The effect of Y2O3 on the dynamics of oxidative dissolution of UO2

In this work, we have studied the impact of Y₂O₃ on the kinetics of oxidative dissolution of UO₂ and the consumption of H₂O₂. The second order kinetics of catalytic consumption of H₂O₂ on Y₂O₃ was investigated in aqueous Y₂O₃ powder suspensions by varying the solid surface area to solution volume ratio. The resulting second order rate constant is 10⁻⁸ m s⁻¹, which is of the same magnitude as for the reaction between H₂O₂ and UO₂. Powder experiments with mixtures of UO₂ and Y₂O₃ show that Y₂O₃ has no effect on the oxidative dissolution of UO₂, whereas the consumption of H₂O₂ seems to be slightly slower in the presence of Y₂O₃ and H₂ respectively. UO₂ pellets with solid inclusions of Y₂O₃ show a decrease in oxidative dissolution by a factor of 3.3 and 5.3 under inert and hydrogen atmosphere, respectively. The rate of H₂O₂ consumption is similar for all cases and is well in line with kinetic data from powder experiments. The effects of H₂ and Y₂O₃ on the oxidative dissolution of UO₂ under gamma irradiation are similar to those found in experiments with H₂O₂. No significant difference in dissolution between inert and reducing atmosphere can be observed for pure UO₂.