JP2008008656A - Radiation shield - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation shield which is excellent in the simultaneous shielding performance against durability as well as a neutron beam, γ rays and X rays by clearing up a problem of the deterioration in radiation shielding performance due to ununiform scattering of blended graphite. <P>SOLUTION: The radiation shield is formed by making compositions blended so that the content of one or more kinds among Gd or oxide, nitride, boride, carbide, oxynitride, oxyboride, carbonate, nitroboride, carbonitride, carboboride, carbonate nitride, oxyboride nitride, carboboride nitride, oxyboride nitrocarbide of Gd or complex compounds or mixtures of them which have a large capture cross section for thermal neutrons, is 0.2 to 40 percent by mass, the content of tungsten is 50 to 97.8 percent by mass, and the content of a binding agent such as iron is 2 to 10 percent by mass, and by sintering such compositions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation shielding material that simultaneously shields γ-rays, X-rays and neutron rays. For radiation facilities, radioactive waste, nuclear fuel, radioisotope (RI) storage, transportation containers and related equipment It relates to the radiation shielding material used.

  For shielding γ-rays and X-rays, there is no large difference in mass attenuation coefficient for any substance, and a substance with higher density has a larger linear attenuation coefficient and a smaller shield thickness. , Tungsten, iron, concrete, etc. are used.

  On the other hand, fast neutrons irradiated into a material lose energy due to elastic scattering with atoms in the material to become thermal neutrons, and the thermal neutrons are captured by the nuclei of elements constituting the material. Therefore, for shielding neutrons, water containing hydrogen, polymer materials, materials containing Gd, B, C, Be, etc. are generally used as shielding materials.

  Thermal neutrons are more likely to be captured by nuclei with larger thermal neutron capture cross sections, but in this case there are cases where secondary γ rays are emitted, so the neutron beam shielding is considered including the shielding of secondary γ rays. It must be.

  Therefore, as materials for simultaneously shielding neutron rays, γ rays, and X-rays, Patent Literature 1 and Patent Literature 2 are materials in which neutron ray shielding materials such as Gd and graphite and γ ray shielding materials such as lead and tungsten are combined. Has been proposed.

  That is, in Patent Document 1, a raw material powder made of a mixture of a neutron moderator made of graphite, a neutron absorber made of gadolinium oxide, and a γ-ray shielding material made of tungsten and / or tungsten oxide is made uniform with iron powder. A radiation shielding material formed and processed by mixing and melting iron as a binder material is disclosed.

In Patent Document 2, a raw material powder made of graphite, gadolinium oxide, tungsten and / or tungsten oxide, and iron powder and / or lead powder are mixed at a volume ratio of 90 to 95% and 10 to 5%, respectively. A semiconductor container molded by pressure is disclosed.
Japanese Patent Publication No. 8-27388 Japanese Patent No. 2877292

  A material obtained by combining a neutron shielding material such as Gd or graphite and a γ-ray shielding material such as lead or tungsten is excellent in the ability to simultaneously shield neutron rays, γ-rays, and X-rays. Due to the difference in specific gravity between each other, especially the blended graphite and other blended components, the blended components, especially the graphite, are not uniformly dispersed in the material, and the density is lowered, so that the intended radiation shielding ability is reduced. There is a problem that it cannot be fully demonstrated.

  The problem to be solved in the present invention is to solve the problem of reduction in radiation shielding ability due to non-uniform dispersion of blended graphite, and in addition to the simultaneous shielding ability of neutron rays, γ rays and X rays, the radiation shielding material having excellent durability Is to provide.

  The present invention provides the knowledge that the shielding ability of graphite, particularly fast neutron radiation, can be replaced by Gd or an oxide of Gd and other compounds without using graphite that adversely affects densification in terms of material. Based on the above, the above problems were solved. As a result, the use of graphite, which has conventionally been essential for radiation shielding, especially fast neutron radiation shielding, prevents the decrease in density due to the use of graphite, and is dense, with neutron rays, gamma rays, and X-rays. A radiation shielding material excellent in the simultaneous shielding ability can be obtained.

  In addition to the above Gd or Gd oxide, various nitrides, borides, carbides, oxynitrides, oxyborides, carbonates, nitroborides, carbonitrides, carbonitrides, carbonitrides, acids At least one of boronitrides, carbonitrides, oxyboronitrides, or composite compounds or mixtures thereof (hereinafter collectively referred to as “Gd-containing materials”) can be used. By obtaining a material composed of a binder, a radiation shielding material having reliable performance and durability for simultaneously shielding neutron rays, γ rays, and X rays can be obtained.

