Spent fuel UO2 matrix alteration in aqueous media under oxidizing conditions
Résumé
For underwater interim storage of spent UOX fuel assemblies it is necessary to consider the incidental and unusual scenario starting from the occurrence of a breach in the cladding and the presence of water. On this assumption it is important to compile data on the reactivity of the spent fuel matrix under highly oxidizing conditions and subjected to a mixed * and ** radiation field. Data such as the UO2 fuel matrix alteration rate or the nature of the precipitating secondary phases are important for modeling the behavior of a failed rod in water under incidental scenario, and especially the cladding behavior during interim storage (opening of a rod by enlargement of a defect due to secondary phase precipitation, contamination level in the pool water, etc.). Various spent fuel leaching experiments conducted at different degrees of oxidizing conditions and of accessibility of species at the reaction interface are discussed. The results indicate that despite highly variable oxidizing conditions (presence of an external * irradiation source, addition of H2O2, aerated water) the spent fuel matrix alteration determined from the release of tracer elements such as Cs and Sr is always the same. Conversely, allowing for the alteration conditions (no solution renewal and no complexants), the uranium concentrations in solution do indeed depend on the redox conditions as does the nature of the secondary phases liable to precipitate.