JP7193215B2 - Method for removing radioactive cesium from radioactive cesium-containing material - Google Patents

Description

The present invention relates to a method for removing radioactive cesium from radioactive material containing material.

When radioactive cesium-contaminated waste is incinerated, radioactive cesium is concentrated in bottom ash and fly ash. If the concentration of radioactive cesium is 8000 Bq/kg or less, these incinerated ash can be landfilled at a normal controlled landfill disposal site. However, the radioactive cesium concentration in incineration ash, especially in incineration fly ash, often exceeds 8,000 Bq/kg, and due to the feelings of residents living near landfill disposal sites, even incineration ash below 8,000 Bq/kg cannot be landfilled. is also highly anticipated.

For example, most of the radioactive cesium in incineration ash is present in water-soluble forms such as cesium chloride. Therefore, there is a method of removing the cesium in the incineration ash by washing the incineration ash with water and separating the solid and liquid to transfer the radioactive cesium to the liquid layer. The radioactive cesium that has migrated to the liquid layer is further adsorbed by an adsorbent such as zeolite or Prussian blue, and removed from the liquid layer (hereinafter referred to as "conventional method 1").

Moreover, the following method is known as a method of removing radioactive cesium from incinerated ash (see Patent Document 1). In this method, (1) Inorganic calcium compound or 500 ° C. or higher is added so that the ratio of inorganic calcium compound or organic calcium compound in the mixture of incinerated ash and inorganic calcium compound or organic calcium compound is 3% by mass or more and 30% by mass. Add an organic calcium compound that generates calcium oxide in an oxidizing atmosphere, and add more than 0.5% by mass to 10% by mass or less with respect to the mass of the mixture of incinerated ash and inorganic calcium compound or organic calcium compound. and (2) a heating step of volatilizing radioactive cesium from the incineration ash after the addition step by heat-treating at 1000° C. or higher and 1200° C. or lower for 30 minutes or more and 120 minutes or less. and (3) a recovery step of recovering radioactive cesium volatilized from the incineration ash by the heating step.

A system for treating radioactive cesium-contaminated fly ash is also known (see Patent Document 2). This system includes a first column filled with a zeolite adsorbent or a silicotitanic acid adsorbent, a first pipe for inputting the transported fly ash extract to the beginning of the first column, and a ferrocyanic A second column filled with an adsorbent and a second pipe connecting the end of the first column and the beginning of the second column are provided.

JP 2014-174090 JP 2015-1447

Conventional method 1 uses a chelating agent in the washed fly ash obtained after solid-liquid separation to prevent the elution of heavy metals when radioactive cesium is removed from the incinerated fly ash to a level at which it can be disposed of in landfills by water washing or the like. is added. In order to uniformly mix the chelating agent with the washed fly ash after solid-liquid separation, it is necessary to install a new mixing tank (problem of chelating treatment).

In addition, when the radioactive cesium contained in the fly ash is extracted by washing with water, the slurry is conveyed to a device such as a filter press for solid-liquid separation. If the washed fly ash obtained after this process exceeds 8000 Bq/kg, or if the radioactivity concentration of the washed fly ash does not decrease to the target concentration level even if it is 8000 Bq/kg or less, the washed fly ash The ash is returned to the fly ash washing tank and treated by water washing or the like again. This not only complicates the operation, but also increases equipment costs (problems in the cleaning process).

In addition, radioactive cesium in the fly ash cleaning solution is removed by adsorption with adsorbents such as zeolite and Prussian blue. After adsorption treatment, radioactive cesium is disposed of as radioactive contaminated waste together with the adsorbent. It is difficult to adjust (problem of adjustment of concentration ratio).

It is also possible to store the radioactive cesium in the fly ash cleaning solution in its original state (liquid) in a closed container, etc., but from a long-term perspective, there is an unavoidable risk of leakage due to cracks or breakage of the container. Therefore, the fly ash cleaning solution is treated with an adsorbent such as zeolite to transfer the radioactive cesium to the solid phase. However, in this method, the solid phase (adsorbent) must also be discarded after the adsorption treatment, so it is difficult to say that this method is optimal from the viewpoint of volume reduction (problems in solidifying the eluent).

In view of the above problems, the present invention provides a method capable of reducing the concentration of radioactive cesium in radioactive cesium-containing materials by separating radioactive cesium from radioactive cesium-containing materials (e.g., incineration ash) and concentrating and recovering them. With the goal.

The method for removing radioactive cesium from the radioactive cesium-containing material of the present invention comprises
an extraction step of extracting radioactive cesium from a radioactive cesium-containing substance with a washing solution;
an adsorption step in which the radioactive cesium-containing cleaning solution extracted in the extraction step is passed through two or more adsorption means arranged in series to adsorb radioactive cesium to the adsorption means;
An elution step of eluting (desorbing) radioactive cesium adsorbed to the most upstream adsorption means by passing an eluent only through the most upstream adsorption means in the immediately preceding adsorption step among the adsorption means. When,
a temporary storage step of storing the radioactive cesium-containing eluent (recovered eluent) eluted from the adsorption means in the elution step in a recovered eluent tank;
Until the radioactivity concentration of the recovered eluent stored in the temporary storage step is equal to or less than a predetermined concentration, the recovered eluent is repeatedly used in the elution step, and the recovered eluent containing high-concentration radioactive cesium (radioactive cesium a repeated step (sometimes referred to as a "concentration step") to obtain an eluent with a concentrated concentration (hereinafter also referred to as a "concentrated recovered eluent");
When the radioactivity concentration of the recovered eluent containing high-concentration radioactive cesium stored in the temporary storage step exceeds a predetermined concentration, the eluent for adsorbing the recovered eluent containing high-concentration radioactive cesium to the immobilizing agent. and a immobilizing step.
It is preferable that the adsorption means has an adsorbent that is highly selective for radioactive cesium and capable of adsorption and desorption.

