JP5794932B2 - Removal method of radioactive material in soil - Google Patents

Description

  The present invention relates to a method for removing soil-containing radioactive substances.

For example, assuming that a large amount of radioactive material is released from a nuclear power plant, spent nuclear fuel reprocessing plant, nuclear fuel processing facility, or other nuclear fuel handling facility, the radioactive material is released. Material must be removed quickly and efficiently enough. In particular, when radioactive cesium, strontium, etc., which have a relatively long half-life, are scattered over a wide range, the amount of removal objects such as soil in the scattering area also becomes enormous.
However, even with this soil as an example, a method that can quickly and efficiently remove radioactive materials contained in the soil and that can treat the soil in a large amount at a low cost has not yet been established.
By the way, radioactive cesium, strontium and the like are mainly cationized and taken into the soil. On the other hand, the silicate compound constituting the soil has an anion portion that is negatively charged by replacing silicon with aluminum. Therefore, radioactive cesium, strontium, etc. that are cationized and incorporated into the soil are chemically strongly adsorbed by certain soil minerals (silicate compounds), for example, adsorbed on the interlayer of layered silicate minerals. Cesium ions can hardly be separated by washing with water.
Conventionally, a method of eluting cesium contained in soil with carboxylic acid is known (for example, see Patent Document 1).

JP-A-6-51096

However, silicate minerals constituting general soil are composed of a plurality of different types depending on the structure of the anion portion, and the ratio of each silicate mineral mixed in the soil is also varied. In other words, since the adsorption capacity of radioactive materials in the soil differs depending on the type and proportion of silicate minerals that make up the soil, elution of radioactive materials with carboxylic acid is effective for soil in one region. Even if it exists, the elution by the carboxylic acid concerned with the soil in other areas is not always effective as well.
It is also possible to analyze the components of the soil from which radioactive substances are to be removed for each region, identify the type and proportion of the silicate minerals that make up, and find and use carboxylic acids that are effective for removal. However, it is not suitable for a method for removing soil-containing radioactive materials, which requires a large amount of soil to be processed quickly and efficiently.

  Then, the subject of this invention is providing the removal method of the soil containing radioactive substance which can process a lot of soil quickly and efficiently.

The soil-containing radioactive material removal method that solves the above problems includes a pulverization step of pulverizing the soil so that the silicate mineral layer of the silicate mineral contained in the soil breaks, and the pulverized soil in the pulverization step. And a contact step of bringing a cleaning liquid of a radioactive substance into contact.

  According to the method for removing a soil-containing radioactive substance of the present invention, a large amount of soil can be treated quickly and efficiently.

It is composition explanatory drawing of the removal apparatus which enforces the removal method of the soil content radioactive substance concerning the embodiment of the present invention. It is a flowchart for demonstrating the removal method of the soil containing radioactive substance which concerns on embodiment of this invention. (A) is the conceptual diagram which showed typically the soil containing radioactive cesium adsorbed | sucked to the silicate mineral of soil. (B) is the conceptual diagram which showed the mode at the time of making the aqueous solution of the ammonium salt as a chemical | medical solution contact the grind | pulverized soil. (C) is the conceptual diagram which showed the mode at the time of making the aqueous solution of the potassium salt as a chemical | medical solution contact the grind | pulverized soil.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
The removal method of the soil-containing radioactive substance of the present invention and the removal apparatus for carrying out this removal method are as follows: a radioactive substance cleaning liquid (radioactive substance elution chemical solution; hereinafter simply referred to as “chemical solution”) Main feature is contact.
In the present embodiment, the removal device and a separation method in soil containing radioactive cesium ⁽¹³⁴ Cs, ¹³⁷ Cs) by way of example, first, after the described removal apparatus for implementing the method of removing soil containing radioactive cesium present invention, A method for removing the soil-containing radioactive material will be described.

