Development of Leak-Before-Break Computer Code AP3

Abstract

Leak-Before-Break (LBB) is a widely-accepted methodology to demonstrate that a postulated through-wall crack can be detected by the available leakage monitoring systems in a timely manner while not challenging the pipe's capability to withstand any design loading without catastrophic break of the component. During the past three decades, LBB has been successfully applied to the design, fitness-for-service, risk-informed in-service inspection, high energy line break assessment and large-break loss-of-coolant accident reclassification of CANDU™ primary heat transport system piping.

AP³ (Assessment of Postulated Pipe ruPture) version 1.0 is a Tier Level II computer code and was developed in compliance with the CSA Standard N286.7-16. AP³ performs LBB assessments for circumferential and axial cracks subject to fatigue and stress corrosion cracking mechanisms following the U.S. NRC Standard Review Plan (SRP) 3.6.3 and past Canadian practices. The flaw models are based on recognized standards/codes, such as ASME BPVC Section XI and ASME FFS-1, and on state-of-the-art research. The present paper describes key elements of the development process of the AP³ computer code and the code capabilities. An LBB benchmarking problem is used to demonstrate the code accuracy of AP³.