GB2365103A

GB2365103A - Device and method for servicing heat exchanger

Info

Publication number: GB2365103A
Application number: GB0115117A
Authority: GB
Inventors: Jean-Claude Ferlay; Marc Gely; Dominique Jouin; Roger Rousson
Original assignee: Framatome ANP SAS
Current assignee: Areva NP SAS
Priority date: 2000-06-30
Filing date: 2001-06-20
Publication date: 2002-02-13
Anticipated expiration: 2021-06-20
Also published as: GB2365103B; CH693467A5; FR2811064B1; FR2811064A1; ZA200105388B; GB0115117D0

Abstract

The device of the invention 10 comprises an attachment plate 14 having at least one means for fixing it against the underside 4a of the tube plate 4, which means is intended to be introduced into a hole 6 in the tube plate, a turret 15 comprising a part mounted so that it can rotate about an axis perpendicular to the attachment plate 14 and at least one tool 24 for carrying out interventions in the water box 2 of the heat exchanger and carried by a means for supporting the tool 24 in terms of translation with respect to the rotary part of the turret 15 and means for moving and actuating the tool 24, these means being remote controlled. The device 10 comprises a guide beam 16 mounted so that it can move in terms of translation on the rotary part of the turret 15 in its longitudinal direction 16a, and a carriage 20 for supporting the tool 24 and mounted so that it can move on means of guidance of the beam 16. The device additionally comprises a head plate 36 allowing the attachment plate 14 to be fitted automatically inside the water box from outside the water box by pulling on a lifting cable. The method for carrying out interventions may be implemented in particular for plugging tubes 5 of a steam generator.

Description

2365103 Device And Method For Servicing Heat Exchanger The invention

relates to a device and to a method for carrying out intervention operations in the water box of a heat exchanger and, in particular, of a steam generator of a pressurized-water nuclear reactor. 5 Pressurized-water nuclear reactors comprise a primary circuit in which the pressurized water that cools the nuclear reactor flows, and which generally consists of a number of loops, each of which carries a steam generator which, through exchange of heat between the pressurized water that cools the nuclear reactor and the feedwater, heats up the feedwater and vaporizes it so as to produce steam which is sent to the turbine of the nuclear power station.

Steam generators in pressurized-water nuclear reactors comprise a wrapper of cylindrical overall shape arranged with its axis vertical and in which there is a bundle of heat-exchange tubes and a water box of essentially hemispherical shape constituting the lower part of the steam generator, below the wrapper containing the bundle.

A thick tube plate, arranged horizontally and through which vertical holes arranged in a grid pattern pass, marks the boundary between the upper part of the steam generator wrapper and the water box. The tubes of the steam generator bundle are engaged and fixed in a sealed manner via their end part into the holes in the tube plate. The water box is delimited, on the one hand, by the hemispherical wall constituting the bottom part of the steam generator wrapper and, on the other hand, by the horizontal underside of the tube plate onto which the holes for the passage and fixing of the bundle tubes open.

Each of the tubes of the bundle is bent at its top and has two straight branches the ends of which are engaged in holes passingthrough the tube plate on each side of a partition that divides the water box into two compartments, each connected, by a nozzle, to a pipe of the primary circuit, so that the water for cooling the reactor enters the water box inside one of the 2 compartments, to be distributed into each of the tubes of the bundle, the pressurized cooling water that has flowed through the tubes of the bundle being collected in the second compartment of the water box to be picked up by a pipe of the primary circuit which is connected to the second compartment of the water box.

In order to allow access to the water box, the hemispherical outer casing of the water box has an inspection opening or manhole passing through it in each of the two parts of the hemispherical wall delimiting one compartment of the water box.

The cooling water flowing through the tubes of the bundle in the upper part of the steam generator delimited by the vertical cylindrical wrapper of the steam generator, heats up and vaporizes feedwater which is introduced into the steam generator wrapper in its upper part. The steam formed in the steam generator is collected at the top of the steam generator wrapper. 20 When the nuclear reactor is in operation, the walls of the heat-exchange tubes of the steam generator bundle experience mechanical and thermal stresses which may, after a certain running time, lead to the appearance of cracks or crack initiators. These cracks or crack initiators must be detected so as to avoid any leak of pressurized cooling water into the interior volume of the steam generator wrapper into which the feedwater is introduced.

It is therefore necessary periodically, for example during programmed shutdowns of the nuclear reactor for refuelling the reactor with fuel assemblies, to perform inspections on the steam generator tubes.

When one or more cracked tubes are detected, an intervention operation has to be performed on this or these tubes in order to prevent the risk of leakage when the steam generator is brought back into operation.

3 One of the interventions most commonly performed consists in introducing and fixing a watertight blanking plug into each of the ends of the defective tube, opening into one compartment of the 5 water box.

Use is commonly made of blanking plugs of a mechanical type which comprise a cylindrical shell, the external surface of which may exhibit means of attachment to the inside of the tube that is to be plugged, and an expander means which is moved inside the shell or body of the plug to expand it inside the tube.

The plug has to be fixed by screwing at the end of a fitting tool which inserts the plug in the unexpanded state into the end of the tube, inside the tube plate, and expands the body of the plug in the end part of the tube that is being blanked off.

During a previous operation of inspecting the tubes of the bundle, the underside of the tube plate is marked around the defective tube so that all the ends of defective tubes opening into the compartment of the water box can be plugged from inside the water box.

A similar operation is performed in the second compartment of the water box, so that the defective tubes can be plugged at both ends.

one technique employed for plugging the tubes consists in getting operators working inside the steam generator water box to fit the plugs using a hand tool. This technique has the drawback of making the operators work in an area of the nuclear reactor containing deposits of activated materials which are carried into the water box by the nuclear reactor cooling water flowing in contact with the fuel assemblies in the core. As a result of this, the doses received by the operators may be high, 'even in the case of operations performed very quickly with the minimum presence of each of the operators inside the steam generator water box.

The root of the problem is that a pressurizedwater nuclear reactor steam generator comprises several thousands of tubes and it may be necessary to plug several dozen tubes during a steam generator 5 maintenance operation.

It is therefore necessary to employ a great many operators, each of whom receive high doses of radiation while they are working inside the nuclear reactor water box, and this means that these operators are no longer available to perform other operations in irradiated or contaminated areas.

Furthermore, the manual operations inside the steam generator water box require the use of fully trained and very experienced personnel, to guarantee that the plugging work is carried out to a high standard of quality.

In order to avoid the drawbacks associated with the need to ask operators to enter steam generator water boxes, methods and devices controlled remotely from outside the water box have been conceived of, for placing the plugging tooling under the underside of the tube plate and for operating the tooling in order to plug a tube.

These methods and devices make it possible to reduce the length of time for which operators need to be present in the steam generator water box or even make it possible to eliminate the need for operators to get into the water box.

There has, for example, been proposed the use of a robot arm of an anthropomorphic type which is introduced into the water box through the manhole and which comprises an attachment part which is fixed to the wall of the water box near the manhole. A remotely controlled tube-plugging tool is fixed to the end of the arm, so that it can be moved inside the water box so as to introduce a plug into the end parts of each of the defective tubes identified beforehand.

