Document: NRC Regulatory Guide
Document ID: 0cfc3978-32da-4370-9f31-8a3547d82846
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and Storage Facility for Boiling and Pressurized Water Reactors (Rev. 0)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0833/ML083300022.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.25
CFR Part: 
CFR Title: 

Content:
of radioactive material available for release to the environment will be evaluated on an individual case basis. 4 These efficiencies are based upon a 2-inch charcoal bed depth with ¼ second residence time. Efficiencies may be different for other systems and must be calculated on an individual case basis. 5 Credit for mixing will be allowed in some cases; the amount of credit will be evaluated on an individual case basis. 6 Credit for an elevated release will be given only if the point of release is (a) more than two and one-half times the height of any structure close enough to affect the dispersion of the plume or (b) located far enough from any structure which could affect the dispersion of the plume. For those plants without stacks the atmospheric diffusion factors assuming ground level release given in regulatory position 2.b. should be used. RG-1.25, Page 4 2. The assumptions for atmospheric diffusion are: a. Ground Level Releases (1) The basic equation for atmospheric diffusion from a ground level point source is: z yσ σ u π 1 Q / χ = Where: χ = the short term average centerline value of the ground level concentration (curies/m3) Q = amount of material released (curies/sec) u = windspeed (meters/sec) σy = 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.] σz = 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.] (2) For ground level releases, atmospheric diffusion factors7 used in evaluating the radiological consequences of the accident addressed in this guide are based on the following assumptions: (a) windspeed of 1 meter/sec; (b) uniform wind direction; (c) Pasquill diffusion category F.