KR101444078B1 - Nondestructive Testing Apparatus and Method for Penetration Nozzle of Control Rod Drive Mechanism of Reactor Vessel Head - Google Patents

Abstract

An apparatus and method for non-destructive inspection of a reactor head control rod drive apparatus are provided. The nondestructive inspection apparatus according to the embodiment of the present invention detects ultrasonic waves generated by scanning a laser to a welding portion between a reactor upper head and a control rod driving device pipe, and a control rod driving device pipe, and images the sensed ultrasonic waves , There is no change in the position of the ultrasonic sensor for detecting the ultrasonic waves while the laser is scanned at a plurality of points in the specific region, and the damage visualization based on the ultrasonic wave imaging is performed. As a result, the inspection time is significantly reduced, leading to a shortening of inspection time, resulting in a direct economic effect.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-destructive testing apparatus,

The present invention relates to a non-destructive inspection apparatus and method, and more particularly, to an apparatus and method for nondestructive inspection of a control rod drive pipe tube provided in a reactor head.

As shown in FIG. 1 (a), a control rod drive mechanism (CRDM) of a reactor includes a reactor vessel head (RVH) and a plurality of penetration nozzles provided therein . As shown in Fig. 1 (b), the pipe tubes of the control rod drive apparatus are installed through the different welding on the reactor head.

However, two types of cracks are generated in the pipe tube through long-term use.

First, cracks are generated in the welds, and the growth of cracks propagates into the welds on the inner side of the upper head and the inside of the welds, thereby causing pressure in the reactor and leakage of the primary coolant.

Second, the residual stress due to welding and the pressure inside the reactor cause cracks in the tube.

Accordingly, ultrasonic inspection, eddy current inspection, visual inspection, and penetration inspection techniques have been applied to detect cracks in the upper pipe tube of the reactor or welds.

It is a reality that the crack detection technique in the inside of the upper head pipe and the weld part using the eddy current flaw detection technique is not suitable for the inspection of the area other than one point. In addition, since the contact of the probe is made at each inspection point, the reliability of the inspection result is low due to an error that occurs when the probe contact state changes each time.

The pulse / echo ultrasonic inspection technique is a point-by-point inspection based on the movement of a contact probe such as an eddy current probe.

In addition, there is a problem that the penetration testing method requires much time to clean the test surface before and after the test, and to apply and visualize the penetrant.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for nondestructive inspection of a reactor upper head control rod driving apparatus using laser ultrasonic waves and capable of performing sensing at a point without moving during high speed laser scanning and scanning. And to provide a non-destructive inspection apparatus and method for a pipe upper-head control rod drive pipe for a reactor based on ultrasonic wave propagation imaging performed.

According to an aspect of the present invention, there is provided a nondestructive inspection apparatus comprising: a Q-switched diode pumped solid state laser for generating a laser beam pulse; An LMS (Laser Mirror Scanner) which irradiates laser beam pulses generated by the laser to an upper head of the reactor, a welded portion of the pipe, or the inside of the pipe; An ultrasonic sensor for detecting ultrasonic waves generated by the laser; And an image processing apparatus for imaging the ultrasonic waves sensed by the ultrasonic sensor. While the laser is scanned at a plurality of points of a specific region by the LMS, the positions of the ultrasonic sensors are the same.

The LMS can irradiate the laser to the region where the pipe is welded by the different welding at the upper head of the reactor.

The ultrasonic sensor may be a plurality of ultrasonic sensors, or may be a contact ultrasonic sensor or a near-contact non-contact ultrasonic sensor.

The nondestructive inspection apparatus according to an embodiment of the present invention may further include a robot arm for installing the ultrasonic sensor in the vicinity of the specific region.

Further, in the nondestructive inspection apparatus according to an embodiment of the present invention, the LMS can irradiate the laser beam into a pipe tube provided in the upper head of the reactor.

The nondestructive inspection apparatus according to an embodiment of the present invention may further include a laser mirror (LM) for reflecting a laser beam scanned by the LMS to the inner surface of the tube.

In addition, the image processing apparatus can process the adjacent scanning signals to grasp the cracks in a plurality of directions.

