Containment structure testing is intended to assure the leak-tight integrity of the containment structure under all design basis conditions. In Korea, ILRT testing frequency for PWR-type plants had been 1 every 5 years following the requirements of operating license. However, the utility had performed more frequently ILRT than the requirements due to the refueling outage of 18 months. The feasibility study of reducing the frequency of ILRT from 1 every 5 years to 1 every 10 years was performed with the method of performance-based containment leak-test program (NUREG-1493). To verify the justification of relaxation of test frequency, two activities were conducted. First, the recent 3 periods experiences of containment leakage-rate test were reviewed. And, Level 3 PSA for Ulchin Units 3 &4 as pilot plants was performed.

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