Radiation shield and radiation shielding structure

Abstract

To provide a radiation shield which efficiently blocks a neutron, an X-ray, and a γ-ray.SOLUTION: A radiation shield includes a concrete. The concrete includes: a first aggregate which has an average particle diameter and an average length or thickness of less than 5 mm and which is made of a first sintered compact of a first gadolinium compound; and a second aggregate which has the average particle diameter and the average length or thickness of 5 mm or more and which is made of a second sintered compact of a second gadolinium compound. The ratio of both of the first and second aggregates to the concrete is 85 vol.% or more and 90 vol.% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate to radiation shields and structures. [Background technology]

[0002] Materials used for radiation shielding are made of substances that scatter or absorb radiation when it hits the shielding material, thereby reducing the amount of radiation that penetrates. Radiation is a general term for α-rays, β-rays, γ-rays, X-rays, neutron rays, etc. Among them, neutron rays react with materials and directly or secondarily emit α-rays, β-rays, γ-rays, and X-rays. Therefore, in order to shield neutron rays, it is necessary to consider not only shielding neutrons but also shielding α-rays, β-rays, γ-rays, and X-rays. The interaction between these radiations and materials varies depending on the type of radiation and the magnitude of energy. Among them, gamma rays, X-rays, and neutron rays have a high tendency to penetrate materials, so materials that shield them are being researched and developed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-128447 [Non-patent literature]

[0004] [Non-Patent Document 1] Kiyoshi Okada, “Cement and Concrete as Construction Materials for Shielding”, Materials Testing, Japan Society for Materials Testing, December 1956, Vol. 5, No. 39, p. 743-748 Summary of the Invention

[0005] One of the problems that the invention aims to solve is to efficiently block neutrons, X-rays, and gamma rays.

[0006] The radiation shield of the embodiment includes concrete. The concrete has a first aggregate having an average particle size, an average length, or an average thickness of less than 5 mm and made of a first sintered body of a first gadolinium compound, and a second aggregate having an average particle size, an average length, or an average thickness of 5 mm or more and made of a second sintered body of a second gadolinium compound. The ratio of both the first aggregate and the second aggregate to the concrete is 85 volume % or more and 90 volume % or less. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of radiation shielding concrete 1. [Diagram 2] FIG. 2 is a diagram showing large size coarse aggregate 5. [Diagram 3] FIG. 2 is a diagram showing medium-sized coarse aggregate 6 and large-sized fine aggregate 7. [Figure 4] FIG. 13 is a diagram showing small size fine aggregate 8. [Diagram 5] FIG. 2 is a diagram showing the relationship between neutron energy and reaction cross section in boron isotopes. [Figure 6] FIG. 2 is a diagram showing the relationship between neutron energy and reaction cross section in boron isotopes. [Figure 7] FIG. 2 is a diagram showing the relationship between neutron energy and reaction cross section in boron isotopes. [Figure 8] FIG. 2 is a diagram showing the relationship between neutron energy and reaction cross section in boron isotopes. [Figure 9] FIG. 1 is a diagram showing the relationship between neutron energy and reaction cross section in gadolinium isotopes. [Figure 10] FIG. 1 is a diagram showing the relationship between neutron energy and reaction cross section in gadolinium isotopes. [Figure 11] FIG. 1 is a diagram showing the relationship between neutron energy and reaction cross section in gadolinium isotopes. [Figure 12] FIG. 1 is a diagram showing the relationship between neutron energy and reaction cross section in gadolinium isotopes. [Figure 13] FIG. 1 is a diagram showing the relationship between neutron energy and reaction cross section in gadolinium isotopes. [Figure 14] FIG. 1 is a diagram showing the relationship between neutron energy and reaction cross section in gadolinium isotopes. [Figure 15] FIG. 1 is a diagram showing a comparison of the thermal neutron transmittance of boron compounds and gadolinium compounds. [Figure 16] FIG. 2 is a schematic diagram for explaining neutron capture gamma rays of gadolinium. [Figure 17] FIG. 2 is a schematic diagram for explaining neutron capture gamma rays of gadolinium. [Figure 18] This is a graph showing the gamma ray energy and transmission rate of a 5 cm thick shielding material. [Figure 19] 1 is a schematic top view showing an example of the structure of a concrete block 10. FIG. [Figure 20] 2 is a schematic front view showing another structural example of the concrete block 10. FIG. [Figure 21] 2 is a schematic side view showing another structural example of the concrete block 10. FIG. [Figure 22] FIG. 1 is a schematic diagram showing a structural example of a concrete block structure. [Diagram 23] FIG. 1 is a schematic diagram showing a structural example of a concrete block structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiment of the present invention will be described in detail. Note that the configuration described below is an example and does not limit the scope of the present invention in any way. In addition, in the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, in the drawings referred to in the following description, the size and thickness of each component are values ​​for convenience of explanation, and do not necessarily indicate the actual dimensions or ratios.

