Self-sealing capacity of argillite samples

Abstract

Many countries are currently facing the issue of finding a proper solution to store radioactive wastes coming from nuclear energy production plants. The possibility to store them in underground tunnels is largely considered and investigated. In France, Andra (Agence Nationale pour la gestion des Déchets Radioactifs) selected the Callovo-Oxfordian rock clay (COx) situated in the Meuse/Haute Marne site (France) between 400 and 600 m depth as possible host rock deposit. The excavation of the storage tunnels is expected to create a fractured zone around galleries. However, the factures will be then gradually re-saturated by the underground water coming from the surrounding rock mass and the fractures are expected to self-seal in contact with water, thanks to the swelling potential of COx. The capacity of self-sealing of COx, i.e. closing of fractures after water contact and possibly restoring of hydraulic permeability, is thus of primary interest for the safety of the storage system with respect to water, gas and solutes transport. In the work presented in this paper, the self-sealing behaviour of the COx argillite was investigated through x-ray tomography. The tested samples show significantly different responses depending on the zone where they have been collected on site. The results of mineralogical analyses (x-ray diffraction) are used to understand the observed phenomena.