JP4131814B2 - Method and apparatus for chemical decontamination of activated parts - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention chemically dissolves metal oxides containing radioactive substances attached to the surface of structural parts such as pipes, equipment, and structural members installed in radiation handling facilities such as nuclear power generation facilities, and surfaces of structural parts and the like The present invention relates to a method and an apparatus for chemical decontamination of an activated part to be removed from an air.
[0002]
[Prior art]
In a radiation handling facility, a structural part that comes into contact with a fluid containing a radioactive substance has an oxide film containing a radionuclide attached or generated on the inner surface thereof during operation. When the operation period becomes longer, the radiation dose around pipes and equipment increases, and the radiation dose to workers increases during periodic inspection work or dismantling work during facility decommissioning. In order to reduce the exposure of workers, a chemical decontamination method that chemically dissolves and removes an oxide film has been put into practical use.
[0003]
Various chemical decontamination methods have been proposed so far, including the process of oxidizing and dissolving chromium-based oxides in oxide films with oxidizing agents, and reducing and dissolving iron-based oxides, the main component in oxide films, with reducing agents. A method that combines the steps to perform is known.
[0004]
Patent Document 1 below describes a chemical decontamination method using a permanganic acid aqueous solution as an oxidizing agent and a dicarboxylic acid (oxalic acid) aqueous solution as a reducing agent. This decontamination method uses permanganic acid with low concentration and high oxidizing power, and oxalic acid that can be decomposed into carbon dioxide gas and water, resulting in the generation of secondary waste compared to the conventional chemical decontamination method. Can be reduced. This method has already been used in the decontamination work of nuclear power generation facilities.
[0005]
Patent Document 2 below describes a chemical decontamination method using an aqueous ozone solution as an oxidizing agent and an aqueous oxalic acid solution as a reducing agent. Since ozone is decomposed into oxygen and oxalic acid is decomposed into carbon dioxide and water, it is attracting attention as a decontamination technique that can further reduce secondary waste.
[0006]
Patent Document 3 below proposes a method of decontaminating stainless steel metal waste in an organic acid (oxalic acid or formic acid) aqueous solution. In this method, a metal having a negative potential relative to the oxidation-reduction potential of stainless steel is brought into contact to dissolve and decontaminate the stainless steel base material. Since the organic acid aqueous solution is treated alone, the decontamination operation is simple, and the metal base material is dissolved, so that it is effective as a method for decontaminating the radioactive level of the metal waste to the level of general industrial waste.
[0007]
Regarding the treatment method of the decontamination waste liquid, Patent Literature 4 discloses a treatment method of an oxalic acid aqueous solution. Since Fe ³⁺ in the oxalic acid aqueous solution forms a complex with oxalic acid and becomes an anion, it is reduced to Fe ²⁺ by irradiation with ultraviolet rays (hν) as shown in the following formula (1).
[Fe (C ₂ O ₄ ) ₃ ] ^3- + hν → Fe (C ₂ O ₄ ) ₂ + 2CO ₂ (1)
[0008]
Thereby, Fe ²⁺ in the oxalic acid aqueous solution can be separated by the cationic resin. In addition, when decomposing oxalic acid, the hydroxyl radical (OH.) Generated by the reaction of hydrogen peroxide (H ₂ O ₂ ) and Fe ²⁺ as shown in the following formulas (2) and (3) Decomposes oxalic acid into carbon dioxide and water with the oxidizing power of.
^{_{H 2 O 2 + Fe 2+ →}} Fe 3+ + OH - + OH · ... (2)
H ₂ C ₂ O ₄ + 2OH · → 2CO ₂ + 2H ₂ O (3)
[0009]
[Patent Document 1]
Japanese Patent Publication No. 3-10919 [Patent Document 2]
JP 2000-81498 A [Patent Document 3]
Japanese Patent Laid-Open No. 9-11690 [Patent Document 4]
Japanese National Patent Publication No. 9-510784 [0010]
[Problems to be solved by the invention]
The techniques described in Patent Documents 1 to 4 described above are effective decontamination techniques for reducing the exposure of workers in periodic inspections and inspections of nuclear power plants and the like. However, when oxalic acid is used as a reducing agent, Fe ³⁺ An ultraviolet device that reduces the amount of Fe to Fe ²⁺ is required. As the decontamination system increases, the amount of the decontamination solution increases, and accordingly, the scale of the ultraviolet device also increases and the cost of the device increases. Moreover, when the decomposition time of oxalic acid is long, there is a problem that the whole decontamination period is prolonged.
