Uranium

Uranium (chemical symbol: U) is a heavy, radioactive metal, meaning its atoms spontaneously decay and release energy. It belongs to the actinide group and is the heaviest element found in significant quantities on Earth. Uranium is dense, pale silvery-white in colour, and tarnishes rapidly in air.

It occurs in rocks and soil worldwide, but only in small, concentrated deposits (ore bodies) is it economical to extract commercially. The most important isotopes are U-238, which constitutes the vast majority of natural uranium, and U-235, which accounts for less than one per cent but can sustain a chain nuclear reaction.

Chemical and radioactive properties

Uranium has atomic number 92, meaning its nucleus contains 92 protons. The decay of its isotopes is slow and proceeds over long periods; consequently, natural uranium still exists in the Earth despite the planet's age in billions of years. When U-238 decays, it produces a chain of other elements, including radium and radon gas. The radiation uranium emits is mostly alpha particles, which cannot penetrate skin but are hazardous if inhaled or ingested.

Mining and enrichment

Uranium ore is extracted through open-pit mining, underground mining, or in-situ leaching, in which liquid is injected into the ground to dissolve and extract the metal. The ore is then processed into a product called yellowcake. For use in standard reactors, the proportion of U-235 must be increased—a process called enrichment, typically performed using rapidly spinning machines called centrifuges. The degree of enrichment determines whether the fuel is intended for civilian nuclear power or other purposes.

Uses

The primary use is as fuel for nuclear reactors that generate electricity. In these reactors, the splitting of U-235 atoms releases heat, which is used to boil water and drive turbines. Depleted uranium—uranium with low fissile content—is employed for shielding and military equipment. Additionally, the rate of uranium decay is used to determine the age of rocks and geological formations.

Policy and oversight

Because the technology for enrichment can be applied to both civilian fuel and weapons, the trade and processing of uranium are governed by international agreements and oversight by the International Atomic Energy Agency (IAEA). Some countries have restrictions on the level of enrichment permitted and limits on stockpiles.