WO2019123788A1

WO2019123788A1 - Corrosion suppression method for carbon steel members in plant

Info

Publication number: WO2019123788A1
Application number: PCT/JP2018/037763
Authority: WO
Inventors: 秀幸細川; 伊藤　剛; 太田　信之; 大内　智; 慎太郎柳澤; 誠長瀬; 石田　一成
Original assignee: 日立Ｇｅニュークリア・エナジー株式会社
Priority date: 2017-12-20
Filing date: 2018-10-10
Publication date: 2019-06-27
Also published as: JP6868545B2; JP2019108600A

Abstract

Provided is a corrosion suppression method for carbon steel members in a plant that can further extend the length of time where corrosion is suppressed in the carbon steel members in the plant. A circulation pipe of a film-forming device is connected to a carbon steel-made cleaning system pipe communicating with a reactor pressure vessel of a nuclear plant in a stopped state (S1). A film-forming solution prepared by injection of nickel ions (S4) and injection of a reducing agent (S5) is supplied to the cleaning system pipe from the circulation pipe and a nickel metal film is formed on the inside surface of the cleaning system pipe. Subsequently, an aqueous solution containing platinum ions and a reducing agent is supplied to the cleaning system pipe from the circulation pipe, causing platinum to adhere to the nickel metal film. The film-forming device is disconnected from the cleaning system pipe (S15) and the nuclear plant is activated (S16). Oxygen-containing reactor water in a range of 130˚C to under 200˚C is brought into contact with the platinum-adhered nickel metal film inside the cleaning system pipe to transform the nickel metal film into a stable nickel ferrite film wherein no elution occurs even when the platinum exerts action.

Description

Corrosion control method of carbon steel member of plant

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

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

In addition, since the corrosion products that are the source of radioactive corrosion products are generated on the surfaces of the component parts of the BWR plant, such as RPV and recirculation piping, which come in contact with the reactor water, the main component that contacts the reactor water For example, stainless steel, nickel base alloy and the like with low corrosion are used. In addition, low-alloy steel RPV is coated with stainless steel on its inner surface to prevent low-alloy steel from coming into direct contact with furnace water. Furthermore, a part of the reactor water is purified by the filter demineralizer of the reactor purification system to actively remove metal impurities slightly present in the reactor water.

On the other hand, for components such as the reactor purification system, residual heat removal system, reactor isolation cooling system, core spray system and water supply system communicated to RPV, from the viewpoint of reducing the production 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 caused by the above. Of these systems, in the residual heat removal system, the reactor isolation cooling system, and the core spray system, the cooling water that has flowed through the system is temporarily included in the cooling water because it is temporarily returned to the reactor water. The effect of corrosion products in the system on the reactor water is small. However, since there is a temperature range (130 ° C to 180 ° C) where the amount of corrosion increases in the reactor water purification system and the water supply system, the inflow of corrosion products into the reactor water and the load on the purification device increase. I am concerned. In addition, if the amount of corrosion of the system is increased, the soundness of the components will be affected, so an inspection for soundness confirmation will be required, leading to an increase in regular inspection work. For this reason, studies on corrosion inhibition of carbon steel members of nuclear power plants have been conducted.

As a method of suppressing the corrosion of carbon steel members constituting a nuclear power plant, for example, a method of injecting oxygen into a water supply system to form a passivation film consisting of an oxide film on the surface of carbon steel members, ammonia and hydrazine etc. A method of adjusting the pH of the feed water to the alkaline side by adding a chemical to the feed water has been proposed in BWR plants and pressurized water nuclear power plants (hereinafter referred to as PWR plants) (see, for example, JP-A-2000-292589). . However, in the method of injecting oxygen and alkaline chemicals and the like, it is necessary to continue to inject the chemical during operation of the nuclear power plant in order to continuously obtain the effect of suppressing the corrosion of the carbon steel member. If you stop injecting the drug, the effect is lost. In addition, in the case of injecting an alkaline agent, since the agent is a load of the ion exchange resin in the reactor water purification apparatus provided in the reactor purification system, the amount of radioactive waste may be increased.

JP-A-2006-38483 and JP-A-2012-247322 have a range of 60 ° C. to 100 ° C. including iron (II) ion, an oxidant and a pH adjuster (hydrazine) during shutdown of a nuclear power plant. It is described that a film forming solution 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, during shutdown of a nuclear power plant, an aqueous solution containing a noble metal (e.g. platinum) is brought into contact with the magnetite film to deposit the noble metal on the magnetite film.

JP2007-182604A and JP2007-192672A do not inject a chemical during operation, and as a method of suppressing corrosion of a carbon steel member by surface treatment, on the surface of a carbon steel member of a nuclear power plant A method of forming a ferrite film is described. In this method, a film forming solution containing iron (II) ions and an oxidant, having a pH in the range of 5.5 to 9.0, and a temperature range of normal temperature to 100 ° C. Contact with the surface of the member to form a ferrite film on this surface.

Furthermore, a nickel metal film is formed on the surface of the carbon steel member, and contains nickel ions, iron (II) ions, an oxidizing agent and a pH adjuster, the pH is in the range of 5.5 to 9.0, and the temperature is 60 A method is proposed to form a nickel ferrite film on the surface of the nickel metal film using a film forming solution in the range of 100 ° C. to 100 ° C. and then convert the nickel metal film to a nickel ferrite film by high temperature water (For example, JP-A-2011-32551).

JP-A-2015-158486 discloses an aqueous solution containing a complex ion-forming agent, a noble metal ion and a reducing agent when attaching a noble metal to the inner surface of a recirculation system piping which is a component of a BWR plant. It is stated to be in contact with

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

However, carbon can be obtained by the respective 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 described in detail later. is there. Therefore, the nickel ferrite film can not suppress the corrosion of the carbon steel member for a long time.

An object of the present invention is to provide a method of inhibiting corrosion of a carbon steel member of a plant, which can further extend a period during which corrosion of the carbon steel member of the plant is inhibited.

A feature of the present invention for achieving the above object is to form a nickel metal film on a surface of a carbon steel member of a plant in contact with water, cover the surface with a nickel metal film, and deposit a noble metal on the surface of the nickel metal film. The contact of the noble metal with the nickel metal film on which the noble metal is attached is brought into contact with water containing an oxidizing agent at 130 ° C. or more and less than 200 ° C. The formation of the nickel metal film and the deposition of the noble metal are performed after plant shutdown and before plant start-up It is about to be done.

The corrosion potential of the nickel metal coating and the carbon steel member in contact with the water is lowered by the action of the noble metal adhering to the nickel metal coating. Such a decrease in corrosion potential and water in a temperature range of 130 ° C. or more and less than 200 ° C. containing an oxidizing agent to the nickel metal film makes the nickel metal film also contact by the action of the deposited noble metal It is converted to a stable nickel ferrite film which does not elute. Since the surface of the carbon steel member is covered with the stable nickel ferrite to which the noble metal adheres, the corrosion of the carbon steel member of the plant can be suppressed for a longer period of time.

According to the present invention, since a stable nickel ferrite film which does not dissolve in the water which contacts even by the action of the deposited noble metal is formed on the surface of the carbon steel member, corrosion of the carbon steel member of the plant is prolonged over a longer period. It can be suppressed.

It is a flowchart which shows the procedure of the corrosion-control method of the carbon steel member of the plant of Example 1 applied to the purification system piping of a boiling water type nuclear power plant which is one suitable Example of this invention. It is explanatory drawing which shows the state which connected the film-forming apparatus used when enforcing the corrosion suppression method of the carbon steel member of the plant of Example 1 to the purification system piping of a boiling water type nuclear plant. It is a detailed block diagram of the film formation apparatus shown in FIG. It is sectional drawing of purification system piping of a boiling water type nuclear plant before the corrosion suppression method of the carbon steel member of the plant shown by FIG. 1 is started. It is explanatory drawing which shows the state in which the nickel metal film was formed in the inner surface of purification system piping by the corrosion suppression method of the carbon steel member of the plant shown by FIG. It is explanatory drawing which shows the state which made the noble metal adhere on the surface of the nickel metal film formed in the inner surface of purification system piping by the corrosion suppression method of the carbon steel member of the plant shown by FIG. In the method for suppressing corrosion of carbon steel members of a plant shown in FIG. 1, the nickel metal film formed on the inner surface of the purification system pipe and having platinum adhered is brought into contact with water containing oxygen in a temperature range of 130 ° C. or more and 200 ° C. It is an explanatory view showing a 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 more and less than 200 ° C. and Fe ²⁺ in the purification system piping are formed on the inner surface of the purification system piping. It is an explanatory view showing a state of being transferred to a nickel metal film to which platinum is attached. It is explanatory drawing which shows the state by which the nickel metal film formed in the inner surface of purification system piping was converted into the nickel ferrite film in the corrosion suppression method of the carbon steel member of the plant shown by FIG. It is explanatory drawing which showed the result of the real machine simulation environmental corrosion test by a carbon steel test piece. It is explanatory drawing which shows the laser Raman spectrum analysis result of the oxide film formed in the carbon steel test piece by the real machine simulation environmental corrosion test using the carbon steel test piece which formed the nickel metal film which adhered platinum. It is explanatory drawing which shows the corrosion-control method of the carbon steel member of the plant of Example 2 applied to the feed water piping of a boiling water type nuclear plant which is another Example of this invention. It is explanatory drawing which shows the corrosion-control method of the carbon steel member of the plant of Example 3 applied to the purification system piping of a boiling water type nuclear power plant which is another Example of this invention. It is a flowchart which shows the procedure of the corrosion-control method of the carbon steel member of the plant of Example 4 applied to the purification system piping of a boiling water type nuclear plant which is another Example of this invention. 14 is a heating system connected to a purification system piping to convert a nickel metal film formed on the inner surface of the purification system piping into a nickel ferrite film in the method for suppressing adhesion of radionuclides to carbon steel members of the plant shown in FIG. FIG. It is explanatory drawing which shows the corrosion-control method of the carbon steel member of the plant of Example 5 applied to the feed water piping 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 method of preventing corrosion of a carbon steel member described in JP-A-2011-32551. In JP-A-2011-32551, a nickel metal film is formed on the surface of a carbon steel member of a BWR plant while the BWR plant is stopped, a nickel ferrite film is formed on the surface of the nickel metal film, and further 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 studies by the inventors, the inventors finally deposit a noble metal on the surface of the nickel metal film formed on the surface of the carbon steel member, and 130 ° C. or more (preferably, 130 ° C. or more and less than 200 ° C. Water 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 a fixed ratio, thereby further preventing the corrosion of the carbon steel member I found the conclusion that it can be enhanced.

