Patent Number: 062822543
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated a spent fuel pit 10 which contains a plurality of spent nuclear fuel racks 12. The pit 10 is a sealed enclosure comprised of concrete 14 and a sealed metallic liner 16. The spent fuel pit 10 is filled with a shielding medium, such as water containing boric acid 18. Each fuel rack 12 includes a plurality of vertically oriented spaced apart fuel cells 20. Each cell 20 is sized to receive a fuel assembly 50 (described below). Each cell 20 has a metallic can 22 affixed to the top of the cell 20. The can 22 may include a square funnel to guide a fuel assembly 50 into its storage position. As shown in FIG. 2, the can 22 includes two bores 24, 26 in raised plates 25, 27 at diagonally opposite corners. The remaining corners of the can 22 define standoff plates 28, 30. Referring to FIG. 2, a poison rod assembly 40 is shown partially extracted from a fuel cell 20. Each fuel assembly 50 is formed in part from fuel rods 52 which are intermixed with poison rods 42. The fuel rods 52 are generally positioned on the periphery of the fuel assembly 50 and the poison rods 42 are generally positioned in an inner portion of the fuel assembly 50. The poison rods 42 are joined at their top portions by a support web 44. A T-shaped bar 46 is attached to the support web 44 extending upwardly, forming an easily accessible handle for lifting the poison rod assembly 40. When the poison rod assembly 40 is positioned within the fuel assembly 50, each poison rod 42 is disposed within a thimble 48 mounted in the fuel assembly 50. Referring to FIG. 1, a poison rod assembly transfer device 70 of the present invention is illustrated within a spent fuel pit 10. The transfer device 70 is suspended within the spent fuel pit 10 by an overhead crane 60. The overhead crane 60 is coupled to a moveable walkway 62 and gantry 63. The moveable walkway 62 and gantry 63 are mounted on walkway rails 64 located above the water line 18 of the spent fuel pit 10. The crane 60, moveable walkway 62 and gantry 63 are used to lift the transfer device 70 and a poison rod assembly 40 and move them between fuel cells 20. The transfer device 70 is seated on a fuel cell 20 and attached to a poison rod assembly 40 as detailed below. As shown in FIGS. 3, 4a, 4b and 5, the transfer device 70 includes an outer member 200 that is divided into two portions, a frame assembly 80, located at the lower end of the transfer device 70, and an upper portion 90. In the preferred embodiment, the upper portion 90 is tubular, including an inner tubular member 230 and outer tubular member 250, described in detail below. Generally, and as will be described in detail below, the frame assembly 80 is fixed to the fixed outer tubular member 250 of upper portion 90. The frame assembly 80 and the outer tubular member 250 are of an appropriate length so that the top of the outer tubular member 250 is adjacent to the walkway 62 when the transfer device 70 is seated on a fuel cell 20. An inner tubular member 230 is slidably disposed within the outer tubular member 250 and supports a gripper assembly 210. Gripper assembly 210 is disposed within the frame assembly 80. As shown in FIG. 3, the inner tubular member 230 may be raised and lowered between an upper position 228 and a lower position 229 by a winch (not shown) as described in Hornak et al., U.S. Pat. No. 5,325,408. Alternatively, inner tubular member 230 and outer tubular member 250 may be linked by an interlock device 280 as described in attorney docket number NSD 98-004A, filed concurrently herewith. When an interlock device 280 is used, the interlock device 280 locks the inner tubular member 230 in either an upper position 228 or a lower position 229. The inner tubular member 230 is attached to the crane 60 so that, when the inner tubular member 230 is not locked in place, and the crane 60 is raised, frame 80 and outer tubular member 250 remain stationary and inner tubular member 230 and gripper assembly 210 move vertically. When the interlock device 280 is engaged, however inner tubular member 230 is locked to outer tubular member 250 and raising the crane 60 raises the entire transfer device 70. Thus, lifting of a poison rod assembly 40 is accomplished by an operator using crane 