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:
lly diluted effluent becomes a definite possibility. The situation is less serious for a discharge in deep water. In this case, ambient water can move under as well as around the jet; pressure drag is reduced, and fresh dilution water is availabl- nn the jet's downstream side. The influence of ambient stratification on thermal discharges depends directly upon the density of the heated effluent relative to the vertical density profile of the ambient water. As a result, the heated effluent can assume any of a number of different configurations. If the heated effluent is less dense than the ambient water, the effluent forms a surface layer analogous to the unstratified cage. Moreover, natural stratification can enhance effects due to buoyancy and can inhibit vertical mixing, effectively thinning the surface layer while increasing its horizontal extent. If the effluent has an intermediate density relative to the density range of the stratified ambient, the discharge jet tends to rise or fall to the point of neutral density, depending on whether the exit port is submerged or at the surface. Usually, when the effluent sinks to the level of density compensation, the phenomenon is referred to as a "sinking plume." Note that effluent dilution by entrainment continually influences the density along the discharge trajectory. Dilution may be sufficiently pronounced to affect the level at which the plume equilibrates. Once the neutral density level has been achieved, the effluent is free to disperse horizontally, regulated by natural diffusion and any residual jet momentum. Under certain conditions the effluent may be more dense than the receiving water and, as a result, flow to the bottom. During the winter months this can occur if the ambient water has equilibrated at a temperature below the point of maximum water density. Should the effluent form a bottom layer, dispersion can be inhibited by bathymetry and bottom friction. b. Turbulent Diffusion With the decay of jet