Document: NRC Regulatory Guide
Document ID: 14983af3-17d8-4f7b-866e-8d603a0f811c
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss of Coolant Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739614.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.4
CFR Part: 
CFR Title: 

Content:
o account specific meteorological, topographical, and other characteristics which may affect the maximum plume concentration. These site related characteristics must be evaluated on an individual case basis. In the case of beta radiation, the receptor is assumed to be exposed to an infinite cloud at the maximum ground level concentration at that distance from the reactor. In the case of gamma radiation, the receptor is assumed to be exposed to only one-half the cloud owing to the presence of the ground. 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. The atmospheric diffusion model should be as follows: (1) The basic equation for atmospheric diffusion from a ground level point source is: 1 XIQ = u SrUayoz 1.4-2 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) ay = the horizontal standard deviation of the plume (meters) [See Figure V-i, 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, Nudear Safety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.] (2) For time periods of greater than 8 hours the plume should be assumed to meander and spread uniformly over a 22.50 sector. The resultant equation is: 2.032 x/Q = uu OzU Where x = distance from point of release to the receptor; other variables are as given in g(l). (3) The atmospheric diffusion model 2 for ground level releases is based