In Belgium, EUROBITUM bituminized radioactive waste containing large amount of soluble salts (NaNO3) is to be disposed of in a final repository in a clay formation. Since the emplacement of the waste will induce many interdependent processes that could negatively affect the interesting radionuclide retarding properties of the clay, the study of the compatibility of EUROBITUM is very complex. To better structure the research and to identify possible knowledge gaps, NIRAS/ONDRAF, the Belgian Radioactive Waste Management Agency, developed the safety functions and safety statements approach. In this paper, we present the application of this approach for the case of EUROBITUM. The approach is illustrated with new and old results on water uptake, swelling, swelling pressure build-up, and ageing, obtained from tests performed in the laboratories of SCK•CEN, the Belgian Nuclear Research Centre.

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