Developing RETRAN input for redundant networks

Complex valve and instrument networks are frequently found in nuclear power plants; the complexity of such networks is often due to built-in, safety-related redundance. When developing RETRAN input to model a redundant network, it is generally assumed that the performance of such a network can be accurately represented by the performance characteristics of its individual components. This approach, however, can introduce a substantial amount of conservatism into the RETRAN calculations because a redundant network tends to outperform its components. To help utility engineers evaluate the performance of redundant networks, the Electric Power Research Institute has sponsored the development of the Plant Network Simulation (PLANETS) computer program. The PLANETS code can be used to develop both conservative and best-estimate network characteristics for RETRAN input. This paper reports that analyses have shown that the use of network inputs can significantly reduce calculated event consequences as well as provide added safety or operating margin