Key principles
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Learn about the key basic principles to better understand our research on nuclear fuel and the fuel cycle.

The Research Institute for Nuclear Systems for Low-Carbon Energy Production (IRESNE) has a strong department devoted to nuclear fuel studies and the fuel cycle.

Portion d'assemblage combustible composé de tronçons de gaine de combustible avec bouchons et d'une portion de grille d'espacement des crayons.

What do we mean by nuclear fuel cycle?
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The nuclear cycle refers to the life cycle of the nuclear fuel


The fuel cycle starts with the mining, manufacturing, reprocessing and then recycling of fuel used in nuclear power plants. All these phases are analysed in depth to find ways of optimising the cycle and limiting the volume and toxicity of the nuclear waste produced.​

IRESNE - Un institut du CEA

What are the institute’s objectives?
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The institute’s roadmap states several objectives:


  • Meeting the needs of its industry partners EDF, Orano and the French national radioactive waste management agency (Andra)


  • Studying the possibilities of recycling the nuclear fuel from pressurised water reactors multiple times


  • Preparing and developing material management options for the future fleet of nuclear reactors, known as the fourth generation.
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Prélèvement d'échantillons par analyse lors des essais de validation des performances du procédé d'extraction sélective de l'uranium.

A closed fuel cycle
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France has chosen to work towards closing this fuel cycle


This configuration makes it possible to recycle any material that can be recovered from the spent fuel (uranium and plutonium) and to optimise the management of final waste. Nuclear fuels retain most of the uranium-238 and part of the uranium-235 that was initially contained in the fuel. It also contains highly radioactive fission products, plutonium and minor actinides.


In a closed-cycle configuration, the uranium and plutonium are removed from the spent fuel so they can be reused in new fuel assemblies. This reprocessing makes it possible to reduce the level of radioactivity by a factor of ten in nuclear waste because the plutonium has been removed. ​​

Pressage des poudres UO2 et PuO2 pour constituer un comprimé cru de MOX.

MOX fuel
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The new fuel manufactured with the recycled plutonium from spent fuel is called MOX, which is a mixture of plutonium and depleted uranium oxide. However, this fuel can only be reused once in a PWR because of the existence of plutonium isotopes that can prove difficult to use in the PWR technology. This is what we call "once-through” recycling.


IRESNE is currently leading research in the field of multiple recycling and its feasibility for this reactor technology.​​

Le mur d'images de la DES, permet de visualiser en immersion 3D des résultats de simulations de fonctionnement ou des procédés liés aux réacteurs nucléaires. modélisation en soutien à la conception d'un réacteur à nutrons rapides refroidis au sodium. Etude de la tenue mécanique des structures à la propagation d'une onde de pression.

Fast reactors
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This reactor technology allows the full recycling of spent fuel, which is a strong advantage.

Such reactors can be designed to:

  • Regenerate plutonium and therefore supply its own fuel, i.e. fast breeder mode.


  • Consume plutonium, i.e. burner mode.


  • Produce as much plutonium as it uses.


Fast reactors also produce four times fewer minor actinides than PWRs. They can burn these elements and thus transform them into fission products with much shorter half-lives. This is known as transmutation.


Studies on transmutation are underway all over the world, and more specifically at the CEA.​

Learn more about research on nuclear fuel and the fuel cycle at IRESNE.