JP6868545B2 - Corrosion control method for carbon steel parts of plants - Google Patents

Description

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

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

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

On the other hand, the components such as the reactor purification system, residual heat removal system, reactor isolation cooling system, core spray system and water supply system, which are connected to the RPV, are used from the viewpoint of reducing the manufacturing cost of the plant or high temperature water. Carbon steel members are mainly used from the viewpoint of avoiding stress corrosion cracking of stainless steel due to the above. Of these systems, the residual heat removal system, the reactor isolation cooling system, and the core spray system are included in the cooling water because the cooling water that has flowed through the system is temporarily returned to the reactor water. , The effect of system corrosion products on reactor water is small. However, since there is a temperature range (130 ° C to 180 ° C) in which the amount of corrosion increases in the furnace water purification system and the water supply system, the amount of corrosion products flowing into the furnace water increases and the load on the purification device increases. I am concerned. In addition, if the amount of corrosion of the system increases, it affects the soundness of the components, so it is necessary to inspect the soundness confirmation, which leads to an increase in periodic inspection work. For this reason, studies have been conducted on the suppression of corrosion of carbon steel members of nuclear power plants.

As a method of suppressing corrosion of carbon steel members constituting a nuclear power plant, for example, a method of injecting oxygen into a water supply system to form an inactive film composed of an oxide film on the surface of the carbon steel member, and ammonia and hydrazine, etc. A method of adding a chemical to the water supply to adjust the pH of the water supply to the alkaline side has been proposed in a BWR plant and a pressurized water reactor (hereinafter referred to as a PWR plant) (see, for example, Japanese Patent Application Laid-Open No. 2000-292589). .. However, in the method of injecting oxygen and alkaline chemicals, it is necessary to continue injecting the chemicals during the operation of the nuclear power plant in order to continuously obtain the effect of suppressing corrosion of the carbon steel member. If the injection of the drug is stopped, the effect will not be obtained. Further, when an alkaline chemical is injected, the chemical becomes a load on the ion exchange resin in the reactor water purification device provided in the reactor water purification system, so that the amount of radioactive waste may increase.

JP-A-2006-38483 and JP-A-2012-247322 are in the range of 60 ° C. to 100 ° C. containing iron (II) ions, an oxidizing agent and a pH adjuster (hydrazine) while the nuclear power plant is shut down. It is described that the film forming liquid is brought into contact with the surface of a stainless steel component of a nuclear power plant to form a magnetite film on this surface. Furthermore, these publications also describe that an aqueous solution containing a noble metal (for example, platinum) is brought into contact with the magnetite film and the noble metal is adhered onto the magnetite film while the nuclear power plant is shut down.

JP-A-2007-182604 and JP-A-2007-192672 provide methods for suppressing corrosion of carbon steel members by surface treatment without injecting chemicals during their operation on the surface of carbon steel members of a nuclear power plant. Describes a method for forming a ferrite film. In this method, a film-forming solution containing iron (II) ions and an oxidizer and having a pH in the range of 5.5 to 9.0 and a temperature range of room temperature to 100 ° C. is applied to carbon steel while the nuclear plant is shut down. It is brought into contact with the surface of the member to form a ferrite film on this surface.

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

Japanese Patent Application Laid-Open No. 2015-158486 describes that when a noble metal is attached to the inner surface of a recirculation system pipe which is a component of a BWR plant, an aqueous solution containing a complex ion forming agent, a noble metal ion and a reducing agent is applied to the inner surface of the recirculation system pipe. It is described that it is brought into contact with.

Japanese Unexamined Patent Publication No. 2000-292589 Japanese Unexamined Patent Publication No. 2006-38483 Japanese Unexamined Patent Publication No. 2012-247322 JP-A-2007-182604 JP-A-2007-192672 Japanese Unexamined Patent Publication No. 2011-32551 Japanese Unexamined Patent Publication No. 2015-158486

However, carbon is produced by the methods described in JP-A-2006-38483, JP-A-2012-247322, JP-A-2007-182604, JP-A-2007-192672, and JP-A-2011-32551. When a noble metal adheres to the surface of the nickel ferrite film, the nickel ferrite film formed on the surface of the steel member may be eluted by the action of the noble metal and eventually disappear, as will be described in detail later. is there. Therefore, the nickel ferrite film cannot suppress the corrosion of the carbon steel member for a long period of time.

An object of the present invention is to provide a method for suppressing corrosion of carbon steel members of a plant, which can further extend the period during which corrosion of carbon steel members of the plant is suppressed.

The feature of the present invention that achieves the above-mentioned object is to form a nickel metal film on the surface of the carbon steel member of the plant in contact with water, cover the surface with the nickel metal film, and attach the noble metal to the surface of the nickel metal film. The nickel metal film to which this noble metal is attached is brought into contact with water containing an oxidizing agent at 130 ° C. or higher and lower than 200 ° C., and the nickel metal film is formed and the noble metal is attached after the plant is shut down and before the plant is started. To be done.

The corrosion potential of the nickel metal film and the carbon steel member that come into contact with water is lowered by the action of the noble metal adhering to the nickel metal film. Due to such a decrease in the corrosion potential and contact of water in the temperature range of 130 ° C. or higher and lower than 200 ° C. containing an oxidizing agent with the nickel metal film, the nickel metal film also comes into contact with the water by the action of the attached noble metal. It is converted into a stable nickel-ferrite film that does not elute in. Since the surface of the carbon steel member is covered with stable nickel ferrite to which the noble metal is attached, corrosion of the carbon steel member of the plant can be suppressed for a longer period of time.

According to the present invention, a stable nickel ferrite film that does not elute in the contacting water due to the action of the attached noble metal is formed on the surface of the carbon steel member, so that the carbon steel member of the plant is corroded over a longer period of time. It can be suppressed.

It is a flowchart which shows the procedure of the corrosion suppression method of the carbon steel member of the plant of Example 1 applied to the purification system piping of a boiling water reactor which is a preferable example of this invention. It is explanatory drawing which shows the state which connected the film forming apparatus used when carrying out the method of suppressing corrosion of the carbon steel member of the plant of Example 1 to the purification system piping of a boiling water reactor. It is a detailed block diagram of the film forming apparatus shown in FIG. It is sectional drawing of the purification system piping of a boiling water type nuclear power plant before the corrosion control method of the carbon steel member of a plant shown in FIG. 1 is started. It is explanatory drawing which shows the state which the nickel metal film was formed on the inner surface of the purification system pipe by the corrosion suppression method of the carbon steel member of a plant shown in FIG. It is explanatory drawing which shows the state which the noble metal adhered to the surface of the nickel metal film formed on the inner surface of the purification system pipe by the corrosion suppression method of the carbon steel member of a plant shown in FIG. In the method for suppressing corrosion of carbon steel members of a plant shown in FIG. 1, water in a temperature range of 130 ° C. or higher and lower than 200 ° C. containing oxygen is brought into contact with a nickel metal film formed on the inner surface of a purification system pipe and to which platinum is adhered. It is explanatory drawing which shows the state. In the method for suppressing corrosion of carbon steel members of a plant shown in FIG. 1, oxygen contained in water in a temperature range of 130 ° C. or higher and lower than 200 ° C. and Fe ²⁺ in the purification system piping are formed on the inner surface of the purification system piping. It is explanatory drawing which shows the state which is transferred to the nickel metal film to which platinum is adhered. It is explanatory drawing which shows the state which the nickel metal film formed on the inner surface of a purification system pipe was converted into a nickel ferrite film in the method of suppressing corrosion of the carbon steel member of a plant shown in FIG. It is explanatory drawing which showed the result of the actual machine simulated environmental corrosion test by the carbon steel test piece. It is explanatory drawing which shows the laser Raman spectrum analysis result of the oxide film formed on the carbon steel test piece by the actual machine simulated environmental corrosion test using the carbon steel test piece which formed the nickel metal film with platinum attached. It is explanatory drawing which shows the corrosion suppression method of the carbon steel member of the plant of Example 2 applied to the water supply pipe of the boiling water type nuclear power plant which is another Example of this invention. It is explanatory drawing which shows the corrosion suppression method of the carbon steel member of the plant of Example 3 applied to the purification system piping of the boiling water reactor which is another Example of this invention. It is a flowchart which shows the procedure of the corrosion suppression method of the carbon steel member of the plant of Example 4 applied to the purification system piping of the boiling water reactor which is another Example of this invention. In the method for suppressing the adhesion of radionuclides to the carbon steel member of the plant shown in FIG. 14, 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. It is a block diagram. It is explanatory drawing which shows the corrosion suppression method of the carbon steel member of the plant of Example 5 applied to the water supply pipe of a thermal power plant which is another Example of this invention.

The inventors conducted detailed studies and experiments to further enhance the effect of the anticorrosion method for carbon steel members described in Japanese Patent Application Laid-Open No. 2011-32551. According to Japanese Patent Application Laid-Open No. 2011-32551, a nickel metal film is formed on the surface of a carbon steel member of a BWR plant, a nickel ferrite film is formed on the surface of the nickel metal film, and further, a nickel ferrite film is formed on the surface of the nickel metal film while the BWR plant is stopped. During the operation, water containing oxygen at 150 ° C. or higher is brought into contact with the surface of the nickel ferrite film to convert the above nickel metal film into a nickel ferrite film. As a result of the examination by the inventors, the inventors finally adhere the noble metal to the surface of the nickel metal film formed on the surface of the carbon steel member, and the temperature is 130 ° C. or higher (preferably 130 ° C. or higher and lower than 200 ° C.). ) Is brought into contact with the surface of the nickel metal film to convert the nickel metal film into a stable nickel ferrite film whose Ni content is close to the constant ratio, thereby further enhancing the anticorrosion effect of the carbon steel member. We have found the conclusion that it can be enhanced.

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

There are two cases in which the noble metal adheres to the surface of the ferrite film formed on the surface of the carbon steel member. In the first case, the noble metal injected into the furnace water during the operation of the nuclear power plant in order to reduce the dissolved oxygen concentration in the furnace water adheres to the surface of the ferrite film formed on the constituent members. In the second case, as described in JP-A-2006-38483 and JP-A-2012-247322, noble metal ions are contained on the surface of the ferrite film formed on the constituent members during the shutdown of the nuclear power plant. The solution is brought into contact and the noble metal is attached to the surface of the ferrite film.

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

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

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

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

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

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

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

The formation of a nickel metal film on the surface of the carbon steel member is possible by bringing an aqueous solution containing nickel ions and a reducing agent into contact with the surface of the carbon steel member. The 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. Further, the noble metal can be attached to the surface of the nickel metal film formed on the surface of the carbon steel member by bringing an aqueous solution containing a noble metal ion (for example, platinum ion) and a reducing agent into contact with the formed nickel metal film. Is. The nickel ions contained in the aqueous solution can be attached to the surface of the carbon steel member even when ^{Fe 2+ is eluted from the carbon steel member.}

By forming a nickel metal film on the surface of the carbon steel member in this way, ^{it is possible to prevent the elution of Fe 2+} from the carbon steel member, and to attach more precious metal to the carbon steel member in a short time. Can be done.

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

Furthermore, the results of studies on the suppression of corrosion of carbon steel members will be described below. _{The inventors do not form an unstable Ni 0.7} Fe _2.3 O ₄ film on the surface of the carbon steel member in the low temperature range of 60 ° C to 100 ° C, but stable nickel ferrite that is not eluted by the attached noble metal. We aimed to form a film on the surface of carbon steel members. Therefore, the inventors have variously examined whether the nickel metal film formed on the surface of the carbon steel member can be used for forming the stable nickel ferrite film in order to effectively adhere the noble metal to the carbon steel member. did. As a result, high-temperature (130 ° C. or higher) water with platinum attached to the nickel metal film is brought into contact with the surface of the nickel metal film formed on the surface of the carbon steel member to which the noble metal is attached. The nickel metal film covers the surface of the carbon steel member and is a stable nickel ferrite film that does not elute even by the action of noble metals (a nickel ferrite film in which x is 0 in _{Ni 1-x} Fe _{2 + x} O _{4, that is, NiFe. 2} O ₄ film) could be converted.

