JP2018054538A - Method for depositing precious metal on carbon steel member in nuclear power plant and method for preventing attachment of radioactive nuclide to carbon steel member in nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing attachment of a radioactive nuclide to a carbon steel member in a nuclear power plant, which enables the effect to prevent attachment to last for a long period of time.SOLUTION: In a method for preventing attachment of a radioactive nuclide to a carbon steel member in a nuclear power plant, first film formation liquid containing nickel formate and hydrazine is injected (S4 and S5) through circulation piping of a film formulation device and introduced into carbon steel piping in a purification system after a reducing decontamination process in a BWR plant so as to form a nickel metal film on an inner periphery of the piping. Next, second film formation liquid prepared by injecting iron formate and hydrogen peroxide is introduced (S6 and S7) into the carbon steel piping in the purification system so as to form a NiFeOfilm on a surface of the nickel metal film. Then, solution containing platinum ions and hydrazine is prepared and introduced (S10 and S11) into the carbon steel piping in a purification system so as to enable platinum to deposit on the surface of the NiFeOfilm. Last, furnace water with a temperature not less than 200°C is introduced into the carbon steel piping in the purification system by starting up the BWR plant so as to convert the nickel metal film into a stable NiFeOfilm which is insoluble even with an action of platinum.SELECTED DRAWING: Figure 13

Description

  The present invention relates to a method for adhering a noble metal to a carbon steel member of a nuclear power plant and a method for suppressing the attachment of a radionuclide to a carbon steel member of a nuclear power plant, and in particular, a nuclear power plant suitable for application to a boiling water nuclear power plant. The present invention relates to a method for adhering noble metals to carbon steel members and a method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant.

  As a nuclear power plant, for example, a boiling water nuclear power plant (hereinafter referred to as a BWR plant) and a pressurized water nuclear power plant (hereinafter referred to as a PWR plant) are known. For example, in a BWR plant, steam generated in a reactor pressure vessel (referred to as RPV) is guided to a turbine to rotate the turbine. Steam discharged from the turbine is condensed into water by the condenser. This water is supplied to the RPV through the water supply pipe as water supply. In order to suppress generation | occurrence | production of the radioactive corrosion product in RPV, the metal impurity contained in feed water is removed with the filtration desalination apparatus provided in the feed water piping.

  In the BWR plant and the PWR plant, main components such as RPV use stainless steel and a nickel-based alloy in a portion in contact with water in order to suppress corrosion. Components such as the reactor purification system, residual heat removal system, reactor isolation cooling system, core spray system, and water supply system are caused by high-temperature water flowing through the water supply system from the viewpoint of reducing the required manufacturing cost of the plant. From the viewpoint of avoiding stress corrosion cracking of stainless steel, carbon steel members are mainly used.

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

However, even if the above-mentioned corrosion prevention measures are taken, the presence of very few metal impurities in the reactor water is inevitable, so some of the metal impurities are contained in the fuel assembly as metal oxides. Adhere to the outer surface of The metal element contained in the metal impurities attached to the outer surface of the fuel rod causes a nuclear reaction by irradiation of neutrons emitted from the nuclear fuel material in the fuel rod, and becomes a radionuclide such as cobalt 60, cobalt 58, chromium 51, manganese 54, etc. Become. Some radionuclides adhering to the outer surface of the fuel rod in the form of oxides elute as ions in the reactor water depending on the solubility of the incorporated oxide, and re-released into the reactor water as insoluble solids called clads Is done. The radionuclide that has not been removed by the reactor purification system is accumulated on the surface of the component that contacts the reactor water while circulating in the recirculation system together with the reactor water. As a result, radiation is emitted from the surface of the component member, which causes radiation exposure of workers during regular inspection work. The exposure dose of the employee is managed so that it does not exceed the prescribed value for each person. However, in recent years, this limit has been reduced, and it has become necessary to make the exposure dose of each person as low as possible economically. A chemical decontamination method has been proposed in which an oxide film containing radionuclides such as 60 and cobalt 58 is removed by dissolution using a chemical (Japanese Patent Laid-Open No. 2000-105295).

  Various methods for reducing the attachment of radionuclides to piping have been studied. For example, in order to suppress the attachment of radionuclides to the surface of a component of a nuclear power plant, Japanese Patent Laid-Open No. 8-220293 discloses that metal ions such as zinc and nickel are injected into reactor water, and zinc and It describes the deposition of nickel.

  A method for suppressing the attachment of radionuclides to a surface of a constituent member after operation of the plant by forming a magnetite film that is a kind of ferrite film on the surface of the constituent member of a nuclear power plant after chemical decontamination This is proposed in Japanese Patent Laid-Open No. 2006-38483. Furthermore, in Japanese Patent Application Laid-Open No. 2006-38483, after forming a magnetite film on the surface of a constituent member, the nuclear power plant is started, and the reactor water into which the noble metal has been injected is brought into contact with the magnetite film so that the noble metal is deposited on the magnetite film. It is described that it is adhered (see FIGS. 17 and 18).

  Japanese Patent Application Laid-Open No. 2007-182604 discloses a film forming solution in the range of 60 ° C. to 100 ° C. containing iron (II) ions, nickel ions, an oxidizing agent and a pH adjusting agent (for example, hydrazine) while the nuclear power plant is shut down After chemical decontamination, it is described that a surface of a carbon steel constituent member of a nuclear power plant is brought into contact with and a nickel ferrite film is formed on this surface (see FIG. 6). The formation of the nickel ferrite film suppresses corrosion of the carbon steel constituent member and suppresses the attachment of the radionuclide to the constituent member.

  Further, JP 2012-247322 A discloses a film forming solution in the range of 60 ° C. to 100 ° C. containing iron (II) ions, an oxidizing agent, and a pH adjusting agent (hydrazine) while the operation of the nuclear power plant is stopped. It is described that the plant is brought into contact with the surface of a chemically decontaminated component made of stainless steel, and a magnetite film is formed on this surface. Japanese Patent Application Laid-Open No. 2012-247322 also describes that during operation stop, an aqueous solution containing a noble metal (for example, platinum) is brought into contact with the formed magnetite film, and the noble metal is deposited on the magnetite film (FIG. 1).

  Japanese Patent Application Laid-Open No. 2014-44190 describes a method for attaching a noble metal to a component of a nuclear power plant. In this noble metal adhesion method, in the chemical decontamination performed during the shutdown of the nuclear power plant, a noble metal (for example, platinum ) (See FIG. 1 and FIG. 3), or precious metal is attached to the surface of the component member (see FIG. 16) in the purification process after the reductive decontamination process. The adhesion of the radionuclide to the surface is suppressed by the adhesion of the noble metal to the surface of the constituent member.

JP-A-8-220293 JP 2000-105295 A JP 2006-38483 A JP 2007-182604 A JP 2012-247322 A JP 2014-44190 A

  It has been desired to reduce the time required for adhesion of noble metals to carbon steel components (carbon steel members) in nuclear power plants.

  In addition, when metal ions such as zinc and nickel are injected into the reactor water to deposit metal such as zinc and nickel on the surface of nuclear plant components, radionuclides will adhere to stainless steel components. Although the suppression effect is expressed, the carbon steel component (carbon steel member) has a lower radionuclide adhesion suppression effect than the stainless steel component. Even in the case of noble metal adhesion, when the noble metal is adhered to the surface of the carbon steel component, the effect of suppressing the attachment of the radionuclide is lower than when the noble metal is adhered to the surface of the stainless steel component. .

  It is desired that the attachment of the radionuclide to the carbon steel member of the nuclear power plant is suppressed, and that the adhesion suppressing effect is sustained for a long time.

  A first object of the present invention is to provide a method for attaching a noble metal to a carbon steel member of a nuclear power plant that can shorten the time required for the noble metal to adhere to the carbon steel member.

  The second object of the present invention is to provide a method for suppressing the attachment of radionuclides to carbon steel members of a nuclear power plant that can maintain the effect of suppressing the attachment of radionuclides to carbon steel members over a longer period. It is in.

  A feature of the first invention for achieving the first object described above is that a nickel metal film is formed on a surface of a carbon steel member of a nuclear power plant in contact with cooling water, and the surface is covered with the nickel metal film. A first nickel ferrite film is formed on the surface in a temperature range of 60 ° C. to 100 ° C., a noble metal is adhered to the surface of the first nickel ferrite film formed in the temperature range, and a nickel metal film is formed and a noble metal is adhered. Is performed after the nuclear power plant is shut down and before the nuclear plant is started.

Since the surface of a carbon steel member in a nuclear power plant is covered with at least a nickel metal film, it is possible to prevent the elution of Fe ²⁺ from the carbon steel member into the film-forming aqueous solution, and noble metal adheres to the surface of the carbon steel member. The time required for adhesion of the noble metal to the surface of the carbon steel member can be shortened without being inhibited by the elution of Fe ²⁺ .

  Preferably, the formation of the nickel metal film is performed by supplying the first film forming aqueous solution through the second pipe to the first pipe which is a carbon steel member and communicated with the reactor pressure vessel. Is brought into contact with the inner surface of the first pipe, and the first nickel ferrite film is formed by supplying the second film-forming aqueous solution to the first pipe through the second pipe. The aqueous solution is formed by contacting the surface of the formed first nickel ferrite film, and the adhesion of the noble metal is performed by supplying an aqueous solution containing noble metal ions and a reducing agent to the first pipe through the second pipe. It is desirable to carry out by bringing the aqueous solution into contact with the surface of the formed first nickel ferrite film.

  A feature of the second invention for achieving the second object is that a nickel metal film is formed on a surface of a carbon steel member of a nuclear power plant in contact with cooling water, and the surface is covered with the nickel metal film. A first nickel ferrite film is formed on the surface, and a noble metal is adhered to the surface of the first nickel ferrite film. The formation of the nickel metal film and the deposition of the noble metal are performed after the nuclear plant is shut down and before the nuclear plant is started. The nickel metal film is changed to the second nickel ferrite film by bringing water having a temperature range of 200 ° C. or higher and 330 ° C. or lower containing an oxidizing agent (oxygen, hydrogen peroxide, etc.) into contact with the first nickel ferrite film to which the noble metal is adhered. The first nickel ferrite film is formed when the cooling water is in contact with the first nickel ferrite film. A nickel ferrite film that elutes into the cooling water by the action of the noble metal adhering to the surface of the first nickel ferrite film, and the second nickel ferrite film is formed when the cooling water is in contact with the second nickel ferrite film. The nickel ferrite film does not elute into the cooling water due to the action of the noble metal adhering to the surface.

The corrosion potential of the nickel metal film and the carbon steel member in contact with the water is lowered by the action of the noble metal adhering to the first nickel ferrite film. The carbon steel member and the nickel metal film are 200 ° C. or higher and 330 ° C. due to such a decrease in the corrosion potential and the contact of the water in the temperature range of 200 ° C. or higher and 330 ° C. or lower containing the oxidizing agent with the first nickel ferrite film. Since the temperature is in the following range, the oxidant contained in the water and oxygen constituting a part of the water molecules migrate to the nickel metal film, and the Fe ² from the carbon steel member to the nickel metal film. The transition of ⁺ converts the nickel metal film into a stable nickel ferrite film that does not elute into the cooling water in contact with the nuclear power plant, even by the action of the deposited precious metal. The effect of suppressing the adhesion of radionuclides to the carbon steel member by such a stable nickel ferrite film covering the surface of the carbon steel member can be maintained for a longer period.

  Preferably, during operation of the nuclear power plant, cooling water having a temperature range of 200 ° C. or higher and 330 ° C. or lower in the reactor pressure vessel, which is water having a temperature range of 200 ° C. or higher and 330 ° C. or lower containing an oxidizing agent, It is desirable to contact the metal film.

  According to the first invention, the time required for the adhesion of the noble metal to the carbon steel member of the nuclear power plant can be shortened.

  According to the 2nd invention, the adhesion suppression effect of the radionuclide to the carbon steel member of a nuclear power plant can be maintained over a longer period.

It is a flowchart which shows the procedure of the adhesion method of the noble metal to the carbon steel member of the nuclear power plant of Example 1 applied to the purification system piping of the boiling water nuclear power plant which is a preferable example of this invention. It is explanatory drawing which shows the state which connected the film formation apparatus used when implementing the adhesion method of the noble metal to the carbon steel member of the nuclear power plant shown in FIG. 1 to the purification system piping of the boiling water nuclear power plant. It is a detailed block diagram of the film forming apparatus shown in FIG. It is sectional drawing of purification system piping before the adhesion method of the noble metal to the carbon steel member of the nuclear power plant shown in FIG. 1 is started. It is explanatory drawing which shows the state by which the nickel metal membrane | film | coat was formed in the inner surface of purification system piping by the adhesion method of the noble metal to the carbon steel member of the nuclear power plant shown in FIG. Explanatory view showing a state in which further forming a nickel ferrite (Ni _0.7 Fe _2.3 O ₄₎ film on the formed nickel metal film surface cleaning system pipe inner surface by deposition method of the noble metal on the carbon steel member of a nuclear power plant shown in FIG. 1 It is. A state in which noble metal (for example, platinum) is adhered to the surface of the Ni _0.7 Fe _2.3 O ₄ film on the nickel metal film formed on the inner surface of the purification system pipe by the method of adhering the noble metal to the carbon steel member of the nuclear power plant shown in FIG. It is explanatory drawing which shows. It is explanatory drawing which shows the result of the Co-60 adhesion test to a carbon steel test piece. It is explanatory drawing which shows the laser Raman spectrum analysis result of the oxide film formed in the carbon steel test piece by the Co-60 adhesion test using the carbon steel test piece which formed the nickel metal film which adhered platinum. It is explanatory drawing which shows the result of the Auger spectrum analysis of the oxide film formed in the carbon steel test piece by the Co-60 adhesion test using the carbon steel test piece which formed the nickel metal film which adhered platinum. It is a flowchart which shows the procedure of the attachment suppression method of the radionuclide 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 suitable Example of this invention. . The heating system 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 the nickel ferrite film in the method for suppressing the attachment of radionuclides to the carbon steel member of the nuclear power plant shown in FIG. It is a block diagram. It is a flowchart which shows the procedure of the attachment suppression method of the radionuclide to the carbon steel member of the nuclear power plant of Example 3 applied to the purification system piping of the boiling water nuclear power plant which is another suitable Example of this invention. . In each of the methods for suppressing the attachment of radionuclides to carbon steel members of a nuclear power plant shown in FIGS. 10 and 12, Ni _0.7 Fe _2.3 O with platinum attached on the nickel metal film formed on the inner surface of the purification system pipe It is explanatory drawing which shows the state which contacts the water of the temperature range of 200 to 330 degreeC containing oxygen to ₄ film | membranes. In each of the methods for suppressing attachment of radionuclides to carbon steel members of a nuclear power plant shown in FIGS. 10 and 12, oxygen contained in water in a temperature range of 200 ° C. to 330 ° C. and Fe ² in the purification system pipe ⁺ is formed on the clean system pipe inner surface is an explanatory view showing a state in which the platinum to migrate to the nickel metal film covered with Ni _0.7 Fe _2.3 O ₄ film deposited. In each of the methods for suppressing the attachment of radionuclides to carbon steel members of the nuclear power plant shown in FIGS. 10 and 12, the Ni _0.7 Fe _2.3 O ₄ film formed on the inner surface of the purification system pipe and covered with platinum is covered. the nickel metal film was an explanatory view showing a state in which instead of the nickel ferrite (Ni ₇ Fe ₂ O ₄₎ film. The Ni _0.7 Fe _2.3 O ₄ film in the state shown in FIG. 16 formed in each of the methods for suppressing the attachment of radionuclides to carbon steel members of the nuclear power plant shown in FIGS. It is explanatory drawing which shows the state eluted to the reactor water.

