Multi-element rare earth nickel-based alloy material for thermal neutron shielding and preparation method thereof

Abstract

The application provides a multi-element rare earth nickel-based alloy material for thermal neutron shielding and a preparation method thereof. According to mass percentage, the material comprises the following components: Fe: 3.5-4.5%, Cr: 6.5-7.5%, Mo: 16.5-17.5%, Gd: 1.0-3.0%, Er: 0.05-0.2%, and the rest components are Ni and other trace elements. The alloy material has the advantages of excellent strength-plasticity matching, good processing forming, strong corrosion resistance, low cost and the like.

Description

Technical Field

[0001] This invention relates to the field of nickel-based alloy materials technology, specifically to a multi-element rare-earth nickel-based alloy material for thermal neutron shielding and its preparation method. Background Technology

[0002] Nuclear energy, as a clean energy source with low energy consumption, low cost, and high efficiency, is widely used in energy, medical, and military fields, and has become an inevitable choice for countries around the world to cope with energy and environmental pressures. However, because nuclear reactions produce radioactive materials that are extremely harmful to human health and the environment, the use of nuclear energy must be based on absolute safety. In recent years, with the continuous development and application of nuclear energy technology, the safe storage, transportation, and disposal of large quantities of spent reactor fuel have become a focus of attention. Spent fuel generally refers to nuclear fuel in nuclear fuel assemblies that have undergone nuclear reactions in a nuclear reactor through neutron bombardment, reached the design burn-up level, and are no longer used in the reactor. As can be seen from this definition, spent fuel contains a large number of unfissile and newly generated fissile nuclides, unused fissile nuclides, fission products, and transuranium elements, and still has strong radioactivity. In order to protect the ecological environment and human safety, spent fuel must be properly disposed of. Meanwhile, spent fuel from nuclear power plants still has a high calorific value after being unloaded from the reactor, and needs to be cooled in spent fuel pools for more than 5 years before it can be transported off-site for storage, processing, or disposal. In the storage and subsequent transportation of spent fuel, in order to ensure that the spent fuel is in a subcritical safety state and to prevent the release of radioactive materials into the environment, neutron shielding materials need to be used in storage and transportation devices such as racks or baskets.

[0003] According to my country's development plan and medium-to-long-term outlook for nuclear power, my country's installed nuclear power capacity will reach 70 million kilowatts by 2025 and 120 million kilowatts by 2030, accounting for approximately 8% of the country's total electricity generation. At that time, the accumulated spent fuel stockpile in my country's nuclear power plants will reach 23,000 tons. With the rapid development of my country's nuclear industry, the total amount of spent fuel discharged from reactors continues to rise, leading to a continuous increase in demand for high-performance neutron shielding materials for spent fuel storage and transportation.

[0004] When developing neutron shielding materials for spent fuel storage, priority should be given to materials with sufficiently high thermal neutron absorption capacity, high stability under neutron irradiation with minimal irradiation damage, stable physicochemical properties during storage, and good corrosion and seismic resistance. Simultaneously, integrated functional / structural design should be considered, meaning the material should possess high strength and toughness, while also being readily available from raw materials and having a simple processing method for industrial production. Currently, the most widely used materials for spent fuel storage in reactors are boron-based materials, such as boron-containing stainless steel, boron-aluminum alloys, boron carbide-aluminum composites, and boron-containing polyethylene composites. However, due to the low solubility of boron in stainless steel and aluminum, the plasticity and impact toughness of boron steel (boron-aluminum) decrease significantly with the addition of boron, especially in cast high-boron steel, which has poor machinability and weldability. Furthermore, boron generates helium after absorbing thermal neutrons, causing the material to swell and reducing its mechanical properties. As for boron-containing polyethylene materials, their strength is not high, their radiation resistance and corrosion resistance are relatively poor, and they are prone to aging and becoming brittle under strong radiation environments, so they are generally not used as structural materials.

