Corrosion test method for coating zirconium alloy fuel cladding tube

Abstract

The invention discloses a coating zirconium alloy fuel cladding tube corrosion test method, which comprises the following steps: providing a corrosion medium for simulating a pressurized water reactor primary loop water chemical environment, and arranging a coating-free contrast sample, the unit area corrosion rate of a zirconium alloy base material in a corrosion medium and the total mass change of a single-coating target sample in the corrosion medium are obtained by combining a weighing method, and microscopic parameters such as the thickness of a coating corrosion layer, the cross section content of key elements, spatial distribution and the like are measured so as to quantify the coating corrosion consumption; and deducting the base material corrosion mass change from the total mass change of the target sample according to the base material corrosion rate of the comparison sample, separating the coating corrosion mass change, and obtaining a coating corrosion evolution model in combination with the real coating corrosion rate calculated after microscopic parameter verification. The method breaks through the limitation that a traditional weighing method cannot split the independent corrosion behavior of the coating, and provides a basis for corrosion mechanism research, coating corrosion stage division, rate prediction and failure critical time judgment.

Description

Technical Field

[0001] This application relates to the field of reactor material corrosion testing technology, and in particular to a corrosion testing method for coated zirconium alloy fuel cladding tubes. Background Technology

[0002] With the continuous development of nuclear energy technology, pressurized water reactor nuclear power plants, as the current mainstream reactor type, have placed more stringent requirements on the performance of fuel cladding materials. As the first barrier to prevent the leakage of radioactive materials, the fuel cladding tubes need to operate in a high-temperature, high-pressure water environment for extended periods, and their corrosion performance directly affects the safe operation and economic benefits of the nuclear power plant.

[0003] In recent years, research and development of coated zirconium alloy cladding has been widely carried out both domestically and internationally to improve its corrosion resistance and accident resistance. By preparing ceramic coatings, such as Cr, FeCrAl, and MAX phases, on the surface of zirconium alloys, the high-temperature oxidation rate can be significantly reduced, extending the safety margin under accident conditions. However, existing studies on the corrosion performance of coated zirconium alloy clad tubes generally use test environments that deviate from actual operating conditions, resulting in significant discrepancies between test data and the actual service behavior of the clad tubes, thus failing to provide a reliable basis for coating design. Furthermore, traditional zirconium alloy corrosion test standards are formulated for uncoated homogeneous substrates, while coated zirconium alloy clad tubes have an asymmetric structure with a single-sided coating. Existing test methods do not consider key factors such as the coating-substrate interface, tubular geometric constraints, and the coupling effect of corrosion between the inner and outer walls, making it difficult to directly use the test results to evaluate the comprehensive corrosion performance of the coated tubes. These problems severely restrict the engineering application of coated zirconium alloy clad tubes.

[0004] Therefore, the urgent need to develop a corrosion testing method that can realistically simulate the chemical conditions of the primary loop water in a pressurized water reactor and is specifically designed for the characteristics of single-sided coated zirconium alloy fuel cladding tubes has become a key research focus in this field. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art.

[0006] Therefore, the first objective of this application is to propose a corrosion test method for coated zirconium alloy fuel cladding tubes.

[0007] To achieve the above objectives, the first aspect of this application provides a corrosion testing method for a coated zirconium alloy fuel cladding tube, comprising: Multiple sets of test samples are provided, each set of test samples includes a single-coated target sample with zirconium alloy fuel cladding tube as the substrate and an uncoated control sample. A reaction vessel simulating the chemical environment of the primary loop water in a pressurized water reactor is provided, and multiple sets of the test samples are placed inside the reaction vessel for corrosion. According to the preset corrosion time nodes, each group of test samples is taken out in sequence, and the macroscopic quality and microstructure of each group of test samples before and after corrosion are measured to obtain the corrosion parameters of the test samples. Based on the corrosion parameters of each group of test samples at different corrosion time points, the coating corrosion evolution model of the target sample is obtained.

[0008] Optionally, the corrosion parameters of the sample to be tested include at least the corrosion rate, corrosion layer thickness, and the content and spatial distribution of key elements in the corrosion cross section of the target sample.

[0009] Optionally, the key elements of the target sample include at least oxygen and coating key elements, wherein the coating key elements include Cr.

[0010] Optionally, the step of measuring the macroscopic mass of each group of test samples before and after corrosion and obtaining the corrosion rate of the target sample includes: The mass changes of the target sample and the control sample in each group of test samples before and after corrosion were measured and obtained respectively. The corrosion rate of the comparative sample is calculated based on the mass change of the comparative sample before and after corrosion and the surface area of ​​the comparative sample. The change in substrate mass of the target sample is calculated based on the corrosion rate of the comparative sample and the substrate surface area of ​​the target sample. The change in coating mass of the target sample is calculated based on the change in mass of the target sample before and after corrosion and the change in mass of the target sample substrate. The corrosion rate of the coating on the target sample is calculated based on the change in coating mass and the surface area of ​​the coating on the target sample.

