Porous electrically insulating ceramic barrier for magnetic confinement fusion reactor and method of manufacturing and use thereof

Abstract

The application belongs to the field of magnetic confinement fusion reactors, and specifically discloses a porous electrically insulating ceramic barrier for a magnetic confinement fusion reactor, a preparation method and application thereof. Along the flow direction of liquid metal, the ceramic barrier comprises a first porous layer with first connected pores, a second porous layer with second connected pores and a third porous layer with third connected pores, and the average pore diameters of the first connected pores, the second connected pores and the third connected pores decrease in gradient; further comprising a tritium-blocking coating arranged on the side of the first porous layer away from the second porous layer; and an edge densification region arranged in the edge region of the ceramic barrier, and the surface of the edge densification region is sequentially provided with a metallization layer and an electroplating layer. The ceramic barrier can greatly reduce the MHD effect under a strong magnetic field, eliminate the problem of electrochemical corrosion, and simultaneously realize reliable sealing under a high pressure of 0-15 MPa and a stable breakthrough pressure of above 0.5 MPa.

Description

Technical Field

[0001] This application belongs to the field of magnetic confinement fusion reactor technology, specifically relating to a porous electrically insulating ceramic barrier for magnetic confinement fusion reactors, its preparation method, and its application. Background Technology

[0002] Magnetic confinement fusion reactors operate in extremely strong magnetic field environments (the CFETR's central magnetic field reaches 14T). Liquid Pb-17Li eutectic alloys, used as both a coolant and a tritium breeder in the cladding, generate strong induced currents by cutting magnetic field lines during their flow. Porous metal barriers (such as 316H stainless steel or RAFM steel) in dynamic differential pressure tracking safety relief devices suffer from three inherent and insurmountable drawbacks under these conditions: Magnetohydrodynamic (MHD) effects lead to system failure: Metal barriers are good conductors, and induced currents will form closed eddy currents inside the barrier, which not only causes additional energy loss (the local MHD voltage drop can reach more than 30% of the total voltage drop), but also causes local overheating of the barrier (the temperature can rise to more than 50°C); at the same time, the interaction between the eddy currents and the magnetic field will change the flow characteristics of the liquid metal, resulting in unstable discharge flow and seriously affecting the reliability of the safety discharge system.

[0003] Electrochemical corrosion accelerates barrier failure: Different metal components (such as stainless steel barriers and Hastelloy pipes) form galvanic cells in high-temperature liquid lithium-lead, resulting in electrochemical corrosion. Experiments show that the electrochemical corrosion rate of 316H stainless steel in flowing lithium-lead at 500℃ can reach 1~2μm / year, which leads to a gradual increase in the pore size of porous barriers and a year-by-year decrease in breakthrough pressure. Typically, after 3 years of operation, it can no longer meet the gas seal requirements.

[0004] Tritium permeation risk is difficult to control: Hydrogen isotopes have extremely high solubility and diffusion coefficient in metallic materials, and a large amount of tritium will permeate into the metal barrier and remain there, affecting the tritium multiplication rate.

[0005] Porous silicon nitride ceramics possess excellent electrical insulation, chemical stability, and low tritium permeability, theoretically making them an ideal material to replace metal barriers. However, existing porous ceramic barriers face three major technical challenges in engineering applications, preventing their large-scale application to date: High brittleness and poor impact resistance: Ceramic materials have low fracture toughness (KIC≈5~6MPa) (m^0.5), traditional single-structure porous ceramics are prone to brittle fracture under system pressure fluctuations and water hammer impacts, leading to catastrophic leaks.

[0006] High-pressure sealing between ceramics and metals is difficult: the coefficient of thermal expansion of silicon nitride ceramics is approximately 3 × 10⁻⁶. -6 / ℃) and 316H stainless steel (approximately 16×10) -6The difference in temperature (°C) is huge. Conventional welding or bonding methods will generate huge interfacial stress during temperature cycling, causing the sealing joint to crack and failing to meet the high pressure sealing requirements of 10MPa and above.

[0007] In addition, the single-aperture barriers used in existing liquid metal circuits have the following inherent drawbacks that cannot be overcome: The fundamental contradiction between breakthrough pressure and discharge resistance: According to the capillary action principle, the breakthrough pressure of liquid metal is inversely proportional to the pore size. To obtain sufficient liquid resistance, the pore size needs to be reduced, but reducing the pore size will lead to a quadratic decrease in gas permeability, resulting in a sharp increase in discharge resistance under accident conditions. Conversely, increasing the pore size can reduce discharge resistance, but it will lead to insufficient breakthrough pressure, and liquid metal will easily permeate and contaminate the gas seal chamber during normal operation. Under the same boundary conditions with the same total thickness and overall porosity, the argon permeability of the barrier with a single pore size of 2.5 μm is lower than that of the gradient structure of this application, and its contamination capacity is also lower.

[0008] Impurities can clog the system and shorten its lifespan: During the operation of the liquid metal circuit, intermetallic compound particles of Fe, Cr, and Ni are generated (after filtration, the residual particle size is mostly 1μm~5μm). The barrier surface with a single pore size structure is prone to forming a filter cake layer, which clogs the pores, leading to an increase in the gas supply frequency of the gas seal system and ultimately causing the gas seal to fail.

[0009] Therefore, there is an urgent need to develop a porous electrically insulating ceramic barrier suitable for the strong magnetic field environment of fusion reactors, to fundamentally solve the inherent defects of existing metal barriers, and to provide a long-life, highly reliable core component for the safe release device of liquid metal circuits. Summary of the Invention

[0010] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to propose a porous electrically insulating ceramic barrier for magnetic confinement fusion reactors, its preparation method, and its application. The ceramic barrier of this application can significantly reduce the MHD effect under strong magnetic fields, eliminate electrochemical corrosion problems, and simultaneously achieve reliable sealing under high pressure of 0-15 MPa and a stable breakthrough pressure above 0.5 MPa, meeting the 30-year design life requirement of fusion reactors. Furthermore, the ceramic barrier of this application can significantly reduce gas passage resistance and significantly improve pollution tolerance while maintaining sufficient breakthrough pressure, thus simultaneously meeting the comprehensive requirements of "high breakthrough pressure, low discharge resistance, and high pollution tolerance," providing a reliable core component for the safe discharge device of liquid metal loops.

[0011] In one aspect of this application, a porous electrically insulating ceramic barrier for magnetic confinement fusion reactors is proposed, the ceramic barrier being used in a liquid metal loop safety release device. According to an embodiment of this application, along the flow direction of the liquid metal, the ceramic barrier comprises: A first porous layer, the first porous layer having a first interconnected pore; A second porous layer is disposed on one side of the first porous layer. The second porous layer has a second interconnecting pore, and the average pore diameter of the second interconnecting pore is smaller than the average pore diameter of the first interconnecting pore. A third porous layer is disposed on the side of the second porous layer away from the first porous layer. The third porous layer has a third interconnecting pore, and the average pore diameter of the third interconnecting pore is smaller than the average pore diameter of the second interconnecting pore. A tritium-blocking coating is disposed on the surface of the first porous layer away from the second porous layer; An edge densification region is provided at the edge of the ceramic barrier and extends along the flow direction of the liquid metal. The surface of the edge densification region is sequentially provided with a metallization layer and an electroplating layer.

