Wikipedia:Today's featured article/December 2, 2017

Chicago Pile-1 was the world's first artificial nuclear reactor. Its construction was part of the Manhattan Project, the Allied effort to create atomic bombs during World War II. It was built by the project's Metallurgical Laboratory at the University of Chicago, under the west viewing stands of the original Stagg Field. The first human-made self-sustaining nuclear chain reaction was initiated there on 2 December 1942, supervised by Enrico Fermi, who described the apparatus as "a crude pile of black bricks and wooden timbers". It contained 45,000 graphite blocks weighing 400 ST used as neutron moderators, and was fueled by 6 ST of uranium metal and 50 ST of uranium oxide. In the pile, some of the free neutrons produced by the natural decay of uranium were absorbed by other uranium atoms, causing nuclear fission of those atoms, and the release of additional free neutrons. Unlike most subsequent nuclear reactors, it had no radiation shielding or cooling system as it only operated at very low power – about one-half watt. The site is now a National Historic Landmark.