Patent Number: 
Section: description

The installation described below is of general structure comparable to that disclosed in U.S. Pat. No. 5,317,609 to which reference can be made. Consequently, the description below relates essentially to those elements of the installation which are original. The complete installation can be constituted by apparatuses arranged in a hall provided with handling means, for example winches carried by a monorail. The installation includes means for feeding empty skeleton structures (not shown) and also means for feeding vessels containing rods to be loaded. These vessels are provided with biological protection when the rods they transport are radioactive, as applies in particular for so-called xe2x80x9cMOXxe2x80x9d rods containing pellets of uranium and plutonium oxide. Rods are transferred from a xe2x80x9cwaterfallxe2x80x9d carriage to follow a sinuous path therein, one after another. The waterfall carriage makes it possible to bring rods into rod-receiving magazines in a disposition corresponding to that of the rods in an assembly for loading. The order in which rods are fed to the waterfall carriage can be arranged so that the reception magazine receives rods of different kinds depending on their final locations in the assembly. FIG. 1 shows the position of the waterfall carriage 10 fitted with biological shielding when it is for receiving MOX rods, beside an inlet table 12 which is separated by a cleaning location from an indexing machine 14 of a reception magazine filled with rods coming from the carriage 10. In an advantageous embodiment, the magazine comprises an elongate receptacle in which a plurality of sets of pairs of grooves are formed. Each set is for receiving a particular set of perforated plates corresponding to a determined array of rods in the assembly for loading. An overhead crane that moves in direction 18 serves to bring the magazines 16 into the position shown by chain-dotted lines, on a support 20. The installation also has a rigid structure for receiving each skeleton structure in turn, which structure is constituted by a swingable bench 22 designed to receive biological protection 24 when the installation handles rods containing MOX fuel. The bench can be stationary or it can be mounted on rails enabling it to be brought into alignment with the reception magazine 16 and with a pulling bench 26 which is movable transversely on rails 28 enabling it to be brought into the position shown in dashed lines by being moved along double-headed arrow 30. The skeleton structures for loading can be brought onto the rocking bench 22 by means of a carriage 32. Finally, additional zones enable the usual operations of inspection and cleaning to be performed on complete assemblies, which the crane means can transport in a vertical position in the direction shown by dashed-line arrows 34. The essential apparatuses of the installation are described below in succession. Pulling Bench (FIGS. 2 to 5) The pulling bench 26 is for inserting rods into successive sheets into the skeleton structure of an assembly while the skeleton structure is supported horizontally. The bench can be regarded as comprising a frame 36, a carriage 38 that is movable along the frame, and a removable block 40 for selecting pulling elements. This block is selected from a plurality of blocks corresponding to different distributions of rods in an assembly. The bench 26 can also have removable safety arms 42 whose function is described below. The frame 36 includes a cradle 44 that is movable in the y direction by a motor 48 driving toothed wheels. The pulling bench can thus be taken from the working position in which it is shown in continuous lines in FIG. 1 to the rest position shown in dashed lines. On the cradle, there is mounted a beam 50 carrying the carriage. A motor 52 actuating actuators 54 serves to move the beam 50 vertically (z direction) to adjust the height of the pulling elements 56 (which are constituted by bars) so as to bring them level with each sheet of rods to be loaded. The carriage 38 is mounted on the beam 50 via bearings enabling it to move along the bench (x direction). These movements are driven by rotating a drive screw 58, itself driven by a motor. Pulling elements carried by the carriage are distributed to occupy a complete horizontal sheet. To enable the invention to be implemented, the pulling elements are connected to the carriage 38 by connection means which: in the pulling direction, i.e. when the carriage is tending to pull the rods from the magazine towards a structure, serve to provide a positive connection, via a mechanical abutment; and in the pushing direction, serve to perform resilient locking only, e.g. by means of a spring biased ball engaging into a recess in the pulling element. For safety reasons, a force sensor can be mounted between the pulling elements and the mechanical abutment of the positive connection, so as to measure the pulling force. In addition, the carriage is provided with a mechanism enabling the