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Depleted Uranium (DU) is uranium primarily composed of the isotope uranium-238. In nature, uranium atoms exist as uranium-238 (99.275 percent), uranium-235 (0.711 percent), and a very small amount of uranium-234 (0.0058 percent). Uranium-235 is important because of the high probability of fissioning when bombarded with slow neutrons and generating the heat in nuclear reactors, used as a source of power, and to provide the fissile material for nuclear weapons. Natural uranium may be processed, or enriched, which separates the U-235 from the U-238. The waste material left over from this enrichment process is composed primarily of uranium-238 and is called Depleted Uranium or DU. Depleted uranium contains less than one third as much uranium-235 and uranium-234 as natural uranium, and is weakly radioactive. Because the half-life of U-238 is about 4.5 billion years, it produces an extremely small amount of radiation. Another, less common, source of depleted uranium is reprocessed spent reactor fuel. DU created by enrichment can be distinguished from that created in a reactor by the percentage of uranium-236, produced by neutron capture from uranium-235 in nuclear reactor, present in the material. An external radiation dose from depleted uranium is about 60 percent of that from the same mass of uranium with a natural isotopic ratio. In the past it has been called by the names Q-metal, depletalloy, and D-38, but these have fallen into disuse.
At standard temperature and pressure (STP) it is a very dense metal solid. The primary civilian uses of depleted uranium are due to its very high density and include counterweights in aircraft, radiation shields in medical radiation therapy machines, containers for the transport of radioactive materials and shielding material in industrial radiography devices. The primary military uses of depleted uranium are also due to its very high density and include defensive armor plate, armour-piercing and projectiles.
The use of depleted uranium in armor-penetrating munitions remains a source of controversy because of the numerous unanswered questions about its long-term health effects. Depleted uranium is less toxic than other heavy metals such as arsenic and mercury and is only very weakly radioactive because of its relatively long half life (4.5 billion years). While there are risks involved with any radiation exposure, no conclusive epidemiological data have correlated DU exposure to specific human health effects such as cancer. However, the UK government has attributed birth defect claims from a 1991 Gulf War combat veteran to depleted uranium poisoning, and studies using cultured cells and laboratory rodents continue to suggest the possibility of leukemogenic, genetic, reproductive, and neurological effects from chronic exposure. Until issues of concern are resolved with further research, the use of depleted uranium by the military will continue to be controversial.
Enriched uranium was first manufactured in the 1940s when the U.S. and USSR began their nuclear weapons and nuclear power programs. It was at this time that depleted uranium was first stored as an unusable waste product. There was some hope that the enrichment process would be improved and fissionable isotopes of U-235 could, at some future date, be extracted from the depleted uranium. This re-enrichment recovery of the residual uranium-235 contained in the depleted uranium is no longer a matter of the future: it has been practised for several years now. Also, it is possible to design civilian power reactors with unenriched fuel, but only about 10 percent of reactors ever built utilize that technology, and both nuclear weapons production and naval reactors require the concentrated isotope.
In the 1970s, The Pentagon reported that the Soviet military had developed armor plating for Warsaw Pact tanks that NATO ammunition couldn't penetrate. The Pentagon began searching for material to make denser bullets. After testing various metals, ordnance researchers settled on depleted uranium. DU was useful in ammunition not only because of its unique physical properties and effectiveness, but also because it was cheap and readily available. Tungsten, the only other candidate, had to be sourced from China. With DU stockpiles estimated to be more than 500,000 tons, the financial burden of housing this amount of low-level radioactive waste was very apparent. It was therefore more economical to use depleted uranium rather than storing it. Thus, from the late 1970s, the U.S., the Soviet Union, Britain, and France began converting their stockpiles of depleted uranium into kinetic energy penetrators.
Photographic evidence of destroyed equipment suggests that DU was first used during the 1973 Arab-Israeli war. Various written reports cite information that was obtained as a consequence of that use. However, while clearing the decades-old Hawaii Stryker firing range, workers have found depleted uranium ammunition from the 1960s.
