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:
e,” 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 modeling should be used only for those situations in which the activity being released is homogeneously throughout the building and when the assumed release rate from the building surface would be reasonably constant over the surface of the building. b. ARCON uses two initial diffusion coefficients entered by the user to represent the area source. There are insufficient field measurements to mechanistically model these initial diffusion coefficients. The following deterministic equations should be used in the absence of site-specific empirical data: ߪ௒బୀௐ௜ௗ௧௛ ೌೝ೐ೌ ೞ೚ೠೝ೎೐ ଺ ߪ௓బୀு௘௜௚௛௧ ೌೝ೐ೌ ೞ೚ೠೝ೎೐ ଺ c. The height and width of the area source (e.g., the building surface) are taken as the maximum vertical and horizontal dimensions of the above-grade building cross-sectional area perpendicular to the line of sight from the building center to the EAB or LPZ boundary. These dimensions are projected onto a vertical plane perpendicular to the line of sight and located at the closest point on the building surface to the EAB or LPZ boundary. The release height is set at the vertical center of the projected plane but may also be considered as a ground-level source to reduce the distance to the EAB or LPZ. The source to receptor distance (slant path) is measured from this point to the receptor location. Section 3.2.4, “Diffuse Area Sources,” of RG 1.194, describes other scenarios, primarily for large light-water reactors requiring the use of a diffuse area source can be found in Section 3.2.4, “Diffuse Area Sources,” of RG 1.194. 2.4 Determining the 95-Percentile and 99.5-Percentile χ/Q Values This RG provides a method for applicants and licensees to use ARCON for offsite (EAB and LPZ) χ/Q