Reliability Evaluation Methodologies of Fault Tolerant Techniques of Digital I and C Systems in Nuclear Power Plants

Since the reactor protection system was replaced from analog to digital, digital reactor protection system has 4 redundant channels and each channel has several modules. It is necessary for various fault tolerant techniques to improve availability and reliability due to using complex components in DPPS. To use the digital system, it is necessary to improve the reliability and availability of a system through fault-tolerant techniques. Several researches make an effort to effects of fault tolerant techniques. However, the effects of fault tolerant techniques have not been properly considered yet in most fault tree models. Various fault-tolerant techniques, which used in digital system in NPPs, should reflect in fault tree analysis for getting lower system unavailability and more reliable PSA. When fault-tolerant techniques are modeled in fault tree, categorizing the module to detect by each fault tolerant techniques, fault coverage, detection period and the fault recovery should be considered. Further work will concentrate on various aspects for fault tree modeling. We will find other important factors, and found a new theory to construct the fault tree model