Patent Number: 060470372
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 6 to 13, a control rod exchange multi-lift tool 100 according to a preferred embodiment of the present invention will be described. The multi-lift tool 100 according to the present invention is designed to save valuable outage time in a BWR by combining several lifts into one during control rod exchange or shuffle operations. This is accomplished with a single tool which combines existing technologies to lift the fuel support piece 25, the blade guide 49, and the control rod 20 all at once. When the multi-lift tool 100 of the present invention is used to exchange a control rod 20, the fuel support piece 25 and the blade guide 49 remain on the tool 100. The fuel support piece 25 forms the lower member of the tool frame as the control rod 20 is lifted from the guide tube 24. The blade guide 49 centers the whole lift and prevents hang-ups. With the multi-lift tool 100, reinsertion of the fuel support piece 25, the blade guide 49, and the control rod 20 is accomplished with a single operation. The multi-lift tool 100 also functions to unlatch the control rod 20 from the control rod drive 30 before lifting the control rod 20 from the guide tube 24. The multi-lift tool 100 comprises a frame 101 made of square electropolished stainless steel tubes 101a, 101b. The tubes 101a, 101b are connected at the top by a bolted structure 101c which houses a blade guide grapple hook 102 with its operating cylinder 103. The tool 100 also includes sheaves or rollers 104 which transfer the lift cable 105 from an off-center control rod grapple 106 through the top of the tool 100 at a point generally along the central longitudinal axis of the tool 100. The bottom of the tubes 101a, 101b of the frame 101 connect to a fuel support piece grapple 107. A control rod lifter 108 in the form of a small trolley is provided which travels the length of the tubes 101a, 101b of the frame 101 on one side of the tool 100. The control rod lifter 108 supports the control rod grapple 106 and is operable to lower the control rod 20 into its cell for latching the control rod 20 to the control rod drive 30 at the bottom of the cell. The control rod lifter 108 can also lower the control rod 20 into a storage or transfer container. The control rod lifter 108 is connected directly to the lift cable 105 and is movable on cam rollers 108a along the length of the frame 101 by raising and lowering the lift cable 105. A lowered position of the control rod lifter 108 is shown in dashed lines in FIG. 7. When the control rod lifter 108 reaches its upper limit on the frame 101, the lifter 108 abuts a stop 108s and the whole assembly of the multi-lift tool 100, along with the blade guide 49 and the fuel support piece 25, can then be raised by the lift cable 105. The control rod grapple 106 is operated by a cylinder 109 to selectively engage and disengage with the control rod lifting handle 52. A bypass arrangement 105a is connected to the lift cable 105 above the tool 100 for guiding pressure lines 109a leading to the cylinder 109 around the sheaves 104. An unlatching handle grapple 110 is provided at the lower end of the multi-lift tool 100 just above the fuel support piece grapple 107. The unlatching handle grapple 110 is operated by two cylinders 111 and 112. The first cylinder 111 positions a D-ring finger 110a into selective engagement with the unlatching handle 53 on the control rod 20. The second cylinder 112 provides a lifting force for disengaging the unlatching handle 53. The fuel support piece 25 is grappled at the lower end of the tool 100 by the fuel support piece grapple 107. The grapple 107 comprises two cylindrical members 113 having tapered lower ends. Each cylindrical member 113 has three latches 114 which are operated by a respective cylinder 115 to move into locking engagement with the fuel support piece 25. The cylinders 115, like the other cylinders 103, 109, 111, 112 of the tool 100, cannot be activated while there is a load on the support device. The weight of the total lift according to the present invention is preferably under 1,000 pounds, which is within the lift capacity of the conventional hoists 46a, 46b, 46c provided for exchanging and shuffling the control rods 20 in a BWR. Only the weight of the control rod 20 is on the hoist during unlatching (i.e., when lifting the unlatching handle 53). The multi-lift tool 100 itself weighs approximately 400 pounds. An in-vessel storage station 200 according to the present invention is shown in FIGS. 12a and 12b for storing two control rods 20 and one fuel support piece 25. The storage station 200 comprises a frame 201 which hangs from the reactor flange and is retained by hooks which go around the studs on the reactor vessel. The storage station 200 is easily lowered into position with a cable which can be attached to the handrail for easy retrieval during removal. Alternate locations outside the reactor can be arranged according to individual plant preferences. The top of the storage station 200 has three openings 202 which simulate the core support plate openings. The lower end has two cups 203 which can receive