JP2001056203A - Non-contact displacement measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of errors caused by the contact of a detector with an object to be measured when, for example, a change in the external form of the object to be measured such as a fuel cladding pipe in a nuclear reactor is measured. SOLUTION: Electromagnetic induction type detectors 1 to 3 are arranged at an interval of 120 degrees in the peripheral direction of a fuel cladding pipe 40. Amplitude of oscillation signals of oscillation circuits 1 to 3 is changed in accordance with displacement of a gap among them. Magnitude of the amplitude is detected in rectifying circuits 1 to 3. Size of the gap is obtained from the magnitude of the amplitude detected based on a calibration curve for the gap vs. magnitude of amplitude which is stored in advance in a signal computing circuit 44. Furthermore, displacement of a diameter of the fuel cladding pipe is obtained based on obtained size of gap in three directions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-contact displacement measuring device. The present invention is suitable, for example, for measuring the change over time of the diameter of a cylindrical metal.

[0002]

2. Description of the Related Art It is very important to know the details of the behavior of fuel failure in designing conditions for maintaining the integrity of fuel in a nuclear reactor or designing a high burn-up fuel. PCMI (Pellet cladding-Interaction) during reactor reactivity accident
This may cause deformation of the cladding tube and further damage to the cladding tube. Until now, the change in the outer shape of the cladding tube at the time of the fuel rod breakage experiment was determined from the change in the value by attaching a contact type micrometer or strain gauge to the cladding tube surface.

[0003]

In the conventional contact-type detector, since the surface temperature of the fuel cladding tube is inevitably reduced due to the cooling effect, the change in the outer shape of the fuel cladding tube at the actual temperature can be accurately detected. It could not be measured.

The present invention relates to a non-contact displacement measurement method which does not cause an error caused by a detector coming into contact with an object to be measured when measuring a change in the outer shape of the object to be measured such as a fuel cladding tube of a nuclear reactor. To provide equipment.

[0005]

In order to solve the above-mentioned problems, a non-contact displacement measuring instrument according to the present invention includes a plurality of electromagnetic induction type detectors, and is electrically connected to the plurality of electromagnetic induction type detectors. An oscillation circuit for generating a high-frequency signal; signal detection means for detecting a magnitude of the high-frequency signal generated by the oscillation circuit; and the plurality of electromagnetic inductions based on the magnitude of the high-frequency signal detected by the signal detection means. Means for determining a gap between each of the pattern detectors and the object to be measured.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of the present invention will be described below with reference to the drawings, in a case where the present invention is applied to an application for measuring a change in outer shape of a fuel cladding tube (or fuel rod) of a nuclear reactor. explain.

As non-contact type sensors, there are an electrostatic type, an electromagnetic induction type, an optical sensor type, an ultrasonic type, and the like. In the experiment, the conditions of the experiment are water under high radiation, bubbles are generated, and the change speed is high. Therefore, it is considered that an electromagnetic induction type using a high-frequency magnetic field is appropriate.

First, as a problem in measurement, there is the generation of noise synchronized with the reactor output specific to the pulse output type reactor. Radiation measurement is detected by an interaction with a substance. However, current is generated in all detectors and signal lines due to ionized ions generated by high radiation generated during pulse operation, resulting in pulsed noise.

As a second problem, there is a problem of temperature compensation. Water temperature is 100 ° C because it is an experiment under atmospheric pressure
Although it does not rise above, it is necessary to compensate for the output change due to the temperature.

[0010] As a method of solving these problems,
The compensation was made by using a dummy sensor. That is, by setting one dummy sensor under the same environmental condition, a dummy signal (output change due to radiation noise and temperature) not including a displacement signal is detected and the displacement signal is corrected. The pulse-like noise can be removed to some extent by subtracting the signal of the dummy sensor from the experience so far. The temperature compensation may be performed in the same manner, but it is necessary to obtain the detector temperature characteristics in advance and grasp the degree of the temperature.

Further, since a minute displacement in the radial direction of the cladding tube of the cylindrical fuel is measured, the reliability in one direction is low and the displacement in three directions is measured, the change is calculated, and the time change of the diameter is measured. To analyze the cladding failure behavior of the fuel.

