JP5358554B2 - Corrosion potential sensor and corrosion potential sensor installation structure - Google Patents

Description

  The present invention relates to a corrosion potential sensor and an installation structure of the corrosion potential sensor, and in particular, corrosion of structural members made of carbon steel, iron-base alloy, nickel-base alloy, or the like, in which the reactor coolant is in contact with the surface. The present invention relates to a corrosion potential sensor suitable for measuring a potential and an installation structure of the corrosion potential sensor.

  Structural members made of stainless steel or nickel-base alloys that make up nuclear plant equipment and piping exhibit stress corrosion cracking (SCC) susceptibility under certain conditions. Therefore, in order to maintain the soundness of the nuclear power plant, SCC prevention measures are applied to the structural members. In recent years, preventive measures for SCC have been applied to nuclear power plants from the viewpoint of improving the utilization factor of nuclear power plants and improving the economic efficiency such as extending the life.

  As an SCC prevention measure, a technique for improving the corrosion resistance of the material, improving the stress, or relaxing the corrosive environment is applied. In boiling water reactors (BWR), hydrogen injection is widely performed at home and abroad as one of the SCC measures based on the improvement of the corrosive environment of reactor cooling water (reactor water) that contacts the surface of structural members. . An example of this hydrogen injection is described in, for example, Japanese Patent No. 2687780. In the reactor water, there are oxygen and hydrogen peroxide that are generated by radiolysis of water in the reactor pressure vessel (inside the reactor) and cause corrosion, and these form a corrosive environment. In hydrogen injection, hydrogen is added to the reactor water through a water supply system, and reacted with oxygen and hydrogen peroxide to be reduced to water. As a result, the oxygen concentration and the hydrogen peroxide concentration in the reactor water are lowered, and the corrosion potential (ECP) of the structural member is lowered. Therefore, the occurrence of SCC and the SCC progress rate in the structural member are alleviated.

  Further, as a technique for accelerating the decrease in the corrosion potential of the structural member during hydrogen injection, for example, a noble metal injection technique described in JP-A-4-223299 is known. This technique injects a platinum group noble metal element into the reactor water and utilizes the catalytic action of the platinum group noble metal element on the electrochemical reaction of hydrogen to significantly lower the corrosion potential of the structural member at the time of hydrogen injection.

  In these corrosion environment mitigation techniques, it is necessary to accurately know the corrosion potential of the structural member. Therefore, a corrosion potential sensor is installed in the reactor or in the piping to measure the corrosion potential of the structural member. The corrosion potential sensor generates a constant potential (reference potential) that serves as a reference for measuring the corrosion potential under the use conditions. For this reason, the corrosion potential sensor is also called a reference electrode, a reference electrode, or a verification electrode. By measuring the potential difference between the potential of the structural member under the conditions of the temperature, oxygen concentration, hydrogen peroxide concentration and flow rate of the reactor water and the reference potential of the corrosion potential sensor using a potentiometer, It is possible to know the corrosion potential of the material.

  The corrosion potential is usually displayed by indicating what kind of reference electrode is used as a reference. A standard hydrogen electrode potential is widely used as a reference, which means that the redox reaction of hydrogen at each temperature is set to 0 V as a reference. SHE (versus Standard Hydrogen Electrode) is attached immediately after V which is a unit of potential difference, and Vvs. It is expressed as SHE. In order to accurately measure the corrosion potential (ECP), the installation of a corrosion potential sensor is indispensable, and the corrosion potential sensor is required to be usable under the operating conditions of the reactor.

  The conventional technology of the corrosion potential sensor is described in Proceedings of International Symposium on Plant Aging and Life Prediction of Corrodible Structures, May 15-18, 1995, Sapporo Japan, p413 JSCE-NACE (1995). It is also described in Japanese Patent No. 65785, Japanese Patent Application Laid-Open No. 2000-146871 and Japanese Patent Application Laid-Open No. 2009-42111.

  The corrosion potential sensor described in JP 2000-65785 A includes an electrode, an oxygen ion conductor (insulator), and a metal body (sensor housing). The oxygen ion conductor is made of zirconium oxide (zirconia) and has a tubular shape (a test tubular shape) in which one end is opened and the other end is closed. The open end of the oxygen ion conductor is joined to the metal body by brazing. The electrode that generates the reference potential of the corrosion potential sensor includes a catalyst (platinum), silver oxide, and a lead wire. The catalyst, silver oxide and lead are placed in a closed oxygen ion conductor at one end, the catalyst is placed at the closed end of the oxygen ion conductor, and the silver oxide packed bed is adjacent to the catalyst packed bed. Placed in.

  In the corrosion potential sensor described in Japanese Patent Application Laid-Open No. 2000-146891, a lid is fixed to one end of a cylindrical insulator, the other end of the insulator is sealed with an inner sleeve, and an outer sleeve is an outer surface of the insulator. Is attached. A silver-silver chloride electrode is disposed in the insulator, and a lead wire connected to the electrode is drawn out of the outer sleeve.

  Japanese Unexamined Patent Application Publication No. 2009-42111 describes a corrosion potential sensor. This corrosion potential sensor has a platinum electrode, a zirconia insulator, a metal sensor housing, and a lead wire. An electrode for generating a reference potential is attached to one end of the insulator by brazing, and a sensor housing is attached to the other end of the sensor insulator.

  In addition, the corrosion potential sensor described in Japanese Patent Application Laid-Open No. 2001-166082 includes a structural member of a nuclear power plant that measures the corrosion potential, for example, a test piece made of the same material as the recirculation piping, and a reference electrode. It arrange | positions so that it may contact the reactor water which flows in recirculation system piping.

