Nuclear Fuel Uranium Enrichment Fuel Fabrication MOX Seminar

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

Ends of the Nuclear Fuel Cycle

The Reactor: Core of the Nuclear Fuel Cycle

The Nuclear Fuel Cycle

Uranium Mining and Milling

Yellow Cake Final Product of Milling Step – 70 to 80 % uranium

Conversion, Enrichment and Fuel Fabrication

Natural Uranium 235 U only fissile nuclide – only 1 atom of 235 U in 140 atoms of 238 U

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, UF 6 gas is used as the feed material • Molecules of UF 6 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

Enrichment: UF 6 Feed Container

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 UF 6 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

Enrichment: Centrifuge Process

Enrichment: Gaseous Diffusion Process • involves forcing UF 6 under pressure through a porous membranes • as 235 U molecules are lighter than the 238 U molecules they move faster and have a slightly better chance of passing through the pores in the membrane • the UF 6 which diffuses through the membrane is thus slightly enriched, while the gas which did not pass through is depleted in 235 U • this process is repeated many times in a series of diffusion stages called a cascade • enriched UF 6 is withdrawn from one end of the cascade and depleted UF 6 is removed at the other end • the gas must be processed through some 1400 stages to obtain a product with a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% 235 U

Enrichment: Gaseous Diffusion Process The large Tricastin enrichment plant in France (beyond cooling towers). The nuclear reactors in the foreground provide power for it.

Conversion, Enrichment and Fuel Fabrication

Conversion and Nuclear Fuel Fabrication • UF 6, in solid form in containers, is heated to gaseous form, and the UF 6 gas is chemically processed to form LEU uranium dioxide (UO 2) 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

UO 2, Pellets and Fuel Assembly

Fuel Rods

Fuel Assembly

MOX Fuel

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

MOX Fuel: Glove Boxes

IAEA Thank you for your attention …atoms for peace.