JP2013170888A - Radiation shield vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation shield vessel that accommodates a substance containing radioactive materials, and shields radiation rays emitted from the accommodated substance containing the radioactive materials.SOLUTION: A radiation shield vessel 1 for accommodating a substance 2 containing radioactive materials, includes: a pair of layers 10 and 11; and a radiation ray absorption layer 12 that is provided between the pair of layers 10 and 11 and absorbs radiation rays. The pair of layers 10 and 11 are a solid layer, and the radiation ray absorption layer 12 is a fluid layer.

Description

  The present invention relates to a radiation shielding container that contains a substance containing a radioactive substance and shields radiation emitted from the contained substance containing the radioactive substance.

  In Japan, it is thought that after the great earthquake of March 11, 2011, there was an accident at a nuclear power plant and a large amount of radioactive material was scattered. Since then, radioactive materials have been confirmed from incineration ash at garbage incineration plants, sludge from sewage treatment plants, rivers, oceans, rubble from disaster areas, and a large amount of low-level radioactive waste has been generated. Furthermore, as the decontamination work becomes full-scale, low-level radioactive waste is considered to continue to increase.

  At present, low-level radioactive waste is to be disposed at a deep depth, in a shallow pit, or in a shallow trench. However, low-level radioactive waste must be temporarily stored until it is processed at the repository. Furthermore, low-level radioactive waste needs to be transported from a decontamination work site where decontamination work is performed to a temporary storage, or from a temporary storage to a disposal site. At this time, a stable radiation shielding performance is desired for the storage container for storing the low-level radioactive waste.

  The present invention has been made on the basis of the background as described above, and includes a radiation shielding container that contains a substance containing a radioactive substance and stably shields radiation emitted from the contained substance containing the radioactive substance. The purpose is to provide.

  A radiation shielding container according to the present invention includes a container main body having a storage portion that stores a substance containing a radioactive substance, and a lid that closes the storage portion of the container main body. At least one surface of the container body and / or the lid includes a pair of layers and a radiation absorbing layer that is provided between the pair of layers and absorbs radiation. Further, the pair of layers is a solid layer, and the radiation absorbing layer is a fluid layer.

  In the present invention, radiation emitted from a substance containing a radioactive substance housed in a housing part of the container body can be reduced by the radiation absorbing layer provided on at least one surface of the container body and / or the lid. Therefore, in this invention, it can be used as a storage container for storing a substance containing a radioactive substance during storage and transportation.

  Further, in the present invention, since the radiation absorbing layer is a fluid layer, it is not limited to injecting the radiation absorbing layer between the pair of layers in advance, but after being transported to a storage work site that stores a substance containing a radioactive substance. The radiation absorbing layer can be injected between the pair of layers. Therefore, in this invention, it can be conveyed to the accommodation work site in the weight-reduced state which does not provide the radiation absorption layer between a pair of layers.

  In addition, when the radiation absorbing layer, which is a fluid, is composed of water as a main component, even when the radiation emitted from a substance containing a radioactive substance contains neutron rays, not only γ rays but also neutron rays It is also possible to effectively attenuate the radiation intensity.

It is sectional drawing which showed the radiation shielding container to which this invention is applied. It is sectional drawing which showed the container main body and the cover body. It is sectional drawing which showed the radiation shielding container which provided the new layer in the container main body and the cover body. It is sectional drawing which showed the radiation shielding container which provided the engaging part and the to-be-engaged part in the container main body and the cover body. It is sectional drawing which showed the radiation shielding container which piled up the container main body in multiple numbers. It is sectional drawing which showed the radiation shielding container which provided the side surface of the container main body at an acute angle (obtuse angle) with respect to the bottom face.

  Hereinafter, a radiation shielding container to which the present invention is applied will be described with reference to the drawings.

  As shown in FIG. 1, a radiation shielding container 1 to which the present invention is applied includes a container body 3 having a housing part 3 a that houses a substance 2 containing a radioactive substance, and a lid 4 that closes the housing part 3 a of the container body 3. And.

  As shown in FIG. 1, the container body 3 is provided in a bottomed cylindrical shape having an opening formed in the upper portion, and has a housing portion 3 a inside. Furthermore, the substance 2 containing a radioactive substance is accommodated in the accommodating part 3a of the container body 3. For example, the substance 2 containing a radioactive substance accommodated in the accommodating part 3a is composed of incineration ash from a garbage incineration site, sludge from a sewage treatment plant, rivers, oceans, debris from a disaster area, etc. Low level radioactive waste. These are merely examples, and the substance 2 containing a radioactive substance is not limited to these.