[0012] The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to embodiments of this application can significantly reduce the MHD effect under strong magnetic fields, essentially eliminate electrochemical corrosion problems, and simultaneously achieve reliable high-pressure sealing of 0-15 MPa and stable breakthrough pressure above 0.5 MPa, meeting the 30-year design life requirement of fusion reactors. Furthermore, the ceramic barrier of this application can significantly reduce gas passage resistance and significantly improve pollution tolerance while maintaining sufficient breakthrough pressure, thus simultaneously meeting the comprehensive requirements of "high breakthrough pressure, low discharge resistance, and high pollution tolerance," providing a reliable core component for the safe discharge device of liquid metal loops.

[0013] In addition, the porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to the above embodiments of this application may also have the following additional technical features: In some embodiments of this application, the average pore size of the first porous layer is 5 μm to 10 μm, the thickness of the first porous layer is 0.5 mm to 1.0 mm, and the maximum pore size of the first porous layer is ≤ 1.1 times the average pore size of the first porous layer; the average pore size of the second porous layer is 3 μm to 5 μm, the thickness of the second porous layer is 0.5 mm to 1.0 mm, and the maximum pore size of the second porous layer is ≤ 1.1 times the average pore size of the second porous layer; the average pore size of the third porous layer is 2 μm to 2.5 μm, the thickness of the third porous layer is 1 mm to 1.5 mm, and the maximum pore size of the third porous layer is ≤ 1.1 times the average pore size of the third porous layer; the overall porosity of the ceramic barrier is 30% to 35%, and the closed-cell rate is < 3%; the volume resistivity of the ceramic barrier at 300°C is ≥ 1 × 10⁻⁶. 14 Ω cm.

[0014] In some embodiments of this application, the radial width of the edge densification region on one side is 6mm to 8mm; the density of the edge densification region is ≥99.3%.

[0015] In some embodiments of this application, the thickness of the metallization layer is 50 μm to 70 μm; the material of the metallization layer includes a Mo-Mn mixture; the thickness of the electroplating layer is 5 μm to 8 μm; and the material of the electroplating layer is selected from at least one of nickel and gold.

[0016] In some embodiments of this application, the materials of the first porous layer, the second porous layer and the third porous layer are each independently selected from at least one of silicon nitride and silicon carbide.

[0017] In some embodiments of this application, the thickness of the tritium-blocking coating is 30 μm to 40 μm; the tritium-blocking coating is a composite coating containing boron nitride nanoparticles.

[0018] In a second aspect, this application proposes a method for preparing a porous electrically insulating ceramic barrier for magnetic confinement fusion reactors. According to embodiments of this application, the method includes: (1) The ceramic powder and sintering aid are mixed and ball-milled, and the first granulated powder, the second granulated powder and the third granulated powder are prepared by spray granulation technology, wherein the particle size of the first granulated powder is larger than the particle size of the second granulated powder, and the particle size of the second granulated powder is larger than the particle size of the third granulated powder. (2) The first granulated powder, the second granulated powder and the third granulated powder are respectively filled into the mold in layers. Each layer is compacted by vertical vibration, and the interlayer bonding surface is roughened to obtain the first green body. (3) A densifying agent is coated on the edge region of the first green blank to obtain a second green blank; (4) The second green body is subjected to cold isostatic pressing to obtain the third green body; (5) The third green body is placed in a gas pressure sintering furnace for the first sintering to obtain the first porous green body structure; (6) The first porous blank structure is processed to a preset size; (7) Apply metallization paste to the densified edge region of the first porous preform structure and perform a second sintering to form a metallization layer; (8) Electroplating is performed on the surface of the metallized layer to form an electroplated layer, thereby obtaining a second porous preform structure; (9) A tritium barrier coating is deposited on the liquid metal-facing side of the second porous preform structure to obtain the ceramic barrier.

[0019] The method for preparing a porous electrically insulating ceramic barrier for magnetically confined fusion reactors according to embodiments of this application can significantly reduce the MHD effect under strong magnetic fields, eliminate electrochemical corrosion problems, and simultaneously achieve reliable high-pressure sealing of 0-15 MPa and stable breakthrough pressure above 0.5 MPa, meeting the 30-year design life requirement of fusion reactors. Furthermore, the ceramic barrier prepared by the above method can significantly reduce gas passage resistance and significantly improve pollution tolerance while maintaining sufficient breakthrough pressure, thus simultaneously meeting the comprehensive requirements of "high breakthrough pressure, low discharge resistance, and high pollution tolerance," providing a reliable core component for the safe discharge device of liquid metal loops.

[0020] In addition, the method for preparing a porous electrically insulating ceramic barrier for a magnetically confined fusion reactor according to the above embodiments of this application may also have the following additional technical features: In some embodiments of this application, the particle size D50 of the first granulated powder is 6μm~7μm, the particle size range of the first granulated powder is 5μm~10μm, and the D90 / D10 of the first granulated powder is <1.5; the particle size D50 of the second granulated powder is 3.5μm~4μm, the particle size range of the second granulated powder is 3μm~5μm, and the D90 / D10 of the second granulated powder is <1.5; the particle size D50 of the third granulated powder is 2.2μm~2.5μm, the particle size range of the third granulated powder is 2μm~3μm, and the D90 / D10 of the third granulated powder is <1.5.

[0021] In some embodiments of this application, in step (1), the type of ceramic powder is selected from at least one of silicon nitride and silicon carbide; based on the total mass of the ceramic powder and the sintering aid being 100wt%, the amount of the sintering aid added is 3wt%~11wt%; the sintering aid includes at least one of Y2O3-Al2O3 mixture and B4C-C mixture.

[0022] In some embodiments of this application, in step (3), the densifying agent is a Y2O3-Al2O3-SiO2 densifying agent with added hexagonal boron nitride as a thickener; in step (4), cold isostatic pressing is performed under a pressure of 180MPa~220MPa; in step (5), the temperature for the first sintering is 1800℃~2100℃ and the time is 2h~3h.

[0023] In some embodiments of this application, in step (7), the metallization slurry comprises 72wt%~78wt% Mo, 12wt%~15wt% Mn, 5wt%~8wt% borosilicate glass phase and 5wt%~5.5wt% organic binder; the second sintering temperature is 1420℃~1440℃ and the time is 10min~12min.

[0024] In a third aspect, this application proposes a safe release device for a liquid metal loop, comprising a porous electrically insulating ceramic barrier for a magnetic confinement fusion reactor as described in the above embodiments, or a porous electrically insulating ceramic barrier for a magnetic confinement fusion reactor prepared by the method described in the above embodiments. The porous electrically insulating ceramic barrier is disposed between the liquid metal loop and the inert gas chamber. The decreasing direction of the pore size gradient of the porous electrically insulating ceramic barrier is consistent with the flow direction of the liquid metal, and the first porous layer faces the liquid metal loop. Under normal operating conditions, the porous electrically insulating ceramic barrier for a magnetic confinement fusion reactor allows inert gas to pass freely in both directions, but completely prevents the penetration of liquid metal under a pressure difference of 0.02 MPa to 0.05 MPa. Under accident conditions, when the pressure difference between the two sides exceeds the breakthrough pressure, the liquid metal can be rapidly released through the ceramic barrier.

[0025] In some embodiments of this application, the liquid metal is a Pb-17Li eutectic alloy; the safety relief device is a dynamic differential pressure tracking safety relief device.

[0026] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0027] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the structure of a porous electrically insulating ceramic barrier for a magnetically confined fusion reactor according to an embodiment of this application.

