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:
currents Is discussed below, but only to the extent that advection affects dispersion proceses a.Esiralninnet Consider first the hypothetical case of a nonbuoyant discharge into a stagnant homogeneous environment. (in the context of this discussion, a stagnant environment is one in which the magnitude of the Initia discharge velocity is much greater than any local ambient velocity.) The injection of a fluid as a jet into another fluid results in the generation of turbulent eddies due to shearing stresees; caused by the velocity difference between the two fields. Shearing stresses so produced represen t the lateral flux of momentum, and they are directly proportional to the velocity vector difference. Eddy motion along the jet boundary yields a net mixing of jet fluid with ambient fluid, in effect broadening and diluting the jet at increasing centerline distances from the outfall. This mixing and dilution is called entrainment, and the constant of proportionality relating jet volume flux to velocity is referred to as the entrainment coefficient. Note that for a submerged jet discharging into an infinite medium, entrainment largely propagates transversely to the discharge direction. If the jet exits at the suirface, entrainment is constrained by the sir-water interface; if the vertical extent of the jet is equivalent: to the receiving water depth, vertical enitrainment is nonexistent. The entrainment-Induced transfer of jet momentum to the ambient medium progresses outward fronm the jet boundary, in effect altering the transverse velocity profile from a top-hat shape at the discharge point to a normal or Gaussian distribution. Laboratory 4.4-6 e xpe rimental data have indicated that suitably time-averaged Gaussian velocity profiles are similar:' that is, each transverse 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