Sample records for becquerelite
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Neptunium incorporation into select uranyl phases and thermal analysis of select uranyl phases
NASA Astrophysics Data System (ADS)
Klingensmith, Amanda Leigh
Alteration of spent nuclear fuel in a geological repository under oxidizing conditions is likely to result in abundant uranyl compounds. The proposed repository at Yucca Mountain, Nevada is intended to store about 70,000 metric tons of spent nuclear fuel in the unsaturated zone of a welded tuff sequence. Following failure of canisters that encapsulate the waste, contents may be exposed both to air and water and undergo repetitive wetting and drying events. Incorporation of radionuclides into the uranyl alteration phases may significantly reduce their mobility, thereby impacting repository performance. Of particular interest is 237Np owing to its long half-life (2.14 x 106 years) and potential mobility in groundwater. Powders of the synthetic uranyl phase soddyite, (UO2) 2(SiO4)(H2O)2, a framework type structure, and uranophane, Ca[(UO2)(SiO3OH)]2(H 2O)5, kasolite, Pb[(UO2)(SiO4)]H 2O, Na compreignacite, Na2[(UO2)3O 2(OH)3]2(H2O)7, and becquerelite, Ca[(UO2)3O2(OH)3]2(H 2O)8, all of which are sheet type structures, were synthesized in the presence of Np5+ under varying temperature and pH conditions. Uranophane, kasolite, boltwoodite K[(UO2)(SiO3OH)](H 2O)1.5, and Na boltwoodite K,Na[(UO2)(SiO 3OH)](H2O)1.5 were synthesized in the presence of Np as well as P, Ca and/or Mg. Single crystals of Na metaschoepite, Na[(UO 2)4O2(OH)5]˙5H2O were synthesized in the presence of Np5+ and laser ablation verified that Np can be incorporated within the structure of a uranyl phase. Incorporation of Np5+ into soddyite increased steadily with synthesis temperature. Np incorporation into uranophane, becquerelite, and kasolite was not dependent on synthesis temperature. Np uptake in uranophane and kasolite was found to be dependent on synthesis pH, with an increase in Np uptake with higher pH. Uranophane, boltwoodite and Na boltwoodite showed an increase in Np incorporation in the presence of P. Boltwoodite showed an even higher Np uptake when Mg and P were both present in the synthesis. Thermal analysis was completed for the uranyl phases soddyite, becquerelite, Na compreignacite, uranophane, and kasolite. TGA curves for becquerelite, Na compreignacite and uranophane showed loss of interlayer water groups by 100°C. Soddyite and kasolite showed more gradual TGA curves and retention of water groups up to 400°C for soddyite and 550°C for kasolite, with agreement shown by high temperature powder XRD data.
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Felipe-Sotelo, M; Hinchliff, J; Field, L P; Milodowski, A E; Preedy, O; Read, D
2017-07-01
The solubility of uranium and thorium has been measured under the conditions anticipated in a cementitious, geological disposal facility for low and intermediate level radioactive waste. Similar solubilities were obtained for thorium in all media, comprising NaOH, Ca(OH) 2 and water equilibrated with a cement designed as repository backfill (NRVB, Nirex Reference Vault Backfill). In contrast, the solubility of U(VI) was one order of magnitude higher in NaOH than in the remaining solutions. The presence of cellulose degradation products (CDP) results in a comparable solubility increase for both elements. Extended X-ray Absorption Fine Structure (EXAFS) data suggest that the solubility-limiting phase for uranium corresponds to a becquerelite-type solid whereas thermodynamic modelling predicts a poorly crystalline, hydrated calcium uranate phase. The solubility-limiting phase for thorium was ThO 2 of intermediate crystallinity. No breakthrough of either uranium or thorium was observed in diffusion experiments involving NRVB after three years. Nevertheless, backscattering electron microscopy and microfocus X-ray fluorescence confirmed that uranium had penetrated about 40 μm into the cement, implying active diffusion governed by slow dissolution-precipitation kinetics. Precise identification of the uranium solid proved difficult, displaying characteristics of both calcium uranate and becquerelite. Copyright © 2017 Elsevier Ltd. All rights reserved.
