JP2016164494A - Surface processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface processing method for forming a stable oxide film on a nuclear power plant constitution member while reducing a waste liquid processing load at a low cost.SOLUTION: The surface processing method includes: a film forming step S20 to expose a nuclear power plant constitution member to a first temperature area while being in contact with a solution which contains peroxide iron ion to thereby form a primary oxide film over the surface of the nuclear power plant constitution member; and a film degeneration step S30, subsequently to the film forming step S20 to expose the nuclear power plant constitution member to a second temperature area higher than the first temperature area while being in contact with a solution containing zinc to thereby denature the primary oxide film into a secondary oxide film.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a surface treatment method for forming an oxide film on a nuclear plant component.

An oxide film containing a radionuclide is gradually formed in a portion that comes into contact with the reactor water among parts such as piping and various devices constituting the nuclear power plant. For this reason, the radiation dose increases with the passage of time around such components. Therefore, in nuclear power plants, chemical cleaning (chemical decontamination) of parts is performed in order to remove oxide films containing radionuclides from such parts during periodic inspections.
After chemical cleaning, the surface dose rate may exceed the dose rate before chemical cleaning because, for example, after the operation for one year, the parts are in a surface state in which radionuclides are likely to be captured. In order to suppress this recontamination, various surface treatment methods have been proposed. Patent Document 1 describes a technique for depositing a zinc oxide film using electrolysis.

JP 2012-225711 A

  By the way, the surface treatment method described in Patent Document 1 is difficult to introduce additional equipment such as an electrolyzer and to secure an installation space. Moreover, since a high concentration electrolytic solution is used, there is a problem that the load of waste liquid treatment increases.

  An object of the present invention is to provide a surface treatment method capable of forming a stable oxide film at a lower cost and while reducing a waste liquid treatment load.

  According to the first aspect of the present invention, the surface treatment method exposes the surface of the nuclear plant component to the nuclear plant component by exposing the nuclear plant component to the first temperature region while contacting the solution containing the perferrate ions. A film forming step for forming a primary oxide film on the substrate, and after the film forming step, the nuclear plant component is exposed to a second temperature region higher than the first temperature region while contacting with a solution containing zinc. And a film modification step of modifying the primary oxide film into a secondary oxide film.

  According to such a configuration, an oxide film can be easily formed in the film forming process, and a stable oxide film can be formed by forming a high temperature / reducing atmosphere in the film modification process. In addition, since an apparatus such as an electrolysis apparatus is not used, a film can be formed at a lower cost. Moreover, since a high concentration electrolytic solution is not used, the waste liquid processing load can be reduced.

  In the surface treatment method, the coating modification step includes a member installation step of incorporating the nuclear plant component into the nuclear plant, a plant startup step of starting the nuclear plant, and a solution containing the zinc as reactor water of the nuclear plant And an injecting step of injecting.

  According to such a configuration, by using the nuclear reactor water, the solution containing zinc can be heated to a high temperature without providing a separate heating device.

  In the surface treatment method, the first temperature region may be 30 ° C to 100 ° C, and the second temperature region may be 100 ° C to 360 ° C.

  According to such a configuration, the film forming step can be performed using an existing cleaning facility that cannot increase the temperature of the chemical to 100 ° C. or higher by suppressing the first temperature region to 100 ° C. or lower. .

  In the surface treatment method, the nuclear plant component may include Cr.

According to such a configuration, FeCr ₂ O ₄ can also be formed as an oxide film.

  According to the present invention, an oxide film can be easily formed in the film forming step, and a stable oxide film can be formed by forming a high temperature / reducing atmosphere in the film modification step. In addition, since an apparatus such as an electrolysis apparatus is not used, a film can be formed at a lower cost. Moreover, since a high concentration electrolytic solution is not used, the waste liquid processing load can be reduced.

It is a systematic diagram of a nuclear power plant. It is a systematic diagram of the decontamination equipment for enforcing the surface treatment method of the first embodiment of the present invention. It is a flowchart explaining the surface treatment method of 1st embodiment of this invention.

(First embodiment)
Hereinafter, a surface treatment method according to a first embodiment of the present invention will be described in detail with reference to the drawings.
First, the application target of the surface treatment method of this embodiment will be described. The application target of the surface treatment method of the present embodiment is parts (nuclear plant constituent members) such as pipes, containers, and various devices constituting the nuclear power plant, and parts that are in contact with reactor water.