[0011] Optionally, before the step of measuring the microstructure of each group of test samples before and after corrosion, the method further includes: At least 12 measurement points are obtained at equal angles along the circumference of the cross-section of the sample to be tested, and at least 4 test samples are cut at each measurement point. Each test sample is then subjected to pretreatment by grinding and polishing.

[0012] Optionally, the step of measuring the microstructure of each group of test samples before and after corrosion and obtaining the corrosion layer thickness of the target sample includes: Each of the test samples was placed in a microscopic detection device in sequence, and the corrosion cross section of each test sample was image-characterized to obtain the corrosion layer thickness of each test sample. The corrosion layer thickness of the target sample is obtained based on the average value of the corrosion layer thickness of multiple test samples.

[0013] Optionally, the step of sequentially placing each of the test samples in a microscopic detection device and obtaining the content and spatial distribution of key elements of the target sample in the corrosion cross section includes: Energy dispersive X-ray spectroscopy was used to perform line scanning on the corrosion cross section of each test sample to obtain the content distribution of key elements in the corrosion cross section of each test sample, and surface scanning was also performed on the corrosion cross section of each test sample to obtain the spatial distribution of key elements in the corrosion cross section of each test sample.

[0014] Optionally, the microscopic detection device includes at least a scanning electron microscope and a transmission electron microscope.

[0015] Optionally, the step of providing a reaction vessel simulating the chemical environment of the primary loop water in a pressurized water reactor includes: The step of providing a reaction vessel simulating the chemical environment of the primary loop water in a pressurized water reactor includes: A reaction vessel and a circulating controlled water chemical corrosion testing system are provided, and the circulating controlled water chemical corrosion testing system is connected to the reaction vessel to provide the reaction vessel with a high-temperature, high-pressure dynamic circulating water chemical environment simulating the primary loop of a pressurized water reactor; wherein... The circulating controllable water chemical corrosion test system includes a water tank, a circulating water loop connecting the water tank to the reaction vessel, and a control component connected to the circulating water loop. The circulating water loop is used to export the aqueous solution stored in the water tank and transport it to the reaction vessel, and to cool the aqueous solution output from the reaction vessel and then transport it back to the water tank. The control component is used to input and regulate the temperature, pressure, and chemical parameters of the aqueous solution in the reaction vessel, providing the reaction vessel with a high-temperature and high-pressure dynamic circulating water chemical environment simulating the primary loop of a pressurized water reactor.

[0016] Optionally, the control component includes at least an oxygen control device and a purification device; wherein, The oxygen control device is used to drive inert gas to contact the aqueous solution input into the reaction vessel in a bubbling manner, and to control the dissolved oxygen concentration of the aqueous solution input into the reaction vessel to be less than a first concentration threshold. The purification device includes an unsaturated nucleus-grade mixed bed resin unit and a B-Li presaturated mixed bed resin unit. The unsaturated nucleus-grade mixed bed resin unit is connected in parallel to the circulation branch between the inlet and outlet of the water tank, so that when the reaction vessel is in bypass mode, the aqueous solution stored in the water tank can be input into the unsaturated nucleus-grade mixed bed resin unit through the circulation branch to purify the aqueous solution stored in the water tank. The B-Li presaturated mixed bed resin unit is located at one end of the circulating water loop near the reaction vessel, so that when the circulation branch is in bypass mode, the aqueous solution stored in the water tank can be input into the B-Li presaturated mixed bed resin unit through the circulating water loop to purify the aqueous solution delivered to the reaction vessel.

[0017] The corrosion testing method for coated zirconium alloy fuel cladding tubes provided in this application has at least the following beneficial effects: This application discloses a corrosion testing method for coated zirconium alloy fuel cladding tubes. The method includes providing a corrosive medium simulating the chemical environment of the primary loop water in a pressurized water reactor, setting up an uncoated control sample, and using a gravimetric method to obtain the corrosion rate per unit area of ​​the zirconium alloy substrate in the corrosive medium and the total mass change of the single-coated target sample in the corrosive medium. It also measures microscopic parameters such as the thickness of the corroded coating, the cross-sectional content and spatial distribution of key elements to quantify the coating corrosion consumption. Based on the substrate corrosion rate of the control sample, the substrate corrosion mass change is subtracted from the total mass change of the target sample to separate the coating corrosion mass change. The actual corrosion rate of the coating is calculated after verification with the microscopic parameters to obtain a coating corrosion evolution model. This method overcomes the limitation of traditional gravimetric methods in being unable to separate the individual corrosion behavior of the coating, providing a basis for corrosion mechanism research, coating corrosion stage division, rate prediction, and failure critical time determination. It has significant supporting value for coating process optimization and engineering service life assessment.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic flowchart illustrating a corrosion test method for a coated zirconium alloy fuel cladding tube according to an embodiment of this application.

[0020] Figure 2 This is a schematic diagram of the cross-sectional structure of a set of samples to be tested according to an embodiment of this application.

[0021] Figure 3This is a schematic diagram of the corrosion cross-sectional structure of a target sample according to an embodiment of this application.

