JP4959196B2 - Nuclear power plant replacement member and nuclear power plant member handling method - Google Patents

Description

  The present invention relates to an exchange member for a nuclear power plant such as a boiling water nuclear power plant (hereinafter referred to as “BWR”) and a pressurized water nuclear power plant (hereinafter referred to as “PWR”), and a method of handling the nuclear power plant member. In particular, the present invention relates to an exchange member that comes into contact with primary cooling water of a nuclear power plant capable of suppressing adhesion of radionuclides and a method for handling a member for a nuclear power plant.

  Since BWR removes heat generated in the core, cooling water in the reactor pressure vessel (hereinafter referred to as “reactor water”) is forcibly circulated by a recirculation pump. The steam generated in the nuclear reactor is sent to the turbine after moisture is removed by a separator and a dryer provided in the upper part of the core. Part of this steam is extracted as turbine bleed air and used as a heat source for high and low pressure heaters. On the other hand, most of the steam is condensed in the condenser. At that time, in the condenser, oxygen and hydrogen generated by radiolysis of water in the core are almost completely removed. The condensate is generally heated to near 200 ° C. by multistage low-pressure and high-pressure heaters and supplied to the reactor again. In order to suppress the production of radioactive corrosion products in the reactor, mainly metal impurities in the condensate are removed. Furthermore, for the purpose of maintaining the purity of the reactor water, the entire amount of condensate is treated by an ion exchange resin filtration device such as a demineralizer provided between the condenser and the low-pressure heater. At that time, in order to reduce the amount of metal impurities generated by the corrosion of the primary structural material, it is a principle to use stainless steel such as stainless steel and stellite steel for the main structure. In addition, the inner wall of the pressure vessel is made of stainless steel in the carbon steel reactor pressure vessel, preventing the carbon steel from coming into direct contact with the reactor water. In addition to such material considerations, a portion of the reactor water is purified by a reactor water purification device to positively remove metal impurities generated in the reactor water.

  However, even if the above-described countermeasures against corrosion are taken, the presence of very few metal impurities in the reactor water is inevitable, so some metal impurities adhere to the surface of the fuel rod as metal oxides. The metal element adhering to the fuel rod surface undergoes a nuclear reaction when irradiated with neutrons emitted from the fuel, and radionuclides such as cobalt 60, cobalt 58, chromium 51, manganese 54, and the like are generated. Most of these radionuclides continue to adhere to the fuel rod surface in the form of oxides, but some radionuclides elute in cooling water according to the solubility of the incorporated oxides, or insoluble solids called clads Or re-released into the reactor water. The radioactive material in the reactor water is removed by the reactor water purification system, but what cannot be removed is accumulated on the surface of the water contact portion of the component 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.

  As one of the solutions to such a problem, there is a technique for forming a preliminary oxide film on the inner surface of the pipe in high-temperature water before a full-scale operation of the nuclear power plant. However, this method is intended for a new plant, and since radionuclides already exist in the reactor water in an already-operated plant, the radionuclides are taken into the preliminary oxide film.

  On the other hand, chemical decontamination is performed on pipes and the like in which radionuclides are attached and the dose is increased. However, when chemical decontamination is carried out, the reactor water containing the radionuclide comes in contact with the new surface of the metal where the oxide film grows fast, so the deposition rate of the radionuclide is faster than the non-decontaminated place, and the decontamination effect. Will soon get smaller.

  As a method for solving this problem, there is a technique in which an oxide film is formed in advance on the surface of a pipe in contact with the primary system (see, for example, Patent Document 1). However, in this method, since it is necessary to form an oxide film in an atmosphere of a high temperature (for example, 500 ° C.) in the gas phase, an apparatus for forming the film becomes large and the cost may increase.

JP-A-7-288910

  This invention makes it a subject to provide the replacement | exchange member which contacts the primary cooling water of the nuclear power plant which can suppress adhesion of a radionuclide, and the replacement | exchange method of the replacement | exchange member.

  A metal member in contact with the primary cooling water of the water-cooled nuclear power plant is removed from a predetermined location, and a new metal member having a ferrite film formed on the surface is attached to the predetermined location.

  ADVANTAGE OF THE INVENTION According to this invention, the replacement | exchange member which contacts the primary cooling water of the nuclear power plant which can suppress attachment of a radionuclide, and the replacement | exchange method of the replacement | exchange member can be provided.

