WO2009103922A2

WO2009103922A2 - Device and method for detecting and measuring the clogging ratio of water passages in the secondary circuit of a pressurised-water nuclear reactor

Info

Publication number: WO2009103922A2
Application number: PCT/FR2009/050232
Authority: WO
Inventors: Bernard Sartre; Sébastien HERMOSILLA-LARA; Marc Piriou; Stéphane BOURGOIS
Original assignee: Areva Np
Priority date: 2008-02-18
Filing date: 2009-02-13
Publication date: 2009-08-27
Also published as: WO2009103922A3; FR2927724B1; FR2927724A1; FR2927723A1; FR2927723B1

Abstract

The invention relates to a device for detecting and measuring the clogging ratio, by deposits having a high magnetite concentration, of water passages of a secondary circuit in the strut plates of a steam generator, characterised in that the device includes a probe (20) including a Foucault-current detector (50) connected to a body (21) bearing two magnetic-field detectors (24) and containing at least one magnetic dipole (30) generating a continuous magnetic field coaxial to said body (21) and having a north-south orientation that coincides with the longitudinal axis of the body (21).

Description

Apparatus and method for detecting and measuring the clogging rate of water passages in a secondary circuit of a pressurized water nuclear reactor.

The present invention relates to a device and a method for detecting and measuring the clogging rate of the water passages of a secondary circuit in spacer plates of a steam generator of a pressurized water nuclear reactor.

The pressurized water nuclear reactors comprise steam generators which provide heating and vaporization of feed water by the heat transported by the water under cooling pressure of the reactor core. The pressurized water reactors comprise, on each of their primary branches, a steam generator having a primary part in which circulates water under reactor cooling pressure and a secondary part receiving feed water which is heated. and vaporized progressively and emerges from the secondary part of the steam generator in the form of steam which is sent to a turbine associated with the nuclear reactor to drive an alternator producing the electric current.

Such steam generators comprise an outer envelope, called a pressure envelope, of generally cylindrical shape arranged with its vertical axis and integral with a substantially horizontal tubular plate whose lower face or inlet face constitutes a wall of the water box supply of the steam generator, in pressurized water constituting the primary fluid.

The steam generator also comprises a bundle of U-shaped curved tubes each having two straight parallel branches, the ends of which are fixed in holes passing through the tubular plate between the lower face of the tube plate and the upper face from which the tubes of the tube. beam are held in the secondary part of the steam generator in which an inner envelope, called the beam envelope, arranged in a coaxial position inside the pressure envelope, defines an annular space with this pressure envelope.

The tubes of the bundle are furthermore maintained in a regular arrangement in transverse planes perpendicular to the axis of the bundle, by spacers plates which are distributed at regular distances according to the height of the beam.

The spacer plates are traversed by a network of openings which is identical to the network of openings of the steam generator tube plate.

These spacer plates which hold the tubes of the bundle of tubes in the bundle envelope, have secondary water passages along the tubes of the bundle, through the thickness of each spacer plate and which are in the form of lobes, called tri-or quad-folate passages.

During the operation of the steam generator, the feed water circulating in contact with the outer surface of the tubes of the bundle and inside the secondary circuit of the reactor, is charged with impurities of various nature and in particular of the magnetite type, which can be deposited in the form of sludge in different parts of the steam generator and in particular in the interstices between the tubes of the bundle and the passages of the spacer plates which are reserved to allow the circulation of the cooling water around the tubes of the beam.

Deposits accumulating between the passages of the spacer plates and the outer surface of the tubes of the bundle progressively clog those passages preventing a circulation of cooling water and can produce some embedding of the tubes in the passages, so that the The tubes are rigidly fixed in the spacer plate and can no longer move in the axial direction common to the passage and the tube and are also immobilized in the radial directions.

Under these conditions, the thermal efficiency of the steam generator is largely degraded and at the extreme, the tubes may be stressed against the spacer plates and crack causing then a primary water leak in the circuit secondary, which would lead to the shutdown of the nuclear reactor.

