CA2673904A1

CA2673904A1 - Tube support system for nuclear steam generators

Info

Publication number: CA2673904A1
Application number: CA2673904A
Authority: CA
Inventors: Richard G. Klarner; Robert S. Horvath; Ghasem V. Asadi; Thomas Waring
Original assignee: Babcock and Wilcox Canada Ltd
Current assignee: BWXT Canada Ltd
Priority date: 2008-11-07
Filing date: 2009-07-24
Publication date: 2010-05-07
Anticipated expiration: 2029-07-24
Also published as: KR101645170B1; KR20100051546A; CA2673904C; JP5512235B2; JP2010112703A

Abstract

A method and apparatus in a steam generator that employs tube support plates within a shroud that is in turn disposed within a shell. The tube support plates are made of a material having a coefficient of thermal expansion lower than that of the shroud. The tube support plates are aligned during fabrication, with minimal clearances between components. Using a tube support displacement system, a controlled misalignment is then imposed on one or more tube support plates, as the steam generator heats up. Displacement to produce misalignment is produced only when the steam generator is heated. The tube support plate displacement system has a linking bar and a restraining mechanism, and only the linking bar is internal to the steam generator shell, threadably engaged to the linking bar connected to the shell, thereby minimizing the potential of loose parts. The tube support plate displacement system can be used to provide controlled misalignments on one or more tube support plates, in the same or varying amounts and directions, and with one or more apparatus being provided for any individual tube support plate.

Description

TUBE SUPPORT SYSTEM FOR NUCLEAR STEAM GENERATORS
FIELD AND BACKGROUND OF INVENTION

[0001] The present invention relates generally to nuclear steam generators, and in particular to a new and useful tube support system and method for use in nuclear steam generators which employ tube support plates to retain the tube array spacing within the steam generator.

[0002] The pressurized steam generators, or heat exchangers, associated with nuclear power stations transfer the reactor-produced heat from the primary coolant to the secondary coolant, which in turn drives. the plant turbines. These steam generators may be as long as 75 feet and have an outside diameter of about 12 feet.
Within one of these steam generators, straight tubes, through which the primary coolant flows, may be 5/8 inch in outside diameter, but have an effective length of as long as 52 feet between the tube-end mountings and the opposing faces of the tube sheets. Typically, there may be a bundle of more than 15,000 tubes in one of these steam generators. It is clear that there is a need to provide structural support for these tubes, such as a tube support plate, in the span between the tube sheets to ensure tube separation, adequate rigidity, and the like.

[0003] U.S. patent 4,503,903 describes apparatus and a method for providing radial support of a tube support plate within a heat exchanger, such as a U-tube steam generator having an inner shell and an outer shell. The apparatus is rigidly attached to the inner shell, and is used to centrally locate the tube support plate within the inner shell.

[0004] U.S. patent 5,497,827 describes apparatus and method for radially holding a tube support within a U-tube steam generator. Abutments radially separate an inner bundle envelope, or inner shell, from an outer pressure envelope. Each abutment is fixed to the inner bundle envelope by welding, and contacts the inner face of the pressure envelope. The abutments maintain the different coaxial envelopes of the steam generator and the assembly of the bundle by spacer plates in the radial directions. This is done to avoid relative displacements and shocks between the envelopes and the bundle in the case of external stresses, such as those accompanying an earthquake. In one variant, elastic pressure used to make contact with a spacer plate is obtained by a spiral spring. The spring is located internal to the pressure envelope.

[0005] U.S. Patent 4,204,305 describes a nuclear steam generator commonly referred to as a Once Through Steam Generator (OTSG), the text of which is hereby incorporated by reference as though fully set forth herein. An OTSG contains a tube bundle consisting of straight tubes. The tubes are laterally supported at several points along their lengths by tube support plates. The tubes pass through tube support plate holes having three bights or flow passages, and also having three tube contact surfaces for the purpose of laterally supporting the tubes. It is generally recognized that after a heat exchanger is assembled, the tubes will contact one or two of the inwardly protruding lands of the tube support plate holes. This contact provides lateral support to the tube bundle to sustain lateral forces such as seismic _ loads, as well as provides support to mitigate tube vibration during normal operation.

[0006] U.S. patent 6,914,955 B2 describes a tube support plate suitable for use in the aforementioned OTSG.

