Corrosion potential sensor

Abstract

To provide a corrosion potential sensor capable of achieving further extended service life by removing the oxide layer through pickling.SOLUTION: A disclosed corrosion potential sensor 10 includes: a first electrode part 1 having a cylindrical shape; a second electrode part 2 having a cylindrical shape with a base, which is connected to the first electrode part 1 with the first electrode part 1 overlapped on the outside; a conductor 3 with the second electrode part 2 overlapped and connected to the second electrode part 2 on the outside extending a part of the second electrode part 2 through opening 5; and an insulation body 4 with the conductor 3 extending thereinside from the opening 5 of the second electrode part 2. A joint 6 fixing the first electrode part 1 and the second electrode part 2 is located on the tip side of the corrosion potential sensor 10 than the opening 5 of the second electrode part 2.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electrochemical corrosion potential sensor. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a corrosion potential sensor that uses a zirconium electrode to measure the corrosion potential of a metal material in contact with reactor water is known (see, for example, Patent Document 1). This corrosion potential sensor is configured so that a metal cap made of zirconium, which serves as the electrode, covers the brazed portion between an electrode fixing body made of an alloy of iron and nickel, or the like, and a tubular insulator made of zirconia, sapphire, or the like. According to such an electrochemical corrosion potential sensor, the reactor water in contact with the brazed portion can be stagnated to reduce the dissolved oxygen concentration, thereby suppressing corrosion of the brazed portion and extending the life of the electrochemical corrosion potential sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5002606 Summary of the Invention [Problem to be solved by the invention]

[0004] When a zirconium electrode is brazed or welded in the atmosphere, an oxide layer containing zirconium nitride, zirconium oxide, etc. is formed on the heated electrode surface. If such an oxide layer could be removed from the brazed portion of a conventional electrochemical corrosion potential sensor (see, for example, Patent Document 1) by pickling or the like, the electrochemical corrosion potential sensor could be expected to have a longer life. However, in the conventional electrochemical corrosion potential sensor, since the joint is formed near the opening of the metal cap, there is a risk that the acid solution during pickling may penetrate into the inside of the electrochemical corrosion potential sensor through the opening of the metal cap. Therefore, it is difficult to further extend the service life of the conventional electrochemical corrosion potential sensor by removing the oxide layer formed at the joint by pickling.

[0005] An object of the present invention is to provide an electrochemical corrosion potential sensor capable of achieving a longer service life by removing an oxide layer through pickling. [Means for solving the problem]

[0006] The electrochemical corrosion potential sensor of the present invention comprises a cylindrical first electrode portion, a bottomed cylindrical second electrode portion connected to the first electrode portion and overlapping with the first electrode portion so that the first electrode portion is on the outside, a conductor connected to the second electrode portion and overlapping with the second electrode portion so that the second electrode portion is on the outside and having a portion extending from an opening of the second electrode portion, and an insulator through which the conductor extending from the opening of the second electrode portion passes, and is characterized in that a joint fixing the first electrode portion and the second electrode portion is located toward the tip of the electrochemical corrosion potential sensor relative to the opening of the second electrode portion. Effect of the Invention

[0007] According to the present invention, it is possible to provide an electrochemical corrosion potential sensor capable of achieving a further extension of its life by removing the oxide layer by pickling. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a configuration explanatory diagram of an electrochemical corrosion potential sensor according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a partially enlarged view of part II in FIG. [Figure 3A] 3 is a cross-sectional view taken along line IIIA-IIIA in FIG. 2 at a joint between a first electrode portion and a second electrode portion which constitute the electrochemical corrosion potential sensor of the first embodiment. [Figure 3B] FIG. 3B is a cross-sectional view showing a first modified example of the joint portion of FIG. 3A. [Figure 3C]FIG. 3B is a cross-sectional view showing a second modified example of the joint in FIG. 3A. [Figure 4] 4 is a diagram showing a state of pickling applied to the electrochemical corrosion potential sensor according to the first embodiment. FIG. [Diagram 5] 1 is a configuration explanatory diagram of a boiling water reactor plant in which an electrochemical corrosion potential sensor according to a first embodiment is installed; [Figure 6] 6 is a schematic diagram showing an electrochemical corrosion potential sensor according to a first embodiment installed in a recirculation system pipe in the boiling water reactor plant of FIG. 5. FIG. [Figure 7] FIG. 5 is a configuration explanatory diagram of an electrochemical corrosion potential sensor according to a second embodiment of the present invention. [Figure 8] FIG. 11 is a configuration explanatory diagram of an electrochemical corrosion potential sensor according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the electrochemical corrosion potential sensor of the present invention will be described in detail with reference to the accompanying drawings. First Embodiment Fig. 1 is a diagram illustrating the configuration of an electrochemical corrosion potential sensor 10 according to the present embodiment. Fig. 2 is a partially enlarged view of part II in Fig. 1.

[0010] As shown in Fig. 1, the electrochemical corrosion potential sensor 10 includes an electrode 11, a conductor 3, an insulator 4, a metal housing 12, and a conducting wire 22. In Fig. 1, reference numeral 13 denotes a mineral insulated cable (MI (Mineral Insulated) cable). Reference numeral H1 denotes a hollow portion of the insulator 4, and reference numeral H2 denotes a hollow portion of the metal housing 12. Reference numeral 3b denotes a core wire constituting the conductor 3.

