Document: NUREG-0800
Document ID: 1c401e6c-8c2d-47df-b05f-2978939cbd15
Document Type: srp
Title: CONTROL ROOM HABITABILITY SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550069.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.4
CFR Part: 
CFR Title: 

Content:
with filtered recirculated air and a positive pressure. This system is essentially the same as the preceding one. However, an additional operational mode is possible. Makeup air for pressurization is admitted. It is filtered before entering the emergency zone. Pressurization reduces the unfiltered inleakage that is assumed to occur when the emergency zone is not pressurized. Assuming a filter fan capacity of 2400 L/s (5000 cfm) and a filter efficiency of 95%, the following protection factors result (flows in L/s (cfm)): 4 Normally 5 L/s (10 cfm) infiltration is assumed for conservatism. This flow could be reduced or eliminated if the applicant provides assurance that backflow (primarily as a result of ingress and egress) will not occur. This may mean installing two-door vestibules or equivalent. 6.4-13 Revision 3 - March 2007 Makeup Air Recirculated Air IPF (Assuming No Infiltration) IPF (Assuming Infiltration4) 190 (400) 2200 (4600) 238 159 350 (750) 2000 (4250) 128 101 470 (1000) 1900 (4000) 96 80 For method of operation, the following methods have been considered: (1) automatic isolation with subsequent manual control of pressurization. (2) automatic isolation with immediate automatic pressurization. The first is advantageous in the case of external puff releases. Simple isolation would maintain the buildup of the unfilterable noble gases. It would also protect the filters from excessive concentrations in the case of a chlorine release. However, the second method does ensure that infiltration (unfiltered) is reduced to near zero immediately upon accident detection. This would be beneficial in the case where the contamination transport path to the emergency zone is mainly inside the building. Method (i) should be used in the case of a toxic gas release and either method (i) or (ii) should be used in the case of a radiological release, provided GDC 19 can be satisfied. A substantial time delay should be assumed where manual isolation is assumed, e.g., 20 minutes