JP2009210307A - Adhesion suppression method of radioactive nuclide on nuclear power plant constituting member, and ferrite film forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesion suppression method of a radioactive nuclide on a nuclear power plant constituting member, can suppress adhesion of the radioactive nuclide. <P>SOLUTION: After bringing coating formation liquid containing iron(II) ions into contact with a surface (for example, a surface of a recirculation system pipe) where the nuclear power plant constituting member is brought into contact with a cooling material, processing liquid to which an oxidizing agent for oxidizing a part of the iron(II) ions into iron(III) ions and a pH adjusting agent for adjusting pH of solution to 5.5-9.0 are added substantially simultaneously is supplied from a circulation pipe to the recirculation system pipe, to thereby form a ferrite coating on the surface of the recirculation system pipe. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for suppressing radionuclide adhesion to a nuclear plant component and a ferrite film forming apparatus, and more particularly, to suppress adhesion of a radionuclide to a nuclear plant component suitable for application to a boiling water nuclear power plant. The present invention relates to a method and a ferrite film forming apparatus.

  For example, a boiling water nuclear power plant (hereinafter abbreviated as a BWR plant) has a nuclear reactor with a reactor core built in a reactor pressure vessel (RPV). The cooling water supplied to the core by the recirculation pump (or internal pump) is heated by the heat generated by the fission of each fuel material in the fuel assembly loaded in the core, and a part thereof becomes steam. This steam is led from the nuclear reactor to the turbine and rotates the turbine. The steam exhausted from the turbine is condensed in a condenser to become water. This water is supplied to the reactor as feed water. In order to suppress the generation of radioactive corrosion products in the nuclear reactor, metal impurities are mainly removed by a filtration and desalination apparatus provided in the water supply pipe.

  In addition, since corrosion products that are the source of radioactive corrosion products are also generated from water contact parts such as RPV and recirculation piping, the primary primary components are made of stainless steel and nickel bases with low corrosion. Stainless steel such as alloy is used. In addition, the low alloy steel RPV has a stainless steel overlay on the inner surface, preventing the low alloy steel from coming into direct contact with the reactor water (cooling water present in the RPV). Reactor water is cooling water present in the nuclear reactor. Furthermore, a part of the reactor water is purified by a filter demineralizer of the reactor purification system to positively remove metal impurities that are slightly present in the reactor water.

  However, even if the above-described corrosion countermeasures are taken, the presence of very few metal impurities in the reactor water is inevitable, so some metal impurities are converted into metal oxides to the fuel rods contained in the fuel assembly. Adhere to the surface. Metal impurities (for example, metal elements) adhering to the surface of the fuel rod cause a nuclear reaction when irradiated with neutrons emitted from the nuclear fuel in the fuel rod, and become radioactive nuclides such as cobalt 60, cobalt 58, chromium 51, manganese 54, and the like. Become. Most of these radionuclides remain attached to the fuel rod surface in the form of oxides, but some radionuclides elute as ions in the reactor water depending on the solubility of the incorporated oxides. Or re-released into the reactor water as an insoluble solid called clad. Radioactive material in the reactor water is removed by the reactor purification system. However, the radioactive material that has not been removed accumulates on the surface of the component that contacts the reactor water while circulating in the recirculation system together with the reactor water. As a result, radiation is radiated from the surface of the component member, which causes radiation exposure of workers during regular inspection work. The exposure dose of the employee is managed so that it does not exceed the prescribed value for each person. In recent years, this regulation value has been lowered, and it has become necessary to make the exposure dose of each person as low as economically possible.

  Thus, various methods for reducing the adhesion of radionuclides to piping and methods for reducing the concentration of radionuclides in the reactor water have been studied. For example, in Patent Documents 1, 2, and 3, a radionuclide adheres to the surface of a component after the plant is operated by forming a magnetite film as a ferrite film on the surface of the nuclear plant component after chemical decontamination. A method of suppressing this is disclosed. In this method, a formic acid aqueous solution containing iron (II) ions, hydrogen peroxide and hydrazine, and a treatment liquid heated to a temperature ranging from room temperature to 100 ° C. are brought into contact with the surface of the component member to form a ferrite film on the surface. To form.

JP 2006-38483 A JP 2007-192745 A JP 2007-24644 A

  The method of forming a ferrite film described in Patent Document 1 can remarkably suppress the amount of radionuclide adhering to the nuclear plant components, and can reduce the surface dose rate of the recirculation system piping of the nuclear plant. On the other hand, in order to suppress the adhesion of radioactive cobalt, a certain amount of ferrite film is required.

  An object of the present invention is to provide a method and an apparatus for forming a ferrite film that can easily and surely form a ferrite film necessary for suppressing the attachment of a radionuclide to a nuclear plant component that can further suppress the attachment of a radionuclide. There is.

  The feature of the present invention that achieves the above-described object is that after a film forming liquid containing iron (II) ions is brought into contact with a surface where a component of a nuclear power plant is in contact with a coolant, a part of the iron (II) ions is By substantially simultaneously adding an oxidizing agent that oxidizes iron (III) ions and a pH adjusting agent that adjusts the pH of the solution to 5.5 to 9.0, the ferrite film necessary to suppress the adhesion of radioactive cobalt is ensured. It is to make it form.

By substantially simultaneously adding an oxidizing agent and a pH adjuster to a film-forming solution containing iron (II) ions, generation of ferric hydroxide Fe (OH) ₃ does not occur, and the amount of ferrite film generated is improved. . This facilitates the formation of a ferrite film effective for suppressing the adhesion of radioactive cobalt ions, and at the same time shortens the film processing time.

  The 1st chemical | medical agent containing an iron (II) ion will not be specifically limited if it is a compound containing the iron (II) ion, or its aqueous solution. For example, an aqueous solution of a salt of iron and an organic acid or an inorganic acid can be used as the first drug containing iron (II) ions. In particular, organic acids and carbonic acid are preferable substances for use in the first drug because they can be decomposed into carbon dioxide and water after use. Examples of the organic acid include formic acid, acetic acid, malonic acid, diglycolic acid, and oxalic acid. From the viewpoint of the production amount and uniformity of the ferrite film, it is preferable to use an aqueous solution of iron (II) formate as the first agent. Furthermore, an aqueous solution containing iron (II) ions eluted from the iron electrode by electrolysis using metallic iron as the electrode can also be used as the first agent.

  As the second agent, an oxidizing agent having an action of oxidizing iron (II) ions to iron (III) ions or an aqueous solution thereof can be used. In order to form ferrite from a solution containing iron (II) ions, it is necessary to first oxidize a part thereof to iron (III) ions. Examples of the oxidizing agent include hydrogen peroxide.

  The third drug is a pH adjuster that adjusts the pH of the treatment liquid or an aqueous solution thereof. The pH of the treatment liquid is adjusted to 5.5 to 9.0 with the pH adjuster. As the pH adjuster, for example, a base such as hydrazine can be used.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to construct more reliably the ferrite membrane | film | coat quantity which can suppress adhesion of the radionuclide to a nuclear power plant structural member.

  Inventors examined the method of performing the method of forming the ferrite film described in patent documents 1 more efficiently. As a result, the inventors have found that the amount of ferrite film formation increases as the addition time interval between the oxidizing agent and the pH adjuster added to cause the ferritization reaction to the film forming solution containing iron (II) ions is shorter. I found.

That is, the inventors used stainless steel, which is a nuclear plant component, as a test piece, immersed in a film-forming solution containing iron (II) ions prepared by dissolving iron with formic acid, and then used hydrogen peroxide as an oxidizing agent. When a hydrazine was added as a pH adjusting agent to form a ferrite film, the relationship between the time interval from the addition of the oxidizing agent to the addition of the pH adjusting agent and the amount of the ferrite film was examined. The result is shown in FIG. The horizontal axis in FIG. 2 indicates the time interval from the introduction of an oxidizing agent (for example, H ₂ O ₂ ) to the introduction of a pH adjuster (for example, N ₂ H ₄ ), and the vertical axis represents a ferrite film. Indicates the relative value of the quantity. From this result, it was found that the amount of ferrite film increased when the time interval was short, and the amount of ferrite film increased most when the oxidizing agent pH adjuster was added simultaneously. On the other hand, as shown in FIG. 3, it is known that the more the amount of ferrite film, the more the adhesion of radioactive cobalt is suppressed (Patent Document 2). Therefore, it is effective to increase the amount of ferrite film in order to further reduce the amount of radioactive cobalt deposited. For this purpose, it is desirable that the time interval for adding the oxidizing agent and the pH adjusting agent is shorter, preferably at the same time. Became clear. The inventors consider this result as follows.

