Metal coating thickness eddy current measuring probe and probe coil design method

Abstract

The invention relates to the technical field of fuel rod coating thickness eddy current probe detection, and provides a metal coating thickness eddy current measuring probe and a probe coil design method, and the probe comprises a coil detection module and a signal cable; wherein the coil detection module comprises a probe shell, a focusing magnetic core, a detection coil unit and a contact layer; the contact layer is arranged at the head of the probe shell to contact a to-be-detected fuel rod; the focusing magnetic core is fixedly connected in the head of the probe shell; the detection coil unit comprises a measuring coil and a balance coil which coaxially sleeve the focusing magnetic core, the measuring coil and the balance coil are in differential connection, and the measuring coil is arranged on one side close to the head of the probe shell; and one end of the signal cable passes through the tail part of the probe shell and is connected with the detection coil unit. The probe is directly attached to the fuel rod to be detected, the probe is high in detection sensitivity, good in stability and good in temperature drift resistance, the problem that remote transmission of weak signals in eddy current detection is difficult is effectively solved, and the coating thickness is accurately measured.

Description

Technical Field

[0001] The invention relates to the technical field of eddy current probe detection of fuel rod coating thickness, and in particular to a metal coating thickness eddy current measurement probe and a probe coil design method. Background Art

[0002] In the development of accident-resistant fuel assemblies for nuclear power plants, the coating thickness on the surface of the fuel rods and its changes after operation in the reactor are crucial to evaluating the performance of the fuel assemblies. The surface of the fuel rods usually has a protective coating, such as a chromium coating on zirconium alloys, which mainly serves to improve corrosion resistance and reduce the risk of hydrogen embrittlement, thereby enhancing the stability of the fuel cladding in high temperature and high pressure environments. The thickness of the coating directly affects the fuel rods' oxidation resistance, corrosion resistance, and behavior under accident conditions.

[0003] In the prior art, non-destructive detection methods are usually used to measure the coating thickness on the surface of fuel rods, such as the eddy current method, which measures the thickness of metal coatings based on the principle of electromagnetic induction. The probe can penetrate the coating and substrate to accurately measure the thickness of the coating without damaging the fuel rods themselves. However, under actual application conditions, especially in the high-level, deep-water, and high-temperature environment of spent fuel pools in nuclear power plants, the eddy current signal is weak and the signal attenuation is obvious under extreme environmental conditions. The reliability of the measurement results is difficult to guarantee. Summary of the invention

[0004] In view of the shortcomings of the above-mentioned prior art, the present invention provides a metal coating thickness eddy current measurement probe and a probe coil design method, which solves the technical problem that when the probe in the prior art adopts the eddy current method to measure the high-precision coating thickness, the signal attenuation is obvious under extreme environmental conditions and the measurement result accuracy is poor.

[0005] In one aspect, the present invention provides a metal coating thickness eddy current measurement probe, comprising a coil detection module and a signal cable;

[0006] The coil detection module includes a probe housing, a focusing magnetic core, a detection coil unit and a contact layer;

[0007] The contact layer is arranged at the head of the probe housing and is used for contacting the fuel rod to be tested;

[0008] The focusing magnetic core is arranged in the probe housing and is fixedly connected to the head of the probe housing;

[0009] The detection coil unit comprises a measuring coil and a balancing coil, wherein the measuring coil and the balancing coil are coaxially sleeved on the focusing magnetic core, and the measuring coil is differentially connected to the balancing coil, and the measuring coil is arranged on one side close to the head of the probe housing;

[0010] One end of the signal cable passes through the tail of the probe housing and is connected to the detection coil unit.

[0011] Optionally, a stainless steel sleeve is provided in the probe housing, and the stainless steel sleeve is located at the head of the probe housing;

[0012] The measuring coil and the balancing coil are both arranged in the stainless steel sleeve, and the measuring coil and the balancing coil are fixed and sealed in the stainless steel sleeve by a packaging medium;

[0013] The contact layer is fixedly connected to one side of the stainless steel sleeve close to the head of the probe housing.

