JP2014173905A - Radioactive cesium elution processing method and radioactive cesium elution processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactive cesium elution processing method which allows efficient and effective elution of radioactive cesium from an object substance by reducing a precipitation amount of calcium oxalate resulting from a reaction between the object substance and an oxalic acid and a radioactive cesium elution processor.SOLUTION: The radioactive cesium elution processing method is a processing method of mixing an object substance containing calcium and radioactive cesium and an eluant containing oxalic acid which includes a mixing step S1 of mixing an elution accelerator which reduces a precipitation amount of calcium oxalate resulting from a reaction between the object substance and oxalic acid, an eluant containing oxalic acid and the object substance.

Description

  Embodiments described herein relate generally to a radioactive cesium elution processing method and a radioactive cesium elution processing apparatus.

In a nuclear power plant, if a severe accident occurs in which radioactive material is scattered outside the building, it is radioactively contaminated over a wide area. The effects of such radioactive contamination extend to sludge generated in soil and sewage treatment plants, sludge incineration ash obtained by incineration of this sludge, and incineration ash and fly ash generated in general waste incineration sites in various places. Most of the radionuclides contained in radioactive contaminants derived from severe accidents at nuclear power plants are ¹³⁴ Cs and ¹³⁷ Cs of radioactive cesium, and contaminated objects contain these nuclides. Among radioactive cesiums, particularly ¹³⁷ Cs has a half-life of 30.2 years, and is a nuclide that is feared to release relatively high-intensity radiation to the environment over a long period of time.

  Therefore, a technique for eluting radioactive cesium from a contaminated target substance is desired. So far, a technique has been proposed in which sludge incineration ash, soil, and the like are immersed in an aqueous oxalic acid solution and the radioactive cesium is eluted to the liquid phase side (see Non-Patent Document 1). By eluting the radioactive cesium from the target substance to the liquid phase side, it becomes possible to concentrate the radioactive cesium, and it is possible to greatly reduce the amount managed and treated as radioactive waste.

Kanae Matsuyama, 5 others, "Development of radiocesium elution technology from sewage sludge incineration ash", Abstracts of the 1st Environmental Radioactivity Decontamination Research Presentation, Environmental Radioactivity Decontamination Research Society, page 52

  For example, when a target substance containing calcium and radioactive cesium, such as sludge incineration ash contaminated with radioactive cesium, is mixed with an eluent containing oxalic acid and treated, the calcium component and oxalic acid component in the object react. Calcium oxalate is deposited. Since calcium oxalate adsorbs the radioactive cesium eluted in the eluent, the proportion of radioactive cesium eluted in the eluent (the elution rate of radioactive cesium) is reduced.

  The present invention provides an elution of radioactive cesium capable of efficiently and effectively eluting radioactive cesium from the target substance by reducing the amount of calcium oxalate deposited due to the reaction between the target substance and oxalic acid. It is an object of the present invention to provide a processing method and a radioactive cesium elution processing apparatus.

  In order to achieve the above object, the radioactive cesium elution treatment method according to the embodiment is a treatment method in which a target substance containing calcium and radioactive cesium and an eluent containing oxalic acid are mixed to elute the radioactive cesium from the target substance. In this case, a mixing step of mixing an elution accelerator that reduces the amount of calcium oxalate deposited due to the reaction between the target substance and oxalic acid, an eluent containing oxalic acid, and the target substance is provided.

  Further, the radioactive cesium elution processing apparatus of the embodiment is a processing apparatus for mixing a target substance containing calcium and radioactive cesium and an eluent containing oxalic acid to elute the radioactive cesium from the target substance. An elution accelerator for reducing the amount of calcium oxalate precipitated due to the reaction between the substance and oxalic acid, an cesium elution tank into which the eluent containing oxalic acid and the target substance are charged are provided.

The block diagram of the elution processing apparatus of the radioactive cesium in 1st Embodiment. The block diagram of the 1st waste liquid processing mechanism in 1st Embodiment. The flowchart of the elution processing method of radioactive cesium in 1st Embodiment. The graph which shows the elution rate of radioactive cesium by the process using a 1st eluent. The block diagram of the elution processing apparatus of the radioactive cesium in 2nd Embodiment. The flowchart of the elution processing method of the radioactive cesium in 2nd Embodiment. The graph which shows the elution rate of the radioactive cesium by the elution process of the radioactive cesium in 2nd Embodiment.

