Depleted uranium
Depleted uranium (DU) is uranium which has had most of the fissile isotope U-235 and the highly radioactive but rare isotope U-234 removed, and consists of mostly U-238. The U-235 is concentrated into enriched uranium through the process of isotope separation for use in nuclear reactors and nuclear weapons. The remaining U-238 is 60% as radioactive as natural uranium. It is waste material from this enrichment process. During the Manhattan Project depleted uranium had the codename tuballoy, a term that is still occasionally used. Uranium is mined mainly for its U-235 content, so the excess U-238 can be obtained cheaply and is used for its extremely high density, only slightly less than that of tungsten.
Military applications
A major use of DU is as the head of a kinetic projectile fired to penetrate armour, so it is used by tanks and other military platforms. Depleted uranium is very dense: at 19.05 g/cm³ it is 70% denser than lead, allowing it to penetrate most conventional armor. A DU projectile burns and melts as it penetrates steel, becoming 'sharper' rather than blunting. As the projectile passes through armor, the heat build-up causes it to catch fire and disintegrate into fine particles on re-encountering air, causing it to emerge from the other side of the armor accompanied by a white-hot ball of fire and a shower of molten shrapnel. DU is also used as a component in some vehicular armor, specifically in M1A1HA and M1A2 Abrams tanks built after 1998.
Armor piercing projectiles made from depleted uranium are far less expensive to manufacture than those made from tungsten, due to the fact that depleted uranium can be cast easily, whereas tungsten's tremendous hardness and very high melting point make it extremely difficult to manufacture anything from it.
Currently the US military is the primary user of DU in combat, though DU armor-piercing munitions were invented by the Soviets in the late 1970s and are still mass-produced in Russia today (as well as 17 other countries, including Pakistan). 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 caliber by the M1 Abrams and M60A3 tanks and in 25 mm by the M242 mounted on the M2 Bradley and the LAV-AT; some late-production Abrams tanks have DU rods as reinforcements as part of its armour plating in the front of the hull and the front of the turret. The US Navy uses it in its 20 mm CIWS (though it has switched to tungsten for this appliction) and the 25 mm Mk38 machine gun. The Air Force uses it in 30 mm caliber on the A-10 Thunderbolt II and the Marine Corps in 25 mm on their AV-8B Harrier and also in the 20 mm electric Gatling gun mounted on AH-1 helicopter gunships. The Russian military mainly uses DU munitions in tank main gun ammunition, mostly for the 115 mm guns in the T62 tank and the 125 mm guns in the T64, T72, T80, and T90 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 other countries.
Civilian applications
Depleted uranium is also used in 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, such as in aircraft ballast (a 747 may contain 400-1,500kg). Tungsten could also be used, but the difficulty in working it makes anything made from tungsten extremely expensive and a mix of tungsten and uranium weights in aircraft is not unusual.
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 under the front axle to achieve a better balance.
Health concerns
Environmental groups have raised concerns about the use of this material; arguing that not only is it dangerously radioactive, but it is also as toxic as lead. Such issues are of concern to those fired upon by DU weapons, to those firing DU weapons, to those protected by DU armour-plating, and to civilians and troops operating in a theatre where DU is used. The health effects of depleted uranium have been postulated to be one of the possible causes of Gulf war syndrome. Government officials have disputed this claim.
Studies of scientific bodies have resulted in mixed conclusions. Studies showing detrimental health affects have claimed the following:
- Toxic material from shot DU ammunition does disperse into the air much more easily and widely than expected (since uranium is one of the heaviest metals there is, this came rather unexpectedly). Also DU disperses into the 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 penetrators recovered by the UNEP team had decreased in mass by 10-15% due to corrosion. This rapid corrosion speed underlines the importance of monitoring the water quality at the DU sites on an annual basis."
- While DU studies from the military sector mainly evaluated external exposure to DU materials, newer studies took inhalation of particles from the remains of used ammunition into consideration. These studies indicate that the battlefield use of DU ammunition may have grave consequences, especially if used near population centers.
- Small amounts of radiation may even be more harmful to the body than bigger doses may be. Damaged cells resulting from lower doses of radiation seem to be less efficiently repaired by the body. This seems to be a possible source of cancer. This may lead to controversy in the future if the facts become more clear (proven by more studies) and more commonly known, since this may be important to people living in the vicinity of nuclear power plants as well.
- While DU is minimally radioactive (and its radioactivity figures are often cited by advocates of its use) its decay product - 234 Th - and its own daughter 234 Pa - are beta particle emitters with half-lives of several weeks (234 Pa decays to 234 U, with a half-life of hundreds millenia; this isotope does not build to equilibrium concentration for a significant amount of time). When the two first isotopes in the decay chain reach their (tiny) equilibrium concentrations (over the months following manufacture), a DU fragment will emit 3 times the radiation due to DU itself, and most of this will be beta radiation - which can penetrate the skin or cause damage if ingested or inhaled.
These facts together may indicate that DU ammunition is actually quite a health problem and endangers the civilian population if left on the battlefield, as asserted in a 1997 report by Green EU parliamentarians - the European Committee on Radiation Risk (ECRR) - which found that DU posed serious health risks. However, other studies have shown that DU ammunition has no measurable detrimental health effects, either in the short or long term. Critics of these studies point to the fact that they come primarily from either "Green" groups who are opposed to anything vaguely nuclear, or the US and UK -- both supporters of DU.
The Vienna-based 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." The US military watchdog group Federation of American Scientists has come to similar conclusions.