the lower end of the control rods 20. The storage station 200 is constructed of electropolished stainless steel which is welded or bolted together for ease of decontamination and movement. A plurality of pads 204 made of delrin or other suitable material interface with the reactor. A sequence of moves involved in changing or shuffling a control rod using the multi-lift tool 100 according to the present invention will now be described with reference to FIG. 13 of the drawings. With the control rod fully inserted in the control cell, two diagonally opposed fuel assemblies 26 are removed one at a time from the control cell with the main grapple and transported to storage in the spent fuel pool, to an in-vessel storage rack, or to another core location as part of a fuel shuffle. A blade guide 49 is transported on the main grapple from a storage location and inserted into the open holes of the control cell. The remaining two fuel assemblies 26 are then removed one at a time from the cell with the main grapple and are stored in the pool or another location. The operation up to this point is the same as in the conventional procedures. The multi-lift tool 100 is then placed into the cell with the control rod 20 fully inserted. The cylinders on the multi-lift tool 100 are actuated to grapple the fuel support piece 25, the blade guide 49, and the control rod 20. Video cameras are inserted into the open holes of the control cell (i.e., the holes without the blade guide 49 positioned therein) to verify the latching operations. The multi-lift tool 100 is then actuated to grapple the unlatching handle and unlatch the control rod 20 from the control rod drive 30 with the control room giving a continuous withdraw signal. The control rod drive 30 is then withdrawn to the overtravel position. The whole assembly is then lifted from the control cell and moved to a new control rod storage position. This is represented by step (1) in FIG. 13. This storage position can include, for example, the in-vessel storage station 200 or a suitable rack in the spent fuel pool. The old control rod 20 and fuel support piece 25 are then discharged, and the multi-lift tool 100 is moved to another part of the storage station and attached to a replacement control rod 20 and fuel support piece 25 for the cell. The multi-lift tool 100 then carries the assembly comprising the new control rod, the original blade guide 49, and the new fuel support piece 25 to a position above the control cell. This is represented by step (2) in FIG. 13. The multi-lift tool 100 then places the new assembly into the control cell and lowers the control rod 20, thereby seating the fuel support piece 25, the blade guide 49, and the control rod 20 in the control cell. The placement and alignment of the fuel support piece 25 onto the anti-rotation pin is verified with a camera in one of the two open holes of the control cell. The multi-lift tool 100 is then withdrawn. With the control rod 20 raised to its fully inserted position, two fuel assemblies 26 are installed in the positions not occupied by the blade guide 49. The blade guide 49 is then removed, and two more fuel assemblies 26 are installed in the positions from which the blade guide 49 was removed. A number of interlocks and safety features are built into the multi-lift tool 100 according to the present invention. For example, the control rod grapple 106 has a retaining barb 116. The operating cylinder 109 does not have the power to overcome the weight of the control rod 20 against the control rod grapple 106 with the retaining barb 116 at its outer edge. The lift cable 105 is attached directly to the control rod grapple 106 so that its function cannot be bypassed when the tool 100 is moved under load. Due to the sliding trolley arrangement, the control rod 20 cannot be lowered out of the lift assembly without the bottom end of the assembly being supported. The blade guide grapple 102 also has a barb 117 to retain the handle of the blade guide 49. While the fuel support piece 25 is attached, the blade guide grapple 102 is redundant since the fuel support piece 25 prevents the blade guide 49 from being lowered. The blade guide grapple 102 is barbed to prevent the blade guide 49 from moving and is hinged in a way which would support the blade guide 49 if the power is shut off. The multi-lift tool 100 lifts the blade guide 49 with the control rod 20. Since this assembly is never completely below the grid 51, there is a greatly reduced chance of any type of hang-up either going down through the grid 51 or in the removal process. No hoist overloads are necessary for this reason. When the tool 100 is empty, the tubes 101a, 101b of the frame 101 function as a guide to locate the tool 100 centrally in the grid opening. The unlatching handle grapple 110 can be left in its unlatched position for added lifting safety during transport if desired. The fuel support piece 25 is grappled by the two bullet nosed grapples 107. Each bullet nose 113 has three latches 114 which cannot be actuated when the weight of the fuel support piece 25 is on them. This is a double redundant system since the latches 114 must move up in order