According to this configuration, by arranging two or more adsorption means in series, more radioactive cesium is adsorbed to the upstream adsorption means. Therefore, when eluting (desorbing) radioactive cesium from the adsorption means, only the adsorption means on the upstream side is washed for elution processing. Thereby, cleaning time can be shortened.

In addition, the method of the present invention is
It may further include an adsorption means cleaning step of cleaning the adsorption means after elution in the elution step.

In addition, the method of the present invention is
It may further include a liquid passage line switching step of switching the liquid passage line for the radioactive cesium-containing washing liquid between the adsorption means so that the adsorption means after elution in the elution step is arranged on the most downstream side.

Also, in the next adsorption step, the most upstream adsorption means is arranged at the most downstream side, and the second most upstream adsorption means in the immediately preceding adsorption step becomes the most upstream adsorption means. , the liquid permeation line is switched. As a result, the more upstream the adsorption means, the more radioactive cesium is adsorbed. treatment), the adsorption efficiency can be improved, and the time can be shortened and the elution efficiency can be increased compared to performing the elution treatment for all the adsorption means.

In addition, the method of the present invention may be configured such that the adsorption treatment (step) is performed by other adsorption means during the elution treatment (desorption treatment of radioactive cesium). Each adsorption means is connected by a liquid passage line (pipe), and a valve is provided on the liquid passage line (pipe) so as to switch the liquid passage line so that the above processing can be performed. While the elution process is being performed by one adsorption means, the adsorption process can be performed by the other adsorption means.

By using the recovered eluent (hereinafter sometimes referred to as "recovered eluent") as the eluent again through the above repeated steps, the recovered eluent temporarily stored in the recovered eluent tank can be reused as it is. The amount of radioactive waste can be reduced (the volume can be reduced) compared to disposal without use. Repeated use can increase the concentration of radioactive cesium in the recovered eluent in proportion to the number of repetitions. The number of times the eluent (recovered eluent) is used is preferably set based on the results of experiments in advance, and is preferably 2 or more and 10 or less, for example. By repeatedly using the eluent (recovered eluent), the amount of eluent used can be reduced, and the radioactive cesium concentration (concentration range) in the eluent can be arbitrarily adjusted.

According to the eluent immobilization step, the recovered eluent containing high concentration radioactive cesium (concentrated recovered eluent) is brought into contact with the immobilizing agent as it is or after neutralization treatment, and the radioactive cesium is adsorbed on the immobilizing agent. Let This makes it possible to stabilize and immobilize radioactive cesium. As the immobilizing agent, for example, zeolite, Prussian blue, or the like, which adsorbs and immobilizes cesium, is preferable. Adsorption (immobilization) to an immobilizing agent may be performed by a flow-through type method such as a column. A method of solid-liquid stirring the concentrated recovered eluent and the adsorbent with a stirrer, pump, or the like is more preferable. Adsorbing the cesium in the concentrated recovery eluate to these fixatives rather than directly adsorbing the cesium in the washing liquid after the washing process can reduce the amount of fixative used and reduce the final waste. It is possible to make it easier. When the cleaning liquid is adsorbed to zeolite as it is, alkali metals (Na, K) are also adsorbed to zeolite, so the amount of cesium adsorbed decreases (adsorption performance is low). On the other hand, in the case of the concentrated recovered eluent, cesium can be efficiently adsorbed because there are few competing alkali metals. In addition, the risk of leakage can be reduced by immobilizing liquid radioactive cesium.

Moreover, the method of the present invention may include a cleaning liquid storage step of storing the radioactive cesium-containing cleaning liquid extracted in the extraction step in a cleaning liquid tank.

In addition, the method of the present invention is a step that is carried out in advance before the next elution step. ~ n (the number of adsorption means)), the amount of radioactive cesium adsorbed by the adsorption means in the next adsorption step is calculated (estimated), and the radioactive a first calculation step of precalculating (predicting) the radioactivity concentration (Sv(n+1)) in the eluent of cesium;
By adding the radioactivity concentration (Sv(n+2)) of the recovered eluent tank and the radioactivity concentration (Sv(n+1)) of the eluent calculated in the first calculation step, after the next elution step a second calculation step of calculating the radioactivity concentration (Sv(n+2)') of the eluent in the recovered eluent tank of
In the repeating step, if the radioactivity concentration (Sv(n+2)') calculated in the second calculating step does not exceed a predetermined concentration, the elution step with the recovered eluent is repeated.
The predetermined concentration may be set differently depending on the radiation shielding structure. For example, it may be set so that the exposure dose of workers outside the shielding structure does not exceed 25 μSv/h.

In addition, when the repeating step is repeated a predetermined number of times (for example, obtained from experimental values), or when the radioactivity concentration calculated in the second calculating step exceeds a predetermined concentration, the next elution step is Use fresh eluent. Add new eluent to the eluent tank (or new recovered eluent tank). When elution treatment (process) is performed with a new eluent, the eluent is sent to a newly installed recovered eluent tank. The concentrated recovered eluent in the immediately preceding recovered eluent tank (the recovered eluent that has been repeated a predetermined number of times or the recovered eluent in which the radioactivity concentration calculated in the second calculation step has reached a predetermined concentration) is supplied to the eluent immobilization step. be done.

