Method for identifying oxygen corrosion evolution and oxygen corrosion evolution of material in high-level radioactive waste geological disposal environment

Abstract

The invention relates to the field of metal corrosion behavior monitoring and characterization, in particular to a method for identifying oxygen corrosion evolution and oxygen corrosion evolution of a material in a high-level radioactive waste geological disposal environment. The method comprises two indexes: one index is an oxidation-reduction potential reflecting the overall oxidation-reduction characteristics of a corrosion system, namely an Eh value; the other one is a time constant reflecting the kinetic characteristics of reduction reaction (ORR) of dissolved oxygen in the corrosion system, namely an ORR-log (tau / s) value; the Eh value is measured by adopting an Eh electrode, and the ORR-log (tau / s) value is obtained by performing electrochemical impedance spectroscopy (EIS) measurement on a working electrode made of a metal material and then performing relaxation time distribution function analysis on EIS data. The method is suitable for identifying and researching the oxygen corrosion evolution of the disposal container candidate material in the high-level radioactive waste geological disposal environment, and has the characteristics of simple method, easily available parameters, strong operability, high accuracy, good long-term stability and real-time measurement.

Description

Technical Field

[0001] The present invention relates to the field of monitoring and characterization of metal corrosion behavior, and particularly to a method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste. Background Art

[0002] High-level radioactive waste (HLW) mainly refers to high-level liquid waste generated from spent fuel reprocessing and its solidified body. HLW is a special type of waste that poses a potentially huge threat to the environment. The radionuclides contained in HLW are characterized by strong radioactivity, high toxicity, long half-life, and heat generation. Once they enter the human living environment, they are extremely harmful and difficult to eliminate. Therefore, the safe disposal of HLW has become a major issue affecting the sustainable development of nuclear energy, environmental protection, and the well-being of future generations, and is also a major scientific, technical, and engineering challenge.

[0003] Currently, the internationally recognized method for the safe disposal of HLW is deep geological disposal, that is, burying HLW in a stable geological body about 400 - 1000 m deep from the surface to effectively isolate it from the biosphere. The disposal container is generally composed of metal materials, and its main safety function is to contain HLW, prevent groundwater intrusion, and the containment time is not less than 1000 years. Therefore, it is very necessary to study the corrosion evolution behavior of the disposal container materials in the geological disposal repository environment.

[0004] Since it is inevitable that a certain amount of oxygen will remain in the disposal repository for a considerable period of time after it is closed during the disposal process, the consumption and evolution characteristics of dissolved oxygen will be directly related to the corrosion rate characteristics of the disposal container materials. In order to better study the aerobic / anaerobic corrosion evolution behavior and its evolution characteristics of the packaging container materials in the geological disposal repository environment, it is very necessary to develop and design a method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste. Summary of the Invention

[0005] Aiming at the engineering requirements of the geological disposal of high-level radioactive waste, the purpose of the present invention is to provide a method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste. The principle of this identification method is clear, the steps are simple, the parameters are easy to obtain, and the identification method has high accuracy, strong operability, and good long-term stability, and is suitable for the research on the identification of aerobic / anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste.

[0006] A method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste includes two indicators. One is the redox potential, i.e., the Eh value, which reflects the overall redox characteristics of the corrosion system; the other is the time constant, i.e., the ORR-log(τ / s) value, which reflects the kinetic characteristics of the reduction reaction (ORR) of dissolved oxygen in the corrosion system.

[0007] The materials in the geological disposal environment of high-level radioactive waste are used to simulate the materials of high-level radioactive waste geological disposal containers, including low-carbon steel, copper, cast iron, nickel-based alloys, and titanium alloys;

[0008] The geological disposal environment of high-level radioactive waste includes the groundwater environment of the surrounding rock strata of the disposal repository and the backfill material environment around the disposal container, including the environment containing bentonite with different water contents;

[0009] The corrosion system is used to simulate the closed environment characteristics of the high-level radioactive waste geological disposal repository. According to the environment where the disposal repository is located and the characteristics of the groundwater in the surrounding rock strata, the environmental parameters of the closed system are different, including SO42- concentration, Cl- concentration, HCO3- / CO32- concentration, pH value, pressure, and water content of the backfill material;

[0010] The Eh value is used to reflect the overall oxidizing property of the corrosion system and is related to the dissolved oxygen content and the overall oxidizing property of all oxidizing substances containing Fe(III) substances in the corrosion system; measured by an Eh electrode, the evolution characteristics of the Eh value with corrosion time can be obtained;

[0011] The ORR-log(τ / s) value is used to reflect the ease of occurrence of ORR of dissolved oxygen in the corrosion system and is related to the dissolved oxygen content; by performing relaxation time distribution (DRT) analysis on the measured electrochemical impedance spectrum (EIS), the evolution characteristics of the ORR-log(τ / s) value with corrosion time are obtained.

