CORROSION POTENTIAL SENSOR AND METHOD FOR MANUFACTURING THE SAME

Abstract

To provide a corrosion potential sensor capable of measuring ECP of structural members more accurately than before regardless of the distance between the corrosion potential sensor and the structural member, and a manufacturing method of a corrosion potential sensor.SOLUTION: A corrosion potential sensor 1 includes: a hollow metal housing 2; a reference electrode 5 that is provided in the longitudinal direction of the metal housing 2 and protrudes from one end of the metal housing 2; an insulator 3 formed at one end of the metal housing 2 and covering at least part of the reference electrode 5; a first metal oxide film 6a that covers the junction between the metal housing 2 and the insulator 3; and a second metal oxide coating 6b covering at least part of the periphery of one end of the metal housing 2 on which the first metal oxide coating 6a is formed.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an electrochemical corrosion potential sensor and a method for manufacturing an electrochemical corrosion potential sensor. [Background technology]

[0002] Patent Document 1 describes an example of an electrochemical corrosion potential sensor capable of more accurately measuring the electrochemical corrosion potential of structural components. The electrochemical corrosion potential sensor in Patent Document 1 includes a reference electrode, an insulator, a measured electrode, and a sensor body. The zirconium metal reference electrode is fixed within a zirconium oxide insulator. A stainless steel sensor body is attached to the insulator, surrounding one end of the insulator. The measured electrode is attached to the surface of the insulator so as to cover the side and the periphery of the tip of the insulator. The measured electrode is made of the same material as the structural component of the nuclear power plant, which is the object of electrochemical corrosion potential measurement. A zirconium electrode wire penetrates the insulator and is connected to the reference electrode. The core wire of a mineral-insulated cable inserted into the sensor body is connected to the zirconium electrode wire, and the metal outer tube of the mineral-insulated cable is connected to the sensor body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-079830 Summary of the Invention [Problem to be solved by the invention]

[0004] In nuclear power plants, structural components such as equipment and piping are constructed from structural materials such as stainless steel and nickel-based alloys. These structural materials are susceptible to stress corrosion cracking (SCC) under certain conditions. Therefore, to maintain the integrity of nuclear power plants, SCC countermeasures are applied to the structural components of nuclear power plants.

[0005] In recent years, SCC countermeasures have also been applied to structural components of nuclear power plants from the perspective of improving economic efficiency, such as improving the capacity factor and extending the life of the nuclear power plants.

[0006] As countermeasures against SCC, technologies aimed at improving the corrosion resistance of materials, improving stress, or mitigating the corrosive environment are being applied. In boiling water reactors (BWRs), hydrogen injection is widely used both domestically and internationally as one of the SCC countermeasures based on improving the corrosive environment of the reactor coolant (reactor water) to which structural components are exposed.

[0007] Reactor water contains oxygen and hydrogen peroxide, which are produced by radiolysis of water inside the reactor pressure vessel (inside the reactor), and these oxygen and hydrogen peroxide cause corrosion, creating a corrosive environment for the reactor water. Hydrogen injection involves adding hydrogen to the reactor water by adding hydrogen to the feedwater, which then reacts with the oxygen and hydrogen peroxide, turning them back into water. As a result of the reduction in the oxygen and hydrogen peroxide concentrations in the reactor water, the electrochemical corrosion potential (ECP) of structural components is reduced, suppressing the occurrence of SCC.

[0008] Furthermore, one technology that promotes the reduction of ECP during hydrogen injection is to inject platinum group precious metal elements into the reactor water, and the catalytic action of the platinum group precious metal elements on the electrochemical reaction of hydrogen significantly reduces the ECP of structural components during hydrogen injection.

[0009] To apply these techniques, it is necessary to accurately know the ECP of structural components that come into contact with reactor water in nuclear power plants. ECP is expressed as the potential relative to a reference electrode. The standard hydrogen electrode potential is widely used as the reference, and "vs.SHE (versus Standard Hydrogen Electrode)" is added after V, the unit of potential difference, with 0 V as the reference at each temperature.

