EP0568434A1 - Distributing and partitioning device for feed and recirculation water in the secondary side of a steam generator - Google Patents

Abstract

In a steam generator used in a nuclear reactor, the feed of secondary water takes place by at least one nozzle (48) which opens directly into the bottom of an annular recirculation space (32) formed between the external casing (10) and an internal casing (26) surrounding inverted U-shaped tubes (24), on the side of the cold branches of these tubes. A perforated collar (56) placed in the annular space (32), above the nozzle (48), creates a loss of head or a flow limitation which prevents the rising of the feed water and controls the circumferential distribution of the recirculation water which descends from the separators (28). <IMAGE>

Description

The invention relates to a steam generator designed for use in a pressurized water nuclear reactor and in which means are provided for ensuring a controlled distribution of the feed water injected at the bottom of the steam generator and of the recirculation from the condensation of secondary water vapor in the upper part of the generator.

As illustrated in particular in document FR-A-2 477 265, a steam generator equipping a nuclear power plant usually comprises an outer envelope, of vertical axis, the interior space of which is divided into two parts, in the direction of the height, by a horizontal plate called "tube plate" (in English "tube sheet"). The ends of the tubes of an inverted U-shaped tube bundle are fixed on the tube plate and open below it respectively in an intake manifold and in a collector for evacuating the water circulating in the circuit. reactor primary, called "primary water". The water circulating in the secondary circuit of the reactor, called "secondary water" or "edible water" is injected into the part of the steam generator located above the tube plate.

In the steam generator described more precisely in the document FR-A-2 477 265, the injection of drinking water is ensured by a main supply manifold of semi-toric shape, located above a space recirculation ring formed between the outer casing and an inner casing covering the tube bundle and the lower edge of which is spaced from the tube plate.

Food water introduced into the steam generator by the main supply manifold descends into this annular space, then rises between the bundle tubes inside the interior envelope. The heat taken from the primary water circulating inside the tubes then has the effect of vaporizing the drinking water when it reaches the upper region of the inner envelope. The steam thus formed then passes through separators and dryers which lower the humidity level of the steam before it escapes towards the turbines of the secondary circuit used to drive the electric generators of the power plant.

The condensed water retained in the separators, generally called "recirculation water", descends by gravity into the annular recirculation space, in order to effect a new passage in the interior envelope of the generator.

The location of the main supply collector of the steam generator above the annular recirculation space leads, as illustrated in document FR-A-2 477 265, to equip this collector with inverted J-shaped tubes, to avoid pressure surges and water hammer which could occur when the pumps in the secondary circuit are restarted, following dewatering of the supply manifold. However, this technique has the disadvantage of complicating the manufacture of the steam generator and, consequently, of lengthening the duration and the cost of this manufacture.

Furthermore and as illustrated in particular by documents US-A-3 804 069, 3 896 770 and 3 916 843, it has also been envisaged to ensure the supply of drinking water to a steam generator by directly connecting a pipe. water intake on a lower part of the inner envelope, so as to make penetrate the drinking water directly at the base of the cold branches of the bundle tubes. Deflectors placed opposite the intake manifold and around the cold branches then form a device for preheating the food water circulating between the tubes.

If the solution described in these latter documents avoids the drawbacks posed by the installation of the main supply manifold in the upper part, it has the drawback of subjecting the lower parts of the cold branches of the tubes to significant transverse flows and of not allowing a controlled distribution of the feed water flow over the section of the steam generator.

In addition, if migrant bodies such as objects (welding rods, screws, bolts, etc.) inadvertently introduced into the secondary circuit during their production enter the steam generator through the water intake manifold food, they can get stuck between the bundle tubes and therefore damage these tubes.

• l'obtention d'un rendement maximal du générateur de vapeur en fonctionnement normal ;
• la nécessité d'assurer un fonctionnement satisfaisant du générateur de vapeur lors d'un incident nécessitant l'utilisation d'un collecteur d'alimentation de secours, généralement placé au-dessus de l'espace annulaire de recirculation ; et
• la limitation à des valeurs aussi faibles que possible des contraintes thermiques subies notamment par l'enveloppe extérieure et la plaque à tubes du générateur de vapeur.