[0028] Figure label: 10 - First porous layer, 20 - Second porous layer, 30 - Third porous layer, 40 - Tritium barrier coating, 50 - Edge densification region. Detailed Implementation

[0029] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0030] In the description of the embodiments of this application, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0031] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0032] In the description of this application, unless otherwise stated, "multiple" means two or more. "A variety" means two or more. In this document, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] In one aspect of this application, a porous electrically insulating ceramic barrier for magnetic confinement fusion reactors is proposed, which is used in a safety release device for a liquid metal loop. According to an embodiment of this application, refer to the appendix... Figure 1 Along the flow direction of the liquid metal (i.e., direction A), the ceramic barrier includes: a first porous layer 10 (i.e., the liquid metal-facing side layer), the first porous layer 10 having first interconnected pores; a second porous layer 20 (i.e., an intermediate transition layer), the second porous layer 20 being disposed on one side of the first porous layer 10, the second porous layer 20 having second interconnected pores, the average pore size of the second interconnected pores being smaller than the average pore size of the first interconnected pores; and a third porous layer 30 (i.e., the gas seal-facing side layer), the third porous layer 30 being disposed on the side of the second porous layer 20 away from the first porous layer 10. The three-porous layer 30 has a third interconnected pore, the average pore diameter of which is smaller than the average pore diameter of the second interconnected pore; a tritium barrier coating 40 is disposed on the surface of the first porous layer 10 away from the second porous layer 20 (the tritium barrier coating 40 is deposited only on the outer surface of the first porous layer 10 facing the liquid metal, and is not coated on the inner wall of the pores); an edge densification region 50 is disposed at the edge region of the ceramic barrier and extends along the flow direction of the liquid metal, and a metallization layer and an electroplating layer are sequentially disposed on the surface of the edge densification region 50. Therefore, the ceramic barrier of this application can greatly reduce the MHD effect under strong magnetic fields, eliminate electrochemical corrosion problems, and simultaneously achieve reliable high-pressure sealing of 0~15MPa and stable breakthrough pressure above 0.5MPa, meeting the 30-year design life requirement of the fusion reactor. In addition, the ceramic barrier of this application can significantly reduce gas passage resistance and significantly improve fouling capacity while maintaining sufficient breakthrough pressure. It can simultaneously meet the comprehensive requirements of "high breakthrough pressure, low discharge resistance, and high fouling capacity", providing a reliable core component for the safe discharge device of liquid metal circuit.

[0035] The following details the beneficial effects achievable by the porous electrically insulating ceramic barrier for magnetic confinement fusion reactors proposed in this application: The release process of liquid metal consists of three stages, and its core principle is as follows: Phase 1: Liquid metal wetting and filling of the first porous layer. When an accident overpressure occurs, the liquid metal, at a pressure differential far below the core breakthrough pressure, easily overcomes the capillary resistance of the first porous layer (average pore size 5μm~10μm), rapidly wetting and filling its pores. The large pore size of the first porous layer means it poses almost no flow resistance.

[0036] Second stage: Liquid metal penetrates the second porous layer. The liquid metal then enters the second porous layer (average pore size 3μm~5μm). Although the capillary resistance of the second porous layer is higher than that of the first porous layer, it is still significantly lower than that of the third porous layer, allowing the liquid metal to penetrate smoothly under this pressure difference.

[0037] The third stage: The liquid metal finally breaks through the third porous layer. When the liquid metal reaches the third porous layer (average pore size 2μm~2.5μm), it faces the maximum capillary resistance of the entire barrier, which is the so-called "breakthrough pressure". Once the system pressure difference exceeds this threshold, the liquid metal breaks through this layer and enters the gas-sealed chamber, realizing the release. Since the first and second porous layers have been filled in the early stage and their flow resistance is much lower than that of the fine pore layer (i.e., the third porous layer), the rate bottleneck of the entire release process is still controlled by the third porous layer.

[0038] According to Darcy's law, the permeability of a porous medium is proportional to the square of its pore size. Under steady-state venting conditions, the liquid metal flows sequentially through the first, second, and third porous layers, forming a series of flow resistances. The third porous layer, with the smallest pore size, accounts for the majority of the total flow resistance and is the bottleneck controlling the rate of the entire venting process. The first and second porous layers, due to their large pore size, have much lower flow resistance than the third porous layer. Therefore, the gradient structure of the porous ceramic barrier in this application ensures liquid resistance without creating an additional flow bottleneck during the venting process.

[0039] Therefore, the porous electrically insulating ceramic barrier for magnetic confinement fusion reactors proposed in this application can achieve the following beneficial effects: First, it greatly reduces the MHD effect under strong magnetic fields: ceramic materials have high volume resistivity, especially porous silicon nitride ceramics with a volume resistivity ≥1×10⁻⁶ at 300℃. 14 Ω cm is a complete electrical insulator, which blocks the path of induced current and eliminates the problems of MHD voltage drop and local overheating.

[0040] Secondly, it eliminates electrochemical corrosion at its source: ceramic materials (especially silicon nitride ceramics) exhibit excellent chemical stability, exhibiting no electrochemical corrosion in flowing liquid lithium-lead at 500℃, with a uniform corrosion rate of <0.08μm / year, more than 15 times lower than 316H stainless steel. During long-term operation, the pore size and breakthrough pressure remain almost unchanged, solving the performance degradation problem of metal barriers caused by corrosion.

[0041] Third, naturally higher breakthrough pressure and safety margin: The contact angle between ceramic materials and Pb-17Li is larger. For example, the contact angle between silicon nitride and Pb-17Li is 148°~152°, which is 18°~22° higher than that of 316H stainless steel. According to the capillary action formula, the breakthrough pressure is increased by about 30% for the same pore size. Based on the Young-Laplace formula engineering calculation, the Pb-17Li breakthrough pressure of the ceramic barrier in this application is stable at 0.57MPa~0.60MPa at 300℃, forming a sufficient safety margin with the dynamic gas seal pressure difference (0.02MPa~0.05MPa).

[0042] Fourth, excellent intrinsic tritium barrier properties: Ceramic materials (especially silicon nitride ceramics) have extremely low solubility and diffusion coefficients for hydrogen isotopes. The intrinsic tritium permeability of silicon nitride ceramics is approximately 8 × 10⁻⁶. -14 mol / (m s The tritium content (Pa^0.5) is three orders of magnitude lower than that of uncoated 316H stainless steel, significantly reducing the risk of radioactive tritium leakage. Furthermore, the tritium-blocking coating further reduces the hydrogen isotope solubility and diffusion coefficient of the ceramic barrier.

[0043] Fifth, it can achieve reliable sealing under high pressures above 16MPa: This application sets a densified region at the edge of the ceramic barrier, and sequentially sets a metallization layer and an electroplating layer on the surface of the densified region, and then uses AgCu... 28 Ti3 active brazing filler metal is used to braze the metallized and electroplated edge densified region to the 316H stainless steel flange, effectively solving the problem of mismatched thermal expansion coefficients between ceramics and metals. The joint of the Mo-Mn metallized ceramic seal has a shear strength ≥120MPa and can withstand 16MPa hydrostatic pressure without leakage, meeting the maximum operating pressure requirement of 15MPa for fusion reactors.

[0044] Sixth, this application fundamentally resolves the inherent contradiction between breakthrough pressure and discharge resistance in liquid metal circuit safety systems: It pioneers a three-layer functional zoning gradient structure with a coarse upper layer and a fine lower layer. The first porous layer effectively intercepts corrosion product particles, providing high contamination capacity. The second porous layer, with its gradient pore size, prevents stress concentration between layers and also assists in intercepting fine particles. The third porous layer provides the primary breakthrough pressure, becoming the core liquid-blocking layer. Given that the breakthrough pressure of the ceramic barrier is determined by the third porous layer, the introduction of the first and second porous layers significantly reduces gas flow resistance.

