A multi-layer clad structural metal-coated fuel sphere and method of manufacture

Abstract

The present application relates to the technical fields of reactor fuel element, in particular to a kind of multilayer coating structure metal coating fuel ball and preparation method, comprising: fuel ball core, inner dense metal layer, intermediate foam metal layer and outer dense metal layer;The outer surface of the fuel ball core is sequentially coated with inner dense metal layer, intermediate foam metal layer and outer dense metal layer from inside to outside.This application effectively improves the thermal conductivity of multilayer coating structure dispersion fuel coating layer, reduces the core temperature, and the multilayer structure metal coating layer designed can effectively improve the containment capacity of coating layer to fissile gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reactor fuel elements, in particular to a multi-layer coated structure metal coated fuel sphere and a preparation method. BACKGROUND

[0002] Multi-layer coated fuel particles are widely used in high temperature gas cooled reactors, dispersion fuel elements, light water reactors and other reactors, and have excellent fission product containment capability, high inherent safety and high burnup and lifetime. By dispersing multi-layer coated fuel particles in a ceramic or metal matrix, a dispersion fuel pellet can be obtained, which can further improve the safety characteristics of the reactor. Multi-layer coated dispersion fuel has attracted widespread attention in the field of accident tolerant fuel and has become a research hotspot.

[0003] Dispersion fuel pellets are formed by dispersing fuel spheres or fuel particles in a metal or ceramic matrix with high thermal conductivity. The composite fuel has a large heat exchange area, which can effectively reduce the operating temperature of the reactor core and improve safety performance. In addition, the metal or ceramic matrix has good fission product containment capability, which can effectively reduce the release of radioactive fission products. Even in the case of cladding damage, the excellent corrosion resistance of the metal or ceramic matrix still effectively ensures the containment of fission products.

[0004] Traditional dispersion fuel pellets are formed by directly dispersing fuel spheres or fuel particles in a metal or ceramic matrix. In existing literature, UO2 particles are dispersed in a stainless steel matrix by rolling. This method has simple preparation process and controllable fuel element thickness, and is commonly used in power reactors. However, during the rolling process, UO2 particles agglomerate, and after irradiation, the fuel particles release fission gas, and the dispersion fuel has weak ability to contain fission gas, thus causing fuel particle cracks to penetrate and communicate, resulting in failure of the fuel element. In order to improve the ability of fuel particles or dispersion fuel pellets to contain fission products, the concepts of full ceramic coated dispersion fuel and metal matrix coated dispersion fuel have been proposed internationally. They are formed by dispersing TRISO particles of high temperature gas cooled reactors into ceramic or metal matrices, respectively, and preparing dispersion fuel pellets by hot pressing or isostatic pressing. This dispersion fuel pellet has the advantages of strong fission product containment capability and high thermal conductivity. However, TRISO particles are coated with ceramic materials such as loose pyrolytic carbon, dense pyrolytic carbon and SiC layer, and the loose pyrolytic carbon densifies in the irradiation environment. In the later stage of service, the structural integrity of the coating layer is difficult to maintain due to the swelling and deformation of the fuel core. In addition, due to the low plasticity of the ceramic coating layer, the coating layer cracks under large deformation conditions, thereby losing the fission product containment capability. In addition, for the loose pyrolytic carbon layer, the fuel particle cracking weakens its ability to hinder fission propagation.

[0005] In order to improve the shortcomings of TRISO particles, the prior art uses a loose SiC layer to replace the loose pyrolytic carbon layer to alleviate the reduction of gap heat transfer, the reduction of fission product containment capacity, and the poor compatibility with the nuclear core caused by the densification of the loose pyrolytic carbon layer, but the loose SiC is still a ceramic material, and the swelling process of the fuel ball causes extrusion to the loose SiC layer, resulting in damage and cracking of the loose layer. In addition, the porosity of the loose SiC layer is relatively low, and the amount of fission gas contained is less. The international optimization design for multi-layer coated fuel particles includes using a loose SiC layer to replace the loose pyrolytic carbon layer to improve the thermal conductivity of the coating layer; and using ZrC to replace the SiC layer to improve the service temperature of the multi-layer coated fuel ball.

