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:
internally generated missiles, and it is necessary to shield the ECCS strainers, debris interceptors, and other credited design features from impacts of ruptured high-energy piping and associated jet impingement loads. ECCS strainers should be designed to minimize or prevent blockage by large pieces of debris (e.g., partially torn insulation blankets or damaged reflective metallic insulation cassettes). For example, despite their large and complex surface area, ECCS strainers located in pits below the containment floor grade could be susceptible to blockage by large debris pieces that accumulate at the relatively restricted pit openings. The installation of trash racks, curbs, or interceptors may prevent this type of accumulation. Consistent with the plant licensing-basis single-failure criterion, redundant ECCS strainers should be separated to the extent practicable to reduce the probability that a single event will render more than one train inoperable. It is generally expected that the water surface will be above the top of the ECCS strainer after completion of the injection phase and before the start of the ECCS recirculation phase. However, because of uncertainties about the time-dependent water coverage on the strainer and the amount of floating debris that may accumulate, horizontally oriented strainer surfaces may become significantly blocked. Therefore, in the computation of available strainer surface area, no credit may be taken for horizontal strainer surfaces unless plant evaluations that account for water level changes and uncertainties demonstrate that the horizontal surface will be submerged at the time of recirculation. For certain sump designs, the top of the sump structure should preferably be a solid cover plate that will provide additional protection 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