[0009] One embodiment relates to a radiation shielding body that blocks radiation and a manufacturing method thereof, and more specifically, to a radiation shielding concrete and a manufacturing method for radiation shielding concrete, particularly radiation generated from nuclear reactors or accelerators, radioisotope sources, and radioactive waste, particularly neutrons and secondary gamma rays and X-rays generated by reacting with neutrons.

[0010] X-rays and gamma rays are called different names depending on how they are generated (hereafter, X-rays and gamma rays will be collectively referred to as gamma rays), but their reaction with materials depends on the atomic number Z, and for gamma rays of the same energy, the larger the atomic number Z and density, the larger the reaction cross section and the higher the shielding ability. Therefore, tungsten, bismuth, lead, and molybdenum are used as gamma ray shielding materials rather than light elements such as carbon and aluminum. In the case of X-rays and gamma rays, if the density is about the same, elements with similar atomic numbers Z have almost the same transmittance (shielding effect). In addition, the amount of penetration of X-rays varies with the energy of the absorption edge depending on the orbit of the electron shell such as the K shell or L shell of the atom, but there is no distinction between isotopes. Furthermore, the higher the energy of X-rays and gamma rays, the higher the transmittance (the worse the shielding efficiency).

[0011] On the other hand, the reaction rate of neutron rays is not related to the atomic number Z, and varies with specific element isotopes. Therefore, even for the same element, the reaction and absorption rates change depending on the isotope and the neutron energy, and the rate of neutron transmission (shielding effect) differs. This reaction rate is expressed as the neutron cross section (unit: barn (b), 1b = 10 -24 cm 2 ) is used. The value defined by multiplying the neutron cross section by the atomic number density ρ is the macroscopic cross section Σ(cm -1 ) and corresponds to the linear attenuation coefficient of X-rays.

[0012] The above elements are, for example, hydrogen, lithium, boron, etc., which have a low reaction rate with gamma rays. In the case of lithium, lithium-6 (Li-6), an isotope with a natural abundance of 7.6%, reacts, and in the case of boron, boron-10 (B-10), an isotope with a natural abundance of 20%, reacts, while lithium-7 (Li-7), with a natural abundance of 92.4%, and B-11, with a natural abundance of 80%, hardly react with neutrons. Lithium and boron compounds are mainly used as neutron shielding materials. In the case of gamma rays, it depends on the size of the atomic number Z, but does not particularly depend on the abundance rate of the isotope. Therefore, in order to increase the reaction rate with neutrons, the proportion of the reactive isotope may be concentrated and used, such as using the isotope B-10 enriched to 90% or more from natural boron.

[0013] In both the case of gamma rays and neutrons, except for the case of resonance absorption specific to neutron isotopes, the higher the radiation energy, the lower the reaction rate and the smaller the shielding ability. For this reason, a thicker shield is required to block high-energy radiation.

[0014] In addition to cement and concrete, shielding materials that are in practical use may also be made by putting radiation-reactive materials into resin or rubber. Concrete is advantageous as a shielding material because of its excellent structural strength, shielding ability, workability, and adaptability. On the other hand, its disadvantage is that the shielding body is thicker than denser materials. To compensate for this disadvantage, research on various heavy concretes and special cements was started in 1956.

[0015] Concrete is composed of cement, water, coarse aggregate, fine aggregate, and admixtures. The largest volumetric proportion is coarse aggregate, followed by fine aggregate, with cement, water, and admixtures filling the gaps between them. Commonly used coarse and fine aggregates are gravel and sand, but their chemical composition varies depending on where they are collected, and they are rock minerals such as oxides of aluminum and calcium, silicates, and carbonates. Sand is also divided into river sand and sea sand, and although the salt content differs, it is basically formed when the particles become smaller due to the weathering of rocks. Well-known cements include Portland cement and alumina cement. These cements harden through a chemical reaction with water, and once hardened, they have the property of not losing their strength even in water.

[0016] Heavy concrete is used for radiation shielding. As mentioned above, the higher the atomic number Z and the higher the density, the greater the effect of shielding gamma rays. Therefore, the coarse and fine aggregates have a high iron composition ratio and a density of 3 to 4 g / cm3. 3 Limonite (2Fe2O3 3H2O), density 4.6-5.1g / cm 3 of magnetite (Fe3O4), density 4.2-4.4g / cm 3 Barite (BaSO4), with an even higher density of 7.5g / cm 3 Galena (PbS) is used, with a density of 7.6-7.8g / cm 3 Iron blocks, iron pieces, and steel balls are also used. Aggregates made from these materials have a higher shielding effect against gamma rays than general lightweight aggregates, but they have a lower shielding effect against thermal neutrons. Aggregates with a density of 2.42 g / cm3 are used for absorbing thermal neutrons. 3 of colmanite (also known as colemanite) (B2O3), with a density of 2.9 g / cm 3 of tumbleweed (B2O3), density 2.25g / cm 3 Pyrex (B2O3), density 2.5g / cm 3 The aggregates made from these materials are lightweight aggregates, and because they are poor at shielding against gamma radiation, they are mixed with heavy aggregates. This further reduces the proportion of isotopes present in the total volume that react with neutrons, and requires the shield to be thicker.

