Uranium in nature

Uranium is a fairly common element on Earth. For example, there is uranium in granite everywhere. There are also small amounts of uranium in sea water.

The average uranium concentration in the Earth´s crust is four grammes per tonne and in sea water three milligrammes per tonne. Uranium is mined only from deposits where its concentration is much higher than the average. The uranium concentration in deposits exploited today is generally dozens of kilos per tonne of ore.

The biggest known uranium reserves are in Australia, North America, Kazakhstan, Russia, South Africa, Niger and Namibia.

Nature´s own nuclear reactors have been operating for millions of years in the world´s richest uranium deposits. The best known of these is Oklo in Gabon, where a natural reactor was in operation almost two billion years ago, when the concentration of the fissile U-235 isotope of uranium was more than 3% - Nature´s own light-water reactor fuel. The Oklo reactor is thought to have run for hundreds of thousands of years, creating the same radioactive substances as modern nuclear power plants. This nuclear waste, however, has already decayed into stable elements which have remained at their location of origin.

Oklo natural reactor