A space dosimeter or a radioactivity concentration meter is installed in each of the washing liquid tank (preferably in its lower part), each adsorption means (preferably its liquid passage outlet, its outlet side piping), and the collected eluent tank (preferably in its lower part). Install. Obtain the correlation between the indicated values of the air dosimeter and the radioactivity concentration meter in advance, and convert the indicated value of the air dosimeter into the radioactivity concentration.

For example, a description will be given of a repeated process when the number of adsorption means is three. Three adsorption means are arranged in series, and the adsorption means are designated as K1, K2, and K3 from the upstream side of the liquid flow, and the indicated values of the respective radioactivity concentrations are designated as Sv1, Sv2, and Sv3. In the first adsorption process, the liquid passage lines are configured so that liquids are passed through the adsorption means in the order of K1, K2, and K3 from the upstream side. A liquid feed line can be configured by automatically or manually opening or closing each gate valve installed in each line.
For example, before the m-th elution step (or before the m-th adsorption step, that is, after the (m-1)th elution step), the washing liquid tank before the m-th adsorption step (after the m-1th adsorption step) From the integrated value of the radioactivity concentration (Sv0) measured in and the radioactivity concentration (Sv1, Sv2, Sv3) measured by each adsorption means (K1, K2, K3), the radioactive cesium adsorbed by each adsorption means The amount is calculated, and the radioactivity concentration (Sv4) of the eluate after the m-th elution step is calculated. Next, the radioactivity concentration (Sv5) of the recovered eluent in the recovered eluent tank and the above-mentioned radioactivity concentration (Sv4) are added, and the radioactivity concentration ( Sv5') is calculated.

(Concentration adjustment of radioactive cesium in the eluent)
For example, a radioactivity concentration meter is installed in the washing liquid layer, the recovered eluent tank, and each adsorption means.
(1) Radioactivity concentration in washing liquid tank (washing liquid) after extraction process: A [Bq/kg]
Fluid flow rate of cleaning liquid: B [kg]
(2) Radioactivity concentration at the outlet of each adsorption means: C [Bq/kg]
(3) Radioactivity concentration of recovered eluent tank (recovered eluent): Ta [Bq/kg]
Here, the adsorption amount X of radioactive cesium per time is
X = (AC) x B [kg]
The radioactivity concentration in the collected eluate is calculated from the adsorption amount X. This is done before the mth elution step.
(4) The radioactivity concentration Tm in the recovered eluent calculated before the m-th elution step is
Tm = (E x D + X)/D
Here, the m (1 to n)-th adsorption amount of radioactive cesium is (Am−Cm)×Bm [kg], and the amount of recovered eluent in the recovered eluent tank after the m-th elution step: D [kg ] and the amount of the eluent in the recovered eluent tank before the m-th elution step (after the (m-1)th elution step): E [kg].
Next, the radioactivity concentration (Ta) in the collected eluent tank measured with a radioactivity meter and the radioactivity concentration Tm ((E × D + X) ÷ D) in the collected eluent are added, and the m-th elution step Calculate the radioactivity concentration Ts in the later collected eluent bath.
Then, the recovered eluent may be reused until the radioactivity concentration Ts in the recovered eluent tank reaches a predetermined concentration. When the radioactivity concentration Ts reaches a predetermined concentration, a new recovered eluent may be passed through the adsorption means and recovered in another container after the elution step.
By the above operation, the radioactivity concentration in the recovered eluent tank can be adjusted to the desired concentration level.

In addition, before the next elution step, the radioactivity concentration after the adsorption step of the adsorption means on the most upstream side (adsorption means used in the next elution step) and the radioactivity concentration used in the next elution step (recovered eluent tank The radioactivity concentration of the recovered eluent in the recovered eluent tank after the next elution step may be obtained by adding the radioactivity concentration of the recovered eluate (inside). The radioactivity concentration is determined based on the radioactivity concentration meter or air dosimeter installed in the adsorption means and the eluent collection tank.

The extraction step includes a washing step of washing the radioactive cesium-containing substance with a neutral to alkaline (pH 7 or higher, substantially pH 7 or higher) washing liquid in a washing container to extract radioactive cesium into the washing liquid; A solid-liquid separation step of separating the solid content from the radioactive cesium-containing washing liquid obtained in the washing step by filtering means (for example, a filter press device) may be included.

Examples of the radioactive cesium-containing material include incineration fly ash and molten fly ash. In the washing step, it is preferable to stir the radioactive cesium-containing substance with the washing liquid for a predetermined time in the washing container. The predetermined time may be determined experimentally in advance, or the state of the slurry may be determined visually or from an image captured by a camera. Solids are recovered in a solids recovery tank. Solids can be landfilled.

According to this configuration, the radioactive cesium is extracted into a neutral to alkaline washing liquid, and then the solid content (or SS content) is separated. Assuming that the amount of radioactive cesium in the radioactive cesium-containing substance before the washing step is 100%, the amount of radioactive cesium in the separated solid content is 20% or less, preferably 15% or less, more preferably 10% or less. preferable. By measuring the radioactivity concentration, the amount of radioactive cesium can be calculated. Solids are recovered in a solids recovery tank. Solids are landfilled.

Further, the extraction step may include a crushing step of pre-crushing the radioactive cesium-containing substance before the washing step, and the washing step is to wash the radioactive cesium-containing substance crushed in the crushing step with a washing solution. You may

According to this configuration, the radioactive cesium-containing substance is in the form of a solid substance with a particle size of several centimeters to several tens of centimeters or more, such as chelate-processed fly ash and cement-solidified fly ash. By crushing, radioactive cesium can be effectively extracted into the cleaning solution.