[0017] Radiation shielding concrete is required to be able to shield not only alpha rays, beta rays, gamma rays, and X-rays, but also neutron rays. In addition, unlike normal concrete structures, radiation is irradiated, so radiation deterioration must be taken into consideration. When high doses of radiation are irradiated to concrete, the radiation energy is absorbed and heat is generated. As a result, aggregates and cement pastes expand and contract repeatedly, causing embrittlement and cracking. Radiolysis also occurs, and in resins that contain water and hydrogen, chemical bonds are broken, hydrogen gas is generated, and the resins become liberated and embrittlement occurs. Ionization caused by radiation causes chemical reactions with other substances at the molecular level, leading to deterioration.

[0018] In particular, in the case of neutrons, they may change into other nuclides. For example, boron, which is often used as a neutron absorber, emits alpha rays when its isotope B-10 reacts with neutrons, becoming the lithium isotope Li-7, which then emits prompt gamma rays of 478 keV. Furthermore, in the case of neutrons, the energy levels handled vary from thermal neutrons (around 0.025 eV) from nuclear reactors, to accelerator neutron sources, radioisotope (RI) neutron sources, and high-energy neutrons from the sun in the space environment. As the energy increases, the reaction methods change, making shielding difficult even with lithium or boron, and ingenuity is required, such as mixing a neutron moderator to reduce the energy before shielding. Radiation shielding concrete centered on heavy aggregates can be used to shield gamma rays, but in order to shield neutrons as well, an optimal combination with conventional lightweight aggregates containing lithium and boron is required.

[0019] Neutron scattering can be broadly divided into two types: coherent scattering and incoherent scattering. For many elements, coherent scattering is dominant. For elements with a large coherent cross section, scattering is mainly due to diffraction, and Bragg edges appear depending on the difference in neutron energy. Incoherent scattering is scattering with atomic motion, and the cross section increases in inverse proportion to the neutron velocity v, which is equivalent to the neutron energy. This is called the "1 / v law", and for example, elements such as B-10 and Li-6 correspond to the 1 / v law, and as the energy increases (the velocity v increases), the reaction becomes more difficult and the shielding efficiency decreases. In addition to these scattering cross sections, there is also an absorption cross section due to resonance capture that appears in different neutron energy ranges depending on the element isotope.

[0020] Generally, neutron beams emitted from a neutron source contain neutrons of various energies, and at energies less than 1 MeV, reactions occur in the resonance region, such as the 1 / v law and resonance absorption (mainly reactions in which gamma rays are emitted in reaction with neutrons, hereafter referred to as (n,γ) reactions), but at energies of 1 MeV or more, threshold reactions different from these reactions occur (such as the (n,2n) reaction in which two neutrons are emitted in reaction with one neutron, the (n,p) reaction in which a proton is emitted in reaction with a neutron, and the (n,α) reaction in which alpha rays are emitted in reaction with a neutron). In particular, unlike reactions with gamma rays, reactions with neutrons can change elements, such as boron becoming lithium or sulfur becoming phosphorus, and elements that were not originally radioactive can become radioactive. The half-life is the time it takes for a substance to become radioactive and the proportion of radiation emitted by the substance to be reduced by half as it decays. If the half-life is on the order of milliseconds or nanoseconds, the material is no longer radioactive almost instantly, so this is not a problem. However, if a material is irradiated at a high dose and has a long half-life, the shielding itself will become a source of radiation for a long period of time and will no longer function satisfactorily as a shield.

[0021] The neutron reactant of colmanite (also known as colemanite) (B2O3), tumburite (B2O3), Pyrex (registered trademark) (B2O3), and boron carbide (B4C), which are used as neutron shielding materials, is boron. Natural boron has two isotopes: boron-10 (B-10), which has a natural abundance of 19.9%, and boron-11 (B-11), which has a natural abundance of 80.1%. The nuclear data JENDL-4.0, which shows the reaction rate with neutron energy (cross section, unit: barns), can be viewed on the homepage of each data research group of the Japan Atomic Energy Agency (https: / / wwwndc.jaea.go.jp / jendl / j40 / J40_J.html#Reports). (Reference: K. Shibata, O. Iwamoto, T. Nakagawa, N. Iwamoto, A. Ichihara, S. Kunieda, S. Chiba, K. Furutaka, N. Otuka, T. Ohsawa, T. Murata, H. Matsunobu, A. Zukeran, S. Kamada, and J. Katakura: "JENDL-4.0: A New Library for Nuclear Science and Engineering," J. Nucl. Sci. Technol. 48(1), 1-30 (2011).)

