Deep geological disposal in argillaceous formations: studies at the Tournemire test site

Abstract Deep argillaceous formations are potential host media for radioactive waste disposal. The French Institute of Protection and Nuclear Safety (IPSN) is developing in situ studies concerning the confining properties of this kind of geological barrier at the Tournemire tunnel site (Aveyron, France). The past research programme covered physical and physico-chemical properties of the consolidated argillaceous medium, diffusive and convective transport; rock and water chemistry and long-term behaviour of the host rock. Investigations conclude that fluid circulations in the unperturbed matrix are very slow. However, past tectonic events have induced fractures which might accelerate these circulations. The hydraulic role of fractures in this type of rocks is poorly known. A detailed study of the role of these fractures is presently under way. Moreover, the 100-year old tunnel exhibits a very clear `Excavation-Damaged Zone' (EDZ), with large fractures which might drain water rather quickly over long distances. The mechanical, hydraulic and physico-chemical properties of the EDZ are being investigated. The present paper summarizes the results obtained so far at Tournemire, and the current research orientations.