The Influence of Seasonal Variation on AP1000 Reliability Under LOOP Accident

Abstract The benchmark PSA (Probabilistic Safety Assessment) is mainly used to evaluate the average safety level of nuclear power plants, cannot reflect the current risk level of the plant. The risk level of power plants might change under different plant configurations and environmental factors. At present, passive safety technology is being increasingly implemented in advanced reactors. The safety function of passive system is accomplished mainly based on the natural force, which increases the influence of environmental factors on nuclear power plant reliability. Environmental factors vary significantly with the seasons. Therefore, the impact of seasonal changes on the plant reliability is evaluated to consider environmental factors into the analysis of plant reliability. This paper presents a methodological approach to analyze the impact of seasonal variations on the reliability of the AP1000 nuclear power plant under LOOP (Loss of Offsite Power) accident. AP1000 reactor is a typical passive nuclear reactor. The influence of environmental factors on LOOP accident is obvious, and the importance of LOOP accident to is very significant to the reliability of power plant. Initial event and passive system should be considered seriously in the evaluation. The Fault Tree (FT) tool is employed to calculate the frequency of LOOP accident during different seasons. A combination method of Thermal-Hydraulic (T-H) model and probabilistic model is utilized to calculate the failure probability of the Passive Containment Cooling System (PCCS) physical processes. The FT method is used to combine the system functional failure with device fault. Finally, the nuclear power plant reliability under different seasons is evaluated based on the Event Tree (ET) tool.