The methodology followed in Belgium to investigate the compatibility with geological disposal of Eurobitum bituminized intermediate-level radioactive waste

In Belgium, Eurobitum bituminized radioactive waste containing large amounts of NaNO3 is to be disposed of in an underground repository in a geologically stable clay formation. The Boom Clay is studied as a potential host formation because of its favourable properties to delay the migration of the leached radionuclides to the biosphere. The emplacement of Eurobitum will induce multiple processes that could have a significant effect on the key properties of the clay. Also because several of these processes are interdependent, the study of the compatibility of Eurobitum with geological disposal is complex. To better structure the research and to identify possible knowledge gaps, the Belgian Radioactive Waste Management Agency ONDRAF/NIRAS developed the safety functions and safety statements approach. In this paper, this methodology is explained, with reference to the disposal of Eurobitum. Experimental results obtained at the Belgian Nuclear Research Centre SCK•CEN are presented and discussed in the light of the safety functions and safety statements approach. The importance of the interdependence of the processes is highlighted. Special attention is given to the evolution of the disposal design as a result of the improved understanding of key processes.