| 摘要 |
PROBLEM TO BE SOLVED: To constantly maintain the soundness of a clad pipe over a long time by providing a sleeve with sufficient strength in the radial direction of reduced-diameter part at an annular space between the outer-periphery surface of the reduced-diameter part and the inner-periphery surface of the clad pipe. SOLUTION: In a control rod, both the ends of a clad pipe 11 being made of stainless steel are enclosed by upper and lower end stoppers 12 and 13. A rod-shaped neutron absorption body 14 is accommodated inside the clad pipe 11. Also, the neutron absorption body 14 has a reduced-diameter part 14a with a smaller diameter as compared with other parts at the side of the lower end stopper, and a sleeve 16 is provided between the outer-periphery surface of the reduced-diameter part 14a and the inner-periphery surface of the clad pipe 11. The sleeve 16 is formed by a material that is the same as the clad pipe 11 or a material with thermal coefficient of expansion that is smaller than that of the clad pipe 11, and has sufficient strength for the diameter direction of the reduced-diameter part 14a, thus preventing the reduced-diameter part of the neutron absorption body from being expanded in the diameter direction by impact being generated by the step drive of a control rod cluster.
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