[0045] The breakthrough pressure in this invention can be based on the Yang-Laplace formula P. break=2γ·|cosθ| / r, i.e., the capillary action formula, is used for engineering calculations. The ideal application condition of this formula is a uniform straight cylindrical channel. The actual sintered porous material of this invention has a curved, variable diameter three-dimensional network structure. Therefore, this invention adopts the pore diameter parameter r in the maximum pore diameter calculation formula. This method is a common engineering approximation calculation method in the field of porous materials. The deviation between the calculation result and the actual measured breakthrough pressure is ≤10%, which meets the engineering design requirements.

[0046] Seventh, ultra-long service life and low maintenance cost: The first porous layer can effectively intercept most of the corrosion product particles (with a particle size of approximately 1μm~5μm) in liquid metal, forming a surface filter cake layer, without clogging the core liquid-blocking third porous layer. The gradient pore structure of the ceramic barrier in this application provides three times the fouling capacity of a single-pore structure. Combined with a negligible corrosion rate, the design service life of the ceramic barrier can reach more than 10 years, more than three times that of a metal barrier, significantly reducing maintenance frequency and personnel radiation exposure. At the same time, the three-layer gradient structure of the ceramic barrier in this application effectively alleviates stress concentration through the gradient transition between layers, and its impact resistance is 30% higher than that of a single-structure porous ceramic. It can withstand water hammer pressure impacts of up to 2MPa without brittle fracture.

[0047] Eighth, the activation characteristics of ceramic materials meet safety requirements, especially Si3N4 materials, although ¹ 4 N will produce a small amount of long-half-lived ¹ through the (n,p) reaction. 4 C, but its overall activation level is lower than that of traditional metal structural materials such as RAFM steel and 316H stainless steel, meeting the safety requirements of fusion reactor materials.

[0048] The high-precision electrically insulating porous ceramic barrier of this application, which has the selective permeability characteristic of "gas-through but liquid-through", is particularly suitable for dynamic differential pressure tracking safety relief devices in the high-temperature and high-pressure liquid Pb-17Li eutectic alloy loop of tokamak-type magnetic confinement fusion reactors (3~14T strong magnetic field), and can also be used in the relevant insulation and isolation systems of fourth-generation lead-based fast reactors.

[0049] According to some specific embodiments of this application, the above-mentioned ceramic barrier is formed by sintering three porous ceramic layers with uniform pore size and tight interlayer bonding in sequence along the direction of liquid metal flow. The pore size of the porous ceramic layers decreases in a stepwise manner along the direction of liquid metal flow, forming a functional partition structure of "upstream coarse pore filtration - intermediate transition - downstream fine pore liquid blocking".

[0050] It should be noted that in this application, "upstream" and "downstream" refer to the flow direction of the liquid metal.

[0051] According to some specific embodiments of this application, the average pore size of the first porous layer is 5μm to 10μm (for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.), which further ensures that the first porous layer effectively intercepts corrosion product particles and provides high dirt-holding capacity. Furthermore, the maximum pore size of the first porous layer is ≤ 1.1 times the average pore size of the first porous layer, indicating that the pore size distribution uniformity of the first porous layer is significantly better than that of traditional sintered porous materials.

[0052] According to some specific embodiments of this application, the average pore size of the second porous layer is 3μm to 5μm (e.g., it can be 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc.). This further ensures that the second porous layer has a gradient pore size, alleviating interlayer stress concentration and assisting in the interception of fine particles. Furthermore, the maximum pore size of the second porous layer is ≤ 1.1 times the average pore size of the second porous layer, indicating that the pore size distribution uniformity of the second porous layer is significantly better than that of traditional sintered porous materials.

[0053] According to some specific embodiments of this application, the average pore size of the third porous layer is 2μm to 2.5μm (e.g., it can be 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, etc.). This further ensures that the third porous layer provides the main breakthrough pressure, becoming the core liquid-blocking layer. Furthermore, the maximum pore size of the third porous layer is ≤ 1.1 times the average pore size of the third porous layer. This demonstrates that the pore size distribution uniformity of the third porous layer is significantly better than that of traditional sintered porous materials, while also ensuring high batch-to-batch consistency of the breakthrough pressure of the ceramic barrier.

[0054] According to some specific embodiments of this application, the overall porosity of the ceramic barrier is 30%~35% (for example, it can be 30%, 31%, 32%, 33%, 34%, 35%, etc.), and the closed-pore rate is <3%. The closed-pore rate is determined by the mercury porosimetry method according to GB / T 21650.1.

[0055] According to some specific embodiments of this application, the volume resistivity of the above-mentioned ceramic barrier at 300°C is ≥1×10⁻⁶. 14 Ω cm is a completely electrical insulator, and its volume resistivity is determined using the GB / T 1410 method for testing high-temperature insulation resistance.

[0056] According to some specific embodiments of this application, the thickness of the first porous layer is 0.5mm to 1.0mm (for example, it can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, etc.), thereby further ensuring that the first porous layer effectively intercepts corrosion product particles and provides high dirt-holding capacity.

[0057] According to some specific embodiments of this application, the thickness of the second porous layer is 0.5mm to 1.0mm (for example, it can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, etc.), thereby further ensuring that the second porous layer has a pore size gradient transition, alleviating interlayer stress concentration, and at the same time assisting in the interception of fine particles.

[0058] According to some specific embodiments of this application, the thickness of the third porous layer is 1mm to 1.5mm (for example, it can be 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, etc.), thereby further ensuring that the third porous layer provides the main breakthrough pressure and becomes the core liquid-resistant layer.

[0059] In the embodiments of this application, the materials of the first porous layer, the second porous layer, and the third porous layer are not particularly limited. As some preferred embodiments, the materials of the first porous layer, the second porous layer, and the third porous layer are each independently selected from at least one of silicon nitride (e.g., α-Si3N4) and silicon carbide, thereby exhibiting excellent high-temperature mechanical properties and radiation resistance. As another preferred embodiment, the materials of the first porous layer, the second porous layer, and the third porous layer are the same.

[0060] According to some specific embodiments of this application, the thickness of the above-mentioned tritium barrier coating is 30μm~40μm (for example, it can be 30μm, 32μm, 34μm, 36μm, 38μm, 40μm, etc.). This can further reduce the solubility and diffusion coefficient of hydrogen isotopes in the ceramic barrier, ensuring that all hydrogen isotopes are mixed with argon gas through the pores and then connected to the tritium recovery system of the main circuit through the exhaust system, thereby improving tritium production efficiency, while not causing radioactive material residue or pollution.

[0061] According to some specific embodiments of this application, the tritium-blocking coating is a composite coating containing boron nitride nanoparticles. It should be noted that the aforementioned tritium-blocking coating is not applied to the inner wall of the pores to avoid premature blockage of the pores due to coating defects.

[0062] In the embodiments of this application, the aforementioned edge densification region is disposed at the edge of the ceramic barrier and extends along the flow direction of the liquid metal. A metallization layer and an electroplating layer are sequentially disposed on the surface of the edge densification region, and then AgCu is applied. 28 Ti3 active brazing filler metal connects the metallized and electroplated edge densified region to a 316H stainless steel flange, effectively solving the problem of direct welding and sealing of porous ceramic surfaces. The metallization layer forms a metallurgical bond with the ceramic substrate, while the electroplating layer improves wettability with the brazing filler metal.

