Typical Sequence Analysis of SLOCA Accidents in a Third Generation Nuclear Power Plant Based on RISMC Method
Authors: Feng Churan , Zhan Jingxiang , Yan Lin , Wang Yiming , Zhou Jinghua 
Published: November 2024

Abstract
It is an important scientific issue for the sustainable development of nuclear energy to scientifically recognize the factors and rules of nuclear accidents, and to take design, operation and management measures to ensure that staff, the public and the environment are protected from radioactive hazards. At present, there are two safety analysis methods, deterministic theory and probabilistic theory, which are used to recognize which faults and accidents will lead to core damage and accident evolution law. However, the single deterministic theory or probabilistic theory do not reflect the objective influence of the interaction between the equipment system failure and the system performance of the nuclear power plant on the occurrence and evolution of nuclear accidents, and the determination of the safety margin of the nuclear power plant will be biased, and the calculated safety margin is insufficient or unnecessarily conservative compared with the real value. The Risk Informed Safety Margin Characterization (RISMC) methodology is based on the coupling of deterministic theory and probabilistic theory. The accident which may lead to core damage will be researched realistically. The evolution law of the accident, the possibility of occurrence and the consequences are studied. The method aims at studying the influence of thermal parameters and model uncertainty, random failure uncertainty on the accident process of nuclear power plants under different accident scenarios. In this paper, advanced pressurized water reactor nuclear power plant SLOCA (small LOCA) is taken as the research object. Based on the theory of RISMC, the development process of the accident is studied. Based on the theory of RISMC, the research object and accident process are studied. Based on the dynamic characteristics analysis of SLOCA accidents, the typical scenario of SLOCA accidents with the failure of medium pressure safety injection (case 1) and SLOCA accidents with the failure of auxiliary feed water (case 2) were selected for analysis. Combined with probabilistic theory analysis, deterministic analysis and engineering judgment, the key dynamic characteristic parameters of SLOCA accidents are analyzed. Then, the coupling method of dynamic PSA and dynamic simulation model and the one-to-one mapping relationship in modeling are explored. Through RISMC model, the frequency of each sequence and the conditional failure probability under this specific condition are calculated, and the CDF value based on RISMC method is finally obtained. The calculation results show that, compared with the traditional PSA analysis results. For case 1 and case2, conditional probability of core damage is reduced by 48% and 5% respectively. This paper verifies the feasibility of this method based on RISMC case analysis, evaluates the accident risk more realistically, and further explores the margin of success criteria for auxiliary feedwater system secondary side heat and feed bleed operation under SLOCA accidents, which can lay a foundation for the RISMC analysis method in the design optimization of new nuclear power plants and the potential exploitation of in-service nuclear power plants.