JP2014010040A - Method of attenuating radiation dose from soil, radiation-attenuating material, and method of manufacturing radiation-attenuating material - Google Patents

Abstract

The present invention provides a method for attenuating radiation dose from soil, a radiation attenuating material, and a method for producing the radiation attenuating material.
The method for attenuating the radiation dose from soil according to the present invention is a particulate radiation comprising 100 parts by mass of an elastomer and 10 parts by mass to 120 parts by mass of a carbon material comprising at least one of graphene and carbon nanotubes. The attenuation member 50a is sprayed on the soil 1 contaminated with a radioactive substance. Since the carbon material 50a made of at least one of graphene and carbon nanotubes has a radiation R shielding effect, the radiation dose from the soil 1 can be attenuated by spraying the particulate radiation attenuation member 50a on the soil 1. .
[Selection] Figure 3

Description

  The present invention relates to a method for attenuating radiation dose from soil, a radiation attenuating material, and a method for producing a radiation attenuating material.

  The soil contamination of radioactive materials due to the accident at the TEPCO's Fukushima Daiichi Nuclear Power Station, which occurred in conjunction with the 2011 off the Pacific coast of Tohoku Earthquake on March 11, 2011, is a serious problem. Decontamination of contaminated soil is an urgent issue. It is. At present, decontamination work such as removal of contaminated soil and removal with an adsorbent is being carried out, but the area contaminated by radioactive materials is very wide and the decontamination work is not progressing.

  Many of the decontamination work currently being conducted in Fukushima Prefecture is that the surface of the building is washed with water using a high-pressure washing machine, etc., the soil surface is wiped off, and the wiped soil is buried. Is. Although such decontamination methods have certain effects, the contaminated areas are very wide and it is difficult to decontaminate all contaminated soil surfaces as well.

  In addition to natural minerals such as zeolite, cesium adsorbents include radioactive cesium adsorbents using Prussian blue, which is a pigment (see, for example, Non-Patent Document 1). Such adsorbents can adsorb radioactive substances in contaminated soil and remove them together with adsorbents, but since they do not have the ability to shield radiation, they can be removed from radioactive cesium adsorbed on adsorbents during storage and transportation. There are concerns about the external effects of radiation.

National Institute of Advanced Industrial Science and Technology (AIST) Press Release August 24, 2011 "Developing various forms of cesium adsorbents using Prussian Blue"

  Therefore, the present invention provides a method for attenuating the radiation dose from soil, a radiation attenuating material, and a method for producing the radiation attenuating material.

The method for attenuating the radiation dose from the soil according to the present invention comprises:
A particulate radiation attenuation member in which 10 parts by mass or more and 120 parts by mass or less of a carbon material composed of at least one of graphene and carbon nanotubes is blended in 100 parts by mass of an elastomer is sprayed on soil contaminated with a radioactive substance.

According to the method for attenuating the radiation dose from the soil according to the present invention, since the carbon material composed of at least one of graphene and carbon nanotubes has a radiation shielding effect, by spraying particulate radiation attenuation members on the soil Can attenuate the radiation dose from the soil. Further, according to the method for attenuating the radiation dose from the soil according to the present invention, the specific gravity of the particulate radiation attenuating member is not as large as that of metal particles, so it is difficult to settle into the ground due to rain or the like, and it may remain near the ground surface. Therefore, radiation can be attenuated efficiently. In particular, in the decontamination work, by carrying out the method for attenuating the radiation dose from the soil according to the present invention, the soil on which the radiation attenuating member is dispersed is transported and stored for the decontamination operator when stored. The influence of radiation from the soil can be reduced.

In the method for attenuating radiation dose from soil according to the present invention,
When the carbon material is graphene, the carbon material can be blended in an amount of 10 to 80 parts by mass with respect to 100 parts by mass of the elastomer.

In the method for attenuating radiation dose from soil according to the present invention,
The radiation attenuation member may further include 5 parts by mass or more and 100 parts by mass or less of one or more kinds of radioactive substance adsorbents selected from activated carbon, zeolite, and Prussian blue.