The inventors used a carbon steel test piece A to which nickel and platinum were not attached, and a carbon steel test piece B in which a nickel metal film was formed on the surface and platinum was attached to the nickel metal film surface. , The amount of corrosion of the test piece was determined by immersing it in simulated water simulating the conditions of the furnace water during operation of the BWR plant. 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 circulated in the circulation pipe. 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 the simulated water flowing in the circulation pipe for 500 hours. After 500 hours have passed, each of the test pieces A and B is taken out from the circulation pipe, the oxide film formed in high temperature water is dissolved and removed by the cathode dissolution method, and the amount of metal remaining in the test piece is determined and tested. The amount of corrosion was determined from the difference from the amount of metal in the previous test piece.

The measurement result of the amount of corrosion in each test piece is shown in FIG. As is clear from FIG. 10, in the test piece B in which platinum is attached to the surface of the nickel metal film, the amount of corrosion is significantly reduced as compared with the test piece A in which nickel and platinum are not attached.

Furthermore, the chemical composition on each surface of the test pieces A and B taken out from the circulation pipe was analyzed by Raman spectroscopy. The analysis result is shown in FIG. _{A film mainly composed of Fe 3} O ₄ was formed on the 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 in which the amount of corrosion was significantly reduced. The NiFe ₂ O _4, in _{Ni 1-x Fe 2 + x} O 4 x is in the form a 0.

A nickel metal film is formed on the surface, and the nickel metal film of the carbon steel member (test piece B) having a noble metal (for example, platinum) adhered to the surface of the nickel metal film comes into contact with water containing oxygen at 130 ° C. or higher. The reason why it is converted into a _{stable nickel ferrite film (NiFe 2} O ₄ film) covering the surface of the carbon steel member will be described. When water of 130 ° C. or higher comes into contact with the nickel metal film on the carbon steel member, the nickel metal film and the carbon steel member are heated to 130 ° C. or higher. The oxygen contained in the water moves into the nickel metal film, and Fe contained in the carbon steel member becomes Fe ²⁺ and moves into the nickel metal film. Nickel in the nickel metal film reacts with ^{oxygen and Fe 2+} transferred into the nickel metal film in a high temperature environment of 130 ° C. or higher, and nickel ferrite in which x is 0 in _{Ni 1-x} Fe _{2 + x} O ₄ Is generated. At this time, the ease of incorporating nickel and iron into the ferrite structure is affected by the noble metal, and if the noble metal is present, nickel is more easily incorporated than iron. Therefore, Ni _1-x Fe ₂₊ Nickel ferrite in which x is 0 is produced in _x O _4. This nickel ferrite film covers the surface of the carbon steel member.

_{In Ni 1-x} Fe _{2 + x} O ₄ produced as described above from the nickel metal contained in the nickel metal film covering the surface of the carbon steel member in a high temperature environment of 130 ° C. or higher, x is 0. A certain nickel ferrite has a large crystal growth, and even if a noble metal adheres to it _{, it is stable without being eluted in water like a Ni 0.7} Fe _2.3 O ₄ film, and acts to suppress corrosion of the base carbon steel. In this _{stable nickel ferrite in which x is 0 in Ni 1-x} Fe _{2 + x} O ₄ , the corrosion potential of the carbon steel member and the nickel metal film is lowered by the action of a noble metal such as platinum adhering to the nickel metal film. Is generated for. As described above, the nickel ferrite film formed from the nickel metal covering the surface of the carbon steel member in the presence of platinum in a high temperature environment of 130 ° C. or higher is formed in a low temperature range of 60 ° C. to 100 ° C. Corrosion of carbon steel members can be suppressed for a longer period of time than the Ni _0.7 Fe _2.3 O _{4 film.}

When the temperature of the oxygen-containing water in contact with the nickel metal film is less than 130 ° C., the nickel metal film is not converted into _{a stable nickel ferrite film (NiFe 2} O _{4 film).} In order to convert the nickel metal film into a stable nickel ferrite film that does not elute due to the action of the noble metal, it is necessary to raise the temperature of the water containing oxygen that comes into contact with the nickel metal film to 130 ° C. or higher. Further, in order to shorten the time required for the temperature of the water containing oxygen to rise, the temperature of the water may be set to less than 200 ° C. That is, the oxygen-containing water that comes into contact with the nickel metal film is heated to a temperature range of 130 ° C. or higher and lower than 200 ° C. in order to convert _{the nickel metal film into a stable nickel ferrite (NiFe 2} O _{4) film.}

The inventors have made contact with a nickel metal film having a noble metal adhered to its surface with water containing oxygen and having a temperature within the temperature range of 130 ° C. or higher and lower than 200 ° C., even when the surface of the carbon steel member is contacted. _They found that the formed nickel metal film could be converted into a stable nickel ferrite film (NiFe 2 O _{4 film).}

In addition, in order to form a nickel metal film on the surface of the carbon steel member, nickel ions, formic acid and a reducing agent (for example, hydrazine) are contained, and the pH is 4.0 to 11.0 (4.0 or more and 11.0 or less). ), When an aqueous solution in the temperature range of 60 ° C. or higher and 100 ° C. or lower is brought into contact with the surface of the corresponding carbon steel member, until the surface of the carbon steel member is completely covered with the nickel metal film. ^{Fe 2+} elutes from the carbon steel member into the aqueous solution. The eluted Fe ²⁺ is precipitated in the aqueous solution as iron hydroxide and magnetite.

After the formation of the nickel metal film on the surface of the carbon steel member is completed, the aqueous solution containing the precipitated iron hydroxide and magnetite, nickel ion, formic acid and hydrazine is used in the decomposition step of formic acid and hydrazine to form the cation exchange resin tower and It is supplied to the disassembly device. ^{Nickel ions and Fe 2+} contained in the aqueous solution are removed by a cation exchange resin column, and formic acid and hydrazine are decomposed by a decomposition apparatus. After decomposition of formic acid and hydrazine, the aqueous solution is guided to the mixed bed resin tower, impurities contained in the aqueous solution are removed by the ion exchange resin in the mixed bed resin tower, and the aqueous solution is purified.

^{Even after purifying the aqueous solution, Fe 2+} that could not be completely removed by the cation exchange resin tower and the mixed bed resin tower may be present in the aqueous solution. After purification of the aqueous solution, Fe ²⁺ present in the aqueous solution is oxidized by oxygen dissolved in the aqueous solution and hydrogen peroxide supplied to the aqueous solution to decompose formic acid and hydrazine contained in the aqueous solution. ^It becomes 3+ and precipitates as iron hydroxide and magnetite. After that, when the noble metal ion and the reducing agent are injected into the aqueous solution, a part of the injected noble metal ion adheres as a noble metal to the iron hydroxide and magnetite precipitated by the action of the reducing agent, and the carbon steel member The amount of noble metal adhering to the nickel metal film formed on the surface is reduced, and the time required for adhering a predetermined amount of noble metal to the surface of the nickel metal film becomes long.

^{Iron ions (Fe 3+} ) remaining in the aqueous solution are precipitated as iron hydroxide and magnetite, and in order to prevent the noble metal from adhering to iron hydroxide and magnetite, a complex ion forming agent (for example, ammonia) and the noble metal are added to the aqueous solution. Each of the ion (for example, platinum ion) and the reducing agent (for example, hydrazine) is injected, and the iron ion remaining in the aqueous solution and the injected complex ion forming agent, for example, ammonia form an iron-ammonia complex ion. It is known to suppress the precipitation of iron ions (see JP-A-2015-158486). The iron ion and ammonia generate an iron-ammonia complex ion by each reaction represented by the formulas (1) to (3).

Fe ³⁺ + NH ₃ → [Fe (NH ₃ )] ³⁺ …… (1)
Fe ³⁺ + 2NH ₃ → [Fe (NH ₃ ) ₂ ] ³⁺ …… (2)
Fe ³⁺ + 3NH ₃ → [Fe (NH ₃ ) ₃ ] ³⁺ …… (3)
In this way, when iron-ammonia complex ions are generated in the aqueous solution, even if the reducing agent hydrazine is injected and the pH of the aqueous solution becomes alkaline of about 8 or more, iron ions are produced in the aqueous solution. Precipitation is suppressed. By injecting a complex ion forming agent into an aqueous solution, the noble metal ions contained in the aqueous solution are efficiently adhered to the surface of the nickel metal film formed on the surface of the carbon steel member of the plant with the help of the reducing agent. Can be done. Therefore, the time required for the noble metal to adhere to the surface of the carbon steel member can be further shortened.

As the complex ion forming agent, even when the pH of the aqueous solution is increased by injecting a reducing agent (for example, hydrazine), ^{the solubility of Fe 3+} is increased by the formation of complex ions, and the precipitation of iron hydroxide and magnetite is suppressed. Any substance can be used as long as it can be used, and at least one of monoamines such as ammonia and hydroxylamine, cyanide compounds, urea and thiocyan compounds is used.

As described above, even when iron ions (Fe ³⁺ ) remain in the purified aqueous solution, iron ions such as ammonia that suppress the precipitation of iron ions in the aqueous solution are used. By injecting a substance that forms complex ions (complex ion forming agent) into the aqueous solution, platinum ions (noble metal ions) and reducing agents (for example, hydrazine) form platinum ions as platinum on the surface of the carbon steel member. It can be attached to the surface of the nickel metal film.

Based on the above-mentioned examination results, the inventors were able to newly create the invention described below.

A film-forming aqueous solution containing nickel ions and a reducing agent is brought into contact with the surface of the carbon steel member to form a nickel metal film on the surface of the carbon steel member, and a noble metal is attached to the surface of the nickel metal film to contain oxygen at 130 ° C. Water in a temperature range of more than 200 ° C. is brought into contact with a nickel metal film to which a noble metal is attached, and based on the nickel metal contained in the nickel metal film, oxygen contained in water, and iron contained in a carbon steel member, 130 A nickel ferrite film is formed on the surface of a carbon steel member by utilizing the catalytic action of a noble metal at a high temperature of ° C. or higher and lower than 200 ° C.

The present invention relates to a method for suppressing corrosion of carbon steel members of a plant. According to the present invention, a nickel metal film formed on the surface of a carbon steel member to which a noble metal is attached is brought into contact with water in the range of 130 ° C. or higher and lower than 200 ° C., and the nickel metal contained in the nickel metal film is brought into contact with the nickel metal film. Based on this, a stable nickel ferrite film is formed on the surface of the carbon steel member at a high temperature in the range of 130 ° C. or higher and lower than 200 ° C. by utilizing the catalytic action of the noble metal. Even if the noble metal is attached, it does not elute into water, and corrosion of the carbon steel member can be suppressed for a longer period of time (specifically, over a plurality of operation cycles).

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

The method for suppressing corrosion of the carbon steel member of the plant of Example 1 which is a preferred embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3. The method for suppressing corrosion of carbon steel members of this embodiment is applied to a carbon steel purification system pipe (carbon steel member) of a boiling water reactor (BWR plant).

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

The recirculation system includes a stainless steel recirculation system pipe 6 and a recirculation pump 7 installed in the recirculation system pipe 6. In the water supply system, a condensate pump 12, a condensate purifier (for example, a condensate desalinator) 13, a low-pressure feed water heater 14, a feed water pump 15, and a high-pressure feed water supply are connected to a feed water pipe 11 connecting the condenser 10 and the RPV 3. The heater 16 is installed in this order from the condenser 10 toward the RPV3. In the reactor purification system, the purification system pump 19, the regenerated heat exchanger 20, the non-regenerated heat exchanger 21, and the reactor water purification device 22 are connected to the purification system pipe 18 connecting the recirculation system pipe 6 and the water supply pipe 11 in this order. It is installed. The bypass pipe 28 that bypasses the furnace water purification device 22 is connected to the purification system pipe 18 on the upstream side and the downstream side of the furnace water purification device 22. The valve 27 is provided in the purification system pipe 18 on the furnace water purification device 22 side of the connection point between the bypass pipe 28 and the purification system pipe 18. The purification system pipe 18 is connected to the recirculation system pipe 6 upstream of the recirculation pump 7. The reactor 2 is installed in the reactor containment vessel 90 arranged in the reactor building (not shown).

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

A part of the furnace water flowing in the recirculation system pipe 6 flows into the purification system pipe 18 by driving the purification system pump 19, is cooled by the regenerated heat exchanger 20 and the non-regenerating heat exchanger 21, and then is cooled in the furnace. It is purified by the water purification device 22. The purified furnace water is heated by the regenerative heat exchanger 20 and returned to the RPV3 via the purification system pipe 18 and the water supply pipe 11.

