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(11) | EP 0 186 957 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Anti-vibration bars for nuclear steam generators |
| (57) A method of installing tubular anti-vibration bars (15) into a tube bundle (11) of
a steam generator (18) wherein the tube bundle (11) comprises rows of tubes (13),
with the anti-vibration bars (15) received between adjacent rows of the tube bundle
(11) for stabilizing the tubes (13) against vibration. The anti-vibration bars (15)
are first inserted between adjacent rows of the tube bundle (11) and a pressurized
fluid is then introduced into the anti-vibration bars (15) which are thus expanded
into contact with the tubes of the adjacent rows for support. |
[0001] This invention relates to mechanisms for supporting the tubes of a nuclear steam generator to prevent vibration and, more particularly, to anti-vibration bars as disposed between rows of the tubes of a nuclear steam generator.
[0002] This invention relates to a novel method of installing and design of anti-vibration bars installed in the U-bend region of the tube bundle of nuclear steam generators to control tube vibration caused by the steam/ water mixture flowing by the U-shaped tubes. In the absence of anti-vibration bars, the U-shaped tubes would vibrate and, if not controlled, would leak resulting in the loss of the primary coolant into the steam supplied to the turbine generator.
[0003] Anti-vibration bars of the prior art are typically of uniform cross-section, e.g., square or cylinder. On the other hand, the U-shaped tubes are of substantially uniform cylindrical cross-section with the result that there is a gap/clearance between the anti-vibration bars and the U-shaped tubes. Gaps between the U-shaped tubes and the anti-vibration bars are not desirable for tube performance or from a reliability point of view and are difficult to make small. The U-shaped tubes and the anti-vibration bars have dimensioned tolerances and are assembled such that close contact therebetween is difficult to maintain. For example, normal tolerances occur in the outer diameters of the anti-vibration bars and the U-shaped tubes. The forming of the U-shaped tubes results in oval cross-sections in their bend areas and their straight portions may not be aligned precisely parallel with each other. Further, the openings within the tube support plate 14 may not be precisely spaced so that the spacing between adjacent U-shaped tubes in the region of their bends may not be uniform.
[0004] It is the principal object of this invention to provide new and improved anti-vibration bars that have decreased clearance from the U-shaped tubes of a nuclear steam generator, whereby the degree of tube support is improved.
[0005] With this object in view, the present invention resides in a method of forming and installing anti-vibration bars into a tube bundle of a steam generator, which tube bundle is comprised of rows of tubes, each of which carries a high temperature coolant, with each of said anti-vibration bars having a tubular configuration and being disposed between adjacent rows of said tube bundle for stabilizing said tubes so as to prevent vibration thereof, characterized in that after insertion of at least one anti-vibration bar between adjacent rows of said tube bundle a pressurized fluid is admitted to said inserted anti-vibration bar, and said anti-vibration bar is expanded thereby to minimize any gaps between said anti-vibration bar and the tubes of said adjacent rows.
[0006] The invention will become more readily apparent from the following description of a preferred embodiment thereof showing, by way of example only, in the accompanying drawings, wherein:
Figures 1A and 1B are respectively a perspective view of a nuclear steam generator, wherein its U-shaped tubes are supported by an upper tube support assembly in accordance with the teachings of this invention, and a cross-sectioned view particularly showing the anti-vibration bars of this invention and the manner in which they are assembled into the upper tube support assembly;
Figure 2 is a perspective view of a test rig for receiving first and second rows of test tubes between which are disposed an anti-vibration bar;
Figures 3 and 5 show plan views of the rows of test tubes illustrating, respectively, an anti-vibration bar before and after deformation, whereas Figures 4 and 6 are side views, respectively, of the arrangements of Figures 3 and 5 showing the anti-vibration bar in cross-section;
Figure 7 is a schematic diagram of the test rig of Figure 2 as coupled to a controllable source of pressurized fluid;
Figures 8A and 8B show, respectively, an oval shaped anti-vibration bar and such a bar in contact with a U-shaped tube;
Figures 9A and 9B show, respectively, a second embodiment of this invention in the form of a hollow rectangularly shaped anti-vibration bar and the manner in which it contacts a U-shaped tube; and
Figures 10A and lOB show, respectively, a third embodiment of this invention in the form of a rectangularly shaped anti-vibration bar with foldable side portions and the manner in which such a vibration bar contacts a U-shaped tube.
