A boron-containing spherical fuel element for high-temperature gas-cooled reactor

Abstract

The present invention discloses a boron-containing spherical fuel element for a high-temperature gas-cooled reactor, which includes a fuel zone and a fuel-free zone from the inside out; the fuel zone includes coated fuel particles and a graphite matrix; the coated fuel particles are, from the inside out, concentric UO2 cores, loose pyrolytic carbon layers, inner dense pyrolytic carbon layers, SiC layers, ZrB2 layers, and outer dense pyrolytic carbon layers; wherein the thickness of the ZrB2 layer is 5 to 20 μm; the coated fuel particles are dispersed in the graphite matrix. The boron-containing spherical fuel element for a high-temperature gas-cooled reactor in the embodiment of the present invention avoids the risk of failure of the SiC coating by coating the surface of the SiC layer in the coated fuel particles with a ZrB2 coating, and can improve the performance of the spherical fuel element. 235 U enrichment can reduce the number of fuel elements loaded and increase the fuel burnup depth at the same reactor power level, thereby enhancing the economic value of high-temperature gas-cooled reactors.

Description

Technical Field

[0001] The present invention belongs to the technical field of design of pebble bed type high temperature gas-cooled reactor fuel elements, and in particular, the present invention relates to a boron-containing spherical fuel element for a high temperature gas-cooled reactor. Background Art

[0002] A pebble-bed high-temperature gas-cooled reactor (HTGR) uses helium as a coolant and graphite as a neutron moderator. It is a fourth-generation advanced reactor type distinguished by its inherent safety. It consists of a core composed of spherical fuel elements stacked within a reactor pressure vessel. Each spherical fuel element consists of a fuel region and a fuel-free region. The fuel region is a spherical structure consisting of fuel particles dispersed within a graphite matrix. The fuel-free region is a spherical shell of a defined thickness, made of the same graphite matrix, surrounding the fuel region. There is no physical boundary between the fuel and fuel-free regions. The fuel particles are coated with a fully ceramic triple isotropically coated (TRISO) structure, with the fuel core at its center. Four coatings cover the fuel core: from the inside out, the first layer is low-density pyrolytic carbon, the second is high-density isotropic pyrolytic carbon, the third is silicon carbide, and the fourth is high-density isotropic pyrolytic carbon.

[0003] At present, the fuel core in the pebble bed high temperature gas cooled reactor fuel element is low enrichment ( 235 In order to achieve a flat core power distribution and uniform unloading burnup, a fuel circulation method is adopted in which spherical fuel elements pass through the core multiple times. If the spherical fuel elements pass through the core less frequently, the power peak will be too high and located at the top of the core active area, which is not conducive to pebble bed high-temperature gas-cooled reactors. Therefore, it is necessary to further optimize the fuel elements in existing high-temperature gas-cooled reactors. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, an embodiment of the present invention provides a boron-containing spherical fuel element for a high-temperature gas-cooled reactor.

[0005] In one aspect, an embodiment of the present invention provides a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element includes a fuel region and a fuel-free region from the inside out.

[0006] The fuel zone includes coated fuel particles and a graphite matrix;

[0007] The coated fuel particles are composed of a concentric UO2 core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer and an outer dense pyrolytic carbon layer from the inside to the outside; wherein the thickness of the ZrB2 layer is 5 to 20 μm;

[0008] The coated fuel particles are dispersed in the graphite matrix.

[0009] In the boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to the embodiment of the present invention, a ZrB2 coating of a certain thickness is applied on the SiC layer in the coating fuel particles. The ZrB2 material has a large thermal neutron absorption cross section ( 10 B thermal neutron microscopic absorption cross section is 3840 barns, 1 barn = 10 -24 cm 2 ), it can compensate for the reactivity of new fuel when the pebble bed type high temperature gas cooled reactor is initially loaded, and will be consumed preferentially as the fuel is burned up, to ensure the fuel backup reactivity of the pebble bed type high temperature gas cooled reactor during the transition cycle and the equilibrium cycle, and to meet the continuous operation of the pebble bed type high temperature gas cooled reactor.

[0010] In some embodiments of the present invention, the thickness of the ZrB2 layer is preferably 10 to 15 μm.

[0011] In some embodiments of the present invention, the boron element in the ZrB2 layer can be natural boron ( 10 B abundance is 20%), and boron enrichment can also be used.

