THM numerical modelling of the excavation damage zone in nuclear waste disposal

The PhD thesis focuses on the effect of temperature on the THM modelling in near and far field, with the objective of developing the thermal-mechanical model and numerical application.

The current studied solution for the long-term management of long-lived high activity nuclear wastes is the geological disposal in deep rock layers. In Europe, the host rocks considered for the nuclear disposal are mainly clay rock and granite. Among the remaining issues under investigation, the characterization of in-situ THM behavior of the clay host rock is significant for the design of the underground nuclear waste disposal facility and for the long-term safety.

The heat generated by the radioactive waste must not affect the favorable properties of clay host rock for containment, especially its transport properties. In the near field characterized by an excavation damaged zone (EDZ), due to the discrepancy of thermal expansion between water and clay rock, over-pressure of pore water could induce fracture re-opening or propagation, altering the permeability. In the far field, the zone located half-way between two parallel galleries will be subjected to the thermal loading from both sides. Depending on the distance between the cells and the intensity of the thermal load, this could induce tensile or even shear failure and/or reactivate old fractures/faults.

Thus, the main objective of the thesis is to improve the knowledge of the THM behavior of clay host rocks to help optimize the repository design.