(Soil-containing radioactive cesium removal equipment)
As shown in FIG. 1, a removal device 10 that performs the removal method according to the present embodiment includes a pulverizer 1 that pulverizes soil S containing radioactive cesium, a classification device 2 that classifies pulverized soil S, and classification. The soil S and the chemical solution R, which are mixed and stirred to wash the soil S with the chemical solution R and elute the radioactive cesium into the chemical solution R, and the soil S and the chemical solution R extracted from the cleaning device 3 A dehydrator 6 that separates the chemical solution R from the slurry mixture, a collection device 5 that receives the chemical solution R separated by the dehydrator 6 and collects radioactive cesium in the chemical solution R, and a cleaning device 3 And a gas purification device 4 for receiving the radioactive cesium contained in the vapor V and receiving the vapor V generated in the above. In addition, about the chemical | medical solution R, it demonstrates concretely later with the removal method which concerns on this embodiment.

The crusher 1 is configured to crush silicate minerals in the soil S. Although the crushing apparatus 1 in this embodiment assumes the rotor double blade type biaxial crusher provided with the rotary crushing blades 1a and 1b, as the crushing apparatus 1, it is not limited to this, For example, A ball mill, a hammer mill, a press crusher, etc. can also be used.
In addition, although the dry-type thing is assumed as the grinding | pulverization apparatus 1 in this embodiment, a wet-type thing can be used so that it may demonstrate in detail later.

  In the present embodiment, it is assumed that the pulverization of the soil S in the pulverization apparatus 1 is performed only once, but the soil S can be repeatedly applied to the pulverization apparatus 1 and pulverized twice or more. By pulverizing twice or more, the silicate mineral in the soil becomes finer, and the radioactive cesium can be more efficiently removed from the soil S in the cleaning step (see FIG. 2) described later. it can.

The classifier 2 classifies the soil S pulverized by the pulverizer 1. Incidentally, the classification device (sieving shaker) 2 in the present embodiment has a sieve 2a having an opening of 2000 μm, a sieve 2b having an opening of 1180 μm, a sieve 2c having an opening of 300 μm, and a mesh from the top to the bottom. A sieve 2d having an opening of 75 μm is provided in this order.
And in the removal apparatus 10 in this embodiment, it supplies to the washing | cleaning apparatus 3 mentioned later, and wash | cleans the soil S with a particle diameter of 75 micrometers or less obtained under the sieving of the sieve 2d.

  The classifier 2 is not limited to such a sieve shaker, and for example, a dry classifier such as a dry cyclone, a centrifugal classifier, or an inertia classifier can be used. Moreover, as the classifier 2, wet classifiers, such as a liquid cyclone and a wet vibration sieving machine, can also be used, for example.

The cleaning device 3 mixes and agitates the soil S composed of fine particles having a particle diameter of 75 μm or less supplied from the classification device 2 and the chemical solution R stored in the chemical solution tank 9, thereby changing the soil S to the chemical solution R. It is configured to elute radioactive cesium.
Such a cleaning device 3 has a hopper H that receives the soil S supplied from the classification device 2, a soil S that is received via the hopper H, and a storage tank that stores the chemical solution R supplied from the chemical solution tank 9. 3a, the stirring device 3c for mixing and stirring the soil S and the chemical solution R in the storage tank 3a, and the temperature of the mixture of the soil S and the chemical solution R in the storage tank 3a to a predetermined temperature (mixing stirring temperature described later) And a jacket tank 3b in which a heat medium circulation pipe (not shown) to be set and an electric heater are arranged.

  The dehydrating device 6 receives a slurry-like mixture of the soil S extracted from the vicinity of the bottom of the storage tank 3a of the cleaning device 3 through the predetermined pipe 20 and the chemical solution R containing radioactive cesium, from the soil S. The chemical solution R containing radioactive cesium is separated. The dehydrating device 6 in this embodiment is assumed to be a screw press type, but is not limited to this, and other dehydrating devices such as a rotary filter press type can also be used. In addition, the code | symbol F is a feeder which is provided in the middle of the piping 20 and conveys the slurry-like mixture of the soil S and the chemical | medical solution R in FIG.

