JP5787588B2 - Chemical cleaning method - Google Patents

Description

  The present invention relates to a chemical cleaning method for cleaning a component by chemically dissolving and removing a metal in an oxide film formed on the surface of the component constituting the nuclear power plant.

  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 of parts is performed in order to remove oxide films containing radionuclides from such parts during periodic inspections and the like.

  As a method for chemically cleaning the parts constituting the nuclear power plant, for example, there is a method described in Patent Document 1 below.

  In this cleaning method, the part is first attached to a permanganate aqueous solution to oxidize and dissolve the chromium-based oxide contained in the oxide film of the part, and then the iron-based oxide that is the main component of the oxide film of the part. To reduce and dissolve. Then, an aqueous solution containing various ions is brought into contact with an anion exchange resin or a cation exchange resin to remove impurities containing radionuclides from the aqueous solution.

Japanese Patent Publication No. 3-10919

  According to the chemical cleaning method described in Patent Document 1, it is possible to remove the oxide film containing the radionuclide from the parts constituting the nuclear power plant. By the way, in such chemical cleaning, it is desired to reduce the amount of secondary waste containing radionuclides as much as possible.

  Accordingly, an object of the present invention is to provide a chemical cleaning method that can reduce the amount of secondary waste.

The chemical cleaning method according to the invention for achieving the above object comprises an oxidation step of oxidizing and dissolving a metal in an oxide film formed on the surface of a part constituting a nuclear power plant using an oxidizing solution. In the chemical cleaning method for cleaning a part, in the oxidation step, an aqueous solution containing at least one peroxide of perferroic acid and perboric acid is used as the solution.

  In the chemical cleaning method, the chromium-based oxide in the oxide film formed on the surface of the component can be efficiently oxidized and dissolved by using an aqueous solution containing a peroxide having a high standard oxidation-reduction potential. For this reason, in the said chemical cleaning method, the quantity of the chemical | medical agent (peroxide) in aqueous solution can be decreased, As a result, the quantity of the secondary waste containing a radionuclide can be decreased.

  Here, in the chemical cleaning method, after performing the oxidation step, dicarboxylic acid is put into the solution, and other metals in the oxide film are reduced and dissolved, and the solution containing the dicarboxylic acid is removed. A reduction step may be performed.

  In the chemical cleaning method, it is possible to further reduce and dissolve the iron-based oxide which is a main component in the oxide film of the part.

  In the chemical cleaning method, a waste liquid treatment step may be performed in which the solution removed in the reduction step is heated to evaporate water in the solution.

  In the chemical cleaning method, the amount of secondary waste containing radionuclides can be reduced as compared with the case where the solution removed in the reduction step is treated using an ion exchange resin.

  In the chemical cleaning method, the oxidation step and the reduction step after the oxidation step may be one decontamination step, and the decontamination step may be performed a plurality of times.

  In the chemical cleaning method, the oxide film formed on the surface of the component can be more reliably removed.

  In the chemical cleaning method, a film forming step of forming an oxide film on the surface of the part after the reduction step may be performed. In this case, in the film formation step, the component after the reduction step is attached to an aqueous solution containing zinc ions and at least one compound selected from oxoacid salts of chlorine compounds. A zinc oxide film may be formed on the surface.

  In the chemical cleaning method, by forming an oxide film on the surface of the component, an oxide film containing a radionuclide can be hardly formed on the surface of the oxide film.

  In the chemical cleaning method, the concentration of the peroxide in the aqueous solution used in the oxidation step is preferably 200 to 300 ppm. Furthermore, the temperature of the aqueous solution used in the oxidation step is preferably 20 ° C. or higher and lower than 100 ° C.

  In the present invention, the chromium-based oxide in the oxide film formed on the surface of the component can be efficiently oxidized and dissolved. Therefore, according to the present invention, the amount of the chemical in the aqueous solution used when oxidizing and dissolving the chromium-based oxide in the oxide film can be reduced, and as a result, the amount of secondary waste containing radionuclides can be reduced. Can be reduced.

It is a flowchart which shows the chemical cleaning method in one Embodiment which concerns on this invention. It is a systematic diagram of the cleaning equipment for enforcing the chemical cleaning method in one embodiment concerning the present invention. It is a systematic diagram of a nuclear power plant.

