JP3972050B1 - Method for treating solution after formation of ferrite film - Google Patents

Abstract

A processing time required for discarding a solution used for forming a ferrite film is shortened.
A film forming apparatus is connected to a piping system for forming a film (S1). Chemical decontamination of the piping inner surface of the piping system is performed (S2). After decontamination, the temperature of the film-forming aqueous solution (including the organic acid solution containing iron (II) ions, the oxidizing agent, and the pH adjusting agent) used for forming the ferrite film is adjusted (S3) to form a ferrite film on the inner surface of the pipe (S4). The waste liquid treatment method after forming the ferrite film has the following steps. A pH adjuster (hydrazine) is injected into the waste liquid so that the pH of the waste liquid becomes 6.5 or more (S6). An oxidizing agent (H ₂ O ₂ ) is injected into the waste liquid (S7). Iron (II) ions in the waste liquid are precipitated as magnetite solid particles. The solid particles are removed with a filter (S8). Thereafter, the organic acid (formic acid) and the pH adjuster in the waste liquid are decomposed using an oxidizing agent and a catalyst (S10).
[Selection] Figure 1

Description

  The present invention relates to a method for treating a solution after forming a ferrite film, and in particular, treating a solution after forming a ferrite film suitable for treating a solution used when forming a philite film on a component of a nuclear power plant. Regarding the method.

  For example, a boiling water nuclear power plant (hereinafter abbreviated as a BWR plant) has a nuclear reactor with a reactor core built in a reactor pressure vessel (RPV). The cooling water supplied to the core by the recirculation pump (or internal pump) is heated by the heat generated by the fission of each fuel material in the fuel assembly loaded in the core, and a part thereof becomes steam. This steam is led from the nuclear reactor to the turbine and rotates the turbine. The steam exhausted from the turbine is condensed in a condenser to become water. This water is supplied to the reactor as feed water. In order to suppress the generation of radioactive corrosion products in the nuclear reactor, metal impurities are mainly removed by a filtration and desalination apparatus provided in the water supply pipe.

  In addition, since corrosion products that are the source of radioactive corrosion products are also generated from water contact parts such as RPV and recirculation piping, the primary primary components are made of stainless steel and nickel bases with low corrosion. Stainless steel such as alloy is used. In addition, the low alloy steel RPV has a stainless steel overlay on the inner surface to prevent the low alloy steel from coming into direct contact with the reactor water. Reactor water is cooling water present in the nuclear reactor. Furthermore, a part of the reactor water is purified by a filter demineralizer of the reactor purification system to positively remove metal impurities that are slightly present in the reactor water.

  However, even if the above-described corrosion countermeasures are taken, the presence of very few metal impurities in the reactor water is inevitable, so some metal impurities are converted into metal oxides to the fuel rods contained in the fuel assembly. Adhere to the surface. Metal impurities (for example, metal elements) adhering to the surface of the fuel rod cause a nuclear reaction when irradiated with neutrons emitted from the nuclear fuel in the fuel rod, and become radioactive nuclides such as cobalt 60, cobalt 58, chromium 51, and manganese 54. Become. Most of these radionuclides remain attached to the fuel rod surface in the form of oxides, but some of the radionuclides elute into the reactor water depending on the solubility of the incorporated oxide, and the cladding Re-released into the reactor water as an insoluble solid called Radioactive material in the reactor water is removed by the reactor purification system. However, the radioactive material that has not been removed accumulates on the surface of the component that contacts the reactor water while circulating in the recirculation system together with the reactor water. As a result, radiation is radiated from the surface of the component member, which causes radiation exposure of workers during regular inspection work. The exposure dose of the employee is managed so that it does not exceed the prescribed value for each person. In recent years, this regulation value has been lowered, and it has become necessary to make the exposure dose of each person as low as economically possible.

  Thus, various methods for reducing the adhesion of radionuclides to piping and methods for reducing the concentration of radionuclides in the reactor water have been studied. For example, by injecting metal ions such as zinc into the reactor water, and forming a dense oxide film containing zinc on the inner surface of the recirculation piping that contacts the reactor water, cobalt 60 and cobalt 58 in the oxide film, etc. A method for suppressing the uptake of radionuclides has been proposed (Patent Document 1).

  It is also proposed that an oxide film be formed on the inner surfaces of the recirculation system piping and the purification system piping of the reactor purification system before the radionuclide is dissolved or released in the cooling water. (Patent Document 2).

  However, in the method of injecting metal ions such as zinc into the reactor water in Patent Document 1, it is necessary to continuously inject zinc ions separated from expensive isotopes during operation in order to avoid activation of zinc itself. In the method of forming an oxide film in Patent Document 2, for example, it is necessary to form an oxide film in a BWR operating temperature range (250 to 300 ° C.). It is assumed that the oxide film is formed on the surface of, for example, a stainless steel component in such a high temperature atmosphere. The formed oxide film includes an inner layer rich in chromium components and an outer layer rich in iron components located outside the inner layer. Since the outer layer has a crystal film structure that is not necessarily dense, radionuclides such as cobalt in the reactor water easily pass through the outer layer and be taken into the inner layer, thereby reducing the effect of suppressing the attachment of the radionuclide to the constituent members.

  Therefore, as a method that can more effectively suppress the attachment of radionuclides, a method of forming a dense ferrite film on the surface of a component at a low temperature of 100 ° C. or less has been proposed (Patent Document 3). According to this method, since a ferrite film with less radionuclide uptake can be formed on the surface of the component member, adhesion of the radionuclide can be suppressed.

JP 58-79196 A JP-A-62-95498 JP 2006-38483 A

  By the way, after using the method described in Patent Document 3 to form a ferrite film on the surface of a component such as a pipe of a nuclear power plant that comes into contact with the reactor water, the solution used to form this ferrite film (hereinafter referred to as the ferrite film) It is necessary to purify and drain the waste liquid). That is, the waste liquid contains iron (II) ions and the like as a raw material for the film in addition to the particulate matter (for example, iron oxide) generated at the time of forming the ferrite film. For this reason, after adding a chemical | medical agent to a waste liquid and depositing iron (II) ion, it is necessary to remove this deposit. However, when the waste liquid on which iron (II) ions are deposited is filtered through a filter, there is a problem that the processing time becomes longer due to clogging of the filter depending on the size of the precipitate.

  An object of the present invention is to provide a method for treating a solution after forming a ferrite film, which can shorten the time required for treating the solution used for forming the ferrite film.

  A feature of the present invention that achieves the above-described object is that a first agent containing iron (II) ions, a second agent that oxidizes the iron (II) ions to iron (III) ions, and a pH adjusting agent. 3 is a method of treating a solution used when forming a ferrite film on the surface of a metal member constituting a plant, and when the solution is treated, a pH adjuster is used to treat the solution. The pH is adjusted to 6.5 or more, and then an oxidizing agent is supplied to the solution, and solids generated by the reaction between the supplied oxidizing agent and iron (II) ions are removed from the solution.

  Since the pH of the solution used for forming the ferrite film is set to 6.5 or more and an oxidizing agent is supplied to the solution, iron (II) ions contained in the solution can be precipitated as a solid matter. . For this reason, since the precipitated solid matter can be easily removed from the solution, the processing time of the solution after forming the ferrite film can be shortened.