The nondestructive inspection apparatus according to an embodiment of the present invention may further include a laser ultrasonic receiver for receiving ultrasonic waves generated by the laser and transmitting the ultrasonic waves to the image processing apparatus.

The laser ultrasound receiver may be plural.

According to another aspect of the present invention, there is provided a nondestructive inspection method comprising: generating a laser; Scanning the laser generated in the generating step with the upper head of the reactor; Sensing ultrasound generated by the laser; And an imaging step of imaging the ultrasonic waves sensed by the sensing step, wherein during the scanning of the laser at a plurality of points of a specific area in the irradiation step, the position of the ultrasonic sensor for sensing the ultrasonic waves in the sensing step is Is fixed.

In the irradiating step, the laser may be scanned and irradiated onto the region where the tube is welded by different welding at the upper head of the reactor or inside the tube of the tube provided at the upper head of the reactor.

As described above, according to the embodiments of the present invention, density inspection can be performed through automatic scanning using laser beams at a few hundred points per second per micrometer, so that area inspection can be performed instead of point inspection, The position of the sensor does not change during scanning and the generation of ultrasonic waves is made in a noncontact manner. Therefore, the reliability of the inspection is very high and the inspection time is significantly reduced, leading to a shortening of the inspection time and a direct economic effect.

1 is a view showing a control rod driving apparatus of a nuclear reactor,
FIG. 2 is a view provided for explaining crack occurrence and leakage in a control rod drive weld portion of a nuclear reactor,
3 is a view provided in the explanation of the reactor upper head control rod drive device pipe-tube weld portion nondestructive inspection apparatus according to an embodiment of the present invention,
FIG. 4 is a photograph showing a physical model and artificial cracks of a control rod driving apparatus manufactured to verify the effectiveness of the non-destructive testing apparatus according to an embodiment of the present invention,
FIG. 5 is a block diagram of an embodiment of the present invention provided in the description of ultrasound spectral imaging (USI) and ultrasound propagation imaging (UWPI)
Fig. 6 is a view provided to explain a dispersion ultrasonic wave by a laser beam irradiated to the periphery of a crack, Fig.
FIG. 7 is a diagram provided in the description of the similarity of adjacent signals in the horizontal /
8 is a diagram provided in the description of a near-wave diffraction wave propagation imaging technique,
FIG. 9 is a view showing an experimental result on the real object shown in FIG. 4,
FIG. 10 is a view for explaining a nondestructive inspection apparatus for a nuclear reactor upper head control rod drive pipe in accordance with another embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a view for explaining a nuclear reactor non-destructive inspection apparatus for a pipe upper head control rod driving apparatus according to an embodiment of the present invention. The 'Nondestructive Inspection Apparatus' (hereinafter abbreviated as 'Nondestructive Inspection Apparatus') is an apparatus for overhauling a weld between a pipe tube and an upper head according to the present embodiment.

To this end, the nondestructive testing apparatus according to the present embodiment performs a high-speed automated high-density laser ultrasonic scanning under an open reactor upper head, and the generated laser ultrasonic waves are contacted or contacted through capacitive and piezoelectric air-coupled transducers Collect or remotely collect with a laser ultrasonic receiver.

At the time of collection, ultrasonic reception is performed at a fixed point for one inspection area (including a plurality of laser irradiation points). Ultrasonic signals collected through scanning are visualized by applying multiple image processing techniques based on ultrasonic wave imaging.

Fig. 3 (a) shows a system configuration of the nondestructive inspection apparatus. 3, a non-destructive inspection apparatus includes an LMS (Laser Mirror Scanner) 110, a Q-switched diode-pumped solid state laser (QL) 120, a QL controller 130, a PC An ultrasound sensor 150, and a sensor system 160.

Due to the nature of the reactor vessel, it is essential to avoid direct human access. To this end, the robot arm 170 is used below the opened reactor vessel head as shown in FIG. 3 (b) to bring the ultrasonic sensor 150 into contact with the inner surface of the reactor vessel head. 3 (d) shows in detail the mechanism of the end portion of the robot arm 170 for contacting the ultrasonic sensor 150 with the inner surface of the reactor vessel head.

