A quantitative study on risk issues in safety feature control system design in digitalized nuclear power plant

Risk assessment for the engineered safety feature component control system (ESF-CCS) designed as part of the Korean Nuclear Instrumentation and Control (I and C) System project for application to the advanced pressurized reactor (APR1400) by using newly developed safety-class microprocessor-based modules was performed for risk-informed design feedback. The fault-tree models were developed to assess the failure probability of a system function, which is used to generate an automated control signal for complicated accident-mitigation equipment. The developed fault trees were combined with a plant risk model. This study aims at providing risk information of design issues: the risk effects of the ESF-CCS failure in consideration of an operator's manual action failure, the effect of input-signal diversity on ESF-CCS unavailability, and the risk effects of the network communication used for safety-critical information transmission in the ESF-CCS. Based on the case studies and cutset analysis, we quantitatively address these risk issues. (author)