CORE FOR FAST REACTOR

PURPOSE:To operate with the little fluctuation of output and the little fluctuation of reactivity over a long period of time, without stopping a reactor within the life period of fuel. CONSTITUTION:A fuel assembly where minor actinide elements are added 15 to 24wt% to fuel of a fast reactor is constructed, and a core is constructed by making an addition ratio of minor actinide elements to the inside core 3 to 8% less at weight ratio than that to the outside core. By this, the core where both the swing of the burning reactivity and the fluctuation of an output distribution are little can be constructed, and continuing to keep the reactivity can be made because the minor actinide nuclides convert into higher nuclides of fissionability while burning, from the view point of the reactivity also.