Method for dismantling, compacting and shearing a spent nuclear fuel assembly frame skeleton.

Abstract: Method and apparatus for dismantling, shearing and compacting a fuel assembly skeleton. A frame (28) is provided which can be placed into the transfer canal (7) of a fuel-handling building for severing a bottom nozzle from the thimble tubes and grids of the skeleton. After compacting the remainder of the skeleton, the thimble tubes and grids are further severed into shorter pieces, and the shortened compacted severed pieces are placed into a container (30) for off-site shipment or on-site storage.

Description: This invention relates to a method for dismantling, shearing, and compacting a fuel assembly frame skeleton. Heretofore, because of a lack of spent fuel reprocessing capability and lack of or insufficient Away-From-Reactor (AFR) storage facilities, it is necessary to have extended storage capability at reactor sites. This is presently being accomplished by storage-rack densification and trans-shipment between stations. Both fuel assembly reconstitution and fuel assembly consolidation result in frame skeletons that must be disposed of. For example, a method of disposing of nuclear waste is disclosed in US-A-3,763,770 which proposes to shear spent nuclear fuel bundles into units of predetermined length. This apparatus generally includes a pair of orthogonally related "gags" to clamp and collapse the bundle or a pair of parallely-acting horizontal gags co-operating with a vertical restraint for compressing predetermined lengths of the fuel bundles. Then a shear blade is used to sever predetermined lengths which are dropped through a chute to a dissolution apparatus. US-A-4,056,052 to Weil et al. is concerned with a method for shearing spent nuclear fuel assemblies of the shrouded pin-type wherein a plurality of long metal tubes packed with ceramic fuel are supported in a spaced-apart relationship. Spent fuel nuclear assemblies are first compacted between specially provided gag compactors into short segments so that they are amenable to chemical processing. Compression takes place so as to form the assemblies into specially formed compacts. Shearing then takes place with specially contoured blades which are adapted to mate with the contoured surface of the compacts of the compressed fuel assemblies. A method for remotely dismantling, compacting and shearing a spent fuel assembly frame skeleton is known from document FR-A-2 324 094, wherein the assembly skeleton comprising the bottom nozzle, thimble tubes and grids is removed from the spent fuel pit and placed into a shearing device in which the bottom nozzle is removed from the assembly skeleton, sections of the assembly skeleton are compacted in a direction normal to the longitudinal axis of the skeleton, and each compacted section is cut before the next section is compacted, whereby individual pieces of compacted skeleton are formed so as to reduce the length of the compacted skeleton. However, none of the prior art known to the inventors is concerned with remotely dismantling and compacting an irradiated skeleton for off-site shipment or on-site storage. It is therefore the principal object of the present invention to provide a method for remotely dismantling and compacting a fuel assembly frame skeleton. With this object in view, the present invention resides in a method for remotely dismantling, compacting and shearing a spent fuel assembly frame skeleton, wherein, after the top nozzle and the fuel rods have been removed from the fuel assembly in a spent fuel pit, the assembly skeleton comprising the bottom nozzle, thimble tubes and grids is moved from the spent fuel pit and placed into a bottom nozzle removal fixture of a skeleton conveyor, in which removal fixture the bottom nozzle is removed from the assembly skeleton, the assembly skeleton is then conveyed from the bottom nozzle removal fixture to a compactor separate from the bottom nozzle removal fixture, wherein the remainder of the assembly skeleton is compacted in a direction normal to the longitudinal axis of the skeleton, and the compacted skeleton is conveyed from the compactor to a skeleton shear separate from the compactor, in which the compacted assembly skeleton is cut into individual pieces so as to reduce the length of the