Japanese Patent No. 2687780 JP-A-4-223299 JP 2000-65785 A Japanese Patent Laid-Open No. 2000-146891 JP 2009-42111 A

Proceedings of International Symposium on Plant Aging and Life Prediction of Corrodible Structures, May 15-18, 1995, Sapporo Japan, p413 JSCE-NACE (1995)

  When measuring the corrosion potential at a site where the flow rate of reactor water is high, such as the recirculation piping of a boiling water nuclear plant, which is a nuclear power plant, under the environmental conditions of the site, the corrosion potential sensor ( ECP sensor) must be installed directly in the recirculation piping. To install the corrosion potential sensor in the recirculation system piping, insert the corrosion potential sensor into the cylindrical measurement seat provided in the recirculation system piping, and the top of the corrosion potential sensor flows in the recirculation system piping. The test is performed by contacting the reactor water and attaching the corrosion potential sensor to the measurement seat.

  However, as shown in FIG. 3 (A), when the corrosion potential sensor is attached to the measurement seat in a state where the top of the corrosion potential sensor reaches the inner side of the inner surface of the recirculation piping, recirculation is performed. The flow of the reactor water flowing in the system piping hits the corrosion potential sensor and is disturbed at the top of the corrosion potential sensor. Furthermore, since the corrosion potential sensor is in a state orthogonal to the flow of the high flow rate reactor water in the recirculation system piping, the corrosion potential sensor is damaged by flow vibration or the electrode is electrically connected from the housing in the corrosion potential sensor. There is a possibility that the insulator used for the purpose of insulative insulation will corrode and thin.

  Therefore, as shown in FIG. 3B (see FIG. 3 of Japanese Patent Laid-Open No. 2009-42111), the tip of the top of the corrosion potential sensor is arranged with the position of the inner surface of the recirculation system pipe aligned to corrode. It is required to attach the potential sensor to the measurement seat. In order to evaluate the influence of the flow accelerated corrosion (FAC) of the carbon steel pipe, it is more strictly required to align the tip of the top of the head with the position of the inner surface of the recirculation pipe.

  When the corrosion potential sensor is attached to the measurement seat as shown in FIG. 3B, the corrosion potential sensor is inserted between the corrosion potential sensor and the inner surface of the measurement seat and in the recirculation piping. An annular gap is formed between the inner surfaces of the insertion holes. These gaps are also filled with reactor water flowing through the recirculation system piping. The corrosion potential of the recirculation system pipe by the corrosion potential sensor is obtained by measuring the potential difference between the potential detection part of the corrosion potential sensor and the inner surface of the recirculation system pipe.

  Based on the results of the study by the inventors, the following findings could be obtained. That is, if the width of the gap formed between the top of the corrosion potential sensor and the inner surface of the insertion hole of the structural member (for example, piping) into which the top is inserted is sufficiently wide, the side of the top of the head is inserted. The potential difference from the inner surface of the hole indicates the corrosion potential of the surface (for example, the inner surface of the pipe) in contact with the flowing water of the structural member. However, when the width of the gap formed between the top of the corrosion potential sensor and the inner surface of the insertion hole is narrow, the potential difference between the side of the top and the inner surface of the insertion hole causes the flow of the structural member. The corrosion potential of the inner surface of the insertion hole, or the corrosion potential of the inner surface of the insertion hole and the surface of the structural member that is in contact with flowing water, not the corrosion potential of the surface that is in contact with the water (for example, the inner surface of the pipe) Indicates a mixed corrosion potential. When the width of the gap is narrow, the water in the gap remains stagnant without being affected by the flow of water flowing along the surface of the structural member, and dissolved oxygen and excess contained in the flowing water. The environment is likely to accumulate hydrogen oxide. For this reason, the corrosion potential of the inner surface of the insertion hole is different from the corrosion potential of the surface of the structural member in contact with the flowing water.

  The inventors of the present invention, even when the top of the top of the corrosion potential sensor is aligned with the surface of the structural member in contact with the flowing water, the top of the top of the corrosion potential sensor and the insertion hole of the corrosion potential sensor formed in the structural member. When the width of the gap formed between the inner surface and the inner surface becomes narrower, a new finding that the accuracy of the measured corrosion potential of the piping is reduced is found, and based on this finding, the top of the corrosion potential sensor, Regardless of the width of the gap formed between the inner surface of the insertion hole of the corrosion potential sensor formed on the structural member, it has been recognized that the corrosion potential of the structural member needs to be accurately measured.

  The objective of this invention is providing the installation structure of the corrosion potential sensor which can measure the corrosion potential of a structural member accurately, and a corrosion potential sensor.

In order to achieve the above-described object, the present invention is characterized in that a reference electrode disposed in any of a casing, a space formed in the casing, and an end of the casing as a part of the casing, and a reference electrode A connected first conducting wire, a potential detection unit formed on the outer surface of the casing, and an electrode member disposed outside the casing facing the potential detection unit in a state of being separated from the outer surface of the casing;
The casing is attached to the cylindrical metal member and the metal member and has at least an electric potential detection unit and an insulating member disposed between the metal member, the electrode member is attached to the metal member, and the casing is an object for measuring the corrosion potential. A plurality of openings formed in the electrode member when attached to the surface of the electrode member are arranged so that water that contacts the surface of the object to be measured for corrosion potential passes, and the portion facing the potential detection part of the electrode member is the object to be measured for corrosion potential The potentiometer is connected to the first conductor outside the casing, and the second conductor connected to the corrosion potential measurement object is connected to the potentiometer .

When the electrode member is attached to the metal member and the casing is attached to the corrosion potential measurement object, a plurality of openings formed in the electrode member are arranged so that water that contacts the surface of the corrosion potential measurement object passes through. Since the portion of the electrode member that faces the potential detection portion is made of the same material as the corrosion potential measurement object, the inner surface of the hole formed in the structural member of the plant into which the tip of the corrosion potential sensor is inserted The corrosion potential of the structural member can be accurately measured regardless of the width of the gap formed between the casing and the casing of the corrosion potential sensor.