[0011] 2, the electrode 11 has a first electrode part 1 and a second electrode part 2. The first electrode part 1 and the second electrode part 2 are made of metallic zirconium. In this embodiment, the first electrode portion 1 is formed in a cylindrical shape. Specifically, the first electrode portion 1 has a cylindrical shape that is open at both ends. The inner diameter of the opening 1a on one end side of the first electrode unit 1 is larger than the inner diameter of the opening 1b on the other end side. A second electrode 2 is inserted through an opening 1a into the inside of the first electrode 1. An insulator 4 is inserted through an opening 1b.

[0012] The second electrode unit 2 is formed in a cylindrical shape with a bottom. Specifically, the second electrode unit 2 has a cylindrical main body 2a that is fitted into the first electrode unit 1, and a flange portion 2b that contacts an end face on one end side of the first electrode unit 1. The main body portion 2 a has an opening 5 on the side facing the opening 1 b of the first electrode portion 1 . Further, an internal thread 2a1 is formed on the inner peripheral surface of the main body 2a. An external thread 3a1 of the conductor 3, which will be described later, is engaged with the internal thread 2a1. The flange portion 2b is integrated with the main body portion 2a to form the bottom of the second electrode portion 2 so as to close the opening on one end side of the main body portion 2a. The flange portion 2b is formed in a disk shape having an outer diameter equal to the outer diameter of the first electrode portion 1. As a result, the outer peripheral surface of the flange portion 2b and the outer peripheral surface of the first electrode portion 1 are flush with each other in the axial direction.

[0013] The conductor 3 has a conductor body 3a and a core wire 3b. The conductor body 3a is formed in a substantially cylindrical shape. A male thread 3a1 that meshes with the female thread 2a1 of the second electrode portion 2 is formed on the outer circumferential surface of the conductor body 3a. In this embodiment, the nominal diameter of the male thread 3a1 is larger than the inner diameter of the opening 1b of the first electrode portion 1. The conductor body 3a has the male thread 3a1 meshed with the female thread 2a1, so that most of the conductor body 3a is disposed inside the second electrode portion 2. That is, the second electrode portion 2 and the conductor 3 are screwed together by a male thread 3a1 and a female thread 2a1. Moreover, the conductor body 3a has, on the side facing the opening 1b of the first electrode portion 1, a recess 3c into which one end of an insulator 4, which will be described later, is fitted. The core wire 3b is formed so as to extend from the conductor body 3a. Specifically, the core wire 3b extends in a direction away from the conductor body 3a at the center of the recess 3c of the conductor body 3a.

[0014] In this embodiment, the conductor 3 (conductor body 3a) is assumed to have a contact portion 3d with the insulator 4 formed of an FeNi alloy or an FeNiCo alloy, as shown by the imaginary line (double-dashed line) in Fig. 1. In such a conductor 3, the portions other than the contact portion 3d, including the core wire 3b, may be made of other metals, such as nickel, stainless steel, etc. The contact portion 3d with the insulator 4 and the portion other than the contact portion 3d are integrally joined by brazing or welding with silver or the like to form the conductor 3. As an example of such a joint, as shown in Fig. 2, the part 3e of the conductor body 3a outside the long dashed line can be made of an FeNi alloy and can be a threaded part that meshes with the female thread 2a1. The part 3f of the conductor body 3a inside the long dashed line and the core wire 3b can be a single nickel wire 3g. The nickel wire 3g (inner part 3f) is inserted into a hole (not shown) drilled in the axial direction in the center of the threaded part that is the outer part 3e. The conductor 3 is formed by joining the outer part 3e and the inner part 3f by brazing at a joint point 3h on the sensor tip side indicated by a short dashed line. The conductor 3 may have the contact portion 3d entirely made of an FeNi alloy or an FeNiCo alloy.

[0015] The insulator 4 is formed in a substantially cylindrical shape. The core wire 3b of the conductor 3 is inserted into the hollow portion H1 of the insulator 4. The insulator 4 has a small diameter portion 4b connected to the conductor body 3a and a large diameter portion 4a having an outer diameter larger than that of the small diameter portion 4b. The outer diameter of the large diameter portion 4a is slightly smaller than the inner diameter of the opening 1b of the first electrode portion 1. In this embodiment, the insulator 4 is preferably made of stabilized zirconia or sapphire, although the material of the insulator 4 is not limited to these.

[0016] The outer peripheral surface of the tip of the small diameter portion 4b (one end of the insulator 4) is metallized. For the metallization, it is preferable to use at least one metal selected from tungsten, titanium, molybdenum, and manganese. Among them, a tungsten layer, a titanium layer, and a molybdenum-manganese layer are preferable as the metallization layer. The tip of the small diameter portion 4b is fitted into the recess 3c of the conductor body 3a and joined to the conductor body 3a by brazing or the like in a state in which the metallized layer is in contact with the conductor body 3a.

[0017] Returning to FIG. 1, the other end of the insulator 4 is connected to one end of a metal housing 12 . The metal housing 12 has a cylindrical shape with a larger diameter than the large diameter portion 4a (see FIG. 2) of the insulator 4. The metal housing 12 also has a hollow portion H2 that passes through the metal housing 12 in the longitudinal direction so as to communicate with the hollow portion H1 of the insulator 4.