[0014] Optionally, the contact layer is a sapphire wafer, and the sapphire wafer includes a flat end and an arc-shaped convex end;

[0015] A clamping structure is provided in the stainless steel sleeve, and an arc-shaped fixing structure is provided on one side of the stainless steel sleeve close to the head of the probe housing, and the arc-shaped fixing structure has the same arc as the arc-shaped protruding end of the sapphire wafer;

[0016] The plane end of the sapphire wafer is clamped on the clamping structure, and the arc-shaped protruding end of the sapphire wafer is fixedly connected to the arc-shaped fixing structure.

[0017] Optionally, the probe housing is made of 304L stainless steel.

[0018] Optionally, the measuring coil and the balancing coil include a coil body, and the coil body includes an internal conductor, an insulating layer and a protective layer;

[0019] The material of the internal conductor is annealed copper material;

[0020] The insulating layer covers the surface of the internal conductor, and the insulating layer is an enamel layer;

[0021] The protective layer covers the surface of the insulating layer, and the material of the protective layer is polyimide material.

[0022] Optionally, the coil detection module further includes a positioning member;

[0023] One end of the positioning member is in relative contact with the balancing coil, and is used to fix the balancing coil and the measuring coil on the head of the probe housing;

[0024] The other end of the positioning member is packaged with the tail of the probe housing through a packaging medium;

[0025] A through hole for the focusing magnetic core to pass through is opened at the center of the positioning piece.

[0026] Optionally, the metal coating thickness eddy current measuring probe further includes an eddy current meter;

[0027] The other end of the signal cable is connected to the eddy current instrument through a four-core connector;

[0028] The eddy current instrument excites the detection coil unit through the signal cable to generate an alternating electromagnetic field, and analyzes the impedance change generated by the detection coil unit.

[0029] Optionally, the signal cable is a coaxial cable made of pure copper, and the outer layer of the coaxial cable is made of polyurethane.

[0030] Another aspect of the present invention provides a probe coil design method, which is applied to design a measuring coil in any one of the above-mentioned metal coating thickness eddy current measurement probes, and the method comprises:

[0031] Determine a preset coil model, and obtain initial parameters of the coil model, wherein the initial parameters include an initial width of the coil and an outer diameter of the wire;

[0032] Obtaining an estimated thickness of the fuel rod coating to be measured, determining an effective penetration depth of a measuring coil based on the estimated thickness, calculating a detection frequency of the measuring coil using a skin depth formula, and determining a resonant frequency of the measuring coil based on the detection frequency;

[0033] The inner radius and the outer radius of the measuring coil are calculated according to the diameter of the fuel rod to be measured, the estimated thickness and the initial width of the coil, and the initial height and the total number of initial turns of the measuring coil are calculated based on the resonant frequency of the measuring coil;

[0034] Performing simulation calculation on the coil model, reducing the initial height of the coil to within a preset parameter range to obtain a target coil height, and determining a target coil width and a target total number of turns of the measuring coil;

[0035] Based on the resonant frequency and the preset quality factor, target parameters of the measuring coil are determined, and the measuring coil is designed based on the target parameters, wherein the target parameters include the coil inner radius, the coil outer radius, the coil target height, the coil target width, and the target total number of turns.

[0036] Optionally, the step of calculating the inner radius and the outer radius of the measuring coil according to the diameter of the fuel rod to be measured, the estimated thickness and the initial width of the coil, and calculating the initial height and the initial total number of turns of the measuring coil based on the resonant frequency of the measuring coil comprises:

[0037] Determine the median diameter of the measuring coil according to the diameter of the fuel rod to be measured and the estimated thickness, and calculate the inner radius and outer radius of the measuring coil according to the initial width of the coil, wherein the median diameter of the coil is equal to one-half of the sum of the inner radius and the outer radius of the coil, and the initial width of the coil is equal to the difference between the outer radius and the inner radius of the coil;

[0038] The number of layers of the measuring coil is calculated according to the initial width of the coil and the outer diameter of the wire, and the number of turns of the coil is calculated according to the calculation formula of the resonant frequency and the number of layers of the measuring coil, the outer radius of the coil and the inner radius of the coil;

[0039] The initial height of the coil is obtained by calculating the product of the layer turns of the coil and the outer diameter of the wire, and the initial total number of turns of the coil is obtained by calculating the product of the layer turns of the coil and the number of layers of the coil.

