Decay Heat Removal and Operators Intervention During A Very Small LOCA

Abstract

Sample calculations were done for KORI-1 to develop a better understanding of what happens after very small LOCA (≤0.05 ft²). For s water-side break with the break size larger than 0.006 ft², fluid-loss through break exceeds the makeup. If the break size is larger than 0.008ft², decay heat can be completely removed through break. Based on these results, it was concluded that KORI-1 is fairly safe for the whole spectrum of sizes in very small LOCA. However, for the reactor with 900 MWe or 1200 MWe, a certain spectrum of sizes in very small LOCA should be carefully considered. In the accident sequence the transition from natural circulation to pool boiling or from pool boiling to natural circulation may be troublesome to the operator or in the safety analysis. Operators intervention was discussed; primary pump shutoff, HPI pump shutoff, break isolation, and opening relief valve. It was proved that continuous operation of HPI pumps after shutdown will not threaten the integrity of the primary system.