uranium-235 in uranium hexafluoride. Almost all natural uranium contains about 99.3 percent uranium-238 and about 0.7 percent uranium-235 by mass. Enrichment increases the mass percentage of uranium-235, the fissile (i.e., the component of the nuclear fuel that can be induced to fission with thermal [low-energy] neutrons) component of nuclear fuel, to between about 4 and 5 percent. In the United States, uranium enrichment is currently being carried out in gaseous diffusion and centrifuge plants. New plants that use laser enrichment technologies are under construction.

Fuel fabrication facilities: Facilities that are used to convert enriched uranium hexafluoride into a uranium dioxide (U02) solid and fabricate it into nuclear fuel for civilian reactors.

Some of the fuel facilities being considered in this study have had or currently have dual civilian and defense missions. Prior to the USNRC assuming regulatory control, some of these facilities were previously regulated by the U.S. Department of Energy and its predecessor agencies.

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FIGURE S.1 Schematic depiction of the nuclear fuel cycle. SOURCE: USNRC.

The NCI investigation also did not attempt to estimate radiation exposures resulting from the operation of nuclear facilities. However, NCI investigators noted that such exposures are likely to be “too small to result in detectable harm” (Jablon et al., 1991, p. 1407). Absent reliable information about radiation exposures, it is difficult to provide scientifically supportable explanations for any observed associations between a nuclear facility and cancer incidence or mortality.



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