A nuclear power equipment damage detection system based on fiber grating acoustic emission sensor

Abstract

The present invention discloses a nuclear power equipment damage detection system based on a fiber grating acoustic emission sensor, which includes a fiber grating acoustic emission sensor, a connecting boss, an anti-radiation cable, and a high-frequency demodulation module. The fiber grating acoustic emission sensor in the present invention is composed of a metal shell, a metal bottom shell, a top negative thermal expansion joint, a fiber Bragg grating, a diaphragm, and a coupling agent. The present invention uses optical fiber to transmit signals and selects optical fibers with strong anti-electromagnetic interference and anti-radiation capabilities; the top negative thermal expansion joint can achieve temperature compensation for the surrounding environment; the fiber grating high-frequency demodulation system realizes multi-channel transmission of optical signals through a spectrometer, matches the slope of the FBG reflection spectrum with the central wavelength of a tunable laser light source, and converts it into corresponding optical power changes through a photodetector, thereby realizing high-frequency, multi-channel demodulation; utilizing the advantages of fiber grating distributed measurement, multi-channel distributed measurement of nuclear power equipment structural damage acoustic emission signals can be realized.

Description

Technical Field

[0001] The invention relates to the field of equipment monitoring, and in particular to a nuclear power equipment damage detection system based on a fiber grating acoustic emission sensor. Background Art

[0002] In recent years, the development of global nuclear energy has become an irreversible trend of the times. Nuclear energy has begun to be widely used in the industrial field, and the investment proportion has increased year by year. Among them, the reactor pressure vessel is one of the most important equipment in a nuclear power plant. It is the key to ensure the normal and safe operation of the nuclear power system. The local defects of the pressure vessel make the safety of the reactor pressure vessel an unstable factor, which is prone to major accidents, such as the Fukushima nuclear power plant incident, which caused immeasurable economic losses and social impact. Therefore, damage detection of reactor pressure vessels has become an urgent problem to be solved, but the working environment of reactor pressure vessels is relatively harsh and complex. In a strong radiation environment, the detection range is large and the measurement defect requirements are high. Therefore, the research on acoustic emission signal perception technology of structural damage in nuclear environment has become one of the research hotspots in the industry and academia, which has very important contemporary and practical significance for the detection of structural damage.

[0003] As a medium for optical signal transmission, optical fiber has the characteristics of anti-electromagnetic interference, ultra-high voltage insulation, explosion-proof and flame-proof, and has broad application prospects in extremely harsh environments such as nuclear radiation, high temperature and high pressure. In addition, optical fiber sensors also have the characteristics of small size and high sensitivity, but many acoustic emission sensors designed based on the principle of optical fiber sensing have the disadvantages of small resonant frequency and low sensitive point under the resonant frequency, which do not meet the high resonant frequency requirements of sensors in nuclear radiation environments. Summary of the invention

[0004] The purpose of the present invention is to provide a nuclear power equipment damage detection system based on a fiber grating acoustic emission sensor, which has the advantage of being able to detect equipment structure damage in a nuclear radiation environment.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] A nuclear power equipment damage detection system based on a fiber Bragg grating acoustic emission sensor comprises a sensing module, a demodulation module and an analysis module. The sensing module comprises a housing unit, a signal sensing unit and a transmission cable. The housing unit comprises a metal shell, a metal bottom shell and a boss base. The upper end of the metal bottom shell is threadedly connected to the lower end of the metal shell, and the boss base is threadedly connected to the lower end of the metal bottom shell. The signal sensing unit comprises a negative thermal expansion joint, a fiber Bragg grating, a diaphragm and a coupling agent. One end of the negative thermal expansion joint is fixedly connected to the transmission cable, the diaphragm is fixed in the housing unit, the negative thermal expansion joint is connected to the diaphragm through an optical fiber, the fiber Bragg grating is located on the optical fiber, and the coupling agent is filled in the space between the diaphragm and the metal bottom shell. The sensing module is used to detect an object to obtain damage information of the object. The demodulation module is used to demodulate the sensing light signal and generate electronic information. The analysis module is used to analyze the electronic information and draw a damage conclusion.

[0007] Preferably, a high temperature glue is provided in the negative thermal expansion joint, and the high temperature glue is used to fill the negative thermal expansion joint.

[0008] Preferably, the transmission cable is an anti-radiation cable, which includes an inner core, an anti-radiation layer and a protective layer. The anti-radiation layer is wrapped around the surface of the inner core, and the protective layer is located at the outer edge of the anti-radiation layer. The anti-radiation layer includes a metal layer, a polyimide coating and an aluminum coating from the inside to the outside, and the protective layer includes a waterproof layer and a polyethylene outer sheath layer.

