JP5645759B2 - Dose reduction method for nuclear plant components - Google Patents

Description

  The present invention relates to a method for reducing the dose of nuclear plant components, and more particularly to a method for reducing the dose of nuclear plant components 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 (RPV). Cooling water supplied to the core by the recirculation pump (or internal pump) is heated by heat generated by nuclear 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 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 generated from the water contact parts of BWR plant components such as RPV and recirculation piping, the main primary components are made of stainless steel with little corrosion. Stainless steels such as steel and 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. 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, and metal impurities slightly contained in the reactor water are positively removed.

  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 by irradiation of neutrons released by fission of the nuclear fuel material in the fuel rod, such as cobalt 60, cobalt 58, chromium 51, manganese 54, etc. Become a radionuclide.

  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. Radioactive material in the reactor water is removed by a reactor purification system connected to the reactor. 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 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 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. The formation of the ferrite film on the surface of the component member that contacts the reactor water prevents the radionuclide from adhering to the surface of the component member after the operation of the nuclear power plant is started. 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. 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 reduction of the ferrite film formed on the surface of the nuclear plant component by the method described in JP-A-2006-38483. As a result, the deposition of radionuclides on the prepared ferrite coating itself is much less than the deposition of radionuclides that occur as the corrosion coating grows. Incorporation of some radionuclides into the ferrite film formed on the surface of the plant component was observed.

  An object of the present invention is to provide a method for reducing the dose of a nuclear plant constituent member that can suppress stress corrosion cracking of the nuclear plant constituent member and further suppress the incorporation of radionuclides into the ferrite film.

A feature of the present invention that achieves the above-described object is that the pH includes iron (II) ions and an oxidizing agent that oxidizes iron (II) ions to iron (III) ions when the operation of the nuclear power plant is stopped. Is brought into contact with the surface of the nuclear plant stainless steel component that contacts the reactor water to form a ferrite film on the surface .
During operation of the nuclear power plant, the corrosion potential of the constituent members is adjusted within a range of −0.2 V to +0.2 V to form a hematite film on the surface layer of the ferrite film,
After that, during the operation of the nuclear power plant, the first state where the corrosion potential of the component member is −0.5 V and the second state where the corrosion potential of the component member is within the range of −0.2 V to +0.2 V are alternated. It repeatedly,
After the reactor power reaches the rated power, the second period in which the second state is formed is shorter than the first period in which the first state is formed.

  After the ferrite film is formed on the surface of the constituent member, the corrosion potential of the constituent member is adjusted within the range of −0.2 V to +0.2 V, so that the hematite film covering the ferrite film is formed on the surface portion of the ferrite film. Incorporation of radionuclides (for example, radioactive Co ions) into the ferrite film can be further suppressed. After the hematite film is formed on the surface layer of the ferrite film, the first state in which the corrosion potential of the constituent member is −0.5V and the corrosion potential of the constituent member is in the range of −0.2V to + 0.2V. Since the two states are repeated alternately, the hematite film covering the ferrite film can be maintained, and the first state in which the corrosion potential of the component member becomes −0.5 V is generated, thereby causing the stress of the component member Corrosion cracking can be suppressed.

  According to the present invention, it is possible to suppress the stress corrosion cracking of the nuclear plant component, and to reduce the dose of the nuclear plant component that can further suppress the incorporation of the radionuclide into the ferrite film formed on the surface of the nuclear plant component. Further reduction can be achieved.

It is a flowchart which shows the process of 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 block diagram of the BWR plant to which the film formation apparatus used when implementing the dose reduction method of the nuclear power plant structural member shown in FIG. 1 is connected. It is a detailed block diagram of the film formation apparatus shown by FIG. It is a characteristic view which shows each change of the condenser vacuum degree, the reactor water temperature, and the reactor pressure at the time of starting of a BWR plant. It is explanatory drawing which shows the influence which the surface state of a test piece and the quality of immersion water have on the adhesion amount of Co-60 to a test piece. It is explanatory drawing which shows the Raman spectrum of the film | membrane formed in the 2nd test piece and the 3rd test piece shown in FIG. It is a flowchart which shows the process of the dose reduction method of the nuclear power plant structural member of Example 2 which is another Example of this invention. It is a block diagram of the boiling water nuclear power plant to which the process shown in FIG. 7 of the dose reduction method of a nuclear power plant structural member is applied. It is a characteristic view which shows the relationship between feed water hydrogen concentration and the corrosion potential of recirculation system piping. It is a flowchart which shows the process of the dose reduction method of the nuclear power plant structural member of Example 3 which is another Example of this invention. It is a block diagram of the boiling water nuclear power plant to which the dose reduction method of the nuclear power plant structural member of Example 4 which is another Example of this invention is applied.

  The inventors examined a method for further suppressing the incorporation of radionuclides into the ferrite film formed on the nuclear plant component. In this study, the inventors aimed to improve the adhesion suppression performance of the radionuclide of the ferrite film described in JP-A-2006-38483.

  Therefore, the inventors conducted the Co-60 experiment described below in order to confirm the adhesion conditions of Co-60 to the ferrite film. In this experiment, a stainless steel test piece (first test piece) polished with a # 600 water-resistant abrasive paper and a stainless steel test piece (second test piece) formed with a ferrite film were used. The corrosion potential of a test piece 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 is −0 including Co-60, simulating the hydrogen injection conditions (hereinafter referred to as HWC conditions) of a BWR plant These two types of test pieces were immersed for a predetermined time in high-temperature high-pressure pure water (simulated reactor water) at 5 V. In addition, another test piece (third test piece) made of stainless steel on which a ferrite film was formed was immersed in the high-temperature high-pressure pure water for 12 hours, and then hydrogen peroxide was injected into the high-temperature high-pressure pure water. In a state where the corrosion potential of the test piece was adjusted to −0.2 V, the third test piece was immersed in high-temperature high-pressure pure water containing hydrogen peroxide for 50 hours. Further, after that, the injection of hydrogen peroxide was stopped, the corrosion potential of the third test piece was set to −0.5 V, and the total immersion time for the third test piece was the same as the first test piece and the second test piece. Until this time, the immersion of the third test piece in the high-temperature high-pressure pure water was continued.

  After the predetermined time had elapsed, the amount of Co-60 adhesion on each test piece was measured. The measurement results are shown in FIG. The second test piece that was only subjected to the ferrite film treatment as a measure for suppressing Co-60 adhesion exhibited a Co-60 adhesion suppression effect that was reduced by about 60% compared to the first test piece that did not form a ferrite film. Furthermore, after the ferrite film treatment, the third test piece immersed for 50 hours in high-temperature high-pressure pure water where the corrosion potential becomes high shows a Co-60 adhesion suppressing effect that is about 25% less than the second test piece. It was. The inventors considered this result as follows.

  The formation of the ferrite film on the second and third test pieces is performed as follows (see JP-A-2006-38483). An aqueous solution containing iron (II) ions that are ferrite materials, hydrogen peroxide that oxidizes iron (II) ions, and hydrazine that is a pH adjuster that promotes the ferritization reaction is used as the mother of the second and third test pieces. By making contact with the surface of the stainless steel material, the reaction represented by the formula (1) occurs, and a film of magnetite, which is a kind of ferrite, is formed on the surface.

3Fe ²⁺ + H ₂ O ₂ + 6OH ⁻ → Fe ₃ O ₄ + 4H ₂ O (1)
The structure of this magnetite is represented by Fe (III) [Fe (II) Fe (III)] O ₄ . The brackets indicate the metal ions located at the center of the octahedral structure of oxygen. In magnetite, Fe (II) ions are present in this part. (1) The above-mentioned high-temperature high-pressure pure water satisfying the HWC condition (corrosion potential of the second test piece) is applied to the second test piece having a magnetite film, which is a ferrite film formed based on the reaction of the formula (1). The first test film (formed on the second test piece) obtained by dipping in −0.5 V) and the third test piece on which this magnetite film is formed are set to have a corrosion potential of −0. High-temperature high-pressure pure water with different hydrogen peroxide concentrations so that the corrosion potential of the third test piece is alternately changed to -0.2V and -0.5V. Each of the Raman spectra of the second film (formed on the third test piece) obtained by soaking in was measured.

