FR2983337A1 - Probe for inspecting e.g. tubes of spacer plates of steam generator of pressurized nuclear reactor, has sensor and detector that are connected to amplification and visualization system to realize variations of signals - Google Patents

Abstract

The probe (20) has an elongated body (21) comprising an eddy current sensor (24) for detecting and measuring thickness of clogging of an external wall of a tube to be inspected and for detecting metallurgical defects in the wall. A magnetic field detector (30) detects and measures clogging level by deposits having high magnetite concentration. The sensor and the detector are connected to an amplification and visualization system by a connection unit to realize variations of signals transmitted by the sensor and the detector. An independent claim is also included for a method for inspecting tubes and waterways of spacer plates of a steam generator of a pressurized nuclear reactor.

Description

The present invention relates to a probe for inspection of tubes and water passages in plates. The invention relates to a probe for inspecting tubes and water passages of the spacer plates of a steam generator of a pressurized-water nuclear reactor. spacers of a steam generator of a pressurized water nuclear reactor. The invention also relates to a method for inspecting tubes and water passages in spacer plates of a steam generator of a pressurized water nuclear reactor using such a probe. The pressurized water nuclear reactors comprise steam generators which provide heating and vaporization of feed water by the heat transported by the cooling water of the reactor core.

The pressurized water reactors have on each of their primary branch, a steam generator having a primary portion in which circulates water under reactor cooling pressure and a secondary portion receiving feed water which is heated and progressively vaporized 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 pressure envelope, of generally cylindrical shape, arranged with its vertical axis and secured to a substantially horizontal tube plate whose lower face or inlet face constitutes a wall of the box. supply water 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 parallel straight branches between them whose ends are fixed in holes passing through the tubular plate between the lower inlet face of the tube plate and the upper outlet face. from which the tubes of the bundle are held in the secondary part of the steam generator in which an inner envelope, called the bundle envelope, arranged in a coaxial position inside the pressure envelope, delimits an annular space with this envelope pressure.

The tubes of the beam are further maintained in a regular position in transverse planes perpendicular to the axis of the beam, by spacer plates which are distributed at regular distances along the beam height. 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 lobe-shaped, 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 formed between the tubes of the bundle and the passages of the spacers plates reserved for them to allow the circulation of the cooling water around the tubes 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 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 that causes the shutdown of the nuclear reactor. Similarly, the deposits foul the outer surface of the tubes after a certain time of operation of the steam generator may also affect the thermal efficiency of the steam generator. In addition, during the operation of the steam generator, the tubes of the beam are subjected to very significant stresses of mechanical, hydraulic and thermal origin. Some parts of these tubes are very sensitive to corrosion and wear caused by contacting these tubes with the pressurized water constituting the primary fluid of the reactor and with the supply water of the steam generator. These stresses can cause in some tubes of the steam generator, the appearance of cracks or microcracks. It is therefore necessary to perform, during the shutdown of the nuclear reactor, inspections to detect these cracks or fissures. Thus, three main types of control are usually performed: - the measurement of the clogging rate of the spacer plates of the steam generator, - the measurement of clogging of the outer wall of the tubes, and - the search for cracking indication, corrosions, wear or deformation in the tubes of the steam generator. Until now, the operators use for each of these types of control, a specific dedicated probe. Therefore, each control operation requires the successive passage of at least two different probes in a given tube to acquire all the parameters, which increases the duration of the control operations and subjects the operators to a significant dosimetry. In addition, the length of the sensor for detecting the clogging of the water passages of the spacer plates does not allow its passage through the portions of the tubes of small radius of curvature, located in the center of the beam.