  Hereinafter, an embodiment of a chemical cleaning method according to the present invention will be described in detail with reference to the drawings.

  First, the application object of the chemical cleaning method of this embodiment is demonstrated.

  The application target of the chemical cleaning method of the present embodiment is parts such as piping, containers, and various devices that constitute a nuclear power plant, and parts that are in contact with reactor water.

  An example of the nuclear power plant is a nuclear power plant P including a pressurized water reactor 50 as shown in FIG.

  The nuclear power plant P includes a pressurized water reactor 50 in which fuel rods 51 and the like are accommodated, and a pressurizer 52 that pressurizes the primary cooling water in order to suppress boiling of the primary cooling water (light water) in the pressurized water reactor 50. 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 the steam generator 53 A steam turbine 56 driven by the generated steam, a generator 57 that generates electric power by driving the steam turbine 56, a condenser 58 that returns steam from the steam turbine 56 to water, and water from the condenser 58 is steamed And a water supply pump 59 that returns to the 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 parts for the primary cooling system are formed of stainless steel containing Cr and Ni with Fe as a main component, Ni-base alloy, 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 in the reactor water adheres to the reactor water contact surface of the component, and forms an oxide film mainly composed of 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 the present embodiment, a method for chemically cleaning the component described above and removing the oxide film adhering to the reactor water contact surface of the component is presented.

  Next, cleaning equipment for carrying out the chemical cleaning method of the present embodiment will be described with reference to FIG.

  The cleaning equipment E of the present embodiment includes a decontamination equipment 10 for removing the oxide film from the surface of the part 1, a waste liquid treatment equipment 20 for treating a waste liquid generated by removing the oxide film, and a part from which the oxide film has been removed. 1 is provided with a water washing facility 30 for washing 1 and a film forming facility 40 for forming a new film on the surface of the component 1.

  The decontamination equipment 10 stores a decontamination tank 11 into which a component 1 on which an oxide film containing a radionuclide is formed, an oxidizing liquid tank 14 in which a peroxodisulfuric acid aqueous solution is stored, and an oxalic acid aqueous solution. A reducing liquid tank 17, a circulation line 12 for circulating the liquid in the decontamination tank 11, a circulation pump 13 provided in the circulation line 12, and an oxidizing liquid tank 14 in the circulation line 12. An oxidizing liquid line 15 for supplying the peroxodisulfuric acid, an oxidizing liquid supply pump 16 provided in the oxidizing liquid line 15, and oxalic acid in the reducing liquid tank 17 in the circulation line 12. A reducing liquid line 18 for supplying and a reducing liquid supply pump 19 provided in the reducing liquid line 18 are provided.

  The waste liquid treatment facility 20 is a neutralization tank 21 for neutralizing the waste liquid generated by the treatment in the decontamination equipment 10, and an evaporation for concentrating the waste liquid by evaporating water in the waste liquid neutralized in the neutralization tank 21. The apparatus 24, the neutralization waste liquid line 22 for sending the liquid in the neutralization tank 21 to the evaporation apparatus 24, and the waste liquid pump 23 provided in the neutralization waste liquid line 22 are provided.

  The neutralization tank 21 of the waste liquid treatment equipment 20 and the circulation line 12 of the decontamination equipment 10 are connected by a waste liquid line 28. The evaporation device 24 of the waste liquid treatment facility 20 includes a waste liquid evaporation tank 25 and a heater 26 that heats the waste liquid in the waste liquid evaporation tank 25.

  The rinsing equipment 30 includes a rinsing tank 31 into which the component 1 from which the oxide film has been removed is charged, ion-exchange resins 34 and 35 that remove impurities from water in contact with the component 1 in the rinsing tank 31, and the rinsing tank 31. The water purification line 32 for sending the water to the ion exchange resins 34 and 35 and the water pump 33 provided in the water purification line 32 are provided. Examples of the ion exchange resins 34 and 35 include an anion exchange resin 34 and a cation exchange resin 35.