  Preferably, it is desirable to decompose the organic acid contained in the first drug after the step of removing the solid matter. Since the organic acid is decomposed after removing the solid matter, the decomposition efficiency of the organic acid can be improved. Thereby, the processing time of the solution after forming the ferrite film can be further shortened.

  According to the present invention, it is possible to shorten the waste liquid treatment time after the formation of the ferrite film.

The inventors of the present invention have made various studies in order to precipitate iron (II) ions that are dissolved in the waste liquid after the film formation process of the ferrite film. As a result, the inventors simply added an oxidizing agent to the waste liquid to oxidize iron (II) ions, so that the fineness of magnetite (Fe ₃ O ₄ ) and ferric hydroxide (Fe (OH) ₃ ). New particles were found to be deposited and the filtration time of the waste liquid was prolonged.

Examining this cause, first, hydrogen peroxide and iron (II) ions generate iron (II) ions, hydroxy radicals and hydroxide ions by the Fenton reaction of the formula (1). Here, the hydroxy radical oxidizes iron (II) ion, formic acid, hydrazine and the like to become a hydroxide ion. Further, the iron (III) ion is hydrolyzed with unreacted iron (II) ion as shown in the formula (2) to generate iron oxide magnetite (Fe ₃ O ₄ ), or (3) As shown in the formula, it hydrolyzes itself to produce ferric hydroxide.

Fe ²⁺ + H ₂ O ₂ → Fe ³⁺ + OH · + OH ⁻ (1)
2Fe ³⁺ + Fe ²⁺ + 4H ₂ O → Fe ₃ O ₄ + 8H ⁺ (2)
Fe ³⁺ + 3H ₂ O → Fe (OH) ₃ + 3H ⁺ (3)
Which of the reactions (2) and (3) is dominant depends on the concentration of iron (II) ions contained in the waste liquid and the pH of the waste liquid. Whichever reaction occurs, the pH of the waste liquid decreases because hydrogen ions are released. Considering the Fenton reaction and the hydroxide ions generated by the subsequent reduction of hydroxy radicals, 1 to 2 moles of hydrogen ions are generated from 1 mole of iron (II) ions.

As shown in FIG. 2, when hydrogen peroxide is added to the waste liquid, the pH decreases to about 4.5 with the generation of hydrogen ions. Further, based on FIG. 3 showing the form of the iron compound in the iron-water system in terms of the relationship between the electric potential and the pH, it can be seen that when the pH of the waste liquid shifts from 6.5 to the low pH side, it enters the region where magnetite dissolves. . When the waste liquid (pH 4.5) to which hydrogen peroxide was added was evaluated, it was found that iron (II) ions contained in the waste liquid were precipitated not as magnetite but as Fe (OH) ₃ . When this waste liquid was filtered with a filter having an opening of 1 μm, it took about 20 hours.

  On the other hand, basic hydrazine is added to the waste liquid in advance so that the pH of the waste liquid when hydrogen peroxide is added is 6.5 or more. When hydrogen peroxide was added so that 2/3 of the initial iron (II) ion concentration became iron (III) ions with the hydrazine added, it was found that only magnetite was produced. When this waste liquid was filtered by the same method as described above, the filtration was completed in about 3 hours.

Changes in the concentration of precipitated iron over time when only hydrogen peroxide is added to the waste liquid and when hydrazine (N ₂ H ₄ ) is added and maintained at pH 6.5 or higher before adding hydrogen peroxide to the waste liquid Is shown in FIG. Moreover, the time change of the particle size of the deposited particles is shown in FIG. That is, by reacting iron (II) ions and an oxidant at a predetermined ratio in a state where the pH of the waste liquid is 6.5 or more, the iron oxide in which the particle size of the precipitated particles is larger than that of ferric hydroxide. In other words, it was found that magnetite can be precipitated and that the particle size can be grown greatly in a short time. By these actions, the removal time of the waste liquid is remarkably shortened.

  From the above examination results, the inventors have applied a pH adjuster so that the pH of the waste liquid does not fall below 6.5 when treating the solution (waste liquid) used in forming the ferrite film on the surface of the metal member. The solution was supplied into the waste liquid, and the oxidant was supplied into the waste liquid supplied with the pH adjusting agent to precipitate the iron ions in the waste liquid as a solid, and the new idea was reached that the waste liquid should be filtered. . The amount of hydroxide ions supplied to the waste liquid may be adjusted based on the measured value of the concentration of iron (II) ions contained in the waste liquid. According to this, for example, the supply amount of the pH adjusting agent can be adjusted according to the change in the iron (II) ion concentration in the waste liquid. The supply amount of the oxidizing agent may also be adjusted based on the measured value of the iron (II) ion concentration in the waste liquid. According to this, for example, iron (II) ions and iron (III) ions can be reacted at an optimum ratio based on the formula (2), so that magnetite can be efficiently generated.

  Further, the supply amount of hydroxide ions and oxidant may be adjusted based on the measured value by measuring the pH of the waste liquid. According to this, the pH of the waste liquid can be easily managed.

  In the treatment of the waste liquid, it is preferable to use the third chemical agent as the pH adjusting agent and the second chemical agent as the oxidizing agent. Thereby, since the chemical | medical agent used for a ferrite membrane | film | coat formation and the chemical | medical agent used for a waste liquid process can be made shared, the supply equipment of a chemical | medical agent can be reduced in size. Here, the 2nd chemical | medical agent contains at least 1 among hydrogen peroxide, oxygen, and ozone, for example. As the third drug, hydrazine can be used. That is, hydrazine reacts with water to generate hydroxide ions.

  In addition, after contaminants including an oxide film adhering to the surface of the metal member are chemically removed by repeating oxidation dissolution using permanganate ions and reduction dissolution using organic acid (for example, oxalic acid). A ferrite film may be formed on the surface of the metal member in contact with the reactor water. The chemical component contained in the filtered waste liquid may be decomposed, and the decomposed waste liquid may be drained through an ion exchange resin. Moreover, the filter used for filtration of a waste liquid can shorten the filtration processing time by using a thing with the opening of 1 micrometer thru | or 10 micrometers.

  Examples of the present invention will be described below.

  A method for treating a solution after forming a ferrite film, which is a preferred embodiment of the present invention, will be described below with reference to the drawings. This processing method is an example in which the solution used for forming the ferrite film applied to the BWR plant is discarded. Before explaining the treatment of the solution after the formation of the ferrite film in this embodiment, that is, the treatment of the waste liquid, the film formation used for the treatment of the waste liquid is described based on the schematic configuration of the BWR plant based on FIG. A schematic configuration of the apparatus will be described with reference to FIG. The film forming apparatus shown in FIG. 7 is also used when forming a ferrite film.

  A BWR plant, which is a nuclear power plant, includes a nuclear reactor 1, a turbine 3, a condenser 4, a recirculation system, a nuclear reactor purification system, a water supply system, and the like. The nuclear reactor 1 has a nuclear reactor pressure vessel (hereinafter referred to as RPV) 12 containing a core 13, and a jet pump 14 is installed in the RPV 12. The core 13 is loaded with a large number of fuel assemblies (not shown). The fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel. In the recirculation system, a recirculation pump 21 is installed in the recirculation system pipe 22. In the feed water system, a condensate pump 5, a condensate purification device 6, a feed water pump 7, a low pressure feed water heater 8, and a high pressure feed water heater 9 are installed in a feed water pipe 10 that connects the condenser 4 and the RPV 12. In the reactor purification system, a purification system pump 24, a regenerative heat exchanger 25, a non-regenerative heat exchanger 26 and a reactor water purification device 27 are installed in a purification system pipe 20 that connects the recirculation system pipe 22 and the feed water pipe 10. ing. The purification system pipe 20 is connected to the recirculation system pipe 22 upstream from the recirculation pump 21.