[0040] The metal coating thickness eddy current measurement probe provided by the present invention is provided with a focusing magnetic core to enhance the coil inductance, improve the magnetic field concentration of the measuring coil, and effectively improve the detection sensitivity and resolution of the probe; a balancing coil and a measuring coil are coaxially arranged, and the balancing coil and the measuring coil are differentially connected to achieve differential temperature balance, and overcome the influence of signal drift caused by the temperature of the fuel rod and the water temperature on the coating thickness measurement; the setting of the contact layer ensures good contact between the probe and the fuel rod to be measured, and at the same time plays a role in protecting the probe head and extending the service life of the probe; the signal cable is directly connected to the detection coil unit to ensure the effective transmission of the signal and improve the signal transmission quality. The above-mentioned probe is directly fitted with the fuel rod to be measured, and the probe has high detection sensitivity, good stability, and good temperature drift resistance, which effectively overcomes the problem of difficulty in remote transmission of weak signals of eddy current detection, and is accurate for coating thickness measurement.

[0041] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0042] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 A schematic diagram of the structure of an eddy current measuring probe for metal coating thickness in one embodiment provided in the present application;

[0045] Figure 2 A schematic diagram of the structure of a detection coil unit and a focusing magnetic core in an eddy current measurement probe for metal coating thickness in an embodiment provided in the present application;

[0046] Figure 3 A schematic diagram of a flow chart of a probe coil design method in an embodiment provided in the present application;

[0047] Figure 4 A schematic diagram of initial parameters of a coil model in an embodiment provided in the present application.

[0048] In the figure:

[0049] 1. Detection coil unit; 101. Measuring coil; 102. Balance coil; 2. Probe housing; 3. Focusing magnetic core; 4. Contact layer; 5. Positioning piece. DETAILED DESCRIPTION

[0050] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0051] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0052] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] In one aspect, the present invention provides a metal coating thickness eddy current measurement probe, such as Figure 1 and Figure 2 As shown, it includes a coil detection module and a signal cable; wherein the coil detection module includes a probe housing 2, a focusing core 3, a detection coil unit 1 and a contact layer 4; the contact layer 4 is arranged at the head of the probe housing 2, and is used to contact the fuel rod to be tested; the focusing core 3 is arranged in the probe housing 2, and is fixedly connected to the head of the probe housing 2; the detection coil unit 1 includes a measuring coil 101 and a balancing coil 102, the measuring coil 101 and the balancing coil 102 are coaxially sleeved on the focusing core 3, and the measuring coil 101 is differentially connected to the balancing coil 102, and the measuring coil 101 is arranged on a side close to the head of the probe housing 2; one end of the signal cable passes through the tail of the probe housing 2 and is connected to the detection coil unit 1.

[0054] The metal coating thickness eddy current measuring probe provided by the present invention is provided with a focusing magnetic core 3, which enhances the coil inductance, improves the magnetic field concentration of the measuring coil 101, and effectively improves the detection sensitivity and resolution of the probe; a balancing coil 102 and a measuring coil 101 are coaxially arranged, and the balancing coil 102 and the measuring coil 101 are differentially connected to achieve differential temperature balance, and overcome the influence of signal drift caused by the temperature of the fuel rod and the water temperature on the coating thickness measurement; the setting of the contact layer 4 ensures good contact between the probe and the fuel rod to be measured, and at the same time plays a role in protecting the probe head and extending the service life of the probe; the signal cable is directly connected to the detection coil unit 1 to ensure the effective transmission of the signal and improve the signal transmission quality. The above-mentioned probe is directly fitted with the fuel rod to be measured, and the probe has high detection sensitivity, good stability, and good temperature drift resistance, which effectively overcomes the problem of difficulty in remote transmission of weak signals of eddy current detection, and is accurate for coating thickness measurement.

[0055] Furthermore, a stainless steel sleeve is provided in the probe housing 2, and the stainless steel sleeve is located at the head of the probe housing 2; the measuring coil 101 and the balancing coil 102 are both provided in the stainless steel sleeve, and the measuring coil 101 and the balancing coil 102 are fixed and sealed by a packaging medium in the stainless steel sleeve; the contact layer 4 is fixedly connected to one side of the stainless steel sleeve close to the head of the probe housing 2.