  The inventors have made various studies on measures that can suppress adhesion of radionuclides to carbon steel components of nuclear power plants, that is, carbon components.

  As described above, when nickel or platinum is attached to the surface of the carbon steel member that contacts the reactor water, compared to when nickel or platinum is attached to the surface of the stainless steel component that contacts the reactor water. As a result, the effect of suppressing the attachment of the radionuclide to the surface is reduced.

  In order to improve the decrease in the effect of suppressing the adhesion of such radionuclides, the inventors attached a noble metal (for example, platinum) to the surface of the carbon steel component that contacts the reactor water, and then carbon. When nickel was adhered to the surface of the steel member on which the noble metal was adhered, it was found that the amount of radionuclide adhered to the surface of the carbon steel member was significantly reduced (see Japanese Patent Application No. 2015-41991).

  Based on such new knowledge, the inventors thought that adhering noble metal and nickel to the surface of a carbon steel member would lead to suppression of radionuclide adhesion to the surface. Accordingly, the inventors have examined a countermeasure that can further suppress the attachment of radionuclide to the surface of the carbon steel member on the premise that the noble metal and nickel are attached to the surface of the carbon steel member.

  By the way, as described in JP 2006-38483 A and JP 2012-247322 A, the inventors include iron (II) ions, an oxidizing agent, and a pH adjusting agent (for example, hydrazine). A film forming liquid in a low temperature range of 60 ° C. to 100 ° C. (60 ° C. or more and 100 ° C. or less) is brought into contact with the surface of the structural member of the nuclear power plant to form a magnetite film on the surface of the structural member. In the case of depositing the magnetite film, the phenomenon that the magnetite film elutes into the reactor water by the action of precious metal during the operation of the nuclear power plant in one operation cycle (for example, a period of one year) immediately after the magnetite film is formed is found. It was. Even when a noble metal is deposited on the nickel ferrite film formed on the surface of the carbon steel member in contact with the reactor water in a low temperature range of 60 ° C. to 100 ° C., the nickel ferrite film is not removed during operation of the nuclear power plant. The phenomenon of elution into the reactor water by the action of precious metals was found. Such elution of the ferrite film from the surface of the carbon steel member eventually leads to the disappearance of the ferrite film on the carbon steel member, and after the ferrite film disappears, that is, at the end of its one operating cycle. Nuclide was found to adhere to the surface of the carbon steel member. As a result, suppression of adhesion of the radionuclide to the surface of the carbon steel member over a long period of time is inhibited. In addition, 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, and a ferrite film must be formed every time the operation cycle is stopped. Disappear.

  Considering the elution of ferrite films such as magnetite films and nickel ferrite films with precious metals attached to the surface, not only will the radionuclide adherence to the surface of the carbon steel member be further suppressed, but also the radionuclides on the surface The inventors thought that the suppression of adhesion over a long period of time was also important.

The inventors of the present invention have the reason why the nickel ferrite film formed on the surface of the carbon steel member in contact with the reactor water in a low temperature range of 60 ° C. to 100 ° C. elutes when the noble metal is deposited on the film. Was examined. As a result of this study, the nickel ferrite film formed on the surface of the carbon steel member in such a low temperature range during the shutdown of the nuclear power plant is a Ni _0.7 Fe _2.3 O ₄ film and is unstable. I understood. 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 . For this reason, when, for example, platinum is deposited on the Ni _0.7 Fe _2.3 O ₄ film, which is an unstable film, Ni _0.7 Fe _2.3 O ₄ is caused by the action of the platinum during operation of the nuclear power plant. It was found that it elutes in the reactor water. In addition, since the unstable Ni _0.7 Fe _2.3 O ₄ film is formed in the low temperature range described above, many small particles of Ni _0.7 Fe _2.3 O ₄ are adhered to the surface of the carbon steel member. ing. For this reason as well, a Ni _0.7 Fe _2.3 O ₄ film with platinum adhering to the upper surface is eluted.

By the way, when the noble metal is attached to the surface of the carbon steel member, if the 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. For this reason, the inventors examined measures to prevent the elution of Fe ²⁺ from the carbon steel member when the noble metal is adhered to the surface of the carbon steel member. 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 that covers the surface of the carbon steel member is a substance that contributes to the formation of a stable nickel ferrite film that suppresses the attachment of radionuclides to the carbon steel member and does not elute due to the action of the attached noble metal, as will be described later. is there. 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, the elution of Fe ²⁺ from the carbon steel member can be prevented, and the nickel metal film surface of the noble metal Adhesion to the carbon steel, specifically, adhesion of the noble metal to the carbon steel member could be performed in a short time. In addition, the amount of precious metal attached to the carbon steel member has also increased.

Further, the surface of the carbon steel member was covered with the above nickel metal film, a Ni _0.7 Fe _2.3 O ₄ film was formed on the nickel metal film, and a noble metal was deposited on the Ni _0.7 Fe _2.3 O ₄ film. Even in this case, elution of Fe ²⁺ from the carbon steel member can be prevented, and adhesion of the noble metal to the carbon steel member can be performed in a short time. The Ni _0.7 Fe _2.3 O ₄ film covering the nickel metal film has a temperature range of 60 ° C. to 100 ° C. (60 ° C. or more and 100 ° C. or less) containing iron (II) ions, nickel ions, an oxidizing agent and a pH adjusting agent. It is formed by bringing a film-forming aqueous solution into contact with a nickel metal film. Also in this case, the time required for adhesion of the noble metal to the carbon steel member can be shortened. Formation of the Ni _0.7 Fe _2.3 O ₄ film covering the nickel metal film increases the amount of noble metal attached to the carbon steel member.

  The nickel metal film can be formed on the surface of the carbon steel member by bringing an aqueous solution containing nickel ions and a reducing agent into contact with the surface of the carbon steel member. Nickel ions contained in the aqueous solution are replaced with Fe contained in the carbon steel member, and the substituted nickel ions become nickel metal by the action of the reducing agent, and a nickel metal film is formed on the surface of the carbon steel member. Moreover, adhesion of the noble metal to the surface of the nickel metal film formed on the surface of the carbon steel member is possible by contacting the nickel metal film formed with an aqueous solution containing noble metal ions (for example, platinum ions) and a reducing agent. is there.

In this way, 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 noble metal to the carbon steel member in a short time. Can do.

Furthermore, the examination result regarding the adhesion control over the long term of the radionuclide on the surface of a carbon steel member is demonstrated below. The inventors have not formed an unstable Ni _0.7 Fe _2.3 O ₄ film in contact with the surface of a carbon steel member in a low temperature range of 60 ° C. to 100 ° C. We aimed to form a simple nickel ferrite film on the surface of carbon steel members. Therefore, the inventors made a nickel metal film formed on the surface of the carbon steel member in order to effectively attach the noble metal to the carbon steel member, and applied the stable nickel ferrite film to the surface of the carbon steel member. Various studies were made on whether it could be used for formation. As a result, high temperature (200 ° C. or higher) water containing an oxidant is brought into contact with the surface of the nickel metal film formed on the surface of the carbon steel member on the side to which the noble metal is adhered. , A stable nickel ferrite film that covers the surface of a carbon steel member and does not elute even by the action of a noble metal (a nickel ferrite film in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ , that is, a NiFe ₂ O ₄ film) I was able to change it. When the nickel metal film on the surface of the carbon steel member is converted to the stable nickel ferrite (NiFe ₂ O ₄ ) film, a Ni _0.7 Fe _2.3 O ₄ film is formed on the surface of the stable nickel ferrite film and the stable The nickel ferrite film is covered, and a noble metal (for example, platinum) is deposited on the Ni _0.7 Fe _2.3 O ₄ film.

The inventors formed a Ni _0.7 Fe _2.3 O ₄ film on a test piece A made of carbon steel to which nickel and platinum were not attached and a nickel metal film formed on the surface, and the surface of the Ni _0.7 Fe _2.3 O ₄ film. An experiment was conducted to confirm the adhesion of Co-60, which is a radionuclide, using a test piece B made of carbon steel with platinum attached thereto. In this experiment, the test pieces A and B were installed in a closed loop circulation pipe, and simulated water simulating the reactor water in the reactor was caused to flow through the circulation pipe and circulated. The simulated water that circulates contains Co-60, and the temperature of the simulated water is 280 ° C. Each of the test pieces A and B installed in the circulation pipe was immersed in simulated water flowing in the circulation pipe for 500 hours. After 500 hours, each of the test pieces A and B was taken out from the circulation pipe, and the amount of Co-60 attached to each test piece was measured.

The measurement result of the Co-60 adhesion amount in each test piece is shown in FIG. As is clear from FIG. 8, in the test piece B in which a Ni _0.7 Fe _2.3 O ₄ film was formed on a nickel metal film formed on the surface and platinum was adhered to the Ni _0.7 Fe _2.3 O ₄ film surface, Compared with the test piece A in which no film was formed and platinum was not adhered, the adhesion amount of Co-60 was significantly reduced.

And the composition in each surface of the test pieces A and B taken out from the circulation piping was analyzed by Raman spectroscopy. The analysis results are shown in FIG. A film mainly composed of Fe ₃ O ₄ was directly formed on the surface of the test piece A which is substantially carbon steel. An oxide film containing nickel ferrite (NiFe ₂ O ₄ ) as a main component was formed on the surface of the test piece B on which the amount of Co-60 deposited was greatly reduced. This NiFe ₂ O ₄ is a form in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ . This NiFe ₂ O ₄ film could be distinguished from the Ni _0.7 Fe _2.3 O ₄ film by the difference in the peak width of the Raman spectrum obtained by Raman spectroscopy.

Moreover, the result of the Auger spectrum of the surface of the test piece B taken out from the circulation piping was shown in FIG. From the results shown in FIG. 10, it was confirmed that NiFe ₂ O ₄ having a uniform composition was formed on the surface of the base material (carbon steel) of the test piece B. By the formation of this NiFe ₂ O ₄ , the adhesion amount of Co-60 was remarkably suppressed in the test piece B.

A nickel metal film is formed on a carbon steel member (test piece B) in which a noble metal (for example, platinum) is adhered on a Ni _0.7 Fe _2.3 O ₄ film formed on the surface of the nickel metal film. Nickel ferrite film covering the surface of a carbon steel member by contact with water at 200 ° C. or higher and water at 200 ° C. or higher containing an oxidizing agent (nickel ferrite in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ The reason why the film is converted to a film will be described. When water at 200 ° C. or higher containing an oxidizer contacts the nickel metal film on the carbon steel member, the nickel metal film and the carbon steel member are heated to 200 ° C. or higher. Oxygen contained in the water moves into the nickel metal film through the Ni _0.7 Fe _2.3 O ₄ film, and Fe contained in the carbon steel member becomes Fe ²⁺ and moves into the nickel metal film. Nickel ferrite in which nickel in the nickel metal film reacts with oxygen and Fe ²⁺ transferred into the nickel metal film in a high temperature environment of 200 ° C. or higher, and x is 0 in Ni _1-x Fe _{2 + x} O ₄ Is generated. This stable nickel ferrite film covers the surface of the carbon steel member.

Ni _1-x Fe _{2 + x} O ₄ produced as described above in a high-temperature environment of 200 ° C. or more from nickel metal contained in the nickel metal film covering the surface of the carbon steel member has zero x. Certain nickel ferrites have large crystals, are stable and do not elute into water, like Ni _0.7 Fe _2.3 O ₄ film, due to the action of attached noble metals, and also take in radionuclides such as Co-60. Absent. This stable nickel ferrite in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ is a carbon steel member due to the action of a noble metal such as platinum attached to the Ni _0.7 Fe _2.3 O ₄ film covering the nickel metal film. And the corrosion potential of the nickel metal film is reduced. Thus, in a high temperature environment of 200 ° C. or higher, the stable nickel ferrite film generated from the nickel metal covering the surface of the carbon steel member is formed in a low temperature range of 60 ° C. to 100 ° C. It is possible to suppress the attachment of the radionuclide to the carbon steel member over a longer period than the _0.7 Fe _2.3 O ₄ coating.

  The nickel metal film is converted into a stable nickel ferrite film that does not elute due to the action of the deposited noble metal by bringing water at 200 ° C. or more containing an oxidant into contact with the nickel metal film formed on the surface of the carbon steel member. be able to. However, the temperature of the water containing the oxidizing agent is preferably in the range of 200 ° C. or higher and 330 ° C. or lower in order to avoid an excessively high temperature from the viewpoint of implementation.

  Based on the examination results described above, the inventors were able to create two new inventions (1) and (2) described below.

(1) A film-forming aqueous solution containing nickel ions and a reducing agent is brought into contact with the surface of the carbon steel member in contact with the cooling water, a nickel metal film is formed on the surface of the carbon steel member, and Ni _0.7 is formed on the surface of the nickel metal film. An Fe _2.3 O ₄ film (first nickel ferrite film) is formed, and a noble metal is adhered to the surface of the first nickel ferrite film.

(2) A film-forming aqueous solution containing nickel ions and a reducing agent is brought into contact with the surface of the carbon steel member, a nickel metal film is formed on the surface of the carbon steel member, and a Ni _0.7 Fe _2.3 O ₄ film is formed on the surface of the nickel metal film. (First nickel ferrite film) is formed, a noble metal is attached to the surface of the first nickel ferrite film, and water in a temperature range of 200 ° C. to 330 ° C. containing an oxidizing agent is added to the first nickel ferrite to which the noble metal is attached. The above-mentioned stable nickel ferrite film (second nickel ferrite film) is formed on the surface of the carbon steel member in the temperature range of 200 ° C. or higher and 330 ° C. or lower based on the nickel metal contained in the nickel metal film. To do.

