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:
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 realistic set of χ/Q values than the preferred method described above. Figures 2-1 and 2-2 depict a square EAB/LPZ boundary; however, the same principles would apply to EAB and LPZ boundaries of any other shape. DG-4030, Page 12 Figure 2-2. Example of how to use the closest point of a building withing each of the 16 directional sectors from the PBA to the EAB/LPZ boundaries 2.2.2 Direction from Source to Receptor Traditionally, the ARCON code has been run by calculating a relative concentration for only one specific direction per code execution or, put otherwise, one source-receptor pair. This source -receptor pair, within the existing code, assumes a release point from a location within or near the plant boundary. 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 direction from the nearest building edge to the EAB or LPZ. When the combinations of source (release point) and receptor pairs have been identified, the direction and distance between the release point and the receptor location should be determined. Wind direction data are recorded as the direction from which the wind blows (e.g., a north wind blows from the north, a wind blowing out of the west is recorded with a direction of 270 degrees). The direction input to ARCON is the wind direction (in degrees) that would carry the plume from the release point to the receptor location.2 For example, an analyst standing at the receptor location facing west to the release point would enter 270 degrees; an analyst facing north would enter 360 degrees. 2.3 Release Characteristics A 95th-percentile overall site χ/Q value, or a 99.5th-percentile relative