EP0067739A1 - Method and apparatus for removing sludge from the top surface of the tube sheet of a steam generator - Google Patents

Abstract

Method and device for unclogging the upper face of the tube plate of a steam generator comprising, in a cylindrical enclosure (1), a bundle of tubes (7) bent in an inverted U shape and connected to a tube plate (2 ), in which unclogging is obtained by two jets of water under high pressure coming from the heads (11, 12) and which can be directed towards the tube plate, these two jets of water moving simultaneously and symmetrically with respect to the diametrical line of delimitation of two zones in the form of a semi-disc of the tube plate, at the same time, means are provided (21) for discharging the separated sludge by carrying out a suction of this sludge all along the peripheral zone of the tube plate .

Description

The present invention relates to a method and a device for unclogging the upper face of the tube plate of a steam generator.

The steam generators of pressurized water nuclear reactors generally comprise a cylindrical envelope of great height inside which is disposed vertically a bundle composed of a large number of bent tubes in the shape of an inverted U. Each tube is connected by its two ends to a tubular plate arranged horizontally in the vicinity of the lower part of the steam generators, above the lower curved bottom of this generator.

The lower part of the steam generator located under the tube plate forms two substantially identical compartments delimited by the lower curved bottom and by a vertical partition, one of the compartments communicates by the tube plate with one of the ends of all the tubes, the other compartment communicates with the other end of all the tubes. The pressurized water bringing the heat from the core of the nuclear reactor to the steam generator is introduced into one of the compartments, circulates in the tubes, returns to the other compartment and returns to the core of the nuclear reactor. Passing through the tubes, this water gives up part of its heat by vaporizing edible water which is contained in the envelope of the generator and which surrounds the tubes. The steam produced is taken from the upper part of the steam generator and sent to the turbine associated with the electric generator. Then, this vapor is condensed in the form of drinking water which is reintroduced into the steam generator.

Despite the treatments carried out with potable water, its presence in the steam generator causes it to operate, over long periods of time, to form a deposit of sludge which accumulates on the tube plate around the base of the U-shaped tubes, in particular at the place of the tight connection of the tubes and the tube plate which is produced by swaging and welding.

This sludge is mainly composed of iron oxide, in particular magnetite, which is the cause of corrosion phenomena of the tubes at the level of the tube plate. A leak at the level of the tubes which causes a passage of the primary water in the vapor circuit being considered as me a serious accident in the case of a nuclear reactor, special care must be taken to avoid these corrosion phenomena. Consequently, there is provision for periodic unclogging of the upper face of the tube plate in order to eliminate the sludge which is deposited there.

To carry out this operation, it has already been proposed to place inside the generator, above the tube plate, a mobile lance sending a jet of water under high pressure in the direction of the base of the tubes. It is known to arrange this lance so that it moves in a diametrical direction of the steam generator, passing through the central zone which is devoid of tubes.

On the other hand, various installations have been proposed for removing the sludge formed during the unclogging operation. It is thus known (French hrevet application n ° 2.352.269 of May 13, 1977) to cause the circulation of a water jet on the periphery of the tubular plate, this water jet being intercepted and evacuated outside the steam generator after having traversed a half-turn, causing in its passage and thus evacuating the sludge as they reach the periphery of the tube plate.

It has also been proposed to carry out the evacuation of slurries, by introducing through the same orifice as that which is used for the passage of the launching head, a flexible suction pipe which is guided so as to be disposed approximately on the area tubular plate device.

Finally, it has been proposed to give the tubular plate a funnel shape so as to evacuate the sludge by gravity, the lowest point of the tubular plate being in the center and comprising at this location an evacuation.

These different arrangements have certain drawbacks, however. The evacuation process by peripheral water circulation does not make it possible to obtain a homogeneous drainage because the evacuation takes place only at one point; the evacuation device using a flexible tube temporarily inserted into the steam generator is not very reliable because this tube can twist or be arranged irregularly on the tube plate; and the device using a tubular plate in the form of a funnel may be of interest since the tubular plate being a centerpiece it is preferable to give it a geometric shape that is as simple as possible, for example a planar shape. This latter process is furthermore limited to a steam generator, the water tank of which comprises a central column.

