JP2013044588A - Method and system for treatment of waste resin of nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and system for treatment of waste resins including a used ion exchange resin as a radioactive waste in a nuclear power plant.SOLUTION: A waste resin is immersed in about 10 g/L oxalic acid aqueous solution and metal-clad on the waste resin surface is dissolved in the oxalic acid aqueous solution and metal ions adsorbed by the waste resin are eluted in the oxalic acid aqueous solution so that the radiation dose is reduced to smoothly treat the waste resin.

Description

  The present invention relates to a waste resin treatment method and processing system including filter sludge such as used ion exchange resin and cellulose filter aid among radioactive waste generated from a cooling water purification system of a nuclear power plant.

  Filter sludges such as powder ion exchange resins and cellulose filter aids used in nuclear reactor nuclear reactor cooling water purification systems and fuel pool cooling water purification systems are used as radioactive waste after use. It is stored for a long time in the storage tank. These used ion exchange resins and filter sludges are called waste resin, but waste resin is a waste that is regularly generated during the operation of nuclear power plants, thus ensuring a storage space for waste. In order to achieve this, volume reduction technology that efficiently reduces the volume of waste resin currently stored is required.

  The ion exchange resin is based on styrene-divinylbenzene and is chemically stable. Cellulosic filter sludge is also a stable material. Since these are chemically stable, they can be stored for a long time. On the other hand, the decomposition process is difficult due to its stability, and when the volume is reduced, a thermal decomposition process at a high temperature is usually required.

  There exists patent document 1 as a volume reduction processing technique of waste resin. Patent Document 1 describes a method for reducing the volume of an ion exchange resin by thermally decomposing it with plasma. Patent Document 2 discloses a treatment method in which ion exchange resin is dried and heated and incinerated using microwaves to reduce the volume, and unburned components in exhaust gas generated during thermal decomposition are also thermally decomposed by microwaves. Have been described.

  Patent Document 3 discloses a method for eluting radioactive nuclides in radioactive waste sludge using sulfuric acid, nitric acid, oxalic acid or the like in a treatment means for radioactive waste sludge comprising filters such as used ion exchange resins and filter aids. Is disclosed. Patent Document 4 discloses a configuration in which a radioactive substance is eluted using an inorganic acid such as sulfuric acid and an organic acid such as oxalic acid in a method for treating a radioactive ion exchange resin. Patent Document 5 discloses a configuration using oxalic acid and tetramethylammonium hydroxide in a method for regenerating a condensate purification system ion exchange resin for a nuclear reactor.

JP 2001-305287 A JP 59-46899 A JP-A-4-136800 JP 61-254899 A Japanese Patent Laid-Open No. 7-16477

  Although the thermal decomposition treatment described in Patent Documents 1 and 2 can reduce the volume of waste resin at a high ratio, it is necessary to remotely perform operations such as decompression and atmosphere control because the radiation dose of the waste resin is high. In addition, an advanced exhaust gas treatment system is required, and the entire treatment system may be complicated.

  Moreover, although the processing method of patent document 3, 4, 5 mentions use of an oxalic acid, it does not mention the optimal density | concentration.

  Further, in order to reduce the radiation dose of the waste resin, it is necessary to elute the radioactive metal ions adsorbed on the ion exchange resin and to dissolve and remove the radionuclide incorporated in the clad adhering to the resin surface together with the clad. One process is required. As the method, immersion treatment with sulfuric acid is conceivable. In sulfuric acid, in order to turn the waste liquid remaining after treating the resin into waste, it is necessary to remove the sulfuric acid from the waste liquid by a method such as electrodialysis. Moreover, it is difficult to completely remove the sulfuric acid component.

  An object of the present invention is to provide a processing method and a processing system for efficiently reducing the volume of spent radioactive waste of ion exchange resin with a simple system.

  The present invention relates to a waste resin treatment method including a spent ion exchange resin generated in a cooling water purification system of a nuclear power plant, wherein the waste resin is immersed in an aqueous oxalic acid solution of about 10 g / L and the metal clad on the surface of the waste resin. Is dissolved in an aqueous oxalic acid solution, and metal ions adsorbed on the waste resin are eluted into the aqueous oxalic acid solution.

