JP2020098183A - Method for inhibiting adherence of radionuclide to carbon steel member of nuclear power plant - Google Patents

Abstract

To provide a method for inhibiting adherence of radionuclides to a carbon steel member, with which the adherence of radionuclides to a carbon steel member of a nuclear power plant is further restricted.SOLUTION: A formic acid Ni aqueous solution is infused (S5) into a circulation pipeline of a film forming device connected to a purification system pipeline made of carbon steel. The aqueous solution containing formic acid Ni is led to the purification system pipeline, and a Ni metal film is formed on an inner surface thereof. A platinum ion aqueous solution and hydrazine are infused (S10, S11) into the circulation pipeline, and the aqueous solution containing platinum ions and hydrazine is supplied to the purification system pipeline so that platinum is adhered to a surface of the Ni metal film. The film forming device is removed from the purification system pipeline and a BWR plant is started up (S16). Reactor water of 130°C or more containing infused oxygen is brought into contact with the Ni metal film, and a corrosion potential of the purification system pipeline is set (S18) to a high corrosion potential of 0 mV or higher. A crystal grain boundary density of a Ni ferrite film converted from the Ni metal film is reduced, so that adherence of radionuclides to the purification system pipeline is further restricted.SELECTED DRAWING: Figure 1

Description

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

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

In BWR plants and PWR plants, main constituent members such as RPV use stainless steel, nickel-based alloys, and the like for the water contact portions in contact with water in order to suppress corrosion. Components such as the reactor cleaning system, residual heat removal system, reactor isolation cooling system, core spray system and water supply system are used to reduce the manufacturing cost of the plant or stress of stainless steel caused by high temperature water. From the viewpoint of avoiding corrosion cracking, carbon steel members are mainly used.

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

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

Chemicals for removing oxide films containing radioactive nuclides such as cobalt 60 and cobalt 58 formed on the surface of a component of a nuclear power plant that has experienced operation, for example, the surface of pipes in contact with reactor water, by dissolution using chemicals A decontamination method has been proposed (Japanese Patent Laid-Open No. 2000-105295).

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

JP-A-2007-182604 discloses a film forming liquid in the range of 60°C to 100°C containing iron (II) ions, nickel ions, an oxidizing agent and a pH adjusting agent (for example, hydrazine) while the nuclear power plant is not operating. Is brought into contact with the surface of a carbon steel structural member of a nuclear power plant after chemical decontamination, and a nickel ferrite film is formed on this surface. The formation of the nickel ferrite film suppresses the corrosion of the carbon steel structural member and suppresses the adhesion of the radionuclide to the structural member.

JP2012-247322A discloses that a film forming liquid containing iron (II) ions, an oxidizing agent and a pH adjusting agent (hydrazine) in a range of 60°C to 100°C is supplied to a nuclear power plant while the nuclear power plant is not operating. , Making contact with the surface of a chemically decontaminated stainless steel component, and forming a magnetite film on this surface. Japanese Unexamined Patent Application Publication No. 2012-247322 also describes that an aqueous solution containing a noble metal (for example, platinum) is brought into contact with the formed magnetite film during operation stop to deposit the noble metal on the magnetite film.

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

Japanese Unexamined Patent Application Publication No. 2014-44190 describes a method of depositing a noble metal on a component of a nuclear power plant. In this noble metal deposition method, in the chemical decontamination performed while the nuclear power plant is out of operation, the noble metal (for example, platinum ), or a noble metal is attached to the surfaces of the constituent members in the purification step after the step of decomposing the reducing decontaminating agent. The adhesion of the noble metal to the surface of the constituent member suppresses the adhesion of the radionuclide to the surface.

JP-A-2018-48831 discloses that a nickel metal film is formed on the surface of a carbon steel member, a noble metal is attached to the surface of the nickel metal film, and the surface of the nickel metal film to which the noble metal is attached contains oxygen. A stable nickel ferrite film (Ni _1-x Fe _2+x O ₄ in which the nickel metal film that covers the surface of the carbon steel member and does not elute by the action of the noble metal is x It is described that the nickel ferrite film is 0).

JP-A-2000-105295 JP, 2006-38483, A JP, 2007-182604, A JP2012-247322A JP, 2011-32551, A JP, 2014-44190, A JP, 2018-48831, A

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

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

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

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

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

(A2) Preferably, in (A1) above, when the period for injecting the oxidant into the reactor water has passed a predetermined period, hydrogen is injected into the reactor water to reduce the corrosion potential of the carbon steel member to less than 0 mV. It is desirable to do.

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

According to the present invention, it is possible to further suppress the attachment of radionuclides to the carbon steel member of a nuclear power plant.

It is a flow chart which shows the procedure of the adhesion control method of a radionuclide to the structural member of the nuclear power plant of Example 1 applied to the purification system piping of a boiling water nuclear power plant which is one suitable example of the present invention. It is explanatory drawing which shows the state which connected the purification|cleaning system piping of the boiling water nuclear power plant with the precious metal injection apparatus used when implementing the adhesion suppression method of the radionuclide to the structural member of the nuclear power plant of Example 1. It is a detailed block diagram of the precious metal injection apparatus shown in FIG. It is sectional drawing of the purification|cleaning system piping of the boiling water nuclear power plant before the method of suppressing the adhesion of radionuclides to the structural members of the nuclear power plant shown in 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 the purification|cleaning system piping by the adhesion suppression method of the radionuclide to the structural member of the nuclear power plant shown in FIG. Explanatory diagram showing a state in which precious metal particles containing nickel metal are attached to the surface of a nickel metal coating formed on the inner surface of the purification system pipe by the method of suppressing the attachment of radionuclides to the structural members of the nuclear power plant shown in FIG. 1. Is. It is explanatory drawing which shows the state which contacts the reactor water which has the temperature within the temperature range of 130 degreeC or more and 330 degreeC or less with the nickel metal film which adhered the noble metal formed in the inner surface of purification system piping. It is explanatory drawing which shows typically the state of the nickel ferrite film|membrane when the nickel metal film|membrane which adhered the noble metal formed in the purification|cleaning system piping inside was converted into nickel ferrite by low potential environmental water quality. It is explanatory drawing which shows typically the state of the nickel ferrite film|membrane when the nickel metal film|membrane which adhered the noble metal formed in the purification|cleaning system piping inside was converted into nickel ferrite with high potential environmental water quality. It is explanatory drawing which compared the Co-60 adhesion speed by the difference of the conversion water quality conditions of the nickel metal film which the noble metal adhered to the nickel ferrite film. Each of the polished carbon steel test piece and the carbon steel test piece on which the nickel metal film to which the noble metal is adhered is brought into contact with simulated reactor water containing Co-60. It is explanatory drawing which shows the laser Raman spectrum analysis result of the formed film. It is a characteristic view which shows the relationship between pH of the film formation aqueous solution which contacts the surface of a carbon steel test piece, and the amount of the nickel metal film formed on the surface of the carbon steel test piece. It is a characteristic view which shows the relationship between the density|concentration of the formic acid and the density|concentration of ammonia which are inject|poured into a film formation aqueous solution using pH of a film formation aqueous solution as a parameter. It is explanatory drawing which shows the adhesion suppression method of the radionuclide to the structural member of the nuclear power plant of Example 2 applied to the purification|cleaning system piping of the boiling water nuclear power plant which is another suitable Example of this invention.

