JP7104616B2 - Method of suppressing adhesion of radionuclides to carbon steel components of nuclear power plants - Google Patents

Description

The present invention relates to a method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant, and more particularly to a method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant suitable for application to a boiling water type nuclear power plant. ..

As nuclear power plants, for example, boiling water reactors (hereinafter referred to as BWR plants) and pressurized water reactors (hereinafter referred to as PWR plants) are known. For example, in a BWR plant, steam generated in a reactor pressure vessel (referred to as RPV) is guided to a turbine to rotate the turbine. The steam discharged from the turbine is condensed by the condenser to become water. This water is supplied to the RPV as water supply through a water supply pipe. In order to suppress the generation of radioactive corrosion products in the RPV, metal impurities contained in the water supply are removed by a filtration desalting device provided in the water supply pipe.

In BWR plants and PWR plants, the main components such as RPV use stainless steel, nickel-based alloy, or the like at the water contact portion with which water comes into contact in order to suppress corrosion. The components of the reactor purification system, residual heat removal system, reactor isolation cooling system, core spray system, water supply system, etc. are designed from the viewpoint of reducing the manufacturing cost of the plant, or the stress of stainless steel caused by high temperature water. From the viewpoint of avoiding corrosion cracks, carbon steel members are mainly used.

Further, a part of the furnace water (cooling water existing in the RPV) is purified by the reactor water purification device of the reactor purification system, and the metal impurities slightly present in the reactor water are positively removed.

However, even if the above-mentioned corrosion prevention measures are taken, the presence of a very small amount of metal impurities in the furnace water is unavoidable. Therefore, some metal impurities are contained as metal oxides in the fuel assembly. Adheres to the outer surface of. The metal elements contained in the metal impurities adhering to the outer surface of the fuel rod cause a nuclear reaction by irradiation with neutrons emitted from the nuclear fuel material in the fuel rod, and become radioactive nuclei such as cobalt-60, cobalt 58, chromium 51, and manganese 54. Become. Some radionuclides adhering to the outer surface of the fuel rods in the form of oxides elute as ions in the furnace water depending on the solubility of the incorporated oxides, and are re-introduced into the furnace water as insoluble solids called clad. It is released. Some of the radionuclides in the reactor water are removed by the reactor purification system. However, the radionuclides that have not been removed are accumulated on the surface of the structural member in contact with the furnace water while circulating in the recirculation system and the like together with the furnace water. As a result, radiation is emitted from the surface of the structural member, which causes radiation exposure of workers during regular inspection work. The exposure dose of the employee is controlled so as not to exceed the specified value for each person. However, in recent years, this regulation value has been lowered, and it has become necessary to reduce the exposure dose of each person as economically as possible.

Chemistry that removes oxide films containing radionuclides such as cobalt-60 and cobalt58 formed on the surface of pipes that come into contact with the reactor water of nuclear plant components that have experienced operation by dissolution with chemicals. A decontamination method has been proposed (Japanese Patent Laid-Open No. 2000-105295).

In addition, various methods for reducing the adhesion of radionuclides to pipes have been studied. For example, by forming a magnetite film, which is a kind of ferrite film, on the surface of the structural members of a nuclear power plant after chemical decontamination, it is possible to prevent radionuclides from adhering to the surface of the structural members after the operation of the plant. The method is proposed in JP-A-2006-38483. Further, in Japanese Patent Application Laid-Open No. 2006-38883, after forming a magnetite film on the surface of a structural member, a nuclear power plant is started, and the furnace water in which the noble metal is injected is brought into contact with the magnetite film to form a noble metal on the magnetite film. It is described that it is attached.

Japanese Patent Application Laid-Open No. 2007-182604 describes a film-forming solution in the range of 60 ° C. to 100 ° C. containing iron (II) ions, nickel ions, oxidizing agents and pH adjusters (for example, hydrazine) while the nuclear power plant is shut down. Is described in that, after chemical decontamination, the surface is brought into contact with the surface of a carbon steel structural member of a nuclear plant to form a nickel ferrite film on the surface. The formation of the nickel ferrite film suppresses the corrosion of the structural member made of carbon steel and suppresses the adhesion of radionuclides to the structural member.

Japanese Patent Application Laid-Open No. 2012-247322 states that a film-forming solution in the range of 60 ° C. to 100 ° C. containing iron (II) ions, an oxidizing agent and a pH adjuster (hydrazine) is applied to a nuclear power plant while the operation of the nuclear power plant is stopped. , It is described that the surface of a chemically decontaminated stainless steel component is brought into contact with the surface to form a magnetite film on the surface. Japanese Patent Application Laid-Open No. 2012-247322 also describes that an aqueous solution containing a noble metal (for example, platinum) is brought into contact with the formed magnetite film to adhere the noble metal onto the magnetite film while the operation is stopped.

Further, a nickel metal film is formed on the surface of the carbon steel member, which contains nickel ions, iron (II) ions, an oxidizing agent and a pH adjusting agent, has a pH in the range of 5.5 to 9.0, and has a temperature of 60. A method has been proposed in which a nickel ferrite film is formed on the surface of the nickel metal film using a film forming liquid in the range of ° C. to 100 ° C., and then the nickel metal film is converted into a nickel ferrite film with high temperature water. (For example, Japanese Patent Application Laid-Open No. 2011-32551).

Japanese Unexamined Patent Publication No. 2014-44190 describes a method for attaching a precious metal to a constituent member of a nuclear power plant. In this noble metal attachment method, in the chemical decontamination carried out while the operation of the nuclear power plant is stopped, the noble metal (for example, platinum) is applied to the surface of the stainless steel component in a state where a part of the reduction decontamination agent is decomposed. ), Or the noble metal is attached to the surface of the constituent members in the purification step after the reduction decontamination agent decomposition step. The adhesion of the noble metal to the surface of the constituent member suppresses the adhesion of the radionuclide to the surface.

Japanese Unexamined Patent Publication No. 2018-48831 describes that a nickel metal film is formed on the surface of a carbon steel member, a noble metal is attached to the surface of the nickel metal film, and oxygen is contained on the surface of the nickel metal film to which the noble metal is attached. A stable nickel-ferrite film that covers the surface of the carbon steel member and does not elute even by the action of noble metal (x in Ni _1-x Fe _{2 + x} O ₄ ) It is described that it is converted to a nickel ferrite film (0).

Japanese Unexamined Patent Publication No. 2000-105295 Japanese Unexamined Patent Publication No. 2006-38483 JP-A-2007-182604 Japanese Unexamined Patent Publication No. 2012-247322 Japanese Unexamined Patent Publication No. 2011-32551 Japanese Unexamined Patent Publication No. 2014-44190 Japanese Unexamined Patent Publication No. 2018-48831

In a nuclear power plant, in order to reduce the radiation exposure of workers, a technique for suppressing the adhesion of radionuclides to structural materials is desired, and the adhesion of radionuclides to carbon steel members is also suppressed, and the effect of suppressing the adhesion is long-term. It is hoped that it will last for a long time.

An object of the present invention is to provide a method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant, which can further suppress the adhesion of radionuclides to carbon steel members of a nuclear power plant.

A feature of the present invention that achieves the above object is that a film-forming liquid containing nickel ions and a reducing agent is brought into contact with the first surface of a carbon steel member of a nuclear power plant to form a nickel metal film on the first surface. A noble metal is attached to the second surface of the nickel metal film, a nuclear plant is started, and the first surface of the nickel metal film is brought into contact with furnace water having a temperature within the range of 130 ° C. or higher and 330 ° C. or lower. Is to make the corrosion potential of the carbon steel member 0 mV or more by injecting.

According to the present invention, the second surface of the nickel metal film to which the noble metal is attached, which is formed on the first surface of the carbon steel member, is brought into contact with the furnace water having a temperature within the range of 130 ° C. or higher and 330 ° C. or lower. By injecting oxygen into the carbon steel member to raise the corrosion potential of the carbon steel member to 0 mV or more, nickel ferrite crystals having a large particle size are contained in the nickel ferrite film formed on the first surface of the nickel ferrite. The density of nickel ferrite crystal grain boundaries in the film is further reduced. Therefore, the adhesion of radionuclides (for example, Co-60) to the carbon steel member is further suppressed.

(A1) A film-forming liquid containing nickel ions and a reducing agent is brought into contact with the first surface of a carbon steel member of a nuclear power plant to form a nickel metal film on the first surface, and a noble metal is formed on the second surface of the nickel metal film. The carbon steel member is made by contacting the second surface of the nickel metal film with furnace water at a temperature within the range of 130 ° C or higher and 330 ° C or lower, and injecting an oxidizing agent into the furnace water. A more preferable method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear power plant having a corrosion potential of 0 mV or more will be described below.

(A2) Preferably, in the above (A1), when the period for injecting the oxidizing agent into the furnace water elapses, the corrosion potential of the carbon steel member is reduced to less than 0 mV by injecting hydrogen into the furnace water. It is desirable to do.

(A3) Preferably, in the above (A2), it is desirable to set the corrosion potential of the carbon steel member within the range of −300 mV or less and −500 mV or more by injecting hydrogen.

According to the present invention, the adhesion of radionuclides to carbon steel members of a nuclear power plant can be further suppressed.

It is a flowchart which shows the procedure of the method of suppressing the adhesion of a radionuclide to the structural member of the nuclear power plant of Example 1 applied to the purification system piping of the boiling water type nuclear power plant which is a preferable example of this invention. It is explanatory drawing which shows the state which connected the noble metal injection apparatus used when carrying out the method of suppressing the adhesion of a radionuclide to the structural member of the nuclear power plant of Example 1 to the purification system pipe of a boiling water type nuclear power plant. It is a detailed block diagram of the precious metal injection apparatus shown in FIG. It is sectional drawing of the purification system piping of a boiling water type nuclear power plant before the method of suppressing the adhesion of a radionuclide to the structural member of a nuclear power plant shown in FIG. 1 is started. It is explanatory drawing which shows the state which the nickel metal film was formed on the inner surface of the purification system pipe by the method of suppressing the adhesion of a radionuclide to the structural member of a nuclear power plant shown in FIG. Explanatory drawing showing a state in which noble metal particles containing nickel metal are attached to the surface of a nickel metal film formed on the inner surface of a purification system pipe by the method of suppressing the adhesion of radionuclides to the structural members of a nuclear power plant shown in FIG. Is. It is explanatory drawing which shows the state which brings the furnace water which has the temperature in the temperature range of 130 degreeC or more and 330 degreeC or less into contact with the nickel metal film which adhered the noble metal formed on the inner surface of a purification system pipe. It is explanatory drawing which shows typically the state of the nickel ferrite film when the nickel metal film which adhered the noble metal formed on the inner surface of a purification system pipe is converted into nickel ferrite in the low potential environment water quality. It is explanatory drawing which shows typically the state of the nickel ferrite film when the nickel metal film which adhered the noble metal formed on the inner surface of a purification system pipe is converted into nickel ferrite by the high potential environmental water quality. It is explanatory drawing which compared the Co-60 adhesion rate by the difference of the conversion water quality condition of the nickel metal film to which the noble metal adhered to the nickel ferrite film. On the surface of each test piece after the Co-60 adhesion test in which simulated furnace water containing Co-60 is brought into contact with each of the polished carbon steel test piece and the carbon steel test piece having a nickel metal film to which a noble metal is attached. It is explanatory drawing which shows the laser Raman spectrum analysis result of the formed film. It is a characteristic figure which shows the relationship between the pH of the film-forming aqueous solution which comes into contact with the surface of a carbon steel test piece, and the amount of a nickel metal film formed on the surface of a carbon steel test piece. It is a characteristic diagram which shows the relationship between the concentration of formic acid to be injected into a film-forming aqueous solution and the concentration of ammonia, with the pH of the film-forming aqueous solution as a parameter. It is explanatory drawing which shows the method of suppressing the adhesion of a radionuclide to the structural member of the nuclear power plant of Example 2 applied to the purification system piping of the boiling water type nuclear power plant which is another preferable example of this invention.

As described in JP-A-2018-48831, a ferrite film is applied to the surface of the structural member of a nuclear power plant by the methods described in JP-A-2006-38483 and JP-A-2012-247322. When a magnetite film, which is a kind of magnetite film, is formed, there arises a problem that the formed magnetite film is eluted into the furnace water by the action of the attached noble metal. At the end of the operation cycle in which the ferrite film disappears due to the elution of the ferrite film formed on the surface of the carbon steel member, the effect of suppressing the adhesion of radionuclides by the ferrite film disappears, so the operation of the nuclear plant in this operation cycle is stopped. After that, it is necessary to form a ferrite film again on the surface of the carbon steel member. The reason why the ferrite film formed on the surface of the carbon steel member elutes due to the action of the noble metal attached is described in paragraph 0036 of JP-A-2018-48831. The nickel ferrite film that elutes into the furnace water due to the action of the attached noble metal is an unstable nickel ferrite film (a nickel ferrite film in which x is, for example, 0.3 in Ni _1-x Fe _{2 + x} O ₄ ). That is, Ni _0.7 Fe _2.3 O ₄ film).

In order to solve such a problem, in Japanese Patent Application Laid-Open No. 2018-48831, a nickel metal film is formed on the surface of a carbon steel member, a noble metal is attached to the surface of the nickel metal film, and nickel to which the noble metal is attached. The surface of the metal film is brought into contact with water containing oxygen and having a temperature in the temperature range of 200 ° C. or higher and 330 ° C. As a result, the nickel metal film covers the surface of the carbon steel member and is a stable nickel ferrite film that does not elute even by the action of the adhered noble metal (x in Ni _1-x Fe _{2 + x} O ₄ is 0, for example. It is converted into a certain nickel ferrite film, that is, a NiFe ₂ O ₄ film) (see paragraphs 0037 to 0040 of JP-A-2018-48831). Due to the stable nickel ferrite film covering the surface of the carbon steel member, the effect of suppressing the adhesion of radionuclides to the carbon steel member can be maintained for a longer period of time.

The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant described in JP-A-2018-48831 suppresses the adhesion of radionuclides to the carbon steel members. However, the inventors have conducted various studies with the aim of realizing measures that can further suppress the adhesion of radionuclides to the carbon constituents of a nuclear power plant than the adhesion suppression method described in JP-A-2018-48831. gone. As a result, the inventors have found an effective method capable of further suppressing the adhesion of radionuclides to carbon constituents. The results of this study will be described below.

It is desirable to form a nickel metal film on the cooling water of the carbon steel member of the nuclear plant, that is, the surface in contact with the furnace water, following the chemical decontamination of the surface. The advantage of this is that the functions of heating, injecting, circulating and purifying the chemical solution used in chemical decontamination can be utilized for the formation of the nickel metal film. Nickel formate was used as the chemical used, as formic acid that can be decomposed into water or carbon dioxide was used as the counter anion of nickel. When the carbon steel is immersed in an aqueous solution of nickel formate, a substitution plating reaction represented by the following formula (1) occurs to form a nickel metal film on the surface of the carbon steel.

