JP2013164269A - Radiation amount reducing method for nuclear power plant constitution member and nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation amount reducing method for a nuclear power plant constitution member that can suppress adherence of a radionuclide at the time of execution of a hydrogen injection and at the time of non-execution of the hydrogen injection.SOLUTION: A radiation amount reducing method for a nuclear power plant constitution member comprises the steps of: polishing an inner surface of piping for replacement (S2); immersing the piping in mixed solution of 3% HF and 10% HNOand forming a passive film containing Cr as a principal component on the inner surface of the piping (S3); supplying film formation liquid whose pH value containing iron (II)ion, hydrogen peroxide and hydrazine is within a range of 5.5 to 9.0 into the piping in which the passive film is formed on the inner surface and forming a ferrite film by covering a surface of the passive film (S4); stopping operation of a reactor and executing chemical decontamination of an inner surface of recirculation system piping to be connected to the piping (S5); cutting and removing a replacement portion of the recirculation system piping (S6); and connecting the piping in which the passive film and the ferrite film are formed thereon to the cut portion of the recirculation system piping (S7).

Description

  The present invention relates to a nuclear plant plant component dose reduction method and a nuclear plant, and more particularly to a nuclear plant plant component dose rate reduction method and a nuclear plant suitable for application to a boiling water nuclear plant.

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

  In addition, corrosion products that are the source of radioactive corrosion products are generated on the surface of the BWR plant components such as RPV and recirculation piping that come into contact with the reactor water. Fewer stainless steels and stainless steels such as nickel-base alloys are used. In addition, the low alloy steel RPV has a stainless steel overlay on the inner surface to prevent the low alloy steel from coming into direct contact with the reactor water. 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. Impurities (for example, metal elements) adhering to the surface of the fuel rod cause a nuclear reaction by irradiation of neutrons released by fission of nuclear fuel material in the fuel rod, and radioactive such as cobalt 60, cobalt 58, chromium 51, manganese 54, etc. Become a nuclide.

  These radionuclides remain mostly attached to the fuel rod surface in the form of oxides. However, some radionuclides are eluted as ions in the reactor water depending on the solubility of the incorporated oxide, or re-released into the reactor water as an insoluble solid called a clad. The radioactive material contained in the reactor water is removed by the reactor purification system communicated with the RPV. The radioactive material that has not been removed by the reactor purification system is accumulated on the surface of the nuclear plant component (for example, piping) 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 worker 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 reduce the exposure dose of each person as much as possible.

  Therefore, various methods for reducing the adhesion of radionuclides to the surface of the piping in contact with the reactor water and methods for reducing the concentration of radionuclides in the reactor water have been studied. For example, in JP-A-2006-38483, JP-A-2007-192745, and JP-A-2007-24644, a magnetite film that is a ferrite film is formed on the surface of a nuclear plant component that contacts the reactor water, A method for suppressing the attachment of the radionuclide to the constituent member has been proposed. Formation of a ferrite film on the surface of the nuclear plant component that contacts the reactor water prevents the radionuclide from adhering to the surface of the nuclear component after the operation of the nuclear plant. In this radionuclide adhesion suppression 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 constituent member to obtain the surface. A ferrite film is formed on the surface.

  JP 2000-105295 A describes chemical decontamination including oxidative decontamination and reductive decontamination.

JP 2006-38483 A JP 2007-192745 A JP 2007-24644 A JP 2000-105295 A

  The method for suppressing the attachment of radionuclides to nuclear plant components described in Japanese Patent Application Laid-Open No. 2006-38483 suppresses the corrosion of nuclear plant components by forming a ferrite film, and the radioactivity generated as the corrosion film grows. It is possible to reduce the surface dose rate of the recirculation piping of the nuclear power plant by suppressing the adhesion of nuclides. The inventors conducted a detailed study on the dose rate reduction of the ferrite film formed on the surface of the nuclear plant component by the method described in Japanese Patent Application Laid-Open No. 2006-38483. As a result, it was found that the dose rate reduction effect by the ferrite film was dependent on the corrosion potential, and was −0.5 Vvs. In SHE, -0.2Vvs. It was found that the effect was reduced compared to SHE. From the result of the test piece subjected to the passive film treatment performed at the same time, -0.2 Vvs. Although the dose rate reduction effect is not seen in SHE, -0.5 Vvs. In SHE, the dose rate reduction effect exceeding the ferrite film was recognized.

  An object of the present invention is to provide a nuclear power plant dose reduction method and a nuclear power plant capable of suppressing the attachment of radionuclides when hydrogen injection is performed and when hydrogen injection is not performed.

  A feature of the present invention that achieves the above-described object is that a passive film including at least a part of elements contained in the stainless steel is formed on the first surface of a nuclear power plant component made of stainless steel so as to cover the first surface. The second surface of the passive film is to cover the second surface and form a ferrite film.

  A passive film containing at least a part of the elements contained in the stainless steel is formed on the first surface of the nuclear power plant component made of stainless steel so as to cover the first surface, and this passive film is formed on the second surface of the passive film. Since the ferrite film is formed so as to cover the second surface, it is possible to suppress the attachment of radionuclides to the nuclear plant components when hydrogen injection into the nuclear reactor is performed and when hydrogen injection is not performed. In particular, even when hydrogen injection into the coolant in the reactor is interrupted and the corrosion potential is increased, the passive film is covered with a ferrite film, so it is possible to suppress the elution of elements contained in the passive film. The adhesion of the radionuclide to the nuclear plant component can be suppressed by the ferrite film. Moreover, in the state in which hydrogen injection is performed, adhesion of the radionuclide to the nuclear plant constituent member can be suppressed by the passive film.

  ADVANTAGE OF THE INVENTION According to this invention, adhesion of a radionuclide to a nuclear power plant structural member can be suppressed when hydrogen injection is performed and when hydrogen injection is not performed.

It is a flowchart which shows the process implemented in the dose reduction method of the nuclear power plant structural member of Example 1 which is one suitable Example of this invention. It is a detailed block diagram of the membrane | film | coat formation apparatus used in the dose reduction method of the nuclear power plant structural member of Example 1. FIG. It is a block diagram of the boiling water type nuclear power plant to which the dose reduction method of the nuclear power plant structural member of Example 1 is applied. It is a detailed block diagram of the decontamination apparatus connected to the boiling water type nuclear power plant shown in FIG. 3 in the dose reduction method of the nuclear power plant structural member of Example 1. FIG. It is explanatory drawing which shows the dependence of the corrosion potential of Co-60 adhesion amount, and the surface state of a metal sample. It is a flowchart which shows the process implemented in the dose reduction method of the nuclear power plant structural member of Example 2 which is another Example of this invention. It is a detailed block diagram of the chemical decontamination apparatus used in the dose reduction method of the nuclear power plant structural member of Example 2. It is a flowchart which shows the process implemented in the dose reduction method of the nuclear power plant structural member of Example 3 which is another Example of this invention. It is a detailed block diagram of the membrane | film | coat formation apparatus used in the dose reduction method of the nuclear power plant structural member of Example 3. FIG. It is a block diagram of the recirculation system to which the dose reduction method of the nuclear power plant structural member of Example 3 is applied. It is explanatory drawing which shows the connection state of the film formation apparatus shown in FIG. 9 to the recirculation system shown in FIG.

  The inventors studied various measures that can suppress the incorporation of radionuclides when hydrogen injection is performed and when hydrogen injection is not performed. In the process of studying this countermeasure, the inventors paid attention to the formation of a passive film on the surface of the nuclear plant component that contacts the reactor water.

  However, the inventors have found that the corrosion potential is −0.5 Vvs. In SHE, the accumulation of radioactive Co-60 in a stainless steel member formed with a passive film is less than that in a stainless steel member without a passive film, but this passive film has a high corrosion potential. It has been found that when exposed to the environment, Cr oxide contained in the passive film is oxidized and eluted as hexavalent chromate ions in high-temperature water, so that the effect of suppressing the accumulation of radioactive Co-60 is lost. For this reason, in the actual operation condition of the boiling water nuclear power plant that may interrupt the hydrogen injection into the reactor water only by forming the passive film on the surface of the stainless steel member in contact with the reactor water, the radioactive Co- It proved difficult to continue to suppress the accumulation of 60. Accordingly, the inventors have newly developed a method for further covering the surface of the passive film that is formed on the surface of the nuclear plant component that contacts the reactor water and is easily eluted in an environment with a high corrosion potential with a ferrite film. I figured it out. Corrosion potential experienced with actual water quality of boiling water nuclear power plant -0.5Vvs. SHE ~ + 0.2 vs. When the oxide formed in the SHE environment is analyzed, ferrite is observed. If the surface of the passive film is coated with this ferrite, the ferrite layer prevents contact with the passive film and the high potential reactor water when exposed to high potential reactor water where hydrogen injection is interrupted. The elution of Cr from the dynamic film does not occur, and the passive film is maintained on the surface of the nuclear plant component.

