Plutonium See Also: Chemical Elements Radioactive Element, first produced artificially by Glenn Seaborg and colleagues in 1940 by deuteron bombardment of Uranium oxide (see Oxidation and Reduction). It is a silver-gray Transuranium Element in the Actinide Series and is found in very small quantities in nature in association with uranium ores. Plutonium is a fission fuel for Nuclear Reactors and weapons (see Atomic Bomb; Nuclear Energy). It is an extremely dangerous poison, collecting in bones and altering the production of white blood cells.