[0005] To address the issues with neutron shielding in boron-based alloys and composites, rare earth elements with large thermal neutron absorption cross-sections (such as gadolinium (Gd)) can be used to replace boron in the alloy matrix, effectively solving the radiation swelling problem of boron-based materials. Nickel-based alloys, on the other hand, possess excellent high-temperature strength, good oxidation resistance, and corrosion resistance, and are widely used in aerospace, nuclear energy, and chemical industries. Therefore, adding trace amounts of rare earth elements to nickel-based alloys has become an effective way to develop new high-strength, high-toughness, and high-neutron-shielding alloys. The Idaho National Laboratory and other institutions have developed a Ni-Cr-Mo-Gd nickel-based superalloy containing Gd, which exhibits good neutron shielding performance. However, due to the extremely low solubility of Gd in the nickel matrix, it easily forms large-sized (30–40 μm) Ni5Gd intermediate compounds and Gd2O3, causing significant anisotropy and reducing the alloy's plasticity (P. McConnell, C. Robino, R. Mizia, J. DuPont, G. Wachs, W. Hurt, A New Ni-Cr-Mo-Based Gadolinium Structural Alloy for Neutron Adsorption Application in Radioactive Material Packages, in: Vol. 7 Opera. Appl. Compon., ASMEDC, Vancouver, BC, Canada, 2006: pp. 453–462.). In summary, there is an urgent need to develop a novel rare-earth nickel-based alloy for thermal neutron shielding, integrating structure and function, for materials used in spent fuel storage tanks in nuclear power plants. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a multi-element rare-earth nickel-based alloy material for thermal neutron shielding and its preparation method.

[0007] According to one aspect of the present invention, a multi-element rare-earth nickel-based alloy material for thermal neutron shielding is provided, wherein the material comprises, by mass percentage:

[0008] Fe: 3.5-4.5%,

[0009] Cr: 6.5-7.5%,

[0010] Mo: 16.5–17.5%,

[0011] Gd: 1.0~3.0%,

[0012] Er: 0.05~0.2%,

[0013] The remaining components are Ni and other trace elements.

[0014] Furthermore, the microstructure of the nickel-based alloy material includes a face-centered cubic matrix γ-(Ni solid solution) phase and a rare earth-rich second phase Ni5(Gd,Er) intermetallic compound.

[0015] Furthermore, the space group of the rare earth-rich second phase Ni5(Gd,Er) intermetallic compound crystal structure in the nickel-based alloy material is P6 / mmm, which is incoherent with the face-centered cubic matrix γ-(Ni solid solution) phase.

[0016] Preferably, the material comprises, by weight percentage:

[0017] Fe: 4.0~4.1%,

[0018] Cr: 6.8–7.2%,

[0019] Mo: 16.7–17.2%,

[0020] Gd: 1.0~1.5%,

[0021] Er: 0.05~0.2%,

[0022] The remaining components are Ni and other trace elements.

[0023] According to another aspect of the present invention, a method for preparing the above-mentioned multi-element rare-earth nickel-based alloy material for thermal neutron shielding is provided, comprising:

[0024] The various metal raw materials are mixed and smelted to obtain alloy ingots;

[0025] The alloy ingot is homogenized and annealed to produce an alloy plate of a predetermined thickness.

[0026] Optionally, the mixing and smelting of the various metal raw materials is carried out using vacuum arc melting or vacuum induction melting processes.

[0027] Optionally, the step of mixing and smelting the various metal raw materials to obtain an alloy ingot includes: obtaining the alloy ingot by direct cooling or suction casting after smelting.

[0028] Optionally, the alloy ingot is subjected to homogenization annealing treatment, wherein the homogenization annealing treatment temperature is 1150-1200℃ and the time is 1-5h.

[0029] Optionally, the alloy plate is made with a preset thickness, wherein the thickness of the alloy plate is 5 to 10 mm.

[0030] Optionally, the process of producing an alloy sheet of a predetermined thickness includes: obtaining an alloy sheet of a predetermined thickness through rolling or forging.

[0031] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0032] 1. This invention uses Ni-Fe-Cr-Mo as the alloy matrix and introduces a second rare earth element (Er) on the basis of adding rare earth Gd to form a multi-element rare earth nickel-based alloy material. Under the premise of satisfying neutron shielding performance, the addition of Er element effectively refines the size of Ni5Gd intermetallic compound, thereby significantly improving the strength and plasticity matching of the alloy.

