Ultrathin nuclear fuel oxide film eddy current detection probe

Abstract

The invention relates to the technical field of nuclear power fuel pool edge detection, and provides an ultra-thin nuclear fuel oxidation film eddy current detection probe which comprises a thin sheet base body used for being inserted into a fuel assembly, one end of the thin sheet base body is connected with an elastic sheet, and a detection piece attached to the surface of a fuel rod is installed on the elastic sheet. The detection piece comprises a magnetic core, a detection coil and a shielding layer, the detection coil is wound outside the magnetic core, the shielding layer wraps the magnetic core and the detection coil, the other end of the sheet base body is provided with a connector used for being externally connected with an eddy current instrument, and the detection coil is connected with the connector through a cable. A thin sheet base body capable of being inserted into a fuel assembly serves as a carrier, a detection piece comprising a magnetic core, a detection coil and a shielding layer is attached to a fuel rod through an elastic piece, a connector is connected through a cable, and then the detection piece is externally connected with an eddy current instrument, so that a probe extends into a narrow gap in the fuel assembly, coil inductance is improved, electromagnetic interference is resisted, and a deepwater high-level environment is adapted. The problems of detection adaptability and precision of the narrow gap in the fuel assembly are solved.

Description

Technical Field

[0001] This invention relates to the field of nuclear power fuel pool edge detection technology, and more specifically, to an ultra-thin nuclear fuel oxide film eddy current detection probe. Background Technology

[0002] In the operation and maintenance of nuclear power plants, ensuring the safe and stable operation of the nuclear reactor is of paramount importance. As the core component of the nuclear reactor, the performance and lifespan of nuclear fuel assemblies directly affect the safety and economic efficiency of the entire nuclear power plant. During long-term operation, an oxide film inevitably forms on the surface of the fuel assemblies. Variations in the thickness of this oxide film not only affect the heat exchange capacity of the fuel assemblies but may also accelerate the corrosion rate of the fuel rods, thereby impacting the safe operation of the reactor. For example, when the oxide film thickness exceeds a certain threshold, the thermal resistance of the fuel assembly increases significantly, leading to a rise in fuel rod temperature, which may trigger a series of safety issues. Therefore, accurately measuring the thickness of the oxide film on the nuclear fuel assemblies is crucial for timely assessment of their performance status, implementation of effective maintenance measures, and ensuring the safe and stable operation of the reactor.

[0003] Currently, the industry primarily uses eddy current testing technology to measure the oxide film thickness of fuel assemblies. The principle is based on the lift-off effect of eddy current detection, calculating the oxide film thickness by analyzing the impedance differences in eddy current signals generated by oxide films of different thicknesses. However, in practical applications, due to the unique internal structure of fuel assemblies and the small internal space (the gap between fuel rods is only 3.2 mm, and the gap between the guide tube and the fuel rod is even narrower at 1.6 mm), conventional placement-type eddy current testing probes are too large to fit into the narrow gaps for internal measurement. Furthermore, the testing environment is complex; measurements must be performed in the deep-water, high-level radioactive environment of a spent fuel pool in a nuclear power plant. A temperature gradient exists between the water and the fuel rods, and when the probe is in direct contact with the fuel rods, it is susceptible to temperature drift, leading to signal distortion and making it difficult to guarantee measurement accuracy. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-thin eddy current detection probe for nuclear fuel oxide film, which solves the problems of difficulty in measuring narrow gaps in nuclear fuel assemblies and signal distortion caused by temperature drift in deep-water high-level radioactive environments.

[0005] This invention is achieved through the following technical solution: an ultra-thin nuclear fuel oxide film eddy current detection probe, comprising a thin sheet substrate for insertion into a fuel assembly, an elastic sheet connected to one end of the thin sheet substrate, a detection element mounted on the elastic sheet and conforming to the surface of the fuel rod, the detection element comprising a magnetic core, a detection coil and a shielding layer, the detection coil being wound around the magnetic core, the shielding layer enclosing the magnetic core and the detection coil, and a connector for external eddy current instrument provided at the other end of the thin sheet substrate, the detection coil being connected to the connector via a cable.

[0006] Furthermore, the elastic sheet has a first circular groove for installing the test piece, the first circular groove is filled with waterproof sealant for bonding the test piece, and a first limiting groove is radially formed in the first circular groove.

[0007] Furthermore, a reference element is mounted on one end of the sheet substrate for testing. The reference element has the same structure as the testing element. The testing surface of the testing element extends beyond the surface of the sheet substrate, while the testing surface of the reference element is flush with the surface of the sheet substrate.