[0011]
In addition, the technique described in Patent Document 3 uses formic acid as a decontamination agent, but formic acid dissolves a metal base material electrochemically, so decontamination for maintaining the soundness of equipment. I can not use it. Further, simply formic acid treatment alone has a problem in that sufficient decontamination performance cannot be obtained because the oxide film and iron oxide formed on the surface of the device cannot be dissolved and removed.
[0012]
Therefore, the present invention does not require a process and apparatus for reducing trivalent iron ions to divalent iron ions, has a higher decomposition rate than oxalic acid, and has a decontamination performance equivalent to that of oxalic acid. An object of the present invention is to provide a chemical decontamination method and apparatus.
[0013]
[Means for Solving the Problems]
The invention according to claim 1 is a chemical decontamination method, wherein the surface of a radioactive component having a radioactive oxide film on the surface is a reducing property in which formic acid and oxalic acid having a concentration of about 1/10 of the concentration of formic acid are dissolved. A reduction dissolution process for contacting with the decontamination liquid and an oxidation dissolution process for contacting the surface of the activated component with the oxidizing decontamination liquid in which the oxidizing agent is dissolved are provided.
[0014]
The invention according to claim 2 is configured such that the reduction dissolution step and the oxidation dissolution step are alternately performed a plurality of times .
[0015]
The invention according to claim 3 is configured such that the oxidizing agent that constitutes the oxidizing decontamination solution is ozone, permanganic acid, or permanganate .
[0016]
According to a fourth aspect of the present invention, the formic acid remaining in the reducing decontamination solution is decomposed into hydrogen peroxide and oxalic acid is decomposed into carbon dioxide and water by ozone dissolved in the oxidizing decontamination solution. To do.
The invention according to claim 5 is configured such that hydrogen peroxide or ozone remaining in the reducing decontamination solution is decomposed into water or oxygen by ultraviolet rays.
[0017]
According to a sixth aspect of the present invention, the reducing decontamination solution includes carbonic acid, carbonate or hydrogen carbonate, boric acid or borate, sulfuric acid or sulfate, phosphoric acid or phosphate or phosphoric acid as a corrosion inhibitor for the activated component. One of the hydrogen salts is added.
[0018]
The invention according to claim 7 is a chemical decontamination apparatus, containing a deactivation tank having a radioactive oxide film on the surface and contacting the surface with a decontamination liquid, and connected to the decontamination tank A circulation system that circulates a decontamination liquid, and the circulation system injects into the decontamination liquid a reducing agent composed of formic acid and oxalic acid having a concentration of about 1/10 of the concentration of formic acid and hydrogen peroxide. A configuration comprising an injection device, an ion exchange device that separates and removes Fe ²⁺ ions and Fe ³⁺ ions in the decontamination solution by a cationic resin, and an ozone generator that injects ozone into the decontamination solution And
[0019]
The invention according to claim 8 is also a chemical decontamination apparatus, containing a deactivation tank having a radioactive oxide film on its surface and bringing the surface into contact with a decontamination liquid, and connected to the decontamination tank A circulation system that circulates a decontamination solution, and the circulation system comprises a reducing agent comprising formic acid and oxalic acid having a concentration of about 1/10 of the concentration of formic acid , hydrogen peroxide, and permanganic acid in the decontamination solution. Or it is set as the structure provided with the chemical | medical agent injection | pouring apparatus which inject | pours the oxidizing agent which consists of permanganate, and the ion exchange apparatus which isolate | separates and removes Fe2 ⁺ ion and Fe3 ⁺ ion in the said decontamination liquid with a cation resin. .
