Patent Number: 050248030
Section: description

DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows schematically a portion 1 of the enclosure of a nuclear reactor, notably of the so-called pressurized water type, including thick concrete protection walls 2 defining an inner zone 3 filled with water. A portion of the reactor shell is shown at 4, reference 5 denoting a nuclear fuel assembly adapted to be introduced or removed from the reactor core. The reactor structure as well as the means used for loading or unloading the core with the fuel assembly are well known in the art and therefore require no particular description, said means moreover having no direct relation with the object of the present invention. In FIG. 1, a fuel assembly 5 shown in solid lines is mounted in a substantially horizontal position, carried by a conveying carrier 6 brought into the inner zone 3, in a space (I) of the latter which forms a conventional a loading-unloading station. The mechanism allowing gripping the fuel assembly 5 on its carrier, transferring it from its horizontal position to a vertical position, and then transferring it so as to place it in vertical alignment with the core above shell 4, is schematically denoted as a whole by reference numeral 7. The conveying carrier 6 moves on a rolling path 8 provided in the bottom of enclosure 1, so as to pass from space (I) and from the loading-unloading station to a space (II) situated on the other side of the protection wall 2 with respect to space (I) and forming a receiving or removal station for the fuel assemblies, to selectively allow the positioning on the carrier of a new fuel assembly to be introduced in the core, or reversely receiving and removing a used fuel assembly removed from said core. During its transfer from space (I) toward space (II) or vice versa, the conveying carrier 6 passes through a guiding tunnel 9 provided in a passage 10 formed in the lower portion of wall 2, whereby said tunnel can be opened or closed by the closing block 11 of a lock-gate mounted at the lower end of a control stem 12, operated from the outside of the enclosure by a control mechanism 13. Space (II), where the removal or receiving station is placed, is filled with water 14 to a height necessary to provide a convenient protection to the outer environment during handling of the fuel assemblies 5, and particularly those extracted from the core which are highly radio-active. The control of the reciprocating movements of conveying carrier 6 from one to the other of spaces (I) and (II) is provided by means of a handling chain 15 the details of which will be explained hereinafter. Moreover, one of the ends of carrier 6 is connected to a traction cable 16 allowing the carrier to be returned inside space (II) to the receiving or removal station when an incident occurs on handling chain 15. Cable 16 is returned on a guide pulley 17 toward a control winch 18 provided at the upper portion of enclosure 1. FIGS. 2 and 3 show in greater detail a particular embodiment of the conveying carrier 6 and of the fuel assembly 5 monted in the latter inside a carrying structure 19 (FIG. 2), provided with side trunnions 20 pivoting inside bearings 21 so as to allow assembly 5 to be lifted respect to the carrier for loading or unloading operations, briefly mentioned hereinabove. Carrier 6 includes a support chassis 22 provided laterally with wheels 23 for the displacement of the carrier on path 8, particularly on carrying walls 24 conveniently arranged for receiving and guiding said wheels. The operating chain 15 is a chain of the "push-pull" type and includes successive links (FIGS. 3 and 4) each formed with two parallel side flanges, respectively 25 and 26. Between the flanges of any one of the chain links, preferably at the end of the chain, a fastening member 27 is engaged underneath the chassis 22 of carrier 6, flanges 25 and 26 being rigidly connected to said fastening member 27 by a connection means the details of which will be explained hereinafter. Flanges 25 and 26 extend into tongues 25a and 25a through which extends a connection shaft 28, including substantially in its central portion a double flange 29 defining a groove in which the teeth 30 of a control wheel 31 are successively engaged. The latter is rigidly connected to a horizontal shaft 32 and rotates inside a casing 33 provided between the carrier walls 24 of the rolling path 8. At one end of shaft 32 is supported a bevel pinion 34 in mesh with a pinion of same profile 35 keyed at the end of a control shaft 36, driven by an appropriate motor reduction 37 (FIG. 3). Chain 15, the detailed description of which does not directly refer to the invention, allows, depending on the direction of rotation of wheel 31, displacement of the conveying carrier 6 to the right or to the left in FIG. 1, respectively in the direction of spaces (I) or (II). When the chain winds itself into a spiral, it pulls the carrier to the removal or receiving station in space (II); on the contrary, when the chain is unwound, it becomes rigid and forms a one arm jack of the carrier toward space (I) in the direction of the loading and unloading station. According to the invention, the connection between the fastening member 27 rigidly connected to the carrier and the end link of chain 15, notably with the side flanges 25 and 26 of said link, is provided by means of a transverse spindle 38 penetrating bores in register, respectively 39 and 40, formed in the flanges on the one hand and in the fastening member on the other hand, as shown in FIG. 4. Moreover, spindle 38 is secured against motion with