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Sample records for minor uranium isotopes

  1. Increasing the Accuracy in the Measurement of the Minor Isotopes of Uranium: Care in Selection of Reference Materials, Baselines and Detector Calibration

    NASA Astrophysics Data System (ADS)

    Poths, J.; Koepf, A.; Boulyga, S. F.

    2008-12-01

    The minor isotopes of uranium (U-233, U-234, U-236) are increasingly useful for tracing a variety of processes: movement of anthropogenic nuclides in the environment (ref 1), sources of uranium ores (ref 2), and nuclear material attribution (ref 3). We report on improved accuracy for U-234/238 and U-236/238 by supplementing total evaporation protocol TIMS measurement on Faraday detectors (ref 4)with multiplier measurement for the minor isotopes. Measurement of small signals on Faraday detectors alone is limited by noise floors of the amplifiers and accurate measurement of the baseline offsets. The combined detector approach improves the reproducibility to better than ±1% (relative) for the U-234/238 at natural abundance, and yields a detection limit for U-236/U-238 of <0.2 ppm. We have quantified contribution of different factors to the uncertainties associated with these peak jumping measurement on a single detector, with an aim of further improvement. The uncertainties in the certified values for U-234 and U-236 in the uranium standard NBS U005, if used for mass bias correction, dominates the uncertainty in their isotopic ratio measurements. Software limitations in baseline measurement drives the detection limit for the U-236/U-238 ratio. This is a topic for discussion with the instrument manufacturers. Finally, deviation from linearity of the response of the electron multiplier with count rate limits the accuracy and reproducibility of these minor isotope measurements. References: (1) P. Steier et al(2008) Nuc Inst Meth(B), 266, 2246-2250. (2) E. Keegan et al (2008) Appl Geochem 23, 765-777. (3) K. Mayer et al (1998) IAEA-CN-98/11, in Advances in Destructive and Non-destructive Analysis for Environmental Monitoring and Nuclear Forensics. (4) S. Richter and S. Goldberg(2003) Int J Mass Spectrom, 229, 181-197.

  2. The terrestrial uranium isotope cycle

    NASA Astrophysics Data System (ADS)

    Andersen, Morten B.; Elliott, Tim; Freymuth, Heye; Sims, Kenneth W. W.; Niu, Yaoling; Kelley, Katherine A.

    2015-01-01

    Changing conditions on the Earth's surface can have a remarkable influence on the composition of its overwhelmingly more massive interior. The global distribution of uranium is a notable example. In early Earth history, the continental crust was enriched in uranium. Yet after the initial rise in atmospheric oxygen, about 2.4 billion years ago, the aqueous mobility of oxidized uranium resulted in its significant transport to the oceans and, ultimately, by means of subduction, back to the mantle. Here we explore the isotopic characteristics of this global uranium cycle. We show that the subducted flux of uranium is isotopically distinct, with high 238U/235U ratios, as a result of alteration processes at the bottom of an oxic ocean. We also find that mid-ocean-ridge basalts (MORBs) have 238U/235U ratios higher than does the bulk Earth, confirming the widespread pollution of the upper mantle with this recycled uranium. Although many ocean island basalts (OIBs) are argued to contain a recycled component, their uranium isotopic compositions do not differ from those of the bulk Earth. Because subducted uranium was probably isotopically unfractionated before full oceanic oxidation, about 600 million years ago, this observation reflects the greater antiquity of OIB sources. Elemental and isotope systematics of uranium in OIBs are strikingly consistent with previous OIB lead model ages, indicating that these mantle reservoirs formed between 2.4 and 1.8 billion years ago. In contrast, the uranium isotopic composition of MORB requires the convective stirring of recycled uranium throughout the upper mantle within the past 600 million years.

  3. The terrestrial uranium isotope cycle.

    PubMed

    Andersen, Morten B; Elliott, Tim; Freymuth, Heye; Sims, Kenneth W W; Niu, Yaoling; Kelley, Katherine A

    2015-01-15

    Changing conditions on the Earth's surface can have a remarkable influence on the composition of its overwhelmingly more massive interior. The global distribution of uranium is a notable example. In early Earth history, the continental crust was enriched in uranium. Yet after the initial rise in atmospheric oxygen, about 2.4 billion years ago, the aqueous mobility of oxidized uranium resulted in its significant transport to the oceans and, ultimately, by means of subduction, back to the mantle. Here we explore the isotopic characteristics of this global uranium cycle. We show that the subducted flux of uranium is isotopically distinct, with high (238)U/(235)U ratios, as a result of alteration processes at the bottom of an oxic ocean. We also find that mid-ocean-ridge basalts (MORBs) have (238)U/(235)U ratios higher than does the bulk Earth, confirming the widespread pollution of the upper mantle with this recycled uranium. Although many ocean island basalts (OIBs) are argued to contain a recycled component, their uranium isotopic compositions do not differ from those of the bulk Earth. Because subducted uranium was probably isotopically unfractionated before full oceanic oxidation, about 600 million years ago, this observation reflects the greater antiquity of OIB sources. Elemental and isotope systematics of uranium in OIBs are strikingly consistent with previous OIB lead model ages, indicating that these mantle reservoirs formed between 2.4 and 1.8 billion years ago. In contrast, the uranium isotopic composition of MORB requires the convective stirring of recycled uranium throughout the upper mantle within the past 600 million years. PMID:25592542

  4. Ultratrace Uranium Fingerprinting with Isotope Selective Laser Ionization Spectrometry

    SciTech Connect

    Ziegler, Summer L.; Bushaw, Bruce A.

    2008-08-01

    Uranium isotope ratios can provide source information for tracking uranium contamination in a variety of fields, ranging from occupational bioassay to monitoring aftereffects of nuclear accidents. We describe the development of Isotope Selective Laser Ionization Spectrometry (ISLIS) for ultratrace measurement of the minor isotopes 234U, 235U, and 236U with respect to 238U. Optical isotopic selectivity in three-step excitation with single-mode continuous wave lasers is capable of measuring the minor isotopes at relative abundances below 1 ppm, and is not limited by isobaric interferences such as 235UH+ during measurement of 236U. This relative abundance limit approaches the threshold for measurement of uranium minor isotopes with conventional mass spectrometry, typically 10-7, but without mass spectrometric analysis of the laser-created ions. Uranyl nitrate standards from an international blind comparison were used to test analytical performance for different isotopic compositions and with quantities ranging from 11 ng to 10 µg total uranium. Isotopic ratio determination was demonstrated over a linear dynamic range of 7 orders of magnitude with a few percent relative precision and detection limits below 500 fg for the minor isotopes.

  5. NUSIMEP-7: uranium isotope amount ratios in uranium particles.

    PubMed

    Truyens, J; Stefaniak, E A; Aregbe, Y

    2013-11-01

    The Institute for Reference Materials and Measurements (IRMM) has extensive experience in the development of isotopic reference materials and the organization of interlaboratory comparisons (ILC) for nuclear measurements in compliance with the respective international guidelines (ISO Guide 34:2009 and ISO/IEC 17043:2010). The IRMM Nuclear Signatures Interlaboratory Measurement Evaluation Program (NUSIMEP) is an external quality control program with the objective of providing materials for measurements of trace amounts of nuclear materials in environmental matrices. Measurements of the isotopic ratios of the elements uranium and plutonium in small amounts, typical of those found in environmental samples, are required for nuclear safeguards and security, for the control of environmental contamination and for the detection of nuclear proliferation. The measurement results of participants in NUSIMEP are evaluated according to international guidelines in comparison to independent external certified reference values with demonstrated metrological traceability and uncertainty. NUSIMEP-7 focused on measurements of uranium isotope amount ratios in uranium particles aiming to support European Safeguards Directorate General for Energy (DG ENER), the International Atomic Energy Agency's (IAEA) network of analytical laboratories for environmental sampling (NWAL) and laboratories in the field of particle analysis. Each participant was provided two certified test samples: one with single and one with double isotopic enrichment. These NUSIMEP test samples were prepared by controlled hydrolysis of certified uranium hexafluoride in a specially designed aerosol deposition chamber at IRMM. Laboratories participating in NUSIMEP-7 received the test samples of uranium particles on two graphite disks with undisclosed isotopic ratio values n((234)U)/n((238)U), n((235)U)/n((238)U) and n((236)U)/n((238)U). The uranium isotope ratios had to be measured using their routine analytical

  6. Ultratrace uranium fingerprinting with isotope selective laser ionization spectrometry.

    PubMed

    Ziegler, Summer L; Bushaw, Bruce A

    2008-08-01

    Uranium isotope ratios can provide source information for tracking uranium contamination in a variety of fields, ranging from occupational bioassay to monitoring aftereffects of nuclear accidents. We describe the development of isotope selective laser ionization spectrometry for ultratrace measurement of the minor isotopes (234)U, (235)U, and (236)U with respect to (238)U. The inherent isotopic selectivity of three-step excitation with single-mode continuous wave lasers results in measurement of the minor isotopes at relative abundances below 1 ppm and is not limited by isobaric interferences such as (235)UH(+) during measurement of (236)U. This relative abundance limit is attained without mass spectrometric analysis of the laser-created ions. Uranyl nitrate standards from an international blind comparison were used to test analytical performance for different isotopic compositions and with quantities ranging from 11 ng to 10 microg total uranium. Isotopic ratio determination was demonstrated over a linear dynamic range of 7 orders of magnitude with a few percent relative precision and detection limits below 500 fg for the minor isotopes. PMID:18613650

  7. Uranium isotopes fingerprint biotic reduction.

    PubMed

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-05-01

    Knowledge of paleo-redox conditions in the Earth's history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth's crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium. PMID:25902522

  8. Uranium isotopes fingerprint biotic reduction

    SciTech Connect

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-04-20

    Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. In addition, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

  9. Uranium isotopes fingerprint biotic reduction

    DOE PAGESBeta

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-04-20

    Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U),more » i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. In addition, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.« less

  10. Uranium isotopes fingerprint biotic reduction

    PubMed Central

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-01-01

    Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium. PMID:25902522

  11. Isotopic Compositions of Uranium Reference Materials

    NASA Astrophysics Data System (ADS)

    Jacobsen, B.; Borg, L. E.; Williams, R. W.; Brennecka, G.; Hutcheon, I. D.

    2009-12-01

    Uranium isotopic compositions of a variety of U standard materials were measured at Lawrence Livermore National Laboratory and are reported here. Both thermal ionization mass spectrometry (TIMS) and multi-collector inductively couple plasma mass spectrometry (MC-ICPMS) were used to determine ratios of the naturally occurring isotopes of U. Establishing an internally coherent set of isotopic values for a range of U standards is essential for inter-laboratory comparison of small differences in 238U/235U, as well as the minor isotopes of U. Differences of ~1.3‰ are now being observed in 238U/235U in natural samples, and may play an important role in understanding U geochemistry where tracing the origin of U is aided by U isotopic compositions. The 238U/235U ratios were measured with a TRITON TIMS using a mixed 233U-236U isotopic tracer to correct for instrument fractionation. This tracer was extremely pure and resulted in only very minor corrections on the measured 238U/235U ratios of ~0.03. The values obtained for 238U/235U are: IRMM184 = 137.698 ± 0.020 (n=15), SRM950a = 137.870 ± 0.018 (n=8), and CRM112a = 137.866 ± 0.030 (n=16). Uncertainties represent 2 s.d. of the population. Our measured value for IRMM184 is in near-perfect agreement with the certified value of 137.697 ± 0.042. However, the U isotopic compositions of SRM950a and CRM112a are not certified. Minor isotopes of U were determined with a Nu Plasma HR MC-ICPMS and mass bias was corrected by sample/standard bracketing to IRMM184, using its certified 238U/235U ratio. Thus, the isotopic compositions determined using both instruments are compatible. The values obtained for 234U/235U are: SRM950a = (7.437 ± 0.043)x10-3 (n=18), and CRM112a = (7.281 ± 0.050)x10-3 (n=16), both of which are in good agreement with published values. The value for 236U/235U in SRM950a was determined to be (8.48 ± 2.63)x10-6, whereas 236U was not detected in CRM112a. We are currently obtaining the U isotopic composition of

  12. ISOTOPIC COMPOSITIONS OF URANIUM REFERENCE MATERIALS

    SciTech Connect

    Jacobsen, B; Borg, L; Williams, R; Brennecka, G; Hutcheon, I

    2009-09-03

    Uranium isotopic compositions of a variety of U standard materials were measured at Lawrence Livermore National Laboratory and are reported here. Both thermal ionization mass spectrometry (TIMS) and multi-collector inductively couple plasma mass spectrometry (MC-ICPMS) were used to determine ratios of the naturally occurring isotopes of U. Establishing an internally coherent set of isotopic values for a range of U standards is essential for inter-laboratory comparison of small differences in {sup 238}U/{sup 235}U, as well as the minor isotopes of U. Differences of {approx} 1.3{per_thousand} are now being observed in {sup 238}U/{sup 235}U in natural samples, and may play an important role in understanding U geochemistry where tracing the origin of U is aided by U isotopic compositions. The {sup 238}U/{sup 235}U ratios were measured with a TRITON TIMS using a mixed {sup 233}U-{sup 236}U isotopic tracer to correct for instrument fractionation. this tracer was extremely pure and resulted in only very minor corrections on the measured {sup 238}U/{sup 235}U ratios of {approx} 0.03. The values obtained for {sup 238}U/{sup 235}U are: IRMM184 = 137.698 {+-} 0.020 (n = 15), SRM950a = 137.870 {+-} 0.018 (n = 8), and CRM112a = 137.866 {+-} 0.030 (n = 16). Uncertainties represent 2 s.d. of the population. The measured value for IRMM184 is in near-perfect agreement with the certified value of 137.697 {+-} 0.042. However, the U isotopic compositions of SRM950a and CRM112a are not certified. Minor isotopes of U were determined with a Nu Plasma HR MC-ICPMS and mass bias was corrected by sample/standard bracketing to IRMM184, using its certified {sup 238}U/{sup 235}U ratio. Thus, the isotopic compositions determined using both instruments are compatible. The values obtained for {sup 234}U/{sup 235}U are: SRM950a = (7.437 {+-} 0.043) x 10{sup -3} (n = 18), and CRM112a = (7.281 {+-} 0.050) x 10{sup -3} (n = 16), both of which are in good agreement with published values. The value for

  13. Uranium Isotopic Analysis with the FRAM Isotopic Analysis Code

    SciTech Connect

    Duc T. Vo; Thomas E. Sampson

    1999-05-01

    FRAM is the acronym for Fixed-energy Response-function Analysis with Multiple efficiency. This software was developed at Los Alamos National Laboratory originally for plutonium isotopic analysis. Later, it was adapted for uranium isotopic analysis in addition to plutonium. It is a code based on a self-calibration using several gamma-ray peaks for determining the isotopic ratios. The versatile-parameter database structure governs all facets of the data analysis. User editing of the parameter sets allows great flexibility in handling data with different isotopic distributions, interfering isotopes, and different acquisition parameters such as energy calibration and detector type.

  14. Uranium and plutonium isotopes in the atmosphere

    SciTech Connect

    Sakuragi, Y.; Meason, J.L.; Kuroda, P.K.

    1983-04-20

    Uranium 234 and 235 were found to be highly enriched relative to uranium 238 in several rain samples collected at Fayetteville, Arkansas, during the months of April and May 1980. The anomalous uranium appears to have originated from the Soviet satellite Cosmos-954, which fell over Canada on January 24, 1978. The uranium fallout occurred just about the time Mount St. Helens erupted on May 18, 1980. The concentration of /sup 238/U in rain increased markedly after the eruption of Mount St. Helens, and it appeared as if a large quantity of natural uranium was injected into the atmosphere by the volcanic eruption. The pattern of variation of the concentrations of uranium in rain after the eruption of Mount St. Helens was found to be similar to that of plutonium isotopes.

  15. AMS of the Minor Plutonium Isotopes.

    PubMed

    Steier, P; Hrnecek, E; Priller, A; Quinto, F; Srncik, M; Wallner, A; Wallner, G; Winkler, S

    2013-01-01

    VERA, the Vienna Environmental Research Accelerator, is especially equipped for the measurement of actinides, and performs a growing number of measurements on environmental samples. While AMS is not the optimum method for each particular plutonium isotope, the possibility to measure (239)Pu, (240)Pu, (241)Pu, (242)Pu and (244)Pu on the same AMS sputter target is a great simplification. We have obtained a first result on the global fallout value of (244)Pu/(239)Pu = (5.7 ± 1.0) × 10(-5) based on soil samples from Salzburg prefecture, Austria. Furthermore, we suggest using the (242)Pu/(240)Pu ratio as an estimate of the initial (241)Pu/(239)Pu ratio, which allows dating of the time of irradiation based solely on Pu isotopes. We have checked the validity of this estimate using literature data, simulations, and environmental samples from soil from the Salzburg prefecture (Austria), from the shut down Garigliano Nuclear Power Plant (Sessa Aurunca, Italy) and from the Irish Sea near the Sellafield nuclear facility. The maximum deviation of the estimated dates from the expected ages is 6 years, while relative dating of material from the same source seems to be possible with a precision of less than 2 years. Additional information carried by the minor plutonium isotopes may allow further improvements of the precision of the method. PMID:23565016

  16. AMS of the Minor Plutonium Isotopes

    PubMed Central

    Steier, P.; Hrnecek, E.; Priller, A.; Quinto, F.; Srncik, M.; Wallner, A.; Wallner, G.; Winkler, S.

    2013-01-01

    VERA, the Vienna Environmental Research Accelerator, is especially equipped for the measurement of actinides, and performs a growing number of measurements on environmental samples. While AMS is not the optimum method for each particular plutonium isotope, the possibility to measure 239Pu, 240Pu, 241Pu, 242Pu and 244Pu on the same AMS sputter target is a great simplification. We have obtained a first result on the global fallout value of 244Pu/239Pu = (5.7 ± 1.0) × 10−5 based on soil samples from Salzburg prefecture, Austria. Furthermore, we suggest using the 242Pu/240Pu ratio as an estimate of the initial 241Pu/239Pu ratio, which allows dating of the time of irradiation based solely on Pu isotopes. We have checked the validity of this estimate using literature data, simulations, and environmental samples from soil from the Salzburg prefecture (Austria), from the shut down Garigliano Nuclear Power Plant (Sessa Aurunca, Italy) and from the Irish Sea near the Sellafield nuclear facility. The maximum deviation of the estimated dates from the expected ages is 6 years, while relative dating of material from the same source seems to be possible with a precision of less than 2 years. Additional information carried by the minor plutonium isotopes may allow further improvements of the precision of the method. PMID:23565016

  17. Investigating Uranium Isotopic Distributions in Environmental Samples Using AMS and MC-ICPMS

    SciTech Connect

    Buchholz, B A; Brown, T A; Hamilton, T F; Hutcheon, I D; Marchetti, A A; Martinelli, R E; Ramon, E C; Tumey, S J; Williams, R W

    2005-12-09

    Major, minor, and trace uranium isotopes were measured at Lawrence Livermore National Laboratory in environmentally acquired samples using different instruments to span large variations in concentrations. Multi-collector inductively-coupled plasma mass spectrometry (MC-ICPMS) can be used to measure major and minor isotopes: {sup 238}U, {sup 235}U, {sup 234}U and {sup 236}U. Accelerator mass spectrometry (AMS) can be used to measure minor and trace isotopes: {sup 234}U, {sup 236}U, and {sup 233}U. The main limit of quantification for minor or trace uranium isotopes is the abundance sensitivity of the measurement technique; i.e., the ability to measure a minor or trace isotope of mass M in the presence of a major isotope at M{+-}1 mass units. The abundance sensitivity for {sup 236}U/{sup 235}U isotope ratio measurements using MC-ICPMS is around {approx}2x10{sup -6}. This compares with a {sup 236}U/{sup 235}U abundance sensitivity of {approx}1x10{sup -7} for the current AMS system, with the expectation of 2-3 orders of magnitude improvement in sensitivity with the addition of another high energy filter. Comparing {sup 236}U/{sup 234}U from MC-ICPMS and AMS produced agreement within {approx}10% for samples at {sup 236}U levels high enough to be measurable by both techniques.

  18. Investigating uranium isotopic distributions in environmental samples using AMS and MC-ICPMS

    NASA Astrophysics Data System (ADS)

    Buchholz, B. A.; Brown, T. A.; Hamilton, T. F.; Hutcheon, I. D.; Marchetti, A. A.; Martinelli, R. E.; Ramon, E. C.; Tumey, S. J.; Williams, R. W.

    2007-06-01

    Major, minor and trace uranium isotopes were measured at Lawrence Livermore National Laboratory in environmentally acquired samples using different instruments to span large variations in concentrations. Multi-collector inductively-coupled plasma mass spectrometry (MC-ICPMS) can be used to measure major and minor isotopes: 238U, 235U, 234U and 236U. Accelerator mass spectrometry (AMS) can be used to measure minor and trace isotopes: 234U, 236U and 233U. The main limit of quantification for minor or trace uranium isotopes is the abundance sensitivity of the measurement technique; i.e. the ability to measure a minor or trace isotope of mass M in the presence of a major isotope at M ± 1 mass units. The abundance sensitivity for 236U/235U isotope ratio measurements using MC-ICPMS is around ∼2 × 10-6. This compares with a 236U/235U abundance sensitivity of ∼1 × 10-7 for the current AMS system, with the expectation of 2-3 orders of magnitude improvement in sensitivity with the addition of another high energy filter. Comparing 236U/234U from MC-ICPMS and AMS produced agreement within ∼10% for samples at 236U levels high enough to be measurable by both techniques.

  19. Isotopic fractionation of uranium in sandstone

    USGS Publications Warehouse

    Rosholt, J.N.; Shields, W.R.; Garner, E.L.

    1963-01-01

    Relatively unoxidized black uranium ores from sandstone deposits in the western United States show deviations in the uranium-235 to uranium-234 ratio throughout a range from 40 percent excess uranium-234 to 40 percent deficient uranium-234 with respect to a reference uranium-235 to uranium-234 ratio. The deficient uranium-234 is leached preferentially to uranium-238 and the excess uranium-234 is believed to result from deposition of uranium-234 enriched in solutions from leached deposits.

  20. Advances in Multicollector ICPMS for precise and accurate isotope ratio measurements of Uranium isotopes

    NASA Astrophysics Data System (ADS)

    Bouman, C.; Lloyd, N. S.; Schwieters, J.

    2011-12-01

    The accurate and precise determination of uranium isotopes is challenging, because of the large dynamic range posed by the U isotope abundances and the limited available sample material. Various mass spectrometric techniques are used for the measurement of U isotopes, where TIMS is the most accepted and accurate one. Multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) can offer higher productivity compared to TIMS, but is traditionally limited by low efficiency of sample utilisation. This contribution will discuss progress in MC-ICPMS for detecting 234U, 235U, 236U and 238U in various uranium reference materials from IRMM and NBL. The Thermo Scientific NEPTUNE Plus with Jet Interface offers a modified dry plasma ICP interface using a large interface pump combined with a special set of sample and skimmer cones giving ultimate sensitivity for all elements across the mass range. For uranium, an ion yield of > 3 % was reported previously [1]. The NEPTUNE Plus also offers Multi Ion Counting using discrete dynode electron multipliers as well as two high abundance-sensitivity filters to discriminate against peak tailing effects on 234U and 236U originating from the major uranium beams. These improvements in sensitivity and dynamic range allow accurate measurements of 234U, 235U and 236U abundances on very small samples and at low concentration. In our approach, minor U isotopes 234U and 236U were detected on ion counters with high abundance sensitivity filters, whereas 235U and 238U were detected on Faraday Cups using a high gain current amplifier (10e12 Ohm) for 235U. Precisions and accuracies for 234U and 236U were down to ~1%. For 235U, subpermil levels were reached.

  1. Uranium isotope ratio measurements in field settings

    SciTech Connect

    Shaw, R.W.; Barshick, C.M.; Young, J.P.; Ramsey, J.M.

    1997-06-01

    The authors have developed a technique for uranium isotope ratio measurements of powder samples in field settings. Such a method will be invaluable for environmental studies, radioactive waste operations, and decommissioning and decontamination operations. Immediate field data can help guide an ongoing sampling campaign. The measurement encompasses glow discharge sputtering from pressed sample hollow cathodes, high resolution laser spectroscopy using conveniently tunable diode lasers, and optogalvanic detection. At 10% {sup 235}U enrichment and above, the measurement precision for {sup 235}U/({sup 235}U+{sup 238}U) isotope ratios was {+-}3%; it declined to {+-}15% for 0.3% (i.e., depleted) samples. A prototype instrument was constructed and is described.

  2. Determination of the concentration and isotopic composition of uranium in environmental air filters

    SciTech Connect

    Russ, G.P. III; Bazan, J.M.

    1994-08-26

    For many years, Lawrence Livermore National Laboratory has collected monthly air-particulate filter samples from a variety of environmental monitoring stations on and off site. Historically the concentration and isotopic composition of uranium collected on these filters was determined by isotope dilution using a {sup 233}U spike and thermal ionization mass spectrometry (TIMS). For samples containing as little as 10 nanograms of uranium, ICP-MS is now used to make these measurements to the required level of precision, about 5% in the measured 235/238 and 233/238. Unless particular care is taken to control bias in the mass filter, variable mass bias limits accuracy to a few percent. Measurements of the minor isotopes 236 (if present) and 234 are also possible and provide useful information for identifying the source of the uranium. The advantage of ICP-MS is in rapid analysis, {approximately}12 minutes of instrument time per sample.

  3. Discovery of actinium, thorium, protactinium, and uranium isotopes

    NASA Astrophysics Data System (ADS)

    Fry, C.; Thoennessen, M.

    2013-05-01

    Thirty-one actinium, thirty-one thorium, twenty-eight protactinium, and twenty-three uranium isotopes have so far been observed; the discovery of these isotopes is described. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

  4. Evaluating the status of uranium isotope ratio measurements using an inter-laboratory comparison campaign

    NASA Astrophysics Data System (ADS)

    Richter, S.; Alonso, A.; Truyens, J.; Kühn, H.; Verbruggen, A.; Wellum, R.

    2007-07-01

    The REIMEP 18 (Regular European Inter-laboratory Measurement Evaluation Programme) campaign for the measurement isotopic ratios of uranium in nitric acid solution was completed in December 2006. The task for all participating laboratories was to measure the uranium isotopic composition of four uranium samples ranging from depleted to slightly enriched uranium. With 71 participating laboratories REIMEP 18 has become the largest nuclear isotopic measurement campaign organized by IRMM so far. Participation in this kind of measurement campaign is an integral part of the external quality control required for nuclear safeguards laboratories worldwide. For the first time also a significant number of academic laboratories, mainly from the geochemistry area was included. Certification measurements were carried out at IRMM using state-of-the-art mass spectrometric methodology. A MAT511 UF6-gas source mass spectrometer (GSMS) was used to determine the n(235U)/n(238U) ratios and a TRITON thermal-ionization mass-spectrometer (TIMS) for the minor isotope ratios n(234U)/n(238U) and n(236U)/n(238U). Verification measurements on ampouled samples were performed successfully prior to sample shipping and showed good agreement with the certified ratios. The results of the REIMEP 18 campaign confirm in general the excellent capability of nuclear safeguards and scientific laboratories in measuring isotopic abundances of uranium, although some problems were discovered for the measurements of the minor isotope ratios n(234U)/n(238U) and n(236U)/n(238U) and the calculation of measurement uncertainties for isotope ratios in general. This paper describes the outcome of the REIMEP 18 campaign. It includes a graphical evaluation and discussion of the results, an evaluation of the applied measurement and calibration techniques and a discussion of conclusions and actions to be taken.

  5. Uranium Isotope Systematic in Saanich Inlet

    NASA Astrophysics Data System (ADS)

    Amini, M.; Holmden, C.; Francois, R.

    2008-12-01

    As a redox-sensitive element Uranium has become the focus of stable isotope studies. Based on the nuclear field shift effect [1], U isotope fractionation was predicted as a function of U(IV)-U(VI) exchange reactions with the insoluble reduced U(IV) species being heavier than the soluble oxidized U(VI) species. Recently, variations in 238U/235U were reported in low temperature aqueous and sedimentary environments [2,3] indicating that U deposited in well-oxygenated environments is characterized by light isotopic composition, whereas suboxic and anoxic deposits tend towards a heavy isotopic signature. U isotope fractionation has been hence proposed as a promising new paleo-redox proxy. In order to test the efficacy of U isotope fractionation to record oxidation states in marine systems, we are investigating sediment samples deposited over a range of redox conditions in the seasonally anoxic Saanich Inlet, on the east coast of Vancouver Island. We have also made δ238U measurements for water samples from above and below the redoxcline. The measurements were carried out by MC-ICPMS using 233U/236U-double spike technique. The data are reported as δ238U relative to NBL 112a with a 238U/235U ratio of 137.88 (2sd). External precision is better than 0.10 permil (2sd). Eleven analyses of seawater performed over the course of this work yielded δ238U of -0.41±0.07 permil (2sd). No clear difference in δ238U values has been found, thus far, in water samples collected at 10m (O2~380μM) and 200m (O2~1μM) depths from a single location in the middle of the inlet. The mean of two measurements of the deepwater sample yielded -0.43±0.01 permil (2sd). Two measurements of the shallow water sample yielded a mean value of -0.38±0.03 permil (2sd). The δ238U values for HF-HNO3 digestions of the organic rich sediments, one taken in the middle of the basin (3.11% organic carbon) below seasonally anoxic bottom waters (-0.22±0.01 permil, n=2), and the other taken from the sill (1

  6. Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits

    NASA Astrophysics Data System (ADS)

    Uvarova, Yulia A.; Kyser, T. Kurt; Geagea, Majdi Lahd; Chipley, Don

    2014-12-01

    Variations in 238U/235U and 234U/238U ratios were measured in uranium minerals from a spectrum of uranium deposit types, as well as diagenetic phosphates in uranium-rich basins and peraluminous rhyolites and associated autunite mineralisation from Macusani Meseta, Peru. Mean δ238U values of uranium minerals relative to NBL CRM 112-A are 0.02‰ for metasomatic deposits, 0.16‰ for intrusive, 0.18‰ for calcrete, 0.18‰ for volcanic, 0.29‰ for quartz-pebble conglomerate, 0.29‰ for sandstone-hosted, 0.44‰ for unconformity-type, and 0.56‰ for vein, with a total range in δ238U values from -0.30‰ to 1.52‰. Uranium mineralisation associated with igneous systems, including low-temperature calcretes that are sourced from U-rich minerals in igneous systems, have low δ238U values of ca. 0.1‰, near those of their igneous sources, whereas uranium minerals in basin-hosted deposits have higher and more variable values. High-grade unconformity-related deposits have δ238U values around 0.2‰, whereas lower grade unconformity-type deposits in the Athabasca, Kombolgie and Otish basins have higher δ238U values. The δ234U values for most samples are around 0‰, in secular equilibrium, but some samples have δ234U values much lower or higher than 0‰ associated with addition or removal of 234U during the past 2.5 Ma. These δ238U and δ234U values suggest that there are at least two different mechanisms responsible for 238U/235U and 234U/238U variations. The 234U/238U disequilibria ratios indicate recent fluid interaction with the uranium minerals and preferential migration of 234U. Fractionation between 235U and 238U is a result of nuclear-field effects with enrichment of 238U in the reduced insoluble species (mostly UO2) and 235U in oxidised mobile species as uranyl ion, UO22+, and its complexes. Therefore, isotopic fractionation effects should be reflected in 238U/235U ratios in uranium ore minerals formed either by reduction of uranium to UO2 or chemical

  7. High precision and high accuracy isotopic measurement of uranium using lead and thorium calibration solutions by inductively coupled plasma-multiple collector-mass spectrometry

    SciTech Connect

    Bowen, I.; Walder, A.J.; Hodgson, T.; Parrish, R.R. |

    1998-12-31

    A novel method for the high accuracy and high precision measurement of uranium isotopic composition by Inductively Coupled Plasma-Multiple Collector-Mass Spectrometry is discussed. Uranium isotopic samples are spiked with either thorium or lead for use as internal calibration reference materials. This method eliminates the necessity to periodically measure uranium standards to correct for changing mass bias when samples are measured over long time periods. This technique has generated among the highest levels of analytical precision on both the major and minor isotopes of uranium. Sample throughput has also been demonstrated to exceed Thermal Ionization Mass Spectrometry by a factor of four to five.

  8. Tables for determining lead, uranium, and thorium isotope ages

    NASA Technical Reports Server (NTRS)

    Schonfeld, E.

    1974-01-01

    Tables for determining lead, uranium, and thorium isotope ages are presented in the form of computer printouts. Decay constants, analytical expressions for the functions evaluated, and the precision of the calculations are briefly discussed.

  9. Polyatomic interferences on high precision uranium isotope ratio measurements by MC-ICP-MS: Applications to environmental sampling for nuclear safeguards

    DOE PAGESBeta

    Pollington, Anthony D.; Kinman, William S.; Hanson, Susan K.; Steiner, Robert E.

    2015-09-04

    Modern mass spectrometry and separation techniques have made measurement of major uranium isotope ratios a routine task; however accurate and precise measurement of the minor uranium isotopes remains a challenge as sample size decreases. One particular challenge is the presence of isobaric interferences and their impact on the accuracy of minor isotope 234U and 236U measurements. Furthermore, we present techniques used for routine U isotopic analysis of environmental nuclear safeguards samples and evaluate polyatomic interferences that negatively impact accuracy as well as methods to mitigate their impacts.

  10. Polyatomic interferences on high precision uranium isotope ratio measurements by MC-ICP-MS: Applications to environmental sampling for nuclear safeguards

    SciTech Connect

    Pollington, Anthony D.; Kinman, William S.; Hanson, Susan K.; Steiner, Robert E.

    2015-09-04

    Modern mass spectrometry and separation techniques have made measurement of major uranium isotope ratios a routine task; however accurate and precise measurement of the minor uranium isotopes remains a challenge as sample size decreases. One particular challenge is the presence of isobaric interferences and their impact on the accuracy of minor isotope 234U and 236U measurements. Furthermore, we present techniques used for routine U isotopic analysis of environmental nuclear safeguards samples and evaluate polyatomic interferences that negatively impact accuracy as well as methods to mitigate their impacts.

  11. Isotopic evidence of natural uranium and spent fuel uranium releases into the environment.

    PubMed

    Pourcelot, L; Boulet, B; Le Corre, C; Loyen, J; Fayolle, C; Tournieux, D; Van Hecke, W; Martinez, B; Petit, J

    2011-02-01

    Uranium and plutonium isotopes were measured in soils, sediments and waters in an area subject to the past and present discharges from the uranium conversion plant of Malvési (France). The isotopes (236)U and (239)Pu are well known activation products of uranium and they prove to be powerful tracers of spent fuel releases in soils and sediments. On the other hand (234)U and (238)U activities measured in waters can be used to distinguish between releases and background uranium sources. Such findings contribute to improve the monitoring of the actinides releases by nuclear fuel facilities (mining sites, conversion, enrichment and fuel plants, reprocessing plants). PMID:21132170

  12. Uranium Isotope Ratios in Modern and Precambrian Soils

    NASA Astrophysics Data System (ADS)

    DeCorte, B.; Planavsky, N.; Wang, X.; Auerbach, D. J.; Knudsen, A. C.

    2015-12-01

    Uranium isotopes (δ238U values) are an emerging paleoredox proxy that can help to better understand the redox evolution of Earth's surface environment. Recently, uranium isotopes have been used to reconstruct ocean and atmospheric redox conditions (Montoya-Pino et al., 2010; Brennecka et al., 2011; Kendall et al., 2013; Dahl et al., 2014). However, to date, there have not been studies on paleosols, despite that paleosols are, arguably better suited to directly tracking the redox conditions of the atmosphere. Sedimentary δ238U variability requires the formation of the soluble, oxidized form of U, U(VI). The formation of U(VI) is generally thought to require oxygen levels orders of magnitude higher than prebiotic levels. Without significant U mobility, it would have been impossible to develop isotopically distinct pools of uranium in ancient Earth environments. Conversely, an active U redox cycle leads to significant variability in δ238U values. Here we present a temporally and geographically expansive uranium isotope record from paleosols and modern soils to better constrain atmospheric oxygen levels during the Precambrian. Preliminary U isotope measurements of paleosols are unfractionated (relative to igneous rocks), possibly because of limited fractionation during oxidation (e.g., {Wang, 2015 #478}) or insufficient atmospheric oxygen levels to oxidize U(IV)-bearing minerals in the bedrock. Further U isotope measurements of paleosols with comparison to modern soils will resolve this issue.

  13. Uranium isotopes in surface waters from southern Africa

    NASA Astrophysics Data System (ADS)

    Kronfeld, J.; Vogel, J. C.

    1991-07-01

    The 234U/ 238U activity ratio in river water in southern Africa is generally higher than that reported for rivers in other regions of the world. This is interpreted as due to the prevailing environmental conditions: in this warm dry region mechanical weathering predominates over chemical weathering, causing the isotope activity ratio of leached uranium to be, on average, 2.03 ± 0.42 as compared to a ratio of 1.20 for river water in the more humid tropical and temperate regions. The isotopic composition of leachable uranium from river sediment is similar to that in the water. Rivers draining the Witwatersrand gold and uranium mining area clearly show pollution inputs characterised by high uranium content and low activity ratios.

  14. Origin of uranium isotope variations in early solar nebula condensates

    PubMed Central

    Tissot, François L. H.; Dauphas, Nicolas; Grossman, Lawrence

    2016-01-01

    High-temperature condensates found in meteorites display uranium isotopic variations (235U/238U), which complicate dating the solar system’s formation and whose origin remains mysterious. It is possible that these variations are due to the decay of the short-lived radionuclide 247Cm (t1/2 = 15.6 My) into 235U, but they could also be due to uranium kinetic isotopic fractionation during condensation. We report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of 235U reaching ~+6% relative to average solar system composition, which can only be due to the decay of 247Cm. This allows us to constrain the 247Cm/235U ratio at solar system formation to (1.1 ± 0.3) × 10−4. This value provides new clues on the universality of the nucleosynthetic r-process of rapid neutron capture. PMID:26973874

  15. Isotopic uranium concentrations in Pullman soils of the Texas Panhandle

    SciTech Connect

    Booker, J.D.; Honea, J.H.; Gabocy, T.A.

    1995-12-31

    The study of the historic isotopic uranium data (1988 to 1994) from Pullman soils near the US Department of Energy`s Pantex Plant was undertaken to provide a range of values for native concentrations of uranium isotopes in Pullman soils of the Texas Panhandle. Offsite and onsite soil monitoring locations have been sampled since 1978. The Bushland, Texas site is used as a control location because it is upwind of the plant. Data sets for 1988 to 1993 which show significant differences from the control data set in median differences of U-234 and U-238 are summarized and discussed. Maximum uranium concentrations at Firing Sites demonstrate substantial contamination. U-234 and U-238 isotopic activity ratio results for some offsite sample locations were significantly higher than those of the control location.