The plugging device may comprise a means for supplying the tool with plugs so that a great many successive plugging operations can be performed inside the water box compartment into which the anthropomorphic arm is introduced. It is also possible to provide an arm, the end part of which can easily be brought up to the manhole between two successive plugging operations, so that a new plug can be placed on the fitting tool by hand.

Various devices allowing a robot arm to be introduced inside one compartment of the water box through the manhole without the need for operators to be present near the manhole, or partially inside the water box have also been conceived of.

The device for carrying out interventions inside a steam generator water box comprising a robot arm of anthropomorphic type is extremely complex as regards its structure and requires lengthy and difficult operations, particularly to introduce and position it inside the steam generator water box.

After the robot arm and the plugging tooling have been introduced into the water box, all the successive operations of fitting and fixing the plugs inside the end parts of the defective tubes can be controlled remotely, from an intervention station outside the reactor building. In this case, the operators tasked with the plugging operations are not subjected to any dose of radiation during the intervention.

The positioning and plugging operations are monitored remotely, from images provided by at least one video camera carried by the robot arm.

This method and this device therefore offer significant advantages as far as the quality with which plugging can be performed is concerned and in respect of the zero or low radiation doses received by the operators tasked with the plugging operations. However, the device used is very complex and positioning it inside the water box of the steam generator is an operation which may be lengthy and difficult, which means that this method and this device cannot be used profitably unless the number of tubes to be plugged is relatively high, for example several dozen tubes.

The operations of plugging tubes in a steam generator can be carried out only within certain limits, as plugging a high proportion of the tubes of the steam generator will result in an excessive reduction in the heat-exchange area of the steam generator which then has to operate under conditions far removed from its optimum operating conditions.

Particularly in nuclear power stations under French control, therefore, operations of replacing steam generators in their entirety have been performed. Furthermore, the choice and treatment of the alloys used in the tubes of the heat-exchange bundles of steam generators and the in-situ stress -relieving treatments performed on tubes in steam generators have made it possible to limit very significantly the amount of cracks which appear in steam generator tubes.

As a result of this, the number of defective tubes detected that need to be plugged during nuclear power station maintenance operations may be very low, for example of the order of four or five tubes.

In the case of intervention operations for plugging such a low number of tubes, the use of a device involving a robot arm controlled from outside the reactor building may prove expensive and therefore not very profitable.

Devices for performing interventions inside the water boxes of steam generators with a far simpler and more lightweight structure have therefore been envisaged. These can be set in place inside the water box prior to the intervention, in a relatively short length of time, from outside the water box, or with low operator intervention inside the water box.

There have, for"example, been proposed devices for carrying out intervention operations inside a steam generator water box, for example for inspecting and/or plugging tubes, which comprise a plate for attaching the device to the underside of the tube plate, by expanding pegs introduced into the holes in the tube plate, and a turret mounted so that it can rotate on the attachment plate, about an axis perpendicular to the plate, that is to say about an axis perpendicular to the tube plate during the inter-vention. The intervention device also comprises one 'or two telescopic arms which rotate as one with the turret or part of the turret, so that they can be moved in terms of rotation about the axis of the turret, to sweep across one or two annular areas whose width in the radial direction is defined by the travel of the telescopic arm or arms. A device such as this allows an intervention tool or inspection means to be positioned in any tube inside the area or one of the two areas swept by the device with polar positioning of the tooling.

The device can be introduced into the water box through a manhole and set in plate and fixed by means of the attachment plate under the tube plate of the steam generator using a guide rail passing through the manhole.

The arms of the device carrying the tools are equipped with expanding fingers which can be fixed inside holes in the tube plate. The attachment plate can thus be moved remotely from one working position to another using the attachment devices of the arms and the means for moving these arms telescopically.

When such a device is being used to plug tubes, it has been proposed that use be made of an arm mounted so that it can pivot about a horizontal axis at the end of which the plugging tool is fixed and which comprises two attachment heads for attaching the device under the tube plate, one head of which is arranged at a fixed end of the arm and the other of which is placed on a pivoting part of the arm so that the arm can either be attached or released so that it can be moved by pivoting it between a position in which the plugging tool is in a service position in the end of a tube, and a reload or refit position in the opening of the steam 8 generator water box manhole, for reloading or refitting a tool.

These devices have the drawback of generally requiring numerous movements in order to perform operations in a number of tubes distributed across the entire area of the tube plate, which means that these many movements increase the complexity and duration of the operations inside the water box.

Furthermore, positioning the device inside the water box in an initial phase of the intervention is a complex operation which may involve the presence of at least one operator inside the water box.

These devices too can be used only to perform operations, for example inspections, plugging operations or lining inside the end parts of the tubes of the steam generator bundle, from underneath the tube plate.

It may be necessary, in some instances, to have means that allow inspections to be made in other parts of the water box, for example on the partition dividing the water box or in the regions where the partition meets the hemispherical wall of the water box.

The object of the invention is therefore to propose a device for performing intervention operations in the water box of a steam generator comprising a wall of essentially hemispherical shape, through which there passes at least one inspection opening and which is delimited, at its upper part, by an essentially horizontal flat underside of a tube plate through which there pass a number of vertical holes in each of which there is crimped one end of a tube of an exchange bundle of the steam generator, comprising an attachment plate having at least one means for fixing it against the underside of the tube plate, which means is intended to be introduced into a hole in the tube plate, a turret mounted so that it can move on the attachment plate about an axis perpendicular to the attachment plate, at least one tool for performing interventions in the water box, means for supporting 9 and moving the intervention tool in terms of translation with respect to the turret and means for remotely controlling the movement of the turret in terms of rotation and the movement of the intervention tool in terms of translation and the actuation of the intervention tool, this device being of a simple structure, being able to perform a great many interventions in all the areas of the water box with small movements and being able to be introduced rapidly, by simple operations, into the water box without the need for operators to be present inside the water box.

To this end, the means for supporting and moving the intervention tool comprise a guide beam extending in a longitudinal direction, mounted so that it can move in terms of translation on the turret in the longitudinal direction and comprising means for its rectilinear guidance in longitudinal direction and at least one carriage for supporting the intervention tool which is mounted so that it can move on the means of guidance of the guide beam, the device additionally comprising means controlled remotely from outside the water box for moving the beam in terms of translation with respect to the turret and for moving the carriage in terms of translation along the means of guidance of the beam.

In order to allow for a good understanding of the invention, one embodiment of an intervention device according to the invention, its implementation for plugging tubes of a steam generator, and the operations involved in positioning the device inside the steam generator water box will now be described by way of example with reference to the appended figures.

Figure 1 is a view in section on a vertical plane of the lower part of a steam generator comprising a water box in which an intervention operation is being performed using a device according to the invention.

- Figure 2 is a part view in side elevation of a first side of the intervention device in position in the steam generator water box.

Figure 3 is a part view in side elevation of a 5 second side of the device depicted in Figure 2.

Figure 4 is a view in elevation and in part section, on a vertical plane perpendicular to the longitudinal axis of the beam, of the intervention device.

Figure 5 is a partial view from above of the intervention device.

Figure 6 is a view in section and in elevation of the water box of the steam generator during the implementation of a first stage of the positioning of the intervention device under the tube plate of the steam generator.

