JPH0466896A - Ultrasonic inspection device for weld part of nuclear fuel rod - Google Patents

Abstract

PURPOSE:To enable on-line inspection without requiring much time by synchronizing rotation of a probe and generation of ultra sonic wave, by forming two dimensional image and by extracting a quantity of two dimensional features. CONSTITUTION:First of all, a fuel rod 3 is positioned at specified position by a pusher 47 of coarsely movable mechanism, and then is pressed and fixed to an axial driving table 45 by a fixing cylinder 48. After releasing hold of the pusher 47, a motor 26 is made to rotate by indication from a processing unit 300 and therewith a pulse motor 55 rotates proportionally to the number of the rotation, to move the fuel rod 3 axially. Then, output signal of an ultrasonic flaw detector 200 is input to the device 300 by each pulse generation. Since the number of the pulses during one turn of a rotating body is set at the device 300, the output signals of the one-turn operation are displayed as a matrix and the matrix are formed at a memory in the device 300, as a two-dimensional image. After completion of predetermined number of rotation, the rotation is stopped by indication from the device 300 and the fuel rod 3 is withdrawn to an original position by the pusher 47.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an ultrasonic inspection device for end plug welds on nuclear fuel rods.

(Prior Art) X-ray radiography is generally used to inspect welds of nuclear fuel rods (hereinafter also referred to as fuel rods). That is, as shown in FIG. 8, the welded portion 3al of the fuel rod 3:
After exposing the film 401 to a shadow corresponding to the X-ray transmittance of the welded area by irradiating radiation from the X-ray tube 400, the film is developed and this shading image is visually inspected to confirm that there is no thinning. Inspections were made to ensure that the melt penetration was sufficient and that there were no defects such as bores.

(Invention or problem solving section@) However, in the case of X-ray radiography, one
Since the irradiation was from all directions, only two points could be confirmed: no thinning of the weld, and sufficient penetration, so the measurement accuracy cannot be said to be high. For this reason, it is a time-consuming process that requires irradiation and imaging from multiple directions multiple times for confirmation. Also, the film must be carefully visually inspected by a skilled person.

Furthermore, there are other problems such as development, visual inspection, and inspection and determination are labor intensive and time consuming, making them inefficient, requiring time to obtain results, and making automation difficult.

Additionally, ultrasonic testing has been attempted as an alternative to X-ray radiography, but conventional ultrasonic testing is similar to tube inspection using ultrasonic waves of approximately 15 MHz or less, as shown in Figure 9. It is something.

That is, using two devices, as shown in FIG.
One probe 2a is arranged so that the ultrasonic waves are incident perpendicularly to the welding part 3a, and the other one is arranged so that the ultrasonic waves are incident to the welding part from an oblique direction as shown in Fig. 11. Probe 2
b, the fuel rods were rotated, and an attempt was made to determine whether the detection signal of the ultrasonic flaw detector exceeded a certain alarm level range.

However, in this case, as shown in Fig. 4(a), the cross section 3C of the welded part has a more complicated shape than the pipe;
When using the oblique angle method in which ultrasonic waves with a normal frequency of MHz or less are incident from an oblique direction, there is interference such as reflection of ultrasonic echoes from the notch 3d, and it is difficult to detect only those above this detection level as defects. This poses a problem in that the sensitivity for detecting defects such as bores becomes low. Furthermore, if a vertical method in which ultrasonic waves are incident perpendicularly is used, the resolution is poor and it is difficult to detect defects such as bores, and for this reason, the ultrasonic inspection method could not be adopted.

Furthermore, since the fuel rods are filled with pellets of uranium dioxide or the like, and the pellets are made of ceramic, there is a concern that when the fuel rods are rotated, they may break due to impact.

In view of these points, it is an object of the present invention to provide an ultrasonic inspection device for nuclear fuel rod welds that does not have the above-mentioned disadvantages.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides an apparatus for inspecting end plug welds of nuclear fuel rods using ultrasonic waves. A rotating body supported and attached to the rotating body,
A probe that transmits and receives ultrasonic waves in the axial direction of a rotating body, a nozzle that injects an ultrasonic transmission liquid from the probe side toward the object to be inspected, and A rotatable signal coupling mounted on the opposite side of the mounting position, an ultrasonic flaw detector connected to the probe via the signal coupling, and connected to the rotating body via the rotatable water supply coupling. a liquid supply device that supplies an ultrasonic transmission liquid to the nozzle; a holding device that holds the fuel rod concentrically with the rotating body and moves and positions the fuel rod; and a holding device that moves the fuel rod and the rotating body relative to each other in an axial direction. It is characterized by having a means.

