JP2014062735A - Decontamination method for buildings, soil, or plants contaminated with radioactive materials - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method for buildings, plants, or soil that prevents radioactive materials from spreading peripherally, since a water jet, which is being considered to be used for decontamination of buildings in a wide area contaminated with radioactive materials generated by Fukushima Daiichi Nuclear Power Plant severely damaged by the Great East Japan Earthquake, has a risk of further spreading of radioactive materials.SOLUTION: When decontamination is conducted for buildings, plants, or soil, the following steps are carried out sequentially: a first step in which spray coating of a washing agent is applied to surfaces of buildings or the like to let it reach every corner of them without allowing it to spread peripherally; a second step in which the applied washing agent is removed to clean the buildings or the like; and a third step in which the removed washing agent mixed with radioactive materials is treated as radioactive waste. Thus, decontamination of the buildings or the like can be carried out easily at low cost without spreading of the radioactive materials in their circumference environment.

Description

  The present invention relates to a method for removing radioactive substances from buildings, soil, or plants such as trees and flowers contaminated with radioactive substances without scattering them around.

  The Fukushima Daiichi Nuclear Power Station reactor was destroyed by the Great East Japan Earthquake on March 11, 2011, and the radioactive material was scattered and the surrounding area was contaminated with radioactive material. More than half a year later, decontamination work is now close-up, and decontamination work using a water jet is performed as a decontamination method. However, cleaning with water jets may disperse radioactive materials more extensively to neighbors, the atmosphere, surrounding areas, or side trenches and even sewage treatment plants, even if the building or facility is decontaminated.

  However, in Japan, there is no experience of radioactive materials scattered outside the power plant facilities due to accidents at nuclear power plants so far, so that radioactive materials adhering to and deposited on buildings etc. can be safely removed without scattering to the surroundings. At present, no method has been presented.

  An object of the present invention is to provide a method for safely removing radioactive substances adhering to and accumulating on buildings such as buildings, facilities and structures in the above-described situation without scattering them around. Is.

  Even when decontaminating with a water jet, if the surroundings of the building are covered with a curing sheet, etc., and the building is completely isolated from the surroundings, the risk of scattering radioactive materials in the vicinity is greatly reduced. . However, implementing this is enormous and time consuming and not realistic. Another object of the present invention is to provide a decontamination method for buildings and the like that is inexpensive and hassle-free without isolating and curing the buildings and the like.

  In order to achieve the above-mentioned object, the present invention, when decontaminating a building contaminated with radioactive substances, sprays the surface of the building without spraying it around the surface of the building and sprays it on every corner. The first step to disperse, the second step to remove and clean the applied cleaning agent, and the third step to treat the mixture of removed radioactive material and cleaning agent as radioactive waste, are carried out sequentially To do.

  The first step is the most dangerous step that may scatter radioactive materials around. In this step, it is preferable to use an airless sprayer so that radioactive materials are not scattered around. Further, it is suitable to spray the cleaning agent at a discharge pressure of 0.5 MPa or less, preferably 0.3 MPa or less. When the discharge pressure exceeds 0.3 MPa, the tendency of the cleaning agent to scatter appears around, and when the discharge pressure exceeds 0.5 MPa, the tendency becomes remarkable.

The amount of the cleaning agent applied is preferably as small as possible in order to minimize the amount of waste and to prevent the cleaning agent from falling off, but if it is too small, the effect of decontamination is lost. As a guideline, 0.1 to ² kg / m ² is preferable, but the optimum coating amount varies depending on the material, surface state, etc. of the target building surface, and the present invention is not limited to this value.

  After the cleaning agent is applied, air blowing, brushing, additional spraying of the cleaning agent, etc. are performed as appropriate so that buildings such as uneven parts, corners, openings around buildings, tops of crosspieces, cross beams, and eaves Disperse the cleaning agent in every corner of the object.

  The second step is a very important step in that the efficiency of the decontamination work, the presence / absence of scattering of radioactive material to the surroundings, and the result of the decontamination depend on whether this is appropriate. In the present invention, the cleaning agent applied to the building and the radioactive material captured by the cleaning agent are removed by suction using a water-resistant vacuum cleaner. A water-resistant vacuum cleaner is a type of vacuum cleaner that sucks dry garbage, damp trash and water with a single unit, and a water-circulating type vacuum cleaner that sucks waste water and circulates it while washing with water. included.