[0010] ECP is measured by installing a corrosion potential sensor inside the reactor or on piping connected to the reactor, and measuring the potential difference between this corrosion potential sensor and the structural components. The corrosion potential sensor generates a constant potential (reference potential) that serves as the basis for ECP measurement under the conditions of use. For this reason, the corrosion potential sensor is also called a standard electrode or reference electrode. The ECP of a structural component can be determined by using an electrometer to measure the potential difference between the potential of the structural component under the conditions of reactor water temperature, oxygen concentration, hydrogen peroxide concentration, and reactor water flow rate and the reference potential of the corrosion potential sensor.

[0011] When attempting to measure the ECP of a BWR plant in situ, the corrosion potential sensor must be installed directly on piping or equipment and immersed in the reactor water. For example, when installing a corrosion potential sensor on a recirculation system piping, the sensor is inserted into a cylindrical measurement seat (flange) on the recirculation system piping so that the tip of the corrosion potential sensor (detection part) comes into contact with the reactor water flowing through the recirculation system piping. The measurement seat is made of the same material as the recirculation system piping: 304 stainless steel or 316NG steel (nuclear grade of 316L steel).

[0012] However, if the EP sensor is attached to the measurement seat with its detection section reaching inside the inner surface of the recirculation system piping, the flow of reactor water in the recirculation system piping will hit the EP sensor and disturb the tip of the EP sensor. Furthermore, since the EP sensor is perpendicular to the high-velocity reactor water flow in the recirculation system piping, there is a risk that the EP sensor will be damaged by flow vibrations.

[0013] Therefore, it is necessary to align the tip of the electrochemical corrosion potential sensor with the inner surface of the recirculation system piping and attach the electrochemical corrosion potential sensor to the measurement seat. When the electrochemical corrosion potential sensor is attached to the measurement seat in this manner, the space between the electrochemical corrosion potential sensor and the inner surface of the measurement seat is also filled with reactor water flowing through the recirculation system piping.

[0014] When the tip of the corrosion potential sensor is inserted into a measurement seat provided in the recirculation system piping and attached to the measurement seat, and the tip is aligned with the position of the inner surface of the recirculation system piping, if the width of the gap formed between the tip of the corrosion potential sensor and the inner surface of the measurement seat is large, the corrosion potential sensor will measure the ECP of the surface of the metal casing of the corrosion potential sensor, rather than the ECP of the inner surface of the recirculation system piping.

[0015] The reason for this is that ECP is measured by measuring the potential difference between the corrosion potential sensor and the surface of the piping and structural materials, but the piping and structural materials, the signal wire of the corrosion potential sensor, and the corrosion potential sensor housing are all installed in a state where they are electrically conductive in the reactor water.

[0016] Because BWR reactor water is pure water and has high liquid resistance, if the distance between the tip of the ECP sensor and the piping surface becomes longer than the distance between the tip of the ECP sensor and the ECP sensor housing, the ECP sensor housing becomes the closest ground surface to the tip of the ECP sensor. As a result, the ECP sensor measures the potential of the ECP sensor housing. As a result, the ECP sensor cannot accurately measure the ECP of the structural components.

[0017] Therefore, in order for the corrosion potential sensor to accurately measure the ECP of a structural component, the distance between the side of the detection part at the tip of the corrosion potential sensor and the inner surface of the measurement seat must be sufficiently smaller than the distance between the detection part at the tip of the corrosion potential sensor and the metal casing of the corrosion potential sensor.

[0018] Therefore, as in the above-mentioned Patent Document 1, an electrochemical corrosion potential sensor has been developed that includes an insulator, a reference electrode disposed within the insulator, and a metal housing attached to the insulator and surrounding one end of the insulator, and that has a cage-shaped or cylindrical electrode to be measured disposed on the side of the detection section of the electrochemical corrosion potential sensor. The electrode to be measured is made of the same material as the object to be ECP measured, such as a recirculation system pipe. This allows the potential difference between the detection section of the electrochemical corrosion potential sensor and the electrode to be measured to more accurately measure the ECP of the object to be ECP measured.

[0019] However, boiling water nuclear power plants use a variety of metallic materials, such as carbon steel, stainless steel, and nickel-based alloys, for their structural components, and it is necessary to change the material of the electrode to be measured by the corrosion potential sensor to suit each ECP measurement target, which is extremely difficult.

