Patent ID: 7844025

Claim:
A fuel assembly for a pressurized water nuclear reactor, comprising: fuel rods which are arranged at nodes of a substantially regular network having a polygonal outer contour, the fuel rods containing uranium which is enriched in isotope 235 and not containing any plutonium before the assembly is used in a reactor, wherein the rods are distributed in at least: a first central group which is constituted by fuel rods which have a first level of enrichment e 1 in uranium 235; and an outer peripheral layer of fuel rods distributed in: a second group of fuel rods that extend along faces of the outer contour of the network and that have a second level of enrichment e 2 in uranium 235 strictly less than the first level of enrichment e 1 ; and a third group of fuel rods that are arranged at corners of the outer contour of the network and that have a third level of enrichment e 3 in uranium 235 that is strictly less than the second level of enrichment e 2 wherein the outer peripheral layer of fuel rods defines an outer periphery of the fuel assembly.