  16. Origin of uranium isotope variations in early solar nebula condensates.

    PubMed

    Tissot, François L H; Dauphas, Nicolas; Grossman, Lawrence

    2016-03-01

    High-temperature condensates found in meteorites display uranium isotopic variations ((235)U/(238)U), which complicate dating the solar system's formation and whose origin remains mysterious. It is possible that these variations are due to the decay of the short-lived radionuclide (247)Cm (t 1/2 = 15.6 My) into (235)U, but they could also be due to uranium kinetic isotopic fractionation during condensation. We report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of (235)U reaching ~+6% relative to average solar system composition, which can only be due to the decay of (247)Cm. This allows us to constrain the (247)Cm/(235)U ratio at solar system formation to (1.1 ± 0.3) × 10(-4). This value provides new clues on the universality of the nucleosynthetic r-process of rapid neutron capture. PMID:26973874

  17. Uranium isotope measurements by quadrupole ICP-MS for process monitoring of enrichment

    SciTech Connect

    Policke, T.A.; Bolin, R.N.; Harris, T.L.

    1998-12-31

    Historically, uranium isotopic ratio measurements in the nuclear industry have been performed using Thermal Ionization Mass Spectrometry (TIMS); primarily due to the high level of precision that can be achieved. TIMS analysis, however, requires sample purification and intricate sample loading. Quadrupole (low resolution, single detector) inductively coupled plasma--mass spectrometry, Q-ICP-MS, overcomes these disadvantages and is a cost-effective alternative, i.e., in terms of initial capital, maintenance, and operating costs. This paper presents a simple, single standard approach for measuring uranium isotope content in various solid and liquid nuclear materials along with some comparison data of Q-ICP-MS and TIMS. Intensity ratios of {sup 234}U, {sup 235}U, {sup 236}U, and {sup 238}U to total U intensity are produced, providing the enrichment level or percent {sup 235}U. A detailed description of the instrument and data collection parameters are also provided. Optimal precision and accuracy are achieved through the use of a single standard which is closely matched to the enrichment and concentration of the samples. Depending upon the standard chosen, enrichments between depleted and 97% can be quantified. Standard deviations for the major uranium isotopes are typically within 0.02 absolute and at least an order of magnitude lower for the minor U isotope abundances.

  18. Enhanced Method for Molybdenum Separation and Isotopic Determination in Geological Samples and Uranium-Rich Materials

    NASA Astrophysics Data System (ADS)

    Migeon, V.; Bourdon, B.; Pili, E.

    2014-12-01

    Molybdenum (Mo) shares analogous geochemical properties with uranium. Mo ispresent as a minor or a trace element in uranium ores under two main oxidation states: +IVand +VI. Mo has seven stable isotopes (92, 94, 95, 96, 97, 98 and 100). In natural systems,Mo and Mo isotopes were shown to fractionate during redox reactions. Because Morepresents an impurity difficult to separate in the nuclear fuel cycle, it has the potential to beused as an indicator of the origins of uranium concentrates, in the framework of nuclearforensics. This work focuses on developing an enhanced separation method for Mo from auranium-rich matrix (uranium ore, uranium concentrate) in order to analyze the massfractionation induced by processes typical of the nuclear fuel cycle. Purification of Mo forisotope ratio measurements is performed with a three-step separation on ion-exchange resins,with yields between 45 and 82%. Matrix and isobaric interferences (Zr, Ru) were reduced ingeological and uranium standards, such as U/Mo ≤ 2*10-4, Zr/Mo ≤ 1*10-3, Ru/Mo ≤ 6*10-4and Fe/Mo ≤ 4*10-3. Mo isotopic compositions were measured on a Neptune Plus MC-ICPMSequipped with Jet cones, for a concentration of 30 ng/ml. The achieved sensitivity is~1200-1800 V/ppm with interferences below 10 mV and an overall reproducibility of 0.02 ‰on the δ98Mo values. A double spike, with 97Mo and 100Mo, was added to the samples beforethe purification. It allows for correction of the chemical and instrumental mass fractionations,without requiring a quantitative yield. For igneous rocks, δ98Mo values range between -0.55and -0.03 ‰, relative to the NIST-SRM 3134 molybdenum standard. Fractionation amonguranium ore concentrates is higher, with δ98Mo ranging between 0.02 and -2.84 ‰.

  19. Evolution of isotopic composition of reprocessed uranium during the multiple recycling in light water reactors with natural uranium feed

    SciTech Connect

    Smirnov, A. Yu. Sulaberidze, G. A.; Alekseev, P. N.; Dudnikov, A. A.; Nevinitsa, V. A. Proselkov, V. N.; Chibinyaev, A. V.

    2012-12-15

    A complex approach based on the consistent modeling of neutron-physics processes and processes of cascade separation of isotopes is applied for analyzing physical problems of the multiple usage of reprocessed uranium in the fuel cycle of light water reactors. A number of scenarios of multiple recycling of reprocessed uranium in light water reactors are considered. In the process, an excess absorption of neutrons by the {sup 236}U isotope is compensated by re-enrichment in the {sup 235}U isotope. Specific consumptions of natural uranium for re-enrichment of the reprocessed uranium depending on the content of the {sup 232}U isotope are obtained.

  20. Uranium isotopes in ground water as a prospecting technique

    SciTech Connect

    Cowart, J.B.; Osmond, J.K.

    1980-02-01

    The isotopic concentrations of dissolved uranium were determined for 300 ground water samples near eight known uranium accumulations to see if new approaches to prospecting could be developed. It is concluded that a plot of /sup 234/U//sup 238/U activity ratio (A.R.) versus uranium concentration (C) can be used to identify redox fronts, to locate uranium accumulations, and to determine whether such accumulations are being augmented or depleted by contemporary aquifer/ground water conditions. In aquifers exhibiting flow-through hydrologic systems, up-dip ground water samples are characterized by high uranium concentration values (> 1 to 4 ppB) and down-dip samples by low uranium concentration values (less than 1 ppB). The boundary between these two regimes can usually be identified as a redox front on the basis of regional water chemistry and known uranium accumulations. Close proximity to uranium accumulations is usually indicated either by very high uranium concentrations in the ground water or by a combination of high concentration and high activity ratio values. Ground waters down-dip from such accumulations often exhibit low uranium concentration values but retain their high A.R. values. This serves as a regional indicator of possible uranium accumulations where conditions favor the continued augmentation of the deposit by precipitation from ground water. Where the accumulation is being dispersed and depleted by the ground water system, low A.R. values are observed. Results from the Gulf Coast District of Texas and the Wyoming districts are presented.

  1. Pulsed CO laser for isotope separation of uranium

    SciTech Connect

    Baranov, Igor Y.; Koptev, Andrey V.

    2012-07-30

    This article proposes a technical solution for using a CO laser facility for the industrial separation of uranium used in the production of fuel for nuclear power plants, employing a method of laser isotope separation of uranium with condensation repression in a free jet. The laser operation with nanosecond pulse irradiation can provide an acceptable efficiency in the separating unit and a high efficiency of the laser with the wavelength of 5.3 {mu}m. In the present work we also introduce a calculation model and define the parameters of a mode-locked CO laser with a RF discharge in the supersonic stream. The average pulsed CO laser power of 3 kW is sufficient for efficient industrial isotope separation of uranium in one stage.

  2. Uranium isotope separation from 1941 to the present

    NASA Astrophysics Data System (ADS)

    Maier-Komor, Peter

    2010-02-01

    Uranium isotope separation was the key development for the preparation of highly enriched isotopes in general and thus became the seed for target development and preparation for nuclear and applied physics. In 1941 (year of birth of the author) large-scale development for uranium isotope separation was started after the US authorities were warned that NAZI Germany had started its program for enrichment of uranium and might have confiscated all uranium and uranium mines in their sphere of influence. Within the framework of the Manhattan Projects the first electromagnetic mass separators (Calutrons) were installed and further developed for high throughput. The military aim of the Navy Department was to develop nuclear propulsion for submarines with practically unlimited range. Parallel to this the army worked on the development of the atomic bomb. Also in 1941 plutonium was discovered and the production of 239Pu was included into the atomic bomb program. 235U enrichment starting with natural uranium was performed in two steps with different techniques of mass separation in Oak Ridge. The first step was gas diffusion which was limited to low enrichment. The second step for high enrichment was performed with electromagnetic mass spectrometers (Calutrons). The theory for the much more effective enrichment with centrifugal separation was developed also during the Second World War, but technical problems e.g. development of high speed ball and needle bearings could not be solved before the end of the war. Spying accelerated the development of uranium separation in the Soviet Union, but also later in China, India, Pakistan, Iran and Iraq. In this paper, the physical and chemical procedures are outlined which lead to the success of the project. Some security aspects and Non-Proliferation measures are discussed.

  3. High-Resolution Triple Resonance Autoionization of Uranium Isotopes

    SciTech Connect

    Schumann, Philipp G.; Wendt, K; Bushaw, Bruce A.

    2005-11-01

    The near-threshold autoionization (AI) spectrum of uranium has been investigated by triple-resonance excitation with single-mode continuous lasers. Spectra were recorded over the first {approx}30 cm-1 above the first ionization limit at a resolution of 3x10-4 cm 1 using intermediate states with different J values (6, 7, 8) to assign AI level total angular momentum JAI = 5 to 9. Resonances with widths ranging from 8 MHz to 30 GHz were observed; the strongest ones have JAI = 9 and widths of {approx} 60 MHz. Hyperfine structures for 235U and isotope shifts for 234,235U have been measured in the two intermediate levels and in the final AI level for the most favorable excitation path. These measurements were performed using aqueous samples containing sub-milligram quantities of uranium at natural isotopic abundances, indicating the potential of this approach for trace isotope ratio determinations.

  4. Certification of the Uranium Isotopic Ratios in Nbl Crm 112-A, Uranium Assay Standard (Invited)

    NASA Astrophysics Data System (ADS)

    Mathew, K. J.; Mason, P.; Narayanan, U.

    2010-12-01

    Isotopic reference materials are needed to validate measurement procedures and to calibrate multi-collector ion counting detector systems. New Brunswick Laboratory (NBL) provides a suite of certified isotopic and assay standards for the US and international nuclear safeguards community. NBL Certified Reference Material (CRM) 112-A Uranium Metal Assay Standard with a consensus value of 137.88 for the 238U/235U ratio [National Bureau of Standards -- NBS, currently named National Institute for Standards and Technology, Standard Reference Material (SRM) 960 had been renamed CRM 112-A] is commonly used as a natural uranium isotopic reference material within the earth science community. We have completed the analytical work for characterizing the isotopic composition of NBL CRM 112-A Uranium Assay Standard and NBL CRM 145 (uranyl nitrate solution prepared from CRM 112-A). The 235U/238U isotopic ratios were characterized using the total evaporation (TE) and the modified total evaporation (MTE) methods. The 234U/238U isotope ratios were characterized using a conventional analysis technique and verified using the ratios measured in the MTE analytical technique. The analysis plan for the characterization work was developed such that isotopic ratios that are traceable to NBL CRM U030-A are obtained. NBL is preparing a certificate of Analysis and will issue a certificate for Uranium Assay and Isotopics. The results of the CRM 112-A certification measurements will be discussed. These results will be compared with the average values from Richter et al (2010). A comparison of the precision and accuracy of the measurement methods (TE, MTE and Conventional) employed in the certification will be presented. The uncertainties in the 235U/238U and 234U/238U ratios, calculated according to the Guide to the Expression of Uncertainty in Measurements (GUM) and the dominant contributors to the combined standard uncertainty will be discussed.

  5. Utilizing Isotopic Uranium Ratios in Groundwater Evaluations at FUSRAP Sites

    SciTech Connect

    Frederick, W.T.; Keil, K.G.; Rhodes, M.C.; Peterson, J.M.; MacDonell, M.M.

    2007-07-01

    The U.S. Army Corps of Engineers Buffalo District is evaluating environmental radioactive contamination at several Formerly Utilized Sites Remedial Action Program (FUSRAP) sites throughout New York, Pennsylvania, Ohio, and Indiana. The investigations follow the process defined in the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). Groundwater data from the Niagara Falls Storage Site (NFSS) in Lewiston, New York were evaluated for isotopic uranium ratios, specifically uranium-234 versus uranium-238 (U- 234 and U-238, respectively), and the results were presented at Waste Management 2006. Since uranium naturally occurs in all groundwater, it can be difficult to distinguish where low-concentration impacts from past releases differ from the high end of a site-specific natural background range. In natural groundwater, the ratio of U-234 to U-238 exceeds 1 (unity) due to the alpha particle recoil effect, in which U-234 is preferentially mobilized to groundwater from adjacent rock or soil. This process is very slow and may take hundreds to thousands of years before a measurable increase is seen in the natural isotopic ratio. If site releases are the source of uranium being measured in groundwater, the U-234 to U-238 ratio is commonly closer to 1, which normally reflects FUSRAP-related, uranium-contaminated wastes and soils. This lower ratio occurs because not enough residence time has elapsed since the 1940's and 1950's for the alpha particle recoil effect to have significantly altered the contamination-derived ratio. An evaluation of NFSS-specific and regional groundwater data indicate that an isotopic ratio of 1.2 has been identified as a signature value to help distinguish natural groundwater, which may have a broad background range, from zones impacted by past releases. (authors)

  6. Uranium isotopic composition and uranium concentration in special reference material SRM A (uranium in KCl/LiCl salt matrix)

    SciTech Connect

    Graczyk, D.G.; Essling, A.M.; Sabau, C.S.; Smith, F.P.; Bowers, D.L.; Ackerman, J.P.

    1997-07-01

    To help assure that analysis data of known quality will be produced in support of demonstration programs at the Fuel Conditioning Facility at Argonne National Laboratory-West (Idaho Falls, ID), a special reference material has been prepared and characterized. Designated SRM A, the material consists of individual units of LiCl/KCl eutectic salt containing a nominal concentration of 2.5 wt. % enriched uranium. Analyses were performed at Argonne National Laboratory-East (Argonne, IL) to determine the uniformity of the material and to establish reference values for the uranium concentration and uranium isotopic composition. Ten units from a batch of approximately 190 units were analyzed by the mass spectrometric isotope dilution technique to determine their uranium concentration. These measurements provided a mean value of 2.5058 {+-} 0.0052 wt. % U, where the uncertainty includes estimated limits to both random and systematic errors that might have affected the measurements. Evidence was found of a small, apparently random, non-uniformity in uranium content of the individual SRM A units, which exhibits a standard deviation of 0.078% of the mean uranium concentration. Isotopic analysis of the uranium from three units, by means of thermal ionization mass spectrometry with a special, internal-standard procedure, indicated that the uranium isotopy is uniform among the pellets with a composition corresponding to 0.1115 {+-} 0.0006 wt. % {sup 234}U, 19.8336 {+-} 0.0059 wt. % {sup 235}U, 0.1337 {+-} 0.0006 wt. % {sup 236}U, and 79.9171 {+-} 0.0057 wt. % {sup 238}U.

  7. Isotopic analysis of uranium in natural waters by alpha spectrometry

    USGS Publications Warehouse

    Edwards, K.W.

    1968-01-01

    A method is described for the determination of U234/U238 activity ratios for uranium present in natural waters. The uranium is coprecipitated from solution with aluminum phosphate, extracted into ethyl acetate, further purified by ion exchange, and finally electroplated on a titanium disc for counting. The individual isotopes are determined by measurement of the alpha-particle energy spectrum using a high resolution low-background alpha spectrometer. Overall chemical recovery of about 90 percent and a counting efficiency of 25 percent allow analyses of water samples containing as little as 0.10 ?g/l of uranium. The accuracy of the method is limited, on most samples, primarily by counting statistics.

  8. Disequilibrium of uranium isotopes in some Syrian groundwater.

    PubMed

    Abdul-Hadi, A; Alhassanieh, O; Ghafar, M

    2001-07-01

    Uranium concentration in groundwater samples from three areas of Syria was determined using alpha-spectrometry and INAA. It was in the range of 0-6.13 microg/l in the phosphate areas, and lower than 1 ppb in the volcanic areas. The activity ratio of 234U/238U was investigated, and disequilibrium of uranium isotopes was found to occur (234U/238U = 0.52-2.02). The excess of 234U was calculated. This excess can be interpreted by higher mobility of 234U, which more readily forms the soluble (UO2)2+ ion in comparison with 238U, most of which remains in the insoluble 4+ state. This excess increases with increase in uranium concentration. Thorium concentration was measured using INAA, it was found to be in the rang 0-1.15 microg/l. PMID:11339524

  9. Separation of uranium isotopes by chemical exchange

    DOEpatents

    Ogle, P.R. Jr.

    1974-02-26

    A chemical exchange method is provided for separating /sup 235/U from / sup 238/U comprising contacting a first phase containing UF/sub 6/ with a second phase containing a compound selected from the group consisting of NOUF/sub 6/, NOUF/sub 7/, and NO/sub 2/UF/sub 7/ until the U Fsub 6/ in the first phase becomes enriched in the /sup 235/U isotope. (Official Gazette)

  10. Nuclear Volume-Dependent Fractionation of Uranium Isotopes

    NASA Astrophysics Data System (ADS)

    Weyer, S.; Schauble, E. A.; Anbar, A. D.

    2007-12-01

    Chemical reactions can fractionate isotopes because the magnitudes of equilibrium and rate constants are subtly sensitive to nuclear mass. Geoscientists have exploited this fact to learn about modern environmental processes and past environmental conditions by precisely measuring variations in the isotope compositions of a wide range of elements in natural materials. Here we present evidence from natural terrestrial samples that processes related to ¡°nuclear volume¡± rather than ¡°nuclear mass¡± significantly fractionate the isotope composition of the heaviest primordial element ¨C uranium. The isotopic composition of U in nature is generally assumed to be invariant. Here, we report variations of the 238U/235U isotope ratio in natural samples (basalts, granites, seawater, corals, black shales, suboxic sediments, ferro-manganese crusts/nodules and BIFs), which span a range of δ238U values of ~ 1.3 ‰, exceeding by far the analytical precision of our method (¡Ö 0.06‰, 2SD, based on replicate measurements of individual samples). The largest isotope variations found in our survey are between oxidized and reduced depositional environments, with seawater and suboxic sediments falling in between. U isotopes were analyzed with MC-ICP-MS. A mixed 236U-233U isotopic tracer (double spike) was used to correct for isotope fractionation during sample purification and instrumental mass bias. Sediments formed in oxic environments, such as manganese crusts from the Atlantic and Pacific oceans, display δ238U of -0.54 to -0.62 ‰, slightly lighter than that of seawater (-0.41 ‰). However, sediments from reducing environments, such as black shales from the Black Sea (unit I and unit II) and the Cariaco basin, display heavy U isotope compositions with δ238U of up to +0.43 ‰ (0.84 ‰ heavier than seawater). Uranium enrichment in these sediments probably occurred during the reduction of soluble U(VI) (from seawater) to insoluble U(IV). Intriguingly, isotope

  11. Analysis on uranium isotope in the facilities of nuclear fuel materials using depleted uranium

    SciTech Connect

    Jong seon Jeon; Ki chut Jung; Sang gyu Park; Tae hyun Kim; Jae min Lee

    2007-07-01

    This study checked the degree of contamination of depleted uranium used as a chemical catalyst in the manufacturing process within the facilities of nuclear fuel materials to analyze the environmental sample for abandoning their industrial factory sites and investigated how many times of contamination were made compared to (natural) abundance of isotopes if contamination was made within the facilities. In order to analyze the degree of uranium contamination, the researcher of this study divided the upper and lower parts of 20 points from the surface of the earth within the factory site made of concrete and extracted 40 samples from the surface of the earth and 15 samples for checking air and surface water contamination. The study checked the concentration of uranium existing in small quantity in the samples by liquefying a large amount of samples using pre-treatable acid percolation. (authors)

  12. 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

  13. Uranium isotopes quantitatively determined by modified method of atomic absorption spectrophotometry

    NASA Technical Reports Server (NTRS)

    Lee, G. H.

    1967-01-01

    Hollow-cathode discharge tubes determine the quantities of uranium isotopes in a sample by using atomic absorption spectrophotometry. Dissociation of the uranium atoms allows a large number of ground state atoms to be produced, absorbing the incident radiation that is different for the two major isotopes.

  14. Uranium and strontium isotopes in Boulder Zone waters, South Florida

    SciTech Connect

    Cowart, J.B. . Dept. of Geology)

    1993-03-01

    The Boulder Zone of southern peninsular Florida, which is at a depth of approximately 1,000 m, is a cavernous, dolomitized zone which contains anomalously cool water which appears to be of marine composition. Samples of this water, as they have become available, have been analyzed for uranium concentration, U-234/U-238 alpha activity ratio, and, in a few cases, Sr-87/Sr-86 ratio and concentration. Boulder Zone samples collected in the vicinity of Ft. Lauderdale have analyzed values of the above mentioned parameters which are virtually indistinguishable from those of sea water. In a fan-like radial pattern, the uranium concentrations decrease and the U-234/U-238 activity ratios increase away from the apex at Ft. Lauderdale. It has been hypothesized by others that the Ft. Lauderdale area is the location on land that is nearest to an intake area where sea water moves into the Boulder Zone. The isotopic and concentration values reported here are consistent with this hypothesis. Waters collected from well located near the Atlantic coast north of Ft. Lauderdale do not display the same U and Sr isotopic pattern as those in the remainder of south Florida. This may be due to increased mixing between water bearing units which have been fractured and/or faulted by the extention of a flexure which has been postulated in the northern part of the study area.

  15. Utilizing Isotopic Uranium Ratios in Groundwater Evaluations at NFSS

    SciTech Connect

    Rhodes, M.C.; Keil, K.G.; Frederick, W.T.; Papura, T.R.; Leithner, J.S.; Peterson, J.M.; MacDonell, M.M.

    2006-07-01

    The U.S. Army Corps of Engineers (USACE) Buffalo District is currently evaluating environmental contamination at the Niagara Falls Storage Site (NFSS) under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) as part of its Formerly Utilized Sites Remedial Action Program (FUSRAP). The NFSS is located in the Town of Lewiston in western New York and has been used to store uranium-contaminated materials since 1944. Most of the radioactive materials are currently contained in an on-site structure, but past contamination remains in soil and groundwater. As a naturally occurring radionuclide, uranium is present in all groundwater. Because contamination levels at the site are quite low, it can be difficult to distinguish zones that have been impacted by the past releases from those at the high end of the natural background range. The differences in the isotopic ratio of uranium-234 (U-234) to uranium-238 (U-238) between natural groundwater systems and affected areas are being used in an innovative way to better define the nature and extent of groundwater contamination at NFSS. In natural groundwater, the ratio of U-234 to U-238 exceeds 1 due to the alpha particle recoil effect, in which U-234 is preferentially mobilized to groundwater from adjacent rock or soil. This process is very slow, and it can be hundreds to thousands of years before a measurable impact is seen in the isotopic ratio. Thus, as a result of the recoil effect, the ratio of U-234 to U-238 will be higher in natural groundwater than in contaminated groundwater. This means that if site releases were the source of the uranium being measured in groundwater at NFSS, the ratio of U-234 to U-238 would be expected to be very close to 1 (the same ratio that exists in wastes and soil at the site), because not enough time has elapsed for the alpha particle recoil effect to have significantly altered that ratio. From an evaluation of site and regional groundwater data, an isotopic ratio

  16. U-Pb isotope systematics and age of uranium mineralization, Midnite mine, Washington.

    USGS Publications Warehouse

    Ludwig, K. R.; Nash, J.T.; Naeser, C.W.

    1981-01-01

    Uranium ores at the Midnite mine, near Spokane, Washington, occur in phyllites and calcsilicates of the Proterozoic Togo Formation, near the margins of an anomalously uraniferous, porphyritic quartz monzonite of Late Cretaceous age. The present geometry of the ore zones is tabular, with the thickest zones above depressions in the pluton-country rock contact. Analyses of high-grade ores from the mine define a 207 Pb/ 204 Pb- 235 U/ 204 Pb isochron indicating an age of mineralization of 51.0 + or - 0.5 m.y. This age coincides with a time of regional volcanic activity (Sanpoil Volcanics), shallow intrusive activity, erosion, and faulting. U-Th-Pb isotopic ages of zircons from the porphyritic quartz monzonite in the mine indicate an age of about 75 m.y., hence the present orebodies were formed about 24 m.y. after its intrusion. The 51-m.y. time of mineralization probably represents a period of mobilization and redeposition of uranium by supergene ground waters, perhaps aided by mild heating and ground preparation and preserved by a capping of newly accumulated, impermeable volcanic rocks. It seems most likely that the initial concentration of uranium occurred about 75 m.y. ago, probably from relatively mild hydrothermal fluids in the contact-metamorphic aureole of the U-rich porphyritic quartz monzonite.Pitchblende, coffinitc, pyrite, marcasite, and hisingerite are the most common minerals in the uranium-bearing veinlets, with minor sphalerite and chalcopyrite. Coffinitc with associated marcasite is paragenetically later than pitchblende, though textural and isotopic evidence suggests no large difference in the times of pitchblende and colfinite formation.The U-Pb isotope systematics of total ores and of pitchblende-coffinite and pyrite-marcasite separates show that whereas open system behavior for U and Pb is essentially negligible for large (200-500 g) ore samples, Pb migration has occurred on a scale of 1 to 10 mm (out of pitchblende and coffinite and into pyrite

  17. Application of Uranium Isotope Dilution Mass Spectrometry in the preparation of New Certified Reference Materials

    NASA Astrophysics Data System (ADS)

    Hasözbek, A.; Mathew, K. J.; Orlowicz, G.; Srinivasan, B.; Narayanan, U.

    2012-04-01

    Proven measurement techniques play a critical role in the preparation of Certified Reference Materials (CRMs) - those requiring high accuracy and precision in the measurement results. Isotope Dilution Mass Spectrometry (IDMS) is one such measurement method commonly used in the quantitative analysis of uranium in nuclear safeguards and isotope geology applications. In this project, we evaluated the possibility of using some of the uranium isotopic and assay CRMs made earlier by the New Brunswick laboratory as IDMS spikes to define the uranium mass fraction in future preparations of CRMs. Uranium solutions prepared from CRM 112-A (a highly pure uranium metal assay standard) and CRM 115 (a highly pure uranium oxide isotopic and assay standard) were used as spikes in the determination of uranium. Two different thermal ionization mass spectrometer instruments (MAT 261 and TRITON) were used for the isotopic measurements. Standard IDMS equation was used for data reduction to yield results for uranium mass fraction along with uncertainties, the latter calculated according to GUM. The results show that uranium mass fraction measurements can be made with the required accuracy and precision for defining the uranium concentration in new CRMs as well as in routine samples analyses.

  18. Minor actinide transmutation in thorium and uranium matrices in heavy water moderated reactors

    SciTech Connect

    Bhatti, Zaki; Hyland, B.; Edwards, G.W.R.

    2013-07-01

    The irradiation of Th{sup 232} breeds fewer of the problematic minor actinides (Np, Am, Cm) than the irradiation of U{sup 238}. This characteristic makes thorium an attractive potential matrix for the transmutation of these minor actinides, as these species can be transmuted without the creation of new actinides as is the case with a uranium fuel matrix. Minor actinides are the main contributors to long term decay heat and radiotoxicity of spent fuel, so reducing their concentration can greatly increase the capacity of a long term deep geological repository. Mixing minor actinides with thorium, three times more common in the Earth's crust than natural uranium, has the additional advantage of improving the sustainability of the fuel cycle. In this work, lattice cell calculations have been performed to determine the results of transmuting minor actinides from light water reactor spent fuel in a thorium matrix. 15-year-cooled group-extracted transuranic elements (Np, Pu, Am, Cm) from light water reactor (LWR) spent fuel were used as the fissile component in a thorium-based fuel in a heavy water moderated reactor (HWR). The minor actinide (MA) transmutation rates, spent fuel activity, decay heat and radiotoxicity, are compared with those obtained when the MA were mixed instead with natural uranium and taken to the same burnup. Each bundle contained a central pin containing a burnable neutron absorber whose initial concentration was adjusted to have the same reactivity response (in units of the delayed neutron fraction β) for coolant voiding as standard NU fuel. (authors)

  19. Uranium Stable Isotopes: A Proxy For Productivity Or Ocean Oxygenation?

    NASA Astrophysics Data System (ADS)

    Severmann, S.

    2015-12-01

    Uranium elemental abundances in sediments have traditionally been used to reconstruct primary productivity and carbon flux in the ocean. 238U/235U isotope compositions, in contrast, are currently understood to reflect the extent of bottom water anoxia in the ocean. A review of our current understanding of authigenic U enrichment mechanism into reducing sediments suggests that a revision of this interpretation is warranted. Specifically, the current interpretation of U isotope effects in suboxic vs. anoxic deposits has not taken into account the well-documented linear relationship with organic C burial rates. Although organic C rain rates (i.e., surface productivity) and bottom water oxygenation are clearly related, distinction between these two environmental controls is conceptually important as it relates to the mechanism of enhanced C burial and ultimately the strength of the biological pump. Here we will review new and existing data to test the hypothesis that the isotope composition of authigenic U in reducing sediments are best described by their relationship with parameters related to organic carbon delivery and burial, rather than bottom water oxygen concentration.

  20. Femtosecond Laser Ablation Multicollector ICPMS Analysis of Uranium Isotopes in NIST Glass

    SciTech Connect

    Duffin, Andrew M.; Springer, Kellen WE; Ward, Jesse D.; Jarman, Kenneth D.; Robinson, John W.; Endres, Mackenzie C.; Hart, Garret L.; Gonzalez, Jhanis J.; Oropeza, Dayana; Russo, Richard; Willingham, David G.; Naes, Benjamin E.; Fahey, Albert J.; Eiden, Gregory C.

    2015-02-06

    We have utilized femtosecond laser ablation coupled to multi-collector inductively couple plasma mass spectrometry to measure the uranium isotopic content of NIST 61x (x=0,2,4,6) glasses. The uranium content of these glasses is a linear two-component mixing between isotopically natural uranium and the isotopically depleted spike used in preparing the glasses. Laser ablation results match extremely well, generally within a few ppm, with solution analysis following sample dissolution and chemical separation. In addition to isotopic data, sample utilization efficiency measurements indicate that over 1% of ablated uranium atoms reach a mass spectrometer detector, making this technique extremely efficient. Laser sampling also allows for spatial analysis and our data indicate that rare uranium concentration inhomogeneities exist in NIST 616 glass.

  1. Isotopic Analysis of Uranium in NIST SRM Glass by Femtosecond Laser Ablation

    SciTech Connect

    Duffin, Andrew M.; Hart, Garret L.; Hanlen, Richard C.; Eiden, Gregory C.

    2013-05-19

    We employed femtosecond Laser Ablation Multicollector Inductively Coupled Mass Spectrometry for the 11 determination of uranium isotope ratios in a series of standard reference material glasses (NIST 610, 612, 614, and 12 616). This uranium concentration in this series of SRM glasses is a combination of isotopically natural uranium in 13 the materials used to make the glass matrix and isotopically depleted uranium added to increase the uranium 14 elemental concentration across the series. Results for NIST 610 are in excellent agreement with literature values. 15 However, other than atom percent 235U, little information is available for the remaining glasses. We present atom 16 percent and isotope ratios for 234U, 235U, 236U, and 238U for all four glasses. Our results show deviations from the 17 certificate values for the atom percent 235U, indicating the need for further examination of the uranium isotopes in 18 NIST 610-616. Our results are fully consistent with a two isotopic component mixing between the depleted 19 uranium spike and natural uranium in the bulk glass.

  2. Determination of uranium isotopes in environmental samples by anion exchange in sulfuric and hydrochloric acid media.

    PubMed

    Popov, L

    2016-09-01

    Method for determination of uranium isotopes in various environmental samples is presented. The major advantages of the method are the low cost of the analysis, high radiochemical yields and good decontamination factors from the matrix elements, natural and man-made radionuclides. The separation and purification of uranium is attained by adsorption with strong base anion exchange resin in sulfuric and hydrochloric acid media. Uranium is electrodeposited on a stainless steel disk and measured by alpha spectrometry. The analytical method has been applied for the determination of concentrations of uranium isotopes in mineral, spring and tap waters from Bulgaria. The analytical quality was checked by analyzing reference materials. PMID:27451111

  3. Innovative lasers for uranium isotope separation. [Progress report

    SciTech Connect

    Brake, M.L.; Gilgenbach, R.M.

    1991-06-01

    Copper vapor lasers have important applications to uranium atomic vapor laser isotope separation (AVLIS). The authors have spent the first two years of their project investigating two innovative methods of exciting/pumping copper vapor lasers which have the potential to improve the efficiency and scaling of large laser systems used in uranium isotope separation. Experimental research has focused on the laser discharge kinetics of (1) microwave, and (2) electron beam excitation/pumping of large-volume copper vapor lasers. During the first year, the experiments have been designed and constructed and initial data has been taken. During the second year these experiments have been diagnosed. Highlights of some of the second year results as well as plans for the future include the following: Microwave resonant cavity produced copper vapor plasmas at 2.45 GHz, have been investigated. A CW (0--500 W) signal heats and vaporizes the copper chloride to provide the atomic copper vapor. A pulsed (5 kW, 0.5--5kHz) signal is added to the incoming CW signal via a hybrid mixer to excite the copper states to the laser levels. An enhancement of the visible radiation has been observed during the pulsed pardon of the signal. Electrical probe measurements have been implemented on the system to verify the results of the electromagnetic model formulated last year. Laser gain measurements have been initiated with the use of a commercial copper vapor laser. Measurements of the spatial profile of the emission are also currently being made. The authors plan to increase the amount of pulsed microwave power to the system by implementing a high power magnetron. A laser cavity will be designed and added to this system.

  4. Valence-associated uranium isotope fractionation of uranium enriched phosphate in a shallow aquifer, Lee County, Florida

    SciTech Connect

    Weinberg, J.M. ); Levine, B.R. ); Cowart, J.B. . Geology Dept.)

    1993-03-01

    The source of anomalously high concentrations of uranium, characterized by U-234/U-238 activity ratios significantly less than unity, in shallow groundwaters of Lee County, Florida, was investigated. Uranium in cores samples was separated into U(IV) and U(VI) oxidation state fractions, and uranium analyses were conducted by alpha spectrometry. Uranium mobility was also studied in selected leaching experiments. Results indicate that mobilization of unusually soluble uranium, present in uranium enriched phosphate of the Pliocene age Tamiami Formation at determined concentrations of up to 729 ppm, is the source for high uranium concentrations in groundwater. In leaching experiments, approximately one-third of the uranium present in the uranium enriched phosphate was mobilized into the aqueous phase. Results of previous investigations suggest that U-234, produced in rock by U-238 decay, is selectively oxidized to U(VI). The uranium enriched phosphate studied in this investigation is characterized by selective reduction of U-234, with a pattern of increasing isotopic fractionation with core depth. As a consequence, U-234/U-238 activity ratios greater than 1.0 in the U(IV) fraction, and less than 1.0 in the U(VI) fraction have developed in the rock phase. In leaching experiments, the U(VI) fraction from the rock was preferentially mobilized into the aqueous phase, suggesting that U-234/U-238 activity ratios of leaching groundwaters are strongly influenced by the isotopic characteristics of the U(VI) fraction of rock. It is suggested that preferential leaching of U(VI), present in selectivity reduced uranium enriched phosphate, is the source for low activity ratio groundwaters in Lee County.

  5. Uranium disequilibrium in groundwater: An isotope dilution approach in hydrologic investigations

    USGS Publications Warehouse

    Osmond, J.K.; Rydell, H.S.; Kaufman, M.I.

    1968-01-01

    The distribution and environmental disequilibrium patterns of naturally occurring uranium isotopes (U234 and U238) in waters of the Floridan aquifer suggest that variations in the ratios of isotopic activity and concentrations can be used quantitatively to evaluate mixing proportions of waters from differing sources. Uranium is probably unique in its potential for this approach, which seems to have general usefulness in hydrologic investigations.

  6. Uranium disequilibrium in groundwater: an isotope dilution approach in hydrologic investigations.

    PubMed

    Osmond, J K; Rydell, H S; Kaufman, M I

    1968-11-29

    The distribution and environmental disequilibrium patterns of naturally occurring uranium isotopes (U(234) and U(238)) in waters of the Floridan aquifer suggest that variations in the ratios of isotopic activity and concentrations can be used quantitatively to evaluate mixing proportions of waters from differing sources. Uranium is probably unique in its potential for this approach, which seems to have general usefulness in hydrologic investigations. PMID:4880720

  7. High-Precision Isotope Analysis of Uranium and Thorium by TIMS

    NASA Astrophysics Data System (ADS)

    Neymark, L. A.; Paces, J. B.

    2006-12-01

    The U.S. Geological Survey (USGS) Yucca Mountain Project Branch laboratory in Denver, Colorado, conducts routine high-precision isotope analyses of uranium (U) and thorium (Th) using thermal ionization mass- spectrometry (TIMS). The measurements are conducted by a ThermoFinnigan Triton\\texttrademark equipped with a Faraday multi-collector system and an energy filter in front of an active-film-type secondary electron multiplier (SEM). The abundance sensitivity of the instrument (signal at mass 237 over 238U in natural U) with the energy filter is about 15 ppb and peak tails are reduced by a factor of about 100 relative to the Faraday cup measurements. Since instrument installation in April 2004, more than 500 rock and water samples have been analyzed in support of isotope-geochemical studies for the U.S. Department of Energy`s Yucca Mountain Project. Isotope ratios of sub-nanogram to microgram U and Th samples are measured on graphite-coated single- filament and double-filament assemblies using zone-refined rhenium filaments. Ion beams less than 5 mV are measured with the SEM, which is corrected for non-linearity on the basis of measurements of NIST U-500 and 4321B standards with ion beams ranging from 0.01 to 8 mV. Inter-calibration between the SEM and the Faraday multi-collector is performed for every mass cycle using a 5 mV beam switched between Faraday cup and SEM (bridging technique), because SEM-Faraday inter-calibrations prior to the measurement failed to produce acceptable results. Either natural (^{235}U) or artificial (^{236}U, ^{229}Th) isotopes were used for the bridging. Separate runs are conducted for minor isotopes using SEM only. These techniques result in high within-run precisions of less than 0.1 to 0.2 percent for 234U/238U and 0.2 to 0.5 percent for 230Th/238U. The performance of the instrument is monitored using several U and Th isotope standards. The mean measured 234U/238U in NIST SRM 4321B is (52.879±0.004)×10-6 (95 percent confidence, n

  8. Uranium isotopic composition and absolute ages of Allende chondrules

    NASA Astrophysics Data System (ADS)

    Brennecka, G. A.; Budde, G.; Kleine, T.

    2015-11-01

    A handful of events, such as the condensation of refractory inclusions and the formation of chondrules, represent important stages in the formation and evolution of the early solar system and thus are critical to understanding its development. Compared to the refractory inclusions, chondrules appear to have a protracted period of formation that spans millions of years. As such, understanding chondrule formation requires a catalog of reliable ages, free from as many assumptions as possible. The Pb-Pb chronometer has this potential; however, because common individual chondrules have extremely low uranium contents, obtaining U-corrected Pb-Pb ages of individual chondrules is unrealistic in the vast majority of cases at this time. Thus, in order to obtain the most accurate 238U/235U ratio possible for chondrules, we separated and pooled thousands of individual chondrules from the Allende meteorite. In this work, we demonstrate that no discernible differences exist in the 238U/235U compositions between chondrule groups when separated by size and magnetic susceptibility, suggesting that no systematic U-isotope variation exists between groups of chondrules. Consequently, chondrules are likely to have a common 238U/235U ratio for any given meteorite. A weighted average of the six groups of chondrule separates from Allende results in a 238U/235U ratio of 137.786 ± 0.004 (±0.016 including propagated uncertainty on the U standard [Richter et al. 2010]). Although it is still possible that individual chondrules have significant U isotope variation within a given meteorite, this value represents our best estimate of the 238U/235U ratio for Allende chondrules and should be used for absolute dating of these objects, unless such chondrules can be measured individually.