end clamp of the pulling elements to be opened and closed. FIG. 4 shows only one bell crank 60 of this transmission mechanism, which can be conventional. The clamps can be opened and closed by a mechanism similar to that described in above-mentioned U.S. Pat. No. 5,317,609. The block 40 for selecting pulling elements (FIG. 5) has a row of through holes in the same disposition as the pulling elements. Each hole in the selection block is provided with a retractable cover 61 preventing the corresponding pulling element from advancing when it is placed facing the hole by a pneumatic actuator such as 62. When the carriage moves towards the magazine containing rods in order to take hold of the rods, those elements which are in register with a cover become temporarily separated from the carriage and stop moving. This disposition is simple to implement when all of the assemblies to be loaded have the same rod distribution pitch, even if the rods are replaced by other elements at different locations. If, on the contrary, provision is made for loading assemblies having pitches that are very different, it can be necessary either to provide a plurality of different connection means, at appropriate pitches, or else to ensure that the pulling elements are very flexible. Rocking Bench (FIGS. 6 and 7) The rocking bench 22 holds the skeleton structure of the assembly for loading while the rods are being inserted, and optionally while the bottom and top nozzles are being mounted and guide tubes are fixed in the nozzles. It also serves to swing a loaded assembly from the horizontal position to the vertical position so as to enable it to be taken and transported without deforming by handling means such as an overhead crane. The rocking bench 22 can be regarded as comprising a frame 64 and an upending beam 66. The beam is designed to receive the skeleton structure 68 of the assembly for loading, represented in FIG. 6 by the grids 70 and the virtual envelope or outline 72 of the pull bars of a PWR assembly. The beam also carries an insert magazine 74 and a system 76 for extracting inserts. They can be of relatively conventional structure, and in particular of the structure described in above-mentioned U.S. Pat. No. 5,317,609, and they are designed so as to be easily replaceable depending on the nature of the assembly to be built up, for example by fixing them using eccentric clamping means. The frame 64 is typically rigidly secured to the ground. It is generally built as an all-welded structure. The beam 66 pivots relative to the frame 64 about a horizontal axis 78. To minimize its weight, the beam is advantageously constituted by an all-welded structure or a one-piece machined element whose configuration equalizes stresses and which can be designed by the finite element computation technique. An actuator 80, e.g. an electrical actuator, serves to move the beam 66 from the horizontal position in which it is shown in continuous lines in FIG. 7 to the vertical position shown in chain-dotted lines. When the actuator is extended and the beam is in the horizontal position, the end of the beam rests on a support 82 which is generally fixed to the ground. When the beam is in its vertical position, it enables a winch (not shown) to take hold of the top nozzle of the assembly and move it with minimum stress. To provide biological protection for operators who need to penetrate temporarily into the enclosure, the upending bench 22 is provided with a biological protection hood 24. In order to facilitate handling and upending of the beam, the hood is made up of a plurality of parts capable of sliding relative to one another between the position shown in FIG. 8 where they are placed side by side, and a position in which they overlap. In the embodiment of FIGS. 8 and 9, the hood is made up of a bottom inner part 84, a top inner part 86, and a middle outer part 90. Each of the inner parts carries a closure hatch 92 suspended from a linkage 94 that can be moved vertically by motors 96. These parts can be provided with wheels 98 resting on rails placed on the ground. The component parts of the protection hood can be provided with rings enabling them to be lifted by an overhead crane. The reception magazine 16 can also be covered by a biological protection hood 100 (FIG. 8) that can be closed by means of a hatch 102. The insert magazine 74 (FIG. 10) is similar in structure to that described in document U.S. Pat. No. 5,317,609. However a special type of magazine is provided for each type of assembly to be loaded. It comprises a receptacle 110 having an end wall pierced by passages distributed in the same array as the rods to be loaded and intended for receiving inserts. To enable rapid disassembly, the receptacle 110 can have a stand 111 which engages in a socket fixed to the upending beam 66 by screws. A centering pin 112 fixed to the beam engages in a housing of the receptacle to guarantee accurate assembly, and a pressure screw 112 retains the receptacle. The receptacle 110 and a slideway (not shown) parallel