[0033] 2. This invention successfully prepared a multi-element rare-earth nickel-based alloy material through smelting. The resulting alloy sample had a yield strength ≥380MPa, tensile strength ≥770MPa, and elongation at break ≥29%. Calculations show that the thermal neutron attenuation coefficient of a 5mm thick plate is ≤1.3×10⁻⁶. -4 At the same thickness, this multi-element rare-earth nickel-based alloy exhibits higher neutron shielding efficiency. The multi-element rare-earth nickel-based alloy of this invention possesses advantages such as excellent strength-plasticity matching, good machinability, strong corrosion resistance, and low cost. It can be used as a special alloy material for spent fuel storage and transportation tanks in nuclear power plants, and is particularly suitable for the preparation of small, lightweight spent fuel storage and transportation tanks, providing a new approach for next-generation high-temperature alloy materials for thermal neutron shielding with integrated structure and function. Attached Figure Description

[0034] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0035] Figure 1The scanning electron microscope morphology of the nickel-based alloy material in Example 1 of this invention;

[0036] Figure 2 The scanning electron microscope morphology of the nickel-based alloy material in Example 2 of this invention;

[0037] Figure 3 The image shows the scanning electron microscope (SEM) morphology of the nickel-based alloy material in the comparative examples of this invention.

[0038] Figure 4 The tensile property curves of the nickel-based alloy materials in Examples 1, 2 and the comparative examples of the present invention are shown. Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0040] This invention provides a multi-element rare earth nickel-based alloy material for thermal neutron shielding, comprising, by mass percentage: Fe: 3.5-4.5%, Cr: 6.5-7.5%, Mo: 16.5-17.5%, Gd: 1.0-3.0%, Er: 0.05-0.2%, with the remainder being Ni and other trace elements. Trace elements refer to elements that are difficult to avoid during the high-temperature alloy smelting process, including elements such as C and Si, which exist in small amounts (ppm level).

[0041] In this embodiment of the invention, when the alloy material contains Er, the microstructure of the nickel-based alloy material includes a face-centered cubic matrix γ-(Ni solid solution) phase and a rare-earth-rich second phase Ni5(Gd,Er) intermetallic compound. The space group of the rare-earth-rich second phase Ni5(Gd,Er) intermetallic compound in the microstructure of the nickel-based alloy material is P6 / mmm, which is incoherent with the face-centered cubic matrix γ-(Ni solid solution) phase.

[0042] In some preferred embodiments, the alloy material comprises, by mass percentage: Fe: 4.0–4.1%, Cr: 6.8–7.2%, Mo: 16.7–17.2%, Gd: 1.0–1.5%, Er: 0.05–0.2%, with the remainder being Ni and other trace elements.

[0043] This invention uses Ni-Fe-Cr-Mo as the alloy matrix and introduces a second rare earth element (Er) in addition to the rare earth element Gd to form a multi-element rare earth nickel-based alloy material. While meeting neutron shielding performance requirements, the addition of Er effectively refines the size of the Ni5Gd intermetallic compound, improving alloy strength while maintaining good elongation. This multi-element rare earth nickel-based alloy exhibits excellent strength-ductility matching, good machinability, strong corrosion resistance, and low cost. It can be used as a special alloy material for spent fuel storage and transportation tanks in nuclear power plants, and is particularly suitable for the preparation of small, lightweight spent fuel storage and transportation tanks.

[0044] This invention also provides a method for preparing the above-mentioned multi-element rare-earth nickel-based alloy material for thermal neutron shielding, the method comprising:

[0045] The various metal raw materials are mixed and smelted to obtain alloy ingots;

[0046] After homogenization annealing, the alloy ingot is made into an alloy plate of a predetermined thickness.

[0047] In some embodiments, the various metal raw materials are mixed and smelted, wherein: the metal raw materials are mixed and placed in a mold or crucible, and smelted using vacuum arc melting or vacuum induction melting processes to ensure that the alloy composition is accurate and the structure is uniform.

