JP2001343481A - Crack diagnostic method for reactor core internal structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack diagnostic method for reactor core internal structure, capable of totally diagnosing cracks on the core internal surface remotely and in non-contact manner and reducing the exposure dose of workers and drastically reducing work man-hours. SOLUTION: A surface wave is generated on the surface of reactor core internal structure, a laser light is cast on the surface and based on the speckle pattern of laser holography that reflection light from the surface forms, cracks existing on the surface of the core internals are surveyed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for remotely and non-contactly diagnosing a crack existing on the surface of a reactor internal structure in the air or underwater.

[0002]

2. Description of the Related Art In the case of an operating nuclear power plant structure, if an opening crack occurs in the material surface of the structure (particularly, the surface of a welded portion) due to long-term operation, the reactor water in the nuclear reactor is conventionally discharged. The shield is installed by draining the water, and then the surface of the material is subjected to liquid dye flaw detection (PT) to perform crack detection. In particular, since reactor internals are activated, it is required to install shields to reduce the exposure of workers as a measure to eliminate the radiation shielding effect by draining reactor water. .

[0003]

Since water drain (drainage) is indispensable in the conventional PT, a large-scale shielding operation is required to reduce the exposure of the worker. Also,
In the case of PT, an operation of directly contacting the site to be inspected is required, and the number of operation steps cannot be reduced so much for the application of a staining solution.

An object of the present invention is to provide a macroscopic diagnosis of cracks on the surface of a reactor internal structure in a remote non-contact manner, and to reduce the amount of exposure of an operator and greatly reduce the number of work steps. It is to provide a diagnostic method.

[0005]

An embodiment for achieving the above object is to generate a surface wave on a surface of a reactor internal structure, irradiate the surface with laser light, and reflect light from the surface. Cracks present on the surface of the furnace internals are detected based on a speckle pattern formed by laser holography formed by the laser beam.

[0006] Preferably, the crack diagnosis is performed in the reactor water by using a laser beam having a wavelength with little attenuation in the water. As a wavelength having little attenuation in water, a wavelength in the range of 500 to 600 nm can be used. For example, 533 nm N
d: The second harmonic of YAG is realistic, but a ruby laser with a wavelength of 694 nm, which is excellent in coherence, is also effective in some cases.

[0007] Surface waves include hammering by dropping an iron ball on the surface of a structure, hammering by irradiating a pulse laser,
It can be generated by mechanical hammering of the surface (hit by a hammer) or the like. Crack diagnosis is performed by detecting, via a speckle pattern, a phenomenon in which the surface wave is diffracted by a crack existing on the surface of the structure.

[0008] Hammering is instantaneously performed with a small load that does not damage the material surface, and generates a surface wave.
This generates a shear wave surface wave of several hundred kHz to several MHz. Surface waves propagate through the surface of the material at a depth approximately equal to the wavelength from the surface, and are reflected and diffracted by surface cracks. The propagating surface wave, reflected wave and diffraction wave are detected from the speckle pattern of laser holography, and the position of the surface crack,
Find the shape and dimensions. When hammering of the material surface is impossible, a surface wave can be generated by a continuous vibrator such as a vibrator.

According to this embodiment, the phenomenon in which a surface wave propagating on the surface of a furnace internal structure is reflected and diffracted by a crack existing on the surface in water or in the air using a speckle pattern by laser holography. It can be observed indirectly. Therefore, it is possible to diagnose a crack on the surface of the furnace internal structure without remote contact. This makes it possible to reduce the amount of exposure of the worker at the time of crack diagnosis as compared with the related art, and to significantly reduce the number of work steps. Further, this embodiment can be carried out in a state where the reactor water is held in the reactor pressure vessel. Accordingly, radiation shielding by the reactor water can be obtained, so that the amount of exposure of workers involved in flaw detection work can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is an example in which the present invention is applied to diagnosis of a surface crack of a material. FIG. 1 is a principle diagram of the crack diagnosis according to the present embodiment. FIG. 2 is a schematic configuration diagram of one embodiment of a laser holography apparatus to which the present invention is applied. FIG. 3 is a configuration diagram of the holographic receiver used in the present embodiment.