In addition, the rotatable signal coupling is a coaxial connector for high-frequency transmission, is arranged coaxially with the axis of the rotating body, and is rotatably electrically coupled to the sliding part via mercury, etc. It is characterized by

Additionally, it is equipped with a processing device such as a computer that stores and analyzes the output signal from the ultrasonic flaw detector, and a means for detecting the rotation angle of the rotating body and generating pulses according to the rotation angle, and a predetermined distance according to the rotation. It has a means for shifting the relative axial position of the fuel rod and the probe, and generates ultrasonic pulses synchronized with the pulses according to the rotation angle, and when the ultrasonic pulses are incident on the object to be inspected, the individual ultrasonic pulses are The output signals from the ultrasonic flaw detector corresponding to the sonic pulses are input to a computer or other processing device, and from these signals a two-dimensional image of the inspection target part is formed in the storage section of the computer or other processing device. The present invention is characterized in that an inspection judgment such as a pass/fail judgment is made on the object to be inspected based on the special @ quantity.

The present invention is also characterized in that the signal input to the processing device, such as a computer, is a wall thickness value of the object to be inspected, or a value corresponding to the wall thickness value and the echo height from within a predetermined internal depth range.

Further, it is characterized in that an ultrasonic flaw detector having an ultrasonic frequency of approximately 3 OMHz or more is used.

(Operation) The welded part of the nuclear fuel rod held in the nuclear fuel rod holding mechanism is set in a position facing the probe, and the probe is operated while the ultrasonic transmission liquid is injected and supplied from the nozzle toward the welded part. The entire surface of the welded area is scanned by rotating a rotating body equipped with a probe and a nozzle around its axis, and moving the fuel rod and probe relative to each other in the axial direction. Since values corresponding to the rotational position and the axial movement position can be obtained, a two-dimensional image can be formed by the processing device and two-dimensional feature quantities can be extracted.

Furthermore, since high frequency waves of 30 MHz or more are used, high resolution can be obtained. Furthermore, since a coaxial rotatable coupling is used, high-frequency signals can be transmitted between the ultrasonic flaw detector and the probe without problems such as noise, attenuation, and reflection.

Furthermore, since there is basically no need to rotate the fuel rods,
There is no fear of chipping the beret.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 6.

In FIG. 1, reference numeral 20 denotes a pedestal fixed to a base 21, and is rotatably supported by the pedestal 20 via a rotating body 22 or a bearing 23 so as to be rotatable around a horizontal axis.

A probe 24 is attached to one end of the rotating body 22.
The rotating body 2 is fixed so as to face the central axis of the
A rotatable signal coupling 35 is attached to the other end of 2.

The rotating part 34 of the coupling is fixed to the rotating body so that it can rotate with the rotation of the rotating body 22, and the fixing part of the coupling is fixed to the base 21 via a support.

A coaxial cable 33 from the probe 24 is connected to the rotating part 34, a coaxial cable 36 from the ultrasonic flaw detector 200 is connected to the fixed part, and the probe is fixed to a rotating body that is rotatably supported. This allows signal transmission between the probe 24 and the ultrasonic flaw detector 200.

Furthermore, as shown in FIG. 2, this rotatable signal coupling 35 has a coaxial structure centered on the central axis of rotation, and is in a state where impedance matching is achieved and mercury 38. 39 and are electrically coupled to each other, so that the signal has a high frequency of 30 MHz or more and there is no noise, reflection, or abnormal attenuation even when the rotating body 22 rotates at high speed.

A pulley 25 is fixed to the rotating body 22, and a belt 28 is wound between the pulley 25 and a pulley 27 fixed to a motor 26.