  The cooling water in the RPV 12 is boosted by the recirculation pump 21, and jetted into the jet pump 14 through the recirculation system pipe 22. The cooling water existing around is also sucked into the jet pump 14 and supplied to the core 13. The cooling water supplied to the core 13 is heated by the heat generated by the fission of each fuel material in the fuel rod, and a part thereof becomes steam. This steam is guided from the RPV 12 through the main steam pipe 2 to the turbine 3 to rotate the turbine 3. A generator (not shown) connected to the turbine 3 rotates to generate electric power. The steam discharged from the turbine 3 is condensed by the condenser 4 to become water. This water is supplied into the RPV 12 through the water supply pipe 10 as water supply. The feed water flowing through the feed water pipe 10 is boosted by the condensate pump 5, impurities are removed by the condensate purification device 6, further boosted by the feed water pump 7, and heated by the low pressure feed water heater 8 and the high pressure feed water heater 9. . Extracted steam extracted from the main steam pipe 2 and the turbine 3 by the extracted pipe 15 is supplied to the low-pressure feed water heater 8 and the high-pressure feed water heater 9, respectively, and serves as a heating source for the feed water.

  A part of the cooling water flowing in the recirculation system pipe 22 flows into the purification system pipe 20 by the drive of the purification system pump 24 and is purified by the reactor water purification device 27. The purified cooling water is returned into the RPV 12 through the purification system pipe 20 and the water supply pipe 10.

  After the operation of the BWR plant is stopped, the circulation pipe 35 of the film forming apparatus 30 is connected to the recirculation system pipe 22 and the purification system pipe 20. The film forming apparatus 30 is a temporary facility, and is removed from the recirculation system pipe 22 and the purification system pipe 20 after the processing of the solution used for forming the ferrite film is completed. The film forming apparatus 30 is used both for forming a ferrite film on the inner surface of the recirculation pipe 22 and for treating the solution used for forming the film. Furthermore, the film forming apparatus 30 is also used when performing chemical decontamination in the recirculation piping 22.

  A detailed configuration of the film forming apparatus 30 will be described with reference to FIG. The film forming apparatus 30 includes a surge tank 31, a circulation pipe 35, chemical liquid tanks 40, 45, 46, a filter 51, a decomposition apparatus 64, and a cation exchange resin tower 60. From the upstream, the opening / closing valve 47, the circulation pump 48, the heater 53, the valves 55, 56, 57, the surge tank 31, the circulation pump 32, the valves 49, 33, and the opening / closing valve 34 are provided in the circulation pipe 35 in this order from the upstream. ing. A pipe 66 that bypasses the heater 53 and the valve 55 is connected to the circulation pipe 35. A cooler 58 and a valve 59 are installed in the pipe 66. A cation exchange resin tower 60 and a valve 61 are installed in a pipe 67 that is connected to the circulation pipe 35 at both ends and bypasses the valve 56. The mixed bed resin tower 62 and the valve 63 are installed in a pipe 68 that is connected to the circulation pipe 35 at both ends and bypasses the valve 56. A pipe 69 that bypasses the valve 57 and is provided with the valve 65 and the decomposition device 64 is connected to the circulation pipe 35. The decomposition apparatus 64 is filled with, for example, an activated carbon catalyst in which ruthenium is impregnated on the surface of the activated carbon. A pipe 71 that bypasses the valve 49 and is provided with the filter 51 and the valve 50 is connected to the circulation pipe 35. A pipe 70 provided with the valve 36 and the ejector 37 is connected to the circulation pipe 35 between the valve 33 and the valve 49, and further connected to the surge tank 31. Surge tank for permanganic acid for oxidizing and dissolving pollutants on the inner surface of piping (for example, recirculation system piping 22) subject to chemical decontamination, and oxalic acid for reducing and dissolving contaminants in the piping. The ejector 37 is provided with a hopper (not shown) for supplying the inside of the ejector 31.

  The iron (II) ion implantation apparatus includes a chemical solution tank 45, an injection pump 43, and an injection pipe 72. The chemical tank 45 is connected to the circulation pipe 35 by an injection pipe 72 having an injection pump 43 and a valve 41. The chemical liquid tank 45 is filled with a medicine containing divalent iron (II) ions prepared by dissolving iron with formic acid. This drug contains formic acid. In addition, as a chemical | medical agent which dissolves iron, the organic acid or carbonic acid which becomes a counter anion of iron (II) ion can be used not only formic acid. The oxidant injection device includes a chemical tank 46, an injection pump 44, and an injection pipe 73. The chemical tank 46 is connected to the circulation pipe 35 by an injection pipe 73 having an injection pump 44 and a valve 42. The chemical tank 46 is filled with hydrogen peroxide which is an oxidant. The pH adjuster injection device includes a chemical tank 40, an injection pump 39, and an injection pipe 74. The chemical tank 40 is connected to the circulation pipe 35 by an injection pipe 74 having an injection pump 39 and a valve 38. The chemical tank 40 is filled with hydrazine which is a pH adjusting agent. The first connection point to the circulation pipe 35 of the oxidant injection device is downstream of the second connection point to the circulation pipe 35 of the iron (II) ion injection device and to the circulation pipe 35 of the pH adjuster injection device. Is located upstream of the third connection point. The position of the third connection point is preferably as close as possible to the target site for chemical decontamination and ferrite film formation in the circulation pipe 35. A pipe 75 provided with a valve 54 communicates the pipe 73 and the pipe 69. The surge tank 31 is filled with water used for processing. In order to remove oxygen contained in the aqueous solution, chemical gas tank 45 and surge tank 31 are preferably bubbled with an inert gas such as nitrogen or argon.

  The decomposition device 64 can decompose an organic acid (for example, formic acid) used as a counter anion of iron (II) ions and a hydrazine as a pH adjusting agent. That is, as the counter anion of the iron (II) ion, an organic acid that can be decomposed into water or carbon dioxide in consideration of reduction of the amount of waste, or carbonic acid that can be released as a gas and does not increase waste is used.

  The processing method of the solution after forming the ferrite film in the present embodiment will be described in detail with reference to FIG. The procedure shown in FIG. 1 includes not only a solution processing method but also chemical decontamination and formation of a ferrite film. First, the film forming apparatus 30 is connected to the piping system to be coated (Step S1). That is, after the operation of the BWR plant is stopped for the periodic inspection of the BWR plant, the circulation pipe 35 is connected to the recirculation system pipe 22 and the purification system pipe 20 as described above. The piping system to be coated is, for example, the recirculation piping 22. A valve 23 is provided in the purification system pipe 20. The bonnet of the valve 23 is opened to close the reactor water purification device 26 side of the purification system pipe 20. One end of the circulation pipe 35 is connected to the flange of the valve 23. The other end of the circulation pipe 35 is connected to a recirculation system pipe 22 downstream of the recirculation pump 21, for example, a branch pipe connected to the recirculation system pipe 22 (a branch pipe from which a drain pipe or an instrumentation pipe is separated). Connecting. In this way, the film forming apparatus 30 is connected to the recirculation piping 22. In addition, both ends of the recirculation system pipe 22 are sealed with plugs as shown in FIG. 8 so that the decontamination solution and the film-forming aqueous solution supplied into the recirculation system pipe 22 do not flow into the RPV 12. .