60 to position the transfer device 70 over a fuel cell 20 containing a poison rod assembly 40. Once the transfer device 70 is seated on the fuel cell 20, the operator lowers inner tubular member 230 and gripper assembly 210 until the gripper assembly 210 engages the T-bar 46 of the poison rod assembly 40. When the gripper assembly 210 has engaged the T-bar 46, the operator lifts inner tubular member 230, gripper assembly 210 and the poison rod assembly 70. Once the poison rod assembly 40 is withdrawn from fuel cell 20, the operator may lift the transfer device 70 off fuel cell 20 and use the moveable gantry 63 to reposition the crane 60 and transfer device 70 above another fuel cell 20. The transfer device 70 is lowered onto a second fuel cell 20 and, with the assistance of comb assemblies 120, the poison rod assembly 40 can be guided into the new fuel cell 20. When the poison rod assembly 40 is positioned within the second fuel cell 20, the gripper assembly 210 is disengaged from the poison rod assembly 40 and the transfer device 70 removed. As shown in FIG. 4a, 4b, 4c and 5, the frame assembly 80 includes two C-members 82, 84 held in spaced relation by a plurality of braces 86. The C-members 82, 84 define a, preferably square, frame cavity 88. Each C-member 82, 84 has an upper end 92, located at frame assembly upper end 91, and a lower end 94, 96 located at frame assembly lower end 95. At the lower end 94, 96 of the C-members 82, 84 is a mounting plate 100. Mounting plate 100 has an upper surface 102, an opening 104 and a lower surface 106. The C-members 82, 84 are attached to the mounting plate upper surface 102. The mounting plate opening 104 communicates with the frame cavity 88. The frame assembly 80 further includes a square pedestal 110 attached to the mounting plate lower surface 106. The pedestal 110 has an upper surface 111, a lower surface 112 with openings 113, 114 therethrough. The upper surface pedestal opening 113 and lower surface pedestal opening 114 are sized to allow the poison rod assembly 40 to pass therethrough. The upper surface pedestal opening 113 communicates with the mounting plate opening 104. In operation, the poison rod assembly 40 will be lifted through the pedestal 110 and mounting plate 100 by gripper assembly 210 into a position within the frame cavity 88. The pedestal lower surface 112 has at least one projection 116. In the preferred embodiment, there are two pedestal projections 116 extending downwardly from diagonally opposite corners. The projections 116 are sized to engage the bore holes 24, 26 on the fuel rod assembly can 22. Thus, mounting of the transfer device 70 is accomplished by the operator lowering the device 70 until projections 116 are seated within bore holes 24, 26. Once the projections 116 are so seated, the transfer device 70 is resting on the fuel cell 20. Once the transfer device 70 is seated on a fuel cell 20, removal of the poison rod assembly 40 can be performed by the lifting assembly 220. The lifting assembly 220 includes an outer tubular member 250, an inner tubular member 230, a platform 240, and a gripper assembly 210. Outer tubular member 250 is fixed at its lower end 252 to frame 80. Thus, when the transfer device 70 is seated on a fuel cell 20, frame 80 and, therefore outer tubular member 250, are fixed in place. As shown in FIG. 6, a platform 240 is mounted at the upper end 232 of inner tubular member 230. The lifting platform 240 may include a winch (not shown) to raise and lower the inner tubular member 230, or the inner tubular member 230 may be coupled directly to crane 60 by bail 246. As noted above, inner tubular member 230 is slidably disposed within outer tubular member- 250. Thus, as shown diagrammatically in FIG. 3, when frame 80 and outer tubular member 250 are fixed in place, inner tubular member 230 can slide between an upper position 228 and a lower position 229 within outer tubular member 250. As shown in FIG. 3, in the upper position 228, the inner tubular member 230 is raised so that the gripper 212 (described below) is adjacent to the top of frame 80. In the lower position 229, the gripper 212 is adjacent to the lower end of frame 80, but spaced above pedestal 110. Coupling the poison rod assembly 40 to the transfer device 70 is accomplished by a