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EP-4738385-A1 - NEUTRON SHIELDING MULTILAYER STRUCTURE

EP4738385A1EP 4738385 A1EP4738385 A1EP 4738385A1EP-4738385-A1

Abstract

A new multilayer structure having neutron-shielding properties is provided. The multilayer structure comprises: two or more first layers made of a resin or elastomer, and two or more second layers formed of inorganic fiber bundles containing neutron-absorbing elements and a resin or elastomer, the first and second layers being laminated alternately. Even if the total content of neutron-absorbing elements is the same, the multilayer structure of the present invention exhibits superior neutron-shielding performance compared with conventional particle-dispersion-type structures.

Inventors

  • FUKAZAWA, HIROSHI

Assignees

  • Nippon Fiber Corporation

Dates

Publication Date
20260506
Application Date
20240603

Claims (15)

  1. A multilayer structure having neutron-shielding properties, which is disposed between a neutron source and an object to be protected, wherein the multilayer structure comprises: at least one first layer made of a resin or an elastomer, and at least one second layer formed of neutron-absorbing inorganic fiber bundles and the resin or elastomer, the first and second layers being laminated alternately.
  2. The multilayer structure according to Claim 1, wherein the total mass of one or more elements selected from gadolinium, samarium, and cadmium contained in the inorganic fiber bundles is 10 mass% or more.
  3. The multilayer structure according to Claim 2, wherein the inorganic fiber bundles are selected from fiber cloths, rovings, roving cloths, chopped strand mats, milled fibers, nonwoven fabrics, or filament mats.
  4. The multilayer structure according to Claim 3, wherein the resin or elastomer constituting the first layer and the resin or elastomer constituting the second layer are identical.
  5. The multilayer structure according to Claim 4, wherein the outermost layer closest to the object to be protected is the second layer.
  6. The multilayer structure according to Claim 4, wherein the outermost layer closest to the neutron source is the first layer.
  7. The multilayer structure according to Claim 5 or Claim 6, wherein both the first layer and the second layer are provided in plural numbers.
  8. The multilayer structure according to Claim 7, wherein the thickness of each first layer gradually increases from the layer closest to the object to be protected toward the layer closest to the neutron source.
  9. The multilayer structure according to Claim 7, wherein the thickness of each second layer gradually increases from the layer closest to the neutron source toward the layer closest to the object to be protected.
  10. The multilayer structure according to Claim 7, wherein, for the plurality of second layers, from the layer closest to the neutron source toward the layer closest to the object to be protected, i) the content of inorganic fiber bundles per unit volume increases, or ii) the volume porosity of the inorganic fiber bundles decreases, or iii) the content of neutron-absorbing elements (gadolinium, samarium, or cadmium) contained in the inorganic fiber bundles increases.
  11. A multilayer structure having neutron-shielding properties, which is disposed between a neutron source and an object to be protected, wherein the multilayer structure comprises two or more layers each formed of neutron-absorbing inorganic fiber bundles and a resin or elastomer, and wherein, from the layer closest to the neutron source toward the layer closest to the object to be protected, i) the content of inorganic fiber bundles per unit volume increases, or ii) the volume porosity of the inorganic fiber bundles decreases, or iii) the content of neutron-absorbing elements (gadolinium, samarium, or cadmium) contained in the inorganic fiber bundles increases.
  12. The multilayer structure according to Claim 10, wherein the resin is a cured product of bisphenol-A type epoxy resin or hydrogenated bisphenol-A type epoxy resin.
  13. The multilayer structure according to Claim 11, wherein the resin is a cured product of bisphenol-A type epoxy resin or hydrogenated bisphenol-A type epoxy resin.
  14. A method for producing the multilayer structure according to Claim 10, wherein the multilayer structure is manufactured by an infusion molding process.
  15. A method for producing the multilayer structure according to Claim 11, wherein the multilayer structure is manufactured by an infusion molding process.