  The above examination results conducted by the inventors will be described in more detail.

  The inventors have made a stainless steel polished test piece (hereinafter referred to as a first test piece) and a test piece (hereinafter referred to as a second test piece) in which a magnetite film which is a type of ferrite film is formed on the surface of the polished test piece. ), Using these three test pieces, which were treated with hydrofluoric acid to form a passive film containing Cr oxide on the surface (hereinafter referred to as the third test piece). A Co-60 adhesion test was conducted to confirm the amount of Co-60 adhered to the surface. In the Co-60 adhesion test, high-temperature high-pressure pure water containing Co-60 having a temperature of 280 ° C., a pressure of 7 MPa, a dissolved oxygen concentration of 5 ppb or less, and a dissolved hydrogen concentration of 50 ppb was used, which simulates the conditions of boiling water reactor water. The three test pieces described above were immersed in the high-temperature high-pressure pure water for a predetermined time. At this time, in order to investigate the influence of the corrosion potential, 5 ppb of hydrogen peroxide was injected into the high-temperature and high-pressure pure water so that the corrosion potential was -0.2 Vvs. The corrosion potential was set to -0.5 V vs. SHE without adding hydrogen peroxide to high-temperature high-pressure pure water. Each test was performed under the condition of SHE.

The test results are shown in FIG. -0.2Vvs. In the case of SHE, the amount of Co-60 deposited on the second test piece on which the magnetite film was formed was reduced to about 1/20 that of the first test piece on which only polishing was performed. On the other hand, -0.5 Vvs. In the case of SHE, the Co-60 adhesion amount of the second test piece is about 1/4 of the Co-60 adhesion amount of the first test piece. Reduced. The amount of Co-60 deposited on the third test piece on which the passive film was formed was -0.5 Vvs. In SHE, the adhesion amount of Co-60 of the first test piece was about 1/10, and the Co-60 adhesion suppression effect of the third test piece exceeded that of the second test piece. However, -0.2Vs. In SHE, the amount of Co-60 adhered to the third test piece was not significantly different from the amount of Co-60 adhered to the first test piece, and the Co-60 adhesion inhibiting effect of the third test piece was hardly produced. This is -0.2 Vvs. In order to realize SHE, the trivalent Cr contained in the passive film formed on the third test piece is oxidized to hexavalent and eluted as CrO ₄ ²⁻ by hydrogen peroxide injected into high-temperature high-pressure pure water. However, it is considered that the passive film no longer functions as a protective film. An example of a reaction in which trivalent Cr is oxidized and dissolved is a reaction represented by Formula (1).

4FeCr ₂ O ₄ + 14H ₂ O ₂ = 2Fe ₂ O ₃ + 8CrO ₄ ²⁻ + 16H ⁺ + 6H ₂ O (1)
Co-60 adhesion to the surface of the first test piece, which is a polished test piece made of stainless steel, is caused when stainless steel is corroded by high-temperature water, and when an oxide film formed by the corrosion grows, Co-60 in the reactor water grows. Generated by incorporation into the growing oxide film. Both the magnetite film and the passive film prevent high-temperature water from coming into direct contact with the stainless steel surfaces of the second and third test pieces, and suppress the corrosion of each stainless steel. The growth of the oxide film is suppressed, and the adhesion of Co-60 that should be taken into the oxide film is suppressed. Therefore, it can be said that the adhesion inhibition effect of Co-60 shown in FIG. 5 reflects the corrosion inhibition effect. This corrosion inhibiting effect is affected by the corrosion potential in the magnetite film and the passive film. The corrosion inhibitory effect is -0.5 Vvs. In SHE, the passive film becomes larger than the magnetite film, and is -0.2 Vvs. In SHE, the magnetite film is larger than the passive film.

  Based on the test results shown in FIG. 5, the inventors combined a magnetite film and a passive film, so that −0.2 Vvs. SHE and -0.5 Vvs. We have devised a new method for reducing the dose of nuclear plant components that is effective in suppressing corrosion of nuclear plant components at each SHE corrosion potential and also effective in suppressing Co-60 adhesion. In a newly devised method for reducing the dose of nuclear plant components, a passive film is formed on the surface of a nuclear plant component, for example, a stainless steel member, and a ferrite film, for example, magnetite, is further formed on the surface of the passive film. Form a film. Since a two-layered film of a passive film and a ferrite film is formed on the surface of such a nuclear plant component, and the surface of the passive film is covered with a ferrite film, -0.5 Vvs. SHE produces a corrosion inhibiting effect due to a passive film, and is -0.2 Vvs. In SHE, the corrosion suppression effect by a magnetite film arises. Furthermore, since the magnetite film covers the passive film even if it is once exposed to an environment of -0.2 V, the passive film does not come into contact with high-temperature water containing hydrogen peroxide, and again, -0.5 V vs. . Even if it changes to the environment of SHE, it can prevent that the chromium contained in a passive film elutes to high temperature water. Therefore, -0.5 Vvs. Even in SHE, the passive film can suppress the corrosion of the nuclear plant components.

  Examples of the present invention reflecting the above-described examination results will be described below.

  A dose reduction method for a nuclear plant component according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. 1, 2, 3, and 4. The method for reducing the dose of nuclear plant components of this embodiment is an example applied to a boiling water nuclear plant (BWR plant).

  A schematic configuration of a BWR plant that is a nuclear power plant to which the method for reducing the dose of nuclear plant components according to the present embodiment is applied will be described with reference to FIG. The BWR plant includes a reactor 49, a turbine 56, a condenser 57, a recirculation system, a reactor purification system, a water supply system, and the like. A reactor 49 installed in the reactor containment vessel 11 has a reactor pressure vessel (hereinafter referred to as RPV) 50 containing a core 51, and a jet pump 52 is installed in the RPV 50. The core 51 is loaded with a plurality of fuel assemblies (not shown). Each fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material. The recirculation system has a recirculation pump 53 and a stainless steel recirculation system pipe 54, and the recirculation pump 53 is installed in the recirculation system pipe 54. The water supply system is configured by installing a condensate pump 59, a condensate purification device 60, a low pressure feed water heater 61, a feed water pump 63 and a high pressure feed water heater 62 in a feed water pipe 58 connecting the condenser 57 and the RPV 50. The A hydrogen injection device 66 is connected to the feed water pipe 58 between the condensate purification device 60 and the low pressure feed water heater 61. In the reactor water purification system, a purification system pump 68, a regenerative heat exchanger 69, a non-regenerative heat exchanger 70, and a reactor water purification device 71 are installed in a purification system pipe 67 that connects the recirculation system pipe 54 and the feed water pipe 58. Configured. The purification system pipe 67 is connected to the recirculation system pipe 54 upstream from the recirculation pump 53.

  Cooling water in the RPV 50 (hereinafter referred to as “reactor water”) is pressurized by a recirculation pump 53, passes through a recirculation system pipe 54, and from a nozzle (not shown) of the jet pump 52 to a bell mouth (not shown) of the jet pump 52. ) The reactor water present around the nozzle is also sucked into the bell mouth by the action of the jet flow jetted from the nozzle. Reactor water discharged from the jet pump 52 is supplied to the core 51 and heated by heat generated by nuclear fission of nuclear fuel material in the fuel rods. Part of the heated reactor water becomes steam. This steam is guided from the RPV 50 through the main steam pipe 55 to the turbine 56 to rotate the turbine 56. A generator (not shown) connected to the turbine 56 is rotated to generate electric power. The steam discharged from the turbine 56 is condensed in the condenser 57 to become water.

  This water is supplied into the RPV 50 through the water supply pipe 58 as water supply. The feed water flowing through the feed water pipe 58 is boosted by the condensate pump 59, impurities are removed by the condensate purification device 60, further boosted by the feed water pump 63, and heated by the low pressure feed water heater 61 and the high pressure feed water heater 62. . Extracted steam extracted from the main steam pipe 55 and the turbine 56 by the extracted pipe 64 is supplied to the low-pressure feed water heater 61 and the high-pressure feed water heater 62, respectively, and serves as a heating source for the feed water.

  A detailed configuration of the film forming apparatus 1 used in the method for reducing the dose of nuclear plant components according to the present embodiment will be described with reference to FIG. The film forming apparatus 1 includes a surge tank 17 in which a heater 19 is installed, a circulation pipe 2, an iron (II) ion implanter 3, an oxidant injector 7, a pH adjuster injector 12, a chromium ion implanter 88, A filter 21, a decomposition device 25, and a cation exchange resin tower 23 are provided.

