Rare earth aluminates dense ceramic gray control rod neutron capture material and method of making

Abstract

This invention relates to a rare-earth aluminate dense ceramic gray control rod neutron trapping material and its preparation method. The chemical composition of the rare-earth aluminate dense ceramic gray control rod neutron trapping material is Ln. a x Ln b 1‑x AlO3 or Ln a 3y Ln b 3‑3y Al5O 12 Among them, Ln a For Tm 3+ 、Tb 3+ Dy 3+ Gd 3+ 、Sm 3+ Eu 3+ At least one of them, Ln b For Pr 3+ La 3+ At least one of the following, 0 < x < 0.5, 0 < y ≤ 0.5; preferably, the rare earth aluminate dense ceramic gray control rod neutron trapping material exists in the form of a ceramic block.

Description

Technical Field

[0001] This invention relates to a rare-earth aluminate dense ceramic gray control rod neutron trapping material and its preparation method, belonging to the field of nuclear energy and nuclear technology. Background Technology

[0002] Nuclear power plants typically control reactor power by raising and lowering control rod assemblies. Control rods used in nuclear power plants are generally divided into two categories: black control rods and gray control rods. Gray control rods have weaker neutron trapping capabilities, and therefore their reactivity value is lower than that of black control rods. However, during reactor operation, if mechanical compensation (MSHIM) operating mode is used for reactivity control, the neutron trapping capability of the gray control rods must remain stable over a long period.

[0003] Neutron traps loaded in the control rod bundle cladding of nuclear reactors are mainly classified into two categories based on their material form: metal-based and ceramic-based (or powdered). Ceramic-based neutron trapping materials include boron-based neutron trapping materials, such as natural boron and boron-based materials. 10 Enriched boron carbide (B4C), boric acid, and lanthanide-based neutron trapping materials are used. While rare earth metals and mono-rare earth oxides theoretically meet the requirements for neutron trapping value in gray control rods, they cannot meet the engineering requirements for neutron trapping material dimensions, stability, etc., and suffer from severe self-shielding effects. For example, pure metal Tm rods (density 9.32 g / cm³) are problematic. 3 When used as the core of the ash control rod, the calculated core diameter is only 3mm, which is significantly smaller than the cladding tube with an inner diameter of 9mm. Furthermore, the rare earth metal has poor stability and is easily damaged by oxygen or hydrogen (water vapor) corrosion.

[0004] Perovskite and garnet-structured rare-earth aluminate ceramics exhibit significantly superior chemical properties, high-temperature stability, and oxidation resistance (CN102534789.A). Currently, perovskite and garnet-phase rare-earth aluminate ceramics and crystals are mainly used in optical thin films (CN202110408169.0), with no reported research in the field of gray control rod neutron trapping materials. On the other hand, different rare-earth elements can be doped by substituting elements from the same group, allowing for the design of materials with different neutron trapping values ​​and properties, providing new directions and selection options for control rod design. These rare-earth aluminate ceramic neutron trapping materials generally have melting points exceeding 2000℃. Even under severe accident conditions such as 1200℃ or contact with moderators like water, they maintain their crystal form and structure without damage and retain basic functions, which is of great significance for nuclear reactor safety. Summary of the Invention

[0005] Therefore, the present invention provides a rare earth aluminate ceramic gray control rod neutron trapping material and its preparation method.

[0006] On one hand, the present invention provides a rare-earth aluminate ceramic gray control rod neutron trapping material, wherein the chemical composition of the rare-earth aluminate dense ceramic gray control rod neutron trapping material is Ln a x Ln b 1-x AlO3 or / and Ln a 3y Ln b 3-3y Al5O 12 ; where Ln a For Tm 3+ 、Tb 3+ Dy 3+ Gd 3+ 、Sm 3+ Eu 3+ At least one of them, Ln b For Pr 3+ La 3+ At least one of the following, 0 < x < 0.5, 0 < y ≤ 0.5; preferably, the rare earth aluminate dense ceramic gray control rod neutron trapping material exists in the form of a ceramic block.

