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:
te χ/Q values to support control room and technical support center habitability dose assessments. Some of the regulatory positions in this RG represent procedures acceptable to the staff beyond those previously found acceptable to determine χ/Q values. The NRC recently updated the ARCON96 user interface to improve its functionality on modern personal computers and renamed the latest version of the code as ARCON 2.0. As described in RG 1.194, the ARCON96 code uses an improved building wake dispersion algorithm; assessment of ground-level, elevated, and diffuse source release modes; hour-by-hour meteorological observations; sector averaging; and directional dependence of dispersion conditions. ARCON was initially developed and has historically only been used for determining onsite χ/Q values at air intakes and points of ingress and egress to the control room and technical support center. In the mid-1980s, the NRC staff determined that its DBA atmospheric dispersion modeling guidance, which included RG 1.145 and PAVAN, significantly overpredicted concentrations during light winds in the vicinity of buildings and embarked on a series of studies that ultimately resulted in the ARCON96 model. The ARCON model is based on field measurements taken at seven reactor sites. The downwind distances of the field measurements ranged from locations on and adjacent to buildings out to distances of 1,200 m (3937 ft). The results were a set of revised diffusion coefficients that had low wind speed and building wake corrections. The resulting dispersion algorithms improved model performance by reducing overpredictions without significantly increasing underpredictions. The staff subsequently endorsed, in large part, ARCON96 in RG 1.194 as a method for determining atmospheric relative concentrations in support of design-basis radiological habitability assessments for the control room DG-4030, Page 6 Both the ARCON96 and ARCON 2.0 versions of the model calculate χ/Q values using hourly