Apparatus for removing keys from a support grid a of nuclear fuel assembly

Abstract: An apparatus is presented for removing the keys (6, 9) smoothly and reliably from support grids (1) of a fuel assembly. The apparatus performs the task of removing the keys (6, 9), which had been inserted into the grid (1) through the opening sections (8) of the grid (1), and enables mechanization and automation of the key removal operation. The apparatus has a robotic arm (14) including a pair of parallel grid support members (15) freely movably disposed at the end of the robotic arm (14) for clamping onto the side edges of the grid (1). The apparatus further includes a key rotation device (16) disposed on the grid support members (15) for engaging with and rotating the keys (6, 9); a key moving device (17) disposed on the grid support members (15) so as to hold the keys (6, 9) and move the keys (6, 9) in the direction of the key axis.

Description: Background of the Invention Field of the Invention The present invention relates to an apparatus for assembling a fuel assembly and more specifically relates to an apparatus for mechanically or automatically removing the keys which had been inserted into the supporting grids of a fuel assembly for deflecting the springs away from the dimples to enable smooth loading of the fuel rods into the supporting grids. Background Technology In general, pressurized light water nuclear reactors utilize a type of fuel assembly comprising: an upper nozzle and a lower nozzle; a plurality of supporting grids for supporting the fuel rods (shortened to grids henceforth) disposed between the nozzles with a certain spacing; instrumentation pipes and control rod guide pipes inserted into and attached to the grid cells of the grids; and a plurality of fuel rods inserted into and held elastically in the grid cells between the springs and the dimples formed inside the grid cells. As shown in Figure 5, the grid 1 is made by intersecting a plurality of straps 1a which cross each other at right angles. As shown in Figure 2, the arrangement of the dimples 2 and springs 3 is symmetrical with respect to an axis at right angles to the paper passing through the center O formed by the intersection of a line X-X and a line Y-Y. The dimples 2 and the springs 3 are disposed so that they are symmetrical in each of the four quadrants. The reference numerals 4 and 5 designate, respectively, those grid cells 7 for housing control rod guide pipe and those housing instrumentation pipes. In Figures 3 and 4, the reference numeral 6 refers to an inner key. When assembling such a fuel assembly, there is a danger of introducing scratches on the surface of the fuel rods if the rods are inserted into the grid cells with the springs and dimples protruding out into the grid cells, because they are formed on the inside walls of the grid cells. To prevent damaging the surface of the fuel rods, there have been various methods suggested to deal with the prevention of surface damage problem. For example, a method proposed in a US-A-5,068,081 (Japanese Patent Application No. S64-957) proposed the following fuel assembly. In this fuel assembly, insertion openings 8 are formed in the grids 1, and the spring deflection jigs (not shown) are inserted into the grid cells 7 through the insertion openings 8 to deflect the springs 3 away from the dimples 2 formed in each wall of the grid cell 7 for elastically holding the fuel rod. The keys 6 are inserted through the key insertion openings 8 to keep the springs 3 in the deflected position, so as to allow the fuel rods to be inserted into the grid cells 7 smoothly without the danger of causing surface damages. To remove the keys 6 from the fuel assembly, the keys are first moved along the direction of the key axis, and the hook 6a is disengaged from the rib 1b of the strap 1a. Next, the keys 6 are rotated about the key axis through 90 degrees thereby orienting the keys 6 so that the hook 6a would not interfere with the rim section 8a of the insertion openings 8, and the keys 6 are removed from the grid 1 by withdrawing the keys 6 along the direction of the key axis 6. Further, an improvement in the key design such as the one shown in Figure 6 has also been made. The key 9' shown in Figure 6 has a protrusion sections 9'a disposed at regular intervals so as to contact the rim section 8a of the insertion openings 8 to enable to deactivate the spring 3. The protrusion section 9'a has a tapered section 9'b so that it can be moved in the key axis direction via the tapered section 9'b to disengage the protrusion section 9a from the rim section 8a of the insertion openings 8. Next, the key 9 is rotated 90 degrees about the key axis so that the protrusion section 9a will not interfere with the rim section 8a of the insertion openings 8, and the key 9 is removed from the grid 1. However, such insertion and removal operations for the keys 6, 9 are based on manual approach, causing operational problems because the tasks are cumbersome, the operations are lengthy and the efficiency is low. Furthermore, the workers involved in the key removal operation are required to work in the proximity of the fuel rods, and are particularly vulnerable to radiation exposure. From these viewpoints, there has been a need to automate the key removal operation. Summary of the Invention The present invention was made in view of the background technology described above, and an objective is to present a key removal apparatus which performs the task of key removal smoothly and reliably, and would enable mechanization and automation of the key removal operation. The