The inventors have recently investigated the simultaneous formation of the noble metal injection technology, which is being introduced as a countermeasure against stress corrosion cracking, and the above-described ferrite film formation technology. Ferrite film formation techniques include iron (II) ions, an oxidant and a pH adjuster (for example, hydrazine) as described in the aforementioned JP-A-2006-38483 and JP-A-2012-247322. There is one in which a film forming solution in a low temperature range of 60 ° C. to 100 ° C. is brought into contact with the surface of a component of a nuclear power plant to form a magnetite film on the surface of the component. Noble metals were deposited on the surface of the magnetite film in contact with the reactor water, and the effect was examined. During operation of the nuclear plant under the hydrogen injection simulation conditions, the effect of the noble metal to which the magnetite film was deposited was added to the reactor water. We found a phenomenon of elution. In addition, even in the case where a noble metal is deposited on a nickel ferrite film formed on the surface of a carbon steel member in contact with reactor water at a low temperature range of 60 ° C. to 100 ° C., operation under hydrogen injection simulation conditions of a nuclear power plant The phenomenon was found that the nickel ferrite film eluted in the reactor water due to the action of the noble metal to which the nickel ferrite film was attached.

In addition, there are two cases in the adhesion of the noble metal 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 reactor water during operation of the nuclear power plant in order to reduce the concentration of dissolved oxygen in the reactor water adheres to the surface of the ferrite film formed on the component. In the second case, as described in JP-A-2006-38483 and JP-A-2012-247322, the surface of the ferrite film formed on the component includes a noble metal ion during shutdown of the nuclear power plant. The solution is brought into contact, and a noble metal is deposited on the surface of the ferrite film.

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

The inventors have found that when a noble metal is deposited on a nickel ferrite film formed on a surface of a carbon steel member in contact with furnace water at a low temperature range of 60 ° C. to 100 ° C., the reason for the nickel ferrite to elute is Study was carried out. According to this examination, the nickel ferrite film formed on the surface of the carbon steel member at such a low temperature range during shutdown of the nuclear power plant is a film of Ni _0.7 Fe _2.3 O ₄ and is unstable I understood. Note that Ni _0.7 Fe _2.3 O ₄ is a form in the case where x is 0.3 in Ni _1-x Fe _{2 + x} O ₄ . Therefore, for example, when platinum is deposited on the unstable film Ni _0.7 Fe _2.3 O ₄ film, the reaction of the Ni _0.7 Fe _2.3 O ₄ causes the reactor to operate during operation of the nuclear power plant. It was found to elute in water. In addition, since an unstable Ni _0.7 Fe _2.3 O ₄ film is formed in the above-mentioned low temperature range, a large number of small particles of Ni _0.7 Fe _2.3 O ₄ adhere to the surface of the carbon steel member. ing. Also for this reason, a film of Ni _0.7 Fe _2.3 O ₄ with platinum adhering to the upper surface is eluted.

As described in JP 2011-32551 A, water containing oxygen at 150 ° C. or more is brought into contact with a nickel ferrite film covering a nickel metal film formed on the surface of a carbon steel member of a BWR plant, When the nickel metal film is converted to a nickel ferrite film, the nickel ferrite film converted from the nickel metal film becomes an unstable nickel ferrite film, for example, a film of Ni _0.7 Fe _2.3 O ₄ .

The reason is described below. In JP-A-2011-32551, as described above, a film-forming aqueous solution (film-forming solution) containing nickel ions, iron (II) ions and an oxidant and having a pH in the range of 5.5 to 9.0 A nickel ferrite film is formed on the nickel metal film in contact with the nickel metal film. Therefore, the nickel ferrite contained in the nickel ferrite film is a nickel ferrite having a large amount of Fe, that is, a nickel ferrite having less Ni and more Fe than Ni _0.7 Fe _2.3 O ₄ .

JP-A-2011-32551 discloses that a nickel ferrite film containing nickel ferrite having a high iron content and formed on a nickel metal film is brought into contact with water containing oxygen at 150 ° C. Iron ions from nickel ferrite with high iron content, oxygen contained in water at 150 ° C., and iron contained in carbon steel members are transferred to the nickel metal film and react with the nickel in the nickel metal film, as described above unstable nickel ferrite (e.g., Ni _0.7 Fe _2.3 O ₄₎ is generated. 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, a 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 is large and the amount of nickel is insufficient. The nickel ferrite film originally covering the nickel metal film reacts with the nickel metal transferred from the nickel metal film after contact with high temperature water to form a film of Ni _0.7 Fe _2.3 O ₄ . The nickel content of 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 a nickel ferrite film which is unstable in a reducing environment.

For this reason, when a noble metal such as platinum injected during operation of the BWR plant adheres to the surface of the unstable nickel film, this nickel ferrite film elutes in the reactor water by the action of the noble metal (eg platinum). Eventually, at the end of the operation cycle, the nickel ferrite film originally covering the nickel metal film and the nickel ferrite film converted from the nickel metal film may disappear and the carbon steel member may be exposed to contact with the reactor water There is.

By the way, when 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 can not be attached to the surface of the carbon steel member. For this reason, the inventors examined measures to prevent the elution of Fe ²⁺ from the carbon steel member when a noble metal is attached to the surface of the carbon steel member. Then, the inventors found that covering the surface of the carbon steel member with a nickel metal film can prevent the elution of Fe ²⁺ from the carbon steel member. Nickel metal which covers the surface of a carbon steel member is a substance which contributes to formation of a stable nickel ferrite film which controls corrosion of a carbon steel member, as mentioned 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, elution of Fe ²⁺ from the carbon steel member can be prevented, and the nickel metal film surface of noble metal The adhesion to the skin could be made in a short time. At the same time, the adhesion amount of the noble metal to the carbon steel member also increased.

The formation of a nickel metal film on the surface of a 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 ion contained in the aqueous solution is substituted with Fe contained in the carbon steel member, and the substituted nickel ion becomes nickel metal by the action of the reducing agent, and a nickel metal film is formed on the surface of the carbon steel member. In addition, adhesion of a noble metal to the surface of a nickel metal film formed on the surface of a carbon steel member is possible by bringing an aqueous solution containing noble metal ions (eg, platinum ions) and a reducing agent into contact with the formed nickel metal film. It is. The adhesion of nickel ions contained in the aqueous solution to the surface of the carbon steel member is possible even when Fe ²⁺ is eluted from the carbon steel member.

Thus, by forming a nickel metal film on the surface of the carbon steel member, elution of Fe ²⁺ from the carbon steel member can be prevented, and more noble metal can be attached to the carbon steel member in a short time. Can.

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

Furthermore, the examination result regarding corrosion suppression of a carbon steel member is demonstrated below. The present inventors did not form an unstable Ni _0.7 Fe _2.3 O ₄ film on the surface of a carbon steel member in a low temperature range of 60 ° C. to 100 ° C., but did not form a stable nickel ferrite even by the deposited noble metal. We aimed at the formation of the coating on the surface of carbon steel member. Therefore, the inventors variously examined whether the nickel metal film formed on the surface of the carbon steel member can be utilized for the formation of the stable nickel ferrite film in order to effectively adhere the noble metal to the carbon steel member. did. As a result, by bringing high temperature (130 ° C. or more) water into contact with the noble metal-deposited surface of the nickel metal coating formed on the surface of the carbon steel member while platinum is attached to the nickel metal coating, A stable nickel ferrite film (a nickel ferrite film in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ which covers the surface of a carbon steel member and does not dissolve even by the action of a noble metal, ie, NiFe It could be converted to a ₂ O ₄ film).

The inventors used a test piece A made of carbon steel not having nickel and platinum attached, and a test piece B made of carbon steel having a nickel metal film formed on the surface and platinum attached to the surface of the nickel metal film. Then, it was immersed in simulated water simulating the conditions of the reactor water during operation of the BWR plant to determine the corrosion amount of the test piece. In this experiment, test pieces A and B were placed in a closed loop circulation pipe, and simulated water simulating 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 removed 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. The amount of corrosion was determined from the difference with the previous test piece metal amount.

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

Furthermore, the chemical composition on each surface of the test pieces A and B removed from the circulation pipe was analyzed by Raman spectroscopy. The analysis results are 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 mainly composed of nickel ferrite (NiFe ₂ O ₄ ) was formed on the surface of the test piece B in which the amount of corrosion was significantly reduced. This NiFe ₂ O ₄ is a form in which x is 0 in Ni _1-x Fe _{2 + x} O ₄ .

A nickel metal film of a carbon steel member (test piece B) in which a nickel metal film is formed on the surface and a noble metal (for example, platinum) is attached to the surface of the nickel metal film is in contact with oxygen containing water of 130 ° C. or more. The reason for conversion to a stable nickel ferrite film (NiFe ₂ O ₄ film) covering the surface of a carbon steel member will be described. When water at 130 ° C. or more contacts the nickel metal film on the carbon steel member, the nickel metal film and the carbon steel member are heated to 130 ° C. or more. Oxygen contained in the water is transferred into the nickel metal film, and Fe contained in the carbon steel member is converted into Fe ²⁺ and transferred into the nickel metal film. Nickel ferrite in which nickel in the nickel metal film reacts with oxygen and Fe ²⁺ transferred to the nickel metal film in a high temperature environment of 130 ° C. or more, and x is 0 in Ni _1-x Fe _{2 + x} O ₄ Is generated. At this time, the ease with which each of nickel and iron is incorporated into the ferrite structure is affected by the noble metal, and in the presence of the noble metal, nickel is more easily incorporated than iron, so Ni _{1 -x} Fe 2 _{+ A} nickel ferrite is formed where x is 0 at _x O ₄ . The nickel ferrite film covers the surface of the carbon steel member.

X is 0 in Ni _1-x Fe _{2 + x} O ₄ generated as described above from a nickel metal contained in a nickel metal film covering the surface of a carbon steel member in a high temperature environment of 130 ° C. or higher Some nickel ferrites are large in crystal growth, and do not elute into water like the Ni _0.7 Fe _2.3 O ₄ film even if precious metals are attached, and they are stable against corrosion of the base carbon steel. In this Ni _1-x Fe _{2 + x} O ₄ , a stable nickel ferrite in which x is 0 is reduced in the corrosion potential of the carbon steel member and the nickel metal film by the action of a noble metal such as platinum attached to the nickel metal film. Generated to Thus, in a high temperature environment of 130 ° C. or higher, the nickel ferrite film formed in the presence of platinum from nickel metal covering the surface of a carbon steel member is formed in a low temperature range of 60 ° C. to 100 ° C. The corrosion of the carbon steel member can be suppressed for a longer period of time than the Ni _0.7 Fe _2.3 O ₄ coating.

