Patent Number: 
Section: claims

1. A passage selector of a reactor in-core nuclear-measuring apparatus, comprising:a passage selecting guide tube;a plurality of detector passages;a drive motor;an index device that is driven by said drive motor, the index device including an output shaft that makes a rotary output of a fixed predetermined index number;a central rotating shaft that is rotated so as to cause the passage selecting guide tube to be aligned to a detector passage; anda speed-increasing and decreasing device that comprises a first gear directly connected to the output shaft of the index device and a second gear that is meshed with said first gear and directly connected to said central rotating shaft; andwherein when a stop number (index number) of the index device is Y where a teeth number of the first gear is Z1, and a teeth number of the second gear is Z2, the stop number (index number) of the central rotating shaft is Y×Z2/Z1. 2. A passage selector of a reactor in-core nuclear-measuring apparatus, comprising:a passage selecting guide tube;a plurality of detector passages;a drive motor;an index device that is driven by said drive motor, the index device including an output shaft that makes a rotary output of a fixed predetermined index number;a central rotating shaft that is rotated so as to cause the passage selecting guide tube to be aligned to a detector passage; anda speed-increasing and decreasing device that comprises a first gear directly connected to the output shaft of the index device and a second gear that is meshed with said first gear and directly connected to said central rotating shaft; andwherein when an input shaft of the index device makes one revolution by the drive motor, an output shaft of the index device makes 1/Y revolution in accordance with an index number Y that is specific to the index device, where a teeth number of the first gear is Z1, and a teeth number of the second gear is Z2, the revolutions of the central rotating shaft is set to be 1/Y×Z1/Z2.