The invention according to claim 9 is configured such that the circulation system includes a liquid phase decomposition apparatus for decomposing hydrogen peroxide and ozone remaining in the decontamination liquid with ultraviolet rays.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method and an apparatus for chemical decontamination of activation parts according to an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the chemical decontamination method of the activated component of the present embodiment includes a step S1 of setting the activated component in the chemical decontamination apparatus, and the oxide on the surface of the activated component of formic acid and oxalic acid. Step S2 for reducing and dissolving with a decontamination solution comprising a mixed aqueous solution, Separation step S3 for separating and removing metal ions such as iron dissolved in the decontamination solution by the step S2 from the decontamination solution with an ion exchange resin, and the step A reducing agent decomposition step S4 in which formic acid and oxalic acid remaining without being consumed in S2 are decomposed by ozone or hydrogen peroxide, and a separation step S5 in which ozone and hydrogen peroxide remaining in step S4 are separated and removed from the decontamination solution. And step S6 for oxidizing and dissolving the oxide film on the surface of the activated component with a decontamination solution in which ozone is dissolved; and a separation step S7 for separating and removing the oxidation product in the step S6 from the decontamination solution; Comprising the step S8 for discharging decontaminated effluent. The oxidation dissolution step S6 and the separation step S7 may be performed before the reduction dissolution step S2.
[0021]
FIG. 2 is an example of a chemical decontamination apparatus that decontaminates used equipment generated as a replacement part in a periodic inspection of a nuclear power plant. That is, the activation component chemical decontamination apparatus of the present embodiment includes a decontamination tank 1 that stores the decontamination liquid 1a, and a circulation system 2 that is connected to the decontamination tank 1 and circulates the decontamination liquid 1a. The circulation system 2 is connected to a circulation pump 3, a heater 4, a drug injection device 5, a liquid phase decomposition device 6, a cation resin tower 7, a mixed bed resin tower 8, a mixer 9 and an ozone generator 10. Has been. The mixed bed resin tower 8 is filled with a cationic resin and an anionic resin. Further, a vapor phase decomposition tower 11 and an exhaust blower 12 are connected to the decontamination tank 1.
[0022]
The activation part 13 which is a decontamination object is installed in the decontamination tank 1, and is immersed in the decontamination liquid 1a. Or although not shown in figure, the shower of the decontamination liquid 1a is received. The decontamination liquid 1 a is pumped by the circulation pump 3, circulated in the circulation system 2, and returned to the decontamination tank 1.
[0023]
When the oxide film on the surface of the activated component 13 is reduced and dissolved, a reducing aqueous solution in which formic acid and oxalic acid are mixed is supplied from the chemical injection device 5 to the circulation system 2. Iron ions dissolved in the reducing decontamination solution are separated and removed by the cation resin tower 7.
[0024]
The reductive decontamination liquid after the reductive decontamination is injected with the ozone gas from the ozone generator 10 into the circulation system 2 through the mixer 9 or the hydrogen peroxide is supplied from the chemical injection device 5 to produce carbon dioxide gas. Decomposes into water. Further, the metal ions dissolved in the decontamination solution 1a are removed by the cation resin tower 7. When ozone or hydrogen peroxide remains when the decontamination liquid 1a is passed through the cation resin tower 7, ultraviolet light is irradiated from the liquid phase decomposition apparatus 6 to decompose ozone into oxygen, Hydrogen peroxide decomposes into oxygen and water.
[0025]
When the oxide film on the surface of the activation component 13 is oxidized and dissolved, ozone gas from the ozone generator 10 is injected into the circulation system 2 through the mixer 9, and ozone water is supplied to the decontamination liquid 1a. The ozone gas discharged from the decontamination tank 1 is sucked into the exhaust blower 12, decomposed in the vapor phase decomposition tower 11, and discharged into the existing exhaust system. The decontamination liquid in the apparatus after completion of decontamination is purified by passing water through the mixed bed resin tower 8.
[0026]
Although the oxide film formed on the surface of stainless steel can be dissolved and removed by formic acid alone and in combination with the oxidation treatment, iron oxide hardly dissolves by this formic acid alone. In order to dissolve this iron oxide, about 1/10 of oxalic acid is added to the formic acid concentration in this embodiment. Formic acid can be decomposed in a short time with hydrogen peroxide alone as described later, and if it is a low concentration oxalic acid, it can be decomposed in a short time with ozone, permanganic acid and potassium permanganate used for the oxidation treatment, The decontamination period can be greatly shortened.