In addition, the extraction step includes a washing step of washing the radioactive cesium-containing substance with an acidic washing liquid in the washing container to extract the radioactive cesium into the washing liquid, and a solid solid from the radioactive cesium-containing washing liquid obtained in the washing step. and a neutralization step (or alkalizing step) for neutralizing (or alkalizing) the washing liquid from which the solid content has been separated in the solid-liquid separation step. . In the neutralization step (or alkalization step), for example, in a cleaning liquid tank, the cleaning liquid is measured with a pH measuring instrument, a neutralizing agent (or alkaline agent) is filled according to the measurement result, stirred and mixed, and the pH is adjusted. It is done by

According to this configuration, radioactive cesium-containing substances such as sludge incineration ash and soil are washed with an acidic washing liquid. In addition, for example, in the case of solid matter (for example, main ash) with a particle size of several cm to several tens of cm or more as the radioactive cesium-containing substance, a crushing step of crushing the radioactive cesium-containing substance in advance is performed before the washing step. It is preferred that If the adsorbent used in the adsorption process is neutral to alkaline, adsorbs cesium, and is eluted with acid, it is necessary to neutralize (or alkalinize) the washing solution after the solid content is separated. There is

Further, the extraction step includes a solid-liquid separation step of separating solids from leachate containing radioactive cesium, and a neutralization step of neutralizing the leachate from which solids have been separated in the solid-liquid separation step. may contain.

According to this configuration, after the solid content (for example, SS content) is separated from the leachate containing radioactive cesium, if the leachate is acidic, the pH is adjusted and then the adsorption step is performed. The leachate is, for example, sewage that oozes out together with rainwater from decomposed sludge and waste at a waste disposal site.

In addition, the two or more adsorption means used in the adsorption step may be neutral to alkaline to adsorb radioactive cesium and acidic to desorb radioactive cesium, and the eluent used in the elution step may be acidic, and the cleaning liquid for the adsorption means used in the step of cleaning the adsorption means may be neutral or alkaline. In another embodiment, the adsorbent of the adsorption means is acidic to adsorb radioactive cesium and is neutral to alkaline to desorb radioactive cesium, the eluent is neutral to alkaline, and the adsorption means cleaning solutions are acidic.

According to this configuration, a crown ether (for example, dibenzo-20-crown-6-ether) is preferable as the adsorbent of the adsorption means because it selectively adsorbs water-soluble cesium. Other adsorbents include, for example, zeolite, Prussian blue, ferrocyanide (nickel, cobalt, iron) granules, and the like. However, zeolite is inferior in selective adsorption because it also adsorbs sodium and potassium in addition to cesium, and cannot be used repeatedly. Prussian blue selectively adsorbs cesium, but cannot be used repeatedly. It is preferable to select an adsorbent that can switch between adsorption and desorption depending on pH fluctuations.

The cleaning step includes a chelating treatment step of adding a chelating agent to the cleaning container for cleaning and/or adding a chelating agent on a liquid feed line from the cleaning container to the filtering means. good too.
The chelating agent is preferably added in an amount of 5 to 10% by weight with respect to 100% by weight of the radioactive cesium-containing substance. The properties of the chelating agent are not particularly limited, and are exemplified by liquid or powder. It is preferred to add both a liquid chelate and a powder chelate. When adding to both the cleaning container and the liquid feed line, the amount added to the cleaning container is large, preferably 51 to 80% of the total amount added. The chelating agent added to the liquid feed line is mixed and stirred with the slurry in the pipe.

According to this configuration, the chelating agent is stirred and mixed at the same time in the washing vessel, so there is no need to install a separate mixing vessel and stirring device for mixing the chelating agent. Since the slurry to which the chelating agent has been added is subjected to solid-liquid separation, the elution of heavy metals can be suppressed without adding the chelating agent to the newly separated solid content.

Further, in the washing step, after stirring the radioactive cesium-containing substance and the washing solution for a predetermined time, the stirring is stopped, and the radioactivity concentration of the radioactive cesium-containing substance sedimented at the bottom of the washing container reaches a predetermined value (e.g., 8000 Bq/Kg ) In the following cases, after stirring again to obtain a slurry washing liquid, the slurry washing liquid is fed to the filtering means and the solid-liquid separation step is performed, and the predetermined value (for example, 8000 Bq/Kg) is exceeded. In some cases, the washing step may be repeated.

Further, in the washing step, after stirring the radioactive cesium-containing substance and the washing solution for a predetermined time, the stirring is stopped, and the radioactivity concentration of the radioactive cesium-containing substance sedimented at the bottom of the washing container reaches a predetermined value (e.g., 8000 Bq/Kg ), the cleaning conditions may be changed and the cleaning process may be performed again,
The cleaning conditions include increasing the amount of cleaning liquid, extending the stirring time, changing the stirring speed, heating and stirring the cleaning liquid, and changing the cleaning liquid (for example, neutral water, weakly alkaline water, weakly acidic water, acidic liquid). cleaning solution) may be characterized by combining one or two or more of the treatments.

An air dosimeter (Sv/h) or radioactivity concentration meter (Bq/kg) is installed inside or on the outer wall of the lower part of the cleaning vessel, and the air dosimeter or radioactivity concentration meter for the sedimented radioactive cesium-containing material is Measure the indicated value. If an air dosimeter is installed, the radioactivity concentration is converted based on the correlation between the air dose measured in advance and the radioactivity concentration. Also, the dry activity concentration of sedimented radioactive cesium-bearing material, based on conversion factors for measurements of wet material (e.g. wet incinerator ash) and dry material (e.g. dry incinerator ash) of activity concentration. is preferably calculated. If the radioactivity concentration calculated above or the indicated value of the radioactivity concentration meter is less than a predetermined value (8000 Bq/kg), the cleaning liquid is stirred again and made into a slurry to the solid-liquid separation means (filtration means) in the latter stage. Send liquid. On the other hand, if the calculated radioactivity concentration or the indicated value of the radioactivity concentration meter exceeds the predetermined value (8000Bq/kg) or if the radioactivity concentration cannot be removed to the predetermined value, solid-liquid separation of the slurry washing liquid Do not send to the means, but perform the cleaning treatment again. When performing the cleaning treatment again, it is preferable to change the cleaning conditions.

