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Radioactive waste

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A Russian fissile material storage facility

Radioactive waste is waste material containing radioactive chemical elements that does not have a practical purpose. It is sometimes the product of a nuclear process, such as nuclear fission. The majority of radioactive waste in mass and volume terms is low level waste which is often items such as used protective clothing which is only slightly contaminated.

Nuclear waste explodes very easily and should not be thrown in a fire or kept under your bed and if you have nuclear waste you should throw it in the lake and nothing bad will happen so you should run really fast and and swim in hot lava 10 times backwards over the feilds and if you meet a magic butterfly you should chop off your toes and feed them to ducks if you know how to ride a swing set you should be able to get their faster that way but if you want to soup it up you can take it to cherry picker lane but that all i know about nuclear waste bye

Basic overview

Physics

The radioactivity of all nuclear waste diminishes with time. All radioisotopes contained in the waste have a half-life - the time it takes for any radionuclide to lose half of its radioactivity. Eventually all radioactive waste decays into non-radioactive elements; for example, after 40 years 99.9% of radiation in spent nuclear fuel disappears [1].

The faster a radioisotope is decaying, the more radioactive it will be. The energy and the type of the ionizing radiation emitted by a pure radioactive substance are important factors in deciding how dangerous it will be. The chemical properties of the radioactive element will determine how mobile the substance is and how likely it is to spread into the environment and contaminate human bodies. This is further complicated by the fact that many radioisotopes decay immediately to a stable state, but rather to a radioactive decay product leading to decay chains.

Biochemistry

Depending on the decay mode and the biochemistry of an element, the threat due to exposure to a given activity of a radioisotope will differ. For instance 131I is a short-lived beta and gamma emitter but because it concentrates in the thyroid gland, it is more able to cause injury than 99mTcO4- which is spread throughout the body and is rapidly excreted. In a similar way, the alpha emitting actinides and radium are considered very harmful as they tend to have long biological half-lives and their radiation has a high linear energy transfer value. Because of these differences the rules often differ according to the radioisotope and the nature that the activity is in.

Philosophy

The main objective in managing and disposing of radioactive (or other) waste is to protect people and the environment. This means isolating or diluting the waste so that the rate or concentration of any radionuclides returned to the biosphere is harmless. To achieve this the preferred technology to date has been deep and secure burial for the more dangerous wastes; transmutation, long-term retrievable storage, and removal to space have also been suggested.

The phrase which sums up the area is ' Isolate from man and his environment ' until the waste has decayed such that it no longer poses a threat.

For instance a vial containing 1 Ci of 32P or 99mTc if left in a shielded place to decay, then after a year it would contain only a trace of activity. But 1 Ci of used nuclear fuel (1 year after irradiation in a reactor) or 137Cs would have a longer lifetime, as a result this waste would need to be isolated from humans for longer.

Fiction

In fiction, radioactive waste is often cited as the reason for gaining super-human powers and abilities. In reality, contact with radioactive waste is not good, and would be vastly more likely to cause serious harm or death rather than an improvement. It is interesting to note that the treatment of an adult animal with radiation or some other mutation causing effect, such as a cytotoxic anti-cancer drug, that it is impossible to cause that adult animal to become a mutant. It has more likely that a cancer will be induced in the animal, in humans it has been calculated that a 1 sievert dose has a 5% chance of causing cancer and a 1% chance of causing a mutation in a gamete (e.g. egg) or a gamete forming cell such as those in the testis which can be passed to the next generation. If a developing organism such as a unborn child is irradiated then it is possible to induce a deformity or birth defect but it is unlikely that this defect will be in a gamete or a gamete forming cell.

Types of radioactive waste

Removal of very low-level waste

Although not significantly radioactive, uranium mill tailings are waste. They are byproduct material from the rough processing of uranium-bearing ore. They are sometimes referred to as 11(e)2 wastes, from the section of the U.S. Atomic Energy Act that defines them. Uranium mill tailings typically also contain chemically-hazardous heavy metals such as lead and arsenic. Vast mounds of uranium mill tailings are left at many old mining sites, especially in Colorado, New Mexico, and Utah.

