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:
to the corresponding χ/Q value generated by ARCON and the higher value determined through the use of PAVAN. The χ/Q values generated by ARCON for the 2–8-hour and the 8–24-hour intervals may be used without adjustment. For the 24–96-hour and 96–20-hour intervals, the following expressions may be used to determine the effective χ/Q. This deterministic approach assumes that the stack plume reverses direction for 1 hour of each day for the duration of the event. The plume is assumed to fold over itself such that the ground-level concentration is at its maximum value at the receptor location. ቀ ఞ ொቁ ଶସ→ଽ଺௛௥= ଵ∙ቀഖ ೂቁ మర→వల ೓ೝ ುಲೇಲಿ ାଶଷ∙ቀഖ ೂቁ మర→వల ೓ೝ ಲೃ಴ೀಿ ଶସ (1) ቀ ఞ ொቁ ଽ଺→଻ଶ଴௛௥= ଵ∙ቀഖ ೂቁ వల→ళమబ ೓ೝ ುಲೇಲಿ ାଶଷ∙ቀഖ ೂቁ వల→ళమబ ೓ೝ ಲೃ಴ೀಿ ଶସ (2) Fumigation is an atmospheric effect that occurs when a plume, initially embedded in an elevated relatively non-turbulent layer of the atmosphere, encounters a turbulent mixing layer. As described in NUREG/CR- 3352, “Fumigation Potential at Inland and Coastal Power Plant Sites”, issued October 1983 (Ref. 18), this fumigation effect can lead to ground-level concentrations, when and where the plume comes to the ground, that are higher than the concentrations before or after the fumigation episode. Therefore, at sites where fumigation is a potential concern, this effect will be addressed on a case-by-case basis. 2.3.3 Vent Releases The ARCON calculation of vent releases includes an algorithm to model mixed-mode releases as described in RG 1.111, “Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents 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