EP0648974B1 - Steam generator with radial support for tube inner shell and tube support plate - Google Patents

Description

The present invention relates to a steam generator comprising a device radial support of the beam envelope and spacer plates of the steam generator according to the preamble of claims 1 and 4. Such a steam generator is described in document US-A-4,503,903.

Heat exchangers such as steam generators of a water nuclear reactor under pressure have a tube bundle made up by a very large number of small diameter tubes arranged vertically inside an envelope of generally cylindrical shape itself disposed inside the envelope under rigid pressure external thickness of the steam generator.

Pressurized water from the nuclear reactor circulates inside the small diameter tubes and the water to be vaporized is introduced inside the envelope of the bundle where it comes into contact with the outer surface of the tubes. Steam is recovered at the top of the beam envelope then it is generally dried in separators steam-water arranged in the outer envelope of the steam generator above the envelope of the beam.

Steam generators are very tall units in which the different coaxial envelopes are arranged with generally small radial spacing.

It is known to use spacer plates through which the bundle tubes pass, distributed depending on the height of the beam, to maintain the tubes in fixed radial positions one by compared to others. These spacer plates are connected between them by vertical tie rods, the assembly being placed inside the bundle envelope.

It is therefore important to maintain the different coaxial envelopes of the steam generators, and the whole beam by the spacer plates in radial directions, so as to avoid relative displacements and shocks between these envelopes and the beam in the event of external stresses such as those accompanying an earthquake.

This radial support is obtained by stops attached to the bundle envelope at the spacer plates and at the rate of several stops by spacer plate. These stops are then regularly distributed around the periphery of spacer plates.

We know by document FR-A-2 511 491 such a holding device. It is made up of parts having a thickness greater than the thickness of the beam casing and drilled with tapped holes inside which one can screw studs threaded whose end protruding into space existing between the beam envelope and the envelope rigid outer bears against the surface inside of this outer shell. The support of these stops is made after adjusting the studs, by introducing wedge-shaped wedging pieces between the outer edge of the spacer plates and the interior surface of the support device directed towards the beam.

Such stops have the disadvantage of occupying much of the width of the placeholder between the beam envelope and the external envelope and thus appreciably limit the section of passage for the water to vaporize circulating in this space without ensuring a perfect seal. These stops also have the disadvantage of requiring the introduction of wedging parts in notches machined at the peripheral part of spacer plates. These notches decrease accordingly the distance between the peripheral tubes of the beam and the edge of the spacer plates. If we want maintain sufficient distance between tubes peripherals and plaque, then you have to decrease the number of tubes in the bundle. On the other hand, the stops must have shapes that do not facilitate their fixing by welding in the wall of the envelope beam.

Other radial holding devices the bundle casing and spacer plates of a steam generator have been disclosed by the patent FR-A-2,562,996 by FRAMATOME and by patents American US-A-4,503,903, US-A-4,583,584, US-A-4 690 206 and US-A-4 768 582. All these devices are not entirely satisfactory. Their mounting is generally complicated by the use of shims for some people. Some of these devices only offer insufficient range for satisfactory support spacer plates.

To remedy these drawbacks, it is proposed, according to the present invention, a device allowing the radial maintenance of the bundle envelope and spacer plates of a steam generator and which ensures a simpler and faster assembly than those known so far. This new device maintenance also ensures better timing of spacer plates, thanks to a greater range with these. These advantages are notably obtained by the use of elastic positioning stops.

The invention therefore relates to a generator of steam comprising a pressure envelope of form stretched along a given axis, a bundle envelope steam generator tubes, also shaped elongated along the same axis and contained in the envelope pressure so as to leave an annular space between the two envelopes, spacer plates being arranged at given intervals and transversely to said axis in the beam envelope for supporting said tubes by means of a device holding device, the holding device being constituted of stops passing through the wall of the bundle envelope and fixed to this wall at the level of spacer plates, the stops being distributed at the periphery of each spacer plate to separate radially the envelope beam of the envelope pressure and to exercise maintenance constraints rigid between the spacer plates and the casing beam, each stop comprising a first part attached to the beam casing and comprising means allowing their possible sliding on the face internal pressure envelope along said axis and means for varying their radial dimension with respect to said axis, each stop also comprising a second part which can be moved radially relative to to the first room and having means to exercise said rigid holding constraint on the plate spacer, fixing means being provided for immobilize the second part relative to the envelope beam after contacting the second part and the spacer plate, characterized in that each stop includes means for bringing the second piece in contact with the corresponding spacer plate by introduction of a fluid between the second part and the first piece.