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

(First embodiment)
A first embodiment will be described with reference to FIGS. FIG. 1 is a block diagram of an elution processing apparatus for radioactive cesium in the first embodiment. FIG. 2 is a block diagram of the first waste liquid treatment mechanism in the first embodiment. FIG. 3 is a flowchart of the radioactive cesium elution processing method according to the first embodiment. FIG. 4 is a graph showing the elution rate of radioactive cesium by the treatment using the first eluent.

  In this embodiment, the target substance that elutes radioactive cesium is incinerated ash generated after incineration of sludge.

(About incineration ash)
Hereinafter, the incineration ash will be described. Incineration ash is mainly composed of SiO, Ca ₉ Al (PO ₄ ) ₇ , Ca ₁₉ Fe ₂ (PO ₄ ) ₁₄ , Fe ₂ O ₃ , Al (PO ₃ ) _3, etc., and part of radioactive cesium Is incorporated into the structure of incineration ash. A part of the components of the incineration ash dissolves in the oxalic acid aqueous solution. For example, Ca ₉ Al (PO ₄ ) ₇ , Ca ₁₉ Fe ₂ (PO ₄ ) ₁₄ , Al (PO ₃ ) _3, etc. are dissolved. When the components that have formed the structure of the incinerated ash are dissolved, radioactive cesium is also eluted into the oxalic acid aqueous solution.

  Moreover, the calcium component eluted in the oxalic acid aqueous solution reacts with the oxalic acid component according to the following formula and precipitates as calcium oxalate.

^{_{(COOH) 2 + Ca 2+ →}} Ca (COOH) 2 ↓ + 2H +
And when calcium oxalate precipitates, it adsorbs a part of radioactive cesium eluted in the oxalic acid aqueous solution.

(About the elution processing apparatus of 1st Embodiment)
Below, the structure of the elution processing apparatus 10 of 1st Embodiment is demonstrated. The arrows connecting the respective components shown in FIG. 1 indicate the moving direction of the substance. In addition, it is assumed that the components connected by the arrows are connected via a pipe, a conveyor, or the like (not shown).

  The elution processing apparatus 10 according to the first embodiment includes an incineration ash storage tank 13 that stores incineration ash, and a first eluent tank 12 that stores a first eluent. The incineration ash storage tank 13 and the first eluent tank 12 are connected to the first cesium elution tank 11. The first cesium elution tank 11 is provided with a mixer or the like for stirring the contents.

In addition, a first solid-liquid separation device 14 is connected to the first cesium elution tank 11. A first waste liquid treatment mechanism 30 and a decontaminated incineration ash treatment mechanism 50 are connected to the first solid-liquid separator 14. Further, a first measuring instrument is provided between the first solid-liquid separator 14 and the first waste liquid treatment mechanism 30 and between the first solid-liquid separator 14 and the decontaminated incineration ash treatment mechanism 50, respectively. 15 and the 2nd measuring device 16 are provided. Hereafter, each structure is demonstrated. First, the first eluent is an aqueous oxalic acid solution and an elution accelerator. An elution promoter is a substance that reduces the amount of calcium oxalate deposited due to the reaction between incinerated ash and oxalic acid, and is a solution containing hydrochloric acid or sulfuric acid. By adding an elution accelerator, the amount of calcium oxalate deposited is reduced and the elution rate of radioactive cesium is improved.

  It has been confirmed that the elution rate of radioactive cesium is improved by the addition of an elution accelerator as described in Example 1 described later. Here, it is described that the mechanism by which the elution rate of radioactive cesium is improved by the addition of an elution accelerator is estimated.

  For example, hydrochloric acid reacts with calcium oxalate to form calcium chloride and oxalic acid having higher solubility than calcium oxalate. Since the adsorbed radioactive cesium elutes when calcium oxalate reacts with hydrochloric acid, it is estimated that the total amount of radioactive cesium present in calcium oxalate decreases and the elution rate of radioactive cesium improves.

