A by-product of uranium enrichment, the most common chemical form of which is depleted uranium hexafluoride (DUF6). Natural uranium is composed of three isotopes: uranium-238 (99.284 percent); uranium-235 (0.711 percent); and uranium-234 (0.005 percent), all of which are radioactive. The purpose of uranium enrichment is to concentrate uranium-235, the fissile isotope, in one stream. The other stream which is low in uranium-235, is called 'depleted uranium' which contains about 0.2 to 0.3 percent uranium-235.