Reprocessing
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The reprocessing facility at La Hague, France, processes spent nuclear fuel from France and several other countries around the world.
Spent nuclear fuel from a light water reactor typically contains about 96% uranium, around 1% plutonium and approximately 3% fission products and other radioactive elements. Most of the uranium and plutonium can potentially be recovered and recycled into fresh nuclear fuel, reducing the requirement for newly mined uranium. Reprocessing also concentrates the highly radioactive waste: reprocessing one tonne of spent nuclear fuel typically produces around 100—150 kg of vitrified high-level waste.
Uranium
Nuclear reprocessing was developed in part to recover the uranium contained in spent fuel. Reprocessed uranium from typical PWR fuel consists predominantly of 238U and contains about 1% 235U, which is still more than in natural uranium. It also contains extremely small quantities of 232U, whose decay products emit intense gamma radiation and make fuel handling more difficult. About 0.4—0.6% of reprocessed uranium consists of 236U, which acts as a neutron absorber and reduces the reactivity of the fuel.
Recovered uranium can be converted and re-enriched for reuse as nuclear fuel. Because of the presence of 236U and other isotopes, a somewhat higher 235U enrichment is required than for equivalent fuel produced from natural uranium. The resulting fuel can subsequently be reprocessed and recycled again, although the accumulation of undesirable uranium isotopes makes repeated recycling progressively more demanding.
Changes in the composition of uranium fuel during irradiation in a nuclear reactor.
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Spent nuclear fuel also contains valuable fission products, including platinum-group metals such as ruthenium, rhodium and palladium. Their recovery for industrial use has been investigated, although radioactive contamination and the complexity of separation currently limit practical applications.
MOX
Sellafield is one of the largest nuclear sites in Great Britain. Once a major centre for spent fuel reprocessing, it is now focused primarily on nuclear waste management, spent fuel storage and decommissioning.
MOX is an acronym for mixed oxide fuel, a mixture of uranium oxide and plutonium oxide (UO2 and PuO2). It is manufactured using plutonium recovered during the reprocessing of spent nuclear fuel, mixed mainly with depleted uranium. MOX currently accounts for almost 5% of newly manufactured nuclear fuel worldwide and has been used in dozens of light water reactors, particularly in Europe and Japan. Depending on the reactor design and licence, MOX may replace part or, in specially designed reactors, potentially all of the conventional uranium fuel in the core.
MOX fuel is typically manufactured by mixing plutonium oxide with depleted uranium oxide. The required plutonium content depends on its isotopic composition and the reactor in which the fuel will be used. MOX containing about 7% reactor-grade plutonium can have a fissile content comparable to conventional uranium fuel enriched to around 4.5% 235U. If weapons-grade plutonium containing more than 90% 239Pu is used, a lower plutonium concentration of around 5% can provide a similar fissile content.
In France, plutonium recovered from spent fuel at the Orano La Hague reprocessing plant is used to manufacture MOX fuel at the Melox plant in Marcoule.
Changes in the composition of MOX fuel during irradiation in a nuclear reactor.
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Plutonium
The spent fuel reprocessing facility at La Hague is subject to stringent nuclear safety and security requirements.
Recovered plutonium contains a mixture of isotopes whose composition depends primarily on the fuel burnup and irradiation history. In typical spent light water reactor fuel, the fissile isotopes 239Pu and 241Pu make up roughly two-thirds of the plutonium. Around 70 tonnes of plutonium are contained in the spent fuel discharged from the world’s reactors each year, although only part of this material is recovered through reprocessing.
Separated plutonium is preferably fabricated into fresh fuel without prolonged storage. The isotope 241Pu has a half-life of about 14 years and decays into 241Am, a strong gamma emitter that increases radiation exposure during subsequent fuel fabrication. Recovered plutonium is therefore commonly recycled relatively soon after separation, primarily in the form of MOX fuel.
Repeated recycling of plutonium in thermal reactors is limited by changes in its isotopic composition, whereas fast reactors can potentially support multiple plutonium recycling cycles.
A single recycling of plutonium as MOX fuel can increase the energy obtained from the original uranium by about 12%; if the recovered uranium is also recycled, the increase can reach about 22%.
The La Hague nuclear fuel reprocessing site in Normandy, France, contrasts with the surrounding rural landscape.
Reprocessing Method
Most commercial reprocessing facilities use the PUREX (Plutonium Uranium Reduction EXtraction) process. After the fuel assemblies are dismantled, the fuel rods are remotely cut into short sections and the fuel is dissolved in hot nitric acid. Uranium and plutonium are then separated from the fission products and other radioactive elements by solvent extraction and subsequently purified for possible reuse.
Commercial and state-operated reprocessing facilities exist in several countries, including France, Russia and India, while Japan has developed the large Rokkasho reprocessing plant. France’s La Hague facility is the world’s largest commercial reprocessing centre, with a licensed capacity of 1,700 tonnes of spent fuel per year.
Weapons-grade plutonium recovered from dismantled nuclear weapons can be mixed with depleted uranium to produce MOX fuel for use in suitable nuclear reactors.
After uranium and plutonium have been separated, the remaining highly radioactive waste stream contains most of the fission products and minor actinides. It is concentrated and mixed with glass-forming materials before being melted to form durable borosilicate glass in a process known as vitrification. The vitrified high-level waste is poured into robust containers and stored pending eventual geological disposal. When foreign spent fuel is reprocessed under commercial contracts, the resulting high-level waste is generally returned to the country of origin.
The first nuclear fuel reprocessing facilities were constructed to produce weapons-grade plutonium.
The Orano La Hague reprocessing facility is one of several major nuclear facilities located on the Cotentin Peninsula in Normandy, north-western France.