[0007] In this disclosure, the inventors selected Pr and La, whose thermal neutron trapping cross-sections are 11.4 and 8.98 Å, respectively, which are the smallest among the 17 lanthanide rare earth elements except for Y and Ce. From a nuclear physics perspective, they are suitable dilution elements. Al and O have very small neutron trapping cross-sections, but in this invention, they provide stable crystal structures through the formation of aluminum-oxygen tetrahedra and octahedra. Compared to neutron trapping materials in powder form, the rare earth aluminate ceramics of this invention have higher structural and spatial stability, as well as excellent thermal and mechanical properties. This invention introduces Tm (10⁵ Å), Tb (23 Å), Dy (950 Å), and Gd (4.9 × 10⁻⁶ Å) with different neutron trapping cross-sections into rare earth aluminate ceramics of perovskite or garnet phases. 4 One or more of rare earth elements, such as Sm (5900 BE), Eu (4570 BE), etc., are used to form neutron trapping materials with different trapping properties and stable structures by utilizing the trapping cross-section and trapping spectral characteristics of these rare earth element combinations. These materials are then applied to the manufacture of neutron trapping materials for reactor gray control rods.

[0008] Specifically, the rare earth aluminate ceramics (Ln) disclosed herein a x Ln b 1-x AlO3 or Ln a 3y Ln b 3-3y Al5O 12) contains Ln b Rare earth elements praseodymium (Pr) and lanthanum (La) are used as diluent elements or the first component, while rare earth element Ln... a Thulium (Tm), terbium (Tb), dysprosium (Dy), gadolinium (Gd), samarium (Sm), europium (Eu) are used as capturing elements or secondary components. Rare earth aluminates are in the perovskite phase (LnAlO3) or garnet phase (Ln3Al5O3). 12 The relative density of rare earth aluminate ceramics ranges from 96% to 100%. The first component and aluminate structure can modulate the neutron-trapping properties introduced by the second component element, resulting in a chemically and structurally stable perovskite crystal structure (ABO3) or garnet structure (A3B5O). 12 With chemical properties similar to lanthanide rare earth ions, combined with the mechanical and thermophysical properties of dense advanced ceramics, these rare earth elements provide a carrier and foundation for the second component elements. Due to their different neutron capture cross-sections and characteristics, these rare earth elements can be used to design material compositions with varying reactivity values ​​according to the requirements of reactor nuclear physics. On the other hand, a class of structurally stable rare earth-based ceramic neutron trappers has been prepared using a two-step method and by adding sintering aids and binders.

[0009] Ideally, 0 < x < 0.5 or 0 < y ≤ 0.5.

[0010] Preferably, the neutron-capturing material of the rare-earth aluminate dense ceramic gray control rod has a perovskite phase and / or garnet phase.

[0011] Preferably, the neutron-capturing material of the rare-earth aluminate dense ceramic gray control rod is cylindrical or annular in shape; The relative density of the neutron-capturing material in the rare-earth aluminate dense ceramic gray control rod is 96-100%. The weight gain rate of the neutron-trapping material in the rare-earth aluminate dense ceramic gray control rod does not exceed 3.26 × 10⁻⁶. - 3 mg / (cm 2 ·h).

[0012] On the other hand, the present invention provides a method for preparing a rare-earth aluminate dense ceramic gray control rod neutron trapping material, comprising: (1) The chemical composition of the rare earth aluminate dense ceramic gray control rod neutron trapping material is Ln a x Ln b 1- x AlO3 or / Ln a 3y Ln b 3-3y Al5O 12 Weigh out Ln respectively aoxide powder, Ln b The oxide powder and alumina powder are mixed and then calcined and refined to obtain the raw material powder; the raw material powder contains Ln a x Ln b 1-x AlO3 powder and / or Ln a 3y Ln b 3-3y Al5O 12 Powder; (2) Mix the raw material powder, sintering aid and binder to obtain a mixed powder; (3) The mixed powder is pressed, debonded and sintered to obtain rare earth aluminate dense ceramic gray control rod neutron capture material.

[0013] Preferably, in step (1), the calcination temperature is 1000-1300℃ and the time is 2-4 hours; the particle size of the raw material powder is 100nm-3μm.

[0014] Preferably, in step (2), the sintering aid is at least one of silicon oxide powder, magnesium oxide powder, silicon oxide precursor, and magnesium oxide precursor; the amount of sintering aid added is 0.05 to 2 wt% of the raw material powder mass; Preferably, the silicon oxide precursor is selected from at least one of silicic acid, tetraethyl orthosilicate, and methyl orthosilicate; Preferably, the magnesium oxide precursor is selected from at least one of magnesium hydroxide, magnesium oxide, and magnesium carbonate.

