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Depleted uranium (DU) is uranium which contains mostly Uranium-238 and a reduced proportion of the isotope Uranium-235. It is a byproduct of the enriching of natural uranium for use in nuclear reactors. DU is what is left over when most of the fissile radioactive isotopes of uranium are removed. The names Q-metal, depletalloy, and D-38, once applied to depleted uranium, have fallen into disuse.

As a radioactive byproduct otherwise requiring long term storage as low level nuclear waste, depleted uranium is an inexpensive but controlled material. It is useful for its extremely high density, which is only slightly less than that of tungsten. However, it has extremely poor corrosion properties, is pyrophoric (it will burn spontaneously when small particles are exposed to air), and since like all heavy metals toxic, as well as being radioactive, the facilities for processing it need to monitor and filter airborne particles.

Production and availability

Natural uranium metal contains about 0.71% U-235, 99.28% U-238, and about 0.0054% U-234. Depleted uranium contains only 0.2% to 0.4% U-235, the remainder having been removed and concentrated into enriched uranium through the process of isotope separation. The enrichment process does not create U-235 but merely separates the different isotopes of uranium. Therefore the process leaves large amounts of U-238 uranium as a byproduct. This byproduct is refered to as depleted uranium. 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.

The Nuclear Regulatory Commission (NRC) defines depleted uranium as uranium in which the percentage of the U isotope by weight is less than 0.711 percent (See 10 CFR 40.4.) The military specifications designate that the DU used by DoD contain less than 0.3 percent U (AEPI, 1995). In actuality, DoD uses only DU that contains approximately 0.2 percent U (AEPI, 1995).

World Depleted Uranium Inventory
Country Organization DU Stocks (000 Kg) Reported
United States USA DOE 480,000 2002
Russia Russia FAEA 460,000 1996
France France COGEMA 190,000 2001
United Kingdom UK BNFL 30,000 2001
Germany Germany URENCO 16,000 1999
Japan Japan JNFL 10,000 2001
China China CNNC 2,000 2000
South Korea South Korea KAERI 200 2002
South Africa South Africa NECSA 73 2001
TOTAL 1,188,273 2002
Source: WISE Uranium Project

Health concerns

Main article: Health and environmental effects of depleted uranium

The major health impact of depleted uranium relate to its chemical toxicity as a heavy metal rather than to its radioactivity, which is relatively low. As with any heavy metal, the overall hazard depends on the amount of exposure.

However the fact that considerable amounts are being stored in the much more dangerous form of uranium hexafluoride and significant quantities of the metal are being distributed in the environment in the form of fumes and fragments as spent munitions has has raised some valid concerns.

Nuclear energy applications

In a nuclear reactor, uranium-238 can be used to breed plutonium, which itself can be used in a nuclear weapon or as a reactor fuel source. In fact, in a typical nuclear reactor, up to a third of the generated power does come from the fission of Plutonium-239 (not supplied as a fuel to the reactor, but transmuted from Uranium-238).

Breeder reactors

Depleted uranium is not usable directly as nuclear fuel. Depleted uranium can be used as a source material for creating the element plutonium. Breeder reactors carry out such a process of transmutation to convert "fertile" isotopes such as U-238 into fissile plutonium. It has been estimated that there is anywhere from 10,000 to five billion years worth of Uranium-238 for use in these power plants . Breeder technology has been used in several reactors .

As of December 2005, the only breeder reactor producing power is BN-600 in Beloyarsk, Russia. The electricity output of BN-600 is 600 megawatts. Russia has planned to build another unit, BN-800, at Beloyarsk nuclear power plant. Also, Japan's Monju breeder reactor is planned for restart, having been shut down since 1995, and both China and India have announced intentions to build breeder reactors.

Radiation shielding

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. However, DU is not as effective as ordinary water for stopping fast neutrons. Both metallic depleted uranium and depleted uranium dioxide are being used as materials for radiation shielding. Depleted uranium is about five times better gamma ray shield than lead, so a shield with the same effectivity can be packed into a thinner layer.