[0063] As some specific embodiments, for ceramic barriers with diameters of DN50 to DN125, the radial width of the aforementioned edge densification region on one side is 6mm to 8mm (e.g., 6mm, 6.5mm, 7mm, 7.5mm, 8mm, etc.). As further specific embodiments, the aforementioned edge densification region is a densified annular region with a density ≥99.3%, preferably ≥99.5%. It is understood that if the aforementioned porous electrically insulating ceramic barrier for magnetic confinement fusion reactors is cylindrical, then the aforementioned edge densification region is an annular region.

[0064] According to some specific embodiments of this application, the thickness of the metallization layer is 50μm to 70μm, for example, it can be 50μm, 55μm, 60μm, 65μm, 70μm, etc., thereby further ensuring that the metallization layer forms a metallurgical bond with the ceramic substrate.

[0065] In the embodiments of this application, the type of material of the metallization layer is not particularly limited. As some preferred embodiments, the material of the metallization layer includes a Mo-Mn mixture. As some specific embodiments, the mass ratio of Mo to Mn in the Mo-Mn mixture is (72~78):(12~15).

[0066] According to some specific embodiments of this application, the thickness of the above-mentioned electroplated layer is 5μm to 8μm, for example, it can be 5μm, 6μm, 7μm, 8μm, etc., thereby further improving the wettability with the solder.

[0067] In the embodiments of this application, the type of material of the electroplated layer is not particularly limited. As some preferred embodiments, the material of the electroplated layer is selected from at least one of nickel and gold.

[0068] In a second aspect, this application proposes a method for preparing a porous electrically insulating ceramic barrier for a magnetically confined fusion reactor. According to an embodiment of this application, the method includes the following steps: S100: Ceramic powder and sintering aid are mixed and ball-milled, and the first granulated powder, the second granulated powder and the third granulated powder are prepared by spray granulation technology; In some specific embodiments, ceramic powder and sintering aid are mixed and ball-milled, and then spray granulation technology is used to prepare three types of granulated powder with narrow particle size distributions: first granulated powder (coarse powder), second granulated powder (medium powder), and third granulated powder (fine powder). Then, according to the designed layer thickness, the first granulated powder (coarse powder), second granulated powder (medium powder), and third granulated powder (fine powder) are respectively filled into a mold and vibrated vertically to roughen the interlayer bonding surfaces, achieving a surface roughness Ra of 3.2 μm to 6.3 μm to enhance the interlayer mechanical interlocking, thus obtaining a first green body. The first granulated powder layer forms a first porous layer after subsequent sintering, the second granulated powder forms a second porous layer, and the third granulated powder forms a third porous layer. Furthermore, the particle size of the first granulated powder is larger than that of the second granulated powder, and the particle size of the second granulated powder is larger than that of the third granulated powder. This ensures that the average pore size of the first porous layer formed by sintering the first granulated powder layer is larger than that of the second porous layer formed by sintering the second granulated powder, and the average pore size of the second porous layer formed by sintering the second granulated powder is larger than that of the third porous layer formed by sintering the third granulated powder, thus ensuring the formation of a three-layer functional zoning gradient structure with "coarse upper layer and fine lower layer".

[0069] According to some specific embodiments of this application, the particle size D50 of the first granulated powder is 6μm~7μm (for example, it can be 6μm, 6.2μm, 6.4μm, 6.6μm, 6.8μm, 7μm, etc.), the particle size range of the first granulated powder is 5μm~10μm, and the D90 / D10 of the first granulated powder is <1.5. Therefore, it can be ensured that a first porous layer with a uniform pore size distribution is formed, which can effectively intercept corrosion product particles and provide high dirt holding capacity.

[0070] According to some specific embodiments of this application, the particle size D50 of the second granulated powder is 3.5μm~4μm (for example, it can be 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, etc.), the particle size range of the second granulated powder is 3μm~5μm, and the D90 / D10 of the second granulated powder is <1.5. Therefore, it can be ensured that a second porous layer with a uniform pore size distribution is formed, preventing interlayer stress concentration, and at the same time assisting in the interception of fine particles.

[0071] According to some specific embodiments of this application, the particle size D50 of the third granulated powder is 2.2μm~2.5μm (for example, it can be 2.2μm, 2.3μm, 2.4μm, 2.5μm, etc.), the particle size range of the third granulated powder is 2μm~3μm, and the D90 / D10 of the third granulated powder is <1.5. Thus, it can be ensured that a third porous layer with a uniform pore size distribution is formed, further ensuring that the main breakthrough pressure is provided and becoming the core liquid-resistant layer.

[0072] It should be noted that D50 represents the particle size corresponding to a cumulative volume fraction of 50% for powder particles, D10 represents the particle size corresponding to a cumulative volume fraction of 10% for powder particles, and D90 represents the particle size corresponding to a cumulative volume fraction of 90% for powder particles.

[0073] In the embodiments of this application, the type of ceramic powder is not particularly limited. As some preferred embodiments, the ceramic powder is selected from at least one of silicon nitride (e.g., α-Si3N4) and silicon carbide, thereby exhibiting excellent high-temperature mechanical properties and radiation resistance.

[0074] According to some specific embodiments of this application, based on a total mass of 100 wt% for ceramic powder and sintering aid, the amount of sintering aid added is 3 wt% to 11 wt%. As some specific embodiments, based on a total mass of 100 wt% for ceramic powder and sintering aid, the sintering aid includes 5 wt% to 7 wt% Y₂O₃ and 2 wt% to 4 wt% Al₂O₃. As still some specific embodiments, based on a total mass of 100 wt% for ceramic powder and sintering aid, the sintering aid includes 2 wt% B₄C and 1 wt% C.

[0075] S200: The first granulated powder, the second granulated powder, and the third granulated powder are filled into the mold in layers. Each layer is compacted by vertical vibration. The interlayer bonding surface is roughened so that the surface roughness Ra reaches 3.2μm~6.3μm to enhance the mechanical interlocking between layers and obtain the first green body.

[0076] S300: A densifying agent is applied to the edge region of the first green body to obtain a second green body; According to some specific embodiments of this application, a densifying agent of Y2O3-Al2O3-SiO2 (mass ratio of Y2O3, Al2O3, and SiO2 is 5:3:2) with 15wt% high-purity hexagonal boron nitride microparticles as a thickener is coated on the edge region of the first green body, and the penetration depth is controlled to be ≤0.5mm, which can achieve densification of the edge region and obtain a second green body.

[0077] S400: The second green body is cold isostatically pressed to obtain the third green body; According to some specific embodiments of this application, the mold containing powder is sealed and placed in a cold isostatic press. The pressure is increased to 180MPa~220MPa (e.g., 180MPa, 190MPa, 200MPa, 210MPa, 220MPa, etc.) at a rate of 5MPa / min~8MPa / min (e.g., 5MPa / min, 6MPa / min, 7MPa / min, 8MPa / min), and held for 10min~20min (e.g., 10min, 12min, 14min, 16min, 18min, 20min, etc.). Then the pressure is reduced at a rate of 3MPa / min~5MPa / min (e.g., 3MPa / min, 4MPa / min, 5MPa / min, etc.) to obtain a third green compact with uniform density.

[0078] S500: The third green body is placed in the gas pressure sintering furnace for the first sintering to obtain the first porous green body structure; According to some specific embodiments of this application, a third green body is placed in a gas pressure sintering furnace and sintered for the first time under a high-purity nitrogen atmosphere of 3MPa, so as to achieve simultaneous sintering of the porous body and the densified edge, and obtain a first porous green body structure.

