Download - Adelfang presentation 2.2 (1)
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Nuclear Fuel, Uranium Enrichment, Fuel Fabrication, MOX
Seminar on Nuclear Science and Technology
for Diplomats
P. Adelfang
(+)Division of Nuclear Fuel Cycle and Waste Technology (NEFW)Department of Nuclear Energy (NE)
IAEA, Vienna, February 6-8, 2007
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Ends of the Nuclear Fuel Cycle
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The Reactor: Core of the Nuclear Fuel Cycle
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The Nuclear Fuel Cycle
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Uranium Mining and Milling
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Yellow Cake
Final Product of Milling Step – 70 to 80 % uranium
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Conversion, Enrichment and Fuel Fabrication
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Natural Uranium
235U only fissile nuclide – only 1 atom of 235U in 140 atoms of 238U
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Enrichment
• A number of enrichment processes have been demonstrated in the laboratory
• Only two, the gaseous diffusion process and the centrifuge process, are operating on a commercial scale
• In both of these, UF6 gas is used as the feed material
• Molecules of UF6 with U-235 atoms are about one percent lighter than the rest, and this difference in mass is the basis of both processes
• Large commercial enrichment plants are in operation in France, Germany, Netherlands, UK, USA, and Russia, with smaller plants elsewhere
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Enrichment: UF6 Feed Container
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Enrichment: Centrifuge Process • vacuum tubes, each containing a
rotor one to two metres long and 15-20 cm diameter.
• rotors are spun rapidly, at 50,000 to 70,000 rpm
• heavier molecules with U-238 increase in concentration towards the cylinder's outer wall
• there is a corresponding increase in concentration of U-235 molecules near the centre.
• enriched gas forms part of the feed for the next stages, depleted UF6 gas goes back to the previous stage (cascade)
• very high speeds:, outer wall spinning cylinder 400 and 500 metres per second= 1 million times the acceleration of gravity
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Enrichment: Centrifuge Process
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Enrichment: Gaseous Diffusion Process
• involves forcing UF6 under pressure through a porous membranes
• as 235U molecules are lighter than the 238U molecules they move faster and have a slightly better chance of passing through the pores in the membrane
• the UF6 which diffuses through the membrane is thus slightly enriched, while the gas which did not pass through is depleted in 235U
• this process is repeated many times in a series of diffusion stages called a cascade
• enriched UF6 is withdrawn from one end of the cascade and depleted UF6 is removed at the other end
• the gas must be processed through some 1400 stages to obtain a product with a concentration of 3% to 4% 235U
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Enrichment: Gaseous Diffusion Process
The large Tricastin enrichment plant in France (beyond cooling towers). The nuclear reactors in the foreground provide power for it.
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Conversion, Enrichment and Fuel Fabrication
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Conversion and Nuclear Fuel Fabrication
• UF6, in solid form in containers, is heated to gaseous form, and the UF6 gas is chemically processed to form LEU uranium dioxide (UO2) powder
• this powder is then pressed into pellets, sintered into ceramic form (fuel pellets)
• pellets are then loaded into Zircaloy tubes that are afterwards hermetically closed (fuel rods)
• rods are constructed into fuel assemblies• fuel assemblies are made with different
dimensions and number of fuel rods, depending on the type reactor
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UO2, Pellets and Fuel Assembly
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Fuel Rods
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Fuel Assembly
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MOX Fuel
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MOX Fuel
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MOX Fuel• Plutonium, made in power reactors and from dismantled nuclear
weapons, is a valuable energy source when integrated in the nuclear fuel cycle
• Over one third of the energy produced in most nuclear power plants comes from plutonium. It is created there as a by-product.
• 'MOX' is derived from 'mixed oxides', and refers to reactor fuel made from a mixture of plutonium and uranium oxide
• For use in a light water reactor, the proportion of plutonium is about 5%. This is a similar fissile content as low enriched uranium fuel
• MOX is formed into ceramic fuel pellets, extremely stable and durable, and which are sealed in metal (usually zirconium) tubes, which in turn are assembled into fuel elements
• In most cases a part of the reactor core can be loaded with MOX fuel elements without engineering or operational modifications to the reactor
• Plutonium is radiologically hazardous, particularly if inhaled, so must be handled with appropriate precautions
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MOX Fuel: Glove Boxes
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MOX Fuel: Glove Boxes
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IAEA
…atoms for peace.
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