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

In order to solve such a problem, in JP-A-2018-48831, a nickel metal film is formed on the surface of a carbon steel member, a noble metal is adhered to the surface of the nickel metal film, and nickel having the noble metal adhered thereto is formed. Water containing oxygen and having a temperature within the temperature range of 200° C. to 330° C. is brought into contact with the surface of the metal film. As a result, the nickel metal coating covers the surface of the carbon steel member and is a stable nickel ferrite coating that does not elute even by the action of the attached noble metal ( _{x in} Ni _1-x Fe _2+x O ₄ is, for example, 0). It is converted into a certain nickel ferrite film, that is, a NiFe ₂ O ₄ film) (see paragraphs 0037 to 0040 of JP-A-2018-48831). By the stable nickel ferrite film covering the surface of the carbon steel member, the effect of suppressing the adhesion of the radionuclide to the carbon steel member can be maintained for a longer period.

The method of suppressing the attachment of radionuclides to carbon steel members of a nuclear power plant described in JP-A-2018-48831 suppresses the adhesion of radionuclides to the carbon steel members. However, the inventors have made various studies with the aim of realizing a measure capable of further suppressing the adhesion of radionuclides to carbon constituent members of a nuclear power plant as compared with the adhesion suppression method described in Japanese Unexamined Patent Application Publication No. 2018-48831. went. As a result, the inventors have found an effective method that can further suppress the attachment of the radionuclide to the carbon constituent member. The results of this examination will be described below.

It is desirable that the formation of the nickel metal film on the surface of the carbon steel member of the nuclear power plant that comes into contact with the cooling water, that is, the reactor water, be performed subsequent to the chemical decontamination of the surface. The advantage thereof is that the functions of raising the temperature, injecting, circulating and purifying the chemical used in the chemical decontamination can be utilized for the formation of the nickel metal film. Regarding the chemical to be used, nickel formate was used by using formic acid capable of decomposing into water or carbon dioxide as a counter anion of nickel. When carbon steel is immersed in an aqueous solution of nickel formate, a displacement plating reaction represented by the following formula (1) occurs and a nickel metal film is formed on the surface of carbon steel.

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

2Ni ²⁺ +N ₂ H ₄ → Ni+N ₂ +2H ⁺ +H ₂ (2)
In this way, after forming a nickel metal film on the surface of the carbon steel member of the nuclear power plant that is out of operation, the surface of this nickel metal film contains hydrazine as a reducing agent, and hexahydroxoplatinic acid of a platinum aqueous solution. The aqueous sodium solution is brought into contact to deposit platinum on the surface of the nickel metal coating. After that, the nuclear power plant is restarted, and hydrogen is injected into reactor water of the nuclear power plant for the purpose of suppressing stress corrosion cracking. By injecting hydrogen, reactor water of a corrosive environment mitigating water quality that reduces the corrosion potential of the member in contact with the reactor water to −230 mV or less is generated. When the hydrogen-containing reactor water of this corrosive environment mitigating water is brought into contact with the nickel metal film formed on the surface of the carbon steel member and having platinum adhered thereto, the action of platinum and hydrogen causes the carbon steel member and the nickel metal film to react. The corrosion potential of No. 1 drops to about -500 mV. In such a corrosive environment, an oxidation reaction by oxygen contained in the reactor water at a high temperature (a temperature within a temperature range of 130° C. to 330° C.) in contact with the nickel metal film, and carbon steel as a base material of the carbon steel member The reaction represented by the following formula (3) occurs due to the action of iron ions formed by the oxidation reaction of the above, and the above nickel metal film is converted into a stable nickel ferrite film that does not elute even by the action of the attached platinum. To be done.

2Ni+2Fe+2O ₂ →NiFe ₂ O ₄ (3)
This stable nickel ferrite film contributes to the suppression of adhesion of radionuclide (for example, Co-60). However, the inventors conducted the following experiment in order to find a method of further enhancing the Co-60 adhesion suppressing effect of this nickel ferrite film. In this experiment, the conversion of the nickel metal film into the nickel ferrite film was performed in a high corrosion potential environment of 0 mV or higher, instead of in a low corrosion potential environment of -500 mV. In the experiment, the inventors used carbon steel polishing test pieces as the test pieces A and C, and formed nickel metal coatings on the surfaces of the carbon steel polishing test pieces as the test pieces B and D. A test piece having platinum adhered to the surface of this coating was used.

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

In this Co-60 adhesion experiment, the immersion time of each of the test pieces A and B in the simulated water flowing in the circulation pipe was 500 hours, 1000 hours, and 1500 hours. For this reason, each of the test pieces A and B is used in three pieces corresponding to three kinds of immersion times. Each time each immersion time of 500 hours, 1000 hours, and 1500 hours passed, the test pieces A and B were taken out one by one from the circulation pipe, and the Co-60 adhesion amount of each taken-out test piece was measured. Based on the amount of Co-60 deposition on each of the test pieces A and B at each immersion time, the average Co-60 deposition rate on each of the test pieces A and B at time intervals t ₁ , t ₂ and t _3. I asked. The time section t ₁ is 0 hours<t ₁ ≦500 hours, the time section t ₂ is 500 hours<t ₂ ≦1000 hours, and the time section t ₃ is 1000 hours<t ₃ ≦1500 hours.

On the other hand, also in the Co-60 adhesion experiment using the test pieces C and D, each of the test pieces C and D is immersed in the above-described simulated water containing Co-60 and circulating at 280° C. in the circulation pipe. In the Co-60 adhesion experiment using the test pieces C and D, in the first 500 hours, a simulated water of a corrosive environment forming water quality (normal reactor water quality environment (NWC)) in which dissolved oxygen exists and dissolved hydrogen does not exist ( A temperature of 280° C.) was used to generate an environment in which the circulation pipe had a high corrosion potential within the range of 0 mV or more and +200 mV or less, and under this environment, the Co-60 adhesion experiment was performed. When the first 500 hours have passed, hydrogen is injected into the simulated water that circulates in the circulation pipe, and the simulated water of the corrosion environment mitigating water quality that contains 100 ppb oxygen and 40 ppb hydrogen causes the circulation pipe to have a low corrosion potential of -500 mV. An environment was created and Co-60 adhesion experiments on test pieces C and D were performed in this environment. The immersion time for immersing each of the test pieces C and D in the simulated water having a corrosive environment relaxing water quality was set to two kinds of 1000 hours and 1500 hours.

Each time the immersion time of 500 hours, 1000 hours, and 1500 hours passed, the test pieces C and D were taken out one by one from the circulation pipe, and the Co-60 adhesion amount in each taken-out test piece was measured. Based on the Co-60 deposition amount on each of the test pieces C and D at each immersion time, the average Co-60 deposition rate on each of the test pieces C and D at time intervals t ₁ , t ₂ and t _3. I asked.

Co-60 deposition rates for each of the test pieces A, B, C and D are shown in FIG. As is clear from FIG. 10, in the test pieces B and D in which the nickel metal film was formed on the surface and platinum was attached to the surface of the nickel metal film, the nickel metal film was not formed on the surface and platinum was also attached. The deposition rate of Co-60, that is, the amount of Co-60 deposited was remarkably reduced as compared with the test pieces A and C which were not tested.

Then, the compositions on the respective surfaces of the test pieces A, B, C and D taken out from the circulation pipe were analyzed by Raman spectroscopy. The result of this analysis is shown in FIG. On the respective surfaces of the test pieces A and C which were substantially carbon steel, a film mainly composed of Fe ₃ O ₄ was formed. An oxide film containing nickel ferrite (NiFe ₂ O ₄ ) as a main component was formed on each surface of the test pieces B and D in which the amount of Co-60 deposited was significantly reduced. This NiFe ₂ O ₄ has a form in which x is 0 in Ni _1-x Fe _2+x O ₄ .

