JP2008304388A - Method for treating solution after ferrite membrane formation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the processing time required for disposal of solution having been used for forming a ferrite film. <P>SOLUTION: A film forming device is connected to a pipe system for film formation. Chemistry decontamination of the pipe inner surface of the pipe system is carried out. After the completion of the decontamination, film forming aqueous solution to be used for ferrite film formation (containing organic acid solution containing iron (II) ion, oxidizer, and pH adjustor) is adjusted in temperature, and the ferrite film is formed on the pipe inner surface. The method for treating the used film forming aqueous solution (waste liquid) after the ferrite film formation is as follows. Solid particles contained in the waste liquid is removed by a filter. A pH adjustor (hydrazine) is injected into the waste liquid so that the pH of the waste liquid circulating in a place for film formation (for example, recirculating system pipe). Iron (II) ions contained in the waste liquid are removed by cation-exchange resin while the pH is maintained and organic acid (formic acid) contained in the waste liquid is decomposed using the oxidizer and catalyst. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 radionuclides elute into the reactor water depending on the solubility of the incorporated oxides, or It is released again into the reactor water as an insoluble solid called clad. 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 has been proposed that an oxide film be formed on the inner surface 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 solution containing iron (II) ions, hydrogen peroxide and hydrazine is brought into contact with the surface of the constituent member at a low temperature of 100 ° C. or less, and ferrite is deposited on the surface. A method for forming a dense film has been proposed (Patent Document 3). Since iron (II) ions are used after dissolved in formic acid, the solution contains formic acid. 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 forming a ferrite film on the surface of a component such as a pipe of a nuclear power plant in contact with the reactor water using the method described in Patent Document 3, the solution used for forming this ferrite film ( Hereinafter, it is necessary to purify and drain the waste liquid). That is, the waste liquid contains iron (II) ions or the like as a raw material for the ferrite film in addition to the particulate matter (for example, iron oxide) generated during the formation of the ferrite film. It is necessary to remove these particulate matter and ions before draining. A filter may be used to remove the particulate matter, but if all the ionic components are removed with an ion exchange resin, the amount of secondary waste increases. For this reason, the organic acid and pH adjuster contained in the waste liquid are decomposed. However, since there is a difference in the easiness of decomposition of the organic acid and the pH adjuster, the pH is lowered during the decomposition process, and the formed ferrite film may be dissolved.

  The objective of this invention is providing the processing method of the solution after the ferrite film formation which can suppress the melt | dissolution of the formed ferrite film and can shorten the time which a waste liquid process requires.

  A feature of the present invention that achieves the above-described object is that a solution containing iron (II) ions, an organic acid, and a pH adjuster is used for forming a ferrite film on the surface of a metal member constituting a plant. When processing after film formation, the pH of the solution is adjusted to 4 or more and 10 or less using a pH adjuster, and in parallel with the removal of iron (II) ions contained in the solution with a cation exchange resin, The purpose is to decompose the organic acid contained in the solution.

  The pH of the solution used for forming the ferrite film is set to 4 to 10, and the organic acid contained in the first chemical contained in this solution is decomposed, so that the dissolution of the formed ferrite film is suppressed. can do. Further, in parallel with the removal of iron (II) ions contained in the solution, the organic acid contained in the solution is decomposed, so that the processing time of the solution can be shortened.

  ADVANTAGE OF THE INVENTION According to this invention, melt | dissolution of the ferrite film formed at the time of the waste liquid process after film-forming of a ferrite film can be suppressed.

  The inventors of the present invention examined the application of the same apparatus as the decomposition of organic acids used in chemical decontamination as a process of decomposing and removing organic acids dissolved in the waste liquid after the ferrite film formation treatment. As a result, the inventors have found a new finding that the ferrite film formed by the film formation treatment dissolves during the process of decomposing the organic acid and the pH adjuster contained in the waste liquid.

  The inventors examined this cause. In the decomposition apparatus, formic acid is decomposed according to the equation (1) and hydrazine is decomposed according to the equation (2) due to the addition of hydrogen peroxide and the presence of a catalyst.

HCOOH + H ₂ O ₂ → CO ₂ + 2H ₂ O (1)
N ₂ H ₄ + 2H ₂ O ₂ → N ₂ + 4H ₂ O (2)
The decomposition rates of formic acid and hydrazine are different as shown in FIG. 2, and the decomposition rate of hydrazine used as a pH adjuster is higher than the decomposition rate of formic acid. Therefore, the ratio of formic acid contained in the waste liquid is larger at the outlet of the decomposition apparatus than at the inlet. That is, the inventors have newly found that the pH of the waste liquid discharged from the decomposition apparatus is shifted to the acidic side. The inventors have found that the shift of the pH of the waste liquid to the acidic side results in the dissolution of the ferrite film formed on the surface of the structural member of the nuclear power plant.

