THM coupling sensitivity analysis in geological nuclear waste storage

A deep geological repository involving a multi-barrier system constitutes one of the most promising options to isolate high-level radioactive waste from the human environment. In order to certify the efficiency of waste isolation, it is essential to understand the behaviour of the confining geomaterials under a variety of environmental conditions. The efficiency of an Engineered Barrier System (EBS) is largely based on the complex behaviour of bentonite. To contribute to a better understanding of the processes involved in the EBS, a case study for sensitivity analysis has been defined and is studied using a thermo-hydro-mechanical (THM) finite element approach including a consistent thermo-plastic constitutive model for unsaturated soils. The model also features a coupled THM approach of the water retention curve. Various couplings were studied separately and in combination in order to determine the significance of each. The same principle is applied to physical phenomena such as vapour diffusion. This study clearly highlights the effects that need to be taken into consideration for a correct assessment of EBS behaviour.