Method for on-line measurement of thickness of oxidized corrosion products based on photoacoustic effect

Abstract

The application discloses an online measurement method for the thickness of oxidation corrosion products based on the photoacoustic effect, which comprises the following steps: modulating laser irradiation of a specific frequency on the CRUD surface of a fuel cladding, monitoring the sound wave signals emitted by the CRUD surface by using a piezoelectric sensor, and establishing an online conversion model of the sound wave signals and the CRUD thickness, so that intuitive real-time thickness data can be obtained. The thickness of the CRUD is measured online and in situ without destroying the original environment of the CRUD, so that the measurement data can accurately reflect the real thickness of the CRUD in the growth environment. Through the method, the dynamic growth behavior characteristics of the CRUD thickness can be obtained, so that more accurate monitoring and guidance can be provided for the safe operation and fuel management of a reactor.

Description

Technical Field

[0001] This invention relates to a technology in the field of reactor control, specifically a method for online measurement of the thickness of oxidation corrosion products based on photoacoustic effects. Background Technology

[0002] During pressurized water reactor (PWR) operation, the fuel cladding surface is deposited with corrosion products (CRUD), and the resulting corrosion layer significantly affects the temperature distribution and thermal expansion of the fuel rods. Therefore, accurately measuring the thickness of CRUD is crucial for ensuring the safe operation of the fuel rods. Currently, the measurement of the thickness of CRUD on the PWR fuel cladding surface mainly relies on traditional offline measurement methods, such as atomic concentration spectrometry (ACS) and scanning electron microscopy (SEM). Offline measurement methods require removing the sample from its actual operating environment and undergoing complex sample preparation processes. These operations not only disrupt the natural equilibrium between the CRUD and its surrounding environment, leading to redissolution or changes in composition, but may also alter its microstructure, thus affecting the accuracy of the measurement results. Furthermore, offline measurement methods cannot capture the dynamic growth process of CRUD on the fuel rod surface over time, and cannot provide real-time information on the thickness of CRUD during formation and evolution, limiting their application value in corrosion monitoring and prediction. Summary of the Invention

[0003] This invention addresses the shortcomings of existing measurement methods, which are mostly offline and may disrupt the original CRUD environment during operation, leading to inaccurate results. Furthermore, offline measurement methods cannot monitor the dynamic changes in fouling layer thickness. To address these limitations, this invention proposes an online method for measuring the thickness of oxidation corrosion products based on the photoacoustic effect. This method performs online, in-situ measurement of the CRUD thickness without disrupting its original environment, ensuring that the measurement data accurately reflects the true thickness of the CRUD in its growth environment. This method allows for the acquisition of dynamic growth behavior characteristics of the CRUD thickness, thereby providing more precise monitoring and guidance for safe reactor operation and fuel management.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to an online method for measuring the thickness of oxidation corrosion products based on photoacoustic effect. By modulating a laser of a specific frequency to irradiate the CRUD surface of a fuel cladding, and using a piezoelectric sensor to monitor the acoustic wave signal emitted from the CRUD surface, an online conversion model between the acoustic wave signal and the CRUD thickness is established to obtain intuitive real-time thickness data.

[0006] This invention relates to a system for implementing the above-mentioned method, comprising: a test section, a PWM pulsed laser emitter, a signal acquisition and processing module, and a motion control and data analysis module. The test section simulates the actual environment of a fuel rod in a sealed working medium. The PWM pulsed laser emitter emits pulsed lasers according to parameters set by a laser control station, obtaining a pulsed laser beam capable of exciting a photoacoustic effect. The signal acquisition and processing module amplifies and performs phase-locked loop extraction on the acoustic signal information received by a piezoelectric sensor, obtaining an amplified electrical signal synchronized with the laser modulation frequency, and outputting it to an oscilloscope for waveform display. The motion control and data analysis module precisely moves the laser emitter and processes the electrical signal according to the experimental scanning path and control command information, obtaining photoacoustic signal data corresponding to different measurement points and their relationship with the CRUD thickness.