  Among these water-resistant vacuum cleaners, a water-absorbing vacuum cleaner equipped with a waste water container is most suitable for decontamination work of buildings. In the present invention, the cleaning agent to be sucked contains a surfactant and easily foams in the waste water container. If this foam comes into contact with the motor at the top of the vacuum cleaner, it causes electric leakage. It is more suitable if it is a water-absorbing vacuum cleaner having a structure that cannot contact the motor, for example, a cyclone type water-absorbing vacuum cleaner. In addition, it is effective to prevent the generation of bubbles by applying an antifoaming agent or an antifoaming agent solution to the bottom of the wastewater container in advance. Thereby, it can carry out efficiently, without scattering a radioactive substance around.

  Furthermore, in order to minimize bubbles in the water-absorbing cleaner, it is preferable to provide a storage tank on the way from the suction port to the water-absorbing cleaner. The storage tank is provided with a lid for removing the accumulated waste water. The lid is structured to be sealed with a storage tank so as not to prevent suction when closed.

  In the second step, cleaning work such as washing, brushing, wiping, etc. is performed as necessary to completely decontaminate the building contaminated with radioactive substances.

  The third step is an important step in the final stage. If this step is not properly performed, all the steps so far are wasted and radioactive materials are scattered around. Paper, cloth, cotton, etc. used for wiping and cleaning work should be stored and sealed in a radioactive waste container or bag. Also, the sludge water collected in the waste water container of the vacuum cleaner, the waste water that has been used to clean the used devices and equipment, etc. are stored and sealed in a radioactive waste container. The radioactive waste container or bag is stored in a predetermined place. If the wash water used and the waste liquid collected in the waste water tank of the water supply vacuum cleaner are collected in a plastic tank and lime, zeolite, activated carbon, etc. are added to adsorb and precipitate the radioactive material, only the precipitate is radioactively discarded. It can also be a thing.

  The cleaning agent must contain a component that is effective for trapping radioactive materials and must be a liquid that is harmless to the environment and the human body. In the present invention, the cleaning agent is an aqueous solution containing a surfactant as a main component.

  Surfactants include anionic surfactants such as fatty acid salts, alkyl sulfates, and alkyl benzene sulfonates, quaternary ammonium salt cationic surfactants, fatty acid-based, higher alcohol-based, alkylphenol-based nonions, etc. Any of amphoteric surfactants such as surfactants, amino acids, betaines, and amine oxides can be used.

  The concentration of the surfactant is preferably as low as possible from the viewpoint of saving resources, and is generally 1% by weight or less, preferably 0.5% by weight or less.

  As described above, the cleaning agent is an aqueous solution containing a surfactant as a main component, but the present invention is not limited thereto.

  The radioactive material scattered by the nuclear power plant is iodine 131, cesium 137, xenon 133, krypton 88, etc., as long as the pressure vessel and the containment vessel are not damaged. The half-lives of these radioactive substances are mainly 8 days for iodine 131, 5.3 days for xenon 133 and 2.8 hours for krypton 88, whereas cesium 137 is overwhelmingly 30 years. The target of decontamination is considered to be cesium 137. Cesium is a group 1 element and a member of alkali metals. Therefore, adding an acid such as dilute hydrochloric acid, dilute sulfuric acid, citric acid, oxalic acid, tartaric acid, etc. to the cleaning agent has a reasonable basis for the acid to react with the alkali and make decontamination more effective. An acid may be contained. Further, salts or chelating agents such as sodium citrate, sodium tartrate, sodium phosphate, ammonium carbonate, ammonium citrate, EDTA may be effective, and these may be contained.

  Further, since the porous substance fine powder has an action of adsorbing dust, the cleaning substance may contain the porous substance fine powder. Porous materials include zeolite, diatomaceous earth, activated carbon, etc., all of which can be used.

  When the porous substance fine powder is contained, a water-soluble thickener may be added to prevent sedimentation. Water-soluble thickeners include polysaccharides such as starch, polyvinyl alcohol, methylcellulose, sodium polyacrylate, etc., all of which can be used.

  A preferable method for achieving the object of the present invention is to apply a foamed cleaning agent to the surface of the building when decontaminating the building contaminated with radioactive substances, and to remove all the corners. The first step of spreading, the second step of removing and cleaning the applied cleaning agent, and the third step of treating the mixture of the removed radioactive substance and the cleaning agent as radioactive waste are sequentially performed. Is. Thereby, the object of the present invention can be realized more effectively.

  A preferable first step is to spray the cleaning agent while foaming it using a foam generating device.

