Fuel assembly

Purpose: To provide a fuel assembly suitable to the control of rapid increase in the local power peaking after the extraction of control rods in a BWR type reactor. Constitution: The fuel rod situated nearest to the center axis of a control rod inserted into a fuel channel is constituted as a special rod having neutron moderating effects. Specifically, this rod comprises carbon or beryllium pellets sealed in a cladding tube with the same diameter as that of a fuel rod, and the uranium enrichment degree for the fuel rods near the special rod is made lower. Since rapid increase in the local power peakings are thus suppressed even at the extraction of the control rod, and the local power peakings are not increased also in the state where the control rod is not inserted, it enables such a control rod pattern exchange planning that an identical control rod is inserted for a long time. (Seki, T.)