Secret Military Facilities

K-25 Gaseous Diffusion Plant

The K-25 Plant was built on the western end of town to separate uranium 235 from uranium 238 by a more economical method called gaseous diffusion. This plant was one of the largest scale-ups of laboratory equipment in history and involved process systems of unprecedented vacuum tightness and cleanliness. The original K-25 Plant covered more than 1,500 acres and was the forerunner of similar facilities in Paducah, Kentucky and Portsmouth, Ohio. The facility was completed at a cost of $500 million and operated by 12,000 workers. Today, these plants are a source of enriched uranium which is used to fuel both military and civilian nuclear power reactors.

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X-10 (Graphite Reactor)

The X-10 Plant, located in the city’s southwest corner, was the site where a graphite-moderated nuclear reactor was constructed as a pilot facility for the larger plutonium production complex in Hanford, Washington. This reactor, later used to produce radioisotopes, was closed in 1963. It has been designated a National Historic Landmark and is open to the public on special DOE Public Bus Tours that are conducted from June through September each year. The X-10 area became the Oak Ridge National Laboratory (ORNL) in 1948. ORNL has gained worldwide recognition for its research in the basic sciences, energy systems, environmental technology and safety.

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Y-12 National Security Complex

The Y-12 Plant was built in Bear Creek Valley to separate the uranium 235 isotope from natural uranium in sufficient quantity and quality to produce the fissionable material for atomic weapons. It was the first to accomplish this goal. This plant utilized an electromagnetic process developed at the University of California at Berkeley and had the unusual distinction of using $300 million worth of silver borrowed from the U.S. Treasury. The silver was used as a substitute for copper in the fabrication of equipment for the plant. The facility was built for $427 million and employed 22,000 workers. Uranium separation by the electromagnetic process ended in 1947 at the Y-12 Plant. However, research & development and specialized production continue today at this facility which is still identified by its wartime code name.

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S-50 Thermal Diffusion Plant

S-50 was a third, much smaller plant built at Oak Ridge to help produce the highly enriched U-235 for the first atomic bomb.
Oppenheimer at Los Alamos learned in 1944 that the huge power house being built for the K-25 uranium enriching plant was going to be ready to produce high pressure steam almost six months before K-25 would need it. He suggested to General Groves that it be used to provide heat for a third enriching process called Liquid Thermal Diffusion. This process had been under development by the U.S.Navy and their pilot plant under construction in Philadelphia. It was copied and expanded many times over on the banks of the Clinch River next to the K-25 Powerhouse. Groves seized on every possible avenue to provide enriched feed material to Y-12’s Calutrons and thus shorten the war.

The S-50 plant was built in less than 70 days, starting up in September 1944. The amount of enriching it did was very important although it sounds small, only enriching from 0.7% U-235 to a little over 0.9%.

The S-50 plant fed this slightly enriched UF6 to Y-12 early, and then to K-25 when it got started in the early spring of 1945 where it was enriched further and then sent to Y-12. S-50 operated successfully, but was a far more difficult process to operate than either Y-12’s or K-25’s, so was shut down about a month after war’s end and taken down soon after. It’s cost was $16 million for capital and operations, and about 1,600 employees worked there at the peak.

In his memoirs, General K. D. Nichols tells that he had an estimate made of the value of the enriching done by S-50 during its year long operation. The assessment was that if it had not produced those thousands of pounds of slightly enriched uranium for Y-12, that Y-12 would have taken nine more days to deliver the required amount of product to Los Alamos. Nichols’ comment was that considering the cost of the war ($250M/day) and the lives being lost each day, shortening the war by nine days seemed to him a good return on investment.

After the thermal diffusion process was no longer needed, the S-50 building became the location for the Nuclear Energy Powered Aircraft experiment until 1951 after which it was taken out of operation and demolished, becoming the first significant Manhattan Project facility to be decommissioned and demolished.

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