An Evaluation of Post-LOCA Debris on Multi-Stage Safety-Related Pumps in PWR ECCS in Support of Generic Safety Issue 191 Closure

Abstract

The U.S. Nuclear Regulatory Commission (NRC) issued Generic Safety Issue (GSI) 191 covering the ability of nuclear reactor containment building (RCB) sumps to support long-term core cooling post-accident for Pressurized Water Reactors (PWRs). The issue is that a postulated Loss-of-Coolant Accident (LOCA) for a PWR would result in the initial escape of high-pressure, high-temperature subcooled coolant from the pipe break location in the form of a two-phase jet. The impingement of the jet may damage materials used inside the RCB, resulting in the generation of debris. The debris transported to and through the sump screen when the Emergency Core Cooling (ECC) and the Containment Spray (CS) Systems are realigned to draw suction from the containment sump will be ingested by pumps in the flow path. Since wear affects the dynamics of the pump and hence vibration, the extent to which any pump can survive the abrasive nature of the ingested debris depends on how well one can predict the wear of pump critical dimensions using the debris mix and pump design parameters. This paper describes the issues to be considered in pump assessment and presents wear models that can be used to assess pump operability and performance. It shows that depending on assumptions made relative to the wear pattern, different results can be reached using the wear models. The question of what makes sense is discussed.