  The measured Raman spectra of the first film and the second film are shown in FIG. From the magnetite film formed before being immersed in high-temperature high-pressure pure water, a peak of only magnetite was observed (see the third Raman spectrum from the top in FIG. 6). A second test piece (see the first Raman spectrum in FIG. 6) and a third test piece (see the second Raman spectrum from the top in FIG. 6) formed with this magnetite film and immersed in the high-temperature high-pressure pure water described above. Then, although the shape of the spectrum was different depending on the site, hematite was observed in addition to magnetite. In the second test piece, as shown in FIG. 3, a site where no hematite peak was observed was observed, but in the third test piece, a hematite peak was observed in all the observed sites. The formation of hematite is considered to be due to the oxidation of iron (II) ions contained in magnetite to iron (III) ions as shown in the formula (2).

4Fe ₃ O ₄ + O ₂ → 6Fe ₂ O ₃ (2)
Since hematite generation requires an oxidizing agent such as oxygen and hydrogen peroxide, it is considered that only the very surface layer portion of the magnetite film that is easily in contact with the oxidizing agent is hematized when magnetite is hematized.

  The inventors considered that the incorporation of Co ions into magnetite is performed by an ion exchange reaction as in the chemical reaction represented by the formula (3).

Fe (III) [Fe (II) Fe (III)] O ₄ + Co ²⁺ → Fe (III) [Co (II) Fe (III)] O ₄ + Fe ²⁺ (3)
On the other hand, the inventors thought that the incorporation of Co ions into hematite is performed by a solid-phase reaction like the chemical reaction of the formula (4).

Co ²⁺ + 2H ₂ O → Co (OH) ₂ + H ⁺ (4)
Fe ₂ O ₃ + Co (OH) ₂ → Fe (III) [Co (II) Fe (III)] O ₄ + H ₂ O (5)
The reaction of formula (5) is a reaction accompanied by a crystal structure change from hematite having a corundum crystal structure to a magnetite having a spinel crystal structure, whereas the reaction of formula (3) is not accompanied by a crystal structure change. The reaction of the formula (5) is less likely to occur than the reaction of (3). For this reason, the third test piece exposed to high-temperature high-pressure pure water with a corrosion potential of −0.2 V, where the hematiteization of the surface of the magnetite film formed on the surface of the stainless steel material has progressed, is more likely to occur. It is considered that the uptake of Co is suppressed more than that of the second test piece that is not exposed to the high-temperature high-pressure pure water at −0.2V.

  The inventors examined conditions for forming a hematite film on the surface layer of the formed ferrite film. As a result, in order to form a hematite film on the surface layer of the ferrite film formed on the surface of the nuclear plant component member, water that brings the corrosion potential of the structural member within the range of -0.2V to + 0.2V is used. It was found that it was necessary to contact the surface of the ferrite film. By bringing water having a corrosion potential of the structural member of −0.2 V or more into contact with the ferrite film formed on the surface of the structural member, hematite is stabilized rather than magnetite. Therefore, water that reduces the corrosion injection potential of the structural member to -0.2 V, which is a normal hydrogen injection condition, by reducing the hydrogen injection amount to reduce the corrosion potential of the structural member to -0.5 V is applied to the ferrite film. By contacting, the magnetite in the formed ferrite film chemically changes to hematite. On the other hand, when water having a corrosion potential of the structural member in the range of −0.4 V or more and less than −0.2 V is brought into contact with the ferrite film, the formation of hematite in the ferrite film becomes incomplete. Moreover, since it is not considered in the operation of a normal nuclear power plant that the corrosion potential of the structural member exceeds +0.2 V, the corrosion potential +0.2 V was set as the upper limit.

  When changing the corrosion potential of a structural member from -0.5V to a range of -0.2V to + 0.2V, and adjusting the corrosion potential of a structural member to a range of -0.2V to + 0.2V Control the amount of hydrogen injected into the reactor water. The corrosion potential of structural members varies depending on the ratio of dissolved hydrogen concentration and oxidizer concentration in the reactor water, but the relationship between the ratio of dissolved hydrogen concentration and oxidizer concentration varies depending on the type of nuclear power plant, and the corrosion potential depends on this. Also changes. For this reason, the dissolved hydrogen concentration for adjusting the corrosion potential of the structural member from -0.2 V to +0.2 V is not uniquely determined. However, generally, when the dissolved hydrogen concentration in the reactor water exceeds 50 ppb, the structural member When the corrosion potential is −0.5 V or less and the dissolved hydrogen concentration in the reactor water is less than 50 ppb, the corrosion potential of the structural member increases rapidly. The dissolved hydrogen concentration in the reactor water can be controlled by the concentration of hydrogen injected into the feed water. FIG. 9 shows an example of the relationship between the hydrogen concentration in the feed water and the corrosion potential of the recirculation piping. The corrosion potential of the recirculation piping is greatly changed when the hydrogen concentration in the feed water is in the range of 0.3 ppm to 0.4 ppm. When the hydrogen concentration in the feed water is lower than 0.3 ppm, the corrosion potential of the recirculation piping is 0.0 V or higher, and when the hydrogen concentration is higher than 0.6 ppm, the corrosion potential is -0.5 V or lower. It has become.

  Hematite is more effective than magnetite for suppressing the incorporation of Co ions into the oxide film. However, from the viewpoint of suppressing stress corrosion cracking of the structural member, the corrosion potential of the structural member is more stable than the reactor water in which the hematite is stabilized and the structural member has a corrosion potential in the range of −0.2V to + 0.2V. It is more preferable to bring the reactor water having a -0.5V into contact with the ferrite film formed on the structural member. Even in the reactor water in which the corrosion potential of the structural member falls within the range of -0.2V to + 0.2V, the structure It is preferable to bring the reactor water in which the corrosion potential of the member is −0.2 V into contact with the ferrite film. For this reason, in order to achieve both the suppression of adhesion of Co ions and the suppression of stress corrosion cracking, it is necessary to maintain the contact between the reactor water and the ferrite film so that the corrosion potential of the structural member is -0.5 V after the formation of hematite. is there. Once formed, the hematite is gradually reduced to magnetite in an environment where the corrosion potential is −0.5V.

6Fe ₂ O ₃ + 2H ₂ → 4Fe ₃ O ₄ + 2H ₂ O (6)
Therefore, in order to maintain the hematite layer formed on the surface of the component of the nuclear power plant and having the effect of suppressing the adhesion of Co ions, the magnetite generated by the above reduction existing on the surface of the component is structured. It is good to expose again to the reactor water which makes the corrosion potential of a member the range of -0.2V- + 0.2V. Therefore, in order to continue the state in which the suppression of adhesion of Co ions and the suppression of stress corrosion cracking are continued, the reactor water in contact with the ferrite film formed on the surface of the component member has a corrosion potential of −0. Continued operation of the nuclear power plant by adjusting the concentration of hydrogen injected into the reactor water so as to repeat the state of 2V to + 0.2V and the state where the corrosion potential of structural members is -0.5V. It is desirable to do.

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

  A method for reducing the dose of a nuclear plant component according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. The present embodiment is an example in which the method for reducing the dose of nuclear plant components is applied to a BWR plant.

  A schematic configuration of the BWR plant will be described with reference to FIG. The BWR 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 installed in the nuclear reactor containment vessel 11 has a nuclear reactor pressure vessel (hereinafter referred to as RPV) 12 containing a core 13, and a jet pump 14 is installed in the RPV 12. The core 13 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 21 and a stainless steel recirculation pipe 22, and the recirculation pump 21 is installed in the recirculation pipe 22. The feed water system is configured by installing a condensate pump 5, a condensate purification device 6, a low pressure feed water heater 8, a feed water pump 7, and a high pressure feed water heater 9 in a feed water pipe 10 connecting the condenser 4 and the RPV 12. The A hydrogen injection device 16 is connected to the water supply pipe 10 between the condenser 4 and the condensate pump 5. 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.

  Cooling water (hereinafter referred to as “reactor water”) in the RPV 12 is pressurized by the recirculation pump 21, passes through the recirculation system pipe 22, and from the nozzle (not shown) of the jet pump 14 to the bell mouth (not shown) of the jet pump 14. ) 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 14 is supplied to the core 13 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 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.

