A method and system for on-line monitoring of material behavior in lead-bismuth fast reactor

Abstract

The application discloses a kind of lead bismuth fast reactor material service behavior online monitoring method and system, it is related to nuclear reactor material corrosion online monitoring technical field, specifically includes: exposing the electrochemical impedance spectroscopy probe integrated with three electrode system in liquid lead bismuth environment, applies sinusoidal potential disturbance and gathers electrochemical impedance spectroscopy data, obtains constant phase element parameter and oxide film resistance by equivalent circuit model fitting, conversion equivalent capacitance, determine the range of effective dielectric constant in combination with multilayer phase composition, and estimate the thickness range of oxide film based on equivalent capacitance, effective dielectric constant range and the effective exposure area of working electrode, to realize the online quantitative monitoring of oxide film thickness and corrosion state early warning in the service process of lead bismuth fast reactor material.

Description

Technical Field

[0001] This invention relates to the field of nuclear energy system service safety monitoring and liquid metal corrosion protection technology, and particularly to an online monitoring method and system for the service behavior of lead-bismuth fast reactor materials. Background Technology

[0002] Liquid lead-bismuth eutectic (LBE) possesses characteristics such as a low melting point, a high boiling point, good thermal conductivity, and good neutronics properties, and is often used as a liquid metal coolant in lead-cooled fast reactors and accelerator-driven subcritical systems. In the high-temperature operating environment of LBE fast reactors, structural and cladding materials are in long-term direct contact with liquid lead-bismuth. The material surfaces typically rely on a controlled oxygen environment to form a protective oxide film to reduce the impact of liquid metal corrosion on the material's service life. The continuity, density, and thickness of this oxide film are directly related to the material's corrosion resistance. An oxide film that is too thin may fail to form an effective barrier, while an oxide film that is too thick or cracks or peels may cause localized corrosion risks. Therefore, continuous monitoring of the oxide film condition is an important aspect of the service safety assessment of LBE fast reactor materials.

[0003] In existing online corrosion detection schemes for lead-bismuth fast reactors, some devices use contact between the metal sample to be tested and liquid lead-bismuth to form an impedance probe. Electrochemical impedance spectroscopy data is then acquired via an electrochemical workstation, and the formation or thickening of an oxide film is determined based on changes in the shape of the impedance spectrum in the Nyquist plot. This type of scheme can reflect changes in the corrosion state of the material surface to some extent, but its judgment is mainly based on qualitative changes in impedance spectrum morphology or capacitive arc radius, making it difficult to directly provide numerical results for oxide film thickness, and also difficult to form quantitative inputs for corrosion margin assessment and remaining life prediction. Traditional post-corrosion characterization methods mainly rely on scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. These methods require removing the sample from the service or experimental environment and performing cutting, mounting, and grinding. While these methods can obtain information on film morphology, elemental distribution, and phase composition, they can only reflect the final state of corrosion at a specific time point and cannot continuously track the growth, densification, degradation, and failure processes of the oxide film on the same sample.

[0004] Existing laboratory electrochemical impedance spectroscopy studies have shown that the impedance response of oxide films on material surfaces in liquid lead-bismuth environments is correlated with film resistance, film capacitance, film defects, and film thickness. For oxide films close to the dielectric layer, the capacitance and film thickness can be correlated using... To characterize, among which, For oxide film capacitors, The vacuum permittivity, The relative permittivity of the oxide film is... The effective exposed area of ​​the working electrode. The oxide film thickness is given. The oxide film formed on the surface of actual lead-bismuth fast reactor materials is usually not a single homogeneous film, but a multilayered mixed film containing an outer oxide layer, an inner spinel phase, chromium-rich oxide, or other enriched phases. This type of multilayered film suffers from problems such as non-unique dielectric constants, non-uniform thickness, complex defect distribution, and changing interface states. Simply relying on changes in impedance spectral patterns is insufficient to obtain a film thickness range suitable for engineering judgment. Existing technologies also suffer from insufficient electrode system integration, easy interference between polarization and measurement pathways, insufficient automatic switching capability across multiple monitoring locations, and inadequate data fitting and early warning linkage.

[0005] Therefore, how to achieve online, continuous, non-destructive, and quantitative monitoring of the thickness of multilayer oxide films on the surface of lead-bismuth fast reactor structural materials, and to use this information for early warning of material corrosion status, has become an urgent technical challenge to be solved. Summary of the Invention

[0006] The main objective of this invention is to provide an online monitoring method and system for the service behavior of lead-bismuth fast reactor materials, which aims to achieve online, continuous, non-destructive, and quantitative monitoring of the thickness of multilayer oxide films on the surface of lead-bismuth fast reactor structural materials, and to provide early warning of material corrosion status based on this.

