Qualification of Strategies for Modernizing Test Frequency of Safety Systems at Nuclear Power Facilities With Extended Time of Fuel Campaigns

A risk-informed method for qualifying (substantiating) strategies for increasing the test periodicity of passive safety systems in the regimes of increasing the time of fuel campaigns of nuclear power facilities has been developed. The qualification criterion is the probability of failure of accident management systems for groups of initial accident events with a “tight” and “loose” reactor circuit. The qualification conditions are not to exceed the probability of failure of accident management systems of the modernized test strategy as to the design test strategy. Based on the developed method, it was recognized that a reasonable increase in the test periodicity of passive safety systems in the general case depends on the modernization of reliability indicators and the test periodicity of active safety systems at reactor power. Based on the qualification results, it was recognized that to increase the reliability of the emergency feed system of steam generators is the most reasonable strategy for increasing the test periodicity of passive safety systems. This can be provided with an emergency feed pump with a steam drive from the steam generators which get the required conditions for feeding steam generators at all accident stages at a pressure in the steam generators of at least 0.3 MPa. The developed method for qualifying strategies for test periodicity of passive safety systems in modes of increasing the time of fuel campaigns of nuclear power facilities can be implemented using sufficient operational data on the reliability of safety systems over the entire operation life.