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Chicago Pile-1 (CP-1) was the world's first artificial nuclear reactor. CP-1 was built on a rackets court, under the abandoned west stands of the original Alonzo Stagg Field stadium, at the University of Chicagomarker. The first artificial, self-sustaining, nuclear chain reaction was initiated within CP-1, on December 2, 1942. The site was designated a National Historic Landmark in 1965 and was added to the newly created National Register of Historic Places a little over a year later. The site was named a Chicago Landmark in 1971. It is one of the four Chicago Registered Historic Places from the original October 15, 1966 National Register of Historic Places list.


The reactor was a pile of uranium and graphite blocks, assembled under the supervision of the renowned Italian physicist Enrico Fermi, in collaboration with Leo Szilard, discoverer of the chain reaction. It contained a critical mass of fissile material, together with control rods, and was built as a part of Manhattan Project by the University of Chicago Metallurgical Laboratory. 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.

A labor strike prevented construction of the pile at the Argonne National Laboratorymarker, so Fermi and his associates Martin Whittaker and Walter Zinn set about building the pile (the term "nuclear reactor" was not used until 1952) in a racquets court under the abandoned west stands of the university's Stagg Field. The pile consisted of uranium pellets as a neutron–producing "core", separated from one another by graphite blocks to slow the neutrons. Fermi himself described the apparatus as "a crude pile of black bricks and wooden timbers." The controls consisted of cadmium-coated rods that absorbed neutrons. Withdrawing the rods would increase neutron activity in the pile, leading to a self-sustaining chain reaction. Re-inserting the rods would damp the reaction.

First nuclear reaction

On December 2, 1942, CP-1 was ready for a demonstration. Before a group of dignitaries, a young scientist named George Weil worked the final control rod while Fermi carefully monitored the neutron activity. The pile reached the critical mass for self-sustaining reaction at 3:25 p.m. Fermi shut it down 28 minutes later.

Operation of CP-1 was terminated in February 1943. The reactor was then dismantled and moved to Red Gate Woodsmarker, the former site of Argonne National Laboratorymarker, where it was reconstructed using the original materials, plus an enlarged radiation shield, and renamed Chicago Pile-2 (CP-2). CP-2 began operation in March 1943 and was later buried at the same site, now known as the Site A/Plot M Disposal Site.

Significance and commemoration

The site of the first man-made nuclear reaction received designation as a National Historic Landmark on February 18, 1965. On October 15, 1966, which is the day that the National Historic Preservation Act of 1966 was enacted creating the National Register of Historic Places, it was added to that as well. The site was named a Chicago Landmark on October 27, 1971.A small graphite block from the pile is on display at the Museum of Science and Industrymarker in Chicago. The old Stagg Field plot of land is currently home to the Regenstein Librarymarker at the University of Chicago. A Henry Moore sculpture, Nuclear Energymarker, in a small quadrangle commemorates the nuclear experiment.

See also


  1. Natural nuclear reactors existed approx. 1.5 billion years ago in Oklo, Africa.
  2. tif.
  3. The space is commonly misidentified as having been a squash court.
  4. National Register Information System, National Register of Historic Places, National Park Service. Retrieved 11 February 2007.

External links

  • CP-1 Goes Critical Describes in detail the construction and activation of CP-1. US Department of Energy, Office of History and Heritage Resources.
  • Photos of CP-1 The University of Chicago Library Archive. Includes photos and sketches of CP-1.

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