  The lid body 4 is provided in a plate shape having a plan view shape substantially the same as the plan view shape of the container body 3. The lid 4 is disposed on the upper surface 3b of the container body 3, and closes and seals the accommodating portion 3a of the container body 3. In addition, a protrusion 4 a is provided on the surface of the lid body 4 that faces the housing portion 3 a of the container body 3. The protrusion 4a is fitted in the vicinity of the upper portion in the accommodating portion 3a to improve the sealing performance of the accommodating portion 3a and prevent the lid 4 from being displaced from the container body 3.

  Further, as shown in FIG. 2, each of the container body 3 and the lid body 4 includes an inner layer 10, an outer layer 11, and a radiation absorbing layer 12 that is provided between the inner layer 10 and the outer layer 11 and absorbs radiation. .

  The inner layer 10 is a solid layer provided on the housing 3a side. The inner layer 10 is formed of a material containing at least one element having a first period to a seventh period in the element periodic table shown in Table 1 below. More specifically, the inner layer 10 is mainly made of, for example, metals mainly composed of iron-based materials and lead-based materials, ceramics mainly composed of ceramic materials and porcelain materials, and glassy materials such as plate glass and glass cullet. Glass, concrete, asphalt as components, polymer compounds such as natural resins, synthetic resins and rubbers, trees, or composite materials composed of them, for example, made into fiber reinforcement, etc. . Of course, the surface of the inner layer 10 includes a rust preventive layer, a corrosion resistant layer, a water resistant layer, a waterproof layer, a gas barrier layer, a buffer layer, a chemical resistant layer having acid resistance and base resistance, a corrosion resistant layer, a heat resistant layer, an ultraviolet resistant layer, etc. It is also good to provide.

  The outer layer 11 is a solid layer provided on the outer side with a predetermined distance from the inner layer 10. The outer layer 11 is formed of a material containing at least one element having the first to seventh periods in the periodic table of elements shown in Table 1 above. More specifically, the outer layer 11 is mainly composed of, for example, metals mainly composed of iron-based materials and lead-based materials, ceramics mainly composed of ceramic materials and porcelain materials, and glassy materials such as plate glass and glass cullet. Glass, concrete, asphalt as components, polymer compounds such as natural resins, synthetic resins and rubbers, trees, or composite materials composed of them, for example, made into fiber reinforcement, etc. . Of course, the surface of the outer layer 11 includes a rust preventive layer, a corrosion resistant layer, a water resistant layer, a waterproof layer, a gas barrier layer, a buffer layer, a chemical resistant layer having acid resistance and base resistance, a corrosion resistant layer, a heat resistant layer, an ultraviolet resistant layer, and the like. It is also good to provide.

  The radiation absorbing layer 12 is a fluid layer provided between the inner layer 10 and the outer layer 11. The radiation absorbing layer 12 is formed of a material containing at least one element having a first period to a seventh period in the periodic table of elements shown in Table 1 above. For example, the radiation absorbing layer 12 is water or seawater that is easily available. In particular, when the radiation absorbing layer 12 is composed of a fluid containing water as a main component, the number of hydrogen atoms contained in water molecules is very large. The hydrogen atoms are very close to the mass of the neutron beam and are almost stationary due to the van der Waals force in a large amount of water molecules and hydrogen bonds. When a neutron beam that has come into collision collides, the kinetic energy of the neutron beam is remarkably attenuated, and most of the strong kinetic energy possessed as radiation is lost by collision with hydrogen atoms on the average of about 18 times. Therefore, when the radiation absorbing layer 12 is composed of a fluid containing water as a main component, it is preferable because not only γ rays, which are a kind of radiation, can be attenuated but also the kinetic energy of neutron rays can be absorbed. .

  The radiation absorbing layer 12 may be injected between the inner layer 10 and the outer layer 11 in advance, and after transporting the radiation shielding container 1 to a storage work site that contains the substance 2 containing a radioactive substance, the inner layer 10 and the outer layer 11 may be injected. Further, the radiation absorbing layer 12 may be injected between the inner layer 10 and the outer layer 11 after the transportation to the housing work site and before the substance 2 containing the radioactive substance is housed in the housing portion 3a. It may be injected between 10 and the outer layer 11.

  Further, the radiation absorbing layer 12 is provided so as to have a thickness defined by the following formula (1).

