China in Nigeria

DTIC Science & Technology

2012-11-02

African policy on democracy, good governance and human rights while China’ policy is resource and business oriented. Nigeria benefits from the combination...infrastructure, governance , AFRICOM 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE...www.allacademic.com/ meta /p251834_index.html. 32 Paradise, “China and International Harmony: The Role of Confucius Institutes in Bolstering Beijing’s Soft Power,” 648

Confucius as Transformational Leader: Lessons for ESL Leadership

ERIC Educational Resources Information Center

Bi, Leilei; Ehrich, John; Ehrich, Lisa C.

2012-01-01

Purpose: This paper aims to explore the leadership values and practices of Confucius in the light of transformational leadership theory. Design/methodology/approach: This paper is literature based. Findings: The paper discusses four key dimensions of transformational leadership theory: idealized influence, inspirational motivation, intellectual…

Beyond Rote-Memorisation: Confucius' Concept of Thinking

ERIC Educational Resources Information Center

Tan, Charlene

2015-01-01

Confucian education is often associated with rote-memorisation that is characterised by sheer repetition of facts with no or little understanding of the content learnt. But does Confucian education necessarily promote rote-memorisation? What does Confucius himself have to say about education? This article aims to answer the above questions by…

Two Key Theories in Education: Confucius and John Dewey

ERIC Educational Resources Information Center

Bonnie, Michael G.

2010-01-01

The following describes the philosophies of Confucius (Confucianism) and John Dewey (pragmatism/instrumentalism/experimentalism) and their views toward vocational, technical, general academic instruction, and the development of morals and values as espoused throughout Asia and America during a span of history from 551 BCE to 1949 CE. This is not…

From the Teachings of Confucius to Western Influences: How Adult Education Is Shaped in Taiwan

ERIC Educational Resources Information Center

Wang, Victor C. X.; Farmer, Lesley S. J

2010-01-01

This article reports the results of a study designed to determine whether the teachings of Confucius (liberal and behavioral teaching approaches) or Western teaching approaches (humanistic, progressive, radical and analytic teaching approaches) shaped adult education in Taiwan. Thirty-nine randomly selected adult educators from three premium…

Exploring an East~West Epistemological Convergence of Embodied Democracy in Education through Cultural Humanism in Confucius~Makiguchi~Dewey

ERIC Educational Resources Information Center

He, Ming Fang

2016-01-01

This article explores an East~West epistemological convergence of embodied democracy in education through cultural humanism illuminated in five main themes in the works of John Dewey (1859-1952), Confucius (551-479 B.C.), and Tsunesaburo Makiguchi (1871-1944): "human-nature interconnection," "self-cultivation," "value…

The bioethical principles and Confucius' moral philosophy.

PubMed

Tsai, D F-C

2005-03-01

This paper examines whether the modern bioethical principles of respect for autonomy, beneficence, non-maleficence, and justice proposed by Beauchamp and Childress are existent in, compatible with, or acceptable to the leading Chinese moral philosophy-the ethics of Confucius. The author concludes that the moral values which the four prima facie principles uphold are expressly identifiable in Confucius' teachings. However, Confucius' emphasis on the filial piety, family values, the "love of gradation", altruism of people, and the "role specified relation oriented ethics" will inevitably influence the "specification" and application of these bioethical principles and hence tend to grant "beneficence" a favourable position that diminishes the respect for individual rights and autonomy. In contrast, the centrality of respect for autonomy and its stance of "first among equals" are more and more stressed in Western liberal viewpoints. Nevertheless, if the Confucian "doctrine of Mean" (chung-yung) and a balanced "two dimensional personhood" approach are properly employed, this will require both theorists and clinicians, who are facing medical ethical dilemmas, of searching to attain due mean out of competing moral principles thus preventing "giving beneficence a priority" or "asserting autonomy must triumph".

East-West Epistemological Convergence of Humanism in Language, Identity, and Education: Confucius-Makiguchi-Dewey

ERIC Educational Resources Information Center

He, Ming Fang

2013-01-01

In this article, the author explores an East-West epistemological convergence of humanism illuminated in three main themes in the works of Confucius (551-479 BC), Makiguchi Tsunesaburo (1871-1944), and John Dewey (1859-1952): "human-nature interconnection," "associated self-cultivation," and "value creation." She contends that these thinkers'…

Analysing Institutional Influences on Teaching-Learning Practices of English as Second Language Programme in a Pakistani University

ERIC Educational Resources Information Center

Rind, Irfan Ahmed; Kadiwal, Laila

2016-01-01

This paper examines the institutional influences on the teaching-learning practices within English as Second Language (ESL) programme in the University of Sindh (UoS), Pakistan. The study uses qualitative case study approach, basing its findings on documentary review, observations, and responses of teachers and students. The analysis of the data…

Confucius Say: Naming as Social Code in Ancient China.

ERIC Educational Resources Information Center

Hagemann, Julie Ann

Confucius (551-479 B.C.) believed in the power of language to regulate society. Concerned about civil war and the moral and social decay of his time, he advocated a peaceful society with a mild and moderate form of law and order and with an emphasis on the well-being of individuals through compassion, kindness, and justice. This form of law…

Can Virtue Be Taught and How? Confucius on the Paradox of Moral Education

ERIC Educational Resources Information Center

Huang, Yong

2011-01-01

In this paper I shall first examine an apparent paradox in Confucius' view on whether everyone is perfectible through education: on the one hand, he states that education should be provided to all, on the other hand, he says that common people cannot be made to know things. To understand this apparent paradox, I shall argue that education for…

Greening academia: Developing sustainable waste management at Higher Education Institutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, N.; Williams, I.D., E-mail: idw@soton.ac.uk; Kemp, S.

Higher Education Institutions (HEIs) are often the size of small municipalities. Worldwide, the higher education (HE) sector has expanded phenomenally; for example, since the 1960s, the United Kingdom (UK) HE system has expanded sixfold to >2.4 million students. As a consequence, the overall production of waste at HEIs throughout the world is very large and presents significant challenges as the associated legislative, economic and environmental pressures can be difficult to control and manage. This paper critically reviews why sustainable waste management has become a key issue for the worldwide HE sector to address and describes some of the benefits, barriers,more » practical and logistical problems. As a practical illustration of some of the issues and problems, the four-phase waste management strategy developed over 15 years by one of the largest universities in Southern England - the University of Southampton (UoS) - is outlined as a case study. The UoS is committed to protecting the environment by developing practices that are safe, sustainable and environmentally friendly and has developed a practical, staged approach to manage waste in an increasingly sustainable fashion. At each stage, the approach taken to the development of infrastructure (I), service provision (S) and behavior change (B) is explained, taking into account the Political, Economic, Social, Technological, Legal and Environmental (PESTLE) factors. Signposts to lessons learned, good practice and useful resources that other institutions - both nationally and internationally - can access are provided. As a result of the strategy developed at the UoS, from 2004 to 2008 waste costs fell by around Pounds 125k and a recycling rate of 72% was achieved. The holistic approach taken - recognizing the PESTLE factors and the importance of a concerted ISB approach - provides a realistic, successful and practical example for other institutions wishing to effectively and sustainably manage their waste.« less

Sustainability Assessment of University of Gondar, Gondar, North-West Ethiopia

ERIC Educational Resources Information Center

Moges, Haimanot Gebrehiwot; Kifle, Desalegn Woldeyohannes; Lotz-Sisitka, Heila; Woldyohhanes, Solomon Meseret

2014-01-01

The purpose of this article is to provide an overview of the cross-institutional assessment of sustainable development practices in the University of Gondar (UoG). The focus of the assessment was the level of UoG academic departments' integration of sustainability concerns in teaching, research and community service. Management contributions to…

Greening academia: developing sustainable waste management at Higher Education Institutions.

PubMed

Zhang, N; Williams, I D; Kemp, S; Smith, N F

2011-07-01

Higher Education Institutions (HEIs) are often the size of small municipalities. Worldwide, the higher education (HE) sector has expanded phenomenally; for example, since the 1960s, the United Kingdom (UK) HE system has expanded sixfold to >2.4 million students. As a consequence, the overall production of waste at HEIs throughout the world is very large and presents significant challenges as the associated legislative, economic and environmental pressures can be difficult to control and manage. This paper critically reviews why sustainable waste management has become a key issue for the worldwide HE sector to address and describes some of the benefits, barriers, practical and logistical problems. As a practical illustration of some of the issues and problems, the four-phase waste management strategy developed over 15 years by one of the largest universities in Southern England--the University of Southampton (UoS)--is outlined as a case study. The UoS is committed to protecting the environment by developing practices that are safe, sustainable and environmentally friendly and has developed a practical, staged approach to manage waste in an increasingly sustainable fashion. At each stage, the approach taken to the development of infrastructure (I), service provision (S) and behavior change (B) is explained, taking into account the Political, Economic, Social, Technological, Legal and Environmental (PESTLE) factors. Signposts to lessons learned, good practice and useful resources that other institutions--both nationally and internationally--can access are provided. As a result of the strategy developed at the UoS, from 2004 to 2008 waste costs fell by around £125k and a recycling rate of 72% was achieved. The holistic approach taken--recognizing the PESTLE factors and the importance of a concerted ISB approach--provides a realistic, successful and practical example for other institutions wishing to effectively and sustainably manage their waste. Copyright © 2011 Elsevier Ltd. All rights reserved.

Endoscopic Spatulation of the Intramural Ureter: A Technique to Prevent Stenosis of the Ureterovesical Junction in Patients Undergoing Resection of the Ureteral Orifice.

PubMed

Creta, Massimiliano; Mirone, Vincenzo; Di Meo, Sergio; Buonopane, Roberto; Fusco, Ferdinando; Imperatore, Vittorio

2016-08-01

Wide resection of the ureteral orifice (UO) may result in scarring and stenosis of the ureterovesical junction (UVJ). We aimed to describe a technique of endoscopic spatulation of the intramural ureter in patients undergoing resection of the UO at the time of transurethral resection of bladder tumor (TURBT) and compare the surgical and oncological outcomes of this procedure with those of patients undergoing conventional UO resection. The clinical records of patients who underwent TURBT at a single institution were retrospectively analyzed. Patients who underwent conventional UO resection or UO resection followed by endoscopic spatulation of the intramural ureter were included in the analysis. The two groups were compared in terms of intra- and postoperative outcomes. A total of 227 patients were included in the final comparative analyses. Of them, 104 underwent conventional UO resection and 123 underwent UO resection followed by endoscopic spatulation of the intramural ureter. The two groups were comparable for demographic and clinical features. There were not statistically significant differences in terms of mean operative times. The incidence of transient postoperative hydronephrosis as well as UVJ scarring and stenosis was significantly lower in patients undergoing endoscopic spatulation of the intramural ureter. The two groups were similar in terms of incidence of vesicoureteral reflux (VUR) and upper urinary tract cancer recurrence. Endoscopic spatulation of the intramural ureter after UO resection is a safe and quick procedure that significantly reduces the incidence of transient early postoperative hydronephrosis and late UVJ stricture if compared with UO resection alone. This procedure is quick to perform, safe, and does not increase the risk of VUR.

UO{sub 2} and PuO{sub 2} utilization in high temperature engineering test reactor with helium coolant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waris, Abdul, E-mail: awaris@fi.itb.ac.id; Novitrian,; Pramuditya, Syeilendra

High temperature engineering test reactor (HTTR) is one of high temperature gas cooled reactor (HTGR) types which has been developed by Japanese Atomic Energy Research Institute (JAERI). The HTTR is a graphite moderator, helium gas coolant, 30 MW thermal output and 950 °C outlet coolant temperature for high temperature test operation. Original HTTR uses UO{sub 2} fuel. In this study, we have evaluated the use of UO{sub 2} and PuO{sub 2} in form of mixed oxide (MOX) fuel in HTTR. The reactor cell calculation was performed by using SRAC 2002 code, with nuclear data library was derived from JENDL3.2. Themore » result shows that HTTR can obtain its criticality condition if the enrichment of {sup 235}U in loaded fuel is 18.0% or above.« less

NASA’s Universe of Learning: Connecting Scientists, Educators, and Learners

NASA Astrophysics Data System (ADS)

Smith, Denise A.; Lestition, Kathleen; Squires, Gordon K.; Greene, W. M.; Biferno, Anya A.; Cominsky, Lynn R.; Goodman, Irene; Walker, Allyson; Universe of Learning Team

2017-01-01

NASA’s Universe of Learning (UoL) is one of 27 competitively awarded education programs selected by NASA’s Science Mission Directorate (SMD) in its newly restructured education effort. Through these 27 programs, SMD aims to infuse NASA science experts and content more effectively and efficiently into learning environments serving audiences of all ages. UoL is a unique partnership between the Space Telescope Science Institute, Chandra X-ray Center, IPAC at Caltech, Jet Propulsion Laboratory Exoplanet Exploration Program, and Sonoma State University that will connect the scientists, engineers, science, technology and adventure of NASA Astrophysics with audience needs, proven infrastructure, and a network of partners to advance SMD education objectives. External evaluation is provided through a partnership with Goodman Research Group and Cornerstone Evaluation Associates. The multi-institutional team is working to develop and deliver a unified, consolidated and externally evaluated suite of education products, programs, and professional development offerings that spans the full spectrum of NASA Astrophysics, including the Cosmic Origins, Physics of the Cosmos, and Exoplanet Exploration themes. Products and programs focus on out-of-school-time learning environments and include enabling educational use of Astrophysics mission data and offering participatory experiences; creating multimedia and immersive experiences; designing exhibits and community programs; and producing resources for special needs and underserved/underrepresented audiences. The UoL team also works with a network of partners to provide professional learning experiences for informal educators, pre-service educators, and undergraduate instructors. This presentation will provide an overview of the UoL team’s approach to partnering scientists and educators to engage learners in Astrophysics discoveries and data; progress to date; and pathways for science community involvement.

Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate.

PubMed

Kim, B H; Lee, Y B; Prelas, M A; Ghosh, T K

Two types of ammonium uranyl nitrate (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O and NH 4 UO 2 (NO 3 ) 3 , were thermally decomposed and reduced in a TG-DTA unit in nitrogen, air, and hydrogen atmospheres. Various intermediate phases produced by the thermal decomposition and reduction process were investigated by an X-ray diffraction analysis and a TG/DTA analysis. Both (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O and NH 4 UO 2 (NO 3 ) 3 decomposed to amorphous UO 3 regardless of the atmosphere used. The amorphous UO 3 from (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O was crystallized to γ-UO 3 regardless of the atmosphere used without a change in weight. The amorphous UO 3 obtained from decomposition of NH 4 UO 2 (NO 3 ) 3 was crystallized to α-UO 3 under a nitrogen and air atmosphere, and to β-UO 3 under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O and NH 4 UO 2 (NO 3 ) 3 were as follows: under a nitrogen atmosphere: (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O → (NH 4 ) 2 UO 2 (NO 3 ) 4 ·H 2 O → (NH 4 ) 2 UO 2 (NO 3 ) 4  → NH 4 UO 2 (NO 3 ) 3  → A-UO 3  → γ-UO 3  → U 3 O 8 , NH 4 UO 2 (NO 3 ) 3  → A-UO 3  → α-UO 3  → U 3 O 8 ; under an air atmosphere: (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O → (NH 4 ) 2 UO 2 (NO 3 ) 4 ·H 2 O → (NH 4 ) 2 UO 2 (NO 3 ) 4  → NH 4 UO 2 (NO 3 ) 3  → A-UO 3  → γ-UO 3  → U 3 O 8 , NH 4 UO 2 (NO 3 ) 3  → A-UO 3  → α-UO 3  → U 3 O 8 ; and under a hydrogen atmosphere: (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O → (NH 4 ) 2 UO 2 (NO 3 ) 4 ·H 2 O → (NH 4 ) 2 UO 2 (NO 3 ) 4  → NH 4 UO 2 (NO 3 ) 3  → A-UO 3  → γ-UO 3  → α-U 3 O 8  → UO 2 , NH 4 UO 2 (NO 3 ) 3  → A-UO 3  → β-UO 3  → α-U 3 O 8  → UO 2 .

The Highest State of Being and Knowing.

ERIC Educational Resources Information Center

Clarken, Rodney H.

This paper identifies the most influential paradigmatic individuals in human history, Socrates, Confucius, Buddha, Jesus, Muhammad, and Baha'u'llah, and presents their individual conceptions of the highest state of being and knowing, comparing the commonalities of those conceptualizations. Each proposes a state that might be described as…

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchetti, M.; University of Montpellier, IES, UMR 5214, F-34000, Montpellier; Laux, D.

During irradiation UO{sub 2} nuclear fuel experiences the development of a non-uniform distribution of porosity which contributes to establish varying mechanical properties along the radius of the pellet. Radial variations of the porosity and of elastic properties in high burnup UO{sub 2} pellet can be investigated via high frequency acoustic microscopy. Ultrasound waves are generated by a piezoelectric transducer and focused on the sample, after having travelled through a coupling liquid. The elastic properties of the material are related to the velocity of the generated Rayleigh surface wave (VR). A 67 MWd/kgU UO{sub 2} pellet was characterized using the acousticmore » microscope installed in the hot cells of the Institute of Transuranium Elements: 90 MHz frequency was applied, methanol was used as coupling liquid and VR was measured at different radial positions. By comparing the porosity values obtained via acoustic microscopy with those determined using ceramographic image analysis a good agreement was found, especially in the areas close to the centre. In addition Young's modulus was calculated and its radial profile was correlated to the corresponding burnup profile. (authors)« less

Confucius: Philosopher of Twenty-First Century Skills

ERIC Educational Resources Information Center

Tan, Leonard

2016-01-01

In this article, I examine the Partnership for twenty-first Century Skills (P21) framework from a Confucian perspective. Given that this framework has attracted attention around the world, including Confucian-heritage societies, an analysis of how key ideas compare with Confucian values appears important and timely. As I shall show, although…

Pedagogy: East and West, Then and Now

ERIC Educational Resources Information Center

Cheng, Kai-Ming

2011-01-01

This is the first of six commentaries discussing Zongjie Wu's essay, "Interpretation, autonomy, and transformation". Wu's analyses of pedagogy have opened a new window for looking at the essence of education. The comparison of Confucius's pedagogy with contemporary teaching in China provides a striking contrast. However, perhaps it is…

Gifted Sixth-Graders and Primary Source Philosophy.

ERIC Educational Resources Information Center

White, David A.; Schlaggar, Sheila

1993-01-01

A sixth-grade gifted class studied the history of philosophy, including selections from such philosophers as Plato, Confucius, Buddha, Marcus Aurelius, and Moses Maimonides. Readings drew on fundamental features of child experience, such as their sense of justice, concern for moral values, and questions about reality. The paper describes classroom…

Of Chrysanthemums and Confucius: Some Impressions of Recent Japanese Educational Reforms.

ERIC Educational Resources Information Center

Janesick, Valerie J.

1993-01-01

Although Japanese public school curriculum is based on the U.S. model imposed during the postwar occupation years, it reflects a long, rich history of group solidarity and consensus, a strong aesthetic sense, and the spiritual influences of Shinto, Buddhism, and Confucianism. Japan's new 10-year education reform plan's emphasis on individual…

Westernization and Social Transformations in Chinese Music Education, 1895-1949.

ERIC Educational Resources Information Center

Ho, Wai-Chung

2003-01-01

Discusses four fields of education in Chinese culture during the time of Confucius: (1) morals, (2) law, (3) politics, and (4) music. Identifies three traditional Chinese music types: (1) refined, (2) popular, and (3) foreign. States music was used to promote social harmony, reinforce nationalist views and actions, and shape attitudes and beliefs…

Older Adult Education: New Public Pedagogy in 21st Century Taiwan

ERIC Educational Resources Information Center

Lee, Ya-hui

2015-01-01

The lifelong learning concept of "never too late to learn" advocated by Confucius has gradually become rooted in the lives of Taiwanese adults and seniors. In response to the impact of population ageing and low fertility rates, numerous elementary schools, junior high schools, and universities have allocated resources and space to…

Nursing's values from a Confucian perspective.

PubMed

Chao, Y M

1995-01-01

Confucius' sayings-derived from his 450 recorded brief conversations and observations-colourfully expound such basic virtues as a child's duty toward his/her parents, love between brothers, devotion to family tradition, reliability in friendships, loyalty to superiors and justice to all men. How five major values of Confucian beliefs fit into nursing practices are elaborated below.

Confucianism on the Comeback: Current Trends in Culture, Values, Politics, and Economy

ERIC Educational Resources Information Center

Angle, Stephen C.

2010-01-01

There is ample evidence that Confucianism is undergoing a multi-faceted revival in contemporary China. This can be seen in government slogans, in a runaway best seller on the "Analects" (the compendium of Confucius's teachings), in educational experiments, and in academic activities. The twentieth century was a bad century for…

Confucius Comes Back

ERIC Educational Resources Information Center

Mooney, Paul

2007-01-01

For more than 2,500 years, Confucian thought held sway in China, advocating a state guided by highly ethical scholar-bureaucrats and a society ruled by morality and a strong emphasis on hierarchical relationships. But by the end of the 19th century, the Chinese state, powerless to fight off foreign encroachment and growing public dissatisfaction,…

Confucius, Mao, and Modernization: Social Studies in the People's Republic of China.

ERIC Educational Resources Information Center

Fouts, Jeffrey T.; Chan, Jack C. K.

1996-01-01

Describes the communist Chinese national curriculum in social studies, a broad term that includes moral and political education, as well as traditional subjects. Includes a sample moral and political education lesson, " Socialism is Good," and lists of several textbook contents and curriculum guides. Provides a brief educational history.…

An Introduction to Chinese Literature.

ERIC Educational Resources Information Center

Kane, Tony

This unit will introduce secondary level students to Chinese literature. The first part of the unit discusses poetry which has always been the most highly prized form of Chinese literature. The discussion examines the "Complete Tang Poems," the "Book of Songs" compiled by Confucius, the "Songs of Chu," and the "Li Sao." Students learn about the…

OOPS! A Miracle Created by Confucius

ERIC Educational Resources Information Center

Chang, Agnes; Chu, Lucifer

2007-01-01

The story is told of the conception and creation of OOPS (Opensource Opencourseware Prototype System), which is a massive, worldwide volunteer project that translates OER into Mandarin. The founder and leader, Lucifer Chu, describes how the project grew from his own solo translation work to over 2,400 volunteers in 22 countries. In 2005 and 2006…

"Ren-li", Reciprocity, Judgment, and the Question of Openness to the Other in the Confucian "Lunyu"

ERIC Educational Resources Information Center

Wu, Meiyao

2013-01-01

Here the author takes "ren"-humanity to be, as Confucius says, an underlying, ineffable, potentially universal human quality, and draws a distinction between three different types of moral capacity in the "Lunyu": the man of "ren's" capacity for "li"-proper interactions, his capacity for total…

A Transcultural Theory of Thinking for Instrumental Music Education: Philosophical Insights from Confucius and Dewey

ERIC Educational Resources Information Center

Tan, Leonard

2016-01-01

In music education, thinking is often construed in terms of acquiring conceptual knowledge of musical elements. Research has found, however, that instrumental music educators have largely neglected conceptual teaching and learning. This begs the following questions: What is the nature of thinking in instrumental music education? How should…

The Confucian View of the Relationship between Knowledge and Action and Its Relevance to Action Research

ERIC Educational Resources Information Center

Tsai, Ching-tien

2014-01-01

There are marked similarities between Confucian ideas about the relationship between action, knowledge and learning, and contemporary educational thinking about action research. Examples can be seen in the relationship between action and research. First, Confucius emphasized the importance of "action" which was different from…

Human embryonic stem cell research debates: a Confucian argument

PubMed Central

Tsai, D

2005-01-01

The author proposes that the "gradualist" position is more plausible than the other two positions. Confucius's moral principle of jen, which proposes a unique theory of "love of gradation", and the principle of yi, which advocates "due treatment for persons", are then explored. The author then argues that our moral obligations to do good to other living organisms, persons, and our families are different. Putting together the "gradualist" position on the human embryo, and Confucius's theories of "love of gradation" and "due treatment for persons", the author concludes that the early embryo has less ethical significance than the later fetus and adult human. The moral obligation we have toward persons is clearer and stronger than that which we have toward human embryos. Embryo research is justifiable if it brings enormous welfare to human persons that cannot be otherwise achieved. The "love of gradation" requires us, however, to extend love and respect towards other entities according to their different status. We should therefore be very cautious in using human embryos for research, acknowledging the gradualist nature of their moral status. PMID:16269558

Unusual ion UO(4)(-) formed upon collision induced dissociation of [UO(2)(NO(3))(3)](-), [UO(2)(ClO(4))(3)](-), [UO(2)(CH(3)COO)(3)](-) ions.

PubMed

Sokalska, Marzena; Prussakowska, Małgorzata; Hoffmann, Marcin; Gierczyk, Błazej; Frański, Rafał

2010-10-01

The following ions [UO(2)(NO(3))(3)](-), [UO(2)(ClO(4))(3)](-), [UO(2)(CH(3)COO)(3)](-) were generated from respective salts (UO(2)(NO(3))(2), UO(2)(ClO(4))(3), UO(2)(CH(3)COO)(2)) by laser desorption/ionization (LDI). Collision induced dissociation of the ions has led, among others, to the formation of UO(4)(-) ion (m/z 302). The undertaken quantum mechanical calculations showed this ion is most likely to possess square planar geometry as suggested by MP2 results or strongly deformed geometry in between tetrahedral and square planar as indicated by DFT results. Interestingly, geometrical parameters and analysis of electron density suggest it is an U(VI) compound, in which oxygen atoms bear unpaired electron and negative charge. Copyright © 2010 American Society for Mass Spectrometry. Published by Elsevier Inc. All rights reserved.

High resolution photoelectron imaging of UO(-) and UO2(-) and the low-lying electronic states and vibrational frequencies of UO and UO2.

PubMed

Czekner, Joseph; Lopez, Gary V; Wang, Lai-Sheng

2014-12-28

We report a study of the electronic and vibrational structures of the gaseous uranium monoxide and dioxide molecules using high-resolution photoelectron imaging. Vibrationally resolved photoelectron spectra are obtained for both UO(-) and UO2(-). The spectra for UO2(-) are consistent with, but much better resolved than a recent study using a magnetic-bottle photoelectron analyzer [W. L. Li et al., J. Chem. Phys. 140, 094306 (2014)]. The electron affinity (EA) of UO is reported for the first time as 1.1407(7) eV, whereas a much more accurate EA is obtained for UO2 as 1.1688(6) eV. The symmetric stretching modes for the neutral and anionic ground states, and two neutral excited states for UO2 are observed, as well as the bending mode for the neutral ground state. These vibrational frequencies are consistent with previous experimental and theoretical results. The stretching vibrational modes for the ground state and one excited state are observed for UO. The current results for UO and UO2 are compared with previous theoretical calculations including relativistic effects and spin-orbit coupling. The accurate experimental data reported here provide more stringent tests for future theoretical methods for actinide-containing species.

Electronic spectrum of the UO and UO(+) molecules.

PubMed

Tyagi, Rajni; Zhang, Zhiyong; Pitzer, Russell M

2014-12-18

Electronic theory calculations are applied to the study of the UO molecule and the UO(+) ion. Relativistic effective core potentials are used along with the accompanying valence spin-orbit operators. Polarized double-ς and triple-ς basis sets are used. Molecular orbitals are obtained from state-averaged multiconfiguration self-consistent field calculations and then used in multireference spin-orbit configuration interaction calculations with a number of millions of terms. The ground state of UO has open shells of 5f(3)7s(1), angular momentum Ω = 4, and a spin-orbit-induced avoided crossing near the equilibrium internuclear distance. Many UO excited states are studied with rotational constants, intensities, and experimental comparisons. The ground state of UO(+) is of 5f(3) nature with Ω = 9/2. Many UO(+) excited states are also studied. The open-shell nature of both UO and UO(+) leads to many low-lying excited states.

The UO2 ex-ADU powder preparation and pellet sintering for optimum efficiency: experimental and modeling studies

NASA Astrophysics Data System (ADS)

Hung, Nguyen Trong; Thuan, Le Ba; Van Tung, Nguyen; Thuy, Nguyen Thanh; Lee, Jin-Young; Jyothi, Rajesh Kumar

2017-12-01

The UO2 nuclear fuel pellet process for light water reactors (LWR) includes the conversion of uranium hexafluoride (UF6) into UO2 powder and the fabrication of UO2 pellets from such UO2 powder. In the paper, studies on UO2 pellet process from ammonium diuranate-derived uranium dioxide powder (UO2 ex-ADU powder) were reported. The UO2 ex-ADU powders were converted from ADU at various temperatures of 973 K, 1023 K and 1073 K and then UO2 pellets prepared from the powders were sintered at temperatures of 1923 K, 1973 K and 2023 K for times of 4 h, 6 h and 8 h. Response surface methodology (RSM) based on quadratic central composite design (CCD) type of face centered (CCF) improved by Box and Hunter was used to model the UO2 pellet process, using MODDE 5.0 software as an assessing tool. On the base of the proposed model, the relationship between the technological parameters and density of the UO2 pellet product was suggested to control the UO2 ex-ADU pellet process as desired levels.

In the Image of Confucius: The Education and Preparation of Teachers in Taiwan.

ERIC Educational Resources Information Center

Smith, Douglas C.

This book reviews both preservice and inservice teacher education in the Republic of China and provides detailed analyses. In the first chapter, an overview of the educational system's structure in modern Taiwan and the United States is presented and comparisons drawn. Features of Chinese educational and intellectual thought and philosophy are…

Investigating Morals and Values in Today's Society.

ERIC Educational Resources Information Center

Garnett, Paul D.

This responsibility education activity book for grades 5-10 offers a set of materials that reflect students' interests and motivation for values education. The book is built around three moral principles: (1) "Do unto others as you would have them do unto you" (Confucius, 513 B.C.); (2) "The end does not justify the means" (Immanuel Kant, "The…

Cooperative Learning in a Hong Kong Primary School: Perceptions, Problems and Accommodation

ERIC Educational Resources Information Center

Chan, Kam Wing

2014-01-01

Some educators may see cooperative learning as a Western pedagogy that is difficult to use in Eastern countries with a Confucian Heritage, while others argue that the philosophy of Confucius parallels the elements of cooperative learning. This article reports the key findings of a 2-year longitudinal study that investigated the perceptions of…

Socratic Knowledge, Christian Love, Confucian Virtue and Buddhist Emptiness: Guiding Principles for Education

ERIC Educational Resources Information Center

Clarken, Rodney

2010-01-01

Socrates' view of knowledge, Jesus' conception of love, Confucius' idea of virtue and Buddha's path of emptiness provide valuable insights and guiding principles to help us achieve a well-rounded education. Each of these individuals caused a transformation in the individual and collective lives of their followers and their respective societies…

Effects of Cognitive Styles on an MSN Virtual Learning Companion System as an Adjunct to Classroom Instructions

ERIC Educational Resources Information Center

Hsieh, Sheng-Wen

2011-01-01

This study designed a chatbot system, Confucius, as a MSN virtual learning companion to examine how specific application design variables within educational software affect the learning process of subjects as defined by the cognitive continuum of field-dependent and field-independent learners. 104 college students participated in a 12 week…

Foucault, Confucius and the In-Service Learning of Experienced Teachers in an Era of Managerialism

ERIC Educational Resources Information Center

Huang, Hua

2018-01-01

By drawing on Foucault's theory of subjectification, this study presents a case study of two experienced teachers' in-service learning in the managerialist climate of Macau. The results indicate that the prevailing policies and administrative strategies on in-service learning served as the apparatus of managerialism working on teachers and…

Conceptions of Lifelong Learning in Confucian Culture: Their Impact on Adult Learners

ERIC Educational Resources Information Center

Zhang, Weiyuan

2008-01-01

The philosophy and practice of lifelong learning has a long history in China, being traceable to Confucius's idea (circa 500 BC) of "education for all". However, very little research has been done on the development of the Confucian idea of lifelong learning in ancient China, or on its influence on current practices of lifelong learning…

High resolution photoelectron imaging of UO{sup −} and UO{sub 2}{sup −} and the low-lying electronic states and vibrational frequencies of UO and UO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Czekner, Joseph; Lopez, Gary V.; Wang, Lai-Sheng

2014-12-28

We report a study of the electronic and vibrational structures of the gaseous uranium monoxide and dioxide molecules using high-resolution photoelectron imaging. Vibrationally resolved photoelectron spectra are obtained for both UO{sup −} and UO{sub 2}{sup −}. The spectra for UO{sub 2}{sup −} are consistent with, but much better resolved than a recent study using a magnetic-bottle photoelectron analyzer [W. L. Li et al., J. Chem. Phys. 140, 094306 (2014)]. The electron affinity (EA) of UO is reported for the first time as 1.1407(7) eV, whereas a much more accurate EA is obtained for UO{sub 2} as 1.1688(6) eV. The symmetricmore » stretching modes for the neutral and anionic ground states, and two neutral excited states for UO{sub 2} are observed, as well as the bending mode for the neutral ground state. These vibrational frequencies are consistent with previous experimental and theoretical results. The stretching vibrational modes for the ground state and one excited state are observed for UO. The current results for UO and UO{sub 2} are compared with previous theoretical calculations including relativistic effects and spin-orbit coupling. The accurate experimental data reported here provide more stringent tests for future theoretical methods for actinide-containing species.« less

Grain growth and pore coarsening in dense nano-crystalline UO 2+x fuel pellets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Tiankai; Mo, Kun; Yun, Di

Dense nano-sized UO 2+x pellets are synthesized by spark plasma sintering with controlled stoichiometries (UO 2.03 and UO 2.11) and grain sizes (~100 nm), and subsequently isothermally annealed to study their effects on grain growth kinetics and microstructure stability. The grain growth kinetics is determined and analyzed focusing on the interaction between grain boundary migration, pore growth and coalescence. Grains grow much bigger in nano-sized UO 2.11 than UO 2.03 upon thermal annealing, consistent with the fact that hyper-stoichiometric UO 2+x is beneficial for sintering due to enhanced U ion diffusion from excessive O ion interstitials. The activation energies ofmore » the grain growth for UO 2.03 and UO 2.11 are determined as ~1.0 and 1.3~2.0 eV, respectively. As compared with the micron-sized UO 2 in which volumetric diffusion dominates the grain coarsening with an activation energy of ~3.0 eV, the enhanced grain growth kinetics in nano-sized UO 2+x suggests that grain boundary diffusion controls grain growth. Lastly, the higher activation energy of more hyper-stoichiometric nano-sized UO 2.11 may be attributed to the excessive O interstitials pinning grain boundary migration.« less

Grain growth and pore coarsening in dense nano-crystalline UO 2+x fuel pellets

DOE PAGES

Yao, Tiankai; Mo, Kun; Yun, Di; ...

2017-03-25

Dense nano-sized UO 2+x pellets are synthesized by spark plasma sintering with controlled stoichiometries (UO 2.03 and UO 2.11) and grain sizes (~100 nm), and subsequently isothermally annealed to study their effects on grain growth kinetics and microstructure stability. The grain growth kinetics is determined and analyzed focusing on the interaction between grain boundary migration, pore growth and coalescence. Grains grow much bigger in nano-sized UO 2.11 than UO 2.03 upon thermal annealing, consistent with the fact that hyper-stoichiometric UO 2+x is beneficial for sintering due to enhanced U ion diffusion from excessive O ion interstitials. The activation energies ofmore » the grain growth for UO 2.03 and UO 2.11 are determined as ~1.0 and 1.3~2.0 eV, respectively. As compared with the micron-sized UO 2 in which volumetric diffusion dominates the grain coarsening with an activation energy of ~3.0 eV, the enhanced grain growth kinetics in nano-sized UO 2+x suggests that grain boundary diffusion controls grain growth. Lastly, the higher activation energy of more hyper-stoichiometric nano-sized UO 2.11 may be attributed to the excessive O interstitials pinning grain boundary migration.« less

Local structure and charge distribution in the UO(2)-U(4)O(9) system.

PubMed

Conradson, Steven D; Manara, Dario; Wastin, Franck; Clark, David L; Lander, Gerard H; Morales, Luis A; Rebizant, Jean; Rondinella, Vincenzo V

2004-11-01

Analysis of X-ray absorption fine structure spectra of UO(2+x) for x = 0-0.20 (UO(2)--U(4)O(9)) reveals that the adventitious O atoms are incorporated as oxo groups with U--O distances of 1.74 A, most likely associated with U(VI), that occur in clusters so that the UO(2) fraction of the material largely remains intact. In addition to the formation of some additional longer U--O bonds, the U sublattice consists of an ordered portion that displays the original U--U distance and a spectroscopically silent, glassy part. This is very different from previous models derived from neutron diffraction that maintained long U--O distances and high U--O coordination numbers. UO(2+x) also differs from PuO(2+x) in its substantially shorter An-oxo distances and no sign of stable coordination with H(2)O and its hydrolysis products.

Fabrication of micro-cell UO2-Mo pellet with enhanced thermal conductivity

NASA Astrophysics Data System (ADS)

Kim, Dong-Joo; Rhee, Young Woo; Kim, Jong Hun; Kim, Keon Sik; Oh, Jang Soo; Yang, Jae Ho; Koo, Yang-Hyun; Song, Kun-Woo

2015-07-01

As one of accident tolerant fuel pellets which should have features of good thermal conductivity and high fission product retention, a micro-cell UO2-Mo pellet has been studied in the aspect of fabrication and thermal property. It was intended to develop the compatible process with conventional UO2 pellet fabrication process. The effects of processing parameters such as the size and density of UO2 granule and the size of Mo powder have been studied to produce sound and dense pellet with completely connected uniform Mo cell-walls. The micro-cell UO2-Mo pellet consists of many Mo micro-cells and UO2 in them. The thermal conductivity of the micro-cell UO2-Mo pellet was measured and compared to those of the UO2 pellet and the UO2-Mo pellet with dispersed form of Mo particles. The thermal conductivity of the micro-cell UO2-Mo pellet was much enhanced and was found to be influenced by the Mo volumetric fraction and pellet integrity. A continuous Mo micro-cell works as a heat conducting channel in the pellet, greatly enhancing the thermal conductivity of the micro cell UO2-Mo pellet.

The influence of unilateral oophorectomy on the age of menopause.

PubMed

Rosendahl, M; Simonsen, M K; Kjer, J J

2017-12-01

To determine the age of menopause after premenopausal unilateral oophorectomy (UO) and to establish whether UO at a young age leads to menopause at a younger age than if UO occurs at an older age. A cohort of 28 731 women, of whom 17 781 (62%) were menopausal, was investigated. Information on menopause was obtained from self-reported questionnaires. Surgical data were obtained from the National Patient Register to avoid recollection bias. Age of menopause after UO/not UO was determined using Kaplan-Meier curves. Cox regression was used to identify factors of importance for early menopause. UO was performed in 1148 women. Women with UO after the age of 45 years, premenopausal hysterectomy, bilateral oophorectomy and cancer were excluded, leaving 236 in the analysis. Menopause occurred 1.8 years earlier after UO compared to women with two intact ovaries (mean 49.5 vs. 51.3 years), and younger age at UO was significantly linearly correlated to younger age at menopause. UO (hazard ratio 1.23) and smoking (hazard ratio 1.12) significantly decreased the age of menopause. Premenopausal unilateral oophorectomy significantly reduces the age of menopause by 1.8 years. Younger age at UO leads to significantly younger age at menopause.

Dissolution of Biogenic and Synthetic UO2 under Varied Reducing Conditions

PubMed Central

ULRICH, KAI – UWE; SINGH, ABHAS; SCHOFIELD, ELEANOR J.; BARGAR, JOHN R.; VEERAMANI, HARISH; SHARP, JONATHAN O.; LATMANI, RIZLAN BERNIER -; GIAMMAR, DANIEL E.

2008-01-01

The chemical stability of biogenic UO2, a nanoparticulate product of environmental bioremediation, may be impacted by the particles’ surface free energy, structural defects, and compositional variability in analogy to abiotic UO2+x (0 ≤ x ≤ 0.25). This study quantifies and compares intrinsic solubility and dissolution rate constants of biogenic nano-UO2 and synthetic bulk UO2.00, taking molecular-scale structure into account. Rates were determined under anoxic conditions as a function of pH and dissolved inorganic carbon in continuous-flow experiments. The dissolution rates of biogenic and synthetic UO2 solids were lowest at near neutral pH and increased with decreasing pH. Similar surface area-normalized rates of biogenic and synthetic UO2 suggest comparable reactive surface site densities. This finding is consistent with the identified structural homology of biogenic UO2 and stoichiometric UO2.00. Compared to carbonate-free anoxic conditions, dissolved inorganic carbon accelerated the dissolution rate of biogenic UO2 by 3 orders of magnitude. This phenomenon suggests continuous surface oxidation of U(IV) to U(VI), with detachment of U(VI) as the rate-determining step in dissolution. Although reducing conditions were maintained throughout the experiments, the UO2 surface can be oxidized by water and radiogenic oxidants. Even in anoxic aquifers, UO2 dissolution may be controlled by surface U(VI) rather than U(IV) phases. PMID:18754482

Silencing expression of UO-44 (CUZD1) using small interfering RNA sensitizes human ovarian cancer cells to cisplatin in vitro.

PubMed

Leong, C T C; Ong, C K; Tay, S K; Huynh, H

2007-02-08

Ovarian cancer is currently the second leading cause of gynecological malignancy and cisplatin or cisplatin-based regimens have been the standard of care for the treatment of advance epithelial ovarian cancers. However, the efficacy of cisplatin treatment is often limited by the development of drug resistance either through the inhibition of apoptotic genes or activation of antiapoptotic genes. We have previously reported the overexpression of human UO-44 (HuUO-44) in ovarian cancers and the HuUO-44 antisera markedly inhibited NIH-OVCAR3 ovarian cancer cell attachment and proliferation (Oncogene 23: 5707-5718, 2004). In the present study, we observed through the cancer cell line profiling array that the expression of HuUO-44 was suppressed in the ovarian cancer cell line (SKOV-3) after treatment with several chemotherapeutic drugs. Similarly, this suppression in HuUO-44 expression was also correlated to the cisplatin sensitivity in two other ovarian cancer cell lines NIH-OVCAR3 and OV-90 in a dose-dependent manner. To elucidate the function of HuUO-44 in cisplatin chemoresistance in ovarian cancer cell, small interfering RNAs (siRNAs) were employed to mediate HuUO-44 silencing in ovarian cancer cell line, NIH-OVCAR3. HuUO-44 RNA interference (RNAi) resulted in the inhibition of cell growth and proliferation. Importantly, HuUO-44 RNAi significantly increased sensitivity of NIH-OVCAR3 to cytotoxic stress induced by cisplatin (P<0.01). Strikingly, we have also demonstrated that overexpression of HuUO-44 significantly conferred cisplatin resistance in NIH-OVCAR3 cells (P<0.05). Taken together, UO-44 is involved in conferring cisplatin resistance; the described HuUO-44-specific siRNA oligonucleotides that can potently silence HuUO-44 gene expression may prove to be valuable pretreatment targets for antitumor therapy or other pathological conditions that involves aberrant HuUO-44 expression.

UO(2) 2+ speciation determines uranium toxicity and bioaccumulation in an environmental Pseudomonas sp. isolate.

PubMed

Vanengelen, Michael R; Field, Erin K; Gerlach, Robin; Lee, Brady D; Apel, William A; Peyton, Brent M

2010-04-01

In the present study, experiments were performed to investigate how representative cellulosic breakdown products, when serving as growth substrates under aerobic conditions, affect hexavalent uranyl cation (UO(2) (2+)) toxicity and bioaccumulation within a Pseudomonas sp. isolate (designated isolate A). Isolate A taken from the Cold Test Pit South (CTPS) region of the Idaho National Laboratory (INL), Idaho Falls, ID, USA. The INL houses low-level uranium-contaminated cellulosic material and understanding how this material, and specifically its breakdown products, affect U-bacterial interactions is important for understanding UO(2) (2+) fate and mobility. Toxicity was modeled using a generalized Monod expression. Butyrate, dextrose, ethanol, and lactate served as growth substrates. The potential contribution of bicarbonate species present in high concentrations was also investigated and compared with toxicity and bioaccumulation patterns seen in low-bicarbonate conditions. Isolate A was significantly more sensitive to UO(2) (2+) and accumulated significantly more UO(2) (2+) in low-bicarbonate concentrations. In addition, UO(2) (2+) growth inhibition and bioaccumulation varied depending on the growth substrate. In the presence of high bicarbonate concentrations, sensitivity to UO(2) (2+) inhibition was greatly mitigated, and did not vary between the four substrates tested. The extent of UO(2) (2+) accumulation was also diminished. The observed patterns were related to UO(2) (2+) aqueous complexation, as predicted by MINTEQ (ver. 2.52) (Easton, PA, USA). In the low- bicarbonate medium, the presence of positively charged and unstable UO(2) (2+)-hydroxide complexes explained both the greater sensitivity of isolate A to UO(2) (2+), and the ability of isolate A to accumulate significant amounts of UO(2) (2+). The exclusive presence of negatively charged and stable UO(2) (2+)-carbonate complexes in the high bi-carbonate medium explained the diminished sensitivity of isolate A to UO(2) (2+) toxicity, and limited ability of isolate A to accumulate UO(2) (2+). (c) 2010 SETAC.

Applying Syundz's Philosophical Concepts to Teaching Leadership in Higher Education and Lifelong Learning

ERIC Educational Resources Information Center

Ko, Hsin Chi

2016-01-01

Syundz (c. 314-237 BC), born in China during the Warring States Period, was a realist philosopher who contributed to the Hundred Schools of Thought, a period of cultural and philosophical development that flourished from the 6th century to 221 BC. Syundz commented on many ideas, particularly those of Confucius and Mencius, and a collection of…

How do you keep the music playing?

PubMed

Baumann, Steven L

2008-10-01

The classical Chinese philosophy of Confucius is here reconsidered in light of the current challenge of sustaining loving relationships not only in words but in actions, and providing a life worth living for frail older adults. The Ox Mountain Parable of Meng Tzu (Mencius) is described and linked to the nursing home reform movement known as "The Eden Alternative." Implications for nursing are considered.

The Confucius-Dewey Synthesis: Administration of Higher Education in Taiwan's Universities, Colleges, and Teachers Colleges--An Evaluation.

ERIC Educational Resources Information Center

Smith, Douglas C.

Perspectives on higher education in Taiwan are presented, based in part on the views of a sample of Chinese scholars. After briefly reviewing the origins of Chinese higher education, attention is directed at the current system. The nine layers in the contemporary educational structure in Taiwan are identified. Chinese students seeking college…

Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)-ethylenediamine-N,N'-diacetic acid-fluoride system: A potentiometric, NMR and X-ray crystallographic study.

PubMed

Palladino, Giuseppe; Szabó, Zoltán; Fischer, Andreas; Grenthe, Ingmar

2006-11-21

The structure, thermodynamics and kinetics of the binary and ternary uranium(VI)-ethylenediamine-N,N'-diacetate (in the following denoted EDDA) fluoride systems have been studied using potentiometry, 1H, 19F NMR spectroscopy and X-ray diffraction. The UO2(2+)-EDDA system could be studied up to -log[H3O+] = 3.4 where the formation of two binary complexes UO2(EDDA)(aq) and UO2(H3EDDA)3+ were identified, with equilibrium constants logbeta(UO2EDDA) = 11.63 +/- 0.02 and logbeta(UO2H3EDDA3+) = 1.77 +/- 0.04, respectively. In the ternary system the complexes UO2(EDDA)F-, UO2(EDDA)(OH)- and (UO2)2(mu-OH)2(HEDDA)2F2(aq) were identified; the latter through 19F NMR. 1H NMR spectra indicate that the EDDA ligand is chelate bonded in UO2(EDDA)(aq), UO2(EDDA)F- and UO2(EDDA)(OH)- while only one carboxylate group is coordinated in UO2(H3EDDA)3+. The rate and mechanism of the fluoride exchange between UO2(EDDA)F- and free fluoride was studied by 19F NMR spectroscopy. Three reactions contribute to the exchange; (i) site exchange between UO2(EDDA)F- and free fluoride without any net chemical exchange, (ii) replacement of the coordinated fluoride with OH- and (iii) the self dissociation of the coordinated fluoride forming UO2(EDDA)(aq); these reactions seem to follow associative mechanisms. (1)H NMR spectra show that the exchange between the free and chelate bonded EDDA is slow and consists of several steps, protonation/deprotonation and chelate ring opening/ring closure, the mechanism cannot be elucidated from the available data. The structure (UO2)2(EDDA)2(mu-H2EDDA) was determined by single crystal X-ray diffraction and contains two UO2(EDDA) units with tetracoordinated EDDA linked by H2EDDA in the "zwitterion" form, coordinated through a single carboxylate oxygen from each end to the two uranium atoms. The geometry of the complexes indicates that there is no geometric constraint for an associative ligand substitution mechanism.

NASA’s Universe of Learning: Girls STEAM Ahead

NASA Astrophysics Data System (ADS)

Marcucci, Emma; Meinke, Bonnie K.; Smith, Denise A.; Ryer, Holly; Slivinski, Carolyn; Kenney, Jessica; Arcand, Kimberly K.; Cominsky, Lynn R.; Girls STEAM Ahead with NASA Team

2017-10-01

NASA Science Mission Directorate’s Universe of Learning (UoL) program enables scientists and engineers to more effectively engage with learners of all ages. The Girls STEAM Ahead with NASA education program within UoL, expands upon the former program, NASA Science4Girls and Their Families, in celebration of National Women’s History Month. The initiative partners the NASA’s Universe of Learning science education program resources with public libraries to provide NASA-themed activities for girls and their families, including hands-on activities for engaging girls, complementary exhibits, and professional development for library partner staff. The science-institute-embedded partners in NASA’s UoL are uniquely poised to foster collaboration between scientists with content expertise and educators with pedagogy expertise. The thematic topics related to NASA Astrophysics enable audiences to experience the full range of NASA scientific and technical disciplines and the different career skills each requires. The events focus on engaging underserved and underrepresented audiences in Science, Technology, Engineering, and Mathematics (STEM) via use of research-based best practices, collaborations with libraries, partnerships with local and national organizations (e.g. National Girls Collaborative Project or NGCP), and remote engagement of audiences. This presentation will provide an overview of the program progress related to engaging girls and their families in NASA-based science programming.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamashita, T.; Fujino, T.; Masaki, N.

The structural parameters of ..cap alpha..- and ..beta..-CdUO/sub 4/ crystals are determined by x-ray powder diffraction technique. ..cap alpha..-CdUO/sub 4/ is rhombohedral and cell parameters are a = 6.233(3) A and ..cap alpha.. = 36.12(5)/sup 0/. ..beta..-CdUO/sub 4/ crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514(2) A. The space groups are R3m for ..cap alpha..-CdUO/sub 4/ and Cmmm for ..beta..-CdUO/sub 4/. ..cap alpha..-CdUO/sub 4/: 1U in (000), 1Cd in (1/2 1/2 1/2), 2O(1) in +-(uuu), 2O(2) in +-(vvv); u = 0.113, v= 0.350, Z = 1. ..beta..-CdUO/sub 4/: 2U in (000; 1/2more » 1/2 0), 2Cd in (1/2 0 1/2; 0 1/2 1/2), 40(1) in (0, +-y, 0; 1/2, 1/2 +-y, 0), 4O(2) in (+-x, 0, 1/2; 1/2 +-x, 1/2, 1/2); x = 0.159, y = 0.278, Z = 2. ..beta..-CdUO/sub 4/ contains collinear uranyl UO/sub 2//sup 2 +/ groups with a U-O(1) distance of 1.91 A, located either along or parallel to the c axis whereas the U-O(1) bond length in ..cap alpha..-CdUO/sub 4/ is 1.98 A which is longer than the usual uranyl bond length.« less

METHOD FOR PREPARATION OF UO$sub 2$ PARTICLES

DOEpatents

Johnson, J.R.; Taylor, A.J.

1959-09-22

A method is described for the preparation of highdensity UO/sub 2/ particles within the size range of 40 to 100 microns. In accordance with the invention UO/sub 2/ particles are autoclaved with an aqueous solution of uranyl ions. The resulting crystals are reduced to UO/sub 2/ and the UO/sub 2/ is heated to at least 1000 deg C to effect densification. The resulting UO/sub 2/ particles are screened, and oversize particles are crushed and screened to recover the particles within the desired size range.

Structure and cation ordering in La 2UO 6, Ce 2UO 6, LaUO 4, and CeUO 4 by first principles calculations

DOE PAGES

Casillas-Trujillo, Luis; Xu, H.; McMurray, Jake W.; ...

2016-07-06

In the present work, we have used density functional theory (DFT) and DFT+U to investigate the crystal structure and phase stability of four model compounds in the Ln 2O 3-UO 2-UO 3 ternary oxide system: La2UO 6, Ce 2UO 6, LaUO 4, CeUO 4, due to the highly-correlated nature of the f-electrons in uranium. We have considered both hypothetical ordered compounds and compounds in which the cations randomly occupy atomic sites in a fluorite-like lattice. We determined that ordered compounds are stable and are energetically favored compared to disordered configurations, though the ordering tendencies are weak. To model and analyzemore » the structures of these complex oxides, we have used supercells based on a layered atomic model. In the layer model, the supercell is composed of alternating planes of anions and cations. We have considered two different ordering motifs for the cations, namely single species (isoatomic) cation layers versus mixed species cation layers. Energy differences between various ordered cationic arrangements were found to be small. This may have implications regarding radiation stability, since cationic arrangements should be able to change under irradiation with little cost in energy.« less

Excision of uranium oxide chains and ribbons in the novel one-dimensional uranyl iodates K(2)[(UO(2))3(IO(3))(4)O(2)] and Ba[(UO(2)2(IO(3))(2)O(2)](H(2)O).

PubMed

Bean, A C; Ruf, M; Albrecht-Schmitt, T E

2001-07-30

The alkali metal and alkaline-earth metal uranyl iodates K(2)[(UO(2))(3)(IO(3))(4)O(2)] and Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) have been prepared from the hydrothermal reactions of KCl or BaCl(2) with UO(3) and I(2)O(5) at 425 and 180 degrees C, respectively. While K(2)[(UO(2))(3)(IO(3))(4)O(2)] can be synthesized under both mild and supercritical conditions, the yield increases from <5% to 73% as the temperature is raised from 180 to 425 degrees C. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), however, has only been isolated from reactions performed in the mild temperature regime. Thermal measurements (DSC) indicate that K(2)[(UO(2))(3)(IO(3))(4)O(2)] is more stable than Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) and that both compounds decompose through thermal disproportionation at 579 and 575 degrees C, respectively. The difference in the thermal behavior of these compounds provides a basis for the divergence of their preparation temperatures. The structure of K(2)[(UO(2))(3)(IO(3))(4)O(2)] is composed of [(UO(2))(3)(IO(3))(4)O(2)](2)(-) chains built from the edge-sharing UO(7) pentagonal bipyramids and UO(6) octahedra. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) consists of one-dimensional [(UO(2))(2)(IO(3))(2)O(2)](2)(-) ribbons formed from the edge sharing of distorted UO(7) pentagonal bipyramids. In both compounds the iodate groups occur in both bridging and monodentate binding modes and further serve to terminate the edges of the uranium oxide chains. The K(+) or Ba(2+) cations separate the chains or ribbons in these compounds forming bonds with terminal oxygen atoms from the iodate ligands. Crystallographic data: K(2)[(UO(2))(3)(IO(3))(4)O(2)], triclinic, space group P_1, a = 7.0372(5) A, b = 7.7727(5) A, c = 8.9851(6) A, alpha = 93.386(1) degrees, beta = 105.668(1) degrees, gamma = 91.339(1) degrees, Z = 1; Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), monoclinic, space group P2(1)/c, a = 8.062(4) A, b = 6.940(3) A, c = 21.67(1), beta= 98.05(1) degrees, Z = 4.

To Learn, To Die/To Teach, To Kill: The Role of the Teacher in Contemporary Taiwan ESL Classrooms.

ERIC Educational Resources Information Center

Cornberg, David

This paper examines the teacher's role in contemporary English as a Second Language (ESL) classrooms in Taiwan. Key figures in this exploration are Confucius, Chuang Tzu, Lao Tzu, Socrates, and Plato. The paper explains how the power of the student meets the power of the teachers. Students' power flows through their freedom and responsibility to…

The crystal structures of α- and β-CdUO 4

NASA Astrophysics Data System (ADS)

Yamashita, Toshiyuki; Fujino, Takeo; Masaki, Norio; Tagawa, Hiroaki

1981-04-01

The structural parameters of α- and β-CdUO 4 crystals are determined by X-ray powder diffraction technique. α-CdUO 4 is rhombohedral and cell parameters are a = 6.233(3) Å and α = 36.12(5)°. β-CdUO 4 crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514 (2) Å. The space groups are R overline3m for α-CdUO 4 and Cmmm for β-CdUO 4. α-CdUO 4: 1U in (000), 1Cd in ( {1}/{2}{1}/{2}{1}/{2}), 2O(1) in ±( uuu), 2O(2) in ±( vvv); u = 0.113, v = 0.350, Z = 1. β-CdUO 4: 2U in ( 000; {1}/{2}{1}/{2} 0 ), 2Cd in ( {1}/{2} 0 {1}/{2}; 0 {1}/{2}, {1}/{2}), 4O(1) in ( 0, ±y, 0; {1}/{2}, {1}/{2} ±y, 0 ), 4O(2) in ( ±x, 0, {1}/{2}; {1}/{2} ±x, {1}/{2}, {1}/{2}); x = 0.159, y = 0.278, Z = 2. β-CdUO 4 contains collinear uranyl UO 2+2 groups with a UO(1) distance of 1.91 Å, located either along or parallel to the c axis whereas the UO(1) bond length in α-CdUO 4 is 1.98 Å which is longer than the usual uranyl bond length.

The synthesis and crystal structure of α-Ca 3UO 6

NASA Astrophysics Data System (ADS)

Holc, J.; Golic̆, L.

1983-07-01

Single crystals of α-Ca 3UO 6 were grown from a UO 3CaCl 2CaO melt by the slow cooling method from 950°C. The crystal structure was determined by means of X-ray diffraction with R = 0.032 and Rw = 0.019. The structure of α-Ca 3UO 6 is of Mg 3TeO 6 type. α-Ca 3UO 6 is rhombohedral with a = 6.729 (1)Å, α = 90.30 (1)°, Z = 2, Dc = 4.955 g/cm 3, Dm = 4.79 g/cm 3, space group R overline3. Uranium and calcium atoms are six-coordinated. At 1200°C rhombohedral α-Ca 3UO 6 irreversibly transforms to monoclinic β-Ca 3UO 6.

Complete reduction of high-density UO2 to metallic U in molten Li2O-LiCl

NASA Astrophysics Data System (ADS)

Choi, Eun-Young; Lee, Jeong

2017-10-01

The large size and high density of spent fuel pellets make it difficult to use the pellets directly in electrolytic reduction (also called as oxide reduction, OR) for pyroprocessing owing to the slow diffusion of molten Li2O-LiCl salt electrolyte into the pellets. In this study, we investigated complete OR of high-density UO2 to metallic U without any remaining UO2. Only partial reductions near the surface of high-density UO2 pellets were observed under operation conditions employing fast electrolysis rate that allowed previously complete reduction of low-density UO2 pellets. Complete reduction of high-density UO2 pellets was observed at fast electrolysis rate when the pellet size was reduced. The complete reduction of high-density UO2 pellets without size reduction was achieved at slow electrolysis rate, which allowed sufficient chemical reduction of UO2 with the lithium metal generated by the cathode reaction.

Induction of UO-44 gene expression by tamoxifen in the rat uterus and ovary.

PubMed

Huynh, H; Ng, C Y; Lim, K B; Ong, C K; Ong, C S; Tran, E; Tuyen Nguyen, T T; Chan, T W

2001-07-01

A complementary DNA, uterine-ovarian-specific gene 44 (UO-44), has been isolated from tamoxifen-induced rat uterine complementary DNA library using differential display techniques. UO-44 transcripts are found to be abundant in the uterus and ovary. UO-44 gene expression in the uterus is strictly regulated by estrogens, tamoxifen, and GH, whereas the pure antiestrogen ICI 182780 is inhibitory. Treatment of ovariectomized rats and hypophysectomized rats with tamoxifen and GH, respectively, resulted in up-regulation of UO-44 expression in a dose-dependent manner. In situ hybridization revealed that UO-44 gene expression was restricted to the luminal and glandular epithelial cells of the uterus and to granulosa cells of medium-size ovarian follicles. Transfection studies showed that UO-44 was a membrane-associated protein. Because estrogens, tamoxifen, and GH are stimulators of uterine luminal epithelial cell growth in vivo, UO-44 protein may serve as a mediator of the effect of these compounds in inducing epithelial proliferation and differentiation in these tissues.

A charge-optimized many-body potential for the U-UO2-O2 system

NASA Astrophysics Data System (ADS)

Li, Yangzhong; Liang, Tao; Sinnott, Susan B.; Phillpot, Simon R.

2013-12-01

Building on previous charge-optimized many-body (COMB) potentials for metallic α-U and gaseous O2, we have developed a new potential for UO2, which also allows the simulation of U-UO2-O2 systems. The UO2 lattice parameter, elastic constants and formation energies of stoichiometric and non-stoichiometric intrinsic defects are well reproduced. Moreover, this is the first rigid-ion potential that produces the correct deviation of the Cauchy relation, as well as the first classical interatomic potential that is able to determine the defect energies of non-stoichiometric intrinsic point defects in UO2 with an appropriate reference state. The oxygen molecule interstitial in the α-U structure is shown to decompose, with some U-O bonds approaching the natural bond length of perfect UO2. Finally, we demonstrate the capability of this COMB potential to simulate a complex system by performing a simulation of the α-U + O2 → UO2 phase transformation. We also identify a possible mechanism for uranium oxidation and the orientation of the resulting fluorite UO2 structure relative to the coordinate system of orthorhombic α-U.

First-principles investigation of the physical properties of cubic and orthorhombic phase Na3UO4

NASA Astrophysics Data System (ADS)

Chen, Haichuan; Tian, Wenyan

2017-11-01

The anisotropic elastic properties, Vickers hardness, Debye temperature and the minimum thermal conductivity of c-Na3UO4 and o-Na3UO4 have been investigated by means of the first principles calculations. The lattice parameters are in good agreement with the available experimental data and the theoretical results. The elastic constants satisfy the mechanical stability criteria show that both of them are mechanically stable. The value of B / G and Cauchy pressure reveal that the c-Na3UO4 holds a ductile behavior while the o-Na3UO4 behaves a brittle manner. The elastic anisotropy of c-Na3UO4 is less weak than that of o-Na3UO4. The hardness shows that both of them can be classified as ;soft materials;. Finally, the Debye temperature is 452.6 K and 388.4 K, and the minimum thermal conductivities kmin is 0.883 W m-1 K-1 and 0.753 W m-1 K-1 of c-Na3UO4 and o-Na3UO4, respectively. Due to relatively lower thermal conductivity, and thereby they are suitable to be used as thermal insulating materials.

Advancing Cancer Survivorship in a Country with 1.35 Billion People: The China Lymphoma Project

PubMed Central

Coughlin, Steven; Reno, Jamie

2016-01-01

Rates of lymphoma are rising rapidly and lymphoma is now the ninth most common cancer among Chinese males. The China Lymphoma Project was founded to increase awareness of lymphoma in China, including the survivability of the disease and the availability of potentially life-saving treatments, and to provide social support for men, women, and children in China who are living with the disease. The project is working with China government officials, several of the top cancer hospitals in China and the U.S., internationally known oncologists and cancer researchers, pharmaceutical and biotech companies in China and the U.S., healthcare and environmental companies, the Confucius Institute at San Diego State University, and the Asian Heritage Society. Advances in e-Health are being utilized to provide patient education and social support. The project will provide free e-books that profile lymphoma survivors (e.g., Kai-Fu Lee, creator of Google China), new videos, websites, pamphlets, blogs, video logs (vlogs), peer-to-peer counseling and support, and information about the latest treatments and oncology clinical trials. PMID:27570834

Advancing Cancer Survivorship in a Country with 1.35 Billion People: The China Lymphoma Project.

PubMed

Coughlin, Steven; Reno, Jamie

Rates of lymphoma are rising rapidly and lymphoma is now the ninth most common cancer among Chinese males. The China Lymphoma Project was founded to increase awareness of lymphoma in China, including the survivability of the disease and the availability of potentially life-saving treatments, and to provide social support for men, women, and children in China who are living with the disease. The project is working with China government officials, several of the top cancer hospitals in China and the U.S., internationally known oncologists and cancer researchers, pharmaceutical and biotech companies in China and the U.S., healthcare and environmental companies, the Confucius Institute at San Diego State University, and the Asian Heritage Society. Advances in e-Health are being utilized to provide patient education and social support. The project will provide free e-books that profile lymphoma survivors (e.g., Kai-Fu Lee, creator of Google China), new videos, websites, pamphlets, blogs, video logs (vlogs), peer-to-peer counseling and support, and information about the latest treatments and oncology clinical trials.

Surface reactions of ethanol over UO 2(100) thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

S. D. Senanayake; Mudiyanselage, K.; Burrell, A. K.

2015-10-08

The study of the reactions of oxygenates on well-defined oxide surfaces is important for the fundamental understanding of heterogeneous chemical pathways that are influenced by atomic geometry, electronic structure, and chemical composition. In this work, an ordered uranium oxide thin film surface terminated in the (100) orientation is prepared on a LaAlO 3 substrate and studied for its reactivity with a C-2 oxygenate, ethanol (CH 3CH 2OH). With the use of synchrotron X-ray photoelectron spectroscopy (XPS), we have probed the adsorption and desorption processes observed in the valence band, C 1s, O 1s, and U 4f to investigate the bondingmore » mode, surface composition, electronic structure, and probable chemical changes to the stoichiometric-UO 2(100) [smooth-UO 2(100)] and Ar +-sputtered UO 2(100) [rough-UO 2(100)] surfaces. Unlike UO 2(111) single crystal and UO 2 thin film, Ar-ion-sputtering of this UO 2(100) did not result in noticeable reduction of U cations. Upon ethanol adsorption (saturation occurred at 0.5 ML), only the ethoxy (CH 3CH 2O –) species is formed on smooth-UO 2(100) whereas initially formed ethoxy species are partially oxidized to surface acetate (CH3COO–) on the Ar +-sputtered UO 2(100) surface. Furthermore, all ethoxy and acetate species are removed from the surface between 600 and 700 K.« less

Women in Science and Technology: The Institutional Ecology Approach. Volume III: Discussion Papers (The Ten Factors of Influence) Used in the UO WISTA Survey.

ERIC Educational Resources Information Center

Byrne, Eileen M.

This document is a "methodological annex" to volume I of the Women in Science and Technology in Australia (WISTA) final research report. The 10 discussion papers that make up this document deal with the 10 core factors of influence that formed one main axis of the study's theoretical framework for inquiry. A diagram illustrates this…

Environmental modeling of uranium interstitial compositions of non-stoichiometric oxides: experimental and theoretical analysis.

PubMed

Ivanova, Bojidarka

2016-10-01

Study of uranium interstitial compositions of non-stoichiometric oxides UO2+x (x ∈ 0.1-0.02) in gas and condense phases has been presented, using various soft-ionization mass spectrometric methods such as ESI-, APCI-, and MALDI-MS at a wide dynamic temperature gradient (∈ 25-300 °C). Linearly polarized vibrational spectroscopy has been utilized in order to assign unambiguously, the vibrational frequencies of uranium non-stoichiometric oxides. Experimental design has involved xUO2.66·yUO2.33, xUO2.66·yUO2.33/SiO2, xUO2.66·yUO2.33/SiO2 (NaOH) and SiO2/x'NaOH·y'UO2(NO3)2·6H2O, multicomponent systems (x = 1, y ∈ 0.1-1.0 and x' = 1, y' ∈ 0.1-0.6) as well as phase transitions UO2(NO3)2·6H2O → {U4O9(UO2.25)} → U3O7(UO2.33) → U3O8(UO2.66) → {UO3}, thus ensuring a maximal representativeness to real environmental conditions, where diverse chemical, geochemical and biochemical reactions, including complexation and sorption onto minerals have occurred. Experimental factors such as UV-irradiation, pH, temperature, concentration levels, solvent types and ion strength have been taken into consideration, too. As far as uranium speciation represents a challenging analytical task in terms of chemical identification diverse coordination species, mechanistic aspects relating incorporation of oxygen into UO 2+x form the shown full methods validation significantly impacts the field of environmental radioanalytical chemistry. UO2 is the most commonly used fuel in nuclear reactors around the globe; however, a large non-stoichiometric range ∈ UO1.65-UO2.25 has occurred due to radiolysis of water on UO2 surface yielding to H2O2, OH(·), and more. Each of those compositions has different oxygen diffusion. And in this respect enormous effort has been concentrated to study the potential impact of hazardous radionuclide on the environment, encompassing from the reprocessing to the disposal stages of the fuel waste, including the waste itself, the processes in the waste containers, the clay around the containers, and geological processes. In a broader sense, thereby, this study contributes to field of environmental analysis highlighting the great ability of various soft-ionization MS methods, particularly, MALDI-MS one, for direct assay of complex multicomponent heterogeneous mixtures at fmol-attomol concentration ranges, along with it the great instrumental features allowing, not only meaningful quantitative, but also structural information of the analytes, thus making the method indispensable for environmental speciation of radionuclides, generally.

Incidence, time trends, laterality, indications, and pathological findings of unilateral oophorectomy before menopause

PubMed Central

Laughlin-Tommaso, Shannon K.; Stewart, Elizabeth A.; Grossardt, Brandon R.; Rocca, Liliana Gazzuola; Rocca, Walter A.

2013-01-01

Objective Unilateral oophorectomy (UO) is common, yet it remains understudied. We investigated trends in incidence rates, indications, and pathological differences in the right and left ovary in women younger than 50 years. Methods The Rochester Epidemiology Project medical records-linkage system was used to identify all women who underwent UO between 1950 and 2007 in Olmsted County, Minnesota (n=1,838). We studied incidence rates, indications, and pathology of UO by laterality and investigated trends over time. Results Pooling all oophorectomies over a 58-year period, the incidence of UO was higher than the incidence of bilateral oophorectomy through age 39 years; however, bilateral oophorectomy surpassed UO thereafter. The incidence of UO increased from 1950 to 1974 but decreased thereafter, and was surpassed by the rate of bilateral oophorectomy after 1979. Prior to 1985, left ovaries were removed more frequently than right ovaries both with and without a medical indication for UO. Ovaries removed with a medical indication showed pathologic differences between right and left, with endometriosis more common on the left. Ovaries removed without a medical indication did not differ in pathology by side. Conclusion There have been major trends in UO over 6 decades. Medically-indicated UO has been more common on the left due, in part, to the higher prevalence of endometriosis. However, UO without a medical indication has also been more common on the left as a result of surgical preferences and traditions. The long-term consequences of right or left UO on timing of menopause, morbidity, and mortality need further study. PMID:24067261

Urine output on ICU entry is associated with hospital mortality in unselected critically ill patients.

PubMed

Zhang, Zhongheng; Xu, Xiao; Ni, Hongying; Deng, Hongsheng

2014-02-01

Urine output (UO) is routinely measured in the intensive care unit (ICU) but its prognostic value remains debated. The study aimed to investigate the association between day 1 UO and hospital mortality. Clinical data were abstracted from the Multiparameter Intelligent Monitoring in Intensive Care II (version 2.6) database. UO was recorded for the first 24 h after ICU entry, and was classified into three categories: UO >0.5, 0.3-0.5 and ≤0.3 ml/kg per hour. The primary endpoint was the hospital mortality. Four models were built to adjust for the hazards ratio of mortality. A total of 21,207 unselected ICU patients including 2,401 non-survivors and 18,806 survivors were included (mortality rate 11.3 %). Mortality rate increased progressively across UO categories: >0.5 (7.67 %), 0.3-0.5 (11.27 %) and ≤0.3 ml/kg/h (18.29 %), and this relationship remained statistically significant after rigorous control of confounding factors with the Cox proportional hazards regression model. With UO >0.5 as the referent group, the hazards ratios for UO 0.3-0.5 and UO ≤0.3 were 1.41 (95 % CI 1.29-1.54) and 1.52 (95 % CI 1.38-1.67), respectively. UO obtained on ICU entry is an independent predictor of mortality irrespective of diuretic use. It would be interesting to examine whether strategies to increase UO would improve clinical outcome.

Structure of complexes of uranyl succinate with carbamide and dimethylurea

NASA Astrophysics Data System (ADS)

Serezhkina, L. B.; Grigor'ev, M. S.; Seliverstova, N. V.; Serezhkin, V. N.

2017-09-01

Three new succinate-containing complexes of uranyl with carbamide ( Urea) and N,N'-dimethylurea ( s-Dmur) are synthesized and studied by IR spectroscopy and X-ray diffraction. Structures of the same type, [UO2( Urea)4(H2O)][(UO2)2(C4H4O4)3] · 3H2O and [UO2( Urea)4(H2O)][(UO2)2(C4H4O4)3] · 2 Urea contain two sorts of uranium-containing complex groups, namely, mononuclear [UO2( Urea)4(H2O)]2+ cations and two-dimensional [(UO2)2(C4H4O4)3]2- anions described by crystal-chemical formulas AM 5 1 and A 2 Q 3 02, respectively ( A = UO2 2+, M 1 = Urea or H2O, Q 02 = C4H4O4 2-), and differ only in the nature of noncoordinated molecules—water and carbamide. The main structural groups of the [(UO2)2(C4H4O4)2( s-Dmur)3] crystals are [(UO2)2(C4H4O4)2( s-Dmur)3] chains belonging to the A 2 Q 2 02 M 3 1 ( A = UO2 2+, Q 02 = C4H4O4 2-, M 1 = s-Dmur) crystal-chemical group. Specific features of intermolecular interactions in the crystal structures are revealed using the Voronoi-Dirichlet method of molecular polyhedra.

Severe anemia in cats with urethral obstruction: 17 cases (2002-2011).

PubMed

Beer, Kari Santoro; Drobatz, Kenneth J

2016-05-01

To characterize clinical parameters of cats with severe anemia due to suspected urinary bladder hemorrhage associated with urethral obstruction. Retrospective case-control study. University teaching hospital. Seventeen cats with urethral obstruction and severe anemia (group "UO-A") that required transfusion were identified via medical record database search. Thirty cats with urethral obstruction and mild or no anemia (group "UO") were included as controls. None. The median PCV of all cases at presentation was 28% (range, 9%-47%). Seven cats had PCV ≤20% at presentation, and all transfused cats had PCV ≤20% at the time of transfusion. Three cats did not receive a transfusion despite PCV ≤18%. Cats in the UO-A group had a significantly longer duration of clinical signs (P = 0.001), and were more likely to have a history of previous urethral obstruction (P = 0.011), have a heart murmur (P = 0.002), have a gallop rhythm (P = 0.005), and have lower blood pressure (P = 0.007) compared to those in the UO group. Additionally, UO-A cats had significantly lower pH, more negative base excess, higher BUN, and higher creatinine compared to UO cats. Duration of urinary catheterization was significantly (P = 0.016) longer in UO-A cats. All UO cats survived to discharge, whereas 4/17 (23.5%) UO-A cats were euthanized (P = 0.013). A history of previous urethral obstruction and longer duration of clinical signs may be important risk factors for severe anemia in UO cats. Additionally, UO-A cats appeared to be more severely affected, as evidenced by lower blood pressure, more severe metabolic acidosis, higher BUN and creatinine, and worse outcome. © Veterinary Emergency and Critical Care Society 2016.

Hydrothermal syntheses, structures, and properties of the new uranyl selenites Ag(2)(UO(2))(SeO(3))(2), M[(UO(2))(HSeO(3))(SeO(3))] (M = K, Rb, Cs, Tl), and Pb(UO(2))(SeO(3))(2).

