Patent Number: 048246328
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIGS. 1 and 2 show a partial section of a nuclear reactor upper core plate 10 with two fuel assembly alignment pins, one misaligned or bent 12 and the other relatively straight 14. FIG. 1 shows the straightening device, generally designated at 16, which has been positioned by a refueling machine auxiliary hoist (not shown) so as to place the straightening means, generally designated at 19, under the upper core plate 10. The upper core plate 10, and the upper internals structure of which it is a part, is supported for this purpose, outside of the reactor vessel, upon a support structure (not shown) within a refueling cavity of the containment area of a nuclear power plant. The straightening device 16 generally comprises an elongated mast 22 having a bail 25, or other support means, secured to its top end and a cross member 28 secured to the bottom end, generally perpendicularly disposed to the elongated mast 22. Secured to one end of the cross member 28, the left hand side of FIG. 1, is the straightening means 19. On the opposite end of the cross member 28 is a counterweight 31 matched to the weight of the straightening means 19 (which in this example is about 295 kg or 650 lbs.) so as to keep the cross member 28 horizontal in a generally perpendicular orientation with respect to the elongated mast 22. Preferably, the elongated mast 22 is comprised of a plurality of segments 32. Since plants have differing sized containment buildings, the use of segments 32 having different lengths allows the straightening device 16 to be used in a number of different plants. The cross member 28 would also be made of segments so that the straightening means 19 can reach all fuel assembly alignment pins regardless of their radial position on the upper or lower core plate 10. These segments may either be rigidly secured end to end, or may be telescoping. The device 16 is supported and positioned by the bail 25 by means of the plant's overhead crane (not shown). The straightening means or assembly 19 is secured to the cross member 28 by a baseplate 34, and generally comprises a housing 37, a means 40 of interconnecting said housing 37 with said baseplate 34 for providing both angular and translational compliance for the housing 37, as shown in FIG. 3. Preferably, the interconnecting means 40 is comprised of four axially compressible and laterally deformable compression springs 41 connected between the housing 37 and the baseplate 34. Also secured to the baseplate 34, on a side opposite the housing 37, is a hydraulic ram 44 or other means for lifting the housing 37 into full planar contact with a bottom surface 47 of the upper core plate 10. Shown in greater detail in FIG. 2, the housing 37 of the pin straightening assembly 19 has two generally parallel vertical holes 50 and 51 disposed therein. A die insert 54 is adapted to be secured within a first hole 50, the die insert 54 also having a bore 55 disposed therein for receiving a bent fuel assembly alignment pin 12. Preferably, the bore 55 has a frusto-conical opening 56 to facilitate the entry of the bent pin 12 into the bore 55 of the die insert 54. The die insert 54 is secured to the housing 37 by a set screw 57. Also, the die insert 54 is preferably made of a hardened material, most preferredly 17-4 ph stainless steel, to prevent its deformation as the pin 12 is bent back into alignment. The other bore 51 is adapted to receive. the other pin 14 and is an aid to alignment of the housing 37 with respect to the upper core plate 10. The bore 51 is of a diameter which is greater than that of the fuel assembly alignment pin 14 to allow compliance of the housing 37 as the bent pin 12 is inserted into the die insert 54. This is especially true if the other pin 14 happens to be misaligned as well. A most important feature of the straightening assembly 19 is a wedge-shaped adjustable shim 61 disposed on an upper surface of the housing 37. The shim 61 also has two holes 62 and 63 which are concentric with the two holes 50 and 51 in the housing 37. The shim 61 is a plate which is secured to the top of the housing 37 by set screws 64. The purpose of the adjustable shim 61 is to compensate for expected spring back in the pin 12. This is accomplished by bending the pin 12 a predetermined amount past a centerline, generally designated at 66, which corresponds to a correct alignment of the bent pin 12 (see FIG. 4). For a typical stainless steel pin, having a diameter of about 22 mm, the pin 12 should be bent past the centerline 66 at an angle which is about 15% to 25%, and preferably about 20%, greater than and opposite to an angle at which the pin 12 was originally bent. For example, if the pin 12 were misaligned at an angle 67 of 3.degree., the adjustable shim 61 would have an included angle 68 of about 3.6.degree.. (The predetermined angle at which the pin 12 is bent back beyond the original centerline 66 is dependent upon the material of the pin 12). At this value the spring back of the pin 12 will cause it to align exactly with the desired centerline 66, after the straightening assembly 19 is lowered from the upper core plate 10 and out of engagement with the pins 12 and 14 (FIG. 5). Alternatively, the hardened die insert 54 may have a bore 55 which is slanted at an angle opposite to that of the bent pin 12 in order to compensate for spring back in the pin 12, instead of using an adjustable shim 61. This included angle for the adjustable shim 61 or die insert 54 mainly is a function of the material of which the alignment pin 12 is constructed. The angle which will adequately compensate for expected springback of a pin 12 can thus be functionally derived for whatever material the pin 12 is constructed. When a bent pin 12 is discovered, its angle of misalignment 67 is determined. This can be accomplished either by the use of high resolution photography to determine bend angles and direction, or by making a mold of the bent pin 12. In the second method, a putty-like substance is applied to the bent pin 12, and allowed to harden. The mold is then removed and the angle 67 and direction of bent pin 12 measured. An adjustable shim 61 is then chosen which has an included angle which is about 20% greater than and opposite to the misalignment angle 