  When hydrogen peroxide is added to an iron formate aqueous solution containing iron (II) ions, ferric hydroxide is generated as shown in the chemical reaction formula (Formula 1).

2Fe ²⁺ + H ₂ O ₂ + 4H ₂ O → 2Fe (OH) ₃ + 4H ⁺ (Formula 1)

  When a pH adjusting agent such as hydrazine is added to this aqueous solution to adjust the pH of the solution from 5.5 to 9.0, ferrous hydroxide is generated as shown in the following (Chemical Formula 2). As shown in Chemical formula 3), magnetite is produced from ferric hydroxide.

Fe ²⁺ + 2OH ⁻ → 2Fe (OH) ₂ ...... (Chemical formula 2)
Fe ²⁺ + 2Fe (OH) ₃ → Fe ₃ O ₄ + 2H ₂ O + 2H ⁺ (chemical formula 3)

  When the time interval from the addition of hydrogen peroxide as an oxidizing agent to the addition of hydrazine as a pH adjusting agent becomes longer, the ferric hydroxide fine particles generated in (Chemical Formula 1) repeatedly collide in the solution. It is thought that grain growth occurs during this time. In this case, even if the ferritization reaction of (Chemical Formula 3) occurs by adding a pH adjuster, ferritization occurs only on the surface of the ferric hydroxide particles, and the ferric hydroxide trapped inside is It becomes difficult to contribute to the ferritization reaction. For this reason, in order to promote ferritization efficiently, hydrogen peroxide as an oxidizing agent is added before ferric hydroxide particles grow, and then hydrazine as a pH adjusting agent is added within a short time. It is considered better to do.

  Moreover, when hydrogen peroxide as an oxidizing agent and hydrazine as a pH adjusting agent are added simultaneously, ferric hydroxide produced in (Chemical Formula 1) does not occur, and magnetite is directly generated as shown in (Chemical Formula 4). Therefore, it is more efficient in forming the magnetite film.

3Fe ²⁺ + H ₂ O ₂ + 2H ₂ O → Fe ₃ O ₄ + 4H ⁺ (Chemical formula 4)

  As a method for simultaneously adding an oxidizing agent and a pH adjusting agent, there is a method in which an oxidizing agent and a pH adjusting agent are mixed and then added to a film forming solution containing iron (II) ions. At this time, when hydrogen peroxide is used as the oxidizing agent and hydrazine is used as the pH adjusting agent, if the concentration of both is high, a decomposition reaction occurs, making it difficult to control the concentration. Therefore, the inventors investigated the relationship between the concentration of hydrogen peroxide and hydrazine in equimolar mixing and the temperature rise resulting from the heat generated by the decomposition reaction. The result is shown in FIG. The horizontal axis of FIG. 4 shows the concentration of hydrogen peroxide and hydrazine at equimolar mixing, and the vertical axis shows the rising temperature. From this result, it can be seen that the 0.5 mol / L equimolar mixed solution hardly raises the temperature and the decomposition reaction is slight, but the 2 mol / L equimolar mixed solution causes a violent decomposition reaction. Therefore, when a mixed solution of both is used as a method of adding hydrogen peroxide and hydrazine at the same time, it is desirable that the mixing concentration be 0.5 mol / L or less.

  The present invention has been made based on the above examination results obtained by the inventors.

  The metal base material used as the above sample simulates a nuclear plant component. The nuclear plant component is a metal member that makes up the nuclear plant and contacts the reactor water containing radioactive material generated in the nuclear power plant nuclear reactor. Examples of the nuclear plant constituent member include, but are not limited to, a metal member constituting a reactor water recirculation system or reactor water purification system of a BWR plant. The ferrite film can also be formed on the surface of a metal member in contact with the reactor water in a nuclear power plant (PWR plant) having a pressurized water reactor (PWR). Stainless steel is mainly used for these metal members.

  Examples of the present invention will be described below.

  A method for suppressing the attachment of radionuclides to structural members of a nuclear power plant according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS.

  Example 1 is an example applied to a BWR power plant (hereinafter referred to as a BWR plant). The schematic configuration of this BWR plant is based on FIG. 5, and the schematic configuration of a film forming apparatus (ferrite film forming apparatus) 30 used when forming a ferrite film on the surface of the constituent members of the BWR plant is based on FIG. Each will be explained. FIG. 1 is a flow chart showing a method for suppressing radionuclide adhesion used in Example 1. In FIG. 5, the block diagram of the whole system | strain at the time of applying the radionuclide adhesion suppression method of Example 1 to the recirculation piping of a nuclear power plant is shown. In FIG. 6, the schematic block diagram of the film forming apparatus 30 of Example 1 is shown.

  As shown in FIG. 5, the BWR plant that is a nuclear power plant includes a reactor 1, a turbine 3, a condenser 4, a recirculation system, a reactor purification system, a water supply system, and the like. The nuclear reactor 1 has a nuclear reactor pressure vessel (hereinafter referred to as RPV) 12 in which a core 13 is built, and a jet pump 14 is installed in the RPV 12. The nuclear reactor 1 is installed in a nuclear reactor containment vessel 11. The core 13 is loaded with a large number of fuel assemblies (not shown). The fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel. The recirculation system has a recirculation pump 21 and a recirculation system pipe 22, and the recirculation pump 21 is installed in the recirculation system pipe 22. The feed water system is configured by installing a condensate pump 5, a condensate purification device 6, a feed water pump 7, a low pressure feed water heater 8, and a high pressure feed water heater 9 in a feed water pipe 10 connecting the condenser 4 and the RPV 12. The In the reactor purification system, a purification system pump 24, a regenerative heat exchanger 25, a non-regenerative heat exchanger 26 and a reactor water purification device 27 are installed in a purification system pipe 20 that connects the recirculation system pipe 22 and the feed water pipe 10. Configured. The purification system pipe 20 is connected to the recirculation system pipe 22 upstream from the recirculation pump 21.

  The cooling water in the RPV 12 is boosted by the recirculation pump 21, and jetted into the jet pump 14 through the recirculation system pipe 22. The cooling water existing around is also sucked into the jet pump 14 and supplied to the core 13. The cooling water supplied to the core 13 is heated by the heat generated by the fission of each fuel material in the fuel rod, and a part thereof becomes steam. This steam is guided from the RPV 12 through the main steam pipe 2 to the turbine 3 to rotate the turbine 3. A generator (not shown) connected to the turbine 3 is rotated to generate electric power. The steam discharged from the turbine 3 is condensed by the condenser 4 to become water. This water is supplied into the RPV 12 through the water supply pipe 10 as water supply. The feed water flowing through the feed water pipe 10 is boosted by the condensate pump 5, impurities are removed by the condensate purification device 6, further boosted by the feed water pump 7, and heated by the low pressure feed water heater 8 and the high pressure feed water heater 9. . Extracted steam extracted from the main steam pipe 2 and the turbine 3 in the extracted pipe 15 is supplied to the low-pressure feed water heater 8 and the high-pressure feed water heater 9, respectively, and serves as a heating source for the feed water.

  A part of the cooling water flowing in the recirculation system pipe 22 flows into the purification system pipe 20 by the drive of the purification system pump 24 and is purified by the reactor water purification device 27. The purified cooling water is returned into the RPV 12 through the purification system pipe 20 and the water supply pipe 10.

  After the operation of the BWR plant is stopped, the circulation pipe 35 of the film forming apparatus 30 is connected to the recirculation system pipe 22 and the purification system pipe 20. The film forming apparatus 30 is a temporary facility, and is removed from the recirculation system pipe 22 and the purification system pipe 20 after the processing of the solution used for forming the ferrite film is completed. The film forming apparatus 30 is used for both the formation of a ferrite film on the inner surface of the recirculation pipe 22 and the treatment of the solution (waste liquid) used for forming this film. Furthermore, the film forming apparatus 30 is also used when performing chemical decontamination in the recirculation piping 22.