  The film forming facility 40 is a three-electrode electrolytic device. The three-electrode electrolytic apparatus includes an electrolytic bath 41 filled with an electrolytic solution, a counter electrode 42 for the part 1 as a working electrode placed in the electrolytic solution, a KCl bath 43 filled with a KCl saturated solution, and the KCl bath 43 A reference electrode 44 placed in the electrode, a Lugin tube 45 for reducing the distance between the reference electrode 44 and the component 1 as a working electrode, and a potentiostat 46 for controlling the current flowing through each electrode.

  Next, a chemical cleaning method for the component 1 using the cleaning equipment E described above will be described with reference to the flowchart shown in FIG.

  First, an oxidation step (S1) is performed in which the chromium oxide contained in the oxide film of the component 1 is oxidized and dissolved with a peroxodisulfuric acid aqueous solution.

  In this oxidation step (S 1), first, a peroxodisulfuric acid aqueous solution is stored in the oxidizing liquid tank 14 of the decontamination equipment 10. The concentration of the peroxodisulfuric acid aqueous solution is preferably 200 to 300 ppm, and here is 300 ppm. The temperature of the aqueous peroxodisulfuric acid solution is preferably from room temperature (20 ° C.) to less than 100 ° C. (temperature limit at which the aqueous solution does not boil), and is 90 ° C. here.

  Next, the component 1 in which the oxide film containing a radionuclide is formed is put into the decontamination tank 11 of the decontamination equipment 10. Subsequently, the peroxodisulfuric acid aqueous solution in the oxidizing liquid tank 14 is supplied into the decontamination tank 11 through the oxidizing liquid line 15 and the circulation line 12. Then, the circulation pump 13 is driven to circulate the peroxodisulfuric acid aqueous solution in the decontamination tank 11 and the circulation line 12. The time for putting the component 1 in the circulating peroxodisulfuric acid aqueous solution is about 5 to 10 hours. This time depends on the concentration and temperature of the peroxodisulfuric acid aqueous solution. If the concentration and temperature are high, the time can be shortened. For this reason, the temperature of the peroxodisulfuric acid aqueous solution may be room temperature, although it takes a long time to put on the component 1 in order to save the trouble of heating the peroxodisulfuric acid aqueous solution. In order to shorten the time for putting 1 on, the temperature may be close to 100 ° C. as in this embodiment.

In this oxidation step (S1), Cr ³⁺ present as Cr ₂ O ₃ or FeCr ₂ O ₄ in the oxide film becomes Cr ⁶⁺ and is eluted into the aqueous solution. That is, Cr in the oxide film is oxidized and dissolved.

  Next, a reduction step (S2) is performed in which oxalic acid is placed in a peroxodisulfuric acid aqueous solution, and the iron-based oxide, which is the main component of the oxide film of the component 1, is reduced and dissolved with the oxalic acid aqueous solution.

  In this reduction step (S 2), first, an oxalic acid aqueous solution is stored in the reducing liquid tank 17 of the decontamination equipment 10. The concentration of the oxalic acid aqueous solution is such a concentration that the oxalic acid concentration in the aqueous solution after mixing the oxalic acid aqueous solution in the peroxodisulfuric acid aqueous solution after the oxidation step (S1) becomes 2000 ppm. The temperature of the oxalic acid aqueous solution is preferably from room temperature (20 ° C.) to less than 100 ° C. (temperature limit at which the aqueous solution does not boil), and is 90 ° C. here.

  Next, the oxalic acid aqueous solution in the reducing liquid tank 17 is supplied into the decontamination tank 11 through the reducing liquid line 18 and the circulation line 12, and the solution in the aqueous solution in the decontamination tank 11 and the circulation line 12 is supplied. As described above, the oxalic acid concentration is adjusted to 2000 ppm. Then, the circulation pump 13 is driven to circulate an oxalic acid aqueous solution (including peroxodisulfuric acid) in the decontamination tank 11 and the circulation line 12. The time for putting the component 1 in the circulating oxalic acid aqueous solution is also about 5 to 10 hours. This time also depends on the concentration and temperature of the oxalic acid aqueous solution, and the time can be shortened if the concentration and temperature are high.