Fe + Ni ²⁺ → Fe ²⁺ + Ni… (1)
Furthermore, when a reducing agent is injected into the nickel formate aqueous solution, nickel ions are reduced to nickel metal by the action of the reducing agent, and this nickel metal is deposited on the surface of carbon steel. When, for example, hydrazine is used as the reducing agent, a nickel metal is produced on the surface of carbon steel by the reaction represented by the formula (2).

2 Ni ²⁺ + N ₂ H ₄ → Ni + N ₂ + 2H ⁺ + H ₂ … (2)
In this way, after forming a nickel metal film on the surface of the carbon steel member of the nuclear power plant that has been shut down, hexahydroxoplatinic acid in a platinum aqueous solution containing hydrazine, which is a reducing agent, on the surface of the nickel metal film. The aqueous sodium solution is brought into contact to attach platinum to the surface of the nickel metal film. After that, the nuclear plant is restarted, and hydrogen is injected into the reactor water of the nuclear plant for the purpose of suppressing stress corrosion cracking. By injecting hydrogen, furnace water of corrosive environment mitigation water quality that lowers the corrosion potential of the member in contact with the furnace water to -230 mV or less is generated. When the furnace water containing hydrogen of this corrosive environment mitigation water quality is brought into contact with the nickel metal film formed on the surface of the carbon steel member and to which platinum is adhered, the carbon steel member and the nickel metal film are formed by the action of platinum and hydrogen. The corrosion potential of the steel drops to about -500 mV. In such a corrosive environment, the oxidation reaction by oxygen contained in the high temperature (temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower) in contact with the nickel metal film, and the carbon steel which is the base material of the carbon steel member. Due to the action of iron ions formed by the oxidation reaction of, the reaction represented by the following formula (3) occurs, and the above nickel metal film is converted to a stable nickel ferrite film that does not elute even by the action of attached platinum. Will be done.

2Ni + 2Fe + 2O ₂ → NiFe ₂ O ₄ … (3)
This stable nickel ferrite film contributes to the suppression of adhesion of radionuclides (for example, Co-60). However, the inventors conducted the following experiments in order to find a method for further enhancing the Co-60 adhesion suppressing effect of the nickel ferrite film. In this experiment, the conversion of the nickel metal film to the nickel ferrite film was carried out in a high corrosion potential environment of 0 mV or more, not in a low corrosion potential environment of −500 mV. In that experiment, the inventors used carbon steel polishing test pieces as test pieces A and C, and formed a nickel metal film on the surface of the carbon steel polishing test pieces as test pieces B and D. A test piece having platinum adhered to the surface of this film was used.

The Co-60 adhesion experiment using each test piece will be specifically described. In the Co-60 adhesion experiment using test pieces A and B, test pieces A and B were installed in a closed-loop circulation pipe, and the circulation pipe contained Co-60 simulating the reactor water in the reactor. Simulated water was circulated. The test pieces A and B were immersed in simulated water in the circulation pipe. For the test pieces A and B, simulated water having a temperature of 280 ° C., which is a corrosive environment mitigating water in which dissolved hydrogen is present, is used as simulated water, and this simulated water is circulated in the circulation pipe to form a circulation pipe. An environment with a low corrosion potential of −500 mV was created, and a Co-60 adhesion experiment was conducted in this environment.

In this Co-60 adhesion experiment, the immersion time of each of the test pieces A and B in the simulated water flowing in the circulation pipe was set to 500 hours, 1000 hours, and 1500 hours. Therefore, each of the test pieces A and B is used three times corresponding to three different immersion times. Each time the immersion time of 500 hours, 1000 hours, and 1500 hours passed, the test pieces A and B were taken out from the circulation pipe one by one, and the amount of Co-60 adhered to each of the taken out test pieces was measured. The average Co-60 adhesion rate for _each of the test pieces A and B in the _{time intervals} t1, t2 and t3, based on the amount of Co-60 adhered to each of the test pieces A and B at each immersion time. Asked. The time interval t ₁ is 0 hours <t ₁ ≤ 500 hours, the time interval t ₂ is 500 hours <t ₂ ≤ 1000 hours, and the time interval t ₃ is 1000 hours <t ₃ ≤ 1500 hours.

On the other hand, also in the Co-60 adhesion experiment using the test pieces C and D, each of the test pieces C and D is immersed in the above-mentioned simulated water at 280 ° C. containing Co-60, which circulates in the circulation pipe. In the Co-60 adhesion experiment using the test pieces C and D, in the first 500 hours, simulated water (normally in-core water quality environment (NWC)) with dissolved oxygen and no dissolved hydrogen was used. Using a temperature of 280 ° C.), an environment was created in which the circulation pipe had a high corrosion potential within the range of 0 mV or more and + 200 mV or less, and a Co-60 adhesion experiment was conducted in this environment. When the first 500 hours have passed, hydrogen is injected into the simulated water circulating in the circulating pipe, and the simulated water of the corrosive environment mitigation water containing 100 ppb of oxygen and 40 ppb of hydrogen causes the circulating pipe to have a low corrosion potential of -500 mV. An environment was generated, and a Co-60 adhesion experiment was performed on the test pieces C and D in this environment. The immersion time for immersing each of the test pieces C and D in the simulated water of the corrosive environment mitigation water quality was 1000 hours and 1500 hours.

Each time the immersion time of 500 hours, 1000 hours, and 1500 hours passed, the test pieces C and D were taken out from the circulation pipe one by one, and the amount of Co-60 adhered to each of the taken out test pieces was measured. Average Co-60 adhesion rate for _each of the test pieces _C and D in the time _intervals t1, t2 and t3 based on the amount of Co-60 adhered to each of the test pieces C and D at each immersion time. Asked.

The Co-60 adhesion rate for each of the test pieces A, B, C and D is shown in FIG. As is clear from FIG. 10, in the test pieces B and D in which a nickel metal film was formed on the surface and platinum was adhered to the surface of the nickel metal film, the nickel metal film was not formed on the surface and platinum also adhered to the surface. The adhesion rate of Co-60, that is, the adhesion amount of Co-60 was significantly reduced as compared with the test pieces A and C which were not used.

Then, the composition on each surface of the test pieces A, B, C and D taken out from the circulation pipe was analyzed by Raman spectroscopy. The analysis result is shown in FIG. A film mainly composed of Fe ₃ O ₄ was formed on the surfaces of the test pieces A and C, which are substantially carbon steel. An oxide film containing nickel ferrite (NiFe ₂ O ₄ ) as a main component was formed on the surfaces of the test pieces B and D in which the amount of Co-60 adhered was significantly reduced. This Ni Fe ₂ O ₄ has a form in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ .

The Co-60 adhesion rate for each of the test pieces A, B, C and D will be specifically described with reference to FIG. Comparing the polishing test piece A immersed only in the simulated water of the corrosive environment mitigation water quality and the test piece B having the nickel metal film formed, the test piece B is more than the test piece A in the time intervals t ₂ and t ₃ . The Co-60 adhesion rate becomes low. Comparing the difference in the adhesion rates between the test piece B and the test piece A, the difference becomes smaller as the time elapses from the time interval t ₂ to the time interval t ₃ . On the other hand, in the time interval t ₁ in which each of the polishing test piece C and the test piece D on which the nickel metal film is formed is immersed in the simulated water of the corrosive environment forming water quality, the respective Co-60 adhesion rates are the same. When the immersion time elapses more than the time interval t ₁ and reaches the time interval t ₂ , the Co-60 adhesion rate of the test piece D drops sharply and becomes almost the same as that of the test piece B, and the time interval t ₃ Then, the Co-60 adhesion rate of the test piece D becomes smaller than that of the test piece B because the Co-60 adhesion rate of the test piece B increases.

Since the nickel metal film formed on each of the test pieces B and D comes into contact with simulated water at 280 ° C., the nickel metal film is converted into a stable nickel ferrite film.

As a result, the inventors formed a nickel metal film on the surface of the carbon steel member, and then contacted the surface of the nickel metal film with the furnace water of the corrosive environment mitigation water quality from the beginning. By first contacting the film with the furnace water of the corrosive environment forming water quality and then contacting the furnace water of the corrosive environment mitigation water quality, the nickel metal film is effective in suppressing the adhesion of radioactive nuclei over a longer period of time. It was found that it can be converted into a stable nickel ferrite film.

A nickel metal film is formed on the surface, and the nickel metal film of the carbon steel member (test pieces B and D) having a noble metal (for example, platinum) adhered to the surface of the nickel metal film is 130 ° C. or higher and 330 ° C. or lower containing oxygen. A stable nickel ferrite film covering the surface of the carbon steel member (0 ≤ x in Ni _1-x Fe _{2 + x} O ₄ ) that does not elute due to the action of the adhered noble metal due to contact with water at a temperature within the temperature range of The reason for conversion to nickel ferrite satisfying <0.3, for example, NiFe ₂ O ₄ ) will be described.

Corrosion of water having a temperature in the temperature range of 130 ° C. or higher and 330 ° C. or lower, which is generated by injection of oxygen (oxidizing agent) and makes the corrosion potential of the carbon steel member within the range of 0 mV or more + 200 mV or less. When the water of the environment-forming water quality comes into contact with the nickel metal film formed on the surface of the carbon steel member, the nickel metal film formed on the surface of the carbon steel member is formed, for example, in Ni _1-x Fe _{2 + x} O ₄ . It is converted to a stable nickel ferrite film in which x is 0. Specifically, the nickel metal film and the carbon steel member are heated to 130 ° C. or higher by the water of the corrosive environment forming water quality. Oxygen contained in the water moves into the nickel metal film, and Fe contained in the carbon steel member becomes Fe ²⁺ and moves into the nickel metal film. Nickel in the nickel metal film reacts with oxygen and Fe ²⁺ transferred into the nickel metal film in a high temperature environment of 130 ° C. or higher, and noble metals such as platinum adhering to the surface of the nickel metal film and carbon steel members Corrosion environment formation that makes the corrosion potential within the range of 0 mV or more and + 200 mV or less Due to the action of water in the water quality, the nickel metal film is stable with x being 0 in, for example, Ni _1-x Fe _{2 + x} O ₄ . Converted to a good nickel ferrite film. This stable nickel-ferrite film covers the surface of the carbon steel member.

By the way, the unstable nickel ferrite that elutes due to the action of the noble metal adhering to the surface is a nickel ferrite that satisfies 0.3 ≦ x <0 in Ni _1-x Fe _{2 + x} O ₄ , for example, Ni _0.7 Fe _2.3 O. It is ₄ . As described above, Ni _0.7 Fe _2.3 O ₄ is nickel ferrite having x of 0.3 in Ni _1-x Fe _{2 + x} O ₄ .

In Ni _1-x Fe _{2 + x} O ₄ produced as described above from the nickel metal contained in the nickel metal film covering the surface of the carbon steel member in a high temperature environment of 130 ° C. or higher, x is 0. A certain nickel ferrite has a large crystal growth, and even if a noble metal adheres to it, it is stable without being eluted in water like a Ni _0.7 Fe _2.3 O ₄ film. The inventors have found that in a stable nickel ferrite film, the density of grain boundaries decreases due to the enlargement of nickel ferrite crystals, and the diffusion of radionuclides such as Co-60 through the grain boundaries into the nickel ferrite film. I thought it was suppressed. As described above, the stable nickel ferrite film formed from the nickel metal covering the surface of the carbon steel member in a high temperature environment of 130 ° C. or higher is Ni produced in a low temperature range of 60 ° C. to 100 ° C. It is possible to suppress the adhesion of radioactive nuclei to carbon steel members for a longer period of time than the _0.7 Fe _2.3 O ₄ film.

In addition, even in the prior application, Japanese Patent Application No. 2018-49244 (application date: March 16, 2018), the specification states that "from the nickel metal contained in the nickel metal film covering the surface of the carbon steel member, 130 Nickel ferrite in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ produced as described above in a high temperature environment in the temperature range of ° C. or higher and 330 ° C. or lower has large crystal growth. (See paragraph 0064, lines 2-4), the stable nickel ferrite crystals converted from nickel metal become larger, and the adhesion of radioactive nuclei to the carbon steel member can be suppressed.

However, the present invention is not implemented in Japanese Patent Application No. 2018-49244, "Injection of an oxidizing agent (for example, oxygen) into the furnace water during the operation of the BWR plant 1 before hydrogen injection into the furnace water". Is carried out to set the corrosion potential of the carbon steel member within the range of 0 mV or more and + 200 mV or less. Therefore, in the present invention, nickel ferrite crystals contained in the stable nickel ferrite generated from the nickel metal film are formed. It is larger than the stable nickel ferrite crystal produced in Japanese Patent Application No. 2018-49244. Therefore, in the present invention, the grain boundary density per unit volume in the stable nickel ferrite film is further lower than the grain boundary density in Japanese Patent Application No. 2018-49244, and the radionuclide adheres to the carbon steel member. It is further suppressed than its adhesion in Japanese Patent Application No. 2018-49244.

The effect of reducing the rate of attachment of radionuclides to carbon steel members, that is, the effect of suppressing the attachment of radionuclides to carbon steel members in Japanese Patent Application No. 2018-49244 is the effect of suppressing the attachment of radionuclides to the carbon steel member, which is obtained by the test piece B shown in FIG. Corresponds to the suppression effect. On the other hand, the effect of suppressing the adhesion of radionuclides to the carbon steel member in the present invention corresponds to the effect of suppressing the adhesion of radionuclides obtained in the test piece D shown in FIG. The longer the contact time of the furnace water with the stable nickel ferrite film formed on the surface of the carbon steel member, the more the effect of suppressing the adhesion of radionuclides to the carbon steel member is obtained in the present invention. It will be larger than 49244.

Based on the above-mentioned examination results, the inventors were able to newly create the invention described below. That is, the inventors bring a film-forming aqueous solution containing nickel ions and a reducing agent into contact with the surface of the carbon steel member to form a nickel metal film on the surface of the carbon steel member, and attach the noble metal to the surface of the nickel metal film. It has a temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower including oxygen, and the corrosion potential of the carbon steel member generated by injection of the oxidizing agent is 0 mV or higher (specifically, the range of 0 mV or higher + 200 mV or lower). By contacting the water of the corrosive environment formation water quality to make it the inner corrosion potential) with the nickel metal film on which the noble metal adheres to the surface, as a result, stable nickel ferrite with a large particle size (for example, NiFe ₂ O ₄ ) Crystals will be contained in the stable nickel ferrite film converted from the nickel metal film, and the density of the nickel ferrite crystal grain boundaries of this nickel ferrite film will be further reduced. I came up with a new method of suppressing adhesion. As is clear from the comparison between the adhesion rate of Co-60 of the test piece B and the adhesion rate of Co-60 of the test piece D in the time interval t ₃ shown in FIG. 10, the corrosion potential of the carbon steel member is 0 mV or more. Due to a new method of suppressing the adhesion of the radioactive nuclei, the water of the corrosive environment forming water that makes the corrosion potential within the range of +200 mV or less is formed on the surface of the carbon steel member and is brought into contact with the nickel metal film to which the noble metal is attached. For example, a nickel metal film is formed on the surface of a carbon steel member, precious gold (for example, platinum) is adhered to the surface of the nickel metal film, and dissolved hydrogen is present on the nickel metal film. Compared with the case where water having a temperature of 280 ° C. is brought into contact with the material (test piece B), the adhesion of radioactive nuclei to the carbon steel member can be remarkably suppressed.

