Sure!
There are essentially 3 main water systems that we use; Primary Water (this is the water inside the reactor used for cooling) is a closed system. Or at least at closed as we can make it. There is some leakage, but it is rigorously monitored and identified. And it is an awful small amount, like less than a teaspoon per hour or something like that... it's shiny-pipe stuff so not my department (Chemistry and RadCon take care of that).
The condensate system is pumped through the steam generators to generate (eventually) superheated steam. It's also a more-or-less closed system.
This steam is fed to the turbine where it then passes across tubes below the turbine in the condenser (where it accumulates in the hotwell as condensate to repeat the cycle).
In order to have an efficient transfer of energy from steam to condensate, we use river water from upstream of Watts Bar dam that is piped through the condenser. As river temperature increases efficiency decreases. And why power plants can crank out several more megawatts during the winter months.
There are other factors as well; tube leaks, clogged tubes (things have been known to get past strainers), backpressure, condenser vacuum, environmental conditions (big thunderstorm - drop in atmospheric pressure) etc.
Anyway... after the river water (called condenser circ water or CCW) passes through the condenser it is pumped over to the cooling tower. Here there are lift pumps that send it up into the interior to be sprayed onto some diffusers to eventually rain down into a basin under the tower (oddly enough called a cooling tower basin). This water will eventually flow wind up back in the Tennessee River (normally spending some time in one holding pond or another. The big plume rising up out of our cooling towers is nothing more than water vapor. This water here participated in the transfer of energy as one medium (steam rolling the turbine at around 770 degrees F) to another (condensate in the hotwell at around 94 F).
The water has to be held on site because we are only permitted to discharge water once it's cooled down to some temp that I don't care to know. We cannot just discharge it to the river, that temperature shock would kill off some wild life and fishes, clams and the greenies would just love that...)
So there you have it. I'll admit it's over-simplified, but it'd need a thread of it's own to explain fully.