  Reactor water in the RPV 12 is irradiated with radiation generated as a result of nuclear fission of nuclear fuel material and undergoes radiolysis to generate oxidizing species such as hydrogen peroxide and oxygen. This oxidizing chemical species raises the corrosion potential of the components in contact with the reactor water. For this reason, hydrogen is injected into the feed water from the hydrogen injection device 16 as an environmental mitigation measure against stress corrosion cracking. Feed water containing hydrogen is supplied to the RPV 12, and this hydrogen and oxidizing species are reacted in the reactor water in the RPV 12, thereby reducing the concentration of oxidizing species and lowering the corrosion potential. In this way, the operation of the BWR plant performed while injecting hydrogen into the reactor water is the hydrogen injection water quality operation (HWC: Hydrogen Water Chemistry), and the operation of the BWR plant without hydrogen injection is the normal water quality operation (NWC: Normal Water Chemistry). I'm calling.

  A part of the reactor 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 reactor water is returned to the RPV 12 through the purification system pipe 20 and the water supply pipe 10.

  The BWR plant is stopped after the operation in one operation cycle is completed. After this operation stop, a periodic inspection is performed on the BWR plant. After the periodic inspection is completed, the BWR plant is started again. During this periodical inspection, some fuel assemblies in the core 13 are replaced with new fuel assemblies. That is, a part of the fuel assembly in the core is taken out from the RPV 12 as a spent fuel assembly, and a new fuel assembly with zero burnup is loaded into the core 13.

  Formation of a ferrite film on the inner surface of the piping system connected to the RPV 12 (for example, the recirculation system piping 22 and the purification system piping 20) in contact with the reactor water during the periodical inspection in which the operation of the BWR plant is stopped Is done. For forming the ferrite film, a film forming apparatus 30 which is a temporary facility is used. After the operation of the BWR plant is stopped, the circulation pipe 35 of the film forming apparatus 30 is connected to, for example, the recirculation pipe 22 that is a film formation target. The film forming apparatus 30 is removed from the recirculation system pipe 22 after the formation of the ferrite film, specifically, after the processing of the solution used for forming the ferrite film is completed and before the operation of the BWR plant is started. While the operation of the BWR plant is stopped, the film forming apparatus 30 dissolves and removes the oxide film containing the radionuclide formed on the inner surface of the recirculation system pipe 22 and ferrite on the pipe surface after the oxide film is dissolved and removed. It is used to form a film and to treat the solution (waste liquid) used to form this film.

  A 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, an iron (II) ion implanter 81, an oxidant injector 82, a pH adjuster injector 83, a filter 54, a decomposition treatment device 67, a cation exchange resin tower 63, and A mixed bed resin tower 65 is provided. 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 connected to the circulation pipe 35 at both ends 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 pipe 71 and bypassing the cation exchange resin tower 63 and the valve 64. 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. Surges potassium permanganate to oxidize and dissolve contaminants on the inner surface of piping (for example, recirculation piping 22) that is subject to chemical decontamination, and oxalic acid to reduce and dissolve contaminants in the piping. A hopper (not shown) for supplying the fuel into the tank 31 is provided in the ejector 37. The piping that is the target of chemical decontamination is the piping that is the target for film formation (for example, the recirculation piping 22).

  The iron (II) ion implantation apparatus 81 includes a chemical liquid 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 provided with 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 also 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 injector 82 includes a chemical tank 48, an injection pump 45, a valve 42, and an injection pipe 76. The chemical tank 48 is connected to the circulation pipe 35 by an injection pipe 76 in which an injection pump 45 and a valve 42 are installed. The chemical tank 48 is filled with, for example, hydrogen peroxide that is an oxidizing agent (second chemical).

  The pH adjusting agent injection device 83 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, for example, hydrazine, which is a pH adjuster (third drug).

  A pipe 78 provided with a valve 57 is connected to the injection pipe 76 and further connected to the pipe 73 upstream of the decomposition processing device 67. The surge tank 31 is initially filled with water used for processing. The chemical tank 47 and the surge tank 31 are each provided with an inert gas injection device (not shown) for bubbling an inert gas such as nitrogen or argon into the solution in order to remove oxygen contained in the solution existing inside. Are preferably connected).

  The second connection point 79 between the injection pipe 76 and the circulation pipe 35 of the oxidant injection apparatus 82 and the third connection point 80 of the injection pipe 77 and the circulation pipe 35 of the pH adjuster injection apparatus 83 are an iron (II) ion implantation apparatus. 81 is arranged downstream of the first connection point 78 of the injection pipe 75 and the circulation pipe 35. It is preferable that the pH adjuster injection device 83 is connected to the circulation pipe 35 at a position as close as possible to the film formation target portion. Thus, since the piping system of the film forming apparatus 30 is configured, after injecting iron (II) ions into the circulation pipe 35, the oxidant injecting device 82 and the pH adjusting agent injecting device 83 are started. An oxidizing agent and a pH adjusting agent can be added to the aqueous solution containing iron (II) ions in the circulation pipe 35.

  The decomposition processing device 67 decomposes an organic acid (for example, formic acid) used as a counter anion of iron (II) ions and hydrazine that is a pH adjusting agent. That is, as the counter anion of the iron (II) ion, an organic 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.

  Corrosion potential (range of −0.2V to + 0.2V) in which a ferrite film is formed in the recirculation piping 22 using the film forming apparatus 30 and a hematite film is formed on the surface layer of the formed ferrite film after the plant is started. 1 and the corrosion potential (−0.5 V) that suppresses stress corrosion cracking are repeatedly generated, the steps shown in FIG. The In the present embodiment, the formation of the ferrite film on the surface of the BWR plant component in contact with the reactor water is performed, for example, within the period of periodic inspection (maintenance inspection) of the BWR plant after the operation of the BWR plant is stopped. Is called. A method for reducing the dose of nuclear plant components according to the present embodiment will be specifically described along the procedure shown in FIG.

  First, the film forming apparatus 30 is connected to the piping system to be coated (Step S1). After the BWR plant is stopped for periodic inspection, as described above, the circulation pipe 35 is connected to, for example, the recirculation system pipe 22 to be coated. A valve 23 is provided in the purification system pipe 20 connected to the recirculation system pipe 22. 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.

  Chemical decontamination is performed on the inner surface of the piping system to be coated (step S2). On the inner surface of the recirculation system pipe 22 that is in contact with the reactor water of the operated BWR plant, an oxide film (contaminant) incorporating the radionuclide is formed. For this reason, in a BWR plant that has experienced operation, before forming a ferrite film on the inner surface of the piping system, it is possible to remove the oxide film (contaminants) that incorporates radionuclides formed on the inner surface of the piping system. preferable. 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. However, the removal of the oxide film in advance means that the formed ferrite film is radioactive. This prevents covering the oxide film incorporating the nuclide and reduces the dose of the piping system. In the present embodiment, the oxide film formed on the inner surface of the piping system and incorporating the radionuclide is removed by chemical decontamination.

  The chemical decontamination performed in step S2 is a known method (see Japanese Patent Laid-Open No. 2000-105295), but will be briefly described. First, the on-off valve 50, the valves 52, 58, 59, 60 and 33, and the on-off valve 34 are opened, and the other pumps are closed, and the circulation pumps 32 and 51 are started to recirculate the film formation target. The water in the surge tank 31 is circulated in the system piping 22. And it heats with the heater 56 and raises the temperature of the circulating water to about 90 degreeC. The potassium permanganate supplied from the hopper communicated with the ejector 37 is supplied into the surge tank 31 by the water flowing through the pipe 74 by opening the valve 36. In the surge tank 31, an oxidative decontamination solution is generated by potassium permanganate. This oxidative decontamination solution is supplied into the recirculation system pipe 22 through the circulation pipe 35 and dissolves contaminants such as an oxide film formed on the inner surface of the recirculation system pipe 22. In this way, oxidative decontamination of the inner surface of the recirculation system pipe 22 is performed.

