Modelling bentonite re-saturation with an advanced COMSOL-VIPER code: a synthesis of developments

Bentonite is foreseen as a geotechnical barrier material in deep geological repositories for radioactive waste. Understanding and modeling its hydration behavior is crucial for the long-term safety assessment of the geotechnical barrier. This paper synthesizes recent advancements in the development of the VIPER-based thermo-hydraulic modeling approach for the resaturation of compacted bentonite under confined conditions. Beginning with an alternative equation-based implementation in COMSOL Multiphysics®, the approach was successively advanced to be applicable to higher dimensions, enhanced by a dedicated COMSOL custom interface, and validated under both isothermal and non-isothermal conditions. Further development introduced a Neumann boundary condition to simulate realistic limited water supply rates (LWSR), representing host-rock controlled inflow as known from several potential host rocks. Together, these works demonstrate a comprehensive evolution toward a robust, scalable, and realistic COMSOL-VIPER simulation framework for bentonite saturation processes. The paper encompasses the theoretical foundations, model developments, boundary condition innovations, and validation against experiments including the FEBEX in-situ test.