FUEL ASSEMBLY FOR BOILING WATER TYPE ATOMIC REACTOR

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PROBLEM TO BE SOLVED : To provide a fuel assembly for boiling water type atomic reactors, in which the void coefficient becomes a proper value and the adjustment of reactivity can be realized in a proper flammable poison amount in a reactor core having high burnup and continuously operating for a long term. SOLUTION : A fuel assembly for boiling water type atomic reactors, comprising a plurality of fuel bars 101 aligned in a square grid form, and a channel box 104 which encloses the outer periphery of these fuel bars as a whole, wherein the fuel bars 101 includes a plurality of first fuel bars (groups 1 to 4) to which no flammable poison is added, at least one second fuel bar (G) to which gadolinium alone is added as a flammable poison, and at least one third fuel bar (Er) to which a rare earth oxide alone, other than gadolinium, is added as a flammable poison.