The SKI regulation SKIFS 2004:2 allows for the use of Leak Before Break (LBB) as one way to provide assurance that adequate protection exists against the local dynamic consequences of a pipe break. The way to demonstrate that LBB prevails relies on a deterministic procedure for which a leakage crack is postulated in certain sections of the pipe based on the leak detection capability of the plant. It shall then be demonstrated that certain margins exist against the critical crack length at which a pipe break can be expected. It is well-known that the crack morphology has a large influence on the leakage flow rate and hence on the LBB- margins. SKI has therefore initiated a project to investigate the influence of the crack morphology on LBB-margins applied on pipe systems in a Swedish PWR-plant.