Patent Number: 047028785
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, shown in FIGS. 1 and 2 is a portion of a conventional nuclear steam generator, generally indicated by the numeral 10, having an outer cylindrical shell 11 provided with an opening 12, generally referred to as a handhole, located approximately 18 inches from the tube sheet 13 adjacent the bottom of the shell. Generally the handhole is only six inches in diameter. As shown in FIG. 2, the steam generator further includes a plurality of closely spaced vertical tubes 14 supported by and extending upwardly from the tube sheet 13. The vertical tubes 14 are associated by pairs with a U-bend at the top (not shown) so as to straddle two sides of an aisle 15 extending centrally across the shell. The tubes 14 are surrounded by a wrapper barrel 16 spaced approximately two inches from the interior wall of the shell 11 to form an annulus 17, therewith. As shown in FIG. 1, the wrapper barrel 16, and consequently the annulus 17, extend downwardly to a point six inches above the tube sheet 13. As further shown in FIG. 1 an inspection hole 18 is provided below the handhole 12 in the shell and is located at a point just above the tube sheet 13. As shown in FIGS. 1 and 2, the search and retrieval device of the present invention includes a guide tube, generally indicated by the numeral 20, having a straight main segment 21 and an upper segment 22 bent at a right angle to the main segment. The guide tube further includes a lower segment 23 also bent at a right angle to the main segment and extending in a direction rotated 90.degree. from the direction of the upper segment 22. The lower segment 23 of the guide tube 20 rests on and is parallel to the surface of the tube sheet 13. The upper segment 22 and the lower segment 23 may be constructed as separate parts from the main segment 21 of the guide tube 20 to facilitate insertion of the guide tube into the steam generator. The guide tube is secured at its upper end to the shell 11 by means of a guide plate 24 fastened to the shell by suitable means such as bolts 25. Referring particularly to FIGS. 3 and 4, the search and retrieval device also includes a sled, generally indicated by the numeral 30, which comprises a flat front plate 31, an intermediate plate 32 angled upwardly at approximately a 30.degree. angle and a back plate 33 attached to the intermediate plate and positioned in a plane above but parallel to the plane of the front plate 31. Mounted on the back plate 33 is an upstanding bracket 34 for receiving and securely holding the end of a flexible steel tube 36 which extends from the back plate 33 of the sled 30 up through the guide tube 20 to the outside of the shell of the steam generator. Preferably, the flexible tube 36 has a diameter of one inch. While the flexible tube 36 preferably is constructed of steel, it also may be constructed of other suitable materials which are flexible enough to permit insertion through the guide tube 20 and the annulus 17 but yet is sufficiently rigid to permit pushing of the sled 30 around the periphery of the shell 11 on the tube sheet 13. An inspection probe 40 and a gripper 41 are associated with the sled 30 as most clearly shown in FIG. 2. The probe may be of any suitable type which permits inspection of the surface of the tube sheet 13. For example, the probe may comprise either a fiberscope or a miniature TV camera and preferably has a diameter of 3/8 inch. The gripper may be of any type suitable for picking up small objects from the surface of the tube sheet. The gripper shown in FIG. 2 has a plurality of prongs 42 which may closed and opened to grasp and release objects. The probe 40 is connected to a flexible probe cable 43 which extends from the probe back through the flexible tube 36 to the outside of the steam generator. The gripper 41 is connected to a flexible gripper shaft 44 which also extends back through the flexible tube 22 to the outside of the steam generator. The gripper shaft 44 preferably has a diameter of 1/4 inch. As shown in FIG. 5, the gripper shaft 44 consists of an inner shaft 45 slidably received within an outer shaft 46. The inner shaft 45 is connected to the end of gripper 41 whereby when the inner shaft is pushed forwardly the gripper prongs 42 are opened and when the inner shaft 45 is pulled backwardly the prongs 42 close to grasp an object. The probe cable 43 and the gripper shaft 44 constitute control means for the probe 40 and the gripper 41. Adjusting means, generally indicated by the numeral 50, are mounted on the sled 30 for changing the operating positions and direction of the probe and the gripper. The adjusting means 50 is comprised of a rotatable turret 51 having a circular passageway 52 extending through the upper portion thereof and a worm wheel 53 fixedly attached to the lower portion thereof by any suitable