[0007] Technical effect

[0008] This invention constructs a collaborative measurement system including pulsed laser excitation, acoustic signal acquisition and processing, motion control, and real-time data analysis. It achieves dynamic scanning photoacoustic measurement of CRUD thickness in a simulated coolant environment. It can analyze the correspondence between thickness and acoustic amplitude at different locations in real time. This overcomes the problems of traditional offline methods that require destroying the original CRUD environment, resulting in large measurement errors and the inability to capture the dynamic changes of the fouling layer. It realizes non-contact, high-precision, and in-situ online measurement of CRUD thickness on the surface of simulated fuel rods. Attached Figure Description

[0009] Figure 1 This is a flowchart of the present invention;

[0010] Figure 2 This is a schematic diagram of the measurement process for an example.

[0011] Figure 3 This is a schematic diagram of a one-dimensional calculation model for laser thickness measurement in an embodiment.

[0012] Figure 4 This is a schematic diagram of the original data for repeatability in the embodiment;

[0013] In the figure: f is the laser modulation frequency, and DR is the laser duty cycle;

[0014] Figure 5 This is a schematic diagram of the original data for comparing laser parameters (duty cycle) in the example embodiment;

[0015] In the figure: (a) transient data; (b) frequency domain data;

[0016] Figure 6 This is a schematic diagram of the original data for comparing laser parameters (pulse frequency) in the example embodiment;

[0017] In the figure: (a) instantaneous data; (b) frequency domain data;

[0018] Figure 7 This is a schematic diagram of the instantaneous raw data of electrical signals under different CRUD thickness conditions in the example;

[0019] In the figure: δ represents the CRUD thickness, and 1st and 2nd represent the first and second experiments, respectively;

[0020] Figure 8 This is a schematic diagram of intermediate Fast Fourier Transform (FFT) data of electrical signals under different CRUD thickness conditions in this embodiment.

[0021] In the diagram: 1st and 2nd represent the first and second experiments, respectively;

[0022] Figure 9 A schematic diagram illustrating the experimental results showing the relationship between different CRUD thicknesses and electrical signal amplitude.

[0023] In the diagram: 1st and 2nd represent the first and second experiments, respectively. Detailed Implementation

[0024] like Figure 1 As shown in the figure, this embodiment relates to an online method for measuring the thickness of oxidation corrosion products based on photoacoustic effect. By irradiating the CRUD surface of the fuel cladding with a laser and monitoring the acoustic wave signal emitted by the CRUD surface using a piezoelectric sensor, an online conversion model between the acoustic wave signal and the CRUD thickness is established to obtain intuitive real-time thickness data.

[0025] The laser irradiation refers to irradiation using a pulsed laser with a wavelength of 532nm, a modulation frequency of 700Hz, and a laser power of 3W, with a spot diameter on the order of millimeters.

[0026] The online conversion model is obtained in the following way:

[0027] Step 1, according to Figure 3 After simplifying the one-dimensional laser thickness measurement model shown, the heat flux density generated by laser irradiation is calculated to obtain the temperature distribution on the CRUD surface and inside, as follows: Where: q is the heat flux density generated on the laser-irradiated surface, P peak is the peak power of the laser, and D is the duty cycle, which is the ratio of the pulse's on-time to the total period time.

[0028] The laser thickness measurement one-dimensional model includes: a dielectric layer I, a fouling layer II, and a simulated fuel rod layer III. The one-dimensional heat transfer equations along the radial direction for these three regions include: , , , , where: Qtotal The total heat gained on the CRUD surface comprises two parts: the energy qA input by the laser. laser And the heat lost by CRUD through convective heat transfer with water, hA laser (T surface -T f A laser T represents the area of ​​the laser spot. surface T represents the surface temperature of the CRUD. f T represents the temperature of the water. wall To simulate the inner surface temperature of the fuel rod; k crud and k rod r1 and r2 are the thermal conductivity of the CRUD and the simulated fuel rod, respectively; r0 and r1 are the inner and outer diameters of the simulated fuel rod, respectively; r2 is the outer diameter of the CRUD; L crud L rod These represent the axial lengths of the CRUD and simulated fuel rods, respectively.

[0029] Step 2: Calculate the thermal expansion of the CRUD surface to obtain the one-dimensional temperature field change of the CRUD caused by PWM laser irradiation. Specifically, the CRUD surface temperature is obtained based on the one-dimensional laser thickness measurement model in Step 1. The temperature distribution inside the CRUD can be derived from the internal heat conduction differential equation and the corresponding boundary conditions, including: ; CRUD top face (r=r2): ; CRUD bottom face (r=r1): Based on the thermal resistance model, the simulated fuel rod outer surface temperature T can be obtained. inner That is, the temperature at the point where the CRUD and the simulated fuel rod are in close contact: This leads to the radial temperature distribution inside the CRUD. , where T(r) is the temperature inside the CRUD at a position with radius r.

