JP2017044609A - Corrosive environment sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosive environment sensor capable of measuring accurate conductivity of furnace water under corrosive environment in a narrow installation space.SOLUTION: A corrosive environment sensor comprises: a cylindrical metal housing 21; an insulation member 22 which is formed of an insulation material having radiation resistance and heat resistance, and is attached to the metal housing 21; a pair of metal electrodes 24, 25 one surface of which opposes to each other at a predetermined gap, and which are attached to the insulation member 22 in an electrically insulated state from the metal housing 21; a pair of conducting wires 28, 29 which are electrically connected to the pair of metal electrodes 24, 25 respectively, and extend into the insulation member 22 and the metal housing 21 in an insulated state from the metal housing 21; and an insulation covering part 26 which is formed of an insulation material having radiation resistance and heat resistance, and covers surfaces opposing to each other, attaching portions to the insulation member 22, and surfaces excluding a connection part of the pair of conducting wires 28, 29 out of each surface of the pair of metal electrodes 24, 25.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a corrosive environment sensor, and more particularly to a sensor capable of measuring at least the electrical conductivity of reactor cooling water that comes into contact with a metallic structural member in a nuclear power plant during service.

  In nuclear power plants, stainless steel, nickel-base alloys, and the like are called structural materials and are used as materials for structural members such as in-reactor equipment and piping. These structural materials exhibit susceptibility to stress corrosion cracking (SCC) under certain conditions. Therefore, in nuclear power plants, SCC suppression measures are applied to maintain the soundness. In recent years, SCC suppression measures have also been applied from the viewpoint of improving the facility utilization factor of the plant and improving economic efficiency such as extending the service life.

  As one of the measures for suppressing SCC, there is a technique for reducing the corrosive environment. In boiling water nuclear power plants, hydrogen injection is widely used to improve the corrosive environment of reactor cooling water (hereinafter referred to as reactor water) in contact with structural members of the plant. The reactor water in the nuclear reactor contains oxygen and hydrogen peroxide generated by radiolysis of the reactor water. Oxygen and hydrogen peroxide cause corrosion of structural members and form a corrosive environment. Hydrogen injection is a technique in which hydrogen is injected into the reactor water through a water supply pipe or the like, and this hydrogen is reacted with oxygen and hydrogen peroxide in the reactor water to return to the water. As a result of the decrease in the concentration of oxygen and hydrogen peroxide in the reactor water due to this reaction, the corrosion potential (ECP: Electrochemical Corrosion Potential) of the structural member in contact with the reactor water decreases, and the occurrence and progress of SCC in the structural member. Alleviated.

  Furthermore, as a technique for further promoting the reduction of the corrosion potential when hydrogen injection is performed, a technique for injecting a platinum group noble metal element into the reactor water (noble metal injection technique) is known. The noble metal injection technique is used in combination with the hydrogen injection technique and utilizes the catalytic action of the platinum group noble metal element on the electrochemical reaction of hydrogen, and further increases the reduction range of the corrosion potential due to hydrogen injection.

  In order to confirm the above-described mitigating effect of the corrosive environment, it is necessary to measure the corrosion potential of the structural member. Therefore, a corrosion potential sensor is installed in the reactor or in a pipe connected to the reactor to measure the corrosion potential of the structural member (for example, see Patent Document 1). The corrosion potential sensor generates a constant potential (reference potential) that serves as a reference for measuring the corrosion potential regardless of the oxygen and hydrogen peroxide concentrations in the reactor water under use conditions. For this reason, the corrosion potential sensor is called a reference electrode, a reference electrode, or a reference electrode. The reference potential of this corrosion potential sensor and the concentration of oxygen, hydrogen peroxide, and hydrogen contained in the reactor water in contact with the structural member, the temperature of the reactor water, and the flow rate of the reactor water The corrosion potential of the structural member can be known by measuring the potential difference from the potential with a potentiometer.

  In addition, electrical conductivity (hereinafter referred to as conductivity) is an important factor in managing and controlling the possibility of occurrence and progress of corrosion of structural members. For example, it is said that the susceptibility of intergranular stress corrosion cracking of stainless steel at simulated reactor temperatures can be organized by the corrosion potential measured in high temperature water and the conductivity measured at room temperature. Further, in order to evaluate an index called Wagner length, which is known as an important factor representing the ease of progress of corrosion, a value of conductivity is required. The corrosion reaction proceeds by coupling the anode reaction in which the metal material elutes to emit electrons and the cathode reaction in which the electrons released into the metal material by the anode reaction are received on the solution side in contact with the metal material. To do. This distance capable of coupling is referred to as Wagner length, and is represented by Lw = Rp · κ. Here, Lw represents Wagner length, Rp represents polarization resistance, and κ represents conductivity. If the distance that can be coupled is increased, the cathode reaction occurs in a wider range, so that more metal is eluted. In other words, the Wagner length is an important factor indicating the ease of corrosion in a corrosion mode such as local corrosion where the anode and cathode are separated. It is necessary to measure the rate.

In boiling water reactors, pure water is used as the reactor water, so the conductivity of the reactor water is ideally determined by the concentrations of H ⁺ and OH ⁻ generated by the dissociation of water. However, the reactor water may contain trace amounts of impurities such as seawater-derived Cl ⁻ and SO ₄ ²⁻ eluted from the ion exchange resin. These trace amounts of impurities can cause corrosion to occur and progress. Therefore, in a boiling water reactor, in order to monitor the change in the conductivity of the reactor water caused by a small amount of impurities, for example, the reactor water sampled from the feed water piping etc. via the sampling piping and cooled to near room temperature. Conductivity is measured continuously. Furthermore, the upper limit conductivity level that does not affect the corrosion behavior is specified, and the water quality of the reactor water is maintained and managed so that the measured room temperature conductivity is within the specified range. Confirmed experimentally in advance the correlation between the corrosion behavior in the actual environment at high temperature (reactor water temperature during operation of the reactor power plant, for example, about 280 ° C) and the conductivity of the reactor water at room temperature. By measuring the electrical conductivity at room temperature, engineering can control and manage corrosion. Controlling and managing corrosion by measuring room temperature conductivity in this way is technically difficult to measure conductivity in high-temperature high-pressure water, and conducts corrosion tests while measuring room-temperature conductivity. This is because most of the knowledge for correlating the corrosion behavior with the electrical conductivity at room temperature has been obtained.

