Fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging

Abstract

The invention relates to the technical field of nondestructive testing, and particularly provides a fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging, which comprises the following steps: arranging a pair of signal receiving and transmitting devices at two ends of a to-be-detected area of a fuel rod cladding for transmitting an input signal f (t) and receiving and acquiring wave field data; performing narrowband signal extraction on the obtained wave field data, and extracting a wave packet signal h (t) when frequency dispersion does not occur in each spiral path according to spiral guided wave propagation characteristics; calculating a signal difference coefficient SDC of each spiral path by comparing the difference between f (t) and h (t); calculating the damage probability of each point position in the detection area by using the SDC; and judging the damage probability of all the point positions in the detection area through the damage probability threshold, and determining the damage position. According to the invention, only one pair of signal receiving and transmitting devices is arranged, so that the defects of the scanning area in the fuel rod cladding can be accurately detected and positioned by utilizing spiral guided waves.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a method for detecting fuel rod cladding damage based on probabilistic imaging of multiple diffraction guided waves. Background Technology

[0002] With the continued growth of global energy demand, nuclear energy, as a highly efficient and clean energy source, is playing an increasingly important role in the global energy mix. Ensuring the safe operation of nuclear reactors is a crucial task for the nuclear energy industry. One of the core components of a nuclear reactor is the nuclear fuel rod, whose primary function is to encapsulate the nuclear fuel and prevent the leakage of radioactive materials. The fuel rod cladding is typically made of zirconium alloy, which possesses excellent corrosion resistance and mechanical properties. During reactor operation, the fuel rod cladding is exposed to various factors, such as high temperature, high pressure, coolant flow, and radiation. These factors may cause damage to the cladding surface or interior, such as corrosion, fatigue-induced cracks, and wear. If this damage is not detected and addressed promptly, it is highly likely to lead to fuel rod leakage and subsequently a nuclear accident. Therefore, timely and effective defect detection of the nuclear fuel rod cladding is essential.

[0003] In recent years, with the increasing demand for non-destructive testing of pipe structures, many scholars have proposed methods for large-scale pipe inspection based on ultrasonic array technology, greatly enhancing the versatility of ultrasonic guided wave-based structural health inspection methods. However, ultrasonic guided wave inspection based on array technology usually requires the deployment of a large number of signal receiving and transmitting devices to obtain relatively accurate defect information. In reality, the fuel rod cladding assemblies are densely packed, making it impossible to deploy a large number of signal receiving and transmitting devices. Therefore, a fuel rod cladding damage detection method based on probabilistic imaging of multiple diffraction guided waves, which significantly reduces the number of signal receiving and transmitting devices, has become a research direction. Summary of the Invention

[0004] The purpose of this invention is to provide a fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging. This method can use only a pair of signal receiving and transmitting devices to send and receive signals. By comparing the difference between the input signal f(t) and the wave packet signal h(t) when no dispersion occurs in each helical path, the probability of damage at each point in the detection area can be calculated, thereby accurately obtaining defect information. This reduces the complexity of the testing device, reduces the amount of data to be processed, and facilitates the quick and easy detection of nuclear fuel rod cladding damage.

[0005] This invention proposes a method for detecting fuel rod cladding damage based on probabilistic imaging of multiple diffraction guided waves, which includes the following steps: S1. A pair of signal receiving and transmitting devices are installed at both ends of the fuel rod cladding inspection area; S2. Transmit the input signal f(t) through the signal transmitting device S0; S3. Acquire wavefield data through signal receiving device R0, and extract narrowband signals from the acquired wavefield data; S4. Based on the propagation characteristics of helical guided waves, extract the wave packet signal h(t) of each helical path when no dispersion occurs; h(t) ; ; ; ; in, The Fourier transform of the output signals superimposed with all different modes and different propagation distances. This is to compensate for the propagation phase delay; t0 is the input signal. Duration; P i Let i be the propagation distance, i be the number of revolutions in the direction of propagation of the helical waveguide, and let i be negative when the propagation direction is left-handed and positive when the propagation direction is right-handed. Let 'b' be the length of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area, and 'b' be the width of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area. Let be the ordinate of the launch device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area. The vertical coordinate of the receiving device is located within the rectangle of the expanded cylindrical area of ​​the fuel rod cladding inspection zone. S5. By comparing the difference between the input signals f(t) and h(t), calculate the signal difference coefficient SDC for each spiral path; S6. Calculate the probability of damage at each point within the detection area using the signal difference coefficient SDC of each spiral path. S7. Determine the location of damage by judging the probability of damage at all points within the detection area using the damage probability threshold.

