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The Nuclear Fuel Cycle

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The Nuclear Fuel Cycle THE COLLECTION > From the uranium mine> toI wNTasRtOeD dUisCpToIsOaN l 1 > The atom 2 > Radioactivity 3 > Radiation and man 4 > Energy 5 > Nuclear energy: fusion and fission 6 > How a nuclear reactor works 7 > The nuclear fuel cycle 7 > The nuclear fuel cycle FROM RESEARCH 8 > Microelectronics 9 > The laser: a concentrate of light TO INDUSTRY 10 > Medical imaging 11 > Nuclear astrophysics 12 > Hydrogen 7 >>TThhee nnuucclleeaarr ffuueell ccyyccllee UPSTREAM THE REACTOR: PREPARING THE FUEL IN THE REACTOR: FUEL CONSUMPTION DOWNSTREAM THE REACTOR: REPROCESSING NUCLEAR WASTE NUCLEAR WASTE © Commissariat à l’’Énergie Atomique et aux Energies Alternatives, 2005 Communication Division Bâtiment Siège - 91191 Gif-sur-Yvette cedex www.cea.fr ISSN 1637-5408. From the uranium mine to waste disposal 7 > The nuclear fuel cycle From the uranium mine to waste disposal 7 > The nuclear fuel cycle 2 > CONTENTS > INTRODUCTION 3 Uranium ore is extracted from open-pit mines – such as the McClear mines in Canada seen here – or underground workings. a m e g o C © “The nuclear fuel cycle includes an erray UPSTREAM THE REACTOR: of industrial operations, from uranium PREPARING THE FUEL 4 e mining to the disposal of radioactive l Extracting uranium from the ore 5 waste.” c Concentrating and refining uranium 6 y Enriching uranium 6 c Enrichment methods 8 l introduction uel is a material that can be burnt to pro - IN THE REACTOR: FUEL CONSUMPTION 9 Fvide heat. The most familiar fuels are wood, e Preparing fuel assemblies 10 coal, natural gas and oil. By analogy, the ura - e g a nium used in nuclear power plants is called Per unit or mass (e.g. per kilo), nuclear fuel s e u Uranium-235 consumption 10 L . P / “nuclear fuel”, because it gives off heat too, supplies far more energy than a fossil fuel (coal a f Fuel degradation 11 m e g although, in this case, the heat is obtained or oil). When used in a pressurised water reactor, o C DOWNSTREAM THE REACTOR: © through fission and not combustion. a kilo of uranium generates 10,000 times more r REPROCESSING NUCLEAR Spent fuel is stored in a pool on the site, where it will After being used in the reactor, spent nuclear energy than a kilo of coal or oil in a conven - WASTE 12 remain for three years. a fuel can be reprocessed to extract recyclable tional power station. Also, the fuel will remain The purpose of reprocessing 13 energy material, which is why we speak of the in the reactor for a long time (several years), e Extracting fission products 13 nuclear fuel cycle. This cycle includes all the unlike conventional fuels, which are burnt up l Recycling fuel materials 14 following industrial operations: quickly. Nuclear fuel also differs from others in • uranium mining, that uranium has to undergo many processes c NUCLEAR WASTE 16 • fuel fabrication, between the time it is mined and the time it u Nuclear waste production • use in the reactor, goes into the reactor. in France 17 • reprocessing the fuel unloaded from the For the sake of simplicity, the following pages n Sorting and disposing reactor, will only look at nuclear fuel used in pressurised of radioactive waste 18 • waste treatment and disposal. water reactors (or PWRs), because nuclear Research on long-lived power plants consisting of one or more PWRs e waste 19 are the most widely used around the world (see h How a nuclear reactor works booklet). T Designed and produced by Spécifique – Cover photo by © CEA/Roquemaure - Illustrations by YUVANOE - Printed by Imprimerie de Montligeon - 03/2005 From the uranium mine to waste disposal 7 > The nuclear fuel cycle From the uranium mine to waste disposal 7 > The nuclear fuel cycle 4 > UPSTREAM THE REACTOR: PREPARING THE FUEL 5 AFTER MINING , THE URANIUM IS PURIFIED , CONCENTRATED AND ENRICHED . Upstream the Simplified diagram of the fuel cycle in France today reactoor: prepparing Storage Fuel fabrication U-235 depleted MOX fuel uranium UO 2 + PuO 2 the fuel Enrichment UO 2 fuel U-235 Pure natural Conversion enriched uranium uranium Concentration Plutonium Recycled uranium PWRs with thermal Ore neutrons Spent UO 2 fuel extraction Spent MOX fuel Waste Natural Reprocessing uranium plants Storage Ultimate disposal 3% of spent fuel Storage 0.5% of natural uranium mined EXTRACTING URANIUM with the highest uranium content are known as FROM THE ORE uranium ores, which often include uraninite Uranium is a relatively common metal in the and pitchblende. Earth’s crust (it is 50 times more common than The nuclear fuel cycle thus begins at the open- mercury, for example). Like most metals, it can - pit mines or underground workings where the e g a s not be mined directly in its pure