JPH07218474A - Underwater eddy current tester - Google Patents

Abstract

PURPOSE:To enhance the workability and test accuracy at a time when the measurement of the thickness of the oxide film on the surface of a material to be tested such as a fuel rod and the detection of the surface damage of the material to be tested are performed in the water of a fuel pool by utilizing an eddy current. CONSTITUTION:A chasis 7, a pair of upper and lower frames 5, 6 fixing the chasis 7 to a fuel handle 25 and an operation head 100 moving along the fuel rod 26 of the fuel handle in an up-and-down vertical direction between the frames 5, 6 and also moved in the lateral direction crossing the up-and-down vertical direction at a right angle and a before-and-behind direction are provided and a test coil 10 and a standard coil 13 are attached to the operation head 100 and a sensitivity calibrating test piece 12 is provided in the vicinity of the operation head 100. An air sump is provided to the chasis 7 and feed screws 17, 20 moving the operation head 100 in the up-and-down vertical direction and the lateral direction are provided to the chasis 7 and two motors 16, 19 driven by the screws are arranged to the operation head 100 in a left-and-right symmetric state. A Manganin wire is used in the test coil 10 and guide rollers are provided above and under the test coil 10 to be held by a coil spring 11 and a slide rod.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current test which is one of non-destructive inspection methods, and more particularly, to a flaw detection test by remote operation in water such as in a fuel storage pool of a nuclear reactor or a nuclear power plant. The present invention relates to an underwater eddy current test device for performing a measurement test stably and accurately.

[0002]

2. Description of the Related Art The eddy current flaw detection method, which is one of the nondestructive inspection methods, is widely used for inspecting material flaws as well as measuring coating films on material surfaces. The principle is that when a coil excited by an alternating current from an eddy current flaw detector is brought close to a test material that is an electric conductor, an eddy current is generated in the test material due to an alternating magnetic field formed by the coil. The new magnetic field created by this eddy current interferes with the magnetic field of the coil and consequently changes the impedance of the coil.

When the test material has a flaw, or when the eddy current changes due to a change in the distance between the test coil and the test material, the impedance of the coil changes due to the change. Therefore, by measuring the change in the impedance of the coil, it is possible to detect a material flaw or measure the gap between the coil and the test material.

The structure of a general eddy current test apparatus is shown in FIG. 6, and usually comprises two test coils or a test coil and a standard coil, an eddy current flaw detector, a test coil operating device and a control device. The eddy current flaw detector 43 is provided with a bridge circuit 33 including two coils 29 and 30 and impedance elements 31 and 32, and an alternating current is supplied from a bridge power supply 34. Bridge circuit 3 associated with impedance change of test coil 29 or 30
The output voltage e ₀ of No. ₃ is amplified by the amplifier 35 and then phase-detected by the phase signals supplied from the phase-shift circuits 36 and 37 to be decomposed into two components having different phases by 90 °, and the phase detectors 38 and 39, respectively. And signal processing devices 40, 41
And is displayed on the display unit 42.

In order to perform an underwater test, the test coil operating device 44 is used underwater and is remotely operated by the control device 45 from the outside.

The eddy current test is classified into two methods depending on how the two coils are used. That is, one is a method called a self-comparison method and the other is a standard comparison method.

The self-comparison method has two coils placed close to each other on the surface of the test material and provides a signal due to the difference in impedance caused by the difference in state between two adjacent points in the test material. . This method is not easily affected by background signals such as changes in the characteristics of the material that change slowly, and is suitable for detecting minute scratches in the material.

In the standard comparison method, of the two coils, one is called the test coil and is placed on the surface of the test material, and the other is called the standard coil and is placed on the surface of the standard test piece. This method is suitable for measuring the wall thickness of slowly changing materials because the change in the test material is measured based on the standard test piece.This method is used to measure the oxide film thickness of fuel rods for nuclear power generation. Is going on.

Not only the oxide film thickness but also various film thicknesses are calibrated in advance or periodically. Calibration is usually performed at two or more points using a test piece of which film thickness is known. A method for calibrating the zero point will be described.

