If they operate properly, very little. But depleted uranium, spent uranium and thorium could be used in the CANDU reactor, which has a proven safety record, and since it has been in use since the 1960s, cost certainty.

http://en.wikipedia.org/wiki/CANDU_react...

http://www.the-weinberg-foundation.org/2...

Depleted uranium, spent fuel piles. Probably the worst potential impact is the production of weapons grade fissile material.

They would make the surrounding water warmer. Usually the fish like that.

You have to do something with all of those spent fuel rods.