compacted skeleton. With this invention, remote dismantling of the fuel assembly frame skeleton is facilitated and the costs are reduced because the volume for eventual storage is reduced while the fuel rods and top nozzle can be removed and saved. During the compacting step, the skeleton is compacted so that a cross-section taken along its axial length is 5 cm x 25 cm. After compacting and shearing into 40 cm lengths along the axial length of the skeleton, the individual portions are fed by means of a chute to the scrap transfer bin, also under water and supported by the superstructure. The compacted and sheared skeleton assembly may also be placed into a container which is adapted to hold four skeletons for off-site removal. The invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example only, in the accompanying drawings, wherein: Fig 1 is a schematic perspective view illustrating the general arrangement of a single station containing a skeleton conveyor including cutting and compaction equipment supported by a frame for compacting a fuel cell assembly frame skeleton after all the fuel rods are removed; Fig 2 is an elevational view of a fuel cell frame assembly skeleton; Fig 3 is a schematic arrangement illustrating the steps in the compaction process after all the fuel rods have been removed from the fuel cell assembly to leave the fuel cell frame assembly skeleton, as shown in Fig 2, which is then placed into a nozzle-removal fixture for removal of the bottom nozzle and then dropping it into a scrap storage bin, and then the remaining parts consist of a unit of thimble tubes and grids which is moved into the compactor for compaction, and then after compaction, the unit is moved to a shear which cuts the compacted thimble tubes and grids to form smaller units for deposit into the scrap storage bin; Fig 4 is a partial plan view of the fuel cell assembly frame skeleton looking downwardly into the fuel transfer canal as shown in Fig 1; Fig 5 is a sectional view taken on line 5-5 of Fig 4 illustrating an overhead crane mechanism positioned above the skeleton conveyor for taking the fuel cell assembly frame skeleton, after the fuel rods have been removed therefrom, from the fuel pit to the spent fuel skeleton conveyor disassembly station; Fig 6 is a plan view of the bottom nozzle-removal fixture of a skeleton conveyor with the skeleton lowered and in place on the bottom nozzle-removal fixture; Fig 7 is an elevational view in section of the bottom nozzle-removal fixture of Fig 6, but omitting the skeleton for purposes of simplicity; Fig 8 is a plan view of the compactor with parts remaining from the skeleton after removal from the bottom nozzle-removal fixture in place for compaction; Fig 9 is an elevational view, partly in section of the compactor of Fig 8 without the partial skeleton; Fig 10 is a plan view of the shear for shearing the remaining part of the skeleton after the bottom nozzle has been removed; and Fig 11 is an elevational view of the shear of Fig 10. Referring now more particularly to the accompanying drawings, a spent fuel assembly 2 including fuel rods 6, top nozzle 8 and fuel cell assembly frame skeleton 10 (Fig 2) is intended to hang in the transfer canal 12 (fig 1) adjacent to the spent fuel pit 14 of the fuel-handling building 16. Connecting fuel transfer canal 12 and spent fuel pit 14 is fuel handling slot 18. In Fig 1, there is shown a skeleton conveyor 20, which generally includes as components a nozzle shear or removal fixture 22, a compactor 24, and a skeleton shear 26. All of the aforesaid components are supported within a frame 28 which hangs from the curb 31 of the transfer canal 12 of the spent fuel pit 14. A transfer container or scrap storage bin 30 is supported at the bottom of the frame 28 to receive compacted skeleton pieces 32 (see Fig 3) and the bottom nozzle 34. Spent fuel assemblies 2 are dismantled, and the fuel rods 6 and top nozzle 8 are removed therefrom to leave the fuel cell frame skeleton 10 in spent fuel pit 14. A crane mechanism 36 (Fig 5) is slidable on casters 38 along and on top of ledges or wall 40 to the transfer canal 12, adjacent the spent fuel pit 14, to raise the fuel cell assembly frame skeleton 10 from the fuel pit 14 and move it to the skeleton conveyor 20. Removal of the top nozzle 8 