The conductivity is obtained by immersing a pair of insoluble metal electrodes in a solution to be evaluated, and passing a current between the two electrodes and measuring the resistance. One surface of a pair of metal electrodes having the same area is faced in parallel at a distance L, and the solution existing between the two electrodes is a rectangular parallelepiped, and the surface parallel to the pair of metal electrodes is cut off. When the area is A, the electrical conductivity κ can be calculated from the relationship of the following formula (I) by actually measuring the resistance R between the two electrodes.
R = κ ⁻¹ · L · A ⁻¹ Formula (I)
Here, R represents the resistance of the solution, L represents the distance between the two electrodes, and A represents the cross-sectional area of the conducting portion (current path) between the two electrodes.

As can be seen from the equation (I), in order to obtain the conductivity κ from the measured resistance R, the geometric shape L · A ⁻¹ of the path of the current flowing between the two electrodes needs to be known. This constant indicating the influence of the geometric shape is generally called a cell constant, and is an essential parameter for measuring conductivity. As described above, when the shape of the solution existing between the two electrodes is a simple shape such as a rectangular parallelepiped, the cell constant L · A ⁻¹ can be calculated from the geometric condition. On the other hand, when the shape of the solution between the two electrodes is a complicated shape such as a cylindrical shape, the cell constant L · A is obtained by measuring the resistance R between the two electrodes in a solution having a known conductivity κ. ^-1 is experimentally obtained in advance.

When measuring the electrical conductivity of reactor water at room temperature, a pair of metal electrodes are surrounded by a container-like or cylindrical member formed of an insulating material such as a polymer resin or glass, so that two currents are supplied. The current path is defined so as to flow reliably through the reactor water sandwiched between them. For this reason, the cell constant L · A ⁻¹ can be determined from geometric conditions or experiments, and the accurate conductivity of room temperature reactor water can be calculated from the measured resistance between the two electrodes using equation (I). Can do.

JP 2009-42111 A

  In order to control and manage the corrosion of structural members by measuring the electrical conductivity at room temperature, it is necessary to experimentally confirm the correlation between the corrosion behavior at high temperature and the electrical conductivity at room temperature in advance. Such an experiment is complicated. When analyzing the details of corrosion behavior by evaluating the Wagner length, it is necessary to grasp the conductivity of the reactor water in a corrosive environment during operation of the nuclear power plant. In other words, there is a demand for measuring the conductivity of the reactor water not at room temperature but at actual temperature and actual pressure in a corrosive environment.

  Even when measuring the conductivity of reactor water in the reactor or the piping through which reactor water flows during the rated operation of a nuclear power plant, basically a pair of insoluble metal electrodes is immersed in the reactor water. From the measured resistance between the two electrodes, it can be calculated using the above formula (I). However, sensors that measure the conductivity of reactor water at room temperature do not have specifications that measure the conductivity of high-temperature and high-pressure reactor water in a reactor that is exposed to radiation. It cannot be used for measurement.

Therefore, it is conceivable to measure the conductivity of the reactor water in a high-temperature and high-pressure corrosive environment by installing two corrosion potential sensors described in Patent Document 1 that can be installed in the nuclear reactor so as to face each other. However, in high-temperature and high-pressure reactor water that is irradiated with radiation, unlike measurements at room temperature, cylinders made of insulating materials with poor radiation resistance and heat resistance, such as polymer resins and glass, etc. Therefore, the surroundings of the electrodes of the two corrosion potential sensors cannot be surrounded, and the current path between the two electrodes cannot be defined. For this reason, the cell constant L · A ⁻¹ is not determined, and the conductivity of the reactor water cannot be calculated from the above formula (I).

  In addition, when there is a metal member such as a piping member or a structural member near one electrode of the corrosion potential sensor rather than the distance between the electrodes of the two corrosion potential sensors, the current is such that the resistance becomes the smallest. It flows between the two electrodes via a metal member near the corrosion potential sensor. Therefore, a value smaller than the resistance value when the current flows only through the reactor water existing between the two electrodes is measured, and thus the calculated conductivity includes an error.

  Furthermore, since steady-state reactor water is close to pure water and has high electrical resistance, it is necessary to bring the electrodes of the two corrosion potential sensors close to about several millimeters. In addition, since there are many in-reactor equipment in the reactor, and it is necessary to install the corrosion potential sensor in a narrow area so as not to be directly exposed to the flow of reactor water. The degree of freedom in installing the corrosion potential sensor is low. That is, it is difficult to install two corrosion potential sensors at positions close to several millimeters suitable for measuring the conductivity of the reactor water.

  Thus, when measuring the conductivity of reactor water in a high temperature and high pressure corrosive environment in a nuclear reactor, it is difficult to define the path of the current flowing between the two electrodes, and in a narrow installation space. It is also difficult to arrange the two electrodes at a position suitable for measuring the conductivity of the reactor water.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a corrosive environment sensor capable of measuring the accurate conductivity of reactor water in a corrosive environment in a narrow installation space. It is.

In order to solve the above problems, for example, the configuration described in the claims is adopted.
The present application includes a plurality of means for solving the above-mentioned problems. For example, a cylindrical metal casing disposed in a structural member through which reactor cooling water in a corrosive environment in a nuclear reactor plant flows. And an insulating member formed of an insulating material having radiation resistance and heat resistance and attached to the metal casing, and one surface thereof facing each other with a predetermined interval, and the metal casing A pair of metal electrodes attached to the insulating member in an electrically insulated state, and the insulation in a state electrically connected to the pair of metal electrodes and electrically insulated from the metal casing A pair of conductive wires extending inside the member and the metal casing, and an insulating material having radiation resistance and heat resistance, the surfaces of the pair of metal electrodes facing each other, Attaching part to insulation member, Further comprising an insulating coating portion covering the surface except the connection portion of the fine the set of conductors and said.

