By Jeff Danner Jeff has worked in both the chemical and biotech industries and is the veteran of thousands of science debates at cocktail parties and holiday dinners across the nation. In his Common Science blog, Jeff aims to make technological and scientific concepts accessible to all.

Depleted Uranium

By Jeff Danner Posted May 6, 2013 at 9:00 am

I recently heard a story on the radio about a study which estimated that the cost for the clean up from the use of depleted uranium weapons in Iraq would be 30-45 million dollars.  Human exposure to depleted uranium occurs in war zones via embedded shrapnel, inhalation of dust, or ingestion of water contaminated by dust.   While I listened to the story, I assumed the health and environmental issues relating to depleted uranium stem from its radioactivity.  It turns out I was wrong.

The primary health risks of depleted uranium stem from it being a toxic heavy metal, like mercury or arsenic, rather than from its low-level radioactivity.   Those exposed to depleted uranium suffer a long list of health problems ranging from neurological damage to a variety of cancers.  In addition, contamination by depleted uranium to both men and women results in increased rates of health issues for their offspring as tragically evidenced by a notable increase in the rates of childhood leukemia in Basra, Iraq.

Uranium ore contains approximately 0.7% of the isotope uranium-235 (U-235), with the remainder being uranium-238 (U-238).   Compare to U-238, U-235 has three fewer neutrons in its nucleus to act as spacers between the positively-charged protons.  The lower number of spacers in the nucleus of a U-235 atom renders it unstable, since the protons are too close together, and causes it to spontaneously break apart (radioactive decay).  This releases both particles and energy.  Since U-238 has a sufficient number of spacers (neutrons) in its nucleus, it is stable and does not undergo radioactive decay.  In a nuclear reactor, the energy from radioactive decay of U-235 is utilized to generate electricity.

Due to the low concentration of U-235, uranium ore in its natural state is neither useful as fuel nor does it pose a significant health hazard.  In order to generate fuel for nuclear reactors, uranium ore is processed to create enriched uranium with high levels of U-235.  The enrichment process leaves behind the bulk of the uranium ore, now called depleted uranium, which has less than 0.4% U-235.  Depleted uranium is very dense, weighing in at 19 grams per cubic centimeter.  This is 19 times denser than water, 1.7 times denser than lead, and approximately equal to the density of tungsten and gold.

Between the 1940s and the 1970s, the nuclear power industry in the U.S. generated significant amounts of depleted uranium, a byproduct with limited use.  Then in the 1970s, the Soviets started to manufacture armor for their military equipment that NATO munitions could not pierce, generating, in typical Cold War fashion, a race to develop bigger and better weapons.

Piercing armored vehicles with projectiles is primarily a question of momentum, which is equal to the mass of the projectile multiplied by its velocity.  Other factors, such as the shape of the projectile and hardness of the metal used to make it also influence performance in armor piercing, but to a lesser extent.  Using a very dense material, like depleted uranium, allows you to make a heavy projectile which is still small enough to have low wind resistance, allowing it to travel at high velocity.  Therefore, projectiles made of depleted uranium hit their targets with very high momentum, allowing them to pierce even the most advanced armor.

Depleted uranium is also used to make weapons because it is pyrophoric, meaning that in the proper conditions, it will spontaneously ignite when exposed to air.  When a depleted uranium shell breaks through the armor of a tank or other military vehicle, it heats up due to the friction from breaking through the wall and also disintegrates into dust.  The hot depleted uranium dust bursts into flames, which kills the occupants and often causes munitions within the vehicle to explode. (When I write these columns, I pick a topic which interests me and then just follow the science where it leads me.  In this case, the images of an incendiary, depleted uranium shell exploding within a tank occupied by several of my fellow human beings fills me with horror.  Whatever your personal philosophy on ethical behavior, somehow this just has to be wrong.)

The U.S. Army and Air Force used depleted uranium weapons in Iraq in 1991 and 2003 and in Bosnia in the 1990s. The U.S. Navy stopped using depleted uranium weapons in 1993, with they switched to tungsten.  Tungsten is heavy enough to pierce armor but does not present long-term health risks.

There have been several attempts by the United Nations to ban the use of depleted uranium, all of which have been blocked by the permanent members of the Security Council.  I believe it is a mistake for the U.S. to oppose this ban.  With our overwhelming global military superiority and our field-tested experience that we can make armor-piercing weapons with tungsten, we should join effort to ban these weapons.  One of our primary foreign policy goals should be to communicate to our fellow human beings around the world that, while we may sometimes enter into military combat with their governments, we are always a friend of the people.  We can start by denouncing the use of depleted uranium weapons and helping the parents of Basra.

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