If the temperature of the water containing oxygen brought into contact with the nickel metal film is less than 130 ° C., the nickel metal film is not converted to a stable nickel ferrite film (NiFe ₂ O ₄ film). In order to convert the nickel metal film into a stable nickel ferrite film which is not eluted by the action of a noble metal, the temperature of water containing oxygen to be brought into contact with the nickel metal film needs to be 130 ° C. or more. Furthermore, in order to reduce the time required for the temperature rise of the water containing oxygen, the temperature of the water may be less than 200 ° C. That is, water containing oxygen to be brought into contact with the nickel metal film is heated to a temperature range of 130 ° C. or more and less 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 the surface of the carbon steel member even when the nickel metal film having a noble metal attached to the surface is contacted with water containing oxygen and having a temperature within the temperature range of 130 ° C. or more and less than 200 ° C. It has been found that the formed nickel metal film can be converted to a stable nickel ferrite film (NiFe ₂ O ₄ film).

In addition, in order to form a nickel metal film on the surface of a carbon steel member, it contains a nickel ion, formic acid and a reducing agent (for example, hydrazine) and has a pH of 4.0 to 11.0 (4.0 to 11.0). When the aqueous solution in the temperature range of 60 ° C. to 100 ° C. is brought into contact with the surface of the corresponding carbon steel member, 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⁺ precipitates 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 precipitated aqueous solution of iron hydroxide and magnetite, nickel ion, formic acid and hydrazine is a cation exchange resin tower and It is supplied to the disassembling device. Nickel ions and Fe ²⁺ contained in the aqueous solution are removed in a cation exchange resin column, and formic acid and hydrazine are decomposed in a decomposition apparatus. After decomposition of formic acid and hydrazine, the aqueous solution is introduced into the mixed bed resin tower, and the impurities contained in the aqueous solution are removed by the ion exchange resin in the mixed bed resin tower to purify the aqueous solution.

Even after purification of the aqueous solution, Fe ^{2+ ions} that could not be 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. Thereafter, when a noble metal ion and a reducing agent are injected into the aqueous solution, a part of the injected noble metal ion adheres to iron hydroxide and magnetite deposited by the action of the reducing agent as a noble metal. The amount of precious metal deposited on the nickel metal film formed on the surface is reduced, and the time required to deposit a predetermined amount of precious metal on the surface of the nickel metal film becomes long.

In order to prevent iron ions (Fe ³⁺ ) remaining in the aqueous solution from precipitating as iron hydroxide and magnetite and attaching the noble metal to the iron hydroxide and magnetite, a complex ion forming agent (for example, ammonia) in the aqueous solution, noble metal The ion (eg, platinum ion) and the reductant (eg, hydrazine) are each injected, and the iron ion remaining in the aqueous solution and the injected complex ion forming agent, eg, ammonia form iron-ammonia complex ion, It is known to suppress the precipitation of iron ions (see JP-A-2015-158486). The iron ion and ammonia form an iron-ammonia complex ion by each of the reactions shown in the formulas (1) to (3).

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

Even when the pH of the aqueous solution is increased by the injection of a reducing agent (for example, hydrazine) as a complex ion forming agent, the formation of complex ions increases the solubility of Fe ³⁺ and suppresses the precipitation of iron hydroxide and magnetite Any substance can be used, and at least one of ammonia, monoamines such as hydroxylamine, a cyan compound, urea, and a thiocyan compound is used.

As described above, even if iron ions (Fe ³⁺ ) remain in the aqueous solution after purification, iron ions such as ammonia, which suppress precipitation of iron ions in the aqueous solution, A substance that forms complex ions (complex ion forming agent) is injected into the aqueous solution to form platinum ions (precious metal ions) and a reducing agent (for example, hydrazine) on the surface of the carbon steel member with platinum ions as platinum. It can be attached to the surface of the nickel metal film.

Based on the above-described 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 a carbon steel member to form a nickel metal film on the surface of the carbon steel member, a noble metal is deposited on the surface of the nickel metal film, oxygen is included 130 ° C. Water in a temperature range of not less than 200 ° C. is brought into contact with the nickel metal film to which the noble metal is attached, and nickel metal contained in the nickel metal film, oxygen contained in water and iron contained in the carbon steel member A nickel ferrite film is formed on the surface of a carbon steel member by using the catalytic action of a noble metal at high temperatures of not less than 200 ° C. and not less than 200 ° C.

The present invention relates to a method of inhibiting corrosion of a carbon steel member of a plant. According to the present invention, the nickel metal film formed on the surface of the carbon steel member and having the noble metal attached thereto is brought into contact with water within the range of 130 ° C. or more and less than 200 ° C. Since the stable nickel ferrite film is formed on the surface of the carbon steel member under the high temperature within the range of 130 ° C. or more and less than 200 ° C. by utilizing the catalytic action of the noble metal, the formed nickel ferrite film is Even if precious metals are attached, they do not elute in water, and corrosion of carbon steel members can be suppressed over a long period of time (specifically, over a plurality of operation cycles).

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

A method of inhibiting corrosion of a carbon steel member of a plant according to a first embodiment which is a preferred embodiment of the present invention will be described with reference to FIG. 1, FIG. 2 and FIG. The method of suppressing corrosion of a carbon steel member of the present embodiment is applied to a carbon steel purification system pipe (carbon steel member) of a boiling water nuclear power plant (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 nuclear reactor 2 is a steam generator and has a reactor pressure vessel (hereinafter referred to as RPV) 3 containing a core 4 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 downcomer formed between it and the inner surface. The core 4 is loaded with a number of fuel assemblies (not shown). The fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material.

The recirculation system has a stainless steel recirculation system pipe 6 and a recirculation pump 7 installed in the recirculation system pipe 6. The water supply system includes a condensate pump 12, a condensate purification apparatus (for example, a condensate demineralizer) 13, a low pressure feed water heater 14, a feed water pump 15, and a high pressure feed water to a feed water pipe 11 connecting the condenser 10 and the RPV 3 The heater 16 is installed and arranged in this order from the condenser 10 toward the RPV 3. The reactor purification system comprises a purification system pipe 18 connecting the recirculation system pipe 6 and the water supply pipe 11, with the purification system pump 19, the regenerative heat exchanger 20, the non-regeneration heat exchanger 21 and the reactor water purification device 22 in this order. It has been installed. The bypass piping 28 bypassing the reactor water purification device 22 is connected to the purification system piping 18 on the upstream side and the downstream side of the reactor water purification device 22. The valve 27 is provided in the purification system pipe 18 on the side of the reactor water purification device 22 with respect to the connection point between the bypass pipe 28 and the purification system pipe 18. The purification system piping 18 is connected to the recirculation system piping 6 upstream of the recirculation pump 7. The reactor 2 is installed in a reactor containment vessel 90 disposed in a reactor building (not shown).

The cooling water in the RPV 3 (hereinafter referred to as “furnace water”) is pressurized by the recirculation pump 7 and is jetted into the jet pump 5 through the recirculation system pipe 6. Reactor water present in the downcomer around the nozzle of the jet pump 5 is also drawn 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 thereof becomes steam. The steam is led from the RPV 3 through the main steam piping 8 to the turbine 9 to rotate the turbine 9. A generator (not shown) connected to the turbine 9 rotates to generate electric power. The steam discharged from the turbine 9 is condensed by the condenser 10 into water. This water is supplied to the RPV 3 through the water supply pipe 11 as water supply. The feed water flowing through the feed water pipe 11 is pressurized by the condensate pump 12, impurities are removed by the condensate purification device 13, and the pressure is further boosted by the feed pump 15. The feedwater is heated by the low pressure feedwater heater 14 and the high pressure feedwater heater 16 and introduced into the RPV 3. Extracted steam extracted from the turbine 9 in 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 of the feed water.

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

In the method of suppressing corrosion of carbon steel members of the plant of this embodiment, the

film forming devices

30 and 31A are used, and as shown in FIG. 2, these

film forming devices

30 and 31A are used for the purification system piping 18 of the BWR plant. Connected

The detailed configuration of the

film forming devices

30 and 30A will be described with reference to FIG. The configuration of each of the

film forming devices

30 and 30A is the same.

The

film forming devices

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

An on-off valve 62, a circulation pump 35,

valves

63, 66, 69 and 74, a surge tank 32, a circulation pump 34, a valve 77 and an on-off valve 78 are provided in the circulation pipe 31 in this order from the upstream. A pipe 65 bypassing 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 a pipe 68 which bypasses the valve 66 and is connected to the circulation pipe 31 at both ends. 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 which bypasses the valve 69. The mixed bed resin tower 54 and the valve 72 are installed on the piping 73 whose both ends are connected to the piping 71 and which bypasses the cation exchange resin tower 53 and the valve 70. The cation exchange resin column 53 is filled with a cation exchange resin, and the mixed bed resin column 54 is filled with a cation exchange resin and an anion exchange resin.

A pipe 76 in which the valve 75 and the decomposition device 55 located downstream of the valve 75 are installed bypasses the valve 74 and is connected to the circulation pipe 31. The decomposition device 55 is filled with an activated carbon catalyst in which, for example, ruthenium is attached to the surface of activated carbon. A surge tank 32 is installed in the circulation pipe 31 between the valve 74 and the circulation pump 34. A heater 33 is disposed in the surge tank 32. A 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 is further connected to the surge tank 32. A hopper (not shown) for supplying oxalic acid (reduction decontaminant) used to reduce and dissolve the contaminants on the inner surface of the purification system pipe 18 is provided in the ejector 61.

A nickel ion implantation apparatus 36 has a chemical solution tank 37, an injection pump 38 and an injection pipe 39. The chemical solution tank 37 is connected to the circulation pipe 31 by an injection pipe 39 having an injection pump 38 and a valve 40. An aqueous solution of nickel formate (an aqueous solution containing nickel ions) prepared by dissolving nickel formate (Ni (HCOO) ₂ · 2 H ₂ O) in a dilute aqueous solution of formic acid is filled in the chemical solution tank 37.

A platinum ion implantation device (noble metal ion implantation device) 46 has a chemical solution tank 47, an injection pump 48 and an injection pipe 49. The chemical solution 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 (eg, sodium hexahydroxoplatinate hydrate (Na ₂ [Pt (OH) ₆ ] .nH ₂ O) in water (eg, sodium hexahydroxoplatinate) Hydrate aqueous solution) is filled in the drug solution tank 47. The aqueous solution containing platinum ions is a kind of aqueous solution containing precious metal ions.

The reducing agent injection device 41 has a chemical solution tank 42, an injection pump 43 and an injection pipe 44. The chemical solution 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 solution 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 order from the valve 77 to the on-off valve 78.

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

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

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

As described above, while the operation of the BWR plant 1 is stopped, a carbon steel piping system communicated with the RPV 12, which is one of the carbon steel members in the BWR plant 1, for example, the purification system piping 18 The target method of inhibiting corrosion of carbon steel members of the plant of this embodiment is implemented. In this method of suppressing corrosion of a carbon steel member, the adhesion treatment of nickel metal to the inner surface of the purification system piping 18 in contact with the reactor water, the adhesion treatment of noble metal such as platinum to the adhered nickel metal and the noble metal are adhered. The conversion of nickel metal into stable nickel ferrite is carried out.

