JP2010150633A - Method for suppressing stress corrosion crack of plant constituting member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for suppressing the stress corrosion crack of a plant constituting member which can further suppress the propagation of a crack. <P>SOLUTION: A nozzle 11 is arranged so as to face a crack 1 generated in a reactor core shroud 6 found by eddy current flaw examination or the like. Oxygen is blown into pure water 13 within a chemical tank 12 from a nitrogen-oxygen feeder 14. The pure water 13 containing oxygen is pressurized by the pump 15, is passed through a high pressure hose 21, is introduced into a heater 16, and is heated to 553K. The heated pure water 13 is injected from the nozzle 11 toward the opening part of the crack 1, and is made to flow into the crack 1 generated in the reactor core shroud 6. The pure water 13 made to flow into the crack 1 is fluidized within the crack 1, reaches the tip of the crack 1, is inverted and is made to flow out to the outside of the crack 1. By the temperature of the pure water 13 and the action of oxygen, an oxide film 2 is formed on the whole of the inside face of the crack 1 from the opening of the crack 1 to the tip of the crack 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for suppressing stress corrosion cracking of plant components, and more particularly to a method for suppressing stress corrosion cracking of plant components suitable for application to a boiling water nuclear power plant.

  In a boiling water nuclear power plant, cooling water (coolant) is heated by heat generated by nuclear reaction of nuclear fuel material in a nuclear reactor to generate steam. This steam is supplied to the turbine to rotate the turbine. The generator connected to the turbine also rotates to generate electricity. In a boiling water nuclear power plant, suppression of stress corrosion cracking of plant components is an important issue from the viewpoint of improving the operating rate.

It is known that stress corrosion cracking is caused by a combination of material factors, stress factors, and environmental factors. Among them, environmental factors are formed by hydrogen peroxide and oxygen generated by radiolysis of cooling water. The cathode reaction shown by the formulas (1) and (2) takes away electrons from the surface of the plant component that contacts the cooling water, and hydrogen peroxide and oxygen are reduced to water. As a result of the anodic reaction of formula (3), which is this counter reaction, the metal of the plant component is eluted.
O ₂ + 4H ⁺ + 4e ⁻ = 2H ₂ O (1)
^{_{H 2 O 2 + 2H + +}} 2e - = 2H 2 O (2)
^{M = M n + + ne -} (3)
In stress corrosion cracking, more metal elutes from easily leaching sites such as grain boundaries of plant components. When attention is paid to the environment inside the crack in which stress corrosion cracking occurs, an oxide film is gradually formed in the vicinity of the crack tip after the new surface is exposed by the progress of the crack. In the boiling water nuclear power plant, an oxide film is formed on the surface of the plant component by the above-described oxygen and hydrogen peroxide. These oxidizing agents enter the crack by diffusion. However, these oxidizing agents are consumed by forming an oxide film on the inner surface of the crack before reaching the crack tip. For this reason, the oxidizer does not reach the crack tip in the crack that has propagated to a certain depth or more. Even if the oxidant reaches the crack tip, the concentration of the oxidant at the crack tip is extremely low compared to the vicinity of the opening of the crack. Therefore, the oxide film formed in the vicinity of the crack tip is thinner than the vicinity of the crack opening. For this reason, the cathode reaction site is fixed in the vicinity of the crack opening, and the anode reaction site, that is, the aforementioned “easily eluted site” is fixed to the crack tip. For this reason, a cathodic reaction mainly occurs near the crack opening, and an anodic reaction mainly occurs at the crack tip, thereby forming an electrical closed circuit. Along the flow of electricity in this closed circuit, sulfate ions and chloride ions move into the crack and are concentrated. This makes the pH in the crack acidic, creating an environment in the crack that is more susceptible to corrosion.

  From the above, the following four methods can be considered as methods for suppressing stress corrosion cracking. First, focusing on the cathode side, (A) reducing the concentration of oxidizing species such as oxygen and hydrogen peroxide at the cathode reaction site, or (B) oxygen and hydrogen peroxide on the surface of the plant component. Reducing the amount of oxidized species reached and reducing the cathode current. Further, focusing on the anode side, (C) reducing the anode current by suppressing metal elution at the anode reaction site, or (D) increasing the anode current in place of metal elution. It is done. By applying any one or more of these methods, the development of stress corrosion cracking can be suppressed.

  The stress corrosion cracking suppression method for reducing the concentration of oxidizing species such as oxygen and hydrogen peroxide at the cathode reaction site, which is the method of (A), is to inject hydrogen into the feed water and introduce it into the reactor. A technique for reducing hydrogen peroxide and oxygen to water by reacting with hydrogen peroxide and oxygen contained in cooling water in the reactor is known. This technique is generally called hydrogen injection and is used in many boiling water nuclear power plants. However, when hydrogen is excessively injected, an event occurs in which the surface dose rate of the main steam system (for example, main steam pipe) increases. For this reason, the amount of hydrogen injected is suppressed to such an extent that the surface dose rate of the main steam system does not increase. In this case, there may be a portion where the occurrence of stress corrosion cracking and the suppression of the development are insufficient.