ｘ：放射線吸収層の厚さ
μ：放射線吸収層を構成する物質固有のγ線に対する減衰係数
ε：比例定数（原始減衰係数）
ｅ：自然対数の底
ρ：放射線吸収層を構成する物質の質量体積密度
Ｉ_０：放射線遮蔽容器に透過前の放射線強度
Ｉ：放射線遮蔽容器に透過後の放射線強度

x: thickness of the radiation absorbing layer μ: attenuation coefficient with respect to γ rays specific to the material constituting the radiation absorbing layer ε: proportional constant (primary attenuation coefficient)
e: base of natural logarithm ρ: mass volume density of the substance constituting the radiation absorbing layer I ₀ : radiation intensity before transmission through the radiation shielding container I: radiation intensity after transmission through the radiation shielding container

  Here, the primitive damping coefficient ε will be described. The mechanism of γ-ray decay in matter is due to the photoelectric effect of matter (including electrons) and light (γ-rays) and the Compton effect, which is the scattering phenomenon of matter (including electrons) and light (γ-rays). Is considered dominant. That is, the γ-ray attenuation coefficient μ is a function of the number of atomic nucleons and electrons, and is considered to be proportional to the mass volume density ρ of the material constituting the radiation absorbing layer. That is, it is expressed as μ∝ρ. Therefore, the attenuation coefficient μ determined by the substance is expressed as μ = ερ. Here, ε is a primitive attenuation coefficient treated as a proportional constant.

  Table 2 below summarizes the attenuation of γ rays. The left column of Table 2 summarizes the actual measured values of the linear absorption coefficient (attenuation coefficient with respect to γ-rays) of various substances for each magnitude of γ-ray energy (refer to the Mitsui Kinzoku Engineering Co., Ltd. website). The right column of Table 2 shows values obtained by dividing the values in the left column by the respective mass volume densities ρ. As can be seen from Table 2, the magnitude of attenuation differs depending on the magnitude of γ-ray energy. On the other hand, when the same energy level is compared between materials, the primitive attenuation coefficient ε is considered to be substantially constant.

Specifically, the radiation absorbing layer 12 is, for example, water, and the energy of γ rays emitted from the substance 2 containing the radioactive substance accommodated in the accommodating portion 3a is 2 MeV, and the γ rays are attenuated to 1/20. The thickness of the radiation absorbing layer 12 necessary for this is calculated. If the primitive attenuation coefficient of water ε = 0.048 cm ² / g when the energy of γ rays in Table 2 is 2 MeV, the attenuation coefficient μ of water is μ = ερ = 0.048 × 1.00 = 0. 048 (cm ⁻¹ ). Therefore, the thickness x of the radiation absorbing layer 12 is calculated as x = − (1 / 0.048) log _e (1/20) = 62.4 (cm).

  That is, in the radiation shielding container 1, the radiation absorbing layer 12 is water, the energy of γ rays emitted from the substance 2 containing the radioactive substance accommodated in the accommodating portion 3a is 2 MeV, and the γ rays are reduced to 20 minutes. The thickness of the radiation absorbing layer 12 required to attenuate to 1 is 62.4 cm. In other words, when the radiation absorbing layer 12 is water, the radiation shielding container 1 is released from the substance 2 containing the radioactive substance accommodated in the accommodating portion 3a by setting the thickness of the radiation absorbing layer 12 to 62.4 cm. Γ-rays with 2 MeV energy can be attenuated to 1/20.

  As described above, the radiation shielding container 1 is formed from the substance 2 containing the radioactive substance accommodated in the accommodating portion 3a of the container body 3 by the radiation absorbing layer 12 composed of the fluid layer provided on the container body 3 and the lid body 4. The emitted radiation can be reduced. Therefore, the radiation shielding container 1 can be used as a storage container for storing a substance containing a radioactive substance during storage and transportation.

  Moreover, since the radiation absorption layer 12 is a fluid layer, the radiation shielding container 1 is not limited to injecting the radiation absorption layer 12 between the inner layer 10 and the outer layer 11 in advance, and contains a substance 2 containing a radioactive substance. The radiation absorbing layer 12 can be injected between the inner layer 10 and the outer layer 11 after being transported to the receiving work site. Therefore, the radiation shielding container 1 can be transported to the accommodation work site in a lightened state in which the radiation absorbing layer 12 is not provided between the inner layer 10 and the outer layer 11. Of course, as the fluid constituting the radiation absorbing layer 12, in addition to a liquid phase, a gel, a slurry, a powder, a granule, a mixture thereof, or a space between the inner layer 10 and the outer layer 11 is used. At the time of injection, it may be a fluid that hardens and solidifies after injection.

