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Depleted uranium (DU) is uranium which contains a reduced proportion of the fissile isotope U-235 and (usually) the highly radioactive but rare isotope U-234, compared to natural uranium.

Uranium enrichment process

Natural uranium contains nominally 0.7110% U-235 (+/- 0.1% variation) and 99.28305% U-238 (and 0.0054% U-234), while depleted uranium contains only 0.2 to 0.4 weight-percent U-235. The U-235 is concentrated into enriched uranium through the process of isotope separation for use in nuclear reactors and nuclear weapons.

The enrichment process does not create U-235 but merely separates the different isotopes of uranium. Therefore the process leaves large amounts of depleted uranium as a waste product. For example producing 1 kg of 5% enriched uranium requires 11.8 kg of natural uranium, leaving about 10.8 kg of depleted uranium with 0.3% U-235.

• Nuclear weapons usually use uranium containing 90% or more of U-235 (a lower grade is possible but makes the weapon less efficient).
• Commercial light water nuclear reactor fuel is usually enriched up to a maximum of 5% (the 5% limit is set by the currently licensed transport containers — in the future the 5% limit may be increased up to 7% for improved fuel economy).
• Research reactor fuel is today limited to maximum 20% (most older research reactors have been or will be converted down to this lower enrichment level).

US stockpiles

The United States Department of Energy currently has an inventory of 704,000 tons of depleted uranium hexafluoride (stored in 58,000 metal cylinders), corresponding to 476,000 tonnes of uranium . It encourages the use of DU as a means of disposing of the stock, and plans to eventually convert the remaining inventory to a less toxic form, probably either uranium metal or oxide.

Uses and availability

As a product otherwise requiring long term storage as low level radioactive waste, depleted uranium can be obtained cheaply. It is useful for its extremely high density, which is only slightly less than that of tungsten. As well as a lower initial cost, depleted uranium is easier to roll, machine and cast than tungsten. However, it has extremely poor corrosion properties, can burn, spalls easily, and since it is toxic and radioactive the facilities for processing it need to monitor and filter dust and airborne particles. One disadvantage of DU is that it needs to be correctly handled when an object containing it is scrapped. The uranium is normally leased from the manufacturer and subsequently returned at the end of the object's life.

Nuclear applications

Depleted uranium is natural uranium that is somewhat depleted in the isotope U-235 and is not normally usable directly as nuclear fuel. Depleted uranium can be used as a source material for creating the element plutonium. Theoretically, breeder reactors could carry out a process of transmutation to convert "fertile" isotopes such as U-238 into fissile material, although no known operating reactors are currently used for this purpose.

DU is also used as a radiation shield — its alpha radiation is easily stopped by the non-radioactive casing of the shielding and the uranium's high atomic weight and high number of electrons is highly effective in absorbing gamma radiation and x-rays.

Military applications

Projectile weapons

One use of DU is for kinetic energy penetrators for the anti-tank role. Kinetic energy penetrator rounds consist of a long, relatively thin flechette surrounded by a discarding sabot. Two materials lend themselves to flechette construction: tungsten and depleted uranium, the latter in designated alloys known as staballoys.

Depleted uranium is favoured for flechette construction due to two particular properties: being self-sharpening and pyrophoric. On impact with a hard target, such as an armoured vehicle, the nose of the flechette rod fractures in such a way that it remains sharp. Further, the impact and subsequent release of heat energy causes it to disintegrate to dust and combust when it reaches air (compare to ferrocerium). Against an armoured vehicle this is devastating, piercing the hull to create an extremely hot ball of dust and gas in the interior, killing or injuring the crew and igniting fuel and ammunition.

Depleted uranium also has the advantage of being easy to melt and cast into shape; a difficult and costly process for tungsten.

Depleted uranium is also very dense: at 19050 kg/m³, it is 70% denser than lead. Thus a given weight of it has a smaller diameter than an equivalent lead projectile, with less aerodynamic drag and better penetration due to a higher pressure at point of impact.

The US Army uses the DU in an alloy with around 3.5% titanium. It is used by the US Army in 120 mm or 105 mm calibre by the M1 Abrams and M60A3 tanks and in 25 mm calibre by the M242 mounted on the M2 Bradley.

The US Navy used it in its 20 mm Phalanx CIWS guns (though it has now switched to armor-piercing tungsten alloys for this application, primarily because multiple stray DU rounds hit friendly ships; those that strike metal often burn, so the incindary effect of uranium presented an easily avoidable danger. Tungsten costs 5-10x that of depleted uranium rounds, and its shrapnel is also chemically toxic, causing cancer but not birth defects.)