As shown in FIG. 1, the surface wave generating section 11 of the inspection target material 2 having a surface crack is hammered by hitting an iron ball.
, A surface wave 3 which is a concentric shock wave is generated and propagates concentrically on the surface. The surface wave 3 propagating concentrically on the surface of the inspection target material 2 is reflected by the surface crack 19,
Diffracts at the edge of the surface crack and continues to propagate further. The reflection of the surface wave at the surface crack 19 and the diffracted wave 20 are detected by the distortion of the speckle pattern 10 by laser holography.

As a method of generating a shock wave in the surface wave generating section 11, an iron ball is hit in this embodiment, but hammering by a pulse laser or hammering by a robot arm may be used.

In the laser holography, a coherent laser beam irradiated from a laser 1 is divided into an irradiation laser beam 6 and a reference laser beam 8 by a beam splitter 4,
The irradiation laser light 6 is expanded on the inspection target material 2 by the irradiation optical system 5, and the reference laser light 8 is irradiated on the imaging plate by the reference optical system 9.

The irradiation laser beam 6 is expanded coherently by an irradiation optical system (beam expander) 5 and is evenly applied to a region of a predetermined size set on the inspection target material 2. When the reflected laser light 7 of the irradiation laser light from the inspection target material and the reference laser light 8 are combined on the imaging screen 10a on the same scale, a concentric speckle pattern distorted by the surface crack 19 of the inspection target material 2 10 is projected. This speckle pattern 10
The concentric distortion (speckle pattern distortion) 30 is caused by the reflection of the surface wave 3 by the surface crack 19 and the diffraction at the edge of the surface crack.

FIG. 2 shows the principle and configuration of a laser holography apparatus that draws a speckle pattern 10. Laser light for irradiating the inspection target material 2 is generated by the laser 1. Since the laser beam 6 emitted from the laser 1 is preferably a solid-state laser in the visible light region, the wavelength is 40
0 nm to 1060 nm is conceivable. It is considered that a wavelength around 500 nm to 600 nm is optimal for a diagnostic device,
In water, the second harmonic of Nd: YAG having a small attenuation of 533 nm is suitable, and in the air, a He-Ne laser or a ruby laser having a wavelength of 633 nm which is inexpensive and can obtain high energy is suitable.

The laser beam 6 is applied to the irradiation laser beam 6 for irradiating the inspection target material 2 and the reference laser beam 8 to be synthesized for forming the speckle pattern 10 by the beam splitter 4.
Divided. The irradiation laser beam 6 partially transmitted by the beam splitter 4 is irradiated with the beam expander of the irradiation optical system 5 while being coherently expanded to the inspection target range. Irradiated laser light 6 that has been enlarged and uniformly applied to the inspection range is reflected on the surface of inspection target material 2 to become incoherent reflected laser light 7, and is projected on imaging screen 10 a by reflection optical system 21.

On the other hand, the reference laser beam 8 partially reflected by the beam splitter 4 is once condensed by the reference optical system 9 while being coherent, then reflected by the beam splitter 4 and projected on an imaging screen 10a. Is done. In this case, the optical system is adjusted so that the reflected laser light 7 has the same scale as the image. By superimposing the pattern image of the reflected laser light 7 and the reference laser light 8 on the imaging screen 10a, partial interference of the laser light occurs and an interference fringe called a speckle pattern is drawn. The interference fringes are attenuated when the laser beams are overlapped with a shift of a half wavelength.

