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:
ri- 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, periodic verification testing is required in addition to the calculations and the acceptance test. A question that often arises is whether "pressurization' or "isolation and recirculation" of the control room is to be pre- ferred. Which design gives the lowest doses depends upon the assumptions as to unfiltered inleakage. Isolation limits the entrance of noble gases (not filterable) and, in addition, it *Nonmally 10 cOm infiltration is assumed for conservatism. This flow could be reduced or eliminated if the applicant provides assurance that backflow (pri- marily as a result of ingress and egress) will not occur. This Way mean installing two-door vestibules or equivalent. 6.4-9 Rev. 2 - July 1981 is a better approach when the accident involves a short-term "puff release. If infiltration is 25 cfm or less, XisolationU would be best in any event. A second question related to the first involves the method of operation. The following possibilities have been considered: (1) automatic isolation with subsequent manual control of pressurization. (ii) automatic isolation with immediate automatic pressurization. The first is advantageous in the case of external puff releases. Simple isolation would minimize 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 guarantee that infiltration (unfiltered) is reduced to near zero imediately 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 (M) 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 (Ref. 3) can be