The Co-60 deposition rate for each of the test pieces A, B, C and D will be specifically described with reference to FIG. Comparing the polishing test piece A immersed in only simulated water of corrosive environment mitigating water quality with the test piece B having the nickel metal film formed thereon, the test piece B is more than the test piece A in the time sections t ₂ and t _3. Co-60 deposition rate is low. Comparing the difference in the adhesion speed between the test piece B and the test piece A, the difference becomes smaller as time passes from the time section t ₂ to the time section t ₃ . On the other hand, in the time section t ₁ in which the polishing test piece C and the test piece D on which the nickel metal film is formed are immersed in simulated water of corrosive environment forming water quality, the respective Co-60 deposition rates are the same. When the immersion time further elapses after the time section t ₁ and the time section t ₂ is reached, the Co-60 adhesion rate of the test piece D rapidly decreases to almost the same as that of the test piece B, and the time section t ₃ Then, the Co-60 adhesion rate of the test piece D becomes smaller than that of the test piece B because the Co-60 adhesion rate of the test piece B increases.

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

As a result, the inventors formed a nickel metal film on the surface of the carbon steel member, and then formed the nickel metal film formed on the surface of the nickel metal film, rather than contacting the surface of the nickel metal film with the reactor water having a mitigating environment for corrosive environment from the beginning. By first contacting the coating with reactor water of corrosive environment forming water quality, and then contacting with reactor water of corrosive environment mitigating water quality, the nickel metal coating is effective for suppressing the adhesion of radionuclides for a longer period of time. It was found that it can be converted into a stable nickel ferrite film.

The nickel metal film of a carbon steel member (test pieces B and D) having a nickel metal film formed on the surface and a noble metal (for example, platinum) attached to the surface of the nickel metal film contains oxygen at 130°C to 330°C. Stable nickel ferrite film (Ni _1-x Fe _2+x O ₄ 0≦x for Ni _1-x Fe _2+x O ₄₎ that does not elute even by the action of the noble metal that has adhered to it when it comes into contact with water at a temperature within the temperature range The reason for conversion into nickel ferrite satisfying <0.3, for example, NiFe ₂ O ₄ ) will be described.

Corrosion that is water having a temperature within the range of 130°C to 330°C and is generated by the injection of oxygen (oxidizer) to make the corrosion potential of the carbon steel member within the range of 0 mV to +200 mV. When the water of the environment forming water quality comes into contact with the nickel metal coating formed on the surface of the carbon steel member, the nickel metal coating formed on the surface of the carbon steel member becomes, for example, in Ni _1-x Fe _2+x O ₄ . It is converted to a stable nickel ferrite film with x=0. Specifically, the nickel metal film and the carbon steel member are heated to 130° C. or higher by the water of the corrosive environment forming water quality. Oxygen contained in the water migrates into the nickel metal film, and Fe contained in the carbon steel member becomes Fe ²⁺ and migrates into the nickel metal film. Nickel in the nickel metal film reacts with oxygen and Fe ²⁺ transferred into the nickel metal film in a high temperature environment of 130° C. or higher, and precious metals such as platinum adhered to the surface of the nickel metal film and carbon steel members By the action of water of a corrosive environment-forming water quality, which makes the corrosion potential within the range of 0 mV or more and +200 mV or less, the nickel metal film has a stability such that x is 0 in Ni _1-x Fe _2+x O ₄ It is converted into a nickel ferrite film. This stable nickel ferrite film covers the surface of the carbon steel member.

Incidentally, unstable nickel ferrite eluted by the action of the noble metal attached to the surface is a nickel ferrite satisfying 0.3≦x<0 in Ni _1-x Fe _2+x O ₄ , for example, Ni _0.7 Fe _2.3 O. _{Is 4} . As described above, Ni _0.7 Fe _2.3 O ₄ is nickel ferrite in which x is 0.3 in Ni _1-x Fe _2+x O ₄ .

In the Ni _1-x Fe _2+x O ₄ produced as described above from the nickel metal contained in the nickel metal film covering the surface of the carbon steel member in a high temperature environment of 130° C. or more, x is 0. A certain nickel ferrite has large crystal growth, and even if a noble metal adheres, it is stable without elution in water like a Ni _0.7 Fe _2.3 O ₄ film. In the stable nickel ferrite film, the inventors of the present invention reduced the density of crystal grain boundaries due to the large size of nickel ferrite crystals, and the diffusion of radionuclides such as Co-60 into the nickel ferrite film through the grain boundaries. I thought it was suppressed. As described above, in a high temperature environment of 130° C. or higher, the stable nickel ferrite film formed from the nickel metal covering the surface of the carbon steel member has a low temperature range of 60° C. to 100° C. Adhesion of radionuclides to carbon steel members can be suppressed for a longer period of time than the _0.7 Fe _2.3 O ₄ coating.

Note that Japanese Patent Application No. 2018-49244 (filing date: March 16, 2018), which is a prior application, also describes in the specification that "from the nickel metal contained in the nickel metal coating covering the surface of the carbon steel member, 130 Ni _1-x Fe _2+x O ₄ produced as described above in a high temperature environment within a temperature range of ℃ to 330 ℃, nickel ferrite with x=0 in Ni _1-x Fe _2+x O ₄ has large crystal growth. (See paragraph 0064, lines 2 to 4), the size of stable nickel ferrite crystals converted from nickel metal becomes large, and the adhesion of radionuclides to carbon steel members can be suppressed.

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

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

Based on the above-described examination results, the inventors were able to newly create the invention described below. That is, the inventors have brought a film-forming aqueous solution containing nickel ions and a reducing agent into contact with the surface of a carbon steel member to form a nickel metal film on the surface of the carbon steel member and attach a noble metal to the surface of the nickel metal film. And has a temperature within a temperature range of 130° C. or higher and 330° C. or lower containing oxygen, and the corrosion potential of the carbon steel member generated by the injection of the oxidizing agent is 0 mV or higher (specifically, a range of 0 mV or higher and +200 mV or lower). (Corrosion potential inside) by contacting water of a corrosive environment forming water quality with a nickel metal film having a precious metal adhered to the surface thereof, resulting in stable nickel ferrite having a large particle size (eg, NiFe ₂ O ₄ ). Will be included in the stable nickel ferrite film converted from the nickel metal film, further reducing the density of the nickel ferrite crystal grain boundaries of this nickel ferrite film. We came up with the idea of a new method of suppressing adhesion. As is clear from the comparison between the deposition rate of Co-60 of the test piece B and the deposition rate of Co-60 of the test piece D in the time section t ₃ shown in FIG. 10, the corrosion potential of the carbon steel member was 0 mV or more. Corrosion environment forming water with a corrosion potential within the range of +200 mV or less The water of the water quality is formed on the surface of the carbon steel member and is brought into contact with the nickel metal film to which the noble metal is adhered. For example, a nickel metal film is formed on the surface of a carbon steel member, noble gold (for example, platinum) is attached to the surface of this nickel metal film, and the nickel metal film has a corrosion environment mitigating water quality in which dissolved hydrogen exists, Adhesion of the radionuclide to the carbon steel member can be significantly suppressed as compared with the case where water having a temperature of 280° C. is contacted (test piece B).

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

Furthermore, in order to investigate the amount of nickel metal film formed on the surface of carbon steel by each reaction of formula (1) and formula (2), a carbon steel test piece is dipped in a nickel formate aqueous solution at 90° C. When 60 minutes have passed from the start, the test case was taken out from the nickel formate aqueous solution, and another carbon steel test piece was immersed in the nickel formate aqueous solution, and 60 minutes had elapsed from the start of immersion. , Hydrazine (reducing agent) was injected into the nickel formate aqueous solution in which the test piece was immersed, and the test piece immersed in the formic acid solution containing hydrazine was immersed in the formic acid solution containing hydrazine for 4 hours. Then, the amounts of the nickel metal film formed on the respective test pieces were compared for each of the second cases taken out of the formic acid aqueous solution containing hydrazine.

