Patent Number: 042808740
Section: abstract

The core of a nuclear reactor is constituted by two sorts of fuel assemblies: first fuel assemblies each of which contains both fissile material and gadolinea and second fuel assemblies each of which contains only the fissile material. The ratio of the number of the first fuel assemblies to that of the second fuel assemblies are selected to be 1:3. The enrichment of the fissile material is larger at the upper part of the reactor core than at the lower part of the same. The fuel assembly containing both of the fissile material and the gadolinea includes first fuel rods each of which contain both the fissile material and the gadolinea, and second fuel rods which contains only the fissile material. The number of the first fuel rods and the concentration of gadolinea are substantially in proportion to the power density at positions in the reactor core where the fuel assembly is placed.