In addition, a common point in these unclogging methods is to launch the cleaning water using a single launching head which moves either along a diameter of the steam generator, or along 'a radius of this generator. In the latter case, the cleaning operation is carried out in two stages: introduction of the lance through an orifice formed in the envelope of the steam generator and cleaning of the corresponding tubular half-plate, then introduction through a diametrically opposite orifice and cleaning the other tubular half-plate. By operating in one or the other of these ways, there may be a displacement of the sludge from an area being cleaned towards an already cleaned area.

The present invention relates to a method and a device for unclogging intended to overcome these various drawbacks.

The present invention therefore relates to a method of unclogging the upper face of the tube plate of a steam generator comprising, in a cylindrical enclosure with vertical axis, a vertical bundle of bent tubes in the shape of an inverted U, connected to each of their ends lower than the flat horizontal tubular plate integral with the enclosure of the steam generator, a high temperature fluid being brought to the tubes of the bundle above the tubular plate to supply heat allowing the vaporization of the drinking water introduced into the steam generator.

According to an essential characteristic of the invention, provision is made in the enclosure containing the bundle of tubes, two jets of water under high pressure which can be directed towards different points of the tube plate, one of the jets of water sweeping a first zone in the form of a half-disc of the tube plate, the other water jet sweeping the complementary zone in the form of a half-disc of the tube plate, these two jets of water moving simultaneously and symmetrically by relative to the diametrical line of delimitation of the two zones of the tubular plate, provision is also made for discharging the sludge detached by the water jets by performing a suction of this sludge all along the peripheral zone of the tubular plate.

According to a particular embodiment of the invention relating to an unclogging device in accordance with said method, provision is made for two launching heads projecting water under high pressure in the direction of the tube plate, these two heads moving independently l one from the other along the same horizontal axis located above the pla that tubular, these two heads being driven in an oscillating movement around said same axis, the displacement of the heads along this axis being carried out step by step, by a value equal to the distance separating two rows of tubes, so that the water jets leaving the lances pass successively between each row of tubes.

According to an advantageous arrangement, it is provided that the launching heads are movable in a diametrical direction of the steam generator located in the free space left between the bundle of tubes; and means are provided for simultaneous displacement of the two launching heads so that their position always remains symmetrical with respect to the central axis of the steam generator in order to symmetrically sweep the entire tubular plate.

According to another advantageous arrangement, there is provided a sludge evacuation device consisting of at least one tube situated above the tubular plate, at a relatively small distance, and disposed at the periphery of the tubular plate, in the vicinity of the vertical cylindrical envelope of the steam generator, this tube comprising orifices directed towards the bottom of the steam generator, and at least one connection of this evacuation tube to a conduit opening out of the steam generator and connected to a suction device.

• La figure 1 représente une vue en coupe par un plan vertical de symétrie de la partie inférieure du générateur de vapeur dans laquelle se trouve le dispositif de décolmatage et de récupération de boues.
• La figure 2 est une demi-vue simplifiée en coupe suivant A-A de la figure 1.
• La figure 3 est une vue en coupe suivant B-B de la figure 1.
• La figure 4 est une vue suivant la même coupe que la figure 3 d'une variante du dispositif de décolmatage.
• La figure 5 est une vue en coupe de la tête de lançage.
• La figure 6 est une vue en coupe partielle suivant C-C de la figure 3.
• La figure 7 est une vue en coupe partielle suivant D-D de la figure 3.

Other advantages specific to this invention will become apparent from the detailed description of the embodiment which follows, illustrated by the appended figures.

• FIG. 1 represents a view in section through a vertical plane of symmetry of the lower part of the steam generator in which is the device for unclogging and recovering sludge.
• FIG. 2 is a simplified half-view in section along AA in FIG. 1.
• FIG. 3 is a sectional view along BB of FIG. 1.
• Figure 4 is a view along the same section as Figure 3 of a variant of the unclogging device.
• Figure 5 is a sectional view of the launching head.
• FIG. 6 is a partial sectional view along CC of FIG. 3.
• FIG. 7 is a partial sectional view along DD of FIG. 3.