[0012] An Eh electrode is used to measure the overall oxidizing property of the corrosion system; the Eh electrode can be obtained by self-making or by commercial purchase, but during use, it is necessary to periodically perform cathodic polarization with a small external potential on the Eh electrode to ensure the cleanliness of the Eh electrode surface, thereby ensuring the measurement accuracy of the Eh electrode.

[0013] Taking dissolved oxygen as an example, there is the following relationship between its redox potential and the corrosion rate of the disposal container material, According to the measured Eh value that can reflect the overall chemical property of the corrosion system, an evolution curve of the Eh value with corrosion time is plotted.

[0014] The candidate material is processed and prepared into a working electrode for corrosion electrochemistry testing, and EIS data is collected for the working electrode using a traditional three-electrode system or a two-electrode system; based on the relationship, DRT analysis is performed on the EIS data to obtain the number of time constants included in the EIS spectrum and the corresponding log(τ / s) values, and an evolution spectrum of the log(τ / s) value with corrosion time is plotted, and then the evolution law of the ORR-log(τ / s) value with corrosion time is obtained.

[0015] When Eh > -640 mV (vs. SSC); when the ORR-log(τ / s) value is less than 1.2, the disposal container material is in the stage of aerobic corrosion.

[0016] When Eh < -640 mV (vs. SSC); when the ORR-log(τ / s) value is greater than 1.2 to 1.5, the disposal container material enters the stage of anaerobic corrosion.

[0017] The present invention utilizes the sensitivity of the Eh electrode to oxidizing substances in the corrosion system, especially to the dissolved oxygen content. By measuring with a commercially purchased or self-made Eh electrode, the Eh value that can reflect the overall oxidizing property of the corrosion system is obtained, and the evolution curve of the Eh value with the corrosion time is plotted, so that the evolution behavior of the content of oxidizing substances in the entire corrosion system with the corrosion time can be identified.

[0018] Since DRT analysis can identify the time constants contained in the EIS spectrum and can be correlated with the electrochemical reactions involved in the corrosion process, the time constant corresponding to ORR can be identified through DRT analysis; since the time constant log(τ / s) corresponding to ORR is closely related to the concentration of oxygen, the dissolved oxygen concentration in the corrosion system can be further judged by the evolution of the ORR-log(τ / s) value.

[0019] By comprehensively considering the evolution behavior of the Eh value and the evolution behavior of the ORR-log(τ / s) value measured during the corrosion process of the materials in the geological disposal environment of high-level radioactive waste, the evolution behavior of aerobic / anaerobic corrosion of the materials in the geological disposal environment of high-level radioactive waste can be identified. Therefore, the present invention is applicable to the identification research on the evolution of aerobic / anaerobic corrosion of materials in the geological disposal environment of high-level radioactive waste, and has the characteristics of simple method, easy-to-obtain parameters, strong operability, high accuracy, good long-term stability and real-time measurement.

[0020] The advantages and beneficial effects of the present invention are:

[0021] The Eh electrode adopted by the present invention has a simple structure, can be commercially purchased or made by oneself, and the Eh test method is simple; the EIS measurement based on the three-electrode system and the two-electrode system is a commonly used method in the field of corrosion electrochemistry, and the DRT analysis method of EIS data is simple and has high accuracy, and can accurately identify the evolution of the time constant log(τ / s) corresponding to ORR during aerobic / anaerobic corrosion. Therefore, only two parameters, namely the Eh value and the ORR-log(τ / s) value, are needed to accurately identify the evolution behavior of aerobic / anaerobic corrosion of materials in the geological disposal environment of high-level radioactive waste, effectively avoiding the disadvantages of low accuracy and complexity of traditional identification methods.

