| 摘要 |
PURPOSE: To obtain a fuel rod structure capable of increasing the weight of a fuel as compared with a fuel bundle containing a partial length fuel rod, improving fuel/moderator ratio and further making the flow of fluid in the bundle more uniform in a boiling water reactor. CONSTITUTION: A fuel bundle has a lower large-diameter tube 24 useful to hold the post of a large-diameter fuel pellet 60 at the lower part of a fuel rod, an upper small-diameter tube 22 useful to hold the post of a small-diameter fuel pellet 51 at the upper part of the rod, and a fuel rod R having a different diameter joint 26 disposed between the upper end of the lower tube 24 and the lower end of the tube 22. In the joint, a transition pellet formed of fuel, fuel containing burnable poison moderator or moderator containing burnable poison is charged.
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