Nuclear fuel assemblies and reactor cores including them

摘要

A nuclear fuel assembly (11) has an array of fuel rods comprising a plurality of first fuel rods (6-9) each containing nuclear fuel material but not containing burnable poison and a plurality of further fuel rods (G1,G2) each containing both nuclear fuel material and burnable poison. The further fuel rods comprise second fuel rods (G2) and third fuel rods (G1), and each second fuel has at said lower region of the fuel assembly a burnable poison concentration which is a minimum burnable poison concentration in the further fuel rods. To increase the effectiveness of the second fuel rods (G2) in controlling axial power peaking, as seen in plan view on said array,the first fuel rods are the nearest neighbours of each said further fuel rod.