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Radioactive waste

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.

Sources of waste NORM
(naturally occurring radioactive material)
Coal
Oil and gas Mineral processing Medical
Industrial Nuclear fuel cycle Front end
Back end Proliferation concerns Nuclear weapons production
Basic overview Physics Biochemistry
Philosophy Fiction Types of radioactive waste
Management of medium level waste Management of high level waste Storage
Vitrification Synroc Geological disposal
Transmutation Reuse of waste Accidents involving radioactive waste
See also



Sources of waste

NORM (naturally occurring radioactive material)
Processing of substances containing natural radioactivity, this is often known as NORM. Much of this waste is alpha particles emitting matter from the decay chains of uranium and thorium.


Coal
Coal contains a small amount of radioactive nuclides, such as uranium and thorium, but it is less than the average concentration of those elements in the Earth's crust. They become more concentrated in the fly ash because they do not burn well. However, the radioactivity of fly ash is still very low. It is about the same as black shale and is less than phosphate rocks, but is more of a concern because a small amount of the fly ash ends up in the atmosphere where it can be inhaled.


Oil and gas
Residues from the oil and gas industry often contain radium and its daughters. The sulphate scale from an oil well can be very radium rich, while the water, oil and gas from a well often contains radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant the area of the plant where propane is processed is often one of the more contaminated areas of the plant as radon has a similar boiling point as propane.


Mineral processing
Wastes from mineral processing can contain natural radioactivity.


Medical

Radioactive medical waste tends to contain beta ray and gamma ray emitters. It can be divided into two main classes. In diagnostic nuclear medicine a number of short-lived gamma emitters such as 99mTc are used.

Many of these can be disposed of by leaving it to decay for a short time before disposal as normal trash. Other isotopes used in medicine, with half-lives in parentheses:

  • 90Y, used for treating lymphoma (2.7 days)
  • 131I, used for thyroid function tests and for treating thyroid cancer (8.0 days)
  • 89Sr, used for treating bone cancer, intravenous injection (52 days)
  • 192Ir, used for brachytherapy (74 days)
  • 60Co, used for brachytherapy and external radiotherapy (5.3 years)
  • 137Cs, used for brachytherapy, external radiotherapy (30 years)

Industrial
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 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 oxide (UO2) concentrate from mining is not very radioactive - only a thousand or so times as radioactive as the granite used in buildings. It is refined from yellow cake (U3O8), then converted to uranium hexafluoride gas (UF6). As a gas, it undergoes enrichment to increase the 235U content from 0.7% to about 3.5% (LEU). It is then turned into a hard ceramic oxide (UO2) for assembly as reactor fuel elements.

The main by-product of enrichment is depleted uranium (DU), principally the 238U isotope, with a 235U content of ~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 the keels of yachts, and anti-tank shells. It is also used (with recycled plutonium) for making mixed oxide fuel (MOX) and to dilute highly enriched uranium from weapons stockpiles which is now being redirected to become reactor fuel. This dilution, also called downblending, means that any nation or group that acquired the finished fuel would have to repeat the (very expensive and complex) enrichment process before assembling a weapon.


Back end
The back end of the of the nuclear fuel cycle, mostly spent fuel rods, often contains fission products that emit beta and gamma radiation, and may contain actinides that emit alpha particles, such as 234U, 237Np, 238Pu and 241Am, and even sometimes some neutron emitters such as Cf. These isotopes are formed in nuclear reactors.

It's 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 High Level Waste above). 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 235U and plutonium present. Currently, in the USA, this used fuel is stored. In other countries (the UK, France, and Japan in particular) the fuel is reprocessed to remove the fission products, and the fuel can then be re-used. The reprocessing process involves handling highly radioactive materials, and the fission products removed from the fuel are a concentrated form of High Level Waste as are the chemicals used in the process.


Proliferation concerns

When dealing with uranium and plutonium, the possibility that they may be used to build nuclear weapons (nuclear proliferation) is often a consideration. Active nuclear reactors and nuclear weapons stockpiles are very carefully safeguarded and controlled. However, high-level waste from nuclear reactors may contain plutonium. Ordinarily, this plutonium is reactor-grade plutonium, containing a mixture of 239Pu (highly suitable for building nuclear weapons) and 240Pu (an undesirable contaminant and highly radioactive); the two isotopes are difficult to separate. Moreover, high-level waste is full of highly radioactive fission products. However, most fission products are relatively short-lived. This is a concern since if the waste is stored, perhaps in deep geological storage, over many years the fission products decay, decreasing the radioactivity of the waste. Moreover, the undesirable contaminant 240Pu decays faster than the 239Pu, and thus the quality of the bomb material increases with time (although its quantity decreases). Thus as time passes, these deep storage areas have the potential to become "plutonium mines", from which material for nuclear weapons can be acquired with relatively little difficulty.

