Modelling the thermo-hydro-chemical behaviour of compacted bentonite for nuclear waste disposal

The long-term safety of nuclear waste repositories in crystalline rock rely to a large extent on the performance of the engineered barrier system to be place in the deposition holes and tunnels. In the KBS-3V repository design [1,2], this system includes a copper canister containing the waste and a buffer surrounding it made of compacted bentonite. In addition, a bentonite backfill will be placed in to seal the deposition tunnels. The long-term performance depends on a number of physical and chemical processes, involving high temperatures, slow water saturation, bentonite swelling, cation exchange, and dissolution/precipitation of accessory minerals and potentially the montmorillonite itself. In this contribution, focus is made on the thermo-hydro-geochemical processes having an impact on the long-term evolution of the system. A recently developed numerical framework to couple multiphysics and geochemistry is presented in which the mechanical coupling could be readily implemented, provided the underlying phenomena governing the interplay between mechanical deformations and chemical reactions are sufficiently well characterized. An interface coupling two existing software, Comsol Multiphysics and the geochemical simulator Phreeqc, has been recently developed to study problems where multiphysics and geochemistry canno