Figure 7 is a view in elevation and in section showing a second step in the positioning of the intervention device under the tube plate of the steam generator.

Figure 8 is a view in section showing the intervention device in a final phase of the operation of positioning the attachment plate under the tube plate of the steam generator.

Figure 9 is a view in section and in elevation showing the water box of the steam generator during an operation of connecting a tool such as a steam generator tube plugging tool to the carriage of the intervention device, on an end part of the beam of the device of the invention, near the manhole.

Figure 10 is a view from beneath of the tube plate, showing the intervention device during a steam generator tube plugging operation in various positions under the tube plate.

Figure 11 is a view in elevation and in section showing an operation of fitting a plug in a steam generator tube.

Figure 1 depicts the lower part of the steam generator denoted overall by the reference 1 and which comprises an outer wrapper la of cylindrical overall shape, in which the heat-exchange bundle of the steam generator consisting of a collection of tubes 5 is placed.

Each of the tubes 5 of the steam generator heat exchange bundle has the shape of a U and has a bent upper part and two straight branches, the lower ends of which are engaged and fixed in vertically directed through holes 6 in a tube plate 4 separating the upper part of the steam generator containing the bundle of tubes 5 from a lower part delimited by an essentially hemispherical wall 3 constituting the steam generator water box 2. The steam generator water box 2 is bounded at its upper part by the horizontal underside 4a of the tube plate 4.

The steam generator water box 2 is divided into two compartments by a vertical partition 7 arranged along a diametral plane of the tube plate 4 constituting a plane of symmetry, on each side of which the ends of the straight branches of each of the tubes 5 of the steam generator bundle are fixed.

The partition 7 divides the steam generator water box 2 into a first compartment and a second compartment which are connected respectively to an inlet pipe and to an outlet pipe for pressurized-water nuclear reactor cooling water which flows through the tubes 5 of the steam generator bundle between the inlet compartment and the outlet compartment, which compartments are separated by the partition 7.

The plane of section of Figure 1 is a plane parallel to the partition, which means that just one of the two compartments of the water box is visible in Figure 1.

An inspection hole 8 or manhole giving access to the inside of the water box compartment, for example for performing inspection or maintenance operations, passes through the wall 3 of the water box 2.

The manhole 8 can be used in particular for introducing into the steam generator water box 2 an intervention device 10 according to the invention which can be used to perf orm an operation such as a tube plugging operation in the corresponding compartment of the water box. The manhole 8 also allows the passage into the water box of cables 9 for powering and remotely controlling means for moving and introducing the plugging tool used, into the tubes which are being plugged and operating this tool in position inside a tube.

Video cables 9' are connected to cameras 12 and 51 allowing operators to be provided with images of the tube plate 14 on display screens at a control station.

The cables 9 and 91 are connected, outside the water box, to control and display units such as lla and lib at the station controlling the intervention performed in the water box.

The operations control centre may be arranged any distance away from the lower part of the steam generator comprising the water box, the operations inside the water box being viewed by virtue of the environment camera 12 fixed inside the water box near the manhole 8 and aimed at the underside 4a of the tube plate 4 in which the intervention is being performed.

As visible particularly in Figures 1, 2 and 3, the intervention device 10 according to the invention mainly comprises an attachment plate 14 making it possible for the intervention device 10 to befixed under the tube plate 4, a turret 15 fixed to the plate 14 and comprising an axis of rotation 13 perpendicular to the plate 14 and a beam 16 fixed to a rotary part 18 of the turret 15 able to move in terms of rotation about the axis 13 via a beam support 17 mounted so that it can rotate on the rotary part 18 of the turret 15 via a bearing 19 which has an axis of rotation perpendicular to the longitudinal direction 16a of the beam 16 and orthogonal to the axis of rotation 13 of the turret 15. The axis of the bearing 19 is horizontal in all phases of positioning and use of the intervention device.

The beam 16 is mounted so that it can move in the direction of its longitudinal axis 16a on the piece 17, via two sets of rollers 21, the axes of rotation of which are perpendicular to the longitudinal direction 16a of the beam 16, collaborating with runway tracks of the beam 16 which are arranged in the longitudinal direction 16a of the beam. The rollers 21 of each of the sets of rollers have axes arranged in one and the same plane perpendicular to the longitudinal axis 16a of the beam 16, the two sets of rollers being spaced apart by a certain distance in the longitudinal direction 16a so as to allow the beam 16 to be effectively guided and supported.

The device 10 additionally comprises a carriage 20 comprising two sets of running rollers 22 whose axes of rotation, perpendicular to the longitudinal direction 16a of the beam 16, are arranged in two planes perpendicular to the longitudinal axis 16a of the beam and spaced apart in the longitudinal direction 16a.

The rollers 22 of the carriage 20 run along guide rails of longitudinal direction of the beam 16, as will be explained later on.

As visible in Figure 3, a tool holder 23, on which a plug-fitting tool 24 is mounted, may be connected to one end of the carriage 20, via a quick coupling 25 of the type used in machine tools, that is to say a coupling made in two parts which fit together, a first element of which comprises locking balls which are received in a groove in a second element of the coupling.

The tool holder 23 can be coupled to the end of the carriage 20 very quickly simply through coaxial engagement of the two elements of the quick coupling 25 and by pushing in the axial direction.

The device 10 for performing interventions inside the water box of a steam generator additionally comprises a rocking actuator 26, the body of which is mounted so that it can pivot about a horizontal axis on the rotary part 18 of the turret 15 and the rod 26a of which is articulated about a horizontal axis to a rear end of the support piece 17 for the rail 16. By actuating the actuator 26, by moving the rod 26a in the deployment or retraction direction, the beam support 17 and the beam 16 are made to pivot about the horizontal axis of the bearing 19 in one direction or the other so as to move the beam between a position which is inclined with respect to the horizontal plane and a position which is practically horizontal and which is the service position of the beam for carrying out an intervention in a tube of the tube plate using the device of the invention.

At its upper part, along longitudinally directed lateral edges, the beam 16 has two racks 27a and 27b used to drive the beam 16 and the carriage 20, respectively, in terms of translation in the direction 16a.

Mounted on the beam support 17 is a drive device allowing the beam to be moved longitudinally and comprising, for example, at least one pinion or worm meshing with at least one rack. In particular, use may be made of a reduction motor 28a of axis perpendicular to the longitudinal direction of the beam 16, the output pinion 29a of which meshes with the longitudinally directed rack 27a arranged on one of the lateral sides of the upper part of the beam 16.

By rotating the shaft of the reduction motor 28a and the output pinion 29a, the beam 16 is made to move, in one direction or the other, depending on the direction of rotation of the reduction motor 28a, in the longitudinal direction 16a.

The carriage 20 carries a drive device allowing it to be moved longitudinally along the beam and comprising, for example; at least one pinion or worm meshing with at least one rack. In particular, use may be made of a reduction motor 28b, the axis of which is perpendicular to the longitudinal direction 16a of the beam 16 and which comprises an output pinion 29b - is - meshing with the second rack 27b of the beam 16 arranged along the second upper lateral edge of the beam 16, in the longitudinal direction.

