Nuclear Fuel

The fuel for nuclear power plants is the processed uranium. It exists in a suitable amount in nature for needs of nuclear energy industry. From two main isotopes, U 238 and U 235, only nuclei of U 235 atoms are utilizable for fission reaction. They occur in amount of approximately 0.7 % in natural uranium. Most of reactors utilizes a slightly enriched uranium, i.e. such, in which, share of uranium 235 is increased up to 2 to 4 % by means of special technology.

Fuel in reactor is fissioned, while a higher number of radioactive fission products is generated. Some of U 238 nuclei in fuel are changed into heavier radioactive elements by nuclear reactions. The most important of them is isotope of plutonium Pu 239, which is fissionable and it is a potential fuel. In nuclear reactor, in which uranium is used as fuel, up to one third of released energy originates from fission of plutonium. After fuel is spent, it is removed from reactor and it is stored for a period of 3–4 years in storage basin of spent fuel located near the reactor. Also unspent uranium, plutonium and other heavy elements remain in the spent fuel. After sufficient cooling and decrease of radiation in the storage basin, spent fuel can be reprocessed, by which unused uranium and plutonium are obtained back for new nuclear fuel.

In reactors WWER 440 uranium dioxide UO₂ in form of fuel pellets is used as fuel. These are loaded in fuel rods, from which a fuel assembly consists of. In reactor there are operational and regulation cartridges. Regulation cartridges consist of operational part and regulation part, which is firmly connected with the drive of the regulation cartridge. Electro motor drives of regulation cartridges are located in the upper block above reactor and they serve for performance of operational or safety vertical movement of the regulation cartridges.