[0056] In this embodiment, a stainless steel sleeve is provided at the head of the probe housing 2, which can improve the mechanical strength and durability of the probe and protect the internal components from the influence of the external environment; the measuring coil 101 and the balancing coil 102 are fixed and sealed by the packaging medium inside the stainless steel sleeve, which can ensure the stability of the coil position during use and prevent deformation or displacement caused by vibration or physical impact, and the packaging medium can also provide additional insulation and protection to prevent pollutants such as moisture and dust from entering the probe, thereby improving the reliability and service life of the probe; the contact layer 4 is fixedly connected to one end of the stainless steel sleeve, ensuring the contact between the probe and the fuel rod to be measured, and reducing the measurement error caused by poor contact. The design of the contact layer 4 can also protect the probe head from wear and damage and extend the service life of the probe.

[0057] Furthermore, the contact layer 4 is a sapphire wafer, which includes a flat end and an arc-shaped protruding end; a clamping structure is arranged inside the stainless steel sleeve, and an arc-shaped fixing structure is arranged on the side of the stainless steel sleeve close to the head of the probe housing 2, and the arc-shaped fixing structure has the same curvature as the arc-shaped protruding end of the sapphire wafer; the flat end of the sapphire wafer is clamped on the clamping structure, and the arc-shaped protruding end of the sapphire wafer is fixedly connected to the arc-shaped fixing structure.

[0058] In the present embodiment, sapphire has extremely high mechanical properties, high hardness, and good wear resistance. When used as the contact layer 4, it can withstand long-term use and friction, reduce wear, and extend the service life of the probe. It is more resistant to radiation than organic matter, and the working environment dose for continuous work can be higher than 100,000 Gy / h. At the same time, sapphire has good thermal stability, can maintain its physical and chemical properties unchanged in a high temperature environment, and the material deformation rate is much lower than other non-metallic materials, and can adapt to the coating thickness detection of nuclear fuel rods under high temperature conditions. The flat end of the sapphire wafer is embedded in the stainless steel sleeve and fixed by a clamping structure, while the arc-shaped convex end of the sapphire wafer is mechanically fixed to the arc-shaped fixing structure by gem inlay, ensuring the accurate installation and positioning of the contact layer 4, so that the sapphire wafer remains stable during use, reducing displacement or damage caused by vibration or physical impact, and always ensuring the integrity and wear resistance of the entire probe. The stainless steel sleeve has good machining performance, which is conducive to the inlay processing of the sapphire wafer.

[0059] Specifically, in the above embodiment, the material of the probe housing 2 is 304L stainless steel.

[0060] In this embodiment, 304L stainless steel has good corrosion resistance, effectively reduces the activation products that can be detached during the detection process, and is conducive to decontamination after the detection is completed; moreover, 304L stainless steel has good high temperature resistance and can work in a high temperature environment without losing its structural integrity; 304L stainless steel is also a high-strength material that can withstand mechanical pressure and impact, thereby protecting the internal electronic components from damage.

[0061] Specifically, in the above embodiment, the measuring coil 101 and the balancing coil 102 include a coil body, which includes an internal conductor, an insulating layer and a protective layer; the material of the internal conductor is annealed copper material; the insulating layer covers the surface of the internal conductor, and the insulating layer is an enamel layer; the protective layer covers the surface of the insulating layer, and the material of the protective layer is a polyimide material.

[0062] In this embodiment, the internal conductor is made of annealed copper material with good conductivity, which helps to reduce energy loss during signal transmission and improve measurement accuracy and sensitivity. The annealed copper material makes the coil less likely to break when bent or twisted, thereby enhancing the durability and reliability of the coil. The enamel layer as an insulating layer can effectively prevent short circuits between the internal conductors of the coil and ensure the stability and accuracy of signal transmission. The enamel layer also has good heat resistance and chemical stability and can withstand higher operating temperatures. Polyimide material as a high-performance protective layer has excellent heat resistance, chemical stability and electrical insulation properties, which can provide additional protection for the coil, especially in high temperature, high humidity or corrosive environments. The coil provided in this application has the characteristics of good radiation resistance and good temperature drift resistance, and the probe material of the coil body has strong radiation resistance and a stable temperature coefficient.

[0063] Specifically, in the above embodiment, the coil detection module also includes a positioning member 5; one end of the positioning member 5 is in relative contact with the balance coil 102, and is used to fix the balance coil 102 and the measuring coil 101 on the head of the probe shell 2; the other end of the positioning member 5 is encapsulated with the tail of the probe shell 2 through a packaging medium; and a through hole is opened in the center of the positioning member 5 for the focusing magnetic core 3 to pass through.