(1) is an invention relating to a method for attaching a noble metal to a carbon steel member of a nuclear power plant. According to the invention of (1), since the surface of the carbon steel member is covered with the nickel metal film, the elution of Fe ²⁺ from the carbon steel member can be prevented, and the noble metal adheres to the surface of the carbon steel member. The time required can be shortened. Furthermore, since the surface of nickel metal is covered with the first nickel ferrite film, the amount of noble metal adhering to the carbon steel member can be increased.

  (2) is an invention relating to a method for suppressing the attachment of radionuclides to carbon steel members of a nuclear power plant. According to the invention of (2), the first nickel ferrite film formed on the surface of the nickel metal film formed on the surface of the carbon steel member and including the noble metal is included at 200 ° C. or higher and 330 ° C. A nickel ferrite film (second nickel ferrite film) is formed on the surface of the carbon steel member in a temperature range of 200 ° C. or higher and 330 ° C. or lower based on nickel metal contained in the nickel metal film by contacting water in the following temperature range. The formed nickel ferrite film does not elute into water even if noble metal is attached, and more specifically, in a plurality of (for example, five) operation cycles. In addition, the attachment of the radionuclide to the carbon steel member can be suppressed.

  As described in Examples 2 and 3, the first nickel ferrite film is a precious metal adhering to the surface of the first nickel ferrite film in a state where the reactor coolant is in contact with the first nickel ferrite film. It is a nickel ferrite film that elutes into the cooling water due to its action (see, for example, FIG. 17). On the other hand, as described in Examples 2 and 3, the second nickel ferrite film is formed of precious metal adhering to the surface of the first nickel ferrite film even when the cooling water is in contact with the second nickel ferrite film. It is a nickel ferrite film that does not elute into the cooling water due to its action (see, for example, FIG. 17).

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

  A method for adhering a noble metal to a carbon steel member of a nuclear power plant according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. The adhesion method of the noble metal to the carbon steel member of the nuclear power plant of this embodiment is applied to a carbon steel purification system pipe (carbon steel member) of a boiling water nuclear power plant (BWR plant).

  A schematic configuration of the BWR plant will be described with reference to FIG. The BWR plant 1 includes a nuclear reactor 2, a turbine 9, a condenser 10, a recirculation system, a nuclear reactor purification system, a water supply system, and the like. The reactor 2 has a reactor pressure vessel (hereinafter referred to as RPV) 3 in which a core 4 is built, and is formed between an outer surface of a core shroud (not shown) surrounding the core 4 in the RPV 3 and an inner surface of the RPV 3. A jet pump 5 is installed in an annular downcomer. A large number of fuel assemblies (not shown) are loaded on the core 4. The fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material. The recirculation system has a stainless steel recirculation system pipe 6 and a recirculation pump 7 installed in the recirculation system pipe 6. The water supply system includes a condensate pump 12, a condensate purification device (for example, a condensate demineralizer) 13, a low-pressure feed water heater 14, a feed water pump 15, and a high-pressure feed water to a feed water pipe 11 that connects the condenser 10 and the RPV 3. The heater 16 is installed in this order from the condenser 10 toward the RPV 3. In the reactor purification system, a purification system pipe 18, a regenerative heat exchanger 20, a non-regenerative heat exchanger 21, and a reactor water purification device 22 are connected in this order to a purification system pipe 18 that connects the recirculation system pipe 6 and the feed water pipe 11. It is installed. The purification system pipe 18 is connected to the recirculation system pipe 6 upstream of the recirculation pump 7. The nuclear reactor 2 is installed in a reactor containment vessel 87A arranged in a nuclear reactor building (not shown).

  Cooling water (hereinafter referred to as “reactor water”) in the RPV 3 is boosted by the recirculation pump 7 and jetted into the jet pump 5 through the recirculation system pipe 6. The reactor water existing around the nozzle of the jet pump 5 in the downcomer is also sucked into the jet pump 5 and supplied to the reactor core 4. The reactor water supplied to the reactor core 4 is heated by heat generated by fission of nuclear fuel material in the fuel rods. Part of the heated reactor water becomes steam. This steam is guided from the RPV 3 through the main steam pipe 8 to the turbine 9 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 through the water supply pipe 11 as water supply. The feed water flowing through the feed water pipe 11 is boosted by the condensate pump 12, impurities are removed by the condensate purification device 13, and further boosted by the feed water 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 RPV 3. The extraction steam extracted from the turbine 9 by the extraction pipe 17 is supplied to the low-pressure feed water heater 14 and the high-pressure feed water heater 16 respectively, and becomes a heating source of the feed water.

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

  In the method of attaching a noble metal to the carbon steel member of the nuclear power plant of this embodiment, a film forming apparatus 30 is used, and this film forming apparatus 30 is connected to the purification system pipe 18 of the BWR plant as shown in FIG. The

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

  The film forming apparatus 30 includes a surge tank 31, circulation pumps 32 and 33, a circulation pipe 34, a nickel ion implantation apparatus 35, a reducing agent implantation apparatus 40, an iron ion implantation apparatus 45, a platinum ion implantation apparatus 50, an oxidant implantation apparatus 55, A heater 58, a cooler 60, a cation exchange resin tower 61, a mixed bed resin tower 62, a decomposition apparatus 63, and an ejector 64 are provided.

  The on-off valve 65, the circulation pump 33, the valves 66, 69, 72, and 77, the surge tank 31, the circulation pump 32, the valve 80, and the on-off valve 81 are provided in the circulation pipe 34 in this order from the upstream. A pipe 68 that bypasses the valve 66 is connected to the circulation pipe 34, and a valve 67 and a filter 59 </ b> A are installed in the pipe 68. A cooler 60 and a valve 70 are installed in a pipe 71 that bypasses the valve 69 and is connected to the circulation pipe 34 at both ends. A cation exchange resin tower 61 and a valve 73 are installed in a pipe 74 having both ends connected to the circulation pipe 34 and bypassing the valve 72. A mixed bed resin tower 62 and a valve 75 are installed in a pipe 76 having both ends connected to the pipe 74 and bypassing the cation exchange resin tower 61 and the valve 73. The cation exchange resin tower 61 is filled with a cation exchange resin, and the mixed bed resin tower 62 is filled with a cation exchange resin and an anion exchange resin.

  A pipe 79 where the valve 78 and the disassembling device 63 located downstream of the valve 78 is installed bypasses the valve 77 and is connected to the circulation pipe 34. The decomposition device 63 is filled with, for example, an activated carbon catalyst in which ruthenium is impregnated on the surface of the activated carbon. A surge tank 31 is installed in the circulation pipe 34 between the valve 77 and the circulation pump 32. A heater 58 is disposed in the surge tank 31. A pipe 83 </ b> A provided with the valve 82 and the ejector 64 is connected to the circulation pipe 34 between the valve 80 and the circulation pump 32, and is further connected to the surge tank 31. The ejector 64 is provided with a hopper (not shown) for supplying oxalic acid (reductive decontamination agent) used for reducing and dissolving contaminants on the inner surface of the recirculation system pipe 6 into the surge tank 31.

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

The iron (II) ion implantation apparatus 45 includes a chemical solution tank 46, an injection pump 47, and an injection pipe 48. The chemical tank 46 is connected to the circulation pipe 34 by an injection pipe 48 having an injection pump 47 and a valve 49. An aqueous solution of iron formate (an aqueous solution containing iron (II) ions) prepared by dissolving iron formate (2Fe (HCOO) · 2H ₂ O) in water is filled in the chemical tank 46.

A platinum ion implantation apparatus (noble metal ion implantation apparatus) 50 includes a chemical tank 51, an injection pump 52, and an injection pipe 53. The chemical tank 51 is connected to the circulation pipe 34 by an injection pipe 53 having an injection pump 52 and a valve 54. 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) Hydrate aqueous solution) is filled in the chemical tank 51. An aqueous solution containing platinum ions is a kind of aqueous solution containing noble metal ions. As an aqueous solution containing noble metal ions, an aqueous solution containing any ion of palladium, rhodium, ruthenium, osmium and iridium may be used in addition to an aqueous solution containing platinum ions.

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

  The oxidant injection device 55 includes a chemical tank 56, an injection pump 57, and an injection pipe 58A. The chemical tank 56 is connected to the circulation pipe 34 by an injection pipe 58 </ b> A having an injection pump 57 and a valve 59. The chemical liquid tank 56 is filled with hydrogen peroxide as an oxidant. As the oxidizing agent, ozone or water in which oxygen is dissolved may be used. Further, one end of the supply pipe 101 having the valve 100 is connected to the injection pipe 58 </ b> A between the injection pump 57 and the valve 59, and the other end of the supply pipe 101 is connected to the pipe 79 upstream of the valve 78.

  Injection pipes 48, 38, 58A, 53 and 43 are connected to the circulation pipe 34 between the valve 80 and the on-off valve 81 in that order from the valve 80 toward the on-off valve 81.

  A pH meter 82A is attached to the circulation pipe 34 between the connection point of the injection pipe 43 and the circulation pipe 34 and the on-off valve 81.

  The BWR plant 1 is stopped after the operation in one operation cycle is completed. After the shutdown, 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 a fuel change is completed, the BWR plant 1 is restarted for operation in the next operation cycle. Maintenance inspection of the BWR plant is performed using a period during which the BWR plant 1 is stopped for fuel replacement.

During the period when the operation of the BWR plant 1 is stopped as described above, a piping system made of carbon steel, for example, the purification system piping 18 connected to the RPV 12, which is one of the carbon steel members in the BWR plant 1, is used. The method for attaching a noble metal to the carbon steel member of the nuclear power plant according to the present embodiment is performed. In this noble metal adhesion method, the formation of a nickel metal film on the inner surface of the purification system pipe 18 in contact with the reactor water, the formation of a Ni _0.7 Fe _2.3 O ₄ film on the surface of the nickel metal film, and the Ni _0.7 Fe _2.3 O precious metals to ₄ film surface, for example, deposition processing of platinum is performed.

  A method for attaching a noble metal to a carbon steel member of a nuclear power plant according to the present embodiment will be described below based on the procedure shown in FIG. In the method for attaching a noble metal to a carbon steel member of a nuclear power plant according to this embodiment, a film forming apparatus 30 is used.

  First, a film forming apparatus is connected to a piping system made of carbon steel for film formation (step S1). When the operation of the BWR plant 1 is stopped, for example, the recirculation system is opened by opening the bonnet of the valve 23 installed in the purification system pipe 18 (first pipe) connected to the recirculation system pipe 6. Seal the pipe 6 side. One end of the circulation pipe 34 (second pipe) of the film forming apparatus 30 on the open / close valve 81 side is connected to the flange of the valve 23, and one end of the circulation pipe 34 is connected to the purification system pipe 18 upstream of the purification system pump 19. Connected. On the other hand, the bonnet of the valve 25 installed in the purification system pipe 18 is opened between the regenerative heat exchanger 20 and the non-regenerative heat exchanger 21 to seal the non-regenerative heat exchanger 21 side. The other end of the circulation pipe 34 on the open / close valve 65 side is connected to the flange of the valve 25, and the other end of the circulation pipe 34 is connected to the purification system pipe 18 on the downstream side of the regenerative heat exchanger 20. Both ends of the circulation pipe 34 are connected to the purification system pipe 18 to form a closed loop including the purification system pipe 18 and the circulation pipe 34.

  In this embodiment, the film forming apparatus 30 is connected to the purification system pipe 18 of the reactor purification system. However, in addition to the purification system pipe 18, the residual heat removal system that is a carbon steel member and communicates with the RPV 3. The film forming apparatus 30 is connected to one of the carbon steel pipes of the reactor isolation cooling system and the core spray system, and the carbon steel pipe is connected with the precious metal to the carbon steel member of the nuclear power plant of this embodiment. An attachment method may be applied.

  Chemical decontamination is performed on the piping system made of carbon steel to be coated (step S2). In the BWR plant 1 that has experienced operation in the previous operation cycle, an oxide film containing a radionuclide is formed on the inner surface of the purification system pipe 18 that contacts the reactor water flowing from the RPV 3. Before forming a nickel metal film, which will be described later, on the inner surface of the purification system pipe 18, it is preferable to remove the oxide film containing the radionuclide from the inner surface. When the nickel metal film is formed on the inner surface of the purification system pipe 18 according to the present embodiment, the dose rate of the purification system pipe 18 is lowered in advance and the adhesion between the formed film and the inner surface of the purification system pipe 18 is reduced. In order to improve the above, it is desirable to remove the oxide film containing the radionuclide formed on the inner surface of the purification system pipe 18. In order to remove the oxide film, chemical decontamination, particularly reductive decontamination using a reductive decontamination solution containing oxalic acid as a reductive decontaminant, is performed on the inner surface of the purification system pipe 18.

  In step S2, the chemical decontamination applied to the inner surface of the purification system pipe 18 is a known reductive decontamination described in Japanese Patent Application Laid-Open No. 2000-105295. This reductive decontamination will be described. First, the on-off valve 65, the valves 66, 69, 72, 77 and 80, and the on-off valve 81 are opened, and the circulation pumps 32 and 33 are driven with the other valves closed. Thereby, the water heated by the heater 58 in the surge tank 31 in the purification system pipe 18 circulates in the closed loop formed by the circulation pipe 34 and the purification system pipe 18. The circulating water is adjusted to 90 ° C. by the heater 58. When the temperature of the water reaches 90 ° C., the valve 82 is opened to guide a part of the water flowing in the circulation pipe 34 into the pipe 83A. A predetermined amount of oxalic acid supplied from the hopper and ejector 64 into the pipe 83A is guided into the surge tank 31 by the water flowing through the pipe 83A. This oxalic acid is dissolved in water in the surge tank 31, and an oxalic acid aqueous solution (reductive decontamination solution) is generated in the surge tank 31.

  The oxalic acid aqueous solution is discharged from the surge tank 31 to the circulation pipe 34 by driving the circulation pump 32. The hydrazine aqueous solution in the chemical tank 41 of the reducing agent injection device 40 is injected into the oxalic acid aqueous solution in the circulation pipe 34 through the injection pipe 43 by opening the valve 44 and driving the injection pump 42. By controlling the injection pump 42 (or the opening of the valve 44) based on the pH value of the oxalic acid aqueous solution measured by the pH meter 82A and adjusting the injection amount of the hydrazine aqueous solution into the circulation pipe 34, the purification system The pH of the oxalic acid aqueous solution supplied to the pipe 18 is adjusted to 2.5. In this embodiment, hydrazine, which is a reducing agent used when depositing nickel metal on the inner surface of the purification system pipe 18 and depositing noble metal, for example, platinum on the nickel metal film, is reduced by decontamination. In the process, it is used as a pH adjuster for adjusting the pH of the oxalic acid aqueous solution.