Low level Waste (LLW) is generated from hospitals and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filters, etc., which contain small amounts of mostly short-lived radioactivity. It does not require shielding during handling and transport and is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal. Low level waste is divided into four classes, class A, B, C and GTCC, which means greater than class C.

Intermediate level Waste (ILW) contains higher amounts of radioactivity and some requires shielding. It typically comprises of resins, chemical sludges and metal fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen for disposal. Generally short lived waste (mainly from reactors) is buried in a shallow repository, while long lived waste (from fuel reprocessing) will be disposed of deep underground. U.S. regulations don't recognize this category of waste; the term is used in Europe and elsewhere.

High level Waste (HLW) arises from the use of uranium fuel in a nuclear reactor and nuclear weapons processing. It contains the fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot. It can be considered the "ash" from "burning" uranium. HLW accounts for over 95% of the total radioactivity produced in the process of nuclear electricity generation.

Transuranic Waste as defined by U.S. regulations is, without regard to source or form, waste that is contaminated with alpha-emitting transuranium radionuclides with half-lives greater than 20 years, and concentrations greater than 100nCi/g but not including High Level Waste. In the U.S. it arises mainly from weapons production, and consists of clothing, tools, rags, residues, debris and other such items contaminated with small amounts of radioactive elements -- mostly plutonium. These elements have an atomic number greater than uranium -- thus transuranic (beyond uranium). Because of the long half-lives of these elements, this waste is not disposed of as either low level or intermediate level waste. It does not have the very high radioactivity of high level waste, nor its high heat generation. The United States currently permanently disposes of transuranic waste of military origin at the Waste Isolation Pilot Plant. [2]

Management of medium level waste

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 [3]. 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[4][5][6]. In order to get better long term performance instead of normal cement (portland cement) a mixture of fly ash or blast furnace slag and portland cement can be used.

Management of High level waste

Storage

High-level radioactive waste is stored temporarily in spent fuel pools and in dry cask storage facilities.

Vitrification

Long-term storage of radioactive waste requires the stabilization of the waste into a form which will not react, nor degrade, for extended periods of time. One way to do this is through vitrification. Currently at Windscale, the high-level waste (PUREX first cycle raffinate) is calcined and mixed with glass and sugar before being melted into glass[7]. The resulting glass is poured into stainless steel containers, after filling a seal is welded onto the cylinder. The cylinder is then washed, after being inspected for external contamination the steel cylinder is placed in a store. The glass inside is a black glossy substance, all this work (in england) is done using hot cell systems. The sugar is added to control the ruthenium chemistry, it is to stop the formation of the volatile RuO4. In the west the glass is normally a borosilicate glass (similar to Pyrex {NB Pyrex is a trade name}), while in the former Soviet block it is normal to use a phosphate glass. The amount of fission products in the glass must be limited because some (palladium, the other Pt group metals, and tellurium) tend to form metallic phases which separate from the glass. In Germany a vitrification plant is in use, this is treating the waste from a small demonstration reprocessing plant which has since been closed down.

The glass formed when placed in water will dissolve very slowly,[8] according to the ITU it will require about 1 million years for 10% of the glass to dissolve in water.

In 1997, in the 20 countries which account for most of the world's nuclear power generation, spent fuel storage capacity at the reactors was 148,000 tonnes, with 59% of this utilized. Away-from-reactor storage capacity was 78,000 tonnes, with 44% utilized. With annual additions of about 12,000 tonnes, issues for final disposal are not urgent.

In 1989 and 1992, France commissioned commercial plants to vitrify HLW left over from reprocessing oxide fuel, although there are adequate facilities elsewhere, notably in the UK and Belgium. The capacity of these western European plants is 2,500 canisters (1000 t) a year, and some have been operating for 18 years.

Synroc

The Australian Synroc (synthetic rock) is a more sophisticated way to immobilize such waste, and this process may eventually come into commercial use for civil wastes (it is currently being developed for US military wastes).