[0027]
Oxide, permanganic acid, and permanganate (potassium permanganate) can be used as the oxidizing agent to oxidize the surface of the activated parts, and the dissolution / removal rate of the oxide film can be improved by combining with formic acid. Can do.
[0028]
Since the equilibrium constant of the complex formation reaction of Fe ²⁺ ions and Fe ³⁺ ions with formic acid is small, both ions can be adsorbed and separated by the cationic resin. Therefore, an apparatus for reducing Fe ³⁺ ions to Fe ²⁺ ions as in the case of using oxalic acid becomes unnecessary.
[0029]
Formic acid can be decomposed in a short time with hydrogen peroxide alone, but oxalic acid is difficult to decompose with hydrogen peroxide alone. Oxalic acid remaining after formic acid decomposition is decomposed by ozone, permanganic acid and potassium permanganate used for the oxidation treatment. Since the oxalic acid concentration is about 1/10 of the formic acid concentration, it can be decomposed in a short time.
[0030]
Hydrogen peroxide or ozone remaining after the decomposition treatment promotes deterioration of the cationic resin. In order to prevent this, ultraviolet rays decompose hydrogen peroxide into water and ozone into oxygen.
[0031]
Furthermore, when the formic acid concentration approaches the detection lower limit value, the ozone concentration in the decontamination solution increases. Since there is concern about equipment corrosion due to the oxidizing power of ozone, a decomposition aid is added to suppress the base metal corrosion of the equipment and maintain the soundness of the equipment material.
[0032]
Next, test data for confirming the oxide film dissolution performance of the chemical decontamination method of the present embodiment using the chemical decontamination apparatus shown in FIG. 2 will be described. The water quality conditions of the primary system of the boiling water nuclear power plant were simulated, and a SUS304 specimen with an oxide film was subjected to an oxide film dissolution test for 3,000 hours.
[0033]
The test results are shown in FIG. In the figure, the vertical axis represents the weight reduction of the oxide film, and the horizontal axis represents the formic acid concentration. A mark indicates the result of treatment with an aqueous ozone solution followed by treatment with an aqueous formic acid solution, and a mark △ indicates the result of treatment with an aqueous permanganate solution followed by treatment with an aqueous formic acid solution. In addition, for comparison with the present embodiment, as a conventional example, the result of treatment with an aqueous oxalic acid solution after treatment with an aqueous ozone solution (▽ mark) and the result of treatment with an aqueous formic acid solution alone (□ mark) are also shown.
[0034]
The ozone treatment conditions are a concentration of 5 ppm and a temperature of 80 ° C. for 2 hours, and the permanganate treatment conditions are a concentration of 300 ppm and a temperature of 95 ° C. for 2 hours. Formic acid treatment conditions are a concentration of 100 to 50,000 ppm, immersion at a temperature of 95 ° C. for 1 hour, and oxalic acid treatment conditions are a concentration of 2000 ppm, a temperature of 95 ° C. for 1 hour.
[0035]
As can be seen from the results of this test, formic acid treatment alone (concentration 2000 ppm) hardly dissolves the oxide film. On the other hand, in the combination of ozone treatment and formic acid treatment of the present embodiment, the oxide film was dissolved together with the formic acid concentration, and an almost constant dissolution amount was exhibited at the formic acid concentration of 1000 ppm or more. When compared with a formic acid concentration of 1000 ppm or more, a result about 5 times larger than that obtained with formic acid alone was obtained. The result is equivalent to the combined use of conventional ozone treatment and oxalic acid treatment.
[0036]
In addition, the combined effect of the permanganic acid treatment and the formic acid treatment of the present embodiment also has an effect of dissolving the oxide film, and although the amount of dissolution is smaller than the combined use of the ozone treatment, a result about three times larger than the formic acid treatment alone is obtained. It was. In addition, potassium permanganate is selected as the permanganate, treated with potassium permanganate at a concentration of 300 ppm (temperature 95 ° C., 2 hours immersion), and then formic acid treated (concentration 2000 ppm, temperature 95 ° C., 1 hour immersion) ), The same effect was obtained.
