Session: MF-12-01 Materials and Fabrication: General Topics I

Paper Number: 62368

Start Time: Wednesday, July 14, 2021, 05:00 PM

62368 - Application of Leak-Before-Break to Small Diameter Stainless Steel Piping in PWRs 

Traditional leak-before-break (LBB) evaluations involve deterministic fracture mechanics principles to demonstrate that flaws in high energy fluid systems will grow predominantly in the through-wall direction (as opposed to the circumferential or axial directions) and leak such that the leakage can be detected by the plant leakage detection system long before the through-wall flaw reaches critical flaw length.  The evaluations are performed using criteria provided in NRC’s Standard Review Plan (SRP) 3.6.3 and technical guidance in NUREG-1061, Volume 3.  LBB has traditionally been applied to large main loop piping in PWRs to address the dynamic effects of  pipe break in General Design Criteria 4, Appendix A of 10CFR50 .    

Recently, however, LBB is being sought for Class 1 pressure boundary piping systems such as the safety injection and residual heat removal systems which have small diameter piping (10 NPS and less) to mitigate the effect of dynamic loads on reactor internals and other concerns.  In NUREG-1061, Volume 3, it is stated that LBB approach means the application of fracture mechanics to demonstrate that high energy fluid piping is unlikely to experience double-ended ruptures or their equivalent as longitudinal or diagonal splits.  In application of traditional LBB to large diameter piping, only circumferential flaws are considered since it is generally believed that the critical crack sizes for axial flaws for such piping are relatively large in comparison to circumferential cracks.  However, this may not be the case for small diameter piping.  This paper examines the application of LBB to small diameter piping by determining the leak rate requirements to meet the criteria specified in SRP 3.6.3 and NUREG-1061,Volume 3 for both circumferential and axial cracks.

Presenting Author: Nathaniel Cofie Structural Integrity Associates, Inc.

Authors:

Nathaniel Cofie Structural Integrity Associates, Inc.
Dilipkumar Dedhia Structural Integrity Associates, Inc.
Do Jun Shim Structural Integrity Associates, Inc.