The oxidative dissolution of unirradiated UO2 by hydrogen peroxide as a function of pH

The dissolution of non-irradiated UO2 was studied as a function of both pH and hydrogen peroxide concentration (simulating radiolytic generated product). At acidic pH and a relatively low hydrogen peroxide concentration (10−5 mol dm−3), the UO2 dissolution rate decreases linearly with pH while at alkaline pH the dissolution rate increases linearly with pH. At higher H2O2 concentrations (10−3 mol dm−3) the dissolution rates are lower than the ones at 10−5 mol dm−3 H2O2, which has been attributed to the precipitation at these conditions of studtite (UO4 · 4H2O, which was identified by X-ray diffraction), together with the possibility of hydrogen peroxide decomposition. In the literature, spent fuel dissolution rates determined in the absence of carbonate fall in the H2O2 concentration range 5 × 10−7– 5 × 10−5 mol dm−3 according to our results, which is in agreement with H2O2 concentrations determined in spent fuel leaching experiments.