CRIEPI and SKB cooperation report no.10. Numerical prediction for the density variation of the bentonite with the progress of its swelling

In a repository of high-level radioactive waste, complex thermal, hydraulic and mechanical (THM) phenomena will take place, involving the radiogenic heating from the vitrified waste, infiltration of ground water and swelling pressure in the buffer. The capability of modeling such coupled phenomena is of particular importance to the repository design and the safety assessment. CRIEPI has developed the THM coupling code LOSTUF for evaluating the phenomena that will take place around the engineered barrier system (EBS). In Task Force on EBS at the Aespoe Hard Rock Laboratory International Joint Committee, CRIEPI makes efforts to verify the capability to model THM processes in both unsaturated and saturated bentonite buffer. In this report, numerical results for Canister Retrieval Test (CRT) which is the full scale in-situ heating and infiltration test of EBS in the shaft deposition hole. Simulation on the canister mid-height and simulation of the entire CRT are conducted. In the comparison between measured data and numerical results, following conclusions are obtained: (1) the swelling model in LOSTUF can reproduce the homogenization of bentonite dry density after the saturation process, (2) calculated swelling pressures are isotropic and their values are in better agreement with measured data in the case where Poisson's ratio is approximately 0.5, (3) LOSTUF can reproduce the THM behavior around the full-scale EBS. (author)