A rare earth element-doped aluminum-based composite material for nuclear spent fuel shielding

Abstract

A rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel comprises, by weight percentage: gadolinium oxide 1 wt.%–10 wt.%, europium oxide 1 wt.%–10 wt.%, samarium oxide 1 wt.%–10 wt.%, dysprosium oxide 1 wt.%–10 wt.%, erbium oxide 1 wt.%–10 wt.%, with the remainder being 6063 aluminum alloy powder. This invention exhibits excellent neutron absorption capacity. The aluminum-based material maintains both low weight and high strength and ductility. Furthermore, the addition of rare-earth elements such as Gd, Eu, and Sm, which have high thermal neutron absorption cross-sections, significantly enhances the material's neutron absorption capacity. The introduction of rare-earth elements such as Gd, which react with neutrons in an (n,γ) reaction, effectively prevents the formation of numerous helium bubbles in the matrix, thus improving the material's practical service life.

Description

Technical Field

[0001] This invention relates to the field of nuclear spent fuel disposal and storage technology, and in particular to an aluminum-based composite material doped with rare earth elements for shielding nuclear spent fuel. Background Technology

[0002] Spent fuel contains unburned U-235, U-233, or Pu-239, as well as various fission products such as Sr-90, Tc-99, and Cs-137. These nuclides still possess high decay activity, continuing to release neutrons and accompanied by extremely strong alpha, beta, and gamma rays. Improper handling will pollute the environment and harm human health. Based on the characteristics of spent fuel, to ensure safety, dry storage of spent fuel requires the use of neutron-absorbing materials to keep it below a subcritical state. This means the neutron-absorbing material must have sufficient neutron-capturing capacity to absorb the neutrons produced by the spent fuel, resulting in a multiplication factor of less than 1. Therefore, high-performance neutron-absorbing materials are essential in the storage of spent fuel.

[0003] Generally, when selecting and preparing neutron-absorbing materials for spent fuel storage, priority should be given to whether the material possesses sufficiently high thermal neutron absorption capacity. Currently, aluminum-based boron carbide composite materials are one of the most studied neutron shielding materials for spent fuel transportation and storage. Boron (B) has a strong thermal neutron absorption capacity. 10 Boron carbide (B) has a thermal neutron absorption cross section of 3800 barns and a natural abundance of approximately 19.9%. Aluminum-based boron carbide neutron absorbers are inexpensive to prepare and exhibit excellent mechanical and thermal neutron absorption properties. However, as the B content increases, the material's thermal neutron absorption capacity, hardness, tensile strength, and yield strength increase, while ductility, impact toughness, and corrosion resistance decrease. Therefore, excessive use of boron carbide may hinder the processing and molding of composite materials. When the boron carbide content exceeds a certain value, the material's plasticity decreases significantly, and its density also decreases. Furthermore, because B reacts with neutrons in an (n,α) reaction to generate helium, radiation damage is significantly increased, leading to helium bubble formation, material swelling and cracking, and accelerating B loss.

[0004] The ability of some existing aluminum-based boron carbide shielding materials to absorb neutrons mainly depends on the boron element. However, boron is not the element with the highest neutron absorption capacity, and the boron content further limits its application. Therefore, developing a new aluminum-based composite material with high thermal neutron absorption capacity and excellent performance is of great significance for the development of new neutron absorbing materials for spent fuel storage. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide an aluminum-based composite material doped with rare earth elements for shielding spent nuclear fuel.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel comprises, by weight percentage, the following components: gadolinium oxide (Gd₂O₃) 1 wt.%–10 wt.%, europium oxide (Eu₂O₃) 1 wt.%–10 wt.%, samarium oxide (Sm₂O₃) 1 wt.%–10 wt.%, dysprosium oxide (Dy₂O₃) 1 wt.%–10 wt.%, erbium oxide (Er₂O₃) 1 wt.%–10 wt.%, with the remainder being 6063 aluminum alloy powder.

[0008] A rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel comprises, by weight percentage, the following components: 10 wt.% gadolinium oxide (Gd₂O₃), 10 wt.% europium oxide (Eu₂O₃), 5 wt.% samarium oxide (Sm₂O₃), 5 wt.% dysprosium oxide (Dy₂O₃), 5 wt.% erbium oxide (Er₂O₃), with the remainder being 6063 aluminum alloy powder.