[0015] Furthermore, preferably, when the sintering aid contains at least one of silicon oxide and silicon oxide precursor, the amount added is 0.2% to 1% of the mass of the raw material powder; When the sintering aid contains magnesium oxide and magnesium oxide precursor, the amount added is 0.05 to 1% of the mass of the raw material powder.

[0016] Preferably, in step (2), the binder is at least one of phenolic resin, PVB, and PVA; the amount of binder added is 1 to 5 wt% of the total mass of the raw material powder and sintering aid.

[0017] Preferably, in step (3), the pressing method is to first dry press and then isostatic press or directly press; the pressure of dry pressing is 10-100 MPa, the pressure of isostatic pressing is 150-200 MPa, and the pressure of direct isostatic pressing is 100-150 MPa.

[0018] Preferably, in step (3), the debonding temperature is 600-800°C and the time is 1-3 hours.

[0019] Preferably, in step (3), the sintering temperature is 1450–1600°C, the time is 3–6 hours, and the atmosphere is vacuum or reducing atmosphere sintering; preferably, the reducing atmosphere is a mixture of hydrogen and inert atmosphere, more preferably, the hydrogen content is 2–5 vol%.

[0020] The beneficial effects of this invention are: (1) Using Pr and La, which have smaller neutron trapping cross sections, as dilution elements or the first component, and rare earth elements such as thulium (Tm), terbium (Tb), dysprosium (Dy), gadolinium (Gd), samarium (Sm), and europium (Eu), which have larger neutron trapping cross sections, as trapping elements or the second component, the shortcomings of metal-based or alloy-based gray control rod trapping bodies in terms of stability and engineering design are overcome, and it has engineering practicality; (2) The aluminate crystal structure of perovskite phase or garnet structure has advantages in chemical and structural stability as well as component control over rare earth metal elements, alloys or rare earth oxides, and is novel. (3) The first and second components of rare earth aluminates with perovskite or garnet structures are combined in different proportions, and the low neutron capture cross section of aluminates is utilized to meet the needs of gray control rod neutron capture materials for reactivity value and properties, which is creative. (4) The dense ceramic bulk material prepared by the two-step method (instead of single crystal, non-transparent optical ceramic, and non-powder) can be processed into cylinders, rings and other gray control rod shell tubes that can be installed. The processing requirements are the same as those of ordinary ceramics, which is creative and practical. (5) Using rare earth oxides that are industrially prepared in large quantities and stored and transported stably as raw materials, it is possible to obtain materials that are more suitable for loading into metal shells and operating under harsh conditions such as high temperature, which meets the safety requirements of neutron capture materials and has practicality and creativity. (6) The pre-synthesis step can also avoid the problem of ceramic cracking caused by excessive shrinkage due to direct one-step synthesis, which is easy to prepare in batches, improves the yield, and the process is feasible and practical. (7) The obtained rare earth aluminate ceramic neutron trapping material has high density, water corrosion resistance, good mechanical properties and thermal properties (service life ≥ 20 years); (8) Utilizing the nuclear physics properties of the two components and the stability of the aluminate crystal framework (containing aluminum-oxygen tetrahedrons, octahedrons, and Al and O with very small neutron capture cross sections that can be ignored and can also play a dilution role), the rare earth components such as Tm, which have higher neutron capture value, play the main role in neutron capture. Attached Figure Description

