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:
risk as a small fraction (0.1%) of other risks to which the public is exposed. Procedures outlined in the “Framework for Risk-Informed Changes to the Technical Requirements of 10 CFR Part 50,” an attachment to SECY-00-0198 (Ref. 19), may also be used as guidelines for quantifying risks. If the level of risk associated with the release of a toxic chemical is not acceptable, then a detailed control room habitability evaluation should be performed. A method acceptable to the NRC staff for evaluating the CR habitability is described in Section C.3 below. 3. CONTROL ROOM HABITABILITY EVALUATION When performing a detailed evaluation of CR habitability during a hazardous chemical release using this guidance, the metric applicants and licensees should use for each chemical is the IDHL that can be tolerated without physical incapacitation of a CR operator. In deriving the toxicity level in the CR, the detailed calculations should consider several factors, such as accident type; release characterization (e.g., release rate, duration); atmospheric dispersion characteristics, including prevailing meteorological conditions at the site; and the air exchange rate of the CR. The checklist for the determinations of the toxicity level (i.e., concentration) in the CR, based on the toxic chemical and CR air quality parameter values, is as follows: (1) name of the most hazardous chemical, (2) type of source (stationary or mobile) during the accidental release; (3) maximum quantity or concentration measured (if available); (4) IDLH values (i.e., ppm or mg/m3); (5) average continuous release rate of hazardous chemical; (6) vapor pressure (torr) of hazardous chemical (at local ambient plant temperature); (7) fraction of chemical flashed and rate of boiloff when spilling occurs; (8) total plume travel distance between the CR and the chemicals; and (9) local meteorological data. For determining the air quality in the CR for habitability evaluation, the NRC recommends the following 7