Holder For U-tube Bundles Of Steam Generators

Abstract

In substantially upright U-tube bundles of steam generators, tube holders located at substantially horizontally extending turns of the U-tube bundles and comprising a plurality of wave-shaped bands disposed substantially parallel to one another between respective rows of tubes located in the same plane, the waves of each of said bands forming respective bulges, adjacent bands being disposed relative to one another so that the bulges thereof alternately face away from and toward one another, the respective pairs of bulges facing away from one another defining spaces therebetween respectively for receiving individual tubes therein, the bulges facing toward one another being firmly secured to and prestressed toward one another.

Description

Our invention relates to holder for U-tube bundles of steam generators.

In pressurized water nuclear reactors, the heating surfaces of the related steam generators generally are formed of upright tightly packed bundles of U-tubes. An upwardly directed flow of water being vaporized is produced by natural circulation between these tubes. The provision of a holder for the rectilinearly extending legs of the U-tube bundles causes no great difficulty. The U-bend of the tube bundles, however, is traversed by the vaporizing water in transverse direction. In addition thereto, the velocity of the water-steam mixture flowing past the bend in the tube bundles is at its greatest thereat so that these bend sections of the tubes are subjected to the greatest stress.

It is accordingly an object of our invention to provide a holder for U-tube bundles at the bends thereof, in order to minimize the occurrence of vibrations therein. This objective is pursued, furthermore, while taking great pains to avoid welding of the tubes and to keep them free from temper color and other damage.

With the foregoing and other objects in view, we provide according to our invention, in substantially upright U-tube bundles of steam generators, tube holders located at substantially horizontally extending turns of the U-tube bundles and comprising a plurality of wave-shaped bands disposed substantially parallel to one another between respective rows of tubes located in the same plane, the waves of each of the bands forming respective bulges, adjacent bands being disposed relative to one another so that the bulges thereof alternately face away from and toward one another, the respective pairs of bulges facing away from one another defining spaces therebetween respectively for receiving individual tubes therein, the bulges facing toward one another being firmly secured to and prestressed toward one another.

The individual tubes of the bundles are clamped between the respective holder bands with such force only as to hold the tubes very gently and without damage therebetween. Relative thermal expansions have thereby, moreover, virtually no effect thereon. Furthermore, any tendency of the tubes to become deformed into an oval cross section due to bending of the tubes presents no difficulty when the tubes are held by the holder of our invention. Since the tubes are firmly clamped, no striking or rubbing thereof can consequently occur and, above all, the natural frequency of the tubes is increased, thereby reducing the tendency of the tubes to vibrate.

In accordance with another feature of our invention, the holder bands are formed of material that is softer or more yieldable than the material of which the tubes are formed.

In accordance with further features of our invention, the individual holder bands are connected together at the closest adjacent portions thereof, namely at the bulges thereof facing toward one another. Thus, the holder bands are held together by screw connections. Also the bulges of adjacent bands facing toward one another are connected to one another by crosspieces welded intermediate thereto. In another embodiment of our invention, a pin is welded to one of the bulges facing toward one another and the free end of the pin is received in a corresponding bore formed in a member welded to the other of the mutually facing bulges, the free end of the pin being welded within the bore to the member wherein the bore is formed. In yet another embodiment of our invention, the bulges of adjacent bands facing toward one another are formed with respective outward bends therein located almost in contact with one another, the pairs of adjacent outward bends being connected to one another by direct welds.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in holder for U-tube bundles of steam generators, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is a fragmentary longitudinal view of the upper bend of a vertically disposed U-tube bundle;

FIG. 2 is a cross-sectional view of FIG. 1 taken along the line II--II in the direction of the arrows;

FIG. 3 is an enlarged fragmentary view of FIG. 2; and

FIGS. 4 and 5 are sectional views of FIG. 3 taken respectively along the lines VI--VI and V--V in the direction of the arrows.

Referring now to the drawing and first, particularly, to FIG. 1 thereof, there is shown in section, the upper portion of a U-tube bundle of a steam generator, wherein only the uppermost and the lowermost row of the parallel-extending tubes 1 are illustrated.

In the sectional view of FIG. 2, the arrangement of the individual tubes 1 in the upper bend of the tube bundle is clearly shown. These tubes 1 are held in place by holder bands 2 which are connected to one another by crosspieces 3.