  Alternatively, hydrochloric acid is presumed to react with the calcium component before the calcium component eluted from the incinerated ash reacts with the oxalic acid component, resulting in highly soluble calcium chloride and oxalic acid. Since the amount of precipitated calcium oxalate is reduced, the total amount of radioactive cesium present in the calcium oxalate decreases, and it is estimated that the elution rate of radioactive cesium is improved.

  On the other hand, it is presumed that sulfuric acid reacts with the calcium component to become calcium sulfate before the calcium component eluted from the incineration ash reacts with the oxalic acid component. Therefore, it is estimated that the precipitation amount of calcium oxalate decreases, the total amount of radioactive cesium existing in calcium oxalate decreases, and the elution rate of radioactive cesium improves. In addition, calcium sulfate may be less likely to adsorb radioactive cesium compared to calcium oxalate.

  Alternatively, it is presumed that sulfuric acid reacts with calcium oxalate to become calcium sulfate, and adsorbed radioactive cesium elutes when calcium oxalate and sulfuric acid react. Therefore, it is estimated that the total amount of radioactive cesium present in calcium oxalate is reduced, and the elution rate of radioactive cesium is improved.

  Next, the first solid-liquid separator 14 will be described. The first solid-liquid separation device 14 is a device that separates a mixture of a liquid and a solid into a liquid phase and a solid phase, and uses, for example, means such as centrifugation, filtration, and pressure filtration. The liquid phase and the solid phase separated by the first solid-liquid separator 14 are referred to as a first liquid phase and a first solid phase, respectively. Note that the first solid phase is incinerated ash from which the liquid phase has been separated after being mixed with the first eluent. In addition, the first solid phase portion may contain a liquid, and the first liquid phase may contain some solid.

  Next, the first measuring instrument 15 and the second measuring instrument 16 will be described. The first measuring instrument 15 and the second measuring instrument 16 are radiation detectors, for example, NaI scintillation detectors. The first measuring instrument 15 and the second measuring instrument 16 respectively monitor the radiation dose of the first liquid phase or the first solid phase.

  Next, the first waste liquid treatment mechanism 30 will be described with reference to FIG. The first waste liquid treatment mechanism 30 is a mechanism for removing radioactive cesium contained in the first liquid phase. The first waste liquid treatment mechanism 30 includes a first cesium adsorption column 40 that contains a cesium adsorbent therein. The first liquid phase is introduced into the first cesium adsorption column 40 from the top, and the liquid phase that has passed through the first cesium adsorption column 40 is released from the bottom. A first decontaminated waste liquid treatment mechanism 43 is connected to the first cesium adsorption column 40. The liquid phase that has passed through the first cesium adsorption column 40 is input to the waste liquid treatment mechanism 43. The first decontaminated waste liquid treatment mechanism 43 is a mechanism for finally treating the waste liquid from which radioactive cesium has been removed. It is assumed that a UV irradiation device for decomposing oxalic acid and a device for making the waste liquid into a form that can be carried out to the outside are provided. The apparatus for making the waste liquid into a form that can be carried out to the outside is, for example, a filling machine that fills an airtight tank with the liquid.

  Although not shown, the first waste liquid treatment mechanism 30 may be provided with an adsorbent treatment mechanism. The adsorbent processing mechanism is a mechanism for making the cesium adsorbent accommodated in the first cesium adsorption column 40 into a form suitable for carrying out and storing. A dryer for drying the cesium adsorbent, a filling machine for filling the container, a solidifying device, and the like are provided.

  The container filled with the cesium adsorbent is, for example, a stainless steel container that can be hermetically sealed after being filled with the cesium adsorbent. The solidification device is, for example, a vitrification device that melts and vitrifies a cesium adsorbent, or a device that compresses and solidifies a cesium adsorbent.

  Note that the cesium adsorbent includes, for example, at least one of the group consisting of ferrocyanide, silicotitanate, and zeolite.

  Further, the adsorbent processing mechanism may be provided in the elution processing apparatus 10 of the first embodiment separately from the first waste liquid processing mechanism 30.

  Next, the decontaminated incineration ash processing mechanism 50 will be described. The decontaminated incineration ash processing mechanism 50 is a mechanism for making the incineration ash after elution processing of radioactive cesium into a form suitable for carrying out and storing. For example, it is assumed that a washing machine for washing the incinerated ash after the elution treatment, a drying machine for drying, an apparatus for solidification, a filling machine for filling containers, and the like are provided. The solidification device, the filling machine, and the container for filling are the same as those provided in the first adsorbent processing mechanism 44.

