JP2001166082A - Method for detecting corrosive environment and method for operating nuclear power plant using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more surely suppress corrosion of a component by detecting electrochemical phenomena of the component with excellent precision in a nuclear reactor component and a piping contacting to reactor water or cooling water. SOLUTION: An electrochemical sensor according to this method consists of a reference electrode and a test specimen, and reference electrodes 9 and test specimens 10 made of the same material to the component are arranged in a reactor core part 2, a primary loop recirculation system, and a feed water line. Potential difference between the reference electrode 9 and the test specimen 10 is measured to detect the corrosive environment based on excessive voltage change in the test specimen 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear power plant, and more particularly to a method of detecting a corrosive environment and a nuclear power plant suitable for maintaining the integrity of constituent materials in a reactor structure and piping in contact with reactor water or cooling water. The present invention relates to an operation method of a power plant.

[0002]

2. Description of the Related Art Generally, in a boiling water nuclear power plant (hereinafter, referred to as a BWR plant), steam generated in a nuclear reactor is sent to a turbine through a main steam pipe.
So I finish my work. This steam is condensed in the condenser and returned to the reactor through the condensing pipe and the water supply pipe. Normally, when water is returned to the reactor, and when the reactor water returned to the reactor flows through the reactor, equipment conditions such as equipment and piping that the water and reactor water come into contact with impair the quality of the water and reactor water. Every effort has been made to ensure that the quality of the water supply and reactor water is reduced below the standards set by the standards.

[0003] One of the main purposes of maintaining the quality of feedwater and reactor water is to protect the materials in contact with it from corrosion. For this purpose, it is necessary to detect the values of the electric conductivity, pH, dissolved oxygen concentration and dissolved hydrogen concentration, and to suppress a decrease in water quality. Usually, the corrosion behavior is influenced by the temperature, so the temperature is also an important measurement item.

[0004]

As described above, the conductivity of the feed water and the reactor water must be reduced to enable the corrosion of the constituent materials to be suppressed.
It is important to properly maintain the pH, dissolved oxygen concentration and dissolved hydrogen concentration. However, it is not clear what kind of electrochemical phenomena actually occurs when the constituent material itself affected by water quality comes into contact with water supply and reactor water, and it is not possible to confirm the effectiveness of corrosion suppression. For example, according to data obtained in the laboratory, the decrease in conductivity due to the removal of impurities is clear, and the improvement in water quality due to hydrogen injection, noble metal injection, and the like also shows no doubt. However, the shapes and materials of the constituent materials are quite various, and it cannot be said that it is appropriate to estimate only the phenomena actually occurring in the constituent materials during the operation of the plant based only on the water quality data and the material test data.

Accordingly, an object of the present invention is to accurately detect an electrochemical phenomenon of a constituent material in a reactor internal structure or piping in contact with reactor water or cooling water, and to more reliably suppress corrosion of the constituent material. An object of the present invention is to provide a method for detecting a corrosive environment and a method for operating a nuclear power plant using the method.

[0006]

According to the method for detecting a corrosive environment according to the present invention, a reference electrode and a test piece of the same material as a constituent material are formed in a reactor water or cooling water flow area around a reactor internal structure, equipment or piping. The sensor is characterized by measuring a potential difference between a reference electrode and a test piece, and detecting a corrosive environment based on an excessive change in potential of the test piece.

[0007] In the method of the present invention, a potential change can be easily detected by an electrochemical sensor, and it is possible to reliably detect that an excessive potential change leads to an environment where corrosion is likely to proceed.

Another method of detecting a corrosive environment differs from that described above in that an electrical test is performed by using a reference test piece and a test piece of the same material as a constituent material in a reactor water or cooling water flow area around a reactor structure, equipment, or piping. A chemical sensor is provided, a current flowing between the reference test piece and the test piece is measured, and a corrosive environment is detected based on an excessive current value change of the test piece.

In the method of the present invention, a change in current can be easily detected by an electrochemical sensor, and it is possible to reliably detect that an environment in which a crack easily develops from an excessive current change.