(effect)
As described above, according to the present invention, it is possible to effectively reduce the concentration of radioactive cesium in radioactive cesium-containing substances by separating radioactive cesium from radioactive cesium-containing substances (for example, incineration ash) and concentrating and collecting them. It becomes possible.

1 is a diagram showing the overall configuration of a radioactive cesium removal system according to Embodiment 1. FIG. FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining repeated processing of each step of adsorption, elution, and washing; FIG. 4 is a diagram for explaining a structure;

(Overall system configuration)
FIG. 1 is a diagram showing the overall configuration of a radioactive cesium removal system. A radioactive cesium-containing substance (eg, incineration fly ash) and cleaning water (water is used in this embodiment) are put into the cleaning container 11 and stirred by the stirring device 12 for a predetermined time (eg, 60 to 120 minutes). Mix and extract the radioactive cesium into the wash water (wash step). The compounding ratio of radioactive cesium-containing substance:washing water is 1:5-10. Washing water containing radioactive cesium is sent from the washing container 11 to the filter 15, and the solid content and water are separated by the filter 15 (solid-liquid separation step). The solid content separated by the filter 15 is sent to the solid content collection tank 16 , and the cleaning liquid containing radioactive cesium is sent to the cleaning liquid tank 17 . Solids are landfilled.

(Washing process)
Both the liquid chelate and the powder chelate are added to the washing vessel 11 in the washing step. Liquid chelates and powder chelates add 5-10% by weight to 100% by weight of the radioactive cesium-containing material. The mixing ratio of liquid chelate and powder chelate is liquid:powder=4-2:6-8 when the total amount of chelate is 10.

A space dosimeter (Sv/h) 13 is installed on the lower outer wall of the cleaning container 11 . Stirring is stopped after stirring and mixing after a predetermined time. The radioactivity concentration of the radioactive cesium-containing material that has sedimented to the bottom of the cleaning container 11 after a predetermined time has elapsed is calculated. Measure the air dosimeter indication of the sedimenting radioactive cesium-containing material. Radioactivity concentration is converted based on the correlation between air dose and radioactivity concentration measured in advance. Also, the dry activity concentration of sedimented radioactive cesium-bearing material, based on conversion factors for measurements of wet material (e.g. wet incinerator ash) and dry material (e.g. dry incinerator ash) of activity concentration. Calculate When the radioactivity concentration calculated above is 8000 Bq/kg or less, the washing liquid is stirred again and made into a slurry, and the washing liquid is fed to the filter 15 in the subsequent stage. On the other hand, when the calculated radioactivity concentration exceeds 8000 Bq/kg, the washing treatment is performed again without sending the slurry washing water to the filter 15 . In this embodiment, stirring is performed for the same time as the immediately preceding stirring time. The stirring speed is also the same. As another embodiment, the cleaning conditions may be changed. Increase the amount of cleaning liquid, extend the stirring time, change the stirring speed, heat and stir the cleaning liquid, change the cleaning liquid (for example, neutral water, weakly alkaline water, weakly acidic water, acidic cleaning liquid). , or a combination of two or more.

The washing water (neutral to alkaline) containing radioactive cesium stored in the washing liquid tank 17 is sent to the adsorption means 20 . The adsorption means 20 is composed of three columns filled with an adsorbent (crown ether adsorbent). The first column 21, the second column 22, and the third column 23 are arranged in series, and washing water is passed through each column in order to adsorb radioactive cesium on the adsorbent (first adsorption step, see FIG. 2A). ). Washing water (cesium-removed treated water) that has passed through each column is sent to the treated tank 43 and is subjected to wastewater treatment. A liquid passing line is configured to pass liquids through the washing liquid tank 17, the first column 21, the second column 22, the third column 23, and the treated tank 43 in this order.

The eluent (acidic) in the eluent tank 30 is passed through the first column 21 (first elution step, see FIG. 2B) and sent to the recovered eluent tank 40 (temporary storage step). Before the liquid passage, the liquid passage line from the first column 21 to the second column 22 is closed, and the liquid passage line L1 for sending from the first column 21 to the recovered eluent tank 40 is opened (liquid passage line switching step ). As an eluent, for example, a 0.1-2.0M hydrochloric acid solution is used. Also, nitric acid or sulfuric acid may be used instead of hydrochloric acid. The pH concentration of the eluent is set so that the pH of the collected eluent at the column outlet (on the liquid passage line L1) is less than 5. The collected eluent tank 40 is preferably shielded with a structure 52, which will be described later. It is preferable that the outer surface dose of the recovered eluent tank 40 is less than 2.5 μSv/h.

After the first elution step, the first column 21 is washed (first column washing step, see FIG. 2C). Water (or an alkaline solution) is passed through the first column 21 from the column washing liquid tank 32 and sent to the recovery tank 33 . Before washing, the liquid passage line to the eluent tank 30 and the liquid passage line L1 are closed, and the liquid passage line to the column washing liquid tank 32, the first column 21, and the recovery tank 33 is opened. Alkaline solutions instead of water include, for example, NaOH and _NaHCO3 .