  As a nuclear power plant, for example, there is a nuclear power plant P including a pressurized water reactor 50 as shown in FIG.

  The nuclear power plant P pressurizes the primary cooling water in order to suppress boiling of the pressurized water reactor 50 in which the fuel rods 51 and the like are accommodated and the primary cooling water (light water, reactor water) in the pressurized water reactor 50. A pressurizer 52, a steam generator 53 that turns the secondary cooling water into steam by the heat of the primary cooling water, a coolant pump 54 that returns the primary cooling water from the steam generator 53 to the pressurized water reactor 50, and steam generation A steam turbine 56 driven by steam generated in the condenser 53, a generator 57 that generates electric power by driving the steam turbine 56, a condenser 58 for returning steam from the steam turbine 56 to water, and a condenser 58 And a water supply pump 59 for returning water to the steam generator 53.

  The pressurized water reactor 50 and the steam generator 53 are connected by primary cooling water pipes 55a and 55b. The steam generator 53 and the steam turbine 56 are connected by a steam pipe 61, and the condenser 58 and the steam turbine 56 are connected by a water supply pipe 62.

  In this nuclear power plant P, the parts in contact with the reactor water, that is, the primary cooling water are parts of the primary cooling system. The components of the primary cooling system include a pressurized water reactor 50, a pressurizer 52, a steam generator 53, a coolant pump 54, primary cooling water pipes 55a and 55b that connect them, and primary cooling water pipes 55a and 55b. There are various valves provided. These primary cooling system components are formed of stainless steel containing iron (Fe) as a main component and containing chromium (Cr) and nickel (Ni), a Ni-base alloy, a Co-base alloy, and the like.

  The metal elements forming these components are slightly dissolved in the reactor water, and a part of them adheres to the surface of the fuel rod 51 in the pressurized water reactor 50. The metal element adhering to the surface of the fuel rod 51 undergoes a nuclear reaction when irradiated with neutrons from the fuel, and becomes a radionuclide such as chromium, nickel, cobalt, and the like. Most of these radionuclides remain attached to the surface of the fuel rod 51 in the form of oxides, but part of them are eluted into the reactor water or released as insoluble solids. The radionuclide eluted or released into the reactor water adheres to the reactor water contact surface of the component, and forms an oxide film mainly composed of iron (Fe) on the reactor water contact surface. For this reason, the worker who works in the vicinity of the part is exposed to radiation from the radionuclide in the oxide film formed on the part.

In addition, the nuclear power plant P includes a decontamination facility 10 that chemically cleans the parts described above and removes an oxide film adhering to the reactor water contact surface of the parts.
FIG. 2 is a system diagram of the decontamination equipment 10 for carrying out the surface treatment method of the present embodiment. In the following description, a single device is processed, but a system configuration in which the entire pipe inner surface of the system is processed may be used.
The decontamination equipment 10 includes a treatment tank 11 into which a component 1 on which an oxide film containing a radionuclide is formed, a circulation line 12 for circulating the liquid in the treatment tank 11, and a circulation line 12. It has a circulation pump 13 provided, a chemical tank 14 for storing chemicals and supplying them to the circulation line 12, and a waste liquid treatment facility 20 for treating waste liquid generated by removing the oxide film. .

Further, the treatment tank 11 is provided with a spray 15 for spraying chemicals circulating through the circulation line 12.
The waste liquid treatment facility 20 uses, for example, a waste liquid treatment resin such as an ion exchange resin to remove impurities in the waste liquid.
The surface treatment method of the present embodiment is characterized in that a zinc oxide film (for example, ZnFe ₂ O ₄ ) is formed on the component 1 by utilizing the decontamination equipment 10 provided as an existing equipment in the nuclear power plant P. It is said.

Next, details of the surface treatment method of the present embodiment will be described with reference to the flowchart shown in FIG.
As shown in FIG. 3, the surface treatment method of the present embodiment includes a surface cleaning step S10 for cleaning the part 1, a film forming step S20 for forming a primary oxide film on the part 1, and two primary oxide films formed. And a film modification step S30 for modifying the next oxide film.
The coating modification step S30 includes a member installation step S31 for installing the component 1 in the treatment tank 11, a plant startup step S32 for starting the nuclear power plant P, and an injection step S33 for injecting reactor water.

