2014:44 Technical Note, Independent evaluation of the number of critical canister positions in the KBS-3 repository at Forsmark – Main Review Phase

Independent calculations were carried out to estimate Ncrit, the number of canisters in critical positions that can be expected in the proposed repository at Forsmark, based on statistical simulations of SKB's geological discrete-fracture network (Geo-DFN) models, and taking into account SKB's full-perimeter criterion (FPC) and extended full-perimeter criterion (EFPC) to screen out canister positions that can be identified as potentially intersected by large fractures. Degree-of-utilization factors DoU for the deposition tunnels are also obtained from the simulations of the proposed repository layout D2.

Three different Geo-DFN alternatives as developed by Fox et al. (2007) were assessed: (1) r0-fixed model, (2) OSM+TFM (outcrop-scale model + tectonic fault model), and (3) TCM (tectonic continuum model). Consequences of variation of fracture intensity (P32) were also scoped by considering a 25% increase in fracture intensity for each of the three Geo-DFN alternatives.  Stochastic realizations of the Geo-DFN models were used as the basis for explicit simulation of the deposition-hole screening process along deposition tunnels in the Forsmark repository layout, using FPC and EFPC.