[0022] In the thermal neutron region, the cross section of B-10 is about six orders of magnitude larger than that of B-11. However, in the high energy region above 1 MeV, the cross section of B-10 is almost the same as that of B-11. B-10 reacts with neutrons to emit alpha rays and become Li-7. More precisely, this reaction is 10 B(n,α) 7* This is described as the Li reaction. 7*Li is given an initial recoil energy of 840 keV by the (n,α) reaction, and while moving with a short life of 0.105 ps, it emits a prompt gamma ray of 478 keV and becomes Li-7 in the ground state. Therefore, when natural minerals are used from the viewpoint of radiation shielding, the shielding efficiency is determined by the product of the number of boron atoms present in the mineral, the proportion of the isotope B-10, which has a high reaction rate with neutrons, and the cross section, which depends on the neutron energy. In addition, since the cross section decreases as the neutron energy increases, it is important to reduce the energy of high-energy neutrons by the number of collisions with neutrons using a moderator such as hydrogen or carbon to allow efficient reaction. Furthermore, since it emits a prompt gamma ray of 478 keV, shielding against this gamma ray must also be considered. The density of minerals containing boron is about 2.5 g / cm 3 Its atomic number, Z, is also small at Z=5, so the mass attenuation coefficient μ / ρ (μ: linear absorption coefficient, ρ: material density), which is important in interactions with X-rays and gamma rays, is generally said to be proportional to the third or fourth power of Z. Therefore, its shielding effect against gamma rays is low.

[0023] In one embodiment, attention is focused on gadolinium (Gd), which has the largest reaction cross section for thermal neutrons among all elements, and the fact that it has a high shielding effect against gamma rays due to its atomic number Z=64. Gadolinium is a rare earth element and a rare metal. There are six types of naturally occurring isotopes: gadolinium-154 (Gd-154) with a natural abundance of 2.18%, gadolinium-155 (Gd-155) with a natural abundance of 14.80%, gadolinium-156 (Gd-156) with a natural abundance of 20.47%, gadolinium-157 (Gd-157) with a natural abundance of 15.65%, gadolinium-158 (Gd-158) with a natural abundance of 24.84%, and gadolinium (Gd-160) with a natural abundance of 21.86%. In the thermal neutron region where the neutron energy is 0.0253 eV, the reaction cross section of Gd-157 is 66 times larger than that of B-10, and the reaction cross section of Gd-155 is 15.8 times larger than that of B-10. In the energy region from 100 eV to around 1 keV, Gd-157 and Gd-155, like other Gd isotopes, have multiple resonance absorption peaks and have larger reaction cross sections than B-10.

[0024] The main reaction of gadolinium, unlike boron, is the (n,γ) reaction, which reacts with neutrons and emits gamma rays (data marked as capture in the diagram showing the cross section). In the case of boron, it is the (n,α) reaction. 7* Li is produced and emits prompt gamma rays of 478 keV in the process of becoming Li-7. In the case of Gd, 154 Gd(n,γ) 155 Gd reaction, 155 Gd(n,γ) 156 Gd reaction, 156 Gd(n,γ) 157 Gd reaction, 157 Gd(n,γ) 158 The Gd reactions produce Gd-155, Gd-156, Gd-157, and Gd-158, respectively. These are stable isotopes and do not emit beta or gamma rays upon decay. 158 Gd(n,γ) 159Gadolinium-159 (Gd-159) produced by the Gd reaction decays into the stable isotope terbium (Tb-159) through beta decay. This decay releases beta rays with energies of 970.6keV (62%), 912.6keV (26%), 607.09keV (12%), and 622.42keV (0.31%), and gamma rays with energies of 363.55keV (11.4%), 58keV (2.15%), 348.16keV (0.234%), and 226.01keV (0.215%). Gd-157 and Gd-155, which have particularly large reaction cross sections in the thermal neutron region, emit neutron capture gamma rays of 8MeV in the (n,gamma) reaction.

[0025] The gamma ray emission modes are broadly divided into two: (1) continuous spectrum (93.8%) and (2) discrete spectrum (6.2%). Most are (1) continuous spectrum, with a high emission rate across a range of energies from high to low, from unstable compound nuclei to the stable ground level, rather than a single energy of 8 MeV. (2) discrete spectrum is 5.62 MeV + 2.25 MeV (1.3%), 5.88 MeV + 1.99 MeV (1.6%), 6.74 MeV + 1.11 MeV (3.2%), and 7.87 MeV (0.02%). The discrete spectrum has higher energies, but its rate is low.

[0026] In radiation shielding technology, it is preferable that the purpose of shielding is to prevent people and devices such as detection equipment from being damaged by radiation. High-energy gamma rays that penetrate materials with a large atomic number Z penetrate human tissues and thin-film detector elements that are made of light elements. In other words, if the linear energy transfer (LET) by radiation in the material to be protected is small, little energy is transferred to the material that it penetrates, and no damage occurs. LET indicates how much energy the radiation transfers to the material while passing through it. Conversely, the larger the LET, the more energy is transferred to the material, which inevitably leads to greater damage to human cells and tissues. This is expressed as a larger relative biological effectiveness (RBE), and the larger the LET, the larger the RBE.

