WO2012165025A1 - Method for cleaning and decontaminating dust, earth, sand, and soil contaminated by radioactive substance - Google Patents

Abstract

Provided is a method for decontaminating contaminated dust, contaminated earth and sand, and contaminated soil in an outside environment contaminated by a radioactive substance, in which oxidation/reduction processing technology is applied and contamination by the radioactive substance is removed, and waste water used in the decontamination is purified and made reusable. Said method has: a collection stage in which the dust, earth, sand, and soil that has been contaminated by the radioactive substance is collected; a cleaning stage in which the collected dust, earth, sand, and soil that has been contaminated by the radioactive substance is cleaned using reduction-treated water; a solid/liquid separation stage in which the dust, earth, sand, and soil that has completed the cleaning stage is solid/liquid separated from the cleaning waste water; an adsorption treatment stage in which the solid/liquid separated cleaning waste water is adsorption treated using an absorption agent; and a microbubble processing stage in which the adsorption treated cleaning waste water is microbubble processed by cavitation.

Description

Cleaning and decontamination methods for dust, soil and soil contaminated with radioactive materials

The present invention relates to a decontamination method for an outdoor environment contaminated with radioactive substances. More specifically, the present invention relates to a method for removing contamination by radioactive substances by applying oxidation / reduction treatment technology and purifying waste water used for decontamination. The present invention relates to a method for cleaning and decontaminating dust, earth and sand, and soil in an outdoor environment contaminated with radioactive materials that can be reused.

At a nuclear power plant, the concrete surface of the inner wall and the exposed metal surface are oxidized due to high temperature exposure for a long period of time. As the time passes, radioactive materials are taken into the oxidized materials, and highly concentrated radioactive materials accumulate on the walls and metal surfaces of nuclear power plants. Such contamination by radioactive substances is not easy because the contaminants are taken into the walls and the like.

On the other hand, even in the case of leakage of low-level radioactivity due to cracks in cooling water pipes due to power plant accidents, radioactive substances are chemically adsorbed on concrete surfaces such as floors, walls, ceilings, and removed easily. Is difficult. Such contamination, unlike contamination in the reactor, has a large effect on the human body even at low levels, and its removal is performed by elution with a chelating agent, organic acid, etc. Since there is a residual radioactive material, there is a need for a technique for removing this to the limit.

Radioactive radiation removal treatment at nuclear power plants consists of high-level spent nuclear fuel solidified with concrete, buried deep in the ground, and exposed to low-level radiation such as clothing, gloves, and other contaminated equipment that has come into contact with radioactive materials, such as buried concrete. It was said that active pollutants were packed in drums and hardened with concrete, and buried deep in the ground, so that no contamination spread outside the nuclear power plant.
However, the accident at the Fukushima nuclear power plant caused by the Great East Japan Earthquake in 2011 caused many radioactive materials to be scattered in the vicinity, causing contamination by radioactive materials on a scale that had not been envisaged in the past, and due to radioactive materials in outdoor and indoor environments. There is an increasing need for techniques for the removal of contamination.

Although there are very few prior arts for the removal of contamination by radioactive material, typical ones are outlined below.
Patent Document 1 discloses that the elution of metal ions from the corrosion film becomes large at an appropriate water temperature, and that the elution of metal ions is further promoted by the presence of hydrogen peroxide. A method of shutting down a boiling water reactor plant is described that removes material and reduces the air dose rate of the piping.

Patent Document 2 discloses a method for removing radioactivity on a cementitious surface, in which a cementitious surface contaminated with a radioactive substance is degraded by applying microorganisms, and residues containing the radioactive substance are removed by suction, scraping, or the like. Patent Document 3 describes a radioactivity removal apparatus in a reactor pressure vessel that removes radioactivity by adsorbing it to an ion cladding, and Patent Document 4 injects a noble metal solution and hydrogen into a nuclear reactor. An apparatus and method for attaching a noble metal to a nuclear reactor structure material in which a noble metal is attached to the structural material and an oxide film on the surface of the nuclear reactor structure is removed by a shot peening method are described.