The collection device 5 collects radioactive cesium in the chemical solution R by passing the chemical solution R separated from the soil S by the dehydrating device 6. The collection device 5 is not particularly limited as long as it can collect radioactive cesium contained in the chemical solution R. For example, a radioactive cesium adsorption device, a radioactive cesium coagulation precipitation device, a radioactive cesium membrane separation device, and the like. Can be mentioned.
And the collection apparatus 5 in this embodiment returns the chemical | medical solution R after collecting radioactive cesium to the said chemical | medical solution tank 9. FIG. Incidentally, the chemical solution R returned from the collection device 5 to the chemical solution tank 9 is mixed with the chemical solution Rn newly added to the chemical solution tank 9 and supplied again to the storage tank 3a of the cleaning device 3 and the soil S. It will be reused for mixing and stirring.

The gas purification device 4 is included in the steam V by causing the steam V generated by heating the mixture of the soil S and the chemical R in the storage tank 3a of the cleaning device 3 to be heated in the jacket tank 3b. It removes radioactive cesium and purifies the vapor V.
The gas purification device 4 includes a filler 4a such as Raschig ring provided in the purification tower 4b, a chemical R stored in the bottom of the purification tower 4b, and the chemical R pumped up by a pump P. A spray nozzle 4c for spraying at the top. Further, a pipe 22 is branched through a three-way valve 4d in the middle of the pipe 21 that pumps the chemical solution R toward the top of the purification tower 4b by the pump P. The pipe 22 joins a pipe 23 that connects the dehydrating device 6 and the collecting device 5.

  Further, in this gas purification device 4, when the concentration of radioactive cesium in the chemical liquid R stored at the bottom of the purification tower 4b increases, the chemical liquid R stored at the bottom of the purification tower 4b passes through the three-way valve 4d and the pipe 22. The radioactive cesium contained in the chemical solution R is removed by flowing through the collection device 5. Incidentally, a new chemical solution R is replenished to the bottom of the purification tower 4b via a pipe (not shown) so that the chemical solution R is sufficiently stored even if the chemical solution R is extracted to the collection device 5 side. It has become.

(Removal method of soil-containing radioactive cesium)
Next, a method removing the soil containing radioactive cesium ⁽¹³⁴ Cs, ¹³⁷ Cs).
In the removal method according to the present embodiment, the chemical solution R is brought into contact with the pulverizing step of pulverizing the soil S so that the silicate mineral contained in the soil S is crushed, and the soil S pulverized in the pulverizing step. And a contacting step.

FIG. 2 is a flowchart for explaining a method for removing a soil-containing radioactive substance (radiocesium) according to an embodiment of the present invention.
As shown in FIG. 2, in the removal method according to the present embodiment, the soil S (see FIG. 1) is first collected (step S1).
Next, the collected soil S is pulverized by being supplied to the pulverizing apparatus 1 (see FIG. 1) (the pulverizing step of step S2). In this crushing step, as described above, the silicate mineral of the soil S is crushed. And in this embodiment, it is desirable that many particles having a particle diameter of 75 μm or less, which will be described later, are formed in the soil S by crushing the silicate mineral in this crushing step. Incidentally, the “particle diameter of 75 μm or less” in the present invention refers to the range of the particle diameter of the soil S that has passed through a sieve having an opening of 75 μm according to JIS Z 8801 (ISO 3310).

Next, the soil S pulverized by the pulverizer 1 (see FIG. 1) is supplied to the classifier 2 (see FIG. 1) and classified (classifying step of step S3). This classification step in step S3 corresponds to the “fine-grain classification step” in the claims. And the particle | grains of the soil S exceeding 2000 micrometers of particle diameter remain on the sieve 2a (refer FIG. 1) of the classification apparatus 2, and the soil exceeding the particle diameter of 1180 micrometers on the sieve 2b (refer FIG. 1) of the classification apparatus 2 S particles remain, and on the sieve 2c (see FIG. 1) of the classification device 2, particles of soil S having a particle diameter exceeding 300 μm remain, and on the sieve 2d (see FIG. 1) of the classification device 2, the particle diameter Particles of soil S exceeding 75 μm will remain.
As described above, the classifying device 2 supplies the particles of the soil S having a particle diameter of 75 μm or less obtained under the sieve 2d to the hopper H of the cleaning device 3 (see FIG. 1).

