Document: NRC Regulatory Guide
Document ID: 6f0a99f2-d25a-44e3-b7f2-3286449a9752
Document Type: regulatory_guide
Title: Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident (Rev. 5)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2126/ML21266A185.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.82
CFR Part: 
CFR Title: 

Content:
tection from LOCA-generated loads and the direct impact of water drainage. If a cover plate is installed, it should be designed to vent any trapped air. It is possible that ECCS sump strainers in some plants may not be submerged completely at the time of recirculation, either because of unique designs or because of uncertainties in water level estimates. ECCSs and CSSs with partially submerged strainers may be subject to failure criteria other than NPSH margin, as discussed in Section C.1.3.11.3 and Appendix A of this guide. For partially submerged strainers, calculations should consider only the portion of the strainer that is expected to be submerged as a function of time. A complex geometry and location at the containment floor level will reduce the deposition or settling of debris on strainer surfaces, ensuring the greatest possible free flow through the strainer. DG-1385, Page 11 Boiling-Water Reactors In BWRs, the suppression pool, also referred to as the wetwell, serves as the water source for long-term recirculation cooling. This source, the related pump suction inlets, and the piping between them are important safety components. Figure 1 shows the features and relationships of the suppression pool or wetwell pertinent to this guide. Figure 1: Conceptual features of a BWR Mark II containment (other BWR containments are similar in function) Concerns related to the performance of the suppression pool hydraulics and ECCS pump suction strainers include air ingestion effects, blockage of suction strainers by debris, and the combined effects of these items on the operability of the ECCS pumps (e.g., the impact on NPSHa at the pump inlets). NUREG-0897, Revision 1, provides data on the performance and air ingestion characteristics of some types of BWR suction strainer configurations. Currently operating BWR strainer designs are based on guidance from sources such as the Boiling Water Reactor Owners’ Group (BWROG) Utility Resolution Guide (URG), issued October 1998