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:
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 the data set around the exclusion area boundary and around the outer LPZ bound- ary should be determined as follows (Ref. 10): Using the xJQ values calculated according to regulatory position 1, an overall cumulative probability distribution for all directions combined should be constructed. A plot of X/Q versus probability of being exceeded should be made, and an upper bound curve should be drawn. The 2-hour X/Q value that is exceeded 5 percent of the time should be selected from this curve as representing the dispersion condition indicative of the type of release being considered. In addition, for the outer LPZ boundary the maximum of the 16 annual average X/Q values should be used along with the 5 percent 2-hour X/Q value to deter- mine X/Q values for the intermediate time periods by logarithmic interpolation. 4. SELECTION OF X/Q VALUES TO BE USED IN EVALUATIONS The X/Q value for exclusion area boundary or outer LPZ boundary evaluations should be the maximum sector X/Q 1.145-5 (regulatory position 2) or the 5 percent overall site xIQ (regulatory position 3), whichever is higher. All direction- dependent sector values should be presented for considera- tion of the appropriateness of the exclusion area and outer LPZ boundaries. Where the basic meteorological data necessary for the analyses described herein substantially deviate from the regulatory position stated in Regulatory Guide 1.23, consideration should be given to the resulting uncertainties in dispersion estimates. D. IMPLEMENTATION The purpose of this section is to provide information to applicants regarding the NRC staff plans for using this regulatory guide. Except in those cases in which an applicant proposes an acceptable alternative method for complying with specified portions of the Commission's