  Preferably, the electrode member is a capture electrode member that covers the tip of the casing including the potential detection portion on the insulating member side from the attachment portion of the insulating member to the metal member.

A corrosion potential sensor having the above-described features is attached to a cylindrical support seat installed on a structural member that is an object to be measured for corrosion potential in the plant, and is disposed in the support seat.
The tip of the portion of the casing located in the support seat is arranged at the position of the surface in contact with the water of the structural member in the axial direction of the corrosion potential sensor,
The electrode member is disposed closer to the central axis side of the corrosion potential sensor than the inner surface of the hole with the tip of the portion of the casing located in the support seat being inserted into the hole formed in the structural member. By doing so, the above-described object can be achieved.

  According to the present invention, the structure is formed regardless of the width of the gap formed between the inner surface of the hole formed in the structural member of the plant and into which the tip of the corrosion potential sensor is inserted and the casing of the corrosion potential sensor. The corrosion potential of the member can be measured with high accuracy.

It is a longitudinal cross-sectional view which shows the structure which installed the corrosion potential sensor of Example 1 which is one suitable Example of this invention in the recirculation system piping of a boiling water nuclear power plant. It is a perspective view which shows the capture electrode member shown in FIG. It is explanatory drawing which shows the installation state to the piping of a corrosion potential sensor, (A) is explanatory drawing which shows the state which has arrange | positioned the front-end | tip of a corrosion-potential sensor inside the inner surface of piping, (B) is the front-end | tip of a corrosion potential sensor It is explanatory drawing which shows the state which has arrange | positioned in the position of the inner surface of piping. It is explanatory drawing which shows the power line which generate | occur | produces between the top part of a corrosion potential sensor, and recirculation system piping, (A) is explanatory drawing which shows the power line which generate | occur | produces with the conventional corrosion potential sensor, (B) is an example of this invention It is explanatory drawing which shows the power line which generate | occur | produces with the corrosion potential sensor which is. A characteristic diagram showing the change in corrosion potential of the surface of a stainless steel specimen with a platinum layer formed on a part of the surface under the reactor water conditions of a boiling water nuclear power plant from the boundary between the platinum layer and stainless steel. is there. It is a longitudinal cross-sectional view which shows the structure which installed the corrosion potential sensor of Example 2 which is another Example of this invention in the recirculation system piping of a boiling water nuclear power plant. It is a longitudinal cross-sectional view which shows the structure which installed the corrosion potential sensor of Example 3 which is another Example of this invention in the recirculation system piping of a boiling water nuclear power plant. It is a perspective view which shows the capture electrode member shown in FIG.

  When the corrosion potential sensor is installed in a structural member of a nuclear power plant and the tip portion of this corrosion potential is placed in a hole formed in the structural member, the inventors corrode the inner surface of the hole facing the corrosion potential sensor. The structure of a corrosion potential sensor that can suppress the influence of the potential and can accurately measure the corrosion potential of the surface of the structural member in contact with the flowing water was examined.

  The corrosion potential sensor described in Japanese Patent Application Laid-Open No. 2009-42111 utilizes an electrode reaction of hydrogen on an electrode attached to the tip of a zirconia insulator, that is, on platinum. The tip surface of the electrode (platinum) in the axial direction of the corrosion potential sensor and the side surface of the electrode (platinum) serve as a potential detection unit.

  As shown in FIG. 4A, this corrosion potential sensor is inserted into a measurement seat and a hole formed in the pipe, which are installed in a pipe (for example, a recirculation system pipe) by welding. A sensor housing of the corrosion potential sensor is attached to the measurement seat through an adapter. At this time, the tip of the electrode attached to the insulator is disposed at the position of the inner surface of the pipe. Potential detection portions are formed on the tip and side surfaces of the electrode, respectively. The corrosion potential of the pipe is measured by connecting the lead wire connected to the electrode and arranged in the zirconia insulator and sensor housing, and the wiring connected to the pipe, for example, to an electrometer and connecting the electrode with the electrometer. This is done by measuring the potential difference between the pipes. When the width of the gap between the electrode and the hole formed in the pipe is small, the distance between the side surface of the electrode and the inner surface of the hole is the shortest. ) Are more than power lines (arrows indicated by curves in FIG. 4A) from the tip of the electrode having a long distance to the inner surface of the pipe. For this reason, the measured corrosion potential of the pipe is a mixed potential of the corrosion potential of the inner surface of the hole and the corrosion potential of the inner surface of the pipe, and the contribution of the electrode tip in the measurement of the corrosion potential is smaller than the contribution of the electrode side surface. .

  Therefore, the inventors based on the above power line generation situation, as shown in FIG. 4 (B), the electrode's tip and side surfaces are positioned at substantially equal distances. Other electrodes were arranged so as to face the tip and side surfaces. For convenience, the electrode provided at the tip of the insulator of the corrosion potential sensor is referred to as a first electrode, and the electrode disposed opposite to the first electrode is referred to as a second electrode. The second electrode was attached to the sensor housing of the corrosion potential sensor using a plurality of support bars. The portion of the second electrode facing the side surface of the first electrode and the support rod are disposed between the corrosion potential sensor and the inner surface of the hole formed in the pipe. The corrosion potential sensor shown in FIG. 4B is also attached to the measurement seat via an adapter. In the corrosion potential sensor shown in FIG. 4 (B), the lead wire connected to the first electrode and disposed in the zirconia insulator and the sensor housing, and the wiring connected to the pipe are connected to the electrometer (potential measuring device). Is done. The second electrode is electrically connected to the pipe via a support bar, a sensor housing, an adapter, and a measurement seat.

