Fault-tree modeling for the signal generation failures of the engineered safety features in digitalized nuclear power plant

A safety assessment for the engineered safety feature actuation system designed in the Korean Nuclear I&C System (KNICS) project by using newly developed safety-critical-class microprocessor-based modules was performed. Fault-tree models were developed to assess the failure probability of a system function which is to generate an automated actuation signal for accident-mitigation equipment. The quantification results show that the failures of digital output module, network module and processor module are dominant reasons for a system unavailability. The application of a redundancy in the signal generation system effectively improves the system function failure probability. Another important finding from this study is that a careful design of a manual actuation signal path is very important.