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

Deep argillaceous formations are potential host media for radioactive waste disposal. The French institute of Protection and Nuclear Safety (ZPSN) 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 o f the consolidated argillaceous medium, diffusive and convective transport; rock and water chemistry and long-term behaviour of the host rock. Investi gations conclude that fluid circulations in the unperturbed matrix are very slow. However, past tectonic events have induced fractures which might acc elerate 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 clea r 'Excavation-Damaged Zone' (EDZ), with large fractures which might drain w ater rather quickly over long distances. The mechanical, hydraulic and phys ico-chemical properties of the EDZ are being investigated. The present pape r summarizes the results obtained so far at Tournemire, and the current res earch orientations. (C) 1998 Elsevier Science B.V. All rights reserved.