[0008] Furthermore, a second circular groove for mounting the reference component is formed on the thin film substrate. The second circular groove is filled with waterproof sealant for bonding the reference component. A second limiting groove is formed radially in the second circular groove.

[0009] Furthermore, the detection coil uses enameled wire with a polyimide coating.

[0010] Furthermore, the detection coil is fitted with a sleeve.

[0011] Furthermore, the thin film substrate is made of austenitic stainless steel.

[0012] Furthermore, the thin substrate has grooves for laying cables.

[0013] Furthermore, the connections between cables and connectors are sealed with epoxy resin.

[0014] The present invention has at least the following advantages and beneficial effects: by using a thin substrate that can be inserted into the fuel assembly as a carrier, and using an elastic sheet to make the detection component containing the magnetic core, detection coil and shielding layer fit against the fuel rod, and then connecting it to an eddy current meter through a cable connector, the probe can be inserted into a narrow gap inside the fuel assembly, thereby improving the coil inductance, resisting electromagnetic interference, adapting to deep-water high-level discharge environments, and solving the problems of adaptability and accuracy of narrow gap detection inside the fuel assembly. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an ultra-thin nuclear fuel oxide film eddy current detection probe provided by the present invention.

[0016] Figure 2 This is a cross-sectional view of the position of the detection element in an ultra-thin nuclear fuel oxide film eddy current detection probe provided by the present invention.

[0017] Figure 3 This is a cross-sectional view of the reference component position in an ultra-thin nuclear fuel oxide film eddy current detection probe provided by the present invention.

[0018] Figure 4 This is a cross-sectional view of the detection element or reference element in an ultra-thin nuclear fuel oxide film eddy current detection probe provided by the present invention.

[0019] Reference numerals: 1-Thin sheet substrate, 10-Wire groove, 11-Connector, 12-Cable, 13-Second circular groove, 14-Second limiting groove, 2-Elastic sheet, 21-First circular groove, 22-First limiting groove, 3-Detection element, 31-Magnetic core, 32-Detection coil, 33-Shielding layer, 34-Sleeve, 4-Reference element. Detailed Implementation

[0020] The specific implementation method is described below with reference to the accompanying drawings.

[0021] Example like Figures 1 to 4 As shown in this embodiment, an ultra-thin eddy current detection probe for nuclear fuel oxide film is disclosed. It includes a thin substrate 1 for insertion into a fuel assembly. One end of the thin substrate 1 is connected to an elastic sheet 2. A detection element 3, which conforms to the surface of the fuel rod, is mounted on the elastic sheet 2. The detection element 3 includes a magnetic core 31, a detection coil 32, and a shielding layer 33. The detection coil 32 is wound around the magnetic core 31, and the shielding layer 33 encloses the magnetic core 31 and the detection coil 32. The other end of the thin substrate 1 is provided with a connector 11 for connecting an external eddy current analyzer. The detection coil 32 is connected to the connector 11 via a cable 12. Specifically, the thin substrate 1 has a thin blade structure, allowing it to smoothly extend into the fuel rod gap and the gap between the guide tube and the fuel rod inside the fuel assembly. The elastic sheet 2 is Z-shaped and movably engages with the thin substrate 1, ensuring that the detection element 3 fits tightly against the fuel rod surface while preventing excessive wear on the fuel rod through its rebound, thus ensuring signal coupling stability. The addition of the magnetic core 31 in the detection component 3 effectively improves the inductance performance of the detection coil 32. The shielding layer 33 can be made of a high-strength polymer material with temperature and wear resistance (such as polyetheretherketone), which reduces electromagnetic interference. Combined with the connection of the cable 12 to the external eddy current instrument, it realizes long-distance underwater signal transmission, which is suitable for the deep-water high-level radioactive working environment of the spent fuel pool of nuclear power plants, meets the core requirement of accurate measurement of oxide film thickness, and solves the problems of adaptability and detection accuracy of narrow gap detection inside nuclear fuel assemblies.

[0022] Furthermore, in a specific implementation, a first circular groove 21 for installing the detection element 3 is provided on the elastic sheet 2 provided in the embodiment of the present invention. The first circular groove 21 is filled with waterproof sealant for bonding the detection element 3. A first limiting groove 22 is radially provided in the first circular groove 21. Specifically, the design of the first circular groove 21 provides precise installation positioning for the detection element 3, ensuring the relative position of the detection coil 32 and the surface of the fuel rod is stable, laying the foundation for measurement accuracy. The filled waterproof sealant not only achieves a firm bond between the detection element 3 and the elastic sheet 2, but also prevents water from the pool from invading the interior of the detection element 3, meeting the waterproof requirements of the probe for underwater operation. The radially provided first limiting groove 22 further restricts the radial displacement of the detection element 3, avoiding the displacement of the detection element 3 due to vibration or bonding pressure during the detection process, ensuring the consistency of the bonding between the detection coil 32 and the surface being tested, effectively reducing the measurement error caused by installation deviation, and improving the stability of the probe in complex detection scenarios.