  As Gd-containing material, Gd may be added as it is, but Gd oxide, nitride, boride, carbide, acid, which helps to disperse uniformly in a chemically stable oxide or material. Of nitrides, oxyborides, carbonates, nitroborides, carbonitrides, carbonitrides, carbonitrides, oxyboronitrides, carbonitrides, oxyborocarbides, or complex compounds or mixtures thereof When added in the form, a material capable of uniformly dispersing the Gd-containing material in the radiation shielding material and reliably shielding neutrons can be obtained. In particular, borides and carbides of Gd have a greater effect on neutron deceleration and shielding than Gd alone, and the mixed dispersion of raw materials is more uneven due to the difference in specific gravity than the conventional one in which graphite or boron is added to Gd alone. Therefore, the neutron shielding effect is improved. In particular, when the radiation shielding material is used in a thin shape, the performance is exhibited. A solid solution containing boron, such as borohydride of Gd, or a solid solution containing carbon, such as carbonitride, has the same effect.

  As the radiation shielding material of the present invention, it is desirable to use a heat-resistant or corrosion-resistant binder, and specifically, at least one or more of Fe, Ti, Cu, Ni, Cr, and Co are used. It is desirable. Depending on the selection of the binder, it can be used at 400 ° C. or higher. Further, if a corrosion-resistant alloy such as a stainless alloy is formed by selecting a plurality of types of the binders, a radiation shielding material suitable for an environment where corrosion resistance is required can be obtained.

  Further, the composition is such that the content of the Gd-containing material is 0.2 to 40% by mass, the content of tungsten is 50 to 97.8% by mass, and the content of the binder is 2 to 10% by mass. If the configuration has a higher density, the effect of shielding γ rays and X-rays is improved. In addition, since elements with a large thermal neutron capture cross-sectional area or substances containing a large amount of such elements are more effective for shielding neutron radiation, it is possible to use a combination of these inorganic substances or combine them to create a better radiation shielding material. Manufacturing is possible.

  When the content of the Gd-containing material is less than 0.2% by mass, the shielding effect of neutron beams is lowered. When the content of the Gd-containing material is more than 40% by mass, the shielding effect of γ rays and X rays is lowered. Further, if the tungsten content is less than 50% by mass, the shielding effect of γ rays and X-rays is not sufficient, and if it is more than 97.8% by mass, the shielding of neutrons is not sufficient and sintering is difficult. . If the content of the binder is less than 2% by mass, sintering at 1500 ° C. or lower is not sufficient, and a material that can withstand bending and pulling cannot be obtained. On the other hand, if it is more than 10% by mass, the shielding efficiency of γ rays and X rays is poor, so it is necessary to use a thick material.

  The density of the radiation shielding material of the present invention after sintering is desirably 10 or more. Below this value, γ-ray and X-ray shielding ability is inferior to lead, and in order to obtain simultaneous shielding ability of γ-ray, X-ray and neutron ray, the material itself must be used thickly, which is not practical. It is.

  Furthermore, the surface of the radiation shielding material of the present invention is coated with Ti or stainless steel by plating, spraying, ion plating, vapor deposition, etc., and the corrosion resistance is improved, making it possible to use as a radiation shielding material for a long time in various environments. Become.

  The radiation shielding material of the present invention has a simultaneous shielding ability of γ-rays, X-rays and neutrons, and is a radiation comprising a sintered body containing graphite, gadolinium oxide, tungsten and / or tungsten oxide with conventional iron or lead as a binder material. It is superior to shielding materials and has excellent durability.

  Moreover, by setting the mixing ratio of the raw materials to the ratio of the present invention, it is possible to design an optimal radiation shielding material, and it is possible to produce a radiation shielding material having sufficient mechanical strength and heat resistance for use. is there.

  Furthermore, if the surface of the radiation shielding material of the present invention is coated with Ti or stainless steel, the corrosion resistance is improved and it can be used in various environments.

  The radiation shielding material of the present invention can be produced by the following method.

  First, a tungsten powder, a powder containing Gg, and a powder composed of at least one of Fe, Ti, Cu, Ni, Cr, and Co are uniformly mixed by a ball mill mixer, an attritor, a rough machine, or the like. Other mixing methods may be used as long as they can be mixed uniformly.

  Next, the mixed powder is sieved, the coarse particle size powder is pulverized, sieved again, the average particle size is adjusted to 1 to 30 μm, then filled in the mold of the press machine and press-molded at a pressure of 20 to 200 MPa. When the sintering is performed at 1200 to 1700 ° C. in a non-oxidizing atmosphere, the radiation shielding material of the present invention can be obtained. Alternatively, when the raw material powder adjusted in particle size is filled in a carbon mold of a hot press apparatus and hot pressing is performed at a pressure of 1 to 20 MPa in a temperature range of 850 to 1300 ° C., the radiation shielding material of the present invention is obtained. Obtainable.