[0009] A rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel comprises, by weight percentage, the following components: 5 wt.% gadolinium oxide (Gd₂O₃), 5 wt.% europium oxide (Eu₂O₃), 5 wt.% samarium oxide (Sm₂O₃), 5 wt.% dysprosium oxide (Dy₂O₃), 5 wt.% erbium oxide (Er₂O₃), with the remainder being 6063 aluminum alloy powder.

[0010] The gadolinium oxide (Gd2O3), europium oxide (Eu2O3), samarium oxide (Sm2O3), dysprosium oxide (Dy2O3), erbium oxide (Er2O3), and 6063 aluminum alloy powders are all powders with a purity of 99.0% or higher and are dried.

[0011] The aluminum-based composite material is prepared under inert gas protection by a powder metallurgy process, including gadolinium oxide (Gd2O3) powder, europium oxide (Eu2O3) powder, samarium oxide (Sm2O3) powder, dysprosium oxide (Dy2O3) powder, erbium oxide (Er2O3) powder, and 6063 aluminum alloy powder, through ball milling-cold isostatic pressing-sintering or ball milling-hot isostatic pressing sintering.

[0012] A material for spent fuel storage racks is made of the aforementioned aluminum-based composite material doped with rare earth elements for shielding spent nuclear fuel.

[0013] An application of an aluminum-based composite plate for preparing spent fuel storage racks, wherein the composition of the aluminum-based composite plate is the same as that of the aluminum-based composite material doped with rare earth elements used for shielding spent nuclear fuel.

[0014] The application of a rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel in shielding materials, wherein the shielding material is made of the aforementioned rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel.

[0015] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0016] 1. This invention possesses excellent neutron absorption capabilities. The aluminum-based material used maintains both low weight and high strength and ductility. Furthermore, the addition of rare earth elements such as Gd, Eu, and Sm, which have high thermal neutron absorption cross-sections, significantly enhances the material's neutron absorption capacity. Composite materials using boron readily undergo (n, α) reactions with neutrons to produce helium (He), which can cause irradiation swelling and cracking, reducing the material's service life. This invention, by introducing rare earth elements such as Gd that react with neutrons (n, γ), effectively avoids the formation of numerous helium bubbles in the matrix, thus improving the material's actual service life.

[0017] 2. This invention employs powder metallurgy technology, involving processes such as ball milling-cold isostatic pressing-sintering or ball milling-hot isostatic pressing-sintering. Specifically, ball milling thoroughly refines and uniformly mixes aluminum alloy powder, europium oxide powder, samarium oxide powder, dysprosium oxide powder, and erbium oxide powder. The mixture is then pre-pressed into a blank using cold isostatic pressing and sintered under inert gas protection or hot isostatic pressing to obtain the desired aluminum-based composite material. The resulting composite material exhibits stable structure, high material utilization, and requires simple equipment and processes, making it easy to operate and significantly reducing preparation costs. This provides a practical and theoretical foundation for the further development of novel neutron-absorbing materials for spent fuel storage. Attached Figure Description

[0018] Figure 1 The image is a scanning electron microscope image of the mixed powder of Al-10wt.%Gd2O3-10wt.%Eu2O3-5wt.%Sm2O3-5wt.%Dy2O3-5wt.%Er2O3 in Example 1 after ball milling for 24 hours.

[0019] Figure 2 The images show the bright-field transmission electron microscope images and selected area electron diffraction patterns of the mixed powder with mass percentages of Al-10wt.%Gd2O3-10wt.%Eu2O3-5wt.%Sm2O3-5wt.%Dy2O3-5wt.%Er2O3 after ball milling for 24 hours, as well as the mixed powder with mass percentages of Al-10wt.%Gd2O3-10wt.%Eu2O3-5wt.%Sm2O3-5wt.%Dy2O3-5wt.%Er2O3.

[0020] Figure 3 The image is a scanning electron microscope image of the mixed powder of Al-5wt.%Gd2O3-5wt.%Eu2O3-5wt.%Sm2O3-5wt.%Dy2O3-5wt.%Er2O3 in Example 2 after ball milling for 24 hours.

[0021] Figure 4 The images and selected area electron diffraction patterns of the mixed powder with mass percentages of Al-5wt.%Gd2O3-5wt.%Eu2O3-5wt.%Sm2O3-5wt.%Dy2O3-5wt.%Er2O3 in Example 2 after ball milling for 24 hours are shown in the bright field image and selected area electron diffraction pattern.