[0006] Although ZrCl4 or ZrI4 is used as a zirconium source in the prior art, and a Zr metal coating is prepared by gas phase reduction deposition on a fluidized bed device; or a Cu and Ni metal coating is deposited on the surface of hollow glass microspheres by electroless plating to obtain hollow glass microsphere coatings with good wave absorption performance. However, they are all single metal coatings, and there is no research on multi-layer structure metal coatings on the surface of fuel balls, so it is necessary to design a multi-layer coated structure metal coating fuel ball and a preparation method to improve the shortcomings of the prior art. SUMMARY

[0007] The application discloses a multi-layer coated structure metal coating fuel ball and a preparation method thereof, and relates to the field of nuclear fuel materials.

[0008] The technical scheme of the application is as follows:

[0009] A multi-layer coated structure metal coating fuel ball, comprising a fuel ball core, an inner dense metal layer, an intermediate foam metal layer, and an outer dense metal layer; and the outer surface of the fuel ball core is coated with the inner dense metal layer, the intermediate foam metal layer, and the outer dense metal layer from inside to outside.

[0010] The diameter of the fuel ball core is 100-800 mu m, the fuel ball core is in a spherical shape, and the ratio of the maximum radius of the fuel ball core to the minimum radius is less than 1.2.

[0011] The thickness of the inner dense metal layer is 5-10 mu m, and the inner dense metal layer is made of metal materials including Cr, stainless steel, and Nb alloy.

[0012] The thickness of the intermediate foam metal layer is 50-100 mu m, the porosity of the foam is not less than 80%, and the intermediate foam metal layer is made of metal materials including Nb, Zr, and stainless steel alloy.

[0013] The outer dense metal layer is made of high-strength alloy material, and the thickness is 10-20 microns.

[0014] A preparation method of the multi-layer coated structure metal-coated fuel sphere, comprising the following steps:

[0015] Step one, surface treatment of the fuel sphere core before coating the metal coating, comprising: high-temperature pretreatment of the fuel sphere core, the treatment temperature is 1400-1700 DEG C, to ensure the surface smoothness of the fuel sphere core;

[0016] Step two, preparation of the multi-layer metal coating and coating the multi-layer metal coating on the surface of the fuel sphere core, the preparation of the multi-layer metal coating comprises: preparation of the inner dense metal layer, preparation of the intermediate foam metal layer and preparation of the outer dense metal layer;

[0017] The preparation of the inner dense metal layer adopts the fluidized bed chemical vapor deposition method, and the deposition temperature is 800-850 DEG C;

[0018] The preparation of the intermediate foam metal layer adopts the chemical deposition method, by increasing the deposition temperature and the deposition rate, and at the same time, inert gas is introduced in the reducing atmosphere for foaming, and then high-temperature heat treatment is carried out, to obtain the foam metal coating; the chemical deposition temperature of the foam metal material is 1000-1200 DEG C, and the H2 / Ar ratio is 1:3; the deposition time of the foam alloy is 20-30 hours;

[0019] The preparation of the outer dense metal layer adopts the chemical deposition method, and the deposition temperature is 1000-1100 DEG C;

[0020] The prepared inner dense metal layer, intermediate foam metal layer and outer dense metal layer are coated on the outer surface of the fuel sphere core from inside to outside;

[0021] Step three, size optimization screening of the fuel sphere after coating the multi-layer metal coating, comprising: the fuel sphere after coating the multi-layer metal coating is screened by using the metal mesh screening method, to obtain the multi-layer coated structure metal-coated fuel sphere with uniform size;

[0022] The mesh size of the metal mesh is customized according to different diameters of the fuel sphere; for the 100-micron fuel sphere, the mesh size is 160-200 microns; for the coated fuel sphere with strict size limit, two-stage screening method is adopted; the upper and lower limit sizes of the mesh hole of the metal mesh of the two-stage screening method are matched with the upper and lower limit requirements of the size of the coated fuel sphere.

