Development of USNRC standard review plan 3.6.3 for leak-before-break applications to nuclear power plants

In the United States, it is now permissible to eliminate the dynamic effects of postulated high energy pipe ruptures from the design basis of nuclear power plants using ‘Leak-Before-Break’ (LBB) technology. To provide review guidance for the implementation of LBB, a new Standard Review Plan (SRP) 3.6.3 was issued for public comment. Based upon public comments received and advances in fracture mechanics application, further development of SRP 3.6.3 is in progress.

SRP 3.6.3 will outline the review procedures and acceptance criteria for LBB licensing applications. A deterministic fracture mechanics evaluation accounting for material toughness will be required. Margins on load, crack size, and leakage will be specified and the load combination methods and leakage detection sensitivity will be described. Piping particularly susceptible to failure from potential degradation mechanisms will be excluded from the application of LBB. The design basis of containment, emergency core cooling systems, and environmental qualification of equipment in the context of LBB applicability will be clarified.