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S-50 Oak Ridge Thermal Diffusion Plant

State: Tennessee
Location: Oak Ridge
Time Period: 1944-1951
Facility Type: Department of Energy
Facility Description: The S-50 Plant at Oak Ridge was constructed in 1944 to enrich uranium feed material for the Y-12 electromagnetic facility using a liquid thermal diffusion process. The process was originally developed at theNaval Research Laboratory in Washington, DC, and tested on a pilot plant level at the Philadelphia Naval Shipyard. Located near the K-25 gaseous diffusion facility, the S-50 Plant operated for a limited period during 1944- 1945. The plant was closed in September 1945 because the thermal diffusion process was not as efficient as the gaseous diffusion.
The S-50 plant was reopened in 1946 as part of the joint Air Force/AEC project to investigate the possibility of developing a nuclear-powered airplane. This project, known as Nuclear Energy for the Propulsion of Aircraft (NEPA), was housed at S-50 and the contractor was the Fairchild Engine and Aircraft Corporation. Fairchild’s NEPA Division at S-50 conducted a number of experiments involving beryllium powder during the time period 1946-1951.
S-50 Oak Ridge Thermal Diffusion Plant is listed as  Department of Energy (DOE) site under the EEOICPA.
Employees of the DOE predecessor agencies and their contractors and subcontractors who were monitored or should have been monitored while working at the S-50 Oak Ridge Thermal Diffusion Plant working for a number of work days aggregating at least 250 work day during the period from July 9, 1944, through December 31, 1951, or in combination with work days within the parameters established for one or more other classes of employees in the SEC.
As of 08/30/2015, the total compensation paid under Parts B and E of the EEOICPA, including medical compensation, for workers suffering from the effects of having worked at the S-50 Oak Ridge Thermal Diffusion Plant is $8,904,608.
S-50 Oak Ridge Thermal Diffusion Plant Workers:
If you or your parent worked at this or any other DOE or AWE facility and became ill, you may be entitled to compensation of up to $400K plus medical benefits from the US Department of Labor. Call EEOICPA Counsel Hugh Stephens at 1-855-EEOICPA (336-4272) or fill out the form to the right, whether your claim has been accepted or denied.
We can help with all OWCP (Federal Workers Compensation) claims, impairments, wage loss and health care. 2495 Main Street, Suite 442 Buffalo, NY.
The S-50 Liquid Thermal Diffusion Plant was a wartime uranium enrichment facility constructed in 1944 adjacent to the K-25 facility in Oak Ridge, Tennessee by H. K. Ferguson Company and operated by Fercleve Corporation, a wholly owned subsidiary of H. K. Ferguson Company that was organized for the sole purpose of operating the Plant. Groundbreaking for the facility was on July 9, 1944, and construction was complete on October 31, 1944. The main process building dimensions were 522 ft long by 62 ft wide by 75 ft high; the building had a concrete floor and foundation, and steel frames, sides, and roof (MED 1947). Uranium enrichment began on September 16, 1944, before construction was complete. Thermal diffusion operations shut down on September 9, 1945 (DOE 2005).
There was a tremendous amount of emphasis placed on high production output at this facility. Processed uranium from the Plant was used as feed material for the Y-12 facility, where it was further enriched; some of this material was used in the bomb dropped over Hiroshima (“Little Boy”). Operations at S-50 generally continued around the clock. The number of individuals employed by Fercleve Corporation reached a maximum of more than 1,500 in April 1945 (MED 1947).
Feed material came from Harshaw Chemical Company of Cleveland, Ohio, in nickel shipping containers as uranium hexafluoride (UF6). The liquid thermal diffusion process at S-50 increased 235U enrichment from natural (0.71%) to 0.85% (MED 1947).
The process to enrich uranium at S-50 consisted of multiple columns, each of which contained three concentric pipes. High-pressure (1,000-psig) steam passed through the innermost nickel pipe, which was inside a copper pipe. UF6 was batch-charged into the gap between the nickel and copper pipes at about 1,500 psig. The nickel and copper pipes were inside the outermost steel pipe. Cold water passed between the steel pipe and the outer wall of the copper pipe. The enrichment process utilized convective flow, whereby the lighter 235U molecules tended to move upward along the hot nickel pipe wall while the heavier 238U molecules moved downward along the cold copper wall (MED 1947). A graph of the production output from S-50 (Percentage of Original Theoretical Maximum Output) showed the racks operated at less than 5% until January 1945, at which time the production increased gradually to a maximum of approximately 90% in June 1945 (MED 1947).
Losses of UF6 were common during S-50 operations, with UF6 often escaping into the air or cooling water (MED 1947). The losses usually resulted from internal or external breaks in columns or other parts of the process, which were caused by failure of the materials under the high operating pressures. Other losses resulted from improper handling of open connections and from operational mistakes due, in part, to the number of new employees at the facility and the emphasis on high production rates. From March through July 1945, monthly losses of UF6 ranged from 247 to 1,826 lb (DOE 2005). Accountability records showing losses for other months of operation are unavailable. The released UF6 would rapidly oxidize and form uranyl fluoride (UO2F2) (DOE 2005), which would either exhaust through the building roof or settle to the process building floor. Operators were required to have a gas mask on their persons at all times for emergencies (MED 1947).
The S-50 Plant ceased enrichment operation in September 1945, shortly after the war ended (MED 1947). The uranium enrichment process used at S-50 was unique in that it was the only production-scale liquid thermal diffusion facility ever built. S-50 closed because it had become evident that the liquid thermal diffusion process would not be competitive with the gaseous diffusion process.
Disassembly of the S-50 process equipment was done in the late 1940s, at which time it was removed from the main process building and transported to the K-25 Powerhouse Area, where it was stored for some time before being either salvaged or buried (DOE 2005).
NIOSH SEC Petition Evaluation Reports
Petition 60 (Jan 1, 1944 to Dec 31, 1951)
SEC Petition Evaluation Report, Petition SEC-00060,
Rev # 08-04-06, Report Submittal Date __________

Technical Basis Documents
Site Profile
Summary Site Profile for the S-50 Liquid Thermal Diffusion Project