[0018] Although not shown, the metal casing 12 in this embodiment is assumed to have a portion in contact with the insulator 4 made of an FeNi alloy or an FeNiCo alloy. The portions of the metal casing 12 other than the portion in contact with the insulator 4 can be made of other metals such as nickel, stainless steel, etc. The portion of the metal casing 12 made of an FeNi alloy or an FeNiCo alloy and the portion made of other metals such as nickel, stainless steel, etc. can be joined together by brazing with silver or the like.

[0019] In such a metal casing 12, at least the portion in contact with the insulator 4 needs to be made of an FeNi alloy or an FeNiCo alloy, and the entire metal casing 12 may be made of an FeNi alloy or an FeNiCo alloy.

[0020] In addition, it is preferable that a metallization treatment is applied to the bonding surface of the insulator 4 to the metal housing 12. At least one metal selected from tungsten, titanium, molybdenum, and manganese is preferably used for the metallization treatment. Among them, a tungsten layer, a titanium layer, and a molybdenum-manganese layer are preferable as the metallization treatment layer.

[0021] The core wire 3b extending from the insulator 4 side is inserted into the hollow portion H2 of the metal casing 12. In the hollow portion H2 at the other end of the metal housing 12, the core wire 3b of the conductor 3 is electrically connected to the conductor wire 22. The connection end of the conductor wire 22 to the core wire 3b is supported on the other end of the metal housing 12 by being inserted into the mineral insulated cable 13 fitted into the hollow portion H2. In other words, the mineral insulated cable 13 constitutes an extraction portion of the conductor wire 22.

[0022] The electrochemical corrosion potential sensor 10 as described above can be assembled, for example, in the following manner. The method of assembling the electrochemical corrosion potential sensor 10 will be described with reference to FIGS. 2, first, the conductor body 3a of the conductor 3 is placed in the second electrode portion 2 through the opening 5 of the second electrode portion 2. Specifically, the male thread 3a1 of the conductor body 3a is engaged with the female thread 2a1 of the second electrode portion 2, and the conductor body 3a is placed inside the second electrode portion 2. As a result, the second electrode portion 2 is placed so as to overlap the outside of the conductor body 3a of the conductor 3.

[0023] Next, in this assembly method, one end side of the insulator 4 is fitted into the recess 3c of the conductor 3 (conductor body 3a) fixed to the second electrode portion 2. At this time, the core wire 3b of the conductor 3 is inserted into the hollow portion H1 of the insulator 4. Then, the conductor body 3a of the conductor 3 and the one end side of the insulator 4 are connected by brazing or the like.

[0024] Next, in this assembly method, the insulator 4 is inserted from the opening 1a side to the opening 1b side of the first electrode portion 1, and the large diameter portion 4a of the insulator 4 is pulled out to the outside of the first electrode portion 1. The main body portion 2a of the second electrode portion 2, which is connected to the insulator 4 via the conductor main body 3a of the conductor 3, is fitted into the inside of the first electrode portion 1 from the opening 1a of the first electrode portion 1. As a result, the first electrode portion 1 is arranged so as to overlap the outside of the main body portion 2a of the second electrode portion 2. When the second electrode portion 2 is attached to the first electrode portion 1 in this manner, the first electrode portion 1 and the second electrode portion 2 are not yet fixed to each other.

[0025] Next, in this assembly method, one end of the metal housing 12 is connected to the other end of the insulator 4 by brazing or the like, as shown in Fig. 1. At this time, the core wire 3b of the conductor 3 is inserted into the hollow portion H2 of the insulator 4, and the tip of the core wire 3b is electrically connected to one end of the conductor 22. One end side of the conductor 22 is supported on the other end side of the metal housing 12 by a mineral insulated cable 13 fitted into the hollow portion H2. Although not shown in Fig. 1, the other end side of the conductor 22 is connected to an electrometer 27 (see Fig. 6) described later.

[0026] Next, in this assembly method, the flange portion 2b of the second electrode portion 2 and the first electrode portion 1 are joined by welding, as shown in Fig. 2. As a result, a joint 6 (welded portion) is formed in the electrochemical corrosion potential sensor 10. Specifically, the joint 6 is formed on a side surface of the electrochemical corrosion potential sensor 10 on the tip side of the electrochemical corrosion potential sensor 10. That is, the joint 6 is formed at a position farther from the opening 5 of the second electrode portion 2 on the tip side of the electrochemical corrosion potential sensor 10.

[0027] FIG. 3A is a cross-sectional view taken along line IIIA-IIIA in FIG. 3A, the joint 6 (welded portion) in this embodiment is formed around the entire circumference of the electrochemical corrosion potential sensor 10 along the flange portion 2b on the radial outside of the main body 2a of the second electrode 2. That is, the joint 6 (welded portion) is formed in a continuous ring shape in the circumferential direction of the electrochemical corrosion potential sensor 10.