[0022] Figure 4 This is a schematic diagram of the corrosion cross-sectional structure of another target specimen according to an embodiment of this application. Detailed Implementation

[0023] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0024] According to a first aspect of this application, a corrosion test method for coated zirconium alloy fuel cladding tubes is provided, such as... Figure 1 As shown, the method includes the following steps: S1 provides multiple sets of test samples. Each set of test samples includes a single-coated target sample with a zirconium alloy fuel cladding tube as the substrate and an uncoated control sample. It is understandable that, such as Figure 2 As shown, the single-coated target sample refers to a zirconium alloy fuel cladding tube with a coating on one side, while the uncoated control sample refers to a zirconium alloy fuel cladding tube without a coating. For the pure zirconium alloy cladding tube (control sample), since its entire perimeter is made of the same zirconium alloy substrate, its overall corrosion rate during the corrosion process can be considered uniform. The rate of change in mass per unit area of ​​the substrate can be obtained by weighing, thus directly representing the corrosion rate of the substrate. In contrast, the material distribution of the coated zirconium alloy cladding tube (target sample) is non-uniform. Its outer perimeter is coated, while the end sidewalls and inner wall are still made of zirconium alloy substrate, and there is a significant difference in the corrosion rate between the coating and the zirconium alloy substrate. In this case, the weighing method can only obtain the overall mass change of the coating and the zirconium alloy substrate, and cannot separate the mass changes of the two separately. Therefore, it is impossible to obtain the mass change or corrosion rate of the coating separately by weighing. In other words, the traditional weighing method cannot directly obtain the mass change or corrosion rate of the coating of the target sample during the subsequent corrosion process.

[0025] Since each group of test samples includes a combination of a single-coated target sample and an uncoated control sample, and the single-coated target sample has a coating only on its outer peripheral sidewalls, with the remaining parts being zirconium alloy substrate, while the uncoated control sample is a pure zirconium alloy substrate, the simultaneous corrosion of the two ensures that the substrate corrosion environment remains consistent. Furthermore, the corrosion parameters of the uncoated control sample, such as the substrate corrosion rate, can serve as a benchmark for substrate corrosion, used to calibrate the mass change of the zirconium alloy substrate in the target sample. This allows for the separation of the coating's individual mass change and corrosion rate from the total mass change of the target sample, avoiding misjudging substrate corrosion as coating corrosion due to a lack of control, or failing to quantify the true protective effect of the coating.

[0026] As an example, the coating thickness on the outer peripheral sidewall of the target sample is approximately several micrometers to tens of micrometers, which can effectively improve the corrosion resistance of the zirconium alloy fuel cladding and enhance the economy and safety of nuclear fuel assemblies. Due to limitations in the preparation method, the coating is only formed on the outer peripheral sidewall of the cladding tube substrate, while there is no coating on the inner wall and end sidewalls of the cladding tube. Exemplarily, the substrate of each group of test samples is a tubular sample with a length of 20 mm, an outer diameter of 9.53 mm, a wall thickness of 0.58 mm, and open at both ends.

[0027] It should be noted that multiple sets of test samples refer to multiple control groups of samples set up later according to the duration nodes of the corrosion test, and the specific number of groups can be flexibly configured according to the corrosion test time nodes.

[0028] S2 provides a reaction vessel that simulates the chemical environment of the primary loop water in a pressurized water reactor, and places multiple sets of test samples inside the reaction vessel for corrosion.

[0029] Understandably, traditional nuclear fuel cladding tubes are usually tested in a static high-temperature and high-pressure water chemical environment (hereinafter referred to as the static water chemical environment). However, the static water chemical environment differs significantly from the actual operating environment of the primary loop of a pressurized water reactor nuclear power plant, making it difficult for the test data to accurately reflect the actual corrosion performance of the cladding tubes.

[0030] On the one hand, the environmental conditions and pressure sources are different. The static water chemistry environment is a two-phase gas-liquid environment, and the pressure comes from the volume expansion of steam in a confined space; while the actual service environment of the primary circuit fuel assembly of a pressurized water reactor is flowing liquid high-temperature and high-pressure water. The fundamental difference between the two environmental conditions will directly affect the interaction between the corrosive medium and the cladding tube.

[0031] On the other hand, the precision of dissolved oxygen control varies greatly. Although thermal deoxygenation is used in static water chemistry environments, the residual dissolved oxygen in the environment can still reach the ppm level and will continue to increase over time. In contrast, the dissolved oxygen in the actual service environment of the primary circuit fuel assemblies of pressurized water reactors needs to be strictly controlled at the ppb level, and the dissolved oxygen content has a significant impact on the corrosion behavior of the fuel cladding. This difference means that traditional static test methods cannot accurately simulate the corrosion pattern of the cladding tubes.

[0032] Furthermore, the standards for controlling impurity ion concentrations differ. In long-term testing under static aqueous chemical conditions, impurity ions such as iron and nickel ions accumulate continuously, reaching concentrations far exceeding those under actual operating conditions. In contrast, impurity ions in the actual service environment of pressurized water reactor primary circuit fuel assemblies must be strictly controlled at the ppb level. Moreover, impurity ion concentration is a key indicator for evaluating the corrosion performance of fuel cladding. Excessive accumulation of impurity ions in static aqueous chemical conditions can lead to distorted corrosion performance assessment results.