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

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

In order to control the pH of the film-forming aqueous solution within the range of 3.9 to 4.2, attention has been paid to a pH buffer solution. In addition to adjusting the pH of the film-forming aqueous solution with the nickel formate aqueous solution, the pH of the film-forming aqueous solution is adjusted. Injection of buffer solution was considered. The pH buffer solution is a mixed solution of a weak acid and a weak base, and even if diluted or externally added with an acid or a base, it is not significantly affected by them and the hydrogen ion concentration (pH) does not change so much. Is. Such a pH buffer solution includes, for example, a mixed solution of formic acid contained in nickel formate, which is a weak acid, and ammonia, which is easy to handle for a weak base, for example, ammonia. Each of the weak acid and the weak base is a component of the pH buffer solution. For example, in a mixed solution of formic acid and ammonia, which is an example of a pH buffer solution, each of formic acid and ammonia is a component of the pH buffer solution. It can be said that the pH buffer solution contains one component each of acid and base. By injecting the pH buffer solution into the film-forming aqueous solution, the pH of the film-forming aqueous solution can be kept constant at a certain value, for example, a pH within the range of 3.9 or more and 4.2 or less. Another example of the pH buffer solution is a mixed solution of acetic acid and ammonia. Formic acid and acetic acid contained in the pH buffer solution can be decomposed by the action of a catalyst and an oxidizing agent.

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

^{HCOOH → H + + HCOO - ......} (4)

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

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

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

NH ₄ ⁺ → H ⁺ +NH ₃ (7)

Here, K _A is an acid dissociation multiplier of ammonia, [NH ₃ ] is an ammonia concentration of the film forming aqueous solution, and [NH ₄ ⁺ ] is an ammonia ion concentration of the film forming aqueous solution.

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

[NH ₃ ] _T =[NH ₃ ]+[NH ₄ ⁺ ] (9)
When the ionic product K _{W of} water is expressed as K _W =[H ⁺ ][OH ⁻ ], the ion balance equation is expressed by equation (10). In addition, [OH ⁻ ] is a hydroxide ion concentration.

[H ⁺ ]+[NH ₄ ⁺ ]=[OH ⁻ ]+[HCOO ⁻ ]... (10)
Regarding [NH ₄ ⁺ ], [OH ⁻ ] and [HCOO ⁻ ] of the formula (10), the relation between the formula (5), the formula (6), the formula (8), the formula (9) and the ion product K _W of water. By rearranging using, the equation (11) is obtained.

With K _F =1.12×10 ⁻⁴ , K _A =2.43×10 ⁻⁸ , and K _W =5.379×10 ⁻¹³ , the formic acid total concentration [HCOOH] _T was 800 ppm (17.4 mmol/L). ), the total ammonia concentration [NH ₃ ] _T is 156 ppm when the pH of the film forming aqueous solution is 4.0. Similarly, the total ammonia concentration [NH ₃ ] _T in the formic acid total concentration range of 400 ppm to 1600 ppm when the pH of the film-forming aqueous solution was 4.0 was determined. The relationship between the formic acid concentration and the obtained ammonia concentration when the pH of the film-forming aqueous solution is 4.0 is shown by the solid line in FIG. Similarly, in FIG. 13, the relationship between the formic acid concentration and the ammonia concentration in the case where the pH of the film forming aqueous solution is 3.9 is indicated by a one-dot chain line, and the relationship between the formic acid concentration and the ammonia concentration in the case where the pH of the film forming aqueous solution is 4.2 is shown. The relationships are indicated by broken lines. According to FIG. 13, the respective concentrations of formic acid and ammonia required for pH 3.9 to pH 4.2 may be the concentrations in the region between the alternate long and short dash line (pH 3.9) and the broken line (pH 4.2). I understand.

An example of the present invention, which reflects the above-mentioned examination results, will be described below.

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

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

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

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

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

In the method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant of this embodiment, a film forming device 30 is used, and this film forming device 30 is used in a purification system pipe 18 of a BWR plant as shown in FIG. Connected.

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

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

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

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

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

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

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

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

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

The oxidant supply device 56 has a chemical liquid tank 57, a supply pump 58, and a supply pipe 59. The chemical liquid 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 liquid tank 57. As the oxidant, ozone or water in which oxygen is dissolved may be used.

A pH meter 97 is attached to the circulation pipe 34 between the connection point between the injection pipe 43 and the circulation pipe 34 and the opening/closing valve 78.

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

During the period when the operation of the BWR plant 1 is stopped as described above, the carbon steel piping system, for example, the purification system piping 18, which is one of the carbon steel members in the BWR plant 1 and is connected to the RPV 3 is installed. The targeted method for suppressing radionuclide adhesion to carbon steel members of a nuclear power plant according to this embodiment is implemented. In this method, first, an oxide film incorporating a radionuclide is removed from the inner surface of the purification system pipe 18 by chemical decontamination to form a nickel metal film on the inner surface of the purification system pipe 18 that has been chemically decontaminated, and A noble metal such as platinum is attached to the surface of the formed nickel metal film, and then the nickel metal film to which platinum is attached is converted into a stable nickel ferrite film.

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

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

Chemical decontamination is performed on the carbon steel pipe system to be coated (step S2). In the BWR plant 1 that has experienced the operation in the previous operation cycle, the oxide film containing the radionuclide is formed on the inner surface of the purification system pipe 18 that comes into contact with the reactor water discharged from the RPV 3. Before forming a nickel metal film described below 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. The removal of the oxide film also leads to improvement of the adhesion between the nickel metal film and the inner surface of the purification system pipe 18. In order to remove this oxide film, chemical decontamination, particularly reduction decontamination using a reduction decontamination solution containing oxalic acid as a reduction decontamination agent, is performed on the inner surface of the purification system pipe 18.

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

First, the circulation pumps 32 and 33 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. As a result, the water heated by the heater 51 in the surge tank 31 in the purification system pipe 18 circulates in the closed loop formed by the circulation pipe 34 and the purification system pipe 18. The circulating water is adjusted to 90° C. by the heater 51. When the temperature of this water reaches 90° C., the valve 79 is opened to guide a part of the water flowing in the circulation pipe 34 into the pipe 80. A predetermined amount of oxalic acid supplied from the hopper and ejector 61 into the pipe 80 is guided into the surge tank 31 by the water flowing in the pipe 80. This oxalic acid is dissolved in water in the surge tank 31, and an oxalic acid aqueous solution (reduction decontamination solution) is generated in the surge tank 31.

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

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

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

In reduction decontamination of the surface of a carbon steel member (for example, the purification system pipe 18) using oxalic acid, hardly soluble iron oxalate (II) is formed on the surface of the carbon steel member, and this iron oxalate ( Due to II), dissolution of the oxide film containing the radionuclide formed on the surface of the carbon steel member by oxalic acid may be suppressed. In this case, the valve 69 is fully opened and the valve 70 is closed to stop the supply of the oxalic acid aqueous solution containing hydrazine to the cation exchange resin tower 53, and hydrogen peroxide as an oxidant flows through the circulation pipe 34. Pour into an aqueous solution of oxalic acid containing hydrazine. To inject this hydrogen peroxide into the oxalic acid aqueous solution containing hydrazine, the valve 60 is opened to activate the supply pump 58, and the hydrogen peroxide in the chemical solution tank 57 is circulated through the supply pipe 59 and the pipes 76 and 71. It is supplied to an aqueous oxalic acid solution containing hydrazine. At this time, the valves 72 and 75 are closed. An oxalic acid aqueous solution containing hydrogen peroxide and hydrazine is introduced from the circulation pipe 34 into the purification system pipe 18, and Fe(II) contained in iron oxalate (II) formed on the inner surface of the purification system pipe 18 is By the action of hydrogen peroxide contained in the aqueous oxalic acid solution, it is oxidized to Fe(III), and the iron(II) oxalate is dissolved in the aqueous oxalic acid solution containing hydrazine as an iron(III) oxalate complex. That is, iron oxalate (II), and hydrogen peroxide and oxalic acid contained in the oxalic acid aqueous solution produce an iron (III) oxalate complex, water and hydrogen ions by the reaction shown in the following formula (12). ..