to unlatch and there are two direct support paths (i.e., two bullet noses 113), each with three latches 114. During raising and lowering of the control rod 20, the blades of the control rod 20 are guided by the blade guide 49 which is, at that time, integral with and supported by the tool 100. Thus, all surfaces of the blades of the control rod 20 are protected during movement with the tool 100 in the same manner as during operation of the BWR. Safety interlocks with the hoist are maintained for the control rod 20 withdrawal because the lift cable 105 only lifts the control rod 20 during the unlatching operation. After the control rod 20 is unlatched and the control rod drive 30 is withdrawn, the trolley 108 is raised to the hardstop 108s on the frame 101 and only then does the weight of the other members rest on the lift cable 105 of the hoist. Corrosion resistance is enhanced by the use of stainless steel parts. Where possible these parts are electropolished for ease of decontamination. Aluminum parts can be used for certain components, but must receive a hard anodized coating to resist corrosion. Loose parts are controlled predominantly by lock wiring since most of the construction of the tool 100 embodies bolting methods. In some isolated instances, a locking agent can be used to prevent loosening of parts, particularly if the part is not subjected to significant torque. Bent tab keepers can also be used to prevent loosening of parts on the tool 100. The reactor water will provide sufficient lubrication to permit smooth operation of the moving parts of the tool 100. The cylinders 103, 109, 111, 112, and 115 of the tool 100 are preferably air cylinders which will perform optimally using 90-120 psig air supplies. The end of the lift cable 105 is adaptable for use with any desired hoisting device positioned over the BWR. The core configuration for support of the tool 100 does not need to be changed after initial removal of fuel and installation of the blade guide 49. The tool 100 removes the control rod 20, the blade guide 49, and the fuel support piece 25 together. The control rod drive 30 is retracted during the unlatching of the control rod 20 within the tool 100. The installation of the control rod 20 using the tool 100 takes place in the same manner, except the control rod 20 is lowered to the control rod drive 30. The whole tool 100 is inserted into the control cell guided by the existing blade guide 49 and the control rod 20. Once installed, the top of the tool 100 is still above the grid 51 allowing ease of removal guided by the blade guide 49. The bottom of the assembly of the tool 100, the blade guide 49, and the control rod 20 is stiffened by the fuel support piece 25. Each of the operation cylinders 115 for the fuel support piece grapple 107 has a double ended shaft which can be used to visually determine the position of the latches 114. If the latches 114 are not extended, the cylinders 115 will not stroke. Visual verification is possible through the two fuel positions which are not occupied by the blade guide 49. One cell is removed completely with the fuel support piece 25. The control rod 20 is then placed in an intermediate position such as a so-called gun barrel or in-vessel storage station 200 (FIGS. 12a, 12b). A new control rod 20 is retrieved from the same intermediate position, and the assembly is returned to the original cell as a whole for relatching. The fuel support piece 25 may be released onto the same intermediate position in unusual situations, such as during replacement of the fuel support piece 25. The tool 100 is capable of placing the control rod 20 into the gun barrel, but not with the fuel support piece 25 on the tool. The fuel support piece 25 must be set down on the in-vessel storage station 200 or another gun barrel before the control rod 20 can be lowered fully. Modification of the gun barrel by cutting down the height by 20 inches or adding a spool support piece inside the barrel are alternate solutions. The multi-lift tool 100 according to the present invention solves many of the problems with conventional tools for exchanging and shuffling control rods. For example, the multi-lift tool 100 is not subject to the problem of jamming under the grid 51 because part of the tool 100 always remains above the grid 51. In addition, the blade guide 49 becomes an integral part of the tool 100 during the lift operation providing guidance in the horizontal and rotational directions at all times after the assembly enters the grid 51. Access for video cameras is possible through the two fuel locations not taken up by the blade guide 49. Slack cable is not an issue because the trolley 108 can be made to weigh the necessary amount to draw the lift cable 105 into the tool 100. The multi-lift tool 100 is suited to either of the hoists 47a, 47c available on the refuel bridge. The total weight of the tool 100 with the attached blade guide 49, control rod 20, and fuel support piece 25 is less than 1000 pounds. Therefore, the hoist used can be the one with the most accessibility for the user, thereby improving safety. Moreover, the tool 100 can be designed to be used with any of the