In the method for suppressing corrosion of carbon steel members of the plant of this embodiment, film forming devices 30 and 31A are used, and these film forming devices 30 and 31A are attached to the purification system pipe 18 of the BWR plant as shown in FIG. Be connected.

The detailed configurations of the film forming apparatus 30 and 30A will be described with reference to FIG. The configurations of the film forming apparatus 30 and 30A are the same.

The film forming devices 30 and 30A include a circulation pipe 31, a surge tank 32, a heater 33, a circulation pump 34, 35, a nickel ion injection device 36, a reducing agent injection device 41, a platinum ion injection device 46, a cooler 52, and a cation exchange. It includes a resin tower 53, a mixed bed resin tower 54, a decomposition device 55, an oxidant supply device 56, and an ejector 61.

The on-off valve 62, the circulation pump 35, the valves 63, 66, 69 and 74, the surge tank 32, the circulation pump 34, the valve 77 and the on-off valve 78 are provided in the circulation pipe 31 in this order from the upstream. The pipe 65 that bypasses the valve 63 is connected to the circulation pipe 31, and the valve 64 and the filter 51 are installed in the pipe 65. A cooler 52 and a valve 67 are installed in the pipe 68 whose both ends are connected to the circulation pipe 31 by bypassing the valve 66. The cation exchange resin tower 53 and the valve 70 are installed in the pipe 71 whose both ends are connected to the circulation pipe 31 and bypass the valve 69. The mixed bed resin tower 54 and the valve 72 are installed in the pipe 73 whose both ends are connected to the pipe 71 and bypass the cation exchange resin tower 53 and the valve 70. The cation exchange resin tower 53 is filled with a cation exchange resin, and the mixed bed resin tower 54 is filled with a cation exchange resin and an anion exchange resin.

The pipe 76 in which the valve 75 and the disassembling device 55 located downstream of the valve 75 are installed is connected to the circulation pipe 31 by bypassing the valve 74. The decomposition device 55 is filled with, for example, an activated carbon catalyst in which ruthenium is adhered to the surface of the activated carbon. A surge tank 32 is installed in the circulation pipe 31 between the valve 74 and the circulation pump 34. The heater 33 is arranged in the surge tank 32. The pipe 80 provided with the valve 79 and the ejector 61 is connected to the circulation pipe 31 between the valve 77 and the circulation pump 34, and further connected to the surge tank 32. The ejector 61 is provided with a hopper (not shown) for supplying oxalic acid (reduction decontamination agent) used for reducing and dissolving contaminants on the inner surface of the purification system pipe 18 into the surge tank 32.

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

The platinum ion implanter (precious metal ion implanter) 46 includes a chemical tank 47, an injection pump 48, and an injection pipe 49. The chemical tank 47 is connected to the circulation pipe 31 by an injection pipe 49 having an injection pump 48 and a valve 50. An aqueous solution containing platinum ions prepared by dissolving a platinum complex (for example, sodium hexahydroxoplatinate hydrate (Na ₂ [Pt (OH) ₆ ], nH ₂ O)) in water (for example, sodium hexahydroxoplatinate). Aqueous solution of hydrate) is filled in the chemical tank 47. An aqueous solution containing platinum ions is a type of aqueous solution containing noble metal ions.

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

The injection pipes 39, 49 and 44 are connected to the circulation pipe 31 between the valve 77 and the on-off valve 78 in that order from the valve 77 toward the on-off valve 78.

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

A pH meter 81 is attached to the circulation pipe 31 between the connection point between the injection pipe 44 and the circulation pipe 31 and the on-off valve 78.

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

During the period when the operation of the BWR plant 1 is stopped as described above, the carbon steel piping system connected to the RPV 12 which is one of the carbon steel members in the BWR plant 1, for example, the purification system piping 18 is installed. The targeted method for suppressing corrosion of carbon steel members of the plant of this example is implemented. In this method for suppressing corrosion of carbon steel members, nickel metal adhesion treatment to the inner surface of the purification system pipe 18 in contact with furnace water, precious metal adhesion treatment to the adhered nickel metal, for example, platinum adhesion treatment, and precious metal adhesion are performed. The conversion process of the nickel metal to stable nickel ferrite is performed.

The method for suppressing corrosion of the carbon steel member of the plant of this embodiment will be described below based on the procedure shown in FIG. In the method for suppressing corrosion of carbon steel members of the plant of this embodiment, film forming devices 30 and 30A are used.

First, the film forming apparatus is connected to the carbon steel piping system to be formed (step S1). When the operation of the BWR plant 1 is stopped, for example, the bonnet of the valve 23 installed in the purification system pipe 18 is opened upstream of the purification system pump 19 to seal the recirculation system pipe 6 side. One end of the circulation pipe 31 of the film forming apparatus 30 on the on-off valve 78 side is connected to the flange of the valve 23. Further, the bonnet of the valve 25 installed in the purification system pipe 18 is opened between the regenerated heat exchanger 20 and the non-regenerating heat exchanger 21 to seal the non-regenerating heat exchanger 21 side. The other end of the circulation pipe 31 on the on-off valve 62 side is connected to the flange of the valve 25. Both ends of the circulation pipe 31 are connected to the purification system pipe 18, and a closed loop including the purification system pipe 18 and the circulation pipe 31 is formed. Similarly, one end of the circulation pipe 31 of the film forming apparatus 30A on the on-off valve 78 side is connected to the flange of the valve 32A, and the other end of the circulation pipe 31 on the on-off valve 62 side is connected to the flange of the valve 26. , The film forming apparatus 30A is connected to the purification system pipe 18.

In this embodiment, the film forming apparatus 30 is connected to the purification system pipe 18 of the reactor purification system, but in addition to the purification system pipe 18, it is a carbon steel member and is a residual heat removal system connected to the RPV3. , The film forming device 30 is connected to the carbon steel pipe of any of the reactor isolation cooling system, the core spray system, and the water supply system, and the carbon steel member of the plant of this embodiment is corroded to this carbon steel pipe. Suppression methods may be applied.

Each step of steps S2 to S14 described below is carried out on the portion of the purification system pipe 18 between the valve 23 and the valve 25 by the film forming apparatus 30, and the purification system piping 18 is carried out by the film forming apparatus 30A. It is carried out for the portion between the valve 26 and the valve 32A.

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

In step S2, the chemical decontamination applied to the inner surface of the purification system pipe 18 is the known reduction decontamination described in JP-A-2000-105295. This reduction decontamination will be described. First, the on-off valve 62, the valves 63, 66, 69, 74 and 77, and the on-off valve 78 are opened, respectively, and the circulation pumps 34 and 35 are driven with the other valves closed. As a result, the water heated to 90 ° C. by the heater 33 in the surge tank 32 in the purification system pipe 18 circulates in the closed loop formed by the circulation pipe 31 and the purification system pipe 18. When the temperature of this water reaches 90 ° C., the valve 79 is opened to guide a part of the water flowing in the circulation pipe 31 into the pipe 80. A predetermined amount of oxalic acid supplied from the hopper and the ejector 61 into the pipe 80 is guided into the surge tank 32 by the water flowing in the pipe 80. This oxalic acid dissolves in water in the surge tank 32, and an aqueous oxalic acid solution (reduction decontamination liquid) is generated in the surge tank 32.

This oxalic acid aqueous solution is discharged from the surge tank 32 to the circulation pipe 31 by driving the circulation pump 34. The hydrazine aqueous solution in the chemical tank 42 of the reducing agent injection device 41 is injected into the oxalic acid aqueous solution in the circulation pipe 31 through the injection pipe 44 by opening the valve 45 and driving the injection pump 43. Purification system by controlling the injection pump 43 (or the opening degree of the valve 45) based on the pH value of the oxalic acid aqueous solution measured by the pH meter 81 to adjust the injection amount of the hydrazine aqueous solution into the circulation pipe 31. The pH of the oxalic acid aqueous solution supplied to the pipe 18 is adjusted to 2.5. In this embodiment, hydrazine, which is a reducing agent used when a nickel metal is attached to the inner surface of the purification system pipe 18 and when a noble metal, for example, platinum is attached onto the nickel metal film, is used for reduction decontamination. In the process, it is used as a pH adjuster for adjusting the pH of the aqueous oxalic acid solution.

An aqueous solution of oxalic acid having a pH of 2.5 and 90 ° C. is supplied from the circulation pipe 31 to the purification system pipe 18, and the oxalic acid in the aqueous solution is an oxide film containing radionuclides formed on the inner surface of the purification system pipe 18. Dissolve. The oxalic acid aqueous solution flows through the purification system pipe 18 while dissolving the oxide film, and passes through the purification system pump 19, the regenerated heat exchanger 20, the non-regenerated heat exchanger 21, 21, the bypass pipe 28, and the regenerated heat exchanger 20. It is returned to the circulation pipe 31. The oxalic acid aqueous solution returned to the circulation pipe 31 is boosted by the circulation pump 35 through the on-off valve 62, passes through the valves 63, 66, 68 and 73, and reaches the surge tank 32. In this way, the oxalic acid aqueous solution circulates in the closed loop including the circulation pipe 31 and the purification system pipe 18, carries out reduction decontamination of the inner surface of the purification system pipe 18, and dissolves the oxide film formed on the inner surface thereof. ..

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

In the reduction decontamination of the surface of a carbon steel member (for example, purification system pipe 18) using oxalic acid, sparingly soluble iron (II) oxalate is formed on the surface of the carbon steel member, and this iron oxalate (for example) II) may suppress the dissolution of the oxide film containing radioactive nuclei formed on the surface of the carbon steel member by oxalic acid. In this case, the valve 69 is fully opened, the valve 70 is closed, and the supply of the oxalic acid aqueous solution to the cation exchange resin tower 53 is stopped. Further, the valve 60 is opened to start the supply pump 58, and the hydrogen peroxide in the chemical solution tank 57 is supplied to the oxalic acid aqueous solution flowing in the circulation pipe 31 through the supply pipe 59 and the pipe 76 with the valve 75 closed. To do. An oxalic acid aqueous solution containing hydrogen peroxide is guided from the circulation pipe 31 into the purification system pipe 18. Fe (II) contained in iron (II) oxalate formed on the inner surface of the purification system pipe 18 is oxidized to Fe (III) by the action of the hydrogen peroxide, and the iron (II) oxalate is oxidized. It dissolves in an aqueous oxalic acid solution as an iron (III) acid complex. That is, iron (II) oxalate, and hydrogen peroxide and oxalic acid contained in the aqueous oxalic acid solution generate an iron (III) oxalate complex, water, and hydrogen ions by the reaction represented by the formula (4).

2Fe (COO) ₂ + H ₂ O ₂ + 2 (COOH) ₂ →
2Fe [(COO) ₂ ] ₂ ⁻ + 2H ₂ O + 2H ⁺ … (4)
After it was confirmed that iron (II) oxalate formed on the inner surface of the purification system pipe 18 was dissolved and the hydrogen peroxide injected into the aqueous oxalic acid solution disappeared by the reaction of the formula (4), the circulation pipe 31 A part of the oxalic acid aqueous solution that has passed through the valve 66 is supplied to the cation exchange resin tower 53 through the pipe 71. Metal cations such as radionuclides contained in the oxalic acid aqueous solution are adsorbed on the cation exchange resin in the cation exchange resin tower 53 and removed. The disappearance of hydrogen peroxide in the oxalic acid aqueous solution can be confirmed, for example, by immersing a test paper that reacts with hydrogen peroxide in the oxalic acid aqueous solution sampled from the circulation pipe 31 and observing the color appearing on the test paper.

When the dose rate at the reduction decontamination site of the purification system pipe 18 drops to the set dose rate, or when the reduction decontamination time of the purification system pipe 18 reaches a predetermined time, the oxalic acid contained in the oxalic acid aqueous solution and Decomposes hydrazine (reduction decontamination agent decomposition step). The decrease in the dose rate to the set dose rate at the reduction decontamination site is confirmed by the dose rate obtained based on the output signal of the radiation detector that detects the radiation from the reduction decontamination site of the purification system pipe 18. be able to.

