Production: global size, tailor-made solutions

What is a fuel assembly?

Fuel assemblies are the reactor core, the place where nuclear fission produces energy.

They contribute to reactor safety by ensuring that the radioactive products of fission are contained in sealed tubing (“cladding”) made of zirconium alloy. Cladding is the primary containment barrier.

A fuel assembly can contain 200-500 kilograms of fissile material, depending on the type of assembly. It consists of rods that contain fissile material and a metal frame or “skeleton”—generally made of a zirconium alloy—that includes guide thimbles, spacer grids and end nozzles.

Fuel assemblies last, on average, 3-4 years into the reactor. Used fuel is removed every 12-24 months by replacing 20-50% of the assemblies in the reactor core, depending on management techniques and fuel assembly performance.

Stages of fuel assembly production

Production of a fuel assembly for a pressurized water reactor (PWR):

• After enrichment, uranium hexafluoride (UF₆) is transformed into uranium oxide.
• This black powder is then compressed into small pellets that are placed in a furnace at 1,700°C where they acquire their characteristic strength and density. Each pellet—a cylinder measuring 10-13 millimeters in length and 8-13,5 millimeters in diameter—weighs only 10 grams and can release as much energy as a metric ton of carbon.
• The pellets (about 300) are inserted into long tubing (or cladding) that is 4 meters in length and made of a zirconium alloy. Each tube is sealed at both ends with 2 plugs. This entire unit constitutes a fuel rod.
• The rods are held in a metal structure (the skeleton), usually made of a zirconium alloy, and fastened in “bundles” with square cross-sections to form a fuel assembly. Each assembly contains 264 rods.
• A reactor core holds various quantities of fuel assemblies depending on the type of power plant.
  • A PWR plant holds on the order of 150 to 265 fuel assemblies.
  • For a BWR plant the range is approximately 400 - 800.
• Each stage of assembly production is subject to strict controls.

Seven complementary production sites

Fuel assembly production is spread across 7 sites in France, Germany and the United States and supplies utilities around the world.

Fuel assembly production capacity:

• Germany
  • Karlstein manufactures spacers, nozzles and assembly components.
  • Lingen produces uranium oxide powder, fuel pellets, rods and assemblies.
• Belgium
  • Dessel manufactures assemblies for PWRs, fuel pellets and rods, a full range of small assembly components and assembly of MOX fuel rods.
• United States
  • Richland (Washington) produces uranium oxide (UO₂), assemblies for PWRs and BWRs and burnable poison rods (boron carbide).
  • Erwin (Tennessee) converts low enriched uranyl nitrate into (fissile) uranium oxide and delivers it to the Richland plant to be transformed into pellets for fuel production.
• France
  • Pierrelatte (Drôme) manufactures spacers, called grids, for PWR assemblies as well as Harmoni™ rod cluster control.
  • Romans (Drôme) produces uranium oxide (UO₂), fuel pellets, nozzles, fuel rods and assemblies for PWRs.

Located at the Pierrelatte and Romans sites, Compagnie pour l’Etude et la Réalisation de Combustibles Atomiques (CERCA) is the global leader in manufacturing and supplying fuel for research reactors.  It also provides radioactive standard sources for industry, medicine and research.