[0020] In addition, although the ECP of the test electrode made of the same material as the structural member is measured inside the furnace, it is not the ECP of the actual structural member that is being measured, so care must be taken when treating the measured ECP of the test electrode as the ECP of the structural member.

[0021] An object of the present invention is to provide an electrochemical corrosion potential sensor and a method for manufacturing an electrochemical corrosion potential sensor that can measure the ECP of a structural member more accurately than conventional methods, regardless of the distance between the electrochemical corrosion potential sensor and the structural member. [Means for solving the problem]

[0022] The present invention includes a plurality of means for solving the above problems, and examples thereof include: 1. An electrochemical corrosion potential sensor comprising: a hollow metal housing; a reference electrode provided in a longitudinal direction of the metal housing and protruding from one end of the metal housing; an insulator formed on one end of the metal housing and covering at least a portion of the reference electrode; and a first metal oxide coating covering a joint between the metal housing and the insulator. directly on at least a portion of the first metal oxide coating, and and a second metal oxide coating that covers at least a portion of the outer periphery of one end of the metal casing on the side where the first metal oxide coating is formed. [Effects of the Invention]

[0023] According to the present invention, the ECP of a structural member can be measured more accurately than in the past, regardless of the distance between the electrochemical corrosion potential sensor and the structural member. Objects, configurations, and effects other than those described above will become clear from the following description of the embodiments. [Brief explanation of the drawings]

[0024] [Figure 1]FIG. 2 is an explanatory diagram showing an example of an installation state of an electrochemical corrosion potential sensor on a pipe. [Figure 2] FIG. 1 is an explanatory diagram showing a detection unit at the tip of an electrochemical corrosion potential sensor of a related art and its installation state in a pipe. [Figure 3] 1 is an explanatory diagram showing a detection unit of an electrochemical corrosion potential sensor according to an embodiment and its installation state in a pipe. FIG. [Figure 4] 1 is a characteristic diagram showing the relationship between the distance L between a pipe and an electrochemical corrosion potential sensor and the potential detected by the electrochemical corrosion potential sensor. [Figure 5] 1 is a cross-sectional schematic view of an electrochemical corrosion potential sensor according to an embodiment of the present invention. [Figure 6] FIG. 10 is a cross-sectional schematic view of an electrochemical corrosion potential sensor according to a modified example of the embodiment of the present invention. [Figure 7] FIG. 10 is a cross-sectional schematic view of an electrochemical corrosion potential sensor according to another modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Examples of the electrochemical corrosion potential sensor and the method for manufacturing the electrochemical corrosion potential sensor of the present invention will be described with reference to Figures 1 to 7. In the drawings used in this specification, identical or corresponding components are denoted by the same or similar reference numerals, and repeated description of these components may be omitted.

[0026] First, the background to the invention will be described.

[0027] The inventors have investigated the configuration of an electrochemical corrosion potential sensor that can suppress the influence of ECP on the surface of the metal casing of the electrochemical corrosion potential sensor when installed on a structural component of a nuclear power plant, and can accurately measure the ECP on the surface of the structural component.

[0028] First, an example of the installation location of an electrochemical corrosion potential sensor in a boiling water reactor (BWR) will be described with reference to Figures 1 to 3. Figure 1 is an explanatory diagram showing an example of the installation state of an electrochemical corrosion potential sensor on a pipe, Figure 2 is an explanatory diagram showing the detection unit at the tip of an electrochemical corrosion potential sensor of the reference technology and its installation state on the pipe, and Figure 3 is an explanatory diagram showing the detection unit of an electrochemical corrosion potential sensor of an embodiment and its installation state on the pipe.

[0029] As shown in FIG. 1, the corrosion potential sensor 101 is inserted into a measurement seat 13 welded to a hole formed in the recirculation system piping 12 or the bottom drain piping 12 of a BWR, so that the detection part at the tip of the corrosion potential sensor 101 comes into contact with the reactor water flowing in the piping 12, thereby measuring the ECP of the piping 12.

[0030] The measuring seat 13 installed in the recirculation system piping 12 is called a flange type and has a diameter of approximately φ80 to 300 mm. The measuring seat 13 installed in the bottom drain piping 12 is called a manifold type and has a diameter of approximately φ25 to 30 mm.