When the surface of the inspection target material 2 is flat, the interference fringes have a symmetric and uniform pattern. However, when the surface of the inspection target material 2 generates a surface wave 3 due to impact such as hammering, the surface of the inspection target material 2 has Speckle pattern distortion 30 is generated by out-of-plane vibration due to surface wave propagation of the above. By measuring the speckle pattern distortion 30, it is possible to obtain the fluctuation due to the reflection and diffraction of the surface wave 3 on the surface of the inspection target material.

FIG. 3 shows an overall conceptual diagram of the laser holographic crack diagnosis apparatus. A trigger signal generated when hammering is performed by hitting an iron ball having a diameter of several mm on the surface wave generating portion 11 on the surface of the inspection target material 2 is transmitted to the trigger box 15 through a signal cable, and several tens μm
After a time delay of sec, the laser 1 is operated, and pulse laser light is generated at intervals of several tens of μsec. These μsec (10 ^-6
Time control on the order of seconds) is performed by the control box 14.

When the laser 1 has sufficiently high power or the inspection range (laser beam irradiation range) is smaller than the laser power, the laser 1 of the steady laser beam (CW laser beam) is used.
Can be used.

A laser beam emitted from the laser 1 by a pulse or CW is distributed to an irradiation laser beam 6 and a reference laser beam 8 by a beam splitter 4, and the reference laser beam 8 enters an optical fiber 17 by a condenser lens 18. Transmitted. The incoherent reflected laser light 7 and the coherent reference laser light 8 are interference-synthesized on the same image by the CCD camera 12, and are drawn to an image processing device 16 for image-processing interference fringes (not shown) of the speckle pattern 10. .

Background noise at the time of measurement can be removed by setting a cutoff frequency in the laser measurement system. Also, the hammering method can be performed by thermal shock by irradiating the inspection target material 2 with a pulse laser of several hundred mJ per pulse. In this case, a mechanical structure such as an iron ball dropping device is not required. Becomes

FIG. 5 shows the principle of detecting the surface crack 19 by the speckle pattern 10. Speckle pattern 10
Reflects the situation in which the surface wave propagates concentrically around the position 11a corresponding to the surface wave generator 11. The surface wave is reflected by the surface crack 19, and a speckle pattern 32 of the reflected wave is observed. 19a is a surface crack 19
Is an image corresponding to. On the other hand, the surface wave is concentrically diffracted around the end of the surface crack 19, and a speckle pattern distortion 30 of the diffracted wave is observed.

From the speckle pattern 32 of the reflected wave at the surface crack 19 and the speckle pattern distortion 30 of the diffracted wave at the end of the surface crack 19, the position corresponding to the end of the surface crack 19 (the end of the image 19a). ) 31 can be obtained.

In FIG. 5, the left end and the right end of the speckle pattern 32 of the reflected wave move from the vicinity of the center of the image 19a to the left and right, respectively, and reach the end 31 which is the left end and the right end of the image 19a. When the end of the speckle pattern 32 of the reflected wave reaches the end 31, the speckle pattern 32 of the reflected wave disappears.

As shown in FIG. 5, the speckle pattern distortion 30 includes a speckle pattern 30a generated centering on the left end of the image 19a and a speckle pattern 30b generated centering on the right end of the image 19a. The right end of the speckle pattern 30a moves from the left end of the image 19a to the center, and the left end of the speckle pattern 30b moves from the right end of the image 19a to the center. After the right end of the speckle pattern 30a and the left end of the speckle pattern 30b overlap, as shown in FIG. 5, these two speckle patterns are synthesized and move upward.

Therefore, on the imaging screen 10a, the position where the end of the speckle pattern 32 of the reflected wave disappears, or the speckle patterns 30a and 30b
By calculating the position (center position) serving as the base point at which occurs, the end 31 of the image 19a corresponding to the end of the surface crack 19 can be obtained.

The trace of the movement of the end of the speckle pattern 32 of the reflected wave is traced on the imaging screen 10a, or the speckle pattern 30 is traced.
The shape of the image 19a corresponding to the surface crack 19 can be obtained by tracing the trace of the movement of the right end of a and the left end of 30b.