In the method for attenuating radiation dose from soil according to the present invention,
The radiation attenuation member may further include 20 parts by mass or more and 300 parts by mass or less of a water absorbent resin.

In the method for attenuating radiation dose from soil according to the present invention,
The radiation attenuation member may further include 50 parts by mass or more and 2000 parts by mass or less of metal particles.

The radiation attenuating material according to the present invention is
A carbon material composed of at least one of graphene and carbon nanotubes is blended in an amount of 10 to 120 parts by mass with 100 parts by mass of the elastomer.

  According to the radiation attenuating material according to the present invention, by obtaining a radiation attenuating material that is a composite elastomer composition containing a carbon material composed of at least one of graphene and carbon nanotubes as a radiation shielding material, according to the use environment, Various shapes of radiation attenuating members can be provided. Moreover, according to the radiation attenuation material which concerns on this invention, since specific gravity is comparatively small, it is easy to handle with light weight, and when it installs in soil, it can prevent settling into the ground.

In the radiation attenuation material according to the present invention,
When the carbon material is graphene, the carbon material can be blended in an amount of 10 to 80 parts by mass with respect to 100 parts by mass of the elastomer.

In the radiation attenuation material according to the present invention,
Furthermore, 5 mass parts or more and 100 mass parts or less of 1 or more types of radioactive substance adsorbent selected from activated carbon, a zeolite, and Prussian blue can be included.

In the radiation attenuation material according to the present invention,
Furthermore, 20 mass parts or more and 300 mass parts or less of water absorbing resin can be included.

In the radiation attenuation material according to the present invention,
Furthermore, 50 mass parts or more and 2000 mass parts or less of metal particles can be included.

The method for producing a radiation attenuating material according to the present invention comprises:
Mixing an elastomer and a carbon material comprising at least one of graphene and carbon nanotubes to obtain a first composite material;
Mixing the first composite material and the water absorbent resin to obtain a radiation attenuating material;
It is characterized by including.

According to the method for producing a radiation attenuating material according to the present invention, it is possible to produce a radioactive attenuating material that is light and easy to handle and can prevent sedimentation into the ground when installed on soil.

It is a schematic diagram for demonstrating the manufacturing method of a radiation attenuation material. It is a schematic diagram for demonstrating a radiation attenuation member. It is a schematic diagram for demonstrating the method to attenuate the radiation dose from the soil which concerns on one embodiment of this invention. It is a schematic diagram for demonstrating the method to attenuate the radiation dose from the soil which concerns on one embodiment of this invention. It is a schematic diagram for demonstrating the method to attenuate the radiation dose from the soil which concerns on one embodiment of this invention. It is a schematic diagram for demonstrating the method to attenuate the radiation dose from the soil which concerns on one embodiment of this invention. It is a schematic diagram for demonstrating the method to attenuate the radiation dose from the soil which concerns on one embodiment of this invention. It is a figure which shows the radiation shielding rate with respect to specific gravity of an Example and a comparative example. It is the figure which expanded a part of FIG.

  Hereinafter, embodiments of the present invention will be described in detail.

A. Radiation Attenuating Material A radiation attenuating material according to an embodiment of the present invention is characterized in that 10 parts by mass or more and 120 parts by mass or less of a carbon material composed of at least one of graphene and carbon nanotubes is blended with 100 parts by mass of an elastomer.

  The radiation attenuating material is a composite elastomer composition in which a carbon material composed of at least one of graphene and carbon nanotubes, which are radiation shielding materials, is blended. The radiation attenuating material of the composite elastomer composition can be formed into various shapes according to the use environment. Since the radiation attenuating material has a specific gravity smaller than that of, for example, a metal by using a carbon material, it is lightweight and easy to handle. Therefore, it is possible to prevent sedimentation into the ground when a radiation attenuating material is installed in the soil. Since radioactive materials released from nuclear power plants exist near the surface of the earth, if the specific gravity of the radioactive attenuating material is small, it is difficult to settle into the ground, and the radiation shielding / attenuating effect can be maintained over a long period of time.

