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JANE'S DEFENCE WEEKLY
15 January 2001

The DU debate: what are the risks?

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.