Model Studies of A Cooling Water Discharge Outlet Modification Prairie Island Nuclear Generating Plant

The P~airie Island Nuclear Generating Plant is located on the Mississippi River near Red Wing, Minnesota. 'The general location is shown' in Fig. 1. The plant is situated on. the right bank in the bend of the river about one mile above Lock and Dam No. 3 as shown in the frontispiece. The cooling water is presently discharged through an open canal directly into the Mississippi River. The present outlet is i.n rathe~ close proximity to the plant inlet resulting in some recirculation of the ~armer water. Northern States Power (NSP) also has need for preventing fish from entering the outlet canal where they would be subject to cold shock mortality in case of sudden winter shutdown.. Modification of the di.scharge outlet nas therefore been proposed. The discharge outlet would·be moved further downstream and the cooling water discharged into the river 500 ft downstream of Barney's Point, thus reducing recirculation. This may be seen in the frontispiece and the sketch. in Fig. 2. . Dikes buil·t across a backwater area adjacent to the plant would provide an impoundment area for the plant discharge.. Four pipes with diameters of 8, 7,· 6 ,·.and 5 ft would convey the flow through the embankment and discharge it into the river. The velocity of the flow from the open pipes would be maintained above 8 fps. This high velocity would prevent most of the fish.from swimming through the pipes and entering the impoundment pool. During .operatiop., the pipes would be either closed or wide open, and the number of open pipes would vary from 1 to 4 depending on the plant dipcharge. By proper selection of the pipes to be opened, the·head can be maintained at a fairly constant elevation, thus keeping the discharge ~elocity greater than the required 8 fps.