[0006] As one aspect of this invention, step S4 involves extracting the wave packet signal h(t) from the extracted narrowband signal based on the propagation characteristics of the helical guided wave; specifically, this includes: S41. Calculate the distance the helical guided wave propagates in the pipe; ; Among them, P i Let i be the propagation distance, i be the number of revolutions in the direction of propagation of the helical waveguide, and let i be negative when the propagation direction is left-handed and positive when the propagation direction is right-handed. Let 'b' be the length of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area, and 'b' be the width of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area. Let be the ordinate of the launch device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area. The vertical coordinate is the ordinate of the receiving device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area.

[0007] S42. Obtain the propagation distance P of the spiral guided wave. i The signal received later ; ; in, The Fourier transform of the output signals superimposed with all different modes and different propagation distances, where s represents the mode type. For the Fourier transform of the input signal f(t), The wavenumber-frequency relationship for different modes. It is a wave with frequency 𝜔 that propagates over a distance P. i The phase delay factor, P, was introduced later; 𝑗 is the imaginary unit. i For the distance of propagation; S43. Calculate the signal r(t) after dispersion compensation; ; in, The Fourier transform of the output signals superimposed with all different modes and different propagation distances. To compensate for the propagation phase delay; S44. Extract the wave packet signal h(t) when no dispersion occurs; h(t) ; ; in, Let t0 be a rectangular window function, and t0 be the input signal. Duration.

[0008] As one aspect of this invention, the signal difference coefficient SDC for each spiral path calculated in S5 is: ; Where T is the period of the signal. for The average value over a period of time.

[0009] As one aspect of this invention, step S6, calculating the probability of damage at each point within the detection area using the signal difference coefficient SDC of each spiral path, includes: S61. Calculate the damage weight function for each point on each spiral path: ; ; in, , Let S be the coordinates of the h-th virtual launch device on the S0 side of the rectangle after the cylinder of the fuel rod cladding inspection area is unfolded. , The coordinates of the j-th virtual receiving device on the R0 side of the rectangle after the cylinder of the fuel rod cladding inspection area is unfolded; For shape factor, This is the ratio of the sum of the distances from each point (x, y) to the signal transmitting and receiving devices to the length of the spiral path. S62. Calculate the probability that damage exists at each point within the detection area; .

[0010] As one aspect of this invention, step S7, determining the damage location by judging the probability of damage existing at all point locations within the detection area using a damage probability threshold, includes: S71. Determine the damage probability threshold; S72. Determine whether P(x,y) > damage probability threshold for all point locations. If yes, the point location is damaged; otherwise, the point location is undamaged.

[0011] As one aspect of the present invention, the damage probability threshold in S71 is 0.9.

[0012] As one aspect of this invention, the signal receiving and transmitting device is a pair of PZT ceramic piezoelectric sheets.

[0013] As one aspect of this invention, the number of turns i in the propagation direction of the helical waveguide can be a positive integer between -10 and 10.

[0014] Compared with the prior art, the present invention has the following advantages: 1. In scenarios where fuel rod cladding assemblies are densely arranged and the installation space for array sensors is limited, this invention uses only a pair of sensors to complete non-destructive testing. This significantly reduces the number of non-destructive testing devices without compromising testing quality, greatly enhances the versatility of non-destructive testing devices, and achieves efficient, reliable, and economical non-destructive testing.

[0015] 2. This invention employs a spatially extended physical model to consider the phenomenon of multiple wavefronts forming on a pipe section and their repeated intersections, thereby calculating the propagation distance of each helical path of the helical guided wave in the pipeline. This elevates guided wave nondestructive testing from a "black box" technology based on "one-dimensional time," fraught with ambiguity and false alarms, to a "white box" science based on "three-dimensional space," capable of precise analysis and positioning. By mapping complex signal phenomena one-to-one with clear physical paths, it achieves a leap from "guessing" to "diagnosis," greatly improving the reliability, accuracy, and information content of the detection.