The Air Force uses the 30 mm PGU-14/B amour-piercing round in the GAU-8 Avenger cannon of the A-10 Thunderbolt II.

The 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 Russian military has used DU munitions in tank main gun ammunition since the late 1970s, mostly for the 110 mm guns in the T-62 tank and the 125 mm guns in the T-64, T-72, T-80, and T-90 tanks.

DU munitions (in the form of tank and naval artillery rounds) are also deployed by the armed forces of the UK, Israel, France, China, Russia, Pakistan, and many more. DU rounds are manufactured in 18 countries. DU is also used to make body armour piercing bullets.

Armour plate

Because of its high density, depleted uranium can also be used in tank armour, 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 armour plating in the front of the hull and the front of the turret and there is a program to upgrade the rest.

Nuclear weapons

Nuclear weapons can utilize depleted uranium as a "tamper" material (see Nuclear weapon design). A tamper which surrounds a fissile core works to reflect neutrons and add inertia to the compression of the core. As such, it increases the efficiency of the weapon and reduces the amount of critical mass required. This was the arrangement used in the weapon dropped on Nagasaki, Japan during World War II, called "Fat Man." It is thought that this design is common in other weapons as well.

Thermonuclear weapons

Thermonuclear warheads often have a layer of DU surrounding the main charge of fusion fuel. Initially, this serves as a reaction mass to allow more forceful compression (see inertial confinement fusion) during detonation and allow more complete fusion to occur. The high flux of very energetic neutrons from the resulting fusion reaction causes the U-238 to fission and adds energy to the yield of the weapon. Such weapons are referred to as fission-fusion-fission weapons after the three consecutive stages of the explosion.

A surprising portion of the total explosive yield can come from a final fission stage fueled by DU, producing enormous amounts of radioactive fission products. For example, 77% of the 10.4 megaton yield of the Ivy Mike thermonuclear test in 1952 came from fast fission of the DU tamper. Because DU has no critical mass, it can be added to thermonuclear bombs in almost unlimited quantity. The 1961 Soviet test of Tsar Bomba produced "only" 50 megatons, over 90% from fusion, because the DU final stage was replaced with lead. Had DU been used, the yield would have been 100 megatons, and would have produced fallout equivalent to one third of the global current total since the invention of nuclear weapons.

Civilian applications

Depleted uranium is also used in a number of civilian applications, generally where a high density weight is needed.

Such applications include sailboat keels, as counterweights and sinker bars in oil drills, gyroscope rotors, and in other places where there is a need to place a weight that occupies as little space as possible. Tungsten could be used instead, but it is much more expensive.

Aircraft may also contain depleted uranium counterweights (a Boeing 747 may contain 400 to 1,500 kg). However there is some controversy about its use in this application because of concern about the uranium entering the environment should the aircraft crash, since the metal can oxidise to a fine powder in a fire. This was highlighted by the collision of two Boeing 747s at Tenerife Airport in 1977 when the resulting fire consumed 3000 kg of the material. (Another well-known crash with DU release was the Bijlmermeer disaster in 1992 in Amsterdam.) Consequently its use has been phased out in many newer aircraft, for example both Boeing and McDonnell-Douglas discontinued using DU counterweights in the 1980s.

An unexpected application is in Formula 1 racing cars. The rules state a minimum weight of 600 kg, but builders strive to get the weight as low as possible and then bring it up to the 600 kg mark by placing depleted uranium where needed to achieve a better balance.

Health concerns

Early scientific studies sometimes found no link between depleted uranium and negative health effects such as cancer, liver damage, and birth defects, but newer studies have found and explained such links.

Environmental groups have raised concerns about the use of this material, particularly in munitions because it is radioactive, effectively lasts forever in the environment (its half-life is approximately 4.5 billion years, approximately the age of the Earth), and also it is toxic in the same manner as lead and other heavy metals. The long half-life indicates that depleted uranium is only weakly radioactive. However, all isotopes of uranium are potent chemical toxicants (see Depleted uranium and Gulf War Syndrome below.)

Such issues are of concern to those attacked with DU weapons, those firing DU weapons, those protected by DU armour-plating, civilians and troops operating in a theatre where DU is used, and to people who will live at any time after in such areas or breathing air or drinking water from these areas.