The object of the invention is therefore to propose a device and a method making it possible, by simple means, to implement, detect and estimate the clogging rate of the water passages in the spacer plates of the secondary circuit of the generators of the steam from nuclear power plants under pressure water. The subject of the invention is therefore a device for detecting and measuring the level of clogging by deposits having a high concentration of magnetite type, and water passages of a secondary circuit in spacer plates of a steam generator. a pressurized water nuclear reactor, said steam generator comprising a bundle of primary water circulation tubes, whose vertical branches are held in said water passages of the spacer plates, characterized in that it comprises a probe comprising at least one eddy current detector connected to a generally cylindrical body bearing, on its external face, at least two magnetic field detectors arranged coaxially and solidly to said body and containing at least one magnetic dipole producing a continuous magnetic field coaxial with this body and whose north-south orientation coincides with the longitudinal axis of the body, at least one of said at least two magnetic field detectors being positioned substantially at one of the ends of the magnetic dipole and said eddy current detector and said at least two magnetic field detectors being connected by connection means to a system for amplifying and visualizing variations of the signals transmitted by these detectors during the displacement of the probe in a tube of the steam generator at the passages to be examined in the spacer plates.

According to other features of the invention:

said at least one magnetic dipole is formed by at least one permanent magnet,

said at least one permanent magnet is formed by a circular base cylinder,

said at least one permanent magnet has a length greater than its diameter,

said at least one magnetic dipole is formed by at least one coil powered by a direct current,

said at least one coil contains a field amplifier bar,

said field amplifier is a ferrite bar,

said at least two detectors are disposed substantially at the ends of said at least one magnetic dipole, said at least two detectors are disposed substantially between two magnetic dipoles mounted in opposition,

the detectors are positioned one close to the other,

the detectors are each formed by a coil comprising a number of turns less than 200,

the magnetic field detectors are formed by a multitude of point sensors distributed regularly over at least one circumference of the body of the probe,

the body of the probe comprises, at its periphery, centering means for maintaining said body substantially in the longitudinal axis of the tube in which said probe moves,

the body of the probe comprises an accelerometer or a speed meter connected to a preamplifier,

the body of the probe is made of a non-magnetic material,

the body of the probe is connected to displacement means in the tube,

the eddy current detector is connected to the body by a flexible rod,

the eddy current detector is disposed upstream of the body with respect to the direction of movement of the probe in the tube, and

the eddy current detector operates at low frequency, less than or equal to 100 KHz, and preferably in absolute mode.

The invention also relates to a method for detecting and measuring the level of clogging by deposits having a high concentration of magnetite type, water passages of a secondary circuit in spacer plates of a steam generator. a pressurized water nuclear reactor, using a probe as defined above, characterized in that:

at least one probe is introduced into at least one tube of the tube bundle of the steam generator,

said at least one probe is moved at a determined speed in said at least one tube,

a correlation is made between the signals delivered by said magnetic field detectors and those delivered by said current detector of Foucault to determine the extreme values of the clogging rate of each passage in the spacer plates, and

the variations of the signals transmitted by the eddy current detector and by said magnetic field detectors are amplified and visualized during the displacement of the at least one probe in the tube at the level of each passage to be examined in the spacer plates.

According to other features of the invention:

said at least one probe is moved at a high and constant speed, and

according to the signals transmitted by said eddy current detector and by said magnetic field detectors, a distribution distribution map is established for at least one spacer plate of the steam generator.

The features and advantages of the invention will become apparent from the following description, given by way of example and with reference to the appended drawings, in which:

FIG. 1 is a schematic perspective view of a steam generator of a pressurized water nuclear reactor,

FIG. 2 is a partial schematic top view of a spacer plate of a steam generator of a pressurized water nuclear reactor,

FIG. 3 is a diagrammatic view in vertical section of a passage of a tube of the bundle of tubes in a spacer plate,

FIG. 4 is a schematic view in perspective and partially broken away of a first embodiment of a probe of the detection and measurement device, according to the invention,

FIG. 5 is a schematic view in perspective and partly broken away of a second embodiment of a probe of the detection and measuring device according to the invention,

FIG. 6 is a schematic view of a tube of a steam generator, partially broken away and showing the position of a probe in line with a spacer plate, and

FIG. 7 is a diagram showing the field lines generated by the two permanent magnets of the probe of the detection and measurement device, according to the invention; In FIG. 1, there is shown the lower part of a steam generator of a pressurized water nuclear reactor, generally designated 1.

The steam generator 1 comprises, in a conventional manner, a substantially cylindrical pressure envelope 2 inside which a bundle shell 3 containing a tube bundle 4 of the steam generator 1 is arranged in a coaxial manner.

