Probabilistic Approach to Leak-Before-Break (LBB) for HTGR Pressure Boundary Components

This paper offers definitions and comparisons of two different and complementary approaches to a strategy to achieve high reliability for nuclear power plant pressure vessels and piping systems known as "leak-before-break (LBB)". One approach to LBB is based on deterministic design and inspection principles that are intended to practically eliminate the possibility for catastrophic failures. The other approach uses a probabilistic interpretation of the reliability characteristics of piping systems that are designed to these deterministic principles. When used together, both approaches yield a robust evaluation of piping systems that require a high degree of reliability in preventing catastrophic failures. Such an evaluation has been used to aid in the design and licensing of the PBMR Demonstration Power Plant. Key results of that evaluation are presented in this paper. (author)