[0064] In this embodiment, one end of the positioning member 5 is in relative contact with the balance coil 102, and is used to fix the balance coil 102 and the measuring coil 101 at the head of the probe housing 2, ensuring that the relative position between the coils is stable and unchanged, thereby improving the accuracy and repeatability of the measurement; the other end of the positioning member 5 is encapsulated with the tail of the probe housing 2 through a packaging medium, ensuring the stability of the entire coil detection module structure and reducing displacement or deformation caused by vibration or physical impact. The packaging medium can not only fix the positioning member 5, but also seal the probe as a whole, so that the probe itself can be waterproof and can adapt to a more severe working environment; the through hole opened in the center of the positioning member 5 can ensure the correct installation and positioning of the focusing core 3, thereby ensuring that the relative position between the focusing core 3 and the measuring coil 101 and the balance coil 102 is accurate, thereby improving the magnetic field concentration of the coil, and thereby improving the sensitivity and resolution of the measurement.

[0065] Specifically, in the above embodiment, the metal coating thickness eddy current measurement probe also includes an eddy current meter; the other end of the signal cable is connected to the eddy current meter through a four-core connector; the eddy current meter excites the detection coil unit 1 through the signal cable to generate an alternating electromagnetic field, and analyzes the impedance changes generated by the detection coil unit 1.

[0066] In this embodiment, the probe measures the thickness of the metal coating based on the eddy current skin effect. Specifically, the detection coil unit 1 is excited by the excitation unit in the eddy current meter to generate an electromagnetic field, thereby generating eddy currents on the surface of the fuel rod cladding coating to be measured. Then, the eddy currents generated by the fuel rod cladding coating material generate a spatial electromagnetic field that reacts to the detection coil unit 1 of the coating probe, thereby changing the impedance of the detection coil unit 1. There is a corresponding relationship between the eddy current impedance and the coating thickness. The coating thickness measurement is achieved by detecting and analyzing the eddy current signal impedance of the detection coil unit 1. The measurement signal can be analyzed by the eddy current meter and software to finally obtain information on the coating thickness on the fuel rod surface.

[0067] Specifically, in the above embodiment, the signal cable is a coaxial cable made of pure copper, and the outer layer of the coaxial cable is made of polyurethane.

[0068] In this embodiment, the signal cable uses a 75-ohm coaxial cable of model RG58 / U, the outer layer of which is made of polyurethane, has good impedance matching, and has excellent mechanical strength and electrical insulation; the signal cable can be suitable for long-term work in the weak acid environment of underwater nuclear power, has excellent resistance to chemical corrosion, radiation resistance, and protects the cable from damage by mechanical stress, ensuring the stability of its electrical performance; the signal cable material selected in this application is waterproof, radiation-resistant, and has good shielding and signal transmission properties, can be used in the nuclear power site environment, ensure the stability of the measurement results, and meet the needs of the accident-resistant fuel assembly development project for fuel rod surface coating thickness measurement.

[0069] Specifically, the steps of packaging the metal coating thickness eddy current measurement probe provided by the present application are as follows:

[0070] First, the measuring coil 101 and the balancing coil 102 in the detection coil unit 1 are fixed by the positioning member 5, and then the detection coil unit 1 is welded to the signal cable, and the packaging medium is matched with the stainless steel sleeve to ensure the centering and installation accuracy of the measuring coil 101 and the balancing coil 102, which are fixed by sealant;

[0071] The sapphire wafer is then embedded into a stainless steel sleeve and fixed by injecting sealant;

[0072] Finally, the signal cable is led out from the rear end of the probe housing 2, and the positioning member 5 and the rear end of the probe housing 2 are encapsulated with glue to ensure the waterproof sealing of the probe.

[0073] Specifically, the testing of the metal coating thickness eddy current measurement probe provided in this application requires the use of an eddy current meter and a comparison test block to test the performance of the probe, including measurement accuracy, waterproofness, radiation resistance, temperature resistance and stability, as well as the main and secondary parameters required for various tests such as inductance and resistance to confirm the probe performance parameters.

