Places
"Met Lab"
(Metallurgical
Laboratory)
K-25 GASEOUS DIFFUSION PLANT
(1942 - 1945)
Places > Oak Ridge: Clinton Engineer Works
In 1940, gaseous diffusion was thought to be one of the two
methods (the centrifuge being the other) most likely to provide for large-scale separation of uranium-235. Preliminary research in
gaseous diffusion was centered at Columbia University. The theory of gaseous diffusion
was straightforward. The process would be continuous, not batch, and gaseous diffusion offered less likelihood of mechanical
difficulty than did other methods. There were, nonetheless, many practical problems to implementing this enrichment method on
an industrial scale, the most fundamental being the selection of an appropriate barrier. In the influential July 1941 Maud Report,
British scientists contended that an atomic bomb could be built and called for gaseous diffusion of uranium-235 on a massive scale.
In April 1942, a survey group for selection of an appropriate site for either the gaseous diffusion or the centrifuge full-scale
plant favored a site at Oak Ridge, Tennessee.
The Oak Ridge site for the gaseous diffusion plant, codenamed K-25, consisted of 5,000 acres about 15 miles southwest of the town site. Enclosed on three sides by thickly wooded ridges and on the west by the Clinch River, the site had few roads, a country schoolhouse, and a main rail line several miles to the north. The site also had a readily available water supply, a relatively level area of about 1,000 acres for the plant facilities, and adequate distance from other production plants and any densely populated areas. By March 1943, the Kellex design group completed a plot plan and general arrangement for the plant, but could not finalize the design when the individual components of the diffusion process, such as barriers and sealants, had not yet been developed. Work on the plant, as a result, languished. 
Actual construction began on the last day of May 1943. Survey crews laid out the huge power plant, which would supply a portion of the electrical energy for the plant. The powerhouse was started first, partly because of the long lead-time required for generating equipment and partly as a hedge against failure of the gaseous diffusion process. If all else came to naught, the power plant, which was the largest steam-electric power plant up to that time, could be sold to the Tennessee Valley Authority. Ground was not broken for the process buildings until September. The main plant consisted of a series of 54 contiguous four-story buildings constructed in the shape of a U, almost a half mile long and more than 1,000 feet in width. The enormous area of the buildings (almost 2 million square feet) and the weight of the process equipment they would contain required an extraordinary amount of earth moving. Over the length of the U, original elevations differed by as much as 50 feet, and it was necessary to move almost 3 million cubic yards of earth. It was late October before the first of 200,000 cubic yards of concrete were poured in the process area. At the same time, work began on auxiliary buildings to test the process equipment and the administration building. Construction of the cafeteria, laboratories, and other auxiliary buildings was deferred until 1944. 
Construction at K-25 continued throughout 1944, with the first few stages—without acceptable barrier in the converters—available for testing in April. Although a decision was made on the barrier in January, it was not until late 1944 that the barrier impasse appeared to be headed toward full resolution. K-25 production came online in stages, beginning in February 1945, as the plant was completed. The resulting structure encompassed an area of some 60 acres. The main process equipment, consisting of 2,892 diffusion stages, was on ground level. Piping runs were carried on the second level, and the third level was the operating floor. The basement held auxiliary process equipment. Each diffusion stage consisted of a converter, in which incremental separation of the uranium isotopes took place, together with centrifugal pumps for circulating the process gas (uranium hexafluoride), heat exchangers to remove the heat of compression, piping interconnections, and control instrumentation. The stages were arranged in series and so connected such that the depleted gas fraction leaving a given stage was directed "down" the cascade and the enriched gas fraction leaving the stage was directed "up" the cascade. Feed entered the cascade below the midpoint; enriched product was drawn off at any of various points up the cascade, depending upon the degree of enrichment desired, and depleted "tails" were drawn off at the bottom of the cascade. All of the equipment, if laid end-to-end, would extend about 20 miles, and it was all required to operate virtually leak-free. Completed at a cost of $500 million and employing 12,000 workers, the K-25 plant used 130,000 instruments and 500,000 specialized valves. The K-25 plant provided enriched feed to the Y-12 electromagnetic plant for final enrichment. After the war, gaseous diffusion proved to be the most efficient of the wartime uranium separation processes and became the sole process used during the Cold War. In January 1946, a second gaseous diffusion plant at the site, K-27, became operational. Construction of K-29, K-31, and K-33 followed in the early years of the Cold War. K-25 ceased production in 1964.
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At the S-1 meeting with the Army on June 25, Army representatives recommended that
all full-scale plants be built at the Oak Ridge site. Despite the lack of progress by the Columbia researchers and their industrial
partners, the M.W. Kellogg Company, in developing a suitable barrier, the Lewis Committee reported in early December 1942 that of the
proposed uranium separation methods "the diffusion process is believed to have the best over-all chance of success, and produces
the more certainly usable material." The committee recommended the design and construction of a full-scale gaseous diffusion plant.
The S-1 Executive Committee agreed, and on December 28 President 
The text for this page is original to the Department of Energy's Office of History and Heritage Resources. 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), and Manhattan District History, Book II - Gaseous Diffusion (K-25) Project, Volumes 1 through 5. The diagram of gaseous diffusion is from Hewlett and Anderson, 98. The photograph of K-25 is courtesy the Federation of American Scientists.