Research On Diversity Design And Application Of Security Level Control Systems In Nuclear Power Plants

When nuclear power plant is under an abnormal condition, security level controlsystem can actuate a safety emergency shut down or actuate the equipments ofengineered safety features actuation system to reduce the influence of accidents,providing a powerful guarantee for the safety of nuclear power plants. In recent years,with the rapid development of computer technology, digital control system has beenincreasingly mature. At present, non-safety control system has basically realized thedigitization, and the digitization of security level control system has become aninevitable trend.Due to the application of microprocessor running software, digital systems areeasily subjected to the risk of common cause failure. Common cause failure may leadto unavailability of some safety functions in nuclear security level control system,which is to say when the plant parameters are abnormal, the system can not make thereactor shut down in time, or trigger related security functions, resulting in accidents.Therefore, in the design of nuclear power plant security level control system, the riskof common cause failure should be considered, and correspondingly make the designfor defense in depth and diversity. Through the design of diversity, the system caneffectively deal with the influence of the common cause failure, ensure the safety ofnuclear power plants, and meet the design principle of defense in depth.This paper introduces the development and research status of nuclear powerplant reactor protection system, analyzes the principle of common cause failure andits effective coping methods. Also introduces the definition of diversity design andsix different types of diversity, namely people, design, software, function, signals andequipment diversity. Considering the requirements of regulations and standards, wemake the diversity design of security control system. Mainly analyses and designs thefunction diversity and equipment diversity, including the distribution of protectionfunctions in security level, selection of equipments, and the design of the DiversityActuate system, etc. Diversity design is been using in the Hongyanhe plant protectionsystem, and the results show that the design effectively defense the influence ofCommon cause failure, and guarantees the safe operation of nuclear power plant.