Patent ID: 8744033

Claim:
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; and a 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; and wherein 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.