Further, another method for detecting a corrosive environment is to apply a reference electrode, a reference test piece, and a test piece of the same material as a constituent material to a reactor water or cooling water flow area inside a reactor structure, equipment, or piping. An electrochemical sensor is installed to measure the potential difference between the reference electrode and the test piece and the current flowing between the reference test piece and the test piece. It is characterized by detecting an environment.

In the method of the present invention, the change in potential and the change in current can be easily detected by the electrochemical sensor, so that the corrosion and the crack easily progress due to the excessive change in potential and current. Can be reliably detected.

In the method of the present invention, a crack is desirably formed in the test piece in advance and a stress is applied.

Further, in the method of the present invention, the test piece is desirably treated with a noble metal. Further, the method for operating a nuclear power plant according to the present invention, when an excessive potential change, a current value change or a potential change and a current value change are detected by the above-described corrosive environment detection method, adjusts the hydrogen injection amount to adjust the corrosion potential. It is characterized by lowering.

In the method of the present invention, when minute damage is detected by the electrochemical sensor, the corrosion potential is lowered by quickly changing the hydrogen injection amount. Thus, the progress of corrosion can be suppressed, and the soundness of the constituent materials can be prevented from being impaired.

Further, an operation method different from the above is that when an excessive potential change, a current value change, or a potential change and a current value change are detected by the above-described corrosive environment detection method, the corrosion potential is adjusted while adjusting the hydrogen injection amount. It is characterized by lowering.

In the method of the present invention, when minute damage is detected by the electrochemical sensor, the amount of hydrogen injected is immediately adjusted to lower the corrosion potential. This makes it possible to suppress the progress of the corrosion and prevent the soundness of the constituent materials from being impaired.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the method of the present invention will be described with reference to the drawings. In FIG. 1, a reactor pressure vessel 1 is a vessel made of steel and contains a reactor core 2 therein. Water as a coolant, that is, reactor water is supplied to the reactor core 2. A reactor recirculation system (hereinafter, referred to as a PLR system) is provided outside the reactor pressure vessel 1, and the reactor water extracted by the PLR pump 3 from the reactor core 2 circulates.

On the other hand, a turbine system for recovering the thermal output of the reactor is connected to the reactor pressure vessel 1. The turbine system includes a turbine 4 and a condenser 5. Condensed water condensed in the condenser 5 is extracted by a condensate pump 6, and is treated in a condensate purification device 7 to satisfy water quality standards. In this water treatment, the supplied water can satisfy the water quality standards in terms of conductivity, pH, dissolved oxygen concentration, and the like. Water is supplied into the reactor pressure vessel 1 by a water supply pump 8.

An electrochemical sensor for realizing the method of the present invention comprises a combination of a reference electrode and a test piece, and is arranged as follows. That is, the reference electrode 9 and the test piece 10 made of the same material as the constituent material are arranged in the core 2. A reference electrode 9 and a test piece 10 made of the same material as the constituent material are arranged in the PLR system, and a reference electrode 9 and a test piece 10 made of the same material as the constituent material are arranged in a water supply path through which water flows. Each of the reference electrode 9 and the test piece 10 is attached so as to be in contact with the reactor water and the water supply so as to serve as a sensor for detecting a potential as described later.

Further, the reference electrode 9 and the test piece 10 are connected to a measurement processing device 11 for analyzing a potential difference, a magnitude of a potential variation, and the like based on the detected potential signal. The measurement processing device 11 is connected to a data processing computer 12. In the drawings, reference numeral 13 indicates a containment vessel.

Next, the method of the present invention will be described. A potential signal is provided from the electrochemical sensor to the measurement processing device 11. The potential difference between the reference electrode 9 and the test piece 10 is calculated as the most important value. Further, the magnitude and the cycle of the potential fluctuation are obtained in accordance with the time. FIG. 2 shows an example of the potential change. The constituent material of this example is SUS304 steel. It is data when immersed in a 3.5% NaCl solution at a temperature of 80 ° C. The electric potential of SUS304 steel changes in the base direction from a certain time. The potential drop indicates that slight damage has occurred and this is progressing constantly. In the present embodiment, the occurrence of such a potential change can be easily detected by the electrochemical sensor. When the potential change is excessive, it indicates that there is an environment in which corrosion is likely to progress. Therefore, in operation of the plant, the environment is changed to an environment in which corrosion hardly progresses by, for example, hydrogen injection.

