The Leaching Behavior of Bituminized Radioactive Waste in the Geologic Disposal Conditions of the Boom Clay Formation

Abstract

ABSTRACTAs part of the evaluation of the safety of geologic disposal, the leaching behaviour of two types of bituminized radioactive waste (Eurobitum and CEA bitumen) has been studied as a function of temperature, pressure, leachant composition and bitumen matrix type. Inactive and active bitumen samples were brought into contact with two test media, simulating the geologic disposal environment of the Boom clay formation. At contact with these media, the samples swelled and soluble salts and radionucides were leached. It was found that the leach rate is influenced by temperature, the leachant composition, and the physical characteristics of the bitumen matrix. The release of nitrate is interpreted as a diffusion controlled process, which can however be disturbed by crack formation. The leaching of 60Co, 90Sr, and total β is diffusion controlled. Low leach rates were measured for Pu and Am: the release of Pu and Am is limited by their solubility in the leachant. Pu and Am are preferentially sorbed to the Boom clay, the test container or the bitumen. The leached mobile Pu and Am concentrations are of the order of 10−10 to 1013 M at 23°C. The results of this study suggest that the integrity of bituminized waste packages is seriously affected due to the leaching of soluble salts: a full-size 220 litre Eurobitum drum is predicted to be depleted in NaNO3 in less than 20,000 years.