The ultrasonic sensor 150 can be implemented as an amplifier integrated PZT sensor having a diameter of 4 mm and a center frequency of 350 kHz. In order to increase the ultrasonic wave transmission rate, a gel contact medium is used in a protective film of the sensor. The ultrasonic sensor 150 can be implemented in both contact type or near non-contact type sensors.

3 (c), the ultrasonic sensor 150 may be replaced with the ultrasonic receiver 180. [0034] FIG. This case is useful in that the robot arm 170 is not necessary.

Next, the periphery of the dissimilar welding portion is scanned by the LMS 110 at a high speed laser. To this end, a Q-switched diode-pumped solid state laser (QL) 120 having a wavelength of several hundreds to several thousands of nanometers generates a laser beam pulse for 8 ns under the control of a QL controller 130, 110 scan the laser beam to the inner surface of the reactor vessel head at the same interval.

The laser beam irradiated on the scanning grid point generates ultrasonic waves.

The LMS 110 is provided with a pair of laser mirrors including the wavelength of the laser beam as the operating wavelength, and these mirrors are fixed to two orthogonal galvanomotors having several hundreds of rad / s at the maximum angular velocity. Each mirror can be rotated ± 20 degrees from top to bottom or from left to right.

The pulse repetition frequency (PRF) of the QL controller 130 is synchronized with the movement of the Galvano motors so that the laser pulses are irradiated once at each lattice point. Specifically, as shown in FIG. 3 (e), the laser beam is irradiated to the respective points along the scan path in the region having the width (L _H ) and the length (L _V ) of the constant interval (?).

Ultrasonic waves are generated at the respective points by the laser beam. The generated ultrasonic waves are sensed by the ultrasonic sensor 150, processed by the sensor system 160, and then stored in the PC 140 for data acquisition and image processing do.

In order to verify the effectiveness of the nondestructive testing apparatus according to the embodiment of the present invention, the control rod driving apparatus was manufactured as a real model of actual size as shown in FIG. 4 (a). As shown in Fig. 4 (b), an arc-shaped depth crack was created at the center of the dissimilar metal welding with a maximum depth of 1.5 mm, a length of 15 mm and a width of 0.7 mm.

A plurality of damage visualization algorithms can be applied to the nondestructive inspection apparatus according to the embodiment of the present invention. (UWPI), ultrasonic spectral imaging (USI), wavelet transformed ultrasonic wave propagation imaging (WUPI), and anomalous wave propagation (AWPI) imaging: conversion of anomalous wave propagation images) and local wavelength imaging (LWI).

The UWPI method reorders the 3D data structure into a 1D time-domain signal. That is, as shown in FIG. 5A, one time-domain wave signal is represented by N sampling points, and (L _v /? + 1) And stored in a sheet.

The 2D array, N x (L _v /? + 1), is generated by arranging the signals as shown in Fig. 5 (d). After generating all the horizontal path spreadsheets of (L _H / Δ + 1), this spreadsheet is rearranged into a 3D data array of N × (L _v / Δ + 1) × (L _H / Δ + 1) .

An intensity map on the scanned area representing the amplitude of the signal for each point by the color scale is generated by cutting along the time axis as shown in Fig. 5 (f). The N intensity maps are N stop frames in generating a wave propagation image.

5B is a 1D frequency domain signal converted from a 1D time domain signal by applying a fast Fourier transform (FFT). In the USI scheme, this transformed signal is used to generate ultrasound spectral video. This signal is processed in the same way as UWPI through the arrangement, truncation, and video generation procedures.

Each frame of the USI video represents the spatial distribution of the spectral amplitudes on a color scale. At this time, if the ultrasound induced by the damage shows a frequency change, the damaged area is effectively visualized because it can be identified in the cut frame at each frequency. Also, frequency components found in USI, including damaged parts, are available for WUPI. When the wavelet transformed 1D time domain signal is selected from the wavelet response as shown in FIG. 5C, the center frequency and the damage-related frequency can be selected to visualize the propagation of the fundamental wave and the damage-related wave, respectively.

The WUPI method rearranges the selected frequency and the 1D wavelet transform signal in the same manner of UWPI as shown in (d) to (f) of FIG. 5 to generate wavelet-transformed ultrasonic propagation video.