  The detailed configuration of the film forming apparatus 30 will be described with reference to FIG. The film forming apparatus 30 includes a surge tank 31, a circulation pipe 35, chemical liquid tanks 40, 47, 48, a filter 54, a decomposition treatment device 67, a cation exchange resin tower 63, and a mixed bed resin tower 65. The on-off valve 50, the circulation pump 51, the valve 52, the heater 56, the valves 58, 59, 60, the surge tank 31, the circulation pump 32, the valve 33, and the on-off valve 34 are provided in the circulation pipe 35 in this order from the upstream. . A pipe 69 is provided so as to connect a pipe connecting the circulation pump 51 and the valve 52 and a pipe connecting the valve 52 and the heater 56. That is, the pipe 69 is provided so as to bypass the valve 52. The pipe 69 is provided with a valve 53 and a filter 54. Both ends of a pipe 70 that bypasses the heater 56 and the valve 58 are connected to the circulation pipe 35. A cooler 61 and a valve 62 are installed in the pipe 70. A cation exchange resin tower 63 and a valve 64 are installed in a pipe 71 having both ends connected to the circulation pipe 35 and bypassing the valve 59. A mixed bed resin tower 65 and a valve 66 are installed in a pipe 72 having both ends connected to the circulation pipe 35 and bypassing the valve 59. A pipe 73 in which the valve 68 and the decomposition processing device 67 are installed bypasses the valve 60 and is connected to the circulation pipe 35. The decomposition processing device 67 is filled with, for example, an activated carbon catalyst in which ruthenium is impregnated on the surface of the activated carbon. A pipe 74 provided with the valve 36 and the ejector 37 is connected to the circulation pipe 35 between the valve 33 and the circulation pump 32, and further connected to the surge tank 31. Surge tank for permanganic acid for oxidizing and dissolving pollutants on the inner surface of piping (for example, recirculation system piping 22) subject to chemical decontamination, and oxalic acid for reducing and dissolving contaminants in the piping. The ejector 37 is provided with a hopper (not shown) for supplying the inside of the ejector 31. The pipe to be subjected to chemical decontamination is a pipe to be formed with a ferrite film on the inner surface.

  The iron (II) ion implantation apparatus 100 includes a chemical solution tank 47, a valve 41, an injection pump 44, and an injection pipe 75. The chemical tank 47 is connected to the circulation pipe 35 by an injection pipe 75 having an injection pump 44 and a valve 41. The chemical solution tank 47 is filled with a drug (first drug) containing divalent iron (II) ions prepared by dissolving iron with formic acid. This drug contains formic acid. In addition, as a chemical | medical agent which dissolves iron, the organic acid or carbonic acid which becomes a counter anion of iron (II) ion can be used not only formic acid.

  The oxidant injection device 101 includes a chemical liquid tank 48, an injection pump 45, a valve 42, and an injection pipe 76. The chemical tank 48 is connected to an injection pipe 77 connected to the circulation pipe 35 by an injection pipe 76 in which the injection pump 45 and the valve 42 are installed. The chemical tank 48 is filled with hydrogen peroxide which is an oxidizing agent (second chemical).

  The pH adjusting agent injection device 102 includes a chemical liquid tank 40, an injection pump 39, a valve 38 and an injection pipe 77. The chemical tank 40 is connected to the circulation pipe 35 by an injection pipe 77 in which an injection pump 39 and a valve 38 are installed. The chemical tank 40 is filled with hydrazine which is a pH adjuster (third drug).

  A pipe 78 provided with a valve 57 communicates the pipe 73 and the pipe 76. The surge tank 31 is initially filled with water used for processing. An inert gas injection device (not shown) for bubbling an inert gas such as nitrogen or argon is connected to the chemical liquid tank 47 and the surge tank 31 in order to remove oxygen contained in the solution existing in each of them. It is preferable to do.

  The piping 76 of the oxidant injection device 101 is not directly connected to the circulation piping 35 but is connected to the injection piping 77 of the pH adjuster injection device 102. The second connection point of the injection pipe 77 to the circulation pipe 35 is downstream of the first connection point (connection point of the injection pipe 75 and the circulation pipe 35) to the circulation pipe 35 of the iron (II) ion implantation apparatus 100. Therefore, it is preferable to be as close as possible to the target site for chemical decontamination and ferrite film formation. By configuring the piping system in this manner, after injecting iron (II) ions, the oxidant injecting device 101 and the pH adjusting agent injecting device 102 are started at the same time, so that the iron (II) ions in the circulation piping 35 are started. The oxidant and the pH adjuster can be allowed to act simultaneously.

  The decomposition treatment device 67 can decompose an organic acid (for example, formic acid) used as a counter anion of iron (II) ions and a hydrazine as a pH adjuster. That is, as the counter anion of the iron (II) ion, an organic acid that can be decomposed into water or carbon dioxide in consideration of reduction of the amount of waste, or carbonic acid that can be released as a gas and does not increase waste is used.

  The method for suppressing the attachment of radionuclides to the nuclear plant components of this embodiment, in which a ferrite film is formed in the recirculation system pipe 22 using the film forming apparatus 30, will be described in detail with reference to FIGS. explain. The radionuclide adhesion suppression method of the present embodiment is performed within a period of periodic inspection (maintenance inspection) of the BWR plant in which the operation of the BWR plant is stopped.

  First, the film forming apparatus 30 is connected to the piping system to be coated (Step S1). That is, after the operation of the BWR plant is stopped for the periodic inspection of the BWR plant, the circulation pipe 35 is connected to the recirculation system pipe 22 and the purification system pipe 20 as described above. The piping system to be coated is, for example, the recirculation piping 22. A valve 23 is provided in the purification system pipe 20. The bonnet of the valve 23 is opened to close the reactor water purification device 27 side of the purification system pipe 20. One end of the circulation pipe 35 is connected to the flange of the valve 23. The other end of the circulation pipe 35 is connected to a recirculation system pipe 22 downstream of the recirculation pump 21, for example, a branch pipe connected to the recirculation system pipe 22 (a branch pipe from which a drain pipe or an instrumentation pipe is separated). Connected. In this way, the film forming apparatus 30 is connected to the recirculation piping 22. In addition, as shown in FIG. 8, both ends of the recirculation system pipe 22 are sealed with plugs so that the decontamination solution and the film forming aqueous solution supplied into the recirculation system pipe 22 do not flow into the RPV 12. .

  Chemical decontamination is performed on the film formation target portion (step S2). On the inner surface of the recirculation system pipe 22 that comes into contact with the cooling water, an oxide film (contaminant) incorporating the radionuclide is formed. An example of step S2 is a process of removing the oxide film that has taken in the radionuclide by a chemical process from the inner surface of the recirculation pipe 22 that is a film formation target location. The formation of a ferrite film on the piping system to be coated is intended to suppress the attachment of radionuclides to the piping system. It is preferable to carry out. Since it is sufficient that the surface of the metal member to be coated is exposed before the ferrite film is formed, mechanical decontamination treatment can be applied instead of chemical decontamination.

  The chemical decontamination applied in step S2 is a known method (see Japanese Patent Laid-Open No. 2000-105295), but will be briefly described. First, the valves 33, 34, 50, 52, 58, 59 and 60 are opened, and the other pumps are closed, and the circulation pump 32 and the circulation pump 51 are started to recirculate the piping 22 to be decontaminated. The water in the surge tank 31 is circulated inside. Then, the temperature of the circulating water is raised to about 90 ° C. by the heater 56. After reaching a predetermined temperature, the valve 36 is opened. The required amount of potassium permanganate introduced into the pipe 74 from the hopper connected to the ejector 37 is supplied into the surge tank 31 by the water flowing in the pipe 74. Potassium permanganate dissolves in water in the surge tank 31 to produce an oxidative decontamination solution. This oxidative decontamination solution is supplied to the recirculation system pipe 22 through the valve 34 and the purification system pipe 20 through the circulation pipe 35 by driving of the circulation pump 32. The oxidative decontamination solution oxidizes and dissolves contaminants such as an oxide film formed on the inner surface of the recirculation pipe 22.

