Document: NUREG-0800
Document ID: 8c2fce42-281a-4a50-9de7-513df024f27c
Document Type: srp
Title: CONTROL ROOM HABITABILITY SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340712.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.4
CFR Part: 
CFR Title: 

Content:
rate is the enhancement of the infiltration 6.4-8 Rev. 2 - July 1981 occurring at the dampers or valves upstream of recircula- tion fans. When closed, these dampers typically are exposed to a pressure differential of several-inches water gauge. This is accounted for by an additional infiltration contribution over the base infiltration of 1/8-inch water gauge. The use of an infiltration rate that is based on calculation is acceptable except in the case where the applicant has assumed exceptionally low rates of infiltration. In these cases, more substantial verification or proof may be required. For instance, if an applicant submits an analysis that shows a gross leakage rate of less than 0.06 volume changes per hour, the reviewer would require that the gross leakage be verified by periodic tests as described in Regulatory Position C.5 of Regulatory Guide 1.95 (Ref. 8). (3) Zone isolation 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 unfil- tered inleakage that is assumed to occur when the emergency zone is not pressurized. Assuming a filter fan capacity of 5000 cfm and a filter efficiency of 95%, the following protection factors result (flows in cfm): IPF (Assuming IPF (Assuming Makeup Air Recirculated Air No Infiltration) Infiltration*) 400 4600 238 159 750 4250 128 101 1000 4000 96 80 The makeup flow rate should have adequate margin to assure that the control room will be maintained at a pressure of at least 1/8-inch water gauge. The applicant should indicate that an acceptance test will be performed to verify adequate pressuri- zation. If the makeup rate is less than 0.5 volume changes per hour, supporting calculations are required to verify adequate air flow. If the makeup rate is less than 0.25 volume changes per hour,