Probabilistic safety assessment of BWR shroud-support weldments with multiple through-wall cracks

Abstract

To assure the structural integrity of shroud-support structure of a BWR power plant in Taiwan, a finite element simulation model is built in this paper by referring to evaluation guidelines developed by the Electric Power Research Institute (EPRI). The major purpose is to check whether the collapse load of the shroud-support is reached or not. To be conservative and reflect the reality, it is assumed that circumferential Multiple Through-wall Cracks (MTC) are distributed randomly on either the single side or both sides of two major shroud-support plate weldments. Owing to the randomness, different cracks may exist in the weldments, which result in different collapse loads when elasto-plastic analyses are carried out. Statistical analysis is then applied to treat the simulated collapse loads. Among different possible collapse loads, the minimum load is the critical one and related directly to the safety of the plant. Several techniques to find the minimum load are proposed and numerical calculations are carried out in this paper. It is illustrated and verified by examples that the proposed model can indeed be adopted for the probabilistic safety analysis of BWR shroud-support weldments and the proposed techniques can be used for finding easily those minimum collapse loads.