form, because uranium ore is mined . The largest known ore e L . P / in its natural state it is found in rocks com - deposits are in Australia, the United States, a m e g bined with other chemical elements. The rocks Canada, South Africa and Russia. o C © From the uranium mine to waste disposal 7 > The nuclear fuel cycle From the uranium mine to waste disposal 7 > The nuclear fuel cycle 6 > UPSTREAM THE REACTOR: PREPARING THE FUEL > UPSTREAM THE REACTOR: PREPARING THE FUEL 7 “In order to increase uranium content, ore rocks are broken up and finely ground. The resulting concentrate is called yellow cake.” CONCENTRATING AND REFINING However, this uranium concentrate cannot be nium-235, making only 0.7% of fissile ura - booklet). They can be distinguished, however, URANIUM used in a nuclear reactor as it is. The uranium nium-235. The process of increasing the pro - due to their slightly different mass, uranium-235 The ore generally has a rather low uranium con - oxide must first go through various stages of portion of uranium-235 is called enrichment. being just a little lighter than uranium-238 . tent. For example, in France, one tonne of ore purification (or refining) to get rid of any impu - This is a difficult operation because , like all the This is why the current uranium enrichment contains between 1 and 5 kg of uranium rities. Once it is very pure, it is converted into isotopes of the same element, uranium-235 and process used is based on the difference in (between 0.1 and 0.5%). This makes it essen - uranium tetrafluoride (UF 4), which is composed uranium-238 are very similar and have almost mobility caused by this slight difference in tial to concentrate the uranium in these ores, of four fluorine atoms and one uranium atom. identical chemical properties (see The Atom mass. Of all the enrichment processes studied a job usually carried out on the spot. so far, only two have been developed on an First of all, the rocks are broken up and finely ENRICHING URANIUM industrial scale: gaseous diffusion and the crushed. Then various chemical processes are The fuel used in a PWR must contain between “Before it can be used ultracentrifuge process . used to extract the uranium. 3 and 5% uranium-235, because this is the The resulting concentrate looks like a yellow only uranium isotope that can withstand as nuclear reactor ENRICHMENT METHODS paste and is called yellow cake. It contains about energy-releasing nuclear fission (see How a fuel, natural uranium Gaseous diffusion 75% uranium oxide, i.e. 750 kg per tonne. nuclear reactor works booklet). The problem must be enriched with Before being enriched via this process, the ura - Uranium is a metal that oxidises very quickly when it comes into is that 100 kg of natural uranium contains nium tetrafluoride obtained after extraction contact with oxygen in the air and changes into uranium oxide. 99.3 kg of uranium-238 and 0.7 kg of ura - uranium-235.” from the ore and refining will be transformed Raise boring in frozen ground in the McArthur mine (Canada). COMINAL ore processing plant in Niger. l e o t r c a e M m . a O C / / a a m m e e g g o o C C © © From the uranium mine to waste disposal 7 > The nuclear fuel cycle From the uranium mine to waste disposal 7 > The nuclear fuel cycle 8 > UPSTREAM THE REACTOR: PREPARING THE FUEL 9 FUEL IS USED IN A NUCLEAR REACTOR FOR THREE OR FOUR YEARS . into uranium hexafluoride (UF ), which becomes enough 235 U-enriched uranium for use in In the reactor: 6 a gas when heated to 56°C. nuclear power plants. The gaseous diffusion process consists in passing gaseous UF 6 through a long series of “barriers” Ultracentrifuge process formed by membranes with microscopic pores. Another uranium enrichment process is used fuel consumption Uranium-235 hexafluoride molecules are slightly on a smaller scale by the European Urenco group lighter than uranium-238 hexafluoride mole - (Germany, Netherlands, United Kingdom). It is cules and cross each barrier a little faster, grad - known as the ultracentrifuge process. ually enriching the uranium as they do so. This separation process uses a centrifuge which, However, as the difference in mass between the acting like a high-speed salad spinner, projects two isotopes is very small, the uranium-238 the uranium-238 hexafluoride molecules to its travels hardly slower than the uranium-235. For outer edge more quickly than those of uranium- this reason, the operation has to be repeated 235 hexafluoride, which remain nearer the centre. 1,400 times at the uranium enrichment plant The very slight difference in mass between the in France (the Eurodif plant in Tricastin in the two molecules gradually increases the uranium-235 Rhone valley, which produces more than a third concentration.
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