Thermo-hydro-mechanical behavior of clay rock for deep geological disposal of high-level radioactive waste

In the context of deep geological disposal of radioactive waste in clay formations, the thermo-hydro-mechanical (THM) behavior of the indurated Callovo-Oxfordian and Opalinus clay rocks has been extensively investigated in our laboratory under repository relevant conditions: (1) rock stress covering the range from the lithostatic state to redistributed levels after excavation; (2) variation of the humidity in the openings due to ventilation as well as hydraulic drained and undrained boundary conditions; (3) gas generation from corrosion of metallic components within repositories; and (4) thermal loading from high-level radioactive waste up to the designed maximum temperature of 90 °C and even beyond to 150 °C. Various important aspects concerning the long-term barrier functions of the clay host rocks have been studied: (1) fundamental concept for effective stress in the porous clay-water system; (2) stress-driven deformation and damage as well as resulting permeability changes; (3) moisture influences on mechanical properties; (4) self-sealing of fractures under mechanical load and swelling/slaking of clay minerals upon water uptake; (5) gas migration in fractured and resealed claystones; and (6) thermal impact on the hydro-mechanical behavior and properties. Major findings from the investigations are summarized in this paper.