[0012] In some embodiments of the present invention, the number of the coated fuel particles in each of the boron-containing spherical fuel elements for a high-temperature gas-cooled reactor is 10,000 to 15,000.

[0013] In some embodiments of the present invention, the UO2 core is a sphere with a diameter of 0.5 mm.

[0014] In some embodiments of the present invention, the diameter of the coated fuel particles is any one of 0.8 mm, 0.92 mm, or 1.0 mm.

[0015] Another aspect of the present invention further provides a method for preparing the above-mentioned boron-containing spherical fuel element for a high-temperature gas-cooled reactor, comprising the following steps:

[0016] (1) The UO2 core is prepared by a sol-gel process: first, U3O8 raw material powder is dissolved in nitric acid, then an organic binder is added to obtain a colloid, and then dispersed in ammonia water to obtain gel particles; then, after aging, washing, drying, and roasting, UO3 particles are obtained; finally, after reduction and sintering, dense UO2 ceramic particles are obtained;

[0017] (2) Preparation of coated fuel particles: using chemical vapor deposition to sequentially deposit a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer, and an outer dense pyrolytic carbon layer on the outside of the fuel core;

[0018] (3) Preparation of boron-containing spherical fuel elements: First, a layer of graphite powder is wrapped on the surface of the coated fuel particles and pressed to obtain a fuel area core ball; then, another layer of graphite powder is pressed on the surface of the fuel area core ball as a fuel-free area; and then, after carbonization, turning, and high-temperature purification, a boron-containing spherical fuel element is obtained.

[0019] In the method for preparing boron-containing spherical fuel elements for high-temperature gas-cooled reactors according to the embodiment of the present invention, a burnable poison ZrB2 coating is added to the fuel element, wherein the ZrB2 coating contains 10 The B isotope is a natural isotope with a large thermal neutron absorption cross-section, which can make the fuel element have a large excess reactivity. As the combustible poison is consumed, the excess reactivity is gradually released, achieving the effect of delaying the power peak and flattening the power distribution. Only a small amount of ZrB2 needs to be added to meet the reactivity control requirements.

[0020] In some embodiments of the present invention, in step (1), the organic binder is an ester compound or a mixed solution prepared by dissolving a metal alkoxide in an organic solvent such as methanol, ethanol, propanol or butanol.

[0021] In some embodiments of the present invention, in step (1), the roasting temperature is 500-600° C., and the time is 1.5-2 h; the sintering temperature is 1550-1650° C., and the time is 16-32 h.

[0022] In some embodiments of the present invention, in step (2), chemical vapor deposition of a loose pyrolytic carbon layer is performed at a temperature of 1100-1300°C for 10-30 minutes; chemical vapor deposition of an inner dense pyrolytic carbon layer is performed at a temperature of 1250-1500°C for 15-45 minutes; chemical vapor deposition of a SiC layer is performed at a temperature of 1450-1650°C for 2-5 hours; chemical vapor deposition of a ZrB2 layer is performed at a temperature of 1450-1650°C for 1-2 hours; and chemical vapor deposition of an outer dense pyrolytic carbon layer is performed at a temperature of 1250-1500°C for 15-45 minutes.

[0023] In some embodiments of the present invention, in step (3), the carbonization temperature is 750-850° C., and the time is 30-50 h; the high-temperature purification temperature is 1150-1250° C., and the time is 10-20 h.

[0024] The present invention has the following advantages and beneficial effects:

[0025] (1) The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to the embodiment of the present invention avoids the failure risk of the SiC coating by coating the surface of the SiC layer in the coating fuel particles with a ZrB2 coating, and can improve the efficiency of the spherical fuel element. 235U enrichment can reduce the number of fuel elements loaded and increase the fuel burnup depth at the same reactor power level, thereby enhancing the economic value of high-temperature gas-cooled reactors.

[0026] (2) The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to the embodiment of the present invention can reduce the number of cycles of the spherical fuel element in a pebble-bed high-temperature gas-cooled reactor, reduce the number of operations of the fuel loading and unloading system, and improve reliability. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments derived by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by persons having ordinary skills in the field to which the present invention belongs.

[0029] In one aspect, an embodiment of the present invention provides a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element includes a fuel region and a fuel-free region from the inside out.

