Calibration method and calibration sample for a fuel rod cladding oxide film detection device

Abstract

A calibration method and calibration sample for a fuel rod cladding oxide film detection device, belonging to the field of thin film detection. The method includes the following steps: depositing an accelerated oxidation layer on a sample substrate by physical vapor deposition process to obtain a calibration sample preform, the accelerated oxidation layer includes a cladding component and a doping component, the cladding component is the same as the matrix component of the fuel rod cladding to be detected, and the doping component includes one or more of N, C, and Al; performing oxidation treatment on the calibration sample preform to oxidize at least part of the accelerated oxidation layer into a simulated oxidation layer to obtain a calibration sample; providing multiple calibration samples with simulated oxidation layers of different thicknesses to calibrate the eddy current detection device. This method can effectively improve the calibration efficiency and accuracy of the eddy current detection device and improve the detection accuracy of the oxide film thickness on the surface of the fuel rod cladding.

Description

Technical Field

[0001] The present invention belongs to the field of thin film detection, and particularly relates to a calibration method and a calibration sample for a fuel rod cladding oxide film detection device. Background Art

[0002] Fuel rods are key components in a reactor core, and the fuel rod cladding is the first barrier for radioactive substances generated by fission reactions. When serving in a high-temperature and high-pressure environment for a long time, an oxide layer of a certain thickness will form on the surface of the fuel rod cladding. The oxide layer affects both the thickness of the fuel rod cladding structure and the heat transfer capacity of the fuel rod. Therefore, it is necessary to accurately detect the thickness of the oxide layer on the surface of the fuel rod cladding. Among them, eddy current detection is a commonly used detection method at present, which has the advantages of fast detection speed, simple operation and low cost. However, before using an eddy current detection device to detect the thickness of the fuel rod oxide film, it is first necessary to accurately calibrate the detection device. Since the fuel rod cladding material has strong antioxidant properties under normal conditions, the time cost of forming an oxide layer by direct oxidation is unacceptable; while preparing by spraying method is likely to cause uneven thickness. Therefore, providing an optimized calibration method for a fuel rod cladding oxide film detection device has positive significance for improving calibration efficiency and calibration accuracy. Summary of the Invention

[0003] The purpose of the present invention is to provide a calibration method for a fuel rod cladding oxide film detection device to improve the calibration accuracy of an eddy current detection device. The present invention also provides a calibration sample for a fuel rod cladding oxide film detection device.

[0004] According to an embodiment of one aspect of the present invention, there is provided a calibration method for a fuel rod cladding oxide film detection device, which calibrates an eddy current detection device for detecting a fuel rod cladding oxide film. The method includes the following steps:

[0005] Step a): Provide a calibration sample substrate, and deposit an accelerated oxide layer on the calibration sample substrate by physical vapor deposition process to obtain a calibration sample preform; the accelerated oxide layer includes a cladding component and a doping component, wherein the cladding component is the same as the matrix component of the fuel rod cladding to be detected, and the doping component is configured as one or more combinations of N, C, and Al;

[0006] Step b): Perform oxidation treatment on the calibration sample preform to oxidize at least part of the accelerated oxide layer into a simulated oxide layer to obtain a calibration sample;

[0007] Step c): Provide a plurality of the calibration samples with different thicknesses of the simulated oxide layer, and use the calibration samples to calibrate the eddy current detection device.

[0008] By using this method, calibration samples with different oxide layer thicknesses can be prepared quickly and accurately. The oxidation rate of obtaining the oxide layer by using the calibration sample preform is 3-5 times higher than that of directly conducting a high-temperature oxidation test using the fuel rod cladding material. At the same time, problems such as interface undulation and thickness non-uniformity commonly existing in the spraying preparation process can be effectively avoided, and the calibration efficiency and accuracy of the eddy current detection device can be effectively improved.

[0009] Further, in some embodiments, the material of the fuel rod cladding is zirconium alloy.

[0010] Further, in some embodiments, in step a), the weight ratio of the doping component in the accelerated oxide layer is 0.01%-5%.