FIG. 7 shows a halftone image displayed on the display when the surface crack is detected by the speckle pattern 10 by the surface shock wave of the monopole generated from the surface wave generating section 11 due to the steel ball falling. In this example, the apparatus shown in FIG. 3 was manufactured in a laboratory and tested on a stainless steel plate and a steel plate having a thickness of 20 mm or more.

As is clear from FIG. 7, the position and shape of the surface crack can be observed by the speckle pattern 32 of the reflected wave reflected by the surface crack 19. Thereby, a crack can be found.

Next, a method for obtaining the position, shape and size of the surface crack 19 from the speckle pattern will be described with reference to FIG.
This will be described more specifically. FIG. 6 shows an example in which a surface crack is positioned obliquely. Interval L of speckle pattern 10
₀ has a relationship of L ₀ = v / f with the propagation speed v of the surface wave in the inspection target material 2 and the excitation frequency f of the surface. The propagation speed v is determined by the density ρ and the Young's modulus E of the inspection target material 2;
v = (E / ρ) ^0.5 .

Based on the interval L ₀ determined by the speckle pattern 10 and the speckle pattern 32 of the reflected wave, a position 11 a corresponding to the surface wave generator 11 and a surface crack 19
Distance between the end portion 31 of the image 19a corresponding to L ₁ and L ₂
Ask for. The length LC of the image 19a corresponding to the length of the surface crack 19 is obtained from the following equation.

L _C = ((L ₁ sin θ) ² + (L ₂ −L ₁ cos θ) ² ) ^0.5 θ is formed by two straight lines connecting the position 11a and the end 31 as shown in FIG. Angle.

Therefore, by using the optical system of the holographic receiver 23 to previously adjust the magnification of the distance on the imaging screen 10a to 1 with respect to the distance on the inspection target material 2, the above-mentioned length LC can be obtained. The length of the surface crack 19 can be determined. As described above, the speckle pattern distortion 30 or 3
The shape of the surface crack 19 can be determined by displaying (or determining) the image 19a by tracing the trace of the movement of the end of the second part. Further, the imaging screen 1
By determining the relative position of the image 19a with respect to the position 11a on 0a, the relative position of the surface crack 19 with respect to the surface acoustic wave generation unit 11 on the inspection target material 2 can be determined.

When the magnification of the distance on the imaging screen 10a with respect to the distance on the inspection target material 2 is adjusted to n times, the position, the shape and the size of the surface crack 19 may be obtained in consideration of this magnification. .

In the case of this embodiment, the video signal of the speckle pattern 10 monitored by the CCD camera 12 is
By performing the above-described signal processing using the image processing device 16, the position, shape, and size of the surface crack of the furnace internal structure are obtained.

The case where this is used in FIG. 7 described above will be described. The reflected wave speckle 32 in FIG. 7 has almost the same size as the crack length, and in this case, is about 30 mm. Diagnosis of even smaller dimensions is possible. The shock wave propagated from the surface wave generator 11 is reflected by the surface crack 19 to form a reflected wave speckle 32. These are formed by processing the image of the CCD camera 12 of the apparatus shown in FIG.

Next, a state in which the laser holographic crack diagnosing apparatus is applied to a reactor internal structure of an actual machine will be described with reference to FIG. During the maintenance (periodic inspection) of the reactor vessel 28, the reactor water 29
The holographic receiver 23 and the laser oscillator head 1 which are filled to just below 0 and have been subjected to a 3 atmosphere water resistant treatment.
a is inserted into the furnace from the upper grid plate 24, and is supported by a vertically expandable sensor support rod 25 supported by an upper grid plate support stay 26 supported by the upper grid plate 24. A pulse laser generator (not shown) for performing hammering is attached to the housing of the holographic receiver 23.

