JP6236752B2 - Radioactive substance-containing forest soil immobilization solution using water-soluble or water-dispersible polymer, and radioactive substance decontamination method using the immobilization solution - Google Patents

Description

  The present invention relates to a radioactive material-containing forest soil immobilization solution for immobilizing and removing forest soil including fallen leaves and humus soil contaminated by the adhesion and adsorption of radioactive material, and a radioactive material using the immobilization solution It relates to decontamination methods, and in particular, decontamination of radioactive material-containing forest soil existing in or around nuclear power generation related facilities.

  It is expected that radioactive materials that leak inside the nuclear power generation related facility or for some reason from the nuclear power generation related facility or scatter will contaminate the surrounding environment and have a serious adverse effect on the human body. Some radioactive materials such as cesium have a half-life of several decades or more, and this damage will continue not only at the time of radioactive material scattering and leakage, but also after that. For this reason, it is necessary to quickly decontaminate radioactive materials released from facilities related to nuclear power generation, and safely so as not to be exposed to radiation materials.

  Contamination to the surrounding area due to radioactive substances spreads not only to surrounding residential areas and farmland, but also to forests and forests. In residential and agricultural areas where the ground surface is exposed, radioactive materials that fall with rain are adsorbed by clay components. In that case, it is said that it is effective to decontaminate the surface soil by stripping the surface soil. (I) A method of scraping the surface using a large machine, (ii) High pressure A method of washing with water using a washing machine, (iii) a method of solidifying and decontaminating soil using a polyion complex, and the like are known.

  On the other hand, in the case of mountain forests, thick forests, etc., the ground surface is covered with fallen leaves and humus soil, and the fallen radioactive material is thought to be adsorbed on the humus (such as humic acid) where fallen leaves and humus soil exist . For this reason, in the case of decontamination of forests and forests, it is judged that removal of fallen leaves and humus on the surface is effective as a decontamination method, and it is judged that nearly 90% can be decontaminated.

  As a method for treating contaminated soil, in addition to the above-described removal method, a method of preventing the scattering and outflow of radioactive substances by forming a coating layer on the contaminated soil can be considered (for example, Patent Documents 1 to 3). 4). The coating layers described in Patent Documents 1 to 3 are composed of a composition containing a water-soluble or water-dispersible polymer, clay or gypsum, and water. Patent Document 4 discloses an alternative soil covering material containing an aqueous emulsion resin and water-insoluble particulate matter such as wood flour.

  In addition, the radioactive waste collected by the above decontamination method is generally packaged strictly, and then isolated and stored in a waste treatment facility for a long period of time. For example, in Patent Documents 5 and 6, there is a method for constructing a barrier with a clay material such as bentonite in a radioactive waste geological disposal in which a solidified radioactive waste is cast into a metal container and embedded in the geological formation. It is disclosed.

Japanese Patent Laid-Open No. 4-5000697 JP 2003-117515 A JP-A-2005-28319 JP 2002-186828 A JP 2007-515106 A JP 2006-313074 A

  In the case of forest soil containing radioactive substances including humic soil and fallen leaves, volatilization and release of radioactive substances are easily caused when removing those soils, and the internal exposure of workers is more problematic than before. In addition, if the radioactive material-containing forest soil is to be treated as it is, a large amount of waste is produced in volume, and the treatment work becomes complicated. Furthermore, since the area of the storage place becomes enormous when finally storing and storing, it is difficult to secure the place.

  The decontamination method for peeling the surface soil is not suitable for forest soil including fallen leaves and humus for the following reasons. That is, in the method (i) or (ii) described above, the fallen leaves, humus, and the like rise and float during the removal operation, which increases the risk of internal exposure of the operator. In addition, it is substantially difficult to decontaminate all forest soil including fallen leaves and humus soil to which radioactive substances are attached or adsorbed, because it requires enormous and complicated work. In the method (iii) described above, since the volume of forest soil is large, a large amount of polyion complex is required, which is not only a costly decontamination method, but also the polyion complex itself becomes a large amount of waste. End up. In addition, since the polyion complex has not only a function to solidify forest soil, but also a moisturizing function, this moisturizing function requires high temperature or a long time for drying, and decontamination work is performed immediately after fixing the forest soil. It has become a major obstacle to doing. The place where the forest soil is removed is usually a place with a lot of sunlight and poor ventilation, and therefore, drying of the polyion complex requires a period of at least 4 to 7 days and possibly longer.

  The inventions described in Patent Documents 1 to 4 are merely described or suggested for use as a covering layer, and their application as a decontamination method for radioactive material-containing forest soil is not recognized at all. It is practically impossible to leave forest soil contaminated with radioactive substances in a forest or a mixed forest with the method described in Patent Documents 1 to 4 as it is, in view of safety and storage. . In addition, the solutions for forming the coating layers described in Patent Documents 3 and 4 have compositions whose viscosities are set to high values of 5000 to 20000 cps (mPa · s) and 10,000 to 20000 cps (mPa · s), respectively. It is difficult to ensure sufficient permeability to remove most of the contaminated forest soil.

  Furthermore, the composition constituting the coating layer described in Patent Documents 1 to 4 is a composition containing gypsum, paper, wood powder, or the like, which is a component having no selectivity for radioactive substances such as cesium, The bentonite described in Patent Document 1 is merely used as a thickener or a waterstop material. Therefore, it is unclear whether these compositions can be applied as an immobilized solution for contaminated soil for radioactive material decontamination.

  The inventions described in Patent Documents 5 and 6 relate to a method for storing and preserving radioactive waste collected by a decontamination method, and decontamination for removing or collecting radioactive material-containing forest soil itself. Application as a method is not recognized at all. In addition, Patent Documents 5 and 6 describe or suggest any composition or configuration of an immobilization solution used to remove contaminated forest soil after the solution is applied or spread on the forest soil. Not.

  The present invention has been made to solve such a problem, and by fixing and removing forest soil including fallen leaves and humus soil to which at least a radioactive substance is attached or adsorbed, the amount of the radioactive substance is reduced by the human body. The radioactive material-containing forest soil immobilization solution and the immobilization solution that can be used to reduce the volume of radioactive waste at the same time can be reduced quickly, efficiently and effectively to a level that does not affect The purpose is to provide a method for decontamination of radioactive materials.

  The present inventor can easily and reliably immobilize and remove not only the forest soil contaminated by the attachment or adsorption of radioactive substances, but also the surface layer of the soil in contact with the forest soil as necessary. In view of the above, the present invention focuses on a method for fixing the forest soil with a polymer and finds that the above-mentioned problems can be solved by optimizing the configuration and composition of the immobilization solution containing the polymer. I reached.

