Document: NRC Regulatory Guide
Document ID: bd0ffb9e-22f8-46a4-ab36-f5cffd435ed7
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss of Coolant Accident for Boiling Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739601.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.3
CFR Part: 
CFR Title: 

Content:
.5.2 of Meteorology and Atomic Energy 1968, should be used only in the 0-8 hour period; it is used with a shape factor of 1/2 and the minimum cross-sectional area of the reactor building only. (2) The basic equation for atmospheric diffusion from a ground level point source is: 1 x/Q = 7rUOryc"Z Where (4) The atmospheric diffusion model for ground level releases is based on the information in the table below. Time Following Accident Atmospheric Conditions 0-8 hours Pasquill Type F, windspeed 1 meter/sec, uniform direction 8-24 hours Pasquill Type F, windspeed 1 meter/sec, variable direction within a 22.50 sector 14 days (a) 40% Pasquill Type D, windspeed 3 meter/sec (b) 60% Pasquill Type F, meter/sec (c) wind direction variable sector windspeed 2 within a 22.50 x = the short term average centerline value of the ground level concentration (curie/meter 3) Q = amount of material released (curie/sec) u = windspeed (meter/sec) ay = the horizontal standard deviation of the plume (meters) [See Figure V-1, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.] z= the vertical standard deviation of the plume (meters) [See Figure V-2, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.] (3) For time periods of greater than 8 hours the plume should be assumed to meander and spread unikormly over a 22.50 sector. The resultant equation is: 4-30 days (a) 33.3% Pasquill Type C, windspeed 3 meter/sec (b) 33.3% Pasquill Type D, windspeed 3 meter/sec (c) 33.3% Pasquill Type F, windspeed 2 meter/sec (d) Wind direction 33.3% frequency in a 22.50 sector (5) Figures 3A and 3B give the ground level release atmospheric diffusion factors based on the parameters given in h(4). D. IMPLEMENTATION The purpose of the revision (indicated by a line in the margin) to this guide is to