Environmental Risks of Depleted UF6 Disposal
A discussion of the environmental impacts associated with the disposal of depleted uranium oxide and uranium tetrafluoride.
Impacts Analyzed in the PEIS
The PEIS evaluated the potential environmental impacts associated with the disposal of depleted uranium oxide at a generic low level waste disposal facility. Two forms of uranium oxide were considered, triuranium octaoxide (U3O8) and uranium dioxide (UO2). After completion of the PEIS, as documented in the Oak Ridge National Laboratory study, Assessment of Preferred Depleted Uranium Disposal Forms (ORNL/TM- 2000/161, June 2000), four potential conversion forms (U3O8, UO2, uranium tetrafluoride (UF4), and uranium metal) were evaluated and found to be acceptable for near-surface disposal at low level radioactive waste disposal sites such as those at DOE's Nevada Test Site and Envirocare of Utah, Inc.
The potential environmental impacts from disposal of depleted uranium would depend on the form of the uranium as well as the characteristics of the disposal facility. During the licensing or authorization process for such a disposal facility, which includes an opportunity for public review, analyses are conducted to evaluate risks and demonstrate that the facility meets established performance criteria. The generic results for the PEIS are described below.
Impacts from Construction of Disposal Facility
Disposal as oxide could result in adverse impacts to air, water, and soil quality as a result of construction activities. Potential air quality impacts would be from particulate matter, such impacts could be controlled by good construction practices. Also, construction activities have the potential to result in surface water, groundwater, or soil contamination through spills of construction chemicals. However, by following good engineering practices, concentrations in soil and wastewater (and therefore surface water and groundwater) could be kept well within applicable standards or guidelines.
Impacts After Construction of 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), the PEIS analysis indicated that 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. Over the long-term (e.g., 1,000 years), disposal as uranium oxide in a wet environment could result in groundwater contamination. If the contaminated groundwater discharged to nearby surface waters, aquatic biota might be exposed to elevated concentrations of uranium, possibly resulting in adverse chemical effects. Adverse effects would not be associated with disposal in a dry environment.
Depending on the type of disposal facility, the PEIS indicated that disposal could require excavation of large quantities of soil and rock. Impacts from the excavated materials could be mitigated by contouring and reseeding, or by trucking the excavated material off-site.
No other adverse impacts from disposal were identified in the PEIS for disposal. Socioeconomic impacts were evaluated in terms of jobs and income generated, which are considered positive impacts. Disposal was estimated to result in about 130 to 950 direct jobs and the generation of about $10 to $60 million in direct income per operational year.
For more details on the environmental risks from disposal, see also Section 2.4 and Appendix I of the PEIS.
Disposal as Uranium Tetrafluoride (UF4)
As mentioned above, following the completion of the PEIS, it was suggested that the depleted UF6 could also be converted to UF4 and disposed. Because of differences in the chemical properties of uranium oxide and UF4, it was unclear if the impacts estimated for the disposal of uranium oxide in the PEIS would be representative of the impacts associated with the disposal of depleted UF4. Therefore, the potential impacts of UF4 disposal were evaluated in a separate report, Environmental Impacts of Options for Disposal of Uranium Tetrafluoride (UF4) (ANL/EAD/TM-104). Because of issues identified in the PEIS associated with disposal in a wet environment, the UF4 disposal analyses were limited to the evaluation of disposal in a dry environment.
In order to facilitate comparisons and future decision making, the depleted UF4 disposal analyses were performed and the results were presented at the same level of detail as contained in the PEIS for disposal as an oxide. For the same reasons, the assumptions made and the methodologies used to evaluate environmental impacts were similar to those used in the PEIS. The disposal report found that the potential environmental impacts from disposal of UF4 were, in general, similar to those for disposal as uranium oxide.