Document: NUREG-0800
Document ID: 37e64905-5f3c-4221-9ce6-b3089b164d6f
Document Type: srp
Title: LONG-TERM DIFFUSION ESTIMATES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070237.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.5
CFR Part: 
CFR Title: 

Content:
s, and locations of receptors of interest are identified. Each release should be characterized as 19 continuous or intermittent. 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 standard diffusion model used by the staff is described in NUREG-0324. This model is a straight-line Gaussian model with a specific calculational procedure for estimating X/Q values for intermittent releases. Modifications to the straight-line model to consider the effects of variations in space and time in airflow are also described in NUREG-0324.The diffusion model used by the staff is described in NUREG/CR-2919, a user guide for the XOQDOQ Computer Program. This program provides independent meteorological evaluation of routine or anticipated intermittent releases at nuclear power stations.20 For unusual topographic and meteorological conditions, a variable trajectory model may be used on a case-by-case basis. 2.3.5-5 DRAFT Rev. 3 - April 1996 2. Atmospheric Diffusion Parameters The vertical plume spread parameter, , as a function of distance and atmospheric z stability is reviewed. Atmospheric stability should be defined by measurement of vertical temperature