PSA level 1 analysis by considering redundancy and diversity of emergency diesel generators for APR-1400

Abstract

This paper builds upon the initial Level 1 Probabilistic Safety Assessment (PSA) for Emergency Diesel Generator (EDG) failures in the APR-1400 Nuclear Power Plant (NPP). By incorporating more complex EDG failure scenarios and expanding the scope of fault trees and event trees, it provides a more comprehensive safety performance analysis using AIMS-PSA software. The results highlight the reactor’s safety systems’ resilience in the face of an increasing number of malfunctioning EDGs. An in-depth understanding of the interdependencies and failure probability of the Essential Chilled Water System (ECWS), Component Cooling Water System (CCWS), 480 V bus, and fault trees for the 125 V and 4.16 kV buses has been obtained through this detailed examination. The Core Damage Frequency (CDF) values from the analysis, 1.71E-6 /RY, were found to be significantly lower compared to official literature values of 2.56E-6 /RY and 2.25E-6 /RY, attributed to the exclusion of more extensive operational and environmental aspects of LOOP and common cause failure events. The findings provide critical insights for enhancing nuclear safety frameworks and underscore the need for scenario-based PSAs to address potential vulnerabilities. Overall, the paper not only effectively measures the resilience of the NPP’s safety measures to various failure modes but also provides regulators and plant management with insightful information about the significance of redundancy and diversity in preserving nuclear safety over the NPP’s operational lifetime.