  After the decontamination with the oxidative decontamination liquid is completed, permanganate ions remaining in the oxidative decontamination liquid are decomposed by injecting oxalic acid into the surge tank 31 from the hopper. After the decomposition of potassium permanganate, reductive decontamination solution is used to reduce and dissolve contaminants such as an oxide film formed on the inner surface of the recirculation pipe 22. The reductive decontamination liquid is generated by supplying oxalic acid into the surge tank 31. In order to adjust the pH of the reductive decontamination solution, the valve 38 is opened and hydrazine is supplied from the chemical solution tank 40 into the circulation pipe 35. A reductive decontamination solution containing hydrazine is supplied into the recirculation system pipe 22 by driving the circulation pump 32, and the inner surface of the recirculation system pipe 22 is reductively decontaminated. At the time of reductive decontamination, the valve 64 is opened and the opening of the valve 59 is adjusted, and a part of the reductive decontamination solution is guided to the cation exchange resin tower 63. Metal cations eluted from the inner surface of the recirculation system pipe 22 into the reducing decontamination solution are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 63.

  After the reduction decontamination is completed, in order to decompose the oxalic acid remaining in the decontamination liquid, the valve 68 is opened and the opening of the valve 60 is adjusted, and a part of the reduction decontamination liquid flowing in the circulation pipe 35 is decomposed. Supply to device 67. At this time, the valve 57 is opened to drive the injection pump 45, and the hydrogen peroxide in the chemical tank 48 is guided to the decomposition treatment device 67 through the pipe 78. The decomposition treatment device 67 decomposes oxalic acid and hydrazine contained in the reductive decontamination solution by the action of hydrogen peroxide and activated carbon catalyst. After decomposition of oxalic acid and hydrazine, the valve 58 is closed to stop heating by the heater 56, and at the same time, the valve 62 is opened to supply the decontamination solution to the cooler 61. After the temperature of the decontamination liquid falls to a temperature at which water can be passed through the mixed bed resin tower 65 (for example, 60 ° C.), the valve 64 is closed and the valve 66 is opened to supply the decontamination liquid to the mixed bed resin tower 65. The mixed bed resin tower 65 removes impurities contained in the decontamination liquid that has not been completely decomposed by the decomposition processing device 67.

  By repeating the oxidative dissolution, oxidant decomposition, reductive dissolution, reductant decomposition, and purification operation from the temperature rise, for example, about 2 to 3 times, the metal member (the constituent member of the recirculation piping 22) at the decontamination target location is repeated. The contaminants including the oxide film formed on the surface in contact with the reactor water can be dissolved and removed. After removing contaminants including the oxide film on the metal member and decomposing oxalic acid and hydrazine contained in the reductive decontamination solution, a ferrite film is formed.

  After the decontamination of the film formation target portion and the decomposition treatment of the reductive decontamination liquid are completed, the temperature of the film forming aqueous solution is adjusted (step S3). After the decontamination of the film formation target portion, after the final purification operation by the film forming apparatus 30, the following valve operation is performed. The valve 53 is opened and the valve 52 is closed, and water flow to the filter 54 is started. By opening the valve 59 and closing the valve 66, water flow to the mixed bed resin tower 65 is stopped. Further, the valve 62 is closed, the valve 58 is opened, and the water in the circulation pipe 35 is heated to a predetermined temperature by the heater 56. Valves 50, 60, 33, and 34 are open, and valves 36, 41, 38, 42, 57, 62, 64, 66, and 68 are closed. The flow of water through the filter 54 is for removing fine solids remaining in the water. If this solid substance remains, a ferrite film is also formed on the surface of the solid substance when the ferrite film is formed at the film formation target site, and the drug is wasted. By removing the solid matter, a chemical contained in a film-forming aqueous solution (referred to as a treatment liquid) can be used effectively. If water is passed through the filter 54 during decontamination, the dose rate of the filter 54 may become too high due to the dissolved solid matter containing high-activity radionuclides. For this reason, the water is passed through the filter 54 after the decontamination. When the removal of the solid matter is completed, the valve 52 is opened and the valve 53 is closed.

  The predetermined temperature is preferably about 100 ° C., but is not limited thereto. In short, it is only necessary that the film structure such as crystals of the coating can be densely formed so that the radionuclide contained in the cooling water during operation of the nuclear reactor is not taken into the ferrite coating generated at the coating formation target site. Therefore, the temperature of the treatment liquid is preferably at least 200 ° C. and the lower limit may be room temperature (20 ° C.), but is preferably 60 ° C. or more at which the film formation rate is within the practical range. When the temperature is 100 ° C. or higher, it is not preferable because the boiling of the treatment liquid is suppressed and the pressure has to be increased and the pressure resistance of the temporary equipment is required and the equipment is enlarged.

  In order to form a ferrite film at a film formation target site, iron (II) ions need to be adsorbed on the surface of the metal member at the film formation target site. However, iron (II) ions in the treatment liquid are oxidized to iron (III) ions by dissolved oxygen according to the formula (5). Since iron (III) ions have lower solubility than iron (II) ions, they precipitate as ferric hydroxide according to the formula (6) and do not contribute to the formation of a ferrite film. Therefore, in order to remove dissolved oxygen in the treatment liquid, it is preferable to perform bubbling of inert gas or vacuum degassing as described above.

4Fe ²⁺ + O ₂ + 2H ₂ O → 4Fe ³⁺ + 4OH ⁻ (Chemical formula 5)
Fe ³⁺ + 3OH ⁻ → Fe (OH) ₃ ...... (Chemical formula 6)

  After the temperature of the water circulating in the circulation pipe 35 reaches a predetermined temperature in step S3, a chemical (aqueous solution) containing iron (II) ions is injected into the circulation pipe 35 (step S4). In other words, the valve 41 is opened, the injection pump 43 is driven, and a chemical containing iron (II) ions and formic acid obtained by dissolving iron with formic acid flows from the chemical tank 47 through the circulation pipe 35. Inject into liquid. Hydrogen peroxide as an oxidizing agent and hydrazine as a pH adjusting agent are simultaneously injected into the circulation pipe 35 (step S5). The valve 42 and the valve 38 are opened to drive the injection pump 45 and the injection pump 39 to draw hydrogen peroxide from the chemical tank 48 and hydrazine from the chemical tank 40, and the hydrogen peroxide passing through the injection pipe 76 is connected to the injection pipe 77. The mixed solution of hydrazine and hydrogen peroxide is injected into the treatment liquid containing iron (II) ions in the circulation pipe 35 through the injection pipe 77. Hydrogen peroxide oxidizes iron (II) ions adsorbed on the surface of the metal member at the location where the film is to be formed or iron (II) ions in the treatment solution to iron (III) ions. In order to adjust the pH of the liquid to 5.5 to 9.0, iron (II) ions and iron (III) ions form ferrite. This processing liquid is supplied to the recirculation system pipe 22 through the circulation pipe 35. The formation reaction of the ferrite film occurs on the inner surface of the recirculation piping 22 that comes into contact with the film-forming aqueous solution. A control device (not shown) controls the rotation speed of the injection pump 39 based on the measured pH value of the processing liquid measured by the pH meter 79 and adjusts the injection speed of hydrazine to be injected into the recirculation system pipe 22. To do. By this control, the pH of the treatment liquid is adjusted within the above range.

  By supplying a treatment liquid in which hydrogen peroxide and hydrazine are simultaneously injected into the circulating water in the circulation pipe 35 containing iron (II) ions, the ferrite is applied to the inner surface of the recirculation system pipe 22. A film is formed. The process of forming a ferrite film on the inner surface of the recirculation pipe 22 will be described in detail with reference to FIG.