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Products of in Situ Corrosion of Depleted Uranium Ammunition in Bosnia and Herzegovina Soils.
Wang, Yuheng; von Gunten, Konstantin; Bartova, Barbora; Meisser, Nicolas; Astner, Markus; Burger, Mario; Bernier-Latmani, Rizlan
2016-11-15
Hundreds of tons of depleted uranium (DU) ammunition were used in previous armed conflicts in Iraq, Bosnia and Herzegovina, and Serbia/Kosovo. The majority (>90%) of DU penetrators miss their target and, if left in the environment, corrode in these postconflict zones. Thus, the best way to understand the fate of bulk DU material in the environment is to characterize the corrosion products of intact DU penetrators under field conditions for extended periods of time. However, such studies are scarce. To fill this knowledge gap, we characterized corrosion products formed from two intact DU penetrators that remained in soils in Bosnia and Herzegovina for over seven years. We used a combination of X-ray powder diffraction, electron microscopy, and X-ray absorption spectroscopy. The results show that metaschoepite (UO 3 (H 2 O) 2 ) was a main component of the two DU corrosion products. Moreover, studtite ((UO 2 )O 2 (H 2 O) 2 ·2(H 2 O)) and becquerelite (Ca(UO 2 ) 6 O 4 (OH) 6 ·8(H 2 O)) were also identified in the corrosion products. Their formation through transformation of metaschoepite was a result of the geochemical conditions under which the penetrators corroded. Moreover, we propose that the transformation of metaschoepite to becquerelite or studtite in the DU corrosion products would decrease the potential for mobilization of U from corroded DU penetrators exposed to similar environments in postconflict areas.
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Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments
Perdrial, Nicolas; Vázquez-Ortega, Angélica; Wang, Guohui; ...
2017-12-05
Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. Here, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO 4-reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K 2(UO 2) 6O 4(OH) 6·8H 2O]- and becquerelite [Ca(UO 2) 6O 4(OH) 6·8H 2O]-like species.more » Subsequent further removal of uranium coincided with that of Si and accumulation of boltwoodite, [(K, Na)(UO 2) 2O 4(HSiO 4) 2•0.5(H 2O)]-like species of uranium at 180 and 365 days. When present, PO 4 exerted a direct and strong control over U speciation. Furthermore, the detection of meta-ankoleite, [K 2(UO 2) 2O 4(PO 4) 2·6H 2O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolved U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO 4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO 4 present, nearly all uranium would have precipitated in the upper soil.« less
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Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments
DOE Office of Scientific and Technical Information (OSTI.GOV)
Perdrial, Nicolas; Vázquez-Ortega, Angélica; Wang, Guohui
Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. In this study, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO(4)(-)reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K-2(UO2)(6)O-4(OH)(6)center dot 8H(2)O]-and becquerelite [Ca(UO2)(6)O-4(OH)(6)center dot 8H(2)O]-like species. Subsequent further removal of uranium coincided withmore » that of Si and accumulation of boltwoodite, [(K, Na)(UO2)(2)O-4(HSiO4)(2)center dot 0.5(H2O)]-like species of uranium at 180 and 365 days. When present, PO4 exerted a direct and strong control over U speciation. The detection of meta-ankoleite, [K-2(UO2)(2)O-4(PO4)(2)center dot 6H(2)O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolved U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO4 present, nearly all uranium would have precipitated in the upper soil.« less
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Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments
DOE Office of Scientific and Technical Information (OSTI.GOV)
Perdrial, Nicolas; Vázquez-Ortega, Angélica; Wang, Guohui
Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. Here, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO 4-reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K 2(UO 2) 6O 4(OH) 6·8H 2O]- and becquerelite [Ca(UO 2) 6O 4(OH) 6·8H 2O]-like species.more » Subsequent further removal of uranium coincided with that of Si and accumulation of boltwoodite, [(K, Na)(UO 2) 2O 4(HSiO 4) 2•0.5(H 2O)]-like species of uranium at 180 and 365 days. When present, PO 4 exerted a direct and strong control over U speciation. Furthermore, the detection of meta-ankoleite, [K 2(UO 2) 2O 4(PO 4) 2·6H 2O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolved U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO 4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO 4 present, nearly all uranium would have precipitated in the upper soil.« less
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NASA Astrophysics Data System (ADS)
Burns, Peter C.; Ewing, Rodney C.; Miller, Mark L.
