JP6894862B2 - Method for suppressing radionuclide adhesion to carbon steel components of nuclear power plants - Google Patents

Description

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

For example, a boiling water reactor (hereinafter referred to as a BWR plant) has a nuclear reactor in which a core is arranged in a reactor pressure vessel (hereinafter referred to as RPV). The reactor water supplied to the core by the recirculation pump (or internal pump) is heated by the heat generated by the fission of the nuclear fuel material in the fuel assembly loaded in the core, and a part of it becomes steam. This steam is guided from the RPV to the turbine to rotate the turbine. The steam discharged from the turbine is condensed into water by the condenser. This water is supplied to the reactor as water supply through a water supply pipe. In the water supply, in order to suppress the generation of radioactive corrosion products in the RPV, metal impurities are mainly removed by a filtration desalting device provided in the water supply pipe. The furnace water is the cooling water existing in the RPV.

In addition, since the corrosion products that are the source of radioactive corrosion products are generated on the surface of the components of the BWR plant such as RPV and recirculation system piping that come into contact with the furnace water, they are the main components that come into contact with the furnace water. Uses stainless steel and nickel-based alloys that are less corrosive. Further, the RPV made of low alloy steel is overlaid with stainless steel on the inner surface to prevent the low alloy steel from coming into direct contact with the furnace water. Further, a part of the reactor water is purified by the filtration desalination device of the reactor purification system, and the metal impurities slightly present in the reactor water are positively removed.

In addition, since the corrosion products that are the source of the radioactive corrosion products are also generated from the water contact parts such as RPV and recirculation system piping, the main primary system components are stainless steel and nickel group with less corrosion. Non-corrosive steel such as alloy is used. Further, the RPV made of low alloy steel is overlaid with stainless steel on the inner surface to prevent the low alloy steel from coming into direct contact with the furnace water (cooling water existing in the RPV). The reactor water is the cooling water existing in the reactor. Further, a part of the reactor water is purified by the filtration desalination device of the reactor purification system, and the metal impurities slightly present in the reactor water are positively removed.

Even if the above-mentioned corrosion countermeasures are taken, it is inevitable that a very small amount of metal impurities remain in the furnace water, so that some metal impurities adhere to the surface of the fuel rods contained in the fuel assembly as metal oxides. To do. Metal impurities (for example, metal elements) adhering to the surface of the fuel rods cause a nuclear reaction by irradiation with neutrons generated by nuclear fission of the nuclear fuel material in the fuel rods, and are radioactive such as cobalt-60, cobalt 58, chromium 51, and manganese 54. Become a nuclear species. Most of these radionuclides remain attached to the fuel rod surface in the form of oxides, while some radionuclides elute as ions in the furnace water depending on the solubility of the oxides incorporated. Or, it is re-released into the furnace water as an insoluble solid called a clad. Radioactive materials contained in reactor water are removed by the reactor purification system. However, the radioactive material that has not been removed is accumulated on the surface of the constituent members constituting the BWR plant 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 radiated from the surface of the component member, which causes radiation exposure of the worker during the regular inspection work. The radiation dose of the employee is controlled so as not to exceed the specified value for each person. In recent years, this regulation value has been lowered, and it has become necessary to reduce the exposure dose of each person as economically as possible.

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

In addition, various methods for reducing the adhesion of radionuclides to pipes have been studied. For example, in order to suppress the adhesion of radionuclides to the surface of the constituent members of a nuclear power plant, Japanese Patent Application Laid-Open No. 8-220293 discloses that metal ions such as zinc and nickel are injected into the furnace water, and zinc and zinc and metal ions such as nickel are injected into the surface of the constituent members. It describes that nickel is attached.

A method of forming a magnetite film, which is a kind of ferrite film, on the surface of a nuclear plant component after chemical decontamination to prevent radionuclides from adhering to the surface of the component after the operation of the plant is described in JP-A. It is proposed in Japanese Patent Application Laid-Open No. 2006-38483. Further, in Japanese Patent Application Laid-Open No. 2006-38483, after forming a magnetite film on the surface of a component member, a nuclear power plant is started, and furnace water in which a 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 component 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 carbon steel constituent members and suppresses the adhesion of radionuclides to the constituent members.

Further, Japanese Patent Application Laid-Open No. 2012-247322 uses 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) while the nuclear power plant is shut down. It describes the contacting with the surface of a chemically decontaminated stainless steel component of a plant to form a magnetite film on this 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) on 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. 8-220293 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

As described above, various proposals have been proposed as methods for suppressing the adhesion of radionuclides to the constituent members of a nuclear power plant. Such a radionuclide adhesion control method carried out during the shutdown of a nuclear plant will take the time required to implement the radionuclide bond control method in consideration of the maintenance and inspection of the nuclear plant carried out during the shutdown. It is hoped that it will be further shortened.

Therefore, the inventors have investigated a method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant, which can reduce the number of steps required to implement the method for suppressing radionuclide adhesion.

An object of the present invention is to provide a method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant, which can reduce the number of steps.

The feature of the present invention to achieve the above object is to form a nickel metal film on the surface of the carbon steel member of the nuclear plant in contact with water, cover the surface with the nickel metal film, and cover the noble metal particles containing nickel metal with the nickel metal film. It adheres to the surface of the nickel metal film, and the nickel metal film to which the noble metal particles adhere is brought into contact with water containing oxygen at a temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower to form the nickel metal film and the noble metal. The adhesion of particles is to occur after the shutdown of the nuclear plant and before the start of the nuclear plant.

Since the noble metal particles containing nickel metal are attached to the surface of the nickel metal film formed on the surface of the carbon steel member of the nuclear plant, the number of steps of the method for suppressing the adhesion of radioactive nuclei to the carbon steel member of the nuclear plant is reduced. be able to.

According to the present invention, it is possible to reduce the number of steps of the method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant.

It is a flowchart which shows the procedure of the radionuclide adhesion suppression method to the carbon steel 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 film forming apparatus used when carrying out the radionuclide adhesion suppression method to the carbon steel member of the nuclear power plant of Example 1 to the purification system piping of a boiling water nuclear power plant. It is a detailed block diagram of the film forming apparatus shown in FIG. It is sectional drawing of the purification system piping of the boiling water type nuclear power plant before the method of suppressing the radionuclide adhesion to the carbon steel member of the 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 radionuclide adhesion suppression method to the carbon steel member of the nuclear power plant shown in FIG. Explanatory drawing showing a state in which noble metal particles containing nickel metal are adhered to the surface of a nickel metal film formed on the inner surface of a purification system pipe by the method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant shown in FIG. Is. It is explanatory drawing which shows various forms of the noble metal particle containing a nickel metal shown in FIG. In the method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant shown in FIG. 1, water containing oxygen at 130 ° C. or higher is contained in a nickel metal film formed on the inner surface of a purification system pipe to which precious metal particles containing nickel metal are attached. It is explanatory drawing which shows the state which makes contact. In the method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant shown in FIG. 1, oxygen contained in water at 130 ° C. or higher and Fe ²⁺ in the purification system piping are formed on the inner surface of the purification system piping. It is explanatory drawing which shows the state which shifts to the nickel metal film with platinum attached. FIG. 5 is an explanatory diagram showing a state in which a nickel metal film formed on the inner surface of a purification system pipe is converted into a stable nickel ferrite film in the method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant shown in FIG. It is explanatory drawing which showed the adhesion result ^{of 60} Co to various carbon steel test pieces immersed in the simulated furnace water containing ^{60 Co.} It is an electron micrograph of a state in which platinum particles containing nickel metal are attached to the surface of nickel metal covering a carbon steel test piece. It is explanatory drawing which shows the element composition ratio of the platinum particle containing a nickel metal shown in FIG. It is a flowchart which shows the procedure of the radionuclide adhesion suppression method to the carbon steel 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. .. Heating connected to the purification system pipe in order to convert the nickel metal film formed on the inner surface of the purification system pipe into a stable nickel ferrite film in the method for suppressing the adhesion of radionuclides to the carbon steel member of the plant shown in FIG. It is a block diagram of a system. It is a flowchart which shows the procedure of the radionuclide adhesion suppression method to the carbon steel member of the nuclear power plant of Example 3 applied to the purification system piping of the boiling water reactor which is another Example of this invention.

The inventors conducted detailed studies and experiments in order to further enhance the effect of the anticorrosion method for carbon steel members described in Japanese Patent Application Laid-Open No. 2011-32551. According to Japanese Patent Application Laid-Open No. 2011-32551, a nickel metal film is formed on the surface of a carbon steel member of a BWR plant, a nickel ferrite film is formed on the surface of the nickel metal film, and further, a nickel ferrite film is formed on the surface of the nickel metal film while the BWR plant is stopped. During the operation, water containing oxygen at 150 ° C. or higher is brought into contact with the surface of the nickel ferrite film to convert the above nickel metal film into a nickel ferrite film. As a result of the examination by the inventors, the inventors finally adhered the noble metal to the surface of the nickel metal film formed on the surface of the carbon steel member, and contained oxygen at 130 ° C. or higher (preferably 130 ° C. or higher). Water in the temperature range of 330 ° C. or lower) is brought into contact with the surface of the nickel metal film to convert the nickel metal film into a stable nickel ferrite film having a Ni content close to a constant ratio, thereby forming the carbon steel member. We have found that the effect of suppressing the adhesion of radioactive nuclei can be maintained for a longer period of time.

The inventors examined the simultaneous feasibility of the precious metal injection technology and the above-mentioned ferrite film forming technology, which have been introduced as measures against stress corrosion cracking in recent years. The ferrite film forming technique includes iron (II) ions, an oxidizing agent and a pH adjuster (for example, hydrazine) as described in JP-A-2006-38483 and JP-A-2012-247322 described above. In some cases, a film-forming liquid in a low temperature range of 60 ° C. to 100 ° C. is brought into contact with the surface of a component member of a nuclear plant to form a magnetite film on the surface of the component member. When a noble metal was attached to the surface of the magnetite film in contact with the furnace water and the effect of the noble metal was investigated, the furnace was operated by the action of the noble metal to which the magnetite film was attached during operation of the nuclear power plant under simulated hydrogen injection conditions. We found the phenomenon of elution in water. Further, even when a noble metal is adhered on a nickel ferrite film formed on the surface of a carbon steel member in contact with the furnace water in a low temperature range of 60 ° C. to 100 ° C., the operation under hydrogen injection simulated conditions of a nuclear plant is performed. We found a phenomenon in which the nickel-ferrite film elutes into the furnace water due to the action of the noble metal attached.

Such elution of the ferrite film formed on the surface of the carbon steel member eventually results in the disappearance of the ferrite film on the carbon steel member, and after the ferrite film disappears, that is, at the end of the operation cycle, by the ferrite film. The effect of suppressing the adhesion of radioactive nuclei that has been brought about disappears. Therefore, after stopping the operation of the nuclear power plant in this operation cycle, it is necessary to form a ferrite film again on the surface of the carbon steel member.

The reason why the nickel ferrite elutes when the noble metal is adhered to the nickel ferrite film formed on the surface of the carbon steel member in contact with the furnace water in a low temperature range of 60 ° C. to 100 ° C. will be described below. It was found that the nickel ferrite film formed on the surface of the carbon steel member in such a low temperature range was a film of Ni _0.7 Fe _2.3 O ₄ and was unstable during the shutdown of the nuclear plant. Note that Ni _0.7 Fe _2.3 O ₄ is a form in which x is 0.3 in _{Ni 1-x} Fe _{2 + x} O _4. Therefore, for example, when platinum is adhered on the unstable film Ni _0.7 Fe _2.3 O _{4 film, Ni 0.7} Fe _2.3 O ₄ is produced by the action of the platinum in the reactor during the operation of the nuclear power plant. Elute in water. Further, since the unstable Ni _0.7 Fe _2.3 O ₄ film is formed in the above low temperature range, a large number of small particles _{of Ni 0.7} Fe _2.3 O _{4 are attached to the surface of the carbon steel member.} ing. For this reason as well, a film of _{Ni 0.7} Fe _2.3 O ₄ with platinum attached to the upper surface elutes.

As described in Japanese Patent Application Laid-Open No. 2011-32551, a nickel ferrite film covering a nickel metal film formed on the surface of a carbon steel member of a BWR plant is brought into contact with water containing oxygen at 150 ° C. or higher. When the nickel metal film is converted into a nickel ferrite film, the nickel ferrite film converted from the nickel metal film becomes an unstable nickel ferrite film, for example, a Ni _0.7 Fe _2.3 O ₄ film.

The reason for this will be explained below. In Japanese Patent Application Laid-Open No. 2011-32551, as described above, a film-forming aqueous solution (film-forming solution) containing nickel ion, iron (II) ion and an oxidizing agent and having a pH in the range of 5.5 to 9.0 is used. A nickel ferrite film is formed on the nickel metal film in contact with the nickel metal film. Therefore, the nickel ferrite contained in this nickel ferrite film becomes nickel ferrite having a large amount of Fe, that is, nickel ferrite having less Ni and more Fe _{than Ni 0.7 Fe 2.3} O _4.

