Kinetic Effects of H 2 O 2 Speciation on the Overall Peroxide Consumption at UO 2 -Water Interfaces.

The interfacial radiation chemistry of UO 2 is of key importance in the development of models to predict the corrosion rate of spent nuclear fuel in contact with groundwater. Here, the oxidative dissolution of UO 2 induced by radiolytically produced H 2 O 2 is of particular importance. The difficulty of fitting experimental data to simple first-order kinetics suggests that additional factors need to be considered when describing the surface reaction between H 2 O 2 and UO 2 . It has been known for some time that UO 2 2+ forms stable uranyl peroxo-carbonato complexes in water containing H 2 O 2 and HCO 3 - /CO 3 2- , yet this concept has largely been overlooked in studies where the oxidative dissolution of UO 2 is considered. In this work, we show that uranyl peroxo-carbonato complexes display little to no reactivity toward the solid UO 2 surface in 10 mM bicarbonate solution (pH 8-10). The rate of peroxide consumption and UO 2 2+ dissolution will thus depend on the UO 2 2+ concentration and becomes limited by the free H 2 O 2 fraction. The rate of peroxide consumption and the subsequent UO 2 2+ dissolution can be accurately predicted based on the first-order kinetics with respect to free H 2 O 2 , taking the initial H 2 O 2 surface coverage into account.