[0031] The dimensions of the electrochemical corrosion potential sensor 101 are approximately 150 mm x approximately φ10 mm, so when the electrochemical corrosion potential sensor 101 is installed on the measurement seat 13, the distance between the measurement seat 13 or the pipe 12 and the detection part of the electrochemical corrosion potential sensor 101 is several tens to several hundreds of mm for the flange type and several mm for the manifold type.

[0032] 1 and 2, the electrochemical corrosion potential sensor 101 has a cylindrical insulator 103 made of zirconia (zirconium oxide: ZrO2) located in the detection section of the sensor and joined to a metal housing 102 by a brazing section 104. The area inside the insulator 103 filled with platinum black powder 108 serves as a reference electrode 105 for ECP measurement. A reference electrode 105 made of a platinum core wire is inserted into the insulator 103 filled with platinum black powder 108, and the reference electrode 105 is led to the outside via a metal wire 107 inside a mineral insulated cable.

[0033] As shown in FIG. 1, this electrochemical corrosion potential sensor 101 is inserted into a measurement seat 13 welded to a pipe 12 (for example, a recirculation pipe), or into a hole formed in the pipe 12.

[0034] At this time, the detection unit at the tip of the corrosion potential sensor 101 is positioned on the inner surface of the pipe 12. The ECP of the pipe 12 is measured by connecting a metal wire 107 connected to the reference electrode 105 and disposed within the metal casing 102, and a wiring 15 connected to the pipe 12, to, for example, an electrometer 14, and measuring the potential difference between the reference electrode 105 and the pipe 12 with the electrometer 14.

[0035] 2, when the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12 is small, the electrochemical corrosion potential sensor 101 detects the ECP of the pipe 12. On the other hand, when the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12 is large and exceeds the distance M between the detection unit of the electrochemical corrosion potential sensor 101 and the metal housing 102, the electrochemical corrosion potential sensor 101 detects the ECP of the metal housing 102.

[0036] Therefore, the inventors studied the relationship between the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12, the distance M between the detection unit of the electrochemical corrosion potential sensor 101 and the metal housing 102, and the ECP detected by the electrochemical corrosion potential sensor 101, and came up with the idea of ​​covering the surface of the metal housing 2 of the electrochemical corrosion potential sensor 1 with an insulating metal oxide coating 6, as shown in FIG. 3.

[0037] This allows the ECP of the metal casing 2 to be blocked by the metal oxide coating 6, preventing the corrosion potential sensor 1 from detecting the ECP of the metal casing 2, and enabling the corrosion potential sensor 1 to detect the ECP of the piping 12 even if the distance L between the detection part of the corrosion potential sensor 1 and the piping 12 is greater than the distance M between the detection part of the corrosion potential sensor 1 and the metal casing 2.

[0038] The electrochemical corrosion potential sensor 101 shown in FIG. 2 can detect the ECP of the metal component closest to the detection unit of the electrochemical corrosion potential sensor 101, such as the pipe 12 or the metal casing 102 of the electrochemical corrosion potential sensor 101, because the range of the electric potential is extremely limited in a reactor water environment with low conductivity, such as a BWR.

[0039] The relationship between the distance L between the detection unit of the electrochemical corrosion potential sensor 101 and the pipe 12, and the distance M between the detection unit of the electrochemical corrosion potential sensor 101 and the metal casing 102, and the potential E detected by the electrochemical corrosion potential sensor 101 is expressed by the following equation (1).

[0040]

number

[0041] In formula (1), ECP p ECP of piping 12, ECP m indicates the ECP of the metal housing 2 of the corrosion potential sensor 1, and ρ w indicates the resistivity of the reactor water.

[0042] In contrast, when the surface of the metal housing 2 of the electrochemical corrosion potential sensor 1 is covered with a metal oxide coating 6 as shown in FIG. 3, the potential E detected by the electrochemical corrosion potential sensor 1 is expressed by the following equation (2).

[0043]

number

[0044] In equation (2), ρ c indicates the resistivity of the metal oxide film 6, and N indicates the film thickness of the metal oxide film 6.

