The X-10 Graphite Reactor is a decommissioned nuclear reactor at Oak Ridge National Laboratory in Oak Ridge, Tennessee. Formerly known as the Clinton Pile and X-10 Pile, it was the world's second artificial nuclear reactor (after Enrico Fermi's Chicago Pile-1) and the first intended for continuous operation. It was built during World War II as part of the Manhattan Project. While Chicago Pile-1 demonstrated the feasibility of nuclear reactors, the Manhattan Project's goal of producing enough plutonium for atomic bombs required reactors a thousand times as powerful, along with facilities to chemically separate the plutonium bred in the reactors from uranium and fission products. An intermediate step was considered prudent. The next step for the plutonium project, codenamed X-10, was the construction of a semiworks where techniques and procedures could be developed and training conducted. The centerpiece of this was the X-10 Graphite Reactor. It was air-cooled, used nuclear graphite as a neutron moderator, and pure natural uranium in metal form for fuel. Using designs by the Metallurgical Laboratory, DuPont commenced construction of the plutonium semiworks at the Clinton Engineer Works in Oak Ridge on February 2, 1943. The reactor went critical on November 4, 1943, and produced its first plutonium in early 1944. The reactor and chemical separation plant provided invaluable experience for engineers, technicians, reactor operators, and safety officials who then moved on to the Hanford Site. It supplied the Los Alamos Laboratory with its first significant amounts of plutonium and its first reactor-bred product. Studies of these samples in comparison to those from cyclotrons revealed a higher content of plutonium-240, making the gun-type Thin Man design impossible, leading to the Gadget and Fat Man bombs of the now-ubiquitous implosion-type. X-10 operated as a plutonium production plant until January 1945, when it was turned over to research activities and the production of radioactive isotopes for scientific, medical, industrial and agricultural uses. In August 1948, it became the first nuclear reactor to produce electricity, lighting a single bulb. It was shut down in 1963 and was designated a National Historic Landmark in 1965.
Origins The discovery of nuclear fission by German chemists Otto Hahn and Fritz Strassmann in 1938, followed by its theoretical explanation (and naming) by Lise Meitner and Otto Frisch, opened up the possibility of a controlled nuclear chain reaction with uranium. At Columbia University, Enrico Fermi and Leo Szilard began exploring how this might be done. Szilard drafted a confidential letter to the President of the United States, Franklin D. Roosevelt, explaining the possibility of atomic bombs, and warning of the danger of a German nuclear weapon project. He convinced his old friend and collaborator Albert Einstein to co-sign it, lending his fame to the proposal. This resulted in support by the U.S. government for research into nuclear fission, which became the Manhattan Project. In April 1941, the National Defense Research Committee asked Arthur Compton, a Nobel-Prize-winning physics professor at the University of Chicago, to report on the uranium program. His report, submitted in May 1941, foresaw the prospects of developing radiological weapons, nuclear propulsion for ships, and nuclear weapons using uranium-235 or the recently discovered plutonium. In October he wrote another report on the practicality of an atomic bomb. Niels Bohr and John Wheeler had theorized that heavy isotopes with even atomic numbers and odd number of neutrons were fissile. If so, then plutonium-239 was likely to be fissile. Emilio Segrè and Glenn Seaborg at the University of California produced 28 μg of plutonium in the 60-inch cyclotron there in May 1941 and found that it had 1.7 times the thermal neutron capture cross section of uranium-235. At the time plutonium-239 had been produced in minute quantities using cyclotrons, but it was not possible to produce large quantities that way. Compton discussed with Eugene Wigner from Princeton University how plutonium might be produced in a nuclear reactor, and with Robert Serber how the plutonium produced in a reactor might be separated from uranium. The final draft of Compton's November 1941 report made no mention of using plutonium, but after discussing the latest research with Ernest Lawrence, Compton became convinced that a plutonium bomb was also feasible. In December, Compton was placed in charge of the plutonium project, which was codenamed X-10. Its objectives were to produce reactors to convert uranium to plutonium, to find ways to chemically separate the plutonium from the uranium, and to design and build an atomic bomb. It fell to Compton to decide which of the different types of reactor designs the scientists should pursue, even though a successful reactor had not yet been built. He felt that having teams at Columbia, Princeton, the University of Chicago and the University of California was creating too much duplication and not enough collaboration, and he concentrated the work at the Metallurgical Laboratory at the University of Chicago.
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