The tube bundle 4 consists of a very large number of U-shaped tubes 5, each having two straight branches which are engaged and fixed at their end in a tubular plate 6 fixed to the lower part of the generator pressure envelope. Steam 1.

The pressure envelope 2 is connected to a hemispherical bottom delimiting a two-part water box.

Inside the envelope of the bundle 3 are fixed in successive positions according to the height of the beam of the spacer plates 8 intended to hold the branches of the tubes 5 of the bundle 4 to prevent them from vibrating during the operation of the steam generator .

Each of the spacer plates 8 is pierced with a network of openings similar to the network of openings passing through the tubular plate 6 in which the ends of the tubes 5 of the bundle 4 are fixed. The straight branches of the tubes 5 of the bundle are engaged in the aligned openings of the spacer plates 8 spaced in the longitudinal direction of the tube 5.

Thus and as shown in FIG. 2, each spacer plate 8 is traversed by openings 10 through the tubes 5 of the bundle 4 of the steam generator and these openings have, in the embodiment shown in this figure, a shape with four lobes called quadh-folies. These openings may have a three-lobed shape called tri-folate, as shown in FIG. 5.

As shown in FIG. 6, each opening 10 comprises between the lobes 10a edges which thus ensure the maintenance of the corresponding tube 5 in transverse directions. These edges 10a form between them and with the outer wall of this tube 5, a passage 11 of the supply water of the steam generator flowing in the vertical direction from bottom to top. The circulating water in the secondary circuit and inside the secondary part of the steam generator 1, in contact with the outer surface of the tubes 5 of the bundle 4, is charged with impurities which form deposits (FIG. ) on the spacer plates 8, in particular in the passages 11 between the tubes 5 and the openings 10 of these spacer plates 8 which must maintain the tubes 5 and the passage of the feed water in contact with the outer surface tubes 5.

These deposits have a high concentration of magnetite type and it has been found that the clogging of the passages 11 begins with the lower part, that is to say from the lower face of the tube plate 8, and progresses upwards by accumulation. as the operation of the reactor.

During a shutdown of the nuclear reactor, after a certain period of operation of this reactor, it is necessary to be able to detect the presence of these deposits and also to measure the rate of clogging in the passages 11 of the spacer plates 8.

For this purpose, the device according to the invention consists of a probe shown in Figs. 4 and 5 and designated by general reference 20.

The probe 20 comprises a body 21 of generally cylindrical shape and preferably made of a material having no magnetic characteristics. The body 21 is closed at one of its ends by a conical-shaped head plug 22 and, at the other end thereof, by a tail plug 23.

These plugs, respectively 22 head and tail 23, are fixed on the body 21 by any suitable means, such as by screwing or gluing.

The body 21 of the probe 20 comprises, at its periphery, centering means 31 for maintaining said body substantially in the longitudinal axis of the tube 5 in which this probe 20 moves.

As shown in FIG. 4, the centering means are formed by a ring 31 comprising at each of its ends, a ring 31 has elastic to ensure self-centering of the body 21 in the tube 5.

The body 21 of the probe 20 carries on its external surface, at least two magnetic field detectors 24 disposed coaxially and integral with said body 21. Each detector 24 is constituted by a coil disposed in a groove 25 hollowed in the wall and extends transversely to the longitudinal axis of the body 21. The detectors 24 are connected by conductive wires 26 extending over the along the body 21 to the tail cap 23. The son extend in a central channel 26a formed inside said body to the tail cap 23. This tail cap 23 has an extension 27 located in the axis of the body 21 and provided at its free end with a connector 28 connected to the conductive son 26 of the detectors 24. The extension 27 is constituted by a flexible tube or by any other appropriate element, allowing the passage of the probe 20 in portions of bent tubes.

The body 21 has an inside diameter slightly smaller than the inside diameter of the tube 5.

The body 21 contains at least one magnetic dipole 30 (Figs 4 and 5) producing a continuous magnetic field.

According to a first embodiment, said at least one magnetic dipole is formed by at least one permanent magnet 30 coaxial with this body 21 and whose north-south orientation coincides with the longitudinal axis of said body 21.

The permanent magnet 30 is formed by a circular base cylinder and has a length greater than its diameter.

According to a second embodiment shown in FIGS. 4 and 5, said at least one magnetic dipole is formed by at least one permanent magnet 30 preferably comprising two elementary permanent magnets, respectively 30a and 30b.

