Thermo-hydro-mechanical responses of a high-level radioactive waste repository: Effects of short- and long-term nonlinear behavior of the host rock

This paper aims to model the thermo-hydro-mechanical (THM) responses of a high-level waste (HLW) repository to the heat released from the waste package by considering short- and long-term nonlinear behavior (damage, plasticity, creep) of the host rock. This results from a benchmark exercise involving three modelling teams on the French HLW concept disposal. This work focuses only on the thermo-mechanical pressurization of the host rock. Two representative constitutive models are considered to describe the behavior of the host rock. The first one consists in an anisotropic elasto-plastic-creep model, including stiffness and strength anisotropy. The second model is a double phase field model with both tensile and compressible damage mechanism, associated with plasticity and creep. Parameters of these two models are calibrated based on the data acquired from both laboratory tests on samples and field observation.

Comparisons between poro-elastic and non-linear simulations show that the short-term nonlinear behavior only affects the THM responses in the near field of the host rock, while creep leads to a decrease in fluid pressure build-up and stress in both the near and far fields. An unsaturated condition prescribed on the HLW cell wall before heating reduces the fluid pressure and stress within the host rock.