[0037]
Next, FIG. 4 shows test results for confirming dissolution of iron oxide (Fe ₃ O ₄ ) in the chemical decontamination method of the present embodiment. At a formic acid concentration of 2000 ppm and a temperature of 95 ° C., the horizontal axis represents the oxalic acid concentration and the vertical axis represents the dissolved Fe concentration. As can be seen from the results of this test, iron oxide was not dissolved by formic acid alone, but iron oxide was dissolved by adding oxalic acid, and the iron concentration increased in proportion to the oxalic acid concentration.
[0038]
As described above, in the chemical decontamination method of the present embodiment, stainless steel is obtained by using ozone, permanganic acid or permanganate as the oxidation treatment, and using a mixed decontamination solution of formic acid and oxalic acid as the reduction treatment. The oxide film and iron oxide produced on the surface can be efficiently dissolved.
[0039]
Since the radioactive substance is taken into the oxide film on the surface of the activated part, the radioactive substance can be decontaminated from the surface of the activated part by dissolving and removing the oxide film, thereby reducing the exposure of workers. Although formic acid alone can be combined with oxidation treatment to remove the oxide film on the surface of stainless steel, formic acid alone hardly dissolves iron oxides, so decontamination compared with mixed decontamination solution of formic acid and oxalic acid. The performance is considered inferior.
[0040]
When permanganic acid or permanganate is used for the oxidation treatment in the chemical decontamination apparatus of FIG. 2, the ozone generator 10, the mixer 9 and the gas phase decomposition tower 11 are unnecessary, and only the chemical injection apparatus 5 is used. Can be used for chemical decontamination of activated parts.
[0041]
Next, the third test result will be described with reference to FIGS. FIG. 5 shows the result of separation of Fe ²⁺ ions and Fe ³⁺ ions dissolved in the mixed decontamination solution of formic acid (2000 ppm) and oxalic acid (200 ppm) of the present embodiment by a cationic resin, and FIG. FIG. 7 shows the results of a separation test from a formic acid (2000 ppm) single decontamination solution, and FIG. 7 shows the results of a separation test from a conventional oxalic acid (2000 ppm) single decontamination solution.
[0042]
Explaining the test results from the conventional example, Fe ²⁺ and Fe ³⁺ ions dissolved in the formic acid single decontamination solution of FIG. 6 could be separated by a cationic resin. In the oxalic acid single decontamination solution of FIG. 7, Fe ²⁺ ions could be separated by the cationic resin, but Fe ³⁺ ions could not be separated. This is because Fe ³⁺ forms a complex with oxalic acid and exists as an anion as shown in the formula (1). In order to separate Fe ³⁺ ions, as shown in the above formula (1), it is reduced to a divalent Fe compound by irradiation with ultraviolet rays (hν), or separated with an anion resin in the state of an oxalic acid complex. There is a need to.
[0043]
On the other hand, in the mixed decontamination solution of formic acid and oxalic acid according to the present embodiment shown in FIG. 5, Fe ²⁺ ions and Fe ³⁺ ions could be separated by a cationic resin as in the case of formic acid single decontamination solution. . As shown in the following formula (4), Fe ³⁺ ions complexed with oxalic acid and H ^{+ of} formic acid were replaced, and it is considered that Fe ³⁺ ions could be separated by a cationic resin.
[Fe (C ₂ O ₄ ) ₃ ] ^3- + 6HCOOH + Fe (COOH) ₃ + 3H ₂ C ₂ O ₄ (4)
[0044]
As described above, when a mixed aqueous solution of formic acid and oxalic acid is used as the reducing agent, the UV equipment and Fe ³⁺ ion reduction process are not required compared to the oxalic acid aqueous solution, reducing the overall cost of decontamination work. Is possible.