  When a predetermined time has passed since the part 1 was put on the oxalic acid aqueous solution, the aqueous solution in the decontamination tank 11 and the circulation line 12 was used as a waste liquid via the circulation line 12 of the decontamination equipment 10 and the waste liquid line 28 of the waste liquid treatment equipment 20 It is sent into the neutralization tank 21 of the waste liquid treatment facility 20.

  In the above description, the peroxodisulfuric acid aqueous solution in the oxidizing liquid tank 14 and the oxalic acid aqueous solution in the reducing liquid tank 17 are both 90 ° C. In order to improve the handling of these aqueous solutions, In the process of circulating the aqueous solutions in the decontamination tank 11 and the circulation line 12 in the process of setting the temperature of the aqueous solutions in 14 and 17 to normal temperature, these aqueous solutions are heated by a heater provided in the circulation line 12 and the like, and the oxidation reaction time Alternatively, the reduction reaction time may be shortened.

In this reduction step (S2), Fe ²⁺ present as Fe ₂ O ₃ or the like in the oxide film becomes Fe ³⁺ and is eluted into the aqueous solution. That is, Fe in the oxide film is reduced and dissolved.

  When the reduction step (S2) is completed, it is determined whether or not the oxide film formed on the surface of the component 1 has been sufficiently removed (S3). When the oxide film is not sufficiently removed, the decontamination step is performed a plurality of times, with the oxidation step (S1) and the reduction step (S2) after the oxidation step (S1) as one decontamination step.

  When the oxide film is sufficiently removed, a waste liquid treatment process (S4) for treating the waste liquid generated in the decontamination process (oxidation process + reduction process) is performed.

  In this waste liquid treatment step (S4), first, the acidic waste liquid sent to the neutralization tank 21 of the waste liquid treatment facility 20 is neutralized with an alkaline aqueous solution such as an aqueous sodium hydroxide solution. In this neutralization, the alkaline aqueous solution may be previously placed in the neutralization tank 21 before the waste liquid is sent to the neutralization tank 21, but after the waste liquid enters the neutralization tank 21, the neutralization tank is used. 21 may contain an alkaline aqueous solution.

  Next, the waste liquid neutralized in the neutralization tank 21 is sent to the waste liquid evaporation tank 25, and the waste liquid in the waste liquid evaporation tank 25 is heated by the heater 26 to evaporate water and the like in the waste liquid. Is concentrated to about 20 times, for example. The concentrated waste liquid is subjected to, for example, concrete pit disposal.

  Here, after it is determined that the oxide film formed on the surface of the component 1 has been sufficiently removed, the waste liquid treatment step (S4) is performed, but every time the reduction step (S2) is completed, A waste liquid treatment step (S4) may be performed.

  Further, when the oxide film is sufficiently removed, the decontamination tank 11 in parallel with the waste liquid treatment step (S4), before the waste liquid treatment step (S4), or after the waste liquid treatment step (S4). A component water washing step (S5) for washing the inside component 1 is performed.

  In this component washing step (S5), the component 1 in the decontamination tank 11 is taken out, and the component 1 is put in the washing tank 31 of the washing facility 30 and washed. The water after washing is passed through ion exchange resins 34 and 35 to remove impurities in the water. The ion exchange resins 34 and 35 obtained by treating the washed water a plurality of times are treated separately.

  Next, a film forming step (S6) is performed in which a film is formed on the surface of the component 1 washed in the component water washing step (S5). In this film forming step (S6), a zinc oxide film is formed on the surface of the component 1.

  The electrolytic solution to be placed in the electrolytic tank 41 of the film forming facility 40 is an aqueous solution containing zinc ions and at least one compound selected from oxoacid salts among chlorine compounds. For example, zinc perchlorate, zinc chloride, zinc sulfate, zinc acetate, zinc phosphate, zinc carbonate, zinc carbonate, zinc metal, zinc oxide, and zinc hydroxide can be dissolved in an acidic or alkaline solution. Can be obtained at Examples of at least one compound selected from oxoacid salts of chlorine compounds include hypochlorous acid, sodium hypochlorite, potassium hypochlorite, chlorous acid, sodium chlorite, Examples include potassium chlorate, chloric acid, sodium chlorate, potassium chlorate, perchloric acid, sodium perchlorate, and potassium perchlorate.

