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:
ound. The maximum cloud concentration always should be assumed to be at ground level. (2) The appropriate average beta and gamma energies emitted per disintegration, as given in the Table of Isotopes, Sixth Edition, by C. M. Lederer, J. M. Hollander, I. Perlman; University of California, Berkeley; Lawrence Radiation Laboratory; should be used. g. For BWR's with stacks the atmospheric diffusion model should be as follows: (1) The basic equation for atmospheric diffusion from an elevated release is: exp(-h2 I2oz2) X/Q iu a Sy~z Where 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) y= the horizontal standard deviation of the plume (meters) [See Figure V-l, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.] oz= 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.] h = effective height of release (meters) (2) For time periods of greater than 8 hours the plume from an elevated release should be assumed to meander and spread uniformly over a 22.50 sector. The resultant equation is: 2.032 exp(-h2/2az 2) x/Q a=ux Where x = distance from the release point (meters); other variables are as given in g(l). (3) The atmospheric diffusion model s for an elevated release as a function of the distance from the reactor, is based on the information in the table below. Time Following Accident Atmospheric Conditions 0-8 hours See Figure I(A) Envelope of Pasquill diffusion categories based on Figure A7 Meteorology and Atomic Energy-1968, assuming various stack heights; windspeed 1 meter/sec; uniform direction. 8-24 hours See Figure I(B) Envelope of Pasquill diffusion categories; windspeed 1