  It is assumed that the elution processing apparatus 10 of the first embodiment is configured of a material (for example, stainless steel) that is not easily corroded by the first eluent. In addition, a portion having contact with the eluent or incineration ash may be provided with a coating having high corrosion resistance.

(About the elution processing method of the first embodiment)
Hereinafter, the radioactive cesium elution processing method of this embodiment will be described. First, the mixing step S1 is performed. The mixing step S1 is a step of mixing the first eluent and the incineration ash. In the elution processing apparatus 10 of the first embodiment, the first eluent and the incinerated ash are respectively supplied from the first eluent tank 12 and the incineration ash storage tank 13 to the first cesium elution tank 11. Mix in the cesium elution tank 11. In that case, in order to promote reaction of the 1st eluent and incineration ash, it is good also as what stirs a mixture with a mixer.

  By the mixing step S1, the components of the incineration ash react with oxalic acid and dissolve in the first eluent, and radioactive cesium is also eluted in the first eluent. Moreover, a part of calcium component in incineration ash reacts with an elution promoter.

  Next, separation step S2 is performed. Separation step S2 is a step of separating the incinerated ash mixed with the first eluent into a first liquid phase and a first solid phase. In the elution processing apparatus 10 of the first embodiment, the mixture in the first cesium elution tank 11 is transported to the first solid-liquid separation apparatus 14, and the first liquid-phase separation apparatus 14 performs the first liquid phase. And the first solid phase. The first liquid phase is conveyed to the first waste liquid treatment mechanism 30, and the first solid phase is conveyed to the decontaminated incineration ash treatment mechanism 50.

  By the separation step S2, the first liquid phase mainly contains components eluted from the first eluent and incinerated ash, and radioactive cesium. On the other hand, the first solid phase mainly contains a portion of the incinerated ash that has not been eluted in the first eluent and a precipitate resulting from the calcium component.

  Next, a waste liquid treatment step S3 is performed. The waste liquid treatment step S3 is a step of recovering radioactive cesium from the first liquid phase using a cesium adsorbent.

  In the elution processing apparatus 10 of the first embodiment, this is performed by the first waste liquid processing mechanism 30. First, the first liquid phase is introduced into the first cesium adsorption column 40, and the liquid that has passed through the first cesium adsorption column 40 is processed by the first decontaminated waste liquid treatment mechanism 43. In the first liquid phase charged into the first cesium adsorption column 40, radioactive cesium is removed by adsorbing radioactive cesium to the cesium adsorbent in the process of passing through the column.

  By the waste liquid treatment step S3, radioactive cesium in the first liquid phase is removed. In the first waste liquid treatment solid-liquid separator 42, the oxalic acid component contained in the first liquid phase is decomposed by ultraviolet rays. And the 1st liquid phase from which radioactive cesium was removed and oxalic acid was decomposed | packed is filled with a container etc., for example, is conveyed to the processing plant of the waste liquid containing hydrochloric acid, a sulfuric acid, etc., and is processed. Further, the cesium adsorbent is solidified by an adsorbent treatment mechanism, or is filled in a container or the like after drying, so that it can be taken out. Then, it is transported to a radioactive material storage facility or the like and buried or stored as a radioactive pollutant.

  In parallel with the waste liquid processing step S3, the decontaminated incineration ash processing step S4 is performed. The decontaminated incineration ash processing step S4 is a step in which the first solid phase can be carried out. In the elution processing apparatus 10 according to the first embodiment, the decontamination incineration ash processing mechanism 50 is used. The first solid phase is washed and solidified, or washed and dried to fill a container or the like so that it can be taken out. And it is embed | buried as incineration ash after the elution process of the radioactive cesium, or it is used as a cement material like a general incineration ash.