As a technique for improving the hydrogen injection effect, there is noble metal injection (Japanese Patent No. 3002129). Precious metal injection is a technique for suppressing stress corrosion cracking of a plant component by attaching particles of the precious metal injected into the feed water to the surface of the plant component. Specifically, the aqueous solution containing the noble metal is circulated in the nuclear reactor while the reactor is shut down, and the noble metal is attached to the surface of the plant constituent member in contact with the aqueous solution containing the noble metal. The hydrogen oxidation reaction represented by the formula (4) is promoted on the surface of the plant constituent member by the action of the noble metal attached to the plant constituent member. As a result, the anode current is increased. Instead of the anode current generated by elution of the metal of the plant component, the anode current due to the oxidation reaction of hydrogen increases. For this reason, by the method of (D), the anode current replaced with metal elution is increased, and the stress corrosion cracking is suppressed.
H ₂ = 2H ⁺ + 2e ⁻ (4)
Moreover, the stress corrosion cracking suppression technique using a photocatalyst is described in Unexamined-Japanese-Patent No. 2001-4789. In this technique, a photocatalyst (for example, titanium oxide) injected into the nuclear reactor while the nuclear reactor is shut down is injected into the nuclear reactor, and a photocatalytic film is formed on the surface of the plant component. The photocatalyst on which this film is formed is irradiated with Cherenkov light generated in the reactor core. Electrons excited by the photocatalyst by irradiation with Cherenkov light become the anode current, and therefore stress corrosion cracking is suppressed by the method (D) that increases the anode current instead of metal elution.

  The conventional technology described above is a surface treatment technology for suppressing stress corrosion cracking. On the other hand, Japanese Patent Application Laid-Open No. 9-157828 discloses that application of surface treatment technology suppresses overall corrosion of plant components and suppresses radioactivity incorporation into the oxide film on the surface to reduce exposure. . When the boiling water reactor is shut down, hot water or air containing water vapor is supplied into the carbon steel pipe of the system and brought into contact with the inner surface of the carbon steel pipe for a predetermined time. This is a technique for forming an iron oxide film on the inner surface.

  The dose rate in the vicinity of the pipe depends on the amount of radioactivity taken into the oxide film generated on the inner surface of the pipe during operation of the nuclear reactor. It is known that the formation rate of the oxide film depends on the corrosion rate, but the corrosion rate tends to saturate after several hundred hours. This corresponds to the fact that the increase in the thickness of the oxide film formed on the surface during the operation of the nuclear reactor shows a saturation tendency. Therefore, by pre-applying an oxide film to the inner surface of the carbon steel pipe before the start of the reactor operation, metal elution is suppressed at the anode reaction site, the anode current is reduced, and the corrosion rate is reduced. Therefore, radioactivity uptake is reduced (see (C) above). For this reason, the dose rate of piping made from carbon steel can be reduced.

Japanese Patent No. 3002129 Japanese Patent Laid-Open No. 2001-4789 JP-A-9-157828

  In the prior art described in each of the above-mentioned known examples, a coating is formed by immersing a part or all of the in-furnace equipment to be constructed in cooling water and attaching surface treatment components (noble metal, photocatalyst, etc.) to the surface. Technology to form. By immersing the in-furnace equipment in the cooling water, a film is formed on the surface in contact with the cooling water of the in-furnace equipment. Since a film is formed on the surface of the in-furnace equipment, surface treatment components such as high-temperature water or water vapor, or a noble metal and a photocatalyst (for example, titanium oxide) are evenly distributed on the surface of the in-furnace equipment. However, when a crack exists on the surface of the in-furnace equipment, the penetration of the surface treatment component into the crack largely depends on diffusion in the cooling water. In this case, when the surface treatment component film is formed on the inner surface of the crack in the process of diffusion of the surface treatment component contained in the cooling water in contact with the surface of the furnace equipment into the crack, The concentration of surface treatment components contained in the cooling water in the crack is reduced. For this reason, there is a possibility that the concentration of the surface treatment component in the cooling water existing on the inner surface of the crack does not reach the required concentration at the crack tip. Therefore, the target surface treatment may not be performed at the tip of the crack.

  The objective of this invention is providing the stress corrosion cracking suppression method of the plant structural member which can further suppress progress of a crack.

  A feature of the present invention that achieves the above-described object is that a heated fluid containing an oxidant is disposed from the injector toward the crack, facing the crack generated in the plant component of the nuclear power plant. And an oxide film is formed on the inner surface of the crack by the oxidizing agent contained in the fluid flowing into the crack.

  According to the present invention, since the fluid containing the oxidant is jetted toward the crack, the heated fluid containing the oxidizer flows into the crack, and the inner surface of the crack from the opening of the crack to the tip of the crack An oxide film can be formed entirely. As a result, it is possible to reduce the cathode current by reducing the amount of oxidizing species such as oxygen and hydrogen peroxide that reach the crack inner surface generated in the plant component, or the plant at the anode reaction site of the crack. Since elution of the constituent members can be suppressed and the anode current can be reduced, the crack growth rate can be suppressed. Therefore, stress corrosion cracking of the plant component can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the progress of the crack which arises in the plant structural member of a nuclear power plant can further be suppressed.