The decomposition of oxalic acid and hydrazine is carried out as follows. The oxalic acid aqueous solution containing hydrazine, which has passed through the valve 69 and the valve 70 by opening the valve 75 to partially reduce the opening degree of the valve 74, is supplied to the decomposition device 55 by the pipe 76 through the valve 75. At this time, the hydrogen peroxide in the chemical solution tank 57 is supplied to the decomposition device 55 through the supply pipe 59 and the pipe 76. The oxalic acid and hydrazine contained in the oxalic acid aqueous solution are decomposed in the decomposition apparatus 55 by the action of the activated carbon catalyst and the supplied hydrogen peroxide. The decomposition reaction of oxalic acid and hydrazine in the decomposition apparatus 55 is represented by the formulas (5) and (6).

(COOH) ₂ + H ₂ O ₂ → 2CO ₂ + 2H ₂ O …… (5)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O …… (6)
The decomposition of oxalic acid and hydrazine in the decomposition apparatus 55 is performed while circulating the oxalic acid aqueous solution in a closed loop including the circulation pipe 31 and the purification system pipe 18. The amount of hydrogen peroxide supplied from the chemical tank 57 to the decomposition device 55 is adjusted so that the supplied hydrogen peroxide is not completely consumed by the decomposition device 55 for decomposition of oxalic acid and hydrazine and flows out from the decomposition device 55. The rotation speed of the supply pump 58 is controlled and adjusted.

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

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

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

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

Next, in order to end the oxalic acid decomposition step, the opening degree of the valve 60 is narrowed, the supply amount of hydrogen peroxide is adjusted so that hydrogen peroxide does not flow out from the decomposition device 55, and new formic acid is injected. Close the valve 79 to stop. When the hydrogen peroxide concentration of the oxalic acid aqueous solution becomes 1 ppm or less, the valve 70 is opened to reduce the opening degree of the valve 69, and the oxalic acid aqueous solution is supplied to the cation exchange resin tower 53. As described above, the metal cations in the oxalic acid aqueous solution are removed by the cation exchange resin in the cation exchange resin tower 53, and the metal cation concentration in the oxalic acid aqueous solution decreases. Decomposition of oxalic acid, hydrazine and formic acid is continued in the decomposition apparatus 55. Of oxalic acid, hydrazine and formic acid, hydrazine is decomposed first, then oxalic acid is decomposed, and formic acid remains last. In this state, the decomposition step of oxalic acid is completed.

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

The temperature of the film-forming liquid is adjusted (step S3). Valves 69 and 74 are opened and valves 70 and 75 are closed. Since the circulation pumps 34 and 35 are driven, the remaining aqueous solution containing formic acid circulates in the closed loop including the circulation pipe 31 and the purification system pipe 18. The aqueous solution containing formic acid is heated to 90 ° C. by the heater 33. The temperature of this formic acid aqueous solution (film-forming aqueous solution described later) is preferably in the temperature range of 60 ° C. to 100 ° C. (60 ° C. or higher and 100 ° C. or lower). Further, the valve 64 is opened and the valve 63 is closed. As a result, the formic acid aqueous solution flowing in the circulation pipe 31 is supplied to the filter 51, and the fine solid content remaining in the formic acid aqueous solution is removed by the filter 51. When the fine solid content is not removed, as will be described later, when the nickel formate aqueous solution is injected into the circulation pipe 31, a nickel metal film is formed on the surface of the solid material, and the injected nickel ions are wasted. Will be done.

A nickel ion aqueous solution is injected (step S4). The valve 63 is opened, the valve 64 is closed, and water flow to the filter 51 is stopped. The valve 40 of the nickel ion injection device 36 is opened to drive the injection pump 38, and the nickel formate aqueous solution in the chemical tank 37 is injected into the 90 ° C. aqueous solution containing residual formic acid flowing in the circulation pipe 31 through the injection pipe 39. To do. The nickel ion concentration of the injected nickel formate aqueous solution is, for example, 200 ppm.

Inject the reducing agent (step S5). The valve 45 of the reducing agent injection device 41 is opened to drive the injection pump 43, and an aqueous solution of hydrazine, which is a reducing agent in the chemical solution tank 42, flows through the injection pipe 44 in the circulation pipe 31 and contains nickel ions and formic acid 90. Infused into an aqueous solution at ° C. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 200 ppm. The hydrazine aqueous solution contains nickel ions and formic acid, and the pH of the aqueous solution at 90 ° C. is in the range of 4.0 to 11.0 (4.0 or more and 11.0 or less), for example, 4.0. , The amount of injection into the aqueous solution is adjusted.

An aqueous solution containing nickel ions, formic acid and hydrazine and having a pH of 4.0 and 90 ° C., that is, a film-forming aqueous solution (film-forming liquid) is supplied from the circulation pipe 31 to the purification system pipe 18 by driving the circulation pump 34. .. When the film-forming aqueous solution 83 comes into contact with the inner surface of the purification system pipe 18, a nickel metal film 82 is formed on the inner surface of the purification system pipe 18 (see FIG. 5). The nickel metal film 82 is formed as follows. The contact between the inner surface of the purification system pipe 18 and the film-forming aqueous solution 83 having a pH of 4.0 accelerates the substitution reaction between the nickel ions contained in the film-forming aqueous solution 83 and the Fe (II) ions in the purification system piping 18 for purification. The amount of nickel ions taken into the inner surface of the system pipe 18 increases, and the elution of iron (II) ions into the film-forming aqueous solution 83 increases. Since the nickel ions taken into the inner surface of the purification system pipe 18 become nickel metal by the action of hydrazine contained in the film-forming aqueous solution 83, the nickel metal film 82 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 film-forming aqueous solution 83 in contact with the inner surface of the purification system pipe 18 is 4.0, and is incorporated into the inner surface of the purification system pipe 18. The amount of nickel ions is the highest. When the pH of the film-forming aqueous solution 83 increases to 7 or the like by injecting the reducing agent, the amount of nickel ions taken in becomes nickel metal increases.

The film-forming aqueous solution 83 discharged from the purification system pipe 18 to the circulation pipe 31 is pressurized by the circulation pumps 35 and 34, and the nickel formate aqueous solution from the nickel ion injection device 36 and the hydrazine aqueous solution from the reducing agent injection device 41 are injected, respectively. Then, it is supplied to the purification system pipe 18 again. By circulating the film-forming aqueous solution 83 in the closed loop including the circulation pipe 31 and the purification system pipe 18, the nickel metal film eventually comes into contact with the film-forming aqueous solution 83 between the valve 23 and the valve 25. The entire surface of the inner surface of the purification system pipe 18 and the inner surface of the purification system pipe 18 between the valve 26 and the valve 32A are uniformly covered. At this time, the amount of nickel metal existing on the inner surface of the purification system pipe 18 is, for example, 50 μg to 300 μg (50 to 300 μg / cm ² ) per square centimeter.

In the surge tank 32, a liquid level of a 90 ° C. aqueous solution (or a film-forming aqueous solution) containing residual formic acid is formed, and a space (not shown) exists above the liquid level, and a space (not shown) exists in this space. There is air. Oxygen in the air in the space is supplied to an aqueous solution (or a film-forming aqueous solution) at 90 ° C. containing the remaining formic acid in the surge tank 32 via the liquid surface. Due to the supply of oxygen in the surge tank 32, the aqueous solution will contain a trace amount of oxygen of about 2 ppm. In step S5, a hydrazine aqueous solution containing 200 ppm of hydrazine is injected into the aqueous solution in order to convert the nickel ions taken into the inner surface of the purification system pipe 18 into nickel metal. The film-forming aqueous solution produced in the circulation system pipe 31 by injecting the hydrazine aqueous solution contains a large amount of hydrazine as compared with about 2 ppm of oxygen. Oxygen contained in the film-forming aqueous solution is decomposed by the injected reducing agent, for example, hydrazine to become water, so that the oxygen dissolved in the film-forming aqueous solution disappears. As a result, an oxygen-free film-forming aqueous solution containing nickel ions, formic acid and hydrazine and having a pH of 4.0 and 90 ° C. is supplied into the purification system pipe 18. The nickel ions taken into the inner surface of the purification system pipe 18 become nickel metal by the action of hydrazine contained in the film-forming aqueous solution, and eventually a nickel metal film is formed on the inner surface of the purification system pipe 18.

When oxygen is contained in the film-forming aqueous solution that comes into contact with the inner surface of the purification system piping 18, a nickel metal film containing _{unstable nickel ferrite (Ni 0.7} Fe _2.3 O _{4) is formed on the inner surface of the purification system piping 18.} It is formed. However, by injecting hydrazine to generate an oxygen-free film-forming aqueous solution and supplying this film-forming aqueous solution to the purification system pipe 18, the inner surface of the purification system pipe 18 does not contain unstable nickel ferrite. A metal film can be formed. Further, since the film-forming aqueous solution contains hydrazine, the thickness of the nickel metal film formed on the inner surface of the purification system pipe 18 can be further increased.

As shown in FIG. 10 of JP-A-2006-38483, an inert gas (for example, nitrogen) may be bubbled into the aqueous solution in the surge tank 32, and the dissolved oxygen in the aqueous solution may be discharged. .. An oxygen-free aqueous solution can be supplied from the surge tank 32 to the circulation pipe 31, and by injecting hydrazine into this aqueous solution, an oxygen-free film-forming aqueous solution can be generated in the circulation pipe 31. By injecting the inert gas into the aqueous solution in the surge tank 32, the amount of hydrazine injected into the circulation pipe 31 can be reduced in order to generate the film-forming aqueous solution.

It is determined whether the formation of the nickel metal film is completed (step S6). If the nickel metal film 82 formed on the inner surface of the purification system pipe 18 is insufficient (when the nickel metal present on the inner surface is ^{less than 50 μg / cm 2} ), each of the steps S4 to S6 is repeated. When the nickel metal existing on the inner surface of the purification system pipe 18 reaches 50 μg / cm ² , the injection pump 38 is stopped, the valve 40 is closed, the injection of the nickel formate aqueous solution into the circulation pipe 31 is stopped, and the injection pump 43 is used. Is stopped, the valve 45 is closed, the injection of the hydrazine aqueous solution into the circulation pipe 31 is stopped, and the formation of the nickel metal film on the inner surface of the purification system pipe 18 is completed. When the elapsed time from injecting the nickel formate aqueous solution into the circulation pipe 31 reaches the set time, it is determined ^{that the nickel metal existing on the inner surface of the purification system pipe 18 has reached 50 μg / cm 2.} The set time is determined by measuring in advance the time until the nickel metal on the surface of the carbon steel test piece reaches 50 μg / cm ^2.

Decompose formic acid and reducing agent (step S7). The opening degree of the valve 69 is narrowed down, the valve 70 is opened, and the film-forming aqueous solution 83 containing nickel ions, formic acid, and hydrazine is passed through the cation exchange resin tower 53. As a result, nickel ions are adsorbed on the cation exchange resin, and the nickel ion concentration in the film-forming aqueous solution 83 decreases. Subsequently, the valve 75 is opened to close a part of the opening degree of the valve 74, and a part of the film-forming aqueous solution 83 containing nickel ions, formic acid, and hydrazine boosted by the circulation pump 35 is passed through the pipe 76 to the decomposition device 55. Lead to. Further, the hydrogen peroxide in the chemical solution tank 57 is supplied to the decomposition device 55 through the supply pipe 59 and the pipe 76. Formic acid, which is the counterion of nickel ions, and hydrazine, which is the reducing agent, contained in the film-forming aqueous solution 83 are decomposed into carbon dioxide, nitrogen, and water by the action of the activated carbon catalyst and hydrogen peroxide in the decomposition apparatus 55. ..