  After the oxidative decontamination, permanganate ions remaining in the oxidative decontamination solution are decomposed by oxalic acid injected from the hopper to the surge tank 31. A reductive decontamination solution is generated by further 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 the circulation pump 32 to reduce and dissolve contaminants such as an oxide film formed on the inner surface of the recirculation system pipe 22. 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 completion of the reductive decontamination, the valve 68 is opened and a part of the reductive decontaminating liquid flowing in the circulation pipe 35 is supplied to the decomposition processing device 67. The decomposition treatment device 67 decomposes hydrogen peroxide supplied from the chemical solution tank 48 through the pipe 78 and oxalic acid and hydrazine contained in the reductive decontamination solution by the action of the activated carbon catalyst. After the decomposition of oxalic acid and hydrazine, the valve 58 is closed to stop heating, and the decontamination solution is cooled by the cooler 61 and lowered to 60 ° C., for example. The decontamination liquid that has reached 60 ° C. is supplied to the mixed bed resin tower 65 by closing the valve 64 and opening the valve 66. The mixed bed resin tower 65 removes impurities contained in the decontamination liquid that have not been decomposed by the decomposition processing device 67.

  A ferrite film is formed on the surface of the film formation target portion (step S3). First, after the last purification operation by the film forming apparatus 30 is completed after the above decontamination, 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. The temperature of the film-forming aqueous solution supplied to the recirculation piping 22 that is the target for film formation is adjusted. Valves 50, 60, 33, and 34 are open, and valves 36, 41, 38, 42, 57, 62, 64, 66, and 68 are closed. The heated film-forming aqueous solution circulates in a closed loop path formed by the circulation pipe 35 and the recirculation system pipe 22.

  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 on the film formation target portion, and the drug is wasted. By removing the solid matter, the chemical contained in the film-forming aqueous solution (film-forming 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 of the aqueous solution for forming a film 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 film can be densely formed so that the radionuclide contained in the reactor water during operation of the BWR plant is not taken into the ferrite film formed at the film formation target location. . Therefore, the temperature of the film-forming aqueous solution 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 ferrite film formation rate is within the practical range. When the temperature is 100 ° C. or higher, it is necessary to apply pressure in order to suppress boiling of the film-forming aqueous solution, and pressure resistance of the film-forming apparatus 30 is required. Since the temperature of the film-forming aqueous solution is 200 ° C. or lower, a dense ferrite film can be formed on the inner surface of the piping system to be coated, for example, the inner surface of the recirculation piping 22 that contacts the reactor water.

  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 (for example, the inner surface of the recirculation pipe 22). However, iron (II) ions contained in the film-forming aqueous solution are oxidized to iron (III) ions by dissolved oxygen based on the formula (7). Since iron (III) ions have a lower solubility than iron (II) ions, they are precipitated as ferric hydroxide by the reaction of formula (8) and do not contribute to the formation of a ferrite film. Therefore, in order to remove dissolved oxygen in the film-forming aqueous solution, 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 ⁻ (7)
Fe ³⁺ + 3OH ⁻ → Fe (OH) ₃ (8)
After the temperature of water circulating in the circulation pipe 35 reaches a predetermined temperature, a medicine (aqueous solution) containing iron (II) ions is injected into the circulation pipe 35. That is, the film which flows through the circulation pipe 35 from the chemical tank 47 is obtained by opening the valve 41 and driving the infusion pump 44 to obtain a drug containing iron (II) ions and formic acid prepared by dissolving iron with formic acid. Pour into the forming aqueous solution. Hydrogen peroxide as an oxidant is injected into the circulation pipe 35. Specifically, when the injection pump 45 is driven by opening the valve 42, hydrogen peroxide in the chemical liquid tank 48 flows through the circulation pipe 35 through the injection pipe 76, thereby forming a film containing iron (II) ions. Injected into aqueous solution. Hydrogen peroxide converts iron (II) ions adsorbed on the surface of the metal member (the inner surface of the recirculation pipe 22) at the film formation target and iron (II) ions in the film formation aqueous solution into iron (III). Oxidizes to ions. When the latter iron (II) ions are oxidized to iron (III) ions, the aqueous film-forming solution contains iron (II) ions and iron (III) ions. Subsequently, hydrazine as a pH adjusting agent is injected into the circulation pipe 35. By opening the valve 38 and driving the injection pump 39, hydrazine in the chemical tank 40 flows through the circulation pipe 35 through the injection pipe 77, and iron (II) ions, iron (III) ions, and peroxidation. It is injected into a film-forming aqueous solution (film-forming liquid) containing hydrogen. Hydrazine is injected so that the pH of the film-forming aqueous solution is in the range of 5.5 to 9.0, for example, 7.0. Since the pH of the film-forming aqueous solution is adjusted within the range of 5.5 to 9.0, magnetite which is a kind of ferrite from iron (II) ions and iron (III) ions is based on the reaction formula (9). It is formed on the inner surface of the recirculation pipe 22.

Fe ²⁺ + 2Fe ³⁺ + 2H ₂ O = Fe (III) [Fe (II) Fe (III)] O ₄ + 8H ⁺ (9)
This film-forming aqueous solution is supplied to the recirculation system pipe 22 through the circulation pipe 35. A formation reaction of the magnetite film occurs on the entire inner surface of the recirculation system pipe 22 in contact with the film-forming aqueous solution, and a magnetite film that is a ferrite film is formed on the entire surface. The control device (not shown) controls the rotational 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 amount of hydrazine injected into the recirculation system pipe 22. To do. By this control, the pH of the film-forming aqueous solution is adjusted within the above range. In this embodiment, the pH of the aqueous film forming solution is adjusted to 7.0.

  Since the circulation pumps 32 and 51 are driven, a film-forming aqueous solution having a pH of 7.0 containing hydrazine, iron (II) ions and hydrogen peroxide is recirculated through the open / close valve 34 by the circulation pipe 35. It is supplied into the system piping 22. This film-forming aqueous solution flows through the recirculation pipe 22 and is returned to the open / close valve 50 side of the circulation pipe 35. A chemical containing iron (II) ions and formic acid is injected from the chemical tank 47, hydrogen peroxide from the chemical tank 48, and hydrazine from the chemical tank 40 to the returned film-forming aqueous solution. This film-forming aqueous solution is again introduced into the recirculation system pipe 22.

  It is determined whether or not the formation of the ferrite film on the inner surface of the piping system to be coated is completed. This determination is made at the elapsed time after the start of the ferrite film formation process, that is, the injection of the agent containing iron (II) ions and formic acid is started and the injection of the oxidizing agent and the pH adjusting agent is started. Until this elapsed time reaches the time required to form the ferrite film having a predetermined thickness on the inner surface of the recirculation pipe 22, the determination as to whether the formation of the ferrite film is completed is "NO". In this case, the ferrite film is continuously formed on the inner surface of the recirculation pipe 22. When the determination is “YES”, the injection pumps 39, 44 and 45 are stopped (or the valves 38, 41 and 42 are closed) to stop the injection of each drug into the circulating film-forming aqueous solution. . Thereby, the formation of the ferrite film on the inner surface of the recirculation pipe 22 is completed.

  When the formation of the ferrite film on the inner surface of the piping system is completed, the chemical contained in the film-forming aqueous solution is decomposed (step S4). The film-forming aqueous solution used for forming the ferrite film on the inner surface of the recirculation pipe 22 contains hydrazine and formic acid, which is an organic acid, even after the formation of the ferrite film is completed. Hydrazine and formic acid contained in the film-forming aqueous solution are decomposed by the decomposition treatment device 67 in the same manner as the decomposition of oxalic acid, which is a reducing decontamination agent. In the chemical decomposition treatment, the opening degree of the valves 60 and 68 is adjusted, and a part of the film-forming aqueous solution in the circulation pipe 35 is supplied to the decomposition treatment device 67. By opening the valve 57, hydrogen peroxide is supplied from the chemical solution 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 decomposes into carbon dioxide and water by the reaction of formula (10), and hydrazine decomposes into nitrogen and water by the reaction of formula (11).

HCOOH + H ₂ O ₂ → CO ₂ + 2H ₂ O (10)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O (11)
During the period in which the chemical decomposition is performed, the film-forming aqueous solution is supplied from one end of the circulation pipe 35 to one end of the recirculation system pipe 22 by driving the circulation pumps 32 and 51, and passes through the recirculation system pipe 22. Returned to the other end of the circulation pipe 35.

