Characterization of fractures as water-conducting features in shales. Studies at the Tournemine test site.

Cabrera, J.; De Windt, L.; Moreau-Le Golvan, Y.; Boisson, J.Y. actes du congrès "Characterisation of water-conducting features and their representation in models of radionuclide migration" Barcelona (Spain) 10-12 Jun 1998; OECD-NEA 1999 379 p. p. 295-296

The Institute of Protection and Nuclear Safety (irsn) develops research programs concerning the confining properties of an argillaceous formation at the irsn Tournemine site (Aveyron, France). This well-consolidated argillaceous media of Jurassic age presents a very low permeability. Water circulations seem to be of very minor importance in the shales, with a main diffusive component for transport. However, recent field studies, from radial boreholes around the Tournemine tunnel and two gallery excavations in the argilites, document a fractured zone of tectonic origin associated with a main fault. It is an interesting case to analyze the fractures and faults in argillaceous media and their past present and future roles in possible fluid transfers. Fracture investigation as water-conducting features for transport is supported by different approaches: structural and tectonics analyses, interpretation of the present water circulation and chemistry, characterisation of the circulation and chemistry of the paleo-fluids through studies of the fracture mineral fillings, and experiments on sorption of radionuclides performed at laboratory.