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:
ation 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 Sites: For stack releases at sites located less than 3.2 kilometers from large bodies of water, a furniga- tion condition should be assumed to exist at the exclusion area boundary at the time of the accident and continue for the entire 2-hour period. For each sector, the larger of the 7Selection of the 0.5 percent level is based on an equality without consideration of plume meander, between the S percen directionally independent evaluation of X/Q (the previous evaluatior procedure) and the 0.5 percent directionally dependent evaluation of VQ averaged over a reasonably representative number of existini nuclear power plant sites. See NUREG/CR-2260 for additiona information. 1.145-4 sector fumigation X/Q and the sector nonfumigation X/Q should be used for the 2-hour period. Of these 16 sector values, the highest is the maximum sector X/Q value. c. Modifications: These conservative assumptions do not consider frequency and duration of fumigation conditions as a function of airflow direction. If information can be presented to substantiate the likely directional occurrence and duration of fumigation conditions at a site, the assump- tions of fumigation in all directions and of duration of 1/2 hour and 2 hours for the exclusion area boundary may be modified. Then fumigation need only be considered for airflow directions in which fumigation has been determined to occur and of a duration determined from the study of site conditions.8 2.2 Outer LPZ Boundary 2.2.1 General Method Sector X/Q values for the outer LPZ boundary should be determined for various time periods throughout the course of the postulated accident.9 The time periods should represent appropriate meteorological regimes, e.g., 8 and 16 hours and 3 and 26 days as presented in Section 2.3.4 of Regulatory Guide