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

Oxalic acid contained in the oxalic acid aqueous solution when the dose rate at the reduction decontamination point of the purification system pipe 18 decreases to a set dose rate or when the reduction decontamination time of the purification system pipe 18 reaches a predetermined time. And decompose hydrazine. That is, the reduction decontaminating agent decomposition step is performed. It should be noted that the fact that the dose rate at the reduction decontamination site has decreased 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. can do.

Decomposition of oxalic acid and hydrazine contained in the oxalic acid aqueous solution is performed as follows. The oxalic acid aqueous solution containing hydrazine, which has flown through the cation exchange resin tower 53 and passed through the valve 70 by opening the valve 75 to partially reduce the opening degree of the valve 69, is supplied to the decomposition device 55 through the valve 75 through the pipe 76. To be done. At this time, the valve 95 is closed and the valve 96 is open. Further, by opening the valve 60 and driving the supply pump 58, the hydrogen peroxide in the chemical liquid tank 57 is supplied to the pipe 76 through the supply pipe 59 and flows into the decomposition device 55. Oxalic acid and hydrazine contained in the oxalic acid aqueous solution are decomposed in the decomposition device 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 device 55 is represented by Formula (13) and Formula (14).

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

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

The oxalic acid aqueous solution containing hydrogen peroxide and hydrazine discharged from the decomposition device 55 is introduced from the circulation pipe 34 to the purification system pipe 18. As described above, the iron (II) oxalate formed on the inner surface of the purification system pipe 18, which is a carbon steel member, becomes an iron (III) oxalate complex by the action of hydrogen peroxide thereof, and an aqueous oxalic acid solution containing hydrazine. Dissolves in. Since the decomposition of oxalic acid in oxalic acid aqueous solution containing hydrazine is progressing, there is a shortage of oxalic acid that converts Fe(II) contained in iron(II) oxalate into Fe(III), which is easily dissolved, Fe(OH) ₃ is easily deposited on the inner surface of the pipe 34. Therefore, in order to suppress the precipitation of Fe(OH) ₃ , formic acid is injected into the oxalic acid aqueous solution. The formic acid is injected by, for example, opening the valve 79 and supplying the formic acid to the oxalic acid aqueous solution from the hopper and the ejector 61 described above while guiding the oxalic acid aqueous solution into the surge tank 31 with the oxalic acid aqueous solution flowing in the pipe 80. Be seen. The supplied formic acid is mixed with the oxalic acid aqueous solution.

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

Next, in order to complete the decomposition process of oxalic acid and hydrazine, the hydrogen peroxide concentration of the oxalic acid aqueous solution containing hydrazine flowing in the circulation pipe 34 is reduced to supply the oxalic acid aqueous solution to the cation exchange resin tower 53. Therefore, valve 60 is closed and valve 79 is closed to stop the injection of formic acid. When the injection of hydrogen peroxide and formic acid into the oxalic acid aqueous solution flowing in the circulation pipe 34 is stopped, the concentrations of these in the oxalic acid aqueous solution containing hydrazine also decrease. When the hydrogen peroxide concentration of the oxalic acid aqueous solution containing hydrazine becomes 1 ppm or less, the valve 96 and the valve 70 are opened to reduce the opening degree of the valve 69, and the oxalic acid aqueous solution is supplied to the cation exchange resin tower 53. As described above, the metal cations contained in the oxalic acid aqueous solution are removed by the cation exchange resin in the cation exchange resin tower 53, and the metal cation concentration of the oxalic acid aqueous solution decreases. The decomposition of oxalic acid, hydrazine and formic acid is continued in the decomposition device 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 decomposition process of oxalic acid and hydrazine is completed.

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

The temperature of the film forming liquid is adjusted (step S3). The valves 69 and 74 are opened and the valves 96 and 70 and 75 are closed. Since the circulation pumps 32 and 33 are driven, the remaining aqueous solution containing formic acid circulates in the closed loop including the circulation pipe 34 and the purification system pipe 18. The aqueous solution containing the formic acid is heated to 90° C. by the heater 51. The temperature of this formic acid aqueous solution (the film forming aqueous solution described later) is preferably in the 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. By these valve operations, the formic acid aqueous solution flowing in the circulation pipe 34 is supplied to the filter 50, and the fine solids remaining in the formic acid aqueous solution are removed by the filter 50. When the fine solids are not removed by the filter 50, when the nickel formic acid aqueous solution is injected into the circulation pipe 34 when the nickel metal film described below is formed on the inner surface of the purification system pipe 18, the surface of the solid substance is removed. Also, a nickel metal film is formed, and the implanted nickel ions are excessively consumed. The formic acid aqueous solution is supplied to the filter 50 in order to prevent such excessive consumption of nickel ions.
A pH buffer solution is injected (step S4). The valve 63 is opened and the valve 64 is closed to stop the water flow to the filter 50. The valve 85 of the pH buffer solution injection device 81 is opened to drive the injection pump 83, and the pH buffer solution in the chemical solution tank 82, specifically, the mixed aqueous solution of formic acid and ammonia flows through the injection pipe 84 through the circulation pipe 34. It is poured into a 90° C. aqueous solution containing the remaining formic acid. The respective concentrations of formic acid and ammonia injected are 800 ppm and 156 ppm, for example. By injecting the pH buffer solution, the pH of the aqueous solution containing formic acid and ammonia flowing in the closed loop including the circulation pipe 34 and the purification system pipe 18 becomes within the range of 3.9 or more and 4.2 or less, for example, 4.0. And is kept at 4.0. The pH of the circulating aqueous solution containing formic acid and ammonia (a film forming aqueous solution described later) is 3.9 or more by changing the mixing ratio of formic acid and ammonia contained in the pH buffer solution before being supplied to the chemical liquid tank 82. It is possible to adjust within a pH range of 0.2 or less.

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

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

In order to secure a time for promoting such a displacement plating reaction, for example, after starting the injection of the nickel formate aqueous solution, a reaction time of 60 minutes is provided until the next step (reducing agent injection step in step S6) is performed. During the 60 minutes, the film forming aqueous solution 89 does not contain a reducing agent. Therefore, during the 60 minutes from the start of the injection of the nickel formate aqueous solution to the start of the reducing agent injection in the step S6 described later, the nickel ions taken into the inner surface of the purification system pipe 18 are reduced by the electrons, not the reducing agent. Becomes nickel metal. Eventually, the nickel metal is reduced by the electrons to form a nickel metal film 86 covering the entire inner surface of the purification system pipe 18, and the elution of iron (II) ions from the purification system pipe 18 to the film forming aqueous solution 89 is stopped.

