Uranium mostly consisting of the non-fissionable isotope uranium-238, obtained as a by-product of enriching natural uranium in a nuclear reactor, or obtained from nuclear reprocessing plants. Being radioactive with a half-life of many thousands of years, it therefore needs to be stored for indefinite periods of time. It has a very high density of 19,000 kg m−3 and has found use in various military applications such as coatings for armour-piercing missiles.