  The inventors examined stress corrosion cracking of plant components made of austenitic stainless steel in a boiling water nuclear power plant. The inventors newly found the following matters based on the examination of the internal environment of the crack of the plant component member in which stress corrosion cracking occurs. The new matter that the inventors have grasped is that the crack caused by stress corrosion cracking progresses due to the difference in the thickness of the oxide film inside and outside the crack. By giving, there is a possibility that progress of stress corrosion cracking may be suppressed. Therefore, the inventors conducted an experiment for confirming the effect obtained by applying an oxide film equivalent to that outside the crack in the crack in advance.

  As described above, the corrosion reaction of the plant component in the aqueous solution is explained by the transfer of electric charges performed between the metal constituting the plant component and the component contained in the aqueous solution. The driving force for charge transfer is a potential, and as a result, the amount of electrochemical reaction in which charge transfer is performed can be measured as a current. Accordingly, by evaluating the amount of charge exchanged when the metal is placed at an arbitrary potential, the level of the corrosion rate of the metal can be determined. A diagram obtained by applying a predetermined potential to a metal and measuring the amount of charge exchanged at that time as a current is called a polarization curve. In the case of stress corrosion cracking, in an environment simulating the water quality in the crack, the metal potential at the tip of the crack is more easily eluted by measuring the current at each time while changing the potential of the metal. Can be evaluated.

  Therefore, the inventors determined whether the ease of charge transfer between the metal and water at the crack tip depends on the presence or absence of an oxide film in an environment simulating the inside of a crack in a boiling water reactor during rated operation. It was examined by measuring the polarization curve. Here, the water quality in the crack will be described. As described above, in the cooling water (coolant) in the nuclear reactor, sulfate ions eluted from the ion exchange resin are present at a concentration of 1 ppb or less. It is known that this sulfate ion is concentrated several hundred to several thousand times in the vicinity of the crack tip. For this reason, the anodic polarization curve was measured by adding 1 ppm of sulfuric acid in order to simulate the water quality at the crack tip. The cathodic polarization curve was considered to occur only outside the crack in which sulfuric acid was not concentrated and in the vicinity of the opening of the crack, and was measured in pure water to which sulfuric acid was not added. In order to investigate the difference due to the presence or absence of an oxide film, SUS304 stainless steel previously provided with an oxide film under conditions of 280 ° C., 8 MPa, oxygen concentration 300 ppb, 500 hours, and SUS304 stainless steel not previously provided with an oxide film On the other hand, the polarization curves were measured under conditions simulating the inside of a boiling water reactor during rated operation. The polarization curves of these two types of SUS304 stainless steel were compared. Since the elution rate of the metal when the metal is placed at a predetermined potential can be measured as a current by the polarization curve, the transfer of charge of the anode reaction on the metal surface is inhibited ((C) metal at the anode reaction site. The action of suppressing the elution of the anode and reducing the anode current) was confirmed by forming an oxide film.

Experimental conditions, the pure water conductivity 0.056μS · cm ^-1, pressurized to 8MPa the purpose of preventing boiling temperature controlled at 280 ° C. and led into the hot bath loaded with specimens. Sulfuric acid was added from the upstream side of the high-temperature tank and continuously injected at a flow rate ratio of 1 ppm in the high-temperature tank. A commercially available SUS304 stainless steel wire with a diameter of φ0.5 mm was used as a test piece, a SUS304 stainless steel wire (preliminary oxidation test piece) in which an oxide film was previously formed on the surface, and a polished state in which an oxide film was not previously formed on the surface SUS304 stainless steel wire (non-pre-oxidation test piece) was prepared. The preliminary oxidation test piece was held in pure water at 280 ° C., 8 MPa, and oxygen concentration of 300 ppb for 500 hours to form an oxide film on the surface of the SUS304 stainless steel wire. The polarization curve for each test piece was measured by applying a potential to each test piece using a potentiostat and measuring the current at that time.

  The current measurement results in the above experiment are shown in FIG. FIG. 3 shows the relationship between potential and current density. In the pre-oxidation test piece, the potential range (−0.5 to +0.2 V vs. SHE) that stainless steel can indicate in the reactor pressure vessel of the boiling water reactor due to the influence of the oxide film formed by the pre-oxidation. The current density decreased in the entire area. In the pre-oxidation test piece, the current density was reduced to about 1/3 compared to the non-pre-oxidation test piece. -0.4 V vs. At potentials below SHE, the anode current density of the pre-oxidation specimen was not observed. A decrease in current density in the pre-oxidized specimen indicates that the corrosion rate of the specimen has decreased. That is, even under conditions where sulfuric acid is concentrated to 1 ppm at the crack tip, the oxide film formed in advance by the pre-oxidation treatment suppresses elution of the metal that is the base material of the test piece.

