Document: NRC Regulatory Guide
Document ID: 29acb072-d497-44e6-ac1c-a053c0a468a0
Document Type: regulatory_guide
Title: Meteorological Monitoring Programs for Nuclear Power Plants + HISTORY - HISTORY DG-1164 , Third Proposed Revision 1, published 10/2006 Draft ES 926-4 , Second Proposed Revision 1, entitled "Meteorological Measurement Program for Nuclear Power Plants," published 04/1986 Draft SS 926-4 , First Proposed Revision 1, entitled "Meteorological Programs In Support of Nuclear Power Plants," published 09/1980 Revision 0, entitled "Onsite Meteorological Programs," was issued as Safety Guide 23
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0625/ML062540408.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.23
CFR Part: 
CFR Title: 

Content:
tively drier the air. Wind Direction: The direction from which the wind is blowing. Wind direction is reported in degrees azimuth, measured clockwise from true north and ranging from 0E to 360E (e.g., north is 0E or 360E, east is 90E, etc.). Wind Speed: The rate at which air is moving horizontally past a given point. 2. Meteorological Parameters This section discusses the criteria for a basic meteorological monitoring system. Wind speed, wind direction, and vertical temperature difference should be measured on one open-lattice tower or mast. Wind speed and wind direction should be measured at heights of approximately 10 meters (33 feet) and 60 meters (197 feet) above ground level and at a representative level for releases significantly greater than 60 meters (197 feet).5 Vertical temperature difference (∆T) should be measured between the 10-meter (33-foot) level and 60-meter (197-foot) levels and, if necessary, between the 10-meter (33-foot) level and a higher level that is representative of diffusion conditions from release points significantly greater than 60 meters (197 feet).6 Table 1 provides a definition of Pasquill stability classes as a function of ∆T. 7 While routine release or design-basis accident assessments of offsite dose consequences do not typically consider precipitation, the presence or absence of precipitation and its amount are important for severe accident assessments that are included in the applicant’s environmental report and the staff’s environmental impact assessment pursuant to Subpart A to 10 CFR Part 51. Severe accident dose consequence computer codes, such as Version 2 of the MELCOR Accident Consequence Code System (MACCS2) (see D. Chanin and M.L. Young), account for the efficient removal of particulate radionuclides from the plume by wet deposition. 8 For example, trees 15 meters (49 feet) in height should be no closer than 150 meters (492 feet) from the tower or mast. DG-1164, Page 8 Table 1. Classification of Atmospheric