PubMed

Almond, Philip M; Albrecht-Schmitt, Thomas E

2002-03-11

The transition metal, alkali metal, and main group uranyl selenites, Ag(2)(UO(2))(SeO(3))(2) (1), K[(UO(2))(HSeO(3))(SeO(3))] (2), Rb[(UO(2))(HSeO(3))(SeO(3))] (3), Cs[(UO(2))(HSeO(3))(SeO(3))] (4), Tl[(UO(2))(HSeO(3))(SeO(3))] (5), and Pb(UO(2))(SeO(3))(2) (6), have been prepared from the hydrothermal reactions of AgNO(3), KCl, RbCl, CsCl, TlCl, or Pb(NO(3))(2) with UO(3) and SeO(2) at 180 degrees C for 3 d. The structures of 1-5 contain similar [(UO(2))(SeO(3))(2)](2-) sheets constructed from pentagonal bipyramidal UO(7) units that are joined by bridging SeO(3)(2-) anions. In 1, the selenite oxo ligands that are not utilized within the layers coordinate the Ag(+) cations to create a three-dimensional network structure. In 2-5, half of the selenite ligands are monoprotonated to yield a layer composition of [(UO(2))(HSeO(3))(SeO(3))](1-), and coordination of the K(+), Rb(+), Cs(+), and Tl(+) cations occurs through long ionic contacts. The structure of 6 contains a uranyl selenite layered substructure that differs substantially from those in 1-5 because the selenite anions adopt both bridging and chelating binding modes to the uranyl centers. Furthermore, the Pb(2+) cations form strong covalent bonds with these anions creating a three-dimensional framework. These cations occur as distorted square pyramidal PbO(5) units with stereochemically active lone pairs of electrons. These polyhedra align along the c-axis to create a polar structure. Second-harmonic generation (SHG) measurements revealed a response of 5x alpha-quartz for 6. The diffuse reflectance spectrum of 6 shows optical transitions at 330 and 440 nm. The trailing off of the 440 nm transition to longer wavelengths is responsible for the orange coloration of 6.

Synthesis and crystal structure of two new uranyl oxychloro-vanadate layered compounds: M7(UO 2) 8(VO 4) 2O 8Cl with M=Rb, Cs

NASA Astrophysics Data System (ADS)

Duribreux, I.; Saadi, M.; Obbade, S.; Dion, C.; Abraham, F.

2003-05-01

Two new alkali uranyl oxychloro vanadates M7(UO 2) 8(VO 4) 2O 8Cl with M=Rb, Cs, have been synthesized by solid-state reactions and their structures determined from single-crystal X-ray diffraction data. They crystallize in the orthorhombic system with space groups Pmcn and Pmmn, respectively. The a and b unit cell parameters are almost identical in both compounds while the c parameter in the Rb compound is doubled: Rb— a=21.427(5) Å, b=11.814(3) Å, c=14.203(3) Å, V=3595.1(1) Å 3, Z=4, ρmes=5.93(2) g/cm 3, ρcal=5.82(1) g/cm 3; Cs— a=21.458(3) Å, b=11.773(2) Å, c=7.495(1) Å, V=1893.6(5) Å 3, Z=2, ρmes=6.09(2) g/cm 3, ρcal=6.11(1) g/cm 3. A full-matrix least-squares refinement yielded R1=0.0221, w R2=0.0562 for 2675 independent reflections and R1=0.0386, w R2=0.1042 for 2446 independent reflections, for the Rb and Cs compounds, respectively. Data were collected with Mo( Kα) radiation and a charge coupled device (CCD) detector of a Bruker diffractometer. Both structures are characterized by [(UO 2) 8(VO 4) 2O 8Cl] n7 n- layers parallel to the (001) plane. The layers are built up from VO 4 tetrahedra, UO 7 and UO 6Cl pentagonal bipyramids, and UO 6 distorded octahedra. The UO 7 and UO 6Cl pentagonal bipyramids are associated by sharing opposite equatorial edges to form infinite chains (UO 5-UO 4Cl-UO 5) n parallel to the a axis. These chains are linked together by VO 4 tetrahedra, UO 6 octahedra, UO 7 corner sharing and UO 6Cl, Cl sharing. Both structures differ simply by the symmetry of the layers. The unit cell contains one centrosymmetric layer in the Cs compound, whereas in the two-layer unit cell of the Rb compound, two non-centrosymmetric consecutive layers are related by an inversion center. The layers appear to be held together by the alkali ions. The mobility of the M+ ions within the interlayer space in M7(UO 2) 8(VO 4) 2O 8Cl and carnotite analog compounds is compared.

METHOD OF PREPARING A CERAMIC FUEL ELEMENT

DOEpatents

Ross, W.T.; Bloomster, C.H.; Bardsley, R.E.

1963-09-01

A method is described for preparing a fuel element from -325 mesh PuO/ sub 2/ and -20 mesh UO/sub 2/, and the steps of screening --325 mesh UO/sub 2/ from the -20 mesh UO/sub 2/, mixing PuO/sub 2/ with the --325 mesh UO/sub 2/, blending this mixture with sufficient --20 mesh UO/sub 2/ to obtain the desired composition, introducing the blend into a metal tube, repeating the procedure until the tube is full, and vibrating the tube to compact the powder are included. (AEC)

PROCESS FOR THE PRODUCTION OF AN ACTIVATED FORM OF UO$sub 2$

DOEpatents

Polissar, M.J.

1957-09-24

A process for producing a highly active form of UO/sub 2/ characterized both by rapid oxidation in air and by rapid chlorination with CCl/sub 4/ vapor at an elevated temperature is reported. In accordance with the process, commercial UO/sub 2/, is subjected to a series of oxidation-reduction operations to produce a form of UC/sub 2/ of enhanced reactivity. By treatimg commercial UO/sub 2/ at a temperature between 335 and 485 deg C with methane, then briefly with an oxygen containing gas and followimg this by a second treatment with a methane containing gas, the original relatively stable charge of UO/sub 2/ will be transformed into an active form of UO/sub 2/.

Coordination trends in alkali metal crown ether uranyl halide complexes: the series [A(crown)]2[UO(2)X(4)] where A=Li, Na, K and X=Cl, Br.

PubMed

Danis, J A; Lin, M R; Scott, B L; Eichhorn, B W; Runde, W H

2001-07-02

UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory.

Syntheses and crystal structures of two topologically related modifications of Cs(2)[(UO(2))(2)(MoO(4))(3)].

PubMed

Krivovichev, S V; Cahill, C L; Burns, P C

2002-01-14

Two polymorphs of Cs(2)(UO(2))(2)(MoO(4))(3) have been synthesized by hydrothermal (alpha-phase) and high-temperature (beta-phase) routes. Both were characterized by single-crystal X-ray diffraction: alpha-Cs(2)(UO(2))(2)(MoO(4))(3), orthorhombic, Pna2(1), a = 20.4302(15) A, b = 8.5552(7) A, c = 9.8549(7) A, Z = 4; beta-Cs(2)(UO(2))(2)(MoO(4))(3), tetragonal, P4(2)/n, a = 10.1367(8) A, c = 16.2831(17) A, Z = 4. The structures of both phases consist of linked UO(7) pentagonal bipyramids and MoO(4) tetrahedra: alpha-Cs(2)(UO(2))(2)(MoO(4))(3) is a framework compound with large channels parallel to the c axis. Two cesium sites are located in these channels and are coordinated by 8 and 10 oxygen atoms. The structure of beta-Cs(2)(UO(2))(2)(MoO(4))(3) contains corrugated [(UO(2))(2)(MoO(4))(3)] sheets that are parallel to (001). The cesium cations are located between the sheets and are coordinated by eight oxygen atoms. The structures are topologically related; both can be described in terms of chains of 5-connected UO(7) pentagonal bipyramids and 3- and 4-connected MoO(4) tetrahedra.

China’s Grand Strategy: From Confucius to Contemporary

DTIC Science & Technology

2010-02-02

DISTRIBUTION STATEMENT A: Approved for Public Release. Distribution is Unlimited. Only a work of the United States Government is not subject to...copyright. Based upon the nature of a particular student-author’s employment, a paper may not be a work of the United States Government and may, in fact...Brigadier Subrata Saha 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER Dr Janeen M. Klinger 7. PERFORMING

JPRS Report, China

DTIC Science & Technology

1989-06-14

Wensheng are still single and unmarried . Zhang Hanzhi [4545 0698 0037], the third woman in this group, came from a well-known family. Her father, Zhang...also a "senior translator" originally, who later married Qiao Guanhua [0829 0385 5478]. The Background for Criticizing Lin [Biao], Confucius, and...hopes on reform of the ownership system instead. But can the problem of millions who have jobs but are "unem- ployed" and millions who are still

Design and synthesis of target-responsive hydrogel for portable visual quantitative detection of uranium with a microfluidic distance-based readout device.

PubMed

Huang, Yishun; Fang, Luting; Zhu, Zhi; Ma, Yanli; Zhou, Leiji; Chen, Xi; Xu, Dunming; Yang, Chaoyong

2016-11-15

Due to uranium's increasing exploitation in nuclear energy and its toxicity to human health, it is of great significance to detect uranium contamination. In particular, development of a rapid, sensitive and portable method is important for personal health care for those who frequently come into contact with uranium ore mining or who investigate leaks at nuclear power plants. The most stable form of uranium in water is uranyl ion (UO2(2+)). In this work, a UO2(2+) responsive smart hydrogel was designed and synthesized for rapid, portable, sensitive detection of UO2(2+). A UO2(2+) dependent DNAzyme complex composed of substrate strand and enzyme strand was utilized to crosslink DNA-grafted polyacrylamide chains to form a DNA hydrogel. Colorimetric analysis was achieved by encapsulating gold nanoparticles (AuNPs) in the DNAzyme-crosslinked hydrogel to indicate the concentration of UO2(2+). Without UO2(2+), the enzyme strand is not active. The presence of UO2(2+) in the sample activates the enzyme strand and triggers the cleavage of the substrate strand from the enzyme strand, thereby decreasing the density of crosslinkers and destabilizing the hydrogel, which then releases the encapsulated AuNPs. As low as 100nM UO2(2+) was visually detected by the naked eye. The target-responsive hydrogel was also demonstrated to be applicable in natural water spiked with UO2(2+). Furthermore, to avoid the visual errors caused by naked eye observation, a previously developed volumetric bar-chart chip (V-Chip) was used to quantitatively detect UO2(2+) concentrations in water by encapsulating Au-Pt nanoparticles in the hydrogel. The UO2(2+) concentrations were visually quantified from the travelling distance of ink-bar on the V-Chip. The method can be used for portable and quantitative detection of uranium in field applications without skilled operators and sophisticated instruments. Copyright © 2016 Elsevier B.V. All rights reserved.

A spectroscopic study of uranyl speciation in chloride-bearing solutions at temperatures up to 250 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Migdisov, A. A.; Boukhalfa, H.; Timofeev, A.

The speciation of U in NaCl-bearing solutions at temperatures up to 250 °C and concentrations of NaCl up to 1.5 m has been investigated using an in situ spectroscopic technique. The recorded spectra permit us to identify the species present in the solutions as UO 2 2+, UO 2Cl +, and UO 2Cl 2°. UO 2Cl 3 - is also likely present at high temperatures and NaCl concentrations, but concentrations of this species are insufficient for derivation of the formation constants. No evidence was found for species of higher ligand (Cl-) number. Thermodynamic stability constants derived for these species showmore » fair agreement with published data for 25 °C, but differ significantly from those predicted by an earlier high-temperature study (Dargent et al., 2013), which suggested that UO 2Cl 4 2- and UO 2Cl 5 3- contribute significantly to the mass balance of uranyl chloride complexes, especially at high temperature. In contrast, our data suggest that the main uranyl-chloride complex present in aqueous solutions at T >150 °C and concentrations of NaCl relevant to natural hydrothermal systems is UO 2Cl 2°. The values of the logarithms of thermodynamic formation constants (β) for the reaction UO 2 2+ + Cl - = UO 2Cl + are 0.02, 0.25, 0.55, 1.09, 1.59, and 2.28 derived at 25, 50, 100, 150, 200, and 250 °C, respectively. For the reaction UO 2 2+ + 2Cl - = UO 2Cl 2° the values of log β derived at these temperatures are 0.4, 0.58, 0.74, 1.44, 2.18, and 3.42. Values of the formation constant estimated for uranyl-chloride species predict the high concentrations of U observed by Richard et al. (2011) in fluid inclusions of the giant McArthur River unconformity-type uranium deposit.« less

A spectroscopic study of uranyl speciation in chloride-bearing solutions at temperatures up to 250 °C

DOE PAGES

Migdisov, A. A.; Boukhalfa, H.; Timofeev, A.; ...

2017-10-24

The speciation of U in NaCl-bearing solutions at temperatures up to 250 °C and concentrations of NaCl up to 1.5 m has been investigated using an in situ spectroscopic technique. The recorded spectra permit us to identify the species present in the solutions as UO 2 2+, UO 2Cl +, and UO 2Cl 2°. UO 2Cl 3 - is also likely present at high temperatures and NaCl concentrations, but concentrations of this species are insufficient for derivation of the formation constants. No evidence was found for species of higher ligand (Cl-) number. Thermodynamic stability constants derived for these species showmore » fair agreement with published data for 25 °C, but differ significantly from those predicted by an earlier high-temperature study (Dargent et al., 2013), which suggested that UO 2Cl 4 2- and UO 2Cl 5 3- contribute significantly to the mass balance of uranyl chloride complexes, especially at high temperature. In contrast, our data suggest that the main uranyl-chloride complex present in aqueous solutions at T >150 °C and concentrations of NaCl relevant to natural hydrothermal systems is UO 2Cl 2°. The values of the logarithms of thermodynamic formation constants (β) for the reaction UO 2 2+ + Cl - = UO 2Cl + are 0.02, 0.25, 0.55, 1.09, 1.59, and 2.28 derived at 25, 50, 100, 150, 200, and 250 °C, respectively. For the reaction UO 2 2+ + 2Cl - = UO 2Cl 2° the values of log β derived at these temperatures are 0.4, 0.58, 0.74, 1.44, 2.18, and 3.42. Values of the formation constant estimated for uranyl-chloride species predict the high concentrations of U observed by Richard et al. (2011) in fluid inclusions of the giant McArthur River unconformity-type uranium deposit.« less

A spectroscopic study of uranyl speciation in chloride-bearing solutions at temperatures up to 250 °C

NASA Astrophysics Data System (ADS)

Migdisov, A. A.; Boukhalfa, H.; Timofeev, A.; Runde, W.; Roback, R.; Williams-Jones, A. E.

2018-02-01

The speciation of U in NaCl-bearing solutions at temperatures up to 250 °C and concentrations of NaCl up to 1.5 m has been investigated using an in situ spectroscopic technique. The recorded spectra permit us to identify the species present in the solutions as UO22+, UO2Cl+, and UO2Cl2°. UO2Cl3- is also likely present at high temperatures and NaCl concentrations, but concentrations of this species are insufficient for derivation of the formation constants. No evidence was found for species of higher ligand (Cl-) number. Thermodynamic stability constants derived for these species show fair agreement with published data for 25 °C, but differ significantly from those predicted by an earlier high-temperature study (Dargent et al., 2013), which suggested that UO2Cl42- and UO2Cl53- contribute significantly to the mass balance of uranyl chloride complexes, especially at high temperature. In contrast, our data suggest that the main uranyl-chloride complex present in aqueous solutions at T > 150 °C and concentrations of NaCl relevant to natural hydrothermal systems is UO2Cl2°. The values of the logarithms of thermodynamic formation constants (β) for the reaction UO22+ + Cl- = UO2Cl+ are 0.02, 0.25, 0.55, 1.09, 1.59, and 2.28 derived at 25, 50, 100, 150, 200, and 250 °C, respectively. For the reaction UO22+ + 2Cl- = UO2Cl2° the values of log β derived at these temperatures are 0.4, 0.58, 0.74, 1.44, 2.18, and 3.42. Values of the formation constant estimated for uranyl-chloride species predict the high concentrations of U observed by Richard et al. (2011) in fluid inclusions of the giant McArthur River unconformity-type uranium deposit.

Structural studies of the rhombohedral and orthorhombic monouranates: CaUO{sub 4}, α-SrUO{sub 4}, β-SrUO{sub 4} and BaUO{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, Gabriel; Kennedy, Brendan J., E-mail: kennedyb@chem.usyd.edu.au; Johannessen, Bernt

The structures of some AUO{sub 4} (A=Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L{sub 3}-edge. The smaller Ca cation favours a rhombohedral AUO{sub 4} structure with 8-coordinate UO{sub 8} moieties whilst an orthorhombic structure based on UO{sub 6} groups is found for BaUO{sub 4}. Both the rhombohedral and orthorhombic structures can be stabilised for SrUO{sub 4}. The structural studies suggest that the bonding requirements of the A site cation play a significant role in determining which structure is favoured. In themore » rhombohedral structure, Bond Valence Sums demonstrate the A site is invariably overbonded, which, in the case of rhombohedral α-SrUO{sub 4}, is compensated for by the formation of vacancies in the oxygen sub-lattice. The uranium cation, with its flexible oxidation state, is able to accommodate this by inducing vacancies along its equatorial coordination site as demonstrated by neutron powder diffraction. - Graphical abstract: Diffraction studies of AUO{sub 4} (A = Ca, Sr, or Ba) oxides reveal the importance of the bonding requirements of the A site cation in determining whether the structure is rhombohedral or orthorhombic. - Highlights: • Structures of AUO{sub 4} ( A = Ca Sr, Ba) refined against X-ray and Neutron diffraction. • The alkali cations size has a dramatic effect on the crystal structure. • Smaller cations favouring a rhombohedral structure. • Oxygen vacancies to stabilise the rhombohedral structure in SrUO{sub 4}.« less

Hydrogen suppresses UO 2 corrosion

NASA Astrophysics Data System (ADS)

Carbol, Paul; Fors, Patrik; Gouder, Thomas; Spahiu, Kastriot

2009-08-01

Release of long-lived radionuclides such as plutonium and caesium from spent nuclear fuel in deep geological repositories will depend mainly on the dissolution rate of the UO 2 fuel matrix. This dissolution rate will, in turn, depend on the redox conditions at the fuel surface. Under oxidative conditions UO 2 will be oxidised to the 1000 times more soluble UO 2.67. This may occur in a repository as the reducing deep groundwater becomes locally oxidative at the fuel surface under the effect of α-radiolysis, the process by which α-particles emitted from the fuel split water molecules. On the other hand, the groundwater corrodes canister iron generating large amounts of hydrogen. The role of molecular hydrogen as reductant in a deep bedrock repository is questioned. Here we show evidence of a surface-catalysed reaction, taking place in the H 2-UO 2-H 2O system where molecular hydrogen is able to reduce oxidants originating from α-radiolysis. In our experiment the UO 2 surface remained stoichiometric proving that the expected oxidation of UO 2.00 to UO 2.67 due to radiolytic oxidants was absent. As a consequence, the dissolution of UO 2 stopped when equilibrium was reached between the solid phase and U 4+ species in the aqueous phase. The steady-state concentration of uranium in solution was determined to be 9 × 10 -12 M, about 30 times lower than previously reported for reducing conditions. Our findings show that fuel dissolution is suppressed by H 2. Consequently, radiotoxic nuclides in spent nuclear fuel will remain immobilised in the UO 2 matrix. A mechanism for the surface-catalysed reaction between molecular hydrogen and radiolytic oxidants is proposed.

Molten uranium dioxide structure and dynamics

DOE PAGES

Skinner, L. B.; Parise, J. B.; Benmore, C. J.; ...

2014-11-21

Uranium dioxide (UO 2) is the major nuclear fuel component of fission power reactors. A key concern during severe accidents is the melting and leakage of radioactive UO 2 as it corrodes through its zirconium cladding and steel containment. Yet, the very high temperatures (>3140 kelvin) and chemical reactivity of molten UO 2 have prevented structural studies. In this work, we combine laser heating, sample levitation, and synchrotron x-rays to obtain pair distribution function measurements of hot solid and molten UO 2. The hot solid shows a substantial increase in oxygen disorder around the lambda transition (2670 K) but negligiblemore » U-O coordination change. On melting, the average U-O coordination drops from 8 to 6.7 ± 0.5. Molecular dynamics models refined to this structure predict higher U-U mobility than 8-coordinated melts.« less

Antiferromagnetic-ferromagnetic crossover in UO 2-TiO x multi-phase systems

NASA Astrophysics Data System (ADS)

Nakamura, Akio; Tsutsui, Satoshi; Yoshii, Kenji

2001-05-01

An antiferromagnetic (AF)-weakly ferromagnetic (WF) crossover has been found for UO 2-TiO x multi-phase systems, (1- y)UO 2+ yTiO x ( y=0.05-0.72, x=0, 1.0, 1.5 and 2.0), when these mixtures are heat treated at high temperature in vacuum. From the powder X-ray diffraction and electron-microprobe analyses, their phase assemblies were as follows: for x=0, 1.0 and 1.5, a heterogeneous two-phase mixture of UO 2+TiO x; for x=2.0, that of UO 2+UTi 2O 6 for y<0.67, showing characteristic microstructures, and for y>0.67 that of UTi 2O 6+TiO 2 (plus residual minor UO 2). Magnetic susceptibility ( χ) of the present UO 2 powder was confirmed to exhibit an antiferromagnetic sharp drop at TN (=30.5 K). In contrast, χ of these multi-phase systems was found to exhibit a sharp upturn at the respective TN, while their TN values remained almost constant with varying y. This χ upturn at TN is most pronounced for UO 2+Ti-oxide (titania) systems ( x=1.0, 1.5 and 2.0) over the wide mixture ratio above y˜0.10. These observations indicate that an AF-WF crossover is induced for these multi-phase systems, plausibly due to the interfacial magnetic modification of UO 2 in contact with the oxide partners.

Molecular dynamics simulation of the diffusion of uranium species in clay pores.

PubMed

Liu, Xiao-yu; Wang, Lu-hua; Zheng, Zhong; Kang, Ming-liang; Li, Chun; Liu, Chun-li

2013-01-15

Molecular dynamics simulations were carried out to investigate the diffusive behavior of aqueous uranium species in montmorillonite pores. Three uranium species (UO(2)(2+), UO(2)CO(3), UO(2)(CO(3))(2)(2-)) were confirmed in both the adsorbed and diffuse layers. UO(2)(CO(3))(3)(4-) was neglected in the subsequent analysis due to its scare occurrence. The species-based diffusion coefficients in montmorillonite pores were then calculated, and compared with the water mobility and their diffusivity in aqueous solution/feldspar nanosized fractures. Three factors were considered that affected the diffusive behavior of the uranium species: the mobility of water, the self-diffusion coefficient of the aqueous species, and the electrostatic forces between the negatively charged surface and charged molecules. The mobility of U species in the adsorbed layer decreased in the following sequence: UO(2)(2+)>UO(2)CO(3)>UO(2)(CO(3))(2)(2-). In the diffuse layer, we obtained the highest diffusion coefficient for UO(2)(CO(3))(2)(2-) with the value of 5.48×10(-10) m(2) s(-1), which was faster than UO(2)(2+). For these two charged species, the influence of electrostatic forces on the diffusion of solutes in the diffuse layer is overwhelming, whereas the influence of self-diffusion and water mobility is minor. Our study demonstrated that the negatively charged uranyl carbonate complex must be addressed in the safety assessment of potential radioactive waste disposal systems. Copyright © 2012 Elsevier B.V. All rights reserved.

First identification and thermodynamic characterization of the ternary U(VI) species, UO2(O2)(CO3)2(4-), in UO2-H2O2-K2CO3 solutions.

PubMed

Goff, George S; Brodnax, Lia F; Cisneros, Michael R; Peper, Shane M; Field, Stephanie E; Scott, Brian L; Runde, Wolfgang H

2008-03-17

In alkaline carbonate solutions, hydrogen peroxide can selectively replace one of the carbonate ligands in UO2(CO3)3(4-) to form the ternary mixed U(VI) peroxo-carbonato species UO2(O2)(CO3)2(4-). Orange rectangular plates of K4[UO2(CO3)2(O2)].H2O were isolated and characterized by single crystal X-ray diffraction studies. Crystallographic data: monoclinic, space group P2(1)/ n, a = 6.9670(14) A, b = 9.2158(10) A, c = 18.052(4) A, Z = 4. Spectrophotometric titrations with H 2O 2 were performed in 0.5 M K 2CO 3, with UO2(O2)(CO3)2(4-) concentrations ranging from 0.1 to 0.55 mM. The molar absorptivities (M(-1) cm(-1)) for UO2(CO3)3(4-) and UO2(O2)(CO3)2(4-) were determined to be 23.3 +/- 0.3 at 448.5 nm and 1022.7 +/- 19.0 at 347.5 nm, respectively. Stoichiometric analyses coupled with spectroscopic comparisons between solution and solid state indicate that the stable solution species is UO2(O2)(CO3)2(4-), which has an apparent formation constant of log K' = 4.70 +/- 0.02 relative to the tris-carbonato complex.

Irradiation effects and micro-structural changes in large grain uranium dioxide fuel investigated by micro-beam X-ray diffraction

NASA Astrophysics Data System (ADS)

Mieszczynski, C.; Kuri, G.; Degueldre, C.; Martin, M.; Bertsch, J.; Borca, C. N.; Grolimund, D.; Delafoy, Ch.; Simoni, E.

2014-01-01

Microstructural changes in a set of commercial grade UO2 fuel samples have been investigated using synchrotron based micro-focused X-ray fluorescence (μ-XRF) and X-ray diffraction (μ-XRD) techniques. The results are associated with conventional UO2 materials and relatively larger grain chromia-doped UO2 fuels, irradiated in a commercial light water reactor plant (average burn-up: 40 MW d kg-1). The lattice parameters of UO2 in fresh and irradiated specimens have been measured and compared with theoretical predictions. In the pristine state, the doped fuel has a somewhat smaller lattice parameter than the standard UO2 as a result of chromia doping. Increase in micro-strain and lattice parameter in irradiated materials is highlighted. All irradiated samples behave in a similar manner with UO2 lattice expansion occurring upon irradiation, where any Cr induced effect seems insignificant and accumulated lattice defects prevail. Elastic strain energy densities in the irradiated fuels are also evaluated based on the UO2 crystal lattice strain and non-uniform strain. The μ-XRD patterns further allow the evaluation of the crystalline domain size and sub-grain formation at different locations of the irradiated UO2 pellets.

XPS studies of UO 2 oxidation by alpha radiolysis of water at 100°C

NASA Astrophysics Data System (ADS)

Sunder, S.; Boyer, G. D.; Miller, N. H.

1990-12-01

The effect of alpha radiolysis of water on the oxidation and dissolution of UO 2 was studied at 100°C as a function of alpha-field strength and water chemistry using X-ray photoelectron spectroscopy. In N 2-purged solutions the oxidation of UO 2 increases with the strength of the alpha flux; an alpha flux greater than or equal to that from a 250-μ Ci americium-241 source leads to oxidation of UO 2 beyond the UO 2.33 (U 3O 7) stage, and an alpha flux equal to that from a 5-μ Ci source does not result in UO 2 oxidation beyond the UO 2.33 stage. The presence of dissolved H 2 in water, at a concentration ≥ 1.6 × 10 -4moldm-3, reduces the oxidation and dissolution of UO 2 due to alpha radiolysis at temperatures ≥ 100° C. It is concluded that the radiolysis of groundwater at ~ 100°C, due to the alpha flux associated with used CANDU fuel, is unlikely to make a significant contribution to its oxidative dissolution in the geological disposal vault planned in the Canadian Nuclear Fuel Waste Management Program. CANada Deuterium Uranium. Registered trademark.

Photochemical reduction of UO(2)(2+) in the presence of alcohol studied by density functional theory calculations.

PubMed

Tsushima, Satoru

2009-06-01

A well-known photochemical process of U(VI)O(2)(2+) reduction to U(V)O(2)(+) in the presence of alcohols was studied by density functional theory (DFT) calculations. It was found that the first process which takes place is a photoexcitation of the ground-state UO(2)(2+) to the triplet excited state (*UO(2)(2+)) followed by a significant shortening of the *UO(2)(2+)-to-alcohol O(ax)-H distance. A charge transfer from *UO(2)(2+) to alcohol and hydrogen abstraction takes place in the following step. Consequently, U(VI)O(2)(2+) gets reduced to U(V)O(OH)(2+). The photochemical byproduct RCHOH acts further as a reducing agent toward UO(2)(2+) to yield UO(2)(+) and RCHO (aldehyde). Only a combination of these two reactions can explain a high quantum yield of this reaction. In the absence of alcohol, the lowest-lying triplet state exhibits a different character, and photoreduction is unlikely to take place via the same mechanism. The present results agree well with recent experimental finding [J. Am. Chem. Soc. 2006, 128, 14024] and supports the idea that the O(ax)-H linkage between UO(2)(2+) and the solvent molecule is the key to the photochemical reduction process.

[Effects of UO-126 on proliferation and fbw7 expression of HeLa cells].

PubMed

Sun, Di; Shen, Yi; Wang, Shao-hua; Xiang, Zi-wu; Xie, Ying-shan; Jiang, Xin

2010-02-01

To observe the effects of UO-126 on the expression of F-box and WD repeat domain-containing protein 7(FBW7)and on the proliferation of human cervical cancer cell lines (HeLa cells). HeLa cells were treated with different concentrations of UO-126, MTT assay was used to observe the proliferation of HeLa cells. Immunofluorescence showed the location and expression of FBW7 in HeLa cells. The mRNA and protein expression of FBW7 were detected by RT-PCR and Western blot before and after mitogen-activated protein kinases (MAPK)signal was blocked by UO-126 a MAPK inhibitor. MTT results showed that the concentration range of MAPK signaling pathway inhibitor UO-126 inhibited the proliferation of HeLa cells in a concentration-and time-dependent manner(P<0.05). Immunofluorescence showed that the expression of positive FBW7 had increased after HeLa cells were treated with UO-126. RT-PCR and Western blot exhibited that the FBW7 mRNA and protein expression had significantly increased before and after HeLa cells were treated with UO-126(P<0.05). UO-126 could inhibit HeLa cells proliferation, FBW7 lied downstream of MAPK signaling pathway.

U(v) in metal uranates: A combined experimental and theoretical study of MgUO 4, CrUO 4, and FeUO 4

DOE PAGES

Guo, Xiaofeng; Tiferet, Eitan; Qi, Liang; ...

2016-01-01

Although pentavalent uranium can exist in aqueous solution, its presence in the solid state is uncommon. Metal monouranates, MgUO 4, CrUO 4 and FeUO 4 were synthesized for detailed structural and energetic investigations. Structural characteristics of these uranates used powder X-ray diffraction, synchrotron X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe-Mossbauer spectroscopy. Enthalpies of formation were measured by high temperature oxide melt solution calorimetry. Density functional theory (DFT) calculations provided both structural and energetic information. The measured structural and thermodynamic properties show good consistency with those predicted from DFT. The presence of U 5+ has been solidly confirmed in CrUOmore » 4 and FeUO 4, which are thermodynamically stable compounds, and the origin and stability of U 5+ in the system was elaborated by DFT. Lastly, the structural and thermodynamic behaviour of U 5+ elucidated in this work is relevant to fundamental actinide redox chemistry and to applications in the nuclear industry and radioactive waste disposal.« less

Development of Innovative Accident Tolerant High Thermal Conductivity UO 2-Diamond Composite Fuel Pellets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tulenko, James; Subhash, Ghatu

2016-01-01

The University of Florida (UF) evaluated a composite fuel consisting of UO 2 powder mixed with diamond micro particles as a candidate as an accident-tolerant fuel (ATF). The research group had previous extensive experience researching with diamond micro particles as an addition to reactor coolant for improved plant thermal performance. The purpose of this research work was to utilize diamond micro particles to develop UO 2-Diamond composite fuel pellets with significantly enhanced thermal properties, beyond that already being measured in the previous UF research projects of UO 2 – SiC and UO 2 – Carbon Nanotube fuel pins. UF ismore » proving with the current research results that the addition of diamond micro particles to UO 2 may greatly enhanced the thermal conductivity of the UO 2 pellets producing an accident-tolerant fuel. The Beginning of life benefits have been proven and fuel samples are being irradiated in the ATR reactor to confirm that the thermal conductivity improvements are still present under irradiation.« less

10 CFR Appendix J to Part 110 - Illustrative List of Uranium Conversion Plant Equipment and Plutonium Conversion Plant Equipment...

Code of Federal Regulations, 2013 CFR

2013-01-01

... cracked ammonia gas or hydrogen. (4) Especially Designed or Prepared Systems for the conversion of UO2 to UF4. Conversion of UO2 to UF4 can be performed by reacting UO2 with hydrogen fluoride gas (HF) at 300... hydrolyzed to UO2 using hydrogen and steam. In the second, UF6 is hydrolyzed by solution in water, ammonia is...

10 CFR Appendix J to Part 110 - Illustrative List of Uranium Conversion Plant Equipment and Plutonium Conversion Plant Equipment...

Code of Federal Regulations, 2012 CFR

2012-01-01

... cracked ammonia gas or hydrogen. (4) Especially Designed or Prepared Systems for the conversion of UO2 to UF4. Conversion of UO2 to UF4 can be performed by reacting UO2 with hydrogen fluoride gas (HF) at 300... UO2 using hydrogen and steam. In the second, UF6 is hydrolyzed by solution in water, ammonia is added...

10 CFR Appendix J to Part 110 - Illustrative List of Uranium Conversion Plant Equipment and Plutonium Conversion Plant Equipment...

Code of Federal Regulations, 2014 CFR

2014-01-01

... cracked ammonia gas or hydrogen. (4) Especially Designed or Prepared Systems for the conversion of UO2 to UF4. Conversion of UO2 to UF4 can be performed by reacting UO2 with hydrogen fluoride gas (HF) at 300... hydrolyzed to UO2 using hydrogen and steam. In the second, UF6 is hydrolyzed by solution in water, ammonia is...

On the Role of the Electrical Field in Spark Plasma Sintering of UO2+x

PubMed Central

Tyrpekl, Vaclav; Naji, Mohamed; Holzhäuser, Michael; Freis, Daniel; Prieur, Damien; Martin, Philippe; Cremer, Bert; Murray-Farthing, Mairead; Cologna, Marco

2017-01-01

The electric field has a large effect on the stoichiometry and grain growth of UO2+x during Spark Plasma Sintering. UO2+x is gradually reduced to UO2.00 as a function of sintering temperature and time. A gradient in the oxidation state within the pellets is observed in intermediate conditions. The shape of the gradient depends unequivocally on the direction of the electrical field. The positive surface of the pellet shows a higher oxidation state compared to the negative one. An area with larger grain size is found close to the positive electrode, but not in contact with it. We interpret these findings with the redistribution of defects under an electric field, which affect the stoichiometry of UO2+x and thus the cation diffusivity. The results bear implications for understanding the electric field assisted sintering of UO2 and non-stoichiometric oxides in general. PMID:28422164

On the Role of the Electrical Field in Spark Plasma Sintering of UO2+x

NASA Astrophysics Data System (ADS)

Tyrpekl, Vaclav; Naji, Mohamed; Holzhäuser, Michael; Freis, Daniel; Prieur, Damien; Martin, Philippe; Cremer, Bert; Murray-Farthing, Mairead; Cologna, Marco

2017-04-01

The electric field has a large effect on the stoichiometry and grain growth of UO2+x during Spark Plasma Sintering. UO2+x is gradually reduced to UO2.00 as a function of sintering temperature and time. A gradient in the oxidation state within the pellets is observed in intermediate conditions. The shape of the gradient depends unequivocally on the direction of the electrical field. The positive surface of the pellet shows a higher oxidation state compared to the negative one. An area with larger grain size is found close to the positive electrode, but not in contact with it. We interpret these findings with the redistribution of defects under an electric field, which affect the stoichiometry of UO2+x and thus the cation diffusivity. The results bear implications for understanding the electric field assisted sintering of UO2 and non-stoichiometric oxides in general.

Chemical reactivity of CVC and CVD SiC with UO2 at high temperatures

NASA Astrophysics Data System (ADS)

Silva, Chinthaka M.; Katoh, Yutai; Voit, Stewart L.; Snead, Lance L.

2015-05-01

Two types of silicon carbide (SiC) synthesized using two different vapor deposition processes were embedded in UO2 pellets and evaluated for their potential chemical reaction with UO2. While minor reactivity between chemical-vapor-composited (CVC) SiC and UO2 was observed at comparatively low temperatures of 1100 and 1300 °C, chemical-vapor-deposited (CVD) SiC did not show any such reactivity. However, both CVD and CVC SiCs showed some reaction with UO2 at a higher temperature (1500 °C). Elemental maps supported by phase maps obtained using electron backscatter diffraction indicated that CVC SiC was more reactive than CVD SiC at 1500 °C. Furthermore, this investigation indicated the formation of uranium carbides and uranium silicide chemical phases such as UC, USi2, and U3Si2 as a result of SiC reaction with UO2.

Focus on China. Joint Force Quarterly, Issue 47, 4th Quarter 2007

DTIC Science & Technology

2007-01-01

and the informa- tion age —is creating a paper dragon. This issue of Joint Force Quarterly takes a look at China and Sino-U.S. engagement, as well...Golden Age because “forthwith, multitudes would resort to his dominions.”26 Confucius likened this dynamic almost to an irresistible force of...China’s support from an international perspective. China only recently became comfortable in its “liberal internationalist skin ,” but it has since

U(VI) uranyl cation-cation interactions in framework germanates.

PubMed

Morrison, Jessica M; Moore-Shay, Laura J; Burns, Peter C

2011-03-21

The isomorphous compounds NH(4)[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (1), K[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (2), Li(3)O[(UO(6))(2)(UO(2))(9)(GeO(4))(GeO(3)(OH))] (3), and Ba[(UO(6))(2)(UO(2))(9)(GeO(4))(2)] (4) were synthesized by hydrothermal reaction at 220 °C. The structures were determined using single crystal X-ray diffraction and refined to R(1) = 0.0349 (1), 0.0232 (2), 0.0236 (3), 0.0267 (4). Each are trigonal, P(3)1c. 1: a = 10.2525(5), c = 17.3972(13), V = 1583.69(16) Å(3), Z = 2; 2: a = 10.226(4), c = 17.150(9), V = 1553.1(12) Å(3), Z = 2; 3: a = 10.2668(5), c = 17.0558(11), V = 1556.94(15) Å(3), Z = 2; 4: a = 10.2012(5), c = 17.1570(12), V = 1546.23(15) Å(3), Z = 2. There are three symmetrically independent U sites in each structure, two of which correspond to typical (UO(2))(2+) uranyl ions and the other of which is octahedrally coordinated by six O atoms. One of the uranyl ions donates a cation-cation interaction, and accepts a different cation-cation interaction. The linkages between the U-centered polyhedra result in a relatively dense three-dimensional framework. Ge and low-valence sites are located within cavities in the framework of U-polyhedra. Chemical, thermal, and spectroscopic characterizations are provided.

Formation of ternary CaUO2(CO3)3(2-) and Ca2UO2(CO3)3(aq) complexes under neutral to weakly alkaline conditions.

PubMed

Lee, Jun-Yeop; Yun, Jong-Il

2013-07-21

The chemical behavior of ternary Ca-UO2-CO3 complexes was investigated by using time-resolved laser fluorescence spectroscopy (TRLFS) in combination with EDTA complexation at pH 7-9. A novel TRLFS revealed two distinct fluorescence lifetimes of 12.7 ± 0.2 ns and 29.2 ± 0.4 ns for uranyl complexes which were formed increasingly dependent upon the calcium ion concentration, even though nearly indistinguishable fluorescence peak shapes and positions were measured for both Ca-UO2-CO3 complexes. For identifying the stoichiometric number of complexed calcium ions, slope analysis in terms of relative fluorescence intensity versus calcium concentration was employed in a combination with the complexation reaction of CaEDTA(2-) by adding EDTA. The formation of CaUO2(CO3)3(2-) and Ca2UO2(CO3)3(aq) was identified under given conditions and their formation constants were determined at I = 0.1 M Na/HClO4 medium, and extrapolated to infinitely dilute solution using specific ion interaction theory (SIT). As a result, the formation constants for CaUO2(CO3)3(2-) and Ca2UO2(CO3)3(aq) were found to be log β113(0) = 27.27 ± 0.14 and log β213(0) = 29.81 ± 0.19, respectively, providing that the ternary Ca-UO2-CO3 complexes were predominant uranium(vi) species at neutral to weakly alkaline pH in the presence of Ca(2+) and CO3(2-) ions.

The effect of fuel chemistry on UO2 dissolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casella, Amanda; Hanson, Brady; Miller, William

2016-08-01

The dissolution rate of both unirradiated UO2 and used nuclear fuel has been studied by numerous countries as part of the performance assessment of proposed geologic repositories. In the scenario of waste package failure and groundwater infiltration into the fuel, the effects of variables such as temperature, dissolved oxygen, and water and fuel chemistry on the dissolution rates of the fuel are necessary to provide a quantitative estimate of the potential release over geologic time frames. The primary objective of this research was to determine the influence these parameters have on the dissolution rate of unirradiated UO2 under repository conditionsmore » and compare them to the rates predicted by current dissolution models. Both unirradiated UO2 and UO2 doped with varying concentrations of Gd2O3, to simulate used fuel composition after long time periods where radiolysis has minor contributions to dissolution, were examined. In general, a rise in temperature increased the dissolution rate of UO2 and had a larger effect on pure UO2 than on those doped with Gd2O3. Oxygen dependence was observed in the UO2 samples with no dopant and increased as the temperature rose; in the doped fuels less dependence was observed. The addition of gadolinia into the UO2 matrix showed a significant decrease in the dissolution rate. The matrix stabilization effect resulting from the dopant proved even more beneficial in lowering the dissolution rate at higher temperatures and dissolved O2 concentrations in the leachate where the rates would typically be elevated.« less

Liquid-liquid extraction of uranyl by TBP: the TBP and ions models and related interfacial features revisited by MD and PMF simulations.

PubMed

Benay, G; Wipff, G

2014-03-20

We report a molecular dynamics (MD) study of biphasic systems involved in the liquid-liquid extraction of uranyl nitrate by tri-n-butylphosphate (TBP) to hexane, from "pH neutral" or acidic (3 M nitric acid) aqueous solutions, to assess the model dependence of the surface activity and partitioning of TBP alone, of its UO2(NO3)2(TBP)2 complex, and of UO2(NO3)2 or UO2(2+) uncomplexed. For this purpose, we first compare several electrostatic representations of TBP with regards to its polarity and conformational properties, its interactions with H2O, HNO3, and UO2(NO3)2 species, its relative free energies of solvation in water or oil environments, the properties of the pure TBP liquid and of the pure-TBP/water interface. The free energies of transfer of TBP, UO2(NO3)2, UO2(2+), and the UO2(NO3)2(TBP)2 complex across the water/oil interface are then investigated by potential of mean force (PMF) calculations, comparing different TBP models and two charge models of uranyl nitrate. Describing uranyl and nitrate ions with integer charges (+2 and -1, respectively) is shown to exaggerate the hydrophilicity and surface activity of the UO2(NO3)2(TBP)2 complex. With more appropriate ESP charges, mimicking charge transfer and polarization effects in the UO2(NO3)2 moiety or in the whole complex, the latter is no more surface active. This feature is confirmed by MD, PMF, and mixing-demixing simulations with or without polarization. Furthermore, with ESP charges, pulling the UO2(NO3)2 species to the TBP phase affords the formation of UO2(NO3)2(TBP)2 at the interface, followed by its energetically favorable extraction. The neutral complexes should therefore not accumulate at the interface during the extraction process, but diffuse to the oil phase. A similar feature is found for an UO2(NO3)2(Amide)2 neutral complex with fatty amide extracting ligands, calling for further simulations and experimental studies (e.g., time evolution of the nonlinear spectroscopic signature and of surface tension) on the interfacial landscape upon ion extraction.

Calorimetric determination of energetics of solid solutions of UO 2+ x with CaO and Y 2O 3

NASA Astrophysics Data System (ADS)

Mazeina, Lena; Navrotsky, Alexandra; Greenblatt, Martha

2008-02-01

Quantitative study of thermodynamic properties of solid solutions of UO 2+ x with divalent and trivalent oxides is important for predicting the behavior of oxide fuel. Although early literature work measured vapor pressure in some of these solid solutions, direct calorimetric measurements of enthalpies of formation have been hampered by the refractory nature of such oxides. First measurements of the enthalpies of formation in the systems UO 2+ x-CaO and UO 2+ x-YO 1.5, obtained by high-temperature oxide melt solution calorimetry, are reported. Both systems show significantly negative (exothermic) heats of formation from binary oxides (UO 2, plus O 2 and CaO or YO 1.5, as well as from UO 2 plus UO 3 and CaO or YO 1.5), consistent with reported free energy measurements in the urania-yttria system. The energetic contributions of oxygen content (oxidation of U 4+) and of charge balanced ionic substitution as well as defect clustering are discussed. Behavior of urania-yttria is compared to that of corresponding systems in which the tetravalent ion is Ce, Zr, or Hf. The substantial additional stability in the solid solutions compared to pure UO 2+ x may retard, in both thermodynamic and kinetic sense, the oxidation and leaching of spent fuel to form aqueous U 6+ and solid uranyl phases.

Matrix isolation infrared spectra of O2 and N2 insertion reactions with atomic uranium

NASA Astrophysics Data System (ADS)

Hunt, Rodney D.; Toth, L. Mac; Yustein, Jason T.; Andrews, Lester

1993-10-01

Laser ablation of refractory metals can be an effective source of vapor for matrix isolation IR studies. This combination of techniques was used for the first time to study the mechanisms of U vapor reactions with atmospheric components. U atoms and O2 were codeposited with excess Ar at 12 K. The dominant codeposition products were UO2 and UO3. In contrast, the UO yield was always small because UO2 is formed by an insertion mechanism. This mechanism was verified in the 16O2/18O2 experiments which failed to produce 16OU18O. The effects of UV photolysis and matrix annealings were also examined. The U atoms and O2 reaction requires little or no activation energy since UO2 was formed from cold reagents. New charge-transfer species, (UO2+2)(O2-2) and (UO+2)(O-2), and a weak complex, UO3-O2, were primarily produced under conditions which favored further O2 reactions. Similar U atom and N2 experiments produced only linear NUN which is also produced by an insertion mechanism. This U reaction represents the first time that atom was observed breaking and inserting into the triple bond of N2. Photolysis dramatically increased the NUN yield by 3-fold. Matrix annealings produced weak UN2-N2 and UN2-2N2 complexes.

Simple (17) O NMR method for studying electron self-exchange reaction between UO2 (2+) and U(4+) aqua ions in acidic solution.

PubMed

Bányai, István; Farkas, Ildikó; Tóth, Imre

2016-06-01

(17) O NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of (17) O-enrichment in U(17) OO(2+) ion in the presence of U(4+) ion in aqueous solution. The reactions have been performed at room temperature using I = 5 M ClO4 (-) ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U(4+) and UO2 (2+) aqua ions. The rate equation is given as R = a[H(+) ](-2)  + R', where R' is an acid independent parallel path. R' depends on the concentration of the uranium species according to the following empirical rate equation: R' = k1 [UO(2 +) ](1/2) [U(4 +) ](1/2)  + k2 [UO(2 +) ](3/2) [U(4 +) ](1/2) . The mechanism of the inverse H(+) concentration-dependent path is interpreted as equilibrium formation of reactive UO2 (+) species from UO2 (2+) and U(4+) aqua ions and its electron exchange with UO2 (2+) . The determined rate constant of this reaction path is in agreement with the rate constant of UO2 (2+) -UO2 (+) , one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO(3+) , which loses enrichment mainly by electron exchange with UO2 (2+) ions. One can also conclude that (17) O NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Processing of uranium dioxide nuclear fuel pellets using spark plasma sintering

NASA Astrophysics Data System (ADS)

Ge, Lihao

Uranium dioxide (UO2), one of the most common nuclear fuels, has been applied in most of the nuclear plant these days for electricity generation. The main objective of this research is to introduce a novel method for UO 2 processing using spark plasma sintering technique (SPS). Firstly, an investigation into the influence of processing parameters on densification of UO2 powder during SPS is presented. A broad range of sintering temperatures, hold time and heating rates have been systematically varied to investigate their influence on the sintered pellet densification process. The results revealed that up to 96% theoretical density (TD) pellets can be obtained at a sintering temperature of 1050 °C for 30s hold time and a total run time of only 10 minutes. A systematic study is performed by varying the sintering temperature between 750°C to 1450°C and hold time between 0.5 min to 20 min to obtain UO2 pellets with a range of densities and grain sizes. The microstructure development in terms of grain size, density and porosity distribution is investigated. The Oxygen/Uranium (O/U) ratio of the resulting pellets is found to decrease after SPS. The mechanical and thermal properties of UO2 are evaluated. For comparable density and grain size, Vickers hardness and Young's modulus are in agreement with the literature value. The thermal conductivity of UO2 increases with the density but the grain size in the investigated range has no significant influence. Overall, the mechanical and thermal properties of UO2 are comparable with the one made using conventional sintering methods. Lastly, the influence of chromium dioxide (Cr2O3) and zirconium diboride (ZrB2) on the grain size of doped UO 2 fuel pellet is performed to investigate the feasibility of producing large-grain-size nuclear fuel using SPS. The benefits of using SPS over the conventional sintering of UO2 are summarized. The future work of designing macro-porous UO2 pellet and thorium dioxide (ThO 2) cored UO2 pellet is also proposed.

Prognostic implications of adding urine output to serum creatinine measurements for staging of acute kidney injury after major surgery: a cohort study.

PubMed

Quan, Samuel; Pannu, Neesh; Wilson, Todd; Ball, Chad; Tan, Zhi; Tonelli, Marcello; Hemmelgarn, Brenda R; Dixon, Elijah; James, Matthew T

2016-12-01

Current guidelines recommend staging acute kidney injury (AKI) according to the serum creatinine (SCr) or urine output (UO) criteria that achieve the highest stage. There is little information about the implications of adding UO to SCr measurements for staging AKI outside intensive care units and after cardiac surgery. We performed a cohort study of all adults without end-stage renal disease who underwent major noncardiac surgery between January 2005 and March 2011 in Calgary, AB, Canada. Participants required at least two SCr and UO measurements to be included. We examined the implications of adding UO to SCr to stage AKI based on Kidney Disease: Improving Global Outcomes criteria. Logistic and linear regression models were used to examine the associations between AKI stage and 30-day mortality or hospital length of stay (LOS), respectively. A total of 4229 (17%) surgical patients had sufficient SCr and UO measurements for inclusion in the cohort. The apparent incidence of postoperative AKI substantially increased with the addition of UO to SCr criteria (8.1% with SCr alone versus 64.0% with SCr and UO). Mortality for a given stage of AKI was lower when UO was added to SCr criteria (0.3, 3.2, 1.9 and 3.0% for no AKI and Stages 1, 2 and 3, respectively) versus with SCr alone (1.2, 4.2, 15.4 and 12.8%). However, among participants without AKI based on the SCr criterion, the odds of mortality and mean LOS both significantly increased with lower UO. Models that reclassified AKI stage based on UO in addition SCr criteria had the best discrimination for mortality and LOS. Adding UO to SCr criteria substantially increases the apparent incidence of AKI on hospital wards and significantly changes the prognostic implications of AKI identification and staging. These measures should not be considered equivalent criteria in AKI staging. © The Author 2016. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.

Subsurface Uranium Fate and Transport: Integrated Experiments and Modeling of Coupled Biogeochemical Mechanisms of Nanocrystalline Uraninite Oxidation by Fe(III)-(hydr)oxides - Project Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peyton, Brent M.; Timothy, Ginn R.; Sani, Rajesh K.

2013-08-14

Subsurface bacteria including sulfate reducing bacteria (SRB) reduce soluble U(VI) to insoluble U(IV) with subsequent precipitation of UO 2. We have shown that SRB reduce U(VI) to nanometer-sized UO 2 particles (1-5 nm) which are both intra- and extracellular, with UO 2 inside the cell likely physically shielded from subsequent oxidation processes. We evaluated the UO 2 nanoparticles produced by Desulfovibrio desulfuricans G20 under growth and non-growth conditions in the presence of lactate or pyruvate and sulfate, thiosulfate, or fumarate, using ultrafiltration and HR-TEM. Results showed that a significant mass fraction of bioreduced U (35-60%) existed as a mobile phasemore » when the initial concentration of U(VI) was 160 µM. Further experiments with different initial U(VI) concentrations (25 - 900 M) in MTM with PIPES or bicarbonate buffers indicated that aggregation of uraninite depended on the initial concentrations of U(VI) and type of buffer. It is known that under some conditions SRB-mediated UO 2 nanocrystals can be reoxidized (and thus remobilized) by Fe(III)-(hydr)oxides, common constituents of soils and sediments. To elucidate the mechanism of UO 2 reoxidation by Fe(III) (hydr)oxides, we studied the impact of Fe and U chelating compounds (citrate, NTA, and EDTA) on reoxidation rates. Experiments were conducted in anaerobic batch systems in PIPES buffer. Results showed EDTA significantly accelerated UO 2 reoxidation with an initial rate of 9.5 M day-1 for ferrihydrite. In all cases, bicarbonate increased the rate and extent of UO 2 reoxidation with ferrihydrite. The highest rate of UO 2 reoxidation occurred when the chelator promoted UO 2 and Fe(III) (hydr)oxide dissolution as demonstrated with EDTA. When UO 2 dissolution did not occur, UO 2 reoxidation likely proceeded through an aqueous Fe(III) intermediate as observed for both NTA and citrate. To complement to these laboratory studies, we collected U-bearing samples from a surface seep at the Rifle field site and have measured elevated U concentrations in oxic iron-rich sediments. To translate experimental results into numerical analysis of U fate and transport, a reaction network was developed based on Sani et al. (2004) to simulate U(VI) bioreduction with concomitant UO 2 reoxidation in the presence of hematite or ferrihydrite. The reduction phase considers SRB reduction (using lactate) with the reductive dissolution of Fe(III) solids, which is set to be microbially mediated as well as abiotically driven by sulfide. Model results show the oxidation of HS– by Fe(III) directly competes with UO 2 reoxidation as Fe(III) oxidizes HS– preferentially over UO 2. The majority of Fe reduction is predicted to be abiotic, with ferrihydrite becoming fully consumed by reaction with sulfide. Predicted total dissolved carbonate concentrations from the degradation of lactate are elevated (log(pCO 2) ~ –1) and, in the hematite system, yield close to two orders-of-magnitude higher U(VI) concentrations than under initial carbonate concentrations of 3 mM. Modeling of U(VI) bioreduction with concomitant reoxidation of UO 2 in the presence of ferrihydrite was also extended to a two-dimensional field-scale groundwater flow and biogeochemically reactive transport model for the South Oyster site in eastern Virginia. This model was developed to simulate the field-scale immobilization and subsequent reoxidation of U by a biologically mediated reaction network.« less

Rates and mechanism of fluoride and water exchange in UO(2)F(5)(3-) and [UO(2)F(4)(H(2)O)](2-) studied by NMR spectroscopy and wave function based methods.

PubMed

Vallet, Valérie; Wahlgren, Ulf; Szabó, Zoltán; Grenthe, Ingmar

2002-10-21

The reaction mechanism for the exchange of fluoride in UO(2)F(5)(3-) and UO(2)F(4)(H(2)O)(2-) has been investigated experimentally using (19)F NMR spectroscopy at -5 degrees C, by studying the line broadening of the free fluoride, UO(2)F(4)(2-)(aq) and UO(2)F(5)(3-), and theoretically using quantum chemical methods to calculate the activation energy for different pathways. The new experimental data allowed us to make a more detailed study of chemical equilibria and exchange mechanisms than in previous studies. From the integrals of the different individual peaks in the new NMR spectra, we obtained the stepwise stability constant K(5) = 0.60 +/- 0.05 M(-1) for UO(2)F(5)(3-). The theoretical results indicate that the fluoride exchange pathway of lowest activation energy, 71 kJ/mol, in UO(2)F(5)(3-) is water assisted. The pure dissociative pathway has an activation energy of 75 kJ/mol, while the associative mechanism can be excluded as there is no stable UO(2)F(6)(4-) intermediate. The quantum chemical calculations have been made at the SCF/MP2 levels, using a conductor-like polarizable continuum model (CPCM) to describe the solvent. The effects of different model assumptions on the activation energy have been studied. The activation energy is not strongly dependent on the cavity size or on interactions between the complex and Na(+) counterions. However, the solvation of the complex and the leaving fluoride results in substantial changes in the activation energy. The mechanism for water exchange in UO(2)F(4)(H(2)O)(2-) has also been studied. We could eliminate the associative mechanism, the dissociative mechanism had the lowest activation energy, 39 kJ/mol, while the interchange mechanism has an activation energy that is approximately 50 kJ/mol higher.

Significance of oliguria in critically ill patients with chronic liver disease.

PubMed

Amathieu, Roland; Al-Khafaji, Ali; Sileanu, Florentina E; Foldes, Emily; DeSensi, Rebecca; Hilmi, Ibtesam; Kellum, John A

2017-11-01

Clinical guidelines recommend using Kidney Disease Improving Global Outcomes (KDIGO) criteria for the diagnosis and classification of acute kidney injury (AKI) in patients with chronic liver disease (CLD). Concerns have been raised about the use of urine output (UO) criteria in CLD. We examined the significance of oliguria meeting the urine output criteria for AKI (AKI-UO) and examined its association with clinical outcomes in CLD patients. Using an 8-year clinical database from a large university medical center, 3458 patients with CLD were identified. AKI occurred in 2854 (82.5%) patients when they fulfilled any KDIGO criteria. When serum creatinine (SC) and UO criteria were used, 604 patients (17.5%) had no evidence of AKI and had the lowest hospital mortality rate (5%). Using AKI-UO criteria alone, 2103 patients (60.8%) were classified as stage 2-3 AKI. When only SC criteria were applied, 1281 (61%) of those patients with stage 2-3 AKI-UO were misclassified as either no AKI or AKI stage 1. Patients reclassified with AKI according to UO criteria (AKI-UO) had nearly a 3-fold increased rate of hospital mortality compared with patients without any AKI (14.6% versus 5%; P < 0.001) and more than a 50% increased mortality compared with stage 1 AKI-SC (14.6% versus 9%; P < 0.001). Patients with transient oliguria (AKI-UO stage 1) had increased mortality rates compared with patients without oliguria (14.9% versus 6.9%; P < 0.001). CLD patients have a high incidence of AKI. Compared with creatinine criteria alone, incorporating UO into the diagnostic criteria increased the measured incidence of AKI. Stage 2-3 AKI-UO has a high negative impact on hospital mortality. (Hepatology 2017;66:1592-1600). © 2017 by the American Association for the Study of Liver Diseases.

Sperm DNA quality evaluated by comet assay and sperm chromatin structure assay in stallions after unilateral orchiectomy.

PubMed

Serafini, R; Varner, D D; Bissett, W; Blanchard, T L; Teague, S R; Love, C C

2015-09-15

Unilateral orchiectomy (UO) may interfere with thermoregulation of the remaining testis caused by inflammation surrounding the incision site, thus altering normal spermatogenesis and consequently sperm quality. Two measures of sperm DNA quality (neutral comet assay and the sperm chromatin structure assay [SCSA]) were compared before UO (0 days) and at 14, 30, and 60 days after UO to determine whether sperm DNA changed after a mild testis stress (i.e., UO). The percent DNA in the comet tail was higher at 14 and 60 days compared to 0 days (P < 0.05) after UO. All other comet tail measures (i.e., length, moment, migration) were higher at all time periods after UO compared to 0 days (P < 0.05). Two SCSA measures (mean-αt, mode-αt) increased at 14 days after UO (P < 0.05), whereas two measures (SD-αt and COMP-αt) did not change. This study identified a decrease in sperm DNA quality using both the neutral comet assay and the SCSA, which was not identified using traditional measures of sperm quality. Copyright © 2015 Elsevier Inc. All rights reserved.

Thermodynamic studies of studtite thermal decomposition pathways via amorphous intermediates UO 3, U 2O 7, and UO 4

DOE PAGES

Guo, Xiaofeng; Wu, Di; Xu, Hongwu; ...

2016-09-01

The thermal decomposition of studtite (UO 2)O 2(H 2O) 2·2H 2O results in a series of intermediate X-ray amorphous materials with general composition UO 3+x (x = 0, 0.5, 1). As an extension of a structural study on U 2O 7, this work provides detailed calorimetric data on these amorphous oxygen-rich materials since their energetics and thermal stability are unknown. These were characterized in situ by thermogravimetry, and mass spectrometry. Ex situ X-ray diffraction and infrared spectroscopy characterized their chemical bonding and local structures. This detailed characterization formed the basis for obtaining formation enthalpies by high temperature oxide melt solutionmore » calorimetry. The thermodynamic data demonstrate the metastability of the amorphous UO 3+x materials, and explain their irreversible and spontaneous reactions to generate oxygen and form metaschoepite. Thus, formation of studtite in the nuclear fuel cycle, followed by heat treatment, can produce metastable amorphous UO 3+x materials that pose the risk of significant O 2 gas. Quantitative knowledge of the energy landscape of amorphous UO 3+x was provided for stability analysis and assessment of conditions for decomposition.« less

$sup 18$O enrichment process in UO$sub 2$F$sub 2$ utilizing laser light

DOEpatents

DePoorter, G.L.; Rofer-DePoorter, C.K.

1975-12-01

Photochemical reaction induced by laser light is employed to separate oxygen isotopes. A solution containing UO$sub 2$F$sub 2$, HF, H$sub 2$O and a large excess of CH$sub 3$OH is irradiated with laser light of appropriate wavelength to differentially excite the UO$sub 2$$sup 2+$ ions containing $sup 16$O atoms and cause a reaction to proceed in accordance with the reaction 2 UO$sub 2$F$sub 2$ + CH$sub 3$OH + 4 HF $Yields$ 2 UF$sub 4$ down arrow + HCOOH + 3 H$sub 2$O. Irradiation is discontinued when about 10 percent of the UO$sub 2$F$sub 2$ has reacted, the UF$sub 4$ is filtered from the reaction mixture and the residual CH$sub 3$OH and HF plus the product HCOOH and H$sub 2$O are distilled away from the UO$sub 2$F$sub 2$ which is thereby enriched in the $sup 18$O isotope, or the solution containing the UO$sub 2$F$sub 2$ may be photochemically processed again to provide further enrichment in the $sup 18$O isotope.

Development of UO2/PuO2 dispersed in uranium matrix CERMET fuel system for fast reactors

NASA Astrophysics Data System (ADS)

Sinha, V. P.; Hegde, P. V.; Prasad, G. J.; Pal, S.; Mishra, G. P.

2012-08-01

CERMET fuel with either PuO2 or enriched UO2 dispersed in uranium metal matrix has a strong potential of becoming a fuel for the liquid metal cooled fast breeder reactors (LMR's). In fact it may act as a bridge between the advantages and disadvantages associated with the two extremes of fuel systems (i.e. ceramic fuel and metallic fuel) for fast reactors. At Bhabha Atomic Research Centre (BARC), R & D efforts are on to develop this CERMET fuel by powder metallurgy route. This paper describes the development of flow sheet for preparation of UO2 dispersed in uranium metal matrix pellets for three different compositions i.e. U-20 wt%UO2, U-25 wt%UO2 and U-30 wt%UO2. It was found that the sintered pellets were having excellent integrity and their linear mass was higher than that of carbide fuel pellets used in Fast Breeder Test Reactor programme (FBTR) in India. The pellets were characterized by X-ray diffraction (XRD) technique for phase analysis and lattice parameter determination. The optical microstructures were developed and reported for all the three different U-UO2 compositions.

Chelation of UO(2)(2+) by vitamin B6 complex derivatives: synthesis and characterization of [UO2(beta-pyracinide)2(H2O)] and [UO2(Pyr2en)DMSO]Cl2{Pyr2en=N,N'-ethylenebis(pyridoxylideneiminato)}. A useful modeling of assimilation of uranium by living beings.

PubMed

Back, Davi Fernando; de Oliveira, Gelson Manzoni; Lang, Ernesto Schulz

2006-10-01

The vitamin B(6) derivatives 4-pyridoxic acid (anionic) and the Schiff base N,N'-ethylenebis(pyridoxylideneiminato) react with UO(2)(NO(3))(2) * 6H(2)O to give [UO(2)(beta-pyracinide)(2)(H(2)O)] (beta-pyracin=4-pyridoxic acid) and [UO(2)(Pyr(2)en)DMSO]Cl(2)(Pyr(2)en=N,N'-ethylenebis(pyridoxylideneiminato); DMSO=dimethyl sulfoxide). In both compounds the two uranyl oxo ligands set the axis of distorted pentagonal bipyramides. The ability of vitamin B(6) derivatives to react with UO(2)(2+) allowing the chelation of one uranium atom represents a very specific model of assimilation of uranium by living beings. It could also explain the serious damages caused by heavy or radioactive metals like uranium since their complexation "in vivo" by enzymatic systems like pyridoxal phosphate-containing enzymes would lead to a modification of the prosthetic groups of the metalloenzymes with loss of their catalytic activities.

TOF-SIMS for Rapid Nuclear Forensics Evaluation of Uranium Oxide Particles

DTIC Science & Technology

2011-03-01

Fraction U-238 nU U metal CRM 112-A NBL Metal Assay and Isotopic .000052458 .0072017 --- .9927458 nUO2 UO2 --- NBL Commercial material...0 .992745 dU U metal CRM 115 NBL Uranium Assay .0000076 .0020291 .0000322 .9979311 dUO2 UO2 --- IBI Labs Commercial material --- .002- .0035...U500* U3O8 CRM U500 NBL Isotopic .005181 .49696 .000755 .49711 U900* U3O8 CRM U900 NBL Isotopic .007777 .90196 .003327 .08693 *Sample

Dissolution process for ZrO.sub.2 -UO.sub.2 -CaO fuels

DOEpatents

Paige, Bernice E.

1976-06-22

The present invention provides an improved dissolution process for ZrO.sub.2 -UO.sub.2 -CaO-type pressurized water reactor fuels. The zirconium cladding is dissolved with hydrofluoric acid, immersing the ZrO.sub.2 -UO.sub.2 -CaO fuel wafers in the resulting zirconium-dissolver-product in the dissolver vessel, and nitric acid is added to the dissolver vessel to facilitate dissolution of the uranium from the ZrO.sub.2 -UO.sub.2 -CaO fuel wafers.

China Debates the Future Security Environment

DTIC Science & Technology

2000-01-01

ccx~perafion and avoid confrontation" (zengl~a .x4nren, jianshao mafan, fa~han he~uo, tntgao dzdk~. Quoted in Lu Zhongwei, "On China-U.S.-Japan...and south to Australia." Lu Gua0g~,e , a fellow at the Chinese National Defense Strategic Institute, claims that together with NATO, the U.S...States may not be prepared to face. First, there is the issue of homeland defense. Lu Dehong from the CIISS writes, "It is the first time since the

Biogenic uraninite precipitation and its reoxidation by iron(III) (hydr)oxides: A reaction modeling approach

NASA Astrophysics Data System (ADS)

Spycher, Nicolas F.; Issarangkun, Montarat; Stewart, Brandy D.; Sevinç Şengör, S.; Belding, Eileen; Ginn, Tim R.; Peyton, Brent M.; Sani, Rajesh K.

2011-08-01

One option for immobilizing uranium present in subsurface contaminated groundwater is in situ bioremediation, whereby dissimilatory metal-reducing bacteria and/or sulfate-reducing bacteria are stimulated to catalyze the reduction of soluble U(VI) and precipitate it as uraninite (UO 2). This is typically accomplished by amending groundwater with an organic electron donor. It has been shown, however, that once the electron donor is entirely consumed, Fe(III) (hydr)oxides can reoxidize biogenically produced UO 2, thus potentially impeding cleanup efforts. On the basis of published experiments showing that such reoxidation takes place even under highly reducing conditions (e.g., sulfate-reducing conditions), thermodynamic and kinetic constraints affecting this reoxidation are examined using multicomponent biogeochemical simulations, with particular focus on the role of sulfide and Fe(II) in solution. The solubility of UO 2 and Fe(III) (hydr)oxides are presented, and the effect of nanoscale particle size on stability is discussed. Thermodynamically, sulfide is preferentially oxidized by Fe(III) (hydr)oxides, compared to biogenic UO 2, and for this reason the relative rates of sulfide and UO 2 oxidation play a key role on whether or not UO 2 reoxidizes. The amount of Fe(II) in solution is another important factor, with the precipitation of Fe(II) minerals lowering the Fe +2 activity in solution and increasing the potential for both sulfide and UO 2 reoxidation. The greater (and unintuitive) UO 2 reoxidation by hematite compared to ferrihydrite previously reported in some experiments can be explained by the exhaustion of this mineral from reaction with sulfide. Simulations also confirm previous studies suggesting that carbonate produced by the degradation of organic electron donors used for bioreduction may significantly increase the potential for UO 2 reoxidation through formation of uranyl carbonate aqueous complexes.

Personal past experience with opioid consumption affects attitudes and knowledge related to pain management.

PubMed

Pud, Dorit

2004-12-01

The personal past experience with opioid consumption by hospital health care providers was examined for its influence on their attitudes toward and knowledge of pain management. Data were collected through a questionnaire that elicited demographic information, attitudes toward pain management, barriers to pain relief, and self-assessment of pain management knowledge. The sample ( N = 163) was divided into two groups according to past experience with opioids: 52% of participants had used opioids (UO) for pain relief in the past, and the rest had never done so (NO). UO participants noted that pain control treatment was not sufficient for pain relief, in contrast to NO participants ( p = .013). Pain management was considered a low priority relative to overall treatment by the UO group compared with the NO group ( p = .016). The former group also attributed major responsibility for inappropriate pain relief to the clinical staff (12% of the UO group vs. 1.4% of the NO group; p = .048) rather than to the patients (22.9% of the UO group vs. 32.9% of the NO group; p = .019). UO participants felt extremely competent in their ability to manage several aspects of pain therapy ( p < .05). These aspects included assessing cause of the pain (42.9% of the UO group vs. 29.3% of the NO group), selecting a starting dose for opioid therapy (26.9% of the UO group vs. 13.3% of the NO group), and using opioids intravenously (20.5% of the UO group vs. 8.3% of the NO group). Personal past experience regarding analgesic use is an important factor in evaluating attitudes toward pain and achieving optimal pain management outcomes.

Strong electron correlation in UO{sub 2}{sup −}: A photoelectron spectroscopy and relativistic quantum chemistry study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Wei-Li; Jian, Tian; Lopez, Gary V.

2014-03-07

The electronic structures of actinide systems are extremely complicated and pose considerable challenges both experimentally and theoretically because of significant electron correlation and relativistic effects. Here we report an investigation of the electronic structure and chemical bonding of uranium dioxides, UO{sub 2}{sup −} and UO{sub 2}, using photoelectron spectroscopy and relativistic quantum chemistry. The electron affinity of UO{sub 2} is measured to be 1.159(20) eV. Intense detachment bands are observed from the UO{sub 2}{sup −} low-lying (7sσ{sub g}){sup 2}(5fϕ{sub u}){sup 1} orbitals and the more deeply bound O2p-based molecular orbitals which are separated by a large energy gap from themore » U-based orbitals. Surprisingly, numerous weak photodetachment transitions are observed in the gap region due to extensive two-electron transitions, suggesting strong electron correlations among the (7sσ{sub g}){sup 2}(5fϕ{sub u}){sup 1} electrons in UO{sub 2}{sup −} and the (7sσ{sub g}){sup 1}(5fϕ{sub u}){sup 1} electrons in UO{sub 2}. These observations are interpreted using multi-reference ab initio calculations with inclusion of spin-orbit coupling. The strong electron correlations and spin-orbit couplings generate orders-of-magnitude more detachment transitions from UO{sub 2}{sup −} than expected on the basis of the Koopmans’ theorem. The current experimental data on UO{sub 2}{sup −} provide a long-sought opportunity to arbitrating various relativistic quantum chemistry methods aimed at handling systems with strong electron correlations.« less

Thermal diffusivity and conductivity of thorium- uranium mixed oxides

NASA Astrophysics Data System (ADS)

Saoudi, M.; Staicu, D.; Mouris, J.; Bergeron, A.; Hamilton, H.; Naji, M.; Freis, D.; Cologna, M.

2018-03-01

Thorium-uranium oxide pellets with high densities were prepared at the Canadian Nuclear Laboratories (CNL) by co-milling, pressing, and sintering at 2023 K, with UO2 mass contents of 0, 1.5, 3, 8, 13, 30, 60 and 100%. At the Joint Research Centre, Karlsruhe (JRC-Karlsruhe), thorium-uranium oxide pellets were prepared using the spark plasma sintering (SPS) technique with 79 and 93 wt. % UO2. The thermal diffusivity of (Th1-xUx)O2 (0 ≤ x ≤ 1) was measured at CNL and at JRC-Karlsruhe using the laser flash technique. ThO2 and (Th,U)O2 with 1.5, 3, 8 and 13 wt. % UO2 were found to be semi-transparent to the infrared wavelength of the laser and were coated with graphite for the thermal diffusivity measurements. This semi-transparency decreased with the addition of UO2 and was lost at about 30 wt. % of UO2 in ThO2. The thermal conductivity was deduced using the measured density and literature data for the specific heat capacity. The thermal conductivity for ThO2 is significantly higher than for UO2. The thermal conductivity of (Th,U)O2 decreases rapidly with increasing UO2 content, and for UO2 contents of 60% and higher, the conductivity of the thorium-uranium oxide fuel is close to UO2. As the mass difference between the Th and U atoms is small, the thermal conductivity decrease is attributed to the phonon scattering enhanced by lattice strain due to the introduction of uranium in ThO2 lattice. The new results were compared to the data available in the literature and were evaluated using the classical phonon transport model for oxide systems.

Electrochemical and spectroelectrochemical studies on UO(2)(saloph)L (saloph = N,N'-disalicylidene-o-phenylenediaminate, L=dimethyl sulfoxide or N,N-dimethylformamide).

PubMed

Mizuoka, Koichiro; Kim, Seong-Yun; Hasegawa, Miki; Hoshi, Toshihiko; Uchiyama, Gunzo; Ikeda, Yasuhisa

2003-02-24

To examine properties of pentavalent uranium, U(V), we have carried out electrochemical and spectroelectrochemical studies on UO(2)(saloph)L [saloph = N,N'-disalicylidene-o-phenylenediaminate, L = dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF)]. The electrochemical reactions of UO(2)(saloph)L complexes in L were found to occur quasireversibly. The reduction processes of UO(2)(saloph)L complexes were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from 0 to -1.650 V versus ferrocene/ferrocenium ion redox couple (Fc/Fc(+)) for UO(2)(saloph)DMSO in DMSO have clear isosbestic points and that the evaluated electron stoichiometry equals 1.08. These results indicate that the reduction product of UO(2)(saloph)DMSO is [U(V)O(2)(saloph)DMSO](-), which is considerably stable in DMSO. Furthermore, it was clarified that the absorption spectrum of the [U(V)O(2)(saloph)DMSO](-) complex has a very small molar absorptivity in the visible region and characteristic absorption bands due to the 5f(1) orbital at around 750 and 900 nm. For UO(2)(saloph)DMF in DMF, the clear isosbestic points were not observed in the similar spectral changes. It is proposed that the UO(2)(saloph)DMF complex is reduced to [U(V)O(2)(saloph)DMF](-) accompanied by the dissociation of DMF as a successive reaction. The formal redox potentials of UO(2)(saloph)L in L (E(0), vs Fc/Fc(+)) for U(VI)/U(V) couple were determined to be -1.550 V for L = DMSO and -1.626 V for L = DMF.

Evolution of uranium monoxide in femtosecond laser-induced uranium plasmas

DOE PAGES

Hartig, Kyle C.; Harilal, Sivanandan S.; Phillips, Mark C.; ...

2017-05-09

We report on the observation of uranium monoxide (UO) emission following fs laser ablation (LA) of a uranium metal sample. The formation and evolution of the molecular emission are studied under various ambient air pressures. Observation of UO emission spectra at a rarefied residual air pressure of ~1 Torr indicates that the UO molecule is readily formed in the expanding plasma with trace concentrations of oxygen present within the vacuum chamber. Furthermore, the persistence of the UO emission exceeded that of the atomic emission; however, the molecular emission was delayed in time compared to the atomic emission due to themore » necessary cooling and expansion of the plasma before the UO molecules can form.« less

Non-Destructive Characterization of UO2+x Nuclear Fuels

DOE PAGES

Pokharel, Reeju; Brown, Donald W.; Clausen, Bjørn; ...

