Patent Number: 047524340
Section: claims

1. In a control bar assembly for a nuclear reactor, said control bar assembly having a vertically movable elongate control bar and a drive mechanism for vertically positioning said bar, a coupling device for releasibly coupling said mechanism and said bar, having :  an endmost pommel and a shoulder formed on said bar, said shoulder being formed at a vertical distance under said pommel and facing upwardly,  a vertically movable gripping body included in said mechanism and having a plurality of resilient gripping fingers for locking engagement with said pommel;  a sleeve included in said mechanism and vertically movable with respect to said gripping body between a first position where a downwardly directed endmost face of said sleeve is in abutment against said shoulder and a second position clear of said shoulder, when said gripping fingers are locked on said pommel;  controllable means for moving said sleeve away from said first position toward said second position; and  resilient prestressing means in said mechanism arranged to exert a force in said sleeve biasing said sleeve vertically away from the fingers so as to maintain said downwardly directed endmost face of the sleeve in firm abutment against the shoulder when the fingers are locked on the pommel. 2. The device according to claim 1, wherein said gripper body and said fingers are slidably mounted in the sleeve and said sleeve is formed with a recess allowing the fingers to spread apart and to release the pommel upon application of an external force overcoming the prestress of said prestressing spring. 3. The device according to claim 1, wherein said endmost face of the sleeve and said shoulder have a flaring shape for taking up lateral reactions and causing self centering during engagement of the sleeve on the pommel. 4. The device according to claim 1, wherein the gripper body has a central rod trasversing the whole of the mechanism and having a releasable abutment connection with a tubular rod situated at that end of the mechanism which is remote from said enmost face, the prestressing spring being compressed between said tubular rod and said sleeve. 5. The device according to claim 4, further comprising a tubular control rod fast with the sleeve and which cooperates with external longitudinal drive means, said tubular rod being located within and along said tubular control rod. 6. The device according to claim 2, wherein said sleeve is fast with a slide situated inside the gripper body and having a surface for abutting engagement with one end of the prestressing spring and the other end of the prestressing spring bears on a slider having a releasable abutment connection with the gripper body. 7. The device according to claim 6, wherein the abutment connection comprises locking cams disposed in the slider cooperating with an abutment sleeve fast with the gripper body and wherein a central rod is mounted in the slider for movement between a position in which it holds the cams in engagement against the sleeve and a position in which it allows the cams to retract. 8. The device according to claim 7, wherein the central rod is coaxial to a tube fast with the slider and to a tubular control rod fast with the gripper body and cooperating with longitudinal drive means. 9. The device according to claim 8, whereint he central rod is held in abutment against the tube through a stiffer spring by a less stiff spring and the central rod and the tube project outside the tubular control rod so as to allow the central rod and the tube to be moved with respect to each other with a tool, against the action of the return spring. 10. The device according to claim 1, wherein the sleeve comprises shoes for slidably guiding the sleeve along a fixed tubular guide placed in alignment with the control bar.