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:
vised to provide guidance on control room habitability during a postulated hazardous chemical release, including chlorine. The guide describes assumptions and criteria for screening out release events that need not be considered in the evaluation of control room habitability. The guide also provides guidance on performing detailed evaluations of control room habitability and on screening criteria, including the distance between the release source and the control room, the frequency of shipments (to calculate release frequency from a mobile source), the quantity and duration of a release, toxicity of released chemicals, meteorological conditions (for dispersion calculations), and the rate of air infiltration into the control room. The guide covers both toxic and asphyxiating chemicals, but recognizes that the asphyxiating chemicals should only be considered if their release results in displacement of a significant fraction of the control room air. The Occupational Safety and Health Administration (OSHA) provides guidance on what is considered an oxygen-deficient atmosphere. This revision of Regulatory Guide 1.78 updates specifications of toxicity limits based on more recent data (Regulatory Position 3), brings risk insights into the process, and makes the guidance more performance-based. Consistent with risk-informed regulatory decision-making, this revision encourages licensees to make greater use of risk insights in submitting applications for plant-specific changes to the licensing basis, using the guidance provided in Regulatory Guide 1.174 (Ref. 3). At the same time, the revision continues to provide latitude to the licensees for the use of traditional engineering approaches. Also, consistent with the intent of SECY-00-0191 (Ref. 4) on performance-based initiatives, this revision provides performance-based guidance rather than traditional prescriptive guidance. 1.78-3 The June 1974 version of Regulatory Guide 1.78 specified a 2-minute exposure to given