Document: NRC Regulatory Guide
Document ID: c0dbb594-6262-4b83-96b1-366758ad9676
Document Type: regulatory_guide
Title: Interim Licensing policy on as low as Practicable for Gaseous Radiodine Releases from Light-Water-Cooled Nuclear Power Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1229/ML12298A137.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.42
CFR Part: 
CFR Title: 

Content:
edure (Ref. 1) if data from the appropriate levels are not available. Atmos- pheric stability may be divided into seven classes to represent Pasquill stability classes A (extremely unstable) through G (extremely stable) based, preferably, on onsite vertical temperature gradient measurements as pre- sented in Regulatory Guide 1.23 (Safety Guide 23) or other suitable methods. The Gaussian plume model for long-period averages (Eq. 3.144 of Ref. 2) may be used to determine the annual average relative concentrations (x/Q) at appropriate distances and directions from the source. The joint frequency distribution data should be used as input to these calculations. Vertical plume spread (a z) should be estimated at appropriate distances for each stability class using the curves presented in Reference 2, Figure 3.11. For purposes of estimating az during extremely stable (G) conditions, the following approximation is appropriate: 1.42-Bl (G) = 3 az(F) z 5z For rooftop vent and building emissions, a ground-level release may be assumed, and the vertical plume spread adjusted in accordance with Eq. 3.142 of Ref. 2, where A should be defined as the maximum adja- cent building height either upwind or downwind from the release point. The adjusted spread should be limited to a reduction of up to a factor of /3 of the relative concentration calculated for a ground-level point source. For stack releases, plume rise due to momentum based on the formula in Reference 3 is added to the height of the stack above plant grade, and topographical elevations higher than plant grade along the effluent trajectory are subtracted from the stack height. References 1. Smith, M. (ed.), 1968, Recommended Guide for the Prediction of the Dispersion of Airborne Effluents, American Society of Mechanical Engineers, New York, N.Y. 2. Slade, D. H. (ed.), Meteorology and Atomic Energy-1968, TID-24190, USe^=C Division of Technical Information Extension, Oak Ridge, Tennessee. 3. Briggs, G. A., 1969, Plume Rise,