EP0387131B1 - Apparatus for the stabilization of the tubes of a steam generator tube bundle comprising antivibration bars - Google Patents

Description

The invention relates to a bundle of tubes of a steam generator provided with a tube stabilization device comprising anti-vibration bars interposed between curved parts of the tubes of the steam generator.

The steam generators, in particular the steam generators of the pressurized water nuclear reactors comprise bent U-shaped tubes having two straight branches crimped at their ends in a tubular plate. The curved parts of the bundle tubes which are juxtaposed at its upper part have radii of curvature different from each other and are placed adjacent to form a structure of substantially hemispherical shape called a bun.

During the operation of the generator. steam, pressurized water at high temperature circulates in the bundle tubes and drinking water is brought into contact with the outer surface of these tubes along which it moves in the vertical direction by heating and then vaporizing, to come out as vapor at the top of the generator.

The circulation of fluid in contact with the tubes can cause vibrations which are liable to cause damage to these tubes if they are not effectively maintained.

The right part of the tubes is engaged in spacers located at regular distances from each other according to the height of the beam. These straight parts are therefore effectively maintained by rigid elements. The curved parts of the bundle tubes constituting the bun must also be maintained and generally used for this, spacer bars which are interposed between the adjacent tubes of the bundle and arranged in substantially radial directions of the bun. These spacer bars are generally connected two by two in an articulated manner at one of their ends arranged towards the inside of the bun and placed in an angular manner to form V-shaped structures.

The ends of the antivibration bars opposite their articulated ends are generally projecting from the tubes constituting the outer layer of the bun.

Various means of fixing these ends of the anti-vibration bars have been proposed on fixing elements placed on the upper surface of the bun.

For example, it has been proposed to weld the ends of the antivibration bars on curved elements arranged along meridian planes of the bun.

It has also been proposed to fix the ends of the anti-vibration bars, for example by welding on substantially parallel rings resting on the upper surface of the bun.

In all cases, the fixing of the antivibration bars requires complex operations most often using welds which must be carried out in the vicinity of the tubes of the bundle.

Anti-takeoff stabilization devices are also known for the curved parts of the bundle tubes which consist of stirrups engaged on the last row of tubes and the ends of which protrude from the surface of the bun can be fixed by welding to elements of maintenance of anti-vibration bars located for example in meridian planes.

Structures are also known for holding the tubes of a steam generator in the area of the bun constituted by arches in the form of ring portions surrounding the external surface of the bun and arranged along meridian planes of the bun all passing through the same diameter parallel to the rows of tubes. The arches have cutouts allowing them to adapt perfectly to the upper shape of the bun and are rigidly connected together by hoops of direction perpendicular to the arches which are screwed onto these arches.

The whole of the arches and the hoops constitutes a structure which rests freely on the bun. This structure is maintained on the bun, under the effect of its own weight.

In certain embodiments, provision has been made to drill holes in the arches in order to engage the anti-vibration bars which can be maintained by screw connections.

This arrangement is not satisfactory insofar as the engagement of the anti-vibration bars in the arches is a delicate operation to perform.

The object of the invention is therefore to propose a bundle of tubes of a steam generator comprising bent U-shaped tubes each having two straight branches crimped at their ends in a tubular plate and a curved part between the two straight branches, the curved parts of the tubes having different radii of curvature and being placed adjacent to form a substantially hemispherical structure called a bun and a tube stabilization device comprising anti-vibration bars each disposed between the curved parts of two tubes in position adjacent, in substantially radial directions of the bun and the hoops in the form of a portion of rings surrounding the external surface of the bun, arranged in planes all passing through a diameter of the bun, connected by hoops perpendicular to the arches, the stabilization device allowing quick and easy fixing of the anti-vibration bars on the structure formed by the hoops and the hoops.

For this purpose, each of the hoops comprises a plurality of fixing brackets integral with the hoops of direction perpendicular to the hoops and relative to the anti-vibration bars which are each fixed by an external end to a bracket or a hoop by mechanical screwing means .

In order to clearly understand the invention, a description will now be given, with reference to the appended figures, of an embodiment of a device according to the invention for stabilizing the tubes of the bundle of a steam generator of a pressurized water nuclear reactor.

Figure 1 is a sectional elevation view in partial section of a steam generator of a pressurized water nuclear reactor comprising a device for stabilizing the bundle tubes according to the invention.

Figure 2 is a front view on a larger scale of the upper part of the beam.

Figure 3 is a partial perspective view of the stabilization device according to the invention.

Figure 4 is a half top view of the arches and hoops on which are fixed the anti-vibration bars.

Figure 5 is a sectional view through a plane of symmetry of the upper part of the bundle of the steam generator showing the devices for fixing the anti-vibration bars on a hoop.