  An aqueous oxalic acid solution having a pH of 2.5 and 90 ° C. is supplied from the circulation pipe 34 to the purification system pipe 18 and comes into contact with the oxide film containing the radionuclide formed on the inner surface of the purification system pipe 18. This oxide film is dissolved by oxalic acid. The aqueous oxalic acid solution flows in the purification system pipe 18 while dissolving the oxide film, passes through the purification system pump 19 and the regenerative heat exchanger 20, and is returned to the circulation pipe 34. The oxalic acid aqueous solution returned to the circulation pipe 34 is pressurized by the circulation pump 33 through the open / close valve 65, passes through the valves 63, 66, 68 and 73, and reaches the surge tank 31. As described above, the oxalic acid aqueous solution circulates in the closed loop including the circulation pipe 34 and the purification system pipe 18, performs reductive decontamination of the inner surface of the purification system pipe 18, and dissolves the oxide film formed on the inner surface. .

  As the oxide film dissolves, the radionuclide concentration and Fe concentration of the oxalic acid aqueous solution increase. The cation exchange resin tower 61 is operated in order to suppress the concentration increase of each of the radionuclide and Fe contained in the oxalic acid aqueous solution. That is, by opening the valve 73 and adjusting the opening degree of the valve 72, a part of the oxalic acid aqueous solution returned from the purification system pipe 18 to the circulation pipe 34 is introduced to the cation exchange resin tower 61 through the pipe 74. It is burned. 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 61. The oxalic acid aqueous solution discharged from the cation exchange resin tower 61 and the oxalic acid aqueous solution that has passed through the valve 72 are supplied again from the circulation pipe 34 to the purification system pipe 18 and used for reductive decontamination of the purification system pipe 18.

  In reductive decontamination on the surface of a carbon steel member (for example, purification system pipe 18) using oxalic acid, poorly soluble iron oxalate (II) is formed on the surface of the carbon steel member, and this iron oxalate ( According to II), dissolution of the oxide film containing the radionuclide formed on the surface of the carbon steel member by oxalic acid may be suppressed. In this case, the valve 72 is fully opened, the valve 73 is closed, the supply of the oxalic acid aqueous solution to the cation exchange resin tower 61 is stopped, and the oxalic acid aqueous solution flowing through the circulation pipe 34 is supplied with hydrogen peroxide as an oxidizing agent. Inject. Injecting hydrogen peroxide into the oxalic acid aqueous solution, the valve 59 is opened and the injection pump 57 is activated to convert the hydrogen peroxide in the chemical tank 56 into the oxalic acid aqueous solution flowing in the circulation pipe 34 through the injection pipe 58A. Supply. At this time, the valve 100 is closed. An aqueous oxalic acid solution containing hydrogen peroxide is introduced from the circulation pipe 34 into the purification system pipe 18, and Fe (II) contained in the iron (II) oxalate formed on the inner surface of the purification system pipe 18 is the oxalic acid aqueous solution. Is oxidized to Fe (III) by the action of hydrogen peroxide contained in the iron, and the iron (II) oxalate is dissolved in the oxalic acid aqueous solution as an iron (III) oxalate complex. That is, iron (II) oxalate and hydrogen peroxide and oxalic acid contained in the oxalic acid aqueous solution generate an iron (III) oxalate complex, water, and hydrogen ions by the reaction shown in Formula (1).

2Fe (COO) ₂ + H ₂ O ₂ +2 (COOH) ₂ →
2Fe [(COO) ₂ ] ₂ ⁻ + 2H ₂ O + 2H ⁺ (1)
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 oxalic acid aqueous solution disappeared by the reaction of the formula (1), the valve 73 was opened. Then, the opening degree of the valve 72 is adjusted, and a part of the oxalic acid aqueous solution that has flowed through the circulation pipe 34 and passed through the valve 69 is supplied to the cation exchange resin tower 61 through the pipe 74. Metal cations such as radionuclides contained in the oxalic acid aqueous solution are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 61. The disappearance of hydrogen peroxide in the oxalic acid aqueous solution can be confirmed by attaching a test paper that reacts with hydrogen peroxide to the oxalic acid aqueous solution sampled from the circulation pipe 34 and observing the color that appears on the test paper.

  Oxalic acid contained in the oxalic acid aqueous solution when the dose rate of the reductive decontamination part of the purification system pipe 18 is reduced to the set dose rate or when the decontamination time of the purification system pipe 18 reaches a predetermined time. And decomposes hydrazine. That is, a reductive decontamination decomposition process is performed. In addition, it was confirmed by the dose rate calculated | required based on the output signal of the radiation detector which detects the radiation from the reduction decontamination location of the purification system piping 18 that the dose rate of the reduction decontamination location fell to the set dose rate. can do.

  Decomposition of oxalic acid and hydrazine is performed as follows. The oxalic acid aqueous solution containing hydrazine that has flowed through the circulation pipe 34 and passed through the valve 72 is supplied to the cracking device 63 through the valve 78 and the pipe 79 by opening the valve 78 and partially reducing the opening degree of the valve 77. Is done. At this time, by opening the valve 100 and driving the injection pump 57, the hydrogen peroxide in the chemical tank 56 is supplied to the pipe 79 through the supply pipe 101 and flows into the decomposition device 63. The valve 59 is closed. Oxalic acid and hydrazine contained in the oxalic acid aqueous solution are decomposed in the decomposition device 63 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 63 is expressed by the formulas (2) and (3).

(COOH) ₂ + H ₂ O ₂ → 2CO ₂ + 2H ₂ O (2)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O (3)
The decomposition of the oxalic acid and hydrazine in the decomposition device 63 is performed while circulating the oxalic acid aqueous solution in the closed loop including the circulation pipe 34 and the purification system pipe 18. In order to prevent the supplied hydrogen peroxide from being completely consumed by the decomposition apparatus 63 for the decomposition of oxalic acid and hydrazine and from flowing out of the decomposition apparatus 63, the supply amount of hydrogen peroxide from the chemical tank 56 to the decomposition apparatus 63 is reduced. The rotational speed of the infusion pump 57 is controlled and adjusted.

  Also in the reductive decontamination step, if oxalic acid is present in the oxalic acid aqueous solution, iron (II) oxalate is formed on the inner surface of the purification system pipe 18 that is a carbon steel member that comes into contact with the oxalic acid aqueous solution. There is a possibility. Therefore, when the decomposition of oxalic acid and hydrazine contained in the oxalic acid aqueous solution has progressed to some extent, the rotation speed of the injection pump 57 is increased, and the decomposition device is discharged from the chemical tank 56 so that hydrogen peroxide flows out of the decomposition device 63. The supply amount of hydrogen peroxide to 63 is increased.

The aqueous oxalic acid solution containing hydrogen peroxide discharged from the decomposition apparatus 63 is guided from the circulation pipe 34 to the purification system pipe 18. As described above, the iron (II) oxalate formed on the inner surface of the purification pipe 18 that is a carbon steel member is converted into an iron (III) oxalate complex by the action of hydrogen peroxide and dissolved in the aqueous oxalic acid solution. To do. Since decomposition of oxalic acid and the like in the oxalic acid aqueous solution has progressed, there is a shortage of oxalic acid that converts Fe (II) contained in iron (II) oxalate into easily soluble Fe (III). Fe (OH) ₃ tends to precipitate on the inner surface. For this reason, in order to suppress precipitation of Fe (OH) ₃ , formic acid is injected into the oxalic acid aqueous solution. The formic acid is injected by, for example, supplying the formic acid from the hopper and ejector 64 to the surge tank 31 with the valve 82 opened and the oxalic acid aqueous solution flowing in the pipe 83A. Is called. The supplied formic acid is mixed with an oxalic acid aqueous solution.

The supplied oxalic acid aqueous solution containing formic acid contains hydrogen peroxide discharged from the decomposition device 63 in addition to oxalic acid and hydrazine having a reduced concentration. The aqueous oxalic acid solution containing formic acid and hydrogen peroxide is supplied to the purification system pipe 18. Hydrogen peroxide contained in the oxalic acid aqueous solution dissolves iron (II) oxalate deposited on the inner surface of the purification system pipe 18 and formic acid dissolves Fe (OH) ₃ . Since the oxalic acid aqueous solution circulates in a closed loop including the circulation pipe 34 and the purification system pipe 18, decomposition of oxalic acid and hydrazine is continued in the decomposition apparatus 63.

  Next, in order to finish the decomposition process of oxalic acid, the hydrogen peroxide concentration of the oxalic acid aqueous solution flowing in the circulation pipe 34 is reduced, and the oxalic acid aqueous solution is supplied to the cation exchange resin tower 61. Thus, valve 100 is closed and valve 82 is closed to stop formic acid injection. When the injection of hydrogen peroxide and formic acid into the oxalic acid aqueous solution flowing in the circulation pipe 34 is stopped, these concentrations in the oxalic acid aqueous solution also decrease. When the hydrogen peroxide concentration of the oxalic acid aqueous solution becomes 1 ppm or less, the valve 73 is opened to reduce the opening of the valve 72, and the oxalic acid aqueous solution is supplied to the cation exchange resin tower 61. As described above, the metal cation contained in the oxalic acid aqueous solution is removed by the cation exchange resin in the cation exchange resin tower 61, and the metal cation concentration of the oxalic acid aqueous solution is lowered. The decomposition of oxalic acid, hydrazine and formic acid is continued in the decomposition device 63. Among 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 process of oxalic acid is finished.

  When the chemical decontamination described above is completed, the purification system pipe 18 is in the state shown in FIG. 4 with the oxide film containing the radionuclide removed from the inner surface of the purification system pipe 18. The inner surface is in contact with the aforementioned aqueous solution containing formic acid.

  The temperature of the film forming liquid is adjusted (step S3). Valves 72 and 77 are opened and valves 73 and 78 are closed. Since the circulation pumps 32 and 33 are driven, the remaining aqueous solution containing formic acid circulates in the closed loop including the circulation pipe 34 and the purification system pipe 18. The aqueous solution containing the formic acid is heated to 90 ° C. by the heater 58. The temperature of this aqueous formic acid solution (film formation aqueous solution described later) is preferably in the range of 60 ° C. to 100 ° C. (60 ° C. or higher and 100 ° C. or lower). Further, the valve 67 is opened and the valve 66 is closed. By these valve operations, the formic acid aqueous solution flowing in the circulation pipe 34 is supplied to the filter 59A, and fine solids remaining in the formic acid aqueous solution are removed by the filter 59A. When the fine solid content is not removed by the filter 59A, when the nickel metal film is formed on the inner surface of the purification system pipe 18, when the nickel formic acid aqueous solution is injected into the circulation pipe 34, the surface of the solid is also nickel. A metal film is formed, and the injected nickel ions are wasted. The supply of the formic acid aqueous solution to the filter 59A is to prevent such useless use of nickel ions.

  A nickel ion aqueous solution is injected (step S4). The valve 66 is opened and the valve 67 is closed, and water flow to the filter 59A is stopped. The valve 39 of the nickel ion implanter 35 is opened and the injection pump 37 is driven to inject the nickel formate aqueous solution in the chemical solution tank 36 into the 90 ° C. aqueous solution containing the remaining formic acid flowing through the circulation pipe 34 through the injection pipe 38. Is done. The nickel ion concentration of the injected nickel formate aqueous solution is, for example, 200 ppm.

  A reducing agent is injected (step S5). The valve 44 of the reducing agent injection device 40 is opened to drive the injection pump 42, and an aqueous solution of hydrazine, which is a reducing agent in the chemical tank 41, contains nickel ions and formic acid 90 flowing through the circulation pipe 34 through the injection pipe 43. It is poured into an aqueous solution at ° C. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 200 ppm. The aqueous hydrazine solution was measured with a pH meter 82A so that the pH of the aqueous solution containing nickel ions and formic acid at 90 ° C. was in the range of 4.0 to 11.0 (4.0 to 11.0). For example, the injection amount into the aqueous solution is adjusted to 4.0.

  An aqueous solution containing nickel ions, formic acid and hydrazine and having a pH of 4.0 and a temperature of 90 ° C., that is, a first film-forming aqueous solution (first film-forming liquid) is supplied from the circulation pipe 34 to the purification system pipe 18 by driving the circulation pump 32. To be supplied. When the first film-forming aqueous solution 84 comes into contact with the inner surface of the purification system pipe 18, a nickel metal film 83 is formed on the inner surface of the purification system pipe 18 (see FIG. 5). The nickel metal film 83 is formed as follows. By contact between the inner surface of the purification system pipe 18 and the first film-forming aqueous solution 84 having a pH of 4.0, a substitution reaction between nickel ions contained in the first film-forming aqueous solution 84 and Fe (II) ions in the purification system pipe 18 occurs. The amount of nickel ions that are accelerated and taken into the inner surface of the purification system pipe 18 increases, and the elution of iron (II) ions into the first film-forming aqueous solution 84 increases. Nickel ions taken into the inner surface of the purification system pipe 18 become nickel metal due to the action of hydrazine contained in the first film forming aqueous solution 84, so that a nickel metal film 83 is formed on the inner surface of the purification system pipe 18.

  The substitution reaction between nickel ions and iron (II) ions is most active when the pH of the first film-forming aqueous solution 84 in contact with the inner surface of the purification system pipe 18 is 4.0. The amount of nickel ions taken up is the largest. When the pH of the first film forming aqueous solution 84 is increased to 7 etc. by the injection of the reducing agent, the amount of the nickel ions taken into nickel metal increases.

The first film forming aqueous solution 84 discharged from the purification system pipe 18 to the circulation pipe 34 is pressurized by the circulation pumps 33 and 32, and the nickel formate aqueous solution from the nickel ion implanter 35 and the hydrazine aqueous solution from the reducing agent injector 40 are used. Each is injected and again injected into the purification system pipe 18. Thus, by circulating the first film forming aqueous solution 84 in the closed loop including the circulation pipe 34 and the purification system pipe 18, the nickel metal film 83 eventually becomes the first film formation aqueous solution 84 of the purification system pipe 18. Cover the entire inner surface in contact with the surface uniformly. At this time, the nickel metal existing on the inner surface of the purification system pipe 18 is 50 μg (50 μg / cm ² ) per square centimeter.