Next, in step S4, the mixing and stirring of the soil S and the chemical solution R (see FIG. 1) is performed in the cleaning device 3 (contact process in step S4).
The said chemical | medical solution R is chosen from the chemical | medical agent which can elute the radioactive cesium contained in the soil S, more specifically the radioactive cesium carry | supported by the soil S physically or chemically. Among them, a desirable chemical solution R is a drug capable of eluting radioactive cesium ions bound to the charged group of the silicate mineral constituting the soil S, and is a counter ion (metal) that binds to the charged group of the silicate mineral. Ions, hydrogen ions). Examples of such a chemical solution R include aqueous solutions of salts such as potassium salts, sodium salts, ammonium salts, and magnesium salts, and aqueous solutions of acids such as oxalic acid. In particular, an aqueous salt solution and an aqueous weak acid solution are desirable because they are less corrosive to the removing device (see FIG. 1).

  The concentration of the solute in the chemical solution R (aqueous solution) can be appropriately set according to the target amount of radioactive cesium separated from the soil S, the solubility of the solute in water, etc., but is set to 0.1 mol / L or less. It is desirable to set it to 0.001 mol / L or more and 0.1 mol / L or less.

The mixing ratio of the soil S and the chemical solution R in step S4 is a solid-liquid ratio (soil volume / chemical solution volume), and is preferably 1/30 to 1/10.
The mixing and stirring temperature of the soil S and the chemical solution R in step S4 only needs to be lower than the boiling point of the chemical solution R, and when performing step S4 under atmospheric pressure, an increase in boiling point is expected according to the solute concentration. If an upper limit is set, 100 degrees C or less is desirable and about 15 to 100 degreeC is still more desirable. More desirably, the temperature is about 30 ° C to 80 ° C. The mixing and stirring temperature in step S4 in this embodiment is controlled and set by the jacket tank 3b shown in FIG.
By performing such a contact process, the radioactive cesium contained in the pulverized soil S is eluted in the chemical solution R as will be described in detail later.

  Next, as shown in FIG. 1, the slurry-like mixture of the soil S and the chemical solution R extracted from the vicinity of the bottom of the storage tank 3 a of the cleaning device 3 through the pipe 20 is mixed with the soil S and the radioactive material by the dehydrator 6. Separated into the chemical solution R containing cesium (the separation step in step S5 shown in FIG. 2).

  Next, as described above, the chemical solution R containing radioactive cesium separated by the dehydration device 6 is sent to the collection device 5 (see FIG. 1). And the radioactive cesium Cs contained in the chemical | medical solution R is collected by the collection apparatus at the collection process of step S6 (collection process of step S6). Next, the chemical solution R from which the radioactive cesium has been removed by the collection device 5 is returned to the chemical solution tank 9 again and reused (step S7), and then returned to step S4 and used for the contact process.

  And the soil S isolate | separated from the chemical | medical solution R with the spin-drying | dehydration apparatus 6 (refer FIG. 1) is backfilled to the collection place of the soil S of step S1 (step S8), and the process of the removal method which concerns on this embodiment Ends.

Next, the effect of the soil-containing radioactive cesium removal method according to this embodiment will be described.
As described above, radioactive cesium released into the atmosphere due to an unexpected accident at a nuclear fuel handling facility is carried by the wind and descends to the ground due to rainfall or the like. And the radioactive cesium which fell to the earth surface exists in the soil S mainly as a monovalent cation (Cs ^<+> ).

  The radioactive cesium in the soil S is chemically strongly adsorbed by the silicate mineral. FIG. 3A is a conceptual diagram schematically showing soil-containing radioactive cesium adsorbed on the silicate mineral of the soil. FIG.3 (b) is the conceptual diagram which showed the mode at the time of making the aqueous solution of the ammonium salt as a chemical | medical solution contact the ground soil. FIG.3 (c) is the conceptual diagram which showed the mode at the time of making the aqueous solution of the potassium salt as a chemical | medical solution contact the ground soil. In FIGS. 3A to 3C, the description of the charged group (anion portion) of the silicate mineral layer is omitted.