In Japanese Patent Application Laid-Open No. 2011-32551, a nickel ferrite film containing nickel ferrite having a high iron content formed on the nickel metal film is brought into contact with water at 150 ° C. containing oxygen to form the nickel ferrite film in the nickel ferrite film. Iron ions from nickel ferrite having a high iron content, oxygen contained in water at 150 ° C., and iron contained in the carbon steel member migrate to the nickel metal film and react with nickel in the nickel metal film, as described above. Unstable nickel ferrite (eg Ni _0.7 Fe _2.3 O ₄ ) is produced. As a result, the nickel metal film formed on the surface of the carbon steel member is converted into an _{unstable nickel ferrite film (for example, Ni 0.7} Fe _2.3 O _{4 film).} The conversion of the nickel metal film to the unstable nickel ferrite film is because when the nickel metal film is converted to the nickel ferrite film, the amount of iron supplied to the nickel metal film increases and the amount of nickel becomes insufficient. The nickel ferrite film that originally covered the nickel metal film reacts with the nickel metal transferred from the nickel metal film after contact with high-temperature water to form a Ni _0.7 Fe _2.3 O ₄ film. The Ni content of nickel ferrite in the _{original nickel ferrite film is lower than that of Ni 0.7} Fe _2.3 O ₄ , and the original nickel ferrite film is an unstable nickel ferrite film in a reducing environment.

Therefore, when a noble metal injected during the operation of a BWR plant, for example platinum, adheres to the surface of the unstable nickel film, the nickel ferrite film is eluted into the furnace water by the action of the noble metal (for example, platinum). Eventually, at the end of the operation cycle, the nickel ferrite film that originally covered the nickel metal film and the nickel ferrite film converted from the nickel metal film may disappear, exposing the carbon steel members and coming into contact with the furnace water. There is.

By the way, when the noble metal is attached to the surface of the carbon steel member, if Fe contained in the carbon steel member is ^{eluted as Fe 2+} , the noble metal cannot be attached to the surface of the carbon steel member. Therefore, the inventors have studied measures to prevent the elution ^{of Fe 2+} from the carbon steel member when the noble metal is attached to the surface of the carbon steel member. Then, the inventors have found that the elution ^{of Fe 2+} from the carbon steel member can be prevented by covering the surface of the carbon steel member with a nickel metal film. The nickel metal covering the surface of the carbon steel member is a substance that contributes to the formation of a stable nickel ferrite film that suppresses corrosion of the carbon steel member, as will be described later. By forming a nickel metal film on the surface of the carbon steel member and covering the surface of the carbon steel member with this nickel metal film, ^{it is possible to prevent Fe 2+} from elution from the carbon steel member, and the surface of the nickel metal film of the noble metal. It was possible to adhere to the metal in a short time. At the same time, the amount of noble metal adhering to the carbon steel member also increased.

The formation of a nickel metal film on the surface of a carbon steel member contains an aqueous solution (film formation) containing nickel ions and having a pH in the range of 3.5 to 6.0 and a temperature in the temperature range of 60 ° C. or higher and 100 ° C. or lower. It is possible by bringing an aqueous solution) into contact with the surface of the carbon steel member. The nickel ions contained in the film-forming aqueous solution are replaced with Fe contained in the carbon steel member, and the substituted nickel ions act as electrons generated by elution ^{of Fe 2+ from the carbon steel member into the film-forming aqueous solution.} Becomes nickel metal, and a nickel metal film is formed on the surface of the carbon steel member. The nickel ions contained in the aqueous solution can be attached to the surface of the carbon steel member even when ^{Fe 2+ is eluted from the carbon steel member.}

In the formation of the nickel metal film on the surface of the carbon steel member during the reduction decontamination agent decomposition step, nickel ions and oxalic acid were contained, and the pH was in the range of 3.5 to 6.0 and the temperature was 60 ° C. An aqueous solution (film-forming aqueous solution) having a temperature within the temperature range of 100 ° C. or lower is used. After the reduction decontamination agent decomposition step is completed, for example, in the formation of a nickel metal film on the surface of a carbon steel member after the purification step of chemical decontamination, the pH is 3 which contains nickel ions and does not contain oxalic acid. An aqueous solution (film forming aqueous solution) having a temperature in the range of .5 to 6.0 and a temperature in the range of 60 ° C. or higher and 100 ° C. or lower is used.

When the film-forming aqueous solution having a pH higher than 6.0 comes into contact with the surface of the carbon steel member, the amount of iron (II) ions eluted from the carbon steel member is reduced and the number of electrons generated is also reduced. When the number of electrons is small, the reduction of nickel ions to the nickel metal is suppressed, and the nickel metal is not generated on the surface of the carbon steel member. In order to generate nickel metal on the surface of the carbon steel member, the pH of the film-forming aqueous solution needs to be 6.0 or less. Further, when the pH of the film-forming aqueous solution is made smaller than 3.5, the amount of nickel metal adhering to the surface of the carbon steel member becomes very small. Therefore, by setting the pH of the film-forming aqueous solution that comes into contact with the surface of the carbon steel member within the range of 3.5 or more and 6.0 or less, a nickel metal film can be formed on the surface.

As described above, by forming a nickel metal film on the surface of the carbon steel member, ^{it is possible to prevent the elution of Fe 2+} from the carbon steel member, and to attach more precious metal to the carbon steel member in a short time. be able to. The noble metal can be attached to the surface of the nickel metal film formed on the surface of the carbon steel member by bringing an aqueous solution containing a noble metal ion (for example, platinum ion) and a reducing agent into contact with the formed nickel metal film. Is.

The nickel ion aqueous solution is brought into contact with the surface of the carbon steel member, and the nickel ions incorporated into the carbon steel member are reduced by the reduction of electrons generated by the elution ^{of Fe 2+ from the carbon steel member into the aqueous solution.} It can also be nickel metal. In this case, it is not necessary to inject the reducing agent into the nickel ion aqueous solution, and the step of injecting the reducing agent becomes unnecessary.

As the noble metal to be adhered to the nickel metal film formed on the surface of the carbon steel member, any one of platinum, palladium, rhodium, ruthenium, osmium and iridium may be used. Further, as the reducing agent used when forming the noble metal on the surface of the nickel metal film, any one of hydrazine derivatives such as hydrazine, formhydrazine, hydrazinecarbamide and carbhydrazide and hydroxylamine may be used.

_{The inventors do not form an unstable Ni 0.7} Fe _2.3 O ₄ film on the surface of the carbon steel member in the low temperature range of 60 ° C to 100 ° C, but stable nickel ferrite that is not eluted by the attached noble metal. By forming the film on the surface of the carbon steel member, we aimed to realize a longer-term suppression of the adhesion of radioactive nuclei to the carbon steel member of the nuclear plant. Therefore, the inventors have variously used the nickel metal film formed on the surface of the carbon steel member for the formation of a stable nickel ferrite film in order to effectively attach the noble metal to the carbon steel member. Was examined. As a result, a nickel metal film formed on the surface of the carbon steel member with water having a temperature within the temperature range of 130 ° C. or higher (preferably 130 ° C. or higher and 330 ° C. or lower) with platinum adhered to the nickel metal film. By contacting the surface with the noble metal attached, the nickel metal film covers the surface of the carbon steel member, and a stable nickel ferrite film (Ni _1-x Fe _{2+) that does not elute even by the action of the attached noble metal.} It was possible to convert to a _{nickel ferrite film (NiFe 2} O ₄ film) in which x is 0 in _x O _4.

A nickel metal film formed on the surface of a carbon steel member to which a noble metal (for example, platinum) is attached comes into contact with water having a temperature in the range of 130 ° C. or higher (preferably 130 ° C. or higher and 330 ° C. or lower) containing oxygen. This will explain the reason why it is converted into a _{stable nickel ferrite film (NiFe 2} O ₄ film) that covers the surface of the carbon steel member. When water of 130 ° C. or higher comes into contact with the nickel metal film on the carbon steel member, the nickel metal film and the carbon steel member are heated to 130 ° C. or higher. 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 nickel ferrite in which x is 0 in _{Ni 1-x} Fe _{2 + x} O ₄ Is generated. At this time, the ease of incorporating nickel and iron into the ferrite structure is affected by the noble metal, and when the noble metal is present, nickel is more easily incorporated than iron. Therefore, Ni _1-x Fe _{2+ A} stable nickel ferrite with x 0 is produced at x O _4. This stable nickel-ferrite film covers the surface of the carbon steel member.

The nickel ferrite produced as described above, _{in which x is 0 in Ni 1-x} Fe _{2 + x} O ₄ , has large crystal growth, and even if a noble metal adheres, it is a Ni _0.7 Fe _2.3 O ₄ film. As described above, it is stable without being eluted in water, and acts to suppress the adhesion of radionuclides to the carbon steel of the base material. In this _{stable nickel ferrite in which x is 0 in Ni 1-x} Fe _{2 + x} O ₄ , the corrosion potential of the carbon steel member and the nickel metal film is lowered by the action of a noble metal such as platinum adhering to the nickel metal film. Is generated for. Thus, in a high temperature environment of 130 ° C. or higher, the stable nickel ferrite film formed from the nickel metal covering the surface of the carbon steel member in the presence of platinum has a low temperature range of 60 ° C. to 100 ° C. It is possible to suppress the adhesion of radioactive nuclei to the carbon steel member for a longer period of time than the Ni _0.7 Fe _2.3 O _{4 film produced in.}

When the temperature of the oxygen-containing water in contact with the nickel metal film is less than 130 ° C., the nickel metal film is not converted into _{a stable nickel ferrite film (NiFe 2} O _{4 film).} In order to convert the nickel metal film into a stable nickel ferrite film that does not elute due to the action of the noble metal, the temperature of the oxygen-containing water that comes into contact with the nickel metal film must be within the temperature range of 130 ° C or higher (130 ° C or higher and 330 ° C or lower). Must be at the temperature of.

The inventors have made nickel formed on the surface of a carbon steel member when water containing oxygen at a temperature in the temperature range of 130 ° C. or higher and 330 ° C. or lower is brought into contact with a nickel metal film having a noble metal adhered to the surface. _They found that the metal film could be converted into a stable nickel ferrite film (NiFe 2 O _{4 film).}

By forming a nickel metal film on the surface of the carbon steel member, attaching a noble metal to the surface of the nickel metal film, and bringing water containing oxygen at 200 ° C. or higher into contact with the surface of the nickel metal film to which the noble metal is attached. , 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 noble metal (a nickel ferrite film in which x is 0 in _{Ni 1-x} Fe _{2 + x} O _{4, that is,} The method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear plant, which is converted to _{NiFe 2} O _{4 film), is a prior application in which the two inventors of this application are some of the inventors.} It is described in the specification of Japanese Patent Application No. 2016-182928.

As shown in FIG. 12 of Japanese Patent Application No. 2016-182928, the method for suppressing the adhesion of radioactive nuclei to the carbon steel member of the nuclear power plant of the prior application is described in "injection of nickel ion solution", "injection of reducing agent", and the like. "Judgment of completion of nickel metal film formation" (stop injection of nickel ion solution and reducing agent), "decomposition of reducing agent", "first purification", "injection of platinum ion solution", "injection of reducing agent", "Judgment of completion of platinum adhesion" (stop injection of platinum ion solution), "second purification", "waste liquid treatment", "removal of film forming equipment from piping system", "start of nuclear plant" and "high temperature" The 13 main steps of "contacting the furnace water with the nickel metal film to which platinum is attached" are carried out. The inventors will reduce the number of the 13 main steps shown in FIG. 12 of Japanese Patent Application No. 2016-182928, and realize a simple method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant. And various studies were conducted.

As a result of this study, the inventors have reduced the number of steps by adhering noble metal particles containing nickel metal as the above-mentioned noble metal to the surface of the nickel metal film covering the surface of the carbon steel member, thereby suppressing the adhesion of radionuclides. We found that the method could be realized.

Therefore, the inventors have described a reduction decontamination agent (for example, Shu) contained in the reduction decontamination liquid during chemical decontamination at the time of shutdown before starting the nuclear plant, specifically, in the reduction decontamination liquid decomposition step. After decomposing a part of the acid), the realization of a technique for adhering noble metal particles containing nickel metal to the surface of the nickel metal film covering the surface of the carbon steel member was examined as described above.

In the reduction decontamination agent decomposition step when the operation of the nuclear plant is stopped before starting, after partially decomposing the reduction decontamination agent contained in the reduction decontamination solution, the reduction decontamination solution, specifically, oxalic acid A carbon steel member is an aqueous solution containing oxalic acid, platinum ion and hydrazine, which is formed by injecting each of a noble metal ion aqueous solution (for example, a platinum ion aqueous solution) and a reducing agent aqueous solution (for example, a hydrazine aqueous solution) into the aqueous solution. It has already been confirmed that platinum can be adhered to the inner surface of the purification system pipe by contacting it with the inner surface (see JP-A-2014-4419).

In consideration of the above platinum adhesion technique, the inventors have investigated a method for forming noble metal particles containing nickel metal, for example, platinum particles containing nickel metal. The results of this study will be described below.

The inventors were produced by injecting each of an aqueous solution containing nickel ions (nickel ion aqueous solution), an aqueous solution containing platinum ions (platinum ion aqueous solution), and an aqueous solution containing a reducing agent (reducing agent aqueous solution) into water. By bringing an aqueous solution containing nickel ions, platinum ions and a reducing agent into contact with the surface of the nickel metal film covering the carbon steel member which is a component of the nuclear plant, the reactions of the formulas (1) and (2) are carried out. Based on this, it was considered that platinum particles containing nickel metal could be attached to the nickel metal film covering the surface of the carbon steel member.

Pt ²⁺ + 2e ^2- → Pt …… (1)
Ni ²⁺ + 2e ^2- → Ni …… (2)
Therefore, the inventors conducted experiments to apply an aqueous solution containing nickel ions, platinum ions, and a reducing agent to a nickel metal covering the surface of a carbon steel test piece simulating a carbon steel member which is a component of a nuclear plant. In contact with the film, an attempt was made to form platinum particles containing nickel metal on the surface of the nickel metal film.

