A systematic approach to snubber reduction with minimum effect on piping systems

All nuclear power plants have used shock suppressors (snubbers) in the design of piping and/or equipment support systems to mitigate the dynamic response of piping and components from fluid transient or seismically induced loadings. The purpose of the snubber is to allow the normal thermal growth of piping or equipment while mitigating the more rapid dynamic responses due to fluid transient or seismically induced loadings. The early snubbers were hydraulic but these have proven susceptible to seal degradation resulting in fluid leakage and valve clogging. Subsequent mechanical snubber designs have experienced operability problems as a result of environmentally induced degradation of close-fitting mechanical parts or damage due to excessive vibration. The Nuclear Regulatory Commission has responded to the high snubber failure rate by requiring rigorous inspection programs from licenses of operating nuclear power plants. The inspection programs are generally based on OM-4, a sampling procedure which requires expanded sample populations with increased failure rates. In some cases, this has resulted in almost 100-percent inspection of snubbers during each scheduled outage. Many utilities are considering snubber reduction programs as a means of reducing plant maintenance costs, increasing plant availability, and lowering radiation exposure of plant personnel. This paper describes a systematic approach to maximize the elimination of piping system snubbers while minimizing changes in design loads on the remaining support structures and equipment. Among the things discussed are new analytical techniques, regulatory developments, computer programs, and snubber replacement device