One solution to this problem is to recycle the plutonium and use it as a fuel e.g. in fast reactors. But the very existence of the nuclear fuel reprocessing plant needed to separate the plutonium from the other elements represents, in the minds of some, a proliferation concern. In pyrometallurgical fast reactors, the waste generated is an actinide compound that cannot be used for nuclear weapons.


Nuclear weapons production

Waste from nuclear weapons production is unlikely to contain much beta or gamma activity other than tritium. It is more likely to contain alpha emitting actinides such as 239Pu which is a fissile material used in bombs, some material with much higher specific activities, such as 238Pu or Po, have been used in neutron triggers or thermoelectric power sources used in weapon systems.


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.

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 131I1 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

Low level nuclear waste being processed


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 in some cases requires shielding. ILW includes resins, chemical sludge and metal [nuclear fuel|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 shallow repositories, while long lived waste (from fuel reprocessing) is deposited in deep underground facilities. U.S. regulations do not define 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 fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot. HLW accounts for over 95% of the total radioactivity produced in the process of nuclear electricity generation.


Transuranic Waste (TRUW) as defined by U.S. regulations is, without regard to form or origin, waste that is contaminated with alpha-emitting transuranic radionuclides with half-lives greater than 20 years, and concentrations greater than 100nCi/g, excluding High Level Waste. In the U.S. it arises mainly from weapons production, and consists of clothing, tools, rags, residues, debris and other items contaminated with small amounts of radioactive elements (mainly plutonium). Elements that have an atomic number greater than uranium are called transuranic ("beyond uranium"). Because of their long half-lives, TRUW is disposed more cautiously then either low level or intermediate level waste.


Under U.S. law, TRUW is further categorized into "contact-handled" (CH) and "remote-handled" (RH) on the basis of radiation dose measured at the surface of the waste container. CH TRUW has a surface dose rate not greater than 200 mrem per hour, whereas RH TRUW has a surface dose rate of 200 mrem per hour or greater. CH TRUW does not have the very high radioactivity of high level waste, nor its high heat generation, but RH TRUW can be highly radioactive, with surface dose rates up to 1000 rem per hour. The United States currently permanently disposes of TRUW generated from nuclear power plants and military facilities at the Waste Isolation Pilot Plant.


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. 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. 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
Fissle material storage facilityb at Mayak in Russia
A fissile material storage facility in Mayak, Russia

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. 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 and 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 bloc 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, 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. 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 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 sea-based burial has become 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 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 canceled 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 . 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 teletherapy 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.


Global Nuclear Energy Partnership

The Global Nuclear Energy Partnership (GNEP), announced by U.S. Department of Energy secretary Samuel Bodman on February 6, 2006, is a plan to form an international partnership to see spent nuclear fuel reprocessed in a way that renders the plutonium in it usable for nuclear fuel but not for nuclear weapons.

The plan is part of the Advanced Energy Initiative announced by President Bush in his 2006 State of the Union address.

The Department of Energy said:

The Global Nuclear Energy Partnership has four main goals. First, reduce America’s dependence on foreign sources of fossil fuels and encourage economic growth. Second, recycle nuclear fuel using new proliferation-resistant technologies to recover more energy and reduce waste. Third, encourage prosperity growth and clean development around the world. And fourth, utilize the latest technologies to reduce the risk of nuclear proliferation worldwide.

Through GNEP, the United States will work with other nations possessing advanced nuclear technologies to develop new proliferation-resistant recycling technologies in order to produce more energy, reduce waste and minimize proliferation concerns. Additionally, [the] partner nations will develop a fuel services program to provide nuclear fuel to developing nations allowing them to enjoy the benefits of abundant sources of clean, safe nuclear energy in a cost effective manner in exchange for their commitment to forgo enrichment and reprocessing activities, also alleviating proliferation concerns.

On February 16, 2006 the U.S., France and Japan signed an "arrangement" to research and develop sodium-cooled fast reactors in support of the GNEP.


See also

Pollution
Great Smog of 1952
The Great stink
Waste
Britain’s Domestic Waste
Nuclear waste’s final resting place

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