Non-Subscriber Extract
The DU debate: what are the risks?
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| 15 January 2001 |
Rupert Pengelley JDW Technical Editor
London
What is depleted uranium (DU)?
A waste product of the process of extracting the 235U isotope (used in nuclear weapons and power stations) from natural uranium. DU is chemically transformed into a uranium metal, suitable for further processing by ammunition manufacturers. Reports from the US Department of Defense (DoD) indicate that in this state it has about 0.002% 234U, 0.2% 235U and 99.8% 238U, and about 60% of natural uranium's radioactivity.
Military uses?
DU is a heavy metal that, when alloyed with titanium (up to 0.75% by weight), becomes a material with a density (18,600kg/m3) and ductility suited to making penetrators for kinetic energy anti-tank munitions, or liners for shaped-charge warheads. Plates of DU also form part of the frontal armour of the US Army's M1A1 and M1A2 tanks. It is planned to incorporate additional plates in the turret sides as part of the upgrade programme.
Is it radioactive?
Radiologically, DU emits types of ionising radiation similar to that of natural uranium, but DU is 40% less radioactive than natural uranium, whose specific radioactivity is about 0.67 microCuries/gm.
Although DU emits Alpha and Beta particles and Gamma rays, the 238U isotope - which by weight makes up almost 99.8% of DU - is an alpha emitter. Scientific research indicates most alpha particles are not energetic enough to penetrate skin and are not considered an external health hazard. Internally however, alpha particles can be a hazard if inhaled or ingested in sufficient quantities.
Is it poisonous?
In common with tungsten, DU is toxic. DoD research shows that in combat environments, DU may enter the body through inhalation, ingestion, or wounds - in the form of uranium metal (from flying fragments and unoxidised DU) and uranium particles from DU impacts on target vehicles or fire). The kidney is particularly susceptible to damage from high doses of uranium. Uranium's toxic effects on the kidney resemble those caused by other heavy metals, such as lead or cadmium. As the target organ for uranium, medical experts would expect the kidney to show the most dramatic effects from uranium exposure. The US Veterans Association conducted extensive testing in 1993-94, 1997 and 1999 and documented no kidney abnormalities, even in 1990-91 Gulf War veterans with retained DU fragments who are excreting elevated levels of uranium in their urine.
Why use it?
At the velocities of current kinetic-energy tank and aircraft munitions (1,000-1,800m/s), DU penetrators are superior to those of other heavy metal penetrators made of tungsten alloys because their flow-softening and adiabatic-shear failure modes inhibit the build-up of a large mushroom head on the penetrator. This results in narrower but deeper penetrations (10-20% greater). DU also has significant pyrophoric properties, normally setting the target on fire. DU is also cheaper than tungsten.
What happens when a DU round hits a tank?
When the penetrator hits the tank armour both the penetrator and the armour partially liquify under pressure, the molten materials initially flowing outwards. Once the armour has been perforated, the part of the penetrator that has not melted, together with the molten armour and fragments that break away from the inner surface, ricochet around the interior of the vehicle. These, in combination with pyrophoric particles from the DU penetrator, can cause flammable materials and ammunition charges to ignite, further disrupting the target.
Studies in the USA, UK and France show that when an armoured vehicle burns at about 10,000°C, the resulting oxidisation of the materials aboard, including benzene products and depleted uranium, can create particulates that are harmful to the human body; ingested they can affect the lungs and kidneys.
In US Army trials conducted after the 1990-91 Gulf War, it was shown that some 20% of the penetrator mass can be turned into an aerosol as a consequence of target impact. The aerosols contain respirable-sized DU particles. The concentration of airborne DU aerosol decreases with time, but measurable concentrations of respirable particles do remain suspended hours later.
Can tungsten penetrators be improved?
The claim has been made that future tungsten alloy penetrators will perform as well as, or even better than DU penetrators, and at the same time will not be environmentally hazardous. However, this increased performance will only be gained by imparting a higher velocity to the penetrator than is possible with current tank guns.