Example 1
The results of performing the elution process by the elution process method of this embodiment will be described. This elution process was performed in a laboratory. The incinerated ash subjected to the elution treatment is about several tens of grams, using a glass container such as a beaker as the first cesium elution tank 11 and using a centrifuge or the like as the first solid-liquid separation device 14. is there. The concentration of oxalic acid in the first eluent is adjusted to 0.5 mol / l, and any one of 0.1 mol / l hydrochloric acid, 0.1 mol / l sulfuric acid, and 0.5 mol / l sulfuric acid is used. It is adjusted to contain one.

  FIG. 4 shows the elution rate of the incinerated ash after the treatment with the first eluent, that is, the first solid phase radioactive cesium. Further, at the left end of FIG. 4, the result of the elution rate of incinerated ash treated in the same manner using only a 0.5 mol / l oxalic acid aqueous solution is shown for comparison. The elution rate is the ratio of radioactive cesium eluted in the eluent out of the radioactive cesium contained in the object. The elution rate was calculated as follows.

  From the results of FIG. 4, it can be seen that the incineration ash treated with the first eluent has a higher elution rate than the incineration ash treated only with the oxalic acid aqueous solution. That is, the elution rate of radioactive cesium can be improved by adding an elution accelerator to the oxalic acid aqueous solution.

(Second Embodiment)
A second embodiment will be described with reference to FIGS. FIG. 5 is a block diagram of an elution processing apparatus for radioactive cesium in the second embodiment. FIG. 6 is a flowchart of a radioactive cesium elution processing method according to the second embodiment. FIG. 7 shows the elution rate of radioactive cesium by the elution process of radioactive cesium in the second embodiment. In addition, the same code | symbol is attached | subjected to the structure same as 1st Embodiment, and the overlapping description is abbreviate | omitted.

(About the elution processing apparatus of 2nd Embodiment)
The configuration of this embodiment will be described. The elution processing apparatus 9 of the second embodiment has the same configuration as the elution processing apparatus 10 of the first embodiment. Further, a configuration unique to the elution processing apparatus 9 of the second embodiment is provided between the second measuring instrument 16 and the decontaminated incineration ash processing mechanism 50. Hereinafter, a configuration unique to the elution processing apparatus 9 of the second embodiment will be described.

  The elution processing apparatus 9 of the second embodiment includes a second cesium elution tank 18 connected to the first solid-liquid separation apparatus 14 via the second measuring instrument 16. Similarly to the first cesium elution tank 11, the first cesium elution tank 18 is also provided with a mixer or the like for stirring the contents. Connected to the second cesium elution tank 18 is a second eluent tank 19 that contains the second eluent.

  In addition, a second solid-liquid separation device 20 is connected to the second cesium elution tank 18. A second waste liquid treatment mechanism 31 and a decontaminated incineration ash treatment mechanism 50 are connected to the second solid-liquid separator 20. Between the second solid-liquid separator 20 and the second waste liquid treatment mechanism 31, and between the second solid-liquid separator 20 and the decontaminated incineration ash treatment mechanism 50, the third measuring instrument 23 and A fourth measuring instrument 24 is provided.

  The second cesium elution tank 18, the second eluent tank 19, the second solid-liquid separator 20, the third measuring instrument 23, the fourth measuring instrument 24, and the second waste liquid treatment mechanism 31 are the first The first cesium elution tank 11, the first eluent tank 12, the first solid-liquid separation device 14, the first measuring instrument 15, the second measuring instrument 16, and the first waste liquid treatment mechanism 30 in the embodiment. It is the same composition as.

  In the second embodiment, the first eluent and the second eluent contained in the first eluent tank 12 and the second eluent tank 19 are the same as those in the first embodiment. It is different from the eluent. In the second embodiment, the first eluent contained in the first eluent tank 12 is an aqueous oxalic acid solution and does not contain an elution accelerator. Further, the second eluent contained in the second eluent tank 19 is an aqueous solution of an elution accelerator and does not contain an oxalic acid component. Moreover, the elution promoter in this embodiment is a solution containing nitric acid or sodium hydroxide.

  In this embodiment, the effect of improving the elution rate of radioactive cesium by adding an elution accelerator has been confirmed as described in Example 2 below. Here, it is described that the mechanism by which the elution rate of radioactive cesium is improved by the addition of an elution accelerator is estimated.

