Uranium, a radioactive metallic element, is the only natural material capable of sustaining nuclear fission. But only one isotope, uranium–235, which occurs in one molecule out of 40 of natural uranium, can undergo fission under neutron bombardment. Mined in various parts of the world, it must then be converted during purification to uranium dioxide (UO2). Uranium deposits occur throughout the world, with approximately 75 percent of all known uranium deposits in Australia. Other countries with significant deposits are Kazakhstan (17 percent of the world’s total), Canada, United States, South Africa, Namibia, Brazil, Niger, and Russia. Canada is the largest exporter of uranium.
