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:
igure 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 meter/sec; variable direction within a 22.50 sector. 14 days See Figure 1(C) Envelope of Pasquill diffusion categories with the following relationship used to represent maximum plume concentrations as a function of distance: Atmospheric Condition Case 1 40% Pasquill A 60% Pasquill C Atmospheric Condition Case 2 50% Pasquill C 50% Pasquill D Atmospheric Condition Case 3 33.3% Pasquill C 33.3% Pasquill D 33.3% Pasquill E Atmospheric Condition Case 4 33.3% Pasquill D 33.3% Pasquill E 33.3% Pasquill F Atmospheric Condition Case 5 50% Pasquill D 50% Pasquill F wind speed variable (Pasquill Types A, B, E, and F windspeed 2 meter/sec; Pasquill Types C and D windspeed 3 meter/sec); variable direction within a 22.50 sector. 4-30 days See Figure I(D) Same diffusion relations as given above; windspeed variable dependent on Pasquill Type used; wind direction 33.3% frequency in a 22.50 sector. This model should be used until adequate site meteorological data are obtained. In some cases, available information, such as meteorology, topography and geographical location, may dictate the use of a more restrictive model to insure a conservative estimate of potential offsite exposures. 1.3-3 h. For BWR's without stacks the atmospheric diffusion model 6 should be as follows: (1) The 0-8 hour ground level release concentrations 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 in calculating potential exposures. The volumetric building wake correction factor, as defined in section 3-3.5.2 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