Elke Bohnert

Effects of hydrogen and bromide on the corrosion of spent nuclear fuel and γ-irradiated UO2(s) in NaCl brine

Abstract Radiation induced UO2(s) corrosion is studied at elevated hydrogen pressure in NaCl brine containing traces of bromide. Release of Sr, Cs, Tc and actinides was measured in corrosion experiments with spent nuclear fuel pellets in presence of 10−2 mol H2 (kg H2O)−1, and 10−4 and 10−3 mol Br− (kg H2O)−1, respectively. For comparison, depleted UO2(s) pellets were γ-irradiated in NaCl brine at 10−3 mol H2 (kg H2O)−1 and 0−10−4 mol Br− (kg H2O)−1, respectively. In the γ-radiolysis experiments a significant increase in the yield of radiolytic products due to Br− is observed. Both, in the γ-radiolysis experiment with Br− and in that without Br−, the UO2(s) sample was oxidized, and the concentration of dissolved uranium was controlled by precipitation of meta-schoepite and clarkeite. In the spent nuclear fuel corrosion experiment under H2 overpressure, aqueous concentrations of Tc and Np were in the range of solubilities of Tc(IV) and Np(IV) hydroxides, whereas measured U concentrations were between solubilities of U(VI) and U(IV) phases. The release rate of Sr was significantly increased in the presence of Br− traces. Results of the complementary spent nuclear fuel corrosion and γ-radiolysis experiments allow the conclusion that Br− traces reduce significantly the protective hydrogen effect with respect to the release of certain radionuclides and the yield of radiolytic products.