Natural uranium is poor in the fissile isotope, containing as it does only 0.70% of uranium 235. Certain uranium compounds (hexavalent ones) are highly soluble whereas others (tetravalent) are not.Īs a particularly heavy element, uranium isotopes are primarily alpha emitters, though these radiations are sometimes accompanied by gamma rays. Uranium can be found in the Earth crust at 3 parts per million, particularly in granite and volcanic rocks. PHILIPPE LESAGE/COGEMA From a chemical point of view, uranium belongs to the actinide family, a group of atoms whose properties are similar to those of actinium, the 89th element in Mendeleyev’s periodic table. The photograph above shows the ‘yellow cake’ on a filter at a treatment plant in Jouac (Haute-Vienne) at Limousin, France. This high concentration makes it much easier to transport the uranium from the mine to the factory. The concentrated uranium they are handling, also known as ‘Yellow Cake’, takes the form of a bright yellow powder containing about 750kg of uranium per tonne. The radioactivity of uranium is low, and so no particularly high standards of radioprotection are needed: as can be seen with the above workmen. They were all formed billions of years ago by the explosion of heavy stars (supernovae). The nuclei of uranium 235 and 238 are, along with those of thorium 232, the heaviest present in nature. Though both isotopes were at the time of Earth formation equally abundant, natural uranium today consists today of 99.3% uranium 238 and only 0.70% uranium 235. The half-life of uranium 238 is of 4.5 billion years, while uranium 235 has a half-life of ‘only’ 700 million years. HARRY GRUYAERT /MAGNUM /AREVAAll isotopes of uranium are unstable and radioactive, but uranium 238 and uranium 235 have half-lives which are sufficiently long to have allowed them to still be present in the Solar System and indeed on Earth. This high abundance, taken in conjunction with the difficult geological conditions and the harsh climate have made the extraction process an almost entirely automated one. Western Canada is particularly rich in uranium, with anywhere between 28 to 210 kilograms of uranium per tonne as opposed to the usual 3 grams per tonne found elsewhere.
Athabasca plateau in Saskatchewan province, Canada.