  The on-off valve 27, the circulation pump 20, the valve 28, the valves 29, 30 and 31, the surge tank 17, the circulation pump 26, the valve 32 and the on-off valve 33 are provided in the circulation pipe 2 in this order from the upstream. A valve 35 and a filter 21 are installed in a pipe 34 that bypasses the valve 28 and is connected to the circulation pipe 2. A pipe 36 that bypasses the valve 29 is connected to the circulation pipe 2, and a cooler 22 and a valve 37 are installed in the pipe 36. A cation exchange resin tower 23 and a valve 40 are installed in a pipe 38 having both ends connected to the circulation pipe 2 and bypassing the valve 30. The mixed bed resin tower 24 and the valve 6 are installed in a pipe 39 having both ends connected to the pipe 38 and bypassing the cation exchange resin tower 23 and the valve 40.

  A pipe 42 in which the valve 43 and the decomposition apparatus 25 are installed bypasses the valve 31 and is connected to the circulation pipe 2. The decomposition apparatus 25 is filled with, for example, an activated carbon catalyst in which ruthenium is impregnated on the surface of the activated carbon. A surge tank 17 is installed in the circulation pipe 2 between the valve 31 and the circulation pump 26.

  The iron (II) ion implantation apparatus 3 includes a chemical liquid tank 4, an injection pump 5, and an injection pipe 6A. The chemical tank 4 is connected to the circulation pipe 2 by an injection pipe 6 </ b> A having an injection pump 5 and a valve 6. The chemical tank 4 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 carboxylic acid or carbonic acid which becomes a counter anion of iron (II) ion can be used not only formic acid. As a carboxylic acid other than formic acid that dissolves iron, oxalic acid or malonic acid may be used.

  The oxidant injection device 7 includes a chemical liquid tank 8, an injection pump 9, and an injection pipe 11. The chemical tank 8 is connected to the circulation pipe 2 by an injection pipe 11 having an injection pump 9 and a valve 10. The chemical tank 8 is filled with hydrogen peroxide that is an oxidizing agent (second chemical). A pipe 44 provided with a valve 45 connects the injection pipe 11 and the pipe 42 upstream of the decomposition apparatus 25.

  The pH adjuster injection device 12 includes a chemical liquid tank 13, an injection pump 14, and an injection pipe 16. The chemical liquid tank 13 is connected to the circulation pipe 2 by an injection pipe 16 having an injection pump 14 and a valve 15. The chemical tank 13 is filled with hydrazine which is a pH adjuster (third drug).

  In the film forming apparatus 1, a first connection point (connection point between the injection pipe 6 </ b> A and the circulation pipe 2) to the circulation pipe 2 of the iron (II) ion implantation apparatus 3 and a second connection point to the circulation pipe 2 of the oxidant injection apparatus 7. The connection point (the connection point between the injection pipe 11 and the circulation pipe 2) and the third connection point (the connection point between the injection pipe 16 and the circulation pipe 2) to the circulation pipe 2 of the pH adjusting agent injection device 12 are upstream in this order. It is arranged toward the downstream. A pH meter 113 is installed in the circulation pipe 2 between the third connection point and the on-off valve 33.

  Both ends of the pipe 47 provided with the valve 46 are respectively connected to the circulation pipe 2 existing between the pH meter 113 and the on-off valve 33 and the circulation pipe 2 existing between the on-off valve 27 and the circulation pump 20. Before each medicine is injected into the circulation pipe 2, the surge tank 17 is filled with water used for processing. In order to reduce the oxygen concentration contained in the film forming liquid, it is preferable to bubble an inert gas such as nitrogen or argon into the chemical tank 4 and the surge tank 17.

  The decomposition device 25 can decompose carboxylic acid (for example, formic acid) used as a counter anion of iron (II) ions and hydrazine as a pH adjusting agent. That is, as the counter anion of the iron (II) ion, carboxylic acid that can be decomposed into water and 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 detailed structure of the chemical decontamination apparatus 72 used for the dose reduction method of the nuclear power plant structural member of a present Example is demonstrated using FIG. The chemical decontamination device 72 includes a surge tank 74 provided with a heater 75 therein, a circulation pipe 73, a pH adjuster injection device 77, an oxidant injection device 82, a filter 89, a decomposition device 87, a cation exchange resin tower 91, and a mixture. A floor resin tower 92 is provided. The on-off valve 94, the circulation pump 88, the valves 95, 96, 97, 98, the surge tank 74, the circulation pump 93, the valve 99, and the on-off valve 100 are provided in the circulation pipe 73 in this order from upstream to downstream.

  A pipe 101 is connected to the circulation pipe 73 at both ends so as to bypass the valve 95. The pipe 101 is provided with a valve 102 and a filter 89. Both ends of the pipe 103 that bypasses the valve 96 are connected to the circulation pipe 73. A cooler 90 and a valve 104 are installed in the pipe 103. A cation exchange resin tower 91 and a valve 106 are installed in a pipe 105 that is connected to the circulation pipe 73 at both ends and bypasses the valve 97. A mixed bed resin tower 92 and a valve 108 are installed in a pipe 107 having both ends connected to the pipe 105 and bypassing the cation exchange resin tower 91 and the valve 106. A pipe 109 in which the valve 110 and the decomposition device 87 are installed bypasses the valve 98 and is connected to the circulation pipe 73. The decomposition apparatus 87 is filled with, for example, an activated carbon catalyst in which ruthenium is impregnated on the surface of the activated carbon. A pipe 111 provided with the valve 112 and the ejector 76 is connected to the circulation pipe 73 between the valve 99 and the circulation pump 93, and is further connected to the surge tank 74. Surges potassium permanganate to oxidize and dissolve contaminants on the inner surface of piping (for example, recirculation piping 54) that is subject to chemical decontamination, and oxalic acid to reduce and dissolve contaminants in the piping. A hopper (not shown) for supplying the inside of the tank 74 is provided in the ejector 76.

  The pH adjusting agent injection device 77 includes a chemical tank 78, an injection pump 79, and an injection pipe 81. The chemical tank 78 is connected to the circulation pipe 73 by an injection pipe 81 having an injection pump 79 and a valve 80. The chemical tank 78 is filled with hydrazine which is a pH adjusting agent.

  The oxidant injection device 82 includes a chemical liquid tank 83, an injection pump 84, and an injection pipe 86. The chemical tank 84 is connected to the pipe 109 upstream of the decomposition apparatus 87 by an injection pipe 86 having an injection pump 84 and a valve 85. The chemical tank 83 is filled with hydrogen peroxide which is an oxidizing agent. The surge tank 74 is filled with water for circulating the system including the chemical decontamination target.

  Reactor water in the RPV 50 undergoes radiation decomposition due to irradiation of the nuclear fuel material contained in the fuel assembly loaded in the core 51 and undergoes radiolysis, and oxidizing chemical species such as hydrogen peroxide and oxygen. Is produced. This oxidizing species increases the corrosion potential of the nuclear plant configuration in contact with the reactor water. For this reason, in the BWR plant, hydrogen is injected into the feed water from the hydrogen injection device 66 as an environmental mitigation measure against stress corrosion cracking, and this hydrogen reacts with oxidizing chemical species such as hydrogen peroxide and oxygen contained in the reactor water. Thus, an operation is performed in which the oxidizing chemical species concentration of the reactor water is reduced to lower the corrosion potential of the nuclear plant components. The operation performed while injecting hydrogen into the feed water in the BWR plant is called a hydrogen water quality (HWC) operation, and the operation without hydrogen injection in the BWR plant is performed as a normal water quality (NWC) operation. Say. The operation of the BWR plant that lowers the corrosion potential by hydrogen injection is preferably continued during the operation. However, the hydrogen injection may be interrupted, and the operation of the BWR plant when the hydrogen injection is interrupted is the NWC operation. Thus, the corrosion potential of the nuclear plant components becomes high.

  A part of the reactor water flowing in the recirculation system pipe 54 flows into the purification system pipe 67 by driving the purification system pump 68 and is cooled by the regenerative heat exchanger 69 and the non-regenerative heat exchanger 70. It is purified by the water purification device 71. The purified reactor water is heated by the regenerative heat exchanger 69 and returned to the RPV 50 through the purification system pipe 67 and the water supply pipe 58.