[0027] Although it depends on the degree of damage, considering the purpose of such protection by shielding, in the case of gamma rays with high energy, the purpose of shielding can be achieved even if they penetrate gamma ray shielding materials. For example, even though 2MeV and 500keV gamma rays have monochromatic energy (strictly speaking, they have an energy range) at the time of generation, their energy attenuates due to the photoelectric effect and Compton scattering due to the interaction between the gamma rays and materials, and spreads to the lower energy range. In particular, in the low energy range, 500keV gamma rays react more with and attenuate than 2MeV gamma rays as a gamma ray shielding material. And, for gamma rays below a few hundred keV, the lower the energy, the greater the LET and RBE for the human body and devices such as sensors.

[0028] Furthermore, the attenuation rate is calculated in detail. When gamma rays with energies of 50 keV, 100 keV, 500 keV, and 2 MeV are shielded with shielding materials that contain iron, lead, boron carbide, and gadolinium oxide, are 5 cm thick, and have a uniform density, at 2 MeV boron carbide attenuates by 60%, iron and gadolinium oxide by 20%, and lead by less than 10%. At 500 keV, boron carbide attenuates by about 35%, while the other elements, iron, lead, and gadolinium oxide, are attenuated by less than 0.5% (1 / 20). At the even lower energy of 100 keV, boron carbide does not attenuate by less than 10%, but the others, such as iron, are attenuated by 4 x 10-7 (4 x 10 -7 ) or less, gadolinium oxide is 1×10 to the power of -42 (1×10 -42 ) or less for lead, 2 × 10 to the power of -137 (2 × 10 -137 ) or less. If the energy is even lower, the attenuation will be even greater. In reality, concrete shielding is made up of cement, water, coarse aggregate, fine aggregate, and admixtures, so it is difficult to construct it with a uniform density. Even if iron blocks are used for the coarse aggregate, the density will be low due to the fine aggregate, cement, water, and the cement paste portion of the admixture.

[0029] In this way, concrete that blocks neutrons and also blocks gamma rays uses a combination of both neutron absorbing materials containing boron as aggregate because the material alone has a low ability to block gamma rays, while heavy concrete with aggregate containing high density iron and other materials has low neutron shielding performance.

[0030] Therefore, in the embodiment, concrete is used as the radiation shield, and a gadolinium compound is used for the aggregates (coarse aggregate and fine aggregate) that make up the concrete. In particular, to make coarse aggregate and fine aggregate with large particle size, it is preferable to use a material that has been ceramicized by hot isostatic pressing (HIP). For this reason, the density of the aggregate is 6.5 g / cm. 3The above is the case. The volume ratio of cement, fine aggregate (sand), and coarse aggregate (gravel) in typical concrete mix is ​​1:2-3:4-6, where cement is taken as 1. In actual production conditions, fine aggregate and cement paste (cement and water) enter the voids in the coarse aggregate, so the ratio of cement paste and fine aggregate to coarse aggregate is adjusted. Therefore, the volume ratio of fine aggregate to cement is preferably 2 or more and 3 or less. The volume ratio of coarse aggregate to cement is preferably 4 or more and 6 or less. The radiation shielding body of the embodiment may be so-called mortar.

[0031] The volume ratio of water to cement is preferably 0.5 or more and 0.6 or less. The amount of water is approximately 50-60% as a ratio to cement. That is, if the volume of the concrete product is 100%, the aggregate ratio, which is the sum of fine aggregate and coarse aggregate, is 85-90%, and water is about 5%. Therefore, the high-density aggregate becomes a material that shields neutrons and gamma rays, and neutrons with higher energy are scattered by water, slowed down, and absorbed by the aggregate. In particular, this aggregate can be produced from powdered raw materials such as shavings and shavings during the production of scintillators used as detectors for X-rays and gamma rays, without HIP treatment, and from waste materials that have already been HIP treated, or from defective scintillators that have been inspected and replaced due to the end of their product life, so it is not only cheaper than producing it from powdered raw materials, but also effective as a treatment for environmental waste.

[0032] The concrete, which is a radiation shielding body of the embodiment, contains 10% to 90% by volume of gadolinium element. If the content is less than 10% by volume, the radiation shielding effect is insufficient, and even if the thickness of the concrete is increased, it becomes too thick to be practical for effectiveness. If the content exceeds 90% by volume, the strength of the concrete decreases. The preferred content is 30% to 70% by volume. The content of gadolinium element contained in concrete is measured as follows.

[0033] A method for non-destructively analyzing the composition of radiation shielding and measuring the gadolinium element contained therein is X-ray fluorescence analysis, which detects the fluorescent X-rays specific to gadolinium generated by irradiating the target with X-rays. X-ray fluorescence analysis allows accurate and easy determination of the composition and elements. In addition, it is possible to use neutron rays to measure the gadolinium atom number density reacting within the radiation shielding from the ratio of the neutron intensity irradiated to the target and the neutron intensity penetrating the target relative to the thickness of the target, thereby determining the content ratio of gadolinium isotopes. As a method for analyzing the isotope ratio in more detail, it is also possible to determine the amount of transmission of resonance absorption energy specific to gadolinium isotopes using the neutron time-of-flight method.

