Use of probabilistic methods for estimating failure probabilities and directing ISI-efforts

Some general aspects of the role of NDT efforts on the resulting probability of core damage is discussed. A simple model for the estimation of the pipe break probability due to IGSCC is discussed. It is partly based on analytical procedures, partly on service experience from the Swedish BWR program. Estimates of the break probabilities indicate that further studies are urgently needed. It is found that the uncertainties about the initial crack configuration are large contributors to the total uncertainty. Some effects of the in-service inspection are studied and it is found that the detection probabilities influence the failure probabilities. Concluding remarks: - IGSCC seems to be the dominating contributor to pipe failure; - Probabilistic methods can be used to study the effects of ISI; - The need of exhaustive failure statistics is great. (authors)