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

The reactivity of doped UO2 such as SIMFUEL towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. In this work we have studied the mechanistic difference between SIMFUEL and pure UO2. H2O2 can be catalytically decomposed on UO2 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 UO2 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 UO2 and SIMFUEL pellets were calculated. The impact of H2O2 is shown to be slightly reduced.

► The mechanism for the reaction between H2O2 and UO2-based materials was studied.
► H2O2 can be catalytically decomposed on UO2 or oxidize U(IV) to U(VI).
► The catalytic decomposition was shown to involve the formation of hydroxyl radicals.
► Doping of UO2 increases the relative importance of catalytic H2O2 decomposition.
► This can be attributed to effects of dopants on the redox reactivity of UO2-materials.