Studies showing detrimental health effects have claimed the following:

• DU can disperse into the air and water, as mentioned in a United Nations Environment Programme (UNEP) study :

"The most important concern is the potential for future groundwater contamination by corroding penetrators (ammunition tips made out of DU). The munition tips recovered by the UNEP team had already decreased in mass by 10-15% in this way. This rapid corrosion speed underlines the importance of monitoring the water quality at the DU sites on an annual basis."

• Military DU studies mainly evaluated external exposure, but other studies take inhalation risk into consideration. These studies indicate that DU passes into humans more easily than previously thought after battlefield use. (Radioactive particles absorbed into the body are far more harmful than a similar background radiation level outside the body, due to their immediate proximity to delicate structures such as DNA, bone marrow and the like.)

A 1997 report by The European Committee on Radiation Risk (ECRR), formed in 1997 by the Green Group in the European Parliament, suggested that DU posed serious health risks. By contrast, other studies have shown that DU ammunition has no measurable detrimental health effects, either in the short or long term. The International Atomic Energy Agency reports, "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 US military watchdog group Federation of American Scientists has come to similar conclusions.

Depleted Uranium and Gulf War Syndrome

See also: Gulf War Syndrome

Because uranium is a chemical toxicant heavy metal with nephrotoxic (kidney-damaging), teratogenic (birth defect-causing), and potentially carcinogenic properties, there is a connection between uranium exposure and a variety of illnesses. The chemical toxicological hazard posed by uranium dwarfs its radiological hazard because it is only weakly radioactive. In 2002, A.C. Miller, et al., of the U.S. Armed Forces Radiobiology Research Institute, found that the chemical generation of hydroxyl radicals by depleted uranium in vitro exceeds radiolytic generation by one million-fold. Hydroxyl radicals damage DNA and other cellular structures, leading to cancer, immune system damage in white blood cells, birth defects in gonocytes (testes), and other serious health problems. In 2005, uranium metalworkers at a Bethlehem plant near Buffalo, New York, exposed to frequent occupational uranium inhalation risks, were found to have the same patterns of symptoms and illness as Gulf War Syndrome victims,.

The increase in the rate of birth defects in the children of Gulf War veterans and in Iraqis may therefore be attributed to depleted uranium inhalation exposure,. 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. 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". A report written by an Irish petrochemical engineer stated that in Iraq, death rates per 1000 Iraqi children under 5 years of age increased from 2.3 in 1989 to 16.6 in 1993 and cases of leukaemia have more than quadrupled in areas where DU was present. I. Al-Sadoon, et al., writing in the Medical Journal of Basrah University, report a similar increase (see Table 1 here).

However, disputes continue to exist about the role of depleted uranium in Gulf War Syndrome. Some including Dr. Richard Guthrie, an expert in chemical warfare at Sussex University, have argued that a more likely cause for the increase in birth defects was the Iraqi Army’s use of teratogenic mustard agents. Since more recent epidemiological findings have come to light, only the plaintifs in a long-running class action lawsuit continue to assert that sulphur mustards might be responsible. According to the CDC Toxicological Profile, for sulphur mustards to have produced as many birth defects as have been observed, they would have had to have also produced more than 200 times as many cancers as observed.

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. But those studies ignored uranium trioxide gas -- also known as uranyl oxide gas, or UO₃(g) -- which is formed during uranium combustion (R.J. Ackermann, et al., "Free Energies of Formation of Gaseous Uranium, Molybdenum, and Tungsten Trioxides," Journal of Physical Chemistry, vol. 64 (1960) pp. 350-355, "gaseous monomeric uranium trioxide is the principal species produced by the reaction of U₃O₈ with oxygen." U₃O₈ being the dominant aerosol combustion product.) Uranyl ion contamination has been found on and around depleted uranium targets. UO₃ gas remains dissolved in the atmosphere for weeks, but as a monomolecular gas is absorbed immediately upon inhalation, leading to accumulation in tissues including gonocytes (testes) and white corpuscles, but virtually no residual presence in urine other than what might be present from coincident particulate exposure.

In early 2004, the U.K. Pensions Appeal Tribunal Service began attributing birth defect claims from February 1991 Gulf War combat veterans to depleted uranium poisoning ,.

Legal status of military use

In 1996 and 1997, the United Nations Human Rights Commission in Geneva, passed a resolution to ban the use of depleted uranium weapons. The Subcommission adopted resolutions which include depleted uranium weaponry amongst "weapons of mass and indiscriminate destruction, ... incompatible with international humanitarian or human rights law." (Secretary General's Report, 24 June 1997, E/CN. 4/Sub.2/1997/27)

A UN report of 2002 states that DU weapons also potentially breach each of the following laws: The Universal Declaration of Human Rights; the Charter of the United Nations; the Genocide Convention; the Convention Against Torture; the four Geneva Conventions of 1949; the Conventional Weapons Convention of 1980; and the Hague Conventions of 1899 and 1907. All of these laws are designed to spare civilians from unwarranted suffering in or after armed conflicts.