[0030] Step 3: Calculate the periodic thermal expansion of the CRUD due to temperature field changes to obtain the pressure fluctuation amplitude. Specifically, after the CRUD is irradiated by the laser, its temperature rises, leading to thermal expansion. The one-dimensional radial thermal expansion is... Where: α is the coefficient of thermal expansion of the CRUD, T0 is the reference temperature for the thermal expansion of the CRUD, that is, the temperature of the CRUD when it is not irradiated by the laser, and thus the radial thermal expansion of the CRUD is obtained. Where: x(r) is the radial thermal expansion of the CRUD at a position with radius r.

[0031] Step 4: Calculate the coolant ambient pressure fluctuation caused by the periodic thermal expansion of the CRUD, and transmit the pressure fluctuation to a nearby piezoelectric sensor to form a periodic piezoelectric signal. Construct an online conversion model to theoretically derive the quantitative relationship in one dimension between the CRUD thickness and the amplitude of the excited photoacoustic signal under pulsed laser irradiation. Specifically, this includes:

[0032] a) When the surface of the dirt expands, it causes the surrounding fluid to move, resulting in fluctuations in the coolant environment pressure, i.e., the expansion rate of the fluid on the surface of the dirt at a certain moment. This dynamic pressure, driven by the piezoelectric sensor, is transmitted to the surface of the nearby piezoelectric sensor, forming a periodic electrical signal. Where: i is the current time, Δt is the time step, and ρ f The density of the surrounding fluid, specifically the density of water.

[0033] b) Piezoelectric signals caused by fluctuations in coolant ambient pressure Where: ε is the strain matrix of the piezoelectric ceramic, E is the unit electric field strength generated by the piezoelectric effect; d is the piezoelectric coefficient, which varies depending on the sensitivity and model of the piezoelectric sensor. Furthermore, due to the extremely small crystal deformation of the piezoelectric ceramic, the relationship between stress and strain satisfies Hooke's Law: , where σ is the stress matrix of the piezoelectric ceramic and k is the elastic modulus of the piezoelectric ceramic.

[0034] like Figure 2 As shown, the online measurement system for implementing the above method in this embodiment includes: a sealed water working medium environment for placing the simulated fuel rod, a PWM pulsed laser emitter and a piezoelectric sensor set outside the sealed water working medium environment facing the simulated fuel rod, a signal amplifier, a lock-in amplifier, an oscilloscope, and a laser control and data analysis station connected in sequence to the PWM pulsed laser emitter and the oscilloscope respectively.

[0035] The simulated fuel rod is used to simulate the coolant environment in actual fuel rod operation. The sealed aquatic working fluid environment ensures the practical applicability of the experimental results while preventing external interference from affecting the measurement results. The visible material ensures that the laser can directly illuminate the simulated fuel rod.

[0036] The PWM pulsed laser emitter emits a pulsed laser with a wavelength of 532nm, a modulation frequency of 700Hz, and a laser power of 3W. This laser, after being focused, illuminates a simulated fuel rod covering a CRUD, thereby exciting a photoacoustic effect and generating an acoustic signal.

[0037] The PWM pulsed laser emitter is mounted on a three-dimensional linear moving stage. The position of the laser emitter is precisely controlled by the three-dimensional linear moving stage to achieve scanning of different measurement points. The high-precision movement of the moving stage ensures the repeatability of data and the accuracy of measurements during the experiment.

[0038] The piezoelectric sensor is preferably positioned near the simulated fuel rod (with a deflection angle of approximately 90°) to receive the acoustic signal generated by pulsed laser excitation.

[0039] The laser control and data analysis station controls the working status of the laser emitter in real time, including the power and modulation frequency of the PWM laser. It also processes data to display the relationship between thickness and piezoelectric amplitude.

[0040] Since the CRUD thickness of the pressurized water reactor fuel cladding ranges from approximately 0 to 100 μm, four representative thicknesses were selected: 15 μm, 35 μm, 65 μm, and 90 μm, from the bottom to the top of the fuel cladding. To avoid the influence of laser movement on the calculation results, a linear motion stage was used to move the laser irradiation position vertically upwards from the 15 μm thickness condition until it stopped at the top 90 μm condition, and then measurements were taken sequentially downwards, completing one cycle. To reduce measurement error, two cycles of measurement were performed, and the average value of the acoustic signal corresponding to each thickness condition was taken.