  Chemical decontamination is performed on the film formation target portion (step S2). On the inner surface of the recirculation system pipe 22 that comes into contact with the cooling water, an oxide film (contaminant) incorporating the radionuclide is formed. An example of step S2 is a process of removing the oxide film that has taken in the radionuclide by a chemical process from the inner surface of the recirculation pipe 22 that is a film formation target location. The formation of a ferrite film on the piping system to be coated is intended to suppress the attachment of radionuclides to the piping system. It is preferable to carry out. Since it is sufficient that the surface of the metal member to be coated is exposed before the ferrite film is formed, mechanical decontamination treatment can be applied instead of chemical decontamination.

  The chemical decontamination applied in step S2 is a known method (see Japanese Patent Laid-Open No. 2000-105295), but will be briefly described. First, the valves 33, 34, 47, 49, 55, 56, and 57 are opened, and the circulation pump 32 and the circulation pump 48 are activated with the other valves closed, and the recirculation piping 22 to be decontaminated. The water in the surge tank 31 is circulated inside. And the temperature of the water circulated with the heater 53 is raised to about 90 degreeC. After reaching a predetermined temperature, the valve 36 is opened. The surge tank 31 supplies the required amount of potassium permanganate introduced into the pipe 70 from the hopper connected to the ejector 37 into the surge tank 31 by the water flowing in the pipe 70. Potassium permanganate dissolves in water in the surge tank 31 to produce an oxidative decontamination solution. This oxidative decontamination liquid is supplied to the recirculation system pipe 22 through the purification system pipe 20 through the circulation pipe 35 by driving of the circulation pump 32. The oxidative decontamination solution oxidizes and dissolves contaminants such as an oxide film formed on the inner surface of the recirculation pipe 22.

  After the decontamination by the oxidative decontamination liquid is completed, oxalic acid is injected from the hopper into the surge tank 31 in order to decompose permanganate ions remaining in the oxidative decontamination liquid. After the potassium permanganate is decomposed, a reducing decontamination solution is used to reduce and dissolve contaminants such as an oxide film formed on the inner surface of the recirculation pipe 22. The reductive decontamination liquid is generated by supplying oxalic acid into the surge tank 31 as described above. The reductive decontamination liquid flows through the circulation pipe 35 by driving the circulation pump 32. In order to adjust the pH of the reductive decontamination liquid, the valve 38 is opened and the injection pump 39 is driven to supply hydrazine from the chemical liquid tank 40 into the circulation pipe 35. A reductive decontamination solution containing hydrazine is supplied into the recirculation system pipe 22 to reduce and decontaminate the inner surface of the recirculation system pipe 22. After supplying the reductive decontamination liquid to the recirculation system pipe 22, the valve 61 is opened and the opening degree of the valve 56 is adjusted to guide a part of the reductive decontamination liquid to the cation exchange resin tower 60. The metal cation eluted in the reductive decontamination solution by reductive decontamination is adsorbed by the cation exchange resin in the cation exchange resin tower 60 and removed from the reductive decontamination solution.

  After the reduction decontamination is completed, the oxalic acid remaining in the decontamination liquid is decomposed, the valve 65 is opened, the opening degree of the valve 57 is adjusted, and a part of the reduction decontamination liquid flowing in the circulation pipe 35 is decomposed. 64. At this time, the valve 54 is opened to drive the injection pump 44, and the hydrogen peroxide in the chemical tank 46 is guided to the decomposition device 64 through the pipe 75. The decomposition device 64 decomposes oxalic acid and hydrazine contained in the reductive decontamination solution by the action of hydrogen peroxide and activated carbon catalyst. After decomposition of oxalic acid and hydrazine, the valve 55 is closed to stop heating by the heater 53, and at the same time, the valve 59 is opened to supply the decontamination solution to the cooler 58. After the temperature of the decontamination liquid is lowered to a temperature at which water can be passed through the mixed bed resin tower 62 (for example, 60 ° C.), the valve 61 is closed and the valve 63 is opened, and the decontamination liquid is supplied to the mixed bed resin tower 62. The mixed bed resin tower 62 removes impurities contained in the decontamination solution.

  The oxide film formed on the surface of the metal member at the decontamination target site by repeating, for example, about 2 to 3 times, from these series of temperature rises, oxidation dissolution, oxidant decomposition, reduction dissolution, reductant decomposition, and purification operation. Contaminants containing can be dissolved and removed.

  In this way, after removing the contaminants including the oxide film of the metal member, the process is switched to the ferrite film forming process. A method for forming a ferrite film is known (see Patent Document 3), but will be briefly described here.

  After the decontamination of the film forming target portion is completed, the temperature of the film forming aqueous solution is adjusted (step S3). After the decontamination of the film formation target portion, after the final purification operation by the film forming apparatus 30, the following valve operation is performed. The valve 50 is opened, the valve 49 is closed, and water flow to the filter 51 is started. By opening the valve 56 and closing the valve 63, water flow to the mixed bed resin tower 62 is stopped. Further, the valve 55 is opened and the water in the circulation pipe 35 is heated to a predetermined temperature by the heater 53. Valves 47, 57, 33, and 34 are open, and valves 36, 59, 61, 65, 38, 41, 42, and 54 are closed. The water flow through the filter 51 is for removing fine solids remaining in the water. If this solid substance remains, a ferrite film is also formed on the surface of the solid substance when the ferrite film is formed at the film formation target site, and the drug is wasted. By removing the solid matter, the drug contained in the film-forming aqueous solution can be used effectively. When water is passed through the filter 51 during decontamination, the dose rate of the filter 51 may become too high due to the dissolved solid matter containing the high-activity radionuclide. For this reason, water is passed through the filter 51 after the decontamination is completed. When the removal of the solid matter is completed, the valve 49 is opened and the valve 50 is closed.

  The predetermined temperature is preferably about 100 ° C., but is not limited thereto. In short, it is only necessary that the film structure such as crystals of the coating can be densely formed so that the radionuclide contained in the cooling water during operation of the nuclear reactor is not taken into the ferrite coating generated at the coating formation target site. Therefore, the temperature of the aqueous solution for forming a film is preferably at least 200 ° C. and the lower limit may be room temperature, but is preferably 60 ° C. or higher at which the film formation rate is within the practical range. When the temperature is 100 ° C. or higher, pressure must be applied in order to suppress boiling of the film-forming aqueous solution, and the pressure resistance of the temporary equipment is required.

  A ferrite film is formed at a film formation target location (step S4). In order to form a ferrite film, iron (II) ions need to be adsorbed on the surface of the metal member at the film formation target location. However, iron (II) ions in the film-forming aqueous solution are oxidized to iron (III) ions by dissolved oxygen according to the formula (4). Since iron (III) ions have lower solubility than iron (II) ions, they precipitate as iron hydroxide according to the formula (5) and do not contribute to the formation of a ferrite film. Therefore, in order to remove dissolved oxygen in the film-forming aqueous solution, it is preferable to perform bubbling of inert gas or vacuum degassing as described above.