gripper assembly 210 located generally at the bottom 234 of inner tubular member 230. As shown in FIG. 7, the gripper assembly 210 includes gripper 212, a connecting pin 214, a base 216 and inner shaft 218. The gripper base 216 is a cylindrical member attached to inner tubular member bottom 234, having a greater diameter than the inner tubular member 230 and having two support fingers 217 extending downwardly from the base 216. The gripper base 216 provides support for the gripper 212 which is rotatably disposed about the gripper base 216. The gripper 212 incorporates two J-shaped notches 219 which are spaced approximately one hundred and eighty degrees apart. The J-shaped notches 219 are used to latch onto the T-bar 46 of the poison rod assembly 40. The gripper 212 is disposed on the gripper base 216 so that the J-shaped notches 219 are between support fingers 217. Inner shaft 218 is rotatably disposed within inner tubular member 230 and extends from the bottom 234 of inner tubular member 230 through the flange 238 located at the top of inner tubular member 230. A connecting pin 214 connects the inner shaft 218 to the gripper 212. As shown in FIG. 6, a handle 248 is attached to the upper end of inner shaft 218 at lifting platform 240. When the gripper 212 is positioned over a poison rod assembly 40 with T-bar 46 disposed within notch 219, the operator rotates handle 248 causing gripper 212 to rotate thereby latching T-bar 46 into J-shaped notches 219. In operation, the transfer device 70 is seated on a fuel cell 20 as described above. The operator lowers gripper assembly 212 onto the poison rod assembly 40. T-bar 46 will fit into the J-shaped notches 219. The operator then turns handle 248 rotating gripper 212 and latching T-bar 46 in the J-shaped notches 219. The operator then lifts inner tubular member 230, thereby raising gripper assembly 210 and poison rod assembly 40 into frame cavity 88. Once the poison rod assembly is within cavity 88, the operator lifts the transfer device 70 off fuel cell 20 using crane 60. The operator then uses gantry 64 to reposition the transfer device 70 over a different fuel cell 20. The transfer device 70 is then seated on the second fuel cell 20 as described above. Once the transfer device 70 is seated on the second fuel cell, the operator lowers the inner tubular member 230 with the crane 60 or the winch, until poison rod assembly 40 is seated in the new fuel cell 20. One of the most difficult portions of the transfer procedure is the reinsertion of the poison rod assembly 40 into the new fuel cell 20. Because the poison rods 42 are only held by the support web 44 located at the top of the poison rod assembly 40, the lower end of the poison rods 42 are free to move and sway. Without a means to support and guide the poison rods 42, poison rods 42 will not align properly with the thimbles 48 in the second fuel cell 20. To aid in the alignment of the poison rods 42, comb assemblies 120 are used. As shown in FIGS. 8 and 9, a comb assembly 120 of the preferred embodiment, consists of two parallel horizontal plates 122, 124 held in spaced relation by a vertical plate 126. Each horizontal plate 122, 124 has a plurality of slots 128 cut therein. The slots 128 are spaced to correspond to the rows of poison rods 42 in a poison rod assembly 40. Each slot also has a cut-out 129, at the location where each poison rod 42 will be disposed when the comb assembly is in its closed position around a poison rod assembly 40. Each horizontal plate 122, 124 has an outer edge 130, two side edges 132, 134, and an inner edge 136. The inner edge 136, may be uneven and communicates with the slots 128. Adjacent to each slot 128, on the inner edge 136 is an angled portion 140, which will assist in guiding the poison rods 42 into the slots. On the side edges 132, 134 of each plate, adjacent to the outer edge 130, are located projections 138, 139 which are disposed in channels 152 described below. In the preferred embodiment each horizontal plate 122, 124 covers approximately one half of frame cavity 88. Thus, to provide complete coverage in the closed position (described below), two opposing parallel comb assemblies 120a, 120b must be used. As shown in FIG. 10, the separate comb assemblies 120a, 120b are disposed with inner