Description

Technical Field The present invention relates to a multilayer structure excellent in neutron shielding property. Background Art With the advancement of nuclear-related and aerospace technologies, the necessity for neutron-shielding materials has been increasing more than ever before. Neutron-shielding materials are continuously required to improve their performance to protect humans from neutron exposure. Furthermore, as to electronic devices indispensable for the control of nuclear facilities and space-related equipment, the increased integration density of semiconductors mounted therein has resulted in an increasing occurrence of so-called "soft errors." A "soft error" refers to a malfunction of an electronic device caused by the inversion of bit data when neutrons derived from cosmic rays penetrate semiconductor elements. Accordingly, materials capable of effectively shielding neutrons are required not only for protecting humans but also for protecting electronic devices. Concrete has long been known as a representative example of a neutron-shielding material; however, it is unsuitable for precision-machined parts such as housings for electronic devices. As alternative materials, composites combining neutron-shielding substances with resins have been proposed. For example, Japanese Patent Application Laid-Open No. H6-180388 (Patent Document 1) discloses a heat-resistant neutron-shielding material obtained by incorporating inorganic boron compounds and gadolinium oxide as thermal neutron-shielding substances into phenolic resin. Japanese Patent Application Laid-Open No. 2020-30088 (Patent Document 2) discloses a resin composition in which boron carbide, boric acid, gadolinium, or a mixture thereof having a specific particle-size range is incorporated into a curable resin. The inventions disclosed in Patent Documents 1 and 2 both involve adding neutron-absorbing "powdery" raw materials into resin matrices. Meanwhile, the present inventor has developed inorganic fibers containing a high concentration of gadolinium or the like, which exhibit excellent neutron-shielding properties (WO 2022/145401 A1; Patent Document 3). Prior Art Documents Patent Documents Patent Document 1: JP-A H6-180388Patent Document 2: JP-A 2020-30088Patent Document 3: WO 2022/145401 A1 Summary of the Invention Problems to be Solved by the Invention The inventions described in Patent Documents 1 to 3 all employ rare-earth elements such as gadolinium and samarium as neutron-absorbing elements. Therefore, from the viewpoint of effectively utilizing limited natural resources, it is desirable to provide a material that can exhibit excellent neutron-shielding performance while suppressing the consumption of such rare-earth elements. Accordingly, the inventor of the present invention has studied the creation of a neutron-shielding structure capable of maximizing neutron-shielding performance while minimizing the amount of neutron-absorbing elements used. Means for Solving the Problems As a result, the inventor has found that in a composite material in which a matrix such as a resin is filled with a material containing neutron-absorbing elements, the neutron-shielding performance is superior when the material containing the neutron-absorbing elements is filled in the form of a fiber bundle rather than in a particulate form. Based on this finding, the present invention has been completed. That is, the present invention provides a multilayer structure having neutron-shielding properties, wherein the multilayer structure comprises: at least one first layer made of a resin or an elastomer, andat least one second layer formed of neutron-shielding inorganic fiber bundles and a resin or an elastomer,laminated alternately in a stacked manner. In the multilayer structure of the present invention, the first layer serves to attenuate the energy of neutrons (i.e., to slow down the velocity of neutrons), and the second layer serves to absorb the decelerated neutrons. Effects of the Invention In the multilayer structure of the present invention, since the material containing neutron-absorbing elements is incorporated not as a powder but as inorganic fiber bundles, the neutron-shielding performance is significantly improved. Furthermore, because the filler is composed of inorganic fiber bundles, it is possible to effectively position and form the neutron-slowing layer and the neutron-absorbing layer within the structure. Brief Description of Drawings [Fig. 1] Schematic diagram showing the layer structure of the multilayer structure of the present invention.[Fig. 2] Schematic diagram showing a conventional neutron-shielding structure in which the material containing neutron-absorbing elements is in powder form.[Fig. 3] Graph showing the results of PHITS calculations.[Fig. 4] Enlarged view of a part of the graph shown in Fig. 3.[Fig. 5] Schematic diagrams of two examples of multilayer structure models used in PHITS calculations.[Fig. 6] Another graph showing th