  For example, nitric acid reacts with calcium oxalate in the same manner as hydrochloric acid to form calcium nitrate and oxalic acid having high solubility, thereby presuming that calcium oxalate is dissolved. It is presumed that the amount of radioactive cesium present in calcium oxalate is reduced and the elution rate of radioactive cesium is improved by the decrease in the amount of precipitated calcium oxalate.

  Moreover, in the case of sodium hydroxide, calcium oxalate becomes sodium oxalate having high solubility, and the amount of precipitated calcium oxalate is reduced. And when calcium oxalate reacts with sodium hydroxide, the adsorbed radioactive cesium elutes, so it is estimated that the total amount of radioactive cesium present in calcium oxalate decreases and the elution rate of radioactive cesium improves Is done. Note that calcium hydroxide may be less likely to adsorb radioactive cesium than calcium oxalate.

(About the elution processing method of the second embodiment)
Hereinafter, the radioactive cesium elution processing method of this embodiment and its effect | action are demonstrated. First, the first mixing step S5 is performed. The first mixing step S5 is a step of mixing the first eluent and the incineration ash. In the elution processing apparatus 9 of the second embodiment, processing is performed in the same procedure as the mixing step S1 in the elution processing apparatus 10 of the first embodiment.

  By the first mixing step S5, the components of the incineration ash react with oxalic acid and dissolve in the first eluent, and radioactive cesium is also eluted in the first eluent. Moreover, a part of calcium component in incineration ash reacts with the oxalic acid component of the 1st eluent, and precipitates.

  Next, the first separation step S6 is performed. The first separation step S6 is a step of separating the mixture of the first eluent and the incinerated ash into a first liquid phase and a first solid phase. In the elution processing apparatus 9 of the second embodiment, processing is performed in the same procedure as the separation step S2 in the elution processing apparatus 10 of the first embodiment.

  By the first separation step S6, the first liquid phase mainly contains the first eluent, components eluted from the incineration ash, and radioactive cesium. On the other hand, the first solid phase mainly contains a portion of the incinerated ash that has not been eluted in the first eluent, calcium oxalate, and the like.

  Next, the first waste liquid treatment step S7 is performed. The first waste liquid treatment step S7 is a step of recovering radioactive cesium from the first liquid phase using a cesium adsorbent, similarly to the waste liquid treatment step S3 in the elution processing apparatus 10 of the first embodiment. In the elution processing apparatus 9 of the second embodiment, processing is performed in the same procedure as the waste liquid processing step S3 in the elution processing apparatus 10 of the first embodiment.

  In the first waste liquid treatment step S7, radioactive cesium in the first liquid phase is removed and the oxalic acid component is decomposed. And it is conveyed to the processing factory of the waste liquid with which a container etc. are filled and containing nitric acid, sodium hydroxide, etc., and processed. Further, the cesium adsorbent is in a form that can be carried out and is buried as a radioactive pollutant.

  The first solid phase is subsequently processed in the second mixing step S8. The second mixing step S8 is a step of mixing the second eluent and the first solid phase. In the elution processing apparatus 9 of the second embodiment, the second eluent and the first solid are respectively transferred from the first solid-liquid separator 14 and the second eluent tank 18 to the second cesium elution tank 18. Charge and mix.

  In the second mixing step S8, calcium oxalate in the first solid phase reacts with the elution accelerator in the second eluent, and radioactive cesium elutes in the second eluent.

  Next, the second separation step S9 is performed. The second separation step S9 is a step of separating the mixture of the second eluent and the first solid phase into the second liquid phase and the second solid phase. In the elution processing apparatus 9 of the second embodiment, the mixture in the second cesium elution tank 18 is transported to the second solid-liquid separation apparatus 20 and separated into a second liquid phase and a second solid phase. . The second solid phase in the present embodiment is incinerated ash from which the liquid phase portion has been separated after being mixed with the second eluent. The second liquid phase is conveyed to the second waste liquid treatment mechanism 31, and the second solid phase is conveyed to the decontaminated incineration ash treatment mechanism 50.

  In the second separation step S9, the second liquid phase mainly contains the second eluent, the component eluted from the first solid phase, and radioactive cesium. On the other hand, the second solid phase mainly contains a portion of the first solid phase that has not been eluted in the second eluent and a precipitate resulting from the calcium component.

