Document: NRC Regulatory Guide
Document ID: 96baa826-d3bb-478b-8f38-e74500f6d433
Document Type: regulatory_guide
Title: 06/2009 (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0911/ML091170109.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.21
CFR Part: 
CFR Title: 

Content:
aseous effluent dispersion factors (χ/Q) and deposition factors (D/Q) in accordance with Regulatory Guide 1.111, “Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors” (Ref. 28). The use of annual average meteorological conditions to determine χ/Q and D/Q is appropriate for continuous releases and for establishing instantaneous release set points (see NUREG-0133, “Preparation of Radiological Effluent Technical Specifications for Nuclear Power Plants,” issued October 1978 (Ref. 29)). This practice may also be acceptable for calculating doses from intermittent releases if the releases occur randomly and with sufficient frequency to justify the use of annual average meteorological conditions (see Regulatory Guide 1.111). When calculating long-term, annual average frequency distributions, 5 (or more) years of data should be used. If long-term, annual average χ/Q and D/Q values are used in determining dose to individual members of the public, the values should be revalidated or updated periodically (e.g., every 3 to 5 years). If the evaluation indicates the long- term, annual average χ/Q and D/Q are nonconservative by 10 percent or more, either revise the affected values or document the reason why such changes are not deemed necessary. 3.3 Release Height The release height affects the transport and dispersion of radioactive materials especially with respect to “downwash” and building wake effects. For facilities with both ground-level and elevated releases, an evaluation should be made to determine the proper location of the maximum exposed individual member of the public. From a dispersion perspective, when determining the maximum exposure location (submersion and/or deposition), the evaluation should consider the magnitude of release originating as an elevated release and the magnitude of release originating as a ground-level release. For example, a close-in, downwind