Depleted uranium [DU] results from the enriching of natural uranium for use in nuclear reactors. Natural uranium is a slightly radioactive metal that is present in most rocks and soils as well as in many rivers and sea water. Natural uranium consists primarily of a mixture of two isotopes (forms) of uranium, Uranium-235 (U235) and Uranium-238 (U238), in the proportion of about 0.7 and 99.3 percent, respectively. Nuclear reactors require U235 to produce energy, therefore, the natural uranium has to be enriched to obtain the isotope U235 by removing a large part of the U238. Uranium-238 becomes DU, which is 0.7 times as radioactive as natural uranium. Since DU has a half-life of 4.5 billion years, there is very little decay of those DU materials.


The Agency for Toxic Substances and Disease Registry (ATSDR) for the Department of Health and Human Services estimates there are an average of 4 tons of uranium in the top foot of soil in every square mile of land. A heavy metal similar to tungsten and lead, uranium occurs in soils in typical concentrations of a few parts per million (equivalent to about half a teaspoon of uranium in a typical 8-cubic yard dump truck-load of dirt).


The Department of Energy (DOE) recently reported that the DU it provided to DoD for manufacturing armor plates and munitions may contain trace levels (a few parts per billion ) of contaminants including neptunium, plutonium, americium, technitium-99 and uranium-236. From a radiological perspective, these contaminants in DU add less than one percent to the radioactivity of DU itself.


In military applications, when alloyed, Depleted Uranium is ideal for use in armor penetrators. These solid metal projectiles have the speed, mass and physical properties to perform exceptionally well against armored targets. DU provides a substantial performance advantage, well above other competing materials. This allows DU penetrators to defeat an armored target at a significantly greater distance. Also, DU's density and physical properties make it ideal for use as armor plate. DU has been used in weapon systems for many years in both applications.


DU can be used to engage the enemy at greater distances than tungsten penetrators or high explosive anti-tank (HEAT) rounds because of improved ballistic properties. When they strike a target, tungsten penetrators blunt while DU has a self-sharpening property. DU ammunition routinely provides a 25 percent increase in effective range over traditional kinetic energy rounds.


On impact with a hard target (such as a tank) the penetrator may generate a cloud of DU dust within the struck vehicle that ignites spontaneously creating a fire that increases the damage to the target. Due to the pyrophoric nature of DU, many of the DU particles and fragments that are formed during and following impact and perforation will spontaneously ignite, resulting in a shift of the particle size probability distribution function to a smaller mean diameter. As a result of physical differences between DU and its oxides, the oxide particles tend to crumble under relatively weak mechanical forces, further shifting the particle size to an even smaller mean diameter.


The amount of depleted uranium which is transformed into dust will depend upon the type of munition, the nature of the impact, and the type of target. The number of penetrators hitting a target depends upon many factors, including the type and size of the target. On average, not more than 10% of the penetrators fired by planes equipped with large machine guns hit the target (20 - 30 mm rounds). DU munitions which do not hit hard targets will penetrate into the soft ground or remain more or less intact on the surface. These will corrode over time, as metalic DU is not stable under environmental conditions.


US forces also use DU to enhance their tanks’ armor protection. In one noteworthy incident, an M1A1 Abrams Main Battle Tank, its thick steel armor reinforced by a layer of DU sandwiched between two layers of steel, rebuffed a close-in attack by three of Iraq's T-72 tanks. After deflecting three hits from Iraq's tanks, the Abrams’ crew dispatched the T-72s with a single DU round to each of the three Iraqi tanks.


Depleted uranium is also used in numerous commercial applications requiring a very dense material. These include: ballast and counterweights; balancing control devices on aircraft; balancing and vibration damping on aircraft; machinery ballast and counterweights; gyrorotors and other electromechanical counterweights; shielding for medicine and industry; shipping container shielding for radiopharmaceuticals; chemical catalyst; pigments; and, x-ray tubes.


History
The Army uses alloyed DU in the 25, 105, and 120 millimeter (mm) kinetic energy cartridges. The Bradley Fighting Vehicle uses the 25 mm cartridge (not released for use as of May 1995) in its chain gun. The M1 and M60 series tanks use the 105 mm cartridge; the Army also plans to use the 105 mm in the main gun of the XM8 Armored Gun System. The M1A1 and M1A2 Abrams Tank main guns use the 120 mm cartridge. DU is used as an armor component on the M1 series heavy armor (HA) tanks. Small amounts of DU are used as an epoxy catalyst for the M86 Pursuit Deterrent Munition (PDM) and the Area Denial Artillery Munition (ADAM).


During the late 1950s, the primary material used for kinetic energy, armor-piercing projectiles was tungsten carbide. When first fielded, tungsten carbide represented a quantum improvement over its nearest competitor, high carbon steel. Its higher density (approximately 13 gm/cc) gave it superior penetration performance against existing armor targets. With the advent of double and triple plated armor in the 1960s, however, tungsten munitions showed a tendency to break up before penetrating the layered armor. This deficiency spurred the development of new alloys and materials capable of defeating any armored threats.