  The second electrode is made of a metal (for example, SUS316L) made of the same material as the structural member for measuring the corrosion potential, and is in contact with water flowing in the pipe. In the corrosion potential sensor having the second electrode, as shown in FIG. 4B, the power line from the tip and side surfaces of the first electrode to the structural member does not reach the inner surface of the hole formed in the structural member. In order to reach the second electrode close to the first electrode, the electrometer measures the corrosion potential of the second electrode. As a result, in the corrosion potential sensor shown in FIG. 4B, in the measurement of the corrosion potential, the gap formed between the corrosion potential sensor and the inner surface of the hole, that is, the structural member in contact with the reactor water stagnation portion. Since the influence of the corrosion potential in the portion (inner surface of the hole) can be reduced, the contribution of the corrosion potential on the surface of the structural member exposed to the flow of water is increased accordingly.

Therefore, regardless of the wide width gap and the narrow width gap formed between the first electrode of the corrosion potential sensor and the inner surface of the hole portion where the tip of the corrosion potential sensor is inserted. The corrosion potential of the structural member in contact with the flowing water can be accurately measured. In the corrosion potential sensor shown in FIG. 4B, the hole of the structural member into which the tip of the corrosion potential sensor is inserted. The influence of the corrosion potential on the inner surface of the steel can be reduced because the range of potential is extremely limited in the environment of reactor water such as BWR having low conductivity. This will be described in detail with reference to FIG. The characteristic shown in FIG. 5 is that the surface of the specimen of SUS304 stainless steel is formed by depositing a platinum layer by vapor deposition and the remaining part of the surface is left as SUS304 stainless steel. The measurement result of electric potential is shown. The measurement of the corrosion potential distribution shown in FIG. 5 is performed by immersing the test piece in water simulating the BWR reactor water condition at 280 ° C., and placing the corrosion potential sensor along the surface of the test piece on which the platinum layer is formed. I went while scanning.

  Since the water condition in which the test piece was immersed was adjusted so that the stoichiometric ratio of hydrogen to oxygen was 2 or more, the corrosion potential of the platinum layer was −0.4 to −0.3 Vvs. A constant value of SHE was shown. When the corrosion potential sensor is moved along the surface of the test piece from the boundary between the platinum layer and the SUS304 stainless steel on the surface toward the region where the SUS304 stainless steel is exposed, the corrosion potential of the surface gradually increases. On the surface, at a position 12 mm away from the boundary toward the region where the SUS304 stainless steel is exposed, the corrosion potential completely showed the same value as the corrosion potential of SUS304 stainless steel. At this time, the range affected by the corrosion potential of the platinum layer was up to about 5 mm away from the boundary.

  In the region where SUS304 stainless steel is exposed, the region having the same corrosion potential as that of the platinum layer exists in the very vicinity of the boundary. It was found that the corrosion potential of platinum and the corrosion potential of SUS304 stainless steel were mixed in the region where SUS304 stainless steel was exposed between this boundary and a position several mm away from this boundary. From the above, in order to accurately measure the corrosion potential of the surface of the structural member that is in contact with flowing water, the second electrode of the corrosion potential sensor is disposed closer to the first electrode than the inner surface of the hole. I knew I had to.

  Furthermore, in the corrosion potential sensor described in Japanese Patent Application Laid-Open No. 2000-65785, the outer surface of the area where the catalyst (platinum) filled in the ionic conductor made of ceramics contacts, that is, the ionic conductor. The outer surface (the outer surface of the curved surface portion) of the tip portion disposed in the hole portion of the structural member becomes the potential detection portion. Also in such a corrosion potential sensor, the corrosion potential sensor has a curved surface facing the potential detection portion at a predetermined interval away from the potential detection portion formed on the outer surface of the front end portion of the oxygen ion conductor. An electrode may be disposed and the potential detection unit may be covered with the second electrode.

  Examples of the present invention reflecting the above examination results will be described below.

  A corrosion potential sensor according to embodiment 1 which is a preferred embodiment of the present invention will be described with reference to FIGS. The corrosion potential sensor 1 of this embodiment is a silver / silver chloride type corrosion potential sensor having a silver / silver chloride electrode (reference electrode) 7. The corrosion potential sensor 1 has the configuration of a corrosion potential sensor described in Japanese Patent Application Laid-Open No. 2000-146871 and includes a casing 30, a silver / silver chloride electrode 7, a lead wire (conductive wire) 8, and a capture electrode member ( Electrode member) 11 is provided. The casing 30 includes a lid (second insulating member) 2, an insulator (first insulating member) 3, an external sleeve (metal member) 4, and a sensor body (metal member) 5.

The configuration of the casing 30 will be specifically described. A lid 2 made of high purity sapphire is fixed to one end of a cylindrical insulator 3 made of high purity sapphire. The lid 2 is provided with a small diameter portion having a male screw formed on the outer surface, and the male screw of the small diameter portion is engaged with and fixed to a female screw formed on the inner surface of the end portion of the insulator 3. The lid 2 is spot-welded to the insulator 3 at a plurality of locations in the circumferential direction to prevent rotation. One end of a cylindrical outer sleeve 4 made of stainless steel is attached to the outer surface of the insulator 3 via a brazing portion. The outer sleeve 4 surrounds a small diameter portion that is the other end portion of the insulator 3. One end of the stainless steel sensor body 5 is attached to the other end of the stainless steel outer sleeve 4 by brazing. The other end of the sensor body 5 is sealed. The outer sleeve 4 and the sensor body 5 may be integrated as a metal member. A potential detector 27 </ b> A is formed between the lid 2 and the insulator 3 on the outer surface of the casing 30.