[0023] The beneficial effects of the present application are as follows:

[0024] The multilayer metal coated fuel ball designed in the application has an inner layer of dense metal coating, an intermediate layer of foam metal coating and an outermost layer of high-strength metal coating. The main functions of the inner layer of metal coating are: 1) preventing the embrittlement of the foam metal material caused by irradiation damage; and 2) preventing the interaction between the foam metal coating and the UO2 fuel ball.

[0025] The main functions of the intermediate foam metal coating are: 1) the foam metal material can accommodate fission gas; 2) absorbing the swelling of the fuel core; 3) hindering the crack propagation to the dispersed fuel matrix; and 4) the foam metal material can effectively improve the thermal conductivity of the multilayer coated fuel.

[0026] The main functions of the outermost layer of high-strength metal coating are: 1) bearing the internal pressure of fission gas to ensure the integrity of the coated fuel ball; 2) containing fission products to prevent the release of fission products; and 3) the high-strength metal coating has certain compression and shear resistance, which is beneficial to the forming of the dispersed fuel.

[0027] Through the design of the multilayer structure metal coating layer of the application, the thermal conductivity of the multilayer coated structure dispersed fuel coating layer can be effectively improved, the core temperature can be reduced, the multilayer structure metal coating layer designed can effectively improve the containment capacity of the coating layer to fission gas, and under high burnup conditions, the foam metal coating can effectively hinder the crack propagation, thereby improving the failure behavior of the dispersed fuel. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The structure schematic diagram of the multilayer coated structure metal coating fuel ball designed in the application is shown in the figure.

[0029] Figure 2 The micrograph of the intermediate foam metal layer described in the application is shown in the figure.

[0030] Figure 3 The micrograph of the dense metal layer described in the application is shown in the figure.

[0031] 1-fuel ball core, 2-inner layer of dense metal, 3-intermediate layer of foam metal, 4-outer layer of dense metal DETAILED DESCRIPTION

[0032] The multilayer coated structure metal coating fuel ball and the preparation method thereof will be described in detail below in combination with the drawings and examples.

[0033] A multilayer coated structure metal coating fuel ball comprises: a fuel ball core 1, an inner layer of dense metal 2, an intermediate layer of foam metal 3 and an outer layer of dense metal 4; the outer surface of the fuel ball core 1 is coated with the inner layer of dense metal 2, the intermediate layer of foam metal 3 and the outer layer of dense metal 4 from inside to outside.

[0034] The fuel sphere core 1 has a diameter of 100-800 μm, and the fuel sphere core 1 is in a spherical shape, and the ratio of the maximum radius to the minimum radius of the fuel sphere core 1 is less than 1.2.

[0035] The inner dense metal layer 2 has a thickness of 5-10 μm, and the inner dense metal layer 2 is made of metal materials including Cr, stainless steel, and Nb alloy.

[0036] The intermediate foam metal layer 3 has a thickness of 50-100 μm, and a foam porosity of not less than 80%, and the intermediate foam metal layer 3 is made of metal materials including Nb, Zr, and stainless steel alloy.

[0037] The outer dense metal layer 4 is made of high-strength alloy material, has a thickness of 10-20 μm, and is made of metal materials including W, W, and Mo alloy.

[0038] A preparation method of the multi-layer coated metal-coated fuel sphere, comprising the following steps:

[0039] Step one, surface treatment of the fuel sphere core before coating the metal coating, including: high-temperature pretreatment of the fuel sphere core, and the treatment temperature is 1400-1700 °C, so as to ensure the surface smoothness of the fuel sphere core;

[0040] Step two, preparation of the multi-layer metal coating and coating of the multi-layer metal coating on the surface of the fuel sphere core, and the preparation of the multi-layer metal coating includes: preparation of the inner dense metal layer, preparation of the intermediate foam metal layer, and preparation of the outer dense metal layer;

