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:
urfaces. The calculated height of water should not consider quantities of water that do not contribute to the sump or suppression pool (e.g., atmospheric steam, pooled water on floors and in refueling canals, spray droplets and other falling water, holdup in containment coolers, water held up by upstream obstructions, and the volume of empty system piping). In determining the minimum level, licensees should not credit non- leak-tight structures, such as ducting for heating, ventilation, and air conditioning, for the displacement of water. The calculated height should not include the amount of water in enclosed areas that cannot readily be returned to the sump or suppression pool. Minimum water level calculations should consider worst-case break locations (e.g., breaks at high elevations) that could lead to a minimum quantity of reactor coolant reaching the sump or suppression pool. Licensees should consider volume reduction of the reactor coolant inventory as it cools when crediting the contribution of spilled coolant to the sump or suppression pool. The volume of the coolant remaining in the primary system will also decrease as it cools. Therefore, it will be necessary to add more inventory to the primary DG-1385, Page 21 system before it is filled. Licensees should explicitly consider the limiting small-break LOCA water level, because elevated break locations may be possible and certain sources of inventory (e.g., PWR accumulators) may not inject. 1.3.1.7 Licensees should calculate the pipe and fitting resistance and the nominal strainer resistance without blockage by debris in a recognized, defensible method or determine it from applicable experimental data. Calculations of the clean strainer head loss (i.e., the friction head loss caused by the passage of flow through the strainer and any associated connecting pipes and plenums) should consider the distribution of flow through the strainer that produces the highest head loss. For some curvilinear-type strainer