That is, the configuration of the present invention is as follows.
(1) The present invention comprises (a) at least one biodegradable water-soluble or water-dispersible polymer selected from starch, polyvinyl alcohol, carboxymethyl cellulose and acetylated starch , and (b) water as a main component. The viscosity of the solution when the (a) biodegradable water-soluble or water-dispersible polymer is dissolved or dispersed in the aqueous medium (b) containing water as a main component. Provides an immobilizing solution for a forest soil containing a radioactive substance, which is adjusted to 5 to 4000 mPa · s at 4 to 30 ° C.
(2) In the present invention, the viscosity of the solution when the (a) biodegradable water-soluble or water-dispersible polymer is dissolved or dispersed in the aqueous medium (b) containing water as a main component is described above. The radioactive substance-containing forest soil immobilization solution according to (1) above, which is adjusted to 19 to 1000 mPa · s at 4 to 30 ° C., is provided.
(3) In the present invention, (b) the content of the biodegradable water-soluble or water-dispersible polymer is 10 to 10 parts per 100 parts by weight of the aqueous medium mainly composed of water. The radioactive substance-containing forest soil-fixing solution according to (1) or (2) above, which is 90 parts by mass.
( 4 ) The present invention includes the radioactive substance according to any one of (1) to (3) , wherein (a) the biodegradable water-soluble or water-dispersible polymer is starch. Provide an immobilization solution for forest soil.
( 5 ) The present invention provides (a) a biodegradable water-soluble or water-dispersible polymer and (b) an aqueous medium containing water as a main component, and (c) an inorganic radioactive substance adsorbent. The radioactive substance-containing forest soil fixing solution according to any one of the above (1) to (4) , which is contained.
( 6 ) The present invention provides the radioactive material-containing forest soil immobilization solution according to (5) , wherein the (c) inorganic radioactive material adsorbent is bentonite.
( 7 ) The present invention relates to (a) the biodegradable water-soluble or water-dispersible polymer (c) and (c) when 100 parts by mass of the water-based medium (b) is the main component. The content of the inorganic radioactive material adsorbent is 10 to 90 parts by mass and 0.1 to 15 parts by mass, respectively, and the component (c) is blended with a content less than the component (a). The radioactive substance-containing forest soil-immobilizing solution according to (5) or (6) is provided.
( 8 ) The present invention relates to (a) the biodegradable water-soluble or water-dispersible polymer (c) and (c) when 100 parts by weight of the water-based medium (b) is the main component. The radioactive material-containing forest soil fixing solution according to (7) above, wherein the content of the inorganic radioactive material adsorbent is 20 to 60 parts by mass and 0.5 to 5 parts by mass, respectively. To do.
( 9 ) The present invention uses the immobilization solution according to any one of (1) to (4) above, or applies the immobilization solution to the surface of forest soil containing fallen leaves or humus containing a radioactive substance. A step of spraying, the step of immobilizing the forest soil with the component (a) by drying the immobilization solution and volatilizing the aqueous medium mainly composed of water (b), and A method for decontaminating radioactive material, comprising the step of exfoliating and removing the forest soil together with nonvolatile components contained in the immobilization solution.
( 10 ) The present invention uses the immobilization solution according to any one of (5) to (8) above, and applies the immobilization solution to the surface of forest soil containing fallen leaves or humus containing a radioactive substance. A step of spraying, and drying the immobilization solution to volatilize the aqueous medium (b) containing water as a main component, so that the forest soil and the inorganic radioactive substance adsorbent (c) A radioactive substance decontamination method comprising the steps of: fixing the forest soil with the component (a); and stripping and removing the forest soil together with the nonvolatile components contained in the fixing solution.
(11 ) In the present invention, after removing the forest soil containing the fallen leaves or humus containing the radioactive substance together with the nonvolatile component contained in the immobilization solution, the forest soil containing the nonvolatile component is removed for a predetermined time. The radioactive substance decontamination method as described in (9) or (10) above, wherein the volume reduction treatment is performed by promoting the fermentation of the fallen leaves or mulch by storing or leaving.
( 12 ) The present invention removes forest soil containing fallen leaves or humus containing radioactive substances by spraying the entire solution of the immobilization solution according to any one of (5) to (8) above. A radioactive substance decontamination method that removes radioactive substances adhering to the leaves of trees in a forest together, and comprises the following steps (A), (B), (C) and (D): A step of adhering or adhering the immobilization solution to the leaves of the tree; (B) a radioactive substance adhering to the leaves of the tree in the state where the immobilization solution is adhered or adhered to the leaves of the tree; (C) Step of adsorbing to an inorganic radioactive material adsorbent, (C) Sprinkling water throughout the forest, or dissolving the immobilization solution with rainwater, and (c) Adsorbing the inorganic radioactive material Agent in forest soil surface or in forest soil Step thereby moved, and (D) characterized in that the said (c) inorganic forest soil containing radioactive materials adsorbent, the process is removed together with the forest soil containing fallen leaves or leaf mold containing said radioactive substance A radioactive material decontamination method is provided.
[Effect of the invention]

  According to the immobilization solution of the present invention, since it penetrates in the depth direction of the forest soil contaminated with the radioactive material in a short time with certainty, not only the contaminated radioactive material-containing forest soil but also the forest as necessary. Even the surface layer of the soil in contact with the soil can be immobilized by the biodegradable polymer. In addition, since the biodegradable polymer of the present invention is excellent in drying properties, it can reduce the time until it is dried and solidified after coating or spraying, and in addition, it dissolves or disperses uniformly in an aqueous medium. Handling becomes easy in the processing step. Therefore, it is not necessary to consider the environmental load due to the use of an organic solvent or the like, and the safety is excellent. The biodegradable polymer contained in the immobilization solution of the present invention has a function as an adhesive, pressure-sensitive adhesive, or paste for immobilizing radioactive material-containing forest soil, and therefore, the forest soil can be easily detached and removed. In addition, it is possible to prevent the radioactive material from being scattered during decontamination and to reduce the internal exposure of the worker. In particular, a polysaccharide used as a biodegradable polymer, preferably starch, has a high function of firmly immobilizing radioactive substance-containing forest soil. As a result, the radioactive material decontamination method according to the present invention can delaminate the radioactive material-containing forest soil and, if necessary, the surface layer of the soil in contact with the forest soil. Proceed quickly, efficiently and effectively.

  In the present invention, the immobilization solution further contains an inorganic radioactive material adsorbent such as bentonite, and absorbs surrounding moisture when the radioactive material adsorbent dries in the formation of the continuous layer. An effect (sanction effect) occurs, and the adsorption of a radioactive substance such as cesium to the adsorbent is promoted. The adsorbed radioactive material is fixed and stably held between the adsorbent layers and in the pores. Therefore, radioactive substances that contaminate the soil are reduced in speed in the soil and reliably and stably decontaminated. As a result, it is possible to further prevent the radioactive material from being scattered during decontamination and reduce the internal exposure of the worker.