[0011] Further, in some embodiments, in step a), the accelerated oxide layer further includes an oxide layer stabilizing component, and the oxide layer stabilizing component includes one or more combinations of Nb, Cu, and Fe. The weight ratio of the oxide layer stabilizing component in the accelerated oxide layer is 0.1%-1%.

[0012] Further, in some embodiments, the calibration sample substrate is made of metal, ceramic, or polymer material.

[0013] Further, in some embodiments, in step a), the physical vapor deposition process includes magnetron sputtering or multi-arc ion plating.

[0014] Further, in some embodiments, in step a), before the physical vapor deposition, a step of ion cleaning the calibration sample substrate is further included.

[0015] Further, in some embodiments, in step a), the method of adding the doping component into the accelerated oxide layer is to add the doping component into the target of the physical vapor deposition, or to mix the gas raw material including the doping component into the protective gas of the physical vapor deposition.

[0016] Further, in some embodiments, in step b), the oxidation treatment method is to immerse the calibration sample preform in an oxidizing solution for heat treatment.

[0017] Further, in some embodiments, in step b), the oxidizing solution uses a LiOH solution with a concentration not higher than 100 ppm, the oxidation temperature is not lower than 300 °C, and the oxidation treatment pressure is not lower than 15 MPa.

[0018] Further, in some embodiments, in step c), the thickness of the simulated oxide layer of multiple calibration samples is 1 μm - 100 μm.

[0019] Among them, the method for preparing the simulated oxide layers with different thicknesses in multiple calibration samples is as follows:

[0020] Set acceleration oxide layers with different thicknesses on different calibration sample preforms, and fully oxidize the acceleration oxide layers.

[0021] Or

[0022] Set acceleration oxide layers with the same or different thicknesses on different calibration sample preforms, and perform oxidation treatments with different degrees on different calibration sample preforms to at least partially oxidize the acceleration oxide layers to obtain simulated oxide layers with different thicknesses.

[0023] According to an embodiment of another aspect of the present invention, there is provided a calibration sample for a fuel rod cladding oxide film detection device. The calibration sample is manufactured by using steps a) and b) in the calibration method of the fuel rod cladding oxide film detection device provided in any one of the foregoing embodiments, and is used in step c). Description of the Drawings

[0024] Figure 1 It is a comparison curve of oxidation rates for the examples and comparative examples.

[0025] The purpose of the above-mentioned drawings is to make a detailed description of the present invention so that those skilled in the art can understand the technical concept of the present invention, rather than being intended to limit the present invention. Detailed Embodiments

[0026] The present invention will be further described in detail below through specific embodiments in conjunction with the drawings.

[0027] The mention of "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of this article. The phrase that appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments in this article can be combined with other embodiments without structural conflicts.

[0028] In the description of this article, the meaning of "a plurality of" is at least two.

[0029] Pressurized water reactor fuel rods are immersed in the primary coolant, and fuel pellets are contained inside. The heat generated by the fission of the fuel pellets is transferred to the coolant through the cladding of the fuel rods, and then transmitted to the outside through the heat exchange system. In this process, the overall strength and heat transfer performance of the fuel rod cladding play a decisive role in the safety of the reactor core. On the one hand, the fuel rod cladding needs to have mechanical strength meeting the design requirements to contain the radioactive products generated by the fission of the fuel pellets. At the same time, it also needs to have sufficient tolerance to thermal stress, creep during long-term service, and irradiation growth of the fuel pellets and the fuel rod cladding itself. At the same time, due to the high working temperature of the primary circuit, the fuel rod cladding is immersed in the high-temperature and high-pressure coolant for a long time during service. Soluble boron, LiOH and other solvent components are usually added to the coolant to adjust the chemical environment in the primary circuit. Even though zirconium alloy, nuclear-grade stainless steel and other materials with stable chemical properties have been used for the fuel rod cladding, oxidation and corrosion still occur inevitably under long-term service conditions, and an oxide film is formed on the surface. On the one hand, the oxide film will erode the original thickness of the fuel rod cladding, resulting in a thinner wall thickness of the fuel rod cladding. On the other hand, due to the low thermal conductivity of metal oxides, the heat transfer on the surface of the fuel rod will deteriorate, posing a safety risk. Therefore, accurately detecting the thickness of the oxide film on the surface of the fuel rod cladding is very important for ensuring the safe operation of the reactor.