Further, as described above, the water of the corrosive environment forming water quality that makes the corrosion potential of the carbon steel member within the range of 0 mV or more + 200 mV or less is formed on the surface of the carbon steel member and the noble metal is attached to the nickel. When contacting with the metal film, the corrosion potential of the carbon steel member is set to a corrosion potential within the range of 0 mV or more + 200 mV or less. Even if the carbon steel member is brought into contact with a corrosion potential in the range of -300 mV to -500 mV (-300 m or less and -500 mV or more), for example, water having a corrosive environment mitigation water quality of -500 mV. The stable nickel ferrite film formed on the surface is maintained on the surface for a longer period of time, and the adhesion of radioactive nuclei to the carbon steel member can be effectively suppressed for a long period of time. By setting the corrosion potential of the carbon steel member to −300 mV or less, the occurrence of stress corrosion cracking in the stainless steel member of the nuclear power plant can be remarkably suppressed.

Further, in order to investigate the amount of the nickel metal film formed on the surface of the carbon steel by each reaction of the formulas (1) and (2), a test piece made of carbon steel is immersed in a nickel formate aqueous solution at 90 ° C. and immersed. When 60 minutes have passed from the start, the first case in which the test piece was taken out from the nickel formate aqueous solution and another carbon steel test piece were immersed in the nickel formate aqueous solution, and 60 minutes had passed from the start of immersion. Injecting hydrazine (reducing agent) into the nickel formate aqueous solution in which the test piece is immersed, and immersing the test piece immersed in the formic acid aqueous solution containing hydrazine for 4 hours from the start of immersion in the formic acid aqueous solution containing hydrazine. The amount of nickel metal film formed on each test piece was compared for each case of the second case taken out from the formic acid aqueous solution containing hydrazine.

As a result, in the first case in which the test piece was taken out from the nickel formate aqueous solution before the injection of hydrazine and only the reaction of the formula (1) occurred, the amount of the nickel metal film formed on the test piece was the amount of formic acid injected with hydrazine. It was confirmed that the amount of the nickel metal film formed on the test piece reached about 80% in the second case in which the reactions of the formulas (1) and (2) occurred when the test piece was taken out from the nickel aqueous solution. Therefore, it was found that the substitution plating reaction of the formula (1) has a great influence on the formation of the nickel metal film on the carbon steel member, and the substitution plating reaction is important.

Next, when the pH dependence of the film-forming aqueous solution of the substitution plating reaction of the formula (1) was examined, the pH of the film-forming aqueous solution containing nickel formate was 4.0, and the amount of nickel metal film formed on the carbon steel member was maximum. I found a tendency to become. The pH-dependent result of the amount of nickel metal film formed is shown in FIG. As is clear from FIG. 12, the amount of the nickel metal film formed on the surface of the carbon steel member is in the range of 3.9 to 4.2 (3.9 or more and 4.2 or less) in the pH of the film-forming aqueous solution. Since the efficiency of the substitution plating reaction between the iron in the carbon steel member and the nickel ions contained in the film-forming aqueous solution is increased, the amount is 80% or more of the maximum value. Therefore, in order to form the nickel metal film on the surface of the carbon steel member, it is preferable to control the pH of the film-forming aqueous solution in the range of 3.9 or more and 4.2 or less.

In order to control the pH of the film-forming aqueous solution in the range of 3.9 or more and 4.2 or less, a pH buffer solution has attracted attention, and the pH of the film-forming aqueous solution is adjusted together with the pH adjustment of the film-forming aqueous solution by the nickel formate aqueous solution. Injection of a buffer solution was considered. A pH buffer solution is a mixed solution of a weak acid and a weak base, and is a solution that is not significantly affected by the acid or base added even when diluted or externally added, and the hydrogen ion concentration (pH) does not change so much. Is. Examples of such a pH buffer solution include a mixed solution of formic acid contained in nickel formate, which is a weak acid, and ammonia, which is easy to handle for a weak base. Each of the weak acid and the weak base is a component of the pH buffer solution. For example, in a mixed solution of formic acid and ammonia, which is an example of a pH buffer solution, each of formic acid and ammonia is a component of the pH buffer solution. It can be said that the pH buffer solution contains one kind of component each of an acid and a base. By injecting the pH buffer solution into the film-forming aqueous solution, the pH of the film-forming aqueous solution can be kept constant at a certain value, for example, in the range of 3.9 or more and 4.2 or less. Further, as another example of the pH buffer solution, there is a mixed solution of acetic acid and ammonia. Formic acid and acetic acid contained in the pH buffer solution can be decomposed by the action of a catalyst and an oxidizing agent.

By using a mixed solution of formic acid and ammonia as the pH buffer solution, the concentrations of formic acid and ammonia are calculated when the pH of the film-forming aqueous solution is set to 4.0. When the nickel concentration of nickel formate is, for example, 200 ppm, the formic acid concentration associated with the nickel concentration is about 400 ppm. Therefore, in order to provide pH buffering property when injecting nickel formate in a mixed solution of formic acid and ammonia (pH buffering solution), the concentration of formic acid in the mixed solution must be at least higher than the concentration of formic acid associated with nickel formate. There is. In the above mixed solution, for example, when double 800 ppm of formic acid is used, the concentration of ammonia required to bring the pH of the film-forming aqueous solution to 4.0 can be calculated as follows. The acid dissociation reaction formula and the acid dissociation equilibrium formula of formic acid are expressed as the formulas (4) and (5), respectively.

HCOOH → H ⁺ + HCOO ^－ …… (4)

Here, K _F is the acid dissociation multiplier of formic acid, [H ⁺ ] is the hydrogen ion concentration of the film-forming aqueous solution, [HCOO- ^] is the formic acid ion concentration of the film-forming aqueous solution, and [HCOOH] is the formic acid concentration of the film-forming aqueous solution. be.

The total concentration of formic acid [HCOOH] _T is represented by the formula (6).

[HCOOH] _T = [HCOOH] + [HCOO- ^] …… (6)
The acid dissociation reaction formula and the acid dissociation equilibrium formula of ammonia are represented by the formulas (7) and (8), respectively.

NH ₄ ⁺ → H ⁺ + NH ₃ …… (7)

Here, _KA is the acid dissociation multiplier of ammonia, [NH ₃ ] is the ammonia concentration of the film-forming aqueous solution, and [NH ₄₊ ^] is the ammonia ion concentration of the film-forming aqueous solution.

The total concentration of ammonia [NH ₃ ] _T is expressed by the formula (9).

[NH ₃ ] _T = [NH ₃ ] + [NH ₄ ⁺ ] …… (9)
When the ionic product of water K _W is expressed as K _W = [H ⁺ ] [OH- ^] , the ion equilibrium equation is expressed by equation (10). [OH- ^] is the hydroxide ion concentration.

[H ⁺ ] + [NH ₄ ⁺ ] = [OH- ^] + [HCOO- ^] …… (10)
Relationship between [NH ₄ ⁺ ], [OH- ^] , and [HCOO- ^] of equation (10), equation (5), equation (6), equation (8), equation (9), and ionic product of water K _W When arranged using, equation (11) is obtained.

With K _F = 1.12 × 10 ^-4 , KA = 2.43 × 10 ^-8 , and K _W = _5.379 × 10 ^-13 , the total concentration of formic acid [HCOOH] _T is 800 ppm (17.4 mmol / L). ), The total ammonia concentration [NH ₃ ] _T when the pH of the film-forming aqueous solution is 4.0 is 156 ppm. Similarly, the total concentration of ammonia [NH ₃ ] _T in the range of 400 ppm to 1600 ppm of total formic acid concentration when the pH of the film-forming aqueous solution was 4.0 was determined. The relationship between the formic acid concentration and the obtained ammonia concentration when the pH of the film-forming aqueous solution is 4.0 is shown by a solid line in FIG. Similarly, in FIG. 13, the relationship between the formic acid concentration and the ammonia concentration when the pH of the film-forming aqueous solution is 3.9 is shown by a dash-dotted line, and the relationship between the formic acid concentration and the ammonia concentration when the pH of the film-forming aqueous solution is 4.2 is shown. The relationships are shown by broken lines. According to FIG. 13, the respective concentrations of formic acid and ammonia required for pH 3.9 to pH 4.2 may be the concentrations in the region sandwiched between the alternate long and short dash line (pH 3.9) and the broken line (pH 4.2). You can see that.

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

The method of adhering the nickel metal film and the noble metal to the carbon steel member of the nuclear power plant of Example 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. 1, 2 and 3. The method of adhering noble metal to the carbon steel member of the nuclear power plant of this embodiment is applied to a carbon steel purification system pipe (carbon steel member) of a boiling water reactor (BWR plant).

The schematic configuration of this BWR plant 1 will be described with reference to FIG. The BWR plant 1 includes a reactor 2, a turbine 9, a condenser 10, a recirculation system, a reactor purification system, a water supply system, and the like. The reactor 2 has a reactor pressure vessel (hereinafter referred to as RPV) 3 containing the core 4, and is formed between the outer surface of the core shroud (not shown) surrounding the core 4 and the inner surface of the RPV 3 in the RPV 3. A plurality of jet pumps 5 are installed in the annular down-comb. A large number of fuel assemblies (not shown) are loaded in the core 4. The fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material.

The recirculation system includes a stainless steel recirculation system pipe 6 and a recirculation pump 7 installed in the recirculation system pipe 6. In the water supply system, a condensate pump 12, a condensate purification device (for example, a condensate desalting device) 13, a low pressure water supply heater 14, a water supply pump 15, and a high pressure water supply are connected to a water supply pipe 11 connecting the condenser 10 and the RPV 3. The heater 16 is installed in this order from the condenser 10 toward the RPV3. The hydrogen injection device 28 is connected to the water supply pipe 11 between the water recovery pump 12 and the water recovery purification device 13 by a hydrogen injection pipe 29 provided with an on-off valve 99. In the reactor purification system, the purification system pump 19, the regenerated heat exchanger 20, the non-regenerated heat exchanger 21, and the reactor water purification device 22 are connected to the purification system pipe 18 connecting the recirculation system pipe 6 and the water supply pipe 11 in this order. It is installed. The purification system pipe 18 is connected to the recirculation system pipe 6 upstream of the recirculation pump 7. The reactor 2 is installed in the reactor containment vessel 27 arranged in the reactor building (not shown). Then, the oxidant injection device 25 is purified by the oxidant injection pipe 26 provided with the on-off valve 98 at a position as close to the valve 23 as possible between the valve 23 installed in the purification system pipe 18 and the purification system pump 19. It is connected to the system pipe 18.

The cooling water in the RPV 3 (hereinafter referred to as furnace water) is boosted by the recirculation pump 7 and ejected into the jet pump 5 through the recirculation system pipe 6. The furnace water existing around the nozzle of the jet pump 5 in the downkama is also sucked into the jet pump 5 and supplied to the core 4. The reactor water supplied to the core 4 is heated by the heat generated by the nuclear fission of the nuclear fuel material in the fuel rods, and a part of the heated reactor water becomes steam. This steam is guided from the RPV 3 to the turbine 9 through the main steam pipe 8 to rotate the turbine 9. A generator (not shown) connected to the turbine 9 rotates to generate electric power. The steam discharged from the turbine 9 is condensed by the condenser 10 to become water. This water is supplied into the RPV 3 as water supply through the water supply pipe 11. The water supply flowing through the water supply pipe 11 is boosted by the recovery pump 12, impurities are removed by the recovery water purification device 13, and the pressure is further boosted by the water supply pump 15. The water supply is heated by the low-pressure feed water heater 14 and the high-pressure feed water heater 16 and guided into the RPV3. The bleed steam extracted from the turbine 9 in the bleed pipe 17 is supplied to the low-pressure feed water heater 14 and the high-pressure feed water heater 16 as heating sources for the feed water, respectively.

A part of the furnace water flowing in the recirculation system pipe 6 flows into the purification system pipe 18 by driving the purification system pump 19, is cooled by the regenerated heat exchanger 20 and the non-regenerated heat exchanger 21, and then is cooled in the furnace. It is purified by the water purification device 22. The purified furnace water is heated by the regenerative heat exchanger 20 and returned to the RPV 3 via the purification system pipe 18 and the water supply pipe 11.

In the method for suppressing the adhesion of radionuclides to the carbon steel member of the nuclear power plant of this embodiment, the film forming apparatus 30 is used, and as shown in FIG. 2, the film forming apparatus 30 is attached to the purification system pipe 18 of the BWR plant. Be connected.

The detailed configuration of the film forming apparatus 30 will be described with reference to FIG.

The film forming apparatus 30 includes a surge tank 31, circulation pumps 32 and 33, a circulation pipe 34, a nickel ion injection device 35, a reducing agent injection device 40, a platinum ion injection device 45, a heater 51, a cooler 52, and a cation exchange resin tower. 53, a mixed bed resin tower 54, a decomposition device 55, an oxidant supply device 56, an ejector 61, and a buffer solution injection device 81 are provided.

The on-off valve 62, the circulation pump 33, the valves 63, 66, 69 and 74, the surge tank 31, the circulation pump 32, the valve 77 and the on-off valve 78 are provided in the circulation pipe 34 in this order from the upstream. The pipe 65 that bypasses the valve 63 is connected to the circulation pipe 34, and the valve 64 and the filter 50 are installed in the pipe 65. A cooler 52 and a valve 67 are installed in the pipe 68 which bypasses the valve 66 and is connected to the circulation pipe 34 at both ends. The valve 96, the cation exchange resin tower 53, and the valves 70 and 95 are installed in this order from the upstream in the pipe 71 whose both ends are connected to the circulation pipe 34 and bypass the valve 69. The mixed bed resin tower 54 and the valve 72 are installed in the pipe 73 whose both ends are connected to the pipe 71 and bypass the cation exchange resin tower 53 and the valve 70. Specifically, the upstream end of the pipe 73 is connected to the pipe 71 between the valve 96 and the cation exchange resin tower 53, and the downstream end of the pipe 73 is connected to the pipe 71 between the valve 70 and the valve 95. The cation exchange resin tower 53 is filled with a cation exchange resin, and the mixed bed resin tower 54 is filled with a cation exchange resin and an anion exchange resin.