  An inner sleeve (blocking member) 6 is attached to the end of the small diameter portion to seal the insulator 3 in a sealed state. The silver / silver chloride electrode 7 is disposed in the insulator 3 and connected to the lead wire 8. A lead wire 8 passes through the inner sleeve 6 and is disposed in the sensor body 5. The lead wire 8 and the inner sleeve 6 are also sealed. A mineral insulated cable 17 attached to the sensor body 5 includes a lead wire 8.

  The capture electrode member 11 includes an electrode portion 10 and a support portion 31 as shown in FIG. The electrode unit 10 includes an electrode plate 28 that is a disk and a plurality of electrode rods 13. Each electrode bar 13 is vertically attached to one surface of the electrode plate 28, and is disposed at a predetermined interval in the circumferential direction of the casing 30. The distance between the electrode bars 13 is smaller than the diameter of the lid 2. The support portion 31 includes a plurality of support rods 12 and a plurality of annular members 14. The annular members 14 are arranged at a predetermined interval in the axial direction of the casing 30 and are connected to each other by the support rods 12 extending in the axial direction of the casing 30. The above-described element members of the electrode member 10 and the support portion 31 are all made of SUS316L steel, which is the same material as the recirculation pipe 18 that is a corrosion potential measurement object for the corrosion potential sensor 1.

  One surface to which each electrode rod 13 of the electrode plate 28 constituting the electrode portion 10 is attached is arranged facing a flat end surface of the lid 2 constituting the tip portion of the casing 30 at a predetermined interval. The electrode bars 13 are arranged on the side surface of the lid 2 so as to face each other at a predetermined interval, and face the annular potential detection unit 27A. A support portion 31 is attached to the electrode portion 10. Of the annular member 14 constituting the support portion 31, the annular member 14 disposed at a position closest to the electrode plate 28 is attached to the upper end of each electrode rod 13 by welding. Each support bar 12 is joined to the outer surface of the outer sleeve 4 by welding. The distance between the electrode plate 28 and the end surface of the lid 2 and the distance between each electrode bar 13 and the side surface of the lid 2 are equal.

  Each support rod 12 and each annular member 14 surround the insulator 3 at a position away from the outer surface of the insulator 3. The electrode unit 10 covers the front end surface and the side surface of the lid 2 that is the front end portion of the casing 30.

  A zirconia film, which is an insulating film, is formed on the surface of each support rod 12 and each annular member 14 of the support portion 31 by a plasma coating method. Instead of the zirconia film, an alumina, sapphire or diamond film may be formed. The metal surfaces of the electrode plate 28 and each electrode rod 13 constituting the electrode unit 10 are exposed.

  In order to make the exposed metal surface of the electrode part 10 the same as the inner surface of the recirculation system pipe 18 that is the object of corrosion potential measurement, which is in contact with the reactor water, the furnace surface of the boiling water nuclear power plant is previously formed on the exposed metal surface. A pre-oxidation treatment is performed in which simulated water having a dissolved oxygen concentration of 300 ppb simulating water is brought into contact with 500 hours or more. By this treatment, an oxide film is formed in advance on the exposed metal surfaces of the electrode portion 10 and the support rods 12 and 13.

  The installation structure of the corrosion potential sensor 1 in a nuclear power plant is as follows. The corrosion potential sensor 1 is attached to, for example, a cylindrical measurement seat (support seat) 19 attached by welding to a recirculation system pipe 18 connected to a nuclear reactor of a boiling water nuclear power plant. The corrosion potential sensor 1 is inserted into the measurement seat 19, and the sensor body 5 of the corrosion potential sensor 1 passes through the adapter 20 attached to one end of the measurement seat 19 and is attached to the adapter 20 by welding. It is done. In this state, the tip of the lid 2 of the corrosion potential sensor 1 is disposed on the inner surface of the recirculation system pipe 18 in the radial direction of the recirculation system pipe 18. A wiring (conductive wire) 16 connected to the lead wire 8 is connected to a potentiometer (potential difference measuring device) 15. A wiring (conductive wire) 17 connected to the potentiometer 15 is connected to the recirculation piping 18.

  With the corrosion potential sensor 1 attached to the recirculation system pipe 18, the tip of the corrosion potential sensor 1 (the portion of the lid 2) is disposed in a hole formed in the recirculation system pipe 18. An annular gap 21 is formed between the corrosion potential sensor 1 and the measurement seat 19 and between the tip of the corrosion potential sensor 1 and a hole formed in the recirculation system pipe 18.

  The corrosion potential measuring device connects the corrosion potential sensor 1, the potentiometer 15, the wiring 16 connecting the lead wire 8 and the potentiometer 15, and the corrosion potential measurement object (for example, the recirculation system pipe 18) and the potentiometer 15. Wiring 17 is provided.

  By driving a recirculation pump provided in the recirculation system pipe 18, the reactor water in the reactor is sucked up and pressurized, and led to a jet pump arranged in the reactor and cored in the reactor vessel. To be supplied. Reactor water flowing in the recirculation system pipe 18 is in contact with the inner surface of the recirculation system pipe 18 and is opposite to the plane of the electrode plate 28 facing the plane of the tip of the lid 2 of the electrode plate 28. Touch the plane. Further, the reactor water is disposed in the circumferential direction of the electrode plate 28 and passes between adjacent electrode rods 13, and passes between the plane of the tip of the lid 2 and the plane of the electrode plate 28 facing this plane. Flow and touch both planes. Reactor water is also present in the gap 21. An opening through which reactor water flows is formed between the adjacent electrode rods 13.

