JP6026896B2 - Method and system for treating organic waste - Google Patents

Description

  The present invention relates to a processing method and a processing system for organic waste containing a radionuclide generated in a nuclear facility.

  Filter sludge and other organic waste containing cellulosic filter aids, ion exchange resins, etc., generated from nuclear power plant reactor coolant purification systems, fuel pool cooling and purification systems, etc. are stored in storage tanks for long periods. Has been. These waste resins are regularly generated as the nuclear power plant is operated, and are finally processed after volume reduction.

  Since the ion exchange resin is based on styrene / divinylbenzene and is chemically stable, it can be stored for a long time. On the other hand, the decomposition process is difficult because of its stability, and when the volume is reduced, a thermal decomposition process at a high temperature is usually required.

  As thermal decomposition treatment of waste resin (used ion exchange resin), Patent Document 1 describes a treatment method using plasma, and Patent Document 2 describes a treatment method using microwaves. These thermal decomposition treatment methods have a high volume reduction with respect to waste resin. However, since the concentration of the radionuclide contained in the waste resin to be treated is relatively high, a remote operation system such as decompression and atmosphere control and an advanced exhaust gas treatment system are required, and the entire treatment system becomes complicated.

  As a waste resin volume reduction treatment other than thermal decomposition, there is a treatment method in which organic substances in the used ion exchange resin are decomposed with hydrogen peroxide. In Patent Document 3, a cellulose-based filter sludge is hydrolyzed and liquefied using a cellulose-degrading enzyme, and in the presence of iron ions (in the examples, ferrous sulfate is used). A method for treating radioactive waste in which hydrogen peroxide is allowed to act to oxidatively decompose organic matter is disclosed. Patent Document 4 discloses a chemical decomposition method in which a radioactive ion exchange resin is brought into contact with hydrogen peroxide in an aqueous ferric sulfate solution to oxidatively decompose the resin.

  Other volume reduction treatment methods include elution of the radionuclide contained in the used ion-exchange resin with an aqueous sulfuric acid solution, etc. to facilitate incineration or chemical decomposition of the resin, and to dilute the eluent containing the radionuclide. Patent Document 5 discloses a treatment method for transferring radionuclide to an inorganic substance by adding iron ions and alkalis to oxidize them to generate ferrite particles and incorporating the radionuclide into ferrite particles.

  Patent Document 6 discloses a chemical cleaning agent using malonic acid and hydrazine. Further, in this document, as conventional techniques, those containing oxalic acid and ammonium citrate (Japanese Patent Publication No. 45-37360) and those containing oxalic acid and hydrazine (Japanese Patent Laid-Open No. 57-9885) are also disclosed. Have been described.

JP 2001-305287 A JP 59-46899 A JP-A 61-270700 JP 58-161898 A JP-A-63-40900 Japanese Patent Laid-Open No. Sho 62-127483

  Residue waste liquid generated by volume reduction treatment by decomposition using hydrogen peroxide described in Patent Documents 3 and 4 contains a large amount of sulfate groups, so neutralization treatment is required, and volume reduction is reduced. To do.

  In the processing method described in Patent Document 5, since a sulfuric acid aqueous solution is used as a desirable eluent, it is a problem that a large amount of waste sulfuric acid is generated.

  The chemical cleaning agent described in Patent Document 6 is a metal material to be cleaned, and is not used for volume reduction treatment of used ion exchange resins.

  The object of the present invention is to reduce the volume of cellulosic organic matter contained in organic waste when reducing the volume of organic waste generated from nuclear facilities, and from organic waste without using sulfuric acid. The purpose is to increase the elution function of radionuclides and to promote the oxidative decomposition of organic waste residues to reduce the amount of oxidant used.

  The organic waste processing method of the present invention includes a step of decomposing a cellulose organic material contained in an organic waste containing a radionuclide with an enzyme to form a cellulose decomposition product, and the organic waste using a carboxylic acid. It includes a step of chemical decontamination, and a step of oxidizing and decomposing a radionuclide solution containing a carboxylic acid produced by cellulose degradation products and chemical cleaning using hydrogen peroxide or ozone.

  According to the present invention, the cellulosic organic matter contained in the organic waste generated from the nuclear facility can be reduced, and the elution function of the radionuclide from the organic waste can be enhanced without using sulfuric acid. In addition, the amount of the oxidizing agent used can be reduced by promoting the oxidative decomposition of the organic waste residue.