[0079] According to some specific embodiments of this application, the temperature for the first sintering is 1800℃~2100℃ (e.g., 1800℃, 1900℃, 2000℃, 2100℃, etc.), and the time is 2h~3h. During the sintering process, by precisely controlling the powder particle size, molding pressure, and sintering process parameters, a porous ceramic barrier with the target porosity and pore size can be directly obtained without subsequent hot isostatic pressing densification treatment to avoid damaging the porous structure.

[0080] S600: Machining the first porous blank structure to the preset size; In this step, the sintered blank is machined to the design dimensions, with a surface roughness Ra≤1.6μm and an edge sealing surface flatness≤0.02mm.

[0081] S700: Apply metallization paste to the densified edge region of the first porous preform structure, and perform a second sintering to form a metallization layer; According to some specific embodiments of this application, a metallization slurry is coated on the densified edge region of the first porous preform structure, and sintered at 1420°C to 1440°C for 10 to 12 minutes in a humid hydrogen atmosphere with a dew point of 20°C to 30°C to form a metallization layer.

[0082] According to some specific embodiments of this application, the metallization paste comprises 72wt%~78wt% Mo, 12wt%~15wt% Mn, 5wt%~8wt% borosilicate glass phase, and 5wt%~5.5wt% organic binder. As a specific embodiment, the organic binder is ethyl cellulose (EC) with a viscosity of 10~20 mPa. s (25℃, 5% ethanol solution), with a degree of substitution of 2.4~2.6.

[0083] S800: Electroplating is performed on the surface of the metallization layer to form an electroplated layer, resulting in a second porous preform structure; According to some specific embodiments of this application, bright nickel is electroplated on the surface of the metallization layer, with a plating thickness of 5μm~8μm and a plating adhesion strength ≥100N / cm. 2 .

[0084] S900: A tritium barrier coating is deposited on the liquid metal-facing side of the second porous preform structure to obtain a ceramic barrier.

[0085] In this step, either atomic layer deposition (ALD) or plasma-enhanced chemical vapor deposition (PECVD) can be used to deposit a tritium barrier coating on the surface of the first porous layer away from the second porous layer (i.e., the side facing the liquid metal).

[0086] The method for preparing a porous electrically insulating ceramic barrier for magnetically confined fusion reactors according to embodiments of this application can significantly reduce the MHD effect under strong magnetic fields, eliminate electrochemical corrosion problems, and simultaneously achieve reliable high-pressure sealing of 0-15 MPa and stable breakthrough pressure above 0.5 MPa, meeting the 30-year design life requirement of fusion reactors. Furthermore, the ceramic barrier prepared by the above method can significantly reduce gas passage resistance and significantly improve pollution tolerance while maintaining sufficient breakthrough pressure, thus simultaneously meeting the comprehensive requirements of "high breakthrough pressure, low discharge resistance, and high pollution tolerance," providing a reliable core component for the safe discharge device of liquid metal loops.

[0087] In a third aspect of the present application, the present application provides a safety relief device for a liquid metal loop, comprising the porous electrically insulating ceramic barrier for a magnetically confined fusion reactor according to any of the above embodiments or the porous electrically insulating ceramic barrier for a magnetically confined fusion reactor prepared by the method according to any of the above embodiments, wherein the porous electrically insulating ceramic barrier for a magnetically confined fusion reactor is arranged between the liquid metal loop and an inert gas chamber, the pore size gradient decreasing direction of the porous electrically insulating ceramic barrier is consistent with the flow direction of liquid metal, and the first porous layer faces the liquid metal loop. Under normal operating conditions, the insulating ceramic barrier of the present application allows inert gas to freely pass through in both directions, but completely prevents the penetration of liquid metal under a pressure difference of 0.02MPa~0.05MPa; under accident conditions, when the pressure difference on both sides exceeds the breakthrough pressure, liquid metal can quickly pass through the ceramic barrier to achieve relief.

[0088] According to some specific embodiments of the present application, the liquid metal is Pb-17Li eutectic alloy, and the inert gas is high-purity argon with a purity of ≥99.999%.

[0089] According to further specific embodiments of the present application, the safety relief device is a dynamic differential pressure tracking type safety relief device, and a constant slight positive differential pressure of 0.02MPa~0.05MPa is maintained between the gas sealing pressure and the main loop pressure during normal operation.

[0090] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used for explaining the present application, and cannot be construed as limiting the present application. In addition, unless explicitly stated otherwise, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are all easily obtained by those skilled in the art.

[0091] Example 1 This embodiment provides a porous silicon nitride ceramic barrier with gradient pore size for fusion reactors, specifically a porous electrically insulating ceramic barrier matched with the lithium lead blanket loop of fusion reactors, the structure is as Figure 1 shown.

[0092] The overall structure of the barrier is co-sintered from three layers of porous silicon nitride ceramic layers in sequence along the flow direction of liquid metal, and the structural parameters of the three layers are specifically as follows: First porous layer: average pore size 6.83μm, maximum pore size 7.20μm (≤1.1 times the average pore size), thickness 0.5mm; Second porous layer: average pore size 3.68μm, maximum pore size 3.85μm (≤1.1 times the average pore size), thickness 0.5mm; Third porous layer: average pore size 2.31μm, maximum pore size 2.42μm (≤1.1 times the average pore size), thickness 1.0mm.

[0093] Overall barrier parameters: The barrier is cylindrical, with its height aligned with the flow direction of the liquid metal, and a diameter of 50 mm. The overall porosity is 32%, the closed-cell rate is less than 2.5%, and the volume resistivity at 300℃ is 1.2 × 10⁻⁶. 14 Ω cm. A 7mm wide densified annular area is reserved at the edge of the barrier, with a density of 99.3% (density was determined by the water displacement method according to GB / T 3850).

[0094] The specific steps of the preparation process are as follows: Powder preparation: α-Si3N4 powder with a purity of 99.9% and an average particle size of 1.5μm was mixed with 6wt%Y2O3 and 3wt%Al2O3 sintering aids and ball-milled in anhydrous ethanol medium for 24 hours to obtain a uniform mixed slurry. Spray granulation: The mixed slurry is spray granulated to prepare granulated powder with good sphericity and flowability. Then, three types of granulated powder with narrow particle size distribution are obtained by air classification: coarse powder (D50=6.83μm, particle size range of 5μm~10μm, D90 / D10<1.5), medium powder (D50=3.68μm, particle size range of 3μm~5μm, D90 / D10<1.5), and fine powder (D50=2.31μm, particle size range of 2~2.5μm, D90 / D10<1.5). Layered molding: Coarse powder, medium powder and fine powder are filled into the graphite mold in layers in sequence. After each layer is filled, it is compacted by vertical vibration at a frequency of 25Hz for 5 minutes. The interlayer bonding surface is roughened to enhance the mechanical interlocking between layers. Edge densification treatment: A densification agent of Y2O3-Al2O3-SiO2 (mass ratio of Y2O3, Al2O3, and SiO2 is 5:3:2) with 15wt% hexagonal boron nitride thickener is uniformly coated on a 7mm wide area at the edge of the green blank, and the penetration depth is controlled to be ≤0.5mm. Cold isostatic pressing: After sealing the mold, hold the pressure at 200MPa for 15 minutes, with a pressure increase rate of 7MPa / min and a pressure decrease rate of 4MPa / min to obtain the green blank; Gas pressure sintering: The green billet is placed in a gas pressure sintering furnace and heated to 1800°C at a rate of 5°C / min under a high-purity nitrogen atmosphere of 3MPa for the first sintering. The temperature is held for 3 hours and then cooled to room temperature with the furnace. Precision machining: The blank is machined to the design dimensions using a diamond grinding wheel, and the edge sealing surface is precision ground to achieve a flatness of ≤0.02mm and a surface roughness of Ra=1.6μm; Mo-Mn metallization: Mo-Mn metallization paste (containing 75.5 wt% Mo, 13.5 wt% Mn, 6 wt% borosilicate glass phase, and 5 wt% organic binder, with ethyl cellulose (EC) as the organic binder and a viscosity of 10~20 mPa) is screen-printed in the densification edge region. s (25℃, 5% ethanol solution), degree of substitution 2.4~2.6, and then sintered at 1430℃ for 11 minutes in a wet hydrogen atmosphere with a dew point of 25℃; Nickel electroplating: Bright nickel is electroplated on the metallized layer surface, with a coating thickness of 7μm, and the coating adhesion test is qualified; Tritium barrier coating: A tritium barrier coating containing boron nitride nanoparticles with a thickness of 35 μm is deposited on the side of the first porous layer away from the second porous layer using a single-sided mask and PECVD process at a deposition temperature of 380℃. The inner walls of the pores are not coated. Sealing joint structure: The sealing joint adopts a 60μm Mo-Mn metallization layer + a 7μm electroplated nickel layer + a 60μm AgCu layer. 28 The Ti3 brazing filler layer is brazed to the 316H pipe.