Production and availability
Natural uranium metal contains about 0.71 percent U-235, 99.28 percent U-238, and about 0.0054 percent U-234. In order to produce enriched uranium, the process of isotope separation removes a substantial portion of the U-235 for use in nuclear power, weapons, or other uses. The remainder, depleted uranium, contains only 0.2 percent to 0.4 percent U-235. Because natural uranium begins with such a low percentage of U-235, the enrichment process produces large quantities of depleted uranium. For example, producing 1 kg of five percent enriched uranium requires 11.8 kg of natural uranium, and leaves about 10.8 kg of depleted uranium with only 0.3 percent U-235 remaining.
The Nuclear Regulatory Commission (NRC) defines depleted uranium as uranium with a percentage of the 235U isotope that is less than 0.711 percent by weight (See 10 CFR 40.4.) The military specifications designate that the DU used by the U.S. Department of Defense (DoD)contain less than 0.3 percent 235U (AEPI, 1995). In actuality, DoD uses only DU that contains approximately 0.2 percent 235U (AEPI, 1995).
About 95 percent of the depleted uranium produced is stored as uranium hexafluoride, a liquid, (D)UF6, in steel cylinders in open air storage yards close to enrichment plants. Each cylinder holds up to 12.7 tonnes (or 14 US tons) of UF6. In the U.S. 560,000 tonnes of depleted UF6 had accumulated by 1993. In 2005, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, and Paducah, Kentucky. The storage of DUF6 presents environmental, health, and safety risks because of its chemical instability. When UF6 is exposed to water vapor in the air, it reacts with the moisture to produce UO2F2 (uranyl fluoride), a solid, and HF (hydrogen fluoride), a gas, both of which are highly soluble and toxic. The uranyl fluoride solid acts to plug the leak, limiting further escape of depleted UF6. Release of the hydrogen fluoride gas to the atmosphere is also slowed by the plug formation. Storage cylinders must be regularly inspected for signs of corrosion and leaks and are repainted and repaired as necessary. The estimated life time of the steel cylinders is measured in decades.
There have been several accidents involving uranium hexafluoride in the United States, including one in which 31 workers were exposed to a cloud of UF6 and its reaction products. Though some of the more highly exposed workers showed evidence of short-term kidney damage (e.g., protein in the urine), none of these workers had lasting kidney toxicity from the uranium exposure. The U.S. government has been converting DUF6 to solid uranium oxides for use or disposal. Such disposal of the entire DUF6 inventory could cost anywhere from $15 million to $450 million.
Depleted uranium is very dense; at 19050 kg/m³, it is almost 70 percent denser than lead. Thus a given weight of it has a smaller diameter than an equivalent lead projectile, with less aerodynamic drag and deeper penetration due to a higher pressure at point of impact. DU projectile ordnance is often incendiary because of its pyrophoric property.
Because of its high density, depleted uranium can also be used in tank armor, sandwiched between sheets of steel armor plate. For instance, some late-production M1A1HA and M1A2 Abrams tanks built after 1998 have DU reinforcement as part of its armor plating in the front of the hull and the front of the turret and there is a program to upgrade the rest, for example Chobham armour.
Depleted uranium is used as a tamper in fission bombs and as a nuclear fuel in hydrogen bombs.
Most military use of depleted uranium has been as 30 mm and smaller ordnance, primarily the 30 mm PGU-14/B armour-piercing incendiary round from the GAU-8 Avenger cannon of the A-10 Thunderbolt II and M230 of the Apache Helicopter used by the U.S. Air Force. 25 mm DU rounds have been used in the M242 gun mounted on the U.S. Army's Bradley Fighting Vehicle and LAV-AT. The U.S. Marine Corps uses DU in the 25 mm PGU-20 round fired by the GAU-12 Equalizer cannon of the AV-8B Harrier, and also in the 20 mm M197 gun mounted on AH-1 helicopter gunships. The US Navy's Phalanx CIWS's M61 Vulcan gatling gun used 20 mm armor-piercing penetrator rounds with discarding plastic sabots which were made using depleted uranium, later changed to tungsten.