[0009] Preferably, the demodulation module is a high-frequency demodulation module, which includes a tunable laser source, a high-frequency data collector, an amplifier, a photoelectric converter and a fiber optic circulator. The signal sensing unit is connected to a port of the fiber optic circulator through a transmission cable, the fiber optic circulator is connected to the photoelectric converter at the next port according to the rotation direction, the photoelectric converter is connected to the amplifier, the amplifier is connected to the high-frequency data collector, and the high-frequency data collector is connected to the analysis module.

[0010] Preferably, one side of the tunable laser source is connected to an optical splitter, the demodulation module further comprises 12 distributed sensors, and the port of the optical splitter is connected to the 12 distributed sensors via a transmission cable.

[0011] Preferably, the analysis module is a PC-side signal processing device.

[0012] The beneficial effects of the present invention are:

[0013] 1. The present invention can obtain high resonance frequency and high resonance point sensitivity by optimizing the film design and the fiber Bragg grating tension suspension configuration;

[0014] 2. The present invention greatly improves the performance of the sensor by optimizing the design of the outer coating process of the fiber grating;

[0015] 2. The present invention connects the diaphragm and the bottom shell by a coupling agent, which can reduce the attenuation of elastic wave signals and enhance the transmission performance of acoustic emission optical fiber signals;

[0016] 3. The present invention uses the negative expansion coefficient material on the top of the sensor to compensate for the wavelength drift caused by the change in the detection environment temperature, thereby reducing the measurement error caused by the temperature change;

[0017] 4. The present invention uses radiation-resistant cables to enhance the anti-interference ability of optical fibers and prevent the cables from aging prematurely under strong radiation conditions, thereby extending the service life of the sensor;

[0018] 5. The present invention realizes multi-channel transmission of optical signals through an optical splitter, adopts 12 fiber grating acoustic emission sensors to realize distributed measurement, and can realize synchronous data acquisition of 12 channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is an assembly diagram of a fiber Bragg grating acoustic emission sensor according to an embodiment of the present invention;

[0020] Figure 2 is a cross-sectional view of a fiber Bragg grating acoustic emission sensor according to an embodiment of the present invention;

[0021] Figure 3 A dynamic model of a fiber Bragg grating acoustic emission sensor according to an embodiment of the present invention;

[0022] Figure 4 This is a high-frequency demodulation sensing system according to an embodiment of the present invention.

[0023] Figure numerals: 1. Shell unit; 101. Metal shell; 102. Metal bottom shell; 103. Boss base; 2. Signal sensing unit; 201. Negative thermal expansion joint; 202. Fiber Bragg grating; 203. Coupling agent; 204. High temperature glue; 205. Diaphragm; 3. Transmission cable; 401. Tunable laser source; 402. PC-side signal processing equipment; 403. High-frequency data collector; 404. Voltage amplifier; 405. Photoelectric converter; 406. Fiber circulator; 407. Distributed sensor; 408. Optical splitter. DETAILED DESCRIPTION

[0024] The following is only a preferred embodiment of the present invention, and the protection scope is not limited to this embodiment. All technical solutions under the concept of the present invention should belong to the protection scope of the present invention. The same parts are represented by the same figure marks. It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the drawings, and the words "bottom" and "top", "inside" and "outside" refer to the directions toward or away from the geometric center of a specific component, respectively.

[0025] like Figures 1 to 4 As shown, a temperature-compensated acoustic emission fiber Bragg grating sensor suitable for use in a nuclear radiation environment includes a sensing module, a demodulation module and an analysis module. The sensing module includes a housing unit, a signal sensing unit and a transmission cable, and the housing unit contacts the surface of the object to be measured.

[0026] The shell unit comprises a metal shell, a metal bottom shell and a boss base, the upper end of the metal bottom shell is threadedly connected to the lower end of the metal shell, and the boss base is threadedly connected to the lower end of the metal bottom shell.

[0027] The signal sensing unit includes a negative thermal expansion joint, a fiber Bragg grating, a diaphragm and a coupling agent. The top negative expansion joint can eliminate the influence of ambient temperature changes on the FBG wavelength. One end of the negative thermal expansion joint is fixedly connected to the transmission cable. The diaphragm is fixed in the housing unit, and the negative thermal expansion joint is connected to the diaphragm through an optical fiber. The fiber Bragg grating is located on the optical fiber, and the coupling agent is evenly filled in the space between the diaphragm and the metal bottom shell, and the diaphragm and the coupling agent are fully and evenly contacted.

