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:
t of the hourly χ/Qs are below this threshold. This formula and relationship can be expressed as: % ா௫௖௘௘ௗ௔௡௖௘ୀ൬ ಹ೟೚೟ೌ೗షಹೌೡ೒_೔೙೟ ಹ೟೚೟ೌ೗ ൰∗ଵ଴଴ Equation A-1 where, %ா௫௖௘௘ௗ௔௡௖௘ = the percentage of the time that each χ/Q threshold is exceeded ܪ்௢௧௔௟ = the total number of hours in the .LOG file for a given averaging interval ܪ௔௩௚_௜௡௧ = the number of hours exceeded for each χ/Q threshold Equation A-1 should be applied to each line in the .CFD file until the exceedance frequency of each χ/Q in the first column is identified. The 99.5th-percentile χ/Q value will most likely be between two DG-4030, Appendix A, Page A-3 χ/Q threshold values. In Figure A-1, third column, the 99.5th-percentile χ/Q value is bounded by the 2.089 x 10-03 s/m3 χ/Q (99.83th percentile) and 1.905E-03 s/m3 χ/Q (98.31th percentile). Using the two bounding χ/Q threshold values from Equation A-1, a simple linear interpolation can be used to determine the 99.5th-percentile χ/Q using the following equation: ݕ= ݕଵ+ ቂቀ ௫ି௫భ ௫మି௫భቁ∙ሺݕଶ−ݕଵሻቃ Equation A-2 The expressions in Equation A-2 are: y = the resulting 99.5th-percentile χ/Q value y1 = the lesser of the two bounding χ/Q values y2 = the greater of the two bounding χ/Q values x = 99.5 x1 = the lesser of the two exceedance frequencies x2 = the greater of the two exceedance frequencies Based on the χ/Qs in this example, Equation A-2 can be solved as: ݕ= 1.905 ݔ 10ି଴ଷ+ ൤൬99.5 −99.31 99.83 −99.31൰∙ሺ2.089 ݔ 10ି଴ଷ−1.905 ݔ 10ି଴ଷሻ൨ Therefore, y = 99.5th-percentile χ/Q = 1.970 x 10-03 s/m3 Note that for some unique modeling scenarios, this methodology may not produce the most conservative χ/Q values from the CFD output file. Those cases may need to be examined on a case-by- case basis and are discussed in the ARCON 2.0 User’s Guide. DG-4030,