[en] In this study, we performed an importance analysis of the in-service testing(IST) components for Ulchin Units 3 using the PSA and the integrated importance analysis method developed in this study. The quantitative importance analysis using PSA was performed through Level 1 and 2 internal PSA, external PSA, and shutdown/low power operation PSA. The integrated importance analysis method developed in this study was applied to the importance analysis of components neither modeled nor identified as high safety significant components (HSSCs) in PSA. It is basically aimed at having a PSA expert perform an importance analysis using PSA and its related information. It is a substitute for an expert panel in the risk-informed IST. It consists of the simplified failure modes and effects analysis, the quantitative evaluation for the component failure mode assumed to have the most significant effect, and the integrated evaluation procedures of components importance analysis. The final importance analysis results of valves show that 167 (26.55%)of the 629 IST valves is HSSCs and 462(73.45%) is low safety significant components (LSSCs). The final importance analysis of pumps results also show that 28 (40%)of the 40 IST pumps is HSSCs and 12(30%) is LSSCs