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:
n Section 2.3, this method would ensure that the 95th-percentile overall site χ/Q is conservatively determined. The source to receptor distance is the shortest horizontal distance between the release point and the receptor location. ARCON will use this distance and the elevations of the source and receptor to calculate the slant path.1 For an area source such as a building surface, the shortest horizontal distance from the building surface to the EAB or LPZ is used as the source to receptor distance. If the distance to the receptor is less than about 10 m (32.8 ft), the ARCON code should not be used to assess χ/Q values. These situations will need to be addressed on a case-by-case basis. Should the facility be sited on a military or other government facility, where the EAB and/or LPZ boundary falls within a larger controlled area, the applicant will need to clearly identify the locations or areas considered to be onsite and offsite. These cases will also need to be addressed on a case-by-case basis. 1 ARCON calculates the shortest line-of-sight distance from the release point to the receptor location, based on the differences in elevation and the horizontal intervening distance, and uses it used as the source-to-receptor distance. N DG-4030, Page 11 Figure 2-1. Example of limiting and nonlimiting distances from buildings within the PBA to the EAB/LPZ boundaries An alternative method for determining the distance for each source-receptor pair in each 22.5-degree sector is to use the closest point of an applicable building in that sector to the EAB, as shown in Figure 2-2. As with the preferred method, analysts only need to consider the buildings from which radioactive material could potentially be released. Other buildings, such as support buildings and cooling towers, do not need to be used when calculating the distance to the EAB or LPZ. Using the closest point on an applicable building for each sector would create a less conservative but potentially more