Reality → Energy → Nuclear energy → Uranium
The element with the atomic number 92 is a heavy metal [1] used as a nuclear energy source. Mined ores [2] contain 0.2% to 3% uranium metal consisting basically of two radioactive isotopes: 99.3% U-238 (half-life 4.5 billion years) and 0.7% U-235 (half-life 700 million years) [3] . The recovery of uranium from the ore and the subsequent enrichment of the fissile isotope U-235 involves extensive chemical and physical processing [4] . The enriched reactor-grade uranium contains 3% to 5% U-235, but the 'depleted' uranium still contains a large proportion of the fissile material [5] .
Uranium mining has to struggle with complex geological conditions, health risks, sharp drop in prices and uncertain markets.
At the mine site, yellowcake (consisting basically of uranium oxides) is extracted from the ore through a complex hydrometallurgical process. At the enrichment plant, the yellow cake is transformed into uranium hexafluoride through a series of chemical processes. The hexafluorides of the two uranium isotopes are then separated in gas centrifuges (as the difference in density is only 1%, a large number of cascading centrifuges and long operating times are involved).
The depleted uranium still contains about one quarter of the U-235 contained in the natural uranium feedstock. For each kg of reactor-grade uranium produced about 6 kg of depleted uranium are rejected, of which only a small portion is being used (mainly by the military for protective armor plating and high penetration bullets, making use of the metal’s high density). The bulk of the depleted uranium (about 95 %) is stored as waste in the form of uranium hexafluoride at the enrichment plant.