The method of suppressing the corrosion of carbon steel members of the plant of the present embodiment will be described below based on the procedure shown in FIG. In the method of suppressing corrosion of a carbon steel member of a plant of the present embodiment, the

film forming devices

30 and 30A are used.

First, a film forming apparatus is connected to a carbon steel piping system to be subjected to film formation (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 piping 18 is opened upstream of the purification system pump 19 to seal the recirculation system piping 6 side. One end of the circulation pipe 31 of the film forming apparatus 30 on the side of the on-off valve 78 is connected to the flange of the valve 23. Furthermore, the bonnet of the valve 25 installed in the purification system pipe 18 between the regenerative heat exchanger 20 and the non-regenerating heat exchanger 21 is opened to seal the non-regenerating heat exchanger 21 side. The other end of the circulation pipe 31 on the side of the on-off valve 62 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 on-off valve 78 side of the circulation piping 31 of the film forming apparatus 30A is connected to the flange of the valve 32A, and the other end on the on-off valve 62 side of the circulation piping 31 is connected to the flange of the valve 26 The film forming device 30A is connected to the purification system pipe 18.

In the present 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, a residual heat removal system which is a carbon steel member and communicated with the RPV 3 The film forming apparatus 30 is connected to any carbon steel piping of the reactor isolation cooling system, core spray system, or water supply system, and the carbon steel members of the plant of this embodiment are corroded to the carbon steel piping. A suppression method may be applied.

The steps S2 to S14 described below are performed by the film forming device 30 on the portion of the purification system piping 18 between the valve 23 and the valve 25. The film forming device 30A performs the purification system piping 18 , Between the valve 26 and the valve 32A.

Chemical decontamination is carried out on a carbon steel piping system to be subjected to film formation (step S2). In the BWR plant 1 that has experienced the operation in the previous operation cycle, an oxide film containing a radionuclide is formed on the inner surface of the purification system pipe 18 in contact with the reactor water flowing from the RPV 3. Before forming a nickel metal film to be described later on the inner surface of the purification system pipe 18, it is preferable to remove the oxide film containing the radionuclide from the inner surface also in order to lower the dose rate of the purification system pipe 18. The removal of the oxide film improves the adhesion between the nickel metal film and the inner surface of the purification system pipe 18. In order to remove the oxide film, a chemical decontamination, in particular, a reduction decontamination using a reduction decontamination solution containing oxalic acid which is a reduction decontamination agent is performed on the inner surface of the purification system pipe 18.

The chemical decontamination to be applied to the inner surface of the purification system pipe 18 in step S2 is a known reductive decontamination described in JP-A-2000-105295. This reduction decontamination will be described. First, the circulation pumps 34 and 35 are driven with the on-off valve 62, the

valves

63, 66, 69, 74 and 77, and the on-off valve 78 opened and the other valves closed. Thus, 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 the water reaches 90 ° C., the valve 79 is opened to introduce 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 ejector 61 into the pipe 80 is introduced into the surge tank 32 by the water flowing through the pipe 80. The oxalic acid is dissolved in water in the surge tank 32, and an oxalic acid aqueous solution (reduction decontamination solution) is generated in the surge tank 32.

The oxalic acid aqueous solution is discharged from the surge tank 32 to the circulation pipe 31 by driving the circulation pump 34. The hydrazine solution in the chemical solution 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 aqueous solution of oxalic acid 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 aqueous solution of oxalic acid supplied to the pipe 18 is adjusted to 2.5. In this embodiment, when nickel metal is attached to the inner surface of the purification system pipe 18 and a noble metal such as platinum is attached on the nickel metal film, hydrazine which is a reducing agent used for reduction decontamination is used. In the process, it is used as a pH adjuster to adjust the pH of an aqueous solution of oxalic acid.

An oxalic acid aqueous solution 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 formed on the inner surface of the purification system pipe 18. Dissolve. The oxalic acid aqueous solution flows in the purification system pipe 18 while dissolving the oxide film, and passes through the purification system pump 19 and the regenerative heat exchanger 20, the non-regenerating heat exchanger 21, the bypass piping 28 and the regenerative heat exchanger 20. It is returned to the circulation pipe 31. The aqueous solution of oxalic acid returned to the circulation pipe 31 is pressurized by the circulation pump 35 through the on-off valve 62 and passes through the

valves

63, 66, 68 and 73 to reach the surge tank 32. As described above, the aqueous solution of oxalic acid circulates in the closed loop including the circulation pipe 31 and the purification system pipe 18 to carry out reduction decontamination of the inner surface of the purification system pipe 18 to dissolve the oxide film formed on the inner surface. .

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

In reduction decontamination of the surface of a carbon steel member (for example, purification system piping 18) using oxalic acid, poorly soluble iron (II) oxalate is formed on the surface of the carbon steel member, and this iron oxalate ( The dissolution by oxalic acid of the oxide film containing the radionuclide formed on the surface of the carbon steel member may be suppressed by II). In this case, the valve 69 is fully opened and the valve 70 is closed to stop the supply of the oxalic acid aqueous solution to the cation exchange resin column 53. 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 aqueous solution of oxalic acid flowing in the circulation pipe 31 through the supply pipe 59 and the pipe 76 in the state where the valve 75 is closed. Do. An aqueous solution of oxalic acid containing hydrogen peroxide is led 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 hydrogen peroxide, and the iron (II) oxalate is oxidized It is dissolved in an aqueous solution of oxalic acid as an iron (III) complex. That is, iron oxalate (II) and hydrogen peroxide and oxalic acid contained in an aqueous solution of oxalic acid form an iron (III) oxalate complex, water and hydrogen ions by the reaction shown in formula (4).

_{_{2Fe (COO) 2 + H 2}} O 2 +2 (COOH) 2 →
_{_{2Fe [(COO) 2] 2}} - + 2H 2 O + 2H + ... (4)
The iron (II) oxalate formed on the inner surface of the purification system piping 18 is dissolved, and it is confirmed that the hydrogen peroxide injected into the oxalic acid aqueous solution has disappeared by the reaction of formula (4). Part of the aqueous oxalic acid 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 radionuclide contained in the aqueous solution of oxalic acid are adsorbed to 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 reacting 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 of the reduction decontamination site of the purification system pipe 18 decreases to the set dose rate, or when the reduction decontamination time of the purification system pipe 18 reaches a predetermined time, oxalic acid contained in the aqueous solution of oxalic acid and Decompose hydrazine (Reductive decontamination reagent decomposition process). The decrease of the dose rate at the reduction decontamination site to the set dose rate is confirmed by the dose rate obtained based on the output signal of the radiation detector that detects the radiation from the reduction decontamination site of the purification system pipe 18 be able to.

Decomposition of oxalic acid and hydrazine is carried out as follows. The valve 75 is opened to partially reduce the opening degree of the valve 74, and the oxalic acid aqueous solution containing hydrazine which has passed through the valve 69 and the valve 70 is supplied to the disassembling apparatus 55 through the valve 75 and the pipe 76. 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 Formula (5) and Formula (6).

(COOH) ₂ + H ₂ O ₂ → 2CO ₂ + 2H ₂ O ...... (5)
N ₂ H ₄ + ₂ H ₂ O ₂ → N ₂ + 4 H 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 supply amount of hydrogen peroxide from the chemical solution tank 57 to the decomposition device 55 is set so that the supplied hydrogen peroxide is not completely consumed by the decomposition device 55 for decomposition of oxalic acid and hydrazine and does not flow out of the decomposition device 55. The rotational speed of the feed pump 58 is controlled and adjusted.

Also in the reduction decontamination reagent decomposition process, oxalic acid may exist in the aqueous solution of oxalic acid discharged from the decomposition apparatus 55, and iron (II) oxalate may be formed on the inner surface of the purification system pipe 18 is there. Therefore, when the decomposition of oxalic acid and hydrazine contained in the aqueous oxalic acid solution proceeds to a certain extent, the amount of hydrogen peroxide supplied from the chemical solution tank 57 to the decomposition device 55 is set so that the hydrogen peroxide flows out from the decomposition device 55. increase. At this time, in order to prevent the hydrogen peroxide from flowing into the cation exchange resin tower 53, the valve 70 is closed in advance.

As described above, the iron (II) oxalate formed on the inner surface of the purification system pipe 18 in the reduction decontamination reagent decomposition process becomes an iron (III) oxalate complex by the action of hydrogen peroxide in the aqueous solution of oxalic acid. Dissolve in aqueous oxalic acid solution. As decomposition of oxalic acid and the like in the aqueous oxalic acid solution proceeds, oxalic acid which converts Fe (II) contained in iron (II) oxalate to Fe (III) runs short, and Fe on the inner surface of the circulation pipe 31 It becomes easy to precipitate (OH) ₃ . For this reason, formic acid is injected into an aqueous solution of oxalic acid to suppress precipitation of Fe (OH) ₃ . The injection of formic acid is performed, for example, by supplying formic acid from the hopper and ejector 61 described above to the aqueous solution of oxalic acid flowing in the pipe 80 and guiding it to the surge tank 32. The supplied formic acid is mixed with the aqueous oxalic acid solution.

Note that the injection of an oxidant into the aqueous solution of oxalic acid to dissolve iron (II) oxalate, and the injection of formic acid into the aqueous solution of oxalic acid to suppress precipitation of iron hydroxide Will be done after the

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

Next, in order to complete the decomposition process of oxalic acid, the opening degree of the valve 60 is squeezed to adjust the supply amount of hydrogen peroxide to such an extent that hydrogen peroxide does not flow out from the decomposition device 55 and inject new formic acid Close the valve 79 to stop it. 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 aqueous oxalic acid solution are removed by the cation exchange resin in the cation exchange resin tower 53, and the metal cation concentration of the aqueous oxalic acid solution decreases. The decomposition of oxalic acid, hydrazine and formic acid is continued in the decomposition unit 55. Among oxalic acid, hydrazine and formic acid, hydrazine is decomposed first, then oxalic acid is decomposed, and formic acid remains last. In this state, the oxalic acid decomposition process is completed.

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

The temperature of the film forming solution 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 the formic acid is heated by the heater 33 to 90.degree. The temperature of the formic acid aqueous solution (the film-forming aqueous solution described later) is desirably in the temperature range of 60 ° C. to 100 ° C. (60 ° C. or more and 100 ° C. or less). 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 fine solid content is not removed, as described later, when an aqueous solution of nickel formate is injected into the circulation pipe 31, a nickel metal film is also formed on the surface of the solid, and the injected nickel ions are wasted. Be done.

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

A reducing agent is injected (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 the reducing agent in the chemical solution tank 42, flows through the injection piping 44 through the circulation piping 31 including nickel ions and formic acid 90 Injected into an aqueous solution of ° C. The hydrazine concentration of the aqueous hydrazine solution to be injected is, for example, 200 ppm. The aqueous hydrazine solution contains nickel ions and formic acid so that 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 injection amount to the aqueous solution is adjusted.

