Estimating the potential for spalling around a deep nuclear waste repository in crystalline rock

Stress-induced brittle failure (spalling) is probable at a deep geological repository for nuclear waste in crystalline rock. In the early stages of repository design it is unlikely that orientation and magnitudes of the principal stresses and the rock mass strength will be accurately known. A simple methodology is developed for estimating if spalling will occur and the severity of the hazard. The methodology is calibrated to case studies and applied to a site in Sweden. Results from the methodology are expressed in terms of a factor of safety for the mean input values and the probability of spalling based on input parameter distributions. It is shown based on the calibration studies that a factor of safety of 1.25 using the mean values should be adequate to reduce the probability of yielding to negligible levels. The methodology is proposed as a screening tool in the early design stages of a project to identify potential spalling problems.