A-1. Elastomer The elastomer used for the radiation attenuating material can be selected from natural rubber, synthetic rubber and thermoplastic elastomer having high rubber elasticity at room temperature. For example, natural rubber (NR); epoxidized natural rubber (ENR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPR, EPDM), butyl rubber (IIR), Chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber (Q), fluorine rubber (FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO, CEO), urethane rubber (U ), Synthetic rubber such as polysulfide rubber (T); olefin (TPO), polyvinyl chloride (TPVC), polyester (TPEE), polyurethane (TPU), polyamide (TPEA), styrene (SBS), etc. Thermoplastic elastomers; and mixtures thereof It can be used. In particular, when carbon nanotubes are blended, highly polar elastomers that easily generate free radicals during elastomer kneading, such as natural rubber (NR) and nitrile rubber (NBR), can be used. Even in the case of an elastomer having a low polarity, such as ethylene propylene rubber (EPDM), free radicals are generated by setting the kneading temperature to a relatively high temperature (for example, 50 ° C. to 150 ° C. in the case of EPDM). It can also be used when blending nanotubes. In particular, when used for a radiation attenuating member that is spread on soil, for example, synthetic rubber having excellent weather resistance can be used, and nitrile rubber (NBR) having excellent water resistance can be used. Also, a plurality of types of rubber can be mixed and used, for example, synthetic rubber and natural rubber can be used in combination.

A-2. Carbon material A carbon material consists of at least one of a graphene and a carbon nanotube. A carbon material composed of at least one of graphene and carbon nanotubes is considered to have a higher electron density due to a difference in the crystal structure of carbon and a higher radiation shielding effect than a carbon material such as carbon black. Thus, a high radiation shielding effect can be obtained by uniformly dispersing the carbon material having a minute size in the elastomer. Since the carbon material of a minute size has a large surface area and can be widely dispersed and distributed in the radiation attenuating material, it can simply be excellent in radiation shielding efficiency per specific gravity.

The radiation shielding effect due to the minute size of the carbon material can also be explained by the mean free path equation.
Mean free process = 1 / μ
= 1 / (nσ)
(Where n is the number of carbon material particles that the radiation collides with, and σ is the cross-sectional area of the carbon material particles)
Thus, it can be seen that the number of carbon material particles increases if the carbon material becomes a minute size even with the same blending amount, so that the collision probability increases and the radiation shielding ability also increases.

  The compounding amount of the carbon material composed of at least one of graphene and carbon nanotubes is 10 parts by mass or more and 120 parts by mass or less, and further 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the elastomer. If the amount of the carbon material composed of at least one of graphene and carbon nanotubes is 10 parts by mass or more, an effect of shielding radiation can be obtained, and if it is 120 parts by mass or less, processing is possible. Since the elastomer and the carbon material are only converted into carbon by incineration, it is considered that the impact on the environment is small compared to other radiation shielding materials such as metal. In addition, the average particle diameter, average diameter, and average length of the substance blended in the elastomer in this specification are measured by measuring the particle diameter, diameter, and length at a plurality of locations using imaging of the substance with an electron microscope. It can be obtained by calculating as an arithmetic average value.

  The carbon nanotube is a single-layer or multi-layer fibrous material in which a graphene structure sheet is formed into a cylindrical shape. The carbon nanotubes can have an average diameter of 0.5 nm to 500 nm, and further 0.5 nm to 100 nm. The carbon nanotubes can be straight fibers or curved fibers. The compounding amount of the carbon nanotube can be appropriately set according to the shape and use of the material. However, in order to obtain the celllation by the carbon nanotube, the proportion of the carbon nanotube is 10 parts by mass to 120 parts by mass with respect to 100 parts by mass of the elastomer. Furthermore, carbon nanotubes having an average diameter of 0.5 nm to 20 nm can be included at a ratio of 10 parts by mass to 80 parts by mass, and carbon nanotubes having an average diameter of 60 nm to 200 nm. It can be contained at a ratio of 10 parts by mass or more and 120 parts by mass or less. If the carbon nanotube is 10 parts by mass or more, a celllation structure can be obtained, and a radioactive substance adsorption ability can be obtained. If the carbon nanotube is 120 parts by mass or less, workability is possible. It is considered that the fibrous carbon nanotubes are not used in the form of agglomerated particles, but are defibrated and dispersed to form a three-dimensional network structure in the radiation attenuating material, which increases the probability of collision with radiation. .