It is a figure which shows the process of the radioactive substance decontamination method using the fixed solution by this invention. It is a figure which shows the radioactive substance decontamination method of this invention which removes together the radioactive substance adhering to the leaf of the tree in a forest, when removing forest soil.

Fixing solution of the present invention contains an aqueous medium mainly containing (a) a biodegradable water-soluble or water-dispersible high content element,及 Beauty (b) water, and a viscosity at 4 to 30 ° C. Is adjusted to the range of 5 to 4000 mPa · s, and is applied to or sprayed onto the forest soil surface contaminated with radioactive materials attached or adsorbed by spraying, pouring or brushing, etc., and then dried. The method is applied to a method for decontamination of forest soil containing radioactive substances, which comprises a step of peeling and removing forest soil fixed with a biodegradable polymer. In the present invention, forest soil includes fallen leaves or humus, and is distinguished from ordinary soil that forms a lower layer in contact with the forest soil.

  As described above, most of the radioactive substances in forest soil are attached to or adsorbed on fallen leaves or humus. The immobilization solution of the present invention is used for immobilization of forest soil containing fallen leaves or humus containing a radioactive substance, and further, decontamination of not only the forest soil but also forest soil containing a radioactive substance. In order to ensure, it can also be used to immobilize the surface part of the soil that contacts the forest soil and forms the lower layer.

  Each component of the above (a) and (b) exhibits the following functions in order to achieve the object of the present invention. That is, the contaminated forest soil is fixed by the function of the component (a) serving as an adhesive, an adhesive, or a paste of the contaminated forest soil. The component (a) is water-soluble or water-dispersible, and (b) it is used by being dissolved or dispersed in an aqueous medium. Even if a large amount is applied or sprayed for decontamination, the occurrence of environmental problems becomes very small. In addition, when the immobilized radioactive substance-containing forest soil is treated as it is, the volume of waste or disposal can be reduced by fermenting fallen leaves and humus. Since it is degradable, it becomes a nutrient for bacteria and microorganisms at this stage of fermentation, and has the effect of allowing the fermentation to proceed smoothly, as well as decomposition of the component (a).

  And the viscosity range of the immobilization solution containing each component of (a) and (b) is to improve the permeability to the radioactive soil containing forest soil, the thickness of the radioactive soil containing forest soil to be immobilized after drying. It is stipulated to satisfy all conditions such as optimization and suppression of the residue of removal of forest soil, and the like when removing and removing the immobilized radioactive substance-containing forest soil. In particular, the immobilization solution of the present invention improves the permeability to forest soil and optimizes the thickness of the radioactive substance-containing forest soil immobilized by the component (a) described above. It is characterized in that the viscosity is specified to be low based on a completely different technical idea from the coating layers described in 3 and 4.

  In the present invention, examples of (a) biodegradable water-soluble or water-dispersible polymers include natural polysaccharide polymers or chemically synthesized polymers such as polyvinyl alcohol.

  The polysaccharide is not particularly limited as long as it is substantially water-soluble and can be rigidized (cured) by dehydration after plasticization (melting). For example, the following polysaccharides can be used.

(A) Starches (A1) Unmodified starch on ground stems such as corn starch and wheat starch,
(A2) Unmodified starch of rhizomes such as tapioca and potato starch,
(A3) Low-level esterification, low-level etherification, cross-linking, oxidation, acid treatment, dextrinization, and pregelatinized starch of each above-ground stem and rhizome starch,
(B) Cellulose Carboxymethylcellulose (CMC), methylcellulose (MC), hydroxyethylcellulose, hydroxypropylcellulose, cationized cellulose, etc. (C) Seaweed polysaccharide agar, alginic acid, carrageenan, etc. (D) Microbial polysaccharide pullulan, dextran, xanthan gum (E) Other plant polysaccharides such as mannan, gum arabic, guar gum, tragacanth gum, locust gum, tamarind, etc.

  Further, after the reactive hydroxyl group of the above starch is ester-substituted (including organic acids, inorganic acids, and further graft-substituted products) and ether-substituted (including graft-substituted products) are dispersed in water, then a plasticizer Emulsion water (emulsion water composed of water, plasticizer and dispersion stabilizer) may be added to form a water-dispersible polymer solution.

  Polyvinyl alcohol (PVA) has a degree of polymerization of preferably 1000 to 5000, and more preferably 1700 to 2400. Furthermore, the saponification degree of PVA is preferably 85 to 99%, more preferably 87 to 93% because the solution is water-soluble.

  In the present invention, the function as an adhesive, pressure-sensitive adhesive or paste that strongly fixes radioactive substance-containing soil is high, high safety, ease of handling with an aqueous medium, high functionality for promoting fermentation, From the viewpoint of low price and the like, one or more of the above-mentioned polysaccharides are suitable as the component (a). Furthermore, among the above polysaccharides, it is more preferable to use starch having the highest function as an adhesive, pressure-sensitive adhesive, or paste for fixing radioactive substance-containing soil. Starch may be used in combination with polysaccharides other than starch as described above or polyvinyl alcohol.

  In the immobilization solution of the present invention, any of the above compounds is an essential component as the component (a), but other biodegradable polymers may be used as a subcomponent. Examples of the secondary biodegradable polymer include natural polymers such as chitosan and casein, and chemically synthesized polymers such as polylactic acid, polycaprolactan, and polyaspartic acid. The content of these biodegradable polymers is preferably less than 100 parts by mass and more preferably 50 parts by mass or less with respect to 100 parts by mass of the component (a). These contents are determined from the performance as an adhesive, a pressure-sensitive adhesive, or a paste that strongly fixes the radioactive substance-containing soil.

  The aqueous medium (b) containing water as a main component used in the present invention is a medium in which water accounts for 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. Since the radioactive substance decontamination solution of the present invention is intended for decontamination of soil, it is necessary to use an aqueous medium mainly composed of water in consideration of ease of handling, workability, and reduction of environmental load on the periphery. is there. In addition to water, for example, water-soluble alcohols such as methyl alcohol, ethyl alcohol, and 2-propanol, ethers such as diethyl ether and tetrahydrofuran, or ketones such as acetone, methyl ethyl ketone, and cyclohexanone are used in a small amount. May be. These solvents are used when it is necessary to adjust the viscosity with respect to the radioactive substance decontamination solution of the present invention or to dissolve components other than the above (a) as necessary. Among these solvents, ethyl alcohol is preferable in order to reduce the influence on the human body and the environmental load.