By rotating the shaft and the output pinion of the reduction motor in one direction or the other. the carriage 20 is made to move in one direction or the other in the longitudinal direction 16a of the beam.

As visible in Figures 4 and 5, the plate 14 which has the overall shape of a triangle has three expanding pegs 30 for fixing the plate 14 under the underside of the steam generator tube plate 4 and which are arranged in locations near the vertices of the triangular plate 14.

Each of the attachment fingers 30 comprises an expanding sleeve 30a and an expander insert 30b of frustoconical overall shape comprising an actuating rod that can move in the axial direction of the sleeve 30a, this actuating rod being secured to the rod of an actuator 30c carried by the plate 14.

The sleeves 30a of the expanding fixing pegs 30 have a nominal outside diameter very slightly smaller than the inside diameter of the tubes 5 of the steam generator tube bundle in the part which is engaged and crimped inside the holes 6 passing through the tube plate 4. Each sleeve 30a comprises a number of segments in the form of independent cylindrical sectors urged towards each other by a spring; the sectors can be moved one with respect to the next as the expander insert 30b of the chuck is moved in the axial direction to diametrically expand the sleeve 30a and fix the plate whose fingers 30 in the unexpanded state have been already introduced into the end parts of three tubes of the steam generator bundle.

The downwards movement of the rod and of the expander insert 30b allowsthe sleeve 30a to be expanded inside a tube and the upwards movement of the rod of the actuator and of the expander insert 30b allows the sleeve 30a to be released, which can then contract through elasticity so that the plate 14 can be separated from the steam generator tube plate.

The turret 15 comprises an annular piece 15a fixed under the plate 14 which comprises, on its outer face, a toothed wheel 31 having as its axis the axis 13 of the turret and with which there meshes a pinion 32 secured to the output shaft of a rotational-drive reduction motor fixed to the rotary part 18 of the turret 15 which is mounted so that it can rotate about the axis 13 on the piece 15a via a rolling bearing 33.

The reduction motor which drives the pinion 32 is fixed to the rotary part 18 of the turret 15 with its axis vertical, that is to say parallel to the axis 13 of the turret itself perpendicular to the attachment plate 14. Rotating the reduction motor and the pinion 32 in one direction or the other makes it possible to rotate about the axis 13, in one direction or the other, the rotary part 18 of the turret 15 and the beam support 17 and the beam 16 which are mounted on the rotary part 18 of the turret, via the horizontal-axis pivot bearing 19.

The beam 16 has a cross section visible in Figure 4 which is symmetric with respect to an axis of the plane of symmetry of the beam in a longitudinal direction. The beam has a cross section in the overall shape of a I, the perforated web of which has oblong openings in the longitudinal direction spaced uniformly along the length of the beam, and the f langes of which carry the guide tracks for the sets of rollers 21 and 22 for the beam support 17 and the carriage 20, respectively.

The guide tracks of one set of rollers 21 or 22 comprise two tracks, of which the parts for engagement with the rollers, which have a cross section of essentially triangular shape, point towards one another and have longitudinally directed straight edges.

The upper rollers of the sets of rollers 21 mounted on the beam support 17 engage with a first guide track 34 and the lower rollers of the sets of rollers 21 engage with a second guide track 34', of which the triangularsection guide part is arranged facing, in the vertical direction, the corresponding guide part of the f irst guide track 34, the edges of the guide parts of the tracks 34 and 341 being parallel.

The rollers 21 have a groove of triangular cross section for guiding and centring the guide parts of the tracks 34 and 341. The beam 16 rests on the upper rollers of the sets of rollers 21 which, with the lower rollers, guide it in its longitudinal movements.

The upper rollers of the sets of rollers 22 of the carriage 20 engage via a groove of triangular cross section, with a guide part of triangular cross section of an upper guide track 35 and the lower rollers of the sets of rollers 22 are themselves engaged, via their groove of triangular cross section, with a triangular guide part of a lower guide track 35' arranged opposite the guide track 35 in the vertical direction.

The guide tracks 34 and 35 are fixed to the top flange of the beam 16 and the lower tracks 341, 351 are fixed to the lower flange of the beam 16. The carriage rests via the lower rollers of its sets of rollers 22 on the lower guide track 35', the upper rollers 22 guiding the carriage on the upper guide track 35, the guide part of which has an edge facing towards the edge of the guide part of the lower track 351 and parallel to this lower edge.

Figure 5 shows the attachment plate 14 of essentially triangular shape, to which is fixed the turret 15 carrying, via the horizontal-axis bearing 19, the beam support 17 on which the beam 16 is mounted so that it can move in the longitudinal direction 16a.

The tool support 23 is f ixed to the end of the carriage 20 in a configuration parallel to the beam 16.

The various movements of the intervention device which allow the tool 24 to be positioned vertically in line with an end part of any tube of the steam generator comprise rotating about the axis 13 of the turret the assembly consisting of the rotary part 18 of the turret, the beam support 17, the beam 16, the carriage 20 carried by the beam 16 and the tool holder 23 and the tool 24, it being possible for this rotation to have a total travel of 3600, moving the beam 16 in translation in its entirety in the longitudinal direction 16a on the beam support 17, and moving the carriage 20 along the beam 16. The translational travel of the beam essentially corresponds to the total length of the beam in the direction 16a. Moving the carriage in terms of translation along the beam also makes it possible for the carriage, tool holder 23 and tool 24 to be moved in the longitudinal direction 16a along practically the entire length of the beam 16.

is These various movements and, in particular, the double movement of the tool in the longitudinal direction 16a, or double movement, make the tool 24 easier to position in the working position in any tube of the tube plate without moving the attachment plate 14 or, as the case may be, with a very low number of movements.

In addition, mounting the beam support 17 so that it can pivot on the horizontal-axis bearing 19 allows the beam to be orientated inside the steam generator water box, for example so as to change a tool or so as to f it a plug on a plugging tool, in close proximity to the water box manhole.

A complete intervention in the water box of a steam generator, for example for plugging steam generator bundle tubes, will now be described with reference to Figures 1 to 5 and Figures 6 to 9. This intervention involves, first of all, introducing and positioning the intervention device 10 inside the water box. These operations will be described in particular with reference to Figure-s 6 to 9.

As depicted in Figure 6, a positioning plate 36 known as a head plate is first of all positioned and fixed against the underside of the tube plate 4, this head plate allowing the attachment plate 14 of the - 19 intervention device 10 to be positioned under the tube plate 4 quickly and automatically.

Figure 7 depicts the positioning plate or head plate 36 fixed in its service position against the underside 4a of the tube plate 4. The positioning plate 36, or head plate, comprises a support plate 36a on the upper side, or f irst side, of which is mounted, at one end of the support plate, a positioning peg 37 having the shape and size that allows it to be introduced easily into a tube 5 of the steam generator from the underside 4a of the tube plate 4, an expanding fixing finger 38, also projecting vertically above the upper side of the support plate 36a, and bearing stops 39 intended to come into contact with the underside 4a of the tube plate around the opening of a tube 5.