  The graphene is a graphene structure sheet, and includes a sheet in which a plurality of graphene structure sheets are stacked. Graphene includes graphene oxide or redox graphene and a graphene plate having a structure in which oxygen atoms, hydroxyl groups, or other molecules having a relatively high electron affinity are adsorbed on or at an end of the graphene layer. The graphene may have an average thickness of 0.5 nm to 100 nm and a flat plate area of 0.01 μm to 300 μm. Here, the average thickness and the average area can be obtained by measuring a plurality of locations using imaging of the substance with an electron microscope and calculating the arithmetic average value thereof. The blending amount of the graphene is 10 parts by mass or more and 80 parts by mass or less, and further 20 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the elastomer. If the blending amount of graphene is 10 parts by mass or more, an effect of shielding radiation is obtained, and if it is 80 parts by mass or less, processing is possible.

A-3. Other compounding agents The radiation attenuating material may further include a radiation shielding material other than the carbon material composed of at least one of graphene and carbon nanotubes. The radiation attenuating material can include, for example, metal particles, metal oxide particles, and the like. Examples of the metal particles having excellent radiation shielding performance include lead, iron, copper, and tungsten. Examples of the metal oxide particles having excellent radiation shielding performance include lead oxide and ferrite. The total amount of the radiation shielding material other than the carbon material composed of at least one of graphene and carbon nanotubes may be 50 to 2000 parts by mass with respect to 100 parts by mass of the elastomer, and further 100 parts by mass to 1500 parts by mass. Can be. When the blending amount of the entire radiation shielding material is 50 parts by mass or more, radiation shielding ability is obtained, and if it is 2000 parts by mass or less, processing is possible. However, when metal particles are included in the radiation attenuating material, care should be taken not to affect the surrounding environment by metal ions flowing into the soil.

  The radiation attenuating material can further include a radioactive substance adsorbing material other than a carbon material made of at least one of graphene and carbon nanotubes. The radioactive substance adsorbing material may be one or more selected from activated carbon, zeolite, and Prussian blue. The mixing amount of the radioactive substance adsorbing material is preferably as much as possible, but the mixing ratio with other compounding agents is appropriately adjusted, and is 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the elastomer. Furthermore, it can be 10 parts by mass or more and 60 parts by mass or less. A plurality of types of radioactive material adsorbents can be used simultaneously.

  The radiation attenuating material may further include a water-absorbing resin that can retain a large amount of water with excellent water absorption. For example, the water-absorbent resin can absorb 100 to 1000 times the weight of its own weight, and has a property that it is difficult to remove water even under pressure. As the water-absorbing resin, those widely used as water-absorbing materials such as paper diapers and sanitary products can be adopted. As the water absorbent resin, for example, sodium polyacrylate can be employed. The compounding amount of the water absorbent resin can be 20 parts by mass or more and 300 parts by mass or less, and further 40 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the elastomer. If the blending amount of the water-absorbing resin is 20 parts by mass or more, a relatively excellent water absorbing ability is obtained, and if it is 300 parts by mass or less, the resin is hardly eluted.

B. Manufacturing method of radiation attenuating material The manufacturing method of the radiation attenuating material which concerns on one embodiment of this invention mixes the elastomer and the carbon material which consists of at least one of a graphene and a carbon nanotube, and obtains the 1st composite material, And a step of mixing the first composite material and the water absorbent resin to obtain a radiation attenuating material. In this mixing step, a compounding agent other than the carbon material composed of at least one of graphene and carbon nanotubes, for example, the radiation shielding material and the radioactive substance adsorbing material described in the above A can be blended. In addition, although the case where a water absorbing resin is mix | blended is demonstrated here, a water absorbing resin can also be used. A well-known mixing method can be used for the mixing process in the manufacturing method of a radiation attenuation material. In particular, when blending carbon nanotubes that easily aggregate and are not easily defibrated, a strong kneading step at a low temperature of 0 to 50 ° C. can be employed.