2017-10-27

This article describes the effect of fabrication conditions on as-sintered microstructures of various stoichiometric ratios of uranium dioxide, UO 2+x, with the aim of enhancing the understanding of fabrication process and developing and validating a predictive microstructurebased model for fuel performance. We demonstrate the ability of novel, non-destructive methods such as near-field high-energy X-ray diffraction microscopy (nf-HEDM) and micro-computed tomography (μ-CT) to probe bulk samples of high-Z materials by non-destructively characterizing three samples: UO 2.00, UO 2.11, and UO 2.16, which were sintered at 1450°C for 4 hours. The measured 3D microstructures revealed that grain size and porosity were influencedmore » by deviation from stoichiometry.« less

Effect of the ZrCl4 concentration in the (NaCl-KCl)eqiv-UO2Cl2-ZrCl4 melt and the electrolysis current density on the quantitative composition of UO2-ZrO2 cathode deposits. Calculation and experiment

NASA Astrophysics Data System (ADS)

Krotov, V. E.; Filatov, E. C.

2014-08-01

A method is proposed for calculating the ZrO2 content in the (NaCl-KCl)eqiv-UO2Cl2-ZrCl4 melt. Based on the known composition of a UO2-ZrO2 cathode deposit, the content is calculated at current densities of 0.08-0.63 A/cm2 and ZrCl4 concentrations of 0-12.3 wt %. The calculated and experimental ZrO2 contents in UO2-ZrO2 cathode deposits are in qualitative and adequate quantitative agreement.

Tandem dissolution of UO 3 in amide-based acidic ionic liquid and in situ electrodeposition of UO 2 with regeneration of the ionic liquid: a closed cycle

DOE PAGES

Wanigasekara, Eranda; Freiderich, John W.; Sun, Xiao-Guang; ...

2016-05-19

A closed cycle is demonstrated for the tandem dissolution and electroreduction of UO 3 to UO 2 with regeneration of the acidic ionic liquid. The dissolution is achieved by use of the acidic ionic liquid N,N-dimethylacetimidium bis(trifluoromethanesulfonimide) in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonimide) serving as the diluent. Bulk electrolysis performed at 1.0 V vs. Ag reference yields a dark brown-black uranium deposit (UO 2) on the cathode. Anodic oxidation of water in the presence of dimethylacetamide regenerates the acidic ionic liquid. We have demonstrated the individual steps in the cycle together with a sequential dissolution, electroreduction, and regeneration cycle.

Tandem dissolution of UO 3 in amide-based acidic ionic liquid and in situ electrodeposition of UO 2 with regeneration of the ionic liquid: a closed cycle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wanigasekara, Eranda; Freiderich, John W.; Sun, Xiao-Guang

A closed cycle is demonstrated for the tandem dissolution and electroreduction of UO 3 to UO 2 with regeneration of the acidic ionic liquid. The dissolution is achieved by use of the acidic ionic liquid N,N-dimethylacetimidium bis(trifluoromethanesulfonimide) in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonimide) serving as the diluent. Bulk electrolysis performed at 1.0 V vs. Ag reference yields a dark brown-black uranium deposit (UO 2) on the cathode. Anodic oxidation of water in the presence of dimethylacetamide regenerates the acidic ionic liquid. We have demonstrated the individual steps in the cycle together with a sequential dissolution, electroreduction, and regeneration cycle.

Evolution of uranium monoxide in femtosecond laser-induced uranium plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartig, Kyle C.; Harilal, Sivanandan S.; Phillips, Mark C.

We report on the observation of uranium monoxide (UO) emission following fs laser ablation (LA) of a uranium metal sample. The formation and evolution of the molecular emission are studied under various ambient air pressures. Observation of UO emission spectra at a rarefied residual air pressure of ~1 Torr indicates that the UO molecule is readily formed in the expanding plasma with trace concentrations of oxygen present within the vacuum chamber. Furthermore, the persistence of the UO emission exceeded that of the atomic emission; however, the molecular emission was delayed in time compared to the atomic emission due to themore » necessary cooling and expansion of the plasma before the UO molecules can form.« less

An Anonymous Referee Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tobin, J. G.

2015-06-08

This is a combined experimental and theoretical study of the compound UO 2, UO 2(NO 3) 2(H 20) 6 and UO 0.75Pu 0.25O 2, using resonant inelastic x-ray scattering (RXIS), high resolution x-ray absorption (XAS) and LDA and LDA-U calculations.

Numerical characterization of micro-cell UO2sbnd Mo pellet for enhanced thermal performance

NASA Astrophysics Data System (ADS)

Lee, Heung Soo; Kim, Dong-Joo; Kim, Sun Woo; Yang, Jae Ho; Koo, Yang-Hyun; Kim, Dong Rip

2016-08-01

Metallic micro-cell UO2 pellet with high thermal conductivity has received attention as a promising accident-tolerant fuel. Although experimental demonstrations have been successful, studies on the potency of current metallic micro-cell UO2 fuels for further enhancement of thermal performance are lacking. Here, we numerically investigated the thermal conductivities of micro-cell UO2sbnd Mo pellets in terms of the amount of Mo content, the unit cell size, and the aspect ratio of the micro-cells. The results showed good agreement with experimental measurements, and more importantly, indicated the importance of optimizing the unit cell geometries of the micro-cell pellets for greater increases in thermal conductivity. Consequently, the micro-cell UO2sbnd Mo pellets (5 vol% Mo) with modified geometries increased the thermal conductivity of the current UO2 pellets by about 2.5 times, and lowered the temperature gradient within the pellets by 62.9% under a linear heat generation rate of 200 W/cm.

Chemical reactivity of CVC and CVD SiC with UO 2 at high temperatures

DOE PAGES

Silva, Chinthaka M.; Katoh, Yutai; Voit, Stewart L.; ...

2015-02-11

Two types of silicon carbide (SiC) synthesized using two different vapor deposition processes were embedded in UO 2 pellets and evaluated for their potential chemical reaction with UO 2. While minor reactivity between chemical-vapor-composited (CVC) SiC and UO 2 was observed at comparatively low temperatures of 1100 and 1300 C, chemical-vapor-deposited (CVD) SiC did not show any such reactivity, according to microstructural investigations. But, both CVD and CVC SiCs showed some reaction with UO 2 at a higher temperature (1500 C). Elemental maps supported by phase maps obtained using electron backscatter diffraction indicated that CVC SiC was more reactive thanmore » CVD SiC at 1500 C. Moreover, this investigation indicated the formation of uranium carbides and uranium silicide chemical phases such as UC, USi 2, and U 3Si 2 as a result of SiC reaction with UO 2.« less

Gas-phase reactions of uranate ions, UO(2)(-), UO(3)(-), UO(4)(-), and UO(4)H(-), with methanol: a convergence of experiment and theory.

PubMed

Michelini, Maria Del Carmen; Marçalo, Joaquim; Russo, Nino; Gibson, John K

2010-04-19

Bimolecular reactions of uranium oxide molecular anions with methanol have been studied experimentally, by Fourier transform ion cyclotron resonance mass spectrometry, and computationally, by density functional theory (DFT). The primary goals were to provide fundamental insights into mechanistic and structural details of model reactions of uranium oxides with organics, and to examine the validity of theoretical modeling of these types of reactions. The ions UO(3)(-), UO(4)(-), and UO(4)H(-) each reacted with methanol to give a singular product; the primary products each exhibited sequential reactions with two additional methanol molecules to again give singular products. The observed reactions were elimination of water, formaldehyde, or hydrogen, and in one case addition of a methanol molecule. The potential energy profiles were computed for each reaction, and isotopic labeling experiments were performed to probe the validity of the computed mechanisms and structures-in each case where the experiments could be compared with the theory there was concurrence, clearly establishing the efficacy of the employed DFT methodologies for these and related reaction systems. The DFT results were furthermore in accord with the surprisingly inert nature of UO(2)(-). The results provide a basis to understand mechanisms of key reactions of uranium oxides with organics, and a foundation to extend DFT methodologies to more complex actinide systems which are not amenable to such direct experimental studies.

Theoretical investigations of geometry, electronic structure and stability of UO(6): octahedral uranium hexoxide and its isomers.

PubMed

Xiao, Hai; Hu, Han-Shi; Schwarz, W H Eugen; Li, Jun

2010-08-26

The existence of a novel octahedral UO(6) complex had been suggested by Pyykko et al. [Pyykko, P.; Runeberg, N.; Straka, M.; Dyall, K. G. Chem. Phys. Lett. 2000, 328, 415]. We have now investigated the stability, the geometric and electronic structures, and the vibrations of various UO(6) molecules, using spin-orbit density functional and scalar-relativistic coupled-cluster approaches. We find four different (meta-)stable species, namely (3)D(2h)-UO(2)(eta(2)-O(2)(*))(2) at lowest energy, (3)C(2v)-UO(4)(*)(eta(2)-O(2)(*)) and (1)D(3)-U(eta(2)-O(2))(3) at medium energies, and (1)O(h)-UO(6) at highest energy. The decay of O(h)-UO(6) occurs via an activated spin-flip mechanism. The UO(6) species correspond to local minima on singlet and triplet energy surfaces and might be trapped in noble gas matrices. Experimentally, the four species might be identified through their vibrational spectra. Uranium is best described as coordinated by oxygen atoms in various oxidation states as oxo O(2-), oxido(1) O(*-), peroxido O(2)(2-), and superoxido O(2)(*-) ligands. The occurrence of monovalent oxygen is remarkable. The resulting characterization of the central ion as U(VI) in all four cases does not fully reflect the electronic differences, nor the "valence-activity" of the U-6p(6) semicore shell.

Transient Ureteral Obstruction Prevents against Kidney Ischemia/Reperfusion Injury via Hypoxia-Inducible Factor (HIF)-2α Activation

PubMed Central

Chen, Xiao-Song; Zhang, Ming; Xu, Long-Mei; Zhang, Jian-Jun; Xia, Qiang

2012-01-01

Although the protective effect of transient ureteral obstruction (UO) prior to ischemia on subsequent renal ischemia/reperfusion (I/R) injury has been documented, the underlying molecular mechanism remains to be understood. We showed in the current study that 24 h of UO led to renal tubular hypoxia in the ipsilateral kidney in mice, with the accumulation of hypoxia-inducible factor (HIF)-2α, which lasted for a week after the release of UO. To address the functions of HIF-2α in UO-mediated protection of renal IRI, we utilized the Mx-Cre/loxP recombination system to knock out target genes. Inactivation of HIF-2α, but not HIF-1α blunted the renal protective effects of UO, as demonstrated by much higher serum creatinine level and severer histological damage. UO failed to prevent postischemic neutrophil infiltration and apoptosis induction in HIF-2α knockout mice, which also diminished the postobstructive up-regulation of the protective molecule, heat shock protein (HSP)-27. The renal protective effects of UO were associated with the improvement of the postischemic recovery of intra-renal microvascular blood flow, which was also dependent on the activation of HIF-2α. Our results demonstrated that UO protected the kidney via activation of HIF-2α, which reduced tubular damages via preservation of adequate renal microvascular perfusion after ischemia. Thus, preconditional HIF-2α activation might serve as a novel therapeutic strategy for the treatment of ischemic acute renal failure. PMID:22295069

Project CHECO Southeast Asia Report. VNAF Improvement and Modernization Program, July 1971 - December 1973

DTIC Science & Technology

1975-01-01

Thus it’s not too difficult to understand that Vietnamese who follow Confucius, Mencius and Mo Tzu or who subscribe to Taoism , Buddhism or other...Bombing System, improving the Air Liaison Officer (ALO)/FAC system, improving the airlift control system, improving the food distribution system, and...to have to sustain many, many places that are surrounded and cannot get food and supplies other than by airlift, then they don’t have the capability

Method for producing UO$sub 2$ loaded refractory metals

DOEpatents

Baker, R.D.; Hayter, S.W.; Lewis, H.D.

1973-12-11

A finely divided dispersion of UO/sub 2/ in tungsten or molybdenum is prepared by co-precipitating the metals from mixed aqueous solution with oxine. The co-precipitate thus formed is separated from the solution, dried, calcined, and finally reduced to UO/sub 2/ and refractory metal. (Official Gazette)

Sintering Uranium Dioxide of Domestic Production. Report No. 78; SINTERIZACION DE DIOXIDO DE URANIO DE PRODUCCION NACIONAL. Informe No. 78

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carrea, A.J.

1963-01-01

After a brief indication of the uranium- oxygen equilibrium and the methods for the preparation of UO/sub 2/, the sintering of UO/sub 2/ is considered. The effects of various sintering atmospheres on the properties of the product are discussed and tabulated. The method used for the processing of domestic ores for the preparation of UO/sub 2/ and the fabricition of the sintered UO/sub 2/are described. The properties of the product obtained are illustrated graphically. (J.S.R.)

PREPARATION OF HIGH DENSITY UO$sub 2$

DOEpatents

Googin, J.M.

1959-09-29

A method is presented for the preparation of highdensity UO/sub 2/ from UF/sub 6/. In accordance with the invention, UF/sub 6/ is reacted with water and concentrated ammonium hydroxide is added to the resulting aqueous solution of UO/ sub 2/F/sub 2/. The resulting precipitate is calcined to U/sub 3/O/sub 8/ an d the U/sub 3/O/sub 8/ is reduced to UO/sub 2/ with a gaseous mixture comprised of carbon monoxide and carbon dioxide at a temperature of from 1600 to 1900 deg C.

Thermal reactions of uranium metal, UO 2, U 3O 8, UF 4, and UO 2F 2 with NF 3 to produce UF 6

NASA Astrophysics Data System (ADS)

McNamara, Bruce; Scheele, Randall; Kozelisky, Anne; Edwards, Matthew

2009-11-01

This paper demonstrates that NF 3 fluorinates uranium metal, UO 2, UF 4, UO 3, U 3O 8, and UO 2F 2·2H 2O to produce the volatile UF 6 at temperatures between 100 and 550 °C. Thermogravimetric and differential thermal analysis reaction profiles are described that reflect changes in the uranium fluorination/oxidation state, physiochemical effects, and instances of discrete chemical speciation. Large differences in the onset temperatures for each system investigated implicate changes in mode of the NF 3 gas-solid surface interaction. These studies also demonstrate that NF 3 is a potential replacement fluorinating agent in the existing nuclear fuel cycle and in actinide volatility reprocessing.

Effects of Beryllium and Compaction Pressure on the Thermal Diffusivity of Uranium Dioxide Fuel Pellets

NASA Astrophysics Data System (ADS)

Camarano, D. M.; Mansur, F. A.; Santos, A. M. M.; Ferraz, W. B.; Ferreira, R. A. N.

2017-09-01

In nuclear reactors, the performance of uranium dioxide (UO2) fuel is strongly dependent on the thermal conductivity, which directly affects the fuel pellet temperature, the fission gas release and the fuel rod mechanical behavior during reactor operation. The use of additives to improve UO2 fuel performance has been investigated, and beryllium oxide (BeO) appears as a suitable additive because of its high thermal conductivity and excellent chemical compatibility with UO2. In this paper, UO2-BeO pellets were manufactured by mechanical mixing, pressing and sintering processes varying the BeO contents and compaction pressures. Pellets with BeO contents of 2 wt%, 3 wt%, 5 wt% and 7 wt% BeO were pressed at 400 MPa, 500 MPa and 600 MPa. The laser flash method was applied to determine the thermal diffusivity, and the results showed that the thermal diffusivity tends to increase with BeO content. Comparing thermal diffusivity results of UO2 with UO2-BeO pellets, it was observed that there was an increase in thermal diffusivity of at least 18 % for the UO2-2 wt% BeO pellet pressed at 400 MPa. The maximum relative expanded uncertainty (coverage factor k = 2) of the thermal diffusivity measurements was estimated to be 9 %.

[La(UO{sub 2})V{sub 2}O{sub 7}][(UO{sub 2})(VO{sub 4})] the first lanthanum uranyl-vanadate with structure built from two types of sheets based upon the uranophane anion-topology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mer, A.; Obbade, S.; Rivenet, M.

2012-01-15

The new lanthanum uranyl vanadate divanadate, [La(UO{sub 2})V{sub 2}O{sub 7}][(UO{sub 2})(VO{sub 4})] was obtained by reaction at 800 Degree-Sign C between lanthanum chloride, uranium oxide (U{sub 3}O{sub 8}) and vanadium oxide (V{sub 2}O{sub 5}) and the structure was determined from single-crystal X-ray diffraction data. This compound crystallizes in the orthorhombic system with space group P2{sub 1}2{sub 1}2{sub 1} and unit-cell parameters a=6.9470(2) A, b=7.0934(2) A, c=25.7464(6) A, V=1268.73(5) A{sup 3}, Z=4. A full matrix least-squares refinement yielded R{sub 1}=0.0219 for 5493 independent reflections. The crystal structure is characterized by the stacking of uranophane-type sheets {sup 2}{sub {infinity}}[(UO{sub 2})(VO{sub 4})]{sup -}more » and double layers {sup 2}{sub {infinity}}[La(UO{sub 2})(V{sub 2}O{sub 7})]{sup +} connected through La-O bonds involving the uranyl oxygen of the uranyl-vanadate sheets. The double layers result from the connection of two {sup 2}{sub {infinity}}[La(UO{sub 2})(VO{sub 4}){sub 2}]{sup -} sheets derived from the uranophane anion-topology by replacing half of the uranyl ions by lanthanum atoms and connected through the formation of divanadate entities. - Graphical abstract: A view of the three-dimensional structure of [La(UO{sub 2})V{sub 2}O{sub 7}][(UO{sub 2})(VO{sub 4})]. Highlights: Black-Right-Pointing-Pointer New lanthanum uranyl vanadate divanadate has been synthesized. Black-Right-Pointing-Pointer Structure was determined from single-crystal X-ray diffraction data. Black-Right-Pointing-Pointer Structure is characterized by uranophane-type sheets and double layers {sup 2}{sub {infinity}}[La(UO{sub 2})(V{sub 2}O{sub 7})]{sup +}.« less

Microstructure and mechanical properties of eutectic B2O3-UO2 ceramic composites solidified at different cooling rates

NASA Astrophysics Data System (ADS)

Yusufu, Aikebaier; Uno, Masayoshi

2018-02-01

The removal of nuclear debris from damaged reactors by drilling or cutting requires an understanding of various properties of the solidified debris, such as mechanical properties (hardness, fractural features, strength, etc.) and microstructural properties like porosity, which have a significant impact on the mechanical properties. In this study, B2O3-UO2 composites were prepared by the eutectic reaction as solidified samples of mock fuel debris with a wide variety of porosities, and the porosity dependence of the mechanical properties under compression were characterized to obtain fundamental data on the complicated fuel debris. The porous eutectic B2O3-UO2 (B2O3/UO2 atomic ratio = 0.225:0.775) samples were successfully prepared by solidification of the molten phase below 2073 K, and the porosity increased as the pore network developed as the cooling rate was decreased. The nano- and microhardness as well as Young's moduli of the eutectic B2O3-UO2 samples were higher than those of UO2. However, the compressive strengths of the eutectic B2O3-UO2 samples were lower than that of UO2, and they decreased as the porosity increased. All samples showed typical brittle fracturing behavior. The low-porosity samples showed a linear elastic step up to a sudden rupture, whereas the high-porosity samples exhibited two main regimes: a linear elastic region that can be attributed to pore-edge bending or face stretching; a zigzag step that is related to the progression of pore collapse.

Colloids from the aqueous corrosion of uranium nuclear fuel

NASA Astrophysics Data System (ADS)

Kaminski, M. D.; Dimitrijevic, N. M.; Mertz, C. J.; Goldberg, M. M.

2005-12-01

Colloids may enhance the subsurface transport of radionuclides and potentially compromise the long-term safe operation of the proposed radioactive waste repository at Yucca Mountain. Little data is available on colloid formation for the many different waste forms expected to be buried in the repository. This work expands the sparse database on colloids formed during the corrosion of metallic uranium nuclear fuel. We characterized spherical UO 2 and nickel-rich montmorilonite smectite-clay colloids formed during the corrosion of uranium metal fuel under bathtub conditions at 90 °C. Iron and chromium oxides and calcium carbonate colloids were present but were a minor population. The estimated upper concentration of the UO 2 and clays was 4 × 10 11 and 7 × 10 11-3 × 10 12 particles/L, respectively. However, oxygen eventually oxidized the UO 2 colloids, forming long filaments of weeksite K 2(UO 2) 2Si 6O 15 · 4H 2O that settled from solution, reducing the UO 2 colloid population and leaving predominantly clay colloids. The smectite colloids were not affected by oxygen. Plutonium was not directly observed within the UO 2 colloids but partitioned completely to the colloid size fraction. The plutonium concentration in the colloidal fraction was slightly higher than the value used in the viability assessment model, and does not change in concentration with exposure to oxygen. This paper provides conclusive evidence for single-phase radioactive colloids composed of UO 2. However, its impact on repository safety is probably small since oxygen and silica availability will oxidize and effectively precipitate the UO 2 colloids from concentrated solutions.

On the mechanical stability of uranyl peroxide hydrates: Implications for nuclear fuel degradation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weck, Philippe F.; Kim, Eunja; Buck, Edgar C.

The mechanical properties and stability of studtite, (UO2)(O2)(H2O)2·2H2O, and metastudtite, (UO2)(O2)(H2O)2, two important corrosion phases observed on spent nuclear fuel exposed to water, have been investigated using density functional perturbation theory. While (UO2)(O2)(H2O)2 satisfies the necessary and sufficient Born criteria for mechanical stability, (UO2)(O2)(H2O)2·2H2O is found to be mechanically metastable, which might be the underlying cause of the irreversibility of the studtite to metastudtite transformation. According to Pugh’s and Poisson’s ratios and the Cauchy pressure, both phases are considered ductile and shear modulus is the parameter limiting their mechanical stability. Debye temperatures of 294 and 271 K are predicted formore » polycrystalline (UO2)(O2)(H2O)2·2H2O and (UO2)(O2)(H2O)2, suggesting a lower micro-hardness of metastudtite.« less

An evaluation of UO2-CNT composites made by SPS as an accident tolerant nuclear fuel pellet and the feasibility of SPS as an economical fabrication process for the nuclear fuel cycle

NASA Astrophysics Data System (ADS)

Cartas, Andrew R.

The innovative and advanced purpose of this study is to understand and establish proper sintering procedures for Spark Plasma Sintering process in order to fabricate high density, high thermal conductivity UO2 -CNT pellets. Mixing quality and chemical reactions have been investigated by field emission scanning electron microscopy (FESEM), wavelength dispersive spectroscopy (WDS), and X-ray diffraction (XRD). The effect of various types of CNTs on the mixing and sintering quality of UO2-CNT pellets with SPS processing have been examined. The Archimedes Immersion Method, laser flash method, and FE-SEM will be used to investigate the density, thermal conductivity, grain size, pinning effects, and CNT dispersion of fabricated UO2-CNT pellets. Pre-fabricated CNT's were added to UO 2 powder and dispersed via sonication and/or ball milling and then made into composite nuclear pellets. An investigation of the economic impact of SPS on the nuclear fuel cycle for producing pure and composite UO2 fuels was conducted.

Synthesis and sintering of UN-UO2 fuel composites

NASA Astrophysics Data System (ADS)

Jaques, Brian J.; Watkins, Jennifer; Croteau, Joseph R.; Alanko, Gordon A.; Tyburska-Püschel, Beata; Meyer, Mitch; Xu, Peng; Lahoda, Edward J.; Butt, Darryl P.

2015-11-01

The design and development of an economical, accident tolerant fuel (ATF) for use in the current light water reactor (LWR) fleet is highly desirable for the future of nuclear power. Uranium mononitride has been identified as an alternative fuel with higher uranium density and thermal conductivity when compared to the benchmark, UO2, which could also provide significant economic benefits. However, UN by itself reacts with water at reactor operating temperatures. In order to reduce its reactivity, the addition of UO2 to UN has been suggested. In order to avoid carbon impurities, UN was synthesized from elemental uranium using a hydride-dehydride-nitride thermal synthesis route prior to mixing with up to 10 wt% UO2 in a planetary ball mill. UN and UN - UO2 composite pellets were sintered in Ar - (0-1 at%) N2 to study the effects of nitrogen concentration on the evolved phases and microstructure. UN and UN-UO2 composite pellets were also sintered in Ar - 100 ppm N2 to assess the effects of temperature (1700-2000 °C) on the final grain morphology and phase concentration.

Polymorphism in Alkali Metal Uranyl Nitrates: Synthesis and Crystal Structure of γ-K(UO2)(NO3)3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jouffret, Laurent J.; Krivovichev, Sergey V.; Burns, Peter C.

2011-07-20

Single crystals of γ-K(UO2)(NO3)3 were prepared from aqueous solutions by evaporation. The crystal structure [orthorhombic, Pbca (61), a = 9.2559(3) Å, b = 12.1753(3) Å, c = 15.8076(5) Å, V = 1781.41(9) Å3, Z = 8] was determined by direct methods and refined to R1 = 0.0267 on the basis of 3657 unique observed reflections. The structure is composed of isolated anionic uranyl trinitrate units, [(UO2)(NO3)3]–, that are linked through eleven-coordinated K+ cations. Both known polymorphs of K(UO2)(NO3)3 (α- and γ-phases) can be considered as based upon sheets of isolated complex [(UO2)(NO3)3]– ions separated by K+ cations. The existence ofmore » polymorphism in the two K[UO2(NO3)3] polymorphs is due to the different packing modes of uranyl trinitrate clusters that adopt the same two-dimensional but different three-dimensional arrangements.« less

Precisely Determining Ultralow level UO22+ in Natural Water with Plasmonic Nanowire Interstice Sensor

NASA Astrophysics Data System (ADS)

Gwak, Raekeun; Kim, Hongki; Yoo, Seung Min; Lee, Sang Yup; Lee, Gyoung-Ja; Lee, Min-Ku; Rhee, Chang-Kyu; Kang, Taejoon; Kim, Bongsoo

2016-01-01

Uranium is an essential raw material in nuclear energy generation; however, its use raises concerns about the possibility of severe damage to human health and the natural environment. In this work, we report an ultrasensitive uranyl ion (UO22+) detection method in natural water that uses a plasmonic nanowire interstice (PNI) sensor combined with a DNAzyme-cleaved reaction. UO22+ induces the cleavage of DNAzymes into enzyme strands and released strands, which include Raman-active molecules. A PNI sensor can capture the released strands, providing strong surface-enhanced Raman scattering signal. The combination of a PNI sensor and a DNAzyme-cleaved reaction significantly improves the UO22+ detection performance, resulting in a detection limit of 1 pM and high selectivity. More importantly, the PNI sensor operates perfectly, even in UO22+-contaminated natural water samples. This suggests the potential usefulness of a PNI sensor in practical UO22+-sensing applications. We anticipate that diverse toxic metal ions can be detected by applying various ion-specific DNA-based ligands to PNI sensors.

On the mechanical stability of uranyl peroxide hydrates: Implications for nuclear fuel degradation

DOE PAGES

Weck, Philippe F.; Kim, Eunja; Buck, Edgar C.

2015-09-11

The mechanical properties and stability of studtite, (UO 2)(O 2)(H 2O) 2·2H 2O, and metastudtite, (UO 2)(O 2)(H 2O) 2, two important corrosion phases observed on spent nuclear fuel exposed to water, have been investigated using density functional perturbation theory. While (UO 2)(O 2)(H 2O) 2 satisfies the necessary and sufficient Born criteria for mechanical stability, (UO 2)(O 2)(H 2O) 2·2H 2O is found to be mechanically metastable, which might be the underlying cause of the irreversibility of the studtite to metastudtite transformation. According to Pugh's and Poisson's ratios and the Cauchy pressure, both phases are considered ductile and shearmore » modulus is the parameter limiting their mechanical stability. Furthermore, debye temperatures of 294 and 271 K are predicted for polycrystalline (UO 2)(O 2)(H 2O) 2·2H 2O and (UO 2)(O 2)(H 2O) 2, suggesting a lower micro-hardness of metastudtite.« less

A Fock space coupled cluster study on the electronic structure of the UO(2), UO(2) (+), U(4+), and U(5+) species.

PubMed

Infante, Ivan; Eliav, Ephraim; Vilkas, Marius J; Ishikawa, Yasuyuki; Kaldor, Uzi; Visscher, Lucas

2007-09-28

The ground and excited states of the UO(2) molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach (DC-IHFSCC). This method is unique in describing dynamic and nondynamic correlation energies at relatively low computational cost. Spin-orbit coupling effects have been fully included by utilizing the four-component Dirac-Coulomb Hamiltonian from the outset. Complementary calculations on the ionized systems UO(2) (+) and UO(2) (2+) as well as on the ions U(4+) and U(5+) were performed to assess the accuracy of this method. The latter calculations improve upon previously published theoretical work. Our calculations confirm the assignment of the ground state of the UO(2) molecule as a (3)Phi(2u) state that arises from the 5f(1)7s(1) configuration. The first state from the 5f(2) configuration is found above 10,000 cm(-1), whereas the first state from the 5f(1)6d(1) configuration is found at 5,047 cm(-1).

Thermal transport in UO 2 with defects and fission products by molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiang-Yang; Cooper, Michael William Donald; Mcclellan, Kenneth James

2015-10-14

The importance of the thermal transport in nuclear fuel has motivated a wide range of experimental and modelling studies. In this report, the reduction of thermal transport in UO 2 due to defects and fission products has been investigated using non-equilibrium MD simulations, with two sets of empirical potentials for studying the degregation of UO 2 thermal conductivity including a Buckingham type interatomic potential and a recently developed EAM type interatomic potential. Additional parameters for U 5+ and Zr 4+ in UO 2 have been developed for the EAM potential. The thermal conductivity results from MD simulations are then correctedmore » for the spin-phonon scattering through Callaway model formulations. To validate the modelling results, comparison was made with experimental measurements on single crystal hyper-stoichiometric UO 2+x samples.« less

Six uranyl-organic frameworks with naphthalene-dicarboxylic acid and bipyridyl-based spacers: syntheses, structures, and properties.

PubMed

Xu, Wei; Ren, Ya-Nan; Xie, Miao; Zhou, Lin-Xia; Zheng, Yue-Qing

2018-03-28

A new series of uranium coordination polymers have been hydrothermally synthesized by using 1,4-naphthalene dicarboxylic acid (H 2 NDC), namely, (H 3 O) 2 [(UO 2 ) 2 (NDC) 3 ]·H 2 O (1), (H 2 -bpp)[(UO 2 ) 2 (NDC) 3 ]·EtOH·5H 2 O (2), (H 2 -bpe) 2/2 [(UO 2 ) 2 (NDC) 3 ]·EtOH (3), (H 2 -bpp)[(UO 2 ) 2 (NDC) 3 ]·5H 2 O (4), (H 2 -bpp)[(UO 2 )(HNDC)(NDC)] 2 ·2H 2 O (5), and (H 2 -bpy)[(UO 2 )(NDC) 2 ] (6) [bpp = 1,3-di(4-pyridyl) propane, bpe = 4,4'-vinylenedipyridine, bpy = 4,4'-bipyridine]. Single-crystal X-ray diffraction demonstrates that complex 1 represents the uranyl-organic polycatenated framework derived from a simple two-dimensional honeycomb grid network structure via a H 2 NDC linker. Complexes 2-4 contain the dinuclear motifs of the two UO 7 pentagonal and one UO 8 hexagonal bipyramids which are linked by NDC 2- anions creating a (UO 2 ) 4 (NDC) 2 unit, and further extend to a 2D layer through NDC 2- anions. Complex 5 displays a 1D zigzag double chain structure, in which the carboxylate groups of the NDC 2- anions adopt a chelate mode and further extends to a 2D framework via hydrogen bonds. The 1D structure of complex 6 is similar to the zigzag chain of complex 5. In addition, powder X-ray diffraction, elemental analysis, IR, thermal stability and luminescence properties of all complexes have also been investigated in this paper. The photocatalytic properties of the six complexes for the degradation of tetracycline hydrochloride (TC) under UV irradiation have been examined. Moreover, density functional theory (DFT) calculations were carried out to explore the electronic structural and bonding properties of the uranyl complexes 1-6.

Supplemental Environmental Impact Statement, Guam and Commonwealth of the Northern Mariana Islands Military Relocation (2012 Roadmap Adjustments)

DTIC Science & Technology

2015-07-01

Improvements & Traffic Signal Activation RF C-32 UoG UoG Wind Turbine University Drive 2013 Complete A 70-foot (21.3 m) wind turbine RC C-33 UoG... turbine Talofofo 2013 Contract approved 15 MW solar / wind turbine farm to help power 2,200 homes P S-5 GovGuam GWA Santa Rita Springs Booster...Rehabilitation of Asan Springs P B X X B B B C-31 GovGuam Route 26/25 Intersection Improvements RF B B X X B B B C-32 UoG Wind Turbine P

Uranium migration in spark plasma sintered W/UO2 CERMETS

NASA Astrophysics Data System (ADS)

Tucker, Dennis S.; Wu, Yaqiao; Burns, Jatuporn

2018-03-01

W/UO2 CERMET samples were sintered in a Spark Plasma Sintering (SPS) furnace at various temperature under vacuum and pressure. High Resolution Transmission Electron Microscopy (HRTEM) with Energy Dispersive Spectroscopy (EDS) was performed on the samples to determine interface structures and uranium diffusion from the UO2 particles into the tungsten matrix. Local Electrode Atom Probe (LEAP) was also performed to determine stoichiometry of the UO2 particles. It was seen that uranium diffused approximately 10-15 nm into the tungsten matrix. This is explained in terms of production of oxygen vacancies and Fick's law of diffusion.

SEPARATION OF URANIUM AND PLUTONIUM OXIDES

DOEpatents

Benedict, G.E.; Lyon, W.L.

1961-12-01

ABS>A method of separating a mixture of UO/sub 2/ and PuO/sub 2/ is given which comprises immersing the mixture in a fused NaCl-KCl bath, chlorinating with chlorine or phosgene, and preferentially electrolytically or chemically reducing the UO/sub 2/Cl/sub 2/ so produced to UO/sub 2/ and filtering it out. (AEC)

Microbes make average 2 nanometer diameter crystalline UO2 particles.

NASA Astrophysics Data System (ADS)

Suzuki, Y.; Kelly, S. D.; Kemner, K. M.; Banfield, J. F.

2001-12-01

It is well known that phylogenetically diverse groups of microorganisms are capable of catalyzing the reduction of highly soluble U(VI) to highly insoluble U(IV), which rapidly precipitates as uraninite (UO2). Because biological uraninite is highly insoluble, microbial uranyl reduction is being intensively studied as the basis for a cost-effective in-situ bioremediation strategy. Previous studies have described UO2 biomineralization products as amorphous or poorly crystalline. The objective of this study is to characterize the nanocrystalline uraninite in detail in order to determine the particle size, crystallinity, and size-related structural characteristics, and to examine the implications of these for reoxidation and transport. In this study, we obtained U-contaminated sediment and water from an inactive U mine and incubated them anaerobically with nutrients to stimulate reductive precipitation of UO2 by indigenous anaerobic bacteria, mainly Gram-positive spore-forming Desulfosporosinus and Clostridium spp. as revealed by RNA-based phylogenetic analysis. Desulfosporosinus sp. was isolated from the sediment and UO2 was precipitated by this isolate from a simple solution that contains only U and electron donors. We characterized UO2 formed in both of the experiments by high resolution-TEM (HRTEM) and X-ray absorption fine structure analysis (XAFS). The results from HRTEM showed that both the pure and the mixed cultures of microorganisms precipitated around 1.5 - 3 nm crystalline UO2 particles. Some particles as small as around 1 nm could be imaged. Rare particles around 10 nm in diameter were also present. Particles adhere to cells and form colloidal aggregates with low fractal dimension. In some cases, coarsening by oriented attachment on \\{111\\} is evident. Our preliminary results from XAFS for the incubated U-contaminated sample also indicated an average diameter of UO2 of 2 nm. In nanoparticles, the U-U distance obtained by XAFS was 0.373 nm, 0.012 nm smaller than found in the bulk structure of UO2 (0.385 nm). This indicates contraction within the nanoparticles due to tensile surface stress. Microbially formed UO2 is highly reactive, thus will be oxidized quickly as redox conditions change. Our findings support a growing number of studies that indicate that biominerals formed as the result of enzyme-mediated redox reactions are nanoparticulate. Preliminary results suggest that these particles will be readily transported through sandy aquifers, especially when conditions prevent high degrees of flocculation. Thus, despite its low (but size-dependent) solubility, UO2 nanoparticle transport may exert a fundamental control on mobility of U in contaminated environments.

Mixed-metal uranium(VI) iodates: hydrothermal syntheses, structures, and reactivity of Rb[UO(2)(CrO(4))(IO(3))(H(2)O)], A(2)[UO(2)(CrO(4))(IO(3))(2)] (A = K, Rb, Cs), and K(2)[UO(2)(MoO(4))(IO(3))(2)].

PubMed

Sykora, Richard E; McDaniel, Steven M; Wells, Daniel M; Albrecht-Schmitt, Thomas E

2002-10-07

The reactions of the molecular transition metal iodates A[CrO(3)(IO(3))] (A = K, Rb, Cs) with UO(3) under mild hydrothermal conditions provide access to four new, one-dimensional, uranyl chromatoiodates, Rb[UO(2)(CrO(4))(IO(3))(H(2)O)] (1) and A(2)[UO(2)(CrO(4))(IO(3))(2)] (A = K (2), Rb (3), Cs (4)). Under basic conditions, MoO(3), UO(3), and KIO(4) can be reacted to form K(2)[UO(2)(MoO(4))(IO(3))(2)] (5), which is isostructural with 2 and 3. The structure of 1 consists of one-dimensional[UO(2)(CrO(4))(IO(3))(H(2)O)](-) ribbons that contain uranyl moieties bound by bridging chromate and iodate anions as well as a terminal water molecule to create [UO(7)] pentagonal bipyramidal environments around the U(VI) centers. These ribbons are separated from one another by Rb(+) cations. When the iodate content is increased in the hydrothermal reactions, the terminal water molecule is replaced by a monodentate iodate anion to yield 2-4. These ribbons can be further modified by replacing tetrahedral chromate anions with MoO(4)(2)(-) anions to yield isostructural, one-dimensional [UO(2)(MoO(4))(IO(3))(2)](2)(-) ribbons. Crystallographic data: 1, triclinic, space group P(-)1, a = 7.3133(5) A, b = 8.0561(6) A, c = 8.4870(6) A, alpha = 88.740(1) degrees, beta = 87.075(1) degrees, gamma = 71.672(1) degrees, Z = 2; 2, monoclinic, space group P2(1)/c, a = 11.1337(5) A, b = 7.2884(4) A, c = 15.5661(7) A, beta = 107.977(1) degrees, Z = 4; 3, monoclinic, space group P2(1)/c, a = 11.3463(6) A, b = 7.3263(4) A, c = 15.9332(8) A, beta = 108.173(1) degrees, Z = 4; 4, monoclinic, space group P2(1)/n, a = 7.3929(5) A, b = 8.1346(6) A, c = 22.126(2) A, beta = 90.647(1) degrees, Z = 4; 5, monoclinic, space group P2(1)/c, a = 11.3717(6) A, b = 7.2903(4) A, c = 15.7122(8) A, beta = 108.167(1) degrees, Z = 4.

From Layered Structures to Cubic Frameworks. Expanding the Structural Diversity of Uranyl Carboxyphosphonates via the Incorporation of Cobalt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alsobrook, Andrea N.; Hauser, Brad G.; Hupp, Joseph T.

2011-02-08

Five heterobimetallic U(VI)/Co(II) carboxyphosphonates have been synthesized under mild hydrothermal conditions by reacting UO 3, Co(CH 3CO 2) 2·4H 2O, and triethyl phosphonoacetate. These compounds, Co(H 2O) 4[(UO 2) 2(PO 3CH 2CO 2) 2(H 2O) 2] (CoUPAA-1), [Co(H 2O) 6][UO 2(PO 3CH 2CO 2)] 2·8H 2O (CoUPAA-2), Co(H 2O) 4[UO 2(PO 3CH 2CO 2)] 2·4H 2O (CoUPAA-3), Co(H 2O) 4[(UO 2) 62CH 2CO 2) 2O 2(OH) 3(H 2O) 3] 2·3H 2O (CoUPAA-4), and Co 2(UO 2) 6(PO 3CH 2CO 2) 3O 3(OH)(H 2O) 2·16H 2O (CoUPAA-5), range from two- to three-dimensional structures. CoUPAA-1 to CoUPAA-3 all possess uranyl carboxyphosphonate layersmore » that are separated by the Co(II) cation with varying degrees of hydration. CoUPAA-4 contains both UO 7 pentagonal bipyramids and UO 8 hexagonal bipyramids within the uranyl carboxyphosphonate plane. Unlike the first four low-symmetry compounds, CoUPAA-5 is a cubic, three-dimensional network with large cavities approximately 16 Å in diameter that are filled with cocrystallized water molecules. Differential gas absorption measurements performed on CoUPAA-5 displayed a surface area uptake for CO 2 of 40 m 2 g -1 at 273 K, and no uptake for N 2 at 77 K.« less

How to Adapt Chemical Risk Assessment for Unconventional Hydrocarbon Extraction Related to the Water System.

PubMed

Faber, Ann-Hélène; Annevelink, Mark; Gilissen, Herman Kasper; Schot, Paul; van Rijswick, Marleen; de Voogt, Pim; van Wezel, Annemarie

2017-12-27

We identify uncertainties and knowledge gaps of chemical risk assessment related to unconventional drillings and propose adaptations. We discuss how chemical risk assessment in the context of unconventional oil and gas (UO&G) activities differs from conventional chemical risk assessment and the implications for existing legislation. A UO&G suspect list of 1,386 chemicals that might be expected in the UO&G water samples was prepared which can be used for LC-HRMS suspect screening. We actualize information on reported concentrations in UO&G-related water. Most information relates to shale gas operations, followed by coal-bed methane, while only little is available for tight gas and conventional gas. The limited research on conventional oil and gas recovery hampers comparison whether risks related to unconventional activities are in fact higher than those related to conventional activities. No study analyzed the whole cycle from fracturing fluid, flowback and produced water, and surface water and groundwater. Generally target screening has been used, probably missing contaminants of concern. Almost half of the organic compounds analyzed in surface water and groundwater exceed TTC values, so further risk assessment is needed, and risks cannot be waived. No specific exposure scenarios toward groundwater aquifers exist for UO&G-related activities. Human errors in various stages of the life cycle of UO&G production play an important role in the exposure. Neither at the international level nor at the US federal and the EU levels, specific regulations for UO&G-related activities are in place to protect environmental and human health. UO&G activities are mostly regulated through general environmental, spatial planning, and mining legislation.

Intensive Monitoring of Urine Output Is Associated With Increased Detection of Acute Kidney Injury and Improved Outcomes.

PubMed

Jin, Kui; Murugan, Raghavan; Sileanu, Florentina E; Foldes, Emily; Priyanka, Priyanka; Clermont, Gilles; Kellum, John A

2017-11-01

Urine output (UO) is a vital sign for critically ill patients, but standards for monitoring and reporting vary widely between ICUs. Careful monitoring of UO could lead to earlier recognition of acute kidney injury (AKI) and better fluid management. We sought to determine if the intensity of UO monitoring is associated with outcomes in patients with and those without AKI. This was a retrospective cohort study including 15,724 adults admitted to ICUs from 2000 to 2008. Intensive UO monitoring was defined as hourly recordings and no gaps > 3 hours for the first 48 hours after ICU admission. Intensive monitoring for UO was conducted in 4,049 patients (26%), and we found significantly higher rates of AKI (OR, 1.22; P < .001) in these patients. After adjustment for age and severity of illness, intensive UO monitoring was associated with improved survival but only among patients experiencing AKI. With or without AKI, patients with intensive monitoring also had less cumulative fluid volume (2.98 L vs 3.78 L; P < .001) and less fluid overload (2.49% vs 5.68%; P < .001) over the first 72 hours of ICU stay. In this large ICU population, intensive monitoring of UO was associated with improved detection of AKI and reduced 30-day mortality in patients experiencing AKI, as well as less fluid overload for all patients. Our results should help inform clinical decisions and ICU policy about frequency of monitoring of UO, especially for patients at high risk of AKI or fluid overload, or both. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

UO₂²⁺ uptake by proteins: understanding the binding features of the super uranyl binding protein and design of a protein with higher affinity.

PubMed

Odoh, Samuel O; Bondarevsky, Gary D; Karpus, Jason; Cui, Qiang; He, Chuan; Spezia, Riccardo; Gagliardi, Laura

2014-12-17

The capture of uranyl, UO2(2+), by a recently engineered protein (Zhou et al. Nat. Chem. 2014, 6, 236) with high selectivity and femtomolar sensitivity has been examined by a combination of density functional theory, molecular dynamics, and free-energy simulations. It was found that UO2(2+) is coordinated to five carboxylate oxygen atoms from four amino acid residues of the super uranyl binding protein (SUP). A network of hydrogen bonds between the amino acid residues coordinated to UO2(2+) and residues in its second coordination sphere also affects the protein's uranyl binding affinity. Free-energy simulations show how UO2(2+) capture is governed by the nature of the amino acid residues in the binding site, the integrity and strength of the second-sphere hydrogen bond network, and the number of water molecules in the first coordination sphere. Alteration of any of these three factors through mutations generally results in a reduction of the binding free energy of UO2(2+) to the aqueous protein as well as of the difference between the binding free energies of UO2(2+) and other ions (Ca(2+), Cu(2+), Mg(2+), and Zn(2+)), a proxy for the protein's selectivity over these ions. The results of our free-energy simulations confirmed the previously reported experimental results and allowed us to discover a mutant of SUP, specifically the GLU64ASP mutant, that not only binds UO2(2+) more strongly than SUP but that is also more selective for UO2(2+) over other ions. The predictions from the computations were confirmed experimentally.

Density functional theory calculations of UO2 oxidation: evolution of UO(2+x), U4O(9-y), U3O7, and U3O8.

PubMed

Andersson, D A; Baldinozzi, G; Desgranges, L; Conradson, D R; Conradson, S D

2013-03-04

Formation of hyperstoichiometric uranium dioxide, UO2+x, derived from the fluorite structure was investigated by means of density functional theory (DFT) calculations. Oxidation was modeled by adding oxygen atoms to UO2 fluorite supercells. For each compound ab initio molecular dynamics simulations were performed to allow the ions to optimize their local geometry. A similar approach was used for studying the reduction of U3O8. In agreement with the experimental phase diagram we identify stable line compounds at the U4O9-y and U3O7 stoichiometries. Although the transition from fluorite to the layered U3O8 structure occurs at U3O7 (UO2.333) or U3O7.333 (UO2.444), our calculated low temperature phase diagram indicates that the fluorite derived compounds are favored up to UO2.5, that is, as long as the charge-compensation for adding oxygen atoms occurs via formation of U(5+) ions, after which the U3O8-y phase becomes more stable. The most stable fluorite UO2+x phases at low temperature (0 K) are based on ordering of split quad-interstitial oxygen clusters. Most existing crystallographic models of U4O9 and U3O7, however, apply the cuboctahedral cluster. To better understand these discrepancies, the new structural models are analyzed in terms of existing neutron diffraction data. DFT calculations were also performed on the experimental cuboctahedral based U4O9-y structure, which enable comparisons between the properties of this phase with the quad-interstitial ones in detail.

Failure of ESI Spectra to Represent Metal-Complex Solution Composition: A Study of Lanthanide-Carboxylate Complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, Luther W.; Campbell, James A.; Clark, Sue B.

2014-01-21

Electrospray ionization - mass spectrometry (ESI-MS) was used for the characterization of uranyl complexed to tributyl phosphate (TBP) and dibutyl phosphate (DBP). The stoichiometry of uranyl with TBP and DBP was determined, and the gas phase speciation was found to be dependent on the cone voltage applied to induce fragmentation on the gas phase complexes. To quantitatively compare the gas phase distribution of species to solution, apparent stability constants were calculated. With a cone voltage of 80V, the apparent stability constants for the complexes UO2(NO3)2•2TBP, UO2(NO3)2(H2O)•2TBP, and UO2(DBP)+ were determined. With a lower cone voltage applied, larger complexes were observedmore » and stability constants for the complexes UO2(NO3)2•3TBP and UO2(DBP)42- were determined.« less

Advances in the Development of a WCl6 CVD System for Coating UO2 Powders with Tungsten

NASA Technical Reports Server (NTRS)

Mireles, Omar R.; Tieman, Alyssa; Broadway, Jeramie; Hickman, Robert

2013-01-01

W-UO2 CERMET fuels are under development to enable Nuclear Thermal Propulsion (NTP) for deep space exploration. Research efforts with an emphasis on fuel fabrication, testing, and identification of potential risks is underway. One primary risk is fuel loss due to CTE mismatch between W and UO2 and the grain boundary structure of W particles resulting in higher thermal stresses. Mechanical failure can result in significant reduction of the UO2 by hot hydrogen. Fuel loss can be mitigated if the UO2 particles are coated with a layer of high density tungsten before the consolidation process. This paper discusses the work to date, results, and advances of a fluidized bed chemical vapor deposition (CVD) system that utilizes the H2-WCl6 reduction process. Keywords: Space, Nuclear, Thermal, Propulsion, Fuel, CERMET, CVD, Tungsten, Uranium

Direct Electrodeposition of UO2 from Uranyl Bis(trifluoromethanesulfonyl)imide Dissolved in 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide Room Temperature Ionic Liquid System

DOE PAGES

Freiderich, John W.; Wanigasekara, Eranda P.; Sun, Xiao-Guang; ...

2013-11-11

Our study demonstrates a direct electrodeposition of UO 2 at a Pt cathode from a solution of uranyl bis(trifluoromethanesulfonyl)imide [UO 2(NTf 2) 2)] in a bulk room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM +NTf 2 –). Cyclic voltammetry (CV) studies revealed two reduction waves corresponding to the conversion of uranium(VI) to uranium(IV), and a mechanism for the overall electroreduction is proposed. A controlled-potential experiment was performed, holding the reduction potential at–1.0 V for 24 h to obtain a brown-black deposit of UO 2 on the Pt cathode. The Faradaic efficiency of the reduction process was determined to be >80%. Themore » UO 2deposit was characterized by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).« less

Uranyl Ion Complexes with Long-Chain Aliphatic α,ω-Dicarboxylates and 3d-Block Metal Counterions.

PubMed

Thuéry, Pierre; Harrowfield, Jack

2016-03-07

Twelve new complexes were obtained from reaction of uranyl ions with the aliphatic dicarboxylic acids HOOC-(CH2)n-2-COOH (H2Cn; n = 7-10 and 12) under solvo-hydrothermal conditions, in the presence of 3d-block metal ions (Mn(2+), Fe(3+), Co(2+), Ni(2+), and Cu(2+)) and 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen). In contrast to previously reported triple-stranded helicates obtained with C9(2-) and C12(2-), all these complexes crystallize as polymeric one-dimensional (1D) or two-dimensional (2D) species. [Fe(bipy)3][(UO2)2(C7)3]·3H2O (1), [Cu(phen)2]2[(UO2)3(C7)4(H2O)2]·2H2O (2), and [Cu(bipy)2]2[(UO2)2(C9)3] (6), in which the 3d cation was reduced in situ, are 1D ladderlike polymers displaying tetra- or hexanuclear rings, of sufficient width to encompass two counterions in 2 and 6. The three complexes [Co(phen)3][(UO2)3(C8)3(O)]·H2O (3), [Ni(phen)3][(UO2)3(C8)3(O)]·H2O (4) and [Co(phen)3][(UO2)3(C9)3(O)]·H2O (5) contain bis(μ3-oxo)-bridged tetranuclear secondary building units, and they crystallize as deeply furrowed 2D assemblies. Depending on the nature of the counterion, C10(2-) gives [Ni(bipy)3][(UO2)2(C10)3]·2H2O (7), a 2D network displaying elongated decanuclear rings containing the counterions, or [Mn(phen)3][(UO2)2(C10)3]·6H2O (8), [Co(phen)3][(UO2)2(C10)3]·7H2O (9), and [Ni(phen)3][(UO2)2(C10)3]·7H2O (10), which consist of 2D assemblies with honeycomb topology; the hexanuclear rings in 8-10 are chairlike and occupied by one counterion and two uranyl groups from neighboring layers. Two complexes of the ligand with the longest chain, C12(2-), are reported. [UO2(C12)(bipy)] (11) is a neutral 1D species in which bipy chelates the uranyl ion and plays an important role in the packing through π-stacking interactions. Two polymeric units, 1D and 2D, coexist in the complex [Ni(bipy)3][(UO2)2(C12)3][UO2(C12)(H2O)2]·H2O (12); the 2D network has the honeycomb topology, but the hexanuclear rings are markedly convoluted, with local features akin to those in helicates, and the counterions are embedded in intralayer cavities. Emission spectra measured in the solid state show in most cases various degrees of quenching, with intense and well-resolved uranyl emission being observed only for complexes 2 and 11.

In situ synchrotron investigation of grain growth behavior of nano-grained UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, Yinbin; Yao, Tiankai; Lian, Jie

Here, we report on the study of grain growth kinetics in nano-grained UO 2 samples. Dense nano-grained UO 2 samples with well-controlled stoichiometry and grain size were fabricated using the spark plasma sintering technique. To determine the grain growth kinetics at elevated temperatures, a synchrotron wide-angle X-ray scattering (WAXS) study was performed in situ to measure the real-time grain size evolution based on the modified Williamson-Hall analysis. The unique grain growth kinetics of nanocrystalline UO 2 at 730 °C and 820 °C were observed and explained by the difference in mobility of various grain boundaries.

In situ synchrotron investigation of grain growth behavior of nano-grained UO 2

DOE PAGES

Miao, Yinbin; Yao, Tiankai; Lian, Jie; ...

2017-01-09

Here, we report on the study of grain growth kinetics in nano-grained UO 2 samples. Dense nano-grained UO 2 samples with well-controlled stoichiometry and grain size were fabricated using the spark plasma sintering technique. To determine the grain growth kinetics at elevated temperatures, a synchrotron wide-angle X-ray scattering (WAXS) study was performed in situ to measure the real-time grain size evolution based on the modified Williamson-Hall analysis. The unique grain growth kinetics of nanocrystalline UO 2 at 730 °C and 820 °C were observed and explained by the difference in mobility of various grain boundaries.

Synthesis and sintering of UN-UO 2 fuel composites

DOE PAGES

Jaques, Brian J.; Watkins, Jennifer; Croteau, Joseph R.; ...

2015-06-17

In this study, the design and development of an economical, accident tolerant fuel (ATF) for use in the current light water reactor (LWR) fleet is highly desirable for the future of nuclear power. Uranium mononitride has been identified as an alternative fuel with higher uranium density and thermal conductivity when compared to the benchmark, UO 2, which could also provide significant economic benefits. However, UN by itself reacts with water at reactor operating temperatures. In order to reduce its reactivity, the addition of UO 2 to UN has been suggested. In order to avoid carbon impurities, UN was synthesized frommore » elemental uranium using a hydride-dehydride-nitride thermal synthesis route prior to mixing with up to 10 wt% UO 2 in a planetary ball mill. UN and UN – UO 2 composite pellets were sintered in Ar – (0–1 at%) N 2 to study the effects of nitrogen concentration on the evolved phases and microstructure. UN and UN-UO 2 composite pellets were also sintered in Ar – 100 ppm N 2 to assess the effects of temperature (1700–2000 °C) on the final grain morphology and phase concentration.« less

Oxo-exchange of gas-phase uranyl, neptunyl, and plutonyl with water and methanol.

PubMed

Lucena, Ana F; Odoh, Samuel O; Zhao, Jing; Marçalo, Joaquim; Schreckenbach, Georg; Gibson, John K

2014-02-17

A challenge in actinide chemistry is activation of the strong bonds in the actinyl ions, AnO2(+) and AnO2(2+), where An = U, Np, or Pu. Actinyl activation in oxo-exchange with water in solution is well established, but the exchange mechanisms are unknown. Gas-phase actinyl oxo-exchange is a means to probe these processes in detail for simple systems, which are amenable to computational modeling. Gas-phase exchange reactions of UO2(+), NpO2(+), PuO2(+), and UO2(2+) with water and methanol were studied by experiment and density functional theory (DFT); reported for the first time are experimental results for UO2(2+) and for methanol exchange, as well as exchange rate constants. Key findings are faster exchange of UO2(2+) versus UO2(+) and faster exchange with methanol versus water; faster exchange of UO2(+) versus PuO2(+) was quantified. Computed potential energy profiles (PEPs) are in accord with the observed kinetics, validating the utility of DFT to model these exchange processes. The seemingly enigmatic result of faster exchange for uranyl, which has the strongest oxo-bonds, may reflect reduced covalency in uranyl as compared with plutonyl.

Ruthenium Nanoparticles Mediated Electrocatalytic Reduction of UO22+ Ions for Its Rapid and Sensitive Detection in Natural Waters.

PubMed

Gupta, Ruma; Sundararajan, Mahesh; Gamare, Jayashree S

2017-08-01

Reduction of UO 2 2+ ions to U 4+ ions is difficult due to involvement of two axially bonded oxygen atoms, and often requires a catalyst to lower the activation barrier. The noble metal nanoparticles (NPs) exhibit high electrocatalytic activity, and could be employed for the sensitive and rapid quantifications of U0 2 2+ ions in the aqueous matrix. Therefore, the Pd, Ru, and Rh NPs decorated glassy carbon electrode were examined for their efficacy toward electrocatalytic reduction of UO 2 2+ ions and observed that Ru NPs mediate efficiently the electro-reduction of UO 2 2+ ions. The mechanism of the electroreduction of UO 2 2+ by the RuNPs/GC was studied using density functional theory calculations which pointed different approach of 5f metal ions electroreduction unlike 4p metal ions such as As(III). RuNP decorated on the glassy carbon would be hydrated, which in turn assist to adsorb the uranyl sulfates through hydrogen bonding thus facilitated electro-reduction. Differential pulse voltammetric (DPV) technique, was used for rapid and sensitive quantification of UO 2 2+ ions. The RuNPs/GC based DPV technique could be used to determine the concentration of uranyl in a few minutes with a detection limit of 1.95 ppb. The RuNPs/GC based DPV was evaluated for its analytical performance using seawater as well lake water and groundwater spiked with known amounts of UO 2 2+ .

Towards a Quantitative Framework for Evaluating Vulnerability of Drinking Water Wells to Contamination from Unconventional Oil & Gas Development

NASA Astrophysics Data System (ADS)

Soriano, M., Jr.; Deziel, N. C.; Saiers, J. E.

2017-12-01

The rapid expansion of unconventional oil and gas (UO&G) production, made possible by advances in hydraulic fracturing (fracking), has triggered concerns over risks this extraction poses to water resources and public health. Concerns are particularly acute within communities that host UO&G development and rely heavily on shallow aquifers as sources of drinking water. This research aims to develop a quantitative framework to evaluate the vulnerability of drinking water wells to contamination from UO&G activities. The concept of well vulnerability is explored through application of backwards travel time probability modeling to estimate the likelihood that capture zones of drinking water wells circumscribe source locations of UO&G contamination. Sources of UO&G contamination considered in this analysis include gas well pads and documented sites of UO&G wastewater and chemical spills. The modeling approach is illustrated for a portion of Susquehanna County, Pennsylvania, where more than one thousand shale gas wells have been completed since 2005. Data from a network of eight multi-level groundwater monitoring wells installed in the study site in 2015 are used to evaluate the model. The well vulnerability concept is proposed as a physically based quantitative tool for policy-makers dealing with the management of contamination risks of drinking water wells. In particular, the model can be used to identify adequate setback distances of UO&G activities from drinking water wells and other critical receptors.

Learning considered within a cultural context. Confucian and Socratic approaches.

PubMed

Tweed, Roger G; Lehman, Darrin R

2002-02-01

A Confucian-Socratic framework is used to analyze culture's influence on academic learning. Socrates, a Western exemplar, valued private and public questioning of widely accepted knowledge and expected students to evaluate others' beliefs and to generate and express their own hypotheses. Confucius, an Eastern exemplar, valued effortful, respectful, and pragmatic acquisition of essential knowledge as well as behavioral reform. Expressions of these approaches in modern postsecondary contexts are discussed, as are the effects these approaches may have for students who either fit or do not fit the cultural ideal.

The thermodynamic properties of gaseous UO2(OH)2

NASA Astrophysics Data System (ADS)

Konings, R. J. M.; Kovács, A.; Beneš, O.

2017-12-01

Quantum chemical calculations of the molecular properties of the UO2(OH)2 molecule are presented. From the results the thermodynamic properties of this gaseous species have been calculated, and these have been used to re-evaluate the existing literature study on the volatilization of U3O8 in steam, allowing to derive the enthalpy of formation of the UO2(OH)2 molecule.

Composite thermochemistry of gas phase U(VI)-containing molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bross, David H.; Peterson, Kirk A., E-mail: kipeters@wsu.edu

Reaction energies have been calculated for a series of reactions involving UF{sub 6}, UO{sub 3}, UO{sub 2}(OH){sub 2}, and UO{sub 2}F{sub 2} using coupled cluster singles and doubles with perturbative triples, CCSD(T), with a series of correlation consistent basis sets, including newly developed pseudopotential (PP)- and all-electron (AE) Douglas-Kroll-Hess-based sets for the U atom. The energies were calculated using a Feller-Peterson-Dixon composite approach in which CCSD(T) complete basis set (CBS) limits were combined with a series of additive contributions for spin-orbit coupling, outer-core correlation, and quantum electrodynamics effects. The calculated reaction enthalpies (both PP and AE) were combined with themore » accurately known heat of formation of UF{sub 6} to determine the enthalpies of formation of UO{sub 3}, UO{sub 2}(OH){sub 2}, and UO{sub 2}F{sub 2}. The contribution to the reaction enthalpies due to correlation of the 5s5p5d electrons of U was observed to be very slowly convergent with basis set and at the CBS limit their impact on the final enthalpies was on the order of 1 kcal/mol or less. For these closed shell molecules, spin-orbit effects contributed about 1 kcal/mol to the final enthalpies. Interestingly, the PP and AE approaches yielded quite different spin-orbit contributions (similar magnitude but opposite in sign), but the total scalar plus spin-orbit results from the two approaches agreed to within ∼1 kcal/mol of each other. The final composite heat of formation for UO{sub 2}F{sub 2} was in excellent agreement with experiment, while the two results obtained for UO{sub 3} were just outside the ±2.4 kcal/mol error bars of the currently recommended experimental value. An improved enthalpy of formation (298 K) for UO{sub 2}(OH){sub 2} is predicted from this work to be −288.7 ± 3 kcal/mol, compared to the currently accepted experimental value of −292.7 ± 6 kcal/mol.« less

Oxide particle size distribution from shearing irradiated and unirradiated LWR fuels in Zircaloy and stainless steel cladding: significance for risk assessment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, W. Jr.; West, G.A.; Stacy, R.G.

1979-03-22

Sieve fractionation was performed with oxide particles dislodged during shearing of unirradiated or irradiated fuel bundles or single rods of UO/sub 2/ or 96 to 97% ThO/sub 2/--3 to 4% UO/sub 2/. Analyses of these data by nonlinear least-squares techniques demonstrated that the particle size distribution is lognormal. Variables involved in the numerical analyses include lognormal median size, lognormal standard deviation, and shear cut length. Sieve-fractionation data are presented for unirradiated bundles of stainless-steel-clad or Zircaloy-2-clad UO/sub 2/ or ThO/sub 2/--UO/sub 2/ sheared into lengths from 0.5 to 2.0 in. Data are also presented for irradiated single rods (sheared intomore » lengths of 0.25 to 2.0 in.) of Zircaloy-2-clad UO/sub 2/ from BWRs and of Zircaloy-4-clad UO/sub 2/ from PWRs. Median particle sizes of UO/sub 2/ from shearing irradiated stainless-steel-clad fuel ranged from 103 to 182 ..mu..m; particle sizes of ThO/sub 2/--UO/sub 2/, under these same conditions, ranged from 137 to 202 ..mu..m. Similarly, median particle sizes of UO/sub 2/ from shearing unirradiated Zircaloy-2-clad fuel ranged from 230 to 957 ..mu..m. Irradiation levels of fuels from reactors ranged from 9,000 to 28,000 MWd/MTU. In general, particle sizes from shearing these irradiated fuels are larger than those from the unirradiated fuels; however, unirradiated fuel from vendors was not available for performing comparative shearing experiments. In addition, variations in particle size parameters pertaining to samples of a single vendor varied as much as those between different vendors. The fraction of fuel dislodged from the cladding is nearly proportional to the reciprocal of the shear cut length, until the cut length attains some minimum value below which all fuel is dislodged. Particles of fuel are generally elongated with a long-to-short axis ratio usually less than 3. Using parameters of the lognormal distribution estimates can be made of fractions of dislodged fuel having dimensions less than specified values.« less

Disseminating NASA-based science through NASA's Universe of Learning: Girls STEAM Ahead

NASA Astrophysics Data System (ADS)

Marcucci, E.; Meinke, B. K.; Smith, D. A.; Ryer, H.; Slivinski, C.; Kenney, J.; Arcand, K.; Cominsky, L.

2017-12-01

The Girls STEAM Ahead with NASA (GSAWN) initiative partners the NASA's Universe of Learning (UoL) resources with public libraries to provide NASA-themed activities for girls and their families. The program expands upon the legacy program, NASA Science4Girls and Their Families, in celebration of National Women's History Month. Program resources include hands-on activities for engaging girls, such as coding experiences and use of remote telescopes, complementary exhibits, and professional development for library partner staff. The science-institute-embedded partners in NASA's UoL are uniquely poised to foster collaboration between scientists with content expertise and educators with pedagogy expertise. The thematic topics related to NASA Astrophysics enable audiences to experience the full range of NASA scientific and technical disciplines and the different career skills each requires. For example, an activity may focus on understanding exoplanets, methods of their detection, and characteristics that can be determined remotely. The events focus on engaging underserved and underrepresented audiences in Science, Technology, Engineering, and Mathematics (STEM) via use of research-based best practices, collaborations with libraries, partnerships with local and national organizations (e.g. National Girls Collaborative Project or NGCP), and remote engagement of audiences. NASA's UoL collaborated with another NASA STEM Activation partner, NASA@ My Library, to announce GSAWN to their extensive STAR_Net network of libraries. This partnership between NASA SMD-funded Science learning and literacy teams has included NASA@ My Library hosting a professional development webinar featuring a GSAWN activity, a newsletter and blog post about the program, and plans for future exhibit development. This presentation will provide an overview of the program's progress to engage girls and their families through the development and dissemination of NASA-based science programming.

Dissolution of Uranium Oxides Under Alkaline Oxidizing Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Steven C.; Peper, Shane M.; Douglas, Matthew

2009-11-01

Bench scale experiments were conducted to determine the dissolution characteristics of uranium oxide powders (UO2, U3O8, and UO3) in aqueous peroxide-carbonate solutions. Experimental parameters included H2O2 concentration, carbonate counter cation (NH4+, Na+, K+, and Rb+), and pH. Results indicate the dissolution rate of UO2 in 1 M (NH4)2CO3 increases linearly with peroxide concentration ranging from 0.05 – 2 M. The three uranium oxide powders exhibited different dissolution patterns however, UO3 exhibited prompt complete dissolution. Carbonate counter cation affected the dissolution kinetics. There is minimal impact of solution pH, over the range 8.8 to 10.6, on initial dissolution rate.

Biosensing for the Environment and Defence: Aqueous Uranyl Detection Using Bacterial Surface Layer Proteins

PubMed Central

Conroy, David J.R.; Millner, Paul A.; Stewart, Douglas I.; Pollmann, Katrin

2010-01-01

The fabrication of novel uranyl (UO22+) binding protein based sensors is reported. The new biosensor responds to picomolar levels of aqueous uranyl ions within minutes using Lysinibacillus sphaericus JG-A12 S-layer protein tethered to gold electrodes. In comparison to traditional self assembled monolayer based biosensors the porous bioconjugated layer gave greater stability, longer electrode life span and a denser protein layer. Biosensors responded specifically to UO22+ ions and showed minor interference from Ni2+, Cs+, Cd2+ and Co2+. Chemical modification of JG-A12 protein phosphate and carboxyl groups prevented UO22+ binding, showing that both moieties are involved in the recognition to UO22+. PMID:22399904

Developing uranium dicarbide-graphite porous materials for the SPES project

NASA Astrophysics Data System (ADS)

Biasetto, L.; Zanonato, P.; Carturan, S.; Di Bernardo, P.; Colombo, P.; Andrighetto, A.; Prete, G.

2010-09-01

Uranium carbide dispersed in graphite was produced under vacuum by means of carbothermic reduction of different uranium oxides (UO 2, U 3O 8 and UO 3), using graphite as the source of carbon. The thermal process was monitored by mass spectrometry and the gas evolution confirmed the reduction of the U 3O 8 and UO 3 oxides to UO 2 before the carbothermic reaction, that started to occur at T > 1000 °C. XRD analysis confirmed the formation of α-UC 2 and of a minor amount of UC. The morphology of the produced uranium carbide was not affected by the oxides employed as the source of uranium.

UO2 fuel pellets fabrication via Spark Plasma Sintering using non-standard molybdenum die

NASA Astrophysics Data System (ADS)

Papynov, E. K.; Shichalin, O. O.; Mironenko, A. Yu; Tananaev, I. G.; Avramenko, V. A.; Sergienko, V. I.

2018-02-01

The article investigates spark plasma sintering (SPS) of commercial uranium dioxide (UO2) powder of ceramic origin into highly dense fuel pellets using non-standard die instead of usual graphite die. An alternative and formerly unknown method has been suggested to fabricate UO2 fuel pellets by SPS for excluding of typical problems related to undesirable carbon diffusion. Influence of SPS parameters on chemical composition and quality of UO2 pellets has been studied. Also main advantages and drawbacks have been revealed for SPS consolidation of UO2 in non-standard molybdenum die. The method is very promising due to high quality of the final product (density 97.5-98.4% from theoretical, absence of carbon traces, mean grain size below 3 μm) and mild sintering conditions (temperature 1100 ºC, pressure 141.5 MPa, sintering time 25 min). The results are interesting for development and probable application of SPS in large-scale production of nuclear ceramic fuel.

Development Status of a CVD System to Deposit Tungsten onto UO2 Powder via the WCI6 Process

NASA Technical Reports Server (NTRS)

Mireles, O. R.; Kimberlin, A.; Broadway, J.; Hickman, R.

2014-01-01

Nuclear Thermal Propulsion (NTP) is under development for deep space exploration. NTP's high specific impulse (> 850 second) enables a large range of destinations, shorter trip durations, and improved reliability. W-60vol%UO2 CERMET fuel development efforts emphasize fabrication, performance testing and process optimization to meet service life requirements. Fuel elements must be able to survive operation in excess of 2850 K, exposure to flowing hydrogen (H2), vibration, acoustic, and radiation conditions. CTE mismatch between W and UO2 result in high thermal stresses and lead to mechanical failure as a result UO2 reduction by hot hydrogen (H2) [1]. Improved powder metallurgy fabrication process control and mitigated fuel loss can be attained by coating UO2 starting powders within a layer of high density tungsten [2]. This paper discusses the advances of a fluidized bed chemical vapor deposition (CVD) system that utilizes the H2-WCl6 reduction process.

LOW-TEMPERATURE MAGNETIC PROPERTIES OF SOME URANIUM OXIDES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leask, M.J.M.; Roberts, L.E.J.; Walter, A.J.

1963-10-01

The magnetic susceptibilities of UO/sub 2/, UO/sub 2.1/, U/sub 4/O/sub 9/ , U/s ub 3/O/sub 7/, and U/sub 3/O/sub 8/ at temperatures between 1.5 and 44 deg K were determined using an a-c inductance method. The susceptibility Of U/sub 3/ O/sub 8/ rises to a sharp maximum at 4.2 deg K, with smaller effects at 8 and at 25.3 deg K. The susceptibility of UO/sub 2/ reaches a maximum at 29 deg K and remains constant between 25 and 2 deg K. A maximum in the susceptibility- temperature plot for U/sub 4/O/sub 9/ at 6.4 deg K occurs also-in themore » plots for UO/sub 2.1/ an d U/sub 3/O/sub 7/ and appears to be primarily due to the inclusion of interstitial oxygen ions in the UO/sub 2/ lattice, independent of the precise nature of subsequent ordering effects. (auth)« less

Probing the electronic structure of UO+ with high-resolution photoelectron spectroscopy.

PubMed

Goncharov, Vasiliy; Kaledin, Leonid A; Heaven, Michael C

2006-10-07

The pulsed field ionization-zero kinetic energy photoelectron technique has been used to observe the low-lying energy levels of UO+. Rotationally resolved spectra were recorded for the ground state and the first nine electronically excited states. Extensive vibrational progressions were characterized. Omega+ assignments were unambiguously determined from the first rotational lines identified in each vibronic band. Term energies, vibrational frequencies, and anharmonicity constants for low-lying energy levels of UO+ are reported. In addition, accurate values for the ionization energies for UO [48,643.8(2) cm(-1)] and U [49,957.6(2) cm(-1)] were determined. The pattern of low-lying electronic states for UO+ indicates that they originate from the U3+(5f3)O2- configuration, where the uranium ion-centered interactions between the 5f electrons are significantly stronger than interactions with the intramolecular electric field. The latter lifts the degeneracy of U3+ ion-core states, but the atomic angular momentum quantum numbers remain reasonably well defined.

Thermally activated flux flow in FeSe0.5Te0.5 superconducting single crystal

NASA Astrophysics Data System (ADS)

Hamad, R. M.; Kayed, T. S.; Kunwar, S.; Ziq, Kh A.

2017-07-01

The current-voltage (J-E) isotherms of single crystal FeSe0.5Te0.5 sample have been measured at several temperatures near the transition temperature (Tc) and under applied magnetic fields (H). A power law (E ˜ Jβ ) has been used to fit the data and evaluate the activation energy Uo (T) using β = Uo/kBT. At low current density (J << Jc), the initial behaviour is associated with thermally activated flux Flow (TAFF) while at J >> Jc vortex flux flow (FF) behavior is expected. The effects of applied magnetic field on FF and TAFF also been investigated. We found that Uo(FF) was reduced with by about an order of magnitude in magnetic fields as low as ˜1.5 Tesla-the reduction in Uo(TAFF) is even faster than in Uo(FF)-hence reflecting the low pinning nature (defects, vacancies etc.) of FeSe0.5Te0.5 superconductor.

Amoeba behavior of UO/sub 2/ coated particle fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner-Loeffler, M.

1977-09-01

The data extracted from numerous irradiation tests were used to derive amoeba endurance parameters for UO/sub 2/. The data do not yet allow an unambiguous definition of the controlling mechanism, which may be due to either gaseous or solid-state diffusion processes. Adequate data on the amoeba effect are available for design of a steam-raising high-temperature gas-cooled reactor using UO/sub 2/ fuel.

Characterization of Actinides Complexed to Nuclear Fuel Constituents Using ESI-MS.

PubMed

McDonald, Luther W; Campbell, James A; Vercouter, Thomas; Clark, Sue B

2016-03-01

Electrospray ionization-mass spectrometry (ESI-MS) was tested for its use in monitoring spent nuclear fuel (SNF) constituents including U, Pu, dibutyl phosphate (DBP), and tributyl phosphate (TBP). Both positive and negative ion modes were used to evaluate the speciation of U and Pu with TBP and DBP. Furthermore, apparent stability constants were determined for U complexed to TBP and DBP. In positive ion mode, TBP produced a strong signal with and without complexation to U or Pu, but, in negative ion mode, no TBP, U-TBP, or Pu-TBP complexes were observed. Apparent stability constants were determined for [UO2(NO3)2(TBP)2], [UO2(NO3)2(H2O)(TBP)2], and [UO2(NO3)2(TBP)3]. In contrast DBP, U-DBP, and Pu-DBP complexes were observed in both positive and negative ion modes. Apparent stability constants were determined for the species [UO2(DBP)], [UO2(DBP)3], and [UO2(DBP)4]. Analyzing mixtures of U or Pu with TBP and DBP yielded the formation of ternary complexes whose stoichiometry was directly related to the ratio of TBP to DBP. The ESI-MS protocols used in this study will further demonstrate the utility of ESI-MS and its applicability to process control monitoring in SNF reprocessing facilities.

