Patent Number: 048851230
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention is shown in FIGS. 1a, 1b, 1c, 2 and 3. The first embodiment is described below. The apparatus for handling the core constituent elements of the present invention is provided on a small rotating plug 4 at the position where a conventional control rod drive mechanism is provided, in place of the conventional control rod drive mechanism. The same number of apparatuses for handling the core constituent elements as that of the conventional control rod drive mechanism are provided at the same positions. The apparatus for handling the core constituent elements has the arrangement described below. A cylindrical frame 40 is vertically provided in the small rotating plug 4 of a fast breeder reactor, and a first elevating drive mechanism is provided in an upper portion of the frame. The first elevating drive mechanism comprises a horizontal frame 50 which is fixed to the cylindrical frame 40 at an upper position of the frame and is provided with a first motor 42, a gear 51 which is provided on the rotary drive shaft of the first motor 42, and gears 52 which each engage with the gear 51 and which are each provided on a screw shaft 53 that is rotatably supported by the frame 50. A lower screw portion of each of the screw shafts 53 is screwed into a first elevating frame 54 which is connected to a sleeve 57 by a side frame 54a. The first elevating frame 54 supports a second elevating drive mechanism that comprises a frame 60 which is provided on the first elevating frame 54 and has a second motor 61, a gear 62 which is provided on the rotating drive shaft of the second motor 61, and other gears 63 which each engage with the gear 62 and which are each provided on a screw shaft 64 which has an upper portion rotatably supported by the frame 60 and a lower screw portion screwed into a second elevating frame 65. The second elevating frame 65 comprises a top frame 66, a cylindrical side frame 67 which is connected to the top frame 66, a frame 55 which is provided at the lower end of the side frame, bellows 70 which connect the frame 55 to an operational shaft 69, a gripper support frame 59 which has an upper end fixed to the frame 55, and bellows 58 which are connected to the frame 55 and one sleeve 56 of the sleeves 56, 57. The second elevating frame 65 supports a third elevating drive mechanism which comprises a frame 71 which is provided on a top plate 66 and has a third motor 72, a gear 73 which is provided on the rotary drive shaft of the third motor 72, and other gears which each engage with the gear 73 and which are each provided on a screw shaft 75 which has an upper portion rotatably supported by a frame 71 and a lower screw portion screwed into an operational shaft support frame 76. The upper end of the operational shaft 69 is fixed to the operational shaft support frame 76. The side frame 67 is, as shown in FIG. 1c, divided into an upper frame 77 and a lower frame 78 which are connected to each other by a magnetic link mechanism 79. This magnetic link mechanism 79 comprises an electromagnet 80 supported by the frame 77, a cylindrical body frame 81 attracted by the electromagnet 80, and links 82, 83 connecting the body frame 81 to the magnet side. Each of the links 82 engages with a projection of the frame 78. The operational shaft 69 comprises an upper operational shaft 84 and a lower operational shaft 85 which are connected to each other by the lower end of the upper shaft being tightly inserted into the upper end of the lower shaft at an intermediate position of the operational shaft 69. As shown in FIG. 2, the gripper support frame 59 has a lower end of an external diameter that can be inserted into a handling head 16 of each of control rod assemblies 13, and fuel assemblies 11, 12, but the upper portion thereof has a large external diameter which cannot be inserted into the handling head 16. As shown in FIG. 2, three grippers 87 are provided on shafts 86 at equal angular intervals within the gripper support frame 59, and are rotatable around the shafts 86 so that the state shown in FIG. 2 can be changed to the state shown in FIG. 3 or vice versa. Each of the grippers 87 has a shape in which projections 88, 89 projecting inwards are provided in the upper end and an intermediate portion of the gripper 87, respectively, an upper hook 90 projects outwards, and a lower hook 91 projects inwards. Since the hooks 90, 91 are separated from each other in the longitudinal direction but are not much separated from each other in the lateral direction, the grippers 87 can be inserted into the narrow handling head 16 even when the hooks 90, 91 are projecting outward and inward, respectively. A handling head 19 provided at the upper end of a control rod 18 contained in each of the control rod assemblies 13 has a shape having a projection which projects outward in the lateral direction and so can be supported by the lower hooks 91. The handling head 16 of each of the control rod assemblies 13 and the fuel assemblies 11, 12 has a shape having a projection which projects inward in the lateral direction and so can be supported by the upper hooks 90. The lower end of the operational shaft 69 is provided with an operational head 92 which comprises an upper portion 93, a lower portion 94, and an intermediate portion 95 having a greater diameter than those of the upper and lower portions. A description will now be made of the operation of the first embodiment as configured above. When the first motor 42 is driven, the torque of the motor 42 is transmitted to each of the gears so as to rotate the screw shafts. When the screw shafts are rotated, the first elevating frame 54 and the structural portions below the frame 54 can be moved either upward or downward. In a state wherein the first elevating frame 54 has been moved downward, the lower end of the gripper support frame 59 is inserted in the handling head 16. When the third motor 76 is then driven, each of the gears 73, 74 is rotated so as to rotate the screw shafts 75. When the frame 71 is moved downward by the rotation of the screw shafts 75, the operational shaft 69 moves downward, with the bellows 70 extending so that the intermediate portion 95 of the operational head 92 abuts against the projections 88. Consequently, each of the grippers 87 rotates around its shaft 86 so as to close the lower ends of the grippers 87. When the grippers 87 are closed, the handling head 19 of the control rod 18 is supported by the hooks 90 of the grippers 87 so as to be gripped thereby. When the second motor 61 is then driven so as to rotate each of the gears 62, 63, the screw shafts 64 are rotated so that the second elevating frame 65 is moved either upward or downward. In the state wherein the handling head 19 of the control rod 18 is gripped by the grippers 87, the longitudinal movement of the second elevating frame 65 causes the control