  Here, as the electrolytic solution, for example, a 1% by weight aqueous ammonia solution containing zinc chloride and sodium chlorite at a rate of 0.05 mol / L and adjusted to pH 5 is used. In addition, about 1-7 are suitable for pH of electrolyte solution, and 5-6 are especially preferable. The temperature of the electrolytic solution is preferably from room temperature (20 ° C.) to less than 100 ° C. (temperature limit at which the aqueous solution does not boil), particularly preferably 50 to 90 ° C., and here 80 ° C.

  The working electrode is the component 1 washed with water in the component washing step (S5). The counter electrode 42 is a platinum electrode, and the reference electrode 44 is a platinum electrode in a KCl saturated solution.

  In the film forming step (S6), as described above, the component 1 washed in the component water washing step (S5) is used as a working electrode, and this is placed in the electrolytic solution in the electrolytic bath 41. The working electrode potential is about -0.1 to -2.0 V, preferably -0.7 to -1.3 V, based on the Ag / AgCl electrode. When a zinc oxide film having a target thickness is formed on the surface of the component 1, the component 1 is pulled up from the electrolytic solution, and the film formation step (S6) is completed.

  Thus, when a zinc oxide film is formed on the surface of the component 1, it is difficult to form an oxide film containing a radionuclide on the surface of the zinc oxide film. For this reason, by forming a zinc oxide film on the surface of the component 1, the chemical cleaning cycle of the component 1 can be lengthened.

  This completes the entire chemical cleaning process for the component 1.

  As described above, in the oxidation step (S1) of the present embodiment, a peroxodisulfuric acid aqueous solution is used in place of the conventionally used permanganic acid aqueous solution. Here, the standard oxidation-reduction potential of permanganic acid is 1.695V, and the standard oxidation-reduction potential of peroxodisulfuric acid is 2.01V. Therefore, in the oxidation step (S1), it is more efficient to use the peroxodisulfuric acid aqueous solution than the permanganic acid aqueous solution to oxidize and dissolve the chromium oxide contained in the oxide film of the component 1 can do. In other words, in this embodiment, even if the amount of the solute (peroxodisulfuric acid) in the oxidizing aqueous solution is reduced, an effect equivalent to or higher than that in the case of using the permanganic acid aqueous solution can be obtained.

  In the present embodiment, the waste liquid produced in the decontamination process (oxidation process + reduction process) is not used with an ion exchange resin, but the water in the waste liquid is evaporated to concentrate the waste liquid. Disposal of a large amount of ion exchange resin becomes unnecessary.

  As described above, in this embodiment, the amount of the chemical (peroxodisulfuric acid) used in the oxidation step (S1) can be reduced, and the waste liquid can be removed without using an ion exchange resin in the waste liquid treatment step (S4). Since it is treated, the amount of secondary waste containing radionuclides can be reduced.

  Next, a modification of the embodiment described above will be described.

  In the oxidation step (S1) of the above embodiment, an aqueous solution of peroxodisulfuric acid is used. Instead of this peroxodisulfuric acid, an aqueous solution of persulfuric acid, perferric acid, or perboric acid may be used. Further, an aqueous solution containing two or more peroxides of peroxodisulfuric acid, persulfuric acid, perferroic acid, and perboric acid may be used. The standard redox potentials of these peroxides are all higher than the standard redox potential of permanganic acid. For example, the standard redox potential of perferic acid is 2.20V. Therefore, it is more efficient to use these aqueous solutions than to use the permanganic acid aqueous solution as in the case of using the peroxodisulfuric acid aqueous solution. It can be oxidized and dissolved.

  Moreover, in the reduction | restoration process (S2) of the above embodiment, although the oxalic acid which is 1 type of dicarboxylic acid is used, you may add a citric acid to this oxalic acid further. Further, instead of oxalic acid, other dicarboxylic acids may be used. For example, mesooxalic acid, malonic acid, didroxyfumaric acid, dihydroxytartaric acid and the like may be used.