The new knowledge obtained by the experiment and the examination by the inventors will be described below. First, the mechanism of adhesion of radionuclides to the reactor plant surface of the atomic plant will be described. FIG. 1 is an explanatory view schematically showing the attachment mechanism of radionuclides on the surface of a furnace material. Among the radionuclides in the reactor water, cobalt 60, cobalt 58, chromium 51, manganese 54, and the like become problems during periodic inspection. Of particular concern is cobalt 60, a radioactive isotope of cobalt, which has a relatively long half-life. Most of these radionuclides of cobalt exist as cobalt (II) ions in the reactor water. On the other hand, in stainless steel or the like under reactor water conditions, wet corrosion caused by water and dry corrosion caused by diffusion of oxygen, electrons, and ions in a high temperature atmosphere occur simultaneously. Of these, the radionuclide is taken up mainly in the process of wet erosion. In the wet corrosion process, iron elutes through an oxide film formed by dry etching from a base material such as stainless steel and becomes iron (II) ions. This iron (II) ion is oxidized by dissolved oxygen in water to become iron (III) ion. Since the solubility of iron (III) ions is very low, it precipitates again as an oxide solid. At this time, if a divalent metal ion is present in the vicinity, a part of the ferrite precipitates as a spinel oxide containing the divalent metal ion. When a divalent metal ion does not exist, it precipitates as hematite which is a corundum type oxide. The ferrite is mainly in the form of nickel ferrite formed between nickel ions, which are divalent metals having the largest abundance in the reactor water. This also contains cobalt ions, resulting in the deposition of radionuclides on the furnace material surface. In particular, in a new replacement member or a reused member after decontamination targeted by the present invention, the surface becomes a new surface of the metal, so that the corrosion rate is high, and the radionuclide exists in the reactor water of the existing plant, so that the radioactive material is radioactive. Nuclide is easily attached.

FIG. 2 is a diagram showing the relationship between the presence or absence of an oxide film and the amount of cobalt 58 deposited. For sample A in which an oxide film was not formed on stainless steel and sample B in which an oxide film was previously formed on stainless steel, the sample was immersed in cooling water under nuclear plant operating conditions and adhered to each of samples A and B. It is the experimental result which compared the relative value of the amount of cobalt. Here, A1 and B1 indicate inner layer oxide films mainly composed of chromium, and A2 and B2 indicate outer layer oxide films mainly composed of iron. From this result, in the case of stainless steel (sample B) on which an oxide film is formed in advance, radioactive cobalt is incorporated in the inner layer oxide film B1 containing chromium as a main component. That is, even if an oxide film is formed in advance in high-temperature water under BWR in-service conditions and the growth rate of the oxide film formed during in-service operation is slowed down to suppress cobalt uptake, the effect of suppressing radionuclide adhesion Is small. On the other hand, in the case of stainless steel (sample A) having no oxide film formed on the surface, cobalt is likely to be taken in during the growth of the outer layer oxide film A2 containing iron as a main component. However, as shown in Sample B, when an oxide film is applied in advance, it is difficult for cobalt to be taken into the outer layer oxide film B2 whose growth has been delayed. Outer oxide film A2, mainly composed of iron
From the analysis by laser Raman spectrum, B2 was found to be a ferrite film containing magnetite as a main component (hereinafter referred to as “magnetite film” as appropriate). As a result of further studies by the inventors, it was obtained as a new finding that if a magnetite film can be formed as an oxide film, the adhesion of cobalt can be suppressed. As the ferrite film, both magnetite, Ni ferrite and Zn ferrite are considered to have the same effect.

  However, when an oxide film is formed in high-temperature water, dissolved oxygen in the cooling water diffuses into the metal base material, so it is difficult to suppress the formation of the inner layer oxide film B1 mainly composed of chromium. Therefore, the inner layer oxide film B1 becomes a radioactive cobalt uptake source, making it difficult to suppress the attachment of the radionuclide. Therefore, when the inventors examined these problems, only magnetite films such as outer layer oxide films A2 and B2 were formed under a temperature condition where the diffusion rate of dissolved oxygen into the metal base material was slow (for example, 100 ° C. or less). It was concluded that the radionuclide cobalt uptake could be suppressed if this could be achieved.

  Since the test which confirms the cobalt inhibitory effect with respect to the stainless steel which formed the magnetite film | membrane based on the said inventors' new knowledge was conducted, the content is shown below. FIG. 3 is a diagram showing the relationship between the stainless steel surface condition and the amount of cobalt deposited. In FIG. 3, sample C is a sample obtained by mechanically polishing the surface of stainless steel, sample D is a sample in which an oxide film is previously formed on the surface of stainless steel under BWR service conditions, and sample E is under a condition of 100 ° C. or less. This is a sample in which a magnetite film is formed on the surface of stainless steel. The vertical axis shows the relative value of the amount of cobalt 60 deposited after these samples C, D, and E are immersed in high-temperature water under the BWR operating conditions. From the experimental results shown in FIG. 3, it was found that Sample E, on which a magnetite film was formed, had a much smaller amount of cobalt deposited than the other Samples C and D.

  Furthermore, since the relationship between the magnetite film thickness on the stainless steel surface and the cobalt 60 adhesion amount was investigated, the result is shown in FIG. In FIG. 4, the vertical axis indicates the relative value of the amount of cobalt adhered to the stainless steel on which the magnetite film is formed, and the horizontal axis indicates the thickness of the magnetite film.