  As the foam generation device, air from the air compressor is introduced into the cleaning agent container of the foam generation device, and the pressure tank type foam generation device that injects the foaming cleaning agent from the nozzle with that pressure, and the air of the air compressor is driven by air There is an air-driven pump type foam generating device that feeds into the pump and injects the foaming detergent from the nozzle by the driving force of the pump, but any type can be used. However, in the case of an air-driven pump, it pulsates and the foam state is likely to become unstable. Therefore, in order to implement the present invention in a better form, a pressure tank type foam generator is preferable. When the foamed cleaning agent is sprayed on the surface of the building, it absorbs the energy of collision and is less likely to scatter. Moreover, since the foamed cleaning agent has a large effect of capturing fine dust, it is a suitable cleaning agent for capturing and removing radioactive substances.

  After application of the foamed detergent, air blowing, brushing, additional spraying of the cleaning agent and spraying of the defoaming agent, etc. are performed as appropriate, so that the irregularities, corners, openings around the building, Disperse the detergent and defoam all the way to the corners of the building. In particular, air blowing from an air compressor using an air hose is an extremely effective method in that the applied foaming detergent can be easily distributed to the details of the building.

  The detergent for foaming may be an aqueous solution containing the surfactant as a main component or a solution obtained by adding a foaming agent to the aqueous solution.

  Examples of the foaming agent include surfactants such as detergents, aqueous emulsions of oils such as pine oil and eucalyptus oil, egg white, gelatin and the like, all of which can be used.

The amount of foamed detergent applied should be as small as possible in order to minimize the amount of waste and to prevent the detergent from dripping. Disappear. As a guideline, 0.05 to 1 kg / m ² is preferable, but the optimum coating amount varies depending on the material, surface state, etc. of the target building surface, and the present invention is not limited to this value.

  Antifoaming agents include fatty acid-based, higher alcohol-based, alkylphenol-based nonionic surfactants, hydrophilic organic solvents such as ethyl alcohol, silicone oil or aqueous emulsions thereof, and silicone resin fine powder. Is possible.

  The details of soil decontamination are as follows. There is a high possibility that radioactive cesium is concentrated and fixed near the surface of the soil. In addition, the radiation dose represented by the numerical value of the air dose rate is strongly influenced by radioactive cesium existing near the soil surface. Thus, removing very thin layers of soil reduces the air dose rate to less than half. The first cleaning step, which is a preferred first step of the present invention, is sprayed while foaming using a foam generating device, and is thoroughly distributed over the soil surface. A very thin layer of soil along with the foaming detergent is also removed by suction. As described above, the method of the present invention makes it possible to easily and effectively decontaminate the ground, that is, the soil. Moreover, radioactive materials are not scattered around.

  Further, details of decontamination of plants such as trees and flowers are as follows. In the case of plants such as trees and flowers, radioactive cesium is concentrated and deposited at the root of the plant, as well as the branches and leaves. Therefore, if the grass and soil at the base are intensively decontaminated, the effect of decontamination is dramatically increased. As described above, the cleaning agent used in the invention is an aqueous solution mainly composed of a surfactant. If this cleaning agent is used and the method of the present invention is carried out, the plant can be decontaminated. That is, the cleaning agent, which is a preferred first step of the present invention, is sprayed onto the plant body and its roots while foaming using a foam generator. And, when removing the soil at the root of the plant together with the foaming detergent using a water-absorbing vacuum cleaner, which is a preferred second step, by spraying water on the plant body and its root with a sprayer, It can be easily and effectively decontaminated without harming the plant. Moreover, radioactive materials are not scattered around.

  As mentioned above, the spraying agent is sprayed and applied to buildings and the like contaminated with radioactive materials without splashing the surroundings, and the applied cleaning agent is removed in a first step that spreads all over the corner. Adhering to and depositing on buildings such as buildings, facilities, and buildings by sequentially performing the second step of cleaning and the third step of treating the mixture of removed radioactive material and cleaning agent as radioactive waste It is possible to achieve the object of the present invention to perform the radioactive material safely without being scattered around, without being troublesome.

  In addition, as a preferable method for decontaminating radioactive substances, a first step of applying a foaming detergent on the surface of buildings, plants or soil contaminated with radioactive substances and spreading them all over the corners, By sequentially performing the second step of removing and cleaning the applied cleaning agent and the third step of treating the mixture of the removed radioactive material and the cleaning agent as radioactive waste, the building, facility, and work are performed. It is possible to more effectively achieve the object of the present invention in which radioactive materials attached to and accumulated on buildings such as objects are safely and inexpensively performed without being scattered around. .