  More specifically, an example using the open roll method in which thinning with a roll interval of 0.5 mm or less is described with reference to FIG.

  FIG. 1 is a diagram schematically showing an open roll method using two rolls. In FIG. 1, the code | symbol 10 shows a 1st roll and the code | symbol 20 shows a 2nd roll. The first roll 10 and the second roll 20 are arranged at a predetermined interval d, for example, 1.5 mm. The first and second rolls rotate in the normal direction or the reverse direction. In the illustrated example, the first roll 10 and the second roll 20 rotate in the direction indicated by the arrow.

  First, when the elastomer 30 is wound around the first roll 10 in a state where the first and second rolls 10 and 20 are rotated, a so-called bank 32 in which the elastomer is accumulated between the rolls 10 and 20 is formed. For example, when the carbon nanotube 40 as a carbon material is added to the bank 32 and the first and second rolls 10 and 20 are rotated, a mixture of the elastomer 30 and the carbon nanotube 40 is obtained. Remove this mixture from the open roll. Further, the distance d between the first roll 10 and the second roll 20 is preferably set to 0.5 mm or less, more preferably 0.1 to 0.5 mm, and the obtained mixture is put into an open roll. And do thinness. The number of thinning is preferably about 3 to 10 times. When the surface speed of the first roll 10 is V1, and the surface speed of the second roll 20 is V2, the ratio of the surface speeds (V1 / V2) in thinness is 1.05 to 3.00. It is preferably 1.05 to 1.2. By using such a surface velocity ratio, a desired shear force can be obtained.

  Due to the shearing force thus obtained, a high shearing force acts on the elastomer 30 and the aggregated carbon nanotubes 40 are separated from each other so as to be pulled out one by one to the elastomer molecules, and dispersed in the elastomer 30. A first composite material is obtained.

  In this process, in order to obtain as high a shearing force as possible, the mixing of the elastomer with the carbon nanotubes and the second carbon nanotubes can be performed at 0 to 50 ° C., and at a relatively low temperature of 5 to 30 ° C. It can be carried out. Such thinness at low temperature allows the carbon nanotubes to be efficiently dispersed in the matrix because the elastomer has rubber elasticity.

  At this time, the elastomer of the present embodiment has the above-described characteristics, that is, the elasticity expressed by the molecular shape (molecular length) and molecular motion of the elastomer, the viscosity, and the chemical properties of the carbon nanotube and the second carbon nanotube. Since the dispersion of the carbon nanotubes is facilitated by having the interaction, the first composite material excellent in dispersibility and dispersion stability (the carbon nanotubes are difficult to reaggregate) can be obtained.

  Further, although not shown, the first composite material and the water absorbent resin are mixed to obtain a radioactive shielding material. The mixing method here may be continued by the open roll method, or other mixing methods may be used.

  Here, an example of a carbon nanotube has been described, but even when graphene is used, it can be manufactured in the same manner.

The step of dispersing the carbon material in the elastomer by a shearing force is not limited to the open roll method, and a closed kneading method or a multi-screw extrusion kneading method can also be used. In short, in this step, it is sufficient that a shearing force capable of separating the agglomerated carbon material can be applied to the elastomer.

  The radiation attenuating material can be formed in various forms of radiation attenuating members depending on the application. FIG. 2 is a schematic diagram for explaining the radiation attenuation members 50a, 50b, and 50c. For example, as shown in FIG. 2, (A) the radioactive attenuation material can be pulverized by a pulverizer to form a particulate radiation attenuation member 50a. The sheet-like radiation attenuation member 50b can be formed into a sheet-like sheet having the above-described structure, or (C) the radiation attenuation member 50c is formed by forming the radioactive attenuation material into a predetermined shape, for example, a cylindrical block as shown in the figure. You can also. The particulate radiation attenuating member 50a can have an average particle size of 100 μm or more and 5 mm or less. If the average particle size is 100 μm or more, it is larger than the particle size of sand (for example, about 10 μm). It can be manufactured by pulverizing with a general pulverizer, and radiation can be shielded relatively efficiently if the average particle size is 5 mm or less. The sheet-like radiation attenuating member 50b can be used as a single sheet, and a plurality of sheets can be laminated and used according to the application. The radiation attenuation member 50c formed into a predetermined shape such as a cylindrical block can be used for a lid of a simple container for storing soil containing radioactive material, for example.