The pipe 76 in which the valve 75 and the disassembling device 55 located downstream of the valve 75 are installed is connected to the pipe 73 downstream of the valve 72, and is connected to the circulation pipe 34 between the surge tank 31 and the valve 74. The decomposition device 55 is filled with, for example, an activated carbon catalyst in which ruthenium is adhered to the surface of the activated carbon. A surge tank 31 is installed in the circulation pipe 34 between the valve 74 and the circulation pump 32. The heater 51 is arranged in the surge tank 31. The pipe 80 provided with the valve 79 and the ejector 61 is connected to the circulation pipe 34 between the valve 77 and the circulation pump 32, and further connected to the surge tank 31. The ejector 61 is provided with a hopper (not shown) for supplying oxalic acid (reduction decontamination agent) used for reducing and dissolving contaminants on the inner surface of the recirculation system pipe 6 into the surge tank 31.

The nickel ion implanter 35 includes a chemical tank 36, an injection pump 37, and an injection pipe 38. The chemical tank 36 is connected to the circulation pipe 34 by an injection pipe 38 having an injection pump 37 and a valve 39. A nickel formate aqueous solution (an aqueous solution containing nickel ions) prepared by dissolving nickel formate (Ni (HCOO) _{2.2H 2 O} ) in water is filled in the chemical tank 36.

The platinum ion implanter (precious metal ion implanter) 45 includes a chemical solution tank 46, an injection pump 47, and an injection pipe 48. The chemical tank 46 is connected to the circulation pipe 34 by an injection pipe 48 having an injection pump 47 and a valve 49. An aqueous solution containing platinum ions prepared by dissolving a platinum complex (for example, sodium hexahydroxoplatinate hydrate (Na ₂ [Pt (OH) ₆ ] · nH ₂ O)) in water (for example, sodium hexahydroxoplatinate). The aqueous solution of hydrate) is filled in the chemical tank 46. An aqueous solution containing platinum ions is a type of aqueous solution containing noble metal ions. As the aqueous solution containing noble metal ions, an aqueous solution containing any one of palladium, rhodium, ruthenium, osmium and iridium ions may be used in addition to the aqueous solution containing platinum ions.

The reducing agent injection device 40 includes a chemical solution tank 41, an injection pump 42, and an injection pipe 43. The chemical tank 41 is connected to the circulation pipe 34 by an injection pipe 43 having an injection pump 42 and a valve 44. An aqueous solution of hydrazine, which is a reducing agent, is filled in the chemical tank 41. As the reducing agent, any one of hydrazine derivatives such as hydrazine, formhydrazine, hydrazinecarbamide and carbhydrazide and hydroxylamine may be used.

The buffer solution injection device 81 includes a chemical solution tank 82, an injection pump 83, and an injection pipe 84. The chemical tank 82 is connected to the circulation pipe 34 by an injection pipe 84 having an injection pump 83 and a valve 85. A mixed aqueous solution of formic acid and ammonia, which is a pH buffer solution, is filled in the chemical tank 82.

The injection pipes 38, 84, 48 and 43 are connected to the circulation pipe 34 between the valve 77 and the on-off valve 78 in that order from the valve 77 toward the on-off valve 78.

The oxidant supply device 56 includes a chemical solution tank 57, a supply pump 58, and a supply pipe 59. The chemical tank 57 is connected to the pipe 76 upstream of the valve 75 by a supply pipe 59 having a supply pump 58 and a valve 60. Hydrogen peroxide, which is an oxidizing agent, is filled in the chemical tank 57. As the oxidizing agent, ozone or water in which oxygen is dissolved may be used.

A pH meter 97 is attached to the circulation pipe 34 between the connection point between the injection pipe 43 and the circulation pipe 34 and the on-off valve 78.

The BWR plant 1 is shut down after the operation in one operation cycle is completed. After this operation is stopped, a part of the fuel assembly loaded in the core 4 is taken out as a used fuel assembly, and a new fuel assembly having a burnup of 0 GWd / t is loaded in the core 4. After such refueling is complete, the BWR plant 1 is restarted for operation in the next run cycle. Maintenance and inspection of the BWR plant 1 is performed using the period during which the BWR plant 1 is stopped for refueling.

During the period when the operation of the BWR plant 1 is stopped as described above, the carbon steel piping system connected to the RPV3, which is one of the carbon steel members in the BWR plant 1, for example, the purification system piping 18 is installed. The targeted method for suppressing radionuclide adhesion to carbon steel members of the nuclear plant of this example is implemented. In this method, first, the oxide film incorporating the radionuclides is removed from the inner surface of the purification system pipe 18 by chemical decontamination, a nickel metal film is formed on the inner surface of the purification system pipe 18 subjected to chemical decontamination, and then A noble metal, for example, platinum is attached to the surface of the formed nickel metal film, and then the nickel metal film to which the platinum is attached is converted into a stable nickel ferrite film.

The method for suppressing the adhesion of radionuclides to the carbon steel members of the nuclear power plant of this embodiment will be described below based on the procedure shown in FIG. In the method for suppressing the adhesion of radionuclides to the carbon steel member of the nuclear power plant of the present embodiment, the film forming apparatus 30 is used for forming the nickel metal film and adhering the noble metal to the nickel metal film.

First, the film forming apparatus is connected to the carbon steel piping system to be formed (step S1). When the operation of the BWR plant 1 is stopped, for example, the bonnet of the valve 23 provided in the purification system pipe 18 connected to the recirculation system pipe 6 is opened to block the recirculation system pipe 6 side. .. One end of the circulation pipe 34 of the film forming apparatus 30 on the on-off valve 78 side is connected to the flange of the valve 23, and one end of the circulation pipe 34 is connected to the purification system pipe 18 on the upstream side of the purification system pump 19. On the other hand, the bonnet of the valve 24 installed in the purification system pipe 18 is opened between the regenerated heat exchanger 20 and the non-regenerating heat exchanger 21 to block the non-regenerating heat exchanger 21 side. The other end of the circulation pipe 34 on the on-off valve 62 side is connected to the flange of the valve 24, and the other end of the circulation pipe 34 is connected to the purification system pipe 18 on the downstream side of the regenerative heat exchanger 20. Both ends of the circulation pipe 34 are connected to the purification system pipe 18, and a closed loop including the purification system pipe 18 and the circulation pipe 34 is formed.

Chemical decontamination of the carbon steel piping system to be filmed is carried out (step S2). In the BWR plant 1 which has experienced the operation in the previous operation cycle, an oxide film containing radionuclides is formed on the inner surface of the purification system pipe 18 in contact with the furnace water discharged from the RPV3. Before forming the nickel metal film described later on the inner surface of the purification system pipe 18, it is preferable to remove the oxide film containing radionuclides from the inner surface thereof. The removal of this oxide film also leads to improvement of the adhesion between the nickel metal film and the inner surface of the purification system pipe 18. In order to remove this oxide film, chemical decontamination, particularly reduction decontamination using a reduction decontamination liquid containing oxalic acid as a reduction decontamination agent, is carried out on the inner surface of the purification system pipe 18.

In step S2, the chemical decontamination applied to the inner surface of the purification system pipe 18 is the known reduction decontamination described in JP-A-2000-105295. Oxidative decontamination is not performed on the carbon steel purification system pipe 18. Among the chemical decontamination steps, the reduction decontamination immediately before the nickel metal film and the noble metal adhesion step is performed will be described.

First, the on-off valve 62, the valves 63, 66, 69, 74 and 77, and the on-off valve 78 are opened, respectively, and the circulation pumps 32 and 33 are driven with the other valves closed. As a result, the water heated by the heater 51 in the surge tank 31 in the purification system pipe 18 circulates in the closed loop formed by the circulation pipe 34 and the purification system pipe 18. The circulating water is adjusted to 90 ° C. by the heater 51. When the temperature of this water reaches 90 ° C., the valve 79 is opened to guide a part of the water flowing in the circulation pipe 34 into the pipe 80. A predetermined amount of oxalic acid supplied from the hopper and the ejector 61 into the pipe 80 is guided into the surge tank 31 by the water flowing in the pipe 80. This oxalic acid dissolves in water in the surge tank 31, and an aqueous oxalic acid solution (reduction decontamination liquid) is generated in the surge tank 31.

This oxalic acid aqueous solution is discharged from the surge tank 31 to the circulation pipe 34 by driving the circulation pump 32. The hydrazine aqueous solution in the chemical tank 41 of the reducing agent injection device 40 is injected into the oxalic acid aqueous solution in the circulation pipe 34 through the injection pipe 43 by opening the valve 44 and driving the injection pump 42. Purification system by controlling the injection pump 42 (or the opening degree of the valve 44) based on the pH value of the oxalic acid aqueous solution measured by the pH meter 97 to adjust the injection amount of the hydrazine aqueous solution into the circulation pipe 34. The pH of the oxalic acid aqueous solution supplied to the pipe 18 is adjusted to 2.5. In this embodiment, hydrazine, which is a reducing agent used when a nickel metal is attached to the inner surface of the purification system pipe 18 and when a noble metal, for example, platinum is attached onto the nickel metal film, is used for reduction decontamination. In the process, it is used as a pH adjuster for adjusting the pH of the aqueous oxalic acid solution.

An oxalic acid aqueous solution (reduction decontamination aqueous solution) containing hydrazine at a pH of 2.5 and 90 ° C. was supplied from the circulation pipe 34 to the purification system pipe 18, and the radionuclide formed on the inner surface of the purification system pipe 18 was released. Contact the containing oxide film. This oxide film is dissolved by oxalic acid. The oxalic acid aqueous solution containing hydrazine flows in the purification system pipe 18 while dissolving the oxide film, passes through the purification system pump 19 and the regenerative heat exchanger 20, and is returned to the circulation pipe 34. The oxalic acid aqueous solution containing hydrazine returned to the circulation pipe 34 is boosted by the circulation pump 33 through the on-off valve 62, passes through the valves 63, 66, 69 and 74, and reaches the surge tank 31. As described above, the oxalic acid aqueous solution containing hydrazine circulates in the closed loop including the circulation pipe 34 and the purification system pipe 18, and the inner surface of the purification system pipe 18 is reduced and decontaminated to form an oxide film on the inner surface thereof. Dissolve.

With the dissolution of the oxide film, the radionuclide concentration and Fe concentration of the oxalic acid aqueous solution containing hydrazine increase. A cation exchange resin tower 53 is used in order to suppress an increase in the concentration of radionuclides and the concentration of Fe contained in the aqueous oxalic acid solution containing hydrazine. That is, a part of the oxalic acid aqueous solution containing hydrazine returned from the purification system pipe 18 to the circulation pipe 34 by opening the valves 70, 95 and 96 to adjust the opening degree of the valve 69 passes through the pipe 71. It is guided to the cation exchange resin tower 53. Radionuclear species and metal cations such as Fe contained in the oxalic acid aqueous solution containing hydrazine are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 53. The hydrazine-containing aqueous oxalic acid solution discharged from the cation exchange resin column 53 passes through the valve 95 and is mixed with the hydrazine-containing aqueous oxalic acid solution that has passed through the valve 69. These mixed oxalic acid aqueous solutions are supplied again from the circulation pipe 34 to the purification system pipe 18, and are used for reduction decontamination of the purification system pipe 18. The cation exchange resin uses a hydrazine-plated resin.

In the reduction decontamination of the surface of a carbon steel member (for example, purification system pipe 18) using oxalic acid, sparingly soluble iron (II) oxalate is formed on the surface of the carbon steel member, and this iron oxalate (for example, iron oxalate) is formed. II) may suppress the dissolution of the oxide film containing radioactive nuclei formed on the surface of the carbon steel member by oxalic acid. In this case, the valve 69 is fully opened, the valve 70 is closed, the supply of the oxalic acid aqueous solution containing hydrazine to the cation exchange resin tower 53 is stopped, and hydrogen peroxide, which is an oxidizing agent, flows through the circulation pipe 34. Inject into an oxalic acid aqueous solution containing hydrazine. To inject the hydrogen peroxide into the hydrazine-containing aqueous solution of oxalic acid, the valve 60 is opened to start the supply pump 58, and the hydrogen peroxide in the chemical solution tank 57 is circulated through the supply pipe 59, the pipes 76 and 71, and the like. It is supplied to an aqueous oxalic acid solution containing hydrazine flowing inside. At this time, the valves 72 and 75 are closed. An aqueous solution of oxalic acid containing hydrogen peroxide and hydrazine is guided from the circulation pipe 34 into the purification system pipe 18, and Fe (II) contained in iron (II) oxalate formed on the inner surface of the purification system pipe 18 is the Fe (II) thereof. By the action of hydrogen peroxide contained in the oxalic acid aqueous solution, it is oxidized to Fe (III), and the iron oxalate (II) is dissolved in the oxalic acid aqueous solution containing hydrazine as an iron (III) oxalate complex. That is, iron (II) oxalate, and hydrogen peroxide and oxalic acid contained in the aqueous oxalic acid solution generate an iron (III) oxalate complex, water, and hydrogen ions by the reaction represented by the following formula (12). ..

2Fe (COO) ₂ + H ₂ O ₂ + 2 (COOH) ₂ →
2Fe [(COO) ₂ ^] _2- + 2H ₂ O + 2H ⁺ … (12)
After confirming that the iron (II) oxalate formed on the inner surface of the purification system pipe 18 was dissolved and the hydrogen hydrogen injected into the oxalic acid aqueous solution containing hydrazine disappeared by the reaction of the formula (12), the valve 70 is opened to adjust the opening degree of the valve 69, and a part of the oxalic acid aqueous solution containing hydrazine that has flowed through the circulation pipe 34 and passed through the valve 66 is supplied to the cation exchange resin tower 53 through the pipe 71. Metal cations such as radioactive nuclei contained in the oxalic acid aqueous solution containing hydrazine are adsorbed on the cation exchange resin in the cation exchange resin tower 53 and removed. The disappearance of hydrogen peroxide in the hydrazine-containing aqueous solution of oxalic acid can be confirmed by immersing a test paper that reacts with hydrogen peroxide in the aqueous solution of oxalic acid sampled from the circulation pipe 34 and observing the color appearing on the test paper. ..

Oxalic acid contained in the oxalic acid aqueous solution when the dose rate at the reduction decontamination site of the purification system pipe 18 drops to the set dose rate, or when the reduction decontamination time of the purification system pipe 18 reaches a predetermined time. And decompose hydrazine. That is, the reduction decontamination agent decomposition step is carried out. The fact that the dose rate at the reduction decontamination site has dropped to the set dose rate is confirmed by the dose rate obtained based on the output signal of the radiation detector that detects the radiation from the reduction decontamination site of the purification system piping 18. can do.