[0030] The fuel zone includes coated fuel particles and a graphite matrix;

[0031] The coated fuel particles are composed of a concentric UO2 core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer and an outer dense pyrolytic carbon layer from the inside to the outside; wherein the thickness of the ZrB2 layer is 5 to 20 μm;

[0032] The coated fuel particles are dispersed in the graphite matrix.

[0033] In the boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to the embodiment of the present invention, a ZrB2 coating of a certain thickness is applied on the SiC layer in the coating fuel particles. The ZrB2 material has a large thermal neutron absorption cross section ( 10 B thermal neutron microscopic absorption cross section is 3840 barns, 1 barn = 10 -24 cm 2 ), can compensate for the reactivity of new fuel when the pebble bed type high temperature gas cooled reactor is initially loaded, and will be consumed preferentially as the fuel is consumed, so as to ensure the fuel backup reactivity of the pebble bed type high temperature gas cooled reactor during the transition cycle and the balance cycle, and meet the continuous operation of the pebble bed type high temperature gas cooled reactor; and the boron-containing spherical fuel element for the high temperature gas cooled reactor according to the embodiment of the present invention can improve the 235U enrichment can achieve the purpose of increasing fuel consumption and improving the economy of pebble bed high temperature gas-cooled reactor; and zirconium boride (ZrB2) is also commonly used as a neutron burnable poison in commercial pressurized water reactors, with rich application experience.

[0034] The present invention adopts reasonable design and preferably coats the surface of the SiC layer with a burnable poison ZrB2 coating, rather than directly mixing UO2 and ZrB2 as the fuel core of the coated fuel particles. This is mainly because ZrB2 will produce helium when irradiated by neutrons (as shown in formula (1): 10 B absorbs neutrons to produce (n, α) reaction, producing lithium and helium). If UO2 and ZrB2 are mixed as the fuel core of the coated fuel particles, and then a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer and an outer dense pyrolytic carbon layer are sequentially deposited on the outside of the fuel core, the helium generated will cause the internal pressure of the coated fuel particles to increase due to the density of the SiC coating, bringing failure risk to the SiC coating. In the embodiment of the present invention, a ZrB2 coating is added to the surface of the SiC coating. The helium generated after neutron irradiation can be released into the outer dense pyrolytic carbon coating, and can also be further released into the graphite matrix in the spherical fuel element and released outside the spherical fuel element. Since the high-temperature gas-cooled reactor itself uses helium as a coolant, the small amount of helium released by the spherical fuel element will not affect the entire high-temperature gas-cooled reactor primary coolant system.

[0035] B+n→Li+He↑ (1)

[0036] In some embodiments of the present invention, the thickness of the ZrB2 layer is preferably 10 to 15 μm, for example, 10 μm, 11 μm, 12 μm, 12.5 μm, 14 μm, 15 μm, etc.

[0037] In some embodiments of the present invention, the boron element in the ZrB2 layer can be natural boron ( 10 B abundance is 20%), and boron enrichment can also be used.

[0038] In some embodiments of the present invention, the number of coated fuel particles in each boron-containing spherical fuel element for a high-temperature gas-cooled reactor is 10,000 to 15,000.

[0039] In some embodiments of the present invention, the UO2 core is a sphere with a diameter of 0.5 mm.

[0040] In some embodiments of the present invention, the diameter of the coated fuel particles is any one of 0.8 mm, 0.92 mm, or 1.0 mm.

[0041] Another aspect of the present invention further provides a method for preparing the above-mentioned boron-containing spherical fuel element for a high-temperature gas-cooled reactor, comprising the following steps:

[0042] (1) The UO2 core is prepared by a sol-gel process: first, U3O8 raw material powder is dissolved in nitric acid, then an organic binder is added to obtain a colloid, and then dispersed in ammonia water to obtain gel particles; then, after aging, washing, drying, and roasting, UO3 particles are obtained; finally, after reduction and sintering, dense UO2 ceramic particles are obtained;

[0043] (2) Preparation of coated fuel particles: using chemical vapor deposition to sequentially deposit a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer, and an outer dense pyrolytic carbon layer on the outside of the fuel core;

[0044] (3) Preparation of boron-containing spherical fuel elements: First, a layer of graphite powder is wrapped on the surface of the coated fuel particles and pressed to obtain a fuel area core ball; then, another layer of graphite powder is pressed on the surface of the fuel area core ball as a fuel-free area; and then, after carbonization, turning, and high-temperature purification, a boron-containing spherical fuel element is obtained.

