uranium (U) /yo̅o̅rā″nē·əm/ [planet Uranus] , a heavy, radioactive metallic element. Its atomic number is 92; its atomic mass is 238.03. Uranium is the heaviest of the natural elements. Isotopes of uranium are used in nuclear power plants to provide neutrons for the nuclear reactions that result in release of energy. The toxicity of uranium varies according to its chemical form and route of exposure.
