The relative impact of radiolysis products in radiation induced oxidative dissolution of UO2

The relative impact of radiolysis products in radiation induced oxidative dissolution of UO ₂ has been studied experimentally. The experiments were performed by γ-irradiating an aqueous solution containing HCO 3 - and a UO ₂-pellet. The U(VI) concentration in the solution was measured as a function of irradiation time. The aqueous solution was saturated with Ar, N ₂O, N ₂O/O ₂ (80/20), air and O ₂ in order to vary the conditions and the initial oxidant yields. The measured rate of oxidation was significantly higher for the O ₂ - and air saturated systems compared to the other systems. Using oxidant concentrations derived from numerical simulations of the corresponding homogeneous systems and previously determined rate constants for oxidation of UO ₂ , the relative trend in rate of oxidation in the different systems was reproduced. The results from the simulations were also used to estimate the relative impact of the oxidative radiolysis products as a function of irradiation time, both for γ- and α-irradiated systems. For γ-irradiated systems saturated with Ar, air or O ₂, the most important oxidant is H ₂O ₂ while for N ₂O- and N ₂O/O ₂-saturated systems the most important oxidant is CO 3 - . For α-irradiated systems the most important oxidant was found to be H ₂O ₂.