Advantageously, the first part comprises a cavity in which the second part is housed forming a piston in this cavity, said fluid being introduced into the cavity, in the space between the first room and the second room. This facilitates assembly operations of the steam generator.

This fluid can be introduced through a conduit crossing the second room.

The invention also relates to a generator of steam including a pressure envelope of elongated shape given axis, an envelope of the bundle of tubes of the steam generator, also elongated according to the same axis and contained in the pressure envelope so as to leave an annular space between the two envelopes, with spacer plates arranged at given intervals and across the audit axis in the beam envelope to support said beams tubes by means of a holding device, the holding device consisting of stops crossing the wall of the bundle envelope and fixed at this wall at the level of the spacer plates, the stops being distributed around the periphery of each spacer plate to radially separate the casing pressure envelope beam and to exercise rigid support constraints between spacer plates and the bundle shell, each stop comprising a first part fixed on the beam envelope and comprising means allowing their possible sliding on the internal face the pressure envelope along said axis and means to vary their radial dimension with respect said axis, each stop also comprising a second part that can be moved radially relative to to the first room and having means to exercise said rigid holding constraint on the plate spacer, fixing means being provided for immobilize the second room in relation to the beam envelope after contacting the second piece and spacer plate, characterized in that the means for varying the radial dimension with respect to said axis consist of elastic means connecting the second part at the first room and tending to push aside the second piece of this first piece in a radial direction with respect to said axis between a first position corresponding to a minimum radial dimension of the stop and a second position corresponding to the contact with the spacer plate.

These elastic means may include a spring arranged between the first part and the second room.

Preferably, the means allowing the possible sliding of a stop on the internal face of the pressure envelope and the means to make vary their radial dimension are constituted by at minus a screw screwed into the first part, the contact between said screw and the inner face of the envelope pressure taking place at a convex end of the opinion.

• la figure 1 représente une vue en coupe verticale d'un générateur de vapeur utilisé dans les réacteurs nucléaires à eau pressurisée ;
• la figure 2 représente une butée connue de maintien radial de l'enveloppe de faisceau et des plaques-entretoises d'un générateur de vapeur ;
• la figure 3 représente, selon la coupe III-III de la figure 4, une butée de maintien radial selon l'invention dans une vue correspondant à celle de la figure 2 ;
• la figure 4 est une vue de la butée de maintien radial selon la flèche IV de la figure 3 ;
• la figure 5 représente une variante de butée de maintien radial selon l'invention.

The invention will be better understood and other advantages and features will appear on reading the description which follows, given by way of nonlimiting example, accompanied by the appended drawings among which:

• Figure 1 shows a vertical sectional view of a steam generator used in pressurized water nuclear reactors;
• FIG. 2 represents a known stop for radial retention of the bundle envelope and of the spacer plates of a steam generator;
• 3 shows, according to section III-III of Figure 4, a radial retaining stop according to the invention in a view corresponding to that of Figure 2;
• Figure 4 is a view of the radial retaining stop according to arrow IV of Figure 3;
• FIG. 5 represents a variant of radial retention stop according to the invention.

In Figure 1, which is an axial sectional view, we see a steam generator whose external envelope 1, resistant to pressure, contains in its lower part of smaller diameter a tubular bundle 2 comprising a set of bent tubes in the shape of an inverted U. These tubes are traversed by pressurized water forming part of the primary circuit and introduced into the steam generator under the tubular plate 3 by an inlet orifice 4. The pressurized water traverses the tubes of the tubular bundle 2 then returns under the tube plate 3 to exit through the orifice 5.

The tubular bundle 2 is surrounded, until near its lower part, by an envelope of beam 6 constituting the vaporization enclosure inside which the food water in contact with the tube bundle 2, traversed by water at high temperature coming from the reactor core, gradually vaporizes while rising inside of enclosure 6. The tallest part of the dome of steam is provided with a steam outlet 7 towards the turbine.

