JPH0569186B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an inspection device for an object to be measured such as a nuclear reactor fuel assembly, and in particular, to an inspection device for inspecting objects to be measured such as nuclear reactor fuel assemblies. This invention relates to an inspection device suitable for flaw detection, wall thickness measurement, etc.

[Technical background of the invention and its problems]

A light water reactor such as a boiling water reactor is equipped with a large number of fuel assemblies to form a core. Each fuel assembly contains a fuel bundle of multiple fuel rods within a channel box. Each fuel rod has a fuel cladding tube filled with nuclear fuel such as fuel pellets.

By the way, in recent nuclear reactors, in order to effectively utilize uranium resources and improve fuel economy, there is a trend to use nuclear fuel to a high burnup and to lengthen the operating period of the reactor. However, if the reactor is operated for a long period of time, the fuel cladding tubes of the fuel rods will be subjected to a higher load than before, resulting in damage to the fuel rods.
There is a risk that the radioactive materials inside may leak out. In reality, fuel rod damage is extremely low from a safety standpoint.
Although it is almost non-existent, considering the high combustion rate of nuclear fuel,
In order to determine the cause of fuel rod damage and maintain the integrity of the fuel rods, it is necessary to conduct detailed inspections of fuel cladding for corrosion and changes in wall thickness.

Similar to the inspection of fuel rods, the channel boxes and spacers that are component parts of fuel assemblies are also required to be inspected for corrosion and changes in wall thickness in order to extend their service life.

Currently, after the components of a fuel assembly are put into use in a nuclear reactor, they are transported into a large hot cell, where they are inspected in post-irradiation tests and the like. For fuel inspection within the hot cell, the fuel assembly is disassembled and each fuel rod is inspected with high accuracy.

However, due to the difficulties involved in transporting nuclear power plants to hot cells, only a limited number of specific fuel assemblies are actually inspected, and many fuel assemblies remain uninspected in spent fuel storage pools. stored in

For this reason, when many fuel assemblies need to be inspected, there is a tendency to conduct fuel inspections at the reactor site. In order to carry out fuel inspections at the reactor site, a large drive system must be installed in the fuel storage pool to handle the fuel bundles, fuel rods, and channel boxes that are the components of the fuel assembly.

However, since there is no reprocessing plant in Japan, a large amount of spent fuel is stored and stored in fuel storage pools. For this reason, there is not enough space to accommodate a large inspection drive device, making it difficult to install the inspection drive device.

Therefore, a simple device with an inspection probe such as an ultrasonic probe or an eddy current sensor attached to the tip of an operation pole is used in the fuel storage pool as a device to inspect the fuel bundles and channel boxes of fuel assemblies. It is being In this inspection device, an operating pole is submerged in a fuel storage pool, and an inspection probe is brought into contact with or close to the fuel bundle or channel box from above the storage pool to make measurements.

However, in order to measure the entire length of the fuel handle or channel box with the above inspection device, the length of the operation pole must be several meters or more, and a joint part must be provided in the middle or the tip must be inspected. When the probe is brought into contact with or close to the fuel bundle or channel box, the operating pole is bent or deflected, resulting in poor position repeatability between the inspection probe and the object to be measured, which poses problems in terms of measurement and inspection accuracy.

[Purpose of the invention]

This invention has been made in consideration of the above-mentioned points, and is an inspection device that can efficiently and accurately measure flaw detection and wall thickness measurement of objects to be measured such as fuel bundles and channel boxes of fuel assemblies. The main purpose is to provide

Another object of the invention is to accurately inspect fuel rods and channel boxes in fuel bundles without using large inspection drives in fuel storage pools or disassembling fuel assemblies into individual components. It is an object of the present invention to provide an inspection device capable of carrying out the inspection.

