Hazardous waste may be “destroyed.” For example, by incinerating it at a high temperature, flammable wastes can sometimes be burned as energy sources. For example, many cement kilns burn hazardous wastes like used oils or solvents. Today, incineration treatments not only reduce the amount of hazardous waste but also generate energy from the gases released in the process. It is known that this particular waste treatment releases toxic gases produced by the combustion of by‐product or other materials which can affect the environment. However, current technology has developed more efficient incinerator units that control these emissions to a point where this treatment is considered a more beneficial option. There are different types of incinerators which vary depending on the characteristics of the waste. Starved air incineration is another method used to treat hazardous wastes. Just like in common incineration, burning occurs, however, controlling the amount of oxygen allowed proves to be significant to reduce the amount of harmful by‐products produced. Starved air incineration is an improvement of the traditional incinerators in terms of air pollution. Through using this technology, it is possible to control the combustion rate of the waste and therefore reduce the air pollutants produced in the process (see a Case Study on WtE in Sections 7.13.1.1 and 7.13.3).
Hazardous Waste Landfill (Sequestering, Isolation, etc.)
Hazardous waste may be sequestered in an hazardous waste landfill or permanent disposal facility. “In terms of hazardous waste, a landfill is defined as a disposal facility or part of a facility where hazardous waste is placed or on land and which is not a pile, a land treatment facility, a surface impoundment, an underground injection well, a salt dome formation, a salt bed formation, an underground mine, a cave, or a corrective action management unit” (Title 40 CFR 260.10).
Pyrolysis
Some hazardous waste types may be eliminated using pyrolysis in an ultrahigh temperature electrical arc, in inert conditions to avoid combustion. This treatment method may be preferable to high‐temperature incineration in some circumstances such as in the destruction of concentrated organic waste types, including PCBs, pesticides, and other persistent organic pollutants (RCRA, USEPA, Title 40 CFR 261).
Radioactive Waste
Radioactive waste is waste that contains radioactive material. Radioactive waste is usually a by‐product of nuclear power generation and other applications of nuclear fission or nuclear technology such as research and medicine. Radioactive waste is hazardous to all forms of life and the environment, and it is regulated by government agencies in order to protect human health and the environment.
Radioactivity naturally decays over time; therefore, radioactive waste has to be isolated and confined in appropriate disposal facilities for a sufficient period until it no longer poses a threat. The time radioactive waste must be stored for depends on the type of waste and radioactive isotopes. Current approaches to managing radioactive waste have been segregation and storage for short‐lived waste, near‐surface disposal for low and some intermediate level waste, and deep burial or partitioning/transmutation for the high‐level waste.
A summary of the amounts of radioactive waste and management approaches for most developed countries are presented and reviewed periodically as part of the International Atomic Energy Agency (IAEA) Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management (IAEA 2007).
Sources
Radioactive waste comes from a number of sources. In countries with nuclear power plants, nuclear armament or nuclear fuel treatment plants, the majority of waste originates from the nuclear fuel cycle and nuclear weapons reprocessing. Other sources include medical and industrial wastes as well as naturally occurring radioactive materials (NORM) that can be concentrated as a result of the processing or consumption of coal, oil, and gas and some minerals as discussed below.
Nuclear Fuel Cycle
Front End
Waste from the front end of the nuclear fuel cycle is usually alpha‐emitting waste from the extraction of uranium. It often contains radium and its decay products.
Uranium dioxide (UO2) concentrate from mining is a thousand or so times as radioactive as the granite used in buildings. It is refined from yellowcake (U3O8), then converted to uranium hexafluoride gas (UF6). As a gas, it undergoes enrichment to increase the U‐235 content from 0.7% to about 4.4% low enriched uranium (LEU). It is then turned into a hard ceramic oxide (UO2) for assembly as reactor fuel elements (Cochran 1999).
The main by‐product of enrichment is depleted uranium (DU), principally the U‐238 isotope, with a U‐235 content of approximately 0.3%. It is stored either as UF6 or as U3O8. Some is used in applications where its extremely high density makes it valuable such as antitank shells, and on at least one occasion even a sailboat keel (IHS Jane’s 360). It is also used with plutonium for making mixed oxide fuel and to dilute, or downblend, highly enriched uranium from weapons stockpiles which is now being redirected to become reactor fuel.
Back End
The back‐end of the nuclear fuel cycle, mostly spent fuel rods, contains fission products that emit beta and gamma radiation, and actinides that emit alpha particles, such as uranium‐234 (half‐life 245 000 years), neptunium‐237 (2.144 million years), plutonium‐238 (87.7 years), and americium‐241 (432 years), and even sometimes some neutron emitters such as californium (half‐life of 898 years for Cf‐251). These isotopes are formed in nuclear reactors.
It is important to distinguish the processing of uranium to make fuel from the reprocessing of used fuel. Used fuel contains the highly radioactive products of fission (see Section 3.25.2). Many of these are neutron absorbers, called neutron poisons in this context. These eventually build up to a level where they absorb so many neutrons that the chain reaction stops, even with the control rods completely removed. At that point, the fuel has to be replaced in the reactor with fresh fuel, even though there is still a substantial quantity of uranium‐235 and plutonium present. In the United States, this used fuel is usually “stored,” while in other countries such as Russia, the United Kingdom, France, Japan, and India, the fuel is reprocessed to remove the fission products, and the fuel can then be reused, thus cutting costs, reducing health risks, saving time, and in general being far safer (Regulation of TENORM 2012). The fission products removed from the fuel are a concentrated form of high‐level waste as are the chemicals used in the process. While these countries reprocess the fuel carrying out single plutonium cycles, India is the only country known to be planning multiple plutonium recycling schemes.
Nuclear Industry
Industrial source waste can contain alpha, beta, neutron, or gamma emitters. Gamma emitters are used in radiography, while neutron emitting sources are used in a range of applications, such as oil well logging (Nuclear Logging 2009).
Annual release of uranium and thorium radioisotopes from coal combustion, predicted by ORNL, cumulatively amount to 2.9 million T over the 1937–2040 period, from the combustion of an estimated 637 billion T of coal worldwide (Gabbard 1993).
Substances containing natural radioactivity are known as NORM. After human processing that exposes or concentrates this natural radioactivity (such as mining bringing coal to the surface or burning it to produce concentrated ash), it becomes technologically enhanced NORM (TENORM) (USEPA, June 6 2006c). A lot of this waste is alpha particle‐emitting matter from the decay chains of uranium and thorium. The main source of radiation in the human body is potassium‐40 (°K), typically 17 mg in the body at a time and 0.4 mg/day intake (Radio activity in nature, Idaho State University). Most rocks, due to their components, have a low level of radioactivity. Usually ranging from 1 to 13 mSv annually depending on location, average radiation exposure from natural radioisotopes is 2.0 mSv/person a year worldwide (UNSCEAR 2008). This makes up the majority of typical total dosage (with mean annual exposure from other sources amounting to 0.6 mSv from medical tests averaged over the whole populace, 0.4 mSv from cosmic rays, 0.005 mSv from the legacy of past atmospheric nuclear testing, 0.005 mSv occupational exposure, 0.002 mSv from the Chernobyl disaster, and 0.0002 mSv from the nuclear fuel cycle) (UNSCEAR 2008).
TENORM is not regulated as restrictively as nuclear reactor waste, though there are no significant differences in the radiological risks of these materials (Regulation of TENORM, Aug 1 2012).
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