As shown in FIG. 3A, radioactive cesium ions Cs ⁺ in the soil S (hereinafter simply referred to as “radiocesium Cs ⁺ ”) are charged groups (for example, silicate mineral layer L in the soil S). (The same is true in FIGS. 3B and 3C). Incidentally, although not shown, there is a radioactive cesium Cs ⁺ that is not chemically adsorbed in the soil S in this way. And this radioactive cesium which is not chemically adsorbed (illustration omitted) may be separated from soil S by water washing.

However, radioactive cesium Cs ⁺ chemically adsorbed on a charged group (not shown) of the silicate mineral layer L (for example, radioactive cesium Cs ⁺ adsorbed on a charged portion present at a site called a freid edge site) ) Enters three-dimensionally between the layers of the silicate mineral layer L and can hardly be separated by washing with water. Moreover, as described above, the method of separating radioactive cesium in soil with carboxylic acid (see, for example, Patent Document 1) is not effective for various soils S containing a wide variety of silicate minerals.

On the other hand, in the soil-containing radioactive cesium removal method according to the present embodiment, the soil S is pulverized (the pulverization step of step S2 in FIG. 2). Thus, as shown in FIG. 3B or FIG. 3C, the silicate mineral layer L of the soil S is broken by the silica bond (≡Si—O—Si≡) indicated by reference numeral 8. Arise. In particular, in the pulverization step (step S2 in FIG. 2), the fracture 8 is reliably formed by pulverizing the soil S so that particles of the soil S having a particle diameter of 75 μm or less increase. As a result, a fixed site in which radioactive cesium Cs ⁺ is bonded to a charged group (not shown) in the silicate mineral layer L of the soil S is exposed. Further, the formation of the fracture 8 in the silicate mineral layer L weakens the ability of the silicate mineral layer L to adsorb radioactive cesium Cs ⁺ . This is because the silica bond (≡Si—O—Si≡) is partially cut by forming the fracture 8 of the silicate mineral layer L by the pulverization process of step S2, and the silicate mineral layer L This is thought to be due to the weakening of the charge of the anion portion.

When the aqueous solution of ammonium salt as the chemical solution R comes into contact with the ground soil S in this way, as shown in FIG. 3B, the radioactive cesium Cs ⁺ adsorbed on the silicate mineral layer L is converted to ammonium. It is ion-exchanged with ions NH ₄ ⁺ and is eluted from the silicate mineral layer L into the chemical solution R. Further, when an aqueous solution of potassium salt as the chemical solution R comes into contact with the crushed soil S, as shown in FIG. 3C, the radioactive cesium Cs ⁺ adsorbed on the silicate mineral layer L is converted to potassium ion K ^+. And is eluted from the silicate mineral layer L into the chemical solution R.

Therefore, according to the method for removing soil-containing radioactive cesium according to the present embodiment, the radioactive cesium Cs ⁺ contained in the soil S is efficiently separated by having a contact step of bringing the chemical solution R into contact with the crushed soil S. be able to.

In addition, as described above, the method for removing soil-containing radioactive cesium according to the present embodiment is different in that the adsorption ability of radioactive cesium Cs ⁺ in the soil S varies depending on the type and ratio of the silicate mineral constituting the soil S. According to the present invention, the silicate mineral in the soil S is crushed by the pulverization process of the soil S (step S2 in FIG. 2), and the fixing site of the radioactive cesium Cs ⁺ is exposed. Compared with the method of separating from (for example, refer to Patent Document 1), the method can be applied to soil S having various adsorption capacities.

In addition, according to the method for removing soil-containing radioactive cesium according to the present embodiment, the radioactive cesium Cs ⁺ can be separated from the soil S by bringing the chemical solution R into contact with the pulverized soil S. Can be processed in large quantities.

  Further, according to the method for removing soil-containing radioactive cesium according to this embodiment, the chemical solution R is selected from the group consisting of an aqueous salt solution and a weak acid, preferably the group consisting of an aqueous salt solution. The corrosion durability of the removing device (see FIG. 1) to be improved can be improved.

  Moreover, according to the removal method of the soil containing radioactive cesium which concerns on this embodiment, since the chemical | medical solution R is circulated and reused, the cost required for isolation | separation of a radioactive cesium can be reduced.