4Fe ²⁺ + O ₂ + 2H ₂ O → 4Fe ³⁺ + 4OH ⁻ (4)
Fe ³⁺ + 3OH ⁻ → Fe (OH) ₃ (5)
After the temperature of the water circulating in the circulation pipe 35 reaches a predetermined temperature, a drug containing iron (II) ions prepared by opening the valve 41 and driving the injection pump 43 and dissolving iron with formic acid is used as a chemical solution. Injection from the tank 45 into the circulation pipe 35. Subsequently, the valve 42 is opened and the injection pump 44 is driven to inject oxidant hydrogen peroxide into the circulation pipe 35 from the chemical tank 46. Hydrogen peroxide ferritizes iron (II) ions adsorbed on the surface of the metal member at the film formation target location. Finally, the valve 38 is opened and the injection pump 39 is driven to inject hydrazine from the chemical tank 40 into the circulation pipe 35. By injecting a chemical containing iron (II) ions, hydrogen peroxide, and hydrazine, a film-forming aqueous solution is generated in the circulation pipe 35 along with the water in the circulation pipe 35. This film-forming aqueous solution is supplied to the recirculation system pipe 22 through the circulation pipe 35. The formation reaction of the ferrite film occurs on the inner surface of the recirculation piping 22 that comes into contact with the film-forming aqueous solution. Hydrazine is used to adjust the pH of the film-forming aqueous solution to 5.5 to 9.0, which is a reaction initiation condition. The pH of the film-forming aqueous solution is measured by a pH meter 66. A control device (not shown) controls the rotation speed of the injection pump 39 based on the measured pH value, and adjusts the injection speed of hydrazine to be injected into the circulation pipe 22. As a result, a ferrite film containing magnetite as a main component (hereinafter referred to as magnetite film) is formed on the inner surface of the recirculation pipe 22.

  The oxidizing agent in the film-forming aqueous solution causes an oxidation reaction of iron (II) ions contained in the aqueous solution. For this reason, the abundance ratio of iron (II) ions and iron (III) ions in the film-forming aqueous solution is a condition suitable for the formation reaction of the ferrite film. However, when the film-forming aqueous solution is acidic, the ferrite film is not formed. For this reason, the production | generation reaction of a ferrite membrane | film | coat is started by adding pH adjuster (for example, hydrazine) and adjusting the pH of film-forming aqueous solution to 5.5 thru | or 9.0. Therefore, in order to prevent the formation of a useless ferrite film on the inner surface of the circulation pipe 35, the injection point of the pH adjusting agent is preferably close to the film formation target location.

  When chemicals are injected in the order of oxidant, iron ion, and pH adjuster, hydrogen peroxide easily decomposes on the metal surface at a high temperature, so some of the oxidant that is injected first is wasted. Will be consumed. When iron ions, a pH adjuster, and an oxidizing agent are injected in this order, the formation of a ferrite film at the film formation target site is recognized, but the magnetite particles that form the ferrite film become larger. From the viewpoint of effectively using a chemical and forming a denser ferrite film, it is desirable to inject the chemical solution in the order of iron (II) ions, an oxidizing agent, and a pH adjusting agent.

  After the formation of the ferrite film on the inner surface of the recirculation system pipe 22 is completed, the processing of the used film forming aqueous solution (hereinafter referred to as waste liquid) (processing of steps S5 to S10 shown in FIG. 1) is performed in the film forming apparatus 30. Is executed. During the period during which the waste liquid is being processed, the waste liquid is supplied from one end of the circulation pipe 35 to one end of the recirculation system pipe 22 by driving the circulation pump 32, and passes through the recirculation system pipe 22 to the circulation pipe 35. Returned to the other end. The waste liquid returned to the circulation pipe 35 through the valve 47 is returned to the surge tank 31 through the heater 53 and the valves 55, 56, 57 by driving of the circulation pump 48.

  In the waste liquid treatment process, first, the concentration of iron (II) ions remaining in the waste liquid is measured (step S5). In the film-forming aqueous solution remaining in the recirculation system pipe 22 and the film-forming apparatus 30, for example, particulate matter such as magnetite generated with the formation of the ferrite film, iron (II that has not contributed to the formation of the ferrite film) ) Ions etc. remain. Particulate matter such as magnetite can be easily separated and removed by filtration, but iron (II) ions and the like need to be separated after adding a chemical to precipitate. Therefore, the concentration of iron (II) ions present in the waste liquid is measured. The iron (II) ion concentration can be measured by absorptiometry using, for example, o-phenanthroline in the waste liquid collected by opening the sampling valve 76 (see FIG. 7).

Next, a pH adjuster is injected (step S6). Iron (II) ions present in the waste liquid are oxidized and precipitated as magnetite (Fe ₃ O ₄ ) generated according to the formulas (1) and (2). When iron (II) ions are oxidized, the reaction of the formula (3) proceeds simultaneously, and ferric hydroxide (Fe (OH) ₃ ) is also generated. However, in this example, iron (II) ions are precipitated as a magnetite that is an iron oxide at a high ratio.

  That is, according to the formulas (1) to (3), 1 to 2 mol of hydrogen ions are generated per 1 mol of iron (II) ions. A predetermined amount of basic substance is injected based on the measured value of the iron (II) ion concentration so as not to neutralize the hydrogen ions and lower the pH of the waste liquid. Here, hydrazine used at the time of chemical decontamination and formation of a ferrite film is used.

This hydrazine exhibits an equilibrium reaction of the formula (6) in water, and the dissociation constant Ka is Ka = [N ₂ H ₄ ] [H ⁺ ] / [N ₂ H ₅ ⁺ ] = 1.07 × 10 ^−7. . And since the total concentration [N ₂ H ₄ ] _T of hydrazine is [N ₂ H ₄ ] _T = [N ₂ H ₄ ] + [N ₂ H ₅ ⁺ ], the hydrazine consumed H ⁺ The ratio of [N ₂ H ₅ ⁺ ] to the total concentration [N ₂ H ₄ ] _T is [N ₂ H ₅ ⁺ ] / [N ₂ H ₄ ] _T = [H ⁺ ] / ([H ⁺ ] + Ka )

N ₂ H ₅ ⁺ = N ₂ H ₄ + H ⁺ (6)
If the waste liquid after adding hydrogen peroxide is to be maintained at pH 7, for example, about half of the added hydrazine can consume hydrogen ions. Therefore, since the maximum amount of hydrogen ions generated when hydrogen peroxide is added is 2 mol per mol of iron (II) ions, the amount of hydrazine injected into the circulation pipe 35 is more than four times the iron (II) ion concentration. It becomes. The injection of hydrazine in step S6 is performed by opening the valve 38 and driving the injection pump 39 while processing the waste liquid, specifically while processing the waste liquid. Hydrazine is injected from the chemical solution tank 40 into the circulation pipe 35. Hydrazine is injected so that the pH of the waste liquid is 6.5 or higher. Preferably, hydrazine is injected so that the pH of the waste liquid is 6.5 or more and pH 9 or less.

  An oxidizing agent is injected (step S7). As shown in the formula (2), iron (II) ions and iron (III) ions are reacted to generate magnetite, and this is deposited. Is added from the chemical tank 46 into the circulation pipe 35. The predetermined amount of hydrogen peroxide to be added is 1 to 2 times the iron (II) ion concentration from the equation (1). However, if the hydroxy radical generated by the formula (1) reacts with unreacted iron (II) ions, it may be 1 time. However, when it reacts with hydrazine and organic acids, the amount of iron (III) ions generated is insufficient. This lowers the magnetite production rate. On the other hand, when hydrogen peroxide is added twice, the amount of iron (III) ions produced becomes excessive, and a large amount of ferric hydroxide is produced. Therefore, in order to suppress the production of ferric hydroxide and produce magnetite, for example, the following method is used.