[0030] At present, eddy current testing is a commonly used method for detecting the thickness of fuel rod cladding. It can utilize the difference in electrical conductivity between the fuel rod cladding material and the oxide film to achieve fast and accurate thickness detection in a non-destructive manner. Eddy current testing is fast, does not require a coupling agent, is easy to operate and has a low cost. However, before using an eddy current testing device to detect the oxide film thickness, the testing device needs to be accurately calibrated first. The calibration work usually requires a series of calibration samples with oxide films of different thicknesses to be provided. The thickness of the oxide film in the calibration samples is usually in the range of 0 - 100 μm. The calibration samples need to be prepared by pre-oxidizing the same material as the fuel rod cladding in advance. Due to the differences in the electrical properties of different materials, the structures and properties of the oxide films formed after oxidation are also different. Therefore, calibration samples of different grades of alloys cannot replace each other. At present, there are the following several manufacturing methods for calibration samples:

[0031] 1) High-temperature oxidation. Depending on the oxidation environment, it can be further divided into oxidation in a liquid environment (such as oxidation treatment in a high-temperature and high-pressure LiOH solution), oxidation in a gas environment (such as oxidation treatment in a high-temperature and high-pressure steam environment), and oxidation treatment in supercritical water with a high oxygen content. However, according to the design requirements, alloy materials used to manufacture fuel rod claddings, such as various zirconium alloys or nuclear-grade stainless steel materials, themselves have strong oxidation resistance. If the cladding material is directly used for oxidation treatment to prepare calibration samples, whether it is oxidation treatment using a solution under high-temperature and high-pressure conditions or oxidation treatment in a gas environment, the required manufacturing cycle is too long, and the cost and efficiency are both unacceptable.

[0032] 2) Direct preparation of an oxidation coating. For example, processes such as micro-arc oxidation, cold spraying, or magnetron sputtering are used to directly prepare an oxidation coating on the surface of the sample substrate. Currently, the oxidation films obtained by micro-arc oxidation and cold spraying preparation processes are prone to relatively significant cross-sectional undulations between the film and the substrate, the thickness of the oxidation film is uneven, and the sample accuracy cannot meet the calibration requirements; while the magnetron sputtering process can form a dense, uniform, and thickness-controllable oxidation layer, but the oxide target is prone to poisoning during the preparation process, and the sputtering preparation process cannot be continuously and efficiently completed.

[0033] The above factors lead to the problems of slow preparation and high cost of calibration samples in the calibration of the current fuel rod cladding oxidation film detection device, affecting the efficiency and accuracy of calibration.

[0034] To solve the above problems, an embodiment of the present invention provides a calibration method for a fuel rod cladding oxidation film detection device, which can effectively improve the calibration efficiency and accuracy of the fuel rod cladding oxidation film detection device.

[0035] The method includes the following steps:

[0036] Step a): Provide a calibration sample substrate, and deposit an accelerated oxidation layer on the calibration sample substrate using a physical vapor deposition process to obtain a calibration sample preform. Among them, the accelerated oxidation layer includes a cladding component and a doping component. The cladding component is the same as the matrix component of the fuel rod cladding to be tested. For a zirconium alloy cladding, Zr is used as the cladding component; the doping component is configured as one or a combination of N, C, and Al. By adding a doping component to the cladding component, the doping component can generate vacancies or other forms of oxygen ion channels in the cladding component, improving the diffusion rate of oxygen in the accelerated oxidation layer, thereby effectively increasing the oxidation rate.

[0037] In a preferred embodiment, the calibration sample substrate is made of the same metal material as the fuel rod cladding. For example, in some embodiments, a zirconium alloy sheet can be used.

