Analysis of Normal Operation Function Effect on Qualitative Risk Importance in CANDU

Development of the Maintenance Effectiveness Monitoring Program consists of three major steps: scoping functions, determining importance and establishing performance criteria. Once the scoping of functions is completed, those functions are categorized into High Safety Significance (HSS) or Low Safety Significance (LSS) according to their importance. The Maintenance Rule (MR), which is U.S. 10CFR 50.65, monitor the safety related systems and their support system's performance in Light Water Reactor (LWR) plants. Industry guidance for the development of the MR program provides instructions only for PWR plants and does not mention CANDU plants. CANDU systems are different from PWRs in many aspects. In developing CANDU MR, it was necessary to reflect the specific characteristics of CANDU and compare them with PWR functions. Industry guidelines provide a method to provide a method to determine risk importance. KHNP adopted a combination of two different approaches: qualitative risk analysis using expert judgment and quantitative risk analysis using the Probabilistic Safety Analysis (PSA). This paper presents the effect of three additional Normal-Operation (NO) function questionnaires added for CANDU for determining the qualitative risk importance