The basic principle of the present invention will be described with reference to FIG. The electromagnetic induction type detector 10 (corresponding to the above-described sensor) in FIG. 1 is a sensor in which a magnetic core 14 which is an iron core is used in a coil 12 and is generally called a probe coil or a probe coil. The induced electromotive force is
In addition to the general magnetic metal conductor 16 to be measured,
Also occurs inside the. A high frequency signal (250 KHz to 1.3 MHz) from the oscillation circuit 20 is applied to the electromagnetic induction type detector 10 via the excitation circuit 22 and the coaxial cable 24,
A magnetic force is generated at the tip of the electromagnetic induction type detector 10, and when the magnetic metal conductor 16 approaches the electromagnetic induction type detector 10, an electromagnetic induction action by the magnetic force from the tip causes the magnetic metal conductor 16.
An induced electromotive force is generated on the surface of the substrate, and a current based on the electromotive force, that is, an eddy current is generated. Since the eddy current is generated so as to prevent the change of the magnetic flux passing through the magnetic metal conductor 16, if the eddy current occurs,
The back electromotive force due to the eddy current cancels the magnetic flux, and the magnetic flux becomes small.

The eddy current signal induced in the magnetic metal conductor 16 is affected by the shape and size of the magnetic metal conductor 16, conductivity and permeability, existence of cracks, and relative position. Here, when the magnetic metal conductor 16 approaches the electromagnetic induction type detector 10, the magnitude of the eddy current changes according to the distance, and the electromagnetic induction type detector 1
The fact that the impedance of 0 changes, thereby changing the output amplitude of the oscillation circuit 20 is used. Oscillation circuit 2
The change of the output amplitude of 0 is output as a displacement signal, that is, a gap signal through a normal rectifier circuit 26 using, for example, a diode.

The electromagnetic induction type detector 10 for detecting the displacement of the surface of the fuel cladding tube is desirably small in order to minimize mutual interference in detecting the displacement in three directions.

Rectifier circuit 26 of the circuit shown in FIG.
Can be represented by an equivalent circuit as shown in FIG. The influence of the inductance L and the capacitance C differs depending on the frequency. Even if the frequency is kept constant, L and C of the signal cable and the wiring of the coaxial cable 24 also have a large effect, so it is important to select the oscillation frequency of the oscillation circuit 20 and to obtain a calibration curve based on the frequency.

FIG. 3 shows the change in the outer shape of the cylindrical fuel cladding for a nuclear reactor in the circumferential direction by using three electromagnetic induction type detectors.
A non-contact displacement measuring device according to a preferred embodiment of the present invention which measures the change of the eddy current from three directions and measures the change of the outer shape, that is, the change of the diameter in a non-contact manner, is shown in a block diagram form. The fuel cladding tube 40 for the reactor, which is the object to be measured,
It is made of a magnetic metal whose material is Zr-4 and has a cylindrical shape. Three small electromagnetic induction type detectors 10a, 1
Ob and 10c are arranged at the same height position in the circumferential direction of the cylindrical fuel cladding tube 40 and at an angle of 120 degrees to each other as shown in the plan view of FIG. The gap between each of the electromagnetic induction type detectors 10a to 10c and the fuel cladding tube 40 is about 0.5 to 1.0 mm. Each of the electromagnetic induction type detectors 10a to 10c is connected to the displacement amplifier 42 via a coaxial cable (not shown). The displacement amplifier 42 has the same oscillation circuits 1, 2 as the oscillation circuit 20 shown in FIG. 1 corresponding to the three electromagnetic induction detectors 10a to 10c.
And 3, the same exciting circuits 1, 2 and 3 as the exciting circuit 22 and the same rectifying circuits 1, 2 and 3 as the rectifying circuit 26 are provided. In order to clarify the correspondence, electromagnetic induction type detector 1
0a, 10b, and 10c are also referred to as electromagnetic induction type detectors 1, 2, and 3, respectively. The electromagnetic induction type detectors 1 to 3, the oscillation circuits 1 to 3, the excitation circuits 1 to 3, and the rectification circuits 1 to 3 are connected as shown in FIG. The oscillation circuits 1 to 3 generate high-frequency signals of several hundred kHz,
Each of the high frequency signals of the two oscillating circuits has a different frequency so as not to interfere with each other in the measurement. The excitation circuits 1 to 3 excite the electromagnetic induction type detectors 1 to 3 with high frequency signals from the oscillation circuits 1 to 3. The amplitude of the high-frequency signals of the excitation circuits 1 to 3 is determined by the fuel cladding tube 40 and the electromagnetic induction type detectors 1 to 3.
Since the component changes due to a change in the gap between the components, the component is rectified by the rectifier circuits 1 to 3 and further amplified. The signals rectified and amplified by the rectifier circuits 1 to 3 are output to the signal operation circuit 44.

In the signal operation circuit 44, a calibration curve representing the relationship between the gap and the output voltage of the displacement amplifier 42 as shown in FIG.

