Fuel functional characteristics
Plutonium fuel fabrication for PWRs and BWRs

A distinction must be made between EPRs and BWRs.

• In a BWR, the fuel assembly consists of a bundle of fuel rods enclosed in a casing; reactor physics dictates a zoning of rods of different fissile content (²³⁵U enrichment or plutonium content) and the use of consumable poisons, usually gadolinium in the form of Gd₂O₃ in UO₂ rods. A MOX BWR assembly contains MOX rods and UO₂ rods. Most existing boiling reactors can accommodate up to 50% or 60% MOX assemblies without modification; the design of a 100% MOX core in a BWR requires only minor modifications; this is the case with the ABWR-type BWR that Hitachi, under license from General Electric, built at Ohma (Japan) for EPDC.