[0007] For a general description of the characteristics of nuclear steam generators, the reader is referred to Chapter 48 of Steam/Its Generation and Use, 41st Edition, The Babcock & Wilcox Company, Barberton, Ohio, U.S.A., 2005, the text of which is hereby incorporated by reference as though fully set forth herein.

SUMMARY OF INVENTION

[0008] The present invention is drawn to an improved method and apparatus for supporting tubes in a steam generator.

[0009] According to the invention, there is provided a tube bundle support system and method which advantageously permits tube support plates to be installed in an aligned configuration that is compatible with normal fabrication processes. A
controlled misalignment is then imposed on one or more tube support plates as the steam generator heats up, i.e. in the hot condition. The tube support plates are made from a material having a lower coefficient of thermal expansion than the shroud that surrounds the tubes. As a result, radial clearances open adjacent to the tube support plate as the steam generator heats up. These radial clearances provide space for lateral shifting or displacement of the individual tube support plates by an associated tube support plate displacement system.

[0010] Each tube support displacement system advantageously has only one part located inside the steam generator shell, thereby minimizing the potential of loose parts.

[0011] The method and apparatus can be readily retrofit to existing steam generators, since few internal alterations are required. Conversely, the invention can be easily removed, restoring the steam generator to its original condition.

[0012] The normal load paths used for the transmission of seismic loads between tubes, supports, shroud and shell are advantageously unaltered.

[0013] Accordingly, one aspect of the invention is drawn to a method of assembling and operating a steam generator having a plurality of tubes in a spaced parallel relation for flow of a fluid there through and the tubes transfer heat with a fluid flowing over the tubes, and also having a plurality of tube support plates disposed transverse to the tubes. The method of assembling and operating the steam generator includes the steps of 1) aligning the tube support plates; 2) inserting the tubes through the aligned tube support plates; and 3) while heating up the steam generator, displacing at least one support plate out of alignment in a lateral direction transverse to the tubes, thereby increasing tube support effectiveness.

[0014] The method may include displacing adjacent support plates in the same lateral direction transverse to the tubes.

[0015] The method may include displacing only every other support plate in the same lateral direction transverse to the tubes.

[0016] The method may include displacing alternating support plates in a first lateral direction transverse to the tubes and displacing the remaining support plates in a lateral direction transverse to the tubes and opposite the first direction.

[0017] The method may include displacing a first plurality of support plates in a first lateral direction transverse to the tubes and a remaining plurality of support plates in a lateral direction transverse to the tubes and opposite the first direction.

[0018] The method may include displacing one or more tube support plates, in the same or varying amounts and directions, and providing one or more displacements for any individual tube support plate.

[0019] Another aspect of the invention is drawn to a tube support system for use in a heat exchanger having a plurality of tubes in spaced parallel relation for flow of fluid there through in indirect heat transfer relation with a fluid flowing there over, and also having a cylindrical shroud that is disposed within a cylindrical pressure shell and surrounds the tubes. The tube support system includes a tube support plate disposed transverse to the tubes that is made of a material having a lower coefficient of thermal expansion than the shroud. The tube support system also includes means for displacing the tube support plate in a lateral direction transverse to the tubes. The means for displacing the tube support plate includes a restraining mechanism connected to the shell at one end, and a linking bar connected to the tube support plate at the other end. The linking bar may be installed slack or with some tension, and as the radial clearance between the tube support plate and the shroud that surrounds the tubes opens up during heating, the tension or increasing tension in the linking bar pulls on the tube support plate, thereby displacing the tube support plate.

[0020] Yet another aspect of the invention is drawn to a tube support displacement system for use in a heat exchanger having a plurality of tubes in spaced parallel relation for flow of fluid there through in indirect heat transfer relation with a fluid flowing there over, the heat exchanger further having tube support plates arranged transverse to the tubes and a cylindrical shroud, the shroud disposed within a cylindrical pressure shell and surrounding the tubes. The tube support displacement system may include within the linkage system a threaded engagement or other adjustable mechanism to change the length or amount of tension in the linkage during its installation, or afterwards.

[0021] The tube support plate displacement system can be used to provide controlled misalignments on one or more tube support plates, in the same or varying amounts and directions, and with one or more apparatus being provided for any individual tube support plate.

