The heat from the reactor heats up pipes of water which make steam which drive a turbine, and the warm water left over goes to a cooling tower. But why on earth would they do that when it would be much more efficient to run that water back to the reactor heat and in turn make steam even easier? Basically what's the logic behind saying quot;eh...seems we have hot water left over, let's cool it down, then reheat some new waterquot; - why not heat the already warm water? ? ?
Hot water is not used to generate electricity, high pressure steam is. What comes out of the turbine would need to be condensed back to water to recycle it and by the time you've done that it will it have lost quite a lot of it heat anyway. Better to use a heat exchanger where the steam is passed through a coil located inside a huge water tank. This way the steam condenses and passes its energy to heat the water indirectly and then this could be sent to the reactor or local homes for heating. By doing it this way the heat of the steam from after the turbine can be used to heat water, if you let it condense to water by itself the heat is lost to the atmosphere instead.
i dunno, to reduce the carbon footprint
easier to use a fresh cold supply of water than to try to run miles of tubing to cool off hot water. simple thermodynamics.
They DO reuse the heated water. The entire steam cycle is intended to be as closed of a system as practical. The water is pumped to high pressure, then boiled to steam, then expanded in the turbine, and then chilled back to the initial state in the condenser. All of this water is intended to remain in the system. Occasionally, a little additional feedwater is needed to make up for the unintentional losses (simply because it is impractical to build a 100% sealed system). When you are looking at the steam rising out of the cooling tower, that steam is actually unrelated to the steam that flows through the most active components. The cooling tower is the least nuclear and least power plant-like part of a nuclear power plant, yet somehow it has become its notorious symbol. The cooling tower is simply a device that is used to aid the condenser in rejecting heat. The alternative is if a naturally flowing source of cold water is available, such that it can be used to pass through the shell over the condenser piping instead. But, because there are limits to how hot you can heat up rivers, and because there might not be a much needed river nearby, the cooling tower is put to use so that AIR can be used to cool the condenser with much less feedwater involved. Air is a VERY BAD conductor of heat, so passing air over the condenser tubes is impractical if you want them to cool off effectively. The cooling tower uses a stream of feedwater (of much less flowrate than would otherwise be used if water alone were supplied), and uses it to flow across the condenser and evaporate in to the air. Both the air and the water are used as the coolant, in a creative manner that takes advantage of the favorable features of each. That is what a cooling tower does.