In the bridge circuit according to the standard comparison method, the standard coil is placed on the standard test piece, and the test coil is placed on the test material to measure the thickness of the oxide film. Oxide film thickness 0 before or during measurement
The zero point calibration is performed by placing the test coil on the surface of the (zero) zero point calibration test piece.

Measurement of the oxide film thickness of fuel rods in the fuel pool of a nuclear power plant by such a method has been conventionally performed. For example, JP-A-60-46401, JP-A-62-119497, and JP-A-63-1382.
No. 02, etc. are known, but the positioning control of the test coil is mainly a method in which the test coil is attached to the tip of a long rod, and the tester manually lowers it and operates it. Buoyancy was not considered so much. In addition, the measurement system including the test coil is calibrated in the atmosphere, and then the test coil is placed in water.
In addition, the standard coil in the standard comparison method is placed in the atmosphere and the test coil is placed in water, and fluctuations in water temperature or differences between air temperature and water temperature cause errors in measured values. Was measured and corrected.

[0012]

As described above, in the conventional underwater eddy current test apparatus used by remote control in water, the weight of the apparatus is large and the balance between weight and buoyancy in water is not taken into consideration. In addition, it is difficult to handle and operate in water, and the device supporting mechanism is large and heavy.

Further, if the test sensitivity is calibrated in the atmosphere, it is affected by the difference between the air temperature and the water temperature, which causes a measurement error.
If the standard test piece of the standard comparison method is placed in the air and only the test coil is placed in water, this will again be a measurement error due to the effect of the temperature difference. Further, if there is a difference between the temperature of the surface of the test material and the water temperature, a temperature difference will occur between the test coil and the standard coil, causing a measurement error.

Further, in the conventional test coil holding system,
Even if the test coil is simply brought close to the flat test material surface,
It was difficult to make the two contact at a right angle with stability.

An object of the present invention is to eliminate such conventional defects and improve operability and test accuracy.

[0016]

The above object of the present invention is to make the chassis portion, which is a main structural portion of the underwater eddy current testing device, have a hollow structure, and to use this as an air reservoir to generate buoyancy in water. In addition to the chassis, a water-tight case of the electric motor is used as an air reservoir to generate buoyancy, and the electric motors, which are the main components of the operating device of the underwater eddy current test device, are arranged symmetrically to balance the This is accomplished by attaching vertical and horizontal feed screws to each electric motor so that the test coil can be freely scanned.

Further, the standard test piece set on the standard coil is placed in water close to the test coil, and the sensitivity calibration test piece provided near the test coil is set close to the material to be tested. This is accomplished by allowing the test coil to be calibrated near the material under test.

The conductor of the test coil in the underwater eddy current tester can be achieved by using an electric wire such as a manganin wire having a very small temperature coefficient of electric resistance as compared with a copper wire.

In order to stably contact the test surface and the surface of the test coil at a right angle, two guide rollers are arranged above and below the test coil and held by a coil spring and a slide rod.

[0020]

In the underwater eddy current testing apparatus of the present invention, the chassis of the test coil operating device is made hollow, and this is used as an air reservoir to generate buoyancy and reduce the underwater weight of the device, thus facilitating handling. At the same time, the weight of the entire system can be reduced. Further, in addition to the chassis portion, a water-sealed case of an electric motor for driving the operation head is used as an air reservoir to generate buoyancy, thereby balancing the buoyancy and facilitating stable posture in water.

Further, heavy parts such as an electric motor, which are installed symmetrically with respect to the center line of the device, maintain a good weight balance and contribute to stable operation and posture of the device.

The test coils can be moved to arbitrary test positions on the material to be tested and can be freely scanned by the vertical and horizontal feed screws attached to the two electric motors.

Further, a standard coil used at the same place as the standard test piece for the standard comparison method is placed in the vicinity of the test coil, and a sensitivity calibration test piece is also placed in the vicinity of the material under test for calibration. By doing so, each test piece and coil are placed in the same environment, and as a result, the occurrence of errors due to temperature differences is prevented.

Further, by using a manganin wire or the like having a small temperature coefficient of electric resistance as the material of the test coil, the influence of the temperature difference between the DUT and the test piece for sensitivity calibration can be reduced to further improve the accuracy. .