The inventors further conducted an experiment to examine how the oxide film formed by the preliminary oxidation affects the oxygen concentration dependence of the cathode polarization curve. In this experiment, a pre-oxidation test piece and a non-pre-oxidation test piece were placed in pure water not filled with sulfuric acid having a temperature of 280 ° C. and an electric conductivity of 0.056 μS · cm ⁻¹ filled in a high-temperature tank having a pressure of 8 MPa. It was immersed. The currents flowing through these test pieces were measured, and the respective currents were compared. As a result of this experiment, the formation of an oxide film hinders the transfer of the cathode reaction charge on the metal surface ((B) the cathode current is reduced by reducing the amount of oxidizing species such as oxygen and hydrogen peroxide reaching the material surface. I was able to confirm that. FIG. 4 shows an example of the difference between the cathode polarization curve and the presence or absence of an oxide film, based on the measurement result at an oxygen concentration of 300 ppb. From this result, it was clarified that the pre-oxidized test piece on which the oxide film was formed in advance had a lower current density than the non-pre-oxidized test piece in the entire potential range. The current density in the cathodic polarization curve represents the amount of reduction reaction of oxidizing species such as oxygen on the surface of a metal at an arbitrary potential. Therefore, the decrease in the current density due to the formation of the oxide film means that the amount of oxygen reduction reaction is inhibited by the oxide film. This indicates that the driving force of corrosion is reduced in the constituent member by forming an oxide film on the surface of the plant constituent member.

  Based on the experimental results described above, the inventors have previously formed an oxide film on the surface of the plant constituent member that contacts the cooling water by pre-oxidation treatment, thereby reducing the corrosion driving force of the plant constituent member. It was also found that even when sulfuric acid was concentrated to 1 ppm at the crack tip, the amount of metal eluted from the crack tip per unit time, that is, the corrosion rate was reduced. Based on this fact, it is confirmed that a predetermined thickness of oxidation is detected in the detected crack at any time within the period from when the stress corrosion cracking has occurred in the plant components during periodic inspection to when the reactor is started. It has been found that a film should be formed. By forming this oxide film, the corrosion rate of the plant component can be suppressed, and as a result, the progress of stress corrosion cracking in the plant component can be suppressed.

  The outline of the stress corrosion cracking suppression method for plant components newly considered by the inventors based on the above experimental results will be described below.

  For boiling water reactor plant components that have cracks due to stress corrosion cracking, during the period from when this crack is detected in the crack until the next start of the boiling water reactor A film (for example, an oxide film) having a property of inhibiting charge transfer at the solid-liquid interface is formed on the inner surface of the crack. As a result, the growth rate of cracks existing in the plant components can be reduced, and the boiling water reactor can be operated while maintaining the plant components in a healthy state.

  The oxide film on the inner surface of the crack may be formed on the entire inner surface of the crack by an oxide containing at least one chemical component among the chemical components constituting the plant component. As a result, during the operation of the boiling water reactor, an oxide film having the same electrochemical properties as that of the oxide film formed on the surface of the plant component member in contact with the coolant outside the crack is formed inside the crack. Can be formed. For this reason, it can be avoided that the crack tip is fixed as a portion where the metal that is the base material of the plant component is easily eluted, and the rate of crack propagation can be suppressed.

  Formation of the oxide film on the inner surface of the crack is preferably performed by injecting a high-temperature fluid of 473 K to 873 K containing an oxidizing agent into the crack with a pressure of 8 MPa or less. By injecting the high-temperature fluid into the crack, the atmosphere in the crack is adjusted to a high temperature and a highly oxidized atmosphere. The high temperature and highly oxidizing atmosphere within the crack is maintained for a predetermined period. The reason why the temperature of the hot fluid containing the oxidant injected into the crack is in the range of 473K to 873K is as follows. The oxide film is generated by a chemical reaction, and the reaction rate for forming the oxide film increases as the temperature increases. However, depending on the target material of the plant component, if it exceeds 873K, there is a risk of thermal sensitization. To avoid this, the temperature of the high-temperature fluid to be injected is set to 873K or less. In addition, when the temperature of the high-temperature fluid is less than 473 K, the corrosion rate of the plant constituent members becomes slow, and it takes time to form an oxide film on the crack inner surface. In order to form an oxide film on the inner surface of the crack in a shorter time, the temperature of the high temperature fluid is preferably set to 473K or higher.

  The reason why the pressure of the high-temperature fluid to be injected is set to 8 MPa or less will be described below. In order for the hot fluid to flow in the cracks present in the plant components, the hot fluid is preferably at a higher pressure. However, when the pressure of the injected high temperature fluid exceeds the pressure applied to the plant components during the reactor operation, the high temperature fluid is injected toward the crack while the oxide film is formed on the crack inner surface. The crack may develop. In order to avoid this, the pressure of the hot fluid to be injected needs to be 8 MPa or less.

  At least one of oxygen, hydrogen peroxide, and ozone is used as an oxidant that is introduced into the hot fluid. These substances are chemical substances that do not contain elements other than oxygen and hydrogen. Oxygen, hydrogen peroxide, and ozone adversely affect the corrosion and activation behavior outside the oxide film formation site, even if they remain in the reactor after forming an oxide film on the crack inner surface There is nothing. Therefore, the oxidizing power of the high-temperature fluid injected into the crack can be maintained for a predetermined period when the oxide film is formed, and an oxide film having a predetermined thickness can be formed on the inner surface of the crack.

