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:
rocesses that determine the amount of surface cooling from a heated plume are identical to those that prevail under typical ambient conditions. As a result, heating by a discharge can be regarded as a perturbation on the normal thermal regime. Adoption of this viewpoint leads to the concept of excess temperature, Te, the difference between the observed plume temperature and the natural or ambient water temperature. On the basis of this definition, a heat budget formulation may be applied to excess temperature to yield the rate of heat transfer across the air-water interface due to the plume: H = KTe (A-8) where the heat transfer coefficient, K, is primarily a function of wind speed, ambient temperature, and excess temperature. Tables are available from which K may be estimated, given the aovropriate meteorological parameters.7 Note that Eq. (A-8) is based upon the premise that the ambient water temperature is equal to the equilibrium value (i.e., the temperature at which the net rate of heat transfer across the air-water interface is zero). This condition is rarely achieved in nature, but the equation offers a simplified means of expressing surface heat exchange independent of the full heat budget equation. Since the error introduced by assuming an equilibrium condition is believed to be inconsequential, any disparities are ignored. Surface cooling, whereby the excess heat is passed to the atmosphere, is ultimately responsible for limiting the areal extent of heated plumes. If surface cooling were not utilized in far-field modeling, the iotherms of excess temperature would never achieve closure. 7D. W. Pritchard and H. H. Carter, "Design and Siting Criteria for Once-Through Cooling Systems Based on a First-Order Thermal Plume Model," Chesapeake Bay Institute Technical Report No. 75, 1972. 4.4-9 APPENDIX 8 MATHEMATICAL FORMULATION OF THERMAL DISPERSION 1. FWmxmlont SIul-iNo where AU thermal dispersin pbelso as govewed by the basic laws, of moss, moamtum, and eerly