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:
h normal and accident conditions. The volume of the control room and all other rooms, including the ventilation systems, that share the same ventilating air, during both normal conditions and accident conditions, should be considered. The control room and emergency ventilation system should have low-leakage construction. Low-leakage dampers or valves should be installed on the upstream side of recirculation fans or other locations where negative system pressure exists and where inleakage from contaminated atmospheric ambient air is possible. The inleakage characteristics of the control room envelope during a hazardous chemical challenge should be determined by testing. The testing should be conducted to a recognized industry standard and performed to demonstrate control room envelope inleakage with systems and components configured and operating as they would in the event of a hazardous chemical challenge. Any test determining inleakage should ensure that the control room envelope, its 1.78-10 associated ventilation systems, and ventilation systems in adjacent areas are all aligned, functioning, and performing in a manner consistent with the licensing bases. A comprehensive test identifies all inleakage associated with the envelope. It is not necessary to identify all inleakage sources. However, it is imperative that the testing to determine inleakage be based upon the limiting condition for the type of challenge. This limiting condition may change as systems, components, and operating modes are modified. An effective method that has been used and accepted by the staff to perform a test of envelope inleakage is ASTM E741- 95, “Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution” (Ref. 9). Additional guidance on control room envelope inleakage determination for control room habitability testing is being developed and will be published as a regulatory guide. If credit is taken in the evaluation of the removal of