Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope 235U than natural uranium. The less radioactive and non-fissile 238U is the main component of depleted uranium. It is antonymous to "enriched uranium".
Uranium is notable for the extremely high density of its metallic form: at , uranium is more dense than lead. Because depleted uranium has nearly the same density as natural uranium but far less radioactivity, it is desirable for applications that demand high mass without added radiation hazards. Civilian uses include counterweights in aircraft, radiation shielding in medical radiation therapy, research and industrial radiography equipment, and containers for transporting radioactive materials. Military uses include armor plating and armor-piercing projectiles.
The use of DU in ammunitions is controversial because of concerns about potential long-term health effects. Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by exposure to uranium, a toxic metal. It is only weakly radioactive because of the long radioactive half-life of 238U (4.468 billion years) and the low amounts of 234U (half-life about 246,000 years) and 235U (half-life 700 million years). The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days. The aerosol or spallation frangible powder produced by impact and combustion of depleted uranium munitions (or armour) can potentially contaminate wide areas around the impact sites, leading to possible inhalation by human beings.
The actual level of acute and chronic toxicity of DU is also controversial. Several studies using cultured cells and laboratory rodents suggest the possibility of leukemogenic, genetic, reproductive, and neurological effects from chronic exposure. A 2005 epidemiology review concluded "In aggregate the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU." A 2021 study concluded that DU from exploding munitions did not lead to Gulf War illness in American veterans deployed in the Gulf War. A 2011 study found elevated levels of uranium in soil and hair samples from Fallujah, Iraq, but it was from slightly enriched uranium instead of DU.
Definition Natural uranium contains about 235U. Depleted uranium has lower mass fractions—up to three times less—of 235U and 234U than natural uranium. Since 238U has a much longer half-life than the lighter isotopes, DU is about 40% less radioactive than natural uranium. Most of the alpha radiation comes from 238U and 234UIn natural uranium, about 49% of the radiation comes from 238U, 49% from 234U, and 2% from 235U. In depleted uranium the amounts of 235U and 234U are both reduced, but there is still much more radiation from the 234U than from the 235U. whereas beta radiation comes from decay products 234Th and 234Pa that are formed within a few weeks.
The United States Nuclear Regulatory Commission (NRC) defines depleted uranium as uranium with a percentage of the 235U isotope that is less than 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 235U. In actuality, DoD uses only DU that contains approximately 235U.
History
Enriched uranium was first manufactured in the early 1940s when the United States and the United Kingdom began their nuclear weapons programs. Later in the decade, France and the Soviet Union began their nuclear weapons and nuclear power programs. Depleted uranium was originally stored as an unusable waste product (uranium hexafluoride) in the hope that improved enrichment processes could extract additional quantities of the fissionable 235U isotope. This re-enrichment recovery of the residual uranium-235 is now in practice in some parts of the world; e.g. in 1996 over were upgraded in a Russian plant.
In the 1970s, the Pentagon reported that the Soviet military had developed armor plating for Warsaw Pact tanks that NATO ammunition could not penetrate. The Pentagon began searching for materials to make denser armor-piercing projectiles. After testing various metals, ordnance researchers settled on depleted uranium.
The US and NATO militaries used DU penetrator rounds in the 1991 Gulf War, the Bosnia war, bombing of Serbia, the 2003 invasion of Iraq, and 2015 airstrikes on ISIS in Syria. It is estimated that between of DU were used in the 1991 Gulf War.
Production
Most depleted uranium arises as a by-product of the production of enriched uranium for use as fuel in nuclear reactors and in the manufacture of nuclear weapons. Enrichment processes generate uranium with a higher-than-natural concentration of lower-mass-number uranium isotopes (in particular 235U, which is the uranium isotope supporting the fission chain reaction) with the bulk of the feed ending up as depleted uranium.
Natural uranium metal contains about 235U, 238U, and about 234U. The production of enriched uranium using isotope separation creates depleted uranium containing only 0.2% to 0.4% 235U. Because natural uranium begins with such a low percentage of 235U, enrichment produces large quantities of depleted uranium. For example, producing of enriched uranium requires of natural uranium, and leaves about of depleted uranium having only 235U.
Depleted uranium is further produced by recycling spent nuclear fuel, in which case it contains traces of neptunium and plutonium. These quantities are so small that they are not considered to be of serious radiological significance by the European Committee on Radiation Risk. Documents of the ECRR 2010 No. 2, Brussels, Belgium, 2010. DU from nuclear reprocessing has different isotopic ratios from enrichment-by-product DU, from which it can be distinguished by the presence of 236U.