As shown in FIG. 4, the coating thickness is up to 50 [mu] g / cm ² was reduced cobalt 60 coating weight abruptly, the adhesion amount of cobalt 60 if the film thickness is 90 [mu] g / cm ² or more as compared with the case where there is no coating 1 / 5. Therefore, the thickness of the magnetite film may if 50 [mu] g / cm ² or more, and more preferably as long as 90 [mu] g / cm ² or more.

  As a method for forming a magnetite film, there is a technique for forming a ferrite film on a magnetic recording medium. However, this technology does not relate to corrosion suppression of components of nuclear power plants. Furthermore, in this technique, chlorine is used to form a magnetite film, but it is not preferable to use chlorine from the viewpoint of ensuring the soundness of components of nuclear power plants.

  The present invention has been made on the basis of the new knowledge obtained by the inventor, and an exchange member having a ferrite film formed on the surface thereof is used as an exchange member constituting the primary cooling system of a nuclear power plant. By using the exchange member on which the ferrite film is formed, the radionuclide can be prevented from adhering to the exchange member, so that the radiation exposure of the worker during the regular inspection work can be reduced.

Here, the formation of the ferrite film is performed at a temperature of room temperature to 200 ° C., preferably room temperature to 100 ° C., more preferably 60 ° C. to 100 ° C. Furthermore, from the viewpoint of ensuring the soundness of the components of the nuclear power plant, it is preferable to use a chemical that does not use chlorine when forming the ferrite film. Specifically, the treatment liquid for immersing the replacement member is set to room temperature to 200 ° C., preferably room temperature to 100 ° C., more preferably 60 ° C. to 100 ° C., and iron is dissolved in an organic acid or carbonic acid to obtain iron (II). A solution containing ions is injected into the treatment liquid, an oxidizing agent such as hydrogen peroxide is injected into the treatment liquid, and a chemical for adjusting the pH is injected into the treatment liquid. By forming the ferrite film by the above procedure, it is possible to suppress the attachment of the radionuclide to the replacement member, so that it is possible to reduce the radiation exposure of the worker during the regular inspection work. Furthermore, since the chemical | medical agent containing chlorine is not used, the soundness of the structural member of a nuclear power plant can be ensured.

  Even when there is no object to be treated, the treatment liquid starts to produce magnetite fine particles in the liquid immediately after mixing, and therefore needs to be mixed immediately before the treatment. That is, when the ferrite film is formed, an oxidizing agent and a pH adjuster can be added to a liquid containing divalent iron ions. The order of addition is (1) a liquid containing divalent iron ions. There is a case where a pH adjuster is added after adding an oxidizer and vice versa (2) a case where the pH adjuster is added to a liquid containing divalent iron ions and then the oxidizer is added. It is done. FIG. 5 is a diagram showing the relationship between the order of drug addition and the rate of film formation, and compares the ease with which a magnetite film can be formed depending on the order of drug addition. As shown in FIG. 5, (1) even when adding a pH adjuster after adding an oxidizing agent to a solution containing divalent iron ions, (2) adding a pH adjuster to the solution containing divalent iron ions. It has been found that a film can also be formed when an oxidizing agent is added after the addition. However, when (1) the pH adjusting agent is added after adding the oxidizing agent, the film formation rate is increased and the film is uniform and dense. (2) The oxidizing agent is added after the pH adjusting agent is added. It was found that when added, the magnetite particles became larger and the coating film became non-uniform and mottled as compared with the case where the chemicals were added in the order of (1).

  Here, from the viewpoint of waste reduction during construction, the chemical used is preferably an organic acid that can be decomposed into carbon dioxide and water. Considering the ease of decomposition, examples of organic acids that dissolve divalent iron ions include formic acid, malonic acid, diglycolic acid, and oxalic acid. FIG. 6 is a diagram showing the relationship between the type of organic acid and the amount of film produced. As shown in FIG. 6, as a result of the film formation test, the formation of a magnetite film was confirmed with all acids of formic acid, malonic acid, diglycolic acid and oxalic acid used in the test. In particular, it has been found that it is effective to use formic acid from the viewpoint of film formation speed and uniformity.

  In addition, piping, a valve, a pump, a separator, a dryer, and those components can be applied as an exchange member which contacts the primary cooling water of the nuclear power plant to which the radionuclide adhesion suppression method of the present invention is applied. Furthermore, the replacement member to which the radionuclide adhesion suppression method of the present invention is applied is preferably a member that contacts the primary cooling water of the BWR plant, but is not limited thereto. Further, the present invention is not limited to the BWR plant, but can be applied to a technique for suppressing the attachment of radionuclides to structural members in contact with reactor water in other water-cooled water nuclear plants such as PWR.

