Operating devices for control rods in a nuclear reactor

Device for a control rod in a nuclear reactor of the type comprising a sealed tubular enclosure associated with a variable reluctance stepping drive motor the rotor of which is situated inside the said enclosure and the stator of which is located externally of the latter, rotation of said motor bringing about raising or lowering of said control rod via a transmission means of the screw/nut type, said device having hooking means for hooking said screw in its raised position, said hooking means being controlled by at least one electromagnetic spool surrounding said enclosure, so that said means are in their closed position on said screw when said spools are supplied with power, said means moving to opened position when no longer supplied with power so as to allow the complete assembly of the screw/nut type to fall, said hooking means comprising an integral part of the poles of the rotor of said motor, said electromagnetic spools being constituted by the spools of the stator of said motor, and comprising means for locking said hooking means allowing them to remain in open position even when said spools are again placed under tension when said screw is not in its upper, hooking position.