Finally, the accuracy of the results is subject to a constant rate of passage of the probe, which is difficult to guarantee in the right part of the tubes, and not respected when passing the curved portions where it is necessary to slow down to avoid damaging the probe corresponding. The purpose of the invention is to propose an inspection probe and a method for implementing this probe making it possible to improve the quality and the speed of the controls carried out during the shutdowns on the bundles of tubes of the steam generators. and reduce the dosimetry of the operators involved, while allowing a 100% control of all tubes in the tube bundle of the steam generator. The subject of the invention is therefore an inspection probe for tubes and water passages in spacer plates of a steam generator of a pressurized water nuclear reactor, characterized in that it comprises a body of elongate form comprising an eddy current sensor, on the one hand, for detecting and measuring the thickness of fouling of the outer wall of the inspected tube and, on the other hand, for detecting metallurgical defects in the wall of this tube and a magnetic field detector for detecting and measuring the clogging rate by deposits having a high concentration of magnetic type, water passages of the spacer plates, the eddy current sensor and the magnetic field detector being connected by connection means to a system for amplifying and displaying the variations of the signals transmitted by said sensor and said detector.

According to other characteristics of the invention: the eddy current sensor is placed in front of the magnetic field detector with respect to the direction of movement in the tube to be inspected; the magnetic field detector comprises two elementary permanent magnets of polarity opposed and a single magnetic sensor placed between said magnets, - the single magnetic sensor is Hall-type or magneto-resistive effect type (GMR) or giant magneto-impedance type (GMI) - the magnetic field detector comprises two elementary permanent magnets of opposite polarity and two coils each associated with one of said permanent magnets, - each permanent magnet has a length less than its diameter, and - the eddy current detector operates at a low frequency, less than or equal to 100 KHz, and in absolute mode for the detection and measurement of the fouling thickness of the outer wall of tubes.

The invention also relates to a method for inspecting tubes and water passages in spacer plates of a steam generator of a pressurized water nuclear reactor, using a probe as mentioned above. , characterized in that: - the probe is introduced into a first tube to be inspected by the steam generator, - the probe is moved into said tube, - the variations of the transmitted signals are amplified and visualized simultaneously, on the one hand by the eddy-current sensor for detecting and measuring fouling of the outer wall of the inspected tube and for detecting metallurgical defects in the wall of this tube and secondly for the magnetic field sensor for detecting and measuring the rate clogging by deposits having a high concentration of magnetite type, water passages, and - the operation is repeated in each tube of the steam generator. According to another characteristic of the method, as a function of the variations of the signals transmitted by the eddy current sensor and by the magnetic field detector, a distribution map of the fouling of the deposits of the outer walls of the tubes is simultaneously established. metallurgical of these tubes and deposits in the water passages 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 accompanying drawings, in which: - Figure 1 is a schematic perspective view of a generator FIG. 2 is a partial top schematic view of a spacer plate of a steam generator of a pressurized water nuclear reactor, FIG. schematic view in vertical section of a portion of a tube of tube bundle with the passage of this tube in a spacer plate, - Figure 4 is a schematic elevational view and partially in longitudinal section of an inspection probe according to the invention, and - Figures 5 and 6 are two diagrams of two embodiments of a magnetic detector of the inspection probe, according to the invention. FIG. 1 shows the lower part of a steam generator of a pressurized water nuclear reactor, generally designated by the reference numeral 1. The steam generator 1 comprises, in a conventional manner, an envelope of pressure 2 of substantially cylindrical shape within which is arranged, coaxially, a bundle 3 containing a bundle of tubes 4 of the steam generator 1. The bundle of tubes 4 consists of a very large number of tubes 3 bent U-shaped, each having two straight legs which are engaged and fixed at their ends in a tubular plate 6 fixed to the lower part of the pressure jacket of the steam generator 1. The pressure envelope 2 is connected to a hemispherical bottom delimiting a water box in two parts. The tubes 3 of the bundle of tubes 4 are held in spacer plates 8 so as to prevent them from vibrating during operation of the steam generator.

Each of the spacer plates 8 is pierced with an array of openings similar to the network of openings passing through the tubular plate 6 in which the ends of the tubes 3 of the bundle 4 are fixed. The straight branches of the tubes 3 are engaged in the aligned openings. spacer plates 8 spaced in the longitudinal direction of the tubes 3.