  At the time of sintering, at least one of Fe, Ti, Cu, Ni, Cr, and Co, which are binders, is once liquefied and serves as a binder that connects the tungsten particles and the Gd-containing particles.

  If the obtained sintered body is appropriately subjected to machining, electric discharge machining or the like, the radiation shielding material of the present invention having a desired shape can be obtained.

  Hereinafter, the present invention will be described in detail by way of examples. In addition, this invention is not limited to a following example.

The test of shielding ability evaluated the thickness (1/10 valence layer) of each test material which makes the dose equivalent rate of each radiation 1/10, and evaluated it. In the test, ²⁵² Cf was used as a neutron source, and ⁶⁰ Co was used as a γ-ray source.

Table 1 shows pure iron having an average particle diameter of 1 μm as a binder, Gd ₂ O ₃ particles having an average particle diameter of 1 μm as a neutron absorber, and tungsten powder having an average particle diameter of 145 μm as a γ-ray shielding material. It mixed according to the compounding ratio shown, and it mixed until it became uniform for 4 hours with the ball mill mixer.

  Next, the mixed powder is passed through a sieve made of stainless steel in the order of # 500 and # 1000, the powder with a coarse particle size is pulverized, sieved again, and the average particle size is adjusted to 1 to 30 μm. It was filled and press-molded at a pressure of 20 to 200 MPa to obtain a press-molded body having a shape of 15 × 15 × (1.5 to 2.5) cm, and this was obtained in a hydrogen atmosphere at a temperature range of 1200 to 1700 ° C. Sintering was performed, and the radiation shielding material of the present invention having a shape of 10 × 10 × (1 to 2) cm was produced using a surface grinder. Similarly, the radiation of the present invention can also be obtained by filling the carbon powder of the hot press apparatus with the raw material powder having the above particle size adjusted and performing hot pressing at a pressure of 1 to 20 MPa in a temperature range of 850 to 1300 ° C. A shielding material could be obtained.

And about the obtained radiation shielding material of this invention, the density and shielding ability were measured. As a comparative example, 50 wt% W-20 _wt% Gd ₂ O 3 -20 wt% Fe-10 wt% C of _{W-Gd 2 O 3 -Fe-} C based material containing conventional graphite, nickel, Similar measurements were performed for tungsten, lead, epoxy resin, polyethylene, concrete, and carbon steel (SS41). The results are shown in Table 1.

  Table 1 shows that the radiation shielding material of the present invention can shield both neutron rays and γ rays (including X-rays) with a practical thickness.

However, Example No. As can be seen from FIG. 1, when the content of Gd ₂ O ₃ is less than 0.2% by mass, the neutron shielding ability is lowered, so that the content of Gd ₂ O ₃ is preferably 0.2% by mass or more. In addition, Example No. As can be seen from FIG. 14, when the content of Gd ₂ O ₃ exceeds 40% by mass, it may be in an unsintered state. Therefore, the content of Gd ₂ O ₃ is 0.2% by mass or more and 40% by mass or less. It turns out that is desirable.

  In addition, Example No. As can be seen from FIG. 6, when the Fe content is less than 2.0% by mass, it may be unsintered and cannot be used as a radiation shielding material. % Or more is desirable. However, if the amount of the binder exceeds 10% by mass, the density decreases and the ability to shield γ rays (including X-rays) decreases, so the content of the binder is 2.0% by mass or more and 10% by mass. % Or less is desirable.

  Furthermore, Example No. As can be seen from FIG. 1, the neutron shielding ability decreases when the amount of W exceeds 97.8% by mass, so that the content of W is preferably 97.8% by mass or less. In addition, Example No. As can be seen from FIG. 14, when the amount of W is less than 50% by mass, it may be unsintered. Therefore, it is understood that the content of W is preferably 50% by mass or more and 97.8% by mass or less.

  The radiation shielding material of the present invention is No. Comparative Example No. 1 except for Example 1 It has a neutron shielding ability superior to that of 19 epoxy resins, and also increases the gamma ray shielding ability due to the increase in density, and has both high performance of gamma ray, X-ray shielding ability and neutron ray shielding ability. Is.

Comparative Example No. 15 W-Gd ₂ O ₃ —Fe—C-based material has excellent neutron shielding ability, but contains graphite, so the density decreases, and the dispersion of graphite in the material becomes non-uniform due to the difference in specific gravity, The γ-ray shielding ability was smaller than ¼ of the γ-ray shielding ability of the radiation shielding material of the present invention.