According to the present invention, a pair of metal electrodes are provided on one metal casing so that one surface faces each other, and most of the surfaces other than the surfaces facing the pair of metal electrodes are radiation resistant. And since it covered with the heat-resistant insulation coating part, a pair of metal electrodes can be arrange | positioned in a narrow installation space, and the path | route of the electric current which flows between a pair of metal electrodes can be prescribed | regulated reliably. That is, it is possible to measure the exact conductivity of the reactor cooling water in a corrosive environment in a narrow installation space such as in the reactor. As a result, based on the conductivity measured in a corrosive environment such as in a nuclear reactor, it is possible to perform effective water chemistry management to suppress corrosion, and maintain or improve the soundness of the structural members in the reactor. Can be planned.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a system diagram showing a boiling water reactor plant in which an embodiment of a corrosive environment sensor of the present invention is installed. FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a corrosive environment measuring device showing a first embodiment of a corrosive environment sensor of the present invention in a cross-sectional state. FIG. 2 is a longitudinal sectional view showing an enlarged electrode part constituting a part of the first embodiment of the corrosive environment sensor of the present invention shown in FIG. 2 and a sectional view of the longitudinal sectional view seen from the arrow AA. is there. It is explanatory drawing which shows the measuring method of the corrosive environment in the reactor of a boiling water reactor plant using the corrosive environment measuring apparatus provided with 1st Embodiment of the corrosive environment sensor of this invention. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the corrosion environment sensor of this invention. It is the longitudinal cross-sectional view which expands and shows the electrode part which comprises a part of 2nd Embodiment of the corrosion environment sensor of this invention shown in FIG. 5, and its side view. It is explanatory drawing which shows the measuring method of the corrosive environment in piping of a boiling water reactor plant using the corrosive environment measuring apparatus provided with 2nd Embodiment of the corrosive environment sensor of this invention.

Hereinafter, embodiments of a corrosive environment sensor of the present invention will be described with reference to the drawings.
First, the configuration of a boiling water reactor plant in which an embodiment of the corrosion environment sensor of the present invention is installed will be described with reference to FIG. FIG. 1 is a system diagram showing a boiling water reactor plant in which an embodiment of a corrosive environment sensor of the present invention is installed. In FIG. 1, the arrows indicate the flow direction of the reactor cooling water or the injection direction of the aqueous solution containing hydrogen and noble metals.

  In FIG. 1, a boiling water reactor plant is installed outside a reactor pressure vessel 102 containing a reactor core 101, a reactor containment vessel 103 containing the reactor pressure vessel 102, and a reactor containment vessel 103. The turbine 104 driven by the steam generated in the reactor pressure vessel 102, the condenser 105 installed immediately below the turbine 104 and returning the steam discharged from the turbine 104 to the condensate, and the condenser 105 are obtained. And a water supply system for supplying the condensed water into the reactor pressure vessel 102. Both ends of a main steam pipe 107 that supplies steam generated in the reactor pressure vessel 102 to the turbine 104 are connected to the reactor pressure vessel 102 and the turbine 104, respectively. The water supply system has a water supply pipe 109 connected to the condenser 105 and the reactor pressure vessel 102, and a water supply pump 110 provided in the water supply pipe 109.

  The boiling water reactor plant includes, for example, two recirculation systems that forcibly circulate reactor cooling water (hereinafter referred to as reactor water) in the reactor pressure vessel 102. Each recirculation system has a recirculation system pipe 112 having both ends connected to the upper and lower sides of the lower part of the reactor pressure vessel 102 and a recirculation pump 113 provided in the recirculation system pipe 112. It is disposed in the furnace containment vessel 103.

  The boiling water reactor plant further includes a reactor purification system for removing or diluting reactor water impurities. The nuclear reactor purification system includes a purification system pipe 115 connected to the recirculation system pipe 112 and the water supply pipe 109, a purification device 116 provided in the purification system pipe 115, and upstream of the purification device 116 in the purification system pipe 115. And a purification system pump 117 provided on the side.

  A core 101 in the reactor pressure vessel 102 is loaded with a plurality of fuel assemblies (not shown) having a plurality of fuel rods containing nuclear fuel material. A steam-water separator 121 and a steam dryer 122 are installed above the core 101 in the reactor pressure vessel 102. One end of a bottom drain pipe 123 is connected to the bottom of the reactor pressure vessel 102. The other end of the bottom drain pipe 123 is connected to the upstream side of the purification system pump 117 in the purification system pipe 115.

  Connected to the water supply pipe 109 is a hydrogen injection device 125 for adding hydrogen to the water supply. Further, a noble metal injection device 126 for adding a noble metal such as platinum to the reactor water is connected to the purification system pipe 115 downstream of the purification device 116.

  In the boiling water reactor plant configured as described above, the reactor water in the reactor pressure vessel 102 is generated by the heat generated by the nuclear fission of the nuclear fuel material contained in the fuel assembly (not shown) in the core 101. It is heated and part becomes steam. The steam is separated from the water by the steam separator 121 and the steam dryer 122, then discharged from the reactor pressure vessel 102, supplied to the turbine 104 through the main steam pipe 107, and rotates the turbine 104. As a result, a generator (not shown) connected to the turbine 104 rotates to generate electric power.

  The steam discharged from the turbine 104 is condensed by the condenser 105 to become water. This condensed water is boosted by feed water pump 110 as feed water, and is supplied to reactor pressure vessel 102 through feed water pipe 109. Hydrogen is added from the hydrogen injection device 125 to the water supply flowing through the water supply pipe 109. The added hydrogen is introduced into the reactor pressure vessel 102 together with the feed water.

  Of the reactor water heated by the core 101, the reactor water separated by the steam / water separator 121 and the steam dryer 122 without being steamed is a downcomer 129 formed between the reactor pressure vessel 102 and the reactor core 101. Go down inside. At this time, the reactor water in the downcomer 129 is mixed with the feed water containing hydrogen supplied into the reactor pressure vessel 102 via the feed water pipe 109. The reactor water mixed with the feed water flows into the recirculation system pipe 112 by the recirculation pump 113. Reactor water in the recirculation piping 112 is supplied into a jet pump (not shown) installed in the downcomer 129. This reactor water is discharged from the jet pump and supplied to the reactor core 101.

