A nuclear reactor control rod anti-ejection lock for use with magnetic jacking type control rod drives and having a spring pressed pawl which ratchets to allow insertion of the control rod but prevents ejection or withdrawal unless the control rod drive is in an upper position or the latch mechanism of the drive is in latched position. The drive comprises two axially spaced axially movable drive members around the rod and magnets selectively alternately moving the members in two opposite directions along or with the rod. Each member carries a latch or gripper and an axially movable sleeve, selectively magnetically operated, to operate the latch to connect or disconnect the rod and respective drive member. A push rod connects each sleeve and the pawl and disables the pawl when either sleeve is in position to latch the control rod and a drive member. The stroke of the drive member may be made less than the stroke of the sleeve and a lost motion incorporated in the push rod connection so that the drive member will not disable the pawl.