The orientation of the poles of the two elementary permanent magnets 30 and 30b is opposite.

By way of example, the orientation of the poles of the elementary permanent magnets 30a and 30b, in the direction of the head cap 22 towards the tail cap 23, is North-South for the magnet 30a and South-North for the like 30b.

In general, at least one of said at least two detectors 24 is positioned substantially in line with one of the ends of the magnetic dipole.

According to a preferred embodiment, each detector 24 is placed substantially between the elementary permanent magnets 30a and 30b and in particular at the right of one end of an elementary permanent magnet 30a. and 30b, these elementary magnets being magnetized along the longitudinal axis and mounted in opposition.

According to one variant, each elementary permanent magnet 30a or 30b may also be composed of two elementary permanent magnets and whose orientation of the poles is North-South, North-South and South-North and South-North, South-North.

According to a third embodiment, said at least one magnetic dipole is formed by at least one coil, not shown, fed by a direct current.

This type of winding is generally formed by a cylindrical support on which an electric wire is wound externally with spirally contiguous turns from the north pole to the south pole.

The coil which is fed by a direct current can be mounted on a field amplifier, such as for example a ferrite bar placed inside the winding.

But, the preferential solution lies in at least one permanent magnet as magnetic dipole because it does not require a power supply and moreover the permanent magnet produces a strong magnetic field.

In the embodiment shown in Figs. 4 and 5, the body 21 comprises two detectors 24 disposed between two magnetic dipoles each formed by an elementary permanent magnet 30a and 30b.

The two detectors 24 are arranged close to each other.

The two detectors 24 are identical and they are each formed by a coil having a maximum of 200 turns.

According to a variant shown in FIG. 5, the magnetic field detectors are formed by multielements, such as for example micro-coils 40 disposed at the periphery of the body 21 and distributed regularly along two parallel circumferences of the body 21 of the probe 20.

These multielements can also consist of Hall effect probes or probes type GMR (magneto-resistance giant effect).

As shown in Figs. 4 to 6, the probe 20 also comprises a detector 50 with eddy currents of known type. This detector 50 comprises a tapered end-piece 51 and is disposed at a determined distance from the head cap 22 upstream of the body 21 with respect to the direction of movement of the probe 20 in the tube 5, as it is will see later. The detector 50 is connected to the head cap 22 of the body 21 by a flexible tube 52.

The eddy current detector 50 is connected to the connector 28 by conducting wires 50a, which are arranged in the flexible tube 52, in the central channel 26a of the body 21, and in the flexible tube 27 to said connector 28.

Preferably, the detector 50 operates at a low frequency, less than or equal to 100 KHz, and preferably in absolute mode rather than in differential mode for the simplicity of its signal and for its less influence at the inter-biting distance, so for better accuracy.

By way of example, the preferred geometry of the eddy current detector 50 is of the order of 2 mm for the thickness of the coils and of the order of 3 mm for the inter-winding space.

Finally, the probe 20 may also include an accelerometer 53 or a speedometer disposed inside the body 21, connected to a preamplifier 54, as shown in Figs. 4 and 5.

The connector 28 is connected by appropriate means of known type to a system for amplifying and displaying or recording the variations of the signals transmitted by the detectors 24.

In the following, the operation of the probe 20 will be described with a permanent magnet 30, the operation with a coil powered by a direct current being identical.

Detection and measurement of the clogging rate by magnetite-type deposits in the water passages 11 of the secondary circuit of a spacer plate 8 is carried out as follows.

From one of the steam generator water boxes (shown in Fig. 1), a probe 20 is introduced into a tube 5 of the bundle 4. This probe 20 is connected to the amplification and visualization system of the variations of the signals transmitted by the detectors 24.

The probe 20 is moved by appropriate means of known type, such as a pole, or by means of a shooter placed outside the water box of the steam generator, inside the tube 5 which it is desired to examine the clogging of the passages 11 of the spacer plates 8 in which said tube 5 is placed.

This probe 20 is moved in the tube 5 at a high and constant speed and the accelerometer 53 and its preamplifier 54 make it possible to give an indication of the constancy of the speed of displacement of the probe 20 in the tube 5 to the right of the spacer plates 8 or to enslave the speed of displacement of this probe to a constant value so as to increase the accuracy of the detection and measurement of the clogging rate of the passages 10 of these spacer plates 8.

The magnet 30 placed in the body 21 of the probe 20 emits a continuous magnetic field.