[0045]
Next, the fourth test result will be described with reference to FIG. FIG. 8 shows the decomposition test results of the mixed aqueous solution of formic acid and oxalic acid (Δ mark, ▽ mark), the conventional oxalic acid single aqueous solution (□ mark), and the formic acid single aqueous solution (◯ mark) of the present embodiment. The test conditions were 2000 ppm for both formic acid alone and oxalic acid alone aqueous solution, the mixed aqueous solution was 2000 ppm formic acid and 100 ppm oxalic acid, the temperature was 90 ° C., and 20 ppm Fe ion was dissolved in each aqueous solution.
[0046]
In the decomposition method, the mixed aqueous solution first decomposes formic acid with hydrogen peroxide (addition amount: 1.5 times equivalent) (△ mark), and then with ozone (O ₃ generation amount / liquid amount: 75 g / h / m ³ ). Oxalic acid was decomposed (▽ mark). Oxalic acid single aqueous solution is a combination of ultraviolet light (output / liquid amount: 3 kw / m ³ ) and hydrogen peroxide (addition amount: 1.5 times equivalent), formic acid single aqueous solution is hydrogen peroxide (addition amount: 1.5 times equivalent) Just disassembled.
[0047]
Explaining the test results from the conventional example, the aqueous solution of oxalic acid alone was decomposed to an organic carbon concentration of 10 ppm or less in 10 hours by the combined use of hydrogen peroxide and ultraviolet rays. Formic acid was decomposed with hydrogen peroxide alone to an organic carbon concentration of 10 ppm or less in 2 hours.
[0048]
On the other hand, in the mixed aqueous solution of the present embodiment, formic acid is decomposed by hydrogen peroxide alone, but oxalic acid is not decomposed by hydrogen peroxide alone. Therefore, after decomposition of formic acid, oxalic acid was subsequently decomposed by ozone used for oxidation treatment, and the organic carbon concentration was decomposed to 10 ppm or less in a total of less than 4 hours. Oxalic acid can also be decomposed by other oxidizing aqueous solutions such as permanganic acid and potassium permanganate.
[0049]
Here, the reason why formic acid is not decomposed with an oxidizing aqueous solution is that it can be decomposed by ozone alone, but it takes about the same time as the decomposition of oxalic acid by hydrogen peroxide and ultraviolet rays, so it does not shorten the decomposition time. is there. In addition, decomposition reaction is very slow in permanganic acid and potassium permanganate, and the above decomposition time is required.
[0050]
As described above, the mixed aqueous solution of formic acid and oxalic acid can be decomposed in about half the time of oxalic acid, which has a proven track record as a decontaminant, although the decomposition time is slower than that of formic acid alone. In addition, as shown in the above formulas (2) and (3), the decomposition of oxalic acid requires an ultraviolet device in order to generate Fe ²⁺ ions. Since the Fe ³⁺ ion reduction process is not required, the overall cost of decontamination work can be reduced.
[0051]
The concentration range of formic acid and oxalic acid used for the reducing decontamination agent is preferably 1000 ppm to 5000 ppm for formic acid and 50 ppm to 300 ppm for oxalic acid in consideration of decontamination performance and reduction time.
[0052]
Next, as a fifth test result, the decomposition treatment of hydrogen peroxide and ozone remaining after the completion of the decomposition treatment of the mixed decontamination solution of formic acid and oxalic acid will be described. Iron ions and radioactive substances that elute in the decontamination solution are separated by the ion exchange resin. However, if hydrogen peroxide and ozone remain in the decontamination solution, the oxidative degradation of the ion exchange resin is promoted. there is a possibility. In order to prevent this, the decontamination solution is irradiated with ultraviolet rays (hν), and hydrogen peroxide and ozone are decomposed into water and oxygen by the reactions shown in the following formulas (5) and (6).
Decomposition of hydrogen peroxide: H ₂ O ₂ + hν → O ₂ + 2H ⁺ + 2e ⁻ (5)
Decomposition of ozone: O ₃ + hν → O + O ₂ (6)
[0053]
In order to confirm the above reaction, a decomposition test was carried out by ultraviolet rays of hydrogen peroxide and ozone remaining in the decontamination solution (formic acid concentration of 10 ppm or less). The hydrogen peroxide decomposition test results are shown in FIG. 9, and the ozone decomposition test results are shown in FIG. At an ultraviolet output of 3 kw / m ³ , hydrogen peroxide with an initial concentration of 20 ppm was decomposed to 1 ppm or less in 1.5 hours, and ozone with an initial concentration of 5.5 ppm was decomposed to 0.1 ppm or less in 12 minutes.