When the elapsed time after injecting the nickel formate aqueous solution into the circulation pipe 34 becomes the first set time, it is determined that the nickel metal present on the inner surface of the purification system pipe 18 has reached 50 μg / cm ² . The first set time is obtained by measuring in advance the time until the nickel metal on the surface of the carbon steel test piece reaches 50 μg / cm ² . In the period until the elapsed time from the injection of the nickel formate aqueous solution into the circulation pipe 34 reaches the first set time, the first film-forming aqueous solution 84 circulates in the closed loop, and nickel on the inner surface of the purification system pipe 18 Metal adhesion continues.

Iron (II) ion water is injected (step S6). When the elapsed time from the start of the injection of the nickel formate aqueous solution has reached the first set time (that is, when the nickel metal present on the inner surface of the purification system pipe 18 has reached 50 μg / cm ² ), iron (II) ion implantation The valve 49 of the device 45 is opened and the injection pump 47 is driven to inject the iron formate aqueous solution in the chemical solution tank 46 into the first film forming aqueous solution 84 flowing through the circulation pipe 34 through the injection pipe 48. The iron (II) ion concentration of the iron formate aqueous solution injected into the circulation pipe 34 is, for example, 200 ppm.

  An oxidizing agent is injected (step S7). The valve 59 of the oxidant injector 55 is opened and the injection pump 57 is driven to inject hydrogen peroxide in the chemical tank 56 into the first film-forming aqueous solution 84 flowing in the circulation pipe 34 through the injection pipe 58A. At this time, the valve 100 is closed.

  After the elapsed time from the start of the injection of the nickel formate aqueous solution reaches the first set time, the iron formate solution and the hydrogen peroxide are injected into the first film-forming aqueous solution 84 flowing in the circulation pipe 34, so that the circulation pipe 34 , Nickel ions, iron (II) ions, formic acid, hydrogen peroxide and hydrazine, and an aqueous solution having a pH of, for example, 7.0 and 90 ° C., that is, a second film-forming aqueous solution 86 (see FIG. 6) is generated. . Even after the elapsed time reaches the first set time, the injection of the nickel formate aqueous solution in step S4 and the injection of the hydrazine aqueous solution in step S5 are continued. In order to increase the pH of the second film forming aqueous solution 86 to 7.0, the rotational speed of the injection pump 42 of the reducing agent injection device 40 is increased, and the injection amount of the hydrazine aqueous solution from the chemical tank 41 to the circulation pipe 34 is increased. To do. Hydrazine contained in the hydrazine aqueous solution injected into the circulation pipe 34 after the injection of the iron formate aqueous solution into the circulation pipe 34 is started functions as a pH adjuster.

The second film-forming aqueous solution 86 having a pH of 7.0 and 90 ° C. is supplied from the circulation pipe 34 to the purification system pipe 18 by the driven circulation pump 32 and the nickel metal film 83 formed on the inner surface of the purification system pipe 18. Contact the surface (see FIG. 6). Then, the nickel film (Ni _0.7 Fe _2.3 O ₄ ) film 85 is formed on the surface of the nickel metal film 83 by the contact of the second film forming aqueous solution 86 with the surface of the nickel metal film 83 (see FIG. 6). ). In order to form the Ni _0.7 Fe _2.3 O ₄ film (first nickel ferrite film) 85 on the surface of the nickel metal film 83, the pH of the second film-forming aqueous solution measured by the pH meter 82A is adjusted by injecting the hydrazine aqueous solution. It is necessary to adjust to the range of 5.5 to 9.0. The temperature of the second film-forming liquid used for forming the Ni _0.7 Fe _2.3 O ₄ film 85 is adjusted to a range of 60 ° C. to 100 ° C..

Steps S4 to S7 are performed, and the second film-forming aqueous solution 86 having a pH of, for example, 7.0 and 90 ° C. is circulated through the closed loop including the circulation pipe 34 and the purification system pipe 18 to the surface of the nickel metal film 83. The formation of the Ni _0.7 Fe _2.3 O ₄ film 85 is continued. When the elapsed time since the injection of the iron formate aqueous solution into the circulation pipe 34 has reached the second set time, the thickness of the Ni _0.7 Fe _2.3 O ₄ film 85 covering the surface of the nickel metal film 83 becomes the set thickness. It determines with having reached, the infusion pumps 37, 42, 47, 52, and 57 are each stopped, and each of the valves 39, 44, 49, 54, and 59 is closed. Therefore, the nickel formate aqueous solution by the nickel ion implanter 35, the hydrazine aqueous solution by the reducing agent implanter 40, the iron formate aqueous solution by the iron (II) ion implanter 45, and the peroxide aqueous solution by the oxidant injector 55, respectively. Injection into the circulation pipe 34 is stopped. Thereby, the formation of the Ni _0.7 Fe _2.3 O ₄ film 85 on the surface of the nickel metal film 83 formed on the inner surface of the purification system pipe 18 is completed. The second set time is obtained by measuring in advance the time until the thickness of the Ni _0.7 Fe _2.3 O ₄ film 85 covering the surface of the nickel metal film 83 reaches the set thickness.

  The reducing agent (and pH adjusting agent) is decomposed (step S8). A part of the second film-forming aqueous solution 86 containing nickel ion, iron (II) ion, hydrogen peroxide and hydrazine boosted by the circulation pump 33 is opened by opening the valve 78 and closing part of the opening of the valve 77. The pipe 79 is led to the decomposition device 63. Further, the valve 100 is opened and the injection pump 57 is driven to supply the hydrogen peroxide in the chemical solution tank 56 to the decomposition device 63 through the supply pipe 101 and the pipe 79. Hydrazine, which is a reducing agent and a pH adjusting agent, contained in the second film forming aqueous solution 86 is decomposed into nitrogen and water by the action of the activated carbon catalyst and hydrogen peroxide in the decomposition device 63, and the second film forming aqueous solution 86. The formic acid contained in is also decomposed.

  The film-forming aqueous solution in which the reducing agent (and pH adjusting agent) is decomposed is purified (step S9). After the hydrazine (reducing agent and pH adjusting agent) is decomposed, the valve 77 is opened and the valve 78 is closed to stop the supply of the second film-forming aqueous solution containing no hydrazine to the decomposing device 63 and the valve 70 is opened. The valve 69 is closed, the valve 75 is opened, and a part of the opening degree of the valve 72 is closed. At this time, the valve 73 is closed and the circulation pumps 33 and 32 are driven. The second film-forming aqueous solution that does not contain hydrazine and is returned to the circulation pipe 34 from the purification system pipe 18 is cooled to 60 ° C. by the cooler 60. Furthermore, a 60 ° C. second film-forming aqueous solution containing no hydrazine is guided to the mixed bed resin tower 62, and nickel ions, iron (II) ions, other cations and anions remaining in the second film-forming aqueous solution are introduced. The ions are adsorbed and removed by the cation exchange resin and the anion exchange resin in the mixed bed resin tower 62 (first purification step). The 60 ° C. second film-forming aqueous solution not containing hydrazine is circulated through the circulation pipe 34 and the purification system pipe 18 until the above-described ions are substantially eliminated. The second film-forming aqueous solution in which each ion is substantially lost becomes substantially 60 ° C. water.

A platinum ion aqueous solution is injected (step S10). After the first purification step is completed, the valve 72 is opened to close the valve 75, and the valve 54 is opened to drive the infusion pump 52. The water flowing in the circulation pipe 34 is kept at 60 ° C. by heating by the heater 58. An aqueous solution (for example, sodium hexahydroxoplatinate sodium hydrate (Na ₂ [Pt (OH) ₆ ] · nH ₂ ) containing platinum ions in the chemical solution tank 51 through the injection pipe 53 into 60 ° C. water flowing in the circulation pipe 34. O) aqueous solution) is injected. The concentration of platinum ions in this aqueous solution to be injected is, for example, 1 ppm. Platinum is in an ionic state in an aqueous solution of sodium hexahydroxoplatinate sodium hydrate. An aqueous solution containing platinum ions at 60 ° C. is supplied from the circulation pipe 34 to the purification system pipe 18 by the drive of the circulation pumps 32 and 33, and is returned from the purification system pipe 18 to the circulation pipe 34. The aqueous solution containing platinum ions circulates in the closed loop including the circulation pipe 34 and the purification system pipe 18.

Immediately after the start of injection, platinum at the connection point of an aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O injected from the chemical tank 46 through the connection point of the circulation pipe 34 and the injection pipe 53 into the circulation pipe 34. The injection rate of the aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O into the circulation pipe 34 is calculated in advance so that the concentration becomes a set concentration, for example, 1 ppm. A predetermined amount of platinum is deposited on the Ni _0.7 Fe _2.3 O ₄ film formed on the surface of the nickel metal film covering the inner surface of the purification system pipe 18 with the platinum ion in flowing water at 60 ° C. being the set concentration. The amount of the aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O required to fill the chemical tank 51 is calculated, and the calculated aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O The amount of chemical tank 5 To fill in. Calculated _{Na 2 [Pt (OH) 6} ] · nH 2 the rotational speed of the infusion pump 52 is controlled in accordance with the injection rate of O solution to the circulation pipe 34 of the, _Na 2 in the chemical liquid tank 51 [Pt (OH ) ₆ ] · nH ₂ O aqueous solution is injected into the circulation pipe 34.

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

The aqueous hydrazine solution is injected into the circulation pipe 34 after the aqueous solution of Na ₂ [Pt (OH) ₆ ] .nH ₂ O at 60 ° C. reaches the connection point between the injection pipe 43 and the circulation pipe 34 where the hydrazine aqueous solution is injected. Is done. In this case, an aqueous solution containing platinum ions and hydrazine at 60 ° C. is supplied from the circulation pipe 34 to the purification system pipe 18. However, more preferably, the hydrazine aqueous solution is added to the circulation pipe immediately after the predetermined amount of Na ₂ [Pt (OH) ₆ ] · nH ₂ O filled in the chemical tank 51 is completely injected into the circulation pipe 34. 34 is preferably injected. In this case, a 60 ° C. aqueous solution containing platinum ions is supplied from the circulation pipe 34 to the purification system pipe 18, and after the injection of the platinum ion aqueous solution into the circulation pipe 34 is completed, the platinum ions and hydrazine are contained at 60 ° C. An aqueous solution 88 (see FIG. 7) is supplied from the circulation pipe 34 to the purification system pipe 18.

In the case of the injection of the former hydrazine aqueous solution, the reduction reaction to convert platinum ions into platinum by hydrazine first occurs in the aqueous solution containing hydrazine and platinum ions flowing in the circulation pipe 34, whereas the latter. In the case of injection of the hydrazine aqueous solution, platinum ions have already been adsorbed on the surface of the Ni _0.7 Fe _2.3 O ₄ film formed on the surface of the nickel metal film 83 covering the inner surface of the purification system pipe 18. Since the adsorbed platinum ions are reduced by hydrazine, the amount of platinum 87 adhering to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the surface of the nickel metal film 83 formed on the inner surface of the purification system pipe 18 is reduced. Further increase (see FIG. 7).

Immediately after the start of the injection of the hydrazine aqueous solution, the hydrazine concentration at the connection point of the hydrazine aqueous solution injected from the chemical solution tank 41 through the connection point of the circulation pipe 34 and the injection pipe 43 is set in advance so as to become a set concentration, for example, 100 ppm. Then, the injection rate of the hydrazine aqueous solution into the circulation pipe 34 is calculated, and the nickel metal film on the inner surface of the purification system pipe 18 is set by setting the hydrazine concentration of the aqueous solution containing platinum ions at 60 ° C. flowing through the circulation pipe 34 to the set concentration. The amount of the hydrazine aqueous solution filled in the chemical tank 41 necessary for reducing the platinum ions adsorbed on the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the surface of 83 to platinum 87 was calculated. The chemical tank 41 is filled with the amount of the hydrazine aqueous solution. The rotational speed of the injection pump 42 is controlled in accordance with the calculated injection speed of the hydrazine aqueous solution into the circulation pipe 34, and the hydrazine aqueous solution in the chemical liquid tank 41 is injected into the circulation pipe 34.

When the entire amount of the aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O (aqueous solution containing platinum ions) in the chemical tank 46 is injected into the circulation pipe 34, the driving of the injection pump 52 is stopped. Valve 54 is closed. Thereby, injection | pouring of the aqueous solution containing platinum ion to the circulation piping 34 is stopped. Further, when the entire amount of the hydrazine aqueous solution (reducing agent aqueous solution) in the chemical tank 41 is injected into the circulation pipe 34, the driving of the injection pump 42 is stopped and the valve 44 is closed. Thereby, injection | pouring of the hydrazine aqueous solution to the circulation piping 34 is stopped.

Since the platinum ions adsorbed on the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 are reduced by the injected hydrazine to become platinum 87, the Ni _0.7 Fe _2.3 O formed on the surface of the nickel metal film 83 on the inner surface of the purification system pipe 18. Platinum 87 adheres to the surface of the ₄ film 85 (see FIG. 7).

It is determined whether or not the adhesion of platinum is completed (step S12). When the elapsed time from the injection of the platinum ion aqueous solution and the reducing agent aqueous solution reaches a predetermined time, a predetermined amount to the surface of the Ni _0.7 Fe _2.3 O ₄ coating 85 formed on the surface of the nickel metal coating 83 on the inner surface of the purification system pipe 18 It is determined that the platinum deposition is complete. When the elapsed time does not reach the predetermined time, steps S10 to S12 are repeated.

The fact that a predetermined amount of platinum has adhered to the surface of the nickel metal film 80 formed on the inner surface of the purification system pipe 18 is described in Example 3 (FIGS. 10, 11, and 12) of Japanese Patent Application Laid-Open No. 2014-44190. As described above, the quartz vibrating electrode device is installed in the circulation pipe 34 on the upstream side of the circulation pump 33, and measurement is performed by the quartz vibrating electrode device. The quartz crystal vibrating electrode device has a quartz crystal mounted in a recess formed in the electrode holder, and a carbon steel metal member (same as the composition of the purification system pipe 18) is attached to the crystal surface on the open end side of the electrode holder. The surface of the crystal existing between the metal member and the electrode holder is covered with a seal member. Such an electrode holder is disposed in the circulation pipe 34, and the surface of the metal member is in contact with the first film forming aqueous solution 84 that flows in the circulation pipe 34. A nickel metal film 83 is formed on the surface of the metal member in contact with the first film forming aqueous solution 84. After it is determined that a predetermined amount (50 μg / cm ² ) of nickel metal has adhered to the inner surface of the purification system pipe 18 and the formation of the nickel metal film 83 has been completed, the second film forming aqueous solution 86 is transferred to the purification system pipe 18. It is supplied and returned to the circulation pipe 34, and comes into contact with the surface of the nickel metal film 83 formed on the surface of the metal member arranged in the circulation pipe 34. A Ni _0.7 Fe _2.3 O ₄ film 85 is formed on the surface of the nickel metal film 83 that contacts the second film forming aqueous solution 86 and covers the surface of the metal member.

