Patent Number: 056429550
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS During the installation procedure, the tie rod/lower spring assembly (items 54 and 56 in FIG. 2) is lowered into the downcomer annulus 16. This is accomplished using a crane (not shown) on the refueling floor of the reactor. First, the tie rod/lower spring assembly must be raised from horizontal position on the refueling floor to a vertical position suspended from the end of the crane cable. This is accomplished by means of a tie rod adaptor which couples the upper end of the tie rod to the end of the cable. When the cable is wound, the upper end of the tie rod is lifted off the refueling floor into an upright position with all of the weight of the tie rod being supported by the cable. The tie rod/lower spring assembly can then be lowered into the annulus by unwinding the cable. Referring to FIGS. 3A and 3B, when vertical access to the downcomer annulus 16 is limited by internal reactor structures such as the feedwater sparger 14 and core spray header 15, the tie rod adaptor 100 is coupled to the end of the cable 84 via a rigid frame or strongback 90 specially designed, in accordance with the present invention, to bypass the obstruction. Maneuvering of the tie rod/lower spring assembly must be done with extreme care to avoid damaging reactor hardware such as the jet pump sensing lines. Referring to FIGS. 5A and 5B, the tie rod adaptor 100 comprises a frame 102 having a hole 104 for receiving a conventional coupling mechanism, such as a clevis pin, which must be strong enough to bear the entire weight of the tie rod/lower spring assembly. A circular cylindrical shield 106 for protecting the threads of the tie rod is connected to the frame 102 by means of a mounting plate 108. The frame 102 has an axial recess 114 shaped for receiving the upper end of the tie rod, and a pair of circular cylindrical holes 116a and 116b which communicate with axial recess 114. Each hole 116a and 116b has a respective bushing 118a and 118b in which a respective locking pin 120a and 120b is slidably mounted. Each locking pin is slidable from a first position whereat the locking pin does not interfere with axial recess 114 to a second position whereat the locking pin interferes with axial recess 114, as seen in FIG. 5B. Each locking pin 120a, 120b slides from the interfering position to the non-interfering position in response to actuation of a respective pneumatic cylinder 122a, 122b. The piston of pneumatic cylinder 122a is connected to a reduced-diameter end of locking pin 120a; the piston of pneumatic cylinder 122b is connected to a reduced-diameter end of locking pin 120b. As best seen in FIG. 5B, each cylinder is protected against damage by a respective U-shaped cylinder shield 126a, 126b attached to frame 102 via screws. Each locking pin 120a and 120b is disposed radially relative to the axis of the tie rod and is configured to fit with little play inside a respective one of circular cylindrical radial holes 58a and 58b formed in the topmost portion of the tie rod upper end, as shown in FIG. 4, and inside a respective one of the bushings 118a and 118b. The front end of each locking pin is chamfered to facilitate entry of the locking pin into the radial holes 58a and 58b. In the preferred embodiment, the holes 58a and 58b are mutually perpendicular, as are the locking pins 120a and 120b. Each locking pin is capable of supporting the entire weight of the tie rod, which is in excess of 1,000 pounds. Each pneumatic cylinder is connected to a separate source of pressurized fluid via a respective pneumatic line (not shown). Each piston is retracted when pressurized fluid, e.g., air, is supplied to the cylinder and extended when the supply of pressurized fluid is cut off. When the pistons are extended, they interlock the adaptor to the tie rod via locking pins 120a and 120b which extend into tie rod holes 58a and 58b (see FIG. 4) respectively. Each cylinder has a spring return which urges the locking pins to engage tie rod holes 58a and 58b when pneumatic pressure is discontinued. As a safeguard to prevent dropping the tie rod into the annulus, each locking pin is latched in the locking position by a respective latch 128. The exposed end of each latch shaft is integrally joined with a respective eyebolt 124a and 124b. The tie rod cannot be disengaged from the lifting apparatus until each latch 128 has been manually unlatched by an operator using a handling pole to lift the eyebolts. Then pressurized fluid can be supplied to disengage the locking pins 120a and 120b from the holes in the tie rod. When both locking pins are retracted, the tie rod lifting apparatus can be disengaged from the tie rod and removed from the annulus. The hole 104 of tie rod adaptor 100 is coupled by a first clevis pin (not shown) to an apertured clevis 90a (see FIGS. 6A and 6B) which forms the lower end of the strongback 90. The upper end of strongback 90, in turn, has an apertured clevis 90h which is coupled by a second clevis pin (also not shown) to a cable 84 by a cable adaptor 86 (see FIGS. 3A and 3B). The strongback must have a height sufficient to span the distance between a point above the feedwater sparget 14 to a point below the core spray elbow 19, thereby allowing a shorter cable to be used. Because the cable ends at a point above and the strongback circumvents the piping obstructions, the tie rod/lower spring assembly 54/56 can be freely suspended without the supporting hardware or cable bearing against the piping. Thus, the cable stays plumb and the position of the tie rod/lower spring assembly relative to the gusset plate 58 can be freely adjusted by displacing the cable adaptor, e.g., by displacing the crane or by exerting a lateral force on the cable. To circumvent the piping obstructions, the strongback 90 is designed to have a first rigid linear member 90c which is parallel to and offset from the reference axis A (see FIG. 6A). Strongback 90 further comprises a second rigid linear member 90e which is also parallel to and offset from the reference axis A. The rigid linear members 90c and 90e are mutually parallel and define a midsection plane. The bottom end of rigid linear member 90e is connected by a welded joint to the top end of an oblique rigid linear member 90d; the top end of rigid linear member 90c is connected by a welded joint to the bottom end of oblique rigid linear member 90d. Similarly, the bottom end of rigid linear member 90c is connected by a welded joint to the top end of an oblique rigid linear member 90b. The bottom end of rigid linear member 90b is joined to or integrally formed with the lower clevis 90a; the top end of rigid linear member 90e is connected by a welded joint to the bottom end of an oblique rigid linear member 90f. The top end of oblique rigid linear member 90f is in turn connected by a welded joint to the bottom end of a rigid linear member 90g which is coaxial with reference axis A. The top end of rigid linear member 90g is joined to or integrally formed with the upper clevis 90h. Preferably, each rigid linear member is a tube having a square cross section. Each of the welded joints connecting an oblique rigid linear member to a vertical rigid linear member is reinforced by a respective channel welded to both rigid linear members and spanning the welded joint. These reinforcing ribs bear the designations 90i-90m in FIGS. 6A and 6B. Finally, a coupling 90n is attached to oblique tube 90f such that the axis of a hexagonal socket in the head of the coupling is generally vertical and accessible from above by a tool which can be manipulated remotely to cause the strongback 90 to rotate about reference axis A during positioning of the tie rod/lower spring assembly relative to the gusset plate. The preferred embodiment of the strongback in accordance with the present invention has been disclosed for the purpose of illustration. Variations and modifications of the disclosed structure which fall within the concept of this invention will be readily apparent to persons skilled in the art of tooling design. For example, it will be apparent that not all tubes of the welded strongback assembly need to be straight. Nor does the tube cross section need to be square. All such variations and modifications are intended to be encompassed by the claims set forth hereinafter.