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:
e 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. (3) Figure 1 is a plot of atmospheric diffusion factors (χ/Q) versus distance derived by use of the equation for a ground level release given in regulatory position 2.a.(1) above under the meteorological conditions given in regulatory position 2.a.(2) above. (4) Atmospheric diffusion factors for ground level releases may be reduced by a factor ranging from one to a maximum of three (see Figure 2) for additional dispersion produced by the turbulent wake of the reactor building. The volumetric building wake correction as defined in Subdivision 3-3.5.2 of Meteorology and Atomic Energy–1968, is used with a shape factor of ½ and the minimum cross-sectional area of the reactor building only. 7 These diffusion factors should be used until adequate site meteorological data are obtained. In some cases, available information on such site conditions as meteorology, topography and geographical location may dictate the use of more restrictive parameters to insure a conservative estimate of potential offsite exposures. RG-1.25, Page 5 b. Elevated Releases (1) The basic equation for atmospheric diffusion from an elevated release is: z y 2 z h σ σ u π σ 2 / e Q / χ 2 − = 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