[0021] Figure 1Flowchart of the two-step preparation process for rare earth aluminate ceramic neutron trapping materials; Figure 2 The Pr6O used in Example 1 11 Scanning electron microscope images of powder raw materials; Figure 3 This is a scanning electron microscope image of the Tm2O3 powder used in Example 1; Figure 4 Tm synthesized in Example 1 0.05 Pr 0.95 Scanning electron microscope image of AlO3 powder; Figure 5 For example, Tm in Example 1 0.05 Pr 0.95 XRD pattern of AlO3 ceramics; Figure 6 Photograph of PrAlO3 ceramic in Comparative Example 1; Figure 7 For example, Tm in Example 2 0.1 Pr 0.9 Photographs of rare earth aluminate neutron-trapping materials of AlO3; Figure 8 For example, Tm in Example 4 0.05 Pr 0.95 Water corrosion resistance of AlO3 ceramic neutron trapping materials; Figure 9 For example, Tm in Example 6 0.2 Pr 0.8 Neutron trapping properties of AlO3 ceramic neutron trapping materials; Figure 10 Tb in Example 7 0.1 Dy 0.1 Pr 0.8 Neutron trapping properties of AlO3 ceramic neutron trapping materials; Figure 11 Tb in Example 8 0.1 Dy 0.2 La 0.7 Photographs of AlO3 ceramic neutron trapping materials; Figure 12 The neutron trapping performance of the ceramic neutron trapping material in Example 9 is shown. Detailed Implementation

[0022] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0023] In this field, no design or fabrication of neutron-absorbing materials has been considered from the perspective of water corrosion resistance. In this disclosure, rare-earth aluminate dense ceramics (Ln...)a x Ln b 1-x AlO3 or Ln a 3y Ln b 3-3y Al5O 12 In the rare earth element Ln, (0 < x ≤ 0.5, 0 < y ≤ 0.5) b (Pr, La) as diluents or the first rare earth component, with rare earth Ln a (Tm, Tb, Dy, Gd, Sm, Eu) are used as the captured component or the second rare earth component. Among them, the captured component (Tm) 3+ 、Tb 3+ Dy 3+ Gd 3+ 、Sm 3+ Eu 3+ Lanthanide rare earth ions and diluted components (Pr) 3+ La 3+ It occupies the A site in the crystal lattice, while the B site is entirely Al. 3+ The neutron capture value of the gray control rod is adjusted by changing the ratio of the elements in the first and second components and by modifying the aluminate composition. A dense perovskite phase or garnet ceramic body with high structural and chemical stability and tunable Ln-site composition is used as the core of the control rod. Preferably, the crystal configuration of the aluminate is a perovskite phase (LnAlO3) or a garnet phase (Ln3Al5O3). 12 Crystal phase, first component Ln b and aluminates (-AlO3 or -Al5O) 12 ) Component adjustment of the second component Ln a The neutron-trapping value introduced by the elements. Pr and La each have unique characteristics in nuclear physics; in this invention, they are utilized as framework elements due to their relatively small neutron absorption cross-sections. When Ln... b =Pr, the weight gain rate of the neutron trapping material in the rare earth aluminate dense ceramic gray control rod does not exceed 3.05 × 10 -3 mg / (cm 2 ·h). When Ln b =La, the weight gain rate of the neutron trapping material in the rare earth aluminate dense ceramic gray control rod does not exceed 3.26 × 10 -3 mg / (cm 2 ·h).

[0024] Moreover, the chemically and crystal-structure-stable perovskite crystal structure (ABO3) or garnet structure (A3B5O) 12The invention leverages the similar chemical properties of rare earth ions (such as lanthanides) and dense, advanced ceramics with excellent mechanical, corrosion-resistant, and thermal properties to provide a carrier and foundation for the second component element, while also diluting its neutron capture value. Through material design and reactor nuclear physics calculations, this invention provides a feasible scheme for obtaining the neutron capture value of gray control rods. In this invention, rare earth aluminate ceramics possess a stable crystal structure and tunable neutron absorption performance. Innovations in material preparation schemes and technologies improve material performance and reliability, while also demonstrating high practicality.

[0025] In one embodiment of the present invention, a two-step method is used to prepare rare earth aluminate ceramics with high density and excellent mechanical properties, namely, pre-synthesizing powders with specific crystal forms and sintering ceramics, and adding sintering aids to prepare neutron trapping materials for gray control rods.

[0026] In this invention, lanthanide elements such as Tm are introduced into a specific aluminate crystal structure through pre-synthesis of powder and lattice element substitution to act as neutron trappers, thereby controlling the neutron trapping value and characteristics. This can be used in reactor ash control rods. This type of material comprehensively utilizes the stability of the chemical and perovskite crystal framework structure, the fault tolerance of ceramics, and the neutron trapping characteristics of rare earth elements. The main process steps for preparing rare earth aluminate dense ceramic neutron trapping materials are described below. Figure 1 .