  As a fluid injected into the crack, a fluid containing any one or more of water, water vapor, air, nitrogen gas and argon gas is used. Water, water vapor, air, and nitrogen gas are components that are always dissolved in the cooling water in the reactor during regular inspection. Even if these substances remain in the reactor after the formation of the oxide film on the inner surface of the crack, they do not adversely affect the corrosion behavior and activation behavior other than at the oxide film formation site. Argon gas is an inert gas and does not cause a chemical reaction with other parts when an oxide film is formed on the inner surface of the crack. For this reason, the argon gas can be released into the atmosphere from the upper part of the reactor. Argon gas also does not adversely affect the corrosion behavior and activation behavior outside the oxide film formation site.

  A surface treatment device is used to inject the hot fluid into the crack. This surface treatment device gives a predetermined temperature, pressure, and supply rate to the injected high-temperature fluid. By using this surface treatment apparatus, a high-temperature fluid can be caused to flow in a narrow portion typified by a crack, and an oxide film can be formed in the narrow portion.

  FIG. 5 schematically shows a longitudinal cross section of a crack before and after implementing a new method for suppressing stress corrosion cracking of plant components considered by the inventors. Before implementing this new method for suppressing the development of stress corrosion cracking, as shown in FIG. 5A, the oxide film 2 is formed on the surface of the plant component that contacts the cooling water and in the vicinity of the opening of the crack 1. It is formed on the inner surface. The thickness of the oxide film 2 formed near the tip of the crack 1 is extremely thin. On the other hand, after the above-described new stress corrosion crack growth suppression method is implemented, the oxide film 2 having the same thickness as the oxide film 2 formed on the outside of the crack 1 on the entire inner surface of the crack 1 It is formed over the entire inner surface (see FIG. 5B). An oxide film 2 having the same thickness is also formed near the tip of the crack 1.

  An embodiment of the present invention based on the above examination results will be described below.

  A method for suppressing stress corrosion cracking of a plant component applied to a boiling water reactor, which is a preferred embodiment of the present invention, will be described with reference to FIGS. FIG. 1 is an enlarged view of a portion I in FIG.

  The surface treatment apparatus 10 used in the method for suppressing stress corrosion cracking of plant components according to the present embodiment includes a nozzle 11, a chemical solution tank 12, an oxygen / nitrogen supply device 14, a pump 15, a heater 16, and a nozzle moving device 26. Yes. The nozzle moving device 26 includes a turning device 27, a horizontal direction moving device 29, and a vertical direction moving device 30. The swivel device 27 is turnably installed on an annular rail (not shown) provided on the operation floor 31 so as to surround the upper end of the reactor well 7. The swivel device 27 has a rail holding member 28 straddling the reactor well 7. The horizontal movement device 29 is installed on a linear rail (not shown) provided on the rail holding member 28 and moves above the reactor well 7. The vertical movement device 30 is attached to the horizontal movement device 29 and moves in the axial direction of the reactor pressure vessel 5. A fixing jig 23 is provided at the lower end of the vertical movement device 30.

  The nozzle 11 and the heater 16 are attached to a fixing jig (fixing member) 23. The chemical liquid tank 12 and the pump 15 are placed on the operation floor 31. An oxygen / nitrogen supply device 14 is connected to the chemical tank 12 filled with pure water 13. An oxygen concentration sensor 17 is attached to the chemical tank 12 and connected to the notation device 18. The pump 15 is connected to a pipe 20 attached to the bottom of the chemical tank 12. Further, the pump 15 is connected to the heater 16 by a flexible high-pressure hose 21 to which a pressure gauge 19 is attached. The nozzle 11 and the heater 16 are connected by a pipe 22. A nozzle position detector 25 that detects the amount of movement of the vertical movement device 30 in the axial direction of the reactor pressure vessel 5, that is, the position of the nozzle 11 in the axial direction, is installed in the horizontal movement device 29. The nozzle position detector 25 is connected to a control device 24 placed on the operation floor 31.

  After the operation of the boiling water reactor is stopped, periodic inspection of the boiling water reactor is carried out. Before performing this periodic inspection, the cooling water 32 is filled in the reactor well 7 located above the reactor pressure vessel 5 of the boiling water reactor. Thereafter, the lid (not shown) of the reactor pressure vessel 5 is removed. A steam dryer (not shown) and a steam / water separator (not shown) installed in the reactor pressure vessel 5 are removed and taken out of the reactor pressure vessel 5. A core shroud 6 surrounds the core in the reactor pressure vessel 5. All the fuel assemblies loaded in the core are sequentially taken out of the reactor pressure vessel 5 and stored in a fuel storage pool (not shown).

  An eddy current flaw detector (or ultrasonic flaw detector) is carried into the core shroud 6, and the eddy current flaw detector (or ultrasonic flaw detector) is scanned along the inner surface of the core shroud 6. The eddy current flaw detector (or ultrasonic flaw detector) is scanned in the axial direction and the circumferential direction of the reactor pressure vessel 5, and eddy current flaw detection (or ultrasonic flaw detection) is performed on the core shroud 6. In this embodiment, when a crack 1 is detected in the core shroud 6 by this flaw detection, an oxide film is formed on the inner surface of the detected crack 1.