(Second and Third Embodiments) In the second embodiment, a reference test piece 14 as shown in FIG. 3A is used instead of an electrochemical sensor comprising a reference electrode 9 and a test piece 10. And a test piece 10 of the same material as the constituent material. In the third embodiment, an electrochemical sensor including a reference electrode 9, a reference test piece 14, and a test piece 10 as shown in FIG. 3B is used.

In the case of the electrochemical sensor shown in FIG.
A current value flowing between the reference test piece 14 and the test piece 10 is measured. In the case of the electrochemical sensor shown in FIG. 3B, the potential difference between the reference electrode 9 and the test piece 10 is measured, and the current flowing between the reference test piece 14 and the test piece 10 is measured.

FIG. 4 shows the relationship between the current and the load between the CT test piece and the cathode plate. This raises the water temperature to 252
It is a value when kept at ° C. It can be seen that the crack developed by the load and the current value changed. Also, when the load was removed, the growth of the cracks stopped, and at this time, it was found that the current value was stable.

In the second and third embodiments, the occurrence of such a change in the current value can be easily detected by the electrochemical sensor. If the change in the current value is excessive, it indicates that the environment is in an environment where cracks are likely to develop. Therefore, in operation of the plant, the environment is changed to an environment in which cracks are unlikely to grow by, for example, hydrogen injection.

The reference electrode 9 and the reference test piece 14 of the first, second and third embodiments can be formed using test pieces of the same material as the constituent material.

Alternatively, the reference electrode 9 and the reference test piece 14 may be made of platinum.

Further, the reference electrode 9 is replaced with A
g / AgCl or Fe / Fe ₃ O ₄ .

On the other hand, the test piece 10 of the first, second, and third embodiments can be configured as follows. That is, in FIG. 5, the flat plate 15 is bent into a U-shape, and both ends of the flat plate 15 are fixed with bolts 16 and nuts 17 as fastening members, and a stress is previously applied to the material. Flat plate 1
5 is connected with a lead wire 18 in advance.

The use of such a test piece 10 makes it possible to detect the occurrence of stress corrosion cracking.

Further, in FIG. 6, a slit 20 is cut in the flat plate 19, a fine crack 21 is cut in advance at the tip of the slit 20, and a portion of the slit 20 is
To apply stress to the material. Such a test piece 10
It is possible to detect the progress of stress corrosion cracking by using the.

7 (a) and 7 (b), the test piece 10 may be constructed by superimposing a second flat plate 23 of the same material on the first flat plate 22. The lead wire 18 is connected to the first flat plate 22. By using such a test piece 10, occurrence of crevice corrosion can be detected.

Further, in FIGS. 8A and 8B, the first
The test piece 10 may be formed by stacking a second flat plate 23 of the same material on the flat plate 22 and joining both members by spot welding 24. The use of such a test piece 10 makes it possible to detect the occurrence of crevice corrosion or stress corrosion cracking in crevice corrosion.

In FIG. 9, the test piece 10 may be constructed by stacking a second flat plate 23 of the same material on the first flat plate 22 and connecting both members with bolts 25 and nuts 26. The use of such a test piece 10 makes it possible to detect the occurrence of crevice corrosion.

10 (a) and 10 (b), a Teflon sheet 27 is placed on the first flat plate 22, and a second flat plate 23 made of the same material as the first flat plate 22 is placed thereon. You may comprise. The use of such a test piece 10 makes it possible to detect the occurrence of crevice corrosion. The same effect can be obtained by using graphite wool or mica instead of the Teflon sheet 27 described above.

In FIG. 11, the test piece 10 may be formed by joining the first member 28 and the second member 29 with a welding joint 30.

Further, the test piece 10 subjected to the sensitizing heat treatment was used.
Alternatively, it is possible to use the test pieces 10 subjected to the noble metal treatment instead of the test pieces 10 described above.

