Combined effect of H2O2 and HCO3- on UO2(s) dissolution rates under anoxic conditions

Abstract

The influence of both hydrogen peroxide (H 2 O 2 ) and bicarbonate (HC0 3 -) on the dissolution of UO 2 has been studied in this work. Two different series of experiments have been carried out using a flow-through reactor. In the first series, the influence of H 2 O 2 concentration (between 10- 6 and 5 x 10- 4 mol dm -3 ) on the dissolution rate of U0 2 has been studied at a fixed bicarbonate concentration of 2 x 10 -3 mol dm -3 . An increase in the dissolution rate is observed as the concentration of hydrogen peroxide increases. In the second series, the influence of bicarbonate (between 10 -4 and 10 -2 mol dm -3 ) on the dissolution rate of U0 2 has been studied in the presence of a fixed hydrogen peroxide concentration (10 -4 mol dm -3 ). The main result was that UO 2 dissolution rates increased with bicarbonate concentration. From the experimental data, an oxidative dissolution model has been developed that can reproduce spent nuclear fuel dissolution rates obtained under relatively low oxygen concentrations. Under these conditions, the influence of radiolysis products, rather than 0 2 concentration, is expected to determine the oxidative dissolution rates of the fuel.