THCM numerical simulations of the engineered barrier system for radioactive waste disposal

Abstract

The final disposal of high-level radioactive waste in geological repositories envisages an engineered barrier system with a bentonite buffer, which will be subjected to strongly coupled thermal, hydrodynamic, geochemical and mechanical (THCM) processes. This paper presents coupled THCM numerical simulations of laboratory and in situ tests performed with compacted Full-scale Engineered Barrier Experiment (Febex) bentonite having different space and time scales. The simulations of the heating and hydration tests fit the measured temperature, water content and water intake data and reproduce the trends of the geochemical data. Although simulation results of the tests display similar trends, they show differences due to geometry and initial and confining conditions. The changes in porosity due to mineral dissolution/precipitation are not relevant in these tests but become relevant in long-term simulations, which show that the precipitation of corrosion products reduces significantly the porosity of the bentonite near the canister and causes pore clogging. The thickness of the bentonite alteration band is simulated to be smaller than 7 cm after 1 Ma.