In response to the new operational requirements, a succession of metal alloys were evaluated. Initially, the UK Government developed a higher density tungsten alloy consisting of 93 percent tungsten and 7 percent binder tungsten alloy (WA). The new WA alloy had a density of 17 gm/cc versus 13 gm/cc for tungsten carbide. From 1965 to 1972, the US Army conducted a parallel development program for the 152mm XM578 cartridge which was co-developed with the MBT-70 Tank. The XM578 cartridge used a tungsten alloy that was slightly denser than the British alloy consisting of 97.5 percent tungsten and 2.5 percent binder, which had a density of 18.5 gm/cc.


Throughout the 1960s and early 1970s, the Army developed a successive series of improved 105 mm rounds (the primary main gun caliber on M-60 and developmental XM-1 series tanks) using the denser 97.5% tungsten alloy. The first of these rounds were the XM735 and XM774 cartridges derived from the XM578 cartridge program. These alloys proved sufficient to meet the Army’s operational requirements. At the same time, the Army continued to investigate applications for depleted uranium [DU].


One of the Army’s first uses of DU was as a ballistic weight in the spotting round for the Davy Crockett missile warhead. Additionally, in the early 1960s, the Army tested a four-alloy "UQuad" containing DU in experimental tests on the 105mm and 120mm Delta Armor Piercing Fin Stabilized, Discarding Sabots (APFSDS). Tungsten continued to be favored over DU, however, for two main reasons: 1) DU was still developmental, and inconsistencies with the alloys in the manufacturing process were a persistent problem; and 2) penetration tests against older Soviet tanks and similar targets failed to show the clear penetration superiority of the DU round.


In the mid-1970s, as it became clear that the latest-generation armors might prove impervious to tungsten carbide penetrators, the Army’s focus on improved tungsten alloys began to shift. At the same time, parallel Air Force and Navy tests using smaller-caliber (20-, 25-, and 30mm) ammunition had demonstrated quite convincingly the clear penetration superiority of DU rounds.


In 1973, the Army evaluated alternatives for improving the lethality of its 105mm M68 tank gun. This effort grew into the XM774 Cartridge Program which, after an extensive developmental testing and evaluation program, selected depleted uranium alloyed with ¾ percent by weight titanium (U-3/4Ti). The selection of U-3/4Ti derived in part from improved designs and alloys that allowed the DU core to withstand high acceleration without breaking up. In the 1960s, tungsten alloys used in the XM578 projectile had to be encased in a steel jacket to withstand the extreme firing velocities of the 152mm gun, reducing the penetrating effectiveness of the tungsten cartridge. The new U-3/4Ti alloy overcame these early limitations for large caliber munitions.


Development of U-3/4Ti ushered in a new generation of penetrators for the Army. Since the selection of DU for the XM774 cartridge, all major developments in tank ammunition have selected DU, including the 105mm M833 series and the 120mm M829 series (the latter being the primary anti-armor round used in the Gulf War). This pattern continues today, with the latest generation of the 105mm M900 series and the 25mm M919 for the Bradley Fighting Vehicle.


In the early 1970s, the Air Force developed the GAU-8/A air to surface gun system for the A-10 close air support aircraft. This unique aircraft, designed to counter the massive Soviet/Warsaw Pact armored formations spearheading an attack into NATO’s Central Region, was literally designed and built around the GAU-8. This large, heavy, eight-barreled 30-mm cannon was designed to blast through the top armor of even the heaviest enemy tanks. To further exploit the new cannon’s tremendous striking power, the Air Force opted to use the depleted uranium U-3/4Ti, a 30mm API round. A comprehensive Environmental Assessment of the GAU-8 ammunition was released on January 18, 1976. The report stated that the proposed action was expected to have no significant environmental impact and that the "biomedical and toxicological hazards of the use of depleted uranium (DU) in this program are practically negligible." The A-10 aircraft was deployed to United States Air Forces in Europe (USAFE) in 1978.


The Navy’s Phalanx Close-In Weapon System, or CIWS was designed for terminal (last-ditch) defense against sea-skimming missiles. The Navy evaluated a wide range of materials before deciding on DU alloyed with 2 percent molybdenum (DU-2Mo). Phalanx production started in 1978, with orders for 23 USN and 14 Foreign Military Sales systems; however, subsequent budget cuts reduced these numbers. In 1988 the Navy opted to transition the CIWS 20mm round from DU to tungsten. The Navy made the decision based on live fire tests that showed that tungsten met the Navy’s performance requirements while offering reduced probabilities of radiation exposure and environmental impact. It should be noted that the "soft" targets the CIWS was designed to defeat—anti-ship missiles at close range—are far easier to destroy than "hard" targets like tanks. Substantial stocks of DU ammunition delivered prior to that date remain in the inventory.