The apparatus for producing a ferrite film for carrying out the method for adhering a radionuclide of the present invention sucks a processing tank in which a film formation target (exchange member) is immersed, a surge tank for storing the processing liquid, and a processing liquid in the surge tank. A circulation pump, a first chemical liquid tank for storing iron (II) ions to be injected into the processing liquid, a second chemical liquid tank for storing an oxidant to be injected into the processing liquid, and adjusting the processing liquid to a predetermined pH A third chemical tank that stores the pH adjusting agent and a heating unit that superheats the temperature of the treatment liquid to a predetermined temperature can be provided.

  The first embodiment will be described below with reference to FIGS. In the first embodiment, a metal pipe that is in contact with the primary cooling water is used as a replacement member, and the deposition of a radionuclide is suppressed by forming a ferrite film on the inner surface of the pipe. Is reduced. FIG. 7 is a flowchart showing the procedure of the radionuclide adhesion suppression process for the piping that is a constituent member of the nuclear power plant according to the present embodiment. FIG. 8 shows a system configuration diagram of a film forming apparatus for carrying out the radionuclide adhesion suppressing method according to the present embodiment.

  First, the replacement member (pipe) which is a construction target is immersed in the construction tank 10 filled with water used for processing (S1). Next, the valves 13, 14, 27, 30, 35, 36 are opened, the circulation pumps 12, 28 are started, water flow to the filter 31 is started, and the processing liquid is brought to a predetermined temperature by the heater 32. Adjust (S2). If fine solids in water remain, film formation occurs on the surface of the solids during the formation of the ferrite film, and useless chemicals are used. In order to prevent this, water is passed through the filter 31.

  The temperature of the treatment liquid at this time is preferably about 100 ° C., but is not limited thereto. It suffices if the film structure such as crystals can be formed densely to such an extent that the radionuclide in the reactor water at the time of in-service operation of the reactor is hardly taken into the formed ferrite film. Therefore, at least the design temperature of the system is preferable and the lower limit may be room temperature, but 60 ° C. or higher is preferable in consideration of the film formation rate. When the temperature is 100 ° C. or higher, the treatment liquid must be pressurized in order to suppress boiling of the treatment liquid, and the pressure resistance of the temporary equipment is required, which increases the equipment cost.

  In order to form a ferrite film, iron (II) ions need to be adsorbed on the surface of the film formation target part. However, iron (II) ions in the solution are oxidized by dissolved oxygen into iron (III) ions according to chemical formula 1. Furthermore, since iron (III) ions are less soluble than iron (II) ions, they are precipitated as iron (III) hydroxide according to chemical formula 2. That is, when dissolved oxygen is present in the treatment liquid, iron (II) ions in the treatment liquid are unlikely to contribute to the formation of the ferrite film. Therefore, in order to remove dissolved oxygen in the treatment liquid, it is preferable to perform bubbling of inert gas or vacuum deaeration.

(Formula 1) 4FE ²⁺ + O ₂ + 2H ₂ O → 4FE ³⁺ + 4OH ⁻
(Chemical formula 2) Fe (OH) ^3- → FE (OH)

Thereafter, when the temperature of the circulated processing solution reaches a predetermined temperature, the valve 21 is opened to start the injection pump 23, and iron (II) ions prepared by dissolving iron with formic acid from the chemical solution tank 25 are contained. The drug is injected into the treatment liquid (S3). Subsequently, in order to ferritize the iron (II) ions adsorbed on the surface of the replacement member (pipe) to be processed, the valve 22 is opened, the injection pump 24 is started, and the oxidant stored in the chemical tank 26 The hydrogen peroxide solution is injected into the treatment liquid (S4). Further, in order to adjust the pH of the treatment liquid to 5.5 to 9.0 which is a reaction start condition, the valve 18 is opened, the injection pump 19 is started, and hydrazine as a pH adjusting agent is discharged from the chemical tank 20 to the treatment liquid. It is injected into the inside (S5). Thereby, it becomes a processing liquid in which the formation reaction of the ferrite film occurs, and a ferrite film containing magnetite as a main component is formed at the site to be processed.

  Steps S3, S4, and S5 are continuous, that is, when the liquid into which the iron ions are injected reaches the oxidant injection point, the injection of the oxidant is started, and the treatment liquid in which the iron ions and the oxidant are mixed is adjusted in pH. Preferably, the pH adjusting agent is injected immediately when the agent injection point is reached. If only iron ions are injected first and the system is circulated, the dissolved oxygen remaining in the system causes an oxidation reaction, leading to loss of chemicals due to useless reactions and inhibition of the reaction.

  When an oxidizing agent is supplied to iron ions, the iron ion oxidation reaction is started, and the abundance ratio of iron (II) ions to iron (III) ions is a condition suitable for the film formation reaction. However, as it is, the film is not formed because the treatment liquid is acidic. By adding a pH adjuster to the treatment liquid, a film forming reaction is started. Therefore, in order to prevent the formation of a useless film on the site to be treated, the injection point of the pH adjuster is preferably provided near the construction tank 10 where the object to be treated exists.

