Radioactive waste



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Radioactive wastes are 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 km²) site.[2] 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.[2]

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.[2] In other countries with lower ability or will to maintain environmental integrity the issue would be more problematic.

The nature and significance of radioactive waste

Radioactive waste typically comprises a number of ionizing radiation which can be harmful to human health and to the environment. Those isotopes emit different types and levels of radiation, which last for different periods of time.

Physics

Medium-lived
fission products
t½(y)Yield%KeVβ
155Eu4.76.0330252γ
85Kr10.76.2717687γ
113mCd14.1.0003316
90Sr28.95.75182826β
137Cs30.236.08991176γ
121mSn43.9.00003390γ
151Sm90.420377
Long-lived
fission products
t½(my)Yield%KeVβ
99Tc.2116.0507294
126Sn.230.02364050γ
79Se.295.0508151
93Zr1.536.295691γ
135Cs2.3 6.3333269
107Pd6.5 .162933
129I15.7 .6576194γ

The radioactivity of all nuclear waste diminishes with time. All radioisotopes contained in the waste have a 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 two tables show some of the major radioisotopes, their half-lives, and their radiation yield as a proportion of the yield of fission of Uranium-235.

The faster a 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

Exposure to high levels of radioactive waste may cause serious harm or death. Treatment of an adult animal with 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.

Depending on the decay mode and the 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: management options for waste are discussed below.

Radioactivity by definition reduces over time, so in principle the waste needs to be isolated for a particular period of time until its components have decayed such that it no longer poses a threat. In practice this can mean periods of hundreds of thousands of years, depending on the nature of the waste involved.

Sources of waste

Radioactive waste comes from a number of sources. The majority originates from the nuclear fuel cycle and nuclear weapon reprocessing, however 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.

Nuclear fuel cycle

Main articles: Spent nuclear fuel

Front end

Waste from the front end of the radium and its decay products.

ceramic oxide (UO2) for assembly as reactor fuel elements.

The main by-product of enrichment is 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 californium (Cf). These isotopes are formed in nuclear reactors.

It is important to distinguish the processing of uranium to make fuel from the 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 article: 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 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 109 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 in the minds of some, the very existence of the nuclear fuel reprocessing plant needed to separate the plutonium from the other elements represents 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 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 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 PUREX type extraction process would be one possible method of making the separation.

Medical

Radioactive medical waste tends to contain 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)
  • intravenous injection (52 days)
  • 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 radiography while neutron emitting sources are used in a range of applications, such as oil well logging.[1]

Naturally occurring radioactive material (NORM)

Processing of substances containing natural radioactivity; this is often known as NORM. A lot of this waste is 40K).

Coal

Coal contains a small amount of radioactive uranium, barium and thorium, around or slightly more than the average concentration of those elements in the Earth's crust[5][6]. They become more concentrated in the 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.[7]

Oil and gas

Residues from the oil and gas industry often contain 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.[8]

Types of radioactive 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 arsenic. Vast mounds of uranium mill tailings are left at many old mining sites, especially in Colorado, New Mexico, and Utah.

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 deep underground facilities. U.S. regulations do not define this category of waste; the term is used in Europe and elsewhere.

  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-story structure built on top of a basketball court.[9]

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 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 Waste Isolation Pilot Plant.[10]

Management of waste

  Nuclear waste requires sophisticated treatment and management in order 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[11].

Initial treatment of waste

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 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[2]. 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. [3] 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 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.

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 portland cement, gravel and sand).

Synroc

The Australian caesium will be fixed in the hollandite.

Long term management of waste

Storage

High-level radioactive waste is stored temporarily in dry cask storage facilities. This allows the shorter-lived isotopes to decay before further handling.

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.

Geological disposal

The process of selecting appropriate 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, with some of the main concerns being the long distance transportation of the waste from across the United States to this area, and the possibility of accidents over time that could 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 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.[14]

The Finnish government has already started building a vault to store nuclear waste 500 to 1000 meters below ground, not far from the Olkiluoto Nuclear Power Plant.