Probing the Oxygen Environment in UO22+ by Solid-State O-17 Nuclear Magnetic Resonance Spectroscopy and Relativistic Density Functional Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Herman M.; De Jong, Wibe A.; Soderquist, Chuck Z.

A combined theoretical and solid-state O-17 NMR study of the electronic structure of the uranyl ion UO22+ in (NH4)4UO2(CO3)3 and rutherfordine UO2CO3 is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens, and the latter exemplifying a uranyl environment without hydrogens. A fully relativistic ab initio treatment reveals unique features of the U-O covalent bond, including the finding of O-17 chemical shift anisotropies that are among the largest ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state O-17 NMR measurementsmore » in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the O-17 echo signal of UO22+. The William R. Wiley environmental Molecular Sciences Laboratory is a US Department of Energy national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington. PNNL is operated by Battelle for the US Department of Energy.« less

PUREX/UO{sub 3} deactivation project management plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Washenfelder, D.J.

1993-12-01

From 1955 through 1990, the Plutonium-Uranium Extraction Plant (PUREX) provided the United States Department of Energy Hanford Site with nuclear fuel reprocessing capability. It operated in sequence with the Uranium Trioxide (UO{sub 3}) Plant, which converted the PUREX liquid uranium nitrate product to solid UO{sub 3} powder. Final UO{sub 3} Plant operation ended in 1993. In December 1992, planning was initiated for the deactivation of PUREX and UO{sub 3} Plant. The objective of deactivation planning was to identify the activities needed to establish a passively safe, environmentally secure configuration at both plants, and ensure that the configuration could be retainedmore » during the post-deactivation period. The PUREX/UO{sub 3} Deactivation Project management plan represents completion of the planning efforts. It presents the deactivation approach to be used for the two plants, and the supporting technical, cost, and schedule baselines. Deactivation activities concentrate on removal, reduction, and stabilization of the radioactive and chemical materials remaining at the plants, and the shutdown of the utilities and effluents. When deactivation is completed, the two plants will be left unoccupied and locked, pending eventual decontamination and decommissioning. Deactivation is expected to cost $233.8 million, require 5 years to complete, and yield $36 million in annual surveillance and maintenance cost savings.« less

XPS study of the surface chemistry of UO2 (111) single crystal film

NASA Astrophysics Data System (ADS)

Maslakov, Konstantin I.; Teterin, Yury A.; Popel, Aleksej J.; Teterin, Anton Yu.; Ivanov, Kirill E.; Kalmykov, Stepan N.; Petrov, Vladimir G.; Springell, Ross; Scott, Thomas B.; Farnan, Ian

2018-03-01

A (111) air-exposed surface of UO2 thin film (150 nm) on (111) YSZ (yttria-stabilized zirconia) before and after the Ar+ etching and subsequent in situ annealing in the spectrometer analytic chamber was studied by XPS technique. The U 5f, U 4f and O 1s electron peak intensities were employed for determining the oxygen coefficient kO = 2 + x of a UO2+x oxide on the surface. It was found that initial surface (several nm) had kO = 2.20. A 20 s Ar+ etching led to formation of oxide UO2.12, whose composition does not depend significantly on the etching time (up to 180 s). Ar+ etching and subsequent annealing at temperatures 100-380 °C in vacuum was established to result in formation of stable well-organized structure UO2.12 reflected in the U 4f XPS spectra as high intensity (∼28% of the basic peak) shake-up satellites 6.9 eV away from the basic peaks, and virtually did not change the oxygen coefficient of the sample surface. This agrees with the suggestion that a stable (self-assembling) phase with the oxygen coefficient kO ≈ 2.12 forms on the UO2 surface.

Near Surface Stoichiometry in UO 2 : A Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Jianguo; Valderrama, Billy; Henderson, Hunter B.

2015-01-01

The mechanisms of oxygen stoichiometry variation in UO 2at different temperature and oxygen partial pressure are important for understanding the dynamics of microstructure in these crystals. However, very limited experimental studies have been performed to understand the atomic structure of UO 2near surface and defect effects of near surface on stoichiometry in which the system can exchange atoms with the external reservoir. In this study, the near (110) surface relaxation and stoichiometry in UO 2have been studied with density functional theory (DFT) calculations. On the basis of the point-defect model (PDM), a general expression for the near surface stoichiometric variationmore » is derived by using DFT total-energy calculations and atomistic thermodynamics, in an attempt to pin down the mechanisms of oxygen exchange between the gas environment and defected UO 2. By using the derived expression, it is observed that, under poor oxygen conditions, the stoichiometry of near surface is switched from hyperstoichiometric at 300 K with a depth around 3 nm to near-stoichiometric at 1000 K and hypostoichiometric at 2000 K. Furthermore, at very poor oxygen concentrations and high temperatures, our results also suggest that the bulk of the UO 2prefers to be hypostoichiometric, although the surface is near-stoichiometric.« less

Near surface stoichiometry in UO 2: A density functional theory study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Jianguo; Valderrama, Billy; Henderson, Hunter B.

2015-08-01

The mechanisms of oxygen stoichiometry variation in UO 2 at different temperature and oxygen partial pressure are important for understanding the dynamics of microstructure in these crystals. However, very limited experimental studies have been performed to understand the atomic structure of UO 2 near surface and defect effects of near surface on stoichiometry in which the system can exchange atoms with the external reservoir. In this study, the near (110) surface relaxation and stoichiometry in UO 2 have been studied with density functional theory (DFT) calculations. On the basis of the point-defect model (PDM), a general expression for the nearmore » surface stoichiometric variation is derived by using DFT total-energy calculations and atomistic thermodynamics, in an attempt to pin down the mechanisms of oxygen exchange between the gas environment and defected UO 2. By using the derived expression, it is observed that, under poor oxygen conditions, the stoichiometry of near surface is switched from hyperstoichiometric at 300 K with a depth around 3 nm to near-stoichiometric at 1000 K and hypostoichiometric at 2000 K. Furthermore, at very poor oxygen concentrations and high temperatures, our results also suggest that the bulk of the UO 2 prefers to be hypostoichiometric, although the surface is near-stoichiometric.« less

Excited States and Luminescent Properties of UO 2F 2 and Its Solvated Complexes in Aqueous Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Jing; Wang, Zheming; Pan, Duoqiang

2014-07-21

The electronic absorption and emission spectra of free UO 2F 2 and its water solvated complexes below 32 000 cm –1 are investigated at the levels of ab initio CASPT2 and CCSD(T) with inclusion of scalar relativistic and spin–orbit coupling effects. The influence of the water coordination on the electronic spectra of UO 2F 2 is explored by investigating the excited states of solvated complexes (H 2O) nUO 2F 2 (n = 1–3). In these uranyl complexes, water coordination is found to have appreciable influence on the 3Δ (Ω = 1 g) character of the luminescent state and on themore » electronic spectral shape. The simulated luminescence spectral curves based on the calculated spectral parameters of (H 2O) nUO 2F 2 from CCSD(T) approach agree well with experimental spectra in aqueous solution at both near-liquid-helium temperature and room temperature. The possible luminescence spectra of free UO 2F 2 in gas phase are predicted on the basis of CASPT2 and CCSD(T) results, respectively, by considering three symmetric vibration modes. Finally, the effect of competition between spin–orbit coupling and ligand field repulsion on the luminescent state properties is discussed.« less

The U(VI) speciation influenced by a novel Paenibacillus isolate from Mont Terri Opalinus clay.

PubMed

Lütke, Laura; Moll, Henry; Bachvarova, Velina; Selenska-Pobell, Sonja; Bernhard, Gert

2013-05-21

Bacterial cell walls have a high density of ionizable functional groups available for U(VI) binding, hence have a great potential to affect the speciation of this contaminant in the environment. The studied strain of the genus Paenibacillus is a novel isolate originating from the Mont Terri Opalinus clay formations (Switzerland) which are currently investigated as a potential host rock for future nuclear waste storage. U(VI) binding to the cell surface functional groups was studied by potentiometry combined with time-resolved laser-induced fluorescence spectroscopy (TRLFS). Four bacterial U(VI) surface complexes were identified: R-COO-UO2(+), R-O-PO3-UO2, R-O-PO3H-UO2(+), and (R-O-PO3)2-UO2(2-). The corresponding complex stability constants were calculated to be 5.33 ± 0.08, 8.89 ± 0.04, 12.92 ± 0.05, and 13.62 ± 0.08, respectively. Hence UO2(2+) displays a moderate to strong interaction with the bacterial surface functional groups. In the acidic pH range (pH 3) UO2(2+) binding onto the cell envelope is governed by coordination to hydrogen phosphoryl sites. Upon increasing the pH an increasing coordination of UO2(2+) to carboxylic and deprotonated phosphoryl sites was found. At a pH greater than 7 uranyl hydroxides dominate the speciation. Additionally the bacteria-mediated release of inorganic phosphate in dependence on [U(VI)] at different pH values was studied to assess the influence of phosphate release on U(VI) mobilization.

Complexation of uranium(VI) with glutarimidoxioxime: thermodynamic and computational studies.

PubMed

Endrizzi, Francesco; Melchior, Andrea; Tolazzi, Marilena; Rao, Linfeng

2015-08-21

The complex formation between a cyclic ligand glutarimidoxioxime (denoted as HL(III) in this paper) and UO2(2+) is studied by potentiometry and microcalorimetry. Glutarimidoxioxime (HL(III)), together with glutarimidedioxime (H2L(I)) and glutardiamidoxime (H2L(II)), belongs to a family of amidoxime derivatives with prospective applications as binding agents for the recovery of uranium from seawater. An optimized procedure of synthesis that leads to the preparation of glutarimidoxioxime in the absence of other amidoxime byproducts is described in this paper. Speciation models based on the thermodynamic results from this study indicate that, compared with H2L(I) and H2L(II), HL(III) forms a much weaker complex with UO2(2+), UO2(L(III))(+), and cannot effectively compete with the hydrolysis equilibria of UO2(2+) under neutral or alkaline conditions. DFT computations, taking into account the solvation by including discrete hydration water molecules and bulk solvent effects, were performed to evaluate the structures and energies of the possible isomers of UO2(L(III))(+). Differing from the tridentate or η(2)-coordination modes previously found in the U(vi) complexes with amidoxime-related ligands, a bidentate mode, involving the oxygen of the oxime group and the nitrogen of the imino group, is found to be the most probable mode in UO2(L(III))(+). The bidentate coordination mode seems to be stabilized by the formation of a hydrogen bond between the carbonyl group of HL(III) and a water molecule in the hydration sphere of UO2(2+).

Perrhenate complexation by uranyl in traditional solvents and in ionic liquids: a joint molecular dynamics/spectroscopic study.

PubMed

Chaumont, Alain; Klimchuk, Olga; Gaillard, Clotilde; Billard, Isabelle; Ouadi, Ali; Hennig, Christoph; Wipff, Georges

2012-03-15

The complexation of perrhenate (ReO(4)(-)) anions by the uranyl (UO(2)(2+)) cation has been investigated by joint molecular dynamics simulations and spectroscopic (UV-vis, TRLFS, and EXAFS) studies in aqueous solution, acetonitrile, and three ionic liquids (ILs), namely, [Bmi][Tf(2)N], [Me(3)BuN][Tf(2)N], and [Bu(3)MeN][Tf(2)N] that are based on the same Tf(2)N(-) anion (bis(trifluoromethylsulfonyl)imide) and either Bmi(+) (1-butyl,3-methylimidazolium), Me(3)BuN(+), or Bu(3)MeN(+) cations. They show that ReO(4)(-) behaves as a weak ligand in aqueous solution and as a strong ligand in acetonitrile and in the ILs. According to MD simulations in aqueous solution, the UO(2)(ReO(4))(2) complex quickly dissociates to form UO(2)(H(2)O)(5)(2+), while in acetonitrile, a stable UO(2)(ReO(4))(5)(3-) species forms from dissociated ions. In the ILs, the UO(2)(ReO(4))(n)(2-n) complexes (n = 1 to 5) remained stable along the dynamics, and to assess their relative stabilities, we computed the free energy profiles for stepwise ReO(4)(-) complexation to uranyl. In the two studied ILs, complexation is favored, leading to the UO(2)(ReO(4))(5)(3-) species in [Bmi][Tf(2)N] and to UO(2)(ReO(4))(4)(2-) in [Bu(3)MeN][Tf(2)N]. Furthermore, in both acetonitrile and [Bmi][Tf(2)N] solutions, MD and PMF simulations support the formation of dimeric uranyl complexes [UO(2)(ReO(4))(4)](2)(4-) with two bridging ReO(4)(-) ligands. The simulation results are qualitatively consistent with spectroscopic observations in the different solvents, without firmly concluding, however, on the precise composition and structure of the complexes in the solutions. © 2012 American Chemical Society

Uranyl carboxyphosphonates that incorporate Cd(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alsobrook, Andrea N.; Alekseev, Evgeny V.; Depmeier, Wulf

2011-05-15

The hydrothermal treatment of UO{sub 3}, Cd(CH{sub 3}CO{sub 2}){sub 2}.2H{sub 2}O, and triethyl phosphonoacetate results in the formation of Cd{sub 2}[(UO{sub 2}){sub 6}(PO{sub 3}CH{sub 2}CO{sub 2}){sub 3}O{sub 3}(OH)(H{sub 2}O){sub 2}].16H{sub 2}O (CdUPAA-1), [Cd{sub 3}(UO{sub 2}){sub 6}(PO{sub 3}CH{sub 2}CO{sub 2}){sub 6}(H{sub 2}O){sub 13}].6H{sub 2}O (CdUPAA-2), and Cd(H{sub 2}O){sub 2}[(UO{sub 2})(PO{sub 3}CH{sub 2}CO{sub 2})(H{sub 2}O)]{sub 2} (CdUPAA-3). CdUPAA-1 adopts a cubic three-dimensional structure constructed from planar uranyl oxide clusters containing both UO{sub 7} pentagonal bipyramids and UO{sub 8} hexagonal bipyramids that are linked by Cd(II) cations and phosphonoacetate to yield large cavities approximately 16 A across that are filled with disordered watermore » molecules. CdUPAA-2 forms a rhombohedral three-dimensional channel structure that is assembled from UO{sub 7} pentagonal bipyramids that are bridged by phosphonoacetate. CdUPAA-3 is layered with the hydrated Cd(II) cations incorporated directly into the layers linking one-dimensional uranyl phosphonate substructures together. In this structure, there are complex networks of hydrogen bonds that exist within the sheets, and also stitch the sheets together. -- Graphical abstract: A view of part of the cubic structure of Cd{sub 2}[(UO{sub 2}){sub 6}(PO{sub 3}CH{sub 2}CO{sub 2}){sub 3}O{sub 3}(OH)(H{sub 2}O){sub 2}].16H{sub 2}O. Display Omitted highlights: > High symmetry uranyl compounds. > Three-dimensional structures. > Porous materials. > Heterobimetallic compounds.« less

Incorporation mechanisms of actinide elements into the structures of U 6+ phases formed during the oxidation of spent nuclear fuel

NASA Astrophysics Data System (ADS)

Burns, Peter C.; Ewing, Rodney C.; Miller, Mark L.

1997-05-01

Uranyl oxide hydrate and uranyl silicate phases will form due to the corrosion and alteration of spent nuclear fuel under oxidizing conditions in silica-bearing solution. The actinide elements in the spent fuel may be incorporated into the structures of these secondary U6+ phases during the long-term corrosion of the UO 2 in spent fuel. The incorporation of actinide elements into the crystal structures of the alteration products may decrease actinide mobility. The crystal chemistry of the various oxidation states of the actinide elements of environmental concern is examined to identify possible incorporation mechanisms. The substitutions Pu 6+U 6+ and (Pu 5+, Np 5+)U 6+ should readily occur in many U 6+ structures, although structural modification may be required to satisfy local bond-valence requirements. Crystal-chemical characteristics of the U 6+ phases indicate that An 4+ (An: actinide)U 6+ substitution is likely to occur in the sheets of uranyl polyhedra that occur in the structures of the minerals schoepite, [(UO 2) 8O 2(OH) 12](H 2O) 12, ianthinite, [U 24+ (UO 2) 4O 6(OH) 4(H 2O) 4](H 2O) 5, becquerelite, Ca[(UO 2) 3O 2(OH) 3] 2(H 2O) 8, compreignacite, K 2[(UO 2) 3O 2(OH) 3] 2(H 2O) 8, α-uranophane, Ca[(UO 2)(SiO 3OH)] 2(H 2O) 5, and boltwoodite, K(H 2O)[(UO 2)(SiO 4)], all of which are likely to form due to the oxidation and alteration of the UO 2 in spent fuel. The incorporation of An 3+ into the sheets of the structures of α-uranophane and boltwoodite, as well as interlayer sites of various uranyl phases, may occur.

Renal pelvic and ureteral ultrasonographic characteristics of cats with chronic kidney disease in comparison with normal cats, and cats with pyelonephritis or ureteral obstruction.

PubMed

Quimby, Jessica M; Dowers, Kristy; Herndon, Andrea K; Randall, Elissa K

2017-08-01

Objectives The objective was to describe ultrasonographic characteristics of cats with stable chronic kidney disease (CKD) and determine if these were significantly different from cats with pyelonephritis (Pyelo) and ureteral obstruction (UO), to aid in clinical assessment during uremic crisis. Methods Sixty-six cats with stable CKD were prospectively enrolled, as well as normal control cats (n = 10), cats with a clinical diagnosis of Pyelo (n = 13) and cats with UO confirmed by surgical resolution (n = 11). Renal ultrasound was performed and routine still images and cine loops were obtained. Analysis included degree of pelvic dilation, and presence and degree of ureteral dilation. Measurements were compared between groups using non-parametric one-way ANOVA with Dunn's post-hoc analysis. Results In total, 66.6% of CKD cats had measurable renal pelvic dilation compared with 30.0% of normal cats, 84.6% of Pyelo cats and 100% of UO cats. There was no statistically significant difference in renal pelvic widths between CKD cats and normal cats, or CKD cats and Pyelo cats. On almost all measurement categories, UO cats had significantly greater renal pelvic widths compared with CKD cats and normal cats ( P <0.05) but not Pyelo cats. Six percent of stable CKD cats had measurable proximal ureteral dilation on one or both sides vs 46.2% of Pyelo cats and 81.8% of UO cats. There was no statistically significant difference in proximal ureteral width between normal and CKD cats, or between Pyelo and UO cats. There was a statistically significant difference in proximal ureteral width between CKD and Pyelo cats, CKD and UO cats, normal and UO cats, and normal and Pyelo cats. Conclusions and relevance No significant difference in renal pelvic widths between CKD cats and Pyelo cats was seen. These data suggest CKD cats should have a baseline ultrasonography performed so that abnormalities documented during a uremic crisis can be better interpreted.

A prospective randomized comparison of unsedated ultrathin versus standard esophagogastroduodenoscopy in routine outpatient gastroenterology practice: does it work better through the nose?

PubMed

Birkner, B; Fritz, N; Schatke, W; Hasford, J

2003-08-01

In an outpatient gastroenterological practice setting, highly effective diagnostic procedures and patient satisfaction play an important role. Ultrathin endoscopy in unsedated patients has been shown to be more cost-effective and time-efficient in comparison with standard endoscopy. A prospective randomized study was carried out in unsedated patients to compare performance, feasibility, safety, and patient tolerance between ultrathin transnasal (UT), ultrathin oral (UO), and standard (SO) esophagogastroduodenoscopy (EGD). A total of 200 of 600 eligible patients consented to participate in the study, and were randomly assigned to undergo UT, UO, or SO. Patients reported their tolerance of the procedure (anxiety, pain, gagging, and overall satisfaction; Likert scale 1-10), and the endoscopists reported the effectiveness of the procedure (handling, picture quality, and overall performance; Likert scale 1-10). Statistics were calculated using the Kruskal-Wallis test. After randomization, 65, 67, and 68 patients were allocated to the UT, UO, and SO groups, respectively. Failure to achieve complete EGD by the intended route occurred in 14 patients (22 %) in the UT group. Compared to the SO group, patients in the UT and UO groups rated anxiety before the procedure as being more intense - median score (10 % quantile estimate; 90 % quantile estimate): UT, 2.0 (1.0; 4.0); UO, 2.0 (1.0; 4.0); SO, 0.0 (0.0; 2.0); p < 0.0001), whereas SO patients experienced a higher level of anxiety during the procedure ( P < 0.0001). Pain during insertion of the endoscope was the least intense in the UO group: UT, 2.0 (1.0; 5.0); UO, 1.0 (1.0; 3.0); SO, 2.0 (1.0; 4.0); P < 0.001). Gagging during insertion was more pronounced in the UO group: UT, 2.0 (1.0; 4.0); UO, 3.0 (1.0; 7.0); SO, 2.0 (1.0; 5.0); P < 0.01). The patients' score for the overall assessment was better in the SO group ( P < 0.0001). The endoscopists' overall assessment for ultrathin EGD was poorer than for standard EGD: UT, 3.0 (2.0; 5.0); UO, 3.0 (2.0; 5.0); SO, 2.0 (1.0; 3.0); P < 0.0001). Ultrathin endoscopy through both the transnasal and oral routes has limited use in routine outpatient practice. Techniques for reducing pain and gagging may improve patient tolerance. Further technical improvements are needed to allow routine implementation.

Membrane optode for uranium(VI) ions preconcentration and quantification based on a synergistic combination of 4-(2-thiazolylazo)-resorcinol with 8-hydroxyquinaldine

NASA Astrophysics Data System (ADS)

Kalyan, Y.; Pandey, A. K.; Naidu, G. R. K.; Reddy, A. V. R.

2009-12-01

A membrane optode was developed utilizing the 8-hydroxyquinaldine (HQ) facilitated preconcentration of UO 22+ ions and subsequent colored complex formation of UO 22+ with 4-(2-thiazolylazo)-resorcinol (TAR) in optode matrix. The composition of the membrane optode was optimized by scanning several extractants immobilized in different plasticized polymer matrices. It was observed that the chelating agent HQ along with an indicator TAR immobilized in the tri-(2-ethylhexyl)phosphate (TEHP) plasticized cellulose triacetate matrix (CTA) was best suited as an optode for the UO 22+ ions in aqueous samples. On sorption of UO 22+ in the optode matrix, TAR changes color of the optode from yellow to magenta having a maximum absorbance ( λmax) at 546 nm. The uptake of UO 22+ ions in the optode was found to be pH dependent and was maximum (>90%) at pH above 3. The acetate buffer (0.1 mol L -1 sodium acetate + 0.1 mol L -1 acetic acid) was found to be necessary for the stable response. The optimum equilibration time for the optode (2 cm × 1 cm) was found to be 30 min in 10 mL aqueous sample containing acetate buffer (pH 4.75). The equilibration time was found to increase with increase in aqueous sample volume. The optode response was found to be linear in the UO 22+ ions concentration range of 0.01-0.11 μmol L -1 in tap water as well as aqueous solutions containing 0.1 mol L -1 NaCl or NaNO 3. The tolerance to the presence of several cations and anions in the determination of UO 22+ ion was studied. It was observed that the optode in the presence of buffer can tolerate presence of large amounts of interfering cations (Ce 4+, V 4+, Eu 3+, Al 3+, Fe 3+, Ni 2+, Cd 2+, Co 2+, Pb 2+, Hg 2+, Cu 2+ and Th 4+ ions) without hindering the sorption of UO 22+ ions in the optode matrix. The present work indicated that 50 ppb UO 22+ ions in 100 mL sample can easily be quantified using this optode. The optode was found to be fully reversible, can readily be regenerated by equilibrating it with 0.1 mol L -1 HNO 3 and reusable up to three cycles. The applicability of the developed optode in real samples was studied by determining uranium in the ground water samples spiked with a known quantity of UO 22+ ions.

A study on recovery of uranium in the anode basket residues delivered from the pyrochemical process of used nuclear fuel

NASA Astrophysics Data System (ADS)

Eun, H. C.; Kim, T. J.; Jang, J. H.; Kim, G. Y.; Park, S. B.; Yoon, D. S.; Kim, S. H.; Paek, S. W.; Lee, S. J.

2018-04-01

In this study, the chlorination of uranium oxide (UO2) using ammonium chloride and zirconium as chemical agents was conducted to recover the uranium in the anode basket residues from the pyrochemical process of used nuclear fuel. The chlorination of UO2 was predicted using thermodynamic equilibrium calculations. The experimental conditions for the chlorination were determined using a chlorination test with cerium oxide (CeO2). In the chlorination test, it was confirmed that UO2 was chlorinated into UCl3 at 320 °C, some UO2 remained without changes in the chemical form, and ZrO2, Zr2O, and ZrCl2 were generated as byproducts.

Experimental evaluation of thermal ratcheting behavior in UO2 fuel elements

NASA Technical Reports Server (NTRS)

Phillips, W. M.

1973-01-01

The effects of thermal cycling of UO2 at high temperatures has been experimentally evaluated to determine the rates of distortion of UO2/clad fuel elements. Two capsules were rested in the 1500 C range, one with a 50 C thermal cycle, the other with a 100 C thermal cycle. It was observed that eight hours at the lower cycle temperature produced sufficient UO2 redistribution to cause clad distortion. The amount of distortion produced by the 100 C cycle was less than double that produced by the 50 C, indicating smaller thermal cycles would result in clad distortion. An incubation period was observed to occur before the onset of distortion with cycling similar to fuel swelling observed in-pile at these temperatures.

Onset conditions for flash sintering of UO 2

DOE PAGES

Raftery, Alicia M.; Pereira da Silva, João Gustavo; Byler, Darrin D.; ...

2017-06-22

In this paper, flash sintering was demonstrated on stoichiometric and non-stoichiometric uranium dioxide pellets at temperatures ranging from room temperature (26°C) up to 600°C. The onset conditions for flash sintering were determined for three stoichiometries (UO 2.00, UO 2.08, and UO 2.16) and analyzed against an established thermal runaway model. The presence of excess oxygen was found to enhance the flash sintering onset behavior of uranium dioxide, lowering the field required to flash and shortening the time required for a flash to occur. Finally, the results from this study highlight the effect of stoichiometry on the flash sintering behavior ofmore » uranium dioxide and will serve as the foundation for future studies on this material.« less

Onset conditions for flash sintering of UO2

NASA Astrophysics Data System (ADS)

Raftery, Alicia M.; Pereira da Silva, João Gustavo; Byler, Darrin D.; Andersson, David A.; Uberuaga, Blas P.; Stanek, Christopher R.; McClellan, Kenneth J.

2017-09-01

In this work, flash sintering was demonstrated on stoichiometric and non-stoichiometric uranium dioxide pellets at temperatures ranging from room temperature (26 °C) up to 600 °C . The onset conditions for flash sintering were determined for three stoichiometries (UO2.00, UO2.08, and UO2.16) and analyzed against an established thermal runaway model. The presence of excess oxygen was found to enhance the flash sintering onset behavior of uranium dioxide, lowering the field required to flash and shortening the time required for a flash to occur. The results from this study highlight the effect of stoichiometry on the flash sintering behavior of uranium dioxide and will serve as the foundation for future studies on this material.

Determination of successive complexation constants in an ionic liquid: complexation of UO(2)(2+) with NO(3)(-) in C(4)-mimTf(2)N studied by UV-Vis spectroscopy.

PubMed

Georg, Sylvia; Billard, Isabelle; Ouadi, Ali; Gaillard, Clotilde; Petitjean, Laetitia; Picquet, Michel; Solov'ev, Vitaly

2010-04-01

The complexation of UO(2)(2+) with NO(3)(-) has been investigated in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide by UV-vis spectroscopy at T = 18.5 degrees C. The complexation is evidenced through the appearance of four peaks at 425, 438, 453, and 467 nm. EXAFS data indicate that the trinitrato complex, UO(2)(NO(3))(3)(-), is dominating the speciation for a reagent ratio of [NO(3)(-)]/[UO(2)(2+)] > 3. Assuming three successive complexation steps, the conditional stability constants are calculated, the individual absorption spectra are derived, and a speciation plot is presented.

Expanding the remarkable structural diversity of uranyl tellurites: hydrothermal preparation and structures of K[UO(2)Te(2)O(5)(OH)], Tl(3)[(UO(2))(2)[Te(2)O(5)(OH)](Te(2)O(6))].2H(2)O, beta-Tl(2)[UO(2)(TeO(3))(2)], and Sr(3)[UO(2)(TeO(3))(2)](TeO(3))(2).

PubMed

Almond, Philip M; Albrecht-Schmitt, Thomas E

2002-10-21

The reactions of UO(2)(C(2)H(3)O(2))(2).2H(2)O with K(2)TeO(3).H(2)O, Na(2)TeO(3) and TlCl, or Na(2)TeO(3) and Sr(OH)(2).8H(2)O under mild hydrothermal conditions yield K[UO(2)Te(2)O(5)(OH)] (1), Tl(3)[(UO(2))(2)[Te(2)O(5)(OH)](Te(2)O(6))].2H(2)O (2) and beta-Tl(2)[UO(2)(TeO(3))(2)] (3), or Sr(3)[UO(2)(TeO(3))(2)](TeO(3))(2) (4), respectively. The structure of 1 consists of tetragonal bipyramidal U(VI) centers that are bound by terminal oxo groups and tellurite anions. These UO(6) units span between one-dimensional chains of corner-sharing, square pyramidal TeO(4) polyhedra to create two-dimensional layers. Alternating corner-shared oxygen atoms in the tellurium oxide chains are protonated to create short/long bonding patterns. The one-dimensional chains of corner-sharing TeO(4) units found in 1 are also present in 2. However, in 2 there are two distinct chains present, one where alternating corner-shared oxygen atoms are protonated, and one where the chains are unprotonated. The uranyl moieties in 2 are bound by five oxygen atoms from the tellurite chains to create seven-coordinate pentagonal bipyramidal U(VI). The structures of 3 and 4 both contain one-dimensional [UO(2)(TeO(3))(2)](2-) chains constructed from tetragonal bipyramidal U(VI) centers that are bridged by tellurite anions. The chains differ between 3 and 4 in that all of the pyramidal tellurite anions in 3 have the same orientation, whereas the tellurite anions in 4 have opposite orientations on each side of the chain. In 4, there are also additional isolated TeO(3)(2-) anions present. Crystallographic data: 1, orthorhombic, space group Cmcm, a = 7.9993(5) A, b = 8.7416(6) A, c = 11.4413(8) A, Z = 4; 2, orthorhombic, space group Pbam, a = 10.0623(8) A, b = 23.024(2) A, c = 7.9389(6) A, Z = 4; 3, monoclinic, space group P2(1)/n, a = 5.4766(4) A, b = 8.2348(6) A, c = 20.849(3) A, beta = 92.329(1) degrees, Z = 4; 4, monoclinic, space group C2/c, a = 20.546(1) A, b = 5.6571(3) A, c = 13.0979(8) A, beta = 94.416(1) degrees, Z = 4.

Methodology for Producing a Uniform Distribution of UO2 in a Tungsten Matrix

NASA Technical Reports Server (NTRS)

Tucker, Dennis S.; O'Conner, Andrew; Hickman, Rickman; Broadway, Jeramie; Belancik, Grace

2015-01-01

Current work at NASA's Marshall Space Flight Center (MSFC) is focused on the development CERMET fuel materials for Nuclear Thermal Propulsion (NTP). The CERMETs consist of uranium dioxide (UO2) fuel particles embedded in a tungsten (W) metal matrix. Initial testing of W-UO2 samples fabricated from fine angular powders performed reasonably well, but suffered from significant fuel loss during repeated thermal cycling due to agglomeration of the UO2 (1). The blended powder mixtures resulted in a non-uniform dispersion of the UO2 particles in the tungsten matrix, which allows rapid vaporization of the interconnected UO2 from the sample edges into the bulk material. Also, the angular powders create areas of stress concentrations due to thermal expansion mismatch, which eventually cracks the tungsten matrix. Evenly coating spherical UO2 particles with chemical vapor deposited (CVD) tungsten prior to consolidation was previously demonstrated to provide improved performance. However, the CVD processing technology is expensive and not currently available. In order to reduce cost and enhance performance, a powder coating process has been developed at MSFC to produce a uniform distribution of the spherical UO2 particles in a tungsten matrix. The method involves utilization of a polyethylene binder during mixing which leads to fine tungsten powders clinging to the larger UO2 spherical particles. This process was developed using HfO2 as a surrogate for UO2. Enough powder was mixed to make 8 discs (2cm diameter x 8mm thickness) using spark plasma sintering. A uniaxial pressure of 50 MPa was used at four different temperatures (2 samples at each temperature). The first two samples were heated to 1400C and 1500C respectively for 5 minutes. Densities for these samples were less than 85% of theoretical, so the time at temperature was increased to 20 minutes for the remaining samples. The highest densities were achieved for the two samples sintered at 1700C (approx. 92% of theoretical). Scanning electron microscopy (SEM) of the mixed powders and the sintered samples along with energy dispersive x-ray analysis was obtained. The SEM of the powders clearly show the fine W powder adhered to the larger HfO2 particles and a uniform distribution of HfO2 particles in a tungsten matrix upon densification. Vicker's Microhardness testing was also performed on all samples using 0.5, 1.0 and 2.0 kg loads. Five indents were made at each load level. All indents were placed in the tungsten matrix to assist as a proxy in measuring densification. The highest hardness value was obtained for the 1700C specimens. The hardness average for these samples was 312.14 MPa. This powder processing method has been applied to W/UO2 powders with the SEM of the powders appearing similar to the W/HfO2 powder images.

Effects of calcium and phosphate on uranium(IV) oxidation: Comparison between nanoparticulate uraninite and amorphous UIV-phosphate

NASA Astrophysics Data System (ADS)

Latta, Drew E.; Kemner, Kenneth M.; Mishra, Bhoopesh; Boyanov, Maxim I.

2016-02-01

The mobility of uranium in subsurface environments depends strongly on its redox state, with UIV phases being significantly less soluble than UVI minerals. This study compares the oxidation kinetics and mechanisms of two potential products of UVI reduction in natural systems, a nanoparticulate UO2 phase and an amorphous UIV-Ca-PO4 analog to ningyoite (CaUIV(PO4)2·1-2H2O). The valence of U was tracked by X-ray absorption near-edge spectroscopy (XANES), showing similar oxidation rate constants for UIVO2 and UIV-phosphate in solutions equilibrated with atmospheric O2 and CO2 at pH 7.0 (kobs,UO2 = 0.17 ± 0.075 h-1 vs. kobs,UIVPO4 = 0.30 ± 0.25 h-1). Addition of up to 400 μM Ca and PO4 decreased the oxidation rate constant by an order of magnitude for both UO2 and UIV-phosphate. The intermediates and products of oxidation were tracked by electron microscopy, powder X-ray diffraction (pXRD), and extended X-ray absorption fine-structure spectroscopy (EXAFS). In the absence of Ca or PO4, the product of UO2 oxidation is Na-uranyl oxyhydroxide (under environmentally relevant concentrations of sodium, 15 mM NaClO4 and low carbonate concentration), resulting in low concentrations of dissolved UVI (<2.5 × 10-7 M). Oxidation of UIV-phosphate produced a Na-autunite phase (Na2(UO2)PO4·xH2O), resulting in similarly low dissolved U concentrations (<7.3 × 10-8 M). When Ca and PO4 are present in the solution, the EXAFS data and the solubility of the UVI phase resulting from oxidation of UO2 and UIV-phosphate are consistent with the precipitation of Na-autunite. Bicarbonate extractions and Ca K-edge X-ray absorption spectroscopy of oxidized solids indicate the formation of a Ca-UVI-PO4 layer on the UO2 surface and suggest a passivation layer mechanism for the decreased rate of UO2 oxidation in the presence of Ca and PO4. Interestingly, the extractions were unable to remove all of the oxidized U from partially oxidized UO2 solids, suggesting that oxidized U is distributed between the interior of the UO2 nanoparticles and the labile surface layer. Accounting for the entire pool of oxidized U by XANES is the likely reason for the higher UO2 oxidation rate constants determined here relative to prior studies. Our results suggest that the natural presence or addition of Ca and PO4 in groundwater could slow the rates of UIV oxidation, but that the rates are still fast enough to cause complete oxidation of UIV within days under fully oxygenated conditions.

Effects of calcium and phosphate on uranium(IV) oxidation: Comparison between nanoparticulate uraninite and amorphous U IV–phosphate

DOE PAGES

Latta, Drew E.; Kemner, Kenneth M.; Mishra, Bhoopesh; ...

2015-11-17

The mobility of uranium in subsurface environments depends strongly on its redox state, with U IV phases being significantly less soluble than U VI minerals. This study compares the oxidation kinetics and mechanisms of two potential products of U VI reduction in natural systems, a nanoparticulate UO 2 phase and an amorphous U IV–Ca–PO 4 analog to ningyoite (CaU IV(PO 4) 2·1–2H 2O). The valence of U was tracked by X-ray absorption near-edge spectroscopy (XANES), showing similar oxidation rate constants for U IVO 2 and U IV–phosphate in solutions equilibrated with atmospheric O 2 and CO 2 at pH 7.0more » (k obs,UO2 = 0.17 ± 0.075 h -1 vs. k obs,U IV PO4 = 0.30 ± 0.25 h -1). Addition of up to 400 μM Ca and PO 4 decreased the oxidation rate constant by an order of magnitude for both UO 2 and U IV–phosphate. The intermediates and products of oxidation were tracked by electron microscopy, powder X-ray diffraction (pXRD), and extended X-ray absorption fine-structure spectroscopy (EXAFS). In the absence of Ca or PO 4, the product of UO 2 oxidation is Na–uranyl oxyhydroxide (under environmentally relevant concentrations of sodium, 15 mM NaClO 4 and low carbonate concentration), resulting in low concentrations of dissolved U VI (<2.5 × 10 -7 M). Oxidation of U IV–phosphate produced a Na-autunite phase (Na 2(UO 2)PO 4·xH 2O), resulting in similarly low dissolved U concentrations (<7.3 × 10 -8 M). When Ca and PO 4 are present in the solution, the EXAFS data and the solubility of the UVI phase resulting from oxidation of UO 2 and UIV–phosphate are consistent with the precipitation of Na-autunite. Bicarbonate extractions and Ca K-edge X-ray absorption spectroscopy of oxidized solids indicate the formation of a Ca–UVI–PO 4 layer on the UO 2 surface and suggest a passivation layer mechanism for the decreased rate of UO 2 oxidation in the presence of Ca and PO 4. Interestingly, the extractions were unable to remove all of the oxidized U from partially oxidized UO 2 solids, suggesting that oxidized U is distributed between the interior of the UO 2 nanoparticles and the labile surface layer. Accounting for the entire pool of oxidized U by XANES is the likely reason for the higher UO 2 oxidation rate constants determined here relative to prior studies. In conclusion, our results suggest that the natural presence or addition of Ca and PO 4 in groundwater could slow the rates of U IV oxidation, but that the rates are still fast enough to cause complete oxidation of U IV within days under fully oxygenated conditions.« less

Magnetic beads-based DNAzyme recognition and AuNPs-based enzymatic catalysis amplification for visual detection of trace uranyl ion in aqueous environment.

PubMed

Zhang, Hongyan; Lin, Ling; Zeng, Xiaoxue; Ruan, Yajuan; Wu, Yongning; Lin, Minggui; He, Ye; Fu, FengFu

2016-04-15

We herein developed a novel biosensor for the visual detection of trace uranyl ion (UO2(2+)) in aqueous environment with high sensitivity and specificity by using DNAzyme-functionalized magnetic beads (MBs) for UO2(2+) recognition and gold nano-particles (AuNPs)-based enzymatic catalysis oxidation of TMB (3,3',5,5'-tetramethylbenzidine sulfate) for signal generation. The utilization of MBs facilitates the magnetic separation and collection of sensing system from complex sample solution, which leads to more convenient experimental operation and more strong resistibility of the biosensor to the matrix of sample, and the utilization of AuNPs-based enzymatic catalysis amplification greatly improved the sensitivity of the biosensor. Compared with the previous DNAzyme-based UO2(2+) sensors, the proposed biosensor has outstanding advantages such as relative high sensitivity and specificity, operation convenience, low cost and more strong resistibility to the matrix of sample. It can be used to detect as low as 0.02 ppb (74 pM) of UO2(2+) in aqueous environment by only naked-eye observation and 1.89 ppt (7.0 pM) of UO2(2+) by UV-visible spectrophotometer with a recovery of 93-99% and a RSD ≤ 5.0% (n=6) within 3h. Especially, the visual detection limit of 0.02 ppb (74 pM) is much lower than the maximum allowable level of UO2(2+) (130 nM) in the drinking water defined by the U.S. Environmental Protection Agency (EPA), indicating that our method meets the requirement of rapid and on-site detection of UO2(2+) in the aqueous environment by only naked-eye observation. Copyright © 2015 Elsevier B.V. All rights reserved.

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO 2) 4(VO 4) 3 ( A=Li, Na)

NASA Astrophysics Data System (ADS)

Obbade, S.; Dion, C.; Rivenet, M.; Saadi, M.; Abraham, F.

2004-06-01

A new sodium uranyl vanadate Na(UO 2) 4(VO 4) 3 has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I4 1/ amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å 3, Z=4 with ρmes=5.36(3) g/cm 3 and ρcal=5.40(2) g/cm 3. A full-matrix least-squares refinement on the basis of F2 yielded R1=0.028 and w R2=0.056 for 52 parameters with 474 independent reflections with I⩾2 σ( I) collected on a BRUKER AXS diffractometer with Mo Kα radiation and a CCD detector. The crystal structure is characterized by ∞2[(UO 2) 2(VO 4)] sheets parallel to (001) formed by corner-shared UO 6 distorted octahedra and V(2)O 4 tetrahedra, connected by V(1)O 4 tetrahedra to ∞1[UO 5] 4- chains of edge-shared UO 7 pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO 2) 4(VO 4) 3 has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.

Comparative studies of mononuclear Ni(II) and UO2(II) complexes having bifunctional coordinated groups: Synthesis, thermal analysis, X-ray diffraction, surface morphology studies and biological evaluation

NASA Astrophysics Data System (ADS)

Fahem, Abeer A.

2012-03-01

Two Schiff base ligands derived from condensation of phthalaldehyde and o-phenylenediamine in 1:2 (L1) and 2:1 (L2) having bifunctional coordinated groups (NH2 and CHO groups, respectively) and their metal complexes with Ni(II) and UO2(II) have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibilities and spectral data (IR, 1H NMR, mass and solid reflectance) as well as thermal, XRPD and SEM analysis. The formula [Ni(L1)Cl2]·2.5H2O, [UO2(L1)(NO3)2]·2H2O, [Ni(L2)Cl2]·1.5H2O and [UO2(L2)(NO3)2] have been suggested for the complexes. The vibrational spectral data show that the ligands behave as neutral ligands and coordinated to the metal ions in a tetradentate manner. The Ni(II) complexes are six coordinate with octahedral geometry and the ligand field parameters: Dq, B, β and LFSE were calculated while, UO2(II) complexes are eight coordinate with dodecahedral geometry and the force constant, FUsbnd O and bond length, RUsbnd O were calculated. The thermal decomposition of complexes ended with metal chloride/nitrate as a final product and the highest thermal stability is displayed by [UO2(L2)(NO3)2] complex. The X-ray powder diffraction data revealed the formation of nano sized crystalline complexes. The SEM analysis provides the morphology of the synthesized compounds and SEM image of [UO2(L2)(NO3)2] complex exhibits nano rod structure. The growth-inhibiting potential of the ligands and their complexes has been assessed against a variety of bacterial and fungal strains.

Are Surrogate Assumptions and Use of Diuretics Associated with Diagnosis and Staging of Acute Kidney Injury after Cardiac Surgery?

PubMed Central

Hussein, Hayder K.; Prabhu, Mahesh; Kanagasundaram, N. Suren

2012-01-01

Summary Background and objectives This study measured the association between the Acute Kidney Injury Network (AKIN) diagnostic and staging criteria and surrogates for baseline serum creatinine (SCr) and body weight, compared urine output (UO) with SCr criteria, and assessed the relationships between use of diuretics and calibration between criteria and prediction of outcomes. Design, setting, participants, & measurements This was a retrospective cohort study using prospective measurements of SCr, hourly UO, body weight, and drug administration records from 5701 patients admitted, after cardiac surgery, to a cardiac intensive care unit between 1995 and 2006. Results More patients (n=2424, 42.5%) met SCr diagnostic criteria with calculated SCr assuming a baseline estimated GFR of 75 ml/min per 1.73 m2 than with known baseline SCr (n=1043, 18.3%). Fewer patients (n=484, 8.5%) met UO diagnostic criteria with assumed body weight (70 kg) than with known weight (n=624, 10.9%). Agreement between SCr and UO criteria was fair (κ=0.28; 95% confidence interval 0.25–0.31). UO diagnostic criteria were specific (0.95; 0.94–0.95) but insensitive (0.36; 0.33–0.39) compared with SCr. Intravenous diuretics were associated with higher probability of falling below the UO diagnostic threshold compared with SCr, higher 30-day mortality (relative risk, 2.27; 1.08–4.76), and the need for renal support (4.35; 1.82–10.4) compared with no diuretics. Conclusions Common surrogates for baseline estimated GFR and body weight were associated with misclassification of AKIN stage. UO criteria were insensitive compared with SCr. Intravenous diuretic use further reduced agreement and confounded association between AKIN stage and 30-day mortality or need for renal support. PMID:22246280

The effect of ion irradiation on the dissolution of UO 2 and UO 2 -based simulant fuel

DOE PAGES

Popel, Aleksej J.; Wietsma, Thomas W.; Engelhard, Mark H.; ...

2017-11-21

Our aim is to study the separate effect of fission fragment damage on the dissolution of simulant UK advanced gas-cooled reactor nuclear fuel in water. Plain UO 2 and UO 2 samples, doped with inactive fission products to simulate 43 GWd/tU of burn-up, were fabricated. A set of these samples were then irradiated with 92 MeV 129Xe 23+ ions to a fluence of 4.8 × 10 15 ions/cm 2 to simulate the fission damage that occurs within nuclear fuels. The primary effect of the irradiation on the UO 2 samples, observed by scanning electron microscopy, was to induce a smootheningmore » of the surface features and formation of hollow blisters, which was attributed to multiple overlap of ion tracks. Dissolution experiments were conducted in single-pass flow-through (SPFT) mode under anoxic conditions (<0.1 O 2 ppm in Ar) to study the effect of the induced irradiation damage on the dissolution of the UO 2 matrix with data collection capturing six minute intervals for several hours. These time-resolved data showed that the irradiated samples showed a higher initial release of uranium than unirradiated samples, but that the uranium concentrations converged towards ~10 -9 mol/l after a few hours. And apart from the initial spike in uranium concentration, attributed to irradiation induced surficial micro-structural changes, no noticeable difference in uranium chemistry as measured by X-ray electron spectroscopy or ‘effective solubility’ was observed between the irradiated, doped and undoped samples in this work. Some secondary phase formation was observed on the surface of UO 2 samples after the dissolution experiment.« less

The effect of ion irradiation on the dissolution of UO 2 and UO 2 -based simulant fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popel, Aleksej J.; Wietsma, Thomas W.; Engelhard, Mark H.

Our aim is to study the separate effect of fission fragment damage on the dissolution of simulant UK advanced gas-cooled reactor nuclear fuel in water. Plain UO 2 and UO 2 samples, doped with inactive fission products to simulate 43 GWd/tU of burn-up, were fabricated. A set of these samples were then irradiated with 92 MeV 129Xe 23+ ions to a fluence of 4.8 × 10 15 ions/cm 2 to simulate the fission damage that occurs within nuclear fuels. The primary effect of the irradiation on the UO 2 samples, observed by scanning electron microscopy, was to induce a smootheningmore » of the surface features and formation of hollow blisters, which was attributed to multiple overlap of ion tracks. Dissolution experiments were conducted in single-pass flow-through (SPFT) mode under anoxic conditions (<0.1 O 2 ppm in Ar) to study the effect of the induced irradiation damage on the dissolution of the UO 2 matrix with data collection capturing six minute intervals for several hours. These time-resolved data showed that the irradiated samples showed a higher initial release of uranium than unirradiated samples, but that the uranium concentrations converged towards ~10 -9 mol/l after a few hours. And apart from the initial spike in uranium concentration, attributed to irradiation induced surficial micro-structural changes, no noticeable difference in uranium chemistry as measured by X-ray electron spectroscopy or ‘effective solubility’ was observed between the irradiated, doped and undoped samples in this work. Some secondary phase formation was observed on the surface of UO 2 samples after the dissolution experiment.« less

Synthesis and X-ray diffraction study of new uranyl malonate and oxalate complexes with carbamide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medvedkov, Ya. A.; Serezhkina, L. B., E-mail: Lserezh@samsu.ru; Grigor’ev, M. S.

2016-05-15

Two new malonate-containing uranyl complexes with carbamide of the formulas [UO{sub 2}(C{sub 3}H{sub 2}O{sub 4})(Urea){sub 2}] (I) and [UO{sub 2}(C{sub 3}H{sub 2}O{sub 4})(Urea){sub 3}] (II), where Urea is carbamide, and one uranyl oxalate complex of the formula [UO{sub 2}(C{sub 2}O{sub 4})(Urea){sub 3}] (III) were synthesized, and their crystals were studied by X-ray diffraction. The main structural units in crystals I are the electroneutral chains [UO{sub 2}(C{sub 3}H{sub 2}O{sub 4})(Urea){sub 2}]{sub ∞} belonging to the crystal-chemical group AT{sup 11}M{sub 2}{sup 1} (A = UO{sub 2}{sup 2+}, T{sup 11} = C{sub 3}H{sub 2}O{sub 4}{sup 2-}, M{sup 1} = Urea) of uranyl complexes.more » Crystals II and III are composed of the molecular complexes [UO{sub 2}(L)(Urea){sub 3}], where L = C{sub 3}H{sub 2}O{sub 4}{sup 2-} or C{sub 2}O{sub 4}{sup 2-}, belonging to the crystal-chemical group AB{sup 01}M{sub 3}{sup 1} (A = UO{sub 2}{sup 2+}, B{sup 01} = C{sub 3}H{sub 2}O{sub 4}{sup 2-} or C{sub 2}O{sub 4}{sup 2-}, M{sup 1} = Urea). The characteristic features of the packing of the uranium-containing complexes are discussed in terms of molecular Voronoi–Dirichlet polyhedra. The effect of the Urea: U ratio on the structure of uranium-containing structural units is considered.« less

Enhanced thermal conductivity oxide nuclear fuels by co-sintering with BeO: II. Fuel performance and neutronics

NASA Astrophysics Data System (ADS)

McCoy, Kevin; Mays, Claude

2008-04-01

The fuel rod performance and neutronics of enhanced thermal conductivity oxide (ECO) nuclear fuel with BeO have been compared to those of standard UO 2 fuel. The standards of comparison were that the ECO fuel should have the same infinite neutron-multiplication factor kinf at end of life and provide the same energy extraction per fuel assembly over its lifetime. The BeO displaces some uranium, so equivalence with standard UO 2 fuel was obtained by increasing the burnup and slightly increasing the enrichment. The COPERNIC fuel rod performance code was adapted to account for the effect of BeO on thermal properties. The materials considered were standard UO 2, UO 2 with 4.0 vol.% BeO, and UO 2 with 9.6 vol.% BeO. The smaller amount of BeO was assumed to provide increases in thermal conductivity of 0, 5, or 10%, whereas the larger amount was assumed to provide an increase of 50%. A significant improvement in performance was seen, as evidenced by reduced temperatures, internal rod pressures, and fission gas release, even with modest (5-10%) increases in thermal conductivity. The benefits increased monotonically with increasing thermal conductivity. Improvements in LOCA initialization performance were also seen. A neutronic calculation considered a transition from standard UO 2 fuel to ECO fuel. The calculation indicated that only a small increase in enrichment is required to maintain the kinf at end of life. The smallness of the change was attributed to the neutron-multiplication reaction of Be with fast neutrons and the moderating effect of BeO. Adoption of ECO fuel was predicted to provide a net reduction in uranium cost. Requirements for industrial hygiene were found to be comparable to those for processing of UO 2.

Crystal Chemistry of the Potassium and Rubidium Uranyl Borate Families Derived from Boric Acid Fluxes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shuao; Alekseev, Evgeny V.; Stritzinger, Jared T.

2010-07-19

The reaction of uranyl nitrate with a large excess of molten boric acid in the presence of potassium or rubidium nitrate results in the formation of three new potassium uranyl borates, K{sub 2}[(UO{sub 2}){sub 2}B{sub 12}O{sub 19}(OH){sub 4}]·0.3H{sub 2}O (KUBO-1), K[(UO{sub 2}){sub 2}B{sub 10}O{sub 15}(OH){sub 5}] (KUBO-2), and K[(UO{sub 2}){sub 2}B{sub 10}O{sub 16}(OH){sub 3}]·0.7H{sub 2}O (KUBO-3) and two new rubidium uranyl borates Rb{sub 2}[(UO{sub 2}){sub 2}B{sub 13}O{sub 20}(OH){sub 5}] (RbUBO-1) and Rb[(UO{sub 2}){sub 2}B{sub 10}O{sub 16}(OH){sub 3}]·0.7H{sub 2}O (RbUBO-2). The latter is isotypic with KUBO-3. These compounds share a common structural motif consisting of a linear uranyl, UO{sub 2}{sup 2+},more » cation surrounded by BO{sub 3} triangles and BO{sub 4} tetrahedra to create an UO{sub 8} hexagonal bipyramidal environment around uranium. The borate anions bridge between uranyl units to create sheets. Additional BO{sub 3} triangles extend from the polyborate layers and are directed approximately perpendicular to the sheets. All of these compounds adopt layered structures. With the exception of KUBO-1, the structures are all centrosymmetric. All of these compounds fluoresce when irradiated with long-wavelength UV light. The fluorescence spectrum yields well-defined vibronically coupled charge-transfer features.« less

Structural properties of lanthanide and actinide compounds within the plane wave pseudopotential approach

PubMed

Pickard; Winkler; Chen; Payne; Lee; Lin; White; Milman; Vanderbilt

2000-12-11

We show that plane wave ultrasoft pseudopotential methods readily extend to the calculation of the structural properties of lanthanide and actinide containing compounds. This is demonstrated through a series of calculations performed on UO, UO2, UO3, U3O8, UC2, alpha-CeC2, CeB6, CeSe, CeO2, NdB6, TmOI, LaBi, LaTiO3, YbO, and elemental Lu.

Uncloaking the thermodynamics of the studtite to metastudtite shear-induced transformation

DOE PAGES

Weck, Philippe F.; Kim, Eunja

2016-07-11

The interplay between thermodynamics and mechanical properties in the transformation of studtite, (UO 2)(O 2)(H 2O) 2·2H 2O, into metastudtite, (UO 2)(O 2)(H 2O) 2, two important corrosion phases observed on the surface of uranium dioxide exposed to water, is revealed using density functional perturbation theory. Phonon calculations within the quasi-harmonic approximation predict that the standard entropy change for the (UO 2)(O 2)(H 2O) 2·2H 2O → (UO 2)(O 2)(H 2O) 2 + 2H 2O reaction is ΔS 0 = +80 J·mol –1·K –1 for the production of water in the liquid state and +389 J·mol–1·K–1 for water vapor. Similarmore » to bulk H 2O(l), the bulk modulus of (UO 2)(O 2)(H 2O) 2·2H 2O increases with temperature, contrasting with (UO 2)(O 2)(H 2O) 2 which features the typical Anderson–Gruneisen temperature dependence of oxide solids. Upon removal of interstitial H 2O in studtite, the most important changes in the shear modulus, the parameter limiting the mechanical stability, arise in the planes normal to chain propagation directions. Lastly, the present findings have important implications for the dehydration of other hygroscopic materials.« less

Uncloaking the thermodynamics of the studtite to metastudtite shear-induced transformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weck, Philippe F.; Kim, Eunja

The interplay between thermodynamics and mechanical properties in the transformation of studtite, (UO 2)(O 2)(H 2O) 2·2H 2O, into metastudtite, (UO 2)(O 2)(H 2O) 2, two important corrosion phases observed on the surface of uranium dioxide exposed to water, is revealed using density functional perturbation theory. Phonon calculations within the quasi-harmonic approximation predict that the standard entropy change for the (UO 2)(O 2)(H 2O) 2·2H 2O → (UO 2)(O 2)(H 2O) 2 + 2H 2O reaction is ΔS 0 = +80 J·mol –1·K –1 for the production of water in the liquid state and +389 J·mol–1·K–1 for water vapor. Similarmore » to bulk H 2O(l), the bulk modulus of (UO 2)(O 2)(H 2O) 2·2H 2O increases with temperature, contrasting with (UO 2)(O 2)(H 2O) 2 which features the typical Anderson–Gruneisen temperature dependence of oxide solids. Upon removal of interstitial H 2O in studtite, the most important changes in the shear modulus, the parameter limiting the mechanical stability, arise in the planes normal to chain propagation directions. Lastly, the present findings have important implications for the dehydration of other hygroscopic materials.« less

Free energies and mechanisms of water exchange around Uranyl from first principles molecular dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atta-Fynn, Raymond; Bylaska, Eric J.; De Jong, Wibe A.

2012-02-01

From density functional theory (DFT) based ab initio (Car-Parrinello) metadynamics, we compute the activation energies and mechanisms of water exchange between the first and second hydration shells of aqueous Uranyl (UO{sub 2}{sup 2+}) using the primary hydration number of U as the reaction coordinate. The free energy and activation barrier of the water dissociation reaction [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+}(aq) {yields} [UO{sub 2}(OH{sub 2})4]{sup 2+}(aq) + H{sub 2}O are 0.7 kcal and 4.7 kcal/mol respectively. The free energy is in good agreement with previous theoretical (-2.7 to +1.2 kcal/mol) and experimental (0.5 to 2.2 kcal/mol) data. The associative reaction [UO{submore » 2}(OH{sub 2}){sub 5}]{sup 2+}(aq) + H{sub 2}O {yields} [UO{sub 2}(OH{sub 2})6]{sup 2+}(aq) is short-lived with a free energy and activation barrier of +7.9 kcal/mol and +8.9 kca/mol respectively; it is therefore classified as associative-interchange. On the basis of the free energy differences and activation barriers, we predict that the dominant exchange mechanism between [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+}(aq) and bulk water is dissociative.« less

Experimental studies of Micro- and Nano-grained UO 2: Grain Growth Behavior, Sufrace Morphology, and Fracture Toughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, Yinbin; Mo, Kun; Jamison, Laura M.

This activity is supported by the US Nuclear Energy Advanced Modeling and Simulation (NEAMS) Fuels Product Line (FPL) and aims at providing experimental data for the validation of the mesoscale simulation code MARMOT. MARMOT is a mesoscale multiphysics code that predicts the coevolution of microstructure and properties within reactor fuel during its lifetime in the reactor. It is an important component of the Moose-Bison-Marmot (MBM) code suite that has been developed by Idaho National Laboratory (INL) to enable next generation fuel performance modeling capability as part of the NEAMS Program FPL. In order to ensure the accuracy of the microstructure-basedmore » materials models being developed within the MARMOT code, extensive validation efforts must be carried out. In this report, we summarize the experimental efforts in FY16 including the following important experiments: (1) in-situ grain growth measurement of nano-grained UO 2; (2) investigation of surface morphology in micrograined UO 2; (3) Nano-indentation experiments on nano- and micro-grained UO 2. The highlight of this year is: we have successfully demonstrated our capability to in-situ measure grain size development while maintaining the stoichiometry of nano-grained UO 2 materials; the experiment is, for the first time, using synchrotron X-ray diffraction to in-situ measure grain growth behavior of UO 2.« less

Characterization of Actinides Complexed to Nuclear Fuel Constituents Using ESI-MS

DOE PAGES

McDonald, Luther W.; Campbell, James A.; Vercouter, Thomas; ...

2016-03-01

Electrospray ionization-mass spectrometry (ESI-MS) was tested for its use in monitoring spent nuclear fuel (SNF) constituents including U, Pu, dibutyl phosphate (DBP), and tributyl phosphate (TBP). Both positive and negative ion modes were used to evaluate the speciation of U and Pu with TBP and DBP. Furthermore, apparent stability constants were determined for U complexed to TBP and DBP. In positive ion mode, TBP produced a strong signal with and without complexation to U or Pu, but, in negative ion mode, no TBP, U-TBP, or Pu-TBP complexes were observed. Apparent stability constants were determined for [UO 2(NO 3) 2(TBP) 2],more » [UO 2(NO 3) 2(H 2O)(TBP) 2], and [UO 2(NO 3) 2(TBP) 3]. In contrast DBP, U-DBP, and Pu-DBP complexes were observed in both positive and negative ion modes. Apparent stability constants were determined for the species [UO 2(DBP)], [UO 2(DBP) 3], and [UO 2(DBP) 4]. Analyzing mixtures of U or Pu with TBP and DBP yielded the formation of ternary complexes whose stoichiometry was directly related to the ratio of TBP to DBP. The ESI-MS protocols used in this study will further demonstrate the utility of ESI-MS and its applicability to process control monitoring in SNF reprocessing facilities.« less

ON THE REACTION OF COMPONENETS IN MeNO$sub 3$-UO$sub 2$(NO$sub 3$)$sub 2$- H$sub 2$O TYPE SYSTEMS (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yakimov, M.A.; Nosova, N.F.; Degtyarev, A.Ya.

1963-01-01

Solubility in ternary systems TlNO/sub 3/--UO/sub 2/(NO/sub 3/)/sub 2/-- H/sub 2/ O and CsNO/sub 3/--UO/sub 2/(NO/sub 3/)/sub 2/--H/sub 2/O at 0 to 25 c- C was studi ed by the isothermal method. The first system did not form solid phase compounds; the second system formed two compounds Cs/sub 2/UO/ sub 2/(NO/sub 3/)/sub 4/ and CsUO/sub 2/(NO/sub 3/)/sub 3/ at 25 c- and of water vapor pressure over the systems at 25 c- showed that water activity in the ternary systems at certain concentrations does not exceed the water activity in binary uranyl nitratewater system (at identical uranyl nitrate concentrations) confirmingmore » the observed complex formation in the solution. The mechanism of complex formation was analyzed and expanded for alkali metal - metal salt-complexing agent water systems. (R.V.J.)« less

Neutronics Benchmarks for the Utilization of Mixed-Oxide Fuel: Joint U.S./Russian Progress Report for Fiscal Year 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akkurt, H

2001-01-11

In 1967, a series of critical experiments were conducted at the Westinghouse Reactor Evaluation Center (WREC) using mixed-oxide (MOX) PuO{sub 2}-UO{sub 2} and/or UO{sub 2} fuels in various lattices and configurations . These experiments were performed under the joint sponsorship of the Empire State Atomic Development Associates (ESADA) plutonium program and Westinghouse . The purpose of these experiments was to develop experimental data to validate analytical methods used in the design of a plutonium-bearing replacement fuel for water reactors. Three different fuels were used during the experimental program: two MOX fuels and a low-enriched UO{sub 2} fuel. The MOX fuelsmore » were distinguished by their {sup 240}Pu content: 8 wt% {sup 240}Pu and 24 wt% {sup 240}Pu. Both MOX fuels contained 2.0 wt % PuO{sub 2} in natural UO{sub 2} . The UO{sub 2} fuel with 2.72 wt % enrichment was used for comparison with the plutonium data and for use in multiregion experiments.« less

METHOD FOR PREPARATION OF SPHERICAL UO$sub 4$

DOEpatents

Gregory, J.F. Jr.; Levey, R.P. Jr.

1962-06-01

A method is given for continuously precipitating ura nium peroxide in the form of spherical particles. Seed crystals are formed in a first reaction zone by introducing an acidified aqueous uranyl nitrate solution and an aqueous hydrogen peroxide solution at a ratio of 5 to 20 per cent of the stoichiometric amount required for complete precipitation. After a mean residence time of 2 to 5 minutes in the first reaction zone, the resulting mixture is introduced into a second reaction zone, together with a large excess of hydrogen peroxide solution. The resulting UO4 is rapidly separated from the mother liquor after an over-all residence time of 5 to 11 minutes. The first reaction is maintained at a temperature of 85 to 90 deg C and the second zone above 50 deg C. Additional reaction zones may be employed for further crystal growth. The UO/sub 4/ is converted to U/sub 3/O/sub 8/ or UO/sub 2/ by heating in air or hydrogen atmosphere. This method is particularly useful for the preparation of spherical UO/sub 2/ particles 10 to 25 microns in diameter. (AEC)

Probing the oxygen environment in UO(2)(2+) by solid-state 17O nuclear magnetic resonance spectroscopy and relativistic density functional calculations.

PubMed

Cho, Herman; de Jong, Wibe A; Soderquist, Chuck Z

2010-02-28

A combined theoretical and solid-state (17)O nuclear magnetic resonance (NMR) study of the electronic structure of the uranyl ion UO(2)(2+) in (NH(4))(4)UO(2)(CO(3))(3) and rutherfordine (UO(2)CO(3)) is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens and the latter exemplifying a uranyl environment without hydrogens. Relativistic density functional calculations reveal unique features of the U-O covalent bond, including the finding of (17)O chemical shift anisotropies that are among the largest for oxygen ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state (17)O NMR measurements in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the (17)O echo signal of U (17)O(2)(2+).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaques, Brian J.; Watkins, Jennifer; Croteau, Joseph R.

In this study, the design and development of an economical, accident tolerant fuel (ATF) for use in the current light water reactor (LWR) fleet is highly desirable for the future of nuclear power. Uranium mononitride has been identified as an alternative fuel with higher uranium density and thermal conductivity when compared to the benchmark, UO 2, which could also provide significant economic benefits. However, UN by itself reacts with water at reactor operating temperatures. In order to reduce its reactivity, the addition of UO 2 to UN has been suggested. In order to avoid carbon impurities, UN was synthesized frommore » elemental uranium using a hydride-dehydride-nitride thermal synthesis route prior to mixing with up to 10 wt% UO 2 in a planetary ball mill. UN and UN – UO 2 composite pellets were sintered in Ar – (0–1 at%) N 2 to study the effects of nitrogen concentration on the evolved phases and microstructure. UN and UN-UO 2 composite pellets were also sintered in Ar – 100 ppm N 2 to assess the effects of temperature (1700–2000 °C) on the final grain morphology and phase concentration.« less

Estimated critical conditions for UO{sub 2}F{sub 2}--H{sub 2}O systems in fully water-reflected spherical geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jordan, W.C.; Turner, J.C.

1992-12-01

The purpose of this report is to document reference calculations performed using the SCALE-4.0 code system to determine the critical parameters of UO{sub 2}F{sub 2}-H{sub 2}O spheres. The calculations are an extension of those documented in ORNL/CSD/TM-284. Specifically, the data for low-enriched UO{sub 2}F{sub 2}-H{sub 2}O spheres have been extended to highly enriched uranium. These calculations, together with those reported in ORNL/CSD/TM-284, provide a consistent set of critical parameters (k{sub {infinity}}, volume, mass, mass of water) for UO{sub 2}F{sub 2} and water over the full range of enrichment and moderation ratio.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, Yinbin; Mo, Kun; Yao, Tiankai

Here coordinated experimental efforts to quantitatively correlate crystallographic orientation and surface faceting features in UO2 are reported upon. A sintered polycrystalline UO2 sample was thermally etched to induce the formation of surface faceting features. Synchrotron Laue microdiffraction was used to obtain a precise crystallographic orientation map for the UO2 surface grains. Scanning electron microscopy (SEM) was utilized to collect the detailed information on the surface morphology of the sample. The surface faceting features were found to be highly dependent on the crystallographic orientation. In most cases, Triple-plane structures containing one {100} plane and two {111} planes were found to dominatemore » the surface of UO2. The orientation-faceting relationship established in this study revealed a practical and efficient method of determining crystallographic orientation based on the surface features captured by SEM images.« less

Reduced live-birth rates after IVF/ICSI in women with previous unilateral oophorectomy: results of a multicentre cohort study.

PubMed

Lind, Tekla; Holte, Jan; Olofsson, Jan I; Hadziosmanovic, Nermin; Gudmundsson, Johannes; Nedstrand, Elizabeth; Lood, Mikael; Berglund, Lars; Rodriguez-Wallberg, Kenny

2018-02-01

Is there a reduced live-birth rate (LBR) after IVF/ICSI treatment in women with a previous unilateral oophorectomy (UO)? A significantly reduced LBR after IVF/ICSI was found in women with previous UO when compared with women with intact ovaries in this large multicentre cohort, both crudely and after adjustment for age, BMI, fertility centre and calendar period and regardless of whether the analysis was based on transfer of embryos in the fresh cycle only or on cumulative results including transfers using frozen-thawed embryos. Similar pregnancy rates after IVF/ICSI have been previously reported in case-control studies and small cohort studies of women with previous UO versus women without ovarian surgery. In all previous studies multiple embryos were transferred. No study has previously evaluated LBR in a large cohort of women with a history of UO. This research was a multicentre cohort study, including five reproductive medicine centres in Sweden: Carl von Linné Clinic (A), Karolinska University Hospital (B), Uppsala University Hospital (C), Linköping University Hospital (D) and Örebro University Hospital (E). The women underwent IVF/ICSI between January 1999 and November 2015. Single embryo transfer (SET) was performed in approximately 70% of all treatments, without any significant difference between UO exposed women versus controls (68% versus 71%), respectively (P = 0.32), and a maximum of two embryos were transferred in the remaining cases. The dataset included all consecutive treatments and fresh and frozen-thawed cycles. The exposed cohort included 154 women with UO who underwent 301 IVF/ICSI cycles and the unexposed control cohort consisted of 22 693 women who underwent 41 545 IVF/ICSI cycles. Overall, at the five centres (A-E), the exposed cohort underwent 151, 34, 35, 41 and 40 treatments, respectively, and they were compared with controls of the same centre (18 484, 8371, 5575, 4670 and 4445, respectively). The primary outcome was LBR, which was analysed per started cycle, per ovum pick-up (OPU) and per embryo transfer (ET). Secondary outcomes included the numbers of oocytes retrieved and supernumerary embryos obtained, the Ovarian Sensitivity Index (OSI), embryo quality scores and cumulative pregnancy rates. We used a Generalized Estimating Equation (GEE) model for statistical analysis in order to account for repeated treatments. The exposed (UO) and control women's groups were comparable with regard to age and performance of IVF or ICSI. Significant differences in LBR, both crude and age-adjusted, were observed between the UO and control groups: LBR per started cycle (18.6% versus 25.4%, P = 0.007 and P = 0.014, respectively), LBR/OPU (20.3% versus 27.1%, P = 0.012 and P = 0.015, respectively) and LBR/ET (23.0% versus 29.7%, P = 0.022 and P = 0.025, respectively). The differences in LBR remained significant after inclusion of both fresh and frozen-thawed transfers (both crude and age-adjusted data): LBR/OPU (26.1% versus 34.4%, P = 0.005 and P = 0.006, respectively) and LBR/ET (28.3% versus 37.1%, P = 0.006 and P = 0.006, respectively). The crude cancellation rate was significantly higher among women with a history of UO than in controls (18.9% versus 14.5%, P = 0.034 and age-adjusted, P = 0.178). In a multivariate GEE model, the cumulative odds ratios for LBR (fresh and frozen-thawed)/OPU (OR 0.70, 95% CI 0.52-0.94, P = 0.016) and LBR (fresh and frozen-thawed)/ET (OR 0.68, 95% CI 0.51-0.92, P = 0.012) were approximately 30% lower in the group of women with UO when adjusted for age, BMI, reproductive centre, calendar period and number of embryos transferred when appropriate. The OSI was significantly lower in women with a history of UO than in controls (3.6 versus 6.0) and the difference was significant for both crude and age-adjusted data (P = <0.001 for both). Significantly fewer oocytes were retrieved in treatments of women with UO than in controls (7.2 versus 9.9, P = <0.001, respectively). Due to the nature of the topic, this is a retrospective analysis, with all its inherent limitations. Furthermore, the cause for UO was not possible to obtain in all cases. A diagnosis of endometriosis was also more common in the UO group, i.e. a selection bias in terms of poorer patient characteristics in the UO group cannot be completely ruled out. However, adjustment for all known confounders did not affect the general results. To date, this is the largest cohort investigated and the first study indicating an association of achieving reduced live birth after IVF/ICSI in women with previous UO. These findings are novel and contradict the earlier notion that IVF/ICSI treatment is not affected, or is only marginally affected by previous UO. None. Not applicable. © The Author 2017. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com

Functionalized UO[sub 2] salenes. Neutral receptors for anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudkevich, D.M.; Verboom, W.; Brzozka, Z.

1994-05-18

A novel class of neutral receptors for anions that contain a unique combination of an immobilized Lewis acidic binding site (UO[sub 2][sup 2+]) and additional amide C(O)NH groups, which can form a favorable H-bond with a coordinated anion guest, has been developed. The unique combination of a Lewis acidic UO[sub 2] center and amide C(O)NH groups in one receptor leads to highly specific H[sub 2]PO[sub 4[sup [minus

A clinical measure of maximal and rapid stepping in older women.

PubMed

Medell, J L; Alexander, N B

2000-08-01

In older adults, clinical measures have been used to assess fall risk based on the ability to maintain stance or to complete a functional task. However, in an impending fall situation, a stepping response is often used when strategies to maintain stance are inadequate. We examined how maximal and rapid stepping performance might differ among healthy young, healthy older, and balance-impaired older adults, and how this stepping performance related to other measures of balance and fall risk. Young (Y; n = 12; mean age, 21 years), unimpaired older (UO; n = 12; mean age, 69 years), and balance-impaired older women IO; n = 10; mean age, 77 years) were tested in their ability to take a maximal step (Maximum Step Length or MSL) and in their ability to take rapid steps in three directions (front, side, and back), termed the Rapid Step Test (RST). Time to complete the RST and stepping errors occurring during the RST were noted. The IO group, compared with the Y and UO groups, demonstrated significantly poorer balance and higher fall risk, based on performance on tasks such as unipedal stance. Mean MSL was significantly higher (by 16%) in the Y than in the UO group and in the UO (by 30%) than in the IO group. Mean RST time was significantly faster in the Y group versus the UO group (by 24%) and in the UO group versus the IO group (by 15%). Mean RST errors tended to be higher in the UO than in the Y group, but were significantly higher only in the UO versus the IO group. Both MSL and RST time correlated strongly (0.5 to 0.8) with other measures of balance and fall risk including unipedal stance, tandem walk, leg strength, and the Activities-Specific Balance Confidence (ABC) scale. We found substantial declines in the ability of both unimpaired and balance-impaired older adults to step maximally and to step rapidly. Stepping performance is closely related to other measures of balance and fall risk and might be considered in future studies as a predictor of falls and fall-related injuries.

Time-Resolved Infrared Reflectance Studies of the Dehydration-Induced Transformation of Uranyl Nitrate Hexahydrate to the Trihydrate Form

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Timothy J.; Sweet, Lucas E.; Meier, David E.

Uranyl nitrate is a key species in the nuclear fuel cycle. However, this species is known to exist in different states of hydration, including the hexahydrate ([UO2(NO3)2(H2O)6] often called UNH), the trihydrate [UO2(NO3)2(H2O)3 or UNT], and in very dry environments the dihydrate form [UO2(NO3)2(H2O)2]. Their relative stabilities depend on both water vapor pressure and temperature. In the 1950s and 1960s the different phases were studied by infrared transmission spectroscopy, but were limited both by instrumental resolution and by the ability to prepare the samples for transmission. We have revisited this problem using time-resolved reflectance spectroscopy, which requires no sample preparationmore » and allows dynamic analysis while the sample is exposed to a flow of N2 gas. Samples of known hydration state were prepared and confirmed via X-ray diffraction patterns of known species. In reflectance mode the hexahydrate UO2(NO3)2(H2O)6 has a distinct uranyl asymmetric stretch band at 949.0 cm-1 that shifts to shorter wavelengths and broadens as the sample desiccates and recrystallizes to the trihydrate, first as a shoulder growing in on the blue edge but ultimately results in a doublet band with reflectance peaks at 966 and 957 cm-1. The data are consistent with transformation from UNH to UNT as UNT has two inequivalent UO22+ sites. The dehydration of UO2(NO3)2(H2O)6 to UO2(NO3)2(H2O)3 is both a structural and morphological change that has the lustrous lime green UO2(NO3)2(H2O)6 crystals changing to the matte greenish yellow of the trihydrate solid. The phase transformation and crystal structures were confirmed by density functional theory calculations and optical microscopy methods, both of which showed a transformation with two distinct sites for the uranyl cation in the trihydrate, with but one in the hexahydrate.« less

Use of spectroscopic techniques for uranium(VI)/montmorillonite interaction modeling.