  9. Dry Blending to Achieve Isotopic Dilution of Highly Enriched Uranium Oxide Materials

    SciTech Connect

    Henry, Roger Neil; Chipman, Nathan Alan; Rajamani, R. K.

    2001-04-01

    The end of the cold war produced large amounts of excess fissile materials in the United States and Russia. The Department of Energy has initiated numerous activities to focus on identifying material management strategies for disposition of these excess materials. To date, many of these planning strategies have included isotopic dilution of highly enriched uranium as a means of reducing the proliferation and safety risks. Isotopic dilution by dry blending highly enriched uranium with natural and/or depleted uranium has been identified as one non-aqueous method to achieve these risk (proliferation and criticality safety) reductions. This paper reviews the technology of dry blending as applied to free flowing oxide materials.

  10. Isotopic investigation of the colloidal mobility of depleted uranium in a podzolic soil.

    PubMed

    Harguindeguy, S; Crançon, P; Pointurier, F; Potin-Gautier, M; Lespes, G

    2014-05-01

    The mobility and colloidal migration of uranium were investigated in a soil where limited amounts of anthropogenic uranium (depleted in the 235U isotope) were deposited, adding to the naturally occurring uranium. The colloidal fraction was assumed to correspond to the operational fraction between 10 kDa and 1.2 μm after (ultra)filtration. Experimental leaching tests indicate that approximately 8-15% of uranium is desorbed from the soil. Significant enrichment of the leachate in the depleted uranium (DU) content indicates that uranium from recent anthropogenic DU deposit is weakly bound to soil aggregates and more mobile than geologically occurring natural uranium (NU). Moreover, 80% of uranium in leachates was located in the colloidal fractions. Nevertheless, the percentage of DU in the colloidal and dissolved fractions suggests that NU is mainly associated with the non-mobile coarser fractions of the soil. A field investigation revealed that the calculated percentages of DU in soil and groundwater samples result in the enhanced mobility of uranium downstream from the deposit area. Colloidal uranium represents between 10% and 32% of uranium in surface water and between 68% and 90% of uranium in groundwater where physicochemical parameters are similar to those of the leachates. Finally, as observed in batch leaching tests, the colloidal fractions of groundwater contain slightly less DU than the dissolved fraction, indicating that DU is primarily associated with macromolecules in dissolved fraction. PMID:24387914

  11. 77 FR 53236 - Proposed International Isotopes Fluorine Extraction Process and Depleted Uranium Deconversion...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-31

    ...Notice is hereby given that the U.S. Nuclear Regulatory Commission (NRC or the Commission) has published the Final Environmental Impact Statement (EIS) for the proposed International Isotopes Fluorine Extraction Process and Depleted Uranium Deconversion Plant (INIS) in Lea County, New Mexico. On December 30, 2009, International Isotopes Fluorine Products, Inc. (IIFP), a wholly-owned subsidiary......

  12. Isotopic composition analysis and age dating of uranium samples by high resolution gamma ray spectrometry

    NASA Astrophysics Data System (ADS)

    Apostol, A. I.; Pantelica, A.; Sima, O.; Fugaru, V.

    2016-09-01

    Non-destructive methods were applied to determine the isotopic composition and the time elapsed since last chemical purification of nine uranium samples. The applied methods are based on measuring gamma and X radiations of uranium samples by high resolution low energy gamma spectrometric system with planar high purity germanium detector and low background gamma spectrometric system with coaxial high purity germanium detector. The "Multigroup γ-ray Analysis Method for Uranium" (MGAU) code was used for the precise determination of samples' isotopic composition. The age of the samples was determined from the isotopic ratio 214Bi/234U. This ratio was calculated from the analyzed spectra of each uranium sample, using relative detection efficiency. Special attention is paid to the coincidence summing corrections that have to be taken into account when performing this type of analysis. In addition, an alternative approach for the age determination using full energy peak efficiencies obtained by Monte Carlo simulations with the GESPECOR code is described.

  13. Use of uranium isotopes as a temporal and spatial tracer of nuclear contamination in the environment.

    PubMed

    Tortorello, R; Widom, E; Renwick, W H

    2013-10-01

    The Fernald Feed Materials Production Center (FFMPC) was established in 1951 to process natural uranium (U) ore, enriched uranium (EU) and depleted uranium (DU). This study tests the utility of U isotopic ratios in sediment cores and lichens as indicators of the aerial extent, degree and timing of anthropogenic U contamination, using the FFMPC as a test case. An 80-cm-long sediment core was extracted from an impoundment located approximately 6.7 km southwest of the FFMPC. Elemental concentrations of thorium (2.7-6.2 μg g(-1)) and U (0.33-1.33 μg g(-1)) as well as major and minor U isotopes were analyzed in the core. The lack of measurable (137)Cs in the deepest sample as well as a natural (235)U/(238)U signature and no measurable (236)U, are consistent with pre-FFMPC activity. Anomalously elevated U with respect to Th concentrations occur in seven consecutive samples immediately above the base of the core (62-76 cm depth). Samples with elevated U concentrations also show variable (235)U/(238)U (0.00645-0.00748), and all contain measurable (236)U ((236)U/(238)U = 2.1 × 10(-6)-3.6 × 10(-5)). Correspondence between the known releases of U dust from the FFMPC through time and variations in sediment core U concentrations, (235)U/(238)U and (236)U/(238)U ratios provide evidence for distinct releases of both DU and EU. Furthermore, these relationships demonstrate that the sediment core serves as a robust archive of past environmental U contamination events. Samples in the upper 40 cm display natural (235)U/(238)U, but measurable (236)U/(238)U ((236)U/(238)U = 5.68 × 10(-6)-1.43 × 10(-5)), further indicating the continued presence of anthropogenic U in present-day sediment. Three local lichen samples were also analyzed, and all display either EU or DU signatures coupled with elevated (236)U/(238)U, recording airborne U contamination from the FFMPC. PMID:23871969

  14. Spent fuel temperature and age determination from the analysis of uranium and plutonium isotopics

    SciTech Connect

    Scott, Mark R; Eccleston, George W; Bedell, Jeffrey J; Lockard, Chanelle M

    2009-01-01

    The capability to determine the age (time since irradiation) of spent fuel can be useful for verification and safeguards. While the age of spent fuel can be determined based on measurements of short-lived fission products, these measurements are not routinely done nor generally reported. As an alternative, age can also be determined if the uranium (U) and plutonium (Pu) isotopic values are available. Uranium isotopics are not strongly affected by fuel temperature, and bumup is determined from the {sup 235}U and {sup 236}U isotopic values. Age is calculated after estimating the {sup 241}Pu at the end of irradiation while accounting for the fuel temperature, which is determined from {sup 239}Pu or {sup 240}Pu. Burnup and age determinations are calibrated to reactor models that provide uranium and plutonium isotopics over the range of fuel irradiation. The reactor model must contain sufficient fidelity on details of the reactor type, fuel burnup, irradiation history, initial fuel enrichment and fuel temperature to obtain accurate isotopic calculations. If the latter four are unknown, they can be derived from the uranium and plutonium isotopics. Fuel temperature has a significant affect on the production of plutonium isotopics; therefore, one group cross section reactor models, such as ORIGEN, cannot be used for these calculations. Multi-group cross section set codes, such as Oak Ridge National Laboratory's TRITON code, must be used.

  15. Uranium and cadmium provoke different oxidative stress responses in Lemna minor L.

    PubMed

    Horemans, N; Van Hees, M; Van Hoeck, A; Saenen, E; De Meutter, T; Nauts, R; Blust, R; Vandenhove, H

    2015-01-01

    Common duckweed (Lemna minor L.) is ideally suited to test the impact of metals on freshwater vascular plants. Literature on cadmium (Cd) and uranium (U) oxidative responses in L. minor are sparse or, for U, non-existent. It was hypothesised that both metals impose concentration-dependent oxidative stress and growth retardation on L. minor. Using a standardised 7-day growth inhibition test, the adverse impact of these metals on L. minor growth was confirmed, with EC50 values for Cd and U of 24.1 ± 2.8 and 29.5 ± 1.9 μm, respectively, and EC10 values of 1.5 ± 0.2 and 6.5 ± 0.9 μm, respectively. The metal-induced oxidative stress response was compared through assessing the activity of different antioxidative enzymes [catalase, glutathione reductase, superoxide dismutase (SOD), ascorbate peroxidase (APOD), guaiacol peroxidase (GPOD) and syringaldizyne peroxidase (SPOD)]. Significant changes in almost all antioxidative enzymes indicated their importance in counteracting the U- and Cd-imposed oxidative burden. However, some striking differences were also observed. For activity of APODs and SODs, a biphasic but opposite response at low Cd compared to U concentrations was found. In addition, Cd (0.5-20 μm) strongly enhanced plant GPOD activity, whereas U inhibited it. Finally, in contrast to Cd, U up to 10 μm increased the level of chlorophyll a and b and carotenoids. In conclusion, although U and Cd induce similar growth arrest in L. minor, the U-induced oxidative stress responses, studied here for the first time, differ greatly from those of Cd. PMID:25073449

  16. Isotope fractionation of 238U and 235U during biologically-mediated uranium reduction

    NASA Astrophysics Data System (ADS)

    Stirling, Claudine H.; Andersen, Morten B.; Warthmann, Rolf; Halliday, Alex N.

    2015-08-01

    A series of laboratory-controlled microbial experiments using gram-negative sulphate-reducing bacteria (Desulfovibrio brasiliensis) inoculated with natural uranium were performed to investigate 238U/235U fractionation during bacterially-mediated U reduction. Control experiments, without bacteria to drive U reduction, were conducted in parallel. Paired measurements of 238U/235U and U concentration for both the residual growth medium solution and the accumulated biologically-mediated precipitate were obtained using multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS). The control experiments show that only minor (<0.1‰), if any 238U/235U fractionation occurs during co-precipitation with calcite. This implies that carbonate sediments are capable of faithfully recording the signature of the global ocean during Earth's major climatic events, including oxygenation and de-oxygenation transitions in the marine environment. The results for the microbial experiments demonstrate that the 238U/235U composition of the unreacted growth medium containing U(VI) is isotopically lighter than the composition of the U(IV)-bearing precipitate as U(VI) is consumed, in agreement with field-based observations of microbially-mediated U reduction. Uranium isotopic shifts of up to 0.8‰ were observed between the liquid and solid phases. These observations can be modelled using a Rayleigh distillation approach describing kinetic uptake in a closed system, which yields a fractionation factor α of 0.99923 ± 0.00004 (ε = -0.77 ± 04‰) for U(VI)-U(IV) reduction mediated by the D. brasiliensis microbe. This fractionation behaviour is consistent with that observed in field-based redox environments, which give rise to similar α values. Competing processes such as U co-precipitation (e.g. adsorption) may act to lower the apparent value for α and possibly play a secondary role both in the microbial experiments of this study and in natural U reduction settings where

  17. Study of uranium and thorium isotopes in ground waters and solids of two uranium mines, south Texas

    SciTech Connect

    San Juan, F.C. Jr.

    1982-01-01

    Isotopic analysis was carried out on water and solid samples taken from both the ore zones and the general vicinity of two uranium mines in south Texas. The uranium deposits were of the roll-front type. The ore-bearing formations were the Catahoula Formation of Miocene age in Duval County and the Upper Jackson formation of Eocene age in Karnes County. Solid samples were analyzed for /sup 234/U, /sup 238/U and /sup 230/Th, water for /sup 234/U and /sup 239/U. In order to test several models which have been proposed to explain the fractionation of various nuclides in the vicinity of a reduction-oxidation front, plots incorporating uranium concentration and /sup 234/U//sup 238/U activity ratio (AR) of the water and /sup 234/U//sup 238/U and /sup 230/Th//sup 238/U - /sup 234/U//sup 238/U of the solid were used. The integration of data from each of these models, including contour maps of various isotopic parameters and statistical plots helped in predicting the presence, the stage of deposition (dispersing, stable or accumulating) and the degree of radioactive disequilibrium of the deposits under study. The isotopic data were also useful in determining the position of the redox boundary and the environment of a sample. These methods may be useful in prospecting studies of other possible uranium deposits, both in the oxidized and/or the reduced environment.

  18. Static, Mixed-Array Total Evaporation for Improved Quantitation of Plutonium Minor Isotopes in Small Samples

    NASA Astrophysics Data System (ADS)

    Stanley, F. E.; Byerly, Benjamin L.; Thomas, Mariam R.; Spencer, Khalil J.

    2016-06-01

    Actinide isotope measurements are a critical signature capability in the modern nuclear forensics "toolbox", especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10-6) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Results are presented for small sample (~20 ng) applications involving a well-known plutonium isotope reference material, CRM-126a, and compared with traditional total evaporation methods.

  19. The minor sulfur isotope composition of Cretaceous and Cenozoic seawater sulfate

    NASA Astrophysics Data System (ADS)

    Masterson, A. L.; Wing, Boswell A.; Paytan, Adina; Farquhar, James; Johnston, David T.

    2016-06-01

    The last 125 Myr capture major changes in the chemical composition of the ocean and associated geochemical and biogeochemical cycling. The sulfur isotopic composition of seawater sulfate, as proxied in marine barite, is one of the more perplexing geochemical records through this interval. Numerous analytical and geochemical modeling approaches have targeted this record. In this study we extend the empirical isotope record of seawater sulfate to therefore include the two minor sulfur isotopes, 33S and 36S. These data record a distribution of values around means of Δ33S and Δ36S of 0.043 ± 0.016‰ and -0.39 ± 0.15‰, which regardless of δ34S-based binning strategy is consistent with a signal population of values throughout this interval. We demonstrate with simple box modeling that substantial changes in pyrite burial and evaporite sulfate weathering can be accommodated within the range of our observed isotopic values.

  20. Static, mixed-array total evaporation for improved quantitation of plutonium minor isotopes in small samples

    DOE PAGESBeta

    Stanley, F. E.; Byerly, Benjamin L.; Thomas, Mariam R.; Spencer, Khalil J.

    2016-06-01

    Actinide isotope measurements are a critical signature capability in the modern nuclear forensics “toolbox”, especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10-6) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Furthermore, results are presented for small sample (~20 ng) applications involving a well-known plutoniummore » isotope reference material, CRM-126a, and compared with traditional total evaporation methods.« less

  1. Static, Mixed-Array Total Evaporation for Improved Quantitation of Plutonium Minor Isotopes in Small Samples.

    PubMed

    Stanley, F E; Byerly, Benjamin L; Thomas, Mariam R; Spencer, Khalil J

    2016-06-01

    Actinide isotope measurements are a critical signature capability in the modern nuclear forensics "toolbox", especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10(-6)) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Results are presented for small sample (~20 ng) applications involving a well-known plutonium isotope reference material, CRM-126a, and compared with traditional total evaporation methods. Graphical Abstract ᅟ. PMID:27032649

  2. Static, Mixed-Array Total Evaporation for Improved Quantitation of Plutonium Minor Isotopes in Small Samples

    NASA Astrophysics Data System (ADS)

    Stanley, F. E.; Byerly, Benjamin L.; Thomas, Mariam R.; Spencer, Khalil J.

    2016-03-01

    Actinide isotope measurements are a critical signature capability in the modern nuclear forensics "toolbox", especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10-6) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Results are presented for small sample (~20 ng) applications involving a well-known plutonium isotope reference material, CRM-126a, and compared with traditional total evaporation methods.

  3. METHOD OF SEPARATING ISOTOPES OF URANIUM IN A CALUTRON

    DOEpatents

    Jenkins, F.A.

    1958-05-01

    Mass separation devices of the calutron type and the use of uranium hexachloride as a charge material in the calutron ion source are described. The method for using this material in a mass separator includes heating the uranium hexachloride to a temperature in the range of 60 to 100 d C in a vacuum and thereby forming a vapor of the material. The vaporized uranium hexachloride is then ionized in a vapor ionizing device for subsequent mass separation processing.

  4. Uranium and Calcium Isotope Ratio Measurements using the Modified Total Evaporation Method in TIMS

    NASA Astrophysics Data System (ADS)

    Richter, S.; Kuehn, H.; Berglund, M.; Hennessy, C.

    2010-12-01

    A new version of the "modified total evaporation" (MTE) method for isotopic analysis by multi-collector thermal ionization mass spectrometry (TIMS), with high analytical performance and designed in a more user-friendly and routinely applicable way, is described in detail. It is mainly being used for nuclear safeguards measurements of U and Pu and nuclear metrology, but can readily be applied to other scientific tasks in geochemistry, e.g. for Sr, Nd and Ca, as well. The development of the MTE method was organized in collaboration of several "key nuclear mass spectrometry laboratories", namely the New Brunswick Laboratory (NBL), the Institute for Transuranium Elements (ITU), the Safeguards Analytical Laboratory (now Safeguards Analytical Services, SGAS) of the International Atomic Energy Agency (IAEA) and the Institute for Reference Materials and Measurements (IRMM), with IRMM taking the leading role. The manufacturer of the TRITON TIMS instrument, Thermo Fisher Scientific, integrated this method into the software of the instrument. The development has now reached its goal to become a user-friendly and routinely useable method for uranium isotope ratio measurements with high precision and accuracy. Due to the use of the “total evaporation” (TE) method the measurement of the "major" uranium isotope ratio 235U/238U is routinely being performed with a precision of 0.01% to 0.02%. The use of a (certified) reference material measured under comparable conditions is emphasized to achieve an accuracy at a level of 0.02% - depending on the stated uncertainty of the certified value of the reference material. In contrast to the total evaporation method (TE), in the MTE method the total evaporation sequence is interrupted on a regular basis to allow for correction for background from peak tailing, internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, and ion source re-focusing. Therefore, the most significant improvement using the

  5. The jackknife as an approach for uncertainty assessment in gamma spectrometric measurements of uranium isotope ratios

    NASA Astrophysics Data System (ADS)

    Ramebäck, H.; Vesterlund, A.; Tovedal, A.; Nygren, U.; Wallberg, L.; Holm, E.; Ekberg, C.; Skarnemark, G.

    2010-08-01

    The jackknife as an approach for uncertainty estimation in gamma spectrometric uranium isotope ratio measurements was evaluated. Five different materials ranging from depleted uranium (DU) to high enriched uranium (HEU) were measured using gamma spectrometry. High resolution inductively coupled plasma mass spectrometry (ICP-SFMS) was used as a reference method for comparing the results obtained with the gamma spectrometric method. The relative combined uncertainty in the gamma spectrometric measurements of the 238U/ 235U isotope ratio using the jackknife was about 10-20% ( k = 2), which proved to be fit-for-purpose in order to distinguish between different uranium categories. Moreover, the enrichment of 235U in HEU could be measured with an uncertainty of 1-2%.

  6. Neutron-rich isotope production using a uranium carbide - carbon nanotubes SPES target prototype

    NASA Astrophysics Data System (ADS)

    Corradetti, S.; Biasetto, L.; Manzolaro, M.; Scarpa, D.; Carturan, S.; Andrighetto, A.; Prete, G.; Vasquez, J.; Zanonato, P.; Colombo, P.; Jost, C. U.; Stracener, D. W.

    2013-05-01

    The SPES (Selective Production of Exotic Species) project, under development at the Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro (INFN-LNL), is a new-generation Isotope Separation On-Line (ISOL) facility for the production of radioactive ion beams by means of the proton-induced fission of uranium. In the framework of the research on the SPES target, seven uranium carbide discs, obtained by reacting uranium oxide with graphite and carbon nanotubes, were irradiated with protons at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory (ORNL). In the following, the yields of several fission products obtained during the experiment are presented and discussed. The experimental results are then compared to those obtained using a standard uranium carbide target. The reported data highlights the capability of the new type of SPES target to produce and release isotopes of interest for the nuclear physics community.

  7. Laser ablation inductively coupled plasma mass spectrometry measurement of isotope ratios in depleted uranium contaminated soils.

    PubMed

    Seltzer, Michael D

    2003-09-01

    Laser ablation of pressed soil pellets was examined as a means of direct sample introduction to enable inductively coupled plasma mass spectrometry (ICP-MS) screening of soils for residual depleted uranium (DU) contamination. Differentiation between depleted uranium, an anthropogenic contaminant, and naturally occurring uranium was accomplished on the basis of measured 235U/238U isotope ratios. The amount of sample preparation required for laser ablation is considerably less than that typically required for aqueous sample introduction. The amount of hazardous laboratory waste generated is diminished accordingly. During the present investigation, 235U/238U isotope ratios measured for field samples were in good agreement with those derived from gamma spectrometry measurements. However, substantial compensation was required to mitigate the effects of impaired pulse counting attributed to sample inhomogeneity and sporadic introduction of uranium analyte into the plasma. PMID:14611049

  8. Rapid determination of uranium isotopes in urine by inductively coupled plasma-mass spectrometry.

    PubMed

    Shi, Y; Dai, X; Collins, R; Kramer-Tremblay, S

    2011-08-01

    Following a radiological or nuclear emergency involving uranium exposure, rapid analytical methods are needed to analyze the concentration of uranium isotopes in human urine samples for early dose assessment. The inductively coupled plasma mass spectrometry (ICP-MS) technique, with its high sample throughput and high sensitivity, has advantages over alpha spectrometry for uranium urinalysis after minimum sample preparation. In this work, a rapid sample preparation method using an anion exchange chromatographic column was developed to separate uranium from the urine matrix. A high-resolution sector field ICP-MS instrument, coupled with a high sensitivity desolvation sample introduction inlet, was used to determine uranium isotopes in the samples. The method can analyze up to 24 urine samples in two hours with the limits of detection of 0.0014, 0.10, and 2.0 pg mL(-1) for (234)U, (235)U, and (238)U, respectively, which meet the requirement for isotopic analysis of uranium in a radiation emergency. PMID:21709502

  9. Distribution of uranium isotopes in surface water of the Llobregat river basin (Northeast Spain).

    PubMed

    Camacho, A; Devesa, R; Vallés, I; Serrano, I; Soler, J; Blázquez, S; Ortega, X; Matia, L

    2010-12-01

    A study is presented on the distribution of (234)U, (238)U, (235)U isotopes in surface water of the Llobregat river basin (Northeast Spain), from 2001 to 2006. Sixty-six superficial water samples were collected at 16 points distributed throughout the Llobregat river basin. Uranium isotopes were measured by alpha spectrometry (PIPS detectors). The test procedure was validated according to the quality requirements of the ISO17025 standard. The activity concentration for the total dissolved uranium ranges from 20 to 261mBqL(-1). The highest concentrations of uranium were detected in an area with formations of sedimentary rock, limestone and lignite. A high degree of radioactive disequilibrium was noted among the uranium isotopes. The (234)U/(238)U activity ratio varied between 1.1 and 1.9 and the waters with the lowest uranium activity registered the highest level of (234)U/(238)U activity ratio. Correlations between uranium activity in the tested water and chemical and physical characteristics of the aquifer were found. PMID:20870317

  10. Uranium Isotopic and Quantitative Analysis Using a Mechanically-Cooled HPGe Detector

    SciTech Connect

    Solodov, Alexander A

    2008-01-01

    A new, portable high-resolution spectroscopy system based on a high-purity germanium detector cooled with a miniature Stirling-cycle cooler, ORTEC trans-SPEC, has recently become commercially available. The use of a long-life mechanical cooling system eliminates the need for liquid nitrogen. The purpose of this study was to determine the applicability of this new instrument for isotopic and quantitative analyses of uranium samples. The results of the performance of the trans-SPEC with the combination of PC-FRAM and ISOTOPIC software packages are described in this paper. An optimal set of analysis parameters for uranium measurements is proposed.

  11. Method and apparatus for storing hydrogen isotopes. [stored as uranium hydride in a block of copper

    DOEpatents

    McMullen, J.W.; Wheeler, M.G.; Cullingford, H.S.; Sherman, R.H.

    1982-08-10

    An improved method and apparatus for storing isotopes of hydrogen (especially tritium) are provided. The hydrogen gas is stored as hydrides of material (for example uranium) within boreholes in a block of copper. The mass of the block is critically important to the operation, as is the selection of copper, because no cooling pipes are used. Because no cooling pipes are used, there can be no failure due to cooling pipes. And because copper is used instead of stainless steel, a significantly higher temperature can be reached before the eutectic formation of uranium with copper occurs, (the eutectic of uranium with the iron in stainless steel forms at a significantly lower temperature).

  12. Simultaneous determination of the quantity and isotopic ratios of uranium in individual micro-particles by isotope dilution thermal ionization mass spectrometry (ID-TIMS).

    PubMed

    Park, Jong-Ho; Choi, Eun-Ju

    2016-11-01

    A method to determine the quantity and isotopic ratios of uranium in individual micro-particles simultaneously by isotope dilution thermal ionization mass spectrometry (ID-TIMS) has been developed. This method consists of sequential sample and spike loading, ID-TIMS for isotopic measurement, and application of a series of mathematical procedures to remove the contribution of uranium in the spike. The homogeneity of evaporation and ionization of uranium content was confirmed by the consistent ratio of n((233)U)/n((238)U) determined by TIMS measurements. Verification of the method was performed using U030 solution droplets and U030 particles. Good agreements of resulting uranium quantity, n((235)U)/n((238)U), and n((236)U)/n((238)U) with the estimated or certified values showed the validity of this newly developed method for particle analysis when simultaneous determination of the quantity and isotopic ratios of uranium is required. PMID:27591656

  13. Syndepositional diagenesis of modern platform carbonates: Evidence from isotopic and minor element data

    NASA Astrophysics Data System (ADS)

    Patterson, William P.; Walter, Lynn M.

    1994-02-01

    Physical, elemental, and stable isotopic evidence documents significant syndepositional diagenesis off biogenic carbonate in modern sediment pore water. Halimeda (aragonite) and Neogoniolithon (high-Mg calcite) fragments from sediment cores and experimental substrates were compared with fresh samples to determine the magnitude of minor element (Sr, Mg), and stable isotopic (C and O) compositional shifts. Although no significant shift in bulk sediment mineralogy is apparent, experimental substrates and natural biogenic grains exhibit significant diagenetic changes. These changes include dissolution textures, net loss of mass, changes in minor element composition, and progressive evolution toward carbon and oxygen isotopic equilibrium with p ore water. Our results demonstrate that carbonate sediment can undergo rapid syndepositional dissolution and reprecipitation. Pore waters likely are buffered chemically and isotopically by most abundant carbonate grain types. In turn, compositions of less abundant carbonate grains may shift toward equilibrium with respect to pore water. Therefore, many components of shelf limestone have compositions controlled by chemically evolved pore waters rather than by seawater from which the biotic carbonate originally precipitated.

  14. Uranium Measurement Improvements at the Savannah River Technology Center

    SciTech Connect

    Shick, C. Jr.

    2002-02-13

    Uranium isotope ratio and isotope dilution methods by mass spectrometry are used to achieve sensitivity, precision and accuracy for various applications. This report presents recent progress made at SRTC in the analysis of minor isotopes of uranium. Comparison of routine measurements of NBL certified uranium (U005a) using the SRTC Three Stage Mass Spectrometer (3SMS) and the SRTC Single Stage Mass Spectrometer (SSMS). As expected, the three stage mass spectrometer yielded superior sensitivity, precision, and accuracy for this application.

  15. Isotope ratios of uranium using high resolution inductively coupled plasma-mass spectrometry (ICP-MS)

    SciTech Connect

    Hearn, R.; Wildner, H.

    1998-12-31

    Actinide element isotope ratios have been determined in environmental samples using high resolution ICP-MS with ultrasonic nebulization. Precisions as low as 0.1% RSD have been achieved using various methods of acquisition. The methodology has been used for environmental monitoring of uranium isotope ratios as an indicator of nuclear activity. Also, it has been applied to calcite dating studies as a measure of past geochemical disturbances.

  16. Graphite Isotope Ratio Method Development Report: Irradiation Test Demonstration of Uranium as a Low Fluence Indicator

    SciTech Connect

    Reid, B.D.; Gerlach, D.C.; Love, E.F.; McNeece, J.P.; Livingston, J.V.; Greenwood, L.R.; Petersen, S.L.; Morgan, W.C.

    1999-10-20

    This report describes an irradiation test designed to investigate the suitability of uranium as a graphite isotope ratio method (GIRM) low fluence indicator. GIRM is a demonstrated concept that gives a graphite-moderated reactor's lifetime production based on measuring changes in the isotopic ratio of elements known to exist in trace quantities within reactor-grade graphite. Appendix I of this report provides a tutorial on the GIRM concept.

  17. Isotopes of uranium and plutonium in the atmosphere. [Cosmos-954 fall in Canada

    SciTech Connect

    Sakuragi, Y.

    1982-01-01

    The activities of /sup 234/U, /sup 235/U and /sup 238/U were measured in 24 individual rain samples and two composite rains collected at Fayetteville, Arkansas, during the months of March 1979 and March 1980 through May 1981. Uranium-234 and -235 were found to be highly enriched in several rain samples collected during the months of April and May 1980. Uranium-238 concentrations, on the other hand, were unusually high during the months of July, August and early September 1980. The concentrations of /sup 238/Pu and /sup 238/ /sup 240/Pu were measured in 76 individual rain samples and two composite rains which were collected at Fayetteville, Arkansas, during the period from February 1979 through December 1980. Plutonium-238 and plutonium-239,240 concentrations were found to be extremely high during the months of July, August and early September 1980. The anomalous uranium highly enriched in the light isotopes of uranium appears to have originated from the Soviet satellite Cosmos-954 which fell over Canada on 24 January 1978. The uranium fallout occurred just about the time Mount St. Helens erupted on 18 May 1980 and began to inject a large amount of natural uranium into the atmosphere. The pattern of variations of the concentrations of /sup 238/U in rain after the eruption of Mount St. Helens was found to be similar to that of plutonium isotopes.

  18. Spatial heterogeneity of uranium isotope variations in a Phanerozoic, epicontintental black shale (Hushpuckney Shale, Swope Formation)

    NASA Astrophysics Data System (ADS)

    Herrmann, A. D.; Gordon, G. W.; Romaniello, S. J.; Algeo, T. J.; Anbar, A. D.

    2012-12-01

    It has recently been shown that substantial variations in the 238U/235U ratio exist in nature. The isotopic composition of seawater is ultimately driven by the relative sizes and isotopic signatures of the major sources and sinks. Rivers are the major sources of uranium to the ocean, and reducing sediments (mainly anoxic and suboxic sediments) are the major sinks. Under reducing conditions heavy uranium isotopes are sequestered preferentially. Because of the long residence time of uranium in the global ocean, and the relatively large fractionation during removal of uranium under reducing conditions, it has been suggested that the isotope composition of seawater might reflect changes in the redox state of the ocean and that such changes might be mirrored in black shales. Here we present uranium isotope variations of a Pennsylvanian black shale (Hushpuckney Shale; Swope Formation) from two cores from the same depositional basin (Late Paleozoic Midcontinent Sea; LPMS) to test whether global marine redox conditions can be determined from a single section in epicontinental settings. If uranium isotopes in epicontinental black shales can be used to quantify changes in redox changes of the global ocean, then contemporaneous black shales sections should have the same isotope trends and magnitudes. The Hushpuckney shale is one of several cyclothem core intervals that were deposited over large areas (tens of thousands of square kilometers) on continental crust during early transgression in response to the deglaciation of large icesheets in the southern hemisphere. The two cores investigated for this study represent a transect through the LPMS from close to the open ocean (SE Kansas) towards the shoreline (Iowa). The Hushpuckney shale can be easily identified and correlated in these two cores. Thus, it offers an excellent opportunity to test whether the uranium isotopic composition is similar across the basin and how much local redox conditions can play a role in faithfully

  19. Status of Uranium Atomic Vapor Laser Isotope Separation Program

    SciTech Connect

    Chen, Hao-Lin; Feinberg, R.M.

    1993-06-01

    This report discusses demonstrations of plant-scale hardware embodying AVLIS technology which were completed in 1992. These demonstrations, designed to provide key economic and technical bases for plant deployment, produced significant quantities of low enriched uranium which could be used for civilian power reactor fuel. We are working with industry to address the integration of AVLIS into the fuel cycle. To prepare for deployment, a conceptual design and cost estimate for a uranium enrichment plant were also completed. The U-AVLIS technology is ready for commercialization.

  20. Investigation of the Photochemical Method for Uranium Isotope Separation

    DOE R&D Accomplishments Database

    Urey, H. C.

    1943-07-10

    To find a process for successful photochemical separation of isotopes several conditions have to be fulfilled. First, the different isotopes have to show some differences in the spectrum. Secondly, and equally important, this difference must be capable of being exploited in a photochemical process. Parts A and B outline the physical and chemical conditions, and the extent to which one might expect to find them fulfilled. Part C deals with the applicability of the process.

  1. Uranium isotope fractionation during coprecipitation with aragonite and calcite

    NASA Astrophysics Data System (ADS)

    Chen, Xinming; Romaniello, Stephen J.; Herrmann, Achim D.; Wasylenki, Laura E.; Anbar, Ariel D.

    2016-09-01

    Natural variations in 238U/235U of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ∼7.5 and ∼8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ∼8.5, with heavier U isotopes preferentially enriched in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007 + 0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ∼7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3(aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2 , Ca2+, or Mg2+ concentrations. In general, these effects are likely to be small (<0.13‰), but are nevertheless potentially significant because of the small natural range of

  2. A method for the rapid radiochemical analysis of uranium and thorium isotopes in impure carbonates.

    PubMed

    Elyahyaoui, A; Zarki, R; Chiadli, A

    2003-01-01

    A simple method combining solvent extraction and electrodeposition procedures is described for the determination of the isotopic composition and content of uranium and thorium in travertine samples. The actinide elements are extracted with diethyl ether from a calcium nitrate solution. The isolation of the elements and the alpha source preparation are performed in two steps after the sample digestion. The acid leaching of samples is performed using both partial and total dissolution methods. High recoveries of both uranium and thorium and good alpha-spectra are obtained with both partial and total dissolution methods. PMID:12485673

  3. Influence of nutrient medium composition on uranium toxicity and choice of the most sensitive growth related endpoint in Lemna minor.

    PubMed

    Horemans, Nele; Van Hees, May; Saenen, Eline; Van Hoeck, Arne; Smolders, Valérie; Blust, Ronny; Vandenhove, Hildegarde

    2016-01-01

    Uranium (U) toxicity is known to be highly dependent on U speciation and bioavailability. To assess the impact of uranium on plants, a growth inhibition test was set up in the freshwater macrophyte Lemna minor. First growth media with different compositions were tested in order to find a medium fit for testing U toxicity in L. minor. Following arguments were used for medium selection: the ability to sustain L. minor growth, a high solubility of U in the medium and a high percentage of the more toxic U-species namely UO2(2+). Based on these selection criteria a with a low phosphate concentration of 0.5 mg L(-1) and supplemented with 5 mM MES (2-(N-morpholino)ethanesulfonic acid) to ensure pH stability was chosen. This medium also showed highest U toxicity compared to the other tested media. Subsequently a full dose response curve for U was established by exposing L. minor plants to U concentrations ranging from 0.05 μM up to 150 μM for 7 days. Uranium was shown to adversely affect growth of L. minor in a dose dependent manner with EC10, EC30 and EC50 values ranging between 1.6 and 4.8 μM, 7.7-16.4 μM and 19.4-37.2 μM U, respectively, depending on the growth endpoint. Four different growth related endpoints were tested: frond area, frond number, fresh weight and dry weight. Although differences in relative growth rates and associated ECx-values calculated on different endpoints are small (maximal twofold difference), frond area is recommended to be used to measure U-induced growth effects as it is a sensitive growth endpoint and easy to measure in vivo allowing for measurements over time. PMID:26187266

  4. Analysis of Concentrated Uranium Ores Using Stable Isotopes and Elemental Concentrations

    NASA Astrophysics Data System (ADS)

    Miller, D. L.; Riciputi, L. R.; Buerger, S.; Horita, J.; Bostick, D.

    2006-12-01

    The illicit trafficking of nuclear materials presents a continuing threat to national and international security. Various geochemical characteristics of yellowcake (concentrated uranium ore) could potentially provide information on the geologic, geographic, and processing origin of the ore. We have been focusing on investigating the potential of stable isotope analyses, namely carbon, nitrogen, and oxygen, to provide "forensic" information about ore environment and artificial processing methods used to concentrate the uranium ore. Stable isotope analysis of carbon and nitrogen was performed using a Costech elemental analyzer (EA) attached to a Finnigan Mat 252 mass spectrometer. Carbon and nitrogen isotopes can be characteristic of the processing agents used to concentrate the uranium ore. Oxygen analysis was performed using a ThermoFinnigan thermal conversion elemental analyzer (TCEA) attached to a Finnigan Mat 252 mass spectrometer at ORNL. In addition to the stable isotope analyses, elemental concentrations were analyzed using time-of-flight ICP-MS, and uranium isotope composition measured using MC-ICP-MS. Results from a number of yellowcake samples will be presented, illustrating the potential of geochemical characteristics to distinguish among different types of samples. Research sponsored by the Office of Nonproliferation and International Security (NA-24), National Nuclear Security Administration (NNSA), U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE- AC05-00OR22725. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

  5. MEASUREMENTS OF RADON, THORON, ISOTOPIC URANIUM AND THORIUM TO DETERMINE OCCUPATIONAL & ENVIRONMENTAL EXPOSURE & RISK AT FERNALD FEED MATERIALS PRODUCTION CENTER.

    EPA Science Inventory

    The research at the Fernald Environmental Restoration Management Corporation (FERMCO) site will provide radionuclide data, and realistic risk evaluation for isotopic radon, thorium, uranium and lead exposure.We have developed and tested a passive radon monitor with proven accur...

  6. Uranium Isotopic Fractionation Induced by U(VI) Adsorption Onto Common Aquifer Minerals

    NASA Astrophysics Data System (ADS)

    Jemison, N.; Johnson, T. M.; Shiel, A. E.; Lundstrom, C.

    2014-12-01

    Mining and processing of uranium (U) ore for nuclear energy and weapons has led to U contamination of groundwater. Reduction of soluble, mobile U(VI) to UO2 decreases uranium groundwater concentrations and is an important driver of natural and stimulated attenuation. 238U/235U measurements can be used to monitor and perhaps quantify U(VI) reduction; biological reduction of U(VI) has been shown to produce a ~1.0‰ isotopic fractionation in both laboratory and field settings, with the reduced product enriched in 238U. However, adsorption of U(VI) onto minerals may complicate the use of 238U/235U in this application; adsorption of U(VI) onto Mn oxides induces an isotopic fractionation of 0.2‰ with the sorbed U(VI) depleted in 238U. At present, the isotopic shift produced by adsorption of U(VI) onto other minerals has not yet been explored. This study measures U isotopic fractionation during adsorption onto goethite, birnessite, quartz, illite, and complex aquifer materials. In addition, the effect of U speciation on fractionation is also examined by adsorption of uranyl (UO22+), uranyl carbonato (such as UO2(CO3)22- and UO2(CO3)34-), and calcium uranyl carbonato (Ca2UO2(CO3)3(aq) and CaUO2(CO3)32-) ions to goethite and birnessite. Experiments are carried out with a multi-stage, batch approach, in which a U(VI)-bearing solution is exposed to three stages of adsorption, and the final solution is analyzed by a double-spike MC-ICP-MS method. This increases our ability to resolve among sorbents the extent of fractionation. Early results suggest that uranium adsorption to different minerals produces different isotopic fractionations, with quartz producing little to no fractionation (<0 .05‰), while goethite produces a 0.16‰ isotopic shift (adsorbed U(VI) depleted in 238U).

