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:
nd, data from sites in open terrain (noncoastal) may indicate no directional preference for fumigation conditions but may indicate durations much less than 1/2 hour. In this case, fumigation should be considered for all directions, but with dura- tions of less than 1/2 hour. 9See § 100.11 of 10 CFR Part 100. 1oThe X(Qs are based on 1-hour averaged data but are assumed to apply for 2 hours. These are then the maximum sector X/Q values. However, if the highest sector X/Qs do not all occur in the same sector, the 16 (sets of) values will be used in dose assessments requiring time-integrated concentration considerations. The set of XJQ values resulting in the highest time- integrated dose within a sector should be considered the maximum sector X/Q values. 2.2.2 Fumigation Conditions for Stack Releases Determination of sector X/Q values for fumigation conditions at the outer LPZ boundary involves the follow- ing assumptions concerning the duration of fumigation for inland and coastal sites: a. Inland Sites: For stack releases at sites located 3.2 kilometers or more from large bodies of water, a fumigation condition should be assumed to exist at the outer LPZ boundary at the time of the accident and continue for 1/2 hour. Sector xJQ values for fumigation should be deter- mined as for the exclusion area boundary in regulatory position 2.1.2. b. Coastal Sites: For stack releases at sites located less than 3.2 kilometers from large bodies of water, a fumiga- tion condition should be assumed to exist at the outer LPZ boundary following the arrival of the plume and continue for a 4-hour period (Ref. 11). Sector X/Q values for fumiga- tion should be determined as for the exclusion area bound- ary in regulatory position 2.1.2. c. The modifications discussed in regulatory posi- tion 2.1.2 may also be considered for the outer LPZ boundary. 3. DETERMINATION OF 5 PERCENT OVERALL SITE X/Q VALUE The X/Q values that are exceeded no more than 5 per- cent of the total number of hours in