In addition, the existing steam generators in which the introduction of drinking water takes place at the bottom of the secondary part does not make it possible to effect a controlled distribution of the distribution of drinking water and recirculating water. on the periphery of the steam generator, whereas this controlled distribution would be desirable in order to reconcile certain contradictory imperatives as best as possible, including:

• obtaining maximum efficiency of the steam generator in normal operation;
• the need to ensure satisfactory operation of the steam generator during an incident requiring the use of a supply manifold emergency, generally placed above the annular recirculation space; and
• limiting the thermal stresses undergone as low as possible, in particular by the outer casing and the tube plate of the steam generator.

The invention specifically relates to a steam generator whose original design sees the main supply manifold located at the bottom of the secondary part, while ensuring a controlled distribution of the distribution of drinking water and recirculating water on the periphery of the secondary part of the generator and allowing possible trapping of migrant bodies from the food water circuit, likely to penetrate into the bundle of tubes and damage them.

• une enveloppe extérieure, d'axe vertical ;
• une plaque tubulaire horizontale fixée de façon étanche à l'intérieur de l'enveloppe extérieure ;
• un faisceau de tubes en U inversé comprenant des branches chaudes et des branches froides et ayant chacun deux extrémités fixées sur la plaque à tubes et débouchant en dessous de cette dernière, respectivement dans un collecteur d'admission et dans un collecteur d'évacuation de fluide primaire ;
• une enveloppe intérieure coiffant le faisceau de tubes, dont un bord inférieur est espacé de la plaque à tubes, et formant avec l'enveloppe extérieure un espace annulaire de recirculation ;
• des moyens d'alimentation en eau secondaire ; et
• des moyens de séparation d'eau de recirculation apte à redescendre par ledit espace et de vapeur secondaire apte à être extraite du générateur de vapeur, ces moyens de séparation étant situés au-dessus de l'enveloppe intérieure ;

caractérisé par le fait que les moyens d'alimentation en eau secondaire comprennent au moins une tubulure d'alimentation débouchant directement dans l'espace annulaire de recirculation, au moins une collerette perforée étant placée dans l'espace annulaire de recirculation, à un niveau supérieur à celui de la tubulure d'alimentation, de façon à s'opposer à une remontée d'eau secondaire dans ledit espace et à assurer une répartition circonférentielle contrôlée de l'eau de recirculation descendant dans cet espace.According to the invention, this result is obtained by means of a steam generator comprising:

• an outer envelope, of vertical axis;
• a horizontal tubular plate fixed in a sealed manner inside the outer envelope;
• a bundle of inverted U-shaped tubes comprising hot branches and cold branches and each having two ends fixed on the tube plate and emerging below the latter, respectively in an intake manifold and in a fluid discharge manifold primary;
• an inner envelope covering the bundle of tubes, a lower edge of which is spaced from the tube plate, and forming with the outer envelope an annular recirculation space;
• secondary water supply means; and
• means for separating recirculating water capable of descending through said space and secondary steam capable of being extracted from the steam generator, these separation means being located above the inner envelope;

characterized in that the secondary water supply means comprise at least one supply pipe opening directly into the annular recirculation space, at least one perforated flange being placed in the annular recirculation space, at a higher level to that of the supply pipe, so as to oppose a rise of secondary water in said space and to ensure a controlled circumferential distribution of the recirculating water descending in this space.

The perforated flange which is placed in the annular recirculation space above the supply pipe generates a flow limitation or a pressure loss high enough to impose on the drinking water which enters the annular space a movement down and to control the proportion of recirculating water that enters this space, especially in the region above the supply pipe.

Preferably, in order to prevent migrant bodies from the secondary circuit and entering the steam generator via the supply pipe from reaching the tube of the bundle, first means for trapping migrant bodies are placed in the annular recirculation space, at a level lower than that of the supply pipe.

In the same spirit, when an emergency supply manifold is placed above the annular recirculation space, second means for trapping migrant bodies are placed in the annular recirculation space, below this collector emergency power.

In order to contribute to the downward orientation food water which enters the steam generator through the supply pipe, a deflector is advantageously placed inside the annular recirculation space, in the extension of this supply pipe.

The invention can be applied equally to economizer steam generators or to boiler-type steam generators.

In the case of an economizer steam generator comprising an intermediate skirt at least partially lining the inner envelope around the cold branches of the tubes, so as to delimit with the inner envelope an overheating zone belonging to the annular space recirculation, the supply tube opens directly into this overheating zone and the perforated flange is also placed in this overheating zone.

In the case of an economiser steam generator without an intermediate skirt and in which the annular recirculation space is separated into a first region surrounding the cold branches of the tubes and a second region surrounding the hot branches of the tubes by vertical partitions , the supply pipe opens into the first region and the perforated flange is placed above this first region.