The decomposition of oxalic acid and hydrazine contained in the oxalic acid aqueous solution is carried out as follows. The oxalic acid aqueous solution containing hydrazine, which opened the valve 75 to partially reduce the opening degree of the valve 69, flowed through the cation exchange resin tower 53 and passed through the valve 70, was supplied to the decomposition device 55 through the valve 75 by the pipe 76. Will be done. At this time, the valve 95 is closed and the valve 96 is open. Further, by opening the valve 60 and driving the supply pump 58, the hydrogen peroxide in the chemical solution tank 57 is supplied to the pipe 76 through the supply pipe 59 and flows into the decomposition device 55. The oxalic acid and hydrazine contained in the oxalic acid aqueous solution are decomposed in the decomposition apparatus 55 by the action of the activated carbon catalyst and the supplied hydrogen peroxide. The decomposition reaction of oxalic acid and hydrazine in the decomposition apparatus 55 is represented by the formulas (13) and (14).

(COOH) ₂ + H ₂ O ₂ → 2CO ₂ + 2H ₂ O …… (13)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O …… (14)
The decomposition of oxalic acid and hydrazine in the decomposition apparatus 55 is carried out while circulating the oxalic acid aqueous solution in a closed loop including the circulation pipe 34 and the purification system pipe 18. The amount of hydrogen peroxide supplied from the chemical tank 57 to the decomposition device 55 is adjusted so that the supplied hydrogen peroxide is not completely consumed by the decomposition device 55 for decomposition of oxalic acid and hydrazine and flows out from the decomposition device 55. The rotation speed of the supply pump 58 is controlled and adjusted.

Even in the reduction decontamination agent decomposition step, if oxalic acid is present in the oxalic acid aqueous solution containing hydrazine, iron oxalate (II) is formed on the inner surface of the purification system pipe 18 which is a carbon steel member and comes into contact with the oxalic acid aqueous solution. May be formed. Therefore, when the decomposition of oxalic acid and hydrazine contained in the oxalic acid aqueous solution has progressed to some extent, the rotation speed of the supply pump 58 is increased, and the decomposition device from the chemical solution tank 57 so that hydrogen peroxide flows out from the decomposition device 55. Increase the supply of hydrogen peroxide to 55. At that time, the valves 96 and 70 are closed so that hydrogen peroxide does not flow into the cation exchange resin column 53.

The oxalic acid aqueous solution containing hydrogen peroxide and hydrazine discharged from the decomposition device 55 is guided from the circulation pipe 34 to the purification system pipe 18. As described above, iron (II) oxalate formed on the inner surface of the purification system pipe 18 which is a carbon steel member becomes an iron (III) oxalate complex by the action of hydrogen peroxide, and is an oxalic acid aqueous solution containing hydrazine. Dissolve in. Since the decomposition of oxalic acid and the like in the oxalic acid aqueous solution containing hydrazine is progressing, the oxalic acid that converts Fe (II) contained in iron oxalate (II) into easily soluble Fe (III) is insufficient and circulates. Fe (OH) ₃ is likely to be deposited on the inner surface of the pipe 34. Therefore, formic acid is injected into the oxalic acid aqueous solution in order to suppress the precipitation of Fe (OH) ₃ . Formic acid is injected, for example, by opening the valve 79 and supplying formic acid to the oxalic acid aqueous solution from the above-mentioned hopper and ejector 61 in a state where the oxalic acid aqueous solution is flowing in the pipe 80 and guiding the formic acid to the surge tank 31. Will be. The supplied formic acid is mixed with the oxalic acid aqueous solution.

The supplied aqueous solution of oxalic acid containing hydrazine containing formic acid contains hydrogen peroxide discharged from the decomposition apparatus 55 in addition to the reduced concentrations of oxalic acid and hydrazine. The oxalic acid aqueous solution containing hydrazine containing formic acid and hydrogen peroxide is supplied to the purification system pipe 18. Hydrogen peroxide contained in the oxalic acid aqueous solution containing hydrazine dissolves iron (II) oxalate precipitated on the inner surface of the purification system pipe 18, and formic acid dissolves Fe (OH) ₃ . Since this oxalic acid aqueous solution circulates in a closed loop including the circulation pipe 34 and the purification system pipe 18, decomposition of oxalic acid and hydrazine is also continued in the decomposition apparatus 55.

Next, in order to complete the step of decomposing oxalic acid and hydrazine, the hydrogen peroxide concentration of the oxalic acid aqueous solution containing hydrazine flowing in the circulation pipe 34 is lowered to supply the oxalic acid aqueous solution to the cation exchange resin tower 53. Therefore, the valve 60 is closed and the valve 79 is closed to stop the injection of formic acid. When the injection of hydrogen peroxide and formic acid into the oxalic acid aqueous solution flowing in the circulation pipe 34 is stopped, the concentrations of these in the oxalic acid aqueous solution containing hydrazine also decrease. When the hydrogen peroxide concentration of the oxalic acid aqueous solution containing hydrazine becomes 1 ppm or less, the valves 96 and 70 are opened to reduce the opening degree of the valve 69, and the oxalic acid aqueous solution is supplied to the cation exchange resin column 53. As described above, the metal cations contained in the oxalic acid aqueous solution are removed by the cation exchange resin in the cation exchange resin tower 53, and the metal cation concentration of the oxalic acid aqueous solution decreases. Decomposition of oxalic acid, hydrazine and formic acid is continued in the decomposition apparatus 55. Of oxalic acid, hydrazine and formic acid, hydrazine is decomposed first, then oxalic acid is decomposed, and formic acid remains last. In this state, the decomposition step of oxalic acid and hydrazine is completed.

When the chemical decontamination described above is completed, the purification system pipe 18 is in the state shown in FIG. 4 after the oxide film containing radionuclides has been removed from the inner surface of the purification system pipe 18. The inner surface is in contact with the above-mentioned aqueous solution containing residual formic acid.

The temperature of the film forming liquid is adjusted (step S3). Valves 69 and 74 are opened and valves 96, 70 and 75 are closed. Since the circulation pumps 32 and 33 are driven, the remaining aqueous solution containing formic acid circulates in the closed loop including the circulation pipe 34 and the purification system pipe 18. The aqueous solution containing formic acid is heated to 90 ° C. by the heater 51. The temperature of this formic acid aqueous solution (film-forming aqueous solution described later) is preferably in the range of 60 ° C. to 100 ° C. (60 ° C. or higher and 100 ° C. or lower). Further, the valve 64 is opened and the valve 63 is closed. By these valve operations, the formic acid aqueous solution flowing in the circulation pipe 34 is supplied to the filter 50, and the fine solid content remaining in the formic acid aqueous solution is removed by the filter 50. When the fine solid content is not removed by the filter 50, when the nickel formic acid aqueous solution is injected into the circulation pipe 34 when the nickel metal film described later is formed on the inner surface of the purification system pipe 18, the surface of the solid matter is covered. Also, a nickel metal film is formed, and the injected nickel ions are consumed extra. The supply of the formic acid aqueous solution to the filter 50 is to prevent such extra consumption of nickel ions.
Inject the pH buffer solution (step S4). The valve 63 is opened, the valve 64 is closed, and water flow to the filter 50 is stopped. The valve 85 of the pH buffer solution injection device 81 is opened to drive the injection pump 83, and the pH buffer solution in the chemical tank 82, specifically, a mixed aqueous solution of formic acid and ammonia flows through the injection pipe 84 through the circulation pipe 34. It is injected into an aqueous solution at 90 ° C. containing the remaining formic acid. The concentrations of formic acid and ammonia injected are, for example, 800 ppm and 156 ppm. By injecting the pH buffer solution, the pH of the aqueous solution containing formic acid and ammonia flowing in the closed loop including the circulation pipe 34 and the purification system pipe 18 is set to the range of 3.9 or more and 4.2 or less, for example, 4.0. And it is kept at 4.0. The pH of the circulating aqueous solution containing formic acid and ammonia (the film-forming aqueous solution described later) is 3.9 or more by changing the mixing ratio of formic acid and ammonia contained in the pH buffer solution in advance before supplying the solution to the chemical tank 82. It can be adjusted within the pH range of .2 or less.

A nickel ion aqueous solution is injected (step S5). The valve 39 of the nickel ion injection device 35 is opened to drive the injection pump 37, and the nickel formate aqueous solution in the chemical tank 36 is injected into the 90 ° C. aqueous solution containing formic acid and ammonia flowing in the circulation pipe 34 through the injection pipe 38. do. The nickel ion concentration of the injected nickel formate aqueous solution is, for example, 200 ppm. Since the pH of the 90 ° C. aqueous solution containing formic acid and ammonia is buffered at 4.0 in step S4, the 90 ° C. aqueous solution containing nickel ions, formic acid and ammonia produced by injecting the nickel formate aqueous solution (film-forming aqueous solution (film-forming aqueous solution (film forming aqueous solution)). The pH of the film-forming solution)) hardly fluctuates from 4.0.

The 90 ° C. film-forming aqueous solution is supplied from the circulation pipe 34 to the purification system pipe 18, and comes into contact with the inner surface of the purification system pipe 18. When the film-forming aqueous solution 89 having a pH of 4.0 at 90 ° C. comes into contact with the inner surface of the purification system pipe 18, a substitution plating reaction occurs between the iron contained in the purification system pipe 18 and the nickel ions contained in the film-forming aqueous solution 89. Is generated, and a nickel metal film 86 is formed on the inner surface of the purification system pipe 18 (see FIG. 5). This substitution plating reaction will be specifically described. The iron contained in the purification system pipe 18 becomes iron (II) ions and elutes into the film-forming aqueous solution 89 that comes into contact with the inner surface thereof. Nickel ions contained in the film-forming aqueous solution 89 are taken into the inner surface of the purification system pipe 18 by replacement with the eluted iron (II) ions, and are reduced by the electrons generated by the elution of the iron (II) ions to nickel. Become metal. Therefore, the above-mentioned nickel metal film 86 is formed on the inner surface of the purification system pipe 18.

In order to secure a time for advancing such a substitution plating reaction, for example, a reaction time of 60 minutes is provided from the start of injection of the nickel formate aqueous solution to the execution of the next step (reducing agent injection step in step S6). In this 60 minutes, the film-forming aqueous solution 89 does not contain a reducing agent. Therefore, in 60 minutes from the start of injection of the nickel formate aqueous solution to the start of injection of the reducing agent by the step S6 described later, the nickel ions taken into the inner surface of the purification system pipe 18 are reduced by electrons instead of the reducing agent. Becomes nickel metal. Eventually, the nickel metal is reduced by electrons to form a nickel metal film 86 that covers the entire inner surface of the purification system pipe 18, and the elution of iron (II) ions from the purification system pipe 18 to the film-forming aqueous solution 89 is stopped.

Inject the reducing agent (step S6). When 60 minutes have passed from the start of injection of the nickel formate aqueous solution, the valve 44 of the reducing agent injection device 40 is opened to drive the injection pump 42, and the aqueous solution of the reducing agent hydrazine in the chemical solution tank 41 is passed through the injection pipe 43. It is injected into a film-forming aqueous solution at 90 ° C. containing nickel ions, formic acid and ammonia flowing in the circulation pipe 34. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 200 ppm. An aqueous solution at 90 ° C. containing nickel ions, formic acid, ammonia and hydrazine, that is, a film-forming aqueous solution (film-forming solution) 89 is supplied from the circulation pipe 34 to the purification system pipe 18. The film-forming aqueous solution 89 comes into contact with the inner surface of the purification system pipe 18, specifically, the surface of the nickel metal film 86 formed by covering the entire inner surface of the purification system pipe 18 by the reducing action of electrons in the step S5. As a result, the nickel ions adsorbed on the surface of the nickel metal film 86 become nickel metal by the reducing action of hydrazine contained in the film-forming aqueous solution 89, not by the reducing action by electrons. Therefore, the thickness of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 increases. When the pH of the film-forming aqueous solution 89 increases to 7 mag by injecting hydrazine, which is a reducing agent, the amount of nickel ions adsorbed on the surface of the nickel metal film 86 increases, and the amount of nickel metal produced by the action of hydrazine. Increases.

The film-forming aqueous solution 89 discharged from the purification system pipe 18 to the circulation pipe 34 is pressurized by the circulation pumps 33 and 32, and the nickel formate aqueous solution from the nickel ion injection device 35 and the hydrazine aqueous solution from the reducing agent injection device 40 are injected, respectively. Then, it is guided to the purification system pipe 18 again. By circulating the film-forming aqueous solution 89 in the closed loop including the circulation pipe 34 and the purification system pipe 18, the entire inner surface of the purification system pipe 18 in contact with the film-forming aqueous solution 89 is set uniformly. It is covered with a thick nickel metal film 86. At this time, the nickel metal existing on the inner surface of the purification system pipe 18 is, for example, in the range of 50 μg to 300 μg (50 μg / cm ² or more and 300 μg / cm ² or less) per square centimeter. The amount of the nickel metal film 86 covering the entire corresponding inner surface of the purification system pipe 18 per square centimeter varies depending on the temperature of the film-forming aqueous solution 89 in contact with the inner surface. When the temperature of the film-forming aqueous solution 89 is 60 ° C., the amount is 50 μg / cm ² , and in this example where the temperature of the film-forming aqueous solution 89 is 90 ° C., the amount is 250 μg / cm ² .

It is determined whether the formation of the nickel metal film is completed (step S7). When the nickel metal film 86 formed on the inner surface of the purification system pipe 18 is insufficient (when the nickel metal present on the inner surface is less than 250 μg / cm ² ), each step of steps S5 to S7 is repeated. When the nickel metal existing on the inner surface of the purification system pipe 18 reaches 250 μg / cm ² , the injection pump 37 is stopped, the valve 39 is closed, the injection of the nickel formate aqueous solution into the circulation pipe 34 is stopped, and the injection pump is used. The 42 is stopped, the valve 44 is closed, the injection of the hydrazine aqueous solution into the circulation pipe 34 is stopped, and the formation of the nickel metal film 86 on the inner surface of the purification system pipe 18 is completed. When the elapsed time from injecting the nickel formate aqueous solution into the circulation pipe 34 reached the set time, the nickel metal contained in the nickel metal film 86 formed on the inner surface of the purification system pipe 18 became 250 μg / cm ² . judge. The set time is determined by measuring in advance the time until the nickel metal on the surface of the carbon steel test piece reaches 250 μg / cm ² .

Decompose formic acid and reducing agent (step S8). The valves 96 and 70 are opened to close a part of the opening degree of the valve 69, and a part of the film-forming aqueous solution 89 containing nickel ions, formic acid, ammonia and hydrazine is guided to the cation exchange resin tower 53 through the pipe 71. Further, the valve 95 is left closed, and the valve 75 is opened to guide the film-forming aqueous solution 89 from which the nickel ions and ammonia coming out of the cation exchange resin tower 53 are removed to the decomposition apparatus 55 through the pipe 76. Further, the hydrogen peroxide in the chemical solution tank 57 is supplied to the decomposition device 55 through the supply pipe 59 and the pipe 76. Formic acid and hydrazine, which is a reducing agent, contained in the film-forming aqueous solution 89 are decomposed into carbon dioxide, nitrogen and water by the action of the activated carbon catalyst and hydrogen peroxide in the decomposition apparatus 55.

