On December 18, 1941, 11 days after the Japanese attack on Pearl Harbor, the decision was made to focus atomic energy research on the development of a weapon for the war. The Army was assigned the responsibility for this design and construction project of unprecedented size. The headquarters for the project was established in New York and named the Manhattan Engineer District. In September 1942 an isolated area in east Tennessee was selected as the site for the development of the full scale production facilities for uranium separation and for the construction of an experimental nuclear pile that would be used to produce plutonium for research in the war effort. An air-cooled experimental pile, a chemical separation plant, and supporting laboratories were constructed by the Du Pont Co. at the X-10 site. This facility was officially named the Clinton Laboratories---later renamed Oak Ridge National Laboratory (ORNL)---and will be referred to in this report as the X-10 facility. By the summer of 1944 the primary goal of the war effort was achieved and the laboratory was transformed into the first well rounded institution for nuclear research short history of ORNL.
The major portion of the war effort at the Oak Ridge Site was devoted to obtaining enriched uranium. Part of this work was done at the Y-12 location using an electromagnetic separation process. The Tennessee Eastman Corporation operated the facilities at the Y-12 site from June 1943 to May 1947 and is referred to as the TEC facility. In May of 1947 work at the Y-12 site changed from uranium enrichment to nuclear materials fabrication and Union Carbide Corporation became the operating contractor. There was also a significant change in the workforce with only 6.7% of the workers staying on to work in the new operations. In this report Y-12 facility refers to the plant at the Y-12 site that began operation in May 1947 and continued until the end of this study. The main purpose of the facility at the K-25 site was to produce enriched uranium via the gaseous diffusion process. In support of the enrichment process the K-25 facility (later named the Oak Ridge Gaseous Diffusion Plant) also operated a plant that produced barrier material, ran a feed mill operation, and conducted laboratory research.
A more detailed description of these facilities and the potential for occupational exposure to hazardous material is given by Watkins et al [2,3]. A total of 118,588 workers are known to have been employed at one of the four nuclear facilities in Oak Ridge between 1943 and 1984. The study cohort consists of 106,020 workers that were employed for at least thirty days and whose records did not have any critical errors (e.g. unknown sex, race, date of birth, or employment dates).