Further, a water supply coupling 29 is attached to the rotating body 22. That is, the rotary water barrel 29a of the water supply coupling 29 is attached to the rotating body 22, and the fixed water barrel 29a is attached to the rotating body 22.
b is fixed to the base 21 via a support. An example of an ultrasonic transmission liquid is supplied from the rotating water barrel 29a via the vibrator 40 to the nozzle 39 disposed at the tip of the probe 24 so as to surround the ultrasonic irradiation port at the tip of the probe. It is now possible to send some water. Rotating water barrel 29a
and the fixed water barrel 29b are slidably connected by a seal 31, and in a state where the rotating water barrel 29a rotates together with the rotating body 22, water is passed from a water supply pump (not shown) through a pipe 32, 40 without leaking. Stroke so that water can be supplied to the nozzle 39.

Further, the nozzle opening 39a of the nozzle 39 is directed toward the central axis of the rotating body concentrically with the probe 24.

Incidentally, the water receiver of the probe 24 mounting portion of the rotating body 22 is disposed in a tank 41, and the water receiver is connected to the tank 41 via a waste water vibrator 42. Therefore, waste water can be stored in a tank (not shown) and the water can be circulated using a pump.

Furthermore, a fuel rod holding device 43 is disposed on the opposite side of the water receiver from the rotating body 22 with respect to the tank 41 .

That is, a pedestal 44 is provided on the base 21, and an axial X table 45 that supports the fuel rod 3 on the same axis as the rotating body 22 and is movable in the axial direction is provided on the pedestal 44. The fuel rods 3 are mounted on the mount 44.
A support roller 46 for supporting the fuel rod and a coarse movement mechanism button 47 for the fuel rod are provided.

In addition, in the figure, reference numeral 48 is a clamp provided on the axial direction X table 45, and 4 are balance weights for smooth rotation.

Further, another pulley 54 is fixed to the rotating body 22 and is wound around the pulley 52 of the rotary encoder 53 via a belt 51 so that rotation can be transmitted to the rotary encoder 53.

The pulse output of the rotary encoder is inputted to the ultrasonic probe [H2O0] via the amplifier 310 as necessary, and an electric pulse synchronized with this pulse is generated, thereby causing the probe 24 to generate high-frequency ultrasonic waves. can do. By selecting the diameter of each pulley and the number of pulses generated per rotation of the rotary encoder, it is possible to set the number of ultrasonic pulses required during one rotation of the rotating body.

In addition, this pulse is applied to the pulse motor 55 that moves the fuel rod 3 in the axial direction via the frequency division stem 320 via the motor controller 330. be.

Therefore, in order to inspect the welded part of the fuel rod, first, the fuel rod is positioned at a predetermined position using the coarse movement mechanism button 47.
It is pressed and fixed to the axial direction drive table 45 by a fixed cylinder 48. After releasing the holding of the bushing 47, when the motor 26 is rotated in response to a command from the processing device, the pulse motor 55 rotates in proportion to the number of rotations, and the fuel rod 3 is moved in the axial direction. On the other hand, the output signal of the ultrasonic flaw detector 200 is manually input to the processing device 300 every time a pulse is generated. Rotating body 1
Since the number of pulses during rotation is set in the processing device, if the output signal is displayed as a matrix for one rotation operation for each set value, it can be formed as a two-dimensional image in the memory in the processing device. After completion of rotation at a predetermined number of rotations, the rotation can be stopped in response to an instruction from the processing device, the clamp 48 can be released, and the fuel rod can be pulled out to the original position by the coarse movement gear 47. Furthermore, by providing a fuel rod exchange mechanism, it is possible to perform automatic inspections one after another.

By the way, as shown in FIG. 3, when the ultrasonic flaw detector 200 receives an external pulse 201 as a trigger, it generates a pulse 202 that activates the probe after a certain period of time. This pulse is converted into an ultrasonic pulse by the probe 24 directed toward the fuel rod weld, propagates through the water injected from the nozzle, and enters the fuel rod weld. A portion of the ultrasonic waves is reflected by the surface of the fuel rod weld and is converted into a pulse signal 203 by the probe 24.Also, as shown in FIG. If there is a reflective defect, the ultrasonic wave will be reflected from the bottom surface of the defect and sent to the probe 2 as a pulse signal 204 delayed by the sound wave propagation time from the pulse.
Converted by 4.