After the thickness of the Ni _0.7 Fe _2.3 O ₄ film 85 reaches a predetermined thickness, a 60 ° C. aqueous solution 84 containing platinum ions and hydrazine is supplied to the purification system pipe 18 and returned to the circulation pipe 34, and the inside of the circulation pipe 34. In contact with the Ni _0.7 Fe _2.3 O ₄ coating 85 covering the surface of the metal member disposed on the surface. For this reason, platinum 87 adheres to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85. The crystal is vibrated by the application of voltage to the crystal, and the metal member on which the Ni _0.7 Fe _2.3 O ₄ film 85 or the like having platinum 87 adhered together with the crystal is also vibrated. The frequency of the quartz crystal including the metal member is measured by a frequency measuring device, and decreases by the amount of platinum 87 attached. Based on the frequency measured by the frequency measuring device, the difference in frequency before and after platinum 87 is deposited, that is, platinum deposited on the surface of the Ni _0.7 Fe _2.3 O ₄ film 85. A weight of 81 is required. When this weight reaches the set weight, it is determined that a predetermined amount of platinum 87 is attached to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 that covers the nickel metal film 83 formed on the inner surface of the purification system pipe 18.

Similarly, determination as to whether or not the formation of the nickel metal film 80 on the inner surface of the purification system pipe 18 is completed may be performed based on the frequency of the quartz crystal including the metal member measured by the frequency measuring device. Based on the measured frequency of the crystal, the inner surface of the purification system pipe 18 is the difference in frequency before and after the nickel metal film 83 is formed on the surface of the metal member. The weight of the nickel metal film 83 formed on the substrate is determined. When the weight of the nickel metal film 83 reaches the set weight, it is determined that the nickel metal contained in the nickel metal film 83 formed on the inner surface of the purification system pipe 18 has reached 50 μg / cm ² .

Further, the determination of whether the thickness of the Ni _0.7 Fe _2.3 O ₄ coating 85 formed on the surface of the nickel metal coating 83 has reached a predetermined thickness is also based on the frequency of the quartz crystal including the metal member measured by the frequency measuring device. You may go. Based on the measured vibration frequency of the crystal, the frequency before the Ni _0.7 Fe _2.3 O ₄ film 85 is formed on the surface of the nickel metal film 83 on the metal member and after the film 85 is formed. The difference is the weight of the Ni _0.7 Fe _2.3 O ₄ coating 85 formed on the inner surface of the purification system pipe 18. When the weight of the Ni _0.7 Fe _2.3 O ₄ film 85 reaches the set weight, it is determined that the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the inner surface of the purification system pipe 18 has a predetermined thickness.

The aqueous solution remaining in the purification system pipe and the circulation pipe is purified (step S13). After it is determined that the adhesion of platinum 87 to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the surface of the nickel metal film 83 on the inner surface of the purification system pipe 18 is completed, the valve 75 is opened to open the valve 72. A 60 ° C. aqueous solution containing platinum ions and hydrazine and pressurized by the circulation pump 33 is supplied to the mixed bed resin tower 62. Platinum ions, other metal cations (for example, sodium ions), hydrazine and OH groups contained in the aqueous solution are adsorbed by the ion exchange resin in the mixed bed resin tower 62 and removed from the aqueous solution (second purification). Process).

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

  Thus, the method for attaching the noble metal to the carbon steel member of the nuclear power plant according to this embodiment is completed. And the membrane | film | coat formation apparatus 30 connected to the purification system piping 18 is removed from the purification system piping 18, and the purification system piping 18 is restored.

In this embodiment, formation of the nickel metal film 83 covering the inner surface of the purifying system pipe 18, formed of Ni _0.7 Fe _2.3 O ₄ film 85 to the surface of the nickel metal film 83, and Ni _0.7 Fe _2.3 the surface of the O ₄ coating 85 The noble metal (for example, platinum 87) can be attached to the BWR plant 1 during the operation stop period of the BWR plant 1 before starting the BWR plant 1 in the next operation cycle.

In this embodiment, the Ni _0.7 Fe _2.3 O ₄ film (first nickel ferrite film) 85 formed on the inner surface of the purification system pipe 18 that is a carbon steel member and covers the inner surface is 60 ° C. to 100 ° C. A nickel ferrite film formed in a temperature range, in which reactor water (cooling water) in the reactor 2 is in contact with the Ni _0.7 Fe _2.3 O ₄ film 85 as described in Examples 2 and 3. This is a nickel ferrite film that elutes into the reactor water by the action of the noble metal adhering to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 (see, for example, FIG. 17).

According to the present embodiment, the first film-forming aqueous solution containing nickel ions and a reducing agent (for example, hydrazine) is brought into contact with the inner surface of the purification system pipe 18, and the inner surface of the purification system pipe 18 in contact with the reactor water is A nickel metal film 83 covering the inner surface can be formed. Further, a second film-forming aqueous solution containing nickel ions, iron (II) ions, hydrogen peroxide and a pH adjuster (for example, hydrazine) is brought into contact with the surface of the nickel metal film 83 on the inner surface of the purification system pipe 18, and this surface is contacted. A covering Ni _0.7 Fe _2.3 O ₄ film 85 can be formed. These nickel metal film 83 and Ni _0.7 Fe _2.3 O ₄ film 85 can prevent elution of Fe ²⁺ from the purification system pipe 18 to the aqueous solution containing platinum ions flowing in the purification system pipe 18. The adhesion of the noble metal (for example, platinum) to the inner surface of the system pipe 18 is not hindered by the elution of Fe ²⁺ , and the adhesion of the noble metal to the inner surface (specifically, nickel metal on the inner surface of the purification system pipe 18) It is possible to shorten the time required for the noble metal adhesion) to the surface of the Ni _0.7 Fe _2.3 O ₄ coating 85 formed on the surface of the coating 83. Further, the noble metal can be efficiently attached to the inner surface of the purification system pipe 18, and the amount of the noble metal attached to the inner surface of the purification system pipe 18 is increased.

In this embodiment, the nickel metal film 83 formed on the inner surface of the purification system pipe 18 contains 50 μg / cm ² of nickel metal. Thus, when 50 μg / cm ² of nickel metal is present, at least the nickel metal film 83 covers the entire inner surface of the purification system pipe 18 that is in contact with the first film forming aqueous solution, and in the next operation cycle. After the start of the BWR plant 1, the nickel metal film 83 prevents the reactor water flowing in the purification system pipe 18 from coming into contact with the base material of the purification system pipe 18. For this reason, the radionuclide contained in the reactor water is not taken into the base material of the purification system pipe 18.

  The nickel metal film 83 formed on the inner surface of the purification system pipe 18 not only shortens the time required for the platinum to adhere to the purification system pipe 18 but also attaches platinum as described in Examples 2 and 3 below. In combination with the decrease in the corrosion potential of the purification system pipe 18 and the nickel metal film 83 due to 87, it is possible to form a stable nickel ferrite film that does not elute into the reactor water due to the adhered platinum on the inner surface of the purification system pipe 18 To contribute.

  The nickel metal film 83 is formed on the inner surface of the purification system pipe 18 by replacing the nickel ions contained in the first film formation aqueous solution with the iron ions contained in the purification system pipe 18 and being taken into the inner surface of the purification system pipe 18. Nickel ions taken into the inner surface are reduced to nickel metal by hydrazine (reducing agent) contained in the first film-forming aqueous solution. Thus, the nickel metal produced by the action of the reducing agent from the nickel ions taken into the purification system pipe 18 by the substitution reaction has very strong adhesion to the base material of the purification system pipe 18. For this reason, the formed nickel metal film 83 is not peeled off from the purification system pipe 18.

  In this embodiment, after reducing and decontaminating the inner surface of the purification system pipe 18, the nickel metal film 83 is formed on the inner surface of the purification system pipe 18, so that the oxidation containing the radionuclide formed on the inner surface of the purification system pipe 18 is performed. The nickel metal film is not formed on the film, the radiation emitted from the purification system pipe 18 is reduced, and the surface dose rate of the purification system pipe 18 is significantly reduced.

  During reductive decontamination of the inner surface of the purification system pipe 18 using an oxalic acid aqueous solution and decomposition of oxalic acid, iron (II) oxalate formed on the inner surface of the purification system pipe 18 that is a carbon steel member is It is removed by the action of an oxidizing agent (for example, hydrogen peroxide) injected into the acid aqueous solution. By removing the iron (II) oxalate, the adhesion between the purification system pipe 18 and the nickel metal film 83 is improved, and the nickel metal film 83 can be prevented from peeling off from the inner surface of the purification system pipe 18.

  A method for suppressing the attachment of radionuclide 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. 11 and 12. The method for suppressing the attachment of radionuclide to the carbon steel member of this embodiment is applied to the purification system piping of the BWR plant.

  In the method for suppressing the attachment of radionuclide to the carbon steel member of the present embodiment, each of the steps S1 to S14 and the new steps S15 to S18 in the method for attaching the noble metal to the carbon steel member of the nuclear power plant of the first embodiment. Each step is performed. In the method for suppressing the attachment of radionuclide to the carbon steel member of the present embodiment, the film forming apparatus 30 used in the first embodiment is used in each step of Steps S1 to S14, and a new heating system 92 is used in Steps S16 and S16. Used in each step of S17.

  The configuration of the heating system 92 will be described with reference to FIG. The heating system 92 has a pressure resistant structure and includes a circulation pipe 93, a circulation pump 94, a heater (heating device) 95, and a valve 96 that is a pressure increasing device. A circulation pump 94 is provided in the circulation pipe 93, and a heater 95 is provided in the circulation pipe 93 upstream of the circulation pump 94. The heater 95 may be disposed downstream of the circulation pump 94. The pipe 97 bypasses the circulation pump 94, one end of the pipe 97 is connected to the circulation pipe 93 upstream of the circulation pump 94, and the other end of the pipe 97 is connected to the circulation pipe 93 downstream of the circulation pump 94. Connected. A valve 96 is provided in the pipe 97. An on-off valve 98 is provided at the upstream end of the circulation pipe 93, and an on-off valve 99 is provided at the downstream end of the circulation pipe.

  The film forming apparatus is removed from the piping system (step S15). In the method for suppressing the attachment of radionuclide to the carbon steel member of the present embodiment, after each of the steps S1 to S14 is performed, the film forming apparatus 30 connected to the purification system pipe 18 is removed from the purification system pipe 18. It is. One end of the circulation pipe 34 of the film forming apparatus 30 is removed from the flange of the valve 23, and the other end of the circulation pipe 34 is removed from the flange of the valve 25.

  The heating system is connected to the piping system (step S16). One end of the circulation pipe 93 (third pipe) of the circulation pipe 93 of the heating system 92 on the on-off valve 99 side is connected to the flange of the valve 23, and one end of the circulation pipe 93 is upstream of the purification system pump 19. Connected to the pipe 18. The other end of the circulation pipe 93 on the on-off valve 98 side is connected to the flange of the valve 25, and the other end of the circulation pipe 93 is connected to the purification system pipe 18 between the regenerative heat exchanger 20 and the non-regenerative heat exchanger 21. Is done. Both ends of the circulation pipe 93 are connected to the purification system pipe 18 to form a closed loop including the purification system pipe 18 and the circulation pipe 93.

Water containing oxygen at 200 ° C. or higher is brought into contact with the Ni _0.7 Fe _2.3 O ₄ film to which platinum is attached (step S17). Water containing oxygen which is an oxidant is filled in a closed loop including the circulation pipe 93 and the purification system pipe 18. Instead of water containing oxygen, water containing hydrogen peroxide as an oxidizing agent or water containing oxygen and hydrogen peroxide may be used. The circulation pump 94 is driven to circulate oxygen-containing water in the closed loop. The rotational speed of the circulation pump 94 is increased to a certain rotational speed, and then the valve 96 is gradually closed while the opening degree is decreased to increase the pressure of water containing oxygen discharged from the circulation pump 94. Water containing oxygen circulating in the closed loop is heated by the heater 95, and the temperature of the water is raised. In this way, the temperature of the water is raised while increasing the pressure of the water discharged from the circulation pump 94. After the valve 96 is fully closed, the rotational speed of the circulation pump 94 is further increased. By such an operation, the pressure of the water circulating in the closed loop rises to 1.6 MPa, for example, and the temperature of the water rises to about 201 ° C. The pressure and temperature of the water circulating in the closed loop is maintained at each of the above values. Note that when the pressure of water circulating in the closed loop is increased to 6 MPa, the temperature of the water can be increased to about 276 ° C. by the heater 95.

Water 89 to about 201 ° C. containing oxygen is supplied to the purifying system piping 18 from the circulation pipe 93, formed on the surface of the nickel metal film 83 covering the inner surface of the cleaning system piping 18, Ni _0.7 Fe platinum 87 is attached _2.3 Contact the O ₄ film 85 (see FIG. 13). 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 93 are connected. When the water 89 of about 201 ° C. comes into contact with the Ni _0.7 Fe _2.3 O ₄ film 85, the purification system pipe 18 and the nickel metal film 83 are heated, and the respective temperatures become about 201 ° C.

Since each of the water 89 containing oxygen, the purification system pipe 18, the nickel metal film 83, and the Ni _0.7 Fe _2.3 O ₄ film 85 reaches about 201 ° C. of 200 ° C. or higher, oxygen that is an oxidizing agent contained in the water 89 (O ₂ ) and oxygen constituting a part of water molecules contained in the water 89 at about 201 ° C. migrate into the nickel metal film 83 through the Ni _0.7 Fe _2.3 O ₄ film 85 and are contained in the purification system pipe 18. Fe becomes Fe ²⁺ and moves into the nickel metal film 83 (see FIG. 15). Oxygen constituting a part of water molecules contained in the water 89 easily moves alone in the water 89 at 200 ° C. or higher, and easily enters the Ni _0.7 Fe _2.3 O ₄ film 85. Due to the action of platinum 87 adhering to the nickel metal film 83, the corrosion potential of the purification system pipe 18, the nickel metal film 83 and the Ni _0.7 Fe _2.3 O ₄ film 85 is lowered. Oxygen in which nickel in the nickel metal film 83 has migrated into the nickel metal film 83 due to a decrease in the corrosion potential of the nickel metal film 83 and the formation of a high temperature environment of about 201 ° C. reacts with part of the oxygen constituting the water molecule) and Fe ^2+, and nickel ferrite x is 0 in _{Ni 1-x Fe 2 + x} O 4 (NiFe 2 O 4) is generated. For this reason, the nickel metal film 83 formed on the inner surface of the purification system pipe 18 is converted into the nickel ferrite film 91, and the nickel ferrite film (second nickel ferrite film) 91 covers the inner surface of the purification system pipe 18. (See FIG. 16). The nickel ferrite film 91 covers the entire inner surface of the purification system pipe 18 covered by the nickel metal film 83. Platinum 87 adheres to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the surface of the nickel ferrite film 91. Nickel ferrite in which x is 0 in the produced Ni _1-x Fe _{2 + x} O ₄ is formed in a high temperature environment of about 201 ° C., and thus has a larger crystal than Ni _0.7 Fe _2.3 O ₄ . .

