A numerical modelling campaign aiming at the simulation of the development of the distinct fracture network under different geomechanical boundary conditions in a repository for spent nuclear fuel at Forsmark, Sweden, was carried out. The models included the KBS-3V deposition concept with backfill of the tunnel, readjustment of water head, swelling of the bentonite buffer and a full sequence of heat generation and cooling phase of the canisters. A subsequent glaciation scenario regarded an increase in vertical load due to the ice sheet and an increase of fluid pressure due to a hydraulic connection from the surface of the ice cover. The numerical simulations were run for two different Distinct Fracture Network (DFN) models and two stress regimes (i.e. a low magnitude and a high magnitude stress field). From the simulations it results that the understanding of the stress field at Forsmark appears to be critical for the propagation of the fractures. The low magnitude stress field (Ask et al. 2007) enhances the propagation of existing fractures in the network. On the other hand, the high magnitude stress field (Martin 2007) tends to close the existing fractures and mobilise the frictional resistance of the fracture with less propagation of the fractures. The numerical results show that during the operation, closure and thermal phase of the repository no major DFN alterations are to be expected. However, an increase of water head seems to have the most pronounced impact on the DFN evolution.
In preparation for the review of the license application for disposal of spent nuclear fuel by the Swedish Nuclear Fuel and Waste Management Company (SKB), the Swedish Radiation Safety Authority (SSM) is conducting studies to evaluate the performance of the multi-barrier principle on which the KBS-3 system is based.