The radiation measurement result before and behind the decontamination process by the method which concerns on this invention is shown. The radiation measurement result before and behind the decontamination process by the method which concerns on this invention is shown.

  Hereinafter, embodiments of the present invention will be described with respect to decontamination of buildings. However, the present invention relates to radioactive substances, and it was extremely difficult to conduct experiments to demonstrate the effects of the present invention.Fortunately, people who understand and cooperate with the purpose of the present invention appear and can be realized. It is a thing.

The experiment was carried out by borrowing two agricultural storage rooms in Nasu-machi, Nasu-gun, Tochigi Prefecture, which is about 100 km away from the Fukushima Daiichi nuclear power plant and is relatively lightly contaminated with radioactive materials. The two storerooms are about 1km apart, and if they are named A and B buildings, both buildings A and B are steel prefabricated prefab stores and there are no buildings in the surroundings and they are isolated in the field. It is built. A building is frontage 2.7 m, depth 1.8 m, a height 1.8 m, surface area of about 26m ^2, B building is frontage 3.6 m, depth 1.8 m, height 1.8 m, at a surface area of about 33m ² is there. Each storeroom has a simple structure in which a concrete block is placed on the ground and placed on it.

  In order to avoid the influence from the ground as much as possible, the radiation dose generated from the storage room and its surroundings was measured at the following position with a space radiation dose meter (FLUKE Survey Meter 451P). As for the building part, the roof was measured at two locations at a height of 50 cm from the roof surface, the wall was measured at 50 cm from the wall surface, and 1.5 m from the ground at one location in the east, west, south, and north. About the periphery, it measured one place each in the east, west, south, and north at the position of 50cm in height 5m away from the building. The results are shown in FIGS.

In building A, decontamination was performed by the method of claim 1 of the present invention. First, a blue sheet with a width of about 4m was laid on the ground around the storeroom, and necessary materials and equipment were placed on it. As for the electric power, a power source of AC100V was secured by a small private generator. Before spraying, an aqueous solution containing 0.5% by weight of nonyltrimethylammonium salt as a cationic surfactant, 3% by weight of zeolite fine powder, and 5% by weight of polyvinyl alcohol as a thickener is first used as a cleaning agent. Got ready. A detergent aqueous solution was put into the container of Seiwa Sangyo's airless sprayer “Tobanai TB-7” and the discharge pressure of the sprayer was adjusted. When the discharge pressure was 0.1 MPa, the discharge rate was 2 kg / min. The coating amount was set to 500 g / m ^2, and it was calculated that the surface of building A should be sprayed for a total of about 7 minutes as a guideline, and then the roof, eaves, and walls were sprayed sequentially from top to bottom. After spraying, a small blower was blown or brushed, and the area where the cleaning agent was not applied was sprayed with a manual sprayer to spread the cleaning agent to every corner of the building surface. (First step).

  Next, using a vacuum cleaner manufactured by Hitachi Industrial Equipment Systems (CV-980WF2), the roof, eaves, and walls, and the mixture of the radioactive material trapped in the cleaning agent and the cleaning agent were sequentially removed from the top to the bottom. At this time, a suction port suitable for the concave portion or narrow portion was used. Furthermore, cleaning and polishing were carried out by spraying water with a watering can or the like, and wiping with paper, cloth, cotton or the like (second step).

  Finally, the sludge water collected in the container of the water-absorbing vacuum cleaner, the cleaning water of the used equipment, equipment, etc. are absorbed into water-absorbing substances such as paper, cloth, cotton, water-absorbing polymer, and the paper, cloth, It was housed and sealed in a radioactive waste container together with cotton. The cleaning agent that fell from the wall surface and accumulated in the blue sheet was also wiped clean with paper, cloth, cotton, etc., and stored and sealed in a radioactive waste container. The storage of the sealed radioactive waste container was entrusted to the local person who attended the experiment (third step).

  The result of measuring the radiation dose at each place after the decontamination work is shown in FIG. Since the natural radiation dose in Japan is said to be about 0.11 μSv / h, it can be said that decontamination has been successful if the value is around this value. As for the building part, the radiation dose on the walls is higher than that on the roof, but this time the ground was not decontaminated, so it is considered that the building was affected by radiation from the ground. If only the roof is seen, it decreases from 0.41 μSv / h before the treatment to 0.14 μSv / h after the treatment, which is slightly higher than 0.11 μSv / h, but the effect of the decontamination treatment is clear. As for the surrounding area, the radiation dose before and after treatment did not change or the result increased in mind, but there may have been some scattering of radioactive material when spraying the cleaning agent on the building.