[0022] The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For a better understanding of the present invention, and the operating advantages attained by its use, reference is made to the accompanying drawings and descriptive matter, forming a part of this disclosure, in which a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the accompanying drawings, forming a part of this specification, and in which like reference numbers are used to refer to the same or functionally similar elements:

[0024] FIG. 1 is a sectional side view of a once-through steam generator whereon the principles of the invention may be practiced;

[0025] FIG. 2 is a side view of one embodiment of a linkage mechanism of the tube support displacement system according to the present invention;

[0026] FIG. 3 is a partial sectional plan view of the linkage mechanism of the tube support plate displacement system according to the present invention; and

[0027] FIG. 4 is a sectional side view of a tube support plate arrangement incorporating a plurality of tube support plate displacement systems according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] FIG. 1 depicts a prior art once-through steam generator 10 comprising a vertically elongated, cylindrical pressure vessel or shell 11 closed at its opposite ends by an upper head 12 and a lower head 13.

[0029] The upper head includes an upper tube sheet 14, a primary coolant inlet 15, a manway 16 and a hand hole 17. The manway 16 and the hand hole 17 are used for inspection and repair during times when the steam generator 10 is not in operation. The lower head 13 includes drain 18, a coolant outlet 20, a hand hole 21, a manway 22 and a lower tube sheet 23.

[0030] The steam generator 10 is supported on a conical or cylindrical skirt which engages the outer surface of the lower head 13 in order to support the steam generator 10 above structural flooring 25.

[0031] The overall length of a typical steam generator of the sort under consideration is about 75 feet between the flooring 25 and the upper extreme end of the primary coolant inlet 15. The overall diameter of the unit 10 moreover, is in excess of 12 feet.

[0032] Within the shell 11, a lower cylindrical tube shroud, wrapper or baffle encloses a bundle of heat exchanger tubes 27, a portion of which is illustrated in FIG. 1. In a steam generator of the type under consideration moreover, the number of tubes enclosed within the shroud 26 is in excess of 15,000, each of the tubes having an outside diameter of 5/8 inch. It has been found that Alloy 690 is a preferred tube material for use in steam generators of the type described. The individual tubes 27 in the tube bundle each are anchored in respective holes formed in the upper and lower tube sheets 14 and 23 through belling, expanding or seal welding the tube ends within the tube sheets.

[0033] The lower shroud 26 is aligned within the shell 11 by means of shroud alignment pins. The lower shroud 26 is secured by bolts to the lower tubesheet or by welding to lugs projecting from the lower' end of the shell 11. The lower edge of the shroud 26 has a group of rectangular water ports 30 or, alternatively, a single full circumferential opening (not shown) to accommodate the inlet feedwater flow to the riser chamber 19. The upper end of the shroud 26 also establishes fluid communication between the riser chamber 19 within the shroud 26 and annular downcomer space 31 that is formed between the outer surface of the lower shroud 26 and the inner surface of the cylindrical shell 11 through a gap or steam bleed port 32.

[0034] A support rod system 28 is secured at the uppermost support plate 45B, and consists of threaded segments spanning between the lower tubesheet 23 and the lowest support plate 45A and thereafter between all support plates 45 up to the uppermost support plate 45B.

[0035] A hollow, toroid shaped secondary coolant feedwater inlet header 34 circumscribes the outer surface of the shell 11. The header 34 is in fluid communication with the annular downcomer space 31 through an array of radially disposed feedwater inlet nozzles 35. As shown by the direction of the FIG. 1 arrows, feedwater flows from the header 34 into the steam generator unit 10 byway of the nozzles 35 and 36. The feedwater is discharged from the nozzles downwardly through the annular downcomer 31 end through the water ports 30 into the riser chamber 19. Within the riser chamber 19, the secondary coolant feedwater flows upwardly within the shroud 26 in a direction that is counter to the downward flow of the primary coolant within the tubes 27. An annular plate 37, welded between the inner surface of the shell 11 and the outer surface of the bottom edge of an upper cylindrical shroud, baffle or wrapper 33 insures that feedwater entering the downcomer 31 will flow downwardly toward the water ports 30 in the direction indicated by the arrows. The secondary fluid absorbs heat from the primary fluid through the tubes 27 in the tube bundle and rises to steam within the chamber that is defined by the shrouds 26 and 33.