  The corrosion potential sensor 1 measures the corrosion potential of the recirculation piping 18 as follows. When the boiling water nuclear power plant is operated with the corrosion potential sensor 1 attached to the recirculation system pipe 18 as described above, the reactor water flowing in the recirculation system pipe 18 is formed in the lid 2. It penetrates into the area | region in which the silver / silver chloride electrode 7 in the insulator 3 is arrange | positioned through the clearance gap between the female screw and the female screw formed in the insulator 3. For this reason, the silver / silver chloride electrode 7 is immersed in the reactor water in the insulator 3. Since the inner sleeve 6 seals the end portion of the insulator 3 on the side of the mineral insulated cable 17, it is possible to prevent the reactor water that has entered the insulator 3 from coming into contact with the mineral insulated cable 17.

  The electric potential detector 27A formed on the outer surface of the casing 30 is silver through the water present in the gap between the male screw formed on the lid 2 and the female screw formed on the insulator 3, and the water in the insulator 3. / Electrically connected to the silver chloride electrode 7. The potential detection unit 27 </ b> A is also electrically connected to the electrode unit 10 through the reactor water flowing between the lid 2 and the electrode unit 10.

  In this embodiment, the silver / silver chloride electrode 7 serves as a reference electrode, and the potential difference between the potential detection unit 27A and the electrode unit 10 is measured by the potentiometer 15. The potentiometer 15 is electrically connected to the electrode portion 10 by a wiring 17, a recirculation pipe 18, an adapter 20, a sensor body 5 and a support rod 12, and further, a wiring 16, a lead wire 8, a silver / silver chloride electrode 7. In addition, the reactor water that has entered the insulator 3 and the water present in the gap between the male screw formed on the lid 2 and the female screw formed on the insulator 3 are electrically connected to the potential detector 27A. . Furthermore, the electric potential detection unit 27A and the electrode unit 10, specifically, the electric potential detection unit 27A and each electrode bar 13 are electrically connected through the reactor water existing between them. Therefore, a power line is generated between the potential detection unit 27A and the electrode unit 10, and the potential difference between the potential detection unit 27A and the electrode unit 10 whose material is the same as that of the recirculation pipe 18 is measured by the potentiometer 15. The Based on the measured potential difference, the corrosion potential of the recirculation pipe 18 is obtained.

According to the corrosion potential line sensor 1 of the present embodiment, the conductor closest to the potential detection unit 27A is not the recirculation piping 18 but the electrode portion 10 made of the same material as the recirculation piping 18. For this reason, the potentiometer 15 is not the corrosion potential of the inner surface of the hole formed in the recirculation pipe 18 and into which the tip of the corrosion potential sensor 1 is inserted, but closer to the potential detection unit 27A than the inner surface. The corrosion potential of the electrode part 10 made of the same material as that of the recirculation pipe 18 is measured. Therefore, the corrosion potential sensor 1 can reduce the influence of the gap in which the reactor water stagnate regardless of the width of the gap 21, and corrodes the inner surface of the recirculation pipe 18 that contacts the flowing reactor water. The potential can be measured with high accuracy. In particular, reactor water flowing through the recirculation pipe 18 is, as mentioned above, since the flow through the plurality of openings formed in the electrode portions 10 (the gap between the mutually adjacent electrode rod 13), potential detection Part 27A is exposed to the flowing reactor water. Since the reactor water existing between the potential detection unit 27 and the electrode unit 10 is in a flowing state and does not stagnate, the corrosion potential of the electrode unit 10 indicating the corrosion potential of the recirculation pipe 18 is accurately measured. be able to.

  In this embodiment, since the capture electrode member 11, that is, the electrode portion 10 surrounds the lid 2, even if the lid 2 falls off the insulator 3 for some reason, the fallen lid 2 is removed by the capture electrode member 11. Can be captured. Therefore, it is possible to prevent the dropped lid 2 from being carried along the flow of the reactor water flowing in the recirculation pipe 18. Even when the insulator 3 is detached from the outer sleeve 4, the detached outer sleeve 4 can be captured by the capture electrode member 11.

  In this embodiment, since the electrode unit 10 facing the lid 2 is used as a potential detection unit capturing unit that captures the dropped lid 2, the electrode unit 10 and the potential detection unit capturing unit are provided separately. The configuration of the corrosion potential sensor 1 can be simplified. Further, since the configuration of the potential detection unit capturing means is used as a part of the electrical circuit for measuring the potential difference between the potential detection unit 27A and the electrode unit 10, the configuration of the electrical circuit connecting the electrode unit 10 and the potentiometer 15 Can be simplified.

  Since the plurality of electrode rods 13 arranged so as to form a gap between the capture electrode member 11 are used, the reactor water can be easily supplied between the lid 2 and the electrode portion 10. Moreover, since each surface of each support rod 12 and each annular member 14 is covered with a zirconia film, the support portion 31 can be used as a part of an electric circuit connecting the electrode portion 10 and the potentiometer 15. .

  By forming a part of the end face of the insulator 3 of the corrosion potential sensor 1 of this embodiment so as to face the electrode plate 28, it is formed on the outer surface of the casing 30 between the insulator 3 and the lid 2. It is also possible to make the potential detector 27A face the electrode plate 28.

  The corrosion potential sensor 1 of the present embodiment is installed in other piping of the boiling water nuclear power plant (for example, reactor purification system piping, drain piping connected to the bottom of the reactor, water supply piping, etc.) and the corresponding piping. It can be used to measure the corrosion potential. Furthermore, it can also be used for measuring the corrosion potential of pipes and the like in pressurized water nuclear plants and thermal power plants.

  A corrosion potential sensor according to embodiment 2, which is another embodiment of the present invention, will be described with reference to FIG. The corrosion potential sensor 1A of the present embodiment has the configuration of a corrosion potential sensor described in Japanese Patent Application Laid-Open No. 2009-42111, and includes a casing 30A, a capture electrode member 11, and a lead wire 8. A casing 30 </ b> A used in this embodiment includes an electrode 29, an insulator 3, an external sleeve 4, and a sensor body 5. The casing 30A has a configuration in which the silver / silver chloride electrode 7 is deleted from the casing 30 used in the first embodiment and the lid 2 is replaced with an electrode 29 made of zirconium.

