'Radioactive waste' are
waste types containing
radioactive chemical elements that do not have a practical purpose. It is sometimes the product of a nuclear process, such as
nuclear fission. However, other industries not directly connected to the nuclear industry can produce large quantities of radioactive waste. For instance, over the past 20 years it is estimated that just the oil-producing endeavors of the US have accumulated 8 million tons of radioactive wastes.
[1] The majority of radioactive waste is "
low-level waste", meaning it has low levels of radioactivity per
mass or
volume. This type of waste often consists of used protective clothing, which is only slightly contaminated but still dangerous in case of
radioactive contamination of a human body through
ingestion,
inhalation,
absorption, or
injection.
In the
United States alone, the
Department of Energy states that there are "millions of gallons of radioactive waste" as well as "thousands of tons of
spent nuclear fuel and material" and also "huge quantities of contaminated soil and water".
[2] Despite these copious quantities of waste, the DOE has a goal of cleaning all presently contaminated sites successfully by 2025.
The
Fernald, Ohio site for example had "31 million pounds of uranium product", "2.5 billion pounds of waste", "2.75 million cubic yards of contaminated soil and debris", and a "223 acre portion of the underlying Great Miami Aquifer had uranium levels above drinking standards".
The United States currently has at least 108 sites it currently designates as areas that are contaminated and unusable, sometimes many thousands of acres
[3] The DOE wishes to try and clean or mitigate many or all by 2025, however the task can be difficult and it acknowledges that some will never be completely remediated, and just in one of these 108 larger designations,
Oak Ridge National Laboratory, there were for example at least "167 known contaminant release sites" in one of the three subdivisions of the site.
Some of the U.S. sites were smaller in nature, however, and cleanup issues were simpler to address, and the DOE has successfully completed cleanup, or at least closure, of several sites.
The issue of disposal methods for nuclear waste was one of the most pressing current problems the international nuclear industry faced when trying to establish a long term energy production plan, yet there was hope it could be safely solved. In the U.S., the DOE acknowledged much progress in addressing the waste problems of the industry, and successful remediation of some contaminated sites, yet also major uncertainties and sometimes complications and setbacks in handling the issue properly, cost effectively, and in the projected time frame.
In other countries with lower ability or will to maintain environmental integrity the issue would be more problematic.
Sources of waste
NORM (naturally occurring radioactive material)
Processing of substances containing natural radioactivity; this is often known as NORM. A lot of this waste is
alpha particles emitting matter from the decay chains of
uranium and
thorium. The main source of radiation in the human body is
potassium-40 (
40K).
Coal
Coal contains a small amount of radioactive nuclides, such as uranium and thorium, around or slightly more than the average concentration of those elements in the
Earth's crust[4][5]. They become more concentrated in the
fly ash because they do not burn well
5. 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.
[1].
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.
[6]
Mineral processing
Wastes from mineral processing can contain natural radioactivity; the largest source of this are phosphate mining operations.
Medical
Radioactive
medical waste tends to contain
beta particle 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
technetium-99m 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:
★
Y-90, used for treating
lymphoma (2.7 days)
★
I-131, used for
thyroid function tests and for treating
thyroid cancer (8.0 days)
★
Sr-89, used for treating
bone cancer,
intravenous injection (52 days)
★
Ir-192, used for
brachytherapy (74 days)
★
Co-60, used for brachytherapy and external radiotherapy (5.3 years)
★
Cs-137, 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.
[2]
Nuclear fuel cycle
Main articles: Nuclear fuel cycle,
Spent nuclear fuel
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 (UO
2) 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
yellowcake (U
3O
8), then converted to
uranium hexafluoride gas (UF
6). As a gas, it undergoes
enrichment to increase the
U-235 content from 0.7% to about 4.4% (LEU). It is then turned into a hard
ceramic oxide (UO
2) for assembly as reactor fuel elements.