A reducing agent is injected (step S6). When 60 minutes have passed from the start of the injection of the nickel formate aqueous solution, the valve 44 of the reducing agent injection device 40 is opened to drive the injection pump 42, and the aqueous solution of hydrazine as the reducing agent in the chemical solution tank 41 is introduced through the injection pipe 43. It is injected into a film-forming aqueous solution containing nickel ions, formic acid and ammonia flowing in the circulation pipe 34 and having a temperature of 90. The hydrazine concentration of the injected hydrazine aqueous solution is, for example, 200 ppm. A 90° C. aqueous solution containing nickel ions, formic acid, ammonia, and hydrazine, that is, a film forming aqueous solution (film forming liquid) 89 is supplied from the circulation pipe 34 to the purification system pipe 18. This film-forming aqueous solution 89 contacts the inner surface of the purification system pipe 18, specifically, the surface of the nickel metal film 86 formed over the entire inner surface of the purification system pipe 18 by the reducing action of electrons in the step S5. By doing so, the nickel ions adsorbed on the surface of the nickel metal film 86 become nickel metal by the reducing action of hydrazine contained in the film forming aqueous solution 89, not by the reducing action of electrons. Therefore, the thickness of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 increases. When the pH of the film forming aqueous solution 89 is increased to 7 etc. by injecting hydrazine as a reducing agent, the amount of nickel ions adsorbed on the surface of the nickel metal film 86 increases, and the amount of nickel metal produced by the action of hydrazine. Will increase.

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

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

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

Nickel ions and ammonia are removed, and the film-forming aqueous solution in which formic acid and the reducing agent are decomposed is purified (step S9). After the formic acid and hydrazine (reducing agent) are decomposed, the valve 69 is opened to close the valves 96, 70 and 75 to stop the supply of the film-forming aqueous solution 89 to the cation exchange resin tower 53 and the decomposition device 55, The valve 67 is opened to partially close the opening of the valve 66, and the valves 72 and 95 are opened. At this time, the valve 69 is closed and the circulation pumps 33 and 32 are driven. The film forming aqueous solution 89 returned from the purification system pipe 18 to the circulation pipe 34 to remove nickel ions and ammonia and decompose hydrazine and formic acid is cooled by the cooler 52 to 60° C. Further, the 60° C. film-forming aqueous solution discharged from the cooler 52 is introduced into the mixed-bed resin tower 54, and nickel ions, other cations and anions remaining in the film-forming aqueous solution 89 are mixed in the mixed-bed resin. It is adsorbed and removed by the cation exchange resin and the anion exchange resin in the tower 54 (first purification step). The film-forming aqueous solution cooled to 60° C. is circulated through the circulation pipe 34 and the purification system pipe 18 until the respective ions described above are substantially eliminated. The film-forming aqueous solution in which each ion is substantially removed is substantially 60° C. water. After the cleaning is completed, the valve 66 is opened and the valves 67, 72 and 95 are closed.

To facilitate the following platinum adhesion to the surface of the nickel metal film 86 in the process in step S10, its 60 ° C. water, after purification slightly remaining Fe ³⁺ ions iron hydroxide circulating (III ) Injecting ammonia for the purpose of suppressing precipitation due to formation. A portion of the water of 60° C. flowing in the circulation pipe 34 is introduced into the ejector 61 through the pipe 80 by opening the valve 79, and the ammonia water sucked by the ejector 61 from the hopper (not shown) is passed through the pipe 80. Mix in. The water mixed with ammonia is guided to the surge tank 31. When a predetermined amount of ammonia, for example, 50 ppm of ammonia is mixed in the water, the valve 79 is closed and the mixing of ammonia is completed.

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

Immediately after the start of the injection, the platinum at the connection point of the aqueous solution of Na ₂ [Pt(OH) ₆ ].nH ₂ O, which is injected into the circulation pipe 34 from the chemical liquid tank 46 through the connection point between the circulation pipe 34 and the injection pipe 48. The injection rate of the aqueous solution of Na ₂ [Pt(OH) ₆ ].nH ₂ O into the circulation pipe 34 is calculated in advance so that the concentration becomes a set concentration, for example, 1 ppm. The chemical solution tank 46 necessary for adhering 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 platinum ion of water containing ammonia at 60° C. flowing at a set concentration thereof is filled. The amount of the aqueous solution of Na ₂ [Pt(OH) ₆ ].nH ₂ O is calculated, and the calculated amount of the aqueous solution of Na ₂ [Pt(OH) ₆ ].nH ₂ O is filled in the chemical liquid tank 46. The rotation speed of the injection pump 47 is controlled according to the calculated injection speed of the aqueous solution of Na ₂ [Pt(OH) ₆ ].nH ₂ O into the circulation pipe 34, and the Na ₂ [Pt(OH ₆ ].nH ₂ O aqueous solution is injected into the circulation pipe 34.

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

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

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

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

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

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

It is determined whether the platinum adhesion 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 predetermined amount of platinum 87 has been attached to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18. To do. When the elapsed time does not reach the predetermined time, the steps S10 to S12 are repeated.

The aqueous solution remaining in the purification system piping and the circulation piping is purified (step S13). After it is determined that the work of adhering the platinum 87 to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 is completed, the valves 96, 72, 95 are opened to partially open the valve 69. Is closed, and a 60° C. aqueous solution containing platinum ions, ammonia, and hydrazine, which has been pressurized by the circulation pump 33, is supplied to the mixed bed resin tower 54. Platinum ions, other metal cations (for example, sodium ions), ammonia, hydrazine and OH groups contained in the aqueous solution are adsorbed by the ion exchange resin in the mixed bed resin tower 54 and removed from the aqueous solution (first 2 purification process).

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

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

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

Reactor water having a temperature in the range of 330° C. higher than 130° 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 in the RPV 3 is pressurized by the recirculation pump 7 and jetted into the jet pump 5 through the recirculation system pipe 6. Reactor water existing around the nozzle of the jet pump 5 in the downcomer is also sucked into the jet pump 5 and supplied to the core 4. The reactor water discharged from the core is returned into the downcomer. A control rod (not shown) is withdrawn from the core 4 to change the core 4 from a subcritical state to a critical state, and further withdrawal of the control rod eventually causes the reactor water in the core 4 to undergo nuclear fission of the nuclear fuel material in the fuel rod. It is heated by the heat generated in (nuclear heating). No steam is generated in the core 4, and steam is not yet supplied to the turbine 9. Further, the control rod is pulled out from the reactor core 4, the pressure inside the RPV 3 is raised to the rated pressure in the temperature raising step of the reactor 2, and the reactor water is heated by the heat generated by the nuclear fission, so that the reactor water inside the RPV 3 is heated. The temperature is raised to the rated temperature (280°C). After the pressure in the RPV 3 reaches the rated pressure and the reactor water temperature rises to the rated temperature, the reactor output is rated by the control rod being withdrawn from the core 4 and the flow rate of the reactor water supplied to the core 4 increasing. (100% output). The rated operation of the BWR plant 1 maintaining the rated output is continued until the end of the operation cycle. When the reactor power rises to, for example, 10% power, steam generated in the core 4 is supplied to the turbine 9 through the main steam pipe 8 to start power generation, and thereafter, the operation of the BWR plant 1 is completed. , Power generation is continued.

The reactor water 91 contains oxygen and hydrogen peroxide. Oxygen and hydrogen peroxide are produced by radiolysis of reactor water 91 in RPV3. The reactor water 91 in the RPV 3 is introduced from the recirculation system pipe 6 into the purification system pipe 18 and comes into contact with the nickel metal coating 86 to which the platinum 87 is attached, which is formed on the inner surface of the purification system pipe 18 (FIG. 7). reference). In the temperature raising/pressurizing step of the nuclear reactor 2, the temperature of the reactor water 91 contacting the nickel metal film 86 rises due to the heating of the reactor water by the heat generated by the above-mentioned nuclear fission, and eventually reaches 130° C. or more and 280° C. Rise to. When the temperature of the reactor water 91 becomes 130° C. or higher, the temperature of each of the nickel metal film 86 formed on the inner surface and the purification system pipe 18 surrounded by the heat insulating material also becomes 130° C. or higher. In this embodiment, reactor water having a temperature within the temperature range of 130° C. to 280° C., which is within the temperature range of 130° C. to 330° C., is brought into contact with the nickel metal coating 86 to which the platinum 87 is attached.

