Document: NRC Regulatory Guide
Document ID: f4c5fb1d-efb9-4168-9804-5ad3f6f64d06
Document Type: regulatory_guide
Title: Reporting Procedure for Mathematical Models Selected To Predict Heated Effluent Dispersion in Natural Water Bodies
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML0037/ML003739535.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-4.4
CFR Part: 
CFR Title: 

Content:
ow not being collinear. In keeping with the usual definition of the near-field as being the region where dilution by jet entrainment dominates the dilution due to turbulent diffusion, terms describing the latter are usually dropped from Eqs. (B-27) and (B-28). Formally, this'amounts to the approximations dT. 2w lm(r <) « Q-- 2wrlim(ru'v) « <E[u.], However, since the turbulent transport terms involve undetermined eddy coefficients and since the form of the entrainment function E is not well 4.4-15 established, a proper scale analysis to substantiate the above inequalities is very difficult. On physical rounds, it does not appear to be reasonable that the entrainment is always independent of the ambient turbulence level. b. Far-Field Modeling The far-field is generally assumed to be that region of ihe thermal plume sufficiently removed from the discharge that (0) ambient turbulence dominates the mixing process and (2) the excess temperature is transported by the ambient flow as a passive contaminant. The first of these assumptions results in the use of eddy coefficients to represent the mixing. This introduces an indeterminancy into the problem in that the values of these coefficients are not known beforehand. The second assumption eliminates the effects of discharge momentum and removes the nonlinearity due to buoyancy coupling between the heat energy and momentum equations. This results in a considerable mathematical simplification in that the convective velocity field in Eq. (&-14) is known through either direct observation or prior solution of the appropriately simplified momentum equations. For discussion purposes, mathematical models of the fAr-field region may be divided roughly into deterministic, stochastic, and phenomenological types. (1) Delemnistic Models Since the actual motion and temperature always have stochastic components, deterministic methods must relate these components to time-averaged quantities in order that closure of the governing equations