The Hanford Environmental Dose Reconstruction Project: A Review of Four Documents (1994)

After President Roosevelt's 1941 directive to the Department of War to develop nuclear weapons, the Hanford site in southeast Washington state was selected as part of the national effort known as the Manhattan Engineer District Project. Construction started at Hanford in 1943 and a nuclear reactor for the production of plutonium, the B reactor, became operational in September 1944. Two additional reactors for the production of plutonium, the D and F reactors, became operational in 1945. The reactors were fueled with natural uranium, and part of this uranium was converted into plutonium by the reactor neutron flux. Irradiated fuel was removed from the reactors and stored for radioactive decay for a variable time. It was then sent to two bismuth-phosphate separation plants, the T and B plants. The mixture of materials—including uranium, plutonium, and other chemicals and radionuclides—was chemically treated to extract and purify the plutonium. Purified plutonium was then formed into metallic disks and shipped to other nuclear facilities for use in the production of nuclear weapons. The bismuth-phosphate separation plants were succeeded by two plants, a Redox and, later a Purex separation facility. The location of the Hanford site is shown in Figure 1. A series of contractors oversaw the work at Hanford, two of which were the Battelle Memorial Institute and the General Electric Company.

The plutonium-production process created many nuclides, including the radioactive isotope of iodine, iodine-131, the long-lived iodine-129 (half-life, 10⁷ years), and other iodine radionuclides and their precursors such as tellurium-131. The graphite-moderated reactors were cooled with purified river water flowing through them continuously. The water was held for a short period and released to the river; this constituted one pathway for release of radioactivity. A second avenue for release would be a small airborne release at the reactor. A third and more important avenue would be releases related to processing of the fuel elements.

Some of the iodine-131, was released to the atmosphere during the processing of fuel from the reactors. Carried by the wind, the iodine-131 was distributed to the ground and rivers and entered the food chain. This relatively short-lived radioisotope (half-life, 8.04 days) has received considerable attention during dose-reconstruction studies because it was judged to be the largest contributor (over 90% of the effective dose) to the historical radiation dose attributable to the Hanford nuclear facility (Napier, 1991).

Over the last 2 decades, concerns increased about the potential impact of the activities at Hanford on the surrounding population. Continuing declassification of historical Hanford documents, including the release of additional information about episodic releases of iodine-131 (such as the intentional release called the Green Run), has made the public more concerned about the possibility of health effects in residents of the area surrounding the Hanford site. Documents describing specific releases of radioactive materials were made available to the public in 1986.

In 1986, the DOE directed a full study of the release of radioactive materials from Hanford and of the radiation dose received by the surrounding population. The scientific work of the HEDR project was contracted to PNL, and the project was expected to be completed in 1995. The goal of the HEDR project was to determine how much radioactive material was released, how people were exposed, and what radiation dose people might have received. Originally funded by the DOE, the project is currently funded by CDC. The study is being conducted under the direction of the TSP which was created in 1988 and was formed in part to provide independent oversight and to facilitate public discussion of past nuclear activities at Hanford.