Thus, as shown in FIG. 2, each spacer plate 8 is traversed by openings 10 through which the tubes 3 of the bundle 4 of the steam generator pass, and these openings have in the embodiment shown in this figure, a shape comprising four lobes called quadri-folies. These openings may have a three-lobed shape, called tri-folies.

Conventionally, each opening 10 comprises, between the lobes, edges 10a which thus ensure the maintenance of the corresponding tube 3 by transverse directions. These edges 10a form between them and with the outer wall of this tube 3, a passage 11 (Figure 3) 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 3 of the bundle 4, is charged with impurities which form deposits 15 (FIG. 3) on the spacer plates 8, in particular in the passages 11 between the tubes 3 and the openings 10 of these spacer plates 8 which must maintain the tubes 3 and the passage of the feed water in contact with the outer surface of the tubes 3.

These deposits have a high concentration of magnetite type and it has been found that the clogging of the passages 11 is located in the lower part, that is to say from the lower face of the spacer plate 8. Under these conditions, the thermal efficiency of the steam generator is largely degraded and, in the extreme, the tubes 3 may be stressed to the right of the spacer plates 8 and to crack causing then a primary water leakage in the secondary circuit which causes the shutdown of the nuclear reactor. Similarly, these deposits shown schematically by reference 16 in Figure 3 can also foul the outer surface of the tubes 3 and after a certain time of operation of the steam generator, disrupt the thermal efficiency of the steam generator. In addition, during the operation of the steam generator, the tubes 3 of the beam 4 are subjected to very large stresses of thermal, hydraulic and mechanical origin. Parts of these tubes are very sensitive to corrosion and wear caused by contacting these tubes with the pressurized water constituting the primary flow of the reactor and with the supply water of the steam generator. These stresses can cause in some tubes 3 of the steam generator, the appearance of cracks 17 or microcracks. During a shutdown of the nuclear reactor, after a certain operating time of this reactor, three types of control are generally carried out: - the detection of deposits 15 and the measurement of the clogging rate of the passages 11 of the spacer plates 8, - the detection of deposits 16 and measurement of the fouling of the outer wall of the tubes 3, and - the search for possible metallurgical defects 17 in the tubes 3 of the steam generator.

These different detections are carried out by means of an inspection probe designated by the general reference 20 and shown schematically in FIG. 4. The probe 20 is formed by a body 21 of generally elongate shape and preferably made of a material having no magnetic characteristic.

The body 21 of the probe 20 comprises, at its front part, with respect to the direction of displacement in the tube 3 to be inspected, a nose 22 allowing the centering of this body 21 in said tube 3 in order to maintain said body substantially in the axis of the tube in which this probe 20 moves. The body 21 of the probe 20 contains a known type of eddy-current sensor 24, the purpose of which is, on the one hand, to detect the deposits 16 on the outer surface of the tube. 3 tube inspected and measure the thickness of these deposits 16 and, secondly, to detect metallurgical defects 17 in the wall of this tube 3. The sensor 24 is covered with a resin forming a protective layer 25. The nose 22 and the eddy current sensor 24 are interconnected by a flexible tube 23 or by any other appropriate element, allowing the passage of the probe 20 in bent portions of the tube 3. A centering ball 26 is placed on the flexible tube 23 between the nose 22 and the eddy current sensor 24. This centering ball 26 and the nose 22 have an outer diameter slightly smaller than the inside diameter of the tube 3 of the tube bundle 4 in order to maintain the body 21 of the probe 20 substantially in the longitudinal axis of the tube 3 in which The body 21 of the probe 20 also contains a magnetic field detector 30 whose purpose is to detect and measure the clogging rate by deposits having a high concentration of magnetic type, water passages. The magnetic field detector 30 is covered with a resin forming a protective layer 31. The eddy current sensor 24 and the magnetic field sensor 30 are interconnected by a flexible tube 32 or by any other suitable element, allowing the passage of the probe 20 in bent portions of tubes 3. One or more balls of centering 33 are optionally mounted on the flexible tube 32. Preferably, the eddy current sensor 24 is placed in front of the magnetic field sensor 30 with respect to the direction of movement in the tube 3 to be inspected. A reverse arrangement is also possible. According to a first embodiment shown in FIG. 5, the magnetic field detector 30 comprises two elementary permanent magnets 35 of opposite polarity and a single magnetic sensor 36 placed between said magnets 35. The single magnetic sensor 36 is of the effect type Hall or magneto-resistance type with giant effect (GMR) or magneto-giant impedance type (GMI). As shown in FIG. 5, each permanent magnet 35 has a length less than its diameter and, with respect to the direction of movement of the probe 20 in the inspected tube 3, the orientation of the poles of the first magnet is North-South and orientation of the poles of the second South-North magnet. In another example, the orientation of the first magnet is South-North and the orientation of the second magnet is North-South. Each permanent magnet 35 has a central orifice 37 for the passage of conductive wires 29 coming from the eddy current sensor 24. According to a second embodiment shown in FIG. 6, the magnetic field detector 30 also comprises two elementary permanent magnets 35 of opposite polarity and two coils 38 each associated with one of said permanent magnets 35 and supplied with a direct current. In this case also, each permanent magnet 35 has a length less than its diameter and, with respect to the direction of movement of the probe 20 in the tube 3 inspected, the orientation of the poles of the first magnet is North-South and the orientation poles of the second magnet is South-North. Each permanent magnet 35 has a central orifice 37 for the passage of conductive wires 29 (Figure 4) from the eddy current sensor 24.