  First, the opening degree of the valve 42 is controlled in the waste liquid based on the measured value of the iron (II) ion concentration, and an amount of hydrogen peroxide equivalent to the measured value is added. Thereafter, the iron (II) ion concentration is measured again, and the amount of hydrogen peroxide equivalent to the measured value of the iron (II) ion concentration remaining in the waste liquid is controlled by controlling the opening degree of the valve 42 and the circulation pipe 35. Add to the waste liquid flowing through. In this way, by gradually adding hydrogen peroxide to the waste liquid, hydrogen peroxide can be added without excess or deficiency with respect to magnetite production.

In the hydrazine injection in step S6 and the hydrogen peroxide injection in step S7, the opening of the valves 39 and 42 is controlled by a control device (not shown) using the measured value of the pH meter 66, and the respective injection amounts are adjusted. May be. When hydrogen peroxide is started to be injected in step S7, the pH of the waste liquid starts to decrease due to the generation of H ⁺ according to the equations (2) and (3). When the measured value of this pH becomes, for example, pH 6.5 or lower at which a stable region of iron (II) ions is generated, the injection of oxidant is interrupted and hydrazine is added until, for example, pH 7, and then, The injection of hydrogen peroxide may be resumed.

  The precipitated particles in the waste liquid are removed with a filter (step S8). In step S7, iron (II) ions dissolved in the waste liquid are precipitated as magnetite by the reaction according to the formulas (1) and (2). At the same time, ferric hydroxide may be slightly precipitated by the reaction of formula (3). The precipitated particles (solid matter) of magnetite and ferric hydroxide are removed by the filter 51. That is, the removal of these precipitated particles is performed by opening the valve 50 and closing the valve 49 simultaneously with the addition of hydrogen peroxide to the waste water, and allowing the waste liquid to flow through the filter 51. By supplying the waste liquid to the filter 51, the concentration of the precipitated particles precipitated in the waste liquid gradually decreases.

  The installation positions of the valves 49 and 50 and the filter 51 in the film forming apparatus 30 may be anywhere as long as the precipitated particles generated in the waste liquid can be removed. However, as for those installation positions, as shown in FIG. 7, the exit side of the surge tank 31 is more preferable. This is because the precipitated particles grow within the staying period of the waste liquid in the surge tank 31, so that the precipitated particles are easily removed by the filter 51. As the amount of the precipitated particles to be removed increases, the amount of the precipitated particles conveyed into the radioactivity adhesion suppression target portion, that is, the recirculation system pipe 22, is remarkably reduced.

  It is clear from the results shown in FIG. 5 that the deposited particles in the waste liquid can be completely removed by using the filter 51 having an opening of 0.05 μm or less. In this case, since the filter 51 is immediately clogged and the differential pressure increases, the replacement frequency of the filter 51 increases, and the amount of the filter 51 that becomes radioactive solid waste increases. The characteristics shown in FIG. 4 have been confirmed by using a filter having an opening of 1 μm. Even with a filter 51 having an opening of 1 μm, the precipitated particles can be effectively removed from the waste liquid. That is, fine precipitated particles are allowed to permeate, and after the precipitated particles grow and have a large particle size, the precipitated particles are removed by the filter 51. Thereby, since the exchange frequency of the filter 51 by a differential pressure rise can be suppressed remarkably, the generation amount of filter waste can be suppressed. However, if the openings are too large, the removal efficiency of the precipitated particles is deteriorated. Since a filter having a mesh size of 10 μm required about 20 hours to remove the precipitated particles, the filter mesh size is preferably 1 μm to 10 μm.

  It is determined whether the concentration of precipitated iron contained in the waste liquid is equal to or lower than a set concentration (step S9). If the concentration of precipitated iron contained in the waste liquid (the concentration of precipitated particles) is equal to or higher than a set concentration (for example, 1 ppm), the supply of the waste liquid to the filter 51 is continued. The concentration of precipitated iron can be measured by, for example, atomic absorption spectrophotometry of the waste liquid collected by opening the sampling valve 76. When the deposited iron concentration becomes lower than the set concentration, the decomposition process of the chemical contained in the waste liquid is executed in step S10 described later.

  When the determination in step S9 is “Yes”, decomposition of the medicine is performed (step S10). In the waste liquid, hydrazine and formic acid which is an organic acid remain. Hydrazine and formic acid are decomposed by the film forming apparatus 30 after the removal of the precipitated particles in step S8 is completed. These decomposition | disassembly is performed using the decomposition | disassembly apparatus 64 similarly to decomposition | disassembly of oxalic acid in chemical decontamination. The opening degree of the valves 57 and 65 is adjusted, and a part of the waste liquid is supplied to the decomposition device 64. The valve 54 is opened, and hydrogen peroxide is supplied from the chemical solution tank 46 through the pipe 75 to the decomposition device 64. Hydrazine and formic acid are decomposed in the decomposition apparatus 64 by the action of hydrogen peroxide and activated carbon catalyst. Hydrazine decomposes into nitrogen and water, and formic acid decomposes into carbon dioxide and water. It is also possible to use an ultraviolet irradiation device instead of the decomposition processing device 64 using a catalyst. An ultraviolet irradiation device can also decompose hydrazine, formic acid and oxalic acid in the presence of an oxidizing agent.

  By decomposing hydrazine and formic acid into gas and water in the decomposition apparatus 64 as described above, removal of hydrazine and formic acid by the mixed bed resin tower 62 by the cation exchange resin tower 60 can be avoided, so that these ion exchange resins are discarded. The quantity can be significantly reduced. In this embodiment, the precipitated particles are removed from the waste liquid in step S8 before the chemical decomposition step, so that the decomposition efficiency of formic acid and hydrazine is improved, and the time required for the decomposition can be remarkably shortened. In this embodiment, the amount of radioactive solid waste such as ion exchange resin and filter 51 can be suppressed, and the treatment time of the waste liquid of the film-forming aqueous solution generated after the formation of the ferrite film can be remarkably shortened. .

  In this example, when treating the waste liquid generated after the formation of the ferrite film, particulate magnetite, which is an iron oxide that can be easily filtered from iron (II) ions contained in the waste liquid, is generated and deposited. As described above, the waste liquid treatment time can be shortened.

  In addition, according to the present embodiment, after removing contaminants including an oxide film adhering to the surface of the constituent member (for example, the recirculation system pipe 22) that is the target of film formation, which contacts the cooling water, Since the ferrite film is formed on the surface, the ferrite film can be directly formed on the surface. Therefore, the attachment of the radionuclide to the surface can be effectively suppressed. In addition, after the chemical component contained in the waste liquid that has passed through the filter 51 is decomposed, the waste liquid is drained through the ion exchange resins of the cation exchange resin tower 60 and the mixed bed resin tower 62. For this reason, the waste amount of used ion exchange resin can be reduced.