  The BWR plant is stopped after the operation in one operation cycle is completed. After this shutdown, a periodic inspection is performed on the BWR plant. After this periodic inspection is completed, the BWR plant is started again. During this periodical inspection, some fuel assemblies in the core 51 are replaced with new fuel assemblies. That is, a part of the fuel assembly in the core 51 is taken out from the RPV 50 as a spent fuel assembly, and a new fuel assembly having a burnup of 0 GWd / t is loaded into the core 51.

  The method for reducing the dose of the nuclear plant component according to the first embodiment, which is performed by the process shown in FIG. 1, will be specifically described below.

  For example, in the previous periodic inspection of the BWR plant, it has been discovered that cracks that have not penetrated due to stress corrosion cracking have occurred in the recirculation system pipe 54. Assuming that it is determined that it is necessary to perform the periodic inspection, the operation of the BWR plant is resumed after the end of the previous periodic inspection, and the operation of the BWR plant is performed in the next operation cycle. During the periodical inspection after the operation of the BWR plant in the operation cycle is stopped, the replacement work of the cracked portion of the recirculation system pipe 54 is performed. For this reason, it is necessary to prepare a replacement pipe for replacement before the operation of the BWR plant is stopped prior to replacing the cracked portion of the recirculation system pipe 54. On the other hand, each process of step S2-S4 shown in FIG. 1 is implemented.

  First, replacement piping corresponding to the nuclear plant component to be replaced is prepared (step S1). A stainless steel pipe used for the recirculation pipe 54 that is a nuclear plant component to be replaced is prepared. The length of the stainless steel pipe corresponds to the length of the recirculation system pipe 54 that is cut including the cracked portion of the recirculation system pipe 54. The inner surface of the replacement pipe is polished (step S2). In order to adjust the inner surface roughness of the stainless steel pipe that is the replacement pipe, the inner surface is subjected to, for example, mechanical polishing to reduce irregularities and reduce the substantial surface area. If there are many irregularities on the inner surface of the stainless steel pipe, the surface area increases and the oxide film that takes in Co-60 increases. Therefore, mechanical polishing on the inner surface of the stainless steel pipe takes in Co-60 by smoothing the inner surface. This is to reduce the surface area.

Passivation processing is performed on the inner surface of the replacement pipe (step S3). This passivation treatment may be performed by an existing method, and is the same as, for example, the formation of a passive film on the surface of the third test piece obtained from the test result shown in FIG. That is, in the third test piece, a mixed solution (passive film forming solution) of 3% HF (hydrogen fluoride) and 10% HNO ₃ (nitric acid) is heated to 60 ° C., and a stainless steel polishing test is performed. The piece was immersed in this mixed solution for 10 minutes to form a passive film containing Cr oxide on the surface of the polished test piece. Also in step S3 of this embodiment, the stainless steel pipe (replacement pipe) whose inner surface is mechanically polished is immersed in the heated mixed solution for 10 minutes to form a passive film containing Cr oxide on the inner surface of the stainless steel pipe. Form.

  Other methods for forming the passive film include, for example, a method in which stainless steel piping is immersed in hot concentrated nitric acid and the inner surface of the stainless steel piping is oxidized by the oxidizing power of nitric acid, or the stainless steel piping is used as an anode for the electrolyte. There is electropolishing performed by flowing a current between a cathode immersed in the electrolyte and the stainless steel pipe. In either method, there is a difference in degree, but a passive film containing Cr oxide is formed on the inner surface of the stainless steel pipe.

  A magnetite film is formed (step S4). In step S3, a ferrite film, for example, a magnetite film, is formed on the inner surface of the stainless steel pipe (replacement pipe) having the passive film formed on the inner surface. The formation of this magnetite film will be described with reference to FIG.

  Both ends of the stainless steel pipe 48 having the passive film formed on the inner surface are separately connected to both ends of the circulation pipe 2 of the film forming apparatus 1 to form a closed loop by the circulation pipe 2 and the stainless steel pipe 48. The amount of water that can circulate in the closed loop is supplied to the surge tank 17. Thereafter, the valves 27, 28, 29, 30, 31, 32, and 33 are opened, and the circulation pumps 20 and 26 are driven with the other valves closed. Thereby, the water in the surge tank 17 is circulated in the closed loop of the circulation pipe 2 and the stainless steel pipe 48. The water circulating through the heater 19 in the surge tank 17 is heated, and when the temperature of this water reaches 90 ° C., the valve 6 is opened to drive the injection pump 5 and a chemical solution containing iron (II) ions and formic acid. (First drug) is injected from the chemical tank 4 through the injection pipe 6A into the film forming liquid (water when the first drug is injected for the first time), which is an aqueous solution flowing in the circulation pipe 2. . The second drug to be injected here contains, for example, iron (II) ions prepared by dissolving iron with formic acid and this formic acid. Part of the injected iron (II) ions becomes ferrous hydroxide in the film forming solution.

  The valve 10 is opened to drive the injection pump 9, and hydrogen peroxide, which is an oxidant, flows from the chemical tank 8 through the injection pipe 11 to the iron (II) ions, formic acid, and hydroxide hydroxide flowing through the circulation pipe 2. Pour into a film-forming solution containing iron. As the oxidizing agent, in addition to hydrogen peroxide, a chemical in which ozone or oxygen is dissolved may be used.

  By opening the valve 15 and driving the injection pump 14, a pH adjusting agent (for example, hydrazine) is injected from the chemical solution tank 13 into the film forming liquid flowing in the circulation pipe 2 through the injection pipe 16. The pH meter 113 measures the pH of the film forming liquid flowing through the circulation pipe 2. A control device (not shown) controls the rotational speed of the infusion pump 14 (or the opening of the valve 15) based on the measured pH value to adjust the amount of hydrazine injected to adjust the pH of the film forming solution to 5 Adjust to a value in the range of .5 to 9.0, for example, 7.0. That is, the pH of the film-forming solution that is an aqueous solution containing hydrazine, iron (II) ions, chromium ions, ferrous hydroxide, formic acid and hydrogen peroxide is adjusted to 7.0.

This film forming liquid is supplied into the stainless steel pipe 48 through the circulation pipe 2 and comes into contact with the surface of the passive film formed on the inner surface of the stainless steel pipe 48. A part of iron (II) ions (Fe ²⁺ ) contained in the film forming solution is oxidized to iron (III) ions (Fe ³⁺ ) by hydrogen peroxide, and the pH of the film forming solution is 7.0. The reaction of the formula (2) occurs on the surface of the passive film in the stainless steel pipe 48 that comes into contact with the film forming liquid, and a magnetite film is formed on the surface of the passive film.

Fe ²⁺ + 2Fe ³⁺ + 2H ₂ O = Fe (III) [Fe (II) Fe (III)] O ₄ + 8H ⁺ (2)
Since the supply of the film forming liquid into the stainless steel pipe 48 is continued and the magnetite formation reaction represented by the formula (2) is continued, the surface of the passive film formed on the inner surface of the stainless steel pipe 48 is the magnetite film. It will be covered with.

  The film forming liquid supplied from one end into the stainless steel pipe 48 is returned to the circulation pipe 2 from the other end of the stainless steel pipe 48. With respect to the film forming liquid returned to the circulation pipe 2, the chemical liquid containing iron (II) ions and formic acid is injected by the iron (II) ion implanter 3, the hydrogen peroxide is injected by the oxidant injector 7, and the pH. Injection of hydrazine by the adjusting agent injection device 12 is performed. The film forming liquid into which these chemicals are injected is supplied to the stainless steel pipe 48 again.

As is clear from the reaction shown in the formula (2), when the magnetite formation reaction proceeds, H ⁺ is released, so that the pH of the film-forming solution is lowered. For this reason, in order to maintain pH at 7.0 which is a set value, hydrazine is inject | poured into the film formation liquid which flows in the circulation piping 2 from the pH adjuster injection apparatus 12. FIG. As described above, the injection amount of hydrazine is performed by controlling the rotation speed of the injection pump 14 based on the measured pH value of the film forming solution measured by the pH meter 113.

  When a magnetite film having a predetermined thickness is formed covering the surface of the passive film formed on the inner surface of the stainless steel pipe 48, the injection pumps 5, 9, and 14 are stopped and the valves 6, 10, and 15 are closed, The formation of the magnetite film is finished. Then, the chemicals (hydrazine and formic acid) contained in the film forming solution are decomposed. When the chemical is decomposed, the valve 43 is opened to reduce the opening of the valve 31, and a part of the film forming liquid flowing through the circulation pipe 2 is supplied to the decomposition device 25. By opening the valve 45 and driving the injection pump 9, hydrogen peroxide is supplied from the chemical solution tank 8 to the decomposition device 25 through the pipe 44. Hydrazine and formic acid are decomposed in the decomposition apparatus 25 by the action of hydrogen peroxide and activated carbon catalyst. Hydrazine decomposes into nitrogen and water, and formic acid decomposes into carbon dioxide and water. After the decomposition of each chemical contained in the film forming liquid is completed, the aqueous solution in the circulation pipe 2 and the stainless steel pipe 48 is discharged to the outside. The stainless steel pipe 48 having the passive film and the magnetite film formed on the inner surface is removed from the circulation pipe 2.