[0048] In some embodiments, the various metal raw materials are mixed and smelted to obtain an alloy ingot, including: obtaining the alloy ingot by direct cooling or suction casting after arc melting. The smelting-suction casting process can further refine the grain size and Ni5Gd phase size of the nickel-based alloy, thereby significantly improving the strength-ductility balance of the alloy.

[0049] In some embodiments, the alloy ingot is subjected to homogenization annealing treatment, wherein the homogenization annealing treatment temperature is 1150-1200℃, preferably 1180℃, and the time is 1-5h, which can effectively eliminate alloy component segregation and make the microstructure more uniform.

[0050] In some embodiments, an alloy plate of a predetermined thickness is prepared, wherein the thickness of the alloy plate is 5 to 10 mm, to facilitate the fabrication of miniaturized neutron shielding devices such as spent fuel tanks in the later stages.

[0051] In some embodiments, the alloy sheet of a predetermined thickness is prepared by: rolling or forging to obtain the alloy sheet of the predetermined thickness. The deformation treatment such as rolling or forging can introduce a large number of dislocations, and the grains can be refined by annealing and recrystallization, thereby eliminating casting segregation and dendrites, making the microstructure more uniform, and thus optimizing and improving the mechanical properties.

[0052] The technical solutions of this application will be further described below with reference to embodiments and comparative examples.

[0053] Example 1

[0054] In this embodiment, the multi-element rare earth nickel-based alloy material for thermal neutron shielding comprises the following composition by mass percentage: Fe: 4.0%, Cr: 7.0%, Mo: 17.0%, Gd: 1.0%, Er: 0.05%, and the remainder being Ni and other trace elements.

[0055] The preparation method of the multi-element rare-earth nickel-based alloy material for thermal neutron shielding in this embodiment includes the following steps:

[0056] I. A vacuum arc melting process is adopted. The total mass of the raw materials is 80g. The main components are composed of the following mass percentages: Fe: 4.0%, Cr: 7.0%, Mo: 17.0%, Gd: 1.0%, Er: 0.05%, and the remaining components are Ni and other trace elements. The metal raw materials are mixed in a crucible and subjected to arc melting. The arc voltage is about 40V and the current is 200-300A. The melting is repeated 4 times to ensure that the raw materials are fully fused. Then, the mixture is placed in a suction casting station for suction casting. After cooling, a uniform alloy ingot is obtained. The alloy ingot is 90mm long, 15mm wide, and 5mm thick.

[0057] II. After homogenizing and annealing the alloy ingot prepared in step I at 1180℃ for 1 hour, a 5mm thick alloy plate is obtained by cold rolling with a rolling depth of about 50%. No intermediate annealing is required during the cold rolling process.

[0058] The alloy samples prepared in this embodiment were subjected to microstructure analysis and mechanical property testing, and the results are as follows: Figure 1 and Figure 4 As shown in the figure, analysis reveals that the microstructure of this multi-element rare-earth nickel-based alloy mainly consists of a face-centered cubic matrix γ-(Ni solid solution) phase and a rare-earth-rich second phase, Ni5(Gd,Er) intermetallic compound. Transmission electron microscopy results show that the space group of the rare-earth-rich phase crystal structure is P6 / mmm, and it is incoherent with the matrix γ phase. Mechanical property tests show that the room temperature tensile yield strength of the multi-element rare-earth nickel-based alloy sheet prepared in this embodiment is 432 MPa, the tensile strength is 830 MPa, and the elongation at break is 36%. Theoretical calculations indicate that the thermal neutron decay coefficient of the 5 mm thick alloy sheet is 1.22 × 10⁻⁶. -4 .

[0059] Example 2

[0060] The thermal neutron shielding multi-element rare earth nickel-based alloy material in this embodiment comprises the following composition by mass percentage: Fe: 4.1%, Cr: 6.8%, Mo: 17.2%, Gd: 1.0%, Er: 0.2%, and the remainder being Ni and other trace elements.

