Leaching of zirconolite ceramics under H+ and He2+ irradiation

Abstract

Zirconolite is a candidate host material for conditioning minor tri- and tetra-valent actinides arising from enhanced nuclear spent fuel reprocessing and partitioning, which can be disposed in a geological repository for nuclear waste. Its chemical durability has been studied here under charged particle-induced radiolysis (He2+ and proton external beams) to identify possible effects on dissolution rates and mechanisms in pure water. Two geometries of experiments have been used to evaluate the influence of the following parameters: solid irradiation, Linear Energy Transfer (LET) at the interface and total deposited energy. Preliminary results on the elemental releases due to the enhanced dissolution of the zirconolite surface during charged particle-induced irradiation are first presented. Then, we focus on H2O2 production which is one of the major molecular species, created under water radiolysis, and likely to interact with the zirconolite surface. In presence of zirconolite, first results indicate an apparent consumption of the radiolytic hydrogen peroxide or its precursors compared to the production in pure water calculated from the primary yield G H2O2 . The measured H2O2 concentration varies linearly with the total deposited energy in water over the irradiation duration (between 1 h and 6 h) and in the conditions of our experiments. Moreover, the H2O2 concentration decreases when the local density of the deposited energy close to the interface increases. Thus, we suggest that the mechanism(s) leading to the consumption of H2O2 or its precursors involve zirconolite surface reactions.