A non-potable water supply device depicted keeps water level 8 food in the steam generator to a certain distance above tube bundle 2 and below cyclones 10 constituting the first stage of the vapor separator and communicating with the top of the vaporization enclosure 6 via the tubular columns 11. These tubular columns are welded to the roof 9 of the vaporization enclosure 6 and allow communication with the interior of this enclosure. This food water goes first in the space between the outer envelope 1 and enclosure 6 to reach the lower end of this enclosure.

At the outlet of cyclones 10, the vapor, which has abandoned most of the entrained water, passes through the secondary separators 12 formed by baffles allowing more complete drying steam before exiting through port 7.

Beam tubes are held laterally by spacer plates 13 arranged transversely inside the envelope of harness 6. Tie rods 14 attached to their part lower on the tube plate 1 allow maintain the axial spacing of the spacer plates 13.

Figure 2 is an enlargement of the area marked II in Figure 1. It allows you to see one retaining stops for a spacer plate 13. The stop 15 is fixed to the bundle envelope 6. To achieve this fixation, the casing 6 is pierced a radial opening 16 allowing passage and fixing a structure comprising a sheath radial 17 welded to the casing 6 by one of its ends and slightly protruding in space ring between pressure envelope 1 and the beam envelope 6. The structure further comprises an annular plate 18 welded to the end of the sheath 17 which is in the annular space and partially closing the sheath 17. The structure finally includes a second sheath 19 placed in alignment of the first sleeve 17 and welded to the edge of the hole in the annular plate 18.

The stop includes a shaped part 20 general cylindrical which is engaged in the structure described above until contact with the internal wall of the pressure envelope 1. The part 20 comprises a portion 21 of large diameter, this diameter being very slightly smaller than the inside diameter of the sheath 17, and a portion 22 of small diameter, this diameter being slightly less than the diameter inside of the sheath 19. The face of the part 20 directed inward of the bundle envelope 6 is machined to constitute a bearing surface 23 inclined by relative to the vertical of an angle close to 5 °. The angle of inclination of this bearing surface corresponds to the machining angle of the shims 24 interposed between the spacer plate 13 and part 20.

The end of part 22 of part 20 directed to the pressure casing is machined to constitute a spherical bearing surface on the envelope pressure.

For the installation of the support stops, the parts 20 are placed in their housings and contact with pressure casing 1. Each part 20 is then welded by a circular weld bead 25 on the inner face of the sheath 17. Next comes place and weld a set of shims 24 between the surface support 23 and the edge of the spacer plate 13 for provide rigid support between spacer plates and the bundle casing.

We will now describe two variants of the holding device according to the invention which does not employ no shims like the device of the prior art, in relation to Figures 3 to 5.

In these figures, we recognize the envelope pressure 1, the beam envelope 6 and a spacer plate 13.

Figures 3 and 4 illustrate a first variant. A first circular piece 31 is fixed by a weld bead 34 on a axial and circular opening made on the envelope beam 6 at a spacer plate 13. This part occupies part of the annular space 33 separating the two envelopes. The welding of the first piece 31 of each stop on the envelope of beam is made prior to assembly operations of the steam generator.

The first part 31 has in its center a circular cavity 35 on the inside of the generator steam. The peripheral part of part 31, in crown shape 37, has four threaded holes 36 regularly arranged on this crown. In these threaded holes 36, we screw four screws 38 for the adjusting the position of the beam envelope 6 with respect to the pressure envelope 1. The contact between the pressure jacket and each end of the screw 38 is made on a curved face 39.

The second part 32, of cylindrical shape, acts as a piston in the cavity 35 of the first Exhibit 31. It is intended to come to bear on the spacer plate 13 by its rear face 41.

A conduit 42 passes right through the part 32, connecting the rear face 41 of this part to the cavity 35. The duct 42 communicates with the face rear 41 through an orifice 43 adapted to receive a nozzle compressed air supply.

During assembly, the bundle envelope 6 is positioning in the pressure envelope 1 in respecting the spacing required between the two envelopes by means of rods through a hole provided for this purpose in the beam envelope. Screws 38, for example of the hexagon socket type, are then adjusted by means of an Allen key to get into contact with the wall internal pressure envelope. They can then be stopped by a welding point made between each of the screws 38 and the first part 31.