[0028] Fig. 3B is a cross-sectional view showing a first modified example of the joint 6 in Fig. 3A. Fig. 3C is a cross-sectional view showing a second modified example of the joint 6 in Fig. 3A. The joint 6 shown in Figs. 3B and 3C is shown in a cross section corresponding to the IIIA-IIIA cross section in Fig. 2. As shown in FIG. 3B, the joints 6 (welded parts) of the first modified example are formed on the radial outside of the main body 2a of the second electrode portion 2 at two locations 180 degrees apart in the circumferential direction of the flange portion 2b. As shown in FIG. 3C, the joints 6 (welded parts) of the second modified example are formed on the radial outside of the main body 2a of the second electrode portion 2 at four locations spaced 90 degrees apart in the circumferential direction of the flange portion 2b. In this embodiment, the joints 6 (welded parts) may be any joints that join the first electrode 1 and the second electrode 2 at the tip side of the electrochemical corrosion potential sensor 10 as shown in Fig. 2, and there is no limit to the number of joints 6. However, it is preferable that the joints 6 (welded parts) are continuous in the circumferential direction of the electrochemical corrosion potential sensor 10 as shown in Fig. 3A, or are composed of spot welds arranged at two or more places in the circumferential direction of the electrochemical corrosion potential sensor 10 as shown in Figs. 3B and 3C.

[0029] Next, in this assembly method, the electrochemical corrosion potential sensor 10 (see FIG. 1) is subjected to an acid cleaning treatment. FIG. 4 is a diagram showing the state of pickling performed on the electrochemical corrosion potential sensor 10. As shown in FIG. 4, in this pickling treatment step, the joint 6 (welded portion) of the electrochemical corrosion potential sensor 10 is immersed in an acid pickling bath 7. Specifically, only the tip of the electrochemical corrosion potential sensor 10, which serves as an etching target region 8 having an oxide layer (not shown) formed near the joint 6 by heating during welding of the electrochemical corrosion potential sensor 10, is immersed in the acid pickling bath 7. In other words, the tip of the electrochemical corrosion potential sensor 10 is immersed in the acid pickling bath 7 so that the liquid level of the acid pickling bath 7 is below the opening 5 of the second electrode portion 2.

[0030] After the electrochemical corrosion potential sensor 10 is immersed in the pickling bath 7 for a predetermined time, the acid solution adhering to the electrochemical corrosion potential sensor 10 is washed away with pure water. This removes an oxide layer (not shown) formed on the electrode 11 in the vicinity of the joint 6. That is, the joint 6 has a pickled portion from which the oxide layer has been removed. In this embodiment, the acid solution filled in the pickling bath 7 is assumed to be an aqueous solution of hydrofluoric and nitric acid, but is not limited to this as long as it can remove the oxide layer. The immersion time of the electrochemical corrosion potential sensor 10 can be appropriately set depending on the type of acid solution used, but when a hydrofluoric / nitric acid solution is used, it can be set to about one minute. In FIG. 4, reference numeral 1 denotes a first electrode portion, reference numeral 3 denotes a conductor, reference numeral 4 denotes an insulator, reference numeral 12 denotes a metal housing, reference numeral 13 denotes a mineral insulated cable, and reference numeral 22 denotes a conductor.

[0031] Next, a boiling water reactor plant (BWR (Boiling Water Reactor) plant) in which the electrochemical corrosion potential sensor 10 (see FIG. 1) of the present embodiment is installed will be described. FIG. 5 is a diagram illustrating the configuration of a boiling water reactor plant P (hereinafter, sometimes simply referred to as "BWR plant P") in which the electrochemical corrosion potential sensor 10 (see FIG. 1) is installed.

[0032] The BWR plant P includes a nuclear reactor, a feedwater system, a recirculation system, a main steam system, a turbine 37, a condenser 38, and a reactor cleanup system. The reactor 30 has a reactor pressure vessel 31. A reactor core 32 is disposed in the reactor pressure vessel 31. A plurality of fuel assemblies (not shown) are loaded in the reactor core 32. The feedwater system has a feedwater piping 39 that connects a condenser 38 and the reactor pressure vessel 31. A feedwater pump 40 is provided in the feedwater piping 39.

[0033] The main steam system has a main steam pipe 36 that connects the reactor pressure vessel 31 and a turbine 37 . The recirculation system has a recirculation system piping 34 connected to the reactor pressure vessel 31, and a recirculation pump 35 provided in the recirculation system piping 34. The reactor pressure vessel 31 and the recirculation system are installed in a reactor containment vessel 46. The reactor cleanup system has a cleanup system piping 41 connected to the recirculation system piping 34 and a feedwater piping 39, a cleanup system pump 42 provided in the cleanup system piping 41, and a cleanup device 43. A hydrogen injection device 45 is connected to the feedwater piping 39.

[0034] The cooling water (reactor water) in the reactor pressure vessel 31 is heated by heat generated by nuclear fission of the nuclear fuel material contained in the fuel assemblies in the reactor core 32, and a part of it becomes steam. This steam is discharged from the reactor pressure vessel 31 and supplied to the turbine 37 through the main steam pipe 36. This rotates the turbine 37. Electricity is generated by the rotation of the generator connected to the turbine 37. The steam discharged from the turbine 37 becomes condensed water in the condenser 38. This condensed water, that is, feed water, is pressurized by the feed water pump 40 and supplied to the reactor pressure vessel 31 through the feed water pipe 39. Hydrogen is injected from the hydrogen injection device 45 into the feed water flowing in the feed water pipe 39, and is led into the reactor pressure vessel 31 together with the feed water. The reactor water contains this hydrogen.