  In addition, you may make it provide the further layer 13 in the inner layer 10 and the outer layer 11, as shown in FIG. Specifically, the further layer 13 is formed on the surface of the inner layer 10 on the accommodating portion 3a side, the surface of the inner layer 10 on the radiation absorbing layer 12 side, the surface of the outer layer 11 on the radiation absorbing layer 12 side, and the surface of the outer layer 11 on the outer side. One layer or a plurality of layers are provided. Further, the additional layer 13 may be provided in one or more layers on at least one of these surfaces. Such a further layer 13 is a solid layer or a fluid layer, and is formed of a material containing at least one element of the first period to the seventh period of the element periodic table shown in Table 1 above. Therefore, the radiation shielding container 1 can improve mechanical strength and durability.

Further, in the container body 3 and the lid body 4, the inner layer 10 and / or the outer layer 11 may be used as an absorption layer that absorbs radiation similarly to the radiation absorption layer 12. Further, when the container body 3 and the lid body 4 are provided with the additional layer 13, the additional layer 13 may be used as an absorption layer that absorbs radiation similarly to the radiation absorption layer 12. However, the further layer 13 is not limited to fluid but may be solid. At this time, the container body 3 and the lid body 4 are provided so as to satisfy the following expression (2). Of course, the ratio I _n / I ₀ here is an attenuation rate and is a set value that can be preset as a reference, and the radiation intensity before attenuation emitted from the substance containing the radioactive substance contained in the container body 3 Is a ratio of the radiation intensity which is attenuated while passing through the n radiation absorbing layers 12 and is transmitted to the outside. Even when the radiation absorbing layer 12 is multi-layered in this way, the radiation shielding container 1 reduces the radiation emitted from the substance 2 containing the radioactive substance housed in the housing portion 3a of the container body 3. I can do it. Furthermore, the radiation shielding container 1 can be adjusted such that the thickness of the radiation absorbing layer 12 is reduced by using the inner layer 10, the outer layer 11 and the further layer 13 as the absorbing layer, thereby reducing the overall size. I can do it.

ｎ：放射線吸収層１２の層数
ｘ_ｊ：ｊ番目の層の厚さ
μ_ｊ：ｊ番目の層を構成する物質固有のγ線に対する減衰係数
ε_ｊ：ｊ番目の層を構成する物質固有の比例定数（原始減衰係数）
ρ_ｊ：ｊ番目の層を構成する物質固有の質量体積密度
Ｉ_０：放射線遮蔽容器透過前の放射線強度
Ｉ_ｎ：ｎ層の放射線吸収層を有する放射線遮蔽容器透過後の放射線強度

n: number of radiation absorbing layers 12 x _j : thickness of j-th layer μ _j : attenuation coefficient for γ-rays specific to the material constituting the j-th layer ε _j : specific to the material constituting the j-th layer Proportional constant (primary damping coefficient)
ρ _j : Mass volume density specific to the substance constituting the j-th layer I ₀ : Radiation intensity before passing through the radiation shielding container I _n : Radiation intensity after passing through the radiation shielding container having n radiation absorbing layers

  Moreover, the radiation absorption layer 12 should just be provided in at least one surface of the container main body 3. FIG. For example, the radiation shielding container 1 has a radiation absorbing layer 12 on the bottom surface of the container body 3 when the floor of the storage place is shielded or when the radiation shielding container 1 is stored and transported by being stacked on another radiation shielding container 1. The radiation absorbing layer 12 may be provided only on the surface excluding the bottom surface. Further, for example, when the radiation shielding container 1 is stored and transported in a state in which the side surface is in contact with another radiation shielding container 1, the side surface is removed without providing the radiation absorbing layer 12 on the side surface. The radiation absorbing layer 12 may be provided only on the surface. Furthermore, the radiation shielding container 1 does not include the radiation absorbing layer 12 in the lid body 4 when the other radiation shielding containers 1 are stacked and stored and transported, for example. The absorption layer 12 may be provided.

  Further, the radiation shielding container 1 is engaged with the container main body 3 and / or the lid 4, the engaging portion 20 that engages with the other radiation shielding container 1, and the engaging portion 20 of the other radiation shielding container 1. The engaged portion 21 may be included. For example, as shown in FIG. 4, the engaging portion 20 is a convex portion provided on the bottom surface and the side surface of the container body 3, and the engaged portion 21 is provided on the side surface of the lid body 4 and the container body 3. Recessed portion. Therefore, when the radiation shielding container 1 is stored or transported by stacking or arranging a plurality of the radiation shielding containers 1, the engaging portion 20 and the engaged portion 21 are engaged with each other, thereby preventing the displacement. The engaging portion 20 and the engaged portion 21 are not limited to those described above, and can be prevented from slipping by engaging the radiation shielding container 1 with another radiation shielding container 1. Any thing can be used.