[0074] Another aspect of the present invention provides a probe coil design method, such as Figure 3 As shown, the method is applied to design the measuring coil in the above-mentioned metal coating thickness eddy current measuring probe, and the method includes:

[0075] Step S301, determining a preset coil model, and obtaining initial parameters of the coil model, wherein the initial parameters include an initial width of the coil and an outer diameter of the wire;

[0076] Step S302, obtaining an estimated thickness of the fuel rod coating to be tested, determining the effective penetration depth of the measuring coil based on the estimated thickness, and calculating the detection frequency of the measuring coil using the skin depth formula, and determining the resonant frequency of the measuring coil according to the detection frequency;

[0077] Step S303, calculating the inner radius and outer radius of the measuring coil according to the diameter, estimated thickness and initial width of the fuel rod to be measured, and calculating the initial height and total initial number of turns of the measuring coil based on the resonant frequency of the measuring coil;

[0078] Step S304, performing simulation calculation on the coil model, reducing the initial height of the coil to within a preset parameter range to obtain a target height of the coil, and determining a target width and a target total number of turns of the measuring coil;

[0079] Step S305, determining target parameters of the measuring coil based on the resonant frequency and the preset quality factor, and designing the measuring coil based on the target parameters, wherein the target parameters include coil inner radius, coil outer radius, coil target height, coil target width, and target total number of turns.

[0080] The present invention provides a probe coil design method, which determines the effective penetration depth based on the estimated coating thickness, and uses the skin depth formula to calculate the detection frequency of the measuring coil, which can ensure that the coil works at the optimal frequency to obtain the highest measurement sensitivity and accuracy; by calculating the inner radius, outer radius, height and total number of turns of the coil, the geometric dimensions of the coil can be ensured to match the size of the fuel rod to be measured, thereby improving the accuracy and reliability of the measurement; simulation calculation of the coil model helps to verify the effectiveness of the coil design, and adjusting the size and parameters of the coil according to the simulation results can further optimize its performance; by adjusting the height of the coil, it can ensure that the coil is in closer contact with the fuel rod, reduce the influence of the air gap, and improve the accuracy of the measurement; finally, by determining the target parameters of the coil based on the resonant frequency and the preset quality factor, it can ensure that the coil has good selectivity and energy conversion efficiency, thereby improving the quality of the measurement signal. The above method is customized according to the specific size of the fuel rod to be measured and the estimated coating thickness, ensuring that the probe can provide the best measurement performance for a specific application scenario.

[0081] Further, step S303 includes first determining the middle diameter of the measuring coil according to the diameter and estimated thickness of the fuel rod to be measured, and calculating the inner radius and outer radius of the measuring coil according to the initial width of the coil, wherein the middle diameter of the coil is equal to one-half of the sum of the inner radius and the outer radius of the coil, and the initial width of the coil is equal to the difference between the outer radius and the inner radius of the coil; then calculating the number of layers of the measuring coil according to the initial width of the coil and the outer diameter of the wire, and calculating the layer turns of the coil according to the number of layers of the measuring coil, the outer radius of the coil and the inner radius of the coil based on the calculation formula of the resonant frequency; finally calculating the product of the layer turns of the coil and the outer diameter of the wire to obtain the initial height of the coil, and calculating the product of the layer turns of the coil and the number of layers of the coil to obtain the initial total number of turns of the coil.

[0082] This application provides a probe coil design method, and the specific design steps are as follows:

[0083] First, determine the preset coil model, the preset coil model is as follows Figure 4 As shown, the outer diameter d of the wire can be determined in the preset coil model 0 and the initial coil width W 0 , wherein the outer diameter of the wire includes the insulating layer, preferably, the outer diameter of the wire d 0 =0.18mm, initial coil width W 00.5-1mm;

[0084] Then, the estimated thickness of the fuel rod coating to be tested is obtained, and the effective penetration depth of the measuring coil is determined based on the estimated thickness, that is, the estimated thickness is within 2 / 3 of the effective penetration depth, and then the detection frequency of the measuring coil is calculated using the skin depth formula. The specific formula is as follows:

[0085]

[0086] Among them, δ is the effective penetration depth, f is the detection frequency, μ is the magnetic permeability, and σ is the electrical conductivity of the conductor;

[0087] Based on the above formula, the detection frequency f is obtained, and according to the relationship between the resonant frequency and the detection frequency, that is:

[0088] f R =3f,

[0089] Find the resonant frequency f R ;

