Abstract: A neutron absorbing bar for use in a PWR has an integrated damping device comprising a cluster of vertical absorbent rods fixed to the arms of a spider having a central pommel connectable to a drive mechanism. A damping device in the pommel includes a cylinder slidably receiving piston urged into a downward projecting position by springs contained in the cylinder. The cylinder and the piston are so formed that the leak flow at a cross-sectional area offered to the liquid driven out of the cylinder by the piston gradually decrease as the latter moves from an outermost position. The piston carries a hydromechanical damper damping the initial impact of the bar upon a scram.

Abstract: A nuclear reactor control bar drive device with mobile valve is provided, comprising a cluster guide placed above the core, a casing containing a drive mechanism connected to the inside of the reactor by a sheath passing sealingly through the lid of a vessel containing the core, a control shaft movable vertically in the sheath, connecting the mechanism to the bar and passing, with radial clearance, through an upper plate for closing the guide, as well as a thermal protection sleeve interposed radially between the shaft and the sheath and able to bear by an end piece on said upper plate. The sleeve is pierced, below the sheath, with a calibrated passage for intake of fluid into the guide through the clearance and a non return valve is disposed between the sleeve and the sheath, is movable vertically with respect thereto and co-operates with a seat of the sheath for allowing the fluid to flow only towards the drive mechanism.

Abstract: Mechanism for displacing and securing the rod of a nuclear reactor control bar, comprising an enclosure coaxial with the rod and forming a hydraulic cylinder in which the rod slides while defining a decompression chamber, a device for mechanically securing the rod in its high position, and a positive displacement reciprocating pump inserted between the decompression chamber and the inside of the tank, whose piston is actuated electromagnetically means and causes at each backward and forward movement lifting of given amplitude of the rod and the device for securing the rod in the high position disengagable also electromagnetically.

Abstract: The device comprises a vertical shaft (36) movable along its axis under the action of a fluid pressure difference and having means for supporting at least one head (28) of the cluster and a first resilient finger (42) for securing and retaining the head on the support means. It comprises a high position securing mechanism carried by a fixed tube (20) for guiding the cluster and having at least one resilient finger for securing the head and retaining the head against the action of gravity and a vertically movable bolt urged resiliently to a position in which it prevents disengagement of a second resilient finger and cooperating with a mechanism controlling a second cluster so as to be brought into a position in which it releases the second resilient finger when the second cluster passes beyond the highest position assumed during normal operation.

Abstract: Device and method for retaining a linearly movable element in a nuclear reactor. The device comprises, for each shaft, a base fixed to the top part of the reactor internals and coaxial with a shaft guide tube; several grippers or catches spaced apart about the axis of the base and mounted for pivotal movement about a horizontal axis towards a position into and out of engagement with a portion, having circumferential grooves, of the shaft contained in the tube; a slide movable axially on the base towards a top position where it causes engagement of the catches in a groove of the rod, and out of such position; and springs bearing on the base and tending to engage the catches on the shaft. The slide is dimensioned so as to be held by the corresponding sleeve projecting through the reactor vessel cover in a position sufficiently distant from the low position for the catches to be released, whatever the temperature in the reactor.

Abstract: A coupling device between a nuclear reactor control rod and an actuating mechanism has a gripper body having resilient gripping fingers, belonging to the mechanism and, on the bar, a terminal pommel for engagement by the fingers and a shoulder directed towards the pommel. The coupling device comprises an additional member, such as a sleeve, movable with respect to the gripper body between a position in which it allows resilient fingers to be released from the pommel and another position in which it locks the resilient fingers onto the pommel. The sleeve has an end face bearing on the shoulder of the pommel. A prestressed spring exerts a force tending to move the sleeve away from the fingers so as to hold the end face of the sleeve firmly applied against the shoulder when the fingers are locked on the pommel.

Abstract: The electromagnetic device is suitable for use in actuating a pressurized water reactor control bar. It comprises a shaft and a fluid-tight casing in which are movable longitudinally a first and a second sets of grippers for gripping the shaft, staggered in the longitudinal direction. The first set of grippers is associated with a movable pole co-operating with a holding coil, carried by the casing and movable by energization and de-energization of the coil between a position in which the first set of grippers holds the shaft and a position in which it releases it. The second set of grippers is associated with a movable plunger co-operating with a transfer coil and movable by energization and de-energization of the transfer coil to and from a position in abutment against an other pole. The other pole is movable between two positions spaced apart by a given step.