The expanding fixing finger 38 is made in a similar way to the expanding finger 30 of the attachment plate 14. However, the expander insert 38b, of the expanding sleeve 38a of the finger 38 is moved in the axial direction by a rod 38c having a threaded part engaged in a tapped opening of an actuating peg 40 projecting under the support plate 36 and mounted so that it can rotate about a vertical axis on the head plate so that the fixing finger 38 can be expanded by an axial movement of the expander insert 38b secured to the rod 38c, by rotating the actuating peg 40 about its axis so as to move the rod 38c. The actuating peg 40 has a shaped external surface, for example of hexagonal cross section.

On the second side, or underside, of the support plate 36a there is also mounted the yoke from which a pulley 41 is suspended so that it can rotate about a horizontal axis and over which there runs a cable 42 for suspending and lifting part of the intervention device 10 -comprising, in particular, the attachment plate 14 and the beam 16 on which the carriage 20 is mounted. Mounted on the plate 14 so that they can rotate, about axes parallel to the head plate and to the attachment plate and parallel to each other and to the axis of rotation of the pulley 41, are two relay pulleys 43 and 44 over which the cable 42 runs, of which cable the end of the suspension strand running over the second pulley 44 is fixed to a fixing point 45 on the support plate 36a. Thus, when the head plate 36 is fixed under the second side of the tube plate 4, in an arrangement perfectly parallel to the horizontal underside 4a of the tube plate, the attachment plate 14 can be suspended from and lifted up inside the steam generator water box 2 in a configuration which is perfectly horizontal and vertically aligned with the head plate 36, the two vertical strands of the cable 42 defining a fixed vertical plane in which the intervention device can be lifted by pulling on the cable 42 from outside the water box through the manhole 8.

The attachment plate 14 comprises, on its upper side, a guide piece 46 comprising an axial guide opening 47 with a frustoconical inlet part and a prismatic engagement part of hexagonal cross section, the shape and size of which correspond to the shape and size of the actuating and guide peg 40.

When the plate 14 is suspended via the cable 42 from the head plate 36 inside the steam generator water box 2, the axis of the opening 46 is perfectly aligned with the vertical axis of the actuating and guide peg of the head plate 36.

Figure 6 depicts the head plate 36 during positioning and fixing under the tube plate 4, inside the steam generator water box 2. To do this, use is made of a pole 46, to the end of which an automatic screwing device 48 is fixed, this screwing device comprising a control means 48'. The head plate 36 is positioned on the upper part of the automatic screwing device 48 which comprises a hollow screwing tool the cross section of which corresponds to the cross section of the actuating and guide peg 40 of the head plate 36.

The actuating peg 40 is engaged in the hollow screwing piece of the automatic screwing device 48 and the assembly consisting of the end of the pole 47, the automatic screwing device 48 and the head plate 36 resting on the screwing device 48 is introduced into the steam generator water box through the manhole 8.

The head plate 36 rests on the screwing device, in a position such that its support plate 36a is essentially horizontal.

The operations of positioning the head plate 36 are monitored using the environment camera 12 located inside the water box near the manhole. The head plate is lifted up manually on the end of the pole 47 so as to offer up the head plate fixing finger 38 in vertical alignment with the end part of a predetermined tube 5. The positioning peg 37 of the head plate 36 is offered up in line with the end part of a second tube 5 of the steam generator. The.positioning peg 37 allows the head plate 36 to be placed under; the steam generator tube plate 4 in a satisfactory orientation.

The fixing peg 38, which is in a contracted state, is introduced into the end part of the first tube 5 and at the same time the positioning peg is introduced into the end part of the second tube of the steam generator by using the pole 47 to move the head plate 36 in the vertical direction. The head plate is in position when the stops 39 have come into contact with the underside 4a of the tube plate 4 around the first tube 5 of the steam generator.

The screwing device 48 is then actuated remotely, via the control device 48', so as to expand the fixing finger 38. The automatic screwing device 48 is preset so that it effectively fixes the head plate 36 by expanding the fixing finger 38, the screwing device stopping automatically at the end of expansion.

The screwing device 48 is then detached from the actuating finger 40-of the head plate 36 by pulling on the pole 47, and the pole 47 is extracted from the steam generator water box 2 through the manhole 8.

The cable 42 connect ed at one of its ends to the attachment point 45 of the head plate 36 is engaged - 22 on the pulleys 44, 43 and 41, the attachment plate 14 on which the beam 16 is mounted being connected by the cable 42 to the head plate 36 and brought near to the manhole 8, outside the steam generator water box 2.

The strands of cable running over the pulleys 43 and 44 are then passed through the manhole 8.

The attachment plate, to which the beam 16 is fixed, is introduced into the steam generator water box manually, the rail 16 being in an inclined position with respect to the plate 14, as depicted in Figure 7.

The plate 14 to which the beam 16 is fixed is then lifted up into an inclined position inside the water box by pulling on the end strand of the cable 42 running out through the manhole 8.

is As depicted in Figure 8, the beam 16 is made to turn about the axis of the articulation 19 by controlling the actuator 26, so as to place the beam in an essentially horizontal position, that is to say a position with its longitudinal axis 16a in a horizontal plane.

The position of the beam 16 on the beam support and of the carriage on the beam are adjusted in such a way that the load raised by the winch consisting of the cable 42 and the pulleys 41, 43 and 44 is balanced, the beam being in a horizontal position.

The lifting of the attachment plate 14 is continued, the vertical strands of the lifting cable 42 defining a perfectly fixed vertical lifting plane.

In addition, the axis of the centring piece 46 is perfectly aligned with the axis of the peg 40 for positioning and guiding the head plate 36.

Once the intervention device 10 has been lifted, the centring piece 46 engages, via its frustoconical part, on the positioning peg 40 so as to position the attachment' plate 14 with respect to the array of tubes of the tube plate 4, once the device 10 has finished being moved vertically inside the water box. The orientation of the a ttachment plate 14 is also perfectly defined by the fixed vertical plane of lifting of the attachment plate as defined by the strands of cable running through the grooves of the pulleys 43 and 44 secured to the attachment plate. Thus, the three fixing fingers 30 of the attachment plate 14, in the retracted position, engage in the end parts of three tubes of the steam generator bundle.

The positions of the three fixing fingers 30 on the attachment plate 14 correspond to positions of the ends of three tubes of the steam generator bundle, which are arranged in the array of openings in the tube plate.

When the attachment plate 14 has come into abutment against the head plate 36, via the centring piece 46, the fingers 30 are engaged in three tubes of the steam generator bundle in a fixing position, as depicted in Figures 2 and 3. The actuators of the three fixing fingers are then remotely actuated so as to expand them inside the three tubes. The attachment plate is therefore fixed in place under the tube plate 4, as depicted in Figures 2 and 3.

The beam 16 is then moved in terms of translation in its longitudinal direction 16a by remotely actuating the motor 28a secured to the beam support 17, so that one of the ends of the beam reaches a position of abutment at the end of its travel, this end of the beam then being near to the bearing via which the beam support 17 is articulated to the rotary part 18 of the turret 15. The beam is then pivoted into a position like the one depicted in Figure 9 by remotely actuating the actuator 26, so that its rod 26a is retracted into the actuator body. The actuator 26 causes the beam 16 to pivot about the horizontal axis articulation bearing 19, so that the opposite end of the beam to the end near the articulation 19 and near the attachment plate 14 is located near the interior wall of the steam generator water box, near the manhole 8. It may be necessary to rotate the turret 15 about the axis 13 in order to bring the end of the beam 16 into coincidence with the manhole 8.