[0045] In the method for preparing boron-containing spherical fuel elements for high-temperature gas-cooled reactors according to the embodiment of the present invention, a burnable poison ZrB2 coating is added to the fuel element, wherein the ZrB2 coating contains 10 The B isotope is a natural isotope with a large thermal neutron absorption cross-section, which can make the fuel element have a large excess reactivity. As the combustible poison is consumed, the excess reactivity is gradually released, achieving the effect of delaying the power peak and flattening the power distribution. Only a small amount of ZrB2 needs to be added to meet the reactivity control requirements.

[0046] In some embodiments of the present invention, in step (1), the organic binder is an ester compound or a mixed solution prepared by dissolving a metal alkoxide in an organic solvent such as methanol, ethanol, propanol or butanol.

[0047] In some embodiments of the present invention, in step (1), the calcination temperature is 500-600° C., for example, 500° C., 520° C., 550° C., 580° C., 600° C., etc.; the calcination time is 1.5-2 h, for example, 1.5 h, 1.6 h, 1.8 h, 2 h, etc.;

[0048] The sintering temperature is 1550-1650°C, for example, 1550°C, 1580°C, 1600°C, 1620°C, 1650°C, etc.; the sintering time is 16-32h, for example, 16h, 18h, 20h, 24h, 28h, 30h, 32h, etc.

[0049] In some embodiments of the present invention, in step (2), chemical vapor deposition of a loose pyrolytic carbon layer is performed at a temperature of 1100-1300°C for 10-30 minutes; chemical vapor deposition of an inner dense pyrolytic carbon layer is performed at a temperature of 1250-1500°C for 15-45 minutes; chemical vapor deposition of a SiC layer is performed at a temperature of 1450-1650°C for 2-5 hours; chemical vapor deposition of a ZrB2 layer is performed at a temperature of 1450-1650°C for 1-2 hours; and chemical vapor deposition of an outer dense pyrolytic carbon layer is performed at a temperature of 1250-1500°C for 15-45 minutes.

[0050] In some embodiments of the present invention, in step (3), the carbonization temperature is 750-850°C, for example, 750°C, 780°C, 800°C, 820°C, 835°C, 850°C, etc.; the time is 30-50h, for example, 30h, 35h, 40h, 42h, 45h, 48h, 50h, etc.

[0051] In some embodiments of the present invention, in step (3), the temperature of high-temperature purification is 1150-1250°C, for example, it can be 1150°C, 1180°C, 1200°C, 1220°C, 1250°C, etc.; the time is 10-20h, for example, it can be 10h, 12h, 15h, 18h, 20h, etc.

[0052] The technical solutions of the present invention are further described in detail below with reference to specific examples. Experimental methods without specific conditions specified in the examples are conventional methods and conventional conditions well known in the art.

[0053] Example 1

[0054] This embodiment provides a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element includes a fuel region and a fuel-free region from the inside to the outside.

[0055] The fuel zone includes coated fuel particles and a graphite matrix;

[0056] The coated fuel particles are composed of a concentric UO2 core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer and an outer dense pyrolytic carbon layer from the inside to the outside;

[0057] The boron element in the ZrB2 layer is natural boron, and the coating thickness of the ZrB2 layer is 20 μm;

[0058] The coated fuel particles are dispersed in the graphite matrix.

[0059] The method for preparing the boron-containing spherical fuel element comprises the following steps:

[0060] (1) UO2 cores were prepared using a sol-gel process: 10 g of U3O8 raw material powder was mixed with nitric acid at a molar concentration of 16 mol / L to dissolve the U3O8 raw material powder; 5 g of polyvinyl alcohol was then added and mixed to obtain a colloid; the obtained colloid was dispersed in 10 ml of 25% ammonia water to obtain gel particles; the colloid was then aged, washed, dried, and calcined at 600°C for 1.5 h to obtain UO3 particles; and finally, the sol-gel process was reduced and sintered at 1600°C for 24 h to obtain dense UO2 ceramic particles. The diameter of the UO2 core was 0.50 mm.

[0061] (2) Preparation of coated fuel particles: Using chemical vapor deposition, a loose pyrolytic carbon layer is deposited on the outside of the fuel core at 1250°C for 15 minutes; then an inner dense pyrolytic carbon layer is deposited at 1350°C for 30 minutes; then a SiC layer is deposited at 1600°C for 3 hours; then a ZrB2 layer is deposited at 1600°C for 1.5 hours; and finally an outer dense pyrolytic carbon layer is deposited at 1350°C for 30 minutes to obtain coated fuel particles with a diameter of 0.92 mm.