  During the period of the regular inspection, the stress corrosion cracking suppressing method for the plant constituent members of the present embodiment is carried out using the surface treatment apparatus 10 as follows.

  The nozzle 11 is moved in the cooling water 32 so as to oppose the detected position of the crack 1. The movement of the nozzle 11 is performed with respect to the axial direction and the circumferential direction of the reactor pressure vessel 5 using the nozzle moving device 26. The nozzle 11 is moved in the axial direction of the reactor pressure vessel 5 by the movement of the vertical movement device 30 in the core shroud 5, and is moved in the circumferential direction of the reactor pressure vessel 5 by the turning of the turning device 27. Further, the nozzle 11 is moved close to the inner surface of the core shroud 6 by the movement of the horizontal movement device 29. By such movement of the nozzle 11, the nozzle 11 provided on the fixing jig 23 is opposed to the crack 1 formed in the core shroud 6 from the inside of the core shroud 6.

  Oxygen and nitrogen are blown into the pure water 13 in the chemical tank 12 by the nitrogen / oxygen supply device 14 and dissolved in the pure water 13. The oxygen concentration sensor 17 measures the oxygen concentration of the pure water 13 in the chemical tank 12 and outputs the measured oxygen concentration to the display device 18. The display device 18 displays the oxygen concentration measurement value. The operator adjusts the nitrogen / oxygen supply device 14 while monitoring the oxygen concentration of the pure water 13 displayed on the display device 18 to control the amount of oxygen and nitrogen blown from the nitrogen / oxygen supply device 14 into the pure water 13. To do. Thereby, the oxygen concentration of the pure water 4 in the chemical solution tank 12 is adjusted in advance to 8 ppm.

  During operation of the boiling water reactor, an oxide film 2 is formed on the surface of the core shroud. An oxide film 2 is formed on the inner surface of the crack 1 both in the crack 1 and in the vicinity of the crack opening. However, the oxide film 2 is extremely thin near the tip of the crack 1 (see FIG. 5A).

  The pump 15 is driven, and pure water (chemical liquid) 13 containing nitrogen and oxygen of a predetermined concentration in the chemical liquid tank 12 is supplied to the pump 15 through the pipe 20. This pure water 13 is pressurized by a pump 15 and guided to a heater 16 through a high-pressure hose 21. In the heater 16, the pure water 13 containing oxygen or the like is heated until the temperature reaches 553K. The heated pure water 13 reaches the nozzle 11 through the pipe 22 and is jetted from the nozzle 11 toward the opening of the crack 1 generated in the core shroud 6.

  In the cooling water 32, water pressure is applied to the outlet of the nozzle 11. Therefore, in order to eject the pure water 13 from the nozzle 11 at a predetermined flow rate, the pure water 13 ejected from the nozzle 11 based on the position (water depth) in the axial direction of the reactor pressure vessel 5 where the nozzle 11 is located. It is necessary to adjust the pressure. The pressure control of the pure water 13 is performed by controlling the rotation speed of the pump 15 by the control device 24. The position of the nozzle 11 in the axial direction of the reactor pressure vessel 5 is detected by a nozzle position detector 25. The detected position of the nozzle 11 in the axial direction of the reactor pressure vessel 5 is transmitted from the nozzle position detector 25 to the control device 24. The control device 24 obtains the water depth from the liquid level of the cooling water 32 in the reactor well 7 to the nozzle 11 based on the input nozzle position, and obtains the water pressure at the nozzle position based on this water depth. The control device 24 controls the rotation speed of the pump 15 based on the obtained pressure so that the pressure of the pure water 13 ejected from the nozzle 11 is higher than the water pressure at the nozzle position and becomes a set pressure of 8 MPa or less. Adjust. In order to eject the pure water 13 from the nozzle 11, the pressure of the pure water 13 supplied to the nozzle 11 needs to be higher than the water pressure at the nozzle position. In this embodiment, the pressure of the pure water 13 ejected from the nozzle 11 is adjusted to 8 MPa. The pressure of the pressurized pure water 13 is measured by a pressure gauge 19. The pressure measured by the pressure gauge 19 is displayed on the display device 18.

  The injection of heated pure water 13 from the nozzle 11 is continuously performed for a set time. Pure water 13 containing oxygen at 553 K injected from the nozzle 11 flows into the crack 1 generated in the core shroud 6. The pure water 13 that has flowed into the crack 1 flows through the crack 1 and reaches the tip of the crack 1. The high-pressure pure water 13 that has reached the tip of the crack 1 turns in the opposite direction and flows toward the opening of the crack 1. Thus, since the pure water 13 containing oxygen injected from the nozzle 11 flows in the crack 1 at 553 K, the temperature of the pure water 13 and the action of oxygen cause the opening of the crack 1 to the tip of the crack 1. An oxide film 2 is formed on the entire inner surface of the crack 1 (see FIG. 5B). Since the nozzle 11 does not cover the entire opening of the crack 1, the pure water 13 that has flowed into the crack 1 flows through the crack 1 and flows out of the crack 1 as described above.

