Leaching behaviour of UO2 containing α-emitting actinides

Abstract

After a few hundred years in a geologic repository, α-emissions will dominate the radiation field in and around spent nuclear fuel. In the event of a failure of the spent fuel container, the dissolution of the uranium dioxide matrix in contact with groundwater could be enhanced by α-radiolysis, which could create oxidizing conditions at the fuel surface. The radioactivity (hence the radiolysis) of the irradiated fuel available nowadays is characterized by strong β- and γ-contributions, which are not representative of aged fuel in a repository. A possible way to single out the effects of α-radiolysis on the dissolution behaviour of irradiated fuel is to study unirradiated UO2 doped with a short-lived α-emitter. UO2 containing ~0.1 and ~10 wt.% of 238PuO2 was fabricated and leached. Previous results of static (batch and sequential) leaching tests on monoliths at room temperature in demineralized water under anoxic atmosphere showed that the amounts of U released were higher in the case of UO2 containing 238Pu than in the case of undoped UO2. This work presents results of leaching experiments performed under similar conditions on materials of the same composition, but crushed to give samples with two different particle size distributions to investigate the effects of different surface areas. The U release data, normalized to the geometric surface area, showed enhanced U dissolution from α-doped UO2 also in the case of crushed materials, except for the initial release after 1 h of leaching. Under these experimental conditions, the concentration of U measured in the leachates for the two doped materials did not show a clear dependence on α-activity.