80 years ago now (about 3:48pm Chicago time) #ChicagoPile 1, built from stacks of graphite bricks and lumps of uranium assembled in a rackets court under the seating of #StaggField at the University of Chicago, reached criticality and became the world's first self-sustaining #nuclear reactor. It ran for 5 minutes at a power of ½ a watt. Safety measures included cadmium-clad wooden control rods, an axe, and 3 guys above the reactor with jugs of cadmium solution.