In Building B, decontamination was performed by the method of claim 10 of the present invention. First, a blue sheet with a width of about 4m was laid on the ground around the storeroom, and necessary materials and equipment were placed on it. As for the electric power, a power source of AC100V was secured by a small private generator. Before spraying, first prepare a detergent with 1% by weight of citric acid and 1% by weight of gelatin in an aqueous solution of 0.5% by weight of nonyltrimethylammonium salt, a cationic surfactant. did. In addition, an aqueous solution of 25% by weight of ethyl alcohol was prepared as an antifoaming agent. In this experiment, a commercially available air bubble generator for car wash was used as a foaming detergent sprayer. The discharge pressure of this apparatus was 0.4 MPa, and the discharge rate was about 200 g / min. The coating amount was set to 200 g / m ^2, and it was calculated that the surface of Building B should be sprayed for a total of approximately 33 minutes as a guideline, and then the roof, eaves, and walls were sprayed sequentially from top to bottom. In order from the place where spraying is finished, blow a small blower, apply brush, or spray a foamed detergent to the place where the detergent is not applied, or defoam with a manual sprayer The spray was sprayed to the corners of the building surface while spraying the aqueous solution to remove the bubbles (first step).

  Next, using a vacuum cleaner manufactured by Hitachi Industrial Equipment Systems (CV-980WF2), the cleaning agent and the mixture of radioactive materials captured by the cleaning agent were removed from the roof, eaves, and walls sequentially from top to bottom. At this time, a suction port suitable for the concave portion or narrow portion was used. Moreover, an antifoaming agent was sometimes sprayed to the waste water container of the water absorption cleaner, and the foam in the container was erased. Furthermore, cleaning and polishing were carried out by spraying water with a watering can or the like, and wiping with paper, cloth, cotton or the like (second step).

  Finally, the sludge water collected in the container of the water-absorbing vacuum cleaner, the cleaning water of the used equipment, equipment, etc. are absorbed into water-absorbing substances such as paper, cloth, cotton, water-absorbing polymer, and the paper, cloth, It was housed and sealed in a radioactive waste container together with cotton. There was almost no dripping off of the foamed cleaning agent, but the dirt on the blue sheet laid on the ground was wiped clean with paper, cloth, cotton, etc., and stored and sealed in a container for radioactive waste. The storage of the sealed radioactive waste container was entrusted to the local person who attended the experiment (third step).

  FIG. 2 shows the result of measuring the radiation dose at each place after the decontamination work. Since the natural radiation dose in Japan is said to be 0.11 μSv / h, it can be said that decontamination has been successful if it is around this value. As for the building part, the radiation dose on the walls is higher than that on the roof, but this time the ground was not decontaminated, so it is considered that the building was affected by radiation from the ground. If only the roof is seen, it decreased from 0.48 μSv / h before the treatment to 0.11 μSv / h, which is the same as the amount of natural radiation after the treatment, so that it was possible to completely decontaminate as intended. In the surrounding area, the radiation dose before and after treatment does not change at all, but this is considered to mean that radioactive materials were not scattered around the building when spraying the cleaning agent on the building. Also, as mentioned above, it is a noteworthy advantage that there was little dripping of the foamed cleaning agent.

  Next, the case where the radioactive substance decontamination method according to the present invention is applied to the ground will be described in detail.

The method of decontamination on the ground is basically the same as the method described above for buildings, but decontamination is performed with the following points in mind.
1) If the contaminated soil on the ground is soft, spray the foaming detergent onto the ground, and then remove the detergent together with the topsoil by suction. By this method, the work of topsoil cutting by human power can be omitted and the work efficiency can be improved.
2) On the other hand, when decontamination is insufficient by the above method, such as when the soil contaminated on the ground is hard, scraping off the top soil, covering the contaminated soil with soil that is not radioactively contaminated, and the upper soil contaminated with radiation And any of the treatments such as replacement with uncontaminated lower soil, or a combination of these treatments.

  Next, the case where the radioactive substance decontamination method according to the present invention is applied to plants such as trees and flowers will be described in detail.