The main by-product of enrichment is
depleted uranium (DU), principally the
U-238 isotope, with a U-235 content of ~0.3%. It is stored, either as UF
6 or as U
3O
8. 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 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,
neptunium-237,
plutonium-238 and
americium-241, and even sometimes some neutron emitters such as
californium (Cf). 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 high level waste below). 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. Currently, in the U.S., this used fuel is stored. In other countries, such as the United Kingdom, France, and Japan, the fuel is reprocessed to remove the fission products, and the fuel can then be re-used. This reprocessing 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
Main articles: nuclear proliferation
When dealing with uranium and plutonium, the possibility that they may be used to build
nuclear weapons is often a concern. 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
plutonium-239 (highly suitable for building nuclear weapons),
plutonium-240 (an undesirable contaminant and highly radioactive),
plutonium-241, and
plutonium-238; these 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 and making the plutonium easier to access. Moreover, the undesirable contaminant Pu-240 decays faster than the Pu-239, and thus the quality of the bomb material increases with time (although its quantity decreases). Thus, some have argued, 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. Critics of the latter idea point out that the half-life of Pu-240 is 6,560 years and Pu-239 is 24,110 years, and thus the relative enrichment of one isotope to the other with time occurs with a half-life of 9,000 years (that is, it takes 9000 years for the ''fraction'' of Pu-240 in a sample of mixed plutonium isotopes, to spontaneously decrease by half-- a typical enrichment needed to turn reactor-grade into weapons-grade Pu). Thus "weapons grade plutonium mines" would be a problem for the very far future (>9,000 years from now), so that there remains a great deal of time for technology to advance to solve this problem, before it becomes acute.
Pu-239 decays to
U-235 which is suitable for weapons and which has a very long half life (roughly 10
9 years). Thus plutonium may decay and leave uranium-235. However, modern reactors are only moderately enriched with U-235 relative to U-238, so the U-238 continues to serve as denaturation agent for any U-235 produced by plutonium decay.
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 reprocessing
Waste from
nuclear weapons reprocessing (as opposed to production, which requires primary processing from reactor fuel) is unlikely to contain much beta or gamma activity other than
tritium and
americium. It is more likely to contain alpha emitting actinides such as Pu-239 which is a fissile material used in bombs, plus some material with much higher specific activities, such as Pu-238 or Po.
In the past the neutron trigger for a bomb tended to be
beryllium and a high activity alpha emitter such as
polonium; an alternative to polonium is
Pu-238. For reasons of national security, details of the design of modern bombs are normally not released to the open literature. It is likely however that a D-T
fusion reaction in either an electrically driven device or a D-T fusion reaction driven by the chemical explosives would be used to start up a modern device.
Some designs might well contain a
radioisotope thermoelectric generator using Pu-238 to provide a longlasting source of electrical power for the electronics in the device.
It is likely that the fissile material of an old bomb which is due for refitting will contain decay products of the plutonium isotopes used in it, these are likely to include alpha-emitting
Np-236 from Pu-240 impurities, plus some U-235 from decay of the Pu-239; however, due to the relatively long half-life of these Pu isotopes, these wastes from radioactive decay of bomb core material would be very small, and in any case, far less dangerous (even in terms of simple radioactivity) than the Pu-239 itself.
The beta decay of
Pu-241 forms
Am-241; the in-growth of americium is likely to be a greater problem than the decay of Pu-239 and Pu-240 as the americium is a gamma emitter (increasing external-exposure to workers) and is an alpha emitter which can cause the generation of
heat. The plutonium could be separated from the americium by several different processes; these would include
pyrochemical processes and aqueous/organic
solvent extraction. A truncated
PUREX type extraction process would be one possible method of making the separation.
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 and eventually all radioactive waste decays into non-radioactive elements. Certain radioactive elements (such as plutonium-239) in “spent” fuel will remain hazardous to humans and other living beings for hundreds of thousands of years. Other radioisotopes will remain hazardous for millions of years. Thus, these wastes must be shielded for centuries and isolated from the living environment for hundreds of millennia
[3]. Some elements, such as
Iodine-131, have a short half-life (around 8 days in this case) and thus they will cease to be a problem much more quickly than other, longer-lived, decay products but their activity is much greater initially.
The faster a
radioisotope decays, 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 do not decay immediately to a stable state but rather to a radioactive
decay product leading to
decay chains.
Chemistry
The chemical properties of the radioactive substance and the other substances found within (and near) the waste store has a great effect upon the ability of the waste to cause harm to humans or other organisms. For instance
TcO4- tends to
adsorb on the surfaces of steel objects which reduces its ability to move out of the waste store in water.
Pharmacokinetics
Depending on the decay mode and the
pharmacokinetics of an element (how the body processes it and how quickly), the threat due to exposure to a given activity of a
radioisotope will differ. For instance I-131 is a short-lived
beta and
gamma emitter but because it concentrates in the
thyroid gland, it is more able to cause injury than
cesium-137 which, being water soluble, is rapidly excreted in urine. 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 such differences, the rules determining biological injury differ widely according to the radioisotope, and sometimes also the nature of the chemical compound which contains the radioisotope.