[0033] Therefore, this application provides a method to place multiple sets of test samples in a reaction vessel and provide the reaction vessel with a dynamic circulating water chemical environment that simulates the high temperature and high pressure of the primary loop of a pressurized water reactor, so as to simulate the actual service conditions of the fuel cladding tube in the reactor, ensure that the corrosion data obtained by the test has engineering reference value, and solve the problem that the data of the existing test cannot be directly used for coating performance evaluation due to the distortion of the environmental simulation.

[0034] As an example, the reaction vessel is connected to a circulating controlled water chemical corrosion testing system, which is used to provide the reaction vessel with a dynamic water chemical environment highly consistent with the primary loop of a pressurized water reactor nuclear power plant.

[0035] The controlled-flow water chemical corrosion testing system includes a water tank, a circulating water loop connecting the water tank to the reaction vessel, and control components connected to the circulating water loop. The circulating water loop is used to export the aqueous solution stored in the water tank and deliver it to the reaction vessel, and to cool and return the aqueous solution output from the reaction vessel to the water tank. The control components are used to regulate the temperature, pressure, and chemical parameters of the aqueous solution input to the reaction vessel, providing the reaction vessel with a high-temperature, high-pressure, dynamic circulating water chemical environment simulating the primary loop of a pressurized water reactor. Through the controlled-flow water chemical corrosion testing system, continuous circulation of the water chemical environment medium in the reaction vessel can be achieved, with online measurable and controllable oxygen content and real-time monitoring of water chemical parameters, reaching a dynamic water chemical environment highly consistent with the primary loop of a nuclear power plant, providing reliable conditions for the corrosion performance testing and evaluation of fuel cladding tubes.

[0036] The circulating water circuit includes a low-pressure circuit and a high-pressure circuit. The low-pressure circuit is responsible for drawing out the aqueous solution in the water tank, completing water quality purification and parameter monitoring, and sending the water in the low-pressure circuit to the high-pressure circuit after heating and pressurizing. It also returns the aqueous solution flowing out of the reaction vessel outlet and cooled by the heat exchanger to the water tank, realizing the continuous dynamic circulation of the water chemical environment medium. The high-pressure circuit is responsible for providing a high-temperature and high-pressure water chemical environment for the reaction vessel.

[0037] The control components include an online chemical dosing device, heating device, pressurizing device, temperature control device, online water chemistry monitoring device, oxygen control device, purification device, and safety protection device. Specifically, the pressurizing device is crucial for precise pressure control. It provides pressure boosting power through a high-pressure pump, and combined with a high-pressure back pressure valve, the pressure value inside the reaction vessel can be arbitrarily set within a range below 25 MPa, adapting to typical test conditions for nuclear fuel cladding tubes (18.6 MPa). Furthermore, the pulsation damper built into the reaction vessel effectively eliminates pressure fluctuations, ensuring that the pressure fluctuation range inside the reaction vessel is less than 0.2 MPa, guaranteeing long-term pressure stability during the test and preventing pressure fluctuations from interfering with the corrosion behavior of the cladding tubes.

[0038] The temperature control device is crucial for achieving uniformity and stability of temperature within the reaction vessel. This includes using a preheater to preheat the aqueous solution before it enters the reaction vessel, effectively reducing the temperature difference between the inlet water and the aqueous solution inside the reaction vessel, thus avoiding localized water flow disturbances and temperature unevenness caused by the temperature difference; using a heater (resistance wire) wrapped around the outer circumference of the reaction vessel to provide a heat source, with a matching fiber insulation jacket that significantly reduces heat loss and maintains long-term temperature stability; and using a combination of digital temperature control device and temperature control software to achieve online temperature measurement and precise temperature control at multiple points inside the reaction vessel, including the inlet, outlet, and interior, with over-temperature protection, which can stably maintain the typical test temperature (360℃) of the cladding tube, meeting the temperature control requirements for long-term corrosion tests.

[0039] The oxygen control device is used to control the dissolved oxygen content in water. This includes bubbling deoxygenation by introducing an inert gas (such as argon) into the aqueous solution and using a mass flow meter to precisely control the amount of inert gas introduced, avoiding fluctuations in deoxygenation effect caused by excessive or insufficient gas. It also uses a dissolved oxygen probe to collect the dissolved oxygen concentration signal in the water in real time and transmits the signal to a dissolved oxygen meter for online monitoring and data display. Ultimately, the dissolved oxygen concentration in the water is controlled within a first concentration threshold, for example, no more than 5 ppb, which fully matches the ppb-level control standard for dissolved oxygen in the primary loop of a pressurized water reactor. This solves the problem of dissolved oxygen residue reaching ppm level and continuously increasing in conventional static aquatic chemical environments.

[0040] The purification unit and water quality control components are the core of ensuring that the water quality meets the primary loop standards. The purification unit includes an unsaturated nucleo-grade mixed bed resin unit and a B-Li saturated mixed bed resin unit. The unsaturated nucleo-grade mixed bed resin unit is connected in parallel to the circulation branch between the inlet and outlet of the water tank, while the B-Li pre-saturated mixed bed resin unit is located at the end of the circulating water loop closer to the reaction vessel.