  7. Theoretical investigations of uranium isotope fractionation caused by nuclear volume effects

    NASA Astrophysics Data System (ADS)

    Yang, S.

    2015-12-01

    Because the half-life times of uranium isotopes are all very long, e.g., 4.5Ga for 238U and 0.7Ga for 235U, people actually treat uranium isotope system as a stable one in many young geologic systems (e.g., Bopp et al., 2010; Basu et al., 2014). There is an increasing trend of using U isotope method to study surface geochemistry problems. For example, people start to use U isotopes as a new tracer to determine the change of redox conditions (Holmden et al., 2015; Wang et al., 2015). However, there are only a few equilibrium U isotope fractionation factors available right now. The new enterprise of U isotope method requires a much expanded data-base of equilibrium U isotope fractionation factor. Many evidences showed that heavy isotope systems could be significantly fractionated as the consequence of the nuclear volume effect (NVE) or so-called nuclear field shift effect,which is a driving force of mass-independent fractionation induced by differences in nuclear size and nuclear shape of isotopes. Here we theoretically estimate the magnitude of equilibrium isotope fractionation factors of U-bearing gaseous and solid compounds caused by NVE via density functional theory (DFT) quantum chemistry methods with careful evaluation on quantum relativistic effects. Our calculation results show the NVE drives 238U/235U fractionations can be up to -4.43‰ between U(VI) and U(IV) species, or can be up to -1.68‰ between U(IV) and U(III) species, at room temperature. The U4+-bearing species or phases tend to enrich heavier isotopes (i.e., 238U) relative to the oxidized phases (U6+-bearing), and enrich lighter isotopes (i.e., 235U) relative to the reduced U(III) phases (U3+-bearing), which generally agree with the recent experimental results (Wang et al., 2015). Our results provide a base for broad applications of equilibrium U isotope fractionation in surface environments.

  8. The Schwartzwalder uranium deposit, II: Age of uranium mineralization and lead isotope constraints on genesis.

    USGS Publications Warehouse

    Ludwig, K. R.; Wallace, A.R.; Simmons, K.R.

    1985-01-01

    Schwartzwalder ores have high amounts of initial (common) Pb that was both variable and relatively radiogenic in its isotope ratios. Assuming the common Pb in these ores to have sources of similar age and similar Th/U, samples with initial Pb isotope ratios are identified - and others with variable initial ratios are normalized - to obtain U-Pb isochrons yielding an early Laramide age of 69.3 + or - 1.1 m.y. for the ores. The initial Pb-isotope systematics indicate local sources of U, dispersed in concentrations <100 ppm, in rocks of 1730 + or - 130 m.y. age. -G.J.N.

  9. Uranium isotopic ratio measurements of U3O8 reference materials by atom probe tomography.

    PubMed

    Fahey, Albert J; Perea, Daniel E; Bartrand, Jonah; Arey, Bruce W; Thevuthasan, Suntharampillai

    2016-03-01

    We report results of measurements of isotopic ratios obtained with atom probe tomography on U3O8 reference materials certified for their isotopic abundances of uranium. The results show good agreement with the certified values. High backgrounds due to tails from adjacent peaks complicate the measurement of the integrated peak areas as well as the fact that only oxides of uranium appear in the spectrum, the most intense of which is doubly charged. In addition, lack of knowledge of other instrumental parameters, such as the dead time, may bias the results. Isotopic ratio measurements can be performed at the nanometer-scale with the expectation of sensible results. The abundance sensitivity and mass resolving power of the mass spectrometer are not sufficient to compete with magnetic-sector instruments but are not far from measurements made by ToF-SIMS of other isotopic systems. The agreement of the major isotope ratios is more than sufficient to distinguish most anthropogenic compositions from natural. PMID:26774651

  10. Uranium Isotopic Ratio Measurements of U3O8 Reference Materials by Atom Probe Tomography

    SciTech Connect

    Fahey, Albert J.; Perea, Daniel E.; Bartrand, Jonah AG; Arey, Bruce W.; Thevuthasan, Suntharampillai

    2016-01-01

    We report results of measurements of isotopic ratios obtained with atom probe tomography on U3O8 reference materials certified for their isotopic abundances of uranium. The results show good agreement with the certified values. High backgrounds due to tails from adjacent peaks complicate the measurement of the integrated peak areas as well as the fact that only oxides of uranium appear in the spectrum, the most intense of which is doubly charged. In addition, lack of knowledge of other instrumental parameters, such as the dead time, may bias the results. Isotopic ratio measurements can be performed at the nanometer-scale with the expectation of sensible results. The abundance sensitivity and mass resolving power of the mass spectrometer are not sufficient to compete with magnetic-sector instruments but are not far from measurements made by ToF-SIMS of other isotopic systems. The agreement of the major isotope ratios is more than sufficient to distinguish most anthropogenic compositions from natural.

  11. Improving precision in resonance ionization mass spectrometry : influence of laser bandwidth in uranium isotope ratio measurements.

    SciTech Connect

    Isselhardt, B. H.; Savina, M. R.; Knight, K. B.; Pellin, M. J.; Hutcheon, I. D.; Prussin, S. G.

    2011-03-01

    The use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of {sup 235}U/{sup 238}U ratios by resonance ionization mass spectrometry (RIMS) to decrease laser-induced isotopic fractionation. By broadening the bandwidth of the first laser in a three-color, three-photon ionization process from a bandwidth of 1.8 GHz to about 10 GHz, the variation in sequential relative isotope abundance measurements decreased from 10% to less than 0.5%. This procedure was demonstrated for the direct interrogation of uranium oxide targets with essentially no sample preparation.

  12. A new series of uranium isotope reference materials for investigating the linearity of secondary electron multipliers in isotope mass spectrometry

    NASA Astrophysics Data System (ADS)

    Richter, S.; Alonso, A.; Aregbe, Y.; Eykens, R.; Kehoe, F.; Kühn, He; Kivel, N.; Verbruggen, A.; Wellum, R.; Taylor, P. D. P.

    2009-04-01

    A new series of gravimetrically prepared uranium isotope reference materials, the so-called IRMM-074 series, with the n(235U)/n(238U) isotope ratio held constant at unity and the n(233U)/n(238U) isotope ratios varying from 1.0 to 10-6 has been prepared and certified. This series is suited for calibration of secondary electron multipliers used widely in isotope mass spectrometry, in particular for techniques such as thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), accelerator mass spectrometry (AMS) and resonance ionization mass spectrometry (RIMS). The new IRMM-074 was prepared as a replacement for the already exhausted IRMM-072 predecessor series. Uranium materials with high isotopic enrichments of 233U, 235U and 238U were purified using identical methods involving separation on anion and cation column followed by a precipitation as peroxide. The oxides were calcined to convert them to U3O8 simultaneously, in an oven installed in a glove-box that provided a controlled low-humidity environment. The oxides of 235U and 238U were weighed and mixed with a mole ratio n(235U)/n(238U) = 1.0 and then dissolved. The 233U oxide was dissolved to form a separate solution with the same concentration and 6rom this primary solution three dilutions were made by weighing. A weighed amount of the n(235U)/n(238U) solution and weighed amounts of the 233U solutions were mixed in various proportions in order to achieve n(233U)/n(238U) isotope ratios varying from 1.0 to 10-6. The methods for the preparation, the mixing and the mixing calculations are described. The expanded uncertainties (coverage factor k = 2) of the certified isotope ratios for the IRMM-074 series are 0.015% for the n(235U)/n(238U) ratio and 0.025% for the n(233U)/n(238U) ratios, which constitutes an improvement compared to those of the predecessor IRMM-072 series. In addition, recent observations regarding the linearity response of secondary electron multipliers (SEMs

  13. Trace elements and Pb isotopes in soils and sediments impacted by uranium mining.

    PubMed

    Cuvier, A; Pourcelot, L; Probst, A; Prunier, J; Le Roux, G

    2016-10-01

    The purpose of this study is to evaluate the contamination in As, Ba, Co, Cu, Mn, Ni, Sr, V, Zn and REE, in a high uranium activity (up to 21,000Bq∙kg(-1)) area, downstream of a former uranium mine. Different geochemical proxies like enrichment factor and fractions from a sequential extraction procedure are used to evaluate the level of contamination, the mobility and the availability of the potential contaminants. Pb isotope ratios are determined in the total samples and in the sequential leachates to identify the sources of the contaminants and to determine the mobility of radiogenic Pb in the context of uranium mining. In spite of the large uranium contamination measured in the soils and the sediments (EF≫40), trace element contamination is low to moderate (2isotopic signature of the contaminated soils is strongly radiogenic. Measurements performed on the sequential leachates reveal inputs of radiogenic Pb in the most mobile fractions of the contaminated soil. Inputs of low-mobile radiogenic Pb from mining activities may also contribute to the Pb signature recorded in the residual phase of the contaminated samples. We demonstrate that Pb isotopes are efficient tools to trace the origin and the mobility of the contaminants in environments affected by uranium mining. PMID:27220101

  14. Uranium-thorium isotope geochemistry of saline ground waters from central Missouri

    SciTech Connect

    Banner, J.L.; Chen, J.H.; Wasserburg, G.J.

    1989-03-01

    The isotopic and elemental distributions of uranium and thorium were examined in a suite of saline ground waters from central Missouri using mass spectrometric techniques. The waters were sampled from natural springs and artesian wells in Mississippian and Ordovician aquifers and have a wide range in salinity (5 to 26 /per thousand/), deltaD (/minus/108 to /minus/45 /per thousand/), and delta/sup 18/O (/minus/14.7 to /minus/6.5 /per thousand/) values. The suite of samples has a large range in /sup 238/U (50 to 200 x 10/sup /minus/12/g/g) and /sup 232/Th (0.3 to 9.1 x 10/sup /minus/12/g/g) concentrations and extremely high /sup 234/U//sup 238/U activity ratios ranging from 2.15 to 16.0. These isotopic compositions represent pronounced uranium-series disequilibrium compared with the value of modern seawater (1.15) or the equilibrium value (1.00). For such /sup 234/U-enriched waters, /sup 234/U//sup 238/U isotope ratios can be determined with a precision of /+-/ 10 /per thousand/ (2sigma) on 10 mL of sample and less than /+-/5 /per thousand/ on 100 mL. In contrast to the large /sup 234/U enrichments, /sup 230/Th//sup 238/U activity ratios in the ground waters are significantly lower than the equilibrium value. The more saline samples have markedly higher /sup 234/U//sup 238/U activity ratios and lower deltaD and delta/sup 18/O values. Unfiltered and filtered (< 0.1 ..mu..m) aliquots of a saline sample have the same isotopic composition and concentration of uranium, indicating uranium essentially occurs entirely as a dissolved species. The filtered/unfiltered concentration ratio for thorium in this sample is 0.29, demonstrating the predominant association of thorium with particulates.

  15. Uranium and lead isotopic stability in a metamict zircon under experimental hydrothermal conditions

    USGS Publications Warehouse

    Pidgeon, R.T.; O'Neil, J.R.; Silver, L.T.

    1966-01-01

    Disturbance of the uranium-lead isotopic system in a metamict Ceylon zircon has been produced in a 2 molal NaCl solution at 500??C and 1000 bars fluid pressure. Loss of radiogenic lead to the extent of 61 percent in 13 days was the most significant effect. The experimental results support the episodic rather than continuous lead-loss interpretation of natural zircon systems utilized in geochronology.

  16. The importance of colloids and mires for the transport of uranium isotopes through the Kalix River watershed and Baltic Sea

    SciTech Connect

    Porcelli, D.; Wasserburg, G.J.; Andersson, P.S.

    1997-10-01

    The importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire-rich Kalix River drainage basin in northern Sweden and the Baltic Sea. Ultrafiltration techniques were used to separate uranium and other elements associated with colloids > 10 kD and >3 kD from {open_quotes}solute{close_quotes} uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples. Uranium concentrations in 0.45 {mu}m-filtered Kalix River water samples increased by a factor of 3 from near the headwaters in the Caledonides to the river mouth while major cation concentrations were relatively constant. {sup 234}U {sup 238}U ratios were high ({delta}{sup 234}U = 770-1500) throughout the basin, without showing any simple pattern, and required a supply of {sup 234}U-rich water. Throughout the Kalix River, a large fraction (30-90%) of the uranium is carried by >10 kD colloids, which is compatible with uranium complexation with humic acids. No isotopic differences were found between colloid-associated and solute uranium. Within the Baltic Sea, about half of the uranium is removed at low salinities. The proportion that is lost is equivalent to that of river-derived colloid-bound uranium, suggesting that while solute uranium behaves conservatively during estuarine mixing, colloid-bound uranium is lost due to rapid flocculation of colloidal material. The association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior. Mire peats in the Kalix River highly concentrate uranium and are potentially a significant source of recoil {sup 234}U to the mirewaters and river waters. However, mirewater data clearly demonstrate that only small {sup 234}U/{sup 238}U shifts are generated relative to inflowing groundwater. 63 refs., 8 figs., 3 tabs.

  17. Uranium isotope composition of a laterite profile during extreme weathering of basalt in Guangdong, South China

    NASA Astrophysics Data System (ADS)

    Huang, J.; Zhou, Z.; Gong, Y.; Lundstrom, C.; Huang, F.

    2015-12-01

    Rock weathering and soil formation in the critical zone are important for material cycle from the solid Earth to superficial system. Laterite is a major type of soil in South China forming at hot-humid climate, which has strong effect on the global uranium cycle. Uranium is closely related to the environmental redox condition because U is stable at U(Ⅳ) in anoxic condition and U(Ⅵ) as soluble uranyl ion (UO22+) under oxic circumstance. In order to understand the behavior of U isotopes during crust weathering, here we report uranium isotopic compositions of soil and base rock samples from a laterite profile originated from extreme weathering of basalt in Guangdong, South China. The uranium isotopic data were measured on a Nu Plasma MC-ICP-MS at the University of Illinois at Urbana-Champaign using the double spike method. The δ238U of BCR-1 is -0.29±0.03‰ (relative to the international standard CRM-112A), corresponding to a 238U/235U ratio of 137.911±0.004. Our result of BCR-1 agrees with previous analyses (e.g., -0.28‰ in Weyer et al. 2008) [1]. U contents of the laterite profile decrease from 1.9 ppm to 0.9 ppm with depth, and peak at 160 - 170 cm (2.3 ppm), much higher than the U content of base rocks (~0.5 ppm). In contrary, U/Th of laterites is lower than that of base rock (0.27) except the peak at the depth of 160-170 cm (0.38), indicating significant U loss during weathering. Notably, U isotope compositions of soils show a small variation from -0.38 to -0.28‰, consistent with the base rock within analytical error (0.05‰ to 0.08‰, 2sd). Such small variation can be explained by a "rind effect" (Wang et al., 2015) [2], by which U(Ⅳ) can be completely oxidized to U(VI) layer by layer during basalt weathering by dissolved oxygen. Therefore, our study indicates that U loss during basalt weathering at the hot-humid climate does not change U isotope composition of superficial water system. [1] Weyer S. et al. (2008) Natural fractionation of 238U/235

  18. Uranium Isotope Fractionation During Coprecipitation with Aragonite and Calcite

    NASA Astrophysics Data System (ADS)

    Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Wasylenki, L. E.; Anbar, A. D.

    2014-12-01

    Natural variations in the 238U/235U ratio of marine carbonates may provide a useful way of constraining past variations in ocean redox conditions. However, before applying this novel redox proxy, it is essential to explore possible isotopic fractionation during U coprecipitation with aragonite and calcite. We investigated these effects in laboratory experiments. Aragonite and calcite coprecipitation experiments were conducted at pH 8.5±0.1 using a constant addition method [1]. More than 90% of the U was incorporated into the solid phase at the end of each experiment. Samples were purified using UTEVA chemistry and δ238/235U was measured using 233U-236U double-spike MC-ICP-MS with a precision of ±0.10‰ [2]. The aragonite experiment demonstrated a 238U/235U Rayleigh fractionation factor of α=1.00008±0.00002 with the 238U preferentially incorporated. In contrast, the calcite experiment demonstrated no resolvable U isotope fractionation (α=1.00001±0.00003). To determine if U isotopes are affected during the early diagenetic conversion of aragonite to calcite, natural carbonate samples were collected along an aragonite-calcite transition across a single coral head in the Key Largo limestone, and characterized for U concentration and δ238/235U [3]. We found that the mean δ238/235U in aragonite (-0.33±0.07‰ 2se) was slightly heavier than that in calcite (-0.37±0.02‰ 2se). Further work is needed to address the mechanisms leading to differential isotopic fractionation of U(VI) during incorporation into aragonite and calcite. Possible drivers include differences in coordination in the crystal structure or equilibrium isotopic fractionation between various aqueous U(VI) species prior to incorporation. [1] Reeder et al. (2001) GCA 65, 3491-3503. [2] Weyer et al., (2008) GCA 72, 345-359. [3] Gill et al., (2008) GCA 72, 4699-4722.

  19. Uranium isotopes in groundwater from the continental intercalaire aquifer in Algerian Tunisian Sahara (Northern Africa).

    PubMed

    Chkir, N; Guendouz, A; Zouari, K; Hadj Ammar, F; Moulla, A S

    2009-08-01

    The disequilibrium between (234)U and (238)U is commonly used as a tracer of groundwater flow. This paper aims to identify uranium contents and uranium isotopic disequilibria variation in groundwater sampled from deep Continental Intercalaire aquifer (southern Algeria and Tunisia). Large variations in both U contents (0.006-3.39ppb) and (234)U/(238)U activity ratios (0.4-15.38) are observed. We conduct a first assessment in order to verify whether the results of our investigation support and complete previous hydrogeological and isotopic studies. The dissolved U content and (234)U/(238)U activity ratio data were plotted on a two-dimensional diagram that was successfully utilized on sharing the CI aquifer into different compartments submitted to different oxidising/reducing conditions and leads also to distinguished two preferential flow paths in the Nefzaoua/Chott Fejej discharge area. Uranium isotopes disequilibrium indicate that ranium chemistry is mainly controlled by water-rock interaction enhanced by long residence time recognised for this aquifer. PMID:19559509

  20. Absorption spectroscopy of uranium plasma for remote isotope analysis of next-generation nuclear fuel

    NASA Astrophysics Data System (ADS)

    Miyabe, M.; Oba, M.; Iimura, H.; Akaoka, K.; Maruyama, Y.; Ohba, H.; Tampo, M.; Wakaida, I.

    2013-07-01

    To determine experimental conditions suitable for isotope analysis, we studied the plume dynamics of uranium. A uranium oxide sample was ablated by 2nd harmonic radiation from a Nd:YAG laser at a fluence of 0.5 J/cm2. The temporal evolution of the ablation plume was investigated in vacuum and helium environments. In vacuum, the flow velocity perpendicular to the sample surface was determined to be 2.7 km/s for neutral atoms and 4.0 km/s for singly charged atoms. These velocities are about 20 % lower than those of cerium measured under similar conditions. From the evolution of the plume in helium, we found that an observation time of 3-5 μs and an observation height of about 2.5 mm are most suited for obtaining higher sensitivity. Observation times less than 3 μs were unsuitable for precise isotope analysis since the spectral modifications arising from the Doppler splitting effect are different between the two uranium isotopes. Using the established conditions, we evaluated the calibration curve linearity, limit of detection, and precision for three samples having different abundances of 235U.

  1. Isotopic Tracking of Hanford 300 Area Derived Uranium in the Columbia River

    SciTech Connect

    Christensen, John N.; Dresel, P. Evan; Conrad, Mark E.; Patton, Gregory W.; DePaolo, Donald J.

    2010-10-31

    Our objectives in this study are to quantify the discharge rate of uranium (U) to the Columbia River from the Hanford Site's 300 Area, and to follow that U down river to constrain its fate. Uranium from the Hanford Site has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates. Our data on river water samples indicate that as much as 3.2 kg/day can enter the Columbia River from the 300 Area, which is only a small fraction of the total load of dissolved natural background U carried by the Columbia River. This very low-level of Hanford derived U can be discerned, despite dilution to < 1 percent of natural background U, 350 km downstream from the Hanford Site. These results indicate that isotopic methods can allow the amounts of U from the 300 Area of the Hanford Site entering the Columbia River to be measured accurately to ascertain whether they are an environmental concern, or are insignificant relative to natural uranium background in the Columbia River.

  2. Isotopic Anomalies in a Uranium Cluster Formed by Lais

    NASA Astrophysics Data System (ADS)

    van de Walle, J.; Tarento, R. J.; Joyes, P.

    A study of a Au-U liquid alloy ion source (LAIS) where uranium is enriched in its lighter element (20% 235U, 80% 238U) has been performed by high resolution mass spectrometry. Monoatomic species Au+, Au2+, U2+, U3+ and polyatomic species Au+n, Up+n, AunU+ are observed. The monoatomic results are well explained by the Kingham postionization process. Au+n and AunU+ species present an interesting odd-even effect characteristic of monovalent elements. The main result of this preliminary letter is a heteroisotope anomaly which appears in U+2, U+3 and U4+3 emission where only homoisotopes are detected. A similar phenomenon was reported for Cu+2 and Ge+2 in a previous work and was attributed to a higher state of excitation of emitted heteroisotope aggregates which explode as they fly to the collector.1,2

  3. Improving the Sensitivity of Uranium Isotope Ratio Measurements

    NASA Astrophysics Data System (ADS)

    Friedrich, J.; Snow, J.

    2003-12-01

    Accurate and precise measurements of natural and anthropogenic 235/238 U isotope ratios are important for a range of investigations where the amount of sample is extremely restricted and/or the analyte is only present in ultra-trace quantities. Examples include biological, cosmochemical, environmental, geological, and radiological studies. We have developed and validated a novel method using our Nu Instruments Nu Plasma Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS) and a 233U, 236U mixed double spike for the measurement of 235U/238U ratios. Our multi-dynamic technique employs the installed quadrupole zoom optics and fixed positioning of the ion counting detectors such that rather than the commonly used mass dispersion of 1 or 2, we utilize a mass dispersion of 1.5. Using this configuration, we can simultaneously monitor the 235U and 238U ion beams in the first cycle followed by a second cycle that simultaneously monitors the 233U and 236U beams. This innovative approach allows us to correct for the considerable, but consistent, instrumental mass fractionation and ion-counter amplification bias within each sequence. Since we were hesitant to use a U500 (235U, 238U equal atom) solution for spike calibration because of possible enriched U laboratory and instrumentation contamination, we used a U960 (terrestrial 235U/238U) solution for isotopic calibration of the spike. This standardization corrected for the small amounts of 235U and 238U in the spike solution by using a U960 standard solution. With a mean intraday 2-sigma precision of 1.5 permil and an overall 2-sigma precision of 2.25 permil using individual sample sizes of 350 pg (8.8 x10 E11 atoms), we are confident our technique will be useful for identifying U isotopic anomalies present in many sample types.

  4. CO-laser-induced photochemical reaction of UF6 with HCl for the isotope separation of uranium hexafluoride

    NASA Astrophysics Data System (ADS)

    Ding, Hong-Bin; Shen, Z. Y.; Zhang, Cun H.

    1993-05-01

    In this paper, we report the results of CO-laser induced photochemical reaction of UF6 with HCl for the isotope separation of uranium hexafluoride, we also discussed that the molecular collision inducing V-T, V-V relaxation process affects on the selectivity of the isotope separation. The obtained quantum coefficiency of the reaction is about 0.34.

  5. Separation Of Uranium And Plutonium Isotopes For Measurement By Multi Collector Inductively Coupled Plasma Mass Spectroscopy

    SciTech Connect

    Martinelli, R E; Hamilton, T F; Williams, R W; Kehl, S R

    2009-03-29

    Uranium (U) and plutonium (Pu) isotopes in coral soils, contaminated by nuclear weapons testing in the northern Marshall Islands, were isolated by ion-exchange chromatography and analyzed by mass spectrometry. The soil samples were spiked with {sup 233}U and {sup 242}Pu tracers, dissolved in minerals acids, and U and Pu isotopes isolated and purified on commercially available ion-exchange columns. The ion-exchange technique employed a TEVA{reg_sign} column coupled to a UTEVA{reg_sign} column. U and Pu isotope fractions were then further isolated using separate elution schemes, and the purified fractions containing U and Pu isotopes analyzed sequentially using multi-collector inductively coupled plasma mass spectrometer (MCICP-MS). High precision measurements of {sup 234}U/{sup 235}U, {sup 238}U/{sup 235}U, {sup 236}U/{sup 235}U, and {sup 240}Pu/{sup 239}Pu in soil samples were attained using the described methodology and instrumentation, and provide a basis for conducting more detailed assessments of the behavior and transfer of uranium and plutonium in the environment.

  6. U-Pb systems and U isotopic composition of the sandstone-hosted paleovalley Dybryn uranium deposit, Vitim uranium district, Russia

    NASA Astrophysics Data System (ADS)

    Golubev, V. N.; Chernyshev, I. V.; Chugaev, A. V.; Eremina, A. V.; Baranova, A. N.; Krupskaya, V. V.

    2013-11-01

    The isotopic (U-Pb, 238U-235U, 234U-238U) and chemical study of whole-rock samples and finegrained fractions of rocks in a vertical section of the terrigenous sequence at the Dybryn uranium deposit in the Khiagda ore field shows that a wide U-Pb isotopic age range (26.9-6.5 Ma) is caused by oxidation and disturbance of the U-Pb isotopic system in combination with protracted uranium ore deposition. The oxidation of rocks resulted in the loss of uranium relative to lead and eventually to an overestimated 206Pb/238U age at sites with a low U content. The 238U/235U ratios in the studied samples are within the range of 137.74-137.88. Samples with a high uranium content are characterized by a decreasing 238U/235U ratio with a decrease in 207Pb/235U and 206Pb/238U ages. A nonequilibrium 234U/238U ratio in most studied samples furnishes evidence for young (<1.5 Ma) transformation of the Miocene uranium ore, which is responsible for uranium migration and its redeposition.

  7. Fission track-secondary ion mass spectrometry as a tool for detecting the isotopic signature of individual uranium containing particles.

    PubMed

    Esaka, Fumitaka; Lee, Chi-Gyu; Magara, Masaaki; Kimura, Takaumi

    2012-04-01

    A fission track technique was used as a sample preparation method for subsequent isotope abundance ratio analysis of individual uranium containing particles with secondary ion mass spectrometry (SIMS) to measure the particles with higher enriched uranium efficiently. A polycarbonate film containing particles was irradiated with thermal neutrons and etched with 6M NaOH solution. Each uranium containing particle was then identified by observing fission tracks created and a portion of the film having a uranium containing particle was cut out and put onto a glassy carbon planchet. The polycarbonate film, which gave the increases of background signals on the uranium mass region in SIMS analysis, was removed by plasma ashing with 200 W for 20 min. In the analysis of swipe samples having particles containing natural (NBL CRM 950a) or low enriched uranium (NBL CRM U100) with the fission track-SIMS method, uranium isotope abundance ratios were successfully determined. This method was then applied to the analysis of a real inspection swipe sample taken at a nuclear facility. As a consequence, the range of (235)U/(238)U isotope abundance ratio between 0.0276 and 0.0438 was obtained, which was higher than that measured by SIMS without using a fission track technique (0.0225 and 0.0341). This indicates that the fission track-SIMS method is a powerful tool to identify the particle with higher enriched uranium in environmental samples efficiently. PMID:22405310

  8. Oxygen isotopic measurements by secondary ion mass spectrometry in uranium oxide microparticles: a nuclear forensic diagnostic.

    PubMed

    Tamborini, G; Phinney, D; Blidstein, O; Betti, M

    2002-12-01

    To exploit oxygen isotopic measurement by SIMS as a diagnostic tool in nuclear forensics, the magnitude and reproducibility of 0-isotope instrumental mass discrimination for O-isotope standards in the SIMS laboratory at the Institute for Transuranium Elements has been evaluated. Tests for matrix-dependent discrimination effects on three different O-isotope standards with substantially different matrix compositions have been performed. The results were checked by an interlaboratory comparison of O-isotope discrimination with those obtained in the SIMS laboratory at the Lawrence Livermore National Laboratory on two standards. The results from the two laboratories are in very good agreement, indicating statistically indistinguishable instrumental mass discrimination factors for 180/160 ratios on the Cameca 6f and 3f, when the analyses are performed under the experimental conditions described. The 2sigma(mean) uncertainties of these factors are in the range of 0.3-0.9%. In accordance with the tested methodology, 0-isotope compositions were measured in three particulate uranium oxide samples of nuclear forensics interest. PMID:12498207

  9. A Heterogeneous Sodium Fast Reactor Designed to Transmute Minor Actinide Actinide Waste Isotopes into Plutonium Fuel

    SciTech Connect

    Samuel E. Bays

    2011-02-01

    An axial heterogeneous sodium fast reactor design is developed for converting minor actinide waste isotopes into plutonium fuel. The reactor design incorporates zirconium hydride moderating rods in an axial blanket above the active core. The blanket design traps the active core’s axial leakage for the purpose of transmuting Am-241 into Pu-238. This Pu-238 is then co-recycled with the spent driver fuel to make new driver fuel. Because Pu-238 is significantly more fissile than Am-241 in a fast neutron spectrum, the fissile worth of the initial minor actinide material is upgraded by its preconditioning via transmutation in the axial targets. Because, the Am-241 neutron capture worth is significantly stronger in a moderated epithermal spectrum than the fast spectrum, the axial targets serve as a neutron trap which recovers the axial leakage lost by the active core. The sodium fast reactor proposed by this work is designed as an overall transuranic burner. Therefore, a low transuranic conversion ratio is achieved by a degree of core flattening which increases axial leakage. Unlike a traditional “pancake” design, neutron leakage is recovered by the axial target/blanket system. This heterogeneous core design is constrained to have sodium void and Doppler reactivity worth similar to that of an equivalent homogeneous design. Because minor actinides are irradiated only once in the axial target region; elemental partitioning is not required. This fact enables the use of metal targets with electrochemical reprocessing. Therefore, the irradiation environment of both drivers and targets was constrained to ensure applicability of the established experience database for metal alloy sodium fast reactor fuels.

  10. Groundwater salinization in the Saloum (Senegal) delta aquifer: minor elements and isotopic indicators.

    PubMed

    Faye, Serigne; Maloszewski, Piotr; Stichler, Willibald; Trimborn, Peter; Cissé Faye, Seynabou; Bécaye Gaye, Cheikh

    2005-05-01

    The hydrochemistry of minor elements bromide (Br), boron (B), strontium (Sr), environmental stable isotopes (18O and 2H) together with major-ion chemistry (chloride, sodium, calcium) has been used to constrain the source(s), relative age, and processes of salinization in the Continental Terminal (CT) aquifer in the Saloum (mid-west Senegal) region. Seventy-one groundwater wells which include 24 wells contaminated by saltwater and three sites along the hypersaline Saloum River were sampled to obtain additional information on the hydrochemical characteristics of the groundwater defined in previous studies. Use of Br against Cl confirms the Saloum River saline water intrusion up to a contribution of 7% into the aquifer. In addition to this recent intrusion, a relatively ancient intrusion of the Saloum River water which had reached at least as far as 20 km south from the source was evidenced. The high molar ratio values of Sr/Cl and Sr/Ca indicate an additional input of strontium presumably derived from carbonate precipitation/dissolution reactions and also via adsorption reactions. The variable B concentrations (7-650 microg/L) found in the groundwater samples were tested against the binary mixing model to evaluate the processes of salinization which are responsible for the investigated system. Sorption of B and depletion of Na occur as the Saloum river water intrudes the aquifer (salinization) in the northern part of the region, whereas B desorption and Na enrichment occur as the fresh groundwater flushing displaces the saline waters in the coastal strip (refreshening). In the central zone where ancient intrusion prevailed, the process of freshening of the saline groundwater is indicated by the changes in major-ion chemistry as well as B desorption and Na enrichment. In addition to these processes, stable isotopes reveal that mixing with recently infiltrating waters and evaporation contribute to the changes in isotopic signature. PMID:15862849

  11. Process for producing enriched uranium having a .sup.235 U content of at least 4 wt. % via combination of a gaseous diffusion process and an atomic vapor laser isotope separation process to eliminate uranium hexafluoride tails storage

    DOEpatents

    Horton, James A.; Hayden, Jr., Howard W.

    1995-01-01

    An uranium enrichment process capable of producing an enriched uranium, having a .sup.235 U content greater than about 4 wt. %, is disclosed which will consume less energy and produce metallic uranium tails having a lower .sup.235 U content than the tails normally produced in a gaseous diffusion separation process and, therefore, eliminate UF.sub.6 tails storage and sharply reduce fluorine use. The uranium enrichment process comprises feeding metallic uranium into an atomic vapor laser isotope separation process to produce an enriched metallic uranium isotopic mixture having a .sup.235 U content of at least about 2 wt. % and a metallic uranium residue containing from about 0.1 wt. % to about 0.2 wt. % .sup.235 U; fluorinating this enriched metallic uranium isotopic mixture to form UF.sub.6 ; processing the resultant isotopic mixture of UF.sub.6 in a gaseous diffusion process to produce a final enriched uranium product having a .sup.235 U content of at least 4 wt. %, and up to 93.5 wt. % or higher, of the total uranium content of the product, and a low .sup.235 U content UF.sub.6 having a .sup.235 U content of about 0.71 wt. % of the total uranium content of the low .sup.235 U content UF.sub.6 ; and converting this low .sup.235 U content UF.sub.6 to metallic uranium for recycle to the atomic vapor laser isotope separation process.

  12. Process for producing enriched uranium having a {sup 235}U content of at least 4 wt. % via combination of a gaseous diffusion process and an atomic vapor laser isotope separation process to eliminate uranium hexafluoride tails storage

    DOEpatents

    Horton, J.A.; Hayden, H.W. Jr.

    1995-05-30

    An uranium enrichment process capable of producing an enriched uranium, having a {sup 235}U content greater than about 4 wt. %, is disclosed which will consume less energy and produce metallic uranium tails having a lower {sup 235}U content than the tails normally produced in a gaseous diffusion separation process and, therefore, eliminate UF{sub 6} tails storage and sharply reduce fluorine use. The uranium enrichment process comprises feeding metallic uranium into an atomic vapor laser isotope separation process to produce an enriched metallic uranium isotopic mixture having a {sup 235} U content of at least about 2 wt. % and a metallic uranium residue containing from about 0.1 wt. % to about 0.2 wt. % {sup 235} U; fluorinating this enriched metallic uranium isotopic mixture to form UF{sub 6}; processing the resultant isotopic mixture of UF{sub 6} in a gaseous diffusion process to produce a final enriched uranium product having a {sup 235}U content of at least 4 wt. %, and up to 93.5 wt. % or higher, of the total uranium content of the product, and a low {sup 235}U content UF{sub 6} having a {sup 235}U content of about 0.71 wt. % of the total uranium content of the low {sup 235}U content UF{sub 6}; and converting this low {sup 235}U content UF{sub 6} to metallic uranium for recycle to the atomic vapor laser isotope separation process. 4 figs.

  13. Uranium series isotopes in the Avon Valley, Nova Scotia.

    PubMed

    Kronfeld, J; Godfrey-Smith, D I; Johannessen, D; Zentilli, M

    2004-01-01

    An U-series isotopic study was carried out in the waters of the Avon Valley, Nova Scotia. The fresh and acidic recharge waters flow rapidly through the watershed composed of a granitic highland and a sedimentary, largely carbonate, lowland plain, before draining to the sea. There is no significant anthropogenic pollution; but, naturally elevated U levels can be encountered within the bedrock. Nonetheless, the U concentrations of the surface and groundwater are low (generally within the range of several hundredths to several tenths of a microg l(-1)), except in the proximity to weathering of U mineralization. The dissolved U in the surface waters appears to be stabilized by organic rather than inorganic complexes. Both the groundwaters and surface waters have similar (234)U/(238)U activity ratios that rarely deviate from secular equilibrium by more than 20% throughout the watershed. The magnitude of the (234)U/(238)U activity ratio is not determined by lithology but rather by the weathering mechanism, the high rate of flushing, and the leaching of local U mineralization. Dissolved Ra is consistently absent. The dissolved Rn concentrations, though variable, are measurable even in surface waters. This may be due to a continual degassing from the U-enriched bedrock or release from local sites of U mineralization underlying the surface water sources. PMID:15050364

  14. Uranium, plutonium, and thorium isotopes in the atmosphere and the lithosphere

    SciTech Connect

    Essien, I.O.

    1983-01-01

    Concentration of /sup 238/U in rain and snow collected at Fayetteville (36/sup 0/N, 94/sup 0/W), Arkansas, showed a marked increase during the summer months of 1980, while Mount St. Helens remained active. This observed increase of /sup 238/U can be explained as due to the fallout of natural uranium from the eruption of Mount St. Helens. Large increases in the concentration of thorium isotopes detected in rain and snow samples during the last months of 1982 and early months of 1983 probably originated from the eruption of El Chichon volcano, which occurred on 28 March 1982. About 450 Ci of /sup 232/Th is estimated to have been injected into the atmosphere by this eruption. Isotopic anomalies were observed in atmospheric samples such as rain and snow. These anomalies can be attributed to various natural as well as man-made sources: nuclear weapon tests, nuclear accidents involving the burn-up of nuclear powered satellites, and volcanic eruptions. The variation of /sup 234/U//sup 238/U ratios in radioactive minerals when leached with nitric acid were also noticed and this variation, while /sup 235/U//sup 238/U remained fairly constant, can be explained in terms of the ..cap alpha..-recoil effect and changes in oxidation state of uranium. Difference found in /sup 239/Pu//sup 238/U ratios in terrestrial samples and uranium minerals can be explained as due to fallout contamination.

  15. Rapid fusion method for the determination of refractory thorium and uranium isotopes in soil samples

    SciTech Connect

    Maxwell, Sherrod L.; Hutchison, Jay B.; McAlister, Daniel R.

    2015-02-14

    Recently, approximately 80% of participating laboratories failed to accurately determine uranium isotopes in soil samples in the U.S Department of Energy Mixed Analyte Performance Evaluation Program (MAPEP) Session 30, due to incomplete dissolution of refractory particles in the samples. Failing laboratories employed acid dissolution methods, including hydrofluoric acid, to recover uranium from the soil matrix. The failures illustrate the importance of rugged soil dissolution methods for the accurate measurement of analytes in the sample matrix. A new rapid fusion method has been developed by the Savannah River National Laboratory (SRNL) to prepare 1-2 g soil sample aliquots very quickly, with total dissolution of refractory particles. Soil samples are fused with sodium hydroxide at 600 ºC in zirconium crucibles to enable complete dissolution of the sample. Uranium and thorium are separated on stacked TEVA and TRU extraction chromatographic resin cartridges, prior to isotopic measurements by alpha spectrometry on cerium fluoride microprecipitation sources. Plutonium can also be separated and measured using this method. Batches of 12 samples can be prepared for measurement in <5 hours.

  16. Rapid fusion method for the determination of refractory thorium and uranium isotopes in soil samples

    DOE PAGESBeta

    Maxwell, Sherrod L.; Hutchison, Jay B.; McAlister, Daniel R.