hoists 47a, 47b, 47c available on the refuel floor by making it usable with either a rigid pole system fitting or a threaded connection on the end of the lift cable. No batteries or electrical connections are required for the verification processes associated with the multi-lift tool 100. All of the grapples 102, 106, 107 can be observed at the same time through the frame for positive verification of engagement. The position of the fuel support piece grapples 107 is observed by the position of the top of the double ended actuation cylinders 115. Therefore, it is not necessary to use sensors with the tool 100. Rotational positioning of the fuel support piece 25 is controlled at the entrance to the grid 51. After this point, there is no possibility of the fuel support piece 25 rotating due to the presence of the blade guide 49 as part of the assembly. Engagement with the grid 51 is maintained throughout the lowering and raising of the assembly. The unlatching handle 53 is grappled by the unlatching handle grapple 110 using the two cylinders 111, 112. The cylinders 111, 112 are directly connected to the frame 101 which, in turn, is stiffened by the presence of the fuel support piece 25. The two cylinders 111, 112 are operated to provide easy access and unlatching of the control rod 20. Since the tool 100 does all the operations associated with the control rod 20 changeout, no time is wasted changing out between tools, as in the conventional changeout procedures. Additional savings are realized in dose reduction. The unlatching operations are accomplished with an unlatching handle grapple 110 designed for maximum vertical flexibility. The vertical height depends on the vertical cylinder 112 operating the unlatching handle grapple 110. The unlatching handle grapple 110 is designed to sustain the weight of the control rod 20, however this is not the primary method of supporting the control rod 20. The main control rod grapple 106 is at the top of the multi-lift tool 100. When both grapples 106 and 110 are latched there is redundancy in the lift. The unlatching handle grapple 110 can be eliminated from the lift sequence if desired due to the unique application of the trolley lift. The blade guide 49 becomes an integral part of the positioning of the control rod 20 within the tool 100 and provides the necessary guidance. Two fuel positions are essentially open in the control cell to allow camera access to the entire length of the tool 100. This same access provides clearance to insert a conventional rigid pole system for remedial action should that ever be required. The multi-lift tool 100 has no unguided air hoses below the grid 51 because a portion of the tool 100 is always above the grid 51. Only the air hose cluster, the lift cable 105, and a guide rope (not shown) extend to the surface. The guide rope is used to counter rotation of the tool 100 before it enters the grid 51. The rotation is usually caused by the lift cable 105 unwinding as it is played out from the hoist. The multi-lift tool 100 according to the present invention has the potential of changing a two hour exchange of the control rod 20 into a half hour exercise without hangups. This adds a great deal of consistency to the operation. Since the unlatching of the control rod 20 takes place with the control rod 20 in the up position, some communication time can be saved with the control rod drive operation. Unlatching is allowed with the control rod 20 inserted because the blade guide 49 travels with and becomes part of the multi-lift tool 100. The following Table 1 shows a comparison of the typical times required for the control rod replacement procedures using the conventional tools and using the improved multi-lift tool 100 of the present invention. TABLE 1 ______________________________________ Time Comparison for Blade Replacement Operations Current Time Multi-Lift Operation (min) Time (min) ______________________________________ a. BG cell to hanging 5 b. FSP cell to hanging 13 c. CR cell to pool rack 36 15 d. CR pool rack to cell 27 15 e. FSP hanging to cell 20 f. BG hanging to cell 8 Total Time 109 30 ______________________________________ The savings noted in the above table results in 79 minutes per cell exchange, or approximately one hour. If this exchange is made while the BWR is on critical path at a rate of approximately $10,400 per hour, the savings is as follows: ______________________________________ 10 Blades Replaced $104,000 Savings 20 Blades Replaced $208,000 Savings ______________________________________ Thus, the cost of the new multi-lift tool 100 can be easily justified in just one outage. Similarly, a control rod shuffle can be accomplished very quickly changing a cell operation from 4 hours to around 1 hour due to the elimination of steps. The use of two multi-lift tools according to the present invention could further enhance this operation or the exchange noted above. It will be appreciated that the present invention is not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made without departing from the scope and spirit thereof. It is intended that the scope of the invention only be limited by the appended claims.