An aqueous solution containing a nickel ion, formic acid and hydrazine and having a pH of 4.0 and a temperature of 90 ° C., ie, a film forming aqueous solution (film forming solution) is supplied from the circulation piping 31 to the purification system piping 18 by driving the circulation pump 34. . A nickel metal film 82 is formed on the inner surface of the purification system pipe 18 by the film forming aqueous solution 83 contacting the inner surface of the purification system pipe 18 (see FIG. 5). The formation of the nickel metal film 82 is performed as follows. By the contact between the inner surface of the purification system pipe 18 and the film formation aqueous solution 83 of pH 4.0, the substitution reaction between the nickel ions contained in the film formation aqueous solution 83 and the Fe (II) ions in the purification system piping 18 is accelerated and purification is performed. The amount of nickel ions taken into the inner surface of the system piping 18 increases, and the elution of iron (II) ions into the film-forming aqueous solution 83 increases. The nickel ions taken into the inner surface of the purification system pipe 18 become nickel metal by the action of the hydrazine contained in the film forming aqueous solution 83, so 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 taken into the inner surface of the purification system pipe 18 The amount of nickel ions is the highest. When the pH of the aqueous solution for film formation 83 is increased to 7 or the like by the injection of the reducing agent, the amount of the incorporated nickel ions to be 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. It is supplied to the purification system pipe 18 again. Thus, 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 is in contact with the film-forming aqueous solution 83 eventually, between the valve 23 and the valve 25. The entire surfaces 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, for example, 50 μg to 300 μg (50 to 300 μg / cm ² ) of nickel metal per square centimeter are present on the inner surface of the purification system pipe 18.

In the surge tank 32, a liquid surface of a 90 ° C. aqueous solution (or a film formation aqueous solution) containing the remaining formic acid is formed, and a space (not shown) exists above the liquid surface. There is air. Oxygen in the air in the space is supplied to the 90 ° C. aqueous solution (or film-forming aqueous solution) containing the remaining formic acid in the surge tank 32 through the liquid surface. Due to the supply of oxygen in the surge tank 32, the aqueous solution contains about 2 ppm of a trace amount of oxygen. In order to convert the nickel ions incorporated into the inner surface of the purification system pipe 18 into nickel metal, in step S5, an aqueous hydrazine solution containing 200 ppm of hydrazine is injected into the aqueous solution. The film-forming aqueous solution produced in the circulation pipe 31 by injection of the hydrazine aqueous solution contains a large amount of hydrazine as compared to about 2 ppm of oxygen. Since the oxygen contained in the aqueous solution for film formation is decomposed by the injected reducing agent, for example, hydrazine, to become water, the oxygen dissolved in the aqueous solution for film formation 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 piping 18. The nickel ions taken into the inner surface of the purification system pipe 18 become nickel metal by the action of the 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.

If oxygen is contained in the film forming aqueous solution in contact with the inner surface of the purification system pipe 18, the inner surface of the purification system pipe 18 is a nickel metal film containing unstable nickel ferrite (Ni _0.7 Fe _2.3 O ₄ ) It is formed. However, by injecting hydrazine, a film-forming aqueous solution containing no oxygen is generated, and the film-forming aqueous solution is supplied to the purification system pipe 18 so that the inner surface of the purification system pipe 18 does not contain unstable nickel ferrite. A metal film can be formed. Furthermore, since the aqueous solution for film formation contains hydrazine, the thickness of the nickel metal film formed on the inner surface of the purification system pipe 18 can be 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 aqueous solution containing no oxygen can be supplied from the surge tank 32 to the circulation pipe 31. By injecting hydrazine into this aqueous solution, a film-forming aqueous solution containing no oxygen can be generated in the circulation pipe 31. By injecting an inert gas into the aqueous solution in the surge tank 32, it is possible to reduce the amount of hydrazine injected into the circulation pipe 31 for the generation of the film-forming aqueous solution.

It is determined whether the formation of the nickel metal film is completed (step S6). When 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 ), the steps S4 to S6 are repeated. When the nickel metal present on the inner surface of the purification system pipe 18 reaches 50 μg / cm ² , the injection pump 38 is stopped and the valve 40 is closed to stop the injection of the aqueous solution of nickel formate into the circulation pipe 31 and the injection pump 43 To stop the injection of the aqueous hydrazine solution into the circulation pipe 31, and the formation of the nickel metal film on the inner surface of the purification system pipe 18 is ended. When the elapsed time from the injection of the aqueous solution of nickel formate into the circulation pipe 31 becomes the set time, it is determined that the amount of nickel metal present on the inner surface of the purification system pipe 18 has become 50 μg / cm ² . The set time is determined by measuring in advance the time taken for the nickel metal on the surface of the carbon steel test piece to reach 50 μg / cm ² .

The formic acid decomposes the reducing agent (step S7). The opening degree of the valve 69 is squeezed, and the valve 70 is opened to pass a film forming aqueous solution 83 containing nickel ions, formic acid and hydrazine to the cation exchange resin tower 53. As a result, nickel ions are adsorbed to the cation exchange resin, and the concentration of nickel ions 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 pressurized by the circulation pump 35 is decomposed through the pipe 76 Lead to Furthermore, 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 a counter ion of nickel ions, and hydrazine, which is a reducing agent, contained in the aqueous solution for film formation 83 are decomposed into carbon dioxide, nitrogen and water in the decomposition apparatus 55 by the action of the activated carbon catalyst and hydrogen peroxide. .

The film-forming aqueous solution in which formic acid and the reducing agent are decomposed is purified (step S8). After the formic acid and hydrazine (reductant) are decomposed, the valve 74 is opened and the valve 75 is closed to stop the supply of the formic acid, the aqueous solution of film formation 83 having reduced hydrazine concentration to the decomposition device 55, and the valve 67 is opened. The valve 66 is closed, the valve 72 is opened, and a part of the opening 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 reduced in concentration of formic acid and hydrazine returned to the circulation pipe 31 from the purification system pipe 18 is cooled to 60 ° C. by the cooler 52. Further, formic acid, a film forming aqueous solution 83 having a reduced concentration of hydrazine and at 60 ° C. is led 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). The aqueous solution for film formation at 60 ° C. in which the concentrations of formic acid and hydrazine are reduced is circulated in the circulation piping 31 and the purification system piping 18 until the above-described ions are substantially eliminated. The film-forming aqueous solution substantially free of each ion is water substantially at 60 ° C., but contains a trace amount of iron ion (Fe ³⁺ ) remaining.

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

A platinum ion aqueous solution is injected (step S10). After the end of the ammonia injection, the valve 50 is opened to drive the injection pump 48. The aqueous solution at 60 ° C. containing ammonia, which flows in the circulation pipe 31, is kept at 60 ° C. by heating by the heater 33. An aqueous solution containing ammonia at 60 ° C. flowing through the circulation pipe 31 through the injection pipe 49 and containing the platinum ion in the chemical solution tank 47 (eg, sodium hexahydroxoplatinate hydrate (Na ₂ [Pt (OH) ₆ Aqueous solution of n H ₂ O) is injected. The concentration of platinum ions in this aqueous solution to be injected is, for example, 1 ppm. In an aqueous solution of sodium hexahydroxoplatinate hydrate, platinum is in an ionic state. A 60 ° C. aqueous solution containing platinum ions and ammonia is supplied from the circulation piping 31 to the purification system piping 18 by driving the circulation pumps 34 and 33, and is returned from the purification system piping 18 to the circulation piping 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 an aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O, which is injected from the chemical solution tank 47 through the connection point of the circulation pipe 31 and the injection pipe 49 into the circulation pipe 31 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. The chemical solution tank 47 necessary for depositing a predetermined amount of platinum on the surface of the nickel metal film formed on the inner surface of the purification system pipe 18 with the preset concentration of platinum ions in the aqueous solution of 60 ° C. flowing and flowing. 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 The . The rotational speed of the injection pump 48 is controlled in accordance with the calculated injection rate of the aqueous solution of Na ₂ [Pt (OH) ₆ ] · nH ₂ O into the circulation pipe 31, and Na ₂ [Pt (OH ₆ ) The nH ₂ O aqueous solution is injected into the circulation pipe 31.

A reducing agent is injected (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 the reducing agent in the chemical solution tank 42, flows through the injection pipe 44 through the circulation pipe 31. Injected into an aqueous solution of ° C. The hydrazine concentration of the aqueous hydrazine solution to be injected is, for example, 100 ppm.

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

In the case of the injection of hydrazine aqueous solution in the former case, the reduction reaction of platinum ion to platinum with hydrazine first occurs in the aqueous solution containing hydrazine and platinum ion, which flows in circulation pipe 31, while the latter In the case of injection of a hydrazine aqueous 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 adhesion amount of platinum 84 to the surface of the nickel metal film 82 formed on the inner surface of the purification system pipe 18 further increases (see FIG. 6).

Immediately after the start of injection of the hydrazine aqueous solution, the concentration of hydrazine at the connection point of the aqueous hydrazine 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 to 100 ppm, for example. The rate of injection of the hydrazine aqueous solution into the circulation pipe 31 is calculated, and the hydrazine in the aqueous solution containing platinum ions at 60.degree. C. flowing in the circulation pipe 31 is formed at the set concentration to form the inner surface of the purification system pipe 18 The amount of aqueous hydrazine solution to be filled in the chemical solution tank 42 is calculated to reduce platinum ions adsorbed on the surface of the nickel metal film 82 to platinum 84, and the calculated amount of aqueous hydrazine solution is filled in the chemical solution tank 42 Do. The rotational speed of the injection pump 43 is controlled in accordance with the calculated injection rate of the aqueous hydrazine solution into the circulation pipe 31, and the aqueous hydrazine solution in the chemical solution tank 42 is injected into the circulation pipe 31.

When the entire aqueous solution (aqueous solution containing platinum ions) of Na ₂ [Pt (OH) ₆ ] .nH ₂ O in the chemical solution tank 47 is injected into the circulation pipe 31, the driving of the injection pump 48 is stopped. And the valve 50 is closed. Thus, the injection of the aqueous solution containing platinum ions into the circulation pipe 31 is stopped. In addition, when the entire hydrazine solution (reducing agent aqueous solution) in the chemical solution tank 42 is injected into the circulation pipe 31, the driving of the injection pump 43 is stopped and the valve 45 is closed. Thus, the injection of the hydrazine aqueous solution into the circulation pipe 31 is stopped.

The platinum ions adsorbed on the surface of the nickel metal film 82 are reduced by the injected hydrazine to become platinum 84, and 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, ammonia contained in the aqueous solution 85 in contact with the nickel metal film 82 reacts with a trace amount of iron ion (Fe ³⁺ ) contained in the aqueous solution 85 to generate iron-ammonia complex ion. For this reason, 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. The platinum ion contained in the aqueous solution 85 is not attached to iron hydroxide and magnetite as platinum, and the amount of platinum attached on the nickel metal film 82 is increased.

