An Approach to Evaluate the HCLPF Capacities in the Modification Design of SSCs

Abstract

High-Confidence-of-Low-Probability-of-Failure (HCLPF) capacities of critical Structures, Systems, or Components (SSCs) are used to determine the core damage frequency of a nuclear power plant in the Seismic Probabilistic Risk Assessment (SPRA) or the Seismic Margin Assessment (SMA). To maintain the validity of the conclusions in the SPRA or SMA, the minimum HCLPF capacities need to be satisfied during the modification design of these critical SSCs. 

Generally, after the modification design of these critical SSCs, a seismic assessment is performed to determine their HCLPF capacities. However the design may need to be modified several times before the minimum HCLPF capacities are met. To improve the design’s efficiency, a simplified approach based on the Conservative Deterministic Failure Margin (CDFM) method is proposed. In this approach, the minimum HCLPF capacities of SSCs can be satisfied in the modification design process by adding load combinations that are related to the minimum HCLPF seismic demand.