[0095] Performance verification: Breakthrough pressure: In this embodiment, the breakthrough pressure is based on the Yang-Laplace formula P. break =2γ·|cosθ| / r, i.e., the capillary action formula, is used for engineering calculations. The ideal application condition for this formula is a uniform straight cylindrical channel. In this embodiment, the actual sintered porous material has a curved, variable-diameter three-dimensional network structure. Therefore, this embodiment uses the pore size parameter r in the maximum pore size calculation formula measured by the bubble point method. This method is a commonly used engineering approximation calculation method in the field of porous materials. The deviation between the calculated result and the actual measured breakthrough pressure is ≤10%, meeting the engineering design requirements. The maximum capillary resistance that liquid metal cannot pass through the pores is P. break At 500℃, the surface tension of Pb-17Li is γ=0.422N / m, the contact angle between silicon nitride and Pb-17Li is 148°~152°, the maximum pore size of the core liquid-blocking layer (i.e. the third porous layer) is 2.42μm, and the theoretical expected value of the initial breakthrough pressure is 0.57~0.60MPa, which is more than 11 times the working pressure difference of dynamic gas seal (0.02~0.05MPa), with sufficient safety margin.

[0096] Gas release performance: Based on Darcy's law and the performance characteristics of porous filter materials, under the same boundary conditions with the same total thickness and overall porosity, the argon permeability of this embodiment is increased by more than 45% and the release resistance is reduced by more than 40% compared with a single fine-pore structure at the same breakthrough pressure. This conclusion can be verified by air permeability test.

[0097] Electrical insulation properties: The volume resistivity of porous silicon nitride ceramic at 300℃ is ≥1×10⁻⁶. 14 Ω cm (tested according to GB / T 1410) can completely block the induced current path and completely eliminate the MHD effect.

[0098] Sealing performance: The theoretical expected shear strength of the ceramic-metal joint is ≥120MPa, and it can withstand 16MPa hydrostatic pressure without leakage, meeting the maximum operating pressure requirement of 15MPa for fusion reactors.

[0099] Corrosion resistance: The uniform corrosion rate of silicon nitride in liquid lithium lead at 500℃ is <0.08μm / year, the pore size change over 30 years is <1%, and the pressure drop is negligible.

[0100] Example 2: This embodiment provides a DN80 diameter silicon carbide gradient porous ceramic barrier (650℃ high-temperature condition model). The overall structure of the barrier is formed by co-sintering three porous silicon carbide ceramic layers sequentially along the flow direction of liquid metal. The specific parameters of the three-layer structure are as follows: First porous layer: average pore size 7.5 μm, maximum pore size 8.2 μm (≤ 1.1 times the average pore size), thickness 0.7 mm; The second porous layer has an average pore size of 4.2 μm, a maximum pore size of 4.6 μm (≤ 1.1 times the average pore size), and a thickness of 0.7 mm. The third porous layer has an average pore size of 2.4 μm, a maximum pore size of 2.6 μm (≤ 1.1 times the average pore size), and a thickness of 1.2 mm. Overall parameters: diameter 80mm, designed porosity 33%, closed pore rate ≤2.5%.

[0101] Functional layer: A 40μm thick tritium barrier coating containing boron nitride nanoparticles is coated on the side of the first porous layer away from the second porous layer; a 7mm wide densification area is reserved at the edge with a density ≥99.3%, and a Ti-Ni-Ag multilayer metallization process is used to adapt to high-temperature brazing.

[0102] Preparation process (adjusted to suit the properties of silicon carbide materials): Using the same powder ceramic process as in Example 1, the sintering aid was adjusted to 2wt% B4C + 1wt% C to adapt to silicon carbide material, the first sintering temperature was adjusted to 2050℃, and the remaining process parameters were all industry-standard and were adjusted for adaptability, which can stably prepare the ceramic.

[0103] Performance verification: Liquid resistance breakthrough pressure: Based on engineering calculations using the Yang-Laplace formula, the theoretically expected initial breakthrough pressure at 650℃ Pb-17Li is 0.60~0.65MPa, which meets the safety requirements for high-temperature operating conditions.

[0104] High temperature resistance: Silicon carbide has a maximum operating temperature of 650℃, which is 100℃ higher than silicon nitride, and is compatible with the ultra-high temperature liquid metal loop of the fourth-generation fast reactor.

[0105] Corrosion resistance: Silicon carbide corrodes at a rate of <0.05 μm / year in liquid lithium lead at 600℃.

[0106] Example 3: This embodiment provides a large-size silicon nitride gradient porous ceramic barrier with a DN125 diameter (high-flow-rate main circuit type). The overall structure of the barrier is formed by co-sintering three porous silicon nitride ceramic layers sequentially along the liquid metal flow direction. The specific parameters of the three-layer structure are as follows: First porous layer: average pore size 7.0 μm, maximum pore size 7.7 μm (≤ 1.1 times the average pore size), thickness 0.8 mm; Second porous layer: average pore size 4.0 μm, maximum pore size 4.4 μm (≤ 1.1 times the average pore size), thickness 0.8 mm; The third porous layer has an average pore size of 2.3 μm, a maximum pore size of 2.5 μm (≤ 1.1 times the average pore size), and a thickness of 1.4 mm. Overall parameters: diameter 125mm, porosity 33%, closed pore rate ≤2.5%.

[0107] Functional layer: An 8mm wide densification area is reserved at the edge to meet the high-pressure sealing requirements of large-size barriers.

[0108] Preparation process: Using the same powder ceramic process as in Example 1, the cold isostatic pressing holding time was adjusted to 20 min to ensure uniform density of large-sized green bodies. The remaining process parameters are all industry-standard and have been adapted to ensure stable preparation.

[0109] Performance verification: Discharge flow rate: Under a DN125 diameter, the theoretical expected discharge flow rate under an 8MPa pressure difference is above 4.5L / s, which meets the requirements for large flow rate main circuit emergency discharge. It can be calculated based on Darcy's law that the flow rate is proportional to the square of the diameter.

[0110] Impact resistance: The gradient structure in this embodiment can alleviate stress concentration through the pore size gradient transition, and the impact resistance is improved by 30% compared with the single-structure porous ceramic, and it can withstand the impact of 2MPa water hammer.

