Depleted uranium

History

Enriched uranium was first manufactured in the early 1940s when the United States and Britain 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 U-235 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 6000 metric tonnes were upgraded in a Russian plant.

It is possible to design civilian power-generating reactors using unenriched fuel, but only about 10% of those ever built (such as the CANDU reactor) utilize that technology. Thus most civilian reactors as well as all naval reactors and nuclear weapons production require fuel containing concentrated U-235 and generate depleted Uranium.

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 material 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 315 and 350 tons of DU were used in the 1991 Gulf War.

Production and availability

Natural uranium metal contains about 0.71% U-235, 99.28% U-238, and about 0.0054% U-234. The production of enriched uranium using isotope separation creates depleted uranium containing only 0.2% to 0.4% U-235. Because natural uranium begins with such a low percentage of U-235, enrichment produces large quantities of depleted uranium. For example, producing 1 kg of 5% enriched uranium requires 11.8 kg of natural uranium, and leaves about 10.8 kg of depleted uranium having only 0.3% U-235.

The Nuclear Regulatory Commission (NRC) defines depleted uranium as uranium with a percentage of the ²³⁵U isotope that is less than 0.711% 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 0.3% ²³⁵U (AEPI, 1995). In actuality, DoD uses only DU that contains approximately 0.2% ²³⁵U (AEPI, 1995).

Depleted uranium is further produced by recycling spent nuclear fuel, in which case it contains traces of neptunium and plutonium and has therefore been called "dirty DU" although the quantities are so small that they are considered to be not of serious radiological significance (even) by ECRR.

Uranium hexafluoride

Some depleted uranium is stored as uranium hexafluoride, a crystalline solid, (D)UF₆, in steel cylinders in open air storage yards close to enrichment plants. Each cylinder holds up to 12.7 tonnes (14 short tons) of UF₆. In the U.S. 560,000 tonnes of depleted UF₆ had accumulated by 1993. In 2008, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, and Paducah, Kentucky.

The storage of DUF₆ presents environmental, health, and safety risks because of its chemical instability. When UF₆ is exposed to water vapor in the air, it reacts with the moisture to produce UO₂F₂ (uranyl fluoride), a solid, and HF (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 UF₆. Release of the hydrogen fluoride gas to the atmosphere is also slowed by the plug formation. Storage cylinders are regularly inspected for signs of corrosion and leaks, and are repainted and repaired as necessary.

A tenfold jump in uranium prices has transformed approximately one-third of the U.S. depleted uranium inventory into an asset worth $7.6 billion, assuming DOE re-enriches it. This estimate is based on February 2008 market price for uranium and enrichment services, and DOE's access to sufficient uranium enrichment capacity.

There have been several accidents involving uranium hexafluoride in the United States, including one in which 32 workers were exposed to a cloud of UF₆ and its reaction products. One person died; while a few workers with higher exposure experienced short-term kidney damage (e.g., protein in the urine), none of them showed lasting damage from the exposure to uranium. The U.S. government has been converting depleted UF₆ to solid uranium oxides for use or disposal. Such disposal of the entire DUF₆ inventory could cost anywhere from $15 million to $450 million.

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 84% as dense as 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 less aerodynamic drag and deeper penetration due to a higher pressure at point of impact. DU projectile ordnance is often inherently incendiary because uranium is flammable.

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 M1A1HA 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 hull and the front of the turret, and there is a program to upgrade the rest.

Nuclear weapons

Depleted uranium is used as a tamper in fission bombs.

Ammunition

Most military use of depleted uranium has been as 30 mm caliber ordnance, primarily the 30 mm PGU-14/B armour-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 also 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 made using depleted uranium, later changed to tungsten.

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, Challenger 2, 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.

According to 2005 research, at least some of the most promising tungsten alloys that have been considered as replacement for depleted uranium in penetrator ammunitions, such as tungsten-cobalt or tungsten-nickel-cobalt alloys, also possess carcinogenic properties: rats implanted with a pellet of such alloys developed lethal rhabdomyosarcoma within a few weeks.

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 nose of the rod fractures in such a way that it remains sharp. The impact and subsequent release of heat energy causes it to ignite. When a DU penetrator reaches the interior of an armored vehicle it catches fire, often igniting ammunition and fuel, killing the crew 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. The Russian military has used DU ammunition 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 ammunition is 180 g in 20 mm projectiles, 200 g in 25 mm ones, 280 g in 30 mm, 3.5 kg in 105 mm, and 4.5 kg in 120 mm penetrators. DU was used during the mid-1990s in the U.S. to make hand grenades, cluster bombs, and land mines, but those applications have been discontinued, according to Alliant Techsystems. The US Navy used DU in its 20 mm Phalanx CIWS guns, but switched in the late 1990s to armor-piercing tungsten.

Only the US and the UK have acknowledged using DU weapons.

In a three-week period of conflict in Iraq during 2003, it was estimated that over 1000 tons of depleted uranium munitions were used.