    2015-02-14

    Recently, approximately 80% of participating laboratories failed to accurately determine uranium isotopes in soil samples in the U.S Department of Energy Mixed Analyte Performance Evaluation Program (MAPEP) Session 30, due to incomplete dissolution of refractory particles in the samples. Failing laboratories employed acid dissolution methods, including hydrofluoric acid, to recover uranium from the soil matrix. The failures illustrate the importance of rugged soil dissolution methods for the accurate measurement of analytes in the sample matrix. A new rapid fusion method has been developed by the Savannah River National Laboratory (SRNL) to prepare 1-2 g soil sample aliquots very quickly, withmore » total dissolution of refractory particles. Soil samples are fused with sodium hydroxide at 600 ºC in zirconium crucibles to enable complete dissolution of the sample. Uranium and thorium are separated on stacked TEVA and TRU extraction chromatographic resin cartridges, prior to isotopic measurements by alpha spectrometry on cerium fluoride microprecipitation sources. Plutonium can also be separated and measured using this method. Batches of 12 samples can be prepared for measurement in <5 hours.« less

  17. Natural uranium and thorium isotopes in sediment cores off Malaysian ports

    NASA Astrophysics Data System (ADS)

    Yusoff, Abdul Hafidz; Sabuti, Asnor Azrin; Mohamed, Che Abd Rahim

    2015-06-01

    Sediment cores collected from three Malaysian marine ports, namely, Kota Kinabalu, Labuan and Klang were analyzed to determine the radioactivities of 234U, 238U, 230Th, 232Th and total organic carbon (TOC) content. The objectives of this study were to determine the factors that control the activity of uranium isotopes and identify the possible origin of uranium and thorium in these areas. The activities of 234U and 238U show high positive correlation with TOC at the middle of sediment core from Kota Kinabalu port. This result suggests that activity of uranium at Kota Kinabalu port was influenced by organic carbon. The 234U/238U value at the upper layer of Kota Kinabalu port was ≥1.14 while the ratio value at Labuan and Klang port was ≤ 1.14. These results suggest a reduction process occurred at Kota Kinabalu port where mobile U(VI) was converted to immobile U(IV) by organic carbon. Therefore, it can be concluded that the major input of uranium at Kota Kinabalu port is by sorptive uptake of authigenic uranium from the water column whereas the major inputs of uranium to Labuan and Klang port are of detrital origin. The ratio of 230Th/232Th was used to estimate the origin of thorium. Low ratio value (lt; 1.5) at Labuan and Klang ports support the suggestion that thorium from both areas were come from detrital input while the high ratio (> 1.5) of 230Th/232Th at Kota Kinabalu port suggest the anthropogenic input of 230Th to this area. The source of 230Th is probably from phosphate fertilizers used in the oil-palm cultivation in Kota Kinabalu that is adjacent to the Kota Kinabalu port.

  18. Design Study for a Low-Enriched Uranium Core for the High Flux Isotope Reactor, Annual report for FY 2009

    SciTech Connect

    Chandler, David; Freels, James D; Ilas, Germina; Miller, James Henry; Primm, Trent; Sease, John D; Guida, Tracey; Jolly, Brian C

    2010-02-01

    This report documents progress made during FY 2009 in studies of converting the High Flux Isotope Reactor (HFIR) from high enriched uranium (HEU) fuel to low enriched uranium (LEU) fuel. Conversion from HEU to LEU will require a change in fuel form from uranium oxide to a uranium-molybdenum alloy. With axial and radial grading of the fuel foil and an increase in reactor power to 100 MW, calculations indicate that the HFIR can be operated with LEU fuel with no degradation in reactor performance from the current level. Results of selected benchmark studies imply that calculations of LEU performance are accurate. Studies are reported of the application of a silicon coating to surrogates for spheres of uranium-molybdenum alloy. A discussion of difficulties with preparing a fuel specification for the uranium-molybdenum alloy is provided. A description of the progress in developing a finite element thermal hydraulics model of the LEU core is provided.

  19. Determining the isotopic concentration of uranium from vector representation of the gamma spectrum

    NASA Astrophysics Data System (ADS)

    White, Tristan Glover

    Gamma emissions from Uranium-235 in a source of interest were compared to gamma emissions from Protactinium-234m (which is in equilibrium with Uranium-238) in order to determine the isotopic composition of the source. The 144 keV gamma ray from U-235 was compared with 1001 keV gamma ray from Pa-234m. Two analytical methods were compared: the relative activity method and the vector representation method. The relative activity method is similar to the (standard) relative intensity method, but accounts for more variables. Calculations were performed using both methods in order to evaluate precision and accuracy. Relative activity compares the number of counts under one gamma-ray peak from a reference source to the number of counts under another peak from an unknown source. This method is sensitive to systematic errors in the efficiency calibration of the detector when two different peaks with different energies are used. Vector representation compares the count ratio of two gamma-ray peaks from one source to the count ratio of the same two gamma-ray peaks from another source. Vector representation was found to be practical for analyzing depleted uranium, but not highly enriched uranium (HEU), due to different branching ratios and detector efficiency.

  20. Equilibrium uranium isotope fractionation by nuclear volume and mass-dependent processes

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.

    2006-12-01

    Uranium serves as a geochemical tracer of oxidation near the Earth's surface, and is also the basis for several isotopic geochronometers. It is thus important to understand possible non-radiogenic and non-radioactive isotopic fractionation of uranium in natural systems. This study presents theoretical estimates of equilibrium uranium isotope fractionations in U-bearing molecules and complexes, calculated using first-principles computational chemistry. Ion-exchange experiments (1,2) have indicated that mass-dependent mechanisms, alone, cannot explain 238U/234U and 238U/^{235}U fractionations, so nuclear volume (i.e., field shift) fractionation effects are also considered in theoretical calculations. The results indicate that equilibrium isotopic fractionation is likely when U4+ and U6+ species equilibrate. Nuclear volume fractionation leads to higher 238U/^{235}U in U4+-bearing species, overwhelming a smaller mass- dependent fractionation in the opposite direction. The calculated net fractionation between U(H2O)_94+ and UO2Cl3(H2O)_2^- is approximately 1 per mil at 20-150°C, in agreement with earlier experiments. These results also reproduce the apparent non mass-dependent signature observed in 238U/234U relative to 238U/^{235}U. In addition to redox reactions, significant fractionation is expected between different U6+-bearing uranyl complexes (e.g., UO2(H2O)_52+, UO2(NO3)_3^-, UO2(CO3)(H2O)3). These results suggest that U-isotope composition could be used as a proxy for the oxidation state and speciation of natural waters, and that U-isotope ratios are not constant in materials formed or equilibrated at low temperatures. More generally, nuclear volume fractionations are expected to partially cancel or reverse mass-dependent fractionations caused by redox transitions among the high oxidation states (≥+2) of lanthanides, actinides, and heavy transition elements. References: 1. Nomura, Higuchi and Fujii, 1996, J. Am. Chem. Soc., v. 118, p. 9127-9130. 2. Bigeleisen

  1. Establishing Specifications for Low Enriched Uranium Fuel Operations Conducted Outside the High Flux Isotope Reactor Site

    SciTech Connect

    Pinkston, Daniel; Primm, Trent; Renfro, David G; Sease, John D

    2010-10-01

    The National Nuclear Security Administration (NNSA) has funded staff at Oak Ridge National Laboratory (ORNL) to study the conversion of the High Flux Isotope Reactor (HFIR) from the current, high enriched uranium fuel to low enriched uranium fuel. The LEU fuel form is a metal alloy that has never been used in HFIR or any HFIR-like reactor. This report provides documentation of a process for the creation of a fuel specification that will meet all applicable regulations and guidelines to which UT-Battelle, LLC (UTB) the operating contractor for ORNL - must adhere. This process will allow UTB to purchase LEU fuel for HFIR and be assured of the quality of the fuel being procured.

  2. Testing the Ortec's Isotopic and Eberlines Snap software for Uranium waste measurements

    SciTech Connect

    Vo, Duc T.; Seo, P. N.; Li, T. K.

    2003-01-01

    Uranium enrichment plants normally generate lots of wastes. The wastes are in various matrices such as clothing, glass, concrete, aluminum, and steel, etc. They are in the quantity of a few grams to many kilograms and generally stored in 55-gallon drums. For accountability, it is important to determine the amount of uranium in the waste drums to a certain level of accuracy. There are several commercially available systems that can accurately determine the uranium mass in the waste drums, such as Tomographic-Gamma-Scanner1 (TGS) or Segmented Gamma-Ray Scanner2 (SGS). However, those systems are too cumbersome and expensive. Cheap and simple single detector systems are also available commercially from several companies. The workhorse of these systems is the software, which would work with any germanium detector system. We mocked up waste drums containing several hundred grams to several kilograms of uranium with different isotopic compositions in various matrices. We acquired data using a coaxial germanium detector. We tested two different software codes from two companies, the Ortec's Isotopic software and the Eberline's Snap software. The results with the germanium detector were very encouraging, which led us to test with the NaI detectors. The NaI detectors have much worse resolution than the germanium detectors. However, they are very cheap, can be very large in detector size and, thus, efficient for a given counting time, and are simpler because of not requiring liquid nitrogen for cooling. The results, advantages, and disadvantages of the two software codes and the two detector systems will be discussed.

  3. Quantifying Uranium Isotope Ratios Using Resonance Ionization Mass Spectrometry: The Influence of Laser Parameters on Relative Ionization Probability

    SciTech Connect

    Isselhardt, Brett H.

    2011-09-01

    Resonance Ionization Mass Spectrometry (RIMS) has been developed as a method to measure relative uranium isotope abundances. In this approach, RIMS is used as an element-selective ionization process to provide a distinction between uranium atoms and potential isobars without the aid of chemical purification and separation. We explore the laser parameters critical to the ionization process and their effects on the measured isotope ratio. Specifically, the use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of 235U/238U ratios to decrease laser-induced isotopic fractionation. By broadening the bandwidth of the first laser in a 3-color, 3-photon ionization process from a bandwidth of 1.8 GHz to about 10 GHz, the variation in sequential relative isotope abundance measurements decreased from >10% to less than 0.5%. This procedure was demonstrated for the direct interrogation of uranium oxide targets with essentially no sample preparation. A rate equation model for predicting the relative ionization probability has been developed to study the effect of variation in laser parameters on the measured isotope ratio. This work demonstrates that RIMS can be used for the robust measurement of uranium isotope ratios.

  4. Development of a portable mass spectrometric system for determination of isotopic composition of solid uranium samples using fluorine volatilization

    NASA Astrophysics Data System (ADS)

    Loge, G.

    1994-09-01

    Using hardware and materials supplied by LANL, a prototype quadrupole mass spectrometer system designed for portable field analysis of isotopic composition of solid uranium samples was assembled and tested. The system contained the capability for fluorine volatilization of solid uranium samples with gas introduction, which was successfully tested and demonstrated using 100 mg samples of U3O8. Determination of precision and accuracy for measuring isotopic composition was performed using isotopic standards. Use with soil samples containing uranium were also attempted. Silicates in the soil forming SiF4 were found to be a kinetic bottleneck to the formation of UF6. This could be avoided by performing some sort of chemical separation as a pre-treatment step, which was demonstrated using nitric acid.

  5. Isotopic analysis of uranium in U3O8 by passive gamma-ray spectrometry

    PubMed

    Nir-El

    2000-03-01

    Passive gamma-ray spectrometry was applied to analyze the isotopic composition of uranium in U3O8. Depleted and enriched U3O8 standard reference materials were used to calibrate the system. An independent calibration was performed by standard gamma-ray point sources. U3O8 SRM samples of the 950 series were analyzed. The present results show that the isotopic abundances of 235U in SRMs 950, 950a and 950b are higher by +3.6, +0.9 and +0.9% (relative deviation) than the natural value 0.7200%, while relative precisions were +/-0.4, +/-0.7 and +/-0.3%, respectively. PMID:10724436

  6. Isotopic determination of uranium in soil by laser induced breakdown spectroscopy

    NASA Astrophysics Data System (ADS)

    Chan, George C.-Y.; Choi, Inhee; Mao, Xianglei; Zorba, Vassilia; Lam, Oanh P.; Shuh, David K.; Russo, Richard E.

    2016-08-01

    Laser-induced breakdown spectroscopy (LIBS) operated under ambient pressure has been evaluated for isotopic analysis of uranium in real-world samples such as soil, with U concentrations in the single digit percentage levels. The study addresses the requirements for spectral decomposition of 235U and 238U atomic emission peaks that are only partially resolved. Although non-linear least-square fitting algorithms are typically able to locate the optimal combination of fitting parameters that best describes the experimental spectrum even when all fitting parameters are treated as free independent variables, the analytical results of such an unconstrained free-parameter approach are ambiguous. In this work, five spectral decomposition algorithms were examined, with different known physical properties (e.g., isotopic splitting, hyperfine structure) of the spectral lines sequentially incorporated into the candidate algorithms as constraints. It was found that incorporation of such spectral-line constraints into the decomposition algorithm is essential for the best isotopic analysis. The isotopic abundance of 235U was determined from a simple two-component Lorentzian fit on the U II 424.437 nm spectral profile. For six replicate measurements, each with only fifteen laser shots, on a soil sample with U concentration at 1.1% w/w, the determined 235U isotopic abundance was (64.6 ± 4.8)%, and agreed well with the certified value of 64.4%. Another studied U line - U I 682.691 nm possesses hyperfine structure that is comparatively broad and at a significant fraction as the isotopic shift. Thus, 235U isotopic analysis with this U I line was performed with spectral decomposition involving individual hyperfine components. For the soil sample with 1.1% w/w U, the determined 235U isotopic abundance was (60.9 ± 2.0)%, which exhibited a relative bias about 6% from the certified value. The bias was attributed to the spectral resolution of our measurement system - the measured line

  7. High Precision Measurements of 235U/238U Isotopic Fractionations Resulting From Uranium Reduction Induced by Zero Valent Iron

    NASA Astrophysics Data System (ADS)

    Rademacher, L.; Lundstrom, C.; Johnson, T.

    2003-12-01

    Uranium is a widespread natural and anthropogenic contaminant in surface and subsurface waters. Like several other inorganic contaminants, uranium is mobile under oxidizing conditions but may be immobilized by chemical reduction. U(VI) moves with groundwater as (UO2)2+ and as soluble complexes with carbonate, phosphate, and fluoride. In many groundwater systems, uranium undergoes chemical reduction to U(IV), which is insoluble and immobile. Therefore, understanding the extent of reduction is essential for predicting the mobility of uranium in groundwater. Mass dependent isotopic fractionations of redox sensitive contaminants frequently found in groundwater (including chromate, selenate, and nitrate) have proven exceptionally useful for estimating the rate and extent of reduction and immobilization. Until recently, however, analytical limitations have prevented these techniques from being applied to heavier redox sensitive elements, such as uranium. The advent of highly sensitive multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS) enables high precision measurements of previously undetected variations in many elements. Laboratory reduction experiments with zero valent iron (ZVI) were performed in a controlled environment to test the hypothesis that uranium isotopes, specifically 235U/238U, behave similarly to other redox sensitive contaminants and produce a mass dependent fractionation during the transformation between valence states. Because of the large abundance differences between 235U and 238U, initial experiments used U500, an enriched uranium standard with approximately equal parts 235U and 238U. Results suggest that the highly sensitive MC-ICP-MS distinguishes 235U/238Uvariations to approximately + 0.02per mil. Measured isotopic fractionations between the 235U/238U of the initial and final experimental solutions (~70% reduced) are approximately 1.1 per mil, and increase with decreasing concentration. Measured variations in 235U/238U

  8. Time Constraints on Soil Evolution from Uranium-series Isotopes in the South-eastern Australian Highlands: Evidences for a Coupling Between Soil Erosion and Production

    NASA Astrophysics Data System (ADS)

    Puthiyaveetil Othayoth, S.; Dosseto, A.; Hesse, P. P.; Handley, H. K.

    2011-12-01

    The evolution of soil resources (steady-state, aggradation or degradation) is determined by the balance between soil production and denudation rates. The uranium-series isotopic composition of four soil profiles from Frogs Hollow, a location in the upper catchment area of the Murrumbidgee River in southeastern Australia, has been determined to constrain the soil production rate in this region. The results are compared with previous estimates of soil residence time at this site, estimated from cosmogenic radionuclides and soil elemental chemistry data. Soil is increasingly weathered from bottom to top, which is evident from the decrease in (234U/238U) ratios and increase in relative quartz content with decreasing soil depth. The observed variations in mineralogy and geochemistry between the four soil profiles reflect differences in the degree of weathering. Sequential leaching was conducted to assess how uranium-series isotopes are distributed between primary and secondary minerals. Leached and unleached aliquots show similar mineralogy with minor variation in the relative mineral abundances whereas the elemental and isotopic compositions of uranium and thorium show notable differences. The unleached samples show more systematic variations in uranium-series isotopic compositions with depth when compared to leached samples. Soil residence times are calculated by modeling soil uranium-series isotopic composition using the model from (Dosseto et al., 2008). Inferred values vary from 3 to 30 kyr for profiles F1 (unleached aliquots) and F2. A negative correlation is observed between muscovite abundance and calculated soil residence times. The slope of this correlation is similar for different soil profiles and for both leached and unleached aliquots. Thus, we were able to apply this relationship to profiles where the residence time could not be calculated due to scatter in U-series isotope compositions. The inferred soil residence times range from 3 to 33 kyr for leached

  9. Mechanisms of magma generation beneath hawaii and mid-ocean ridges: uranium/thorium and samarium/neodymium isotopic evidence.

    PubMed

    Sims, K W; Depaolo, D J; Murrell, M T; Baldridge, W S; Goldstein, S J; Clague, D A

    1995-01-27

    Measurements of uranium/thorium and samarium/neodymium isotopes and concentrations in a suite of Hawaiian basalts show that uranium/thorium fractionation varies systematically with samarium/neodymium fractionation and major-element composition; these correlations can be understood in terms of simple batch melting models with a garnet-bearing peridotite magma source and melt fractions of 0.25 to 6.5 percent. Midocean ridge basalts shows a systematic but much different relation between uranium/thorium fractionation and samarium/neodymium fractionation, which, although broadly consistent with melting of a garnet-bearing peridotite source, requires a more complex melting model. PMID:17788786

  10. DESIGN STUDY FOR A LOW-ENRICHED URANIUM CORE FOR THE HIGH FLUX ISOTOPE REACTOR, ANNUAL REPORT FOR FY 2010

    SciTech Connect

    Cook, David Howard; Freels, James D; Ilas, Germina; Jolly, Brian C; Miller, James Henry; Primm, Trent; Renfro, David G; Sease, John D; Pinkston, Daniel

    2011-02-01

    This report documents progress made during FY 2010 in studies of converting the High Flux Isotope Reactor (HFIR) from high enriched uranium (HEU) fuel to low enriched uranium (LEU) fuel. Conversion from HEU to LEU will require a change in fuel form from uranium oxide to a uranium-molybdenum alloy. With axial and radial grading of the fuel foil and an increase in reactor power to 100 MW, calculations indicate that the HFIR can be operated with LEU fuel with no degradation in performance to users from the current level. Studies are reported of support to a thermal hydraulic test loop design, the implementation of finite element, thermal hydraulic analysis capability, and infrastructure tasks at HFIR to upgrade the facility for operation at 100 MW. A discussion of difficulties with preparing a fuel specification for the uranium-molybdenum alloy is provided. Continuing development in the definition of the fuel fabrication process is described.

  11. Partial Safety Analysis for a Reduced Uranium Enrichment Core for the High Flux Isotope Reactor

    SciTech Connect

    Primm, Trent; Gehin, Jess C

    2009-04-01

    A computational model of the reactor core of the High Flux Isotope Rector (HFIR) was developed in order to analyze non-destructive accidents caused by transients during reactor operation. The reactor model was built for the latest version of the nuclear analysis software package called Program for the Analysis of Reactor Transients (PARET). Analyses performed with the model constructed were compared with previous data obtained with other tools in order to benchmark the code. Finally, the model was used to analyze the behavior of the reactor under transients using a different nuclear fuel with lower enrichment of uranium (LEU) than the fuel currently used, which has a high enrichment of uranium (HEU). The study shows that the presence of fertile isotopes in LEU fuel, which increases the neutron resonance absorption, reduces the impact of transients on the fuel and enhances the negative reactivity feedback, thus, within the limitations of this study, making LEU fuel appear to be a safe alternative fuel for the reactor core.

  12. Reaction paths and host phases of uranium isotopes (235U; 238U), Saanich Inlet

    NASA Astrophysics Data System (ADS)

    Amini, M.; Holmden, C. E.; Francois, R. H.

    2009-12-01

    In recent times, Uranium has become increasingly the focus of stable isotope fractionation studies. Variations in 238U/235U have been reported as a result of redox reactions [1,2] from the nuclear field shift effect [3], and a mass-dependent, microbially-mediated, kinetic isotope effect [4]. The 238U/235U variability caused by changes in environmental redox conditions leads to an increase in the 238U/235U ratios of the reduced U species sequestered into marine sediments. This points to U isotope variability as a new tool to study ancient ocean redox changes. However, the process by which reduced sediments become enriched in the heavy isotopes of U is not yet known, and hence the utility of 238U/235U as a redox tracer remains to be demonstrated. In order to further constrain sedimentary U enrichment and related isotope effect, we are investigating U isotopic compositions of water samples and fresh surface sediment grab samples over a range of redox conditions in the seasonally anoxic Saanich Inlet, on the east coast of Vancouver Island. U was sequentially extracted from sediments in order to characterize specific fractions for their isotopic composition. The measurements were carried out by MC-ICPMS using 233U/236U-double spike technique. The data are reported as δ238U relative to NBL 112a with a 238U/235U ratio of 137.88 (2sd). External precision is better than 0.10‰ (2sd). Fifteeen analyses of seawater yielded δ238U of -0.42±0.08‰ (2sd). The results for the water samples indicate a homogenous δ238U value throughout the Saanich Inlet water column that matches the global seawater signature. All of the water samples from above and below average -0.42±0.05‰ (2sd). In contrast, a plankton net sample yielded a distinctly different, (about 0.5‰ lighter) isotope value. Bacterial reduction experiments [4] have also shown isotope enrichment factors of about -0.3‰. In addition, metal isotope fractionation occurs during adsorption with the light isotope being

  13. Sulfur Isotopes as Indicators of Bacterial Sulfate Reduction Processes Influencing Field Scale Uranium Bioremediation

    NASA Astrophysics Data System (ADS)

    Druhan, J. L.; Conrad, M. E.; Williams, K. H.; N'guessan, L.; Long, P. E.; Hubbard, S. S.

    2007-12-01

    An in-situ acetate amendment at a DOE Uranium Mill Tailings Remedial Action (UMTRA) site near Rifle, CO demonstrated successful reduction of aqueous U(VI), to less soluble U(IV) through stimulated microbial activity. U(VI) reduction rates were highest during iron reduction and decreased with the onset of sulfate reduction. However, sustained U(IV) attenuation was observed following subsequent termination of the acetate amendment. These findings illustrate the importance of the transition between iron and sulfate reducing conditions in stimulating bioreduction of uranium. The sulfur isotope compositions of sulfate and sulfide were measured through this transition in order to explore the utility of these data in tracking the extent of microbial sulfate reduction and to assess the stability of sulfide precipitates. Samples for isotopic analyses and aqueous measurements of sulfate, ferrous iron, U(VI) and acetate were collected in one background well and three monitoring wells down-gradient of the acetate injection. Results show an increase of up to 7‰ in the δ34S of sulfate at the onset of sulfate reduction, followed by a return to background δ34S values of -8‰ following cessation of the acetate amendment. The δ34S values of sulfide increased from roughly -20‰ at the onset of sulfate reduction to a maximum of -0.8‰ during peak sulfate removal, followed by a gradual return to values of roughly -28‰ upon cessation of the acetate amendment. These data present a unique perspective on the processes governing the bioreduction experiment in that the sulfate isotopes are a function of both transport and mixing processes, whereas the sulfide isotopes represent biogenic sulfide that is rapidly removed from the aqueous phase. Thus a comparable enrichment in sulfate isotopic data noted in the closest and furthest wells from the injection gallery suggest bioreduction in both of these locations, while a larger increase in sulfide isotopic values in the closest well

  14. Uranium and thorium isotopes and their state of equilibria in lungs from uranium miners.

    PubMed

    Wrenn, M E; Singh, N P; Saccomanno, G

    1983-01-01

    Radiochemical analysis of seven lungs obtained at autopsy show that concentrations ranged between 6 and 63 pCi/kg for 238U and 6-66 pCi/kg, for 234U. Similarly, 230Th ranged from 17 to 54 pCi/kg, two orders of magnitude higher than 230Th observed in the lungs of the general population from the Western mining region. For individual lungs, 238U and 234U were close to equilibrium with an average ratio of 238U/234U of 0.94 and a range of 0.80-1.02. Surprisingly, 230Th was close to equilibrium with 234U with a 230Th/234U ratio of 1.1 and a range from 0.54 to 2.6. Equilibrium between U and Th isotopes is in contrast to the disequilibrium reported in beagles which chronically inhaled carnotite, where the 230Th/234U ratio was observed to range from 5.4 to 7.4 with an average of 6.3. The average radiation dose rate to lung from each of the three radionuclides was calculated as follows: D = 18.7 CE where D = dose rate in mrad/year, C = activity concentration in tissue in pCi/g and E = energy absorbed per disintegration in MeV. The combined radiation dose rate (at death) due to three long-lived radionuclides 238U, 234U and 230Th varied from 2.5 to 14.2 mrad/yr with a mean of 9.6 mrad/yr. The concentration of 226Ra and daughters in the lung was not determined. An upper limit to the dose rate from the whole chain, calculated assuming 226Ra through 210Po are in equilibrium with 238U, 234U and 230Th, would be 30 mrad/yr. PMID:6862915

  15. Heterogeneous sodium fast reactor designed for transmuting minor actinide waste isotopes into plutonium fuel

    NASA Astrophysics Data System (ADS)

    Bays, Samuel Eugene

    2008-10-01

    In the past several years there has been a renewed interest in sodium fast reactor (SFR) technology for the purpose of destroying transuranic waste (TRU) produced by light water reactors (LWR). The utility of SFRs as waste burners is due to the fact that higher neutron energies allow all of the actinides, including the minor actinides (MA), to contribute to fission. It is well understood that many of the design issues of LWR spent nuclear fuel (SNF) disposal in a geologic repository are linked to MAs. Because the probability of fission for essentially all the "non-fissile" MAs is nearly zero at low neutron energies, these isotopes act as a neutron capture sink in most thermal reactor systems. Furthermore, because most of the isotopes produced by these capture reactions are also non-fissile, they too are neutron sinks in most thermal reactor systems. Conversely, with high neutron energies, the MAs can produce neutrons by fast fission. Additionally, capture reactions transmute the MAs into mostly plutonium isotopes, which can fission more readily at any energy. The transmutation of non-fissile into fissile atoms is the premise of the plutonium breeder reactor. In a breeder reactor, not only does the non-fissile "fertile" U-238 atom contribute fast fission neutrons, but also transmutes into fissile Pu-239. The fissile value of the plutonium produced by MA transmutation can only be realized in fast neutron spectra. This is due to the fact that the predominate isotope produced by MA transmutation, Pu-238, is itself not fissile. However, the Pu-238 fission cross section is significantly larger than the original transmutation parent, predominately: Np-237 and Am-241, in the fast energy range. Also, Pu-238's fission cross section and fission-to-capture ratio is almost as high as that of fissile Pu-239 in the fast neutron spectrum. It is also important to note that a neutron absorption in Pu-238, that does not cause fission, will instead produce fissile Pu-239. Given this

  16. Weathering and transport of sediments in the Bolivian Andes: Time constraints from uranium-series isotopes

    NASA Astrophysics Data System (ADS)

    Dosseto, A.; Bourdon, B.; Gaillardet, J.; Maurice-Bourgoin, L.; Allègre, C. J.

    2006-08-01

    Rivers from the upper Rio Madeira basin (Bolivia) have been studied with uranium-series isotopes in order to constrain the timescales of weathering and sediment transfer from the Andes through the Amazon tropical plain. Uranium (U), thorium (Th) and radium (Ra) isotopes ( 238U- 234U- 230Th- 226Ra and 232Th) have been analyzed in the suspended load (> 0.2 μm) of rivers. Increasing 230Th excesses relative to 238U in suspended particles from the Andes to the tropical plain is interpreted as an increasing duration of weathering during sediment transport and storage in the foreland basin. Model calculations for ( 230Th/ 238U) and ( 226Ra/ 230Th) activity ratios in suspended particles using a continuous weathering model indicates that: (i) the timescale for production, storage and transport of sediments in the Andean Cordillera is only a few kyr, (ii) the storage time of suspended sediments in the foreland basin is 5 ± 1 kyr and (iii) the average transfer time of suspended sediments from the Andes to the confluence of Rio Madeira with the Amazon River is 17 ± 3 kyr. An implication of these short timescales is that the bedrock eroded must have lost part of its uranium during one or several past erosion cycles. This demonstrates the recycling of sediments through several erosion cycles before transfer to the oceans. The calculation of long-term (> 1 kyr), steady-state erosion rates indicates that they are much lower than present-day rates. This increase in denudation rates must be recent and could be explained by an increase in precipitation ˜ 4 ka ago, as suggested by palaeoclimatic evidences and the draining of transient sedimentary basins encountered on the Altiplano and easily eroded. This suggests that climatic variability rather than tectonics alone produces high erosion rates.

  17. Uranium Bio-accumulation and Cycling as revealed by Uranium Isotopes in Naturally Reduced Sediments from the Upper Colorado River Basin

    NASA Astrophysics Data System (ADS)

    Lefebvre, Pierre; Noël, Vincent; Jemison, Noah; Weaver, Karrie; Bargar, John; Maher, Kate

    2016-04-01

    Uranium (U) groundwater contamination following oxidized U(VI) releases from weathering of mine tailings is a major concern at numerous sites across the Upper Colorado River Basin (CRB), USA. Uranium(IV)-bearing solids accumulated within naturally reduced zones (NRZs) characterized by elevated organic carbon and iron sulfide compounds. Subsequent re-oxidation of U(IV)solid to U(VI)aqueous then controls the release to groundwater and surface water, resulting in plume persistence and raising public health concerns. Thus, understanding the extent of uranium oxidation and reduction within NRZs is critical for assessing the persistence of the groundwater contamination. In this study, we measured solid-phase uranium isotope fractionation (δ238/235U) of sedimentary core samples from four study sites (Shiprock, NM, Grand Junction, Rifle and Naturita, CO) using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). We observe a strong correlation between U accumulation and the extent of isotopic fractionation, with Δ238U up to +1.8 ‰ between uranium-enriched and low concentration zones. The enrichment in the heavy isotopes within the NRZs appears to be especially important in the vadose zone, which is subject to variations in water table depth. According to previous studies, this isotopic signature is consistent with biotic reduction processes associated with metal-reducing bacteria. Positive correlations between the amount of iron sulfides and the accumulation of reduced uranium underline the importance of sulfate-reducing conditions for U(IV) retention. Furthermore, the positive fractionation associated with U reduction observed across all sites despite some variations in magnitude due to site characteristics, shows a regional trend across the Colorado River Basin. The maximum extent of 238U enrichment observed in the NRZ proximal to the water table further suggests that the redox cycling of uranium, with net release of U(VI) to the groundwater by

  18. Uranium isotope fractionation in Saanich Inlet: A modern analog study of a paleoredox tracer

    NASA Astrophysics Data System (ADS)

    Holmden, C.; Amini, M.; Francois, R.

    2015-03-01

    Uranium isotope fractionation was studied in the sediment and water of Saanich Inlet, a seasonally anoxic fjord on the east coast of Vancouver Island. The concentration of dissolved U is the same above and below the redoxcline at ˜120 m depth, with an average δ238U value of -0.45 ± 0.06‰ (2 s.e.), which is indistinguishable from seawater values reported in other studies. This finding is consistent with water renewal times for the inlet that are roughly seasonal in frequency, thus hiding the impact of the U losses to the anoxic sediment of the inlet. Complete digests of the anoxic sediment yielded higher δ238U values than seawater (-0.21 ± 0.11‰ (2 s.e.)). By contrast, complete digests of the sediment trap samples yielded lower δ238U values than seawater (-0.52 ± 0.10‰ (2 s.e.)), and marine plankton from the inlet yielded the lowest δ238U value of -1.24 ± 0.17‰ (2σ). Cross-plots of δ238U and δ234U vs. Th/U reveal strong correlations indicative of two-component mixing when the data from traps and anoxic inlet sediment are combined. One mixing end-member is fractionated uranium of seawater origin, with a δ238U value of 0.17 ± 0.14‰ (2σ). The other is detrital uranium with a δ238U value of -0.83 ± 0.12‰ (2σ). The detrital end-member is lower than the range of δ238U values reported in the literature for granitoid igneous rocks (-0.44‰ to -0.17‰, 2σ) (Telus et al., 2012), suggesting that continental weathering fractionates uranium isotopes, with preferential release of 238U. Development and application of U isotopes as a paleoredox proxy has its basis in the nuclear volume fractionation. The data from Saanich Inlet meets this expectation, with a positive fractionation factor (Δaq(VI)sed(IV)) of 0.62 ± 0.17‰ (2σ) calculated as the difference in δ238U between authigenic U in anoxic sediments and sediment traps (+0.17‰) and U dissolved in seawater (-0.45‰). However, it is widely believed that U(VI) reduction in the marine

  19. Uranium isotopes distinguish two geochemically distinct stages during the later Cambrian SPICE event

    NASA Astrophysics Data System (ADS)

    Dahl, Tais W.; Boyle, Richard A.; Canfield, Donald E.; Connelly, James N.; Gill, Benjamin C.; Lenton, Timothy M.; Bizzarro, Martin

    2014-09-01

    Anoxic marine zones were common in early Paleozoic oceans (542-400 Ma), and present a potential link to atmospheric pO2 via feedbacks linking global marine phosphorous recycling, primary production and organic carbon burial. Uranium (U) isotopes in carbonate rocks track the extent of ocean anoxia, whereas carbon (C) and sulfur (S) isotopes track the burial of organic carbon and pyrite sulfur (primary long-term sources of atmospheric oxygen). In combination, these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million-year time scales. Here we report high-precision uranium isotopic data in marine carbonates deposited during the Late Cambrian ‘SPICE’ event, at ca. 499 Ma, documenting a well-defined -0.18‰ negative δ238U excursion that occurs at the onset of the SPICE event's positive δ13C and δ34S excursions, but peaks (and tails off) before them. Dynamic modelling shows that the different response of the U reservoir cannot be attributed solely to differences in residence times or reservoir sizes - suggesting that two chemically distinct ocean states occurred within the SPICE event. The first ocean stage involved a global expansion of euxinic waters, triggering the spike in U burial, and peaking in conjunction with a well-known trilobite extinction event. During the second stage widespread euxinia waned, causing U removal to tail off, but enhanced organic carbon and pyrite burial continued, coinciding with evidence for severe sulfate depletion in the oceans (Gill et al., 2011). We discuss scenarios for how an interval of elevated pyrite and organic carbon burial could have been sustained without widespread euxinia in the water column (both non-sulfidic anoxia and/or a more oxygenated ocean state are possibilities). Either way, the SPICE event encompasses two different stages of elevated organic carbon and pyrite burial maintained by high nutrient fluxes to the ocean, and potentially sustained by

  20. The isotopic composition of uranium and lead in Allende inclusions and meteoritic phosphates

    NASA Technical Reports Server (NTRS)

    Chen, J. H.; Wasserburg, G. J.

    1981-01-01

    The isotopic compositions of uranium and lead in Ca-Al-rich inclusions from the Allende chondrite and in whitlockite from the St. Severin chondrite and the Angra dos Reis achondrite are reported. Isoptopic analysis of acid soluble fractions of the Allende inclusions and the meteoritic whitlockite, which show isotopic anomalies in other elements, reveals U-235/U-238 ratios from 1/137.6 to 1/138.3, within 20 per mil of normal terrestrial U abundances. The Pb isotopic compositions of five coarse-grained Allende inclusions give a mean Pb-207/Pb-206 model age of 4.559 + or - 0.015 AE, in agreement with the U results. Pb isotope ratios of two fine-grained inclusions and a coarse-grained inclusion with strong mass fractionation and some nonlinear isotopic anomalies indicate that the U-Pb systems of these inclusions have evolved differently from the rest of Allende. Th/U abundance ratios in the Allende inclusions and meteoritic phosphate are found to range from 3.8 to 96, presumably indicating an optimal case for Cm/U fractionation, although the normal U concentrations do not support claims of abundant live Cm-247 or Cm-247/U-238 fractionation at the time of meteorite formation, in contrast to previous results. A limiting Cm-247/U-235 ratio of 0.004 at the time of meteorite formation is calculated which implies that the last major r process contribution at the protosolar nebula was approximately 100 million years prior to Al-26 formation and injection.

  1. Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon

    SciTech Connect

    La Tourrette, T.Z.; Burnett, D.S. ); Bacon C.R. )

    1991-02-01

    Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO{sub 2}), are interpreted to be portions of the magma chamber walls that were torn off during eruption. The glass is clear and well homogenized for all measured elements except Zr. Results for Fe-Ti oxides give D{sub U}{sup oxide/liq} {approx} 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are modestly well equilibrated with the melt for many of the minor elements, while those that are inclusions in relict plagioclase are not. Uranium and ytterbium inhomogeneities in zircons indicate that the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons faster that the zircons were dissolving. Based on the authors measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractional during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in the authors samples. This demonstrates an actual case of nonequilibrium source retention of accessory phases, which in general could be an important trace element fractionation mechanism. Their results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites.

  2. Concentrations and activity ratios of uranium isotopes in groundwater from Donana National Park, South of Spain

    SciTech Connect

    Bolivar, J. P.; Olias, M.; Gonzalez-Garcia, F.; Garcia-Tenorio, R.

    2008-08-07

    The levels and distribution of natural radionuclides in groundwaters from the unconfined Almonte-Marismas aquifer, upon which Donana National Park is located, have been analysed. Most sampled points were multiple piezometers trying to study the vertical distribution of the hydrogeochemical characteristics in the aquifer. Temperature, pH, electrical conductivity, dissolved oxygen and redox potential were determined in the field. A large number of parameters, physico-chemical properties, major and minor ions, trace elements and natural radionuclides (U-isotopes, Th-isotopes, Ra-isotopes and {sup 210}Po), were also analysed. In the southern zone, where aeolian sands crop out, water composition is of the sodium chloride type, and the lower U-isotopes concentrations have been obtained. As water circulates through the aquifer, bicarbonate and calcium concentrations increase slightly, and higher radionuclides concentrations were measured. Finally, we have demonstrated that {sup 234}U/{sup 238}U activity ratios can be used as markers of the type of groundwater and bedrock, as it has been the case for old waters with marine origin confined by a marsh in the south-east part of aquifer.

  3. Third Minima in Thorium and Uranium Isotopes in a Self-Consistent Theory

    SciTech Connect

    McDonnell, J. D.

    2013-01-01

    Background: Well-developed third minima, corresponding to strongly elongated and reflection-asymmetric shapes associated with dimolecular configurations, have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential-energy surfaces in the third minimum region.

    Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular (cluster) states. We study the isentropic potential-energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects.