[0062] (3) Preparation of boron-containing spherical fuel elements: First, a layer of graphite powder is wrapped on the surface of the coated fuel particles, and the fuel core ball is pressed; then another layer of graphite powder is pressed on the surface of the fuel core ball as a fuel-free area; then, it is carbonized at 800°C for 40 hours, then turned, and finally purified at 1200°C for 15 hours to obtain a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element contains 12,000 coated fuel particles.

[0063] Example 2

[0064] This embodiment provides a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element includes a fuel region and a fuel-free region from the inside to the outside.

[0065] The fuel zone includes coated fuel particles and a graphite matrix;

[0066] The coated fuel particles are composed of a concentric UO2 core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer and an outer dense pyrolytic carbon layer from the inside to the outside;

[0067] Among them, the boron element in the ZrB2 layer is 10 The boron-enriched ZrB2 layer has a B abundance of 40% and a coating thickness of 10 μm.

[0068] The coated fuel particles are dispersed in the graphite matrix.

[0069] The method for preparing the boron-containing spherical fuel element comprises the following steps:

[0070] (1) UO2 cores were prepared using a sol-gel process: 10 g of U3O8 raw material powder was mixed with nitric acid at a molar concentration of 16 mol / L to dissolve the U3O8 raw material powder; 5 g of polyvinyl alcohol was then added and mixed to obtain a colloid; the obtained colloid was dispersed in 10 ml of 25% ammonia water to obtain gel particles; the colloid was then aged, washed, dried, and calcined at 600°C for 1.5 h to obtain UO3 particles; and finally, the sol-gel process was reduced and sintered at 1600°C for 24 h to obtain dense UO2 ceramic particles. The diameter of the UO2 core was 0.50 mm.

[0071] (2) Preparation of coated fuel particles: Using chemical vapor deposition, a loose pyrolytic carbon layer is deposited on the outside of the fuel core at 1250°C for 10 minutes; then an inner dense pyrolytic carbon layer is deposited at 1350°C for 15 minutes; then a SiC layer is deposited at 1600°C for 2 hours; then a ZrB2 layer is deposited at 1600°C for 1 hour; and finally an outer dense pyrolytic carbon layer is deposited at 1350°C for 15 minutes to obtain coated fuel particles with a diameter of 0.80 mm.

[0072] (3) Preparation of boron-containing spherical fuel elements: First, a layer of graphite powder is wrapped on the surface of the coated fuel particles, and the fuel core ball is pressed; then another layer of graphite powder is pressed on the surface of the fuel core ball as a fuel-free area; then, it is carbonized at 800°C for 40 hours, then turned, and finally purified at 1200°C for 15 hours to obtain a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element contains 15,000 coated fuel particles.

[0073] Example 3

[0074] This embodiment provides a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element includes a fuel region and a fuel-free region from the inside to the outside.

[0075] The fuel zone includes coated fuel particles and a graphite matrix;

[0076] The coated fuel particles are composed of a concentric UO2 core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer and an outer dense pyrolytic carbon layer from the inside to the outside;

[0077] Among them, the boron element in the ZrB2 layer is 10 The boron-enriched content is 60%, and the coating thickness of the ZrB2 layer is 5 μm;

[0078] The coated fuel particles are dispersed in the graphite matrix.

[0079] The method for preparing the boron-containing spherical fuel element comprises the following steps:

[0080] (1) UO2 cores were prepared using a sol-gel process: 10 g of U3O8 raw material powder was mixed with nitric acid at a molar concentration of 16 mol / L to dissolve the U3O8 raw material powder; 5 g of polyvinyl alcohol was then added and mixed to obtain a colloid; the obtained colloid was dispersed in 10 ml of 25% ammonia water to obtain gel particles; the colloid was then aged, washed, dried, and calcined at 600°C for 1.5 h to obtain UO3 particles; and finally, the sol-gel process was reduced and sintered at 1600°C for 24 h to obtain dense UO2 ceramic particles. The diameter of the UO2 core was 0.50 mm.