[0111] Comparative Example 1 (Single Aperture Structure): Single-aperture 316H stainless steel porous metal barrier (comparison benchmark) This comparative example provides a 316H stainless steel porous barrier with a single pore size of 2.5μm and a total thickness of 2.0mm, an overall porosity of 33%, and a surface coating of 40μm thick tritium-blocking coating containing boron nitride nanoparticles.

[0112] Performance comparison: Electrical insulation performance: 316H stainless steel is a good conductor, but it will produce a strong MHD effect under a strong magnetic field. The MHD voltage drop accounts for more than 30% of the total voltage drop, and local overheating can reach 50°C. It is completely unsuitable for the strong magnetic field environment of fusion reactors.

[0113] Corrosion resistance: The electrochemical corrosion rate of 316H stainless steel in liquid lithium lead at 500℃ is 1~2μm / year. After 3 years of operation, the pore size increases by more than 10%, and the pressure drop is more than 30%.

[0114] Tritium permeability: The intrinsic tritium permeability of 316H stainless steel is three orders of magnitude higher than that of silicon nitride ceramics, and the risk of radioactive tritium leakage is significantly higher than that of ceramic barriers.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A porous electrically insulating ceramic barrier for a magnetic confinement fusion reactor, wherein the ceramic barrier is used in a liquid metal loop safety release device, characterized in that, Along the flow direction of the liquid metal, the ceramic barrier comprises: A first porous layer, the first porous layer having a first interconnected pore; A second porous layer is disposed on one side of the first porous layer. The second porous layer has a second interconnecting pore, and the average pore diameter of the second interconnecting pore is smaller than the average pore diameter of the first interconnecting pore. A third porous layer is disposed on the side of the second porous layer away from the first porous layer. The third porous layer has a third interconnecting pore, and the average pore diameter of the third interconnecting pore is smaller than the average pore diameter of the second interconnecting pore. A tritium-blocking coating is disposed on the surface of the first porous layer away from the second porous layer; An edge densification region is provided at the edge of the ceramic barrier and extends along the flow direction of the liquid metal. A metallization layer and an electroplating layer are sequentially provided on the surface of the edge densification region. The average pore size of the first porous layer is 5μm~10μm, the thickness of the first porous layer is 0.5mm~1.0mm, and the maximum pore size of the first porous layer is ≤1.1 times the average pore size of the first porous layer; The average pore size of the second porous layer is 3μm~5μm, the thickness of the second porous layer is 0.5mm~1.0mm, and the maximum pore size of the second porous layer is ≤1.1 times the average pore size of the second porous layer; The average pore size of the third porous layer is 2μm~2.5μm, the thickness of the third porous layer is 1mm~1.5mm, and the maximum pore size of the third porous layer is ≤1.1 times the average pore size of the third porous layer; The overall porosity of the ceramic barrier is 30%~35%, and the closed-pore rate is <3%.

2. The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to claim 1, characterized in that, The ceramic barrier has a volume resistivity ≥1×10⁻⁶ at 300℃. 14 Ω cm.

3. The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to claim 1, characterized in that, The radial width of the edge densification region on one side is 6mm~8mm; The density of the edge densification region is ≥99.3%.

4. The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to claim 1, characterized in that, The thickness of the metallization layer is 50μm~70μm; The metallization layer is made of a Mo-Mn mixture; The thickness of the electroplated layer is 5μm~8μm; The material of the electroplated layer is selected from at least one of nickel and gold.

5. The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to any one of claims 1 to 4, characterized in that, The materials of the first porous layer, the second porous layer and the third porous layer are each independently selected from at least one of silicon nitride and silicon carbide.

6. The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors according to any one of claims 1 to 4, characterized in that, The thickness of the tritium-blocking coating is 30μm~40μm; The tritium-blocking coating is a composite coating containing boron nitride nanoparticles.

7. A method for preparing a porous electrically insulating ceramic barrier for a magnetically confined fusion reactor according to any one of claims 1 to 6, characterized in that, include: (1) The ceramic powder and sintering aid are mixed and ball-milled, and the first granulated powder, the second granulated powder and the third granulated powder are prepared by spray granulation technology, wherein the particle size of the first granulated powder is larger than the particle size of the second granulated powder, and the particle size of the second granulated powder is larger than the particle size of the third granulated powder. (2) The first granulated powder, the second granulated powder and the third granulated powder are respectively filled into the mold in layers. Each layer is compacted by vertical vibration, and the interlayer bonding surface is roughened to obtain the first green body. (3) A densifying agent is coated on the edge region of the first green blank to obtain a second green blank; (4) The second green body is subjected to cold isostatic pressing to obtain the third green body; (5) The third green body is placed in a gas pressure sintering furnace for the first sintering to obtain the first porous green body structure; (6) The first porous blank structure is processed to a preset size; (7) Apply metallization paste to the densified edge region of the first porous preform structure and perform a second sintering to form a metallization layer; (8) Electroplating is performed on the surface of the metallized layer to form an electroplated layer, thereby obtaining a second porous preform structure; (9) A tritium barrier coating is deposited on the liquid metal-facing side of the second porous preform structure to obtain the ceramic barrier.

8. The method according to claim 7, characterized in that, The particle size D50 of the first granulated powder is 6μm~7μm, the particle size range of the first granulated powder is 5μm~10μm, and the D90 / D10 of the first granulated powder is <1.5; The particle size D50 of the second granulated powder is 3.5μm~4μm, the particle size range of the second granulated powder is 3μm~5μm, and the D90 / D10 of the second granulated powder is <1.5; The particle size D50 of the third granulated powder is 2.2μm~2.5μm, the particle size range of the third granulated powder is 2μm~3μm, and the D90 / D10 of the third granulated powder is <1.

5.

9. The method according to claim 7, characterized in that, In step (1), the ceramic powder is selected from at least one of silicon nitride and silicon carbide; Based on a total mass of 100 wt% for the ceramic powder and the sintering aid, the amount of the sintering aid added is 3 wt% to 11 wt%. The sintering aid includes at least one of a Y2O3-Al2O3 mixture and a B4C-C mixture.

10. The method according to any one of claims 7 to 9, characterized in that, In step (3), the densifying agent is a Y2O3-Al2O3-SiO2 densifying agent with added hexagonal boron nitride as a thickener; In step (4), cold isostatic pressing is performed under a pressure of 180MPa~220MPa; In step (5), the temperature for the first sintering is 1800℃~2100℃ and the time is 2h~3h.

11. The method according to any one of claims 7 to 9, characterized in that, In step (7), the metallization slurry comprises 72wt%~78wt% Mo, 12wt%~15wt% Mn, 5wt%~8wt% borosilicate glass phase and 5wt%~5.5wt% organic binder; The second sintering temperature is 1420℃~1440℃, and the time is 10min~12min.

12. A safety relief device for a liquid metal circuit, characterized in that, The porous electrically insulating ceramic barrier for magnetic confinement fusion reactors as described in any one of claims 1 to 6, or the porous electrically insulating ceramic barrier for magnetic confinement fusion reactors prepared by any one of claims 7 to 11, wherein the pore size gradient of the porous electrically insulating ceramic barrier decreases in the same direction as the liquid metal flow direction, and the first porous layer faces the liquid metal circuit.

13. The liquid metal circuit safety relief device according to claim 12, characterized in that, The magnetically confined fusion reactor uses a porous electrically insulating ceramic barrier positioned between the liquid metal loop and the inert gas chamber.

14. The liquid metal circuit safety relief device according to claim 12 or 13, characterized in that, The liquid metal is a Pb-17Li eutectic alloy; The safety relief device is a dynamic differential pressure tracking safety relief device.

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