  According to the new knowledge obtained from the above study, it is desirable to suppress a decrease in pH of the waste liquid in order to prevent dissolution of the ferrite film. Equilibriumally, based on the relationship between the potential and pH in FIG. 3, the dissolution of the ferrite film can occur if the pH of the waste liquid is stable at 6.5 or higher, regardless of the potential of the magnetite of the formed film. Absent. However, if the pH of the solution being decomposed is to be maintained at 6.5 or more, it is necessary to inject a large amount of a pH adjuster (for example, hydrazine) into the waste liquid. In nuclear power plants, the dissolution of the formed ferrite film that occurs during a finite decomposition time should be negligibly small. If the pH of the waste liquid can be controlled to the lowest possible value, the amount of hydrazine to be injected is reduced, which is useless. Eliminates the use of drugs. Therefore, the inventors changed the lower limit value of pH during decomposition of formic acid and hydrazine contained in the waste liquid, and conducted an experiment to examine the relationship between the lower limit value and dissolution of the formed ferrite film. This experiment yielded the results shown in FIG. Based on this result, while the formic acid and hydrazine contained in the waste liquid are being decomposed, the piping inside the nuclear power plant in which the ferrite film is formed is maintained at a pH of 4 or higher, thereby maintaining the piping. It was newly found that the dissolution of the ferrite film formed on the inner surface of the system is negligible. When performing a decomposition treatment of an organic acid (for example, formic acid) and a pH adjuster (for example, hydrazine), which are chemicals contained in the waste liquid, the pH of the waste liquid is desirably 4 or more and 10 or less. In order to reduce the amount of solid radioactive waste (used cation exchange resin) generated by the decomposition of the drug, the pH of the waste liquid at the time of the drug decomposition is preferably in the range of 4-7. Thereby, the amount of the pH adjusting agent injected into the waste liquid at the time of drug decomposition can also be reduced.

  Organic acids are used to dissolve iron and generate iron (II) ions necessary for the formation of a dense ferrite film. In addition to formic acid, malonic acid, diglycolic acid, oxalic acid, and the like exist.

  From the above examination results, the inventors have solved the dissolution of the ferrite film formed on the surface of the structural member of the nuclear power plant when treating the solution (waste liquid) used in forming the ferrite film. In order to suppress it, it came to the new idea that the organic acid contained in the waste liquid should be decomposed while supplying the pH adjuster into the waste liquid so that the pH of the waste liquid does not become less than 4. The supply amount of the pH adjuster to the waste liquid may be adjusted based on the pH indication value of the waste liquid supplied to the formation target portion of the ferrite film.

  As a pH adjuster used for the treatment of the waste liquid, it is preferable to use a third agent used at the time of film formation. 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, as the third drug, for example, hydrazine can be used.

  Prior to the decomposition of the organic acid in the waste liquid, the organic acid decomposition efficiency can be maintained high by removing particulate matter such as magnetite particles generated in the solution during the formation of the ferrite film contained in the waste liquid with a filter. Therefore, the decomposition processing time can be shortened.

  It is also possible to remove iron (II) ions contained in the waste liquid by injecting an oxidant into particles and then removing them with the above-mentioned filter. It should be removed by passing water. According to this, it is not necessary to wait for the growth of the particles as compared with the case where the iron (II) ions are made into particles, and the removal of the iron (II) ions and the decomposition and removal of the organic acid and the pH adjuster are simultaneously performed. The processing time of the waste liquid can be shortened.

  In addition, the contaminants including the oxide film adhering to the surface of the structural member of the nuclear power plant are chemically treated by repeatedly oxidizing and dissolving using permanganate ions and reducing and dissolving using an organic acid (for example, oxalic acid). After the removal, a ferrite film may be formed on the surface of the structural member in contact with the cooling water (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.