  The reference electrode 29 is attached to the end of the insulator 3 and seals the insulator 3. Lead wire 8 is connected to electrode 29. Other configurations of the corrosion potential sensor 1A of the present embodiment are the same as those of the corrosion potential sensor 1. Similarly to the corrosion potential sensor 1, the corrosion potential sensor 1 </ b> A of the present embodiment is attached to the measurement seat 19 of the recirculation pipe 18 and is disposed in the measurement seat 19. In the present embodiment, the outer surface of the electrode 29 becomes the potential detection unit 27B. The electrode plate 28 of the electrode unit 10 is disposed at a predetermined interval from the end surface of the electrode 29, and each electrode bar 13 is disposed at a predetermined interval from the side surface of the electrode 29. The electrode plate 28 and each electrode bar 13 of the electrode unit 10 are opposed to the potential detection unit 27B.

  Since this embodiment also includes the capture electrode member 11 as in the first embodiment, each effect produced in the first embodiment can be obtained. The capture electrode member 11 captures the electrode 29 dropped from the insulator 3 in the same manner as the lid 2 dropped in the first embodiment. Furthermore, the capture electrode member 11 can also capture the insulator 3 and the electrode 29 that have fallen from the external sleeve 4.

  A corrosion potential sensor according to embodiment 3, which is another embodiment of the present invention, will be described with reference to FIGS. The corrosion potential sensor 1B of the present embodiment has the configuration of a corrosion potential sensor disclosed in Japanese Patent Laid-Open No. 2000-65785, and includes a casing 30B, a lead wire 8, and a capture electrode member 11A. The casing 30 </ b> B used in this embodiment includes an electrode, an insulator 3 </ b> A, and a sensor body 5.

  The insulator 3A is made of zirconium oxide (zirconia), and has a tubular shape (test tubular shape) in which one end is opened and the other end is closed. The insulator 3A acts as a solid electrolyte for oxygen ions, and an equilibrium is established between the outside and the inside of the corrosion potential sensor 1B via the oxygen ions. The open end of the insulator 3A is inserted into the sensor body 5 and joined to the sensor body 5 by brazing. The electrode that generates the reference potential of the corrosion potential sensor 1 </ b> B includes a platinum powder 23, a silver wire 24, and a silver oxide powder 25. The platinum powder 23, the silver wire 24, and the silver oxide powder 25 are disposed in the insulator 3A that is closed at one end, and the platinum powder 23 is disposed at the closed end of the insulator 3A to fill the silver oxide powder 25. A layer is placed next to the packed bed of platinum powder 23.

  The silver oxide powder 25 is used to keep the oxygen partial pressure constant in the corrosion potential sensor 1A. Part of silver oxide decomposes into silver and oxygen at high temperatures. Since the volume in the corrosion potential sensor 1B is constant, the reaction in which silver and oxygen are combined to form silver oxide at a certain partial pressure of oxygen is balanced at a non-negligible rate. As a result, silver oxide, silver and oxygen are equilibrated at the operating temperature and the oxygen partial pressure is kept constant. Such an action of making the oxygen partial pressure constant can be obtained by a combination of a metal oxide such as nickel / nickel oxide, iron / iron oxide, mercury / mercury oxide and the like in addition to silver oxide. A system having a high oxygen partial pressure is preferable, but if it is easily decomposed, the corrosion potential sensor becomes unstable.

  In addition, the platinum powder 23 has a catalytic action in which oxygen ions that have entered the corrosion potential sensor 1A through the insulator 3A quickly obtain electrons to become oxygen ions, and react the oxygen ions and electrons to generate a current at that position. It is responsible for collecting current.

  Each filled layer of the platinum powder 23 and the silver oxide powder 25 is in contact with the inner surface of the insulator 3A. The outer surface of the distal end portion of the insulator 3A where the filling portion of the platinum powder 23 is located has a curved surface and has a hemispherical shape. The open end of the insulator 3A is sealed by a sapphire piston (blocking member) 26 inserted into the insulator 3A. The sapphire piston 26 is fixed to the insulator 3 </ b> A and holds a packed layer of platinum powder 23 and a packed layer of silver oxide powder 25. The silver wire 24 is disposed in a packed layer of silver oxide powder 25. The lead wire 8 that passes through the sapphire piston 26 and reaches the packed layer of the silver oxide powder 25 is connected to the silver wire 24. Similar to the first embodiment, the mineral insulated cable 17 attached to the sensor body 5 includes a lead wire 8.

  The potential detection unit 27C in the present embodiment is an outer surface of the insulator 3A facing the inner surface of the insulator 3A with which the filling portion of the platinum powder 23 comes into contact, and includes a hemispherical surface that is an outer surface of the tip portion described above. Yes.

  The capture electrode member 11A includes an electrode portion 10A and a support portion 31 as shown in FIG. The electrode portion 10 </ b> A includes a wire mesh electrode 22. The support portion 31 includes a plurality of support rods 12 and a plurality of annular members 14 as in the first embodiment. The electrode 22, each support rod 12, and each annular member 14 are made of SUS316L steel, which is the same material as the recirculation pipe 18 that is a corrosion potential measurement object for the corrosion potential sensor 1B. The wire mesh electrode 22 has a hemispherical shape similar to the tip of the insulator 3A (potential detector 27C), and covers the tip of the insulator 3A. For this reason, the dimension between the outer surface of the front-end | tip part of 3 A of insulators and the electrode 22 is equal over the whole front-end | tip part of 3 A of insulators.

  The electrode 22 has a metal surface exposed. A zirconia film is formed on the entire surface of the support portion 31 by a plasma coating method.

