Depleted uranium is a byproduct of the uranium enrichment process used to generate fuel for nuclear power plants. Depleted uranium is so named because it has been partially depleted of radioisotopes, the abundance of both 235U and 234U is lower than natural (it may also contain 236U). The ratio of 238U to 235U in natural uranium is 137.88; in depleted uranium, it is 314.95 (Roth et al., 2003). The chemical properties of depleted uranium are the same as those of the enriched and natural forms (ATSDR, 1999b).
The need for enriched nuclear fuel has been present for decades, so depleted uranium, a byproduct of the enrichment process, is abundant and inexpensive. The chemical and physical properties of depleted uranium make it ideal for several military and commercial uses. It is 67% denser than lead (with a density of 18.9 g/cm3), has a high melting point (2070°F, 1132°C), is highly pyrophoric, has a tensile strength comparable with that of most steels, and is chemically highly reactive (Kirk, 1981). It is used in commercial products, such as radiation shielding in medical equipment, aircraft counterweights, rotors, flywheels, ship ballasts, and gyroscopes (Cantaluppi and Degetto, 2000; Betti, 2003; Sztajnkrycer and Otten, 2004).
The US Army began researching the use of depleted uranium for military applications in the early 1970s (Bleise et al., 2003), and depleted uranium is now used both offensively and defensively. In the Gulf War, heavy-armor tanks had a layer of depleted-uranium armor to increase protection, and depleted uranium was used in kinetic-energy cartridges and ammunition rounds 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) (DOD, 2000). The Army used an estimated 9,500 depleted-uranium tank rounds during the Gulf War, many in training and practice (DOD, 2000).
The US military has continued to use depleted-uranium weapons. Ammunition containing depleted uranium was used in Bosnia-Herzegovina in 1994-1995 and in Kosovo in 1999 (Cantaluppi and Degetto, 2000; Bleise et al., 2003). According to North Atlantic Treaty Organization records, about 10,800 depleted-uranium rounds were fired in Bosnia-Herzegovina and about 30,000 in Kosovo (Bleise et al., 2003). Depleted-uranium–containing weapons have been used in Operation Iraqi Freedom (OIF), which began in 2003 (Burkart et al., 2005; NRC, 2008).
The Gulf War marked the first time that depleted-uranium munitions and armor were extensively used by the US military (DOD, 2000). The Iraqi forces