[Summary of the invention]

In order to achieve the above-mentioned object, an inspection device according to the present invention includes: a main body frame assembly having a frame structure that is suspended so as to be vertically movable; , an elevating mechanism for elevating and lowering the vertically movable table; an L-shaped guide mechanism attached to one side of the main body frame assembly that can engage with the object to be measured; and a mechanism for fixing the main frame assembly to the object to be measured. a frame fixing mechanism; a table moving mechanism that horizontally moves a horizontally moving table installed on the vertically movable table; and a holder advancing/retracting mechanism that moves a holder provided on the horizontally moving table toward and away from the measurement target;
The present invention is characterized by comprising an inspection probe such as an ultrasonic probe supported by the holder.

[Embodiments of the invention]

Hereinafter, preferred embodiments of the inspection device according to the present invention will be described with reference to the accompanying drawings.

1 and 2, reference numeral 1 indicates the main body frame assembly of the inspection device according to the present invention, and this main body frame assembly 1 is suspended from a jig crane, hoist, etc. (not shown) in the fuel storage pool. It is suspended from a hanging rope 2 so that it can be raised and lowered freely. The main body frame assembly 1 has a frame structure, and is constructed by connecting a rectangular upper substrate 3 and a lower substrate 4 with vertical guide posts 5. Vertical guide posts 5 are provided at the four corners of both substrates 3 and 4, and a vertical movable table 6 is supported by each guide post 5 so as to be movable up and down. The vertical movable table 6 is raised and lowered between the upper substrate 3 and the lower substrate 4 by a lifting mechanism 7.

The elevating mechanism 7 includes an elevating drive motor 8 installed on the upper substrate 3 and a power transmission mechanism 9 that transmits the motor driving force to the vertical movable table 6. The power transmission mechanism 9 spans a power transmission wire 12 between a drive pulley (drive sheave) 10 mounted on the output shaft of the drive motor 8 and a driven pulley (driven sheave) 11 provided on the lower substrate 4. It consists of: Of these, the power transmission wire 12 is fixed to the vertical movable table 6 via a wire clip 13.

On the other hand, on one side of the main body frame assembly 1, there is provided an L that can be engaged with a fuel bundle 15 as an object to be measured.
A mold guide mechanism 16 is provided. The L-shaped guide mechanisms 16 are provided at four corners of the main body frame assembly 1 on the upper, lower, left and right corners. Each L-shaped guide mechanism 16 has a guide roller 1 supported by an L-shaped frame 17.
8 and 19, and these guide rollers 18 and 19 are engaged with the fuel bundle 15 from the outside so as to be able to freely roll in the vertical direction.

A frame fixing mechanism 20 that is paired with the L-shaped guide mechanism 16 is provided adjacent to the L-shaped guide mechanism 16 . The frame fixing mechanism 20 is the fuel bundle 1
The fuel rod has a comb-shaped catch member 22 that can be engaged with each of the fuel rods 21 of No. 5, and a member drive mechanism 23 that rotates the catch member 22 about a fulcrum.
The member drive mechanism 23 includes an actuator such as an air actuator, and the catch member 22 is rotated by this actuator.
The main body frame assembly 1 is fixed to the fuel bundle 15 by a pair of frame fixing mechanisms 20 provided on the left and right sides of the main body frame assembly 1 . Specifically, the catch members 22 of the left and right frame fixing mechanisms 20 have comb-like portions that connect to the fuel bundle 15.
from both sides to fix the main body frame assembly 1. Note that the reference numeral 24 is a fuel cladding tube for calibration, and this fuel cladding tube 24 is provided between the upper and lower frame fixing mechanisms 20, 20.

Further, on the vertically movable table 6 of the main body frame assembly 1, there is a horizontally movable table 25 movable in the Y-axis direction.
is provided via a table moving mechanism 26. The table moving mechanism 26 includes a screw shaft 28 that is stretched between support frames 27, 27, and a shaft drive mechanism 29 that drives the screw shaft 28. The support frames 27, 27 are installed on both sides of the vertically movable base 6 so as to extend in the X-axis direction, and the drive mechanism 29 is configured to transmit driving force from a reversibly rotatable drive motor 30 to a power transmission mechanism such as a bevel gear mechanism. 31 to the screw shaft 28. A horizontally moving table 25 is screwed onto the screw shaft 28.
The movable table 25 is moved in the horizontal direction (Y-axis direction) by driving the screw shaft 28,
Its movement is guided by horizontal guide rods 32, 32 mounted in parallel relation to the screw shaft 28. This guide rod 32 is mounted between the support frames 27, 27.

