Document: NRC Regulatory Guide
Document ID: de79d411-4fc9-456e-a5a0-f4a910ca4c9a
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating a Control Rod Ejection Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2111/ML21119A157.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.77
CFR Part: 
CFR Title: 

Content:
to don personal protection equipment (PPE) such as respirators and protective clothing within 2 minutes, so that they will not be subjected to risk from prolonged exposure more than two minutes at the chemical’s IDLH value. Table 1, “Selected IDHL Values for Twenty-Nine Hazardous Chemicals,” has the same IDHL values from Revision 1 of RG 1.78. Promulgated by OSHA, the IDLH concept was established originally for use in assigning respiratory and face-mask equipment as part of the Standards Completion Program, a joint project with the National Institute for Occupational Safety Health (NIOSH) during the mid-1970s. The IDLH values define the levels of chemical concentration that are likely to cause death or immediate or delayed permanent adverse health effects if no PPE is afforded within 30 minutes. The IDLH values are used to: (1) ensure that the worker can identify and escape from a given contaminated environment in the event of failure of the respiratory protection equipment; and (2) determine the required minimum air-purifying factor (APF) for a PPE to provide sufficient protection consistent with the criterion of Appendix A, “Assigned Protection Factors for Respirators,” to 10 CFR Part 20. Further, Table 2, “Minimum Chemical Weights That Require Consideration in CR Habitability Evaluation,” of this RG illustrates the importance of distance between the release source and the CR to determine the mass (i.e., weight) of chemicals, regardless of what kind of toxic chemicals are identified. The frequency of shipments from a mobile source, the quantity and duration of a release, the toxicity of released chemicals, meteorological conditions (for dispersion calculations), and the rate of air infiltration into the CR are also documented from NUREG/CR-6624. Further, RG 1.78, Revision 1, covered both toxic and asphyxiating chemicals and recognized that the asphyxiating chemicals should only be DG-1387, Page 5 considered in CR habitability determinations if their