They do all kinds of heat transfer and pre heating on power plants. The more energy they recover the better their profit margins. Even at the coal plant I worked at, they were only able to economically get the flue gas temp down to ~350 F. The nuke plants typically have a double closed loop cooling system to isolate the water that have been in contact with nuclear fuel.

Nice graphic showing the process:
http://science.howstuffworks.com/nuclear-power2.htm

I have not heard much about the sodium reactors outside of the research stage. I know there was a lot of problem with corrosion due to how caustic the molten sodium is.