Further, by using the coil spring for the holding portion of the test coil, the test coil can obtain a considerable degree of freedom with respect to the movement of the fulcrum of the coil spring and the inclination of the axis, and the test coil is vertically sandwiched. It becomes much easier to follow the inclined test surface together with the two guide rollers provided in the. Also, by attaching a slide rod around the coil spring, it is possible to prevent the test coil and the guide roller from sagging due to the weight of the test coil and the test coil from swinging.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below mainly with reference to FIGS. First, FIG. 5 shows an outline of a fuel bundle which is a test target product. It is used in a nuclear power plant and the fuel bundle 25 is a thin tubular fuel rod 26.
Are bundled into a substantially square shape by a spacer 27 and housed in a case 28 called a channel box. The example described below is an underwater eddy current test suitable for measuring the thickness of an oxide film formed on the outer surface of each fuel rod 26 constituting the fuel bundle 25 in the water of the spent fuel storage pool. Related to the device.

FIG. 1 is a side view of a test coil operating device, which is a main component of an underwater eddy current test apparatus. The entire apparatus is suspended by a wire rope 1 and lowered into the water of a fuel pool in which a fuel handle 25 is inserted. After that, the position is adjusted with the operation rod 2, and the fuel bundle 25 is fixed by grasping the fuel bundle 25 with the upper and lower clamps 3 and 4.

The clamps 3 and 4 are attached to the chassis 7 by the upper and lower frames 5 and 6. The chassis 7 is in the shape of a hollow box, and the inside of the chassis 7 serves as an air reservoir, which causes buoyancy in water and significantly reduces the apparent weight of the entire apparatus. Therefore, an air supply hole 8 is provided in the upper part of the chassis 7 and an air escape hole 9 is provided in the lower part, so that a constant buoyancy can be maintained by adjusting the pressure of the supplied air according to the water depth. It is also possible to make the air reservoir a closed structure so that it is not affected by pressure changes due to water depth. 10 in the figure
Reference numeral 1 is a flexible wiring cable for connecting an external power supply and an operating device.

An operating head 1 is provided between the upper and lower frames 5 and 6.
00 is provided and engages with upper and lower vertical test coil feed screws 17 mounted parallel to the chassis 7, and can be moved up and down in the device by an electric motor 16 housed in a water-sealed case 15. . A test coil 10, a coil spring 11 holding the test coil 10, a sensitivity calibration test piece 12, a standard coil 13, a standard test piece 14 and the like are incorporated in the operation head 100.

At the time of measurement, the test coil 10 is ejected to the fuel bundle position by the air pressure, comes into contact with the fuel rod 26, and then moves up and down to perform the measurement. A clad removing device 18 for removing the clad adhering to the surface of the fuel rod 26 is mounted on the test coil 10.

As described above, the measurement of the oxide film thickness by this underwater eddy current test apparatus is performed by the eddy current test method by the standard comparison method. The standard coil 13 and the standard test piece 14 required at that time are tested. It is installed on the operation head 100 near the coil 10 so that there is no temperature difference between them in water and that measurement can be performed in the same environment so that measurement error does not occur. There is. Similarly, the sensitivity calibration test piece 12 also includes the test coil 1
It is provided adjacent to the fuel rod 26 of the material to be tested and calibrated near the material to be tested in water, so that not only the ambient temperature but also other conditions are calibrated in the same manner as the actual measurement. Care is taken so that no error occurs.

FIG. 2 is a plan view taken along the line AA of FIG. 1 and shows a state in which the fuel bundle 25 is clamped. Operating head 1
The end portion of the 00 test coil 10 is attached to the electric motor 19
The lateral test coil feed screw 20 is also configured so that it can be moved left and right in the apparatus.

The two electric motors 16 and 19 for moving the operating head 100 up and down and to the left and right are of the same size. By installing these electric motors at symmetrical positions, the weight in water is reduced. The imbalance prevents the device from tilting. The cases accommodating the electric motors 16 and 19 are also made to have the same size to form an air pocket, and the buoyancy thereof is also balanced. These lightweight,
By keeping the balance, the posture is stabilized and the operability is improved.