(Explanation of repeating process)
After the first column washing step and before the second adsorption step, each liquid feeding line is switched. As shown in FIG. 3A, a liquid passage line is configured to pass the washing liquid tank 17, the second column 22, the third column 23, the first column 21, and the treated tank 43 in this order. Other fluid lines are closed. In the second adsorption step, washing water is passed through each column in order to adsorb radioactive cesium on the adsorbent (see FIG. 3A).

Next, each liquid passage line is switched before the second elution step. As shown in FIG. 3B, the recovered eluent is sent from the recovered eluent tank 40 to the eluent tank 30 through the liquid feed line L2. The eluent tank 30 , the second column 22 , and the recovered eluent tank 40 constitute a liquid feed line through which the recovered eluent is passed in this order. Other fluid lines are closed. In the second elution step, the recovered eluent (acidic) from the eluent tank 30 is passed through the second column 22 and sent to the recovered eluent tank 40 . Since the recovered eluent is reused, the concentration of radioactive cesium in the eluent increases in proportion to the number of times it is reused.

Next, each liquid feed line is switched before the second column washing step. As shown in FIG. 3C , a liquid passage line through which the column cleaning liquid flows is configured in the order of the column cleaning liquid tank 32 , the second column 22 , and the recovery tank 33 . Other fluid lines are closed. In the second column cleaning step, water (or alkaline solution) is passed through the second column 22 from the column cleaning liquid tank 32 and sent to the recovery tank 33 .

After the second column washing step and before the third adsorption step, each liquid feed line is switched. As shown in FIG. 4A, a liquid passage line is configured to pass liquid through the washing liquid tank 17, the third column 23, the first column 21, the second column 22, and the treated tank 43 in this order. Other fluid lines are closed. In the third adsorption step, washing water is passed through each column in order to adsorb radioactive cesium on the adsorbent (see FIG. 4A).

Next, each liquid passage line is switched before the third elution step. As shown in FIG. 4B, the recovered eluent is sent from the recovered eluent tank 40 to the eluent tank 30 through the liquid feed line L2. The eluent tank 30, the third column 23, and the recovered eluent tank 40 constitute a liquid feed line through which the recovered eluent is passed in this order. Other fluid lines are closed. In the third elution step, the recovered eluent (acidic) from the eluent tank 30 is passed through the third column 23 and sent to the recovered eluent tank 40 . Since the recovered eluent is reused, the concentration of radioactive cesium in the eluent increases in proportion to the number of times it is reused.

Next, each liquid feed line is switched before the third column washing step. As shown in FIG. 4C, the column cleaning liquid tank 32, the third column 23, and the recovery tank 33 constitute liquid passage lines through which the column cleaning liquid is passed in this order. Other fluid lines are closed. In the third column cleaning step, water (or alkaline solution) is passed through the third column 23 from the column cleaning liquid tank 32 and sent to the recovery tank 33 .

Further, when the adsorption, elution, and column washing steps are repeated, the first column 21 is arranged at the uppermost stream again, and the treatment is performed in the manner described above.

Further, as another embodiment, the number of columns of the adsorption means is not limited to the above three, and may be two, four or more. Further, the eluent tank 30 and the recovered eluent tank 40 may be separate bodies as described above, but they may be configured in the same tank.

(Cesium concentration adjustment in recovered eluent)
A method for adjusting the number of times the recovered eluent is reused and the cesium concentration in the recovered eluent will be described. In this embodiment, by predicting in advance the concentration of radioactive cesium that will be adsorbed in the next adsorption step and eluted in the elution step, it is determined whether to reuse the recovered eluate in the next elution step. That is, the cesium concentration (radioactivity concentration) is adjusted.

A space dosimeter 18 for the cleaning solution is provided at the bottom of the cleaning solution tank 17, a first space dosimeter 24 is provided at the liquid passage outlet of the first column 21, a second space dosimeter 25 is provided at the liquid passage outlet of the second column 22, and a third column. A third space dosimeter 26 is installed at the liquid passage outlet of 23, and a fourth space dosimeter 41 is installed below the recovered eluent tank. Obtain the correlation between the indicated values of the air dosimeter and the radioactivity concentration meter in advance, and convert the indicated value of the air dosimeter into the radioactivity concentration.

Before the m-th elution step (or before the m-th adsorption step), the radioactivity concentration (Sv0) calculated based on the cleaning liquid space dosimeter 18 of the cleaning liquid tank 17 before the m-th adsorption step and each column ( 21, 22, 23), the following adsorption Calculate the amount of radioactive cesium adsorbed on each column in the process. Next, from this amount of radioactive cesium, the radioactivity concentration (Sv4) in the (collected) eluent after the m-th elution step is calculated. Next, the radioactivity concentration (Sv5) calculated based on the fourth space dosimeter 41 of the recovered eluent tank 40 and the radioactivity concentration (Sv4) calculated above are added, and after the m-th elution step The radioactivity concentration (Sv5') in the recovered eluent in the recovered eluent tank 40 is calculated.

For example, before the third elution step, the radioactivity concentration (Sv0) calculated based on the cleaning liquid space dosimeter 18 in the cleaning liquid tank 17 before the third adsorption step and the respective columns (21, 22, 23) From the integrated value with the radioactivity concentration (Sv1, Sv2, Sv3) calculated based on the first, second, and third space dosimeters (24, 25, 26), the third column 23 in the next adsorption step Calculate the amount of radioactive cesium to be adsorbed. Next, from this calculated amount of radioactive cesium, the radioactivity concentration (Sv4) in the (collected) eluate after the third elution step is calculated. Next, the radioactivity concentration (Sv5) calculated based on the fourth space dosimeter 41 of the recovered eluent tank 40 and the radioactivity concentration (Sv4) calculated above are added, and after the third elution step The radioactivity concentration (Sv5') in the recovered eluate in the recovered eluent tank 40 is calculated (estimated). It is determined whether or not the calculated radioactivity concentration (Sv5') exceeds a predetermined concentration (eg, 8000 Bq/kg). If the determination result does not exceed the predetermined concentration, the recovered eluent is reused in the third elution step as well. On the other hand, if the determination result exceeds the predetermined concentration, a new eluent is used in the third elution step. The recovered eluent in the recovered eluent tank 40 thus far is supplied to the eluent solidification step while being stored in the recovered eluent tank 40 . A new recovered eluent bath is then installed.