    Methods: We use the finite-temperature superfluid nuclear density functional theory. We consider two Skyrme energy density functionals: a traditional functional SkM and a recent functional UNEDF1 optimized for fission studies.

    Results: We predict very shallow or no third minima in the potential-energy surfaces of 232Th and 232U. In the lighter Th and U isotopes with N = 136 and 138, the third minima are better developed. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly magic 132Sn and a lighter deformed Zr or Mo fragment. The potential-energy surfaces for 228,232Th and 232U at several excitation energies are presented. We also study isotopic chains to demonstrate the evolution of the depth of the third minimum with neutron number.

    Conclusions: We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr andMo isotopes around N = 58.We demonstrate that the depth of

  4. Third minima in thorium and uranium isotopes in a self-consistent theory

    NASA Astrophysics Data System (ADS)

    McDonnell, J. D.; Nazarewicz, W.; Sheikh, J. A.

    2013-05-01

    Background: Well-developed third minima, corresponding to strongly elongated and reflection-asymmetric shapes associated with dimolecular configurations, have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential-energy surfaces in the third minimum region.Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular (cluster) states. We study the isentropic potential-energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects.Methods: We use the finite-temperature superfluid nuclear density functional theory. We consider two Skyrme energy density functionals: a traditional functional SkM* and a recent functional UNEDF1 optimized for fission studies.Results: We predict very shallow or no third minima in the potential-energy surfaces of 232Th and 232U. In the lighter Th and U isotopes with N=136 and 138, the third minima are better developed. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly magic 132Sn and a lighter deformed Zr or Mo fragment. The potential-energy surfaces for 228,232Th and 232U at several excitation energies are presented. We also study isotopic chains to demonstrate the evolution of the depth of the third minimum with neutron number.Conclusions: We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr and Mo isotopes around N=58. We demonstrate that the depth of the third minimum

  5. Isotopic composition ( 238U/ 235U) of some commonly used uranium reference materials

    NASA Astrophysics Data System (ADS)

    Condon, Daniel J.; McLean, Noah; Noble, Stephen R.; Bowring, Samuel A.

    2010-12-01

    We have determined 238U/ 235U ratios for a suite of commonly used natural (CRM 112a, SRM 950a, and HU-1) and synthetic (IRMM 184 and CRM U500) uranium reference materials by thermal ionisation mass-spectrometry (TIMS) using the IRMM 3636 233U- 236U double spike to accurately correct for mass fractionation. Total uncertainty on the 238U/ 235U determinations is estimated to be <0.02% (2σ). These natural 238U/ 235U values are different from the widely used 'consensus' value (137.88), with each standard having lower 238U/ 235U values by up to 0.08%. The 238U/ 235U ratio determined for CRM U500 and IRMM 184 are within error of their certified values; however, the total uncertainty for CRM U500 is substantially reduced (from 0.1% to 0.02%). These reference materials are commonly used to assess mass-spectrometer performance and accuracy, calibrate isotope tracers employed in U, U-Th and U-Pb isotopic studies, and as a reference for terrestrial and meteoritic 238U/ 235U variations. These new 238U/ 235U values will thus provide greater accuracy and reduced uncertainty for a wide variety of isotopic determinations.

  6. Isotopic analysis of single uranium and plutonium particles by chemical treatment and mass spectrometry

    NASA Astrophysics Data System (ADS)

    Shinonaga, T.; Esaka, F.; Magara, M.; Klose, D.; Donohue, D.

    2008-11-01

    The isotopic composition of single uranium and plutonium particles was measured with an inductively coupled plasma mass spectrometer (ICP-MS) and a thermal ionization mass spectrometer (TIMS). Particles deposited on a carbon planchet were first analyzed with an energy dispersive X-ray spectrometer (EDX) attached to a scanning electron microscope (SEM) and then transferred on to a silicon wafer using a manipulator. The particle on the silicon wafer was dissolved with nitric acid and the isotopic ratios of U and Pu were measured with ICP-MS and TIMS. The results obtained by both methods for particles of certified reference materials showed good agreement with the certified values within the expected uncertainty. The measurement uncertainties obtained in this study were similar for both mass spectrometric methods. This study was performed to establish the method of particle analysis with SEM, EDX, the particle manipulation and chemical preparation technique, and the measurement of isotopic ratios of U and Pu in a single particle by mass spectrometry.

  7. Isotopic Tracking of Hanford 300 Area Derived Uranium in the Columbia River

    SciTech Connect

    Christensen, John N.; Dresel, P. Evan; Conrad, Mark E.; Patton, Gregory W.; DePaolo, Donald J.

    2010-12-01

    A portion of the subsurface contamination at the Hanford Site, the former plutonium production facility in Washington State, affects the Columbia River. A component of this contamination, uranium (U), has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates. Our data on river water samples indicate that as much as 3.2 kg/day can enter the Columbia River from the 300 Area of the Hanford Site, which is only a small fraction of the total load of dissolved natural background U carried by the Columbia River. This very low–level contamination can be discerned, despite further dilution to <1% of natural background U, as far as 350 km downstream from the Hanford Site. These results indicate that isotopic methods can allow the amounts of U contamination from the Hanford Site to be measured accurately enough to ascertain where they are an environmental concern, and where they are insignificant.

  8. Determination of total and isotopic uranium and total thorium in soils by inductively coupled plasma-mass spectrometry

    SciTech Connect

    Bolin, R.N.

    1995-12-31

    Inductively coupled plasma-mass spectrometry (ICP-MS), using standard sample introduction by peristaltic pumping, is presented as a method to determine total and isotopic uranium ({sup 234}U, {sup 235}U, {sup 236}U, and {sup 238}U) and thorium ({sup 232}Th) in soil samples. Initial sample preparation consists of oven drying to determine moisture content, and grinding and mixing the soil to make it homogeneous. This is followed by a nitric/hydrofluoric acid digestion to bring the uranium into solution. Bismuth ({sup 209}Bi) is added prior to digestion to monitor for losses due to sample preparation and analysis. An addition digestion, using nitric/perchloric acid is performed if the total thorium concentration is required on the sample. The uranium and thorium content of this solution and the {sup 235}U/{sup 238}U ratio are measured on an initial pass through the ICP-MS. The total uranium measurement is based on the {sup 238}U isotope measurement with correction for the presence of the U isotopes. To determine the concentration of the less abundant {sup 234}U and {sup 236}U isotopes, the digestate is further concentrated by using a solid phase extraction column (TRU.Spec by EiChrom Industries, Inc.) before a second pass through the ICP-MS.

  9. The uranium isotopic composition of the Earth and the Solar System

    NASA Astrophysics Data System (ADS)

    Goldmann, Alexander; Brennecka, Gregory; Noordmann, Janine; Weyer, Stefan; Wadhwa, Meenakshi

    2015-01-01

    Recent high-precision mass spectrometric studies of the uranium isotopic composition of terrestrial and meteoritic materials have shown significant variation in the 238U/235U ratio, which was previously assumed to be invariant (=137.88). In this study, we have investigated 27 bulk meteorite samples from different meteorite groups and types, including carbonaceous (CM1 and CV3), enstatite (EH4) and ordinary (H-, L-, and LL-) chondrites, as well as a variety of achondrites (angrites, eucrites, and ungrouped) to constrain the distribution of U isotopic heterogeneities and to determine the average 238U/235U for the Solar System. The investigated bulk meteorites show a range in 238U/235U between 137.711 and 137.891 (1.3‰) with the largest variations among ordinary chondrites (OCs). However, the U isotope compositions of 20 of the 27 meteorites analyzed here overlap within analytical uncertainties with the narrow range defined by terrestrial basalts (137.778-137.803), which are likely the best representatives for the U isotope composition of the bulk silicate Earth. Furthermore, the average 238U/235U of all investigated meteorite groups overlaps with that of terrestrial basalts (137.795 ± 0.013). The bulk meteorite samples studied here do not show a negative correlation of 238U/235U with Nd/U or Th/U (used as proxies for the Cm/U ratio), as would be expected if radiogenic 235U was generated by the decay of extant 247Cm in the early Solar System. Rather, ordinary chondrites show a positive correlation of 238U/235U with Nd/U and with 1/U. The following conclusions can be drawn from this study: (1) The Solar System has a broadly homogeneous U isotope composition, and bulk samples of only a limited number of meteorites display detectable U isotope variations; (2) Bulk planetary differentiation has no significant effect on the 238U/235U ratio since the Earth, achondrites, and chondrites have indistinguishable U isotope compositions in average. (3) The cause of U isotopic

  10. Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

    NASA Astrophysics Data System (ADS)

    Tissot, François L. H.; Dauphas, Nicolas

    2015-10-01

    The 238U/235U isotopic composition of uranium in seawater can provide important insights into the modern U budget of the oceans. Using the double spike technique and a new data reduction method, we analyzed an array of seawater samples and 41 geostandards covering a broad range of geological settings relevant to low and high temperature geochemistry. Analyses of 18 seawater samples from geographically diverse sites from the Atlantic and Pacific oceans, Mediterranean Sea, Gulf of Mexico, Persian Gulf, and English Channel, together with literature data (n = 17), yield a δ238U value for modern seawater of -0.392 ± 0.005‰ relative to CRM-112a. Measurements of the uranium isotopic compositions of river water, lake water, evaporites, modern coral, shales, and various igneous rocks (n = 64), together with compilations of literature data (n = 380), allow us to estimate the uranium isotopic compositions of the various reservoirs involved in the modern oceanic uranium budget, as well as the fractionation factors associated with U incorporation into those reservoirs. Because the incorporation of U into anoxic/euxinic sediments is accompanied by large isotopic fractionation (ΔAnoxic/Euxinic-SW = +0.6‰), the size of the anoxic/euxinic sink strongly influences the δ238U value of seawater. Keeping all other fluxes constant, the flux of uranium in the anoxic/euxinic sink is constrained to be 7.0 ± 3.1 Mmol/yr (or 14 ± 3% of the total flux out of the ocean). This translates into an areal extent of anoxia into the modern ocean of 0.21 ± 0.09% of the total seafloor. This agrees with independent estimates and rules out a recent uranium budget estimate by Henderson and Anderson (2003). Using the mass fractions and isotopic compositions of various rock types in Earth's crust, we further calculate an average δ238U isotopic composition for the continental crust of -0.29 ± 0.03‰ corresponding to a 238U/235U isotopic ratio of 137.797 ± 0.005. We discuss the implications of

  11. Age of uranium mineralization at the Jabiluka and Ranger deposits, Northern Territory, Australia: New U- Pb isotope evidence.

    USGS Publications Warehouse

    Ludwig, K. R.; Grauch, R.I.; Nutt, C.J.; Nash, J.T.; Frishman, D.; Simmons, K.R.

    1987-01-01

    The Ranger and Jabiluka uranium deposits are the largest in the Alligator Rivers uranium field, which contains at least 20% of the world's low-cost uranium reserves. Ore occurs in early Proterozoic metasediments, below an unconformity with sandstones of the 1.65 b.y.-old Kombolgie Formation. This study has used U-Pb isotope data from a large number of whole-rock drill core samples with a variety of mineral assemblages and textures. Both Ranger and Jabiluka reflect a common, profound isotopic disturbance at about 400 to 600 m.y. This disturbance, which was especially pronounced at Jabiluka, may correspond to the development of basins and associated basalt flows to the W and SW.-from Authors

  12. Uranium isotopic data in uraninite spent fuel from the Bangombe natural nuclear reactor (Gabon) and its surroundings

    PubMed

    Fernandez-Diaz; Quejido; Crespo; Perez del Villar L; Martin-Sanchez; Lozano

    2000-07-01

    In the framework of the "Oklo-Natural Analogue Phase II" Project, uraninite from the Bangombe natural reactor and samples from its host rock were analyzed to determine their uranium isotopic composition by thermal ionisation mass spectrometry, inductively coupled plasma mass spectrometry and alpha spectrometry. There were several objectives for this work: (i) to validate the 235U/238U isotopic ratios obtained by these techniques; (ii) to test the use of the 235U/238U ratio of uraninite as a tracer of migration/retention processes of uranium from the source term to the far field; (iii) to evaluate the most recent migration/retention processes of uranium in the system by U-series disequilibrium. PMID:10879844

  13. Experimental investigation of uranium-series isotope mobility in a basaltic weathering profile

    NASA Astrophysics Data System (ADS)

    Dosseto, Anthony; Menozzi, Davide; Kinsley, Leslie

    2015-04-01

    The measurement of uranium (U)-series isotopes in regolith can be used to determine the formation rate of weathering profiles. This approach aims at following how the U-series isotope composition of primary minerals (i.e. those derived from the parent material) vary during the development of the weathering profile. Nevertheless, regolith samples are a complex mixture of primary minerals, secondary minerals that are the residue of primary mineral weathering, secondary minerals that precipitate from pore water, minerals derived from atmospheric deposition and organic matter. In this study, firstly we aim at isolating primary minerals and the secondary minerals derived from them, by evaluating a sequential extraction procedure designed to eliminate carbonates, Fe-Mn oxides and organic matter. Secondly, we investigate the behaviour of U-series isotopes during primary mineral dissolution by applying a mild HF/HCl etching solution to the residues of the sequential extraction. These experiments were performed on bedrock, saprolite and soil derived from a basaltic weathering profile in south-eastern Australia. Results show that up to 50% of U is removed during sequential extraction, suggesting that (i) there is a large pool of labile U in the bedrock and (ii) secondary phases and organic matter account for a large fraction of the U budget in bulk saprolite and soil. Sequential extraction has little impact on the (234U/238U) activity ratio of bedrock and saprolite, whilst it shows a decrease in soil. This suggests that the pool of U removed from bedrock and saprolite has a (234U/238U) similar to that of primary minerals; but in the soil, the U removed (mostly from organic matter) is enriched in 234U. This is expected as organic matter uptakes U from pore solutions, which are generally enriched in 234U. During HF/HCl etching, the (234U/238U) of bedrock and saprolite is greater than 1. Sheng and Kuroda [1] previously proposed that (234U/238U) >1 in rocks could be explained by

  14. Application of Inductively Coupled Plasma Mass Spectrometry to the determination of uranium isotope ratios in individual particles for nuclear safeguards

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao Zhi; Esaka, Fumitaka; Esaka, Konomi T.; Magara, Masaaki; Sakurai, Satoshi; Usuda, Shigekazu; Watanabe, Kazuo

    2007-10-01

    The capability of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of uranium isotope ratios in individual particles was determined. For this purpose, we developed an experimental procedure including single particle transfer with a manipulator, chemical dissolution and isotope ratio analysis, and applied to the analysis of individual uranium particles in certified reference materials (NBL CRM U050 and U350). As the result, the 235U/ 238U isotope ratio for the particle with the diameter between 0.5 and 3.9 μm was successfully determined with the deviation from the certified ratio within 1.8%. The relative standard deviation (R.S.D.) of the 235U/ 238U isotope ratio was within 4.2%. Although the analysis of 234U/ 238U and 236U/ 238U isotope ratios gave the results with inferior precision, the R.S.D. within 20% was possible for the measurement of the particle with the diameter more than 2.1 μm. The developed procedure was successfully applied to the analysis of a simulated environmental sample prepared from a mixture of indoor dust (NIST SRM 2583) and uranium particles (NBL CRM U050, U350 and U950a). From the results, the proposed procedure was found to be an alternative analytical tool for nuclear safeguards.

  15. Fuel Grading Study on a Low-Enriched Uranium Fuel Design for the High Flux Isotope Reactor

    SciTech Connect

    Ilas, Germina; Primm, Trent

    2009-11-01

    An engineering design study that would enable the conversion of the High Flux Isotope Reactor (HFIR) from high-enriched uranium to low-enriched uranium fuel is ongoing at Oak Ridge National Laboratory. The computational models used to search for a low-enriched uranium (LEU) fuel design that would meet the requirements for the conversion study, and the recent results obtained with these models during FY 2009, are documented and discussed in this report. Estimates of relevant reactor performance parameters for the LEU fuel core are presented and compared with the corresponding data for the currently operating high-enriched uranium fuel core. These studies indicate that the LEU fuel design would maintain the current performance of the HFIR with respect to the neutron flux to the central target region, reflector, and beam tube locations.

  16. Design Study for a Low-Enriched Uranium Core for the High Flux Isotope Reactor, Annual Report for FY 2008

    SciTech Connect

    Primm, Trent; Chandler, David; Ilas, Germina; Miller, James Henry; Sease, John D; Jolly, Brian C

    2009-03-01

    This report documents progress made during FY 2008 in studies of converting the High Flux Isotope Reactor (HFIR) from highly enriched uranium (HEU) fuel to low-enriched uranium (LEU) fuel. Conversion from HEU to LEU will require a change in fuel form from uranium oxide to a uranium-molybdenum alloy. With axial and radial grading of the fuel foil and an increase in reactor power to 100 MW, calculations indicate that the HFIR can be operated with LEU fuel with no degradation in reactor performance from the current level. Results of selected benchmark studies imply that calculations of LEU performance are accurate. Scoping experiments with various manufacturing methods for forming the LEU alloy profile are presented.

  17. Applications with Near-Barrier Photo-Fission Reactions in Uranium Isotopes

    NASA Astrophysics Data System (ADS)

    Johnson, M. S.; Hall, J. M.; McNabb, D. P.; Tuffley, M. J.; Ahmed, M. W.; Stave, S.; Weller, H. R.; Karwowski, H. J.; Tompkins, J. R.

    2010-11-01

    Homeland security programs are developing compact, linearly polarized, quasi-monoenergetic photon sources to probe containers for special nuclear material (SNM). These sources are important in national security applications within the commerce system because of the low dose compared to current bremsstrahlung-based sources used for radiography, and important safety concern. Basic radiography only offers density distributions in cargo containers and does not distinguish fissionable materials from non-fissionable, high-Z materials. One possible usage of quasi-monoenergetic sources is to look for photo-neutrons, which may be subject to lower backgrounds, especially near the barrier where photo-fission neutrons have a high energy tail relative to (g,n). For this presentation, we discuss the results of recent near-barrier photo-fission resonance measurements in uranium isotopes. We will present our study of the neutron data and discuss its viability as a signature for SNM detection applications.

  18. On the accuracy of gamma spectrometric isotope ratio measurements of uranium

    NASA Astrophysics Data System (ADS)

    Ramebäck, H.; Lagerkvist, P.; Holmgren, S.; Jonsson, S.; Sandström, B.; Tovedal, A.; Vesterlund, A.; Vidmar, T.; Kastlander, J.

    2016-04-01

    The isotopic composition of uranium was measured using high resolution gamma spectrometry. Two acid solutions and two samples in the form of UO2 pellets were measured. The measurements were done in close geometries, i.e. directly on the endcap of the high purity germanium detector (HPGe). Applying no corrections for count losses due to true coincidence summing (TCS) resulted in up to about 40% deviation in the abundance of 235U from the results obtained with mass spectrometry. However, after correction for TCS, excellent agreement was achieved between the results obtained using two different measurement methods, or a certified value. Moreover, after corrections, the fitted relative response curves correlated excellently with simulated responses, for the different geometries, of the HPGe detector.

  19. Comparison of the isotopic abundance of U235 and U238 and the radium activity ratios in Colorado Plateau uranium ores

    USGS Publications Warehouse

    Senftle, F.E.; Stieff, L.; Cuttitta, F.; Kuroda, P.K.

    1957-01-01

    The isotopic abundances of uranium and the radium activity ratios of eleven samples of uranium ore from the Colorado Plateau have been measured. No significant variation in the isotopic abundance of the uranium was noted; with'in the experimental error, the average U235/U238 ratio is 137.7. There is a significant variation in the Ra226/Ra223 activity ratios (0.048-0.143), which indicates a relatively recent alteration of the ore samples. The variations do not, however, explain the lead-uranium and lead-lead age discrepancies. ?? 1957.

  20. A new ground-level fallout record of uranium and plutonium isotopes for northern temperate latitudes

    NASA Astrophysics Data System (ADS)

    Warneke, Thorsten; Croudace, Ian W.; Warwick, Phillip E.; Taylor, Rex N.

    2002-11-01

    Plutonium and uranium isotope ratios can be used to differentiate the sources of nuclear contamination from nuclear weapon establishments (Environ. Sci. Technol. 34 (2000) 4496; Internal Report for AWRE Aldermaston, UK (1961)), weapon fallout (Geochim. Cosmochim. Acta 51 (1987) 2623; Earth Planet. Sci. Lett. 63 (1983) 202; Earth Planet. Sci. Lett. 22 (1974) 111; Geochim. Cosmochim. Acta 64 (2000) 989), reprocessing plants, reactor or satellite accidents (Science 105 (1979) 583; Science 238 (1987) 512) and in addition they provide markers for post-1952 geochronology of environmental systems. A good record of plutonium and uranium isotope ratios of the background resulting from atmospheric nuclear testing is essential for source characterisation studies. Using recently developed mass spectrometric techniques (J. Anal. At. Spectrom. 16 (2001) 279) we present here the first complete records between 1952 and the present day of northern temperate latitude 240Pu/ 239Pu and 238U/ 235U atom ratios for atmospheric deposition. Such information was not derived directly during the period of atmospheric testing because suitable mass spectrometric capability was not available. The currently derived records are based on an annual herbage archive and a core from an Alpine glacier. These studies reveal hitherto unseen fluctuations in the 238U/ 235U atmospheric fallout record, some of which are directly related to nuclear testing. In addition, they also provide the first evidence that plutonium contamination originating from Nevada Desert atmospheric weapon tests in 1952 and 1953 extended eastwards as far as northwestern Europe. The results presented here demonstrate that we now have the capability to detect and precisely identify sources of plutonium in the environment with implications for the development of atmospheric transport models, recent geochronology and environmental studies.

  1. Innovative lasers for uranium isotope separation. Final report, September 1, 1989--April 1, 1993

    SciTech Connect

    Brake, M.L.; Gilgenbach, R.M.

    1993-07-01

    Copper vapor laser have important applications to uranium atomic vapor laser isotope separation (AVLIS). We have investigated two innovative methods of exciting/pumping copper vapor lasers which have the potential to improve the efficiency and scaling of large laser systems used in uranium isotope separation. Experimental research has focused on the laser discharge kinetics of (1) microwave, and (2) electron beam excitation/pumping of large-volume copper vapor lasers. Microwave resonant cavity produced copper vapor plasmas at 2.45 GHz, have been investigated in three separate experimental configurations. The first examined the application of CW (0-500W) power and was found to be an excellent method for producing an atomic copper vapor from copper chloride. The second used a pulsed (5kW, 0.5--5 kHz) signal superimposed on the CW signal to attempt to produce vaporization, dissociation and excitation to the laser states. Enhanced emission of the optical radiation was observed but power densities were found to be too low to achieve lasing. In a third experiment we attempted to increase the applied power by using a high power magnetron to produce 100 kW of pulsed power. Unfortunately, difficulties with the magnetron power supply were encountered leaving inconclusive results. Detailed modeling of the electromagnetics of the system were found to match the diagnostics results well. An electron beam pumped copper vapor system (350 kV, 1.0 kA, 300 ns) was investigated in three separate copper chloride heating systems, external chamber, externally heated chamber and an internally heated chamber. Since atomic copper spectral lines were not observed, it is assumed that a single pulse accelerator is not capable of both dissociating the copper chloride and exciting atomic copper and a repetitively pulsed electron beam generator is needed.

  2. A Metal Stable Isotope Approach to Understanding Uranium Mobility Across Roll Front Redox Boundaries

    NASA Astrophysics Data System (ADS)

    Brown, S. T.; Basu, A.; Christensen, J. N.; DePaolo, D. J.; Heikoop, J. M.; Reimus, P. W.; Maher, K.; Weaver, K. L.

    2015-12-01

    Sedimentary roll-front uranium (U) ore deposits are the principal source of U for nuclear fuel in the USA and an important part of the current all-of-the-above energy strategy. Mining of roll-front U ore in the USA is primarily by in situ alkaline oxidative dissolution of U minerals. There are significant environmental benefits to in situ mining including no mine tailings or radioactive dust, however, the long-term immobilization of U in the aquifer after the completion of mining remains uncertain. We have utilized the metal stable isotopes U, Se and Mo in groundwater from roll-front mines in Texas and Wyoming to quantify the aquifer redox conditions and predict the onset of U reduction after post mining aquifer restoration. Supporting information from the geochemistry of groundwater and aquifer sediments are used to understand the transport of U prior to and after in situ mining. Groundwater was collected across 4 mining units at the Rosita mine in the Texas coastal plain and 2 mining units at the Smith Ranch mine in the Powder River Basin, Wyoming. In general, the sampled waters are moderately reducing and ore zone wells contain the highest aqueous U concentrations. The lowest U concentrations occur in monitoring wells downgradient of the ore zone. 238U/235U is lowest in downgradient wells and is correlated with aqueous U concentrations. Rayleigh distillation models of the 238U/235U are consistent with U isotope fractionation factors of 1.0004-1.001, similar to lab-based studies. Based on these results we conclude that redox reactions continue to affect U distribution in the ore zone and downgradient regions. We also measured aqueous selenium isotope (δ82Se) and molybdenum isotope (δ98Mo) compositions in the Rosita groundwater. Se(VI) primarily occurs in the upgradient wells and is absent in most ore zone and downgradient wells. Rayleigh distillation models suggest reduction of Se(VI) along the groundwater flow path and when superimposed on the U isotope data

  3. Sulfur isotopes as indicators of amended bacterial sulfate reduction processes influencing field scale uranium bioremediation.

    PubMed

    Druhan, Jennifer L; Conrad, Mark E; Williams, Kenneth H; N'Guessan, Lucie; Long, Philip E; Hubbard, Susan S

    2008-11-01

    Aqueous uranium (U(VI)) concentrations in a contaminated aquifer in Rifle Colorado have been successfully lowered through electron donor amended bioreduction. Samples collected during the acetate amendment experiment were analyzed for aqueous concentrations of Fe(ll), sulfate, sulfide, acetate, U(VI), and delta(34)S of sulfate and sulfide to explore the utility of sulfur isotopes as indicators of in situ acetate amended sulfate and uranium bioreduction processes. Enrichment of up to 7% per hundred in delta(34)S of sulfate in down-gradient monitoring wells indicates a transition to elevated bacterial sulfate reduction. A depletion in Fe(II), sulfate, and sulfide concentrations atthe height of sulfate reduction, along with an increase in the delta(34)S of sulfide to levels approaching the delta(34)S values of sulfate, indicates sulfate limited conditions concurrent with a rebound in U(VI) concentrations. Upon cessation of acetate amendment, sulfate and sulfide concentrations increased, while delta(34)S values of sulfide returned to less than -20% per hundred and sulfate delta(34)S decreased to near-background values, indicating lower levels of sulfate reduction accompanied by a corresponding drop in U(VI). Results indicate a transition between electron donor and sulfate-limited conditions at the height of sulfate reduction and suggest stability of biogenic FeS precipitates following the end of acetate amendment. PMID:19031870

  4. Performance testing of the upgraded uranium isotopics multi-group analysis code MGAU

    NASA Astrophysics Data System (ADS)

    Berlizov, A. N.; Gunnink, R.; Zsigrai, J.; Nguyen, C. T.; Tryshyn, V. V.

    2007-06-01

    The paper describes recent developments of the MGAU (Multi-Group Analysis for Uranium) method, which resulted in the creation of an upgraded version 4.0 of the MGAU code. The major improvements concerned the procedure of the intrinsic efficiency calibration, particularly in the 120-205 keV region. The results of the tests carried out with the use of certified reference uranium isotopic materials SRM 969 and CRM 146 showed a significantly improved performance of the upgraded MGAU code for the accurate characterization of 235U and 234U abundances. The relative systematic biases of the abundances measured were evaluated not to exceed 1% and 3% over the concentration intervals 0.32-93.2 and 0.002-0.98 mass% for 235U and 234U, respectively. The influence of an up to 4-5 mm steel equivalent absorber and sample thickness on the measurement results was found to be much smaller than in previous versions of the code.

  5. Sulfur Isotopes as Indicators of Amended Bacterial Sulfate Reduction Processes Influencing Field Scale Uranium Bioremediation

    SciTech Connect

    Druhan, Jennifer L.; Conrad, Mark E.; Williams, Kenneth H.; N'Guessan, A. Lucie; Long, Philip E.; Hubbard, Susan S.

    2008-11-01

    Aqueous uranium (U(VI)) concentrations in a contaminated aquifer in Rifle Colorado have been successfully lowered through electron donor amended bioreduction. Samples collected during the acetate amendment experiment were analyzed for aqueous concentrations of Fe(II), sulfate, sulfide, acetate, U(VI), and δ34S of sulfate and sulfide to explore the utility of sulfur isotopes as indicators of in situ acetate amended sulfate and uranium bioreduction processes. Enrichment of up to 7‰ in δ34S of sulfate in down-gradient monitoring wells indicates a transition to elevated bacterial sulfate reduction. A depletion in Fe(II), sulfate, and sulfide concentrations at the height of sulfate reduction, along with an increase in the δ34S of sulfide to levels approaching the d34S values of sulfate, indicates sulfate limited conditions concurrent with a rebound in U(VI) concentrations. Upon cessation of acetate amendment, sulfate and sulfide concentrations increased, while δ34S values of sulfide returned to less than -20‰ and sulfate δ34S decreased to near-background values, indicating lower levels of sulfate reduction accompanied by a corresponding drop in U(VI). Results indicate a transition between electron donor and sulfate-limited conditions at the height of sulfate reduction and suggest stability of biogenic FeS precipitates following the end of acetate amendment.

  6. Depleted uranium mobility across a weapons testing site: isotopic investigation of porewater, earthworms, and soils.

    PubMed

    Oliver, Ian W; Graham, Margaret C; MacKenzie, Angus B; Ellam, Robert M; Farmer, John G

    2008-12-15

    The mobility and bioavailability of depleted uranium (DU) in soils at a UK Ministry of Defence (UK MoD) weapons testing range were investigated. Soil and vegetation were collected near a test-firing position and at eight points along a transect line extending approximately 200 m down-slope, perpendicular to the firing line, toward a small stream. Earthworms and porewaters were subsequently separated from the soils and both total filtered porewater (<0.2 microm) and discrete size fractions (0.2 microm-100 kDa, 100-30 kDa, 30-3 kDa, and <3 kDa)obtainedvia centrifugal ultrafiltration were examined. Uranium concentrations were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) for soils and ICP-mass spectrometry (MS) for earthworms and porewaters, while 235U:238U atom ratios were determined by multicollector (MC)-ICP-MS. Comparison of the porewater and earthworm isotopic values with those of the soil solids indicated that DU released into the environment during weapons test-firing operations was more labile and more bioavailable than naturally occurring U in the soils at the testing range. Importantly, DU was shown to be present in soil porewater even at a distance of approximately 185 m from the test-firing position and, along the extent of the transect was apparently associated with organic colloids. PMID:19174886

  7. On monitoring anthropogenic airborne uranium concentrations and (235)U/(238)U isotopic ratio by Lichen - bio-indicator technique.

    PubMed

    Golubev, A V; Golubeva, V N; Krylov, N G; Kuznetsova, V F; Mavrin, S V; Aleinikov, A Yu; Hoppes, W G; Surano, K A

    2005-01-01

    Lichens are widely used to assess the atmospheric pollution by heavy metals and radionuclides. However, few studies are available in publications on using lichens to qualitatively assess the atmospheric pollution levels. The paper presents research results applying epiphytic lichens as bio-monitors of quantitative atmospheric contamination with uranium. The observations were conducted during 2.5 years in the natural environment. Two experimental sites were used: one in the vicinity of a uranium contamination source, the other one - at a sufficient distance away to represent the background conditions. Air and lichens were sampled at both sites monthly. Epiphytic lichens Hypogimnia physodes were used as bio-indicators. Lichen samples were taken from various trees at about 1.5m from the ground. Air was sampled with filters at sampling stations. The uranium content in lichen and air samples as well as isotopic mass ratios (235)U/(238)U were measured by mass-spectrometer technique after uranium pre-extraction. Measured content of uranium were 1.45 mgkg(-1) in lichen at 2.09 E-04 microgm(-3) in air and 0.106 mgkg(-1) in lichen at 1.13 E-05 microgm(-3) in air. The relationship of the uranium content in atmosphere and that in lichens was determined, C(AIR)=exp(1.1 x C(LICHEN)-12). The possibility of separate identification of natural and man-made uranium in lichens was demonstrated in principle. PMID:16083999

  8. Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon

    USGS Publications Warehouse

    Tourrette, T.Z.L.; Burnett, D.S.; Bacon, C.R.

    1991-01-01

    Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO2), are interpreted to be portions of the magma chamber walls that were torn off during eruption. The glass is clear and well homogenized for all measured elements except Zr. Results for Fe-Ti oxides give DUoxide/liq ??? 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are moderately well equilibrated with the melt for many of the minor elements, while those that are inclusions in relict plagioclase are not. Uranium and ytterbium inhomogeneities in zircons indicate that the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons faster than the zircons were dissolving. Minimum U, Y, and P concentrations in zircons give maximum DUzrc/liq = 13,DYzrc/liq = 23, and DPzrc/liq = 1, but these are considerably lower than reported by other workers for U and Y. Based on our measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractionation during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in our samples. This demonstrates an actual case of non-equilibrium source retention of accessory phases, which in general could be an important trace-element fractionation mechanism. Our results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites. Rough calculations based on Zr gradients in the glass indicate that the samples could have been partially molten for 800 to 8000 years. ?? 1991.

  9. Uranium Isotope Evidence for Temporary Ocean Oxygenation Following the Sturtian Glaciation

    NASA Astrophysics Data System (ADS)

    Lau, K. V.; Maher, K.; Macdonald, F. A.; Payne, J.

    2015-12-01

    The link between widespread ocean oxygenation in the Neoproterozoic and the rise of animals has long been debated, largely because the timing and nature of oxygenation of the oceans remain poorly constrained. Strata deposited during the Cryogenian non-glacial interlude (660 to 635 Ma), between the Sturtian and Marinoan Snowball Earth glaciations, contain the earliest fossil evidence of animals. To quantitatively estimate patterns of seafloor oxygenation during this critical interval, we present uranium isotope (δ238U) data from limestone of the Taishir Formation (Fm) in Mongolia in two stratigraphic sections that are separated by ~75 km across the basin. The Taishir Fm hosts two large δ13C excursions that co-vary in total organic and inorganic (carbonate) carbon: a basal carbonate δ13C excursion to -4‰ in the Sturtian cap carbonate, followed by a rise to enriched values of +8‰, a second negative δ13C excursion to -7‰ referred to as the Taishir excursion, followed by a second rise to +10‰. Above the Sturtian glacial deposits, in the stratigraphic interval below the Taishir excursion, δ238U compositions have a mean value that is similar to that of modern seawater. After the Taishir excursion, the δ238U record exhibits a step decrease of ~0.3‰, and δ238U remains approximately constant until the erosional unconformity at the base of the Marinoan glacial deposits. We use a box model to constrain the uranium cycle behavior that best explains our observations. In the model, the best explanation for the less negative post-Sturtian values of δ238U is extensive oxygenation of the seafloor. Moreover, the model demonstrates that the higher δ238U values of the post-Sturtian limestones are inconsistent with an increased flux of uranium to the oceans due to post-Snowball weathering as the primary driver of the excursion. Thus, we favor a scenario in which there was a rise in oxygen levels following the Sturtian glaciation followed by a decrease in seafloor

  10. Optimized Chemical Separation and Measurement by TE TIMS Using Carburized Filaments for Uranium Isotope Ratio Measurements Applied to Plutonium Chronometry.

    PubMed

    Sturm, Monika; Richter, Stephan; Aregbe, Yetunde; Wellum, Roger; Prohaska, Thomas

    2016-06-21

    An optimized method is described for U/Pu separation and subsequent measurement of the amount contents of uranium isotopes by total evaporation (TE) TIMS with a double filament setup combined with filament carburization for age determination of plutonium samples. The use of carburized filaments improved the signal behavior for total evaporation TIMS measurements of uranium. Elevated uranium ion formation by passive heating during rhenium signal optimization at the start of the total evaporation measurement procedure was found to be a result from byproducts of the separation procedure deposited on the filament. This was avoided using carburized filaments. Hence, loss of sample before the actual TE data acquisition was prevented, and automated measurement sequences could be accomplished. Furthermore, separation of residual plutonium in the separated uranium fraction was achieved directly on the filament by use of the carburized filaments. Although the analytical approach was originally tailored to achieve reliable results only for the (238)Pu/(234)U, (239)Pu/(235)U, and (240)Pu/(236)U chronometers, the optimization of the procedure additionally allowed the use of the (242)Pu/(238)U isotope amount ratio as a highly sensitive indicator for residual uranium present in the sample, which is not of radiogenic origin. The sample preparation method described in this article has been successfully applied for the age determination of CRM NBS 947 and other sulfate and oxide plutonium samples. PMID:27240571

  11. The Effect of Redox Mechanisms on the Fractionation of Uranium `Stable' Isotopes

    NASA Astrophysics Data System (ADS)

    Kaltenbach, A.; Stirling, C. H.; Porcelli, D.; Hilton, D. R.; Kulongoski, J. T.

    2010-12-01

    Uranium is the heaviest naturally occurring element. It consists of three natural isotopes, 238U, 235U and 234U and has four oxidation states, U(III)-U(VI), of which only U(IV) and U(VI) are common. In the oxidized, hexavalent condition, U(VI) exists as uranyl ion (UO22+), which forms soluble, non-reactive complexes with carbonates. In the reduced condition, tetravalent U(IV) forms immobile minerals with hydroxides, fluorides and phosphates that are removed from the water column. In the recent years, isotopic fractionation between 235U and 238U has been detected in a range of terrestrial environments. Changes to U concentrations in natural waters occur due to biological uptake, adsorption/desorption to/from particulates and surfaces, diffusion into sediments, and chemically and biologically induced redox mechanisms (Swarzenski et al., 1999, Mar. Chem. 67, 181). The largest isotopic shifts evidently occur during the reduction of U(VI) to U(IV) in waters, during which precipitation changes the dissolved U concentration. However, the exact mechanisms controlling 235U/238U fractionation remain unclear. Some results implicate mass-dependent zero-point energy effects (preferential removal of 235U over 238U) (Rademacher et al., 2006, Environ. Sci. Technol. 40, 6943) as the main cause for the isotopic variations measured, while others suggest volume-dependent nuclear field shift effects (preferential removal of 238U over 235U) (Weyer et al., 2008, GCA 72, 345, Bopp et al., 2010, Environ. Sci. Technol. 44, 5927), which are predicted to be of the opposite sign and up to three times larger than mass-dependent effects. In this study, profiles of two different water masses were examined for their uranium concentration and their 235U/238U isotopic composition to determine the magnitude of the natural isotopic shifts as well as their origins. One set of samples was collected from a 160 m depth profile in the Framvaren Fjord, an anoxic basin. In this basin, the biogeochemical

  12. Uranium isotopes distinguish two geochemically distinct stages during the later Cambrian SPICE event

    PubMed Central

    Dahl, Tais W.; Boyle, Richard A.; Canfield, Donald E.; Connelly, James N.; Gill, Benjamin C.; Lenton, Timothy M.; Bizzarro, Martin

    2015-01-01

    Anoxic marine zones were common in early Paleozoic oceans (542–400 Ma), and present a potential link to atmospheric pO2 via feedbacks linking global marine phosphorous recycling, primary production and organic carbon burial. Uranium (U) isotopes in carbonate rocks track the extent of ocean anoxia, whereas carbon (C) and sulfur (S) isotopes track the burial of organic carbon and pyrite sulfur (primary long-term sources of atmospheric oxygen). In combination, these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million-year time scales. Here we report high-precision uranium isotopic data in marine carbonates deposited during the Late Cambrian ‘SPICE’ event, at ca. 499 Ma, documenting a well-defined −0.18‰ negative δ238U excursion that occurs at the onset of the SPICE event’s positive δ13C and δ34S excursions, but peaks (and tails off) before them. Dynamic modelling shows that the different response of the U reservoir cannot be attributed solely to differences in residence times or reservoir sizes - suggesting that two chemically distinct ocean states occurred within the SPICE event. The first ocean stage involved a global expansion of euxinic waters, triggering the spike in U burial, and peaking in conjunction with a well-known trilobite extinction event. During the second stage widespread euxinia waned, causing U removal to tail off, but enhanced organic carbon and pyrite burial continued, coinciding with evidence for severe sulfate depletion in the oceans (Gill et al., 2011). We discuss scenarios for how an interval of elevated pyrite and organic carbon burial could have been sustained without widespread euxinia in the water column (both non-sulfidic anoxia and/or a more oxygenated ocean state are possibilities). Either way, the SPICE event encompasses two different stages of elevated organic carbon and pyrite burial maintained by high nutrient fluxes to the ocean, and potentially

  13. Uranium Isotopes in Fine-grained Clastic Sediments: A New Perspective on Erosion and Sedimentation

    NASA Astrophysics Data System (ADS)

    Depaolo, D. J.; Maher, K.; Christensen, J. N.; McManus, J.

