METHOD OF QUALIFICATION OF PASSIVE SAFETY SYSTEMS OF MODULAR NUCLEAR REACTORS WITH CIRCULATION CIRCUIT FLOWS

Abstract

Low-power modular reactors are a promising direction for increasing the safety of nuclear power, because accident management in modular reactors is carried out only by passive safety systems (without electric pumps). Critical for the safety of modular reactors are accidents with a violation of the tightness of the natural circulation circuits of passive safety systems. The main limitations of using traditional accident modeling approaches with deterministic codes to qualify the reliability and operability of passive safety systems of modular reactors are related to the possibility of negative effects of "code differences" and "code user differences", as well as the unfoundedness of code verification/validation results. An original qualification method has been developed to ensure the safety conditions of the passive safety systems of the Westinghouse low-power modular reactor (SMR) in the event of accidents with a violation of the tightness of the natural circulation circuits. The assumptions adopted in the developed method ensure the conservatism of qualification results. Based on the preliminary calculation qualification of the natural circulation circuits of the SMR passive safety systems, it was established that for the relative sizes of the leaks, greater than 5% of the pipeline cross-section, a violation of safety conditions and drainage of the active zone may occur less than 24 hours after the start of the accident. It is necessary to modernize the SMR with regard to systems for diagnosing leaks in natural circulation circuits of passive safety systems and isolating damaged sections of circuits.