As a result of conducting various experiments, the inventors obtained an aqueous solution containing nickel ion, platinum ion and a reducing agent, which was produced by injecting each of nickel ion, platinum ion and a reducing agent into water. It was possible to form platinum particles containing nickel metal on this surface by contacting the surface of the nickel metal film covering the nickel metal. The concentration of nickel ions in the aqueous solution is preferably in the range of 50 ppm to 600 ppm, the concentration of platinum ions is preferably in the range of 0.5 ppm to 5 ppm, and the concentration of hydrazine (reducing agent) is preferably in the range of 10 ppm to 100 ppm. ..

The inventors observed the surface of a nickel metal film on which platinum particles containing nickel metal adhered to the surface covering a test piece made of carbon steel with an electron microscope. A micrograph of the surface is shown in FIG. It can be clearly seen that a large number of platinum particles 84 containing nickel metal are attached to the surface of the nickel metal film. The diameter of the platinum particles 84 containing nickel metal is in the range of 2 nm to 100 nm. Adjusting the diameter of the nickel metal-containing platinum particles 84 adhering to the surface of the nickel metal film by changing the platinum concentration in the aqueous solution containing nickel ions, platinum ions and a reducing agent that comes into contact with the surface of the nickel metal film. Can be done. Furthermore, the inventors analyzed the composition of platinum particles 84 containing nickel metal adhering to the surface of the nickel metal film. The result of this composition analysis is shown in FIG. As is clear from FIG. 13, the platinum particles 84 containing nickel metal contain substantially the same amount of nickel and platinum.

The inventors have each of a carbon steel test piece A, a carbon steel test piece B having platinum adhered to the surface, and a carbon steel test piece C having platinum particles containing nickel metal adhered to the surface. , simulating the conditions of the reactor water during operation of the BWR plant, immersed in simulated reactor water containing ⁶⁰ Co, was calculated coating weight of ⁶⁰ Co to each specimen. ^{The results of 60} Co adhesion to these test pieces are shown in FIG. ^{The amount of 60} Co attached to the test piece B was reduced to 1/3 of the amount attached to the test piece A. ^{The amount of 60} Co attached to the test piece C was 1/10 of the amount attached to the test piece A. As a result, it was found that the platinum particles containing nickel metal had the greatest effect of suppressing the adhesion of ^{60 Co.}

As shown in FIG. 7, the platinum particles 84 containing a nickel metal have three forms. In the first form, the platinum particles 84 containing nickel metal cover the entire surface of the platinum particles 85 with a film of nickel metal 86 (see FIG. 7A). In the platinum particles 84 containing nickel metal in the second form, a plurality of fine particles of nickel metal 86 are attached to the surface of the platinum particles 85 (see FIG. 7B). In the platinum particles 84 containing nickel metal in the third form, the platinum particles 85 and the nickel metal 86 particles are attached to each other (see FIG. 7C). Precious metal particles containing nickel metal other than platinum particles containing nickel metal also have the same three forms.

The nickel metal film covering the surface of the carbon steel member and to which the noble metal particles containing nickel metal are adhered contains oxygen at a temperature within the temperature range of 130 ° C. or higher (preferably 130 ° C. or higher and 330 ° C. or lower). By contacting with water, the nickel metal can be converted into the above-mentioned stable nickel ferrite film (NiFe ₂ O _{4 film).} At this time, the water at that temperature that comes into contact with the nickel metal film also comes into contact with the nickel metal of the noble metal particles containing the nickel metal adhering to the nickel metal film. Similar to the nickel metal film covering the surface of the carbon steel member, this nickel metal is also produced by the migration of oxygen contained in the water and iron contained in the carbon steel member into the nickel metal of the noble metal particles containing the nickel metal. , Stable nickel ferrite (NiFe ₂ O ₄ ). This stable nickel ferrite is incorporated into the stable nickel ferrite film converted from the nickel metal film, and the nickel metal of the noble metal particles containing the nickel metal disappears in due course. As a result, the noble metal particles of the noble metal particles containing the nickel metal remain attached to the surface of the stable nickel ferrite film covering the surface of the carbon steel member.

The formation of the nickel metal film on the surface of the carbon steel member with the noble metal particles containing nickel metal attached to the surface is caused by the partial decomposition of the reduction decontamination agent in the reduction decontamination agent decomposition step in the reduction decontamination liquid. It is carried out either at the stage where the reduction decontamination agent still remains or after the entire process of chemical decontamination is completed.

An example of a method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant, which reflects the above examination results, will be described below.

The method for suppressing the adhesion of radionuclides 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 for suppressing the adhesion of radioactive nuclei to carbon steel members of a 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 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 is a steam generator, has a reactor pressure vessel (hereinafter referred to as RPV) 3 in which the core 4 is built, and has an outer surface of a core shroud (not shown) surrounding the core 4 in the RPV 3 and the RPV 3. The jet pump 5 is installed in an annular down core formed between the inner surface and the inner surface. A large number of fuel assemblies (not shown) are loaded in the core 4. The fuel assembly contains multiple fuel rods filled with multiple 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 purifier (for example, a condensate desalinator) 13, a low-pressure feed water heater 14, a feed water pump 15, and a high-pressure feed water supply are connected to a feed water 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 drain water recovery pipe 27 connected to the high-pressure feed water heater 16 and the low-pressure feed water heater 14 is connected to the condenser 10. 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 26 arranged in the reactor building (not shown).

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 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 condensate pump 12, impurities are removed by the condensate purification device 13, and the pressure is further boosted by the water supply pump 15. The feed water 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, respectively, and serves as a heating source for the feed water.

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-regenerating 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 RPV3 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, a film forming apparatus 30 is used, and the film forming apparatus 30 is connected to the purification system pipe 18 of the BWR plant as shown in FIG. Will be done.

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

The film forming apparatus 30 includes a circulation pipe 31, a surge tank 32, a heater 33, a circulation pump 34, 35, a nickel ion implanter 36, a reducing agent implanter 41, a platinum ion implanter 46, 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, and an ejector 61 are provided.

The on-off valve 62, the circulation pump 35, the valves 63, 66, 69 and 74, the surge tank 32, the circulation pump 34, the valve 77 and the on-off valve 78 are provided in the circulation pipe 31 in this order from the upstream. The pipe 65 that bypasses the valve 63 is connected to the circulation pipe 31, and the valve 64 and the filter 51 are installed in the pipe 65. A cooler 52 and a valve 67 are installed in the pipe 68 whose both ends are connected to the circulation pipe 31 by bypassing the valve 66. The cation exchange resin tower 53 and the valve 70 are installed in the pipe 71 whose both ends are connected to the circulation pipe 31 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. 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 circulation pipe 31 by bypassing 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 32 is installed in the circulation pipe 31 between the valve 74 and the circulation pump 34. The heater 33 is arranged in the surge tank 32. The pipe 80 provided with the valve 79 and the ejector 61 is connected to the circulation pipe 31 between the valve 77 and the circulation pump 34, and further connected to the surge tank 32. 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 purification system pipe 18 into the surge tank 32.

The nickel ion implanter 36 includes a chemical tank 37, an injection pump 38, and an injection pipe 39. The chemical tank 37 is connected to the circulation pipe 31 by an injection pipe 39 having an injection pump 38 and a valve 40. Nickel formic acid _{(Ni (HCOO) 2 · 2H} 2 O) a nickel formate aqueous solution prepared by dissolving in a dilute aqueous solution of formic acid (referred to nickel ions in water) is filled in the chemical tank 37.

The platinum ion implanter (precious metal ion implanter) 46 includes a chemical tank 47, an injection pump 48, and an injection pipe 49. The chemical tank 47 is connected to the circulation pipe 31 by an injection pipe 49 having an injection pump 48 and a valve 50. 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). A hydrate aqueous solution) (referred to as a platinum ion aqueous solution) is filled in the chemical tank 47. The platinum ion aqueous solution is a kind of aqueous solution containing noble metal ions.

The reducing agent injection device 41 includes a chemical liquid tank 42, an injection pump 43, and an injection pipe 44. The chemical tank 42 is connected to the circulation pipe 31 by an injection pipe 44 having an injection pump 43 and a valve 45. An aqueous solution of hydrazine, which is a reducing agent (referred to as an aqueous solution of hydrazine), is filled in the chemical tank 42.

The injection pipes 39, 49 and 44 are connected to the circulation pipe 31 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 the supply pipe 59 having the supply pump 58 and the valve 60. Hydrogen peroxide, which is an oxidizing agent, is filled in the chemical tank 57. As the oxidizing agent, an aqueous solution in which ozone is dissolved may be used.

A pH meter 81 is attached to the circulation pipe 31 between the connection point between the injection pipe 44 and the circulation pipe 31 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 stop, a part of the fuel assembly loaded in the core 4 is taken out as a spent 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 RPV 12 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 the adhesion of radioactive nuclei to carbon steel members of the nuclear power plant of this example is implemented. In this method of suppressing the adhesion of radioactive nuclei to the carbon steel member, a treatment of forming a nickel metal film on the inner surface of the purification system pipe 18 in contact with the furnace water, a noble metal particle containing nickel metal on the formed nickel metal film, for example. , The adhesion treatment of platinum particles containing nickel metal, and the conversion treatment of the nickel metal film to which the noble metal particles containing nickel metal are attached into a stable nickel ferrite film are performed.

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 this embodiment, the film forming apparatus 30 is used.

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 installed in the purification system pipe 18 is opened upstream of the purification system pump 19 to block the recirculation system pipe 6 side. One end of the circulation pipe 31 of the film forming apparatus 30 on the on-off valve 78 side is connected to the flange of the valve 23. Further, the bonnet of the valve 25 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 31 on the on-off valve 62 side is connected to the flange of the valve 25. Both ends of the circulation pipe 31 are connected to the purification system pipe 18, and a closed loop including the purification system pipe 18 and the circulation pipe 31 is formed.

In this embodiment, the film forming apparatus 30 is connected to the purification system pipe 18 of the reactor purification system, but in addition to the purification system pipe 18, it is a carbon steel member and is a residual heat removal system connected to the RPV3. , Connect the film forming device 30 to the carbon steel pipe of any of the reactor isolation cooling system, core spray system, and water supply system, and connect this carbon steel pipe to the carbon steel member of the nuclear power plant of this embodiment. The method for suppressing the adhesion of radioactive nuclei of the above may be applied.

Reduction decontamination is performed on the carbon steel piping system to be filmed (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 flowing from the RPV3. In order to reduce the dose rate of the purification system pipe 18 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 improves 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.

The reduction decontamination applied to the inner surface of the purification system pipe 18 in step S2 is the known reduction decontamination described in JP-A-2000-105295. This reduction decontamination 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 34 and 35 are driven with the other valves closed. As a result, the water heated to 90 ° C. by the heater 33 in the surge tank 32 in the purification system pipe 18 circulates in the closed loop formed by the circulation pipe 31 and the purification system pipe 18. 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 31 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 32 by the water flowing in the pipe 80. This oxalic acid dissolves in water in the surge tank 32, and an aqueous oxalic acid solution (reduction decontamination liquid) is generated in the surge tank 32.

This oxalic acid aqueous solution is discharged from the surge tank 32 to the circulation pipe 31 by driving the circulation pump 34. The hydrazine aqueous solution in the chemical tank 42 of the reducing agent injection device 41 is injected into the oxalic acid aqueous solution in the circulation pipe 31 through the injection pipe 44 by opening the valve 45 and driving the injection pump 43. Purification system by controlling the injection pump 43 (or the opening degree of the valve 45) based on the pH value of the oxalic acid aqueous solution measured by the pH meter 81 to adjust the injection amount of the hydrazine aqueous solution into the circulation pipe 31. The pH of the oxalic acid aqueous solution supplied to the pipe 18 is adjusted to 2.5. At this time, the oxalic acid concentration of the oxalic acid aqueous solution is 200 ppm. 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 aqueous solution of oxalic acid having a pH of 2.5 and 90 ° C. is supplied from the circulation pipe 31 to the purification system pipe 18, and the oxalic acid in the aqueous solution is an oxide film containing radionuclides formed on the inner surface of the purification system pipe 18. Dissolve. The oxalic acid aqueous solution flows through the purification system pipe 18 while dissolving the oxide film, passes through the purification system pump 19, the regenerative heat exchanger 20 and the non-regenerative heat exchanger 21, and is returned to the circulation pipe 31. The oxalic acid aqueous solution returned to the circulation pipe 31 is boosted by the circulation pump 35 through the on-off valve 62, passes through the valves 63, 66, 68 and 73, and reaches the surge tank 32. In this way, the oxalic acid aqueous solution circulates in the closed loop including the circulation pipe 31 and the purification system pipe 18, carries out reduction decontamination of the inner surface of the purification system pipe 18, and dissolves the oxide film formed on the inner surface thereof. ..

With the dissolution of the oxide film, the radionuclide concentration and Fe concentration of the oxalic acid aqueous solution increase. By opening the valve 70 and adjusting the opening degree of the valve 69 in order to suppress the increase in these concentrations, a part of the oxalic acid aqueous solution returned to the circulation pipe 31 is guided to the cation exchange resin tower 53 by the pipe 71. .. Radionuclides and metal cations such as Fe contained in the oxalic acid aqueous solution are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 53. The oxalic acid aqueous solution discharged from the cation exchange resin tower 53 and the oxalic acid aqueous solution that has passed through the valve 69 are resupplied to the purification system pipe 18 from the circulation pipe 31 and used for reduction decontamination of the purification system pipe 18.