edges 136 abutting each other. This, however, only provides slots 128 extending in a single direction. To align the poison rods 42 and prevent the poison rods 42 from swaying, the comb assemblies slots 128 must form a grid having an opening at each intersection. To form the grid, two additional comb assemblies 129c, 129d are disposed immediately above or below and perpendicular to comb assemblies 120a, 120b. Thus, two parallel comb assemblies 120a, 129b abut each other's inner edge 136 while overlaying a second pair of parallel, abutting comb assemblies 120c, 120d which are perpendicular to the first pair 120a, 120b. While there are four comb assemblies 120 on the transfer device 70, one on each side of the square frame 80, each comb assembly 120 is mounted on the frame in a similar manner. As noted above, however, to form a grid when the comb assemblies 120 are in the closed position, two assemblies must overlay the other two. Thus, when disposed within the frame as detailed below, two parallel comb assemblies 120 are disposed immediately above another two parallel comb assemblies 120. The following description will address only one of the four comb assemblies noting that each has a similar mounting assembly. As shown on FIGS. 4a, 4b, 4c, 5, and 12, the comb assembly mounting means includes a plurality of rail assemblies 150 and a comb moving assembly 99. In the preferred embodiment, there are two rail assemblies 150 for each comb assembly 120. Each rail assembly 150 includes two comb rails 154, 156 defining channels 152. The comb rails 154, 156 are attached to the frame 80 by a plurality of mounting bands 158, 159, 160. The mounting bands 158, 159, 160 are attached to spacer assemblies 162, 163, 164, 165 which extend outside the frame 80. The upper end 170, 172 of comb rails 154, 156 are located outside frame 80. The lower end 171, 173 of comb rails 154, 156 curve inward and pass within frame 80. As shown in FIG. 11, the lower end of C-members 82, 84 have cut outs 87 sized to allow a comb assembly 120 to pass therethrough. The lower portion, 171, 173 of comb rails 154, 156 are attached to mounting plate upper surface 102. The mounting plate 100 has channels 108 which communicate with rail channels 152. The mounting plate channels 108 further communicate with channels 118 located in the pedestal 110. Thus, there is a continuous channel from the top of the comb rails 154, 156 to within the pedestal 110. As shown in FIG. 12, comb assembly 120 can travel the length of the channel 152, 108, 118. As the rail assemblies 150 are located outside of the frame 80 at the upper end 170, 172, and inside the frame at the lower end 171, 173, the comb assembly 120 may be disposed in an open position outside the frame 80 while located at the top of the rail assembly 170, 172, or in a closed position within the pedestal 110 when the comb assembly 120 is at the rail lower end 171, 173. As noted above, to form a grid, the comb assemblies 120 must overlay each other in the pedestal. This is accomplished by having certain pedestal channels 118a, 118b, which are located on opposite sides of pedestal 110, extend downwardly more than pedestal channels 118c, 118d, which are located on the sides of pedestal 110 perpendicular to channels 118a, 118b. As described above, lifting of the poison rod assembly 40 is accomplished by gripper assembly 210. When initiating the lifting of a poison rod assembly 40, the comb assembly 120 must be in the open position where the comb assemblies are located at the rail upper ends 170, 172. When the comb assemblies are in the open position the gripper assembly 210 and poison rod assembly support web 44 may pass through the lower end of the frame assembly 80. When lifting a poison rod assembly 40, the comb assemblies 120 should be lowered into the closed position within the pedestal 110 as soon as the gripper assembly 210 and support web 44 pass through the lower end of frame 80. Movement of the comb assemblies 120 is controlled by a comb moving assembly 99 that is disengagably coupled to the poison rod assembly lifting assembly 220. The comb moving assembly 99 and coupling means includes a pusher plate 180, which is mounted on inner tubular member 230, and a pair of slide plates 270, 271 connected by a plurality of cables 198, 199 