[0007] A nuclear steam generator 8 of the type found in the prior art is shown in Figures 1A and 1B of the attached drawings, as comprising a bundle 11 of a large number of vertically oriented U-shaped tubes 13. The tubes 13 are disposed in a lower, cylindrically shaped shell 9 of the steam generator 8, whose bottom end is associated with a channel head 17, typically of a hemi-spherical configuration as shown in Figure 1A. The channel head 17 is divided by a partition 18 into a first half typically known as a hot leg 20, and a second half typically known as a cold leg 22. The high-temperature coolant water from the nuclear reactor is introduced into the steam generator 8, through a primary coolant inlet 24 into the hot leg 20. The high-temperature coolant passes from the hot leg 20 into the exposed openings of the plurality of U-shaped tubes 13, passing therethrough to be introduced into the cold leg 22 and, finally, exiting from the steam generator 8 through a primary coolant outlet 26.
[0008] That portion of the steam generator 8, primarily including the tube bundle 11 and the channel head 22 is referred to as an evaporator section 10. As shown in Figure lA, the steam generator 8 further includes a steam drum section 32 comprising an upper shell 30, which contains a moisture separator 34. Feedwater enters. the steam generator 8 through inlet nozzle 28 disposed in the upper shell 30 to be distributed and mixed with the water removed by the moisture separator 34. This feedwater travels down an annular channel surrounding the tube bundle 11 and is introduced into the bottom of the tube bundle 11. The mixture of feedwater and recirculating water boils as the high temperature coolant is circulated through the U-shaped tubes 13 of the tube bundle 11. The steam so produced rises into the steam drum section 32. The moisture separator 34 removes the entrained water from the steam before the steam exits from the steam generator 8 through a steam outlet 36 to a turbine generator (not shown).
[0009] As shown in Figure lA, the U-shaped tubes 13 are supported in the configuration of the tube bundle 11 by a series of lower tube supports 12 and an upper tube support plate 14. As shown in Figures 1A and 1B, the upper tube support assembly 14 comprises a plurality of retainer rings 16a, 16b and 16c. As best shown in Figure lA, each of the retainer rings 16 is of generally oval configuration. The major and minor diameters of the retainer rings 16a, b and c are progressively smaller, noting that the retainer 16c is disposed at the upper-most portion of the tube bundle 11. A plurality of sets of anti-vibration bars 15 is disposed between adjacent rows of the U-shaped tubes 13. One such set of anti-vibration bars 15 is shown in Figure 1B, it being understood that successive sets of similar anti-vibration bars 15 are disposed behind and in front of the illustrated set. Each of the anti-vibration bars 15a, 15b and 15c is of a V-shaped configuration with the ends thereof extending to the circumference of the tube bundle 11 and connected to a corresponding one of the retainer rings 16. For example, one end of the anti-vibration bar 15a is secured as by tack-welding to the retainer ring 16a and, in similar fashion, the other end of the anti-vibration bar 15a is secured to the same retainer ring 16a. Figure 1B illustrates a cross-sectioned view taken through the tube bundle 11 showing that the anti-vibration bars 15a, 15b and 15c are disposed to support the upper ends of the U-shaped tubes 13, noting the arrangement of the U-shaped tubes 13a to 13n in a row.
[0010] Referring now to Figure 2, there is shown a test rig 40 for receiving and imparting a series of indentations 50 to an anti-vibration bar 15. The test rig 40 comprises an upper plate 42a, front and back plates 42d and 42b and a lower plate 42c, rigidly held together by bolts as shown. The upper plate 42b has first and second rows of openings 46 and 48, for respectively receiving first and second rows of test tubes 13" and 13'. As illustrated in Figures 2 and 3, the anti-vibration bar 15 is disposed between the first and second rows of test tubes 13' and 13". Each of the. first set of openings 48 has a configuration and dimension substantially similar to those of the test tubes 13 for rigidly disposing the test tubes 13, whereas each of the second set of openings 46 is of substantially oval configuration to permit the second set of test tubes 13" to be directed toward the first rows of test tube 13' whereby the spacings between corresponding pairs of the test tubes 13' and 13" may be variably set, thus duplicating the inconsistent spacings between U-shaped tubes 13 of a typical tube bundle 11. As illustrated in Figure 2, a set of micrometer heads 44a, 44b and 44c may be manually rotated to variably set the spacings between opposing test tubes 13' and 13".
