The huge (and they _are_ huge) cost of cleanup from places like Hanford has to be understood in the context under which it was created.
The people at Hanford were tasked with creating weapons to kill people, a million at a time. Given that criterion, is it any wonder that they weren't worried about a few salmon, or clean groundwater. They believed at the time that "Nuculer war, toe to toe with the Rooskies" was right around the corner, and they were dealing with the possibility of hundreds of millions of dead. All other reasons just didn't matter.
That turned out not to be the case, but hindsight is always so excellent.
Now, the pendulum has swung so far the other way, we want to clean up Hanford (as an example) well enough that we could build a school on the location. That doesn't seem like a realistic goal. As for a plutonium contaminated waste facility, I should point out that Los Alamos had quite the plutonium problem. They solved it by painting the walls coral - bright bleedin' orange - and then painting over with white paint. The rule was simple - if you see orange, call the safety people. It was (and is) not a perfect solution, but it was (and is) a workable one.