What are the potential health risks from disposal of depleted uranium as an oxide?
Once depleted uranium has been converted from UF6 to the oxide form, the risk associated with handling at a disposal facility is greatly decreased because the corrosive fluorine component has been removed, and because the oxide form is not reactive. Under normal operating conditions at a disposal facility, there would be a small increase in cancer risk for workers due to exposure to external radiation from the uranium oxide; however, good work practices would minimize the exposure and the risk.
Even under extreme accident conditions, such as if a receiving building were damaged in an earthquake, the risk of immediate chemical injury to the general public and to workers from exposure to released uranium oxide would be very small. Because uranium oxide is insoluble, amounts inhaled would reside in the lungs for a long period of time, so increased cancer risk from radiation would be the predominant risk from oxide exposure. The most serious accident for a disposal facility modeled in the PEIS was an earthquake damaging a receiving building. The probability of earthquakes depends on the location of the facility, and the probability of damage depends on the structural characteristics of the buildings. In the PEIS, the estimated frequency of this type of accident at a disposal facility was between once in 100 years and once in 10,000 years. However, if such an accident did occur, it was estimated that 370 pounds of uranium oxide could be released, resulting in an increased cancer risk of about 0.05 (1 chance in 20) for the most exposed worker. The increased cancer risk for the most exposed member of the general public would be 0.0005 (1 chance in 2000). No immediate chemical health effects would be expected for the general public from accidental exposures, but irreversible or fatal effects among workers very near the accident scene would be possible.
The PEIS also considered the potential long-term impacts to groundwater and human health from a disposal facility. Although design criteria are such that disposal facilities would not be expected to fail (i.e., release material to the environment) until several hundred years after closure, for purposes of analysis, it was assumed that a disposal facility would fail 100 years after closure. If the disposal facility was located in a dry environment (typical of the western United States), no measurable groundwater contamination would have occurred even by 1,000 years after facility failure, because of the small amount of rainfall and large distance to the groundwater table typical of a dry environment. If the disposal facility was located in a wet environment (typical of the eastern United States), the estimated dose from the use of groundwater at 1,000 years after the assumed failure of the facility would be about 100 mrem/yr, which would exceed the regulatory dose limit of 25 mrem/yr. In addition, the groundwater concentrations would be great enough to cause potential adverse kidney effects from chemical exposures. Based on these results, a dry environment would be preferred for disposal of depleted uranium.
(For more details on risks from disposal, see also Appendix I of the PEIS.)
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