A holder advancing/retracting mechanism 34 is installed on the horizontally moving table 25. The holder advancing/retracting mechanism 34 is a fixed block 35 vertically installed on the horizontally moving table 25.
A fluid cylinder 36 such as an air cylinder supported by
and the piston rod 37 of this fluid cylinder 36.
A support block 38 is fixed to the tip of the support block 38. This support block 38 has a U-shape as a whole, and is slidably supported on the horizontal movement table 25, and its sliding movement is controlled by movement guide rods 39, 3.
9.

In the support block 38, as shown in FIGS. 3 and 4, a cylindrical holder 40 is swingably supported around a vertical support pin 41 serving as a swing mechanism. A leaf spring 42 is interposed on the rear end surface of the cylindrical holder 40, and the leaf spring 42 elastically restricts the swinging function of the cylindrical holder 40 so that it always faces forward.

On the front end surface of the cylindrical holder 40, a pair of V-shaped or concavely curved engagement rollers 44, 44 is provided vertically. The engagement rollers 44, 44 are adapted to rollably engage with the fuel rods 21 of the fuel bundle 15 and spacers (not shown), and guide the holder 40 as it moves up and down.

The cylindrical holder 40 accommodates an ultrasonic probe 45 as an inspection probe. This ultrasonic probe 45 is separated from the fuel rods 21 of the fuel bundle 15 by a certain distance and performs ultrasonic flaw detection on the fuel rods 21, and
The detection signal is guided to a detector such as an ultrasonic flaw detector (not shown) via a cable 46.

On the other hand, an eddy current probe test coil 50 shown in FIG. 5 may be housed in the cylindrical holder 40 as an inspection probe instead of the ultrasonic probe. In this case, the probe test coil 50 is connected to the spring 51
The fuel bundle 15 is biased by the spring.

Next, an ultrasonic flaw detection inspection of a fuel cladding tube in a fuel storage pool of a boiling water reactor using the inspection apparatus according to the present invention will be explained.

When performing ultrasonic flaw detection, the fuel assembly is placed on an existing fuel channel attachment/detachment machine (not shown) and the channel box is removed. Next, the fuel bundle 15 with the channel box removed
In order to install the inspection device of the present invention, the main body frame assembly 1 is suspended from a jig crane installed on the side of the fuel storage pool, and the frame assembly 1 is submerged within the vertical movable range of the fuel channel attachment/detachment machine. .

The submerged body frame assembly 1 is brought close to the fuel bundle 15 by horizontal movement of the jig crane, and positioned so that the fuel bundle 15 is set between the upper, lower, left, and right L-shaped guide mechanisms 16, 16. At this time, adjustment in the height direction is easily performed by the guide rollers 18, 19 of the L-shaped guide mechanisms 16, 16 engaging with the fuel bundle 15 and rolling. After completing the height adjustment work,
The frame fixing mechanisms 20, 20 are actuated, and the pair of left and right comb-shaped catch members 22, 22 are pressed against each fuel rod 21, 21... of the fuel bundle 15, gripped from both sides, and the main body frame assembly 1 is It is fixed to the bundle 15 and integrated.

After that, the table moving mechanism 26 and the holder advancing/retracting mechanism 34 are operated to move the holder 40 in the X-Y axis direction, and the fuel cladding tube (fuel rod) is ultrasonic tested using the ultrasonic probe 45 as an inspection probe. Before that, the calibration fuel cladding tube 2 with a standard defect in the unirradiated fuel cladding tube is measured.
In step 4, the gain of a detector such as an ultrasonic flaw detector is adjusted.

For this adjustment work, the table moving mechanism 26
is activated to move the horizontal movement table 25 in the Y-axis direction, and the engagement roller 4 is moved to the calibration fuel cladding tube 24.
4 and 44 to a position where they can touch each other. Subsequently, the holder advancing/retracting mechanism 34 is operated to engage the engagement rollers 44, 44 with the calibration fuel cladding tube 24.