Purify the film-forming aqueous solution in which formic acid and the reducing agent are decomposed (step S8). After the formic acid and hydrazine (reducing agent) were decomposed, the valve 74 was opened, the valve 75 was closed, the supply of the film-forming aqueous solution 83 having the reduced concentrations of formic acid and hydrazine to the decomposition device 55 was stopped, and the valve 67 was opened. The valve 66 is closed, the valve 72 is opened, and a part of the opening degree of the valve 69 is closed. At this time, the valve 70 is closed. The circulation pumps 35 and 34 are driven. The film-forming aqueous solution 83 with reduced formic acid and hydrazine concentrations returned from the purification system pipe 18 to the circulation pipe 31 is cooled by the cooler 52 until it reaches 60 ° C. Further, a film-forming aqueous solution 83 at 60 ° C. having reduced concentrations of formic acid and hydrazine is guided to the mixed bed resin tower 54, and nickel ions, other cations and anions remaining in the film-forming aqueous solution 83 are mixed. It is adsorbed and removed by the cation exchange resin and the anion exchange resin in the floor resin tower 54 (first purification step). A 60 ° C. film-forming aqueous solution having reduced concentrations of formic acid and hydrazine is circulated in the circulation pipe 31 and the purification system pipe 18 until each of the above ions is substantially eliminated. The film-forming aqueous solution in which each ion is substantially eliminated is water at substantially 60 ° C., but contains ^{a trace amount of iron ions (Fe 3+) remaining.}

An aqueous solution of the complex ion forming agent is injected (step S9). After the first purification step is completed, the valve 69 is opened, the valve 72 is closed, the valve 79 is opened, water is passed through the ejector 61, and the aqueous ammonia solution, which is the aqueous complex ion forming agent, is sucked from the hopper. This aqueous ammonia solution is supplied to water at 60 ° C. containing a trace amount of iron ions in the surge tank 32. An aqueous solution at 60 ° C. containing a small amount of Fe ³⁺ and ammonia is boosted by the circulation pump 34 from the surge tank 32 and supplied to the purification system pipe 18 by the circulation pipe 31. This 60 ° C. aqueous solution containing ammonia reaches the circulation pump 35 along the formed closed loop, is boosted by the circulation pump 35, and is returned to the surge tank 32.

An aqueous platinum ion solution is injected (step S10). After the ammonia injection is completed, the valve 50 is opened to drive the injection pump 48. The aqueous solution at 60 ° C. containing ammonia flowing in the circulation pipe 31 is maintained at 60 ° C. by heating with the heater 33. An aqueous solution containing platinum ions in a chemical tank 47 through an injection pipe 49 in an aqueous solution containing ammonia at 60 ° C. flowing in the circulation pipe 31 (for example, sodium hexahydroxoplatinate hydrate (Na ₂ [Pt (OH) _{6) 6} ] ・_{An aqueous solution of nH 2} O)) is injected. The concentration of platinum ions in this aqueous solution to be injected is, for example, 1 ppm. In the aqueous solution of sodium hexahydroxoplatinate hydrate, platinum is in an ionic state. An aqueous solution at 60 ° C. containing platinum ions and ammonia is supplied from the circulation pipe 31 to the purification system pipe 18 by driving the circulation pumps 34 and 33, and is returned from the purification system pipe 18 to the circulation pipe 31. The aqueous solution containing platinum ions circulates in a closed loop including the circulation pipe 31 and the purification system pipe 18.

Immediately after the start of injection, platinum at the connection point of the aqueous solution of _{Na 2} [Pt (OH) ₆ ] and nH ₂ O injected into the circulation pipe 31 from the chemical solution tank 47 through the connection point between the circulation pipe 31 and the injection pipe 49. _{The injection rate of the aqueous solution of Na 2} [Pt (OH) ₆ ] · nH ₂ O into the circulation pipe 31 is calculated in advance so that the concentration becomes the set concentration, for example, 1 ppm, and further, the inside of the circulation pipe 31 is A chemical tank 47 required to make a predetermined amount of platinum adhere to the surface of a nickel metal film formed on the inner surface of a purification system pipe 18 by setting the concentration of platinum ions in a flowing aqueous solution containing ammonia at 60 ° C. to the set concentration. the amount of _{Na 2 [Pt (OH) 6} ] · nH 2 O in aqueous solution filled calculated, filling amount of the aqueous solution of the calculated _{Na 2 [Pt (OH) 6} ] · nH 2 O in the chemical tank 47 To do. Calculated _{Na 2 [Pt (OH) 6} ] · nH 2 the rotational speed of the infusion pump 48 is controlled in accordance with the injection rate of O in water to the circulation pipe 31 of the, _Na 2 in the chemical liquid tank 47 [Pt (OH ) _6] · nH to ₂ O aqueous solution is injected into the circulation pipe 31.

Inject the reducing agent (step S11). The valve 45 of the reducing agent injection device 41 is opened to drive the injection pump 43, and an aqueous solution of hydrazine, which is a reducing agent in the chemical solution tank 42, flows through the injection pipe 44 in the circulation pipe 31 and contains platinum ions and ammonia 60. Infused into an aqueous solution at ° C. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 100 ppm.

The hydrazine aqueous solution is a _{circulation pipe after the 60 ° C. aqueous solution containing ammonia and Na 2} [Pt (OH) ₆ ] and nH ₂ O reaches the connection point between the injection pipe 44 and the circulation pipe 31 which is the injection point of the hydrazine aqueous solution. Injected into 31. In this case, an aqueous solution at 60 ° C. containing platinum ions, hydrazine and ammonia is supplied from the circulation pipe 31 to the purification system pipe 18. However, more preferably, the hydrazine aqueous solution is circulated immediately after all _{the predetermined amounts of Na 2} [Pt (OH) ₆ ] and nH ₂ O aqueous solutions filled in the chemical tank 47 have been injected into the circulation pipe 31. It is desirable to inject into 31. In this case, an aqueous solution at 60 ° C. containing ammonia and platinum ions is supplied from the circulation pipe 31 to the purification system pipe 18, and after the injection of the platinum ion aqueous solution into the circulation pipe 31 is completed, platinum ions, hydrazine and ammonia A 60 ° C. aqueous solution 85 (see FIG. 6) containing the above is supplied from the circulation pipe 31 to the purification system pipe 18.

In the case of the former injection of the hydrazine aqueous solution, the reduction reaction of converting platinum ions to platinum by hydrazine first occurs in the aqueous solution containing hydrazine and platinum ions flowing in the circulation pipe 31, whereas the latter In the case of injecting an aqueous hydrazine solution, platinum ions are already adsorbed on the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18, and the adsorbed platinum ions are reduced by hydrazine. The amount of platinum 84 adhered to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18 is further increased (see FIG. 6).

Immediately after the start of injection of the hydrazine aqueous solution, the hydrazine concentration at the connection point of the hydrazine aqueous solution injected from the chemical solution tank 42 through the connection point of the circulation pipe 31 and the injection pipe 44 is set in advance so as to be a set concentration, for example, 100 ppm. , The injection speed of the hydrazine aqueous solution into the circulation pipe 31 is calculated, and the hydrazine in the aqueous solution containing platinum ions at 60 ° C. flowing in the circulation pipe 31 is set to the set concentration, and is formed on the inner surface of the purification system pipe 18. The amount of the hydrazine aqueous solution to be filled in the chemical tank 42 required to reduce the platinum ions adsorbed on the surface of the nickel metal film 82 to the platinum 84 was calculated, and the calculated amount of the hydrazine aqueous solution was filled into the chemical tank 42. To do. The rotation speed of the injection pump 43 is controlled according to the calculated injection speed of the hydrazine aqueous solution into the circulation pipe 31, and the hydrazine aqueous solution in the chemical tank 42 is injected into the circulation pipe 31.

_{When the entire amount of the aqueous solution of Na 2} [Pt (OH) ₆ ] and nH ₂ O (the aqueous solution containing platinum ions) in the chemical tank 47 was injected into the circulation pipe 31, the drive of the injection pump 48 was stopped. And close the valve 50. As a result, the injection of the aqueous solution containing platinum ions into the circulation pipe 31 is stopped. Further, when the entire amount of the hydrazine aqueous solution (reducing agent aqueous solution) in the chemical liquid tank 42 is injected into the circulation pipe 31, the drive of the injection pump 43 is stopped and the valve 45 is closed. As a result, the injection of the hydrazine aqueous solution into the circulation pipe 31 is stopped.

Since the platinum ions adsorbed on the surface of the nickel metal film 82 are reduced by the injected hydrazine to become platinum 84, the platinum 84 adheres to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18 (see FIG. 6). ).

In this embodiment, the ammonia contained in the aqueous solution 85 in contact with the nickel metal film 82 ^{reacts with a trace amount of iron ions (Fe 3+} ) contained in the aqueous solution 85 to generate iron-ammonia complex ions. Therefore, the iron ion concentration in the aqueous solution 85 decreases, and the iron ions contained in the aqueous solution 85 do not precipitate as iron hydroxide and magnetite. Platinum ions contained in the aqueous solution 85 do not adhere to iron hydroxide and magnetite as platinum, and the amount of platinum adhering to the nickel metal film 82 increases.

It is determined whether the adhesion of platinum is completed (step S12). When the elapsed time from the injection of the platinum ion aqueous solution and the reducing agent aqueous solution reaches a predetermined time, it is determined that the adhesion of a predetermined amount of platinum to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18 is completed. .. When the elapsed time does not reach the predetermined time, each step of steps S10 to S12 is repeated.

The aqueous solution remaining in the purification system pipe 18 and the circulation pipe 31 is purified (step S13). After it was determined that the adhesion of platinum 84 to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18 was completed, the valve 72 was opened, a part of the opening of the valve 69 was closed, and the circulation pump 35 was used. A pressurized 60 ° C. aqueous solution containing platinum ions, hydrazine, and ammonia is supplied to the mixed bed resin tower 54. Platinum ions, other metal cations (for example, sodium ions), hydrazine, ammonia and OH groups contained in the aqueous solution are adsorbed on the ion exchange resin in the mixed bed resin tower 54 and removed from the aqueous solution (No. 1). 2 Purification process).

Treat the waste liquid (step S14). After the second purification step is completed, the circulation pipe 31 and the waste liquid treatment device (not shown) are connected by a high pressure hose (not shown) having a pump (not shown). After the completion of the second purification step, the aqueous solution which is a radioactive waste liquid remaining in the purification system pipe 18 and the circulation pipe 31 drives the pump and passes through the circulation pipe 31 to the waste liquid treatment device (not shown) through the high pressure hose. It is discharged and processed by a waste liquid treatment device. After the aqueous solution in the purification system pipe 18 and the circulation pipe 31 is discharged, the cleaning water is supplied into the purification system pipe 18 and the circulation pipe 31, and the circulation pumps 34 and 35 are driven to clean the inside of these pipes. After the cleaning is completed, the cleaning water in the purification system pipe 18 and the circulation pipe 31 is discharged to the above-mentioned waste liquid treatment device.

As described above, the portion of the purification system piping 18 between the valve 23 and the valve 25 upstream of the non-regenerative heat exchanger 21 and the portion between the valve 26 and the valve 32A downstream of the regenerative heat exchanger 20 respectively. Each process of forming the nickel metal film 82 on the inner surface of the metal film 82 and adhering the platinum 84 on the nickel metal film 82 is completed. A nickel metal film 82 to which platinum 84 is attached is not formed on the inner surface of the purification system pipe 18 at a portion downstream of the valve 25 and upstream of the valve 26.

The film forming apparatus is removed from the piping system (step S15). After each step of steps S1 to S14 is performed, each of the film forming apparatus 30 and 30A is removed from the purification system pipe 18, and the purification system pipe 18 is restored.

The nuclear plant is started (step S16). After the refueling and maintenance and inspection of the BWR plant 1 are completed, there is a purification system pipe 18 having a nickel metal film 82 to which platinum 84 is attached formed on the inner surface in order to start operation in the next operation cycle. BWR plant 1 is started.

The furnace water in the temperature range of 130 ° C. or higher and lower than 200 ° C. is brought into contact with the nickel metal film to which platinum is attached (step S17). When the BWR plant 1 is started, the reactor water existing in the downcomer in the RPV3 is supplied to the 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. The furnace water in the downcomer flows into the purification system pipe 18 via the recirculation system pipe 6, and eventually flows into the water supply pipe 11 and is returned to the RPV3.

A control rod (not shown) is pulled out from the core 4, the core 4 changes from a subcritical state to a critical state, and the reactor water in the core 4 is heated by the heat generated by the nuclear fission of the nuclear fuel material in the fuel rod. No steam is generated in the core 4. Further, the control rods are pulled out from the core 4, and in the process of raising and lowering the temperature of the reactor 2, the pressure in the RPV 3 is raised to the rated pressure, and the heat generated by the fission heats the reactor water to heat the reactor water in the RPV 3. The temperature becomes the rated temperature (280 ° C.). After the pressure in the RPV3 reaches the rated pressure and the reactor water temperature rises to the rated temperature, the reactor output is rated by further pulling out the control rods from the core 4 and increasing the flow rate of the reactor water supplied to the core 4. It is increased to the output (100% output). The rated operation of the BWR plant 1, which maintains the rated output, is continued until the end of the operation cycle. When the reactor power rises to, for example, 10%, the steam generated in the core 4 is supplied to the turbine 9 through the main steam pipe 8 to start power generation.

