Growth and Alteration of Uranium-Rich Microlite

Gieré, Reto; Swope, R. Jeffrey; Buck, Edgar C.; Guggenheim, R.; Mathys, Daniel; Reusser, Éric

doi:10.1557/proc-608-519

Cited by 6 publications

(2 citation statements)

References 12 publications

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“…Drever, 1997). Recently, however, cation exchange has been demonstrated for other minerals including boltwoodite (Burns, 1999), pyrochlore (Gieré et al, 2000(Gieré et al, , 2001, and becquerelite (Burns and Li, 2002). All three minerals are of potential importance in nuclearwaste repositories as primary and secondary hosts of radionuclides.…”

Section: Discussionmentioning

confidence: 99%

“…All three minerals are of potential importance in nuclearwaste repositories as primary and secondary hosts of radionuclides. In the study of Gieré et al (2000Gieré et al ( , 2001 it was demonstrated that during lowtemperature oxidative weathering of microlitepyrochlore (a possible primary host phase for high-level radioactive waste) the A-site cations can exchange with uids whilst the uraniumhosted B-site cations do not exchange, retaining the original abundances of substituted uranium. Burns (1999) and Burns and Li (2002) demonstrated that for the uranyl phases boltwoodite and becquerelite that ion exchange with aqueous uids could retard the mobility of Cs + and Sr 2+ , respectively, in groundwaters responsible for alteration of radioactive waste in a nuclear repository.…”

Section: Discussionmentioning

confidence: 99%

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Ion exchange between aqueous fluid and spent nuclear fuel alteration products: Implications for the mobility of Cs in the probable repository at Yucca Mountain

Hoskin¹,

Burns²

2003

Mineral. mag.

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Compreignacite, a naturally occurring potassium uranyl oxide hydrate, is an expected alteration product of spent nuclear fuel subjected to oxidative corrosion in the presence of water. Ion-exchange experiments were performed using natural crystals of compreignacite in a 2 M CsCl solution at 180ºC for 24 h, and in a 100 ppm CsCl solution at 90ºC for 14 days. Exchange of Cs into crystals of compreignacite was demonstrated by crystal-structure analysis for a crystal from 2 M solution and chemical analysis for crystals from both exchange experiments. The structure of Cs-exchanged compreignacite is hexagonal, space group P62m, a = 14.1014 (18) It was solved by direct methods and refined on the basis of F 2 for all unique reflections to a final R1 = 6.37%. The structure determination demonstrated almost complete exchange of Cs for K in the interlayer of the structure, as confirmed by compositional analysis of the crystals, and provided the formula Cs 6 [(UO 2 ) 12 (OH) 10 O 10 ](H 2 O) 3.5 , Z = 2. The structure of Cs-exchanged compreignacite contains a-U 3 O 8 -type sheets of uranyl pentagonal bipyramids that are topologically identical, although compositionally distinct, to those in compreignacite. Compreignacite crystals placed in 100 ppm CsCl solution also incorporated substantial Cs by ion exchange. Ion exchange experiments, using Csexchanged compreignacite from earlier experiments, in 2 M KCl solution at 90ºC for 14 days showed that compreignacite will retain significant Cs in the presence of a solution rich in K. These experiments indicate that formation of compreignacite structure-type phases in a geological repository due to alteration of nuclear waste may significantly impact upon the mobility of Cs, either by direct incorporation of Cs into growing crystals, or by exchange of Cs into earlier-formed crystals of compreignacite when they contact Cs-bearing solutions.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Ion exchange between aqueous fluid and spent nuclear fuel alteration products: Implications for the mobility of Cs in the probable repository at Yucca Mountain

Hoskin¹,

Burns²

2003

Mineral. mag.

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Nuclear waste forms

Stefanovsky¹,

Yudintsev

Gieré

et al. 2004

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This review describes nuclear waste forms for high-level waste (HLW), that is, glasses, ceramics, and glass-ceramics, as well as for low- and intermediate-level waste (LILW), that is, cement, bitumen, glass, glassy slags, and ceramics. Ceramic waste forms have the highest chemical durability and radiation resistance, and are recommended for HLW and actinide (ACT) immobilization. Most radiation-resistant materials are based on phases with a fluorite-related structure (cubic zirconia-based solid solutions, pyrochlore, zirconolite, murataite). Glass is also a suitable matrix for HLW containing fission and corrosion products, and process contaminants such as Na salts. Within the framework of the HLW partitioning concept providing separation of short-lived (Cs, Sr) and long-lived (rare earth element-ACT) fractions, glass may be used for immobilization of the Cs-Sr-bearing fraction, whereas the rare earth-ACT fraction may be incorporated in ceramics. Glass-based materials or clay-based ceramics are the most promising LILW forms, but cement and bitumen may also be applied as matrices for low-level wastes (LLW).

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Study of Natural Minerals of U-Ryrochlore-Type Structure as Analogues of Plutonium Ceramic Waste-form

et al. 2002

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At present, crystalline ceramic based on titanate pyrochlore, (Ca,Gd,Hf,Pu,U)2Ti2O7, is considered as the US candidate waste form for the immobilization of weapons grade plutonium. Naturally occuring U-bearing minerals with pyrochlore-type structure: hatchettolite, betafite, and ellsworthite, were studied in orders to understand long-term radiation damage effects in Pu ceramic waste forms. Chemical shifts (δ) of U(Lδ1)– and U(Lβ1) – X-ray emission lines were measured by X-ray spectrometry. Calculations were performed on the basis of a two-dimensional δLá1- and δLδ1- correlation diagram. It was shown that 100% of uranium in hatchettolite and, probably, 95-100% of uranium in betafite are in the form of (UO2)2+. formal calculation shows that in ellsworthite only 20% of uranium is in the form of U4+ and 80% of the rest is in the forms of U5+ and U6+. The conversion of the initial U4+ ion originally occurring in the pyrochlore structure of natural minerals to (UO2)2+ due to metamict decay causes a significant increase in uranium mobility.

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Growth and Alteration of Uranium-Rich Microlite

Cited by 6 publications

References 12 publications

Ion exchange between aqueous fluid and spent nuclear fuel alteration products: Implications for the mobility of Cs in the probable repository at Yucca Mountain

Ion exchange between aqueous fluid and spent nuclear fuel alteration products: Implications for the mobility of Cs in the probable repository at Yucca Mountain

Nuclear waste forms

Study of Natural Minerals of U-Ryrochlore-Type Structure as Analogues of Plutonium Ceramic Waste-form

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