Geological disposal

The process of selecting appropriate deep final repositories is now under way in several countries with the first expected to be commissioned some time after 2010. In Switzerland, the Grimsel Test Site is an international research facility investigating the open questions in radioactive waste disposal ([9]). Sweden is well advanced with plans for direct disposal of spent fuel, since its Parliament decided that this is acceptably safe, using the KBS-3 technology. In Germany, there is a political discussion about the search for an Endlager (final repository) for radioactive waste, accompanied by loud protests especially in the Gorleben village in the Wendland area, which was seen ideal for the final repository until 1990 because of its location next to the border to the former GDR. Gorleben is presently being used to store radioactive waste non-permanently, with a decision on final disposal to be made at some future time. The US has opted for a final repository at Yucca Mountain in Nevada, but this project is widely opposed and is a hotly debated topic. There is also a proposal for an international HLW repository in optimum geology, with Australia or Russia as possible locations; however, the proposal for a global repository for Australia has raised fierce domestic political objections, making such a dump unlikely. In Russia, which is fiscally desperate and minimally democratic, the plan might have a greater chance of success.

Sea-based options for disposal of radioactive waste [10] 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 vexing problem of disposal of radioactive waste, they are currently not being seriously considered because of the legal barrier of the Law of the Sea and because in North America and Europe burial sea-based burial has become a taboo from fear that such a repository could leak and cause widespread damage, though the evidence that this would happen is lacking. Dumping of radioactive waste from ships has reinforced this taboo. However, sea-based approaches might come under consideration in the future by individual countries or groups of countries that cannot find other acceptable solutions. A more feasible approach termed Remix & Return [11] would blend high-level waste with mine and mill tailings down to the level of the original radioactivity of the uranium ore, then replace it in empty uranium mines. This approach has the merits of totally eliminating the problem of high-level waste, of placing the material back where it belongs in the natural order of things, of providing jobs for miners who would double as disposal staff, and of facilitating a cradle-to-grave cycle for all radioactive materials.

Transmutation

There have been proposals for reactors that consume nuclear waste and transmute it to other, less-harmful nuclear waste. In particular, the Integral Fast Reactor was a proposed nuclear reactor with a nuclear fuel cycle that produced no transuranic waste; in fact, it could consume transuranic waste. It proceeded as far as large-scale tests but was then cancelled by the US Government. Another approach, considered safer but requiring more development, is to dedicate subcritical reactors to the transmutation of the left-over transuranic elements.

Reuse of waste

Another option is to find applications of the isotopes in nuclear waste so as to reuse them. [12] . Already, cesium 137, strontium 90, technetium 99, and a few other isotopes are extracted for certain industrial applications such as food irradiation and RTGs.

Accidents involving radioactive waste

While radioactive waste is not as sensitive to disruption as an active nuclear reactor, it is often treated as regular waste and forgotten. A number of incidents have occurred when radioactive material was disposed of improperly or simply abandoned.

Perhaps the worst is the Goiânia accident, in which a teletheraphy equipment containing caesium chloride (137Cs) previously used in cancer treatment in a hospital, was left behind when the hospital was abandoned. Scavengers collected the equipment, smashed it open, and the mysterious glowing solid was passed around. Several people were killed, and many more suffered radiation poisoning, before the solid was recognized as radioactive.

Scavenging of abandoned radioactive material has been the cause of several other cases of radiation exposure, mostly in developing nations, which usually have less regulation of dangerous substances and a market for scavenged goods and scrap metal. The scavengers and those who buy the material are almost always unaware that the material is radioactive and it is selected for its aesthetics or scrap value. A few are aware of the radioactivity, but are either ignorant of the risk or believe that the material's value outweighs the danger. Irresponsibility on the part of the radioactive material's owners, usually a hospital, university or military, and the absence of regulation concerning radioactive waste, or a lack of enforcement of such regulations, have been significant factors in radiation exposures.

Transportation accidents involving spent nuclear fuel from power plants are unlikely to have serious consequences due to the strength of the spent nuclear fuel shipping casks.

See also

References

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