The furnace water 86 contains oxygen and hydrogen peroxide. Oxygen and hydrogen peroxide are produced by radiolysis of furnace water 86 in RPV3. The furnace water 86 containing oxygen in the RPV3 is guided from the recirculation system pipe 6 into the purification system pipe 18 in a state where the purification system pump 19 is driven, and is formed on the inner surface of the purification system pipe 18. , Contact with the nickel metal film 82 to which platinum 84 is attached (see FIG. 7). Due to the heating of the furnace water by the heat generated by the above-mentioned nuclear fission, the temperature of the furnace water 86 in contact with the nickel metal film 82 rises and eventually reaches 130 ° C. or higher, and finally reaches 280 ° C. at the rated output. To rise.

The temperature of the furnace water 86 differs greatly before and after the regenerated heat exchanger 20 and the non-regenerated heat exchanger 21. When the temperature of the furnace water 86 in the RPV3 is 280 ° C., the furnace water 86 at about 280 ° C. flows in the portion of the purification system pipe 18 upstream of the regenerated heat exchanger 20. As a result of heat exchange in the regenerative heat exchanger 20, the temperature of the furnace water 86 flowing out from the regenerative heat exchanger 20 to the valve 25 side drops to a range of about 200 ° C. to 150 ° C. Further, in the non-regenerative heat exchanger 21, the furnace water 86 drops to a temperature in the range of 50 ° C. to about room temperature, and is supplied to the furnace water purification device 22 containing the ion exchange resin within this temperature range. Since the furnace water 86 flowing out of the furnace water purification device 22 is used as water supply, it is heated in the range of about 150 ° C. to 200 ° C. by the regenerative heat exchanger 20 and then joins the water supply flowing through the water supply pipe 11.

The part of the purification system pipe 18 between the valve 23 and the regenerative heat exchanger 20 during the period when the BWR plant 1 is started and the pressure in the RPV 3 rises to the rated pressure (the temperature of the furnace water at this time is 280 ° C.). The furnace water 86 flowing through the purification system pipe 18, the furnace water 86 flowing through the portion of the purification system pipe 18 between the regenerative heat exchanger 20 and the valve 25, and the furnace water flowing through the portion of the purification system pipe 18 between the valve 26 and the valve 32A. 86 has a temperature within the temperature range of 130 ° C. or higher and lower than 200 ° C., although there is a time lag. In the process of raising and boosting the temperature of the reactor 2, the temperature of the reactor water in the RPV3 rises to a higher temperature exceeding 130 ° C. as the pressure in the RPV3 rises.

Therefore, the surface of the nickel metal film 82 to which platinum 84 is attached is formed on the inner surface of the purification system pipe 18 between the valve 23 and the valve 25 and the inner surface of the purification system pipe 18 between the valve 26 and the valve 32A. However, by contacting with the furnace water 86 containing oxygen in the temperature range of 130 ° C. or higher and lower than 200 ° C., the purification system pipe 18 and its nickel metal film 82 are heated to the same temperature as the furnace water 86. The oxygen contained in the furnace water 86 is transferred into the nickel metal film formed on the inner surface of the purification system pipe 18 between the valve 23 and the valve 25 and between the valve 26 and the valve 32A, and is a carbon steel member. Fe contained in the purification system pipe 18 becomes Fe ²⁺ and moves into the nickel metal film (see FIG. 8). In a high temperature environment of 130 ° C. or higher and lower than 200 ° C., oxygen contained in the furnace water 86 and Fe ²⁺ from the purification system pipe 18 are likely to move into the nickel metal film. When the oxygen concentration of the furnace water is low, the water molecules of the furnace water are decomposed by the corrosion of iron to generate oxygen, and this oxygen functions in the same manner as the oxygen contained in the above-mentioned furnace water 86. Due to the action of the platinum 84 adhering to the nickel metal film 82, the corrosion potentials of the purification system pipe 18 and the nickel metal film 82 are lowered, and a high temperature environment of 130 ° C. or higher and lower than 200 ° C. is formed, so that the inside of the nickel metal film 82 is formed. nickel reacts with the migrated oxygen and Fe ²⁺ in the nickel metal film _{82, Ni 1-x Fe 2} + x O 4 stable nickel ferrite x is 0 in (NiFe ₂ O ₄₎ is generated. At this time, the ease of incorporating nickel and iron into the ferrite structure is affected by platinum (precious metal), and in the presence of platinum, nickel is more easily incorporated than iron, so Ni _1-x Fe _{2 + x} Stable nickel ferrite with x 0 at O _{4 is produced.} Then, the nickel metal film 82 formed on the inner surface of the purification system pipe 18 _{is converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 87, and is converted between the valve 23 and the valve 25 and between the valve 26 and the valve 32A, respectively. The inner surface of the purification system pipe 18 in the above is covered with a stable nickel ferrite film 87 having platinum 84 adhered to the surface (see FIG. 9). _{Ni 1-x} Fe _{2 + x} O ₄ produced as described above from the nickel metal contained in the nickel metal film 82 covering the inner surface of the purification system pipe 18 in a high temperature environment of 130 ° C. or higher and lower than 200 ° C. In nickel ferrite (NiFe ₂ O ₄ ) in which x is 0, the crystal grows large, and even if a noble metal adheres, it is stable without being eluted in water like a _{Ni 0.7} Fe _2.3 O _{4 film, and the mother} It suppresses corrosion of carbon steel, which is a material, that is, purification system piping 18.

According to this embodiment, the corrosion potential of the purification system pipe 18 and the nickel metal film 82 is lowered by the platinum 84 adhering to the nickel metal film 82, and in a high temperature environment of 130 ° C. or higher and lower than 200 ° C., as described above. As described above, the nickel ferrite film 87 generated from the nickel metal film 82 and having _{x of 0 in Ni 1-x} Fe _{2 + x} O ₄ has the action of the adhered platinum 84 even during the operation of the BWR plant 1. It is a stable nickel ferrite film that does not elute into the furnace water. The stable nickel ferrite film 87 thus generated, which does not elute into the furnace water due to the action of the adhered platinum 84, is more than _{the Ni 0.7} Fe _2.3 O _{4 film formed in the low temperature range of 60 ° C to 100 ° C.} Corrosion of the purification system pipe 18 can be suppressed for a long period of time. Specifically, the stable nickel ferrite film 87 formed on the inner surface of the purification system pipe 18 does not elute due to the action of the adhered platinum 84, and has a plurality of operation cycles, for example, five operation cycles (for example, five operation cycles). The inner surface of the purification system pipe 18 can be covered for 5 years). In this way, since the stable nickel ferrite film 87 can cover the inner surface of the purification system pipe 18 for a long period of time, corrosion of the purification system pipe 18 is suppressed for a long period of time.

Carbon steel members tend to be particularly corroded when in contact with water at temperatures in the range of 150 ° C to 200 ° C. During the rated operation of the BWR plant 1, the purification system pipe 18 is located upstream of the furnace water purification device 22 between the regenerated heat exchanger 20 and the non-regenerating heat exchanger 21 and downstream of the furnace water purification device 22. On the side, the portion between the regenerative heat exchanger 20 and the connection point between the purification system pipe 18 and the water supply pipe 11 comes into contact with the furnace water 86 having a temperature in the range of 150 ° C. to 200 ° C. Therefore, in the purification system piping 18, corrosion increases in these parts. In this embodiment, since a stable nickel ferrite film 87 is formed on the inner surface of the purification system pipe 18 between the valve 23 and the valve 25 and between the valve 26 and the valve 32A, those portions where corrosion increases. Corrosion is suppressed over a long period of time by the formed stable nickel ferrite film 87. The purification system pipe 18 between the valve 23 and the regenerative heat exchanger 20 also has a stable nickel ferrite film 87 formed on the inner surface, so that corrosion is suppressed.

In order to suppress corrosion in the portion of the purification system piping 18 where corrosion increases, the valve 25 should be as close to the non-regenerative heat exchanger 21 as possible, and the valve 26 should be as close to the regenerated heat exchanger 20 as possible. 32A should be installed in the purification system pipe 18 as close to the connection point between the purification system pipe 18 and the water supply pipe 11 as possible.

Further, the stable nickel ferrite film 87 formed on the inner surface of the purification system pipe 18 can suppress the adhesion of radionuclides to the purification system pipe 18 over a plurality of operation cycles. Therefore, the number of times of chemical decontamination performed on the purification system pipe 18 can be reduced. In particular, since a stable nickel ferrite film 87 is formed on the inner surface of the purification system pipe 18 between the valve 23 and the non-regenerative heat exchanger 21 on the upstream side of the furnace water purification device 22, purification is particularly performed. Adhesion of radionuclides to the inner surface of that portion of the system pipe 18 can be suppressed.

According to this embodiment, a film-forming aqueous solution containing nickel ions and a reducing agent (for example, hydrazine) is brought into contact with the inner surface of the purification system pipe 18, and the inner surface of the purification system pipe 18 is brought into contact with the furnace water. A nickel metal film 82 can be formed to cover the film. ^{The nickel metal film 82 can prevent the elution of Fe 2+} from the purification system pipe 18 into the film-forming aqueous solution during the noble metal adhesion treatment, and the precious metal (for example, platinum) adheres to the inner surface of the purification system pipe 18. Is ^{no longer hindered by the elution of Fe 2+} , and is required for the adhesion of the noble metal to the inner surface thereof (specifically, the adhesion of the noble metal to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18). You can save time. Further, the noble metal can be efficiently adhered to the inner surface thereof, and the amount of the noble metal adhering to the inner surface of the purification system pipe 18 increases.

In this embodiment, the nickel metal film 82 formed on the inner surface of the purification system pipe 18 contains 50 μg / cm ² of nickel metal. In this way, in the ^{presence of 50 μg / cm 2} of nickel metal, the nickel metal film 82 covers the entire inner surface of the purification system piping 18 in contact with the film-forming aqueous solution, and the BWR plant in the next operation cycle After the start-up, the contact of the furnace water flowing in the purification system pipe 18 with the base material of the purification system pipe 18 is blocked by the nickel metal film 82. Therefore, the corrosion of the purification system pipe 18 by the furnace water is suppressed, and further, the radionuclide contained in the furnace water is not taken into the base material of the purification system pipe 18.

The nickel metal film 82 formed on the inner surface of the purification system pipe 18 not only shortens the time required for platinum to adhere to the purification system pipe 18, but also, in combination with the action of the adhered platinum 84, purifies the system pipe. It contributes to the formation of a stable nickel ferrite film 87 on the inner surface of 18 which is not eluted into the furnace water even by the adhered platinum.

In the formation of the nickel metal film 82 on the inner surface of the purification system pipe 18, the nickel ions contained in the film forming aqueous solution are replaced with the iron ions contained in the purification system pipe 18 and taken into the inner surface of the purification system pipe 18 to form the film. The nickel ions incorporated on the inner surface of the hydrazine (reducing agent) contained in the aqueous solution are reduced to nickel metal. As described above, 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 strong adhesion to the base material of the purification system pipe 18. Therefore, the formed nickel metal film 82 does not come off from the purification system pipe 18.

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

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

A method for suppressing corrosion of carbon steel members of the plant of Example 2 which is another embodiment of the present invention will be described with reference to FIG. The method for suppressing corrosion of carbon steel members of the plant of this embodiment is applied to a carbon steel water supply pipe of a BWR plant.

In this embodiment, each step of steps S1 to S17 in the method for suppressing corrosion of carbon steel members of the plant of Example 1 is carried out. Each step of steps S1 to S15 is carried out while the operation of the BWR plant 1 is stopped. In step S1 of this embodiment, one end of the circulation pipe 31 of the film forming apparatus 30 on the on-off valve 78 side is connected to the first valve (not shown) provided in the water supply pipe 11 at the outlet of the low-pressure feed water heater 14. The other end of the circulation pipe 31 on the on-off valve 62 side is connected to a second valve (not shown) provided in the water supply pipe 11 at the inlet of the high-pressure feed water heater 16. The first valve is provided in the water supply pipe 11 at a position as close as possible to the outlet of the low-pressure feed water heater 14, and the second valve is provided at a position as close as possible to the inlet of the high-pressure feed water heater 16. The connection of both ends of the circulation pipe 31 to the first valve and the second valve is performed in the same manner as the connection to each of the valve 23 and the valve 25 of the circulation pipe 31 in the first embodiment. Although no radionuclides are attached to the inner surface of the feed water pipe 11 to be constructed, an oxide film is formed due to the flow of high-temperature water. Therefore, in step S2, the low-pressure feed water heater 14 and the high-pressure feed water heater Chemical decontamination is carried out for the purpose of removing the oxide film on the inner surface of the water supply pipe 11 between 16.

