Uranium with a percentage of uranium-235 lower than the 0. 7 percent (by mass) contained in natural uranium. (The normal residual U-235 content in depleted uranium is 0. 2?. 3 percent, with U-238 comprising the remaining 98. 7?8. 8 percent. ) Depleted uranium is produced during uranium isotope separation and is typically found in spent fuel elements or byproduct tailings or residues. Depleted uranium can be blended with highly-enriched uranium, such as that from weapons, to make reactor fuel. For further detail, see Background Information on Depleted Uranium and Fact Sheet on Depleted Uranium and Other Waste Disposal.