PubMed

Kowal-Fouchard, A; Drot, R; Simoni, E; Ehrhardt, J J

2004-03-01

To experimentally identify both clay sorption sites and sorption equilibria and to understand the retention mechanisms at a molecular level, we have characterized the structure of hexavalent uranium surface complexes resulting from the interaction between the uranyl ions and the surface retention groups of a montmorillonite clay. We have performed laser-induced fluorescence spectroscopy (LIFS) and X-ray photoelectron spectroscopy (XPS) on uranyl ion loaded montmorillonite. These structural results were then compared to those obtained from the study of uranyl ions sorbed onto an alumina and also from U(VI) sorbed on an amorphous silica. This experimental approach allowed for a clear determination of the reactive surface sites of montmorillonite for U(VI) sorption. The lifetime values and the U4f XPS spectra of uranium(VI) sorbed on montmorillonite have shown that this ion is sorbed on both exchange and edge sites. The comparison of U(VI)/clay and U(VI)/oxide systems has determined that the interaction between uranyl ions and montmorillonite edge sites occurs via both [triple bond]AlOH and [triple bond]SiOH surface groups and involves three distinct surface complexes. The surface complexation modeling of the U(VI)/montmorillonite sorption edges was determined using the constant capacitance model and the above experimental constraints. The following equilibria were found to account for the uranyl sorption mechanisms onto montmorillonite for metal concentrations ranged from 10(-6) to 10(-3) M and two ionic strengths (0.1 and 0.5 M): 2[triple bond]XNa + UO2(2+) <==> ([triple bond]X)2UO2 + 2Na+, log K0(exch) = 3.0; [triple bond]Al(OH)2 + UO2(2+) <==> [triple bond]Al(OH)2UO2(2+), log K0(Al) = 14.9; [triple bond]Si(OH)2 + UO2(2+) <==> [triple bond]SiO2UO2 + 2H+, log K0(Si1) = -3.8; and [triple bond]Si(OH)2 + 3UO2(2+) + 5H2O <==> [triple bond]SiO2(UO2)3(OH)5- + 7H+, log K0(Si2) = -20.0.

PRESSURIZED WATER REACTOR PROGRAM TECHNICAL PROGRESS REPORT FOR THE PERIOD MAY 5, 1955 TO JUNE 16, 1955

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

The current PWR plant and core parameters are listed. Resign requirements are briefly summarized for a radiation monitoring system, a fuel handling water system, a coolant purification system, an electrical power distribution system, and component shielding. Results of studies on thermal bowing and stressing of UO/sub 2/ are reported. A graph is presented of reactor power vs. reactor flow for various hot channel conditions. Development of U-- Mo and U-Nb alloys has been stopped because of the recent selection of UO/sub 2/ fuel material for the PWR core and blanket. The fabrication characteristics of UO/sub 2/ powders are being studied.more » Seamless Zircaloy-2 tubing has been tested to determine elastic limits, bursting pressures, and corrosion resistance. Fabrication techniques and tests for corrosion and defects in Zircaloy-clad U-Mo and UO/sub 2/ fuel rods are described. The preparation of UO/sub 2/ by various methods is being studied to determine which method produces a material most suitable for PWR fuel elements. The stability of UO/sub 2/ compacts in high temperature water and steam is being determined. Surface area and density measurements have been performed on samples of UO/sub 2/ powder prepared by various methods. Revelopment work on U-- Mo and U--Nb alloys has included studies of the effect on corrosion behavior of additions to the test water, additions to the alloys, homogenization of the alloys, annealing times, cladding, and fabrication techniques. Data are presented on relaxation in spring materials after exposure to a corrosive environment. Results are reported from loop and autoclave tests on fission product and crud deposition. Results of irradiation and corrosion testing of clad and unclad U--Mo and U-Nh alloys are described. The UO/sub 2/ irradiation program has included studies of dimensional changes, release of fission gases, and activity in the water surrounding the samples. A review of the methods of calculating reactor physics parameters has been completed, and the established procedures have been applied to determination of PWR reference design parameters. Critical experiments and primary loop shielding analyses are described. (D.E.B.)« less

Time-resolved infrared reflectance studies of the dehydration-induced transformation of uranyl nitrate hexahydrate to the trihydrate form

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Timothy J.; Sweet, Lucas E.; Meier, David E.

2015-09-08

Uranyl nitrate is a key species in the nuclear fuel cycle. However, this species is known to exist in different states of hydration, including the hexahydrate ([UO 2(NO 3) 2(H 2O) 6] often called UNH), the trihydrate [UO 2(NO 3) 2(H 2O) 3 or UNT], and in very dry environments the dihydrate form [UO 2(NO 3) 2(H 2O) 2]. Their relative stabilities depend on both water vapor pressure and temperature. In the 1950s and 1960s, the different phases were studied by infrared transmission spectroscopy but were limited both by instrumental resolution and by the ability to prepare the samples formore » transmission. We have revisited this problem using time-resolved reflectance spectroscopy, which requires no sample preparation and allows dynamic analysis while the sample is exposed to a flow of N 2 gas. Samples of known hydration state were prepared and confirmed via X-ray diffraction patterns of known species. In reflectance mode the hexahydrate UO 2(NO 3) 2(H 2O) 6 has a distinct uranyl asymmetric stretch band at 949.0 cm –1 that shifts to shorter wavelengths and broadens as the sample desiccates and recrystallizes to the trihydrate, first as a shoulder growing in on the blue edge but ultimately results in a doublet band with reflectance peaks at 966 and 957 cm –1. The data are consistent with transformation from UNH to UNT as UNT has two inequivalent UO 2 2+ sites. The dehydration of UO 2(NO 3) 2(H 2O) 6 to UO 2(NO 3) 2(H 2O) 3 is both a structural and morphological change that has the lustrous lime green UO 2(NO 3) 2(H 2O) 6 crystals changing to the matte greenish yellow of the trihydrate solid. As a result, the phase transformation and crystal structures were confirmed by density functional theory calculations and optical microscopy methods, both of which showed a transformation with two distinct sites for the uranyl cation in the trihydrate, with only one in the hexahydrate.« less

Electrospray ionization of uranyl-citrate complexes

NASA Astrophysics Data System (ADS)

Somogyi, Árpád; Pasilis, Sofie P.; Pemberton, Jeanne E.

2007-09-01

Results presented here demonstrate the usefulness of electrospray ionization and gas-phase ion-molecule reactions to predict structural and electronic differences in complex inorganic ions. Electrospray ionization of uranyl citrate solutions generates positively and negatively charged ions that participate in further ion-molecule reactions in 3D ion trap and FT-ICR mass analyzers. Most ions observed are derived from the major solution uranyl-citrate complexes and involve species of {(UO2)2Cit2}2-, (UO2)3Cit2, and {(UO2)3Cit3}3-, where Cit indicates the citrate trianion, C6H5O73-. In a 3D ion trap operated at relatively high pressure, complex adducts containing solvent molecules, alkali and ammonium cations, and nitrate or chloride anions are dominant, and proton/alkali cation (Na+, K+) exchange is observed for up to six exchangeable protons in an excess of alkali cations. Adduct formation in a FT-ICR cell that is operated at lower pressures is less dominant, and direct detection of positive and negative ions of the major solution complexes is possible. Multiply charged ions are also detected, suggesting the presence of uranium in different oxidation states. Changes in uranium oxidation state are detected by He-CID and SORI-CID fragmentation, and certain fragments undergo association reactions in trapping analyzers, forming "exotic" species such as [(UO2)4O3]-, [(UO2)4O4]-, and [(UO2)4O5]-. Ion-molecule reactions with D2O in the FT-ICR cell indicate substantial differences in H/D exchange rate and D2O accommodation for different ion structures and charge states. Most notably, the positively charged ions [H2(UO2)2Cit2(H)]+ and [(UO2)2(Cit)]+ accommodate two and three D2O molecules, respectively, which reflects well the structural differences, i.e., tighter uranyl-citrate coordination in the former ion than in the latter. The corresponding negatively charged ions accommodate zero or two D2O molecules, which can be rationalized using suggested solution phase structures and charge state distributions.

PREPARATION OF UO$sub 2$ FOR NUCLEAR REACTOR FUEL PELLETS

DOEpatents

Googin, J.M.

1962-06-01

A method is given for preparing high-density UO/sub 2/ compacts. An aqueous uranyl fluoride solution is contacted with an aqueous ammonium hydroxide solution at an ammonium to-uranium ratio of 25: 1 to 30:1 to form a precipitate. The precipitate is separated from the- mother liquor, dried, and contacted with steam at a uniform temperature within the range of 400 to 650 deg C to produce U/ sub 3/O/sub 8/. The U/sub 3/O/sub 8/ is red uced to UO/sub 2/ with hydrogen at a uniform temperature within the range of 550 to 600 deg C. The UO/sub 2/ is then compressed into compacts and sintered. High-density compacts are fabricated to close tolerances without use of a binder and without machining or grinding. (AEC)

First-principles molecular dynamics simulation of the Ca 2UO 2(CO 3) 3 complex in water

DOE PAGES

Priest, Chad; Tian, Ziqi; Jiang, De-en

2016-01-22

Recent experiments have shown that the neutral Ca 2UO 2(CO 3) 3 complex is the dominant species of uranium in many uranyl-containing streams. However, the structure and solvation of such a species in water has not been investigated from first principles. Herein we present a first principles molecular dynamics perspective of the Ca 2UO 2(CO 3) 3 complex in water based on density functional theory and Born–Oppenheimer approximation. We find that the Ca 2UO 2(CO 3) 3 complex is very stable in our simulation timeframe for three different concentrations considered and that the key distances from our simulation are inmore » good agreement with the experimental data from extended X-ray absorption fine structure (EXAFS) spectroscopy. More important, we find that the two Ca ions bind differently in the complex, as a result of the hydrogen-bonding network around the whole complex. Furthermore, this finding invites confirmation from time-resolved EXAFS and has implications in understanding the dissociative equilibrium of the Ca 2UO 2(CO 3) 3 complex in water.« less

Theoretical investigation of thermodynamic stability and mobility of the oxygen vacancy in ThO 2 –UO 2 solid solutions

DOE PAGES

Liu, B.; Aidhy, D. S.; Zhang, Y.; ...

2014-10-16

The thermodynamic stability and the migration energy barriers of oxygen vacancies in ThO 2 –UO 2 solid solutions are investigated by density functional theory calculations. In pure ThO 2, the formation energy of oxygen vacancy is 7.58 eV and 1.46 eV under O rich and O poor conditions, respectively, while its migration energy barrier is 1.97 eV. The addition of UO 2 into ThO 2 significantly decreases the energetics of formation and migration of the oxygen vacancy. Among the range of UO 2-ThO 2 solid solutions studied in this work, UO 2 exhibits the lowest formation energy (5.99 eV andmore » -0.13 eV under O rich and O poor conditions, respectively) and Th 0.25U0 .75O 2 exhibits the lowest migration energy barrier (~ 1 eV). Moreover, by considering chemical potential, the phase diagram of oxygen vacancy as a function of both temperature and oxygen partial pressure is shown, which could help to gain experimental control over oxygen vacancy concentration.« less

Use of UO 2 films for electrochemical studies

NASA Astrophysics Data System (ADS)

Miserque, F.; Gouder, T.; Wegen, D. H.; Bottomley, P. D. W.

2001-10-01

UO 2 films have been prepared by dc reactive sputtering of a uranium metal target in an Ar/O 2 atmosphere. We have used the films deposited on gold substrates as working electrodes for electrochemical investigations as simulating the surfaces of fuel pellets. Film composition was determined by photoelectron spectroscopy (XPS and UPS) and X-ray diffraction (XRD). The oxide stoichiometry as a function of deposition conditions was determined and the appropriate conditions for UO 2.0 formation established. AC impedance and cyclic voltammetry measurements were performed. A double RC electrical equivalent circuit was used to fit the data from impedance measurements, similar to those used in unirradiated UO 2 or spent fuel pellets. However due to the porosity or adhesion defects on the thin films that permitted a direct contact between the solution and the gold substrate, we were obliged to add a contribution simulating the water-gold system. Cyclic voltammetry measurements show the influence of pH on the dissolution mechanism. Alkaline solutions permit the formation of an oxidised layer (UO 2.33) which is not present in the acidic solutions. In both pH=2 and pH=6 solutions, a U VI species layer is formed.

Spectroscopy of the UO+2 cation and the delayed ionization of UO2.

PubMed

Merritt, Jeremy M; Han, Jiande; Heaven, Michael C

2008-02-28

Vibronically resolved spectra for the UO+2 cation have been recorded using the pulsed field ionization zero electron kinetic energy (PFI-ZEKE) technique. For the ground state, long progressions in both the bending and symmetric stretch vibrations were observed. Bend and stretch progressions of the first electronically excited state were also observed, and the origin was found at an energy of 2678 cm(-1) above the ground state zero-point level. This observation is consistent with a recent theoretical prediction [Infante et al., J. Chem. Phys. 127, 124308 (2007)]. The ionization energy for UO2, derived from the PFI-ZEKE spectrum, namely, 6.127(1) eV, is in excellent agreement with the value obtained from an earlier photoionization efficiency measurement. Delayed ionization of UO2 in the gas phase has been reported previously [Han et al., J. Chem. Phys. 120, 5155 (2004)]. Here, we extend the characterization of the delayed ionization process by performing a quantitative study of the ionization rate as a function of the energy above the ionization threshold. The ionization rate was found to be 5 x 10(6) s(-1) at threshold, and increased linearly with increasing energy in the range investigated (0-1200 cm(-1)).

Analysis of the vibrational frequencies of the UO/sup 2 +//sub 2/ ion in complexes containing acido-ligands

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kobets, L.V.; Umreiko, D.S.

1986-02-01

This paper presents an analysis of the vibrational frequencies of the UO/sup 2 +//sub 2/ ion in its complexes with acido-ligands that shows that in the series of the compounds indicated the correlation of UO/sup 2 +//sub 2/ with the nature of the anions and in particular with their basicity is limited in nature and may not be considered without taking account of the specific structures. If neutral ligands are present in the complexes, the situation is probably even more complicated.

Modelling oxygen self-diffusion in UO 2 under pressure

DOE PAGES

Cooper, Michael William D.; Grimes, R. W.; Fitzpatrick, M. E.; ...

2015-10-22

Access to values for oxygen self-diffusion over a range of temperatures and pressures in UO 2 is important to nuclear fuel applications. Here, elastic and expansivity data are used in the framework of a thermodynamic model, the cBΩ model, to derive the oxygen self-diffusion coefficient in UO 2 over a range of pressures (0–10 GPa) and temperatures (300–1900 K). Furthermore, the significant reduction in oxygen self-diffusion as a function of increasing hydrostatic pressure, and the associated increase in activation energy, is identified.

Electrolytic process for preparing uranium metal

DOEpatents

Haas, Paul A.

1990-01-01

An electrolytic process for making uranium from uranium oxide using Cl.sub.2 anode product from an electrolytic cell to react with UO.sub.2 to form uranium chlorides. The chlorides are used in low concentrations in a melt comprising fluorides and chlorides of potassium, sodium and barium in the electrolytic cell. The electrolysis produces Cl.sub.2 at the anode that reacts with UO.sub.2 in the feed reactor to form soluble UCl.sub.4, available for a continuous process in the electrolytic cell, rather than having insoluble UO.sub.2 fouling the cell.

Infrared spectroscopy of extreme coordination: the carbonyls of U(+) and UO(2)(+).

PubMed

Ricks, Allen M; Gagliardi, Laura; Duncan, Michael A

2010-11-17

Uranium and uranium dioxide carbonyl cations produced by laser vaporization are studied with mass-selected ion infrared spectroscopy in the C-O stretching region. Dissociation patterns, spectra, and quantum chemical calculations establish that the fully coordinated ions are U(CO)(8)(+) and UO(2)(CO)(5)(+), with D(4d) square antiprism and D(5h) pentagonal bipyramid structures. Back-bonding in U(CO)(8)(+) causes a red-shifted CO stretch, but back-donation is inefficient for UO(2)(CO)(5)(+), producing a blue-shifted CO stretch characteristic of nonclassical carbonyls.

In situ speciation of uranium in treated acid mine drainage using the diffusion gradients in thin films technique (DGT).

PubMed

Pedrobom, Jorge Henrique; Eismann, Carlos Eduardo; Menegário, Amauri A; Galhardi, Juliana Aparecida; Luko, Karen Silva; Dourado, Thiago de Araujo; Kiang, Chang Hung

2017-02-01

The exchange membranes P81 and DE81 and Chelex-100 resin were used to perform in situ speciation of uranium in treated acid mine drainage at the Osamu Utsumi mining site, Poços de Caldas city, Southeast Brazil. To investigate possible chemical modifications in the samples during analysis, the three ligands were deployed in situ and in a laboratory (in lab). The results obtained in situ were also compared to a speciation performed using Visual MINTEQ software. Chelex-100 retained total labile U for a period of up to 48 h. The labile U fraction determined by Chelex 100 ranged from 107 ± 6% to 147 ± 44% in situ and from 115 ± 22% to 191 ± 5% in lab. DE81 retained anionic U species up to 8 h, with labile fractions ranging from 37 ± 2% to 76 ± 3% in situ and 34 ± 12% to 180 ± 17% in lab. P81 exhibited a lower efficiency in retaining U species, with concentrations ranging from 6± 2% to 19± 2% in situ and 3± 2% to 18± 2% in lab. The speciation obtained from MINTEQ suggests that the major U species were UO 2 OH + , UO 2 (OH) 3- , UO 2 (OH) 2(aq) , Ca 2 UO 2 (CO 3 ) 3(aq) , CaUO 2 (CO 3 ) 3 2- , UO 2 (CO 3 ) 2 2- , and UO 2 (CO 3 ) 3 4- . This result is in accordance with the results obtained in situ. Differences concerning speciation and the total and soluble U concentrations were observed between the deployments performed in situ and in the laboratory, indicating that U speciation must be performed in situ. Copyright © 2016 Elsevier Ltd. All rights reserved.

Synthesis and crystal structure analysis of uranyl triple acetates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klepov, Vladislav V., E-mail: vladislavklepov@gmail.com; Department of Chemistry, Samara National Research University, 443086 Samara; Serezhkina, Larisa B.

2016-12-15

Single crystals of triple acetates NaR[UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 3}·6H{sub 2}O (R=Mg, Co, Ni, Zn), well-known for their use as reagents for sodium determination, were grown from aqueous solutions and their structural and spectroscopic properties were studied. Crystal structures of the mentioned phases are based upon (Na[UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 3}){sup 2–} clusters and [R(H{sub 2}O){sub 6}]{sup 2+} aqua-complexes. The cooling of a single crystal of NaMg[UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 3}·6H{sub 2}O from 300 to 100 K leads to a phase transition from trigonal to monoclinic crystal system. Intermolecular interactions between the structural units and their mutual packing were studiedmore » and compared from the point of view of the stereoatomic model of crystal structures based on Voronoi-Dirichlet tessellation. Using this method we compared the crystal structures of the triple acetates with Na[UO{sub 2}(CH{sub 3}COO){sub 3}] and [R(H{sub 2}O){sub 6}][UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 2} and proposed reasons of triple acetates stability. Infrared and Raman spectra were collected and their bands were assigned. - Graphical abstract: Single crystals of uranium based triple acetates, analytical reagents for sodium determination, were synthesized and structurally, spectroscopically and topologically characterized. The structures were compared with the structures of compounds from preceding families [M(H{sub 2}O){sub 6})][UO{sub 2}(CH{sub 3}COO){sub 3}]{sub 2} (M = Mg, Co, Ni, Zn) and Na[UO{sub 2}(CH{sub 3}COO){sub 3}]. Analysis was performed with the method of molecular Voronoi-Dirichlet polyhedra to reveal a large contribution of the hydrogen bonds into intermolecular interactions which can be a reason of low solubility of studied complexes.« less

A thermal conductivity model for U-­Si compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yongfeng; Andersson, Anders David Ragnar

U 3Si 2 is a candidate for accident tolerant nuclear fuel being developed as an alternative to UO 2 in commercial light water reactors (LWRs). One of its main benefits compared to UO 2 is higher thermal conductivity that increases with temperature. This increase is contrary to UO 2, for which the thermal conductivity decreases with temperature. The reason for the difference is the electronic origin of thermal conductivity in U 3Si 2, as compared to the phonon mechanism responsible for thermal transport in UO 2. The phonon thermal conductivity in UO 2 is unusually low for a fluorite oxidemore » due to the strong interaction with the spins in the paramagnetic phase. The thermal conductivity of U 3Si 2 as well as other U-­Si compounds has been measured experimentally [1-­4]. However, for fuel performance simulations it is also critical to model the degradation of the thermal conductivity due to damage and microstructure evolution caused by the reactor environment (irradiation and high temperature). For UO 2 this reduction is substantial and it has been the topic of extensive NEAMS research resulting in several publications [5, 6]. There are no data or models for the evolution of the U 3Si 2 thermal conductivity under irradiation. We know that the intrinsic thermal conductivities of UO 2 (semi-conductor) and U 3Si 2 (metal) are very different, and we do not necessarily expect the dependence on damage to be the same either, which could present another advantage for the silicide fuel. In this report we summarize the first step in developing a model for the thermal conductivity of U-­Si compounds with the goal of capturing the effect of damage in U 3Si 2. Next year, we will focus on lattice damage. We will also attempt to assess the impact of fission gas bubbles.« less

Efficient uranium capture by polysulfide/layered double hydroxide composites.

PubMed

Ma, Shulan; Huang, Lu; Ma, Lijiao; Shim, Yurina; Islam, Saiful M; Wang, Pengli; Zhao, Li-Dong; Wang, Shichao; Sun, Genban; Yang, Xiaojing; Kanatzidis, Mercouri G

2015-03-18

There is a need to develop highly selective and efficient materials for capturing uranium (normally as UO2(2+)) from nuclear waste and from seawater. We demonstrate the promising adsorption performance of S(x)-LDH composites (LDH is Mg/Al layered double hydroxide, [S(x)](2-) is polysulfide with x = 2, 4) for uranyl ions from a variety of aqueous solutions including seawater. We report high removal capacities (q(m) = 330 mg/g), large K(d)(U) values (10(4)-10(6) mL/g at 1-300 ppm U concentration), and high % removals (>95% at 1-100 ppm, or ∼80% for ppb level seawater) for UO2(2+) species. The S(x)-LDHs are exceptionally efficient for selectively and rapidly capturing UO2(2+) both at high (ppm) and trace (ppb) quantities from the U-containing water including seawater. The maximum adsorption coeffcient value K(d)(U) of 3.4 × 10(6) mL/g (using a V/m ratio of 1000 mL/g) observed is among the highest reported for U adsorbents. In the presence of very high concentrations of competitive ions such as Ca(2+)/Na(+), S(x)-LDH exhibits superior selectivity for UO2(2+), over previously reported sorbents. Under low U concentrations, (S4)(2-) coordinates to UO2(2+) forming anionic complexes retaining in the LDH gallery. At high U concentrations, (S4)(2-) binds to UO2(2+) to generate neutral UO2S4 salts outside the gallery, with NO3(-) entering the interlayer to form NO3-LDH. In the presence of high Cl(-) concentration, Cl(-) preferentially replaces [S4](2-) and intercalates into LDH. Detailed comparison of U removal efficiency of S(x)-LDH with various known sorbents is reported. The excellent uranium adsorption ability along with the environmentally safe, low-cost constituents points to the high potential of S(x)-LDH materials for selective uranium capture.

Urea Synthesis and Excretion in Aedes aegypti Mosquitoes Are Regulated by a Unique Cross-Talk Mechanism

PubMed Central

Isoe, Jun; Scaraffia, Patricia Y.

2013-01-01

Aedes aegypti mosquitoes do not have a typical functional urea cycle for ammonia disposal such as the one present in most terrestrial vertebrates. However, they can synthesize urea by two different pathways, argininolysis and uricolysis. We investigated how formation of urea by these two pathways is regulated in females of A. aegypti. The expression of arginase (AR) and urate oxidase (UO), either separately or simultaneously (ARUO) was silenced by RNAi. The amounts of several nitrogen compounds were quantified in excreta using mass spectrometry. Injection of mosquitoes with either dsRNA-AR or dsRNA-UO significantly decreased the expressions of AR or UO in the fat body (FB) and Malpighian tubules (MT). Surprisingly, the expression level of AR was increased when UO was silenced and vice versa, suggesting a cross-talk regulation between pathways. In agreement with these data, the amount of urea measured 48 h after blood feeding remained unchanged in those mosquitoes injected with dsRNA-AR or dsRNA-UO. However, allantoin significantly increased in the excreta of dsRNA-AR-injected females. The knockdown of ARUO mainly led to a decrease in urea and allantoin excretion, and an increase in arginine excretion. In addition, dsRNA-AR-injected mosquitoes treated with a specific nitric oxide synthase inhibitor showed an increase of UO expression in FB and MT and a significant increase in the excretion of nitrogen compounds. Interestingly, both a temporary delay in the digestion of a blood meal and a significant reduction in the expression of several genes involved in ammonia metabolism were observed in dsRNA-AR, UO or ARUO-injected females. These results reveal that urea synthesis and excretion in A. aegypti are tightly regulated by a unique cross-talk signaling mechanism. This process allows blood-fed mosquitoes to regulate the synthesis and/or excretion of nitrogen waste products, and avoid toxic effects that could result from a lethal concentration of ammonia in their tissues. PMID:23755226

Topologically identical, but geometrically isomeric layers in hydrous α-, β-Rb[UO2(AsO3OH)(AsO2(OH)2)]·H2O and anhydrous Rb[UO2(AsO3OH)(AsO2(OH)2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Na; Klepov, Vladislav V.; Villa, Eric M.

The hydrothermal reaction of uranyl nitrate with rubidium nitrate and arsenic (III) oxide results in the formation of polymorphic α- and β-Rb[UO2(AsO3OH)(AsO2(OH)2)]·H2O (α-, β-RbUAs) and the anhydrous phase Rb[UO2(AsO3OH)(AsO2(OH)2)] (RbUAs). These phases were structurally, chemically and spectroscopically characterized. The structures of all three compounds are based upon topologically identical, but geometrically isomeric layers. The layers are linked with each other by means of the Rb cations and hydrogen bonding. Dehydration experiments demonstrate that water deintercalation from hydrous α- and β-RbUAs yields anhydrous RbUAs via topotactic reactions.

Canadian experience in irradiation and testing of MOX fuel

NASA Astrophysics Data System (ADS)

Yatabe, S.; Floyd, M.; Dimayuga, F.

2018-04-01

Experimental irradiation and performance testing of Mixed OXide (MOX) fuel at the Canadian Nuclear Laboratories (CNL) has taken place for more than 40 years. These experiments investigated MOX fuel behaviour and compared it with UO2 behaviour to develop and verify fuel performance models. This article compares the performance of MOX of various concentrations and homogeneities, under different irradiation conditions. These results can be applied to future fuel designs. MOX fuel irradiated by CNL was found to be comparable in performance to similarly designed and operated UO2 fuel. MOX differs in behaviour from UO2 fuel in several ways. Fission-gas release, grain growth and the thickness of zirconium oxide on the inner sheath appear to be related to MOX fuel homogeneity. Columnar grains formed at the pellet centre begin to develop at lower powers in MOX than in UO2 fuel.

Off-stoichiometric defect clustering in irradiated oxides

NASA Astrophysics Data System (ADS)

Khalil, Sarah; Allen, Todd; EL-Azab, Anter

2017-04-01

A cluster dynamics model describing the formation of vacancy and interstitial clusters in irradiated oxides has been developed. The model, which tracks the composition of the oxide matrix and the defect clusters, was applied to the early stage formation of voids and dislocation loops in UO2, and the effects of irradiation temperature and dose rate on the evolution of their densities and composition was investigated. The results show that Frenkel defects dominate the nucleation process in irradiated UO2. The results also show that oxygen vacancies drive vacancy clustering while the migration energy of uranium vacancies is a rate-limiting factor for the nucleation and growth of voids. In a stoichiometric UO2 under irradiation, off-stoichiometric vacancy clusters exist with a higher concentration of hyper-stoichiometric clusters. Similarly, off-stoichiometric interstitial clusters form with a higher concentration of hyper-stoichiometric clusters. The UO2 matrix was found to be hyper-stoichiometric due to the accumulation of uranium vacancies.

Calculational note for the radiological and toxicological effects of a UO{sub 3} release from the T-hopper storage pad

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldberg, H.J.

1998-06-18

UO{sub 3} powder is stored at the T-hopper storage area associated with the 2714-U building in the 200 west area. The T-hopper containers and 13 drums containing this material are used to store the powder on pads immediately north of the building. An interim safety basis document (WHC,1996) was issued in 1996 for the UO{sub 3} powder storage area. In this document the isotope {sup 99}Tc was not included in the source term used to calculate the radiological consequences of a postulated release of the powder. A calculations note (HNF, 1998) was issued to remedy that deficiency. The present documentmore » is a revision to that document to reflect updated data concerning the solubility of UO{sub 3} in simulated lung fluid and to utilize more realistic powder release fractions.« less

Simulations of Xe and U diffusion in UO2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersson, Anders D.; Vyas, Shyam; Tonks, Michael R.

2012-09-10

Diffusion of xenon (Xe) and uranium (U) in UO{sub 2} is controlled by vacancy mechanisms and under irradiation the formation of mobile vacancy clusters is important. Based on the vacancy and cluster diffusion mechanisms established from density functional theory (DFT) calculations, we derive continuum thermodynamic and diffusion models for Xe and U in UO{sub 2}. In order to capture the effects of irradiation, vacancies (Va) are explicitly coupled to the Xe and U dynamics. Segregation of defects to grain boundaries in UO{sub 2} is described by combining the bulk diffusion model with models of the interaction between Xe atoms andmore » vacancies with grain boundaries, which were derived from atomistic calculations. The diffusion and segregation models were implemented in the MOOSE-Bison-Marmot (MBM) finite element (FEM) framework and the Xe/U redistribution was simulated for a few simple microstructures.« less

Molecular dynamics simulation of premelting and melting phase transitions in stoichiometric uranium dioxide

NASA Astrophysics Data System (ADS)

Yakub, Eugene; Ronchi, Claudio; Staicu, Dragos

2007-09-01

Results of molecular dynamics (MD) simulation of UO2 in a wide temperature range are presented and discussed. A new approach to the calibration of a partly ionic Busing-Ida-type model is proposed. A potential parameter set is obtained reproducing the experimental density of solid UO2 in a wide range of temperatures. A conventional simulation of the high-temperature stoichiometric UO2 on large MD cells, based on a novel fast method of computation of Coulomb forces, reveals characteristic features of a premelting λ transition at a temperature near to that experimentally observed (Tλ=2670K ). A strong deviation from the Arrhenius behavior of the oxygen self-diffusion coefficient was found in the vicinity of the transition point. Predictions for liquid UO2, based on the same potential parameter set, are in good agreement with existing experimental data and theoretical calculations.

Molybdenum-UO2 cerment irradiation at 1145 K

NASA Technical Reports Server (NTRS)

Mcdonald, G.

1971-01-01

Two molybdenum-UO2 cermet fuel pins were fission heated in a helium-cooled loop at a temperature of 1145 K and to a total burnup of 5.3 % of the U-235. After irradiation the fuel pins were measured to check dimensional stability, punctured at the plenums to determine fission gas release, and examined metallographically to determine the effect of irradiation. Burnup was determined in several sections of the fuel pin. The results of the postirradiation examination indicated: (1) There was no visible change in the fuel pins on irradiation under the above conditions. (2) The maximum swelling of the fuel pins was less than 1%. (3) There was no migration of UO2 and no visible interaction between the molybdenum and the UO2. (4) Approximately 12% of the fission gas formed was released from the cermet cone into the gas plenum.

Thermodynamic assessment of oxygen diffusion in non-stoichiometric UO2±x from experimental data and Frenkel pair modeling

NASA Astrophysics Data System (ADS)

Berthinier, C.; Rado, C.; Chatillon, C.; Hodaj, F.

2013-02-01

The self and chemical diffusion of oxygen in the non-stoichiometric domain of the UO2 compound is analyzed from the point of view of experimental determinations and modeling from Frenkel pair defects. The correlation between the self-diffusion and the chemical diffusion coefficients is analyzed using the Darken coefficient calculated from a thermodynamic description of the UO2±x phase. This description was obtained from an optimization of thermodynamic and phase diagram data and modeling with different point defects, including the Frenkel pair point defects. The proposed diffusion coefficients correspond to the 300-2300 K temperature range and to the full composition range of the non stoichiometric UO2 compound. These values will be used for the simulation of the oxidation and ignition of the uranium carbide in different oxygen atmospheres that starts at temperatures as low as 400 K.

Synthesis and structural features of U VI and V IV chelate complexes with (hhmmbH)Cl·H 2O [hhmmb = {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide], a new Schiff base ligand derived from vitamin B6

NASA Astrophysics Data System (ADS)

Back, Davi Fernando; Ballin, Marco Aurélio; de Oliveira, Gelson Manzoni

2009-10-01

The Schiff base ligand {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide hydrochloride monohydrated {(hhmmbH)Cl·H 2O} ( 1) was prepared by reaction of pyridoxine hydrochloride with benzoic acid hydrazide. The reaction of 1 with [VO(acac) 2] and triethylamine yields the neutral vanadium IV complex [VO 2(hhmmb)]·Py ( 2), with a distorted quadratic pyramidal configuration. The Schiff base 1 reacts also with UO 2(NO 3) 2·6H 2O and triethylamine under deprotonation giving the uranium VI cationic complexes [UO 2(hhmmb)(H 2O)Cl] + ( 3) and [UO 2(hhmmb)(CH 3OH)Cl] + ( 4), both showing the classical pentagonal bipyrimidal geometry of UO22+ complexes. The structural features of all compounds are discussed.

Thermodynamics of fission products in UO(2 ± x).

PubMed

Nerikar, P V; Liu, X-Y; Uberuaga, B P; Stanek, C R; Phillpot, S R; Sinnott, S B

2009-10-28

The stabilities of selected fission products-Xe, Cs, and Sr-are investigated as a function of non-stoichiometry x in UO(2 ± x). In particular, density functional theory (DFT) is used to calculate the incorporation and solution energies of these fission products at the anion and cation vacancy sites, at the divacancy, and at the bound Schottky defect. In order to reproduce the correct insulating state of UO(2), the DFT calculations are performed using spin polarization and with the Hubbard U term. In general, higher charge defects are more soluble in the fuel matrix and the solubility of fission products increases as the hyperstoichiometry increases. The solubility of fission product oxides is also explored. Cs(2)O is observed as a second stable phase and SrO is found to be soluble in the UO(2) matrix for all stoichiometries. These observations mirror experimentally observed phenomena.

A Uranyl Peroxide Dimer in the Gas Phase

DOE PAGES

Dau, Phuong D.; Dau, Phuong V.; Rao, Linfeng; ...

2017-03-14

For this study, the gas-phase uranyl peroxide dimer, [(UO 2) 2(O2)(L) 2] 2+ where L = 2,2'-trifluoroethylazanediyl)bis(N,N'-dimethylacetamide), was synthesized by electrospray ionization of a solution of UO 2 2+ and L. Collision-induced dissociation of this dimer resulted in endothermic O atom elimination to give [(UO 2) 2(O)(L) 2] 2+, which was found to spontaneously react with water via exothermic hydrolytic chemisorption to yield [(UO 2) 2(OH) 2(L) 2] 2+. Density functional theory computations of the energies for the gas-phase reactions are in accord with observations. The structures of the observed uranyl dimer were computed, with that of the peroxide ofmore » particular interest, as a basis to evaluate the formation of condensed phase uranyl peroxides with bent structures. The computed dihedral angle in [(UO 2) 2(O 2)(L) 2] 2+ is 145°, indicating a substantial deviation from the planar structure with a dihedral angle of 180°. Energies needed to induce bending in the most elementary gas-phase uranyl peroxide complex, [(UO 2) 2(O 2)] 2+, were computed. It was found that bending from the lowest-energy planar structure to dihedral angles up to 140° required energies of <10 kJ/mol. The gas-phase results demonstrate the inherent stability of the uranyl peroxide moiety and support the notion that the uranyl-peroxide-uranyl structural unit is intrinsically planar, with only minor energy perturbations needed to form the bent structures found in studtite and uranyl peroxide nanostructures.« less

Adsorption characteristics of UO(2)(2+) and Th(4+) ions from simulated radioactive solutions onto chitosan/clinoptilolite sorbents.

PubMed

Humelnicu, Doina; Dinu, Maria Valentina; Drăgan, Ecaterina Stela

2011-01-15

Adsorption features of UO(2)(2+) and Th(4+) ions from simulated radioactive solutions onto a novel chitosan/clinoptilolite (CS/CPL) composite as beads have been investigated compared with chitosan cross-linked with epichlorohydrin. The effects of contact time, the initial metal ion concentration, sorbent mass and temperature on the adsorption capacity of the CS-based sorbents were investigated. The adsorption kinetics was well described by the pseudo-second order equation, and the adsorption isotherms were better fitted by the Sips model. The maximum experimental adsorption capacities were 328.32 mg Th(4+)/g composite, and 408.62 mg UO(2)(2+)/g composite. The overall adsorption tendency of CS/CPL composite toward UO(2)(2+) and Th(4+) radiocations in the presence of Cu(2+), Fe(2+) and Al(3+), under competitive conditions, followed the order: Cu(2+)>UO(2)(2+)>Fe(2+)>Al(3+), and Cu(2+)>Th(4+)>Fe(2+)>Al(3+), respectively. The negative values of Gibbs free energy of adsorption indicated the spontaneity of the adsorption of radioactive ions on both the CS/CPL composite and the cross-linked CS. The desorption level of UO(2)(2+) from the composite CS/CPL, by using 0.1M Na(2)CO(3), was around 92%, and that of Th(4+) ions, performed by 0.1M HCl, was around 85%, both values being higher than the desorption level of radiocations from the cross-linked CS, which were 89% and 83%, respectively. Copyright © 2010 Elsevier B.V. All rights reserved.

Synthesis and structure of R{sub 2}[UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}] (R = Rb or Cs)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serezhkin, V. N., E-mail: lserezh@samsu.ru; Peresypkina, E. V.; Grigor’eva, V. A.

2015-01-15

Crystals Rb{sub 2}[UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}] (I) and Cs{sub 2}[UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}] (II) have been synthesized and studied by IR spectroscopy and X-ray diffraction. Crystals I are monoclinic, with the following parameters: a = 12.2118(5) Å, b = 10.2545(3) Å, c = 11.8754(4) Å, β = 110.287(1)°, sp. gr. C2/c, Z = 4, and R = 0.0523. Crystals II are orthorhombic, with a = 13.7309(3) Å, b = 10.5749(2) Å, c = 10.1891(2) Å, sp. gr. Pnma, Z = 4, and R = 0.0411. The basic structural units of crystals I and II are one-core complexes [UO{submore » 2}(NO{sub 3}){sub 2}(NCS){sub 2}]{sup 2−}, which belong to the crystallochemical group cis-AB{sub 2}{sup 01}M{sub 2}{sup 1} (A = UO{sub 2}{sup 2+}, B{sup 01} = NO{sub 3}{sup −}, M{sup 1} = NCS{sup −}), which are combined into a framework via electrostatic interactions with ions of alkaline metals R (R = Rb or Cs). The structural features of crystals I and II, which condition the formation of [UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}]{sup 2−} complexes with a cis rather than a trans position of isothiocyanate ions in the coordination sphere of uranyl ions, are discussed.« less

The experience of stuttering among Ultra-Orthodox and Secular/Traditional Jews.

PubMed

Freud, Debora; Ezrati-Vinacour, Ruth; Katz-Bernstein, Nitza; Fostick, Leah

2017-12-01

This groundbreaking research compares the experience of stuttering among adult male People Who Stutter (PWS) from the ultra-Orthodox (UO) Jewish community in Israel to those from Secular/Traditional (ST) backgrounds. Participants were 32 UO and 31 ST PWS, aged 18-67 years. Self-report questionnaires utilized: Perceived Stuttering Severity (PSS); Overall Assessment of the Speaker's Experience of Stuttering (OASES-A); Students' Life Satisfaction Scale (SLSS); Situation Avoidance Behavior Checklist (SABC). Demographic, religious, and stuttering information was collected. Groups were compared on scales, and correlations between scales and the PSS. Subjective stuttering severity ratings were significantly higher among the UO. A significant group effect was found for the OASES-A quality of life subscale, but not other subscales. Significant positive correlations were found between: 1) PSS and OASES-A Total Impact; 2) PSS and 3 OASES subscales; and 3) PSS and SABC (indicating increased avoidance with increased stuttering severity rating). A significant negative correlation was found between the PSS and SLSS, indicating lower life satisfaction with higher rates of stuttering severity among the ST. Interestingly, when tested by group, significant correlations between the PSS and all other study measures were observed only among the ST. UO participants showed higher subjective stuttering severity ratings, yet less impact on quality of life, and no correlation between subjective stuttering and other measures of stuttering experience. These novel findings may result from the combined protective effect of religiosity and socio-cultural characteristics on UO PWS' well-being, despite heightened concern about social consequences of stuttering within UO society. Copyright © 2017 Elsevier Inc. All rights reserved.

The mechanism for water exchange in [UO(2)(H(2)O)(5)](2+) and [UO(2)(oxalate)(2)(H(2)O)](2-), as studied by quantum chemical methods.

PubMed

Vallet, V; Wahlgren, U; Schimmelpfennig, B; Szabó, Z; Grenthe, I

2001-12-05

The mechanisms for the exchange of water between [UO(2)(H(2)O)(5)](2+), [UO(2)(oxalate)(2)(H(2)O)](2)(-)(,) and water solvent along dissociative (D), associative (A) and interchange (I) pathways have been investigated with quantum chemical methods. The choice of exchange mechanism is based on the computed activation energy and the geometry of the identified transition states and intermediates. These quantities were calculated both in the gas phase and with a polarizable continuum model for the solvent. There is a significant and predictable difference between the activation energy of the gas phase and solvent models: the energy barrier for the D-mechanism increases in the solvent as compared to the gas phase, while it decreases for the A- and I-mechanisms. The calculated activation energy, Delta U(++), for the water exchange in [UO(2)(H(2)O)(5)](2+) is 74, 19, and 21 kJ/mol, respectively, for the D-, A-, and I-mechanisms in the solvent, as compared to the experimental value Delta H(++) = 26 +/- 1 kJ/mol. This indicates that the D-mechanism for this system can be ruled out. The energy barrier between the intermediates and the transition states is small, indicating a lifetime for the intermediate approximately 10(-10) s, making it very difficult to distinguish between the A- and I-mechanisms experimentally. There is no direct experimental information on the rate and mechanism of water exchange in [UO(2)(oxalate)(2)(H(2)O)](2-) containing two bidentate oxalate ions. The activation energy and the geometry of transition states and intermediates along the D-, A-, and I-pathways were calculated both in the gas phase and in a water solvent model, using a single-point MP2 calculation with the gas phase geometry. The activation energy, Delta U(++), in the solvent for the D-, A-, and I-mechanisms is 56, 12, and 53 kJ/mol, respectively. This indicates that the water exchange follows an associative reaction mechanism. The geometry of the A- and I-transition states for both [UO(2)(H(2)O)(5)](2+) and [UO(2)(oxalate)(2)(H(2)O)](2-) indicates that the entering/leaving water molecules are located outside the plane formed by the spectator ligands.

Using reusable learning objects (rlos) in injection skills teaching: Evaluations from multiple user types.

PubMed

Williams, Julia; O'Connor, Mórna; Windle, Richard; Wharrad, Heather J

2015-12-01

Clinical skills are a critical component of pre-registration nurse education in the United Kingdom, yet there is widespread concern about the clinical skills displayed by newly-qualified nurses. Novel means of supporting clinical skills education are required to address this. A package of Reusable Learning Objects (RLOs) was developed to supplement pre-registration teaching on the clinical skill of administering injection medication. RLOs are electronic resources addressing a single learning objective whose interactivity facilitates learning. This article evaluates a package of five injection RLOs across three studies: (1) questionnaires administered to pre-registration nursing students at University of Nottingham (UoN) (n=46) evaluating the RLO package as a whole; (2) individual RLOs evaluated in online questionnaires by educators and students from UoN; from other national and international institutions; and healthcare professionals (n=265); (3) qualitative evaluation of the RLO package by UoN injection skills tutors (n=6). Data from all studies were assessed for (1) access to, (2) usefulness, (3) impact and (4) integration of the RLOs. Study one found that pre-registration nursing students rate the RLO package highly across all categories, particularly underscoring the value of their self-test elements. Study two found high ratings in online assessments of individual RLOs by multiple users. The global reach is particularly encouraging here. Tutors reported insufficient levels of student-RLO access, which might be explained by the timing of their student exposure. Tutors integrate RLOs into teaching and agree on their use as teaching supplements, not substitutes for face-to-face education. This evaluation encompasses the first years postpackage release. Encouraging data on evaluative categories in this early review suggest that future evaluations are warranted to track progress as the package is adopted and evaluated more widely. Copyright © 2015 Elsevier Ltd. All rights reserved.

Fabrication of Natural Uranium UO 2 Disks (Phase II): Texas A&M Work for Others Summary Document

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerczak, Tyler J.; Baldwin, Charles A.; Schmidlin, Joshua E.

The steps to fabricate natural UO 2 disks for an irradiation campaign led by Texas A&M University are outlined. The process was initiated with stoichiometry adjustment of parent, U 3O 8 powder. The next stage of sample preparation involved exploratory pellet pressing and sintering to achieve the desired natural UO 2 pellet densities. Ideal densities were achieved through the use of a bimodal powder size blend. The steps involved with disk fabrication are also presented, describing the coring and thinning process executed to achieve final dimensionality.

Extreme Performance Scalable Operating Systems Final Progress Report (July 1, 2008 - October 31, 2011)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malony, Allen D; Shende, Sameer

This is the final progress report for the FastOS (Phase 2) (FastOS-2) project with Argonne National Laboratory and the University of Oregon (UO). The project started at UO on July 1, 2008 and ran until April 30, 2010, at which time a six-month no-cost extension began. The FastOS-2 work at UO delivered excellent results in all research work areas: * scalable parallel monitoring * kernel-level performance measurement * parallel I/0 system measurement * large-scale and hybrid application performance measurement * onlne scalable performance data reduction and analysis * binary instrumentation

Oxidation kinetics for conversion of U 3O 8 to ε-UO 3 with NO 2

DOE PAGES

Johnson, J. A.; Rawn, C. J.; Spencer, B. B.; ...

2017-04-04

The oxidation kinetics of U 3O 8 powder to ε-UO 3 in an NO 2 environment was measured by in situ x-ray diffraction (XRD). Experiments were performed at temperatures of 195, 210, 235, and 250°C using a custom designed and fabricated sample isolation stage. Data were refined to quantify phase fractions using a newly proposed structure for the ε-UO 3 polymorph. The kinetics data were modeled using a shrinking core approach. A proposed two-step reaction process is presented based on the developed models.

Structural and electronic properties of half-metallic rare-earth perovskites

NASA Astrophysics Data System (ADS)

Khandy, Shakeel Ahmad; Islam, Ishtihadah; Bhat, Tahir Mohiuddin; Yousuf, Saleem; Gupta, Dinesh C.

2018-05-01

Systemic investigation of structural parameters and electronic properties inclusive of band profiles for BaPaO3 and BaUO3 have been performed. The empirical as well as DFT calculated lattice constants are in agreement with the previously reported results. The critical energy values confirm that the BaPaO3 has lesser migration energy than BaUO3. Both, these materials show a semiconducting, direct band gap in the low spin state with 2.3 eV for BaUO3 and for BaPaO3, its value is 3.9 eV.

SINGLE-STEP CONVERSION OF UO$sub 3$ TO UF$sub 4$

DOEpatents

Moore, J.E.

1960-07-12

A description is given of the preparation of uranium tetrafluoride by reacting a hexavalent uranium compound with a pclysaccharide and gaseous hydrogen fluoride at an elevated temperature. Uranium trioxide and starch are combined with water to form a doughy mixture. which is extruded into pellets and dried. The pellets are then contacted with HF at a temperature from 500 to 700 deg C in a moving bed reactor to prcduce UF/sub 4/. Reduction of the hexavalent uranium to UO/sub 2/ and conversion of the UO/sub 2/ to UF/sub 4/ are accomplished simultaneously in this process.

Communication: Relativistic Fock-space coupled cluster study of small building blocks of larger uranium complexes.

PubMed

Tecmer, Paweł; Gomes, André Severo Pereira; Knecht, Stefan; Visscher, Lucas

2014-07-28

We present a study of the electronic structure of the [UO2](+), [UO2](2 +), [UO2](3 +), NUO, [NUO](+), [NUO](2 +), [NUN](-), NUN, and [NUN](+) molecules with the intermediate Hamiltonian Fock-space coupled cluster method. The accuracy of mean-field approaches based on the eXact-2-Component Hamiltonian to incorporate spin-orbit coupling and Gaunt interactions are compared to results obtained with the Dirac-Coulomb Hamiltonian. Furthermore, we assess the reliability of calculations employing approximate density functionals in describing electronic spectra and quantities useful in rationalizing Uranium (VI) species reactivity (hardness, electronegativity, and electrophilicity).

Communication: Relativistic Fock-space coupled cluster study of small building blocks of larger uranium complexes

NASA Astrophysics Data System (ADS)

Tecmer, Paweł; Severo Pereira Gomes, André; Knecht, Stefan; Visscher, Lucas

2014-07-01

We present a study of the electronic structure of the [UO2]+, [UO2]2 +, [UO2]3 +, NUO, [NUO]+, [NUO]2 +, [NUN]-, NUN, and [NUN]+ molecules with the intermediate Hamiltonian Fock-space coupled cluster method. The accuracy of mean-field approaches based on the eXact-2-Component Hamiltonian to incorporate spin-orbit coupling and Gaunt interactions are compared to results obtained with the Dirac-Coulomb Hamiltonian. Furthermore, we assess the reliability of calculations employing approximate density functionals in describing electronic spectra and quantities useful in rationalizing Uranium (VI) species reactivity (hardness, electronegativity, and electrophilicity).

Inductance Calculations of Variable Pitch Helical Inductors

DTIC Science & Technology

2015-08-01

8217 ’ Integral solution using Simpson’s Rule ’ Dim i As Integer Dim Pi As Double, uo As Double, kc As Double Dim a As Double, amax As Double, da As...Double Dim steps As Integer Dim func1a As Double, func1b As Double ’ On Error GoTo err_TorisV1 steps = 1000 Pi = 3.14159 uo = 4 * Pi * 0.0000001...As Double ’ ’ Integral solution using Simpson’s Rule ’ Dim i As Integer Dim Pi As Double, uo As Double, kc As Double Dim a As Double, amax As

UO(2) Oxidative Corrosion by Nonclassical Diffusion.

PubMed

Stubbs, Joanne E; Chaka, Anne M; Ilton, Eugene S; Biwer, Craig A; Engelhard, Mark H; Bargar, John R; Eng, Peter J

2015-06-19

Using x-ray scattering, spectroscopy, and density-functional theory, we determine the structure of the oxidation front when a UO(2) (111) surface is exposed to oxygen at ambient conditions. In contrast to classical diffusion and previously reported bulk UO(2+x) structures, we find oxygen interstitials order into a nanoscale superlattice with three-layer periodicity and uranium in three oxidation states: IV, V, and VI. This oscillatory diffusion profile is driven by the nature of the electron transfer process, and has implications for understanding the initial stages of oxidative corrosion in materials at the atomistic level.

Speciation of residual carbon contained in UO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ziouane, Yannis; Arab-Chapelet, Bénédicte; Tamain, Christelle

2016-12-15

UO{sub 2} powders were synthesized thanks to oxalic precipitation (platelet morphology) and sol-gel route and completely characterized. A secondary phase was found depending on the calcination atmospheres. This phase has been identified by Raman spectroscopy as graphitic material (i.e. carbon-based secondary compound) and quantified by thermogravimetric analyses. Its amount varies with the calcination atmosphere. The presence of this secondary phase has no significant effect on the lattice parameter and its specific surface area. - Graphical abstract: Figure 2: Raman spectroscopy of the three UO{sub 2} powders and of the dissolution residues.

Seaweed supplements normalise metabolic, cardiovascular and liver responses in high-carbohydrate, high-fat fed rats.

PubMed

Kumar, Senthil Arun; Magnusson, Marie; Ward, Leigh C; Paul, Nicholas A; Brown, Lindsay

2015-02-02

Increased seaweed consumption may be linked to the lower incidence of metabolic syndrome in eastern Asia. This study investigated the responses to two tropical green seaweeds, Ulva ohnoi (UO) and Derbesia tenuissima (DT), in a rat model of human metabolic syndrome. Male Wistar rats (330-340 g) were fed either a corn starch-rich diet or a high-carbohydrate, high-fat diet with 25% fructose in drinking water, for 16 weeks. High-carbohydrate, high-fat diet-fed rats showed the signs of metabolic syndrome leading to abdominal obesity, cardiovascular remodelling and non-alcoholic fatty liver disease. Food was supplemented with 5% dried UO or DT for the final 8 weeks only. UO lowered total final body fat mass by 24%, systolic blood pressure by 29 mmHg, and improved glucose utilisation and insulin sensitivity. In contrast, DT did not change total body fat mass but decreased plasma triglycerides by 38% and total cholesterol by 17%. UO contained 18.1% soluble fibre as part of 40.9% total fibre, and increased magnesium, while DT contained 23.4% total fibre, essentially as insoluble fibre. UO was more effective in reducing metabolic syndrome than DT, possibly due to the increased intake of soluble fibre and magnesium.

Characterization of UO2(2+) binding to osteopontin, a highly phosphorylated protein: insights into potential mechanisms of uranyl accumulation in bones.

PubMed

Qi, Lei; Basset, Christian; Averseng, Olivier; Quéméneur, Eric; Hagège, Agnès; Vidaud, Claude

2014-01-01

Bones are one of the few organs in which uranyl (UO2(2+)) accumulates. This large dioxo-cation displays affinity for carboxylates, phenolates and phosphorylated functional groups in proteins. The noncollagenous protein osteopontin (OPN) plays an important role in bone homeostasis. It is mainly found in the extracellular matrix of mineralized tissues but also in body fluids such as milk, blood and urine. Furthermore, OPN is an intrinsically disordered protein, which, like other proteins of the SIBLING family, contains a polyaspartic acid sequence and numerous patterns of alternating acidic and phosphorylated residues. All these properties led to the hypothesis that this protein could be prone to UO2(2+) binding. In this work, a simple purification procedure enabling highly purified bovine (bOPN) and human OPN (hOPN) to be obtained was developed. Various biophysical approaches were set up to study the impact of phosphorylations on the affinity of OPN for UO2(2+) as well as the formation of stable complexes originating from structural changes induced by the binding of this metal cation. The results obtained suggest a new mechanism of the interaction of UO2(2+) with bone metabolism and a new role for OPN as a metal transporter.

Ab initio DFT+U study of He atom incorporation into UO(2) crystals.

PubMed

Gryaznov, Denis; Heifets, Eugene; Kotomin, Eugene

2009-09-07

We present and discuss results of the density functional theory (DFT) for perfect UO(2) crystals with He atoms in octahedral interstitial positions therein. We have calculated basic bulk crystal properties and He incorporation energies into the low temperature anti-ferromagnetic UO(2) phase using several exchange-correlation functionals within the spin-polarized local density (LDA) and generalized gradient (GGA) approximations. In all DFT calculations we included the on-site correlation corrections using the Hubbard model (DFT+U approach). We analysed a potential crystalline symmetry reduction from tetragonal down to orthorhombic structure and confirmed the presence of the Jahn-Teller effect in a perfect UO(2). We discuss also the problem of a conducting electronic state arising when He is placed into a tetragonal antiferromagnetic phase of UO(2) commonly used in defect modelling. Consequently, we found a specific monoclinic lattice distortion which allowed us to restore the semiconducting state and properly estimate He incorporation energies. Unlike the bulk properties, the He incorporation energy strongly depends on several factors, including the supercell size, the use of spin polarization, the exchange-correlation functionals and on-site correlation corrections. We compare our results for the He incorporation with the previous shell model and ab initio DFT calculations.

First-principles study of defects and phase transition in UO(2).

PubMed

Yu, Jianguo; Devanathan, Ram; Weber, William J

2009-10-28

Defect properties and phase transition in UO(2) have been studied from first principles by the all-electron projector-augmented-wave (PAW) method. The generalized gradient approximation with empirical self-interaction correction, (GGA)+U, formalism has been used to account for the strong on-site Coulomb repulsion among the localized U 5f electrons. The Hubbard parameter U(eff), magnetic ordering, chemical potential and heat of formation have been systematically examined. By choosing an appropriate U(eff) = 3.0 eV it is possible to consistently describe structural properties of UO(2) and model the phase transition processes. The phase transition pressure for UO(2) is about 20 GPa, which is less than the experimental value of 42 GPa but better than the LDA+U value of 7.8 GPa. Meanwhile our results for the formation energies of intrinsic defects partly confirm earlier calculations for the intrinsic charge neutral defects but reveal large variations depending on the determination of the chemical potential and whether the environment is O-rich or U-rich. Moreover, the results for extrinsic defects of Xe, which are representative of mobile insoluble fission product in UO(2), are consistent with experimental data in which Xe prefers to be trapped by Schottky defects.

Seaweed Supplements Normalise Metabolic, Cardiovascular and Liver Responses in High-Carbohydrate, High-Fat Fed Rats

PubMed Central

Kumar, Senthil Arun; Magnusson, Marie; Ward, Leigh C.; Paul, Nicholas A.; Brown, Lindsay

2015-01-01

Increased seaweed consumption may be linked to the lower incidence of metabolic syndrome in eastern Asia. This study investigated the responses to two tropical green seaweeds, Ulva ohnoi (UO) and Derbesia tenuissima (DT), in a rat model of human metabolic syndrome. Male Wistar rats (330–340 g) were fed either a corn starch-rich diet or a high-carbohydrate, high-fat diet with 25% fructose in drinking water, for 16 weeks. High-carbohydrate, high-fat diet-fed rats showed the signs of metabolic syndrome leading to abdominal obesity, cardiovascular remodelling and non-alcoholic fatty liver disease. Food was supplemented with 5% dried UO or DT for the final 8 weeks only. UO lowered total final body fat mass by 24%, systolic blood pressure by 29 mmHg, and improved glucose utilisation and insulin sensitivity. In contrast, DT did not change total body fat mass but decreased plasma triglycerides by 38% and total cholesterol by 17%. UO contained 18.1% soluble fibre as part of 40.9% total fibre, and increased magnesium, while DT contained 23.4% total fibre, essentially as insoluble fibre. UO was more effective in reducing metabolic syndrome than DT, possibly due to the increased intake of soluble fibre and magnesium. PMID:25648511

Behaviour of complexes of f-elements in the environment - An experimental and theoretical analysis

NASA Astrophysics Data System (ADS)

Ivanova, Bojidarka; Spiteller, Michael

2017-01-01

The paper provides a comprehensive study of lanthanide and actinide complexes to a matter of key area in the field of the chemistry, i.e. environmental analytical chemistry. The content has involved: (i) solution and sorption behaviour of lanthanides (Lnn+, Ln = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Py, Ho, Er, Tm, Yb and Lu) onto Y(O)O(H) minerals (Y = Fe, Mn or Si); (ii) ligand exchange processes with participation of inorganic OH-, F-, Cl-, Br-, SO42-, SO32-, IO3-, NO32-, CO32- and/or HCO3- ligands as well as mixed ligand complexes, including solvent molecules such as {[LnOR]2+}, {[Ln(OR)2]+} (R = CH3OH, CH3CH2CH2OH) and {[Ln(CH3CN)x(H2O)z]3+} (x = 6-8, z = 0-4); (iii) the actinide speciation has involved different oxidation states (+4)-(+6) and ions {[UOH]3+}, {[UX]3+} (X = F or Cl), {[UFx]y+/-} (x = 2-6, y = 0-2), {[U(CO3)x]y-} (x = 4 or 5, y = 4 or 6), {[U(SO4)]2+], {[U(NO3)]3+}, {[U(NO3)2]2+}, [[UO2(CO3)3]5-}, {[(UO2)x(OH)z]y+/-} (x = 1-4, y = 1 or 2, z = 1-7), {[UO2Fx]y+/-} (x = 1-4, y = 1 or 2), {[UO2(CO3)x]y-} (x = 2, or 3, y = 2, or 4), {[(UO2)2(CO3)(OH)3]-}, {[(UO2)3O(OH)2(HCO3)]+}, {[(UO2)11(CO3)6(OH)12]2-}, {[UO2(SO4)x]y-}, (x = 2 or 3, y = 2 or 4), {[UO2SiO(OH)3]+}, {[AnCx]y+/-} (x,y = 1 and 2), {[CAnH]+/-}, {[CxAny]0} (x,y = 2 and 3), {[AnHx]y+} (x = 1-3, y = 0-5), {[AnXn]m+/-} (n = 1-6, m = 1-4, X = F-, Br-, I-), {[AnOxFz]y+/-} (x, z = 1 or 2, y = 0, 1 and 2), {[AnNx]y+} (x = 1 and 2), {[AnxOz(OH)n]y+/-} (x = 1-3, z = 1-4, y = 0, 1 or 2, n = 0 or 1) and Ann+ (n = 0-6) at An = Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No and Lr, respectively. Correlation analysis between thermodynamic parameters, accounting for different surface interactions of adsorbed species and experimental mass spectrometric data, including liquid, semi-liquid and solid-state measurements in a large set of experimental conditions such as pH = 2-13, low and intermediate ionic strength, solvent type, ε = 0-78.0, variety of solvent proton accepting and donating numbers and T = 25-400 °C has carried out.

NMR shielding calculations across the periodic table: diamagnetic uranium compounds. 2. Ligand and metal NMR.

PubMed

Schreckenbach, Georg

2002-12-16

In this and a previous article (J. Phys. Chem. A 2000, 104, 8244), the range of application for relativistic density functional theory (DFT) is extended to the calculation of nuclear magnetic resonance (NMR) shieldings and chemical shifts in diamagnetic actinide compounds. Two relativistic DFT methods are used, ZORA ("zeroth-order regular approximation") and the quasirelativistic (QR) method. In the given second paper, NMR shieldings and chemical shifts are calculated and discussed for a wide range of compounds. The molecules studied comprise uranyl complexes, [UO(2)L(n)](+/-)(q); UF(6); inorganic UF(6) derivatives, UF(6-n)Cl(n), n = 0-6; and organometallic UF(6) derivatives, UF(6-n)(OCH(3))(n), n = 0-5. Uranyl complexes include [UO(2)F(4)](2-), [UO(2)Cl(4)](2-), [UO(2)(OH)(4)](2-), [UO(2)(CO(3))(3)](4-), and [UO(2)(H(2)O)(5)](2+). For the ligand NMR, moderate (e.g., (19)F NMR chemical shifts in UF(6-n)Cl(n)) to excellent agreement [e.g., (19)F chemical shift tensor in UF(6) or (1)H NMR in UF(6-n)(OCH(3))(n)] has been found between theory and experiment. The methods have been used to calculate the experimentally unknown (235)U NMR chemical shifts. A large chemical shift range of at least 21,000 ppm has been predicted for the (235)U nucleus. ZORA spin-orbit appears to be the most accurate method for predicting actinide metal chemical shifts. Trends in the (235)U NMR chemical shifts of UF(6-n)L(n) molecules are analyzed and explained in terms of the calculated electronic structure. It is argued that the energy separation and interaction between occupied and virtual orbitals with f-character are the determining factors.

Uranyl extraction by N,N-dialkylamide ligands studied using static and dynamic DFT simulations.

PubMed

Sieffert, Nicolas; Wipff, Georges

2015-02-14

We report DFT static and dynamic studies on uranyl complexes [UO(2)(NO(3))x(H(2)O)(y)L(z)](2-x) involved in the uranyl extraction from water to an "oil" phase (hexane) by an amide ligand L (N,N-dimethylacetamide). Static DFT results "in solution" (continuum SMD models for water and hexane) predict that the stepwise formation of [UO(2)(NO(3))(2)L(2)] from the UO(2)(H(2)O)(5)(2+) species is energetically favourable, and allow us to compare cis/trans isomers of penta- and hexa-coordinated complexes and key intermediates in the two solvents. DFT-MD simulations of [UO(2)(NO(3))(2)L(2)], [UO(2)(NO(3))(2)(H(2)O)L(2)], and [UO(2)(NO(3))(H(2)O)L(2)](+) species in explicit solvent environments (water, hexane, or the water/hexane interface) represented at the MM or full-DFT level reveal a versatile solvent dependent binding mode of nitrates, also evidenced by metadynamics simulations. In water and at the interface, the latter exchange from bi- to monodentate, via in plane rotational motions in some cases. Remarkably, structures of complexes at the interface are more "water-like" than gas phase- or hexane-like. Thus, the order of U-O(NO(3))/U-O(L) bond distances observed in the gas phase (U-O(nit) < U-OL) is inverted at the interface and in water. Overall, the results are consistent with the experimental observation of uranyl extraction from nitric acid solutions by amide analogues (bearing "fatty" substituents), and allow us to propose possible extraction mechanisms, involving complexation of L "right at the interface". They also point to the importance of the solvent environment and the dynamics on the structure and stability of the complexes.

Highly Preorganized Ligand 1,10-Phenanthroline-2,9-dicarboxylic Acid for the Selective Recovery of Uranium from Seawater in the Presence of Competing Vanadium Species

DOE PAGES

Lashley, Mark A.; Ivanov, Alexander S.; Bryantsev, Vyacheslav S.; ...

2016-09-30

Studies of the complexation of new promising ligands with uranyl (UO 2 2+) and other seawater cations can aid the development of more efficient, selective, and robust sorbents for the recovery of uranium from seawater. Here, we propose that the ligand design principles based on structural preorganization can be successfully applied to obtain a dramatic enhancement in UO 2 2+ ion binding affinity and selectivity. This concept is exemplified through the investigation of the com-plexes of UO 2 2+, VO 2+, and VO 2+ with the highly preorganized ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) using a combination of fluores-cence and absorbance techniques,more » along with den-sity functional theory (DFT) calculations. Moreover, the measured stability constant value, log K1, of 16.5 for the UO 2 2+/PDA complex is very high compared to uranyl complexes with other dicarboxylic ligands. Moreover, PDA exhibits strong selectivity for uranyl over vanadium ions, since the determined sta-bility constant values of the PDA complexes of the vanadium ions are quite low (V(IV) log K1 = 7.4, V(V) = 7.3). Finally, the structures of the corresponding UO 2 2+, VO 2+, and VO 2+ complexes with PDA were identified by systematic DFT calculations, and helped to interpret the stronger binding affinity for uranium over the vanadium ions. Due to its high chemical stability, selectivity, and structural preor-ganization for UO 2 2+ complexation, PDA is a very promising candidate that can be potentially used in the development of novel adsorbent materials for the selective extraction of uranium from sea-water.« less

Highly Preorganized Ligand 1,10-Phenanthroline-2,9-dicarboxylic Acid for the Selective Recovery of Uranium from Seawater in the Presence of Competing Vanadium Species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lashley, Mark A.; Ivanov, Alexander S.; Bryantsev, Vyacheslav S.

Studies of the complexation of new promising ligands with uranyl (UO 2 2+) and other seawater cations can aid the development of more efficient, selective, and robust sorbents for the recovery of uranium from seawater. Here, we propose that the ligand design principles based on structural preorganization can be successfully applied to obtain a dramatic enhancement in UO 2 2+ ion binding affinity and selectivity. This concept is exemplified through the investigation of the com-plexes of UO 2 2+, VO 2+, and VO 2+ with the highly preorganized ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) using a combination of fluores-cence and absorbance techniques,more » along with den-sity functional theory (DFT) calculations. Moreover, the measured stability constant value, log K1, of 16.5 for the UO 2 2+/PDA complex is very high compared to uranyl complexes with other dicarboxylic ligands. Moreover, PDA exhibits strong selectivity for uranyl over vanadium ions, since the determined sta-bility constant values of the PDA complexes of the vanadium ions are quite low (V(IV) log K1 = 7.4, V(V) = 7.3). Finally, the structures of the corresponding UO 2 2+, VO 2+, and VO 2+ complexes with PDA were identified by systematic DFT calculations, and helped to interpret the stronger binding affinity for uranium over the vanadium ions. Due to its high chemical stability, selectivity, and structural preor-ganization for UO 2 2+ complexation, PDA is a very promising candidate that can be potentially used in the development of novel adsorbent materials for the selective extraction of uranium from sea-water.« less

Uranium bioprecipitation mediated by yeasts utilizing organic phosphorus substrates.

PubMed

Liang, Xinjin; Csetenyi, Laszlo; Gadd, Geoffrey Michael

2016-06-01

In this research, we have demonstrated the ability of several yeast species to mediate U(VI) biomineralization through uranium phosphate biomineral formation when utilizing an organic source of phosphorus (glycerol 2-phosphate disodium salt hydrate (C3H7Na2O6P·xH2O (G2P)) or phytic acid sodium salt hydrate (C6H18O24P6·xNa(+)·yH2O (PyA))) in the presence of soluble UO2(NO3)2. The formation of meta-ankoleite (K2(UO2)2(PO4)2·6(H2O)), chernikovite ((H3O)2(UO2)2(PO4)2·6(H2O)), bassetite (Fe(++)(UO2)2(PO4)2·8(H2O)), and uramphite ((NH4)(UO2)(PO4)·3(H2O)) on cell surfaces was confirmed by X-ray diffraction in yeasts grown in a defined liquid medium amended with uranium and an organic phosphorus source, as well as in yeasts pre-grown in organic phosphorus-containing media and then subsequently exposed to UO2(NO3)2. The resulting minerals depended on the yeast species as well as physico-chemical conditions. The results obtained in this study demonstrate that phosphatase-mediated uranium biomineralization can occur in yeasts supplied with an organic phosphate substrate as sole source of phosphorus. Further understanding of yeast interactions with uranium may be relevant to development of potential treatment methods for uranium waste and utilization of organic phosphate sources and for prediction of microbial impacts on the fate of uranium in the environment.

c-Type Cytochrome-Dependent Formation of U(IV) Nanoparticles by Shewanella oneidensis

PubMed Central

Marshall, Matthew J; Dohnalkova, Alice C; Kennedy, David W; Shi, Liang; Wang, Zheming; Boyanov, Maxim I; Lai, Barry; Kemner, Kenneth M; McLean, Jeffrey S; Reed, Samantha B; Culley, David E; Bailey, Vanessa L; Simonson, Cody J; Saffarini, Daad A; Romine, Margaret F; Zachara, John M

2006-01-01

Modern approaches for bioremediation of radionuclide contaminated environments are based on the ability of microorganisms to effectively catalyze changes in the oxidation states of metals that in turn influence their solubility. Although microbial metal reduction has been identified as an effective means for immobilizing highly-soluble uranium(VI) complexes in situ, the biomolecular mechanisms of U(VI) reduction are not well understood. Here, we show that c-type cytochromes of a dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1, are essential for the reduction of U(VI) and formation of extracelluar UO 2 nanoparticles. In particular, the outer membrane (OM) decaheme cytochrome MtrC (metal reduction), previously implicated in Mn(IV) and Fe(III) reduction, directly transferred electrons to U(VI). Additionally, deletions of mtrC and/or omcA significantly affected the in vivo U(VI) reduction rate relative to wild-type MR-1. Similar to the wild-type, the mutants accumulated UO 2 nanoparticles extracellularly to high densities in association with an extracellular polymeric substance (EPS). In wild-type cells, this UO 2-EPS matrix exhibited glycocalyx-like properties and contained multiple elements of the OM, polysaccharide, and heme-containing proteins. Using a novel combination of methods including synchrotron-based X-ray fluorescence microscopy and high-resolution immune-electron microscopy, we demonstrate a close association of the extracellular UO 2 nanoparticles with MtrC and OmcA (outer membrane cytochrome). This is the first study to our knowledge to directly localize the OM-associated cytochromes with EPS, which contains biogenic UO 2 nanoparticles. In the environment, such association of UO 2 nanoparticles with biopolymers may exert a strong influence on subsequent behavior including susceptibility to oxidation by O 2 or transport in soils and sediments. PMID:16875436

Topologically identical, but geometrically isomeric layers in hydrous α-, β-Rb[UO{sub 2}(AsO{sub 3}OH)(AsO{sub 2}(OH){sub 2})]·H{sub 2}O and anhydrous Rb[UO{sub 2}(AsO{sub 3}OH)(AsO{sub 2}(OH){sub 2})

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Na; Klepov, Vladislav V.; Villa, Eric M.

2014-07-01

The hydrothermal reaction of uranyl nitrate with rubidium nitrate and arsenic (III) oxide results in the formation of polymorphic α- and β-Rb[UO{sub 2}(AsO{sub 3}OH)(AsO{sub 2}(OH){sub 2})]·H{sub 2}O (α-, β-RbUAs) and the anhydrous phase Rb[UO{sub 2}(AsO{sub 3}OH)(AsO{sub 2}(OH){sub 2})] (RbUAs). These phases were structurally, chemically and spectroscopically characterized. The structures of all three compounds are based upon topologically identical, but geometrically isomeric layers. The layers are linked with each other by means of the Rb cations and hydrogen bonding. Dehydration experiments demonstrate that water deintercalation from hydrous α- and β-RbUAs yields anhydrous RbUAs via topotactic reactions. - Graphical abstract: Three differentmore » layer geometries observed in the structures of Rb[UO{sub 2}(AsO{sub 3}OH)(AsO{sub 2}(OH){sub 2})] and α- and β- Rb[UO{sub 2}(AsO{sub 3}OH)(AsO{sub 2}(OH){sub 2})]·H{sub 2}O. Two different coordination environments of uranium polyhedra (types I and II) are shown schematically on the top of the figure. - Highlights: • Three new uranyl arsenates were synthesized from the hydrothermal reactions. • The phases consist of the topologically identical but geometrically different layers. • Topotactic transitions were observed in the processes of mono-hyrates dehydration.« less

Characterization of Oxygen Defect Clusters in UO2+ x Using Neutron Scattering and PDF Analysis.

PubMed

Ma, Yue; Garcia, Philippe; Lechelle, Jacques; Miard, Audrey; Desgranges, Lionel; Baldinozzi, Gianguido; Simeone, David; Fischer, Henry E

2018-06-18

In hyper-stoichiometric uranium oxide, both neutron diffraction work and, more recently, theoretical analyses report the existence of clusters such as the 2:2:2 cluster, comprising two anion vacancies and two types of anion interstitials. However, little is known about whether there exists a region of low deviation-from-stoichiometry in which defects remain isolated, or indeed whether at high deviation-from-stoichiometry defect clusters prevail that contain more excess oxygen atoms than the di-interstitial cluster. In this study, we report pair distribution function (PDF) analyses of UO 2 and UO 2+ x ( x ≈ 0.007 and x ≈ 0.16) samples obtained from high-temperature in situ neutron scattering experiments. PDF refinement for the lower deviation from stoichiometry sample suggests the system is too dilute to differentiate between isolated defects and di-interstitial clusters. For the UO 2.16 sample, several defect structures are tested, and it is found that the data are best represented assuming the presence of center-occupied cuboctahedra.

Recovery of UO[sub 2]/PuO[sub 2] in IFR electrorefining process

DOEpatents

Tomczuk, Z.; Miller, W.E.

1994-10-18

A process is described for converting PuO[sub 2] and UO[sub 2] present in an electrorefiner to the chlorides, by contacting the PuO[sub 2] and UO[sub 2] with Li metal in the presence of an alkali metal chloride salt substantially free of rare earth and actinide chlorides for a time and at a temperature sufficient to convert the UO[sub 2] and PuO[sub 2] to metals while converting Li metal to Li[sub 2]O. Li[sub 2]O is removed either by reducing with rare earth metals or by providing an oxygen electrode for transporting O[sub 2] out of the electrorefiner and a cathode, and thereafter applying an emf to the electrorefiner electrodes sufficient to cause the Li[sub 2]O to disassociate to O[sub 2] and Li metal but insufficient to decompose the alkali metal chloride salt. The U and Pu and excess lithium are then converted to chlorides by reaction with CdCl[sub 2].

