Document: NUREG-0800
Document ID: dc7fdaed-8abd-4b49-b5df-dcf64a9b93b0
Document Type: srp
Title: SHORT-TERM DISPERSION ESTIMATES FOR ACCIDENTAL ATMOSPHERIC
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070235.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.4
CFR Part: 
CFR Title: 

Content:
priateness of atmospheric dispersion model assumptions and input data, and adequate documentation of this information. The staff makes an independent evaluation of atmospheric dispersion for pertinent distances, usually the exclusion area boundary and the low population zone outer boundary, using the appropriate meteorological data and dispersion model. Two probabilistic approaches are available for evaluating atmospheric transport and diffusion characteristics. a. A direction-dependent probabilistic approach using the X/Q values which are exceeded 0.5% of the time in each of 16 directions from the plant. This methodology is described in Regulatory Guide 1.145. b. A direction-independent probabilistic approach using the X/Q value which is exceeded 5% of the time. This methodology is described in Reference 13Ref. 14.27 These values are assumed to represent conditions for a 2-hour period. X/Q values for time periods greater than 2 hours are estimated for the LPZ distance by assuming a logarithmic relationship between the "2-hour" value and the annual average value. These values of X/Q based on appropriate models for appropriate time intervals and distances are used in the analyses presented in Chapter 15 for dose assessment of design basis accidents. 2.3.4-7 DRAFT Rev. 2 - April 1996 X/Q values based on site-specific meteorological data are calculated, as needed, for control room dose calculations and onsite and offsite releases of hazardous airborne materials. These estimates are made on a case-by-case basis since the mode of release, and therefore the dispersion models, vary. For standard design certification reviews under 10 CFR Part 52, the procedures above should be followed, as modified by the procedures in SRP Section 14.3 (proposed), to verify that the design set forth in the standard safety analysis report, including inspections, tests, analysis, and acceptance criteria (ITAAC), site interface requirements and combined license action items, meet the