Development of state-based integrated dependability model of RPS in NPPs considering CCF and periodic testing effects at the early design phase

Abstract

In the design process of safety critical digital systems, the quantitative analysis of their dependability is essential step to enhance the safety of nuclear power plants. Earlier this analysis can be performed, higher safety can be achieved in a more cost effective manner. In this paper, we present an integrated dependability evaluation model of the reactor protection system in nuclear power plants based on the Markov model. The complex interrelationship among dependability parameters such as architecture, channel-level failure, repair, common cause failure and periodic surveillance test are modeled systematically, which cannot be achieved by using conventional static methods. To prevent the integrated dependability model of reactor protection system from exploding the state, we treat each channel as the hyper component of which failure rate is the channel-level failure rate studied in the previous work. Using this concept, we simplify the model by incorporating various dependability parameters into the model. Using the model, quantitative results for reliability, availability, safety and spurious trip probability of reactor protection system are presented depending on various channel configurations. From the results, we can obtain insight into which parameters have the greatest effect on dependability and guideline for how to optimize parameters to satisfy the system requirements at the early design phase.