| 摘要 |
PROBLEM TO BE SOLVED: To provide a water rod and nuclear fuel bundle for the fuel bundle of a boiling water reactor wherein nuclear reactor output and the vibration of flow is controlled to bring a more stable operation point. SOLUTION: A water rod 58 for the fuel bundle of a boiling water reactor includes an upper end 62, an outside tube 60 having a lower end 64 supported on a support structure, at least a coolant inlet opening 76 provided in the lower end 64, at least a coolant outlet opening 78 provided in the upper end 62 and an inside tube 80 upwardly extending from the lower end 64, and sized and disposed so as to receive the whole coolant passing at least one coolant inlet opening 76. The inside tube 80 has a smaller cross sectional area than the cross sectional area for the main length part of the outside tube 60, and a chamber 86 is formed between the outside tube 60 and the inside tube 80. The inside tube 80 has an open upper end 84 terminating at a place not reaching the upper end 62.
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