Uranium is a metal of the actinide series: a group of large, radioactive elements, represented as an additional row on the periodic table.
It is the heaviest of the naturally occurring elements and has 92 protons and 92 electrons. Like every element heavier than lead – which has 82 protons and 82 electrons – uranium is unstable and will gradually break down, emitting particles of ionizing radiation.
Like all other elements, the number of neutrons in a uranium atom varies, and several isotopes of slightly different molecular weights exist in nature. All uranium isotopes are unstable, but only one is capable of establishing a nuclear chain reaction. The uranium isotope uranium-235 is a fissionable material; when it is struck by a neutron, the nucleus splits, releasing energy and more neutrons, sparking a chain reaction. It is this particular property that makes uranium an ideal fuel source for nuclear power plants, submarines and weapons, among other things.
However, the radioactive decay of uranium poses a significant danger to people and the environment. Not only is uranium radioactive, but it is also toxic and the products of its decay produce ionizing radiation. Therefore, nuclear waste is handled with great care, first being stabilized and then encased in shielded vaults with reinforced, super-thick walls, either above or below ground.
Natural uranium only contains about 0.7 per cent of the most useful isotope, uranium-235, which is insufficient to sustain a nuclear chain reaction. Through a process known as enrichment however, this proportion can be increased up to around 90 per cent.
In order to enrich the uranium, the uranium-235 atoms must be separated from the uranium-238 isotope that makes up over 99 per cent of the natural metal. This is usually done using a gaseous compound of uranium – uranium hexafluoride. The enrichment processes take advantage of the slight difference (less than two per cent) in mass between the two isotopes to gradually increase the amount of uranium-235. The depleted waste material is less radioactive than natural uranium, but is still hazardous and is kept in secure storage for safety.
Uranium is a commonly found element in the Earth’s crust and ore deposits are distributed across the globe, with the highest concentrations in Australia, Kazakhstan and Canada.
There are three main methods for retrieving uranium. It can be extracted using open-pit mining or underground mine shafts. In pit mines, the ore is exposed by drilling and blasting before being cut directly from the ground, while underground shafts are cut for ore buried deeper down.
The third alternative is in-situ leaching, a form of chemical mining. It uses an acid or alkali to dissolve uranium in the ore into a solution, before pumping the fluid to the surface for processing.
Due to its radioactive properties, mining uranium is a dangerous pursuit. As uranium decays it produces radium, which in turn decays to form carcinogenic radon gas. Inhaled radon gas increases the risk of lung cancer. As a result, advanced ventilation systems are installed in uranium mines and workers wear protective gear.