[0022] Figure 5 The microhardness evolution curves of blocks with different mass percentages of mixed powders after ball milling for 24 hours, followed by cold isostatic pressing pre-pressing, and then sintering at 600℃ for 1 hour, 2 hours, 3 hours and 6 hours respectively, are shown.

[0023] Figure 6 The compressive strength of the block was determined by ball milling mixed powders of different mass percentages for 24 hours, followed by cold isostatic pressing pre-pressing, and then sintering at 600℃ for 6 hours.

[0024] Figure 7 The image shows a scanning electron microscope (SEM) image of a block formed from Al-10wt.%Gd2O3-10wt.%Eu2O3-5wt.%Sm2O3-5wt.%Dy2O3-5wt.%Er2O3, which was ball-milled for 24 hours, then cold isostatically pre-pressed into a blank, and finally sintered at 600°C for 6 hours.

[0025] Figure 8 The image shows a scanning electron microscope (SEM) image of a block formed in Example 2 after ball milling a powder containing Al-5wt.% Gd2O3-5wt.% Eu2O3-5wt.% Sm2O3-5wt.% Dy2O3-5wt.% Er2O3 for 24 hours, followed by cold isostatic pressing and then sintering at 600°C for 6 hours. Detailed Implementation

[0026] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0027] Example 1

[0028] 99.9% pure dried 6063 aluminum alloy powder, 99.9% pure dried gadolinium oxide powder, 99.9% pure dried europium oxide powder, 99.9% pure dried samarium oxide powder, 99.9% pure dried dysprosium oxide powder, and 99.9% pure dried erbium oxide powder were weighed and mixed under inert gas protection according to the following mass percentages: Al - 10wt.% Gd₂O₃ - 10wt.% Eu₂O₃ - 5wt.% Sm₂O₃ - 5wt.% Dy₂O₃ - 5wt.% Er₂O₃. Stearic acid was then added as a process control agent to ensure that the final mass concentration did not exceed 1.5wt.%, thus obtaining an initial mixed powder. This mixture was then placed in a ball mill jar, and the jar lid was tightened. The initial mixed powder was ball-milled for 24 hours at a ball-to-powder ratio of 10:1, a filling factor of 0.5, and a ball milling speed of 500 rpm to obtain ball-milled powder. The mixed powder, which has been ball-milled for 24 hours in a glove box under inert gas argon protection, is loaded into a rubber sleeve and sealed tightly. The sealed rubber sleeve is then placed in the hydraulic cylinder of a cold isostatic pressing instrument and held at a pressure of 280 MPa for 2 hours to obtain a green body. The green body is then placed in a sintering furnace under inert gas protection and sintered at 600°C for 1 to 6 hours to obtain the aluminum-based composite material.

[0029] Figure 1 This is a scanning electron microscope image of the mixed powder after ball milling for 24 hours in this embodiment. It can be observed from the image that most of the particles after ball milling are roughly spherical, and many large particles are formed by the aggregation of small particles.

[0030] Figure 2 The images show a bright-field transmission electron microscope image (a) and a selected area electron diffraction pattern (b) of the mixed powder after ball milling for 24 hours in this embodiment. The gray-white area mainly consists of Al, while the black particles mainly consist of the added rare earth elements (Gd, Eu, Sm, Dy, Er). The selected area electron diffraction pattern is a typical nanocrystalline pattern.

[0031] Example 2

[0032] 99.9% pure dried 6063 aluminum alloy powder, 99.9% pure dried gadolinium oxide powder, 99.9% pure dried europium oxide powder, 99.9% pure dried samarium oxide powder, 99.9% pure dried dysprosium oxide powder, and 99.9% pure dried erbium oxide powder were weighed and mixed under inert gas protection according to the following mass percentages: Al - 5wt.% Gd₂O₃ - 5wt.% Eu₂O₃ - 5wt.% Sm₂O₃ - 5wt.% Dy₂O₃ - 5wt.% Er₂O₃. Stearic acid, a process control agent, was then added to ensure a final mass concentration not exceeding 1.5wt.% to obtain an initial mixed powder. This mixture was then placed in a ball mill jar, and the jar lid was tightened. The initial mixed powder was ball-milled for 24 hours at a ball-to-powder ratio of 10:1, a filling factor of 0.5, and a ball milling speed of 500 rpm to obtain ball-milled powder. The mixed powder, which has been ball-milled for 24 hours in a glove box under inert gas argon protection, is loaded into a rubber sleeve and sealed tightly. The sealed rubber sleeve is then placed in the hydraulic cylinder of a cold isostatic pressing instrument and held at a pressure of 280 MPa for 2 hours to obtain a green body. The green body is then placed in a sintering furnace under inert gas protection and sintered at 600°C for 1 to 6 hours to obtain the aluminum-based composite material.

