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:
margin for the ECCS and containment heat removal pumps. These ECCS safety concerns extend to the CSSs for plants with containment designs in which the CSS draws suction from the water supply used for long-term recirculation. In some plant designs (e.g., PWR sub-atmospheric containments), the CSS draws from the recirculation sump much earlier than the ECCS. In other plant designs, the CSS switches the pump suction to the recirculation sump after the ECCS pumps are switched. Some designs provide CSS through the residual heat removal (RHR) system, either directly or by supplying the CSS pumps from the RHR pump discharge. For some plant designs, high-energy line breaks (HELBs) that are not LOCAs, such as main steamline breaks, require recirculation from the long-term water source. For these plants, non-LOCA HELBs that require recirculation should be evaluated using the same criteria and methodology (as appropriate for the HELB conditions, duration, and consequences) as those for pipe breaks that result in a LOCA. Debris that could affect long-term recirculation cooling can be divided into the following categories: • debris generated directly by LOCA blowdown (e.g., insulation, coatings, and other materials near the break) and subject to transport by blowdown forces DG-1385, Page 6 • preexisting debris or debris created by adverse environmental conditions (e.g., latent debris or dirt and unqualified coatings not influenced by LOCA blowdown) that may be transported to the long-term recirculation water source primarily by washdown • other debris that existed before a LOCA, such as debris in a BWR suppression pool or other storage tanks (e.g., suppression pool sludge), and that may become suspended in the containment sump pool or suppression pool at the start of a LOCA • chemical reaction products generated within the containment or the reactor vessel Licensees1 should evaluate debris generation, debris transport, upstream and downstream effects, and blockage of