[0041] Through specific practical experiments, the CRUD on the surface of fuel rods in a simulated pressurized water reactor primary loop was immersed in a sealing medium (coolant). Under the conditions of a pulsed laser wavelength of 532nm, duty cycle of 0.5 / 1.0, modulation frequency of 181 / 500 / 700 / 1000Hz, and output power of 3W, the thickness of the aforementioned oxidation corrosion products was measured online. The repeatability data, comparisons of laser parameters (duty cycle), comparisons of laser parameters (pulse frequency), instantaneous raw data of electrical signals under different CRUD thicknesses, intermediate Fast Fourier Transform (FFT) data of electrical signals under different CRUD thicknesses, and experimental results showing the relationship between different CRUD thicknesses and electrical signal amplitude were recorded simultaneously. Figures 4-9 As shown.

[0042] like Figure 4As shown, under the condition that the laser parameters remain unchanged, the electrical signal fluctuation characteristics obtained in the two experiments are consistent, with only a certain phase difference (this phase difference originates from the different start times of data recording and has no substantial impact on the measurement results). This indicates that the measurement system has good repeatability. Furthermore, the black and red curves in the figure correspond to the 40ms piezoelectric signal data recorded in the first experiment and the 20ms data recorded in the second experiment, respectively. Data comparison shows that the 40ms data roughly contains two complete 20ms data cycles, therefore the signal period can be determined to be approximately 20ms. Based on these results, the measurement system requires relatively little data, which is beneficial for achieving rapid post-processing of the piezoelectric signal, thus enabling real-time thickness acquisition.

[0043] like Figure 5 As shown, the electrical signals obtained under different conditions—laser off and laser operating at a modulation frequency f=1000Hz with duty cycles DR=0.5 or 1.0—exhibit significant differences. Figure (a) shows that the transient fluctuation characteristics differ among the three conditions. Further analysis using a Fast Fourier Transform (FFT) on the transient data yields the frequency domain distribution shown in Figure (b). When the laser is off, significant peaks appear at 50Hz and 700Hz in the frequency domain. When the laser operates at f=1000Hz and DR=0.5, significant peaks are observed at 50Hz, 650Hz, 700Hz, and 1000Hz. However, when the laser operates at f=1000Hz and DR=1.0, a significant peak is observed only at 50Hz. These results indicate that regardless of whether the laser is on or off, the measurement system possesses fundamental frequency components at 50Hz and 700Hz. These frequency components can be suppressed or selectively enhanced using lock-in amplification techniques. It is also known that a larger duty cycle (DR) is not necessarily better for measurement. When DR=1.0, only the 50Hz frequency component is significant, making it difficult to distinguish the electrical signal intensity corresponding to different CRUD thicknesses. Therefore, selecting a laser duty cycle of 0.5 can significantly enhance the 50Hz and 700Hz fundamental frequency signals while preserving multi-frequency components, thereby improving the efficiency of signal acquisition and subsequent processing.

[0044] like Figure 6As shown, the adaptability of different laser modulation frequencies (181Hz, 500Hz, 750Hz, and 1000Hz) to the measurement system was analyzed under the condition of laser duty cycle DR=0.5. Figure (a) shows the transient fluctuation characteristics of the piezoelectric signal under different modulation frequencies, and it can be seen that their responses are significantly different. The corresponding frequency domain distribution was further obtained using Fast Fourier Transform (FFT), as shown in Figure (b). The frequency domain analysis results show that at each modulation frequency, a significant peak appears at the corresponding frequency, indicating that the modulated laser can effectively excite the CRUD to produce a response at the corresponding frequency. Furthermore, in addition to a significant peak at 50Hz, a second peak appears near 700Hz under all modulation conditions. This frequency coincides with a certain modulation frequency (700Hz), and the peak value is the largest. Therefore, the electrical signal response is strongest when the laser modulation frequency is 700Hz. Thus, selecting this frequency helps to further improve the efficiency of signal acquisition and subsequent processing.

[0045] like Figure 7 As shown, with the increase of CRUD thickness δ, under the conditions of laser modulation frequency f=700Hz and duty cycle DR=0.5, the measured high-frequency transient electrical signal amplitude shows a significant increasing trend. This result indicates that the measurement system can effectively distinguish signals of different CRUD thicknesses and has a sensitive response capability to thickness changes.