(Eluent immobilization step)
In the eluent immobilization step, the recovered eluent containing high-concentration radioactive cesium (high-concentration recovered eluent) stored in the recovered eluent tank 40 is adsorbed to the immobilizing agent. The concentrated recovered eluent is passed through a column (eluent immobilizing means 50) containing an immobilizing agent (zeolite) to adsorb and immobilize radioactive cesium on the immobilizing agent. The column with cesium adsorbed is stored in a concentrated cesium storage tank 51 .

(Structure)
The concentrated cesium storage tank 51, the recovered eluent tank 40, and the eluent solidification means 50 are surrounded by a plurality of structures 52 to block radioactivity.

The structure 52 has a rectangular parallelepiped appearance, and has an opening 521 at its zenith for introducing fluid, and a cavity 523 that is continuous with the opening 522 . Cavity 523 is a configuration surrounded by four side walls and bottom wall 521 . A discharge portion 524 for discharging liquid is provided at the bottom of any side wall 521 . The outlet 524 leads to the cavity 523 and has a valve (not shown).

Cavity 523 contains liquid and surrounds reservoir 51 . There are no particular restrictions on the means for introducing the liquid. If the liquid is water, tap water may be added. For example, one port of a hose may be connected to a faucet and the other port of the hose may be directed toward the opening 522 or the hose may be inserted into the cavity 523 to supply water. A tank containing liquid may be connected to a pump, and the liquid may be introduced using the pump.

The liquid may be a liquid that has a function of shielding radiation, especially radiation cesium, and has a higher specific gravity than water, such as silicon oil.

When removing the structure 52, the valve of the discharge section 14 is opened to discharge the liquid. In this case, it is preferable to connect a pipe such as a hose to the discharge portion 524 to discharge the liquid to a predetermined discharge area.

The structure 52 is constructed of polyvinyl chloride, fiber reinforced plastic, or sheet steel material. The thin steel plate has a thickness of, for example, less than 3 mm, preferably 0.3 mm or more and less than 3.0 mm, more preferably 0.4 mm or more and less than 3.0 mm, and even more preferably 0.5 mm or more and less than 3.0 mm.
The structure 52 is not limited to a rectangular parallelepiped, and may be curved in plan view. In addition, the cylindrical structure of Embodiment 3 above does not have to be circular in plan view, and may be polygonal.

The structure 52 may be combined with another radiation shielding member.

(another embodiment)
Although the air dosimeter is used in the above embodiment, the present invention is not limited to this, and a radioactivity concentration meter may be used.
Moreover, in the case of a radioactive cesium-containing substance in the form of a solid substance with a particle size of several cm to several tens of cm or more, a crushing step of crushing in advance with a crushing device may be performed before the washing step.
Also, in the washing step, the radioactive cesium-containing substance may be washed with an acidic washing liquid.
In addition, a neutralization step (or alkalizing step) may be performed to neutralize (or alkali-treat) the washing liquid from which the solid content has been separated in the solid-liquid separation step.
Alternatively, the solid content may be separated from the leachate containing radioactive cesium, and the leachate from which the solid content has been separated may be neutralized.

11 Washing vessel 12 Stirrer 15 Filter 16 Solid content recovery tank 17 Washing liquid tank 21 First column 22 Second column 23 Third column 30 Eluent tank 32 Column washing liquid tank 40 Collected eluent tank 51 Concentrated cesium storage tank 52 Structure body

Claims (13)