  Any of the comparative examples of nickel, tungsten, lead, epoxy resin, polyethylene, concrete, and carbon steel (SS41) can be evaluated in any case when the gamma ray shielding ability and neutron ray shielding ability are comprehensively evaluated. The advantages are clearly recognized.

In the same manner as in Example 1, Gd or Gd nitride (GdN), boride (Gd ₂ B ₄ ), carbide (Gd ₄ C ₃ ), oxynitride (Gd (ON)) instead of Gd ₂ O ₃ ), Acid boride (Gd (BO)), carbonate (Gd ₂ (CO)), boron nitride (Gd (BN)), carbonitride (Gd (CN)), carbon boride (Gd (CB)) ), Carbonitride (Gd (CON)), oxyboronitride (Gd (OBN)), carbonitride (Gd (CBO)), oxyborocarbide (Gd (OBNC)), or a composite compound thereof At least one kind of powder (including Gd oxide) or a mixture (including Gd oxide) was used, and the same results as in Example 1 were obtained.

Here, Gd (ON) is a solid solution of Gd ₂ O ₃ and GdN, Gd (BO) is a solid solution of Gd ₂ B ₄ and Gd ₂ O _3, and Gd ₂ (CO) is Gd ₄ C ₃ and Gd ₂ O. ₃ , Gd (BN) is a solid solution of Cd ₂ B ₄ and GdN, Gd (CN) is a solid solution of Gd ₄ C ₃ and GdN, Gd (BN) is a solid solution of Gd ₂ B ₄ and GdN, Gd (CB) is a solid solution of Gd ₄ C ₃ and Gd ₂ B ₄ , Gd (CON) is a solid solution of Gd ₄ C ₃ , Gd ₂ O ₃ and GdN, and Gd (OBN) is Gd ₂ O ₃ and Gd ₂ A solid solution of B ₄ and GdN, Gd (CBO) is a solid solution of Gd ₄ Cs, Gd ₂ B ₄ and Gd ₂ O _3, and Gd (OBNC) is Gd ₂ O ₃ , Cd ₂ B ₄ , GdN and Gd ₄ C ₃ is a solid solution. The composite compound is a composite compound of the above-described Cd compound. A mixture is simply a mixture of these. It is preferable to add in the form of a compound rather than adding it in the form of Gd alone because the dispersion becomes uniform and is chemically stable.

  In the same manner as in Example 1, the binding material was changed from Fe to Ti, Cu, Ni, Cr, Co, or one or more of them (including Fe), for example, 5 mass% Fe was 3 mass% Fe-2 mass. Similar results were obtained even when changed to% Ni or the like. In addition to the additives, the use of a binder having a composition such as Fe-12Ni-17Cr-2.5Mo-0.15N, which is synthesized by separately adding Mo, N, etc., improves the corrosion resistance.

  An experiment similar to that in Example 1 was performed on the outermost surface of the same sample as in Example 1 under the condition that seawater is sprayed on a sample having Ti 500 μm arc ion-plated. I found out that I could do it. The uncoated sample was corroded from the surface, and had a life of 1/20 or less of the useful life of the coated sample. Similarly, similar results were obtained for samples coated with stainless steel (SUS304, SUS316L, etc.).

  The radiation shielding material of the present invention comprises a radiation facility, a nuclear power plant protection wall, radioactive waste, nuclear fuel, radioisotope (RI) storage, transport container and transportation equipment, medical radiation protective clothing, medical isotope syringe and It can be used for plungers, radiation shielding screens, radiation shielding packings, and the like.

Claims (4)

  Gd or Gd oxide, nitride, boride, carbide, oxynitride, oxyboride, carbonate, nitroboride, carbonitride, carbonitride, carbonitride, oxyboronitride, carbonitride A radiation shielding material comprising tungsten, a binder, and at least one of an oxide, an oxyboronitride, or a composite compound or mixture thereof.   The radiation shielding material according to claim 1, wherein the binder is made of at least one of Fe, Ti, Cu, Ni, Cr, and Co.   Gd or Gd oxide, nitride, boride, carbide, oxynitride, oxyboride, carbonate, nitroboride, carbonitride, carbonitride, carbonitride, oxyboronitride, carbonitride The content of at least one of the product, oxyboronitrocarbide, or a composite compound or mixture thereof is 0.2 to 40% by mass, the content of tungsten is 50 to 97.8% by mass, and the binder The radiation shielding material according to claim 1 or 2, wherein the content of is 2 to 10% by mass.   The radiation shielding material according to any one of claims 1 to 3, wherein the outermost surface is coated with Ti or stainless steel.