It is a flowchart which shows the processing method of the organic waste of this invention. It is a flowchart which shows the modification of the processing method of organic waste. It is a block diagram which shows the outline | summary of the processing system of organic waste. It is a block diagram which shows the modification of the processing system of organic waste. It is a block diagram which shows the other Example of the processing system of organic waste.

  In the present invention, a chemical decontamination treatment using a carboxylic acid (for example, oxalic acid) which does not contain a sulfo group and is easily decomposed and has a reducing action is proposed. The carboxylic acid used in this chemical decontamination treatment elutes ionic radionuclides adsorbed on the used ion exchange resin, and dissolves and removes the radionuclides incorporated in the cladding contained in organic waste together with the cladding. . Here, the clad refers to metal impurities such as iron rust generated from steel materials of piping of nuclear facilities.

  However, the above-mentioned chemical decontamination treatment with carboxylic acid is carried out in such a manner that the nuclides dissolved in the treatment are used as waste materials simultaneously with the washed spent ion exchange resin or boiling reactor (BWR) as filter sludge ( It becomes a problem that the ability to elute the radionuclide adsorbed on the resin becomes insufficient due to redeposition to a powder ion exchange resin, a filter aid or the like. In particular, the cellulosic organic material that is a filter aid has a fibrous shape and a large volume per unit weight, and therefore has a larger volume ratio than the ion exchange resin. Therefore, the influence on the reattachment of nuclides is great.

  Hereinafter, an organic waste processing method and a processing system according to an embodiment of the present invention will be described.

  Here, the organic waste refers to precipitates in waste liquids that are difficult to reuse, including cellulosic filter aids, ion exchange resins, and the like, and is also called so-called filter sludge. Organic waste contains radionuclides.

  FIG. 1 is a flowchart showing an outline of the processing method.

  In this figure, the processing method includes a cellulose decomposition step S101, a chemical decontamination step S102 with carboxylic acid, and an oxidative decomposition step S103 with hydrogen peroxide or ozone.

  The treatment method is a step of degrading a cellulose organic substance contained in an organic waste containing a radionuclide with a cellulase or other degrading enzyme or a cellulose degrading bacterium to obtain a low molecular weight cellulose degrading product (cellulose degrading step S101). And a step of chemically decontaminating organic waste using carboxylic acid (chemical decontamination step S102), and a radionuclide solution containing cellulose decomposition products and carboxylic acid using hydrogen peroxide or ozone as an oxidizing agent. And oxidative decomposition step (oxidative decomposition step S103).

  The cellulose decomposition step S101 is a pretreatment of the organic waste chemical decontamination step S102.

  After the cellulose decomposition step S101, the organic waste from which the cellulose organic matter is separated is a carboxylic acid that does not contain a sulfo group and is easily decomposed and has a reducing action (an acid having a carboxyl group, Chemical decontamination step S102 is performed by oxalic acid.

  Here, the cellulosic organic substance is a general term for organic substances having a molecular structure of cellulose. A functional group, a molecular chain, or the like may be added to the cellulose organic material.

  In the oxidative decomposition step S103, the cellulose decomposition product (cellulose decomposition solution) generated in the cellulose decomposition step S101 and the radionuclide solution generated in the chemical decontamination step S102 may be performed using the same line of equipment. Good.

  Moreover, you may perform chemical decontamination process S102 in the state which heated the organic waste.

  Furthermore, in the chemical decontamination step S102, fresh carboxylic acid may be supplied continuously or intermittently while the organic waste is immersed in the carboxylic acid.

  Examples 1 to 3 described later are processing systems corresponding to the steps shown in the drawing.

  In the treatment method, since the oxidative decomposition step S103 using hydrogen peroxide or ozone is performed after the chemical decontamination step S102, the carboxylic acid in the radionuclide solution is decomposed, and the radionuclide is peroxidized accordingly. Contact with hydrogen or ozone. For this reason, the metal ion acts as a catalyst, and the oxidative decomposition of the organic matter in the liquid is promoted. As a result, the effect that the amount of the oxidizing agent used is small can be obtained.

  FIG. 2 is a flowchart showing a modification of the processing method.

  In this figure, the clad separation step S100 is performed before the cellulose decomposition step S101.

  On the other hand, a used ion exchange resin, which is one of organic wastes, has pores and adsorbs radionuclides inside the pores.

