Depleted uranium (DU) is uranium primarily composed of the isotope uranium-238 (U-238). Natural uranium is about 99.27 percent U-238, 0.72 percent U-235, and 0.0055 percent U-234. Because U-235 is used for fission in nuclear reactors and nuclear weapons, natural uranium is enriched in U-235 by separating the isotopes by mass. The byproduct of enrichment, called depleted uranium or DU, contains less than one third as much U-235 and U-234 as natural uranium. Because U-234 accounts for about half the radioactivity of natural uranium, the external radiation dose from DU is about 60 percent of that from the same mass of natural uranium. Another less common source of DU is reprocessed spent nuclear reactor fuel, which can be distinguished from DU produced as a byproduct of uranium enrichment by the presence of U-236, produced in reactors. In the past, DU has been called Q-metal, depletalloy, and D-38, but those names are no longer used.
DU is used for its very high density of 19.1 g/cm3. Civilian uses include counterweights in aircraft, radiation shielding in medical radiation therapy and industrial radiography equipment, and containers used to transport radioactive materials. Military uses include defensive armor plating and armor-piercing projectiles.
Depleted uranium munitions are controversial because of unanswered questions about potential long-term health effects. DU is less toxic than other heavy metals such as arsenic and mercury, and is only very weakly radioactive because of its long half-life. While any radiation exposure has risks, 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 DU poisoning, and studies using cultured cells and laboratory rodents continue to suggest the possibility of leukemogenic, genetic, reproductive, and neurological effects from chronic exposure.
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. 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.
As a byproduct of uranium enrichment, DU became less expensive than other high-density ordnance candidates including tungsten in the 1960s. As the next best candidate, tungsten had to be obtained from China. With DU stockpiles estimated to be more than 500,000 tons, it was more economical to use depleted uranium than store 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.
While clearing a decades-old Hawaii firing range in 2005, workers found depleted uranium training rounds from the formerly classified Davey Crockett tactical battlefield nuclear delivery system from the 1960-70s. These training rounds had been forgotten because they had been fired before DU came to the news media's attention, more than 20 years before the Gulf War.
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, enrichment 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 crystalline solid, (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 2008, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio 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. The DOE is constructing two facilities to convert the UF6 to a more stable chemical form for long term storage. These facilities are expected to be in operation by early 2009 and take around 20 years to process the entire US government stock of UF6.
A ten-fold jump in uranium prices has transformed approximately one-third of the U.S. depleted uranium inventory into an asset worth $7.6 billion, assuming DOE re-enriches the tails. This estimate is based on February 2008 market price for uranium and enrichment services, and DOE's access to sufficient uranium enrichment capacity.
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.
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Depleted uranium is very dense; at 19050 kg/m³, it has 1.67 times the density of lead, is only slightly less dense than tungsten and gold, and is 84% as dense as osmium or iridium, which are the densest known substances under standard (i.e., Earth-surface) pressures. Thus a given mass 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.
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 mass of depleted uranium and 0.75 percent by mass of titanium. Another variant can have 3.5 percent by mass 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. 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, also 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. 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. 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. The US Navy used DU in its 20 mm Phalanx CIWS guns, but switched in the late 1990s to armor-piercing tungsten.
It is thought that between 17 and 20 countries have weapons incorporating depleted uranium in their arsenals. They include the U.S., the UK, France, Russia, China, 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.
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":
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:
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.
France and Britain, the Netherlands and the Czech Republic voted against a United Nations General Assembly resolution to hold a debate in 2009 about the effects of the use of armaments and ammunitions containing depleted uranium in 2009. All other European Union nations voted to abstain or in favour. The ambassador from the Netherlands explained his negative vote as being due to the reference in the preamble to the resolution "to potential harmful effects of the use of depleted uranium munitions on human health and the environment [which] cannot, in our view, be supported by conclusive scientific studies conducted by relevant international organizations. None of the other permanent members of the United Nations Security Council supported the resolution as China was absent for the vote, Russia abstained and United States voted against the resolution.
In September 2008, and in response to the the 2007 General Assembly resolution, the UN Secretary General published the views of 15 states alongside those of the IAEA and WHO. The IAEA and WHO evidence differed little from previous statements on the issue. The report was largely split between states concerned about DU's use such as Finland, Cuba, Japan, Serbia, Argentina and Qatar and predominantly NATO members such as Spain and the Netherlands who do not consider the use of DU munitions problematic.
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.
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 in very large quantities. Its use in incendiary ammunition is controversial because of potential adverse health effects and 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.
Although slow, metallic uranium is prone to corrosion and small pieces are pyrophoric at around 600F in air. When depleted uranium munitions penetrate armor or burn, it creates depleted uranium oxides dust that can be inhaled or contaminate wounds. Additionally, fragments of munitions or armor can also become embedded in the body. However, 98% of the depleted uranium ingested is filtered and excreted by the body.