[0023] Furthermore, in a specific implementation, a reference element 4 is mounted on one end of the detection element 3 on the thin film substrate 1 provided in this embodiment of the invention. The structure of the reference element 4 is the same as that of the detection element 3. The detection surface of the detection element 3 extends beyond the surface of the thin film substrate 1, while the detection surface of the reference element 4 is flush with the surface of the thin film substrate 1. The identical design of the reference element 4 and the detection element 3 constructs a differential detection system. The detection surface of the detection element 3 extends beyond the surface of the thin film substrate 1, ensuring that it can fully contact the oxide film of the fuel rod to obtain an effective signal. The detection surface of the reference element 4 is flush with the substrate, placing it in the blank area between the two fuel rods, unaffected by the oxide film, and only sensing changes in ambient temperature. Both are affected by temperature in the same way. Differential processing can cancel the interference of temperature fluctuations on the detection signal in real time, solving the measurement deviation problem caused by temperature changes in the fuel water pool, significantly improving the measurement accuracy and stability of the probe under different temperature environments, and improving the measurement accuracy of the oxide film.

[0024] Furthermore, in a specific implementation, a second circular groove 13 for mounting the reference component 4 is provided on the thin substrate 1 provided in the embodiment of the present invention. The second circular groove 13 is filled with waterproof sealant for bonding the reference component 4. A second limiting groove 14 is radially provided in the second circular groove 13. The second circular groove 13 provides a dedicated installation space for the reference component 4, ensuring a reasonable layout spacing between the reference component 4 and the detection component 3, and ensuring the accuracy of the differential compensation effect. The waterproof sealant filled inside achieves a firm fixation and waterproof sealing of the reference component 4, avoiding the impact of the underwater environment on the performance of the reference coil, echoing the waterproof design of the detection component 3, and improving the overall waterproof reliability of the probe. The second limiting groove 14 effectively restricts the displacement of the reference component 4, preventing changes in the relative position of the reference component 4 and the detection component 3 due to probe movement or vibration during the detection process, ensuring the consistency of the two under the influence of environmental factors, ensuring the stable operation of the differential temperature compensation mechanism, and further enhancing the temperature drift resistance of the probe.

[0025] Furthermore, in specific implementations, the detection coil 32 provided in this embodiment of the invention uses enameled wire with a polyimide coating, matching the high-radiation working environment of nuclear power plants. This material has extremely strong radiation resistance, which can prevent the coil performance from decaying or failing due to the radiation environment, thus extending the probe's service life. Simultaneously, the stability of the polyimide coating ensures that key parameters such as resistance and inductance of the detection coil 32 remain stable during long-term use. Combined with the high conductivity of the oxygen-free copper substrate, this improves the electromagnetic detection sensitivity of the coil, enabling the probe to accurately capture the eddy current signal impedance changes caused by oxide films of different thicknesses, providing material support for high linearity and high precision in oxide film thickness measurement.

[0026] Furthermore, in specific implementations, the detection coil 32 provided in this embodiment of the invention is fitted with a sleeve 34, achieving dual protection and performance optimization. On the one hand, the sleeve 34 effectively protects the polyimide-coated enameled wire, preventing damage to the coating caused by friction between the coil and impurities on the surface or in the gap of the fuel rod during the detection process, thus improving the wear resistance of the coil. On the other hand, the sleeve 34 provides electromagnetic shielding, reducing the impact of electromagnetic interference in the underwater environment on the coil signal and ensuring the purity of signal transmission. Simultaneously, the structural design of the sleeve 34 does not significantly increase the coil thickness, ensuring the overall ultra-thin characteristics of the probe and not affecting its flexible movement in narrow gaps, thus balancing protection and adaptability. In addition, waterproof sealant can be injected between the sleeve 34 and the detection coil 32 for waterproof sealing.

[0027] Furthermore, in specific implementations, the thin-film substrate 1 provided in this embodiment of the invention is made of austenitic stainless steel, which balances the requirements of both strength and flexibility. Through precise mechanical analysis and strength design, the thin-film substrate 1 made of this material can withstand the extrusion and guiding forces when inserted into narrow gaps, avoiding deformation and damage, while also possessing sufficient flexibility to adapt to the curved contours of the fuel rods. In addition, austenitic stainless steel has excellent corrosion resistance and radiation resistance, which can resist the corrosive media and radiation effects in the spent fuel pool environment, extending the service life of the probe. Its ultra-thin processing characteristics further meet the core requirement of overall probe thickness control, providing a structural foundation for the probe to smoothly enter narrow gaps and achieve stable detection.

