As the wide adoption of the Digital Instrument and Control system (D-I&C) for Nuclear Power Plants (NPPs), the maintenance of reliability and the safety of the D-I&C is becoming more and more concerned due to the inherent complexity introduced by the D-I&C. Wherein the main difficulty to evaluate the reliability and safety of the D-I&C lies in how to model the system including both the hardware and software. The main objective of this paper is to conduct on a feasible study to model the D-I&C by taking notice of the advantage of the Colored Petri Net (CPN). A function-centered modeling approach is proposed for formal modeling and analysis of D-I&C by using CPN. The proposed model uses the hierarchical modeling capability of CPN, by which different levels of abstraction can be treated. Therefore, the proposed CPN model represents the dynamic behavior of a large scale D-I&C system used in NPPs. Using the proposed CPN model builder, the analyst can choose the specific level of abstraction for modeling and verifying the D-I&C system design. In the paper, a digital main feed water control system of a conventional Pressurized Water Reactor (PWR) plant is modeled as the example of the whole D-I&C system.