[0041] The preparation of the inner dense metal layer is made by using the fluidized bed chemical vapor deposition method, and the deposition temperature is 800-850 °C;

[0042] The preparation of the intermediate foam metal layer is made by using the chemical deposition method, by increasing the deposition temperature and the deposition rate, and by introducing inert gas for foaming in a reducing atmosphere, and then by high-temperature heat treatment, so as to obtain the foam metal coating; the chemical deposition temperature of the foam metal material is 1000-1200 °C, and the H2 / Ar ratio is 1:3; the deposition time of the foam alloy is 20-30 h;

[0043] The preparation of the outer dense metal layer is made by using the chemical deposition method, and the deposition temperature is 1000-1100 °C;

[0044] The prepared inner dense metal layer, intermediate foam metal layer, and outer dense metal layer are coated on the outer surface of the fuel sphere core from inside to outside;

[0045] Step three, size optimization screening of fuel spheres after coating multi-layer metal coating, including: after coating multi-layer metal coating, the fuel spheres are screened by metal mesh screening method to obtain multi-layer coated metal coating fuel spheres with uniform size;

[0046] The mesh size of the metal mesh is customized for fuel spheres with different diameters; for 100 μm fuel spheres, the mesh size is 160 μm to 200 μm; for coated fuel spheres with strict size limits, a two-stage screening method is used; the upper and lower limit sizes of the mesh size of the metal mesh of the two-stage screening method match the upper and lower limit requirements of the size of the coated fuel spheres.

[0047] Example one

[0048] This example is for the specific design of the structure and material selection of the multi-layer coated metal coating fuel spheres; the fuel sphere core 1 takes UO2 fuel microspheres as the core, the core size is 500 μm, and the density of the UO2 fuel microspheres is 95% ± 1.5%; the inner dense metal layer is a Cr metal layer, the coating thickness is 10 μm, the Cr coating density is not less than 99%, the coating thickness is uniform, and the thickness deviation along the coating circumference is less than 10%; the intermediate loose metal layer is a foam metal Nb, the porosity of the foam metal layer is > 80%, and the foam metal Nb does not have closed pores, the thickness of the foam metal Nb coating is 50 μm; the outer dense metal layer is a W metal layer, the coating thickness is 10 μm, the W metal coating density is > 99%, the coating thickness is uniform, and the thickness deviation along the coating circumference is less than 10%.

[0049] Example two

[0050] The embodiment is directed to a preparation method of a multilayer coated structure metal coating. The inner dense metal layer is an inner dense Cr metal coating. The Cr metal coating is prepared by chemical vapor deposition on a fluidized bed. CrCl5 is used as the main Cr source, and H2 is introduced as a reducing atmosphere. The deposition temperature is 800°C, the molar ratio of H2 to CrCl5 is >0.5, the deposition time is >6 hours, and a Cr metal coating with a thickness of 10 μm and a porosity of less than 1% is obtained. After the Cr coating is deposited, the Cr source gas is turned off, NbCl5 gas is introduced, and H2 is introduced as a reducing gas. A foamed metal Nb coating is prepared on the fluidized bed device. The coating is obtained by rapid deposition. The deposition temperature is 1000°C, the molar ratio of H2 to CrCl5 is >0.5, the molar ratio of H2 to Ar is 1:2, the deposition time is <3 hours, and a foamed Nb metal coating with a porosity of not less than 80% and a thickness of not less than 50 μm is obtained. The outer layer is a dense W metal coating. The W metal coating is obtained by magnetron sputtering or chemical vapor deposition. A W metal plate is used as the target material. The sputtering deposition power is 3 KW. The deposition Ar gas flow rate is 70 sccm. The deposition time is 6 hours. A W metal coating with a thickness of 10 μm and a porosity of less than 1% is obtained.