Patent Document 5 describes a radioactivity removal apparatus that heats and pressurizes an extraction solvent of trifluoroacetylacetone to form a supercritical fluid and performs radioactivity decontamination. Patent Document 6 cleans air with a paper filter. Patent Document 7 describes a chemistry for decontaminating the surface of a steel material contaminated with radioactivity with dicarboxylic acid so that the decontamination solution used therein can be reused. Decontamination methods and chemical decontamination equipment are described.

The above-mentioned prior art relates to the decontamination of nuclear power plants, the surface of steel materials, and simple air cleaning, and can sufficiently cope with the removal of pollution of the outdoor environment due to accidents at nuclear power plants. It was not a thing.

JP-A-5-164890 JP-A-5-215896 JP-A-6-214091 Japanese Patent Laid-Open No. 10-186085 JP-A-10-239493 JP 2005-010013 A JP 2006-098360 A

Due to the accident at the Fukushima nuclear power plant, radioactive material contamination to a wide range of external environments has been confirmed, and the effects of radioactive materials scattered in the air, such as dust, on the human body and the effects on agricultural products due to soil contamination are regarded as problems. It is an urgent issue to decontaminate dust, earth and sand in the outdoor environment, and to suppress inhalation of radioactive materials to the human body by inhalation of dust and intake of radioactive materials from contaminated soil via agricultural crops. .
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to apply an oxidation / reduction treatment technique to remove contamination by dust, soil and radioactive materials in the outdoor environment, and decontamination. It is an object of the present invention to provide a method for cleaning and decontaminating dust, earth and sand, and soil in an outdoor environment contaminated with radioactive substances that can be reused by purifying the wastewater used in the field.

A method for cleaning and decontaminating dust, earth and sand and soil contaminated with a radioactive substance according to an embodiment of the present invention, which is made to achieve the above object, includes a sampling stage for collecting dust, earth and sand and soil contaminated with a radioactive substance. , Washing the dust, soil and soil contaminated with the collected radioactive material with reduced water after reducing treatment, and separating the dust, soil and soil after the washing step and the reduced water used for washing into solid-liquid separation A solid-liquid separation step, an adsorption treatment step for adsorbing the reduced water used for the solid-liquid separated washing with an adsorbent, and a microbubble treatment for treating the reduced water used for the adsorption-treated washing with microbubbles by cavitation And a stage.

The cleaning step of cleaning the collected dust, soil, and soil with reduced water that has been reduced is continuously sprayed with reduced water on the permeable belt conveyor. It is preferable that

It is preferable that the washing step of washing the dust, soil and soil contaminated with the collected radioactive material with the reduced water obtained by reducing and treating the dust, soil and soil is immersed in the reduced water and stirred and washed.

It is preferable that the collecting step for collecting dust, earth and sand and soil contaminated with the radioactive material is by a suction method.

In addition, it is preferable that the collecting step of collecting the dust, earth and sand and soil contaminated with the radioactive material is performed by a backhoe cutter bucket.

In the solid-liquid separation step, it is preferable that dust, earth and sand and soil are separated from washing wastewater by a water-permeable bucket conveyor and passed through a continuous centrifuge.

It is preferable that the adsorption treatment step is performed by passing through a column packed with a cation / anion exchanger and a column packed with zeolite.

According to the present invention, in an outdoor environment, contaminated dust, earth and sand, and soil are collected, washed with reduced water having excellent adsorption of radioactive substances, and radioactive substances are efficiently removed from dust, earth and sand and soil by a simple method. The waste water can be effectively reused by making the waste water of the reduced water used for washing into highly functional biological water.

It is the figure which showed the oxidation-reduction potential of water by the reduction process of water It is an illustration figure of the collection step of dust, earth and sand, and soil in the decontamination method by one Embodiment of this invention. It is an illustration figure of the collection step of dust, earth and sand, and soil in the decontamination method by one Embodiment of this invention. It is an illustration figure in the decontamination method by one Embodiment of this invention of the washing | cleaning step by the reduced water of dust, earth and sand, and soil. It is an illustration figure in the decontamination method by one Embodiment of this invention of the washing | cleaning step by the reduced water of dust, earth and sand, and soil.

