A REVIEW OF THE ANDRAS RESEARCH PROGRAMS ON THE THERMOHYDROMECHANICALBEHAVIOR OF CLAY IN CONNECTION WITH THE RADIOACTIVE-WASTE DISPOSAL PROJECT IN DEEP GEOLOGICAL FORMATIONS

This paper presents the different studies realized or launched by ANDR A in collaboration with different contractors, including laboratory an d in situ experiments, as well as physical and numerical modelizations , related to the thermo-hydromechanical behavior of clays and clayey m aterials. Clays are considered as both potential host rocks and sealin g materials, among other geological formations and materials, respecti vely. The study of a high-level or long-lived nuclear waste disposal c oncept is necessarily a step-by-step procedure, with two main objectiv es: on one hand, ensuring a good disposal design, including feasibilit y of the vaults and their stability during the operating phase with th e eventual continuation of the phase of waste retrievability, i.e. on a long period of time not shorter than one hundred years. On the other hand, the objective is to preserve the long-term clay properties with regard to radionuclide behavior, in particular those properties which influence their containment capacity. Swelling clays as an engineered barrier material have been considered by ANDRA for a long time. Buffe r material as an interface between the nuclear waste packages and the geological barrier and tight core of dams in drifts and shafts are the two types of constructions for which the clay conditioning and perfor mance have been investigated. In both of these applications, the under standing of the THM behavior of the swelling clay is required. In the first case the THM load parameters are much more severe and the geoche mical imbalances are of greater consequences. R & D programmes are nec essarily integrated into the design process of the disposal concept. T he results will allow selection between technical solutions estimated as valuable candidates for validation within the project duration, i.e . 13 years, and those solutions which cannot be. In return the design process indicates what are the more profitable axis for the future R & D efforts.