|Distribution of fuel rods in a MOX assembly|
The core of a PWR adapted to burn plutonium contains 30% of MOX fuel rods arranged in MOX-only assemblies. The cross-section of such assemblies or bundles shows that the fuel rods are not all identical. One distinguishes three areas with rods differing by their enrichment in plutonium and guide tubes in which slide the absorber rods to control the chain reaction. The distributions of the assemblies in the reactor’s core and that of rods in the assemblies are designed not to disturb the neutron flux and reactor operation.