  In addition, since magnetite particles are generated in the treatment liquid after the start of the film formation reaction, it is preferable to start water flow to the filter 31 by closing the valve 29 and opening the valve 30. However, it is not necessary to pass water through the filter when adhesion to coarse particles is not a problem for the coating target.

  The injection order of the chemical solution is iron ion, oxidizing agent, and pH adjusting agent, but may be the order of oxidizing agent, iron ion, and pH adjusting agent. However, since hydrogen peroxide is easily decomposed on a metal surface having a high temperature, if it is injected first, it may be partially consumed. On the other hand, although the formation of a film is recognized in the order of iron ions, pH adjusting agent, and oxidizing agent, the size of the magnetite particles forming the film increases. Thus, it is preferable to inject iron ions, oxidizing agents, and pH adjusting agents in this order from the viewpoint of effectively utilizing the drug and forming a denser film.

When the formation of the magnetite film is completed, the process proceeds to a waste liquid treatment step (S7) in step S6. If the formation of the magnetite film has not been completed, the process returns to step S2 to continue the additional supply of the chemical liquid to the processing liquid that has made a round, thereby forming the magnetite film having a required thickness.

Solids such as ferrite particles, formic acid and hydrazine remain in the treatment liquid after the magnetite film is formed. Therefore, when draining the processing liquid, the valve 29 is closed and the valve 30 is opened to allow water to pass through the filter to remove solids in the processing liquid and to perform the waste liquid processing in step S7. , Remove those impurities. By the way, when these impurities are processed in the cation exchange resin tower 39, the waste of the ion exchange resin increases. Therefore, it is preferable that the waste liquid treatment in step S7 uses the decomposition device 43, and formic acid is decomposed into carbon dioxide and water, and hydrazine is decomposed into nitrogen and water. Thereby, the load of the cation exchange resin tower 39 can be reduced, and the waste amount of the ion exchange resin can be reduced. In the decomposition process, a part of the processing liquid is caused to flow into the decomposition apparatus 43. Therefore, the opening of the valve 36 that bypasses the decomposition apparatus 43 and the valve 44 of the decomposition apparatus 43 is adjusted, and the processing liquid that flows into the decomposition apparatus 43 Hydrogen peroxide is injected into it to decompose formic acid and hydrazine.

  Thereafter, the pipe (exchange member) on which the magnetite film is formed is replaced with a predetermined pipe that is in contact with the primary cooling water of the nuclear power plant (S8).

  According to the present embodiment, while suppressing the waste of the ion exchange resin, a magnetite film is formed on the inner surface of the pipe, thereby suppressing the attachment of the radionuclide (radioactive cobalt ion) to the pipe during the operation of the reactor. Can do. As a result, the dose rate of the pipe inner surface (exchange member) in contact with the primary cooling water can be suppressed, and the exposure of the worker during the regular inspection work can be reduced. In addition, since chemicals such as chlorine are not used in the film forming process, the soundness of the components of the nuclear power plant is not impaired.

  A second embodiment will be described with reference to FIG. In the second embodiment, the medicine used in the first embodiment is not decomposed. FIG. 9 shows a system configuration diagram of a film forming apparatus for carrying out the radionuclide adhesion suppressing method according to the present embodiment. As shown in FIG. 9, in this embodiment, since the chemical is not decomposed, the cation exchange resin tower 39 and the valves 35 and 40 associated therewith are not required in the film forming apparatus in the first embodiment. be able to. Further, the waste liquid treatment step 7 can be eliminated from the work procedure in the first embodiment.

  Therefore, in the present embodiment, the attachment of the radionuclide to the replacement member (pipe) can be suppressed as in the first embodiment. In addition, since chemicals such as chlorine are not used in the film forming process, the soundness of the components of the nuclear power plant is not impaired. Furthermore, since the apparatus and work relating to the waste liquid treatment are unnecessary, the apparatus can be simplified and the working time can be shortened.

  A third embodiment will be described with reference to FIGS. In the third embodiment, the method for forming a ferrite film according to the present invention is applied to a reuse member to which contaminants such as radionuclides are attached. The ferrite film forming method according to the present invention can be applied not only to a new replacement member but also to a reuse member to which contaminants such as radionuclides are attached. In that case, a decontamination process for removing the oxide film containing the radionuclide from the reusable member is required before the ferrite film is formed on the reusable member. FIG. 10 is a flowchart showing the procedure of the radionuclide adhesion suppressing process for the piping that is a constituent member of the nuclear power plant according to this embodiment. FIG. 11 shows a system configuration diagram of a film forming apparatus for carrying out the radionuclide adhesion suppressing method according to this embodiment. In the present embodiment, a pipe in contact with the primary cooling water is used as the reuse member.