DU munitions were first used in the Gulf War of 1991. A total of 320 tons (290,300 kilograms) of DU projectiles were fired by the US during the Gulf War. DU friendly fire and accidental fire incidents contaminated a total of 31 US combat vehicles (16 Abrams tanks and 15 Bradley armored vehicles) in the Gulf during 1990-1991. These incidents, and the resultant cleanup and recovery operations, exposed a number of soldiers to depleted uranium. Those with the highest exposures were in, on, or near vehicles when they were struck.


US Air Force A-10 Thunderbolt II aircraft fired approximately 10,000 30mm DU rounds (3.3 tons of DU) at 12 sites in Bosnia-Herzegovina in 1994-1995. In 1999, they fired nearly 31,000 DU rounds (10.2 tons of DU) at 85 sites in Kosovo.


Health Issues
The major health concerns about DU relate to its chemical properties as a heavy metal rather than to its radioactivity, which is very low. As with all chemicals, the hazard depends mainly upon the amount taken into the body. Medical science recognizes that uranium at high doses can cause kidney damage. However, those levels are far above levels soldiers would have encountered in the Gulf or the Balkans.


Because depleted uranium emits primarily alpha radiation, it is not considered a serious external radiation hazard. The depleted uranium in armor and rounds is covered, further reducing the radiation dose. When breathed or eaten, small amounts of depleted uranium are carried in the blood to body tissues and organs; much the same as the more radioactive natural uranium. Despite this, no radiological health effects are expected because the radioactivity of uranium and depleted uranium are so low.


Most soldiers and civilians will not be exposed to dangerous levels of depleted uranium. However, in certain circumstances the exposures may be high and there would be a risk of heavy metal poisoning that could lead to long-term kidney damage for a few soldiers, as well as the increased risk of lung cancer. A small number of soldiers and civilians might suffer kidney damage from depleted uranium if substantial amounts are breathed in, or swallowed in contaminated soil and water. The kidneys of a few soldiers may be damaged if they inhale large quantities of DU after their vehicle is struck by a penetrator or while working for long periods in contaminated vehicles. Large numbers of corroding DU penetrators buried in the soil may also pose a long-term threat if uranium leaches into water supplies. Long-term sampling, particularly of water and milk, is required to detect any increase in uranium levels around areas where DU has been used on the battlefield.


Anecdotal reports of deaths and illnesses among US veterans of the Gulf War who worked for long periods in heavily contaminated vehicles prompted a number of investigations. The voluntary Veterans Affairs DU Medical Follow-up Program began in 1993-1994 with the medical evaluations of 33 friendly-fire DU-exposed veterans, many with embedded DU fragments. An additional 29 of the friendly-fire victims were added to the follow-up program in 1999. In 1998, the scope of the program was expanded to include Gulf War veterans who may have been exposed to DU through close contact with DU munitions, inhalation of smoke containing DU particulate during a fire at the Doha depot, or by entering or salvaging vehicles or bunkers that were hit with DU projectiles. The published results of these medical evaluations indicate that the presence of retained DU fragments is the only scenario predictive of a high urine uranium level, and those with embedded DU fragments continue to have elevated urine uranium levels ten years after the incident. It is unlikely that an individual without embedded DU fragments would have an elevated urine uranium level, and consequently any uranium-related health effects.


In late 2000 and early 2001, various news reports, mostly European, reported allegations of an increase in leukemia cases related to exposure to DU while serving in the Balkans. Subsequent independent investigations by the World Health Organization, European Commission, European Parliament, United Nations Environment Programme, United Kingdom Royal Society, and the Health Council of the Netherlands have all have discounted any association between depleted uranium and leukemia or other medical problems among Balkans veterans.

Is It Likely That Anyone Could Breathe Enough Depleted Uranium to Do Any Harm?

Not very likely. DU is a low specific activity material, so a large mass has to enter the body to give even a moderate radiation dose. In this context, others have pointed out that to inhale 1 g of any dust in a short time is almost impossible. Even over a long time it is not easy. An air concentration of 10 mg per cubic metre is regarded as noticeably and unpleasantly 'dusty'. An adult breathes about 1 cubic metre an hour during normal daytime activities, so would have to inhale dusty air continuously 8 hours a day for nearly two weeks to inhale 1 g. The dust would have to be very contaminated to be even 10% DU. Generally, away from the immediate site of a DU weapon attack, the concentration in dust will be far less. Hence in almost any normal situation it is unlikely that anyone would inhale even 100 mg of DU. The radiation dose from this would be up to about 10 mSv, similar to the average annual dose from radon in parts of the UK. Thus, even if many people inhaled that amount (which is even more unlikely), the effects would be too small to observe.


With regard to chemical effects, the occupational exposure level is 0.2 mg of soluble uranium per cubic metre (see What are the safe limits for depleted uranium inside the body?). It is unlikely that more than 25% of the DU is soluble or that dust to which people are exposed is more than 10% DU. On this basis 0.2 mg per cubic metre corresponds to 8 mg dust per cubic metre, which people would not normally willingly tolerate for long.