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:
uents in Routine Releases from Light-Water-Cooled Reactors” (Ref. 19), which addresses χ/Q values used in the assessment of routine effluent releases. The development of this algorithm was based in part on limited field experiments. Given the limited experiment set, the results obtained with this algorithm may not be sufficiently conservative for accident evaluations. For this reason, the vent-release mode should not be used in design-basis assessments. This position is consistent with the guidance of RG 1.145 for offsite χ/Q values. These releases should be treated as a ground-level release (Section 2.3.1 of this RG) or as an elevated release (Section 2.3.2 of this RG). DG-4030, Page 15 2.3.4 Point Source Use of a ground-level point source from a building periphery is the preferred method for determining the atmospheric concentrations at the EAB or LPZ. Use of this method will produce the most conservative estimates, since there will be no plume rise for buoyancy or mechanical jet effects, as well as no credit given for diffuse area sources. The point source should be the closest point, along the edge of an applicable building, to the EAB or LPZ following the guidance in Section 2.2.1 and depicted in Figures 2-1 and 2-2. 2.3.5 Diffuse Source—Point Receptor ARCON allows users to enter initial diffusion coefficients that may approximate dimensions of diffuse area sources. The diffusion models in ARCON are based on point source formulations. However, some release sources may be better characterized as area sources. Assessments that deem diffuse area sources to be appropriate should follow the guidance in Section 2.2.1 of this RG and use the shortest distance between the building boundary and the EAB or LPZ. Section 2.5.7, “Example 6—Diffuse Source Release,” of NUREG/CR-6331, Revision 1, shows an example of how to model a diffuse area source. When considering the use of a diffuse area source, analysts should consider the following: a. Diffuse source