Radio active waste

Nuclear waste

Nuclear waste is the radioactive waste left over from nuclear reactors, nuclear research projects, and nuclear bomb production. Nuclear waste is divided into low, medium, and high-level waste by the amount of radioactivity the waste produces.

Sources of waste

Radioactive waste comes from a number of sources. The majority of waste originates from the nuclear fuel cycle and nuclear weapons reprocessing. However, other sources include medical and industrial wastes, as well as naturally occurring radioactive materials (NORM).

Management of waste

Nuclear waste requires sophisticated treatment and management to successfully isolate it from interacting with the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving storage, disposal or transformation of the waste into a non-toxic form. Governments around the world are considering a range of waste management and disposal options, though there has been limited progress toward long-term waste management solutions.

Initial treatment of waste

· Vitrification

Long-term storage of radioactive waste requires the stabilization of the waste into a form which will neither react nor degrade for extended periods of time. One way to do this is through vitrification.

Vitrification is the transformation of a substance into a glass. Usually, it is achieved by rapdily cooling a liquid through the glass transition. In a wider sense, the embedding of material in a glassy matrix is also called vitrification. An important application is the vitrification of radioactive waste to obtain a stable compound that is suitable for ultimate disposal.

· Ion exchange

It is common for medium active wastes in the nuclear industry to be treated with ion exchange or other means to concentrate the radioactivity into a small volume. The much less radioactive bulk (after treatment) is often then discharged. For instance, it is possible to use a ferric hydroxide floc to remove radioactive metals from aqueous mixtures. After the radioisotopes are absorbed onto the ferric hydroxide, the resulting sludge can be placed in a metal drum before being mixed with cement to form a solid waste form.

Long term management of waste

· Geologic disposal

The process of selecting appropriate deep final repositories for high level waste and spent fuel is now under way in several countries with the first expected to be commissioned some time after 2010. The basic concept is to locate a large, stable geologic formation and use mining technology to excavate a tunnel, or large-bore tunnel boring machines to drill a shaft 500–1,000 meters below the surface where rooms or vaults can be excavated for disposal of high-level radioactive waste. The goal is to permanently isolate nuclear waste from the human environment.

Deep borehole disposal is the concept of disposing of high-level radioactive waste from nuclear reactors in extremely deep boreholes. Deep borehole disposal seeks to place the waste as much as five kilometers beneath the surface of the Earth and relies primarily on the immense natural geological barrier to confine the waste safely and permanently so that it should never pose a threat to the environment.

Sea-based options for disposal of radioactive waste include burial beneath a stable abyssal plain, burial in a subduction zone that would slowly carry the waste downward into the Earth's mantle, and burial beneath a remote natural or human-made island. While these approaches all have merit and would facilitate an international solution to the problem of disposal of radioactive waste, they would require an amendment of the Law of the Sea.

· Nuclear transmutation

Nuclear transmutation is the conversion of one chemical element or isotope into another, which occurs through nuclear reactions. Natural transmutation occurs when radioactive elements spontaneously decay over a long period of time and transform into other more stable elements. Artificial transmutation occurs in machinery that has enough energy to cause changes in the nuclear structure of the elements. Machines that can cause artificial transmutation include particle accelerators and tokamak reactors as well as conventional fission power reactors. Nuclear transmutation is considered as a possible mechanism for reducing the volume and hazard of radioactive waste.

· Re-use of waste

Another option is to find applications for the isotopes in nuclear waste so as to re-use them. Already, caesium-137, strontium-90 and a few other isotopes are extracted for certain industrial applications such as food irradiation and radioisotope thermoelectric generators. While re-use does not eliminate the need to manage radioisotopes, it reduces the quantity of waste produced.

· Space disposal

Space disposal is an attractive notion because it permanently removes nuclear waste from the environment. It has significant disadvantages, not least of which is the potential for catastrophic failure of a launch vehicle. The high number of launches that would be required — because no individual rocket would be able to carry very much of the material relative to the material needed to be disposed of—makes the proposal impractical (for both economic and risk-based reasons). To further complicate matters, international agreements on the regulation of such a program would need to be established.

Accidents involving radioactive waste

A number of incidents have occurred when radioactive material was disposed of improperly, shielding during transport was defective, or when it was simply abandoned or even stolen from a waste store.

Goiânia accident

The Goiânia accident was a radioactive contamination accident that occurred on 13 September 1987, at Goiânia, Brazil. Considered one of the worst nuclear disasters in history, it took place after an old nuclear medicine source was scavenged from an abandoned hospital site in the city. It was subsequently handled by many people, resulting in four deaths and serious radioactive contamination of 249 other people. The dispersal of radiation was equivalent to a medium-size dirty bomb.

Kyshtym disaster

The Kyshtym disaster was a radiation contamination incident that occurred on 29 September 1957 at Mayak, a nuclear fuel reprocessing plant in Russia (then a part of the Soviet Union). It measured as a Level 6 disaster on the International Nuclear Event Scale, making it the second most serious nuclear accident ever recorded (after the Chernobyl disaster). The event occurred in the town of Ozyorsk, a closed city built around the Mayak plant.

The Mayak plant was built in a great hurry between 1946 and 1950. Initially Mayak was dumping high-level radioactive waste into a nearby river, which was taking waste to the river Ob, flowing farther down to the Arctic Ocean.

A storage facility for liquid nuclear waste was added around 1953. Because of the high level of radioactivity, the waste was heating itself through decay heat. For that reason, a cooler was built around each bank containing 20 tanks. In September 1957 the cooling system in one of the tanks containing about 70-80 tons of radioactive waste failed, and the temperature in it started to rise, resulting in a non-nuclear explosion of the dried waste having a force estimated at about 70-100 tons of TNT, which threw the concrete lid, weighing 160 tons, into the air.

Even though the Soviet government suppressed information about the figures, it is estimated that the direct exposure to radiation caused at least 200 cases of death from cancer.\l

Mayapuri incident

April 2010 - A 35-year old man was hospitalized in New Delhi after handling radioactive scrap metal. Investigation led to the discovery of an amount of scrap metal containing Cobalt-60 in the New Delhi industrial district of Mayapuri. The 35-year old man later died from his injuries, while six others remained hospitalized.