Document: NRC Regulatory Guide
Document ID: d1045e85-64b0-4a83-8450-067a4fcd130f
Document Type: regulatory_guide
Title: Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants + HISTORY –HISTORY 04/2014 – Periodic Review of Revision 1 – Reviewed with issues for future consideration 02/1983 – Reissued 02/1983 to correct page 1.145-7 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740205.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.145
CFR Part: 
CFR Title: 

Content:
tory guidelines. 1. CALCULATION OF ATMOSPHERIC RELATIVE CON- CENTRATION (X/Q) VALUES Equations and parameters presented in this section should be used unless unusual siting, meteorological, or terrain conditions dictate the use of other models or considerations. Site-specific atmospheric diffusion tests covering a full range of conditions may be used as a basis for modifying the equations and parameters. 1.1 Meteorological Data Input The meteorological data needed for X/Q calculations include windspeed, wind direction, and a measure of atmos- pheric stability. These data should represent hourly averages as defined in Regulatory Guide 1.23. Wind direction should be classed into 16 compass direc- tions (22.5-degree sectors centered on true north, north- northeast, etc.). Atmospheric stability should be determined by vertical AT between the release height and the 10-meter level. Acceptable stability classes are given in Regulatory Guide 1.23. If other well-documented parameters are used to determine plume dispersion (with appropriate justification), the models described in this guide may require modifica- tion. A well-documented parameter is one that is substan- tiated by diffusion data collected in terrain conditions similar to those at the nuclear power plant site being considered. Calms should be defined as hourly average windspeeds below the vane or anemometer starting speed, whichever is higher (to reflect limitations in instrumentation). If the instrumentation program conforms to the regulatory position in Regulatory Guide 1.23, calms should be assigned a windspeed equal to the vane or anemometer starting speed, whichever is higher. Otherwise, consideration of a conservative evaluation of calms, taking into account the limitations of the windspeed measurement system, will be necessary. Wind directions during calm conditions should be assigned in proportion to the directional distribution of noncalm winds with speeds less than 1.5 meters persecond.3 1.2