| 摘要 |
PURPOSE:To measure the length of a radioactive member with high efficiency and high accuracy by supporting the radioactive member vertically in water, irradiating its upper and lower end parts with ultrasonic waves slantingly from above and below, and detecting their reflected waves. CONSTITUTION:A used fuel assembly 1 is conveyed underwater to a fuel storage pool 11 by the crane, etc., of a nuclear fuel replacing device. This assembly 1 is suspended by a supporting device 13 and held vertically. Then, a couple of upper and lower ultrasonic sensors 20 and 21 fitted to a frame 15 slantingly upward and downward emit ultrasonic output waves to the nuclear fuel channel 5 of the assembly 1. End part echoes are received from the upper and lower end parts of the channel 5, their positions are detected by sensors 20 and 21, and an arithmetic processor 19 finds the length of the channel 5 based on the result.
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