Lesson 3 ◆ 3.2 Fuel Assemblies
  • Consists of a circular array of 36 stainless steel clad fuel pins
  • Each pin contains 20 enriched UO2_2 fuel pellets (annular shape)
  • The assembly weighs about 43 kg
  • Enrichment levels vary, up to about 3.5%
  • Stainless steel cladding allows for higher operating temperatures but sacrifices some neutron economy owing to its higher capture cross-section compared to Magnox
  • The assembly is covered with a graphite sheath which serves as a moderator
  • Eight assemblies are stacked end-on-end in a fuel channel, inserted down through the top of the reactor
  • During refuelling, the whole stack is replaced
  • Fuel life is about five years
  • Refuelling can be carried out on-load (while the reactor is running), though not at full power