As a result, oxygen contained in the reactor water 91 migrates into the nickel metal film 86, and Fe contained in the purification system pipe 18 becomes Fe ²⁺ and migrates into the nickel metal film 86 (see FIG. 9). Due to the action of the platinum 87 attached to the metal film 86 and the formation of a high temperature environment of about 130° C. or higher, the corrosion potential of the purification system pipe 18 or the like is within the range of 0 mV to +200 mV as described in the step of step S18 described later. In the state where the corrosion potential becomes, the stable nickel ferrite (NiFe ₂ O ₄ ) in which Ni is 0-x is formed in the nickel metal film 86, for example, in Ni _1-x Fe _2+x O ₄ .

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

In a state where the corrosion potential of the purification system pipe 18 and the nickel metal film 86 formed on the inner surface thereof is maintained at a corrosion potential within the range of 0 mV to +200 mV and is in contact with the reactor water 91 having a temperature of 130° C. or higher. A stable nickel ferrite formation reaction by oxygen transferred from the reactor water 91 into the nickel metal film 86, Fe ²⁺ transferred from the purification system pipe 18 into the nickel metal film 86, and nickel contained in the nickel metal film 86, A part of nickel metal contained in the nickel metal film 86 is promoted by the catalytic action of the platinum 87 attached to the nickel metal film 86, and some of the nickel metal in Ni _1-x Fe _2+x O ₄ is stable, for example, x is 0. Nickel ferrite (NiFe ₂ O ₄ ) is generated. Therefore, in the state where the corrosion potential of the purification system pipe 18 and the like is maintained at the corrosion potential within the range of 0 mV to +200 mV, as described above, stable large crystal nickel ferrite (for example, NiFe ₂ O ₄ ) 88B. (See FIG. 9) is created in the nickel metal coating 86. The stable nickel ferrite 88B does not elute even by the action of the attached platinum 87.

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

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

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

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

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

Hydrogen is injected into the reactor water (step S19). When 100 hours have passed since the injection of oxygen into the reactor water (the period during which the high corrosion potential of the purification system pipe 18 is maintained), hydrogen is supplied from the hydrogen injection device 28 through the hydrogen injection pipe 29 by opening the open/close valve 99. It is injected into the pipe 11. The injected hydrogen is mixed with the feed water flowing in the feed water pipe 11, and is injected into the reactor water 91 in the RPV 3 together with the feed water. Reactor water 91 containing hydrogen is supplied from the RPV 3 to the purification system pipe 18 via the recirculation system pipe 6, and the corrosion potential of the purification system pipe 18 or the like on the inner surface of the purification system pipe 18 is increased by the injection of oxygen. When the corrosion potential is within the range of 0 mV to +200 mV, the surface of the nickel metal coating 86 to which the platinum 87 including the nickel ferrite 88B having a large crystal grain size and having the large crystal grain size is adhered is brought into contact. Due to the contact with the reactor water 91 containing hydrogen, the corrosion potential of the purification system pipe 18 drops to, for example, -500 mV. The amount of hydrogen supplied from the hydrogen injecting device 28 to the water supply pipe 11 is controlled so that the corrosion potential of the purification system pipe 18 is, for example, −500 mV. Adjust the hydrogen concentration of 91. In the present embodiment, the corrosion potential of the purification system pipe 18 is maintained at -500 mV by injecting hydrogen.

The corrosion potential of the purification system pipe 18 decreases to −500 mV because the oxygen contained in the reactor water 91 reacts with the injected hydrogen in the reactor water 91 due to the catalytic action of the platinum 87 and becomes water. This is because the dissolved oxygen concentration of is reduced.

After the hydrogen injection to the reactor water 91 is started, the corrosion potential of the purification system pipe 18 and the like is present on the inner surface of the purification system pipe 18 even when the corrosion potential is a low corrosion potential of −500 mV, for example. The nickel metal remaining in the nickel metal film 86 including the nickel ferrite 88B reacts with oxygen transferred from the reactor water 91 into the nickel metal film 86 and Fe ²⁺ transferred from the purification system pipe 18 into the nickel metal film 86. To generate stable nickel ferrite (for example, NiFe ₂ O ₄ ) 88C in the nickel metal film 86 (see FIG. 9). The crystal grain size of the nickel ferrite 88C is the stable nickel ferrite generated in the step S18. Smaller than that of 88B.

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

According to the present embodiment, a nickel metal film is formed on the inner surface of the purification system pipe 18 which is a carbon steel member, and a nickel metal film is formed on the inner surface of the nickel metal film. The surface of the nickel metal coating 86 to which the platinum 87 is attached formed on the inner surface of the purification system pipe 18 is brought into contact with the reactor water 91 having a temperature within the range of 130° C. to 330° C. In order to bring the corrosion potential of the carbon steel member into the corrosion potential within the range of 0 mV or more and +200 mV or less by the injection of nickel, crystals of nickel ferrite 88B having a large grain size are included in the nickel ferrite film 88A formed on the inner surface of the purification system pipe 18. In this state, the density of nickel ferrite crystal grain boundaries in the nickel ferrite film 88A further decreases. Therefore, the adhesion of the radionuclide (for example, Co-60) to the purification system pipe 18 is further suppressed.

According to the present embodiment, the nickel metal coating 86 is added to the reactor water of the corrosive environment forming water quality that contains the injected oxygen (oxidizer) to make the corrosion potential of the purification system pipe 18 within the range of 0 mV or more and +200 mV or less. The nickel ferrite film 88A containing the crystals of nickel ferrite 88B having a large particle size, which is generated through the process of contacting the surfaces of the above, does not contact the reactor water of the corrosive environment forming water quality, and the corrosion potential of the purification system pipe 18 is By contacting with the reactor water having a corrosion environment mitigating water quality of −500 mV, the effect of suppressing the adhesion of radionuclides can be further enhanced as compared with the nickel ferrite film converted from the nickel metal film 86.

In this embodiment, the corrosion potential of the purification system pipe 18 that is the reactor water having a temperature in the range of 130° C. or higher and 330° C. or lower and that contains the injected oxygen (oxidizer) is 0 mV or higher and +200 mV or lower. The nickel ferrite film formed through the process of contacting the corrosive environment forming water of the reactor water with the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18 and having the precious metal (for example, platinum 87) attached thereto. 88A is a stable nickel ferrite film (for example, NiFe ₂ O ₄ ) which contains crystals of nickel ferrite 88B having a large grain size and does not elute even by the action of the attached platinum 87. Therefore, the effect of suppressing the adhesion of the radionuclide to the purification system pipe 18 by the stable nickel ferrite film 88A covering the inner surface of the purification system pipe 18 can be continued for a longer period. In addition, the nickel ferrite coating 88A further includes reactor water of a corrosive environment mitigating water quality that contains hydrogen to make the corrosion potential of the purification system pipe 18 within the range of −300 mV or less and −500 mV or more, on the inner surface of the purification system pipe 18. Since the process of contacting the surface of the nickel metal film 86 including the crystals of nickel ferrite 88B having a large grain size, to which the noble metal (for example, platinum 87) adheres formed on the It contains crystals of nickel ferrite 88C having a smaller grain size.

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

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

According to this example, 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 in contact with the reactor water. A nickel metal coating 86 may be formed to cover. This nickel metal film 86 can prevent the elution of Fe ²⁺ from the purification system pipe 18 into the film forming aqueous solution, and the adhesion of the noble metal (for example, platinum) to the inner surface of the purification system pipe 18 can be prevented by Fe ²⁺ . It is not hindered by elution, and the time required for the adhesion of the noble metal to the inner surface (specifically, the adhesion of the noble metal to the surface of the nickel metal film 86 formed on the inner surface of the purification system pipe 18) is shortened. be able to. Further, the precious metal can be efficiently attached to the inner surface thereof, and the amount of the precious metal attached to the inner surface of the purification system pipe 18 is increased.

