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

Bogdanov, R.V.; Batrakov, Yuri F.; Puchkova, E. V.; Sergeev, A. S.; Burakov, Boris E.

doi:10.1557/proc-713-jj2.2

Cited by 4 publications

(2 citation statements)

References 9 publications

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“…The dissolution behaviour of different pyrochlore compounds has been studied experimentally by various authors (e.g. Lutze and Ewing, 1988;Roberts et al, 2000;Begg et al, 2001;Bogdanov et al, 2002;Icenhower et al, 2002;Xu et al, 2004). All these experimental studies were conducted at solution temperatures below 100ºC.…”

Section: Comparison With Results From Dissolution Experiments With Symentioning

confidence: 99%

Low-temperature aqueous alteration of crystalline pyrochlore: correspondence between nature and experiment

et al. 2004

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Pyrochlore has been considered as a waste form to immobilize high-level nuclear waste such as excess weapons-grade plutonium. In order to study the aqueous stability of pyrochlore, we have carried out hydrothermal experiments with a natural microlite (Nb + Ta > 2Ti; Ta ⩾ Nb) at 175°C in a neutral and acidic solution for 14 days. The starting material and the experimental products were studied by electron microprobe, backscattered electron (BSE) imaging, powder infrared (IR) and micro-Raman spectroscopy, and powder X-ray diffractrometry (XRD). The microlite has small U (∼200 ppm) and Th (∼800 ppm) contents and is crystalline. The hydrothermal treatment in a solution containing l mol/l HCl and l mol/l CaCl2causes the partial replacement of the microlite (up to ∼10 μm) by a new pyrochlore phase. This new phase is characterized by a larger unit-cell volume and contains a large number of vacancies at theAsite (A= Ca, Na) as well as anion vacancies, molecular water, and possibly OH groups. Analyses of the experimental fluid further revealed that U was also selectively lost to the solution. Treatment in pure water did not produce reaction zones detectable by BSE imaging or powder XRD. However, significant spectral changes in powder IR spectra of the reaction product and the detection of Na and Ca in the solution indicate that the microlite has also reacted in pure water. The experimental alteration features bear a remarkable resemblance to those seen in naturally altered microlite samples, suggesting that short-term experimental results can be applied to natural systems andvice versain order to evaluate the long-term stability of a pyrochlore waste form.

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Section: Comparison With Results From Dissolution Experiments With Symentioning

confidence: 99%

Low-temperature aqueous alteration of crystalline pyrochlore: correspondence between nature and experiment

et al. 2004

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“…Another approach in evaluating the long-term durability of nuclear waste forms has been to look for naturally occurring structural analogues. 32,[110][111][112][113][114][115][116][117] Pyrochlore is a relatively common rare-earth mineral containing up to 30 wt. % UO 2 , 9 wt.…”

Section: Chemical Durabilitymentioning

confidence: 99%

Nuclear waste disposal—pyrochlore (A2B2O7): Nuclear waste form for the immobilization of plutonium and “minor” actinides

Ewing

Weber

Lian

2004

Journal of Applied Physics

1,008

723

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During the past half-century, the nuclear fuel cycle has generated approximately 1400 metric tons of plutonium and substantial quantities of the ''minor'' actinides, such as Np, Am, and Cm. The successful disposition of these actinides has an important impact on the strategy for developing advanced nuclear fuel cycles, weapons proliferation, and the geologic disposal of high-level radioactive waste. During the last decade, there has been substantial interest in the use of the isometric pyrochlore structure-type, A 2 B 2 O 7 , for the immobilization of actinides. Most of the interest has focused on titanate-pyrochlore because of its chemical durability; however, these compositions experience a radiation-induced transition from the crystalline-to-aperiodic state due to radiation damage from the alpha-decay of actinides. Depending on the actinide concentration, the titanate pyrochlore will become amorphous in less than 1000 years of storage. Recently, systematic ion beam irradiations of a variety of pyrochlore compositions has revealed that many zirconate pyrochlores do not become amorphous, but remain crystalline as a defect fluorite structure-type due to disordering of the A-and B-site cations. The zirconate pyrochlores will remain crystalline even to very high doses, greater than 100 displacements per atom. Systematic experimental studies of actinide-doped and ion beam-irradiated pyrochlore, analyses of natural U-and Th-bearing pyrochlore, and simulations of the energetics of the disordering process now provide a rather detailed understanding of the structural and chemical controls on the response of pyrochlore to radiation. These results provide a solid basis for predicting the behavior and durability of pyrochlore used to immobilize plutonium.

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Uranium as a possible criterion for the hydro-chemical alteration of betafite

et al. 2018

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

Cited by 4 publications

References 9 publications

Low-temperature aqueous alteration of crystalline pyrochlore: correspondence between nature and experiment

Low-temperature aqueous alteration of crystalline pyrochlore: correspondence between nature and experiment

Nuclear waste disposal—pyrochlore (A2B2O7): Nuclear waste form for the immobilization of plutonium and “minor” actinides

Uranium as a possible criterion for the hydro-chemical alteration of betafite

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