Recovery of UO.sub.2 /Pu O.sub.2 in IFR electrorefining process

DOEpatents

Tomczuk, Zygmunt; Miller, William E.

1994-01-01

A process for converting PuO.sub.2 and UO.sub.2 present in an electrorefiner to the chlorides, by contacting the PuO.sub.2 and UO.sub.2 with Li metal in the presence of an alkali metal chloride salt substantially free of rare earth and actinide chlorides for a time and at a temperature sufficient to convert the UO.sub.2 and PuO.sub.2 to metals while converting Li metal to Li.sub.2 O. Li.sub.2 O is removed either by reducing with rare earth metals or by providing an oxygen electrode for transporting O.sub.2 out of the electrorefiner and a cathode, and thereafter applying an emf to the electrorefiner electrodes sufficient to cause the Li.sub.2 O to disassociate to O.sub.2 and Li metal but insufficient to decompose the alkali metal chloride salt. The U and Pu and excess lithium are then converted to chlorides by reaction with CdCl.sub.2.

Effect of point defects on the thermal conductivity of UO2: molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiang-Yang; Stanek, Christopher Richard; Andersson, Anders David Ragnar

2015-07-21

The thermal conductivity of uranium dioxide (UO 2) fuel is an important materials property that affects fuel performance since it is a key parameter determining the temperature distribution in the fuel, thus governing, e.g., dimensional changes due to thermal expansion, fission gas release rates, etc. [1] The thermal conductivity of UO 2 nuclear fuel is also affected by fission gas, fission products, defects, and microstructural features such as grain boundaries. Here, molecular dynamics (MD) simulations are carried out to determine quantitatively, the effect of irradiation induced point defects on the thermal conductivity of UO 2, as a function of defectmore » concentrations, for a range of temperatures, 300 – 1500 K. The results will be used to develop enhanced continuum thermal conductivity models for MARMOT and BISON by INL. These models express the thermal conductivity as a function of microstructure state-variables, thus enabling thermal conductivity models with closer connection to the physical state of the fuel [2].« less

MARMOT simulations of Xe segregation to grain boundaries in UO2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersson, Anders D.; Tonks, Michael; Casillas, Luis

2012-06-20

Diffusion of Xe and U in UO{sub 2} is controlled by vacancy mechanisms and under irradiation the formation of mobile vacancy clusters is important. We derive continuum thermodynamic and diffusion models for Xe and U in UO{sub 2} based on the vacancy and cluster diffusion mechanisms established from recent density functional theory (DFT) calculations. Segregation of defects to grain boundaries in UO{sub 2} is described by combining the diffusion model with models of the interaction between Xe atoms and vacancies with grain boundaries derived from separate atomistic calculations. The diffusion and segregation models are implemented in the MOOSE/MARMOT (MBM) finitemore » element (FEM) framework and we simulate Xe redistribution for a few simple microstructures. In this report we focus on segregation to grain boundaries. The U or vacancy diffusion model as well as the coupled diffusion of vacancies and Xe have also been implemented, but results are not included in this report.« less

Recovery and recycling of uranium from rejected coated particles for compact high temperature reactors

NASA Astrophysics Data System (ADS)

Pai, Rajesh V.; Mollick, P. K.; Kumar, Ashok; Banerjee, J.; Radhakrishna, J.; Chakravartty, J. K.

2016-05-01

UO2 microspheres prepared by internal gelation technique were coated with pyrolytic carbon and silicon carbide using CVD technique. The particles which were not meeting the specifications were rejected. The rejected/failed UO2 based coated particles prepared by CVD technique was used for oxidation and recovery and recycling. The oxidation behaviour of sintered UO2 microspheres coated with different layers of carbon and SiC was studied by thermal techniques to develop a method for recycling and recovery of uranium from the failed/rejected coated particles. It was observed that the complete removal of outer carbon from the spheres is difficult. The crushing of microspheres enabled easier accessibility of oxygen and oxidation of carbon and uranium at 800-1000 °C. With the optimized process of multiple crushing using die & plunger and sieving the broken coated layers, we could recycle around fifty percent of the UO2 microspheres which could be directly recoated. The rest of the particles were recycled using a wet recycling method.

Safety evaluation of Lactobacillus delbrueckii subsp. lactis UO 004, a probiotic bacterium.

PubMed

Fernández, M Fernanda; Boris, Soledad; Barbés, Covadonga

2005-03-01

Lactobacillus delbrueckii subsp. lactis UO 004 was evaluated for its use as a potential probiotic from a safety point of view. The strain did not exhibit mucinolytic or other enzymatic activities that might be detrimental, such as those involving glycosidases (beta-D-glucosaminidase or alpha-D-galactosidase) or arylamidases (factor Xa and quimotrypsin-like activities), frequently present in Lactobacillus strains isolated from patients with endocarditis, although it was able to express protein Ca and kallikrein-like activities. On the other hand, the presence of the strain did not interfere with the growth of certain species of normal intestinal microbiota, such as Enterococcus fecalis, Escherichia coli, Bifidobacterium bifidum or Bacteroides fragilis. Moreover, the potential probiotic strain UO 004 is sensitive to antibiotics with transmissible resistance mechanisms in Lactobacillus such as chloramphenicol, erythromycin, tetracycline and vancomycin. In addition, strain L. delbrueckii UO 004 was not able to translocate towards the intestinal barrier of mice or produce changes in their activity or general health status.

Catalysis of aptamer-modified AuPd nanoalloy probe and its application to resonance scattering detection of trace UO(2)2+.

PubMed

Liang, Aihui; Zhang, Yi; Fan, Yanyan; Chen, Chunqiang; Wen, Guiqing; Liu, Qingye; Kang, Caiyan; Jiang, Zhiliang

2011-08-01

AuPd nanoalloy and nanopalladium with a diameter of 5 nm were prepared, using sodium citrate as the stabilizing agent and NaBH(4) as the reductant. The nanocatalyst containing palladium on the surface exhibited a strong catalytic effect on the slow NiP particle reaction between NiCl(2) and NaH(2)PO(2), and the NiP particle system showed a resonance scattering (RS) peak at 508 nm. The RS results showed that the Pd atom on AuPd nanoalloy surface is the catalytic center. Combining the aptamer cracking reaction of double-stranded DNA (dsDNA)-UO(2)(2+), AuPd nanoalloy aggregation, and AuPd nanoalloy catalysis, both AuPd nanoalloy RS probe and AuPd nanoalloy catalytic RS assays were developed for the determination of 40-250 pmol L(-1) UO(2)(2+) and 5.0-50 pmol L(-1) UO(2)(2+), respectively. This journal is © The Royal Society of Chemistry 2011

Neutron diffraction study of the in situ oxidation of UO(2).

PubMed

Desgranges, Lionel; Baldinozzi, Gianguido; Rousseau, Gurvan; Nièpce, Jean-Claude; Calvarin, Gilbert

2009-08-17

This paper discusses uranium oxide crystal structure modifications that are observed during the low-temperature oxidation which transforms UO(2) into U(3)O(8). The symmetries and the structural parameters of UO(2), beta-U(4)O(9), beta-U(3)O(7), and U(3)O(8) were determined by refining neutron diffraction patterns on pure single-phase samples. Neutron diffraction patterns were also collected during the in situ oxidation of powder samples at 483 K. The lattice parameters and relative ratios of the four pure phases were measured during the progression of the isothermal oxidation. The transformation of UO(2) into U(3)O(8) involves a complex modification of the oxygen sublattice and the onset of complex superstructures for U(4)O(9) and U(3)O(7), associated with regular stacks of complex defects known as cuboctahedra, which consist of 13 oxygen atoms. The kinetics of the oxidation process are discussed on the basis of the results of the structural analysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verkerk, B.

In 1959 a fuel development program was undertaken based on UO/sub 2/ in which it was intended to study all variables that could influence the quality of fabricated UO/sub 2/-pellets. Later this program was extended to a study of electrolytic UO/sub 2/ with the fabrication of swaged or vibratory compacted fuel elements in mind, and recently the study of the UO/sub 2/-PuO/sub 2/ system was incorporated in it. In order to obtain a better knowledge of the UO/sub 2/- powders that can be used for sintering purposes, an extensive study was made of various preparation methods. A small plutonium laboratorymore » containing equipment for the preparation of UO/sub 2/-- PuO/sub 2/ pellets containing 1 to 10% PuO/sub 2/ was set up and preliminary experiments were performed. Work on a small scale was done on pressing and sintering of UO/sub 2/ made along various routes. The reduction process was also studied. For the regeneration of scrap, especially for the case of enriched material, a 5-kg batch dissolution and precipitation plant was built. This installation is also used for various precipitation studies on a larger scale. Within the scope of tue fuel development program the study of canning materials is also of great importance. For the ship-propulsion reactor Zircaloy-2 was chosen as canning material. Various welding experiments were done in an argon-arc welding chamber and it was found that under well selected conditions very satisfactory end-cap welds could be obtained. 1n the corrosion program it became clear that proper conditioning is of utmost importance. Means of pre-operation treatment are being studied. In the HFR a low-temperature, low-pressure loop for the irradiation of capsules is in regular operation. The pressurized loop now under construction was designed for testing of fuel rods and clusters as planned for the ship-propulsion reactor, under conditions close to those of the actual reactor. The facilities for the post- irradiation measurements consist of two lead cells. (auth)« less

Uranyl Coordination Polymers Incorporating η5-Cyclopentadienyliron-Functionalized η6-Phthalate Metalloligands: Syntheses, Structures and Photophysical Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerr, Andrew T.; Kumalah, Sayon A.; Holman, K. T.

2013-10-06

The reaction of two η5-cyclopentadienyliron(II)-functionalized terephthalate and phthalate metalloligands, namely [(η5-C5H5)FeII(η6-1,4-HO2CC6H4CO2H)][(η5-C5H5)FeII(η6-1,4-HO2CC6H4CO2)][PF6] and [(η5-C5H5)FeII(η6-1,2-HO2CC6H4CO2H)][(η5-C5H5)FeII(η6-1,2-HO2CC6H4CO2)][PF6]—hereafter [H2 CpFeTP][HCpFeTP][PF6] and [H2 CpFeP][HCpFeP][PF6], respectively—with [UO2(NO3)2]·6H2O under hydrothermal conditions yielded four new coordination polymers; (1) [(UO2)F(HCpFeTP)(PO4H2)]·2H2O, (2) [(UO2)2(CpFeTP)4]·5H2O, (3) [(UO2)2F3(H2O)(CpFeP)], and (4) [H2 CpFeP][UO2F3]. The use of metalloligands has proven to be a viable route towards the incorporation of a secondary metal center into uranyl bearing materials. Depending upon the protonation state, the iron sandwich metalloligands may vary from zwitterionic neutral or monoanionic coordinating species as observed in compounds 1–3, or a positively charged species that hydrogen bonds with anionic [UO2F3]- chains as observed in 4.more » Further, the hydrolysis of the charge balancing PF6 - anion increases the diversity of UO2 2+ coordinating species by contributing both F- and PO4 3- anions (1, 3, 4). The luminescent properties of 1–4 were also studied and revealed the absence of uranyl emission, suggestive of a possible energy transfer from the uranyl cation to the iron(II) metal center.« less

Thermal property change of MOX and UO2 irradiated up to high burnup of 74 GWd/t

NASA Astrophysics Data System (ADS)

Nakae, Nobuo; Akiyama, Hidetoshi; Miura, Hiromichi; Baba, Toshikazu; Kamimura, Katsuichiro; Kurematsu, Shigeru; Kosaka, Yuji; Yoshino, Aya; Kitagawa, Takaaki

2013-09-01

Thermal property is important because it controls fuel behavior under irradiation. The thermal property change at high burnup of more than 70 GWd/t is examined. Two kinds of MOX fuel rods, which were fabricated by MIMAS and SBR methods, and one referenced UO2 fuel rod were used in the experiment. These rods were taken from the pre-irradiated rods (IFA 609/626, of which irradiation test were carried out by Japanese PWR group) and re-fabricated and re-irradiated in HBWR as IFA 702 by JNES. The specification of fuel corresponds to that of 17 × 17 PWR type fuel and the axially averaged linear heat rates (LHR) of MOX rods are 25 kW/m (BOL of IFA 702) and 20 kW/m (EOL of IFA 702). The axial peak burnups achieved are about 74 GWd/t for both of MOX and UO2. Centerline temperature and plenum gas pressure were measured in situ during irradiation. The measured centerline temperature is plotted against LHR at the position where thermocouples are fixed. The slopes of MOX are corresponded to each other, but that of UO2 is higher than those of MOX. This implies that the thermal conductivity of MOX is higher than that of UO2 at high burnup under the condition that the pellet-cladding gap is closed during irradiation. Gap closure is confirmed by the metallography of the postirradiation examinations. It is understood that thermal conductivity of MOX is lower than that of UO2 before irradiation since phonon scattering with plutonium in MOX becomes remarkable. A phonon scattering with plutonium decreases in MOX when burnup proceeds. Thus, thermal conductivity of MOX becomes close to that of UO2. A reverse phenomenon is observed at high burnup region. The phonon scattering with fission products such as Nd and Zr causes a degradation of thermal conductivity of burnt fuel. It might be speculated that this scattering effect causes the phenomenon and the mechanism is discussed here.

Xenon Defects in Uranium Dioxide From First Principles and Interatomic Potentials

NASA Astrophysics Data System (ADS)

Thompson, Alexander

In this thesis, we examine the defect energetics and migration energies of xenon atoms in uranium dioxide (UO2) from first principles and interatomic potentials. We also parameterize new, accurate interatomic potentials for xenon and uranium dioxide. To achieve accurate energetics and provide a foundation for subsequent calculations, we address difficulties in finding consistent energetics within Hubbard U corrected density functional theory (DFT+U). We propose a method of slowly ramping the U parameter in order to guide the calculation into low energy orbital occupations. We find that this method is successful for a variety of materials. We then examine the defect energetics of several noble gas atoms in UO2 for several different defect sites. We show that the energy to incorporate large noble gas atoms into interstitial sites is so large that it is energetically favorable for a Schottky defect cluster to be created to relieve the strain. We find that, thermodynamically, xenon will rarely ever be in the interstitial site of UO2. To study larger defects associated with the migration of xenon in UO 2, we turn to interatomic potentials. We benchmark several previously published potentials against DFT+U defect energetics and migration barriers. Using a combination of molecular dynamics and nudged elastic band calculations, we find a new, low energy migration pathway for xenon in UO2. We create a new potential for xenon that yields accurate defect energetics. We fit this new potential with a method we call Iterative Potential Refinement that parameterizes potentials to first principles data via a genetic algorithm. The potential finds accurate energetics for defects with relatively low amounts of strain (xenon in defect clusters). It is important to find accurate energetics for these sorts of low-strain defects because they essentially represent small xenon bubbles. Finally, we parameterize a new UO2 potential that simultaneously yields accurate vibrational properties and defect energetics, important properties for UO2 because of the high temperature and defective reactor environment.. Previously published potentials could only yield accurate defect energetics or accurate phonons, but never both.

Uranyl coordination in ionic liquids: the competition between ionic liquid anions, uranyl counterions, and Cl- anions investigated by extended X-ray absorption fine structure and UV-visible spectroscopies and molecular dynamics simulations.

PubMed

Gaillard, C; Chaumont, A; Billard, I; Hennig, C; Ouadi, A; Wipff, G

2007-06-11

The first coordination sphere of the uranyl cation in room-temperature ionic liquids (ILs) results from the competition between its initially bound counterions, the IL anions, and other anions (e.g., present as impurities or added to the solution). We present a joined spectroscopic (UV-visible and extended X-ray absorption fine structure)-simulation study of the coordination of uranyl initially introduced either as UO2X2 salts (X-=nitrate NO3-, triflate TfO-, perchlorate ClO4-) or as UO2(SO4) in a series of imidazolium-based ILs (C4mimA, A-=PF6-, Tf2N-, BF4- and C4mim=1-methyl-3-butyl-imidazolium) as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. The addition of Cl- anions promotes the solubilization of the nitrate and triflate salts in the C4mimPF6 and the C4mimBF4 ILs via the formation of chloro complexes, also formed with other salts. The first coordination sphere of uranyl is further investigated by molecular dynamics (MD) simulations on associated versus dissociated forms of UO2X2 salts in C4mimA ILs as a function of A- and X- anions. Furthermore, the comparison of UO2Cl(4)2-, 2 X- complexes with dissociated X- anions, to the UO2X2, 4 Cl- complexes with dissociated chlorides, shows that the former is more stable. The case of fluoro complexes is also considered, as a possible result of fluorinated IL anion's degradation, showing that UO2F42- should be most stable in solution. In all cases, uranyl is found to be solvated as formally anionic UO2XnAmClp2-n-m-p complexes, embedded in a cage of stabilizing IL imidazolium or ammonium cations.

Mechanisms and Rates of U(VI) Reduction by Fe(II) in Homogeneous Aqueous Solution and the Role of U(V) Disproportionation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Richard N.; Rosso, Kevin M.

Molecular-level pathways in the aqueous redox transformation of uranium by iron remain unclear, despite the importance of this knowledge for predicting uranium transport and distribution in natural and engineered environments. As the relative importance of homogeneous versus heterogeneous pathways is difficult to probe experimentally, here we apply computational molecular simulation to isolate rates of key one electron transfer reactions in the homogeneous pathway. By comparison to experimental observations the role of the heterogeneous pathway also becomes clear. Density functional theory (DFT) and Marcus theory calculations for all primary monomeric species at pH values ≤7 show for UO22+ and its hydrolysismore » species UO2OH+ and UO2(OH)20 that reduction by Fe2+ is thermodynamically favorable, though kinetically limited for UO22+. An inner-sphere encounter complex between UO2OH+ and Fe2+ was the most stable for the first hydrolysis species and displayed an electron transfer rate constant ket = 4.3 × 103 s-1. Three stable inner- and outer-sphere encounter complexes between UO2(OH)20 and Fe2+ were found, with electron transfer rate constants ranging from ket = 7.6 × 102 to 7.2 × 104 s-1. Homogeneous reduction of these U(VI) hydrolysis species to U(V) is, therefore, predicted to be facile. In contrast, homogeneous reduction of UO2+ by Fe2+ was found to be thermodynamically unfavorable, suggesting the possible importance of U(V)-U(V) disproportionation as a route to U(IV). Calculations on homogeneous disproportionation, however, while yielding a stable outer-sphere U(V)-U(V) encounter complex, indicate that this electron transfer reaction is not feasible at circumneutral pH. Protonation of both axial O atoms of acceptor U(V) (i.e., by H3O+) was found to be a prerequisite to stabilize U(IV), consistent with the experimental observation that the rate of this reaction is inversely correlated with pH. Thus, despite prevailing notions that U(V) is rapidly eliminated by homogeneous disproportionation, this pathway is irrelevant at environmental conditions.« less

Impact of initial 24-h urine output on short-term outcomes in patients with ST-segment elevation myocardial infarction admitted without cardiogenic shock and renal dysfunction.

PubMed

Huang, Bi; Yang, Yanmin; Zhu, Jun; Liang, Yan; Tan, Huiqiong; Yu, Litian; Gao, Xin; Li, Jiandong; Zhang, Han; Wang, Juan; Wan, Huaibin

2015-05-01

Our study aims to evaluate the prognostic value of initial 24-h urine output (UO) in patients with ST-segment elevation myocardial infarction (STEMI) admitted without cardiogenic shock and renal dysfunction, and to determine the additional risk stratification offered by adding initial 24-h UO to TIMI risk score (TRS). Data from 7078 consecutive STEMI patients in a multi-center registry were retrospectively analyzed. Patients were divided into 4 groups according to initial 24-h UO quartiles. The primary endpoints were 7- and 30-day all-cause mortality. Patients in the lowest UO quartile (≤1020 mL) had significantly higher 7- and 30-day all-cause mortality rates, cardiogenic shock, and major adverse cardiovascular events (MACE) than those in other groups (all P<0.05). After multivariate adjustment, initial 24-h UO≤1020 mL was independently associated with an increased risk in 7-day all-cause mortality (HR=4.649, 95%CI 3.348-6.455) and 30-day all-cause mortality (HR=3.775, 95%CI 2.891-4.931) as well as 7-day MACE (HR=1.845, 95%CI 1.563-2.179) and 30-day MACE (HR=1.818, 95%CI 1.553-2.127). Initial 24-h UO provided additional risk stratification across all TRS groups and improved the discriminatory ability of TRS with respect to 7-day all-cause mortality (c-statistic from 0.704 to 0.764) and 30-day all-cause mortality (c-statistic from 0.706 to 0.743). Reduced initial 24-h UO (≤1020 mL) was associated with an increased risk in 7- and 30-day all-cause mortality and MACE in STEMI patients admitted without cardiogenic shock and renal dysfunction. The combination of initial 24-h UO and TRS improved short-term outcome prediction when compared to TRS alone, particularly in patients with initial 24-h UO≤1020 mL. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Quasielastic neutron scattering with in situ humidity control: Water dynamics in uranyl fluoride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miskowiec, A., E-mail: miskowiecaj@ornl.gov; Trowbridge, L.; Anderson, B.

2016-03-07

The structural phase diagram of uranyl fluoride (UO{sub 2}F{sub 2}), while incomplete, contains at least one anhydrous crystal structure and a second, zeolite-like structure with the formula [(UO{sub 2}F{sub 2})(H{sub 2}O)]{sub 7} ⋅ (H{sub 2}O){sub 4} that can be produced by adding water to the anhydrous structure. While traditional diffraction measurements can easily differentiate these crystals, additional aqueous structures (in general of the form UO{sub 2}F{sub 2} + xH{sub 2}O) have been proposed as well. We present results using a novel sample environment setup to intercalate water during a quasielastic neutron scattering measurement over the course of 86 h. Our sample environment allows low-pressure (<2 atm)more » humid air flow across the sample coupled with a system to control the relative humidity of this air flow between 10% and 70%. The water dynamics in UO{sub 2}F{sub 2} and [(UO{sub 2}F{sub 2})(H{sub 2}O)]{sub 7} ⋅ (H{sub 2}O){sub 4} are sufficiently different to distinguish them, with water in the latter executing a restricted diffusion (D = 2.7 × 10{sup −6} cm{sup 2}/s) within the structure's accessible pores (r = 3.17 Å) such that the dynamics can be used as a fingerprinting tool. We confirm that water vapor pressure is the driving thermodynamic force for the conversion of the anhydrous structure to [(UO{sub 2}F{sub 2})(H{sub 2}O)]{sub 7} ⋅ (H{sub 2}O){sub 4}, and we demonstrate the feasibility of extending this approach to aqueous forms of UO{sub 2}F{sub 2} + xH{sub 2}O. This method has general applicability to systems in which water content itself is a driving variable for structural or dynamical phase transitions.« less

Limit Cycle Solutions of Reaction-Diffusion Equations.

DTIC Science & Technology

1980-06-01

simply matching terms of o(.En), the essential factor in obtaining -OLIveLgence is to mix O(- n -1 ) and O(Cn ) terms. The remainder of this section...determine vn we mix up the terms of the second system, defining vn by: dv0 - I I[ K- I-F(Uo)]V0 - I F (uo)F Uo) , (3.4b) dvn0 (E K F’(u )v0 I FF...0). Substitution of 00 u ’Zi-F- c(aO)E into g =0 gives and c(c() kfc ( CP): 3< 40’ from which cQO() > I b(ool for all 0( follows, giving a majorant

Estimated critical conditions for UO[sub 2]F[sub 2]--H[sub 2]O systems in fully water-reflected spherical geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jordan, W.C.; Turner, J.C.

1992-12-01

The purpose of this report is to document reference calculations performed using the SCALE-4.0 code system to determine the critical parameters of UO[sub 2]F[sub 2]-H[sub 2]O spheres. The calculations are an extension of those documented in ORNL/CSD/TM-284. Specifically, the data for low-enriched UO[sub 2]F[sub 2]-H[sub 2]O spheres have been extended to highly enriched uranium. These calculations, together with those reported in ORNL/CSD/TM-284, provide a consistent set of critical parameters (k[sub [infinity

High density, uniformly distributed W/UO2 for use in Nuclear Thermal Propulsion

NASA Astrophysics Data System (ADS)

Tucker, Dennis S.; Barnes, Marvin W.; Hone, Lance; Cook, Steven

2017-04-01

An inexpensive, quick method has been developed to obtain uniform distributions of UO2 particles in a tungsten matrix utilizing 0.5 wt percent low density polyethylene. Powders were sintered in a Spark Plasma Sintering (SPS) furnace at 1600 °C, 1700 °C, 1750 °C, 1800 °C and 1850 °C using a modified sintering profile. This resulted in a uniform distribution of UO2 particles in a tungsten matrix with high densities, reaching 99.46% of theoretical for the sample sintered at 1850 °C. The powder process is described and the results of this study are given below.

Thermal-stress fracture and fractography in UO/sub 2/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kennedy, C.R.; Bandyopadhyay, G.

1976-01-01

Pressed and sintered UO/sub 2/ pellets were thermally shocked by quenching into a water bath at room temperature. The cracking behavior and strength degradation, as measured by the diametral compression technique, in these quench tests are discussed. Fractography of the thermally shocked specimens by scanning-electron microscopy indicated predominantly intergranular fracture in UO/sub 2/ in severe thermal-shock tests. The implication of this observation is that intergranular cracking may occur during the initial heat up in a reactor. Because fission gas bubbles tend to migrate toward the grain boundary, preferential microcracking along the boundary may strongly affect subsequent fission gas release behavior.

Hypoeutectic melting in the UO2-x-Gd2O3 system

NASA Astrophysics Data System (ADS)

Journeau, Christophe; Fouquart, Pascal; Domenger, Renaud; Allegri, Patrick

2017-05-01

Gadolinium is one of the best neutron absorber materials and its use can be considered as a sacrificial material in a Sodium Fast Reactor core catcher in view of preventing recriticallity. A series of experiments have been conducted in the VITI induction-heated facility to study the melting in the UO2-x-Gd2O3 system with 60-87 mol% gadolinia. These experiments have indicated that the eutectic composition is around 92 mol% Gd2O3 - 8 mol% UO2-x and that the liquidus line is close to that of Popov et al. [Atom. Energ. 110 (2011) pp. 221-229] phase diagram.

Raman spectroscopic investigation of thorium dioxide-uranium dioxide (ThO₂-UO₂) fuel materials.

PubMed

Rao, Rekha; Bhagat, R K; Salke, Nilesh P; Kumar, Arun

2014-01-01

Raman spectroscopic investigations were carried out on proposed nuclear fuel thorium dioxide-uranium dioxide (ThO2-UO2) solid solutions and simulated fuels based on ThO2-UO2. Raman spectra of ThO2-UO2 solid solutions exhibited two-mode behavior in the entire composition range. Variations in mode frequencies and relative intensities of Raman modes enabled estimation of composition, defects, and oxygen stoichiometry in these compounds that are essential for their application. The present study shows that Raman spectroscopy is a simple, promising analytical tool for nondestructive characterization of this important class of nuclear fuel materials.

Performance Measures, Benchmarking and Value.

ERIC Educational Resources Information Center

McGregor, Felicity

This paper discusses performance measurement in university libraries, based on examples from the University of Wollongong (UoW) in Australia. The introduction highlights the integration of information literacy into the curriculum and the outcomes of a 1998 UoW student satisfaction survey. The first section considers performance indicators in…

METHOD OF SEPARATING URANIUM SUSPENSIONS

DOEpatents

Wigner, E.P.; McAdams, W.A.

1958-08-26

A process is presented for separating colloidally dissed uranium oxides from the heavy water medium in upwhich they are contained. The method consists in treating such dispersions with hydrogen peroxide, thereby converting the uranium to non-colloidal UO/sub 4/, and separating the UO/sub 4/ sfter its rapid settling.

Complexes of oxovanadium(IV), dioxovanadium(V) and dioxouranium(VI) with aminoacids in aqueous solution

NASA Astrophysics Data System (ADS)

Lagrange, P.; Schneider, M.; Lagrange, J.

1998-11-01

The equilibria between three oxocations (VO2+, VO2+ and UO22+) and several ?- aminoacids (glycine, serine, asparagine, lysine, aspartic acid and glutamic acid) are studied in aqueous solution. Stoichiometry and stability of the complexes formed are determined from a combination of potentiometric and spectroscopic measurements. Solution structures of the different complexes are proposed based on the thermodynamic results. The oxovanadium(IV) complexes appear less stable than the corresponding dioxouranium(VI) and dioxovanadium(V) complexes. VO2+ can be bound to only one ligand to form monodentate or chelate complexes. UO22+ and VO2+ cations may be chelated by one or two ligands. Les équilibres entre trois oxocations, VO2+, VO2+ et UO22+ et plusieurs α-aminoacides, glycine, sérine, asparagine, lysine et acides aspartique et glutamique, sont étudiés en solution aqueuse par potentiométrie couplée à la spectrophotométrie. Les complexes de VO2+ sont moins stables que les complexes de VO2+ et UO22+ de même stoechiométrie. VO2+ ne peut se lier qu'à un seul ligand pour former soit des complexes monodentés, soit des chélates. UO22+ et VO2+ peuvent être chélatés par un ou deux ligands. Des structures hypothétiques en solution sont proposées.

Functionalized Sugarcane Bagasse for U(VI) Adsorption from Acid and Alkaline Conditions.

PubMed

Su, Shouzheng; Liu, Qi; Liu, Jingyuan; Zhang, Hongsen; Li, Rumin; Jing, Xiaoyan; Wang, Jun

2018-01-15

The highly efficient removal of uranium from mine tailings effluent, radioactive wastewater and enrichment from seawater is of great significance for the development of nuclear industry. In this work, we prepared an efficient U(VI) adsorbent by EDTA modified sugarcane bagasse (MESB) with a simple process. The prepared adsorbent preserves high adsorptive capacity for UO 2 2+ (pH 3.0) and uranyl complexes, such as UO 2 (OH) + , (UO 2 ) 2 (OH) 2 2+ and (UO 2 ) 3 (OH) 5 + (pH 4.0 and pH 5.0) and good repeatability in acidic environment. The maximum adsorption capacity for U(VI) at pH 3.0, 4.0 and 5.0 is 578.0, 925.9 and 1394.1 mg/g and the adsorption capacity loss is only 7% after five cycles. With the pH from 3.0 to 5.0, the inhibitive effects of Na + and K + decreased but increased of Mg 2+ and Ca 2+ . MESB also exhibits good adsorption for [UO 2 (CO 3 ) 3 ] 4- at pH 8.3 from 10 mg/L to 3.3 μg/L. Moreover, MESB could effectively extract U(VI) from simulated seawater in the presence of other metals ions. This work provided a general and efficient uranyl enriched material for nuclear industry.

Diffusion of oxygen interstitials in UO2+x using kinetic Monte Carlo simulations: Role of O/M ratio and sensitivity analysis

NASA Astrophysics Data System (ADS)

Behera, Rakesh K.; Watanabe, Taku; Andersson, David A.; Uberuaga, Blas P.; Deo, Chaitanya S.

2016-04-01

Oxygen interstitials in UO2+x significantly affect the thermophysical properties and microstructural evolution of the oxide nuclear fuel. In hyperstoichiometric Urania (UO2+x), these oxygen interstitials form different types of defect clusters, which have different migration behavior. In this study we have used kinetic Monte Carlo (kMC) to evaluate diffusivities of oxygen interstitials accounting for mono- and di-interstitial clusters. Our results indicate that the predicted diffusivities increase significantly at higher non-stoichiometry (x > 0.01) for di-interstitial clusters compared to a mono-interstitial only model. The diffusivities calculated at higher temperatures compare better with experimental values than at lower temperatures (< 973 K). We have discussed the resulting activation energies achieved for diffusion with all the mono- and di-interstitial models. We have carefully performed sensitivity analysis to estimate the effect of input di-interstitial binding energies on the predicted diffusivities and activation energies. While this article only discusses mono- and di-interstitials in evaluating oxygen diffusion response in UO2+x, future improvements to the model will primarily focus on including energetic definitions of larger stable interstitial clusters reported in the literature. The addition of larger clusters to the kMC model is expected to improve the comparison of oxygen transport in UO2+x with experiment.

The oviductal transcriptome is influenced by a local ovarian effect in the sow.

PubMed

López-Úbeda, Rebeca; Muñoz, Marta; Vieira, Luis; Hunter, Ronald H F; Coy, Pilar; Canovas, Sebastian

2016-07-22

Oviducts participate in fertilization and early embryo development, and they are influenced by systemic and local circulation. Local functional interplay between ovary, oviduct and uterus is important, as deduced from the previously observed differences in hormone concentrations, presence of sperm, or patterns of motility in the oviduct after unilateral ovariectomy (UO). However, the consequences of unilateral ovariectomy on the oviductal transcriptome remain unexplored. In this study, we have investigated the consequences of UO in a higher animal model as the pig. The influence of UO was analyzed on the number of ovulations on the contra ovary, which was increased, and on the ipsilateral oviductal transcriptome. Microarray analysis was performed and the results were validated by PCR. Differentially expressed genes (DEGs) with a fold change ≥ 2 and a false discovery rate of 10 % were analyzed by Ingenuity Pathway Analysis (IPA) to identify the main biofunctions affected by UO. Data revealed two principal effects in the ipsilateral oviduct after UO: i) down-regulation of genes involved in the survival of sperm in the oviduct and early embryonic development, and ii) up-regulation of genes involved in others functions as protection against external agents and tumors. Results showed that unilateral ovariectomy results in an increased number of ovulation points on the contra ovary and changes in the transcriptome of the ipsilateral oviduct with consequences on key biological process that could affect fertility output.

Carbon monoxide reaction with UO2(111) single crystal surfaces: A theoretical and experimental study

NASA Astrophysics Data System (ADS)

Senanayake, S. D.; Soon, A.; Kohlmeyer, A.; Söhnel, T.; Idriss, H.

2005-07-01

The reaction of CO has been investigated on the surfaces of UO2(111) single crystal. Over the stoichiometric surface CO does not adsorb at 300 K and no further reaction is noticed. Over UO2-x (prepared by Ar+ bombardment), CO molecules adsorb and in presence of traces of H2 they couple to form acetylene molecules that desorb in two temperature domains during temperature programmed desorption (TPD). In the presence of excess H2 the coupling product is found to be ethylene. X-ray photoelectron spectroscopy (XPS) of the core level shows the presence of an U 4f line at 377 eV on the UO2-x surface, attributed to U metal. This line disappears upon CO adsorption (5 L and above) at 300 K indicating oxidation of U metal atoms by O from dissociatively adsorbed CO. XPS C 1s shows that the only C containing species formed is carbide. Computation of a α-U metal 2d-periodic slab was also conducted using plane-wave pseudopotential in the density functional theoretical framework. Two modes of CO adsorption were considered: molecular and dissociative. The dissociative adsorption was found more energetically favoured by 0.46 eV. From TPD, XPS and computation results it is strongly suggested that CO is dissociatively adsorbed on UO2-x and that a stable U-C species is formed at 300 K.

Manufacture of a UO2-Based Nuclear Fuel with Improved Thermal Conductivity with the Addition of BeO

NASA Astrophysics Data System (ADS)

Garcia, Chad B.; Brito, Ryan A.; Ortega, Luis H.; Malone, James P.; McDeavitt, Sean M.

2017-12-01

The low thermal conductivity of oxide nuclear fuels is a performance-limiting parameter. Enhancing this property may provide a contribution toward establishing accident-tolerant fuel forms. In this study, the thermal conductivity of UO2 was increased through the fabrication of ceramic-ceramic composite forms with UO2 containing a continuous BeO matrix. Fuel with a higher thermal conductivity will have reduced thermal gradients and lower centerline temperatures in the fuel pin. Lower operational temperatures will reduce fission gas release and reduce fuel restructuring. Additions of BeO were made to UO2 fuel pellets in 2.5, 5, 7.5, and 10 vol pct concentrations with the goals of establishing reliable lab-scale processing procedures, minimizing porosity, and maximizing thermal conductivity. The microstructure was characterized with electron probe microanalysis, and the thermal properties were assessed by light flash analysis and differential scanning calorimetry. Reliable, high-density samples were prepared using compaction pressure between 200 and 225 MPa and sintering times between 4 and 6 hours. It was found that the thermal conductivity of UO2 improved approximately 10 pct for each 1 vol pct BeO added over the measured temperature range 298.15 K to 523.15 K (25 °C to 250 °C) with the maximum observed improvement being ˜ 100 pct, or doubled, at 10 vol pct BeO.

Effect of organic complexing agents on the interactions of Cs(+), Sr(2+) and UO(2)(2+) with silica and natural sand.

PubMed

Reinoso-Maset, Estela; Worsfold, Paul J; Keith-Roach, Miranda J

2013-05-01

Sorption processes play a key role in controlling radionuclide migration through subsurface environments and can be affected by the presence of anthropogenic organic complexing agents found at contaminated sites. The effect of these complexing agents on radionuclide-solid phase interactions is not well known. Therefore the aim of this study was to examine the processes by which EDTA, NTA and picolinate affect the sorption kinetics and equilibria of Cs(+), Sr(2+) and UO2(2+) onto natural sand. The caesium sorption rate and equilibrium were unaffected by the complexing agents. Strontium however showed greater interaction with EDTA and NTA in the presence of desorbed matrix cations than geochemical modelling predicted, with SrNTA(-) enhancing sorption and SrEDTA(2-) showing lower sorption than Sr(2+). Complexing agents reduced UO2(2+) sorption to silica and enhanced the sorption rate in the natural sand system. Elevated concentrations of picolinate reduced the sorption of Sr(2+) and increased the sorption rate of UO2(2+), demonstrating the potential importance of this complexing agent. These experiments provide a direct comparison of the sorption behaviour of Cs(+), Sr(2+) and UO2(2+)onto natural sand and an assessment of the relative effects of EDTA, NTA and picolinate on the selected elements. Copyright © 2013 Elsevier Ltd. All rights reserved.

Structural, spectroscopic and redox properties of uranyl complexes with a maleonitrile containing ligand.

PubMed

Hardwick, Helen C; Royal, Drew S; Helliwell, Madeleine; Pope, Simon J A; Ashton, Lorna; Goodacre, Roy; Sharrad, Clint A

2011-06-14

The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt((Et(2)N)(2))H(2)) in methanol produces [UO(2)(salmnt((Et2N)2))(H(2)O)] (1) where the uranyl equatorial coordination plane is completed by the N(2)O(2) tetradentate cavity of the (salmnt((Et(2)N)(2)))(2-) ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO(2)(salmnt((Et(2)N)(2)))(L)] complexes (L = py, DMSO, DMF, TPPO; 2-5, respectively). X-Ray crystallography of 1-5 show that the (salmnt((Et(2)N)(2)))(2-) ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt((Et(2)N)(2))H(2)). The Raman spectra of 1-5 only display extremely weak bands (819-828 cm(-1)) that can be assigned to the typically symmetric O=U=O stretch. This stretching mode is also observed in the infrared spectra for all complexes 1-5 (818-826 cm(-1)) predominantly caused by the distortion of the tetradentate (salmnt((Et(2)N)(2)))(2-) ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2-5 was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2-5 exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (< 5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO(2)}(2+)/{UO(2)}(+) couple are observed for complexes 2-5 (2: E(1/2) = -1.80 V; 3,5: E(1/2) = -1.78 V; 4: E(1/2) = -1.81 V : vs. ferrocenium/ferrocene {Fc(+)/Fc}, 0.1 M Bu(4)NPF(6)) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO(2)}(2+)/{UO(2)}(+) couple observed to date and indicate the strong electron donating nature of the (salmnt((Et(2)N)(2)))(2-) ligand. Multiple uranyl redox processes are clearly seen for [UO(2)(salmnt((Et(2)N)(2)))(L)] in L (L = py, DMSO, DMF; 2-4: 0.1 M Bu(4)NPF(6)) indicating the relative instability of these complexes when competing ligands are present, but the reversible {UO(2)}(2+)/{UO(2)}(+) couple for the intact complexes can still be assigned and shows the position of this couple can be modulated by the solvation environment. Several redox processes were also observed between +0.2 and +1.2 V (vs. Fc(+)/Fc) that prove the redox active nature of the maleonitrile-containing ligand.

The pressure dependence of oxygen-isotope-exchange rates between solution and apical oxygens on the UO 2(OH) 4 2- ion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harley, Steven J.; Ohlin, C. Andre; Johnson, Rene L.

2011-04-06

The pressure dependence of isotope exchange rate was determined for apical oxygen atoms in the UO 2(OH) 4 2-(aq) ion. The results can be interpreted to indicate an associative character of the reaction.

Towards Distinctive and Developmental Curricula at UoTs: The STEPS process at CUT

ERIC Educational Resources Information Center

Mthembu, T. Z.; Orkin, M.; Gering, M.

2012-01-01

Universities of technology (UoTs) achieve developmental impact through differentiated curricula, allowing graduates to undertake mid-level occupations in the workplace. This mandate differs from that at traditional universities in six respects: diploma-level entrants, labour market focus, workplace-oriented learning, applied research and…

Description and crystal structure of albrechtschraufite, MgCa4F2[UO2(CO3)3]2ṡ17-18H2O

NASA Astrophysics Data System (ADS)

Mereiter, Kurt

2013-04-01

Albrechtschraufite, MgCa4F2[UO2(CO3)3]2ṡ17-18H2O, triclinic, space group Pī, a = 13.569(2), b = 13.419(2), c = 11.622(2) Å, α = 115.82(1), β = 107.61(1), γ = 92.84(1)° (structural unit cell, not reduced), V = 1774.6(5) Å3, Z = 2, D c = 2.69 g/cm3 (for 17.5 H2O), is a mineral that was found in small amounts with schröckingerite, NaCa3F[UO2(CO3)3](SO4)ṡ10H2O, on a museum specimen of uranium ore from Joachimsthal (Jáchymov), Czech Republic. The mineral forms small grain-like subhedral crystals (≤ 0.2 mm) that resemble in appearance liebigite, Ca2[UO2(CO3)3]ṡ ~ 11H2O. Colour pale yellow-green, luster vitreous, transparent, pale bluish green fluorescence under ultraviolet light. Optical data: Biaxial negative, nX = 1.511(2), nY = 1.550(2), nZ = 1.566(2), 2 V = 65(1)° ( λ = 589 nm), r < v weak. After qualitative tests had shown the presence of Ca, U, Mg, CO2 and H2O, the chemical formula was determined by a crystal structure analysis based on X-ray four-circle diffractometer data. The structure was later on refined with data from a CCD diffractometer to R1 = 0.0206 and wR2 = 0.0429 for 9,236 independent observed reflections. The crystal structure contains two independent [UO2(CO3)3]4- anions of which one is bonded to two Mg and six Ca while the second is bonded to only one Mg and three Ca. Magnesium forms a MgF2(Ocarbonate)3(H2O) octahedron that is linked via the F atoms with three Ca atoms so as to provide each F atom with a flat pyramidal coordination by one Mg and two Ca. Calcium is 7- and 8-coordinate forming CaFO6, CaF2O2(H2O)4, CaFO3(H2O)4 and CaO2(H2O)6 coordination polyhedra. The crystal structure is built up from MgCa3F2[UO2(CO3)3]ṡ8H2O layers parallel to (001) which are linked by Ca[UO2(CO3)3]ṡ5H2O moieties into a framework of the composition MgCa4F2[UO2(CO3)3]ṡ13H2O. Five additional water molecules are located in voids of the framework and show large displacement parameters. One of the water positions is partly vacant, leading to a total water content of 17-18H2O per formula unit. The MgCa3F2[UO2(CO3)3]ṡ8H2O layers are pseudosymmetric according to plane group symmetry cmm. The remaining constituents do not sustain this pseudosymmetry and make the entire structure truly triclinic. A characteristic paddle-wheel motif Ca[UO2(CO3)3]4Ca relates the structure of albrechtschraufite partly to that of andersonite and two synthetic alkali calcium uranyl tricarbonates.

A comparison of very short lived halocarbon (VSLS) and DMS aircraft measurements in the tropical west Pacific from CAST, ATTREX and CONTRAST

NASA Astrophysics Data System (ADS)

Andrews, Stephen J.; Carpenter, Lucy J.; Apel, Eric C.; Atlas, Elliot; Donets, Valeria; Hopkins, James R.; Hornbrook, Rebecca S.; Lewis, Alastair C.; Lidster, Richard T.; Lueb, Richard; Minaeian, Jamie; Navarro, Maria; Punjabi, Shalini; Riemer, Daniel; Schauffler, Sue

2016-10-01

We present a comparison of aircraft measurements of halogenated very short lived substances (VSLSs) and dimethyl sulphide (DMS, C2H6S) from a co-ordinated campaign in January-February 2014 in the tropical west Pacific. Measurements were made on the NASA Global Hawk, NCAR Gulfstream-V High-performance Instrumented Airborne Platform for Environmental Research (GV HIAPER) and UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 (see Sect. 2.2) using four separate gas chromatography-mass spectrometry (GC-MS) instruments: one operated by the University of Miami (UoM), one from the National Center for Atmospheric Research (NCAR) and two from the University of York (UoY). DMS was measured on the BAe-146 and GV. The instruments were inter-calibrated for halocarbons during the campaign period using two gas standards on separate scales: a National Oceanic and Atmospheric Administration (NOAA) SX-3581 standard representative of clean low-hydrocarbon air, and an Essex canister prepared by UoM, representative of coastal air, which was higher in VSLS and hydrocarbon content. UoY and NCAR use the NOAA scale/standard for VSLS calibration, and UoM uses a scale based on dilutions of primary standards calibrated by GC with FID (flame ionisation detector) and AED (atomic emission detector). Analysis of the NOAA SX-3581 standard resulted in good agreement for CH2Cl2, CHCl3, CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl, CH3I, CH2ICl and CH2I2 (average relative standard deviation (RSD) < 10 %). Agreement was in general slightly poorer for the UoM Essex canister with an RSD of < 13 %. Analyses of CHBrCl2 and CHBr3 in this standard however showed significant variability, most likely due to co-eluting contaminant peaks, and a high concentration of CHBr3, respectively. These issues highlight the importance of calibration at atmospherically relevant concentrations ( ˜ 0.5-5 ppt for VSLSs; see Fig. 5 for individual ranges). The UoY in situ GC-MS measurements on board the BAe-146 compare favourably with ambient data from NCAR and UoM; however the UoY whole-air samples showed a negative bias for some lower-volatility compounds. This systematic bias could be attributed to sample line losses. Considering their large spatial variability, DMS and CH3I displayed good cross-platform agreement without any sampling bias, likely due to their higher volatility. After a correction was performed based upon the UoY in situ vs. whole-air data, all four instrument datasets show good agreement across a range of VSLSs, with combined mean absolute percentage errors (MAPEs) of the four platforms throughout the vertical profiles ranging between 2.2 (CH2Br2) and 15 (CH3I) % across a large geographic area of the tropical west Pacific. This study shows that the international VSLS calibration scales and instrumental techniques discussed here are in generally good agreement (within ˜ 10 % across a range of VSLSs), but that losses in aircraft sampling lines can add a major source of uncertainty. Overall, the measurement uncertainty of bromocarbons during these campaigns is much less than the uncertainty in the quantity of VSLS bromine estimated to reach the stratosphere of between 2 and 8 pptv.

How we developed eForms: an electronic form and data capture tool to support assessment in mobile medical education.

PubMed

Mooney, Jane S; Cappelli, Tim; Byrne-Davis, Lucie; Lumsden, Colin J

2014-12-01

Mobile learning technologies are being introduced and adopted by an increasing number of medical schools. Following the implementation of these devices, institutions are tasked with the challenge of their integration into curriculum delivery and presented with the opportunity to facilitate data collection from large student cohorts. Since 2011, Manchester Medical School (MMS) has undertaken the largest deployment of iPads within UK Higher Education. Working towards the more efficient collation of students' compulsory workplace-based assessment data led us to evaluate how existing information management software could replace previously paper-based systems. Following an evaluation of six, and a trial of one, commercially available packages, the existing software solutions were found to be inflexible and unfit for purpose. This resulted in the development of a new digital solution that addressed the limitations of the previous system. "University of Manchester (UoM) eForms" consists of an app and a web-based administration system that respectively permit high volume data collection and management. UoM eForms has now replaced the preceding paper-based and electronic systems within MMS for workplace-based assessment administration, due to the improved usability and dynamicity built into its interface and infrastructure. This new system has found many further useful applications, including research data collection, feedback, placement evaluations, quality assurance and interview marking.

Modeling the UO2 ex-AUC pellet process and predicting the fuel rod temperature distribution under steady-state operating condition

NASA Astrophysics Data System (ADS)

Hung, Nguyen Trong; Thuan, Le Ba; Thanh, Tran Chi; Nhuan, Hoang; Khoai, Do Van; Tung, Nguyen Van; Lee, Jin-Young; Jyothi, Rajesh Kumar

2018-06-01

Modeling uranium dioxide pellet process from ammonium uranyl carbonate - derived uranium dioxide powder (UO2 ex-AUC powder) and predicting fuel rod temperature distribution were reported in the paper. Response surface methodology (RSM) and FRAPCON-4.0 code were used to model the process and to predict the fuel rod temperature under steady-state operating condition. Fuel rod design of AP-1000 designed by Westinghouse Electric Corporation, in these the pellet fabrication parameters are from the study, were input data for the code. The predictive data were suggested the relationship between the fabrication parameters of UO2 pellets and their temperature image in nuclear reactor.

Compositional changes at the interface between thorium-doped uranium dioxide and zirconium due to high-temperature annealing

NASA Astrophysics Data System (ADS)

Youn, Young-Sang; Lee, Jeongmook; Kim, Jandee; Kim, Jong-Yun

2018-06-01

Compositional changes at the interface between thorium-doped uranium dioxide (U0.97Th0.03O2) and Zr before and after annealing at 1700 °C for 18 h were studied by X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. At room temperature, the U0.97Th0.03O2 pellet consisted of hyperstoichiometric UO2+x with UO2 and ThO2, and the Zr sample contained Zr with ZrO2. After annealing, the former contained stoichiometric UO2 with ThO2 and the latter consisted of ZrO2 along with ZrO2·2H2O.

Layered uranium(VI) hydroxides: structural and thermodynamic properties of dehydrated schoepite α-UO₂(OH)₂.

PubMed

Weck, Philippe F; Kim, Eunja

2014-12-07

The structure of dehydrated schoepite, α-UO2(OH)2, was investigated using computational approaches that go beyond standard density functional theory and include van der Waals dispersion corrections (DFT-D). Thermal properties of α-UO2(OH)2, were also obtained from phonon frequencies calculated with density functional perturbation theory (DFPT) including van der Waals dispersion corrections. While the isobaric heat capacity computed from first-principles reproduces available calorimetric data to within 5% up to 500 K, some entropy estimates based on calorimetric measurements for UO3·0.85H2O were found to overestimate by up to 23% the values computed in this study.

The Pressure Dependence of Oxygen Isotope Exchange Rates Between Solution and Apical Oxygen Atoms on the [UO2(OH)4]2- Ion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harley, Steven J.; Ohlin, C. André; Johnson, Rene L.

2011-04-06

Under pressure: The pressure dependence of isotope exchange rate was determined for apical oxygen atoms in the [UO2(OH)4]2-(aq) ion (see picture). The results can be interpreted to indicate an associative character of the reaction.

Current Evaluation of Upper Oesophageal Sphincter Opening in Dysphagia Practice: An International SLT Survey

ERIC Educational Resources Information Center

Regan, Julie; Walshe, Margaret; McMahon, Barry P.

2012-01-01

Background: The assessment of adequate upper oesophageal sphincter (UOS) opening during swallowing is an integral component of dysphagia evaluation. Aims: To ascertain speech and language therapists' (SLTs) satisfaction with current methods for assessing UOS function in people with dysphagia and to identify challenges encountered by SLTs with UOS…

Reframing Curriculum and Pedagogical Discourse in Universities of Technology

ERIC Educational Resources Information Center

Ntshoe, I.

2012-01-01

This articles aims to demystify curriculum and pedagogical discourses and related practices of sectoral occupational fields and qualifications of universities of technology (UoTs). The article takes issue with the academic tradition which emphasises distinctiveness of UoT as a sector that should focus exclusively on applied knowledge that is fixed…

Crosscutting Runtime Adaptations of LD Execution

ERIC Educational Resources Information Center

Zarraonandia, Telmo; Dodero, Juan Manuel; Fernandez, Camino

2006-01-01

In this paper, the authors describe a mechanism for the introduction of small variations in the original learning design process defined in a particular Unit of Learning (UoL). The objective is to increase the UoL reusability by offering the designers an alternative to introduce slight variations on the original design instead of creating a new…

Interpenetrated Uranyl-Organic Frameworks with bor and pts Topology: Structure, Spectroscopy, and Computation.

PubMed

Liu, Chao; Chen, Fang-Yuan; Tian, Hong-Rui; Ai, Jing; Yang, Weiting; Pan, Qing-Jiang; Sun, Zhong-Ming

2017-11-20

Two novel three-dimensional interpenetrated uranyl-organic frameworks, (NH 4 ) 4 [(UO 2 ) 4 (L 1 ) 3 ]·6H 2 O (1) and [(UO 2 ) 2 (H 2 O) 2 L 2 ]·2H 2 O (2), where L 1 = tetrakis(3-carboxyphenyl)silicon and L 2 = tetrakis(4-carboxyphenyl)silicon, were synthesized by a combination of two isomeric tetrahedral silicon-centered ligands with 3-connected triangular [(UO 2 )(COO) 3 ] - and 4-connected dinuclear [(UO 2 ) 2 (COO) 4 ] units, respectively. Structural analyses indicate that 1 possesses a 2-fold interpenetrating anion bor network, while 2 exhibits a 3-fold interpenetrated 4,4-connected neutral network with pts topology. Both compounds were characterized by thermogravimetric analysis and IR, UV-vis, and photoluminescence spectroscopy. A relativistic density functional theory (DFT) investigation on 10 model compounds of 1 and 2 shows good agreement of the structural parameters, stretching vibrational frequencies, and absorption with experimental results; the time-dependent DFT calculations unravel that low-energy absorption bands originate from ligand-to-uranium charge transfer.

Results of Uranium Dioxide-Tungsten Irradiation Test and Post-Test Examination

NASA Technical Reports Server (NTRS)

Collins, J. F.; Debogdan, C. E.; Diianni, D. C.

1973-01-01

A uranium dioxide (UO2) fueled capsule was fabricated and irradiated in the NASA Plum Brook Reactor Facility. The capsule consisted of two bulk UO2 specimens clad with chemically vapor deposited tungsten (CVD W) 0.762 and 0.1016 cm (0.030-and 0.040-in.) thick, respectively. The second specimen with 0.1016-cm (0.040-in.) thick cladding was irradiated at temperature for 2607 hours, corresponding to an average burnup of 1.516 x 10 to the 20th power fissions/cu cm. Postirradiation examination showed distortion in the bottom end cap, failure of the weld joint, and fracture of the central vent tube. Diametral growth was 1.3 percent. No evidence of gross interaction between CVD tungsten or arc-cast tungsten cladding and the UO2 fuel was observed. Some of the fission gases passed from the fuel cavity to the gas surrounding the fuel specimen via the vent tube and possibly the end-cap weld failure. Whether the UO2 loss rates through the vent tube were within acceptable limits could not be determined in view of the end-cap weld failure.

Integrated skills, integrated data: Mapping best practice and collections for innovation and engagement

NASA Astrophysics Data System (ADS)

Hosker, Rachel; Knowles, Claire; Rodger, Norman

2015-02-01

In recent years the University of Edinburgh [UoE] has seen change, mergers, external partnerships and innovation at the heart of its growth and activity. Collections at UoE were not immune from these changes and have pioneered projects that both support and highlight unique educational cultures. Technology and the dissemination of collections has not only engendered positive relationships with academics but has created wider opportunities for the use of collections in teaching, learning and research. This momentum and an established commitment to the interoperability of data and standards presented an opportunity to look for a global solution to collections management within the converged, cross disciplinary environment. This included harnessing expertise in the University with systems development for large European projects and wider project management. This session will explore how UoE became the first European contributor to the collections management tool Archives Space. Snapshots of a converged culture and how 'archives' have benefited from this (including how 'techies' and 'archivists' worked together). An upbeat finale will look at what the team at the UoE achieved and are excited about for the future.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valderrama, Billy; He, Lingfeng; Henderson, Hunter B.

Fission products, such as krypton (Kr), are known to be insoluble within UO 2, segregating towards grain boundaries, eventually leading to a lowering of the thermal conductivity and fuel swelling. Recent computational studies have identified that differences in grain boundary structure have a significant effect on the segregation behavior of fission products. However, experimental work supporting these simulations is lacking. Atom probe tomography was used to measure the Kr distribution across grain boundaries in UO 2. Polycrystalline depleted-UO 2 samples was irradiated with 0.7 and 1.8 MeV Kr-ions and annealed to 1000ºC, 1300ºC, and 1600°C for 1 hour to producemore » a Kr-bubble dominated microstructure. The results of this work indicate a strong dependence of Kr concentration as a function of grain boundary structure. Temperature also influences grain boundary chemistry with greater Kr concentration evident at higher temperatures, resulting in a reduced Kr concentration in the bulk. While Kr migration is active at elevated temperatures, no changes in grain size or texture were observed in the irradiated UO 2 samples.« less

Synthesis and an X-ray diffraction study of Rb{sub 2}[(UO{sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serezhkina, L. B., E-mail: Lserezh@ssu.samara.ru; Peresypkina, E. V.; Neklyudova, N. A.

2010-09-15

The synthesis and X-ray diffraction study of compound Rb{sub 2}[(UO{sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 3}], which crystallizes in the monoclinic crystal system, are performed. The unit cell parameters are as follows: a = 7.9996(6) A, b = 8.8259(8) A, c = 11.3220(7) A, {beta} = 105.394(2){sup o}, and V = 770.7(1) A{sup 3}; space group P2{sub 1}/n, Z = 2, and R{sub 1} = 0.0271. [(UO{sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 3}]{sup 2-} layers belonging to the AK{sub 0.5}{sup 02}T{sup 11} crystal chemical group of uranyl complexes (A = UO{sub 2}{sup 2+}, K{sup 02} = C{sub 2}O{sub 4}{sup 2-}, and T{supmore » 11} = C{sub 2}O{sub 4}{sup 2-}) are uranium-containing structural units of the crystals. The layers are connected with outer-sphere rubidium cations by electrostatic interactions.« less

Average structure and local configuration of excess oxygen in UO(2+x).

PubMed

Wang, Jianwei; Ewing, Rodney C; Becker, Udo

2014-03-19

Determination of the local configuration of interacting defects in a crystalline, periodic solid is problematic because defects typically do not have a long-range periodicity. Uranium dioxide, the primary fuel for fission reactors, exists in hyperstoichiometric form, UO(2+x). Those excess oxygen atoms occur as interstitial defects, and these defects are not random but rather partially ordered. The widely-accepted model to date, the Willis cluster based on neutron diffraction, cannot be reconciled with the first-principles molecular dynamics simulations present here. We demonstrate that the Willis cluster is a fair representation of the numerical ratio of different interstitial O atoms; however, the model does not represent the actual local configuration. The simulations show that the average structure of UO(2+x) involves a combination of defect structures including split di-interstitial, di-interstitial, mono-interstitial, and the Willis cluster, and the latter is a transition state that provides for the fast diffusion of the defect cluster. The results provide new insights in differentiating the average structure from the local configuration of defects in a solid and the transport properties of UO(2+x).

Raman spectroscopic studies of defect structures and phase transition in hyper-stoichiometric UO(2+x).

PubMed

He, Heming; Shoesmith, David

2010-07-28

A method to determine the defect structures in hyper-stoichiometric UO(2+x) using a combination of XRD and Raman spectroscopy has been developed. A sequence of phase transitions, from cubic to tetragonal symmetry, occurs with increasing degree of non-stoichiometry. This sequence proceeds from a cubic phase through an intermediate t''-type tetragonal (axial ratio c/a = 1) phase to a final t-type tetragonal (c/a not = 1) phase. Four distinct structural defect regions can be identified in the stoichiometry range, UO(2) to U(3)O(7): (i) a random point defect structure (x (in UO(2+x)) < or = 0.05); (ii) a non-stoichiometry region (0.05 < or = x < or = 0.15) over which point defects are gradually eliminated and replaced by the Willis 2:2:2 cluster; (iii) a mixture of Willis and cuboctahedral clusters (0.15 < or = x < or = 0.23); (iv) the cuboctahedral cluster (x > or = 0.23). The geometry and steric arrangement of these defects is primarily determined by the concentration of the excess-oxygen interstitials.

Comparative density functional study of the complexes [UO2(CO3)3]4- and [(UO2)3(CO3)6]6- in aqueous solution.

PubMed

Schlosser, Florian; Moskaleva, Lyudmila V; Kremleva, Alena; Krüger, Sven; Rösch, Notker

2010-06-28

With a relativistic all-electron density functional method, we studied two anionic uranium(VI) carbonate complexes that are important for uranium speciation and transport in aqueous medium, the mononuclear tris(carbonato) complex [UO(2)(CO(3))(3)](4-) and the trinuclear hexa(carbonato) complex [(UO(2))(3)(CO(3))(6)](6-). Focusing on the structures in solution, we applied for the first time a full solvation treatment to these complexes. We approximated short-range effects by explicit aqua ligands and described long-range electrostatic interactions via a polarizable continuum model. Structures and vibrational frequencies of "gas-phase" models with explicit aqua ligands agree best with experiment. This is accidental because the continuum model of the solvent to some extent overestimates the electrostatic interactions of these highly anionic systems with the bulk solvent. The calculated free energy change when three mono-nuclear complexes associate to the trinuclear complex, agrees well with experiment and supports the formation of the latter species upon acidification of a uranyl carbonate solution.

Peierls-Nabarro modeling of dislocations in UO2

NASA Astrophysics Data System (ADS)

Skelton, Richard; Walker, Andrew M.

2017-11-01

Under conditions of high stress or low temperature, glide of dislocations plays an important role in the deformation of UO2. In this paper, the Peierls-Nabarro model is used to calculate the core widths and Peierls stresses of ½<110> edge and screw dislocations gliding on {100}, {110}, and {111}. The energy of the inelastic displacement field in the dislocation core is parameterized using generalized stacking fault energies, which are calculated atomistically using interatomic potentials. We use seven different interatomic potential models, representing the variety of different models available for UO2. The different models broadly agree on the relative order of the strengths of the different slip systems, with the 1/2<110>{100} edge dislocation predicted to be the weakest slip system and 1/2<110>{110} the strongest. However, the calculated Peierls stresses depend strongly on the interatomic potential used, with values ranging between 2.7 and 12.9 GPa for glide of 1/2<110>{100} edge dislocations, 16.4-32.3 GPa for 1/2<110>{110} edge dislocations, and 6.8-13.6 GPa for 1/2<110>{111} edge dislocations. The glide of 1/2<110> screw dislocations in UO2 is also found to depend on the interatomic potential used, with some models predicting similar Peierls stresses for glide on {100} and {111}, while others predict a unique easy glide direction. Comparison with previous fully atomistic calculations show that the Peierls-Nabarro model can accurately predict dislocation properties in UO2.

Two actinide-organic frameworks constructed by a tripodal flexible ligand: Occurrence of infinite {(UO2)O2(OH)3}4n and hexanuclear {Th6O4(OH)4} motifs

NASA Astrophysics Data System (ADS)

Liang, Lingling; Zhang, Ronglan; Zhao, Jianshe; Liu, Chiyang; Weng, Ng Seik

2016-11-01

Two new actinide metal-organic frameworks were constructed by using a tripodal flexible ligand tris (2-carboxyethyl) isocyanurate (H3tci) under hydrothermal condition. The combination of H3tci and uranyl nitrate hexahydrate in aqueous solution leads to the isolation of [(UO2)2(H2O)4]0.5(tci)2(UO2)4(OH)4·18H2O (1), which contains two distinct UO22+ coordination environments. Four uranyl cations, linked through μ3-OH respectively, result in the edge-sharing ribbons. Then, the layer structure is constructed by U-O clusters linked through other eight-coordinated uranyl unions, giving rise to a porous structure in the space. Topological analysis reveals that complex 1 belongs to a (4, 8)-connected net with a schläfli symbol of (34.26.3)2(34.46.56.68.73.8). Th3(tci)2O2(OH)2(H2O)3·12H2O (2) generated by the reaction of H3tci and thorium nitrate tetrahydrate, possesses nine-fold coodinated Th(IV) centers with a monocapped square antiprismatic geometry. The hexamers "Th6O4(OH)4" motifs are connected together by the carboxylate groups, showing a three-dimensional structures. Complex 2 takes on an 8-connected architecture and the point symbol is (424.64).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rabin, S.A.; Martin, M.M.; Lotts, A.L.

The fabricability of dispersion fuels using UO/sub 2/ or UC as the dispersoid and uranium combined with 10 to 15 wt% Mo as the matrix was investigated. Cores containing l7.8 wt% UO/sub 2/ dispersed in U-- 15 wt.% Mo were successfully fabricated to about 80% of theoretical density by cold pressing at 50 tsi, sintering at 1100 deg C, and cold coining at 50 tsi. Comparable results were obtained with UC as the dispersoid. Core fabrication results varied greatly with the type of matrix powder used. Occluded gases, pour density, and surface cleanliness bore important relations to the fabrication behaviormore » of powders. Suitable pressing and sintering results were obtained with prealloyed, calcium-reduced U--Mo powder and with molybdenum and calcium-reduced uranium as elemental powders. Shotted prealloyed powders were difficult to press and sinter, as were elemental and prealloyed powders prepared by hydriding. The cores containing UO/sub 2/ were picture-frame, hot-roll-clad as miniature plates. Molybdenum, Fansteel 82, and Zr--3 wt% Al were investigated as cladding materials. While each bonded well to itself, only the molybdenum-clad core, rolled at 1150 deg C to 10/1 reduction, resulted in dispersions free of ruptures and UO/sub 2/ fragmentation and in strong bonding to the core, evaluated by metallography, mechanical peel, and thermal shock tests. The matrix phase was homogeneous, but the UO/sub 2/ dispersoid showed stringering characteristic of cores worked by hot rolling. Core densities as high as 99% of theoretical were obtained. (auth)« less

FABRICATION DEVELOPMENT OF UO$sub 2$-STAINLESS STEEL COMPOSITE FUEL PLATES FOR CORE B OF THE ENRICO FERMI FAST BREEDER REACTOR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherubini, J.H.; Beaver, R.J.; Leitten, C.F. Jr.

1961-04-18

The development of an inexpensive composite fuel plate with a high burnup potential for application in a 500 deg C sodium environment as Core B of the Enrico Fermi Fast Breeder Reactor is described. The dispersion fuel product consists of 35 wt.% spheroidal UO/sub 2/ dispersed in type 347B stainless steel powder and clad with wrought type 347 stainless steel. Nominal over-all dimensions of Type II design fuel plates are 18.97 in. long x 2.406 in. wide x 0.112 in. thick with 0.005-in. cladding. Reliable processing methods for achieving a uniform distribution of spheroidal UO/sub 2/ in the matrix powdermore » and cladding the sintered powder compact by roll bonding are described. Examination of experimental plates reveals that the degree of UO/sub 2/ fragmentation and stringering encountered during processing is primarily a function of the degree of cold work employed in the finishing operation snd the starting quality of the UO/sub 2/ powder. Cladding studies indicate that a sound metallurgical bond can be achieved with an 87.5% reduction in thickness at 1200 deg C and that close processing control is required to meet the stringent tolerances specified. The developed process meets all criteria except possibly the surface finish requirement; occasionally, pitting occurs due to scale embedded during hot working. Detailed procedures covering composite plate manufacture are presented. (auth)« less

Unconventional oil and gas development and risk of childhood leukemia: Assessing the evidence.

PubMed

Elliott, Elise G; Trinh, Pauline; Ma, Xiaomei; Leaderer, Brian P; Ward, Mary H; Deziel, Nicole C

2017-01-15

The widespread distribution of unconventional oil and gas (UO&G) wells and other facilities in the United States potentially exposes millions of people to air and water pollutants, including known or suspected carcinogens. Childhood leukemia is a particular concern because of the disease severity, vulnerable population, and short disease latency. A comprehensive review of carcinogens and leukemogens associated with UO&G development is not available and could inform future exposure monitoring studies and human health assessments. The objective of this analysis was to assess the evidence of carcinogenicity of water contaminants and air pollutants related to UO&G development. We obtained a list of 1177 chemicals in hydraulic fracturing fluids and wastewater from the U.S. Environmental Protection Agency and constructed a list of 143 UO&G-related air pollutants through a review of scientific papers published through 2015 using PubMed and ProQuest databases. We assessed carcinogenicity and evidence of increased risk for leukemia/lymphoma of these chemicals using International Agency for Research on Cancer (IARC) monographs. The majority of compounds (>80%) were not evaluated by IARC and therefore could not be reviewed. Of the 111 potential water contaminants and 29 potential air pollutants evaluated by IARC (119 unique compounds), 49 water and 20 air pollutants were known, probable, or possible human carcinogens (55 unique compounds). A total of 17 water and 11 air pollutants (20 unique compounds) had evidence of increased risk for leukemia/lymphoma, including benzene, 1,3-butadiene, cadmium, diesel exhaust, and several polycyclic aromatic hydrocarbons. Though information on the carcinogenicity of compounds associated with UO&G development was limited, our assessment identified 20 known or suspected carcinogens that could be measured in future studies to advance exposure and risk assessments of cancer-causing agents. Our findings support the need for investigation into the relationship between UO&G development and risk of cancer in general and childhood leukemia in particular. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Comparative electronic structure of a lanthanide and actinide diatomic oxide: Nd versus U

NASA Astrophysics Data System (ADS)

Krauss, M.; Stevens, W. J.

2003-01-01

Using a modified version of the Alchemy electronic structure code and relativistic pseudopotentials, the electronic structure of the ground and low lying excited states of UO, NdO, and NdO + have been calculated at the Hartree-Fock (HF) and multiconfiguration self-consistent field (MCSCF) levels of theory. Including results from an earlier study of UO + this provides the information for a comparative analysis of a lanthanide and an actinide diatomic oxide. UO and NdO are both described formally as M +2 O -2 and the cations as M +3 O -2 , but the HF and MCSCF calculations show that these systems are considerably less ionic due to large charge back-transfer in the πorbitals. The electronic states putatively arise from the ligand field (oxygen anion) perturbed f 4 , sf 3 , df 3 , sdf 2 , or s 2 f 2 states of M +2 and f 3 , sf 2 or df 2 states of M +3 . Molecular orbital results show a substantial stabilization of the sf 3 or s 2 f 2 configurations relative to the f 4 or df 3 configurations that are the even or odd parity ground states in the M +2 free ion. The compact f and d orbitals are more destabilized by the anion field than the diffuse s orbital. The ground states of the neutral species are dominated by orbitals arising from the M +2 sf 3 term, and all the potential energy curves arising from this configuration are similar, which allows an estimate of the vibrational frequencies for UO and NdO of 862 cm -1 and 836 cm -1 , respectively. For NdO + and UO + the excitation energies for the Ωstates were calculated with a valence configuration interaction method using ab initio effective spin-orbit operators to couple the molecular orbital configurations. The results for NdO + are very comparable with the results for UO + , and show the vibrational and electronic states to be interleaved.

Structural, spectroscopic and thermal characterization of 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester and its Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes.

PubMed

Mohamed, Gehad G; El-Gamel, Nadia E A

2005-04-01

Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes with the ligand 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester (HL(2)) have been prepared and characterized by elemental analyses, molar conductance, magnetic moment, thermal analysis and spectral data. 1:1 M:HL(2) complexes, with the general formula [M(HL(2))X(2)].nH(2)O (where M = Co(II) (X = Cl, n = 0), Ni(II) (X = Cl, n = 3), Cu(II) (grey colour, X = AcO, n = 1), Cu(II) (yellow colour, X = Cl, n = 0) and Zn(II) (X = Br, n = 0). In addition, the Fe(III) and UO(2)(II) complexes of the type 1:2 M:HL(2) and with the formulae [Fe(L(2))(2)]Cl and [UO(2)(HL(2))(2)](NO(3))(2) are prepared. From the IR data, it is seen that HL(2) ligand behaves as a terdentate ligand coordinated to the metal ions via the pyridyl N, carboxylate O and protonated NH group; except the Fe(III) complex, it coordinates via the deprotonated NH group. This is supported by the molar conductance data, which show that all the complexes are non-electrolytes, while the Fe(III) and UO(2)(II) complexes are 1:1 electrolytes. IR and H1-NMR spectral studies suggest a similar behaviour of the Zn(II) complex in solid and solution states. From the solid reflectance spectral data and magnetic moment measurements, the complexes have a trigonal bipyramidal (Co(II), Ni(II), Cu(II) and Zn(II) complexes) and octahedral (Fe(III), UO(2)(II) complexes) geometrical structures. The thermal behaviour of the complexes is studied and the different dynamic parameters are calculated applying Coats-Redfern equation.

Molecular and polymeric uranyl and thorium hybrid materials featuring methyl substituted pyrazole dicarboxylates and heterocyclic 1,3-diketones

NASA Astrophysics Data System (ADS)

Carter, Korey P.; Kerr, Andrew T.; Taydakov, Ilya V.; Cahill, Christopher L.

2018-02-01

A series of seven novel f-element bearing hybrid materials have been prepared from either methyl substituted 3,4 and 4,5-pyrazoledicarboxylic acids, or heterocyclic 1,3- diketonate ligands using hydrothermal conditions. Compounds 1, [UO2(C6H4N2O4)2(H2O)], and 3, [Th(C6H4N2O4)4(H2O)5]·H2O feature 1-Methyl-1H-pyrazole-3,4-dicarboxylate ligands (SVI-COOH 3,4), whereas 2, [UO2(C6H4N2O4)2(H2O)], and 4, [Th(C6H5N2O4)(OH)(H2O)6]2·2(C6H5N2O4)·3H2O feature 1-Methyl-1H-pyrazole-4,5-dicarboxylate moieties (SVI-COOH 4,5). Compounds 5, [UO2(C13H15N4O2)2(H2O)]·2H2O and 6, [UO2(C11H11N4O2)2(H2O)]·4.5H2O feature 1,3-bis(4-N1-methyl-pyrazolyl)propane-1,3-dione and 1,3-bis(4-N1,3-dimethyl-pyrazolyl)propane-1,3-dione respectively, whereas the heterometallic 7, [UO2(C11H11N4O2)2(CuCl2)(H2O)]·2H2O is formed by using 6 as a metalloligand starting material. Single crystal X-ray diffraction indicates that all coordination to either [UO2]2+ or Th(IV) metal centers is through O-donation as anticipated. Room temperature, solid-state luminescence studies indicate characteristic uranyl emissive behavior for 1 and 2, whereas those for 5 and 6 are weak and poorly resolved.

Botulinum toxin for upper oesophageal sphincter dysfunction in neurological swallowing disorders.

PubMed

Regan, Julie; Murphy, Anne; Chiang, Mindy; McMahon, Barry P; Coughlan, Tara; Walshe, Margaret

2014-05-06

Adequate upper oesophageal sphincter (UOS) opening is critical to safe and efficient swallowing due to the close proximity of the UOS to the airway entrance. Many people with neurological conditions, progressive and non-progressive, present with UOS dysfunction. The consequences for the person include difficulty swallowing food with subsequent choking and aspiration (passage of material into the trachea beyond the level of the true vocal cords). Clinical complications include aspiration pneumonia, weight loss, dehydration and malnutrition. Tube feeding is often indicated but is associated with increased mortality. Quality of life is also frequently impacted. A range of interventions exist that aim to improve UOS function and swallowing. These include compensatory strategies, rehabilitation techniques, pharmacological interventions and surgery. Over the last two decades, botulinum toxin has been gaining popularity as an intervention for UOS dysfunction, with some evidence to suggest that it is successful in improving swallow function. Despite a number of studies investigating its efficacy, there is a lack of consensus regarding whether this intervention is effective in improving swallowing for individuals with UOS dysfunction associated with neurological disease. To establish the efficacy and safety of botulinum toxin use aimed at improving UOS dysfunction in people with swallowing difficulties (dysphagia) associated with non-progressive and progressive neurological disease. We searched the following electronic databases for published trials: the Cochrane Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE (1950 to 2013); EMBASE (1980 to 2013); AMED (Allied and Complementary Medicine) (1941 to 2013); CINAHL (Cumulative Index to Nursing and Allied Health Literature) (1937 to 2013). We also searched major clinical trials registers: CCT (http://www.controlled-trials.com); Clinical Trials (http://www.clinicaltrials.gov); Chinese Clinical Trial Register (www.chictr.org); ACTR (http://www.actr.org.au/. We examined the reference lists of all potentially relevant studies to identify further relevant trials. We handsearched published abstracts of conference proceedings from both the Dysphagia Research Society and the European Society of Swallowing Disorders. Digestive Disease Week (published in Gastroenterology) was also handsearched. Additionally, we searched ProQuest Dissertations & Theses for dissertation abstracts. Only randomised controlled trials were sought. Independent searches were completed by JR, AM, MC and MW. Two review authors (JR and MW) independently inspected titles, abstracts and key words identified from the literature search. No randomised controlled studies were retrieved. Twenty-nine studies were excluded, mainly on the basis of trial design. It was not possible to reach a conclusion on the efficacy and safety of botulinum toxin as an intervention for people with UOS dysfunction and neurological disease. There is insufficient evidence to inform clinical practice. Directions for future research are provided.

