Document: NRC Regulatory Guide
Document ID: c9ebcbb0-96c4-4d29-be51-5acae9cc858a
Document Type: regulatory_guide
Title: Estimating Aquatic Dispersion of Effluents from Accidental and Routine Reactor Releases for the Purpose of Implementing Appendix I (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740390.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.113
CFR Part: 
CFR Title: 

Content:
ase of two-dimensional intratidal models, it is, in general, only necessary to include deviations of velocity and concentration in the vertical direction since, with sufficient resolution, the lateral flow field is simulated correctly. In all cases, the most acceptable procedure for choosing the diffusion coefficient is to adjust the model to match observed prototype conditions, usually through tracer study results. In general, the more refined the model, the less empirical tuning is necessary because the turbu lent transport coefficients are more firmly based on physical principles. (1) Tidally Averaged Models If the tidally averaged model is used, the determination of the diffusion coefficient is empirical and must be based on the observed dispersion of a known tracer, with prototype and model constituent concentrations being matched. The tidally averaged longitudinal dispersion coefficient EL may be determined from Equations (25), (28), or (29) by a trial and error pro cedure where EL is changed until the model concentrations match observed values of the tracer. In the case of tidally averaged numerical models covered under paragraph 4.a(3), it is possible to restructure the finite difference equations to solve for EL with input of observed concentration of the tracer. The calculated values of EL may then be used for subsequent con centration computations. As a rough approximation to the dispersion coefficient, lacking any field data, a formula by Hetling and O'Connell (Ref. 52) based on data in the salinity intrusion region of the Potomac River estuary may be used: EL - 1680 Vmax 4/3 (35) where EL is the sectionally and tidally averaged, one-dimensional longitudinal dispersion coefficient (in ft 2/sec), and Vmax is the maximum tidal velocity (in knots). It must be cautioned that this equation can only be relied upon for order of magnitude estimates and is not necessarily conservative. 1.113-22 (2) One-Dimensional Real-Time Models Less "tuning" is necessary for