  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 FIGS. 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 example, 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. The schematic configuration of the apparatus will be described with reference to FIG. The film forming apparatus shown in FIG. 6 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 in which a core 13 is built, and a jet pump 14 is installed in the RPV 12. The nuclear reactor 1 is installed in a nuclear reactor containment vessel 11. 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. The recirculation system has a recirculation pump 21 and a recirculation system pipe 22, and the recirculation pump 21 is installed in the recirculation system pipe 22. The feed water system is configured by installing 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 in a feed water pipe 10 connecting the condenser 4 and the RPV 12. The 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. Configured. 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 nuclear fission of the nuclear 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 is rotated 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 for both the formation of a ferrite film on the inner surface of the recirculation pipe 22 and the treatment of the solution (waste liquid) used for forming this film. Furthermore, the film forming apparatus 30 is also used when performing chemical decontamination in the recirculation piping 22.

  The 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. Both ends of a pipe 66 that bypasses the heater 53 and the valve 55 are 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 having both ends connected to the circulation pipe 35 and bypassing the valve 56. A mixed bed resin tower 62 and a valve 63 are installed in a pipe 68 having both ends connected to the circulation pipe 35 and bypassing the valve 56. A pipe 69 in which the valve 65 and the decomposition device 64 are installed bypasses the valve 57 and 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. By bypassing the valve 49, a pipe 71 in which the filter 51 and the valve 50 are installed 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 pipe to be subjected to chemical decontamination is a pipe to be formed with a ferrite film on the inner surface.

  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 location 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 and 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 periodic inspection (maintenance inspection) of the 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. Note that both ends of the recirculation system pipe 22 are sealed with plugs (not shown) 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 (reactor water) in the RPV 12, 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 metal surface of the structural member to be coated is exposed before the ferrite film is formed, mechanical decontamination processing can be applied instead of chemical decontamination.

  The chemical decontamination applied in step S2 is performed in the same manner as step S2 described in JP 2006-38483 A. This chemical decontamination will be briefly described. First, with the valves 34, 33, 49, 57, 56, 55 and 47 opened and the other valves closed, the circulation pump 32 and the circulation pump 48 are activated, and the recirculation piping 22 to be decontaminated. The water in the surge tank 31 is circulated inside. The temperature of the circulating water is raised to about 90 ° C. by the heater 53 controlled by the temperature control device 80. After the water temperature reaches the set temperature, the valve 36 is opened. A required amount of potassium permanganate from the hopper connected to the ejector 37 is supplied into the surge tank 31 by using the driving force of the water flowing in the pipe 70. The potassium permanganate aqueous solution (oxidation decontamination solution) generated in the surge tank 31 passes through the circulation pipe 35 and is supplied into the recirculation system pipe 22 through the valve 34 and the purification system pipe 20. 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, permanganate ions remaining in the oxidative decontamination liquid are decomposed by the oxalic acid supplied from the hopper. After the decomposition of potassium permanganate, a reducing decontamination solution that is an aqueous oxalic acid solution is used to reduce and dissolve contaminants such as an oxide film formed on the inner surface of the recirculation system pipe 22. The reductive decontamination liquid is generated by supplying oxalic acid into the surge tank 31. The reductive decontamination liquid containing hydrazine for adjusting the pH supplied from the chemical tank 40 decontaminates the inner surface of the recirculation pipe 22 that forms the ferrite film. At the time of reductive decontamination, a part of the reductive decontamination liquid is guided to the cation exchange resin tower 60. Metal cations eluted from the inner surface of the recirculation system pipe 22 into the reducing decontamination liquid are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 60.

  After the completion of the reductive decontamination, a part of the reductive decontamination liquid flowing in the circulation pipe 35 is supplied to the decomposing device 64 in order to decompose the oxalic acid remaining in the decontamination liquid. At this time, hydrogen peroxide in the chemical solution tank 46 is supplied 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 decomposing oxalic acid and hydrazine, the supply of the decontamination solution to the heater 53 is stopped, and the decontamination solution is supplied to the cooler 58. A decontamination liquid lowered to a temperature at which water can be passed through the mixed bed resin tower 62 (for example, 60 ° C.) is supplied to the mixed bed resin tower 62. The mixed bed resin tower 62 removes impurities contained in the decontamination solution.

  Contamination that includes an oxide film formed on the surface of the structural member at the decontamination target site by repeating, for example, about 2 to 3 times, from temperature rise to oxidative dissolution, oxidant decomposition, reductive dissolution, reductant decomposition, and purification operation. Objects 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 set temperature of the aqueous solution for film formation during the film formation treatment 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. Adjustment of the temperature of the film-forming aqueous solution to the set temperature of 100 ° C. is performed by controlling the heater 53 with the temperature control device 80.

