Surface and electrochemical controls on UO2 dissolution under anoxic conditions

Tan, Beng Thye and Popel, Aleksej and Wilbraham, Richard James and Day, Jason and Lampronti, Giulio and Boxall, Colin and Farnan, Ian (2019) Surface and electrochemical controls on UO2 dissolution under anoxic conditions. Journal of Nuclear Materials, 520. pp. 41-55. ISSN 0022-3115

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Abstract

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.

Item Type:
Journal Article
Journal or Publication Title:
Journal of Nuclear Materials
Additional Information:
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
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/3100/3106
Subjects:
ID Code:
132318
Deposited By:
Deposited On:
28 Mar 2019 13:35
Refereed?:
Yes
Published?:
Published
Last Modified:
01 Oct 2020 03:08