respect to fastening member 27, and therefore flanges 25 and 26 and also chain 15, by means of a pin 41 extending through the fastening element and the spindle, parallel to the link flanges. Spindle 38 is mounted inside a first housing 42 of corresponding shape, provided inside a support block 43. Said spindle 38 includes on on one of its sides a rectilinear rack 44, the housing 42 being open laterally to allow the teeth of a pinion 45 mounted in the support block 43 to mesh with rack 44. Pinion 45 is rigidly connected to shaft 46 extending vertically underneath chassis 22 of the conveying carrier (FIG. 2), said pinion 45 being substantially horizontal when such conditions prevail. The support block 43 also includes a second housing 47 extending perpendicularly to the direction of the first housing 42 so as to intersect the latter. Inside the second housing 42 is mounted a second spindle 48 including, like the first one, a rectilinear rack 49 adapted to mesh with the teeth of pinion 45. As may be seen in FIGS. 4 and 5, the relative position of spindles 38 and 48 is determined by the construction in such manner that, depending on the direction of pinion 45, one of the spindles penetrates inside support block 43 in its associated housing while the other extends outside the block by passing through the end of its own housing, and vice versa. Spindle 48 is rigidly connected outside block 43 to a stem 50, ending into a whorl 51 on which is attached the end of cable 16, the connection between the whorl and the cable being effected by any appropriate means, e.g., by crimping, screwing or other clamping and connection means. Whorl 51 includes one end 52 adapted for come to bear against an abutment 53 formed in alignment underneath chassis 22, with the cable 16 extending freely through said abutment via a passage 54. FIG. 6 shows schematically the control means for cable 16. Said cable is first passed around pulley 17, the position of which is fixed at the bottom of enclosure 14 by a support bracket 55, then upwardly to a second pulley 56. After passing around the latter, cable 16 is tackled on a mobile pulley 57 supporting a counter-weight 57a which exerts force on the cable maintaining it permanently taut. Beyond pulley 57, the cable winds itself on drum 58 of winch 18, controlled by a crank 59 or any equivalent driving means. The operation of the device according to the invention is easily understood from the explanations already given. Under normal operation conditions, the movements of carrier 6 between its two spaces (I) and (II), i.e., the loading and unloading station on the one hand, and the removal-receiving station on the other hand, are provided by means of the push-pull chain 15 which, according to the direction of its winding, causes the displacement of the carrier on its rolling path 8 on one side or the other. When an incident occurs and notably when there is a jamming or blockage of carrier 6 or of chain 15, it is of course important to be able to bring the carrier back rapidly to space (II) so as to be able to proceed, under acceptable conditions, to the necessary repairs and to the immediate removal of the assembly it supports, particularly if it is an irradiated assembly removed from the core. To the effect, this emergency device according to the invention consists in controlling, via winch 18, cable 16 in the direction where the latter exterts a traction force on spindle 48 engaged in its housing 47, the second spindle 38 being in that case in the position shown in FIG. 4 where it rigidly connects fastening member 27 flanges 25 and 26 of the end link of chain 15. The force thus exerted on the cable, transmitted from spindle 48 to spindle 38 via pinion 45, is applied to the connection pin 41 which, when judiciously calculated, can also abruptly break into three fragments, 41a and 41b remaining immobile inside fastening member 27, and 41c captive inside spindle 38 and permitting the removal of said spindle and simultaneously the progressive exit of the other spindle 48, respectively in and out of said block 43. After being broken, fastening member 27 is freed from chain 15, carrier 6 which is rigidly connected to the fastening member being no longer connected to the chain. As the force is still applied on cable 16, whorl 51 comes to bear via its end 52 on abutment 53 provided on chassis 22. At that moment, cable 16 can itself entrain the carrier and bring it back from any position of the latter on its rolling path 8 toward the receiving station (II) in the outer portion of enclosure 3. It should be noted that the whole of these operations is controlled remotely by a single operator, controlling only the drum 58 of winch 18. The contact established between whorl 51 and abutment 53 triggers by any known means a signal which is a confirmation for the operator to start driving the carrier and retracting it, until it reaches its final position. The invention thus provides a simple and particularly safe device enabling, when an incident occurs on the carrier handling chain, the return of the latter to a position which allows recovery of the fuel assembly which it supports. Cable 16 assumes under any circumstances the function imparted to it, which is the return of the carrier, particularly by using a tackle and counter-weight maintaining it permanently in a taut state. Of course, it goes without saying that the system according to the invention for the return, should an incident occur, of any remotely controlled mobile element, particularly of the freight-elevator type, or a loading member for a thermal treatment oven, a rolling mill, etc.