The film-forming aqueous solution from which nickel ions and ammonia have been removed and formic acid and the reducing agent have been decomposed is purified (step S9). After the formic acid and hydrazine (reducing agent) were decomposed, the valve 69 was opened, the valves 96, 70, and 75 were closed, and the supply of the film-forming aqueous solution 89 to the cation exchange resin tower 53 and the decomposition device 55 was stopped. The valve 67 is opened, a part of the opening degree of the valve 66 is closed, and the valves 72 and 95 are opened. At this time, the valve 69 is closed and the circulation pumps 33 and 32 are being driven. The film-forming aqueous solution 89 in which nickel ions and ammonia returned from the purification system pipe 18 to the circulation pipe 34 are purified and hydrazine and formic acid are decomposed is cooled by the cooler 52 until the temperature reaches 60 ° C. Further, the film-forming aqueous solution at 60 ° C. discharged from the cooler 52 is guided to the mixed bed resin tower 54, and the nickel ions, other cations and anions remaining in the film-forming aqueous solution 89 are combined with the mixed bed resin. It is adsorbed and removed by the cation exchange resin and the anion exchange resin in the tower 54 (first purification step). The film-forming aqueous solution cooled to 60 ° C. is circulated in the circulation pipe 34 and the purification system pipe 18 until each of the above ions is substantially eliminated. The film-forming aqueous solution in which each ion is substantially eliminated is water at substantially 60 ° C. After the purification is completed, the valve 66 is opened and the valves 67, 72 and 95 are closed.

In order to facilitate the adhesion of platinum to the surface of the nickel metal film 86 in the step of the next step S10, a small amount of Fe ³⁺ ion iron hydroxide (III) remains after purification in the circulating water at 60 ° C. ) Inject ammonia for the purpose of suppressing precipitation due to formation. A part of the water at 60 ° C. flowing in the circulation pipe 34 is guided to the ejector 61 through the pipe 80 by opening the valve 79, and the ammonia water sucked by the ejector 61 from the hopper (not shown) is taken into the water flowing in the pipe 80. It mixes in. The water mixed with ammonia is guided to the surge tank 31. When a predetermined amount of ammonia, for example, 50 ppm of ammonia is mixed in the water, the valve 79 is closed to end the mixing of ammonia.

An aqueous platinum ion solution is injected (step S10). The valve 49 of the platinum ion implanter 45 is opened to drive the implantation pump 47. The water flowing in the circulation pipe 34 is maintained at 60 ° C. by heating by the heater 51. An aqueous solution containing platinum ions in a chemical tank 46 through an injection pipe 48 in water containing ammonia at 60 ° C. flowing through the circulation pipe 34 (for example, sodium hexahydroxoplatinate hydrate (Na ₂ [Pt (OH) ₆ ]]. -An aqueous solution of nH ₂ O)) is injected. The concentration of platinum ions in this aqueous solution to be injected is, for example, 1 ppm. In the aqueous solution of sodium hexahydroxoplatinate hydrate, platinum is in an ionic state. An aqueous solution containing ammonia and platinum ions at 60 ° C. is supplied from the circulation pipe 34 to the purification system pipe 18 and returned from the purification system pipe 18 to the circulation pipe 34. The aqueous solution containing platinum ions circulates in a closed loop including the circulation pipe 34 and the purification system pipe 18.

Immediately after the start of injection, platinum at the connection point of the aqueous solution of Na ₂ [Pt (OH) ₆ ] and nH ₂ O injected into the circulation pipe 34 from the chemical solution tank 46 through the connection point between the circulation pipe 34 and the injection pipe 48. The injection rate of the aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O into the circulation pipe 34 is calculated in advance so that the concentration becomes the set concentration, for example, 1 ppm, and further, the inside of the circulation pipe 34 is The platinum ion of the flowing water containing ammonia at 60 ° C. is set to the set concentration, and the chemical solution tank 46 required to attach a predetermined amount of platinum to the surface of the nickel metal film formed on the inner surface of the purification system pipe 18 is filled. The amount of the solution of Na ₂ [Pt (OH) ₆ ] and nH ₂ O to be added is calculated, and the calculated amount of the solution of Na ₂ [Pt (OH) ₆ ] and nH ₂ O is filled in the chemical tank 46. The rotation speed of the injection pump 47 is controlled according to the injection speed of the calculated Na ₂ [Pt (OH) ₆ ] · nH ₂ O aqueous solution into the circulation pipe 34, and Na ₂ [Pt (OH) (OH) (OH) in the chemical tank 46 is controlled. ) ₆ ] ・ Inject an aqueous solution of nH ₂ O into the circulation pipe 34.

Inject the reducing agent (step S11). The valve 44 of the reducing agent injection device 40 is opened to drive the injection pump 42, and an aqueous solution of hydrazine, which is a reducing agent in the chemical solution tank 41, flows through the injection pipe 43 in the circulation pipe 34 at 60 ° C. containing platinum ions. Inject into an aqueous solution. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 100 ppm.

The hydrazine aqueous solution is injected into the circulation pipe 34 after the aqueous solution of Na ₂ [Pt (OH) ₆ ] and nH ₂ O at 60 ° C. reaches the connection point between the injection pipe 43 and the circulation pipe 34, which is the injection point of the hydrazine aqueous solution. Will be done. In this case, an aqueous solution containing platinum ions and hydrazine at 60 ° C. is supplied from the circulation pipe 34 to the purification system pipe 18. However, more preferably, the hydrazine aqueous solution is circulated immediately after all the predetermined amounts of Na ₂ [Pt (OH) ₆ ] and nH ₂ O aqueous solutions filled in the chemical tank 46 have been injected into the circulation pipe 34. It is desirable to inject into 34. In this case, a 60 ° C. aqueous solution containing platinum ions is supplied from the circulation pipe 34 to the purification system pipe 18, and after the injection of the platinum ion aqueous solution into the circulation pipe 34 is completed, 60 ° C. containing platinum ions and hydrazine. 90 (see FIG. 6) is supplied from the circulation pipe 34 to the purification system pipe 18.

In the case of the former injection of the hydrazine aqueous solution, the reduction reaction of converting platinum ions to platinum by hydrazine first occurs in the aqueous solution containing hydrazine and platinum ions flowing in the circulation pipe 34, whereas the latter In the case of injecting an aqueous hydrazine solution, platinum ions are already adsorbed on the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18, and the adsorbed platinum ions are reduced by hydrazine. The amount of platinum 87 adhering to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 is further increased (see FIG. 6).

Immediately after the start of injection of the hydrazine aqueous solution, the hydrazine concentration at the connection point of the hydrazine aqueous solution injected from the chemical solution tank 41 through the connection point of the circulation pipe 34 and the injection pipe 43 is set in advance so as to be a set concentration, for example, 100 ppm. , The injection speed of the hydrazine aqueous solution into the circulation pipe 34 is calculated, and the hydrazine in the aqueous solution 90 containing platinum ions at 60 ° C. flowing in the circulation pipe 34 is set to the set concentration and formed on the inner surface of the purification system pipe 18. The amount of the hydrazine aqueous solution to be filled in the chemical solution tank 41 required to reduce the platinum ions adsorbed on the surface of the nickel metal film 86 to platinum 87 was calculated, and the calculated amount of the hydrazine aqueous solution was applied to the chemical solution tank 41. Fill. The rotation speed of the injection pump 42 is controlled according to the calculated injection speed of the hydrazine aqueous solution into the circulation pipe 34, and the hydrazine aqueous solution in the chemical solution tank 41 is injected into the circulation pipe 34.

When the entire amount of the aqueous solution of Na ₂ [Pt (OH) ₆ ] and nH ₂ O (the aqueous solution containing platinum ions) in the chemical tank 46 was injected into the circulation pipe 34, the drive of the injection pump 47 was stopped. And close the valve 49. As a result, the injection of the aqueous solution containing platinum ions into the circulation pipe 34 is stopped. Further, when the entire amount of the hydrazine aqueous solution (reducing agent aqueous solution) in the chemical liquid tank 41 is injected into the circulation pipe 34, the drive of the injection pump 42 is stopped and the valve 44 is closed. As a result, the injection of the hydrazine aqueous solution into the circulation pipe 34 is stopped.

Since the platinum ions adsorbed on the surface of the nickel metal film 86 are reduced by the injected hydrazine to become platinum 87, the platinum 87 adheres to the surface of the nickel metal film 86 formed on the inner surface of the purification system piping 18 (see FIG. 6). ). In this platinum adhesion step, since the nickel metal film 86 is already formed on the surface of the carbon steel pipe, the elution of the underlying iron is suppressed, so that platinum easily adheres to the surface of the nickel metal film 86.

It is determined whether the adhesion of platinum is completed (step S12). When the elapsed time from the injection of the platinum ion aqueous solution and the reducing agent aqueous solution reaches a predetermined time, it is determined that the adhesion of the predetermined amount of platinum 87 to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 is completed. do. When the elapsed time does not reach the predetermined time, each step of steps S10 to S12 is repeated.

Purify the aqueous solution remaining in the purification system piping and the circulation piping (step S13). After it is determined that the work of adhering platinum 87 to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 is completed, the valves 96, 72, and 95 are opened to partially open the valve 69. Is closed, and an aqueous solution at 60 ° C. containing platinum ions, ammonia and hydrazine, which is pressurized by the circulation pump 33, is supplied to the mixed bed resin tower 54. Platinum ions, other metal cations (for example, sodium ions), ammonia, hydrazine and OH groups contained in the aqueous solution are adsorbed on the ion exchange resin in the mixed bed resin tower 54 and removed from the aqueous solution (No. 1). 2 Purification process).

Treat the effluent (step S14). After the second purification step is completed, the circulation pipe 34 and the waste liquid treatment device (not shown) are connected by a high-pressure hose (not shown) having a pump (not shown). After the completion of the second purification step, the aqueous solution, which is a radioactive waste liquid, existing in the purification system pipe 18 and the circulation pipe 34 is discharged from the circulation pipe 34 through the high-pressure hose by driving the pump (not shown). It is discharged to the waste liquid treatment equipment. After the aqueous solution in the purification system pipe 18 and the circulation pipe 34 is discharged, the cleaning water is supplied into the purification system pipe 18 and the circulation pipe 34, and the circulation pumps 32 and 33 are driven to clean the inside of these pipes. After the cleaning is completed, the cleaning water in the purification system pipe 18 and the circulation pipe 34 is discharged to the above-mentioned waste liquid treatment device.

As described above, the adhesion of the nickel metal and the noble metal necessary for the conversion to the nickel ferrite film on the carbon steel member of the nuclear power plant of this embodiment is completed. Then, the film forming apparatus 30 connected to the purification system pipe 18 is removed from the purification system pipe 18, and the purification system pipe 18 is restored (step S15).

The nuclear plant is started (step S16). After the refueling is completed and the maintenance and inspection of the BWR plant 1 is completed, it has a purification system pipe 18 in which a nickel metal film 86 having platinum 87 adhered is formed on the inner surface in order to start operation in the next operation cycle. BWR plant 1 is started.

The furnace water having a temperature in the range of 130 ° C. or higher and 330 ° C. or higher is brought into contact with the nickel metal film to which platinum is attached (step S17). When the BWR plant 1 is started, the furnace water in the RPV 3 is boosted by the recirculation pump 7 and ejected into the jet pump 5 through the recirculation system pipe 6. The furnace water existing around the nozzle of the jet pump 5 in the downkama is also sucked into the jet pump 5 and supplied to the core 4. The reactor water discharged from the core is returned to the downcomer. The control rods (not shown) are pulled out from the core 4 to change the core 4 from the subcritical state to the critical state. It is heated by the heat generated in (nuclear heating). No steam is generated in the core 4, and steam is not yet supplied to the turbine 9. Further, the control rod is pulled out from the core 4, the pressure in the RPV 3 is raised to the rated pressure in the temperature raising and boosting step of the reactor 2, and the reactor water is heated by the heat generated by the nuclear fission, and the reactor water in the RPV 3 is heated. The temperature is raised to the rated temperature (280 ° C.). After the pressure in the RPV3 reaches the rated pressure and the reactor water temperature rises to the rated temperature, the reactor output becomes the rated output due to the withdrawal of the control rods from the core 4 and the increase in the flow rate of the reactor water supplied to the core 4. It is increased to (100% output). The rated operation of the BWR plant 1, which maintains the rated output, is continued until the end of the operation cycle. When the reactor power rises to, for example, 10%, the steam generated in the core 4 is supplied to the turbine 9 through the main steam pipe 8 to start power generation, and thereafter until the operation of the BWR plant 1 is completed. , Power generation will continue.

The furnace water 91 contains oxygen and hydrogen peroxide. Oxygen and hydrogen peroxide are produced by radiolysis of the furnace water 91 in RPV3. The furnace water 91 in the RPV3 is guided from the recirculation system pipe 6 into the purification system pipe 18, and comes into contact with the nickel metal film 86 to which platinum 87 is attached, which is formed on the inner surface of the purification system pipe 18 (FIG. 7). reference). In the heating and boosting step of the reactor 2, the temperature of the reactor water 91 in contact with the nickel metal film 86 rises due to the heating of the reactor water by the heat generated by the above-mentioned nuclear fission, and eventually reaches 130 ° C. or higher and reaches 280 ° C. Ascend to. When the temperature of the furnace water 91 becomes 130 ° C. or higher, the temperature of each of the nickel metal film 86 formed on the inner surface and the purification system pipe 18 surrounded by the heat insulating material also becomes 130 ° C. or higher. In this embodiment, the furnace water having a temperature in the temperature range of 130 ° C. or higher and 280 ° C. or lower, which is in the temperature range of 130 ° C. or higher and 330 ° C. or lower, is brought into contact with the nickel metal film 86 to which platinum 87 is attached.

As a result, the oxygen contained in the furnace water 91 is transferred into the nickel metal film 86, and the Fe contained in the purification system pipe 18 becomes Fe ²⁺ and is transferred into the nickel metal film 86 (see FIG. 9). Due to the action of platinum 87 adhering to the metal film 86 and the formation of a high temperature environment of about 130 ° C. or higher, the corrosion potential of the purification system pipe 18 or the like is within the range of 0 mV to +200 mV as described in the step S18 described later. In the state of the corrosion potential of, in the nickel metal film 86, in Ni _1-x Fe _{2 + x} O ₄ , for example, stable nickel ferrite (Ni Fe ₂ O ₄ ) in which x is 0 is generated.