[0033] Figure 3 The image shows a scanning electron microscope image of the mixed powder after ball milling for 24 hours in this embodiment. It can be observed from the image that most of the particles of the powder of this percentage component after ball milling are also roughly spherical, and many large particles are formed by the aggregation of small particles.

[0034] Figure 4 The images show a bright-field transmission electron microscope image (a) and a selected area electron diffraction pattern (b) of the mixed powder after ball milling for 24 hours in this embodiment. The gray-white area also represents Al, and the black particles are mainly composed of the added rare earth elements (Gd, Eu, Sm, Dy, Er). The selected area electron diffraction pattern is a typical nanocrystalline pattern.

[0035] Figure 5 The microhardness evolution curves of the bulk materials obtained by ball milling mixed powders of different mass percentages for 24 hours, followed by cold isostatic pressing pre-pressing, and then sintering at 600℃ for 1 hour, 2 hours, 3 hours, and 6 hours are shown. The microhardness load was 0.98 N, the holding time was 10 seconds, and the hardness values ​​at more than 9 different locations on the same sample were measured and averaged. The graphs show that the microhardness of the sintered bulk material increases with increasing sintering time. Comparing the microhardness after sintering with different mass percentages, the sample with the composition in Example 1 has a higher hardness value, and the hardness values ​​of all samples are greater than that of pure aluminum (approximately 80 HV). The sample in Example 2 has a higher hardness value after sintering for 6 hours.

[0036] Figure 6The statistical results show that the compressive strength of the blocks obtained by ball milling mixed powders of different mass percentages for 24 hours, followed by cold isostatic pressing pre-pressing, and then sintering at 600℃ for 6 hours are statistically analyzed. The results indicate that the sample in Example 1 has a higher compressive strength of 266 MPa, which is higher than that of the samples with other component ratios shown in the figure. The sample in Example 2 has a certain compressive strength, second only to the sample with the component ratio in Example 1.

[0037] Figure 7 The image shows a scanning electron microscope (SEM) image of the bulk material obtained by ball milling the mixed powder of Example 1 for 24 hours, followed by cold isostatic pressing and sintering at 600°C for 6 hours. The dark areas are mainly the aluminum matrix. The image clearly shows that the composite material has a uniform and dense particle distribution, with no particle agglomeration, indicating good sintering performance.

[0038] Figure 8 The image shows a scanning electron microscope (SEM) image of the bulk material obtained by ball milling the mixed powder for 24 hours in Example 2, followed by cold isostatic pressing and sintering at 600°C for 6 hours. The dark areas are mainly the aluminum matrix. The image clearly shows that the composite material has a uniform and dense particle distribution, with no particle agglomeration, indicating good sintering performance.

[0039] Example 3

[0040] 99.9% pure dried 6063 aluminum alloy powder, 99.9% pure dried gadolinium oxide powder, 99.9% pure dried europium oxide powder, 99.9% pure dried samarium oxide powder, 99.9% pure dried dysprosium oxide powder, and 99.9% pure dried erbium oxide powder were weighed and mixed under inert gas protection according to the following mass percentages: Al - 10wt.% Gd₂O₃ - 5wt.% Eu₂O₃ - 7wt.% Sm₂O₃ - 7wt.% Dy₂O₃ - 5wt.% Er₂O₃. Stearic acid, a process control agent, was then added to ensure a final mass concentration not exceeding 1.5wt.% to obtain an initial mixed powder. This powder was then placed in a ball mill jar, and the jar lid was tightened. The initial mixed powder was ball-milled for 24 hours at a ball-to-powder ratio of 10:1, a filling factor of 0.5, and a ball milling speed of 500 rpm to obtain ball-milled powder. The above-mentioned ball-milled powder was loaded into a casing and degassed and sealed. Then it was placed in a hot isostatic pressing furnace and sintered under a vacuum of 10... -3 Below Pa, the temperature is increased to 610℃ at a heating rate of 10℃ / min, while a pressure of 100MPa is applied and the temperature and pressure are maintained for 3 hours. Finally, the temperature is cooled to room temperature and the cladding is removed to obtain a hot isostatic pressing sintered aluminum matrix composite material.

