Document: NUREG-0800
Document ID: 4e1c316a-99c2-4fd3-9d9b-323791bd85f8
Document Type: srp
Title: SHORT-TERM ATMOSPHERIC DISPERSION ESTIMATES FOR ACCIDENT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070730398.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.4
CFR Part: 
CFR Title: 

Content:
stulated sources and control room receptors. However, if the distance to the receptor is less than about 10 meters, the ARCON96 code should not be used to assess χ/Q values. An acceptable alternative approach would be to define the 0-8 hour χ/Q value as 1/F where F is the higher value of the volumetric flow rate at either the release point (e.g., a vent or stack flow rate) or the intake point (e.g., an air intake flow rate). The χ/Q values for other time intervals can be obtained by adjusting the 0-8 hour χ/Q value for long-term meteorological averaging of wind direction. This can be accomplished by multiplying the 0-8 hour time interval χ/Q value by 0.88 for the 8-24 hour time interval, 0.75 for the 1-4 day time interval, and 0.50 for the 4-30 day time interval. Use of this volumetric flow rate methodology should factor in possible decreases in the flow rate (e.g., due to loss of offsite power or other single failure). In addition, unfiltered inleakage should be considered independently of the control room air intake flow rate. 2.3.4-9 Revision 3 - March 2007 Other modifications to the atmospheric dispersion model which should be considered include restrictions to horizontal or vertical plume spread (e.g., by narrow deep valleys, channeling of airflow, and by persistent low-level temperature inversions). Fumigation conditions should be considered for elevated releases to the EAB and LPZ. In the absence of site-specific information concerning the frequency, duration, and directional preference of fumigation conditions, deterministic approaches such as those described in Regulatory Guide 1.145 may be used. 2. Meteorological Data The meteorological data used in atmospheric dispersion analyses are reviewed for compatibility with the models, representativeness with respect to airflow characteristics of the site and vicinity, and representation of normal annual distribution of meteorological conditions. If adequate onsite meteorological data are not available, the