  Formation of a passive film and a magnetite film on the inner surface of the stainless steel pipe 48, that is, each operation from Steps S1 to S4 is performed in a factory that is not a radiation control area during operation of the BWR plant.

  In steps S3 and S4, the stainless steel pipe 48 having a passive film and a magnetite film formed on the inner surface is subjected to a BWR plant replacement work during a periodical inspection performed in a state where the operation of the BWR plant is stopped. Attach to the appropriate location.

  When the operation of the BWR plant in a certain operation cycle is finished, the operation of the BWR plant is stopped, and the BWR plant is periodically inspected in a state where the operation is stopped. During the period of this periodic inspection, the recirculation piping 54 in which cracks not penetrating due to stress corrosion cracking are replaced with a stainless steel piping 48 having a passive film and a magnetite film formed on the inner surface. Prior to this exchange, chemical decontamination is performed (step S5). In the BWR plant that has undergone operation, an oxide film is formed on the inner surface of the recirculation pipe 54 that contacts the reactor water in the RPV 50. In the BWR plant, this oxide film contains a radionuclide. An example of step S2 is a process of removing the oxide film from the inner surface of the recirculation system pipe 22 that is a film formation target by a chemical process. Chemical decontamination of the recirculation piping 54 is performed using a chemical decontamination apparatus 72 shown in FIG. This chemical decontamination is performed in order to reduce the exposure of workers during the replacement work of the recirculation piping 54.

  Both ends of the circulation pipe 73 of the chemical decontamination apparatus 72, which is temporary equipment, are connected to a stainless steel recirculation pipe 54. The operation of connecting the circulation pipe 73 to the recirculation system pipe 54 will be specifically described. After the operation of the BWR plant is stopped, for example, the bonnet of the valve 71 installed in the purification system pipe 67 connected to the recirculation system pipe 54 is opened to block the purification system pump 68 side. One end of the circulation pipe 73 of the chemical decontamination apparatus 72 is connected to the flange of the valve 71. Accordingly, one end of the circulation pipe 73 is connected to the recirculation system pipe 54 upstream of the recirculation system pump 53. On the other hand, a branch pipe such as a drain pipe or an instrumentation pipe connected to the recirculation system pipe 54 on the downstream side of the recirculation pump 53 is cut off, and the cut off pipe of the circulation pipe 73 of the chemical decontamination apparatus 72 is connected to the cut off branch pipe. Connect the other end. By connecting both ends of the circulation pipe 73 to the recirculation pipe 54, a closed loop including the recirculation pipe 54 and the circulation pipe 73 is formed. Each opening in the RPV 50 at both ends of the recirculation pipe 54 is sealed with a plug (not shown) so that the film forming liquid does not flow into the RPV 50. The chemical decontamination apparatus 72 is removed from the recirculation system pipe 54 after the chemical decontamination of the inner surface of the recirculation system pipe 64 is completed and within the operation stop period of the BWR plant.

  The chemical decontamination performed in step S5 is a known method (see Japanese Patent Laid-Open No. 2000-105295), but will be briefly described. First, the on-off valve 94, the valves 95, 96, 97, 98, and 99, and the on-off valve 100 are opened, and the other pumps are closed, and the circulation pumps 88 and 93 are activated to drain the water in the surge tank 74. Circulation is performed in the circulation pipe 73 and the recirculation system pipe 54. And it heats with the heater 75 and raises the temperature of the circulating water to about 90 degreeC. When the water temperature reaches about 90 ° C., the valve 112 is opened. The potassium permanganate supplied from the hopper communicated with the ejector 76 is supplied into the surge tank 74 by the water flowing in the pipe 111. Potassium permanganate is dissolved in water in the surge tank 17 to produce an oxidative decontamination solution. The oxidative decontamination liquid is supplied into the recirculation system pipe 54 through the circulation pipe 73 and dissolves contaminants such as an oxide film formed on the inner surface of the recirculation system pipe 54. In this way, the oxidative decontamination of the inner surface of the recirculation pipe 54 is performed.

  After completion of oxidative decontamination, permanganate ions contained in the oxidative decontamination solution are decomposed by oxalic acid injected into the surge tank 74 from the hopper. A reductive decontamination solution is generated in the surge tank 74 by further supplying oxalic acid from the hopper. In order to adjust the pH of the reductive decontamination liquid, the valve 80 is opened and hydrazine is supplied from the chemical liquid tank 78 into the circulation pipe 73. A reductive decontamination solution containing hydrazine is supplied into the recirculation system pipe 54 by the circulation pump 93 to reduce and dissolve contaminants such as an oxide film formed on the inner surface of the recirculation system pipe 54. At the time of reductive decontamination, the valve 106 is opened and the opening of the valve 97 is adjusted, and a part of the reductive decontamination liquid is guided to the cation exchange resin tower 91. The metal cation eluted from the inner surface of the recirculation system pipe 54 into the reducing decontamination solution is adsorbed by the cation exchange resin in the cation exchange resin tower 91 and removed.

  After the completion of the reductive decontamination, the valve 110 is opened and a part of the reductive decontaminating liquid flowing in the circulation pipe 73 is supplied to the decomposition device 87. The decomposition device 87 decomposes oxalic acid and hydrazine contained in the reduction decontamination solution by the action of hydrogen peroxide supplied from the chemical tank 83 through the pipe 86 and the activated carbon catalyst in the decomposition device 87. After the decomposition of oxalic acid and hydrazine, the heating by the heater 75 is stopped, the valve 104 is opened and the valve 96 is closed, and the decontamination liquid is cooled by the cooler 90 and lowered to 60 ° C., for example. The decontamination liquid that has reached 60 ° C. is supplied to the mixed bed resin tower 92 by closing the valve 106 and opening the valve 108. The mixed bed resin tower 92 removes impurities contained in the decontamination liquid that have not been decomposed by the decomposition apparatus 87. Thereby, the electrical conductivity of a decontamination liquid falls. After analyzing the concentration of oxalic acid and hydrazine in the decontamination solution and confirming that the respective concentrations have fallen below predetermined values, the on-off valves 94 and 100 are closed to isolate the chemical decontamination device 72 from the recirculation system pipe 54. After that, the water remaining in the recirculation piping 54 is drained.

  The pipe to be replaced is removed (step S6). After draining the purified decontamination liquid in the recirculation system pipe 54, the replacement part of the recirculation system pipe 54 where the crack has occurred is cut and removed from the recirculation system. A new pipe is connected (step S7). The stainless steel pipe 48 formed by each step of steps S1 to S4, forming a passive film on the inner surface and covering the surface of the passive film with a magnetite film, is connected to the corresponding BWR plant in the nuclear power plant from the factory. Carry into the reactor containment vessel. The stainless steel pipe 48 that has been carried in is disposed at the cut portion of the recirculation pipe 54 and both ends of the stainless steel pipe 48 are connected to the respective cut end faces of the opposing recirculation pipe 54 by welding.

  As described above, the replacement work of the recirculation piping 54 that is a component of the nuclear plant to be replaced is completed. Then, after the periodic inspection of the BWR plant is completed, the operation of the BWR plant in the next operation cycle is started.

  A stainless steel pipe 48 in which a passive film is formed on the inner surface and a magnetite film (ferrite film) covering the surface of the passive film is newly connected as the recirculation system pipe 54 by starting operation of the BWR plant. The reactor water at 280 ° C. containing Co-60 flows inside. For this reason, the magnetite film comes into contact with the reactor water. Hydrogen is injected from the hydrogen injection device 66 into the feed water flowing in the feed water pipe 58, and feed water containing hydrogen is supplied into the RPV 50. Thus, by continuously injecting hydrogen into the reactor water, the corrosion potential of the nuclear plant components, such as the stainless steel pipe 48, which comes into contact with the reactor water is low (−0.5 V vs. SHE). ) Is maintained. However, when the hydrogen injection is interrupted, the corrosion potential becomes high (+0.2 V vs. SHE).