[0022] The method steps for the aerobic / anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste provided by the present invention are simple, the principle is clear, the recognition accuracy is high, and the method is simple, the parameters are easy to obtain, and the operability is strong. It is applicable to the recognition research of the aerobic / anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste. Brief Description of the Drawings

[0023] Figure 1 It is the evolution results of two parameters, namely the Eh value and the ORR-log(τ / s) value, with the corrosion time during the aerobic / anaerobic corrosion evolution of Q345R low-carbon steel in the groundwater environment of the sealed Beishan disposal repository with an initial oxygen concentration of 8 ppm.

[0024] Figure 2 For the groundwater environment of the sealed Beishan disposal repository with an initial oxygen concentration of 10 -4 ppb, it is the evolution results of two parameters, namely the Eh value and the ORR-log(τ / s) value, with the corrosion time during the aerobic / anaerobic corrosion evolution of Q345R low-carbon steel.

[0025] Next, the present invention will be further elaborated in detail through examples.

[0026] To facilitate the understanding of the present invention, the present invention will be described more comprehensively with reference to the relevant drawings. The typical embodiments of the present invention are given in the drawings. However, the present invention can be applied to many different scenarios and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0027] It should be noted that all the technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] Example 1

[0029] In this example, the corrosion simulation solution uses the BS-01 groundwater of the Beishan disposal repository, which is boiled and cooled under room temperature and normal pressure conditions and then reserved for use. At this time, the oxygen content in the water is about 8 ppm.

[0030] Two electrodes made of Q345R low-carbon steel, an Eh electrode and an Ag / AgCl reference electrode are exposed together to 400 mL of this groundwater, and then the corrosion system is sealed under room temperature and normal pressure conditions to isolate it from the surrounding air environment. At this time, the initial oxygen content in the corrosion solution is about 8 ppm.

[0031] During the corrosion process, an Eh electrode and an Ag / AgCl reference electrode were used to measure the evolution of the Eh value of the entire corrosion system with corrosion time, and the evolution curve of the Eh value - corrosion time t was recorded; two electrodes made of Q345R low-carbon steel were used as the working electrode and the counter electrode, and Ag / AgCl was used as the reference electrode to measure the evolution of the EIS spectrum of the working electrode with corrosion time. The EIS spectrum was analyzed by DRT to obtain the distribution of log(τ / s) in the full frequency domain, and the evolution curve of log(τ / s) - corrosion time t was recorded.

[0032] As Figure 1 shown, during the entire 40-day corrosion process, when the corrosion time was 20 days, the monitored Eh value reached -680 mV (vs. SSC), and then the Eh value remained stable; correspondingly, the ORR-log(τ / s) value reached 1.2 at 20 days and then transformed into the time constant related to water reduction. Explanation: When Eh > -640 mV (vs. SSC) and the ORR-log(τ / s) value is less than 1.2, the candidate material Q345R low-carbon steel of the disposal container is in the aerobic corrosion stage; when Eh < -640 mV (vs. SSC) and the ORR-log(τ / s) value is greater than 1.2, the candidate material Q345R low-carbon steel of the disposal container enters the anaerobic corrosion stage.

[0033] It can be seen that the results of this embodiment show that the method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste of the present invention can well identify the evolution behavior of aerobic / anaerobic corrosion of materials in the geological disposal environment of high-level radioactive waste.

[0034] Example 2

[0035] In this embodiment, the corrosion simulation solution used the BS-01 groundwater of Beishan disposal repository, which was boiled and cooled under room temperature and atmospheric pressure and then reserved. At this time, the oxygen content in the water was about 8 ppm.

[0036] The corrosion system was prepared in a low-oxygen glove box (the gas-phase oxygen content is less than 0.1 ppm). The corrosion simulation solution, two electrodes made of Q345R low-carbon steel, the Eh electrode and the materials of the Ag / AgCl reference electrode were placed in the glove box. Then the corrosion system was prepared and sealed. At this time, the initial oxygen content in the corrosion solution was about 10 -4 ppb.

[0037] During the corrosion process, an Eh electrode and an Ag / AgCl reference electrode were used to measure the evolution of the Eh value of the entire corrosion system with corrosion time, and the evolution curve of the Eh value - corrosion time t was recorded; two electrodes made of Q345R low-carbon steel were used as the working electrode and the counter electrode, and Ag / AgCl was used as the reference electrode to measure the evolution of the EIS spectrum of the working electrode with corrosion time, and the DRT was used to analyze the EIS spectrum to obtain the distribution of log(τ / s) in the full frequency domain, and the evolution curve of log(τ / s) - corrosion time t was recorded.

