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:
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 dispersion during light wind and stable or neutral conditions and (2) building wake mixing becomes more effective in dispersing effluents than meander effects as the windspeed increases and the atmosphere becomes less stable. Examples of Conditional Use of Diffusion Equations Figures A-1, A-2, and A-3 show plots of XU10/Q (X/Q multiplied by the windspeed U1 )versus downwind distance based on the conditional use (as described in regulatory position 1.3.1) of Equations 1, 2, and 3 during atmos- pheric stability class G. The variable M for Equation 3 equals 6, 3, and 2 respectively in Figures A-1, A-2, and A-3 (M is as defined in regulatory position 1.3.1). In Figure A-I, the XU, IQ from Equation 3 (M=6) is less than the higher value from Equation 1 or 2 at all distances. Therefore, for M = 6, Equation 3 is used for all distances. In Figure A-2, the xU1 0/Q from Equation 3 (M = 3) is less than the higher value from Equation 1 or 2 beyond 0.8 km. Therefore, for M = 3, Equation 3 is used beyond 0.8 km. For distances less than 0.8 kin, the value from Equa- tion 3 equals that from Equation 2. Equation 2 is therefore used for distances less than 0.8 km. In Figure A-3, the XUIO/Q from Equation 3 (M = 2) is never less than the higher value from Equation 1 or 2. Therefore, for M = 2, Equation 3 is not used at all. Instead, Equation 2 is used up to 0.8 km, and Equation 1 is used beyond 0.8 km. 1.145-10 1 02 10-3 Eq. I I 1....I i I I_ _ A I. ,10_-4. _X ___ _ H ____ _ _ __ _ x EEq. 1 = = --- Eq. 3(M=6) I 1Eq. 2 1 0 0.1 1.0 10 PLUME TRAVEL DISTANCE (km) Figure A-1. xU1O/Q as a function of plume travel distance for G stability condition using Equations 1, 2, and 3 (M = 6). 1.145-11 10 1 0 0*0 10 =q. 0.1 1.0 10 PLUME TRAVEL DISTANCE (km) Figure A-2. xU10/Q as a function of plume travel