[0007] To achieve the above objectives, this invention proposes an online monitoring method for the service behavior of lead-bismuth fast reactor materials, comprising the following steps: Step 1: Expose the electrochemical impedance spectroscopy probe, which integrates a three-electrode system, to a liquid lead-bismuth environment. The working electrode material of the three-electrode system is the material to be tested. Step 2: Apply a sinusoidal potential perturbation to the three-electrode system and collect electrochemical impedance spectroscopy data of the working electrode during service. Step 3: Fit the electrochemical impedance spectroscopy data using an equivalent circuit model to obtain the constant-phase element parameters and oxide film resistance characterizing the oxide film. Step 4: Calculate the equivalent capacitance of the oxide film based on the parameters of the constant phase element and the resistance of the oxide film. Step 5: Call the effective dielectric constant information, which includes the composition phases of the oxide film and the relative dielectric constant values ​​of each composition phase, which was established and stored in advance for the oxide film formed by the material under the preset liquid lead-bismuth service conditions of the test material. And determine the effective dielectric constant range of the oxide film based on the effective dielectric constant estimation rule of the composition phase dielectric constant boundary. After establishing the oxide film composition and effective dielectric constant information corresponding to the test material, there is no need to re-perform microscopic characterization in the subsequent online monitoring process. Step 6: Based on the equivalent capacitance, the effective dielectric constant range, and the effective exposed area of ​​the working electrode, quantitatively estimate the thickness range of the oxide film; Step 7: Based on at least one of the following: the thickness range of the oxide film, the change in the resistance of the oxide film, and the detection results of capacitive arcs in the electrochemical impedance spectroscopy data that meet the preset capacitive arc judgment conditions, a material corrosion state early warning is issued.

[0008] Furthermore, in step 1, the quasi-reference electrode and counter electrode of the three-electrode system are both made of a metal or its metal oxide that has chemical stability relative to liquid lead bismuth within the service temperature range of liquid lead bismuth; the gaps between the three-electrode systems are insulated and sealed using high-temperature resistant inorganic ceramic adhesive.

[0009] Further, step 2 specifically includes: continuously monitoring the open-circuit potential of the working electrode, and determining that a stable state has been reached when the drift rate of the open-circuit potential is less than or equal to 1 mV / min; in the stable state, applying a sinusoidal potential perturbation with an amplitude of 10 to 20 mV to the three-electrode system, and... to The electrochemical impedance spectroscopy data were collected within a frequency range of Hz.

[0010] Furthermore, steps 3 and 4 specifically include: selecting a single time constant. An equivalent circuit model is used to fit the electrochemical impedance spectroscopy data to obtain the pseudo-capacitance value of the constant-phase element. and index And extract the oxide film resistance Calculate the equivalent capacitance of the oxide film according to Equation 1 below. : (Equation 1), where, The resistance of the liquid lead-bismuth eutectic environment is given by LBE, which represents the liquid lead-bismuth eutectic environment. For oxide film resistance, A constant-phase element for characterizing the non-ideal capacitive behavior of oxide films. For this constant phase element The pseudo-capacitance value, Indicates oxide film, Indicates parallel connection, The equivalent capacitance of the oxide film is given. Indicates equivalence. For this constant phase element The index.

[0011] Further, in step 5, the effective dielectric constant range of the oxide film is determined based on the effective dielectric constant estimation rule of the constituent phase dielectric constant boundary. Specifically, this includes: reading the effective dielectric constant information corresponding to the material to be tested from a pre-established database of correspondences between materials, oxide film phases and effective dielectric constants; the database of correspondences between materials, oxide film phases and effective dielectric constants includes at least the fields of material type, service environment parameters, oxide film phase name, oxide film phase chemical formula, relative dielectric constant value, effective dielectric constant range and data source; the minimum value among the relative dielectric constants of each constituent phase is taken as the lower limit of the effective dielectric constant, and the maximum value among the relative dielectric constants of each constituent phase is taken as the upper limit of the effective dielectric constant, thereby constituting the effective dielectric constant range.

[0012] Furthermore, in step 6, the formula for estimating the thickness range of the oxide film is shown in Equation 2 below: (Equation 2), where, The vacuum permittivity, Let be the effective relative permittivity of the oxide film, and take the lower limit and the upper limit of the effective permittivity, respectively. The effective exposed area of ​​the working electrode. The equivalent capacitance is denoted as . Indicates equivalence. For oxide film thickness, Representing the oxide film, the two calculated values ​​are... The values ​​represent the lower limit and the upper limit of the thickness, respectively, thereby forming the thickness range through the lower limit and the upper limit of the thickness.

[0013] Further, step 7 specifically includes: when the lower limit of the oxide film thickness is lower than a preset lower limit threshold, or the upper limit of the oxide film thickness is higher than a preset upper limit threshold, or the decrease in the oxide film resistance in adjacent test cycles exceeds a preset resistance decrease ratio threshold, or the rate of change of the equivalent capacitance exceeds a preset capacitance change rate threshold, or when an electrochemical impedance spectroscopy capacitive arc satisfying the preset capacitive arc determination condition is not detected from the electrochemical impedance spectroscopy data, different levels of corrosion warnings are triggered according to the degree of deviation from the corresponding threshold, and warning information is pushed to the operator terminal; wherein, when an electrochemical impedance spectroscopy capacitive arc satisfying the preset capacitive arc determination condition is not detected, the oxide film state on the working electrode surface is marked as passivation film damage; wherein, the preset capacitive arc determination condition includes the real part and the negative imaginary part of the impedance in the Nyquist plot forming a continuous arc response, and the equivalent circuit fitting residual is less than a preset residual threshold; wherein, the capacitive arc diameter or the 0.1 Hz low-frequency impedance modulus is also extracted from the electrochemical impedance spectroscopy data as a judgment index to assist in evaluating the protective performance of the oxide film.