An oxidant is injected into the furnace water (step S18). After the start of the BWR plant 1, at the start of nuclear heating, an oxidizing agent, for example, oxygen, is started to be injected into the furnace water 91 flowing in the purification system pipe 18. Even when the temperature of the furnace water 91 becomes 130 ° C. or higher due to nuclear heating, oxygen is injected into the furnace water 91. As the oxidizing agent, hydrogen peroxide may be used instead of oxygen. By opening the on-off valve 98 provided in the oxidant injection pipe 26, oxygen is supplied from the oxidant injection device 25 to the purification system pipe 18 through the oxidant injection pipe 26. The furnace water 91 of the corrosive environment forming water quality containing the injected oxygen comes into contact with the surface of the nickel metal film 86 to which platinum 87 is attached, which is formed on the inner surface of the purification system pipe 18 (see FIG. 9). The oxygen concentration of the furnace water 91 in which oxygen is injected flowing through the purification system pipe 18 is the corrosion potential of the purification system pipe 18 on which the nickel metal film 86 is formed on the inner surface, from 0 mV to +200 mV (0 mV or more and + 200 mV or less). The concentration should be such that it can be maintained at the high corrosion potential of. As a result, the corrosion potential of the purification system pipe 18 and the nickel metal film 86 formed on the inner surface of the purification system pipe 18 is also maintained at a high corrosion potential of 0 mV to +200 mV.

The corrosion potential of the purification system pipe 18 and the nickel metal film 86 formed on the inner surface thereof is maintained at a corrosion potential in the range of 0 mV to +200 mV, and is in contact with the furnace water 91 having a temperature of 130 ° C. or higher. , Oxygen transferred from the furnace water 91 into the nickel metal film 86, Fe ²⁺ transferred from the purification system pipe 18 into the nickel metal film 86, and a stable nickel ferrite formation reaction by nickel contained in the nickel metal film 86. Promoted by the catalytic action of platinum 87 adhering to the nickel metal film 86, some nickel metals contained in the nickel metal film 86 are stable in Ni _1-x Fe _{2 + x} O ₄ , for example, x is 0. Nickel ferrite (NiFe ₂ O ₄ ) is produced. Therefore, in a state where the corrosion potential of the purification system pipe 18 or the like is maintained at a corrosion potential within the range of 0 mV to +200 mV, as described above, stable nickel ferrite (for example, NiFe ₂ O ₄ ) 88B with large crystals (See FIG. 9) is formed in the nickel metal film 86. This stable nickel ferrite 88B does not elute due to the action of the adhered platinum 87.

In addition, not only oxygen but also hydrogen is generated by the radiolysis of the furnace water 91. This hydrogen in the furnace water 91 reacts with oxygen contained in the furnace water 91 by the action of platinum 87 to become water. Due to such a reaction between hydrogen and oxygen, the corrosion potential of the purification system pipe 18 and the nickel metal film 86 tends to decrease, but compared to the amount of hydrogen generated by radiolysis, the furnace water 91 in the step S18. Since the amount of oxygen injected into is overwhelmingly large, the corrosion potential of the purification system pipe 18 and the nickel metal film 86 becomes a corrosion potential within the range of 0 mV to +200 mV as described above. Radiolysis of the furnace water 91 continues to occur during the operation of the BWR plant 1.

The concentration at which the corrosion potential of the purification system pipe 18 can be maintained at the corrosion potential (high corrosion potential) within the range of 0 mV to +200 mV is, for example, 200 ppb in terms of the dissolved oxygen concentration of the furnace water. When the dissolved oxygen concentration in the furnace water reaches 200 ppb, the corrosion potential of the purification system pipe 18 becomes 0 mV. The period for maintaining the high corrosion potential of the purification system pipe 18 is, for example, a period (predetermined period) within a range of 100 hours or more and 500 hours or less after the purification system pipe 18 reaches the high corrosion potential, for example, 100 hours. Is. The injection of oxygen from the oxidant injection device 25 into the furnace water is continued for the 100 hours. After a predetermined period of time, for example, 100 hours, the injection of oxygen into the furnace water is stopped.

When the period for maintaining the purification system pipe 18 at a high corrosion potential by injecting oxygen into the furnace water is less than 100 hours, the crystal grain size of nickel ferrite contained in the nickel ferrite film converted from the nickel ferrite film is sufficient. Since it does not increase and the density of the grain boundaries of nickel ferrite does not decrease sufficiently, the suppression of adhesion of radionuclides to the purification system pipe 18 is hindered. Further, when the period for maintaining the purification system pipe 18 at a high corrosion potential by injecting oxygen into the furnace water exceeds 500 hours, the dissolved oxygen concentration in the furnace water becomes too high, and stress corrosion in the stainless steel member of the nuclear plant. The probability of cracking increases significantly. In order to solve these problems, the period for maintaining the purification system pipe 18 at a high corrosion potential by injecting oxygen into the furnace water needs to be in the range of 100 hours or more and 500 hours or less.

The furnace water 91 containing the injected oxygen at 130 ° C. or higher comes into contact with the nickel metal film 86 formed on the inner surface of the purification system pipe 18 and to which platinum 87 is attached, and the injection of the oxygen causes corrosion of the purification system pipe 18. Since the potential becomes a corrosion potential in the range of 0 mV to +200 mV, the crystal grain size of the stable nickel ferrite 88B converted from a part of the nickel metal contained in the nickel metal film 86 becomes large as shown in FIG. ..

By the way, oxygen is not injected into the furnace water, and the high corrosion potential in the range of 0 mV to +200 mV is not experienced, and the purification system pipe 18 in which the nickel metal film to which platinum is attached is formed on the inner surface does not contain oxygen. , A furnace water having a temperature of 130 ° C. or higher containing hydrogen having a concentration of hydrogen at which the corrosion potential of the purification system pipe 18 becomes −500 mV is flowed, and when this furnace water comes into contact with the above nickel metal film, the nickel metal film is formed. As shown in FIG. 8, 86 is converted into a nickel ferrite film 88D containing a stable nickel ferrite 88C having a crystal grain size smaller than the crystal grain size of the nickel ferrite 88B shown in FIG.

Hydrogen is injected into the furnace water (step S19). When 100 hours (the period for maintaining the high corrosion potential of the purification system pipe 18) have elapsed from the injection of oxygen into the furnace water, hydrogen is supplied from the hydrogen injection device 28 through the hydrogen injection pipe 29 by opening the on-off valve 99. It is injected into the pipe 11. The injected hydrogen is mixed with the water supply flowing in the water supply pipe 11, and is injected into the furnace water 91 in the RPV3 together with the water supply. The furnace water 91 containing hydrogen is supplied from the RPV 3 to the purification system pipe 18 via the recirculation system pipe 6, and the corrosion potential of the purification system pipe 18 and the like is increased by the above-mentioned oxygen injection on the inner surface of the purification system pipe 18. It comes into contact with the surface of the nickel metal film 86 to which platinum 87 is attached, including nickel ferrite 88B having a large crystal grain size, which is generated when the corrosion potential is in the range of 0 mV to +200 mV. The corrosion potential of the purification system pipe 18 is lowered to, for example, −500 mV by the contact of the furnace water 91 containing hydrogen. The furnace water that contacts the surface of the nickel metal film 86 so that the amount of hydrogen supplied from the hydrogen injection device 28 to the water supply pipe 11 is controlled and the corrosion potential of the purification system pipe 18 is, for example, −500 mV. Adjust the hydrogen concentration of 91. In this embodiment, the corrosion potential of the purification system pipe 18 is maintained at −500 mV by injecting hydrogen.

The corrosion potential of the purification system pipe 18 drops to -500 mV because the oxygen contained in the furnace water 91 reacts with the injected hydrogen in the furnace water 91 by the catalytic action of the platinum 87 to become water, and the furnace water 91 This is because it lowers the dissolved oxygen concentration of.

Even when the corrosion potential of the purification system pipe 18 or the like is, for example, a low corrosion potential of −500 mV after the hydrogen injection into the furnace water 91 is started, it exists on the inner surface of the purification system pipe 18. The nickel metal remaining in the nickel metal film 86 containing nickel ferrite 88B reacts with oxygen transferred from the furnace water 91 into the nickel metal film 86 and Fe ²⁺ transferred from the purification system pipe 18 into the nickel metal film 86. A stable nickel ferrite (for example, NiFe ₂ O ₄ ) 88C is produced in the nickel metal film 86 (see FIG. 9). The crystal grain size of the nickel ferrite 88C is the stable nickel ferrite produced in the step S18. It is smaller than that of 88B.

Eventually, the nickel metal film 86 containing nickel ferrite 88B formed on the inner surface of the purification system pipe 18 is converted into a stable nickel ferrite film 88A containing nickel ferrite 88B and 88C (see FIG. 9). Platinum 87 adheres to the surface, and a stable nickel ferrite film 88A that does not elute even by the action of the platinum 87 covers the entire inner surface of the purification system pipe 18. The nickel ferrite film 88A schematically shown in FIG. 9 is a nickel ferrite 88B crystal except for the three nickel ferrite 88C crystals.

According to this embodiment, the purification system pipe 18 which is a carbon steel member is brought into contact with the inner surface to form a nickel metal film on the inner surface, a noble metal is adhered to the surface of the nickel metal film, and a nuclear power plant is started. The surface of the nickel metal film 86 to which platinum 87 is attached, which is formed on the inner surface of the purification system pipe 18, is brought into contact with the furnace water 91 having a temperature within the range of 130 ° C. or higher and 330 ° C. or lower, and further, oxygen to the furnace water 91 is added. The nickel ferrite film 88A having a large particle size is contained in the nickel ferrite film 88A formed on the inner surface of the purification system pipe 18 in order to make the corrosion potential of the carbon steel member within the range of 0 mV or more and + 200 mV or less by injecting The density of the crystal grain boundaries of nickel ferrite in the nickel ferrite film 88A is further reduced. Therefore, the adhesion of radionuclides (for example, Co-60) to the purification system pipe 18 is further suppressed.

According to this embodiment, the nickel metal film 86 is applied to the corrosive environment-forming water furnace water containing the injected oxygen (oxidizing agent) and setting the corrosion potential of the purification system pipe 18 to the corrosion potential within the range of 0 mV or more and + 200 mV or less. The nickel ferrite film 88A, which is formed through the process of contacting the surfaces of the nickel ferrite 88B and contains crystals of nickel ferrite 88B having a large particle size, has a corrosion potential of the purification system pipe 18 without contacting the furnace water of the corrosive environment forming water quality. By contacting with the furnace water having a corrosive environment mitigation water of −500 mV, the effect of suppressing the adhesion of radioactive nuclei can be further enhanced as compared with the nickel ferrite film converted from the nickel metal film 86.

In this embodiment, the corrosion potential of the purification system pipe 18 including the injected oxygen (oxidizing agent) in the furnace water having a temperature in the range of 130 ° C. or higher and 330 ° C. or lower is set to 0 mV or higher + 200 mV or lower. A nickel ferrite film formed through the process of contacting the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 and to which a noble metal (for example, platinum 87) is attached. 88A is a stable nickel ferrite film (for example, NiFe ₂ O ₄ ) containing crystals of nickel ferrite 88B having a large particle size and which does not elute even by the action of adhered platinum 87. Therefore, the effect of suppressing the adhesion of radionuclides to the purification system pipe 18 by the stable nickel ferrite film 88A covering the inner surface of the purification system pipe 18 can be maintained for a longer period of time. The nickel ferrite film 88A further uses furnace water of corrosive environment mitigation water, which contains hydrogen and makes the corrosion potential of the purification system pipe 18 within the range of -300 mV or less and -500 mV or more, on the inner surface of the purification system pipe 18. The nickel ferrite 88B crystal is formed in the above, and is brought into contact with the surface of the nickel metal film 86 containing the nickel ferrite 88B crystal having a large particle size to which a noble metal (for example, platinum 87) is attached. It contains crystals of nickel ferrite 88C having a smaller particle size than.

Since the film-forming aqueous solution contains one acid and one base component of the pH buffer solution, the pH of the film-forming aqueous solution is not affected by the injection of the nickel formate aqueous solution and the reducing agent (for example, hydrazine). The pH of the film-forming aqueous solution can be maintained at the set value while the film-forming aqueous solution containing one component each of the reducing agent, the pH buffer solution, and the acid and the base is in contact with the surface of the carbon steel member. .. Therefore, it is possible to prevent a decrease in the amount of nickel metal adhering to the inner surface of the purification system pipe 18 due to a change in the pH of the film-forming aqueous solution, and it is possible to increase the amount of nickel metal adhering to the surface thereof. As a result, the time required to form the nickel metal film on the inner surface of the purification system pipe 18 can be shortened.

By setting the pH of the film-forming aqueous solution to a pH in the range of 3.9 or more and 4.2, the amount of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 can be significantly increased (see FIG. 12). ). When the film-forming aqueous solution contains a pH buffer solution, the pH setting value of the film-forming aqueous solution can be set to a pH in the range of 3.9 or more and 4.2, and it is purified in combination with the action of the pH buffer solution. The amount of the nickel metal film 86 formed on the inner surface of the system pipe 18 can be further increased. As a result, the time required to form the nickel metal film 86 on the inner surface of the purification system pipe 18 can be further shortened.

According to this embodiment, a film-forming aqueous solution containing nickel ions and a reducing agent (for example, hydrazine) is brought into contact with the inner surface of the purification system pipe 18, and the inner surface of the purification system pipe 18 is brought into contact with the furnace water. A nickel metal film 86 can be formed to cover the film. The nickel metal film 86 can prevent the elution of Fe ²⁺ from the purification system pipe 18 into the film-forming aqueous solution, and the adhesion of the precious metal (for example, platinum) to the inner surface of the purification system pipe 18 is Fe ²⁺ . It is no longer hindered by elution, and the time required for the noble metal to adhere to the inner surface (specifically, the noble metal to adhere to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18) is shortened. be able to. Further, the noble metal can be efficiently adhered to the inner surface thereof, and the amount of the noble metal adhering to the inner surface of the purification system pipe 18 increases.

In this embodiment, the nickel metal film 86 formed on the inner surface of the purification system pipe 18 contains nickel metal in the range of 50 μg / cm ² or more and 300 μg / cm ² or less. In this way, when nickel metal in the range of 50 μg / cm ² or more and 300 μg / cm ² or less is present, the nickel metal film 86 covers the entire inner surface of the purification system pipe 18 in contact with the film-forming aqueous solution. Therefore, during the operation of the BWR plant 1, the contact of the furnace water flowing in the purification system pipe 18 with the base material of the purification system pipe 18 is blocked by the nickel metal film 86. Therefore, the radionuclides contained in the furnace water are not taken into the base material of the purification system pipe 18.

In the formation of the nickel metal film 86 on the inner surface of the purification system pipe 18, the nickel ions contained in the film-forming aqueous solution are taken into the inner surface of the purification system pipe 18 by the replacement plating reaction with the iron contained in the purification system pipe 18 to purify. Nickel ions adsorbed on the inner surface of the pipe are reduced to nickel metal by the electrons generated by the elution of Fe ²⁺ from the system pipe 18 or the hydrazine (reducing agent) contained in the film-forming aqueous solution. As described above, the nickel metal produced by the substitution plating reaction and the reducing action of the electron or the reducing agent has strong adhesion to the base material of the purification system pipe 18. Therefore, the formed nickel metal film 86 does not come off from the purification system pipe 18.