  Moreover, the radiation shielding container 1 is not limited to providing the container body 3 in a bottomed cylindrical shape with an opening formed in the upper part, and is provided in a cylindrical shape with openings in the upper and lower parts. You may do it. Further, as shown in FIG. 5, the radiation shielding container 1 is formed by stacking a plurality of cylindrical container bodies 3 having openings at the upper and lower parts on a bottomed cylindrical container body 3. A lid 4 may be provided on the upper surface 3b of the container body 3 so that the accommodating portions 3a of the stacked container bodies 3 are closed and sealed.

  Further, as shown in FIG. 6, the radiation shielding container 1 may be provided with the side surface 3c of the container body 3 at an obtuse angle or an acute angle with respect to the bottom surface 3d. Thereby, even if the thickness t1 of the side surface itself of the container main body 3 is smaller than the thickness t2 of the side surface 3e provided substantially perpendicular to the bottom surface 3d, the radiation shielding container 1 transmits the transmission distance through which the radiation passes. Since t3 is substantially the same distance as when the side surface 3e is provided at a substantially right angle with respect to the bottom surface 3d, radiation can be reduced in substantially the same manner as with the side surface 3e provided at a substantially right angle with respect to the bottom surface 3d. I can do it. However, since the scattering effect and the so-called skyshine effect are not dominant radiation intensity, they are omitted here.

  The radiation shielding container 1 may be installed in advance on a transportation means such as a truck bed, a train body, or a ship hull.

DESCRIPTION OF SYMBOLS 1 Radiation shielding container, 2 Substance containing radioactive substance, 3 Container main body, 3a accommodating part, 3b upper surface, 3c side surface, 3d, bottom surface, 3e side surface, 4 cover body, 4a protrusion, 10 inner layer, 11 outer layer, 12 radiation absorption Layers, 13 further layers, 20 engaging parts, 21 engaged parts

Claims (8)

In radiation shielding containers that contain substances containing radioactive substances,
A pair of layers;
A radiation absorbing layer provided between the pair of layers and absorbing radiation;
The radiation shielding container, wherein the pair of layers is a solid layer, and the radiation absorbing layer is a fluid layer. The radiation shielding container according to claim 1, wherein the radiation absorbing layer has a thickness defined by the following formula (1).

x: thickness of the radiation absorbing layer μ: attenuation coefficient with respect to γ rays specific to the material constituting the radiation absorbing layer ε: proportional constant (primary attenuation coefficient)
e: base of natural logarithm ρ: mass volume density of the substance constituting the radiation absorbing layer I ₀ : radiation intensity before transmission through the radiation shielding container I: radiation intensity after transmission through the radiation shielding container The radiation shielding container
A container body having a container for containing a substance containing a radioactive substance;
The radiation shielding container according to claim 1, wherein at least one surface of the container body has the pair of layers and the radiation absorbing layer. The radiation shielding container
A lid that closes the housing portion of the container body;
The radiation shielding container according to claim 1, wherein the lid includes the pair of layers and the radiation absorbing layer.   The radiation shielding container according to claim 1, wherein at least one of the pair of layers is provided with at least one further layer. The pair of layers and the radiation absorbing layer, or the pair of layers, the radiation absorbing layer, and the further layer are provided so as to satisfy the following formula (2): The radiation shielding container according to any one of 3 to 5.

n: number of layers x _j : thickness of the j-th layer μ _j : attenuation coefficient for γ rays specific to the material constituting the j-th layer ε _j : proportional constant (primary attenuation specific to the material constituting the j-th layer) coefficient)
ρ _j : Mass volume density specific to the substance constituting the j-th layer I ₀ : Radiation intensity before passing through the radiation shielding container I _n : Radiation intensity after passing through the radiation shielding container of the n layer   The container main body includes one or both of an engaging portion that engages with another radiation shielding container and / or the lid, and an engaged portion that engages with an engaging portion of another radiation shielding container. The radiation shielding container according to claim 3, wherein the radiation shielding container is provided.   The lid has one or both of an engaging portion that engages with another radiation shielding container and an engaged portion that engages with an engaging portion of another radiation shielding container. The radiation shielding container according to claim 4.

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