  In order to make the exposed metal surface of the electrode 22 the same as the inner surface of the recirculation system pipe 18 that is the object of corrosion potential measurement that is in contact with the reactor water, the exposed metal surface is preliminarily provided with a furnace of a boiling water nuclear power plant. A pre-oxidation treatment is performed in which simulated water having a dissolved oxygen concentration of 300 ppb simulating water is brought into contact with 500 hours or more. By this treatment, an oxide film is formed in advance on the metal exposed surface of the electrode 22.

  The installation structure of the corrosion potential sensor 1B in the nuclear power plant in the present embodiment will be described. In the installation structure of this embodiment, the sensor body 5 of the corrosion potential sensor 1B is attached to the measurement seat 19 attached to the recirculation system pipe 18 via the adapter 20 as in the first embodiment. The corrosion potential sensor 1B is inserted into the measurement seat 19, and the tip of the corrosion potential sensor 1B, that is, the tip of the insulator 3A (portion that is a hemispherical surface) is formed in the recirculation system pipe 18. The tip of the insulator 3 </ b> A (the apex of the hemispherical surface portion) is disposed at the position of the inner surface of the recirculation system pipe 18 in the radial direction of the recirculation system pipe 18. As in the first embodiment, the lead wire 8 is connected to the potentiometer 15 by the wiring 16, and the wiring 17 connected to the recirculation system pipe 18 is also connected to the potentiometer 15.

  As in the first embodiment, the electrode 22 is disposed in an annular gap 21 formed between the insulator 3A as a potential detection unit and the inner surface of the hole formed in the recirculation system pipe 18, It is arranged closer to the insulator 3A than the inner surface of the hole.

  Such a present Example can also obtain each effect which arises in Example 1. FIG.

  In the same manner as in Example 1, Examples 2 and 3 are also installed in other piping of the boiling water nuclear power plant (for example, reactor purification system piping, drain piping connected to the bottom of the reactor, water supply piping, etc.). Can be used to measure the corrosion potential of the corresponding pipes, and can also be used to measure the corrosion potential of pipes in pressurized water nuclear plants and thermal power plants.

  DESCRIPTION OF SYMBOLS 1,1A, 1B ... Corrosion potential sensor, 2 ... Cover, 3, 3A ... Insulator, 4 ... External sleeve, 5 ... Sensor body, 6 ... Internal sleeve, 7 ... Silver / silver chloride electrode, 8 ... Lead wire, 10 , 10A ... electrode part, 11, 11A ... capture electrode member, 12 ... support rod, 13 ... electrode rod, 14 ... annular member, 15 ... potentiometer, 16, 17 ... wiring, 18 ... recirculation piping, 19 ... Measurement seat, 21 ... gap, 22, 29 ... electrode, 23 ... platinum powder, 24 ... silver wire, 25 ... silver oxide powder, 27A, 27B, 27C ... potential detection unit, 28 ... electrode plate, 30, 30A, 30B ... casing, 31 ... support part.

Claims (7)

A reference electrode disposed in one of a casing, a space formed in the casing, and an end portion of the casing as a part of the casing; a first conductor connected to the reference electrode; A potential detection unit formed on the outer surface of the casing; and an electrode member disposed outside the casing so as to face the potential detection unit in a state of being separated from the outer surface of the casing.
The casing has a cylindrical metal member and an insulating member that is attached to the metal member and disposed at least between the potential detection unit and the metal member, and the electrode member is attached to the metal member, When the casing is attached to the corrosion potential measurement object, the plurality of openings formed in the electrode member are arranged so that water that contacts the surface of the corrosion potential measurement object passes, and the potential detection of the electrode member A portion facing the portion is made of the same material as the object for measuring corrosion potential , a potentiometer is connected to the first conductor outside the casing, and a second conductor connected to the object for measuring corrosion potential is A corrosion potential sensor connected to the potentiometer .   2. The capture electrode member according to claim 1, wherein the electrode member is a capture electrode member that covers a tip portion including the potential detection portion of the casing on the insulating member side from an attachment portion of the insulating member to the metal member. Corrosion potential sensor. The casing is attached to an end portion of the first insulating member together with the metal member and the first insulating member which is the insulating member to form the potential detecting unit between the casing and the first insulating member. Has an insulating member,
A reference electrode is disposed in the first insulating member;
A sealing member for sealing a region in the first insulating member in which the reference electrode is disposed is disposed in the metal member and attached to the first insulating member;
The corrosion potential sensor according to claim 2, wherein the first conductive wire connected to the reference electrode reaches the outside of the metal member through the sealing member.   The casing has a reference electrode attached to an end of the insulating member together with the metal member and the insulating member to seal the insulating member, and an outer surface serving as the potential detection unit. The corrosion potential sensor according to claim 2, wherein the connected first conducting wire is disposed in the insulating member and in the metal member and reaches the outside of the metal member. The capture electrode member has an electrode part covering a tip part including the potential detection part, and a support part for attaching the electrode part to the metal member, and an insulating film is formed on the surface of the support part The corrosion potential sensor according to any one of claims 2 to 4 . The corrosion potential sensor according to claim 5 , wherein the insulating coating is formed of at least one material selected from zirconia, alumina, sapphire, and diamond. Disposed corrosion potential sensor according to any one of claims 1 to 5, of the plant, the corrosion potential measured object placed on the structural member is a cylindrical attached to the support seat and the support seat in Has been
The tip of the portion of the casing located in the support seat is disposed at a surface position in contact with water of the structural member in the axial direction of the corrosion potential sensor.
In the state where the tip portion of the casing located in the support seat is inserted into the hole formed in the structural member, the electrode member is located in the center of the corrosion potential sensor rather than the inner surface of the hole. Corrosion potential sensor installation structure characterized by being arranged on the shaft side.

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