Complex technological process of treatment of nuclear fuel from mining of uranium ore to storage of spent nuclear fuel is called the fuel cycle. When mentioning the final permanent storage of spent nuclear fuel, we speak about an open fuel cycle, and in case of reprocessing of utilizable part of spent nuclear fuel to new nuclear fuel, we speak about closed fuel cycle.

Open fuel cycle does not consider reprocessing of SF and it is supposed that fuel will be, after stage of intermediate storage, permanently stored. However, the storage has not been executed yet, so there is still the opportunity of its reprocessing and further utilization. This cycle is used not only by all the countries with reactors of PWR type, but also by other countries with other types of reactors. The main reasons of utilization of open fuel cycle are high expenses connected with technology of SF reprocessing and comparatively low prices of natural uranium as a result of decrease of its consumption and recovery of new deposits.

Reprocessing of fuel, its conversion, or production of new nuclear fuel makes it possible to interconnect the back and the front parts of nuclear fuel processing into a closed fuel cycle. Closed fuel cycle is generally considered to be very prospective and methods of fuel reprocessing are being improved thereinafter.

The front part of fuel cycle comprises:

> Mining and treatment of uranium ore
> Processing of ore
> Refining, conversion and enrichment of uranium
> Production of fuel

The back part of fuel cycle comprises:

> Temporal storage of spent fuel
> Reprocessing of spent fuel
> Definitive storage of spent fuel