The present invention relates to a nuclear fuel fixing device comprising: a fixing bar disposed below nuclear fuel and configured to fix or release the nuclear fuel as it moves up and down; and a magnetic part for selectively moving the fixing bar up and down using magnetic force, The safety locking device of the nuclear fuel fixing device includes: an extension bar extending downwardly from a lower end of the fixing bar and having a recess formed on a side surface thereof; A ball guide having a ball portion formed to correspond to the groove portion, and seating the ball portion on the groove portion as it moves up and down to fix the extension bar so that the movement is restricted at a predetermined height or release the state in which the movement is restricted wealth; and a driving unit configured to selectively move the ball guide unit up and down using magnetic force.
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