In Figure 1, we see the entire lower part of a steam generator essentially consisting of an external cylindrical envelope 1 arranged vertically, closed downwards by a plate 2 disposed horizontally, under this plate is disposed an envelope in the form of a half-sphere 3 comprising a vertical watertight partition 4 which thus delimits two chambers 5, 6; the horizontal plate 2 comprises a series of pipes 7 which pass through it and which are welded to it in a sealed manner. Each of these pipes 7 is in the form of an inverted U, the two lower ends of which each open into one and the other of the chambers 5, 6.

The steam generator works as follows: hot water from the reactor core is introduced into chamber 6, passes through all of the tubes 7, leaves in chamber 5, then returns to the reactor core. When passing through the tubes 7, this hot water gives up its heat to a food water contained in the chamber 8, by transforming this food water into steam which rises towards the upper part of the steam generator and which is sent to the turbines. In normal operation of the generator, there is a long-term deposit of sludge on the upper face 9 of the tubular plate 2. This steam generator furthermore comprises a set of devices making it possible to unclog this sludge on the upper face of the tube plate 2, which we "will describe in more detail later.

The unclogging principle adopted in the present invention is illustrated by schematic figure 2. In this figure, there is a tubular plate 2, on which tubes 7 are fixed vertically, all these tubes being arranged equidistantly so as to form a tube bundle. This tubular beam extends in the major part of the tube plate 2 but does not however extend to the very center of this tube plate. The tubes 7 'closest to the central axis 10 are indeed at a certain distance, in order to respect the minimum radius of curvature of their U shape. In the vicinity of the central axis 10, there is therefore a region devoid of tubes, in which the launching heads 11 and 12 are arranged. In FIG. 2 we distinguish the launching head 11 supplied with water under high pressure, and comprising a series of nozzles. In operation, the launching head is driven in an oscillating movement around the longitudinal axis of the lances, so that the water jets represented by the arrow 13 cover the entire surface of the tubular plate. The water jets which follow direction 13 are in a vertical plane which is perpendicular to the longitudinal axis of the lances 11, 12. During the projection of the water jets, a displacement along the longitudinal axis 14 of the lances 11 allows these water jets to reach all of the connection points between the tubes 7 and the tube plate 2.

Referring to Figure 1 we will describe the arrangement and mode of operation of the launching heads 11, 12. In the casing 1 of the steam generator, above the tube plate, are two openings 15 and 16 allowing the introduction into the steam generator of the launching heads 11, 12, in its openings are arranged bearings 17, 18 which allow the longitudinal displacement along the axis 14 of the straight rods 19, 20 which support the heads of launching 11, 12, as well as their oscillation movement. The rods constitute at the same time a pipe for supplying pressurized water into these launching heads.

Referring to Figures 1 and 3, we will describe the unclogging process specific to our invention. At the start of the unclogging operation, the rods 19, 20 are fully inserted into the steam generator so that the launching heads 11, 12 are almost contiguous at the center of the steam generator. At this time it is sent into the rods 19, 20 the high pressure water which emerges at the launching heads in the form of jets perpendicular to the axis 14. As the tubes are arranged at the tubular plate in regular grids, the water jets can pass between the rows of tubes and thus reach, due to the oscillating movement of the heads, the different zones of the tube plate lying on a line perpendicular to the axis 14. After for a few moments, the rods 19, 20 are moved simultaneously towards the outside of the steam generator by a distance equal to the distance between two rows of consecutive tubes. Successive movements are thus carried out so that the unclogging operation ends when the two launching heads 11, 12 arrive simultaneously at the peripheral zone of the tubular plate. By proceeding in this way, the sludge detached during the passage of a jet of water does not circulate on the tube plate so as to return to an already cleaned area to redeposit there.