[0081] (2) Preparation of coated fuel particles: Using chemical vapor deposition, a loose pyrolytic carbon layer is deposited on the outside of the fuel core at 1250°C for 30 minutes; then an inner dense pyrolytic carbon layer is deposited at 1350°C for 45 minutes; then a SiC layer is deposited at 1600°C for 5 hours; then a ZrB2 layer is deposited at 1600°C for 2 hours; and finally an outer dense pyrolytic carbon layer is deposited at 1350°C for 45 minutes to obtain coated fuel particles with a diameter of 1.0 mm.

[0082] (3) Preparation of boron-containing spherical fuel elements: First, a layer of graphite powder is wrapped on the surface of the coated fuel particles, and the fuel core ball is pressed; then, another layer of graphite powder is pressed on the surface of the fuel core ball as a fuel-free zone; then, the fuel core ball is carbonized at 800°C for 40 hours, and then turned, and finally purified at 1200°C for 15 hours to obtain a boron-containing spherical fuel element for a high-temperature gas-cooled reactor. The boron-containing spherical fuel element contains 10,000 coated fuel particles.

[0083] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0084] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A boron-containing spherical fuel element for a high-temperature gas-cooled reactor, characterized in that: From the inside to the outside, it includes the fuel area and the fuel-free area; The fuel zone includes coated fuel particles and a graphite matrix; The coated fuel particles are composed of a concentric UO2 core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer and an outer dense pyrolytic carbon layer from the inside to the outside; wherein the thickness of the ZrB2 layer is 5 to 20 μm; The coated fuel particles are dispersed in the graphite matrix.

2. The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to claim 1, characterized in that: The thickness of the ZrB2 layer is 10 to 15 μm.

3. The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to claim 1 or 2, characterized in that: The boron element in the ZrB2 layer is natural boron or enriched boron.

4. The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to claim 1, characterized in that: In each of the boron-containing spherical fuel elements for a high-temperature gas-cooled reactor, the number of the coated fuel particles is 10,000 to 15,000.

5. The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to claim 1, characterized in that: The UO2 core is a sphere with a diameter of 0.5 mm.

6. The boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to claim 1, characterized in that: The diameter of the coated fuel particles is any one of 0.8 mm, 0.92 mm, or 1.0 mm.

7. The method for preparing a boron-containing spherical fuel element for a high-temperature gas-cooled reactor according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) The UO2 core is prepared by a sol-gel process: first, U3O8 raw material powder is dissolved in nitric acid, then an organic binder is added to obtain a colloid, and then dispersed in ammonia water to obtain gel particles; then, after aging, washing, drying, and roasting, UO3 particles are obtained; finally, after reduction and sintering, dense UO2 ceramic particles are obtained; (2) Preparation of coated fuel particles: using chemical vapor deposition to sequentially deposit a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer, a ZrB2 layer, and an outer dense pyrolytic carbon layer on the outside of the fuel core; (3) Preparation of boron-containing spherical fuel elements: First, a layer of graphite powder is wrapped on the surface of the coated fuel particles and pressed to obtain a fuel area core ball; then, another layer of graphite powder is pressed on the surface of the fuel area core ball as a fuel-free area; and then, after carbonization, turning, and high-temperature purification, a boron-containing spherical fuel element is obtained.

8. The method for preparing boron-containing spherical fuel elements for high-temperature gas-cooled reactors according to claim 7, characterized in that: In step (1), the roasting temperature is 500-600° C., and the time is 1.5-2 hours; the sintering temperature is 1550-1650° C., and the time is 16-32 hours.

9. The method for preparing boron-containing spherical fuel elements for high-temperature gas-cooled reactors according to claim 7, characterized in that: In step (2), a loose pyrolytic carbon layer is chemically vapor deposited for 10 to 30 minutes at a temperature of 1100 to 1300°C; an inner dense pyrolytic carbon layer is chemically vapor deposited for 15 to 45 minutes at a temperature of 1250 to 1500°C; a SiC layer is chemically vapor deposited for 2 to 5 hours at a temperature of 1450 to 1650°C; a ZrB2 layer is chemically vapor deposited for 1 to 2 hours at a temperature of 1450 to 1650°C; and an outer dense pyrolytic carbon layer is chemically vapor deposited for 15 to 45 minutes at a temperature of 1250 to 1500°C.

10. The method for preparing boron-containing spherical fuel elements for high-temperature gas-cooled reactors according to claim 7, characterized in that: In step (3), the carbonization temperature is 750-850° C., and the time is 30-50 h; the high-temperature purification temperature is 1150-1250° C., and the time is 10-20 h.