For underground disposal of high-level radioactive waste (HLW) the performance of the host rock of the repository in the construction phase and in a short-term perspective–a few thousand years–is of primary importance for predicting the risk of dissemination of radioactivity. The large-scale structure of the host rock determines, together with the rock stresses, how and where groundwater moves, hence controlling dispersion and transport of radionuclides escaped from installed HLW. As concerns underground repositories there are three major stress-related issues, that is: the excavation disturbance by boring and blasting, the risk of shearing of fractures and fracture zones that intersect deposition holes, and the impact of convergence of tunnels and holes. The major principal stress is nearly horizontal and 30–40 MPa, the three principal stresses being about 40, 25, and 10 MPa.