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:
e lower value of these two should then be selected as the appro- priate xJQ value. Examples and a detailed explanation of the rationale for determining the controlling conditions are given in Appendix A to this guide. b. During all other meteorological conditions, plume meander should not be considered. The appropriate X/Q value for these conditions is the higher value calculated from Equation 1 or 2. 1.3.2 Stack Releases This class of release modes includes all release points at levels that are two and one-half times the height of adjacent solid structures or higher (Ref. 9). Nonfumigation condi- tions are treated separately. a. For nonfumigation conditions, the equation for ground-level relative concentration at the plume center- line for stack releases is: 2 1 - Uhe IX/Q = l7hyzexpj7 ] (4) where Ir is 3.14159. U1 0 is windspeed at 10 meters above plant grade,5 in m/sec, ay is lateral plume spread, in mn, a function of atmos- pheric stability and distance (see Fig. 1), Uz is vertical plume spread, in m, a function of atmospheric stability and distance (see Fig. 2), Ty is lateral plume spread with meander and building wake effects, in m, a function of atmospheric stability, windspeed U, and distance [for distances of. 800 meters or less, Z = May, where M is determined from Fig. 3; for Lstances greater than 800 meters, Zy = (M - 1) uy800m + ay], and A is the smallest vertical-plane cross-sectional area of the reactor building, in m2. (Other structures or a directional consideration may be justified when appropriate.) 5The 10-meter level is considered to be representative of the layer through which the plume is mixed when subjected to building wake effects. Uh is windspeed representing conditions at the release height, in m/sec, he is effective stack height, in m: he = h5 - ht, hs is the initial height of the plume (usually the stack height) above plant grade, in m, and ht is the maximum terrain height above plant grade between the release point and the point for