As the test coil 10 and the standard coil 13, a copper wire or the like used as a normal conductor may be used, but in order to improve the measurement accuracy, the temperature coefficient of electric resistance is higher than that of the copper wire in this embodiment. Used a small manganin wire. As a result, as shown in FIG. 4, the variation in the measured value when the temperature changes from 0 ° C. to 20 ° C. is about 5 μm in the coil using the conventional copper wire (shown by the broken line), whereas Approximately 2 μm for the coil using manganin wire (shown by the solid line)
Similarly, the variation of the measured value when the temperature changes to 50 ° C is about 21 μm for the coil using the conventional copper wire.
On the other hand, in the coil using the manganin wire, the influence of the temperature difference was suppressed to about 6 μm, and the variation amount was reduced to about 1/2 to 1/3 although it varied depending on the temperature variation amount. In addition to the manganin wire, it is also effective to improve the measurement accuracy by using a conductor having a small temperature coefficient of electric resistance such as nickelin or constantan.

FIG. 3 is a detailed view around the test coil. (A)
Shows a front view, and (b) shows a top view. The test coil 10 and the upper and lower guide rollers 22 are held by a coil spring 11 and a slide rod 21. The coil spring 11 gives the test coil 10 a degree of freedom, and the slide rod 2
1 has a structure in which it is supported as much as possible to prevent the tip portion from hanging down and restrained as much as possible.

In the measurement operation, the coil spring 11 is pushed forward by the air cylinder 24 to bring the test coil 10 into contact with the fuel rod 26. At that time, the upper and lower guide rollers 22 sandwiching the test coil 10 also come into contact with the fuel rod 26 almost at the same time, and the test coil 10 is positioned and fixed on both sides (two-dot chain line position). Further, the test coil 10 and the guide roller 22 are held by the coil spring 11 and are held with a great degree of freedom with respect to the movement of the fulcrum of the coil spring and the inclination of the shaft. During that time, the test coil 10 is always in contact with the fuel rod 26 at three points and can be fixed and contacted at a stable measurement position substantially at right angles. Further, the test coil 10 positioned between the guide rollers 22 is constantly pressed against the fuel rod 26 by the pressing spring 23 with a constant pressing pressure, and the contact state of the pressed fuel rod 26 is kept constant to perform a stable eddy current test. Can be done.

Prior to measurement, the sensitivity of the test coil 10 is calibrated. The sensitivity calibration test piece 12 is fixed to a fixed portion with respect to the lateral movement of the operation head 100, is projected into the water near the fuel rod 26 of the material under test, and is driven by the electric motor 19 and the lateral test coil feed screw 20. When the test coil 10 is laterally moved, it can be brought into contact with the sensitivity calibration test piece 12 so as to face it. As a result, the test coil 10 is calibrated in the same environment as during measurement, and as a result, it is possible to prevent the occurrence of an error due to a temperature difference or the like.

For the measurement, the test coil 10 is laterally fed by the electric motor 19 and the lateral test coil feed screw 20 described above, the test coil 10 is opposed to a predetermined fuel rod 26 in the fuel handle, and then the electric motor 16 is moved. And the longitudinal test coil feed screw 17 and the test coil 10 to the opposite fuel rod 26
Is performed while scanning up and down along the length direction of. At this time, the standard coil 1 provided on the operation head 100
3 and the standard test piece 14 also move at the same time, and because they are always in the water near the test coil 10, the measurement accuracy of the eddy current test can be improved without causing a temperature difference or the like.

In the measurement scan, after the measurement of the fuel rod 26 facing the test coil 10 is completed, the test coil 10 is moved in the lateral direction by the drive control of the electric motor 19 and the lateral test coil feed screw 20. The next fuel rod 2
6 is made to face, and it measures similarly by vertical scanning.
In this manner, each fuel rod 26 can be sequentially tested and measured by the automatic movement scanning.

Further, based on the measurement result, the clad removing device 18 is operated to remove the oxide film on the surface of the fuel rod 26 at the same time by rotating the tip brush or the like, improving the fuel combustion efficiency and extending the life of the fuel rod. Etc. can be measured.