Finally, in the case of a steam generator of the boiler type having no separation between the hot and cold branches of the tubes, the supply manifold opens into the annular recirculation space, on the side of the cold branches of the tubes, the perforated flange extending over the entire circumference of this annular space. A distribution flange having perforations of variable section then extends over the entire circumference of the annular space, at a level lower than that of the supply manifold.

Optionally, the perforated collar can also perform the function of trapping the migrant bodies introduced into the steam generator by the emergency power collector. This flange then has perforations having a maximum diameter less than a minimum distance between the tubes of the bundles.

Similarly, the distribution flange used in the case of a steam generator of the boiler type can also optionally provide the trapping function for migrant bodies. The perforations of this distribution collar then have a maximum diameter less than the minimum distance between the tubes of the bundle.

• la figure 1 est une vue en coupe verticale illustrant schématiquement un générateur de vapeur à économiseur et à jupe intermédiaire réalisé conformément l'invention ;
• la figure 2 est une vue en coupe selon la ligne II-II de la figure 1 ;
• la figure 3 est une vue en coupe verticale comparable à la figure 1, illustrant un générateur de vapeur à économiseur dépourvu de jupe intermédiaire et réalisé conformément à l'invention ;
• la figure 4 est une vue en coupe selon la ligne IV-IV de la figure 3 ;
• la figure 5 est une vue en coupe verticale comparable aux figures 1 et 3, représentant schématiquement un générateur de vapeur de type bouilleur réalisé conformément à l'invention ; et
• la figure 6 est une ligne en coupe selon la ligne VI-VI de la figure 5.

We will now describe, by way of nonlimiting examples, various embodiments of the invention, with reference to the accompanying drawings, in which:

• Figure 1 is a vertical sectional view schematically illustrating a steam generator economizer and intermediate skirt made according to the invention;
• Figure 2 is a sectional view along the line II-II of Figure 1;
• Figure 3 is a vertical sectional view comparable to Figure 1, illustrating an economizer steam generator without an intermediate skirt and produced in accordance with the invention;
• Figure 4 is a sectional view along line IV-IV of Figure 3;
• Figure 5 is a vertical sectional view comparable to Figures 1 and 3, schematically showing a boiler type steam generator produced in accordance with the invention; and
• FIG. 6 is a line in section along the line VI-VI of FIG. 5.

In FIG. 1, the reference 10 designates the outer casing of revolution, of vertical axis, of a steam generator intended to ensure the transfer of heat between the primary water circuit and the secondary water-steam circuit of a pressurized water nuclear reactor. More precisely, the steam generator illustrated diagrammatically in FIG. 1 is a steam generator with an economizer and an intermediate skirt.

The external envelope 10 defines an enclosed internal space which is separated into a primary lower zone and a secondary upper zone by a horizontal tube plate 12 tightly connected to the external envelope 10.

A vertical partition 14 divides the primary lower zone, usually called a "water box", into an intake manifold 16 and an evacuation manifold 18 of the water circulating in the primary circuit of the reactor. Tubes 20 and 22 form part of the water box and connect the collectors 16 and 18 respectively to this primary circuit.

A bundle of inverted U-shaped tubes 24 is tightly connected to the tube plate 12, in the secondary upper zone delimited by the latter. More precisely, each of the tubes comprises a hot vertical branch whose lower end opens into the intake manifold 16 and a cold vertical branch whose lower end opens into the exhaust manifold 18.

The bundle of tubes 24 is surrounded and capped by an interior envelope 26 arranged coaxially in the exterior envelope 10. The upper part of this interior envelope 26 communicates with water-vapor separators 28, which open at their ends. upper in dryers (not shown) connected to a steam exhaust pipe (not shown) located at the top of the outer casing 10. The lower edge of the inner casing 26 is placed at a determined distance above the tube plate 12, so as to form a passage between an annular recirculation space 32 delimited between the envelopes 10 and 26 and the space 27 inside the interior envelope 26.

Horizontal spacer plates 34, regularly spaced over the entire height of the bundle of tubes 24, maintain these tubes inside the inner casing 26.

In the economizer and intermediate skirt steam generator illustrated in FIGS. 1 to 2, a vertical partition 36 rises in the bundle of tubes, from the tube plate 12, between the hot and cold branches of the tubes 24 , so as to physically separate these two branches over the entire lower part of the space 27 delimited in the inner envelope 26.

