ES361211A1 - Nuclear reactor fuel assembly - Google Patents

Abstract

A nuclear fuel element assembly comprises fuel elements arranged in a plurality of groups including an inner group and at least one outer group arranged concentrically around the inner group, the fuel of the elements of a first one of the groups having an initial predetermined enrichment of fissile Pu, and the initial Pu content (if any) of the fuel of the other or at least one other group being markedly different from that of the first. The Pu may be concentrated in the outer fuel elements of the assembly near the regions of highest neutron moderation, i.e. near zones of lowest thermal neutron energy, which arrangement provides for optimization of fuel cycle costs and fuel reliability. Alternatively, the Pu may be concentrated in the inner fuel elements of the assembly, which arrnagement provides for optimization of power and critical heat flux shaping by taking advantage of the increase in the ratio of the thermal fission cross-section of fissile Pu to that of fissile and of the unique higher heat flux capability of the central fuel elements of a boiling water reactor fuel assembly. In the first of these two embodiments, the outer fuel elements contain 1 to 2 atom per cent fissile Pu mixed with depleted or natural U of 0.25 to 0À71 atom per cent fissile U content, while the inner fuel elements contain U fuel of about 3 atom per cent fissile U content. In the second embodiment, the inner fuel elements contain 1 to 2 atom per cent fissile Pu mixed with U of 0À3 to 2 atom per cent fissile U content, while the outer fuel elements contain U fuel of 2 to 3 atom per cent fissile U content.