[0041] Before the experiment, the entire circulating water loop was rinsed with ultrapure water until the conductivity of the inlet and outlet solutions was ≤0.09 μS / cm, ensuring that the circulating water loop was initially free of impurities. Then, the reaction vessel connected to the circulating water loop was bypassed, allowing the aqueous solution stored in the tank to be fed into the unsaturated nucleo-grade mixed bed resin unit through the circulation branch. This allowed the aqueous solution in the tank to be continuously circulated and purified through the unsaturated nucleo-grade mixed bed resin unit until the conductivity dropped to ≤0.06 μS / cm. Afterward, the unsaturated nucleo-grade mixed bed resin unit on the circulation branch was bypassed again, allowing the purified aqueous solution in the tank to be fed into the B-Li presaturated mixed bed resin unit through the circulating water loop, maintaining the boron and lithium concentrations in the aqueous solution to meet the requirements of the primary loop. Simultaneously, an online dosing system (including a peristaltic pump and dosing tank) was used to inject boron-lithium solution or other reagents into the circulating water loop, with a conductivity meter monitoring the water quality in real time to achieve dynamic adjustment of ion concentration. In addition, during the experiment, the B-Li saturated mixed bed resin unit can continuously deionize the aqueous solution flowing through the reaction vessel, controlling impurity ions such as iron, nickel, chloride, fluorine, and sulfate to the ppb level. At the same time, the system is equipped with an online water intake point, and water is periodically taken for ICP (inductively coupled plasma) detection to confirm that the impurity ion content does not exceed the standard, thus avoiding the problem of impurity ion accumulation during long-term experiments.

[0042] The online water chemistry monitoring device serves as the core of water quality control. It includes using a dissolved oxygen meter to display the dissolved oxygen concentration in water in real time, providing a basis for adjusting the inert gas flow rate of the oxygen control device; using a pH meter to monitor the acidity and alkalinity of the solution online, ensuring that the pH of the water meets the requirements of the primary loop; and using a conductivity meter to provide real-time feedback on the total ion concentration in water, assisting in judging the purification effect of the purification device and the accuracy of the online chemical dosing. Through multi-parameter collaborative monitoring, it ensures that the dynamic water chemistry environment is highly consistent with the primary loop of the pressurized water reactor.

[0043] S3. According to the preset corrosion time nodes, each group of test samples is taken out in sequence, and the macroscopic quality and microstructure of each group of test samples before and after corrosion are measured to obtain the corrosion parameters of the test samples.

[0044] It is understandable that the preset corrosion time nodes refer to the test samples before the start of the corrosion test and after the start of the corrosion test, and the corrosion parameters of the test samples refer to the corrosion rate, corrosion layer thickness, and content and spatial distribution of key elements in the corrosion cross section of the target sample corresponding to different corrosion time nodes.

[0045] Since the corrosion parameters of the test samples at different time points can reflect the changes of the coating from its initial state to gradual corrosion, the core function of combining and simultaneously measuring the macroscopic quality and microstructure parameters of the test samples is to obtain dynamic multidimensional data on the changes of coating corrosion over time. This provides not only an intuitive basis for the corrosion rate, but also reveals the microscopic mechanisms of corrosion, such as element diffusion paths and corrosion layer formation rules. This avoids the limitation that a single macroscopic parameter cannot reflect the causes of microscopic failure, and thus provides comprehensive and continuous data support for the subsequent construction of coating corrosion evolution models.

[0046] As an example, the coating of the target sample is a Cr coating. The preset corrosion time nodes include five corrosion time nodes: before corrosion, 50 days of corrosion, 100 days of corrosion, 200 days of corrosion, and 300 days of corrosion. Each corrosion time node corresponds to a set of test samples.

[0047] The steps for measuring the macroscopic mass of each group of test samples before and after corrosion and obtaining the corrosion rate of the target sample include: First, measuring and obtaining the mass change of the target sample and the control sample in each group of test samples before and after corrosion using a weighing method; second, calculating the corrosion rate of the control sample, i.e., the corrosion rate of the substrate, based on the mass change of the control sample before and after corrosion and the surface area of ​​the control sample; then, calculating the mass change of the substrate of the target sample based on the corrosion rate of the control sample and the substrate surface area of ​​the target sample; next, calculating the mass change of the coating of the target sample based on the mass change of the target sample before and after corrosion and the mass change of the substrate of the target sample; finally, calculating the coating corrosion rate of the target sample based on mass loss based on the coating mass change and the coating surface area of ​​the target sample. The above process is applicable to obtaining the coating corrosion rate at different corrosion time points.

[0048] Further, the steps of measuring the microstructure of each group of test samples before and after corrosion and obtaining the corrosion layer thickness of the target sample include placing the target sample in each group of test samples in a microscopic detection device in sequence, and performing image characterization on the corrosion cross section of each test sample to obtain the corrosion layer thickness of each test sample; then, based on the average corrosion layer thickness of multiple test samples, the corrosion layer thickness of the target sample is obtained.