[0045] Figure 4 is a characteristic diagram showing the relationship between the distance L between the pipe and the electrochemical corrosion potential sensor and the potential detected by the electrochemical corrosion potential sensor. The characteristics shown in Figure 4 show the results of a trial calculation based on equations (1) and (2) of the relationship between the distance L between the pipe 12 and the electrochemical corrosion potential sensor 1 and the potential detected by the electrochemical corrosion potential sensor 1 when the distance M between the detection unit of the electrochemical corrosion potential sensor 1 and the metal housing 2 is 30 mm.

[0046] 4, the horizontal axis represents the distance L between the pipe 12 and the detection unit of the electrochemical corrosion potential sensor 1, and the vertical axis represents the potential detected by the electrochemical corrosion potential sensor 1, with the lower end of the vertical axis corresponding to the ECP of the pipe 12 and the upper end corresponding to the ECP of the metal casing 2 of the electrochemical corrosion potential sensor 1. In other words, the closer the detected potential of the electrochemical corrosion potential sensor 1 is to the lower end of the vertical axis, the more accurately the electrochemical corrosion potential sensor 1 can measure the ECP of the pipe 12, and the closer it is to the upper end, the more the potential detected by the electrochemical corrosion potential sensor 1 becomes a composite potential of the ECP of the pipe 12 and the ECP of the metal casing 2.

[0047] First, we will explain the electrochemical corrosion potential sensor of the reference technology shown in Figure 2, which does not have a metal oxide coating on the surface of the metal housing. If the distance L between the pipe 12 and the electrochemical corrosion potential sensor 101 is within a few millimeters, the amount of ECP contamination originating from the metal housing 102 that constitutes the electrochemical corrosion potential sensor 101 is small, and the electrochemical corrosion potential sensor 101 can accurately measure the ECP of the pipe 12.

[0048] On the other hand, if the distance L between the pipe 12 and the electrochemical corrosion potential sensor 101 exceeds 20 mm, the influence of the ECP of the metal casing 102 that constitutes the electrochemical corrosion potential sensor 101 becomes greater, and the detected potential of the electrochemical corrosion potential sensor 101 becomes a mixture of the ECP of the pipe 12 and the ECP of the metal casing 102.

[0049] Therefore, in order to accurately measure the ECP of the pipe 12 using the electrochemical corrosion potential sensor 101 of the reference technology as shown in FIG. 2, the distance L between the pipe 12 and the electrochemical corrosion potential sensor 101 needs to be within several millimeters. Therefore, if a flange-type measurement seat is used in which the distance between the pipe 12 and the detection part of the electrochemical corrosion potential sensor 101 is several tens to several hundreds of millimeters, the ECP of the pipe 12 may not be accurately measured. This places limitations on the conditions for measuring the electrochemical corrosion potential using the electrochemical corrosion potential sensor.

[0050] On the other hand, in the case of an electrochemical corrosion potential sensor 1 having a metal oxide coating 6 on the surface of a metal housing 2 as shown in FIG. 3, even when the distance L between the piping 12 and the electrochemical corrosion potential sensor 1 is 100 mm, the amount of ECP contamination originating from the metal housing 2 constituting the electrochemical corrosion potential sensor 1 is small, and the electrochemical corrosion potential sensor 1 can accurately measure the ECP of the piping 12.

[0051] Therefore, by using the electrochemical corrosion potential sensor 1 shown in Figure 3, it is possible to accurately measure the ECP of a pipe even in a flange-type measurement seat where the distance between the pipe 12 and the detection part of the electrochemical corrosion potential sensor 1 is several tens to several hundreds of mm.

[0052] The configuration of an electrochemical corrosion potential sensor according to an embodiment of the present invention, which reflects the above-described study results, will be described with reference to Figures 5 to 7. Figures 5 to 7 are cross-sectional schematic diagrams of the electrochemical corrosion potential sensor according to the embodiment.

[0053] The electrochemical corrosion potential sensor 1 of this embodiment shown in FIG. 5 includes an insulator 3 formed at one end of a metal housing 2 and covering at least a portion of a reference electrode 5, a hollow metal housing 2, a reference electrode 5 arranged in the longitudinal direction of the metal housing 2 and protruding from one end of the metal housing 2, a metal wire (lead wire) 7, metal / metal oxide powder 8, a sealing plug 9, a mineral-insulated cable 10, a first metal oxide coating 6a covering the joint between the metal housing 2 and the insulator 3, and a second metal oxide coating 6b covering at least a portion of the outer periphery of one end of the metal housing 2 on the side where the first metal oxide coating 6a is formed.

