Document: NUREG-0800
Document ID: 4e1c316a-99c2-4fd3-9d9b-323791bd85f8
Document Type: srp
Title: SHORT-TERM ATMOSPHERIC DISPERSION ESTIMATES FOR ACCIDENT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070730398.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.4
CFR Part: 
CFR Title: 

Content:
n specific studies under similar conditions may be considered to better represent plume spread over unique terrain features such as deserts (Ref. 22) and large bodies of water (Ref. 26). Such specific studies should meet the criteria for the use of site-specific experimental data is outlined in Regulatory Position 7 in Regulatory Guide 1.194. For situations where a puff diffusion equation is used, σx = σy is usually a good assumption. 4. Cumulative Frequency Distributions of χ/Q Values The cumulative frequency distributions of EAB and LPZ χ/Q values are reviewed for inclusion of pertinent modes and time periods of release, and adequacy of input data in accordance with the guidelines set forth in Section 2.3.4.2 of Regulatory Guide 1.70 and Section 2.3.4.2 of RG 1.206. The methods used to generate these distributions are reviewed for adequacy and conservatism. 2.3.4-10 Revision 3 - March 2007 5. Atmospheric Dispersion Factors Used for Accidents The χ/Q values used for assessment of consequences of atmospheric radioactive releases for design basis accidents and for onsite and offsite releases of hazardous airborne materials are reviewed for appropriateness of atmospheric dispersion model assumptions, input data, and adequate documentation of this information. The staff makes an independent evaluation of atmospheric dispersion for pertinent distances, usually the EAB and the LPZ outer boundary, using the appropriate meteorological data and dispersion model. The definitions for the EAB and LPZ are reviewed in SRP section 2.1.1. Two probabilistic approaches as described in Regulatory Guide 1.145 are available for evaluating atmospheric dispersion characteristics and the more conservative approach is used. a. A direction-dependent probabilistic approach which uses the highest χ/Q value which is exceeded 0.5% of the time in each of 16 compass directions from the plant. b. A direction-independent probabilistic approach which uses the χ/Q value which is exceeded 5% of