After that, each of the above-mentioned steps S3 to S17 is carried out in order. Each step of steps S4 and S5 is carried out, and an aqueous solution containing nickel ions and formic acid and having a pH of 4.0 at 90 ° C. is supplied from the film forming apparatus 30 to the feed water heater 11 between the low pressure feed water heater 14 and the high pressure feed water heater 16. Is supplied to. The aqueous solution circulates in a closed loop including the water supply pipe 11 and the circulation pipe 31. As a result, a nickel metal film is formed on the inner surface of the water supply pipe 11 between the low-pressure feed water heater 14 and the high-pressure feed water heater 16.

After the determination in step S6 becomes "Yes", steps S7 and S8 are carried out. Each step of steps S9 to S11 is carried out, and an aqueous solution at 60 ° C. containing platinum ions, ammonia and hydrazine is supplied to the feed water pipe 11 between the low pressure feed water heater 14 and the high pressure feed water heater 16. Platinum adheres to the surface of the nickel metal film formed on the inner surface of the water supply pipe 11. After the determination in step S12 becomes "Yes", each step of steps S13 to S15 is carried out. In step S15, the circulation pipe 31 is removed from the water supply pipe 11, and the water supply pipe 11 is restored to its original state.

After that, the BWR plant 1 is started in step S16, and step S17 is carried out. In step S17, the steam supplied from the RPV 3 to the turbine 9 is condensed by the condenser 10 in the process of increasing the reactor output after the process of raising and boosting the temperature of the reactor 2 is completed, and the water generated by this condensation is condensed. It is supplied to the RPV 3 as water supply through the water supply pipe 11. The feed water flowing through the feed water pipe 11 is heated by the low-pressure feed water heater 14. Eventually, feed water having a temperature within the temperature range of 130 ° C. or higher and lower than 200 ° C. is discharged from the low-pressure feed water heater 14. Water supply at this temperature comes into contact with the nickel metal film 82 to which platinum 84 is attached, which is formed on the inner surface of the water supply pipe 11 between the low-pressure feed water heater 14 and the high-pressure feed water heater 16. As a result, as described in Example 1, the nickel metal film 82 is _{converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 87. In the rated operation of the BWR plant 1, water supply at 150 ° C. is discharged from the low-pressure feed water heater 14.

In this example, each effect produced in Example 1 can be obtained for the water supply pipe 11 other than the suppression of adhesion of radionuclides.

A method for suppressing corrosion of carbon steel members of the plant of Example 3 which is another embodiment of the present invention will be described with reference to FIG. The method for suppressing corrosion of carbon steel members of the plant of this embodiment is applied to each of the carbon steel purification system piping and the bottom drain piping of the BWR plant.
In this embodiment, each step of steps S1 to S17 in the method for suppressing corrosion of carbon steel members of the plant of Example 1 is carried out. Each step of steps S1 to S15 is carried out while the operation of the BWR plant 1 is stopped. In step S1 of this embodiment, both ends of the circulation pipe 31A of the film forming apparatus 30A are connected to the valves 26 and 32, respectively, as in the first embodiment. The end of the circulation pipe 31 of the film forming apparatus 30 on the on-off valve 78 side is branched into two, one branched end is connected to the valve 23, and the other branched end is connected to the bottom drain pipe 89. It is connected to the provided valve 88. One end of the bottom drain pipe 89 is connected to the bottom of the RPV3, and the other end of the bottom drain pipe 89 is connected to the purification system pipe 18 on the upstream side of the purification system pump 19. The other end of the circulation pipe 31 on the on-off valve 62 side is connected to the valve 25.

After that, each step of steps S2 to S17 described above is carried out in order. Each of the steps S4 and S5 is carried out, and an aqueous solution containing nickel ions and formic acid and having a pH of 4.0 is supplied from the film forming apparatus 30 to the purification system pipe 18 and the bottom drain pipe 89. Further, the aqueous solution is supplied from the film forming apparatus 30A to the portion of the purification system pipe 18 between the valve 26 and the valve 32A. As a result, the nickel metal film is formed on the inner surface of the bottom drain pipe 89, the inner surface of the purification system pipe 18 between the valve 23 and the valve 25, and the inner surface of the purification system pipe 18 between the valve 26 and the valve 32A. Is formed in each.

After the determination in step S6 becomes "Yes", steps S7 and S8 are carried out. Further, each of the steps S9 to S11 is carried out, and platinum is adhered to the surface of the nickel metal film formed on the inner surfaces of the bottom drain pipe 89 and the purification system pipe 18. After the determination in step S12 becomes "Yes", each step of steps S13 to S15 is carried out. In step S15, the circulation pipe 31 is removed from the bottom drain pipe 89 and the purification system pipe 18, and the circulation pipe 31A is removed from the purification system pipe 18, and the bottom drain pipe 89 and the purification system pipe 18 are restored to their original state.

After that, the BWR plant 1 is started in step S16, and step S17 is carried out. In step S17, the furnace water in the RPV3 is guided to the purification system pipe 18, and the furnace water is also supplied to the bottom drain pipe 89 by opening the valve 88. When the nickel metal film having platinum adhered to the inner surfaces of the bottom drain pipe 89 and the purification system pipe 18 comes into contact with furnace water having a temperature within the temperature range of 130 ° C. or higher and lower than 200 ° C., the nickel metal film becomes stable. It is converted into a nickel ferrite (NiFe ₂ O _{4) film.}

In this example, each effect produced in Example 1 can be obtained.

The method for suppressing corrosion of the carbon steel member of the plant of Example 4, which is another preferred embodiment of the present invention, will be described below with reference to FIGS. 14 and 15. The method for suppressing corrosion of carbon steel members of this embodiment is applied to purification system piping of a BWR plant that has experienced operation in at least one operation cycle.

In this embodiment, the steps S1 to S15 and S17 carried out in the first embodiment, and the new steps S18 and S19 are carried out. In this example, the film forming apparatus 30 used in Example 1 is used in each of the steps S1 to S14, and a new heating system 91 is used in each of the steps S18 and S17.

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

The film forming apparatus is removed from the piping system (step S14). In this embodiment, after each step of steps S1 to S13 is performed, the film forming apparatus 30 connected to the purification system pipe 18 is removed from the purification system pipe 18. One end of the circulation pipe 31 of the film forming apparatus 30 is removed from the flange of the valve 23, and the other end of the circulation pipe 31 is removed from the flange of the valve 25.

The heating system is connected to the piping system (step S18). One end of the circulation pipe 92 (third pipe) of the heating system 91 on the on-off valve 98 side is connected to the flange of the valve 23, and the circulation pipe 92 is connected to the purification system pipe 18. The other end of the circulation pipe 92 on the on-off valve 97 side is connected to the flange of the valve 25, and the circulation pipe 92 is connected to the purification system pipe 18 between the regenerative heat exchanger 20 and the non-regenerative heat exchanger 21. Both ends of the circulation pipe 92 are connected to the purification system pipe 18, and a closed loop including the purification system pipe 18 and the circulation pipe 92 is formed.

Next, oxygen-containing water in a temperature range of 130 ° C. or higher and lower than 200 ° C. is brought into contact with the nickel metal film to which platinum is attached (step S17). Water containing oxygen is filled in the closed loop including the circulation pipe 92 and the purification system pipe 18. The circulation pump 93 is driven to circulate oxygenated water in its closed loop. The rotation speed of the circulation pump 93 is increased to a certain rotation speed, and then the opening degree of the valve 95 is gradually decreased to increase the pressure of the water discharged from the circulation pump 93. The heating device 94 heats water containing oxygen circulating in the closed loop to raise the temperature of the water. In this way, the temperature of the water is raised while increasing the pressure of the water discharged from the circulation pump 93. After the valve 95 is fully closed, the rotational speed of the circulation pump 93 is further increased. By such an operation, when the pressure of the water circulating in the closed loop rises to the range of, for example, 0.3 MPa to 1.4 MPa, the temperature of the circulating water is about 133.5 ° C. to about 195.0 ° C. Rise within the range of. The pressure of the circulating water is adjusted, and the temperature of the water is adjusted to a temperature range of 130 ° C. or higher and lower than 200 ° C., for example, 150 ° C. The temperature of the water circulating in the closed loop is maintained at 150 ° C. while converting the nickel metal film formed on the inner surface of the purification system pipe 18 into a stable nickel ferrite film.

Water 86A at 150 ° C. containing oxygen is supplied from the circulation pipe 92 to the purification system pipe 18, and comes into contact with the nickel metal film 82 to which platinum 84 is attached, which is formed on the inner surface of the purification system pipe 18 (see FIG. 7). .. The purification system pipe 18 is surrounded by a heat insulating material (not shown) except for the vicinity of the valves 23 and 25 to which both ends of the circulation pipe 92 are connected. When the water 86A at 150 ° C. comes into contact with the nickel metal film 82, each of the purification system pipe 18 and the nickel metal film 82 is heated, and the respective temperatures reach 150 ° C.

Since each of the oxygen-containing water 86A, the purification system pipe 18 and the nickel metal film 82 reaches 150 ° C., oxygen (O ₂ ) contained in the water 86A and some water molecules contained in the water 86A are formed. Oxygen moves into the nickel metal film 82, and Fe contained in the purification system pipe 18 becomes Fe ²⁺ and moves into the nickel metal film 82 (see FIG. 8). Oxygen contained in the water 86A easily moves independently in the water 86A at 130 ° C. or higher, and easily enters the nickel metal film 82. Due to the action of platinum 84 adhering to the nickel metal film 82, the corrosion potential of the purification system pipe 18 and the nickel metal film 82 is lowered. Due to the decrease in the corrosion potential of the nickel metal film 82 and the formation of a high temperature environment at 150 ° C., the nickel in the nickel metal film 82 reacts with ^{the oxygen and Fe 2+} _{transferred into the nickel metal film 82, and Ni 1-x} Fe. _{In 2 + x} O ₄ , x is 0, and stable nickel ferrite (NiFe ₂ O ₄ ) that does not elute even by the action of platinum is produced. Therefore, the nickel metal film 82 formed on the inner surface of the purification system pipe 18 _{is converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 87, and the nickel ferrite film 87 is formed on the valves 23 and 25 of the purification system pipe 18. It will cover the inner surface of the intervening part (see FIG. 9). Platinum is attached to the surface of the stable nickel ferrite film 87.

The heating system is removed from the piping system (step S19). After the nickel ferrite film 87 is formed so as to cover the inner surface of the purification system pipe 18, the heating system 91 connected to the purification system pipe 18 is removed from the purification system pipe 18. After that, the purification system pipe 18 is restored.

In this embodiment, as in the first embodiment, both ends of the circulation pipe 31A of the film forming apparatus 30A are connected to the valves 26 and 32, respectively, and the purification system pipe 18 is located between the valve 26 and the valve 32A. When a nickel metal film having platinum adhered to the surface is formed on the inner surface of the portion, the film forming device 30A is removed from the purification system pipe (step S15) after the step S14 is completed, and the circulation pipe of another heating system 91 is formed. Both ends of 92 are connected to valves 26 and 32, respectively. Then, water at 150 ° C. containing oxygen is supplied from the heating system 91 to the portion of the purification system pipe 18 between the valve 26 and the valve 32A, as described above. The platinum-adhered nickel metal film formed on the inner surface of the portion of the purification system pipe 18 between the valve 26 and the valve 32A is converted into a stable nickel-ferrite film to which platinum is adhered (step S17). After that, another heating system 91 is also removed from the purification system pipe 18.

A BWR plant having a purification system pipe 18 on which a nickel ferrite film 87 with platinum 84 adhered is formed on the inner surface in order to start operation in the next operation cycle after refueling and maintenance and inspection of the BWR plant 1 are completed. 1 is started. Since the nickel ferrite film 87 is formed in the furnace water flowing in the purification system pipe 18, it does not come into direct contact with the base material of the purification system pipe 18.