On either side of this vertical partition 36 and below the spacer plates 34 is placed a distribution plate 38 having a different permeability on the side of the hot branches and on the side of the cold branches, so as to ensure effective scanning of the tube plate 12 and a distribution as homogeneous as possible of the drinking water, mixed with the recirculating water, which rises inside the interior envelope 26.

The steam generator of FIGS. 1 and 2 further comprises an intermediate skirt 40 which at least partially encircles the internal envelope 26, on the side of the cold branches of the tubes 24, as illustrated in FIG. 2. The two circumferential ends of this skirt 40 are connected to the inner casing 26 by two end partitions 42 (Figure 2), so as to form in the annular recirculation space 32 an overheating zone 44, delimited between the inner casing 26, the skirt 40 and the partitions 42.

The intermediate skirt 40 is connected at its lower end to the tube plate 12 and preferably comprises, near this plate, openings 45, as illustrated diagrammatically in FIG. 1. It can also be seen in this figure, that the skirt 40 can support immediately above the openings 45 a horizontal deflector 46 allowing the stream of food water descending inside the overheating zone 44 to be diverted towards the central part of the steam generator, when it arrives at near the tube plate 12.

The intermediate skirt 40 rises in the annular recirculation space 32 to a sufficient level above the tube plate 12, as illustrated in FIG. 1.

In the embodiment illustrated in FIGS. 1 and 2, the entry of drinking water into the steam generator takes place, on the side of the cold branches of the bundle of tubes 24, by at least one supply tube 48 connected to the outer casing 10 of the steam generator and extended by a thermal sleeve 50 connected directly to the intermediate skirt 40. Thus, the supply pipe 48 opens directly into the overheating zone 44.

In the embodiment illustrated in FIG. 1, the steam generator also comprises an emergency supply manifold 52, of toroidal shape, placed around the internal envelope 26, in the upper part of the annular recirculation space 32. This emergency collector 52 can be supplied, in the event of an incident in the secondary circuit, by a supply pipe (not shown) which passes through sealing the outer envelope 10. It opens inside the steam generator by perforations formed on its upper generator.

According to the invention, a perforated flange 56 is placed in the overheating zone 44, near the upper edge of the intermediate skirt 40, that is to say at a level substantially higher than that of the supply pipe. 48. In the embodiment shown, the perforated collar 56 is a flat and horizontal collar which extends over the whole section of the overheating zone 44. As a variant, this collar can take any shape and orientation, such as '' a curvilinear shape and / or an inclined orientation.

The perforated collar 56 has perforations 57 (FIG. 2) whose shape, number and distribution make it possible to control the distribution of the distribution of drinking water and recirculating water in the secondary part of the steam generator.

Thus, in the case of an economizer steam generator as illustrated in FIGS. 1 to 3, it is possible to give the perforated collar 56 characteristics making it possible to contain in space 44 all of the food water from the side of the cold branches of the bundle of tubes 24, which ensures maximum efficiency is obtained for the steam generator. This result is obtained by giving the flow limitation or the pressure drop induced by the perforated flange 56 a value sufficient to practically prevent the food water introduced into the overheating zone 44 from being able to rise beyond the upper edge. of the intermediate skirt 40.

Furthermore, this limitation of flow rate or this pressure drop also has the effect of lowering the recirculated water preferentially. in the part of the annular recirculation space 32 external to the overheating zone 44 rather than in this overheating zone. This promotes, in combination with the openings 45 formed in the bottom of the skirt 40, the flow of the hotter recirculating water along the outer casing 10 and the tube plate 12, which improves the thermal balance of the outer casing and the tube plate. Concretely and only by way of example, the limitation of flow rate or the pressure drop induced by the perforated flange 56 can result in allowing only about 10% of the recirculating water to pass into the overheating zone 44.

Finally, these same characteristics are not contradictory with the need to ensure downward circulation of the drinking water on the side of the cold branches of the tubes 24 when an incident results in introducing the drinking water into the steam generator by the emergency power collector 52.

In the embodiment shown in FIG. 1, the steam generator also comprises a first device 58 for trapping migrant bodies, placed in the overheating zone 44, at a level lower than that of the supply pipe 48. This The device 58 essentially has the function of preventing migrant bodies which risk being blocked between the tubes 24 of the bundle from entering these tubes. Unlike the perforated flange 56, it is designed so as to cause a flow limitation or a pressure drop as small as possible, so as not to reduce the efficiency of the device. To this end, this device may in particular be in the form of a grid or an equivalent system, providing a very large number of passages whose dimensions are less than the minimum distance separating the tubes 24.