Of course, the complete unclogging operation cannot stop when the sludge is removed, but must simultaneously include an operation for removing the sludge mixed with the water coming from the launching heads.

To proceed with the evacuation of sludge, there is provided according to our invention, a set of means which we will now describe.

Since the water jets intended for unclogging follow directions 13 going from the center of the steam generator towards the outside, the detached sludge is found, under the action of the water jet, projected towards the periphery of the tube plate 2 It is on this peripheral zone of the tubular plate 2 that a tube 21 has been placed which extends approximately over this entire peripheral zone.

In Figure 7 we see the detail of realization of this tube 21. We see in particular that this tube 21 is disposed above the tubular plate 2, at a small and regular distance from this plate. In this tube 21, a row 22 of holes is arranged, arranged longitudinally at the bottom of the tube, which also corresponds to the zone of the tube closest to the tube plate 2.

As this tube 21 is connected to the outside by pumps intended to create a vacuum therein, the sludge 24 arriving in the vicinity of the tube 21 passes into the tube through the orifices 22.

In Figure 6 we distinguish the connection between the tube 21 and the outside of the steam generator. The tube 21 is sealingly connected to the tube plate in which are drilled various bores 25, 26 which create a communication between the interior of tube 21 and the outside of the steam generator, the _port's being connected by a pipe 27 to a pump intended to extract the sludge during the unclogging operation.

The tube 21 is mounted and fixed permanently inside the steam generator. In the embodiment which is described here, as it can be seen in FIG. 3, the tube 21 is formed of several sections, 6 in number, closed at the ends, each section 21, 21 ^t comprising a communication with the outside of the independent generator. A set of pipes (not shown) brings together, by pipes 27, 27 'each tube 21, 21' to a suction device with interposition of a valve on each of the pipes, which allows, by the different setting of each valve, to locally increase the suction capacities in order to obtain good evacuation of the sludge over the entire periphery of the tube plate.

It is also possible, without departing from the scope of the invention, to have at the peripheral part of the tube plate a tube 21 making a complete turn and comprising one or more connections with the exterior of the steam generator.

It is also possible, without departing from the scope of the invention, to constitute a discharge device in a simplified manner, as described in figure 4. In this figure 4 we see indeed that there is no provision at all for a peripheral tube fixed inside the generator, but that only holes provided at the periphery of the plate are provided tubular 2 and which are connected to the ex sorter of the steam generator, in the same way as above, to pipes going to a suction device. Although this simplified sludge removal device shown in FIG. 4 is slightly less effective than that shown in the other figures and comprising a peripheral tube 21, this simplified device has the advantage of not having permanently inside of the steam generator, a whole installation of tubes 21.

Figure 5 shows us a launching head which includes two pairs of lances 29, 29 'and 30, 30'. The first pair of lances 29, 29 'being arranged in a first plane perpendicular to the axis 14 and the second pair of lances 30 being arranged in a second plane perpendicular to the axis 14, the distance separating the lances 29 and 30 being equal to the distance between two consecutive rows of tubes making up the bundle of tubes. In this way, as it appears in FIGS. 3 and 4, each lance carries out the unclogging by the simultaneous sending of two jets on either side of the same tube, which causes a cleaning of great efficiency. On the other hand, the lances 29 and 29 'are arranged diametrically opposite with respect to the axis 14. The same is true of the lances 30 and 30'. This arrangement has the advantage of causing the cancellation of the reaction forces at the level of the launching heads, which allows a lighter and more reliable construction of the rods which support these launching heads.

The unclogging process or device specific to our invention improves the performance of the sludge recovery operation since, due to the symmetrical action of the two heads, the jets move the sludge not only in the direction of the jets but also in a perpendicular direction. Thus, the sludge is pushed back step by step towards areas of higher transparency of the beam, that is to say areas where the number of rows of tubes is lower, areas for which the launching efficiency is increased. .

Thanks to the provisions specific to our invention it is possible to leave permanently inside the steam generator, all of the launching heads connected to their rods 19, 20, provided that they have been provided on the bearings 17, 18 sealing devices to withstand the pressure and temperature conditions prevailing inside the steam generator.

