X-10 GRAPHITE REACTOR

(1943 - 1945)
Places > Oak Ridge: Clinton Engineer Works

In spring 1942, Arthur Compton, head of the Met Lab and plutonium pile (reactor) research, selected the Argonne Forest outside Chicago as the site for a pilot plutonium plant consisting of a plutonium producing reactor and facilities for chemically separating the plutonium. Initial plans called for a 100,000-kilowatt, helium-cooled graphite reactor, later scaled back to 10,000 kilowatts. Compton considered several sites near Chicago for the full-scale production reactors but after inspecting the Oak Ridge site in Tennessee found it acceptable. In September, the S-1 Executive Committee decided to move the pilot plant to the Oak Ridge site as well, on the basis of growing evidence that operations would be on a scale too large for the Argonne site. The production reactors, the pilot plant, and a laboratory were to be built at Oak Ridge (officially known as the Clinton Engineer Works) at a site codenamed X-10. The X-10 area lay between two ridges along a small creek in the isolated Bethel Valley, about 10 miles southwest of the planned community of Oak Ridge.

After bringing on the DuPont Corporation to build and operate the production reactors, General Leslie Groves determined in early December 1942 that available electric power at Oak Ridge was not sufficient for the electromagnetic, gaseous-diffusion, and plutonium plants. The X-10 area itself was not large enough for production reactors and for safety reasons was too close to Knoxville. Groves launched a search for an alternate location for the production reactors that resulted in the selection of the Hanford site. With the production reactors gone, Compton and the Met Lab scientists saw little reason to move any part of the plutonium project to Tennessee, and they began to design a small water-cooled reactor to be built at Argonne. DuPont officials, however, were convinced that a semiworks that would aid in the design, construction, and operation of the then planned helium-cooled production reactors at Hanford was necessary and that the Argonne site would not permit the construction and operation of a semiworks plant on a large enough scale. In January 1943, Groves approved construction by DuPont of a semiworks at the Oak Ridge X-10 site. Compton and the Met Lab reluctantly agreed to operate the facility.

Plans called for a 1,000-kilowatt, air-cooled graphite reactor and separation plant, as well as an extensive research laboratory and a number of support, training, and administrative facilities on the 112-acres semiworks site. DuPont broke ground at the X-10 complex in February 1943, and on November 4, 1943, the X-10 Graphite Reactor went critical for the first time. Much more a piece of highly engineered industrial equipment than the science experiment that CP-1 was, the X-10 reactor consisted of a huge block of graphite, measuring 24 feet on each side, surrounded by several feet of high-density concrete as a radiation shield. The block was pierced by 1,248 horizontal diamond-shaped channels in which rows of cylindrical uranium slugs formed long rods. Cooling air circulated through the channels on all sides of the slugs. After a period of operation, operators pushed fresh slugs into the channels from the face of the pile and the irradiated slugs would fall from the back wall through a chute into an underwater bucket. The bucket of irradiated slugs underwent radioactive decay for several weeks, and then was moved by underground canal into the chemical separation facility next to the reactor where the plutonium was extracted with remote control equipment. The plant consisted of six large underground cells with concrete walls several feet thick. The first irradiated uranium from the reactor was dissolved on December 19, 1943. Chemical separation techniques using the bismuth phosphate process were so successful that the first shipment of 1.5 milligrams of plutonium left Oak Ridge for the Met Lab on December 30. By the spring of 1944, Los Alamos was receiving gram quantities of plutonium that had originated at X-10, and as a result weapons designers at the Los Alamos laboratory were able to conduct fission experiments that heavily influenced bomb design. From 1943-1945, a total of about 326 grams of plutonium was shipped from Oak Ridge to Los Alamos.

In January 1944, irradiation of bismuth "slugs" in the X-10 reactor began to produce polonium-210 for use in the bomb initiators. Separation of polonium from the bismuth was performed at laboratories in Dayton, Ohio, operated by Monsanto Chemical Company. Also in early 1944, Los Alamos asked X-10 to produce hundred-curie quantities of radioactive barium-140 for use in weapons development. The barium decayed to produce radioactive lanthanum-140 ("RaLa"), which was used for implosion diagnostics. A special extraction (hot) laboratory and a second plant for dissolving radioactive irradiated uranium slugs and recovering barium from the solution were built on the X-10 site.

By early 1945, the X-10 reactor's value to the Manhattan Project began to recede. X-10 had provided experimental amounts of plutonium to Los Alamos and invaluable experience for engineers, technicians, reactor operators, and safety officials who then moved on to Hanford, but with the Hanford reactors in full operation X-10 plutonium production was no longer essential. From a peak of over 1500 scientists and workers in June 1944, the X-10 site, officially Clinton Laboratories, reached a stable workforce of about 1300 by the end of the year. After January 1945, the reactor produced radioactive isotopes. Management of Clinton Laboratories transferred from the Met Lab and the University of Chicago to the Monsanto Chemical Company in July 1945. Clinton Laboratories became Clinton National Laboratory in 1947 and Oak Ridge National Laboratory in 1948. The graphite reactor, deactivated in 1963 and a National Historic Landmark, is open to guided tours on a seasonal basis. The Oak Ridge National Laboratory, as one of the Department of Energy's seventeen national laboratories, remains one of the nation's leading federally funded research and development centers.

Sources and notes for this page

The text for this page is original to the Department of Energy's History Program. For further information, see Richard G. Hewlett and Oscar E. Anderson, Jr., The New World, 1939-1946: Volume I, A History of the United States Atomic Energy Commission (Washington: U.S. Atomic Energy Commission, 1972), Manhattan District History, Book IV - Pile Project, Volume 2 - Research Part II - Clinton Laboratories, and Lillian Hoddeson, et. al., Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945 (Cambridge: Cambridge University Press, 1993). The photograph of X-10 is courtesy the Oak Ridge National Laboratory.