  First, the target reuse member (piping) is removed from the system, and the removed reuse member is immersed in the construction tank 10 filled with water used for processing (S1B). Next, using a film forming apparatus, contaminants such as an oxide film that incorporates the radionuclide formed on the surface of the reuse member in contact with the reactor water are decontaminated by chemical treatment (S2B). In carrying out the radionuclide adhesion suppression method of the present invention, it is preferable to perform chemical decontamination, but the method is not necessarily limited thereto. A mechanical decontamination method such as polishing may be applied if the surface of the reusable member that is the subject of ferrite film deposition can be exposed before the radionuclide adhesion suppression method of the present invention is carried out. it can.

  Here, the chemical decontamination in step S2B will be described. First, the valves 13, 14, 27, 29, 34, 35, and 36 are opened, the circulation pump 28 is activated, and the inside of the surge tank 11 is placed in the construction tank 10 in which the pipe to be chemically decontaminated is immersed. Circulate the treatment liquid. And the temperature of a process liquid is heated up to about 90 degreeC with the heater 32. FIG. Next, the valve 16 is opened and a required amount of potassium permanganate is injected into the surge tank 11 from a hopper connected to the ejector 17. The chemical dissolved in the surge tank 11 is used to oxidize and dissolve contaminants such as an oxide film formed on the decontamination target part, and the oxide film containing the radionuclide is removed from the reuse member.

  When the oxidative dissolution of the contaminants is completed, oxalic acid is injected from the hopper into the surge tank 11 in order to decompose permanganate ions remaining in the treatment liquid. Subsequently, oxalic acid is further injected into the treatment liquid in order to reduce and dissolve the contaminants. Further, in order to adjust the pH of the processing liquid, the valve 18 is opened, the injection pump 19 is started, and hydrazine is injected from the chemical liquid tank 20 into the processing liquid. In this way, after injecting oxalic acid and hydrazine, the valve 40 is opened and the opening of the valve 35 is adjusted so that a part of the treatment liquid passes through the cation exchange resin tower 39 and is eluted into the treatment liquid. The metal cation adsorbed on the cation exchange resin is removed from the treatment liquid.

  After the reduction and dissolution is completed, in order to decompose oxalic acid in the processing solution, the opening of the valve 44 on the outlet side of the decomposition device 43 and the valve 36 that bypasses the decomposition device 43 is adjusted, and a part of the processing solution is removed. The gas is passed through the decomposition device 43. At this time, the valve 33 is opened, the injection pump 24 is started, hydrogen peroxide in the chemical solution tank 26 is injected into the processing liquid flowing into the decomposition device 43, and oxalic acid and hydrazine are decomposed by the decomposition device 43. . After the oxalic acid and hydrazine are decomposed, the heater 32 is turned off and the valve 34 is closed to remove impurities in the treatment liquid. At the same time, the valve 38 of the cooler 37 is opened and the processing liquid is passed through the cooler 37 to lower the temperature of the processing liquid. After the temperature of the treatment liquid is lowered to a temperature at which water can be passed through the mixed bed resin tower 41 (for example, 60 ° C.), the valve 40 of the cation exchange resin tower 39 is closed and the valve 42 on the mixed bed resin tower 41 side is opened. The liquid is passed through the mixed bed resin tower 41 to remove impurities in the processing liquid.

  By repeating this series of temperature rise, oxidative dissolution, oxidant decomposition, reduction dissolution, reductant decomposition, and purification operations once or twice, contaminants including the oxide film of reusable parts that are decontamination target parts are removed. It can be dissolved and removed.

  After removing the contaminants including the oxide film of the piping which is the reuse member, the reuse member is taken out from the construction tank 10 and inspected (S3B). In addition, when implementing the radionuclide adhesion suppression method of the present invention, it is preferable to inspect the reusable member, but the present invention is not necessarily limited thereto. If it can be confirmed that the reusable member is healthy, an inspection can be performed after the formation of the ferrite film.

When the inspection of the reuse member is completed, the reuse member is again immersed in the construction tank 10 (S4B), and the process is switched to the ferrite film forming process according to the present invention. The valve 30 is opened and the valve 29 is closed to start water flow to the filter 31, and the processing liquid is adjusted to a predetermined temperature by the heater 32 (S5B). Note that it is not appropriate to conduct water through the filter 31 during decontamination because the dose rate of the filter may become too high due to the dissolved solid matter containing high radioactivity. Further, the water flow to the mixed bed resin tower 41 used in the purification system operation is stopped by opening the valve 35 and closing the valve 42.

Thereafter, after forming a ferrite film on the reuse member to be coated (S6B-S10B) in the same procedure as in Example 1, the reuse member on which the ferrite film is formed is incorporated into the system (S11B). In addition, when handling the reusable member contaminated with the radionuclide as in this embodiment, it is desirable to perform the ferrite film forming operation in the nuclear power plant.

