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:
t 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 1.70, "Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants-LWR Edition," or other time periods appropriate to release durations. For a given sector, the average X/Q values for the various time periods may be approximated by a logarithmic inter- polation between the 2-hour 10 sector X/Q and the annual average (8760-hour) X/Q for the same sector. The 2-hour sector XJQ for the outer LPZ boundary is determined using the general method given for the exclusion area boundary in regulatory position 2.1. The annual average X/Q for a given sector is determined as described in regulatory position 1.4. The logarithmic interpolation procedure produces results that are consistent with studies of variations of average concentrations with time periods up to 100 hours (Ref. 8). Alternative methods should also be consistent with these studies and should produce results that provide a mono- tonic decrease in average X/Q with time. For each time period, the highest of the 16 sector X/Q values should be identified. In most cases, these highest values will occur in the same sector for all time periods. 8For example, examination of site-specific information at a location in a pronounced river valley may indicate that fumigation conditions occur only during the downvalley "drainage flow" regime and persist for durations of about 1/2 hour. Therefore, in this case, airflow directions other than the downvalley directions may be excluded from consideration of fumigation conditions, and the duration of fumigation would still be considered as 1/2 hour. On the other hand, 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