Patent Number: 050646060
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, and particularly to FIG. 5, there is illustrated a front elevational view of a channel box removing apparatus of the present invention generally designated by the numeral 70. As shown, the channel box removing apparatus 70 comprises a frame structure 72 including four elongated, upright, angular support members 74 defining four corners thereof; and a lifting rod 76 mounted to and extending upwardly from the top of the frame structure 72. The lifting rod 76 is normally connected to the lower end of a suspension wire 78 by means of a spring-loaded shock absorber 80 and a cable terminal fitting 82. The suspension wire 78 is connected to an auxiliary hoist, crane or the like (not shown). As seen in FIGS. 5, 6 and 8, the channel box removing apparatus 70 includes a pair of releasable hooks 84 adapted to engage the undersurfaces of clips 86 provided adjacent a pair of diagonally opposed top corners of the channel box 12. Each of the releasable hooks 84 has an upper end pivotally mounted by a pin 88 on the lower portion of the frame structure 72 and a lower end extending downwardly from the bottom of the frame structure. The removal apparatus also includes a bifurcated bracket 90 which is pivotally connected to the releasable hooks 84 by pins 92 in a manner to straddle the hook pair, as best seen in FIGS. 8A and 8B. Vertical movement of the bracket 90 results in the movement of the pair of releasable hooks 84 between an unlatched position (FIG. 8A) and a latched position (FIG. 8B). The channel box removing apparatus 70 also includes a pneumatic control mechanism 94 for controlling the movement of the releasable hooks 84, which comprises a double-acting pneumatic cylinder 96 mounted substantially in the center of the removal apparatus, a piston rod 98 having its lower end operatively connected to the bracket 90, and resilient air hoses 100 leading from two chambers of the pneumatic cylinder 96. The resilient air hoses 100 are in turn connected at their respective upper ends to connector plugs 102. A hand lever 104 having a ring end is provided which permits forced disengagement of the releasable hooks 84 from the channel box. The hand lever 104 is rotatably mounted at the other end to the frame structure 72 by means of a pin 106 (FIG. 9) and also is pivotably connected adjacent the other end to the upper end of a piston rod 108 by a pin 110 (FIG. 9). The channel box removing apparatus 70 includes a bail cap 112 which is adapted for placement on a bail 114 provided on an upper tie plate of the nuclear fuel assembly. The bail cap 112 comprises a pair of spaced support members 116 provided in opposed relationship to each other and having a vertically extending guide slot 118 defined therebetween to slidably receive the bail 114, a connector member 120 securely connecting the pair of support members 116 in their middle portions and adapted for abutting engagement with the top of the bail 114, and a pair of bail guides 122 extending downwardly and outwardly from the bottom ends of the respective support members 116 and having their open lower edges adapted to abut the upper ends of the channel box 12 adjacent a pair of diagonally opposed corners thereof which are different from the pair of corners having the clips 86 provided thereon. The bail cap 112 is provided on the removing apparatus for vertical movement along a guide groove 124 defined in the lower portion thereof. Referring to FIGS. 6 and 8, there is provided a locking mechanism 126 for locking the releasable hooks 84 in the latched position, i.e., in engagement with the undersurfaces of the associated clips 86 of the channel box 12. The locking mechanism 126 includes a pair of swing plates 128 which can selectively double the range of pivotal movement of the releasable hooks 84 and which are pivotally mounted adjacent their upper ends to the frame structure 72 by pins 130. A pin 132 projecting from each releasable hook 84 is loosely received in a slit 134 formed in the swing plate 128 to permit a swinging movement of the lower end of the swing plate 128 beyond the pivotal range of the releasable hook 84. Each swing plate 128 has a stopper pin 136 provided at its lower end. The bail cap 112 has a pair of stopper members 138 integrally formed on the side surfaces thereof. Each stopper member 138 has a groove indicated by phantom lines which can be engaged by the associated stopper pin 136 when the associated releasable hook 84 is in its unlatched position as shown in FIG. 8(A). When the associated releasable hook 84 is in its latched position with the bail cap 112 slightly lowered relative to