Development of Preliminary Multi-unit PSA Models for Seismic Event

About 90% of the nuclear sites in the world have two or more reactor units. During the licensing process of new build units in the site containing more than existing six units in Korea in 2016, the multi-unit issues were arisen as one of the most important challenges in nuclear industries. As a countermeasure for the issues, Korea Hydro & Nuclear Power (KHNP) has started the project on developing methodology of multi-unit Probabilistic Safety Assessment (PSA) and applying it to a reference site by 2020. We have reviewed the previous researches and projects including the project of "Development of the Integrated Risk Assessment Technology for Multiple Units" performed by Korea Atomic Energy Research Institute (KAERI) from 2015 to 2017. Based on these backgrounds at the current status, we have performed the pilot study on development and quantification of preliminary multi-unit PSA for seismic event with some assumptions with focusing on integrating single unit PSA models and quantifying the integrated models. This paper describes the plot study with some assumptions in the early stage of our project, which is for preliminary multi-unit PSA for seismic events, with focusing on integrating single unit PSA models and quantifying the integrated models. Through the pilot study, we derived the results of preliminary multi-unit PSA for seismic events as the form of CDF, and provided the information on the increased risk caused by adding new build two units.