FUEL ASSEMBLY, SPECTRUM SHIFT ROD, NUCLEAR REACTOR AND METHOD FOR CONTROLLING OUTPUT OF NUCLEAR REACTOR

摘要

PURPOSE:To improve the fuel economy of the fuel assembly by disposing fuel rods which constitute one square grating arrangement between the plural fuel rods which constitute the other square grating arrangements. CONSTITUTION:The square grating arrangements 7A and 7B of this fuel assembly are disposed in parallel with the side face of an upper tie plate 2 or lower tie plate 3. The square grating arrangements 7A and 7B are parallel with the side face of a channel box 6 and the fuel rods 4 of the arrangement 7B are disposed at the center of the square shape formed of the arrangement 7A. Namely, the state in which the arrangement 7B is superposed within the arrangement 7A by shifting the mutual pitches by 1/2 is attained. The flow passage area of the coolant in the peripheral part of the fuel assembly is increased according to such fuel rod arrangements, by which the thermal allowance and output peaking are increased and the fuel economy of the fuel assembly is improved.