This document summarizes a seminar on nuclear science and technology for diplomats. It discusses various steps in the nuclear fuel cycle including uranium mining and milling, conversion, enrichment through gaseous diffusion or centrifuge processes, and fuel fabrication. It describes how uranium is enriched to increase the concentration of the fissile U-235 isotope and how this enriched uranium and plutonium are used to produce ceramic fuel pellets and fuel rods that are assembled into fuel for nuclear reactors. The document also provides details on MOX fuel which combines plutonium and uranium to generate energy.

1. 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

2. Ends of the Nuclear Fuel Cycle

3. The Reactor:
Core of the Nuclear Fuel Cycle

4. The Nuclear Fuel Cycle

5. Uranium Mining and Milling

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

7. Conversion, Enrichment and
Fuel Fabrication

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

9. 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

10. Enrichment: UF6 Feed Container

11. 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

12. Enrichment: Centrifuge Process

13. 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

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

15. Conversion, Enrichment and
Fuel Fabrication

16. 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

17. UO2, Pellets and Fuel Assembly

18. Fuel Rods

19. Fuel Assembly

20. MOX Fuel

21. MOX Fuel

22. 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

23. MOX Fuel: Glove Boxes

24. MOX Fuel: Glove Boxes

25. IAEA
TThhaannkk yyoouu ffoorr yyoouurr aatttteennttiioonn
…atoms for peace.