FIG. 4B shows an example of the temporal change of the output voltage of each of the rectifier circuits 1 to 3 caused by the temporal change of the gap for each of the electromagnetic induction type detectors 1 to 3. Show. The signal operation circuit 44 receives the output voltage as shown in FIG. 4B with the passage of time, and stores in advance the electromagnetic induction type detectors 1 to 3 shown in FIG. Using the calibration curve, a displacement signal as shown in FIG. For example, the sum of the output voltages of the rectifier circuits 1 to 3 corresponding to the three electromagnetic induction type detectors 1 to 3 or the average of the output voltages can be used as the method of obtaining the values. Next, the displacement signal is recorded in the displacement signal storage device 46.

When used for elucidation of fuel failure behavior, the electromagnetic induction type detectors 1 to 3 are under high radiation, and their influence is included in the displacement signal. Therefore, in order to eliminate the influence, it is necessary to provide a dummy detector for correction. In FIG. 3, an electromagnetic induction type detector 10d indicated by a broken line
Represents a correction dummy detector 4. The correction dummy detector 4 is located at a position where it does not interfere with the electromagnetic induction type detectors 1 to 3 for displacement detection, and
It is sufficient if they are arranged at appropriate positions that receive the same high radiation as in 3. In FIG. 3, an oscillation circuit 4, an excitation circuit 4, and a rectifier circuit 4 surrounded by a broken line are systems for obtaining a voltage indicating the effect of high radiation on the electromagnetic induction type detector. The signal is supplied to the signal operation circuit 44, and is subtracted from the output voltage (each voltage shown in FIG. 4B) corresponding to each of the electromagnetic induction type detectors 1 to 3.

FIG. 5 shows the result of measurement of the time change of the outer shape of the fuel cladding tube in the reactor fuel failure experiment using the measurement system shown in FIG. In FIG. 5, (A) shows the reactor power,
(B) to (D) show the output voltages from the rectifier circuits 1 to 3 corresponding to the respective electromagnetic induction type detectors 1 to 3, and (E) show the rectifier circuit 4 corresponding to the correction dummy electromagnetic induction type detector 4. (F) shows the change over time of the displacement signal.

In the embodiment shown in FIG.
Separate oscillation circuits, excitation circuits, and rectification circuits are provided for one (or four) electromagnetic induction type detectors. For example, an oscillation circuit is provided for an object to be measured whose time variation is slow. , An excitation circuit and a rectifier circuit, each of which may be connected to each electromagnetic induction type detector in a time division manner by a switching circuit.

In the case where the accuracy is further improved or the variation of the displacement in the circumferential direction is large,
Four or more electromagnetic induction type detectors may be arranged along the circumferential direction.

On the other hand, when accuracy is not required much,
Two electromagnetic induction type detectors may be arranged on the diameter of the cylindrical object to be measured. In addition, the shape of the object to be measured is not limited to a cylindrical shape, and even if the object has a thickness, for example, a polygonal prism, a number of electromagnetic induction type detectors corresponding to the shape are provided around the object to be measured. If arranged, the non-contact displacement measuring device of the present invention can measure the outer shape of the object to be measured.

[0024]

According to the present invention, it is possible to arrange a plurality of electromagnetic induction type detectors around the object to be measured in a non-contact state and measure the displacement of the outer shape of the object to be measured. Also,
Responsiveness is good even for high-speed displacement.

Therefore, when measuring the change in the outer shape of the object to be measured, for example, a fuel cladding tube of a nuclear reactor, there is no error caused by the contact of the detector with the object to be measured. It is very effective for

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a basic principle of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of a configuration excluding a rectifier circuit 26 in the circuit shown in FIG.

FIG. 3 is a graph showing a change in the outer shape of a cylindrical fuel cladding tube for a nuclear reactor in three directions using three electromagnetic induction detectors, and a change in the outer shape, that is, a diameter. FIG. 3 is a block diagram showing a non-contact displacement measuring device according to a preferred embodiment of the present invention for measuring a change in a non-contact type.

4 is a schematic diagram of a measurement signal of the non-contact displacement measuring device shown in FIG.

FIG. 5 is a diagram showing a result of measurement of a temporal change of a fuel cladding outer shape in a reactor fuel failure experiment using the measurement system of FIG. 3;

[Explanation of symbols]

 10, 10a to 10c Electromagnetic induction type detector 20 Oscillation circuit 22 Excitation circuit 26 Rectification circuit 40 Fuel cladding tube for reactor 42 Displacement amplifier 44 Signal operation circuit

Claims (1)

[Claims] A plurality of electromagnetic induction type detectors; an oscillation circuit electrically connected to the plurality of electromagnetic induction type detectors for generating a high frequency signal; and a magnitude of a high frequency signal generated by the oscillation circuit. And a means for calculating a gap between each of the plurality of electromagnetic induction type detectors and the object to be measured based on the magnitude of the high-frequency signal detected by the signal detecting means. Non-contact displacement measuring instrument.