[0054]
As described above, hydrogen peroxide or ozone remaining during or after decomposition of formic acid in the decontamination solution can be decomposed by ultraviolet rays, so that the eluted metal ions can be separated without reducing the exchange capacity of the ion exchange resin. . Therefore, the amount of used ion exchange resin generated as secondary waste can be reduced.
[0055]
In FIG. 2, a liquid phase decomposition apparatus 6 that irradiates ultraviolet rays is used only to decompose hydrogen peroxide or ozone remaining in the decontamination liquid and to ensure the soundness of the ion exchange resin. If there is no residual hydrogen peroxide and ozone, or even if the residual metal ions are not separated by the ion exchange resin, the liquid phase decomposition apparatus 6 is unnecessary.
[0056]
In addition, as a corrosion inhibitor for suppressing the corrosion of stainless steel that comes into contact with ozone water, which is an oxidizing agent, carbonic acid, carbonate, hydrogen carbonate, boric acid, borate, sulfuric acid, sulfate, phosphoric acid, phosphate, phosphoric acid Although it is said that there is an effect by adding a hydrogen salt, also in this embodiment, since the ozone gas is supplied at the time of oxalic acid decomposition, the above-mentioned corrosion inhibitor is a stainless steel base material at the time of oxalic acid decomposition treatment. It was confirmed that it was effective in inhibiting corrosion.
[0057]
According to the chemical decontamination method and apparatus for activated parts of the present embodiment, the following effects can be obtained. That is, a method of decontaminating a structure part of a radiation handling facility as a decontamination object and chemically dissolving an oxide film containing a radioactive substance generated or attached to the surface of the activation part as an individual decontamination object In this process, the reducing decontamination solution in which the monocarboxylic acid formic acid and the dicarboxylic acid oxalic acid are mixed and dissolved and the oxidizing decontamination solution in which the oxidizing agent is dissolved are alternately brought into contact with each other and decontaminated. Substances can be removed efficiently.
[0058]
In addition, since Fe ³⁺ ions eluted in the reducing mixed decontamination solution can be separated by a cationic resin, a reduction device and a reduction process for reducing Fe ³⁺ ions to Fe ²⁺ ions are not necessary. The overall cost of the decontamination apparatus can be reduced.
[0059]
Furthermore, formic acid in the reductive mixed decontamination solution can be decomposed only with hydrogen peroxide, and low-concentration oxalic acid can be decomposed in an oxidizing aqueous solution in a short time, thus producing a divalent Fe compound as a decomposition catalyst. Since the reduction device and the reduction process are not required, the entire cost of the decontamination device can be reduced.
[0060]
【The invention's effect】
According to the present invention, there is no need for a process and apparatus for reducing trivalent iron ions to divalent iron ions, the decomposition rate is faster than with oxalic acid, and the decontamination performance is equivalent to that of oxalic acid. A method and apparatus for chemical decontamination of parts can be provided.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a chemical decontamination method for activated components according to an embodiment of the present invention.
FIG. 2 is a system diagram showing a chemical decontamination apparatus for activation parts according to an embodiment of the present invention.
FIG. 3 is a dissolution curve diagram of an oxide film for explaining the effect of the method and apparatus for chemical decontamination of activated parts according to the embodiment of the present invention.
FIG. 4 is a dissolution curve diagram of an oxide film for explaining the effects of the chemical decontamination method and apparatus for activated parts according to the embodiment of the present invention.
FIG. 5 is a bar graph showing the results of a separation test of iron ions in a reducing mixed aqueous solution with a cation resin and illustrating the effect of the embodiment of the present invention.
FIG. 6 is a bar graph showing the results of a separation test of iron ions in an aqueous formic acid solution using a cation resin and explaining the effect of the embodiment of the present invention.
FIG. 7 is a bar graph showing the results of a separation test of iron ions in an oxalic acid aqueous solution using a cationic resin and illustrating the effect of the embodiment of the present invention.
