Document: NUREG-0800
Document ID: 0b3174a2-1530-473d-8cf7-024c17b62e52
Document Type: srp
Title: LONG-TERM ATMOSPHERIC DISPERSION ESTIMATES FOR ROUTINE RELEASES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070730713.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.5
CFR Part: 
CFR Title: 

Content:
nt. Using the criteria presented in Regulatory Guide 1.111, each release is classified as completely elevated, partially elevated, or completely ground level. Turbulent mixing of the effluent into the wake of plant structures is considered where appropriate in accordance with Regulatory Guide 1.111. Topographic characteristics in the vicinity of the site are examined for restrictions of horizontal and/or vertical plume spread, channeling or other changes in airflow trajectories, and other unusual conditions affecting atmospheric transport and diffusion between the source and receptors of interest. Examples of conditions where modifications to standard approaches may be necessary are narrow, deep valleys; land-sea (lake) breeze regimes; and low-level subsidence inversions of temperature. "Fumigation" may be a concern for infrequent releases of short duration from elevated sources. The atmospheric dispersion and deposition model used by the staff, XOQDOQ, is described in NUREG/CR-2919. This program provides independent meteorological evaluation of routine or anticipated intermittent releases at nuclear power stations. For unusual topographic and meteorological conditions, correction factors to the straight-line Gaussian XOQDOQ model or a variable trajectory model may be used on a case-by-case basis. 2. Atmospheric Diffusion Parameters The vertical plume spread parameter, σz, as a function of distance and atmospheric stability is reviewed. Atmospheric stability should be defined by measurement of vertical temperature gradient, particularly during stable conditions. Other classification schemes (Refs. 14 and 15) may be used to estimate atmospheric stability class or to determine the plume spread parameter directly for unstable and neutral conditions. These alternative classification schemes are reviewed for appropriateness to site, plant, and release characteristics. Standard curves of σz with distance are presented in Regulatory Guide 1.111. Modified plume spread