The decontamination method for plants such as trees and flowers is basically the same as that for buildings described above, but decontamination is performed with the following points in mind.
1) Since plants such as trees and flowers are vulnerable to acid, acidic detergents cannot be used for plants. For this reason, detergents that do not contain acids are used for plants.
2) In plants, the radiation dose tends to be higher in depressions where water tends to accumulate. Therefore, decontamination of the roots is given priority over the upper branches and leaves.
3) Spraying the cleaning agent onto the branches and leaves gives priority to spraying the inside of the branches and leaves that are not easily wetted with rain over the surface that is easily wetted with rain.
4) The amount of spraying cleaning agent in the case of plants differs from the case of a flat surface such as a wall surface of a building, because it has three-dimensional unevenness, and is calculated using the following formula.
Appropriate spraying amount of cleaning agent in the case of plants = α × virtual area × β (1)
Where α is the appropriate spray amount per unit area of the cleaning agent for a solid surface such as a wall, the virtual area is the projected area of the plant on the ground, and β is the effective area due to the unevenness of the plant to which the cleaning agent is sprayed. This is a premium coefficient considering the increase and is based on 1.5, but is not necessarily limited to this value.
5) In order to reduce the influence of the cleaning agent on the plant, spray the cleaning agent that does not contain acid on the plant, and then suck the sludge water at the base of the plant with a water-absorbing vacuum cleaner. Spray to completely remove the cleaning agent from the plant body and roots.

Claims (15)

The first step of spraying and applying the cleaning agent to the surface of the building, soil or plant without splashing it around,
A second step of removing and cleaning the mixture of the radioactive substance and the cleaning agent and a third step of recovering and treating the mixture of the removed radioactive substance and the cleaning agent as radioactive waste;
A method for decontaminating a building, soil or plant contaminated with a radioactive material, characterized by comprising: The method for decontaminating a building, soil, or plant according to claim 1, wherein the cleaning agent is a foamed cleaning agent. The building contaminated with a radioactive substance according to claim 1, wherein the first step is performed by spraying the cleaning agent at a discharge pressure of 0.5 MPa or less using an airless sprayer. A method of decontaminating soil or plants. The cleaning in the second step is performed by sucking and removing the cleaning agent and the radioactive material trapped in the cleaning agent with a water-resistant vacuum cleaner, and performing washing with water, brushing and / or wiping. A method for decontaminating a building, soil, or plant contaminated with the radioactive material according to claim 1 or claim 2. The radioactive substance according to claim 1 or 2, wherein the third step stores and seals the waste water and the washing water in a radioactive waste container or bag together with the water-absorbing substance used for cleaning. A method of decontaminating buildings, soil, or plants contaminated with water. 5. The method for decontaminating a building, soil or plant contaminated with a radioactive substance according to claim 4, wherein the water-resistant vacuum cleaner is a water-absorbing type vacuum cleaner provided with a waste water container. The water-absorbing type vacuum cleaner is provided with a storage tank, and the waste water is temporarily retained in the storage tank before the sucked waste water enters the vacuum cleaner, and the storage tank is provided with a lid, 5. The method for decontaminating a building, soil, or plant contaminated with radioactive material according to claim 4, wherein the lid is sealed so as not to prevent suction when closed. . The method for decontaminating a building, soil, or plant according to claim 6, wherein the water-absorbing vacuum cleaner has a structure in which a motor of the water supply vacuum cleaner does not come into contact with bubbles in a waste water container. The method for decontaminating a building, soil, or plant according to claim 6, wherein an antifoaming agent or an antifoaming agent solution is put in advance in a waste water container of the water-absorbing vacuum cleaner. The method for decontaminating a building, soil, or plant contaminated with a radioactive substance according to claim 1 or 2, wherein the cleaning agent is an aqueous solution containing a surfactant as a main component. 3. The method for decontaminating a building or soil contaminated with a radioactive substance according to claim 1, wherein the cleaning agent contains an acid. 3. The method for decontaminating a plant contaminated with a radioactive substance according to claim 1, wherein the cleaning agent does not contain an acid. The method for decontaminating a building, soil, or plant contaminated with a radioactive substance according to claim 10, wherein the cleaning agent contains fine powder of a porous substance. 3. The method of decontaminating a building, soil or plant contaminated with a radioactive substance according to claim 2, wherein the first step is sprayed while foaming the cleaning agent using a foam generating device. 15. The building and soil according to claim 14, wherein the foam generating device introduces air from an air compressor into a cleaning agent container of the foam generating device, and jets the foaming cleaning agent from the nozzle at the pressure. Or a method of decontaminating plants.

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