  A part of the reactor water flowing into the recirculation system pipe 112 is guided to the purification system pipe 115 and purified by the purification device 116. The purified reactor water is returned into the reactor pressure vessel 102 through the purification system pipe 115 and the feed water pipe 109. An aqueous solution containing a noble metal (for example, platinum) is added from the noble metal injection device 126 to the purified reactor water flowing in the purification system pipe 115. Reactor water containing platinum is introduced into the reactor pressure vessel 102 through the water supply pipe 109. The platinum added to the reactor water adheres to the surface of the reactor internal structure in the reactor pressure vessel 102, the inner surface of the recirculation system piping 112, the purification system piping 115, and the like.

  Thus, in the boiling water reactor plant, hydrogen injection and noble metal injection are performed as a measure for suppressing SCC. By the hydrogen injection, the corrosion potential of the structural member in contact with the reactor water is reduced, and the occurrence and progress of SCC in the structural member is mitigated. Furthermore, by using noble metal injection together with hydrogen injection, the range of reduction of the corrosion potential due to hydrogen injection is further increased.

  In order to confirm the effects of these SCC suppression measures and to manage and control the occurrence and progress of corrosion of structural members, it is necessary to measure the corrosion potential of the structural members in a corrosive environment. In addition, in order to evaluate the Wagner length as an index for managing and controlling the occurrence and progress of corrosion of structural members, it is necessary to measure the conductivity of reactor water at actual temperature and actual pressure in a corrosive environment. is there.

  Therefore, in the reactor pressure vessel 102 (for example, the in-core measurement tube 131 described later), the recirculation system piping 112, and the bottom drain piping 123, respectively, A corrosion environment measuring device 1 capable of measuring the conductivity of the reactor water is installed.

[First Embodiment]
Next, the structure of the corrosive environment measuring apparatus provided with the first embodiment of the corrosive environment sensor of the present invention will be described with reference to FIGS.
FIG. 2 is a block diagram of a corrosive environment measuring apparatus showing the first embodiment of the corrosive environment sensor of the present invention in a cross-sectional state, and FIG. 3 is a first embodiment of the corrosive environment sensor of the present invention shown in FIG. It is the longitudinal cross-sectional view which expands and shows the electrode part which comprises some forms, and sectional drawing which looked at the longitudinal cross-sectional view from the AA arrow. 2 and 3, the same reference numerals as those shown in FIG. 1 are the same parts, and detailed description thereof is omitted.

  In FIG. 2, the corrosive environment measuring apparatus 1 includes a corrosive environment sensor 2 and a measuring instrument 3 connected to the corrosive environment sensor 2. The corrosion environment sensor 2 is, for example, a sensor having both a corrosion potential measurement function equivalent to a platinum type corrosion potential sensor and a conductivity measurement function as a conductivity sensor. The measuring device 3 includes, for example, a potentiometer 5 connected to the corrosive environment sensor 2, a potentiostat 6 connected to the corrosive environment sensor 2, and a frequency response analyzer 7 connected to the potentiostat 6. .

  The corrosive environment sensor 2 is a substantially cylindrical metal casing 21 disposed in a structural member (for example, an in-core measurement tube 131 and a sampling pipe 132 described later) through which reactor water in a corrosive environment in a nuclear reactor plant flows. And a substantially cylindrical insulating member 22 attached to the metal casing 21 such that one end (the lower end in FIG. 2) closes the opening on one side (the upper side in FIG. 2) of the metal casing 21. And an electrode portion 23 attached to the tip end surface (the upper end surface in FIG. 2) of the other end of the insulating member 22, and electrically connected to the electrode portion 23, and extends into the insulating member 22 and the metal casing 21. The first conducting wire 28 and the second conducting wire 29 that are present and are electrically connected to the first conducting wire 28 and the second conducting wire 29 inside the metal casing 21 and also connected to the measuring instrument 3. It is composed of a mineral insulated cable 31.

  The metal casing 21 is filled with an electrical insulator (not shown) that electrically insulates the metal casing 21 from the first conductor 28 and the second conductor 29. The electrical insulator has heat resistance and pressure resistance against the high temperature (for example, about 280 ° C.) and high pressure of the reactor water in the reactor pressure vessel 102 (see FIG. 1) during plant operation, and the core 101 ( It is made of either a resin or an inorganic insulating material that is resistant to radiation emitted from (see FIG. 1).

  The insulating member 22 is formed using any one or more materials of alumina, yttria stabilized zirconia, titania, ceria, aluminum nitride, silicon nitride, cordierite, mullite, steatite, forsterite, and cermet. ing. That is, the insulating member 22 has heat resistance and pressure resistance against the high temperature and high pressure of the reactor water in the reactor pressure vessel 102 during plant operation, and has radiation resistance against the radiation emitted from the core 101. Have.

  As shown in FIGS. 2 and 3, the electrode portion 23 includes a first metal electrode 24 and a second metal electrode 25 attached to the insulating member 22 in a state of being electrically insulated from the metal housing 21. Have. The first metal electrode 24 and the second metal electrode 25 are, for example, rectangular flat plates having the same dimensions. As a specific example, for example, a flat plate with a side of 5 mm and a thickness of 1 mm is used. The first metal electrode 24 and the second metal electrode 25 are arranged in parallel so that one surface of the first metal electrode 24 and the second metal electrode 25 are opposed to each other with a predetermined interval, and the mutually opposed planes overlap each other in the normal direction. . This predetermined interval is set to a range in which the conductivity of the reactor water having a high electric resistance can be measured. Further, the predetermined interval is such that when the corrosive environment sensor 2 is installed in the reactor pressure vessel 102 (see FIG. 1) or the like, the metal structural member existing in the vicinity of the area where the corrosive environment sensor 2 is installed and the first structural member. The distance is set to be the shortest distance than the distance from the metal electrode 24 or the second metal electrode 25. The predetermined interval is, for example, about 1 mm.

