text: how many years has nuclear energy been around for? - when was the first nuclear reactor built? please help...i just don't know!   :( hmmmm.... the first reactor was built in a squash court at uom chicago. it was a very very simple pile. after that... i'm betting the next one was in hanford washington.  you might be asking when was the first nuclear power plant.... a construction built for the porpose of generating electricity for the masses.  best guess... that one the army built that exploded on them.  just a guess though.... you tried wiki or even google yet?