[0028] The coating on the surface of the fiber Bragg grating is stripped off using fiber pliers, and the residual coating on the surface is removed with cotton wool soaked in propanol. A layer of silver film is deposited on the surface of the bare optical fiber as a bonding layer using a magnetron sputtering process, and then a layer of aluminum coating is electroplated on the surface of the silver film to complete the preparation of multi-layer metal-coated optical fiber. The lower end of the optical fiber is laser welded to the center of the diaphragm, and the upper end of the fiber Bragg grating is laser welded to the top negative thermal expansion joint with a negative thermal expansion coefficient, and the cylindrical metal shell is connected to the metal bottom shell by threads. Tightening the threads presses the end face of the cylindrical metal shell against the diaphragm, so that the diaphragm is fixed.

[0029] The transmission cable is an anti-radiation cable, which includes an inner core, an anti-radiation layer and a protective layer. The inner core of the transmission cable is an optical fiber, and the outside of the optical fiber is coated with a metal layer composed of a metal coating material. The metal layer is wrapped with an anti-radiation material polyimide coating and an aluminum coating, and the anti-radiation layer is wrapped with a waterproof material, and finally wrapped with a polyethylene outer sheath.

[0030] The top negative thermal expansion joint is connected to the cylindrical metal shell through threads. A cylindrical hole is provided in the middle of the top negative thermal expansion joint. The transmission cable passes through the cylindrical hole and is connected to the signal receiving and demodulation equipment. The top negative thermal expansion joint is filled with high-temperature glue. The fiber Bragg grating adopts a two-point suspension arrangement, and the fiber Bragg grating is in a tensioned state in the initial state.

[0031] The calculation method of the sound pressure sensitivity of the fiber Bragg grating acoustic emission sensor is as follows:

[0032] According to the relevant knowledge of mechanical system dynamics, the equivalent stiffness K of the diaphragm is:

[0033]

[0034] Where: R is the radius of the diaphragm; r1 is the radius of the optical fiber (including the thickness of the metal coating); d is the thickness of the diaphragm. μ is the Poisson's ratio of the diaphragm, E is the elastic modulus of the diaphragm material, and K is c It is a coefficient related to the ratio of the optical fiber radius and the diaphragm radius. The radius of the optical fiber core is r2.

[0035] The elastic modulus of the metal coating is E1, the elastic modulus of the fiber core is E2, the length of the optical fiber suspended inside the sensor is l, the mass per unit volume length of the coating is ρ1, and the mass per unit volume length of the optical fiber is ρ2. According to the relevant knowledge of elastic mechanics, the equivalent stiffness K1 of FBG when stretched along the axial direction can be expressed as:

[0036]

[0037] The total mass of optical fiber can be expressed as:

[0038]

[0039] Then the natural frequency ω of the optical fiber axial motion can be expressed as:

[0040]

[0041] When the diaphragm is subjected to a uniform load P, the change in the grating pitch can be described as follows:

[0042]

[0043] When strain acts on FBG simultaneously, the relative shift of FBG center wavelength can be expressed as;

[0044]

[0045] Where: P e is the elastic-optic coefficient, and λ is the wavelength of the FBG reflection spectrum.

[0046] Combining equations 1.5 and 1.6, the wavelength offset Δλ of the acoustic emission sensor FBG can be expressed as:

[0047]

[0048] The high-frequency demodulation module is composed of a tunable laser source 401, a high-frequency data collector 403, an amplifier, a photoelectric converter 405, and a fiber circulator 406. The tunable laser source 401 is connected to an optical splitter 408, and each port of the optical splitter 408 is connected to each distributed sensor 407 through an anti-radiation cable 103. The acoustic emission fiber grating sensor 102 module is connected to one port of the three-port fiber circulator 406 through an anti-radiation cable 103, and the fiber circulator 406 is connected to the photoelectric converter 405 according to the next port of the rotation direction, and the photoelectric converter 405 is connected to the amplifier, and then the amplifier is connected to the high-frequency data collector 403, and finally connected to the PC-side signal processing device 402.

[0049] Working principle: First, the acoustic emission fiber Bragg grating sensor 102 is installed on the surface of the workpiece to be measured. The acoustic emission signal is transmitted to the sensor through the workpiece to be measured and the connecting boss. The coupling agent 202 makes the acoustic wave signal act evenly on the diaphragm 203, causing the diaphragm 203 to deform, thereby causing the central wavelength of the fiber Bragg grating to shift. Using negative expansion coefficient materials to compensate for the change in the wavelength of the fiber Bragg grating caused by temperature changes can basically eliminate the influence of temperature on wavelength drift.