The distance between the eddy current sensor 24 and the magnetic field sensor 30 is of the order of 150 mm. The body 21 of the probe 20 has, at its end opposite the nose 22, a connector 40 connected to the son 29 of the eddy current sensor 24. This connector 28 is also connected to conducting wires 39 coming from the magnetic field detector 30. The connector 40 is connected to the body 21 of the probe 20 by a flexible tube 41, or by any other member allowing the passage of the body 21 in bent portions of the tube 3. The sensor 24 and the detector 40 are connected by appropriate means of known type, not shown, to a system for amplifying and displaying or recording the variations of the signals transmitted by this eddy current sensor 24 and by this magnetic field detector 30. Preferably, the eddy current sensor 24 operates at a low frequency, less than or equal to 100 KHz and, preferably, in absolute mode rather than in differential mode for a better accuracy of the detection and measurement of the deposits which foul the outer surface of the tubes. Other frequencies and other modes are used simultaneously for the detection of metallurgical defects.

The probe 20 is moved by appropriate means of known type, such as for example a pole, or by means of a shooter placed outside the water box of the steam generator, within the tube 3 that one wishes inspected. The magnets 35 of the magnetic field detector 30 placed in the body 21 of the probe 20 emit a continuous magnetic field. During the passage of the probe 20 at a spacer plate 8, the eddy current sensor 24 traverses first this spacer plate 8 which sends a signal which is amplified and displayed on a screen, not shown, so as to detect and to characterize where a magnetite deposit may have occurred.

After the passage of the sensor 24 at the spacer plate 8, the magnetic field detector 30 passes through this spacer plate 8. If no deposit 15 is present, the field lines of the two permanent magnets 35 are modified and a current appears in the magnetic sensor 36 or in the coils 38.

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 magnets 35 are differently modified, which makes it appear in the sensor magnetic 36 or in the coils 38 a different current. The signal thus emitted is amplified and visualized indicating the presence of a deposit 15 at the spacer plate 8. Depending on the amplitude of the signals thus transmitted, an operator can determine the clogging rate of a passage 11 of a plate 8. Transmitted signals can also be recorded. The amplitude of the signals is insensitive to the speed of the probe 20 in the tube 3 inspected when the single magnetic sensor 36 is of the Hall effect type or of the giant effect magnetoresistance type (GMR) or giant magnetoimpedance type (GMI type) ). In the case where the magnetic field detector 30 comprises two elementary permanent magnets each associated with a coil, a signal analysis method makes it possible to dispense with the speed of the probe 20 in the tube 3 to be inspected.