In the fragmentary enlarged view of FIG. 2, shown in FIG. 3, the tubes 1 are disposed in individual rows, the tubes of adjacent rows being in staggered relationship to one another. The holder bands 2 are wave-shaped and are disposed between the rows of tubes. The tubes in the respective highest, substantially horizontally extending section of the bend of the bundles are held in spaces defined by opposing bulges 3' of respectively adjacent bands facing away from one another. The bulges 4 of the adjacent bands facing toward one another are joined to each other by a mechanical connecting means. The adjacent bands are closest to each other at the respective bulges 4 thereof which face one another. By suitably adjusting the narrowest spacing of the adjacent bands to one another, these holder bands can be held under a predetermined prestressing so that the tubes 1 are firmly clamped between the holder bands. The tubes 1 need not, therefore, be further fastened to the holder bands.

The connection of the holder bands to one another can be effected in different ways. For example, according to FIG. 4, which is a sectional view of part of FIG. 3, a rectangular crosspiece 5 is welded between the respective bulges 4 of adjacent bands that face toward one another, i.e., at the narrowest spacing between the adjacent bands. The crosspieces 5 are initially welded on one side to the wave-shaped bands. When the bands are assembled, they are further connected, for example, by resistance butt welding.

Another possible way of connecting the adjacent bands in accordance with our invention is shown in FIG. 5 which is another sectional view of part of FIG. 3. In FIG. 5, the connection of adjacent bands is effected with pins 6. Thus, the pins 6 are first welded on one side thereof to bulges 4 of respective prepared bands 2 facing toward corresponding bulges 4 in adjacent bands 2 wherein suitable bores are formed. The free ends of the pins 6 are received in the bores in the course of assembling the holder bands and are welded to the bands in which the bores are formed.

It is furthermore possible, in accordance with our invention, to form additional bends 7 (FIG. 3) in the bulges 3 of adjacent bands facing toward one another so that they are almost in contact with one another, and then to weld the additional bends 7 to one another.

Another means for securing adjacent bands to one another is by screw-fastening, as shown in FIG. 3. Thus, a body or pin 8 formed with a bored internal thread is welded to one bulge of the respective pairs of bulges 4 of adjacent bands facing toward one another. A bore is formed in the other bulge of the respective bulge pairs and a screw 9 is inserted therethrough and into the threaded bore formed in the body or pin 8, and is threaded therein. It is thereby possible to adjust the prestressing of the bands individually according to the respective diameter of the adjacent tubes 1. This can be of particular disadvantage because the tubes 1 of conventionally circular cross-section are deformed in the vicinity of the bend in the tube bundle into a generally oval shape. The ovalness is inversely proportional to the bending radius. But also with the other hereinbefore described connections, the deviations in mass resulting from the respective bending radius can be readily balanced or equalized.

The holder bands should clamp the tubes only by themselves and should not be fastened to the circulation skirt or shell so that relative expansion between the tubes and shell does not stress the welding seams. The thermal expansion of the tubes through the bending radii of different lengths is hardly of any importance and has, in fact, a salutary effect because it produces an additional stress or clamping force.

By means of the aforedescribed arrangement of the holder bands and the construction thereof, the tube bends in the U-tube bundles are securely held without damaging the tubes. In addition, the flow cross-section for the upwardly flowing water-steam mixture is virtually unhampered thereby.

Claims

We claim:

1. In substantially upright U-tube bundles of steam generators, tube holder assembly located at substantially horizontally extending turns of the U-tube bundles and comprising a plurality of wave-shaped bands disposed substantially parallel to one another between respective rows of tubes located in the same plane, the waves of each of said bands forming respective bulges, adjacent bands being disposed relative to one another so that the bulges thereof alternately face away from and toward one another, the respective pairs of bulges facing away from one another defining spaces therebetween respectively for receiving individual tubes therein of such diameter that the bulges facing toward one another are spaced from one another, said bulges facing toward one another being firmly secured to and prestressed toward one another so as to clamp the tubes between the respective pairs of bulges facing away from one another.

2. Tube holder assembly according to claim 1, wherein said holder bands are formed of material softer than the material of the tubes.

3. Tube holder assembly according to claim 1, wherein the bulges facing toward one another are held together by threaded connections.

4. Tube holder assembly according to claim 1, wherein, respectively, one of the bulges facing toward one another is formed with a bore, a pin having an internally threaded bore is welded to the other of the bulges facing toward one another, and a screw extends through the bore in the one bulge and is threadedly secured in the internally threaded bore of said pin.

5. Tube holder assembly according to claim 1, wherein crosspieces are disposed between respective pairs of bulges facing toward one another, said crosspieces being welded respectively to the bulges of said pairs.

6. Tube holder assembly according to claim 1, wherein, respectively, one of the bulges facing toward one another, is formed with a bore, and including a pin welded at one end to the other of said bulges, the other end of the pin being received and welded in the bore formed in said one bulge.

7. Tube holder assembly according to claim 1, wherein the bulges facing toward one another are respectively formed with outwardly directed bends substantially in contact with one another and including respective welds directly connecting adjacent pairs of said outwardly directed bends to one another.