Repositories for high level waste in argillaceous formations - key geologic questions

Research and demonstration studies for the final disposal of high-level and long-lived radioactive waste are performed in several countries. Argillaceous formations, ranging from plastic clays to indurated clay formations or shale, are under consideration for hosting radioactive waste or spent fuel. Rather detailed characterization programs from underground infrastructures (URL, mine, tunnel) have already been developed for several argillaceous formations such as the Boom Clay (Rupelian) in Belgium, the Opalinus Clay (Aalenian) in Switzerland, the Boda Claystone (Upper Permian) in Hungary and the Tounemire Claystone (Toarcian/Domerian) in France. Other potential formations have been considered and/or are being investigated in Canada, France, Germany, Italy, Japan, the United Kingdom and the United States. The key geologic questions are addressed and the significance of the values of some parameters and processes on the feasibility and safety aspects of a global repository system is reviewed.