The measurement of the fouling of the external wall of the tube 3 inspected is performed by the eddy current sensor 24. This eddy current sensor 24 generates a sinusoidal magnetic field which induces eddy currents in the inspected tube 3 and in the deposit 16 adhering to the outer wall of the tube. The presence of this deposit 16 disturbs the eddy currents so that an operator can measure the thickness of this deposit 16 at the position of the eddy current sensor 24.

Conventionally, the eddy current sensor 24 is used to perform a deposition detection 16 or cracks 17 may be present in the tube 3 inspected. Several probes 20 can be used simultaneously in different tubes 3 of the bundle of tubes 4 in order to simultaneously inspect several tubes 3 to draw up a map of the fouling of each spacer plate 8 and the fouling of the outer wall of the tubes 3. The inspection probe according to the invention has the advantage of presenting an insensitivity of the measurement to many influential parameters, such as, for example, the speed of movement of the probe, the presence of fouling near the spacer plates, which degrade the performance of the process. This inspection probe offers the possibility of being able to control the tube bundle tubes in their entirety by simultaneously performing the three checks, which results in a gain in time and dosimetry.

Claims (1)

CLAIMS1.- Inspection probe tubes (3) and water passages (11) in spacer plates (8) of a steam generator (1) of a pressurized water nuclear reactor, characterized in that it comprises a body (21) of elongate shape comprising, an eddy current sensor (24), on the one hand, for detecting and measuring the thickness of fouling of the outer wall of the tube (3). ) to inspect and, on the other hand, to detect metallurgical defects in the wall of this tube (3) and a magnetic field detector (30) for detecting and measuring the clogging rate by deposits having a high concentration of magnetite type, water passages (11), said eddy current sensor (24) and said magnetic field sensor (30) being connected by connection means to an amplification and visualization system of the variations of the signals transmitted by the sensor (24) and the detector (30). 2. A probe according to claim 1, characterized in that the eddy current sensor (24) is placed in front of the magnetic field detector (30) with respect to the direction of movement in the tube (3) to be inspected. 3. A probe according to claim 1 or 2, characterized in that the magnetic field detector (30) comprises two permanent magnets (35) of opposite polarity and a single magnetic sensor (36) placed between said magnets (35). 4. A probe according to claim 3, characterized in that the single magnetic sensor (36) is Hall type or magneto-resistive effect type giant (GMR) or giant magneto-impedance type (GMI). 5. A probe according to claim 1 or 2, characterized in that the magnetic field detector (30) comprises two permanent magnets (35) of opposite polarity and two coils (38) each associated with one of said permanent magnets (35). . 6. A probe according to any one of claims 3 to 5, characterized in that each permanent magnet (35) has a length less than its diameter. 7. A probe according to any one of claims 1 to 6, characterized in that the eddy current sensor (24) operates at low frequency, less than or equal to 100 KHz, and in absolute mode for the detection and measurement the thickness of the fouling of the outer wall of the tubes. 8.- Method for inspecting the tubes (3) and the water passages (11) of the spacer plates (8) of a steam generator of a pressurized water nuclear reactor, by means of a probe ( 20) according to any one of the preceding claims, characterized in that: - the probe (20) is introduced into a first tube (3) to be inspected by the steam generator, - the probe (20) is moved into the tube ( 3), the variations of the signals transmitted on the one hand by the eddy current sensor (24) are amplified and visualized simultaneously in order to detect and measure the fouling of the outer wall of the tube (3) to be inspected and for detecting the metallurgical defects in the outer wall of this tube (3) and, secondly, by the magnetic field detector (30) for detecting and measuring the clogging rate by deposits having a high concentration of magnetite type, water passages (11), and - the operation is repeated in each tube (3) of the generator of steam. 9. A process according to claim 8, characterized in that depending on the variations of the signals transmitted by the eddy current sensor (24) and the magnetic field detector (30), a distribution map of fouling of the outer walls of the tubes (3), cracks of these tubes (3) and deposits in the water passages (11) for at least one spacer plate (8) of the steam generator.