In this embodiment, after the inner surface of the purification system pipe 18 is reduced and decontaminated, a nickel metal film 86 is formed on the inner surface of the purification system pipe 18, so that the oxidation containing radionuclides formed on the inner surface of the purification system pipe 18 No nickel metal film is formed on the film, the radiation emitted from the purification system piping 18 is reduced, and the surface dose rate of the purification system piping 18 is significantly reduced.

Iron (II) oxalate formed on the inner surface of the purification system pipe 18, which is a carbon steel member, during reduction decontamination of the inner surface of the purification system pipe 18 using an oxalic acid aqueous solution and at the time of decomposition of oxalic acid. It is removed by the action of an oxidizing agent (for example, hydrogen peroxide) injected into an acid aqueous solution. By removing the iron (II) oxalate, the adhesion between the purification system pipe 18 and the nickel metal film 86 is improved, and the nickel metal film 86 can be prevented from peeling off from the inner surface of the purification system pipe 18.

In this embodiment, the nickel metal film 86 is formed on the inner surface of the purification system pipe 18, and the platinum 87 is attached to the nickel metal film 86 while the operation of the BWR plant 1 is stopped. The conversion to the nickel ferrite film 88A is performed after the start of the BWR plant 1. Therefore, when the temperature of the furnace water is less than 130 ° C., the nickel metal film 86 is not changed to the nickel ferrite film 88A, and the inner surface of the purification system pipe 18 is covered with the nickel metal film 86 to which platinum 87 is attached. (See Fig. 6). Even in this state, the corrosion potential of the purification system pipe 18 and the nickel metal film 86 in contact with the furnace water 91 is lowered by the action of platinum 87, and the radionuclides are taken into the nickel metal film 86 and the purification system pipe 18. do not have. In this way, the adhesion of radionuclides to the purification system pipe 18 is suppressed.

The platinum 87 adhering to the stable nickel ferrite film 88A not only acts on the conversion of the nickel metal film 86 to the stable nickel ferrite film 88A, but also dissolves in the furnace water 91 during the operation of the BWR plant 1. It also functions as a catalyst for producing water by reacting hydrogen injected into the furnace water 91 by injecting oxygen and hydrogen. Therefore, the dissolved oxygen concentration of the furnace water 91 is reduced, and the occurrence of stress corrosion cracking in the stainless steel structural member of the BWR plant 1 (for example, the recirculation system pipe 6 and the like) is suppressed. Further, in this embodiment, the corrosion potential of the purification system pipe 18 and the nickel ferrite film 88A is −300 mV or less due to the action of the hydrogen injected in the step S19 and the platinum 87 adhering to the nickel ferrite film 88A. The corrosion potential is in the range of -500 mV or higher, for example, -500 mV. In the state of low corrosion potential within the range of -300 mV or less and -500 mV or more, the hydrogen injected into the furnace water is a carbon steel pipe having a stable nickel ferrite film 88A with platinum 87 attached on the inner surface, for example, a purification system. It works effectively to suppress the adhesion of radionuclides to the pipe 18. It has been confirmed by the tests of the inventors that the adhesion of radionuclides to the carbon steel member is suppressed when the carbon steel member is in such a low corrosion potential state.

The method for suppressing the adhesion of radionuclides to the carbon steel member of the nuclear power plant of Example 2 which is another preferred embodiment of the present invention will be described below with reference to FIG. The method for suppressing the adhesion of radionuclides to the carbon steel member of this embodiment is applied to the purification system piping of the BWR plant.

Also in the method for suppressing the adhesion of radionuclides to the carbon steel member of this embodiment, each of the steps S1 to S19 carried out in the method for suppressing the adhesion of radionuclides in the nuclear power plant of Example 1 is carried out. Unlike the first embodiment, this embodiment uses a corrosion potential measuring device having a corrosion potential measuring device 92 and a corrosion potential sensor 93. The corrosion potential sensor 93 is attached to the purification system pipe 18 and is arranged in a cylindrical fixing seat 18A, and is attached to the fixing seat 18A. In the fixing seat 18A, one end on the purification system piping 18 side is open, and the other end on the opposite side to the one end is closed. The corrosion potential sensor 93 is connected to the corrosion potential measuring device 92 arranged outside the purification system pipe 18 and the fixing seat 18A by wiring. The corrosion potential measuring device 92 is connected to the oxidizing agent injection device 25 via an oxygen injection amount control device (not shown) by other wiring.

Of the steps S1 to S18, the step S18 (the injected oxygen-containing furnace water is brought into contact with the nickel metal film to which platinum is attached to bring the corrosion potential of the purification system pipe 18 and the nickel metal film to 0 mV or more. At a high corrosion potential of +200 mV or less), this high corrosion potential is measured using the corrosion potential sensor 93 and the corrosion potential measuring device 92. A carbon steel member covered with a nickel metal film to which platinum is adhered is arranged at the tip of the corrosion potential sensor 93.

The measurement of the corrosion potential of the purification system pipe 18 by the corrosion potential sensor 93 and the corrosion potential measuring device 92 will be described below. The tip of the corrosion potential sensor 93 arranged in the fixing seat 18A, that is, the nickel metal film to which platinum is attached covering the carbon steel member flows in the purification system pipe 18 in the fixing seat 18A. It is in contact with the furnace water. Such a corrosion potential sensor 93 generates an electric potential according to the oxygen concentration contained in the furnace water and the hydrogen concentration contained in the furnace water. The corrosion potential measuring device 92 to which this potential is transmitted measures the corrosion potential of the carbon steel member covered with the nickel metal film. The measured corrosion potential of the carbon steel member existing at the tip of the corrosion potential sensor 93 is the corrosion potential of the purification system pipe 18.

The corrosion potential of the purification system pipe 18 measured by the corrosion potential measuring device 92 is input to the oxygen injection amount control device. The oxygen injection amount control device compares the measured corrosion potential with a predetermined corrosion potential (set corrosion potential) within the range of 0 mV or more and + 200 mV or less, and when the measured corrosion potential is lower than the set corrosion potential, , The opening degree of the on-off valve provided in the oxidizing agent injection pipe 26 is increased to increase the amount of oxygen injected into the furnace water flowing in the purification system pipe 18. When the corrosion potential measured by the corrosion potential measuring device 92 becomes the set corrosion potential due to the increase in the oxygen injection amount, the oxygen injection amount control device is used so that the corrosion potential of the purification system pipe 18 maintains the set corrosion potential. The opening degree of the on-off valve is adjusted.

Further, when the corrosion potential of the purification system pipe 18 measured by the corrosion potential measuring device 92 becomes lower than −500 mV due to hydrogen injection in the step (hydrogen injection step) of step S19, it is measured from the corrosion potential measuring device 92. The oxygen injection amount control device that inputs the corrosion potential increases the opening degree of the on-off valve provided in the oxidizing agent injection pipe 26 to increase the amount of oxygen injected into the furnace water flowing in the purification system pipe 18. The opening degree of the on-off valve is adjusted so as to maintain the corrosion potential of the purification system pipe 18 at −500 mV.

Further, hydrogen injection into the furnace water is started as a measure for suppressing the occurrence of stress corrosion cracks in the stainless steel member of the BWR plant 1 (step S19), but after the hydrogen is injected into the water supply, the water supply containing hydrogen is supplied to the furnace. Since there is a time delay before the hydrogen-containing furnace water mixed with water comes into contact with the stainless steel member, the hydrogen injection into the water supply is a period during which the high corrosion potential of the purification system pipe 18 is maintained, for example. It may be carried out before 100 hours have passed. In this case, the oxygen concentration in the furnace water decreases due to the reaction of hydrogen and oxygen due to the injection of hydrogen, and the corrosion potential of the purification system pipe 18 may drop below 0 mV before 100 hours have elapsed. .. When the corrosion potential of the purification system pipe 18 drops below 0 mV due to hydrogen injection, the corrosion potential of the purification system pipe 18 measured by the corrosion potential measuring device 92 is injected with oxygen using the potential input from the corrosion potential sensor 93. The amount control device inputs, and the oxygen injection amount control device compares the input corrosion potential with the set corrosion potential so that the input corrosion potential becomes the set corrosion potential (corrosion potential within the range of 0 mV or more + 200 mV or less). , The opening degree of the on-off valve provided in the oxidizing agent injection pipe 26 is controlled to adjust the amount of oxygen to be injected into the furnace water flowing in the purification system pipe 18. By this control, the corrosion potential of the purification system pipe 18 is maintained at the set corrosion potential for the 100 hours.

When the period for maintaining the high corrosion potential of the purification system pipe 18 reaches 100 hours, the oxygen injection amount control device reduces the opening degree of the on-off valve provided in the oxidant injection pipe 26 and injects it into the purification system pipe 18. The amount of oxygen generated is reduced, and the corrosion potential of the purification system pipe 18 is lowered to −500 mV.

In this example, all the effects produced in Example 1 can be obtained. Further, in this embodiment, since the corrosion potential of the purification system pipe 18 can be measured by using the corrosion potential measuring device, the oxidizing agent injection device 25 is operated by the oxygen injection amount control device based on the corrosion potential of the purification system pipe 18. The amount of oxygen injected into the purification system pipe 18 can be adjusted, and the corrosion potential of the purification system pipe 18 can be easily adjusted.

Each of Examples 1 and 2 may be applied to a pressurized water nuclear power plant.

1 ... Boiling water type nuclear power plant, 2 ... Reactor, 3 ... Reactor pressure vessel, 4 ... Core, 6 ... Recirculation system piping, 7 ... Recirculation pump, 9 ... Turbine, 11 ... Water supply piping, 18 ... Purification System piping, 25 ... Oxidizing agent injection device, 26 ... Oxidizing agent injection piping, 30 ... Film forming device, 31 ... Surge tank, 32, 33 ... Circulation pump, 34 ... Circulation piping, 35 ... Nickel ion injection device, 36, 41 , 46, 57, 82 ... Chemical tank, 37, 42, 47, 83 ... Injection pump, 40 ... Reducing agent injection device, 45 ... Platinum ion injection device, 51 ... Heater, 52 ... Cooler, 53 ... Cation exchange resin Tower, 54 ... Mixed bed resin tower, 55 ... Decomposition device, 56 ... Oxidizer supply device, 58 ... Supply pump, 81 ... Buffer solution injection device, 86 ... Nickel metal film, 87 ... Platinum, 88A, 88D ... Nickel ferrite film , 92 ... Corrosion potential measuring instrument, 93 ... Corrosion potential sensor.

Claims (15)

A film-forming liquid containing nickel ions is brought into contact with the first surface of the carbon steel member of the nuclear plant in contact with the furnace water to form a nickel metal film on the first surface, and on the second surface of the nickel metal film. The noble metal is attached, and the formation of the nickel metal film and the attachment of the noble metal are performed after the operation of the nuclear plant is stopped and before the start of the nuclear plant, and after the start of the nuclear plant, the nickel to which the noble metal is attached. The corrosion potential of the carbon steel member is set to 0 mV or more by bringing the furnace water having a temperature within the range of 130 ° C. or higher and 330 ° C. or lower into contact with the first surface of the metal film and injecting an oxidizing agent into the furnace water. A method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear power plant. The method for suppressing adhesion of radioactive nuclei to a carbon steel member of a nuclear power plant according to claim 1, wherein the corrosion potential of the carbon steel member is set to a corrosion potential within the range of 0 mV or more and +200 mV or less by injecting the oxidizing agent. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 1 or 2, wherein the injection of the oxidizing agent into the furnace water is performed by an oxidizing agent injection device. The corrosion potential of the carbon steel member on which the nickel metal film is formed is measured by a corrosion potential measuring device, and the oxidizing agent is injected from the oxidizing agent injection device into the furnace water based on the measured corrosion potential. The method for suppressing adhesion of radioactive nuclei to carbon steel members of a nuclear power plant according to claim 3, wherein the amount is adjusted. Claim 1 that the first period for maintaining the corrosion potential of the carbon steel member at 0 mV or more exists before the second period for maintaining the corrosion potential of the carbon steel member at less than 0 mV by hydrogen to the furnace water. The method for suppressing adhesion of radioactive nuclei to carbon steel members of a nuclear power plant according to any one of 4 to 4. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 5, wherein the first period is a period in the range of 100 or more and 500 hours or less. The nuclear plant according to any one of claims 1 to 6, wherein one type of each of an acid and a base of a pH buffer solution is injected into the film-forming liquid that comes into contact with the first surface of the carbon steel member. A method for suppressing the adhesion of radionuclides to carbon steel members. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 7, wherein the pH of the film-forming liquid is in the range of 3.9 or more and 4.2 or less. A film-forming liquid containing nickel ions is supplied to the first pipe through the second pipe connected to the first pipe, which is the first pipe connected to the reactor and is a carbon steel member.
The supplied film-forming liquid is brought into contact with the inner surface of the first pipe to form a nickel metal film on the inner surface of the first pipe.
An aqueous solution containing a noble metal ion and a reducing agent is supplied from the second pipe to the first pipe, the aqueous solution is brought into contact with the surface of the nickel metal film, and the noble metal is adhered to the surface of the nickel metal film.
The formation of the nickel metal film and the adhesion of the noble metal are performed after the operation of the nuclear plant is stopped and before the start of the nuclear plant.
After starting the nuclear power plant, the surface of the nickel metal film to which the noble metal is attached is brought into contact with furnace water having a temperature within the range of 130 ° C. or higher and 330 ° C. or lower.
A method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant, which comprises injecting an oxidizing agent into the furnace water to raise the corrosion potential of the first pipe to 0 mV or more. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 9, wherein the corrosion potential of the first pipe is set to a corrosion potential within the range of 0 mV or more and + 200 mV or less by injecting the oxidizing agent. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 9 or 10, wherein the injection of the oxidant into the furnace water is performed by the oxidant injection device connected to the first pipe. The corrosion potential of the carbon steel member on which the nickel metal film is formed is measured by a corrosion potential measuring device, and the oxidizing agent is injected from the oxidizing agent injection device into the furnace water based on the measured corrosion potential. The method for suppressing adhesion of radioactive nuclei to carbon steel members of a nuclear power plant according to claim 11, wherein the amount is adjusted. 9. The first period for maintaining the corrosion potential of the first pipe at 0 mV or more exists before the second period for maintaining the corrosion potential of the carbon steel member at less than 0 mV due to hydrogen to the furnace water. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to any one of 12 to 12. The carbon of a nuclear power plant according to any one of claims 9 to 13, wherein one type of each of an acid and a base of a pH buffer solution is injected into the film-forming liquid that comes into contact with the inner surface of the first pipe. A method for suppressing the adhesion of radionuclides to steel members. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 14, wherein the pH of the film-forming liquid is in the range of 3.9 or more and 4.2 or less.

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