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

The nickel metal film 86 is formed on the inner surface of the purification system pipe 18 by introducing nickel ions contained in the film forming aqueous solution into the inner surface of the purification system pipe 18 by the displacement plating reaction with the iron contained in the purification system pipe 18, and purifying the nickel metal film 86. Electrons generated by elution of Fe ²⁺ from the system pipe 18 or hydrazine (reducing agent) contained in the film-forming aqueous solution reduces nickel ions adsorbed on the inner surface of the pipe to form nickel metal. As described above, the nickel metal generated by the displacement plating reaction and the reducing action of the electrons or the reducing agent has a strong adhesion to the base material of the purification system pipe 18. Therefore, the formed nickel metal film 86 does not come off from the purification system pipe 18.

In this embodiment, since the nickel metal film 86 is formed on the inner surface of the purification system pipe 18 after the decontamination of the inner surface of the purification system pipe 18, the oxidation containing the radionuclide formed on the inner surface of the purification system pipe 18 is performed. The nickel metal film is not formed on the film, the radiation emitted from the purification system pipe 18 is reduced, and the surface dose rate of the purification system pipe 18 is significantly reduced.

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

In this embodiment, the nickel metal coating 86 is formed on the inner surface of the purification system pipe 18 and the platinum 87 is attached to the nickel metal coating 86 while the BWR plant 1 is stopped. The conversion to the nickel ferrite film 88A is performed after the BWR plant 1 is started. Therefore, when the temperature of the reactor water is lower than 130° C., the nickel metal film 86 is not changed to the nickel ferrite film 88A, and the inner surface of the purification system pipe 18 is covered with the nickel metal film 86 to which the platinum 87 is attached. (See FIG. 6). Even in this state, the corrosion potential of the purification system pipe 18 and the nickel metal film 86 in contact with the reactor water 91 is lowered by the action of the platinum 87, and the incorporation of the radionuclide into the nickel metal film 86 and the purification system pipe 18 occurs. Absent. In this way, the adhesion of radionuclides to the purification system pipe 18 is suppressed.

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

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

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

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

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

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

Further, when the corrosion potential of the purification system pipe 18 measured by the corrosion potential measuring instrument 92 becomes lower than −500 mV due to the hydrogen injection in the step of S19 (hydrogen injecting step), the corrosion potential measuring instrument 92 measures the corrosion potential. The oxygen injection amount control device that inputs the corrosion potential thus increased increases the opening degree of the opening/closing valve provided in the oxidant injection pipe 26 to increase the amount of oxygen injected into the reactor water flowing in the purification system pipe 18. The opening degree of the on-off valve is adjusted so that the corrosion potential of the purification system pipe 18 is maintained at -500 mV.

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

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

This embodiment can obtain all the effects produced in the first embodiment. Further, in this embodiment, since the corrosion potential of the purification system pipe 18 can be measured using the corrosion potential measuring device, the oxidant injection device 25 is controlled by the oxygen injection amount control device based on the corrosion potential of the purification system pipe 18. Therefore, the amount of oxygen injected into the purification system pipe 18 can be adjusted, and the corrosion potential of the purification system pipe 18 can be easily adjusted.

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

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

Claims (15)

A film forming liquid containing nickel ions is brought into contact with a first surface of a carbon steel member of an atomic power plant that comes into contact with reactor water to form a nickel metal film on the first surface, and on the second surface of the nickel metal film. Depositing a noble metal, forming the nickel metal film and depositing the noble metal are performed after the nuclear power plant is stopped and before the nuclear power plant is started, and after the nuclear power plant is started, the nickel to which the noble metal is deposited. The corrosion potential of the carbon steel member is set to 0 mV or more by bringing the reactor water having a temperature in the range of 130° C. or higher and 330° C. or lower into contact with the first surface of the metal film and injecting an oxidizing agent into the reactor water. A method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant, which is characterized by: The method for suppressing adhesion of a radionuclide to a carbon steel member of a nuclear power plant according to claim 1, wherein the corrosion potential of the carbon steel member is set to a corrosion potential within a range of 0 mV or more and +200 mV or less by injecting the oxidant. The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 1, wherein the oxidant injection into the reactor water is performed by an oxidant injection device. A corrosion potential measuring device measures the corrosion potential of the carbon steel member on which the nickel metal coating is formed, and injects the oxidant from the oxidant injecting device into the reactor water based on the measured corrosion potential. The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 3, wherein the amount is adjusted. The first period during which the corrosion potential of the carbon steel member is maintained at 0 mV or higher exists before the second period during which the corrosion potential of the carbon steel member is maintained at less than 0 mV by hydrogen in the reactor water. 5. A method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to any one of items 1 to 4. The method for suppressing adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 5, wherein the first period is a period within a range of 100 to 500 hours. The nuclear power plant according to any one of claims 1 to 6, wherein one component of each of an acid and a base of a pH buffer solution is injected into the film forming liquid that is brought into contact with the first surface of the carbon steel member. Method for suppressing the attachment of radionuclides to carbon steel members of. The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 7, wherein the pH of the film forming liquid is in the range of 3.9 or more and 4.2 or less. A film forming liquid containing nickel ions is supplied to the first pipe through a second pipe connected to the first pipe which is a carbon steel member and which is a first pipe connected to a nuclear reactor,
The supplied film forming liquid is brought into contact with the inner surface of the first pipe to form a nickel metal film on the inner surface of the first pipe,
An aqueous solution containing a noble metal ion and a reducing agent is supplied from the second pipe to the first pipe to bring the aqueous solution into contact with the surface of the nickel metal film, and attach the noble metal to the surface of the nickel metal film,
The formation of the nickel metal film and the deposition of the noble metal are performed after the nuclear power plant is shut down and before the nuclear power plant is started,
After starting the nuclear power plant, contact the surface of the nickel metal coating with the precious metal with reactor water at a temperature in the range of 130° C. to 330° C.,
A method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant, wherein the corrosion potential of the first pipe is set to 0 mV or more by injecting an oxidant into the reactor water. The method for suppressing adhesion of a radionuclide to a carbon steel member of a nuclear power plant according to claim 9, wherein the corrosion potential of the first pipe is set to a corrosion potential within a range of 0 mV or more and +200 mV or less by injecting the oxidant. The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 9 or 10, wherein the injection of the oxidant into the reactor water is performed by an oxidant injection device connected to the first pipe. A corrosion potential measuring device measures the corrosion potential of the carbon steel member on which the nickel metal coating is formed, and injects the oxidant from the oxidant injecting device into the reactor water based on the measured corrosion potential. The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 11, wherein the amount is adjusted. The first period of maintaining the corrosion potential of the first pipe at 0 mV or higher exists before the second period of maintaining the corrosion potential of the carbon steel member at less than 0 mV by hydrogen to the reactor water. 13. A method for suppressing the adhesion of radionuclides to a carbon steel member of a nuclear power plant according to any one of 1 to 12. The carbon of a nuclear power plant according to any one of claims 9 to 13, wherein one component of each of an acid and a base of a pH buffer solution is injected into the film forming liquid that contacts the inner surface of the first pipe. A method for suppressing the adhesion of radionuclides to steel members. The method for suppressing the adhesion of radionuclides to carbon steel members of a nuclear power plant according to claim 14, wherein the film-forming solution has a pH in the range of 3.9 or more and 4.2 or less.

Images