  In the stainless steel pipe 48, since the surface of the passive film mainly composed of Cr oxide formed on the inner surface is covered with the magnetite film, the corrosion potential of the stainless steel pipe 48 is low (−0.5 V vs. SHE). At the time of hydrogen injection, the corrosion of the base material of the stainless steel pipe 48 is suppressed by the action of the passive film, and the adhesion of Co-60 to the stainless steel pipe 48 is also suppressed. In addition, in a state where the hydrogen injection is stopped and the corrosion potential of the stainless steel pipe 48 is increased (+0.2 V vs. SHE), the corrosion of the base material of the stainless steel pipe 48 is suppressed by the magnetite film, Co-60 adhesion is suppressed. At this time, since the passive film mainly composed of Cr oxide is not in direct contact with the high-temperature reactor water, elution of Cr contained in the passive film into the reactor water can be prevented. For this reason, a passive film always exists between the base material of the stainless steel pipe 48 and the magnetite film. For this reason, when hydrogen injection is resumed and the corrosion potential of the stainless steel pipe 48 is lowered, the passive film suppresses the corrosion of the base material of the stainless steel pipe 48, so that Co-60 adheres to the stainless steel pipe 48. Suppression is maintained.

  According to the present embodiment, the inner surface of the stainless steel pipe 48 which is a nuclear plant constituent member is covered with the passive film, and the surface of the passive film is covered with the magnetite film. Therefore, when the hydrogen injection is performed and when the hydrogen injection is not performed, it is possible to suppress the incorporation of the radionuclide into the stainless steel pipe 48, that is, the nuclear plant component.

  In this embodiment, since the passive film and the magnetite film are formed on the inner surface of the stainless steel pipe 48 during the operation of the BWR plant, the inner surface is exposed during the periodic inspection period after the operation of the BWR plant is stopped. It is possible to start the replacement work between the stainless steel pipe 48 in which the passive film and the magnetite film are formed as described above, and the pipe that has cracked due to stress corrosion cracking in the BWR plant. There is no fear of extending.

  The present embodiment can also be applied to stainless steel piping for the reactor purification system and the residual heat removal system.

  A method for reducing the dose of a nuclear plant component according to embodiment 2, which is another embodiment of the present invention, will be described with reference to FIGS. The method for reducing the dose of nuclear plant components of this embodiment is an example applied to a boiling water nuclear plant (BWR plant).

  The method for reducing the dose of the nuclear plant component according to the present embodiment is a method in which a step of forming a ferrite film on the surface of the nuclear plant component subjected to chemical decontamination in the dose reduction method for the nuclear plant component according to the first embodiment is added. It is. The other steps of the method for reducing the dose of nuclear plant components according to the present embodiment are the same as those of the method for reducing the dose of nuclear plant components according to the first embodiment.

  Similarly to the method for reducing the dose of nuclear plant components in Example 1, the method for reducing the dose of nuclear plant components in the present embodiment also causes, for example, cracks that have not penetrated due to stress corrosion cracks in the recirculation piping. This part is replaced with a stainless steel pipe in which a passive film is formed on the inner surface and the surface of the passive film is covered with a ferrite film. As in Example 1, each of the steps S1 to S4 (see FIG. 6) is performed in the factory during operation of the BWR plant, so that a passive film is formed on the inner surface. A stainless steel pipe 48 covered with a coating is produced. In step S <b> 4, using the film forming apparatus 1, a magnetite film that covers the surface of the passive film formed on the inner surface of the stainless steel pipe 48 is formed.

  Similarly to the first embodiment, chemical decontamination is performed on the inner surface of the recirculation piping 54 in a period of a periodic inspection performed after the operation of the BWR plant is stopped (step S5). In the chemical decontamination of the present embodiment, a chemical decontamination apparatus 72A is used instead of the chemical decontamination apparatus 72 used in the first embodiment.

  The chemical decontamination apparatus 72A will be specifically described with reference to FIG. The chemical decontamination apparatus 72A is obtained by replacing the chemical decontamination apparatus 72 (see FIG. 4) used in the first embodiment with the iron (II) ion implantation apparatus 3 of the film forming apparatus 1 (see FIG. 2) used in the first embodiment. In addition, the oxidizing agent injection device 82 provided in the chemical decontamination device 72 is replaced with the oxidizing agent injection device 7. The injection pipe 6 </ b> A of the iron (II) ion implantation apparatus 3 is connected to the circulation pipe 73, and the injection pipe 11 of the oxidant injection apparatus 7 is also connected to the circulation pipe 73. An injection pipe 86 having a valve 85 connected to the injection pipe 11 between the injection pump 9 and the valve 10 is connected to the pipe 109 upstream of the decomposition device 87. Also in the chemical decontamination apparatus 72A, the first connection point (connection point between the injection pipe 6A and the circulation pipe 73) to the circulation pipe 73 of the iron (II) ion implantation apparatus 3 and the circulation pipe 73 of the oxidant injection apparatus 7 are connected. The second connection point (the connection point between the injection pipe 11 and the circulation pipe 73) and the third connection point (the connection point between the injection pipe 81 and the circulation pipe 73) to the circulation pipe 73 of the pH adjusting agent injection device 77 are in this order. It is arranged from upstream to downstream.

  Similarly to the circulation pipe 73 of the chemical decontamination apparatus 72 in the first embodiment, the circulation pipe 73 of the chemical decontamination apparatus 72A communicates with the recirculation system pipe 54 of the chemical decontamination target. In step S5 in this embodiment, the chemical decontamination of the inner surface of the recirculation system pipe 54 in step S5 of this embodiment, which is performed using the chemical decontamination apparatus 72A, is oxalic acid and hydrazine contained in the reductive decontamination solution. In the first embodiment, the chemical decontamination apparatus 72 is used except that hydrogen peroxide in the chemical solution tank 8 of the oxidant injection apparatus 7 is supplied to the decomposition apparatus 87 through the injection pipe 86 when the decomposition apparatus 87 is decomposed. This is the same as the chemical decontamination performed.

  A magnetite film is formed after the decomposition treatment in the decomposition device 25 for oxalic acid and hydrazine contained in the reductive decontamination liquid is completed and the chemical decontamination is completed (step S8). In step S8, the chemical decontamination apparatus 72A connected to the recirculation piping 54 is used when the step S5 is performed. When a magnetite film, which is a ferrite film, is formed on the inner surface of the recirculation pipe 54 using the chemical decontamination device 72A, the valve 112 is closed, and potassium permanganate from the ejector 76 to the surge tank 74 and Oxalic acid is not supplied. In the formation of the magnetite film on the inner surface of the recirculation system pipe 54 using the chemical decontamination apparatus 72A, similarly to the formation of the magnetite film on the inner surface of the stainless steel pipe 48 using the film forming apparatus 1 in the first embodiment. Injecting a chemical solution containing iron (II) ions and formic acid from the iron (II) ion implanter 3 into the circulation pipe 73, injecting hydrogen peroxide from the oxidizer injector 7 into the circulation pipe 73, and injecting a pH adjuster Hydrazine was injected from the device 77 into the circulation pipe 73, and the aqueous solution containing hydrazine, iron (II) ions, chromium ions, ferrous hydroxide, formic acid and hydrogen peroxide had a pH of 7.0 and a temperature of 90 ° C. The film forming liquid is supplied from the circulation pipe 73 into the recirculation system pipe 54. A magnetite film covering the inner surface is formed over the entire inner surface in contact with the film forming liquid on the inner surface of the recirculation system pipe 54 in contact with the film forming liquid. In step S8 of the present embodiment, a magnetite film is also formed on the inner surface of the recirculation system pipe 54 other than the portion to be cut where cracks are not penetrating due to stress corrosion cracking.

  When a magnetite film having a predetermined thickness is formed on the inner surface of the recirculation pipe 54, the injection of each of the chemical solution containing iron (II) ions and formic acid, hydrogen peroxide and hydrazine into the circulation pipe 73 is stopped, and the film is formed. Decomposition of hydrazine and formic acid contained in the liquid is performed by the decomposition device 87. At this time, hydrogen peroxide in the chemical solution tank 8 is supplied to the decomposition device 87 through the injection pipe 86. After the decomposition of hydrazine and formic acid is completed in step S8, both ends of the circulation pipe 73 are removed from the recirculation system pipe 54.

  In the removal of the replacement target pipe in step S <b> 6, the replacement part of the recirculation system pipe 54 that is cracked is cut and removed from the recirculation system pipe 54. In order to connect a new pipe to the cut portion of the recirculation system pipe 54 in step S7, a passive film is formed on the inner surface created by the steps of steps S1 to S4, and the surface of the passive film is formed on the magnetite film. The stainless steel pipe 48 covered with is carried from the factory into the reactor containment vessel of the corresponding BWR plant in the nuclear power plant. The stainless steel pipe 48 that has been carried in is disposed at the cut portion of the recirculation pipe 54 and both ends of the stainless steel pipe 48 are connected to the respective cut end faces of the opposing recirculation pipe 54 by welding.

