Probabilistic Safety Assessment of Multi Unit Site of Nuclear Power Plant

It is a common practice around the world to install multiple units of nuclear power plants on a single site taking advantage of common intake cooling structure, shared components, etc. The accident at the Fukushima Daiichi nuclear power plant highlighted the risks from multiple nuclear reactor unit accidents at a site urging the nuclear community to analyse the multi-unit (MU) risks to avoid re-occurrence of similar accidents. A multi-unit site PSA model has to deal with the dependencies existing between the units on that site. Common cause models used in traditional single unit PSAs were originally developed for arrays of redundant components within a single nuclear power plant. If there are identical, redundant components and systems that are replicated on multiple reactor unit, the common cause failure (CCF) that may impact components on different units needs to be considered. This study is conducted to identify main risk contributors that delineate multi-unit risk from single-unit risks. A case study is performed based on full power level-I PSA model to identify plant vulnerabilities considering risk from shared components, common-cause failure of multi structures and components to calculate multi-unit core damage frequency (MUCDF) based on multi-unit initiating events (MUIEs).