[0016] 3. This invention utilizes the "physical anchoring" effect of a rectangular window, taking the physical duration of the original input signal as a benchmark. By multiplying the dispersion-compensated signal by a rectangular window function with the same duration as the input signal, the accurate positioning of the compensated signal on the time axis is ensured, and the resulting signal is the one without dispersion.

[0017] 4. This invention avoids the limitations of manually comparing and searching for damage features, eliminates the reliance on engineering experience, enables automated judgment of pipeline structure quality, greatly reduces the amount of data that needs to be processed, broadens the application scope of non-destructive testing technology, and provides a new approach to pipeline damage detection technology. Attached Figure Description

[0018] Figure 1 This is a flowchart of the fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging of the present invention. Figure 2 This is a structural diagram of a signal transmission and reception test system according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a pipe unfolded into a flat plate according to one embodiment of the present invention; Figure 4 This is a schematic diagram of helical waveguide path calculation according to an embodiment of the present invention; Figure 5 This is an SDC distribution data diagram according to an embodiment of the present invention; Figure 6 This is one embodiment of the present invention. =1.02 (left) and =1.03 (right) Damage imaging results for two scenarios. Detailed Implementation

[0019] To better understand the technical solution of the present invention, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The same reference numerals in the drawings indicate elements with the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0020] As attached Figure 1 As shown, this invention provides a method for detecting fuel rod cladding damage based on probabilistic imaging of multiple diffraction guided waves, which includes the following steps: S1. A pair of signal receiving and transmitting devices are installed at both ends of the fuel rod cladding inspection area.

[0021] like Figure 2 As shown, the entire testing system of one embodiment of the present invention includes a pair of PZT ceramic piezoelectric sheets, a fuel rod under test, a waveform generator, a signal amplifier, and a computer. The PZT ceramic piezoelectric sheets can both transmit and receive signals. In actual experimental testing, one PZT ceramic piezoelectric sheet is attached to one end (the leftmost end) of the fuel rod cladding area under test, serving as a signal transmitting device S0; simultaneously, the other PZT ceramic piezoelectric sheet is attached to the other end (the rightmost end) of the fuel rod cladding area under test, serving as a signal receiving device R0.

[0022] For a system with a single signal transmitter and receiver on a pipeline, the waves collected by the receiver include not only the direct wave but also other guided waves that propagate through helical paths. These helical guided waves essentially cover the entire area between the transmitter and receiver, carrying far more information than the direct wave. Using these helical guided waves, it is possible to complete the detection of the entire pipeline using only a pair of signal transmitters and receivers.

[0023] S2. Transmit the input signal f(t) through the signal transmitting device S0.

[0024] The excitation section consists of a waveform generator, a signal amplifier, and a ceramic piezoelectric element. The waveform generator and signal amplifier are used to generate and amplify the signal. The waveform generator emits a Chirp signal with a frequency range of 5k-2.5M, which is then output to the PZT for excitation after being amplified by the signal amplifier. The ceramic piezoelectric element (emitting device S0) then deforms on the fuel rod cladding to generate the corresponding guided wave, which emits the input signal f(t).

[0025] S3. Acquire wavefield data through signal receiving device R0, and perform narrowband signal extraction on the acquired wavefield data, including: The receiving part receives the signal through another PZT ceramic piezoelectric element (receiving device R0).

[0026] S31. Obtain wavefield data through signal receiving device R0.

[0027] S32. Narrowband signal extraction is performed on the acquired wavefield data.

[0028] Since the raw signal is excited by the Chirp signal, it has a large bandwidth. Therefore, the received signal needs to be processed by narrowband extraction. Narrowband extraction is an existing technology and will not be described in detail here.

[0029] S4. Based on the propagation characteristics of helical guided waves, extract the wave packet signal h(t) of each helical path of the extracted narrowband signal when no dispersion occurs, specifically including: S41. Calculate the propagation distance of each helical path of the helical guided wave in the pipeline.

[0030] For a guided wave propagating in a pipe, the signal received by the receiver includes not only the direct portion but also a helical portion that rotates several times circumferentially before reaching the target. To facilitate geometric modeling, the thin-walled cylinder is unfolded into a flat plate, such as... Figure 3 As shown.

