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. During the Manhattan Project depleted uranium had the codename tuballoy, a term that is still occasionally used.
Natural uranium contains 0.720% U-235 and 99.2745% U-238 (and 0.0055% 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:
- Nuclear weapons usually use uranium containing perhaps 85% or more of U-235 (a lower grade is possible but makes the weapon less efficient).
- Commercial nuclear reactor fuel is usually enriched to 5% or less.
The enrichment process does not create U-235, the isotopes of uranium are merely separated. Therefore the process leaves large amounts of depleted uranium as a waste product. For example producing 1kg of 5% enriched uranium requires 11.8kg of natural uranium, leaving about 10.8 kg of depleted uranium with 0.3% U-235.
The United States Department of Energy currently has an inventory of 704,000 tonnes of depleted uranium hexafluoride (stored in 58,000 metal cylinders), corresponding to 476,000 tonnes of uranium [1]. 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.
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 (tending to spall on exposure to air) 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 not usable as nuclear fuel, but can be a source material for Plutonium. Theoretically, breeder reactors could carry out a process of transmutation to convert "fertile" isotopes such as U-238 into fissile material, although no 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 is effective in absorbing gamma radiation.
Military applications
Projectile weapons
A 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.
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 a way that leaves it sharp again. Further, the impact and heat energy released on impact causes it to disintegrate to dust and combust when it reaches air. 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 120mm or 105mm calibre by the M1 Abrams and M60A3 tanks and in 25mm calibre by the M242 mounted on the M2 Bradley and the LAV-AT .
The US Navy used it in its 20mm Phalanx CIWS guns (though it has now switched to tungsten for this application, as they are not required to pierce armour).
The Air Force uses the 30mm 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 25mm PGU-20 round fired by the GAU-12 Equalizer cannon of the AV-8B Harrier, and also in the 20mm 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 115mm guns in the T-62 tank and the 125mm 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, Japan, China, Russia, Pakistan, and many more. DU rounds are manufactured in 18 countries.
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. In a fission only weapon, the DU tamper does not undergo any significant nuclear reactions.
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 extremely high flux of neutrons from the resulting fusion reaction causes some amount of transmutation and fission of the resulting Plutonium, which can add fission 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 is produced by the third and final fission stage fueled by the DU.
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 400–1,500kg). However there is some controversy about its use in this application because of concern about the uranium entering the environment should the aircraft crash, particularly as the metal is pyrophoric. This was highlighted by the collision of two Boeing 747s at Tenerife Airport in 1977 when the resulting fire consumed 3000kg of the material. 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 600kg but builders strive to get the weight as low as possible and then bring it up to the 600kg mark by placing depleted uranium where needed to achieve a better balance.
Health concerns
The health effects of depleted uranium have been postulated to be one of the possible causes of Gulf war syndrome (see below). Most scientific studies have found no link between depleted uranium and negative health effects such as cancer, liver damage, and birth defects, but many people point to other evidence that suggests a link.
Environmental groups have raised concerns about the use of this material, particularly in munitions because it is radioactive, effectively lasts forever in the environment, and also it is toxic in the same manner as lead and other heavy metals.
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:
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"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)[[3]]
- While DU is minimally radioactive, its decay products - Thorium 234 and Protactinium 234 - are beta particle emitters with half-lives about 20 days and one minute respectively (Pa 234 decays to Uranium 234, which has a half-life of hundreds of millennia, and this isotope does not build to equilibrium concentration for a very long time). When the two first isotopes in the decay chain reach their (tiny) equilibrium concentrations, a DU fragment will emit three times the radiation due to DU itself, and most of this will be beta radiation.
A 1997 report by the European Committee on Radiation Risk (ECRR) 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." [4] The US military watchdog group Federation of American Scientists has come to similar conclusions.
Critics of these latter studies point to the fact that they come primarily from either "Green" groups who are opposed to nuclear power and uses of its radioactive byproducts, or are 'linked' to the US and UK governments -- both users of weaponary which utilise DU with strong incentive to minimize negative conclusions.
The U.S. Army acknowledges the potential hazards of DU in a training manual, in which it requires that anyone who comes within 25 meters of any DU-contaminated equipment or terrain wear respiratory and skin protection, and states that "contamination will make food and water unsafe for consumption."
Depleted uranium and Gulf War Syndrome
See also: Gulf war syndrome
Although most experts believe there is no connection, some disputes exist about the role, if any, played by depleted uranium in Gulf War Syndrome. Those who claim there are no effects point to the absence of confirmed medical evidence supporting the link and the large body of pathological studies showing no statistically significant effect. Those who believe there are effects point to medical statistics and investigations which they claim have been swept under the carpet.
Critics have attempted attribute an alleged increase in the rate of birth defects in the children of Gulf War veterans and in Iraqis to depleted uranium. 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. Dr Richard Guthrie, an expert in chemical warfare at Sussex University , argues that due to the fact that no pathological evidence exists linking depleted uranium to birth defects, a more likely cause for this increase in birth defects was the Iraqi Army’s use of mustard agents during its war with Iran. Sulphur mustard is also know to cause cancers, leukaemias and birth defects, even for relatively low exposures levels. The children of the residents of Halabja as well as those of Iranian veterans of the Iran Iraq war have developed cancers and birth defects. Neither groups had been exposed to depleted uranium, but both groups had been exposed to sulfur mustard agents.
Further studies by the New England Journal of Medicine analyzing 34,000 babies of Gulf War veterans [5], as well as by the Department of Veterans Affairs [6] found no evidence of an increase in the risk of birth defects among the children of Gulf War veterans.
The Uranium Medical Research Centre in Canada and the United States published a study of 27 Gulf War veterans [7] displaying typical symptoms of Gulf War Syndrome. Of the 27, only those who had DU fragments lodged in their bodies showed any sign of DU in their urine. The Department of Veterans Affairs study had found that in a sample of veterans who did have DU fragments in their body, all showed normal reproductive health and kidney function.
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:
- 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 infect others over a wide range, and future passers-by, with uranium poisoning.
- 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.
- 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.
- 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.
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Last updated: 05-07-2005 08:19:33
Last updated: 05-13-2005 07:56:04