DUCRETE, a concrete made with uranium dioxide aggregate instead of gravel, is investigated as a material for Dry cask storage systems to store radioactive waste.

Downblending

The opposite of enriching is downblending. Surplus highly enriched uranium can be downblended with depleted uranium to turn it into low enriched uranium and thus suitable for use in commercial nuclear fuel.

Depleted uranium is also used (with recycled plutonium) from weapons stockpiles for making mixed oxide fuel (MOX) which is now being redirected to become reactor fuel. This dilution, also called downblending, means that any nation or group that acquired the finished fuel would have to repeat the (very expensive and complex) enrichment and seperation processes before assembling a weapon.

Military applications

Staballoys are metal alloys of a high proportion of depleted uranium with other metals, usually titanium or molybdenum, designed for use in kinetic energy penetrator armor-piercing munitions. They are about twice as dense as lead.

One formulation has a composition of 99.25% of depleted uranium and 0.75% of titanium. Other variant can have 3.5% of titanium.

Incendiary projectile munitions

Depleted uranium is 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 deeper penetration due to a higher pressure at point of impact. DU projectile ordinance is often incendiary because of its pyrophoric property. DU munitions, in the form of ordnance, tank, and naval artillery rounds, are deployed by the armed forces of the United States, United Kingdom, Israel, France, China, Russia, Pakistan, and others. DU munitions are manufactured in 18 countries.

DU penetrator from the PGU-14/B incendiary 30mm round

Most military use of depleted uranium has been as 30 mm and smaller ordnance, primarily the 30mm PGU-14/B amour-piercing incendiary round from AH-64 Apache helicopters and the GAU-8 Avenger cannon of the A-10 Thunderbolt II by the U.S. Army and Air Force. 25 mm DU rounds have been used in the M242 gun mounted on the U.S. Army's Bradley Fighting Vehicle and LAV-AT. 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 also in the 20 mm M197 gun mounted on AH-1 helicopter gunships.

Another use of DU is in kinetic energy penetrators anti-armor role. Kinetic energy penetrator rounds consist of a long, relatively thin penetrator surrounded by discarding sabot. Two materials lend themselves to penetrator construction: tungsten and depleted uranium, the latter in designated alloys known as staballoys. The US Army uses DU in an alloy with around 3.5% titanium. Staballoys, along with lower raw material costs, have the advantage of being easy to melt and cast into shape; a difficult and expensive process for tungsten. Depleted uranium is favoured for the penetrator because it is self-sharpening and pyrophoric. On impact with a hard target, such as an armoured vehicle, the nose of the rod fractures in such a way that it remains sharp. The impact and subsequent release of heat energy causes it to disintegrate to dust and combust when it reaches air because of its pyrophoric properties (compare to ferrocerium). After a disintigrated DU penetrator reaches the interior of an armored vehicle, it explodes, often igniting ammunition and fuel, burning the crew, and causing the vehicle to explode. DU is used by the U.S. Army in 120 mm or 105 mm calibre by the M1 Abrams and M60A3 tanks. The Russian military has used DU munitions in tank main gun ammunition since the late 1970s, mostly for the 115 mm guns in the T-62 tank and the 125 mm guns in the T-64, T-72, T-80, and T-90 tanks.

The DU content in various munitions is 180 g in 20 mm projectiles, 200 g in 25 mm ones, 280g in 30 mm, 3.5 kg in 105 mm, and 4.5 kg in 120 mm penetrators. It is used in the form of Staballoy, alloyed with small proportion of other metals. The US Navy used DU in its 20 mm Phalanx CIWS guns, but switched in the late 1990s to armor-piercing tungsten for this application, because of the fire risk associated with stray pyrophoric rounds. DU was used during the mid-1990s in the U.S. to make 9mm and similar caliber armor piercing bullets, grenades, cluster bombs, and mines, but those applications have been discontinued, according to Alliant Techsystems. Whether or not other nations still make such use of DU is difficult to determine.