above objective is achieved in an apparatus for removing keys from a grid of a fuel assembly having fuel rods inserted in a plurality of grid cells, formed by a plurality of straps of a thin longitudinal strip form intersecting at right angles to each other, having dimples formed on one adjacent pair of wall of the grid cells and springs formed on opposing pair of walls of the grid cells, wherein a plurality of keys which had been inserted in the grid in the longitudinal direction of the strap through opening sections formed near the intersections of the plurality of straps are removed by the apparatus comprising; a robotic arm means disposed so that the end section of the robotic arm is freely movable and the orientation of the robotic arm is changeable within a specific space; a pair of support members disposed at an end of the robotic arm means so as to enable each support member to approach or move away from each member; a key rotation device positioned so as to correspond with the keys inserted into the opening sections of the grid for rotating the keys about the key axis; a key moving device disposed on the support members for holding the ends of the keys inserted in the opening sections of the grid and move the keys in the direction of the key axis. The apparatus of the above construction operates by closing the pair of support members onto the side edges of the grid so as to engage the engaging members with the ends of the keys, and the key rotation device is then rotated through a specific angle, thereby disengaging the keys from the grid. The key moving device is operated next to move the keys along the direction of the key axis, thereby to remove the keys completely from the grid. Brief Description of the Drawings Figure 1 is a perspective view of a first embodiment of the key removal apparatus of the present invention. Figure 2 is an illustration to explain the arrangement of the dimples and springs formed in the grid cells in the central region of the grid. Figure 3 is a cross sectional view of a section through the line IV-IV in Figure 2 showing how the keys are operated. Figure 4 is a view showing the key rotation device attached to the side edge of the grid seen along the direction of the fuel rods. Figure 5 is a partial enlarged view of a perspective cut away section of one type of key design applicable to the key removal apparatus of the embodiment. Figure 6 is a partial enlarged view of a perspective cut away section of another type of key design applicable to the key removal apparatus of the embodiment. Preferred Embodiment of the Invention An embodiment of the key removal apparatus will be explained with reference to Figures 1 to 4. Figures 1 and 2 show a key removal apparatus for removing the inner keys which are disposed in the inner grid cells, and outer keys which are disposed in the outer grid cells of the grid. Both types of keys are used to retract the springs away from the dimples in the grid, before the fuel rods are inserted into the grids. The key removal apparatus is used to remove the inner keys 6 from the grid. In the following description, they are simply referred to as keys. The key removal apparatus comprises: a gate-shaped running bridge (transporting means) 11 movably disposed on a pair of guide rails 10; a robotic arm 14 movably disposed on a traversing rail 13 attached to the bottom surface of the horizontal section 12 of the running bridge 11, where the robotic arm 14 is provided with a pair of grid support members 15, disposed at the tip end of the robotic arm 14, which can move towards or away from each other, and a key rotation device 16 for rotating the keys 6 inserted into the grid 1 about the key axis, and further, the grid support member 15 is provided with a key moving device 17 for moving the keys 6 inserted into the grid 1 along the key axis. The robotic arm 14 is provided with an elbow section 140 which rotates in a horizontal plane, and a pair of elbow sections 141, 142 which rotate in mutually orthogonal planes. The key rotation device 16 comprises: a plurality of engaging members 160 freely rotatably disposed on the pair of grid support members 15, each engaging member 160 having a rectangular-shaped through hole; a timing pulley 161 disposed on the outer peripheral of each engaging member 160; a pair of endless belts 162 applied on each of a set of eight timing pulleys 161; a pair of one-way clutches 163a, 163b engaged with each pair of endless belt 162; a drive shaft 164 attached to each of the one-way clutches 163a, 163b; a drive motor (not shown) connected to the drive shaft 164. The key moving device 17 comprises: a pair of support arms 170 freely rotatably disposed on each of the grid support member 15; a roller member 171 rotatably disposed on the edge of each support arm 170; an arm driving motor 172 attached via a transmission device to each support arm 170; and a drive motor (not shown) engaged with each roller member 171. In Figure 1, the reference numeral 18 refers to a storage box for storing the keys 6. The operation of the key removing apparatus of the construction mentioned above will be explained with reference to Figure 5. First, the grid support members 15 are opened, and the running bridge 11 is moved along the guide rails 10, the robotic arm 14 is moved along the traversing rail 13, the elbow sections 140, 141 and 142 are rotated so as to dispose the grid support members 15 on both side surfaces of the grid 1 which has been disposed with the keys 6 and the outer keys which are disposed on the outer peripheral grid cells 7. Next, the support arms 15 are moved toward the