[0090] Then obtain the diameter of the fuel rod to be tested and the estimated thickness of the coating to determine the median diameter D of the measuring coil. 0 , and the diameter D of the measuring coil 0 It can be expressed as follows:

[0091] D 0 =(Ri+Ro) / 2,

[0092] Among them, Ri is the inner radius of the coil, and Ro is the outer radius of the coil;

[0093] The initial coil width W 0 It can be expressed as follows:

[0094] W 0 =Ro-Ri,

[0095] Therefore, the inner radius Ri and the outer radius Ro of the coil can be specifically calculated;

[0096] According to the initial width W of the coil 0 Specific calculation formula:

[0097] W 0 =N L ·d 0 ,

[0098] The number of layers N of the measuring coil can be obtained L ;

[0099] Based on the resonant frequency f R The calculation formula is:

[0100]

[0101] Among them, ε 0 is the vacuum dielectric constant, ε 0 =8.854x10-3(pF / mm), ε r is the relative dielectric constant, ε r =2.1, d is the interlayer thickness, d = 1.26d 0 -1.15d i , d i is the inner diameter of the wire, d i =0.399mm, k is the coefficient;

[0102] Based on the above formula, the layer turns N of the measuring coil can be obtained. V , and then calculate the initial height of the coil according to the following formula:

[0103] H 0 =N V ·d 0 ,

[0104] Then the initial total number of turns of the coil is obtained:

[0105] N=N L ·N V ,

[0106] After obtaining the above parameters, the coil model is simulated and calculated, and the initial height of the coil is reduced to within the preset parameter range to obtain the target height of the coil. The lower the height of the coil, the higher the sensitivity of the coil detection. After determining the target height of the coil, the target width and total number of turns of the coil are accurately measured.

[0107] Finally, based on the resonant frequency and the preset quality factor, all target parameters of the measurement coil are determined, including the inner radius of the coil, the outer radius of the coil, the target height of the coil, the target width of the coil, and the target total number of turns. The quality factor is used to characterize the quality of the coil, specifically the ratio of the stored energy to the consumed energy. The smaller the resistance, the smaller the coil loss, and the larger the value of the quality factor.

[0108] According to all the target parameters of the measured coil, the resistance and inductance of the coil can be further calculated. The resistance calculation formula of the coil is as follows:

[0109]

[0110] Among them, ρ c is the conductor resistivity;

[0111] The formula for calculating the inductance of the coil is as follows:

[0112]

[0113] Among them, μ r is the relative magnetic permeability of the core.

[0114] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A metal coating thickness eddy current measuring probe, characterized in that: Includes coil detection module and signal cable; The coil detection module comprises a probe housing (2), a focusing magnetic core (3), a detection coil unit (1) and a contact layer (4); The contact layer (4) is arranged at the head of the probe housing (2) and is used for contacting the fuel rod to be tested; The focusing magnetic core (3) is arranged in the probe housing (2) and is fixedly connected to the head of the probe housing (2); The detection coil unit (1) comprises a measuring coil (101) and a balancing coil (102), wherein the measuring coil (101) and the balancing coil (102) are coaxially sleeved on the focusing magnetic core (3), and the measuring coil (101) is differentially connected to the balancing coil (102), and the measuring coil (101) is arranged on one side close to the head of the probe housing (2); One end of the signal cable passes through the tail of the probe housing (2) and is connected to the detection coil unit (1).

2. The metal coating thickness eddy current measuring probe according to claim 1, characterized in that: A stainless steel sleeve is arranged inside the probe housing (2), and the stainless steel sleeve is located at the head of the probe housing (2); The measuring coil (101) and the balancing coil (102) are both arranged in the stainless steel sleeve, and the measuring coil (101) and the balancing coil (102) are fixed and sealed in the stainless steel sleeve by a packaging medium; The contact layer (4) is fixedly connected to a side of the stainless steel sleeve close to the head of the probe housing (2).

3. The metal coating thickness eddy current measuring probe according to claim 2, characterized in that: The contact layer (4) is a sapphire wafer, and the sapphire wafer comprises a flat end and an arc-shaped convex end; A clamping structure is arranged inside the stainless steel sleeve, and an arc-shaped fixing structure is arranged on one side of the stainless steel sleeve close to the head of the probe housing (2), wherein the arc-shaped fixing structure has the same arc as the arc-shaped protruding end of the sapphire wafer; The plane end of the sapphire wafer is clamped on the clamping structure, and the arc-shaped protruding end of the sapphire wafer is fixedly connected to the arc-shaped fixing structure.

