Kinetic Effects of HO Speciation on the Overall Peroxide Consumption at UO-Water Interfaces.

The interfacial radiation chemistry of UO 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 induced by radiolytically produced HO 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 HO and UO. It has been known for some time that UO forms stable uranyl peroxo-carbonato complexes in water containing HO and HCO /CO , yet this concept has largely been overlooked in studies where the oxidative dissolution of UO is considered. In this work, we show that uranyl peroxo-carbonato complexes display little to no reactivity toward the solid UO surface in 10 mM bicarbonate solution (pH 8-10). The rate of peroxide consumption and UO dissolution will thus depend on the UO concentration and becomes limited by the free HO fraction. The rate of peroxide consumption and the subsequent UO dissolution can be accurately predicted based on the first-order kinetics with respect to free HO, taking the initial HO surface coverage into account.