  Before supplying the film-forming aqueous solution to the decomposition treatment device 67, the valve 53 is opened and the valve 52 is closed, and the film-forming aqueous solution is supplied to the filter 54. Magnetite particles contained in the film-forming aqueous solution are removed by the filter 54. After removing the magnetite particles, the opening degree of the valves 59 and 64 is adjusted, and a part of the film-forming aqueous solution is supplied to the cation exchange resin tower 63. Iron (II) ions and hydrazinium ions contained in the film-forming aqueous solution are removed by the cation exchange resin tower 63. Decomposition of formic acid contained in the film-forming aqueous solution and hydrazine that has not been completely removed by the cation exchange resin tower 63 is performed using the decomposition processing device 67 as described above.

  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. Since hydrazine and formic acid are more difficult to decompose, when the chemical decomposition by the decomposition treatment device 67 proceeds to some extent, the pH of the circulating film-forming aqueous solution starts to decrease. When the pH of this film-forming aqueous solution is 4 or less, there is a possibility that the ferrite film formed on the inner surface of the recirculation pipe 22 is dissolved. For this reason, the injection pump 39 is started by opening the valve 38 so that the pH value measured by the pH meter 79 does not become 4 or less, and hydrazine in the chemical solution tank 40 is injected into the film-forming aqueous solution. As the decomposition of the remaining formic acid and the injected hydrazine proceeds while injecting hydrazine, the concentration of formic acid gradually decreases, so the amount of hydrazine injected to maintain pH 4 gradually decreases. When the concentration of formic acid decreases, pH 4 or more can be maintained without injecting hydrazine, so that formic acid is finally decomposed without injecting hydrazine.

  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.

  Since hydrazine and formic acid are decomposed into gas and water by the decomposition treatment device 67 as described above, the removal of hydrazine by the cation exchange resin tower 64 and formic acid by the mixed bed resin tower 65 can be greatly reduced. The amount of exchange resin waste can be significantly reduced.

  The film forming apparatus is removed from the pipe system to be coated (step S5). After the decomposition of the chemical contained in the film-forming aqueous solution is completed, both ends of the circulation pipe 35 connected to the recirculation system pipe 22 are connected to the purification system pipe 20 and the recirculation system pipe 22. Removed from. The valve 28 provided in the purification system pipe 20 and its branch pipes are restored to their original positions. Thereby, the operation of the BWR plant can be started. The ferrite film formed on the inner surface of the recirculation pipe 22 is kept in the same state until the start of the BWR plant.

  After the periodic inspection of the BWR plant is completed, preparations for starting the BWR plant are advanced. When the recirculation pump 21 is activated, the reactor water is circulated through the recirculation system pipe 22, and the reactor water discharged from the jet pump 14 is supplied to the reactor core 13. FIG. 4 shows changes in the condenser vacuum degree, reactor water temperature, and reactor pressure at the start of the BWR plant. The vacuum degree of the condenser 4 is raised before starting the BWR plant. The vacuum degree of the condenser 4 is increased by an air extractor (not shown) provided in an off-gas system (not shown) connected to the condenser 4. Further, the main steam isolation valve provided in the main steam pipe 2 is fully opened, and a bypass valve provided in a turbine path pipe (not shown) connecting the main steam pipe 2 and the condenser 4 is opened to open the reactor water. Deaeration is performed to reduce the dissolved oxygen concentration in the reactor water to about 0.2 ppm.

  Thereafter, the nuclear reactor is activated (step S6). A reactor mode switch provided on an operation panel installed in the central control room is activated, and a plurality of control rods (not shown) inserted into the core 13 are sequentially pulled out. Operation in a certain operation cycle of the nuclear reactor 1 is started. Eventually, the reactor 1 reaches the criticality (step S7). Nuclear fuel material contained in each fuel assembly loaded in the reactor core 13 undergoes fission, and nuclear heating of the reactor water is started. The reactor is heated and raised (step S8). In this temperature raising / pressurizing step, the control rod is further pulled out of the core, the nuclear fission of the nuclear fuel material increases, the temperature of the reactor water rises, and steam is generated. The reactor pressure rises to the rated pressure and the reactor water temperature rises to the rated temperature (for example, 280 ° C.) by the temperature raising / pressurizing step. In the core 13, neutron rays and gamma rays are generated by fission of nuclear fuel material. Neutron rays and gamma rays induce radiolysis of the reactor water, producing hydrogen peroxide and oxygen in the reactor water. After the temperature raising / pressurizing step is completed, the reactor output is increased to the rated output (100% output) by pulling out the control rod and increasing the core flow rate (step S9).

  In this embodiment, since hydrogen injection is not performed during the start-up of the reactor, oxidizing chemical species generated by radiolysis remain in the reactor water. When high-temperature reactor water containing oxidizing chemical species flows in the recirculation system pipe 22, the surface of the ferrite film (for example, magnetite film) formed on the inner surface of the recirculation system pipe 22 in step S3. To touch. When the oxidizing chemical species contained in the reactor water comes into contact with the surface of the ferrite film in a high temperature environment of 280 ° C., iron (II) ions contained in the magnetite constituting the ferrite film are oxidized. As a result, hematite is gradually formed on the surface layer portion of the ferrite film formed on the inner surface of the recirculation pipe 22. The surface layer of the ferrite film formed in step 3 in contact with the reactor water during the period from when the reactor water reaches the rated temperature in the temperature raising and boosting process until the reactor output reaches the rated output (100% output) The part becomes hematite. Since hydrogen injection is not performed, the corrosion potential of the recirculation system pipe 22 which is a constituent member becomes +0.2 V, and the surface of the ferrite film formed on the inner surface of the recirculation system pipe 22 comes into contact with the reactor water. A film-like hematite layer (hematite film) is formed. Thus, the surface layer portion of the ferrite film formed on the inner surface of the recirculation pipe 22 is a hematite film that improves the Co ion adhesion suppressing effect.

  Next, hydrogen injection is started from the viewpoint of suppressing stress corrosion cracking, and hydrogen injection is performed for a predetermined period (step S10). Hydrogen injection is performed for one week (first predetermined period) continuously, for example, so that the hydrogen concentration in the reactor water is maintained at 50 ppb. The hydrogen injection in step S <b> 10 is performed by injecting hydrogen (reducing agent) from the hydrogen injection device 16 into the water supply flowing in the water supply pipe 10. By this hydrogen injection, the nuclear reactor 1 is operated under the HWC condition. Feed water containing hydrogen flowing through the feed water pipe 10 is supplied into the RPV 12, and the injected hydrogen reacts with an oxidant such as oxygen and hydrogen peroxide contained in the reactor water to generate water. For this reason, the oxidizing agent density | concentration of the reactor water in RPV12 falls, and the corrosion potential of reactor water falls. Stress corrosion cracking of the components of the nuclear power plant that come into contact with the reactor water can be suppressed. Hydrogen is injected into the reactor water so that the corrosion potential of the constituent members is lowered to a target potential or lower (for example, −0.5 V).

  The hematite layer formed on the surface of the ferrite film is reduced to magnetite when it continues to be exposed to the reactor water in which the corrosion potential of the recirculation pipe 22 is -0.5V. For this reason, the hydrogen injection amount is decreased (step S11). When hydrogen injection at the rated speed in the first predetermined period is completed, in order to increase the hematite in the ferrite film surface layer, the hydrogen injection amount from the hydrogen injection device 16 to the feed water is decreased, and the hydrogen injection concentration of the reactor water is set. Decrease. Since the potential as low as possible is preferable from the viewpoint of suppressing stress corrosion cracking, for example, hydrogen injection is performed so that the corrosion potential of the recirculation system pipe 22 becomes −0.2 V. The second predetermined time, for example, about 6 hours, is continued at an injection rate ½ of the hydrogen injection amount). By performing the hydrogen injection at a 1/2 injection rate, the corrosion potential of the recirculation system pipe 22 increases from −0.5V to −0.2V. As a result, hematite is generated on the surface portion of the ferrite film formed on the inner surface of the recirculation pipe 22 by the action of the oxidizing chemical species contained in the reactor water, and the hematite layer is maintained on the surface of the ferrite film. .