[0038] Depending on different oxidation conditions and design requirements, the weight ratio of the doping component in the accelerated oxidation layer is 0.01% - 5%. The physical vapor deposition process used to prepare the accelerated oxidation layer can be magnetron sputtering or multi-arc ion plating. The doping component can be added to the target or the gas raw material including the doping component can be mixed into the protective gas for physical vapor deposition. For example, nitrogen gas or gas components containing C or Al can be mixed in an argon protection atmosphere.

[0039] When the thickness of the accelerated oxidation layer to be prepared is relatively thick, in a preferred embodiment, an oxidation layer stabilizing component can also be added to the accelerated oxidation layer to make the stress evenly distributed after the accelerated oxidation layer is oxidized, avoiding cracking and spalling. Specifically, the oxidation layer stabilizing component can be Nb, Cu, or Fe.

[0040] Step b): Oxidize the calibrated sample preform so that at least part of the accelerated oxidation layer is oxidized into a simulated oxidation layer to obtain a calibrated sample. Specifically, when the substrate of the calibrated sample is a conductive material, the accelerated oxidation layer can be completely oxidized; when the substrate of the calibrated sample is an insulating material such as ceramic or polymer material, part of the unoxidized accelerated oxidation layer needs to be retained to generate induced eddy currents during the calibration process.

[0041] In different embodiments, the oxidation treatment of the calibrated sample preform can be carried out in different ways. In some embodiments, high-temperature oxidation can be carried out in an oxidizing atmosphere, and in other embodiments, oxidation treatment can be carried out in supercritical water containing dissolved oxygen. In a preferred embodiment, the calibrated sample preform can be immersed in an oxidizing solution for heating treatment to obtain a simulated oxidation layer.

[0042] Step c): Prepare multiple calibrated samples with different simulated oxidation layer thicknesses by the above method, and use the calibrated samples to calibrate the detection device. To improve the calibration accuracy, in a preferred embodiment, the thickness of the simulated oxidation layer should evenly cover the thickness range of 1 μm - 100 μm.

[0043] In a preferred embodiment, the process of calibrating the detection device for detecting the oxidation film thickness of zirconium alloy fuel rods is as follows:

[0044] First, provide a sample substrate, and the sample substrate is made of the same zirconium alloy as the fuel rod cladding. In the embodiment, a Zr-4 alloy tube is used.

[0045] A Zr alloy target doped with N element with a macroscopically uniform composition is manufactured by melting or powder metallurgy processes. Generally, N has serious harmful effects in zirconium alloys. N can replace oxygen ions in the oxide lattice, generate additional vacancies, promote the diffusion of oxygen ions in the zirconium alloy matrix, and severely deteriorate the corrosion resistance of the zirconium alloy. Therefore, Sn is usually added to conventional zirconium alloys to reduce the vacancy migration rate in the zirconium alloy, and at the same time, the N content in the zirconium alloy needs to be limited to less than 0.01%. In the examples, in order to utilize the effect of N accelerating the oxidation of zirconium alloys, the weight ratio of N in the target should be not less than 0.01%.

[0046] Six Zr-4 alloy tubes are provided, and an accelerated oxidation layer is deposited on the Zr-4 alloy tubes by magnetron sputtering.

[0047] Before starting sputtering, first clean the surface of the substrate to remove surface oil, dust, and oxide layer, and keep the surface of the sample substrate highly clean and dry. Subsequently, place the sample substrate into the vapor deposition furnace, evacuate to below 5×10 -3 Pa, introduce an inert gas such as argon as the protective gas, and control the pressure in the furnace after introducing the protective gas to be 0.1 Pa - 1 Pa. Apply a bias voltage of -400 V to -800 V to the sample substrate to ionize the protective gas and continuously bombard the sample substrate, and perform ion cleaning on the sample substrate for 5 min - 60 min.

[0048] After completing the ion cleaning, apply a bias voltage of -50 V to -300 V to the sample substrate for ion sputtering to obtain a calibrated sample. In some other examples, pure Zr can also be used as the target, and nitrogen can be used as the working gas for ion sputtering to form an accelerated oxidation layer with N doping, where the flow ratio of nitrogen to argon is controlled to be 1:20 - 1:1.