[0034] Gadolinium compounds have a density of, for example, 6.5 g / cm 3 The concrete is made of heavy concrete using water-insoluble ceramic or sintered bodies as coarse and fine aggregates. For example, the density is 7.4 g / cm 3 Gadolinium oxide (Gd2O3: hereafter abbreviated as GO), density 7.09g / cm 3 Gadolinium gallium garnet (Gd3Ga5O 12 : hereafter abbreviated as GGG), density 7.3g / cm 3 Gadolinium oxysulfide (Gd2O2S: hereafter abbreviated as GOS), density 6.7g / cm 3 Gadolinium silicate (Gd2SiO5: hereinafter abbreviated as GSO) is an example of the phosphor material. Also included are phosphor materials in which these are used as base materials and praseodymium, terbium, europium, cerium, etc. are mixed. Note that any combination of the above components and aspects in which the components and expressions of the embodiments are mutually substituted between methods, devices, systems, etc. are also valid aspects of the present invention.

[0035] The radiation shield of the embodiment may further contain at least one selected from the group consisting of tungsten (W), bismuth (Bi), lead (Pb), molybdenum (Mo), and heavy alloy. Heavy alloy is a sintered body of a tungsten-based alloy containing tungsten as a main component and elements such as nickel, copper, and iron, and has high density and high radiation shielding properties. These elements or materials shield gamma rays, and can be contained in the radiation shield together with gadolinium, which shields neutron rays, to enhance the shielding effect against radiation including gamma rays and neutron rays.

[0036] In the method for producing the concrete, which is a radiation shield of the embodiment, powdered aggregate having an average particle size, average length, or average thickness of less than 5 mm is used as it is as fine aggregate, and ceramic or sintered body having an average particle size, average length, or average thickness of 5 mm or more is used as it is as coarse aggregate, or crushed to less than 5 mm and used as fine aggregate. Conversely, in the case of powder having an average particle size, average length, or average thickness of less than 5 mm, ceramic or sintered body is produced by HIP treatment, and crushed or cut to produce coarse aggregate having an average particle size, average length, or average thickness of 5 mm or more, which can be used. The gadolinium compound used here is used as a product such as a phosphor for X-rays or gamma rays, a detector sensor, or a sensitizing screen. In this way, the gadolinium compound is used by collecting waste such as cutting chips and defective products generated during production, or materials discarded when products used are replaced because they do not obtain the specified amount of light emission, or because they are scratched or broken, or when devices are discarded. For example, a sensor consisting of multiple bundles of thin columnar GOS scintillators as X-ray scintillators has a size of 5 mm or more and can be used as is or crushed, and in sensors and intensifying screens where GOS powder is mixed with a binder and applied to a resin or glass surface, the applied paste-like GOS phosphor can be peeled off and crushed to be used, removing the resin or glass on the front and back sides. The gadolinium compounds contained in the fine aggregate and coarse aggregate may be the same or different.

[0037] The gadolinium compound may contain an activator. Examples of the activator include rare earth elements. Examples of rare earth elements that are particularly preferred include praseodymium (Pr), terbium (Tb), europium (Eu), and cerium (Ce).

[0038] As described above, it is possible to provide a radiation shielding body that uses a high-density gadolinium compound as aggregate, and that can scatter high-energy neutron rays with water mixed into cement, absorbing the energy and converting it to low energy. According to the radiation shielding body of the embodiment, it is possible to provide an environmentally friendly and inexpensive radiation shielding concrete that can shield not only gamma rays but also neutrons, with a concrete thickness equal to or thinner than that of conventional gamma ray shielding concrete, at the lowest possible cost and with reduced waste.

[0039] Another embodiment is, for example, a nuclear reactor, an accelerator facility, an RI neutron source facility, a nuclear fuel facility, a nuclear fuel storage facility, a nuclear shelter, and a heavy particle beam facility and a neutron capture therapy (BNCT) facility in the medical field, which are facilities that generate neutrons or facilities that are intended for shielding. In X-ray and gamma-ray facilities, the radiation shield is widely used for radiation shielding or in combination with a building structural material in non-destructive testing facilities such as medical X-ray facilities, airports, ports, and security-related facilities. In particular, since it has a gamma-ray shielding ability comparable to heavy concrete with a high weight density suitable for shielding X-rays and gamma rays and can also shield neutron rays, a facility related to neutrons can be designed with a high radiation shielding effect without preparing a separate gamma-ray shielding material.

