Patent Number: 046876294
Section: abstract

A fuel rod for a nuclear reactor fuel assembly includes a cladding tube and a plurality of fuel pellets contained in the tube and composed of fissile material, such as uranium dioxide, having a single enrichment of U-235. At least some of the fuel pellets have an annular configuration. Some of the annular fuel pellets have an annulus of a first size, whereas other of the annular fuel pellets have an annulus of a second size different from the first size. In such manner, graduation of axial enrichment loading is provided between the annular fuel pellets of the fuel rod. Also, a nuclear fuel assembly includes a multiplicity of fuel rods with a plurality of fuel pellets contained in each of the fuel rods and being composed of fissile uranium having a single U-235 enrichment. Each of the fuel pellets in a majority of the fuel rods has a solid configuration, whereas each of the fuel pellets in a minority of the fuel rods has an annular configuration. Each of the annular fuel pellets of some of the fuel rods has an annulus of a first size. On the other hand, each of the annular fuel pellets of other of the fuel rods has an annulus of a second size, whereby graduation of enrichment loading is provided between the solid and annular fuel pellets of the respective majority and minority of fuel rods. The value of the single U-235 enrichment is at the level of the maximum enrichment loading of the fuel assembly.