In the nondestructive inspection apparatus according to the embodiment of the present invention, an improved AWPI method to which an appropriate AWPI-modified appropriate crack visualization method is applied is applied for area damage evaluation.

In the case of area damage such as thinning, peeling, or separation involving a large area of cracks, if an ultrasonic wave is generated by a laser beam irradiated in the damaged area, an isolated wave (a 2D standing wave Is present along with the scattered waves due to the laser irradiated around the area damage.

As shown in Fig. 6 (a), when the ultrasonic wave is generated by the laser beam irradiated to the periphery of the crack (i or i + 1), the partial ultrasonic component is scattered in the crack to become a dispersed wave.

In an embodiment of the present invention, for a crack at a target adjacent to the surface, such as a primary water stress corrosion crack (PWSCC), the waves generated in and around the cracks, as shown in Figure 6 (b), show significant differences.

FIG. 7A shows horizontal adjacent signals obtained from (40.0, 34.2), (40.1, 34.2) and (40.2, 34.2) of the original region. Similarly, FIG. 7B shows the vertical adjacency signals obtained from (40.0, 34.2), (40.0, 34.3) and (40.0, 34.4). Horizontally or vertically adjacent signals generated on the circle surface show very strong similarities with each other regardless of direction.

Figure 7 (c) shows the signals obtained at (14.0, 12.3), (14.1, 12.3) and (14.2, 12.3), which are three horizontal adjacent points located close to the artificial crack. It can be seen that these adjacent signals also have very strong similarities. Since the 2mm laser beam scans the surface cracks in almost that direction, the interaction between the laser beam and the cracks is not significantly different, and thus the signals generated in close proximity are very similar.

On the other hand, since the laser beam scans the surface cracks almost perpendicular to its direction, as shown in Fig. 7 (d), the vertically adjacent signals are considerably different despite a small interval of 0.1 mm.

As a result, existing AWPI algorithms that do not take into account the directionality of cracks that select two adjacent signals may fail to visualize cracks parallel to the processing direction. Accordingly, the nondestructive testing apparatus according to the embodiment of the present invention proposes a bidirectional AWPI for processing two-directional adjacent signals.

The AWPI algorithm includes signal processing that can match two signals with different arrival times.

When determining the number of sampling points to be moved, if the number of sampling points to be moved is determined when the subtraction signal s (N) _i -s (N + 1) _{i + 1} has the minimum RMS value, It is possible to scan and move the time axis of the second signal.

Here, i represents the movement amount, and T and N represent the sampling interval and the number of data points during signal acquisition. The travel time is expressed as l (T / N) [sec.]. The first signal S (N) _i and the second signal s (N) _{i + 1} are matched if s _RMS calculated at l _max (T / N) <t <T _max I think.

Thus, if two adjacent waves obtained in the original region are similar, even if the time point adjustment is made to minimize their difference (but the two adjacent waves obtained in the damaged region are different even after the time point adjustment) The signal still contains visible residual components. The nature of the residual wave depends on the type of damage that generates the incident wave, the dispersive wave and / or the residual component of the isolated wave.

8A shows the difference between horizontal adjacent waves using the first signal at (14.0, 12.3) and the second signal at (14.1, 12.3) of the surface cracks. Due to the high similarity of the horizontal adjoining wave and its parallel crack direction, a low residual component of the incident wave appears in the difference signal. Therefore, AWPI due to the horizontal adjacent wave differences may fail to enhance the visibility of the anomalous wave components except the incident wave, which is shown in FIG. 9 (d).

8B shows a result obtained by subtracting the vertical adjacent wave using the first signal at (14.0, 12.3) and the second signal at (14.0, 12.4). FIG. Shows the high residual component of the incident wave having a high amplitude even though the signals have the same interval as the signals shown in FIG.

The subtraction results of the vertically adjacent waves shown in FIG. 8 (c) were calculated using the signals at (40.0, 34.2) and (40.0, 34.3) independent of the surface crack position. In the case of processing with vertically adjacent waves as shown in FIG. 8 (b), the remaining components were completely removed by time point adjustment and subtraction.