an extraction step of extracting radioactive cesium from a radioactive cesium-containing substance with a washing solution;
an adsorption step in which the radioactive cesium-containing cleaning solution extracted in the extraction step is passed through two or more adsorption means arranged in series to adsorb radioactive cesium to the adsorption means;
an elution step of eluting the radioactive cesium adsorbed by the most upstream side adsorption means by passing the eluting liquid through only the most upstream side adsorption means in the immediately preceding adsorption step among the said adsorption means;
a temporary storage step of storing the radioactive cesium-containing eluent eluted from the adsorption means in the elution step in a recovered eluent tank;
Repeatedly using the recovered eluent in the elution step until the radioactivity concentration of the recovered eluent stored in the temporary storage step is equal to or less than a predetermined concentration, to obtain a recovered eluent containing high-concentration radioactive cesium. process and
When the radioactivity concentration of the recovered eluent containing high-concentration radioactive cesium stored in the temporary storage step exceeds a predetermined concentration, the eluent for adsorbing the recovered eluent containing high-concentration radioactive cesium to the immobilizing agent. an immobilization step;
an adsorption means cleaning step of cleaning the adsorption means after elution in the elution step;
a cleaning liquid storage step of storing the radioactive cesium-containing cleaning liquid extracted in the extraction step in a cleaning liquid tank;
A step performed in advance before the next elution step, wherein the radioactivity to be adsorbed by the adsorption means in the next adsorption step is determined based on the radioactivity concentration measured in the washing liquid tank and the radioactivity concentration measured by each adsorption means. a first calculation step of calculating the amount of cesium and preliminarily calculating the radioactivity concentration in the eluent of the radioactive cesium eluted in the next elution step;
By adding the radioactivity concentration measured in the collected eluent tank and the radioactivity concentration in the eluent calculated in the first calculation step, the elution of the collected eluent tank after the next elution step and a second calculation step of calculating the radioactivity concentration in the liquid,
In the repeating step, if the radioactivity concentration calculated in the second calculating step does not exceed a predetermined concentration, repeat the elution step with the recovered eluent.
A method for removing radioactive cesium from a material containing radioactive cesium. 2. The method according to claim 1 , further comprising a liquid feeding line switching step of switching the liquid feeding line for the radioactive cesium-containing cleaning liquid between the adsorption means so that the adsorption means after elution in the elution step is arranged on the most downstream side. described method. The extraction step includes
a cleaning step of cleaning the radioactive cesium-containing material with a neutral or alkaline cleaning liquid in the cleaning container to extract the radioactive cesium into the cleaning liquid;
2. The method according to claim 1, further comprising a solid-liquid separation step of separating solid content from the radioactive cesium-containing washing liquid obtained in the washing step by filtering means. The extraction step includes a crushing step of pre-crushing the radioactive cesium-containing material before the washing step,
4. The method according to claim 3 , wherein in the washing step, the radioactive cesium-containing material crushed in the crushing step is washed with a washing liquid. The extraction step includes
a cleaning step of cleaning the radioactive cesium-containing material with an acidic cleaning liquid in the cleaning container and extracting the radioactive cesium into the cleaning liquid;
A solid-liquid separation step of separating solids from the radioactive cesium-containing washing liquid obtained in the washing step;
2. The method according to claim 1, further comprising a neutralization step of neutralizing the cleaning liquid from which the solid content has been separated in the solid-liquid separation step. 6. The method according to claim 5 , wherein the extraction step includes a crushing step of crushing the radioactive cesium-containing material in advance before the washing step. The extraction step includes
A solid-liquid separation step of separating solids from leachate containing radioactive cesium;
2. The method according to claim 1, further comprising a neutralization step of neutralizing leachate from which solid content has been separated in said solid-liquid separation step. The two or more adsorption means used in the adsorption step are configured to adsorb radioactive cesium under neutral and alkaline conditions and desorb radioactive cesium under acidic conditions,
The eluent used in the elution step is acidic,
2. The method according to claim 1 , wherein the adsorption means cleaning liquid used in the adsorption means cleaning step is neutral or alkaline. 4. The method according to claim 3 , wherein in said washing step, washing is performed by adding a chelating agent to said washing container and/or adding a chelating agent on a liquid transfer line from said washing container to said filtering means. an extraction step of extracting radioactive cesium from a radioactive cesium-containing substance with a washing solution;
an adsorption step in which the radioactive cesium-containing cleaning solution extracted in the extraction step is passed through two or more adsorption means arranged in series to adsorb radioactive cesium to the adsorption means;
an elution step of eluting the radioactive cesium adsorbed by the most upstream side adsorption means by passing the eluting liquid through only the most upstream side adsorption means in the immediately preceding adsorption step among the said adsorption means;
a temporary storage step of storing the radioactive cesium-containing eluent eluted from the adsorption means in the elution step in a recovered eluent tank;
Repeatedly using the recovered eluent in the elution step until the radioactivity concentration of the recovered eluent stored in the temporary storage step is equal to or less than a predetermined concentration, to obtain a recovered eluent containing high-concentration radioactive cesium. process and
When the radioactivity concentration of the recovered eluent containing high-concentration radioactive cesium stored in the temporary storage step exceeds a predetermined concentration, the eluent for adsorbing the recovered eluent containing high-concentration radioactive cesium to the immobilizing agent. an immobilization step;
The extraction step includes
a cleaning step of cleaning the radioactive cesium-containing material with a neutral or alkaline cleaning liquid in the cleaning container to extract the radioactive cesium into the cleaning liquid;
a solid-liquid separation step of separating solids from the radioactive cesium-containing washing liquid obtained in the washing step by filtering means,
In the cleaning step, after stirring the radioactive cesium-containing substance and the cleaning solution for a predetermined time, the stirring is stopped, and when the radioactivity concentration of the radioactive cesium-containing substance that has settled to the bottom of the cleaning vessel is equal to or less than a predetermined value, stirring is resumed. After obtaining a slurry-like cleaning liquid, the slurry-like cleaning liquid is sent to the filtering means to perform the solid-liquid separation step, and when the predetermined value is exceeded, the cleaning step is repeated.
A method for removing radioactive cesium from a material containing radioactive cesium. The extraction step includes a crushing step of pre-crushing the radioactive cesium-containing material before the washing step,
11. The method according to claim 10 , wherein in the washing step, the radioactive cesium-containing material crushed in the crushing step is washed with a washing liquid. 11. The method according to claim 10 , wherein in said washing step, washing is performed by adding a chelating agent to said washing container and/or adding a chelating agent on a liquid transfer line from said washing container to said filtering means. In the cleaning step, after the radioactive cesium-containing substance and the cleaning solution are stirred for a predetermined time, the stirring is stopped, and when the radioactivity concentration of the radioactive cesium-containing substance sedimented at the bottom of the cleaning container exceeds a predetermined value, cleaning is performed. Change the conditions and perform the washing process again,
The cleaning conditions are characterized by a combination of one or more of the following: increasing the amount of cleaning liquid, extending the stirring time, changing the stirring speed, heating and stirring the cleaning liquid, and changing the cleaning liquid. Item 11. The method according to Item 10 .

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