Moreover, according to the removal method of the soil containing radioactive cesium which concerns on this embodiment, since the soil S after isolate | separating radioactive cesium Cs ^<+> is refilled in the place which extract | collected the original soil S, this removal method is implemented. It is possible to prevent regional environmental changes.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It can implement with a various form.
In the said embodiment, although the removal method of soil containing radioactive cesium was demonstrated, this invention removes other soil containing radioactive substances, such as radioactive strontium, radioactive barium, radioactive cobalt, uranium, plutonium, and thorium contained in the soil S. Can be applied to. Further, the present invention does not exclude a method for removing soil-containing radioactive iodine having a relatively short half-life.

  Moreover, in the said embodiment, soil S after passing through a grinding | pulverization process (refer step S2 of FIG. 2) and a classification process (refer step S3 of FIG. 2. It corresponds to the "fine-grain classification process" said to a claim). However, the present invention classifies the soil S after collecting the soil S in step S1 shown in FIG. 2. To obtain particles of soil S having a particle diameter exceeding 75 μm (this classification step corresponds to the “coarse particle classification step” in the claims), and soil S composed of particles having a particle diameter exceeding 75 μm (for example, By pulverizing at least one of the soil S obtained on the sieve 2d, the sieve 2c, the sieve 2b, and the sieve 2a in FIG. Has contact process to contact with R It is also possible to adopt a configuration that.

  In this configuration, the soil S after the pulverization step is further classified (classification step), and the soil S consisting only of particles having a particle diameter of 75 μm or less is subjected to the contact step with the chemical solution R. Alternatively, the soil S containing particles having a particle size of 75 μm or less in the particles having a particle size of 75 μm or less without being classified may be subjected to the contact step with the chemical solution R.

Moreover, in the said embodiment, although the dry-type thing is assumed as the grinding | pulverization apparatus 1 used at the grinding | pulverization process of step S2 shown in FIG. 2, this invention can also use a wet-type grinding | pulverization apparatus. At this time, the liquid for wetting the soil S at the time of pulverization may be water, but is preferably the chemical solution R. By crushing the soil S with such a chemical solution R while being moistened, dust can be prevented from being generated, and more efficiently included in the soil S in the contact process with the chemical solution R shown in step S4 of FIG. The radioactive cesium produced can be eluted in the chemical solution R.
In the configuration using such a wet pulverizer, the above-described wet classifier is used in the classification step of step S3 in FIG.

  Moreover, in the removal apparatus 10 of the said embodiment, the measuring apparatus which measures the radiation dose emitted from these soil S with respect to the soil S ground by the grinding apparatus 1 and the soil S classified by the classification apparatus 2 is provided. It can also be configured. And when the radiation dose measured by this measuring apparatus is below a predetermined reference value, the soil S can backfill the soil without going through steps S4 and S5 shown in FIG.

DESCRIPTION OF SYMBOLS 1 Crushing device 2 Classifying device 3 Cleaning device 3a Storage tank 3b Jacket tank 3c Stirring device 4 Gas purification device 4a Filler 4b Purification tower 4c Spray nozzle 5 Collection device 6 Dehydration device 9 Chemical liquid tank 10 Removal device H Hopper R Chemical solution Rn Chemical solution S Soil

Claims (3)

A pulverization step of pulverizing the soil so that the silicate mineral layer of the silicate mineral contained in the soil breaks ;
A method for removing soil-containing radioactive material, the method comprising: contacting the soil pulverized in the pulverizing step with a radioactive liquid cleaning solution. In the removal method of the soil-containing radioactive substance according to claim 1,
After the pulverization step, the method further comprises a fine particle classification step of classifying the soil to obtain particles having a particle size of 75 μm or less, and subjecting the soil particles having a particle size of 75 μm or less to the contact step Method for removing contained radioactive material. In the removal method of the soil-containing radioactive substance according to claim 1,
A soil further comprising a coarse particle classification step of classifying soil to obtain soil particles having a particle size exceeding 75 μm, and subjecting the soil particles having a particle size exceeding 75 μm to the crushing step and the contacting step Method for removing contained radioactive material.

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