[0014] This invention also provides an online monitoring system for the service behavior of lead-bismuth fast reactor materials, comprising: a collector, which is an electrochemical impedance spectroscopy probe with an integrated three-electrode system, the three-electrode system including a working electrode, a quasi-reference electrode, and a counter electrode; an electrochemical workstation electrically connected to the collector for applying a sinusoidal potential perturbation to the collector and collecting electrochemical impedance spectroscopy data; a controller communicatively connected to the electrochemical workstation for controlling the electrochemical workstation to perform electrochemical impedance spectroscopy data acquisition; a processor communicatively connected to the electrochemical workstation and the controller for receiving the electrochemical impedance spectroscopy data, performing equivalent circuit model fitting, equivalent capacitance conversion, determination of the effective dielectric constant range, and estimation of the oxide film thickness range; and a central control module communicatively connected to the processor for receiving the estimation results and the detection results of electrochemical impedance spectroscopy capacitive arc that meet the preset capacitive arc judgment conditions, and performing different levels of corrosion warnings based on the estimation results and the detection results.

[0015] Furthermore, the system also includes a multi-channel switching mechanism driven by the controller and a database; the controller, through the multi-channel switching mechanism, enables multiple acquisition devices deployed at different monitoring locations to connect to the electrochemical workstation in a preset time sequence, thereby realizing multi-channel time-sharing inspection and monitoring; the database is communicatively connected to the processor and the central control module, and is used to store historical electrochemical impedance spectroscopy raw data, fitting parameters, thickness range estimation results, and early warning event records for each channel.

[0016] Furthermore, the electrochemical impedance spectroscopy probe also includes a probe shell, an external sleeve, and a tail sleeve; the probe shell covers the outside of the three-electrode system; the external sleeve is connected to the front end of the probe shell and surrounds the electrode end face exposed to the liquid lead-bismuth environment; the tail sleeve is connected to the tail end of the probe shell and has a three-hole female socket and a male base that is inserted and mated with the three-hole female socket.

[0017] The above technical solution has the following advantages: This method directly exposes an electrochemical impedance spectroscopy probe with an integrated three-electrode system to a liquid lead-bismuth environment, using the analyte as the working electrode. This allows the acquired electrochemical impedance spectroscopy data to reflect the interfacial state changes of the analyte during service. By fitting an equivalent circuit model to the electrochemical impedance spectroscopy data, constant-phase element parameters and oxide film resistance can be obtained. Then, by calculating the equivalent capacitance based on the constant-phase element parameters and oxide film resistance, the influence of non-ideal capacitance behavior on film thickness estimation can be reduced. Finally, by calling pre-calibrated and stored multilayer phase composition information of the oxide film and based on the phase dielectric constant boundary... The effective dielectric constant estimation rule determines the effective dielectric constant range, allowing the dielectric properties of multilayer mixed oxide films to be included in the calculation in the form of a range. Based on the equivalent capacitance, the effective dielectric constant range, and the effective exposed area of ​​the working electrode, the oxide film thickness range is estimated, which can convert the impedance spectrum electrical signal into a quantitative result of film thickness. Then, based on the oxide film thickness range, the change in oxide film resistance, and the detection results of capacitive arcs in electrochemical impedance spectroscopy that meet the preset capacitive arc judgment conditions, an early warning is given. When no capacitive arc that meets the preset capacitive arc judgment conditions is detected, it is marked as passivation film damage, which can realize online judgment of the corrosion state of materials. Attached Figure Description

[0018] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a schematic diagram of the structure of the electrochemical impedance spectroscopy probe provided in an embodiment of the present invention.

[0019] Figure 2 A schematic diagram of the control logic of an online monitoring system for the service behavior of lead-bismuth fast reactor materials provided in an embodiment of the present invention.

[0020] Figure 3 This is a comparison chart of the electrochemical impedance spectroscopy and the estimated range and measured values ​​of oxide film thickness for in-situ online monitoring of silicon-ferrite martensitic steel provided in this embodiment of the invention. Figure 3 (a) Electrochemical impedance spectroscopy of silicon-containing ferritic martensitic steel under in-situ online monitoring provided in an embodiment of the present invention; Figure 3 (b) is Figure 3 (a) A magnified view of a region with low to medium impedance; Figure 3 (c) is a comparison chart of the estimated range and the measured value of oxide film thickness. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides an online monitoring method and system for the service behavior of lead-bismuth fast reactor materials. In the actual service environment of fourth-generation advanced nuclear energy systems such as lead-cooled fast reactors and accelerator-driven subcritical systems, reactor structural materials are in direct contact with high-temperature liquid lead-bismuth eutectic. Typically, it is necessary to control the dissolved oxygen concentration in the liquid lead-bismuth to grow a protective oxide film in situ on the material surface to suppress liquid metal corrosion. However, the growth and densification behavior of the oxide film during long-term high-temperature service is influenced by a combination of physicochemical factors such as temperature and oxygen concentration. Its continuity and thickness characteristics directly determine the protective effect and safe service life of the structural material. Existing conventional corrosion monitoring methods often require offline electron microscopy characterization after reactor shutdown and sampling. This method can only reflect the final corrosion state at a specific time point and cannot achieve continuous tracking and monitoring of the dynamic growth and failure process of the oxide film on the same sample. Furthermore, some current exploratory in-situ monitoring schemes mainly rely on the macroscopic morphology of impedance spectroscopy patterns for qualitative judgment, making it difficult to provide quantitative values ​​for the oxide film thickness. The method and system provided in this embodiment can achieve non-destructive quantitative estimation of the thickness of multilayer mixed oxide films, and can quantitatively calculate the equivalent thickness of complex oxide films online, thereby realizing real-time early warning of material corrosion status.