Another use of depleted uranium is in kinetic energy penetrators anti-armor role. Kinetic energy penetrator rounds consist of a long, relatively thin penetrator surrounded by discarding sabot. Two materials lend themselves to penetrator construction: tungsten and depleted uranium, the latter in designated alloys known as staballoys. Staballoys are metal alloys of depleted uranium with a very small proportion of other metals, usually titanium or molybdenum. One formulation has a composition of 99.25 percent by weight of depleted uranium and 0.75 percent by weight of titanium. Another variant can have 3.5 percent by weight of titanium. Staballoys are about twice as dense as lead and are designed for use in kinetic energy penetrator armor-piercing ammunition. The US Army uses DU in an alloy with around 3.5 percent titanium.
Staballoys, along with lower raw material costs, have the advantage of being easy to melt and cast into shape; a difficult and expensive process for tungsten. Note also that according to recent research, at least some of the most promising tungsten alloys which have been considered as replacement for depleted uranium in penetrator ammunitions, such as tungsten-cobalt or tungsten-nickel-cobalt alloys, possess extreme carcinogenic properties, which by far exceed those (confirmed or suspected) of depleted uranium itself: 100 percent of rats implanted with a pellet of such alloys developed lethal rhabdomyosarcoma within a few weeks. On more properly military grounds, depleted uranium is favored for the penetrator because it is self-sharpening and pyrophoric. On impact with a hard target, such as an armoured vehicle, the nose of the rod fractures in such a way that it remains sharp. The impact and subsequent release of heat energy causes it to disintegrate to dust and burn when it reaches air because of its pyrophoric properties (compare to ferrocerium). When a DU penetrator reaches the interior of an armored vehicle, it catches fire, often igniting ammunition and fuel, killing the crew, and possibly causing the vehicle to explode. DU is used by the U.S. Army in 120 mm or 105 mm cannons employed on the M1 Abrams and M60A3 tanks. The Russian military has used DU ammunition in tank main gun ammunition since the late 1970s, mostly for the 115 mm guns in the T-62 tank and the 125 mm guns in the T-64, T-72, T-80, and T-90 tanks.
The DU content in various ammunition is 180 g in 20 mm projectiles, 200 g in 25 mm ones, 280g in 30 mm, 3.5 kg in 105 mm, and 4.5 kg in 120 mm penetrators. It is used in the form of Staballoy. The US Navy used DU in its 20 mm Phalanx CIWS guns, but switched in the late 1990s to armor-piercing tungsten for this application, because of the fire risk associated with stray pyrophoric rounds. DU was used during the mid-1990s in the U.S. to make 9 mm and similar caliber armor piercing bullets, grenades, cluster bombs, and mines, but those applications have been discontinued, according to Alliant Techsystems. Whether or not other nations still make such use of DU is difficult to determine.
It is thought that between 17 and 20 states have weapons incorporating depleted uranium in their arsenals. They include the U.S., the UK, France, Russia, Greece, Turkey, Israel, Saudi Arabia, Bahrain, Egypt, Kuwait, Pakistan, Thailand, Iraq and Taiwan. DU ammunition is manufactured in 18 countries. Only the US and the UK have acknowledged using DU weapons.
Legal status in weapons
In 1996 the International Court of Justice (ICJ) gave an advisory opinion on the "legality of the threat or use of nuclear weapons". This made it clear, in paragraphs 54, 55 and 56, that international law on poisonous weapons, – the Second Hague Declaration of 29 July 1899, Hague Convention IV of 18 October 1907 and the Geneva Protocol of 17 June 1925 – did not cover nuclear weapons, because their prime or exclusive use was not to poison or asphyxiate. This ICJ opinion was about nuclear weapons, but the sentence "The terms have been understood, in the practice of States, in their ordinary sense as covering weapons whose prime, or even exclusive, effect is to poison or asphyxiate." also removes depleted uranium weaponry from coverage by the same treaties as their primary use is not to poison or asphyxiate, but to destroy materiel and kill soldiers through kinetic energy.