[0031] To calculate the helical guided wave path, a spatially extended physical model is used to consider the phenomenon of multiple wavefronts forming on the pipe segment and their repeated intersections. The pipe is unfolded into a rectangular flat plate, where the width *b* of the unfolded rectangle is the circumference of the circular pipe, and the length *a* of the rectangle is the length of the pipe segment. The unfolded pipe segment plane is assumed to be... After the pipe surface is unfolded, the upper and lower boundaries formed by the unfolded lines are the same line on the pipe. When the wave arrives... After the unfolded line, the expansion will continue from... The unfolding lines re-enter the space Similarly, if the wavefront boundary reaches... After the unfolded line, the expansion will continue from... The unfolding lines re-enter the space Utilizing this characteristic, one can imagine the planar aspect of the pipe section. Copy a series symmetrically from left to right ,...., , ,..., As for the pipe section space The extended space, each being a copy of the original space, connects the unfolded lines, representing the closed pipe surface using periodically distributed planar spaces, such as... Figure 4 As shown, that is, after the cylinder in the fuel rod cladding inspection area is unfolded, multiple virtual launch devices appear on the S0 side of the rectangle, including S 1、 S m、 S -1、 S -m Multiple virtual transmitters appear on the R0 side, including R 1、 R m、 R -1、 R -m wait.

[0032] The propagation distance of each helical path of the helical guided wave is: ; Among them, P iLet i be the propagation distance, and i be the number of times the helical waveguide travels along the propagation direction. Let i be negative when the propagation direction is left-handed and positive when the propagation direction is right-handed. Let 'b' be the length of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area, and 'b' be the width of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area. Let be the ordinate of the launch device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area. The vertical coordinate is the ordinate of the receiving device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area.

[0033] Furthermore, in actual calculations, taking 10 for the number of turns i of the helical waveguide along the propagation direction is sufficient for accuracy. Of course, theoretically, the more i is taken, the more accurate it will be.

[0034] S42. Obtain the signal received after the propagation of the helical guided wave. .

[0035] In general, the waveguide propagation problem is transformed into the frequency domain response problem of a linear time-invariant (LTI) system. For a single mode, since different helical waveguides propagate along different paths, the received signal is the superposition of the signals after that mode has propagated to different distances. The actual received signal can be regarded as the superposition of the output signals of all different modes at different propagation distances, that is, the signal received after the helical waveguide has propagated. for: ; in, The Fourier transform of the output signals superimposed with all different modes and different propagation distances, where s represents the mode type. For the Fourier transform of the input signal f(t), The wavenumber-frequency relationship for different modes. It is a wave with frequency 𝜔 that propagates over a distance P. i The phase delay factor, P, was introduced later; 𝑗 is the imaginary unit. i This represents the propagation distance of each helical path of the helical guided wave.

[0036] S43. Calculate the signal r(t) after dispersion compensation.

[0037] Because different frequency components in a guided wave have different phase velocities, wave dispersion is inevitable during propagation. This dispersion causes the signal envelope to gradually widen and the peak value to gradually decrease as the propagation distance increases. This makes it difficult to separate different guided waves and also increases the difficulty of judging the degree of damage through waveform changes. Therefore, dispersion compensation for the received signal is essential.

[0038] Calculate the signal r(t) after dispersion compensation: ; in, The Fourier transform of the output signals superimposed with all different modes and different propagation distances. This is to compensate for the propagation phase delay.

[0039] S44. Extract the wave packet signal h(t) when no dispersion occurs.

[0040] When it is necessary to separate a waveguide of a specific mode and a specific propagation distance, it is only necessary to give By multiplying by the inverse of the corresponding transfer function, transforming back to the time domain, and then truncating to the same length as the input signal, the signal without dispersion can be obtained.

[0041] At this point, only the signal after dispersion compensation needs to be supplied. Multiply by the input signal Rectangular window functions of the same duration The resulting signal is h(t), that is: h(t) ; ; in, Let t0 be a rectangular window function, and t0 be the input signal. Duration.

[0042] When using a pulse signal as the input signal, the fully compensated signal returns to its initial position for a shorter duration, while the uncompensated signal has a longer duration. This yields the main non-dispersion component of a specific signal. Based on the above steps, wave packets of helical guided waves with different numbers of turns can be extracted when they do not disperse.

[0043] S5. By comparing the difference between the input signals f(t) and h(t), calculate the signal difference coefficient SDC for each spiral path.