The chemical toxicity of depleted uranium is about a million times greater in vivo than its radiological hazard. 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 embedded fragments or shrapnel contamination. Properties such as phase (e.g. particulate or gaseous), oxidation state (e.g. metallic or ceramic), and the solubility of uranium and its compounds influence their absorption, distribution, translocation, elimination and the resulting toxicity. For example, metallic uranium is relatively non-toxic compared to hexavalent uranium(VI) uranyl compounds such as uranium trioxide.
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 slowly 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 point to it as being an immunotoxin, teratogen, neurotoxic, with carcinogenic and leukemogenic potential, there has been no definite link between possible health effects in laboratory animals and humans. A 2005 report by epidemiologists concluded: "the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU.
Early studies of depleted uranium aerosol exposure assumed that uranium combustion product particles would quickly settle out of the air and thus could not affect populations more than a few kilometers from target areas, and that such particles, if inhaled, would remain undissolved in the lung for a great length of time and thus could be detected in urine. Burning uranium droplets violently produce a gaseous vapor comprising about half of the uranium in their original mass. Uranyl ion contamination in uranium oxides has been detected in the residue of DU munitions fires.
External exposure to radiation from depleted uranium is less of a 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 low concentration of 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.
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 are being considered as one of the potential causes by the Research Advisory Committee on Gulf War Veterans' Illnesses, as DU was used in 30 mm and smaller caliber machine-gun bullets on a large scale for the first time in the Gulf War. Veterans of the conflicts in the Gulf, Bosnia and Kosovo have been found to have up to 14 times the usual level of chromosome abnormalities in their genes. Serum-soluble genotoxic teratogens produce congenital disorders, and in white blood cells causes immune system damage.
Human epidemiological evidence is consistent with increased risk of birth defects in the offspring of persons exposed to DU. A 2001 study of 15,000 February 1991 U.S. Gulf War combat veterans and 15,000 control veterans found that the Gulf War veterans were 1.8 (fathers) to 2.8 (mothers) times more likely to have children with birth defects. After examination of children's medical records two years later, the birth defect rate increased by more than 20%:
In early 2004, the UK Pensions Appeal Tribunal Service attributed birth defect claims from a February 1991 Gulf War combat veteran to depleted uranium poisoning. Children of British soldiers who fought in wars in which depleted uranium ammunition was used are at greater risk of suffering genetic diseases such as congenital malformations, commonly called "birth defects," passed on by their fathers. In a study of U.K. troops, "Overall, the risk of any malformation among pregnancies reported by men was 50% higher in Gulf War Veterans (GWV) compared with Non-GWVs.
The U.S. Army has commissioned ongoing research into potential risks of depleted uranium and other projectile weapon materials like tungsten, which the U.S. Navy has used in place of DU since 1993. Studies by the U.S. Armed Forces Radiobiology Research Institute conclude that moderate exposures to either depleted uranium or uranium present a significant toxicological threat.
One particular subgroup of veterans which may be at higher risk comprises those who have retained internally fragments of DU from shrapnel wounds. A laboratory study on rats produced by the Armed Forces Radiobiology Research Institute showed that, after a study period of 6 months, rats treated with depleted uranium coming from implanted pellets, comparable to the average levels in the urine of Desert Storm veterans with retained DU fragments, had developed a significant tendency to lose weight with respect to the control group. Substantial amounts of uranium were accumulating in their brains and central nervous systems, and showed a significant reduction of neuronal activity in the hippocampus in response to external stimuli. The conclusions of the study show that brain damage from chronic uranium intoxication is possible at lower doses than previously thought. Results from computer based neuro-cognitive tests on veterans have indeed showed a correlation between the levels of urinary uranium and "problematic performance" on tests assessing performance accuracy and efficiency.
Studies in 2005 and earlier have concluded that DU ammunition has no measurable detrimental health effects.
A 1999 literature review 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 a RAND report authored by the U.S. Defense department undersecretary charged with evaluating DU hazards considered the debate to be more political than scientific.
A 2001 oncology study 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". Former NATO Secretary General Lord Robertson stated in 2001 that "the existing medical consensus is clear. The hazard from depleted uranium is both very limited, and limited to very specific circumstances".
A 2002 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.” 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".
The International Atomic Energy Agency 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." The IAEA concluded that while depleted uranium is a potential carcinogen, there is no evidence that it has been carcinogenic in humans.
A 2005 study by Sandia National Laboratories’ Al Marshall used mathematical models to analyze potential health effects associated with accidental exposure to depleted uranium during the 1991 Gulf War. Marshall’s study concluded that the reports of cancer risks from DU exposure are not supported by veteran medical statistics, but Marshall did not consider reproductive health effects.
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.
In 2005, uranium metalworkers at a Bethlehem plant near Buffalo, New York, exposed to frequent occupational uranium inhalation, were found to have some of the same patterns of symptoms as Gulf War Syndrome victims.