[0046] like Figure 8 As shown, the obtained piezoelectric signal transient data ( Figure 7 A Fast Fourier Transform (FFT) was performed, and the corresponding frequency domain distribution is shown in Figure (b). Figure (b) shows that as the CRUD thickness δ increases, the signal peak at 700Hz continuously strengthens. This phenomenon further demonstrates that the measurement system can effectively distinguish signals for different CRUD thicknesses, and the extracted signal frequency components are clear and consistent with the laser modulation frequency, exhibiting good frequency selectivity and detection reliability.

[0047] like Figure 9 As shown, extract Figure 8 The signal peak at 700Hz in the frequency domain information was plotted, and its relationship with the CRUD thickness δ was analyzed. A clear, approximately linear correlation was observed between the two. This result demonstrates that the proposed measurement system can effectively establish a reliable correspondence between CRUD thickness and the frequency domain peak value of the electrical signal at 700Hz, exhibiting good linearity. It is suitable for extrapolation detection of thinner or thicker CRUD layers, showing broad application potential.

[0048] Experimental results show that as the CRUD thickness increases, the measured electrical signal amplitude increases approximately linearly. Compared with existing technologies, this invention achieves scanning measurement of the CRUD thickness at different locations on the surface of simulated fuel rods and displays the quantitative relationship between thickness and photoacoustic signal amplitude in real time. Furthermore, the linearity between CRUD thickness and photoacoustic signal amplitude is high, enabling online real-time thickness measurement without disrupting the original CRUD deposition environment. This technology accurately reflects the true thickness of the CRUD in its natural state, providing a high-precision monitoring method for reactor operation and maintenance. This invention is not only applicable to CRUD thickness measurement on the surface of nuclear reactor fuel cladding but can also be applied to other industrial fields, such as measuring fouling on the surface of steam generator heat exchanger tube bundles and detecting surface structures of different materials. Its applicability is not limited by specific CRUD structures, possessing broad application prospects and high practical value, providing a reliable solution for surface monitoring of various industrial equipment and systems.

[0049] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for online measurement of the thickness of oxidation corrosion products based on photoacoustic effect, characterized in that, By modulating a laser of a specific frequency to irradiate the CRUD surface of the fuel cladding, and using a piezoelectric sensor to monitor the acoustic wave signal emitted by the CRUD surface, an online conversion model between the acoustic wave signal and the CRUD thickness is established to obtain intuitive real-time thickness data. The online conversion model is obtained in the following way: Step 1: Based on the simplified one-dimensional model of laser thickness measurement, calculate the heat flux density generated by laser irradiation to obtain the temperature distribution on the CRUD surface and inside. Specifically: , where: A laser Let P be the area of ​​the laser spot, q be the heat flux density generated on the laser-irradiated surface, and P be the area of ​​the laser spot. peak It is the peak power of the laser, and D is the duty cycle, which is the ratio of the pulse on-time to the total period time. Step 2: Calculate the thermal expansion of the CRUD surface to obtain the one-dimensional temperature field change of the CRUD caused by PWM laser irradiation. Specifically, the CRUD surface temperature is obtained based on the one-dimensional laser thickness measurement model in Step 1. The temperature distribution inside the CRUD can be derived from the internal heat conduction differential equation and the corresponding boundary conditions, including: ; CRUD top face r=r2: ; CRUD bottom face r=r1: Based on the thermal resistance model, the simulated fuel rod outer surface temperature T can be obtained. inner That is, the temperature at the point of close contact between the CRUD and the simulated fuel rod satisfies: This leads to the radial temperature distribution inside the CRUD. , where: T f T represents the temperature of the water. wall To simulate the inner surface temperature of the fuel rod, r1 is the simulated outer diameter of the fuel rod, r2 is the outer diameter of the CRUD, and Q... total qA represents the total heat gained by the CRUD surface. laser The energy input to the laser, k crud Let be the thermal conductivity of the CRUD, and T(r) be the temperature inside the CRUD at a position with radius r. Step 3: Calculate the periodic thermal expansion of the CRUD due to temperature field changes to obtain the pressure fluctuation amplitude. Specifically, after the CRUD is irradiated by the laser, its temperature rises, leading to thermal expansion. The one-dimensional radial thermal expansion is... Where: α is the coefficient of thermal expansion of the CRUD, T0 is the reference temperature for the thermal expansion of the CRUD, that is, the temperature of the CRUD when it is not irradiated by the laser, and thus the radial thermal expansion of the CRUD is obtained. Where: x(r) is the radial thermal expansion of the CRUD at a position with radius r; Step 4: Calculate the coolant environmental pressure fluctuation caused by the periodic thermal expansion of the CRUD, and transmit the pressure fluctuation to the nearby piezoelectric sensor to form a periodic piezoelectric signal. Construct an online conversion model and theoretically derive the quantitative relationship in one dimension between the CRUD thickness and the amplitude of the excited photoacoustic signal under pulsed laser irradiation.