Hereinafter, specific examples of embodiments for carrying out the method for cleaning and decontaminating dust, earth and sand, and soil contaminated with radioactive substances of the present invention will be described in detail.

The present invention effectively cleans contaminated dust, soil, and soil by washing the outdoor dust, soil, and soil contaminated with radioactive materials using reduced water with high adsorptivity of radioactive materials as cleaning water. In addition to making it possible to safely dispose of dust and restore the soil, the radioactive water is removed from the reduced water used for washing and microbubble treatment is carried out, resulting in highly functional water with high biological activity. By doing so, the cleaning wastewater is effectively reused.

As shown in FIG. 1, the reduced water used as the washing water in the present invention has a different oxidation-reduction potential (Eh) (under normal temperature and normal pressure) depending on the reduction treatment conditions.
In the embodiment of the present invention, the potential of the reducing water used as the cleaning water is preferably negatively charged from −400 mV to −600 mV from the viewpoint of the cleaning effect and solubility of the ionized radioactive substance.

Next, a method for cleaning and decontaminating dust, soil and soil contaminated with radioactive materials according to an embodiment of the present invention will be described.
The first stage in the decontamination method of this embodiment is a collection stage for collecting dust, soil and soil contaminated with radioactive substances.

Outside, there is a high risk that pollutants will permeate underground due to rain, leading to groundwater contamination.
Although cesium is highly soluble in water, it is a cation, so it is strongly adsorbed on the negatively charged soil, and its mobility is surprisingly low unless anion is supplied by fertilizer. The rate of movement of cations such as cesium 134, 137, strontium 90, cobalt 60, etc. that contaminate the soil is slow because it is adsorbed on the soil, and it varies depending on the fertilization conditions to the soil. It is considered to be about 20-30 cm per year.

Therefore, the surface soil was sampled, cation radioactive materials having a long half-life such as cesium 134, cesium 137, strontium 90 and cobalt 60 adsorbed on the soil were washed with reduced water, and transferred from the washing solution to the adsorbent, Perform decontamination restoration of soil.
On the other hand, radioactive materials of anions such as iodine 131 have a short half-life of 8 days, but they are scattered in quantity and need to be removed. In the case of anions, since many of the substances have a negative charge on the surface, they are hardly adsorbed and easily penetrate into the basement and diffuse easily. Since reduced water has high penetrating power, it can also dissolve and capture anionic radioactive substances, and the cleaning effect of reduced water is great as in the case of cations.

For soil collection, it is sufficient to collect the soil surface by a suction method or heavy machinery at an early stage, but depending on the passage of time, it is necessary to collect contaminated soil of about 10 cm of the topsoil.
FIGS. 2 and 3 are exemplary views of the collection stage of dust and earth and sand in the decontamination method according to an embodiment of the present invention.

The method for collecting the decontamination object in the present embodiment is preferably the following two methods, one using a large vacuum suction machine as shown in FIG. The surface soil is collected by a suction method, and the other is a method of cutting soil with a backhoe bulltozer cutter bucket shown in FIG. 3 and collecting contaminated soil having a surface soil of about 10 cm.

The example of the sampling method by the suction method shown in FIG. 2 is preferable as a method corresponding to the collection of soil at a relatively early stage after contamination, dust attached to an outdoor structure or road surface, and earth and sand. Is possible.

As shown in FIG. 2, a movable large vacuum suction machine equipped with a powerful suction port moving vehicle 3 that can be moved by human power at the tip of a suction hose 2 connected to a movable dust suction storage device 1. And can be collected. At this time, the exhaust of the large vacuum suction machine is supplemented with dust with a filter, etc., then the exhaust is bubbled into the reduced water, and the radioactive fine particles mixed in the exhaust are trapped with the reduced water to produce a clean exhaust. It is desirable to discharge from the viewpoint of preventing the diffusion of contamination.

The example of the collection method using the cutter bucket of the backhoe bulltozer shown in FIG. 3 is preferable as a method corresponding to the collection of the contaminated soil having a surface soil of about 10 cm, and requires a large heavy machine such as a backhoe bulltozer.
As shown in FIG. 3, in this sampling method, the contaminated soil is sampled by the cutter bucket 6 of the backhoe bulltozer 5, but the cutter bucket 6 is provided with a soil sampling cutter 7, and the soil that needs to be collected is collected. Can be cut out accurately. The collected contaminated soil is transported to a place for cleaning treatment by the transport vehicle 4.