  The clad separation step S100 separates the clad from the organic waste by physical operations such as specific gravity separation and centrifugal separation. Thereby, the quantity of the radionuclide contained in organic waste can be reduced in advance. The separated clad and organic waste are preferably treated separately in the chemical decontamination step S102. In addition, it is desirable that the respective radionuclide solution generated in the chemical decontamination step S102 be simultaneously processed in the oxidative decomposition step S103 of the same equipment.

  Example 4 to be described later is a processing system corresponding to the steps shown in the figure.

  The clad separation step S100 may be performed on the upstream side of the chemical decontamination step S102. That is, the cladding separation step S100 may be performed immediately after the cellulose decomposition step S101 and immediately before the chemical decontamination step S102.

  The treatment system uses a cellulose degradation part that decomposes cellulose organic substances contained in organic waste containing radionuclides with enzymes to make cellulose degradation products, and chemical decontamination of organic wastes using carboxylic acid. It includes a decontamination part, and an oxidative decomposition part that oxidizes and decomposes the cellulose decomposition product and the radionuclide solution using hydrogen peroxide or ozone.

  In the treatment system, it is desirable that the chemical decontamination unit has a heater unit for heating the organic waste.

  In the treatment system, the carboxylic acid may be supplied to the organic waste continuously or intermittently.

  Examples will be described below.

  FIG. 3 is a configuration diagram showing an outline of an organic waste treatment system.

  In this figure, the treatment system includes a cellulosic organic matter decomposition treatment system 100 (cellulose decomposition part), an oxidative decomposition treatment system 101 (oxidation decomposition part), and a chemical cleaning treatment system 102 (chemical decontamination part). .

  The cellulosic organic matter decomposition treatment system 100 includes a first receiving tank 3, a decomposition tank 4, a first temperature control device 5 (first temperature control unit), a first stirring device 6, a cellulolytic enzyme tank 7, Exhaust gas equipment 8 (exhaust gas treatment equipment) is provided.

  The oxidative decomposition treatment system 101 includes an oxidative decomposition facility 9, a treated water recovery tank 10, a first analysis / inspection device 11 (first analysis / inspection unit), a water supply tank 12, a cement solidification facility 13, and a concentration treatment. Equipment 14.

  The chemical cleaning system 102 includes a second receiving tank 15, an oxalic acid immersion tank 16, a second stirring device 17, an oxalic acid supply tank 18, a water supply tank 19, a recovery tank 20, a second analysis / inspection. An apparatus 21 (second analysis / inspection unit) and an incineration processing facility 34 are provided.

  You may perform the transfer of the liquid between said each tank, apparatus, etc. using the transfer pump 2, as shown in figure.

  In the cellulose organic matter decomposition treatment system 100, the cellulose organic matter is decomposed and removed from the organic waste.

  In the cellulosic organic matter decomposition treatment system 100, organic waste in the form of a water slurry is introduced from the organic waste storage tank 1 to the first receiving tank 3. Thereafter, a certain amount of the organic waste is extracted from the first receiving tank 3 and transferred to the decomposition tank 4. A 1 wt% cellulase enzyme solution is supplied from the cellulose-degrading enzyme tank 7 to the organic waste transferred to the decomposition tank 4 to decompose the cellulose-based organic matter. The decomposition tank 4 can be heated by a first temperature control device 5 (also a heater unit). The organic waste in the decomposition tank 4 can be agitated and mixed by the first agitator 6.

  A solution (cellulose decomposition solution) in which the decomposed cellulose-based organic substance is dissolved is taken out from the decomposition tank 4, and the solution is transferred to the oxidative decomposition equipment 9 of the oxidative decomposition treatment system 101 to oxidatively decompose the organic substance contained in the solution. . Thereafter, the treated water generated in the oxidative decomposition facility 9 is transferred to the treated water recovery tank 10, and the concentration of the radionuclide of the treated water is measured by the first analysis / inspection apparatus 11. When the measured value is equal to or greater than a preset threshold value, the cement is solidified after being transferred to the cement solidification facility 13 and performing necessary pretreatment (evaporation concentration, etc.). When the measured value is less than the threshold value, it is transferred to the existing concentration processing facility 14 in the power generation facility, and processing such as evaporation concentration is performed. The threshold value to be set differs depending on the facility.

  On the other hand, the organic waste obtained by decomposing and removing the cellulosic organic matter in the decomposition tank 4 is transferred to the second receiving tank 15 of the chemical cleaning processing system 102. Thereafter, a certain amount is extracted from the second receiving tank 15 and transferred to the oxalic acid immersion tank 16. An oxalic acid solution of about 10 g / L is supplied from the oxalic acid supply tank 18 to the organic waste transferred to the oxalic acid immersion tank 16, and the organic waste is immersed in oxalic acid.