Legal status in weapons

In 1996, the International Court of Justice (ICJ) gave an advisory opinion on the "legality of the threat or use of nuclear weapons". This made it clear, in paragraphs 54, 55 and 56, that international law on poisonous weapons—the Second Hague Declaration of 29 July 1899, Hague Convention IV of 18 October 1907 and the Geneva Protocol of 17 June 1925—did not cover nuclear weapons, because their prime or exclusive use was not to poison or asphyxiate. This ICJ opinion was about nuclear weapons, but the sentence "The terms have been understood, in the practice of States, in their ordinary sense as covering weapons whose prime, or even exclusive, effect is to poison or asphyxiate," also removes depleted uranium weaponry from coverage by the same treaties as their primary use is not to poison or asphyxiate, but to destroy materiel and kill soldiers through kinetic energy.

The Sub-Commission on Prevention of Discrimination and Protection of Minorities of the United Nations Human Rights Commission, passed two motions — the first in 1996 and the second in 1997. They listed weapons of mass destruction, or weapons with indiscriminate effect, or of a nature to cause superfluous injury or unnecessary suffering and urged all states to curb the production and the spread of such weapons. Included in the list was weaponry containing depleted uranium. The committee authorized a working paper, in the context of human rights and humanitarian norms, of the weapons.

The requested UN working paper was delivered in 2002 by Y. K. J. Yeung Sik Yuen in accordance with Sub-Commission on the Promotion and Protection of Human Rights resolution 2001/36. He argues that the use of DU in weapons, along with the other weapons listed by the Sub‑Commission, may breach one or more of the following treaties: the Universal Declaration of Human Rights, the Charter of the United Nations, the Genocide Convention, the United Nations Convention Against Torture, the Geneva Conventions including Protocol I, the Convention on Conventional Weapons of 1980, and the Chemical Weapons Convention. Yeung Sik Yuen writes in Paragraph 133 under the title "Legal compliance of weapons containing DU as a new weapon":

Annex II to the Convention on the Physical Protection of Nuclear Material 1980 (which became operative on 8 February 1997) classifies DU as a category II nuclear material. Storage and transport rules are set down for that category which indicates that DU is considered sufficiently "hot" and dangerous to warrant these protections. But since weapons containing DU are relatively new weapons no treaty exists yet to regulate, limit or prohibit its use. The legality or illegality of DU weapons must therefore be tested by recourse to the general rules governing the use of weapons under humanitarian and human rights law which have already been analysed in Part I of this paper, and more particularly at paragraph 35 which states that parties to Protocol I to the Geneva Conventions of 1949 have an obligation to ascertain that new weapons do not violate the laws and customs of war or any other international law. As mentioned, the International Court of Justice considers this rule binding customary humanitarian law.

Louise Arbour, chief prosecutor for the International Criminal Tribunal for the Former Yugoslavia led a committee of staff lawyers to investigate possible treaty prohibitions against the use of DU in weapons. Their findings were that:

There is no specific treaty ban on the use of DU projectiles. There is a developing scientific debate and concern expressed regarding the impact of the use of such projectiles and it is possible that, in future, there will be a consensus view in international legal circles that use of such projectiles violate general principles of the law applicable to use of weapons in armed conflict. No such consensus exists at present.

Requests for a moratorium on military use

A number of academics specializing in international humanitarian law have questioned the legality of the continued use of depleted uranium weapons, highlighting that the effects may breach the principle of distinction (between civilians and military personnel). Some states and the International Coalition to Ban Uranium Weapons, a coalition of more than 155 non-governmental organizations, have asked for a ban on the production and military use of depleted uranium weapons.

The European Parliament has repeatedly passed resolutions requesting an immediate moratorium on the further use of depleted uranium ammunition, but France and Britain – the only EU states that are permanent members of the United Nations Security Council – have consistently rejected calls for a ban, maintaining that its use continues to be legal, and that the health risks are unsubstantiated.

In 2007, France, Britain, the Netherlands, and the Czech Republic voted against a United Nations General Assembly resolution to hold a debate in 2009 about the effects of the use of armaments and ammunitions containing depleted uranium. All other European Union nations voted in favour or abstained. The ambassador from the Netherlands explained his negative vote as being due to the reference in the preamble to the resolution "to potential harmful effects of the use of depleted uranium munitions on human health and the environment [which] cannot, in our view, be supported by conclusive scientific studies conducted by relevant international organizations." None of the other permanent members of the United Nations Security Council supported the resolution as China was absent for the vote, Russia abstained and the United States voted against the resolution.

In September 2008, and in response to the 2007 General Assembly resolution, the UN Secretary General published the views of 15 states alongside those of the International Atomic Energy Agency (IAEA) and World Health Organization (WHO). The IAEA and WHO evidence differed little from previous statements on the issue. The report was largely split between states concerned about depleted uranium's use, such as Finland, Cuba, Japan,