The carriage 20 which can move in the longitudinal direction of the beam 16 is brought to that end of the beam 16 which is located near the manhole 8. At its front part facing towards the manhole, the carriage 20 comprises the quick coupling element 25a allowing a tool holder 23 which has a complementary quick-coupling element 25b to be fixed to the end of the carriage 20.

The quick coupling element 25b of the tool holder 23 is then engaged manually on the quick coupling element 25a of the carriage 20 to fix the tool holder 23 and the tool 24 to the carriage 20. The carriage 20 can then be moved in the longitudinal direction of the beam 16 to place it in a position which will allow subsequent manoeuvres to be performed with ease.

The beam 16 is then returned to a position in which its longitudinal axis is roughly horizontal by operating the actuator 23 in the direction of deploying the actuator rod 26a. The device 10 for carrying out intervention operations in the water box of the steam generator can then be used to plug tubes of the bundle inside that compartment of the water box in which the intervention device has been fitted.

Prior to the plugging operation, an operation of inspecting the tubes of the bundle has been performed.

After the tubes have been inspected, the ends of the defective tubes which have to be blanked off with a plug are marked.

The positions of the tube ends 5 which have to be plugged may therefore be identified using the environment camera 12 fixed near to the manhole 8 so as to envisage a positioning of the rail 16 and of the carriage 20 on the ral-1 16 that will allow an area close to a f irst tube that is to be plugged to be accessed.

Furthermore, as depicted in Figure 3, a close-up camera 51 is fixed to the carriage 20 to show the area of the tube plate 4 located in line with the end of the tool 24. The beam 16 is positioned facing the area of intervention for plugging a tube 5 by rotating the 5 rotary part 18 of the turret 15 about the axis 13 quickly by actuating the motor that drives the turret until a position is reached that makes it possible, via the carriage 20 or by longitudinal movement of the beam 16, for the tool 24 to be brought into line with the position of the tube that is to be plugged.

The operator has a control for rotating the beam 16 quickly, via the turret, and a control for moving it step by step, so as to rotate the beam in successive steps of small size to refine the position of the tool.

The tool is brought into position vertically in line with the tube 5 that is to be plugged by the operator watching a video image provided by the close-up camera 51 on the screen of the monitor at the control station.

When the operator considers the position of the tool 24 to be satisfactory, he makes the tool holder move so as to introduce the rod of the tool 24 on which a plug 50 is screwed into the end of the tube that is to be plugged.

If the tool centring is not satisfactory, the plug 50 comes into abutment on the tube plate and movement halts. The operator repositions the tool more accurately to perform the operation of introducing the tool rod.

The plugging tool is then operated in order to f it the plug 50 inside the tube 5, in the way which will be explained later on, this operation being performed using the plugging tool.

Figure 10 depicts part of the underside 4a of the tube plate 4 at the upper part of the compartment of the water box of the steam generator in which a plugging operation is being performed.

The beam 16, the carriage 20, the tool holder 23 and the tool 24 are depicted in a f irst position 16 in solid line, in which position the tool 24 can fit a plug in a tube 5 of the steam generator, the end of which tube is located in a first area of the tube plate. Broken line has also been used to depict the respective positions 161, 20', 23' and 241 of the beam 16, the carriage 20, the tool holder 23 and the tool 24 that allows tubes to be plugged in a second area of the tube plate 4.

Finally, broken line has again been used to depict the respective positions 1611, 2011, 23" and 2411 of the beam of the carriage of the tool holder and of the tool that allows a plug to be fitted in an end part of a steam generator tube, in a third area of the tube plate 4.

To move from the position 16 to the position 161, the beam 16 has to be rotated through an angle (x by manoeuvring the turret 15 and moving the carriage 20 towards the axis of rotation 13 of the turret, so as to plug the tube in an area located some distance from the edge of the tube plate, this distance being roughly equal to the distance from the plugging area to the edge of the plate in the first position, because of the off-centred position of the turret with respect to the tube plate 4.

To bring the tool into the position 2411 to allow the plugging of a tube in a peripheral part of the tube plate 4, near the diametral central part of the plate where the partition that divides the water box is located, the beam 16 has to be rotated through an angle P and the beam 16 has to be moved in terms of translation along the beam support in the direction of the peripheral part of the tube plate 4. The carriage 20 has been moved into a position near the opposite end of the beam 16 to the turret 15, which means that the tool, in its position 2411, is at a distance from the turret that is greater than the length of the beam 16.

Tubes distant from the turret 15 by a distance greater than the length of the beam can thus be plugged. Tubes can be also be plugged in areas distant from the turret by a distance shorter than the length of the beam 16, by making joint use of the translational movement of the beam 16 with respect to the turret and of the movement of the carriage in the longitudinal direction of the beam 16. This therefore shows the benefit of the twofold movement in the longitudinal direction of the beam, which has been given the name "double movement".

Furthermore, to move the plugging tool from a position that allows a tube in an area to the right of the central position 161 of the beam depicted in Figure 10 to be plugged, for example from a position such as 24 or 24u to a position located to the left of the central position 161 of the beam, there are various ways of effecting movement.

For example, in order, starting from the position 24 of the tool on the beam in the position 16 depicted in Figure 10, to plug a tube in the lefthand part of the tube plate near the attachment plate 14, the carriage 20 can be moved along the beam in its position 16 to a position near to the second end of the beam 16, and the beam 16 is then moved longitudinally on the turret 15 to place the tool and the tool holder in a position entirely outside the area in which the attachment plate 14 is fixed. The tool 24 fixed into the continuation of the carriage 20 and the tool holder 23 can then easily be moved in the vertical direction so as to cause the plug and the actuating rod of the tool 24 to enter the tube that is being plugged, it not being possible to move the rod of the tool 24 vertically and upwards from the tool holder 23 when the latter is placed under the attachment plate 14.

It can therefore be seen that it is possible to reach practically all the positions of tubes passing through the tube plate 4 with just one carefully chosen position for the attachment plate 14. Of course, the position of the attachment plate 14 for plugging a number of defective holes is determined in advance according to the position of the defective tubes on the tube plate, so that the various plugging operations can be carried out with feasible movements of the elements of the device of the invention. 5 It is just as possible to carry out plugging operations on a small numbers of tubes as it is to carry out plugging operations on a great many tubes distributed across the entire tube plate. When a small number of tubes is being plugged, the operation remains perfectly viable, in so far as the fitting of the intervention device inside one compartment of the steam generator water box can be performed in a very short space of time, for example of the order of 10 to 15 minutes.

is Of course, having plugged the tubes in a first compartment of the water box, the intervention device is removed and taken back out of the water box compartment through operations which are the reverse of those described hereinabove, so that it can then be introduced into the second compartment of the water box.

As depicted in Figure 11, a blanking plug 50 may be fitted in an end part of a tube 5 of a pressurized-water nuclear reactor steam generator in a conventional way using a plug 50 comprising a plug body 50a in the shape of a split sleeve inside which an expander insert Sob is placed, the expander insert Sob comprising a tapped part which is screwed, prior to intervention, onto the end part of the rod 24a of the tool 24.

