Clays in radioactive waste disposal

Clays and argillites are considered in some countries as possible host rocks for nuclear waste disposal at great depth. The use of compacted swelling clays as engineered barriers is also considered within the framework of the multi-barrier concept. In relation to these concepts, various research programs have been conducted to assess the thermo-hydro-mechanical properties of radioactive waste disposal at great depth. After introducing the concepts of waste isolation developed in Belgium, France and Switzerland, the paper describes the retention and transfer properties of engineered barriers made up of compacted swelling clays in relation to microstructure features. Some features of the thermo-mechanical behaviors of three possible geological barriers, namely Boom clay (Belgium), Callovo-Oxfordian clay (France) and Opalinus clay (Switzerland), are then described, including the retention and transfer properties, volume change behavior, shear strength and thermal aspects.