  This example uses an oxidizing agent in the decomposition of oxalic acid used in reductive decontamination, the formation of ferrite film and the treatment of the waste liquid of the film formation aqueous solution, the reduction decontamination, the formation of ferrite film and the treatment of the waste liquid of the film formation aqueous solution. The pH adjusting agent is used in Fig. 1, and the decomposition apparatus 64 is used in the decomposition of the oxalic acid used in the reductive decontamination and the treatment of the waste liquid of the film-forming aqueous solution. For this reason, the oxidant tank, the pH adjuster tank, and the decomposition apparatus 64 can be shared for chemical decontamination and ferrite film formation (including treatment of waste liquid), and the apparatus configuration can be simplified.

  When the chemical tank 45 is filled with a drug containing divalent iron (II) ions prepared by dissolving iron with carbonic acid, the drug tank 45 contains the drug containing iron (II) ions and carbonic acid. To the circulation pipe 35. For this reason, the film-forming aqueous solution contains carbonic acid. Even when this film-forming aqueous solution containing carbonic acid is processed by the film-forming apparatus 30, the film-forming aqueous solution can be processed in a shorter time by executing the processes of steps S5 to S10 described above.

  A method for treating a solution after forming a ferrite film, which is another embodiment of the present invention, applied to a BWR plant will be described below with reference to FIG. The configuration of the film forming apparatus 30 shown in FIG. 8 used in the present embodiment has the same configuration as the film forming apparatus 30 (see FIG. 7) used in the first embodiment. In FIG. 8, a part of the configuration of the film forming apparatus 30 is omitted. The solution processing method of the present embodiment also executes the steps S1 to S10 shown in FIG.

  In this embodiment, the connection destination of the circulation pipe 35 of the film forming apparatus 30 is different from the connection destination of the circulation pipe 35 of the film formation apparatus 30 in the first embodiment. In this embodiment, one end of the circulation pipe 35 is connected to the branch pipe 80 connected to the recirculation system pipe 22 via the valve 12. The other end of the circulation pipe 35 is connected via a valve 13 to a branch pipe 81 connected to the recirculation system pipe 22. Also in this embodiment, the recirculation system pipe 22 is a film formation target portion. Both ends of the recirculation piping 22 are sealed by plugs 28 and 29. The connection of the circulation pipe 35 to the recirculation system pipe 22 and the plugging of the both ends of the recirculation system pipe 22 by the plugs 28 and 29 are performed in step S1. A pipe 74 for injecting hydrazine is connected to the circulation pipe 35 in the containment vessel 11 in the vicinity of the film formation target location. After the end of step S1, steps S2 to S10 are executed.

  In this embodiment, when the film forming apparatus 30 is connected to the recirculation system pipe 22, two free liquid levels are generated in the recirculation system pipe 22. The level of the liquid surface of the film-forming aqueous solution (or decontamination liquid) in the recirculation pipe 22 needs to be controlled so that the film-forming aqueous solution does not enter the RPV 12. However, in order to keep the dose rate in the dry well outside the RPV 12 low, it is desirable to make the water level of the film-forming aqueous solution as high as possible. The heights of these free liquid levels can be controlled by finely adjusting the balance of the discharge flow rates of the circulation pumps 32 and 48 using the valves 33 and 47. Although not shown in FIG. 8, the valve 33 is provided at the position shown in FIG. Since a ferrite film is likely to be formed in the vicinity of the liquid surface of the film-forming aqueous solution, the ferrite surface is also efficiently formed on the inner surface of the riser pipe located above the recirculation pipe 22 that tends to be stagnant water by changing the liquid surface. A film can be formed. In the present embodiment, the effects produced in the first embodiment can be obtained.

  A film forming apparatus used in a method for treating a solution after forming a ferrite film according to another embodiment of the present invention will be described below with reference to FIG. This film forming apparatus 30A has a configuration in which nitrogen bubbling devices 86 and 89 are added to the film forming apparatus 30 used in the first embodiment. The nitrogen bubbling device 86 is provided for the surge tank 31, and the nitrogen bubbling device 89 is provided for the chemical liquid tank 45. The nitrogen bubbling device 86 includes a nitrogen storage container 82A, an oxygen storage container 84, a supply pipe 87, and a gas ejection device 88. The gas ejection device 88 is disposed in the surge tank 31 and connected to the supply pipe 87. The nitrogen storage container 82A is connected to the supply pipe 87 via the valve 83, and the oxygen storage container 84 is connected to the supply pipe 87 via the valve 85. The nitrogen bubbling device 89 includes a nitrogen storage container 82B, a supply pipe 90, and a gas ejection device 91. The gas ejection device 91 is disposed in the chemical liquid tank 45 and connected to the supply pipe 90. The nitrogen storage container 82B is connected to the supply pipe 90 via a valve (not shown).

  In the solution processing method according to the present embodiment, each procedure of steps S1 to S10 is executed in the same manner as in the first embodiment. The nitrogen bubbling devices 86 and 89 open the valve 83 and the like in order to prevent the iron (II) ions from being excessively oxidized in the surge tank 31 and the chemical liquid tank 45 during the formation of the ferrite film of Step S4. The nitrogen in the nitrogen storage containers 82A and 82B is purged from the gas jetting devices 88 and 91 into the solution in the respective tanks. In step S7, oxygen from the oxygen storage container 84 is spouted into the solution in the surge tank 31 as an oxidant by opening the valve 85. This oxygen bubbling is continued until the iron (II) ions contained in the waste liquid are exhausted. It is also possible to replace the oxygen with ozone-containing oxygen.

  According to the present embodiment, the same effect as in the first embodiment can be obtained.

  The processing method of the solution after the ferrite film formation which is another Example of this invention applied to the BWR plant is demonstrated below using FIG. The solution processing method in the present embodiment is performed using the film forming apparatus 30 shown in FIG. The solution processing method in the present embodiment can also be performed using the film forming apparatus 30A shown in FIG. The procedure shown in FIG. 10 is performed by the solution processing method in the present embodiment performed using the film forming apparatus 30. This procedure is obtained by adding steps S11 and S12 to the procedure shown in FIG. 1, that is, steps S1 to S10. These steps S11 and S12 are performed between step S9 and step S10.

  Steps S11 and S12 will be specifically described. When the determination in step S9 is “Yes”, the iron (II) ion concentration of the waste liquid is determined (step S11). That is, when the determination in step S9 is “Yes”, the iron (II) ion concentration of the waste liquid is measured. The iron (II) ion concentration can be measured by, for example, absorptiometry using o-phenanthroline for the waste liquid collected by opening the sampling valve 76 (see FIG. 7). When it is determined that the measured value of the iron (II) ion concentration is smaller than the remaining amount of the ion exchange capacity of the cation resin tower 60, the waste liquid is supplied to the cation exchange resin tower 60 (step S12). The remaining amount of the ion exchange capacity can be obtained by subtracting the ion exchange equivalent obtained from the cation concentration when the cation resin tower is passed from the ion exchange capacity of the filled cation resin. The valve 49 is opened and the valve 50 is closed, and the supply of the waste liquid to the filter 51 is stopped. At the same time, the valve 61 is opened to adjust the opening degree of the valves 56 and 61, and the waste liquid is supplied to the cation exchange resin tower 60. Iron (II) ions contained in the waste liquid are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 60. After the iron (II) ions are removed from the waste liquid, decomposition of the chemical contained in the waste liquid (step S10), which is performed in Example 1, is performed. When it is determined in step S11 that the measured value of the iron (II) ion concentration is larger than the remaining amount of the ion exchange capacity of the cation resin tower 60, the measured value becomes smaller than the remaining amount of the ion exchange capacity. The processes in steps S6 to S9 are repeated.