[0061] The preparation method of the multi-element rare-earth nickel-based alloy material for thermal neutron shielding in this embodiment includes the following steps:

[0062] I. A vacuum arc melting process is adopted. The total mass of the raw materials is 80g. The main components are composed of the following mass percentages: Fe: 4.1%, Cr: 6.8%, Mo: 17.2%, Gd: 1.0%, Er: 0.2%, and the remaining components are Ni and other trace elements. The metal raw materials are mixed in a crucible and subjected to arc melting. The arc voltage is about 40V and the current is 200-300A. The melting is repeated 4 times to ensure that the raw materials are fully fused. After cooling, a uniform alloy ingot with a diameter of ~35mm and a height of about 10mm is obtained.

[0063] II. After homogenizing and annealing the alloy ingot prepared in step I at 1180℃ for 1 hour, a 5mm thick alloy plate is obtained by cold rolling with a rolling depth of about 50%. No intermediate annealing is required during the cold rolling process.

[0064] The alloy samples prepared in this embodiment were subjected to microstructure analysis and mechanical property testing, such as... Figure 2 and Figure 4 As shown in the figure, analysis reveals that the microstructure of this multi-element rare-earth nickel-based alloy mainly consists of a face-centered cubic matrix γ-(Ni solid solution) phase and a rare-earth-rich second phase, Ni5(Gd,Er) intermetallic compound. Transmission electron microscopy results show that the space group of the rare-earth-rich phase crystal structure is P6 / mmm, and it is incoherent with the matrix γ phase. Mechanical property tests show that the room temperature tensile yield strength of the multi-element rare-earth nickel-based alloy sheet prepared in this embodiment is 387 MPa, the tensile strength is 770 MPa, and the elongation at break is 29%. Theoretical calculations indicate that the thermal neutron decay coefficient of the 5 mm thick alloy sheet is 1.20 × 10⁻⁶. -4 .

[0065] Comparative Example

[0066] The comparative example of the rare earth nickel-based alloy material for thermal neutron shielding comprises the following composition by mass percentage: Fe: 4.2%, Cr: 6.9%, Mo: 17.1%, Gd: 1.0%, with the remainder being Ni and other trace elements.

[0067] The preparation method of rare-earth nickel-based alloy material for thermal neutron shielding in the comparative example includes the following steps:

[0068] I. A vacuum arc melting process is adopted. The total mass of the raw materials is 80g. The main components are composed of the following mass percentages: Fe: 4.2%, Cr: 6.9%, Mo: 17.1%, Gd: 1.0%, and the remaining components are Ni and other trace elements. The metal raw materials are mixed in a crucible and subjected to arc melting. The arc voltage is about 40V and the current is 200-300A. The melting is repeated 4 times to ensure that the raw materials are fully fused. After cooling, a uniform alloy ingot with a diameter of ~35mm and a height of about 10mm is obtained.

[0069] II. After homogenizing and annealing the alloy ingot prepared in step I at 1180℃ for 1 hour, a 5mm thick alloy plate is obtained by cold rolling with a rolling depth of about 50%. No intermediate annealing is required during the cold rolling process.

[0070] Microstructure analysis and mechanical property testing were performed on the alloy samples prepared in the comparative example. The results are as follows: Figure 3 and Figure 4 As shown in the figure, analysis reveals that the microstructure of this multi-element rare-earth nickel-based alloy mainly consists of a face-centered cubic matrix γ-(Ni solid solution) phase and a rare-earth-rich second phase, Ni5Gd intermetallic compound. Transmission electron microscopy results show that the space group of the rare-earth-rich phase crystal structure is P6 / mmm, and it is incoherent with the matrix γ phase. Furthermore, comparison shows that the addition of Er element effectively refines the Ni5Gd intermetallic compound, making its distribution more dispersed and uniform, which helps improve the neutron shielding performance of the alloy. Mechanical property experiments show that the room temperature tensile yield strength of the comparative rare-earth nickel-based alloy plate is 361 MPa, the tensile strength is 762 MPa, and the elongation at break is 34%. Theoretical calculations indicate that the thermal neutron attenuation coefficient of the 5 mm thick alloy plate is 1.22 × 10⁻⁶. -4 Therefore, it can be seen that, under the same thermal neutron shielding efficiency, the yield and tensile strength of the rare earth nickel-based alloy with 1% Gd added alone are lower than those of the multi-element rare earth nickel-based alloy (Example 1). Although the sample in the comparative example has a slightly higher elongation, its strength is far lower than that of the sample in Example 1. This proves that the addition of multi-element rare earth elements can improve the strength of the alloy material while still maintaining a certain elongation.