[0027] Weigh alumina (Al2O3) powder and first rare earth oxides (Pr2O3, Pr6O3) ​​according to the composition of rare earth aluminate dense ceramic neutron capturing materials. 11 La2O3) powder, second rare earth oxide (Ln) x O y Powders of Tm2O3, Tb4O7, Dy2O3, Gd2O3, Sm2O3, and Eu2O3 were mixed and then calcined at 1000–1300℃ (pre-synthesis) for 2–4 hours, followed by refining treatment (ball milling) to synthesize the perovskite phase Ln. a x Ln b 1-x AlO3 powder or garnet phase Ln a 3y Ln b 3-3y Al5O 12 Powders are used as raw material powders. The main functions of pre-synthesis are: 1) to prevent excessive shrinkage, avoid cracking and microstructural defects; 2) to synthesize the required phases and reduce the formation of impurity phases.

[0028] The refined raw material powder, sintering aid, and binder are mixed and pressed into a green body. After debinding, it is sintered at high temperature to obtain the rare earth aluminate ceramic neutron-capturing material. In an optional embodiment, the sintering aid includes silicon oxide and magnesium oxide, added in an amount of 0.2–1 wt%. The sum of the contents of all components, except for unavoidable trace impurities, is 100 wt%.

[0029] In this invention, rare-earth aluminate dense ceramic neutron-trapping material can be used as a core loaded into a nuclear reactor control rod bundle. The main component of the ceramic material is rare-earth aluminate, which plays a neutron-trapping role. Furthermore, the composition and proportion of the rare-earth aluminate dense ceramic neutron-trapping material can be used in reactor ash control rods, and it can be processed into cylindrical, ring-shaped, or other bulk forms. It possesses excellent resistance to subcritical water corrosion and neutron irradiation, allowing for the control of reactor reactivity based on neutron capture value and burnup control requirements. The dense ceramic form endows the material with excellent mechanical properties, thermophysical properties, and accident tolerance (water corrosion resistance).

[0030] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0031] Example 1: Tm 0.05 Pr 0.95 AlO3 ceramic gray control rod neutron trapping material (preparation feasibility, process) Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.05 Pr 0.95 AlO3 was used to calculate the proportions of the three powders. Pr6O before ball milling. 11 The size of Tm2O3 powder is approximately 3–6 micrometers. Figure 2 ) and 2-5 micrometers ( Figure 3 The powders were mixed and calcined at 1100°C for 2 hours in a 4% argon-hydrogen mixed atmosphere. Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling to refine the powders. SEM images of the refined powders are shown below. Figure 4The particle distribution is relatively uniform. Then, 1% PVA aqueous solution is added as a binder, and 0.4% tetraethyl orthosilicate as a sintering aid. The refined powder is dried at 80–100℃, passed through a 100-mesh sieve, then dry-pressed, and finally isostatically pressed into blocks at 200 MPa. The blocks are then debonded at 600℃ and then... -2 The ceramic material was obtained by sintering at 1500℃ for 3 hours under vacuum at Pa. The standard peak positions of the perovskite phase praseodymium aluminate (PrAlO3) and the XRD pattern of 5% TmAlO3 are shown below. Figure 5 It can be seen that the crystal form remains perovskite after doping. The relative density of the ceramic, measured by the water displacement method, is 98.5%.

[0032] Comparative Example 1: Preparation of Tm without pre-calcination synthesis process 0.05 Pr 0.95 AlO3 ceramics Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.05 Pr 0.95 The proportions of the three powders were calculated using AlO3. After mixing, the powders were ball-milled for refinement, and then a 1% PVA aqueous solution was added as a binder. The refined powder was dried at 80–100°C, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks were then debonded at 600°C and then... -2 Ceramic material was obtained by sintering at 1500℃ for 3 hours under vacuum. The relative density, measured by the water displacement method, was 88%. See the sintered sample below. Figure 6 It is evident that the sintered discs exhibit significant cracking.

