Uranium Mill Tailings
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Sources and Volume
Uranium mill tailings are the radioactive sandlike materials that remain after uranium is extracted by milling ore mined from the earth. Tailings are placed in huge mounds called tailings piles which are located close to the mills where the ore is processed.
The most important radioactive component of uranium mill tailings is radium, which decays to produce radon. Other potentially hazardous substances in the tailings are selenium, molybdenum, uranium, and thorium.
Uranium mill tailings can adversely affect public health. There are four principal ways (or exposure pathways) that the public can be exposed to the hazards from this waste. The first is the diffusion of radon gas directly into indoor air if tailings are misused as a construction material or for backfill around buildings. When people breathe air containing radon, it increases their risk of developing lung cancer. Second, radon gas can diffuse from the piles into the atmosphere where it can be inhaled and small particles can be blown from the piles where they can be inhaled or ingested. Third, many of the radioactive decay products in tailings produce gamma radiation, which poses a health hazard to people in the immediate vicinity of tailings. Finally, the dispersal of tailings by wind or water, or by leaching, can carry radioactive and other toxic materials to surface or ground water that may be used for drinking water.
The NRC and some individual states that have regulatory agreements with the NRC have licensed 26 sites for milling uranium ore. However, most of the mills at these sites are no longer processing ore. Another 24 sites have been abandoned and are currently the responsibility of DOE.
All the tailings piles except for one abandoned site located in Canonsburg, PA, are located in the West, predominantly in arid areas (Figure 6). The licensed tailings piles contain a combined total of approximately 200 million metric tons (MT), with individual piles ranging from about 2 million MT to about 30 million MT. (A metric ton is 2,200 pounds.) The 24 abandoned sites contain a total of about 26 million MT and range in size from about 50 thousand MT to about 3 million MT.
It is unlikely that there will be much additional accumulation of mill tailings in the U.S., because foreign countries now produce uranium much more cheaply than can domestic producers.
Setting Environmental Protection Standards
The EPA issued two sets of standards controlling hazards from uranium mill tailings in 1983, under the authority of the Uranium Mill Tailings Radiation Control Act of 1978. These standards provide for the cleanup and disposal of mill tailings at abandoned sites and the disposal of tailings at licensed sites after cessation of operations. They are implemented by DOE, NRC, and some states through agreements with NRC, and require a combination of active and passive controls to clean up contaminated ground water as well as tailings that have been misused at off-site locations, and to dispose of tailings in a manner that will prevent misuse, limit radon emissions, and protect ground water.
Active controls include building fences, putting up warning signs, and establishing land use restrictions. Passive controls include constructing thick earthen covers, protected by rock and designed to prevent seepage into ground water, over the waste. Earthen covers also effectively limit radon emissions and gamma radiation and, in conjunction with the rock covers, serve to stabilize the piles to prevent dispersion of the tailings through erosion or intrusion. In some cases, piles may be moved to safer locations.
The standards were amended in 1993 to require that all licensed sites that have ceased operation undergo remedial action as soon as possible. The EPA is in the process of enacting revised ground-water protection standards that will require the same treatment of ground water at the abandoned sites as is now required at the licensed sites. In addition, EPA enacted Clean Air Act standards in 1989 limiting radon emissions and restricting the length of time that abandoned piles may remain uncovered with no controls on radon emissions. EPA also requires that any piles that may be constructed in the future meet requirements that limit radon emissions and inhibit ground-water contamination during their operational phase. Licensed mills also are subject to the Uranium Fuel Cycle standard which regulates radionuclide emissions other than radon.