and fuel rods 6 leaves the grids 42 and thimble tubes 44 which are supported by jib crane 46 which is adapted to carry various long handled tools for manipulating skeleton 10 in the skeleton conveyor 20 as skeleton 10 is moved from station to station. Crane mechanism 36 is guided for its movement from above fuel pit 14 to transfer canal 12 by means of a chain-track guide 48. After all the fuel rods 6 have been removed from the fuel cell assembly 2 and reinserted into a new skeleton or other storage container (not shown), skeleton 10 is lifted by a long-handled tool held by jib crane 46. The long-handled tool also may be suspended from the spent fuel pit bridge or a wall of the spent fuel pit 14. Then skeleton 10 can be picked up by a floor or wall-mounted jib crane 52 (Fig 4) and transferred to the skeleton conveyor. The jib crane 52 may be in the form of a long-armed crane which is pivoted on a pivot connection such as pivot connection 54 on ledge or curb 31 adjacent to transfer canal 12, and may be pivoted over the canal and skeleton conveyor 20 towards fuel pit 14 to pick up skeleton 10 and place it into skeleton conveyor 20 for compaction. The bottom 33 of transfer canal 12 is desirably 914 cm (30 feet) below curb 31, and the bottom of the spent fuel pit 14 is about 1219 cm (40 feet) below curb 31. Referring now more particularly to Figs 6 and 7, bottom nozzle shear or removal fixture 22 generally includes a frame structure 60 carrying a bottom nozzle support 62 for supporting bottom nozzle 34 after frame skeleton 10 is lowered by crane mechanism 36 or long arm 52 into frame structure 60. Also supported for movement transversely to the longitudinal axis of the thimble tubes 44, when bottom nozzle 34 is on support 62, is a guillotine blade 64 slidably arranged for controlled and guided movement in oppositely arranged spaced guide and support channels or guideways 66. The front end 68 is angled to its direction of movement, and the rear end 70 is connected with hydraulic cylinder 72 which, when actuated, moves to the dot-dashed position 74 of blade 64 across the top of bottom nozzle 34 for separation thereof from thimbles 44. After bottom nozzle 34 is severed, when blade 64 is moved to its dot-dashed position 74, bottom door 76 is operated by air cylinder 78 to permit nozzle 34 to drop out of bottom nozzle support 62 into container 30 by means of chute or slide 79 (Fig 1). Guillotine blade 64 is strong enough to shear off the bottom nozzle by brute force, free of flying materials. The remainder of skeleton 10 which now consists of only thimble tubes 44 and grids 42 is then moved by crane mechanism 36 into position above compactor 24. At this station, the remainder of skeleton 10 is reduced in width from about 21.6 cm (8.5 inches) to about 5.08 cm (2 inches). Referring now more particularly to Figs 8 and 9, compactor 24 includes a receiving area 80 for receiving the remainder of skeleton 10 composed of grids 42 and thimble tube 44. Receiving area 80 is surrounded by a bearing plate 82 on one side and opposite thereto is a ram plate 84 which is guided for movement by guideways or guide bars 86. Ram plate 84 is movable from its position shown in full outline to the position shown in dot-dashed outline 84'. In order to compact the last short section of the remainder of skeleton 10, when it is released from the crane mechanism or handling tool held by long-armed crane 52 or crane mechanism 36, temporary support 90 is provided which is pivotally connected at pivot 92 to compactor 24 and is swung into place by means of air cylinder 94 when actuated from its neutral position 96 indicated in dashed outline. Referring now to Figs 10 and 11, crane mechanism 36 or long-armed crane 52 moves the compacted assembly to skeleton shear 26, or shear for the skeleton unit after the bottom nozzle has been removed, which includes a funnel-shaped member or container 100 with a shear blade 102 and a hydraulic cylinder 104 connected to blade 102 by means of connecting rod 106 connected at one end to blade 102 and the other end to hydraulic cylinder 104. The individual operating parts and movement means of the skeleton shear are conventional. Blade 102 is contoured to sever the thimble tubes to form small units for placement into scrap storage bin 30. After the shear blade 