[0035] Most of the reactor water that does not become steam is separated from the steam by a steam separator (not shown) installed in the reactor pressure vessel 31. The separated reactor water flows down inside the downcomer 33 formed between the reactor pressure vessel 31 and the reactor core 32, and flows into the recirculation system piping 34. A recirculation pump 35 pressurizes this reactor water. The pressurized reactor water is ejected into a jet pump (not shown) installed in the downcomer 33, and the reactor water in the downcomer 33 is sucked into the jet pump. The reactor water discharged from the jet pump is supplied to the reactor core 32. The feed water containing hydrogen introduced by the feed water piping 39 is mixed in the downcomer 33 with the reactor water separated by the steam separator (not shown). A part of the reactor water that has flowed into the recirculation system piping 34 is led to the purification system piping 41 and purified by a purification device 43 provided in the purification system piping 41. The reactor water discharged from the purification device 43 is returned to the reactor pressure vessel 31 through the purification system piping 41 and the feed water piping 39. A bottom drain piping 44 connected to the bottom of the reactor pressure vessel 31 is connected to the purification system piping 41.

[0036] Next, the mounting structure of the electrochemical corrosion potential sensor 10 (see FIG. 1) to the BWR plant P (see FIG. 5) will be described. The electrochemical corrosion potential sensor 10 (see FIG. 1) can be mounted to a sensor mounting portion 47 of the recirculation system piping 34 and a sensor mounting portion 48 of the bottom drain piping 44 shown in FIG. 5. The mounting structure of the electrochemical corrosion potential sensor 10 at the sensor mounting portion 47 and the mounting structure of the electrochemical corrosion potential sensor 10 at the sensor mounting portion 48 are the same structure. Therefore, hereinafter, only the mounting structure at the sensor mounting portion 47 will be described, and a description of the mounting structure of the electrochemical corrosion potential sensor 10 at the sensor mounting portion 48 will be omitted.

[0037] FIG. 6 is a schematic diagram showing the state in which the corrosion potential sensor 10 is installed in the recirculation pipe 34. As shown in FIG. As shown in FIG. 6, the sensor installation section 47 is composed of a T-shaped branch pipe provided at a location to be measured in the recirculation system piping . The electrochemical corrosion potential sensor 10 is inserted into the sensor installation portion 47 so that the electrode 11 faces the central axis of the recirculation system piping 34 .

[0038] The electrochemical corrosion potential sensor 10 is supported by the sensor installation part 47 by attaching the other end of the metal casing 12 to the end of the sealing side of the sensor installation part 47. The space between the sealing side end of the sensor installation part 47 and the metal casing 12 is sealed with a seal member (not shown) to prevent leakage of reactor water flowing through the recirculation system piping 34. The space between the sealing side end of the sensor installation part 47 and the metal casing 12 may be fixed and sealed by welding the metal parts together. The conductor 22 of the electrochemical corrosion potential sensor 10 is connected to an electrometer 27. The other conductor 23 connected to the electrometer 27 is connected to the recirculation system piping 34 and is also grounded. Incidentally, the electrode 11 of the electrochemical corrosion potential sensor 10 and the recirculation system piping 34 are not in contact with each other.

[0039] The electrochemical corrosion potential sensor 10 measures a potential difference occurring between the electrode 11 of the electrochemical corrosion potential sensor 10 and the recirculation system piping 34 at a closest portion 24 where the electrode 11 and the recirculation system piping 34 are closest to each other. This potential difference is measured by an electrometer 27. The electrometer 27 measures the corrosion potential of the recirculation system piping 34 near the electrode 11 based on the measured potential difference.

[0040] <Action and effect> Next, the effects of the electrochemical corrosion potential sensor 10 (see FIG. 1) according to this embodiment will be described in more detail. In general, from the viewpoint of improving the availability of nuclear power plants, it is an important issue to suppress stress corrosion cracking and flow accelerated corrosion of the structural materials (stainless steel, nickel-based alloy) constituting the reactor internals and pressure boundary members, and the materials (stainless steel, low alloy steel, carbon steel) constituting the piping.

[0041] Stress corrosion cracking occurs when three factors, material, stress, and corrosive environment, meet certain conditions, but can be suppressed by improving one of the factors. Flow accelerated corrosion also occurs when materials and the corrosive environment meet certain conditions, but can be suppressed by improving one of the factors.

[0042] It is desirable to confirm the improvement effect of the corrosive environment improvement technology by measuring it throughout the operation cycle. This is because the flow conditions of the plant may change during plant operation, causing the corrosion potential to fluctuate. Therefore, it is desirable to measure the corrosion potential through at least one operation cycle.

[0043] The so-called corrosion potential sensor must generate a constant potential in the environment in which it is used, and the electrodes must be electrically insulated from the measurement site. The corrosion potential is measured using an electrometer as the potential difference between the measurement site and the corrosion potential sensor. For example, in boiling water reactors, there is an operation method in which hydrogen is injected into the cooling water. This operation method changes the environment in which the corrosion potential sensor comes into contact.

[0044] On the other hand, in order to evaluate the potential at the measurement site based on the potential generated by the electrochemical corrosion potential sensor, it is desirable that the potential generated by the electrochemical corrosion potential sensor be constant regardless of changes in the environment. As an electrochemical corrosion potential sensor that generates a constant potential regardless of changes in the environment, an electrochemical corrosion potential sensor that uses zirconium as an electrode is known (see, for example, Patent Document 1). This electrochemical corrosion potential sensor generates a constant potential when zirconium reacts with oxygen dissolved in the cooling water or with the cooling water itself and corrodes into zirconium oxide. However, zirconium electrodes have the problem of poor adhesion to the insulator that supports them. Furthermore, as described above, conventional electrochemical corrosion potential sensors (eg, see Patent Document 1) have a problem in that it is difficult to further extend the service life by removing the oxide layer formed at the joint by pickling.