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) 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, and the supply of the oxalic acid aqueous solution to the cation exchange resin tower 53 is stopped. Further, the valve 60 is opened to start the supply pump 58, and the hydrogen peroxide in the chemical solution tank 57 is supplied to the oxalic acid aqueous solution flowing in the circulation pipe 31 through the supply pipe 59 and the pipe 76 with the valve 75 closed. To do. An oxalic acid aqueous solution containing hydrogen peroxide is guided from the circulation pipe 31 into the purification system pipe 18. Fe (II) contained in iron (II) oxalate formed on the inner surface of the purification system pipe 18 is oxidized to Fe (III) by the action of the hydrogen peroxide, and the iron (II) oxalate is oxidized. It dissolves in an aqueous oxalic acid solution as an iron (III) acid complex. That is, iron (II) oxalate and hydrogen peroxide and oxalic acid contained in the aqueous solution of oxalic acid generate an iron (III) oxalate complex, water and hydrogen ions by the reaction represented by the formula (3).

2Fe (COO) ₂ + H ₂ O ₂ + 2 (COOH) ₂ →
2Fe [(COO) ₂ ] ₂ ⁻ + 2H ₂ O + 2H ⁺ … (3)
After it was confirmed that the iron (II) oxalate formed on the inner surface of the purification system pipe 18 was dissolved and the hydrogen peroxide injected into the aqueous oxalic acid solution disappeared by the reaction of the formula (3), the circulation pipe 31 A part of the oxalic acid aqueous solution that has passed through the valve 66 is supplied to the cation exchange resin tower 53 through the pipe 71. Metal cations such as radionuclides contained in the oxalic acid aqueous solution are adsorbed on the cation exchange resin in the cation exchange resin tower 53 and removed. The disappearance of hydrogen peroxide in the oxalic acid aqueous solution can be confirmed, for example, by immersing a test paper that reacts with hydrogen peroxide in the oxalic acid aqueous solution sampled from the circulation pipe 31 and observing the color appearing on the test paper.

A decomposition step of the reduction decontamination agent is carried out (step S3). The step S3, which is a step of decomposing the reducing decontamination agent, includes a step of decomposing the reducing decontamination agent and the pH adjuster (step S3A) and a step of decomposing the reducing decontamination agent, formic acid and the reducing agent (step S3C). There is.

First, the reduction decontamination agent and the pH adjuster are decomposed (step S3A). 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, the reduction decontamination process is completed and Shu Decomposition (reduction decontamination agent decomposition step) of oxalic acid and hydrazine (pH adjuster) contained in the acid aqueous solution is started. The decrease in the dose rate to the set dose rate at the reduction decontamination site 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 pipe 18. be able to.

The decomposition of oxalic acid and hydrazine is carried out as follows. The oxalic acid aqueous solution containing hydrazine, which has passed through the valve 69 and the valve 70 by opening the valve 75 to partially reduce the opening degree of the valve 74, is supplied to the decomposition device 55 by the pipe 76 through the valve 75. At this time, 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. 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 (4) and (5).

(COOH) ₂ + H ₂ O ₂ → 2CO ₂ + 2H ₂ O …… (4)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O …… (5)
The decomposition of oxalic acid and hydrazine in the decomposition apparatus 55 is performed while circulating the oxalic acid aqueous solution in a closed loop including the circulation pipe 31 and the purification system pipe 18. The amount of hydrogen peroxide supplied from the chemical tank 57 to the decomposition device 55 so that the supplied hydrogen peroxide is not completely consumed by the decomposition device 55 for decomposition of oxalic acid and hydrazine and does not flow out from the decomposition device 55. Is adjusted by controlling the rotation speed of the supply pump 58.

Even in the reduction decontamination agent decomposition step, oxalic acid may be present in the oxalic acid aqueous solution discharged from the decomposition apparatus 55, and iron (II) oxalate may be formed on the inner surface of the purification system pipe 18. is there. Therefore, the amount of hydrogen peroxide supplied from the chemical tank 57 to the decomposition device 55 is adjusted so that hydrogen peroxide flows out from the decomposition device 55 when the decomposition of oxalic acid and hydrazine contained in the oxalic acid aqueous solution has progressed to some extent. increase. At this time, in order to avoid deterioration of the cation exchange resin in the cation exchange resin tower 53 due to hydrogen peroxide, the valve 70 is closed in advance to prevent the inflow of hydrogen peroxide into the cation exchange resin tower 53.

As described above, the iron (II) oxalate formed on the inner surface of the purification system pipe 18 in the reduction decontamination agent decomposition step becomes an iron (III) oxalate complex by the action of hydrogen peroxide in the oxalic acid aqueous solution. It dissolves in an aqueous solution of oxalic acid. Since the decomposition of oxalic acid and the like in the oxalic acid aqueous solution is progressing, the oxalic acid that converts Fe (II) contained in iron (II) oxalate to Fe (III) is insufficient, and Fe is formed on the inner surface of the circulation pipe 31. (OH) ₃ is likely to precipitate. Therefore, in order _{to suppress the precipitation of Fe (OH) 3} , formic acid is injected into the oxalic acid aqueous solution. The injection of formic acid is performed, for example, by supplying formic acid from the above-mentioned hopper and ejector 61 to the oxalic acid aqueous solution flowing in the pipe 80 and guiding it to the surge tank 32. The supplied formic acid is mixed with the oxalic acid aqueous solution.

The injection of the oxidizing agent into the oxalic acid aqueous solution to dissolve iron (II) oxalate and the injection of formic acid into the oxalic acid aqueous solution to suppress the precipitation of iron hydroxide are the reduction decontamination agent decomposition steps. Is done after is started.

The oxalic acid aqueous solution containing formic acid contains hydrogen peroxide discharged from the decomposition apparatus 55 in addition to the reduced concentrations of oxalic acid and hydrazine. The hydrogen peroxide contained in the oxalic acid aqueous solution dissolves iron (II) oxalate precipitated on the inner surface of the purification system pipe 18, and formic acid dissolves Fe (OH) ₃ . Decomposition of oxalic acid and hydrazine contained in the oxalic acid aqueous solution is also continued in the decomposition apparatus 55.

After the decomposition step of the reduction decontamination agent and the pH adjuster in step 3A is started, the valve 64 is opened and the valve 63 is closed. As a result, the formic acid aqueous solution flowing in the circulation pipe 31 is supplied to the filter 51, and the fine solid content remaining in the formic acid aqueous solution is removed by the filter 51. When the fine solid content is not removed, when the nickel formate aqueous solution is injected into the circulation pipe 31 in the step S4 described later, a ferrite mixed metal film is also formed on the surface of the solid material, and the injected nickel ions are generated. It is wasted. The supply of the formic acid aqueous solution to the filter 51 is to prevent such wasteful consumption of nickel ions. Before the step S4 is started, the valve 63 is opened, the valve 64 is closed, and the supply of the formic acid aqueous solution to the filter 51 is stopped.

In the step S3A, the decomposition of the reduction decontamination agent and the pH adjuster proceeds, a part of the oxalic acid (reduction decontamination agent) contained in the oxalic acid aqueous solution is decomposed (step S3B), and the pH of the oxalic acid aqueous solution is However, when the set pH reaches, for example, 4.0 (the oxalic acid concentration in the oxalic acid aqueous solution is 50 ppm), the injection of formic acid from the above-mentioned ejector 61 is stopped. Further, in a state where the valve 69 is fully opened and the valve 70 is fully closed, the chemical solution tank 57 prevents hydrogen peroxide supplied from the chemical solution tank 57 from flowing out from the decomposition device 55 as described above. The amount of hydrogen peroxide supplied to the decomposition apparatus 55 is adjusted by controlling the rotation speed of the supply pump 58. It is confirmed by the pH meter 81 that the pH of the oxalic acid aqueous solution is 4.0. When the pH of the oxalic acid aqueous solution reached 4.0, the pH adjuster hydrazine contained in the oxalic acid aqueous solution was completely decomposed, and the oxalic acid aqueous solution did not contain hydrazine.

After the pH of the oxalic acid aqueous solution reaches the set pH (for example, 4.0), the decomposition of oxalic acid and the steps S4 to S7 are carried out in parallel.

A nickel ion aqueous solution is injected (step S4). With the water flow to the filter 51 stopped, the valve 40 of the nickel ion injection device 36 was opened to drive the injection pump 38, and the nickel formate aqueous solution in the chemical solution tank 37 was passed through the injection pipe 39 into the circulation pipe 31. Inject into a flowing, 90 ° C. aqueous solution of formic acid. The nickel ion concentration of the injected nickel formate aqueous solution is, for example, 200 ppm. The oxalic acid aqueous solution into which the nickel formate aqueous solution is injected is a film-forming aqueous solution (film-forming solution) at 90 ° C. containing nickel ions, formic acid and oxalic acid. It is desirable that the temperature of this film-forming aqueous solution is within the temperature range of 60 ° C. to 100 ° C. (60 ° C. or higher and 100 ° C. or lower). An aqueous solution of nickel oxalate may be used instead of the aqueous solution of nickel formate.

A liquid level of an oxalic acid aqueous solution (or a film-forming aqueous solution) is formed in the surge tank 32, and a space (not shown) exists above the liquid level. There is air in this space. Oxygen in the air in the space is supplied to the 90 ° C. oxalic acid aqueous solution (or film-forming aqueous solution) in the surge tank 32 via the liquid surface. Due to the supply of oxygen in the surge tank 32, the aqueous solution will contain a trace amount of oxygen of about 2 ppm. Therefore, in order to remove the dissolved oxygen in the oxalic acid aqueous solution (or film-forming aqueous solution), an inert gas (for example, nitrogen gas) is added to the oxalic acid aqueous solution (or film-forming aqueous solution) at 90 ° C. in the surge tank 32. Bubbling. As a result, a 90 ° C. film-forming aqueous solution containing nickel ions, formic acid and oxalic acid and not containing oxygen, which is supplied to the purification system pipe 18, is generated in the circulation pipe 31. The pH of this film-forming aqueous solution is a value in the range of 3.5 to 6.0 (3.5 or more and 6.0 or less), for example, 4.0.

Since the film-forming aqueous solution does not contain oxygen, an unstable nickel ferrite (Ni _0.7 Fe _2.3 O ₄ ) is not mixed, and a highly pure nickel metal film described later is formed on the inner surface of the purification system pipe 18.

A 90 ° C. film-forming aqueous solution (film-forming liquid) containing nickel ions, formic acid and oxalic acid and containing no oxygen is supplied from the circulation pipe 31 to the purification system pipe 18 by driving the circulation pump 34. When the film-forming aqueous solution 83 comes into contact with the inner surface of the purification system pipe 18, a nickel metal film 82 is formed on the inner surface of the purification system pipe 18 (see FIG. 5). The nickel metal film 82 is formed as follows. By contacting the inner surface of the purification system pipe 18 with the film-forming aqueous solution 83 having a pH of 4.0, the nickel ions contained in the film-forming aqueous solution 83 are replaced with ^{Fe (II) ions (Fe 2+) in the purification system piping 18.} Is accelerated and the amount of nickel ions taken into the inner surface of the purification system pipe 18 increases, and the elution of iron (II) ions from the purification system pipe 18 to the film-forming aqueous solution 83 increases. The nickel ions taken into the inner surface of the purification system pipe 18 are reduced by the electrons generated by the elution of iron (II) ions to become nickel metal, and further, since the film-forming aqueous solution does not contain oxygen, it is purified. A high-purity nickel metal film 82 is formed on the inner surface of the system pipe 18. Since nickel ions are reduced by the electrons to become nickel metal, in this embodiment, when the nickel metal film 82 is formed on the surface thereof, the reducing agent that converts nickel ions into nickel metal is injected into the film-forming aqueous solution 83. It becomes unnecessary.

The substitution reaction between nickel ions and iron (II) ions is most active when the pH of the film-forming aqueous solution 83 in contact with the inner surface of the purification system pipe 18 is 4.0, and is incorporated into the inner surface of the purification system pipe 18. The amount of nickel ions is the highest.

It is not necessary to bubbling the inert gas (for example, nitrogen gas) into the 90 ° C. oxalic acid aqueous solution (or film-forming aqueous solution) in the surge tank 32. In this case, a 90 ° C. film-forming aqueous solution containing nickel ions, formic acid, oxalic acid and oxygen comes into contact with the inner surface of the purification system pipe 18. Due to the influence of oxygen contained in the film-forming aqueous solution, _{a nickel metal film in which unstable nickel ferrite (Ni 0.7} Fe _2.3 O ₄ ) is mixed is formed on the inner surface of the purification system pipe 18. Since the amount of oxygen contained in the film-forming aqueous solution is extremely small as described above, the unstable nickel ferrite mixed in the nickel metal film formed on the inner surface of the purification system pipe 18 is also extremely small. In the step S12 described later, the furnace water containing oxygen at a temperature in the range of 130 ° C. or higher and 280 ° C. or lower is brought into contact with the nickel metal film formed on the inner surface of the purification system pipe 18, and the purification system pipe 18 is contacted. When the nickel metal film formed on the inner surface is converted to stable nickel ferrite, a very small amount of unstable nickel ferrite mixed in the nickel metal film is also converted to stable nickel ferrite.