Next, the elevating mechanism 7 is operated to move the ultrasonic probe 45 up and down along the calibration fuel cladding tube 24 while operating the ultrasonic flaw detector, and the ultrasonic flaw detector is calibrated using the signal from the standard defect. .

Thereafter, the ultrasonic probe 45 is separated from the calibration fuel cladding tube 24, and the fuel bundle 15 is inspected in the same manner as the calibration fuel cladding tube 24.
A flaw detection inspection of the outer fuel rod cladding tube 21 can be performed. When performing flaw detection over the entire length of the fuel bundle 15, the height direction of the fuel bundle 15 can be changed using a fuel channel attachment/detachment machine, or the hanging position of the inspection device can be changed using a jig crane. , inspection position and fuel bundle 1
What is necessary is to change the bonding position with 5.

Next, the inspection principle of ultrasonic flaw detection will be explained.

Ultrasonic flaw detection of thin-walled thin tubes such as fuel cladding tubes is performed by an oblique angle flaw detection method in which an ultrasonic beam from an ultrasonic probe 45A is focused underwater, as shown in FIG. For angle flaw detection, a method is adopted in which the ultrasonic beam is directed in the axial direction of the fuel cladding tube 21A, and then the ultrasonic probe 45A is offset horizontally by a predetermined amount δ. At this time, the offset amount δ is expressed by the following equation.

δ＝OD／Z・Cw／Ct・ID／√(OD) ² + (ID) ² ...(1) However, OD: Outer diameter of fuel cladding, ID: Inner diameter of fuel cladding, Cw: Underwater Speed of sound Ct: Speed of sound in the fuel cladding tube.

However, if the fuel cladding is damaged,
Between the echoes of the inner diameter and outer diameter of the fuel cladding tube 21A,
Since echoes are generated due to damage, flaw detection becomes possible. The magnitude of the damage can be measured by comparing the echoes caused by the calibration fuel cladding tube 24, for which the location, size, and depth of the scratches on the calibration fuel cladding tube 24 are known, with the measured echoes.

In flaw detection of thin-walled tubes, the sensitivity for detecting the presence or absence of damage depends on whether or not the offset amount δ can be kept constant, so it is necessary to maintain the offset amount with high accuracy. Actually, a pair of upper and lower V-shaped engagement rollers 4 shown in FIGS. 3 and 4
Ultrasonic probe 45 from the center line connecting between 4 and 44
may be changed by a predetermined amount.

In addition, when measuring the wall thickness of the fuel cladding tube 21 using an ultrasonic probe, a calibration fuel cladding tube with a known wall thickness is used instead of a calibration fuel cladding tube for flaw detection inspection, and a An ultrasonic thickness measuring device is used instead of an ultrasonic flaw detector. Thereby, the wall thickness of the fuel cladding tube 21 can be measured using the same procedure as the flaw detection inspection of the fuel cladding tube of the fuel bundle 15.

When measuring the wall thickness using this fuel cladding tube 21, the ultrasonic beam from the ultrasonic probe 45 is set so that it passes through the center of the tube axis, and the reflection between the pipe surface of the fuel cladding tube 21 and the inner surface of the pipe is measured. This is done by measuring the time difference between echoes. In this case, it is important that the oscillated ultrasonic beam be set so as to face in the axial direction of the fuel cladding tube 21.

Next, in place of the ultrasonic probe 45, an eddy current medium probe test coil 50 (see FIG. 5) is used as an inspection probe to perform flaw detection on the fuel cladding tube 21.
The case of performing wall thickness measurement and oxide film thickness measurement will be explained.

When performing a flaw detection inspection using the eddy current probe test coil 50, a calibration fuel cladding tube for eddy current flaw detection is used in place of the calibration fuel cladding tube 24 for ultrasonic flaw detection, and An eddy current flaw detector is used as a detector instead of an ultrasonic flaw detector.

The principle of flaw detection using eddy current is shown in FIGS. 7 and 8.

