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:
in Regulatory Guide 1.145 for design basis accidental releases. The models are reviewed for suitability to release characteristics, plant configuration, and site topography. The accidents and release characteristics to be considered are obtained from the reviewers of SAR Chapter 15. When the Gaussian assumptions are not applicable (e.g., buoyant gases and close-in estimates made for points among or near buildings), other models and techniques used to make estimates are identified and evaluated. Each release should be charac- terized as either an elevated point source or a ground level point source. Generally the release is considered to be elevated if the release point is at least two and one-half times as high as nearby solid structures. Turbulent mixing of the effluent into the wake of plant structures is usually allowed for ground level releases. The volumetric correction is based on one-half the minimum cross-sectional area of the structure from which the effluent is released. Most accidental releases can be considered as continuous releases (i.e., on the order of several minutes or more). However, some releases such as, from steam line breaks or of hazardous chemicals may be considered as instantaneous (puffs). The general Gaussian diffusion model for con- tinuous releases is used to evaluate releases on the order of several minutes or more. For puff releases, instantaneous point source Gaussian diffusion equations are used with a correction for initial source volume (Ref. 12). Other modifications to the atmospheric dispersion model which should be considered include restrictions to horizontal or vertical plume spread (e.g., by narrow deep valleys, channeling of airflow, and by persistent low-level temperature inversions). Fumigation conditions should be considered for elevated releases. In the absence of site-specific information concerning the frequency, duration, and directional prefer- ence of fumigation conditions, deterministic approaches such as those