  In addition, in the waste resin treatment method of a nuclear power plant, after the metal clad on the surface of the waste resin is dissolved in the oxalic acid aqueous solution and the metal ions adsorbed on the waste resin are eluted, the ion exchange resin taken out from the oxalic acid aqueous solution is removed. While incineration, oxalic acid in the oxalic acid aqueous solution is decomposed with ozone.

  Moreover, in the waste resin treatment method of a nuclear power plant, the waste resin is immersed in an oxalic acid aqueous solution of about 10 g / L and stirred for 12 to 24 hours to dissolve the metal clad on the surface of the waste resin in the oxalic acid aqueous solution. The metal ions adsorbed on the resin are eluted into the oxalic acid aqueous solution.

  Moreover, in the waste resin treatment method of a nuclear power plant, the metal ion hydroxide remaining in the aqueous solution after the oxalic acid in the oxalic acid aqueous solution is decomposed with ozone is solidified.

  Furthermore, in a waste resin treatment system including a used ion exchange resin generated in a cooling water purification system of a nuclear power plant, a waste resin supply device for taking out a certain amount of waste resin from a storage tank of used ion exchange resin, and a waste resin In the oxalic acid immersion tank that immerses a certain amount of waste resin taken out by the supply device in oxalic acid, a transport device that feeds the waste resin after being immersed in oxalic acid in the oxalic acid immersion tank, and an immersion tank An ozonolysis apparatus for decomposing the generated oxalic acid aqueous solution with ozone is provided.

  Further, in the waste resin treatment system of a nuclear power plant, the waste resin supply device has a quantitative container for storing a certain amount of waste resin.

  Furthermore, in the waste resin treatment system of a nuclear power plant, the waste resin supply device has a metering pump for supplying a certain amount of waste resin.

  In the treatment system of the present invention, waste resin is thermally decomposed after reducing the radiation dose of used ion exchange resin or the like by chemical treatment at normal temperature and pressure. By reducing the radiation dose of the waste resin, it is possible to reduce the volume by processing in an existing incinerator provided in a nuclear power plant without introducing a new decomposition treatment system.

  In the present invention, a chemical treatment using oxalic acid that is easier to decompose is proposed. Oxalic acid can dissolve the clad mainly composed of iron oxide. Oxalic acid itself is known for chemical decontamination of piping and the like in nuclear power plants, but the inventors further examined the dissolution treatment conditions of the cladding from the viewpoint of reducing the radiation dose of used ion exchange resins and the like.

  Oxalic acid used for chemical decontamination is usually about 2000 ppm, but under such conditions, the solubility of the clad is less than 1 g / L. That is, in order to dissolve the entire amount of the clad adhering to the resin waste, a large amount of oxalic acid aqueous solution is required, and the equipment capacity of the waste treatment system is increased. On the other hand, when the oxalic acid concentration is increased, there is a concern that the amount of iron dissolved is limited by the solubility product of oxalate ions of iron ions.

  Therefore, prior to the present invention, the dependence of the solubility of hematite (iron oxide), which is the main component of the cladding, on the oxalic acid concentration was confirmed. As a result, the solubility of the clad increases with the oxalic acid concentration, and if a concentrated oxalic acid aqueous solution of about 10 g / L is used, the solubility of the iron clad is about 10 g / L, and the clad can be efficiently dissolved with a small amount of oxalic acid aqueous solution. It was confirmed.

  Next, it was confirmed whether radioactive metal ions such as cobalt adsorbed on the ion exchange resin can be eluted with oxalic acid. Since ion exchange resins used in power plants are strongly acidic or basic ion exchange resins, the distribution coefficient of metal ions between weak acids such as oxalic acid and those ion exchange resins is systematically determined. It has not been investigated. Therefore, as a result of inventor's own experiments and examining the distribution characteristics, when the above oxalic acid aqueous solution of about 10 g / L is used, the distribution coefficient of metal ions is small from both the cation exchange resin and the anion exchange resin. I understood that. From this, it was confirmed that the adsorbed metal ions can be eluted by immersing the ion exchange resin in an aqueous oxalic acid solution of about 10 g / L.

