PNNL

Abstract

We have characterized significant quantities of uranyl peroxide phases on commercial spent nuclear fuel (CSNF) samples formed under immersion conditions over a two-year-period. Milligrams of corroded fuel aggregates were observed at the air water interface in each sample. The bulk fuel and the suspended material were examined by SEM, EDX, and XRD and were found to contain studtite and metastudtite, respectively. The reason for the partitioning of the two phases is unclear at this time. SEM micrographs of the bulk powders indicate extensive corrosion. Indeed, under the conditions that developed in the sample containers, dissolution of the fuel was in some cases as severe as a purposeful etching of the surface with concentrated nitric acid. Radiochemical analyses of the leachates and the aggregate materials indicate that dissolution of the fuel surface by hydrogen peroxide may have resulted in rapid release and increased solubility of radiocontaminants in the fuel matrix.