  The first metal electrode 24 and the second metal electrode 25 are made of, for example, platinum. That is, the first metal electrode 24 and the second metal electrode 25 are insoluble and have a property that an oxide film is difficult to be formed. In addition, it has the property that long-lived radionuclides are not generated even when receiving radiation. Furthermore, it has the property of causing an electrode reaction of hydrogen, and generates a reference potential in the corrosion potential measurement in the reactor water when hydrogen injection is performed.

  A first conducting wire 28 and a second conducting wire 29 are respectively connected to part of the first metal electrode 24 and the second metal electrode 25 attached to the insulating member 22. The first conductive wire 28 and the second conductive wire 29 are formed of the same material as the first metal electrode 24 and the second metal electrode 25 in order to suppress corrosion due to dissimilar metal contact and generation of thermoelectromotive force. It is desirable.

  Of the surfaces of the first metal electrode 24 and the second metal electrode 25, the surfaces excluding the surfaces facing each other, the attachment portion to the insulating member 22, and the connection portion of the pair of conductors 28 and 29 are heat resistant. And an insulating covering portion 26 formed of an insulating material having radiation resistance and the like. The insulation coating portion 26 electrically connects the first metal electrode 24 and the second metal electrode 25 to the metal structural member existing in the vicinity of the installation area of the corrosion environment sensor 2 when measuring the conductivity. The current path is defined so that the current flows reliably in the reactor water existing between the opposing surfaces of the first metal electrode 24 and the second metal electrode 25. As with the insulating member 22, the insulating coating portion 26 is any one of alumina, yttria-stabilized zirconia, titania, ceria, aluminum nitride, silicon nitride, cordierite, mullite, steatite, forsterite, and cermet. It is formed using the above materials. The insulation coating part 26 constitutes an electrode part 23 together with the first metal electrode 24 and the second metal electrode 25.

  As shown in FIG. 2, the mineral insulated cable 31 is disposed in a cylindrical metal outer sheath (sheath) 32 and the outer sheath 32, and is electrically connected to the first conductor 28 and the second conductor 29, respectively. An electrical insulator formed between a first core wire 33 and a second core wire 34 connected to each other and between the outer skin 32 and the first core wire 33 and the second core wire 34 and formed of a mineral such as alumina (see FIG. (Not shown). The electrical insulator electrically insulates the outer skin 32 from the first core wire 33 and the second core wire 34. A part of the mineral insulated cable 31 is disposed inside the metal casing 21, and the remaining part extends to the outside of the metal casing 21. The outer wall 32 of the mineral-insulated cable 31 is attached to the other end (the lower end in FIG. 2) of the metal casing 21.

  The potentiometer 5 has an internal impedance of 100 TΩ or more. One lead wire 41 of the potentiometer 5 is connected to the second core wire 34 of the mineral insulated cable 31 of the corrosion environment sensor 2. The other lead wire 42 is connected to a structural member such as a pipe for measuring the corrosion potential when the corrosion potential is measured. By the potentiometer 5 in which the lead wires 41 and 42 are connected in this manner, the potential of the second metal electrode 25 electrically connected to the second core wire 34 of the mineral insulated cable 31 and the potential of the structural member Measure the potential difference.

  In the potentiostat 6, the counter electrode connecting lead wire 44 and the reference electrode connecting lead wire 45 are both connected to the same first core wire 33 of the mineral insulated cable 31. On the other hand, the working electrode connecting lead wire 46 is connected to the second core wire 34 of the mineral insulated cable 31. The working electrode connection lead 46 of the potentiostat 6 is connected to the second core wire 34 of the mineral insulated cable 31 which is the same as the one lead wire 41 of the potentiometer 5, but the internal impedance of the potentiometer 5 is as high as 100 TΩ or more. Therefore, the current that flows when measuring the conductivity hardly flows to the potentiometer 5 side. For this reason, the measurement of conductivity and the measurement of corrosion potential do not affect each other. That is, the corrosion environment measuring device 1 can measure both the corrosion potential of the structural member and the conductivity of the reactor water by itself.

  The frequency response analyzer 7 has its voltage output terminal connected to the potential input terminal of the potentiostat 6 and its voltage input terminal connected to the current output terminal of the potentiostat 6.

Next, a method for measuring the corrosion potential of the structural member and the electrical conductivity of the reactor water using the corrosive environment measuring apparatus provided with the first embodiment of the corrosive environment sensor of the present invention will be described with reference to FIGS. To do. Here, a method for measuring the corrosion potential of the in-core instrumentation tube 131 and the conductivity of the reactor water by installing the corrosion environment sensor 2 inside the in-core instrumentation tube 131 provided in the reactor pressure vessel 102 will be described. explain.
FIG. 4 is an explanatory diagram showing a method for measuring a corrosive environment in a nuclear reactor of a boiling water reactor plant using the corrosive environment measuring apparatus provided with the first embodiment of the corrosive environment sensor of the present invention. It is. In FIG. 4, the same reference numerals as those shown in FIGS. 1 to 3 are the same parts, and detailed description thereof is omitted.

  As shown in FIG. 4, the in-reactor measurement tube 131 provided in the reactor pressure vessel 102 has a water passage hole 131 a so that the reactor water in the reactor pressure vessel 102 can flow into the in-reactor measurement tube 131. Is provided. The corrosion environment sensor 2 of the corrosion environment measuring device 1 is fixed in the in-furnace measurement tube 131. The corrosion environment sensor 2 detects both the corrosion potential of the in-reactor measuring tube 131 and the conductivity of the reactor water in the reactor pressure vessel 102. When measuring the corrosion potential, the other lead wire 42 of the potentiometer 5 is connected in advance to the in-furnace measurement tube 131.

  The corrosion potential is evaluated by measuring the potential difference between the inner surface of the in-furnace measuring tube 131 and the second metal electrode 25 of the corrosion environment sensor 2 with the potentiometer 5. The structural member in the reactor pressure vessel 102 depends on the oxygen, hydrogen peroxide, and hydrogen concentrations contained in the reactor water in contact with the structural member, the reactor water temperature, and the reactor water flow rate conditions. Generated potential. On the other hand, a reference potential corresponding to the concentration of hydrogen contained in the reactor water is generated at the second metal electrode 25.

