Regulatory perspective on ECCS sump blockage issue

In the event of a loss-of-coolant accident (LOCA) of a nuclear power plants (NPP), piping thermal insulation and other materials in the vicinity of the break will be dislodged by the pipe break and steam/water-jet impingement. A fraction of this fragmented and dislodged insulation and other materials, such as paint chips and concrete dust, will be transported to the containment floor by the steam/water flows induced by the break and by the containment sprays. Some of this debris eventually will be transported to and accumulated on the recirculation sump suction screens in pressurized-water reactor (PWR) containment or on the pump suction strainer in CANDU-type reactor containment. Debris accumulation on the sump screen or strainers could challenge the plant's capability to provide a long-term cooling water to the emergency core cooling system (ECCS) and the containment spray system pumps. The present paper summarizes the safety issue related to the sump blockage and its historical background, layouts the applicable regulatory guide to this issue, and briefs the current status in Korean NPP. Based on those aspects, a perspective on future regulation of the sump blockage issue is suggested