Uranium is a metal with mysterious properties. It provided man with the key that unlocked the tremendous energy of the atom. The natural radiation of uranium has been put to amazing uses in medicine, agriculture, industry, and biology.
A chunk of pure uranium metal looks about the same as a piece of silver or steel. But it is surprisingly heavy for its size. A 0.3 metre cube of uranium weighs over half a tonne. Uranium is the heaviest element found in nature.
Uranium has two very unusual characteristics. It is radioactive, which means its atoms break down slowly, releasing energy in the form of radiation. Some of its atoms are fashionable; that is, they can be made to explode and break in two, releasing vast amounts of energy. Uranium’s fissionability is the basis of all nuclear-power plants and nuclear weapons.
Chemically, uranium is very reactive. A piece of uranium exposed to air quickly develops a blackish coating. This coating is a combination of the uranium and the oxygen in the air. Uranium also forms important compounds with many other elements.
Uranium is widely distributed in small amounts, but is never found in nature in a pure state. Extracting uranium from its ores is a long and complicated process. Mills process hundreds of tonnes of ore a day, but only a few kilos of uranium are collected from each tonne.
The ore is first crushed and screened. Then it is treated with various chemicals to remove impurities. The ore is then put through many refining processes until a bright, claylike material called yellow cake is obtained. This highly purified form of uranium is fissionable.
A kilo of uranium contains as much energy as nearly three million kilos of coal. In nuclear reactors the shattering uranium atoms produce tremendous quantities of heat as the chain reaction builds up. This heat can be used to turn a turbine, which drives an electric generator.