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.
Fiction
In
fiction, radioactive waste is often cited as the reason for gaining
super-human powers and abilities. An example of this fictional scenario is the 1981 movie "
Modern Problems" in which actor
Chevy Chase portrays a jealous, harried air traffic controller Max Fiedler; Max Fiedler, recently dumped by his girlfriend, comes into contact with nuclear waste and is granted the power of telekinesis, which he uses to not only win her back, but to gain a little revenge. A more widely known character affected by a bite from a radioactive spider is
Spider-man. The Spider-man character was developed by
Marvel Comics (see also
Stan Lee).
In most movies and cartoons, radioactive waste in any form is portrayed as
steel barrels labeled with the classic radiation
hazard symbol, and full of thick, glowing,
neon-green liquid. People, animals or objects that have come in contact with radiation or are radioactive themselves are usually shown with a bright green glow around them as well, and sometimes undergo hideous mutations such as the sudden growth of extra body parts, disfigurements, or turning into half-animal hybrids (if a person is bitten by a radioactive animal, much like in
werewolf lore). This is often used for comical effect. Most radioactive material in real life however, is neither green nor luminescent (though some have been known to
glow in the dark).
In
reality, exposure to high levels of radioactive waste may cause serious harm or
death. Treatment of an
adult animal with
radiation or some other
mutation-causing effect, such as a cytotoxic anti-
cancer drug, cannot cause that adult animal to become a mutant. It is 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 an
unborn child is irradiated, then it is possible to induce a
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. Commonly, LLW is designated as such as a precautionary measure if it originated from any region of an 'Active Area', which frequently includes offices with only a remote possibility of being contaminated with radioactive materials. Such LLW typically exhibits no higher radioactivity than one would expect from the same material disposed of in a non-active area, such as a normal office block. Some high activity LLW requires shielding during handling and transport but most LLW 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 reactor
fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen for disposal. As a general rule, short-lived waste (mainly non-fuel materials from reactors) is buried in shallow repositories, while long-lived waste (from fuel and 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 flasks are transported by train in the United Kingdom. Each flask is constructed of 3ft thick solid steel and weighs in excess of 50 tons
'
High Level Waste (HLW)' is produced by
nuclear reactors. It contains
fission products and
transuranic elements generated in the
reactor core. It is highly radioactive and often thermally hot. HLW accounts for over 95% of the total radioactivity produced in the process of nuclear
electricity generation. The amount of HLW worldwide is currently increasing by about 12,000 metric tons every year, which is the equival to about 100 double-decker busses or a two-storey structure built on top of a basketball court
[7].
'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 100
nCi/g (3.7
MBq/kg), excluding High Level Waste. 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 than either low level or intermediate 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).
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 (2
mSv/h), whereas RH TRUW has a surface dose rate of 200
mrem per hour (2 mSv/h) 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 1000000
mrem per hour (10000 mSv/h). The United States currently permanently disposes of TRUW generated from nuclear power plants and military facilities at the
Waste Isolation Pilot Plant.
[8]
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
[4]. 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.
[9] In order to get better long-term performance (mechanical stability) from such forms, they may be made from a mixture of
fly ash, or
blast furnace slag, and
portland cement, instead of normal
concrete (made with
portland cement, gravel and sand).
Management of high level waste
Storage
High-level radioactive waste is stored temporarily in
spent fuel pools and in
dry cask storage facilities. This allows the shorter-lived isotopes to decay before further handling.
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
Sellafield, England the high-level waste (
PUREX first cycle
raffinate) is mixed with
sugar and then calcined.
Calcination involves passing the waste through a heated, rotating tube. The purposes of calcination are to evaporate the water from the waste, and de-nitrate the fission products to assist the stability of the glass produced.
The 'calcine' generated is fed continuously into an induction heated furnace with fragmented
glass[5]. The resulting glass is a new substance in which the waste products are bonded into the glass matrix when it solidifies. This product, as a molten fluid, is poured into
stainless steel cylindrical containers ("cylinders") in a batch process. When cooled, the fluid solidifies ("vitrifies") into the glass. Such glass, after being formed, is very highly resistant to water.
[6] According to the ITU, it will require about 1 million years for 10% of such glass to dissolve in water.
After filling a cylinder, a seal is
welded onto the cylinder. The cylinder is then washed. After being inspected for external contamination, the steel cylinder is stored, usually in an underground repository. In this form, the waste products are expected to be immobilized for a very long period of time (many thousands of years).