Incendiary uranium munitions may be implicated in some aspects of Gulf War syndrome and adverse reproductive outcomes such as congenital malformations. See: Health and environmental effects of depleted uranium.

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

Most modern Nuclear weapons 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 plutonium charge. As such, it increases the efficiency of the weapon and reduces the amount of critical mass required. 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.

The larger portion of the total explosive yield in this design comes from the 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 could have been as much as 100 megatons, and would have produced fallout equivalent to one third of the global total at that time.

The use of U-235 in nuclear weapons has has been superseded by plutonium fueled devices. However the production of plutonium itself requires enriched uranium as a feedstock.

Civilian applications

Civilian applications for depleted uranium are fairly limited and are typically unrelated to its radioactive properties. It primarily finds application as ballast because of its high density. 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. Other relatively minor consumer product uses have included: the manufacture of pigments and glazes; incorporation into dental porcelain used for false teeth to simulate the fluorescence of natural teeth; and in uranium-bearing reagents used in chemistry laboratories.

U.S. Nuclear Regulatory Commission regulations at 10 CFR 40.25 establish mandatory licensing for the use of depleted uranium contained in industrial products or devices for mass-volume applications. Other jurisdictions have similar regulations.

Aircraft

Aircraft may also contain depleted uranium trim weights (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. However the other hazardous material releases from a burning commercial aircraft overshadow the contributions made by DU. Nevertheless, its use has been phased out in many newer aircraft, for example both Boeing and McDonnell-Douglas discontinued using DU counterweights in the 1980s.

Forklifts

It has been stated by forklift industry leaders that the mere substitution of depleted uranium metal for iron counterweights would revolutionize the industry by ushering in design concepts not previously available. Notably reduction in overall length when applied to the crucial right-angle stacking (the amount of space required to execute a 90° turn) dimension of the forklift, results in a 10% increase in usable warehouse floor space.

Catalysts

Uranium oxides are known to have high efficiency and long-term stability when used to destroy volatile organic compounds (VOCs) when compared with some of the commercial catalysts, such as precious metals, TiO2, and Co3O4 catalysts. Much research is being done in this area, DU being favoured for the uranium component due to its low radioactivity. (Hutchings, G. J., et. al., AUranium-Oxide-Based Catalysts for the Destruction of Volatile Chloro-Organic compounds,@ Nature, 384, pp. 341B343, 1996.)

Semiconductors

Main article: Uranium dioxide

Some uranium oxides, namely uranium dioxide, have semiconductor properties similar to other semiconductor materials. Its band gap lies at around 1.3 eV, making them suitable for manufacture of efficient solar cells. Its dielectric constant is about twice as high as of silicon, reducing the quantum tunneling effects in the high-integration integrated circuits and allowing higher integration. Its Seebeck coefficient is very high, making it a promising material for thermoelectric applications; it is also capable of withstanding high temperatures.

The low level of alpha radiation produced in the material is a potential cause of electronic noise, which, while potentially causing problems for high-density integrated circuits, most likely as single-event upsets, should not be a major issue in thermoelectric and photovoltaic applications.

Schottky diodes made of uranium oxide and a p-n-p transistor of uranium dioxide were successfully demonstrated in a laboratory.

Pigments

Uranium was widely used as a coloring matter for porcelain and glass in the 19th century. The total production of uranium pigments was about 260 tonnes (with an uranium contents of ~70%), 150 tonnes of which were used for uranium glass. The practice was believed to be a matter of history, however in 1999 concentrations of 10% depleted uranium were found in "jaune no.17" a yellow enamel powder that was being produced in France by Cristallerie de Saint-Paul, a manufacturer of enamel pigments. The depleted uranium used in the powder was sold by Cogéma's Pierrelatte facility. Cogema has since confirmed that it has made a decision to stop the sale of depleted uranium to producers of enamel and glass.

See also

See also

External links

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