  The immobilization solution of the present invention needs to have a viscosity at 4 to 30 ° C. in the range of 5 to 4000 mPa · s, and preferably 19 to 1000 mPa · s. The construction work is carried out in an external environment of 4 to 30 ° C. throughout the year, and this viscosity range is the workability by coating and impregnation, and the workability when peeling and removing the radioactive material-containing forest soil fixed after drying. Determined from balance.

  If the viscosity is less than 5 mPa · s, the application and penetration of the immobilization solution is excellent, but the viscosity is low, and the radioactive material adhering to or adsorbing on the surface of fallen leaves may be washed away during application or spraying. There is. Moreover, since the content of the polymer is very low in the radioactive substance-containing forest soil fixed after drying, it is impossible to immobilize all the radioactive substance-containing forest soil as a result. In addition, the radioactive substance-containing forest soil fixed after drying has a markedly reduced effect of immobilization by the polymer, and is difficult to separate due to the occurrence of discrete, fractured or cracked during peeling. In addition, when the viscosity exceeds 4000 mPa · s, the operability and workability of the immobilization solution are deteriorated, and the permeability to the forest soil is inferior. Cannot be fixed sufficiently, and the removal of contaminated forest soil is insufficient. In addition, in forest soils containing radioactive substances that are fixed after drying, the content of polymers that function as adhesives, adhesives, or glues is high in the upper part corresponding to the soil surface and lower in the lower part corresponding to the deep part of the soil. As a result, the fixed radioactive substance-containing forest soil is left unremoved due to discrete or the like. In the present invention, the radioactive soil containing forest soil, which is reliably permeable to the thickly deposited radioactive material-containing forest soil and is immobilized by the polymer, can be produced without being discrete, broken, or cracked. The viscosity at 4 to 30 ° C. is preferably set in the range of 19 to 1000 mPa · s so that the film can be sufficiently peeled and removed.

  The immobilization solution of the present invention is not only for viscosity, but also for contamination, so that the forest soil containing radioactive material fixed with the polymer can be sufficiently exfoliated and removed without occurrence of discrete, fracture, or crack. It is preferable to optimize the content of the component (a) that functions as an adhesive, adhesive or paste for forest soil. In the present invention, the content of (a) the water-soluble or water-dispersible polymer is preferably 10 to 90 parts by mass when the total amount of the components (b) is 100 parts by mass.

  When the content of the component (a) is less than 10 parts by mass, the viscosity is low, and there is a risk that radioactive substances adhering to or adsorbing on the surface of fallen leaves or the like may be washed away during application or spraying. Moreover, since the content of the polymer in the forest soil containing radioactive material fixed after drying is low, it is impossible to fix all of the forest soil when the forest soil is thick. In addition, since the content of the component that functions as an adhesive, a pressure-sensitive adhesive, or a paste is insufficient, immobilization becomes insufficient, and the radioactive material-containing forest soil becomes discrete, ruptured or cracked, and peeling becomes difficult. Therefore, efficient decontamination cannot be performed. On the other hand, when the content of the component (a) exceeds 90 parts by mass, the viscosity of the immobilizing solution becomes too high, so that the workability of spraying and pouring is inferior, and the operability and workability are greatly reduced. Furthermore, the permeability to contaminated forest soil is poor, and as a result, the above-mentioned polymer cannot fix the contaminated forest soil thickly, resulting in insufficient removal of the contaminated forest soil. In addition, since the composition of the polymer is large in the upper part corresponding to the forest soil surface and less in the lower part corresponding to the forest soil depth, the composition of the radioactive material-containing forest soil is discrete. Breaking or cracking occurs, leaving behind removal, leading to a significant reduction in decontamination efficiency.

  The immobilization solution of the present invention preferably further contains (c) an inorganic radioactive substance adsorbent. The component (c) is an effective component for selectively adsorbing the radioactive substance and suppressing leakage and scattering of the radioactive substance that easily occurs during the decontamination process.

  In the present invention, (c) the inorganic radioactive substance adsorbent includes inorganic particles having an adsorbing ability to adsorb radioactive substances, such as bentonite, zeolite, mica, vermiculite, smectite, and the like. Although the average particle diameter of these inorganic particles can be in the range of 0.01 to 20 μm, it is preferably 1 to 2 μm. The maximum particle size of these inorganic particles is 100 μm or less, preferably 50 μm or less. When the average particle size is less than 0.01 μm, the aggregation of inorganic particles is likely to occur, and the workability in the adjustment and application of the fixing solution becomes remarkable. Moreover, since inorganic particles having a large diameter are mixed when the thickness exceeds 20 μm, the mechanical strength of the fixed layer containing the above-described radiation-substance-containing forest soil is greatly reduced, and peeling and removal become difficult. For the same reason, the maximum particle size of these inorganic particles is 100 μm or less, preferably 50 μm or less.

  In the present invention, among the above-mentioned inorganic particles, bentonite is preferred from the standpoint of achievement as a radioactive substance adsorbent, handling properties, low cost, and the like. Furthermore, bentonite is particularly useful because the above-described sanction effect is superior to other inorganic particles. Bentonite can be obtained at a low cost because it can be used as it is after adjusting the maximum particle size to 100 μm or less, preferably 50 μm or less by removing coarse particles from those mined in the bentonite mine.

  In the immobilization solution of the present invention containing the component (c), the contents of the components (a) and (c) are as follows when the component (b) is 100 parts by mass. It is preferable to set it as 10-90 mass parts and 0.1-15 mass parts. More preferable content of each component of said (a) and (c) is 20-60 mass parts and 0.5-5 mass parts, respectively. In particular, in the present invention, unlike the composition for forming a coating layer as disclosed in Patent Documents 1 and 2, the content of the component (a) is more than that of the component (c). Characterized by high points. This is to ensure that the forest soil containing radioactive material is securely fixed with a polymer and that the forest soil containing the radioactive material fixed with the polymer is peeled and removed, and the strength and appropriateness do not cause discrete, cracking or breaking. This is to provide a high degree of flexibility and to remove the radioactive material present in the forest soil as easily and reliably as quickly as possible.

  The content of the component (a) is, as described above, the permeability of the contaminated forest soil, the thickness of the radioactive material-containing soil fixed after drying, and the removal of the radioactive material-containing forest soil in delamination removal. It is preferable to set it as the range of 10-90 mass parts from the point of suppression of a discrete, a crack, or a fracture | rupture. Further, in order to optimize the thickness of the radioactive substance-containing soil fixed after drying in a state in which the permeability to the contaminated soil is ensured, in order to facilitate the removal and removal of the radioactive substance-containing soil (a The content of the component is more preferably in the range of 20 to 60 parts by mass.