side surfaces to close the support arms 15 so that the ends of the keys 6 are inserted into the through holes of the engaging members 160 freely rotatably disposed on the support arms 15. Next, by using the arm rotation motor 172 of the key moving device 17, each pair of support arms 170 is rotated down towards each other to hold the keys 6 between the roller members 171. By operating the roller driving motors to rotate the roller members 171, the keys 6 are moved in the direction of the key axis, thereby disengaging the hooks 6a from the ribs 1b. Accordingly, the springs 3 are allowed to extend towards the dimples 2, thus firmly holding the fuel rods therebetween. At this time, the arm driving motor 172 is reversed to separate the pair of roller members 171, thus releasing the clamping of the keys 6 by the roller members 171. Next, the driving shaft 164 is rotated through 90 degrees in one direction by the driving motor, then one of the one-way clutches 163a, 163b, for example 163a, transmits the rotational force of the driving shaft 164 to the belt 162 via the timing pulleys 161. The set of eight engaging members 160 are then rotated via the belt 162 and the timing pulleys 161 in one direction. The result is that the keys 6 engaged with the rectangular through holes of the engaging members 160 are likewise rotated through 90 degrees. The pair of support arms 170 are again operated to rotate the roller members 171 in place by operating the arm driving motor 172 to move the roller members 171 towards each other to again clamp the keys 6 therebetween. By operating the roller driving motor to rotate the roller members 171, the keys 6 are completely removed from the grid 1. The keys 6 thus removed from the grid 1 are stored in the key storage box 18 by separating the grid support member 15 from the grid 1 and operating the running bridge 11 and robotic arm 14 suitably. It has been demonstrated that the key removal apparatus of the present invention enables to remove the keys smoothly and reliably from the grid and to allow mechanization and automation of the removal operation. As mentioned earlier, the key removal apparatus is able to handle two types of keys (6, 9) shown in Figures 5 and 6. However, the operation to remove the keys 9 shown in Figure 6 is basically the same as that described for the keys 6 shown in Figure 5; the keys 9 are first moved in the key axis direction via the tapered section 9b to disengage the protrusion 9a from the rim section 8a, and the keys 9 are rotated through 90 degrees and moved along the key axis to remove the keys 9 completely from the grid 1.

Claims: Apparatus for removing keys (6, 9) from a grid (1) of a fuel assembly having fuel rods inserted in a plurality of grid cells (7), formed by a plurality of straps (1a) of a thin longitudinal strip form intersecting at right angles to each other, having dimples (2) formed on one adjacent pair of walls of said grid cells (7) and springs (3) formed on opposing pair of walls of said grid cells (7), wherein a plurality of keys (6, 9) which had been inserted in said grid (1) in the longitudinal direction of said straps through insertion openings (8) formed near the intersections of said plurality of straps are removed by said apparatus characterized by comprising; (a) a robotic arm means (14) disposed so that the end section of said robotic arm means (14) is freely movable and the orientation of said robotic arm means (14) is changeable within a specific space; (b) a pair of grid support members (15) disposed at an end of said robotic arm means (14) so as to enable each grid support member (15) to approach or move away from each other; (c) a key rotation device (16) disposed on said grid support members (15) for rotating said keys (6, 9) about the key axis; (d) a key moving device (17) disposed on said grid support members (15) for holding the ends of said keys (6, 9) inserted in said insertion openings (8) of said grid (1) and move said keys (6, 9) in the direction of the key axis. Apparatus as claimed in claim 1, wherein said robotic arm means (14) is disposed on a transporting means (11). Apparatus as claimed in claim 2, wherein said transporting means is a gate-shaped running bridge, and said robotic arm means (14) is disposed facing downwards on said gate-shaped running bridge. Apparatus as claimed in claim 1, wherein said robotic arm means (14) comprises at least two elbow sections (140, 141, 142) which are freely rotatably connected to said robotic arm means (14). Apparatus as claimed in claim 1, wherein said pair of grid support members (15) are disposed parallel to each other. Apparatus as claimed in claim 1, wherein said key moving device (17) comprises a pair of rotatable roller members (171) disposed longitudinally parallel to each other on said grid support members (15) so as to enable clamping of said keys (6, 9) between said roller members (171) by rotating the support arms (170) into position. Apparatus as claimed in claim 1, wherein said key rotation device (16) is provided with a plurality of engagement sections (160) which are positioned so as to correspond with the ends of said keys (6, 9) inserted into said insertion openings (8) of said grid (1) and engage with the ends of said keys (6, 9).

Inventors: INADA HITOSHI, MIWA NOBUO, OHUCHI KATSUNORI, INADA, HITOSHI,, MIWA, NOBUO,, OHUCHI, KATSUNORI,, INADA, HITOSHI, C/O TOHKAI SEISAKUSHO, Miwa, Nobuo, c/o Tohkai Seisakusho, OHUCHI, KATSUNORI, C/O TOHKAI SEISAKUSHO
Applicants: MITSUBISHI NUCLEAR FUEL, MITSUBISHI NUCLEAR FUEL CO.
Application year: 1993
Main classification: G21C21
IPC codes: G21C21, G21C3