  Based on the above knowledge, in this invention, the processing method and processing system which reduce the radiation dose of used ion exchange resin by the chemical processing by an oxalic acid are proposed. Used ion exchange resin with reduced radiation dose will be incinerated with existing incineration facilities and reduced in volume. The oxalic acid waste solution in which radioactive metal ions are dissolved decomposes oxalic acid with ozone, and the metal ions are recovered as a precipitate and solidified.

  According to the present invention, in a waste resin treatment method including a used ion exchange resin generated in a cooling water purification system of a nuclear power plant, the waste resin is immersed in an aqueous oxalic acid solution of about 10 g / L and the surface of the waste resin is immersed. By efficiently dissolving the metal clad in the oxalic acid aqueous solution and eluting the metal ions adsorbed on the waste resin into the oxalic acid aqueous solution, waste resin such as used ion exchange resin and filter sludge generated at nuclear power plants It is possible to reduce the radiation dose efficiently and perform the volume reduction process smoothly.

The process figure which shows the waste resin processing method and processing system of Example 1 of this invention. The flowchart which shows the waste resin processing method of Example 1 of this invention. The process figure which shows the waste resin processing method and processing system of Example 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a process diagram in which waste resin is immersed in oxalic acid to reduce the radiation dose and thermally decompose the resin in the waste resin treatment method and treatment system of the present invention.

  A certain amount of the waste resin 6 was extracted from the storage tank 1 in the form of a water slurry. Specifically, pure water is added to the waste resin storage tank 1 to make the waste resin 6 into a slurry state and transferred to the metering container 2, and the amount of resin is managed by the volume or weight of the metering container 2. The metering container 2 was provided with a mesh 2a, whereby excess free water accompanying the resin was separated. In this case, excess water can be further separated and removed by a filter press or the like. The quantitative container 2 that has received a certain amount of the waste resin 6 is sent to the oxalic acid immersion tank 3 by a transfer unit (not shown) such as a bucket conveyor.

  In the oxalic acid immersion tank 3, the waste resin 6 was immersed in a concentrated oxalic acid aqueous solution having an oxalic acid concentration of about 10 g / L. This was immersed for about 12 to 24 hours with stirring to dissolve the metal clad adhering to the surface of the waste resin 6 and to elute the metal ions adsorbed on the waste resin 6. Thereby, the radioactive metal ion in the waste resin 6 moved into the oxalic acid aqueous solution.

  The radiation dose of the waste resin 6 was reduced by the above immersion. The treated waste resin 9 taken out from the oxalic acid immersion layer 3 was incinerated in the existing incinerator 10 using the transport device BC. When taking out the waste resin 9, it is preferable to separate and remove the oxalic acid aqueous solution by a compression means or the like.

  On the other hand, the oxalic acid aqueous solution remaining in the oxalic acid immersion layer 3 was sent to the ozone decomposition tank 4 and gas containing ozone 8 was supplied to decompose oxalic acid. Along with this, the metal ion from which the oxalate ion, which is a counter ion, disappears is hydrolyzed. This can be recovered by the precipitate separator 5 as a hydroxide precipitate. This precipitation is solidified by existing cement solidification equipment 12. The aqueous solution remaining in the precipitation separator 5 is further processed in the low level waste liquid treatment system 11.

  FIG. 2 is a flowchart illustrating the waste resin treatment method according to the first embodiment. In Step S10, a certain amount of waste resin is taken out from the storage tank. A certain amount of waste resin taken out in S20 is immersed in an oxalic acid aqueous solution having a concentration of about 10 g / L. Next, the oxalic acid aqueous solution in which the waste resin is immersed in S30 is stirred for 12 to 24 hours. Thereby, the metal clad on the surface of the waste resin is dissolved in S40, and the metal ions adsorbed on the waste resin are dissolved in S50. Next, the waste resin is incinerated in S60, and oxalic acid is decomposed with ozone in S70. Next, the metal ion hydroxide is solidified. Of the above steps, S40 and S50 actually proceed simultaneously.