As indicated above, the tool holder 23 makes it possible, by vertical movement, to introduce the plug into a tube in a position located a certain distance from the internal side 4a of the tube plate 4. The plug 50 introduced into the -tube 5 is held in place by an end part of a tubular support of the tool 24 in which the rod 24a is mounted so that it can slide.

The plug is expanded by actuating a hydraulic actuator pulling on the rod 24a of the tool 24 on the end of which the expander insert Sob is screwed. The expander insert Sob of frustoconical shape moves downwards and expands the sleeve 50a. The rod 24a is then made to rotate so as to unscrew it and detach it 5 from the expander insert Sob of the plug.

The tool holder and the tool 24 are then made to move downwards to completely extract from the tube 5 the upper part of the tool 24 comprising the rod 24a.

If a second tube-plugging operation needs to be performed, the beam is moved by rotating the turret and by pivoting about the articulation bearing 19, using the actuator 26, so as to bring the opposite end of the beam to the turret up close to the manhole 8. The beam is also moved in terms of translation with respect to the turret so as to move as far away as possible from the turret 15 its end which has to be placed in the opening of the manhole 8.

The carriage 20 is then moved to the end of the beam, into the opening of the manhole 8, so as to access the end of the rod 24a of the tool, onto which a new plug 50 is screwed.

It may thus be seen that the main advantages of the device and of the method of intervention according to the invention are that they make it possible to obtain great flexibility as regards the movements of the tool inside the water box by combining the translational movements of the beam with respect to the rotary part of the turret and of the carriage carrying the tool, in the longitudinal direction of the beam.

These combined movements add to the rotational movements of the beam about the axis of the turret to yield any working position of the tool inside the water box.

Furthermore, mounting the beam on the turret to allow pivoting about -a horizontal axis makes it possible for the end of the beam and the carriage to be placed near to the manhole of the compartment of the water box so that the tool can be reloaded or so that the tool can be changed, without the need to remove the attachment plate. The possibility of pivoting of the beam also allows the intervention device to be introduced into the water box manually without difficulty.

The joint use of a head plate or positioning plate comprising a pulley and a lifting cable for a winch and an attachment plate comprising winching pulleys for the passage of the cable allows the attachment plate to be installed very easily once the head plate, whose size and mass are small, has been positioned beforehand. The attachment plate can be perfectly guided to position and fix it under the tube plate.

Fixing the tool, possibly via a tool holder, on a carriage that can move in the longitudinal direction of the beam, makes it considerably easier for the tool to be fitted, by comparison with a device in which the tool is fixed to an arm such as a telescopic arm moving in terms of translation with respect to a turret fixed under the tube plate. The invention is not strictly limited to the embodiment which has been

described.

Thus, the various elements that make up the intervention device, for example the attachment plate, the turret, the beam and the carriage, may be produced in a form that differs from the one described.

The means of moving the various moving parts of the device may consist of rack and pinion or rack and worm systems, electric reduction motors, pneumatic motors and/or pneumatic or hydraulic actuators. The means driving the movement are connected to control means located outside the water box by any means such as cables or piping which may be grouped together into a bundle or harness in the form of a connecting element known as an umbilical, which allows the various cables and pipes to pass in a grouped fashion through the manhole.

Likewise, the video cables connected to the cameras for viewing the inside of the water box may be associated with the cables for controlling and powering the drive means inside a connecting duct.

The device and the method according to the invention can be used not only for plugging tubes but also for many other interventions inside the water box of a steam generator, such as inspecting or testing tubes of the bundle of the steam generator, the tube plate, or the hemispherical wall, known as the bowl, of the water box, testing the welds of the partition plate, fitting sleeves for repairing tubes or testing welds at the ends of the tubes of the bundle. These interventions can be performed without needing operators to be present at any time inside the steam generator water box. is In particular, the device can be introduced, positioned and fixed inside the water box entirely from outside the water box, certain manual operations merely requiring operators to be present near the manhole for a short period of time. 20 The invention applies to any heat exchanger comprising a water box delimited at its upper part by a tube plate through which there pass openings into which the tubes of the heat exchanger are introduced and fixed.

Claims

1. Device for carrying out intervention operations in the water box (2) of a heat exchanger comprising a wall (3) of essentially hemispherical shape, through which there passes at least one inspection opening (8) and which is delimited, at its upper part, by an essentially horizontal flat underside (4a) of a tube plate (4) through which there pass a number of vertical holes (6), in each of which there is inserted and fixed one end of a tube (5) of an exchange bundle of the steam generator, comprising an attachment plate (14) having at least one means (30) for fixing it against the underside (4a) of the tube plate (4), which means is intended to be introduced into a hole (6) in the tube plate (4), a turret (15) which has a rotary part (18) mounted so that it can rotate with respect to the attachment plate (15) about an axis (13) perpendicular to the attachment plate (14), at least one tool (24) for carrying out interventions in the water box (2), means for supporting and moving the intervention tool in terms of translation with respect to the turret (15) and means for remotely controlling the movement of the turret in terms of rotation and the movement of the invention tool (24) in terms of translation and actuating the intervention tool (24), characterized in that the means for supporting and moving the intervention tool (24) comprise a guide beam (16) extending in a longitudinal direction (16a), mounted so that it can move in terms of translation on the rotary part (18) of the turret (15) in the longitudinal direction (16a) and comprising means (34, 34, 35, 351) of rectilinear guidance in the longitudinal direction (16a) and at least one carriage (20) for supporting the intervention tool (24) ihich is mounted so that it can move on the means of guidance (35, 351) of the guide beam (16), the intervention device (10) additionally comprising means controlled remotely from outside the water box (2), for moving the beam (16) in terms of translation with respect to the rotary part (18) of the turret (15) and for moving the carriage (20) in terms of translation along the means of guidance (35, 351) of the beam (16).

2. Device according to Claim 1, characterized in that the beam (16) is mounted so that it can move in its longitudinal direction (16a) on a beam support (17) which is itself mounted so that it can pivot on the rotary part (18) of the turret (15) about an axis orthogonal to the axis (13) of the turret (15), the device additionally comprising a means (26) of pivoting the beam support (17) with respect to the rotary part (18) of the turret (15).

3. Device according to Claim 2, characterized in 15 that the means (26) of pivoting the beam support (17) with respect to the.rotary part (18) of the turret (15) consists of an actuator (26), the body of which is articulated to the rotary part (18) of the turret (15) and the rod (26a) of which is articulated to the support (17) of the beam (16).

4. Device according to any one of Claims 1 to 3, characterized in that the beam (16) comprises a first set of guide tracks (34, 341) of longitudinal direction (16a), intended to collaborate with at least one set of rollers (21), the axes of rotation of which are perpendicular to the longitudinal direction (16a) of the beam and which are mounted so that they can rotate on the beam support (17) connected to the rotary part (18) of the turret (15).

5. Intervention device according to Claim 4, characterized in that the beam (16) comprises a second set of guide tracks (35, 351) of longitudinal direction, intended to collaborate with at least one set of rollers (22) mounted so that they can rotate on the carriage (20).

