This is the totality of the operations undergone by the uranium before and after its period in the reactor. Uranium is a mineral, quite widespread over the earth’s surface and very abundant in Canada, Australia, Kazakhstan…
But, generally, there are only between 1 and 3 kg of uranium in each ton of the mineral!
In France, the last uranium mines were closed at the end of the 1990’s: the deposits were of mediocre quality (low U235 content), and extraction was not a profitable operation.
The company Cogeman, (part of the Areva group), exploits the uranium cycle industrially in France.
On site, close to the mines, the uranium is concentrated and transformed into a yellow powder, commonly called yellow cake, which contains 75% of uranium. It is in this form that the uranium is marketed.
The powder is subsequently transformed into gas, uranium hexafluoride,
by a chemical process, then enriched to U235. The proportion of U235 in natural radiation is only 0.7%, but for nuclear fuel it must be between 3% and 5%.
Enrichment in France is carried out by gaseous diffusion. Some foreign countries use other processes.
The enriched uranium is then transformed into uranium oxide, in the form of a brown powder which is compacted into small pellets which weigh only 7g each but which contain an enormous quantity of energy (15g, that is to say, 2 pellets, are the equivalent of 1 ton of oil).
These pellets are stacked into very long and very narrow tubes called fuel tubes that are grouped together in bundles called fuel assemblies.
These assemblies remain in the reactor core for 3 to 4 years, during which time they undergo the chain reaction and supply energy.
In France, each reactor consumes about 27 tons of enriched uranium per year.
The proportion of U235 is gradually reduced (uranium 235 is consumed by the fission reaction), and a third of the assemblies are replaced every three or four years, whilst the reactor is deactivated. This is called the reloading operation.
The spent assemblies, containing fission products, give off heat and are very radioactive. They are placed in lagoons, so that they cool down in surroundings that absorb the radiation (water acts as a barrier which stops the propagation of radioactivity).
Some countries consider all the fuel assemblies as waste, and envisage stocking them as they are in order to isolate them permanently from the environment; it is the case of the United States.
In France, the spent fuel is re-treated:
- to recover and to recycle 90% of the matter that can still supply energy; and
- to reduce the final volume of waste to be stored.
Japan, Germany, England and Belgium also re-treat some or all of their spent fuels.
The re-treatment operation means that plutonium is recovered and used in a mixture with uranium to produce a fuel called Mox. This fuel is used in some reactors in France.
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