[0036] The upper shroud 33, also aligned with the shell 11 by means of alignment pins (not shown in FIG. 1), is fixed in an appropriate position because it is welded to the shell 11 through the plate 37, immediately below steam outlet nozzles 40.
The upper shroud 33, furthermore, enshrouds about one third of the tubes 27 of the bundle.

[0037] An auxiliary feedwater header 41 is in fluid communication with the upper portion of the tube bundle through one or more nozzles 42 that penetrate the shell 11 and the upper shroud 33. This auxiliary feedwater system is used, for example, to fill the steam generator 10 in the unlikely event that there is an interruption in the feedwater flow from the header 34. As mentioned above, the feedwater, or secondary coolant that flows upwardly along the tubes 27 in the direction shown by the arrows rises into steam. In the illustrative embodiment, moreover, this steam is superheated before it reaches the top edge of the upper shroud 33. This superheated steam flows in the direction shown by the arrow, over the top of the shroud 33 and downwardly through an annular outlet passageway 43 that is formed between the outer surface of the upper cylindrical shroud 33 and the inner surface of the shell 11. The steam in the passageway 43 leaves the steam generator 10 through steam outlet nozzles 40 which are in communication with the passageway 43. In this foregoing manner, the secondary coolant is raised from the feed water inlet temperature through to a superheated steam temperature at the outlet nozzles 40. The annular plate 37 prevents the steam from mixing with the incoming feedwater in the downcomer 31. The primary coolant, in giving up this heat to the secondary coolant, flows from a nuclear reactor (not shown) to the primary coolant inlet 15 in the upper head 12, through individual tubes 27 in the heat exchanger tube bundle, into the lower head 13 and is discharged through the outlet 20 to complete a loop back to the nuclear reactor which generates the heat from which useful work is ultimately extracted.

[0038] To facilitate fabrication, and specifically the insertion of tubes 27 during the fabrication process, the tube support plates 45 are generally aligned with each other, and also with the upper and lower tube sheets. The alignment of the tube support plates 45 is maintained by tube support plate alignment blocks 104, shown in FIGs. 3 - 4, situated around the perimeter of the tube support plates between the tube support plates and the inner surface of the shroud or baffle 26, 33. The tube support plate alignment blocks 104 are attached to the shroud 26, 33, or a tube support plate 45, but not to both, and fill most, or all, of the available clearance between the tube support plates 45 and shroud 26, 33 at discrete locations around the tube support plate perimeter. The shroud, which is generally a large continuous cylinder, is laterally supported within the OTSG shell 11 by shroud alignment pins 106, shown in FIGs. 3 and 4. This support arrangement provides a lateral load path from the tubes 27, through the tube support plates 45, to the shroud 26, 33, which is supported by the shell 11.

[0039] Turning now to the present invention and referring to FIGs. 2 - 4, there is provided a tube bundle support system 100 and method for precisely aligning tube support plates 45 during fabrication, with minimal clearances between components, and then imposing a controlled misalignment as the steam generator heats up.
Tube support plates 45 are advantageously installed in an aligned configuration that is compatible with normal fabrication processes. Displacement to cause misalignment is produced, only when the heat exchanger is heated. Displacement to misalign tube support plates 45 in the hot condition can advantageously mitigate tube vibration due to either cross flow or axial flow excitation mechanisms.

[0040] Misalignment between the different elevations of tube support plates 45 is partially accomplished during heat up by making the tube support plates 45 from a material having a lower coefficient of thermal expansion than the shroud 26, 33.
Radial clearances 102, shown in FIG. 4, between tube support plates 45 and the shroud 26, 33, open at the positions of the tube support plate alignment blocks 104 as the steam generator heats up. These radial clearances provide space to facilitate lateral shifting or displacement of the individual tube support plates 45.

[0041] As described in greater detail below, lateral shifting or displacement is achieved by means of a tube support plate displacement system 100 having linking bars 112 which, when in tension, pull on the sides of respective tube support plates 45. The difference in thermal expansion between the shroud 11, which is preferably made of carbon steel, and tube support. plates 45, which are preferably made of 410S stainless steel, provides enough operational clearance to allow for effective lateral displacement of tube support plate 45, thereby mitigating flow induced vibration of tubes 27. Radial clearances 102 may be reduced to zero due to the linking bar force.