[0023] Combination Figure 1 and Figure 2The online monitoring system mainly includes a data acquisition unit 20, a controller 30, an electrochemical workstation, a processor 50, a central control module 60, and a database 70. The data acquisition unit 20 is specifically an electrochemical impedance spectroscopy probe 10 suitable for high-temperature liquid lead-bismuth environments. The electrochemical impedance spectroscopy probe 10 integrates a three-electrode system, specifically including a working electrode 11, a quasi-reference electrode 12, and a counter electrode 13. The working electrode 11 is made of the analyte, i.e., the lead-bismuth fast reactor structural material or cladding material obtained from in-situ sampling, and its exposed working area is preferably 1.0 cm². Both the quasi-reference electrode 12 and the counter electrode 13 are made of a metal or its metal oxide that is chemically inert in liquid lead-bismuth, for example, both are made of tungsten or tungsten trioxide. The working area of ​​the quasi-reference electrode 12 is preferably 2.0 cm², and the working area of ​​the counter electrode 13 is preferably 0.5 cm². Compared to traditional dual-electrode systems, this three-electrode system design effectively separates the polarization circuit and the measurement circuit, reducing signal noise interference from the high current in the actual reactor and the fluid environment, and improving the stability of the in-situ electrochemical signal. The electrochemical impedance spectroscopy probe 10 also has a probe shell 14, which tightly encloses the three-electrode system. The probe shell 14 can be made of T91 ferritic martensitic steel tubing. Since the service temperature of liquid lead-bismuth is typically between 300°C and 600°C, the physical gaps between the three electrodes inside the probe are comprehensively insulated and sealed using high-temperature resistant inorganic ceramic adhesive 15. Furthermore, a multi-layered sealing and insulation scheme for the electrodes is constructed using graphite sealing rings. This structure prevents short-circuit failure between electrodes caused by micro-leakage of the high-temperature liquid metal. An external sleeve 16 is connected to the front end of the probe shell 14. The external sleeve 16 circumferentially surrounds the electrode faces exposed in the liquid lead-bismuth environment. It primarily serves to physically protect the initial state of the electrode surfaces and reduce hydrodynamic disturbances in the liquid metal, thereby enhancing the signal-to-noise ratio of the electrochemical measurement. The tail of the probe housing 14 is connected to a tail sleeve 17. The tail sleeve 17 is fitted with a three-hole female connector 18 and a male connector base 19 that is plugged into the three-hole female connector 18. The rear end of the male connector base 19 is used to lead out and connect to an external signal transmission cable.

[0024] Based on the above system hardware architecture, the specific monitoring method in this embodiment includes the following consecutive steps.

[0025] Step 1: Insert the electrochemical impedance spectroscopy probe 10, which integrates the above-mentioned three-electrode system, into the target liquid lead-bismuth environmental monitoring node and expose it for a long period of time.

[0026] Step 2: The controller 30 automatically executes the test instructions of the preset cycle, applies a sinusoidal potential perturbation to the three-electrode system exposed to liquid lead-bismuth, and collects in-situ electrochemical impedance spectroscopy data of the working electrode 11 during high-temperature service. Specifically, the controller 30 first guides the electrochemical workstation to continuously monitor the open-circuit potential of the working electrode 11. When the natural drift rate of the open-circuit potential is less than or equal to 1 mV / min, the system determines that the current solid-liquid interface electrochemical state has reached stability. After confirming that a stable state has been reached, the controller 30 instructs the electrochemical workstation to apply a weak AC excitation signal to the three-electrode system, i.e., a sinusoidal potential perturbation with an amplitude between 10 and 20 mV, preferably 15 mV to ensure it is in the linear polarization region. The frequency scanning range of the excitation signal is set to... to The controller 30 automatically performs the above measurement and data acquisition process every 2 hours to capture the long-term dynamic evolution trend of the oxide film. This allows for the acquisition of high-quality electrochemical impedance spectroscopy data across the entire frequency band.

[0027] Step 3: The processor 50 receives the collected electrochemical impedance spectroscopy data in real time and uses an embedded data analysis algorithm to automatically fit and analyze the impedance spectrum data using a preset equivalent circuit model. In the high-temperature liquid lead-bismuth test system, because liquid lead-bismuth has extremely low resistance as an excellent electronic conductor, the impedance characteristics of the entire system mainly originate from the physical obstruction of the passivation oxide film grown on the surface of the structural material to the internal ion and electron transmembrane transport. Therefore, the processor 50 directly selects a single time constant. The equivalent circuit model is fitted using a nonlinear least squares method. In this model, LBE represents the environmental resistance of liquid lead-bismuth eutectic. Represents the target oxide film resistance. Indicates oxide film, This represents a constant-phase element used to characterize the non-ideal capacitive spatial behavior of oxide films. This indicates a parallel connection. Through iterative fitting, processor 50 can extract the pseudo-capacitance value of the constant-phase element. and dimensionless index Simultaneously obtain the oxide film resistance The value. The index here. The value is constant between 0 and 1, and the degree of deviation from 1 reflects the surface roughness, thickness inhomogeneity, and crystal defect characteristics of the porous multilayer passivation film grown under actual service conditions.

