Oxidation and dissolution of nuclear fuel (UO2) by the products of the alpha radiolysis of water

Oxidation of UO2 nuclear fuel by the products of the alpha radiolysis of water has been measured as a function of strength of the alpha flux and solution pH (0.1 mol L-1 NaClO4, 3.5 &le pH &le 11) using electrochemical techniques. Corrosion potentials were measured using a thin-layer corrosion cell in which an alpha source was brought within 30 μm of a UO2 electrode. Oxidative dissolution (corrosion) rates were then calculated as a function of alpha dose rate from the steady-state values of the corrosion potential using an electrochemical model. The corrosion rate was found to increase with an increase in alpha dose rate and with a decrease in pH for values < 4. A procedure to predict the corrosion rate of used nuclear fuel in groundwater as a function of fuel cooling time is then described. As a consequence of the cell geometry used in corrosion potential measurements these predicted rates are appropriately applied to dissolution in cracks and fissures. The corrosion of fuel, supported solely by the alpha radiolysis of water, is predicted to be unimportant for CANDU reactor fuel with a burnup of 685 GJ/kg U for periods ≥ 600 a. However, for fuel with higher burnups, e.g., a typical PWR fuel (burnup 3888 GJ/kg U (45 MW d/kg U)), corrosion supported by the alpha radiolysis of water could be significant for time periods of approx. 2000 a. For periods greater than this (approx. 600 a (CANDU); approx. 2000 a (PWR)) the oxidative dissolution can be appropriately considered as a chemical as opposed to corrosion reaction.