During the passage of the probe 20 at a spacer plate 8, the eddy current detector 50 passes first through this spacer plate 8 which sends a signal which is amplified and visualized on a screen so as to detect and characterize where a deposit of magnetite could have occurred.

After the passage of the detector 50 at the spacer plate 8, the two detectors 24 and the permanent magnet 30 pass through this spacer plate 8.

If no magnetite deposit is present, the field lines of the permanent magnet 30 are modified and a current appears in the detectors 24.

The detectors 24 are sensitive only to variations in the field lines of the permanent magnet 30. These variations are related to the fact that the permanent magnet 30 moves in the tube 5 and detects the ferromagnetic bodies. Thus, in conventional steam generators, the spacer plates 8 have a magnetic behavior and are thus detected by the detectors 24.

For spacer plates 8 having no magnetic behavior, if there is no magnetite, there will be no modified field lines and therefore no detection by the detectors 24.

On the other hand, if the passage 11 is partially clogged by a deposit of magnetite, during the circulation of the probe 20 at this passage 11, the field lines of the permanent magnet 30 are differently modified, which makes it appear in FIG. the detectors 24 a different current. The signal thus emitted is amplified and visualized thus indicating the presence of a deposit 15 at the level of the spacer plate 8.

Depending on the amplitude of the signals thus tansmitted, an operator can determine the filling rate of a passage 11 of a spacer plate 8.

If the passage 11 is completely clogged by a magnetite deposit, or if the deposition is uniform along the tube 5, during the circulation of the probe 20 at this passage 11, the eddy current detector detects and measures the presence of deposit 15 in said passage 11 while the field lines of the permanent magnet 30 would not have been sufficiently modified to show in the detectors 24 a different current.

The transmitted signals can also be recorded.

The probe 20 is moved over the entire height of the tube 5 thus making it possible to detect or not the presence of deposits 15 in the successive passages of this tube 5 in the different spacer plates 8.

The amplitude of the signals emitted by the magnetic field sensors 24 increases as the speed increases.

Likewise, the deposit detection sensitivity for the probe 20 also increases as the speed increases. For example, when the speed of movement of the probe 20 is multiplied by two, the detection sensitivity of this probe is also multiplied by two.

In a general manner, the device according to the invention makes it possible to carry out a detection and a differential measurement thanks to the presence and the disposition of the two detectors 24, instead of a simple detection.

The location of at least one of the two detectors 24 at the edge of the permanent magnet 30 and, preferably, with a detector 24 mounted on the edge of each elementary permanent magnet 30a and 30b magnetized along the longitudinal axis and mounted in opposition one with respect to the other, makes it possible to benefit from the variations of the radial field. Thus, the field is generally radial because the field lines f are curved at the ends, as shown in FIG. 7.

The assembly formed by said at least one permanent magnet 30 and the two detectors 24 constitutes a leakage flow probe which, depending on the type of clogging in the passages of the spacer plate, makes it possible to obtain two different calibration curves for determining and measure the clogging rate. The eddy current detector 50 provides an indication for determining the curve to be selected and a correlation between the signals of the leakage-flux detectors 24 and those of the eddy current detector 50, to measure the clogging rate with great precision.

Several probes 20 can be used simultaneously in different tubes 5 of the bundle of tubes 4 in order to detect and measure the clogging rate of the passages of several tubes 5 at the same time to map the fouling of each spacer plate 8.

The device according to the invention thus makes it possible, by inexpensive and simple means to implement, to detect the location and to rapidly measure the clogging rate of the water passages of a secondary circuit in the spacer plates of a generator. of steam to determine if cleaning of the passages of these plates is necessary.

The invention is applicable to the detection and measurement of the clogging rate by deposits of magnetic material in passages of any steam generator or heat exchanger comprising a tube bundle maintained by transverse plates in which are provided water passage openings.

