Document: NRC Regulatory Guide
Document ID: d1045e85-64b0-4a83-8450-067a4fcd130f
Document Type: regulatory_guide
Title: Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants + HISTORY –HISTORY 04/2014 – Periodic Review of Revision 1 – Reviewed with issues for future consideration 02/1983 – Reissued 02/1983 to correct page 1.145-7 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740205.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.145
CFR Part: 
CFR Title: 

Content:
ions. The highest ground-level xJQ values from elevated releases are expected to occur during stable conditions with low windspeeds when the effluent plume impacts on a terrain obstruction (i.e., he = 0). However, elevated plumes diffuse upward through the stable layer aloft as well as downward through the fumigation layer. Thus ground-level relative concentrations for elevated releases under fumigation conditions cannot be higher than those produced by nonfumigation, stable atmospheric conditions with he = 0. For the fumigation case that assumes F stability and a windspeed of 2 meters per second, Equation 4 should be used instead of Equation 5 at distances greater than the distance at which the XIQ values determined using Equa- tion 4 with he = 0 and Equation 5 are equal. 1.4 Calculation of X/Q Values at Outer LPZ Boundary Distances Two-hour XjQ values should also be calculated at outer LPZ boundary distances. The procedures described above for exclusion area boundary distances (see regulatory position 1.3) should be used. An annual average (8760-hour) X/Q should be calculated for each sector at the outer LPZ boundary distance for that sector, using the method described in regulatory posi- tion L.c of Regulatory Guide 1.1 11. For stack releases, he should be determined as described in regulatory posi- tion 1.3.2 above. These calculated 2-hour and annual average values are used in regulatory position 2.2 to determine sector X/Q values at outer LPZ boundary distances for various inter- mediate time periods. 6 6See § 100.11 of 10 CFR Part 100. 2. DETERMINATION OF MAXIMUM SECTOR x/Q VALUES The XJQ values calculated in regulatory position 1 are used to determine "sector xJQ values" and "maximum sector XJQ values" for the exclusion area boundary and the outer LPZ boundary. 2.1 Exclusion Area Boundary 2.1.1 General Method Using the XJQ values calculated for each hour of data according to regulatory position 1.3, a cumulative proba- bility distribution of X/Q values