[0038] As Figure 2 shown, during the entire 40-day corrosion process, when the corrosion time was 15 days, the monitored Eh value reached -680 mV (vs. SSC), and then the Eh value remained stable; correspondingly, the ORR-log(τ / s) value reached 1.2 at 15 days, and then transformed into a time constant related to water reduction. Explanation: When Eh > -640 mV (vs. SSC) and the ORR-log(τ / s) value is less than 1.2, the candidate material Q345R low-carbon steel of the disposal container is in the aerobic corrosion stage; when Eh < -640 mV (vs. SSC) and the ORR-log(τ / s) value is greater than 1.2, the candidate material Q345R low-carbon steel of the disposal container enters the anaerobic corrosion stage.

[0039] It can be seen that the results of this embodiment show that the method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste can well identify the aerobic / anaerobic corrosion evolution behavior of materials in the geological disposal environment of high-level radioactive waste.

[0040] The results of the embodiment show that the method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste provided by the present invention is applicable to the identification research of the aerobic / anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste. It can be seen that the method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste of the present invention has the characteristics of simple steps, clear principle, high identification accuracy, and simple method, easy-to-obtain parameters, and strong operability.

[0041] The above-described embodiments only represent one implementation manner of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for identifying the evolution of aerobic and anaerobic corrosion of materials in the geological disposal environment of high-level radioactive waste, characterized in that, It includes two indicators: one is the redox potential, which reflects the overall redox characteristics of the corrosion system, namely the Eh value; the other is the time constant, which reflects the kinetic characteristics of the reduction reaction (ORR) of dissolved oxygen in the corrosion system, namely the ORR-log (τ / s) value; The materials in the high-level radioactive waste geological disposal environment are used to simulate the materials of high-level radioactive waste geological disposal containers, including low-carbon steel, copper, cast iron, nickel-based alloys and titanium alloys; The geological disposal environment of high-level radioactive waste includes the rock formation groundwater environment around the disposal repository and the backfill material environment around the disposal container; The corrosion system is used to simulate the closed environment characteristics of a geological repository for high-level radioactive waste; the environmental parameters of the closed system vary according to the environment in which the repository is located and the characteristics of the surrounding rock formations and groundwater, including SO42- concentration, Cl- concentration, HCO3- / CO32- concentration, pH value, pressure, and moisture content of backfill materials; The Eh value is used to reflect the overall oxidizability of the corrosion system, and is related to the dissolved oxygen content in the corrosion system and the overall oxidizability of all oxidizing substances containing Fe(III) substances. By measuring with an Eh electrode, the evolution characteristics of the Eh value over corrosion time can be obtained. The ORR-log (τ / s) value is used to reflect the difficulty of dissolved oxygen in the corrosion system to undergo ORR, and is related to the dissolved oxygen content. By performing a distribution relaxation time (DRT) analysis on the measured electrochemical impedance spectroscopy (EIS), the evolution characteristics of the ORR-log (τ / s) value with corrosion time are obtained.

2. The method for identifying the evolution of aerobic and anaerobic corrosion of materials in the geological disposal environment of high-level radioactive waste according to claim 1, characterized in that, An Eh electrode is used to measure the overall oxidizability of the corrosion system; the Eh electrode can be made by yourself or purchased commercially. During use, the Eh electrode needs to be regularly subjected to cathodic polarization with a small applied potential to ensure that the surface of the Eh electrode is clean, thereby ensuring the measurement accuracy of the Eh electrode.

3. The method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste according to claim 1, characterized in that, The candidate material is processed into a working electrode for corrosion electrochemistry testing, and EIS data is collected for the working electrode using a traditional three-electrode system or a two-electrode system; based on the relationship, DRT analysis is performed on the EIS data to obtain the number of time constants contained in the EIS spectrum and the corresponding log(τ / s) values, and an evolution spectrum of the log(τ / s) values with corrosion time is plotted, thereby obtaining the evolution law of the ORR-log(τ / s) values with corrosion time.

4. The method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste according to claim 1, characterized in that: When the Eh>-640mV (vs.SSC); the ORR-log (τ / s) value is less than 1.2, the disposal container material is in the aerobic corrosion stage.

5. The method for identifying the aerobic and anaerobic corrosion evolution of materials in the geological disposal environment of high-level radioactive waste according to claim 1, characterized in that: When the Eh<-640mV (vs.SSC); the ORR-log (τ / s) value is greater than 1.2 to 1.5, the disposal container material enters the anaerobic corrosion stage.

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