Claims

1.- Device for detecting and measuring the level of clogging by deposits (15) having a high concentration of magnetite type, passages (11) of water of a secondary circuit in spacer plates (8) of a steam generator (1) of a pressurized water nuclear reactor, said steam generator (1) comprising a bundle (4) of primary water circulation tubes (5), whose vertical branches are maintained in said passages (11) of the spacer plates (8), characterized in that it comprises a probe (20) forming at least one eddy current detector (50) connected to a generally cylindrical body (21) carrying, on its external face, at least two magnetic field detectors (24) arranged coaxially and solidly to said body (21) and containing at least one magnetic dipole (30) producing a continuous magnetic field, coaxial with said body (21) and whose orientation north-south coincides with the longitudinal axis of the body (21), at least one of said at least two magnetic field detectors (24) being positioned substantially at one of the ends of the magnetic dipole (30) and said eddy current detector (50) and said at least two two magnetic field detectors (24) being connected by connecting means (26, 28) to a system for amplifying and displaying the variations of the signals transmitted by said detectors (50, 24) during the displacement of the probe (20). ) in a tube (5) of the steam generator (1) at each passage (11) to be examined in the spacer plates (8).

2. - Device according to claim 1, characterized in that said at least one magnetic dipole is formed by at least one permanent magnet (30).

3. - Device according to claim 2, characterized in that said at least one permanent magnet (30) is formed by a circular base cylinder.

4. - Device according to claim 2 or 3, characterized in that said at least one permanent magnet (30) has a length greater than its diameter.

5. - Device according to claim 1, characterized in that said at least one magnetic dipole (30) is formed by at least one coil supplied with a direct current.

6. - Device according to claim 5, characterized in that said at least one coil contains a field amplifier bar.

7. Device according to claim 6, characterized in that said field amplifier is a ferrite bar.

8. Device according to any one of the preceding claims, characterized in that said at least two detectors (24) are arranged substantially in line with the ends of said at least one magnetic dipole (30).

9. Device according to any one of claims 1 to 7, characterized in that said at least two detectors (24) are disposed substantially between two magnetic dipoles (30) mounted in opposition.

10. - Device according to any one of claims 1 to 7, characterized in that the detectors (24) are positioned close to each other.

11. - Device according to any one of the preceding claims, characterized in that said at least two magnetic field detectors (24) are each formed by a coil having a number of turns less than 200.

12. - Device according to any one of the preceding claims, characterized in that said at least two magnetic field detectors (24) are formed by a plurality of point sensors distributed regularly over at least one circumference of the body (21). of the probe (20).

13. - Device according to any one of the preceding claims, characterized in that the body (21) of the probe (20) comprises, at its periphery, centering means (31) for maintaining said body (21) substantially in the longitudinal axis of the tube (5) in which said probe (20) moves.

14. - Device according to any one of the preceding claims, characterized in that the body (21) of the probe (20) comprises an accelerometer or a speed meter (53) connected to a preamplifier (54).

15. - Device according to any one of the preceding claims, characterized in that the body (21) of the probe (20) is of a non-magnetic material.

16. - Device according to any one of the preceding claims, characterized in that the body (21) of the probe (20) is connected to displacement means in the tube (5).

17. Device according to any one of the preceding claims, characterized in that the eddy current detector (50) is connected to the body (21) by a flexible tube (52).

18. Device according to any one of the preceding claims, characterized in that the eddy current detector (50) is arranged upstream of the body (21) with respect to the direction of movement of the probe (20) in the tube ( 5).

19. Device according to any one of the preceding claims, characterized in that the eddy current detector (50) operates at low frequency, less than or equal to 100 KHz, and in absolute mode.

20. - Method for detecting and measuring the level of clogging by deposits (15) having a high concentration of the magnetite type, passages (11) of water of a secondary circuit in spacer plates (8) of a steam generator (1) of a pressurized water nuclear reactor, by means of a probe (20) according to any one of the preceding claims, characterized in that:

at least one probe (20) is introduced into at least one tube (5) of the tube bundle (4) of the steam generator (1),

said at least one probe (20) is moved at a predetermined speed in said at least one tube (5),

a correlation is made between the signals delivered by said magnetic field detectors (24) and those delivered by said eddy current detector (50) to determine the extreme values of the clogging rate of each passage (11) in the spacer plates (8), and

the variations of the signals transmitted by said eddy current detector (50) and by said magnetic field detectors (24) are amplified and visualized during the displacement of said at least one probe (30) in said at least one tube (5) at each passage (11) to be examined in the spacer plates (8).

21. The method of claim 20, characterized in that said at least one probe (20) is moved at a high and constant speed.

22. - Method according to claim 20 or 21, characterized in that depending on the variations of the signals transmitted by said detector (50) with currents of Foucault and said magnetic field detectors (24), is established a distribution map deposits (15) for at least one spacer plate (8) of the steam generator (1).