[0049] Before measuring the microstructure of each group of test samples before and after corrosion, the process includes obtaining at least multiple measurement points at equal angles along the circumferential direction of the cross-section of the test sample, cutting multiple test samples at each measurement point, and pre-treatment of grinding and polishing the corrosion cross-section of each test sample to ensure that each test sample meets the requirements for microstructure detection.

[0050] like Figure 3 and Figure 4 As shown, the measurement of the microstructure of the test sample before and after corrosion mainly targets the coated sample to obtain the corrosion layer thickness of the target sample after corrosion over a corresponding period of time. For example, a measurement point is taken every 30° along the circumference of the target sample's cross-section, for a total of 12 measurement points. Four test samples are obtained from each measurement point, resulting in a total of 48 test samples. By observing the microstructure of the 48 test samples in each group of test samples and measuring the corrosion layer thickness of each target sample based on the observation results, the average corrosion layer thickness of the target sample in each group of test samples can be obtained, and this average value is used as the corrosion layer thickness of the target sample.

[0051] Since multiple target samples can be set as parallel samples for each group of test samples, the corrosion layer thickness of each target sample can be obtained and the average value can be calculated. This average value can then be used as the corrosion layer thickness of the target sample at the corresponding corrosion time. Then, based on the corrosion layer thickness and corrosion time of the target sample, the coating corrosion rate of the target sample based on thickness loss can be calculated, avoiding deviations in the coating corrosion rate calculation results caused by relying solely on macroscopic mass changes.

[0052] Furthermore, the steps of placing each test sample sequentially in a microscopic detection device and obtaining the content and spatial distribution of key elements of the target sample in the corrosion cross section include using energy dispersive X-ray spectroscopy (EDS) to perform line scanning on the corrosion cross section of each test sample to obtain the content distribution of key elements of each test sample in the corrosion cross section, and performing surface scanning on the corrosion cross section of each test sample to obtain the spatial distribution of key elements of each test sample in the corrosion cross section.

[0053] Line scanning of the corrosion cross-section of each test sample using EDS allows for the acquisition of the content distribution of key elements in the corrosion cross-section, thereby quantifying the depth gradient changes of key elements and directly tracing the penetration path of the corrosive medium and the element migration patterns of the coating. Line scanning is typically performed vertically along the coating surface-corrosion layer-coating-substrate interface-zirconium alloy substrate, accurately capturing abrupt concentration changes of key elements such as O, Cr, Zr, B, and Li. For example, if the O concentration within the coating rapidly decreases from 20 at% at the surface to below 1 at% in the middle, it indicates good coating density and effective oxygen diffusion; if the Cr concentration at the coating-corrosion layer interface drops sharply from 99 at% to 50 at%, it reflects Cr dissolution in the coating, for example, the formation of soluble HCrO4. - These data can be directly used to calculate elemental diffusion coefficients, such as the diffusion rate of O in the coating, and to define the effective protection range of the coating, such as the thickness of the area where Cr has not been lost. This provides a quantitative basis for determining whether the coating has failed and for constructing a coating corrosion kinetic model.

[0054] EDS is used to perform surface scanning on the corrosion cross-section of each test sample to obtain the spatial distribution of key elements in the corrosion cross-section. This allows for the localization of elemental enrichment or deficiency areas, enabling precise identification of corrosion weak points and local reaction patterns. Surface scanning, through global elemental imaging, such as using different colors to mark the distribution of O and Cr elements, can visually present the non-uniform distribution characteristics of key elements. For example, if O element is linearly enriched at microcracks in the coating, it indicates that the crack is a rapid penetration channel for the corrosive medium (high temperature and high pressure hydrochemical environment); if Cr element is missing in islands in the corrosion layer, it indicates local oxidation and dissolution of the coating; if a concentrated distribution of Zr and O is detected at the coating-substrate interface, it confirms the formation of a ZrO2 transition layer at the interface, which may weaken the adhesion between the coating and the substrate. This information can directly identify preferential corrosion areas, such as coating defects and interface transition layers, explain the mechanism of localized corrosion, such as why the corrosion rate is faster at cracks, and provide clear directions for optimizing coating preparation processes, such as reducing surface microcracks and improving interfacial bonding, avoiding the neglect of localized corrosion risks based solely on linear data from line scanning.

[0055] Furthermore, each test sample is placed sequentially in a microscopic detection device, and the corrosion cross-section of each test sample is characterized by images. The characteristics of the corrosion cross-section of the sample can also be observed and analyzed based on the characterized images. The microscopic detection device includes at least a scanning electron microscope (SEM) and a transmission electron microscope (SEM).

[0056] As an example, SEM observation was used to characterize the corrosion cross section of each test sample. This clearly presents the interface structure and overall morphology of the corrosion cross section at the microscopic scale, providing a direct basis for the analysis of coating corrosion kinetics and the evaluation of coating-substrate bonding performance.

[0057] For example, by observing the microstructure of the interface between the corroded layer and the coating, such as the presence of cracks, voids, and an oxide transition layer, the dynamic process of coating corrosion can be deduced. If the interface is defect-free and a continuous and dense oxide layer is formed, it indicates that the coating hinders the penetration of corrosive media by forming a passivation layer, corresponding to slow corrosion kinetics. If gaps or local peeling appear at the interface, it reflects that the corrosive media has penetrated the coating, and the coating's protective function has failed.