Just by injecting a solution containing iron (II) ions prepared by dissolving iron with formic acid into the circulating water in the circulation pipe 35, the pH of the treatment liquid is 3 to 5, so that the surface of the recirculation system pipe 22 has ferrite. Is not formed. For the formation of ferrite, the presence of iron (III) ions and the pH of the treatment solution must be 5.5 to 9.0. By simultaneously injecting hydrogen peroxide and hydrazine, the ferrite forming conditions of the treatment liquid are achieved. Chemical decontamination is performed, and OH ⁻ (O ² —H ⁺ ) groups are adsorbed on the inner surface of the recirculation piping 22 (see FIG. 7A). Iron (II) ions contained in the treatment liquid are replaced with H ^{+ of the} OH ⁻ group adsorbed on the inner surface of the recirculation pipe 22, and the inner surface of the recirculation pipe 22 is combined with O ^2−. (See FIG. 7B). When hydrogen peroxide and hydrazine are simultaneously supplied to such a state, iron (II) ions are oxidized to iron (III) ions by hydrogen peroxide, and at the same time, the pH of the solution is in the ferrite formation region. Thus, a hydrolysis reaction occurs, and a ferrite film (Fe ₃ O ₄ ) 80 is formed on the inner surface of the recirculation piping 22 by a combination of one iron (II) ion and two iron (III) (FIG. 7 ( C)). Since OH ^- groups and iron (II) ions still exist in the treatment liquid, the reactions (A) to (C) shown in FIG. 7 are repeated, and the ferrite film 80 grows.

  Here, a case where hydrogen peroxide as an oxidizing agent and hydrazine as a pH adjusting agent are not injected simultaneously will be described. For example, when hydrazine is injected after hydrogen peroxide is injected, since the pH of the treatment solution after hydrogen peroxide injection is 3 to 5, no ferrite is formed, and most of the generated iron (III) ions are ( Ferric hydroxide gel particles are formed by the hydrolysis reaction of Chemical Formula 6). Thereafter, hydrazine is injected to adjust the pH of the treatment liquid to 5.5 to 9.0, thereby causing the ferritization reaction. At this time, it is not hydrogen peroxide that acts as a source of iron (III) ions, but iron (III) ions that are released from ferric hydroxide already formed in a solution equilibrium. When the time interval from hydrogen peroxide injection to hydrazine injection becomes long, ferric hydroxide particles grow and it becomes difficult to release iron (III) ions. For this reason, the growth of the ferrite film 80 is also slow compared with the case where hydrogen peroxide and hydrazine are injected simultaneously. FIG. 2 illustrates this.

Conversely, when hydrazine is injected first and then hydrogen peroxide is injected later, the problem of ferric hydroxide formation does not occur. However, if hydrazine is injected first and the pH of the treatment liquid is set to 7.0 or more, ferrous hydroxide Fe (OH) ₂ gel particles are not generated. The ferritization reaction also proceeds on the ferrous particles, and the ferritization reaction on the inner surface of the target recirculation system pipe 22 decreases accordingly. Therefore, in order to efficiently form the ferrite film 80 on the inner surface of the recirculation system pipe 22, a method in which hydrogen peroxide and hydrazine are simultaneously injected is most preferable.

  Hydrogenation and hydrazine are injected into the circulating fluid containing iron (II) ions to produce iron (III) ions, and at the same time the ferritization reaction starts when the pH of the treatment solution is adjusted to 5.5 to 9.0 Is done. Therefore, in order to prevent the formation of a useless ferrite film on the inner surface of the circulation pipe 35, the injection point of the mixed solution of hydrogen peroxide and hydrazine is preferably close to the film formation target location in the reactor containment vessel 11.

  It is determined whether the formation of the ferrite film has been completed (step S6). When the formation of the ferrite film is insufficient, the processes of step S4 to step S5 are repeated. When the formation of the ferrite film on the inner surface of the recirculation pipe 22 is sufficient, that is, when the ferrite film having a predetermined thickness is formed, the waste liquid treatment in step S7 is performed.

  The waste liquid treatment (step S7) is a treatment for decomposing hydrazine and formic acid contained in the used treatment liquid (hereinafter referred to as waste liquid) after the formation of the ferrite film on the inner surface of the recirculation pipe 22 is completed. . The decomposition process of the waste liquid is executed in the film forming apparatus 30. During the period during which the waste liquid is being processed, the waste liquid is supplied from one end of the circulation pipe 35 to one end of the recirculation system pipe 22 by driving the circulation pump 32, and passes through the recirculation system pipe 22 to the circulation pipe 35. Returned to the other end. The waste liquid returned to the circulation pipe 35 through the valve 50 is returned to the surge tank 31 through the heater 56 and the valves 52, 58, 59, 60 by driving of the circulation pump 51. Valves 36, 41, 42, 38, 53, 62, 64, 65, 57 are closed.

  First, the ferrite particles contained in the waste liquid are removed using the filter 54. The valve 53 is opened and the valve 52 is closed to remove the particle components contained in the waste liquid. Thereafter, in order to remove iron (II) ions and hydrazinium ions contained in the waste liquid, the openings of the valve 59 and the valve 64 are adjusted, and a part of the waste liquid is passed through the cation exchange resin tower 63. At the same time, the formic acid contained in the treatment liquid and the hydrazine that has not been completely removed by the cation exchange resin tower 63 are decomposed using the decomposition treatment device 67 in the same manner as the decomposition of oxalic acid after chemical decontamination. The opening degree of the valves 60 and 68 is adjusted, and a part of the waste liquid is supplied to the decomposition processing device 67. The valve 57 is opened, and hydrogen peroxide is supplied from the chemical tank 48 through the pipe 78 to the decomposition treatment device 67. Hydrazine and formic acid are decomposed in the decomposition treatment device 67 by the action of hydrogen peroxide and activated carbon catalyst. Formic acid is decomposed into carbon dioxide and water based on the reaction of formula (7), and hydrazine is decomposed into nitrogen and water based on the reaction of formula (8).

HCOOH + H ₂ O ₂ → CO ₂ + 2H ₂ O ⁻ (Chemical formula 7)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O ⁻ (Chemical Formula 8)

  Although hydrazine and formic acid can be treated in the mixed bed resin tower 65, waste of ion exchange resin increases, so that these substances are preferably decomposed in the decomposition processing device 67. Here, since hydrazine and formic acid are more difficult to decompose, the pH of the waste liquid begins to decrease as the decomposition of the waste liquid proceeds to some extent. When the pH of the waste liquid becomes 4 or less, the formed ferrite film may be dissolved. Therefore, the injection pump 39 is started by opening the valve 38 so that the indicated value of the pH meter 79 does not become 4 or less. The hydrazine in the regulator tank 40 is poured into the waste liquid. In addition, it is also possible to use an ultraviolet irradiation device instead of the decomposition processing device 67 using a catalyst. An ultraviolet irradiation device can also decompose hydrazine, formic acid and oxalic acid in the presence of an oxidizing agent.

  By decomposing hydrazine and formic acid into gas and water in the decomposition treatment device 67 as described above, the load of removing hydrazine and formic acid by the mixed bed resin tower 65 by the cation exchange resin tower 64 can be greatly reduced. The amount of ion exchange resin waste can be significantly reduced.

  In the present embodiment, it becomes easier to form a dense ferrite film (porosity of less than 0.03%) formed on the inner surface of the recirculation pipe 22 (see FIG. 2). The ferrite film formation process which suppresses adhesion to the recirculation system piping 22 inner surface of the radionuclide can be performed more easily. By forming the ferrite film on the inner surface of the recirculation pipe 22, corrosion of the base material of the recirculation pipe 22 can be further suppressed. Further suppression of the attachment of the radionuclide to the inner surface of the recirculation system pipe 22 further reduces the surface dose rate of the recirculation system pipe 22. For this reason, it is possible to further reduce the exposure of the worker who performs the inspection during the periodic inspection work of the recirculation pipe 22 and the worker who performs the repair. Since the chemical | medical agent containing chlorine is not used for formation of a ferrite membrane | film | coat, a present Example does not impair the soundness of a nuclear reactor structural member.

  This example uses an oxidizing agent in the decomposition of oxalic acid used in reductive decontamination, the formation of a ferrite film, and the treatment of the waste liquid of the film-forming aqueous solution, the reduction decontamination, the formation of ferrite film, and the treatment of the waste liquid of the film-forming aqueous solution. In the above, a pH adjusting agent is used, and a decomposition treatment device 67 is used in the decomposition of oxalic acid used in the reductive decontamination and the treatment of the waste liquid of the film-forming aqueous solution. For this reason, the oxidant tank, the pH adjuster tank, and the decomposition treatment device 67 can be shared for chemical decontamination and ferrite film formation (including waste liquid treatment), and the device configuration can be simplified.