Therefore, since the crack direction is not known in actual application programs, bidirectional AWPI is required in order not to overlook any directional cracks.

FIG. 9 is a diagram showing an experimental result on the real object shown in FIG. 9, the performance of the AWPI scheme is superior to that of UWPI, USI, and WUPI.

FIG. 10 is a view of a non-destructive inspection apparatus according to another embodiment of the present invention. The nondestructive inspection apparatus according to the present embodiment is different from the nondestructive inspection apparatus shown in Fig. 3 in that it is an apparatus for inspecting the inside of a pipe.

To this end, the LMS 110 of the nondestructive inspection apparatus according to the present embodiment scans and irradiates a laser inside the tube. In addition, the LM (Laser Mirror) 190, which is additionally provided in the nondestructive inspection apparatus according to the present embodiment, reflects the laser beam scanned by the LMS 110 to the inner surface of the tube.

The description of other configurations is omitted because it is inferred from FIG. 3 and the detailed description thereof.

Also, the lower head penetration nozzle of the reactor can be inspected with a similar configuration, so it is omitted.

In the above embodiments, it is assumed that the ultrasonic sensor 150 and the laser ultrasonic receiver 180 are implemented as a single unit, but this is merely an example for convenience of explanation. The number of these can be realized by a plurality of.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention.

110: Laser Mirror Scanner (LMS)
120: Q-switched diode-pumped solid state laser (QL)
130: QL controller 140: PC
150: ultrasonic sensor 160: sensor system
170: Robotic arm 180: Laser ultrasonic receiver
190: Laser Mirror (LM)

Claims (10)

In the nondestructive test apparatus,
A laser for Q-switching a continuous wave laser to generate a laser beam pulse;
An LMS (Laser Mirror Scanner) for scanning the laser beam pulses generated by the laser;
An ultrasonic sensor for detecting ultrasonic waves generated by the laser;
An image processing device for imaging the ultrasonic wave sensed by the ultrasonic sensor;
A robot arm for installing the ultrasonic sensor at a specific position; And
And a LM (Laser Mirror) that reflects the laser scanned and irradiated by the LMS in a pipe tube,
When the LMS scans the laser to a different weld between the upper reactor head and the control rod drive pipe, the ultrasonic sensor installed on the dissimilar welding part detects the ultrasonic wave by the robot arm,
When the LMS irradiates the laser to the inside of a control rod drive pipe tube provided in the upper head of the reactor, the LM scans the laser to the inner surface of the pipe tube, and the ultrasonic sensor senses the ultrasonic wave,
The image processing apparatus processes adjacent ultrasonic waves in a plurality of directions to grasp a crack,
The nondestructive inspection apparatus includes:
Further comprising a controller for adjusting a scanning interval and a time of the laser beam pulses so that a difference between adjacent ultrasonic waves is minimized.
delete The method according to claim 1,
The ultrasonic sensor includes:
A contact type ultrasonic sensor or a non-contact type ultrasonic sensor.
delete delete delete delete The method according to claim 1,
And a laser ultrasonic receiver for receiving ultrasonic waves generated by the laser and transmitting the ultrasonic waves to the image processing apparatus.
Generating a laser;
Irradiating the laser generated in the generating step;
Sensing ultrasound generated by the laser; And
And imaging the ultrasound sensed by the sensing step,
Wherein the position of the ultrasonic sensor for sensing the ultrasonic waves in the sensing step is fixed while scanning the laser to a plurality of points of the specific region in the irradiation step,
In the irradiating step, when the laser beam is scanned and irradiated onto a different weld between the upper head of the reactor and the control rod drive pipe, the ultrasonic sensor installed on the dissimilar welded part by the robot arm detects a part of the pipe, The ultrasound waves, in turn,
Wherein when the laser is irradiated into the control tube drive pipe tube provided in the upper head of the reactor in the irradiating step, a laser mirror (LM) irradiates the laser onto the inner surface of the tube,
Wherein the imaging step comprises:
And processing the adjacent ultrasonic waves in a plurality of directions to grasp the cracks,
Wherein said examining comprises:
Wherein the scanning interval and time of the laser beam pulses are adjusted so that a difference between adjacent ultrasonic waves is minimized.
delete

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