The heating system is removed from the piping system (step S17). After a nickel ferrite film 91 with x being 0 in Ni _1-x Fe _{2 + x} O ₄ is formed to cover the inner surface of the purification system pipe 18, the heating system 92 connected to the purification system pipe 18 is purified. It is removed from the system pipe 18. One end of the circulation pipe 93 of the heating system 92 is removed from the flange of the valve 23, and the other end of the circulation pipe 93 is removed from the flange of the valve 25. Thereafter, the purification system pipe 18 is restored.

Then, after the fuel exchange is completed and the maintenance inspection of the BWR plant 1 is completed, a Ni _0.7 Fe _2.3 O ₄ film 85 with platinum 87 attached is formed on the surface in order to start operation in the next operation cycle. The BWR plant 1 having the purification system pipe 18 having the nickel ferrite film 91 formed on the inner surface is started. The reactor water flowing in the purification system pipe 18 is not directly in contact with the base material of the purification system pipe 18 because the nickel ferrite film 91 is formed.

  In the present embodiment, each effect produced in the first embodiment can be obtained.

Further, in the state in the present embodiment, each of the corrosion potential of Ni _0.7 Fe _2.3 O ₄ purifying system pipe 18 of platinum 87 attached to the film 85, the nickel metal film 83 and Ni _0.7 Fe _2.3 O ₄ film 85 is lowered, Further, in a high temperature environment of about 201 ° C. that is 200 ° C. or higher, as described above, the nickel ferrite film 91 in which Ni is 0 in Ni _1-x Fe _{2 + x} O ₄ produced from the nickel metal film 83. Is a stable nickel ferrite film that does not elute into the reactor water due to the action of the attached platinum 87 even in contact with the reactor water (for example, during operation of the BWR plant 1). Thus, in the present embodiment, a stable nickel ferrite film 91 that does not elute into the reactor water by the action of platinum 87 even during operation of the BWR plant 1 can be generated on the inner surface of the purification system pipe 18. The stable nickel ferrite film 91 that does not elute into the reactor water due to the action of the adhered platinum 87 is a purification system pipe over a longer period than the Ni _0.7 Fe _2.3 O ₄ film produced in a low temperature range of 60 ° C. to 100 ° C. The attachment of the radionuclide to 18 can be suppressed. Specifically, the stable nickel ferrite film 91 formed on the inner surface of the purification system pipe 18 is supplied to the purification system pipe 18 over a plurality of operation cycles, for example, five operation cycles (for example, five years). Attachment of radionuclides can be suppressed. For this reason, the frequency | count of the chemical decontamination implemented with respect to the purification system piping 18 can be decreased.

In During operation BWR plant 1, by the action of the Ni _0.7 Fe _2.3 O ₄ Pt 87 adhering to the surface of the coating 85, the surface of the Ni _0.7 Fe _2.3 O ₄ film 85, the reactor water 90 flowing in the purifying system piping 18 Ni _0.7 Fe _2.3 O ₄ contained in the Ni _0.7 Fe _2.3 O ₄ film 85 at the portion of contact being eluted in the reactor water 90. Therefore, of Ni _0.7 Fe _2.3 O ₄ film 85, while leaving the Ni _0.7 Fe _2.3 O ₄ 85A which is present between the platinum 87 and nickel ferrite film 91 deposited from Ni _0.7 Fe _2.3 O ₄ film 85 Ni _0.7 Fe _2.3 O ₄ elutes and eventually the reactor water 90 comes into contact with the surface of the nickel ferrite film 91 during the operation of the BWR plant 1 (see FIG. 17). Even in such a state, since the nickel ferrite film 91 covers the inner surface of the purification system pipe 18, contact between the inner surface of the purification system pipe 18 and the reactor water 90 can be prevented, and the radionuclide contained in the reactor water 90. However, it is not taken into the base material of the purification system pipe 18.

Ni _0.7 Fe _2.3 O ₄ 85 A remaining between the adhered platinum 87 and the nickel ferrite film 91 reacts with nickel, Fe ²⁺ transferred from the purification system pipe 18, and oxygen and nickel transferred from the reactor water 90. In addition, nickel ferrite (NiFe ₂ O ₄ ) that does not dissolve in the reactor water 90 due to the action of the attached platinum 87 (noble metal), that is, the platinum 87 contained in the nickel ferrite film 91 also enters the reactor water 90. It changes to nickel ferrite that does not elute. This nickel ferrite is a film produced in a reducing environment, has resistance to reduction, and does not elute into the reactor water 90. The reactor water 90 contains nickel.

  As described above, since the adhesion between the nickel metal film 83 and the base material of the purification system pipe 18 is very strong, the adhesion between the nickel ferrite film 91 generated in this embodiment and the base material of the purification system pipe 18 is very strong. Will also be very strong. The nickel ferrite film 91 is also not peeled off from the purification system pipe 18.

In this example, the formation of the nickel metal film 83 on the inner surface of the purification system pipe 18 and the adhesion of platinum 87 to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the surface of the nickel metal film 83 are: Since the operation of the BWR plant 1 is stopped after the operation of the BWR plant 1 is stopped and the BWR plant 1 is not restarted. Further, the conversion of the nickel metal film 83 into the nickel ferrite film 91 is also performed while the operation of the BWR plant 1 is stopped. As in Example 3 to be described later, elution of nickel contained in the nickel metal film 83 into the reactor water does not occur when the BWR plant 1 is started up, and the reactor output becomes 100% output by the nickel ferrite film 91. Of the radionuclide to the purification system pipe 18 at the start-up of the BRW plant 1 can be suppressed.

  When platinum is directly attached to the inner surface of the purification system pipe 18, in order to suppress the occurrence of stress corrosion cracking in a stainless steel component (for example, the recirculation system pipe 6), during operation of the BWR plant Even if hydrogen injection is injected into the reactor water in the RPV 3, when the reactor water containing hydrogen flows into the purification system pipe 18 and contacts the inner surface of the carbon steel purification system pipe 18, the inner surface of the purification system pipe 18 The corrosion potential of the purification system pipe 18 increases due to the action of platinum adhering to the surface. For this reason, an oxide film is formed on the inner surface of the purification system pipe 18, and the radionuclide contained in the reactor water is taken into this oxide film. The radionuclide increases the surface dose rate of the purification system pipe 18.

In contrast, in the present embodiment, a stable nickel ferrite film 91 that does not eluted by the action of the platinum covers the inner surface of the cleaning system piping 18, platinum 87, Ni _0.7 formed on the surface of the nickel ferrite film 91 Since it adheres to the surface of the Fe _2.3 O ₄ film 85 (or the tip of Ni _0.7 Fe _2.3 O ₄ 85A remaining on the surface of the nickel ferrite film 91), even during operation of the BWR plant 1, the platinum 87 By the action, the corrosion potential of the purification system pipe 18 and the nickel ferrite film 91 is lowered, and the radionuclide is not taken into the purification system pipe 18 and the nickel ferrite film 91. Even when hydrogen is injected into the reactor water during the operation of the BWR plant 1, the corrosion potential of the purification system pipe 18 and the nickel ferrite film 91 is lowered, and no radionuclide is taken into them.

  A method for suppressing the attachment of radionuclide to the carbon steel member of the nuclear power plant of Example 3 which is another preferred embodiment of the present invention will be described below with reference to FIG. The method for suppressing the attachment of radionuclide to the carbon steel member of this embodiment is applied to the purification system piping of the BWR plant.

  In the method for suppressing the attachment of radionuclide to the carbon steel member of the present embodiment, the steps S1 to S14 and the new steps S15, S19 in the method for attaching a noble metal to the carbon steel member of the nuclear power plant of the first embodiment Each process of S20 is implemented. In the method for suppressing the attachment of radionuclide to the carbon steel member of this example, the film forming apparatus 30 used in Example 1 is used in each step of Steps S1 to S14. Furthermore, the method for suppressing the attachment of radionuclide to the carbon steel member of the present embodiment is the same as the steps for steps S16 to S18 in steps S16 to S18 in the method for suppressing the attachment of radionuclide to the carbon steel member of Example 2. This is a different method.

  The film forming apparatus is removed from the piping system (step S15). After the steps S1 to S14 are performed, the film forming apparatus 30 connected to the purification system pipe 18 is removed from the purification system pipe 18 as in the second embodiment. Then, the purification system pipe 18 is restored.

The nuclear power plant is activated (step S19). Nickel metal whose surface is covered with a Ni _0.7 Fe _2.3 O ₄ film 85 with platinum 87 attached in order to start operation in the next operation cycle after refueling is completed and maintenance inspection of the BWR plant 1 is completed. The BWR plant 1 having the purification system pipe 18 forming the film 83 on the inner surface is started.

Reactor water at 200 ° C. or higher is brought into contact with a nickel ferrite film (Ni _0.7 Fe _2.3 O ₄ film) to which platinum is attached (step S19). When the BWR plant 1 is started, the reactor water present in the downcomer in the RPV 3 is supplied to the reactor core 4 through the recirculation system pipe 6 and the jet pump 5 as described above. The reactor water discharged from the core is returned to the downcomer. A control rod (not shown) is pulled out from the core 4 to change the core 4 from a subcritical state to a critical state, and the reactor water in the core 4 is heated by heat generated by nuclear fission of nuclear fuel material in the fuel rod. Steam is not generated in the core 4. Further, the control rod is pulled out from the core 4, and the pressure in the RPV 3 is raised to the rated pressure in the temperature raising / pressurizing step of the reactor 2, and the reactor water is heated by the heat generated by the nuclear fission, so that the reactor water in the RPV 3 The temperature is raised to the rated temperature (280 ° C.). After the pressure in the RPV 3 becomes the rated pressure and the reactor water temperature rises to the rated temperature, the reactor power is rated by pulling out more control rods from the reactor core 4 and increasing the flow rate of reactor water supplied to the reactor core 4. Increased to output (100% output). The rated operation of the BWR plant 1 while maintaining the rated output is continued until the end of the operation cycle. When the reactor power rises to, for example, 10% power, steam generated in the core 4 is supplied to the turbine 9 through the main steam pipe 8, and power generation is started.

The reactor water 90 contains oxygen and hydrogen peroxide. Oxygen and hydrogen peroxide are generated by radiolysis of the reactor water 90 in the RPV 3. Reactor water 90 in the RPV 3 is led from the recirculation system pipe 6 into the purification system pipe 18 and contacts the Ni _0.7 Fe _2.3 O ₄ film 85 formed on the inner surface of the purification system pipe 18 with platinum 87 attached thereto. (See FIG. 14). In the temperature raising / pressurizing step of the nuclear reactor 2, the temperature of the reactor water 90 in contact with the nickel metal film 83 rises due to the heating of the reactor water by the heat generated by the nuclear fission described above, and eventually reaches 200 ° C. or higher. Rise to ℃. When the temperature of the reactor water 90 becomes 200 ° C. or higher, the temperature of each of the purification system pipes 18 surrounded by the nickel metal film 83 and the heat insulating material also becomes 200 ° C. or higher. As a result, oxygen which is an oxidant contained in the reactor water 90 and oxygen constituting a part of water molecules contained in the reactor water 90 at 200 ° C. or higher enter the nickel metal coating 83 through the Ni _0.7 Fe _2.3 O ₄ coating 85. Then, Fe contained in the purification system pipe 18 becomes Fe ²⁺ and moves into the nickel metal film 83 (see FIG. 15). Oxygen constituting a part of water molecules contained in the reactor water 90 also easily moves alone in the reactor water 90 at 200 ° C. or higher, and easily enters the Ni _0.7 Fe _2.3 O ₄ film 85. The corrosion potential of the purification system pipe 18 and the nickel metal film 83 is lowered by the action of platinum 87 attached to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85. As in Example 2, the oxygen in the nickel metal film 83 migrated to the reactor water 90 due to the decrease in the corrosion potential of the purification system pipe 18 and the nickel metal film 83 and the formation of a high temperature environment of about 200 ° C. or higher. Nickel ferrite (NiFe ₂ O) in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ which reacts with the oxidant contained therein and oxygen that constitutes a part of water molecules of the reactor water 90) and Fe ^2+. ₄ ) is generated.

  For this reason, the nickel metal film 83 formed on the inner surface of the purification system pipe 18 is converted into a nickel ferrite film 91, and the nickel ferrite film 91 covers the inner surface of the purification system pipe 18 (see FIG. 16). The nickel ferrite film 91 covers the entire inner surface of the purification system pipe 18 covered by the nickel metal film 83. Platinum 87 is adhered on the nickel ferrite film 91.

  In the present embodiment, each effect produced in the second embodiment can be obtained. Further, in the present embodiment, as in the second embodiment, the heating system 92 is connected to the purification system pipe 18 after the film forming apparatus 30 is removed from the purification system pipe 18, and the nickel ferrite film 91 is the purification system pipe. There is no need to remove the heating system 92 from the purification system pipe 18 after it has been formed on the inner surface. After removing the film forming apparatus 30 from the purification system pipe 18, the nickel metal film 83 formed on the inner surface of the purification system pipe 18 can be changed to the nickel ferrite film 91 simply by starting the BWR plant 1. For this reason, the time required for the formation of a stable nickel ferrite film 91 that does not elute into the reactor water 90 due to the attached platinum on the inner surface of the purification system pipe 18 is connected to the purification system pipe 18 of the heating system 92 and heated. Since each operation of removing the system 92 from the purification system pipe 18 is not performed, the operation can be shortened compared to the second embodiment.