  The eluent of the radionuclide generated by the immersion treatment is oxidatively decomposed by the oxidative decomposition treatment system 101. Thereby, the oxalic acid contained in the radionuclide solution is decomposed and removed.

  Before processing the radionuclide solution in the oxidative decomposition treatment system 101, the oxidative decomposition facility 9 that decomposes the cellulose decomposition solution or the treated water collection tank 10 that collects the treated water is washed with water or the like.

  The solution obtained by decomposing and removing oxalic acid is recovered in the treated water recovery tank 10. The recovered solution is subjected to a necessary pretreatment (evaporation concentration, etc.) and then subjected to cement solidification in the cement solidification facility 13.

  Further, the organic waste chemically cleaned in the oxalic acid immersion tank 16 is recovered in the recovery tank 20. Thereafter, the concentration of the radionuclide in the collected organic waste is measured by the second analysis / inspection apparatus 21. When the measured value is equal to or higher than a preset threshold value, the measured value is transferred to the second receiving tank 15 and dipped again in the oxalic acid dipping tank 16. When the measured value is less than the threshold value, the incineration processing facility 34 performs incineration processing or cement solidification processing.

  According to the present embodiment, the cellulose-based organic matter, which is a bulky factor of the organic waste, is decomposed and extracted, and the radionuclide is extracted as a solution with oxalic acid, so that the organic waste can be reduced in volume. In addition, by decomposing and removing the cellulosic organic matter before chemical decontamination, it is possible to prevent the radionuclide from reattaching to the cellulosic organic matter in the organic waste.

  In addition, since chemical waste treatment with oxalic acid is performed after reducing the volume of organic waste, the ability to elute radionuclides with oxalic acid can be improved, and the amount of oxalic acid used can be greatly reduced. be able to.

  FIG. 4 is a configuration diagram showing an outline of an organic waste treatment system.

  The difference from the first embodiment is that a second temperature control device 22 (also a heater unit) is additionally provided in the oxalic acid immersion tank 16 to enable heating. Thereby, oxalic acid immersion can be performed in a heated state. It has been confirmed that when the set temperature is not less than room temperature and not more than 90 ° C., the performance of eluting the radionuclide adsorbed on the organic waste increases. The set temperature is more preferably 40 ° C. or higher and 90 ° C. or lower.

  In this example, the difference from Example 1 or Example 2 is that new oxalic acid is continuously or intermittently applied while the organic waste is immersed in oxalic acid in the chemical cleaning treatment of the organic waste. It is a point to supply repeatedly. Thereby, the function to elute a radionuclide can be improved.

  FIG. 5 is a configuration diagram showing an outline of an organic waste treatment system.

  In this embodiment, the difference from Embodiments 1 to 3 is that organic waste is introduced into the clad separation treatment system 404, and the clad has a greater specific gravity than the organic waste. It is a point which isolate | separates a clad from organic waste by physical operation of.

  In this figure, the organic waste in the form of water slurry from the organic waste storage tank 1 is introduced into the third receiving tank 23 of the cladding separation processing system 404. Thereafter, a certain amount of the organic waste is extracted from the third receiving tank 23 and transferred to the clad separator 24. In the clad separation device 24, the clad is separated from the organic waste by physical operations such as specific gravity separation and centrifugal separation. Thereafter, the organic waste is transferred to the organic waste recovery tank 25, and the clad is transferred to the clad recovery tank 26.

  The chemical cleaning treatment of the organic waste recovered in the organic waste recovery tank 25 and the dissolution treatment of the clad recovered in the clad recovery tank 26 may be performed separately.

  Therefore, one of the organic waste and the clad is introduced into the first receiving tank 3 of the cellulosic organic matter decomposition treatment system 100 and a predetermined treatment in the cellulosic organic matter decomposition treatment system 100 is performed. Then, it introduces into the 2nd receiving tank 15 of the chemical cleaning processing system 102, and performs the predetermined | prescribed process in the chemical cleaning processing system 102. FIG. Thereafter, the other is similarly processed in the cellulosic organic matter decomposition treatment system 100 and the chemical cleaning treatment system 102 of the same system.

  The radionuclide solution or the clad solution obtained by the respective processes in the chemical cleaning system 102 is introduced into the oxidative decomposition processing system 101 and subjected to the oxidative decomposition process.

  By these treatments, it is not necessary to consider the problem that the radionuclide dissolved together with the cladding is adsorbed on the organic waste.