The Sub-Commission on Prevention of Discrimination and Protection of Minorities of the United Nations Human Rights Commission, passed two motions the first in 1996 and the second in 1997. They listed weapons of mass destruction, or weapons with indiscriminate effect, or of a nature to cause superfluous injury or unnecessary suffering and urged all states to curb the production and the spread of such weapons. Included in the list was weaponry containing depleted uranium. The committee authorized a working paper, in the context of human rights and humanitarian norms, of the weapons. The requested UN working paper was delivered in 2002 by Y.K.J. Yeung Sik Yuen in accordance with Sub-Commission on the Promotion and Protection of Human Rights resolution 2001/36. He argues that the use of DU in weapons, along with the other weapons listed by the Sub‑Commission, may breach one or more of the following treaties: The Universal Declaration of Human Rights; the Charter of the United Nations; the Genocide Convention; the United Nations Convention Against Torture; the Geneva Conventions including Protocol I; the Convention on Conventional Weapons of 1980; and the Chemical Weapons Convention. Yeung Sik Yuen writes in Paragraph 133 under the title "Legal compliance of weapons containing DU as a new weapon":
Annex II to the Convention on the Physical Protection of Nuclear Material 1980 (which became operative on 8 February 1997) classifies DU as a category II nuclear material. Storage and transport rules are set down for that category which indicates that DU is considered sufficiently "hot" and dangerous to warrant these protections. But since weapons containing DU are relatively new weapons no treaty exists yet to regulate, limit or prohibit its use. The legality or illegality of DU weapons must therefore be tested by recourse to the general rules governing the use of weapons under humanitarian and human rights law which have already been analysed in Part I of this paper, and more particularly at paragraph 35 which states that parties to Protocol I to the Geneva Conventions of 1949 have an obligation to ascertain that new weapons do not violate the laws and customs of war or any other international law. As mentioned, the International Court of Justice considers this rule binding customary humanitarian law.
In 2001, Carla Del Ponte, the chief prosecutor for the International Criminal Tribunal for the Former Yugoslavia, said that NATO's use of depleted uranium in former Yugoslavia could be investigated as a possible war crime. Louise Arbour, Del Ponte's predecessor as chief prosecutor, had created a small, internal committee, made up of staff lawyers, to assess the allegation. Their findings, that were accepted and endorsed by Del Ponte, concluded that:
There is no specific treaty ban on the use of DU projectiles. There is a developing scientific debate and concern expressed regarding the impact of the use of such projectiles and it is possible that, in future, there will be a consensus view in international legal circles that use of such projectiles violate general principles of the law applicable to use of weapons in armed conflict. No such consensus exists at present.
Requests for a general moratorium of military use
Some states and the International Coalition to Ban Uranium Weapons, a coalition of more than 90 non-governmental organizations, have asked for a ban on the production and military use of depleted uranium weapons. The European Parliament has repeatedly passed resolutions requesting an immediate moratorium on the further use of depleted uranium ammunition, but France and Britain – the only EU states that are also permanent members of the United Nations Security Council – have consistently rejected calls for a ban, maintaining that its use continues to be legal, and that the health risks are entirely unsubstantiated.
Civilian applications for depleted uranium are typically unrelated to its radioactive properties. Depleted uranium has a very high density and is primarily used as shielding material for other radioactive material, and as ballast. Examples include sailboat keels, as counterweights and sinker bars in oil drills, gyroscope rotors, aircraft trim weights, radiography shielding and wherever there is a need for a high density material. Other high density materials are sometimes preferred, since uranium is prone to corrosion.
Shielding in Industrial Radiography Cameras
Industrial radiography cameras include a very high source of gamma radiation. (Typically Ir-192.) Depleted uranium is used in the cameras as a shield to protect individuals from the gamma source. Typically the uranium will be surrounded by polyurethane foam to protect the uranium from the elements, and stainless steel will be used to house the device.
Coloring in consumer products
Consumer product uses have included incorporation into dental porcelain used for false teeth to simulate the fluorescence of natural teeth and uranium-bearing reagents used in chemistry laboratories. (eg. uranyl acetate, used in analytical chemistry and as a stain in electron microscopy). Uranium (both depleted uranium and natural uranium) was widely used as a coloring matter for porcelain and glass in the 19th and early to mid 20th century. The practice was largely discontinued in the late 20th century. In 1999 concentrations of 10% depleted uranium were being used in "jaune no.17" a yellow enamel powder that was being produced in France by Cristallerie de Saint-Paul, a manufacturer of enamel pigments. The depleted uranium used in the powder was sold by Cogéma's Pierrelatte facility. Cogema has since discontinued the sale of depleted uranium to producers of enamel and glass.
