Radiation Induced Dissolution of UO2

Abstract

ABSTRACTIn order to be able to model the effect of water radiolysis on the dissolution of fuel in the disposal vault it is essential to study the oxidation mechanism. Radiolysis of water produces radicals and molecules, amongst them the oxidizing species H2O2 and OH radicals, and, in aerated solutions, O2- as well. These species are probably responsible for the oxidation and dissolution of UO2 observed in a number of experiments. In the present investigation the effect of the oxidizing species has been studied separately using suitable scavengers. A polished specimen of UO2 was immersed in water and irradiated at ambient temperature with Co-60 gamma radiation. After irradiation the amount of uranium which had dissolved, or deposited elsewhere than the sample surface, was measured, and the oxidation of the surface was determined, using ESCA and SIMS. In 50 mM H2O2 (without irradiation) the corrosion rate was 5±3 μg.cm−2d−1 after 6 d exposure at pH 8. Corresponding rates for oxidation by O2- and OH radicals were about 3 μg.cm−2d−1, (dose rate 600±90 Gy/h.)