The film-forming aqueous solution 83 discharged from the purification system pipe 18 to the circulation pipe 31 is boosted by the circulation pump 35 and supplied to the decomposition device 55. At this time, since the valves 70 and 72 are closed, the film-forming aqueous solution 83 returned to the circulation pipe 31 is not supplied to the cation exchange resin tower 53 and the mixed bed resin tower 54. In the decomposition apparatus 55, oxalic acid and formic acid contained in the returned film-forming aqueous solution 83 are decomposed by the action of the activated carbon catalyst and the supplied hydrogen peroxide. The film-forming aqueous solution discharged from the decomposition device 55 is pressurized by the circulation pump 34, and the nickel formate aqueous solution is injected from the nickel ion implantation device 36, and the pH is 4 which contains nickel ions, formic acid and oxalic acid and does not contain oxygen. As a film-forming aqueous solution 83 at 0.0 and 90 ° C., it is supplied to the purification system pipe 18 again. By circulating the film-forming aqueous solution 83 in the closed loop including the circulation pipe 31 and the purification system pipe 18, the nickel metal film eventually comes into contact with the film-forming aqueous solution 83 between the valve 23 and the valve 25. Uniformly covers the entire inner surface of the purification system pipe 18. 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} to 300 μg / cm ^{2) per square centimeter.} The amount of the nickel metal film covering the entire inner surface of the purification system pipe 18 between the above two valves per square centimeter varies depending on the temperature of the film-forming aqueous solution in contact with the inner surface. When the temperature of the film-forming aqueous solution is 60 ° C., the amount is 50 μg / cm ² , and when the temperature of the film-forming aqueous solution is 90 ° C., the amount is 250 μg / cm ² . In this embodiment, since the temperature of the film-forming aqueous solution is 90 ° C., the amount of the nickel metal film formed on the inner surface of the purification system pipe 18 is 250 μg / cm ² .

The first setting is the elapsed time from when the nickel metal existing on the inner surface of the purification system pipe 18 reaches 250 μg / cm ² or when the injection of the nickel formate aqueous solution in the chemical liquid tank 37 into the circulation pipe 31 is started. When the time (for example, 30 minutes) was reached, the nickel metal existing on the inner surface of the purification system pipe 18 ^{became 250 μg / cm 2} , and it was determined that the formation of the nickel metal film 82 on the inner surface of the purification system pipe 18 was completed. To do. The first 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.

The film-forming aqueous solution is supplied from the circulation pipe 31 to the purification system pipe 18, and the nickel metal adheres to the inner surface of the purification system pipe 18, and the film-forming aqueous solution is completed until the formation of the nickel metal film 82 on the inner surface is completed. The oxalic acid and hydrazine (reducing agent) contained in the above are decomposed by the decomposition apparatus 55. The nickel formate aqueous solution is injected from the nickel ion implanter 36 into the film-forming aqueous solution discharged from the decomposition apparatus 55 at a constant injection amount. Therefore, the pH of the film-forming aqueous solution rises by the amount that oxalic acid is decomposed by the decomposition device 55. From another tank filled with formic acid connected to the chemical tank 37 in order to suppress an increase in the pH of the film-forming aqueous solution by decomposition of oxalic acid and maintain the pH at a set value (for example, 4.0). The amount of formic acid supplied to the chemical tank 37 is controlled to adjust the formic acid concentration of the nickel formate aqueous solution in the chemical tank 37. By injecting the nickel formate aqueous solution in the chemical tank 37 having the formic acid concentration adjusted into the circulation pipe 31, the pH of the film-forming aqueous solution supplied to the purification system pipe 18 is maintained at the set value. Further, as described in the reduction decontamination (step S2), formic acid is supplied from the hopper and the ejector 61 to the oxalic acid aqueous solution flowing in the pipe 80 without providing another tank filled with formic acid, and the surge tank 32 The pH of the film-forming aqueous solution may be adjusted by leading to.

Inject the noble metal ion solution (step S5). When the formation of the nickel metal film 82 on the inner surface of the purification system pipe 18 is completed, the film-forming aqueous solution 83 at 90 ° C. containing nickel ions, formic acid and oxalic acid and not containing oxygen is introduced into the chemical solution tank 47 through the injection pipe 49. A noble metal ion aqueous solution, for example, a platinum ion aqueous solution (for example, an aqueous solution of hexahydroxoplatinate sodium hydrate (Na ₂ [Pt (OH) ₆ ], 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. Even after the formation of the nickel metal film 82 on the inner surface of the purification system pipe 18 is completed, the injection of the nickel formate aqueous solution from the chemical solution tank 37 into the film forming aqueous solution 83 is continued.

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 31 from the chemical solution tank 47 through the connection point between the circulation pipe 31 and the injection pipe 49. _{The injection rate of the aqueous solution of Na 2} [Pt (OH) ₆ ] · nH ₂ O into the circulation pipe 31 is calculated in advance so that the concentration becomes the set concentration, for example, 1 ppm, and further, the purification system pipe 18 Calculate and calculate the amount of the aqueous solution of _{Na 2} [Pt (OH) ₆ ] and nH ₂ O to be filled in the chemical tank 47, which is necessary to attach a predetermined amount of platinum to the surface of the nickel metal film formed on the inner surface. The chemical solution tank 47 is filled with the amount of the aqueous solution of _{Na 2} [Pt (OH) ₆ ] and nH _{2 O.} Calculated _{Na 2 [Pt (OH) 6} ] · nH 2 the rotational speed of the infusion pump 48 is controlled in accordance with the injection rate of O in water to the circulation pipe 31 of the, _Na 2 in the chemical liquid tank 47 [Pt (OH ) _6] · nH to ₂ O aqueous solution is injected into the circulation pipe 31.

Inject the reducing agent (step S6). The valve 45 of the reducing agent injection device 41 is opened to drive the injection pump 43, and the aqueous solution of hydrazine, which is the reducing agent in the chemical solution tank 42, flows through the injection pipe 44 and in the circulation pipe 31, nickel ion, formic acid, and oxalic acid. And it is injected into a film-forming aqueous solution at 90 ° C. containing platinum ions and no oxygen. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 100 ppm.

The hydrazine aqueous solution contains nickel ion, formic acid, oxalic acid and Na ₂ [Pt (OH) ₆ ] · nH ₂ O, and an oxygen-free aqueous solution at 90 ° C. is the injection point of the hydrazine aqueous solution. After reaching the connection point of, it is injected into the circulation pipe 31. An aqueous solution 87 (see FIG. 6) at 90 ° C. containing nickel ions, formic acid, oxalic acid, platinum ions and hydrazine and containing no oxygen is supplied from the circulation pipe 31 to the purification system pipe 18. An aqueous solution containing nickel ions, formic acid, oxalic acid, platinum ions and hydrazine and not containing oxygen is simply referred to as an aqueous solution 87. The pH of the aqueous solution 87 is in the range of 6.0 to 9.0 due to the injection of hydrazine (reducing agent) in the step S6. The concentration of nickel ions in the aqueous solution 87 should be in the range of 50 ppm to 600 ppm, the concentration of platinum ions should be in the range of 0.5 ppm to 5 ppm, and the concentration of hydrazine (reducing agent) should be in the range of 10 ppm to 100 ppm. Is preferable.

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 42 through the connection point of the circulation pipe 31 and the injection pipe 44 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 31 was calculated, and the hydrazine in the 90 ° C. aqueous solution 87 flowing in the circulation pipe 31 was set to the set concentration, and the injected nickel ions were injected in the purification system pipe 18. The amount of the hydrazine aqueous solution to be filled in the chemical tank 42 required for reducing each of the platinum ions to nickel metal and platinum is calculated, and the calculated amount of the hydrazine aqueous solution is filled in the chemical tank 42. The rotation speed of the injection pump 43 is controlled according to the calculated injection speed of the hydrazine aqueous solution into the circulation pipe 31, and the hydrazine aqueous solution in the chemical tank 42 is injected into the circulation pipe 31.

The aqueous solution 87 at 90 ° C. is boosted by the circulation pump 34 and supplied from the circulation pipe 31 to the purification system pipe 18, and is brought into contact with the surface of the nickel metal film 82 formed on the inner surface thereof. As a result, platinum particles 84 containing a large number of nickel metals adhere to the surface of the nickel metal film 82 (see FIGS. 6 and 12). The platinum particles 84 containing a nickel metal are produced by the action of nickel ions, platinum ions and hydrazine contained in the aqueous solution 87. The nickel ions and platinum ions contained in the aqueous solution 87 are metallized by the reducing action of hydrazine to become nickel metal and platinum. Theoretically, platinum ions have the property of becoming more metallic than nickel ions by reducing agents. Therefore, the platinum ion is metallized to become platinum, and the nickel ion is changed to nickel metal starting from the generated platinum, so that platinum particles 84 containing the nickel metal are formed. Regarding the adhesion of the nickel metal-containing platinum particles 84 to the surface of the nickel metal film 82, the nickel metal-containing platinum produced by the nickel metal adhering to the surface of the platinum particles in (a) aqueous solution 87. The particles 84 adhere to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18, and (b) the nickel ions and platinum ions contained in the aqueous solution 87 adhere to the surface of the nickel metal film 82. Both forms are assumed, which are reduced by hydrazine (reducing agent) and adhered to the surface of the nickel metal film 82 to form platinum particles 84 containing nickel metal.

Since the aqueous solution 87 returned from the purification system piping 18 to the circulation piping 31 contains platinum particles 84 containing nickel ions, formic acid, oxalic acid, platinum ions, hydrazine and nickel metal, the aqueous solution 87 is transferred to the decomposition apparatus 55. Due to the inflow, platinum particles 84 containing nickel metal also flow into the decomposition apparatus 55. In the decomposition apparatus 55, oxalic acid, formic acid and hydrazine (reducing agent) contained in the aqueous solution 87 are decomposed by the action of the activated carbon catalyst and the supplied hydrogen peroxide. The platinum particles 85 (see FIG. 7) of the nickel metal-containing platinum particles 84 that have flowed into the decomposition apparatus 55 also act as a catalyst in the same manner as ruthenium contained in the activated carbon catalyst, and contribute to the decomposition of oxalic acid, formic acid, and hydrazine. Since the platinum particles 85 act as a catalyst, the decomposition of oxalic acid, formic acid and hydrazine is accelerated.

The aqueous solution 87 discharged from the decomposition apparatus 55 is supplied to the purification system pipe 18 by injecting a nickel formate aqueous solution from the chemical solution tank 37, a platinum ion aqueous solution from the chemical solution tank 47, and a hydrazine aqueous solution from the chemical solution tank 42, respectively. ..

Stop the injection of the nickel ion solution, the noble metal ion solution and the reducing agent solution (step S7). When the elapsed time from the start of supply of the aqueous solution 87 to the purification system pipe 18 reaches the second set time (for example, 1 hour), the circulation pipes 31 of the nickel formate aqueous solution, the platinum ion aqueous solution, and the hydrazine aqueous solution, respectively. Injection into is stopped. The second set time is determined by measuring in advance the time required for ^{the nickel metal-containing platinum particles 84 to reach 0.1 μg / cm 2} on the nickel metal film covering the surface of the carbon steel test piece. The injection stop of the nickel formate aqueous solution is carried out by stopping the injection pump 38 and closing the valve 40. The injection stop of the platinum ion aqueous solution is carried out by stopping the injection pump 48 and closing the valve 50. The injection stop of the hydrazine aqueous solution is carried out by stopping the injection pump 43 and closing the valve 45.

Decomposition of reducing agent decontamination agent, formic acid and reducing agent is carried out (step 3C). Oxalic acid, formic acid and hydrazine (reducing agent) contained in the aqueous solution 87 are decomposed in the decomposition apparatus 55 as described above even after the injection of the nickel formate aqueous solution, the platinum ion aqueous solution and the hydrazine aqueous solution is stopped. When the oxalic acid, formic acid and hydrazine (reducing agent) are decomposed after the injection of the nickel formate aqueous solution, the platinum ion aqueous solution and the hydrazine aqueous solution is stopped, the valve 70 is opened to reduce the opening degree of the valve 69. 87 is supplied to the cation exchange resin tower 53. In the cation exchange resin tower 53, metal cations contained in the aqueous solution 87 such as iron ions, nickel ions and platinum ions are removed, and the concentration of the metal cations contained in the aqueous solution 87 decreases. Further, a part of the platinum particles 84 containing nickel metal is also removed by the cation exchange resin column 53. The decomposition of oxalic acid and formic acid has been continuously carried out since the start of injection of the nickel formate aqueous solution in step S4. Further, the decomposition of hydrazine (reducing agent) has been continuously carried out since the start of injection of the hydrazine aqueous solution in step S6. 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 (step S3) of the reduction decontamination agent is completed. At this time, the aqueous solution 87 does not contain oxalic acid and hydrazine, and the concentrations of iron ions, nickel ions, and platinum ions contained in the aqueous solution 87 are very small. Therefore, the aqueous solution 87 is substantially a formic acid aqueous solution having a low formic acid concentration, which contains platinum particles 84 containing nickel metal. When the decomposition step of the reduction decontamination agent in step S3 is completed, the supply pump 58 is stopped and the valves 60 and 75 are closed.

Purification of the aqueous solution in which the reducing decontamination agent, formic acid and the reducing agent are decomposed is carried out (step S8). After the decomposition of oxalic acid, formic acid and hydrazine is completed, the valve 67 is opened and the valve 66 is closed, the valve 72 is opened and the valve 69 is closed. The heating of the aqueous solution obtained by decomposing oxalic acid, formic acid and hydrazine, that is, the aqueous solution of formic acid containing platinum particles 84 containing nickel metal, by the heater 33 is stopped, and the aqueous solution of formic acid is cooled by the cooler 52 to obtain the temperature of the aqueous solution. Is adjusted to, for example, 60 ° C. A formic acid aqueous solution containing platinum particles 84 containing nickel metal, which has been cooled to 60 ° C., is supplied to the mixed bed resin tower 54. The nickel metal-containing platinum particles 84 and formic acid contained in this aqueous formic acid solution are collected by the cation exchange resin and the anion exchange resin in the mixed bed resin tower 54 and removed from the aqueous solution. Further, other impurities such as nickel ions and platinum ions remaining in the formic acid aqueous solution, that is, metal cations and anions containing radioactive nuclei are removed by the cation exchange resin and the anion exchange resin in the mixed bed resin tower 54. Be done (purification process).