2. The online measurement method for the thickness of oxidation corrosion products based on photoacoustic effect according to claim 1, characterized in that, The laser irradiation refers to irradiation using a pulsed laser with a wavelength of 532nm, a modulation frequency of 700Hz, and a laser power of 3W, with a spot diameter on the order of millimeters.

3. The online measurement method for the thickness of oxidation corrosion products based on photoacoustic effect according to claim 1, characterized in that, The laser thickness measurement one-dimensional model includes: a dielectric layer I, a fouling layer II, and a simulated fuel rod layer III. The one-dimensional heat transfer equations along the radial direction for these three regions include: , , , Where: the total heat Q obtained by the CRUD surface total Energy qA including laser input laser And the heat lost by CRUD through convective heat transfer with water, hA laser (T surface -T f ), k rod r0 is the thermal conductivity of the simulated fuel rod; r0 is the inner diameter of the simulated fuel rod; L crud L rod These represent the axial lengths of the CRUD and simulated fuel rods, respectively.

4. The online measurement method for the thickness of oxidation corrosion products based on photoacoustic effect according to claim 1, characterized in that, Step 4 specifically includes: a) When the surface of the dirt expands, it causes the surrounding fluid to move, resulting in fluctuations in the coolant environment pressure, i.e., the expansion rate of the fluid on the surface of the dirt at a certain moment. This dynamic pressure, driven by the piezoelectric sensor, is transmitted to the surface of the nearby piezoelectric sensor, forming a periodic electrical signal. Where: i is the current time, Δt is the time step, and ρ f The density of the surrounding fluid, specifically the density of water; b) Piezoelectric signals caused by fluctuations in coolant ambient pressure Where: ε is the strain matrix of the piezoelectric ceramic, E is the unit electric field strength generated by the piezoelectric effect; d is the piezoelectric coefficient, which depends on different sensitivities and different models of piezoelectric sensors. Furthermore, due to the extremely small crystal deformation of the piezoelectric ceramic, the relationship between stress and strain satisfies Hooke's Law: , where σ is the stress matrix of the piezoelectric ceramic and k is the elastic modulus of the piezoelectric ceramic.

5. An online system for measuring the thickness of oxidation corrosion products implementing the method of any one of claims 1-4, characterized in that, include: The system comprises an experimental section, a PWM pulsed laser emitter, a signal acquisition and processing module, and a motion control and data analysis module. The experimental section simulates the actual environment of a fuel rod in a sealed working medium. The PWM pulsed laser emitter emits pulsed lasers according to parameters set by the laser control station, producing a pulsed laser beam capable of exciting a photoacoustic effect. The signal acquisition and processing module amplifies and performs phase-locked loop extraction on the acoustic signal received by the piezoelectric sensor, obtaining an amplified electrical signal synchronized with the laser modulation frequency, which is then output to an oscilloscope for waveform display. The motion control and data analysis module precisely moves the laser emitter and processes the electrical signal according to the experimental scanning path and control commands, obtaining photoacoustic signal data corresponding to different measurement points and their relationship with the CRUD thickness.

6. The online thickness measurement system for oxidation corrosion products according to claim 5, characterized in that, The PWM pulsed laser emitter emits a pulsed laser with a wavelength of 532nm, a modulation frequency of 700Hz, and a laser power of 3W. After being focused, the laser irradiates the simulated fuel rods covering the CRUD, thereby exciting the photoacoustic effect and generating an acoustic signal. The PWM pulsed laser emitter is mounted on a three-dimensional linear moving stage. The position of the laser emitter is precisely controlled by the three-dimensional linear moving stage to achieve scanning of different measurement points. The high-precision movement of the moving stage ensures the repeatability of data and the accuracy of measurement during the experiment.

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