6. Device according to any one of Claims 1 to 5, characterized in that the means for moving the beam (16) in terms of translation with respect to the turret (15) comprise at least one pinion or worm meshing with at least one rack (27b) arranged in the longitudinal direction (16a) of the beam (16) and rotated by a reduction motor (28a) f ixed to a beam support (17) on which the beam (16) is mounted so that it can move in terms of translation in the longitudinal direction (16a).

7. Intervention device according to any one of Claims 1 to 6, characterized in that the means of moving the carriage (20) on the guide means (35, 351) of longitudinal direction (16a) of the beam (16) comprise at least one pinion or worm meshing with at least one rack (27b) of longitudinal direction (16a) of the beam (16), which pinion or worm is rotated by a reduction motor (28b) secured to the carriage (20).

8. Intervention device according to any one of Claims 1 to 7, characterized in that it additionally comprises a positioning plate or head plate (36) comprising at least one means (38) of fixing the head plate (36) against the underside (4a) of the tube plate (4), which means is intended to be introduced into and f ixed in an end part of a steam generator tube (5), projecting from a first side of the head plate (36), a pulley (41) for relaying a cable (42) fixed with its axis of rotation parallel to the head plate (36) on the opposite side of the head plate (36) to the fixing means (38), or second side, and a point of attachment (45) of one end of the cable (42) to the second side of the head plate (36), and also a positioning peg (40) projecting from the second side of the head plate (36), the attachment plate (14) comprising two relay pulleys (43, 44) mounted so that they can move about axes parallel to the attachment plate (14) and over which the cable (42) runs so as to suspend the attachment plate (44) from the positioning plate (36) f ixed in place against the underside (4a) of the tube plate (4) so as to position it under the tube plate (4) by pulling on the winch cable (42) that runs over the pulley (41) of the positioning plate (36) and over the pulleys (43, 44) of the attachment plate (14), the attachment plate (14) additionally comprising a guide piece (46) intended to be engaged over the guide peg (40) at the end of the lifting of the attachment plate (14) up inside the steam generator water box (2).

9. Device according to Claim 8, characterized in that the means of guidance (40) of the head plate (36) consists of a finger which has a shaped external surface for engaging with a screwing tool (48) used to manipulate a rod (38c) for expansion of a sleeve (38a) of the means (38) of fixing the head plate (36) inside a tube (5) of the steam generator bundle by means of an expander insert (38b).

10. Device according to either one of Claims 8 and 9, characterized in that the head plate (36) additionally comprises, projecting from its first side, a guide peg (37) in a tube (5) of the steam generator, for fitting the head plate (36) under the tube plate (4).

11. Device according to any one of Claims 1 to 10, characterizedin that it additionally comprises a first video camera (12) or environment camera fixed inside the steam generator water box on the wall (3) of the water box (2) near the inspection hole (6), and a second video camera (51) for zooming in on a part of the water box (2) of the steam generator which is mounted on a tool holder (23) holding the tool (24).

12. Device according to any one of Claims 1 to 8 and 11 to 14, characterized in that the intervention tool (24) is a tool for plugging tubes which is mounted so that it can move on the carriage (20) via a tool holder (23) allowing the tool (24) holding a plug for plugging a tube (50) to be moved in a direction perpendicular to the longitudinal axis (16a) of the beam (16).

13. Method for carrying out intervention operations in the water box (2) of a steam generator comprising a wall (3) of essentially hemispherical shape through which there passes at least one inspection opening (8) and which is delimited, at its upper part, by an 36 - essentially horizontal flat underside (4a) of a tube plate (4) through which there pass a number of vertical holes (6), into each of which one end of a tube (5) of the steam generator (1) is crimped, characterized in 5 that.

- a head plate (36) is introduced into the water box through the inspection opening, this head plate (36) comprising, on an upper first side, at least one first means (38) of fixing the head plate under the tube plate (4) via a hole (6) in the tube plate and, on a second side, or underside, at least one pulley (41) of an attachment means (45) for the guidance and attachment of a lifting cable (42) and a means of guidance (40) projecting downwards from the second side of the head plate (36), the means (38) for fixing the head plate (36) is introduced into a hole (6) in the tube plate (4), and a device (38b, 38c) for expanding the fixing means (38) is actuated remotely to lock it in the hole (6) in the tube plate (4) so as to fix the head plate (36) against the underside (4a) of the tube plate (4), - a tooling support is introduced into the water box (2) through the inspection hole (8), this tooling support comprising an attachment plate (14) comprising at least a second means (30) of fixing the attachment plate under the tube plate (4), a turret (15) having a part (18) mounted so that it can rotate on the attachment plate (14) about an axis (13) perpendicular to the attachment plate (14), a guide beam (16) comprising means (34, 341, 35, 351) of guidance in a longitudinal direction (16a), which is mounted so that it can pivot on the turret (15) about an axis orthogonal to the axis (13) of rotation of the rotary part (18) of the turret (15) and so that it can move in terms of translation on the moving part (18) of the turret (15) in a longitudinal direction (16a) perpendicular to the axis of rotation of the rotary part (18) of the turret (15) and remote- controlled means (31, 28a, 29b) for moving the rotary part (18) of 37 - the turret (15) in terms of rotation and for moving the beam (16) in terms of translation in the longitudinal direction (16a), - the attachment plate (14) and the beam (16) are lifted up inside the water box (2) by pulling on one end of the lifting cable (42) fixed to the head plate (36) and running over the pulley (41) of the head plate (16) and over a set of pulleys (43, 44) of the attachment plate (14), through collaboration between at least one means of guidance (46) of the attachment plate and the means of guidance (40) of the head plate (36), the attachment plate (14) is set in place against the head plate (36) and the at least one fixing means (30) of the attachment plate (14) is engaged in a hole (6) in the tube plate (4), the attachment plate (14) is fixed against the head plate (36) in an arrangement parallel to the tube plate (4), - one end of the beam (16) is placed near the inspection opening (8) by pivoting and translational movement, - a carriage (20), mounted so that it can move on the longitudinal means of guidance (35, 351) of the beam (16), is placed at the end of the beam (16) near the inspection opening (8), - the intervention tooling (24) is fixed to the carriage (20), and the tooling (24) is placed in a place of intervention in the water box (2) by moving the beam (16) by rotation of the rotatable part (18) of the turret (15) and in translation in the longitudinal direction (16a) and by moving the carriage (20) in the longitudinal direction.

14. Method according to Claim 13, where the intervention is an operation of plugging tube (5) end parts of the steam generator bundle from the underside (4a) of the tube plate (4), characterized in that a tube plugging tool (24) is placed in turn in axial 38 - alignment with each of the tubes (6) in which the end of the tube (5) is to be plugged, and a rod (24a) of the tool (24) carrying a plug (50) at its end is introduced into the end part of each of the tubes in turn, after which the plug (50) is expanded inside the tube (5), and the rod (24) is separated, by unscrewing, from the plug (50) in its expanded state for plugging the tube (5), the beam (16) being moved by pivoting so as to position one end of the beam (16), where the carriage (20) carrying the tool (24) is placed, near the inspection opening (8) of the water box (2) of the steam generator (1) so as to f it the rod (24a) of the tool (24) with another plug (50) between two successive operations of plugging two successive tubes (5) of the steam generator bundle.