Plutonium yes, but uranium is easy to work with.
I read a book about the Manhattan Project years back. It was alot about Oppenheimer and the tech stuff and the testing, but there was an interesting aside.
Seems one of the professors (and this might have been at Chicago where the first running reactor was put together) liked to show his class the reaction that happened when two sub-critical masses of uranium were pushed closer. You know, it would heat up and start to emit alot of neutron radiation, I guess it can be pretty exciting.
Until one time when he pushed them too close.
Quite a clean up job ensued. He went to meet his maker.