[0033] Example 2: Tm 0.2 Pr 0.8 AlO3 ceramic neutron trapping material (preparation feasibility, dense structure) Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.2 Pr 0.8 The proportions of the three powders were calculated using AlO3. After mixing, the powders were calcined at 1200°C for 2 hours in an argon-hydrogen mixture atmosphere (4% by volume). Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling. Next, 1% PVA aqueous solution was added as a binder, and 0.2% tetraethyl orthosilicate was added as a sintering aid. The refined powder was dried at 80–100°C, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks underwent a debinding treatment at 600°C and were then... -2 Ceramic material was obtained by sintering at 1500℃ for 3 hours under vacuum at Pa. The relative density, measured by the water displacement method, was 97%. The disc ceramic sample was light green, a characteristic color of trivalent praseodymium ions, see [reference needed]. Figure 7 .

[0034] Example 3: Tm 0.5 Pr 0.5 AlO3 ceramic neutron trapping materials (preparation feasibility, large-scale) Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.5 Pr 0.5 The proportions of the three powders were calculated using AlO3. After mixing, the powders were calcined at 1200°C for 2 hours in an argon-hydrogen mixture atmosphere (4% by volume). Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling. Next, 1% PVA aqueous solution was added as a binder, and 0.4% tetraethyl orthosilicate was added as a sintering aid. The refined powder was dried at 80–100°C, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks underwent a debinding treatment at 600°C and were then... -2 The ceramic material was obtained by sintering at 1520℃ for 3 hours under vacuum. The relative density measured by the water displacement method was 98.5%. The mechanical properties are shown in Table 1, with high compressive strength and increased strength compared to pure PrAlO3.

[0035] Compared to powder materials, the stability of ceramics in Comparative Example 2 is significantly improved. Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.5 Pr 0.5 The AlO3 formula calculates the proportions of the three powders. When used as a simple powder after mixing, the bulk density of the powder changes upon heating or vibration, which alters the axial trapping value of the ash control bar and leads to uneven temperature field distribution. Furthermore, the rare earth oxide Pr6O... 11 Direct use will result in a phase transition and deoxygenation reaction at temperatures above 600℃, transforming it into Pr₂O₃, and after capturing oxygen, it reverts to Pr₆O. 11 It has poor chemical stability.

[0036] Example 4: Tm 0.3 Pr 0.7 AlO3 ceramic neutron trapping materials Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.3 Pr 0.7The proportions of the three powders were calculated using AlO3. After mixing, the powders were calcined at 1200°C for 2 hours in an argon-hydrogen mixture atmosphere (4% by volume). Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling. Next, 0.5% PVB ethanol solution was added as a binder, and 0.4% tetraethyl orthosilicate as a sintering aid. The refined powder was dried at 80–100°C, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks underwent a debinding treatment at 600°C and then... -2 The ceramic material was obtained by sintering at 1520℃ for 3 hours under vacuum. The relative density, measured by the water displacement method, was 99%. After corrosion with deionized water at 360℃ for 100 hours, the weight gain rate was 2.78 × 10⁻⁶. -3 mg / (cm 2 (·h), lower than Ag-In-Cd metal-based neutron trappers, samples before and after corrosion are shown. Figure 8 No obvious changes or damage were observed on the sample surface, indicating that the crystal structure and ceramic form of the material give it excellent water corrosion resistance.

[0037] Example 5: In Example 5, Tm 0.1 Pr 0.9 The preparation process of AlO3 ceramic neutron trapping material is as described in Example 1.

[0038] Example 6: Tm 0.2 Pr 0.8 AlO3 ceramic gray control rod neutron trapping material Pr6O 11 Using Tm2O3 and Al2O3 powders as raw materials, according to Tm 0.2 Pr 0.8 The proportions of the three powders were calculated using AlO3. After mixing, the powders were calcined at 1200°C for 2 hours in an argon-hydrogen mixture atmosphere (4% by volume). Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling. Next, 0.5% PVB ethanol solution was added as a binder, and 0.6% tetraethyl orthosilicate as a sintering aid. The refined powder was dried at 80–100°C, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks underwent a debinding treatment at 600°C and were then... -3 The ceramic material was obtained by sintering at 1480℃ for 3 hours under vacuum (Pa). The relative density, measured by the water displacement method, was 99%. (Tm) 0.2 Pr 0.8 The neutron capture performance curves of AlO3 materials are shown in the figure. Figure 9 It can be seen that the capture value changes very little when the burnup reaches 150 GW / tU, which can meet the operating cycle of 20.47 equivalent full power years. This indicates that the material has a service life of up to 20 years and is a low-loss, long-period neutron capture material.