to the comb assembly 120. As shown on FIG. 13 each slide plate 270, 271 includes a base 272 and two sides 273, 274. The sides 273, 274 each have an outward turning tab 275, 276 which terminate in a cylindrical end 277, 278. Each side 273, 274 also has a projection 279 extending upwardly. The sides 273, 274 of the slide plate 270 are parallel to the sides of frame 80. The base 272 is at approximately 45 degrees from brace 86. As shown in FIG. 14, with this configuration, each slide plate is bent outwardly from the center of the frame cavity 88, thus allowing the gripper assembly 210 to easily pass between the slide plates 270. The cylindrical ends 2177, 278 of each slide plate 270 are disposed within a slide plate track 192a, 192b, 194a, 194b which are disposed on the lower portion of frame 80. Slide plate tracks 194a, 194b are mounted on either C-member 82, 84 of the frame assembly 80 while slide plate tracks 192a, 192b are mounted on the plurality of braces 86. Each slide plate track 192a, 192b, 194a, and 194b has a cylindrical channel 193a, 193b, 195a, 195b. The cylindrical ends 277, 278 of the two slide plates 270, 271 fit within the cylindrical channels 193a, 193b, 195a, 195b. Thus, as shown in FIGS. 4a and 4b, the slide plates 270, 271 are able to travel vertically in slide plate tracks 192a, 192b, 194a, and 194b between an upper position 196 and a lower position 197. As shown on FIG. 15, the pusher plate 180 includes a flat member 182 having a medial hole 183. In the preferred embodiment, the flat member 182 is hour-glass shaped with a circular mid-section. At each corner of the plate 183 there is a downward extending projection 184, 185, 186, 187. As shown on FIG. 15b each downward projection 184, 185, 186, 187 has a cup shaped distal end 190 forming a cavity 191. The cavities 191 of the pusher plate projections 184, 185, 186 and 187 are shaped to fit on top of slide plate projections 279. Pusher plate 180 is horizontally mounted on inner tubular member 230 above gripper assembly 210. As the inner tubular member 230 is lowered, pusher plate 182 descends and cavities 191 will engage with a slide plate projections 279. Cables 198, 199 are attached at one end to slide plates 170 and at the other end to the comb assembly 120, coupling the slide plate 170 to the comb assembly 120. The cables 198, 199 travel over pulleys 202, 204 which are mounted on pulley support plate 206. Pulley support plate 206 is attached to frame assembly 80 above the rail upper portion 170, 172 and above the slide plate tracks 192a, 192b, 194a, 194b. In operation, gravity will pull the comb assembly 120 downward into pedestal 110. As the comb assemblies 120 move downward, the cables 198, 199, which pass over pulleys 202 and 204, will draw each slide plate 270, 271 upwards to its upper position 196. As gripper assembly 210 and outer tubular member 230 descend to pick up a poison rod assembly 40, the pusher plate 182 on the inner tubular member 230 engages slide plate 270 causing slide plate 170 to travel downward in slide plate tracks 192a, 192b, 194a and 194b. As the slide plate 270 is pushed downward by pusher plate 180, the cables 198, 199 are drawn over pulleys 202 and 204 lifting the comb assembly 120. Each comb assembly 120 will be lifted from the lower position in the pedestal 110 to a position at the rail upper portion 170, 172. Thus, as gripper assembly 210 is lowered, each comb assembly 120 is raised to the comb rail upper end 170, 172 where the comb assembly 120 does not block the path of travel of gripper assembly 210. The location of pusher plate 180 on inner tubular member 230 can be adjusted so that each comb assembly 120 is removed from the path of travel of gripper assembly 210 just before the gripper assembly 210 or web 44 pass the comb assembly 120. After the poison rod assembly 40 is inserted into a second fuel cell 20, the operator may turn handle 248 to unlatch the poison rod assembly 40 from gripper assembly 210. The operator may then raise the inner tubular member into its lower position 228 and use crane 60 to lift transfer device 70 off fuel cell 20. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangement disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breath of the appended claims and any and all equivalence thereof.