C. Method for Attenuating Radiation Dose from Soil The method for attenuating the radiation dose from soil according to an embodiment of the present invention includes 20 parts by mass or more of carbon material composed of at least one of graphene and carbon nanotubes in 100 parts by mass of elastomer. The particulate radiation attenuation member blended in an amount of 120 parts by mass or less is sprayed on soil contaminated with a radiation material.

  3-5 is a schematic diagram for demonstrating the method to attenuate the radiation dose from the soil which concerns on one embodiment of this invention.

  As shown in FIG. 3, a particulate radiation attenuation member 50a is sprayed on the ground surface 2 of the soil 1 contaminated by the radioactive material released from the nuclear power plant. Moreover, after sprinkling the particulate radioactive attenuation member 50a on the ground surface 2 of the soil 1 contaminated with radioactive substances, the soil 1 and the radioactive attenuation member 50a can be mixed. For this mixing, equipment and methods used for farmland cultivation can be used. For example, a cultivator or the like can be used for a large land. On the ground surface 2, the contaminated soil 1 and the particulate radioactive attenuation member 50 a exist in a mixed state.

  Radiation R is emitted from the surface 2 of the soil 1. The particulate radiation attenuation member 50a may have an average particle diameter of 100 μm or more so that the particulate radiation attenuation member 50a can be uniformly distributed over the entire surface of the earth. If the average diameter of the particles is 100 μm or more, it is difficult to move due to wind or rain, so that the particles are easily fixed on the ground surface 2. Note that the soil 1 is not limited to the case of being on the ground, but also includes soil in water such as a riverbed or a seabed.

As shown in FIG. 4, the radiation attenuating member 50 a that has been dispersed or dispersed and mixed with the soil is near the ground surface 2, and can attenuate the amount of radiation emitted from the radioactive material in the soil 1. . In addition, since the carbon material composed of at least one of graphene and carbon nanotubes has an effect of adsorbing radioactive substances, it is present in the soil 1 near the ground surface 2 or the ground surface 2 by spraying the particulate radiation attenuation member 50a on the soil. The radioactive substance to be absorbed can be adsorbed and the radiation can be shielded in a fixed state. Furthermore, since the specific gravity of the particulate radiation attenuation member is not as large as that of metal particles, it is difficult to settle into the ground due to rain or the like, and it can stay near the ground surface, so that radiation can be attenuated efficiently. In particular, in the decontamination work, when the soil on which the radiation attenuating member is dispersed is transported and stored, it is possible to reduce the influence of radiation from the transport soil or the storage soil on the decontamination worker.

  When the radiation attenuating member 50a further includes a radiation shielding material, the amount of radiation emitted from the radioactive substance in the vicinity of the ground surface 2 can be attenuated more efficiently.

  By including the radioactive substance adsorbing material in the radiation attenuating member 50a, the radioactive substance in the vicinity of the ground surface 2 is adsorbed and fixed, whereby the amount of radiation emitted from the radioactive substance can be attenuated more efficiently. In addition, when removing soil near the surface 2 in decontamination work, the radioactive substance is immobilized and the radiation dose is attenuated, so the impact on workers is reduced and the soil is moved. It is also possible to prevent the radioactive material from being scattered.