Figure 6 is a detail view of a device for fixing an anti-vibration bar on a bracket, according to a first embodiment.

Figure 7 is a detail view of the means for fixing two antivibration bars on a bracket according to a second embodiment.

Figure 8 is a front view of a stirrup anti-takeoff of the upper tubes of the bun of a steam generator, according to the invention.

In Figure 1, we see a steam generator of a pressurized water nuclear reactor generally designated by the reference 1 and having an outer casing 2 connected at its lower part to a tubular plate 3 of great thickness.

The casing 2 contains the bundle of tubes of the steam generator constituted by tubes 5 bent in a U shape and comprising, at their upper part, semicircular hangers of radius of curvature decreasing from the outside to the inside and constituting the steam generator bun.

The straight parts 5a of the bundle tubes are crimped at their ends into the tube plate 3, so as to open into a water box 7 in two parts separated by a partition 8.

The pressurized water from the nuclear reactor enters one of the parts of the water box 7 through an inlet pipe 6a, flows through the tubes of the bundle then exits through an outlet pipe 6b.

The bundle of tubes 5 is surrounded by a bundle envelope 9 making it possible to channel the feed water entering the envelope of the steam generator by an inlet pipe 11. The feed water of the steam generator circulates first from top to bottom in the annular space located around the bundle envelope 9 then from bottom to top in contact with the tubes 5 of the bundle so as to heat up then to vaporize and to come out in the form of vapor by the upper tube 12 of the steam generator.

The upper part of the bundle of tubes 5 is constituted by the juxtaposition of hangers of semi-circular shape whose radii are decreasing from the outside towards the inside of the bundle.

In addition, the different successive layers of tubes of the bundle parallel to the central layer shown in FIG. 1 include hangers of decreasing diameter, so that the upper part of the bundle constitutes a substantially hemispherical assembly called a bun.

The rectilinear part 5a of the tube 5 is held by spacer plates 10 which prevent the tubes from being vibrated when the steam generator is in operation, under the effect of the circulation of exchange fluids.

The curved parts of the tubes located at the upper end of the bundle are held by anti-vibration bars 15 formed in the form of compasses hinged at their inner end 15a and introduced between the successive rows of tubes 5 at the level of the hangers.

In addition, the device for holding the upper part of the bundle comprises arches 16 on which brackets 17 are fixed perpendicular to the arches. The arches are arranged substantially along diametrical planes of the bun all passing through the same diameter corresponding to the transverse direction of the beam parallel to the water street disposed between the small hangers in the internal part of this beam.

As can be seen in Figures 2 and 3, the arches 16 have cutouts and deflections allowing them to adapt to the external shape of the bun.

The arches 16 are interconnected by hoops 18 bolted to the arches and which maintain the entire structure of the arches which rests on the upper end of the bun. The holding assembly constituted by the arches 16 and the hoops 18 is held on the bun, under the effect of its own weight. Certain anti-vibration bars 5 are connected directly to the hoops 18 by screw connections which will be described in more detail in the following text.

In Figure 4, we see the four arches 16 constituting the upper holding structure of the steam generator connected together by a hoop 18. The hoops 18 have a shape of an arc and are arranged in parallel vertical planes to the layers of tubes.

In Figure 5, we see a hoop 16 consisting of successive parts 16a, 16b, 16c connected together by screw connections.

We also see two assembly hoops 18 of all the hoops on which are fixed anti-vibration bars 15 interposed between the rows of tubes 5 of the bundle.

The other anti-vibration bars inserted between the rows of tubes 5 are fixed to the arches by means of brackets 17.

In FIG. 6, a first type of bracket 17 is seen allowing the fixing of an anti-vibration bar 15, the bracket 17 being connected by screw connections 20 at the end of a hoop 16.

On the bracket 17 is fixed a pin 21 and the anti-vibration bar 15 carries an end cap 22 which can be engaged laterally on the pin 21. The tightening and fixing of the anti-vibration bar is ensured by a screw and cup assembly 23 ensuring the tightening of two jaws of the yoke 22 on the journal 21. The screw head is blocked in rotation by a cup which can be folded down in cavities in the screw head.

In FIG. 7, we see a second type of bracket 17 'fixed by screw connection 20' to the upper end of a hoop 16.

The bracket 17 'allows the attachment of two anti-vibration bars 15a and 15b by means of yokes 22a and 22b engaged on corresponding pins 21a and 21b integral with the yoke 17'. The anti-vibration bars are engaged laterally on the corresponding pins 21a, 21b and clamped in place by screw connections 23a and 23b.

Certain anti-vibration bars 15 are fixed to a pin secured to a hoop 18.