[0040] FIG. 1 is a cross-sectional view showing a schematic configuration of radiation-shielding concrete 1. Radiation-shielding concrete 1 includes cement 2, fine aggregate 3, and coarse aggregate 4. FIG. 2 shows large-size coarse aggregate 5, which is a specific ceramic coarse aggregate for radiation shielding used for the coarse aggregate 4 shown in FIG. 1. The large-size coarse aggregate 5 is a waste material formed by cutting a sintered body when gadolinium oxysulfide (Gd2O2S) is subjected to HIP treatment to produce a scintillator material for X-rays or gamma rays. FIG. 3 shows medium-size coarse aggregate 6, which is a ceramic coarse aggregate for radiation shielding made of the same material as the large-size coarse aggregate 5 but of a different size, and large-size fine aggregate 7, which is a ceramic fine aggregate for radiation shielding that is smaller as a coarse aggregate but larger as a fine aggregate.

[0041] FIG. 4 shows a small-sized fine aggregate (powder) 8. The small-sized fine aggregate 8 is a powder obtained by pulverizing the coarse aggregate or fine aggregate shown in FIG. 2 or FIG. 3 with a hammer, roller mill, ball mill, or other grinding machine, or a powder of the raw material. The coarse aggregate and fine aggregate use gadolinium oxysulfide, but this may be used as a base material and a phosphor containing praseodymium (Pr), terbium (Tb), or europium (Eu) as an activator. Not only waste materials generated by cutting after HIP processing, but also waste materials from defective products or products that have expired can be used as aggregate. In addition, waste materials from the manufacturing process of intensifying screens, in which powder such as gadolinium oxide is mixed with a binder and uniformly coated on a resin material such as polyethylene terephthalate (PET), or waste materials that have expired can be cut or crushed to make aggregate. In particular, when mixed with PET resin, the hydrogen component contained in the PET resin contributes to neutron scattering.

[0042] Figures 5, 6, 7, and 8 are diagrams showing the relationship between neutron energy and reaction cross section for boron isotopes. When boron is used as a neutron absorber, as shown in Figures 5 to 8, natural boron B consists of isotopes B-11 with an abundance of 80.1% and B-10 with an abundance of 19.9%. Of these, the reaction with neutrons is with B-10, which has a natural abundance of 19.9%. Depending on the state of the constituent molecules of the aggregate, for example, in colemanite (B2O3), boron B is 2 / 5 of 2 out of 5 atoms, and furthermore, since the natural abundance is 19.9%, the reaction with neutrons is 8%, and the cross section of the reaction with neutrons is given for this 8%.

[0043] Figures 9, 10, 11, 12, 13, and 14 are diagrams showing the relationship between neutron energy and reaction cross section for gadolinium isotopes. Natural gadolinium (Gd) is mainly composed of six isotopes, as shown in Figures 9 to 14. In particular, in the thermal neutron region with low neutron energy, Gd-155 (natural abundance 14.8%) and Gd-157 (15.65%) have reaction cross sections 10 to 100 times larger than B-10, which together account for 30%, and are larger than boron. In the case of gadolinium oxysulfide (Gd2O2S), the gadolinium atoms are 2 / 5 and the reaction with neutrons is 13.3%, so the reaction rate with neutrons is high.

[0044] These gadolinium isotopes, including other gadolinium isotopes, have resonance absorption peaks that range widely from several eV to several thousand eV, and there are many points where the reaction rate increases even in the high energy region. Figure 15 shows the results of comparing the thermal neutron transmittance of the boron compound boron carbide (B4C) and the gadolinium compounds gadolinium oxysulfide (Gd2O2S) and gadolinium oxide (Gd2O3). Figure 15 shows the analysis results of neutron transmittance for each material thickness. At a thickness of 20 μm, the thermal neutron transmittance of boron carbide is about 0.40, but the thermal neutron transmittance of gadolinium compounds decays to 0.10. This indicates that gadolinium compounds have a high thermal neutron shielding ability.

[0045] For high-energy neutrons, they are moderated by a moderator (hydrogen) and absorbed in the thermal neutron region, enabling efficient shielding. Boron and gadolinium react with neutrons to emit gamma rays. Boron is 478 keV, and gadolinium is a maximum of 8 MeV. Figures 16 and 17 are schematic diagrams for explaining gadolinium neutron capture gamma rays. As shown in Figures 16 and 17, gadolinium neutron capture gamma rays are divided into two types, continuous spectrum (1) and discrete spectrum (2), with the main type being continuous spectrum (1). In this case, the rate of generation in the lower energy region is higher than the rate of 8 MeV actually emitted, including scattering.

[0046] Figure 18 shows the results of calculating the gamma ray energy and attenuation rate when the shielding material is 5 cm thick. At 8 MeV, boron carbide can only block about 20%, but gadolinium oxide, like iron, can block more than 70%. For 2.2 MeV gamma rays emitted when neutrons react with hydrogen, boron carbide blocks about 40% while gadolinium oxide blocks 80%. For 478 keV emitted when neutrons react with boron, which is approximately 500 keV, boron carbide blocks about 6.3% while gadolinium oxide blocks more than 9.8%. For X-rays, which are used in medical applications and are mainly used in X-ray equipment, at around 100 keV, boron carbide blocks less than 90%, while gadolinium oxide absorbs more than iron, at 1 to the power of 42, making it a highly shielding performance.