means such as bolts 54 as shown in FIG. 5. The turret 51 is rotatably attached to the front plate 31 of the sled by shaft 55. A worm gear 56 is rotatably mounted on shaft 57 secured by bracket 58 to the front plate 31 of the sled 30. Bracket 58 is mounted to front plate 31 by any suitable means such as bolts 59. The worm gear 56 meshes with worm wheel 53 whereby rotation of the worm gear causes the worm wheel 53 and consequently turret 51 to rotate. The probe cable 43 and the gripper shaft 44 freely pass through the circular passageway 52 of the turret 51 so that they may slide therethrough. Attached to the end of the shaft 57 on which worm gear 56 is mounted is a universal mechanism 60 which in turn is attached to the end of an actuator cable 61 rotatably received within an outer cable 62 which extends through a flexible tube 36 to the outside of the steam generator as shown in FIGS. 4 and 5. Actuator cable 61 rotates within outer cable 62 in a manner similar to a speedometer cable. Rotation of cable 61 causes the worm gear to also rotate or turn. An emergency pull wire 64 also extends through the flexible tube 36 and is welded to the flexible tube at each end thereof. The emergency pull wire 64 extends outwardly from the outer end of the flexible tube whereby if the flexible tube 36 becomes stuck, the emergency pull wire will prevent unraveling of the flexible tube 36 while the tube is being pulled out. In operation of the search and retrieval device of the present invention, the outer end of the flexible tube 36 is initially inserted through the guide tube 20 and out through the end of the upper segment 22 thereof. The sled 30 and the guide tube 20 having the flexible tube 36 passing therethrough are then inserted through the handhole 12 until the sled 30 is positioned on the surface of the tube sheet 13 and the lower segment 23 of the guide tube 20 is parallel to the surface of the tube sheet. An operator of the device may view the guide tube 20 through the inspection hole 18 to ensure that the guide tube is positioned correctly. Once the sled and the associated components mounted thereon are in position on the periphery of the tube sheet, the probe may be activated to search for any loose objects on the surface of the tube sheet. The sled is moved along the periphery of the tube sheet by pushing the flexible tube through the guide tube 20. Pushing or pulling on the flexible tube 36 causes the sled to slide over the surface of the tube sheet. The sled may be stopped at any point and the turret 51 rotated by turning or rotating actuator cable 61 in order to turn the probe and the gripper inwardly to face the rows of the tubes 14. Both the probe cable 40 and the gripper shaft 44 then may be pushed by any suitable means outside of the shell of the steam generator whereby the probe cable 43 and the gripper shaft 44 slide through the circular passageway 52 of the turret to extend the probe 40 and the gripper 41 to a position among the tubes. When an object to be removed is located by use of the probe, the gripper shaft is then pushed until the gripper comes in contact with the object whereupon the inner shaft 45 of the gripper shaft 44 is pulled to close the prongs 42 and grasp the object. The entire sled assembly is then removed from the steam generator and the object released from the gripper. The above-described operation is then continually repeated until the entire tube sheet has been inspected and cleaned. The flexible tube 36 may be pushed through the guide tube 20 either manually or by automatic means (not shown) located outside the shell of the generator. In addition, the rotation of the actuator cable 61 and the pushing and pulling of the probe cable 43 and the gripper shaft 44 may also be done either manually or by suitable automatic means (not shown) located outside the shell of the generator. It is apparent from the foregoing that many advantageous features are provided by the present invention over the prior art. A device for searching and retrieving objects in the small spaces between the tubes on a tube sheet of a nuclear steam generator is disclosed which is relatively simple and economical in construction and which may be readily maneuvered into and through the small spaces present in a steam generator to retrieve objects which have been dropped on the tube sheet and have to be removed. The present invention permits such removal without having to dismantle any part of the steam generator to provide access to the interior portions thereof. Numerous alterations and modifications of the structure herein disclosed will suggest themselves to those skilled in the art. It is to be understood, however, that the present disclosure relates to the preferred embodiments of the invention which is for purposes of illustration only and is not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.