What Is Uranium?
QUICK ANSWER
Uranium is a radioactive chemical element with atomic number 92 and the symbol U. It is a heavy, silvery-gray metal that occurs naturally in trace amounts in rocks, soil, and water. Uranium is best known as the fuel for nuclear power plants and the source material for nuclear weapons.
Uranium is one of the most consequential elements in modern history. It powers nuclear reactors that supply about 10% of the world's electricity. It was used to build the first atomic bombs. And it has a half-life so long that natural uranium in Earth's crust today has been decaying since before the planet formed. Its energy density is millions of times greater than any chemical fuel.
Where is uranium on the periodic table?
Uranium has atomic number 92, the symbol U, and sits in the actinide series in the bottom row of the periodic table. It is the heaviest naturally occurring element in significant amounts. Natural uranium is made up of three isotopes: U-238 (99.27%), U-235 (0.72%), and U-234 (trace). U-235 is the fissile isotope used in nuclear reactors and weapons. U-238 is fertile, meaning it can be converted into plutonium-239 in reactors. Uranium was discovered by Martin Klaproth in 1789 and named after the planet Uranus.
What are the properties of uranium?
Uranium is a heavy metal with a density of 19.1 g/cm³, almost twice as dense as lead. It is silvery when freshly cut but tarnishes to a dark gray in air. The melting point is 1,135°C. Uranium is malleable, ductile, and slightly paramagnetic. All uranium isotopes are radioactive, though their long half-lives (4.5 billion years for U-238, 700 million years for U-235) mean natural uranium is only weakly radioactive in small quantities. Concentrated uranium and especially enriched uranium become significant radiation hazards requiring careful shielding.
What is uranium used for?
Nuclear reactors use uranium fuel, typically enriched to 3-5% U-235, to generate electricity. About 440 commercial reactors worldwide produce roughly 10% of global electricity. Nuclear weapons require highly enriched uranium (over 90% U-235) or plutonium derived from uranium. Depleted uranium, the U-238 left after enrichment, is used in some military armor and ammunition because of its density. Uranium is also used in medical isotope production, scientific research, and historically in glassware and ceramics for its yellow-green color before its radioactivity was understood.
How is uranium mined and processed?
Uranium is mined either through traditional open-pit and underground methods or through in-situ leaching, which dissolves uranium directly from rock using injected solutions. The mined ore is processed into uranium oxide concentrate called yellowcake. For most reactor fuel, yellowcake is converted to uranium hexafluoride gas and enriched in centrifuges to increase the U-235 fraction. Enriched uranium is then converted to fuel pellets, packed into rods, and assembled into fuel bundles. Kazakhstan, Canada, and Australia produce most of the world's uranium today.
Uranium is the heavy, radioactive element that made nuclear power and nuclear weapons possible. Mined from rocks containing parts-per-million amounts, it provides millions of times more energy per gram than chemical fuels, with all the benefits and dangers that energy density brings.
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