  If the content of component (c) is less than 0.1 parts by mass, the effect of adsorbing the radioactive material cannot be sufficiently obtained, and there is concern about the decontamination ability of the radioactive material, and the decontamination process and long-term storage It is impossible to avoid leakage and scattering of radioactive materials inside. Further, the adsorption effect of the radioactive substance only shows a tendency of saturation when the content of the component (c) exceeds 15 parts by mass. Cause a significant decrease in workability and workability. Furthermore, since the component (c) is inorganic, segregation in the immobilization solution is more likely to occur as the content increases, so that not only handling properties are inferior, but also the forest soil containing the radioactive substance is included. Discrete, broken or cracked fixed layers become noticeable. As described above, bentonite is suitable as the component (c) in the present invention, but bentonite is often used as a thickener or a waterstop material. Therefore, when bentonite is applied as a radioactive substance-containing soil fixing solution that achieves the object of the present invention, when its content increases, the viscosity increases rapidly and the coating workability is greatly reduced. In addition, a certain amount of bentonite is required in order to reliably adsorb radioactive substances by bentonite. Therefore, when bentonite is applied as the component (c), the content is more preferably 0.5 to 5 parts by mass, and particularly preferably 1 to 2 parts by mass.

  In the present invention, the immobilization solution containing the components (a), (b) and (c) above has a viscosity at 4 to 30 ° C. containing the components (a) and (b) above. It is necessary to be in the range of 5 to 4000 mPa · s, preferably 19 to 1000 mPa · s, as in the case of the immobilizing solution. This is determined from the balance between workability by application and impregnation and workability when peeling radioactive material-containing forest soil fixed after drying in construction work performed in an external environment of 4 to 30 ° C throughout the year. It is done. Even in the fixing solution containing the components (a), (b) and (c) above, the range of the viscosity required in the construction work contains the components (a) and (b) above. Same as in the case of the immobilization solution.

  In the present invention, in addition to the above-mentioned components (a) to (c), an adhesive-type or adhesive-type bonding agent can be blended as necessary, and the bonding agent is water-soluble or non-biodegradable. Water dispersible polymers can be used. Examples of water-soluble or water-dispersible polymers that do not have biodegradability include, for example, polyvinyl acetate, polyacrylamide, polyvinyl pyrrolidone, polyacrylic acid and its salts, and polyacrylic acid esters containing hydroxyl groups. 1 type or 2 or more types of molecule | numerators or water-dispersible polymers, such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, styrene-acrylic acid ester copolymer, vinyl acetate-acrylic acid ester copolymer Can be used. These polymers are used for assisting immobilization of radioactive material-containing forest soil by the component (a). The content of these macromolecules in the immobilization solution of the present invention is arbitrarily determined according to the immobilization performance and biodegradability of the radioactive material-containing forest soil, but priority is given to volume reduction of the radioactive material-containing soil. In the case where the component (b) is 100 parts by mass, it is 20 parts by mass or less, preferably 10 parts by mass or less.

  Furthermore, in the present invention, if necessary, a plasticizer for imparting flexibility, a dispersant or surfactant for improving the dispersibility between the polymer and the inorganic radioactive material absorbent, and viscosity adjustment Thickeners, viscosity modifiers, preservatives, colorants, deodorizers, and the like can be added. In particular, the colorant can not only identify the application location of the radioactive substance decontamination solution of the present invention, but also the peeling that occurs when the contaminated soil formed after coating and drying peels a continuous layer fixed with a polymer. It is an additive that can be used to check the rest, and is useful when performing decontamination work efficiently.

  Next, the process of the radioactive substance decontamination method using the immobilization solution according to the present invention will be described with reference to FIG.

(1) Preparation of immobilization solution:
Based on the content as described above, the components (a) to (c) are blended, and the radioactivity in the present invention has a viscosity defined in the range as described above in order to perform application or dispersion. Prepare the immobilization solution for the forest soil containing substances. If necessary, in addition to the components (a) to (c), an adhesive-type or adhesive-type bonding agent, a plasticizer, a dispersant, a surfactant, a thickener, a viscosity modifier, a preservative, and coloring. An agent or deodorant is blended.

(2) Application or application of immobilization solution to radioactive soil containing forest material:
The immobilization solution prepared in the above (1) is applied or dispersed at room temperature (a range of 4 to 30 ° C. throughout the year) to forest soil including fallen leaves and humus soil to which radioactive substances are attached or adsorbed. Application or spraying is performed by spraying, pouring or brushing, etc., depending on the location of the contaminated forest soil and the installation form. used. Moreover, in application | coating or dispersion | distribution, the fixed solution of this invention can be heated previously and viscosity can be adjusted. Furthermore, you may use the coating device or spray apparatus which can be heated at the time of application | coating or dispersion | distribution.

(3) Drying:
After the step (2), the immobilization solution of the present invention is dried to volatilize the aqueous medium as component (b). Drying is performed at an outside air temperature for a predetermined time (usually 1 hour to 1 week), but if necessary, a method of adding hot air to an application or spraying place to accelerate drying may be employed. In the present invention, usually, if the drying time is 2 to 3 days, the peeling can be performed, and if the temperature is high, the peeling operation can be started in the shortest day.

(4) Immobilization of radioactive material-containing forest soil with polymer:
After drying the immobilization solution of the present invention, the radioactive substance-containing forest soil is immobilized with the polymer as the component (a). In some cases, fixing is performed including the surface layer of the soil in contact with the radioactive material-containing forest soil. At this time, the immobilization solution may be dried as long as the above component (b) does not need to be completely removed, and can be easily removed from the radioactive substance-containing forest soil. . The continuous layer formed in this step is finally subjected to a peeling process in the next step (5).

(5) Detachment and removal of radioactive material-containing forest soil fixed with polymer:
The radioactive material-containing forest soil fixed with a polymer can be easily peeled off manually or using suction or the like by a crane for separation and collection or a vacuum vehicle. The radioactive material-containing forest soil fixed with polymer is peeled and removed using a crane that has upper and lower collection claws, and then packed into storage bags and packs to reduce internal exposure of workers. In addition, the decontamination work can be speeded up and simplified. In the present invention, since the above-mentioned radioactive substance-containing forest soil is firmly fixed by the polymer, it is excellent in operability and workability.

(6) Storage / preservation of radioactive material-containing forest soil fixed with polymer:
After peeling and removing in the step (5) above, the radioactive material-containing forest soil fixed with a polymer is transported to a place where the radioactive material has been treated so that it does not scatter or leak outside. Stored and stored after. Alternatively, the radioactive material-containing forest soil packed in a storage bag or pack may not be transported, and the volume reduction treatment by fermentation shown in the next step (7) may be performed locally.

(7) Volume reduction treatment by fermentation of radioactive material-containing forest soil fixed with polymer In the above step (6), fallen leaves and humus contained in radioactive material-containing soil start fermentation immediately after storage. In the state where it is stored as it is, the fermentation is promoted and the volume reduction process is advanced.

