Reactivity of H2O2 towards different UO2-based materials: The relative impact of radiolysis products revisited

The reactivity of doped UO ₂ such as SIMFUEL towards H ₂O ₂ has been shown to be fairly similar to that of pure UO ₂. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H ₂O ₂ is significantly lower for doped UO ₂. In this work we have studied the mechanistic difference between SIMFUEL and pure UO ₂. H ₂O ₂ can be catalytically decomposed on UO ₂ in competition with the redox process in which U(IV) is oxidized. The latter process leads to the dissolution of oxidized uranium. The first step in the catalytic decomposition is the formation of hydroxyl radicals. The presence of hydroxyl radicals was verified using Tris buffer as a radical scavenger. For both UO ₂ and SIMFUEL pellets, significant amounts of hydroxyl radicals were formed. The results also show that the difference in dissolution yield between the two materials can mainly be attributed to differences in the redox reactivity. Based on this, the rate constants for electron transfer were revised and the relative impact of the radiolytic oxidants in oxidative dissolution of UO ₂ and SIMFUEL pellets were calculated. The impact of H ₂O ₂ is shown to be slightly reduced.