[0058] Meanwhile, by observing changes in the interface structure between the coating and the substrate, such as whether a ZrO2 transition layer is formed and whether the interface bonding is tight, the influence of the high-temperature and high-pressure hydrochemical environment on the bonding performance of the two can be directly determined. If the interface remains tight without separation, it indicates that the bonding force between the coating and the substrate has not been damaged by the hydrochemical environment; if an oxide transition layer or separation occurs at the interface, it indicates that the corrosive medium has invaded the interface, which may lead to the later peeling off of the coating.

[0059] As an example, TEM was used to image the corrosion cross-section of each test sample. With its high resolution at the nanoscale, it can accurately capture the micro-nano-scale structural details of the corrosion cross-section, providing core support for in-depth revelation of the coating corrosion mechanism and process optimization.

[0060] For example, TEM can accurately determine the true thickness of the corrosion layer, especially suitable for nanoscale ultrathin corrosion layers, avoiding the measurement deviation caused by the resolution limitation of SEM; by observing the microstructure of the interface between the corrosion layer and the coating, such as the crystal orientation and element diffusion layer thickness at the interface, combined with the analysis of crystal structure and grain boundary state, the phase composition of the corrosion products can be determined, such as whether it is Cr2O3, ZrO2, etc.

[0061] Furthermore, TEM can clearly reveal micro- and nano-scale features such as defects, dislocations, and stress distribution within the corrosion layer and coating, including dislocation accumulation and grain boundary oxidation. This information is crucial for understanding the migration path of corrosive media at the micro- and nano-scale and for studying the root causes of coating failure, fundamentally revealing the corrosion mechanism of coated zirconium alloys. Ultimately, this microstructural data can directly guide coating process optimization, such as adjusting coating deposition parameters to reduce defects and improve interfacial bonding, providing reliable microstructural data for the engineering application of coated zirconium alloy clad tubes.

[0062] It should be noted that the analysis of Cr coatings and corresponding Cr elements and related Cr oxides in the above examples is only for illustrative purposes and should not be construed as a limitation of this application. In actual coating analysis, the coating type can be flexibly set according to the requirements of the working conditions.

[0063] S4. Based on the corrosion parameters of each group of test samples at different corrosion time points, obtain the coating corrosion evolution model of the target sample.

[0064] Understandably, the coating corrosion evolution model of the target sample refers to a quantitative model that describes the entire process of the coating from its initial intact state to localized corrosion and then to complete failure, constructed by using parameter correlation and regularity fitting methods based on the corrosion parameters of each group of test samples at different corrosion time points. The purpose is to achieve the stage division, rate prediction and failure critical time determination of the coating corrosion process, and to provide theoretical and data support for coating process optimization (e.g., improving density and interfacial adhesion) and engineering service life assessment.

[0065] In summary, this application provides a corrosion testing method for coated zirconium alloy fuel cladding tubes. The method includes providing a corrosive medium simulating the chemical environment of the primary loop water in a pressurized water reactor. An uncoated control sample is used, leveraging its uniform material and corrosion characteristics, and employing a weighing method to accurately obtain the corrosion rate per unit area of ​​the zirconium alloy substrate within the corrosive medium—that is, the individual mass change pattern of the substrate—providing baseline data for subsequent corrosion analysis of the target sample. Secondly, the total mass change of the target sample within the corrosive medium is obtained through weighing, while simultaneously measuring microscopic parameters such as the coating corrosion layer thickness and the content and spatial distribution of key elements in the coating and substrate cross-sections. These parameters directly quantify the degree of corrosion consumption of the coating itself, such as the amount of coating thickness reduction and the amount of leaching or oxidation products accumulated in the coating. Finally, combining the substrate corrosion rate given by the uncoated control sample, the corrosion mass change of the substrate is subtracted from the total mass change of the target sample, thus separately separating the coating corrosion mass change data. This data is then verified using microscopic parameters to ultimately calculate the true corrosion rate of the coating under high-temperature, high-pressure water chemical conditions and obtain a coating corrosion evolution model.

[0066] This application overcomes the limitations of traditional gravimetric methods in obtaining the total corrosion effect of coatings and substrates and in being unable to separate the individual corrosion behavior of coatings. It provides a basis for clarifying the penetration path of coated zirconium alloy fuel cladding tubes in corrosive media, the interfacial interaction law between coatings and substrates, and the intrinsic mechanism of corrosion product formation-dissolution. Ultimately, it enables the stage division, rate prediction, and determination of failure critical time of coating corrosion process, providing theoretical and data support for coating process optimization and engineering service life assessment.