    2005-12-01

    High precision uranium isotope measurements may provide a means of determining the timescale associated with the transformation of bedrock to sediment, which includes the time required to mechanically break down rock into transportable fragments, the residence time of sediment particles in soils, streambeds, floodplains, dunes, and moraines, and their transport by wind, rivers and ocean currents to the site of final deposition on the seafloor or in lakes. The interpretation of variations in the 234U/238U ratios in sediments is based on a model for the disruption of the 238U decay series due to the loss of the decay product 234Th by recoil associated with the alpha decay of 238U. This paper presents the results of a study of 234U/238U ratios, as well as O, Nd and Sr isotopes, in fine-grained deep sea sediments, 0 to about 400 ky in age, cored in the North Atlantic Ocean at Ocean Drilling Program Site 984A. The sediments are largely siliciclastic, but have a significant carbonate component that varies between a few and 30 per cent by volume. The O isotope data obtained on separated foraminifera clearly show the last several glacial cycles, and thus provide a detailed temporal framework for the sediments. The Nd and Sr isotopic data show that the provenance of the sediment has oscillated, roughly but not exactly, in concert with the extent of continental ice volume, between a local source - probably volcanic rocks from Iceland - and a continental source. An unexpected finding is that the 234U/238U ratios of the siliciclastic portion of the sediment, isolated by leaching, show large and systematic variations that are correlated with glacial cycles and to some degree with sediment provenance. The U isotope variations are inferred to reflect differences in the transport time of the sediment - the time elapsed between the generation of the small sediment particles on Iceland and the continental source areas, and the time of deposition on the seafloor in the North Atlantic

  14. PREPARING THE HIGH FLUX ISOTOPE REACTOR FOR CONVERSION TO LOW ENRICHED URANIUM FUEL ? RETURN TO 100 MW

    SciTech Connect

    Smith, Kevin Arthur; Primm, Trent

    2009-01-01

    The feasibility of low-enriched uranium (LEU) fuel as a replacement for the current, high enriched uranium (HEU) fuel for the High Flux Isotope Reactor (HFIR) has been under study since 2006. Reactor performance studies have been completed for conceptual plate designs and show that maintaining reactor performance while converting to LEU fuel requires returning the reactor power to 100 MW from 85 MW. The analyses required to up-rate the reactor power and the methods to perform these analyses are discussed. Comments regarding the regulatory approval process are provided along with a conceptual schedule.

  15. Investigation of the oxygen isotopic composition in oxidic uranium compounds as a new property in nuclear forensic science.

    PubMed

    Pajo, L; Mayer, K; Koch, L

    2001-10-01

    The analysis of seized nuclear material aims at identifying the origin of the material. Determination of the n(18O)/n(16O) ratio for the uranium oxide adds another characteristic property to the pattern which enables location of the production area of the material. A method has been developed for n(18O)/n(16O) ratio measurement which uses thermal ionization mass spectrometric (TIMS) analysis of the 238UO+ species. It has been shown that uranium oxides of different geographic origin have significantly different n(18O)/n(16O) ratios, whereas different samples of the same origin have constant oxygen isotopes ratios. PMID:11688648

  16. Isotopic Evidence for Reductive Immobilization of Uranium Across a Roll-Front Mineral Deposit.

    PubMed

    Brown, Shaun T; Basu, Anirban; Christensen, John N; Reimus, Paul; Heikoop, Jeffrey; Simmons, Ardyth; Woldegabriel, Giday; Maher, Kate; Weaver, Karrie; Clay, James; DePaolo, Donald J

    2016-06-21

    We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-Highland in situ recovery (ISR) U mine in eastern Wyoming, USA, where economic U deposits occur in the Paleocene Fort Union formation. To evaluate the fate of aqueous U in and adjacent to the ore body, we investigated the chemical composition and isotope ratios of groundwater samples from the roll-front type ore body and surrounding monitoring wells of a previously mined area. The (238)U/(235)U of groundwater varies by approximately 3‰ and is correlated with U concentrations. Fluid samples down-gradient of the ore zone are the most depleted in (238)U and have the lowest U concentrations. Activity ratios of (234)U/(238)U are ∼5.5 up-gradient of the ore zone, ∼1.0 in the ore zone, and between 2.3 and 3.7 in the down-gradient monitoring wells. High-precision measurements of (234)U/(238)U and (238)U/(235)U allow for development of a conceptual model that evaluates both the migration of U from the ore body and the extent of natural attenuation due to reduction. We find that the premining migration of U down-gradient of the delineated ore body is minimal along eight transects due to reduction in or adjacent to the ore body, whereas two other transects show little or no sign of reduction in the down-gradient region. These results suggest that characterization of U isotopic ratios at the mine planning stage, in conjunction with routine geochemical analyses, can be used to identify where more or less postmining remediation will be necessary. PMID:27203292

  17. Isotopic evidence for reductive immobilization of uranium across a roll-front mineral deposit

    DOE PAGESBeta

    Brown, Shaun T.; Basu, Anirban; Christensen, John N.; Reimus, Paul; Heikoop, Jeffrey; Simmons, Ardyth; Woldegabriel, Giday; Maher, Kate; Weaver, Karrie; Clay, James; et al

    2016-06-21

    We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-Highland in situ recovery (ISR) U mine in eastern Wyoming, USA, where economic U deposits occur in the Paleocene Fort Union formation. To evaluate the fate of aqueous U in and adjacent to the ore body, we investigated the chemical composition and isotope ratios of groundwater samples from the roll-front type ore body and surrounding monitoring wells of a previously mined area. The 238U/235U of groundwater varies by approximatelymore » 3‰ and is correlated with U concentrations. Fluid samples down-gradient of the ore zone are the most depleted in 238U and have the lowest U concentrations. Activity ratios of 234U/238U are ~5.5 up-gradient of the ore zone, ~1.0 in the ore zone, and between 2.3 and 3.7 in the down-gradient monitoring wells. High-precision measurements of 234U/238U and 238U/235U allow for development of a conceptual model that evaluates both the migration of U from the ore body and the extent of natural attenuation due to reduction. We find that the premining migration of U down-gradient of the delineated ore body is minimal along eight transects due to reduction in or adjacent to the ore body, whereas two other transects show little or no sign of reduction in the down-gradient region. Lastly, these results suggest that characterization of U isotopic ratios at the mine planning stage, in conjunction with routine geochemical analyses, can be used to identify where more or less postmining remediation will be necessary.« less

  18. Using Pb isotopes in surface media to distinguish anthropogenic sources from undercover uranium sources

    NASA Astrophysics Data System (ADS)

    Kyser, Kurt; Lahusen, Larry; Drever, Garth; Dunn, Colin; Leduc, Evelyne; Chipley, Don

    2015-09-01

    The response in elemental concentrations and Pb isotopes in various surface media from the Cigar West unconformity-type uranium deposit located at a depth of 450 m were measured to ascertain if element migration from the deposit can be detected at the surface. The media included clay-size fractions separated from the A2, B and C soil horizons, and tree cores and twigs from black spruce (Picea mariana) and jack pine (Pinus banksiana) trees. Lead isotopes were used to trace any effect on the surface media from the deposit at depth because the 207Pb/206Pb ratios in the ore are < 0.1, whereas the background values in the basin are > 0.7 and modern anthropogenic Pb from aerosols are near 0.9. The tree cores record their lowest and therefore most radiogenic 207Pb/206Pb ratios of < 0.7 near the surface projection of the deposit and associated structures, particularly in tree rings that predate any exploration and drilling activity in the area. The median 207Pb/206Pb ratios increase in the order C, B soil horizon clays, tree cores, A2 soil clays and twigs because of the increasing contribution of common Pb with high ratios from anthropogenic sources that affect the shallowest media the most. Although this anthropogenic Pb as well as that from the background dominates the composition of all media at the surface and the contribution from the deposit at depth is diminished toward the surface, ore-related Pb is still present as a few percent of the composition of pathfinder elements and Pb isotopes.

  19. Determination of the origin of elevated uranium at a Former Air Force Landfill using non-parametric statistics analysis and uranium isotope ratio analysis

    SciTech Connect

    Weismann, J.; Young, C.; Masciulli, S.; Caputo, D.

    2007-07-01

    factors so that gross alpha action levels can be applied to future long-term landfill monitoring to track radiological conditions at lower cost. Ratios of isotopic uranium results were calculated to test whether the elevated uranium displayed signatures indicative of military use. Results of all ratio testing strongly supports the conclusion that the uranium found in groundwater, surface water, and sediment at OU 2 is naturally-occurring and has not undergone anthropogenic enrichment or processing. U-234:U-238 ratios also show that a disequilibrium state, i.e., ratio greater than 1, exists throughout OU 2 which is indicative of long-term aqueous transport in aged aquifers. These results all support the conclusion that the elevated uranium observed at OU 2 is due to the high concentrations in the regional watershed. Based on the results of this monitoring program, we concluded that the elevated uranium concentrations measured in OU 2 groundwater, surface water, and sediment are due to the naturally-occurring uranium content of the regional watershed and are not the result of waste burials in the former landfill. Several lines of evidence indicate that natural uranium has been naturally concentrated beneath OU 2 in the geologic past and the higher of uranium concentrations in down-gradient wells is the result of geochemical processes and not the result of a uranium ore disposal. These results therefore provide the data necessary to support radiological closure of OU 2. (authors)

  20. The Behaviour of Uranium and Lithium Isotopes During Basalt Weathering and Erosion

    NASA Astrophysics Data System (ADS)

    Pogge von Strandmann, P. A.; Burton, K. W.; James, R. H.; van Calsteren, P.; Gislason, S.

    2005-12-01

    Basalt weathering rates are higher than for many other silicate rocks, and thus exert a strong control on atmospheric CO2 [1]. Moreover, variations in weathering in response to climatic or tectonic change will inevitably affect chemical fluxes to the oceans. Li isotopes potentially provide key information on weathering rates, but their behaviour in the riverine and estuarine environment remains poorly constrained. While U-series nuclides can give information on both the weathering process and the timescale over which it occurs, comparison of both U and Li provides some insight into the processes which govern the geochemical cycles of each element. This study presents new U and Li isotope data for rivers draining basalt terrains in Iceland and Sao Miguel (Azores). Both of these islands are essentially monolithologic, but have different climatic regimes, and variations in river chemistry are linked to differences in the weathering environment, rather than to rock type. River waters from Iceland were taken from both a large catchment in the west of the island, an associated estuary, and from glacial rivers in the south. The U concentration in the rivers ranges from 0.2 to 20 ng/l, and rises from 3 ng/l to almost 3 μg/l in the estuary, showing conservative behaviour in the mixing zone. Li concentrations range from 0.02 to 1.05 μg/l in the rivers, and rise to 160 μg/l in the estuary. Li also behaves conservatively in the mixing zone. For the Azores U and Li river concentrations range from 3 to 212 ng/l and from 0.09 to 3.5 μg/l, respectively. Highest concentrations are linked to hydrothermal input. Uranium activity ratios (234U/238U) range from 1.13 to 2.14 in Iceland, and from 1.02 to 1.92 in the Azores, showing that silicate weathering can yield a large range of values (down to 1, which is secular equilibrium). Lowest U concentrations typically correspond to highest activity ratios, especially in glacial rivers. The behaviour of U in the catchment shows mixing

  1. Rate equation model of laser induced bias in uranium isotope ratios measured by resonance ionization mass spectrometry

    SciTech Connect

    Isselhardt, B. H.; Prussin, S. G.; Savina, M. R.; Willingham, D. G.; Knight, K. B.; Hutcheon, I. D.

    2015-12-07

    Resonance Ionization Mass Spectrometry (RIMS) has been developed as a method to measure uranium isotope abundances. In this approach, RIMS is used as an element-selective ionization process between uranium atoms and potential isobars without the aid of chemical purification and separation. The use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of the 235U/238U ratio to decrease laser-induced isotopic fractionation. In application, isotope standards are used to identify and correct bias in measured isotope ratios, but understanding laser-induced bias from first-principles can improve the precision and accuracy of experimental measurements. A rate equation model for predicting the relative ionization probability has been developed to study the effect of variations in laser parameters on the measured isotope ratio. The model uses atomic data and empirical descriptions of laser performance to estimate the laser-induced bias expected in experimental measurements of the 235U/238U ratio. Empirical corrections are also included to account for ionization processes that are difficult to calculate from first principles with the available atomic data. As a result, development of this model has highlighted several important considerations for properly interpreting experimental results.

  2. Rate equation model of laser induced bias in uranium isotope ratios measured by resonance ionization mass spectrometry

    DOE PAGESBeta

    Isselhardt, B. H.; Prussin, S. G.; Savina, M. R.; Willingham, D. G.; Knight, K. B.; Hutcheon, I. D.

    2015-12-07

    Resonance Ionization Mass Spectrometry (RIMS) has been developed as a method to measure uranium isotope abundances. In this approach, RIMS is used as an element-selective ionization process between uranium atoms and potential isobars without the aid of chemical purification and separation. The use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of the 235U/238U ratio to decrease laser-induced isotopic fractionation. In application, isotope standards are used to identify and correct bias in measured isotope ratios, but understanding laser-induced bias from first-principles can improve the precision and accuracy of experimental measurements. A rate equationmore » model for predicting the relative ionization probability has been developed to study the effect of variations in laser parameters on the measured isotope ratio. The model uses atomic data and empirical descriptions of laser performance to estimate the laser-induced bias expected in experimental measurements of the 235U/238U ratio. Empirical corrections are also included to account for ionization processes that are difficult to calculate from first principles with the available atomic data. As a result, development of this model has highlighted several important considerations for properly interpreting experimental results.« less

  3. Validation of Electrochemically Modulated Separations Performed On-Line with MC-ICP-MS for Uranium and Plutonium Isotopic Analyses

    SciTech Connect

    Liezers, Martin; Olsen, Khris B.; Mitroshkov, Alexandre V.; Duckworth, Douglas C.

    2010-08-11

    The most time consuming process in uranium or plutonium isotopic analyses is performing the requisite chromatographic separation of the actinides. Filament preparation for thermal ionization (TIMS) adds further delays, but is generally accepted due to the unmatched performance in trace isotopic analyses. Advances in Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) are beginning to rival the performance of TIMS. Methods, such as Electrochemically Modulated Separations (EMS) can efficiently pre-concentrate U or Pu quite selectively from small solution volumes in a matrix of 0.5 M nitric acid. When performed in-line with ICP-MS, the rapid analyte release from the electrode is fast, and large transient analyte signal enhancements of >100 fold can be achieved as compared to more conventional continuous nebulization of the original starting solution. This makes the approach ideal for very low level isotope ratio measurements. In this paper, some aspects of EMS performance are described. These include low level Pu isotope ratio behavior versus concentration by MC-ICP-MS and uranium rejection characteristics that are also important for reliable low level Pu isotope ratio determinations.

  4. Measurement of the isotopic composition of uranium micrometer-size particles by femtosecond laser ablation-inductively coupled plasma mass spectrometry

    NASA Astrophysics Data System (ADS)

    Hubert, Amélie; Claverie, Fanny; Pécheyran, Christophe; Pointurier, Fabien

    In this paper, we will describe and indicate the performance of a new method based on the use of femtosecond laser ablation (fs-LA) coupled to a quadrupole-based inductively coupled plasma mass spectrometer (ICP-QMS) for analyzing the isotopic composition of micrometer-size uranium particles. The fs-LA device was equipped with a high frequency source (till 10 kHz). We applied this method to 1-2 μm diameter-uranium particles of known isotopic composition and we compared this technique with the two techniques currently used for uranium particle analysis: Secondary Ionization Mass Spectrometry (SIMS) and Fission Track Thermal Ionization Mass Spectrometry (FT-TIMS). By optimizing the experimental conditions, we achieved typical accuracy and reproducibility below 4% on 235U/238U for short transient signals of only 15 s related to 10 to 200 pg of uranium. The detection limit (at the 3 sigma level) was ~ 350 ag for the 235U isotope, meaning that 235U/238U isotope ratios in natural uranium particles of ~ 220 nm diameter can be measured. We also showed that the local contamination resulting from the side deposition of ablation debris at ~ 100 μm from the ablation crater represented only a small percentage of the initial uranium signal of the ablated particle. Despite the use of single collector ICP-MS, we were able to demonstrate that fs-LA-ICP-MS is a promising alternative technique for determining uranium isotopic composition in particle analysis.

  5. Constrains on the Uranium Isotopic Composition of Seawater and Implications for Coral U/Th Geochronology

    NASA Astrophysics Data System (ADS)

    Chutcharavan, P. M.; Dutton, A.; Ellwood, M. J.

    2015-12-01

    Coral U-series geochronology is an important tool for calibrating records of sea level change during the late Quaternary and coral 14C dates for the radiocarbon timescale. However, coralline aragonite is highly susceptible to diagenesis, and samples must be carefully screened to ensure a specimen is unaltered. One method used to accept or reject U-series ages is the initial coral 234U/238U activity ratio, which reflects the 234U/238U activity of seawater at the time of coral skeleton formation. Due to the long residence time of uranium in the ocean (~400,000 years), researchers often assume that seawater 234U/238U has remained constant throughout the late Pleistocene. Coral specimens whose U-series ages yield an initial 234U/238U value that is significantly different than modern seawater are considered altered. Several studies have demonstrated that coral initial 234U/238U and, hence, seawater 234U/238U may have varied significantly on glacial-interglacial timescales, but the cause of this variability is subject to debate. To evaluate the pattern and mechanisms of 234U/238U variability in seawater over the last glacial cycle, we draw upon a compilation of U-series measurements of shallow and deep water corals to better define the observed variability. Observed trends from the coral record will be assessed using a simple two-box model of the ocean to determine how changes to the ocean's uranium isotope budget during glacial cycles can explain shifts in seawater 234U/238U. An improved understanding the evolution of seawater 234U/238U composition will enable more robust interpretations of both closed-system and open-system ages for corals. Such interpretations of U-series ages are essential to the development of robust chronologies for climate and sea level change and for improving the calibration of the radiocarbon timescale.

  6. A procedural manual for measurement of uranium and thorium isotopes utilizing the USGS-Stanford Finnegan Mat 262

    USGS Publications Warehouse

    Shamp, Donald D.

    2001-01-01

    Over the past several decades investigators have extensively examined the 238U-234U- 230Th systematics of a variety of geologic materials using alpha spectroscopy. Analytical uncertainty for 230Th by alpha spectroscopy has been limited to about 2% (2σ). The advantage of thermal ionization mass spectroscopy (TIMS), introduced by Edwards and co-workers in the late 1980’s is the increased detectability of these isotopes by a factor of ~200, and decreases in the uncertainty for 230Th to about 5‰ (2σ) error. This report is a procedural manual for using the USGS-Stanford Finnegan-Mat 262 TIMS to collect and isolate Uranium and Thorium isotopic ratio data. Chemical separation of Uranium and Thorium from the sample media is accomplished using acid dissolution and then processed using anion exchange resins. The Finnegan-Mat262 Thermal Ionization Mass Spectrometer (TIMS) utilizes a surface ionization technique in which nitrates of Uranium and Thorium are placed on a source filament. Upon heating, positive ion emission occurs. The ions are then accelerated and focused into a beam which passes through a curved magnetic field dispersing the ions by mass. Faraday cups and/or an ion counter capture the ions and allow for quantitative analysis of the various isotopes.

  7. Behavior of isotope (18O/16O, 234U/238U) systems during the formation of uranium deposits of the "sandstone" type

    NASA Astrophysics Data System (ADS)

    Golubev, V. N.; Dubinina, E. O.; Chernyshev, I. V.; Ikonnikova, T. A.

    2016-01-01

    The uneven character of the distribution of 18O/16O and 234U/238U values was established in the vertical cross section of the productive sequence of the Dybryn uranium deposit (Vitim uranium-ore region, Buryatia). Both a deficiency and an excess of 234U in relation to the equilibrium 234U/238U ratio in the vertical sequence may provide evidence for the extremely low rate of the infiltration water flow. The behavior of oxygen isotope characteristics for different size fractions of terrigenous rocks provides evidence for active uranium redistribution and openness of the isotope system of this element during interaction of terrigenous-sedimentary rocks with infiltration waters.

  8. Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

    NASA Astrophysics Data System (ADS)

    Tissot, François L. H.; Dauphas, Nicolas

    2015-10-01

    The 238U/235U isotopic composition of uranium in seawater can provide important insights into the modern U budget of the oceans. Using the double spike technique and a new data reduction method, we analyzed an array of seawater samples and 41 geostandards covering a broad range of geological settings relevant to low and high temperature geochemistry. Analyses of 18 seawater samples from geographically diverse sites from the Atlantic and Pacific oceans, Mediterranean Sea, Gulf of Mexico, Persian Gulf, and English Channel, together with literature data (n = 17), yield a δ238U value for modern seawater of -0.392 ± 0.005‰ relative to CRM-112a. Measurements of the uranium isotopic compositions of river water, lake water, evaporites, modern coral, shales, and various igneous rocks (n = 64), together with compilations of literature data (n = 380), allow us to estimate the uranium isotopic compositions of the various reservoirs involved in the modern oceanic uranium budget, as well as the fractionation factors associated with U incorporation into those reservoirs. Because the incorporation of U into anoxic/euxinic sediments is accompanied by large isotopic fractionation (ΔAnoxic/Euxinic-SW = +0.6‰), the size of the anoxic/euxinic sink strongly influences the δ238U value of seawater. Keeping all other fluxes constant, the flux of uranium in the anoxic/euxinic sink is constrained to be 7.0 ± 3.1 Mmol/yr (or 14 ± 3% of the total flux out of the ocean). This translates into an areal extent of anoxia into the modern ocean of 0.21 ± 0.09% of the total seafloor. This agrees with independent estimates and rules out a recent uranium budget estimate by Henderson and Anderson (2003). Using the mass fractions and isotopic compositions of various rock types in Earth's crust, we further calculate an average δ238U isotopic composition for the continental crust of -0.29 ± 0.03‰ corresponding to a 238U/235U isotopic ratio of 137.797 ± 0.005. We discuss the implications of

  9. Organic matter and containment of uranium and fissiogenic isotopes at the Oklo natural reactors

    USGS Publications Warehouse

    Nagy, B.; Gauthier-Lafaye, F.; Holliger, P.; Davis, D.W.; Mossman, D.J.; Leventhal, J.S.; Rigali, M.J.; Parnell, J.

    1991-01-01

    SOME of the Precambrian natural fission reactors at Oklo in Gabon contain abundant organic matter1,2, part of which was liquefied at the time of criticality and subsequently converted to a graphitic solid3,4. The liquid organic matter helps to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite5. It is known that in the prevailing reactor environments, precipitated uraninite grains incorporated fission products. We report here observations which show that these uraninite crystals were held immobile within the resolidified, graphitic bitumen. Unlike water-soluble (humic) organic matter, the graphitic bituminous organics at Oklo thus enhanced radionu-clide containment. Uraninite encased in solid graphitic matter in the organic-rich reactor zones lost virtually no fissiogenic lan-thanide isotopes. The first major episode of uranium and lead migration was caused by the intrusion of a swarm of adjacent dolerite dykes about 1,100 Myr after the reactors went critical. Our results from Oklo imply that the use of organic, hydrophobic solids such as graphitic bitumen as a means of immobilizing radionuclides in pretreated nuclear waste warrants further investigation. ?? 1991 Nature Publishing Group.

  10. Isotopic fractionation during leaching of impure carbonates and their effect on uranium series dating

    NASA Astrophysics Data System (ADS)

    Alcaraz Pelegrina, J. M.; Martínez-Aguirre, A.

    2005-12-01

    Experiments were designed to evaluate the behaviour of detritus during the leaching of impure carbonates by applying the U-Th isochron technique. We used one natural detritus and a pure, well-dated CaCO 3, alone and in artificial mixtures. One set of experiments was designed to study the effects of sample pre-treatment on the detritus and a second set to examine the effect of acid attacks on both the carbonate and the detritus fractions in a mixture of constant proportions. For both sets of data, the extracted fraction from the detritus was calculated for 238U, 234U, 230Th and 232Th and their constancy established. These conditions are necessary to apply the L/L method [Schwarcz, H.P., Latham, A.G., 1989. Dirty calcites. 1.-Uranium-series dating of contaminated calcite using leachates alone. Chemical Geology (Isotopes Geoscience Section) 80, 35-43] for U/Th dating. Finally, the L/L method was applied to the artificial impure carbonate and the resulting age is found in agreement with the age of the pure carbonate sample. We concluded that conditions of the L/L method to be applied for ageing impure carbonates hold.

  11. Uranium-lead isotope systematics of Mars inferred from the basaltic shergottite QUE 94201

    SciTech Connect

    Gaffney, A M; Borg, L E; Connelly, J N

    2006-12-22

    Uranium-lead ratios (commonly represented as {sup 238}U/{sup 204}Pb = {mu}) calculated for the sources of martian basalts preserve a record of petrogenetic processes that operated during early planetary differentiation and formation of martian geochemical reservoirs. To better define the range of {mu} values represented by the source regions of martian basalts, we completed U-Pb elemental and isotopic analyses on whole rock, mineral and leachate fractions from the martian meteorite Queen Alexandra Range 94201 (QUE 94201). The whole rock and silicate mineral fractions have unradiogenic Pb isotopic compositions that define a narrow range ({sup 206}Pb/{sup 204}Pb = 11.16-11.61). In contrast, the Pb isotopic compositions of weak HCl leachates are more variable and radiogenic. The intersection of the QUE 94201 data array with terrestrial Pb in {sup 206}Pb/{sup 204}Pb-{sup 207}Pb/{sup 204}Pb-{sup 208}Pb/{sup 204}Pb compositional space is consistent with varying amounts of terrestrial contamination in these fractions. We calculate that only 1-7% contamination is present in the purified silicate mineral and whole rock fractions, whereas the HCl leachates contain up to 86% terrestrial contamination. Despite the contamination, we are able to use the U-Pb data to determine the initial {sup 206}Pb/{sup 204}Pb of QUE 94201 (11.086 {+-} 0.008) and calculate the {mu} value of the QUE 94201 mantle source to be 1.823 {+-} 0.008. This is the lowest {mu} value calculated for any martian basalt source, and, when compared to the highest values determined for martian basalt sources, indicates that {mu} values in martian source reservoirs vary by at least 100%. The range of source {mu} values further indicates that the {mu} value of bulk silicate Mars is approximately three. The amount of variation in the {mu} values of the mantle sources ({mu} {approx} 2-4) is greater than can be explained by igneous processes involving silicate phases alone. We suggest the possibility that a small

  12. Isolation and Puification of Uranium Isotopes for Measurement by Mass-Spectrometry (233, 234, 235, 236, 238U) and Alpha Spectrometry (232U)

    SciTech Connect

    Marinelli, R; Hamilton, T; Brown, T; Marchetti, A; Williams, R; Tumey, S

    2006-05-30

    This report describes a standardized methodology used by researchers from the Center for Accelerator Mass Spectrometry (CAMS) (Energy and Environment Directorate) and the Environmental Radiochemistry Group (Chemistry and Materials Science Directorate) at the Lawrence Livermore National Laboratory (LLNL) for the full isotopic analysis of uranium from solution. The methodology has largely been developed for use in characterizing the uranium composition of selected nuclear materials but may also be applicable to environmental studies and assessments of public, military or occupational exposures to uranium using in-vitro bioassay monitoring techniques. Uranium isotope concentrations and isotopic ratios are measured using a combination of Multi Collector Inductively Coupled Plasma Mass Spectrometry (MC ICP-MS), Accelerator Mass Spectrometry (AMS) and Alpha Spectrometry.

  13. Groundwater Ages and Stable Isotope Fingerprints of Contaminated Water to Examine Potential Solute Sources at a Uranium Processing Mill

    NASA Astrophysics Data System (ADS)

    Hurst, T. G.; Solomon, D. K.

    2007-12-01

    To evaluate sources of high solute concentrations in groundwater near a uranium processing facility, groundwater recharge dates are correlated to specific solute concentrations and depth in the water column. Stable isotopes are also used as potential fingerprints of water sourced from mill tailing cells. Passive diffusion samplers, to be analyzed for 3He/4He ratio, were deployed in 15 different wells with samplers at two depths in the saturated interval. Low-flow purging and sampling was then conducted to isolate sampling points at different depths in the wells, with sampling at multiple depths being completed in 4 of the 15 wells sampled. Laboratory analyses were conducted for CFC recharge age, as well as T/3He recharge age. Contract laboratories analyzed for: deuterium and oxygen-18 isotopes of water; sulfur-34 and oxygen-18 isotopes of sulfate; trace metals uranium, manganese, and selenium; and nitrate and sulfate. Analysis for 235U/238U isotope ratios will be conducted to further identify fingerprint signals of source water. Groundwater recharge ages determined using CFC analysis show some vertical stratification in ages across the water column. Upon initial data processing and analysis, measured CFC ages ranged from 30 to 40 years within the water column of one well to only several years difference in another well. Additional results for trace metal concentrations, stable isotope ratios, and T/3He recharge ages will be reported when results are received. Further post-processing of CFC laboratory analysis and noble gas analyses will provide greater clarity as to groundwater ages within the aquifer and, combined with field pumping data, will allow for a comprehensive groundwater model to be constructed. This study provides great insight to potential mine tailings leakage problems and using isotopes and groundwater age dating techniques as a means of tracing contaminated groundwater to the leakage source. Utilizing stable isotopes of water and sulfate, combined

  14. NUCLEAR ISOTOPIC DILUTION OF HIGHLY ENRICHED URANIUM BY DRY BLENDING VIA THE RM-2 MILL TECHNOLOGY

    SciTech Connect

    Raj K. Rajamani; Sanjeeva Latchireddi; Vikas Devrani; Harappan Sethi; Roger Henry; Nate Chipman

    2003-08-01

    DOE has initiated numerous activities to focus on identifying material management strategies to disposition various excess fissile materials. In particular the INEEL has stored 1,700 Kg of offspec HEU at INTEC in CPP-651 vault facility. Currently, the proposed strategies for dispositioning are (a) aqueous dissolution and down blending to LEU via facilities at SRS followed by shipment of the liquid LEU to NFS for fabrication into LWR fuel for the TVA reactors and (b) dilution of the HEU to 0.9% for discard as a waste stream that would no longer have a criticality or proliferation risk without being processed through some type of enrichment system. Dispositioning this inventory as a waste stream via aqueous processing at SRS has been determined to be too costly. Thus, dry blending is the only proposed disposal process for the uranium oxide materials in the CPP-651 vault. Isotopic dilution of HEU to typically less than 20% by dry blending is the key to solving the dispositioning issue (i.e., proliferation) posed by HEU stored at INEEL. RM-2 mill is a technology developed and successfully tested for producing ultra-fine particles by dry grinding. Grinding action in RM-2 mill produces a two million-fold increase in the number of particles being blended in a centrifugal field. In a previous study, the concept of achieving complete and adequate blending and mixing (i.e., no methods were identified to easily separate and concentrate one titanium compound from the other) in remarkably short processing times was successfully tested with surrogate materials (titanium dioxide and titanium mono-oxide) with different particle sizes, hardness and densities. In the current project, the RM-2 milling technology was thoroughly tested with mixtures of natural uranium oxide (NU) and depleted uranium oxide (DU) stock to prove its performance. The effects of mill operating and design variables on the blending of NU/DU oxides were evaluated. First, NU and DU both made of the same oxide

  15. Direct isotope ratio analysis of individual uranium-plutonium mixed particles with various U/Pu ratios by thermal ionization mass spectrometry.

    PubMed

    Suzuki, Daisuke; Esaka, Fumitaka; Miyamoto, Yutaka; Magara, Masaaki

    2015-02-01

    Uranium and plutonium isotope ratios in individual uranium-plutonium (U-Pu) mixed particles with various U/Pu atomic ratios were analyzed without prior chemical separation by thermal ionization mass spectrometry (TIMS). Prior to measurement, micron-sized particles with U/Pu ratios of 1, 5, 10, 18, and 70 were produced from uranium and plutonium certified reference materials. In the TIMS analysis, the peaks of americium, plutonium, and uranium ion signals were successfully separated by continuously increasing the evaporation filament current. Consequently, the uranium and plutonium isotope ratios, except the (238)Pu/(239)Pu ratio, were successfully determined for the particles at all U/Pu ratios. This indicates that TIMS direct analysis allows for the measurement of individual U-Pu mixed particles without prior chemical separation. PMID:25479434

  16. Uranium*

    NASA Astrophysics Data System (ADS)

    Grenthe, Ingmar; Drożdżyński, Janusz; Fujino, Takeo; Buck, Edgar C.; Albrecht-Schmitt, Thomas E.; Wolf, Stephen F.

    Uranium compounds have been used as colorants since Roman times (Caley, 1948). Uranium was discovered as a chemical element in a pitchblende specimen by Martin Heinrich Klaproth, who published the results of his work in 1789. Pitchblende is an impure uranium oxide, consisting partly of the most reduced oxide uraninite (UO2) and partly of U3O8. Earlier mineralogists had considered this mineral to be a complex oxide of iron and tungsten or of iron and zinc, but Klaproth showed by dissolving it partially in strong acid that the solutions yielded precipitates that were different from those of known elements. Therefore he concluded that it contained a new element (Mellor, 1932); he named it after the planet Uranus, which had been discovered in 1781 by William Herschel, who named it after the ancient Greek deity of the Heavens.

  17. Determination of total and isotopic uranium by inductively coupled plasma-mass spectrometry at the Fernald Environmental Management Project

    SciTech Connect

    Miller, F.L.; Bolin, R.N.; Feller, M.T.; Danahy, R.J.

    1995-04-01

    At the Fernald Environmental Management Project (FEMP) in southwestern Ohio, ICP-mass spectrometry (ICP-MS), with sample introduction by peristaltic pumping, is used to determine total and isotopic uranium (U-234, U-235, U-236 and U-238) in soil samples. These analyses are conducted in support of the environmental cleanup of the FEMP site. Various aspects of the sample preparation and instrumental analysis will be discussed. Initial sample preparation consists of oven drying to determine moisture content, and grinding and rolling to homogenize the sample. This is followed by a nitric/hydrofluoric acid digestion to bring the uranium in the sample into solution. Bismuth is added to the sample prior to digestion to monitor for losses. The total uranium (U-238) content of this solution and the U{sup 235}/U{sup 238} ratio are measured on the first pass through the ICP-MS. To determine the concentration of the less abundant U{sup 234} and U{sup 236} isotopes, the digestate is further concentrated by using Eichrom TRU-Spec extraction columns before the second pass through the ICP-MS. Quality controls for both the sample preparation and instrumental protocols will also be discussed. Finally, an explanation of the calculations used to report the data in either weight percent or activity units will be given.

  18. Design Study for a Low-Enriched Uranium Core for the High Flux Isotope Reactor, Annual Report for FY 2006

    SciTech Connect

    Primm, R. T.; Ellis, R. J.; Gehin, J. C.; Clarno, K. T.; Williams, K. A.; Moses, D. L.

    2006-11-01

    Neutronics and thermal-hydraulics studies show that, for equivalent operating power [85 MW(t)], a low-enriched uranium (LEU) fuel cycle based on uranium-10 wt % molybdenum (U-10Mo) metal foil with radially, “continuously graded” fuel meat thickness results in a 15% reduction in peak thermal flux in the beryllium reflector of the High Flux Isotope Reactor (HFIR) as compared to the current highly enriched uranium (HEU) cycle. The uranium-235 content of the LEU core is almost twice the amount of the HEU core when the length of the fuel cycle is kept the same for both fuels. Because the uranium-238 content of an LEU core is a factor of 4 greater than the uranium-235 content, the LEU HFIR core would weigh 30% more than the HEU core. A minimum U-10Mo foil thickness of 84 μm is required to compensate for power peaking in the LEU core although this value could be increased significantly without much penalty. The maximum U-10Mo foil thickness is 457μm. Annual plutonium production from fueling the HFIR with LEU is predicted to be 2 kg. For dispersion fuels, the operating power for HFIR would be reduced considerably below 85 MW due to thermal considerations and due to the requirement of a 26-d fuel cycle. If an acceptable fuel can be developed, it is estimated that $140 M would be required to implement the conversion of the HFIR site at Oak Ridge National Laboratory from an HEU fuel cycle to an LEU fuel cycle. To complete the conversion by fiscal year 2014 would require that all fuel development and qualification be completed by the end of fiscal year 2009. Technological development areas that could increase the operating power of HFIR are identified as areas for study in the future.

  19. Uranium isotope dynamics across salinity and redox gradients in a coastal aquifer: implications for the oceanic uranium budget

    NASA Astrophysics Data System (ADS)

    Linhoff, B.; Charette, M. A.; Thompson, W. G.

    2014-12-01

    To balance the ocean's uranium budget it may be necessary to invoke submarine groundwater discharge as a major source for uranium. However, uranium removal from seawater has been observed in coastal aquifers where steep redox gradients at the seawater-freshwater mixing zone result in the reduction of soluble U(IV) to insoluble U(IV). We investigated uranium cycling in groundwater within a permeable sand subterranean estuary in Waquoit Bay, MA using major and trace element chemistry as well as ∂234U measurements. Groundwater and sediment samples were collected across the seawater-freshwater mixing zone. In the groundwater samples uranium does not behave conservatively. During mixing it is removed in the intermediate salinities (3-4 m; 2-12 salinity; 0.1 nM U) and enriched in higher salinities (4-6 m; 20-25 salinity; 32 nM) while in salinities >25, uranium is again removed (7-8 m; 8 nM). Geochemical modeling suggests that U is removed at the seawater-freshwater interface by adsorption to Mn-oxides (3-4 m) while in the deeper saline aquifer (7-8 m), U is removed through reduction from U(VI) to U(IV). Surprisingly, while ∂234U is above secular equilibrium in both the freshwater and seawater, within the intermediate salinities ∂234U is depleted below secular equilibrium (as much as ∂234U = -50). Sediment samples were subjected to a partial leach to extract surface-exchangeable U. This leach was analyzed for ∂234U and found to be highly depleted (∂234U -80 - -20). Based on the depleted ∂234U of the sediment leaches and groundwater, we hypothesize that the high U concentrations observed within the intermediate salinities likely have a sediment source. This also implies that U within this intermediate salinity zone must have a long residence time relative to groundwater-surface water exchange rates. This might be possible if redox boundaries and Mn-oxides act as a barrier to U in the intermediate salinities allowing U leached from sediments to accumulate

  20. Study of radioactive isotopes of beryllium, polonium, uranium, and plutonium in the atmosphere

    SciTech Connect

    Lee, S.C.

