<Tr> <Th> Primary use </Th> <Td> Experimental </Td> </Tr> <Tr> <Th> Remarks </Th> <Td> The Chicago Pile - 1 (CP - 1) is the world's first nuclear reactor . </Td> </Tr> <P> Chicago Pile - 1 (CP - 1) was the world's first nuclear reactor . On 2 December 1942, the first human - made self - sustaining nuclear chain reaction was initiated in CP - 1, during an experiment led by Enrico Fermi . The reactor's development was part of the Manhattan Project, the Allied effort to create atomic bombs during World War II . It was built by the Metallurgical Laboratory at the University of Chicago, under the west viewing stands of the original Stagg Field . Fermi described the apparatus as "a crude pile of black bricks and wooden timbers". </P> <P> The reactor was assembled in November 1942, by a team that included Fermi, Leo Szilard (who had previously formulated an idea for non-fission chain reaction), Leona Woods, Herbert L. Anderson, Walter Zinn, Martin D. Whitaker, and George Weil . It contained 45,000 graphite blocks weighing 400 short tons (360 t) used as neutron moderators, and was fueled by 6 short tons (5.4 t) of uranium metal and 50 short tons (45 t) 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 operated at very low power--about one - half watt . The shape of the pile was intended to be roughly spherical, but as work proceeded, Fermi calculated that critical mass could be achieved without finishing the entire pile as planned . </P>

Who built the first nuclear reactor the atomic pile