It will also be noted that the device specific to our invention makes it possible to minimize the number of removable parts located inside the steam generator, which simplifies the operating mode, saves time and reduces the risks of having to recover. elements inside the steam generator in the event of an incident. In addition, the fact of having only the lances to be introduced inside the steam generator makes it possible to use access holes of small diameter.

The device specific to our invention also makes it possible, during the period of operation of the steam generator, to operate the sludge removal device permanently mounted inside the steam generator, in order to carry out the periodic purging operations of potable water, which limits the deposition of sludge and consequently lengthens the period between two unclogging operations, which always require stopping the operation of the steam generator.

Claims (6)

1.- Method for unclogging the upper face of the tubular plate of a steam generator comprising, in a cylindrical enclosure with vertical axis, a vertical bundle of bent tubes in the shape of an inverted U, connected at each of their irlErieure ends to the flat horizontal tubular plate integral with the enclosure of the steam generator, a high temperature fluid being brought to the tubes of the bundle below the tubular plate to supply heat making it possible to vaporize the drinking water introduced into the generator steam on contact with the tubes,
characterized by the fact that it comprises a sludge take-off operation by arranging in the enclosure containing the tube bundle two jets of water under high pressure which can be directed towards different points on the tube plate, one of the jets of water sweeping a first zone in the form of a half-disc of the tube plate, the other water jet sweeping the complementary zone in the form of a half-disc of the tube plate, / two jets of water moving simultaneously and symmetrically relative to the diametrical line delimiting these two zones of the tubular plate, this displacement being made from said diametral line towards the periphery of the steam generator, and that it comprises a simultaneous evacuation of the sludge separated by the jets of water by sucking up this sludge all along the peripheral zone of the tube plate. 2.- Device for unclogging the upper face (9) of the tubular plate (2) of a steam generator comprising, in a cylindrical enclosure with vertical axis, a vertical bundle of tubes (7) bent in the shape of an inverted U , connected at each of their lower ends to the flat horizontal tubular plate integral with the enclosure of the steam generator, a high temperature fluid being brought to the bundle tubes below the tubular plate to supply heat making it possible to vaporize food water introduced into the steam generator in contact with the tubes,
characterized by the fact that it comprises two launching heads (11, 12) projecting water under high pressure in the direction of the tube plate, these two heads / moving independently of one another along of the same horizontal axis (14) located above the tube plate, these heads being driven in an oscillating movement around said same axis, the displacement of the heads being carried out step by step, of an equal value at the distance separating two rows of tubes (7), so that the water jets (13) leaving the lances pass successively between each row of tubes (7). 3. unclogging device according to claim 2, characterized in that the launching heads are movable in a diametrical direction (14) of the steam generator located in the free space left between the bundle of tubes (7), and that means are provided for simultaneous movement of the two launching heads, so that their position always remains symmetrical with respect to the central axis of the steam generator in order to symmetrically sweep the entire tubular plate. 4.- unclogging device according to one of claims 2 or 3, characterized in that the sludge removal device (24) consists of at least one tube (21) located above the tube plate , at a relatively small distance, and arranged at the periphery of the tubular plate (2) in the vicinity of the vertical cylindrical envelope (1) of the steam generator, this tube comprising orifices (22) directed towards the bottom of the steam generator steam, and at least one connection (25, 26) of this evacuation tube (21) to a duct (27) opening out to the outside of the steam generator, and connected to a suction device. 5. Unclogging device according to claim 4, characterized in that the sludge evacuation tube consists of several independent sections (21 '), closed at each end, each section being connected to the suction device by via a separate conduit (27) comprising a valve (not shown), these valves being able to be adjusted differently from one another in order to locally increase the suction capacities. 6.- unclogging device according to one of claims 2 or 3, characterized in that the sludge removal device is a simplified device, comprising only a series of holes (28) formed at the periphery of the tube plate and connected, outside the steam generator, to a suction device.

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