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The nuclear fuel cycle

The nuclear fuel cycle encompasses all the necessary operations for supplying fuel to a nuclear reactor, and for storing, reprocessing and recycling the spent fuel. Uranium in its natural state contains only 0.7% uranium 235, its fissile isotope, the remaining 99.3% being non-fissile uranium 238. Before it can be used in the pressurized water reactors of France’s nuclear power plants, it must be enriched with uranium 235 to reach a concentration of 4 to 5%. Uranium is enriched in the form of a gas and then transformed into an oxide, a black powder that is then compressed into small pellets weighing about 7g each. These pellets are inserted into metal tubes called fuel rods, which are in turn grouped in fuel assemblies and placed in the core of the reactor.
After it is used to generate electricity in the reactor core (2-6 years), the fuel’s uranium 235 is depleted and must be replaced. At this point, its U-238 has also been converted into plutonium and heavier actinides. The fuel is first transferred to a spent fuel pool, where it remains for a few years to allow the most radioactive short-lived fission by-products to decay. The irradiated fuel is then placed in a storage site to await reprocessing or ultimate disposal in a repository.
Reprocessing nuclear fuel involves mechanical and chemical processes to isolate the various elements in the spent fuel, separating those that are potentially reusable, especially uranium and plutonium, from waste products. Known as ultimate or final waste, these waste products are calcined and then vitrified in an inert matrix in preparation for storage.
In France, a part of the plutonium is recycled into MOX (mixed oxide) fuel, a mixture of uranium and plutonium oxides that can be used in certain reactors and in the future EPR.
The uranium, which still represents 95% of the mass of the spent fuel, is also recyclable — it can be re-enriched and used in certain reactors.
The re-enrichment process requires ultracentrifugation, a technology that is only available at the Seversk plant in Russia and the Urenco plant in the Netherlands. At present, France outsources its uranium enrichment primarily to Russia, pending the completion of the Tricastin site at the Georges Besse II plant, which will house an ultracentrifuge. About 10% of the country’s reprocessed uranium (RPU) is re-enriched, while the remainder is stored.
The recycling of part of the spent uranium and plutonium reduces France’s natural uranium needs by about 12% each year.
Countries that have reprocessing plants for nuclear waste include France (at the Hague site), the United Kingdom, Russia and Japan. The US has closed its reprocessing installation for economic reasons. Pro and anti-nuclear factions disagree over the transportation of spent fuel to be reprocessed, that of reprocessed uranium to re-enrichment plants and the risks posed to personnel, the local populations and the environment. Recycling as it is today is not highly cost-effective, since natural uranium can still be obtained at relatively low cost. However, if the use of nuclear power continues to increase around the world, the need for optimal management of natural resources and wastes will require increasingly effective recycling of spent nuclear fuel.