Patent Number: 047568682
Section: claims

1. In a nuclear reactor having a tank containing a pressurized coolant and control bars each provided with a drive rod, a mechanism for longitudinally moving and for securing a drive rod, having an enclosure coaxial with the rod and forming a hydraulic cylinder slidably receiving the rod with which it defines a decompression chamber, and means for mechanically securing the rod in the high position thereof, said mechanism comprising first electromagnetically controlled means placed outside the enclosure, hydraulic means controlled by said electromagnetically controlled means for reducing the pressure of the coolant in the decompression chamber so as to cause step by step lift of the rod with a predetermined step and second electromagnetically controlled means, different from the first ones, also placed outside the enclosure, for controlling hydraulic means communicating the decompression chamber with the tank so as to cause downward movement of the rod and release of said securing means, said hydraulic means being placed in the enclosure. 2. A mechanism according to claim 1, wherein the first and second electromagnetically controlled means comprise a first coil and a second coil which may be independently energized, said second coil causing release of the rod and connecting the compression chamber to the tank when it is energized. 3. In a nuclear reactor having a tank containing pressurized liquid coolant and vertically movable control bars each supported by a drive rod, a mechanism for vertically moving and for securing a drive rod having an enclosure coaxial with the rod and forming a hydraulic cylinder slidably receiving the rod with which it defines a decompression chamber, and means for mechanically securing the rod in the high position thereof, said mechanism comprising a positive displacement reciprocating pump inserted between the decompression chamber and the inside of the tank, whose piston is actuated by first electromagnetically controlled means and, upon reciprocation, causes a lift of predetermined amplitude of the rod, and means for securing the rod in the high position releasable by second electromagnetically controlled means. 4. A mechanism according to claim 3, wherein the pump comprises a pole piece movable by the first electromagnetically controlled means between two predetermined positions, comprising a plunger co-operating with a fixed piece for defining a variable volume pumping chamber connected to the hydraulic cylinder by an intake valve and to the tank by a discharge valve. 5. A mechanism according to claim 4, wherein said plunger defines the pumping chamber with a fixed pole piece belonging to the first elecromagnetically controlled means, one of the predetermined positions corresponding to the abutment of the movable pole piece against the fixed pole piece. 6. A mechanism according to claim 4, wherein the pumping chamber has a section smaller than that of the hydraulic chamber, so that the pressure differential force on the rod is greater than the force exerted by the first electromagnetically controlled means on the movable pole piece. 7. A mechanism according to claim 3, wherein a hydraulic flow path between the discharge valve and the tank comprises an annular space formed between a liner linking said enclosure on the inside and said enclosure. 8. A mechanism according to claim 3, wherein the securing means comprise a pole piece having downwardly directed flexible blades and ending in catches for gripping a bulge on the rod, movable between a low position in which the blades are in a position where they prevent the rod from moving downwards once the bulge has passed upwardly beyond the catches and a high position in which the blades are moved apart by a cam so as to release the rod. 9. A mechanism according to claim 8, wherein the movable pole piece forms a distributor opening a leak path between the cylinder and the tank when in a high position. 10. A mechanism according to claim 3, wherein the securing means are provided for reversing the connections of the hydraulic means with the decompression chamber and with the tank when they are disengaged, so as to accelerate the downward movement of the rod by actuation of said hydraulic means by means of the first electromagnetically controlled means.