Therefore, since the time interval between both pulse signals depends on the wall thickness at that position, by measuring this time interval, the wall thickness can be measured, and abnormalities such as a decrease in the wall thickness of the welded part can be detected. can be detected. Furthermore, if necessary, as shown in FIG.
The peak of the pulse 206 within this range can be detected by cutting out and amplifying the pulse 206 in this range. By excluding values below the noise level from this peak value, defects such as minute porosity can be detected separately from relatively large signals such as surface waves and bottom waves.

Now, as mentioned above, the number of pulses in one rotation is a set value, and as shown in FIG.
It can be expanded into dimensions and stored in the processing device. Moreover, if this is displayed, the values such as the wall thickness can be expanded and displayed in two dimensions as shown in FIG. 4(c) 208. By the way, in order to guarantee the soundness of a welded part, it is necessary to detect basic defects such as insufficient penetration, reduced wall thickness, and porosity, and to distinguish and judge them from healthy ones. In addition, to perform the inspection automatically,
These judgments need to be made automatically.

Therefore, in this embodiment, as shown in FIG. 5, data is searched line by line from the two-dimensional data stored in the processing device, and whether the position is the same as the position of the butt surface 210 before welding or is closer to the end plug. If there is a wall thickness value detection area 212 connected to the area 211 where the tube side wall thickness value was obtained, it is determined that the melt penetration is insufficient. As a result, the so-called Elongate Void 2, which is good as a sound material without reducing the wall thickness, can be used.
Even if there is 13, it can be rejected blindly or passed depending on the need, and an accurate judgment can be made.

Regarding porosity, as shown in FIG.
Pass/fail determination can be made by extracting characteristic data such as the area of each of 214d. As a result, compared to the conventional method of determining only based on the peak value of the entire welded part, it is possible to determine based on the area or a more direct characteristic quantity, thereby improving accuracy.

A well-known image processing algorithm can be used to extract the feature amounts as described above, and in this embodiment, this is realized by a program of a microprocessor built into the processing device 300. Further, a circuit for measuring pulse intervals and peak values is well known, and is realized by a circuit built into the ultrasonic detector rgJa.

Further, in this embodiment, since ultrasonic waves with a high frequency of 30 MHz or higher are used, sufficient wall thickness measurement resolution and sufficient temporal and spatial resolution for porosity detection can be obtained.

Furthermore, since the probe is basically rotated without rotating the fuel rod, there is no concern that pellets within the fuel rod will be damaged by the rotation of the fuel rod.

Above, we have described a fuel rod with a structure in which there is no reflection of bottom waves from the end plug side, but as shown in Fig. may be reflected. Instead of regarding the part where the bottom wave is not reflected as the end plug part, it may be determined that the part is the end plug part by detecting the wall thickness of the hollow.

Moreover, although the case where there is one probe has been described above, a high frequency oblique probe of 30 MHz or more can be additionally arranged together with the nozzle if necessary.

In this case, even if the signal coupling is of a coaxial type, the flaw detection described above is performed by transmitting, receiving, and detecting signals in a time-sharing manner as shown by adding the signal arrangement to Fig. 3(b). I can do it. In this case, since the number of directions of ultrasonic irradiation increases, it is possible to further improve reliability. It is particularly effective to add this when there is a possibility that a vertically long defect may occur.

Furthermore, the probe itself may have one probe or may have multiple transducers. In this case as well, flaw detection and wall thickness measurement are possible by processing the signals in a time-division manner.

In addition, in the above embodiment, rotation is detected by a rotary encoder, and the detected pulse generates an ultrasonic pulse in the probe, and the fuel feed pulse is used as an axial feed pulse and a motor drive pulse. It is sufficient that the generation of sonic pulses is synchronized; for example, a processing device can generate synchronized pulses, which can drive motors in rotation, axial direction, and other directions, or cause a probe to generate ultrasonic waves. You can also do this.

[Effects of the Invention] Since the present invention is configured as described above, it requires visual inspection like the X-ray radiography method, takes time to make judgments such as development, and does not allow online inspection. It is possible to eliminate disadvantages such as large size.

Furthermore, since high-frequency ultrasonic waves of 30 MH or higher are used, high resolution sufficient for inspecting nuclear fuel rod welds can be obtained. Furthermore, since the coaxial rotatable coupling is placed at the rotation axis position, high frequency signals can be transmitted between the ultrasonic flaw detector and the probe without problems such as noise, attenuation, and reflection.