Trim weights in aircraft
Aircraft that contain depleted uranium trim weights (Boeing 747-100 for example) may contain between 400 to 1,500 kg of DU. This application is controversial since the DU may enter the environment if the aircraft were to crash. The metal can also oxidize to a fine powder in a fire. Its use has been phased out in many newer aircraft. Boeing and McDonnell-Douglas discontinued using DU counterweights in the 1980s. Depleted uranium was released during the Bijlmer disaster, in which 152 kg was lost. Counterweights manufactured with cadmium plating are considered non-hazardous while the plating is intact.
NRC general license for use
U.S. Nuclear Regulatory Commission regulations at 10 CFR 40.25 establish a general license for the use of depleted uranium contained in industrial products or devices for mass-volume applications. This general license allows anyone to possess or use depleted uranium for authorized purposes. Generally, a registration form is required, along with a commitment to not abandon the material. Agreement states may have similar, or more stringent, regulations.
DU is considered both a toxic and radioactive hazard that requires long term storage as low level nuclear waste. DU is relatively expensive to store but relatively inexpensive to produce or obtain. Generally the only real costs are those associated with conversion of uranium hexafluoride (UF6) to metal. DU is 67 percent denser than lead, only slightly less than tungsten and gold, and just 16 percent less dense than osmium or iridium, the densest naturally occurring substances known. However, the material is prone to corrosion and small particles are pyrophoric. Its use in ammunition is controversial because of its release into the environment. Besides its residual radioactivity, U-238 is a heavy metal whose compounds are known from laboratory studies to be toxic to mammals in high exposures. Pier Roberto Danesi, then-director of the IAEA Seibersdorf Laboratory, stated in 2002 that "There is a consensus now that DU does not represent a health threat". Former NATO Secretary General Lord Robertson has stated that "the existing medical consensus is clear. The hazard from depleted uranium is both very limited, and limited to very specific circumstances". A 1999 study conducted by the Rand Corporation stated: “No evidence is documented in the literature of cancer or any other negative health effect related to the radiation received from exposure to depleted or natural uranium, whether inhaled or ingested, even at very high doses”, and another RAND report considered the debate to be more political than scientific.
A 2002 Health Physics scientific paper on depleted uranium residue within members of the Canadian Armed Forces found insignificant uranium residue. "The total uranium concentrations were sufficiently low so that isotopic (238U:235U ratio) assays could not be performed directly from urine samples."
Exposure to Depleted Uranium
When depleted uranium munitions penetrate armor or burn, it creates depleted uranium oxide dust that can be inhaled or contaminate wounds. Additionally, fragments of munitions or armor can also become embedded in the body. To address these exposures, the US Department of Defense has instituted a monitoring program and provides medical follow-up for those service members found to have been exposed.
External exposure to radiation from depleted uranium has generally not been considered a major concern because the alpha particle emitted by its isotopes travel only a few centimeters in air or can be stopped by a sheet of paper. Also, the uranium-235 that remains in depleted uranium emits only a small amount of low-energy gamma radiation. According to the World Health Organization, a radiation dose from it would be about 60 percent from purified natural uranium with the same mass. Approximately 90 micrograms of natural uranium, on average, exist in the human body as a result of normal intakes of water, food and air. The majority of this is found in the skeleton, with the rest in various organs and tissues.
The radiological dangers of pure depleted uranium are lower (60 percent) than those of naturally-occurring uranium due to the removal of the more radioactive isotopes, as well as due to its long half-life (4.46 billion years). Depleted uranium differs from natural uranium in its isotopic composition, but its biochemistry is for the most part the same. For further details see Actinides in the environment.
Health effects of DU are determined by factors such as the extent of exposure and whether it was internal or external. Three main pathways exist by which internalization of uranium may occur: inhalation, ingestion, and shrapnel contamination. Properties such as the solubility of uranium and its compounds influence their absorption, distribution, translocation, elimination and the resulting toxicity. The chemical toxicity of depleted uranium is much greater than its radiological toxicity.