the removal apparatus, the stopper pin 136 abuts the stopper member 138. Referring to FIG. 9, there is provided a first indicator mechanism 140 which comprises a red indicator plate 142 in the shape of a right-angled equilateral triangle, the indicator plate 142 being pivotally mounted adjacent its bottom end to the top of the frame structure 72 for swinging movement between an upright and a horizontal position, an actuator link 144 pivotally mounted at its middle portion to the frame structure, the actuator link 144 being engagable with the bail cap 112 in the guide groove 116 provided in the lower portion of the removal apparatus, and a control rod 146 having opposite ends pivotally connected to the rear face of the red indicator plate 142 and one end of the actuator link 144, respectively. The control rod 146 comprises a lower portion 146a, and an upper portion 146b adapted to be vertically moved relative to the lower portion 146a. The upper portion 146b is biased downwardly by a spring 148 and includes a pin 150 provided in the middle portion thereof which causes vertical movement of the upper portion 146b in response to the movement of the hand lever 104 because of its engagement with the pin 150. The lower portion 146a is biased upwardly by a spring 152, the upper end of the lower portion 146a being in engagement with a stopper 154 on the upper portion 146b normally, i.e., when the bail cap 112 is out of engagement with the actuator link 144. Accordingly, with the bail guides 122 of the removal apparatus 70 resting in place on the diagonally opposed corners of the channel box 12, further lowering of the removal apparatus relative to the bail cap 112 until the unlatched hooks 84 are inserted into the channel box 12 will bring the bail cap 112 into engagement with the lower end of the actuator link 144. This will rotate the actuator link 144 in a counter-clockwise direction as viewed in FIG. 9 and accordingly move the lower portion 146a downwardly against the action of the spring 152. In this condition, the piston rod 108 can be lowered by actuation of the pneumatic cylinder 96 to move the releasable hooks 84 to the latched position where they engage the undersurfaces of the associated clips 86 of the channel box 12. This will cause a downward movement of the upper portion 146b by the action of the spring 148, rotating the hand lever 104 in a counter-clockwise direction as viewed in FIG. 9 because of its engagement with the pin 150. As a result, the red indicator plate 142 is moved to its horizontal position indicating that the pair of releasable hooks 84 are in the latched position. Referring to FIG. 10, there is provided a second indicator mechanism 160 comprising a yellow indicator plate 162 in the shape of a right-angled equilateral triangle also, the plate 162 being pivotally mounted adjacent its bottom end to the top of the removal apparatus 70 on the opposite side to the red indicator plate 142 so that the yellow indicator plate 162 can swing between its upright and horizontal positions. The second indicator mechanism 160 also includes an actuator link 164 having its upper end pivotally connected to the yellow indicator plate 162, the lower end of the control rod 164 slidably extending through the guide groove 124 in the lower portion of the removal apparatus and an aligned groove of the bail cap 112 into the vertically extending guide slot 118. The yellow indicator plate 162 normally assumes the horizontal position under the action of the weight of the actuator link 164. However, in lowering the removal apparatus 70, when the lower edges of the bail guide 122 first comes into abutting engagement with the associated corners of the channel box 12, followed by the bail 114 of the channel box 12 being received in the bail cap 112, the bail cap 112 will move upwardly relative to the removal apparatus, causing the bail 114 to come into abutting engagement with the lower end of the control rod 164. As a result, the control rod 164 is moved upward to rotate the yellow indicator plate 162 in a counter-clockwise direction as viewed in FIG. 10 to the upright position. When the releasable hooks 84 are moved to the latched position to engage the undersurfaces of the associated clips 86 of the channel box 12, lifting of the removal apparatus will move the channel box 12 upwardly relative to the fuel assembly proper 14 and, at the same time, cause lowering of the bail cap 112 relative to the removal apparatus. As a result, the bail 114 is disengaged from the actuator link 164, causing the yellow indicator plate 162 to swing to the horizontal position under the action of the weight of the actuator link 164. It should