[0054] The insulator 3 and the metal housing 2 are joined at a brazed portion 4 .

[0055] One end of the reference electrode 5 is connected to a metal wire 7 at a joint 11 inside the insulator 3 or the metal housing 2. The other end of the reference electrode 5, which serves as the detection unit, is disposed inside the insulator 3 filled with metal / metal oxide powder 8 and is covered by the insulator 3 via the metal / metal oxide powder 8. The metal / metal oxide powder 8 inside the insulator 3 is sealed from the metal housing 2 side of the electrochemical corrosion potential sensor 1 by a hollow sealing plug 9.

[0056] In the electrochemical corrosion potential sensor 1 of this embodiment, as shown in FIG. 5, the outer surface of the portion where the insulator 3 and the metal housing 2 are joined by the brazing portion 4 is covered with a first metal oxide coating 6a, and a portion of the outer surface of the metal housing 2 is covered with a second metal oxide coating 6b.

[0057] Furthermore, the second metal oxide coating 6b covers at least a portion of the first metal oxide coating 6a. Fig. 5 shows an embodiment in which one surface of the first metal oxide coating 6a facing the second metal oxide coating 6b is covered with the second metal oxide coating 6b.

[0058] As described above with reference to Figures 2 and 3, the distance M between the detection part (end of reference electrode 5) of corrosion potential sensor 1 and metal casing 2 is approximately 30 mm, so it is necessary to form first metal oxide coating 6a and second metal oxide coating 6b on brazed part 4 and part of the outer surface of metal casing 2 according to the distance L between piping 12 and corrosion potential sensor 1.

[0059] For example, if the distance L between the pipe 12 and the electrochemical corrosion potential sensor 1 is 100 mm, it is desirable to cover the outer periphery of the metal casing 2 from the brazed portion 4 by at least 100 mm in the longitudinal direction with the first metal oxide coating 6a and the second metal oxide coating 6b. The insulating first metal oxide coating 6a and the second metal oxide coating 6b block the potential of the brazed portion 4 and the metal casing 2, thereby suppressing ECP mixing originating from the brazed portion 4 and the metal casing 2, enabling the electrochemical corrosion potential sensor 1 to accurately measure the ECP of the pipe.

[0060] The electrochemical corrosion potential sensor of this embodiment is not limited to the structure shown in FIG. 5. Other embodiments will be described below with reference to FIGS.

[0061] 6 has a configuration in which the second metal oxide coating 6b1 covers the entire outer periphery of the metal casing 2, and is a configuration suitable for installing the electrochemical corrosion potential sensor in a flange-type measurement seat having a diameter of more than 100 mm. In the electrochemical corrosion potential sensor 1A shown in FIG. 6, it is desirable that the brazed portion 4 is also covered with the insulating first metal oxide coating 6a, as shown in FIG.

[0062] The electrochemical corrosion potential sensor 1B shown in FIG. 7 includes an insulator 3b, a metal housing 2, a reference electrode 5b, a metal wire (lead wire) 7, a first metal oxide coating 6a2 covering the joint between the metal housing 2 and the insulator 3b, and a second metal oxide coating 6b2 covering at least a portion of the outer periphery of one end of the metal housing 2 on the side where the first metal oxide coating 6a is formed.

[0063] In the electrochemical corrosion potential sensor 1B shown in FIG. 7, the reference electrode 5b is exposed on the side of the insulator 3b opposite to the metal casing 2, and the reference electrode 5b is in direct contact with the reactor water.

[0064] Even in a configuration in which the reference electrode 5b is in direct contact with reactor water, such as the electrochemical corrosion potential sensor 1B shown in Fig. 7, the second metal oxide coating 6b2 may cover the entire outer periphery of the metal casing 2, as shown in Fig. 6. Alternatively, the junction between the reference electrode 5b and the insulator 3b may be covered with the insulating first metal oxide coating 6a2.

