sought to increase the armor penetration of munitions (OSAGWI, 1998). In addition, depleted uranium is useful as a ballast or counterweight in aircraft and gyroscopes because it lends itself to casting into small but dense weights. Additional uses of depleted uranium include as radiation shielding and as a chemical catalyst (it is a strong reducing agent) (Kirk, 1981; Lide, 1999).
The process of converting uranium ore into enriched uranium, with depleted uranium as a by-product, begins with the mining of uranium-containing ore (work previously conducted in deep underground mines but now mostly in surface mines). Sites of significant uranium deposits include the western United States, Canada, southern Africa, and Australia. The milling process crushes the ore and then leaches uranium from the ore with sulfuric acid or alkaline carbonates (du Preez, 1989). The dissolved uranium precipitates as triuranium octaoxide, U3O8 (termed “yellowcake”); this process does not alter the ratio of radioisotopes of uranium (U.S. AEPI, 1995). The enrichment process converts uranium to its hexafluoride (UF6) form, which is a gas, and separates the various isotopes using gaseous diffusion or centrifuge technology, thereby increasing the percentage of 235U in UF6. The remainder of the UF6 (depleted UF6) has a smaller proportion of both 235U and 234U relative to the enriched UF6. The final steps of the milling process are the reduction of depleted UF6 to uranium tetrafluoride (“green salt”) which is further reduced to depleted uranium metal. The Nuclear Regulatory Commission defines depleted uranium as uranium with less than 0.711 percent 235U by weight (10 CFR 40.4). Department of Defense specifications state that depleted uranium used by DoD must have a 235U concentration of less than 0.3 percent (U.S. AEPI, 1995).
In the Gulf War, weapons systems utilized depleted uranium (frequently alloyed three-fourths of 1 percent with titanium by weight to reduce oxidation) for offensive and defensive purposes (Parkhurst et al., 1995; OSAGWI, 1998). Heavy armor tanks had a layer of DU armor to increase protection. Offensively, depleted uranium increases the penetration effectiveness of the kinetic energy cartridges and ammunition rounds used by the Army (105- and 120-mm tank ammunition), Air Force (armor piercing munitions for the Gatling gun mounted on the A-10 aircraft), Marine Corps (Harrier aircraft and tank munitions), and Navy (rounds for the Phalanx Close-in Weapon System)2 (OSAGWI, 1998). The Army used an estimated 9,500 depleted uranium tank rounds during the Gulf War, many as training and practice rounds (OSAGWI, 1998).
Known exposure of U.S. personnel to depleted uranium during the Gulf War occurred as the result of friendly fire incidents, cleanup operations, and accidents (including fires). DU-containing projectiles struck 21 Army combat vehicles (15 Bradley Fighting Vehicles and 6 Abrams tanks) (U.S. AEPI, 1995). Additionally, U.S. forces used DU rounds to destroy three unoccupied Abrams tanks in order to prevent them from being captured by the enemy, and five