Treat the waste liquid (step S9). After the purification step is completed, the circulation pipe 31 and the waste liquid treatment device (not shown) are connected by a high-pressure hose (not shown) having a pump (not shown). After the purification step is completed, the aqueous solution of radioactive waste liquid remaining in the purification system pipe 18 and the circulation pipe 31 is discharged from the circulation pipe 31 through the high-pressure hose to the waste liquid treatment device (not shown) by driving the pump. , Processed in a waste liquid treatment device. After the aqueous solution in the purification system pipe 18 and the circulation pipe 31 is discharged, the cleaning water is supplied into the purification system pipe 18 and the circulation pipe 31, and the circulation pumps 34 and 35 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 31 is discharged to the above-mentioned waste liquid treatment device.

As described above, the formation of the nickel metal film 82 on the inner surface of the portion between the valve 23 and the valve 25 upstream of the non-regenerative heat exchanger 21 of the purification system pipe 18, and the nickel metal of the platinum particles 84 containing the nickel metal. Each process of adhesion on the film 82 is completed.

The film forming apparatus is removed from the piping system (step S10). After each step of steps S1 to S9 is performed, the film forming apparatus 30 is removed from the purification system pipe 18, and the purification system pipe 18 is restored.

The nuclear plant is started (step S11). After the refueling and maintenance and inspection of the BWR plant 1 are completed, in order to start the operation in the next operation cycle, purification in which a nickel metal film 82 to which platinum particles 84 containing nickel metal are attached is formed on the inner surface. The BWR plant 1 having the system pipe 18 is started.

The furnace water having a temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower is brought into contact with the nickel metal film to which the noble metal particles containing nickel metal are attached (step S12). When the BWR plant 1 is started, as described above, the reactor water discharged from the core flows into the purification system pipe 18 from the downcomer via the recirculation system pipe 6, and eventually flows into the water supply pipe 11. Then, it is returned to the RPV3.

A control rod (not shown) is pulled out from the core 4, the core 4 changes from a subcritical state to a critical state, and the reactor water in the core 4 is heated by the heat generated by the nuclear fission of the nuclear fuel material in the fuel rod. At this time, steam is not generated in the core 4. Further, the control rods are pulled out from the core 4, and in the process of raising and lowering the temperature of the reactor 2, the pressure in the RPV 3 is raised to the rated pressure, and the heat generated by the fission heats the reactor water to heat the reactor water in the RPV 3. The temperature becomes 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 is rated by further pulling out the control rods from the core 4 and increasing the flow rate of the reactor water supplied to the core 4. It is increased to the output (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.

Oxygen and hydrogen peroxide generated by radiolysis of the furnace water 88 in the RPV3 are contained in the furnace water 88. The oxygen-containing furnace water 88 in the RPV3 is guided from the recirculation system pipe 6 into the purification system pipe 18 in a state where the purification system pump 19 is driven, and is formed on the inner surface of the purification system pipe 18. , Contact with the nickel metal film 82 to which the platinum particles 84 containing nickel metal are attached (see FIG. 8). Due to the heating of the furnace water by the heat generated by the above-mentioned nuclear fission, the temperature of the furnace water 88 in contact with the nickel metal film 82 rises and eventually reaches 130 ° C. or higher, and finally reaches 280 ° C. at the rated output. To rise.

The temperature of the furnace water 88 differs greatly before and after the regenerated heat exchanger 20 and the non-regenerated heat exchanger 21. When the temperature of the furnace water 88 in the RPV3 is 280 ° C., the furnace water 88 at about 280 ° C. flows in the portion of the purification system pipe 18 upstream of the regenerated heat exchanger 20. As a result of heat exchange in the regenerative heat exchanger 20, the temperature of the furnace water 88 flowing out from the regenerative heat exchanger 20 to the valve 25 side drops to a range of about 200 ° C. to 150 ° C. Further, in the non-regenerative heat exchanger 21, the furnace water 88 drops to a temperature in the range of 50 ° C. to about room temperature, and is supplied to the furnace water purification device 22 containing the ion exchange resin within this temperature range. Since the furnace water 88 flowing out of the furnace water purification device 22 is used as water supply, it is heated in the range of about 150 ° C. to 200 ° C. by the regenerative heat exchanger 20 and then joins the water supply flowing through the water supply pipe 11.

The part of the purification system pipe 18 between the valve 23 and the regenerated heat exchanger 20 during the period when the BWR plant 1 is started and the pressure in the RPV 3 rises to the rated pressure (the temperature of the furnace water at this time is 280 ° C.). The furnace water 88 flowing through and the furnace water 88 flowing through the portion of the purification system pipe 18 between the regenerative heat exchanger 20 and the valve 25 are in the temperature range of 130 ° C. or higher and 330 ° C. or lower, although there is a time lag. , The temperature is within the temperature range of 130 ° C. or higher and 280 ° C. or lower. In the process of raising and boosting the temperature of the reactor 2, the temperature of the reactor water in the RPV3 rises to a higher temperature exceeding 130 ° C. as the pressure in the RPV3 rises.

Therefore, the surface of the nickel metal film 82 to which the platinum particles 84 containing nickel metal are attached, which is formed on the inner surface of the purification system pipe 18 between the valve 23 and the valve 25, has a temperature range of 130 ° C. or higher and 280 ° C. or lower. Upon contact with the oxygen-containing furnace water 88, the purification system pipe 18 and its nickel metal film 82 are heated to the same temperature as the furnace water 88. Oxygen contained in the furnace water 88 is transferred between the valve 23 and the valve 25 into the nickel metal film 82 formed on the inner surface of the purification system pipe 18, and Fe contained in the purification system pipe 18 becomes Fe ^2+. (See FIG. 9).

Further, the furnace water 88 at that temperature that comes into contact with the nickel metal film 82 also comes into contact with the platinum particles 84 containing nickel metal adhering to the nickel metal film 82. The platinum particles 84 also have the same temperature as the furnace water 88, and the nickel metal 86 contained in the platinum particles 84 also contains oxygen contained in the furnace water 88, similarly to the nickel metal film 82 covering the inner surface of the purification system pipe 18. And the transfer of iron contained in the purification system pipe 18 into the nickel metal 86 results in stable nickel ferrite (NiFe ₂ O ₄ ). This stable nickel ferrite is incorporated into the stable nickel ferrite film 89 converted from the nickel metal film 82, and the nickel metal 86 of the platinum particles 84 containing the nickel metal disappears soon. As a result, the platinum particles 85 of the platinum particles 84 containing nickel metal remain attached to the surface of the stable nickel ferrite film 89 covering the inner surface of the purification system pipe 18 (see FIG. 10).

In this embodiment, since the platinum particles 84 containing nickel metal adhere to the surface of the nickel metal film 82 formed by covering the inner surface of the purification system pipe 18, the method for suppressing the adhesion of radionuclides to the carbon steel member of the nuclear power plant The number of steps can be reduced to 10 steps after "injection of nickel ion aqueous solution (step S4)".

In this embodiment, a part of the oxalic acid contained in the reducing decontamination solution is decomposed (step S3B), and the nickel ion aqueous solution is added to the reducing decontamination solution, that is, the oxalic acid aqueous solution with the oxalic acid remaining. Since it is injected, a nickel metal film 82 can be formed on the inner surface of the purification system pipe 18 during the decomposition of oxalic acid, and further, a nickel ion aqueous solution, platinum ion and hydrazine (reducing agent) are added to the oxalic acid aqueous solution containing nickel ions. Therefore, platinum particles 84 containing nickel metal can be adhered onto the nickel metal film 82 formed on the inner surface of the purification system pipe 18 during the decomposition of oxalic acid. Therefore, in this embodiment, it is possible to shorten the time required for the platinum particles 84 containing nickel metal to adhere to the nickel metal film 82 formed on the inner surface of the purification system pipe 18.

Further, in this embodiment, nickel ions, formic acid, oxalic acid, and platinum ions, which are used for adhering platinum particles 84 containing nickel metal onto the nickel metal film 82 and discharged from the purification system pipe 18 to the circulation pipe 31. , An aqueous solution 87 containing platinum particles 84 containing hydrazine and nickel metal is supplied to the decomposition apparatus 55. The oxalic acid, formic acid and hydrazine contained in the aqueous solution 87 are not only decomposed in the decomposition apparatus 55 by the action of the catalyst (for example, activated carbon catalyst) in the decomposition apparatus 55 and hydrogen peroxide, but also the hydrogen peroxide thereof. It is also decomposed by the action of the platinum particles 85 of the platinum particles 84 containing the nickel metal contained in the aqueous solution 87 and the aqueous solution 87. Therefore, the decomposition of oxalic acid, formic acid, hydrazine (reducing agent) and oxalic acid contained in the aqueous solution 87 is accelerated. Therefore, in this example, the time required for the decomposition of oxalic acid in step S3 can be shortened from the time required for the decomposition of the reducing decontamination agent in the reduction decontamination agent decomposition step of JP-A-2000-105295. ..

In this embodiment as described above, chemical decontamination is performed on the inner surface of the purification system pipe 18, formation of a nickel metal film 82 on the inner surface thereof, and adhesion of platinum particles 84 containing nickel metal on the nickel metal film 82. The time required for this can be shortened.

In a high temperature environment of 130 ° C. or higher and 280 ° C. or lower, oxygen contained in the furnace water 88 and Fe ²⁺ from the purification system pipe 18 are likely to move into the nickel metal film 82 and the nickel metal 86. When the oxygen concentration of the furnace water is low, the water molecules of the furnace water are decomposed by the corrosion of iron to generate oxygen, and this oxygen functions in the same manner as the oxygen contained in the above-mentioned furnace water 88. The action of the platinum particles 85 of the nickel metal-containing platinum particles 84 adhering to the nickel metal film 82 lowers the corrosion potentials of the purification system piping 18 and the nickel metal film 82, respectively, and the temperature range of 130 ° C. or higher and 280 ° C. or lower. Due to the formation of the high temperature environment, each nickel in the nickel metal film 82 and the nickel metal 86 reacts with ^{oxygen and Fe 2+} _{transferred into the nickel metal film 82 and the nickel metal 86, and Ni 1-x} Fe _2+. It is converted to stable nickel ferrite (NiFe ₂ O _{4 ) where x is 0 at x} O _4. At this time, the ease of incorporating nickel and iron into the ferrite structure is affected by the platinum particles 85 (precious metal), and when the platinum particles 85 are present, nickel is more easily incorporated than iron, so Ni _1-x Stable nickel ferrite with x 0 is produced at Fe _{2 + x} O _4. Then, the nickel metal film 82 formed on the inner surface of the purification system pipe 18 _{is converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 89, and the inner surface of the purification system pipe 18 between the valve 23 and the valve 25 is described above. As described above, the surface is covered with a stable nickel ferrite film 89 having platinum particles 85 attached (see FIG. 10). _{Ni 1-x} Fe ₂₊ produced as described above from the nickel metal contained in the nickel metal film 82 covering the inner surface of the purification system pipe 18 in a high temperature environment in the temperature range of 130 ° C. or higher and 280 ° C. or lower. _{Stable nickel ferrite (NiFe 2} O ₄ ) in which x is 0 at _x O ₄ has a large crystal growth. The nickel ferrite film 89 that covers the inner surface of the purification system piping 18 is _{stable without being eluted into water like the Ni 0.7} Fe _2.3 O ₄ film due to the action of the adhered platinum particles 85, and is a carbon steel that is a base material. That is, the adhesion of radionuclides to the purification system pipe 18 is suppressed.

The nickel metal film 82 to which platinum particles 84 containing nickel metal are attached, which is formed on the inner surface of the purification system pipe 18 and covers the inner surface, is formed on the high temperature furnace water 88 in the temperature range of 130 ° C. or higher and 280 ° C. or lower. According to this example in which the platinum particles 85 were converted into a stable nickel ferrite film 89 adhering to the surface by the contact with the platinum particles, the platinum particles were formed on the inner surface of the purification system piping described in JP-A-2014-44190. The adhesion of radionuclides can be reduced by 30% as compared with the case of adhesion. ^{That is, the radionuclide (for example, 60} Co) is stabilized by the nickel contained in the stable nickel ferrite film 89 and the zinc injected into the furnace water in RPV3 after the start of the nuclear plant and incorporated into the stable nickel ferrite film 89. Adhesion to the nickel ferrite film 89 is inhibited, and the amount of radionuclide attached is reduced.

According to this embodiment, the corrosion potential of the purification system pipe 18 and the nickel metal film 82 is lowered by the platinum particles 85 of the platinum particles 84 containing nickel metal adhering to the nickel metal film 82, and the temperature is 130 ° C. or higher and 280 ° C. In a high temperature environment in the above temperature range, as described above, the nickel ferrite film 89 having x 0 in _{Ni 1-x} Fe _{2 + x} O _{4 produced from the nickel metal film 82 is the BWR plant 1.} It is a stable nickel ferrite film that does not elute into the furnace water even during the operation of the above, even by the action of the adhered platinum particles 85. The stable nickel ferrite film 89 thus formed adheres to the purification system piping 18 for a longer period of time than _{the Ni 0.7} Fe _2.3 O ₄ film formed in the low temperature range of 60 ° C. to 100 ° C. Can be suppressed. Specifically, the stable nickel ferrite film 89 that does not elute due to the action of the adhered platinum particles 85 is formed over a plurality of operation cycles, for example, five operation cycles (for example, five years). Can cover the inner surface of. In this embodiment, since the stable nickel ferrite film 89 can cover the inner surface of the purification system pipe 18 for a long period of time, it is possible to suppress the adhesion of radionuclides to the purification system pipe 18 for a long period of time.

