Rights statement: This is the author’s version of a work that was accepted for publication in Journal of Nuclear Materials. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Nuclear Materials, 520, 2019 DOI: 10.1016/j.jnucmat.2019.03.047
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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Surface and electrochemical controls on UO2 dissolution under anoxic conditions
AU - Tan, Beng Thye
AU - Popel, Aleksej
AU - Wilbraham, Richard James
AU - Day, Jason
AU - Lampronti, Giulio
AU - Boxall, Colin
AU - Farnan, Ian
N1 - This is the author’s version of a work that was accepted for publication in Journal of Nuclear Materials. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Nuclear Materials, 520, 2019 DOI: 10.1016/j.jnucmat.2019.03.047
PY - 2019/7/1
Y1 - 2019/7/1
N2 - The escape of radionuclides from underground spent nuclear fuel disposal facilities will likely result from anoxic dissolution of spent nuclear fuel by intruding groundwater. Anoxic dissolution of various forms of uranium dioxide (UO2), namely bulk pellet, powder and thin film, has been investigated. Long-duration static batch dissolution experiments were designed to investigate the release of uranium ions in deionized water and any surface chemistry that may occur on the UO2 surface. The dissolved uranium concentration for anoxic dissolution of nearly stoichiometric UO2 was found to be of the order of 10-9 mol/l for the three different sample types. Further, clusters (~500 nm) of homogeneous uranium-containing precipitates of ~20-100 nm grains were observed in thin film dissolution experiments. Such a low solubility of UO2 across sample types and the observation of secondary phases in deionized water suggest that anoxic UO2 dissolution does not only occur through a U(IV)(solid) to U(VI)(aqueous) process. Thus, we propose that dissolution of uranium under anoxic repository conditions may also proceed via U(IV)(solid) to U(IV)(aqueous), with subsequent U(IV)(precipitates) in a less defective form. Quantitative analysis of surface-sensitive EBSD diffractograms was conducted to elucidate lattice-mismatch induced cracks observed in UO2 thin film studies. Variable temperature anoxic dissolution was conducted, and no increased uranium concentration was observed in elevated temperatures.
AB - The escape of radionuclides from underground spent nuclear fuel disposal facilities will likely result from anoxic dissolution of spent nuclear fuel by intruding groundwater. Anoxic dissolution of various forms of uranium dioxide (UO2), namely bulk pellet, powder and thin film, has been investigated. Long-duration static batch dissolution experiments were designed to investigate the release of uranium ions in deionized water and any surface chemistry that may occur on the UO2 surface. The dissolved uranium concentration for anoxic dissolution of nearly stoichiometric UO2 was found to be of the order of 10-9 mol/l for the three different sample types. Further, clusters (~500 nm) of homogeneous uranium-containing precipitates of ~20-100 nm grains were observed in thin film dissolution experiments. Such a low solubility of UO2 across sample types and the observation of secondary phases in deionized water suggest that anoxic UO2 dissolution does not only occur through a U(IV)(solid) to U(VI)(aqueous) process. Thus, we propose that dissolution of uranium under anoxic repository conditions may also proceed via U(IV)(solid) to U(IV)(aqueous), with subsequent U(IV)(precipitates) in a less defective form. Quantitative analysis of surface-sensitive EBSD diffractograms was conducted to elucidate lattice-mismatch induced cracks observed in UO2 thin film studies. Variable temperature anoxic dissolution was conducted, and no increased uranium concentration was observed in elevated temperatures.
KW - Anoxic dissolution
KW - Geological disposal
KW - Nucleation
KW - Secondary phases
KW - Surface alteration
KW - UO 2
KW - Deionized water
KW - Groundwater
KW - Lattice mismatch
KW - Nuclear fuels
KW - Surface chemistry
KW - Thin films
KW - Uranium dioxide
KW - Electrochemical control
KW - Elevated temperature
KW - Geological disposals
KW - Secondary phasis
KW - Spent nuclear fuels
KW - Uranium concentration
KW - Variable temperature
KW - Dissolution
U2 - 10.1016/j.jnucmat.2019.03.047
DO - 10.1016/j.jnucmat.2019.03.047
M3 - Journal article
VL - 520
SP - 41
EP - 55
JO - Journal of Nuclear Materials
JF - Journal of Nuclear Materials
SN - 0022-3115
ER -