[0042] Tube support plate alignment blocks 104 may be installed with an initial clearance to facilitate tube support plate motion in the hot condition.

[0043] As shown in FIG. 4, by alternating the tension direction of the consecutive tube support plates at different elevations, for example, 45C, 45D, 45F, and 45F, the desired tube support plate misalignment and the loading of tubes 27 within the tube support plate holes 116 can be achieved. Generally the tube support plate 45 is made of a material with a thermal expansion coefficient sufficiently less than that of _ the shroud, so that the resulting radial gap between a tube 27 and its support hole 116 that would result at operating temperatures would be greater than the gap between the tube 27 and its support hole 116 at operating temperatures.

[0044] It may not be necessary to laterally misalign the tube support plates

45 at all elevations of the upright heat exchanger. It may, for example, be acceptable to shift every other tube support plate 45 in the same direction while restraining the remaining tube support plates 45 in their neutral positions to achieve the desired misalignment. Also, there may be more than one tube support displacement system 100 per tube support plate elevation. The tube support displacement system 100 can thus be used to variably displace the plurality of tube support plates, in one or more of a plurality of different directions, to provide controlled misalignments on one or more tube support plates, in the same or varying amounts and directions, and with one or more apparatus being provided for any individual tube support plate.

[0045] Referring now to FIGs. 2 and 3, there is shown the linking bar 112 having a connecting end 124 and with a threaded end 126. The threaded end 126 of the linking bar 112 extends through a restraining plate or disc 113 and threadably engages a restraining nut 115. As shown in FIG 3, the restraining disc 113 is in contact with a lip within a handhole 132 provided on the shell 11.

[0046] As shown, in FIGs. 3 - 4, the tube support displacement system 100 is used to impose lateral displacements to tube support plates 45. The restraining nut 115 is threadably engaged with the linking bar 112. The threaded end 126 of the linking bar 112 and the restraining nut 115 is accessible for adjusting tension in the linking bar 112, or for adjusting the length of the linking bar between the restraining plate or disc 113 and the connecting end 124 engaged with the tube support plate 45. The shell 11 is provided with a hand hole 132 for access to the restraining nut 115. When not in use, the hand hole 132 is sealed by a bolted and gasketed hand hole cover 134.

[0047] In a preferred embodiment, the connecting end 124 of the linking bar 112, as illustrated in Figs. 3 and 4, may comprise a finger that extends into a vacant tube hole in the tube support plate 45. Alternatively, the connecting end 124 of the linking bar 112 may comprise any of the following constructions, alone or in combination at one or more tube support plate 45 elevations:

[0048] (a) a threaded end which is threadably engaged with a drilled and tapped hole provided into an edge or surface of the tube support plate 45;

[0049] (b) an end welded to an edge or surface of the tube support plate 45;

[0050] (c) an end hooked or engaged to one or more tubes 27 extending through the tube support plate 45, with or without an internal stabilizer core inserted into the one or more tubes 27;

[0051] (d) an end hooked or engaged into a new or existing hole in the tube support plate 45, other than a hole normally used for receiving a tube 27;

[0052] (e) an end which is connected to a lip, protrusion, depression, deformation or flange on the tube support plate 45, or to a support rod 28 extending through the tube support plate 45; and

[0053] (f) an end which is clamped tightly to top and bottom surfaces of the tube support plate 45 so as to sandwich the tube support plate 45 therebetween.

[0054] When the shell / shroud / tube support plate assembly heats up, the higher coefficient of thermal expansion of the shell 11 and shroud 26, 33 material relative to the material of tube support plate 45 will cause a dilation of the shroud 26, relative to the tube support plate 45. As shown in FIG. 4, in this hot condition, the linking bar 112 will cause a lateral displacement or offset 136 of the tube support plate 45 relative to the initially centered position 138 within the shroud 26, 33. The tensile force in the linking bar 112 will either be reacted by contact with tubes 27, or by contact with both tubes 27 and tube support plate alignment block(s) 104 on the opposite side of the tube support plate 45. In either case, tube contact forces are achieved, thereby providing the desired effect of increased tube support effectiveness. [0055] Control of the tube-to-support plate contact forces in the hot condition is achieved by controlling the initial cold condition tension in the linking bar 112 or its effective length. The tension or length is adjustable through hand hole 132 which provides access to the restraining nuts 115 of the linking bar 112. In the cold shutdown condition, the hand hole cover 132 can be removed to gain access to the linking bar 112, and the restraining nuts 115 can be adjusted by turning the restraining nuts 115 to obtain the desired length or tension.