In the EU, Covra is negotiating about a European-wide waste disposal system with single disposal sites that can be used by several EU-countries.[15] This EU-wide storage possibility is being researched under the SAPIERR-2 program.[16]

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 [6] 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 [7] would blend high-level waste with 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 transmutation of the left-over transuranic elements.

While transmutation has been banned in the US since 1977 due to the danger of plutonium proliferation [17], work on the method continues in the EU. This has resulted in a practical nuclear research reactor called Myrrha in which transmutation is possible. Additionally, a new research program called ACTINET has been started in the EU to make transmutation possible on a large, industrial scale.

There have also been theoretical studies involving the use of fusion reactors as so called "actinide burners" where a fusion reactor 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[8].

Reuse of waste

Another option is to find applications of the isotopes in nuclear waste so as to food irradiation and radioisotope thermoelectric generators. While re-use does not eliminate the need to manage radioisotopes, it may reduce the quantity of waste produced.

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 — due to the fact that 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.[10]

It has been suggested that through the use of a stationary launch system many of the risks of catastrophic launch failure could be avoided. A promising concept is the use of high power lasers to launch "indestructible" containers from the ground into space. Such a system would require no rocket propellant, with the launch vehicle's payload making up a near entirety of the vehicle's mass. Without the use of rocket fuel on board there would be little chance of the vehicle exploding.[11]

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.[18] 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 blown over the area during a dust storm after the lake had partly dried out.[19] In other cases lakes or ponds with radioactive waste accidentally overflowed into the rivers during exceptional storms.[citation needed]

Scavenging of abandoned radioactive material has been the cause of several other cases of Goiânia accident.[21]

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.

Radioactive waste in fiction and popular culture

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.

In reality, of course, exposure to radioactive waste instead would lead to illness and/or death.

In the science fiction television series, "Space: 1999," a massive nuclear waste dump on the Moon explodes, hurtling the Moon, and the inhabitants of "Moonbase Alpha" out of the Solar System at interstellar speeds.

See also

 Energy Portal

References

  1. ^ Krivtsov, A.I., 2006, Geoenvironmental Problems of Mineral Resources Development, in Geology and Ecosystems, Zekster (Ru), Marker (UK), Ridgeway (UK), Rogachevskayarochmaninoff (Ru), & Vartanyan (Ru), 2006 Springer Inc.,
  2. ^ a b c d e f g 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. ^ Nuclear Information and Resource Service,Radioactive Waste Project, retrieved September 2007
  5. ^ http://www.uic.com.au/nip78.htm
  6. ^ a b http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html
  7. ^ U.S. Geological Survey, Radioactive Elements in Coal and Fly Ash: Abundance, Forms, and Environmental Significance, Fact Sheet FS-163-1997, October 1997, retrieved September 2007
  8. ^ Survey & Identification of NORM Contaminated Equipment
  9. ^ http://www.marathonresources.com.au/nuclearwaste.asp
  10. ^ Why WIPP?
  11. ^ M. I. Ojovan, W.E. Lee. An Introduction to Nuclear Waste Immobilisation, Elsevier Science Publishers B.V., Amsterdam, 315pp. (2005)
  12. ^ Removal of Silicon from High Level Waste Streams via Ferric Flocculation
  13. ^ Uranium Information Centre, Synroc, Nuclear Issues Briefing Paper 21, retrieved September 2007
  14. ^ How is high-level nuclear waste managed in Canada?. The Canadian Nuclear FAQ. Retrieved on June 28, 2006.
  15. ^ EU-wide centralised geological waste disposal sites
  16. ^ SAPIERR-2 program
  17. ^ Transmutation being banned in the US since 1977
  18. ^ http://www.iaea.org/Publications/Magazines/Bulletin/Bull413/article1.pdf
  19. ^ GlobalSecurity.org, Chelyabinsk-65/Ozersk, retrieved September 2007
  20. ^ International Atomic Energy Agency, The radiological accident in Goiânia, 1988, retrieved September 2007
  21. ^ International Atomic Energy Agency, The radiological accident in Goiânia, 1988, retrieved September 2007

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.

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