(A) study on reliability assessment of safety-critical network communication in digitalized Nnclear power plant

Abstract

Recently, the Engineered Safety Feature-Component Control System (ESF-CCS), which uses a network communication system for the transmission of safety-critical information from group controllers (GCs) to loop controllers (LCs), was developed. The use of network communication in control or information transmission system in nuclear power plants (NPPs) provides design flexibility and reduced cost

however, the network communication system has not been applied to ESF-CCS in NPP because the network communication failure risk in the ESF-CCS has yet to be fully quantified. Therefore, the potential hazardous states and failure mechanisms of network communication between GCs and LCs, which includes High Reliability-Safety Data Link (HR-SDL) and High Reliability-Safety Data Network (HR-SDN), were identified and the quantification schemes for various network failure causes were developed in this study. To quantify the network communication risk and estimate the risk effects of network communication failures in the ESF-CCS, a fault-tree model for engineered safety feature (ESF) components considering the failure of network communication between GC and LC was developed and integrated with OPR-1000 PSA model. In this study, the hazardous states of network communication were identified both in protocol-level and system-level. To identified the failure mechanisms of network communication which may induce the hazardous states, potential failure causes were analyzed based on the open systems interconnection model of Profibus protocol. The failure mechanisms include hardware failure, software failure, and the failure caused by medium-related bit error. Based on the identified failure mechanisms, quantification schemes for each network failure cause were proposed. Based on the proposed network communication risk assessment methodology, a fault-tree model for ESF components including the network communication failure in ESF-CCS was developed and integrated with OPR-1000 PSA model. Based on various periodic test intervals for network modules, a sensitivity study was conducted to analyze the risk effect of network failure between GCs and LCs on ESF-CCS signal failure.