It is determined whether the deposition 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 process 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 is judged that the adhesion of platinum 84 to the surface of the nickel metal film 82 formed on the inner surface of the purification system piping 18 is completed, the valve 72 is opened to close a part of the opening degree of the valve 69 and the circulation pump 35 is used. A 60 ° C. aqueous solution containing platinum ions and hydrazine, ammonia, which has been pressurized, is supplied to the mixed bed resin column 54. The platinum ion, other metal cations (eg, sodium ion), hydrazine, ammonia and OH groups contained in the aqueous solution are adsorbed onto the ion exchange resin in the mixed bed resin column 54 and removed from the aqueous solution ( 2 purification process).

The waste liquid is treated (step S14). After the second purification step is completed, the circulation pipe 31 and the waste liquid treatment apparatus (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 radioactive waste liquid remaining in the purification system pipe 18 and the circulation pipe 31 is driven by the pump from the circulation pipe 31 through the high pressure hose to the waste liquid treatment apparatus (not shown) It is discharged and treated by the waste liquid treatment device. After the aqueous solution in the purification system pipe 18 and the circulation pipe 31 is discharged, wash water is supplied into the purification system pipe 18 and the circulation pipe 31 and the circulation pumps 34 and 35 are driven to wash the inside of these pipes. After completion of the cleaning, the cleaning water in the purification system piping 18 and the circulation piping 31 is discharged to the above-described waste liquid treatment apparatus.

As described above, the portion of the purification system piping 18 between the valve 23 and the valve 25 upstream of the non-regeneration heat exchanger 21 and the portion between the valve 26 and the valve 32A downstream of the regeneration heat exchanger 20 The formation of the nickel metal film 82 on the inner surface of the and the deposition of platinum 84 on the nickel metal film 82 are completed. A nickel metal film 82 to which platinum 84 is attached is not formed on the inner surface of a portion of the purification system piping 18 downstream of the valve 25 and upstream of the valve 26.

The film forming apparatus is removed from the piping system (step S15). After the processes of steps S1 to S14 are performed, each of the

film forming devices

30 and 30A is removed from the purification system piping 18, and the purification system piping 18 is restored.

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

The reactor water in the temperature range of 130 ° C. or more and less 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 present in the downcomer in the RPV 3 is supplied to the core 4 through the recirculation system pipe 6 and the jet pump 5 as described above. Reactor water discharged from the core is returned to the downcomer. The reactor water in the downcomer flows into the purification system piping 18 via the recirculation system piping 6 and eventually flows into the water supply piping 11 and is returned into the RPV 3.

Control rods (not shown) are withdrawn from the core 4 to bring the core 4 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 rods. In the core 4, no steam is generated. Further, the control rods are withdrawn from the core 4, and the pressure in the RPV 3 is raised to the rated pressure in the heating and pressurizing process of the reactor 2, and the reactor water is heated by the heat generated by the nuclear fission and the reactor water in the RPV 3 The temperature reaches the rated temperature (280 ° C). After the pressure in RPV 3 reaches the rated pressure and the reactor water temperature rises to the rated temperature, the reactor power is rated by the further withdrawal of control rods from the core 4 and the increase in the flow rate of reactor water supplied to the core 4 It is raised to the output (100% output). The rated operation of the BWR plant 1 maintaining the rated output is continued until the end of the operating cycle. When the reactor power rises, for example, to 10% power, the steam generated in the core 4 is supplied to the turbine 9 through the main steam piping 8 to start power generation.

The reactor water 86 contains oxygen and hydrogen peroxide. Oxygen and hydrogen peroxide are generated by radiolysis of the reactor water 86 in the RPV 3. The reactor water 86 containing oxygen in the RPV 3 is led from the recirculation system piping 6 into the purification system piping 18 with the purification system pump 19 being driven, and is formed on the inner surface of the purification system piping 18 , And contacts the deposited nickel metal film 82 (see FIG. 7). The heating of the reactor water by the heat generated by the above-mentioned nuclear fission causes the temperature of the reactor water 86 in contact with the nickel metal film 82 to rise, eventually to 130 ° C. or more, and finally to 280 ° C. at the rated output. To rise.

The temperature of the reactor water 86 greatly differs before and after the regenerative heat exchanger 20 and the non-regenerative heat exchanger 21. When the temperature of the reactor water 86 in the RPV 3 is 280 ° C., the reactor water 86 of about 280 ° C. flows in the portion of the purification system piping 18 upstream of the regenerative heat exchanger 20. As a result of the heat exchange in the regenerative heat exchanger 20, the temperature of the reactor water 86 flowing out from the regenerative heat exchanger 20 to the valve 25 side falls to a range of about 200 ° C to about 150 ° C. Furthermore, in the non-regenerating heat exchanger 21, the reactor water 86 drops to a temperature in the range of 50 ° C. to about room temperature, and is supplied to the reactor water purification device 22 containing the ion exchange resin within this temperature range. The reactor water 86 that has flowed out of the reactor water purification device 22 is used as water supply, and after being heated to a range of about 150 ° C. to 200 ° C. by the regenerative heat exchanger 20, joins the water supply flowing in the water supply pipe 11.

A portion of the purification system piping 18 between the valve 23 and the regenerative heat exchanger 20 in a 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 furnace, the furnace water 86 flowing through the portion between the regenerative heat exchanger 20 and the valve 25 of the purification system pipe 18, and the furnace water flowing through the portion between the valve 26 and the valve 32A of the purification system pipe 18 86 has a temperature in the temperature range of 130 ° C. or more and less than 200 ° C. although there is a time lag. In the heating and pressurizing process of the reactor 2, as the pressure in the RPV 3 rises, the temperature of the reactor water in the RPV 3 rises to a higher temperature exceeding 130 ° C.

Therefore, the surface of the nickel metal film 82 to which platinum 84 is formed, 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, the purification system piping 18 and its nickel metal film 82 are heated to the same temperature as the furnace water 86 by contacting the furnace water 86 containing oxygen in the temperature range of 130 ° C. or more and less than 200 ° C. Oxygen contained in the reactor water 86 is transferred into the nickel metal film formed on the inner surface of the purification system pipe 18 respectively between the valve 23 and the valve 25 and between the valve 26 and the valve 32A, which is a carbon steel member Fe contained in the purification system pipe 18 is converted to Fe ²⁺ to move into the nickel metal film (see FIG. 8). In a high temperature environment of 130 ° C. or more and less than 200 ° C., oxygen contained in the reactor water 86 and Fe ²⁺ from the purification system pipe 18 are easily transferred into the nickel metal film. When the oxygen concentration of the reactor water is low, the water molecules of the reactor 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 reactor water 86. The corrosion potential of the cleaning system pipe 18 and the nickel metal film 82 is reduced by the action of platinum 84 attached to the nickel metal film 82, and the high temperature environment of 130 ° C. or more and less than 200 ° C. Nickel reacts with oxygen and Fe ²⁺ transferred into the nickel metal film 82 to form a stable nickel ferrite (NiFe ₂ O ₄ ) in which x is 0 in Ni ₁ -xFe _{2 + x} O ₄ . At this time, the ease with which nickel and iron are incorporated into the ferrite structure is affected by platinum (noble metal), and in the presence of platinum, nickel is more easily incorporated than iron, so Ni _1-x Fe _{2 + x.} A stable nickel ferrite with x at 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 between the valve 23 and the valve 25 and between the valve 26 and the valve 32A. The inner surface of the purification system pipe 18 in the above is covered with a stable nickel ferrite film 87 in which platinum 84 is attached 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 more and less than 200 ° C. In nickel ferrite (NiFe ₂ O ₄ ) in which x is 0 in the above, crystals are grown large, and even if a noble metal is attached, it does not dissolve in water like Ni _0.7 Fe _2.3 O ₄ film, and is stable. The corrosion of the carbon steel which is the material, that is, the purification system piping 18 is suppressed.

According to this embodiment, in the state where the corrosion potential of the purification system pipe 18 and the nickel metal film 82 is lowered by the platinum 84 attached to the nickel metal film 82, and in the high temperature environment of 130 ° C. or more and less than 200 ° C. Thus, the nickel ferrite film 87 formed of the nickel metal film 82 and having x of 0 in Ni _1-x Fe _{2 + x} O ₄ has the function of the platinum 84 adhered even during the operation of the BWR plant 1. Is a stable nickel ferrite film which does not elute into reactor water. The thus formed stable nickel ferrite film 87 which does not dissolve into the reactor water by the action of the attached platinum 84 is more than the Ni _0.7 Fe _2.3 O ₄ film formed at a temperature range of 60 ° C. to 100 ° C. Corrosion of the purification system pipe 18 can be suppressed over 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 by the action of the attached platinum 84, and a plurality of operation cycles, for example, five operation cycles (for example, Can cover the inner surface of the purification system piping 18 for five years. As described above, since the stable nickel ferrite film 87 can cover the inner surface of the purification system pipe 18 for a long time, corrosion of the purification system pipe 18 is suppressed for a long time.

Carbon steel members tend to be particularly susceptible to corrosion when contacted with water at a temperature in the range of 150 ° C. to 200 ° C. During rated operation of the BWR plant 1, the purification system piping 18 is a portion between the regenerative heat exchanger 20 and the non-regenerating heat exchanger 21 on the upstream side of the reactor water purification device 22 and the downstream of the reactor water purification device 22. At the side between the regenerative heat exchanger 20 and the connection point between the purification system piping 18 and the water supply piping 11, it contacts the furnace water 86 at a temperature in the range of 150 ° C. to 200 ° C. Therefore, the corrosion of the purification system piping 18 is increased in these parts. In this embodiment, stable nickel ferrite films 87 are 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, respectively. Corrosion is suppressed for a long time by the formed stable nickel ferrite film 87. Also in the purification system pipe 18 between the valve 23 and the regenerative heat exchanger 20, since the stable nickel ferrite film 87 is formed on the inner surface, the corrosion is suppressed.

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

Furthermore, 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. For this reason, 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-regenerating heat exchanger 21 on the upstream side of the reactor water purification apparatus 22, in particular, purification The adhesion of the radionuclide to the inner surface of the portion of the system piping 18 can be suppressed.

According to the present 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 reactor water. A covering nickel metal coating 82 can be formed. By this nickel metal film 82, it is possible to prevent the elution of Fe ²⁺ from the purification system pipe 18 to the film forming aqueous solution during the precious metal adhesion treatment, and adhesion of noble metal (for example, platinum) to the inner surface of the purification system pipe 18 Is not inhibited by the elution of Fe ²⁺ , which is required for the adhesion of the noble metal to its inner surface (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) Time can be shortened. Further, the adhesion of the noble metal to the inner surface can be efficiently performed, and the adhesion amount of the noble metal to the inner surface of the purification system pipe 18 is increased.

