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:
dary. 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 should be constructed for each of the 16 sectors. Each distribution should be de- scribed in terms of probabilities of given XJQ values being exceeded in that sector during the total time. A plot of XJQ versus probability of being exceeded should be made for each sector, and a smooth curve should be drawn to form an upper bound of the computed points. For each of the 16 curves, the XJQ value that is exceeded 0.5 percent 7 of the total number of hours in the data set should be selected (Ref. 10). These are the sector X/Q values. The highest of the 16 sector values is defined as the maximum sector X/Q value. 2.1.2 Fumigation Conditions for Stack Releases Regulatory position 1.3.2 describes procedures for calculating a fumigation XJQ for each sector. These sector fumigation values, and the general (nonfumigation) sector values obtained in regulatory position 2.1.1, are used to determine appropriate sector fumigation x/Qs. Conserva- tive assumptions for fumigation conditions, which differ for inland and coastal sites, are described below. Modifications may be appropriate for specific sites. a. Inland Sites: For stack releases at sites located 3.2 kilometers or more from large bodies of water (e.g., oceans or Great Lakes), a fumigation condition should be assumed to exist at the time of the accident and continue for 1/2 hour (Ref. 11). For each sector, if the sector fumigation X/Q exceeds the sector nonfumigation X/Q, use the fumiga- tion value for the 0 to 1/2-hour time period and the non- fumigation value for the 1/2-hour to 2-hour time period. Otherwise, use the nonfumigation sector value for the entire 0 to 2-hour time period. The 16 (sets of) values thus determined should be used in dose assessments requiring time-integrated concentration considerations. b. Coastal