    1986-01-01

    Radiochemical measurements were carried out for /sup 239.240/Pu in a total of 94 rain and snow samples collected at Fayetteville (36/sup 0/ N, 94/sup 0/W), Arkansas, during the period between May 1983 and November 1985. The concentrations of /sup 7/Be in most of these samples were also measured and these results were compared with previous samples. Average concentrations of cosmic-ray-produced radionuclide /sup 7/Be in rain remained fairly constant year after year. The annual rate of /sup 7/Be deposition at Fayetteville, Arkansas, was calculated from these data to be 5.2 dpm/cm/sup 2//year, which corresponds to a value of 2.8 x 10/sup -2/ atoms/cm/sup 2//second for the /sup 7/Be production rate in the atmosphere. The concentrations of bomb-produced radionuclides such as /sup 89/Sr, /sup 90/Sr and /sup 239.240/Pu in rain have drastically decreased since the last nuclear test explosion was conducted by the government of People's Republic of China in 1980. The concentrations of uranium isotopes and radon daughters in rain, on the other hand, were found to be affected by atmospheric injections of volcanic ashes from the 1980 eruption of Mount St. Helens and the 1982 eruption of El Chichon volcano in Mexico. Moreover, the burnups of the nuclear-powered Soviet satellites have caused marked increases in the levels of /sup 235/U and /sup 234/U in some of the rain samples. A sharp increase in the /sup 210/Po//sup 7/Be ratio in rain samples collected toward the end of 1980 and the beginning of 1981 was attributed to an atmospheric injection of /sup 210/Po from a series of major eruptions of Mount St. Helens.

  1. Low-Enriched Uranium Fuel Conversion Activities for the High Flux Isotope Reactor, Annual Report for FY 2011

    SciTech Connect

    Renfro, David G; Cook, David Howard; Freels, James D; Griffin, Frederick P; Ilas, Germina; Sease, John D; Chandler, David

    2012-03-01

    This report describes progress made during FY11 in ORNL activities to support converting the High Flux Isotope Reactor (HFIR) from high-enriched uranium (HEU) fuel to low-enriched uranium (LEU) fuel. Conversion from HEU to LEU will require a change in fuel form from uranium oxide to a uranium-molybdenum (UMo) alloy. With both radial and axial contouring of the fuel foil and an increase in reactor power to 100 MW, calculations indicate that the HFIR can be operated with LEU fuel with no degradation in performance to users from the current levels achieved with HEU fuel. Studies are continuing to demonstrate that the fuel thermal safety margins can be preserved following conversion. Studies are also continuing to update other aspects of the reactor steady state operation and accident response for the effects of fuel conversion. Technical input has been provided to Oregon State University in support of their hydraulic testing program. The HFIR conversion schedule was revised and provided to the GTRI program. In addition to HFIR conversion activities, technical support was provided directly to the Fuel Fabrication Capability program manager.

  2. Uniform deposition of uranium hexafluoride (UF6): Standardized mass deposits and controlled isotopic ratios using a thermal fluorination method.

    PubMed

    McNamara, Bruce K; O'Hara, Matthew J; Casella, Andrew M; Carter, Jennifer C; Addleman, R Shane; MacFarlan, Paul J

    2016-07-01

    We report a convenient method for the generation of volatile uranium hexafluoride (UF6) from solid uranium oxides and other U compounds, followed by uniform deposition of low levels of UF6 onto sampling coupons. Under laminar flow conditions, UF6 is shown to interact with surfaces within a fixed reactor geometry to a highly predictable degree. We demonstrate the preparation of U deposits that range between approximately 0.01 and 500ngcm(-2). The data suggest the method can be extended to creating depositions at the sub-picogramcm(-2) level. The isotopic composition of the deposits can be customized by selection of the U source materials and we demonstrate a layering technique whereby two U solids, each with a different isotopic composition, are employed to form successive layers of UF6 on a surface. The result is an ultra-thin deposit that bears an isotopic signature that is a composite of the two U sources. The reported deposition method has direct application to the development of unique analytical standards for nuclear safeguards and forensics. Further, the method allows access to very low atomic or molecular coverages of surfaces. PMID:27154668

  3. Molecular marker and stable carbon isotope analyses of carbonaceous Ambassador uranium ores of Mulga Rock in Western Australia

    NASA Astrophysics Data System (ADS)

    Jaraula, C.; Schwark, L.; Moreau, X.; Grice, K.; Bagas, L.

    2013-12-01

    Mulga Rock is a multi-element deposit containing uranium hosted by Eocene peats and lignites deposited in inset valleys incised into Permian rocks of the Gunbarrel Basin and Precambrian rocks of the Yilgarn Craton and Albany-Fraser Orogen. Uranium readily adsorbs onto minerals or phytoclasts to form organo-uranyl complexes. This is important in pre-concentrating uranium in this relatively young ore deposit with rare uraninite [UO2] and coffinite [U(SiO4)1-x(OH)4x], more commonly amorphous and sub-micron uranium-bearing particulates. Organic geochemical and compound-specific stable carbon isotope analyses were conducted to identify possible associations of molecular markers with uranium accumulation and to recognize effect(s) of ionizing radiation on molecular markers. Samples were collected from the Ambassador deposit containing low (<200 ppm) to high (>2000 ppm) uranium concentrations. The bulk rock C/N ratios of 82 to 153, Rock-Eval pyrolysis yields of 316 to 577 mg hydrocarbon/g TOC (Hydrogen Index, HI) and 70 to 102 mg CO2/g TOC (Oxygen Index, OI) are consistent with a terrigenous and predominantly vascular plant OM source deposited in a complex shallow water system, ranging from lacustrine to deltaic, swampy wetland and even shallow lake settings as proposed by previous workers. Organic solvent extracts were separated into saturated hydrocarbon, aromatic hydrocarbon, ketone, and a combined free fatty acid and alcohol fraction. The molecular profiles appear to vary with uranium concentration. In samples with relatively low uranium concentrations, long-chain n-alkanes, alcohols and fatty acids derived from epicuticular plant waxes dominate. The n-alkane distributions (C27 to C31) reveal an odd/even preference (Carbon Preference Index, CPI=1.5) indicative of extant lipids. Average δ13C of -27 to -29 ‰ for long-chain n-alkanes is consistent with a predominant C3 plant source. Samples with relatively higher uranium concentrations contain mostly intermediate

  4. Low-Enriched Uranium Fuel Design with Two-Dimensional Grading for the High Flux Isotope Reactor

    SciTech Connect

    Ilas, Germina; Primm, Trent

    2011-05-01

    An engineering design study of the conversion of the High Flux Isotope Reactor (HFIR) from high-enriched uranium (HEU) to low-enriched uranium (LEU) fuel is ongoing at Oak Ridge National Laboratory. The computational models developed during fiscal year 2010 to search for an LEU fuel design that would meet the requirements for the conversion and the results obtained with these models are documented and discussed in this report. Estimates of relevant reactor performance parameters for the LEU fuel core are presented and compared with the corresponding data for the currently operating HEU fuel core. The results obtained indicate that the LEU fuel design would maintain the current performance of the HFIR with respect to the neutron flux to the central target region, reflector, and beam tube locations under the assumption that the operating power for the reactor fueled with LEU can be increased from the current value of 85 MW to 100 MW.

  5. NGSI FY15 Final Report. Innovative Sample Preparation for in-Field Uranium Isotopic Determinations

    SciTech Connect

    Yoshida, Thomas M.; Meyers, Lisa

    2015-11-10

    Our FY14 Final Report included an introduction to the project, background, literature search of uranium dissolution methods, assessment of commercial off the shelf (COTS) automated sample preparation systems, as well as data and results for dissolution of bulk quantities of uranium oxides, and dissolution of uranium oxides from swipe filter materials using ammonium bifluoride (ABF). Also, discussed were reaction studies of solid ABF with uranium oxide that provided a basis for determining the ABF/uranium oxide dissolution mechanism. This report details the final experiments for optimizing dissolution of U3O8 and UO2 using ABF and steps leading to development of a Standard Operating Procedure (SOP) for dissolution of uranium oxides on swipe filters.

  6. Investigating Uranium Mobility Using Stable Isotope Partitioning of 238U/235U and a Reactive Transport Model

    NASA Astrophysics Data System (ADS)

    Bizjack, M.; Johnson, T. M.; Druhan, J. L.; Shiel, A. E.

    2015-12-01

    We report a numerical reactive transport model which explicitly incorporates the effectively stable isotopes of uranium (U) and the factors that influence their partitioning in bioactive systems. The model reproduces trends observed in U isotope ratios and concentration measurements from a field experiment, thereby improving interpretations of U isotope ratios as a tracer for U reactive transport. A major factor contributing to U storage and transport is its redox state, which is commonly influenced by the availability of organic carbon to support metal-reducing microbial communities. Both laboratory and field experiments have demonstrated that biogenic reduction of U(VI) fractionates the stable isotope ratio 238U/235U, producing an isotopically heavy solid U(IV) product. It has also been shown that other common reactive transport processes involving U do not fractionate isotopes to a consistently measurable level, which suggests the capacity to quantify the extent of bioreduction occurring in groundwater containing U using 238U/235U ratios. A recent study of a U bioremediation experiment at the Rifle IFRC site (Colorado, USA) applied Rayleigh distillation models to quantify U stable isotope fractionation observed during acetate amendment. The application of these simplified models were fit to the observations only by invoking a "memory-effect," or a constant source of low-concentration, unfractionated U(VI). In order to more accurately interpret the measured U isotope ratios, we present a multi-component reactive transport model using the CrunchTope software. This approach is capable of quantifying the cycling and partitioning of individual U isotopes through a realistic network of transport and reaction pathways including reduction, oxidation, and microbial growth. The model incorporates physical heterogeneity of the aquifer sediments through zones of decreased permeability, which replicate the observed bromide tracer, major ion chemistry, U concentration, and U

  7. Determination of lead, uranium, thorium, and thallium in silicate glass standard materials by isotope dilution mass spectrometry

    USGS Publications Warehouse

    Barnes, I.L.; Garner, E.L.; Gramlich, J.W.; Moore, L.J.; Murphy, T.J.; Machlan, L.A.; Shields, W.R.; Tatsumoto, M.; Knight, R.J.

    1973-01-01

    A set of four standard glasses has been prepared which have been doped with 61 different elements at the 500-, 50-, 1-, and 0.02-ppm level. The concentrations of lead, uranium, thorium, and thallium have been determined by isotope dilution mass spectrometry at a number of points in each of the glasses. The results obtained from independent determinations in two laboratories demonstrate the homogeneity of the samples and that precision of the order of 0.5% (95% L.E.) may be obtained by the method even at the 20-ppb level for these elements. The chemical and mass spectrometric procedures necessary are presented.

  8. Determining the isotopic compositions of uranium and fission products in radioactive environmental microsamples using laser ablation ICP-MS with multiple ion counters.

    PubMed

    Boulyga, Sergei F; Prohaska, Thomas

    2008-01-01

    This paper presents the application of a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS)--a Nu Plasma HR--equipped with three ion-counting multipliers and coupled to a laser ablation system (LA) for the rapid and sensitive determination of the 235U/238U, 236U/238U, 145Nd/143Nd, 146Nd/143Nd, 101Ru/(99Ru+99Tc) and 102Ru/(99Ru+99Tc) isotope ratios in microsamples collected in the vicinity of Chernobyl. Microsamples with dimensions ranging from a hundred mum to about 1 mm and with surface alpha activities of 3-38 mBq were first identified using nuclear track radiography. U, Nd and Ru isotope systems were then measured sequentially for the same microsample by LA-MC-ICP-MS. The application of a zoom ion optic for aligning the ion beams into the ion counters allows fast switching between different isotope systems, which enables all of the abovementioned isotope ratios to be measured for the same microsample within a total analysis time of 15-20 min (excluding MC-ICP-MS optimization and calibration). The 101Ru/(99Ru+99Tc) and 102Ru/(99Ru+99Tc) isotope ratios were measured for four microsamples and were found to be significantly lower than the natural ratios, indicating that the microsamples were contaminated with the corresponding fission products (Ru and Tc). A slight depletion in 146Nd of about 3-5% was observed in the contaminated samples, but the Nd isotopic ratios measured in the contaminated samples coincided with natural isotopic composition within the measurement uncertainty, as most of the Nd in the analyzed samples originates from the natural soil load of this element. The 235U/238U and 236U/238U isotope ratios were the most sensitive indicators of irradiated uranium. The present work yielded a significant variation in uranium isotope ratios in microsamples, in contrast with previously published results from the bulk analysis of contaminated samples originating from the vicinity of Chernobyl. Thus, the 235U/238U ratios measured in ten

  9. Method for determination of uranium isotopes in environmental samples by liquid-liquid extraction with triisooctylamine/xylene in hydrochloric media and alpha spectrometry.

    PubMed

    Popov, L

    2012-10-01

    Alternative method for determination of uranium isotopes in various environmental samples is presented. The method is based on total decomposition of the solid materials and preconcentration of liquid samples. The separation of uranium from interfering radionuclides and stable matrix elements is attained by liquid-liquid extraction with triisooctylamine/xylene in hydrochloric media. After the additional removal of stable iron by extraction with diisopropyl ether, purified uranium is electrodeposited on stainless steel disks and measured by alpha spectrometry. The analytical method has been successfully applied to the determination of uranium isotopes in water and bottom sediments from the rivers Danube, Ogosta and Tzibritza in Northwestern Bulgaria. The analytical quality was checked by analyzing reference materials with different matrices. PMID:22871440

  10. Isotopic disequilibrium of uranium: alpha-recoil damage and preferential solution effects

    SciTech Connect

    Fleischer, R.L.

    1980-02-29

    Preferential loss of uranium-234 relative to uranium-238 from rocks into solutions has long been attributed to recoiling alpha-emitting nuclei. Direct evidence has been obtained for two mechanisms, first, recoil ejection from grains, and now release by natural etching of alpha-recoil tracks. The observations have implications for radon emanation and for the storage of alpha-emitting radioactive waste.

  11. Assessment of a sequential phase extraction procedure for uranium-series isotope analysis of soils and sediments.

    PubMed

    Suresh, P O; Dosseto, A; Handley, H K; Hesse, P P

    2014-01-01

    The study of uranium-series (U-series) isotopes in soil and sediment materials has been proposed to quantify rates and timescales of soil production and sediment transport. Previous works have studied bulk soil or sediment material, which is a complex assemblage of primary and secondary minerals and organic compounds. However, the approach relies on the fractionation between U-series isotopes in primary minerals since they were liberated from the parent rock via weathering. In addition, secondary minerals and organic compounds have their own isotopic compositions such that the composition of the bulk material may not reflect that of primary minerals. Hence, there is a need for a sample preparation procedure that allows the isolation of primary minerals in soil or fluvial sediment samples. In this study, a sequential extraction procedure to separate primary minerals from soils and sediments was assessed. The procedure was applied to standard rock sample powders (TML-3 and BCR-2) to test whether it introduced any artefactual radioactive disequilibrium. A new step was introduced to remove the clay-sized fraction (<2 µm). Significant amounts (5-14%) of U and Th were removed from the rock standards during the procedure. No significant alteration in ((234)U/(238)U) and ((230)Th/(238)U) activity ratios of the rock standards occurred during the procedure. Aliquots of soil sample were subjected to the sequential extraction process to test how each step modifies the uranium-series activity ratios and mineralogy. Although no secondary minerals were detected in the unleached soil aliquots, the sequential leaching process removed up to 17% of U and Th and modified their activity ratios by up to 3%. The modification of the activity ratios poses a demand for careful means to avoid redistribution of isotopes back to the residual phase during phase extraction. PMID:24239599

  12. Identifying the sources of subsurface contamination at the Hanford site in Washington using high-precision uranium isotopic measurements

    SciTech Connect

    Christensen, John N.; Dresel, P. Evan; Conrad, Mark E.; Maher, Kate; DePaolo, Donald J.

    2004-03-30

    In the mid-1990s, a groundwater plume of uranium (U) was detected in monitoring wells in the B-BX-BY Waste Management Area (WMA) at the Hanford Site in Washington. This area has been used since the late 1940s to store high-level radioactive waste and other products of U fuel-rod processing. Using multiple collector ICP source magnetic sector mass spectrometry (MC ICPMS) high precision uranium isotopic analyses were conducted of samples of vadose zone contamination and of groundwater. The ratios {sup 236}U/{sup 238}U, {sup 234}U/{sup 238}U and {sup 238}U/{sup 235}U are used to distinguish contaminant sources. Based on the isotopic data, the source of the groundwater contamination appears to be related to a 1951 overflow event at tank BX-102 that spilled high level U waste into the vadose zone. The U isotopic variation of the groundwater plume is a result of mixing between contaminant U from this spill and natural background U. Vadose zone U contamination at tank B-110 likely predates the recorded tank leak and can be ruled out as a source of groundwater contamination, based on the U isotopic composition. The locus of vadose zone contamination is displaced from the initial locus of groundwater contamination, indicating that lateral migration in the vadose zone was at least 8 times greater than vertical migration. The time evolution of the groundwater plume suggests an average U migration rate of {approx}0.7-0.8 m/day showing slight retardation relative to a ground water flow of {approx}1 m/day.

  13. Insights into the Galápagos plume from uranium-series isotopes of recently erupted basalts

    NASA Astrophysics Data System (ADS)

    Handley, Heather K.; Turner, Simon; Berlo, Kim; Beier, Christoph; Saal, Alberto E.

    2011-09-01

    Uranium-series isotopes (238U-230Th-226Ra-210Pb), major element, trace element, and Sr-Nd isotopic data are presented for recent (<60 years old) Galápagos archipelago basalts. Volcanic rocks from all centers studied (Fernandina, Cerro Azul, Sierra Negra, and Wolf Volcano) display 230Th excesses (4%-15%) and steep rare earth element (REE) patterns indicative of residual garnet during partial melting of their mantle source. Rare earth element modeling suggests that only a few percent of garnet is involved. Correlations between (238U/232Th), radiogenic isotopes and Nb/Zr ratio suggest that the U/Th ratio of these Galápagos volcanic rocks is primarily controlled by geochemical source variations and not fractionation during partial melting. The lowest (230Th/238U) ratio is not observed at Fernandina (the supposed center of the plume) but at the more geochemically "depleted" Wolf Volcano, further to the north. Small radium excesses are observed for all samples with (226Ra/230Th) ranging from 1.107 to 1.614. The 226Ra-230Th disequilibria do not correlate with other uranium-series parent-daughter nuclide pairs or geochemical data, suggesting modification at shallow levels on timescales relevant to the half-life of 226Ra (1600 years). The combination of 226Ra and 210Pb excesses is inconsistent with interaction of magma with cumulate material unless decoupling of 210Pb (or an intermediate daughter, such as 222Rn) occurs prior to modification of Ra-Th disequilibria. An intriguing correlation of (210Pb/226Ra)0 with Nb/Zr and radiogenic isotopes requires further investigation but suggests possible control via magmatic degassing and accumulation that may somehow be related to source heterogeneities.

  14. Technical Report on the Behavior of Trace Elements, Stable Isotopes, and Radiogenic Isotopes During the Processing of Uranium Ore to Uranium Ore Concentrate

    SciTech Connect

    Marks, N. E.; Borg, L. E.; Eppich, G. R.; Gaffney, A. M.; Genneti, V. G.; Hutcheon, I. D.; Kristo, M. J.; Lindvall, R. E.; Ramon, C.; Robel, M.; Roberts, S. K.; Schorzman, K. C.; Sharp, M. A.; Singleton, M. J.; Williams, R. W.

    2015-07-09

    The goals of this SP-1 effort were to understand how isotopic and elemental signatures behave during mining, milling, and concentration and to identify analytes that might preserve geologic signatures of the protolith ores. The impurities that are preserved through the concentration process could provide useful forensic signatures and perhaps prove diagnostic of sample origin.

  15. Uranium and thorium isotopes in the rivers of the Amazonian basin: hydrology and weathering processes

    NASA Astrophysics Data System (ADS)

    Marques, Aguinaldo N., Jr.; Al-Gharib, Iyad; Bernat, Michel; Fernex, François

    2003-01-01

    hydroxylamine extracts. As expected, the 1 in the Trombetas and Negro rivers. Such ratios probably result from the binding of dissolved uranium to solid sediment.isotopes were used as tools to evaluate the chemical weathering rate of rocks in the Amazon system, which was estimated to be 2·7 cm 1000 year

  16. Uranium isotopes in Pleistocene permafrost: evaluating the age of ancient ice

    NASA Astrophysics Data System (ADS)

    Ewing, S. A.; Paces, J. B.; O'Donnell, J.; Kanevskiy, M. Z.; Aiken, G.; Jorgenson, T.; Shur, Y.; Striegl, R. G.

    2010-12-01

    The age of ice in permafrost is an indicator of past climate history, and of the resilience and response of high-latitude ecosytems to global change. Methods such as radiocarbon dating and tephrachronology are limited in permafrost because they provide indirect age control, and could overestimate ages when ice is intermittently absent. Development of geochemical indicators of water/ice residence time in permafrost is critical for understanding the circumstances and primary controls of permafrost formation, preservation, and thaw in response to climate change. We analyzed uranium isotopes to evaluate the age of segregated ice in ice-rich loess permafrost (yedoma) cores from central Alaska. Activity ratios of 234U vs. sup>238U (234/238U ARs) in thawed waters exceed 1.000 due to extended contact of ice with mineral surfaces over time. Ice is expected to increase in age with depth at this location based on the presence of deep loess, cryostructures associated with syngenetic permafrost aggracation, high segregated ice content, and frequent wedge ice. These features indicate that permafrost formed syngenetically as loess was deposited. Consequently, (234/238U ARs are expected to increase with depth as recoil 234U, derived from in situ decay of (238U in loess particles, accumulates in ice without being flushed over time. Values of (234/238U ARs measured for ice from a series of five neighboring cores up to 21 m deep increase with depth, consistent with downhole increases in permafrost age. Additional variability of (234/238U ARs with depth can be attributed to variations in surface area of solids determined by analysis of particle size distribution. Radiocarbon analysis of dissolved organic carbon indicates that the ages of ice are greater than ~36ky below the upper few meters, consistent with previous work on soil organic-matter profiles in this area. Using these measured parameters, a model of (234/238U AR evolution indicates minimum ages up to a minimum of ~100ky in

  17. Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

    NASA Astrophysics Data System (ADS)

    Handley, Heather K.; Turner, Simon; Afonso, Juan C.; Dosseto, Anthony; Cohen, Tim

    2013-02-01

    Quantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geometric and surface area measurement with an incorporated fractal correction) and typical assumed input parameter values found in the literature. The calculated recoil loss factors and comminution ages are highly dependent on the method of recoil loss factor determination used and the chosen assumptions. To appraise the ramifications of the assumptions inherent in the comminution age approach and determine individual and combined comminution age uncertainties associated to each variable, Monte Carlo simulations were conducted for a synthetic sediment sample. Using a reasonable associated uncertainty for each input factor and including variations in the source rock and measured (234U/238U) ratios, the total combined uncertainty on comminution age in our simulation (for both methods of recoil loss factor estimation) can amount to ±220-280 ka. The modelling shows that small changes in assumed input values translate into large effects on absolute comminution age. To improve the accuracy of the technique and provide meaningful absolute comminution ages, much tighter constraints are required on the assumptions for input factors such as the fraction of α-recoil lost 234Th and the initial (234U/238U) ratio of the source material. In order to be able to directly compare calculated comminution ages produced by different research groups, the standardisation of pre-treatment procedures, recoil loss factor estimation and assumed input parameter values

  18. Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

    USGS Publications Warehouse

    Ewing, Stephanie A.; Paces, James B.; O'Donnell, J.A.; Jorgenson, M.T.; Kanevskiy, M.Z.; Aiken, George R.; Shur, Y.; Harden, Jennifer W.; Striegl, Rob

    2015-01-01

    The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10–100 ky BP), despite subsequent

  19. Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

    NASA Astrophysics Data System (ADS)

    Ewing, S. A.; Paces, J. B.; O'Donnell, J. A.; Jorgenson, M. T.; Kanevskiy, M. Z.; Aiken, G. R.; Shur, Y.; Harden, J. W.; Striegl, R.

    2015-03-01

    The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10-100 ky BP), despite subsequent fluctuations in

  20. Uranium Isotopes in Calcium Carbonate: A Possible Proxy for Paleo-pH and Carbonate Ion Concentration?

    NASA Astrophysics Data System (ADS)

    Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Wasylenki, L. E.; Anbar, A. D.

    2015-12-01

    Natural variations of 238U/235U in marine carbonates are being explored as a paleoredox proxy. However, in order for this proxy to be robust, it is important to understand how pH and alkalinity affect the fractionation of 238U/235U during coprecipitation with calcite and aragonite. Recent work suggests that the U/Ca ratio of foraminiferal calcite may vary with seawater [CO32-] concentration due to changes in U speciation[1]. Here we explore analogous isotopic consequences in inorganic laboratory co-precipitation experiments. Uranium coprecipitation experiments with calcite and aragonite were performed at pH 8.5 ± 0.1 and 7.5 ± 0.1 using a constant addition method [2]. Dissolved U in the remaining solution was periodically collected throughout the experiments. Samples were purified with UTEVA resin and 238U/235U was determined using a 233U-236U double-spike and MC-ICP-MS, attaining a precision of ± 0.10 ‰ [3]. Small but resolvable U isotope fractionation was observed in aragonite experiments at pH ~8.5, preferentially enriching heavier U isotopes in the solid phase. 238U/235U of the dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00002 - 1.00009. In contrast, no resolvable U isotope fractionation was detected in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among dissolved U species is the most likely mechanism driving these isotope effects. Our quantitative model of this process assumes that charged U species are preferentially incorporated into CaCO3 relative to the neutral U species Ca2UO2(CO3)3(aq), which we hypothesize to have a lighter equilibrium U isotope composition than the charged U species. According to this model, the magnitude of U isotope fractionation should scale with the fraction of the neutral U species in the solution, in agreement with our experimental results. These findings suggest that U isotope variations in

  1. The Role of COMSOL Toward a Low-Enriched Uranium Fuel Design for the High Flux Isotope Reactor

    SciTech Connect

    Freels, James D; Arimilli, Rao V; Lowe, Kirk T; Bodey, Isaac T

    2009-01-01

    Design and safety analyses are underway to convert the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) from a high-enriched uranium (HEU) fuel to a low-enriched uranium (LEU) fuel. The primary constraint for the project is that the overall fuel plate dimensions and the current neutron flux performance must remain unchanged. This allows minimal impact on the facility and cost for the conversion, and provides transparency to the HFIR customer base and research projects that depend on the facility for isotopes and neutron flux. As a consequence, the LEU design demands more accuracy and less margin in the analysis efforts than the original design. Several technical disciplines are required to complete this conversion including nuclear reactor physics, heat transfer, fluid dynamics, structural mechanics, fuel fabrication, and engineering design. The role of COMSOL is to provide the fully-coupled 3D multi-physics analysis for heat transfer, turbulent flow, and structural mechanics of the fuel plates and flow channels. A goal is for COMSOL to simulate the entire fuel element array of fuel plates (171 inner, 369 outer). This paper describes the progress that has been made toward development of benchmark validation models of the existing HEU inner-element fuel plates.

  2. Budgets and behaviors of uranium and thorium series isotopes in the Santa Monica Basin off the California Coast

    SciTech Connect

    Yu, Lei

    1991-12-16

    Samples from three time-series sediment traps deployed in the Santa Monica Basin off the California coast were analyzed to study the flux and scavenging of uranium and thorium series isotopes. Variations of uranium and thorium series isotopes fluxes in the water column were obtained by integrating these time-series deployment results. Mass and radionuclide fluxes measured from bottom sediment traps compare favorably with fluxed determined from sediment core data. This agreement suggests that the near-bottom sediment traps are capable of collecting settling particles representative of the surface sediment. The phase distributions of {sup 234}Th in the water column were calculated by an inverse method using sediment trap data, which help to study the variations of {sup 234}Th scavenging in the water column. Scavenging and radioactive decay of {sup 234}Th are the two principal processes for balancing {sup 234}Th budget in the water column. The residence times of dissolved and particulate {sup 234}Th were determined by a {sup 234}Th scavenging model.

  3. A combined chemical, isotopic and microstructural study of pyrite from roll-front uranium deposits, Lake Eyre Basin, South Australia

    NASA Astrophysics Data System (ADS)

    Ingham, Edwina S.; Cook, Nigel J.; Cliff, John; Ciobanu, Cristiana L.; Huddleston, Adam

    2014-01-01

    The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at Pepegoona, Pepegoona West and Pannikan, Lake Eyre Basin, South Australia. Combined chemical, isotopic and microstructural analysis of pyrite indicates variation in fluid composition, sulfur source and precipitation conditions during a protracted mineralization event. The results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low-temperature hydrothermal systems. In-situ micrometer-scale sulfur isotope analyses of pyrite demonstrated broad-scale isotopic heterogeneity (δ34S = -43.9 to +32.4‰VCDT), indicative of complex, multi-faceted pyrite evolution, and sulfur derived from more than a single source. Preserved textures support this assertion and indicate a genetic model involving more than one phase of pyrite formation. Authigenic pyrite underwent prolonged evolution and recrystallization, evidenced by a genetic relationship between archetypal framboidal aggregates and pyrite euhedra. Secondary hydrothermal pyrite commonly displays hyper-enrichment of several trace elements (Mn, Co, Ni, As, Se, Mo, Sb, W and Tl) in ore-bearing horizons. Hydrothermal fluids of magmatic and meteoric origins supplied metals to the system but the geochemical signature of pyrite suggests a dominantly granitic source and also the influence of mafic rock types. Irregular variation in δ34S, coupled with oscillatory trace element zonation in secondary pyrite, is interpreted in terms of continuous variations in fluid composition and cycles of diagenetic recrystallization. A late-stage oxidizing fluid may have mobilized selenium from pre-existing pyrite. Subsequent restoration of reduced conditions within the aquifer caused ongoing pyrite re-crystallization and precipitation of selenium as native selenium. These results provide the first qualitative constraints on the formation mechanisms of the uranium deposits at Beverley North. Insights into

  4. Establishing a Cost Basis for Converting the High Flux Isotope Reactor from High Enriched to Low Enriched Uranium Fuel

    SciTech Connect

    Primm, Trent; Guida, Tracey

    2010-02-01

    Under the auspices of the Global Threat Reduction Initiative Reduced Enrichment for Research and Test Reactors Program, the National Nuclear Security Administration /Department of Energy (NNSA/DOE) has, as a goal, to convert research reactors worldwide from weapons grade to non-weapons grade uranium. The High Flux Isotope Reactor (HFIR) at Oak Ridge National Lab (ORNL) is one of the candidates for conversion of fuel from high enriched uranium (HEU) to low enriched uranium (LEU). A well documented business model, including tasks, costs, and schedules was developed to plan the conversion of HFIR. Using Microsoft Project, a detailed outline of the conversion program was established and consists of LEU fuel design activities, a fresh fuel shipping cask, improvements to the HFIR reactor building, and spent fuel operations. Current-value costs total $76 million dollars, include over 100 subtasks, and will take over 10 years to complete. The model and schedule follows the path of the fuel from receipt from fuel fabricator to delivery to spent fuel storage and illustrates the duration, start, and completion dates of each subtask to be completed. Assumptions that form the basis of the cost estimate have significant impact on cost and schedule.

  5. Determination of plutonium-239, thorium-232, and natural uranium isotopic concentrations in biological samples using photofission track analysis

    NASA Astrophysics Data System (ADS)

    Parry, James Roswell

    Fission track analysis (FTA) has many uses in the scientific community including but not limited to geological dating, neutron flux mapping, and dose reconstruction. The common method of fission for FTA is through neutrons from a nuclear reactor. This dissertation investigates the use of bremsstrahlung radiation produced from an electron linear accelerator to induce fission in FTA samples. This provides a means of simultaneously measuring the amount of Pu-239, U-nat, and Th-232 in a single sample. The benefit of measuring the three isotopes simultaneously is the possible elimination of costly and time consuming chemical processing for dose reconstruction samples. Samples containing the three isotopes were irradiated in two different bremsstrahlung spectra and a neutron spectrum to determine the amount of Pu-239, U-nat, and Th-232 in the samples. The reaction rate from the calibration samples and the counted fission tracks on the samples were used in determining the concentration of each isotope in the samples. The results were accurate to within a factor of two or three, showing that the method can work to predict the concentrations of multiple isotopes in a sample. The limitations of current accelerators and detectors limits the application of this specific procedure to higher concentrations of isotopes. The method detection limits for Pu-239, U-nat, and Th-232 are 20 pCi, 1 fCi, and 0.4 flCI respectively. Analysis of extremely low concentrations of isotopes would require the use of different detectors such as quartz due to the embrittlement encountered in the Lexan at high exposures. Cracking of the Texan detectors started to appear at a fluence of about 2 x 1018 electrons from the accelerator. This may be partly due to the beam stop not being an adequate thickness. The procedure is likely limited to specialty applications for the near term. However, with the world concerns of exposure to depleted uranium, this procedure may find applications in this area since

  6. Isotopic disequilibrium of uranium: alpha-recoil damage and preferential solution effects.

    PubMed

    Fleischer, R L

    1980-02-29

    Preferential loss of uranium-234 relative to uranium-238 from rocks into solutions has long been attributed to recoiling alpha-emitting nuclei. Direct evidence has been obtained for two mechanisms, first, recoil ejection from grains, and now release by natural etching of alpha-recoil tracks. The observations have implications for radon emanation and for the storage of alpha-emitting radioactive waste. PMID:17830457

  7. Chemical and isotopic studies of granitic Archean rocks, Owl Creek Mountains, Wyoming: Uranium-thorium-lead systematics of an Archean granite from the Owl Creek Mountains, Wyoming

    SciTech Connect

    Stuckless, J.S.; Nkomo, I.T.; Butt, K.A.

    1986-01-01

    Isotopic analyses of apparently unaltered whole-rock samples of a granite from the Owl Creek Mountains, Wyo., yield a lead-lead isochron age of 2730 {plus minus} 35 Ma, which is somewhat older than the age obtained by the rubidium-strontium whole-rock method. Thorium-lead data for the same samples deviate markedly from an isochronal relation; however, calculated initial {sup 208}Pb/{sup 204}Pb ratios correlate with whole-rock {delta}{sup 18}O values and lead to the conclusion that the {sup 232}Th-{sup 208}Pb data are not colinear because of an originally heterogeneous granitic magma. Relationships in the {sup 207}Pb/{sup 235}U-{sup 206}Pb/{sup 238}U system show that uranium was mobilized during early Laramide time or shortly before, such that most surface and shallow drill-core samples lost 60-80 percent of their uranium, and some fractured, deeper drill-core samples gained from 50 to 10,000 percent uranium. Fission-track maps show that much uranium is located along edges and cleavages of biotite and magnetic where it is readily accessible to oxidizing ground water. Furthermore, qualitative comparisons of uranium distribution in samples with excess radiogenic lead and in samples with approximately equilibrium amounts of uranium and lead suggest that the latter contain more uranium in these readily accessible sites. Unlike other granites that have uranium distributions and isotopic systematics similar to those observed in this study, the granite of the Owl Creek Mountains is not associated with economic uranium deposits.

  8. Utilization of non-weapons-grade plutonium and highly enriched uranium with breeding of the 233U isotope in the VVER reactors using thorium and heavy water

    NASA Astrophysics Data System (ADS)

    Marshalkin, V. E.; Povyshev, V. M.

    2015-12-01

    A method for joint utilization of non-weapons-grade plutonium and highly enriched uranium in the thorium-uranium—plutonium oxide fuel of a water-moderated reactor with a varying water composition (D2O, H2O) is proposed. The method is characterized by efficient breeding of the 233U isotope and safe reactor operation and is comparatively simple to implement.

  9. Elemental and Isotopic Analysis of Uranium Oxide an NIST Glass Standards by FEMTOSECOND-LA-ICP-MIC-MS

    SciTech Connect

    Ebert, Chris; Zamzow, Daniel S.; McBay, Eddie H.; Bostick, Debra A.; Bajic, Stanley J.; Baldwin, David P.; Houk, R.S.

    2009-06-01

    The objective of this work was to test and demonstrate the analytical figures of merit of a femtosecond-laser ablation (fs-LA) system coupled with an inductively coupled plasma-multi-ion collector-mass spectrometer (ICP-MIC-MS). The mobile fs-LA sampling system was designed and assembled at Ames Laboratory and shipped to Oak Ridge National Laboratory (ORNL), where it was integrated with an ICP-MIC-MS. The test period of the integrated systems was February 2-6, 2009. Spatially-resolved analysis of particulate samples is accomplished by 100-shot laser ablation using a fs-pulsewidth laser and monitoring selected isotopes in the resulting ICP-MS transient signal. The capability of performing high sensitivity, spatially resolved, isotopic analyses with high accuracy and precision and with virtually no sample preparation makes fs-LA-ICP-MIC-MS valuable for the measurement of actinide isotopes at low concentrations in very small samples for nonproliferation purposes. Femtosecond-LA has been shown to generate particles from the sample that are more representative of the bulk composition, thereby minimizing weaknesses encountered in previous work using nanosecond-LA (ns-LA). The improvement of fs- over ns-LA sampling arises from the different mechanisms for transfer of energy into the sample in these two laser pulse-length regimes. The shorter duration fs-LA pulses induce less heating and cause less damage to the sample than the longer ns pulses. This results in better stoichiometric sampling (i.e., a closer correlation between the composition of the ablated particles and that of the original solid sample), which improves accuracy for both intra- and inter-elemental analysis. The primary samples analyzed in this work are (a) solid uranium oxide powdered samples having different {sup 235}U to {sup 238}U concentration ratios, and (b) glass reference materials (NIST 610, 612, 614, and 616). Solid uranium oxide samples containing {sup 235}U in depleted, natural, and enriched

  10. Desert varnish: potential for age dating via uranium-series isotopes

    SciTech Connect

    Knauss, K.G.; Ku, T.L.

    1980-01-01

    Trace metals and natural radioisotopes are measured in an unusually thick and presumed ancient desert varnish from the Colorado Plateau in Utah. Uranium and thorium concentrations in the sequence: varnish-altered rind-heartrock (Shinarump formation sandstone) indicate that uranium with little accompanying thorium is derived from external sources. The varnish forms a closed system for /sup 230/Th and /sup 231/Pa with equilibrium values for both /sup 230/Th//sup 234/U and /sup 231/Pa//sup 235/U. Selective leaching of the ferromanganese oxides followed by analysis of both the leachate and silicate residue is proposed to allow age determinations.