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:
ees, or nearby terrain with heights exceeding one-half the height of the wind measurement. The separation between the wind sensor and such obstructions should be 10 times the obstruction height.8 Wind sensors should be located on top of the measurement tower or mast or extended outward on a boom to reduce airflow modification and turbulence induced by the supporting structure itself. DG-1164, Page 9 Because the tower structure can affect downwind measurements, sensors on the side of a tower should be mounted at a distance equal to at least twice the longest horizontal dimension of the tower (e.g., the side of a triangular tower). The sensors should be on the upwind side of the mounting object in areas with a dominant prevailing wind direction. In areas with two distinct prevailing wind directions (e.g., mountain valleys), the sensors should be mounted in a direction perpendicular to the primary two directions. Air temperature and humidity measurements should be made to avoid air modification by heat and moisture sources (e.g., ventilation sources, cooling towers, water bodies, large parking lots). For this reason, the tower or mast should not be located on or near permanent manmade surfaces, such as concrete or asphalt, or temporary land disturbances, such as coal piles, plowed fields, or storage areas. Temperature sensors should be mounted in fan-aspirated radiation shields to minimize the adverse influences of thermal radiation and precipitation. The aspirated temperature shields should either be pointed downward or laterally towards the north. Precipitation gauges should be equipped with wind shields to minimize the wind-caused loss of precipitation. Where appropriate, precipitation gauges should also be equipped with heaters to measure water equivalent during freezing conditions. 4. Instrument Accuracy and Range The time-average accuracies for digital systems should meet the criteria listed in Table 2. These accuracies are stated in terms of overall system