  After the hydrogen injection at the ½ injection rate for the second predetermined time, for example, 6 hours, is completed, the hydrogen injection amount is increased (step S12). The increase in the hydrogen injection amount is performed by increasing the hydrogen injection to the rated speed, similarly to step S10, and the corrosion potential of the recirculation system pipe 22 is also reduced to -0.5V. The hydrogen injection at the rated speed in step S12 is continued for a first predetermined time (for example, one week) as in step S10. When hydrogen injection at the rated speed in the first predetermined time is completed, the hydrogen injection amount is decreased again (step S13). Also in step S13, as in step S11, during the second predetermined period (for example, 6 hours), hydrogen injection is performed at a 1/2 injection rate, and the corrosion potential of the recirculation system pipe 22 is -0.2V. To rise. After the hydrogen injection at the 1/2 injection speed in the second predetermined period is completed, the hydrogen injection at the rated speed (step S12) and the recirculation system pipe at which the corrosion potential of the recirculation system pipe 22 decreases to -0.5V. Hydrogen injection at 1/2 speed (Step S13) at which the corrosion potential of 22 increases to −0.2 V is alternately repeated to continue operation of the BWR plant (Step S14). The repetition of hydrogen injection in steps S12 and S13 is continued until the operation of the BWR plant in one operation cycle is completed. Thereby, the hematite layer can be maintained on the surface of the ferrite film formed on the inner surface of the recirculation pipe 22 over the rated operation period of the BWR plant, and stress corrosion is maintained while continuing the adhesion suppression of Co ions. A period of a corrosion potential of −0.5 V that can suppress cracking can be secured for a long time.

  According to the present embodiment, after the period when the corrosion potential of the constituent member (recirculation system pipe 22) is set to -0.5V by hydrogen injection, the period for setting the corrosion potential of the constituent member to -0.2V is provided. By repeating this period, it is possible to continue the state in which the surface of the ferrite film formed on the inner surface of the recirculation pipe 22 is covered with the hematite film, and the reactor water flowing in the recirculation pipe 22 is transferred to the ferrite film. Contact with the surface of the hematite film without contact with the surface. Since contact with the ferrite film of the reactor water can be prevented, dissolution and reprecipitation of the ferrite film do not occur, and uptake of radionuclides into the ferrite film can be prevented. For this reason, the dose of the recirculation piping 22 can be further reduced. Since hematite has a lower solubility in water than ferrite, the incorporation of radionuclides into the hematite film in contact with the reactor water is remarkably suppressed. In particular, after the reactor power reaches the rated power, the period in which the corrosion potential of the component member is set to -0.5 V and the period in which the corrosion potential of the component member is set to -0.2 V are repeated through one operation cycle. After the reactor power reaches the rated power, the hematite film can be retained on the surface of the ferrite film formed on the surface of the constituent member until the operation in one operation cycle is completed. After reaching the rated output, the adhesion of Co ions to the ferrite film can be further suppressed through one operation cycle.

  Further, in this embodiment, since the hematite film is in contact with the reactor water, the inner surface (specifically, the surface of the hematite film) of the recirculation piping 22 of the radionuclide such as Co-60 contained in the reactor water. Adhesion to can be remarkably suppressed.

  In this example, a film-forming aqueous solution (film-forming solution) having a pH in the range of 5.5 to 9.0 containing iron (II) ions and an oxidizing agent that oxidizes iron (II) ions to iron (III) ions. The liquid is preferably adjusted to a temperature in the range of 60 ° C. to 100 ° C. and brought into contact with the inner surface of the pipe (for example, the recirculation system pipe 22) that is the target for film formation. A ferrite film can be formed.

  In this embodiment, since the surface layer portion of the ferrite film formed on the inner surface of the recirculation pipe 2 is changed to hematite, the effect of reducing the amount of Co-60 taken into the ferrite film itself can be obtained.

  In this example, the hematite layer is brought into contact with the surface of the ferrite film with the reactor water containing the oxidizing species after the reactor water temperature reaches the rated temperature and before the hydrogen injection into the reactor water. Since it forms, the effect which reduces the adhesion amount of Co-60 taken in by the ferrite film itself can be acquired.

  In this example, after the hematite layer is formed in the surface layer portion of the ferrite film, hydrogen injection is performed to prevent stress corrosion cracking, and the hematite layer is reduced to the magnetite layer by hydrogen injection. Then, after maintaining the rated hydrogen injection amount for the first predetermined period, the hydrogen injection amount is reduced by half, and the corrosion potential of the recirculation system pipe 22 is increased to around -0.2 V to thereby increase the surface layer of the ferrite film. Hematite is formed again on the part. The hydrogen injection amount reduced to ½ is continued for the second predetermined time, and when the hematite layer becomes thick, the hydrogen injection amount is returned to the rating again to suppress stress corrosion cracking. Considering that the thickness of the hematite layer is reduced by reducing the hematite layer to the magnetite layer, the rated hydrogen injection amount for maintaining the corrosion potential of the recirculation piping 22 at −0.5 V is maintained for the first predetermined period. After that, the amount of hydrogen injection is reduced by half, and the corrosion potential of the recirculation system pipe 22 is increased to around -0.2 V to generate hematite. Thereby, the thickness of the hematite layer whose thickness has decreased in the first predetermined period is increased in the second predetermined period. As described above, by repeating the hydrogen injection at the rated hydrogen injection amount and the hydrogen injection amount of 1/2 (half), while maintaining the hematite layer having the Co ion adhesion suppressing effect, the stress corrosion It is possible to ensure a long maintenance period of a corrosion potential of −0.5 V, which has a crack suppressing effect.

  In this embodiment, the hydrogen injection device 16 is connected to the water supply pipe 10, but the hydrogen injection device 16 may be connected to the purification system pipe 20. In this case, hydrogen is injected into the purification system pipe 20, and this hydrogen is injected into the reactor water in the RPV 12 through the purification system pipe 20 and the water supply pipe 10.

  Both ends of the circulation pipe 35 of the film forming apparatus 30 may be connected to the purification system pipe 20, and a ferrite film may be formed on the inner surface of the purification system pipe 20 during the operation stop period of the BWR plant. After the ferrite film is formed on the inner surface of the purification system pipe 20, both ends of the circulation pipe 35 are removed from the purification system pipe 20, and the operation of the BWR plant is started. In step S8, the NWC condition is satisfied from the state in which the reactor water reaches the rated temperature until the rated output in step S9 is reached. Therefore, during this period, the reactor water containing oxidizing chemical species is discharged from the inner surface of the purification system pipe 20. The hematite film is formed on the surface layer portion of the ferrite film. In the purification system pipe 20 as well, when hydrogen injection is performed to prevent stress corrosion cracking (step S10), the hematite film is reduced to magnetite, and the thickness of the hematite film decreases. Therefore, considering that the hematite layer is reduced to magnetite and the thickness of the hematite layer is reduced, the rated hydrogen injection amount is maintained for the first predetermined period, and then the hydrogen injection amount is halved to purify the piping 20 By setting the corrosion potential of to around −0.2 V, hematite is generated and the thickness of the hematite layer is increased. Thereafter, as in the case of the recirculation system pipe 22 described above, the hydrogen injection is alternately repeated to the rated hydrogen injection amount and a half of the injection amount, thereby obtaining each of the above-mentioned obtained in the recirculation system pipe 22. An effect can be obtained.

  Also for a newly installed BWR plant, a ferrite film can be formed on the inner surface of at least one of the recirculation system pipe 22 and the purification system pipe 20 before the start of operation of the BWR plant. However, before the start of operation of the new BWR plant, the radionuclide is not attached to the inner surface of at least one of the recirculation system pipe 22 and the purification system pipe 20. Therefore, when forming a ferrite film on the inner surface of at least one of the recirculation system pipe 22 and the purification system pipe 20, the steps S1, S3, S4, and S5 are performed, and the chemical removal in step S2 is performed. Dyeing is not carried out.

