Radioactive Waste Management
Radioactive waste management
Radioactive waste materials are produced as by-products of research, nuclear power generation, and nuclear weapons manufacture. Radioactive waste is classified by the U.S. government into five groups: high-level, transuranic (chemical elements heavier than uranium ), spent fuel, uranium mill tailings , and low-level radioactive waste .
The management and disposal of radioactive waste receives attention at all levels of state and local governments, but the regulations sometimes conflict or are confusing. The U.S. Congress passes relevant legislation, the Environmental Protection Agency (EPA) sets applicable environmental standards, and the Nuclear Regulatory Commission (NRC) develops regulations to implement the standards. For high-level radioactive waste , the U.S. Department of Energy (DOE) is responsible for the design, construction and operation of suitable disposal facilities. And courts have recently gotten into the act, ordering states to arrange to have necessary disposal facilities designed, constructed and operated for management of low-level wastes.
The principal federal laws related to the management and disposal of radioactive waste include the Atomic Energy Act (1954), the Uranium Mill Tailings Radiation Control Act (1978), the Low-Level Radioactive Waste Policy Act (1980), the Nuclear Waste Policy Act (1982), the Low-Level Radioactive Waste Policy Amendments Act (1985), and the Nuclear Waste Policy Amendments Act (1987). In addition, the Federal Facility Compliance Act (1992) forces the military to clean up its waste sites.
One of the more difficult aspects of the regulatory quagmire is the problem of dealing with waste, especially spent nuclear fuel and contaminated material such as worn-out reactor parts. Today, the official policy objective for nuclear waste is to dispose of it so that it will never do any appreciable damage to anyone, under any circumstances, for all time. However, for some radioactive waste, "for all time" is measured in thousands of years.
Although radioactive waste carries some hazard for many years, radioactive decay removes most of the hazard after a few hundred years. A well-designed waste storage system can be made safe for a long time, some scientists and policy-makers insist, provided that engineers ensure that erosion , groundwater , earthquakes, and other unpredictable natural or human activities do not breach safety barriers.
Disposal methods for radioactive wastes have varied. Over the past 50 years, low-level wastes have been flushed down drains, dumped into the ocean, and tossed into landfills. Uranium mill tailings have been mounded into small hills at sites throughout the western United States. Storage tanks and barrels at DOE sites hold millions of gallons of radioactive waste and toxic chemicals , the by-products of plutonium production for nuclear weapons.
Over 80% of the total volume of radioactive waste generated in the United States is considered low-level. There is now a shift away from the most common disposal method of shallow land burial. Because of public demand for disposal methods that provide the greatest safety and security, disposal methods now include above- and below-ground vaults and earth-mounded concrete bunkers.
However, the country's 17,000 laboratories, hospitals, and nuclear power plants that produce low-level radioactive byproducts could become de facto disposal sites. The federal low-level radioactive waste policy enacted in 1980 was designed to remedy the inequity of shipping all the nation's low-level radioactive waste to three states (Illinois, Kentucky, and New York) which never agreed to serve as the nation's sole disposal facilities. Its intent was to require every state to either build its own low-level repository or compact with other states to build regional facilities by 1986. The 1980 federal act was amended in 1985, when it became clear that the 1986 target would not be met, and the deadline was postponed to 1993. As of late 1992, however, few states had even determined sites for such facilities. And after 1996, the institutions generating low-level wastes will be held liable for all low-level wastes they produce.
The principal sources of high-level radioactive waste are nuclear power plants, and programs of the U. S. Department of Defense and DOE, especially those dealing with nuclear weapons. These wastes include spent fuel removed from nuclear plants, and fission products separated from military fuel that has been chemically processed to reclaim unused uranium and plutonium. In the United States, commercial nuclear power plant fuel removed from those facilities is stored on-site until a geologic repository is completed. The expected completion date for the repository is 2010.
Typically, waste fuel is stored at the power station in a pressurized buffer storage tube for 28 days, then the fuel rod is broken down to component parts. Irradiated fuel elements then are stored for 80 days in a water-filled pond to allow for further decay. For the nonreusable radioactive waste that remains, about 2.5%, there is no totally safe method for disposal.
Radioactive waste from one of the first nuclear bomb plants is so volatile that the clean-up problems have stymied the experts. The plant at the DOE's Hanford Nuclear Reservation near Richland, Washington, is the nation's largest repository of nuclear waste. There, 177 tanks contain more than 57 million gal (26 million l) of radioactive waste and toxic chemicals, byproducts of plutonium production for nuclear weapons. The DOE and Westinghouse Corporation (the contractor in charge of Hanford's clean-up) are still not sure exactly what mixture of chemicals and radioactive waste each tank contains, but a video taken inside one tank shows the liquid bubbling and roiling from chemical and nuclear reactions. Corrosive, highly radioactive liquids have eaten through Hanford's storage tanks and are being removed to computer-monitored, carbon-steel storage tanks. The cleanup at Hanford could cost as much as $57 billion. The only other country known to have had a waste problem as large as the one at Hanford is the former Soviet Union, where a nuclear waste dump exploded in the nuclear complex at Chelyabinsk in 1957, contaminating thousands of square miles of land.
As the military starts massive clean-up efforts, it has identified 17 nuclear facilities as among the worst of the more than 20,000 suspected toxic sites. For example, since the 1970s, about 77,000 barrels of low-level radioactive wastes have been stored at the Oak Ridge, Tennessee nuclear reservation. Today, some barrels are rusting and leaking radioactivity . Other identified radioactive waste sites include California's Lawrence Livermore National Laboratory and Sandia National Laboratory, Colorado's Rocky Flats nuclear plant , and New Mexico's Los Alamos National Laboratory. The Savannah River nuclear plant in South Carolina has been called especially dangerous. Both the Savannah River site and the Hanford site pose the risk of the kind of massive nuclear waste explosion that occurred at Chelyabinsk.
One new technology in development for the treatment of hazardous and radioactive waste is in situ vitrification (ISV), which utilizes electricity to melt contaminated material in place. This technology was developed primarily to treat radioactive waste, but it also has applications to hazardous chemical wastes. The end-result glass formed by ISV is unaffected by extremes of temperature, is not biotoxic, should remain relatively stable for one million years, and passes government tests that measure the speed of contaminant leaching over time. The process permits treatment of mixtures of various wastes including organic, inorganic, and radioactive. The fact that it is not necessary to excavate the waste prior to treatment is seen as a major advantage of the technology, since excavation along with transportation increases health risks. The technology is currently being used in the United States at Superfund sites.
Incineration is also used for disposal of low-level radioactive waste, but incomplete combustion can produce dioxins and other toxic ash and aerosols. Although finding a site for ash disposal is difficult, the ash is considered a better form for burial than the original waste. It is biologically and structurally more stable, and many of the compounds it contains are insoluble. The residual waste produced by incineration also is less susceptible to leaching by rain and groundwater.
Although progress is slow and the situation is often chaotic in the United States, the state of radioactive waste management in much of the rest of the world is even less advanced. The situation is particularly acute in Eastern Europe and the former Soviet Union, since these countries have generated huge quantities of radioactive waste. In many cases the information-gathering necessary to plan clean-up efforts has not begun or is barely underway, and most, if not all, of the actual clean-up remains.
[Linda Rehkopf ]
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