102 cuts the thimbles into short pieces, they fall down a chute 108 (Fig 1) and end up in a temporary scrap storage bin or transfer container 30. When the skeleton conveyor is positioned in the transfer canal 12, water, although not shown, is contained therein, and it is desirably maintained to a level of about 20.32 cm (8 inches) below edge or curb 31. The frame or superstructure 28 is desirably made to fill within the transfer canal 12, and it is suitably enclosed to prevent debris from falling into the canal or the skeleton conveyor 20. When carrying out the method, it is preferred that the skeleton assembly 10 in its various stages of processing be held by the crane mechanism 36 or long-armed crane 54 as the assembly is moved from compactor 24 to skeleton shear 26. Cutting of the thimble tubes 44 preferably takes place at or near a grid 42. The crane should be preferably 609 cm (20 feet) above curb 31 to provide for ease of transfer from spent fuel pit 14 to transfer canal 12. Cutting should desirably take place along a plane which is perpendicular or orthogonally related to the longitudinal axis of the fuel cell assembly 2. In some instances, it may be desired to save the bottom nozzle, and for this purpose frame structure 28 may be provided with another container such as container 30 adjacent chute 79 so as to separate the bottom nozzles from the remainder of skeleton 10 which is to be compacted and disposed of separate from the bottom nozzle. In order to remove the top nozzle, the thimble tubes 44 are severed from the top nozzle 8 by cutting the thimble tubes 44 from the top nozzle to expose the fuel rods. The fuel rods are then removed from the bottom nozzle grid assembly. In many instances, the top nozzle 8 and the fuel rods 6 can be reused, and the cutting to remove top nozzle 8 is carried out in the fuel pit 14.

Claims: A method for remotely dismantling, compacting and shearing a spent fuel assembly frame skeleton (10), wherein, after the top nozzle (8) and the fuel rods (6) have been removed from the fuel assembly in a spent fuel pit (14), the assembly skeleton (10) comprising the bottom nozzle (34), thimble tubes (44) and grids (42) is moved from the spent fuel pit (14) and placed into a bottom nozzle removal fixture (22) of a skeleton conveyor (20), in which removal fixture the bottom nozzle (34) is removed from the assembly skeleton (10), the assembly skeleton (10) is then conveyed from the bottom nozzle removal fixture to a compactor (24) separate from the bottom nozzle removal fixture (22), wherein the remainder of the assembly skeleton (10) is compacted in a direction normal to the longitudinal axis of the skeleton, and the compacted skeleton (10) is conveyed from the compactor to a skeleton shear (26) separate from the compactor, in which the compacted assembly skeleton (10) is cut into individual pieces so as to reduce the length of the compacted skeleton. A method according to claim 1, characterized in that the bottom nozzle (34) is sheared from the assembly skeleton (10) with a guillotine blade (64) and is dropped into a transfer container (30). A method according to claim 2, characterized in that said skeleton (10) is compacted to a cross-sectional area of 5 x 25 cm in a direction orthogonal to the longitudinal axis of the fuel assembly skeleton (10). A method according to claim 3, characterized in that said compacted skeleton (10) is sheared into pieces 40 cm in length. A method as claimed in any of claims 1 to 4, characterized in that the bottom nozzle (34) is transferred to a transfer container (30) by means of a chute (79) supported on said skeleton conveyor (20) between said nozzle-removal fixture (22) and the transfer container (30). A method according to claim 5, characterized in that prior to moving the remainder of the fuel assembly skeleton (10) from the spent fuel pit (14) to the transfer canal (12), the transfer canal (12) is filled with water to a level above the bottom nozzle-removal fixture (22), the compactor (24), the skeleton shear (26) and the container (30).

Inventors: MEUSCHKE ROBERT EDWARD, SCHULTIES JOSEPH RAYMOND, MEUSCHKE, ROBERT EDWARD, SCHULTIES, JOSEPH RAYMOND
Applicants: WESTINGHOUSE ELECTRIC CORP, WESTINGHOUSE ELECTRIC CORPORATION
Application year: 1983
Main classification: G21C19
IPC codes: G21C19