[0028] Step 4: Based on the extracted constant-phase element fitting parameters and oxide film resistance, processor 50 converts the oxide film resistance into an equivalent pure capacitance using a specific impedance formula, thus obtaining the equivalent capacitance of the oxide film. The specific conversion formula is as follows: ,in, The equivalent capacitance of the oxide film is given. Indicates equivalence. For this constant phase element The pseudo-capacitance value, For oxide film resistance, Indicates oxide film, For this constant phase element The exponent. This conversion step reduces the interference of non-ideal dispersion effects and obtains capacitance parameters that are mapped to the physical thickness of the oxide film.

[0029] Step 5: The processor 50 retrieves the multilayer phase composition information of the oxide film grown on the surface of the working electrode 11, which has been pre-calibrated and stored, and determines the effective dielectric constant range of the complex oxide film based on the effective dielectric constant estimation rule of the phase dielectric constant boundary. Metallic materials formed in situ in liquid lead-bismuth often do not have a single composition due to differences in element diffusion rates, but rather a mixed passivation film structure containing multiple phases, such as a common outer layer rich in magnetite phase and an inner layer rich in iron-chromium spinel phase or rich in chromium oxide phase. The processor 50 calls a pre-established database of correspondences between materials, oxide film phases, and effective dielectric constants. This database was established during the early calibration stage after confirming the multilayer phase composition and layered structure of the passivation film formed by the material under test under preset liquid lead-bismuth service conditions using auxiliary microscopic characterization methods such as scanning electron microscopy (SEM), transmission electron microscopy / selected area electron diffraction (TEM / SAED), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). During the online monitoring stage, it is not necessary to re-characterize the same material system microscopically; instead, the effective dielectric constant range corresponding to the material under test is directly read. The database of correspondences between materials, oxide film phases, and effective dielectric constants includes at least the fields of material type, service environment parameters, oxide film phase name, oxide film phase chemical formula, relative dielectric constant value, effective dielectric constant range, and data source. Subsequently, the processor 50 executes a boundary definition algorithm, taking the minimum value among the relative dielectric constants of all constituent phases as the lower limit of the effective dielectric constant and the maximum value among the relative dielectric constants of all constituent phases as the upper limit of the effective dielectric constant, thereby forming a closed effective dielectric constant range. This effective dielectric constant estimation rule based on the boundary of the dielectric constant of the constituent phases solves the engineering blind spot where the local dielectric properties of multilayer hybrid films are difficult to micro-observe, mapping the microscopic complexity of the material composition to a reasonable tolerance band for macroscopic calculation; taking silicon-ferrite martensitic steel as an example, the oxide film phase includes , and The relative permittivity values ​​of each phase are recorded from the previous calibration data or data source fields, and are denoted as follows: , and The lower limit of the effective dielectric constant is taken as The upper limit of the effective dielectric constant is taken as .

[0030] Step 6: Based on the calculated equivalent capacitance, the determined effective dielectric constant range, and the pre-calibrated effective exposed area of ​​the working electrode 11, the processor 50 quantitatively estimates the physical thickness range of the oxide film. The specific inversion estimation formula for the physical thickness is as follows: In this conversion formula, For a fixed vacuum permittivity, the variable Let the effective relative permittivity of the oxide film be denoted by the corresponding effective lower and upper limits of the permittivity determined in the preceding steps. This refers to the physically effective exposed area of ​​the working electrode 11. This refers to the macroscopic equivalent capacitance obtained from the aforementioned conversion. Indicates equivalence. For oxide film thickness, This represents the oxide film. Processor 50 calculates the two outputs using this formula. The numerical values ​​represent the lower and upper limits of the oxide film thickness, which together constitute the thickness range of the oxide film at the current monitoring moment. This complete data processing chain enables the system to convert impedance spectroscopy signals into estimated oxide film thickness values ​​without disrupting the sample and stopping the reactor for sampling. This provides quantitative benchmark data for subsequent lifetime prediction and corrosion margin assessment. The complete quantitative calculation chain from measured electrochemical impedance spectroscopy parameters to oxide film thickness values ​​established in this embodiment has been experimentally verified on pure iron and silicon-containing ferritic martensitic steels. Figure 3 (a) to Figure 3 As shown in (c), the oxide film thickness estimated by this method is on the same order of magnitude as the actual measurement results by scanning electron microscopy and shows a consistent trend, realizing the transformation from qualitative judgment to quantitative characterization and providing direct data input for corrosion margin assessment and lifetime prediction. Furthermore, this method is not only applicable to the aforementioned conventional structural materials, but can also be extended to various candidate structural material systems for liquid metal-cooled reactors, such as austenitic stainless steel, oxide dispersion strengthened steel (ODS steel), and iron-chromium-aluminum (FeCrAl) alloys.

