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:
rgence relative to the expected pressure drop. In general, flashing across or within the strainer should be avoided. Placement of the ECCS strainers at the lowest floor level practical ensures maximum use of available recirculation coolant. Areas within the containment in which coolant could accumulate during the containment spray period should be provided with drains or flowpaths to the sumps to prevent coolant holdup. Debris may also block the drains or flowpaths themselves, either totally or partially, thus preventing water from reaching the active sump region. If drains or other upstream flowpaths necessary to ensure adequate performance of the ECCS sumps are susceptible to debris blockage, they should be protected by trash racks or other design features to ensure that they will fulfill their intended function. Because debris can migrate to the ECCS strainers through these drains or paths, they are best terminated in a manner that will prevent debris from being transported to and accumulating on the strainers. Containment drainage sumps collect and monitor normal equipment leakage flow for leakage detection systems within containments. They are typically separated from the ECCS water sources and are located at an elevation lower than the ECCS pools to minimize inadvertent spillover into the ECCS from minor leaks or spills within containment. The general floor area adjacent to the ECCS strainers normally slopes away from the ECCS strainers, toward the drainage collection sumps. This slope reduces the tendency for debris to collect against the ECCS strainers. Another way to reduce the accumulation of larger pieces of debris on the strainer may be to elevate the sump strainers slightly above the floor level, on a pedestal. NUREG/CR-6772, “GSI-191: Separate-Effects Characterization of Debris Transport in Water,” issued August 2002 (Ref. 17), provides test results on the transport of various types, sizes, and shapes of debris with variables of flume water depth,