This review study is placed in the context of SSM’s Main Review Phase for SKB’s safety assessment SR-Site. The assignment is titled “Rock Mechanics – Confidence of SKB’s models for predicting the occurrence of spalling”. The report presents the authors’ assessment in response to the questions raised by SSM.
The review concentrated on two main issues: (1) the analysis of the assumptions made by SKB about the stress field at the planned repository for nuclear fuel at Forsmark, and (2) the analysis of the potential for spalling and tensile failure in deposition holes and tunnels in the repository.
The analysis of the available data on the stress field and additional structural geology based approaches yielded the conclusion that the stress field model proposed by SKB (referred to as “most likely”) is unlikely from a structural-geomechanical perspective, i.e. it is inconsistent with strength parameters of the rock mass provided by SKB; however, SKB’s model can be assumed to be conservative. Re-evaluating the available stress related data in combination with additional calculations of possible stress field scenarios lead to the proposal of an alternative stress model.