This presentation gives on overview of the complex thermo-hydro-mechanical and chemical (THMC) processes occurring upon the disposal of heat-producing high-level radioactive waste in geologic repositories. Here, we present initial investigations of repository behavior exposed to strongly elevated temperatures.

An experimentally deformed sample of Opalinus Clay (OPA), which is being considered as host rock for nuclear waste in Switzerland, was studied by electron microscopy to image deformation microstructures. Deformation localised by forming micrometre-thick fractures. Deformation zones show dilatant micro-cracking, granular flow and bending grains, and pore collapse. Our model, with three different stages of damage accumulation, illustrates microstructural deformation in a compressed OPA sample.

The success of the geological storage of carbon dioxide is linked to the availability at depth of a capable reservoir and an impermeable caprock. The sealing capacity of the caprock is a key parameter for long-term CO₂ containment. Faults crosscutting the caprock might represent preferential pathways for CO₂ to escape. A decameter-scale experiment on injection in a fault, monitored by an integrated network of multiparamerter sensors, sheds light on the mobility of fluids within the fault.