Neptunium incorporation into select uranyl phases and thermal analysis of select uranyl phases

NASA Astrophysics Data System (ADS)

Klingensmith, Amanda Leigh

Alteration of spent nuclear fuel in a geological repository under oxidizing conditions is likely to result in abundant uranyl compounds. The proposed repository at Yucca Mountain, Nevada is intended to store about 70,000 metric tons of spent nuclear fuel in the unsaturated zone of a welded tuff sequence. Following failure of canisters that encapsulate the waste, contents may be exposed both to air and water and undergo repetitive wetting and drying events. Incorporation of radionuclides into the uranyl alteration phases may significantly reduce their mobility, thereby impacting repository performance. Of particular interest is 237Np owing to its long half-life (2.14 x 106 years) and potential mobility in groundwater. Powders of the synthetic uranyl phase soddyite, (UO2) 2(SiO4)(H2O)2, a framework type structure, and uranophane, Ca[(UO2)(SiO3OH)]2(H 2O)5, kasolite, Pb[(UO2)(SiO4)]H 2O, Na compreignacite, Na2[(UO2)3O 2(OH)3]2(H2O)7, and becquerelite, Ca[(UO2)3O2(OH)3]2(H 2O)8, all of which are sheet type structures, were synthesized in the presence of Np5+ under varying temperature and pH conditions. Uranophane, kasolite, boltwoodite K[(UO2)(SiO3OH)](H 2O)1.5, and Na boltwoodite K,Na[(UO2)(SiO 3OH)](H2O)1.5 were synthesized in the presence of Np as well as P, Ca and/or Mg. Single crystals of Na metaschoepite, Na[(UO 2)4O2(OH)5]˙5H2O were synthesized in the presence of Np5+ and laser ablation verified that Np can be incorporated within the structure of a uranyl phase. Incorporation of Np5+ into soddyite increased steadily with synthesis temperature. Np incorporation into uranophane, becquerelite, and kasolite was not dependent on synthesis temperature. Np uptake in uranophane and kasolite was found to be dependent on synthesis pH, with an increase in Np uptake with higher pH. Uranophane, boltwoodite and Na boltwoodite showed an increase in Np incorporation in the presence of P. Boltwoodite showed an even higher Np uptake when Mg and P were both present in the synthesis. Thermal analysis was completed for the uranyl phases soddyite, becquerelite, Na compreignacite, uranophane, and kasolite. TGA curves for becquerelite, Na compreignacite and uranophane showed loss of interlayer water groups by 100°C. Soddyite and kasolite showed more gradual TGA curves and retention of water groups up to 400°C for soddyite and 550°C for kasolite, with agreement shown by high temperature powder XRD data.

Molten salt flux synthesis and crystal structure of a new open-framework uranyl phosphate Cs{sub 3}(UO{sub 2}){sub 2}(PO{sub 4})O{sub 2}: Spectroscopic characterization and cationic mobility studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagoubi, S., E-mail: said.yagoubi@cea.fr; Renard, C.; Abraham, F.

2013-04-15

The reaction of triuranyl diphosphate tetrahydrate precursor (UO{sub 2}){sub 3}(PO{sub 4}){sub 2}(H{sub 2}O){sub 4} with a CsI flux at 750 °C yields a yellow single crystals of new compound Cs{sub 3}(UO{sub 2}){sub 2}(PO{sub 4})O{sub 2}. The crystal structure (monoclinic, space group C2/c, a=13.6261 (13) Å, b=8.1081(8) Å, c=12.3983(12) Å, β=114.61(12)°, V=1245.41(20) Å{sup 3} with Z=4) has been solved using direct methods and Fourier difference techniques. A full-matrix least-squares refinement on the basis of F{sup 2} yielded R1=0.028 and wR2=0.071 for 79 parameters and 1352 independent reflections with I≥2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a charge-coupledmore » device detector. The crystal structure is built by two independent uranium atoms in square bipyramidal coordination, connected by two opposite corners to form infinite chains {sup 1}{sub ∞}[UO{sub 5}] and by one phosphorus atom in a tetrahedral environment PO{sub 4}. The two last entities {sup 1}{sub ∞}[UO{sub 5}] and PO{sub 4} are linked by sharing corners to form a three-dimensional structure presenting different types of channels occupied by Cs{sup +} alkaline cations. Their mobility within the tunnels were studied between 280 and 800 °C and compared with other tunneled uranyl minerals. The infrared spectrum shows a good agreement with the values inferred from the single crystal structure analysis of uranyl phosphate compound. - Graphical abstract: Arrhenius plot of the electrical conductivity of tunneled compounds Cs{sub 3}U{sub 2}PO{sub 10} and CsU{sub 2}Nb{sub 2}O{sub 11.5}. Highlights: ► The reaction of (UO{sub 2}){sub 3}(PO{sub 4}){sub 2}(H{sub 2}O){sub 4} in excess of molten CsI leads to single-crystals of new tunneled compound Cs{sub 3}(UO{sub 2}){sub 2}(PO{sub 4})O{sub 2}. ► Ionic conductivity measurements and crystal structure analysis indicate a strong connection of the Cs{sup +} cations to the tunnels. ► A low symmetry in Cs{sub 3}(UO{sub 2}){sub 2}(PO{sub 4})O{sub 2} is the cause of IR activation and splitting of the bands in the IR spectrum.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thangavelu, Sonia G.; Butcher, Ray J.; Cahill, Christopher L.

Thiophene 2,5-dicarboxylic acid (TDC) was reacted with uranyl acetate dihydrate and one (or none) of six N-donor chelating ligands (2,2'-bipyridine (BPY), 4,4'-dimethyl-2,2'-bipyridine (4-MeBPY), 5,5'-dimethyl-2,2'-bipyridine (5-MeBPY), 6,6'-dimethyl-2,2'-bipyridine (6-MeBPY), 4,4',6,6'-tetramethyl-2,2'-bipyridine (4,6-MeBPY), and tetrakis(2-pyridyl)pyrazine (TPPZ) to result in the crystallization of seven uranyl coordination polymers, which were characterized by their crystal structures and luminescence properties. The seven coordination polymers, Na2[(UO2)2(C6H2O4S)3]·4H2O (1), [(UO2)4(C6H2O4S)5(C10H8N2)2]·C10H10N2·3H2O (2), [(UO2)(C6H2O4S)(C12H12N3)] (3), [(UO2)(C6H2O4S)(C12H12N3)]·H2O (4), [(UO2)2(C6H2O4S)3]·(C12H14N2)·5H2O (5), [(UO2)3(CH3CO2)(C6H2O4S)4](C14H17N2)3·(C14H16N2)·H2O (6), and [(UO2)2(C6H2O4S)3](C24H18N6) (7), consist of either uranyl hexagonal bipyramidal or pentagonal bipyramidal coordination geometries. In all structures, structural variations in the local and global structures of 1–7 are influenced by the positionsmore » (or number) of methyl groups or pyridyl rings on the N-donor species, thus resulting in a wide diversity of structures ranging from single chains, double chains, or 2-D sheets. Direct coordination of N-donor ligands to uranyl centers is observed in the chain structures of 2–4 using BPY, 4-MeBPY, and 5-MeBPY, whereas the N-donor species participate as guests (as either neutral or charge balancing species) in the chain and sheet structures of 5–7 using 6-MeBPY, 4,6-MeBPY, and TPPZ, respectively. Compound 1 is the only structure that does not contain any N-donor ligands and thus crystallizes as a 2-D interpenetrating sheet. The luminescent properties of 1–7 are influenced by the direct coordination or noncoordination of N-donor species to uranyl centers. Compounds 2–4 exhibit typical UO22+ emission upon direct coordination of N-donors, but its absence is observed in 1, 5, 6, and 7, when N-donor species participate as guest molecules. These results suggest that direct coordination of N-donor ligands participate as chromophores, thus resulting in possible UO22+ sensitization. The lack of emission in 1, 5, 6, and 7 may be explained by the extended conjugation of the TDC ligands within their structures.« less

A Seven-Step Process To Align Curriculum with Oregon State Content Standards.

ERIC Educational Resources Information Center

Golden, Nancy; Lane, Marilyn

1998-01-01

The University of Oregon (UO) and Captain Robert Gray Elementary School formed a partnership where UO students used the elementary school as a case study for curriculum research. This document gives an overview of the 7-step process the students used to align the school's curriculum with Oregon's content and performance standards. The text opens…

Receptivity of a Cryogenic Coaxial Liquid Jet to Acoustic Disturbances

DTIC Science & Technology

2014-05-21

i iio thc UUU DISTRIBUTION STATEMENT A. Approved for public release; distribution unlimited. PA Clearance 14208 12Place Proper DISTRIBUTION STATEMENT...dynamic pressures are approximately equal. Uc Uo – Uc Uc – Ui (Uo > Ui) 2/12/1 2/12/1 io iioo c UUU St = Uc fnatD If St, D, Uc are held constant then

Progress in high-temperature oven development for 28 GHz electron cyclotron resonance ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohnishi, J., E-mail: ohnishi@riken.jp; Higurashi, Y.; Nakagawa, T.

2016-02-15

We have been developing a high-temperature oven using UO{sub 2} in the 28 GHz superconducting electron cyclotron resonance ion source at RIKEN since 2013. A total of eleven on-line tests were performed. The longest operation time in a single test was 411 h, and the consumption rate of UO{sub 2} was approximately 2.4 mg/h. In these tests, we experienced several problems: the ejection hole of a crucible was blocked with UO{sub 2} and a crucible was damaged because of the reduction of tungsten strength at high temperature. In order to solve these problems, improvements to the crucible shape were mademore » by simulations using ANSYS.« less

Design Evolutuion of Hot Isotatic Press Cans for NTP Cermet Fuel Fabrication

NASA Technical Reports Server (NTRS)

Mireles, O. R.; Broadway, J.; Hickman, R.

2014-01-01

Nuclear Thermal Propulsion (NTP) is under consideration for potential use in deep space exploration missions due to desirable performance properties such as a high specific impulse (> 850 seconds). Tungsten (W)-60vol%UO2 cermet fuel elements are under development, with efforts emphasizing fabrication, performance testing and process optimization to meet NTP service life requirements [1]. Fuel elements incorporate design features that provide redundant protection from crack initiation, crack propagation potentially resulting in hot hydrogen (H2) reduction of UO2 kernels. Fuel erosion and fission product retention barriers include W coated UO2 fuel kernels, W clad internal flow channels and fuel element external W clad resulting in a fully encapsulated fuel element design as shown.

Status Report on Irradiation Capsules Designed to Evaluate FeCrAl-UO 2 Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Field, Kevin G.; Howard, Richard H.

This status report provides the background and current status of a series of irradiation capsules that were designed and are being built to test the interactions between candidate FeCrAl cladding for enhanced accident tolerant applications and prototypical enriched commercial UO 2 fuel in a neutron radiation environment. These capsules will test the degree, if any, of fuel cladding chemical interactions (FCCI) between FeCrAl and UO 2. The capsules are to be irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory to burn-ups of 10, 30, and 50 GWd/MT with a nominal target temperature at the interfaces between themore » pellets and clad of 350°C.« less

Plasma induced grafting carboxymethyl cellulose on multiwalled carbon nanotubes for the removal of UO(2)(2+) from aqueous solution.

PubMed

Shao, Dadong; Jiang, Zhongqing; Wang, Xiangke; Li, Jiaxing; Meng, Yuedong

2009-01-29

Carboxymethyl cellulose (CMC) is grafted on multiwalled carbon nanotubes (MWCNT) by using plasma techniques. The CMC grafted MWCNT (MWCNT-g-CMC) is characterized by using Fourier transform infrared spectra (FT-IR), Raman spectra, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA)-differential thermal analysis (DTA), scanning electron microscopy (SEM), and N(2)-BET methods in detail. The application of MWCNT-g-CMC in the removal of UO(2)(2+) from aqueous solution is investigated. MWCNT-g-CMC has much higher sorption ability in the removal of UO(2)(2+) than raw MWCNT. The MWCNT-g-CMC is a suitable material in the preconcentration and solidification of heavy metal ions from large volume of aqueous solutions.

Determination of trace uranium by resonance fluorescence method coupled with photo-catalytic technology and dual cloud point extraction

NASA Astrophysics Data System (ADS)

Li, Jiekang; Li, Guirong; Han, Qian

2016-12-01

In this paper, two kinds of salophens (Sal) with different solubilities, Sal1 and Sal2, have been respectively synthesized, and they all can combine with uranyl to form stable complexes: [UO22 +-Sal1] and [UO22 +-Sal2]. Among them, [UO22 +-Sal1] was used as ligand to extract uranium in complex samples by dual cloud point extraction (dCPE), and [UO22 +-Sal2] was used as catalyst for the determination of uranium by photocatalytic resonance fluorescence (RF) method. The photocatalytic characteristic of [UO22 +-Sal2] on the oxidized pyronine Y (PRY) by potassium bromate which leads to the decrease of RF intensity of PRY were studied. The reduced value of RF intensity of reaction system (ΔF) is in proportional to the concentration of uranium (c), and a novel photo-catalytic RF method was developed for the determination of trace uranium (VI) after dCPE. The combination of photo-catalytic RF techniques and dCPE procedure endows the presented methods with enhanced sensitivity and selectivity. Under optimal conditions, the linear calibration curves range for 0.067 to 6.57 ng mL- 1, the linear regression equation was ΔF = 438.0 c (ng mL- 1) + 175.6 with the correlation coefficient r = 0.9981. The limit of detection was 0.066 ng mL- 1. The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0-103.5%. The mechanisms of the indicator reaction and dCPE are discussed.

Microscopic Fuel Particles Produced by Self-Assembly of Actinide Nanoclusters on Carbon Nanomaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Na, Chongzheng

2016-10-17

Many consider further development of nuclear power to be essential for sustained development of society; however, the fuel forms currently used are expensive to recycle. In this project, we sought to create the knowledge and knowhow that are needed to produce nanocomposite materials by directly depositing uranium nanoclusters on networks of carbon-­ based nanomaterials. The objectives of the proposed work were to (1) determine the control of uranium nanocluster surface chemistry on nanocomposite formation, (2) determine the control of carbon nanomaterial surface chemistry on nanocomposite formation, and (3) develop protocols for synthesizing uranium-­carbon nanomaterials. After examining a wide variety ofmore » synthetic methods, we show that synthesizing graphene-­supported UO 2 nanocrystals in polar ethylene glycol compounds by polyol reduction under boiling reflux can enable the use of an inexpensive graphene precursor graphene oxide in the production of uranium-carbon nanocomposites in a one-­pot process. We further show that triethylene glycol is the most suitable solvent for producing nanometer-­sized UO 2 crystals compared to monoethylene glycol, diethylene glycol, and polyethylene glycol. Graphene-­supported UO 2 nanocrystals synthesized with triethylene glycol show evidence of heteroepitaxy, which can be beneficial for facilitating heat transfer in nuclear fuel particles. Furthermore, we show that graphene-supported UO 2 nanocrystals synthesized by polyol reduction can be readily stored in alcohols, preventing oxidation from the prevalent oxygen in air. Together, these methods provide a facile approach for preparing and storing graphene-supported UO nanocrystals for further investigation and development under ambient conditions.« less

Dissolution of Uranium(IV) Oxide in Solutions of Ammonium Carbonate and Hydrogen Peroxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Steven C.; Peper, Shane M.; Douglas, Matthew

2009-09-12

Understanding the dissolution characteristics of uranium oxides is of fundamental scientific interest. Bench scale experiments were conducted to determine the optimal dissolution parameters of uranium(IV) oxide (UO2) powder in solutions of ammonium carbonate [(NH4)2CO3] and hydrogen peroxide (H2O2). Experimental parameters included variable peroxide and carbonate concentrations, and temperature. Results indicate the dissolution rate of UO2 in 1 M (NH4)2CO3 increases linearly with peroxide concentration ranging from 0.05 – 2 M (1:1 to 40:1 mol ratio H2O2:U), with no apparent maximum rate reached under the limited conditions used in our study. Temperature ranging studies show the dissolution rate of UO2 inmore » 1 M (NH4)2CO3 and 0.1 M H2O2 (2:1 mol ratio H2O2:U) increases linearly from 15 °C to 60 °C, again with no apparent maximum rate reached. Dissolution of UO2 in solutions with constant [H2O2] and [(NH4)2CO3] ranging from 0.5 to 2 M showed no difference in rate; however dissolution was significantly reduced in 0.05 M (NH4)2CO3 solution. The results of this study demonstrate the influence of [H2O2], [(NH4)2CO3], and temperature on the dissolution of UO2 in peroxide-containing (NH4)2CO3 solutions. Future studies are planned to elucidate the solution and solid state complexes in these systems.« less

Variations of uranium concentrations in a multi-aquifer system under the impact of surface water-groundwater interaction

NASA Astrophysics Data System (ADS)

Wu, Ya; Li, Junxia; Wang, Yanxin; Xie, Xianjun

2018-04-01

Understanding uranium (U) mobility is vital to minimizing its concentrations in potential drinking water sources. In this study, we report spatial-seasonal variations in U speciation and concentrations in a multi-aquifer system under the impact of Sanggan River in Datong basin, northern China. Hydrochemical and H, O, Sr isotopic data, thermodynamic calculations, and geochemical modeling are used to investigate the mechanisms of surface water-groundwater mixing-induced mobilization and natural attenuation of U. In the study site, groundwater U concentrations are up to 30.2 μg/L, and exhibit strong spatial-seasonal variations that are related to pH and Eh values, as well as dissolved Ca2+, HCO3-, and Fe(III) concentrations. For the alkaline aquifers of this site (pH 7.02-8.44), U mobilization is due to the formation and desorption of Ca2UO2(CO3)30 and CaUO2(CO3)32- caused by groundwater Ca2+ elevation via mineral weathering and Na-Ca exchange, incorporated U(VI) release from calcite, and U(IV) oxidation by Fe(OH)3. U immobilization is linked to the adsorption of CaUO2(CO3)32- and UO2(CO3)34- shifted from Ca2UO2(CO3)30 because of HCO3- elevation and Ca2+ depletion, U(VI) co-precipitation with calcite, and U(VI) reduction by adsorbed Fe2+ and FeS. Those results are of great significance for the groundwater resource management of this and similar other surface water-groundwater interaction zones.

The structure of liquid UO2-x in reducing gas atmospheres

NASA Astrophysics Data System (ADS)

Alderman, O. L. G.; Benmore, C. J.; Weber, J. K. R.; Skinner, L. B.; Tamalonis, A. J.; Sendelbach, S.; Hebden, A.; Williamson, M. A.

2017-02-01

High energy X-ray diffraction experiments performed on hypostoichiometric UO2-x liquids in reducing gas mixtures of 95%Ar:5%CO and 95%Ar:5%H2 are compared to that conducted in a pure Ar atmosphere [Skinner et al., Science 346, 984 (2014)]. The measurements are pertinent to severe accident scenarios at nuclear reactors, where core melts can encounter reducing conditions and further shed light on the oxide chemistry of the low valence states of uranium, particularly U(III), which become stable only at very high temperatures and low oxygen potentials. The radioactive samples were melted by floating small spheres of material using an aerodynamic levitator and heating with a laser beam. In the more reducing environments, a 1.7% shift to lower Q-values is observed in the position of the principal peak of the measured X-ray structure factors, compared to the more oxidizing Ar environment. This corresponds to an equivalent elongation in the U-U nearest neighbor distances and the U-U periodicity. The U-O peak (modal) bond-length, as measured from the real-space total correlation functions, is also observed to expand by 0.9-1.6% under reducing conditions, consistent with the presence of 15-27% U3+ cations, assuming constant U-O coordination number. The slightly larger U-U elongation, as compared to the U-O elongation, is interpreted as a slight increase in U-O-U bond angles. Difficulties concerning the determination of the hypostoichiometry, x, are discussed, along with the future directions for related research.

The structure of liquid UO 2-x in reducing gas atmospheres

DOE PAGES

Alderman, O. L. G.; Benmore, C. J.; Weber, J. K. R.; ...

2017-02-22

High energy X-ray diffraction experiments performed on hypostoichiometric UO 2-x liquids in reducing gas mixtures of 95%Ar:5%CO and 95%Ar:5%H 2 are compared to that conducted in a pure Ar atmosphere [Skinner et al., Science 346, 984 (2014)]. The measurements are pertinent to severe accident scenarios at nuclear reactors, where core melts can encounter reducing conditions and further shed light on the oxide chemistry of the low valence states of uranium, particularly U(III), which become stable only at very high temperatures and low oxygen potentials. The radioactive samples were melted by floating small spheres of material using an aerodynamic levitator andmore » heating with a laser beam. In the more reducing environments, a 1.7% shift to lower Q-values is observed in the position of the principal peak of the measured X-ray structure factors, compared to the more oxidizing Ar environment. This corresponds to an equivalent elongation in the U-U nearest neighbor distances and the U-U periodicity. The U-O peak (modal) bond-length, as measured from the real-space total correlation functions, is also observed to expand by 0.9–1.6% under reducing conditions, consistent with the presence of 15–27% U 3+ cations, assuming constant U-O coordination number. The slightly larger U-U elongation, as compared to the U-O elongation, is interpreted as a slight increase in U-O-U bond angles. Difficulties concerning the determination of the hypostoichiometry, x, are discussed, along with the future directions for related research.« less

METHOD AND APPARATUS FOR CALCINING SALT SOLUTIONS

DOEpatents

Lawroski, S.; Jonke, A.A.; Taecker, R.G.

1961-10-31

A method is given for converting uranyl nitrate solution into solid UO/ sub 3/, The solution is sprayed horizontally into a fluidized bed of UO/sub 3/ particles at 310 to 350 deg C by a nozzle of the coaxial air jet type at about 26 psig, Under these conditions the desired conversion takes place, and caking in the bed is avoided.

PREPARATION OF SPHERICAL URANIUM DIOXIDE PARTICLES

DOEpatents

Levey, R.P. Jr.; Smith, A.E.

1963-04-30

This patent relates to the preparation of high-density, spherical UO/sub 2/ particles 80 to 150 microns in diameter. Sinterable UO/sub 2/ powder is wetted with 3 to 5 weight per cent water and tumbled for at least 48 hours. The resulting spherical particles are then sintered. The sintered particles are useful in dispersion-type fuel elements for nuclear reactors. (AEC)

Direct electrochemical reduction of solid uranium oxide in molten fluoride salts

NASA Astrophysics Data System (ADS)

Gibilaro, Mathieu; Cassayre, Laurent; Lemoine, Olivier; Massot, Laurent; Dugne, Olivier; Malmbeck, Rikard; Chamelot, Pierre

2011-07-01

The direct electrochemical reduction of UO 2 solid pellets was carried out in LiF-CaF 2 (+2 mass.% Li 2O) at 850 °C. An inert gold anode was used instead of the usual reactive sacrificial carbon anode. In this case, oxidation of oxide ions present in the melt yields O 2 gas evolution on the anode. Electrochemical characterisations of UO 2 pellets were performed by linear sweep voltammetry at 10 mV/s and reduction waves associated to oxide direct reduction were observed at a potential 150 mV more positive in comparison to the solvent reduction. Subsequent, galvanostatic electrolyses runs were carried out and products were characterised by SEM-EDX, EPMA/WDS, XRD and microhardness measurements. In one of the runs, uranium oxide was partially reduced and three phases were observed: nonreduced UO 2 in the centre, pure metallic uranium on the external layer and an intermediate phase representing the initial stage of reduction taking place at the grain boundaries. In another run, the UO 2 sample was fully reduced. Due to oxygen removal, the U matrix had a typical coral-like structure which is characteristic of the pattern observed after the electroreduction of solid oxides.

Thermochemistry of rare earth doped uranium oxides LnxU1-xO2-0.5x+y (Ln = La, Y, Nd)

NASA Astrophysics Data System (ADS)

Zhang, Lei; Navrotsky, Alexandra

2015-10-01

Lanthanum, yttrium, and neodymium doped uranium dioxide samples in the fluorite structure have been synthesized, characterized in terms of metal ratio and oxygen content, and their enthalpies of formation measured by high temperature oxide melt solution calorimetry. For oxides doped with 10-50 mol % rare earth (Ln) cations, the formation enthalpies from constituent oxides (LnO1.5, UO2 and UO3 in a reaction not involving oxidation or reduction) become increasingly exothermic with increasing rare earth content, while showing no significant dependence on the varying uranium oxidation state. The oxidation enthalpy of LnxU1-xO2-0.5x+y is similar to that of UO2 to UO3 for all three rare earth doped systems. Though this may suggest that the oxidized uranium in these systems is energetically similar to that in the hexavalent state, thermochemical data alone can not constrain whether the uranium is present as U5+, U6+, or a mixture of oxidation states. The formation enthalpies from elements calculated from the calorimetric data are generally consistent with those from free energy measurements.

Phase discrimination of uranium oxides using laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Campbell, Keri R.; Wozniak, Nicholas R.; Colgan, James P.; Judge, Elizabeth J.; Barefield, James E.; Kilcrease, David P.; Wilkerson, Marianne P.; Czerwinski, Ken R.; Clegg, Samuel M.

2017-08-01

Nuclear forensics goals for characterizing samples of interest include qualitative and quantitative analysis of major and trace elements, isotopic analysis, phase identification, and physical analysis. These samples may include uranium oxides UO2, U3O8, and UO3, which play an important role in the front end of the nuclear fuel cycle, from mining to fuel fabrication. The focus of this study is to compare the ratios of the intensities of uranium and oxygen emission lines which can be used to distinguish between different uranium oxide materials using Laser-Induced Breakdown Spectroscopy (LIBS). Measurements at varying laser powers were made under an argon atmosphere at 585 Torr to ensure the oxygen emission intensity was originating from the sample, and not from the atmosphere. Fifteen uranium emission lines were used to compare experimental results with theoretical calculations in order to determine the plasma conditions. Using a laser energy of 26 mJ, the uranium lines 591.539 and 682.692 nm provide the highest degree of discrimination between the uranium oxides. The study presented here suggests that LIBS is useful for discriminating uranium oxide phases, UO2, U3O8, and UO3.

Solubility of uranium oxide in molten salt electrolysis bath of LiF-BaF2 with LaF3 additive

NASA Astrophysics Data System (ADS)

Alangi, Nagaraj; Mukherjee, Jaya; Gantayet, L. M.

2016-03-01

The solubility of UO2 in the molten mixtures of equimolar LiF-BaF2(1:1) with LaF3 as additive was studied in the range of 1423 K-1523 K. The molten fluoride salt mixture LiF-BaF2 LaF3 was equilibrated with a sintered uranium oxide pellet at 1423 K, 1473 K, 1523 K and the salt samples were collected after equilibration. Studies were conducted in the range of 10%-50% by weight additions of LaF3 in the equimolar LiF-BaF2(1:1) base fluoride salt bath. Solubility of UO2 increased with rise in LaF3 concentration in the molten fluoride in the temperature range of 1423 K-1523 K. At a given concentration of LaF3, the UO2 solubility increased monotonously with temperature. With mixed solvent, when UF4 was added as a replacement of part of LaF3 in LiF-BaF2(1:1)-10 wt% LaF3 and LiF-BaF2(1:1)-30 wt% LaF3, there was an enhancement of solubility of UO2.

Carbothermic Synthesis of ~820- m UN Kernels. Investigation of Process Variables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindemer, Terrence; Silva, Chinthaka M; Henry, Jr, John James

2015-06-01

This report details the continued investigation of process variables involved in converting sol-gel-derived, urainia-carbon microspheres to ~820-μm-dia. UN fuel kernels in flow-through, vertical refractory-metal crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO 3-H 2O-C microspheres in Ar and H 2-containing gases, conversion of the resulting UO 2-C kernels to dense UO 2:2UC in the same gases and vacuum, and its conversion in N 2 to in UC 1-xN x. The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO 2:2UC kernel of ~96% theoretical densitymore » was required, but its subsequent conversion to UC 1-xN x at 2123 K was not accompanied by sintering and resulted in ~83-86% of theoretical density. Decreasing the UC 1-xN x kernel carbide component via HCN evolution was shown to be quantitatively consistent with present and past experiments and the only useful application of H2 in the entire process.« less

An Automatic Critical Care Urine Meter

PubMed Central

Otero, Abraham; Fernández, Roemi; Apalkov, Andrey; Armada, Manuel

2012-01-01

Nowadays patients admitted to critical care units have most of their physiological parameters measured automatically by sophisticated commercial monitoring devices. More often than not, these devices supervise whether the values of the parameters they measure lie within a pre-established range, and issue warning of deviations from this range by triggering alarms. The automation of measuring and supervising tasks not only discharges the healthcare staff of a considerable workload but also avoids human errors in these repetitive and monotonous tasks. Arguably, the most relevant physiological parameter that is still measured and supervised manually by critical care unit staff is urine output (UO). In this paper we present a patent-pending device that provides continuous and accurate measurements of patient's UO. The device uses capacitive sensors to take continuous measurements of the height of the column of liquid accumulated in two chambers that make up a plastic container. The first chamber, where the urine inputs, has a small volume. Once it has been filled it overflows into a second bigger chamber. The first chamber provides accurate UO measures of patients whose UO has to be closely supervised, while the second one avoids the need for frequent interventions by the nursing staff to empty the container. PMID:23201988

Further observations on OCOM MOX fuel: microstructure in the vicinity of the pellet rim and fuel — cladding interaction

NASA Astrophysics Data System (ADS)

Walker, C. T.; Goll, W.; Matsumura, T.

1997-06-01

The fuel investigated was manufactured by Siemens-KWU and irradiated at low rating in the KWO reactor in Germany. The MOX agglomerates in the cold outer region of the fuel shared several common features with the high burn-up structure at the rim of UO 2 fuel. It is proposed that in both cases the mechanism producing the microstructure change is recrystallisation. Further, it is shown that surface MOX agglomerates do not noticeably retard cladding creepdown although they swell into the gap. The contracting cladding appears able to push the agglomerates back into the fuel. The thickness of the oxide layer on the inner cladding surface increased at points where contact with surface MOX agglomerates had occurred. Despite this, the mean thickness of the oxide did not differ significantly from that found in UO 2 fuel rods of like design. It is judged that the high burn-up structure will form in the UO 2 matrix when the local burn-up there reaches 60 to 80 GWd/tM. Limiting the MOX scrap addition in the UO 2 matrix will delay its formation.

Enhanced thermal conductivity of uranium dioxide-silicon carbide composite fuel pellets prepared by Spark Plasma Sintering (SPS)

NASA Astrophysics Data System (ADS)

Yeo, S.; Mckenna, E.; Baney, R.; Subhash, G.; Tulenko, J.

2013-02-01

Uranium dioxide (UO2)-10 vol% silicon carbide (SiC) composite fuel pellets were produced by oxidative sintering and Spark Plasma Sintering (SPS) at a range of temperatures from 1400 to 1600 °C. Both SiC whiskers and SiC powder particles were utilized. Oxidative sintering was employed over 4 h and the SPS sintering was employed only for 5 min at the highest hold temperature. It was noted that composite pellets sintered by SPS process revealed smaller grain size, reduced formation of chemical products, higher density, and enhanced interfacial contact compared to the pellets made by oxidative sintering. For given volume of SiC, the pellets with powder particles yielded a smaller grain size than pellets with SiC whiskers. Finally thermal conductivity measurements at 100 °C, 500 °C, and 900 °C revealed that SPS sintered UO2-SiC composites exhibited an increase of up to 62% in thermal conductivity compared to UO2 pellets, while the oxidative sintered composite pellets revealed significantly inferior thermal conductivity values. The current study points to the improved processing capabilities of SPS compared to oxidative sintering of UO2-SiC composites.

Reinvestigation of the uranium(3.5+) rare-earth oxysulfides "(UO)2LnS3" (Ln = Yb, Y).

PubMed

Jin, Geng Bang; Choi, Eun Sang; Ibers, James A

2009-09-07

Dark-red square plates of the previously reported compounds "(UO)(2)LnS(3)" (Ln = Yb, Y) have been synthesized by solid-state reactions of UOS and YbS or Y(2)S(3) with Sb(2)S(3) as a flux at 1273 K. The structure of these isotypic compounds was reinvestigated by single-crystal X-ray diffraction methods and an inductively coupled plasma experiment. The actual formula of "(UO)(2)LnS(3)" (Ln = Yb, Y) is (U(0.5)Ln(0.5)O)(2)LnS(3), that is, ULn(2)O(2)S(3), which can be charge-balanced with U(4+) and Ln(3+). The layered structure comprises (U/Ln)O(4)S(4) square antiprisms alternating with LnS(6) octahedra. U and Ln1 atoms disorder on the eight-coordinate metal position, but Ln2 atoms occupy the six-coordinate metal position exclusively. UYb(2)O(2)S(3) is a modified Curie-Weiss paramagnet between 293 and 32 K, below which part of the paramagnetic moments go through a possible ferromagnetic transition. The band gaps of ULn(2)O(2)S(3) (Ln = Yb, Y) are around 2 eV.

High Pressure Low Temperature X-Ray Diffraction Studies of UO2 and UN single crystals.

NASA Astrophysics Data System (ADS)

Antonio, Daniel; Mast, Daniel; Lavina, Barbara; Gofryk, Krzysztof

Uranium dioxide is the most commonly used nuclear fuel material in commercial reactors, while uranium nitride also has many thermal and physical properties that make it attractive for potential use in reactors. Both have a cubic fcc lattice structure at ambient conditions and transition to antiferromagnetic order at low temperature. UO2 is a Mott insulator that orders in a complex non-collinear 3k magnetic structure at about 30 K, while UN has appreciable conductivity and orders in a simpler 1k magnetic structure below 52 K. Both compounds are characterized by strong magneto-structural interactions, understanding of which is vital for modeling their thermo-physical properties. While UO2 and UN have been extensively studied at and above room temperature, little work has been done to directly study the structure of these materials at low temperatures where magnetic interactions are dominant. In the course of our systematic studies on magneto vibrational behavior of UO2 and UN, here we present our recent results of high pressure X-Ray Diffraction (up to 35 GPa) measured below the Neel temperature using synchrotron radiation. Work supported by the Department of Energy, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division.

Performance Refactoring of Instrumentation, Measurement, and Analysis Technologies for Petascale Computing. The PRIMA Project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malony, Allen D.; Wolf, Felix G.

2014-01-31

The growing number of cores provided by today’s high-­end computing systems present substantial challenges to application developers in their pursuit of parallel efficiency. To find the most effective optimization strategy, application developers need insight into the runtime behavior of their code. The University of Oregon (UO) and the Juelich Supercomputing Centre of Forschungszentrum Juelich (FZJ) develop the performance analysis tools TAU and Scalasca, respectively, which allow high-­performance computing (HPC) users to collect and analyze relevant performance data – even at very large scales. TAU and Scalasca are considered among the most advanced parallel performance systems available, and are used extensivelymore » across HPC centers in the U.S., Germany, and around the world. The TAU and Scalasca groups share a heritage of parallel performance tool research and partnership throughout the past fifteen years. Indeed, the close interactions of the two groups resulted in a cross-­fertilization of tool ideas and technologies that pushed TAU and Scalasca to what they are today. It also produced two performance systems with an increasing degree of functional overlap. While each tool has its specific analysis focus, the tools were implementing measurement infrastructures that were substantially similar. Because each tool provides complementary performance analysis, sharing of measurement results is valuable to provide the user with more facets to understand performance behavior. However, each measurement system was producing performance data in different formats, requiring data interoperability tools to be created. A common measurement and instrumentation system was needed to more closely integrate TAU and Scalasca and to avoid the duplication of development and maintenance effort. The PRIMA (Performance Refactoring of Instrumentation, Measurement, and Analysis) project was proposed over three years ago as a joint international effort between UO and FZJ to accomplish these objectives: (1) refactor TAU and Scalasca performance system components for core code sharing and (2) integrate TAU and Scalasca functionality through data interfaces, formats, and utilities. As presented in this report, the project has completed these goals. In addition to shared technical advances, the groups have worked to engage with users through application performance engineering and tools training. In this regard, the project benefits from the close interactions the teams have with national laboratories in the United States and Germany. We have also sought to enhance our interactions through joint tutorials and outreach. UO has become a member of the Virtual Institute of High-­Productivity Supercomputing (VI-­HPS) established by the Helmholtz Association of German Research Centres as a center of excellence, focusing on HPC tools for diagnosing programming errors and optimizing performance. UO and FZJ have conducted several VI-­HPS training activities together within the past three years.« less

Performance Refactoring of Instrumentation, Measurement, and Analysis Technologies for Petascale Computing: the PRIMA Project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malony, Allen D.; Wolf, Felix G.

2014-01-31

The growing number of cores provided by today’s high-end computing systems present substantial challenges to application developers in their pursuit of parallel efficiency. To find the most effective optimization strategy, application developers need insight into the runtime behavior of their code. The University of Oregon (UO) and the Juelich Supercomputing Centre of Forschungszentrum Juelich (FZJ) develop the performance analysis tools TAU and Scalasca, respectively, which allow high-performance computing (HPC) users to collect and analyze relevant performance data – even at very large scales. TAU and Scalasca are considered among the most advanced parallel performance systems available, and are used extensivelymore » across HPC centers in the U.S., Germany, and around the world. The TAU and Scalasca groups share a heritage of parallel performance tool research and partnership throughout the past fifteen years. Indeed, the close interactions of the two groups resulted in a cross-fertilization of tool ideas and technologies that pushed TAU and Scalasca to what they are today. It also produced two performance systems with an increasing degree of functional overlap. While each tool has its specific analysis focus, the tools were implementing measurement infrastructures that were substantially similar. Because each tool provides complementary performance analysis, sharing of measurement results is valuable to provide the user with more facets to understand performance behavior. However, each measurement system was producing performance data in different formats, requiring data interoperability tools to be created. A common measurement and instrumentation system was needed to more closely integrate TAU and Scalasca and to avoid the duplication of development and maintenance effort. The PRIMA (Performance Refactoring of Instrumentation, Measurement, and Analysis) project was proposed over three years ago as a joint international effort between UO and FZJ to accomplish these objectives: (1) refactor TAU and Scalasca performance system components for core code sharing and (2) integrate TAU and Scalasca functionality through data interfaces, formats, and utilities. As presented in this report, the project has completed these goals. In addition to shared technical advances, the groups have worked to engage with users through application performance engineering and tools training. In this regard, the project benefits from the close interactions the teams have with national laboratories in the United States and Germany. We have also sought to enhance our interactions through joint tutorials and outreach. UO has become a member of the Virtual Institute of High-Productivity Supercomputing (VI-HPS) established by the Helmholtz Association of German Research Centres as a center of excellence, focusing on HPC tools for diagnosing programming errors and optimizing performance. UO and FZJ have conducted several VI-HPS training activities together within the past three years.« less

From {sub {infinity}}{sup 1}[(UO{sub 2}){sub 2}O(MoO{sub 4}){sub 4}]{sup 6-} to {sub {infinity}}{sup 1}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})]{sup 6-} infinite chains in A{sub 6}U{sub 2}Mo{sub 4}O{sub 21} (A=Na, K, Rb, Cs) compounds: Synthesis and crystal structure of Cs{sub 6}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagoubi, S.; Groupe de Radiochimie, Institut de Physique Nucleaire d'Orsay, Universite Paris-Sud XI, 91406 Orsay Cedex; Obbade, S., E-mail: said.obbade@phelma.grenoble-inp.f

2011-05-15

A new caesium uranyl molybdate belonging to the M{sub 6}U{sub 2}Mo{sub 4}O{sub 21} family has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. Contrary to the other alkali uranyl molybdates of this family (A=Na, K, Rb) where molybdenum atoms adopt only tetrahedral coordination and which can be formulated A{sub 6}[(UO{sub 2}){sub 2}O(MoO{sub 4}){sub 4}], the caesium compound Cs{sub 6}U{sub 2}Mo{sub 4}O{sub 21} should be written Cs{sub 6}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})] with molybdenum atoms in tetrahedral and square pyramidal environments. Cs{sub 6}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})] crystallizes in the triclinic symmetry withmore » space group P1-bar and a=10.4275(14) A, b=15.075(2) A, c=17.806(2) A, {alpha}=70.72(1){sup o}, {beta}=80.38(1){sup o} and {gamma}=86.39(1){sup o}, V=2604.7(6) A{sup 3}, Z=4, {rho}{sub mes}=5.02(2) g/cm{sup 3} and {rho}{sub cal}=5.08(3) g/cm{sup 3}. A full-matrix least-squares refinement on the basis of F{sup 2} yielded R{sub 1}=0.0464 and wR{sub 2}=0.0950 for 596 parameters with 6964 independent reflections with I{>=}2{sigma}(I) collected on a BRUKER AXS diffractometer with Mo(K{alpha}) radiation and a CCD detector. The crystal structure of Cs compound is characterized by {sub {infinity}}{sup 1}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})]{sup 6-} parallels chains built from U{sub 2}O{sub 13} dimeric units, MoO{sub 4} tetrahedra and MoO{sub 5} square pyramids, whereas, Na, K and Rb compounds are characterized by {sub {infinity}}{sup 1}[(UO{sub 2}){sub 2}O(MoO{sub 4}){sub 4}]{sup 6-} parallel chains formulated simply of U{sub 2}O{sub 13} units and MoO{sub 4} tetrahedra. Infrared spectroscopy measurements using powdered samples synthesized by solid-state reaction, confirm the structural results. The thermal stability and the electrical conductivity are also studied. The four compounds decompose at low temperature (between 540 and 610 {sup o}C). -- Graphical abstract: The staking of {sub {infinity}}{sup 1}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})]{sup 6-} infinite uranyl molybdate ribbons in the Cs{sub 6}[(UO{sub 2}){sub 2}(MoO{sub 4}){sub 3}(MoO{sub 5})] structure. Display Omitted Highlights: {yields} Cs{sub 6}U{sub 2}Mo{sub 4}O{sub 2} a new compound with bidimensional crystal structure, characterized by infinite uranyl molybdate chains. {yields} Crystal structure similar to these of the compounds containing Na, K, Rb. {yields} Molybdenum atoms surrounded by five oxygen atoms to form an original and strongly distorted MoO{sub 5} environment. {yields} The chains arrangement illustrates the key role of the alkaline ionic radius, in the crystal structure distortion for Cs compound.« less

Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

NASA Astrophysics Data System (ADS)

Odorowski, Mélina; Jegou, Christophe; De Windt, Laurent; Broudic, Véronique; Jouan, Gauthier; Peuget, Sylvain; Martin, Christelle

2017-12-01

In the hypothesis of direct disposal of spent fuel in a geological nuclear waste repository, interactions between the fuel mainly composed of UO2 and its environment must be understood. The dissolution rate of the UO2 matrix, which depends on the redox conditions on the fuel surface, will have a major impact on the release of radionuclides into the environment. The reducing conditions expected for a geological disposal situation would appear to be favorable as regards the solubility and stability of the UO2 matrix, but may be disturbed on the surface of irradiated fuel. In particular, the local redox conditions will result from a competition between the radiolysis effects of water under alpha irradiation (simultaneously producing oxidizing species like H2O2, hydrogen peroxide, and reducing species like H2, hydrogen) and those of redox active species from the environment. In particular, Fe2+, a strongly reducing aqueous species coming from the corrosion of the iron canister or from the host rock, could influence the dissolution of the fuel matrix. The effect of iron on the oxidative dissolution of UO2 was thus investigated under the conditions of the French disposal site, a Callovian-Oxfordian clay formation chosen by the French National Radioactive Waste Management Agency (Andra), here tested under alpha irradiation. For this study, UO2 fuel pellets doped with a radioactive alpha emitter (238/239Pu) were leached in synthetic Callovian-Oxfordian groundwater (representative of the French waste disposal site groundwater) in the presence of a metallic iron foil to simulate the steel canister. The pellets had varying levels of alpha activity, in order to modulate the concentrations of species produced by water radiolysis on the surface and to simulate the activity of aged spent fuel after 50 and 10,000 years of alpha radioactivity decay. The experimental data showed that whatever the sample alpha radioactivity, the presence of iron inhibits the oxidizing dissolution of UO2 and leads to low uranium concentrations (between 4 × 10-10 and 4 × 10-9 M), through a reactional mechanism located in the very first microns of the UO2/water reactional interface. The mechanism involves consumption of oxidizing species, in particular of H2O2 by Fe2+ at the precise place where these species are produced, and is accompanied by the precipitation of an akaganeite-type Fe3+ hydroxide on the surface. The higher the radioactivity of the samples, the greater the precipitation induced. Modeling has been developed, coupling chemistry with transport and based on the main reactional mechanisms identified, which enables accurate reproduction of the mineralogy of the system under study, giving the nature of the phases under observation as well as the location of their precipitation. Obviously without excluding a potential contribution from the hydrogen produced by the anoxic corrosion of the iron foil, this study has shown that iron plays a major role in this oxidizing dissolution inhibition process for the system investigated (localized alpha radiolysis). This inhibitor effect associated with iron is therefore strongly dependent on the location of the redox front, which is found on the surface in the case of alpha irradiation UO2/water reactional interface.

Synchrotron X-ray characterization of mackinawite and uraninite relevant to bio-remediation of groundwater contaminated with uranium

NASA Astrophysics Data System (ADS)

Carpenter, J.; Hyun, S.; Hayes, K. F.

2010-12-01

Uranium (U) originating from mining operations for weapon manufacturing and nuclear energy production is a significant radionuclide contaminant in groundwater local to uranium mining, uranium milling, and uranium mill tailing (UMT) storage sites. In the USA, the Department of Energy (DOE) is currently overseeing approximately 24 Uranium Mill Tailing Remediation Action (UMTRA) sites which have collectively processed over 27 million tons of uranium ore1,2. In-Situ microbial bio-reduction of the highly mobile U6+ ion into the dramatically less mobile U4+ ion has been demonstrated as an effective remedial process to inhibit uranium migration in the aqueous phase3. The resistance of this process to oxidization and possible remobilization of U when bioremediation stops (and oxidants such as oxygen from the air or nitrate in water diffuse into the formation) in the long term is not known. UMTRA site studies3 have shown that iron sulfide solids are produced by sulfate reducing bacteria (SRB) during U bioremediation, and some forms of these iron sulfide solids are known to be effective oxidant scavengers, potentially protecting against re-oxidation and thus remobilization of U. This work is investigating the role of iron sulfide solids in the long-term immobilization of reduced U compounds after bioremediation is completed in groundwater local to UMTRA sites. Re-oxidation tests are being performed in packed media columns loaded with both FeS and U solids. High quality mackinawite (FeS), and uraninite (UO2) have been synthesized in our laboratory via a wet chemistry approach. These synthetic materials are expected to mimic the naturally occurring and biogenic materials present in biologically stimulated UMTRA sites. In order to establish the initial conditions of the prepared experimental columns and to compare synthetic and biogenic FeS and UO2, these synthesized materials have been characterized with synchrotron radiation at the Stanford Synchrotron Radiation Lightsource using synchrotron x-ray powder diffraction (SXRD) and extended x-ray absorption fine structure (EXAFS). SXRD data were collected and analyzed with profile fitting to determine lattice parameters and crystallite size for comparison with published values for both biogenic and synthetic materials. This is particularly of interest for UO2, as there is very little information on particle size and lattice parameters for synthetic UO2 in the literature. Profile fitting of the SXRD data for FeS gives lattice parameters of a = b = 3.668 and a mean crystallite size of 5 to 8 nm. Both of these values are in good agreement with published values. For fresh UO2, lattice parameters were determined as a = b = c = 5.4 nm for both freshly synthesized and aged (3 months) UO2 and particle size was determined to be 3.5 nm for fresh UO2 and 5.83 nm for aged UO2. This suggests a growth mechanism for crystallites over time, and an inferred decrease in reactivity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivenet, Murielle; Vigier, Nicolas; Roussel, Pascal

Six new layered uranyl vanadates (NH{sub 4}){sub 2}[(UO{sub 2}){sub 2}V{sub 2}O{sub 8}] (1), (H{sub 2}EN)[(UO{sub 2}){sub 2}V{sub 2}O{sub 8}] (2), (H{sub 2}DAP)[(UO{sub 2}){sub 2}V{sub 2}O{sub 8}] (3), (H{sub 2}PIP)[(UO{sub 2}){sub 2}(VO{sub 4}){sub 2}].0,8H{sub 2}O (4), (H{sub 2}DMPIP)[(UO{sub 2}){sub 2}V{sub 2}O{sub 8}] (5), (H{sub 2}DABCO)[(UO{sub 2}){sub 2}(VO{sub 4}){sub 2}] (6) were prepared from mild-hydrothermal reactions using 1,2-ethylenediamine (EN); 1,3-diaminopropane (DAP); piperazine (PIP); 1-methylpiperazine (MPIP); 1,4-diazabicyclo[2,2,2]octane (DABCO). The structures of 1, 4, 5 and 6 were solved using single-crystal X-ray diffraction data while the structural models of 2 and 3 were established from powder X-ray diffraction data. In compounds 1, 2, 3more » and 5, the uranyl-vanadate layers are built from dimers of edge-shared UO{sub 7} pentagonal bipyramids and dimers of edge-shared VO{sub 5} square pyramids further connected through edge-sharing. In 1 and 3, the layers are identical to that occurring in the carnotite group of uranyl-vanadates. In 2 and 5, the V{sub 2}O{sub 8} dimers differ in orientation leading to a new type of layer. The layers of compound 4 and 6 are built from chains of edge-shared UO{sub 7} pentagonal bipyramids connected by VO{sub 4} tetrahedra and are of uranophane-type anion topology. For the six compounds, the ammonium or organoammonium cation resides in the space between the inorganic layers. Crystallographic data: 1 monoclinic, space group P2{sub 1}/c with a=6.894(2), b=8.384(3), c=10.473(4) A and {beta}=106.066(5){sup o}, 2 monoclinic, space group P2{sub 1}/a with a=13.9816(6), b=8.6165(3), c=10.4237(3) A and {gamma}=93.125(3){sup o}, 3 orthorhombic, space group Pmcn with a=14.7363(8), b=8.6379(4) and c=10.4385(4) A, 4 monoclinic, space group C2/m with a=15.619(2), b=7.1802(8), c=6.9157(8) A and {beta}=101.500(2){sup o}, 5 monoclinic, space group P2{sub 1}/b with a=9.315(2), b=8.617(2), c=10.5246(2) A and {gamma}=114.776(2){sup o}, 6 monoclinic, space group C2/m with a=17.440(2), b=7.1904(9), c=6.8990(8) A and {beta}=98.196(2){sup o}. - Graphical abstract: The three types of layer in layered uranyl-vanadates using diamine as a structure-directing agent.« less

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x

DOE Office of Scientific and Technical Information (OSTI.GOV)

Conradson, Steven D.; Andersson, David A.; Boland, Kevin S.

Mixed valence O-doped UO 2+x and photoexcited UO 2 containing transitory U 3+ and U 5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Fröhlich-type, nonequilibrium, phonon-coupled Bose-Einstein condensate whose stability and coherence are amplified by collective, anharmonic motions of atoms and charges. Complementary to the available, detailed, real space information from scattering and EXAFS, an outstanding question is the electronic structure. Mapping the Mott gap in UO 2, U 4O 9, and U 3O 7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f statesmore » of the valence band by ~0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2–2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO 2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied U5f states of UO 2 and no hot electrons. 3.1 eV excitation, however, complements the O-doping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO 2 therefore fulfills the criteria for a nonequilibrium condensate. The electron distributions resulting from both excitations persist for 5–10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: (1) the direct formation of both of these long lived (>3–10 ps) excited states without the short lived nonthermal intermediate; (2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and (3) the absence of hot electrons accompanying the insulating UO 2 excited state. This heterogeneous, nonequilibrium, Fröhlich BEC stabilized by a Fano-Feshbach resonance therefore continues to exhibit unique properties.« less

Potassium and magnesium succinatouranilates – Synthesis and crystal structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novikov, S.A., E-mail: serg.alex.novikov@gmail.com; Grigoriev, M.S.; Serezhkina, L.B.

2017-04-15

Single crystal X-ray diffraction has been applied to determine the structures of two new uranyl coordination polymers: K{sub 2}[(UO{sub 2}){sub 2}(C{sub 4}H{sub 4}O{sub 4}){sub 3}] (1) and [Mg(H{sub 2}O){sub 6}] [(UO{sub 2}){sub 2}(C{sub 4}H{sub 4}O{sub 4}){sub 3}]·2H{sub 2}O (2), where C{sub 4}H{sub 4}O{sub 4}{sup 2-} is succinate anion. Crystals of 1 and 2 contain polymeric complex anions [(UO{sub 2}){sub 2}(C{sub 4}H{sub 4}O{sub 4}){sub 3}]{sup 2-} with the same A{sub 2}Q{sup 02}{sub 3} crystallochemical formula (A=UO{sub 2}{sup 2+}, Q{sup 02}=C{sub 4}O{sub 4}H{sub 4}{sup 2-}), and have layered (1) or chain (2) structure. It has been found, that conformation of succinate ionsmore » is one of the factors, which affects the structure of [(UO{sub 2}){sub 2}(C{sub 4}H{sub 4}O{sub 4}){sub 3}]{sup 2-} anions. IR spectra of these new compounds are in good agreement with crystallographic data. Topological analysis of the uranium dicarboxylates with A{sub 2}Q{sup 02}{sub 3} crystallochemical formula has shown the presence of five isomers which differ from each other in coordination sequences and / or dimensionality. - Graphical abstract: Crystal structures of two new uranium(VI) coordination polymers with succinate linkers, namely K{sub 2}[(UO{sub 2}){sub 2}(C{sub 4}H{sub 4}O{sub 4}){sub 3}] (1) and [Mg(H{sub 2}O){sub 6}][(UO{sub 2}){sub 2}(C{sub 4}H{sub 4}O{sub 4}){sub 3}]·2H{sub 2}O (2), were determined by single-crystal XRD. Crystals of studied compounds are based on 2D or 1D structural units with the same composition and crystallochemical formula. Topological isomerism in A{sub 2}Q{sup 02}{sub 3} crystallochemical group and conformations of succinate anions in uranyl complexes are under discussion. - Highlights: • Two new uranium coordination polymers were synthesized. • Their structural units have the same composition and crystallochemical formula. • In spite the same composition and CCF dimensionality of units is different. • Structural features of uranyl CPs are affected by linker conformations.« less

Selection of Nuclear Fuel for TREAT: UO 2 vs U 3O 8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glazoff, Michael Vasily; Van Rooyen, Isabella Johanna; Coryell, Benjamin David

The Transient Reactor Test (TREAT) that resides at the Materials and Fuels Complex (MFC) at Idaho National Laboratory (INL), first achieved criticality in 1959, and successfully performed many transient tests on nuclear fuel until 1994 when its operations were suspended. Resumption of operations at TREAT was approved in February 2014 to meet the U.S. Department of Energy (DOE) Office of Nuclear Energy’s objectives in transient testing of nuclear fuels. The National Nuclear Security Administration’s is converting TREAT from its existing highly enriched uranium (HEU) core to a new core containing low enriched uranium (LEU) (i.e., U-235< 20% by weight). Themore » TREAT Conversion project is currently progressing with conceptual design phase activities. Dimensional stability of the fuel element assemblies, predictable fuel can oxidation and sufficient heat conductivity by the fuel blocks are some of the critical performance requirements of the new LEU fuel. Furthermore, to enable the design team to design fuel block and can specifications, it is amongst the objectives to evaluate TREAT LEU fuel and cladding material’s chemical interaction. This information is important to understand the viability of Zr-based alloys and fuel characteristics for the fabrication of the TREAT LEU fuel and cladding. Also, it is very important to make the right decision on what type of nuclear fuel will be used at TREAT. In particular, one has to consider different oxides of uranium, and most importantly, UO 2 vs U 3O 8. In this report, the results are documented pertaining to the choice mentioned above (UO 2 vs U 3O 8). The conclusion in favor of using UO 2 was made based on the analysis of historical data, up-to-date literature, and self-consistent calculations of phase equilibria and thermodynamic properties in the U-O and U-O-C systems. The report is organized as follows. First, the criteria that were used to make the choice are analyzed. Secondly, existing historical data and current literature were reviewed. This analysis was supplemented by the construction and examination of the U-O and U-O-C phase diagrams at pressure close to negligent, thereby mimicking the conditions in which nuclear fuel is supposed to function inside the zirconium-based cladding in the reactor. Finally, our conclusion in favor of the UO 2 down selection was summarized and explained in the last Section of this document.« less

Summary report on UO 2 thermal conductivity model refinement and assessment studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiang-Yang; Cooper, Michael William Donald; Mcclellan, Kenneth James

Uranium dioxide (UO 2) is the most commonly used fuel in light water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, therefore, governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models were replaced with models that incorporate explicit thermal conductivity degradation mechanisms during fuel burn-up. This approach is able to represent the degradation of thermal conductivity due to eachmore » individual defect type, rather than the overall burn-up measure typically used which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO 2 thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham type interatomic potential and a potential that combines the many-body embedded atom method potential with Morse-Buckingham pair potentials. Potential parameters for UO 2+x and ZrO 2 are developed for the latter potential. Physical insights from the resonant phonon-spin scattering mechanism due to spins on the magnetic uranium ions have been introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high-temperature model typically used in fuel performance codes. The model is validated by comparison to low-temperature experimental measurements on single crystal hyper-stoichiometric UO 2+x samples and high-temperature literature data. Ongoing works include investigation of the effect of phase separation to UO 2+U 4O 9 on the low temperature thermal conductivity of UO 2+x, and modeling of thermal conductivity using the Green-Kubo method. Ultimately, this work will enable more accurate fuel performance simulations as well as extension to new fuel types and operating conditions, all of which improve the fuel economics of nuclear energy and maintain high fuel reliability and safety.« less

Multinuclear NMR Study of the Pressure Dependence for Carbonate Exchange in the UO 2(CO 3) 3 4-(aq) Ion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Rene L.; Harley, Stephen J.; Ohlin, C. André

2011-09-16

Rates of carbonate exchange by two pH-sensitive pathways between aqueous carbonate ion and UO 2(CO 3) 3 4-(aq) (see picture) are measured by high-pressure NMR. To accomplish this, a custom pulse sequence is employed to achieve selective inversion. Rates of chemical exchange are determined by modeling the return to equilibrium.

Building Adaptive Game-Based Learning Resources: The Integration of IMS Learning Design and

ERIC Educational Resources Information Center

Burgos, Daniel; Moreno-Ger, Pablo; Sierra, Jose Luis; Fernandez-Manjon, Baltasar; Specht, Marcus; Koper, Rob

2008-01-01

IMS Learning Design (IMS-LD) is a specification to create units of learning (UoLs), which express a certain pedagogical model or strategy (e.g., adaptive learning with games). However, the authoring process of a UoL remains difficult because of the lack of high-level authoring tools for IMS-LD, even more so when the focus is on specific topics,…

Studies in the Phonology of Asian Languages VI: Complex Syllable Nuclei in Vietnamese.

ERIC Educational Resources Information Center

Han, Mieko S.

This study is the sixth in the series "Studies in the Phonology of Asian Languages." A phonetic and phonemic analysis of the three complex nuclei of Vietnames (Hanoi dialect), spelled (1) ye-, -ie-, -ia, (2) -u'o'-, -u'a, and (3) -uo-, -ua, was carried out using the sound spectrograph. The relative domains of the target qualities of the…

Characterisation of high temperature refractory ceramics for nuclear applications

NASA Astrophysics Data System (ADS)

Bottomley, P. D. W.; Wiss, Th; Janssen, A.; Cremer, B.; Thiele, H.; Manara, D.; Scheindlin, M.; Murray-Farthing, M.; Lajarge, P.; Menna, M.; Bouexière, D.; Rondinella, V. V.

2012-03-01

The ternary oxide ceramic system UO2-ZrO2-FeO is a refractory system that is of great relevance to the nuclear industry as it represents one of the main systems resulting from the interaction of the Zircaloy cladding, the UO2 fuel and the structural elements of a nuclear reactor. It is particularly the high temperature properties that require investigation; that is, when substantial overheating of the nuclear core occurs and interactions can lead to its degradation, melting and result in a severe nuclear accident. There has been much work on the UO2-ZrO2 system and also on the ternary system with FeO but there is still a need to examine 2 further aspects; firstly the effect of sub-oxidized systems, the UO2-Zr and FeO-Zr systems, and secondly the effect of Fe/Zr or Fe/U ratios on the melting point of the U-Zr-Fe oxide system. Samples of UO2-Zr and UO2-ZrO2-FeO were fabricated at ITU and then characterized by optical microscopy (OM) and X-ray diffraction to determine the ceramic's structure and verify the composition. Thereafter the samples are to be melted by laser flash heating and their liquidus and solidus temperatures determined by pyrometry. This programme is currently ongoing. The frozen samples, after testing, were then sectioned, polished and the molten zone micro-analytically examined by OM & SEM-EDS in order to determine its structure and composition and to compare with the existing phase diagrams. Examples of results from these systems will be given. Finally, a reacted Zr-FeO thermite mixture was examined, which had been used to generate high temperatures during tests of reactor melt-concrete interactions. The aim was to assess the reaction and estimate the heat generation from this novel technique. These results allow verification or improvement of the phase diagram and are of primary importance as input to models used to predict materials interactions in a severe nuclear accident.

Extended study on oxidation behaviors of UN0.68 and UN1.66 by XPS

NASA Astrophysics Data System (ADS)

Luo, Lizhu; Hu, Yin; Pan, Qifa; Long, Zhong; Lu, Lei; Liu, Kezhao; Wang, Xiaolin

2018-04-01

The surface oxidation behaviors of UN0.68 and UN1.66 thin films are investigated by X-ray photoelectron spectroscopy (XPS), and the traditional U4f/N1s, O1s, valence band spectra as well as the unconventional U4d and U5d spectra are collected for the understanding of their oxidation behavior in-depth. Similar asymmetrical peak shape of the U4f spectra to uranium is observed for both uranium nitrides, despite of a slight shift to higher energy side for UN1.66 clean surface. However, significant difference among the corresponding spectra of UN0.68 and UN1.66 during oxidation reveals the distinctive properties of each own. The coexistence of UO2-x, UO2 and UO2-x.Ny on UN0.68 surface results in the peculiar features of U4f spectra as well as the others within the XPS energy scale, where peaks of the oxidized species firstly shift to higher energy side compared to the clean surface, and then return closely towards those of stoichiometric UO2. For UN1.66, the generation of U-N-O ternary compounds on the surface is identified with the symmetrical U4f peaks at 379.9eV and 390.8 eV, which locate intermediate between UO2 and UN1.66, and gradually expanding to higher energy side during the progressive oxidation. Furthermore, the formation of N-O species on UN1.66 surface is also detected as an oxidation product. The metallic character of UN1.66 is identified by the intense signal at Fermi level, which is greatly suppressed by the increasing oxygen exposure and implies the weakening metallic properties of the as-generated U-N-O compounds. Higher uranium oxides, such as UO3 and U4O9, are deduced to be the final oxidation products, and a multistage mechanism for UN1.66 following the exposure to oxygen is discussed.

A manpower calculus: the implications of SUO fellowship expansion on oncologic surgeon case volumes.

PubMed

See, William A

2014-01-01

Society of Urologic Oncology (SUO)-accredited fellowship programs have undergone substantial expansion. This study developed a mathematical model to estimate future changes in urologic oncologic surgeon (UOS) manpower and analyzed the effect of those changes on per-UOS case volumes. SUO fellowship program directors were queried as to the number of positions available on an annual basis. Current US UOS manpower was estimated from the SUO membership list. Future manpower was estimated on an annual basis by linear senescence of existing manpower combined with linear growth of newly trained surgeons. Case-volume estimates for the 4 surgical disease sites (prostate, kidney/renal pelvis, bladder, and testes) were obtained from the literature. The future number of major cases was determined from current volumes based upon the US population growth rates and the historic average annual change in disease incidence. Two models were used to predict future per-UOS major case volumes. Model 1 assumed the current distribution of cases between nononcologic surgeons and UOS would continue. Model 2 assumed a progressive redistribution of cases over time such that in 2043 100% of major urologic cancer cases would be performed by UOSs. Over the 30-year period to "manpower steady-state" SUO-accredited UOSs practicing in the United States have the potential to increase from approximately 600 currently to 1,650 in 2043. During this interval, case volumes are predicted to change 0.97-, 2.4-, 1.1-, and 1.5-fold for prostatectomy, nephrectomy, cystectomy, and retroperitoneal lymph node dissection, respectively. The ratio of future to current total annual case volumes is predicted to be 0.47 and 0.9 for models 1 and 2, respectively. The number of annual US practicing graduates necessary to achieve a future to current case-volume ratio greater than 1 is 25 and 49 in models 1 and 2, respectively. The current number of SUO fellowship trainees has the potential to decrease future per-UOS case volumes relative to current levels. Redistribution of existing case volume or a decrease in the annual number of trainees or both would be required to insure sufficient surgical volumes for skill maintenance and optimal patient outcomes. Published by Elsevier Inc.

Analysis of key safety metrics of thorium utilization in LWRs

DOE PAGES

Ade, Brian J.; Bowman, Stephen M.; Worrall, Andrew; ...

2016-04-08

Here, thorium has great potential to stretch nuclear fuel reserves because of its natural abundance and because it is possible to breed the 232Th isotope into a fissile fuel ( 233U). Various scenarios exist for utilization of thorium in the nuclear fuel cycle, including use in different nuclear reactor types (e.g., light water, high-temperature gas-cooled, fast spectrum sodium, and molten salt reactors), along with use in advanced accelerator-driven systems and even in fission-fusion hybrid systems. The most likely near-term application of thorium in the United States is in currently operating light water reactors (LWRs). This use is primarily based onmore » concepts that mix thorium with uranium (UO 2 + ThO 2) or that add fertile thorium (ThO 2) fuel pins to typical LWR fuel assemblies. Utilization of mixed fuel assemblies (PuO 2 + ThO 2) is also possible. The addition of thorium to currently operating LWRs would result in a number of different phenomenological impacts to the nuclear fuel. Thorium and its irradiation products have different nuclear characteristics from those of uranium and its irradiation products. ThO 2, alone or mixed with UO 2 fuel, leads to different chemical and physical properties of the fuel. These key reactor safety–related issues have been studied at Oak Ridge National Laboratory and documented in “Safety and Regulatory Issues of the Thorium Fuel Cycle” (NUREG/CR-7176, U.S. Nuclear Regulatory Commission, 2014). Various reactor analyses were performed using the SCALE code system for comparison of key performance parameters of both ThO 2 + UO 2 and ThO 2 + PuO 2 against those of UO 2 and typical UO 2 + PuO 2 mixed oxide fuels, including reactivity coefficients and power sharing between surrounding UO 2 assemblies and the assembly of interest. The decay heat and radiological source terms for spent fuel after its discharge from the reactor are also presented. Based on this evaluation, potential impacts on safety requirements and identification of knowledge gaps that require additional analysis or research to develop a technical basis for the licensing of thorium fuel are identified.« less

K 2x Sn 4-x S 8-x (x = 0.65–1): a new metal sulfide for rapid and selective removal of Cs + , Sr 2+ and UO 2 2+ ions

DOE PAGES

Sarma, Debajit; Malliakas, Christos D.; Subrahmanyam, K. S.; ...

2015-10-27

The fission of uranium produces radionuclides, 137Cs and 90Sr, which are major constituents of spent nuclear fuel. The half-life of 137Cs and 90Sr is nearly 30 years and thus that makes them harmful to human life and the environment. The selective removal of these radionuclides in the presence of high salt concentrations from industrial nuclear waste is necessary for safe storage. We report the synthesis and crystal structure of K 2xSn 4-xS 8-x (x = 0.65–1, KTS-3) a material which exhibits excellent Cs +, Sr 2+ and UO 2 2+ ion exchange properties in varying conditions. Furthermore, the compound adoptsmore » a layered structure which consists of exchangeable potassium ions sandwiched between infinite layers of octahedral and tetrahedral tin centers. K 2xSn 4-xS 8-x (x = 0.65–1, KTS-3) crystallizes in the monoclinic space group P2 1/c with cell parameters a = 13.092(3) Å, b = 16.882(2) Å, c = 7.375(1) Å and β = 98.10(1)°. Refinement of the single crystal diffraction data revealed the presence of Sn vacancies in the tetrahedra that are long range ordered. The interlayer potassium ions of KTS-3 can be exchanged for Cs +, Sr 2+ and UO 2 2+. KTS-3 exhibits rapid and efficient ion exchange behavior in a broad pH range. The distribution coefficients (K d) for KTS-3 are high for Cs + (5.5 × 10 4), Sr 2+ (3.9 × 10 5) and UO 2 2+ (2.7 × 10 4) at neutral pH (7.4, 6.9, 5.7 ppm Cs +, Sr 2+ and UO 2 2+, respectively; V/m ~ 1000 mL g -1). KTS-3 exhibits impressive Cs +, Sr 2+ and UO 2 2+ ion exchange properties in high salt concentration and over a broad pH range, which coupled with the low cost, environmentally friendly nature and facile synthesis underscores its potential in treating nuclear waste.« less

Analysis of cardiopulmonary stress during endoscopy: Is unsedated transnasal esophagogastroduodenoscopy appropriate for elderly patients?

PubMed Central

Uchiyama, Kazuhiko; Ishikawa, Takeshi; Sakamoto, Naoyuki; Kajikawa, Hirokazu; Takagi, Tomohisa; Handa, Osamu; Tatsumi, Yoshihide; Yagi, Nobuaki; Naito, Yuji; Itoh, Yoshito; Takemura, Shuhei

2014-01-01

BACKGROUND: Transnasal esophagogastroduodenoscopy (EGD) without sedation has been reported to be safe and tolerable. It has recently been used widely in Japan for the detection of upper gastrointestinal disease. Alternatively, transoral examination using a thin endoscope has also been reported to be highly tolerable. OBJECTIVE: To examine the cardiocirculatory effects of transoral versus transnasal EGD in an attempt to determine the most suitable endoscopic methods for patients ≥75 years of age. METHODS: Subjects who underwent monitoring of respiratory and circulatory dynamics without sedation during endoscopic screening examinations were enrolled at the New Ooe Hospital (Kyoto, Japan) between April 2008 and March 2009. A total of 165 patients (age ≥75 years) provided written informed consent and were investigated in the present study. Patients were randomly divided into three subgroups: UO group – thin endoscope; SO group – standard endoscope; and UT group – transnasal EGD. Percutaneous arterial blood oxygen saturation, heart rate and blood pressure were evaluated just before EGD and at five time points during EGD. After transnasal EGD, patients who had previously been examined using transoral EGD with a standard endoscope were asked about preferences for their next examination. RESULTS: There were no statistical differences in the characteristics among the groups. Percutaneous oxygen saturation in the UT group showed a transient drop compared with the SO and UO groups at the beginning of the endoscopic procedure. Heart rate showed no significant differences among the SO, UO and UT groups; Systolic blood pressure in the UO group was lower immediately after insertion compared with the SO and UT groups. The rate pressure product in the UO group was comparable with that in the UT group during endoscopy, and the SO group showed a continuously higher level than the UO and UT groups. More than one-half (54.4%) of patients were ‘willing to choose transnasal EGD for next examination’. CONCLUSIONS: For elderly patients, unsedated transnasal EGD failed to show an advantage over unsedated standard endoscopy. Transoral thin EGD was estimated to be safe and tolerable. PMID:24288691

The Key Role of U28 in the Aqueous Self-Assembly of Uranyl Peroxide Nanocages.

PubMed

Falaise, Clément; Nyman, May

2016-10-04

For 11 years now, the structural diversity and aesthetic beauty of uranyl-peroxide capsules have fascinated researchers from the diverse fields of mineralogy, polyoxometalate chemistry, and nuclear fuel technologies. There is still much to be learned about the mechanisms of the self-assembly process, and the role of solution parameters including pH, alkali template, temperature, time, and others. Here we have exploited the high solubility of the UO2 (2+) /H2 O2 /LiOH aqueous system to address the effect of the hydroxide concentration. Important techniques of this study are single-crystal X-ray diffraction, small-angle X-ray scattering, and Raman spectroscopy. Three key phases dominate the solution speciation as a function of time and the LiOH/UO2 (2+) ratio: the uranyl-triperoxide monomer [UO2 (O2 )3 ](4-) and the two capsules [(UO2 )(O2 )(OH)]24 (24-) (U24 ) and [(UO2 )(O2 )1.5 ]28 (28-) (U28 ). When the LiOH/U ratio is around three, U28 forms rapidly and this cluster can be isolated in high yield and purity. This result was most surprising and challenges the hypothesis that alkali templating is the most important determinant in the cluster geometry. Moreover, analogous experiments with KOH, NH4 OH, and TEAOH (TEA=tetraethylammonium) also rapidly yield U28 , which suggests that U28 is the kinetically favored species. Complete mapping of the pH-time phase space reveals only a narrow window of the U28 dominance, which is why it was previously overlooked as an important kinetic species in this chemical system, as well as others with different counterions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Flash sintering of stoichiometric and hyper-stoichiometric urania

DOE PAGES

Valdez, James Anthony; Byler, Darrin David; Kardoulaki, Erofili; ...

2018-03-29

Flash sintering (FS), a novel fabrication technique belonging to the family of field assisted sintering (FAS) techniques, has been utilized in this study to fabricate uranium dioxide (UO 2) pellets. Stoichiometric (UO 2.00) and hyper-stoichiometric (UO 2.16) pellets were flash sintered at 600 °C within a few (2–3) minutes. This is in sharp contrast to conventional sintering where temperatures hundreds of degrees higher are necessary and the sintering time extends to hours. Relating this in terms of the homologous temperature ratio (T H) for both conditions shows that in the case of flash sintering at 600 °C, T H =more » 0.3 versus T H = 0.6 for conventional sintering at 1600 °C. The highest density achieved for a UO 2.00 pellet was 81% theoretical density (TD) when flash sintered at 600 °C for 184 s at a field of 188 V/cm and a current density of 442 mA/mm 2. For the UO 2.16 pellet, the highest achieved density was 92% TD when flash sintered at 600 °C for 140 s at a field of 188 V/cm and a current density of 632 mA/mm 2. X-ray diffraction (XRD) characterization of the sintered pellets showed the final sintered material to be single cubic fluorite phase. Scanning electron microscopy (SEM) of longitudinal sections revealed non-uniform microstructures with regions of high density where the grain size ranged from 1 to 15 μm. Comparisons between conventionally and flash sintered pellets that achieved equivalent shrinkage strains were also conducted. Lastly, in all cases, the flash sintered pellets achieved similar densification to the conventionally sintered pellets at much lower furnace temperatures and shorter times.« less

Local structure in solid solutions of stabilised zirconia with actinide dioxides (UO{sub 2}, NpO{sub 2})

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walter, Marcus, E-mail: marcus.walter@vkta.d; Somers, Joseph; Bouexiere, Daniel

2011-04-15

The local structure of (Zr,Lu,U)O{sub 2-x} and (Zr,Y,Np)O{sub 2-x} solid solutions has been investigated by extended X-ray absorption fine structure (EXAFS). Samples were prepared by mixing reactive (Zr,Lu)O{sub 2-x} and (Zr,Y)O{sub 2-x} precursor materials with the actinide oxide powders, respectively. Sintering at 1600 {sup o}C in Ar/H{sub 2} yields a fluorite structure with U(IV) and Np(IV). As typical for stabilised zirconia the metal-oxygen and metal-metal distances are characteristic for the different metal ions. The bond lengths increase with actinide concentration, whereas highest adaptation to the bulk stabilised zirconia structure was observed for U---O and Np---O bonds. The Zr---O bond showsmore » only a slight increase from 2.14 A at 6 mol% actinide to 2.18 A at infinite dilution in UO{sub 2} and NpO{sub 2}. The short interatomic distance between Zr and the surrounding oxygen and metal atoms indicate a low relaxation of Zr with respect to the bulk structure, i.e. a strong Pauling behaviour. -- Graphical abstract: Metal-oxygen bond distances in (Zr,Lu,U)O{sub 2-x} solid solutions with different oxygen vacancy concentrations (Lu/Zr=1 and Lu/Zr=0.5). Display Omitted Research Highlights: {yields} EXAFS indicates high U and Np adaption to the bulk structure of stabilised zirconia. {yields} Zr---O bond length is 2.18 A at infinite Zr dilution in UO{sub 2} and NpO{sub 2}. {yields} Low relaxation (strong Pauling behaviour) of Zr explains its low solubility in UO{sub 2}.« less

Both lavender fleur oil and unscented oil aromatherapy reduce preoperative anxiety in breast surgery patients: a randomized trial.