The conductivity is measured by measuring the liquid resistance of the reactor water between the first metal electrode 24 and the second metal electrode 25. The liquid resistance is measured by the electrochemical impedance method using, for example, the potentiostat 6 and the frequency response analyzer 7 simultaneously with the measurement of the corrosion potential by the potentiometer 5 described above. An AC sine wave voltage whose frequency is changed from 1 mHz to 100 kHz using the frequency response analyzer 7 is applied between the first metal electrode 24 and the second metal electrode 25 via the potentiostat 6. . An alternating current flowing between the pair of metal electrodes 24 and 25 by applying a sine wave voltage is measured by the potentiostat 6. The impedance is calculated from the AC voltage between the applied frequency of 1 mHz and 100 kHz and the measured AC current. The Nyquist plot is created by displaying the real component of the calculated impedance on the horizontal axis and the imaginary component on the vertical axis, and the liquid resistance R is calculated from the semicircular intercept on the high frequency side. Based on the measurement result of the liquid resistance R, the conductivity is calculated from the following formula (1).
R = κ− ¹ · L · A ⁻¹ Formula (1)
Here, R is the resistance of the reactor water, κ is the conductivity, L is the distance between the pair of metal electrodes, and A is the cross-sectional area of the conduction portion between the pair of metal electrodes.

In the present embodiment, as shown in FIG. 3, of the surfaces of the metal electrodes 24, 25, the surfaces facing each other, the attachment portion to the insulating member 22, and the connection portion of the pair of conductors 28, 29 are provided. By covering the removed surface with an insulating coating portion 26, a conduction portion (current path) P is defined so that current flows reliably in the reactor water between the first metal electrode 24 and the second metal electrode 25. be able to. For this reason, the cell constant L · A ⁻¹ of the above equation (1) can be determined, and the accurate conductivity can be calculated from the above equation (1) based on the measurement result of the liquid resistance R.

In the present embodiment, the first metal electrode 24 and the second metal electrode 25 are rectangular flat plates having the same dimensions and are arranged in parallel so as to face each other. Path) P can be defined as a substantially rectangular parallelepiped portion existing between two electrodes. Therefore, the cell constant L · A ⁻¹ can be calculated from the geometric shape and arrangement of the first metal electrode 24 and the second metal electrode 25. That is, in the cell constant L · A ⁻¹ , the distance between the first metal electrode 24 and the second metal electrode 25 is L, and the flat plates of the first metal electrode 24 and the second metal electrode 25 are opposed to each other. It can be determined by assuming that the area of one surface is A. As a specific example, as shown in the description of the above configuration, the first metal electrode 24 and the second metal electrode 25 are square plate electrodes having a side of 5 mm, and are arranged in parallel with an interval of 1 mm. In this case, the cell constant L · A ⁻¹ is obtained from L = 1 × 10 ⁻³ (m) and A = 25 × 10 ⁻⁶ (m ² ) to 2.5 × 10 ⁻⁸ (1 / m). Based on the known measurement results of the cell constant L · A ⁻¹ and the liquid resistance R, the conductivity κ is calculated from the above equation (1).

On the other hand, unlike the present embodiment, when the first metal electrode 24 and the second metal electrode 25 are not covered with the insulating coating portion 26, they exist between these metal electrodes 24 and 25. The current conduction part (current path) cannot be defined so that the current flows reliably in the reactor water. For example, a current may flow so as to draw a large arc from the side surface of the first metal electrode 24 to the side surface of the second metal electrode 25. In addition, a current may flow from a plane other than the opposing surfaces of the first and second metal electrodes 24 and 25 to the adjacent metal structural member. That is, since the cell constant L · A ⁻¹ cannot be determined, an accurate conductivity cannot be calculated.

  As a result of the measurement by the corrosive environment measuring device 1, when it is found that the conductivity of the reactor water in the reactor pressure vessel 102 is increased, the boiling water reactor plant is more based on those measured values. Proper water quality management. For example, when conducting the noble metal injection, if the electrical conductivity exceeds a set reference value, the noble metal injection amount is reduced or the noble metal injection is stopped. By performing such an operation, it is possible to suppress an increase in the conductivity of the reactor water, and as a result, it is possible to suppress the occurrence of SCC and the development of cracks in the structural member in a structural member made of stainless steel or the like. .

  According to the first embodiment of the corrosive environment sensor of the present invention described above, a pair of metal electrodes 24 and 25 are provided on one metal casing 21 so that one surface faces each other, Since most of the surfaces of the pair of metal electrodes 24, 25 other than the opposing surfaces are covered with the radiation-resistant and heat-resistant insulating coating portion 26, the pair of metal electrodes 24, 25 can be arranged in a narrow installation space. In addition, the path of the current flowing between the pair of metal electrodes 24 and 25 can be defined reliably. That is, the accurate conductivity of the reactor water (reactor cooling water) in a corrosive environment can be measured in a narrow installation space such as in the reactor. As a result, based on the conductivity measured in a corrosive environment such as in a nuclear reactor, it is possible to perform effective water chemistry management to suppress corrosion, and maintain or improve the soundness of the structural members in the reactor. Can be planned.

  In addition, according to the present embodiment, the first metal electrode 24 and the second metal electrode 25 are each formed using platinum in which an electrode reaction of hydrogen occurs, so that the conductivity of the reactor water in a corrosive environment is increased. In addition to the measurement, it is possible to measure the corrosion potential of the structural member in the furnace.

  Furthermore, according to the present embodiment, the first metal electrode 24 and the second metal electrode 25 are formed such that the surfaces facing each other are planes having the same dimensions, and the facing planes are in the normal direction. Therefore, the cell constant can be calculated from the geometric shape and arrangement of the first metal electrode 24 and the second metal electrode 25. For this reason, it is not necessary to experimentally obtain the cell constant in advance using a solution having a known conductivity.