[0039] Example 7: Tb 0.1 Dy 0.1 Pr 0.8 AlO3 ceramic neutron trapping materials Pr6O 11 Using Tb4O7, Dy2O3, and Al2O3 powders as raw materials, according to Tb 0.1 Dy 0.1 Pr 0.8 The proportions of the three powders were calculated using AlO3. After mixing, the powders were calcined at 1200℃ for 2 hours in an argon-hydrogen mixture atmosphere (4% by volume). Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling. Next, 0.5% PVB ethanol solution was added as a binder, and 0.4% tetraethyl orthosilicate was added as a sintering aid. The refined powder was dried at 80–100℃, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks underwent a debinding treatment at 600℃ and were then... -2 The ceramic material was obtained by sintering at 1520℃ for 3 hours under vacuum (Pa), and the relative density, measured by the water displacement method, was 98.2%. A photograph of the cylindrical ceramic sample can be found below. Figure 10 .

[0040] Example 8: Tb 0.1 Dy 0.2 La 0.7 AlO3 ceramic neutron trapping materials Using Tb4O7, Dy2O3, La2O3, and Al2O3 powders as raw materials, according to Tb 0.1 Dy 0.2 La 0.7 The proportions of the three powders were calculated using AlO3. After mixing, the powders were calcined at 1200°C for 2 hours in an argon-hydrogen mixture atmosphere (4% by volume). Then, alumina grinding balls were added, and ethanol was used as a dispersant for ball milling. Next, 0.5% PVB ethanol solution was added as a binder, and 0.4% tetraethyl orthosilicate as a sintering aid. The refined powder was dried at 80–100°C, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks underwent a debinding treatment at 600°C and then... -2 The ceramic material was obtained by sintering at 1520℃ for 3 hours under vacuum (Pa), and the relative density measured by the water displacement method was 98%. A photograph of the light yellow cylindrical sample can be found here. Figure 11 .

[0041] Example 9: Gd 0.1 Sm 0.2 Eu 0.2 La 2.5 Al5O 12 Ceramic neutron trapping materials Using Gd₂O₃, Sm₂O₃, Eu₂O₃, La₂O₃, and Al₂O₃ powders as raw materials, according to Gd 0.1 Sm 0.2 Eu 0.2 La 2.5 Al5O 12 Calculate the proportions of the three powders. After mixing, the powders are calcined at 1200℃ for 2 hours, then alumina grinding balls are added, and ethanol is used as a dispersant for ball milling. Then, 0.5% PVB ethanol solution is added as a binder, and 0.8% tetraethyl orthosilicate is added as a sintering aid. The refined powder is dried at 80–100℃, passed through a 100-mesh sieve, dry-pressed, and then isostatically pressed into blocks at 200 MPa. The blocks are then debonded at 600℃ and then... -2 The ceramic material was obtained by sintering at 1600℃ for 4 hours under vacuum. The relative density, measured by the water displacement method, was 98.6%, the flexural strength reached 402 MPa, and the fracture toughness reached 1.2 MPa·m. 1 / 2 The microstructure of the dense sample is shown in Figure 12 Scanning electron microscope image.

[0042] Example 10: In this embodiment 10, Tm 0.3 La 0.7 The preparation process of AlO3 ceramic neutron trapping material is as described in Example 1.

[0043] Example 11: In this embodiment 11, Tm 0.2 La 0.8 The preparation process of AlO3 ceramic neutron trapping material is as described in Example 1.

[0044] Comparative Example 3: Tm prepared in Example 4 was selected. 0.5 Pr 0.5 AlO3 raw material powder was used as comparative example 3.

[0045] Comparative Example 4: The preparation process of the PrAlO3 ceramic neutron trapping material in Comparative Example 4 is the same as that in Example 1.

[0046] Comparative Example 5: In this comparative example 5, Tm 0.6 Pr 0.4 The preparation process of AlO3 ceramic neutron trapping material is as described in Example 1.