  Since the radiation attenuating member 50a further includes a water-absorbing resin, the water-absorbing resin can also take in the radioactive substance together with moisture, so that the radioactive substance can be easily adsorbed. Moreover, even if a comparatively small amount of radioactive attenuation member 50a is sprayed by water absorption resin absorbing water or rainwater and increasing the volume, the radiation dose on the ground surface 2 can be attenuated over a wide range. Further, since the radiation attenuating member 50a contains the water-absorbing resin, the radioactive substance dissolved in water can be absorbed together with the water. For example, even if the radioactive attenuating member 10a is sprayed in water, the radiation dose in water Can be expected to attenuate

  As shown in FIG. 5, since the radiation attenuation member 50a has a relatively small specific gravity, the radiation attenuation member 50a is unlikely to settle to the underground due to the rainwater W, and can stay near the ground surface 2 and attenuate the radiation dose over a long period of time. Therefore, for example, when storing the soil removed by decontamination, the radioactive material can be made difficult to move by spraying the radiation attenuating member 50a, so that the radioactive material can be fixed in the storage location.

  In the above-described embodiment, the radiation attenuating member is dispersed and used. For example, after the soil containing a large amount of radioactive material in the vicinity of the ground surface is previously scraped, the removed soil and the radiation attenuating member are mixed. However, it can be stored in a state in which the radiation dose is attenuated.

  6-7 is a schematic diagram for demonstrating the other method of attenuating the radiation dose from the soil which concerns on one embodiment of this invention.

  As shown in FIG. 6, the ground surface 2 of the soil 1 contaminated with the radioactive substance can be covered with a sheet-like radiation attenuation member 50b.

  As shown in FIG. 7, the sheet-like radiation attenuation member 50 b covering the ground surface 2 can attenuate the amount of radiation emitted from the radiation material in the soil 1. For example, by covering the contaminated soil 1 carried out by the decontamination work, the influence of radiation on the surroundings can be reduced during storage or transportation.

Compounding ingredients shown in Tables 1 to 4 were blended with 100 parts by mass of natural rubber, and kneaded using an open roll to obtain a radiation attenuating material. More specifically, a predetermined amount (100 g) of natural rubber (described as “NR” in the table) 100 shown in Tables 1 to 4 is applied to an open roll having a roll diameter of 6 inches (roll temperature: 10 ° C. to 20 ° C.). A part by weight (phr: parts per hindered rubber) was added and wound around a roll. Various compounding agents were added to the natural rubber wound around the roll, kneaded, and the mixture was taken out of the roll. At this time, the roll gap was set to 1.5 mm. The roll gap was narrowed from 1.5 mm to 0.3 mm, and the mixture was introduced to make it thin. At this time, the surface speed ratio of the two rolls was set to 1.1. Thinning was repeated 5 times. The roll was set to a predetermined gap (1.1 mm), and the thinned mixture was charged and dispensed. Further, the unvulcanized mixture was press vulcanized at 170 ° C. for 20 minutes to obtain a sample of a sheet-like radiation attenuation member having a thickness of 10 mm. The specific gravity (g / cm ³ ) of each sample was measured and shown in Tables 1 to 4.

The details of each compounding agent were as follows. The abbreviations are shown in Tables 1 to 4.
FER: Ferrite PbO: Lead oxide W: Tungsten Cu: Copper Fe: Iron CB-1: SAF carbon black CB-2: MT carbon black GR: Graphite G-1: Graphene (thickness: average thickness 2 nm, average surface size 1 μm)
G-2: Graphene (thickness: average thickness 7 nm, average surface size 25 μm)
CNT-1: Multi-wall carbon nanotubes with an average diameter of 70 nm CNT-2: Multi-wall carbon nanotubes with an average diameter of 10 nm CNT-3: Single-wall carbon nanotubes Other compounding agents include processing aids, anti-aging agents, and sulfur Was formulated.

Using these samples, the radiation dose is measured by the test method shown below, the radiation shielding rate (PF:%) is calculated by Equation 1, the specific gravity ρ (g / cm ³ ) of the radiation attenuation member sample and its The product ρt (g / cm ² ) with the sample thickness t (cm) was calculated and shown in Tables 1 to 4. Moreover, the relationship between the radiation shielding rate (%) and specific gravity (g / cm < ³ >) of Table 1-Table 4 was shown in FIG. 8, and a part of FIG. 8 was expanded and shown in FIG.

