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:
w conditions (e.g., within the confines of a narrow valley) must be considered or in coastal and desert areas. (See Ref. 12 for additional infonnation.) For purposes of estimating a y during extremely stable (G) atmospheric stability conditions, without plume meander or other lateral enhancement, the following approximation is appropriate: a (G) -- (F) y 1.145-7 10 000, X00, 1 - l- 2 2 5 135 10 2 5 z Uj 02 U- z 0 01 I-- > 10 E OEAEYUSAL 01 DISTANCE fROM SOURCE Am) Figure 2. Vertical diffusion without meander and building wake effects, oz. vs. downwind distance from source for Pasquill's turbulence types (atmospheric stability) (Ref. 7). The sigma values presented above are for unrestricted flow over relatively flat, uniform terrain. They may require modification before application in situations in which rough terrain or restricted flow conditions (e.g., within the confines of a narrow valley) must be considered or in coastal and desert areas. (See Ref. 12 for additional information.) For purposes of estimating cz during extremely stable (G) atmospheric stability conditions, the following approximation is appropriate: a (G) - _ (F) z 5 z 1.145-8 10 T 1 -1 J Stability j Class ,;- X: at CZ I-C) C- C-) CC) 6 4 . 3 - G I I i . : l l ---. I 14 -- i I - 5 . 3 4 5 2 r ; I - 6 WINDSPEED (m/sec) Figure 3. Correction factors for ay values by atmospheric stability class (see Appendix A to this guide). 1.145-9 APPENDIX A ATMOSPHERIC DIFFUSION MODEL FOR RELEASE THROUGH VENTS AND BUILDING PENETRATIONS Rationale The effects of building wake mixing and ambient plume meander on atmospheric dispersion are expressed in this guide in terms of conditional use of Equations 1, 2, and 3.1 Equations I and 2 are formulations that have been acceptable for evaluating nuclear power plant sites over 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