[0047] Table 1 shows the Tm values ​​in Example 3. 0.3 Pr 0.7 Mechanical properties of AlO3 ceramic neutron-trapping materials:

Claims

1. A method for preparing a rare-earth aluminate dense ceramic gray control rod neutron trapping material, characterized in that, The chemical composition of the rare-earth aluminate dense ceramic gray control rod neutron capture material is Ln a x Ln b 1-x AlO3 or Ln a 3y Ln b 3-3y Al5O 12 ; where Ln a For Tm 3+ 、Tb 3+ Dy 3+ Gd 3+ 、Sm 3+ Eu 3+ At least one of them, Ln b For Pr 3+ La 3+ At least one of the following, 0 < x < 0.5, 0 < y ≤ 0.5; the rare earth aluminate dense ceramic gray control rod neutron trapping material exists in the form of a ceramic block; the crystal phase of the rare earth aluminate dense ceramic gray control rod neutron trapping material is a perovskite phase or a garnet phase; The preparation of the rare-earth aluminate dense ceramic gray control rod neutron trapping material includes: (1) The chemical composition of the neutron trapping material of the rare earth aluminate dense ceramic gray control rod is Ln a x Ln b 1-x AlO3 or Ln a 3y Ln b 3-3y Al5O 12 Weigh out Ln respectively a oxide powder, Ln b The oxide powder and alumina powder are mixed and then calcined and refined to obtain the raw material powder; the raw material powder contains Ln a x Ln b 1-x AlO3 powder or Ln a 3y Ln b 3- 3y Al5O 12 Powder; (2) Mix the raw material powder, sintering aid and binder to obtain a mixed powder; (3) The mixed powder is pressed, debonded and sintered to obtain rare earth aluminate dense ceramic control rod neutron capture material; the debonding temperature is 600-800℃ and the time is 1-3 hours; the sintering temperature is 1450-1600℃ and the time is 3-6 hours, and the atmosphere is vacuum or reducing atmosphere sintering.

2. The preparation method according to claim 1, characterized in that, In step (1), the calcination temperature is 1000-1300℃ and the time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that, The reducing atmosphere is a mixture of hydrogen and an inert atmosphere, with a hydrogen content of 2-5 vol.

4. The preparation method according to claim 1, characterized in that, In step (1), the particle size of the raw material powder is 100 nm to 3 μm.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the sintering aid is at least one of silicon oxide powder, magnesium oxide powder, silicon oxide precursor, and magnesium oxide precursor; the amount of sintering aid added is 0.05 to 2 wt% of the raw material powder.

6. The preparation method according to claim 5, characterized in that, The silicon oxide precursor includes at least one of silicic acid, tetraethyl orthosilicate, and methyl orthosilicate.

7. The preparation method according to claim 5, characterized in that, The magnesium oxide precursor includes at least one of magnesium hydroxide and magnesium carbonate.

8. The preparation method according to claim 5, characterized in that, When the sintering aid contains at least one of silicon oxide and silicon oxide precursor, the amount added is 0.2% to 1% of the mass of the raw material powder; When the sintering aid contains at least one of magnesium oxide and magnesium oxide precursor, the amount added is 0.05 to 1% of the mass of the raw material powder.

9. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the binder is at least one of phenolic resin, PVB, and PVA; the amount of binder added is 1 to 5 wt% of the total mass of the raw material powder and sintering aid.

10. The preparation method according to any one of claims 1-4, characterized in that, In step (3), the pressing method is to first dry press and then isostatic press or directly press; the pressure of dry pressing is 10-100 MPa, the pressure of isostatic pressing is 150-200 MPa, and the pressure of direct isostatic pressing is 100-150 MPa.

11. A rare-earth aluminate dense ceramic gray control rod neutron trapping material prepared by the preparation method according to any one of claims 1-10, characterized in that, The relative density of the neutron-capturing material in the rare-earth aluminate dense ceramic gray control rod is 96-100%.

12. The rare-earth aluminate dense ceramic gray control rod neutron trapping material according to claim 11, characterized in that, The weight gain rate of the neutron-trapping material in the rare-earth aluminate dense ceramic gray control rod does not exceed 3.26 × 10⁻⁶. -3 mg / (cm 2 ·h).

13. The rare-earth aluminate dense ceramic gray control rod neutron trapping material according to claim 11 or 12, characterized in that, The neutron-capturing material in the rare-earth aluminate dense ceramic gray control rod is cylindrical or annular.

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