  The set time for injecting pure water 13 from the nozzle 11 is determined in advance by a preliminary experiment. In this preliminary experiment, the temperature and oxygen concentration were used as parameters to change the injection duration from the nozzle, and pure water containing an oxidant was ejected to the simulated crack formed on the test piece and formed on the inner surface of the simulated crack. Measure the thickness of the oxide film. A set time for injecting pure water 13 from the nozzle 11 is determined in advance based on the relationship between the thickness of the formed oxide film, temperature, oxygen concentration, and injection duration. This set time is set so that the oxide film 2 having a thickness of 10 μm or less is formed over the entire inner surface of the crack 1. If the thickness of the oxide film 2 exceeds 10 μm, cracks may occur. For this reason, it is desirable that the thickness of the oxide film 2 be 10 μm or less. The thickness of the oxide film 2 is preferably 0.001 μm or more. In this embodiment, an oxide film 2 having a thickness of 10 μm is formed over the entire inner surface of the crack 1 from the opening of the crack 1 to the tip of the crack 1.

  While the oxide film 2 is formed on the inner surface of the crack 1, a thermocouple (not shown) is a temperature measuring device in which the temperature of the pure water 13 heated by the heater 16 and supplied to the nozzle 11 is provided in the pipe 22. The amount of heating by the heater 16 is controlled so as to reach a set temperature based on the detected temperature of the pure water 13.

  After the formation of the oxide film 2 on the inner surface of the corresponding crack 1 formed in the core shroud 6 is completed and the periodic inspection is completed, the boiling water reactor is started and then operated at the rated power.

  According to the present embodiment, the entire inner surface of the crack 1 formed due to the stress corrosion cracking generated in the core shroud 6 (the entire inner surface of the crack 1 extending from the opening of the crack 1 to the tip of the crack 1) is predetermined. A thick oxide film 2 can be formed. For this reason, the action of the oxide film 2 formed on the entire inner surface of the crack 1 reduces the arrival amount of oxidizing species such as oxygen and hydrogen peroxide on the inner surface of the crack 1, thereby reducing the cathode current. Furthermore, elution of the core shroud 6 at the anode reaction site in the crack 1 can be suppressed, and the anode current can be reduced. In this embodiment, since the cathode current and the anode current in the crack 1 can be reduced, the crack growth rate from the tip of the crack 1 can be suppressed. That is, according to the present embodiment, stress corrosion cracking of the core shroud 6 can be suppressed.

  In this embodiment, since the temperature of the pure water 13 injected from the nozzle 11 toward the crack 1 is set to 553 K, the oxide film can be formed on the inner surface of the crack in a shorter time, and the heat of the core shroud 6 can be increased. Sensitization can be prevented. Since the pressure of the pure water 13 injected from the nozzle 11 is 8 MPa, it can be made lower than the pressure that the core shroud 6 receives during the rated operation of the boiling water reactor. Thereby, the crack growth rate can be further suppressed.

  In this embodiment, pure water 13 containing nitrogen is injected from the nozzle 11 toward the opening of the crack 1, so that even if this pure water 13 flows inside the crack 1 and flows out of the crack 1, the core shroud 6 does not adversely affect the corrosion behavior and activation behavior of the plant components other than the surface of the crack 1 and the core shroud 6. In this embodiment, since nitrogen is supplied to the pure water 13 in addition to oxygen, the oxygen concentration can be easily adjusted.

  In the present embodiment, since the pressure of the pure water 13 injected from the nozzle 11 is controlled based on the position of the nozzle 11 facing the crack 1 in the axial direction of the reactor pressure vessel 5, it is generated in the core shroud 6. The pressure of the pure water 13 supplied to the nozzle 11 can be adjusted according to the water depth up to a plurality of cracks. For this reason, even when the water depth from the liquid level of the cooling water 32 in the reactor well 7 to the crack 1 is different, the pure water 13 having a required pressure can be injected from the nozzle 11 at a predetermined flow rate.

  An aqueous solution containing any one of molybdic acid, chromic acid and tungstic acid may be used as the oxidizing agent.

  This embodiment can also be applied to the case where the oxide film 2 is formed on the inner surface of a crack generated in a plant component other than the core shroud 6, for example, the shroud support.

  A method for suppressing stress corrosion cracking of a plant component applied to a boiling water reactor, which is another embodiment of the present invention, will be described with reference to FIG. FIG. 6 shows a surface treatment apparatus 10A used in this embodiment. 10 A of surface treatment apparatuses have the structure which provided the cylinder (air supply apparatus) 33 filled with air instead of the chemical | medical solution tank 12 and the oxygen / nitrogen supply apparatus 14 in the surface treatment apparatus 10 used for Example 1. FIG. An oxygen concentration meter 17 is attached to the cylinder 33. The cylinder 33 is connected to the pump (or blower) 15 by the pipe 20. The nozzle 11 is provided with an annular nozzle cover 34 so as to surround the injection port.