thus be noted that when the yellow indicator plate 162 is in the upright position, it provides a visual indication that the bail cap 112 is in the position to fully receive the bail 114. When the yellow indicator plate 162 is in the horizontal position, it indicates that the channel box 12 can be pulled up separately from the fuel assembly. Referring to FIGS. 11(A) and 11(B), there is shown a guide unit 170 removably mounted to the bail cap 112 to facilitate guidance of the removal apparatus into its operative position with the fuel assembly from which the channel box is to be removed. The guide unit 170 comprises a pair of conical guide rollers 172 rotatable about a common horizontal axis, and a pair of support members 174 having their lower ends rotatably supporting the guide rollers 172. The pair of support members 174 of the guide unit 170 are removably and rotatably mounted to the lower end of the bail cap 112 by connector pins or ball lock pins 176. As best seen in FIG. 11(B), the pair of guide rollers 172 can slidably and rotatably engage a pair of diagonally opposed corners of the channel box 12 having no clips attached thereto. It will be appreciated by those skilled in the art that this guide unit can conveniently be used in hoisting and transfering channel boxes separated from their associated fuel assemblies. Removal of the channel box from the associated fuel assembly using the removal apparatus of the present invention is accomplished during refuelling, as follows: (1) About 200 spent fuel assemblies previously transferred from a reactor core (not shown) onto the fuel rack 40 within the spent fuel storage pool 41 are lifted by the main hoist 42 on the refuelling platform car 44 for transfer to the preparation machine 46. (2) At the preparation machine 46, the fastener bolts 16 threaded into the associated clips 86 to secure the channel box to the fuel assembly proper are removed by a conventional bolt wrench (not shown) which is about four meters long. (3) After removal of the fastener bolts, the nuclear fuel assembly is transferred by the main hoist 42 from the preparation machine 46 back to the fuel rack 40. (4) The channel box removing apparatus 70 is suspended from the cable terminal end of the auxiliary hoist 56 and is lowered onto the nuclear fuel assembly placed in the fuel rack 40. Then the channel box 12 is pulled up from the nuclear fuel assembly to be separated therefrom by the auxiliary hoist 56 and is transferred to an unoccupied location in the fuel rack. It will be appreciated that the above steps (1) to (4) of channel box removal are much simpler and less time consuming than the conventional steps (1) to (5) as described above. If a long bolt wrench, e.g., 10 meters long, such as one disclosed in, applicant's copending U.S. application, Ser. No. 07/501,107, entitled: "Bolt Wrench" is used, the step (1) of transferring the nuclear fuel assembly from the fuel rack to the preparation machine as well as the step (3) of transferring the nuclear fuel assembly with the fastener bolts removed from the preparation machine back to the fuel rack can be dispensed with. Now, the manner in which the channel box is separated from the fuel assembly in step (4) will be described in more detail: The removal apparatus of the invention is gradually lowered onto the fuel assembly 10 on the fuel rack 40. During lowering of the removal apparatus, the bail 114 of the upper tie plate of the unclear fuel assembly 10 serves to guide the bail guide 122 of the removal apparatus 70 into a position where the bail cap 112 completely covers the bail 114 while simultaneously the lower edges of the bail guides 122 rest on the top of the channel box 12. Further lowering of the removal apparatus 70 will move the bail cap 112 upwardly relative to the apparatus and cause the pair of releasable hooks 84 to be inserted into the channel box 12. This will cause the bail 114 to move the control rod 164 upwardly, resulting in a swinging movement of the yellow indicator plate 162 to the upright position. In the upright position, the red indicator plate 142 is not visible from just above. Now, the pneumatic cylinder 96 may be activated to move the piston rod 108 downwardly so as to move the pair of releasable hooks 84 into the latched position where the hooks are in lifting engagement with the associated clips 86 of the channel box 12. When the piston rod 108 moves downwardly, the upper portion 146b of the actuator link 146 also is moved downwardly by the action of the spring 148, because the upper portion 146b is operatively connected with the piston rod 108 via the pin 110, the hand lever 104 and the pin 150. Accordingly, the red