[0071] In summary, this invention uses Ni-Fe-Cr-Mo as the alloy matrix and introduces a second rare earth element (Er) on top of the addition of rare earth Gd to form a multi-element rare earth nickel-based alloy material. While meeting neutron shielding performance requirements, the addition of Er effectively refines the size of the Ni5Gd intermetallic compound, improving alloy strength while maintaining good elongation. Furthermore, the melting-casting process further refines the grain size of the nickel-based alloy and the size of the Ni5Gd phase, significantly improving the strength-ductility balance of the alloy. The multi-element rare earth nickel-based alloy material in this invention exhibits excellent strength-ductility balance, good machinability, strong corrosion resistance, and low cost. It can be used as a special alloy material for spent fuel storage tanks in nuclear power plants, especially suitable for the preparation of small, lightweight spent fuel storage tanks, providing a new approach for next-generation high-temperature alloy materials for thermal neutron shielding with integrated structure and function.

[0072] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A multi-element rare-earth nickel-based alloy material for thermal neutron shielding, characterized in that, By weight percentage, including: Fe: 3.5~4.5%, Cr: 6.5~7.5%， Mo: 16.5~17.5%, Gd: 1.0~3.0%, Er: Greater than 0.05% and less than or equal to 0.2%, The remaining components are Ni and other trace elements; The microstructure of nickel-based alloy materials includes a face-centered cubic matrix γ-(Ni solid solution) phase and a rare earth-rich second phase Ni5(Gd,Er) intermetallic compound. The rare earth-rich second phase Ni5(Gd, Er) intermetallic compound crystal structure in the nickel-based alloy material has a space group of P6 / mmm, which is incoherent with the face-centered cubic matrix γ-(Ni solid solution) phase. The alloy specimens formed from the material exhibit a yield strength ≥380 MPa, a tensile strength ≥770 MPa, an elongation at break ≥29%, and a thermal neutron attenuation coefficient ≤1.3×10⁻⁶ for a 5 mm thick plate. -4 .

2. The multi-element rare-earth nickel-based alloy material for thermal neutron shielding according to claim 1, characterized in that, By weight percentage, including: Fe: 4.0~4.1%, Cr: 6.8~7.2%， Mo: 16.7~17.2%, Gd: 1.0~1.5%, Er: Greater than 0.05% and less than or equal to 0.2%, The remaining components are Ni and other trace elements.

3. A method for preparing a multi-element rare-earth nickel-based alloy material for thermal neutron shielding as described in claim 1 or 2, characterized in that, include: The various metal raw materials are mixed and smelted to obtain alloy ingots; The alloy ingot is homogenized and annealed to produce an alloy plate of a predetermined thickness.

4. The preparation method of the multi-element rare-earth nickel-based alloy material for thermal neutron shielding according to claim 3, characterized in that, The process involves mixing and smelting various metal raw materials, wherein the smelting is carried out using vacuum arc melting or vacuum induction melting processes.

5. The method for preparing a multi-element rare-earth nickel-based alloy material for thermal neutron shielding according to claim 3, characterized in that, The process of mixing and smelting various metal raw materials to obtain alloy ingots includes: obtaining alloy ingots by direct cooling or suction casting after smelting.

6. The method for preparing the multi-element rare-earth nickel-based alloy material for thermal neutron shielding according to claim 3, characterized in that, The alloy ingot is subjected to homogenization annealing treatment, wherein the homogenization annealing treatment temperature is 1150~1200℃ and the time is 1~5h.

7. The method for preparing a multi-element rare-earth nickel-based alloy material for thermal neutron shielding according to claim 3, characterized in that, The alloy plate is made with a preset thickness, wherein the thickness of the alloy plate is 5~10mm.

8. The method for preparing a multi-element rare-earth nickel-based alloy material for thermal neutron shielding according to claim 3, characterized in that, The process of producing an alloy sheet of a predetermined thickness includes: obtaining an alloy sheet of a predetermined thickness through rolling or forging.

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