Two kinds of nuclear reactors generate emissions-free electricity: Pressurized Water Reactors and Boiling Water Reactors. FPL's nuclear plants in Florida are pressurized water reactors.
The main difference between the two is that in a boiling water reactor, the reactor core heats water, which turns to steam and drives a steam turbine. In a pressurized water reactor, the reactor core heats but does not boil the water; this hot water then exchanges heat with a lower pressure water system, which turns to steam and drives the turbine. The non-radioactive steam is turned back into water in a condenser with cooling water. The water is then circulated back through the tubes in the reactor to begin the cycle again.
The three separate loops of water in a pressurized water reactor are designed to operate separately, with no mixing of any radioactive water with water that turns the turbine, or water that cools the steam in the condenser.