  As described above, by using the oxalic acid aqueous solution of about 10 g / L, the solubility of the iron clad is about 10 g / L, and the clad can be efficiently dissolved with a small amount of the oxalic acid aqueous solution.

  Moreover, the distribution coefficient of metal ions is small from both the cation exchange resin and the anion exchange resin, and the adsorbed metal ions are eluted by immersing the ion exchange resin in about 10 g / L oxalic acid aqueous solution. it can. Therefore, an efficient waste resin treatment method and treatment system could be realized.

  FIG. 3 is a process diagram showing Embodiment 2 of the present invention. Although the immersion operation of Example 1 was performed by a batch process, it may be performed by a continuous process of collecting overflow while continuously supplying the waste resin 6 to the immersion tank 3. In FIG. 3, a certain amount of the waste resin 6 in the waste resin storage tank 1 is supplied to the oxalic acid immersion tank 3 by the metering pump P, and is continuously processed. The overflowed waste resin is returned to the waste resin storage tank 1 again.

  By adopting this configuration, the process can be efficiently advanced even when the amount of waste resin processed is large. Other configurations are the same as those of the first embodiment.

1: Waste resin storage tank 2: Metering container 3: Oxalic acid immersion tank 4: Ozone decomposition tank 5: Precipitation separator 6: Waste resin 7: Oxalic acid 8: Ozone 9: Waste resin 10 after treatment: Incinerator 11: Low level waste liquid treatment system 12: Cement solidification equipment P: Metering pump

Claims (7)

  In a waste resin treatment method including a spent ion exchange resin generated in a cooling water purification system of a nuclear power plant, the waste resin is immersed in an aqueous oxalic acid solution of about 10 g / L to form a metal cladding on the waste resin surface. A waste resin treatment method for a nuclear power plant, wherein metal ions dissolved in an oxalic acid aqueous solution and adsorbed on the waste resin are eluted into the oxalic acid aqueous solution.   2. The method for treating a waste resin in a nuclear power plant according to claim 1, wherein the metal clad on the surface of the waste resin is dissolved in the oxalic acid aqueous solution and the metal ions adsorbed on the waste resin are eluted into the oxalic acid. A method for treating a waste resin of a nuclear power plant, wherein the ion exchange resin taken out from an aqueous solution is incinerated and oxalic acid in the aqueous oxalic acid solution is decomposed with ozone.   3. The method for treating waste resin of a nuclear power plant according to claim 1 or 2, wherein the waste resin is immersed in an aqueous oxalic acid solution of about 10 g / L and stirred for 12 to 24 hours to form a metal clad on the surface of the waste resin. A waste resin treatment method for a nuclear power plant, wherein metal ions dissolved in the oxalic acid aqueous solution and adsorbed on the waste resin are eluted into the oxalic acid aqueous solution.   4. The method for treating waste resin of a nuclear power plant according to claim 2, wherein the metal ion hydroxide remaining in the aqueous solution after the oxalic acid in the oxalic acid aqueous solution is decomposed with ozone is solidified. Waste resin treatment method for nuclear power plants. In the treatment system of waste resin including used ion exchange resin generated in the cooling water purification system of nuclear power plant,
A waste resin supply device that takes out a certain amount of waste resin from a storage tank of used ion exchange resin, an oxalic acid immersion tank that immerses a certain amount of waste resin taken out by the waste resin supply device in an aqueous oxalic acid solution, A nuclear power plant comprising a transport device for feeding waste resin after being immersed in an oxalic acid aqueous solution in an acid immersion bath to an incinerator, and an ozonolysis treatment device for decomposing the oxalic acid aqueous solution in the immersion bath with ozone. Waste resin treatment system for power plants.   The waste resin treatment system for a nuclear power plant according to claim 5, wherein the waste resin supply device has a metering container for storing a certain amount of the waste resin.   6. The nuclear power plant waste resin treatment system according to claim 5, wherein the waste resin supply device has a metering pump for supplying a certain amount of the waste resin.

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