[0031] Step 7: The central control module 60 receives the thickness range estimation results reported by the processor 50 in real time, and performs automated material corrosion status linkage early warning based on the thickness range fluctuation of the oxide film and the evolution trend of the oxide film resistance. The central control module 60 has a pre-set tiered safety judgment mechanism. This mechanism determines the film thickness safety threshold, resistance reduction ratio threshold, and capacitance change rate threshold based on material type, operating temperature, liquid lead-bismuth oxygen concentration, historical stable operating data, and offline corrosion test results. When the estimated lower limit of oxide film thickness is lower than the preset lower limit threshold, or the upper limit of oxide film thickness is higher than the preset upper limit threshold, or when the decrease in the fitted oxide film resistance in adjacent test cycles exceeds the preset resistance reduction ratio threshold, indicating that the surface protective oxide film has undergone large-area dissolution or rupture and peeling, or when the monitored equivalent capacitance change rate suddenly increases and exceeds the preset capacitance change rate threshold, the central control module 60 will immediately trigger different levels of corrosion warnings. The warning levels are divided into yellow warnings, which suggest strengthening parameter monitoring, and red warnings, which suggest initiating a shutdown and maintenance procedure, based on the severity of the deviation from the baseline parameters. The central control module 60 will also push these multi-dimensional abnormal warning information along with the time of occurrence to the external operator monitoring terminal. Furthermore, to further enhance the robustness of corrosion failure assessment, the main control module 60 will directly extract extremely low-frequency features from the original electrochemical impedance spectroscopy data in the background, such as extracting the 0.1 Hz low-frequency impedance modulus. Alternatively, the chord length and diameter of the fitted capacitive arc in the complex plane diagram can be used as a model-independent independent validation metric to assist in evaluating and confirming the overall shielding and protective performance of the oxide film. Indicates impedance, This represents the impedance modulus at a frequency of 0.1 Hz. The preset capacitive arc judgment condition includes: the real part and the negative imaginary part of the impedance in the Nyquist plot form a continuous arc response, and the equivalent circuit fitting residual is less than a preset residual threshold. All the above-mentioned original spectral data, fitting parameters, quantitative thickness results, and early warning event logs are issued by the central control module 60 and persistently stored in the database 70, providing data support for the long-term corrosion mechanism retrospective analysis of lead-cooled fast reactor materials and the iterative optimization of the digital twin model. Through the above-mentioned closed-loop architecture of "acquisition unit - controller - processor - database - central control module", this embodiment realizes the integrated functions of multi-channel time-sharing inspection acquisition, automatic switching, quantitative calculation, and early warning, transforming electrochemical impedance spectroscopy technology from a laboratory analysis method into an online monitoring system for the service behavior of lead-bismuth fast reactor structural materials that can be deployed in engineering.

[0032] Based on Embodiment 1, Embodiment 2 of this invention further provides an advanced deployment architecture and expansion scheme for an online monitoring system for the service behavior of lead-bismuth fast reactor materials. In the actual engineering operation of large nuclear reactors, due to differences in fluid flow rates and temperature gradients in different parts such as the core region, primary coolant pipes, and heat exchangers, the corrosion kinetics of the material surface exhibit spatial heterogeneity. Relying solely on a single monitoring node cannot comprehensively assess the structural safety status of the entire reactor. Therefore, this embodiment introduces an additional multi-channel switching mechanism. Specifically, the system deploys collectors 20 at multiple key corrosion nodes in the reactor, i.e., deploys multiple electrochemical impedance spectroscopy probes 10. The controller 30 integrates this multi-channel switching mechanism internally or externally. By driving the multi-channel switching mechanism, the controller 30 enables multiple collectors 20 deployed at different monitoring locations to sequentially connect to a single electrochemical workstation according to a preset time sequence. This design of multiplexing and automatic inspection eliminates the need for an expensive electrochemical workstation for each monitoring point, reducing engineering implementation costs. At the same time, it enables parallel online monitoring of the spatial distribution characteristics of multilayer oxide film growth in key parts of the entire reactor loop, providing data support for building a global three-dimensional corrosion digital twin model of the reactor.

[0033] To ensure that the weak AC signal collected by the data acquisition unit 20 can be transmitted to an external data analysis system in the harsh environment of strong radiation and high-frequency mechanical vibration in the reactor, this embodiment features a specific design for the tail wiring structure of the electrochemical impedance spectroscopy probe 10. Combined with... Figure 1 The probe housing 14 has a tail sleeve 17 connected to its tail end. The tail sleeve 17 contains a three-hole female connector 18 and a male connector base 19 that mates with the three-hole female connector 18. The three-hole female connector 18 and the male connector base 19 are three-pin socket structures, corresponding to the independent signal outputs of the working electrode 11, the quasi-reference electrode 12, and the counter electrode 13, respectively. The three-hole female connector 18 and the male connector base 19 are locked together using a high-temperature resistant alloy spring and are externally coated with insulating sealant. This mechanical connection design not only improves the engineering convenience of probe installation and subsequent insertion / removal, but also reduces the feed of external electromagnetic interference to the high-frequency impedance signal from a physical perspective, making it more efficient. Impedance spectrum data measured at the Hz high frequency band are less prone to significant phase shift distortion.