PubMed

Franco, Lola; Blanck, Thomas J J; Dugan, Kimberly; Kline, Richard; Shanmugam, Geetha; Galotti, Angela; von Bergen Granell, Annelise; Wajda, Michael

2016-09-01

The objective of this study was to determine whether lavender fleur oil (LFO) aromatherapy would reduce anxiety when administered to women before undergoing breast surgery. This was a single-site, randomized study comparing the effect of LFO to unscented oil (UO). The study was conducted in the preoperative holding area of the ambulatory surgery department of NYU Langone Medical Center. Ninety three women, 18 years and older, scheduled for breast surgery. Women meeting inclusion/exclusion criteria were randomized to either LFO or UO aromatherapy and were blind to their assigned treatment. Subjects completed a Speilberger State Anxiety Inventory for Adults (STAI) before and after aromatherapy. Vital signs were recorded before and after aromatherapy. STAI-State questions were divided into positive and negative emotions for analysis. Before aromatherapy, there was no significant difference between groups by individual questions or overall average answer of either positive or negative questions. The use of both LFO and UO increased the positive STAI score totals, with the LFO group having a slightly, but statistically significant, greater increase. Both resulted in a statistically significant decrease in the negative score totals after treatment. There were no differences in vital signs between groups for either treatment. Following the conclusion of the trial LFO was analyzed and found to contain a very low content of the 2 major Lavandula angustifolia constituents. Both LFO and UO aromatherapy treatments lowered anxiety before surgery despite no significant changes in vital signs. LFO treatment generated a slight but statistically significant increase in positive feelings compared with UO treatment. It is probable that the beneficial effect observed was due to both aromatherapy with LFO and a placebo effect related to the added attention given to the patients. Copyright © 2016 Elsevier Inc. All rights reserved.

Flash sintering of stoichiometric and hyper-stoichiometric urania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valdez, James Anthony; Byler, Darrin David; Kardoulaki, Erofili

Flash sintering (FS), a novel fabrication technique belonging to the family of field assisted sintering (FAS) techniques, has been utilized in this study to fabricate uranium dioxide (UO 2) pellets. Stoichiometric (UO 2.00) and hyper-stoichiometric (UO 2.16) pellets were flash sintered at 600 °C within a few (2–3) minutes. This is in sharp contrast to conventional sintering where temperatures hundreds of degrees higher are necessary and the sintering time extends to hours. Relating this in terms of the homologous temperature ratio (T H) for both conditions shows that in the case of flash sintering at 600 °C, T H =more » 0.3 versus T H = 0.6 for conventional sintering at 1600 °C. The highest density achieved for a UO 2.00 pellet was 81% theoretical density (TD) when flash sintered at 600 °C for 184 s at a field of 188 V/cm and a current density of 442 mA/mm 2. For the UO 2.16 pellet, the highest achieved density was 92% TD when flash sintered at 600 °C for 140 s at a field of 188 V/cm and a current density of 632 mA/mm 2. X-ray diffraction (XRD) characterization of the sintered pellets showed the final sintered material to be single cubic fluorite phase. Scanning electron microscopy (SEM) of longitudinal sections revealed non-uniform microstructures with regions of high density where the grain size ranged from 1 to 15 μm. Comparisons between conventionally and flash sintered pellets that achieved equivalent shrinkage strains were also conducted. Lastly, in all cases, the flash sintered pellets achieved similar densification to the conventionally sintered pellets at much lower furnace temperatures and shorter times.« less

Dehydration of Uranyl Nitrate Hexahydrate to Uranyl Nitrate Trihydrate under Ambient Conditions as Observed via Dynamic Infrared Reflectance Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Timothy J.; Sweet, Lucas E.; Meier, David E.

2015-05-22

the hexahydrate [UO 2(NO 3) 2(H 2O) 6] (UNH) and the trihydrate [UO 2(NO 3) 2(H 2O) 3] (UNT) forms. Their stabilities depend on both relative humidity and temperature. Both phases have previously been studied by infrared transmission spectroscopy, but the data were limited by both instrumental resolution and the ability to prepare the samples as pellets without desiccating them. We report time-resolved infrared (IR) measurements using an integrating sphere that allow us to observe the transformation from the hexahydrate to the trihydrate simply by flowing dry nitrogen gas over the sample. Hexahydrate samples were prepared and confirmed via knownmore » XRD patterns, then measured in reflectance mode. The hexahydrate has a distinct uranyl asymmetric stretch band at 949.0 cm -1 that shifts to shorter wavelengths and broadens as the sample dehydrates and recrystallizes to the trihydrate, first as a blue edge shoulder but ultimately resulting in a doublet band with reflectance peaks at 966 and 957 cm -1. The data are consistent with transformation from UNH to UNT since UNT has two non-equivalent UO 2 2+ sites. The dehydration of UO 2(NO 3) 2(H 2O) 6 to UO 2(NO 3) 2(H 2O) 3 is both a morphological and structural change that has the lustrous lime green crystals changing to the dull greenish yellow of the trihydrate. Crystal structures and phase transformation were confirmed theoretically using DFT calculations and experimentally via microscopy methods. Both methods showed a transformation with two distinct sites for the uranyl cation in the trihydrate, as opposed to a single crystallographic site in the hexahydrate.« less

MEASURING THE MASS OF 4UO900-40 DYNAMICALLY

NASA Technical Reports Server (NTRS)

Dolan, J. F.; Etzel, Paul B.; Boyd, Patricia T.

2006-01-01

Accurate measurements of neutron star masses are needed to constrain the equation of state of neutron star matter - of importance to both particle physics and the astrophysics of neutron stars - and to identify the evolutionary track of the progenitor stars that form neutron stars. The best measured values of the mass of 4UO900-40 (= Vela XR-l), 1.86 +/- 0.16 Msun (Barziv et al. 2001) and 1.93 +/- 0.20 Msun (Abubekerov et al. 2004), make it a leading candidate for the most massive neutron star known. The direct relationship between the maximum mass of neutron stars and the equation of state of ultra-dense matter makes 4UO900-40 an important neutron star mass to determine accurately. The confidence interval on previous mass estimates, obtained from observations that include parameters determined by non-dynamical methods, are not small enough to significantly restrict possible equations of state. We describe here a purely dynamical method for determining the mass of 4UO900-40, an X-ray pulsar, using the reprocessed UV pulses emitted by its BO.5Ib companion. One can derive the instantaneous radial velocity of each component by simultaneous X-ray and UV observations at the two quadratures of the system. The Doppler shift caused by the primary's rotational velocity and the illumination pattern of the X-rays on the primary, two of the three principal contributors to the uncertainty on the derived mass of the neutron star, almost exactly cancel by symmetry in this method. A heuristic measurement of the mass of 4UO900-40 using observations obtained previously with the High Speed Photometer on HST is given in Appendix A.

Flash sintering of stoichiometric and hyper-stoichiometric urania

NASA Astrophysics Data System (ADS)

Valdez, J. A.; Byler, D. D.; Kardoulaki, E.; Francis, J. S. C.; McClellan, K. J.

2018-07-01

Flash sintering (FS), a novel fabrication technique belonging to the family of field assisted sintering (FAS) techniques, has been utilized in this study to fabricate uranium dioxide (UO2) pellets. Stoichiometric (UO2.00) and hyper-stoichiometric (UO2.16) pellets were flash sintered at 600 °C within a few (2-3) minutes. This is in sharp contrast to conventional sintering where temperatures hundreds of degrees higher are necessary and the sintering time extends to hours. Relating this in terms of the homologous temperature ratio (TH) for both conditions shows that in the case of flash sintering at 600 °C, TH = 0.3 versus TH = 0.6 for conventional sintering at 1600 °C. The highest density achieved for a UO2.00 pellet was 81% theoretical density (TD) when flash sintered at 600 °C for 185 s at a field of 188 V/cm and a current density of 442 mA/mm2. For the UO2.16 pellet, the highest achieved density was 91% TD when flash sintered at 600 °C for 123 s at a field of 188 V/cm and a current density of 632 mA/mm2. X-ray diffraction (XRD) characterization of the sintered pellets showed the final sintered material to be single cubic fluorite phase. Scanning electron microscopy (SEM) of longitudinal sections revealed non-uniform microstructures with regions of high density where the grain size ranged from 1 to 15 μm. Comparisons between conventionally and flash sintered pellets that achieved equivalent shrinkage strains were also conducted. In all cases, the flash sintered pellets achieved similar densification to the conventionally sintered pellets at much lower furnace temperatures and shorter times.

Determination of trace uranium by resonance fluorescence method coupled with photo-catalytic technology and dual cloud point extraction.

PubMed

Li, Jiekang; Li, Guirong; Han, Qian

2016-12-05

In this paper, two kinds of salophens (Sal) with different solubilities, Sal1 and Sal2, have been respectively synthesized, and they all can combine with uranyl to form stable complexes: [UO2(2+)-Sal1] and [UO2(2+)-Sal2]. Among them, [UO2(2+)-Sal1] was used as ligand to extract uranium in complex samples by dual cloud point extraction (dCPE), and [UO2(2+)-Sal2] was used as catalyst for the determination of uranium by photocatalytic resonance fluorescence (RF) method. The photocatalytic characteristic of [UO2(2+)-Sal2] on the oxidized pyronine Y (PRY) by potassium bromate which leads to the decrease of RF intensity of PRY were studied. The reduced value of RF intensity of reaction system (ΔF) is in proportional to the concentration of uranium (c), and a novel photo-catalytic RF method was developed for the determination of trace uranium (VI) after dCPE. The combination of photo-catalytic RF techniques and dCPE procedure endows the presented methods with enhanced sensitivity and selectivity. Under optimal conditions, the linear calibration curves range for 0.067 to 6.57ngmL(-1), the linear regression equation was ΔF=438.0 c (ngmL(-1))+175.6 with the correlation coefficient r=0.9981. The limit of detection was 0.066ngmL(-1). The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0-103.5%. The mechanisms of the indicator reaction and dCPE are discussed. Copyright © 2016 Elsevier B.V. All rights reserved.

Theoretical studies of UO(2)(OH)(H(2)O)(n) (+), UO(2)(OH)(2)(H(2)O)(n), NpO(2)(OH)(H(2)O)(n), and PuO(2)(OH)(H(2)O)(n) (+) (n

PubMed

Cao, Zhiji; Balasubramanian, K

2009-10-28

Extensive ab initio calculations have been carried out to study equilibrium structures, vibrational frequencies, and the nature of chemical bonds of hydrated UO(2)(OH)(+), UO(2)(OH)(2), NpO(2)(OH), and PuO(2)(OH)(+) complexes that contain up to 21 water molecules both in first and second hydration spheres in both aqueous solution and the gas phase. The structures have been further optimized by considering long-range solvent effects through a polarizable continuum dielectric model. The hydrolysis reaction Gibbs free energy of UO(2)(H(2)O)(5) (2+) is computed to be 8.11 kcal/mol at the MP2 level in good agreement with experiments. Our results reveal that it is necessary to include water molecules bound to the complex in the first hydration sphere for proper treatment of the hydrated complex and the dielectric cavity although water molecules in the second hydration sphere do not change the coordination complex. Structural reoptimization of the complex in a dielectric cavity seems inevitable to seek subtle structural variations in the solvent and to correlate with the observed spectra and thermodynamic properties in the aqueous environment. Our computations reveal dramatically different equilibrium structures in the gas phase and solution and also confirm the observed facile exchanges between the complex and bulk solvent. Complete active space multiconfiguration self-consistent field followed by multireference singles+doubles CI (MRSDCI) computations on smaller complexes confirm predominantly single-configurational nature of these species and the validity of B3LYP and MP2 techniques for these complexes in their ground states.

The initial stage of uranium oxidation: mechanism of UO(2) scale formation in the presence of a native lateral stress field.

PubMed

Chernia, Z; Ben-Eliyahu, Y; Kimmel, G; Braun, G; Sariel, J

2006-11-23

In this work, an oxidation model for alpha-uranium is presented. It describes the internally lateral stress field built in the oxide scale during the reaction. The thickness of the elastic, stress-preserving oxide (UO(2+x)) scale is less than 0.5 microm. A lateral, 6.5 GPa stress field has been calculated from strains derived from line shifts (delta(2theta)) as measured by the X-ray diffraction of UO(2). It is shown that in the elastic growth domain, (110) is the main UO(2) growth plane for gas-solid oxidation. The diffusion-limited oxidation mechanism discussed here is based on the known "2:2:2" cluster theory which describes the mechanism of fluorite-based hyperstoichiometric oxides. In this study, it is adapted to describe oxygen-anion hopping. Anion hopping toward the oxide-metal interface proceeds at high rates in the [110] direction, hence making this pipeline route the principal growth direction in UO(2) formation. It is further argued that growth in the pure elastic domain of the oxide scale should be attributed entirely to anion hopping in 110. Anions, diffusing isotropically via grain boundaries and cracks, are shown to have a significant impact on the overall oxidation rate in relatively thick (>0.35 microm) oxide scales if followed by an avalanche break off in the postelastic regime. Stress affects oxidation in the elastic domain by controlling the hopping rate directly. In the postelastic regime, stress weakens hopping, indirectly, by enhancing isotropic diffusion. Surface roughness presents an additional hindering factor for the anion hopping. In comparison to anisotropic hopping, diffusion of isotropic hopping has a lower activation energy barrier. Therefore, a relatively stronger impact at lower temperatures due to isotropic diffusion is displayed.

E-beam and UV induced fabrication of CeO2, Eu2O3 and their mixed oxides with UO2

NASA Astrophysics Data System (ADS)

Pavelková, Tereza; Vaněček, Vojtěch; Jakubec, Ivo; Čuba, Václav

2016-07-01

CeO2, Eu2O3 and mixed oxides of CeO2-UO2, Eu2O3-UO2 were fabricated. The preparative method was based on the irradiation of aqueous solutions containing cerium/europium (and uranyl) nitrates and ammonium formate. In the course of irradiation, the solid phase (precursor) was precipitated. The composition of irradiated solutions significantly affected the properties of precursor formed in the course of the irradiation. However, subsequent heat treatment of (amorphous) precursors at temperatures ≤650 °C invariably resulted in the formation of powder oxides with well-developed nanocrystals with linear crystallite size 13-27 nm and specific surface area 10-46 m2 g-1. The applicability of both ionizing (e-beam) and non-ionizing (UV) radiation was studied.

Evaluation of melting point of UO 2 by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Arima, Tatsumi; Idemitsu, Kazuya; Inagaki, Yaohiro; Tsujita, Yuichi; Kinoshita, Motoyasu; Yakub, Eugene

2009-06-01

The melting point of UO 2 has been evaluated by molecular dynamics simulation (MD) in terms of interatomic potential, pressure and Schottky defect concentration. The Born-Mayer-Huggins potentials with or without a Morse potential were explored in the present study. Two-phase simulation whose supercell at the initial state consisted of solid and liquid phases gave the melting point comparable to the experimental data using the potential proposed by Yakub. The heat of fusion was determined by the difference in enthalpy at the melting point. In addition, MD calculations showed that the melting point increased with pressure applied to the system. Thus, the Clausius-Clapeyron equation was verified. Furthermore, MD calculations clarified that an addition of Schottky defects, which generated the local disorder in the UO 2 crystal, lowered the melting point.

URANIUM DIOXIDE OXIDATION WITH FORMING INTERMEDIATE PHASES (in German)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scheibe, H.; Ermischer, W.

1964-02-01

An experimental study was made of the UO/sub 2/ to U/sub 3/O/sub 8/ oxidation process. At low temperatures, depending on the activity of the powder, the oxidation of UO/sub 2/ yield a U/sub 3/O/sub 7/ shell around the UO/sub 2/ grain (160 to 220 deg C). Further oxidation is determined by the diffusion of oxygen through this shell and yields U/sub 5/O/sub 12/ (280 to 290 deg C). Their follows U/sub 5/O/sub (375 to 400 deg C) and finally U/sub 3/O/sub 8/ as more oxigen is absorbed. No further increase of the oxygen content occurs up to 800 deg C.more » The exothermal effects established through differential thermal analysis may be due to lattice transformation. (OTS)« less

Recuperation of uranyl ions from effluents by means of microbiological collectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cecal, A.; Palamaru, I.; Humelnicu, D.

1997-12-31

This paper deals with the study of bioaccumulation of uranyl ions (UO{sub 2}{sup 2+}) from industrial effluents, using microbiological collectors: Nostoc linkia sp., Tolipotrix sp., Spirulina sp., Porphyridium cruentum and also the glucide extract of P. cruentum. The values of retaining degree of UO{sub 2}{sup 2+} on the biomass, for several experimental conditions, were established between 14.22 and 91.99%.

Evaluation of a biological wastewater treatment system combining an OSA process with ultrasound for sludge reduction.

PubMed

Romero-Pareja, P M; Aragon, C A; Quiroga, J M; Coello, M D

2017-05-01

Sludge production is an undesirable by-product of biological wastewater treatment. The oxic-settling-anaerobic (OSA) process constitutes one of the most promising techniques for reducing the sludge produced at the treatment plant without negative consequences for its overall performance. In the present study, the OSA process is applied in combination with ultrasound treatment, a lysis technique, in a lab-scale wastewater treatment plant to assess whether sludge reduction is enhanced as a result of mechanical treatment. Reported sludge reductions of 45.72% and 78.56% were obtained for the two regimes of combined treatment tested in this study during two respective stages: UO1 and UO2. During the UO1 stage, the general performance and nutrient removal improved, obtaining 47.28% TN removal versus 21.95% in the conventional stage. However, the performance of the system was seriously damaged during the UO2 stage. Increases in dehydrogenase and protease activities were observed during both stages. The advantages of the combined process are not necessarily economic, but operational, as US treatment acts as contributing factor in the OSA process, inducing mechanisms that lead to sludge reduction in the OSA process and improving performance parameters. Copyright © 2016 Elsevier B.V. All rights reserved.

Developing the OORCC: A Multifaceted Astronomical Research and Outreach Facility at the University of Oregon

NASA Astrophysics Data System (ADS)

Kwan, Teiler J.; Bullis, Jeremy; Gustafsson, Annika; Fisher, Robert Scott

2015-01-01

The University of Oregon (UO) owns and operates Pine Mountain Observatory (PMO), located in central Oregon on the summit of Pine Mountain at an elevation of 1980 meters. PMO consists of four telescopes ranging in size from 0.35 - 0.8 meters. The Oregon Observatory Remote Control Center (OORCC) is a remote-observing center within the Department of Physics on the UO campus (~140 miles from the observatory) that has a direct connection to PMO through a dedicated fiber-optic cable. With this facility, we will enable UO undergraduate student researchers, UO faculty, and the non-scientific community to fully control and operate a newly installed robotic telescope on the summit of Pine Mountain from Eugene, or any other authorized site in Oregon. In addition to providing undergraduates with instrumentation and engineering experience, we will implement research by photometrically monitoring bright and variable astronomical sources including main belt comets, Herbig Ae/Be stars, and active galactic nuclei in extragalactic systems. The primary objective with the OORCC is to manage a multifaceted astronomy and astrophysics research facility, extending as a state-wide resource for K-12 STEM activities and public outreach programs. With the OORCC, we intend to bring unique and enriching astronomy exposure to many different groups of people throughout the state of Oregon.

Gas emission from the UO2 samples, containing fission products and burnable absorber

NASA Astrophysics Data System (ADS)

Kopytin, V. P.; Baranov, V. G.; Burlakova, M. A.; Tenishev, A. V.; Kuzmin, R. S.; Pokrovskiy, S. A.; Mikhalchik, V. V.

2016-04-01

The process gas released from the fuel pellets of uranium fuel during fuel burn-up reduces the thermal conductivity of the rod-shell gap, enhances hydrogen embrittlement of the cladding material, causes it's carbonization, as well as transport processes in the fuel. In this study a technique of investigating the thermal desorption of gases from the UO2 fuel material were perfected in the temperature range 300-2000 K for uniform sample heating rate of 15 K/min in vacuum. The characteristic kinetic dependences are acquired for the gas emission from UO2 samples, containing simulators of fission products (SFP) and the burnable neutron absorber (BNA). Depending on the amount of SFP and BNA contained in the sample thermal desorption gas spectra (TDGS) vary. The composition of emitted gas varies, as well as the number of peaks in the TDGS and the peaks shift to higher temperatures. This indicates that introduction of SFPs and BNA alters the sample material structure and cause the creation of so- called traps which have different bonding energies to the gases. The traps can be a grid of dislocations, voids, and contained in the UO2 matrix SFP and BNA. Similar processes will occur in the fuel pellets in the real conditions of the Nuclear Power Plant as well.

Oxygen transport in off-stoichiometric uranium dioxide mediated by defect clustering dynamics

DOE PAGES

Yu, Jianguo; Bai, Xian -Ming; El-Azab, Anter; ...

2015-03-05

In this study, oxygen transport is central to many properties of oxides such as stoichiometric changes, phase transformation and ionic conductivity. In this paper, we report a mechanism for oxygen transport in uranium dioxide (UO 2) in which the kinetics is mediated by defect clustering dynamics. In particular, the kinetic Monte Carlo (KMC) method has been used to investigate the kinetics of oxygen transport in UO 2 under the condition of creation and annihilation of oxygen vacancies and interstitials as well as oxygen interstitial clustering, with variable offstoichiometry and temperature conditions. It is found that in hypo-stoichiometric UO 2-x, oxygenmore » transport is well described by the vacancy diffusion mechanism while in hyper-stoichiometric UO 2+x, oxygen interstitial cluster diffusion contributes significantly to oxygen transport kinetics, particularly at high temperatures and high off-stoichiometry levels. It is also found that diinterstitial clusters and single interstitials play dominant roles in oxygen diffusion while other larger clusters have negligible contributions. However, the formation, coalescence and dissociation of these larger clusters indirectly affects the overall oxygen diffusion due to their interactions with mono and di-interstitials, thus providing a explanation of the experimental observation of saturation or even drop of oxygen diffusivity at high off-stoichiometry.« less

Thermodynamics of fission products in dispersion fuel designs - first principles modeling of defect behavior in bulk and at interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiang-yand; Uberuaga, Blas P; Nerikar, Pankaj

2009-01-01

Density functional theory (DFT) calculations of fission product (Xe, Sr, and Cs) incorporation and segregation in alkaline earth metal oxides, HfO{sub 2} and UO{sub 2} oxides, and the MgO/(U, Hf, Ce)O{sub 2} interfaces have been carried out. In the case of UO{sub 2}, the calculations were performed using spin polarization and with a Hubbard U term characterizing the on-sit Coulomb repulsion between the localized 5f electrons. The fission product solution energies in bulk UO{sub 2{+-}x} have been calculated as a function of non-stoichiometry x, and were compared to that in MgO. These calculations demonstrate that the fission product incorporation energiesmore » in MgO are higher than in HfO{sub 2}. However, this trend is reversed or reduced for alkaline earth oxides with larger cation sizes. The solution energies of fission products in MgO are substantially higher than in UO{sub 2{+-}x}, except for the case of Sr in the hypostoichiometric case. Due to size effects, the thermodynamic driving force of segregation for Xe and Cs from bulk MgO to the MgO/fluorite interface is strong. However, this driving force is relatively weak for Sr.« less

In-situ TEM observation of nano-void formation in UO2 under irradiation

NASA Astrophysics Data System (ADS)

Sabathier, C.; Martin, G.; Michel, A.; Carlot, G.; Maillard, S.; Bachelet, C.; Fortuna, F.; Kaitasov, O.; Oliviero, E.; Garcia, P.

2014-05-01

Transmission electron microscopy (TEM) observations of UO2 polycrystals irradiated in situ with 4 MeV Au ions were performed at room temperature (RT) to better understand the mechanisms of cavity and ultimately fission products nucleation in UO2. Experiments were carried out at the JANNuS Orsay facility that enables in situ ion irradiations inside the microscope to be carried out. The majority of 4 MeV gold ions were transmitted through the thin foil, and the induced radiation defects were investigated by TEM. Observations showed that nano-void formation occurs at ambient temperature in UO2 thin foils irradiated with energetic heavy ions under an essentially nuclear energy loss regime. The diameter and density of nano-objects were measured as a function of the gold irradiation dose at RT. A previous paper has also revealed a similar nano-object population after a Xe implantation performed at 390 keV at 870 K. The nano-object density was modelled using simple concepts derived from Classical Molecular Dynamics simulations. The results are in good agreement, which suggests a mechanism of heterogeneous nucleation induced by energetic cascade overlaps. This indicates that nano-void formation mechanism is controlled by radiation damage. Such nanovoids are likely to act as sinks for mobile fission products during reactor operation.

Analysis and Implementation of Accident Tolerant Nuclear Fuels

NASA Astrophysics Data System (ADS)

Prewitt, Benjamin Joseph

To improve the reliability and robustness of LWR, accident tolerant nuclear fuels and cladding materials are being developed to possibly replace the current UO2/zirconium system. This research highlights UN and U3Si 2, two of the most favorable accident tolerant fuels being developed. To evaluate the commercial feasiblilty of these fuels, two areas of research were conducted. Chemical fabrication routes for both fuels were investigated in detail, considering UO2 and UF6 as potential starting materials. Potential pathways for industrial scale fabrication using these methods were discussed. Neutronic performance of 70%UN-30%U3Si2 composite was evaluated in MNCP using PWR assembly and core models. The results showed comparable performance to an identical UO2 fueled simulation with the same configuration. The parameters simulated for composite and oxide fuel include the following: fuel to moderator ratio curves; energy dependent flux spectra; temperature coefficients for fuel and moderator; delayed neutron fractions; power peaking factors; axial and radial flux profiles in 2D and 3D; burnup; critical boron concentration; and shutdown margin. Overall, the neutronic parameters suggest that the transition from UO2 to composite in existing nuclear systems will not require significant changes in operating procedures or modifications to standards and regulations.

Quantification of process variables for carbothermic synthesis of UC 1-xN x fuel microspheres

DOE PAGES

Lindemer, Terrance B.; Silva, Chinthaka M.; Henry, Jr, John James; ...

2016-11-05

This report details the continued investigation of process variables involved in converting sol-gel-derived, urania-carbon microspheres to ~820-μm-dia. UC 1-xN x fuel kernels in flow-through, vertical Mo and W crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO 3-H 2O-C microspheres in Ar and H 2-containing gases, conversion of the resulting UO 2-C kernels to dense UO2:2UC in the same gases and vacuum, and its conversion in N 2 to UC 1-xN x (x = ~0.85). The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO 2:2UCmore » kernel of ~96% theoretical density was required, but its subsequent conversion to UC 1-xN x at 2123 K was not accompanied by sintering and resulted in ~83-86% of theoretical density. Increasing the UC 1-xN x kernel nitride component to ~0.98 in flowing N 2-H 2 mixtures to evolve HCN was shown to be quantitatively consistent with present and past experiments and the only useful application of H 2 in the entire process.« less

Chemical compatibility between UO2 fuel and SiC cladding for LWRs. Application to ATF (Accident-Tolerant Fuels)

NASA Astrophysics Data System (ADS)

Braun, James; Guéneau, Christine; Alpettaz, Thierry; Sauder, Cédric; Brackx, Emmanuelle; Domenger, Renaud; Gossé, Stéphane; Balbaud-Célérier, Fanny

2017-04-01

Silicon carbide-silicon carbide (SiC/SiC) composites are considered to replace the current zirconium-based cladding materials thanks to their good behavior under irradiation and their resistance under oxidative environments at high temperature. In the present work, a thermodynamic analysis of the UO2±x/SiC system is performed. Moreover, using two different experimental methods, the chemical compatibility of SiC towards uranium dioxide, with various oxygen contents (UO2±x) is investigated in the 1500-1970 K temperature range. The reaction leads to the formation of mainly uranium silicides and carbides phases along with CO and SiO gas release. Knudsen Cell Mass Spectrometry is used to measure the gas release occurring during the reaction between UO2+x and SiC powders as function of time and temperature. These experimental conditions are representative of an open system. Diffusion couple experiments with pellets are also performed to study the reaction kinetics in closed system conditions. In both cases, a limited chemical reaction is observed below 1700 K, whereas the reaction is enhanced at higher temperature due to the decomposition of SiC leading to Si vaporization. The temperature of formation of the liquid phase is found to lie between 1850 < T < 1950 K.

Development of Macroscale Models of UO 2 Fuel Sintering and Densification using Multiscale Modeling and Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenquist, Ian; Tonks, Michael

2016-10-01

Light water reactor fuel pellets are fabricated using sintering to final densities of 95% or greater. During reactor operation, the porosity remaining in the fuel after fabrication decreases further due to irradiation-assisted densification. While empirical models have been developed to describe this densification process, a mechanistic model is needed as part of the ongoing work by the NEAMS program to develop a more predictive fuel performance code. In this work we will develop a phase field model of sintering of UO 2 in the MARMOT code, and validate it by comparing to published sintering data. We will then add themore » capability to capture irradiation effects into the model, and use it to develop a mechanistic model of densification that will go into the BISON code and add another essential piece to the microstructure-based materials models. The final step will be to add the effects of applied fields, to model field-assisted sintering of UO 2. The results of the phase field model will be validated by comparing to data from field-assisted sintering. Tasks over three years: 1. Develop a sintering model for UO 2 in MARMOT 2. Expand model to account for irradiation effects 3. Develop a mechanistic macroscale model of densification for BISON« less

Quantification of process variables for carbothermic synthesis of UC1-xNx fuel microspheres

NASA Astrophysics Data System (ADS)

Lindemer, T. B.; Silva, C. M.; Henry, J. J.; McMurray, J. W.; Voit, S. L.; Collins, J. L.; Hunt, R. D.

2017-01-01

This report details the continued investigation of process variables involved in converting sol-gel-derived, urania-carbon microspheres to ∼820-μm-dia. UC1-xNx fuel kernels in flow-through, vertical Mo and W crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO3-H2O-C microspheres in Ar and H2-containing gases, conversion of the resulting UO2-C kernels to dense UO2:2UC in the same gases and vacuum, and its conversion in N2 to UC1-xNx (x = ∼0.85). The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO2:2UC kernel of ∼96% theoretical density was required, but its subsequent conversion to UC1-xNx at 2123 K was not accompanied by sintering and resulted in ∼83-86% of theoretical density. Increasing the UC1-xNx kernel nitride component to ∼0.98 in flowing N2-H2 mixtures to evolve HCN was shown to be quantitatively consistent with present and past experiments and the only useful application of H2 in the entire process.

Issues in the use of Weapons-Grade MOX Fuel in VVER-1000 Nuclear Reactors: Comparison of UO2 and MOX Fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carbajo, J.J.

2005-05-27

The purpose of this report is to quantify the differences between mixed oxide (MOX) and low-enriched uranium (LEU) fuels and to assess in reasonable detail the potential impacts of MOX fuel use in VVER-1000 nuclear power plants in Russia. This report is a generic tool to assist in the identification of plant modifications that may be required to accommodate receiving, storing, handling, irradiating, and disposing of MOX fuel in VVER-1000 reactors. The report is based on information from work performed by Russian and U.S. institutions. The report quantifies each issue, and the differences between LEU and MOX fuels are describedmore » as accurately as possible, given the current sources of data.« less

Thermal expansion in UO 2 determined by high-energy X-ray diffraction

DOE PAGES

Guthrie, M.; Benmore, C. J.; Skinner, L. B.; ...

2016-06-24

In this study, we present crystallographic analyses of high-energy X-ray diffraction data on polycrystalline UO 2 up to the melting temperature. The Rietveld refinements of our X-ray data are in agreement with previous measurements, but are systematically located around the upper bound of their uncertainty, indicating a slightly steeper trend of thermal expansion compared to established values. This observation is consistent with recent first principles calculations.

Identification and distribution of inclusions in derby and ingot uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwartz, C.M.; Vaughan, D.A.

1953-08-31

Inclusions in derby and ingot uranium have been identified by X-ray diffraction methods. Metallographic and microradiographic examinations have shown that inclusions of MgF2, UO2, UN, and UO are concentrated at the top of derby and ingot metal by gravity separation. UC inclusions are distributed throughout the ingot metal. The amount of the carbide phase in the ingot varies with the temperature maintained during remelt of derby metal.

A U-bearing composite waste form for electrochemical processing wastes

NASA Astrophysics Data System (ADS)

Chen, X.; Ebert, W. L.; Indacochea, J. E.

2018-04-01

Metallic/ceramic composite waste forms are being developed to immobilize combined metallic and oxide waste streams generated during electrochemical recycling of used nuclear fuel. Composites were made for corrosion testing by reacting HT9 steel to represent fuel cladding, Zr and Mo to simulate metallic fuel waste, and a mixture of ZrO2, Nd2O3, and UO2 to represent oxide wastes. More than half of the added UO2 was reduced to metal and formed Fe-Zr-U intermetallics and most of the remaining UO2 and all of the Nd2O3 reacted to form zirconates. Fe-Cr-Mo intermetallics were also formed. Microstructure characterization of the intermetallic and ceramic phases that were generated and tests conducted to evaluate their corrosion behaviors indicate composite waste forms can accommodate both metallic and oxidized waste streams in durable host phases.

Probing Chemical Bonding in Uranium Dioxide by Means of High-Resolution X-ray Absorption Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butorin, Sergei M.; Modin, Anders; Vegelius, Johan R.

Here, a systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO 2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d 3/2 edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree ofmore » the 5f localization in UO 2. The results support the covalent character of UO 2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.« less

Characterization of urania vaporization with transpiration coupled thermogravimetry

DOE PAGES

McMurray, J. W.

2015-12-05

Determining equilibrium vapor pressures of materials is made easier by transpiration measurements. However, the traditional technique involves condensing the volatiles entrained in a carrier gas outside of the hot measurement zone. One potential problem is deposition en route to a cooled collector. Thermogravimetric analysis (TGA) can be used to measure in situ mass loss due to vaporization and therefore obviate the need to analyze the entire gas train due to premature plating of vapor species. Therefore, a transpiration coupled TGA technique was used to determine equilibrium pressures of UO3 gas over fluorite structure UO2+x and U3O8 at T = (1573more » and 1773) K. Moreover, we compared to calculations from models and databases in the open literature. Our study gives clarity to the thermochemical data for UO3 gas and validates the mass loss transpiration method using thermogravimetry for determining equilibrium vapor pressures of non-stoichiometric oxides.« less

Carbothermic reduction of uranium oxides into solvent metallic baths

NASA Astrophysics Data System (ADS)

Guisard Restivo, Thomaz A.; Capocchi, José D. T.

2004-09-01

The carbothermic reduction of UO 2 and U 3O 8 is studied employing tin and silicon solvent metallic baths in thermal analysis equipment, under Ar inert and N 2 reactive atmospheres. The metallic solvents are expected to lower the U activity by several orders of magnitude owing to strong interactions among the metals. The reduction products are composed of the solvent metal matrix and intermetallic U compounds. Silicon is more effective in driving the reduction since there is no residual UO 2 after the reaction. The gaseous product detected by mass spectrometer (MS) during the reduction is CO. A kinetic study for the Si case was accomplished by the stepwise isothermal analysis (SAI) method, leading to the identification of the controlling mechanisms as chemical reaction at the surface and nucleation, for UO 2 and U 3O 8 charges, respectively. One example for another system containing Al 2O 3 is also shown.

A U-bearing composite waste form for electrochemical processing wastes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, X.; Ebert, W. L.; Indacochea, J. E.

Metallic/ceramic composite waste forms are being developed to immobilize combined metallic and oxide waste streams generated during electrochemical recycling of used nuclear fuel. Composites were made for corrosion testing by reacting HT9 steel to represent fuel cladding, Zr and Mo to simulate metallic fuel waste, and a mixture of ZrO2, Nd2O3, and UO2 to represent oxide wastes. More than half of the added UO2 was reduced to metal and formed Fe-Zr-U intermetallics and most of the remaining UO2 and all of the Nd2O3 reacted to form zirconates. Fe-Cr-Mo intermetallics were also formed. Microstructure characterization of the intermetallic and ceramic phasesmore » that were generated and tests conducted to evaluate their corrosion behaviors indicate composite waste forms can accommodate both metallic and oxidized waste streams in durable host phases. (c) 2018 Elsevier B.V. All rights reserved.« less

Ring opening of azetidine cycle: First examples of 1-azetidinepropanamine molecules as a template in hybrid organic-inorganic compounds

NASA Astrophysics Data System (ADS)

Gurzhiy, Vladislav V.; Tyumentseva, Olga S.; Britvin, Sergey N.; Krivovichev, Sergey V.; Tananaev, Ivan G.

2018-01-01

Three novel uranyl selenate and sulfate oxysalts templated by protonated azetidine molecules, [AzH]+, and its ring-opened counterpart 1-azetidinepropanamine, [AzH(CH2)3NH3]2+, have been prepared and studied by X-ray structural analysis. Conformations of azetidinium cations were analysed by means of infrared vibrational assignments supported by the DFT calculations. Crystallization of [AzH]2 [(UO2)2(SeO4)3(H2O)] (I) from highly acidic solutions suggests that low pH does not necessarily result in the opening of azetidine ring. [AzH(CH2)3NH3][(UO2)2(SeO4)3(H2O)](H2O) (II) and [AzH(CH2)3NH3](H5O2)[(UO2)2(SO4)3(HSO4)] (III) are the first structurally characterized crystalline compounds bearing isolated ring-opened azetidine moiety.

Investigation of uranium binding forms in selected German mineral waters.

PubMed

Osman, Alfatih A A; Geipel, Gerhard; Bernhard, Gert; Worch, Eckhard

2013-12-01

Cryogenic time-resolved laser-induced fluorescence spectroscopy was successfully used to identify uranium binding forms in selected German mineral waters of extremely low uranium concentrations (<2.0 μg/L). The measurements were performed at a low temperature of 153 K. The spectroscopic data showed a prevalence of aquatic species Ca2UO2(CO3)3 in all investigated waters, while other uranyl-carbonate complexes, viz, UO2CO3(aq) and UO2(CO3)2 (2-), only existed as minor species. The pH value, alkalinity (CO3 (2-)), and the main water inorganic constituents, specifically the Ca(2+) concentration, showed a clear influence on uranium speciation. Speciation modeling was performed using the most recent thermodynamic data for aqueous complexes of uranium. The modeling results for the main uranium binding form in the investigated waters indicated a good agreement with the spectroscopy measurements.

Probing Chemical Bonding in Uranium Dioxide by Means of High-Resolution X-ray Absorption Spectroscopy

DOE PAGES

Butorin, Sergei M.; Modin, Anders; Vegelius, Johan R.; ...

2016-11-30

Here, a systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO 2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d 3/2 edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree ofmore » the 5f localization in UO 2. The results support the covalent character of UO 2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.« less

Topological ordering in liquid UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benmore, C. J.; Skinner, L. B.; Lee, B.

2015-12-10

A molecular dynamics model of liquid UO2 that is in good agreement with recent high-energy x-ray diffraction data has been analyzed using the Bhatia–Thornton formalism. A pre-peak appears in the topological structure factor S NN(Q) at Q = 1.85(1)Å-1 which is not present in the more common, element specific Faber–Ziman partial structure factors. A radical Voronoi tessellation of the 3D molecular dynamics model shows the presence of a wide distribution of clusters, consistent with presence of highly mobile oxygen atoms. However, 4-fold Voronoi polyhedra (n 4) are found to dominate the structure and the majority of clusters can be describedmore » by the distribution n 3 ≤ n 4 ≥ n 5. It is argued that an open network of 4-fold Voronoi polyhedra could explain the origin of the pre-peak in S NN(Q) and the topological ordering observed in liquid UO2.« less

Simulation of xenon, uranium vacancy and interstitial diffusion and grain boundary segregation in UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersson, Anders D.; Tonks, Michael R.; Casillas, Luis

2014-10-31

In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. Based on the mechanisms established from density functional theory (DFT) and empirical potential calculations 1, continuum models for diffusion of xenon (Xe), uranium (U) vacancies and U interstitials in UO 2 have been derived for both intrinsic conditions and under irradiation. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO 2 ( Σ5 tilt, Σ5more » twist and a high angle random boundary),as derived from atomistic calculations. All models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as redistribution for a few simple microstructures.« less

A Historical Review of Cermet Fuel Development and the Engine Performance Implications

NASA Technical Reports Server (NTRS)

Stewart, Mark E. M.

2015-01-01

This paper reviews test data for cermet fuel samples developed in the 1960's to better quantify Nuclear Thermal Propulsion (NTP) cermet engine performance, and to better understand contemporary fuel testing results. Over 200 cermet (W-UO2) samples were tested by thermally cycling to 2500 deg (2770 K) in hydrogen. The data indicates two issues at high temperatures: the vaporization rate of UO2 and the chemical stability of UO2. The data show that cladding and chemical stabilizers each result in large, order of magnitude improvements in high temperature performance, while other approaches yield smaller, incremental improvements. Data is very limited above 2770 K, and this complicates predictions of engine performance at high Isp. The paper considers how this material performance data translates into engine performance. In particular, the location of maximum temperature within the fuel element and the effect of heat deposition rate are examined.

Self-assembly of [UO{sub 2}X{sub 4}]{sup 2−} (X=Cl, Br) dianions with γ substituted pyridinium cations: Structural systematics and fluorescence properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Surbella, Robert G.; Andrews, Michael B.; Cahill, Christopher L., E-mail: cahill@gwu.edu

2016-04-15

Room temperature self-assembly of [UO{sub 2}X{sub 4}]{sup 2−} (X=Cl, Br) with γ substituted pyridinium cations has resulted in the formation of twelve compounds that were studied via single crystal X-ray diffraction and fluorescence spectroscopy. Systematic variation of electron donating groups on the pyridinium species is shown to influence the presence and/or strength of various supramolecular synthons, including hydrogen bonding and pi interactions. Combinations of such non-covalent interactions (NCIs) have given rise to a range of supramolecular assemblies, and are shown to influence uranyl emission by way of second sphere coordination to equatorial ligands. - Graphical abstract: Supramolecular assembly of themore » [UO{sub 2}Cl{sub 4}]{sup 2−} dianion with pyridinium cations is a viable synthetic route to the growth of uranyl containing single crystals.« less

Thermophysical properties of liquid UO2, ZrO2 and corium by molecular dynamics and predictive models

NASA Astrophysics Data System (ADS)

Kim, Woong Kee; Shim, Ji Hoon; Kaviany, Massoud

2017-08-01

Predicting the fate of accident-melted nuclear fuel-cladding requires the understanding of the thermophysical properties which are lacking or have large scatter due to high-temperature experimental challenges. Using equilibrium classical molecular dynamics (MD), we predict the properties of melted UO2 and ZrO2 and compare them with the available experimental data and the predictive models. The existing interatomic potential models have been developed mainly for the polymorphic solid phases of these oxides, so they cannot be used to predict all the properties accurately. We compare and decipher the distinctions of those MD predictions using the specific property-related autocorrelation decays. The predicted properties are density, specific heat, heat of fusion, compressibility, viscosity, surface tension, and the molecular and electronic thermal conductivities. After the comparisons, we provide readily usable temperature-dependent correlations (including UO2-ZrO2 compounds, i.e. corium melt).

Hydrothermal Synthesis, Crystal Structure, and Photoluminescent Properties of Li[UO2(CH3COO)3]3[Co(H2O)6

NASA Astrophysics Data System (ADS)

AlDamen, Murad A.; Juwhari, Hassan K.; Al-zuheiri, Aya M.; Alnazer, Louy A.

2017-12-01

Single crystal of Li[UO2(CH3COO)3]3[Co(H2O)6] was prepared and found to crystallize in the monoclinic crystal system in the sp. gr. C2/ c, with Z = 2, and unit cell parameters a = 22.1857(15) Å, b = 13.6477(8) Å, c = 15.6921(10) Å, β = 117.842(9)°, V = 4201.3(4) Å3. The crystal was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The single crystal X-ray diffraction analysis revealed that the crystal has a lamellar structure in which a cobalt hydrate is sandwiched within the Li[UO2(CH3COO)3]3 2- chains. Furthermore, the room temperature photoluminescence spectrum of the complex was investigated in the solid state.

Electrical and material properties of hydrothermally grown single crystal (111) UO2

NASA Astrophysics Data System (ADS)

Dugan, Christina L.; Peterson, George Glenn; Mock, Alyssa; Young, Christopher; Mann, J. Matthew; Nastasi, Michael; Schubert, Mathias; Wang, Lu; Mei, Wai-Ning; Tanabe, Iori; Dowben, Peter A.; Petrosky, James

2018-04-01

The semiconductor and optical properties of UO2 are investigated. The very long drift carrier lifetimes, obtained from current-voltage I( V) and capacitance-voltage C( V) measurements, along with the well-defined optical properties provide little evidence of an abundance of material defects away from the surface region. Schottky barrier formation may be possible, but very much dependent on the choice of contact and surface stoichiometry and we find that Ohmic contacts are in fact favored. Depth resolved photoemission provided evidence of a chemical shift at the surface. Density functional theory, with the Heyd-Scuseria-Ernzerhof (HSE) functional, indicates a band gap of a 2.19 eV and an anti-ferromagnetic ground state. Ellipsometry measurements indicates at UO2 is relatively isotropic with a band gap of approximately 2.0 eV band gap, consistent with theoretical expectations.

Topologically and geometrically flexible structural units in seven new organically templated uranyl selenates and selenite–selenates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gurzhiy, Vladislav V., E-mail: vladgeo17@mail.ru; Kovrugin, Vadim M.; Tyumentseva, Olga S.

2015-09-15

Single crystals of seven novel uranyl oxysalts of selenium with protonated methylamine molecules, [C{sub 2}H{sub 8}N]{sub 2}[(UO{sub 2})(SeO{sub 4}){sub 2}(H{sub 2}O)] (I), [C{sub 2}H{sub 8}N]{sub 2}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O)] (II), [C{sub 4}H{sub 15}N{sub 3}][H{sub 3}O]{sub 0.5}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 2.93}(SeO{sub 3}){sub 0.07}(H{sub 2}O)](NO{sub 3}){sub 0.5} (III), [C{sub 2}H{sub 8}N]{sub 3}[H{sub 5}O{sub 2}][(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O){sub 2}]{sub 2}(H{sub 2}O){sub 5} (IV), [C{sub 2}H{sub 8}N]{sub 2}[H{sub 3}O][(UO{sub 2}){sub 3}(SeO{sub 4}){sub 4}(HSeO{sub 3})(H{sub 2}O)](H{sub 2}SeO{sub 3}){sub 0.2} (V), [C{sub 4}H{sub 12}N]{sub 3}[H{sub 3}O][(UO{sub 2}){sub 3}(SeO{sub 4}){sub 5}(H{sub 2}O)] (VI), and [C{sub 2}H{sub 8}N]{sub 3}(C{sub 2}H{sub 7}N)[(UO{sub 2}){sub 3}(SeO{sub 4}){submore » 4}(HSeO{sub 3})(H{sub 2}O)] (VII) have been prepared by isothermal evaporation from aqueous solutions. Their crystal structures have been solved by direct methods and their uranyl selenate and selenite–selenate units investigated using black-and-white graphs from the viewpoints of topology of interpolyhedral linkages and isomeric variations. The crystal structure of IV is based upon complex layers with unique topology, which has not been observed previously in uranyl selenates. Investigations of the statistics and local distribution of the U–O{sub br}–Se bond angles demonstrates that shorter angles associate with undulations, whereas larger angles correspond to planar areas of the uranyl selenite layers. - Graphical abstract: Crystal structures of the seven novel Se-contaning uranyl oxysalts that contain protonated organic molecules as interlayer species have been investigated from the viewpoints of topology of interpolyhedral linkages, isomeric variations and flexibility of structural units. - Highlights: • Single crystals of seven novel uranyl oxysalts were prepared by evaporation method. • The graph theory was used for investigation of topologies of structural units. • The method of orientation matrices was applied to distinguish geometrical isomers. • The flexibility of structural complexes specifies the undulation of layered structural units.« less

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsenovich, Yelena P.; Cardona, Claudia; Lapierre, Robert

2016-10-01

Remediation of uranium in the deep unsaturated zone is a challenging task, especially in the presence of oxygenated, high-carbonate alkalinity soil and pore water composition typical for arid and semi-arid environments of the western regions of the U.S. This study evaluates the effect of various pore water constituencies on changes of uranium concentrations in alkaline conditions, created in the presence of reactive gases such as NH3 to effectively mitigate uranium contamination in the vadose zone sediments. This contaminant is a potential source for groundwater pollution through slow infiltration of soluble and highly mobile uranium species towards the water table. Themore » objective of this research was to evaluate uranium sequestration efficiencies in the alkaline synthetic pore water solutions prepared in a broad range of Si, Al, and bicarbonate concentrations typically present in field systems of the western U.S. regions and identify solid uranium-bearing phases that result from ammonia gas treatment. In previous studies (Szecsody et al. 2012; Zhong et al. 2015), although uranium mobility was greatly decreased, solid phases could not be identified at the low uranium concentrations in field-contaminated sediments. The chemical composition of the synthetic pore water used in the experiments varied for silica (5–250 mM), Al3+ (2.8 or 5 mM), HCO3- (0–100 mM) and U(VI) (0.0021–0.0084 mM) in the solution mixture. Experiment results suggested that solutions with Si concentrations higher than 50 mM exhibited greater removal efficiencies of U(VI). Solutions with higher concentrations of bicarbonate also exhibited greater removal efficiencies for Si, Al, and U(VI). Overall, the silica polymerization reaction leading to the formation of Si gel correlated with the removal of U(VI), Si, and Al from the solution. If no Si polymerization was observed, there was no U removal from the supernatant solution. Speciation modeling indicated that the dominant uranium species in the presence of bicarbonate were anionic uranyl carbonate complexes (UO2(CO3)2-2 and UO2(CO3)3-4) and in the absence of bicarbonate in the solution, U(VI) major species appeared as uranyl-hydroxide (UO2(OH)3- and UO2(OH)4-2) species. The model also predicted the formation of uranium solid phases. Uranyl carbonates as rutherfordine [UO2CO3], cejkaite [Na4(UO2)(CO3)3] and hydrated uranyl silicate phases as Na-boltwoodite [Na(UO2)(SiO4)·1.5H2O] were anticipated for most of the synthetic pore water compositions amended from medium (2.9 mM) to high (100 mM) bicarbonate concentrations.« less

The needs of AIDS-infected individuals in rural China.

PubMed

Lu, Yun Luke; Trout, Shirley K; Lu, Katarina; Creswell, John W

2005-11-01

The purpose of this exploratory case study was to describe the needs and present the voices of 21 AIDS-infected individuals who contracted the disease through the selling of blood in rural China. Data sources included interviews, field notes, and letters. Three themes emerged: living in a vicious circle, awakening from the dead end, and escaping the vicious circle through education. Education emerged as an overarching theme and was identified as the catalyst that would either keep the families of those affected trapped in the vicious circle or rescue them from it. Findings are explained within the theoretical contexts of social capital, motivation theory, and Confucius's philosophy on education. The authors discuss implications for researchers, educators, relief workers, human service workers, policy makers, and human rights advocates. They conclude with suggestions for further study.

Two actinide-organic frameworks constructed by a tripodal flexible ligand: Occurrence of infinite ((UO{sub 2})O{sub 2}(OH){sub 3}){sub 4n} and hexanuclear (Th{sub 6}O{sub 4}(OH){sub 4}) motifs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Lingling; Zhang, Ronglan; Zhao, Jianshe, E-mail: jszhao@nwu.edu.cn

Two new actinide metal-organic frameworks were constructed by using a tripodal flexible ligand tris (2-carboxyethyl) isocyanurate (H{sub 3}tci) under hydrothermal condition. The combination of H{sub 3}tci and uranyl nitrate hexahydrate in aqueous solution leads to the isolation of [(UO{sub 2}){sub 2}(H{sub 2}O){sub 4}]{sub 0.5}(tci){sub 2}(UO{sub 2}){sub 4}(OH){sub 4}·18H{sub 2}O (1), which contains two distinct UO{sub 2}{sup 2+} coordination environments. Four uranyl cations, linked through μ{sub 3}-OH respectively, result in the edge-sharing ribbons. Then, the layer structure is constructed by U-O clusters linked through other eight-coordinated uranyl unions, giving rise to a porous structure in the space. Topological analysis reveals thatmore » complex 1 belongs to a (4, 8)-connected net with a schläfli symbol of (3{sup 4.}2{sup 6.}3){sub 2}(3{sup 4.}4{sup 6.}5{sup 6.}6{sup 8.}7{sup 3.}8). Th{sub 3}(tci){sub 2}O{sub 2}(OH){sub 2}(H{sub 2}O){sub 3}·12H{sub 2}O (2) generated by the reaction of H{sub 3}tci and thorium nitrate tetrahydrate, possesses nine-fold coodinated Th(IV) centers with a monocapped square antiprismatic geometry. The hexamers “Th{sub 6}O{sub 4}(OH){sub 4}” motifs are connected together by the carboxylate groups, showing a three-dimensional structures. Complex 2 takes on an 8-connected architecture and the point symbol is (4{sup 24.}6{sup 4}). - Graphical abstract: Two new 3D actinide metal-organic frameworks were constructed by using a tripodal flexible ligand tris (2-carboxyethyl) isocyanurate (H3tci) and their topological structures were displayed. The infinite ((UO{sub 2})O{sub 2}(OH){sub 3}){sub 4n} and hexanuclear (Th{sub 6}O{sub 4}(OH){sub 4}) motifs were found in the title actinides networks.« less

Analysis and fabrication of tungsten CERMET materials for ultra-high temperature reactor applications via pulsed electric current sintering

NASA Astrophysics Data System (ADS)

Webb, Jonathan A.

The optimized development path for the fabrication of ultra-high temperature W-UO2 CERMET fuel elements were explored within this dissertation. A robust literature search was conducted, which concluded that a W-UO 2 fuel element must contain a fine tungsten microstructure and spherical UO2 kernels throughout the entire consolidation process. Combined Monte Carlo and Computational Fluid Dynamics (CFD) analysis were used to determine the effects of rhenium and gadolinia additions on the performance of W-UO 2 fuel elements at refractory temperatures and in dry and water submerged environments. The computational analysis also led to the design of quasi-optimized fuel elements that can meet thermal-hydraulic and neutronic requirements A rigorous set of experiments were conducted to determine if Pulsed Electric Current Sintering (PECS) can fabricate tungsten and W-Ce02 specimens to the required geometries, densities and microstructures required for high temperature fuel elements as well as determine the mechanisms involved within the PECS consolidation process. The CeO2 acts as a surrogate for UO 2 fuel kernels in these experiments. The experiments seemed to confirm that PECS consolidation takes place via diffusional mass transfer methods; however, the densification process is rapidly accelerated due to the effects of current densities within the consolidating specimen. Fortunately the grain growth proceeds at a traditional rate and the PECS process can yield near fully dense W and W-Ce02 specimens with a finer microstructure than other sintering techniques. PECS consolidation techniques were also shown to be capable of producing W-UO2 segments at near-prototypic geometries; however, great care must be taken to coat the fuel particles with tungsten prior to sintering. Also, great care must be taken to ensure that the particles remain spherical in geometry under the influence of a uniaxial stress as applied during PECS, which involves mixing different fuel kernel sizes in order to reduce the porosity in the initial green compact. Particle mixing techniques were also shown to be capable of producing consolidated CERMETs, but with a less than desirable microstructure. The work presented herin will help in the development of very high temperature reactors for terrestrial and space missions in the future.

Predicting equilibrium uranium isotope fractionation in crystals and solution

NASA Astrophysics Data System (ADS)

Schauble, E. A.

2015-12-01

Despite the rapidly growing interest in using 238U/235U measurements as a proxy for changes in oxygen abundance in surface and near-surface environments, the present theoretical understanding of uranium isotope fractionation is limited to a few simple gas-phase molecules and analogues of dissolved species (e.g., 1,2,3). Understanding uranium isotope fractionation behavior in more complicated species, such as crystals and adsorption complexes, will help in the design and interpretation of experiments and field studies, and may suggest other uses for 38U/235U measurements. In this study, a recently developed first-principles method for estimating the nuclear volume component of field shift fractionation in crystals and complex molecular species (4) is combined with mass-dependent fractionation theory to predict equilibrium 38U/235U fractionations in aqueous and crystalline uranium compounds, including uraninite (UO2). The nuclear field shift effect, caused by the interaction of electrons with the finite volume of the positive charge distribution in uranium nuclei, is estimated using Density Functional Theory and the Projector Augmented Wave method (DFT-PAW). Tests against relativistic electronic structure calculations and Mössbauer isomer shift data indicate that the DFT-PAW method is reasonably accurate, while being much better suited to models of complex and crystalline species. Initial results confirm previous predictions that the nuclear volume effect overwhelms mass depdendent fractionation in U(VI)-U(IV) exchange reactions, leading to higher 238U/235U in U(IV) species (i.e., for UO2 xtal vs. UO22+aq, ln αNV ≈ +1.8‰ , ln αMD ≈ -0.8‰, ln αTotal ≈ +1.0‰ at 25ºC). UO2 and U(H2O)94+, are within ~0.4‰ of each other, while U(VI) species appear to be more variable. This suggests that speciation is likely to significantly affect natural uranium isotope fractionations, in addition to oxidation state. Tentatively, it appears that uranyl-type (UO22+-bearing) structures will tend to have higher 238U/235U than uranate-type structures that lack strong U=O bonds. References: 1. Bigeleisen (1996) JACS 118:3676; 2. Schauble (2006) Eos 87:V21B-0570; 3. Abe et al. (2008) J Chem Phys 128:144309, 129:164309, & Abe et al. (2010) J Chem Phys 133:044309; 4. Schauble (2013) PNAS 110:17714.

Stimulating Creativity by Integrating Research and Teaching Across the Academic Disciplines

NASA Astrophysics Data System (ADS)

Taylor, Richard

2013-03-01

Creativity is a human adventure fueled by the process of exploration. But how do we explore our intellectual interests? In this talk, I'll propose that we seek out our creative opportunities using an inherent natural process. This process might, therefore, exploit search strategies found across diverse natural systems - ranging from the way animals forage for food to the way the human eye locates information embedded within complex patterns. The symbolic significance of this hypothesis lies in its call for educational institutes to provide environments that encourage our natural explorations rather those that stamp restrictive, artificial `order' on the process. To make my case, I'll review some of my own research trajectories followed during my RCSA Cottrell Scholarship at the University of Oregon (UO). My first conclusion will be that it is fundamentally unnatural to declare divides across disciplines. In particular, the infamous `art-science divide' is not a consequence of our natural creative searches but instead arises from our practical inability to accommodate the rapid drive toward academic specialization. Secondly, divides between research and teaching activities are equally unnatural - both endeavors are driven by the same creative strategy and are intertwined within the same natural process. This applies equally to the experiences of professors and students. I will end with specific success stories at the UO. These include a NSF IGERT project (focused on accelerating students' transitions from classroom to research experiences) and a collaboration between architects and professors to design a building (the recently opened Lewis Integrative Science Building) that encourages daily encounters between students and professors across research disciplines.

High Strain Rate Characterization of Materials

DTIC Science & Technology

1983-08-01

r.ev ers old@ If nooeeree and identfyl by block ffloboe) New techniques have been developed to study dynamic tensile f ilure of ductile metals... Paisely conducted the spall experiments. The experi- mental facilitied were located in the Impact Physics Laboratory at the University of Dayton...Elevated Temperature. 16 10 Effect of Temperature on Spall Damage in OFHC Copper (a) 200C (uO - 95 m/s, Shot 545), (b) 4250C (uO - 102 m/a, Shot 541). 17 11

Reactivity-worth estimates of the OSMOSE samples in the MINERVE reactor R1-MOX, R2-UO2 and MORGANE/R configurations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Z.; Klann, R. T.; Nuclear Engineering Division

2007-08-03

An initial series of calculations of the reactivity-worth of the OSMOSE samples in the MINERVE reactor with the R2-UO2 and MORGANE/R core configuration were completed. The calculation model was generated using the lattice physics code DRAGON. In addition, an initial comparison of calculated values to experimental measurements was performed based on preliminary results for the R1-MOX configuration.

Regulation of Heat Stress by HSF1 and GR

DTIC Science & Technology

2015-09-01

0 10 20 30 40 50 0 100 200 300 Location (µm) Fl uo re sc en ce 0 10 20 30 40 50 0 100 200 300 Location (µm) 0 10 20 30 40 50 0 100 200 300 Location...µm) Fl uo re sc en ce 0 10 20 30 40 50 0 100 200 300 Location (µm) 6   4. Impact What was the impact on the development of the principal discipline

[Development of questionnaire to assess food intake in the University of Antioquia, Colombia].

PubMed

Monsalve Álvarez, J Ma; González Zapata, L I

2011-01-01

To design a self-reported semi-quantitative questionnaire of frequency of food intake (QFFI) to assess the usual intake of foods and macronutrients of the academic community from the University of Antioquia (UoA). The design of the questionnaire was done by reviewing and analyzing previous studies on food intake and the established linings for the selling of dietary products at the UoA. For selecting the foods and defining the serving size, we applied the criterion of intake pattern and the weight or size of the most frequent serving for each food, according to what has been reported in previous studies. We undertook a descriptive exploratory study with the QFFI including 154 people of the UoA. The analysis included the comprehension, applicability and comprehensiveness of the instrument for the participants, as well as the calculation of the descriptive parameters in the exploratory component. A semi-quantitative QFFI compounded by 144 foods classified in 9 groups with serving sizes known by the population and 9 categories of frequencies of usual intake within the last year. The exploratory study showed differences in the pattern of intake in the population groups analyzed. The designed QFFI was adequate for the study population since it was easily understood and administered, and it allowed for assessing the usual intake in the community of the UoA.

Development of Xe and Kr empirical potentials for CeO 2, ThO 2, UO 2 and PuO 2, combining DFT with high temperature MD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cooper, M. W. D.; Kuganathan, N.; Burr, P. A.

In this study, the development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO 2, ThO 2, UO 2 and PuO 2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matchingmore » to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO 2, ThO 2, UO 2 and PuO 2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO 2 as well as advanced MOX fuels.« less

Development of Xe and Kr empirical potentials for CeO 2, ThO 2, UO 2 and PuO 2, combining DFT with high temperature MD

DOE PAGES

Cooper, M. W. D.; Kuganathan, N.; Burr, P. A.; ...

2016-08-23

In this study, the development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO 2, ThO 2, UO 2 and PuO 2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matchingmore » to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO 2, ThO 2, UO 2 and PuO 2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO 2 as well as advanced MOX fuels.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehta, Vrajesh; Maillot, Fabien; Wang, Zheming

Uranyl phosphate solids are often found with uranium ores, and their low solubility makes them promising target phases for in situ remediation of uranium-contaminated subsurface environments. The products and solubility of uranium(VI) precipitated with phosphate can be affected by the pH, dissolved inorganic carbon (DIC) concentration, and co-solute composition (e.g. Na+/Ca2+) of the groundwater. Batch experiments were performed to study the effect of these parameters on the products and extent of uranium precipitation induced by phosphate addition. In the absence of co-solute cations, chernikovite [H3O(UO2)(PO4)•3H2O] precipitated despite uranyl orthophosphate [(UO2)3(PO4)2•4H2O] being thermodynamically more favorable under certain conditions. As determined usingmore » X-ray diffraction, electron microscopy, and laser induced fluorescence spectroscopy, the presence of Na+ or Ca2+ as a co-solute led to the precipitation of sodium autunite ([Na2(UO2)2(PO4)2] and autunite [Ca(UO2)2(PO4)2]), which are structurally similar to chernikovite. In the presence of sodium, the dissolved U(VI) concentrations were generally in agreement with equilibrium predictions of sodium autunite solubility. However, in the calcium-containing systems, the observed concentrations were below the predicted solubility of autunite, suggesting the possibility of uranium adsorption to or incorporation in a calcium phosphate precipitate in addition to the precipitation of autunite.« less

Modelling the radiolytic corrosion of α-doped UO2 and spent nuclear fuel

NASA Astrophysics Data System (ADS)

Liu, Nazhen; Qin, Zack; Noël, James J.; Shoesmith, David W.

2017-10-01

A model previously developed to predict the corrosion rate of spent fuel (UO2) inside a failed waste container has been adapted to simulate the rates measured on a wide range of α-doped UO2 and spent fuel specimens. This simulation confirms the validity of the model and demonstrates that the steady-state corrosion rate is controlled by the radiolytic production of H2O2 (which has been shown to be the primary oxidant driving fuel corrosion), irrespective of the reactivity of the UO2 matrix. The model was then used to determine the consequences of corrosion inside a failed container resealed by steel corrosion products. The possible accumulation of O2, produced by H2O2 decomposition, was found to accelerate the corrosion rate in a closed system. However, the simultaneous accumulation of radiolytic H2, which is activated as a reductant on the noble metal (ε) particles in the spent fuel, rapidly overcame this acceleration leading to the eventual suppression of the corrosion rate to insignificant values. Calculations also showed that, while the radiation dose rate, the H2O2 decomposition ratio, and the surface coverage of ε particles all influenced the short term corrosion rate, the influence of the radiolytically produced H2 was the overwhelming influence in reducing the rate to negligible level (i.e., <10-20 mol m-2 s-1).

AGR-2 Irradiation Test Final As-Run Report, Rev 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collin, Blaise P.

2014-08-01

This document presents the as-run analysis of the AGR-2 irradiation experiment. AGR-2 is the second of the planned irradiations for the Advanced Gas Reactor (AGR) Fuel Development and Qualification Program. Funding for this program is provided by the U.S. Department of Energy as part of the Very High Temperature Reactor (VHTR) Technical Development Office (TDO) program. The objectives of the AGR-2 experiment are to: (a) Irradiate UCO (uranium oxycarbide) and UO 2 (uranium dioxide) fuel produced in a large coater. Fuel attributes are based on results obtained from the AGR-1 test and other project activities. (b) Provide irradiated fuel samplesmore » for post-irradiation experiment (PIE) and safety testing. (c) Support the development of an understanding of the relationship between fuel fabrication processes, fuel product properties, and irradiation performance. The primary objective of the test was to irradiate both UCO and UO 2 TRISO (tri-structural isotropic) fuel produced from prototypic scale equipment to obtain normal operation and accident condition fuel performance data. The UCO compacts were subjected to a range of burnups and temperatures typical of anticipated prismatic reactor service conditions in three capsules. The test train also includes compacts containing UO 2 particles produced independently by the United States, South Africa, and France in three separate capsules. The range of burnups and temperatures in these capsules were typical of anticipated pebble bed reactor service conditions. The results discussed in this report pertain only to U.S. produced fuel. In order to achieve the test objectives, the AGR-2 experiment was irradiated in the B-12 position of the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) for a total irradiation duration of 559.2 effective full power days (EFPD). Irradiation began on June 22, 2010, and ended on October 16, 2013, spanning 12 ATR power cycles and approximately three and a half calendar years. The test contained six independently controlled and monitored capsules. Each U.S. capsule contained 12 compacts of either UCO or UO2 AGR coated fuel. No fuel particles failed during the AGR-2 irradiation. Final burnup values on a per compact basis ranged from 7.26 to 13.15% FIMA (fissions per initial heavy-metal atom) for UCO fuel, and 9.01 to 10.69% FIMA for UO 2 fuel, while fast fluence values ranged from 1.94 to 3.47 x 10 25 n/m 2 (E >0.18 MeV) for UCO fuel, and from 3.05 to 3.53 x 10 25 n/m 2 (E >0.18 MeV) for UO 2 fuel. Time-average volume-average (TAVA) temperatures on a capsule basis at the end of irradiation ranged from 987°C in Capsule 6 to 1296°C in Capsule 2 for UCO, and from 996 to 1062°C in UO 2-fueled Capsule 3. By the end of the irradiation, all of the installed thermocouples (TCs) had failed. Fission product release-to-birth (R/B) ratios were quite low. In the UCO capsules, R/B values during the first three cycles were below 10 -6 with the exception of the hotter Capsule 2, in which the R/Bs reached 2 x 10 -6. In the UO 2 capsule (Capsule 3), the R/B values during the first three cycles were below 10 -7. R/B values for all following cycles are not reliable due to gas flow and cross talk issues.« less

Thiocyanate complexes of uranium in multiple oxidation states: a combined structural, magnetic, spectroscopic, spectroelectrochemical, and theoretical study.

PubMed

Hashem, Emtithal; Platts, James A; Hartl, František; Lorusso, Giulia; Evangelisti, Marco; Schulzke, Carola; Baker, Robert J

2014-08-18

A comprehensive study of the complexes A4[U(NCS)8] (A = Cs, Et4N, (n)Bu4N) and A3[UO2(NCS)5] (A = Cs, Et4N) is described, with the crystal structures of [(n)Bu4N]4[U(NCS)8]·2MeCN and Cs3[UO2(NCS)5]·O0.5 reported. The magnetic properties of square antiprismatic Cs4[U(NCS)8] and cubic [Et4N]4[U(NCS)8] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, μeff = 1.21 μB and 0.53 μB, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et4N]4[U(NCS)8] has been explored using IR and UV-vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc(+), followed by an irreversible oxidation to form dithiocyanogen (NCS)2 which upon back reduction regenerates thiocyanate anions coordinating to UO2(2+). NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)8](4-) is delocalized over all NCS(-) ligands. Reduction of the uranyl(VI) complex [Et4N]3[UO2(NCS)5] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)8](4-) (An = Th, U) and [UO2(NCS)5](3-) has been explored by a combination of DFT and QTAIM analysis, and the U-N bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)-NCS ion is more ionic than what was found for U(IV)-Cl complexes.

Agricolaite, a new mineral of uranium from Jáchymov, Czech Republic

NASA Astrophysics Data System (ADS)

Skála, Roman; Ondruš, Petr; Veselovský, František; Císařová, Ivana; Hloušek, Jan

2011-11-01

The new mineral agricolaite, a potassium uranyl carbonate with ideal formula K4(UO2)(CO3)3, occurs in vugs of ankerite gangue in gneisses in the abandoned Giftkiesstollen adit at Jáchymov, Czech Republic. The name is after Georgius Agricola (1494-1555), German scholar and scientist. Agricolaite occurs as isolated equant irregular translucent grains to 0.3 mm with yellow color, pale yellow streak, and vitreous luster. It is brittle with uneven fracture and displays neither cleavage nor parting. Agricolaite is non-fluorescent. Mohs hardness is ~4. It is associated with aragonite, brochantite, posnjakite, malachite, rutherfordine, and "pseudo-voglite". Experimental density is higher than 3.3 g.cm-3, Dcalc is 3.531 g. cm-3. The mineral is monoclinic, space group C2/ c, with a 10.2380(2), b 9.1930(2), c 12.2110(3) Å, β 95.108(2)°, V 1144.71(4) Å3, Z = 4. The strongest lines in the powder X-ray diffraction pattern are d( I)( hkl): 6.061(55)(002), 5.087(57)(200), 3.740(100)(202), 3.393(43)(113), 2.281(52)(402). Average composition based on ten electron microprobe analyses corresponds to (in wt.%) UO3 48.53, K2O 31.49, CO2(calc) 22.04 which gives the empirical formula K3.98(UO2)1.01(CO3)3.00. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R 1 = 0.0184 on the basis of the 1,308 unique reflections with F o > 4 σF o. The structure of agricolaite is identical to that of synthetic K4(UO2)(CO3)3 and consists of separate UO2(CO3)3 groups organized into layers parallel to (100) and two crystallographically non-equivalent sites occupied by K+ cations. Both the mineral and its name were approved by the IMA-CNMNC.

Geochemistry of speleothem records from southern Illinois: Development of (234U)/(238U) as a proxy for paleoprecipitation

USGS Publications Warehouse

Zhou, Juanzuo; Lundstrom, C.C.; Fouke, B.; Panno, S.; Hackley, K.; Curry, B.

2005-01-01

Natural waters universally show fractionation of uranium series (U-series) parent-daughter pairs, with the disequilibrium between 234U and 238U (234U)/(238U) commonly used as a tracer of groundwater flow. Because speleothems provide a temporal record of geochemical variations in groundwater precipitating calcite, (234U)/(238U) variations in speleothems provide a unique method of investigating water-rock interaction processes over millennium time scales. We present high precision Thermal Ionization Mass Spectrometric (TIMS) U-series analyses of speleothems and drip waters from Fogelpole Cave in southern Illinois. Data from all speleothems from the cave show an inverse correlation between (234U)/(238U) and U concentration, following the pattern observed in groundwaters globally. Within a 65-cm-long stalagmite, concordant 234U-238 U-230Th and 235U-231Pa ages for 5 samples indicate accurate chronology from 78.5 ka to 30 ka. Notably, (234U)/(238U)o which differs from most speleothems by having (234U)/(238U)o <1, positively correlates with speleothem growth rate. We generalize this to the observation that speleothems globally show (234U)/ (238U)o deviating farther from secular equilibrium at lower growth rates and approaching secular equilibrium at higher grow rates. Based on the Fogelpole observations, we suggest that groundwater (234U)/(238U) is controlled by the U oxidation state, the U concentration of the water and the fluid velocity. A transport model whereby U-series nuclides react and exchange with mineral surfaces can reproduce the observed trend between growth rate and (234U)/(238U)o. Based on this result, we suggest that (234U)/(238U)o in speleothems may record changes in hydrologic flux with time and thus could provide a useful proxy for long term records of paleoprecipitation. ?? 2005 Elsevier B.V. All rights reserved.

Initial results from safety testing of US AGR-2 irradiation test fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morris, Robert Noel; Hunn, John D.; Baldwin, Charles A.

Two cylindrical compacts containing tristructural isotropic (TRISO)-coated particles with kernels that contained a mixture of uranium carbide and uranium oxide (UCO) and two compacts with UO 2-kernel TRISO particles have undergone 1600°C safety testing. These compacts were irradiated in the US Advanced Gas Reactor Fuel Development and Qualification Program's second irradiation test (AGR-2). The time-dependent releases of several radioisotopes ( 110mAg, 134Cs, 137Cs, 154Eu, 155Eu, 90Sr, and 85Kr) were monitored while heating the fuel specimens to 1600°C in flowing helium for 300 h. The UCO compacts behaved similarly to previously reported 1600°C-safety-tested UCO compacts from the AGR-1 irradiation. No failedmore » TRISO or failed SiC were detected (based on krypton and cesium release), and cesium release through intact SiC was very low. Release behavior of silver, europium, and strontium appeared to be dominated by inventory originally released through intact coating layers during irradiation but retained in the compact matrix until it was released during safety testing. Both UO 2 compacts exhibited cesium release from multiple particles whose SiC failed during the safety test. Europium and strontium release from these two UO 2 compacts appeared to be dominated by release from the particles with failed SiC. Silver release was characteristically like the release from the UCO compacts in that an initial release of the majority of silver trapped in the matrix occurred during ramping to 1600°C. However, additional silver release was observed later in the safety testing due to the UO 2 TRISO with failed SiC. Failure of the SiC layer in the UO 2 fuel appears to have been dominated by CO corrosion, as opposed to the palladium degradation observed in AGR-1 UCO fuel.« less