Uranium is a heavy, metallic, naturally Radioactive Element of Atomic Number 92. It has two principle isotopes of uranium-235 and uranium-238 (and very small quantities of Uranium-234). The proportions of natural uranium by weight are about 0.01% Uranium-234, 0.072% Uranium-235, and 99.27% U-238. Uranium-235 is used in the the nuclear industry because it is fissionable by Thermal Neutrons . Natural uranium is extracted from uranium ore where it starts life as a processed uranium oxide (Yellow Cake). Following this the uranium will undergo a process of enrichment where the concentration of U-235 is increased. A byproduct of this process is depleted uranium which can be used for radiation shielding due to its high density.