  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 (3). Since iron (III) ions have lower solubility than iron (II) ions, they precipitate as iron hydroxide according to the formula (4) 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 ⁻ (3)
Fe ³⁺ + 3OH ⁻ → Fe (OH) ₃ (4)
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. It inject | pours into the film formation aqueous solution which flows in the circulation piping 35 from the tank 45. FIG. Formic acid is also supplied into the circulation pipe 35 from the chemical tank 45. Subsequently, the valve 42 is opened and the injection pump 44 is driven to inject oxidant hydrogen peroxide from the chemical tank 46 into the film-forming aqueous solution flowing in the circulation pipe 35. 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 solution tank 40 into the film-forming aqueous solution flowing in the circulation pipe 35. A film-forming aqueous solution is generated in the circulation pipe 35 by injection of a chemical containing iron (II) ions, hydrogen peroxide, and hydrazine. 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 79. The pH control device 81 controls the rotation speed of the injection pump 39 (or the opening degree of the valve 38) based on the measured pH value, and adjusts the injection speed of hydrazine to be injected into the circulation pipe 22. By this control, the pH of the film-forming aqueous solution is adjusted within the above range. By supplying the film-forming aqueous solution whose pH is adjusted in this way to the recirculation system pipe 22, a ferrite film containing magnetite as a main component (hereinafter referred to as magnetite film) is formed on the inner surface of the recirculation system pipe 22. It is formed.

  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. This waste liquid becomes liquid radioactive waste. 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.

  Examples of the film-forming aqueous solution remaining in the recirculation system pipe 22 and the film-forming apparatus 30 include, for example, particulate matter such as magnetite generated with the formation of the ferrite film, and iron (II) that has not contributed to the formation of the ferrite film. Ions etc. remain. In the waste liquid treatment process, first, particulate matter present in the waste liquid generated during the formation of the ferrite film is removed (step S5). In step S <b> 5, the remaining solid matter (particles) such as magnetite and ferric hydroxide is removed by the filter 51. That is, the removal of these particles is performed by opening the valve 50 and closing the valve 49 and flowing waste liquid through the filter 51. By supplying the waste liquid to the filter 51, the particle concentration 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 particles generated in the waste liquid can be removed. However, the installation position is more preferably downstream from the surge tank 31 as shown in FIG. This can preferentially reduce the particle concentration at the location where the ferrite film is to be formed, so that the particles can be prevented from settling within the location.

  Next, iron (II) ions present in the waste liquid are removed (step S6). The valve 61 is opened and the valve 56 is closed, and the waste liquid is supplied to the cation exchange resin tower 60. Iron (II) ions, which are cation components contained in the waste liquid, are adsorbed and removed by the cation exchange resin in the cation exchange resin tower 60. When the cation exchange resin tower 60 does not break hydrazine, hydrazine is also adsorbed and removed by the cation exchange resin. However, since iron (II) ions are more easily adsorbed to the cation exchange resin than hydrazine, hydrazine does not increase the waste amount of the cation exchange resin.

  The chemical | medical agent contained in a waste liquid is decomposed | disassembled (step S7). For example, when the temperature of the outlet of the cation exchange resin tower 60 becomes the temperature of the waste liquid flowing through the circulation pipe 35 by supplying the waste liquid to the cation exchange resin tower 60, iron ( II) Does not contain ions. This waste liquid is supplied to the decomposition device 64. That is, the valve 65 is opened to adjust the opening degree of the valve 57. A part of the waste liquid containing formic acid and hydrazine discharged from the cation exchange resin tower 60 is supplied to the decomposition device 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 formic acid and hydrazine contained in the waste liquid by the action of hydrogen peroxide and activated carbon catalyst. Hydrazine is decomposed into nitrogen and water, and formic acid is decomposed into carbon dioxide and water. The hydrazine to be decomposed is broken from the cation exchange resin tower 60. In this embodiment, the pH of the waste liquid is adjusted to, for example, 5 when the medicine is decomposed. This pH adjustment is performed by the pH controller 81 controlling the number of revolutions of the infusion pump 39 based on the pH measurement value of the pH meter 79. For convenience of explanation, step S7 has been described after step S6, but in this embodiment, the removal of iron (II) ions and the decomposition of the drug are performed in parallel.

  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 formic acid by the mixed bed resin tower 62 can be avoided, so that the amount of waste of ion exchange resin that becomes radioactive waste can be significantly reduced. .

