In the early nineties, we realized a hydropower plant on the tailrace channel of the cooling system of the thermal power plant located in Ostiglia (MN). The hydropower plant exploits the artificial head produced by the water pumped from Po River (36 m3/s) which overtakes the main embankment. The water returns to the Po River after its transit through the heat exchangers of the thermal generating sets.The complexity of the hydraulic problems related to the generation phase with 4 submerged groups with fixed blades and on the occasion of out of service, required a preliminary study through a physical model in 1:20 scale. Within this model all the operating situations were simulated, varying the water levels in Po river: from the historical minimum level with the risk of cavitation of the machinery, to the maximum flood with complete submersion of all installations. This experience was then very useful for the project of a similar plant on the discharge of a nuclear power plant abroad.