FIG. 8 is a curve diagram showing the results of a decomposition test of a reducing mixed aqueous solution and illustrating the effect of the embodiment of the present invention.
FIG. 9 is a curve diagram showing the results of a decomposition test of residual hydrogen peroxide and explaining the effect of the embodiment of the present invention.
FIG. 10 is a curve diagram showing the results of a residual ozone decomposition test and explaining the effect of the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Decontamination tank, 1a ... Decontamination liquid, 2 ... Circulation system, 3 ... Circulation pump, 4 ... Heater, 5 ... Chemical injection apparatus, 6 ... Liquid phase decomposition apparatus, 7 ... Cationic resin tower, 8 ... Mixed bed resin Tower, 9 ... Mixer, 10 ... Ozone generator, 11 ... Gas phase decomposition tower, 12 ... Exhaust blower, 13 ... Activation part.

Claims (9)

A reduction dissolution step in which the surface of the activation part having a radioactive oxide film on the surface is brought into contact with a reducing decontamination solution in which formic acid and oxalic acid having a concentration of about 1/10 of the concentration of formic acid are dissolved; An oxidative dissolution process in which the surface of the component is brought into contact with an oxidizing decontamination solution in which an oxidizing agent is dissolved, and Fe ²⁺ ions and Fe ³⁺ ions eluted in the reducing decontamination solution are removed by a cationic resin. A chemical decontamination method for activated parts, characterized by separating and removing from a dyeing solution .   2. The method for chemical decontamination of activated parts according to claim 1, wherein the reducing and dissolving step and the oxidizing and dissolving step are alternately performed a plurality of times.   The method of chemical decontamination of activated parts according to claim 1 or 2, wherein the oxidizing agent constituting the oxidizing decontamination solution is ozone, permanganic acid or permanganate.   3. The formic acid remaining in the reducing decontamination solution is decomposed into carbon dioxide and water by hydrogen peroxide and oxalic acid is decomposed into carbon dioxide and water by ozone dissolved in the oxidizing decontamination solution. The chemical decontamination method of the activation component as described. 5. The chemical decontamination method for activated parts according to claim 4 , wherein hydrogen peroxide or ozone remaining in the reducing decontamination solution is decomposed into water or oxygen by ultraviolet rays. Any of carbonic acid, carbonate or hydrogen carbonate, boric acid or borate, sulfuric acid or sulfate, phosphoric acid or phosphate or hydrogen phosphate is added to the reducing decontamination solution as a corrosion inhibitor for the activated component. The method for chemical decontamination of activated parts according to claim 4 . A decontamination tank for containing a radioactive component having a radioactive oxide film on the surface and bringing the surface into contact with a decontamination liquid; and a circulation system connected to the decontamination tank and circulating the decontamination liquid. The system includes a chemical injection device for injecting a reducing agent composed of formic acid and oxalic acid at a concentration about 1/10 of the concentration of formic acid and hydrogen peroxide into the decontamination solution, and Fe ²⁺ ions in the decontamination solution. and Fe ³⁺ and ion ion exchanger for separating and removing by cationic resin, chemical decontamination apparatus of the activation component, wherein a and a ozone generator for injecting ozone into the decontamination liquid. A decontamination tank for containing a radioactive component having a radioactive oxide film on the surface and bringing the surface into contact with a decontamination liquid; and a circulation system connected to the decontamination tank and circulating the decontamination liquid. The system injects into the decontamination solution a formic acid and a reducing agent composed of oxalic acid at a concentration about 1/10 of the concentration of formic acid and an oxidizing agent composed of hydrogen peroxide and permanganic acid or permanganate. A chemical decontamination apparatus for activated parts, comprising: an apparatus; and an ion exchange apparatus that separates and removes Fe ²⁺ ions and Fe ³⁺ ions in the decontamination solution using a cationic resin . 9. The chemical decontamination of a radioactive component according to claim 7 or 8 , wherein the circulation system includes a liquid phase decomposition apparatus for decomposing hydrogen peroxide and ozone remaining in the decontamination liquid with ultraviolet rays. apparatus.

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