  In the first operation cycle of the new BWR plant, the reactor is activated (step S6), and thereafter, the operations of steps S7 to S13 are performed. In step S9, the hematite film is formed on the surface layer portion of the ferrite film formed on the inner surface of at least one of the recirculation system pipe 22 and the purification system pipe 20 of the newly installed BWR plant. Subsequently, hydrogen is injected at the rated speed (step S10), and the corrosion potential of the pipe on which the ferrite film and the hematite film are formed is set to -0.5 V, and a measure for suppressing stress corrosion cracking is performed. When the first predetermined time has elapsed, hydrogen is injected at a rate that is half the rated speed (step S11), and the corrosion potential of the pipe on which the ferrite film and the hematite film are formed is set to -0.2V. Thereafter, the operations in steps S12 and S13 are repeated alternately. Therefore, even in the newly installed BWR plant, it is possible to obtain the same effects as those of the BWR plant that has experienced the operation described above.

  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 according to this embodiment is also applied to a BWR plant that has undergone operation. The BWR plant to which the method for reducing the dose of nuclear plant components according to the present embodiment has a configuration in which the hydrogen injection device 17 is added to the BWR plant to which the first embodiment is applied. A hydrogen injection device 17 is connected to a portion of the purification system pipe 20 that is downstream of the reactor water purification device 27 and downstream of the regenerative heat exchanger 25.

  Even in the method for reducing the dose of nuclear plant components in the present embodiment, the steps S1 to S6 performed in the method for reducing the dose of nuclear plant components in the first embodiment are performed. In step S3, a ferrite film is formed on the inner surface of the recirculation piping 22, for example. After starting the nuclear reactor (step S6), hydrogen injection is performed (step S15). This hydrogen injection is performed by supplying hydrogen from the hydrogen injection device 17 to the purification system pipe 20 before reaching the criticality after the reactor 1 is started. Hydrogen from the hydrogen injection device 17 to the purification system pipe 20 is performed at a rated speed. For this reason, the corrosion potential of the structural members such as the recirculation pipe 22 that comes into contact with the reactor water becomes −0.5V. When the nuclear reactor 1 is activated, water supply to the RPV 12 by the water supply pipe 10 is not performed, but the purification system pump 24 is driven and the reactor water flows into the purification system pipe 20. Hydrogen injected into the reactor water flowing in the purification system pipe 20 is guided into the RPV 1 together with the reactor water. This hydrogen injection is stopped when the temperature rise / pressure increase (step S8) of the reactor is completed and the temperature of the reactor water reaches 280 ° C.

  After the temperature of the reactor water reaches 280 ° C. due to the temperature rise and pressure of the reactor, the reactor power is increased to the rated power in step S9. When the reactor power reaches the rated power, hydrogen injection from the reactor purification system is stopped (step S16). When the reactor power reaches the rated power, the hydrogen injection from the hydrogen injection device 17 to the purification system pipe 20 is stopped. Thereafter, hydrogen injection from the hydrogen injection device 16 to the water supply pipe 10 is performed in step S10. The period (usually several days) from the stop of hydrogen injection from the hydrogen injection device 17 to the purification system pipe 20 (step S16) to the hydrogen injection from the hydrogen injection device 16 to the water supply pipe 10 (step S10) is a furnace. The reactor 1 is operated in a state where the water temperature is substantially maintained at the rated temperature and hydrogen injection is not performed (NWC). During this period, the reactor water containing the oxidizing chemical species generated by the radiolysis of the reactor water comes into contact with the surface of the ferrite film formed on the inner surface of the recirculation system pipe 22. The corrosion potential is + 0.2V. As in the first embodiment, hematite is generated on the surface layer portion of the ferrite film formed on the inner surface of the recirculation pipe 22, and eventually a hematite film covering the entire surface of the ferrite film is formed.

  After hydrogen injection from the hydrogen injection device 16 to the water supply pipe 10 is performed in step S10, steps S11, S12, and S13 are performed as in the first embodiment, and one hydrogen injection in each of steps S12 and S13 is performed. The operation of the BWR plant is continued until the operation cycle is completed (step S14). In steps S <b> 10 to S <b> 13, hydrogen injection is performed not from the hydrogen injection device 17 but from the hydrogen injection device 16.

  In the present embodiment, each effect produced in the first embodiment can be obtained. In this embodiment, hydrogen can be injected into the reactor water in the RPV 12 from the start-up of the reactor, so that the stress corrosion cracking of the nuclear plant components can be further suppressed.

  By starting up the BWR plant, the temperature of the nuclear plant components such as the reactor internal structure rises from about 50 ° C. to 60 ° C. at the time of startup to the rated temperature (280 ° C.) at the end of the temperature raising and boosting process. Due to the thermal expansion of the component member accompanying this temperature change, stress is generated in the component member. For this reason, hydrogen may be injected into the reactor water immediately after the reactor is started from the viewpoint of stress corrosion cracking suppression measures for the components of the nuclear power plant. However, when hydrogen is injected into the reactor water immediately after the reactor is started to reach the rated power operation, a period during which the surface of the ferrite film formed on the inner surface of the recirculation pipe 22 is oxidized cannot be obtained. As a result, a hematite film cannot be formed on the surface layer of the ferrite film. Therefore, in this embodiment, hydrogen injection into the reactor water is performed immediately after the start of the reactor, and when the reactor water temperature reaches the rated temperature, the hydrogen injection from the purification system pipe 20 is stopped and the hydrogen injection is not performed. After a period of time, hydrogen injection into the water supply pipe 10 is started. For this reason, in the period in which hydrogen injection is not performed from the stop of hydrogen injection in step S16 to the start of hydrogen injection in step S10, the magnetite in the surface layer portion of the ferrite film formed on the inner surface of the recirculation system pipe 22 is oxidized to form hematite. Can be generated.

  Also in this embodiment, a ferrite film can be formed on the inner surface of the piping system of a newly installed BWR plant. In this case, the chemical decontamination in step S2 is not necessary as 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 FIG. The method for reducing the dose of nuclear plant components according to this embodiment is also applied to a BWR plant that has undergone operation. The BWR plant to which the method for reducing the dose of nuclear plant components according to the present embodiment is applied has the same configuration as the BWR plant to which the second embodiment is applied, and includes a hydrogen injection device 17.

  The nuclear plant component member dose reduction method in the present embodiment performs steps S1 to S6, S15, and S7 to S9 in the same manner as the nuclear plant component member dose reduction method in the second embodiment. In step S3, a ferrite film is formed on the inner surface of the recirculation piping 22, for example. In this embodiment, step S10 is not performed. When the reactor output reaches the rated output in step S9, hydrogen is injected into the water supply pipe (step S11). Hydrogen is injected from the hydrogen injection device 16 to the feed water flowing in the feed water pipe 10 at a half injection rate. When hydrogen injection by this step S11 is started, hydrogen injection to purification system piping is stopped (step S16). The injection of hydrogen from the hydrogen injection device 17 into the purification system pipe 20 is stopped. As a result, the hydrogen injected from the hydrogen injection device 16 into the water supply pipe 10 at a ½ injection rate is supplied into the RPV 12, and the corrosion potential of the constituent members becomes −0.2V. The magnetite in the surface layer portion of the ferrite film formed on the inner surface of the recirculation pipe 22 is hematized, and a hematite film is formed on the surface of the ferrite film. Hydrogen injection at 1/2 injection rate is performed for 6 hours. When these 6 hours have elapsed, the hydrogen injection in step S12 and the hydrogen injection in step S13 are sequentially performed as in the second embodiment. And each hydrogen injection of step S12 and S13 is repeated until one driving cycle is complete | finished, and the driving | operation of a BWR plant is continued (step S14).

  In the present embodiment, each effect produced in the second embodiment can be obtained. In this embodiment, the hydrogen injection from the purification system pipe 20 after the reactor power reaches the rated power is stopped after the hydrogen injection from the feed water pipe 10 is started, so that the components are exposed to the NWC environment. This can eliminate the period during which stress corrosion cracking of the components of the nuclear power plant can be further suppressed.

  Also in this embodiment, a ferrite film can be formed on the inner surface of the piping system of a newly installed BWR plant. In this case, the chemical decontamination in step S2 is not necessary as in the first embodiment.

  A method for reducing the dose of a nuclear plant component according to embodiment 4, which is another embodiment of the present invention, will be described with reference to FIG. The method for reducing the dose of nuclear plant components according to this embodiment is also applied to a BWR plant that has undergone operation. The BWR plant to which the nuclear plant plant component dose reduction method of the present embodiment is applied has a configuration in which the corrosion potential sensor 18 installed in each recirculation piping 22 is added to the BWR plant to which the second embodiment is applied. .