[0049] When the accelerated oxidation layer is deposited to the set thickness, turn off the vapor deposition furnace and take out the calibrated sample when it cools to below 100°C. In the example, an accelerated oxidation layer with a thickness of 70 ± 1 μm is deposited on the surface of the Zr-4 alloy tube, and the N content is 0.5%.

[0050] The calibration sample was placed in an autoclave and immersed in a 100 ppm LiOH solution, and oxidation treatment was carried out at 360 °C and a pressure of 18.6 MPa. At 30 days, 50 days, 160 days, 240 days, 320 days, and 400 days during the oxidation treatment, a Zr-4 alloy tube of an example was taken out respectively, and the thickness of the oxide film on the surface of the Zr-4 alloy tube was detected by a microscope. The thicknesses of the oxide films were 5.7 μm, 9.5 μm, 38.6 μm, 60.2 μm, 81.8 μm, and 106.1 μm respectively. The thicknesses of the oxide films of all specimens were uniform, and the deviation of the oxide film thickness was within the range of ±2 μm. Taking the original Zr-4 alloy tube as a standard sample with an oxide film thickness of 0 μm, thus, a group of standard specimens with an oxide film thickness range of 0 - 106.1 μm covering the Zr-4 alloy fuel rod was obtained. Among them, the accelerated oxidation layer on the Zr-4 alloy tube of the example oxidized for 400 days was almost completely oxidized, and the thickness of the oxide film formed due to the compositional transformation increased to 106.1 μm.

[0051] The above standard specimens were used for the calibration of the eddy current detection device: the eddy current detection probe was successively closely attached to the standard specimens, and the voltage signals of the standard specimens with different oxide film thicknesses were read; based on the voltage signal - oxide film thickness relationship of different specimens, a standard curve of the voltage signal and the oxide film thickness was established by linear fitting.

[0052] In other examples, the standard specimens can also be prepared in the following way: an accelerated oxidation layer was deposited on the surfaces of multiple Zr-4 alloy tubes, and the accelerated oxidation layers on the surfaces of different Zr-4 alloy tubes had a thickness gradient; these Zr-4 alloy tubes were oxidized under the same conditions to completely oxidize their respective accelerated oxidation layers, and oxide films with different thicknesses were obtained. The advantage of this preparation method is that it does not require frequent opening of the reaction kettle and is suitable for the preparation of a large number of samples.

[0053] While oxidizing the standard specimens of the examples, 6 Zr-4 alloy tubes without deposited accelerated oxidation layers were placed in the reaction kettle as a comparative example. Similarly, at 30 days, 50 days, 160 days, 240 days, 320 days, and 400 days during the oxidation treatment, a Zr-4 alloy tube of the comparative example was taken out respectively, and the thickness of the oxide film on the surface of the Zr-4 alloy tube was detected by a microscope. The thicknesses of the oxide films were 2.7 μm, 3.8 μm, 10.8 μm, 16.1 μm, 21.4 μm, and 27.1 μm respectively, and the deviation of the oxide film thickness was ±2 μm. The curves of the surface oxide films of the examples and the comparative example changing with time are as Figure 1As shown. It can be seen that to form an oxide film with a thickness of 20 μm, the oxidation process of the zirconium alloy in the comparative example takes about 300 days, while in the example, it only takes about 90 days, and the oxidation rate is significantly increased. Based on the extrapolation calculation of the oxidation rate of the comparative example, it can be known that the time required to form an oxide film with a thickness of about 100 μm on the Zr-4 alloy tube in the comparative example exceeds 1500 days, and the time cost is unacceptable for the calibration test. If the eddy current detection device is only calibrated in the range of 0 - 27.1 μm, since there are significant differences in the error range of the eddy current detection device under different oxide film thicknesses, the detection accuracy of the oxide film with a thickness significantly exceeding 27.1 μm will not meet the test requirements.

