The accurate assessment of critical crack size plays a vital role in demonstrating the Leak-Before-Break (LBB) criterion for the safety demonstration of a sodium-cooled Fast Breeder Reactor (FBR) piping system. The advancement of the crack size will increase the stress intensity factor and reduce the load-carrying capacity of the piping system. The prototype-sized pipe bend test revealed that even under a large-size crack growth situation, the ductile pipe bend fails by collapse rather than tearing instability. The critical crack size was realistically estimated based on a prototype-sized pipe bend cyclic test and compared with elastoplastic numerical analysis.
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