The availability assessment for reactor trip system based on Markov model

The reactor trip system (RTS) is one of the most complex systems in reactor protection systems. In this case study, there are four redundant channels in the system, each consists of two functional sub-groups containing more than 100 functional boards. Markov model is used to calculate system availability. It is difficult to establish the board-level Markov model which may incur the state space explosion problem, a Markov model to reflect the state transition between channels is proposed according to the hierarchy of system functions. Besides, multiple channels may simultaneously fail due to the common cause failure (CCF) which may be caused by the network communication, the support systems, the common hardware, the manufacturing defects and software in the digital control system. This paper shows that Markov chain is an effective method to be applied to the availability assessment of digital instrumentation and control systems of nuclear power plants.