Similarly, a second device for trapping migrant bodies 60, comparable to this device 58, is placed at the top of the annular recirculation space 32, below the emergency supply manifold 52, in order to prevent migrant bodies being introduced into the generator vapor by this collector can not get caught between the tubes 24 of the bundle. The characteristics and structure of this device 60 are moreover comparable to those of the device 58. In line with these trapping devices for migrant bodies 58 and 60, inspection openings can be made in the pressure envelope 10 and in the skirt 40 in order to collect any trapped migrant objects.

In the steam generator which has just been described with reference to FIGS. 1 to 3, the drinking water which enters the overheating zone 44 through the supply pipe 48 descends into this zone, in particular under the effect of the limitation of flow rate or of the pressure drop induced by the perforated flange 56, as illustrated by the arrows in FIG. 1. Food water then rises around the tubes 24, inside the inner envelope 26, by mixing with the recirculation water which mostly descends in the regions of the annular space 32 distinct from the overheating zone 44, again under the effect of the flow limitation or the pressure drop induced by the perforated collar 56.

It should be noted that the permeability of the perforated flange 56 can vary circumferentially, so as to allow precise local control of the flows.

In FIGS. 3 and 4, a steam generator with an economiser is shown, devoid of an intermediate skirt. This steam generator has many characteristics identical to the previous one, so that only the characteristics which differ from it will now be described.

First of all and as illustrated in FIG. 4, the vertical partition 36 which separates the hot and cold branches of the tubes 24 from the bundle above the tube plate 12 is extended in the intermediate recirculation space 32, by two complementary vertical partitions 62.

Furthermore, due to the disappearance of the intermediate skirt, the supply pipe (s) 48 open directly into the annular recirculation space 32, on the side of the cold branches of the tubes 24.

In this case, the perforated collar 56 is placed directly in the annular recirculation space 32, at a level substantially higher than that of the supply pipe 48. The perforated collar 56 extends over the entire width of the space 32 and on the half of the circumference of this space situated on the side of the cold branches of the tubes 24, as shown in FIG. 3, up to the vertical partitions 62, which rise for this purpose over a height greater than that of the vertical partition 36 separating the hot and cold branches from the tubes.

As before, the perforated flange 56 induces a flow limitation or a pressure drop sufficient to prevent the food water introduced by the supply pipe 48 from rising above the upper edges of the partitions 62.

In this case, the pressure drop or flow limitation may however be slightly lower than the previous case, so that the sweeping of the external enclosure 10 by the recirculating water is sufficient on the side of the cold branches to avoid thermal stresses too large are generated between this side and the opposite side of the steam generator.

As in the first embodiment, a device for trapping migrant bodies 58 is placed at a level lower than that of the supply pipe 48, in the part of the annular recirculation space 32 surrounding the cold branches of the tubes 24, between the partitions 62.

A second device for trapping migrant bodies 60 is also placed at the top of the annular recirculation space 32, over the entire periphery of this space, just below the emergency power collector 52.

The characteristics and structures of the trapping devices for migrant bodies 58 and 60 are identical to those which have been described in the first embodiment.

Finally, a description will now be given with reference to FIGS. 5 and 6 of a steam generator of the boiler type produced in accordance with the invention. This steam generator differs essentially from that which has just been described with reference to FIGS. 3 and 4 by the fact that it does not include any of the partitions 36 and 62.

The boiler-type steam generator illustrated in FIGS. 5 and 6 essentially presents characteristics similar to those of the steam generators described above, so that only the characteristics which distinguish this generator from the preceding will now be described.

As in the embodiment of FIGS. 3 and 4, the supply pipe 48 opens directly into the annular recirculation space 32. However, in this case, a deflector 64 has been placed in the extension of this pipe 48, in order to d bending downwards as soon as it enters the space 32 the flow of food water introduced through the tube 48.

Furthermore, since the annular recirculation space 32 is not separated into two parts semi-annular as in the case of FIGS. 3 and 4, the perforated flange 56 which is placed at the top of the annular recirculation space, at a level higher than that of the supply pipe 48, occupies the entire periphery of this space.

In this case, the perforated flange 56 mainly has the function of ensuring the desired distribution of the recirculated water which flows in the space 32, between the parts of this space surrounding the cold branches of the tubes 24 and the parts of this space surrounding the hot branches. To this end, the perforations made in the perforated flange 56 can ensure a preferential distribution of the recirculating water on the side of the hot branches or, on the contrary, a substantially uniform distribution of the recirculating water over the entire periphery of the annular space 32.