The only known natural source of uranium with a content significantly different from 0.71% is found in the natural nuclear fission reactor at Oklo, Gabon. It can be "fingerprinted" as different in origin from manmade depleted uranium by the content, which is 55 ppm in uranium from the Oklo Mine as well as all other natural sources, but will be lower in depleted uranium in accordance with the degree of depletion.
Storage
About 95% of the depleted uranium produced until now is stored as uranium hexafluoride, or (D), in steel cylinders in open air storage yards close to enrichment plants. Each cylinder typically holds up to of . In the U.S. of depleted had accumulated by 1993. In 2008, in 57,122 storage cylinders were located near Portsmouth, Ohio; Oak Ridge, Tennessee; and Paducah, Kentucky.
The storage of (D) presents environmental, health, and safety risks because of its chemical instability. When is exposed to water vapor in the air, it reacts with the moisture to produce (uranyl fluoride), a solid, and (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 . Release of the hydrogen fluoride gas to the atmosphere is also slowed by the plug formation. Like any other uranium compound, uranyl fluoride is radioactive, and precautions should be taken. Whether ingested, inhaled, or absorbed through the skin, it is corrosive and may harm internal organs, potentially resulting in death. Effects of exposure may be delayed.
The U.S. government has been converting depleted to solid uranium oxides for use or disposal. Such disposal of the entire D inventory could cost anywhere from million to million.
+ World depleted-uranium inventory (1999) Country Organization Estimated DU stockstonnes (short tons) Reported DOE 2002 Rosatom 1996 Areva NC 2001 BNFL 2001 URENCO 1999 JNFL 2001 CNNC 2000 KAERI 2002 NECSA 2001 DSO National Laboratories 2007 Total 2008
Military applications Depleted uranium is very dense; at 19,050 kg/m3, it is 1.67 times as dense as lead, only slightly less dense than tungsten and gold, and only 16% less than osmium or iridium, which are the densest known substances under standard (i.e., Earth-surface) pressures. Consequently, a DU projectile of given mass has a smaller diameter than an equivalent lead projectile with the same kinetic energy, with less aerodynamic drag and deeper penetration because of a higher pressure at point of impact. DU projectiles are inherently incendiary because they become pyrophoric upon impact with the target.
Armor plate Because of its high density, depleted uranium can also be used in tank armor, sandwiched between sheets of steel armor plate. For instance, some late-production M1A1 and M1A2 Abrams tanks built after 1998 have DU modules integrated into their Chobham armor, as part of the armor plating in the front of the turret, and there is a program to upgrade older tanks.
Nuclear weapons
Depleted uranium can be used as a tamper, or neutron reflector, in fission bombs. A high density tamper like DU makes for a longer-lasting, more energetic, and more efficient explosion.
Ammunition Most military use of depleted uranium has been as 30 mm ordnance, primarily the 30 mm PGU-14/B armor-piercing incendiary round from the GAU-8 Avenger cannon of the A-10 Thunderbolt II used by the United States Air Force. 25 mm DU rounds have been used in the M242 gun mounted on the U.S. Army's Bradley Fighting Vehicle and the Marine Corps's LAV-25.
The U.S. Marine Corps uses DU in the 25 mm PGU-20 round fired by the GAU-12 Equalizer cannon of the AV-8B Harrier, and in the 20 mm M197 gun mounted on AH-1 Cobra helicopter gunships. The United States Navy's Phalanx CIWS's M61 Vulcan Gatling gun used 20 mm armor-piercing penetrator rounds with discarding plastic sabots and a core made using depleted uranium, however they later changed to using tungsten penetrators.
Another use of depleted uranium is in kinetic energy penetrators, anti-armor rounds such as the 120 mm sabot rounds fired from the British Challenger 1 and Challenger 2, as well as the American M1A1 and M1A2 Abrams. Kinetic energy penetrator rounds consist of a long, relatively thin penetrator surrounded by a discarding sabot. 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% by mass of depleted uranium and 0.75% by mass of titanium. Staballoys are approximately 1.67 times 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% titanium.
Depleted uranium is favored for the penetrator because it is self-sharpening and flammable. On impact with a hard target, such as an armored vehicle, the tip of the projectile will be "mushroomed", while the back of the projectile is still a rigid solid. This leads to adiabatic shearing, and together with the spin of the projectile results in a shedding of the mushroomed plastic phase in such a way that it forms a new sharp tip. This shedding of the mushroomed tip improves penetration properties compared to the complete dispersal that takes place with tungsten penetrators, therefore DU penetrators are 20% more effective than tungsten rounds. The impact and subsequent release of heat energy causes it to ignite when in contact with oxygen. When a DU penetrator reaches the interior of an armored vehicle, it catches fire, often igniting ammunition and fuel 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 tank.