For the performance assessment of a future nuclear waste repository, the excavation of the tunnel and deposition hole, thermal loading from waste heat release and the swelling pressure of buffer material are factors to be considered. In this paper, they are modelled numerically by using the three-dimensional distinct element code (3DEC). The modelling is carried out in the vicinity of the tunnel and deposition hole and focused on the stability and safety of the repotory. The results indicate that thermal loading has significant influence on the stability of the tunnel and the effect of excavation and swelling pressure on the deposition hole and waste canister is insignificant.