Reliability Analysis of Digital I and C System in Nuclear Power Plant Using Dynamic Flowgraph Methodology

Because of the high reliability of Digital instrumentation and control (I and C) systems, the analog I and C systems are upgraded by use of digital ones widely in the nuclear power plants (NPPs), especially in NPPs under construction and consideration currently. The operation of digital system the dynamic features distinctly which include time sequence, feedback of signal, etc. According to some studies which been supported by United States Nuclear Regulatory Commission (USNRC), the Dynamic Flowgraph Methodology (DFM) is one of the top two methods with the most positive features and least negative or uncertain features when evaluated against the requirements for the reliability modeling of digital I and C systems. In this paper, the reliability of typical dual-CPU structure of typical digital system will be evaluated by DFM model to demonstrate the availability of DFM and find the difficulties in the process of modeling and quantity