  Next, a second waste liquid treatment step S10 is performed. The second waste liquid treatment step S10 is a step of recovering radioactive cesium from the second liquid phase using a cesium adsorbent.

  In the elution processing apparatus 9 of the second embodiment, the second waste liquid processing mechanism 31 performs processing in the same procedure as the waste liquid processing step S7. By the second waste liquid treatment step S10, radioactive cesium in the second liquid phase is removed. And it fills with a container etc., is conveyed to the processing factory of the waste liquid containing nitric acid, sodium hydroxide, etc., and is processed. Further, the cesium adsorbent is in a form that can be carried out and is buried as a radioactive pollutant.

  Next, decontaminated incineration ash processing step S11 is performed. The decontaminated incineration ash processing step S11 is a step in which the second solid phase can be carried out. The decontaminated incineration ash processing mechanism 50 performs the same procedure as the decontaminated incineration ash processing step S4 of the first embodiment.

(Example 2)
The results of performing the elution process by the elution process method of this embodiment will be described. The elution process was performed in the laboratory as in Example 1.

  First Eluent The concentration of oxalic acid in the first eluent is adjusted to 0.5 mol / l. The elution accelerator of the second eluent is adjusted to be a 1 mol / l sodium hydroxide aqueous solution or a 1 mol / l sulfuric acid aqueous solution.

  FIG. 7 shows the elution rate of the incinerated ash after the treatment with the first eluent and the second eluent, that is, the radioactive cesium in the second solid phase. For comparison, the left end of FIG. 7 shows the result of the elution rate of incinerated ash obtained by treating both the first eluent and the second eluent as 0.5 mol / l oxalic acid aqueous solution. The elution rate was calculated as follows.

  From the results of FIG. 7, it can be seen that the incineration ash treated with oxalic acid and then treated with the second eluent has a higher elution rate than the incinerated ash treated twice with the oxalic acid aqueous solution. In other words, the elution rate of radioactive cesium can be improved by treating with oxalic acid and then treating with an elution accelerator.

  Therefore, radioactive cesium can be effectively eluted by performing the elution processing method and the elution processing of the first embodiment and the second embodiment.

  In addition, more radioactive cesium can be eluted from the incineration ash by one cycle of the elution process, and the number of elution processes repeated until the target elution rate is achieved can be reduced. Therefore, in this embodiment, it is possible to elute radioactive cesium from incineration ash more efficiently.

  In the present embodiment, a part of the component contained in the first eluent is oxalic acid, which can be finally decomposed into carbon dioxide and water, so that there is little burden on the environment.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. Moreover, it is also possible to combine each embodiment. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  For example, in the first embodiment and the second embodiment, the target substance is sludge incineration ash, but it may be incineration ash generated when other than sludge is incinerated, soil, or the like.

Moreover, in each embodiment, although the density | concentration of each component contained in the eluent was described, these are examples and can be changed suitably.

  Moreover, it is considered that hydrochloric acid and sulfuric acid, which are elution accelerators in the first embodiment, have an action of reacting with calcium oxalate to improve the elution rate of radioactive cesium as described in the first embodiment. . Therefore, even if hydrochloric acid and sulfuric acid are used as the elution promoter in the second embodiment, it is estimated that the elution rate is improved.

  Moreover, the elution promoter in 2nd Embodiment is good also as what uses at least 2 sort (s) among hydrochloric acid, a sulfuric acid, and nitric acid. Even in that case, it is estimated that the elution rate is improved.

  In the first embodiment, the first eluent is a mixture of an oxalic acid aqueous solution and an elution accelerator, but the oxalic acid aqueous solution and the elution accelerator are separately added to the first cesium elution tank 11. May be. It mixes in the 1st cesium elution tank 11, As a result, there exists an effect similar to the 1st eluent in 1st Embodiment.

  Further, depending on the composition of the target substance, most or all of the incineration ash may be dissolved in the eluent during the elution process. Even in that case, the radioactive cesium eluted to the liquid phase side can be concentrated, and the amount managed and treated as radioactive waste can be greatly reduced.

  In addition, when all of the target substance is completely dissolved in the eluent, there is no solid phase portion, so it is necessary to perform solid-liquid separation with the first solid-liquid separator 14 or the second solid-liquid separator 20. Will disappear.