In addition, since the probe rotation, axial movement, and ultrasound generation are synchronized, inspection can be performed by forming a two-dimensional image with a processing device and extracting two-dimensional features. In terms of inspection, this method can now be applied to the inspection of nuclear fuel rod welds, which was not applicable using conventional ultrasonic inspection methods.

Furthermore, since there is basically no need to rotate the fuel rods, there is no risk of the pellets being chipped by rotating the fuel rods.

[Brief explanation of the drawing]

1 is a diagram of the ultrasonic inspection apparatus of the present invention, FIG. 2 is a cross-sectional view of the signal coupling, and FIG. 3(a) is a diagram showing the time relationship of the signals of the ultrasonic flaw detector of FIG. 1. Fig. 3(b) is a diagram showing the time relationship of the signals of the ultrasonic flaw detector of the added angle probe, Fig. 4(a) is a vertical cross-sectional view of the fuel rod welded part, Fig. 4(b) ) is a developed view of the side low area of the wall thickness value, Figure 4(c) is a diagram showing the wall thickness of the welded part on a plane, Figures 5 and 6 are diagrams showing the display after processing by the processing equipment, Figure 7 is a vertical cross-sectional view of a fuel rod weld using an end plug with a bore, and Figure 8 is a conventional X
FIGS. 9 to 11 are diagrams showing the wire ridge geometry method, and FIGS. 9 to 11 are diagrams showing the ultrasonic flaw detection methods that have been tried in the past. 3...Nuclear fuel rod, 2a...Fuel rod welded part, 20.
... Frame, 22... Rotating body, 24... Ultrasonic probe, 26... Rotating motor, 29... Water supply coupling, 35... Signal coupling, 3... Nozzle, 41
...Water receiver is tank, 43...Nuclear fuel rod holding mechanism, 47...Coarse movement button, 21]...Thickness display area, 214...Poronty display area.

Claims (1)

[Scope of Claims] 1. An apparatus for inspecting end plug welds of nuclear fuel rods using ultrasonic waves, which comprises: a rotating body rotatably supported on a pedestal so as to be rotatable about the longitudinal axis of the fuel rod; and the rotating body. A probe is attached to the rotor and transmits and receives ultrasonic waves in the axial direction of the rotating body, a nozzle that injects ultrasonic transmission liquid from the probe side toward the object to be inspected, and a A rotatable signal coupling mounted on the opposite side of the probe and the nozzle mounting position, an ultrasonic flaw detector connected to the probe via the signal coupling, and a rotatable water supply coupling. a liquid supply device that is connected to the rotating body and supplies an ultrasonic transmission liquid to the nozzle; a holding device that holds the fuel rod concentrically with the rotating body and moves and positions the fuel rod; and a holding device that connects the fuel rod and the rotating body. 1. A nuclear fuel rod welded part ultrasonic inspection apparatus, comprising means for relatively moving a welded part of a nuclear fuel rod in an axial direction. 2. The rotatable signal coupling has a coaxial structure for high frequency transmission, is arranged coaxially with the axis of the rotating body, and is rotatably electrically coupled to the sliding part via mercury, etc. Claim 1, characterized in that an ultrasonic flaw detector having an ultrasonic frequency of approximately 3OMHz or higher is used.
The ultrasonic testing device described. 3. Also equipped with a processing device such as a computer that stores and analyzes the output signal from the ultrasonic flaw detector, means for detecting the rotation angle of the rotating body and generating pulses according to the rotation angle, and a predetermined distance according to the rotation. It has a means for shifting the relative axial position of the fuel rod and the probe by 100 degrees, and generates ultrasonic pulses synchronized with the pulses according to the rotation angle, makes them incident on the object to be inspected, and each ultrasonic pulse The output signals from the ultrasonic flaw detector corresponding to 2. The ultrasonic inspection apparatus according to claim 1, wherein an inspection judgment such as pass/fail judgment is made on the object to be inspected based on the quantity. 4. According to claim 3, wherein the signal input to the processing device such as a computer is a wall thickness value of the object to be inspected, or a value corresponding to the wall thickness value and the height of an echo from within a predetermined depth range inside the object. Ultrasonic inspection equipment.