  In each Example of Examples 1-3, based on the results of other BWR plants or the calculation results using experimental data, the corrosion potential of the constituent members is -0.5V or -0.2V. The amount of hydrogen injected in step S10 or S11 is controlled. In contrast, in this embodiment, the corrosion potential of the recirculation system pipe 22 is measured by the corrosion potential sensor 18, and the furnace is adjusted so that the measured corrosion potential of the structural member becomes −0.5V or −0.2V. Control the amount of hydrogen injected into the water.

  In the present embodiment, for example, the steps S1 to S14 are performed as in the first embodiment. In steps S10 and S12, the hydrogen injection amount from the hydrogen injection device 16 is not shown in FIG. 2 so that the corrosion potential measured by the corrosion potential sensor 18 is −0.5V. Adjusted by device (or manual). In steps S11 and S13, the hydrogen injection amount from the hydrogen injection device 16 is set to the above-described control device (or manual operation) so that the corrosion potential of the structural member measured by the corrosion potential sensor 18 is -0.2V. ). The hydrogen injection amount at the rated speed corresponds to the hydrogen injection amount at which the corrosion potential of the structural member becomes −0.5 V, and the hydrogen injection amount at half the rated speed reduces the corrosion potential of the structural member to −0. This corresponds to a hydrogen injection amount of 2 V.

  In the present embodiment, each effect produced in the first embodiment can be obtained. In the present embodiment, hydrogen injection is controlled based on the corrosion potential measured by the corrosion potential sensor 18 installed in the recirculation system pipe 22, so that the corrosion potential (−0.5 V and −0. 2V) can be reliably controlled.

  The present embodiment can also be applied to the second and third embodiments.

  The present invention can be applied to a boiling water nuclear power plant.

  DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Main steam piping, 3 ... Turbine, 4 ... Condenser, 7 ... Feed water pump, 10 ... Feed water piping, 12 ... Reactor pressure vessel, 13 ... Core, 14 ... Jet pump, 16, 17 DESCRIPTION OF SYMBOLS ... Hydrogen injection apparatus, 18 ... Corrosion potential sensor, 20 ... Purification system piping, 21 ... Recirculation pump, 22 ... Recirculation system piping, 27 ... Reactor water purification apparatus, 30 ... Film formation apparatus, 31 ... Surge tank, 32, DESCRIPTION OF SYMBOLS 51 ... Circulation pump, 35 ... Circulation piping, 39, 44, 45 ... Injection pump, 40, 47, 48 ... Chemical tank, 56 ... Heater, 61 ... Cooler, 63 ... Cation exchange resin tower, 65 ... Mixed bed resin Tower, 67 ... Decomposition treatment device, 79 ... pH meter, 81 ... Iron (II) ion implantation device, 82 ... Oxidant injection device, 83 ... pH adjuster injection device.

Claims (14)

When the operation of the nuclear power plant is stopped, the pH containing iron (II) ions and an oxidizing agent that oxidizes iron (II) ions to iron (III) ions is within the range of 5.5 to 9.0. A film forming liquid is brought into contact with the surface of the nuclear plant stainless steel component that contacts the reactor water to form a ferrite film on this surface .
During operation of the nuclear power plant, the corrosion potential of the constituent members is adjusted within a range of −0.2 V to +0.2 V to form a hematite film on the surface layer of the ferrite film,
Thereafter, during operation of the nuclear power plant, a first state in which the corrosion potential of the structural member is −0.5 V and a second state in which the corrosion potential of the structural member is within a range of −0.2 V to +0.2 V. It repeatedly alternately,
After the reactor power reaches the rated power, the second period in which the second state is formed is shorter than the first period in which the first state is formed. Dose reduction method. 2. The method for reducing a dose of a nuclear plant component according to claim 1 , wherein the film forming liquid brought into contact with the surface of the component is adjusted to a temperature within a range of 60 ° C. to 100 ° C. 3. By reducing than the amount of hydrogen supplied to the reactor in the first state the amount of hydrogen supplied to the nuclear reactor in the nuclear plant, according to claim 1 or the second state is generated A method for reducing the dose of nuclear plant components according to 2 . Change Previous Symbol the first state of the second state, by increasing than the amount of hydrogen supplied to the reactor the amount of hydrogen supplied to the reactor in the second state, the line A method for reducing the dose of a nuclear plant component according to claim 3 . When the first state is generated by injecting hydrogen into the nuclear reactor before the reactor temperature raising and boosting step, the hydrogen is communicated to the reactor before the reactor temperature raising and boosting step. The method for reducing the dose of nuclear plant components according to claim 3 , wherein reactor water is injected into a piping system of the nuclear power plant that guides the reactor water to the nuclear reactor. When the reactor power reaches the rated power, the reactor water is introduced to the reactor before the temperature raising and boosting step of the reactor, the injection of the hydrogen into the piping system of the nuclear power plant is stopped, and the rated power When the first state and the second state are repeatedly generated after reaching the output, hydrogen is injected into the water supply pipe connected to the reactor after a predetermined time has elapsed since the stop of the hydrogen injection. The dose reduction method of the nuclear power plant structural member of Claim 5 . When the reactor power reaches the rated power, the other piping system connected to the reactor other than the piping system that guides the reactor water to the reactor before the temperature rising / pressurizing step of the reactor, Prior to the temperature raising / pressurizing step of the nuclear reactor, hydrogen is injected with an injection amount smaller than the injection amount of the hydrogen into the piping system for introducing reactor water to the reactor, and after the hydrogen injection, the reactor is heated up. 6. The method for reducing a dose of a nuclear plant component according to claim 5 , wherein injection of the hydrogen into the piping system for guiding reactor water to the nuclear reactor is stopped before a temperature boosting step. When reactor power is generated by repeating each of the first state and the second state after upon reaching the rated output, according to claim 3 in which hydrogen is introduced into the feed water pipe connected to the reactor, 4 and 7 The method for reducing the dose of a nuclear plant component according to any one of the above. When the operation of the nuclear plant is stopped, before the formation of the ferrite film on the surface of the structural member, according to any one of claims 1 to 8 to decontaminate the surface of the structural member Of reducing the dose of nuclear plant components. When the operation of the nuclear power plant is stopped, iron (II) ions, and iron (II) ranges pH of 5.5 to 9.0 comprising an oxidizing agent that oxidizes ions to iron (III) ions The film forming liquid inside is supplied to the piping system, which is a component made of stainless steel of the nuclear power plant, through the piping equipped with a heating device and a pump,
Contacting the inner surface of the piping system with the reactor water of the piping system to form a ferrite film on the inner surface;
When the nuclear power plant is in operation, the corrosion potential of the piping system is adjusted within a range of −0.2 V to +0.2 V to form a hematite film on the surface layer of the ferrite film,
Thereafter, when the nuclear power plant is in operation, the first state in which the corrosion potential of the piping system is −0.5V and the corrosion potential of the component members are in the range of −0.2V to + 0.2V. Just repeat the two-state alternately,
After the reactor power reaches the rated power, the second period in which the second state is formed is shorter than the first period in which the first state is formed. Dose reduction method. Supply of the film forming liquid to the piping system is performed after connecting the piping to the piping system when the operation of the nuclear power plant is stopped,
After formation of the ferrite film to the inner surface of the piping system is finished, dose reduction method of a nuclear power plant components according to claim 1 0 of activating the nuclear plant by removing the pipe from the pipeline. Wherein said film-forming liquid is brought into contact with the inner surface of the pipe system, by the heating device, a nuclear power plant components according to claim 1 0 or 1 1, which is adjusted to a temperature in the range of 60 ° C. to 100 ° C. Dose reduction method. The second state is generated by reducing the amount of hydrogen supplied into the nuclear reactor during operation of the nuclear power plant from the amount of hydrogen supplied into the nuclear reactor in the first state. dose reduction method of a nuclear power plant components according to 1 0 to 1, wherein one of 1 2. The change from the second state to the first state during the operation of the nuclear power plant is that the amount of hydrogen supplied into the reactor is more than the amount of hydrogen supplied into the reactor in the second state. by increasing, dose reduction method of a nuclear power plant components according to claims 1 to 3 to be performed.

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