[0056] As shown in FIG. 4, by alternating the tension direction for consecutive tube support plates at different elevations, e.g. 45C, 45D, and 45E, the desired tube support plate misalignment and the loading of tubes 27 within tube support plate holes can be achieved. It may not be necessary to laterally misalign all tube support plate elevations. It may, for example, be acceptable to shift every other plate in the same direction, while restraining the remaining plates in their neutral positions to achieve the desired misalignment. Also, there may be more than one tube support plate displacement system 100 per tube support plate elevation.

[0057] Additionally, the contact forces between tubes 27 and tube support plates 45 may be controlled by limiting the tension, or length, of the linking rod 112. These can be controlled by either selecting a material for the tube support plate 45 with a desired coefficient of thermal expansion, such that the tension is limited by the maximum radial clearance in the hot condition between the tube support plate and the tube support plate alignment blocks 104, or, alternatively, by adjusting the effective length of the linking bar 112.

[0058] The linking bar 112 may comprise bar of any desired cross-section, or cable, or chain or tubular structures, with materials selected to meet applicable pressure, temperature and stress criteria. Advantages of the invention include:

[0059] The tube support plates 45 are installed in an aligned configuration that is compatible with normal fabrication processes. The desired misalignment occurs only when heating the heat exchanger.

[0060] The misaligned tube support plates 45 in the hot condition can mitigate tube vibration due to either cross flow or axial flow excitation mechanisms.

[0061] Tube to tube support plate contact loads in the hot condition are controlled by controlling the linking bar effective length or tension, the tube support plate displacement, or a combination thereof.

[0062] The normal load paths used for the transmission of seismic loads between tubes 27, tube support plates 45, shroud 26, 33 and shell 11 are unaltered.

[0063] Tube support plate displacement system 110 has only three parts, linking bar 112, restraining plate or disc 113, and restraining nuts 115 which are threadably engaged, and are internal to the steam generator shell 11, thereby minimizing the potential of loose parts.

[0064] The hardware for linking bar 112 tension or length adjustment is readily accessible.

[0065] The linking bar connecting end 124 is situated within the shroud opening 130 and the threaded end 126 is situated within the hand hole 132. The linking bar 112 is threadably engaged with the restraining components 113, 115 thereby preventing each from becoming a loose part.

[0066] Linking bar tension is reacted against the shell 11, which is a stiff anchor point, as opposed to a reaction against the shroud 26, 33 which is relatively flexible.
[0067] The design is capable of being retrofitted to existing designs, since few internal alterations are required. Conversely, the tube support plate displacement system 150 can be easily removed, restoring the support arrangement to its original condition.

[0068] The tube support plate alignment blocks 104 may be installed with an initial clearance to facilitate tube support plate displacement during heat up of the heat exchanger.

[0069] While specific embodiments and/or details of the invention have been shown and described above to illustrate the application of the principles of the invention, it is understood that this invention may be embodied as more fully described in the claims, or as otherwise known by those skilled in the art (including any and all equivalents), without departing from such principles.

Claims

1. A method of assembling and operating a steam generator having a plurality of tubes in spaced parallel relation for flow of fluid there through and the tubes transfer heat with a fluid flowing there over, the steam generator further having a plurality of tube support plates disposed transverse to the tubes, the method comprising the steps of:

aligning the tube support plates;

inserting the tubes through the aligned tube support plates; and while heating up the steam generator, displacing at least one support plate out of alignment in a lateral direction transverse to the tubes, thereby increasing tube support effectiveness.

2. The method of Claim 1, wherein the displacing step further comprises displacing adjacent support plates in the same lateral direction transverse to the tubes.

3. The method of Claim 1, wherein the displacing step further comprises displacing only every other support plate in a lateral direction transverse to the tubes.