[0044] To characterize the difference between the received wave packet and the wave packet transmitted at the time of signal transmission, a signal difference coefficient (SDC) is introduced, the expression of which is: ; Where T is the period of the signal. for The average value over a period of time.

[0045] The larger the SDC, the greater the difference between the two signals, with a maximum SDC of 1; conversely, the smaller the SDC, the smaller the difference between the two signals, with a minimum SDC of 0, where the two signals are completely identical. The SDC distribution calculated in this embodiment of the invention is as follows: Figure 5 As shown.

[0046] S6. Using the signal difference coefficient SDC of each spiral path, calculate the probability of damage at each point within the detection area, including: S61. Calculate the damage weight function for each point on each spiral path: In fact, the SDC calculated for the corresponding path represents the probability of damage existing near that path. Assuming that points with equal probability of damage along a path are distributed on an ellipse, and the probability increases the closer to the path, a weighting function can be given: ; ; in, , Let S be the coordinates of the h-th virtual launch device on the S0 side of the rectangle after the cylinder of the fuel rod cladding inspection area is unfolded. , The coordinates of the j-th virtual receiving device on the R0 side of the rectangle after the cylinder of the fuel rod cladding inspection area is unfolded; This is the shape factor, which controls the size of the ellipse. It needs to be set to a value greater than 1 for experimental use. =1.02 and =1.03 Two cases were studied. It is the ratio of the sum of the distances from each point (x,y) to the signal transmitting and receiving devices to the length of the spiral path.

[0047] S62. Calculate the probability that damage exists at each point within the detection area.

[0048] For each point within the detection area, the probability that damage exists at that point location (x, y) is the sum of the products of the SDC and weights of all sensing paths, i.e.: .

[0049] When a signal comes in, there will be signals from multiple paths. By using dispersion compensation, the signals from different paths are extracted separately, which is h(t). h(t) corresponds one-to-one with the path. One spiral path corresponds to one h(t). Many h(t) can be calculated. For each h(t) and f(t), a difference calculation is performed. One h(t) is used to calculate one SDC, which will give the SDC corresponding to each path. Then, for each SDC, the probability of all points in the detection area is calculated. The sum of all probabilities is the final result.

[0050] S7. Determine the location of damage by judging the probability of damage at each point within the detection area using a damage probability threshold, including: S71. Determine the damage probability threshold.

[0051] After normalizing the damage probability in the detection area, the location of the damage is considered to be where the probability is greater than 0.9 (the choice of this threshold has a significant impact on the accuracy of the final imaging and requires multiple iterations based on experimental conditions). Therefore, the determined damage probability threshold is 0.9.

[0052] S72. Determine whether the probability of damage P(x,y) at each point is greater than the damage threshold. If yes, the point is damaged; otherwise, the point is undamaged.

[0053] Determine whether the probability of damage P(x,y) at each point is greater than the damage probability threshold. Points with a probability greater than 0.9 are considered to have damage; otherwise, the points are considered to have no damage.

[0054] Furthermore, following the damage probability calculation expression in S62 above, the damage probability of the entire fuel rod cladding inspection area cylinder can also be calculated to form a damage probability distribution image. By processing the image and filtering secondary areas, the pipeline defect situation can be obtained.

[0055] In an embodiment of the present invention, to verify the damage detection effect of the method of the present invention, damage points were pre-set in the inspection area of ​​the fuel rod cladding, and then subsequent steps such as setting a pair of signal receiving and transmitting devices at both ends of the inspection area of ​​the fuel rod cladding were performed. Actual testing showed that... (See attached...) Figure 6 As shown, attached Figure 6 Different colors represent different probabilities of damage, with red representing the highest probability. The calculated detection results of this invention show good agreement with the actual pre-set defect locations (225mm axially and approximately 12-13mm circumferentially). (See attached image) Figure 6 The two figures shown are damage locations calculated using the same set of data but with different parameters β, demonstrating that the method of this invention can effectively detect fuel rod cladding damage. (The term "damage location" here refers to...) This is the shape factor, which controls the size of the ellipse. It needs to be set to a value greater than 1 for experimental use. =1.02 and =1.03 Two cases were studied.

