Document: NRC Regulatory Guide
Document ID: 687c884d-2807-4ca3-ac21-69b87c59f4ab
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:
th information related to the topic of this RG. DG-4030, Page 7 C. STAFF REGULATORY GUIDANCE 1. General Considerations ARCON96, as described in NUREG/CR-6331, “Atmospheric Relative Concentrations in Building Wakes,” Revision 1, issued May 1997 (Ref. 13), and ARCON 2.0 that was recently updated by the NRC, provide an acceptable methodology for calculating offsite atmospheric dispersion factors (χ/Q values), subject to the positions in this guide. ARCON χ/Q values are generally determined for each of the following averaging periods: 0– 8 hours (or 0–2 hours and 2–8 hours), 8–24 hours, 24–96 hours, and 96–720 hours. The period of the most adverse release of radioactive materials to the environment should be assumed to occur coincident with the period of most unfavorable atmospheric dispersion. If the 0–2-hour χ/Q is calculated, this value should be used coincident with the limiting portion of the release to the environment. The 2–8-hour χ/Q value is used for the remaining 6 hours of the first 8-hour time period. Part of this 6-hour interval may occur before or after the limiting 2-hour period. The 8–24, 24–96, and 96–720-hour χ/Q values should similarly be used for the remainder of the release duration. Applicants and licensees for certain designs, or the siting of such units that may have different release characteristics, such that averaging periods other than the standard intervals apply, should identify those intervals and may have to modify their use of the ARCON model further. These modifications should be documented and submitted to the NRC as part of the applicant’s licensing action. 2. Calculation of χ/Q Using ARCON This section addresses the use of the ARCON code for calculating χ/Q values for offsite atmospheric dispersion at receptors located at the EAB and LPZ. The ARCON code should be obtained and maintained under an appropriate software quality assurance program that complies with the applicable criteria of Appendix B,