thereto hold a perforated closure plate 114 captive which can be moved by a pneumatic actuator 116 between a position in which it closes the passage and a position in which it opens them. The insert magazine interposed between the pulling bench and the skeleton structure serves to engage inserts on the bars which guide them through the grids of the skeleton structure. The inserts are retained in the magazine by the closure plate while the inserts are being put into place on the pull bars. In one position of the plate, the inserts are locked, and in the other position, the pull bars fitted with the inserts can move freely through the magazine. Clamping Skeleton Structures to the Rocking Bench (FIGS. 11 and 12) To make it possible to switch quickly from loading one type of assembly to another, the upending bench is designed so that different clamping means can be installed and removed quickly. These clamping means hold the skeleton structure in a precise position. FIG. 12 shows one of the clamps 118, out of eight, for example, for locking a PWR assembly skeleton by clamping on its grids simultaneously. The moving elements of the clamps are shown in continuous lines in the positions they occupy when the clamp is closed, and in chain-dotted lines in the positions they occupy when the clamp is open. The clamp can be regarded as comprising a clamp pad 120 fitted with means for installing it quickly on the rocking beam, e.g. constituted by bars 122 engaging beneath a soleplate of the beam and clampable by means of screws. One of the flanks of the pad carries an actuator 124 which actuates a lateral shoe 126 for pressing the grid against the other flank of the pad. The other flank carries a pin 128 on which a lid 130 pivots between a closed position and an open position in which the lid extends the arm of the pad upwards. In this position, a skeleton can be inserted into the pad. Another actuator 134 carried by the lid 130 enables the grid to be pressed down against the bottom of the pad and enables it to be centered exactly in the vertical direction, with horizontal direction centering being performed by the actuator 124. The means for clamping a boiling water reactor assembly skeleton structure can have the structure shown in FIG. 11. To enable each clamp to be placed at a suitable location for assembly, the clamp is mounted on a lockable slide 135 mounted on a slideway 136 which is rigidly mounted on the upending beam. The slide is lockable by means of an eccentric. The clamp can be regarded as having a clamp pad on which two arms 138 and 140 are hinged. A double-acting pneumatic actuator 142 enables the two arms to be pivoted between a position in which they hold the skeleton structure captive and a position (shown in chain-dotted lines in FIG. 11) in which they release it. The arm 138 constitutes one of the side walls of a reception space. The arm 140 constitutes the other side wall and the lid. Each of the arms has shoes, similar to the shoe 126 shown in FIG. 12, serving to lock the skeleton structure in place. Each pivoting arm of each clamp can be provided with means for locking it in closed position, actuated by pneumatic actuators. Sensors make it possible to determine whether or not the clamp is closed. Pins can be provided on the clamp for retaining the skeleton structure in the axial position. Although the actuators of all the clamps can be controlled from a single pneumatic distributor in the example shown in FIG. 12, it is usually necessary for the example shown in FIG. 11 to provide an individual distributor for each clamp. To enable the actuators to be powered electrically and/or pneumatically and to enable the signals delivered by the sensors responsive to the condition of the clamp to be transmitted, the clamp is generally provided with a length of cable terminated by a connector for connection with a general feed cable placed under the beam. The frame 36 can also have a cable path followed by electrical and/or pneumatic connections between the solenoid valves and actuators for moving the pulling or pushing elements, and by a bus line for transferring electrical signals. Further clamps other than those shown in FIGS. 11 and 12 can be provided for assemblies of any other kind, and in particular for assemblies of hexagonal section. The pulling bench 26 can be provided with removable safety arms 42 to ensure that while rods are being pulled they are not pulled too far. FIG. 13 shows two removable arms 42 mounted on the cover block 40. These arms can be placed either in a horizontal working position (in continuous lines in FIG. 13) or in a vertical retracted position. The removable arms carry a photoelectric detector 144 placed on the path of the pulling elements and the rods at a location that is intermediate between the insert magazine 74 and the skeleton structure. During the pulling cycle, the arms are placed in the horizontal position and provide an alarm signal if a rod reaches the line of site of the photoelectric detector during a pulling operation.