A Graded Approach to Analysis of Anticipated Operational Occurrences

Abstract

Regulatory requirements exist to perform analysis for Anticipated Operational Occurrences (AOO) to provide verification that domestic nuclear power plants have sufficient Level 2 defence in depth. Some AOO events were addressed in safety analysis, but the analysis focused on demonstrating safety system effectiveness (Level 3 defence) under design basis accident analysis rules and methodology. A graded approach for determining scope of additional AOO analysis can take many forms. However, a risk-informed methodology has been developed that applies importance measures from Level 2 Probabilistic Safety Assessment (PSA) to identify risk-significant events, and evaluates those events with respect to public dose and the integrity of physical barriers. This graded approach is applied at Point Lepreau Nuclear Generating Station and is reflected in its Licence Conditions Handbook in the context of implementing regulatory document REGDOC-2.4.1 for deterministic safety analysis. This paper describes the methodology for the graded approach and the result of its application.