Patent Number: 056339020
Section: description

DETAILED DESCRIPTION OF THE DRAWINGS FIGS. 1-3 illustrate the preferred form of a cutter apparatus 100 of the present invention for dismantling a storage rack after use for storing nuclear fuel assemblies. The storage rack and its use in a spent fuel pool will be described in greater detail hereinafter. The storage rack essentially is made up of an array of elongated storage cells which are tubular and can be of a circular, square or rectangular cross-section. The apparatus embodies a special construction to enable placement and operation at a required site within a given storage cell for severing the wall of the storage cell generally at each of its opposite ends. It is necessary to sever the end portions from their welded interconnection occurring both at the base of the fuel rack and at the fuel entry end of the storage cells . The apparatus includes a support housing 1 having an internal cavity surrounded by side walls 2, 3, 4, and 5 and end walls 6 and 7. The end walls each support bearing sleeves 8 and 9 that in turn rotatably support a drive shaft 10. The drive shaft has a driven end portion 11 which can be mechanically connected to a crank arm 12. The crank arm is provided with a radially extending bar by which a workman or machine tool can apply torque to the drive shaft it to rotate about its longitudinal central axis 10A. As can be seen from FIG. 3, axis 10A extends along the housing 1 within an upper left quadrant with respect to the geometrical center 10B of housing 1. The location of axis 10A with respect to housing 1 is chosen such that the axis will coincide with a central longitudinal axis of a fuel storage cell when the housing is anchored at a desired site to perform a wall severing operation. The housing is anchored at this site by means of pneumatically powered clamp assemblies 15 and 16 supported by wall 3 and pneumatically powered clamp assemblies 17 and 18 supported by wall 4. Each of the pneumatically powered clamp assemblies includes a cylinder wall 19 affixed by a support base 20 to the housing wall and a piston 21 which can move to and fro along the internal wall of cylinder wall 19 in response to the application of pressurized air at opposite sides of a piston through suitable ducts. The ducts are joined by flexible conduits that extend external of the housing within a protective cavity formed by shields 22 which are shown in FIGS. 1 and 2. The shields at each side of the housing are mounted on a mounting plate 23 provided with a suitable opening to allow passage of the conduits into the interior of housing 1. The conduits as well as other power supply lines for a motor given saw blade extend from the end wall 6 of the housing to a suitable control panel having valving and having a supply of pneumatic pressure for controlling the operation of the pneumatically powered clamp assemblies 15-18. The drive output end of shaft 10 is joined to a collar 25 which together with collar 26 at the opposite end of housing 21 prevents shifting of the drive shaft within the housing. Projecting from collar 25 is a drive output shaft 27 having secured to its projected end a L-shaped carrier 28. One leg of the carrier is secured to the drive output shaft 27 and carries a base portion 29 of a linear bearing 30. The second leg of the carrier supports an actuator 31 while operatively connected to a motor bracket 32 that is supported by the moveable member 33 of the linear bearing 30. Motor bracket 32 carries a drive motor 34. The drive motor has a drive output shaft to which there is affixed by mounting collars 35 a metal cutting saw blade 36 of a type per se well known in the art. Supply lines for fluid power to operate the linear actuator 31 and a line for power to operate drive motor 34 extend from carrier 28 through a suitable opening in end wall 7 of housing 1 where these lines are protected and thence formed as part of a bundle with the air supply lines for actuators 15-18 extending exteriorly of the storage cell. FIG. 5 and 6 illustrate a typical spent fuel pool that is formed within an excavated area by side walls 40 and floor wall 41 usually made of reinforced concrete. The water depth above a storage rack 42 is sufficient to always maintain a protective water barrier to function a moderator against harmful emissions from the stored nuclear fuel even when fuel assemblies are manipulated within the spent fuel pool from storage cell to storage cell. The storage rack 42 embodying a construction per se well known in the art is supported on the floor wall during actual use for supporting nuclear fuel assemblies. The rack essentially consists of tubular storage cells that are joined together to form an array as best shown in FIG. 6. The storage racks which are to be dismantled may take any of the diverse forms of construction but essentially the racks include fuel storage cells of an elongated tubular shape that is round, square or rectangular in cross section. The cutter apparatus as described herein before and shown in FIGS. 1-4 is constructed to allow the apparatus to be passed along the length of the storage cell as can be best seen as in FIG. 7. It to be understood, however, that before the cutter apparatus is passed into a storage cell, the storage rack is first removed from its supporting relation on the floor of the spent fuel pool and placed into a confined area where an enclosed working environment is formed by erection of a tent 43 forming an enclosure about the rack and a suitable work area. There is schematically shown in FIG. 7 only a part of