Development of Technical Basis for Leak-Before-Break Evaluation Procedures (NUREG/CR-6765)

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Publication Information

Manuscript Completed: October 2001
Date Published: May 2002

Prepared by:
P. M. Scott¹, R. J. Olson¹
G. M. Wilkowski²

¹Battelle
505 King Avenue
Columbus, OH 43201

Subcontractor:
²Engineering Mechanics Corporation of Columbus
3518 Riverside Drive
Suite 202
Columbus, OH 43221-1735

C. Santos, Jr., NRC Project Manager

Prepared for:
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code W6854

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Abstract

In the mid 1980's the USNRC began to accept LBB for large-diameter, high quality piping systems as a means of enhancing safety. To aide NRC staff in evaluating LBB submittals, a draft Standard Review Plan (SRP) entitled "Leak-Before-Break Evaluation Procedures" was published in 1987. Because of ongoing research, this draft SRP was never published in final form. Now that that research is nearly complete, the NRC has decided to develop and issue a LBB Regulatory Guide. A final version of SRP 3.6.3 will follow publication of the Regulatory Guide. These documents will address updated, acceptable LBB analyses. Consequently, in 1997 the NRC contracted with Battelle to conduct a study entitled "Technical Support for Regulatory Guide on LBB Evaluation Procedures". During this study, a three-tiered approach to LBB was developed. Level 1 is the simplest level of assessment, designed to provide a conservative LBB evaluation. Level 2 is similar to the draft SRP procedures, except it incorporates enhancements in technology that have resulted from recent research. Level 3 is the most complex level of assessment, where nonlinear stress analyses are used to take advantage of margins that exist when one invokes elastic analysis on a nonlinear problem. Case studies of actual piping systems were conducted to ascertain the relative conservatism of the three levels of assessment.