  As described above, the replacement work of the recirculation piping 54 that is a component of the nuclear plant to be replaced is completed. Then, after the periodic inspection of the BWR plant is completed, the operation of the BWR plant in the next operation cycle is started.

  In the present embodiment, each effect produced in the first embodiment can be obtained. In the present embodiment, a ferrite film is formed on a portion other than the cut portion of the recirculation pipe 54, and the inner surface is covered with the passive film at the cut portion, and the surface of the passive film is further covered with a magnetite film. Since the covering stainless steel pipe 48 is connected, the amount of Co-60 adhering to the recirculation pipe 54 that is a nuclear plant component can be reduced more than in the first embodiment.

  A method for reducing the dose of a nuclear plant component according to embodiment 3, which is another embodiment of the present invention, will be described with reference to FIGS. 8, 9, 10 and 11. FIG. The method for reducing the dose of nuclear plant components of this embodiment is an example applied to a boiling water nuclear plant (BWR plant).

  The nuclear power plant component forming the passive film and the ferrite film in the method for reducing the dose of the nuclear power plant component according to the present embodiment is the same as the passive film and the ferrite in the dose reducing method for each nuclear plant component according to the first and second embodiments. Unlike a replacement nuclear power plant component for forming a film, it is a nuclear power plant component provided in an existing BWR plant, for example, a pipe.

  Further, in the method for reducing the dose of nuclear plant components according to the present embodiment, unlike the dose reduction method for each of the nuclear plant components according to the first and second embodiments, the nuclear plant component that forms the two-layer coating described above, for example, Then, both ends of the circulation pipe 73 of the chemical decontamination apparatus 72 (see FIG. 4) are connected to the recirculation system pipe 54 to perform chemical decontamination of the inner surface of the recirculation system pipe 54. Instead of removing from the recirculation system pipe 54, both ends of the film forming apparatus 1A are connected to the recirculation system pipe 54, and the film forming apparatus 1A forms a passive film on the inner surface of the recirculation system pipe 54. A magnetite film (ferrite film) covering the surface of the dynamic film is formed.

  A film forming apparatus 1A used in the present embodiment will be described with reference to FIG. The film forming apparatus 1A has a configuration in which the pipe 47 provided with the valve 46 in the film forming apparatus 1 used in Example 1 is removed and a passive film forming liquid injection device 115 is added. The passive film forming liquid injection device 115 includes a chemical liquid tank 116, an injection pump 117, and an injection pipe 119. The chemical tank 116 is connected to the circulation pipe 2 by an injection pipe 119 having an injection pump 117 and a valve 118. The chemical tank 116 is filled with an aqueous solution containing hydrofluoric acid and nitric acid which are passive film forming liquids.

  A method for reducing the dose of nuclear plant components according to the third embodiment will be described based on the procedure shown in FIG. In the present embodiment, the nuclear plant constituent member that forms the passive film and the ferrite film is the recirculation pipe 54 that is an existing pipe.

  Here, the detailed configuration of the recirculation system including the recirculation system pipe 54 will be described with reference to FIG. As described above, the recirculation system includes the recirculation system pipe 54 and the recirculation pump 53 provided in the recirculation system pipe 54. A recirculation pump inlet valve 120 is provided in the recirculation system pipe 54 upstream of the recirculation pump 53, and a recirculation pump outlet valve 121 is provided in the recirculation system pipe 54 downstream of the recirculation pump 53. The upstream end of the recirculation system pipe 54 is connected to the RPV 50. A semicircular ring header 24 arranged outside the RPV 50 is provided in the recirculation pipe 54. A plurality of riser tubes 125 are connected to the ring header 24 and penetrate the RPV 50 into the RPV 50. These riser pipes 125 communicate with the nozzles of each jet pump 52. A pipe 122 connected to the residual heat removal system is connected to the recirculation system pipe 54 upstream of the recirculation pump inlet valve 120. A pipe 123 connected to the residual heat removal system is connected to the recirculation system pipe 54 upstream of the recirculation pump outlet valve 121.

  In the present embodiment, the passive film and the ferrite film are formed on the inner surface of the recirculation system pipe 54 in the range between the point A on the upstream side of the recirculation pump inlet valve 120 and the point B on the downstream side of the valve. Form. In this range, the inner surface of the recirculation pipe 54 is not cracked due to stress corrosion cracking.

  Chemical decontamination is performed (step S11). In the period of the periodic inspection after the operation of the BWR plant is stopped, one end of the circulation pipe 73 of the chemical decontamination apparatus 72 shown in FIG. 4 (for example, the end on which the on-off valve 100 is provided) is connected to the pipe 122 ( (See FIG. 10). The other end of the circulation pipe 73 (for example, the end provided with the on-off valve 94) is connected to the pipe 123 (see FIG. 10). The chemical decontamination using the chemical decontamination device 72 may be carried out for the range between the point A and the point B of the recirculation system pipe 54, but the recirculation pump inlet valve of the recirculation system pipe 54 When the film forming operation is performed in the range between A and B near 120, the recirculation system piping is used to reduce radiation exposure caused by radionuclides adhering to the inner surface of the surrounding recirculation piping 54. It is desirable to perform chemical decontamination as widely as possible at 54.

  The inner surface of the recirculation system pipe 54 between the pipe 122 and the pipe 123 is reduced and decontaminated in the same manner as in the first embodiment. As in the first embodiment, the on-off valve 94, the valves 95, 96, 97, 98, 99 and 112, and the on-off valve 100 are opened and the other pumps are closed, and the circulation pumps 88 and 93 are started. Water (about 60 ° C.) in the surge tank 74 heated by the heater 75 is circulated in a closed loop formed by the circulation pipe 73 and the recirculation system pipe 54. The oxidative decontamination solution generated by the potassium permanganate supplied from the ejector 76 is supplied into the recirculation system pipe 54, and the oxidative decontamination of the inner surface of the recirculation system pipe 54 is performed. After completion of oxidative decontamination, the pH of the reductive decontamination solution produced by the oxalic acid supplied from the ejector 76 is adjusted by hydrazine injected from the pH injection device 77 and supplied into the recirculation system pipe 54. The inner surface of the recirculation piping 54 is reduced and decontaminated. After the reduction decontamination is completed, oxalic acid and hydrazine contained in the reduction decontamination solution are decomposed by the decomposition device 87. After the decomposition of these chemicals is completed, the chemical decontamination device 72 is removed from the pipes 122 and 123.

  A film forming apparatus is connected (step S12). After completion of chemical decontamination, the recirculation pump inlet valve 120 is disassembled, and the valve body is taken out from the valve box of the recirculation pump inlet valve 120. A partition member is installed from the inside of the valve box at each position of point A on the upstream side of the valve box and point B on the downstream side of the valve box to seal the recirculation system pipe 54. Subsequently, two pipes are connected to the portion of the valve box from which the valve body is removed, and both ends of the circulation pipe 2 of the film forming apparatus 1A (see FIG. 9) are separately connected to these pipes. The upper part of the valve box into which the two pipes through which the film-forming liquid flows are inserted has a sealed structure so that the film-forming liquid does not leak.

  Perform passivation treatment. (Step S13). After the film forming apparatus 1A is connected, water is supplied to the surge tank 17 in order to circulate the passive film forming liquid to the film forming target part of the circulation pipe 2 and the recirculation system pipe 54 of the film forming apparatus 1A. The circulation pumps 20 and 26 are driven to circulate water through the circulation pipe 2 and the valve box. The circulating water is heated to, for example, 60 ° C. by the heater 19. At this time, the valves 27, 28, 29, 30, 31, 32, and 33 are opened, and the other valves are all closed.

  When a passive film is formed on the inner surface of the recirculation system pipe 54 in the range between the point A and the point B, the valve 118 is opened and the injection pump 117 is driven, and the passive film forming liquid in the chemical tank 116 is For example, an aqueous solution containing hydrofluoric acid and nitric acid is injected into water flowing through the circulation pipe 2 through the injection pipe 119. An aqueous solution containing hydrofluoric acid and nitric acid is injected into the circulation pipe 2 from the chemical tank 116 so that the hydrofluoric acid concentration of the circulating aqueous solution is 3% and the nitric acid concentration is 10%. A passive film forming solution having a hydrofluoric acid concentration of 3% and a nitric acid concentration of 10% is supplied into the valve box by driving of the circulation pumps 20 and 26, and in the range from the point A to the point B of the recirculation piping 54. Contact the inner surface. As a result, a passive film containing Cr as a main component is formed on the inner surface within the range.