[0045] In contrast, the electrochemical corrosion potential sensor 10 of the present embodiment includes a cylindrical first electrode portion 1, a bottomed cylindrical second electrode portion 2 connected to the first electrode portion 1 and overlapping with the first electrode portion 1 so that the first electrode portion 1 is on the outside, a conductor 3 (conductor body 3a) connected to the second electrode portion 2 and overlapping with the second electrode portion 2 so that the second electrode portion 2 is on the outside and having a portion extending out from an opening 5 of the second electrode portion 2, and an insulator 4 through which the conductor 3 (core wire 3b) extending out from the opening 5 of the second electrode portion 2 passes. A joint 6 for fixing the first electrode portion 1 and the second electrode portion 2 is located closer to the tip side of the electrochemical corrosion potential sensor 10 than an opening 5 of the second electrode portion 2.

[0046] In such an electrochemical corrosion potential sensor 10, the joint 6 is formed at a position that determines the sensor life, i.e., at a position farther toward the tip of the electrochemical corrosion potential sensor 10 than the opening 5 of the second electrode 2. This makes it possible to prevent the acid from penetrating into the inside of the electrochemical corrosion potential sensor 10 through the opening 5 of the second electrode 2 when the joint 6 is pickled with an acid. Furthermore, the joint 6 can be pickled easily and sufficiently. This effectively removes the oxide layer formed on the joint 6. The electrochemical corrosion potential sensor 10 can achieve a further longer life.

[0047] In addition, in such an electrochemical corrosion potential sensor 10, the first electrode portion 1 and the second electrode portion 2 are preferably made of zirconium. Zirconium generates a constant potential when corroding in cooling water, so the zirconium electrode generates a constant potential regardless of the water quality. On the other hand, zirconium electrodes are prone to forming an oxide layer on their surfaces when heated in an oxygen atmosphere. According to this electrochemical corrosion potential sensor 10, the oxide layer formed on the electrode 11 can be effectively removed by pickling, so that the sensor can exhibit stable performance regardless of the water quality and achieve a long life.

[0048] In addition, in such an electrochemical corrosion potential sensor 10, the joint 6 is a welded portion between the first electrode portion 1 and the second electrode portion 2. In such an electrochemical corrosion potential sensor 10, an oxide layer is likely to be formed on the electrode 11 in the vicinity of the joint 6 due to heating during welding. According to this electrochemical corrosion potential sensor 10, the oxide layer formed on the electrode 11 can be effectively removed by pickling, so that a longer life can be achieved. Furthermore, since the first electrode portion 1 and the second electrode portion 2 are welded together, even if the screw engagement between the second electrode portion 2 and the conductor body 3a is released, the second electrode portion 2 is prevented from falling off the corrosion potential sensor 10.

[0049] In addition, in such an electrochemical corrosion potential sensor 10, the joint 6 (welded portion) is located on the side surface of the electrode 11 of the electrochemical corrosion potential sensor 10. According to this electrochemical corrosion potential sensor 10, alignment can be easily performed when fitting the first electrode portion 1 and the second electrode portion 2 together. Furthermore, according to this electrochemical corrosion potential sensor 10, when the tip side of the electrochemical corrosion potential sensor 10 is pickled in the pickling bath 7, the joint 6 (welded portion) is on the side surface of the electrode 11 of the electrochemical corrosion potential sensor 10, so that it is easy to confirm whether the joint 6 (welded portion) is immersed in the acid solution. As a result, the oxide layer formed on the electrode 11 can be effectively removed by the pickling.

[0050] In addition, in such an electrochemical corrosion potential sensor 10, the joint 6 (welded portion) is formed in a continuous ring shape in the circumferential direction of the electrochemical corrosion potential sensor 10. In such an electrochemical corrosion potential sensor 10, good bonding strength between the first electrode portion 1 and the second electrode portion 2 is ensured, but the area in which an oxide layer is formed is expanded. According to this corrosion potential sensor 10, the oxide layer formed on the electrode 11 can be effectively removed by pickling, so that a long service life can be achieved while maintaining good bonding strength between the first electrode portion 1 and the second electrode portion 2.

[0051] In addition, in such an electrochemical corrosion potential sensor 10, the joints 6 (welded parts) are spot welded parts arranged at two or more places in the circumferential direction of the electrochemical corrosion potential sensor 10. According to such an electrochemical corrosion potential sensor 10, the area affected by welding is smaller than that of a full circumference weld.

[0052] In addition, in such an electrochemical corrosion potential sensor 10, the joint 6 (welded portion) has a pickled portion. In the case of such an electrochemical corrosion potential sensor 10, after the joint 6 is formed by welding, the surface of the joint 6 is pickled with an acid. According to this electrochemical corrosion potential sensor 10, the effect of removing the oxide layer on the electrode 11 around the joint 6 (welded part) is ensured by the presence of a pickling section. According to this electrochemical corrosion potential sensor 10, the heat-affected area during welding can be treated all at once by immersing the entire area in a tank so that it comes into contact with the acid.