[0041] In this invention, rare earth elements primarily exhibit (n, γ) neutron absorption reactions, which are superior to neutron-absorbing materials that undergo (n, α) reactions. This reaction mode avoids the formation of numerous helium bubbles in the matrix, thus extending the material's service life. Furthermore, many different rare earth elements, such as gadolinium (Gd), europium (Eu), and samarium (Sm), possess high neutron absorption cross-sections, and their addition to the material effectively absorbs neutrons. For example, Gd has... 155 Gd (60900 barns) and 157 Gd (254,000 barns) has two extremely high neutron absorption cross-section isotopes, exhibiting excellent neutron absorption performance and exhibiting no material irradiation swelling problem. This makes Gd an ideal neutron-absorbing element, capable of meeting the functional and structural performance requirements of neutron-absorbing materials. Element europium also has a relatively large thermal neutron absorption cross-section, primarily found in... 151 Eu and 153 Eu has two isotopes, among which 151 Eu has a large thermal neutron absorption cross section of 9190 barns and an abundance of 47.8%. Samarium has many stable isotopes, one of which is… 149 Sm has a thermal neutron absorption cross-section of up to 40,000 barns, exhibiting excellent neutron absorption capacity. Furthermore, dysprosium and erbium also have promising applications in the nuclear industry and possess a certain neutron absorption capacity. Therefore, this invention improves the neutron absorption capacity of the material by adding appropriate proportions of rare earth elements, and the prepared aluminum-based material maintains both low weight and high strength and ductility.

Claims

1. A rare-earth-doped aluminum-based composite material for shielding spent nuclear fuel, characterized in that, The composition comprises the following components by weight percentage: 10 wt.% gadolinium oxide powder, 10 wt.% europium oxide powder, 5 wt.% samarium oxide powder, 5 wt.% dysprosium oxide powder, 5 wt.% erbium oxide powder, with the balance being 6063 aluminum alloy powder; The rare-earth-doped aluminum-based composite material used for shielding spent nuclear fuel is prepared through the following steps: (1) Gadolinium oxide powder, europium oxide powder, samarium oxide powder, dysprosium oxide powder, erbium oxide powder and 6063 aluminum alloy powder were ball-milled for 24 hours under inert gas protection, with a ball-to-material ratio of 10:1 and a rotation speed of 500 rpm; stearic acid was added as a process control agent and its final mass concentration was not more than 1.5 wt.%. (2) The ball-milled powder was cold isostatically pre-pressed at 280 MPa for 2 hours; (3) Under inert gas protection, the aluminum-based composite material doped with rare earth elements was sintered at 600℃ for 6 hours to obtain a rare earth element-doped composite material for nuclear spent fuel shielding. The compressive strength of the rare-earth-doped aluminum-based composite material used for shielding spent nuclear fuel is 266 MPa. The rare-earth-doped aluminum-based composite material used for shielding spent nuclear fuel is used as a material for spent fuel storage racks.

2. The aluminum-based composite material doped with rare earth elements for shielding spent nuclear fuel as described in claim 1, characterized in that: The gadolinium oxide powder, europium oxide powder, samarium oxide powder, dysprosium oxide powder, erbium oxide powder, and 6063 aluminum alloy powder are all powders with a purity of 99.0% or higher and are dried.

3. A material for spent fuel storage racks, characterized in that: The material used for the spent fuel storage rack is made of an aluminum-based composite material doped with rare earth elements for shielding spent nuclear fuel as described in claim 1 or 2.

4. An application of an aluminum-based composite plate in the manufacture of spent fuel storage racks, characterized in that: The composition of the aluminum-based composite plate is the same as that of the aluminum-based composite material doped with rare earth elements for shielding spent nuclear fuel as described in claim 1 or 2.

5. The application of an aluminum-based composite material doped with rare earth elements for shielding spent nuclear fuel as described in claim 1 or 2 in shielding materials.

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