The glass inside a cylinder is usually a black glossy substance. All this work (in the
United Kingdom) is done using
hot cell systems. The sugar is added to control the
ruthenium chemistry and to stop the formation of the volatile RuO
4 containing
radioruthenium. 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.
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. However, a number of nuclear power plants in countries that do not reprocess had nearly filled their spent fuel pools, and resorted to Away-from-reactor storage (AFRS). AFRS capacity in 1997 was 78,000 tonnes, with 44% utilized, and annual additions of about 12,000 tonnes. AFRS cannot be expanded forever, and the lead times for final disposal sites have proven to be unpredictable (see below).
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 United Kingdom 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)
[7] 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 U.S. military wastes). The Synroc contains
pyrochlore and
cryptomelane type minerals. The original form of Synroc (Synroc C) was designed for the liquid high level waste (PUREX raffinate) from a
light water reactor. The main minerals in this Synroc are
hollandite (BaAl
2Ti
6O
16),
zirconolite (CaZrTi
2O
7) and
perovskite (CaTiO
3). The zirconolite and perovskite are hosts for the
actinides. The
strontium and
barium will be fixed in the perovskite. The
caesium will be fixed in the hollandite.
Synroc was invented by the late Prof Ted Ringwood (a
geochemist) at the
Australian National University.
Nuclear waste locations in USA
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. However, many people remain uncomfortable with the immediate
stewardship cessation of this management system. In Switzerland, the Grimsel Test Site is an international research facility investigating the open questions in radioactive waste disposal (
[8]).
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
German Democratic Republic. 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 U.S. has opted for a final repository at
Yucca Mountain in Nevada, but this project is widely opposed and is a hotly debated topic, and one of the main concerns is with the long distance transportation of the waste from across the United States to this area, and the possible several accidents over time that would occur. There is also a proposal for an international HLW repository in optimum geology, with Australia or Russia as possible locations, although the proposal for a global repository for Australia has raised fierce domestic political objections.
The Canadian government, for example, is seriously considering this method of disposal, known as the ''Deep Geological Disposal'' concept. Under the current plan, a vault is to be dug 500 to 1000 meters below ground, under the
Canadian Shield, one of the most stable landforms on the planet. The vaults are to be dug inside geological formations known as ''
batholiths'', formed about a billion years ago. The used fuel bundles will be encased in a corrosion-resistant container, and further surrounded by a layer of ''buffer material'', possibly of a special kind of clay (
bentonite clay). The case itself is designed to last for thousands of years, while the clay would further slow the corrosion rates of the container. The batholiths themselves are chosen for their low ground-water movement rates, geological stability, and low economic value.
[10]
The Finnish government has already started building a vault to store nuclear waste 500 to 1000 meters below ground, not far from the nuclear plant at
Olkiluoto Nuclear Power Plant.
Storing high level nuclear waste above ground for a century or so is considered appropriate by many scientists. This allows for the material to be more easily observed and any problems detected and managed, while the decay over this time period significantly reduces the level of radioactivity and the associated harmful effects to the container material. It is also considered likely that over the next century newer materials will be developed which will not break down as quickly when exposed to a high neutron flux thus increasing the longevity of the container once it is permanently buried.
Sea-based options for disposal of radioactive waste
[9] 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. Dumping of radioactive waste from ships has reinforced this concern, as has contamination of islands in the Pacific. 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
[10] would blend high-level waste with
uranium 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 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 and in fact, could consume transuranic waste. It proceeded as far as large-scale tests but was then canceled by the U.S. Government. Another approach, considered safer but requiring more development, is to dedicate
subcritical reactors to the
transmutation of the left-over transuranic elements.
There have also been theoretical studies involving the use of
fusion reactors as so called "actinide burners" where a fusion reactor
plasma such as in a
tokamak, could be "doped" with a small amount of the "minor" transuranic atoms which would be transmuted (meaning fissioned in the actinide case) to lighter elements upon their successive bombardment by the very high energy neutrons produced by the fusion of
deuterium and
tritium in the reactor. It was recently found by a study done at
MIT, that only 2 or 3 fusion reactors with parameters similar to that of the
International Thermonuclear Experimental Reactor (ITER) could transmute the entire annual
minor actinide production from all of the
light water reactors presently operating in the
United States fleet while simultaneously generating approximately 1
gigawatt of power from each reactor
[11].
