A review of the ANDRAʹs research programmes on the thermo-hydromechanical behavior of clay in connection with the radioactive waste disposal project in deep geological formations

This paper presents the different studies realized or launched by ANDRA in collaboration with different contractors, including laboratory and in situ experiments, as well as physical and numerical modelizations, related to the thermo-hydromechanical behavior of clays and clayey materials. Clays are considered as both potential host rocks and sealing materials, among other geological formations and materials, respectively. udy of a high-level or long-lived nuclear waste disposal concept is necessarily a step-by-step procedure, with two main objectives: on one hand, ensuring a good disposal design, including feasibility of the vaults and their stability during the operating phase with the 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. ng clays as an engineered barrier material have been considered by ANDRA for a long time. Buffer 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 performance have been investigated. In both of these applications, the understanding of the THM behavior of the swelling clay is required. In the first case the THM load parameters are much more severe and the geochemical imbalances are of greater consequences. ; D programmes are necessarily integrated into the design process of the disposal concept. The 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.