Radionuclide behaviour and geochemistry in Boom Clay within the framework of geological disposal of high-level waste

The Boom Clay (BC) formation represents the reference host rock for the geological disposal of high-level and long-lived radioactive waste (HLW) in Belgium. The Belgian concept (i.e. Supercontainer concept) for the geological disposal of HLW considers the installation of a multi-barrier repository system within the tertiary BC formation. This multi-barrier system typically comprises the natural barrier, provided by the host rock and its surroundings (aquifers, biosphere), as well as the engineered barrier system. Predicting the retention/migration behaviour of the safety relevant radionuclides over long time scales is the main aim of performance assessment (PA) calculations. A sound understanding of the underlying geochemical processes and mechanisms is prerequisite to derive consistent sets of parameters required for such calculations and safety evaluations. The lecture aims at giving an overview of the main research activities at SCK•CEN related to the radionuclide retention/migration behaviour, involving experimental studies, geochemical as well as transport modelling.