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 and a few other isotopes are extracted for certain industrial applications such as
food irradiation and
radioisotope thermoelectric generators.
Space disposal
Space disposal is an attractive notion because it permanently removes nuclear waste from the environment. However, it has significant disadvantages, not least of which is the potential for catastrophic failure of a
launch vehicle. Furthermore, the high number of launches that would be required makes the proposal impractical. To further complicate matters, international agreements on the regulation of a such a program would need to be established.
[13]
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.
[11] In the former Soviet Union(a nation possessing a high level of technical expertise and experience with nuclear issues), waste stored in
Lake Karachay was accidentally blown all over the area during a dust storm after the lake had dried out. One still must not stop their car when driving through for any reason. In other cases lakes or ponds with radioactive waste accidentally overflowed into the rivers during exceptional storms.
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 sometimes less general education about radioactivity and its hazards) 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. For details of radioactive scrap see the
Goiânia accident.
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 that article).
See also
★
Global Nuclear Energy Partnership
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Hot cell
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Geomelting
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Radioactive scrap metal
★
Yucca Mountain proposed nuclear-waste storage facility
★
List of nuclear accidents
★
List of Superfund sites in the United States
★
List of topics dealing with environmental issues
★
List of waste management companies
★
List of waste management topics
★
List of solid waste treatment technologies
★
Nuclear power
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Pollution
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Toxic waste
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Remediation
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Recycling
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Superfund
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Stored Waste Examination Pilot Plant
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Waste types
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Waste management
References
1. Krivtsov, A.I., 2006, Geoenvironmental Problems of Mineral Resources Development, in ''Geology and Ecosystems'', Zekster (Ru), Marker (UK), Ridgeway (UK), Rogachevskaya (Ru), & Vartanyan (Ru), 2006 Springer Inc.,
2. U.S. Department of Energy Environmental Management - "Department of Energy Five Year Plan FY 2007-FY 2011 Volume II." Retrieved on 8 April 2007.
3. American Scientist Jan/Feb 2007
4. http://www.uic.com.au/nip78.htm
5. http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html
6. Survey & Identification of NORM Contaminated Equipment
7. http://www.marathonresources.com.au/nuclearwaste.php
8. Why WIPP?
9. Removal of Silicon from High Level Waste Streams via Ferric Flocculation
10. How is high-level nuclear waste managed in Canada?
11. http://www.iaea.org/Publications/Magazines/Bulletin/Bull413/article1.pdf
Fentiman, Audeen W. and James H. Saling. ''Radioactive Waste Management''. New York: Taylor & Francis, 2002. Second ed.
An overview of waste from the nuclear fuel cycle was written by B.V. Babu and S. Karthik, ''Energy Education Science and Technology'', 2005, '14', 93-102.
External links
★
Key Radionuclides and Generation Processes (
DOE)
★
Alsos Digital Library - Radioactive Waste (bibliography)
★
Belgian Nuclear Research Centre - Activities (documents and links)
★
Belgian Nuclear Research Centre - Scientific Reports (documents)
★
Critical Hour: Three Mile Island, The Nuclear Legacy, And National Security (PDF)
★
Environmental Protection Agency - Yucca Mountain (documents)
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Grist.org - How to tell future generations about nuclear waste (article)
★
A discussion on the secrecy surrounding plans for radioactive waste in the UK (article)
★
International Atomic Energy Agency - Nuclear Fuel Cycle and Waste Technology Program (program objectives)
★
International Atomic Energy Agency - Internet Directory of Nuclear Resources (links)
★
Nuclear Files.org - Yucca Mountain (documents)
★
Nuclear Regulatory Commission - Radioactive Waste (documents)
★
Nuclear Regulatory Commission - Spent Fuel Heat Generation Calculation (guide)
★
Oak Ridge National Laboratory - Coal Combustion: Nuclear Resource or Danger (document)
★
Radwaste.org (links)
★
Radwaste Blog (weblog)
★
Surviving on Nuclear Waste (book)
★
The Nuclear Energy Option - Hazards of High-Level Radioactive Waste (book)
★
UNEP Earthwatch - Radioactive Waste (documents and links)
★
Uranium Information Center - Radioactive Waste (briefing papers)
★
United States Geological Survey - Radioactive Elements in Coal and Fly Ash (document)
★
World Nuclear Association - Radioactive Waste (briefing papers)
★
Radioactive Waste Management, by UIC
Accidents
★
Nuclear Waste Drums Lose Lids in Japan Quake - Kyodo.
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