[0034] Regarding the expansion of specific application scenarios, the online monitoring method and system of this embodiment are not limited to liquid lead-bismuth eutectic environments. For other liquid metal coolant reactor types in fourth-generation nuclear energy systems, such as liquid pure lead-cooled fast reactors, liquid sodium-cooled fast reactors, liquid lead-lithium alloy fusion reactor blankets, and high-temperature molten salt reactors, this system can expand its application scenarios by adaptively replacing the front-end probe materials. For example, when the system is applied to a liquid sodium or molten salt environment, the quasi-reference electrode 12 and counter electrode 13 in the three-electrode system can be replaced with chemically inert metal materials such as molybdenum or zirconium, which are more stable in this specific fluid. By replacing the electrode materials and calling the effective dielectric constant database of the corresponding fluid environment, the processor 50 can still perform equivalent capacitance conversion and thickness range estimation, thereby enabling the present invention to be extended to high-temperature liquid metal corrosion monitoring scenarios.

[0035] In addition to performing quantitative film thickness calculations, in certain emergency monitoring situations where real-time computational requirements are extremely high, the processor 50 can directly extract rapid evaluation indicators to determine changes in the material's corrosion rate. Specifically, the processor 50 can directly extract the oxide film resistance derived from the equivalent circuit fitting. The diameter of the capacitive arc in the Nyquist plot, or the impedance modulus at 0.1 Hz. As a direct indicator of the protective performance of oxide films, among them, Indicates impedance, This represents the impedance modulus at a frequency of 0.1 Hz. The processor 50 can achieve rapid qualitative screening of corrosion status by comparing the above direct indicators with empirical corrosion rate relationship curves established in advance through offline plate-mounted experiments. This dual-track operation mechanism, combining precise film thickness quantification with rapid screening of characteristic parameters, ensures both the stability of corrosion margin assessment under normal conditions and the system's early warning response capability under extreme operating conditions.

[0036] In this embodiment, the database 70 not only passively stores data but also deeply integrates with the central control module 60 to form a full-lifecycle corrosion evolution retrospective analysis platform. Traditional post-corrosion characterization methods, such as scanning electron microscopy or transmission electron microscopy, require removing the sample from a high-temperature environment and cutting and grinding it. This destroys the original stress state of the oxide film and can only observe the post-death morphology at a specific time point. However, the database 70 in this system continuously records the original electrochemical impedance spectroscopy data and estimated thickness range of the same probe sample for each cycle from the first day of operation. When the central control module 60 issues a yellow warning, engineers can retrieve the trend curves from the past few months in the database 70 to observe how the oxide film thickness undergoes parabolic growth, a densification plateau, and finally a sudden jump in equivalent capacitance due to microcracks caused by thermal stress or fluid erosion. This continuous online tracking capability captures the dynamic game process of transient oxide film peeling and self-healing, which is difficult to observe continuously with traditional offline characterization, providing in-situ time-series data for the study of liquid metal corrosion mechanisms.

Claims

1. A method for online monitoring of the service behavior of lead-bismuth fast reactor materials, characterized in that, Includes the following steps: Step 1: Expose the electrochemical impedance spectroscopy probe, which integrates a three-electrode system, to a liquid lead-bismuth environment. The working electrode material of the three-electrode system is the material to be tested. Step 2: Apply a sinusoidal potential perturbation to the three-electrode system and collect electrochemical impedance spectroscopy data of the working electrode during service. Step 3: Fit the electrochemical impedance spectroscopy data using an equivalent circuit model to obtain the constant-phase element parameters and oxide film resistance characterizing the oxide film. Step 4: Calculate the equivalent capacitance of the oxide film based on the parameters of the constant phase element and the resistance of the oxide film. Step 5: Call the effective dielectric constant information, which includes the composition phases of the oxide film and the relative dielectric constant values ​​of each composition phase, which was established and stored in advance for the oxide film formed by the material under the preset liquid lead-bismuth service conditions of the test material. And determine the effective dielectric constant range of the oxide film based on the effective dielectric constant estimation rule of the composition phase dielectric constant boundary. After establishing the oxide film composition and effective dielectric constant information corresponding to the test material, there is no need to re-perform microscopic characterization in the subsequent online monitoring process. Step 6: Based on the equivalent capacitance, the effective dielectric constant range, and the effective exposed area of ​​the working electrode, quantitatively estimate the thickness range of the oxide film; Step 7: Based on at least one of the following: the thickness range of the oxide film, the change in the resistance of the oxide film, and the detection results of capacitive arcs in the electrochemical impedance spectroscopy data that meet the preset capacitive arc judgment conditions, a material corrosion state early warning is issued.

2. The method as described in claim 1, characterized in that, In step 1, the quasi-reference electrode and counter electrode of the three-electrode system are both made of a metal or its metal oxide that has chemical stability relative to liquid lead bismuth within the service temperature range of liquid lead bismuth; the gaps between the three-electrode systems are insulated and sealed with high-temperature resistant inorganic ceramic adhesive.

3. The method as described in claim 1, characterized in that, Step 2 specifically includes: continuously monitoring the open-circuit potential of the working electrode, and determining that a stable state has been reached when the drift rate of the open-circuit potential is less than or equal to 1 mV / min; in the stable state, applying a sinusoidal potential perturbation with an amplitude of 10 to 20 mV to the three-electrode system, and... to The electrochemical impedance spectroscopy data were collected within a frequency range of Hz.