Carbon steel members tend to be particularly corroded when in contact with water at temperatures in the temperature range of 150 ° C. to 200 ° C. During the rated operation of the BWR plant 1, the purification system pipe 18 is a portion between the regenerated heat exchanger 20 and the non-regenerating heat exchanger 21 on the upstream side of the furnace water purification device 22, and is in the range of 150 ° C. to 200 ° C. It comes into contact with the furnace water 88 at the temperature inside. Therefore, corrosion increases at that portion of the purification system piping 18. In this embodiment, since a stable nickel ferrite film 89 is formed on the inner surface of the purification system pipe 18 between the valve 23 and the valve 25, corrosion in the portion between the valve 23 and the valve 25 of the purification system pipe 18 is formed. However, it is suppressed for a long period of time by the stable nickel ferrite film 89 formed.

During the rated operation of the BWR plant 1, hydrogen is injected into the furnace water in the RPV 3 through the water supply pipe 11. Hydrogen and oxygen contained in the furnace water are combined into water by the catalytic action of the platinum particles 85 adhering to the stable nickel ferrite film 89 covering the inner surface of the purification system pipe 18. Therefore, the dissolved oxygen concentration in the furnace water is lowered, and the occurrence of stress corrosion cracking in the stainless steel constituent members (for example, the recirculation system pipe 6 and the like) that come into contact with the furnace water can be suppressed.

In order to suppress the adhesion of radionuclides to the purification system pipe 18, the valve 25 should be installed in the purification system pipe 18 as close to the non-regenerative heat exchanger 21 as possible. Since the radionuclides contained in the furnace water are removed by the furnace water purification device 22 provided in the purification system pipe 18, it is stable on the inner surface of the portion of the purification system pipe 18 on the downstream side of the furnace water purification device 22. Even if the nickel ferrite film 89 is not formed, the adhesion of radionuclides to the inner surface of the portion is suppressed.

Further, the stable nickel ferrite film 89 formed on the inner surface of the purification system pipe 18 can suppress the adhesion of radionuclides to the purification system pipe 18 over a plurality of operation cycles. Therefore, the number of times of chemical decontamination performed on the purification system pipe 18 can be reduced. Since a stable nickel ferrite film 89 is formed on the inner surface of the purification system piping 18 between the valve 23 and the non-regenerative heat exchanger 21 on the upstream side of the furnace water purification device 22, the purification system piping is particularly effective. Adhesion of radionuclides to the inner surface of that portion of 18 can be suppressed.

According to this embodiment, the film-forming aqueous solution 83 can be brought into contact with the inner surface of the purification system pipe 18, and a nickel metal film 82 covering the inner surface of the purification system pipe 18 can be formed on the inner surface of the purification system pipe 18 in contact with the furnace water. .. ^{The nickel metal film 82 can prevent Fe 2+} from elution from the purification system pipe 18 into the film-forming aqueous solution 83 during the adhesion treatment of the platinum particles 84 containing nickel metal, and can be applied to the inner surface of the purification system pipe 18. The adhesion of the noble metal particles containing nickel metal (for example, platinum particles containing nickel metal) 84 ^{is no longer hindered by the elution of Fe 2+} , and the adhesion of the noble metal particles to the inner surface thereof (specifically, purification) It is possible to shorten the time required for (adhesion of noble metal particles containing nickel metal) to the surface of the nickel metal film 82 formed on the inner surface of the system pipe 18. Further, the noble metal particles containing nickel metal can be efficiently adhered to the inner surface thereof, and the amount of the noble metal particles containing nickel metal adhering to the inner surface of the purification system pipe 18 is increased.

The nickel metal film 82 formed on the inner surface of the purification system pipe 18 not only shortens the time required for the platinum particles 84 containing nickel metal to adhere to the purification system pipe 18, but also reduces the time required for the platinum particles 84 containing the adhered nickel metal to adhere. Combined with the action of the platinum particles 85, it contributes to the formation of a stable nickel ferrite film 89 that does not elute into the furnace water on the inner surface of the purification system pipe 18.

In the formation of the nickel metal film 82 on the inner surface of the purification system pipe 18, the nickel ions contained in the film-forming aqueous solution are replaced with the iron ions contained in the purification system pipe 18 and taken into the inner surface of the purification system pipe 18, and the purification system Nickel ions taken into the inner surface of the pipe 18 are reduced by the electrons generated by the elution of iron (II) ions to become nickel metal. As described above, the nickel metal generated by the action of electrons from the nickel ions taken into the purification system pipe 18 by the substitution reaction has strong adhesion to the base material of the purification system pipe 18. Therefore, the formed nickel metal film 82 does not come off from the purification system pipe 18.

In this embodiment, since the inner surface of the purification system pipe 18 is reduced and decontaminated and then the nickel metal film 82 is formed on the inner surface of the purification system pipe 18, nickel is formed as compared with the case where the nickel metal film is formed on the oxide film. Contributes to the formation of stable nickel ferrite with a high ratio.

At the time of reduction decontamination of the inner surface of the purification system pipe 18 using the oxalic acid aqueous solution and at the time of decomposition of oxalic acid, iron (II) oxalate formed on the inner surface of the purification system pipe 18 which is a carbon steel member is sewn. It is removed by the action of an oxidizing agent (for example, hydrogen peroxide) injected into an aqueous acid solution. By removing the iron (II) oxalate, the adhesion between the purification system pipe 18 and the nickel metal film 82 is improved, and the nickel metal film 82 can be prevented from peeling off from the inner surface of the purification system pipe 18.

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 FIGS. 14 and 15. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant of this embodiment is applied to a purification system pipe of a BWR plant that has experienced operation in at least one operation cycle.

In this embodiment, the steps S1 to S10 and S12 carried out in the first embodiment and the new steps S13 and S14 are carried out. In this example, the film forming apparatus 30 used in Example 1 is used in each of the steps S1 to S9, and a new heating system 91 is used in each of the steps S13 and S12.

The configuration of the heating system 91 will be described with reference to FIG. The heating system 91 has a pressure-resistant structure and includes a circulation pipe 92, a circulation pump 93, a heating device 94, and a valve 95 which is a booster. The circulation pump 93 is provided in the circulation pipe 92, and the heating device 94 is provided in the circulation pipe 92 upstream of the circulation pump 93. The heating device 94 may be arranged downstream of the circulation pump 93. The pipe 96 bypasses the circulation pump 93, one end of the pipe 96 is connected to the circulation pipe 92 upstream of the circulation pump 93, and the other end of the pipe 96 is connected to the circulation pipe 92 downstream of the circulation pump 93. Be connected. A valve 95 is provided in the pipe 96. The on-off valve 97 is provided at the upstream end of the circulation pipe 92, and the on-off valve 98 is provided at the downstream end of the circulation pipe.

In this embodiment, each step of steps S1 to S9 is carried out in the same manner as in Example 1. After the process of step S9 is completed, the process of step S10 is carried out.

The film forming apparatus is removed from the piping system (step S10). In this embodiment, after each step of steps S1 to S9 is performed, the film forming apparatus 30 connected to the purification system pipe 18 is removed from the purification system pipe 18. One end of the circulation pipe 31 of the film forming apparatus 30 is removed from the flange of the valve 23, and the other end of the circulation pipe 31 is removed from the flange of the valve 25.

The heating system is connected to the piping system (step S13). One end of the circulation pipe 92 (third pipe) of the heating system 91 on the on-off valve 98 side is connected to the flange of the valve 23, and the circulation pipe 92 is connected to the purification system pipe 18. The other end of the circulation pipe 92 on the on-off valve 97 side is connected to the flange of the valve 25, and the circulation pipe 92 is connected to the purification system pipe 18 between the regenerative heat exchanger 20 and the non-regenerative heat exchanger 21. Both ends of the circulation pipe 92 are connected to the purification system pipe 18, and a closed loop including the purification system pipe 18 and the circulation pipe 92 is formed.

Next, water containing oxygen at a temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower is brought into contact with the nickel metal film to which the noble metal particles containing nickel metal are attached (step S12). Water containing oxygen is filled in the closed loop including the circulation pipe 92 and the purification system pipe 18. The circulation pump 93 is driven to circulate oxygenated water in its closed loop. The rotation speed of the circulation pump 93 is increased to a certain rotation speed, and then the opening degree of the valve 95 is gradually decreased to increase the pressure of the water discharged from the circulation pump 93. The heating device 94 heats water containing oxygen circulating in the closed loop to raise the temperature of the water. In this way, the temperature of the water is raised while increasing the pressure of the water discharged from the circulation pump 93. After the valve 95 is fully closed, the rotational speed of the circulation pump 93 is further increased. By such an operation, when the pressure of the water circulating in the closed loop rises to the range of, for example, 0.27 MPa to 12.863 MPa, the temperature of the circulating water is about 130.0 ° C. to 330.0 ° C. Rise within range. The pressure of the circulating water is adjusted, and the temperature of the water is adjusted within the temperature range of 130 ° C. or higher and 330 ° C. or lower, for example, 150 ° C. The temperature of the water circulating in the closed loop is maintained at 150 ° C. while converting the nickel metal film formed on the inner surface of the purification system pipe 18 into a stable nickel ferrite film.

Water 88A at 150 ° C. containing oxygen is supplied from the circulation pipe 92 to the purification system pipe 18, and comes into contact with the nickel metal film 82 formed on the inner surface of the purification system pipe 18 to which the platinum particles 84 containing nickel metal are attached. (See FIG. 8). The purification system pipe 18 is surrounded by a heat insulating material (not shown) except for the vicinity of the valves 23 and 25 to which both ends of the circulation pipe 92 are connected. When the water 88A at 150 ° C. comes into contact with the nickel metal film 82, each of the purification system pipe 18 and the nickel metal film 82 is heated, and the respective temperatures reach 150 ° C.

Since each of the oxygen-containing water 88A, the purification system pipe 18 and the nickel metal film 82 reaches 150 ° C., oxygen (O ₂ ) contained in the water 88A and some water molecules contained in the water 88A are formed. Oxygen moves into the nickel metal film 82, and Fe contained in the purification system pipe 18 becomes Fe ²⁺ and moves into the nickel metal film 82 (see FIG. 9). Oxygen contained in the water 88A easily moves independently in the water 88A at 130 ° C. or higher, and easily enters the nickel metal film 82. The corrosion potential of the purification system pipe 18 and the nickel metal film 82 is lowered by the action of the platinum particles 85 of the platinum particles 84 containing nickel metal adhering to the nickel metal film 82. Due to the decrease in the corrosion potential of the nickel metal film 82 and the formation of a high temperature environment at 150 ° C., the nickel in the nickel metal film 82 reacts with ^{the oxygen and Fe 2+} _{transferred into the nickel metal film 82, and Ni 1-x} Fe. _{In 2 + x} O ₄ , x is 0, and stable nickel ferrite (NiFe ₂ O ₄ ) that does not elute even by the action of platinum is produced. Therefore, the nickel metal film 82 formed on the inner surface of the purification system pipe 18 _{is converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 89, and the nickel ferrite film 89 is formed on the valves 23 and 25 of the purification system pipe 18. It will cover the inner surface of the intervening part (see FIG. 10). As described above, the nickel metal 86 of the platinum particles 84 containing the nickel metal is also _{converted into stable nickel ferrite (NiFe 2} O ₄ ), and the nickel metal film 82 formed on the inner surface of the purification system pipe 18 is stable nickel. It is incorporated into the ferrite film 89. As a result, platinum particles 85 adhere to the surface of the stable nickel ferrite film 89 formed on the inner surface of the purification system pipe 18 in a state where the nickel metal 86 disappears (see FIG. 10).

The heating system is removed from the piping system (step S14). After the nickel ferrite film 89 is formed so as to cover the inner surface of the purification system pipe 18, the heating system 91 connected to the purification system pipe 18 is removed from the purification system pipe 18. After that, the purification system pipe 18 is restored.

After the refueling and maintenance and inspection of the BWR plant 1 are completed, a BWR having a purification system pipe 18 having a nickel ferrite film 89 to which platinum particles 85 are attached is formed on the inner surface in order to start operation in the next operation cycle. Plant 1 is started. Since the nickel ferrite film 89 is formed in the furnace water flowing in the purification system pipe 18, the furnace water does not come into direct contact with the base material of the purification system pipe 18.

In this example, each effect produced in Example 1 can be obtained. Further, in this embodiment, in order to convert the nickel metal film 82 formed on the inner surface of the purification system pipe 18 into a stable nickel ferrite film 89 by using the heating system 91, the conversion process in step S12 is performed by the BWR plant 1. Can be done while the operation is stopped. Therefore, when the BWR plant 1 is started, a stable nickel ferrite film 89 is already formed on the inner surface of the purification system pipe 18, and in this embodiment, the stable nickel ferrite film 89 is already formed on the inner surface of the purification system pipe 18. Adhesion of radionuclides to the purification system pipe 18 can be suppressed even before the film 89 is formed. Further, since the heating system 91 is used in this embodiment, the temperature of the oxygen-containing water 88A can be adjusted to any temperature within the range of 130 ° C. or higher and 330 ° C. or lower.

In each of Example 1 and Example 3 described later, the steps S13 and S14 may be carried out instead of step S11, and the step S12 may be carried out using the heating system 91.

