Document: NUREG-0800
Document ID: 7bbfa5be-36ba-4273-8f24-038130581ae5
Document Type: srp
Title: SHORT-TERM DISPERSION ESTIMATES FOR ACCIDENTAL ATMOSPHERIC RELEASES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340583.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.4
CFR Part: 
CFR Title: 

Content:
bility to the site. Lateral and vertical plume spread parameters, a and oz, as functions of meteorological conditions and topography, are reviewed with respect to the characteristics of the accidental release and distances of interest. For stability typing schemes, the curves of 0y and azas functions of downwind distance and atmospheric stability as presented in reference 16 are acceptable for most sites with the addition of an extremely stable (Type G) class. For elevated releases (Ref. 17) or unusual source, meteorological conditions, or topography (e.g., narrow, deep valleys, channeling of airflow), modification of the 0y and az curves may be appropriate (see Ref. 18). Modifications to these curves which reflect recent atmospheric tracer tests primarily during stable, light wind conditions may be used with the atmospheric dispersion model described in Regulatory Guide 1.145. Modifications based on specific studies under similar conditions may also be considered to better represent plume spread over unique terrain features such as deserts (Ref. 12) and large bodies of water (Ref. 19). For situations where a puff diffusion equation is used, ax =a is usually a good assumption. 4. Cumulative Frequency Distributions of X/Q The cumulative probability distributions of X/Q 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 the Standard Format (Ref. 11). The methods used to generate these distributions are reviewed for adequacy and conservatism. 5. Relative Concentrations Used for Accidents The X/Q values used for assessment of consequences of atmospheric radioactive releases for design basis accidents and other accidents, and for onsite and offsite releases of hazardous airborne gases are reviewed for appropriateness of atmospheric dispersion model assumptions and input data, and adequate documentation of this information. The staff makes an independent