  After the formation of the passive film is completed, the water injection pump 117 is stopped and the valve 118 is closed. Then, the waste liquid of the passive film forming liquid is led to the cooler 22 and cooled by opening the valve 37 and closing the valve 29. After the temperature of the waste liquid circulating through the circulation pipe 2 and the valve box by cooling by the cooler 22 decreases to, for example, 20 ° C., the valve 41 is opened and the valve 30 is closed. As a result, the waste liquid is supplied to the mixed bed resin tower 24, and the fluorine ion and nitrate ion contained in the waste liquid are removed by the ion exchange resin and the anion exchange resin filled in the mixed bed resin tower 24. By circulating the waste liquid through the mixed bed resin tower 24, the waste liquid becomes water that can be reused to form a magnetite film.

  A magnetite film is formed (step S15). In the film forming apparatus 1A, in the same manner as the formation of the magnetite film in Example 1, injection of a chemical solution containing iron (II) ions and formic acid from the iron (II) ion implanter 3 to the circulation pipe 2 is performed, and the oxidant injector 7 Is injected into the circulation pipe 2, and hydrazine is injected into the circulation pipe 2 from the pH adjuster injection device 12. Film formation at a temperature of 90 ° C. at pH 7.0, which is an aqueous solution containing hydrazine, iron (II) ions, chromium ions, ferrous hydroxide, formic acid and hydrogen peroxide, generated in the circulation pipe 2 by these injections The liquid is supplied from the circulation pipe 2 into a valve box provided in the recirculation system pipe 54 and comes into contact with the surface of the passive film formed on the inner surface in the range from the point A to the point B of the recirculation system pipe 54. . As a result, a magnetite film is formed on the individual surfaces covering the surface of the passive film. The film forming liquid circulates in a closed loop formed by the circulation pipe 2 and the valve box. After the formation of the magnetite film is completed, formic acid and hydrazine contained in the film forming solution are decomposed by the decomposition device 25.

  Thereafter, the film forming apparatus is removed (step S15). The film forming apparatus 1A connected to the valve box of the recirculation piping 54 is removed. Then, the recirculation pump inlet valve 120 is assembled by incorporating the valve body into the valve box. After the periodic inspection of the BWR plant is completed, the BWR plant is activated.

  In the present embodiment, in the same manner as in the first embodiment, it is possible to suppress the incorporation of radionuclides into the recirculation system pipe 54 that is a nuclear plant constituent member when hydrogen injection is performed and when hydrogen injection is not performed.

  According to the present embodiment, by using the film forming apparatus 1A having the passive film forming liquid injection apparatus 115, the passive film forming liquid is provided from the passive film forming liquid injection apparatus 115 to the BWR plant. It can be easily brought into contact with the surface of a nuclear plant component, for example, the inner surface of the recirculation piping 54, and a passive film is also formed on the inner surface of the recirculation piping 54 provided in the BWR plant. Can do.

  In this embodiment, a passive film is formed on the inner surface of the recirculation piping 54 between the points A and B, and a magnetite film is formed on the surface of the passive film. After removing from the pipes 122 and 123, the recirculation system is connected between the connection part of the pipe 122 and the connection part of the pipe 123 by separately connecting both ends of the circulation pipe 2 of the film forming apparatus 1 </ b> A to the pipes 122 and 123. A passive film can be formed on the inner surface of the pipe 54, and a magnetite film can be formed on the surface of the passive film. As a result, the area of the recirculation piping 54 that can suppress the attachment of radionuclides can be increased. Further, the pipe 111 having the ejector 76 and the valve 122 provided in the chemical decontamination apparatus 72 is provided in the film forming apparatus 1A in the same manner as the chemical decontamination apparatus 72, so that chemical decontamination, formation of a passive film and The magnetite film can be formed by one film forming apparatus 1 </ b> A having the ejector 76. Therefore, it is not necessary to connect and remove the chemical decontamination apparatus 72 from the foot circulation system pipe 54 as in the third embodiment.

  In the case where cracks that do not penetrate due to stress corrosion cracking occur on a part of the inner surface of the recirculation pipe 54 that is the target of film formation in Example 3, the passive film and magnetite film are formed as follows. It may be formed. In the period of the periodic inspection of the BWR plant, after chemical decontamination of the inner surface of the recirculation system pipe 54 using the chemical decontamination apparatus 72, a portion where the crack in the recirculation system pipe 54 is cracked is cut. Remove new pipes and connect new pipes (stainless steel pipes) by welding. Thereafter, both ends of the circulation pipe 2 of the film forming apparatus 1A shown in FIG. 9 are separately connected to the pipes 122 and 123. Then, similarly to Example 3, a passive film is formed on the inner surface of the recirculation system pipe 54 between the connection part of the pipe 122 and the connection part of the pipe 123 using the film forming apparatus 1A. A magnetite film is formed on the surface of the film. Thereby, each effect generated in the third embodiment can be obtained. Furthermore, a passive film can be formed on the inner surface of the welded portion of the newly connected pipe and the remaining recirculation pipe 54, and a magnetite film can be formed on the surface of the passive film.

  Each of Examples 1 to 3 can be applied to a new nuclear plant. Since the radionuclide is not attached to the nuclear plant components of the newly installed nuclear power plant, it is not necessary to perform the chemical decontamination performed in each embodiment when applied to the newly installed nuclear power plant.

  DESCRIPTION OF SYMBOLS 1,1A ... Film formation apparatus, 2,73 ... Circulation piping, 3 ... Iron (II) ion implantation apparatus, 12, 77 ... pH adjuster injection apparatus, 17, 74 ... Surge tank, 19, 75 ... Heater, 20 , 26, 88, 93 ... circulation pump, 22, 90 ... cooler, 25, 87 ... cracking device, 49 ... nuclear reactor, 50 ... reactor pressure vessel, 51 ... core, 53 ... recirculation pump, 54 ... recirculation System piping, 58 ... water supply piping, 66 ... hydrogen injection device, 72, 72A ... chemical decontamination device, 115 ... passive film forming liquid injection device.

Claims (10)

  A passive film containing at least a part of the elements contained in the stainless steel is formed on the first surface of the nuclear power plant component made of stainless steel so as to cover the first surface, and this passive film is formed on the second surface of the passive film. A method for reducing the dose of a nuclear plant component, wherein a ferrite film is formed covering the second surface.   The method for reducing the dose of a nuclear plant component according to claim 1, wherein the formation of the passive film is performed on the first surface of the nuclear plant component installed in a nuclear plant.   The nuclear power plant configuration in which a nuclear power plant constituent member provided in the nuclear power plant is removed, the passive film is formed on the first surface, and the ferrite film is formed on the second surface of the passive film The method for reducing a dose of a nuclear plant component according to claim 1, wherein a member is attached to the nuclear plant in place of the removed nuclear plant component.   The method for reducing a dose of a nuclear plant component according to claim 3, wherein at least the atomic plant component to be removed is chemically decontaminated before removing the nuclear plant component from the nuclear plant.   The method for reducing a dose of a nuclear plant component according to any one of claims 1 to 4, wherein the formation of the passive film on the first surface is performed after the first surface is polished.   The passive film is formed on the first surface by bringing a passive film-forming solution into contact with the first surface, and the ferrite film is formed on the second surface by iron (II) ions, oxidation. The nuclear power plant configuration according to any one of claims 1 to 5, which is performed by bringing a film forming liquid containing a pH agent and a pH adjuster in a range of 5.5 to 9.0 into contact with the second surface. A method for reducing the dose of a member.   The nuclear plant component is the first pipe of the nuclear power plant, and the formation of the passive film is performed by bringing a passive film forming liquid into contact with the inner surface of the first pipe, which is the first surface. The dose reduction method of the nuclear power plant structural member of any one of Claim 1 thru | or 3.   The ferrite film is formed by connecting a second pipe to the first pipe whose inner surface is covered with the passive film, and a pH containing iron (II) ions, an oxidizing agent and a pH adjusting agent is 5.5 to 5.5. A film forming liquid in a range of 9.0 is supplied into the first pipe through the second pipe, and the film forming liquid is applied to the second surface of the passive film formed on the inner surface of the first pipe. The method for reducing a dose of a nuclear plant component according to claim 7, wherein the method is carried out by contacting.   9. The method for reducing a dose of a nuclear plant component according to claim 8, wherein the formation of the passive film is performed by supplying the passive film forming liquid to the first pipe through the second pipe.   In a nuclear power plant having a nuclear plant component, a first surface of the nuclear plant component is covered with a passive film, and a second surface of the passive film is covered with a ferrite film. Nuclear plant.

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