[0053] In addition, in such an electrochemical corrosion potential sensor 10, the second electrode portion 2 and the conductor 3 are screwed together. According to such an electrochemical corrosion potential sensor 10, the second electrode portion 2 and the conductor 3 can be joined easily. Furthermore, according to this corrosion potential sensor 10, the second electrode portion 2 made of zirconium has poor adhesion to the conductor 3 made of a material other than zirconium, but since the second electrode portion 2 and the conductor 3 are screwed together, the bonding strength between the second electrode portion 2 and the conductor 3 is increased. Furthermore, according to this electrochemical corrosion potential sensor 10, the zirconium (second electrode portion 2) and the conductor 3 are electrically connected, so that the current generated by the corrosion of zirconium can be extracted to the outside through the conductor 3.

[0054] In addition, in such an electrochemical corrosion potential sensor 10, the nominal diameter of the male thread 3a1 formed in the conductor 3 is larger than the inner diameter of the opening 1b of the first electrode portion 1. According to this electrochemical corrosion potential sensor 10, even if the screw engagement between the second electrode 2 and the conductor 3 should come loose, the male thread 3a1 of the conductor 3 is engaged with the opening 1b of the first electrode 1. This prevents the assembly of the first electrode 1 and the second electrode 2 from coming off from the insulator 4.

[0055] In the electrochemical corrosion potential sensor 10, at least a contact portion 3d of the conductor 3 that comes into contact with the insulator 4 is made of an FeNi alloy or an FeNiCo alloy. According to this electrochemical corrosion potential sensor 10, by using the alloy having a small thermal expansion, it is possible to reduce thermal stress caused by temperature changes at the joint between the alloy and the insulator 4. This enables the electrochemical corrosion potential sensor 10 to further improve the reliability of the bonding strength at the bonding portion 6.

[0056] In addition, in such an electrochemical corrosion potential sensor 10, the insulator 4 is made of stabilized zirconia or sapphire. According to this corrosion potential sensor 10, by using ceramics made of stabilized zirconia or sapphire as the insulator 4, the chemical stability and physical strength of the insulator 4 can be improved, and the reliability of the insulating portion 4 can be further improved.

[0057] <Second embodiment> Next, a second embodiment of the electrochemical corrosion potential sensor according to the present invention will be described. FIG. 7 is a diagram illustrating the configuration of an electrochemical corrosion potential sensor 10A according to a second embodiment of the present invention. As shown in Figure 7, the second electrode portion 2 of the corrosion potential sensor 10A does not have a flange portion 2b (see Figure 2) and is composed only of a main body portion 2a, unlike the second electrode portion 2 (see Figure 2) of the corrosion potential sensor 10 of the first embodiment (see Figure 2). As a result, the joint 6 of the electrochemical corrosion potential sensor 10A is located on the tip surface of the electrode 11 of the electrochemical corrosion potential sensor 10. In FIG. 7, reference numeral 3 denotes a conductor, reference numeral 4 denotes an insulator, and reference numeral 5 denotes an opening of the second electrode portion 2. According to the electrochemical corrosion potential sensor 10A of the second embodiment, the joint 6 where the oxide layer is formed is located on the tip surface of the electrochemical corrosion potential sensor 10A, so that the surface of the joint 6 can be easily treated by pickling, polishing, or the like. Furthermore, according to the electrochemical corrosion potential sensor 10A of the second embodiment, since the joint 6 is located on the tip surface of the electrochemical corrosion potential sensor 10A, the etching range during pickling can be minimized.

[0058] <Third embodiment> Next, a corrosion potential sensor according to a third embodiment of the present invention will be described. FIG. 8 is a diagram illustrating the configuration of an electrochemical corrosion potential sensor 10B according to a third embodiment of the present invention. As shown in FIG. 8, the outer peripheral surface of the first electrode 1 of the electrochemical corrosion potential sensor 10B has an uneven portion 9 located closer to the tip of the electrochemical corrosion potential sensor 10 than the opening 5 of the second electrode 2. Specifically, the unevenly processed portion 9 has a configuration in which a plurality of circumferential grooves are repeatedly arranged at predetermined intervals in the axial direction at a position away from the opening 5 of the second electrode portion 2 toward the tip side of the electrochemical corrosion potential sensor 10B. The circumferential groove constituting the unevenly processed portion 9 in this embodiment is assumed to be formed by cutting the outer circumferential surface of the first electrode portion 1. However, the unevenly processed portion 9 is not limited to a circumferential groove, and can also be formed by a plurality of protrusions or recesses. In FIG. 8, reference numeral 3 denotes a conductor and reference numeral 4 denotes an insulator.

[0059] According to the third embodiment of the electrochemical corrosion potential sensor 10B, when the electrochemical corrosion potential sensor 10B is installed in the sensor installation section 47 (see FIG. 6), the uneven surface 9 increases the liquid contact area of ​​the electrode 11. This increases the current due to the corrosion of zirconium, and the potential generated by the zirconium electrode becomes less susceptible to the effects of other reactions. This allows the electrode 11 to generate a constant reference potential more stably. In addition, in the electrochemical corrosion potential sensor 10B of the third embodiment, it is preferable that the unevenly processed portion 9 is also immersed in the pickling bath 7 (see FIG. 4) during pickling.