indicator plate 142 swings to the horizontal position so that the red indicator plate is visible from just above. Next, the removal apparatus 70 is lifted by the auxiliary hoist 56 relative to the bail cap 112 which rests on the channel box 12. This will cause the stopper pins 136 on the pair of releasable hooks 84 to engage the associated stopper members 138 as shown in FIG. 8(B) so that the releasable hooks 84 are effectively locked to prevent their disengagement from the associated clips 86 on the channel box 12 even in the event of a malfunction of the pneumatic cylinder 96, for example. As the removal apparatus 70 is further lifted, the channel box 12 is moved upwardly separately from the nuclear fuel assembly proper 14. This will disengage the lower end of the control rod 164 from engagement with the bail 114 and accordingly cause the yellow indicator plate 162 to swing to the horizontal position under the action of the weight of the control rod 164. In the horizontal position, the yellow indicator plate 162 is visible from just above. It should be noted that the second indicator mechanism 160 provides a visual indication that the channel box 12 has been removed from the nuclear fuel assembly 14. The removal apparatus 70 carrying the channel box 12 is then moved to a position above an intended location in the spent fuel storage pool 41, normally the fuel rack 40, where it is lowered until the channel box reaches the bottom of the fuel rack. When the removal apparatus 70 is further lowered relative to the channel box 12, the stopper pins 136 disengage from the associated stopper members 138. In this condition, the pneumatic cylinder 96 is activated to move the piston rod 108 upwardly so as to move the pair of releasable hooks 84 into the unlatched position as shown in FIG. 8(A). As shown, the pair of releasable hooks 84 are out of engagement with the associated clips 86, so that the removal apparatus 70 can be lifted separately from the channel box 12. It will be appreciated that the hand lever 104 provides an emergency disconnect mechanism for moving the pair of releasable hooks 84 into the unlatched position in the event of a malfunction of the air supply system including a faulty air source or air hoses. That is, if difficulties are experienced in releasing or disengaging the pair of hooks 84 from the clips 86 of the channel box 12, the hand lever 104 may be moved upwardly by hooking the ring portion by suitable means and lifting it to move the piston rod 108 upwardly to thereby unlatch the pair of releasable hooks 84. It will be appreciated that in accordance with the teachings of the present invention there has been provided an improved apparatus for removing a channel box from a nuclear fuel assembly in an efficient and reliable manner. To recapitulate the important features of the invention: (1) The invention can simplify the channel box removal operation by eliminating certain transfer steps which were necessary if the removal apparatus of the conventional type is used. This provides additional advantages of a reduced operation time, a decreased operator's exposure to radioactivities, and a reduced possibility of damage to fuel assemblies during transfer. (2) The provision of the lock mechanism prevents accidental release of the pair of releasable hooks 84 with the consequential fall of the channel box 12, as the releasable hooks cannot be disengaged from the associated clips 86 so long as the stopper pins 136 are in engagement with the stopper members 138 as shown in FIG. 8(B). (3) The use of the first and second indicator mechanisms 140 and 160 provides visual indications that the removal apparatus 70 is in lifting engagement, or out of engagement with the channel box 12, respectively. When the red indicator plate 142 is in the horizontal position, it indicates that the removal apparatus 70 can be lifted to separate the channel box from the fuel assembly proper 14 as the pair of releasable hooks 84 are in positive engagement with the clips 86 of the channel box. On the other hand, when the yellow indicator plate 162 is in the horizontal position, it indicates that the pair of releasable hooks 84 are out of engagement with the associated clips 86 so that the removal apparatus can be lifted separately from the channel box. This enables various underwater operations within the spent fuel storge pool to be performed efficiently and reliably by remote control. Although the present invention has been described in terms of what are at present believed to be its preferred embodiments, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention. It is therefore intended that the appended claims cover such changes.