Statistical evaluation of valve and instrument network performance

Complex valve and instrument networks are frequently encountered in nuclear power plants. The complexity of such networks is often due to redundancy that is built in for safety purposes. When developing transient analysis code input to simulate valves or instruments, it is generally assumed that a redundant network of components has performance characteristics similar to those of its individual components. Typical measures of performance might be the elapsed closing time for an isolation valve network or the opening pressure of the first-opening safety valve in a parallel network. The valve network statistical analysis (VALNET) code has been developed to aid in the evaluation of network performance. The VALNET code can be used to evaluate the performance of series, parallel, and series/parallel networks to establish equivalent component characteristics for input to transient analysis codes. Analyses have shown that, for typical networks as compared to individual components, the network mean performance shifts toward the region of reduced event consequences, and the variation in performance becomes considerably smaller. Thus, the use of conservative network values in safety analyses can significantly reduce calculated event consequences and provide safety margin