4. The method of Claim 1, wherein the displacing step further comprises displacing alternating support plates in a first lateral direction transverse to the tubes and displacing the remaining support plates in a second lateral direction transverse to the tubes and opposite the first direction.

5. The method of Claim 1, wherein the displacing step further comprises alternately displacing a first plurality of support plates in a first lateral direction transverse to the tubes and displacing a remaining plurality of support plates in a second lateral direction transverse to the tubes and opposite the first direction.

6. The method of Claim 1, wherein the displacing step further comprises displacing a plurality of tube support plates.

7. The method of Claim 6, wherein the displacing step further comprises variably displacing the plurality of tube support plates.

8. The method of Claim 6, wherein the displacing step further comprises displacing the plurality of tube support plates in one or more of a plurality of different directions.

9. The method of Claim 1, wherein the displacing step further comprises variably displacing a plurality of tube support plates in one or more of a plurality of different directions.

10. A tube support system for use in a heat exchanger having a plurality of tubes in spaced parallel relation for flow of fluid there through and the tubes transfer heat with a fluid flowing there over, the heat exchanger further -having a cylindrical shroud, the shroud disposed within a cylindrical pressure shell and surrounding the tubes, the tube support system comprising:

a tube support plate disposed transverse to the tubes, the support plate being made of a material having a lower coefficient of thermal expansion than the shroud; and means for displacing the tube support plate in a lateral direction transverse to the tubes.

11. The tube support system of Claim 10, wherein the tube support plate is made of 410S stainless steel and the shroud is made of carbon steel.

12. The tube support system of Claim 10, wherein the means for displacing the tube support plate includes a linking bar having a connecting end connected to the tube support plate.

13. The tube support system of Claim 12, wherein the means for displacing the tube support plate includes a restraining plate, and a restraining nut threadably engaged with the linking bar.

14. The tube support system of Claim 13, wherein the linking bar, is located within the shell.

15. The tube support system of Claim 13, wherein the linking bar is adjustable for length or tension.

16. The tube support system of Claim 13, wherein the restraining plate is connected to the shell.

17. The tube support system of Claim 12 wherein the connecting end comprises a threaded end which is threadably engaged with a drilled and tapped hole provided into an edge or surface of the tube support plate.

18. The tube support system of Claim 12 wherein the connecting end comprises an end welded to an edge or surface of the tube support plate.

19 The tube support system of claim 12 wherein the connecting end comprises an end hooked or engaged to one or more tubes extending through the tube support plate.

20. The tube support system of claim 19 wherein the one or more tubes to which the connecting end is hooked or engaged are provided with an internal stabilizer core inserted into the one or more tubes.

21. The tube support system of claim 12 wherein the connecting end comprises an end hooked or engaged into a new or existing hole in the tube support plate, other than a hole normally used for receiving a tube.

22. The tube support system of claim 12 wherein the connecting end comprises an end which is connected to a lip, protrusion, depression, deformation or flange on the tube support plate, or to a support rod extending through the tube support plate.

23. The tube support system of claim 12 wherein the connecting end comprises an end which is clamped tightly to top and bottom surfaces of the tube support plate so as to sandwich the tube support plate therebetween.

24. The tube support system of claim 10, wherein the tube support plate is made of a material with a thermal expansion coefficient sufficiently less than that of the shroud, so that a resulting radial gap between a tube and its support hole that would result at operating temperatures would be greater than the radial gap between the tube and its support hole.

25. A tube support displacement system for use in a heat exchanger having a plurality of tubes in spaced parallel relation for flow of fluid there through and the tubes transfer heat with a fluid flowing there over, the steam generator further having tube support plates arranged transverse to the tubes and a cylindrical shroud, the shroud disposed within a cylindrical pressure shell and surrounding the tubes, the tube support displacement system including:

a linking bar having an end connected a tube support plate and a mechanism engaged with the linking bar for adjusting the effective length of the linking bar to limit the maximum lateral displacement of the tube support plate when the steam generator is in operation.

26. The tube support displacement system of Claim 25, including access means through the shell for adjusting the effective length or tension on the linking bar.

27. The tube support displacement system of Claim 25, wherein the material of the tube support plate is pre-selected to limit the maximum lateral displacement of the linking bar.

28. The tube support system of Claim 25, wherein the linking bar is the only component of the tube support displacement system located within the inside diameter of the shell.