**Abstract**

Instrumentation and control system (I&Cs) plays a key role in nuclear power plants (NPP) whose failure may cause the major issue in a form of accidents, hazardous radiations, and environmental loss. That is why importantly ensure the reliability of such system in NPP. In this proposed method, we effectively analyze the reliability of the instrumentation and control system. An isolation condenser system of nuclear power plant is taken as a case study to show the analysis. The methodology includes the dynamic behavior of the system using Petri net. The proposed method is validated on operation data of NPP.

**Keywords:** reliability, control system, nuclear power plant, isolation condenser system