The surface cleaning step S <b> 10 is a step for cleaning the component 1 using the decontamination equipment 10.
In the surface cleaning step S10, first, the target component 1 (for example, the coolant pump 54) is removed from the nuclear power plant P.
Next, the component 1 is put into a treatment tank 11 filled with a cleaning chemical (for example, an oxidizing chemical such as an aqueous solution containing permanganate ions), and the chromium-based oxide contained in the oxide film of the component 1 is added. Oxidizes and dissolves.

The film forming step S20 is a step of forming a primary oxide film on the component 1 whose surface has been cleaned.
In the film forming step S <b> 20, first, a heater 16 for heating chemicals is installed in the circulation line 12 of the decontamination equipment 10. The heater 16 is composed of, for example, a heater or the like, and heats chemicals using a power source such as gas or electricity.

Next, a solution containing potassium perferrate (K ₂ FeO ₄ ) (a solution containing perferic acid; hereinafter sometimes simply referred to as a drug) is put into the chemical tank 14, and the ferrate ion is put into the treatment tank 11. A solution containing is stored. In addition, the substance contained in a chemical | medical agent is not restricted to potassium perferrate, You may use a perferroic acid and sodium perferrate.
The concentration of potassium perferrate is preferably 1000 ppm or less. More preferably, the concentration of potassium perferrate is 600 ppm or less.

The storage amount of the solution containing potassium perferrate is appropriately set according to the size of the component 1. The larger the storage amount, the easier the film formation, but a burden is placed on the waste liquid treatment. In the film forming step S20 of the present embodiment, the storage amount was set so that 1/3 of the part 1 was immersed in a solution containing potassium perferrate.
Moreover, the chemical | drug | medicine is heated using the heater 16. FIG. The temperature (first temperature range) of the solution containing potassium perferrate is preferably 30 ° C to 100 ° C. The temperature of the solution containing potassium perferrate is more preferably 60 ° C to 95 ° C.

Next, the component 1 is immersed in the chemical stored in the treatment tank 11, and the chemical is sprayed on the component 1 using the spray 15. That is, the component 1 is exposed to the first temperature region while contacting a solution containing a perferrate ion with the component 1. For example, by allowing 8 hours to pass in this state, a primary oxide film (oxide film not containing zinc) is formed on the component 1.
Moreover, in order to form a primary oxide film having a sufficient thickness, the treatment time is preferably set to 8 hours or more. There is no particular upper limit for the treatment time, but it is preferably 24 hours or less.

The primary oxide film is, for example, Fe ₂ O ₃ (hematite) or Fe ₃ O ₄ (magnetite) which are thermodynamically stable oxide films. Fe ₂ O ₃ adheres a component obtained by self-decomposition of iron (Fe) contained in the chemical as iron oxide to the surface of the component 1. Ions in chemicals can be deposited to form stable oxides.
Moreover, when the component 1 is formed of a metal having chromium (Cr), Fe ₂ CrO ₄ is also formed as a primary oxide film.

Next, a film modification step S30 for modifying the primary oxide film formed on the component 1 in the film formation step S20 is executed.
First, the component 1 is incorporated into the nuclear power plant P as the member installation step S31. That is, the reactor water is brought into contact with the component 1 by introducing the reactor water (cooling water) into the nuclear power plant P.

Subsequently, the nuclear power plant P is started (trial operation and adjustment operation) as a plant starting step S32.
Next, as an injection step S33, a solution having a zinc (Zn) concentration of 5 ppb to 10 ppb (hereinafter referred to as reactor water) is injected. The temperature of the reactor water (second temperature range) is 100 ° C. to 360 ° C., which is higher than the first temperature range. The temperature of the reactor water is preferably 285 ° C.

Thereby, the inside of the component 1 is exposed to the 2nd temperature range higher than a 1st temperature range, making it contact with the reactor water containing zinc. By continuing this state for several days, for example, the primary oxide film formed on the component 1 is denatured into a secondary oxide film. Specifically, since the reactor water has a high temperature, a high temperature / reducing atmosphere is formed. Therefore, a stable zinc oxide film (for example, ZnFe ₂ O ₄ ) is formed by the oxide and zinc formed in the film forming step S20. be able to. In other words, zinc ions contained in the cooling water are taken into the primary oxide film and deposited on the primary oxide film.
Further, when the component 1 is formed of a metal containing Cr, ZnCr ₂ O ₄ is also formed as a zinc oxide film.

