Patent Number: 047524340
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a coupling device between an elongate control bar, with longitudinal movement, intended for a nuclear reactor and a mechanism for driving the bar. It finds a particularly important, although not exclusive, application in light water cooled moderated reactors, using control bars comprising a cluster of parallel elements, containing a neutron absorbing material, which elements have a great length and so considerable flexibility and are suspended, at their upper end, from a piece generally called "spider". Control bar coupling devices are already known of the type comprising 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. In all these known coupling devices, the bar is simply suspended from the drive mechanism. Because of the very slender shape of the elements, because of their construction (generally a stack of pellets in a thin sheath), because of the disymmetrie and of the diversity of means for guiding them, considerable vibrations may appear during operation of the reactor. The coupling device cannot absorb the forces having a torque with respect to an axis passing through the gripping zone. The resilient blades work under poor conditions since, because of their very shape, they are only adapted for withstanding tractive forces. The inevitable clearances risk causing oscilltions and vibrations in the vertical direction. SUMMARY OF THE INVENTION It is an object of the invention to provide a releasable coupling devince in which the pommel of the control bar and the drive mechanism are connected against movement in any direction and any longitudinal clearance is taken up and external torques can be absorbed. To this end, there is provided a device of the above-defined type which comprises a sleeve movable with the mechanism, movable longitudinally with respect to the gripping fingers and having an end face bearingo n the shoulder of the pommel and comprises a prestressed spring exerting 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. The gripper body and the fingers may be slidably received in the sleeve. This latter may then be formed with a recess allowing the fingers to spread apart and to release the pommel when an external force is exerted against that of the prestressed spring and overcomes the prestress. The gripper body may be associated with a central rod passing through the whole of the mechanism and having an abutting connection with a tubular rod, said abutting connection being situated at the end of the mechanism opposite said end face, the prestressed spring then being compressed between said tubular rod and the sleeve. The embodiment which has just been described has the advantage of simplicity. On the other hand, it subjects the tubular rod to compression forces which may cause it to buckle. This buckling may however be limited by disposing the tubular rod under compression inside a drive shaft fast with the sleeve and which co-operates with external drive means for moving it longitudinally. the external drive means may be electromechanical means, numerous embodiments of which are known. Such means are for example described in French Pat. No. 1,371,802. If it is desired to locate all components of the coupling device immediately above the pommel, it is possible to use another embodiment which involves no compression stress on rods or tubes or great length. A device may more especially be used in which the sleeve is fast with a slide situated inside the gripper body and having a surface for abutting connection with one end of the prestressed spring bearing on a slider having a disengageable abutting connection with the gripper body. The invention will be better understood from the following description of particular embodiments, given by way of examples. The description refers to the accompanyng drawings.