1997-05-01
Uranyl oxide hydrate and uranyl silicate phases will form due to the corrosion and alteration of spent nuclear fuel under oxidizing conditions in silica-bearing solution. The actinide elements in the spent fuel may be incorporated into the structures of these secondary U6+ phases during the long-term corrosion of the UO 2 in spent fuel. The incorporation of actinide elements into the crystal structures of the alteration products may decrease actinide mobility. The crystal chemistry of the various oxidation states of the actinide elements of environmental concern is examined to identify possible incorporation mechanisms. The substitutions Pu 6+U 6+ and (Pu 5+, Np 5+)U 6+ should readily occur in many U 6+ structures, although structural modification may be required to satisfy local bond-valence requirements. Crystal-chemical characteristics of the U 6+ phases indicate that An 4+ (An: actinide)U 6+ substitution is likely to occur in the sheets of uranyl polyhedra that occur in the structures of the minerals schoepite, [(UO 2) 8O 2(OH) 12](H 2O) 12, ianthinite, [U 24+ (UO 2) 4O 6(OH) 4(H 2O) 4](H 2O) 5, becquerelite, Ca[(UO 2) 3O 2(OH) 3] 2(H 2O) 8, compreignacite, K 2[(UO 2) 3O 2(OH) 3] 2(H 2O) 8, α-uranophane, Ca[(UO 2)(SiO 3OH)] 2(H 2O) 5, and boltwoodite, K(H 2O)[(UO 2)(SiO 4)], all of which are likely to form due to the oxidation and alteration of the UO 2 in spent fuel. The incorporation of An 3+ into the sheets of the structures of α-uranophane and boltwoodite, as well as interlayer sites of various uranyl phases, may occur.
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Residual waste from Hanford tanks 241-C-203 and 241-C-204. 2. Contaminant release model.
Cantrell, Kirk J; Krupka, Kenneth M; Deutsch, William J; Lindberg, Michael J
2006-06-15
Release of U and 99Tc from residual sludge in Hanford waste tanks 241-C-203 and 241-C-204 atthe U.S. Department of Energy's (DOE) Hanford Site in southeastern Washington state was quantified by water-leaching, selective extractions, empirical solubility measurements, and thermodynamic modeling. A contaminant release model was developed based on these experimental results and solid-phase characterization results presented elsewhere. Uranium release was determined to be controlled by two phases and occurred in three stages. In the first stage, U release is controlled by the solubility of tejkaite, which is suppressed by high concentrations of sodium released from the dissolution of NaNO3 in the residual sludges. Equilibrium solubility calculations indicate the U released during this stage will have a maximum concentration of 0.021 M. When all the NaNO3 has dissolved from the sludge, the solubility of the remaining cejkaite will increase to 0.28 M. After cejkaite has completely dissolved, the majority of the remaining U is in the form of poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H20)0-1]. In contact with Hanford groundwater this phase is not stable, and becquerelite becomes the U solubility controlling phase, with a calculated equilibrium concentration of 1.2 x 10(-4) M. For Tc, a significant fraction of its concentration in the residual sludge was determined to be relatively insoluble (20 wt % for C-203 and 80 wt % for C-204). Because of the low concentrations of Tc in these sludge materials, the characterization studies did not identify any discrete Tc solids phases. Release of the soluble fraction of Tc was found to occur concomitantly with NO3-. It was postulated that a NaNO3-NaTcO4 solid solution could be responsible for this behavior. The Tc release concentrations for the soluble fraction were estimated to be 2.4 x 10-6 M for C-203 and 2.7 x 10(-5) M for C-204. Selective extraction results indicated that the recalcitrant fraction of Tc was associated with Fe oxides. Release of the recalcitrant fraction of Tc was assumed to be controlled by dissolution of Fe oxide in the form of ferrihydrite. Based on this assumption and measured values for the ratio of recalcitrant Tc to total Fe in each bulk sludge, the release concentration of the recalcitrant fraction of Tc was calculated to be 3.9 x 10(-12) M for C-203 and 10.0 x 10(-12) M for C-204.