Comparison of vertical and horizontal deposition hole concept for disposal of radioactive waste based on rock mechanical in situ stress-strength analyses

In Finland, a spent fuel repository is being planned in hard, crystalline rock to the depth of 300–800 m. The repository will consist of parallel deposition tunnels which are interconnected by a central tunnel. The spent fuel canisters will be placed in holes drilled according to the tunnel floor—vertical deposition hole concept or in the tunnel wall-horizontal deposition hole concept. Based on the numerical stress-strength analyses, both concepts are found to be feasible. However, when the maximum horizontal stress is perpendicular to the axis of the deposition hole, the rock in the vicinity of the horizontal deposition hole seems to have more stable behavior than in the case of the vertical deposition hole.