Surface and electrochemical controls on UO2 dissolution under anoxic conditions

JOURNAL OF NUCLEAR MATERIALS

卷:520

Article

Tan, Beng Thye¹  Popel, Aleksej J.¹  Wilbraham, Richard J.²  Day, Jason¹  Lampronti, Giulio, I¹  Boxall, Colin²  Farnan, Ian¹ 

[1] Univ Cambridge, Dept Earth Sci, Downing St, Cambridge CB2 3EQ, England

[2] Univ Lancaster, Engn Dept, Lloyds Register Fdn Ctr Nucl Engn, Bailrigg LA1 4YW, Lancs, England

关键词: UO2;    Anoxic dissolution;    Secondary phases;    Surface alteration;    Nucleation;    Geological disposal;   

DOI  :  10.1016/j.jnucmat.2019.03.047

来源: Elsevier

【 摘 要 】

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 (similar to 500 nm) of homogenous uranium-containing precipitates of similar to 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. (C) 2019 Elsevier B.V. All rights reserved.

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