4. The method as described in claim 1, characterized in that, Steps 3 and 4 specifically include: selecting a single time constant. An equivalent circuit model is used to fit the electrochemical impedance spectroscopy data to obtain the pseudo-capacitance value of the constant-phase element. and index And extract the oxide film resistance Calculate the equivalent capacitance of the oxide film according to Equation 1 below. : (Equation 1), where, The resistance of the liquid lead-bismuth eutectic environment is given by LBE, which represents the liquid lead-bismuth eutectic environment. For oxide film resistance, A constant-phase element for characterizing the non-ideal capacitive behavior of oxide films. For this constant phase element The pseudo-capacitance value, Indicates oxide film, Indicates parallel connection, The equivalent capacitance of the oxide film is given. Indicates equivalence. For this constant phase element The index.

5. The method as described in claim 1, characterized in that, In step 5, the effective dielectric constant range of the oxide film is determined based on the effective dielectric constant estimation rule of the constituent phase dielectric constant boundary. Specifically, this includes: reading the effective dielectric constant information corresponding to the material to be tested from a pre-established database of correspondences between materials, oxide film phases and effective dielectric constants; the database of correspondences between materials, oxide film phases and effective dielectric constants includes at least the fields of material type, service environment parameters, oxide film phase name, oxide film phase chemical formula, relative dielectric constant value, effective dielectric constant range and data source; the minimum value of the relative dielectric constant of each constituent phase is taken as the lower limit of the effective dielectric constant, and the maximum value of the relative dielectric constant of each constituent phase is taken as the upper limit of the effective dielectric constant, thereby constituting the effective dielectric constant range.

6. The method as described in claim 5, characterized in that, In step 6, the formula for estimating the thickness range of the oxide film is shown in Equation 2 below: (Equation 2), where, The vacuum permittivity, Let be the effective relative permittivity of the oxide film, and take the lower limit and the upper limit of the effective permittivity, respectively. The effective exposed area of ​​the working electrode. The equivalent capacitance is denoted as . Indicates equivalence. For oxide film thickness, Representing the oxide film, the two calculated values ​​are... The values ​​represent the lower limit and the upper limit of the thickness, respectively, thereby forming the thickness range through the lower limit and the upper limit of the thickness.

7. The method as described in claim 1, characterized in that, Step 7 specifically includes: when the lower limit of the oxide film thickness is lower than a preset lower limit threshold, or the upper limit of the oxide film thickness is higher than a preset upper limit threshold, or the decrease in the oxide film resistance in adjacent test cycles exceeds a preset resistance decrease ratio threshold, or the change rate of the equivalent capacitance exceeds a preset capacitance change rate threshold, or when an electrochemical impedance spectroscopy capacitive arc satisfying the preset capacitive arc judgment condition is not detected from the electrochemical impedance spectroscopy data, different levels of corrosion warnings are triggered according to the degree of deviation from the corresponding threshold, and warning information is pushed to the operator terminal; wherein, when an electrochemical impedance spectroscopy capacitive arc satisfying the preset capacitive arc judgment condition is not detected, the oxide film state on the working electrode surface is marked as passivation film damage; wherein, the preset capacitive arc judgment condition includes the real part and the negative imaginary part of the impedance in the Nyquist plot forming a continuous arc response, and the equivalent circuit fitting residual is less than a preset residual threshold; wherein, the capacitive arc diameter or the 0.1 Hz low-frequency impedance modulus is also extracted from the electrochemical impedance spectroscopy data as a judgment index to assist in evaluating the protective performance of the oxide film.

8. An online monitoring system for the service behavior of lead-bismuth fast reactor materials, used to implement the method described in any one of claims 1-7, characterized in that, include: The collector is an electrochemical impedance spectroscopy probe with an integrated three-electrode system, which includes a working electrode, a quasi-reference electrode, and a counter electrode. An electrochemical workstation, electrically connected to the data acquisition unit, is used to apply a sinusoidal potential perturbation to the data acquisition unit and acquire electrochemical impedance spectroscopy data; a controller, communicatively connected to the electrochemical workstation, is used to control the electrochemical workstation to perform electrochemical impedance spectroscopy data acquisition; a processor, communicatively connected to both the electrochemical workstation and the controller, is used to receive the electrochemical impedance spectroscopy data and perform equivalent circuit model fitting, equivalent capacitance conversion, determination of the effective dielectric constant range, and estimation of the oxide film thickness range. The main control module, which is communicatively connected to the processor, is used to receive the estimation results and the detection results of the electrochemical impedance spectroscopy capacitive arc that meet the preset capacitive arc judgment conditions, and to execute different levels of corrosion warnings based on the estimation results and the detection results.

9. The system as described in claim 8, characterized in that, The system also includes a multi-channel switching mechanism driven by the controller and a database; the controller, through the multi-channel switching mechanism, enables multiple data acquisition devices deployed at different monitoring locations to connect to the electrochemical workstation in a preset time sequence, thereby realizing multi-channel time-sharing inspection and monitoring; The database is communicatively connected to the processor and the central control module, and is used to store historical electrochemical impedance spectroscopy raw data, fitting parameters, thickness range estimation results, and early warning event records for each channel.

10. The system as described in claim 8, characterized in that, The electrochemical impedance spectroscopy probe further includes a probe shell, an external sleeve, and a tail sleeve; the probe shell covers the outside of the three-electrode system; the external sleeve is connected to the front end of the probe shell and surrounds the electrode end faces exposed to the liquid lead-bismuth environment; the tail sleeve is connected to the tail end of the probe shell and has a three-hole female socket and a male base that is inserted and mated with the three-hole female socket.

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