Document: NRC Regulatory Guide
Document ID: ceaeb6d7-d85a-46d3-a1b6-70059a498965
Document Type: regulatory_guide
Title: 12/2001 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0131/ML013100014.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.78
CFR Part: 
CFR Title: 

Content:
ity. For onsite storage, the capability to manually isolate the control room should be provided. Upon detection of a toxic chemical, a detector should initiate complete closure of isolation dampers to the control room with minimal delay. The isolation time is a function of the control room design, in particular, the inleakage characteristics. If the detectors are upstream from the isolation dampers, credit will be allowed for the travel time between the detectors and the dampers. The isolation system and its components, the recirculating filter system, and the air conditioning system should meet IEEE Std 603-1991, "Criteria for Safety Systems for Nuclear Power Generating Stations" (Ref. 10), since these systems are needed to maintain a habitable environment in the control room during design basis radiological events. For plants that isolate control rooms, steps should be taken to ensure that the isolated exchange rate is not inadvertently increased by design or operating error. Ventilation equipment for the control room and for the adjacent zones should be reviewed to ensure that enhanced air exchange between the isolated control room and the outside will not occur. All doors leading to the control room should be kept closed when not in use. 4.3 Protection System If the evaluation of possible accidents for any hazardous chemical indicates that the applicable toxicity limits may be exceeded in the control room, measures should be in place to provide adequate protection to control room operators. The use of full-face self-contained pressure-demand-type breathing apparatus (or the equivalent) and protective clothing should be considered. Adequate air capacity for the breathing apparatus (at least 6 hours) should be readily available onsite to ensure that sufficient time is available to transport additional bottled air from offsite locations. This offsite supply should be capable of delivering several hundred hours of bottled air. Sufficient units of breathing apparatus