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By Fangbiao Lin and George E. Hecker, Alden Research Laboratory Inc., Holden, MA; and Brennan T. Smith and Paul N. Hopping, Tennessee Valley Authority, Knoxville, TN
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The TVA Browns Ferry Nuclear Power Plant (BFNPP) withdraws its
condenser cooling water from Wheeler Reservoir using a shoreline
intake. Waste heat from the plant increases the cooling water
temperature before it is returned to the reservoir through three multiport
diffusers containing a total of about 22,500 downstream-facing
ports. The ports are 2-inch diameter holes situated 6 inches apart both
vertically and horizontally. The numerous small diffuser ports, the buoyancy
of the heated effluent, and the large scale of the discharge area
present major challenges to developing a reliable three-dimensional CFD
model for predicting the temperature distribution and flow patterns
in Wheeler Reservoir. When different treatment alternatives for plant
waste heat are considered, the change each creates in the temperature
distribution in the reservoir is crucial information for assessing the
environmental impact.
Map and computational domain of the overall river model
FLUENT was recently used to develop an innovative CFD model of
the Wheeler Reservoir area. To simulate the discharge from thousands
of diffuser ports, a two-zone modeling approach was used that consists
of a multiple jet sectional model and an overall river model. The
river model contained about 2 million computational cells for simulating
the cooling water discharged from the thousands of diffuser ports.
The multiple jet sectional model, which simulated the flow from the
individual discharge ports over a one foot slice of the diffuser pipe in
great detail, provided the information for developing sectional
boundary conditions for the diffuser effluent in the river model. The
realizable k-e turbulence model was used and a second-order accurate
solution was obtained.
Temperature contours on the water surface
Temperature comparison at one of the downstream monitoring stations
CFD was used to predict the surface water temperature distribution
as well as the stratification resulting from temperature differences.
Validation of the CFD models was performed using data from field measurements,
hydraulic model tests, and other experiments. For the sectional
diffuser model, the results of a vertical section of diffuser ports
were compared with data from a hydraulic model test of a small segment
of the BFNPP diffuser1. These comparisons verified that the sectional
model simulations can predict the thermal stratification,
expansion, dilution, and near-field behavior of the multiport jets. For
the full-scale river model, comparisons between the temperatures predicted
by FLUENT and measured along the centerlines of the operating
diffusers and at downstream monitoring stations were found to be
in close agreement. Indeed, the validations showed that the overall river
model, based on the two-zone approach, can reproduce the major features
of temperature and flow in the diffuser mixing zone, including
the mixing and temperature rise patterns of thermal plumes.
Reference:
- D.R.F. Harleman, L.C. Hall, and T.G. Curtis, Thermal Diffusion of Condenser Water
in A River During Steady and Unsteady Flows with Application to the T.V.A. Browns
Ferry Nuclear Power Plant, Hydrodynamics Laboratory Report No. 111,
Massachusetts Institute of Technology, Cambridge, MA, September 1968.
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