  It is determined whether the pH of the waste liquid is 4 or more (step S8). When the supply of the waste liquid to the cation exchange resin tower 60 and the decomposition of the hydrazine and formic acid by the decomposition apparatus 64 are started, iron (II) ions and hydrazine, which are cation components contained in the waste liquid, are formate ions that are anion components. Removed faster. For this reason, the pH of the waste liquid flowing in the circulation pipe 35 starts to decrease. The measured pH value measured by the pH meter 79 is input to the pH controller 81. The pH controller 81 determines whether the measured pH value is 4 or more at which the ferrite film does not dissolve. When the pH is less than 4, the injection amount is controlled so as to maintain a pH of 4 or more by injecting the pH adjuster (step S9). Again, hydrazine used during chemical decontamination and ferrite film formation is used as the pH adjuster.

  The injection of hydrazine in step S9 is performed by opening the valve 38 and driving the injection pump 39 while the medicine is being decomposed. The pH control device 81 controls the number of revolutions of the infusion pump 39 so that the input pH measurement value is 5 which is the above pH setting value which is pH 4 or higher. By this control, hydrazine is injected from the chemical tank 40 into the circulation pipe 35. It is desirable to inject hydrazine so that the pH of the waste liquid is 5 or more as in this embodiment. The reason why the pH is 5 or more will be described below. When the decomposition of the chemical progresses and the organic acid concentration in the waste liquid decreases and the injection amount of hydrazine falls below the minimum flow rate of the injection pump 39, the injection pump 39 is turned on and off, and the pH of the waste liquid changes. Will increase. By setting the pH of the waste liquid to 5 or more, even when the fluctuation in pH becomes large as described above, it is possible to have a tolerance for stably maintaining the pH of the waste liquid at pH 4 or higher. The pH of the waste liquid is adjusted by hydrazine injection in step S9, and the processes in steps S6 to S8 are performed.

  The adjustment of the injection amount of hydrazine in step S9 may be performed by the operator adjusting the opening of the valve 38 based on the measured value of the pH meter 79 displayed on the display device.

  If it is determined in step S8 that the pH is 4 or higher, it is determined whether the concentration of the organic acid is equal to or lower than a set value (step S10). In order to make the determination in step S10, the concentration of the organic acid contained in the waste liquid, that is, formic acid, is measured periodically, and the formic acid decomposition process is terminated when the formic acid concentration falls below a set value that can be regarded as the lower limit of analysis. Here, the organic acid concentration can be measured by using, for example, an ion chromatography method for the waste liquid collected by opening the sampling valve 76. If it is determined in step S10 that the formic acid concentration is greater than the set value, the processes in steps S6 to S10 are performed. When the formic acid concentration in the waste liquid becomes equal to or lower than the set value, the injection of hydrazine into the waste liquid is stopped, and the concentration of hydrazine contained in the waste liquid is also lower than the decomposition end set value.

  However, when the pH of the waste liquid is set within a permissible range at the time of formic acid decomposition, that is, for example, when the pH is a value close to 10, even if the formic acid concentration falls below the set value, it is included in the waste liquid. The concentration of hydrazine to be exceeded may exceed the above-mentioned decomposition end setting value. As described above, even when the formic acid concentration becomes equal to or lower than the set value, if the waste liquid contains hydrazine at the decomposition end set value or more, the waste liquid is circulated through the circulation pipe 35. This hydrazine is decomposed by a decomposition apparatus 64 to which hydrogen peroxide is supplied. When the concentration of hydrazine contained in the waste liquid falls below a set value that can be regarded as the lower limit of analysis, the decomposition process of the chemical contained in the waste liquid ends, and the circulation pumps 32 and 48 are stopped.

  After the concentration of formic acid contained in the waste liquid falls below the set value and hydrazine decomposition starts, injection of hydrazine from the chemical tank 40 into the circulation pipe 35 is stopped. Although the hydrazine concentration decreases due to decomposition, since the formic acid concentration of the waste liquid is below the set value, even if this waste liquid comes into contact with the ferrite film formed on the inner surface of the recirculation system pipe 22, the film is dissolved. Never happen.

  In this embodiment, since the pH of the waste liquid can be maintained at 4 or more during the decomposition of the organic acid, dissolution of the ferrite film formed on the film formation target site, for example, the inner surface of the recirculation system pipe 22 can be suppressed. Since the iron (II) ions contained in the waste liquid are removed by the cation exchange resin during the decomposition of the organic acid, it is not necessary to wait for all the iron (II) ions to be particulated and removed by the filter. In this embodiment, since the removal of iron (II) ions and the decomposition and removal of organic acid can be performed together, it is possible to significantly reduce the treatment time of the used film-forming aqueous solution generated after the ferrite film formation, that is, the waste liquid. .

