The fuel in nuclear power plants is made of uranium. Fuel
manufacture begins with the separation of the uranium ore from base rock
and foreign minerals and the processing of the ore into powdered
uranium concentrate (U3O8).
This is done in ore enrichment plants, often located close to or in connection to the mine. The uranium concentrate is transported in barrels to the conversion plant for the next processing stage.
In the conversion process, the uranium concentrate is chemically purified of any impurities and converted into uranium hexafluoride, UF6. In converted uranium, the concentration of isotope U-235 remains unchanged at 0.7 percent. At the conversion plant, the uranium hexafluoride is packed into specially designed transport containers compliant with official regulations and then transported to the isotope enrichment plant.
In isotopic enrichment, the U-235 concentration of the uranium is increased from 0.7 percent to the 3–4 percent required of a nuclear fuel. The enriched uranium is in the form of uranium hexafluoride. About six tonnes of natural uranium is required to produce one tonne of uranium that has been isotope-enriched to three percent. After enrichment, the uranium is transported to the fuel manufacturing plant in special pressure tanks and protective packaging.
In the fuel manufacturing process, the uranium hexafluoride is first converted into uranium dioxide powder, which is then compressed into small pellets. The pellets are condensed by sintering, i.e. heating them to about 1,700 degrees. The fuel pellets of about 1 cm in diameter are then stacked into fuel rods manufactured of a zirconium alloy. After this, the fuel rods are compiled into fuel assemblies. The geometry of the fuel assembly depends on the fuel type.
The fuel is transported to the power plant as fuel assemblies. Due to the low radioactivity of fresh fuel, the packaging does not need to be radiation protected.
Leading uranium suppliers have mining operations in many countries. Kazakhstan, Canada, Australia, and Namibia are the countries that produce the largest amounts of uranium at present.