In all cases, the establishment and fixing of the anti-vibration bars can be ensured very quickly and without requiring welding.

In addition, the assembly of the holding structure constituted by the arches 16, the hoops 18 and the brackets for fixing the anti-vibration bars is integral with the set of anti-vibration bars which constitute a structure of great stability resting on the part top of the steam generator bun.

In FIG. 8, we can see a retaining stirrup 25 constituted in the form of a comb, the successive spaces 26 of which are inserted between two successive teeth 27 have a width slightly greater than the diameter of the tubes 5 of the steam generator.

The comb 25 has end portions 28 pierced with fixing holes 29 and each of the teeth 27 likewise has an oblong hole 30 allowing the fixing of the comb below the last row of tubes of the steam generator, as will be explained below,

Referring to FIG. 5, it can be seen that the upper row 31 of the hangers of the tubes 5 of the bundle comprises a number of hangers identical to the number of spaces 26 located between the teeth of the peinge 25.

The comb 25 can be used to hold the anti-vibration bars anti-take-off by being slid in a horizontal position below the row 31 so that the spaces 26 correspond to the positions of the upper hangers of the tubes 5.

The comb 25 is then turned 90 ° upwards so that its end portions 28 and its teeth 27 come into coincidence with one face of the arch 16 located immediately above the row of hangers 31. The roll bar 16 has holes coming from in coincidence with the holes 29 and the pins coming in coincidence with the holes 27 for the positioning and fixing by screwing of the comb on the hoop 16. The comb 25 thus provides anti-theft support for the anti-vibration bars.

The positioning and fixing of the comb can be carried out quickly and efficiently, without requiring any welding operation.

It is obvious that the invention is not limited to the embodiment which has been described.

This is how we can imagine methods of fixing the anti-vibration bars on the brackets attached to the arches or on the hoops of a different type from that which has been described using end caps of the anti-vibration bars coming to tighten on a journal attached to the gallows or the hoop.

One can imagine the use of any number of brackets allowing the attachment of a single anti-vibration bar or several bars.

The structure constituted by the hoops and the hoops may be different from that which has been described and may include any number of hoops or hoops. In particular, more than two hoops in one or more parts can be used.

The comb-shaped stirrups will preferably be placed on the arches located towards the center of the steam generator's bun, but it is also possible to have such anti-take-off stirrups on all the arches of the holding structure.

The invention applies to all steam generators comprising an upper part constituting a bun of substantially hemispherical shape on which is placed a holding structure comprising hoops and hoops.

Claims (5)

1. Tube bundle of a steam generator, comprising tubes (5) which are bent in a U shape, each having two straight branches crimped at their ends in a tube plate (3) and a curved part between the two straight branches, the curved parts of the tubes (5) having different radii of curvature and being arranged adjacent to one another to form a structure of substantially hemispherical form, called a dome, and means for stabilising the tubes (5), comprising anti-vibration bars (15) which are each arranged in substantially radial directions of the dome between the curved parts of two adjacent tubes (5), and bows (16) in the form of a portion of a ring surrounding the outer surface of the dome and arranged in planes all passing through the same diameter of the dome and connected by means of hoops (18) perpendicular to the bows, characterised in that each of the bows (16) has a plurality of fastening brackets (17,17') fixed to the bow and arranged perpendicular to said bow (16) and to the anti-vibration bars (15) which are each fastened, at an outer end, to a bracket (17,17') or to a hoop (18) by mechanical screwing means (23,23a,23b).
2. Tube bundle according to Claim 1, characterised in that the brackets (17,17') and the hoops (18) have, in a lateral position, pivots (21,21a,21b) perpendicular to the bracket (17,17') or to the hoop (18), and in that the anti-vibration bars (15) have an end fork (22) having two jaws capable of engaging on the pivot (21, 21a,21b) and means (23) for the screw clamping of the jaws on the pivot (21,21a,21b).
3. Tube bundle according to Claim 1 or 2,
   characterised in that it has both brackets for fixing a single anti-vibration bar and brackets for fixing two anti-vibration bars.
4. Tube bundle according to any of Claims 1, 2 and 3, characterised in that it also has an anti-flyoff yoke for the anti-vibration bars (5) of the bundle, arranged in the upper part of the dome and taking the form of a comb (25) having notches (26) which are located between two successive teeth (27) and the width of which is greater than the diameter of a tube (25) of the bundle, and end pieces (28) having holes (29) for fastening the comb to a bow (16).
5. Tube bundle according to Claim 4, characterised in that each of the teeth (27) of the comb has an oblong hole (30) capable of engaging onto a positioning stud formed on the corresponding bow (16).

Images