In the present embodiment, 50 μg / cm ² of nickel metal is present in the nickel metal film 82 formed on the inner surface of the purification system pipe 18. Thus, when 50 μg / cm ² of nickel metal is present, the nickel metal film 82 covers the entire inner surface of the purification system pipe 18 in contact with the film-forming aqueous solution, and the BWR plant in the next operation cycle is After the start-up, the contact of the reactor 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. For this reason, the corrosion of the purification system piping 18 due to the reactor water is suppressed, and further, the radionuclides contained in the reactor water do not take in the base material of the purification system piping 18.

The nickel metal film 82 formed on the inner surface of the purification system piping 18 not only shortens the time required for the adhesion of platinum to the purification system piping 18, but in combination with the action of the adhered platinum 84, the purification system piping This contributes to the formation of a stable nickel ferrite film 87 which does not elute into the reactor water even by the deposited platinum on the inner surface of 18.

In the formation of the nickel metal film 82 on the inner surface of the purification system pipe 18, nickel ions contained in the aqueous solution for film formation are replaced with iron ions contained in the purification system pipe 18 and taken into the inner surface of the purification system pipe 18. The nickel ion incorporated on the inner surface is reduced to a nickel metal by hydrazine (reducing agent) contained in the aqueous solution. As described above, the nickel metal produced by the action of the reducing agent from the nickel ion taken into the purification system pipe 18 by the substitution reaction has strong adhesion to the base material of the purification system pipe 18. For this reason, the formed nickel metal film 82 does not peel off from the purification system pipe 18.

In this embodiment, after the inner surface of the purification system pipe 18 is reduced and decontaminated, nickel metal film 82 is formed on the inner surface of purification system pipe 18, so nickel is formed compared to when nickel metal film is formed on the oxide film. Contributes to the formation of a high ratio of stable nickel ferrite.

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

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

In the present embodiment, the respective steps of steps S1 to S17 in the method of suppressing corrosion of carbon steel members of the plant of Embodiment 1 are performed. The steps S1 to S15 are performed while the BWR plant 1 is shut down. In step S1 of this embodiment, one end of the circulation piping 31 of the film forming apparatus 30 on the side of the on-off valve 78 is connected to a first valve (not shown) provided in the water supply pipe 11 at the outlet of the low pressure water supply heater 14 The other end of the circulation pipe 31 on the side of the on-off valve 62 is connected to the second valve (not shown) provided to the water supply pipe 11 at the inlet of the high-pressure water supply heater 16. The first valve is provided in the water supply pipe 11 as close as possible to the outlet of the low pressure feed water heater 14 and the second valve as close as possible to the inlet of the high pressure feed water heater 16. The connection of the both ends of the circulation pipe 31 to the first valve and the second valve is performed in the same manner as the connection of the circulation pipe 31 to the valve 23 and the valve 25 in the first embodiment. Although the radionuclide is not attached to the inner surface of the water supply pipe 11 to be constructed, the high temperature water flows and an oxide film is formed, so that the low pressure feed water heater 14 and the high pressure feed water heater are formed in step S2. Chemical decontamination is performed on the inner surface of the water supply pipe 11 between 16 for the purpose of removing the oxide film.

Thereafter, the steps S3 to S17 described above are sequentially performed. An aqueous solution containing nickel ions and formic acid and having a pH of 4.0 at 90 ° C. is carried out from the film forming apparatus 30 to the water supply pipe 11 between the low pressure water supply heater 14 and the high pressure water supply heater 16. 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 feed water pipe 11 between the low pressure feed water heater 14 and the high pressure feed water heater 16.

After the determination in step S6 is "Yes", steps S7 and S8 are performed. The respective steps of steps S9 to S11 are performed, and an aqueous solution at 60 ° C. containing platinum ions, ammonia and hydrazine is supplied to the water supply pipe 11 between the low pressure water supply heater 14 and the high pressure water supply 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 is "Yes", each process of steps S13 to S15 is performed. In step S15, the circulation pipe 31 is removed from the water supply pipe 11, and the water supply pipe 11 is restored to the original state.

Thereafter, the BWR plant 1 is activated in step S16, and step S17 is performed. In step S17, the steam supplied from the RPV 3 to the turbine 9 is condensed by the condenser 10 in the reactor power rising process after the heating and pressurizing process of the reactor 2 is completed, and the water generated by this condensation is The water is supplied to the RPV 3 through the water supply pipe 11 as the water supply. The feed water flowing through the feed water pipe 11 is heated by the low pressure feed water heater 14. Soon, the low-pressure feedwater heater 14 discharges the feedwater having a temperature in the temperature range of 130 ° C. or more and less than 200 ° C. The feed water at this temperature contacts the platinum metal 84 deposited nickel metal film 82 formed on the inner surface of the feed water 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, the low-pressure feed water heater 14 discharges the feed water at 150 ° C.

The present embodiment can obtain each effect generated in the first embodiment for the water supply pipe 11 other than the adhesion suppression of the radionuclide.

A method of suppressing corrosion of a carbon steel member of a plant of embodiment 3 which is another embodiment of the present invention will be described with reference to FIG. The method for suppressing the corrosion of carbon steel members of the plant of this embodiment is applied to each of a carbon steel purification system pipe and a bottom drain pipe of a BWR plant. In the present embodiment, the respective steps of steps S1 to S17 in the method of suppressing corrosion of carbon steel members of the plant of Embodiment 1 are performed. The steps S1 to S15 are performed while the BWR plant 1 is shut down. In step S1 of the present 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 piping 31 of the film forming apparatus 30 on the side of the on-off valve 78 is branched into two, one branched end is connected to the valve 23, and the other branched end is connected to the bottom drain piping 89 It is connected to the provided valve 88. One end of the bottom drain pipe 89 is connected to the bottom of the RPV 3, 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 side of the on-off valve 62 is connected to the valve 25.

Thereafter, the steps S2 to S17 described above are sequentially performed. 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 purification system piping 18 and the bottom drain piping 89. In addition, the aqueous solution is supplied from the film forming apparatus 30A to a portion of the purification system pipe 18 between the valve 26 and the valve 32A. As a result, the nickel metal film is the inner surface of the bottom drain pipe 89, the inner surface of the portion of the purification system pipe 18 between the valve 23 and the valve 25, and the inner surface of the portion of the purification system pipe 18 between the valve 26 and the valve 32A. Are formed respectively.

After the determination in step S6 is "Yes", steps S7 and S8 are performed. Further, each step of steps S9 to S11 is carried out, and platinum is attached to the surface of the nickel metal film formed on the inner surface of the bottom drain pipe 89 and the purification system pipe 18. After the determination in step S12 is "Yes", each process of steps S13 to S15 is performed. In step S15, the circulation piping 31 is removed from the bottom drain piping 89 and the purification system piping 18, and the circulation piping 31A is removed from the purification system piping 18, and the bottom drain piping 89 and the purification system piping 18 are restored as they were.

Thereafter, the BWR plant 1 is activated in step S16, and step S17 is performed. In step S17, the reactor water in the RPV 3 is led to the purification system piping 18, and by opening the valve 88, the reactor water is also supplied to the bottom drain piping 89. When the reactor water of a temperature within the temperature range of 130 ° C. or more and less than 200 ° C. comes in contact with the nickel metal film to which platinum is attached formed on the inner surface of the bottom drain pipe 89 and the purification system pipe 18, the nickel metal film is stable. Converted to a nickel ferrite (NiFe ₂ O ₄ ) film.

The present embodiment can obtain each effect produced in the first embodiment.

A method of suppressing corrosion of a carbon steel member of a plant according to a fourth embodiment which is another preferred embodiment of the present invention will be described below with reference to FIGS. The method of inhibiting corrosion of a carbon steel member of the present embodiment is applied to the purification system piping of a BWR plant that has experienced operation in at least one operation cycle.

In this embodiment, the processes of steps S1 to S15 and S17 performed in the first embodiment and the processes of new steps S18 and S19 are performed. In the present embodiment, the film forming apparatus 30 used in the first embodiment 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 is a pressure-resistant structure, and includes a circulation pipe 92, a circulation pump 93, a heating device 94, and a valve 95 that is a pressure booster. A circulation pump 93 is provided in the circulation pipe 92, and a heating device 94 is provided in the circulation pipe 92 upstream of the circulation pump 93. The heating device 94 may be disposed 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 downstream of the circulation pump 93 to the circulation pipe 92. Connected A valve 95 is provided in the pipe 96. An on-off valve 97 is provided at the upstream end of the circulation pipe 92, and an 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 the present embodiment, after each step of steps S1 to S13 is performed, the film forming device 30 connected to the purification system piping 18 is removed from the purification system piping 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 side of the on-off valve 98 is connected to the flange of the valve 23, and the circulation pipe 92 is in communication with the purification system pipe 18. The other end of the circulation pipe 92 on the side of the on-off valve 97 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-regenerating 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 within a temperature range of 130 ° C. or more and less than 200 ° C. is brought into contact with the platinum-deposited nickel metal film (step S17). Water containing oxygen is filled in a closed loop including the circulation pipe 92 and the purification system pipe 18. The circulation pump 93 is driven to circulate oxygen-containing water in the closed loop. The rotational speed of the circulation pump 93 is increased to a certain rotational 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 the water containing oxygen circulating in the closed loop to raise the temperature of the water. Thus, the temperature of the water is raised while the pressure of the water discharged from the circulation pump 93 is increased. 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, for example, the range of 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 regulated, and the temperature of the water is regulated to a temperature range of 130 ° C. or more and less than 200 ° C., for example, 150 ° C. The temperature of water circulating in the closed loop is maintained at 150 ° C. while the nickel metal film formed on the inner surface of the purification system pipe 18 is converted to a stable nickel ferrite film.

150 ° C. water 86 A containing oxygen is supplied from the circulation pipe 92 to the purification system pipe 18 and contacts the nickel metal film 82 formed on the inner surface of the purification system pipe 18 to which platinum 84 is attached (see FIG. 7) . The purification system piping 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 piping 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 to a temperature of 150 ° C.