  In the present invention, when the radioactive substance-containing forest soil fixed with a polymer contains (c) an inorganic radioactive substance adsorbent, by grasping the adsorption behavior of the radioactive substance to the component (c) in advance, Determine the retention period. In other words, if the time (adsorption time) during which radioactive materials are adsorbed to a level that does not affect the human body is known, the radioactive material-containing forest soil fixed with the polymer is stored and preserved at least longer than the adsorption time. Leave in condition. In order to further increase safety, a longer storage / preservation time is set with a margin than the adsorption time. Even at that time, if the fermentation of the radioactive substance-containing soil or the biodegradation of the component (a) has not progressed, the storage / preservation time may be further extended.

  Eventually, it was stored and stored in a sealed state until the period when radiation dose reduction was confirmed to a level that had no impact on the human body, and until the volume reduction of forest soil containing radioactive material was confirmed. Later, it is returned as normal soil or discarded as industrial waste.

  As described above, the radioactive substance decontamination method of the present invention not only quickly, efficiently and effectively reduces radiation from radioactive substance-containing forest soil including fallen leaves and humus soil to which radioactive substance is attached or adsorbed. In order to reduce the volume of the radioactive contaminant itself, the steps (1) to (7) shown in FIG. 1 are included.

  Further, the above-described immobilizing solutions (a), (b) and (c) are not only used for immobilizing and removing forest soil, but also for decontamination of radioactive substances attached to the leaves of trees in the forest. It is also possible to apply the method. FIG. 2 shows a radioactive substance decontamination method for removing together radioactive substances adhering to the leaves of trees in the forest when removing forest soil including fallen leaves or humus containing radioactive substances. In FIG. 2, route (I) is a radioactive material decontamination method for removing forest soil including fallen leaves or humus soil containing radioactive material, as described above, and route (II) is in the forest. This is a method for decontaminating radioactive substances adhering to the leaves of trees.

The route (II) shown in FIG. 2 is composed of the following steps (A), (B), (C), and (D). For example, the above-described (a) to (c) using a helicopter or the like. )) (For example, an aqueous solution containing starch and bentonite) is sprayed on the forest. That is, (A) a step of adhering or adhering an immobilization solution consisting of the above (a) to (c) to the leaves of a forest tree,
(B) In the state where the immobilization solution is adhered or adhered, a radioactive substance (for example, cesium) adhering to the leaf surface of the tree is included in the immobilization solution. (C) Inorganic radioactive substance adsorption Adsorbing to an agent (for example, bentonite),
(C) Dispersing water throughout the forest or dissolving the immobilizing solution by rain and moving the (c) inorganic radioactive material adsorbent onto the forest soil surface or into the forest soil; and (D) removing the forest soil containing the above-mentioned (c) inorganic radioactive material adsorbent together with the forest soil containing fallen leaves or humus containing the radioactive material,
Consists of. At this time, in the forest soil including the fallen leaves, radioactive substances (eg, cesium) in the fallen leaves are adsorbed by (c) an inorganic radioactive material adsorbent (eg, bentonite).

  In the present invention, as shown in the lower part of FIG. 2, the radiation material may be decontaminated using another method even when the forest soil including fallen leaves or humus is not removed. For example, as shown in the route (III) shown in FIG. 2, (c) the inorganic radioactive material adsorbent (bentonite) that adsorbs the radioactive material (cesium) moves in the vertical direction (in the soil) without staying on the soil surface. In this case, (c) an inorganic radioactive material adsorbent (bentonite) is retained in the forest soil as it is. Cesium adsorbed on bentonite is firmly fixed, and hardly migrates into the soil even after adsorption, so that it is possible to significantly reduce the concentration of radioactive substances in the soil.

  When bentonite that adsorbs cesium moves to the foot of the mountain along the slope of the mountain, the bentonite that adsorbs cesium is added to the fixing solution of the present invention or the route (IV) shown in the lower part of FIG. After adsorbing and holding on the soil sprayed with the conventional polyion complex, it may be removed and decontaminated.

  Therefore, according to the present invention, safe and reliable radioactive material decontamination can be performed by selecting at least one of the decontamination methods shown in FIG. 2 according to the radioactive contamination state of the forest. .

  The present invention will be described with reference to examples, but the scope of the present invention is not limited to these examples.

[Examples 1-5, Comparative Examples 1-3]
Starch (corn starch) was dissolved in an aqueous medium to prepare various solutions having different starch contents and different viscosities as shown in Table 1 below. The starch content is expressed in parts by mass when the total amount of the aqueous medium is 100 parts by mass. The viscosity was measured at room temperature (18-25 ° C.) using a spindle type viscometer (TV-20 model, manufactured by Tokimec).

  Preliminary experiments were conducted to examine the degree of immobilization of forest soil with the starch solution shown in Table 1. As an experimental method, 50 g of fallen leaves were placed on a 24.5 cm × 33.0 cm tray, and 20 g of dried soil (soil not containing radioactive material) was sprayed thereon. In this example, the soil sprayed on the fallen leaves in a simulated manner was used in place of the radioactive material-containing forest soil.

The starch solution shown in Table 1 was sprayed in an amount of 5 l (liter) / m ² and dried at 60 ° C. for about 3 hours. Next, a net was put on the tray so as not to suck the fallen leaves, and the suction force of the vacuum cleaner was kept constant, and the soil on the fallen leaf surface was sucked for 1 minute. Then, the difference in weight before and after the suction of the paper pack of the vacuum cleaner was measured and used as the amount of soil suction. In this example, the smaller the amount of soil suction, the stronger the fixation of forest soil with starch.

  The experimental results are shown in Table 1 below. The comprehensive evaluation shown in Table 1 shows the result of comprehensively determining the applicability of the radioactive material-containing forest soil as a fixed solution in view of the viscosity of the fixed solution, workability and workability, and the amount of soil suction. It is a thing. In other words, the best evaluation as a comprehensive evaluation (◎), the one that can be used as an immobilization solution (○), the one that can be used as an immobilization solution (△), and the one that cannot be used The thing was represented by (x). In addition, the amount of soil suction shown in Comparative Example 1 of Table 1 (in the case where an immobilization solution containing starch is not used) is a reference value when estimating the effect of immobilizing forest soil in this example. .

  From Table 1, it can be seen that the immobilization solution of this example can ensure the immobilization of forest soil unlike Comparative Example 1 in which no immobilization solution is used. Moreover, the fixed solution which is excellent in the permeability to forest soil and the fixation property of the forest soil by starch can be obtained by defining the viscosity in the range of 5 to 4000 mPa · s. In order to satisfy such a viscosity range, it is necessary to regulate the starch content in the range of 10 to 90 parts by mass with respect to 100 parts by mass of the aqueous medium. Furthermore, if the viscosity of the immobilization solution is in the range of 19 to 1000 mPa · s, it is optimal as an immobilization solution for radioactive material-containing forest soil.