  In FIG. 5, the clad separation treatment system 404 is disposed in front of the cellulosic organic matter decomposition treatment system 100, but the present invention is not limited to this. In the present invention, the clad separation treatment system 404 may be disposed after the cellulosic organic matter decomposition treatment system 100 as long as the clad can be separated from the organic waste before the chemical cleaning treatment. In other words, the cladding separation treatment system 404 may be disposed between the cellulosic organic matter decomposition treatment system 100 and the chemical cleaning treatment system 102.

  Hereinafter, the effects of the present invention will be described together.

  According to the present invention, it is possible to improve the ability to elute a radionuclide adsorbed on waste resin generated in a nuclear facility with a carboxylic acid that does not contain a sulfo group such as oxalic acid and is easily decomposed and has a reducing action. it can.

  Moreover, according to this invention, the cellulosic organic substance used as a hazardous | toxic substance can be decomposed | disassembled and removed at the time of waste disposal.

  Furthermore, according to the present invention, the equipment cost can be reduced by subjecting the decomposition solution and the solution to the oxidative decomposition treatment in the same equipment.

  Furthermore, according to the present invention, after separating the organic waste and the clad, each of them is chemically decontaminated separately so that the radionuclide dissolved together with the clad is re-adsorbed to the chemically decontaminated resin. Preventing and improving the elution capacity of the processing system.

  According to the present invention, the carboxylic acid in the radionuclide solution produced by chemical decontamination treatment of organic waste is oxidatively decomposed by an oxidizing agent such as ozone or hydrogen peroxide. The ions act as a catalyst, and the amount of oxidant used can be reduced.

  1: organic waste storage tank, 2: transfer pump, 3: first receiving tank, 4: decomposition tank, 5: first temperature control device, 6: first stirring device, 7: cellulolytic enzyme tank, 8: Exhaust gas equipment, 9: oxidative decomposition equipment, 10: treated water recovery tank, 11: first analysis / inspection device, 12: feed water tank, 13: cement solidification equipment, 14: concentration treatment equipment, 15: second receiving tank, 16 : Oxalic acid immersion tank, 17: second stirring device, 18: oxalic acid supply tank, 19: water supply tank, 20: recovery tank, 21: second analysis / inspection device, 34: incineration equipment, 100: cellulosic organic matter Decomposition treatment system, 101: oxidative decomposition treatment system, 102: chemical cleaning treatment system, 404: clad separation treatment system.

Claims (8)

A cellulose decomposing step of decomposing the cellulosic organic matter contained in the organic waste containing the radionuclide with an enzyme to form a cellulose decomposing product; and a chemical decontamination step of chemically decontaminating the organic waste using a carboxylic acid; And the oxidative decomposition step of oxidatively decomposing the radionuclide solution generated in the cellulose decomposition product and the chemical decontamination step using hydrogen peroxide or ozone, and the oxidative decomposition step includes the cellulose decomposition product and the A method for treating organic waste, characterized in that a radionuclide solution is separately oxidized and decomposed, and a cladding separation step is provided upstream of the chemical decontamination step to separate the cladding from the organic waste. .   The method for treating organic waste according to claim 1, wherein the chemical decontamination step is performed in a state where the organic waste is heated.   The method for treating organic waste according to claim 1 or 2, wherein the carboxylic acid is continuously or intermittently supplied to the organic waste. The method for treating organic waste according to any one of claims 1 to 3 , wherein the carboxylic acid is oxalic acid. The method for treating organic waste according to any one of claims 1 to 4 , wherein the enzyme is cellulase. Cellulose-based organic matter contained in organic waste containing radionuclides is decomposed with enzymes to make a cellulose-decomposed product, a cellulose-decomposing part, and a chemical decontamination part for chemically decontaminating the organic-based waste using carboxylic acid , An oxidative decomposition part that oxidatively decomposes the radionuclide solution generated in the cellulose decomposition product and the chemical decontamination part using hydrogen peroxide or ozone, and the oxidative decomposition part includes the cellulose decomposition product and the An organic waste treatment system comprising: a clad separation device for separately oxidizing and decomposing radionuclide solution and separating the clad from the organic waste upstream of the chemical decontamination unit . The organic waste treatment system according to claim 6, wherein the chemical decontamination unit includes a heater unit for heating the organic waste. The organic waste treatment system according to claim 6 or 7 , wherein the carboxylic acid is supplied to the organic waste continuously or intermittently.

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