As in the embodiment of FIGS. 3 and 4, a first device for trapping migrant bodies 58 is placed in the annular recirculation space 32, at a level lower than that of the supply pipe 48. In this case, this device 58 however extends over the entire periphery of the space 32.

In addition, this device for trapping migrant bodies 58 is advantageously in the form of a distribution collar, the perforations of which have a maximum diameter less than the minimum distance between the tubes 24 of the bundle. In addition, these perforations have variable sections over the entire periphery of the device 58, so as to generate flow limitations or variable pressure losses allowing the distribution of the feed water and recirculating water flows penetrating to be controlled. inside the inner envelope 26, at the base of the tube bundle.

In this case, the perforated collar 56, which is placed below the emergency power collector 52, can also constitute a second device for trapping migrant bodies possibly introduced by this collector 52. For this, the perforations which are produced in the collar 56 have a maximum diameter less than the maximum distance between the tubes 24 of the beam.

By way of nonlimiting illustration, the combined effect of the deflector 64 and the distribution flange forming the device for trapping migrant bodies 58 can result in distributing the food water introduced into the generator through the supply pipe 48 according to a proportion of about 80% on the side of the cold branches of the tubes 24 and about 20% on the side of the hot branches.

Of course, the invention is not limited to the embodiments which have just been described by way of examples, but covers all the variants thereof. Thus, the deflector 64 described with reference to FIG. 6 can be used in the other embodiments. Furthermore, the steam generator can comprise several supply pipes 48 without departing from the scope of the invention.

Claims (9)

Steam generator comprising: - an outer casing (10), of vertical axis; - a horizontal tubular plate (12) sealed in the interior of the outer envelope; - a bundle of inverted U-shaped tubes (24) comprising hot branches and cold branches and each having two ends fixed on the tube plate and opening below the latter, respectively in an intake manifold (16) and in a primary fluid discharge manifold (18); - an inner casing (26) covering the bundle of tubes, a lower edge of which is spaced from the tube plate, and forming with the outer casing an annular recirculation space (32); - secondary water supply means; and - Means (28, 30) for separating recirculating water capable of coming back down through said space and of secondary vapor capable of being extracted from the steam generator, these separation means being located above the interior envelope; characterized in that the secondary water supply means comprise at least one supply pipe (48) opening directly into the annular recirculation space, at least one perforated flange (56) being placed in the annular space of recirculation, at a level higher than that of the supply pipe, so as to oppose a rise of secondary water in said space and to ensure a controlled circumferential distribution of the recirculation water descending in this space. Steam generator according to claim 1, characterized in that first means for trapping migrant bodies (58) are placed in the annular recirculation space (32) at a level lower than that of the supply manifold (48). Steam generator according to any one of claims 1 and 2, characterized in that an emergency supply manifold (52) is placed above the annular recirculation space (32), of the second means of trapping migrant bodies (60) being placed in the annular recirculation space, below the emergency supply manifold. Steam generator according to any one of the preceding claims, characterized in that a deflector (64) is placed inside the annular recirculation space (32), in the extension of each supply pipe, in order to divert down the secondary water. Steam generator according to any one of the preceding claims, characterized in that an intermediate skirt (40) at least partially lining the inner envelope (26) around the cold branches of the tubes, to delimit with the inner envelope an overheating zone (44) belonging to the annular recirculation space (32), the supply pipe (48) opens into this overheating zone and said perforated flange (56) is placed in the overheating zone (44) . Steam generator according to any one of claims 1 to 5, characterized in that, a lower part of the annular recirculation space (32) being separated into a first region surrounding the cold branches of the tubes and a second region surrounding the hot branches of the tubes by vertical partitions (62), the supply manifold (48) opens into the first region and the perforated flange (56) is placed above this first region. Steam generator according to any one of claims 1 to 5, characterized in that the supply pipe (48) opens into the annular recirculation space, on the side of the cold branches of the tubes, the perforated flange (56) extending over the entire circumference of this annular space, and a distribution flange (58 ) having perforations of variable section extending over the entire circumference of the annular space, at a level lower than that of the supply pipe. Steam generator according to any one of the preceding claims, characterized in that the perforated collar (56) has perforations having a maximum diameter less than a minimum distance between the tubes of the bundle. Steam generator according to claim 7, characterized in that the perforations of the distribution flange (58) have a maximum diameter less than a minimum distance between the tubes of the bundle.

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