  On the other hand, immobilization solutions (Comparative Examples 2 to 3) in which the viscosity and starch content are out of the above ranges have problems in permeability to forest soil and forest soil fixation by starch. Not suitable for immobilization applications. In particular, Comparative Example 3 was found to be somewhat difficult to apply and spread the coating solution at room temperature, and to be inferior in terms of workability and workability.

  Thus, the immobilization solution that exhibits the effect of the present invention includes the viscosity at the temperature during coating or spraying (usually a temperature range of 4 to 30 ° C.), and the content of the component (a) in order to achieve the viscosity. It can be obtained by defining the amount within a predetermined range.

[Examples 6 to 8]
In place of the starch used in Example 4, polyvinyl alcohol (abbreviated as PVA in Table 2), carboxymethylcellulose (abbreviated as CMC in Table 2) or highly substituted acetylated starch having a polymerization degree of about 2000 was used. An immobilization solution was prepared by dissolving or dispersing in a medium. The content of PVA or CMC was dissolved in an aqueous medium so as to be 60 parts by mass with respect to 100 parts by mass of the aqueous medium. Further, the highly substituted acetylated starch was used as an aqueous dispersion in which a plasticizer emulsion comprising a plasticizer and a dispersion stabilizer was added and emulsified and dispersed in a state of being dispersed in water. The content of the highly substituted acetylated starch was adjusted to 60 parts by weight with respect to 100 parts by weight of the aqueous medium. After measuring the viscosity of the immobilization solution and the amount of soil suction by the same method as in Example 4, comprehensive evaluation was performed in consideration of these physical quantities and the workability and workability of the immobilization solution. The evaluation results are shown in Table 2.

  As shown in Tables 1 and 2, as the component (a) of the present invention, not only water-soluble polymers such as starch, polyvinyl alcohol and carboxymethyl cellulose, but also water-dispersible polymers as shown in Example 8 are used. Can be used. As can be seen from the comprehensive evaluation results shown in Tables 1 and 2, starch (Example 4) has a lower amount of soil suction than the other polymers (Examples 6 to 8), and it fixes forest soil. Is more robust.

  In addition, even if content of the said (a) component is the same, the fixative solution in this invention has a little different viscosity according to the kind of polymer | macromolecule. Usually, the permeability of the solidified solution into the soil is largely determined by the viscosity of the solution. Therefore, the immobilization solution of the present invention is clearly identified by first defining the components constituting the immobilization solution and the viscosity range.

[Examples 9 to 17, Comparative Example 4]
Incorporation of an inorganic radioactive material adsorbent into the immobilization solution of Example 3 or 4 and dilution with an aqueous medium, as shown in Table 3 below, adsorption of starch (corn starch) and inorganic radioactive material Various immobilization solutions having different agent contents and viscosities were prepared. The content of each component shown in Table 3 is the content when the aqueous medium is 100 parts by mass. Examples of the inorganic radioactive material adsorbent include bentonite donmine (manufactured by Volclay Japan KK, abbreviated as bentonite A in Table 3), bentonite black hills (manufactured by American Colloid Company, abbreviated as bentonite B in Table 3), Alternatively, zeolite was used. After measuring the viscosity of the immobilization solution and the amount of soil suction by the same method as in Examples 1 to 6, comprehensive evaluation was performed in consideration of these measurement results, workability and workability of the immobilization solution. The evaluation results are shown in Table 3.

  As shown in Table 3, the immobilization solution of the present invention has a slightly higher viscosity by containing (c) an inorganic radioactive substance adsorbent. The amount of soil absorbed decreases slightly as the viscosity of the solution increases. This is due to the progress of immobilization of forest soil due to the increase in viscosity. However, when the viscosity increases significantly (Examples 15 and 16), conversely, the amount of absorbed soil tends to increase compared to the solution (Example 3) not containing the component (c). . In Examples 15 and 16, since the penetration of the solution into the bottom of the forest soil decreases, it is considered that the forest soil existing near the bottom has not been sufficiently fixed.

  On the other hand, as shown in Comparative Example 4 in Table 3, when the content of bentonite exceeds 15 parts by mass, the viscosity of the solution is greatly increased, so that it is not suitable as an immobilizing solution for radioactive material-containing forest soil. . On the other hand, the amount of the radioactive substance adsorbing effect clearly is 0.1% by mass or more, more preferably 0.5 parts by mass or more. Therefore, in the present invention, the more preferable range of the content of the component (c) is in the range of 0.5 to 5% by mass in view of the adsorption effect of the radioactive substance and the comprehensive evaluation result of the peelability shown in Table 3. It is.

[Example 18]
Using the immobilization solution of Example 3, it was uniformly applied on a forest soil contaminated with a radioactive substance such as cesium at room temperature (about 20 ° C.) with a spray device at a condition of 5 l (liter) / m ^2. The radioactive soil containing forest soil was fixed with starch after standing at room temperature for 1 day, and then stripped off. As a result of measuring each radiation dose for the surface of the contaminated forest soil at the initial stage and the soil surface after the above-described radioactive material-containing forest soil was peeled and removed, the ratio of the radiation dose after the peeling removal to the initial stage is 15%. The decontamination rate was 85%.

[Example 19]
Using the fixing solution of Example 11 (containing 1.0% by mass of bentonite B), the radioactive material-containing forest soil was fixed with starch in the same manner as in Example 18, and then stripped and removed. As a result of measuring each radiation dose for the surface of the contaminated forest soil at the initial stage and the soil surface after the above-mentioned radioactive material-containing forest soil was peeled and removed, the ratio of the radiation dose after the peeling removal to the initial stage was 8%. The decontamination rate was 92%. Thus, it was confirmed that the immobilization solution of the present invention containing an inorganic radioactive substance adsorbent can effectively perform decontamination of contaminated forest soil.

[Comparative Example 5]
Without using the immobilization solution, the same amount of radioactive material-containing forest soil as in Example 18 was peeled and removed from the forest soil contaminated with radioactive materials such as cesium. This process corresponds to Comparative Example 1 described above. As a result of measuring the radiation dose on the soil surface of the contaminated forest soil at the initial stage and the soil surface after removing the predetermined amount of radioactive material-containing forest soil, the ratio of the radiation dose after the stripping removal to the initial stage is 65%. The decontamination rate was 35%. This is because the radioactive materials adhering to or adsorbing to the radioactive soil containing forests are not fixed, and when they are stripped and removed, these radioactive materials are volatilized or released, resulting in The ratio of radiation dose after removal is considered to have increased.