In this example, the formation of the nickel metal film 83 on the inner surface of the purification system pipe 18 and the adhesion of the platinum 87 to the Ni _0.7 Fe _2.3 O ₄ film 85 covering the nickel metal film 83 are the same as in Example 2. Unlike the second embodiment, the conversion of the nickel metal film 83 into the nickel ferrite film 91 is performed when the BWR plant 1 is started up. For this reason, when the temperature of the reactor water is less than 200 ° C., the nickel metal film 83 is not changed to the nickel ferrite film 91, and the inner surface of the purification system pipe 18 has a Ni _0.7 Fe _2.3 O ₄ film 85 to which platinum 87 is attached. Is covered with a nickel metal film 83 formed on the surface (see FIG. 14). Even in this state, the corrosion potential of the Ni _0.7 Fe _2.3 O ₄ coating 85 in contact with the reactor water 90, and the purification system pipe 18 and the nickel metal coating 83 is lowered by the action of the platinum 87, and Ni _0.7 Incorporation of radionuclides into the Fe _2.3 O ₄ film 85, the nickel metal film 83, and the purification system pipe 18 does not occur. Thus, the attachment of the radionuclide to the purification system pipe 18 is suppressed.

During the operation of the BWR plant 1, as described in Example 2, among the Ni _0.7 Fe _2.3 O ₄ film 85, Ni _0.7 Fe _2.3 O ₄ 85 A existing between the deposited platinum 87 and the nickel ferrite film 91 is replaced with Ni _0.7 Fe _2.3 O ₄ 85 A. In a state of being left, Ni _0.7 Fe _2.3 O ₄ is eluted from the Ni _0.7 Fe _2.3 O ₄ film 85, and eventually the reactor water 90 comes into contact with the surface of the nickel ferrite film 91 during the operation of the BWR plant 1 (FIG. 17). reference). Even in such a state, since the nickel ferrite film 91 covers the inner surface of the purification system pipe 18, it is possible to prevent the radionuclide contained in the reactor water 90 from being taken into the base material of the purification system pipe 18. The Ni _0.7 Fe _2.3 O ₄ 85A remaining between the adhered platinum 87 and the nickel ferrite film 91 is the platinum contained in the nickel ferrite film 91 during the operation of the BWR plant 1 as in the second embodiment. The action of 87 also changes to nickel ferrite (NiFe ₂ O ₄ ) that does not elute into the reactor water 90.

  If the reactor water 90 comes into contact with the nickel metal film 83, the nickel contained in the nickel metal film 83 elutes into the reactor water 90 although it is a trace amount. The period during which the reactor water 90 is in contact with the nickel metal film 83 becomes long. For example, the nickel metal film 83 may disappear over a period of one operating cycle. However, in the present embodiment, when the temperature of the reactor water 90 becomes 200 ° C. or higher in the temperature raising / pressurizing step at the start of the BWR plant 1, the nickel metal film 83 is changed to the nickel ferrite film 91 as described above. During almost the most part of the cycle, the stable nickel ferrite film 91 that does not elute due to the action of platinum 87 covers the inner surface of the purification system pipe 18. The adhesion of the radionuclide to the purification system pipe 18 is suppressed. The period when the temperature of the reactor water 90 where the nickel metal film 83 covers the inner surface of the purification system pipe 18 is less than 200 ° C. is an extremely short period in one operation cycle period. For this reason, the amount of nickel eluted from the nickel metal film 83 into the reactor water 90 is very small, and the thickness of the nickel metal film 83 hardly changes until the nickel metal film 83 changes to the nickel ferrite film 91.

In each of the embodiments described above, hydrazine, which is the same substance, is used as the reducing agent and the pH adjusting agent, but different substances may be used as the reducing agent and the pH adjusting agent. In this case, in addition to the reducing agent injection device 40 connected to the circulation pipe 34, it is connected to the circulation pipe 34 as described in Example 5 (see FIG. 15) of JP-A-2015-158486. It is necessary to provide a pH adjusting agent injection device. This pH adjusting agent injection device has a chemical tank, an injection pump, a valve and an injection pipe, and this chemical tank is connected to the circulation pipe 34 by an injection pipe having an injection pump and a valve. The chemical tank 56 of the reducing agent injection device 40 is filled with, for example, a carbohydrazide aqueous solution that is a reducing agent, and the carbohydrazide aqueous solution is injected into the circulation pipe 34 in each step of steps S5 and S11. In the pH adjuster injection device, the chemical tank is filled with a hydrazine aqueous solution that is a pH adjuster, and the hydrazine aqueous solution is injected into the circulation pipe 34 in step S7. When a substance different from the reducing agent is used as the pH adjusting agent, after forming the nickel metal film 83 on the inner surface of the purification system pipe 18, the injection of the reducing agent (eg, carbohydrazide) in step S5 is stopped, Between S6 and Step S7 (between Step S7 and Step S8), hydrazine as a pH adjusting agent is injected into the circulation pipe 34 from the pH adjusting agent injection device, and iron (II) ions, hydrogen peroxide, formic acid, A second film-forming aqueous solution containing carbohydrazide and hydrazine having a pH of, for example, 7 and 90 ° C. is generated, and this second film-forming aqueous solution is supplied from the circulation pipe 34 into the purification system pipe 18. As a result, a Ni _0.7 Fe _2.3 O ₄ film 85 is formed on the surface of the nickel metal film 83. In step S <b> 8, oxalic acid, formic acid, carbohydrazide, and hydrazine are decomposed by the decomposition device 63. In addition to hydrazine, any of formhydrazine, hydrazinecarboxamide, and carbohydrazide may be used as the pH adjuster.

  In Examples 2 and 3, the nickel ferrite film 91 formed on the inner surface of the purification system pipe 18 prevents the radionuclide from adhering to the inner surface of the purification system pipe 18, but the operation of the BWR plant 1 in a plurality of operation cycles. As a result, the radionuclide adheres to and accumulates on the inner surface of the purification system pipe 18 in each operation cycle although it is a very small amount. For this reason, for example, after the operation of the BWR plant 1 over five operation cycles (5 years) is completed, the film forming apparatus 30 is connected to the purification system piping 18 of the BWR plant 1 during the operation stop period of the BWR plant 1 ( Step S1), reductive decontamination is performed on the purification system pipe 18, and the nickel ferrite film 91 to which the radionuclide is attached is removed (step S2).

Further, steps S3 to S15, S18 and S19 in the radionuclide adhesion suppression method of Example 3 are performed on the purification system pipe 18 from which the nickel ferrite film 91 has been removed by reductive decontamination. The As a result, a nickel ferrite film 91 is formed on the inner surface of the purification system pipe 18, and platinum is attached to the surface of the Ni _0.7 Fe _2.3 O ₄ film 85 covering the surface of the nickel ferrite film 91. With the nickel ferrite film 91 formed, the BWR plant 1 is operated without performing reduction decontamination, for example, over the following five operation cycles. In addition, you may implement each process of step S3-S18 in the adhesion control method of the radionuclide of Example 2 with respect to the purification system piping 18 by which reductive decontamination was implemented and the nickel ferrite membrane | film | coat 91 was removed.

  Each of Examples 1 to 3 can be applied to a carbon steel member that comes into contact with the reactor water of a pressurized water nuclear plant and a Canadian heavy water cooled pressure tube nuclear plant.

DESCRIPTION OF SYMBOLS 1 ... Boiling water type nuclear power plant, 2 ... Reactor pressure vessel, 4 ... Reactor core, 6 ... Recirculation system piping, 9 ... Turbine, 11 ... Supply water piping, 18 ... Purification system piping, 30 ... Film formation apparatus, 31 ... Surge Tank, 32, 33, 94 ... circulation pump, 34, 93 ... circulation piping, 35 ... nickel ion implanter, 36, 41, 46, 51, 56 ... chemical tank, 37, 42, 47, 52, 57 ... injection pump 40 ... reducing agent injection device, 45 ... iron (II) ion implantation device, 50 ... platinum ion implantation device, 55 ... oxidant injection device, 58, 95 ... heater, 60 ... cooler, 61 ... cation exchange resin tower , 62 ... mixed bed resin column, 63 ... cracker, 83 ... nickel metal _{film, 85 ... Ni 0.7 Fe 2.3 O} 4 film, 87 ... platinum, 91 ... nickel ferrite film, 92 ... heating system.

Claims (16)

  A nickel metal film is formed on a surface of a carbon steel member of a nuclear power plant in contact with cooling water, the surface is covered with the nickel metal film, and the surface of the nickel metal film is first in a temperature range of 60 ° C. to 100 ° C. A nickel ferrite film is formed, and a noble metal is attached to the surface of the first nickel ferrite film formed in the temperature range. The formation of the nickel metal film and the adhesion of the noble metal are performed after the nuclear power plant is shut down. A method for adhering a noble metal to a carbon steel member of a nuclear power plant, which is performed before starting the nuclear power plant. ^2. The method for attaching a noble metal to a carbon steel member of a nuclear power plant according to claim 1, wherein nickel metal contained in the nickel metal film is present on the surface at a rate of 50 μg / cm ² .   The formation of the nickel metal film is performed by bringing a first film forming aqueous solution containing nickel ions and a reducing agent into contact with the surface of the carbon steel member, and the adhesion of the noble metal is an aqueous solution containing noble metal ions and a reducing agent. The method for adhering a noble metal to a carbon steel member of a nuclear power plant according to claim 1 or 2, wherein the method is carried out by contacting a surface of the formed nickel metal film.   The method for adhering a noble metal to a carbon steel member of a nuclear power plant according to claim 3, wherein the pH of the first film-forming aqueous solution is in the range of 4.0 to 11.0.   The first nickel ferrite film is formed by applying a second film-forming aqueous solution in the range of 60 ° C. to 100 ° C. containing iron (II) ions, nickel ions, an oxidizing agent and a pH adjuster on the surface of the nickel metal film. The method for adhering a noble metal to a carbon steel member of a nuclear power plant according to claim 3 or 4, which is carried out by contact.   The method for attaching a noble metal to a carbon steel member of a nuclear power plant according to claim 5, wherein the pH of the second film-forming aqueous solution is in the range of 5.5 or more and 9.0 or less.   The said reducing agent contained in the said 1st film formation aqueous solution and the said pH adjuster contained in the said 2nd film formation aqueous solution are the same substances, The noble metal of the noble metal to the carbon steel member of the nuclear power plant of Claim 5 or 6 Adhesion method.   The method for attaching a noble metal to a carbon steel member of a nuclear power plant according to claim 1 or 2, wherein the nickel metal film is formed after chemical decontamination is performed on the surface of the carbon steel member.   The method for attaching a noble metal to a carbon steel member of a nuclear power plant according to claim 8, wherein an oxidizing agent is injected into an oxalic acid aqueous solution used for the chemical decontamination of the surface. The formation of the nickel metal film is communicated with a reactor pressure vessel, and the first film formation aqueous solution is supplied to the first pipe which is the carbon steel member through the second pipe. Performed on the inner surface by contacting the inner surface of the first pipe, which is the surface of the carbon steel member,
In forming the first nickel ferrite film, the second film forming aqueous solution is supplied to the first pipe through the second pipe, and the second film forming aqueous solution is brought into contact with the surface of the formed nickel metal film. Is performed on the surface of the nickel metal film by
When the noble metal adheres, the aqueous solution containing the noble metal ions and the reducing agent is supplied to the first pipe through the second pipe, and the aqueous solution is brought into contact with the surface of the formed first nickel ferrite film. The method for attaching a noble metal to a carbon steel member of a nuclear power plant according to any one of claims 5 to 7, wherein   The first film-forming aqueous solution is circulated in a closed loop including the first pipe and the second pipe, the second film-forming aqueous solution is circulated in the closed loop, and the aqueous solution containing the noble metal ions and the reducing agent is circulated. The method for adhering a noble metal to a carbon steel member of a nuclear power plant according to claim 10, wherein the noble metal is circulated in the closed loop.   The method for adhering a noble metal to a carbon steel member of a nuclear power plant according to any one of claims 1 to 11, wherein the noble metal adhered to water in a temperature range of 200 ° C to 330 ° C including an oxidizer. A method for suppressing the attachment of radionuclides to a carbon steel member of a nuclear power plant, wherein the nickel metal film is changed to a second nickel ferrite film in the temperature range by contacting the first nickel ferrite film.   The nuclear power plant is activated, and is heated by nuclear fission of nuclear fuel material in a reactor pressure vessel as water in a temperature range of 200 ° C. or more and 330 ° C. or less containing the oxidant, and is 200 ° C. or more and 330 ° C. or less containing oxidant. The nuclear power plant according to claim 12, wherein cooling water in a temperature range is used, and the conversion of the nickel metal film into the second nickel ferrite film is performed by bringing the cooling water into contact with the first nickel ferrite film. Of suppressing the attachment of radionuclides to carbon steel members.   The method for adhering a noble metal to a carbon steel member of a nuclear power plant according to claim 10 or 11, wherein the second pipe is removed from the first pipe, and then a temperature of 200 ° C or higher and 330 ° C or lower containing an oxidizing agent. A range of water is supplied to the first pipe, the water supplied to the first pipe is brought into contact with the first nickel ferrite film formed on the inner surface of the first pipe and attached with the noble metal, and the temperature is set. A method for suppressing the attachment of a radionuclide to a carbon steel member of a nuclear power plant, wherein the nickel metal film is changed to a second nickel ferrite film in a range.   After the second pipe is removed from the first pipe, the nuclear power plant is started, and the water in the temperature range of 200 ° C. or higher and 330 ° C. or lower containing the oxidizing agent is supplied to the first pipe. The precious metal adheres by supplying cooling water having a temperature range of 200 ° C. or more and 330 ° C. or less containing an oxidant heated by nuclear fission of nuclear fuel material in the reactor pressure vessel of the plant to the first pipe. The radionuclide to the carbon steel member of the nuclear power plant according to claim 14, wherein the conversion of the nickel metal film into the second nickel ferrite film is performed by bringing the cooling water into contact with the first nickel ferrite film. Adhesion control method.   After removing the second pipe from the first pipe, both ends of a third pipe are connected to the first pipe to form a closed loop including the first pipe and the third pipe, and the temperature range The supply of water to the first pipe is performed by heating water containing an oxidant to a temperature range of 200 ° C. or higher and 330 ° C. or lower by a heating device provided in the third pipe, and then supplying the first pipe from the third pipe. The nickel metal coating is converted to the second nickel ferrite coating by supplying the piping to the first nickel ferrite coating formed on the inner surface of the first piping and attached to the noble metal. After the water supplied from the three pipes to the first pipe is brought into contact with the nickel metal film, the nickel metal film is converted into the second nickel ferrite film, and then the third pipe. The first method for suppressing adhesion radionuclide to a carbon steel member of a nuclear plant according to claim 14 detached from the pipe.

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