FRACTURE MECHANICS ANALYSIS OF MULTI-PURPOSE CANISTER UNDER IMPACT LOADING

Multi-purpose canisters (MPCs) made of austenitic stainless steel are used to store spent nuclear fuels (SNF) for long periods. During long-term storage, chloride-induced stress corrosion cracking (CISCC) can occur on the external surface of MPC. In this respect, a structural integrity assessment of MPC with possible CISCC defects under accident scenarios such as drop accidents during transportation needs to be performed. In this paper, fracture mechanics analysis is performed to calculate critical crack sizes under the 9m drop accident suggested at IAEA (International Atomic Energy Agency) SSR-6 (rev. 1). For the MPC model, the KORAD (Korea Radioactive Waste Agency)-21 model was used. Elastic-plastic impact simulation was firstly performed using the strain-rate dependent material properties to identify critical locations showing the highest stresses during impact. The postulated crack is assumed to be the external semi-elliptical longitudinal and circumferential crack. Then fracture mechanics analysis is performed using the failure assessment diagram (FAD) approach. The reference stress was calculated using the method suggested in API 579/ASME FFS-1. The stress intensity factor is calculated using the weight function method in ASME Section XI, Appendix A. Using the FAD approach, the critical crack size is calculated. The sensitivity analysis is performed to investigate the effect of the strain rate on calculated critical crack sizes.