Although the measurement of the oxide film thickness by the standard comparison method has been described above, the thickness of the material other than the oxide film can be measured,
An eddy current test based on the self-comparison method is also performed to inspect the material for minute scratches. In this case, the standard coil 13 and the test coil 10 are paired and the two coils are connected to the operating head 1.
The test material fuel rod 26 is provided in the vicinity of the tip of the fuel cell No. 00 so as to face and contact two adjacent points of the test material fuel rod 26. Accordingly, the contact point can be similarly scanned to inspect the fuel rod 26 for flaws.

[0042]

As described above, according to the underwater eddy current test apparatus of the present invention, the operability in measuring the thickness of the oxide film or the like on the surface of the material to be tested such as the fuel rod in water and inspecting for scratches is improved. It is possible to greatly improve the measurement accuracy.

[Brief description of drawings]

FIG. 1 is a side view of a test coil operating device of an underwater eddy current test apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view taken along the line AA of FIG.

FIG. 3 is a side view of a test coil holding unit used in the test coil operating device.

FIG. 4 is a temperature characteristic diagram of a test coil using a manganin wire.

FIG. 5 is a side view of the fuel bundle of the material under test.

FIG. 6 is a basic configuration diagram of a general eddy current test apparatus.

[Explanation of symbols]

1 ... Wire rope, 2 ... Control rod, 3 ... Upper clamp, 4
… Lower clamp, 5… Upper frame, 6… Lower frame, 7…
Chassis (air reservoir), 8 ... Air adjusting hole, 9 ... Air releasing hole, 10 ... Test coil, 11 ... Coil spring, 12 ... Sensitivity calibration test piece, 13 ... Standard coil, 14 ... Standard test piece,
15 ... Water-sealed case, 16 ... Electric motor (for vertical movement),
17 ... Longitudinal test coil feed screw, 18 ... Cladding remover, 19 ... Electric motor (for lateral movement), 20 ... Lateral test coil feed screw, 21 ... Slide rod, 22 ... Guide roller, 23 ... Press spring, 24 ... air cylinder, 25 ... fuel bundle, 26 ... fuel rod.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor, Yasuhiro Yamanaka 3-1-1, Sachimachi, Hitachi, Ibaraki Hitachi Ltd., Hitachi Works, Hitachi factory 2-1 Hitachi Engineering Co., Ltd.

Claims (9)

[Claims] 1. A test coil and a standard coil are submerged in water to perform a material flaw inspection by an eddy current test on a surface layer of a built structure or an installed structure in water, or a film thickness measurement on a material surface. In an underwater eddy current test device to be performed, a chassis that holds the entire device, a pair of upper and lower frames that fix the chassis to a test portion of the test material, and a test of the test material between the upper and lower frames supported by the chassis. An operation head that moves in the vertical and vertical directions along the section and is movable in three directions, that is, the horizontal direction and the front-back direction orthogonal to the vertical and vertical directions, and the test coil and the standard coil are attached to the operation head. An underwater eddy current test apparatus, characterized in that a test piece for sensitivity calibration is provided near the test coil. 2. The underwater eddy current test apparatus according to claim 1, wherein an air reservoir is provided in a chassis that holds the entire apparatus. 3. A feed screw for moving the operation head vertically and laterally is provided, and two electric motors for driving the feed screws are symmetrically arranged on the operation head. Item 1. The underwater eddy current test apparatus according to Item 1. 4. The underwater eddy current test apparatus according to claim 3, wherein an air reservoir is provided in the water-sealed case of the electric motor. 5. The standard test piece set on the standard coil is provided at a position close to the test coil.
The underwater eddy current test apparatus described. 6. The test piece for sensitivity calibration in the vicinity of the test coil is provided close to the material under test.
The underwater eddy current test apparatus described. 7. The underwater eddy current test apparatus according to claim 1, wherein a material having a small temperature coefficient of electric resistance such as manganin wire is used as the conductor material of the test coil and the standard coil. 8. The underwater eddy current test apparatus according to claim 1, wherein two guide rollers are arranged above and below the test coil and held by a coil spring and a slide rod. 9. The underwater eddy current test apparatus according to claim 8, wherein the test coil is provided with a pressing spring independent of the guide roller.