  As described above, the decontamination method using the immobilization solution of Examples 18 and 19 not only shortens the drying time after the application or application of the immobilization solution, but also exfoliates and removes radioactive soil containing forest soil. It can be seen that an excellent decontamination effect can be obtained by reliably performing the above.

  As shown in the Examples, the radioactive substance-containing forest soil immobilization solution of the present invention comprises (a) a biodegradable water-soluble or water-dispersible polymer, and (b) an aqueous medium mainly composed of water. In addition, since the viscosity of the immobilization solution and the content of each component are optimized, it has excellent permeability to contaminated forest soil, and the drying process after application or spraying is performed in a shorter time than before. Can do. In addition, since the radioactive material-containing forest soil is firmly fixed by the component (a) after the drying step, not only can reliable peeling and removal be performed, but also the internal exposure of the operator can be reduced. . Furthermore, (c) by containing an inorganic radioactive material adsorbent, the radioactive material in the contaminated soil is stably fixed, and its movement is greatly suppressed during the decontamination treatment. The effect of reducing internal exposure and the decontamination effect of forests or thickets can be further enhanced.

  On the other hand, in the decontamination method that does not use the immobilization solution of the present invention, not only there is a risk of internal exposure of the operator, but it is difficult to reliably remove and remove the radioactive material-containing forest soil.

  As described above, the immobilization solution of the present invention has a configuration that can quickly and reliably exfoliate and remove radioactive substance-containing forest soil fixed with a biodegradable polymer. Not only that, but it contains an inorganic radioactive material adsorbent that can stably hold radioactive materials such as cesium ions, thereby preventing volatilization and release of radioactive materials to the outside, reducing internal exposure to workers. However, it is possible to reliably and stably perform decontamination of forests and wooded forests. Therefore, the radioactive substance decontamination method of the present invention using the fixing solution having such characteristics can perform decontamination by stripping and removing the radioactive substance-containing forest soil quickly, efficiently and effectively. In addition, since the radioactive substance decontamination method of the present invention uses an immobilized solution containing a biodegradable polymer that promotes fermentation of fallen leaves and humus, it is also an effective method for reducing the volume of radioactive substance contaminants themselves. It is extremely useful.

Claims (12)

(A) starch, polyvinyl alcohol, at least one biodegradable water-soluble or water-dispersible high content element selected from carboxymethyl cellulose and acetylated starch, 及 Beauty (b) an aqueous medium containing water as a main component, a Contains,
When the (a) biodegradable water-soluble or water-dispersible polymer is dissolved or dispersed in the aqueous medium (b) containing water as a main component, the viscosity of the solution is 5 at 4 to 30 ° C. A radioactive material-containing immobilization solution for forest soil, which is adjusted to ˜4000 mPa · s.   When the (a) biodegradable water-soluble or water-dispersible polymer is dissolved or dispersed in the aqueous medium (b) containing water as a main component, the viscosity of the solution is 19 at 4 to 30 ° C. It adjusted so that it might become -1000mPa * s, The fixing solution of the radioactive substance containing forest soil of Claim 1 characterized by the above-mentioned.   When (b) the aqueous medium containing water as a main component is 100 parts by mass, the content of the (a) biodegradable water-soluble or water-dispersible polymer is 10 to 90 parts by mass. The radioactive substance-containing forest soil immobilization solution according to claim 1 or 2. 4. The radioactive substance-containing forest soil immobilization solution according to claim 1, wherein the (a) biodegradable water-soluble or water-dispersible polymer is starch. The (a) biodegradable water-soluble or water-dispersible polymer and (b) an aqueous medium containing water as a main component further contain (c) an inorganic radioactive substance adsorbent. The radioactive substance containing forest soil immobilization solution in any one of Claims 1-4 . 6. The radioactive substance-containing forest soil immobilization solution according to claim 5 , wherein the (c) inorganic radioactive substance adsorbent is bentonite. When (b) 100 parts by mass of the aqueous medium containing water as a main component is used, (a) the biodegradable water-soluble or water-dispersible polymer and (c) the inorganic radioactive material adsorbent The content of each is 10 to 90 parts by mass and 0.1 to 15 parts by mass, and the component (c) is blended with a content less than the component (a). The radioactive substance-containing forest soil immobilization solution according to claim 5 or 6 . When (b) 100 parts by mass of the aqueous medium containing water as a main component is used, (a) the biodegradable water-soluble or water-dispersible polymer and (c) the inorganic radioactive material adsorbent The radioactive substance-containing forest soil immobilization solution according to claim 7 , wherein the content of each is 20 to 60 parts by mass and 0.5 to 5 parts by mass, respectively. Using the immobilization solution according to any one of claims 1 to 4 , a step of applying or spraying the immobilization solution on the surface of forest soil containing fallen leaves or humus containing a radioactive substance, the immobilization solution (B) fixing the forest soil with the component (a) by volatilizing the aqueous medium mainly containing water (b), and the forest soil with the immobilization solution A method for decontaminating radioactive materials, comprising a step of peeling and removing together with the nonvolatile components contained in the material. Using the immobilization solution according to any one of claims 5 to 8 , a step of applying or spraying the immobilization solution on the surface of forest soil containing fallen leaves or humus containing a radioactive substance, the immobilization solution The forest soil and the inorganic radioactive material adsorbent (c) are immobilized with the component (a) by drying and volatilizing the aqueous medium (b) containing water as a main component. And a step of peeling and removing the forest soil together with the non-volatile components contained in the immobilization solution. After removing and removing the forest soil containing fallen leaves or humus containing the radioactive substance together with the nonvolatile component contained in the immobilization solution, the forest soil containing the nonvolatile component is stored or left for a predetermined time, The radioactive substance decontamination method according to claim 9 or 10 , wherein the volume reduction treatment is performed by promoting fermentation of the fallen leaves or mulch. By fixing solution according to any of claims 5-8 for spraying the whole forests, in removing the forest soil containing the fallen leaves or humus containing radioactive materials, adhered to the leaves of trees in forests A radioactive substance decontamination method for removing radioactive substances in combination, wherein the following steps (A), (B), (C) and (D), that is, (A) the immobilization on the leaves of the tree Attaching or adhering the solution,
(B) a step of adsorbing the radioactive substance adhering to the leaves of the tree to the inorganic radioactive substance adsorbent (c) contained in the immobilization solution in a state where the immobilization solution is adhered or adhered;
(C) Dispersing water throughout the forest or dissolving the immobilizing solution by rain and moving the (c) inorganic radioactive material adsorbent onto the forest soil surface or into the forest soil; and (D) removing the forest soil containing the inorganic radioactive material adsorbent (c) together with the forest soil containing fallen leaves or humus containing the radioactive material;
A radioactive material decontamination method comprising:

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