[0051] Embodiment three

[0052] In the embodiment, the fuel sphere core design size is 500 μm±50 μm, the inner dense metal layer design size is 10 μm±2 μm, the intermediate foamed metal layer design size is 50 μm±10 μm, and the outermost metal layer design size is 10 μm±2 μm. After the multilayer coated structure metal coating fuel sphere coating is completed, the coated fuel sphere is size-sorted by a screen mesh method. Two-stage size sorting is used to optimize the size of the coated fuel sphere. The first stage uses a mesh size of 570 μm, and the second stage uses a mesh size of 660 μm to ensure that the coated fuel sphere size is within the design size tolerance range.

[0053] The embodiments of the application are described in detail above. The application is not limited to the above examples. Within the knowledge of those skilled in the art, various changes can be made without departing from the spirit of the application.

Claims

1. A method for preparing a multi-layered coated metal-coated fuel ball, characterized in that, The multi-layer coated metal-coated fuel ball includes: a fuel ball core (1), an inner dense metal layer (2), an intermediate foam metal layer (3), and an outer dense metal layer (4); the outer surface of the fuel ball core (1) is coated with the inner dense metal layer (2), the intermediate foam metal layer (3), and the outer dense metal layer (4) from the inside to the outside. The preparation method of multilayer coated metal fuel balls includes the following steps: Step 1: Before applying the metal coating, the fuel sphere core is surface treated, including: high-temperature pretreatment of the fuel sphere core at a temperature of 1400℃~1700℃ to ensure the surface smoothness of the fuel sphere core. Step 2: Preparation of multi-layer metal coating and coating the surface of the fuel sphere core with multi-layer metal coating. The preparation of multi-layer metal coating includes: preparation of inner dense metal layer, preparation of middle foam metal layer and preparation of outer dense metal layer. The inner dense metal layer was prepared using a fluidized bed chemical vapor deposition method at a deposition temperature of 800℃~850℃. The intermediate foam metal layer is prepared by chemical deposition, which involves increasing the deposition temperature and deposition rate while introducing an inert gas in a reducing atmosphere for foaming, followed by high-temperature heat treatment to obtain the foam metal coating. The chemical deposition temperature of the foam metal material is 1000℃~1200℃, the H2 / Ar ratio is 1:3, and the deposition time of the foam alloy is 20h~30h. The outer dense metal layer was prepared by chemical deposition at a temperature of 1000℃~1100℃. The inner dense metal layer, the middle foam metal layer and the outer dense metal layer, after being prepared, are coated on the outer surface of the fuel sphere core from the inside to the outside. Step 3: Optimization and screening of fuel ball size after coating with multiple layers of metal, including: screening the fuel balls after coating with multiple layers of metal using a metal mesh sieve to obtain fuel balls with a uniform size and a multi-layer coated structure. The metal mesh size is customized for fuel balls of different diameters; for 100μm fuel balls, the mesh size is 160μm~200μm; for coated fuel balls with strict size limits, a two-stage sieving method is adopted; the upper and lower limits of the mesh size of the metal screen in the two-stage sieving method are respectively matched to the upper and lower limit requirements of the size of the coated fuel balls.

2. The method for preparing a multi-layer coated metal-coated fuel ball according to claim 1, characterized in that: The diameter of the fuel ball core (1) is 100μm~800μm. The fuel ball core (1) is spherical in shape. The ratio of the maximum radius to the minimum radius of the fuel ball core (1) is <1.

2.

3. The method for preparing a multi-layer coated metal-coated fuel ball according to claim 2, characterized in that: The thickness of the inner dense metal layer (2) is 5μm to 10μm, and the inner dense metal layer (2) is made of metal materials including Cr, stainless steel and Nb alloy.

4. The method for preparing a multi-layer coated metal-coated fuel ball according to claim 3, characterized in that: The thickness of the intermediate foam metal layer (3) is 50μm~100μm, the foam porosity is not less than 80%, and the intermediate foam metal layer (3) is made of metal materials including alloys such as Nb, Zr and stainless steel.

5. The method for preparing a multi-layer coated metal-coated fuel ball according to claim 4, characterized in that: The outer dense metal layer (4) is a high-strength alloy material with a thickness of 10μm to 20μm. The metal material used includes W and Mo alloys.

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