  In this embodiment, it is possible to suppress the attachment of the radionuclide to the reuse member during the operation of the nuclear reactor. In addition, since chemicals such as chlorine are not used in the film forming process, the soundness of the components of the nuclear power plant is not impaired.

  A fourth embodiment will be described with reference to FIGS. In the fourth embodiment, when the method for forming a ferrite film according to the present invention is applied, system decontamination is performed on a piping system including a reusable member that is an object of construction. That is, as in Example 3, when applying the method for forming a ferrite film according to the present invention to a reuse member to which contaminants such as radionuclides are attached, it is necessary to remove the oxide film containing the radionuclide from the reuse member. However, this decontamination is performed on a piping system including a reuse member that is a construction target. FIG. 12 is a flowchart showing the procedure of the radionuclide adhesion suppressing process for the piping that is a constituent member of the nuclear power plant according to the present embodiment. FIG. 13 shows a system configuration diagram of a film forming apparatus for carrying out the radionuclide adhesion suppressing method according to this embodiment. The difference between the film forming apparatus in the present embodiment shown in FIG. 13 and the film forming apparatus in the third embodiment shown in FIG. 11 is that the system is connected to the piping system to be decontaminated instead of the construction tank 10. It is. In the present embodiment, a pipe in contact with the primary cooling water is used as the reuse member.

The implementation procedure in the present embodiment will be described focusing on the differences from the third embodiment. First, before removing the reuse member (piping), the piping system including the reuse member is decontaminated using a decontamination apparatus (S1C). Thereafter, the reusable member is removed from the piping system and inspected (S2C). Next, the decontamination apparatus shown in FIG. 13 is removed from the piping system, and the construction tank 10 is installed in the decontamination apparatus as in Example 3 (S3C). After the construction tank 10 is installed in the decontamination apparatus, the reuse member is immersed in the construction tank 10 (S4C), and a ferrite film is formed on the surface of the reuse member (S5C-S10C). After confirming that the ferrite film is formed on the surface of the reuse member, the reuse member is attached to the piping system.

  In this embodiment, it is possible to suppress the attachment of the radionuclide to the reuse member during the operation of the nuclear reactor. Moreover, the exposure at the time of removing a reuse member can be reduced by decontaminating the whole piping system containing an exchange member simultaneously. Since chemicals such as chlorine are not used in the film forming process, the soundness of the components of the nuclear power plant is not impaired.

  A fifth embodiment will be described with reference to FIG. In the fourth embodiment, system decontamination is performed on a piping system including a reuse member that is a construction target, and then the decontaminated reuse member is attached to the piping system, and the present invention is applied to the entire piping system. The method for forming a ferrite film by the above method is carried out. FIG. 14 is a flowchart showing the procedure of the radionuclide adhesion suppression process for the piping that is a constituent member of the nuclear power plant according to this embodiment. In the present embodiment, a pipe in contact with the primary cooling water is used as the reuse member.

  An implementation procedure in the present embodiment will be described focusing on differences from the fourth embodiment. The difference from Example 4 is that the reuse member is decontaminated and a ferrite film is formed in a state where the film forming apparatus is connected to a piping system including the reuse member. Specifically, the following procedure is performed. First, as in Example 4, the entire piping system including the reuse member that forms the ferrite film is decontaminated (S1D). Subsequently, the reuse member is removed and inspected (S2D). Then, after attaching a reuse member to a piping system (S3D), a ferrite membrane | film | coat is formed in the whole piping system (S4D-S9D).

  In the present embodiment, the radionuclide adhesion suppressing process can be performed on the entire piping system including the reuse member. Thereby, since a ferrite membrane | film | coat can be formed in the whole decontaminated piping system, the dose rate rise of not only a reuse member but the whole piping system used as a decontamination object can be suppressed. In addition, since chemical | medical agents, such as chlorine, are not used for the film-forming process, the soundness of the structural member of a nuclear power plant is not impaired.

Explanatory drawing which shows typically the adhesion mechanism of the radionuclide on the furnace material surface. The figure which shows the relationship between the presence or absence of an oxide film, and the adhesion amount of cobalt 58. FIG. The figure which shows the relationship between a stainless steel surface condition and cobalt adhesion amount. The figure which shows the relationship between magnetite film thickness and cobalt adhesion amount. The figure which showed the relationship between the kind of organic acid, and the produced | generated film amount. The figure which showed the relationship between the addition order of a chemical | medical agent, and a film formation rate. The flowchart which shows the procedure of the radionuclide adhesion suppression process in a 1st Example. The line | wire system block diagram of the film-forming apparatus for enforcing the radionuclide adhesion suppression method in a 1st Example. The system block diagram of the film-forming apparatus for implementing the radionuclide adhesion suppression method in a 2nd Example. The flowchart which shows the procedure of the radionuclide adhesion suppression process in a 3rd Example. The system block diagram of the film-forming apparatus for enforcing the radionuclide adhesion suppression method in a 3rd Example. The flowchart which shows the procedure of the radionuclide adhesion suppression process in a 4th Example. The system block diagram of the film-forming apparatus for enforcing the radionuclide adhesion suppression method in a 4th Example. The flowchart which shows the procedure of the radionuclide adhesion suppression process in a 5th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Processing tank, 11 ... Surge tank, 17 ... Ejector, 20, 25, 26 ... Chemical tank, 31 ... Filter, 32 ... Heater, 37 ... Cooler, 39 ... Cation exchange resin tower,
41 ... Mixed bed resin tower, 43 ... Decomposition apparatus.

