Reliability Analysis Model of the Digital Reactor Protection System

In recent years, the rapid progress of digital technology to safety-critical systems such as the digital reactor protection system (RPS) is increased. The proposed method aims to make a quantitative evaluation model for the reliability analysis of digital RPS with 2-out-of-4 architecture using the state transition diagram to be sure that Nuclear power plants (NPP) will be in a state to perform a required tasks under given conditions over a time interval. The detection time of the failure, the repair time of failed components and Mean Time to Repair (MTTR) are used in this study. The Probability of Failure on Demand (PFD) of the digital RPS caused by independent hardware failure is calculated and the effect on the system is analyzed. The results show that the proposed method is more effectiveness and appropriate to model the digital RPS and to analyze reliability than conventional Fault Tree Analysis (FTA) method.