4. The metal coating thickness eddy current measuring probe according to claim 1 or 2, characterized in that: The probe housing (2) is made of 304L stainless steel.

5. The metal coating thickness eddy current measuring probe according to claim 1 or 2, characterized in that: The measuring coil (101) and the balancing coil (102) comprise a coil body, wherein the coil body comprises an internal conductor, an insulating layer and a protective layer; The material of the internal conductor is annealed copper material; The insulating layer covers the surface of the internal conductor, and the insulating layer is an enamel layer; The protective layer covers the surface of the insulating layer, and the material of the protective layer is polyimide material.

6. The metal coating thickness eddy current measuring probe according to claim 1, characterized in that: The coil detection module also includes a positioning member (5); One end of the positioning member (5) is in relative contact with the balancing coil (102) and is used to fix the balancing coil (102) and the measuring coil (101) on the head of the probe housing (2); The other end of the positioning member (5) is encapsulated with the tail of the probe housing (2) via an encapsulation medium; A through hole for the focusing magnetic core (3) to pass through is provided at the center of the positioning member (5).

7. The metal coating thickness eddy current measuring probe according to claim 1, characterized in that: The metal coating thickness eddy current measuring probe also includes an eddy current meter; The other end of the signal cable is connected to the eddy current instrument through a four-core connector; The eddy current meter excites the detection coil unit (1) via the signal cable to generate an alternating electromagnetic field, and analyzes the impedance change generated by the detection coil unit (1).

8. The metal coating thickness eddy current measuring probe according to claim 1 or 7, characterized in that: The signal cable is a coaxial cable made of pure copper, and the outer layer of the coaxial cable is made of polyurethane.

9. A probe coil design method, characterized in that: The method is applied to designing a measuring coil in a metal coating thickness eddy current measuring probe according to any one of claims 1 to 8, and the method comprises: Determine a preset coil model, and obtain initial parameters of the coil model, wherein the initial parameters include an initial width of the coil and an outer diameter of the wire; Obtaining an estimated thickness of the fuel rod coating to be measured, determining an effective penetration depth of a measuring coil based on the estimated thickness, calculating a detection frequency of the measuring coil using a skin depth formula, and determining a resonant frequency of the measuring coil based on the detection frequency; The inner radius and the outer radius of the measuring coil are calculated according to the diameter of the fuel rod to be measured, the estimated thickness and the initial width of the coil, and the initial height and the total number of initial turns of the measuring coil are calculated based on the resonant frequency of the measuring coil; Performing simulation calculation on the coil model, reducing the initial height of the coil to within a preset parameter range to obtain a target coil height, and determining a target coil width and a target total number of turns of the measuring coil; Based on the resonant frequency and the preset quality factor, target parameters of the measuring coil are determined, and the measuring coil is designed based on the target parameters, wherein the target parameters include the coil inner radius, the coil outer radius, the coil target height, the coil target width, and the target total number of turns.

10. The probe coil design method according to claim 9, characterized in that: The step of calculating the inner radius and the outer radius of the measuring coil according to the diameter of the fuel rod to be measured, the estimated thickness and the initial width of the coil, and calculating the initial height and the total initial number of turns of the measuring coil based on the resonant frequency of the measuring coil comprises: Determine the median diameter of the measuring coil according to the diameter of the fuel rod to be measured and the estimated thickness, and calculate the inner radius and outer radius of the measuring coil according to the initial width of the coil, wherein the median diameter of the coil is equal to one-half of the sum of the inner radius and the outer radius of the coil, and the initial width of the coil is equal to the difference between the outer radius and the inner radius of the coil; The number of layers of the measuring coil is calculated according to the initial width of the coil and the outer diameter of the wire, and the number of turns of the coil is calculated according to the calculation formula of the resonant frequency and the number of layers of the measuring coil, the outer radius of the coil and the inner radius of the coil; The initial height of the coil is obtained by calculating the product of the layer turns of the coil and the outer diameter of the wire, and the initial total number of turns of the coil is obtained by calculating the product of the layer turns of the coil and the number of layers of the coil.

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