Document: NRC Regulatory Guide
Document ID: 4e88bc9c-73b4-419d-a312-fe7e31653337
Document Type: regulatory_guide
Title: Use of ARCON Methodology For Calculation Of Accident-Related Offsite Atmospheric Dispersion Factors
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2116/ML21165A005.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.249
CFR Part: 
CFR Title: 

Content:
tely address meteorological conditions that could result in higher χ/Qs. Concentrations greater than those predicted by ARCON could result from diurnal wind direction changes, meander, or stagnation. Therefore, the procedure in the following paragraphs, as well as equations (1) and (2), should be used to assess whether a particular stack-to-receptor configuration is subject to this concern and to determine the appropriate χ/Q values. For stack releases, the maximum ground-level concentration in a sector may occur beyond the EAB or LPZ boundary distance. Therefore, for stack releases, χ/Q calculations should be made in each sector at each minimum boundary distance and at various distances beyond the EAB / LPZ boundary distance to determine the maximum relative concentration for consideration in subsequent calculations. DG-4030, Page 14 In addition to running ARCON to determine the elevated stack χ/Q values for the EAB or LPZ assessment, the analyst should calculate the maximum elevated stack χ/Q value using the methodology of RG 1.145 to determine the maximum χ/Q value at ground-level for the 0–2-hour interval and for the 24– 96-hour and 96–720-hour intervals. The NRC-sponsored code PAVAN, is acceptable to the staff for this assessment, as discussed in RG 1.145 and NUREG/CR-2858 (Ref. 8). For this assessment, the input parameters should be adjusted such that the effective release height is measured from the elevation of the EAB or LPZ receptor. The same release point characterization and meteorological data sets used in ARCON should be used to determine the χ/Q values for several distances in each wind direction sector with the objective of identifying the maximum χ/Q value. The maximum χ/Q value obtained for the 0– 2-hour interval should be compared to the corresponding χ/Q value generated by ARCON and the higher value determined through the use of PAVAN. The χ/Q values generated by ARCON for the 2–8-hour and the 8–24-hour intervals may be