Uranium is pyrophoric when finely divided. It will corrode under the influence of air and water producing insoluble uranium(IV) and soluble uranium (VI) salts. Soluble uranium salts are toxic. Uranium accumulates in several organs, such as the liver, spleen, and kidneys. The World Health Organization has established a daily "tolerated intake" of soluble uranium salts for the general public of 0.5 µg/kg body weight, or 35 µg for a 70 kg adult.
While epidemiological studies on laboratory animals exposed to high levels of depleted uranium point to it as being a possible immunotoxant, teratogen, neurotoxic, and carcinogen and leukemogenic potential, there has been no definite link between possible health effects in laboratory animals and humans.
Studies of depleted uranium aerosol exposure have concluded that uranium combustion product particles would quickly settle out of the air. Measurements made in areas where depleted uranium munitions were used extensively found no significantly higher than average uranium concentrations in the soil, just a few months after contamination. Most studies have shown that DU ammunition has no measurable detrimental health effects, either in the short or long term. The International Atomic Energy Agency, for example, reported in 2003 that, "based on credible scientific evidence, there is no proven link between DU exposure and increases in human cancers or other significant health or environmental impacts," although "Like other heavy metals, DU is potentially poisonous. In sufficient amounts, if DU is ingested or inhaled it can be harmful because of its chemical toxicity. High concentration could cause kidney damage". RAND has also studied the health effects on Depleted Uranium and has concluded that the debate around the issue is more political than technical. The study commented that “the full and unbiased presentation of the facts to governments around the world has resulted in the continued use of DU — even in the face of concerted actions by some to distort the facts and media often more interested in shock value than in presenting the truth”. A 2005 report by researchers at the University of Massachusetts and Tufts University concluded: "In aggregate the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU." However, the IAEA concluded that while depleted uranium is a potential carcinogen, there is no evidence that either natural uranium or DU is carcinogenic, and other studies have concluded that "the present scientific consensus is that DU exposure to humans, in locations where DU ammunition was deployed, is very unlikely to give rise to cancer induction".
Other relevant contamination cases
On October 4, 1992, an El Al Boeing 747-F cargo aircraft Flight 1862, crashed into an apartment building in Amsterdam. Local residents and rescue workers complained of various unexplained health issues which were being attributed to the release of hazardous materials during the crash and subsequent fires. Authorities conducted an epidemiological study in 2000 of those believed to be affected by the accident. The study concluded that there was no evidence to link depleted uranium (used as a counter balance in the plane) to any of the reported health complaints.
Gulf War syndrome and soldier complaints
Increased rates of immune system disorders and other wide-ranging symptoms, including chronic pain, fatigue and memory loss, have been reported in over one quarter of combat veterans of the 1991 Gulf War. Combustion products from depleted uranium munitions were at one time being considered as one of the potential causes by the Research Advisory Committee on Gulf War Veterans' Illnesses, as DU was used in tank kinetic energy penetrator and machine-gun bullets on a large scale for the first time in the Gulf War.
A two-year study headed by Sandia National Laboratories’ Al Marshall analyzed potential health effects associated with accidental exposure to depleted uranium during the 1991 Gulf War. Marshall’s study concluded that the reports of serious health risks from DU exposure are not supported by veteran medical statistics and were consistent with earlier studies from Los Alamos and the New England Journal of Medicine.
The U.S. Army has commissioned ongoing research into potential risks of depleted uranium and other projectile weapon materials like tungsten. Studies by the Armed Forces Radiobiology Research Institute have concluded that even though it was unlikely that future studies will alter the view that moderate exposures to either depleted uranium or uranium present a significant toxicological threat, the research was still useful to quantify risk exposure. A similar study from the Australian defense ministry concluded that “there has been no established increase in mortality or morbidity in workers exposed to uranium in uranium processing industries... studies of Gulf War veterans show that, in those who have retained fragments of depleted uranium following combat related injury, it has been possible to detect elevated urinary uranium levels, but no kidney toxicity or other adverse health effects related to depleted uranium after a decade of follow-up.”
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Depleted_uranium". A list of authors is available in Wikipedia.|