Next, a cleaning step is performed in which dust, soil, and soil contaminated with the collected radioactive material are washed with reduced water subjected to reduction treatment.
The cleaning method of the decontamination object in the embodiment of the present invention is preferably the following two methods, and one is continuous reduction water to the decontamination object moving on the conveyor as shown in FIG. A method corresponding to washing of dust, soil and sand that are covered with radioactive materials on the surface, and another method for reducing water and decontamination in a washing tank equipped with a stirrer as shown in FIG. This is a method corresponding to contaminated soil in which radioactive substances are permeated into the inside, which is washed with stirring.

As shown in FIG. 4, the method of continuously showering the reduced water in the present embodiment is a radioactive material that is continuously decontaminated from the decontamination object supply device 21 on the water-permeable net conveyor 24. Dust, soil and soil contaminated with substances are supplied, and reduced water is continuously supplied to the decontamination target from a reduced water shower device provided at the upper part of the permeable net conveyor 24 and connected to the cavitation reduction treatment tank. This can be done by ringing.

Dust, earth and sand and soil contaminated with radioactive substances, which are decontamination objects, are purified by being continuously showered with reduced water while being transported by the water-permeable net conveyor 24, and the washed product storage tank A26. Washed and contaminated reduced water containing radioactive material contained in the shower is dropped into the washed and contaminated reduced water tank 25 and sent to the solid-liquid separation stage.

In the method of stirring and washing the decontamination object shown in FIG. 5, the collected contaminated soil is introduced from the transport vehicle 4 into a washing tank 27 equipped with a stirring blade 28 and a stirring motor 29, and reduced water is contained in the washing tank 27. Can be carried out by stirring and washing for a certain time.
There are no particular limitations on the amount ratio and time of the reducing water and the decontamination target in the stirring cleaning, and the time is determined by the degree of contamination of the decontamination target.

The radioactive material in the decontamination target such as contaminated soil is moved to the reduced water side by stirring and washing with the reduced water, and the washed product containing the washed contaminated reduced water after the washing is continuously centrifuged by the permeable bucket conveyor 34. 32.

Next, the dust, the earth and sand, and the soil which have finished the washing stage proceed to a solid-liquid separation stage in which washing-contaminated reduced water is separated into solid and liquid.
The method of solid-liquid separation is not particularly limited, but a filtration method or a centrifugal separation method is preferable from the viewpoint of simplicity of equipment and processing efficiency.

In the embodiment shown in FIG. 4, the washed and contaminated reduced water containing fine solids that have passed through the water-permeable net conveyor 24 is sent to the continuous centrifugal separator 32 for solid-liquid separation.
The washed and contaminated reduced water separated from the solid by the continuous centrifugal separator 32 is sent to the washed and contaminated reduced water storage tank 41, and the separated solid is stored in the washed substance storage tank B33.

In the embodiment shown in FIG. 5, the soil that has been stirred and washed is subjected to primary filtration with a water-permeable bucket conveyor 34, sent to a continuous centrifugal separator 32, and solid-liquid separated to become reusable washed soil.
The washed and contaminated reduced water separated by the continuous centrifugal separator 32 is filtered by the filtration device 35 together with the filtrate primarily filtered by the water-permeable bucket conveyor 34 and sent to the washed and contaminated reduced water storage tank 41.

Next, the process proceeds to an adsorption treatment stage in which the washed contaminated reduced water separated into solid and liquid is adsorbed with an adsorbent.
Since the steps after the adsorption processing stage have the same configuration in the embodiment of FIGS. 4 and 5, the steps after the adsorption processing stage will be described with reference to FIG.

According to FIG. 4, the washed contaminated reduced water in the washed contaminated reduced water storage tank 41 passes through the anion exchange resin packed column 42 to adsorb and remove the anionic radioactive substances, and then the cation exchange resin packed column. 43 is used to adsorb and remove the cationic radioactive material.
The water that has passed through the cation exchange resin packed column 43 is further passed through the zeolite packed column 44 to completely remove the radioactive substance from the reduced water.

