Procedures and Techniques for the PSA of Digital I and C System

UCN 5 and 6 nuclear units (OPR-1000) are being constructed and the Korean Next Generation Reactor (APR-1400) is being designed by using digital I and C equipment for the safety functions such as a reactor protection system, an engineered safety feature actuation system, and a safety equipment control system. Even though the use of digital equipment for safety-related functions provides many advantageous features, there are still many arguable safety issues remaining. Design, configuration management and maintenance are important application areas for the probabilistic safety assessment (PSA). Digital I and C systems are natural candidates for PSA applications. From the viewpoint of the PSA, the digital techniques are very different from the conventional techniques of analog I and C systems because of some unique features. This article aims at giving an overview for the important issues of digital system PSA and at presenting the current status of technology development for each issue. Korea Atomic Energy Research Institute (KAERI) has performed an initiative research in order to meet risk information needs for digitalized safety-critical systems in Korea. The technologies presented in this article especially focusing on those developed in the KAERI