[0065] The metal housing 2 in the electrochemical corrosion potential sensors 1, 1A, and 1B shown in Figures 5 to 7 is made of at least one of nickel-based alloys and stainless steels, and in particular can be made of nickel-based alloy 42 (42 alloy) and 316L stainless steel (SUS316L).

[0066] The insulators 3, 3b can be made of at least one of zirconia, yttrium oxide (Y2O3, yttria), aluminum oxide (Al2O3, alumina), partially stabilized zirconia (PSZ), yttria stabilized zirconia (YSZ), and the like.

[0067] The reference electrodes 5, 5b may be made of one or more of iron, silver / silver chloride electrodes, platinum electrodes, zirconium electrodes, and the like.

[0068] Furthermore, the first metal oxide coatings 6a, 6a2 and the second metal oxide coatings 6b, 6b1, 6b2, like the insulators 3, 3b, can be made of at least one of zirconia, yttria, alumina, partially stabilized zirconia, yttria-stabilized zirconia, etc.

[0069] Next, among the manufacturing methods of the electrochemical corrosion potential sensors 1, 1A, and 1B according to this embodiment, a method for forming the first metal oxide coatings 6a and 6a2 and a method for forming the second metal oxide coatings 6b, 6b1, and 6b2 on the outer surface of the metal casing 2 will be described.

[0070] The first metal oxide coating 6a, 6a2 and the second metal oxide coating 6b, 6b1, 6b2 can be formed on the outer surface of the brazing portion 4 and the metal casing 2, respectively, by any of the following methods: physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, sol-gel, metal organic decomposition (MOD), and coating.

[0071] Preferably, the first metal oxide films 6a, 6a2 and the second metal oxide films 6b, 6b1, 6b2 are formed simultaneously by the above-mentioned formation method.

[0072] Next, the effects of this embodiment will be described.

[0073] The electrochemical corrosion potential sensors 1, 1A, 1B of the present embodiment described above include a hollow metal housing 2, a reference electrode 5, 5b arranged in the longitudinal direction of the metal housing 2 and protruding from one end of the metal housing 2, an insulator 3, 3b formed at one end of the metal housing 2 and covering at least a portion of the reference electrode 5, 5b, a first metal oxide coating 6a, 6a2 covering the joint between the metal housing 2 and the insulator 3, 3b, and a second metal oxide coating 6b, 6b1, 6b2 covering at least a portion of the outer periphery of one end of the metal housing 2 on the side where the first metal oxide coating 6a, 6a2 is formed.

[0074] In this way, by covering at least the side of the outer periphery of the metal casing 2 that is closer to the reference electrode 5, 5b with the second metal oxide coating 6b, 6b1, 6b2, the side of the surface of the metal casing 2 that is closer to the reference electrode 5, 5b is insulated, thereby preventing the electrochemical corrosion potential sensors 1, 1A, 1B from measuring the ECP of the surface of the metal casing 2. Therefore, even if the distance between the side of the reference electrode 5, 5b, which is the detection unit of the electrochemical corrosion potential sensor 1, 1A, 1B, and the inner surface of the measurement seat is greater than the distance between the detection unit of the electrochemical corrosion potential sensor 1, 1A, 1B and the metal casing 2, the electrochemical corrosion potential sensor 1, 1A, 1B can accurately measure the ECP of the structural member. This alleviates the constraint on the distance between the electrochemical corrosion potential sensor and the ECP measurement target, which is the ECP measurement target of the plant structural member.

[0075] Such corrosion potential sensors 1, 1A, and 1B can be installed in other piping in a BWR plant (e.g., reactor cleanup system piping, drain piping and feedwater piping connected to the bottom of the reactor, etc.) and used to measure the ECP of the corresponding piping. Furthermore, they can be used to measure the ECP of piping in pressurized water nuclear power plants and thermal power plants, and are particularly suitable for measuring the corrosion potential of structural members made of carbon steel, iron-based alloys, or nickel-based alloys whose surfaces come into contact with reactor cooling water, specifically, for measuring the corrosion potential that serves as an indicator of water chemistry conditions for stress corrosion cracking (SCC) of stainless steel and nickel-based alloys or flow accelerated corrosion (FAC) of carbon steel and nickel-based alloys.