[0060] In this way, by also immersing the unevenly processed portion 9 in the pickling bath 7 (see FIG. 4), even if an oxide layer has been formed on the unevenly processed portion 9 due to heat generated when cutting the unevenly processed portion 9, the oxide layer can be removed. Furthermore, since the unevenly processed portion 9 is formed at a position away from the opening 5 of the second electrode portion 2 toward the tip side of the electrochemical corrosion potential sensor 10B, the acid solution used when pickling the unevenly processed portion 9 does not penetrate into the inside of the electrochemical corrosion potential sensor 10B. Therefore, the oxidation layer can be removed without the acid solution penetrating into the interior of the electrochemical corrosion potential sensor 10B during pickling, thereby achieving a further extension of the life of the electrochemical corrosion potential sensor 10B.

[0061] Although the first to third embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to those having all the configurations of the above-mentioned embodiments. Therefore, it is possible to replace a part of the configuration of an embodiment with another configuration, add a part of the configuration of an embodiment to another form, or omit a part of the configuration of an embodiment.

[0062] Further, the first electrode portion 1 and the second electrode portion 2 of the electrochemical corrosion potential sensors 10, 10A, and 10B are formed into a cylindrical shape or a cylindrical shape with a bottom, but may also be formed into a rectangular tube or a rectangular tube with a bottom.

[0063] In addition, although it is assumed that the oxide layer formed near the joint 6 of the electrochemical corrosion potential sensors 10, 10A, and 10B is removed by pickling, the oxide layer can also be removed by mechanical polishing. That is, the joint 6 of the electrochemical corrosion potential sensors 10, 10A, and 10B has a mechanically polished portion. According to such electrochemical corrosion potential sensors 10, 10A, and 10B, the oxide layer is removed by mechanical polishing, so that a further extension of the service life can be achieved. In addition, in the electrochemical corrosion potential sensors 10, 10A, and 10B, the surface of the joint 6 is mechanically polished after welding to form the joint 6. According to such electrochemical corrosion potential sensors 10, 10A, and 10B, only the heat-affected areas during welding can be targeted for processing, so that areas not affected by the polishing are not affected by the polishing. [Explanation of symbols]

[0064] 1 First electrode part 2 Second electrode part 3 Conductors 3d contact area 4. Insulation 5 Opening 6 Joint 7 Pickling bath 9 Uneven processing section 10. Corrosion potential sensor 10A Corrosion Potential Sensor 10B Corrosion Potential Sensor 11 electrodes 12 Metal case 22 Conductor 47 Sensor installation section 48 Sensor installation section

Claims

1. A cylindrical first electrode portion; a bottomed, cylindrical second electrode portion connected to the first electrode portion so as to overlap with the first electrode portion on the outside; a conductor connected to the second electrode portion so as to overlap with the second electrode portion on the outside and having a portion extending outward from an opening of the second electrode portion; an insulator through which the conductor extending from the opening of the second electrode portion passes; Equipped with A corrosion potential sensor characterized in that a joint that fixes the first electrode portion and the second electrode portion is located closer to the tip of the corrosion potential sensor than an opening of the second electrode portion.

2. 2. The electrochemical corrosion potential sensor according to claim 1, A corrosion potential sensor characterized in that the first electrode portion and the second electrode portion are made of zirconium.

3. 2. The electrochemical corrosion potential sensor according to claim 1, A corrosion potential sensor characterized in that the joint is a welded joint between the first electrode portion and the second electrode portion.

4. 2. The electrochemical corrosion potential sensor according to claim 1, The electrochemical corrosion potential sensor according to claim 1, wherein the joint is located on a side surface of an electrode of the electrochemical corrosion potential sensor.

5. 2. The electrochemical corrosion potential sensor according to claim 1, The electrochemical corrosion potential sensor according to claim 1, wherein the joint is located on a tip surface of an electrode of the electrochemical corrosion potential sensor.

6. The electrochemical corrosion potential sensor according to claim 3, The electrochemical corrosion potential sensor according to claim 1, wherein the welded portion is formed in a continuous ring shape in a circumferential direction of the electrochemical corrosion potential sensor.

7. The electrochemical corrosion potential sensor according to claim 3, The electrochemical corrosion potential sensor is characterized in that the welded portions are spot welded portions arranged at two or more locations in a circumferential direction of the electrochemical corrosion potential sensor.

8. 2. The electrochemical corrosion potential sensor according to claim 1, The electrochemical corrosion potential sensor according to claim 1, wherein the joint portion has an acid-treated portion.

9. 2. The electrochemical corrosion potential sensor according to claim 1, The electrochemical corrosion potential sensor according to claim 1, wherein the joint has a mechanically polished portion.

10. 2. The electrochemical corrosion potential sensor according to claim 1, The corrosion potential sensor is characterized in that the second electrode portion and the conductor are screwed together.

11. 2. The electrochemical corrosion potential sensor according to claim 1, The electrochemical corrosion potential sensor according to claim 1, wherein the outer peripheral surface of the first electrode portion has an uneven portion on the tip side of the electrochemical corrosion potential sensor relative to the opening of the second electrode portion.

12. 2. The electrochemical corrosion potential sensor according to claim 1, 2. The electrochemical corrosion potential sensor according to claim 1, wherein at least a portion of the conductor that comes into contact with the insulator is made of an FeNi alloy or an FeNiCo alloy.

13. 2. The electrochemical corrosion potential sensor according to claim 1, The corrosion potential sensor is characterized in that the insulator is made of stabilized zirconia or sapphire.

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