Since each of the water 86A containing oxygen, the purification system pipe 18 and the nickel metal film 82 reaches 150 ° C., it constitutes oxygen (O ₂ ) contained in the water 86A and some water molecules contained in the water 86A Oxygen is transferred into the nickel metal film 82, and Fe contained in the purification system pipe 18 is converted into Fe ²⁺ to be transferred into the nickel metal film 82 (see FIG. 8). The oxygen contained in the water 86A easily moves alone in the water 86A of 130 ° C. or more, and easily enters the nickel metal film 82. The action of the platinum 84 attached to the nickel metal film 82 lowers the corrosion potential of the purification system pipe 18 and the nickel metal film 82. Due to the reduction of the corrosion potential of the nickel metal film 82 and the formation of a high temperature environment of 150 ° C., the nickel in the nickel metal film 82 reacts with the oxygen and Fe ²⁺ transferred into the nickel metal film 82 to ^obtain Ni _1-x Fe _A stable nickel ferrite (NiFe ₂ O ₄ ), which does not elute by the action of platinum where x is 0 in _{2 + x} O ₄ , is produced. For this reason, the nickel metal film 82 formed on the inner surface of the purification system pipe 18 is converted to a stable nickel ferrite (NiFe ₂ O ₄ ) film 87, and the nickel ferrite film 87 corresponds to the

valves

23 and 25 of the purification system pipe 18. It covers the inner surface of the part in between (see FIG. 9). Platinum adheres 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 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. Thereafter, the purification system piping 18 is restored.

In the present 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 between the valve 26 and the valve 32A. When a nickel metal film on the surface of which platinum adheres is formed on the inner surface of the part, the film forming apparatus 30A is removed from the purification system pipe after the process of step S14 (step S15). The two ends of 92 are connected to

valves

26 and 32, respectively. Then, 150 ° C. water containing oxygen from the heating system 91 is supplied to the portion of the purification system piping 18 between the valve 26 and the valve 32A as described above. The platinum-deposited nickel metal film formed on the inner surface of the portion of the purification system piping 18 between the valve 26 and the valve 32A is converted into a stable nickel ferrite film with platinum attached (step S17). Thereafter, another heating system 91 is also removed from the purification system pipe 18.

A BWR plant having a purification system pipe 18 on the inner surface of which a nickel ferrite film 87 to which platinum 84 is attached is formed to start operation in the next operation cycle after refueling and maintenance inspection of the BWR plant 1 are completed. 1 is activated. The reactor water flowing in the purification system piping 18 is not in direct contact with the base material of the purification system piping 18 because the nickel ferrite film 87 is formed.

The present embodiment can obtain the effects produced in the first embodiment. Furthermore, in the present 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 using the heating system 91, the conversion process in step S17 is processed by the BWR plant 1 It can be done while the operation is stopped. Therefore, when the BWR plant 1 is started, the stable nickel ferrite film 87 is already formed on the inner surface of the purification system pipe 18, so in the present embodiment, the stable nickel ferrite on the inner surface in the first embodiment. Corrosion of the purification system piping 18 can be suppressed even before the film 87 is formed.

Furthermore, in the present embodiment, oxygen-containing water in the temperature range of 130 ° C. or more and less than 200 ° C. is brought into contact with the nickel metal film 82 formed on the inner surface of the purification system pipe 18 using the heating system 91. The time required to heat the water to a predetermined temperature can be shortened. Also, the degree of pressure resistance required of the heating system 91 can be reduced.

A method of suppressing corrosion of a carbon steel member of a plant of embodiment 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 a plant of this embodiment is applied to a carbon steel water supply pipe of a thermal power plant (hereinafter referred to as a thermal 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, which is a steam generating device, a high pressure turbine 9A, a low pressure turbine 9B, a condenser 10, and a water supply system. The high pressure turbine 9A and the low pressure turbine 9B are connected to the boiler 99 by the main steam pipe 8. A moisture separation superheater 100 including a moisture separator 101 and a superheater 102 is installed in the main steam piping 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 upstream of the main steam control valve 110 and provided with an on-off valve 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 further to the generator 103. The low pressure turbine 9 B is in communication with the condenser 10 by the steam passage 105. In the condenser 10, a heat transfer pipe 113 through which seawater flows is disposed. Condenser pump 12, low-pressure feedwater heater 14B, low-pressure feedwater heater 14A, feedwater pump 15 and high-pressure feedwater heater 16 are connected to feedwater pipe 11 connecting condenser 10 and boiler 99 from condenser 10 to boiler It is installed in this order toward 99.

A steam extraction pipe 107 connected to the high pressure turbine 9 A and a steam discharge pipe 112 connected to the superheater 102 are connected to the high pressure feed water heater 16. A bleed pipe 108A connected to the low pressure turbine 9B and a drain pipe 111 connected to the moisture separator 101 are connected to the low pressure feed water heater 14A. A bleed pipe 108B connected to the low pressure turbine 9B at a later stage than the connection point of the bleed pipe 108A is connected to the low pressure feed water heater 14B. A 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 by the boiler 99 is supplied to the high pressure turbine 9A and the low pressure turbine 9B, and 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 pipe 113 by the seawater pump 114 to become water. This water passes through the feed water pipe 11 as feed water, and is heated by the high pressure feed water heater 16 and the low pressure

feed water heaters

14A and 14B and supplied to the boiler 99 along the way.

Also in the present embodiment, each process of steps S1 to S17 implemented in the first embodiment is performed. However, in the present embodiment, not the nuclear power plant but the thermal power plant is started in step S16, and the feed water instead of the reactor water is contacted with the nickel metal film in step S17.

In step S1, the above-described film forming apparatus 30 is connected to the water supply pipe 11 between the low pressure water supply heater 14A and the low pressure water supply 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. Is connected to a second valve (not shown) installed in the water supply pipe 11 at a position close to the outlet of the low pressure water supply heater 14B. In order to remove the oxide film formed on the inner surface of the portion of the water supply pipe 11, reduction decontamination is performed (step S2). Thereafter, the steps S3 to S17 described above are sequentially performed. The steps S4 and S5 are performed, and a nickel metal film is formed on the inner surface of the water supply pipe 11 between the low pressure water supply heater 14B and the low pressure water supply heater 14A.

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

Thereafter, in step S16, the thermal power plant is activated, and step S17 is performed. 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 the condensation is supplied to the boiler 99 through the water supply pipe 11 as the water supply. The feedwater flowing through the feedwater pipe 11 is heated by the low

pressure feedwater heaters

14 B and 14 A and the high pressure feedwater heater 16. Soon, a temperature within the temperature range of 130 ° C. to less than 200 ° C., for example, 160 ° C. of feed water is discharged from the low pressure feed water heater 14B. The feed water at this temperature contacts the nickel metal film 82 with platinum 84 deposited on the inner surface of the portion of the feed water pipe 11 between the low pressure feed water heater 14B and the low pressure feed water heater 14A. 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.

Such a present Example can acquire each effect which arises in Example 1 for water supply piping 11 other than adhesion control of a radionuclide.

In each of the second, third, and fifth embodiments, each step of steps S18 and S19 may be performed instead of step S16, and the step of step S17 may be performed using the heating system 91.

DESCRIPTION OF SYMBOLS 1 ... Boiling water type nuclear power plant, 2 ... Reactor pressure vessel, 4 ... Core, 6: Recirculation system piping, 9 ... Turbine, 9A ... High pressure turbine, 9B ... Low pressure turbine, 11 ... Water supply piping, 14, 14A, 14B: low pressure feed water heater, 16: high pressure feed water 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 solution tank, 38, 43, 48 ... Injection pump, 41 ... Reduction agent injection device, 46 ... Platinum ion injection device, 52 ... Cooler, 53 ... Cation exchange resin Tower, 54: mixed bed resin tower, 55: decomposition device, 56: oxidant supply device, 58: supply pump, 82: nickel metal film, 84: platinum, 87: nickel ferrite film, 89: bottom drain Pipe, 91 ... heating system, 99 ... boiler.

Claims

A nickel metal film is formed on the surface of a carbon steel member of a plant in contact with water, the surface is covered with the nickel metal film, a noble metal is adhered to the surface of the nickel metal film, and the noble metal is adhered. Contact with water containing an oxidizing agent at 130 ° C. or more and less than 200 ° C., and the formation of the nickel metal film and the deposition of the noble metal are performed after the shutdown of the plant and before the start of the plant. Method for suppressing the corrosion of carbon steel members in plants.
The formation of the nickel metal film is performed by bringing a film forming solution containing nickel ions and a reducing agent into contact with the surface of the carbon steel member, and the deposition of the noble metal forms the aqueous solution containing noble metal ions and a reducing agent. The method of inhibiting corrosion of a carbon steel member of a plant according to claim 1, which is performed by contacting the surface of the formed nickel metal film.
The method of suppressing corrosion of a carbon steel member of a plant according to claim 2, wherein the pH of the film forming solution 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 formation of the nickel metal film is performed after removing the oxide film formed on the carbon steel member.
The method for suppressing corrosion of a carbon steel member 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 a carbon steel member of a plant according to claim 5, wherein at least one of formic acid and an oxidizing agent is injected into the reduction decontamination solution used for the chemical decontamination.
The method for suppressing corrosion of carbon steel members of a plant according to claim 6, wherein the timing of injecting formic acid or the oxidizing agent or both into the oxalic acid solution is after the start of the decomposition step of the reducing agent.
The film-forming solution is supplied through a second pipe to a first pipe, which is the carbon steel member, in which the formation of the nickel metal film is communicated to a steam generating apparatus, and the film-forming liquid is used as the carbon steel member. The inner surface of the first pipe being in contact with the inner surface of the first pipe,
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 of inhibiting corrosion of a carbon steel member of a plant according to claim 2, which is performed by contacting the surface of the film.
The carbon steel plant according to claim 8, wherein the film forming solution is circulated in a 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. Corrosion control method for parts.
The method for inhibiting corrosion of carbon steel member of plant according to claim 8 or 9, wherein the contact of the water at 130 ° C or more and less than 200 ° C with the nickel metal film to which the noble metal is attached is performed after the plant is started. .
The plant according to claim 10, wherein the plant is a nuclear plant, and the steam generator is a nuclear reactor, and the water of 130 ° C. or more and less than 200 ° C. is reactor water generated by heating in the nuclear reactor. Corrosion control method of carbon steel member of plant.
The high-pressure feedwater heating apparatus and the low-pressure feedwater heating apparatus disposed at the front stage of the high-pressure feedwater heating apparatus, provided in the plant, are the feedwaters supplied to the steam generator and the water at 130 ° C or more and less than 200 ° C. The method for suppressing corrosion of a carbon steel member of a plant according to claim 10, wherein the feed water is heated by the low pressure feed water 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 oxidizing agent is included. The supply of the water to the first pipe at 130 ° C. or more and less than 200 ° C. circulates the inside of the closed loop, and the water containing the oxidant is heated to 130 ° C. or more 200 by the heating device provided in the third pipe. C. by heating to a temperature range of less than .degree. C. and supplying the first pipe from the third pipe, and the conversion of the nickel metal film to the nickel ferrite film to which the noble metal is attached is the inner surface of the first pipe. The nickel metal film formed on the substrate is brought into contact with the water containing the oxidizing agent supplied from the third pipe, and the nickel metal film is the nickel metal film having the noble metal attached thereto. After being converted into Kel ferrite film, the third pipe corrosion inhibiting method for a carbon steel member of the plant of claim 8 which is detached from the first pipe.
14. 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 corrosion control method of the carbon steel member of the plant as described in a term.