The holographic receiver 23 and the laser oscillation head 1a perform power supply and data transmission / reception via a cable 27. The holographic receiver 23 and the laser oscillation head 1a are set to have a cross-sectional dimension of 290 mm × 290 mm or less because they are inserted from the upper lattice plate 24. Due to the horizontal movement of the position of the upper lattice plate support stay 26 and the expansion and contraction of the sensor support rod 25, it is possible to diagnose the surface defect of the in-furnace structure without remote contact from any position in the furnace.

A surface laser, which is a concentric shock wave centered on the surface wave generation site, is generated on the surface to be inspected by the pulse laser generator, and the surface wave is macroscopically diagnosed by the holographic receiver 23 into a 290 mm × 29 surface defect.
After continuously obtaining a rectangular image of 0 mm or less, the height (depth) of a surface crack is determined only by a conventional UT or a non-contact laser UT that performs non-contact only on the detected surface defect site.
Sizing. Thereby, the number of man-hours for sizing the surface cracks by the UT or the laser UT can be significantly reduced.

In this embodiment, the surface wave is generated using a pulse laser, but hammering by a robot arm may be used. The device for generating the surface may be separate from the holographic receiver.

As described above, according to the present embodiment, the phenomenon in which surface waves are reflected and diffracted by cracks existing on the surface of the furnace internal structure in the reactor water without contact using a speckle pattern by laser holography can be achieved in a non-contact manner. Since it is possible to observe, it is possible to diagnose cracks on the surface of the internal structure of the furnace without remote contact while reducing the amount of exposure of the workers. Along with this, the number of work steps at the time of crack diagnosis can be greatly reduced as compared with the related art.

FIG. 8 shows a high-speed diagnostic system which combines laser holography and laser UT according to the present invention. In the present embodiment, a rectangular image of a CCD camera 12 is stored for a surface crack which is observed macroscopically by the pulse laser 1 for diffusing and irradiating the propagation and reflection of the surface wave generated by the surface wave generation unit 11 with a beam. , Only at the surface crack site
Sizing of the crack depth by T or laser UT is performed. In the laser holography CCD image, as shown in FIG. 7, the reflection surface of the reflected wave speckle 32 of the surface wave reflected wave at the structure surface cracks 19-a, b, c, and d corresponds to the surface shape of the surface crack 19. I do. By measuring the size of the reflection line, the size of the surface opening of the surface crack 19 is determined. On the other hand, it is also necessary to provide data on the height of cracks in structures such as nuclear reactors. It is known that the crack height can be measured by the laser UT receiver 33 from the arrival time difference between the crack edge of the surface wave and the crack bottom. Thus, the scanning of the laser UT receiver 33 is not performed on the entire structure to be inspected.
The sites 19-a, b, c, and d where the crack height diagnosis is performed can be specified by laser holography. As a result, the number of man-hours required for sizing the surface cracks for applying the UT or the laser UT 32 to the entire inspection target site can be reduced as compared with the case where the apparatus of the present embodiment is not used, and the number of man-hours required for inspection can be reduced.

FIG. 9 shows a configuration diagram of a diagnostic system as another embodiment. The speckle pattern 10 of the surface waves 3 generated at a constant pitch on the surface of the reactor vessel 28 is photographed by the holographic receiver 23, and the reflected wave speckle 32 at the surface crack 19 of the reactor vessel 28 is measured and stored. A laser UT receiver 33 installed in parallel with the holographic receiver irradiates a probe laser beam 34 near a portion where a reflected wave speckle 32 is generated to measure a crack height (depth). These continuous laser measurements are performed by scanning the inner surface of the reactor vessel 28 in the weekly direction 35, thereby enabling high-speed crack length diagnosis and laser
Crack height measurement by T measurement can be realized in a shorter time than when the device of the present embodiment is not used.

[0045]

According to the present invention, a reactor internal structure capable of macro-diagnosing a crack on the surface of the internal structure of the reactor without remote contact, and reducing the amount of exposure of the worker and greatly reducing the number of work steps. Can be provided.