  In addition, according to the present embodiment, since the first metal electrode 24 and the second metal electrode 25 that are flat plates are arranged in parallel, the first metal electrode 24 and the second metal electrode 25 flow in the reactor water. By installing the corrosive environment sensor 2 along the direction, the fluidity of the reactor water between the first and second metal electrodes 24 and 25 can be ensured.

  Furthermore, according to the present embodiment, since the insulating coating portion 26 is formed of an insulating material having radiation resistance and heat resistance, it is irradiated with high temperature (about 280 ° C.) high pressure reactor water or irradiation in the nuclear reactor. It is possible to maintain an electrical insulating property against the emitted radiation.

[Second Embodiment]
Next, a second embodiment of the corrosive environment sensor of the present invention will be described with reference to FIGS.
FIG. 5 is a longitudinal sectional view showing a second embodiment of the corrosive environment sensor of the present invention, and FIG. 6 is an electrode part constituting a part of the second embodiment of the corrosive environment sensor of the present invention shown in FIG. FIG. 7 is a longitudinal sectional view showing an enlarged view and a side view thereof, and FIG. 7 shows corrosion in piping of a boiling water reactor plant using a corrosive environment measuring apparatus provided with a second embodiment of the corrosive environment sensor of the present invention. It is explanatory drawing which shows the measuring method of an environment. 5 to 7, the same reference numerals as those shown in FIGS. 1 to 4 are the same parts, and detailed description thereof is omitted.

  The second embodiment of the corrosive environment sensor of the present invention shown in FIGS. 5 and 6 is different from the electrode portion 23 of the first embodiment in shape and constituent material. Specifically, the electrode portion 23A of the corrosive environment sensor 2A is a columnar first metal attached to the central portion in the radial direction of the distal end surface (the upper end surface in FIGS. 5 and 6) of the other end of the insulating member 22. A cylindrical shape attached to the distal end surface of the insulating member 22 concentrically with the first metal electrode 24A, with the electrode 24A facing the outer peripheral surface of the first metal electrode 24A at a predetermined interval. And a second metal electrode 25A. This predetermined interval is set to a range in which the conductivity of the reactor water having a high electric resistance can be measured, as in the case of the first embodiment. Further, when the corrosive environment sensor 2A is installed, a distance that is the shortest than the distance between the metal structural member existing in the vicinity of the area where the corrosive environment sensor 2A is installed and the first metal electrode 24A or the second metal electrode 25A. It is set to become. The predetermined interval is, for example, about 1 mm. The first metal electrode 24A and the second metal electrode 25A have substantially the same height (length in the vertical direction in FIGS. 5 and 6).

  The first metal electrode 24A and the second metal electrode 25A are made of titanium plated with platinum. Titanium electrodes plated with platinum, like platinum electrodes, are insoluble, difficult to form an oxide film, long-lived radionuclides are not generated even when exposed to radiation, and have a hydrogen electrode reaction. It has the properties that occur.

  As in the case of the insulation coating portion 26 of the first embodiment, the insulation coating portion 26A has a surface facing the second metal electrode 25A on the surface of the first metal electrode 24A, the surface facing the insulation member 22. The surface excluding the attachment portion and the connection portion of the first conductor 28, that is, the circular tip surface (the top surface in FIGS. 5 and 6) of the first metal electrode 24 </ b> A is covered. Further, of the surface of the second metal electrode 25A, the surface excluding the surface (inner peripheral surface) facing the first metal electrode 24A, the attachment portion to the insulating member 22, and the connection portion of the second conductor 29, That is, the outer peripheral surface of the second metal electrode 25A and the annular front end surface (the upper end surface in FIGS. 5 and 6) are covered.

  Next, a method for measuring the corrosion potential of the structural member and the electrical conductivity of the reactor water using the corrosive environment measuring apparatus provided with the second embodiment of the corrosive environment sensor of the present invention will be described with reference to FIG. Here, a method for measuring the corrosion potential of the structural member and the conductivity of the reactor water by installing the corrosion environment sensor 2A in the sampling pipe 132 connected to the bottom drain pipe 123 (see FIG. 1) will be described.

First, before installing the corrosive environment sensor 2A in the sampling pipe 132, the cell constant L · A ⁻¹ in the above equation (1) is determined in advance. Specifically, the electrode portion 23A (see FIG. 5) of the corrosive environment sensor 2A is immersed in a 0.0746 g / 1.0 kg KCl aqueous solution whose conductivity κ is known to be 133 μS / cm, and the potentiostat 6 and the frequency The liquid resistance R is measured using the response analyzer 7. The liquid resistance R is measured using the electrochemical impedance method as in the case of the first embodiment described above. Based on the measured liquid resistance R and the known conductivity κ, the cell constant L · A ⁻¹ is calculated from the above equation (1).

  Next, as shown in FIG. 7, the corrosive environment sensor 2A of the corrosive environment measuring apparatus 1A is installed in the branch pipe 132a branched from the sampling pipe 132. The corrosion environment sensor 2 </ b> A detects both the corrosion potential of the sampling pipe 132 and the conductivity of the reactor water flowing in the sampling pipe 132. When measuring the corrosion potential, the other lead wire 42 of the potentiometer 5 is connected in advance to the sampling pipe 132.

  The corrosion potential is evaluated by measuring the potential difference between the inner surface of the sampling pipe 132 and the second metal electrode 25A of the corrosion environment sensor 2A with the potentiometer 5 as in the case of the first embodiment. Is called.

The conductivity is measured by measuring the liquid resistance of the reactor water between the first metal electrode 24A and the second metal electrode 25A. The liquid resistance is measured by the electrochemical impedance method using the potentiostat 6 and the frequency response analyzer 7 simultaneously with the measurement of the corrosion potential by the potentiometer 5 as in the case of the first embodiment. In the present embodiment, since the cell constant L · A ⁻¹ is determined in advance, it is possible to calculate the conductivity κ from the above equation (1) based on the measurement result of the liquid resistance R. .

