Power stations "use" water in a closed loop system. The steam you see rising from them will condense back to water and end up (roughly) where it started!
Nuke' power stations will slightly increase the ambient temperiture of the sea round them! This is NOT the problem with eather type.
Decontamination of places like Winscale are made worse by the fact that thy were built as prototypes, and as such experiments were made with materials and techniques.