Reliability analysis for stiff versus flexible piping systems

This paper describes the program plan and progress to date on a research program entitled, 'Reliability Analysis for Stiff Versus Flexible Piping Systems.' This two and one-half year program was undertaken by the Lawrence Livermore National Laboratory (LLNL) for the U.S. Nuclear Regulatory Commission (NRC) to develop improved requirements for nuclear piping system design. These improvements may involve NRC requirements, industry practice, as well as ASME code specifications. The overall approach to this problem is probabilistic, wherein the reliability of a piping system is evaluated, subject to daily events, transient loads, and postulated seismic events. The reliability model is capable of computing the failure probability of a complete piping system including piping, on-line components, and support devices. The total program is divided into three steps: the first step is to confirm safety concerns introduced by the stiff piping system design; the second step is to develop optimum, or near optimum, piping designs; and the third step is to perform a value impact study and propose changes. (orig.)