  Instead of a drug containing divalent iron (II) ions prepared by dissolving iron with formic acid, a drug containing divalent iron (II) ions prepared by dissolving iron with carbonic acid is used as the first drug. Can be used. In this case, the chemical tank 47 is filled with a medicine containing divalent iron (II) ions prepared by dissolving iron with carbonic acid, and the medicine containing iron (II) ions and carbonic acid is discharged from the chemical tank 47. It is supplied into the circulation pipe 35. For this reason, the treatment liquid contains carbonic acid. This treatment liquid containing carbonic acid can also be treated in the film forming apparatus 30 in the same manner as in the first embodiment. Carbon dioxide can be exhausted in the form of gas as carbon dioxide.

  The first drug used in Example 1 is a first drug in which iron is dissolved in an aqueous formic acid solution, and iron (II) formate precipitated from the solution in which iron is dissolved in this manner. It is possible to use a first drug in which iron is dissolved in an organic acid other than formic acid. As a 1st chemical | medical agent, the solution containing the iron (II) ion eluted from a metal iron electrode by electrolysis can also be used. Although hydrogen peroxide is used as the second agent, an oxidizing agent such as ozone water can be used. The third drug can be used in place of hydrazine as long as it can maintain the pH at 5.5 to 9 and can be decomposed into water and a gas at room temperature.

  If the concentration of hydrogen peroxide and hydrazine at the connection point between the hydrogen peroxide injection pipe 76 and the hydrazine injection pipe 77 is 0.5 mol / L or more, respectively, both start to react as shown in FIG. Does not go well. In order to prevent this, for example, there is a method in which a solution in which both hydrogen peroxide and hydrazine are diluted to 0.5 mol / L or less is put into a hydrogen peroxide tank 48 and a hydrazine tank 40 and operated. If it does in this way, it will not exceed 0.5 mol / L even if it mixes hydrogen peroxide and hydrazine in what ratio, and consumption by both reaction can be disregarded.

The upper limit of the hydrogen peroxide injection amount is determined by the amount of iron (II) ions injected into the treatment liquid. The formation of ferrite Fe ₃ O ₄ requires one iron (II) ion and two iron (III) ions. Since hydrogen peroxide is used to oxidize iron (II) ions to form iron (III) ions, the required amount of hydrogen peroxide is 2/3 of the injected iron (II) ions. ) The amount of ions. The reaction between iron (II) ions and hydrogen peroxide is expressed by the following equation.

2Fe ²⁺ + H ₂ O ₂ → 2Fe ³⁺ + 2OH ⁻ (Chemical formula 9)

From this equation, it can be seen that when hydrogen peroxide having a molar number of 1/3 of the injected iron (II) ions is injected, all of the injected iron (II) ions become ferrite Fe ₃ O ₄ . Accordingly, since the upper limit of the hydrogen peroxide injection amount is 1/3 of the number of moles of iron (II) ions injected, the injection pump 45 is started from the chemical tank 48 containing the oxidizing agent, and the injection pipe 76, valve When the amount of hydrogen peroxide injected through 42 reaches this amount, the hydrogen peroxide injection stops. On the other hand, since hydrazine is for the purpose of adjusting the pH, it is injected when the pH deviates from 5.5 to 9.0 with the generation of ferrite even after the injection of hydrogen peroxide is stopped.

  Next, how to determine the hydrazine injection amount will be described. The final adjustment of the hydrazine injection amount is adjusted by adjusting the indicated value of the pH meter 79 to 5.5 to 9.0. The concentration of hydrazine that falls within the pH is simultaneously with the injected iron (II) concentration. From the concentration of formic acid that is injected counter anion, an approximate value can be obtained using the hydrolysis constant, mass balance equation, and charge balance equation of iron (II) ions. The hydrolysis reaction formula of iron (II) ions, the dissociation reaction formula of formic acid and hydrazine, the respective equilibrium constant formula and the equilibrium constant formula of water are shown below.

Fe ²⁺ + H ₂ O = Fe (OH) ⁺ + H ⁺ (Chemical Formula 10)
Fe ²⁺ + 2H ₂ O = Fe (OH) ₂ + 2H ⁺ (Chemical Formula 11)
Fe ²⁺ + 3H ₂ O = Fe (OH) ₃ ⁻ + 3H ⁺ (Chemical Formula 12)
HCOOH = HCOO ⁻ + H ⁺ (Chemical Formula 13)
N ₂ H ₅ ⁺ = N ₂ H ₄ + H ⁺ (Formula 14)

  In the pH range (5.5 to 9.0) to be adjusted, the solubility of iron (III) ions is very low, so if you ignore the concentration of chemical species related to iron (III) ions, The charge balance equation is as follows.

(Equation 7) using (Equation 1) to (Equation 6) where [Fe] _T is the total concentration of iron, [N ₂ H ₄ ] _T is the total concentration of hydrazine, and [HCOOH] _T is the total concentration of formic acid. When arranged, the following equation is obtained.

From this equation, when the values of [Fe] _T and [HCOOH] _T injected and pH ([H ⁺ ]) 5.5 to 9.0 to be set are substituted, and the respective equilibrium constants examined from the literature are given, [N ₂ H ₄ ] _T can be obtained. The hydrazine injection may be performed with this value as an initial set value, and the injection speed may be finally adjusted with the value of the pH meter.

  A method for suppressing the attachment of radionuclides to nuclear plant components of Example 2 which is another example of the present invention applied to a BWR plant will be described with reference to FIG.

  The configuration of the film forming apparatus 30 shown in FIG. 8 used in the present embodiment has the same configuration as the film forming apparatus 30 (see FIG. 6) used in the first embodiment. FIG. 8 is a schematic configuration diagram showing the relationship between the arrangement of temporary equipment and the medicine injection position. In FIG. 8, a part of the configuration of the film forming apparatus 30 is omitted.

  A method for suppressing the adhesion of radionuclides to the nuclear power plan and the components by forming the ferrite film of the present embodiment will be described. Similarly to the first embodiment, the radionuclide adhesion suppression method of the present embodiment also executes the steps S1 to S7 shown in FIG. In this embodiment, the connection destination of the circulation pipe 35 of the film forming apparatus 30 is different from the connection destination of the circulation pipe 35 of the film formation apparatus 30 in the first embodiment. In this embodiment, one end of the circulation pipe 35 is connected to a branch pipe 82 connected to the recirculation system pipe 22 via a valve 81. The other end of the circulation pipe 35 is connected to a branch pipe 84 connected to the recirculation system pipe 22 via a valve 83. Also in this embodiment, the recirculation system pipe 22 is a film formation target portion. Both ends of the recirculation piping 22 are sealed with plugs 85 and 86. The connection of the recirculation pipe 35 to the recirculation pipe 22 and the plugging of both ends of the recirculation pipe 22 by the plugs 85 and 86 are performed in step S1. A pipe 77 for injecting a mixed solution of hydrogen peroxide and hydrazine is connected to the circulation pipe 35 inside the reactor containment vessel 11 and near the film formation target location.

  After the end of step S1, steps S2 to S6 are executed. As a result, the ferrite film 80 is formed on the inner surface of the recirculation pipe 22 as in the first embodiment. Thereafter, step S7 is executed.

  In this embodiment, when the film forming apparatus 30 is connected to the recirculation system pipe 22, two free liquid levels are generated in the recirculation system pipe 22. It is necessary to control the height of the liquid level in the recirculation system pipe 22 so that the processing liquid does not enter the RPV 12. However, in order to keep the dose rate in the dry well existing outside the RPV 12 in the reactor containment vessel 11 low, it is desirable to make the water level of the treatment liquid as high as possible. The heights of these free liquid levels can be controlled by finely adjusting the balance of the discharge flow rates of the circulation pumps 32 and 51 using the valves 34 and 50. Since the ferrite film is likely to be formed near the liquid level of the treatment liquid, the ferrite film is also effectively applied to the inner surface of the riser pipe located above the recirculation pipe 22 that tends to be retained water by changing the liquid level. Can be formed. In the present embodiment, the effects produced in the first embodiment can be obtained.

