| 摘要 |
A hydraulic control rod driving system in which radial clearance is formed between a piston portion (21) and a cylinder (2), one or two or more step portions (23), each comprising a cylindrical upper part (22a) having a large diameter and a cylindrical lower part (22b) having a smaller diameter arranged adjacent to the lower side of the upper part (22a), are provided on the piston portion (21) along the axial direction thereof. Circumferential grooves (26) for partitioning off respective step portions are provided, and the ratio of the length of each step portion to the maximum outside diameter of the piston portion is set at 0.5 to 1.0. <IMAGE>
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