(Fourth Embodiment) A fourth embodiment of the method of the present invention will be described with reference to FIG. A hydrogen injection device 31 is provided which is connected to a path from the condensate purification device 7 to the water supply pump 8. The means used for detecting the corrosive environment is the same as that of the first embodiment.

In this embodiment, the potential signal and the current signal from each electrochemical sensor are supplied to the measurement processing device 11 during the operation of the plant. When minor damage is detected,
An injection command from the computer 12 is input to the hydrogen injection device 31.

At this time, hydrogen is injected from the hydrogen injection device 31 into the supply water flowing through the water supply path. Thereby, the corrosion potential can be reduced and the progress of corrosion can be stopped.

In a plant in which noble metal is injected, when minute damage is detected, the hydrogen injection device 3
The corrosion potential is lowered while adjusting the amount of hydrogen supplied from 1 to stop the progress of corrosion.

The means used for detecting the corrosive environment is not limited to the one in the first embodiment, but may be any of the second and third means.
Of the embodiment can be used.

(Fifth Embodiment) A fifth embodiment of the method of the present invention will be described with reference to FIG. A hydrogen injection device 32 connected to the PLR system is provided. The means used for detecting the corrosive environment is the same as that of the first embodiment.

In this embodiment, the potential signal and the current signal from each of the electrochemical sensors are supplied to the measurement processing device 11 during the operation of the plant. When minor damage is detected,
An injection command from the computer 12 is input to the hydrogen injection device 32. At this time, hydrogen is injected from the hydrogen injection device 32 into the reactor water flowing in the PLR system. This makes it possible to lower the corrosion potential and stop the progress of corrosion.

The means used for detecting the corrosive environment is not limited to the one in the first embodiment, but may be the second or third means.
Of the embodiment can be used.

(Sixth Embodiment) A sixth embodiment of the present invention will be described with reference to FIGS. An electrochemical sensor is arranged at a weld 35 between a shroud 33 and a shroud support 34, which is one of the welds in the reactor pressure vessel 1. This electrochemical sensor comprises a reference electrode 9 and a test piece 10.

In this embodiment, during operation of the plant, a potential signal from the electrochemical sensor is supplied to the measurement processing device. If a potential change is detected, the welded portion 35 is in an environment where corrosion is likely to proceed. When such a situation can be confirmed, the environment is changed to an environment in which corrosion hardly progresses, for example, by hydrogen injection.

(Seventh Embodiment) A seventh embodiment of the present invention will be described with reference to FIGS. The means used for detecting the corrosive environment is the same as that of the first and second embodiments. In this embodiment mode, the potential or the current value is measured at different time intervals. In the figure, (a) shows the results measured at 1 minute intervals, and (b) shows the results measured at 10 second intervals. The measurement at one-minute intervals results in a gentle curve, and the change cannot be reliably detected. On the other hand, the measurement at 10-second intervals makes it possible to accurately detect a sharp change indicating the occurrence of minute damage. It can be seen from the comparison between the two that the time interval in the measurement is preferably set to 10 seconds or less.

[0049]

According to the method of the present invention, the reactor internal components,
Install an electrochemical sensor in the reactor water or cooling water flow area around the equipment or in the piping to measure the potential difference, current value or potential difference and current value, and based on excessive potential change, current value change or potential change and current value change. Corrosive environment can be detected.

Therefore, according to the present invention, it is possible to quickly change the water quality to an optimal one that does not cause corrosion or the like according to the obtained information on the constituent materials, and to maintain the soundness of the constituent materials.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the method of the present invention.

FIG. 2 is a graph showing a change in potential change of SUS304 steel according to the method of the present invention.

FIG. 3A is a configuration diagram showing an electrochemical sensor according to a second embodiment of the method of the present invention. (B) is a block diagram showing an electrochemical sensor according to a third embodiment.

FIG. 4 is a diagram showing the relationship between current and load between a CT test piece and a cathode plate according to the method of the present invention.

FIG. 5 is a configuration diagram showing an example of a test piece according to the method of the present invention.

FIG. 6 is a configuration diagram showing another example of a test piece according to the method of the present invention.

FIG. 7A is a front view showing another example of the test piece according to the method of the present invention. (B) is a side view of the test piece of (a).