  In the present embodiment, as in the first embodiment, an oxide film is formed on the inner surface of a crack discovered by eddy current flaw detection or the like during the periodic inspection period of the boiling water reactor. The stress corrosion cracking suppressing method of the plant constituent member of the present embodiment that is performed on the crack 1 generated in the core shroud 6 will be described with respect to portions that are different from the first embodiment.

  As in the first embodiment, the swiveling device 27, the horizontal movement device 29, and the vertical movement device 30 are driven so that the nozzle 11 faces the opening of the crack 1 that forms the oxide film 2 on the inner surface. Thereby, the nozzle cover 34 is arrange | positioned between the nozzle 11 and the core shroud 6 (refer FIG. 7). The pump 15 is driven to supply the air in the cylinder 33 to the heater 16 through the pipe 20 and the high pressure hose 21. The air pressurized to 8 MPa by the pump 15 is heated to 873 K by the heater 16. Air of 8 MPa and 873 K is injected from the nozzle 11 toward the opening of the crack 1 and supplied into the crack 1 generated in the core shroud 6. Like the pure water 13 of the first embodiment, this air flows from the opening of the crack 1 toward the tip of the crack 1, flows in the crack 1, reaches the tip of the crack 1, and then opens the opening of the crack 1. It flows toward. Due to the flow of the high-temperature and high-pressure air (including oxygen) in the crack 1, an oxide film 2 is formed on the entire inner surface of the crack 1 from the opening of the crack 1 to the tip of the crack 1, as in the first embodiment. (See FIG. 5B).

  Also in this embodiment, each effect produced in the first embodiment can be obtained. By providing the nozzle cover 34, the crack 1 generated in the core shroud 6 can be covered with the nozzle cover 34, and the pressure of the air supplied into the crack 1 can be further increased. For this reason, the amount of air supplied into the crack 1 can be increased, and the formation of the oxide film 2 on the inner surface of the crack 1 can be promoted.

  The method for suppressing stress corrosion cracking of plant components in Examples 1 and 2 can be applied not only to a boiling water nuclear plant but also to a pressurized water nuclear plant. These embodiments can be applied, for example, when an oxide film is formed on the inner surface of a crack generated in a plant component in a reactor pressure vessel of a pressurized water nuclear plant.

It is a block diagram of the surface treatment apparatus used for the stress corrosion cracking suppression method of the plant structural member of Example 1, which is a preferred embodiment of the present invention. It is a longitudinal cross-sectional view of the boiling water reactor which applies the stress corrosion cracking suppression method of the plant structural member of Example 1. It is a characteristic figure which shows the influence of pre-oxidation on the anodic polarization curve in the aqueous solution which simulated the crack tip. It is a characteristic figure which shows the influence of the pre-oxidation which has on the cathode polarization curve in oxygen concentration 300ppb. It is explanatory drawing which shows the formation state of the oxide film of a crack inner surface, (A) is explanatory drawing which shows the formation state of the oxide film of a crack inner surface before injecting the water containing oxygen toward a crack, and (B ) Is an explanatory view showing the state of formation of an oxide film on the inner surface of the crack after injecting water containing oxygen toward the crack. It is a block diagram of the surface treatment apparatus used for the stress corrosion cracking suppression method of the plant structural member of Example 2 which is another Example of this invention. FIG. 7 is an enlarged longitudinal sectional view of a nozzle tip portion shown in FIG. 6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Crack, 2 ... Oxide film, 5 ... Reactor pressure vessel, 6 ... Core shroud, 10, 10A ... Surface treatment apparatus, 11 ... Nozzle, 12 ... Chemical solution tank, 13 ... Pure water, 14 ... Supply of oxygen and nitrogen Device: 15 ... Pump, 16 ... Heater, 17 ... Oxygen sensor, 21 ... High pressure hose, 26 ... Nozzle moving device, 27 ... Swivel device, 29 ... Horizontal moving device, 30 ... Vertical moving device, 33 ... Cylinder, 34 ... Nozzle cover.

Claims (6)

  An injection device is arranged opposite to a crack generated in a plant component of a nuclear power plant, and a heated fluid containing an oxidant is injected from the injection device toward the crack and flows into the crack. A method for suppressing stress corrosion cracking of a plant constituent member, wherein an oxide film is formed on the inner surface of the crack by the oxidant contained in the fluid.   The stress corrosion cracking suppression method for a plant constituent member according to claim 1, wherein the oxide film contains at least one of metal components contained in the plant constituent member.   The method for suppressing stress corrosion cracking of plant components according to claim 1 or 2, wherein the temperature of the fluid sprayed toward the crack is in a temperature range of 473K to 873K.   The pressure of the said fluid injected in the state which the said plant structural member is contacting with cooling water exists in the range of 8 MPa or less higher than the water pressure in the position where the said injection apparatus is arrange | positioned. A method for suppressing stress corrosion cracking of plant components.   The method for suppressing stress corrosion cracking of a plant component according to any one of claims 1 to 3, wherein the oxidizing agent is at least one of oxygen, hydrogen peroxide, and ozone.   The stress corrosion cracking suppression of the plant component according to any one of claims 1 to 3 and 5, wherein the fluid includes any one or more of water, water vapor, air, nitrogen gas, and argon gas. Method.

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