Next, the process proceeds to a microbubble treatment stage in which microbubble treatment by cavitation is performed on the reduced water after the adsorption treatment.
Reduced water from which radioactive substances have been removed may adversely affect the growth of organisms as it is. Add air or oxygen, and perform microbubble treatment by cavitation to produce highly functional reduced water with high biological activity. It needs to be reusable.

In the microbubble treatment stage, reduced water is ejected vigorously from the microbubble generating pump 45, air or oxygen gas is added, and microbubbles are generated by cavitation in the microbubble generating device 46, so that functional water with high biological activity is obtained. Then, it is stored in the microbubble reduced water storage tank 47 and reused or discharged.

As mentioned above, although embodiment of this invention was described in detail, referring drawings, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the technical scope of this invention, it changes variously. It is possible to implement.

DESCRIPTION OF SYMBOLS 1 Dust suction storage device 2 Suction hose 3 Powerful suction port moving vehicle 4 Transport vehicle 5 Backhoe bulltozer 6 Cutter bucket 7 Soil collection cutter 11 Raw material washing water supply line 12 Raw material washing water supply pump 13 Hydrogen gas supply device 14 Ejector 15 Cavitation reduction Treatment tank 16 Reduction treatment tank operation motor 21 Supply device for decontamination object 22 Reduction water supply port 23 Reduction water shower device 24 Permeable net conveyor 25 Washing contamination reduction water tank 26 Washed product storage tank A
27 Washing tank 28 Stirring blade 29 Stirring motor 31 Washing contaminated reduced water line 32 Continuous centrifugal separator 33 Washed product storage tank B
34 Permeable bucket conveyor 35 Filtration device 41 Washed and contaminated reduced water storage tank 42 Anion exchange resin packed column 43 Cation exchange resin packed column 44 Zeolite packed column 45 Micro bubble generating pump 46 Macro bubble generating device 47 Micro bubble reduced water storage tank

Claims (7)

1. A collection stage for collecting dust, dirt and soil contaminated with radioactive material;
   A washing step of washing the dust, earth and sand and soil contaminated with the collected radioactive material with reduced water obtained by reducing treatment;
   Solid-liquid separation step for solid-liquid separation of the dust, earth and sand, and the reduced water used for washing after the washing step;
   An adsorption treatment step of adsorbing the reduced water used for the solid-liquid separated washing with an adsorbent;
   A microbubble treatment step of microbubble treatment of reduced water used for the adsorption treatment washing by cavitation, and a method for washing and decontaminating dust, soil and soil contaminated with radioactive materials.
2. The cleaning step of cleaning the collected dust, soil and soil with reduced water that has been subjected to reduction treatment continuously sprays the reduced water on the permeable belt conveyor with the reduction treatment. The method for cleaning and decontaminating dust, soil and soil contaminated with a radioactive substance according to claim 1.
3. The washing step of washing dust, soil, and soil contaminated with the collected radioactive material with reduced water subjected to a reduction treatment is performed by immersing in reduced water and stirring and washing. Cleaning and decontamination methods for dust, soil and soil contaminated with radioactive materials.
4. 2. The removal of dust, soil and soil contaminated with radioactive material according to claim 1, wherein the sampling step for collecting the dust, soil and soil contaminated with radioactive material is by a suction method. Dyeing method.
5. 2. The dust, soil and soil contaminated with radioactive material according to claim 1, wherein the collection step of collecting dust, soil and soil contaminated with the radioactive material is performed by a cutter bucket of a backhoe. Cleaning decontamination method.
6. 2. The dust polluted with a radioactive material according to claim 1, wherein the solid-liquid separation step is to separate the dust, earth and sand from the washing wastewater with a permeable bucket conveyor and pass through a centrifuge. , Cleaning and decontamination methods for earth and sand and soil.
7. 2. The radioactive substance according to claim 1, wherein the adsorption treatment step passes through a column filled with a cation exchange resin, a column filled with an anion exchange resin, and a column filled with zeolite. For cleaning and decontamination of collected dust, earth and sand and soil.

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