[0047] Next, an example of a radiation shielding structure will be described. First, a radiation shielding block is prepared. The radiation shielding block is made of concrete, which is the radiation shielding body. The concrete block, which is the radiation shielding block, is manufactured, for example, by the following method. The mixture is made of cement, powder of gadolinium compound as fine aggregate having a size (average particle size) of less than 5 mm, and coarse aggregate of gadolinium compound having a size (average particle size) of 5 mm or more, with the volume ratio being 1:2-3:4-6, assuming that the cement is 1. First, the cement and the fine aggregate powder of the gadolinium compound are mixed well, and 50-60% of water is added to the cement to make a cement paste. The water is not added all at once, but is mixed little by little, and the amount of water added is adjusted based on the state of kneading the coarse aggregate into the cement paste and the state of being put into a mold.

[0048] FIG. 19 is a schematic top view showing a structural example of the concrete block 10. FIG. 20 is a schematic front view showing another structural example of the concrete block 10. FIG. 21 is a schematic side view showing another structural example of the concrete block 10. FIG. 22 and FIG. 23 are schematic views showing a structural example of a concrete block structure that is a radiation shielding structure. When making a large area or a large member, a cement frame is used for production, but since the weight of the produced block becomes heavy, here, any of the concrete blocks 10 shown in FIG. 19 and FIG. 20 are further combined and connected together to form a wall-shaped (plate-shaped) concrete block structure 100 shown in FIG. 22 or a box-shaped concrete block structure 100 shown in FIG. 23. These concrete blocks 10 have a connecting through hole 10a for connecting with other concrete blocks 10.

[0049] Unlike a general concrete block structure, when flat surfaces of blocks are stacked on top of each other, radiation may leak from the gap between the flat surfaces. The blocks 10 shown in Figs. 19, 20, and 21 form an uneven structure on the stacked surfaces to prevent radiation from leaking from the gap. Furthermore, assuming that each concrete block 10 becomes heavy and may fall or collapse when stacked, the concrete blocks 10 are connected vertically or horizontally by bolting through structural materials such as iron or stainless steel into the connecting through holes 10a, and in some cases, the bolts are used to fix the blocks to the floor to form anchors. The size of each piece in Figs. 19, 20, and 21 is standardized to 50 mm or 100 mm, and they can be combined in multiple stages depending on the shielding effect to form a shield.

[0050] The concrete of the radiation shield of the embodiment can be used alone or can be combined with conventional heavy concrete containing boron or iron to form a radiation shield. The radiation shield of the embodiment has a high radiation shielding ability, and for example, after forming a shield around a radiation source using the radiation shielding block of the embodiment, a conventional heavy concrete block can be combined behind it to form a radiation shielding structure, thereby more effectively shielding radiation. Such a combination can provide a margin to the overall thickness of the shield, and can expand the applicability of the shield to installation spaces.

[0051] According to the radiation shield of the embodiment, high-energy neutron rays can be scattered by the water mixed into the cement, and the energy can be absorbed and converted into low-energy rays. In addition to the radiation originally generated, the radiation emitted by reaction with neutrons can also be efficiently absorbed by the high-density gadolinium compound, which is industrially useful. [Explanation of symbols]

[0052] 1...Radiation shielding concrete, 2...Cement, 3...Fine aggregate, 4...Coarse aggregate, 5...Large size coarse aggregate, 6...Medium size coarse aggregate, 7...Large size fine aggregate, 8...Small size fine aggregate, 10...Concrete block, 100...Concrete block structure

Claims

1. 1. A radiation shield comprising concrete, The concrete is A first aggregate having an average particle size, an average length, or an average thickness of less than 5 mm and made of a first sintered body of a first gadolinium compound; A second aggregate having an average particle size, an average length, or an average thickness of 5 mm or more and made of a second sintered body of a second gadolinium compound; having The ratio of the first aggregate and the second aggregate to the concrete is 85% by volume or more and 90% by volume or less. Radiation shielding.

2. 2. The radiation shield of claim 1, wherein the concrete comprises between 10% and 90% gadolinium by volume.

3. Each of the first sintered body and the second sintered body has a density of 6.5 g / cm ３ The radiation shield according to claim 1 or 2, having a density equal to or greater than 100 nm.

4. 4. The radiation shield of claim 1, wherein each of the first and second gadolinium compounds includes at least one gadolinium compound selected from the group consisting of gadolinium oxide, gadolinium gallium garnet, gadolinium oxysulfide, and gadolinium silicate.

5. 5. The radiation shield according to claim 1, wherein the concrete further comprises at least one selected from the group consisting of tungsten, bismuth, lead, molybdenum, and heavy alloy.

6. The present invention comprises a plurality of radiation shielding blocks integrally assembled together, A radiation shielding structure, wherein each of the plurality of radiation shielding blocks has the radiation shield according to claim 1 .

7. A radiation shield according to any one of claims 1 to 5; a second radiation shielding comprising boron or iron; A radiation shielding structure comprising:

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