[0056] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting fuel rod cladding damage based on probabilistic imaging of multiple diffracted guided waves, characterized in that, It includes the following steps: S1. A pair of signal receiving and transmitting devices are installed at both ends of the fuel rod cladding inspection area; S2. Transmit the input signal f(t) through the signal transmitting device S0; S3. Acquire wavefield data through signal receiving device R0, and extract narrowband signals from the acquired wavefield data; S4. Based on the propagation characteristics of helical guided waves, extract the wave packet signal h(t) of each helical path when no dispersion occurs; h(t) ; ； ； ； in, This is the Fourier transform of the received signal after narrowband extraction. This is to compensate for the propagation phase delay; t0 is the input signal. Duration; P i Let i be the propagation distance, i be the number of revolutions in the direction of propagation of the helical waveguide, and let i be negative when the propagation direction is left-handed and positive when the propagation direction is right-handed. Let 'b' be the length of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area, and 'b' be the width of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area. Let be the ordinate of the launch device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area. The vertical coordinate of the receiving device is located within the rectangle of the expanded cylindrical area of ​​the fuel rod cladding inspection zone. S5. By comparing the difference between the input signals f(t) and h(t), calculate the signal difference coefficient SDC for each spiral path; S6. Calculate the probability of damage at each point within the detection area using the signal difference coefficient SDC of each spiral path. S7. Determine the location of damage by judging the probability of damage at all points within the detection area using the damage probability threshold.

2. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 1, characterized in that, S4, based on the characteristics of helical guided wave propagation, extracts the wave packet signal h(t) when no dispersion occurs from the extracted narrowband signal, specifically including: S41. Calculate the distance the helical guided wave propagates in the pipe; ； Among them, P i Let i be the propagation distance, i be the number of revolutions in the direction of propagation of the helical waveguide, and let i be negative when the propagation direction is left-handed and positive when the propagation direction is right-handed. Let 'b' be the length of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area, and 'b' be the width of the rectangle formed by unfolding the cylinder of the fuel rod cladding inspection area. Let be the ordinate of the launch device within the rectangle formed by the unfolding of the cylinder in the fuel rod cladding inspection area. The vertical coordinate of the receiving device is located within the rectangle of the expanded cylindrical area of ​​the fuel rod cladding inspection zone. S42. Obtain the propagation distance P of the spiral guided wave. i The signal received later ; ； in, The Fourier transform of the output signals superimposed with all different modes and different propagation distances, where s represents the mode type. For the Fourier transform of the input signal f(t), The wavenumber-frequency relationship for different modes. A wave with frequency ω travels at a distance P. i The phase delay factor, P, was introduced later; 𝑗 is the imaginary unit. i For the distance of propagation; S43. Calculate the signal r(t) after dispersion compensation; ； in, , To compensate for the propagation phase delay; S44. Extract the wave packet signal h(t) when no dispersion occurs; h(t) ; ； in, Let t0 be a rectangular window function, and t0 be the input signal. Duration.

3. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 1, characterized in that, The signal difference coefficient SDC for each spiral path calculated in S5 is: ； Where T is the period of the signal. for The average value over a period of time.

4. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 1, characterized in that, S6, using the signal difference coefficient SDC of each spiral path, calculates the probability of damage at each point within the detection area, specifically including: S61. Calculate the damage weight function for each point on each spiral path: ； ； in, , Let S be the coordinates of the h-th virtual launch device on the S0 side of the rectangle after the cylinder of the fuel rod cladding inspection area is unfolded. , The coordinates of the j-th virtual receiving device on the R0 side of the rectangle after the cylinder of the fuel rod cladding inspection area is unfolded; For shape factor, This is the ratio of the sum of the distances from each point (x, y) to the signal transmitting and receiving devices to the length of the spiral path. S62. Calculate the probability that damage exists at each point within the detection area; 。 5. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 1, characterized in that, Step S7 involves determining the probability of damage at all points within the detection area using a damage probability threshold to identify the damage location. Specifically, this includes: S71. Determine the damage probability threshold; S72. Determine whether P(x,y) > damage probability threshold for all point locations. If yes, the point location is damaged; otherwise, the point location is undamaged.

6. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 5, characterized in that, The damage probability threshold in S71 is 0.

9.

7. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 1, characterized in that, The signal receiving and transmitting device consists of a pair of PZT ceramic piezoelectric elements.

8. The fuel rod cladding damage detection method based on multiple diffraction guided wave probability imaging according to claim 1, characterized in that, The number of turns i in the direction of propagation of the helical guided wave can be a positive integer between -10 and 10.

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