The method for suppressing the adhesion of radionuclides to the carbon steel member of the nuclear power plant of Example 3 which is another embodiment of the present invention will be described with reference to FIG. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant of this embodiment is applied to a purification system pipe of a BWR plant that has experienced operation in at least one operation cycle.

In this example, each of the steps S4 to S7 carried out in Example 1 is carried out after the step S2A (chemical decontamination step) is completed. In the step 2A, each of the steps S2, S3 and S8 carried out in the first embodiment is carried out. In this embodiment, the steps S1 and S9 to S12 executed in the first embodiment are also carried out. Further, in this embodiment, the steps S8A, S15 and S16 are newly added.

In the method for suppressing the adhesion of radionuclides to the carbon steel member of this example, the step S1 is carried out in the same manner as in Example 1.

Chemical decontamination of the carbon steel piping system to be filmed is carried out (step S2A). In the step 2A, each step of step S2 (reduction decontamination step), S3 (reduction decontamination agent decomposition step) and S8 (purification step) carried out in Example 1 is sequentially carried out in this order. .. This purification step is carried out following the decomposition step of the reducing decontamination agent.

The temperature of the film-forming liquid is adjusted (step S15). Valves 69 and 74 are opened and valves 72 and 75 are closed. Since the circulation pumps 34 and 35 are driven, the remaining aqueous solution containing formic acid circulates in the closed loop including the circulation pipe 31 and the purification system pipe 18. The aqueous solution containing formic acid is heated to 90 ° C. by the heater 33. It is desirable that the temperature of this formic acid aqueous solution (the film-forming aqueous solution described later) is in the temperature 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. As a result, the formic acid aqueous solution flowing in the circulation pipe 31 is supplied to the filter 51, and the fine solid content remaining in the formic acid aqueous solution is removed by the filter 51. When the fine solid content is not removed, as will be described later, when the nickel formate aqueous solution is injected into the circulation pipe 31, a nickel metal film is formed on the surface of the solid material, and the injected nickel ions are wasted. Will be done.

Then, in the step S4, the nickel formate aqueous solution (nickel ion concentration of 200 ppm) in the chemical tank 37 is injected into the formic acid aqueous solution at 90 ° C. flowing in the circulation pipe 31, and the nickel ions and nickel ions are injected in the circulation pipe 31. A 90 ° C. film-forming aqueous solution containing formic acid and not oxygen is produced. In this example, the film-forming aqueous solution does not contain oxalic acid.

Before starting the injection of the nickel formate aqueous solution into the 90 ° C. formic acid aqueous solution, bubbling of an inert gas (for example, nitrogen gas) into the 90 ° C. formic acid aqueous solution existing in the surge tank 32 was started. Removes oxygen dissolved in the formic acid aqueous solution. Therefore, the film-forming aqueous solution produced by injecting the nickel formate aqueous solution does not contain oxygen.

The generated aqueous solution for forming a film at 4.0 and 90 ° C. having a pH in the range of 3.5 or more and 6.0 or less, which contains nickel ions and formic acid and does not contain oxygen, is supplied to the purification system pipe 18, and this purification system It comes into contact with the inner surface of the pipe 18. When the film-forming aqueous solution comes into contact with the inner surface of the purification system piping 18, Fe ²⁺ is eluted from the purification system piping 18 into the film-forming aqueous solution by the action of formic acid, and electrons are generated by the elution of ^{this Fe 2+.} To do. Since the nickel ions taken into the purification system pipe 18 are reduced by the electrons, a nickel metal film 82 is formed on the inner surface of the purification system pipe 18 as in the first embodiment. When the elapsed time from the start of injection of the nickel formate aqueous solution into the circulation pipe 31 in the chemical liquid tank 37 reaches the first set time, the formation of the nickel metal film on the inner surface of the purification system pipe 18 is completed.

After the formation of the nickel metal film is completed, each step of steps S5 (injection of the platinum ion aqueous solution) and S6 (injection of the reducing agent) is carried out in the same manner as in Example 1. In parallel with the execution of each of the steps S5 and S6, the step S4 (injection of the nickel ion aqueous solution) is carried out. Therefore, the aqueous solution 87 is generated, and platinum particles 84 containing a large number of nickel metals adhere to the surface of the nickel metal film 82 (see FIGS. 6 and 12). In this example, the aqueous solution 87 that comes into contact with the surface of the nickel metal film 82 does not contain oxalic acid. Further, when the elapsed time from the start of supply of the aqueous solution 87 to the purification system pipe 18 reaches the above-mentioned second set time, the nickel formate aqueous solution, the platinum ion aqueous solution and the hydrazine aqueous solution are sent to the circulation pipes 31 respectively. The injection is stopped (step S7).

After the step of step S7 is completed, the formic acid and the reducing agent are decomposed (step S16). The step of step S16 is substantially the same as the step of step S3C carried out in the first embodiment. In the step S16, the decomposition of oxalic acid carried out in the step S3C is not substantially carried out. Formic acid and hydrazine (reducing agent) are decomposed in the decomposition apparatus 55 by the action of the platinum particles 85 of the platinum particles 84 containing the activated carbon catalyst, hydrogen peroxide, and nickel metal, in the same manner as in step S3C described above. Decomposition of formic acid and hydrazine (reducing agent) is complete when the conductivity of the oxalic acid-free aqueous solution 87 drops to 20 μSiemens / cm.

Purification of the aqueous solution in which formic acid and the reducing agent are decomposed is carried out (step S8A). In this step S8A, the same processing as in step S8 described above is performed. After the decomposition of the formic acid and the reducing agent is completed, a 60 ° C. formic acid aqueous solution containing platinum particles 84 containing nickel ions, platinum ions and nickel metal is supplied to the mixed bed resin tower 54, and the metal contained in the formic acid aqueous solution is supplied. Platinum particles 84 containing ions (platinum ions and the like), nickel metal, and formic acid are collected by the cation exchange resin and the anion exchange resin in the mixed bed resin tower 54 and removed from the aqueous solution.

After the purification step is completed, each step of steps S9 (waste liquid treatment), S10 (removal of film forming apparatus), S11 (startup of nuclear power plant) and S12 (contact of furnace water at 130 ° C. or higher with nickel metal film) is performed. , It is carried out in the same manner as in Example 1. In step S12, oxygen-containing furnace water having a temperature range of 130 ° C. or higher and 330 ° C. or lower and a temperature range of 130 ° C. or higher and 280 ° C. or lower is formed on the inner surface of the purification system pipe 18 to form nickel metal. The platinum particles 84 containing the platinum particles 84 are brought into contact with the surface of the nickel metal film 82 to which the platinum particles 84 are attached. As a result, the nickel metal film 82 is _{converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 89, and the nickel metal 86 of the platinum particles 84 containing the nickel metal is also converted into a _{stable nickel ferrite (NiFe 2} O _4). .. The stable nickel converted from the nickel metal 86 is taken into the nickel ferrite film 89 and disappears, and the platinum particles 85 of the platinum particles 84 containing the nickel metal are in a state of being attached to the surface of the nickel ferrite film 89.

This embodiment shortens the time required for the platinum particles 84 to adhere to the nickel metal film 82, which is obtained by the adhesion of the platinum particles 84 containing the nickel metal to the nickel metal film 82 during the decomposition of oxalic acid. It is possible to obtain each effect generated in Example 1 other than the effect of being able to do so.

1 ... Boiling water type nuclear power plant, 2 ... Reactor pressure vessel, 4 ... Core, 6 ... Recirculation system piping, 9 ... Turbine, 11 ... Water supply piping, 18 ... Purification system piping, 20 ... Regenerative heat exchanger, 21 ... non-regenerative heat exchanger, 30 ... film forming device, 31,92 ... circulation piping, 33 ... heater, 34,35 ... circulation pump, 36 ... nickel ion injection device, 37,42,47,57 ... chemical tank, 38, 43, 48 ... injection pump, 41 ... reducing agent injection device, 46 ... platinum ion injection device, 52 ... cooler, 53 ... cation exchange resin tower, 54 ... mixed bed resin tower, 55 ... decomposition device, 56 ... oxidation Agent supply device, 58 ... Supply pump, 82 ... Nickel metal film, 84 ... Platinum particles containing nickel metal, 85 ... Platinum particles, 86 ... Nickel metal, 89 ... Nickel ferrite film, 91 ... Heating system.

Claims (14)

A nickel metal film is formed on the surface of the carbon steel member of the nuclear plant in contact with water, the surface is covered with the nickel metal film, and noble metal particles containing nickel metal are attached to the surface of the nickel metal film, and the noble metal particles are attached. Water containing oxygen at a temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower is brought into contact with the nickel metal film to which the nickel metal film is attached, and the formation of the nickel metal film and the adhesion of the noble metal particles are caused by stopping the operation of the nuclear power plant. A method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear power plant, which is performed later before the start-up of the nuclear power plant. The radioactivity of the nuclear power plant according to claim 1, wherein the formation of the nickel metal film and the adhesion of the noble metal particles are performed after the oxide film formed on the carbon steel member is removed by reduction decontamination. Nucleus adhesion suppression method. The nickel metal film is formed by bringing a film-forming liquid containing nickel ions and formic acid into contact with the surface of the carbon steel member, and the noble metal particles are attached to nickel ions, noble metal ions, formic acid and a reducing agent. The method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear power plant according to claim 2, which is performed by bringing the containing aqueous solution into contact with the surface of the nickel metal film. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant according to claim 3, wherein the pH of the film-forming liquid is in the range of 3.5 or more and 6.0 or less. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant according to claim 3 or 4, wherein at least one of formic acid and an oxidizing agent is injected into the reduction decontamination liquid used for the reduction decontamination. The formation of the nickel metal film is communicated to the steam generator, and the film forming liquid is supplied to the first pipe, which is the carbon steel member, through the second pipe, and the film forming liquid is applied to the carbon steel member. It is performed on the inner surface of the first pipe, which is the surface, by contacting the inner surface of the first pipe.
The adhesion of the noble metal particles causes the aqueous solution containing nickel ions, noble metal ions and a reducing agent to be supplied to the first pipe through the second pipe, and the nickel formed on the inner surface of the first pipe. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant according to claim 3, which is performed by contacting the surface of a metal film. The nuclear power plant according to claim 6, wherein the film-forming liquid is circulated in a closed loop including the first pipe and the second pipe, and the aqueous solution containing nickel ions, noble metal ions and a reducing agent is circulated in the closed loop. A method for suppressing the adhesion of radionuclides to carbon steel members. The contact of the water containing oxygen at a temperature in the temperature range of 130 ° C. or higher and 330 ° C. or lower with the nickel metal film to which the noble metal particles are attached is according to claim 6 or 7 after the nuclear power plant is started. The method for suppressing the adhesion of radionuclides to carbon steel members of the nuclear power plant described. The eighth aspect of the present invention, wherein the steam generator is a nuclear reactor, and the water having a temperature within the temperature range of 130 ° C. or higher and 330 ° C. or lower is furnace water containing oxygen generated by heating in the nuclear reactor. A method for suppressing the adhesion of radionuclides to carbon steel components of a nuclear power plant. After removing the second pipe from the first pipe, both ends of the third pipe are connected to the first pipe to form a closed loop including the first pipe and the third pipe, and the temperature is 130 ° C. containing oxygen. The supply of the water having a temperature within the temperature range of 330 ° C. or lower to the first pipe is such that the water containing oxygen circulating in the closed loop is supplied to the first pipe by a heating device provided in the third pipe at 130 ° C. The conversion of the nickel metal film to which the noble metal particles are attached to the nickel ferrite film is carried out by heating to a temperature within the temperature range of 330 ° C. or lower and supplying the third pipe to the first pipe. This is performed by contacting the nickel metal film formed on the inner surface of the first pipe with the water having a temperature in the temperature range of 130 ° C. or higher and 330 ° C. or lower, which contains oxygen and is supplied from the third pipe. The suppression of the adhesion of radioactive nuclei to the carbon steel member of the nuclear power plant according to claim 6, wherein the nickel metal film is converted into the nickel ferrite film to which the noble metal is attached, and then the third pipe is removed from the first pipe. Method. The formation of the nickel metal film and the adhesion of the noble metal particles are carried out in the decomposition step of the reducing decontamination agent contained in the reducing decontamination liquid used for the reduction decontamination, which is carried out after the completion of the reduction decontamination. It is carried out during the period when the reducing decontamination agent remains after decomposing a part of the reducing agent.
The film-forming liquid contains the reducing decontamination agent in addition to nickel ions and formic acid, and the aqueous solution contains the reducing decontamination agent in addition to nickel ions, formic acid and the reducing agent. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant according to any one of 6 to 10. The reduction decontamination agent and formic acid contained in the film-forming liquid are decomposed using a catalyst and an oxidizing agent, and the reduction decontamination agent, formic acid and the reducing agent contained in the aqueous solution are decomposed by the catalyst. The method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear power plant according to claim 11, which is carried out using the oxidizing agent and the noble metal contained in the noble metal particles containing the nickel metal. The formation of the nickel metal film and the adhesion of the noble metal particles are carried out after each of the reduction decontamination and the decomposition steps of the reduction decontamination agent contained in the reduction decontamination liquid used for the reduction decontamination are completed. The method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant according to any one of claims 3, 4 and 6 to 10. The decomposition of formic acid contained in the film-forming liquid is carried out using a catalyst and an oxidizing agent, and the decomposition of the formic acid and the reducing agent contained in the aqueous solution is carried out by the catalyst, the oxidizing agent, and the noble metal containing the nickel metal. The method for suppressing the adhesion of radioactive nuclei to carbon steel members of a nuclear power plant according to claim 13, which is performed using a noble metal contained in particles.

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