[Brief description of the drawings]

FIG. 1 is a principle diagram of crack diagnosis according to the present invention.

FIG. 2 is a schematic configuration diagram of one embodiment of a laser holography apparatus to which the present invention is applied.

FIG. 3 is a schematic configuration diagram of an embodiment of a holographic receiver to which the present invention is applied.

FIG. 4 is a view showing a state in which the laser holographic crack diagnosis device of the present invention is applied to a reactor internal structure.

FIG. 5 is a diagram showing a principle of detecting a surface crack by a speckle pattern.

FIG. 6 is an explanatory diagram of a method for obtaining a position, a shape, and a size of a surface crack from a speckle pattern.

FIG. 7 is a diagram for obtaining the position, shape, and size of a surface crack from a speckle pattern obtained by an actual experiment.

FIG. 8 is an explanatory diagram of a method for reducing the time and man-hours required for surface crack sizing by combining laser holography and UT.

FIG. 9 is an explanatory diagram of a diagnostic system configuration combining laser holography and UT.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser, 2 ... Material to be inspected, 3 ... Surface wave, 4 ... Beam splitter, 5 ... Irradiation optical system, 6 ... Irradiation laser light,
7: reflected laser light, 8: reference laser light, 9: reference optical system, 10: speckle pattern (interference fringe), 11: surface wave generator, 12: CCD camera, 14: control box,
15 Trigger box, 16 Video processing device, 18
Condenser lens, 19: Surface crack, 20: Diffracted wave, 21: Reflection optical system, 22: Power control unit, 23: Holographic receiver, 25: Sensor support rod, 26: Upper lattice plate support stay, 27: Cable, 28 ... Reactor vessel, 29 ... Reactor water, 30 ... Speckle pattern distortion, 31 ...
Surface crack end, 32 ... reflected wave speckle pattern, 33
... Laser UT receiver, 130 ... Operating floor.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // G01N 21/91 G01M 7/00 A (72) Inventor Tetsuya Matsui 7-2 Omikacho, Hitachi City, Ibaraki, Japan No. 1 Hitachi, Ltd. Power and Electric Development Laboratory (72) Inventor Takao Sakai 3-1-1, Sakaicho, Hitachi City, Ibaraki Pref., Japan Nuclear Power Division, Hitachi, Ltd.

Claims (6)

[Claims] A surface wave is generated on a surface of a reactor internal structure, a laser beam is irradiated on the surface, and the surface of the reactor is formed based on a laser holographic speckle pattern formed by reflected light from the surface. A method for diagnosing a crack in a reactor internal structure, comprising detecting a crack present on a surface of the internal structure. 2. A method for generating a surface wave on a surface of an internal structure of a nuclear reactor, irradiating the surface with a laser beam, and reflecting and diffracting a speckle pattern by laser holography formed by light reflected from the surface. A method for diagnosing a crack in a reactor internal structure, comprising determining at least one of a position, a shape, and a size of a crack existing on a surface of the reactor internal structure based on any one of the methods. 3. A method for diagnosing a crack in a nuclear structure according to claim 1, wherein the surface wave is generated by irradiating a pulse laser or hammering the surface of the nuclear structure. 4. A method for diagnosing cracks in a reactor internal structure according to claim 1, wherein said laser beam is a laser beam having a wavelength with little attenuation in water. 5. The method according to claim 1, wherein the laser beam has a wavelength of 500 to 600 nm. 6. A method for generating a surface wave on a surface of an internal structure of a nuclear reactor, irradiating the surface with a laser beam, and reflecting and diffracting a speckle pattern by laser holography formed by light reflected from the surface. At least one of a position, a shape, and a size of a crack existing on the surface of the furnace internal structure is obtained based on any of them, and a crack depth of the crack is obtained by a UT or a laser UT. How to diagnose cracks in objects