Patent Number: 050248030
Section: summary

FIELD OF THE INVENTION The present invention relates to an emergency device which allows, upon the occurence of an incident and particularly the blocking of a conveying carrier transporting nuclear fuel assemblies inside and outside the enclosure of a reactor, automatic detachment of the carrier from the chain or other mechanical control means normally used for its displacement, and then its safe return to a predetermined position. BACKGROUND OF THE INVENTION During loading and unloading of a nuclear reactor with the fuel assemblies forming the core of the latter, a conveying carrier is normally used for supporting and displacing at least one new assembly to be put in position in the core, or the used assembly removed from the latter and to be transferred to a storage well which is outside the reactor enclosure. The carrier moves during its displacement at a convenient depth underneath the level of the protection water, by rolling on rails or similar guiding means between a receiving or removal position of a new or used assembly, provided outside the enclosure, and a loading or unloading position of the assembly, arranged inside said enclosure and in which it is removed from or positioned on the carrier. Between these two positions, the carrier slides or rolls on its rails, usually under the effect of a chain adapted to exert a pushing effort or reversely a traction effort, on the carrier, said chain being preferably controlled in the vicinity of the receiving or removal position of the assemblies outside the enclosure. The chain has the property of winding on itself as the carrier is drawn toward the latter position, enabling it to occupy only a reduced space inside the storage well, and also having sufficient rigidity when unwound to assume the function of a jack stem or arm of the carrier for bringing the latter to its loading or unloading position inside the reactor enclosure. In prior art mechanism of this type the conveying carrier generally includes several controls, which require accurate coordination and necessitate the use of numerous and specialized personnel, distributed in the successive handling stations. Problems result when, for some reason, there is jamming or blockage of these control means, the carrier then running the risk of not being able to be brought back to its receiving or removal position for the new or used elements outside the enclosure. In such a case, it becomes necessary to resort to unblocking means which are heavy and cumbersome and the operation of which is complex, for example by using a pole, possibly telecontrolled, and which, through the head of protective water, acts on a rocker adapted to pivotably disengage the teeth of a drive pinion from a control rack for displacement of the carrier, before it is in position to bring it back, for example by means of a cable connected to the carrier frame and winding itself at its opposite end on the drum of winch. A conveying carrier for nuclear fuel assembly, adapted to be transferred in the reactor building or in an annex building, with a reciprocating motion inside a horizontal communication duct along the axis of which it moves on carrying rails, is known from French patent FR-A-2 234 637. The movement of the carrier is effected with the assistance of a pusher arm having an end rigidly connected to a double chain, which is in turn driven on control pinions. When an incident occurs, particularly when the carrier is immobilized inside the reactor building, it is necessary to bring it back outside of said building; to this effect, one uses a cable provided with a clevis retained by a shearing pin, so that, when traction is applied to the cable, the pin breaks, thereby allowing the clevis to be blocked inside the end of the pusher arm, in order to permit retraction of the latter and that of the carrier due to the cable moving back upwardly. However, in this arrangement the pusher arm always remains rigidly connected to the carrier; if the incident is due to the arm itself, for example when blocked in the communication duct, the device fails and the cable does not allow the carrier to be returned to the annex building. SUMMARY OF THE INVENTION The present invention relates to an emergency device avoiding these disadvantages, by providing a significant simplification of the mechanisms required for control of the displacement of the conveying carrier, particularly when an incident occurs and when the carrier is blocked. The device allows the carrier to be easily disconnected from its control members, particularly from the handling chain, and to be returned to a position outside the reactor enclosure, these operations being effected in a safe and rapid manner from a single station, thereby reducing both the requirement for personnel and the duration of their possible exposure to the effects of a hostile environment. To this effect, the device in consideration, in which the conveying carrier moves under the effect of a push-pull chain actuated by a driving mechanism causing, depending on the direction, its winding on itself in spiral so as to pull the carrier, or its unwinding by forming then a carrier rigid pushing element, including a connecting member between the chain and the carrier, formed of two portions connected to each other by a pin adapted to be broken when required for disconnecting the two portions and to free the carrier from the chain, is characterized in that breakage of the pin is due to the effect of traction exerted remotely from the carrier on a control cable in such manner that, after breaking, the cable can apply a traction on the carrier so as to bring it back freely, independently of the chain, to a predetermined position, the connecting member between the chain and the carrier including a fastening member carried by or rigidly connected to the carrier and connected to the two parallel flanges of a link of the chain by means of a transverse spindle, the fastening member and the spindle being connected by the pin placed parallel to the link flanges. During normal operation, the control of the carrier displacement is effected by the driving of the chain whose structure, which is known per se, is such that according to the direction of its winding or unwinding it pulls or pushes the carrier from one position to another, respectively inside and outside the reactor enclosure. When there is a blockage of the carrier or chain, causing the immobilization of the carrier in some intermediate position, the device according to the invention allows the chain to be separated remotely, safely and rapidly from the carrier, by acting on a cable which first causes the breaking of the connecting pin, then exerts on the carrier a traction force bringing it back to a chosen position, outside the enclosure, where necessary repairs and positioning of a replacement pin may take place. According to another feature of the device the transverse spindle, which extends freely through aligned passages in the link flanges and the fastening member, respectively, is secured against motion with respect to the fastening member by means of the pin during normal operation of the carrier. When an incident occurs, a force exerted on the spindle parallel to itself causes breakage of the pin, the spindle disengaging from the fastening member and from the flanges, while disconnecting these two elements from one another and allowing then the displacement of the carrier independently of the chain. Preferably, the transverse spindle is slidably mounted in a first housing of a support block, carried by the carrier and including a rack actuated by a flat pinion, which is mounted so as to rotate freely on an axis perpendicular to the pinion and rigidly connected to the support block. According to another feature, the pinion actuating the spindle rack is driven in rotation by a second spindle mounted in the support block inside a second housing located in the plane of the first housing but perpendicularly to it, this second spindle also including a rack in mesh with the pinion, such that the rotation of the latter selectively simulaneous and opposite displacements of the spindles, respectively toward the inside and the outside of the support block. According to still to another feature, the second spindle is rigidly connected at its end outside the support block to a connecting end-piece with the traction cable. Advantageously, the end-piece includes a whorl, adapted to come to bear at the end of the stem stroke and under the effect of the pinion on an abutment rigidly connected to the carrier in such manner that a traction effort exerted on the cable once the pin is broken brings the whorl against the abutment, thereby causing the entrainment of the carrier by the cable. Moreover, the pinion support block is mounted inside a tight casing which is supported by the pinion rotation axis, said pinion being in turn disposed underneath the carrier lower face. In a preferred embodiment of the invention, the traction cable is actuated by a winch, situated at a distance from the carrier and on the drum of which is wound the cable, guided toward the carrier up to the connecting end-piece by return pullies. Preferably also, the cable winds itself on a mobile pulley, provided with a counter-weight exerting a constant tension on the cable, which remains permanently taut, whatever the position of the carrier. According still to another feature of the device, the carrier includes wheels moving on rails extending parallel to the working plane of the push-pull chain. Preferably, the chain winds itself on a control toothed wheel, driven by a return mechanism from a reduction motor unit.