[0028] Furthermore, in specific implementations, a cable groove 10 is provided on the thin-film substrate 1 provided in this embodiment of the invention for laying cables 12. This prevents the cables 12 from being piled up haphazardly, which would increase the thickness of the probe and ensure that the probe can maintain its ultra-thin structure and smoothly extend into the narrow gap inside the fuel assembly. At the same time, the cable groove 10 can fix and protect the cables 12, preventing them from being pulled or worn due to probe movement or bending during the detection process, thus avoiding signal transmission interruption or attenuation. The orderly arrangement of the cables 12 also reduces electromagnetic interference between the cables 12, ensuring the stability and accuracy of the detection signal transmission and providing structural support for long-distance underwater signal transmission.

[0029] Furthermore, in specific implementation, the connection between the cable 12 and the connector 11 provided in the embodiments of the present invention is sealed with epoxy resin. The epoxy resin seal design specifically solves the problem of waterproof sealing at the connection between the cable 12 and the connector 11 in underwater environments. Its excellent sealing performance can completely prevent water from entering the connection area, avoiding short circuits, signal attenuation, or component corrosion caused by water ingress, ensuring stable operation of the probe in deep-water environments. Simultaneously, the adhesive properties of epoxy resin enhance the firmness of the connection between the cable 12 and the connector 11, resisting the mechanical impact caused by pulling and vibration during the detection process, preventing loosening of the connection from affecting signal transmission, further strengthening the overall waterproof performance of the probe, ensuring stable signal transmission from the probe to the onshore eddy current meter, and achieving accurate long-distance detection.

Claims

1. An ultra-thin nuclear fuel oxide film eddy current inspection probe characterized by, The utility model relates to a kind of fuel assembly eddy current testing device, including the thin sheet matrix (1) for inserting into fuel assembly, the thin sheet matrix (1) one end is connected with elastic sheet (2), the detection piece (3) that is installed with the surface of fuel rod is attached to the elastic sheet (2), the detection piece (3) includes magnetic core (31), detection coil (32) and shielding layer (33), the detection coil (32) is wound outside the magnetic core (31), the shielding layer (33) is wrapped the magnetic core (31) and the detection coil (32), the thin sheet matrix (1) other end is provided with the connector (11) for external eddy current instrument, the detection coil (32) is connected with the connector (11) by cable (12).

2. The ultra-thin nuclear fuel oxide film eddy current inspection probe according to claim 1, characterized in that, The elastic sheet (2) is provided with a first circular groove (21) for mounting the detection piece (3), the first circular groove (21) is filled with waterproof sealant for bonding the detection piece (3), and the first circular groove (21) is provided with a first limiting groove (22) in the radial direction.

3. The ultra-thin nuclear fuel oxide film eddy current inspection probe of claim 1, wherein, The thin sheet matrix (1) is provided with a reference piece (4) at one end of the detection piece (3), the reference piece (4) has the same structure as the detection piece (3), the detection surface of the detection piece (3) exceeds the surface of the thin sheet matrix (1), and the detection surface of the reference piece (4) is flush with the surface of the thin sheet matrix (1).

4. The ultra-thin nuclear fuel oxide film eddy current inspection probe of claim 3, wherein, The thin sheet matrix (1) is provided with a second circular groove (13) for mounting the reference piece (4), the second circular groove (13) is filled with waterproof sealant for bonding the reference piece (4), and the second circular groove (13) is provided with a second limiting groove (14) in the radial direction.

5. The ultra-thin nuclear fuel oxide film eddy current inspection probe of claim 1, wherein, The detection coil (32) is made of enameled wire containing polyimide coating.

6. The ultra-thin nuclear fuel oxide film eddy current inspection probe according to claim 1 or 5, characterized in that, The detection coil (32) is sleeved with a sleeve (34).

7. The ultra-thin nuclear fuel oxide film eddy current inspection probe of claim 1, wherein, The thin sheet matrix (1) is made of austenitic stainless steel material.

8. The ultra-thin nuclear fuel oxide film eddy current inspection probe of claim 1, wherein, The thin sheet matrix (1) is provided with a wire groove (10) for laying the cable (12).

9. The ultra-thin nuclear fuel oxide film eddy current inspection probe of claim 1, wherein, The connection between the cable (12) and the connector (11) is sealed with epoxy resin.

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