In this example, each effect produced in Example 1 can be obtained. Further, in this embodiment, in order to convert the nickel metal film 82 formed on the inner surface of the purification system pipe 18 into the stable nickel ferrite film 87 by using the heating system 91, the conversion process in step S17 is performed by the BWR plant 1. Can be done while the operation is stopped. Therefore, when the BWR plant 1 is started, a stable nickel ferrite film 87 is already formed on the inner surface of the purification system pipe 18, and therefore, in the present embodiment, the stable nickel ferrite film 87 is formed on the inner surface of the purification system pipe 18. Corrosion of the purification system pipe 18 can be suppressed even before the film 87 is formed.

Further, in this embodiment, the heating system 91 is used to bring oxygen-containing water in a temperature range of 130 ° C. or higher and lower than 200 ° C. into contact with the nickel metal film 82 formed on the inner surface of the purification system pipe 18. The time required to heat the water to a predetermined temperature can be shortened. Further, the degree of pressure resistance required by the heating system 91 can be reduced.

A method for suppressing corrosion of carbon steel members of the plant of Example 5 which is another embodiment of the present invention will be described with reference to FIG. The method for suppressing corrosion of carbon steel members of the plant of this embodiment is applied to a carbon steel water supply pipe of a thermal power plant (hereinafter referred to as a thermal power plant).

The schematic configuration of the thermal power plant will be described with reference to FIG. The thermal power plant 115 includes a boiler 99, a high-pressure turbine 9A, a low-pressure turbine 9B, a condenser 10, and a water supply system, which are steam generators. The high-pressure turbine 9A and the low-pressure turbine 9B are connected to the boiler 99 by the main steam pipe 8. The moisture separation superheater 100 including the moisture separator 101 and the superheater 102 is installed in the main steam pipe 8 between the high pressure turbine 9A and the low pressure turbine 9B. The main steam control valve 110 is installed in the main steam pipe 8 existing between the boiler 99 and the high pressure turbine 9A. A steam supply pipe 106 connected to the main steam pipe 8 and provided with an on-off valve upstream of the main steam control valve 110 is connected to the superheater 102. The high-pressure turbine 9A and the low-pressure turbine 9B are connected to each other by one rotating shaft 104, and are further connected to the generator 103. The low pressure turbine 9B is connected to the condenser 10 by a steam passage 105. A heat transfer tube 113 through which seawater flows is arranged in the condenser 10. In the feed water pipe 11 connecting the condenser 10 and the boiler 99, a condenser pump 12, a low pressure feed water heater 14B, a low pressure feed water heater 14A, a feed pump 15 and a high pressure feed water heater 16 are provided from the condenser 10 to the boiler. It is installed in this order toward 99.

The bleeding pipe 107 connected to the high-pressure turbine 9A and the steam discharge pipe 112 connected to the superheater 102 are connected to the high-pressure feed water heater 16. The bleeding pipe 108A connected to the low-pressure turbine 9B and the drain pipe 111 connected to the moisture separator 101 are connected to the low-pressure feed water heater 14A. The bleeding pipe 108B connected to the low-pressure turbine 9B after the connection point of the bleeding pipe 108A is connected to the low-pressure feed water heater 14B. The drain water recovery pipe 109 connected to the high-pressure feed water heater 16 and the low-pressure feed water heaters 14A and 14B is connected to the condenser 10.

The steam generated in the boiler 99 is supplied to the high-pressure turbine 9A and the low-pressure turbine 9B, and is discharged to the condenser 10 through the steam passage 105. The steam discharged to the condenser 10 is condensed by the seawater supplied into the heat transfer tube 113 by the seawater pump 114 to become water. This water passes through the feed water pipe 11 as water supply, is heated by the high-pressure feed water heater 16 and the low-pressure feed water heaters 14A and 14B on the way, and is supplied to the boiler 99.

Also in this example, each step of steps S1 to S17 carried out in Example 1 is carried out. However, in this embodiment, the thermal power plant is started instead of the nuclear power plant in step S16, and the supply water instead of the furnace water is brought into contact with the nickel metal film in step S17.

In step S1, the film forming apparatus 30 described above is connected to the water supply pipe 11 between the low-pressure feed water heater 14A and the low-pressure feed water heater 14B. That is, one end of the circulation pipe 31 of the film forming apparatus 30 is connected to the first valve (not shown) installed in the water supply pipe 11 at a position close to the inlet of the low-pressure feed water heater 14A, and the other end of the circulation pipe 31. The portion is connected to a second valve (not shown) installed in the water supply pipe 11 at a position near the outlet of the low-pressure feed water heater 14B. Reduction decontamination is carried out in order to remove the oxide film formed on the inner surface of the portion of the water supply pipe 11 (step S2). After that, each of the above-mentioned steps S3 to S17 is carried out in order. Each step of steps S4 and S5 is carried out, and a nickel metal film is formed on the inner surface of the water supply pipe 11 between the low pressure feed water heater 14B and the low pressure feed water heater 14A.

After the determination in step S6 becomes "Yes", steps S7 and S8 are carried out. Further, each of the steps S9 to S11 is carried out, and platinum is adhered to the surface of the nickel metal film formed on the inner surface of the water supply pipe 11. After the determination in step S12 becomes "Yes", each step of steps S13 to S15 is carried out. In step S15, the circulation pipe 31 is removed from the water supply pipe 11, and the water supply pipe 11 is restored to its original state.

After that, the thermal power plant is started in step S16, and step S17 is carried out. In step S17, the steam supplied from the boiler 99 to the high-pressure turbine 9A and the low-pressure turbine 9B is condensed by the condenser 10, and the water generated by this condensation is supplied to the boiler 99 as water supply through the water supply pipe 11. The feed water flowing through the feed water pipe 11 is heated by the low-pressure feed water heaters 14B and 14A and the high-pressure feed water heater 16. Eventually, water supplied at a temperature within the temperature range of 130 ° C. or higher and lower than 200 ° C., for example, 160 ° C., is discharged from the low-pressure feed water heater 14B. The feed water at this temperature comes into contact with the nickel metal film 82 to which platinum 84 is attached, which is formed on the inner surface of the portion between the low-pressure feed water heater 14B and the low-pressure feed water heater 14A of the feed water pipe 11. As a result, as described in Example 1, the nickel metal film 82 is _{converted into a stable nickel ferrite (NiFe 2} O ₄ ) film 87.

In this example, each effect produced in the first embodiment can be obtained for the water supply pipe 11 other than the suppression of the adhesion of radionuclides.

In each of Examples 2, 3 and 5, each step S18 and S19 may be carried out instead of step S16, and the step S17 may be carried out using the heating system 91.

1 ... boiling water type nuclear power plant, 2 ... reactor pressure vessel, 4 ... core, 6 ... recirculation piping, 9 ... turbine, 9A ... high pressure turbine, 9B ... low pressure turbine, 11 ... water supply piping, 14, 14A, 14B ... Low pressure water supply heater, 16 ... High pressure water supply heater, 18 ... Purification system piping, 30, 30A ... Film forming device, 31, 31A, 92 ... Circulation piping, 33 ... Heater, 34, 35 ... Circulation pump, 36 ... Nickel ion injection device, 37, 42, 47, 57 ... Chemical tank, 38, 43, 48 ... Injection pump, 41 ... Reducing agent injection device, 46 ... Platinum ion injection device, 52 ... Cooler, 53 ... Cation exchange resin Tower, 54 ... Mixed bed resin tower, 55 ... Decomposition device, 56 ... Oxidizer supply device, 58 ... Supply pump, 82 ... Nickel metal film, 84 ... Platinum, 87 ... Nickel ferrite film, 89 ... Bottom drain piping, 91 ... Heating system, 99 ... boiler.

Claims (14)

A nickel metal film is formed on the surface of the carbon steel member of the plant in contact with water, the surface is covered with the nickel metal film, a noble metal is attached to the surface of the nickel metal film, and the nickel metal film to which the noble metal is attached is attached. The nickel metal film is formed and the noble metal is adhered to the nickel metal film by contacting it with water containing an oxidizing agent at 130 ° C. or higher and lower than 200 ° C., after the plant is stopped and before the plant is started. How to control corrosion of carbon steel parts of plants. The nickel metal film is formed by bringing a film-forming liquid containing nickel ions and a reducing agent into contact with the surface of the carbon steel member, and the noble metal is attached by forming an aqueous solution containing noble metal ions and a reducing agent. The method for suppressing corrosion of a carbon steel member of a plant according to claim 1, which is performed by bringing the nickel metal film into contact with the surface thereof. The method for suppressing corrosion of carbon steel members of a plant according to claim 2, wherein the pH of the film-forming liquid is in the range of 4.0 or more and 11.0 or less. The method for suppressing corrosion of a carbon steel member of a plant according to any one of claims 1 to 3, wherein the nickel metal film is formed after removing the oxide film formed on the carbon steel member. The method for suppressing corrosion of carbon steel members of a plant according to claim 4, wherein the removal of the oxide film is performed by chemical decontamination. The method for suppressing corrosion of carbon steel members of a plant according to claim 5, wherein at least one of formic acid and an oxidizing agent is injected into the reduction decontamination liquid used for the chemical decontamination. The method for suppressing corrosion of carbon steel members of a plant according to claim 6, wherein the timing for injecting formic acid, an oxidizing agent, or both into the oxalic acid solution is after the start of the decomposition step of the reducing agent. The film-forming liquid is supplied to the first pipe, which is the carbon steel member, in which the formation of the nickel metal film is communicated to the steam generator through the second pipe, and the film-forming liquid is used as the carbon steel member. It is performed on the inner surface by contacting the inner surface of the first pipe, which is the surface of the above.
The adhesion of the noble metal supplies the aqueous solution containing the noble metal ion and the reducing agent to the first pipe through the second pipe, and the aqueous solution is formed on the inner surface of the first pipe. The method for suppressing corrosion of carbon steel members of a plant according to claim 2, which is performed by bringing the film into contact with the surface. The carbon steel of the plant according to claim 8, wherein the film-forming liquid is circulated in the closed loop including the first pipe and the second pipe, and the aqueous solution containing the noble metal ion and the reducing agent is circulated in the closed loop. Method of suppressing corrosion of parts. The method for suppressing corrosion of carbon steel members of a plant according to claim 8 or 9, wherein the contact of the water at 130 ° C. or higher and lower than 200 ° C. with the nickel metal film to which the noble metal is attached is performed after the plant is started. .. The tenth aspect of claim 10, wherein the plant is a nuclear power plant, the steam generator is a nuclear reactor, and the water having a temperature of 130 ° C. or higher and lower than 200 ° C. is furnace water generated by heating in the nuclear reactor. How to control corrosion of carbon steel parts of a plant. The water of 130 ° C. or higher and lower than 200 ° C. is the water supplied to the steam generator, and is a high-pressure water supply heating device provided in the plant and a low-pressure water supply heating device arranged in front of the high-pressure water supply heating device. The method for suppressing corrosion of carbon steel members of a plant according to claim 10, wherein the water is heated by the low-pressure water supply heating device. After removing the second pipe from the first pipe, both ends of the third pipe are connected to the first pipe to form a closed loop including the first pipe and the third pipe, and the oxidant is contained. The supply of the water having a temperature of 130 ° C. or higher and lower than 200 ° C. to the first pipe is such that the water containing the oxidizing agent circulating in the closed loop is supplied to the first pipe at 130 ° C. or higher by a heating device provided in the third pipe. The conversion of the nickel metal film to which the noble metal is attached to the nickel ferrite film is performed by heating to a temperature range of less than ° C. and supplying the third pipe to the first pipe, and the conversion of the nickel metal film to the nickel ferrite film is performed on the inner surface of the first pipe. The nickel metal film formed in the above is brought into contact with the water containing the oxidizing agent supplied from the third pipe, and the nickel metal film is formed on the nickel ferrite film to which the noble metal is attached. The method for suppressing corrosion of carbon steel members of a plant according to claim 8, wherein the third pipe is removed from the first pipe after conversion. Any 1 of claims 8 to 13 in which a complex ion forming agent is injected into the aqueous solution containing the noble metal ion and the reducing agent, and the aqueous solution containing the complex ion forming agent is brought into contact with the surface of the nickel metal film. The method for suppressing corrosion of carbon steel members of a plant according to the section.

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