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Today on SciShow, Hank brings us a little science history, telling us the tale of the world's first human-made nuclear reactor, which was built by a team of scientists and students led by Enrico Fermi in a converted squash court under a football field in Chicago. Yes, that Chicago.

Scientists discovered a natural nuclear reactor that had existed in Africa about two billion years ago, which is why we can't say that this is the world's first EVER nuclear reactor. Read more about that here:
and here:

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Hank Green: The world's first self-sustaining nuclear reaction did not take place in a laboratory nor did it occur in some remote desert, though that might make sense if you're about to attempt to control a power that no one has ever attempted to control before. Instead, on December 2, 1942, a team of 49 scientists and students led by Enrico Fermi activated the world's first nuclear reactor in a converted squash court beneath the football stands on Stagg Field at the University of Chicago. Yes, Chicago Chicago. [SciShow Intro plays] Dubbed Chicago Pile 1, the nuclear reactor built by Fermi's team was hardly the complex machine you might expect. It contained no mechanical parts or wires and in the 20 or so minutes it operated, it generated roughly 1/2 a watt of power, just enough to power a lamp. Four years earlier, German scientists had become the first to accomplish nuclear fission, by bombarding atoms of uranium with neutrons to split their nuclei in two. This caused a release of energy and additional neutrons that then split other nuclei to begin a chain reaction. But no one figured out how to harness that power, which many scientists correctly assumed could be used to build powerful atomic weapons. Fermi's Pile consisted of alternating layers of uranium pellets and graphite. Uranium was the fuel emitting neutrons that every so often would strike the nuclei of other uranium atoms and foster the chain reaction. The graphite acted like a moderator of sorts, slowing down the neutrons, which made it easier for them to strike other uranium nuclei. The key, of course, and this is a very important key, is to figure out a way to start, stop, and regulate this chain reaction. Fermi found his answer in the form of cadmium rods, which naturally absorb neutrons during the fission process. His team quickly discovered that the energy output can be increased or decreased by adjusting these rods, which were the only moving parts of the Pile. It took several weeks to build, and once complete, the Pile contained 380 tons of graphite, 40 tons of uranium oxide, and 6 tons of uranium metal. There were 57 layers in all, just enough to reach critical mass of the stage necessary to sustain a chain reaction. At 2pm on December 2nd, the last cadmium rod was pulled out of the Pile, less than 90 minutes later, Fermi announced that the reactor had achieved critical mass and the world had its first controlled self-sustaining nuclear chain reaction. Those present opened a bottle of Chianti to celebrate, but presumably they didn't get too drunk. Now despite rumors to the contrary, there were never dangers of the reactor causing a nuclear disaster. With so little fuel, the worst case scenario involved the Pile catching fire and causing a little mini meltdown if one can speak of a mini meltdown. Also, the Argonne National Laboratory, which was founded by Fermi and a few others years after the experiment, would like to dispel another myth: that the 49 people present that day all died early from cancer. In fact, that is not true, at least two of those on the squash court are still alive today, more than 70 years later. Thanks for watching this episode of SciShow, if you have any questions or comments or suggestions for us, we're on Facebook and Twitter and down in the comments below, and if you want to keep getting smarter with us here at SciShow, you can go to and subscribe. [SciShow endscreen plays]