67. The straightening procedure, as shown in FIGS. 2-5, is then performed. The plant's auxiliary hoist (not shown) maneuvers the straightening device 16 so that the straightening assembly 19 is generally placed under the upper core plate 10 in an area in which a bent pin 12 is situated. The device 16 is suspended by the hoist by the bail 25. The length of the elongated mast 22 is dependent upon the height of the hoist above the refueling cavity, and the length of the cross member 28 is dependent upon the radial position of the bent pin 12: the closer the pin 12 is to the centerline of the reactor upper internals, the longer the cross member 28 must be. Also, the orientation of the pin 12 determines the orientation of the shim 61 on the housing 37. More exact positioning of the housing 37 and the die insert 54 therein under the bent pin 12 is accomplished by means of remote television cameras (not shown) positioned under the upper core plate 10. When the housing 37 is so positioned (FIG. 2), the hoist lifts the device 16 such that the bent pin 12 enters the bore 55 of the insert 54 (FIG. 3), until the shim 61 contacts the bottom surface 47 of the upper core plate 10. At this time, the hydraulic ram 44 is activated so that piston 70 moves downward into contact with the reactor containment refueling cavity floor 73. In order to protect the floor 73, a block 76 may be placed between the piston 70 and the floor 73. This action forces the ram 44, and the attached baseplate 34 upward. This continues until the springs 41 of the compliant interconnecting means 40 are compressed, thereby forcing the housing 37 and the adjustable shim 61 into full planar contact with the upper core plate 10 (FIG. 4). As the baseplate 34 and housing 37 are forced upward the pin 12 is thus bent back in an opposite direction, past the original centerline 66. To accomplish this, in this example, the ram 44 is activated to a force of about 267 kN (60,000 lbs), which is just below that necessary to lift the internals structure out of its support; although all that is necessary to straighten the bent pin 12 is the force required to bring the housing 37 into full planar contact with the upper core plate 10, by activating the ram 44 to this level such full planar contact is assured. At this point, the ram 44 is deactivated in order to remove the insert 54 out of engagement with the pin 12. When the housing 37 is fully retracted, the pin 12 will spring back a predetermined amount necessary to correctly align the pin 12 with the original designed centerline 66 (see FIG. 5). The device 16 can then be maneuvered to perform the above procedures on any other bent fuel assembly alignment pin. DESCRIPTION OF A SECOND EMBODIMENT Instead of the cross member 28 being comprised of sectional members, it is made of a single elongated boom. The boom would be capable of reaching alignment pins 12, 14 in a number of different plants, regardless of the diameter of the reactor internals structures. Also, the mass of the counterweight 31 is capable of remote adjustment. In this configuration, the transverse position of the elongated mast 22 between the pin straightening assembly 19 and the counterweight 28 on the elongated boom or cross member 28 is also remotely adjustable (FIG. 6). This can be accomplished by any suitable means known in the art, preferably by an electric motor and an associated encoder which would indicate the position of the mast 22 with respect to the cross member 28. In this manner the effective length, L, of the cross member 28 can be remotely adjustable. Since the radial positions of each of the alignment pins is known, the individual size and mass of each of the counterweight 31 members are chosen to balance the cross member 28 as the straightening assembly 19 is positioned under a respective bent alignment pin 12. For example, each set of pins 12, 14 occupies a fixed radial (and linear) position on the reactor internals. The maximum mass of the counterweight 31 is placed on the end of the cross member 28, and the mast 22 remotely positioned at a point on the cross member nearest the counterweight in order to reach those alignment pins which are innermost on the diameter of the reactor internals. As each radial (or linear) row of pins is remotely inspected by television cameras (not shown), the straightening assembly 19 can be positioned thereunder for straightening any bent pins 12 discovered. When such operation is completed for those innermost pins, the mast 22 is then moved to a position on the cross member 28 in order that the straightening assembly 19 can be positioned under the next group of pins; the appropriate weight would be removed from the counterweight 31 to balance the cross member 28. This operation would be repeated until each of the pins 12, 14 has been inspected and, if necessary, straightened. Alternatively, the counterweight 31 can be slidably mounted on the cross member 28, the counterweight not being adjustable, in order to compensate for the bending moment on the cross member 28 produced by the straightening assembly 19. Thus, the mast 22 would always be positioned midway between the straightening assembly 19 and the counterweight. It is also to be understood that the orientation and angle 68 of the adjustable shim 61 (or die insert 54) would be capable of remote adjustment to be able to straighten any bent pin 12, regardless of its misalignment angle 67. Another advantage to this type of arrangement is that the inspecting and straightening of fuel assembly alignment pins can be completed much more quickly. Instead of having to first inspect the reactor internals in order to map the locations of any bent pins to provide for predetermined parameters for the tool 16, the inspecting and straightening procedures can be simultaneously performed. This even further would reduce refueling downtime, as well as reducing individual man-rem exposure for plant maintenance personnel. Although the embodiments discussed refer to vertical pins which project upward or downward from a horizontal wall, it is to be understood that the device may be also used to straighten pins, or other such members, which project horizontally from a vertical wall. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alterations would be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.