Uranium fuel is formed into ceramic pellets then sealed in metal tubes. A fuel bundle is an assembly of 37 fuel elements – which are thin, pencil-like tubes about two feet long – containing 29 uranium dioxide pellets in a metal sheath that is welded together at both ends.

The pencils are assembled into roughly 22-kg fuel bundles. Each reactor has 480 fuel channels that each hold 12 or 13 fuel bundles, placed end to end.