That is, as shown in FIG. 7, when a metal plate 55 is brought close to a coil 50A through which an alternating current is passed, an eddy current is generated on the metal plate 55 due to electromagnetic induction, and if there is a defect in the metal plate 55, an eddy current is generated. flow is disturbed, and the impedance of the coil 50A changes. The presence and size of metal defects can be measured from this change in impedance.

In an actual flaw detection test using eddy current, as shown in FIG. 8, when the bridge circuit 56 is assembled and there is no metal defect, the bridge circuit 56 is set to be in an equilibrium state. With this setting, if a defect such as a flaw exists in the fuel cladding tube 21, the impedance of the probe test coil 50 changes, causing the bridge circuit 56 to become unbalanced.
By outputting this imbalance as a voltage change through the rectifier 57, the presence or absence of a defect is measured, and furthermore, the defect (damage) can be detected by comparing it with the voltage change obtained with a known calibration fuel cladding tube. The size can be estimated.

In order to accurately measure the presence or absence of damage to the fuel cladding tube 21 using an eddy current flaw detection test, it is important to maintain a constant gap between the probe test coil 50 and the fuel cladding tube 21. The probe test coil 50 is constantly pressed into contact with the fuel cladding tube 21 by a spring 51.

When performing wall thickness measurement (or oxide film thickness measurement) using eddy current, a probe test coil for wall thickness measurement (or oxide film thickness measurement), fuel cladding for calibration, and eddy current wall thickness measurement are required. (or an eddy current film thickness meter).

Wall thickness measurement using eddy current utilizes the fact that when an AC power source is applied to a probe test coil, the coil impedance changes as the amount of metal changes within the range of the magnetic field generated by this coil. At this time, the lower the AC frequency acting on the probe test coil, the wider the magnetic field range, and the higher the frequency, the narrower the magnetic field range.

For high-precision thin-walled tubes such as fuel cladding, it is possible to eliminate factors that change the coil impedance, such as the absence of defects in the fuel cladding, and to adjust the AC frequency, which responds sensitively to changes in wall thickness. When set, the coil impedance will change if there is a change in the wall thickness of the fuel cladding. By correlating this change in coil impedance with the known change in impedance of the calibration fuel cladding, the wall thickness of the fuel cladding can be measured.

The oxide film thickness of the fuel cladding tube 21 is measured as follows.

The oxide film that adheres to the fuel cladding tube 21 is an insulator, so when the oxide film adheres, the gap between the fuel cladding tube surface and the probe test coil changes due to the adhered oxide film, and the coil impedance changes according to this change. changes. Therefore, by determining the change in coil impedance in a calibration fuel cladding tube whose oxide film thickness is known and comparing it with this change in coil impedance, the thickness of the oxide film attached to the fuel cladding tube of the fuel bundle can be determined. can be measured.

In the description of the embodiments of the present invention, an example was explained in which the fuel cladding tube in the fuel bundle of the fuel assembly was inspected. However, it is also possible to inspect the channel box or spacer instead of the fuel cladding tube. General long objects can be inspected as objects.

When inspecting a channel box, the frame fixing mechanism 20A of the inspection device is configured as shown in FIG. 58 is formed as an engagement latch surface that engages 58.

〔Effect of the invention〕

As described above, in the inspection device according to the present invention, the main body frame assembly, which is suspended so as to be able to rise and fall, is removably fixed to the object to be measured, such as a fuel bundle, using the L-shaped guide mechanism and the frame fixing mechanism. At the same time, a vertically movable table is provided on the main body frame assembly so as to be movable up and down by an elevating mechanism, a horizontally movable table provided on the vertically movable table is movable by a table movement mechanism, and a holder holding an inspection probe can be moved forward and backward by the holder. Since the mechanism allows the inspection probe to move forward and backward toward the object to be measured, it is possible to stably move the inspection probe three-dimensionally relative to the object to be measured. Therefore, without using a large drive device in the fuel storage pool of a nuclear reactor, it is possible to perform flaw detection, wall thickness measurement, and oxide film thickness measurement of objects to be measured, such as fuel bundles, non-destructively and accurately. It can be done efficiently.