  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. Further, after the decomposition treatment of formic acid and hydrazine is completed, the waste liquid is passed through the filter 51 and the mixed bed resin tower 62 and drained. For this reason, the amount of waste, which is a 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. In Example 1, a pH adjuster is used, and a decomposition apparatus 64 is used in decomposition of oxalic acid used in reductive decontamination and decomposition of formic acid in a 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. As the oxidizing agent used in the formation of the ferrite film and the treatment of the waste liquid of the film-forming aqueous solution, oxygen or ozone may be used in addition to hydrogen peroxide.

  Even when any one of malonic acid, diglycolic acid and oxalic acid is used instead of formic acid, the same effect as in the case of formic acid can be obtained.

  Iron is dissolved in carbonic acid to create iron (II) ions, and the chemicals containing carbonic acid and iron (II) ions are injected from the drug tank 45 into the film-forming aqueous solution flowing in the circulation pipe 35 during the formation of the ferrite film. If so, the carbonic acid is removed from the waste liquid at the stage where the iron (II) ions contained in the waste liquid are removed in step S6. This removal of carbonic acid is performed, for example, by bubbling nitrogen into the waste liquid in the surge tank 31. By bubbling nitrogen into the waste liquid, the carbonic acid dissolved in the waste liquid becomes gaseous, so that the carbonic acid can be easily separated from the waste liquid. Decomposition of hydrazine contained in the waste liquid is performed in step S7.

  In addition, when the temperature of the chemical | medical agent with which the chemical | medical agent tank 45 is filled is low, for example, when the temperature of the chemical | medical agent is as low as 90 degreeC, since carbonic acid does not melt | dissolve in a chemical | medical agent, it melt | dissolved in the film formation aqueous solution which inject | pours this chemical | medical agent. It does not contain carbonic acid. Therefore, in this case, it is not necessary to perform carbonic acid separation by nitrogen bubbling.

  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 figure explaining the relationship between the decomposition rate of formic acid and hydrazine in a decomposition apparatus. 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. It is the figure which showed the relationship between the pH lower limit at the time of decomposition | disassembly, and the weight change of a membrane | film | coat. 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 formation apparatus shown in FIG.

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, 79 ... pH meter, 81 ... pH control device.

Claims (12)

A method for treating a solution containing iron (II) ions, an organic acid, and a pH adjuster used for forming a ferrite film on the surface of a metal member constituting a plant,
When processing the solution, the pH of the solution is adjusted to 4 or more and 10 or less using a pH adjuster, and the iron (II) ions contained in the solution are removed with a cation exchange resin. (II) A method for treating a solution after the formation of a ferrite film, wherein the organic acid contained in the solution is decomposed in parallel with the removal of ions.   The method for treating a solution after forming a ferrite film according to claim 1, wherein the pH of the solution is 4 or more and 7 or less.   The method for treating a solution after the formation of a ferrite film according to claim 1 or 2, wherein the decomposition of the iron (II) ions and the organic acid is performed after removal of solid substances contained in the solution.   The method for treating a solution after forming a ferrite film according to claim 3, wherein the solid matter is removed using a filter device.   The processing method of the solution after the ferrite film formation of any one of Claim 1 thru | or 3 with which the said pH adjuster is removed with the said cation exchange resin.   The processing method of the solution after the ferrite film formation according to any one of claims 1 to 3, wherein the pH adjuster is decomposed.   The method for treating a solution after forming a ferrite film according to any one of claims 1 to 3 and claim 6, wherein the decomposition is performed in a decomposition apparatus having a catalyst and supplied with an oxidizing agent.   The ferrite according to claim 7, wherein a decomposition apparatus used for decomposing an organic acid in a decontamination solution used for chemical decontamination of the surface of the metal member before the formation of the ferrite film is used as the decomposition apparatus. Solution processing method after film formation.   The said oxidizing agent uses the oxidizing agent used at the time of the said ferrite film formation, The said pH adjuster which adjusts the pH of this solution at the time of the process of the said solution uses the pH adjusting agent used at the time of the said ferrite film formation. 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 claim 7 or 9, wherein the oxidizing 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 10, wherein the pH adjuster is hydrazine.   The method for treating a solution after forming a ferrite film according to claim 1, wherein the pH of the solution is 5 or more and 7 or less.

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