Claims (10)

A metal member for a nuclear plant to be exchanged for a metal member in contact with the primary cooling water of the nuclear plant,
The metal member for the nuclear power plant is immersed in a tank, and the temperature is from room temperature to 100 ° C., and the iron (II) ion is adsorbed on the surface of the metal member by contacting with a treatment liquid containing iron (II) ion. Then, an oxidizing agent that oxidizes the adsorbed iron (II) ions is injected into the processing solution, and a pH adjusting agent that adjusts the pH of the processing solution to 5.5 to 9.0 is added to the processing solution. Having a ferrite film formed by injecting and oxidizing the iron (II) ions;
A member for a nuclear power plant, wherein the ferrite film has a thickness of 50 μg / cm 2 or more. A nuclear plant member that is used as a metal member in contact with the primary cooling water of a nuclear power plant, then removed from a predetermined location, and then attached to the predetermined location,
The surface of the metal member for the nuclear power plant is immersed in a tank, the temperature is room temperature to 100 ° C., and the iron (II) ion is brought into contact with the treatment liquid containing iron (II) ions on the surface of the metal member. A pH adjuster that adjusts the pH of the treatment liquid to 5.5 to 9.0 by injecting an oxidizing agent that oxidizes the adsorbed iron (II) ions into the treatment liquid. Having a ferrite film formed by oxidizing the iron (II) ions injected therein,
A member for a nuclear power plant, wherein the ferrite film has a thickness of 50 μg / cm 2 or more.   3. The metal member for a nuclear power plant according to claim 1 or 2, wherein the metal member for a nuclear power plant is at least one of a pipe, a valve, a pump, a separator, and a dryer, or at least one component of a pipe, a valve, a pump, a separator, and a dryer. Components for nuclear power plants.   4. The nuclear plant member according to claim 1, wherein the ferrite film is at least one of magnetite, Ni ferrite, and Zn ferrite. A metal member for a nuclear power plant immersed in a tank has a temperature of room temperature to 100 ° C. and is brought into contact with a treatment liquid containing iron (II) ions to adsorb the iron (II) ions on the surface of the metal member. ,
Injecting an oxidizing agent that oxidizes the adsorbed iron (II) ions into the treatment liquid,
A pH adjusting agent that adjusts the pH of the treatment liquid to 5.5 to 9.0 is injected into the treatment liquid to oxidize the iron (II) ions and have a thickness of 50 μg / cm 2 or more on the surface. Forming a ferrite film,
Remove other metal parts coming into contact with the primary cooling water of the nuclear power plant
A method of handling a nuclear plant member in which the metal member on which the ferrite film is formed is attached to the predetermined place. Remove the metal member in contact with the primary cooling water of the nuclear power plant from the specified location,
Immerse the removed metal member in the tank,
The metal member immersed in the tank has a temperature of room temperature to 100 ° C., and is brought into contact with a treatment liquid containing iron (II) ions to adsorb the iron (II) ions on the surface of the metal member,
Injecting an oxidizing agent that oxidizes the adsorbed iron (II) ions into the treatment liquid,
A pH adjusting agent for adjusting the pH of the treatment liquid to 5.5 to 9.0 is injected into the treatment liquid to oxidize the iron (II) ions, and a thickness of 50 μg / Form a ferrite film of cm2 or more,
A method for handling a nuclear plant member in which the metal member on which a ferrite film is formed is attached to the predetermined location.   The method for handling a nuclear plant member according to claim 6, wherein the radionuclide adhering to the metal member is removed before forming a ferrite film on the surface of the metal member.   The nuclear power unit according to any one of claims 5 to 7, wherein the replacement member is at least one of a pipe, a valve, a pump, a separator, and a dryer, or at least one component of a pipe, a valve, a pump, a separator, and a dryer. How to handle plant components.   9. The method for handling a nuclear plant member according to claim 5, wherein the ferrite film is at least one of magnetite, Ni ferrite, and Zn ferrite. The method of handling a nuclear plant member according to any one of claims 5 to 9, wherein the temperature of the treatment liquid brought into contact with the surface of the metal member is 60 ° C to 100 ° C.

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