In addition, when inspecting the fuel cladding tubes of fuel rods, the iron can be used to measure and inspect the fuel cladding tubes without disassembling the fuel bundle into individual fuel rods, reducing inspection time and work. The required labor can be significantly reduced. By shortening the inspection time, it is now possible to inspect each component of the fuel assembly at each periodic inspection of the reactor, and to track changes in the components of the fuel assembly during each operating cycle of the reactor. be able to. Therefore, the present invention can be useful in investigating the influencing factors due to the occurrence of scratches, changes in wall thickness, and changes in oxide film thickness in the component parts of the fuel assembly, and in evaluating the lifespan of the component parts.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the inspection device according to the present invention, FIG. 2 is a partially cutaway plan view of the inspection device, and FIG. 3 is a holder incorporated in the inspection device and the holder moving forward and backward. A sectional view showing the mechanism,
Fig. 4 is a plan view of Fig. 3 seen from above, Fig. 5 is a sectional view showing a modification of the holder part operated by the holder advance/retreat mechanism of the inspection device, and Fig. 6 is an ultrasonic probe attached to the inspection probe. Figure 7 is a diagram showing the principle of eddy current generation when a probe test coil is used as the inspection probe. Figure 8 is the eddy current method shown in Figure 7. Electrical circuit diagram showing the principle of flaw detection measurement using a probe test coil,
FIG. 9 is a diagram showing a modification of the frame fixing mechanism for gripping the channel box of the fuel assembly. 1... Body frame assembly, 3... Upper board,
4... Lower board, 6... Vertical movable table, 7... Lifting mechanism, 8... Lifting drive motor, 9... Power transmission mechanism, 15... Fuel bundle (object to be measured), 1
6... L-shaped guide mechanism, 17... L-shaped frame,
18, 19... Guide roller, 20, 20A...
Frame fixing mechanism, 22, 22A... Catch member, 23... Member drive mechanism, 24... Fuel cladding tube for calibration, 25... Horizontal moving table, 26
. . . Table moving mechanism, 28 . , 45... Ultrasonic probe (inspection probe),
50... Eddy current probe test coil.

Claims (1)

[Scope of Claims] 1. A main body frame assembly having a frame structure suspended so as to be vertically movable, a vertically movable platform supported by the main body frame assembly in a vertically movable manner, and a lifting mechanism for raising and lowering the vertically movable platform. an L-shaped guide mechanism attached to one side of the main body frame assembly and capable of engaging with the object to be measured; a frame fixing mechanism for fixing the main frame assembly to the object to be measured; a table moving mechanism that moves a horizontally moving table installed in the horizontal direction; a holder advancing and retreating mechanism that moves a holder provided on the horizontally moving table toward and away from the object to be measured; and an ultrasound probe supported by the holder. An inspection device characterized by comprising an inspection probe such as the above. 2. The main body frame assembly is assembled by connecting an upper board and a lower board with vertical guide posts installed vertically at the corners, and a vertical movable base is slidably supported on the vertical guide posts. An inspection device according to claim 1. 3. The inspection device according to claim 1, wherein the objects to be measured are fuel rods of a fuel bundle, components of a fuel assembly such as a fuel channel box, and elongated objects. 4 L-shaped guide mechanisms are provided at four locations on the top, bottom, left and right at one side corner of the main body frame assembly, and each L-shaped guide mechanism has a guide roller arranged in an L-shape on the L-shaped frame. An inspection device according to claim 1. 5. A patent in which the frame fixing mechanism is configured to form a pair with an L-shaped guide mechanism, and has a comb-shaped or concave catch member that catches the object to be measured from the outside, and a member drive mechanism that rotates the catch member around the branch. An inspection device according to claim 1. 6. The holder elevating mechanism includes a cylinder device for advancing and retracting the holder toward the object to be measured, and the holder has a pair of upper and lower contact guide rollers capable of engaging with the object to be measured at the tip of the holder, as set forth in claim 1. Inspection equipment. 7. The inspection device according to claim 1, wherein the inspection probe is swingably supported by the holder.