[0011] As shown in Figures 3 and 4, the oval-shaped, tubular anti-vibration bars 15 have initially a uniform minor diameter before they are compressed as will be explained. The anti-vibration bars 15 of this invention are tubular in character to permit their deformation by the application of fluidized pressure, whereby a minimum gap contact is achieved with the U-shaped tubes 13, thus improving the vibration support provided to these tubes 13. In particular as shown in Figure 5, a series of indentations 50a, 50b and 50c, etc., is provided in the anti-vibration bar 15 by applying a pressurized fluid thereto. The diameter B along the minor axis of the oval-shaped anti-vibration bar 15 is shown in Figure 4 before the application of pressure. As illustrated in Figures 5 and 6, opposing indentations 50a, 50b, 50c, etc., are imparted to the anti-vibration bar 15 and the minor diameter A of the anti-vibration bar 15 therebetween is slightly increased by the application of pressurized fluid with respect to the minor diameter B. The application of the fluidized pressure increases significantly the minor diameter C of the deformed anti-vibration bar 15 at a point approximately midway between adjacent indentations 50. It is realized that deformation may increase slightly the minor diameter A from the original minor diameter B. As particularly illustrated in Figure 5, the surfaces of the indentations 50 tend to conform to the configuration of the opposing test tubes 13' and 13", whereby the size of the gap between the anti-vibration bars 15 and the tubes is minimized. The minimized gap between the tubes and anti-vibration bars 15 improves the support provided by the anti-vibration bars 15 to the test tubes 13, thereby reducing the vibration and the risk of primary coolant leakage. Maintaining the gap size at 3 mil or less is believed to result in the desired tube support and vibration reduction.
[0012] The mechanical deformation of anti-vibration bars 15 is carried out after the assembly and installation of the U-shaped tubes 13 as the tube bundle 11. In a preferred embodiment of this invention, method and apparatus are provided for hydraulically deforming anti-vibration bars 15 as illustrated in Figure 7. Figure 7 illustrates an anti-vibration bar 15 disposed between first and second rows of the test tubes 13' and 13" as supported by the test rig 40 as explained above. A pump 72 supplies a regulated, pressurized fluid, such as water, to the anti-vibration bar 15, whereby the anti-vibration bar 15 is expanded and a series of indentations 50a, 50b, 50c, etc., as shown in Figure 5 is imparted to the anti-vibration bar 15. It is understood that, in the preferred method of compressing and installing the anti-vibration bars 15, the U-shaped tubes 13 are first assembled into the tube bundle 11 as illustrated in Figures 1A and B, and thereafter the pump 72 is coupled sequentially or in another desirable order to each of the anti-vibration bars 15 to impart the desired deformations.
[0013] As shown in Figure 7, the pump 72 is coupled by a conduit 64 and a fluid coupling 64b to the one end of the anti-vibration bar 15. The opposite end of the anti-vibration bar 15 is attached to a fluid coupling 64a, which serves to prevent the leakage of the pressurized fluid, thus serving to permit the increase of pressure within the anti-vibration bar 15. The pump 72 pumps the fluid via the conduit 66 and coupling 64b to the anti-vibration bar 15. A pressure gauge 68 is coupled in circuit between the pump 72 and the anti-vibration bar 15, whereby a measurement of fluid pressure is obtained. Further, a pressure recorder 70 is connected to the pressure gauge 68, whereby a record of the fluid pressure may be kept, primarily, to ascertain the maximum fluid pressure.
[0014] In an illustrative embodiment of this invention, an oval-shaped anti-vibration bar 15', as illustrated in Figures 8A and 8B, having a major diameter of 1 cm and a minor diameter of 0.75 cm was disposed between first and second rows 13' and 13" as positioned by the test rig 40. Fluid pressure was established within the anti-vibration bar 15 and gradually increased by the pump 72 to a maximum pressure. Illustratively, the oval-shaped anti-vibration bar 15' may have a wall thickness of 0.5 mm and be made of that stainless steel known as type 304.
[0015] As illustrated in Figures 2 and 5, the pairs of test tubes 13' and 13" are deposed at six locations 1, 2, 3, 4, 5, and 6, each pair spaced 2.5 cm from an adjacent pair. In order to demonstrate the feasibility of this method of deformation, the spacings of the tube pairs 1 to 6 were set respectively to be 9.4, 8.6, 9.4, 7.6, 9.4 and 7.6 mm as would simulate the variations and spacings found within the tubes 13 of a typical tube bundle 11. The pressure was incrementally raised by the pump 72 in steps of 35 kg/cm2 until a maximum of 350 kg/cm2 was reached, before returning the pressure to 0. The following series of relatively uniformed diameters A and C resulted:
[0016] Further, tests have shown that when the pressure is raised greater than a predetermined maximum, e.g., 350 kg/cm2, for the particular oval-shaped anti-vibration bar 15', that the anti-vibration bar 15' may deform the cylindrical configuration of the tubes 13. Such deformation of the U-shaped tubes 13 may threaten their structural integrity, which must be avoided by limiting the predetermined maximum in view of the particular construction, e.g., material and dimensions, of the anti-vibration bar 15.