rod 18 to move the same amount as the longitudinal movement in the same direction. When the control rod 18 is moved downward so as to be deeply inserted in the core of the reactor, the output of the reactor is decreased; while, when the control rod is shallowly inserted into the core, the output is correspondingly increased. In this way, the output of the reactor is controlled. If the output of the reactor increases abnormally, the temperature of the coolant of the reactor rises above the normal temperature. In this case, the function of the electromagnet 80 of the magnet link mechanism 79 is shut off so that the body frame 81 is moved downward, as shown by the dot-dot-dash lines in FIG. 1c, and the links 82, 83 which were placed at certain angles are aligned along an oblique line. As a result, the engagement between the link 82 and the frame 78 is removed so that the frame 78 is moved downward until it hits the upper end of the lower operational shaft 85. The impact force produced by this collision causes the lower operational shaft 85 to be separated from the upper operational shaft 84 and moved downward together with the frame 78. Consequently, the control rod 18 is also moved downward and is more deeply inserted into the core of the reactor at high speed, regardless of the motors. The output of the reactor is therefore decreased so that a safe state of the reactor is obtained. The control rod assemblies 13 and the fuel assemblies 11, 12, which are the core constituent elements, are handled in the manner described below. The first elevating frame 54 is moved downward by driving the first motor 42 so that the lower end of the gripper support frame 59 is inserted shallowly into each control rod assembly, as shown in FIG. 3. Then the operational shaft 69 is moved downward by driving the third motor 72 so that the upper portion 93 and the lower portion 94 of the operational head 92 are brought into contact with the projections 88 and 89 of the grippers, respectively, and the lower ends of the grippers are opened, as shown in FIG. 3. When the grippers are opened, the hooks 90 and the handling head 16 are engaged with each other. When the first elevating frame 54 is then moved upward by driving the first motor 42, the second elevating frame 65, the operational shaft 69, and the gripper support frame 50 are also moved upward by the same amount at the same time. Thus the grippers 87 are moved upward while they are still open, and the hooks 90 engage with the handling head 16 so that each of the control rod assemblies 13 and the various fuel assemblies 11, 12 can be pulled up out of the core of the reactor. Subsequently, each of the pulled-up control rod assemblies 13 and the fuel assemblies 11, 12 is placed above a pocket provided in the periphery of the core by horizontally rotating the large rotating plug and the small rotating plug 4, and is then made to fall into the pocket by driving the first motor in the reverse direction. The operational shaft is then moved upward by driving the third motor 72 so that the grippers are closed. The gripper support frame 59 is moved upward by driving the first motor 42 or the second motor 61 while the grippers are closed so that the grippers 87 are separated from the handling head 16. Each of new control rod assemblies 13 and various fuel assemblies 11, 12 placed in the pocket can be gripped by the grippers 87 and transferred into the core by an operation which is the reverse of that of the transfer from the reactor core to the pocket. Therefore, in accordance with the first embodiment, it is possible to control the output of the reactor by controlling the position in the core at which each control rod 18 is inserted, and to cause the emergency shutdown of the output of the reactor by inserting the control rods deeply into the core by adding the weight of the structure above each control rod 18 thereto, regardless of the motors which are separated by the magnetic link mechanism 79 in which the function of the magnet might be shut off in an emergency, facilitating the work of exchanging the core constituent elements. Since the control rods and the fuel assemblies, which are core constituent elements, can be handled and exchanged in the space where a conventional control rod drive mechanism is provided, the space required for a conventional fuel exchanger can be removed so that the diameter of the small rotating plug 4 and the diameter of the large rotating plug surrounding the small rotating plug 4 can be greatly reduced. Therefore, the size of the reactor vessel can be reduced and the amount of materials used in the reactor structure can also be reduced, so that the reactor structure can be made more economical. FIG. 4 shows a second embodiment of the present invention. Since in the second embodiment only the first elevating drive mechanism is changed from the first embodiment, only the changed part is described below. Racks 45 are vertically fixed to an upper wall of the frame 40, and pinions 43 which each engage with the racks 45 are rotatably provided on a frame 37. The first motor 42 is provided on the frame 37 which supports the first elevating frame 54, and one of the pinions 43 directly engages with a drive gear 97 which is rotated by the first motor 42 and is engaged with the other pinions 43 through an idle gear 98. In this structure, since each of the pinions 43 is rotated by driving the first motor 42 while the pinions 43 are engaged with the corresponding racks 45, the first frame 54 can be moved upward. Since the other parts are the same as those of the first embodiment, the second embodiment can achieve the same functional effect as the first embodiment. The third embodiment shown in FIG. 5 is also an embodiment in which only the first elevating drive mechanism is changed, but the other parts are the same as those in the first embodiment. Therefore, only the changed part is described below. The first motor 42 is provided on the frame 50 fixed to the frame 40, and one end of a rope 100 is fixed to the lower surface of the frame 50 by means of a rope clamp 99. An intermediate portion of the rope 100 is passed through a pulley 46 provided on the first elevating frame 54 and through a pulley 48 provided on the lower surface of the frame 50, and the other end of the rope 100 is fixed to a balance weight 101. A gear 102 rotated by the first motor 42 is engaged with a gear 103 having a shaft which is common with the pulley 48. Therefore, when the first motor 42 is driven, each of the gears 102, 103 is rotated so as to rotate the pulley 48. The first elevating frame 54 can be thus moved upward. Since the other parts are the same as those in the first embodiment, the third embodiment can achieve the same functional effect as the first embodiment. In accordance with the present invention, it is possible to remove the space required for a conventional fuel exchanger and reduce the size of a reactor.