Design of advanced RPS architecture and reliability analysis using markov model

Abstract

This paper presents the architecture of Reactor Protection System (RPS) in Nuclear Integrated Safety System (NISS), and describes the evaluation and analyses of reliability for the NISS-RPS using the Markov model. The NISS-RPS has 4 channels redundancy like the existing digital RPSs however in a channel, is configured for the Triple Modular Redundancy (TMR) as the passive voting method to enhance the safety and availability. In other words, input/output, bistable logic, coincidence logic modules are configured for TMR and initiation circuit is Dual Modular Redundancy (DRM) as with the existing RPS. Markov models for the NISS-RPS including the existing RPS in operation or under construction in Korean were developed and the reliabilities of them were evaluated and analyzed by using the models. From the reliability analyses for the NISS-RPS, it is obtained that the failure rate of each module in the NISS-RPS should be less than 2 ×; 10-4/hour and the MTTF average increase rate depending on the fault coverage factor (FCF) increment, i. e. ΔMTTF/AFCF, is 4 months/0.1. As results of comparison of other RPSs, the reliability of NISS-RPS is minimally 1.5 times better than the three types of RPS architectures, and the MTTF of NISS-RPS is up to 16,600 hours better than the three.