  In addition to bubbling of the inert gas to the chemical liquid tank 47 and the surge tank 31, it is also possible to supply the inert gas to the respective gas phase regions formed above the free liquid level in the recirculation system pipe 22. It is. The supply of the inert gas (for example, nitrogen gas) is performed by an inert gas supply pipe 87 connected to the plug 85 and an inert gas supply pipe 88 connected to the plug 86 as shown in FIG. . FIG. 9 is a schematic diagram showing a configuration for purging the gas phase above the recirculation pipe with nitrogen. The inert gas supply pipes 87 and 88 are connected to an inert gas cylinder (for example, a nitrogen gas cylinder) (not shown). The inert gas is discharged from each gas phase region by a vent pipe 89 connected to the plug 85 and a vent pipe 90 connected to the plug 86.

  A method for suppressing the attachment of radionuclides to structural members of a nuclear power plant according to embodiment 3, which is another embodiment of the present invention, applied to a BWR plant will be described with reference to FIG.

  The BWR plant of the present embodiment has a configuration in which the film forming apparatus 30 in the BWR plant of the first embodiment is replaced with a film forming apparatus 30A. FIG. 10 shows a configuration diagram of the film forming apparatus 30A of the present embodiment. The film forming apparatus 30A of the present embodiment differs from the film forming apparatus 30 of the first embodiment in that the chemical tank 48 containing the oxidizing agent and the oxidizing agent injection pump 45 are dedicated to the chemical decomposition processing device 67, and the oxidizing agent and A chemical solution tank 91 containing a mixed solution of a pH adjusting agent and a mixed solution injection pump 92 are provided. Other configurations of the BWR plant are the same as those in the first embodiment.

  The ferrite film forming procedure of FIG. 1 is performed using such an apparatus configuration. From step S1 to step S4, the operation of the pump, the valve, etc. is performed as in the first embodiment.

  In Step 3, when the oxidizing agent and the pH adjusting agent are injected at the same time, in Example 3, the mixed solution of hydrogen peroxide and hydrazine filled in the chemical tank 91 containing the mixed solution of the oxidizing agent and the pH adjusting agent is mixed. The chemical solution tank 91 containing the solution is activated, and the chemical solution injection pipe 76 and the valve 42 are passed through the junction with the chemical solution injection pipe 77 and injected into the circulation pipe 35. The concentration of hydrogen peroxide and hydrazine in the chemical solution tank 91 containing the mixed solution is adjusted to be 0.5 mol / L or less so that they do not react with each other. The amount of hydrogen peroxide filled in the chemical solution tank 91 containing the mixed solution is set to 1/3 of the number of moles of iron (II) ions in the same manner as in Example 1, and the amount of hydrazine is also iron as in Example 1. (II) The amount obtained from the amount of formic acid which is a counter anion of ions is filled in the chemical tank 91 containing the mixed solution, the injection pump 92 is started, and the junction with the injection pipe 77 through the injection pipe 76 and the valve 42. And is injected into the circulation pipe 35. If the amount of hydrazine calculated from the amount of iron (II) ions and formic acid is injected, the pH of the treatment liquid in the circulation pipe 35 becomes almost the specified pH. The pH is adjusted to 5.5 to 9.0 by adjusting the amount of hydrazine injected from the chemical solution tank 40 containing the adjusting agent into the circulation pipe 35 through the injection pump 39, the valve 38 and the injection pipe 77.

  It is determined whether the formation of the ferrite film has been completed (step S6). When the formation of the ferrite film is insufficient, the processes of step S4 to step S5 are repeated. When the formation of the ferrite film on the inner surface of the recirculation pipe 22 is sufficient, that is, when the ferrite film having a predetermined thickness is formed, the waste liquid treatment in step S7 is performed. The waste liquid treatment method is the same as that in the first embodiment.

  In the present embodiment, the same effect as that of the first embodiment can be obtained.

  A method for suppressing the attachment of radionuclides to structural members of a nuclear power plant according to embodiment 4, which is another embodiment of the present invention, applied to a BWR plant will be described with reference to FIG.

  The BWR plant of the present embodiment has a configuration in which the film forming apparatus 30A in the BWR plant of the third embodiment is replaced with a film forming apparatus 30B. The block diagram of the film forming apparatus 30B of the present embodiment is shown in FIG. The film forming apparatus 30B of the present embodiment is different from the film forming apparatus 30A of the third embodiment where the injection pipe extending from the chemical tank 91 containing the mixed solution of the oxidizing agent and the pH adjusting agent is divided into two systems. In addition to the same injection pipe 76, an injection pipe 93 connected to the surge tank 31 is provided together with the valve 94. Other configurations of the BWR plant are the same as those in the third embodiment.

  A method for suppressing the adhesion of radionuclides to the nuclear power plan and the components by forming the ferrite film of the present embodiment will be described. Steps S1 to S4 in this embodiment are the same as those in the third embodiment.

  In step S5, the initial operation is the same as that of the third embodiment. However, the treatment liquid into which hydrogen peroxide and hydrazine have been injected passes through the valve 34 to the recirculation system pipe 22, and the recirculation system pipe 22 is connected to the valve 50. Then, the pressure is increased by the circulation pump 51, and the operation different from that of the third embodiment is performed from the point of returning to the surge tank 31 through the valve 52, the heater 56, the valves 58, 59 and 60. When the processing liquid into which hydrogen peroxide and hydrazine are injected returns to the surge tank 31, the processing liquid in the surge tank 31 contains iron (II) ions and formic acid which is a counter anion. On the other hand, hydrogen peroxide and hydrazine are injected into the treatment liquid that has returned to the surge tank 31, but the hydrogen peroxide reacts with iron (II) ions and is almost consumed. Only the hydrazine is injected into the treatment liquid in the tank 31, and the treatment of simultaneously adding hydrogen peroxide and hydrazine to the iron (II) ion to be performed in the present invention is performed in the surge tank 31. This is not possible for treatment liquids. Therefore, when the treatment liquid into which hydrogen peroxide and hydrazine are injected returns to the surge tank 31, a mixed solution of hydrogen peroxide and hydrazine is filled in a chemical tank 91 containing a mixed solution of hydrogen peroxide and hydrazine. Is directly injected into the surge tank 31. Specifically, when the indicated value of the pH meter 95 that detects that hydrogen peroxide and hydrazine injected into the processing liquid have returned to the surge tank 31 has increased from the previous value, the circulation pumps 32 and 51 are stopped. When the valve 94 is opened, the valve 42 is closed at the same time, and the mixed solution of hydrogen peroxide and hydrazine filled in the chemical solution tank 91 containing the mixed solution of hydrogen peroxide and hydrazine is passed through the injection pipe 93 by the injection pump 92. Inject into the surge tank 31. The required amount of hydrogen peroxide and hydrazine to the chemical solution tank 91 containing the mixed solution is calculated in the same manner as in Example 1, and the remaining amount at the time when the injection system of the mixed solution of hydrogen peroxide and hydrazine is switched is the surge tank. Inject into 31. After the injection into the surge tank 31, the valve 94 is closed, the injection pump 92 is stopped, the circulation pumps 32 and 51 are restarted, and the processing liquid is circulated through the recirculation system pipe 22.

  It is determined whether the formation of the ferrite film has been completed (step S6). When the formation of the ferrite film is insufficient, the processes of step S4 to step S5 are repeated. When the formation of the ferrite film on the inner surface of the recirculation pipe 22 is sufficient, that is, when the ferrite film having a predetermined thickness is formed, the waste liquid treatment in step S7 is performed. The waste liquid treatment method is the same as that in the first embodiment.

  In the present embodiment, the same effect as that of the first embodiment can be obtained.

  A method for suppressing the attachment of radionuclides to structural members of a nuclear power plant according to embodiment 5, which is another embodiment of the present invention, applied to a BWR plant will be described with reference to FIG.

  The BWR plant of the present embodiment has a configuration in which the film forming apparatus 30 in the BWR plant of the first embodiment is replaced with a film forming apparatus 30C. As shown in FIG. 6, the film forming apparatus 30 of Example 1 has a configuration in which an injection pipe 76 provided in the oxidizer injection apparatus 101 is connected to an injection pipe 77 provided in the pH adjuster injection apparatus 102. On the other hand, the film forming apparatus 30 </ b> C of this embodiment has a configuration in which the injection pipe 76 of the oxidizer injection apparatus 101 is directly connected to the circulation pipe 35 without the injection pipe 77. FIG. 12 is a configuration diagram showing a positional relationship among the iron (II) ion implantation apparatus 100, the oxidant implantation apparatus 101, and the pH adjuster implantation apparatus 102 in the film forming apparatus 30C of the present embodiment. Other configurations of the BWR plant are the same as those in the first embodiment.