[0050] The tunable laser source 401 is used as a light source, and the light source is transmitted to multiple distributed optical fiber sensors through the optical splitter 408. When there is no external influence, the optical signal is reflected back to the data receiving end through the grating, and the wavelength of the optical signal does not drift; when the acoustic emission signal is detected, the deformation of the diaphragm 203 causes the change of the grating reflection, causing the wavelength of the optical signal to shift. At this time, the optical signal is transmitted to the optical fiber circulator 406 through the radiation-resistant cable 103. Since the optical fiber circulator 406 has a guiding effect on the light source, the reflected light enters the photoelectric converter 405.

[0051] If the initial center wavelength of the FBG in the free state is slightly larger than the center wavelength of the tunable laser, then when subjected to compressive (tensile) stress, the FBG reflection center wavelength decreases (or increases) relative to its initial state, and the area of ​​the corresponding reflection spectrum overlapping the laser spectrum increases (decreases). As the center wavelength changes, the optical power obtained by the photodetector will change accordingly. By detecting the change in the output optical power, the fluctuation of the center wavelength of the FBG reflection spectrum can be inverted and demodulated, thereby obtaining acoustic emission information. In this case, the internal damage of the workpiece to be tested can be judged.

[0052] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A nuclear power equipment damage detection system based on fiber grating acoustic emission sensor, characterized in that: The invention comprises a sensing module, a demodulation module and an analysis module. The sensing module comprises a housing unit (1), a signal sensing unit (2) and a transmission cable (3). The housing unit (1) comprises a metal housing (101), a metal bottom housing (102) and a boss base (103). The upper end of the metal bottom housing (102) is threadedly connected to the lower end of the metal housing (101). The boss base (103) is threadedly connected to the lower end of the metal bottom housing (102). The signal sensing unit (2) comprises a negative thermal expansion joint (201), a fiber Bragg grating (202), a diaphragm (205) and a coupling agent (203). The negative thermal expansion joint (201) is provided with a high temperature glue (204). ), the high temperature glue (204) is used to fill the negative thermal expansion joint (201), one end of the negative thermal expansion joint (201) is fixedly connected to the transmission cable (3), the diaphragm (205) is fixed in the housing unit (1), the negative thermal expansion joint (201) is connected to the diaphragm (205) through an optical fiber, the fiber Bragg grating (202) is located on the optical fiber, the coupling agent (203) is filled in the space between the diaphragm (205) and the metal bottom shell (102), the sensing module is used to detect an object to obtain damage information of the object, the demodulation module is used to demodulate the sensing light signal and generate electronic information, and the analysis module is used to analyze the electronic information and draw a damage conclusion.

2. A nuclear power equipment damage detection system based on fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: The transmission cable (3) is an anti-radiation cable, comprising an inner core, an anti-radiation layer and a protective layer, wherein the anti-radiation layer is wrapped around the surface of the inner core, and the protective layer is located at the outer edge of the anti-radiation layer. The anti-radiation layer comprises a metal layer, a polyimide coating and an aluminum coating in sequence from the inside to the outside, and the protective layer comprises a waterproof layer and a polyethylene outer sheath layer.

3. A nuclear power equipment damage detection system based on fiber Bragg grating acoustic emission sensor according to claim 2, characterized in that: The demodulation module is a high-frequency demodulation module, and the high-frequency demodulation module comprises a tunable laser source (401), a high-frequency data collector (403), a voltage amplifier (404), a photoelectric converter (405) and an optical fiber circulator (406); the signal sensing unit (2) is connected to a port of the optical fiber circulator (406) via a transmission cable (3); the optical fiber circulator (406) is connected to the photoelectric converter (405) at the next port according to the rotation direction; the photoelectric converter (405) is connected to an amplifier; the amplifier is connected to the high-frequency data collector (403); and the high-frequency data collector (403) is connected to an analysis module.

4. A nuclear power equipment damage detection system based on fiber Bragg grating acoustic emission sensor according to claim 3, characterized in that: One side of the tunable laser source (401) is connected to an optical splitter (408), and the demodulation module further includes 12 distributed sensors (407), and a port of the optical splitter (408) is connected to the 12 distributed sensors (407) via a transmission cable (3).

5. A nuclear power equipment damage detection system based on fiber Bragg grating acoustic emission sensor according to claim 1, characterized in that: The analysis module is a PC-side signal processing device (402).

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