  In addition, when all of the incineration ash is completely dissolved in the eluent, it is possible to make all the dissolved components into a solid phase by neutralizing the eluent with sodium hydroxide or the like. It is possible to make incinerated ash after decontamination.

DESCRIPTION OF SYMBOLS 9 ... Elution processing apparatus 10 of 2nd Embodiment ... Elution processing apparatus 11 of 1st Embodiment ... 1st cesium elution tank 12 ... 1st Eluent tank 13... Incinerated ash storage tank 14... First solid-liquid separation device 15... First measuring instrument 16. 2nd cesium elution tank 19 2nd eluent tank 20 2nd solid-liquid separator 23 3rd measuring instrument 24 .. Fourth instrument 30... First waste liquid treatment mechanism 31... Second waste liquid treatment mechanism 40... First cesium adsorption column 43. 1 decontaminated waste liquid processing mechanism 50... Decontaminated incineration ash processing mechanism S1... Mixing step S2... Separation step S3... Waste liquid processing step S4. .. Decontaminated incineration ash treatment step S5... First mixing step S6... Second separation step S7... First waste liquid treatment step S8. 2 mixing step S9... Second separation step S10... Second waste liquid treatment step S11... Decontaminated incineration ash treatment step

Claims (10)

A processing method of mixing a target substance containing calcium and radioactive cesium and an eluent containing oxalic acid to elute the radioactive cesium from the target substance,
Elution of radioactive cesium comprising a mixing step of mixing an elution accelerator for reducing the amount of calcium oxalate precipitated due to the reaction between the target substance and the oxalic acid, an eluent containing the oxalic acid, and the target substance Processing method. The mixing step includes a first mixing step of mixing the eluent containing the oxalic acid and the target substance;
A second mixing step of mixing the target substance separated from the liquid phase after being mixed with the eluent containing the oxalic acid and the elution accelerator;
The elution processing method of radioactive cesium of Claim 1 provided with these.   3. The radioactive cesium elution treatment method according to claim 1, wherein the elution promoter is a solution containing at least one substance selected from hydrochloric acid and sulfuric acid.   The method for elution treatment of radioactive cesium according to claim 2, wherein the elution accelerator is a solution containing at least one substance selected from sodium hydroxide or nitric acid. A separation step of separating a liquid phase from the target substance mixed with the eluent containing the oxalic acid and the elution accelerator;
A waste liquid treatment step of adding a cesium adsorbent to the liquid phase and recovering a solid phase from the mixture of the liquid phase and the cesium adsorbent;
The elution processing method of radioactive cesium as described in any one of Claims 1 thru | or 4 provided with these. A processing apparatus for mixing a target substance containing calcium and radioactive cesium and an eluent containing oxalic acid to elute the radioactive cesium from the target substance,
A cesium elution tank into which an elution accelerator that reduces the amount of calcium oxalate precipitated due to the reaction between the target substance and the oxalic acid, an eluent containing the oxalic acid, and the target substance;
A radioactive cesium elution treatment apparatus comprising: A processing apparatus for mixing a target substance containing calcium and radioactive cesium and an eluent containing oxalic acid to elute the radioactive cesium from the target substance,
A first cesium elution tank for mixing the eluent containing the oxalic acid and the target substance;
A second cesium elution tank for mixing the target substance separated from the liquid phase after being mixed with the eluent containing the oxalic acid and the elution promoter;
A first solid-liquid separation device for separating a liquid phase from the target substance mixed with an eluent containing the oxalic acid;
A radioactive cesium elution treatment apparatus comprising:   8. The radioactive cesium elution apparatus according to claim 6, wherein the elution promoter is a solution containing at least one substance selected from hydrochloric acid and sulfuric acid.   8. The radioactive cesium elution apparatus according to claim 7, wherein the elution promoter is a solution containing at least one substance selected from nitric acid and sodium hydroxide. A solid-liquid separation device for separating a liquid phase from the target substance mixed with the eluent containing the oxalic acid and the elution accelerator;
A cesium adsorption column in which the cesium adsorbent is housed and the liquid phase is charged;
The elution processing apparatus of radioactive cesium as described in any one of Claims 6 thru | or 9 provided with these.

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