Effect of Hydrogen on the Dissolution of Uranium Dioxide in Peroxide-Containing Environments

Abstract

The ability of hydrogen (H2) to scavenge hydroxy radicals (OH•) created by the dissociation of hydrogen peroxide (H2O2) on the surface of uranium dioxide (UIVO2) has been studied in a chloride/bicarbonate (pH = 9.5) solution. The oxidation/reduction of the oxide surface was monitored by measuring the corrosion potential as a function of time in this solution, containing various concentrations of H2O2 sparged with either Ar or an Ar/H2 mixture. The surface oxidation was subsequently determined using X-ray photoelectron spectroscopy. In the absence of H2, the peroxide oxidized the surface to UIV 1–2xUV 2xO2+x with x varying with H2O2 concentration and eventually achieved a composition of UIV 0.34UV 0.66O2.33. At this surface composition, the surface becomes unstable with respect to dissolution, but the dominant reaction is H2O2 decomposition. In the presence of H2, the initial oxidation of the UIVO2 when H2O2 was added was reversed by the ability of H2 to scavenge the OH• with the H• radicals formed. This led to a reduction of the oxidized surface. The efficiency of this process is determined by the relative concentrations of H2O2 and H2.