[0067] In the foregoing descriptions of the embodiments, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0068] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A corrosion test method for a coated zirconium alloy fuel cladding tube, characterized in that, include: Multiple sets of test samples are provided, each set of test samples includes a single-coated target sample with zirconium alloy fuel cladding tube as the substrate and an uncoated control sample. A reaction vessel simulating the chemical environment of the primary loop water in a pressurized water reactor is provided, and multiple sets of the test samples are placed inside the reaction vessel for corrosion. According to the preset corrosion time nodes, each group of test samples is taken out in sequence, and the macroscopic quality and microstructure of each group of test samples before and after corrosion are measured to obtain the corrosion parameters of the test samples. Based on the corrosion parameters of each group of test samples at different corrosion time points, the coating corrosion evolution model of the target sample is obtained.

2. The method according to claim 1, characterized in that, The corrosion parameters of the sample to be tested include at least the corrosion rate, corrosion layer thickness, and the content and spatial distribution of key elements in the corrosion cross section of the target sample.

3. The method according to claim 2, characterized in that, The key elements of the target sample include at least oxygen and coating key elements, with Cr being one of the coating key elements.

4. The method according to claim 2, characterized in that, The step of measuring the macroscopic mass of each group of test samples before and after corrosion and obtaining the corrosion rate of the target sample includes: The mass changes of the target sample and the control sample in each group of test samples before and after corrosion were measured and obtained respectively. The corrosion rate of the comparative sample is calculated based on the mass change of the comparative sample before and after corrosion and the surface area of ​​the comparative sample. The change in substrate mass of the target sample is calculated based on the corrosion rate of the comparative sample and the substrate surface area of ​​the target sample. The change in coating mass of the target sample is calculated based on the change in mass of the target sample before and after corrosion and the change in mass of the target sample substrate. The corrosion rate of the coating on the target sample is calculated based on the change in coating mass and the surface area of ​​the coating on the target sample.

5. The method according to claim 2, characterized in that, Before the step of measuring the microstructure of each group of test samples before and after corrosion, the method further includes: At least 12 measurement points are obtained at equal angles along the circumference of the cross-section of the sample to be tested, and at least 4 test samples are cut at each measurement point. Each test sample is then subjected to pretreatment by grinding and polishing.

6. The method according to claim 5, characterized in that, The step of measuring the microstructure of each group of test samples before and after corrosion, and obtaining the corrosion layer thickness of the target sample, includes: Each of the test samples was placed in a microscopic detection device in sequence, and the corrosion cross section of each test sample was image-characterized to obtain the corrosion layer thickness of each test sample. The corrosion layer thickness of the target sample is obtained based on the average value of the corrosion layer thickness of multiple test samples.

7. The method according to claim 5, characterized in that, The step of sequentially placing each of the test samples in a microscopic detection device and obtaining the content and spatial distribution of key elements of the target sample in the corrosion cross section includes: Energy dispersive X-ray spectroscopy was used to perform line scanning on the corrosion cross section of each test sample to obtain the content distribution of key elements in the corrosion cross section of each test sample, and surface scanning was also performed on the corrosion cross section of each test sample to obtain the spatial distribution of key elements in the corrosion cross section of each test sample.

8. The method according to claim 6 or 7, characterized in that, The microscopic detection equipment includes at least a scanning electron microscope and a transmission electron microscope.

9. The method according to claim 1, characterized in that, The step of providing a reaction vessel simulating the chemical environment of the primary loop water in a pressurized water reactor includes: A reaction vessel and a circulating controlled water chemical corrosion testing system are provided, and the circulating controlled water chemical corrosion testing system is connected to the reaction vessel to provide the reaction vessel with a high-temperature, high-pressure dynamic circulating water chemical environment simulating the primary loop of a pressurized water reactor; wherein... The circulating controllable water chemical corrosion test system includes a water tank, a circulating water loop connecting the water tank to the reaction vessel, and a control component connected to the circulating water loop. The circulating water loop is used to export the aqueous solution stored in the water tank and transport it to the reaction vessel, and to cool the aqueous solution output from the reaction vessel and then transport it back to the water tank. The control component is used to input and regulate the temperature, pressure, and chemical parameters of the aqueous solution in the reaction vessel, providing the reaction vessel with a high-temperature and high-pressure dynamic circulating water chemical environment simulating the primary loop of a pressurized water reactor.

10. The method according to claim 9, characterized in that, The control components include at least an oxygen control device and a purification device; wherein... The oxygen control device is used to drive inert gas to contact the aqueous solution input into the reaction vessel in a bubbling manner, and to control the dissolved oxygen concentration of the aqueous solution input into the reaction vessel to be less than a first concentration threshold. The purification device includes an unsaturated nucleus-grade mixed bed resin unit and a B-Li presaturated mixed bed resin unit. The unsaturated nucleus-grade mixed bed resin unit is connected in parallel to the circulation branch between the inlet and outlet of the water tank, so that when the reaction vessel is in bypass mode, the aqueous solution stored in the water tank can be input into the unsaturated nucleus-grade mixed bed resin unit through the circulation branch to purify the aqueous solution stored in the water tank. The B-Li presaturated mixed bed resin unit is located at one end of the circulating water loop near the reaction vessel, so that when the circulation branch is in bypass mode, the aqueous solution stored in the water tank can be input into the B-Li presaturated mixed bed resin unit through the circulating water loop to purify the aqueous solution delivered to the reaction vessel.

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