Chicago Pile-1 (CP-1) was the world's first human-made nuclear reactor. CP-1 was built on a racquets court, under the abandoned west stands of the original Alonzo Stagg Field stadium, at the University of Chicago. The first artificial, self-sustaining, nuclear chain reaction was initiated within CP-1, on December 2, 1942. The pile produced just 1/2 watts of power.
The site of the first nuclear reaction received designation as a National Historic Landmark in 1965 and 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 Nobel laureate (1938) Enrico Fermi. It contained critical mass of the fissile material, together with control rods, and was built as a part of Manhattan Project research done 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 the construction of the pile at a laboratory in the Argonne forest preserve, so Fermi and his associates Martin Whittaker and Walter Zinn set about building the pile (the world's first artificial "nuclear reactor," although that term 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 to lead to a self-sustaining chain reaction. Re-inserting the rods would damp the reaction.
The completed pile contained 771,000 pounds of graphite, 80,590 pounds of uranium oxide and 12,400 pounds of uranium metal when it went critical. It cost about $2.7 million to produce and build. The pile took the form of a flattened ellipsoid which measured 25 feet wide and 20 feet high.
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 went critical 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 Woods, the former site of Argonne National Laboratory, 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.
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 Industry in Chicago. The old Stagg Field plot of land is currently home to the Regenstein Library. A Henry Moore sculpture, Nuclear Energy, in a small quadrangle commemorates the nuclear experiment.
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