[0017] Referring now to 9A and 9B, there is shown a further embodiment of this invention, in which an anti-vibration bar 15" is configured as a rectangle having relative thick top and bottom sides 15a and 15c as compared to side walls 15b and 15d. Dimensions B and C as shown in Figure 9A are, respectively, 7.5 and 12.5 mm. Figure 9B illustrates the anti-vibration bar 15" after it was pneumatically expanded, whereby the side 15d is curved.
[0018] Referring now to Figures 10A and lOB,.a third embodiment is illustrated, wherein anti-vibration bar 15 "' ' has side walls 15f and 15h interconnected by flexible side walls 15e and 15g. The dimensions B and C are similar to those of the anti-vibration bar 15" as shown in Figure 9A. Of the three illustrative embodiments, the oval-shaped anti-vibration bar 15' is the preferred embodiment in that it is relatively easy and inexpensive to manufacture.
1. A method of forming and installing anti-vibration bars (15) into a tube bundle
(11) of a steam generator (8), which tube bundle is comprised of rows of tubes (13),
each of which carries a high temperature coolant, with each of said anti-vibration
bars (15) having a tubular configuration and being disposed between adjacent rows
of said tube bundle (11) for stabilizing said tubes (13) so as to prevent vibration
thereof, characterized in that after insertion of at least one anti-vibration bar
(15) between adjacent rows of said tube bundle (11) a pressurized fluid is admitted
to said inserted anti-vibration bar (15), and said anti-vibration bar (15) is expanded
thereby to minimize any gaps between said anti-vibration bar (15) and the tubes (13)
of said adjacent rows.
2. A method according to claim 1, characterized in that the pressure of the fluid
is increased to a level sufficient to cause the circumference of said anti-vibration
bars (15) to contact said tubes of said adjacent rows but only to a maximum level
to ensure that said tubes (13) are not deformed.
3. A method as claimed in claim 2, characterized in that the pressure of said pressurized
fluid is increased incrementally up to said maximum level of pressure.
4. A method as claimed in claim 3, characterized in that the pressure of the pressurized
fluid is increased incrementally in steps of 35 kg/cm until said maximum level is
reached.
5. A method as claimed in any of claims 1 to 4, wherein the anti-vibration bars (15)
are made of a stainless steel, characterized in that said maximum level is set at
approximately 350 kg/cm2.
6. An anti-vibration bar (15) for use in the method of claims 1 to 5, characterized
in that each of said anti-vibration bars (15) is hollow and has first and second series
of contact points on its opposing sides to receive and to support the tubes of adjacent
rows, some of said contact points being configured as indentations (50) to receive
the tubes.
7. An anti-vibration bar as claimed in claim 6, wherein said tubes (13) in a row are
spaced from each other by a given, uniform distance, characterized in that said contact
points of said first and second series are spaced from each other by a distance equal
to said given uniform distance and said indentations (50) are formed of a similar
configuration to ensure an intimate contact between said anti-vibration bars (15)
and said tubes (13) of said adjacent rows.
8. An anti-vibration bar as claimed in claim 6 or 7, characterized in that each of
said anti-vibration bars (15) is of oval configuration having in cross-section minor
and major axes.
9. An anti-vibration bar as claimed in claim 6 or 7, characterized in that each of
said anti-vibration bars (15) is in cross-section of a rectangular configuration.
10. An anti-vibration bar as claimed in claim 9, wherein said rectangular configuration
has a length and a width, with said length being greater than said width, characterized
in that said contact points of said first and second series are disposed along said
lengths of said anti-vibration bars (15).
11. An anti-vibration bar as claimed in claim 9, wherein each of said anti-vibration
bars (15) has first and second sides disposed along said length thereof and opposing
each other, and third and fourth sides disposed along said width and opposing each
other, characterized in that said third and fourth sides have walls of a relatively
small thickness and folds therein to facilitate displacement of said first and second
sides into contact with the tubes of the adjacent rows of tubes.
12. An anti-vibration bar as claimed in any of claims 6 to 10, characterized in that
the wall thickness of the hollow anti-vibration bar (15) is approximately 0.5 mm.