Reliability analysis for the reactor protection system of HTR-PM

A high-temperature gas-cooled reactor-pebble bed module (HTR-PM), as a demonstration nuclear power plant (NPP), is now under construction in the Shandong province of China. The reactor protection system (RPS) in an HTR-PM is a safety-related system and is mainly in charge of monitoring safety-related parameters according to the reactor protection requirements. Thus, an RPS is very important to operations during the entire life cycle of an NPP. An RPS for an HTR-PM is completely designed and developed in China, which owns all intellectual property rights. Traditionally, the reliability of an RPS is evaluated based on a failure mode, effects, and criticality analysis (FMECA) and a fault tree analysis (FTA), which are static methods and cannot reflect the reliability of the system's dynamics. In this paper, we propose a dynamic reliability model for the RPS in an HTR-PM based on the Markov chain theory. Using this model, all states and their dynamic transition processes, especially the degradation process from a 2-out-of-4 structure to a 2-out-of-3 structure, are all determined. Moreover, based on this proposed model, an optimal surveillance test interval can be determined.