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The nuclear fuel cycle

The electricity supplied by nuclear power plants is produced by the steam generated by the heat released after the fission of uranium 235 used as nuclear fuel. Before being loaded into the reactor, uranium goes through several processes known as the “nuclear fuel cycle”.
In France, the irradiated fuel is reprocessed and partially recycled before reuse.
The successive steps of the nuclear fuel cycle could be described as follows:
  1. Ore mining
First of all, the uranium ore which contains generally 0,1% of uranium is extracted. The rocks are then crushed and finely ground into a thin powder.

  1. Concentration
After several chemical operations, the uranium is concentrated into a powder containing uranates, called “yellow cake”.
 
  1. Conversion

The yellow cake is then purified and converted by AREVA NC, first into uranium tetrafluoride (UF4) at Malvési, near Narbonne, and further into uranium hexafluoride (UF6) at the Pierrelatte site.

  1. Enrichment

Natural uranium consists mainly of 2 radioactive isotopes in following proportions: 99.3% 238U and 0.70 % 235U. The enrichment process is meant to increase 235U content up to between 3 and 5 %, the necessary level for operating pressurised water reactors (PWR).

Enrichment is now performed by centrifugation.
 
In France, this process is used by SET, an AREVA subsidiary, at the Georges Besse II plant, on the Pierrelatte site.
 
  1. Production of fuel assemblies
After enrichment, uranium hexafluoride (UF6) is transformed into a black powder of uranium oxide (UO2). This powder is then compressed into pellets of one cm long and further sintered in a furnace.
These pellets are encased into 4 m long zirconium tubes to form fuel rods, of which both ends are welded. In a nuclear reactor, about 50.000 rods are arranged into fuel assemblies to form the core of the reactor.
AREVA NP produces nuclear fuel out of natural (Unat) and reprocessed (URe)uranium in its plant located at Romans-sur-Isère.
 
  1. Fuel utilization at nuclear power plants

The assemblies are loaded into the reactor vessel and the fuel will gradually transform with time and become less efficient. The fuel assemblies will eventually have to be pulled out of the reactor vessel and stored in the spent fuel pool for a safe radioactive decay.



  1. Reprocessing
After being unloaded, the nuclear fuel which still contains an important quantity of fissile material will be reprocessed. This operation is performed in France at the AREVA NC site at La Hague in order to recover the fissile portion in the used fuel: plutonium and uranium, which is recycled once only into a new fuel called MOX (Mixed OXide of plutonium and uranium). During this process, the high level radioactive waste is separated and stored in specially designed disposal facilities.