The first embodiment aims to precipitate iron (II) ions contained in the waste liquid as solid particles of Fe ₃ O ₄ and Fe (OH) ₃ and remove them with the filter 51. In contrast, in this example, iron (II) ions were precipitated as solid particles of Fe ₃ O ₄ and Fe (OH) ₃ and removed by the filter 51, and then iron (II) still remaining Ions are removed using the cation resin tower 60. In Example 1, the load on the cation resin tower 60 is reduced as much as possible, and the amount of used ion exchange resin generated, that is, the amount of radioactive solid waste generated is reduced. For this reason, in Example 1, since it is necessary to wait until the particle diameters of the solid particles of Fe ₃ O ₄ and Fe (OH) ₃ can be collected by the filter 51, the time required for processing the waste liquid It becomes longer by that much. However, the time required for the treatment of the waste liquid in Example 1 is still significantly reduced as compared with the prior art. In this embodiment, the solid particles are removed by the filter 51, and then the iron (II) ions remaining in the waste liquid are removed by the cation exchange resin tower 60. For this reason, in this embodiment, it is not necessary to wait for the solid particles to grow to a particle diameter that allows the remaining iron (II) ions to be collected by the filter 51. In the present embodiment, the step of removing iron remaining in the waste liquid can be shortened by a corresponding amount compared to the first embodiment, and the time required for processing the waste liquid can be further shortened.

Since the present embodiment uses the cation exchange resin tower 60, the amount of the radioactive solid waste is increased as compared with the first embodiment. However, if the cation resin tower 60 used in the decontamination process is used, this problem can be substantially solved. That is, in the cation resin tower 60 used in the decontamination process, a cation exchange resin having a cation exchange capacity having a tolerance is used so as to cope with several hundred ppm of the cation component generated by dissolution of the oxide film. On the other hand, the iron (II) ion concentration used in forming the ferrite film is about several hundred ppm. When all of the used iron (II) ions remain as ions, the cation resin tower 60 used for decontamination cannot be used. In this embodiment, since most of the iron (II) ions contained in the waste liquid are precipitated as solid particles of Fe ₃ O ₄ and Fe (OH) ₃ by using an oxidizing agent in step S7 and removed by the filter 51, Thereafter, the concentration of iron (II) ions remaining in the waste liquid becomes extremely low. For example, the concentration is several tens of ppm. If it is several tens of ppm of iron (II) ions, it can be removed by using the remaining cation exchange capacity of the cation resin tower 60 used in the decontamination. Therefore, in this embodiment, the amount of cation exchange resin waste does not increase substantially.

  Each example of the method for treating a solution after forming a ferrite film as described above includes not only a BWR plant but also a pressurized water nuclear power plant including the formation of a ferrite film on the surface of a metal member in contact with cooling water. Can also be applied.

It is a flowchart which shows the procedure of the processing method of the solution after the ferrite film formation of Example 1 which is one suitable Example of this invention. It is a characteristic view showing the time change of pH when hydrogen peroxide is added to the waste liquid generated after formation of a phyllite film. It is explanatory drawing which represented the form of the iron compound in an iron-water system by the relationship between an electric potential and pH. When hydrogen peroxide alone is added to the waste liquid generated after the formation of the ferrite film, and when hydrazine (N ₂ H ₄ ) is added to the waste liquid and hydrogen peroxide is added to maintain the pH at 6.5 or higher. In each, it is the characteristic view which showed the time change of precipitation iron concentration. When hydrogen peroxide alone is added to the waste liquid generated after the formation of the ferrite film, and when hydrazine (N ₂ H ₄ ) is added to the waste liquid and hydrogen peroxide is added to maintain the pH at 6.5 or higher. In each, it is the characteristic view which showed the time change of the particle size of a precipitation particle. It is a block diagram of the BWR plant which connected the film forming apparatus used for the processing method of the solution shown in FIG. It is a detailed block diagram of the film forming apparatus shown in FIG. It is explanatory drawing which shows the connection state of the film formation apparatus and recirculation system piping in the processing method of the solution after the ferrite film formation of Example 2 which is another Example of this invention. It is a block diagram of the film formation apparatus used for the processing method of the solution after the ferrite film formation of Example 3 which is another Example of this invention. It is a flowchart which shows the procedure of the processing method of the solution after the ferrite film formation of Example 3 which is another Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactor, 12 ... Reactor pressure vessel, 20 ... Purification system piping, 21 ... Recirculation pump, 22 ... Recirculation system piping, 30 ... Film formation apparatus, 31 ... Surge tank, 32, 48 ... Circulation pump, 35 ... circulation piping, 39, 43, 44 ... injection pump, 40, 45, 46 ... chemical tank, 51 ... filter, 53 ... heater, 60 ... cation exchange resin tower, 62 ... mixed bed resin tower, 64 ... decomposition apparatus, 66: pH meter, 86, 89 ... Nitrogen bubbling device.

Claims (13)

A metal member comprising a first agent containing iron (II) ions, a second agent that oxidizes the iron (II) ions to iron (III) ions, and a third agent that adjusts the pH. A method for treating a solution used in forming a ferrite film on the surface of
When the solution is treated, the pH of the solution is adjusted to 6.5 or more using a pH adjuster, and then an oxidizing agent is supplied to the solution. The supplied oxidizing agent and the iron (II) A method for treating a solution after the formation of a ferrite film, wherein solids produced by the reaction of ions are removed from the solution.   The method for treating a solution after forming a ferrite film according to claim 1, wherein the step of removing the solid matter includes removing the iron (II) ions from the solution, which is performed after the removal of the solid matter. . Method of processing solution removing the iron (II) ions after the ferrite film formation according to 請 Motomeko 2 Ru performed using ion-exchange resin.

  The method for processing a solution after forming a ferrite film according to any one of claims 1 to 3, wherein the solid matter is removed using a filter device.   5. The ferrite film according to claim 1, wherein after the step of removing the solid matter, the organic acid contained in the first drug and the third drug are decomposed. Method for processing solution after formation.   The method for treating a solution after forming a ferrite film according to claim 5, wherein the decomposition of the organic acid and the third agent is performed by a decomposition apparatus to which the oxidizing agent is supplied.   The method for treating a solution after forming a ferrite film according to claim 6, wherein the decomposition is performed by the action of a catalyst in the decomposition apparatus.   The decomposition apparatus used for decomposition | disassembly of the organic acid in the decontamination liquid used for the chemical decontamination of the said surface of the said metal member before formation of the said ferrite film is used as the said decomposition apparatus. The processing method of the solution after the ferrite film formation of description.   The method for treating a solution after forming a ferrite film according to any one of claims 1 to 8, wherein the second agent is used as the oxidizing agent, and the third agent is used as the pH adjusting agent. .   The iron (II) ion concentration of the solution to be treated is measured, and the supply amount of at least one of the pH adjusting agent and the oxidizing agent to the solution is adjusted based on the measured value of the iron (II) ion concentration A method for treating a solution after forming a ferrite film according to any one of claims 1 to 8.   The method for treating a solution after forming a ferrite film according to any one of claims 1 to 8, wherein the second chemical agent is any one of hydrogen peroxide, oxygen, and ozone.   The method for treating a solution after forming a ferrite film according to any one of claims 1 to 8, wherein the third agent is hydrazine.   The method for treating a solution after forming a ferrite film according to claim 4, wherein the filter device has an opening of 1 μm to 10 μm.

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