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Revision as of 01:49, 15 December 2005
Depleted uranium (DU) results from the enriching of natural uranium for use in nuclear reactors. It is what is left over when most of the highly radioactive isotopes of uranium are removed
Uranium enrichment process
Natural uranium contains nominally 0.71% U-235 (+/-0.1%), 99.28% U-238, and about 0.0054% 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.
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.
- Nuclear marine propulsion reactors usually use uranium containing 90% or more of U-235
- Commercial light water nuclear reactor fuel is usually enriched up to a maximum of 5% (the 5% limit is set by the currently licensed transport containers — in the future the 5% limit may be increased up to 7% for improved fuel economy).
- Research reactor fuel is today limited to maximum 20% (most older research reactors have been or will be converted down to this lower enrichment level).
- The use of U-235 in nuclear weapons has has been superseded by plutonium fueled devices.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.
World stockpiles
Most of the depleted uranium produced to date is being stored as UF6 in steel cylinders in the open air in so-called cylinder yards located adjacent to the enrichment plants. The cylinders contain up to 12.7 tonnes of UF6. In the US alone, 560,000 metric tonnes of depleted UF6 have accumulated until 1993; they are currently stored in 46,422 cylinders. Meanwhile, their number has grown by another 8,000 new cylinders.
- World Depleted Uranium Inventory
- Source: WISE Uranium Project
Uses and availability
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, can burn, spalls easily, 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.
Nuclear energy applications
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 a process of transmutation to convert "fertile" isotopes such as U-238 into fissile material, 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 . Currently (December 2005), the only breeder reactor producing power is BN-600 in Beloyarsk, Russia. (The electricity output of BN-600 is 600 MW - Russia has planned to build another unit, BN-800, at Beloyarsk nuclear power plant.) Also, Japan's Monju reactor is planned for restart (having been shut down since 1995), and both China and India intend to build breeder reactors.
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.
Civilian applications
Current uses
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 include: 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.
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.
An unexpected application is in Formula 1 racing cars. The rules state a minimum weight of 600 kg, but builders strive to get the weight as low as possible and then bring it up to the 600 kg mark by placing depleted uranium where needed to achieve a better balance.
Future applications
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.
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.)
Uranium Oxides have electrical and electronic properties equivalent to or much better than the properties of conventional Si, Ge, and GaAs semiconductor materials. Thus, it appears that a new, higher performance class of semiconductors are possible: uranium oxide-based semiconductors. Uranium oxides have characteristics that could give them significantly better performance than conventional conductor materials: operation at substantially higher temperatures and greater radiation and EMF resistance. The low radioactivity of DU would make its use mandatory in this application. In any case the total mass used would be insignifigent.
Military applications
Projectile weapons
One 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, the latter in designated alloys known as staballoys. 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 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 such a way that it remains sharp. Further, the impact and subsequent release of heat energy causes it to disintegrate to dust and combust when it reaches air (compare to ferrocerium). 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.
The material 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.
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 core. As such, it increases the efficiency of the weapon and reduces the amount of critical mass required. This feature is common to the primary of the Teller-Ulam design as well.
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 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 would have been 100 megatons, and would have produced fallout equivalent to one third of the global total at that time.
Health concerns
Early scientific studies usually found no link between depleted uranium and cancer, and sometimes found no link with increases in the rate of birth defects, but newer studies have found the latter and offered explanation of such links. Some have raised concerns about the use of this material, particularly in munitions, because of its proven mutagenicity, teratogenicity, in mice, and neurotoxicity, and its suspected carcinogenic potential, because it remains radioactive for an exceedingly long time with a half-life of approximately 4.5 billion years (about the age of the Earth); and because it is also toxic in a manner similar to lead and other heavy metals. The primary radiological hazards associated with this material are beta and alpha emissions, however the long half-life indicates that depleted uranium is only weakly radioactive. All isotopes and compounds of uranium are toxic. Please see Gulf War Syndrome.
Such issues are of concern to 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 shown the following:
- Indicateations 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.) Pre-1993 military DU studies mainly evaluated external exposure only.
- DU can disperse into the air and water, United Nations Environment Programme (UNEP) study says in part:
- "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."
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 the use of DU in weapons also is in potential breach of 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. Treaties which were designed to spare civilians from unwarranted suffering in or after armed conflicts.
According to the UN, the resolutions in 1996-97 were passed because the use of DU in ordinance 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.
See Also
External links
United Nations
- "Depleted Uranium: Sources, Exposure and Health Effects," World Health Organization, Ionizing Radiation Unit, 2001 (see Chapter 8, "The Chemical Toxicity of Uranium," in particular.)
- Sub-Commission resolution 1996/16
(resolves and states DU to be "incompatible" with human rights and international law; lists DU as "particularly" one "weapon of mass destruction or indiscriminate effect") - UN High Commission for Human Rights, 1998
(statement that DU is prohibited and contravenes prior UN resolutions) - "Human rights and weapons of mass destruction, or with indiscriminate effect, or of a nature to cause superfluous injury or unnecessary suffering"
(The UN 2002 report)
Scientific bodies
- Depleted Uranium article from the Royal Society
- An Analysis of Uranium Dispersal and Health Effects Using a Gulf War Case Study by Sandia National Laboratories ).
- Depleted Uranium Human Health Fact Sheet from Summary Fact Sheets for Selected Environmental Contaminants to Support Health Risk Analyses by Argonne National Laboratory Environmental Assessment Division
- Uranium Human Health Fact Sheet
Other
- Better World Links on Depleted Uranium Weapons 500+ links
- U.S. Soldiers Contaminated With Depleted Uranium Speak Out - Democracy Now!, April 5, 2004
- Depleted UF6 Management Information Network
- International Atomic Energy Agency Depleted Uranium FAQ
- Proposal for Research on Depleted Uranium ( U.K. Ministry of Defence)
- World Uranium Weapons Conference 2003
- International Coalition to Ban Uranium Weapons
- Campaign Against Depleted Uranium