[0054] The purpose of the above embodiments is to further elaborate on the present invention in combination with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope disclosed by the present invention, optimizing or equivalently replacing the involved method steps, and combining the implementation manners in different embodiments without conflict in structure and principle all fall within the protection scope of the present invention.

Claims

1. A calibration method for a fuel rod cladding oxide film detection device, which calibrates an eddy current detection device used for detecting the oxide film of a fuel rod cladding, characterized in that, The following steps are involved: Step a): Providing a calibration sample substrate, and depositing an accelerated oxidation layer on the calibration sample substrate using a physical vapor deposition process to obtain a calibration sample preform; the accelerated oxidation layer includes a cladding component and a doping component, wherein the cladding component is the same as the matrix composition of the fuel rod cladding to be tested, and the doping component is configured as one or more combinations of N, C, and Al; Step b): performing oxidation treatment on the calibration sample preform to oxidize at least part of the accelerated oxidation layer into a simulated oxidation layer to obtain a calibration sample; Step c): providing a plurality of calibration samples having the simulated oxide layers of different thicknesses, and calibrating the eddy current detection device using the calibration samples.

2. The calibration method of the fuel rod cladding oxide film detection device according to claim 1, wherein, The fuel rod cladding is made of zirconium alloy.

3. The calibration method of the fuel rod cladding oxide film detection device according to claim 1 or 2, characterized in that, In the step a), the weight ratio of the doping component in the accelerated oxidation layer is 0.01%-5%.

4. The calibration method for a fuel rod cladding oxide film detection device according to claim 3, characterized in that: In step a), the accelerated oxidation layer further comprises an oxidation layer stabilizing component, which comprises one or more combinations of Nb, Cu, and Fe. The weight ratio of the oxidation layer stabilizing component in the accelerated oxidation layer is 0.1%-1%.

5. The calibration method of the fuel rod cladding oxide film detection device according to claim 1 or 2, characterized in that The calibration sample substrate is made of metal, ceramic or polymer material.

6. The calibration method of the fuel rod cladding oxide film detection device according to claim 1 or 2, characterized in that: In the step a), the physical vapor deposition process includes magnetron sputtering or multi-arc ion plating.

7. The calibration method of the fuel rod cladding oxide film detection device according to claim 6, characterized in that, In the step a), the step of ion cleaning the calibration sample substrate is further included before performing the physical vapor deposition.

8. The calibration method of the fuel rod cladding oxide film detection device according to claim 1 or 2, characterized in that, In the step a), the method of adding the doping component to the accelerated oxidation layer is to add the doping component into the target material of the physical vapor deposition, or to mix the gas raw material including the doping component into the protective gas of the physical vapor deposition.

9. The calibration method of the fuel rod cladding oxide film detection device according to claim 1 or 2, characterized in that In the step b), the oxidation treatment method is to immerse the calibration sample preform in an oxidizing solution and perform a heating treatment.

10. The calibration method of the fuel rod cladding oxide film detection device according to claim 9, characterized in that In the step b), the oxidizing solution is a LiOH solution with a concentration not higher than 100 ppm, the oxidation temperature is not lower than 300° C., and the oxidation treatment pressure is not lower than 15 MPa.

11. The calibration method of a fuel rod cladding oxide film detection device according to claim 1 or 2, characterized in that: In the step c), the thickness of the simulated oxide layer of the plurality of calibration samples is 1 μm-100 μm, Wherein, the method for preparing the simulated oxide layers with different thicknesses in the plurality of calibration samples is: The accelerated oxidation layers of different thicknesses are provided on different calibration sample preforms, and the accelerated oxidation layers are completely oxidized. or The accelerated oxidation layer having the same thickness is provided on different calibration sample preforms, and the different calibration sample preforms are subjected to oxidation treatments of different degrees to at least partially oxidize the accelerated oxidation layer to obtain the simulated oxidation layers having different thicknesses.

12. A calibration sample for a fuel rod cladding oxide film detection device, characterized in that: The device is manufactured using the steps a) and b) of the fuel rod cladding oxide film detection device calibration method according to any one of claims 1 to 11, and is used in step c).

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