  Further, in the waste liquid treatment step (S4) of the above embodiment, the waste liquid is evaporated and the waste liquid is concentrated. However, the waste liquid may be passed through an ion exchange resin for treatment. However, in this case, as described above, it is necessary to separately process a large amount of ion exchange resin generated after the waste liquid treatment.

  Moreover, in the component water washing process (S5) of the above embodiment, although the water after water washing is processed using the ion exchange resin 34 and 35, the water after this water washing is sent in the waste liquid evaporation tank 25. The waste liquid evaporation tank 25 may be heated together with the waste liquid to be evaporated.

  Moreover, in the above embodiment, the part 1 which contacts primary cooling water is removed from the nuclear power plant P, and this is put into the decontamination tank 11, and the decontamination process is performed, but parts are removed from the nuclear power plant P. You may implement a decontamination process by circulating the oxidizing liquid and reducing liquid which were demonstrated above in the line through which primary cooling water passes, without removing. In this case, a chemical liquid supply pipe for supplying an oxidizing liquid or a reducing liquid is connected to a primary cooling water pipe 55b connecting the pressurized water reactor 50 and the steam generator 53, and a chemical liquid discharge pipe is connected. Good.

  Moreover, although the above embodiment exemplifies the nuclear power plant P provided with the pressurized water reactor 50, the present invention is not limited to this, and water contacts the fuel of the reactor. As long as it is a plant to be used, it may be applied to any nuclear power plant, for example, a nuclear power plant equipped with a boiling water reactor.

  DESCRIPTION OF SYMBOLS 10 ... Decontamination equipment, 11 ... Decontamination tank, 12 ... Circulation line, 14 ... Oxidizing liquid tank, 17 ... Reducing liquid tank, 20 ... Waste liquid processing equipment, 21 ... Neutralization tank, 24 ... Evaporator, 30 ... Water washing equipment, 31 ... Water washing tank, 40 ... Film formation equipment, 41 ... Electrolytic tank, 50 ... Pressurized water reactor, 51 ... Fuel rod, 52 ... Pressurizer, 53 ... Steam generator, 54 ... Coolant pump, 55a, 55b ... Primary cooling water piping, 56 ... Steam turbine, 57 ... Generator, 58 ... Condenser

Claims (8)

In a chemical cleaning method for cleaning a component by performing an oxidation step of oxidizing and dissolving a metal in an oxide film formed on the surface of a component constituting a nuclear power plant using an oxidizing solution,
In the oxidation step, an aqueous solution containing at least one peroxide of perferic acid and perboric acid is used as the solution.
The chemical cleaning method characterized by the above-mentioned. The chemical cleaning method according to claim 1,
After carrying out the oxidation step, put a dicarboxylic acid in the solution, reduce and dissolve other metals in the oxide film, and carry out a reduction step of removing the solution containing the dicarboxylic acid.
The chemical cleaning method characterized by the above-mentioned. The chemical cleaning method according to claim 2,
Performing a waste liquid treatment step of heating the solution removed in the reduction step to evaporate water in the solution;
The chemical cleaning method characterized by the above-mentioned. The chemical cleaning method according to claim 2 or 3,
The oxidation step and the reduction step after the oxidation step are one decontamination step, and the decontamination step is performed a plurality of times.
The chemical cleaning method characterized by the above-mentioned. In the chemical cleaning method according to any one of claims 2 to 4,
Performing a film forming step of forming an oxide film on the surface of the component after the reduction step;
The chemical cleaning method characterized by the above-mentioned. The chemical cleaning method according to claim 5,
In the film forming step, the component after the reduction step is attached to an aqueous solution containing zinc ions and at least one compound selected from oxoacid salts of chlorine compounds, and zinc is applied to the surface of the component. Forming an oxide film,
The chemical cleaning method characterized by the above-mentioned. The chemical cleaning method according to any one of claims 1 to 6,
The concentration of the peroxide in the aqueous solution used in the oxidation step is 200 to 300 ppm.
The chemical cleaning method characterized by the above-mentioned. In the chemical cleaning method according to any one of claims 1 to 7,
The temperature of the aqueous solution used in the oxidation step is 20 ° C. or more and less than 100 ° C.,
The chemical cleaning method characterized by the above-mentioned.

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