First, the radiation dose (I ₀ : Sv / h) of the contaminated soil was measured using a scintillation counter (PA-1000Radi manufactured by HORIBA). Next, the sheet-like radiation attenuation member was installed on the contaminated soil, and the radiation dose (I: Sv / h) was measured. The radiation shielding rate (PF) was calculated | required using Formula 1 from the obtained measured value.
Shielding rate PF (%) = (I ₀ −I) / I ₀ × 100 (Formula 1)
Here, I ₀ was the radiation dose (Sv / h) of the radiation source, and I was the measured radiation dose.

  As a result, the radiation attenuating member using the carbon material composed of at least one of graphene and carbon nanotubes has high radiation shielding even if the amount of the carbon material is relatively small compared to the comparative sample using carbon black or graphene. The effect was obtained. A radiation attenuating member using a carbon material composed of at least one of graphene and carbon nanotubes has a lower specific gravity than a composite material of metal powder or metal particles and an elastomer, but has a high radiation shielding rate (PF). understood.

Further, the radiation attenuating members of Example 3 and Comparative Example 7 were pulverized using a freeze pulverizer to produce particulate radiation attenuating members having an average particle diameter of 100 μm. The particulate radiation attenuation member was dispersed on the contaminated soil, and the radiation shielding rate (PF) was determined in the same manner as in the above example. The measurement results are shown in Table 5.

  The radiation attenuation member of Example 11 had a higher radioactive attenuation effect than Comparative Example 10.

DESCRIPTION OF SYMBOLS 1 Soil, 2 Ground surface, 10 1st roll, 20 2nd roll, d Space | interval of 1st roll 10 and 2nd roll 20, 30 Elastomer, 32 banks, 40 Carbon nanofiber, 50a Radiation attenuation member, 50b Radiation attenuation member, 50c Radiation attenuation member, R radiation, W water

Claims (11)

  Radiation dose from soil, in which a particulate radiation-attenuating member, in which 10 parts by mass or more and 120 parts by mass or less of a carbon material composed of at least one of graphene and carbon nanotubes is blended in 100 parts by mass of elastomer, is sprayed on soil contaminated with radioactive substances How to attenuate. In claim 1,
When the carbon material is graphene, the carbon material is blended in an amount of 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the elastomer. In claim 1 or 2,
The radiation attenuating member is a method for attenuating radiation dose from soil, wherein the radiation attenuating member further contains 5 parts by mass or more and 100 parts by mass or less of one or more kinds of radioactive substance adsorbents selected from activated carbon, zeolite and Prussian blue. In any one of Claims 1-3,
The radiation attenuation member further includes 20 parts by mass or more and 300 parts by mass or less of a water-absorbing resin to attenuate the radiation dose from soil. In any one of Claims 1-4,
The radiation attenuating member further includes 50 parts by mass or more and 2000 parts by mass or less of metal particles to attenuate the radiation dose from the soil.   A radiation attenuating material, in which 10 parts by mass or more and 120 parts by mass or less of a carbon material composed of at least one of graphene and carbon nanotubes is blended with 100 parts by mass of an elastomer. In claim 6,
When the carbon material is graphene, the carbon material is a radiation attenuating material in which 10 parts by mass or more and 80 parts by mass or less are blended with respect to 100 parts by mass of the elastomer. In claim 6 or 7,
Furthermore, the radiation attenuating material containing 5 mass parts or more and 100 mass parts or less of 1 or more types of radioactive substance adsorbents selected from activated carbon, zeolite, and Prussian blue. In any one of Claims 6-8,
Furthermore, the radiation attenuation material containing 20 mass parts or more and 300 mass parts or less of water absorbing resin. In any one of Claims 6-8,
Furthermore, the radiation attenuation | damping material which contains 50 mass parts or more and 2000 mass parts or less of metal particles. Mixing an elastomer and a carbon material comprising at least one of graphene and carbon nanotubes to obtain a first composite material;
Mixing the first composite material and the water absorbent resin to obtain a radiation attenuating material;
A method for producing a radiation attenuating material.

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