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:
profile along the jet beyond the point at which the centerline velocity begins to decay has the general form = Ue-n 2 u (A-1) in which U. is the velocity at distance n normal to the jet centerline, U is the jet centerline velocity, and a 2 is the jet velocity variance along n. This finding has permitted the simplification of many near-field thermal discharge models, although the general applicability of the Gaussian approximation to real discharges remains open to question. For the case of a heated jet, the Gaussian approximation of the transverse temperature profile along the jet takes the form, Tn = Te-n!/2X' aT 2 (A-2) where Tn and T are the temperature in :he transverse direction and the jet centerline temperature; respectively, OT. is the temperature variance along n, and X is an adjustable constant. According to Taylor's theory,' heat diffuses more rapidly than momentum in the transverse flow direction. Therefore, the value of X is always greater than unity. Under most circumstances, heated effluent is less dense than the receiving water in the immediate vicinity of the outfall. As a result of the density disparity, there is a buoyant force on the jet acting both vertically and horizontally. A submerged buoyant jet .ends to rise to the surface; a buoyant jet at the surface fam= a stable density layer. For either case entrainment is reduced, especially in the vertical direction, and the dilution rate decreases. The degree to which buoyancy influences a heated jet is suggested by the densimetric Froude number, defined as Fd U- • 1/2 (A-3) ( P)I where Uo is the initial jet velocity, g the gravitational acceleration, h the vertical thickness of the jet, Ap the density difference between effluent and ambient water, and p the ambient water density. The nondimensional Froude number represents the ratio of inertial forces to buoyant forces in the jet. 'G. N. Abramovich, "The Theory of Turbulent Jets," Mamachusetts Institute of Technology Press, Cambridge,