According to the said embodiment, a zinc oxide film (secondary oxide film) can be formed in the surface of the components 1, and radionuclide adhesion from the outside can be suppressed. In addition, a thermodynamically stable zinc oxide film can be formed.
In addition, by forming the zinc oxide film by the surface treatment method of the present embodiment, it is possible to reduce the dose that becomes a problem at the next opening (periodic inspection work). This makes it possible to reduce the number of decontamination times.

  Further, in the coating modification step S30, the reactor water that rises to about 285 ° C. when the nuclear power plant P is started up is utilized, so that existing facilities can be utilized to the maximum extent. That is, it is not necessary to provide additional equipment in order to increase the temperature of the liquid to be injected for modifying the primary oxide film.

In addition, since the electrolytic solution is not used when forming the oxide film, waste liquid treatment can be facilitated.
Moreover, by spraying the chemical | medical agent on the component 1 using a spray, it becomes unnecessary to immerse the whole component 1 in a chemical | medical agent, and can reduce the quantity of waste liquid.
As an alternative to zinc, a solution containing manganese (Mn), titanium (Ti), and aluminum (Al) can be injected in the injection step S33 to form an oxide film including these.
In addition, as the surface treatment method of the present embodiment, the method of performing the surface treatment after chemically cleaning the nuclear plant components after operating for a certain period of time has been described, but the method is not limited thereto. That is, the surface treatment method of the present embodiment may be performed when surface treatment is performed on a newly manufactured component.

(Second embodiment)
Hereinafter, the surface treatment method of the second embodiment of the present invention will be described. In the present embodiment, differences from the first embodiment described above will be mainly described, and description of similar parts will be omitted.
The surface treatment method of this embodiment is characterized in that a solution containing zinc acetate or zinc oxalate is used together with potassium perferrate in the film forming step S10. The concentration of zinc acetate or zinc oxalate is preferably 100 ppm to 1000 ppm.
In addition, in the injection step S33 of the film modification step S20, reactor water not containing zinc is injected.

Since zinc acetate and zinc oxalate are reducing acids, they are self-decomposed and release zinc. Thereby, zinc reacts with iron oxide of potassium perferrate, and ZnO and Fe ₂ O ₃ adhere to the surface of the primary oxide film. By introducing high-temperature reactor water in the injection step S33 to form a high-temperature / reducing atmosphere, a stable zinc oxide film (ZnFe ₂ O ₄ ) can be formed from oxide and zinc.

  The embodiment of the present invention has been described in detail above, but various modifications can be made without departing from the technical idea of the present invention.

1 Parts (nuclear plant components)
DESCRIPTION OF SYMBOLS 10 Decontamination equipment 11 Processing tank 12 Circulation line 13 Circulation pump 14 Chemical tank 15 Spray 16 Heater 20 Waste liquid processing equipment 50 Pressurized water reactor 51 Fuel rod 52 Pressurizer 53 Steam generator 54 Coolant pump 55a Primary cooling water piping 55b Primary cooling water piping 56 Steam turbine 57 Generator 58 Condenser 59 Water supply pump 61 Steam piping 62 Water supply piping P Nuclear power plant S10 Surface cleaning process S20 Film formation process S30 Film modification process S31 Component installation process S32 Plant start-up process S33 Injection process

Claims (4)

A film forming step of forming a primary oxide film on the surface of the nuclear plant component by exposing the nuclear plant component to a first temperature region while contacting a solution containing a ferrate ion with the nuclear plant component;
After the coating formation step, the primary oxide coating is exposed to a second temperature region higher than the first temperature region while contacting a solution containing zinc with the nuclear plant component, thereby forming the secondary oxide coating. A surface modification method comprising: The film modification step includes
A member installation process for incorporating the nuclear plant components into the nuclear plant;
A plant start-up process for starting up the nuclear power plant;
The surface treatment method according to claim 1, further comprising an injection step of injecting a solution containing zinc as reactor water of the nuclear power plant. The first temperature region is 30 ° C to 100 ° C,
The surface treatment method according to claim 1 or 2, wherein the second temperature region is 100 ° C to 360 ° C.   The surface treatment method according to any one of claims 1 to 3, wherein the nuclear plant component includes Cr.

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