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:
should be specified as a MAT entry, and the functional form of the relation should be presented in the text. c. Natuba Turbulence. Natural water bodies possess a varying degree of natural turbulence. Consequently, the effects of turbulence should be included in any thermal dispersion model which 4.4-3 purports to be valid outsde the near-field region. When dealing with natural turbulence, many models employ an eddy diffualvity or dispersion coefficient to simulate transport by turbulent diffusion. Under this circurmatafice, the assumed initial values of the coefficient in the three orthogonal directions of the model's coordinate system should be specified, and the coefficient's functional form(s) and conditions of application should be discussed in the text. Although wind stress is typically responsible' for considerable induced turbulence occurring in water bodies, this phenomenon can also directly affect the surface velocity distribution. The average and extreme range of observed wind vectors for the worst probable conditions at the prototype should be included. A MAT entry should appear for those models that include wind stress. d. Buoyancy. Buoyant forces accelerate flow in the direction of discharge while enhancing lateral spreading. A detailed discussion of the importance of buoyancy relative to other thermal dispersion mechanisms in the prototype should be presented; the means by which the effects of buoyancy are simulated in each model should also be discussed. e. Recrculation. When only a limited amount of entrainment water is available for mixing, such as in some shallow water discharges, partly diluted effluent may be re-entrained or recirculated into the discharge plume. The inclusion of nonambient dilution water decreases thermal dispersion while increasing plume size. The MAT should indicate if recirculation is fesaible for the prototype and whether the models can simulate this process. Substantiation for the entry should be presented in the text. f.