According to the UN, the resolutions in 1996-97 were passed because DU breaches several international laws concerning inhumane weapons: it is not limited in time or space to the legal field of battle, or to military targets; it continues to act after the war; it is "inhumane" by virtue of its ability to cause prolonged or long term death by cancer and other serious health issues, it causes harm to future civilians and passers by (including unborn children and those breathing the air or drinking water); and it has an "unduly negative" and long term effect on the natural environment and food chain. In detail:

1. Weapons may only be used in the legal field of battle, defined as legal military targets of the enemy in war. Weapons may not have an adverse effect off the legal field of battle. DU shells burn into fine particles which remain in the air or the environment. So they affect others over a wide range, and future passers-by, with uranium poisoning.
2. Weapons can only be used for the duration of an armed conflict. A weapon that is used or continues to act after the war is over violates this criterion.
3. Weapons may not be unduly inhumane. Weapons that cause cancer and illness long after the war are widely considered to be legally "inhumane". Health issues to unborn children and civilians may also be crimes against humanity under international law.
4. Weapons may not have an "unduly negative" effect on the natural environment. The dust from DU impact becomes widespread in the environment, and (as with other heavy metals) becomes highly concentrated within living beings and the food chain.

External links

United Nations

• "Depleted Uranium: Sources, Exposure and Health Effects World Health Organization, Ionizing Radiation Unit, 2001 (see Chapter 8, The Chemical Toxicity of Uranium," in particular.)
• Sub-Commission resolution 1996/16
  (resolves and states DU to be "incompatible" with human rights and international law; lists DU as "particularly" one "weapon of mass destruction or indiscriminate effect")
• UN High Commission for Human Rights, 1998
  (statement that DU is prohibited and contravenes prior UN resolutions)
• "Human rights and weapons of mass destruction, or with indiscriminate effect, or of a nature to cause superfluous injury or unnecessary suffering"
  (The UN 2002 report)
• Post Conflict Assessment Iraq by the United Nations Environment Programme.

Scientific bodies

• Uranium Medical Research Centre, founded in 1997 by Dr. Asaf Durakovic, M.D., formerly Chief of Professional Clinical Services in the U.S. Army's 531st Medical Detachment during the Desert Shield phase of the 1991 Gulf War and head of the Veteran's Administration Nuclear Medicine facility in Wilmington, Delaware.
• Depleted Uranium article from the Royal Society, from 2001; representing a position rejected by the U.K. Pensions Appeal Tribunal Service in 2004.
• An Analysis of Uranium Dispersal and Health Effects Using a Gulf War Case Study by Sandia National Laboratories (operated by Lockheed Martin Corporation for the U.S. Department of Energy's National Nuclear Security Administration). In Section 1.2, this report claims to include complete evaluation of both radiological and nonradiological hazards, but Section 5.2 on p. 72 ignores gonocyte contamination, developmental toxicity, and immunotoxicant risks.
• Depleted Uranium Human Health Fact Sheet from Summary Fact Sheets for Selected Environmental Contaminants to Support Health Risk Analyses by Argonne National Laboratory Environmental Assessment Division (operated by the University of Chicago for the U.S. Department of Energy's Office of Science). This 2001 publication does not address the quick solubility of uranium(VI) trioxide or any of uranium's reproductive, developmental, or immunological toxicological risks.
• Uranium Human Health Fact Sheet, also from Argonne, also showing the radiological and nephrotoxiological risk quantities only, without regard to any developmental, reproductive, or immunotoxicant risks.

Other

• Better World Links on Depleted Uranium Weapons 500+ links
• U.S. Soldiers Contaminated With Depleted Uranium Speak Out - Democracy Now!, April 5, 2004
• Depleted UF6 Management Information Network, Online repository of information about the U.S. Department of Energy's inventory of depleted uranium hexafluoride.
• "After the Dust Settles" (Bulletin of the Atomic Scientists report from 1999)
• Proposal for Research on Depleted Uranium ( U.K. Ministry of Defence )
• World Uranium Weapons Conference 2003
• Guardian Unlimited's Special report on Depleted Uranium
• International Coalition to Ban Uranium Weapons
• My Life Living With Depleted Uranium

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