Thermal evolution and thermally induced stress simulations of spent nuclear fuel repository

In this study, a COMSOL Multiphysics model was created to analyze 1) the heat transfer and 2) the thermal expansion induced stresses in Olkiluoto spent nuclear fuel repository. The temperature field of the near disposal hole area was calculated and the minimum disposal hole spacing for 25 m tunnel spacing was analyzed. With 95 °C maximum allowed temperature in bentonite buffer, the minimum spacing was 8.845 m. The results were verified by comparing them to the results by Ikonen, et al. (2018). The verification showed that the results are very close to previous simulations with the difference in the maximum temperature being less than 0.1 °C.
In the second phase, the temperature field was used to analyze the thermally induced stress in the rock around the disposal hole. The study resulted in a maximal increase in shear stress of 83.7 MPa in the sharp corners of the tunnel floor. The damage caused by the stress was analyzed using different failure criterions and the analysis showed that the damage mainly occurs in the disposal hole walls.