The containment sump (also known as emergency or recirculation sump) in a pressurized water reactor (PWR) is part of the emergency core cooling system. Every nuclear power plant is required by regulations (i.e., 10 CFR 50.46) to have an emergency core cooling system to mitigate a design basis accident. The emergency core cooling system is one of several safety systems required by the NRC.

The NRC identified a potential susceptibility of PWR recirculation sump screens and associated flow paths to debris blockage during loss-of-coolant accidents that require recirculation operation which might impede the long-term operation of the emergency core cooling system or containment spray system. The additional head loss due to the accumulation of debris has the potential to exceed the net positive suction head margin required for the successful operation of the emergency core cooling system and containment spray system pumps. Debris can also pass through sump screens and affect equipment downstream (such as valves, pumps, and nuclear fuel assemblies).

As a result, all operating PWR licensees were requested through Generic Letter (GL) 2004-02 to perform a mechanistic evaluation of the recirculation functions and, as appropriate, to take additional actions (e.g., plant modifications) to ensure system functionality. As licensees pursued development of responses to the GL 2004-02, testing indicated that licensees needed to address additional issues (e.g., chemical effects and in-vessel downstream effects) whose scope was not fully known at the time GL 2004-02 was issued. These issues have required additional testing and plant modifications for many licensees.

PWR Sump Performance

Overview

NRC Activities

Related Information

Reports and Correspondence