the side wall for the tent 43 which extends in a sealed fashion to the floor of the work area where there is also located support bases 44 on which a storage rack is supported by arranging the rack so that the side walls of the storage cell rest on the bases. In this orientation the extended lengths of the storage cells are horizontal not vertical as when used in the spent fuel pool. The volume enclosed in the tent 43 is treated by circulation through a HEPA filtration unit 45 to minimize radiological effects to the operating personnel and prevent emission of radioactive particulates to the environment. The present invention eliminates the need for a large steel building with a substantial bank of large HEPA filter units to compensate for torch cutting effects. In FIG. 7 the spent fuel storage rack has become contaminated because of the storing of radioactive fuel assemblies formerly used in a nuclear reactor. The spent fuel storage rack is a weldment type fabrication made up of an array of elongated storage cells shown in FIG. 7 in the form of tubes 51 having a square cross-sectional configuration. The storage cells may have a rectangular or a circular cross-sectional configuration. The rack 42 further includes a base 53 which encircles the lower most ends with the storage tubes 51 and is provided with support legs 54 by which the rack is supported on the floor on the spent fuel pool. At the top end of the rack, when located in its usual fuel storage position, there is located at the fuel entry ends of the tubes 51, a band 55 that encircles the storage tubes at the lead-in ends. After using cutter apparatus 100 saw cutting at 56-57 to free a selected one of the storage tubes from the base 53 and the band 55 there is formed a tube section 58 usually of a length of 8 feet or greater that can be subdivided and compacted for disposal. A jib crane can be used to transport the tube section to a sawing device such as a crop saw where the subdivided tube section is subdivided into lengths of preferably of 3 to 4 feet after which the tube sections can be processed in a press 60 shown in FIGS. 8 and 9. The press 60 has a movable platen 61 by means of a hydraulic piston and cylinder assemblies 62 displace the platen toward a stationary platen 63 between which the tube section resides. The cylinder assemblies 62 are supported by a cross heads 64 and joined by machine columns 65 to develop the necessary force to crush the tube section 66 which is oriented in the press on a corner edge so that after crushing a plate like residue 67 is formed as typically illustrated in FIG. 10. The plate-like residue has been reduced to a volume requiring a minimum of space for storage. Returning to FIG. 7 the cutting apparatus 100 shown schematically is loaded into a selected one of the fuel storage cells and passed along the length thereof to a site where the cutter saw blade 36 can penetrate the side wall of the storage cell above the base by a short distance typically, for example, 3 or 4 inches. Thereafter, pneumatic pressure is delivered to the clamp assemblies 15-18 causing the pistons to extend from their respective cylinders and into forced engagement with the side wall of the fuel storage cell. The reaction force drives the walls 2 and 5 of housing 1 against the internal wall of the storage cell thus anchoring housing 1 against longitudinal movement within the storage cell. Power is then delivered to the drive motor 34 for a period of time sufficient to bring the rotational speed of the metal cutting saw blade 36 for a cutting operation where upon power is delivered to the linear actuator 30 which displaces mounting bracket 32 and the rotational axis of drive motor 34 in a direction for pressing the metal cutting saw blade against the interior of the storage cell as shown in FIG. 11. Power is continually delivered to the linear actuator 30 until the actuator reaches the end of its stroke, or abuts against an adjustable stop, whereupon the saw blade completes an initial puncture of the side wall and extends partially exteriorly of the storage cell wall as shown in FIG. 12. Thereafter, crank arm 12 is operated by a workman to rotate shaft 10 within housing 1. The rotational axis of 10A of shaft 10 generally coincides with the longitudinal central axis of the storage tube. However, because the rotational axis M of the motor and the saw blade driven thereby is displaced by the linear actuator from axis 10A, the rotation of crank arm 12 imparts a cutting path from the puncture site about an arc whose radius R corresponds to the distance between the rotational axis of a motor and axis 10A. In this fashion the cutter blade proceeds to cut the side wall through the storage cell side wall at a corner area as shown in FIG. 13 and then cutting proceeds with a transversing cut forming a parting line along an adjacent side wall of the storage cell as shown in FIG. 14. The cutting operation proceeds by the continue rotation of shaft 10 to perform the cutting operations along the remaining two side walls of the storage cell. This cutting operation frees an end of the storage cell from the base of the storage rack. A top portion of the storage cell section is freed from the band 55 by repeating the cutting operation as just described at a site adjacent the band whereupon a tube section of the storage cell is freed from the storage rack. The tube section is then subdivided by a crop saw into relatively short pieces which are then crushed and pressed as the processed as described herein before. While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.