Evaluation of the Structural Integrity of a Boiling Water Reactor Core Shroud with an Irregular Distribution of Circumferential Cracks: Elasto-plastic and Plastic Analysis

Three asymmetric cracks were postulated at the circumferential horizontal weld H7 of a boiling water reactor type 5 core shroud after 25 years of operation. They were arranged in an irregular distribution with different depths. Unstable crack propagation can be induced when an earthquake and a loss of coolant accident take place. In this paper, a ductile failure analysis has been reported. It has been done following an elastoplastic analysis and a plastic limit load analysis. The crack conditions after 30 and 60 years of operation were evaluated. The results show that the core shroud will keep its structural integrity during sixty years under normal conditions of operation. On the other hand, its operational life is reduced five years under failure conditions. In general terms, the methodology, which has been developed, can be applied for any number of circumferential cracks located in the same cross section. Fast and reliable outputs can be obtained. It can be applied in any moment of the life of the plant, to support the decision on “Use as is”, “Mandatory Repair”, or “Estimation of the remaining life”.