Multi-Units Nuclear Power Plant Site Initial Event Filtration

Abstract

At present, the probabilistic safety assessment (PSA) method is mainly applied to a single unit, while actual nuclear power plants are usually multi-reactor sites. In the multi-unit level 1 probabilistic safety assessment study, the modeling workload is greatly increased. Also, it is necessary to consider the correlation between units, the probabilistic safety evaluation of multiple reactor sites is confronted with great challenges. Safety assessment of multi-unit sites should begin with a screening of the initial event, and not all events need to be analyzed by building an event tree. This paper described the classification status of initial events at multi-unit and calculated these events’ core damage frequency (CDF) upper and lower bounds. The upper limit of CDF is based on the assumption of complete dependence between units, and the lower limit is based on the assumption of complete independence between units. Taking a two-unit as an example, it screened the initial events and sorted out the characteristics of accidents. We assume that the time limit for simultaneous accidents of two units is 24 hours. The results show that the loss-of-offsite-power (LOOP), loss of heat trap and other events are suitable for modeling and analysis. In addition, given the analysis suggestions for other accidents combined with their characteristics. The analytical methods and results provide the basis for the multi-unit Probabilistic Safety Assessment modeling.