[0076] Furthermore, since the second metal oxide films 6b, 6b1, and 6b2 cover at least a portion of the first metal oxide films 6a and 6a2, the areas where the metal casing 2 is exposed can be reduced, enabling more accurate ECP measurement.

[0077] Furthermore, since the second metal oxide coating 6b1 covers the entire outer periphery of the metal casing 2, the possibility of the reference electrodes 5, 5b measuring the ECP of the metal casing 2 can be further reduced, and a structure can be created in which the ECP of the structural components of the plant can be measured with high accuracy even if the distance to the inner surface of the measurement seat becomes very large.

[0078] Furthermore, by simultaneously forming the first metal oxide films 6a, 6a2 and the second metal oxide films 6b, 6b1, 6b2, the time required for film formation can be shortened, improving the manufacturing efficiency of the electrochemical corrosion potential sensors 1, 1A, 1B.

[0079] <Other> The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to having all of the described configurations. [Explanation of symbols]

[0080] 101, 1, 1A, 1B... Corrosion potential sensor 102,2...Metal housing 103,3,3b...Insulator 104,4...Brazed part 105,5,5b…Reference electrode 6…Metal oxide coating 6a,6a2...first metal oxide coating 6b,6b1,6b2...Second metal oxide coating 107,7...Metal wire 108,8...Metal / metal oxide powder 9...Sealing plug 10...Mineral insulated cable 11... Junction between reference electrode and metal wire 12...Piping 13...Measuring seat 14...Electrometer 15...Wiring

Claims

1. 1. An electrochemical corrosion potential sensor comprising: A hollow metal housing, a reference electrode provided in the longitudinal direction of the metal housing and protruding from one end of the metal housing; an insulator formed at one end of the metal housing and covering at least a portion of the reference electrode; a first metal oxide coating covering a joint between the metal housing and the insulator; a second metal oxide coating that directly covers at least a portion of the first metal oxide coating and at least a portion of the outer periphery of one end of the metal casing on which the first metal oxide coating is formed. A corrosion potential sensor characterized by:

2. The electrochemical corrosion potential sensor according to claim 1, The second metal oxide film covers the entire outer periphery of the metal housing. A corrosion potential sensor characterized by:

3. The electrochemical corrosion potential sensor according to claim 1, The insulator covers the end of the reference electrode. A corrosion potential sensor characterized by:

4. The electrochemical corrosion potential sensor according to claim 1, The reference electrode is exposed on the opposite side of the insulator from the metal housing. A corrosion potential sensor characterized by:

5. The electrochemical corrosion potential sensor according to claim 1, The first metal oxide film and the second metal oxide film contain at least one of zirconium oxide, yttrium oxide, and partially stabilized zirconia. A corrosion potential sensor characterized by:

6. The electrochemical corrosion potential sensor according to claim 1, The reference electrode is made of silver / silver chloride, iron, zirconium, or platinum. A corrosion potential sensor characterized by:

7. The electrochemical corrosion potential sensor according to claim 1, The insulator includes at least one of zirconium oxide, yttrium oxide, and aluminum oxide. A corrosion potential sensor characterized by:

8. A method for manufacturing an electrochemical corrosion potential sensor having a hollow metal housing, a reference electrode provided in a longitudinal direction of the metal housing and protruding from one end of the metal housing, and an insulator formed on the one end of the metal housing and covering at least a portion of the reference electrode, forming a first metal oxide coating that covers a joint between the metal housing and the insulator; forming a second metal oxide film that directly covers at least a portion of the first metal oxide film and at least a portion of the outer periphery of one end of the metal casing on the side where the first metal oxide film is formed.

2. A method for manufacturing an electrochemical corrosion potential sensor comprising:

9. 9. The method for manufacturing an electrochemical corrosion potential sensor according to claim 8, The first metal oxide film and the second metal oxide film are formed by at least one method selected from the group consisting of physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, sol-gel, metal organic decomposition (MOD), and coating.

2. A method for manufacturing an electrochemical corrosion potential sensor comprising:

10. 9. The method for manufacturing an electrochemical corrosion potential sensor according to claim 8, The first metal oxide film and the second metal oxide film are formed simultaneously.

2. A method for manufacturing an electrochemical corrosion potential sensor comprising:

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