FIG. 8A is a front view showing another example of the test piece according to the method of the present invention. (B) is a side view of the test piece of (a).

FIG. 9A is a front view showing another example of the test piece according to the method of the present invention. (B) is a side view of the test piece of (a).

10A is a front view showing another example of the test piece according to the method of the present invention, and FIG. 10B is a side view of the test piece of FIG.

FIG. 11 is a sectional view showing another example of the test piece according to the method of the present invention.

FIG. 12 is a configuration diagram showing a fourth embodiment of the method of the present invention.

FIG. 13 is a configuration diagram showing a fifth embodiment of the method of the present invention.

FIG. 14 is a configuration diagram showing a sixth embodiment of the method of the present invention.

FIGS. 15A and 15B are graphs showing changes in potential or current when measured at different time intervals in the seventh embodiment of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor pressure vessel 2 Reactor core part 9 Reference electrode 10 Test piece 11 Measurement processing device 14 Reference test piece 31 and 32 Hydrogen injection device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G21D 1/00 G21C 17/02 GDB 3/08 G21D 1/00 WF term (reference) 2G024 AD33 AD34 BA12 BA21 CA18 2G050 BA03 CA01 EB03 EC02 2G075 AA03 BA03 CA07 CA13 CA40 DA02 DA14 EA08 FA10 FA12 FC14 FC19 GA34 4K062 AA05 AA10 CA10 DA10 EA04 EA11 FA02 FA04 FA05 FA16 GA10

Claims (8)

[Claims] 1. A method for detecting a corrosive environment of a constituent material in a reactor internal structure, equipment, or piping in contact with reactor water or cooling water, comprising: Or provided an electrochemical sensor consisting of a reference electrode and a test piece of the same material as the constituent material in the cooling water flow area,
A method for detecting a corrosive environment, comprising: measuring a potential difference between the reference electrode and the test piece; and detecting a corrosive environment based on an excessive change in potential of the test piece. 2. A method for detecting a corrosive environment of a constituent material in a reactor internal structure, equipment, or piping in contact with reactor water or cooling water, the method comprising: detecting a corrosive environment of the reactor internal structure, equipment surroundings, or piping. An electrochemical sensor consisting of a reference test piece and a test piece of the same material as the constituent material is provided in a water or cooling water flow area, and a current flowing between the reference test piece and the test piece is measured. A corrosive environment detecting method, wherein a corrosive environment is detected based on an excessive current value change. 3. A method for detecting a corrosive environment of a constituent material in a reactor internal structure, equipment, or piping that comes into contact with reactor water or cooling water, the method comprising detecting a corrosive environment of the reactor internal structure, equipment surroundings, or piping. An electrochemical sensor comprising a reference electrode and a reference test piece and a test piece of the same material as the constituent material is provided in a water or cooling water flow area, and a potential difference between the reference electrode and the test piece and the reference test piece are provided. A method for detecting a corrosive environment, comprising: measuring a current flowing between the test piece and a corrosive environment based on both an excessive change in potential and a change in current value of the test piece. 4. The method for detecting a corrosive environment according to claim 1, wherein a stress is previously applied to the test piece. 5. The method for detecting a corrosive environment according to claim 1, wherein a crack is formed in the test piece in advance, and a stress is applied. 6. The method for detecting a corrosive environment according to claim 1, wherein said test piece is treated with a noble metal. 7. A reactor internal structure of a nuclear power plant,
An operating method for maintaining the quality of reactor water or cooling water at a predetermined level so as to protect equipment and piping from corrosion, and an excessive potential change in the method for detecting a corrosive environment according to claim 1, 2 or 3. A method for operating a nuclear power plant, wherein a change in current value or a change in potential and a change in current value are detected, the amount of hydrogen injected is adjusted to lower the corrosion potential. 8. In a plant in which a noble metal is injected, when an excessive potential change, a current value change, or a potential change and a current value change are detected by the method for detecting a corrosive environment according to claim 1, hydrogen or hydrogen is detected. The method for operating a nuclear power plant according to claim 7, wherein the corrosion potential is lowered while adjusting the injection amount.