  A method for forming a ferrite film using the film forming apparatus 30C of the present embodiment will be described. The ferrite film forming method of the present embodiment is performed by an operation procedure in which Step S5 of Embodiment 1 is replaced with Step S5c. In step S5c, hydrogen peroxide as an oxidizing agent is injected into the circulation pipe 35, and then hydrazine as a pH adjusting agent is injected into the circulation pipe 35 within 5 minutes.

  Details of step S5c of the present embodiment will be described below. First, the valve 42 provided in the oxidant injection device 101 is opened, the injection pump 45 is driven, and hydrogen peroxide is drawn out from the chemical tank 48. The extracted hydrogen peroxide passes through the injection pipe 76 and is injected into the circulation pipe 35. Within 5 minutes after opening the valve 42 of the oxidant injection device 101, the valve 38 provided in the pH adjuster injection device 102 is opened, the injection pump 39 is driven, and hydrazine is drawn from the chemical tank 40 to circulate piping. Inject into 35. The timing for opening the valve 42 of the oxidant injection device 101 may be a timer or may be performed by a person. Hydrogen peroxide and hydrazine are mixed in the circulation pipe 35. The mixed processing liquid is supplied to the recirculation system pipe 22 through the circulation system pipe 35. The formation reaction of the ferrite film occurs on the inner surface of the recirculation pipe 35 that is in contact with the film-forming aqueous solution. The control device (not shown) controls the rotation speed of the injection pump 39 based on the measured pH value of the treatment liquid measured by the pH meter 79 and adjusts the injection speed of hydrazine. By this control, the pH of the treatment liquid is adjusted within a predetermined range.

  The connection point where the oxidant injection device 101 (specifically, the injection pipe 76) is connected to the circulation pipe 35 is the connection point where the pH adjuster injection device 102 (specifically, the injection pipe 77) is connected to the circulation pipe 35. Preferably as close as possible to the point. In addition, the connection point of the oxidant injection device 101 to the circulation pipe 35 is preferably downstream of the connection point of the iron (II) ion implantation apparatus 100 to the circulation pipe 35.

  In the present embodiment, the same effect as that of the first embodiment can be obtained.

It is a flowchart which shows the process sequence of the attachment control method of the radionuclide to the nuclear power plant structural member of Example 1 which is one suitable Example of this invention. It is a figure which shows the relationship between the time interval from oxidizing agent addition to pH adjuster addition, and the amount of ferrite film formation. It is a figure which shows the relationship between the amount of ferrite membrane | film | coat, and the radioactive adhesion amount suppression effect. It is a figure which shows the relationship between the equimolar mixing concentration of hydrogen peroxide and hydrazine, and a temperature rise. It is a block diagram of the BWR plant which connected the film forming apparatus used when performing the process shown in FIG. It is a detailed block diagram of the film forming apparatus of Example 1. It is a schematic diagram of the ferrite membrane | film | coat formed in the inner surface of recirculation piping using the membrane | film | coat formation apparatus shown in FIG. It is a detailed block diagram of the membrane | film | coat formation apparatus used for the adhesion suppression method of the radionuclide to the nuclear power plant structural member of Example 2 which is another Example of this invention. It is explanatory drawing which shows the state which connected inert gas supply piping and vent piping to each plug which seals the both ends of recirculation system piping in Example 2. FIG. It is a detailed block diagram of the film formation apparatus of Example 3. It is a detailed block diagram of the film formation apparatus of Example 4. FIG. 10 is a configuration diagram showing a part of a film forming apparatus of Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reactor 10 Feed water piping 12 Reactor pressure vessel 20 Purification system piping 21 Recirculation pump 22 Recirculation system piping 30 Film formation apparatus 31 Surge tank 32, 51 Circulation pump 35 Circulation piping 39, 44, 45, 92 Injection pump 40, 47, 48, 91 Chemical liquid tank 56 Heater 61 Cooler 63 Cation exchange resin tower 65 Mixed bed resin tower 67 Decomposition treatment device 85, 86 Plug 87, 88 Inert gas supply piping 100 Iron (II) ion implantation device 101 Oxidizing agent Injection device 102 pH adjuster injection device

Claims (7)

  An oxidizing agent and a solution that oxidizes a part of iron (II) ions to iron (III) ions after contacting a film-forming solution containing iron (II) ions with the surface where the components of the nuclear power plant are in contact with the coolant The radioactive material to the nuclear plant constituent member is characterized in that a ferrite film is formed on the surface of the structural member by substantially simultaneously adding a pH adjusting agent that adjusts the pH of the structural member to 5.5 to 9.0. A method for suppressing the attachment of nuclides.   An oxidizing agent and a solution that oxidizes a part of iron (II) ions to iron (III) ions after contacting a film-forming solution containing iron (II) ions with the surface where the components of the nuclear power plant are in contact with the coolant A ferrite film is formed on the surface of the structural member by adding a solution mixed with a pH adjusting agent that adjusts the pH of 5.5 to 9.0 to the film forming liquid containing iron (II) ions. A method for suppressing the attachment of radionuclides to structural components of a nuclear power plant.   The method for suppressing the attachment of a radionuclide to a nuclear plant component according to claim 1, wherein the oxidizing agent is hydrogen peroxide.   The method for suppressing the attachment of a radionuclide to a nuclear plant component according to any one of claims 1 to 3, wherein the pH adjuster is hydrazine. The oxidizing agent is hydrogen peroxide, the pH adjuster is hydrazine,
A mixture of the hydrogen peroxide and the hydrazine, adjusted so that the respective concentrations of the hydrogen peroxide and the hydrazine before contacting with the iron (II) ions are 0.5 mol / L or less, is added to the iron (II) A ferrite film is formed on the surface of the structural member by adding to a film-forming solution containing ions, and the method for suppressing radionuclide adhesion to a nuclear plant component according to claim 2 . A surge tank for storing the processing liquid;
A circulation pump for sucking the processing liquid stored in the surge tank;
A first chemical tank for storing a first drug containing iron (II) ions;
A second chemical tank for storing a second chemical for oxidizing the iron (II) ions to iron (III) ions;
A third chemical tank for storing a third chemical for adjusting the pH of the treatment liquid to 5.5 to 9.0;
A piping system configuration in which the second drug and the third drug merge before the second drug and the third drug reach the treatment liquid;
After mixing the chemicals from the first chemical liquid tank with the processing liquid sucked by the circulation pump, and further mixing the chemicals from the second chemical liquid tank and the third chemical liquid tank before mixing with the processing liquid, this A supply pipe for mixing a mixed solution of the second chemical liquid and the third chemical liquid with the treatment liquid, and supplying the mixed liquid to the piping system to be formed;
A return pipe for returning the treatment liquid returned from the piping system to be deposited to the surge tank;
Heating means for heating the temperature of the treatment liquid to 60 ° C. to 100 ° C.,
The position for injecting the liquid mixture of the second chemical and the third chemical into the treatment liquid is installed in the nuclear reactor containment vessel. Deposition device. A surge tank for storing the processing liquid;
A circulation pump for sucking the processing liquid stored in the surge tank;
A first chemical tank for storing a first drug containing iron (II) ions;
A second chemical tank for storing a second chemical for oxidizing the iron (II) ions to iron (III) ions;
A third chemical tank for storing a third chemical for adjusting the pH of the treatment liquid to 5.5 to 9.0;
A piping system configuration in which the second drug and the third drug merge before the second drug and the third drug reach the treatment liquid;
After the chemicals from the first chemical liquid tank are mixed with the processing liquid sucked by the circulation pump, the chemicals from the second chemical liquid tank and the third chemical liquid tank are mixed before being mixed with the processing liquid, and then processed. A supply pipe for mixing with the liquid and supplying it to the pipe system to be deposited;
A return pipe for returning the treatment liquid returned from the piping system to be deposited to the surge tank;
Heating means for heating the temperature of the treatment liquid to 60 ° C. to 100 ° C.,
The composition for injecting the ferrite film on the surface of the nuclear plant component is characterized in that the injection position of the mixture of the second chemical and the third chemical is installed in the reactor containment vessel and the surge tank. Membrane device.

Images