Document: NRC Regulatory Guide
Document ID: d1045e85-64b0-4a83-8450-067a4fcd130f
Document Type: regulatory_guide
Title: Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants + HISTORY –HISTORY 04/2014 – Periodic Review of Revision 1 – Reviewed with issues for future consideration 02/1983 – Reissued 02/1983 to correct page 1.145-7 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740205.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.145
CFR Part: 
CFR Title: 

Content:
a period of many years (Ref. 7 and Regulatory Guides 1.3 and 1.4). The conditional use of Equations 1 and 2 provides an assessment of atmospheric diffusion, including only the effects of building wake mixing that occur during moderate windspeed conditions (>3 m/sec). These equations have recently been found to provide estimates of ground-level concentrations that are consistently too high during light wind and stable or neutral atmospheric conditions for 1-hour release durations (Refs. I through 6). Equation 3 is an empirical formulation based on NRC staff analysis of atmospheric diffusion experiment results (Ref. 2). The NRC staff examined values of lateral plume spread with meander and building wake effects (:y) by atmospheric stability class (based on AT), calculated from measured ground4evel concentrations from the experi- mental results. Plots of the computed Z; values by atmos- pheric stability class and downwind distance were analyzed conservatively but within the scatter of the data points by virtually enveloping most test data. The resultant analysis is the basis for the correction factors applied to the a values (see Fig. 3 of this guide). Thus, Equation 3 identiges con- servatively the combined effects of increased plume meander and building wake on diffusion in the horizontal crosswind direction under light wind and stable or neutral atmos- pheric conditions, as quantified in Figure 3. These experi- ments also indicate that vertical building wake mixing during light wind and stable conditions is not as complete as during moderate wind, unstable conditions. In addition, | For additional information see NUREG/CR-2260. vertical plume meander is shown to be virtually nonexistent during light wind, stable conditions. However, the experi- mental results for both situations could not be quantified for general application at this time. The conditional use of Equations 1, 2, and 3 is consid- ered appropriate because (1) horizontal plume meander tends to dominate