In the present embodiment, of the surfaces of the first and second metal electrodes 24A and 25A, the opposing surfaces of the first and second metal electrodes 24A and 25A, the attachment portions to the insulating member 22, the first and second Since the surface excluding the connecting portion of the second conductive wires 28 and 29 is covered with the insulating coating portion 26A formed of an insulating material, the reactor water between the first metal electrode 24A and the second metal electrode 25A is surely provided. A current conduction part (current path) can be defined so that a current flows. Therefore, since the cell constant L · A ⁻¹ can be determined, an accurate conductivity can be calculated from the above equation (1) based on the measurement result of the liquid resistance R.

  According to the second embodiment of the corrosive environment sensor of the present invention described above, the same effects as those of the first embodiment described above can be obtained.

  Further, according to the present embodiment, since the first and second metal electrodes 24A and 25A are made of passive metal electrodes plated with platinum, the amount of expensive metal such as platinum used can be reduced. As a result, the material cost can be reduced.

[Other embodiments]
In the above-described first embodiment of the corrosive environment sensor of the present invention, an example in which platinum electrodes are used as the first and second metal electrodes 24 and 25 is shown. Use a metal electrode made of a metal material that has four properties: insolubility, the property of being difficult to form an oxide film, the property of not generating long-lived radionuclides even when exposed to radiation, and the property of causing an electrode reaction of hydrogen. Is also possible. That is, the first and second metal electrodes 24 and 25 can be formed using one or more materials of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium.

  In the second embodiment of the corrosive environment sensor of the present invention described above, an example is shown in which titanium metal electrodes plated with platinum are used as the first and second metal electrodes 24A and 25A. Uses a metal electrode plated with a metal material that has four properties: insoluble, the property that an oxide film is difficult to form, the property that a long-lived radionuclide is not generated even when exposed to radiation, and the property that a hydrogen electrode reaction occurs It is also possible to do. That is, it is also possible to use a passive metal electrode plated with one or more materials of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium.

  In the first embodiment described above, an example in which the metal electrode formed of the metal material is used as the first and second metal electrodes 24 and 25 is shown. As the metal electrode, as in the first and second metal electrodes 24A and 25A of the second embodiment described above, a passive state plated using any one or more of the above metal materials. It is also possible to use metal electrodes.

  In the second embodiment described above, a passive metal electrode plated with any one or more of the above metals is used as the first and second metal electrodes 24A and 25A. Although an example has been shown, a metal electrode formed of any one or more of the above metal materials, such as the first and second metal electrodes 24 and 25 of the first embodiment described above, is used. It is also possible to use it.

  In the above-described embodiment, the example in which the corrosion potential of the structural member is measured using the second metal electrodes 25 and 25A has been shown. However, the corrosion of the structural member using the first metal electrodes 24 and 24A is shown. It is also possible to measure the potential.

  In the above-described first embodiment, the first and second metal electrodes 24 and 25 are formed as rectangular flat plates having the same dimensions. However, the first and second metal electrodes are formed as follows. It is also possible to form on a flat plate of the same size with any outer shape other than a rectangular shape. Further, metal electrodes other than flat plates are also possible as long as the opposing surfaces are planes having the same dimensions and can be arranged in parallel so that the opposing surfaces overlap each other in the normal direction. For example, it is possible to use a pair of semi-cylindrical metal electrodes arranged so that rectangular planes face each other. Also in this case, similarly to the first metal electrode 24 and the second metal electrode 25 which are flat plates, the opposing flat surfaces are arranged along the flow direction of the reactor water, so that a pair of semi-cylindrical metal electrodes are disposed. It is possible to ensure the fluidity of the reactor water present in

  In the above-described second embodiment, the example in which the first metal electrode 24A is formed in a columnar shape is shown, but the first metal electrode can also be formed in a cylindrical shape.

  Further, the present invention is not limited to the first and second embodiments described above, and includes various modifications. The above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. For example, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, or replace another configuration for a part of the configuration of each embodiment.

2, 2A ... Corrosion environment sensor, 21 ... Metal casing, 22 ... Insulating member, 24, 24A ... First metal electrode (pair of metal electrodes), 25, 25A ... Second metal electrode (pair of metal electrodes) , 26, 26A ... insulation coating portion, 28 ... first conducting wire (one set of conducting wires), 29 ... second conducting wire (one set of conducting wires), 131 ... in-core instrumentation tube (structural member), 132 ... Sampling piping (structural members)

Claims (6)

A cylindrical metal casing disposed on a structural member through which reactor cooling water in a corrosive environment in a nuclear reactor plant circulates;
An insulating member formed of an insulating material having radiation resistance and heat resistance, and attached to the metal casing;
A pair of metal electrodes attached to the insulating member in a state where one surface faces each other with a predetermined interval and is electrically insulated from the metal casing,
A pair of conductive wires that are electrically connected to the pair of metal electrodes, respectively, and that are electrically insulated from the metal casing, and extend inside the insulating member and the metal casing;
It is formed of an insulating material having radiation resistance and heat resistance, and the surfaces of the pair of metal electrodes that are opposed to each other, the mounting portion to the insulating member, and the connecting portion of the set of conducting wires are excluded. A corrosive environment sensor comprising an insulating coating covering the surface. The corrosion environment sensor according to claim 1,
The corrosion environment sensor, wherein the pair of metal electrodes are arranged in parallel so that the surfaces facing each other are planes having the same dimension, and the surfaces facing each other overlap each other in the normal direction. The corrosion environment sensor according to claim 1,
The pair of metal electrodes are:
A columnar or cylindrical first metal electrode;
A corrosive environment sensor comprising: a cylindrical second metal electrode disposed concentrically with the first metal electrode on an outer peripheral side of the first metal electrode. The corrosion environment sensor according to any one of claims 1 to 3,
The pair of metal electrodes are formed using at least one material selected from gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium. The corrosion environment sensor according to any one of claims 1 to 3,
The pair of metal electrodes are passive electrodes plated with one or more materials selected from gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium. The corrosion environment sensor according to any one of claims 1 to 3,
The insulating coating portion is formed using any one or more materials of alumina, yttria stabilized zirconia, titania, ceria, aluminum nitride, silicon nitride, cordierite, mullite, steatite, forsterite, and cermet. Corrosion environment sensor characterized by

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