Then the piston 32 is introduced into the cavity 35, then brought into contact with the spacer plate 13, duly positioned, by inflation. The inflation can be done by compressed air under a pressure of 7 bars. The position obtained is then stopped using a weld bead 44 connecting the parts 31 and 32.

Figure 5 illustrates a second variant of achievement. The elastic pressure intended to put the part 32 in contact with the spacer plate 13 in this case is ensured by a coil spring 45 housed in cavity 35.

It is possible in either variant of the invention to provide a far-reaching contact between the edge of the spacer plate 13 and the face rear 41 of part 32.

Claims (8)

1. Steam generator incorporating a pressure envelope (11) elongated in accordance with a given axis, an envelope of the steam generator tube bundle also being elongated according to the same axis and contained in the pressure envelope so as to leave an annular space between the two envelopes, spacer plates (13) being located at given intervals and transversely to the said axis within the bundle envelope in order to support the said tubes by means of a holding device, the holding device being constituted by abutments traversing the bundle envelope wall and fixed to said wall level with the spacer plates, the abutments being distributed on the periphery of each spacer plate in order to radially separate the bundle envelope from the pressure envelope and so as to exert rigid holding stresses between the spacer plates and the bundle envelope, each abutment having a first part (31) fixed to the bundle envelope (6) and incorporating means permitting their optional sliding on the inner face of the pressure envelope according to said axis and means for varying their radial dimension with respect to said axis, each abutment also having a second part (32) radially displaceable with respect to the first part, with means for exerting said rigid holding stress on the spacer plate, fixing means being provided for immobilizing the second part (32) with respect to the bundle envelope after contacting the second part (32) and the spacer plate, characterized in that each abutment comprises means for bringing the second part (32) into contact with the corresponding spacer plate (13) by introducing a fluid between the second part (32) and the first part (31).
2. Steam generator according to claim 1, characterized in that the first part (31) has a cavity (35) housing the second part (32) forming a piston in said cavity, said fluid being introduced into the cavity, in the space between the first part (31) and the second part (32).
3. Steam generator according to claim 2, characterized in that said fluid is introduced by a duct (42) traversing the second part (32).
4. Steam generator comprising a pressure envelope (1) elongated in accordance with a given axis, a steam generator tube bundle envelope, also elongated in accordance with the same axis and contained in the pressure envelope so as to leave an annular space between the two envelopes, spacer plates (13) being positioned at given intervals and transversely with respect to said axis in the bundle envelope in order to support said tubes by means of a holding device, the holding device being constituted by abutments traversing the wall of the bundle envelope and fixed to said wall at the spacer plates, the abutments being distributed on the periphery of each spacer plate so as to radially separate the bundle envelope from the pressure envelope and to exert rigid holding stresses between the spacer plates and the bundle envelope, each abutment having a first part (31) fixed to the bundle envelope (6) and comprising means permitting the possible sliding thereof on the inner face of the pressure envelope in accordance with said axis and means for varying their radial dimension relative to said axis, each abutment also having a second part (32), which is radially displaceable with respect to the first part and having means for exerting said rigid holding stress on the spacer plate, fixing means being provided for immobilizing the second part (32) with respect to the bundle envelope after contacting the second part (32) and the spacer plate (13), characterized in that the means for varying the radial dimension with respect to said axis are constituted by elastic means linking the second part (32) to the first part (31) and tending to move aside the second part from said first part in a radial direction with respect to said axis between a first position corresponding to a minimum radial dimension of the abutment and a second position corresponding to contact with the spacer plate (13).
5. Steam generator according to claim 4, characterized in that the elastic means comprise a spring (45) positioned between the first part (31) and the second part (32).
6. Steam generator according to any one of the claims 1 to 5, characterized in that the means permitting the optional sliding of an abutment on the inner face of the pressure envelope and the means for varying their radial dimension are constituted by at least one screw (38) screwed into the first part (31), the contact between said screw (38) and the inner face of the pressure envelope (1) taking place along a cambered end (39) of the screw.
7. Steam generator according to any one of the claims 1 to 6, characterized in that said fixing means are constituted by a weld made between the first part (31) and the second part (32).
8. Steam generator according to any one of the preceding claims, characterized in that the contact between the second part (32) and the spacer plate (13) takes place along a large bearing surface of the second part exerting a pressure on the edge of the spacer plate.

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