Internal Hydraulics of Thermal Discharge Diffusers

The TVA Browns Ferry Nuclear Plant will discharge its heated condenser cooling water into the Wheeler Reservoir. To protect the plant, and to keep within state and federal temperature limits, the warm effluent will be mixed with the reservoir water through a subsurface diffuser system. The diffusers consist of three approximately 20-ft diameter corrugated steel pipes each with 7,800 2-in. holes in the wall through which all the warm water discharges. The multiple discharge jets create turbulence which promotes the mixing. The writers describe a model study from which was obtained the discharge coefficient for lateral flow through holes drilled in the valley—as viewed from inside the pipe—of the corrugations. Tests were made for various hole sizes and numbers of holes in the axial and circumferential direction. Also described is the method used to compute the pipe diameter and hole configuration necessary to obtain uniform spatial distribution of discharge for a given flow rate and head. A description is included of the diffuser system recommended for the Browns Ferry installation.