Nuclear reactor fuel

Abstract

A nuclear fuel system (210), a nuclear fuel particle (100), and a method of operating the nuclear fuel system are disclosed. The nuclear fuel system includes a matrix (130) material and a plurality of fuel particles (100) disposed within the matrix material, each fuel particle comprising a fuel kernel (110) and a fuel coating (120) overlying a surface of the fuel kernel. The fuel kernel comprises a fissile material comprising one or more of uranium-233, uranium-235, or plutonium-239. The fuel coating is functionally graded in density. The density of the fuel coating increases along an outward radial direction relative to a center of the fuel kernel. The fuel coating comprises a neutron moderating material. A volume fraction of the fuel particles is 35 percent or greater of the volume of the nuclear fuel compact.

Description

Technical Field

[0001] The present disclosure generally relates to nuclear reactors and, more specifically, to particle fuel forms.

Background Art

[0002] The desire for global energy growth and to reduce pollution and emissions has stimulated new activities surrounding the commercialization and design of new reactor technologies. Some of these technologies include reactors designed to operate at high temperatures and use coated particle fuels to support high temperature performance. Coated particle fuel designs often use three layers of coating, often referred to as tri-isotropic (TRISO) fuel. These coatings often include an inner graphite layer, a silicon carbide layer, and an outer graphite layer. These layers are included to retain fission products. The different materials used on each particle introduce manufacturing complexity and cost.

Summary of the Invention

Means for Solving the Problems

[0003] Techniques for the fabrication and use of functionally graded coated particle fuels are disclosed. The disclosed techniques can simplify the fabrication of nuclear particle fuels, reduce costs, and increase the fissile density. Exemplary fuel particles include a single porous coating around a fuel kernel. Many particles can be placed within a matrix that provides retention of fission products.

[0004] In an exemplary implementation, a nuclear fuel system includes a matrix material and a plurality of fuel particles disposed within the matrix material. Each fuel particle includes a fuel kernel and at least one fuel coating covering the surface of the fuel kernel.

[0005] In aspects combinable with the exemplary implementation, the fuel kernel includes a fissile material.

[0006] In another aspect that can be combined with any of the aforementioned aspects, the fissile material comprises one or more of uranium-233, uranium-235, or plutonium-239, uranium oxide, uranium oxycarbide, uranium nitride, uranium silicide, or uranium boride.

[0007] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating is functionally stepped in density.

[0008] In another aspect that can be combined with any of the aforementioned aspects, the density of at least one fuel coating increases along the outward radial direction with respect to the center of the fuel core.

[0009] In another aspect that can be combined with any of the aforementioned aspects, the surface includes the entire surface of the fuel core.

[0010] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating is fabricated using a chemical deposition method or a discharge plasma sintering method.

[0011] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating includes a neutron moderator.

[0012] In another aspect that can be combined with any of the aforementioned aspects, the neutron moderator material comprises one or more of graphite or beryllium.

[0013] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating comprises CERCER material.

[0014] In another aspect that can be combined with any of the aforementioned aspects, the CERCER material comprises one or more borides, nitrides, or silicides.

[0015] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating includes an inner layer and an outer layer.

[0016] In another aspect that can be combined with any of the aforementioned aspects, the outer layer contains the same material composition as the matrix material.

[0017] In another aspect that can be combined with any of the aforementioned aspects, the inner layer comprises a material having a lower density compared to the density of the outer layer material.

[0018] In another aspect that can be combined with any of the aforementioned aspects, the material of the inner layer includes at least one of graphite, silicon carbide, niobium carbide, hafnium carbide, tantalum carbide, titanium carbide, or zirconium carbide.

[0019] In another aspect that can be combined with any of the aforementioned aspects, the material of the inner layer comprises at least one of hafnium nitride, boron nitride, titanium nitride, or zirconium nitride.

[0020] In another aspect that can be combined with any of the aforementioned aspects, the material of the inner layer comprises at least one of hafnium boride, niobium boride, titanium boride, or zirconium boride.

[0021] In another aspect that can be combined with any of the aforementioned aspects, the matrix material is fabricated using a discharge plasma sintering method.

[0022] In another aspect that can be combined with any of the aforementioned aspects, the matrix material comprises one or more of silicon carbide, niobium carbide, hafnium carbide, tantalum carbide, titanium carbide, or zirconium carbide.

[0023] In another aspect that can be combined with any of the aforementioned aspects, the matrix material includes a neutron moderating material.

[0024] In another side that can be combined with any of the previous sides, at least one fuel coating and the matrix material are materially compatible.

[0025] Another side that can be combined with any of the previous sides further includes a nuclear fuel compact manufactured via discharge plasma sintering, and a plurality of fuel particles and matrix material are disposed within the nuclear fuel compact.

[0026] In another side that can be combined with any of the previous sides, the volume fraction of the fuel particles is at least 35 percent of the volume of the nuclear fuel compact.

[0027] In another side that can be combined with any of the previous sides, the volume fraction of the fuel particles is at least 50 percent of the volume of the nuclear fuel compact.

[0028] In another side that can be combined with any of the previous sides, the fuel kernel includes at least one of an oxide, carbide, oxycarbide, boride, or nitride.

[0029] In another side that can be combined with any of the previous sides, at least one fuel coating covering the surface of the fuel kernel includes a single coating layer including a porous material.

[0030] In another exemplary implementation, the nuclear fuel particle includes a fuel kernel and at least one fuel coating covering the surface of the fuel kernel.

[0031] In a side that can be combined with the exemplary implementation, the fuel kernel includes a fissile material.

[0032] In another side that can be combined with any of the previous sides, the fissile material includes one or more of uranium 233, uranium 235, or plutonium 239.

[0033] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating is functionally stepped in density.

[0034] In another aspect that can be combined with any of the aforementioned aspects, the density of at least one fuel coating increases along the outward radial direction with respect to the center of the fuel core.

[0035] In another aspect that can be combined with any of the aforementioned aspects, the surface includes the entire surface of the fuel core.

[0036] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating is fabricated using a chemical deposition method or a discharge plasma sintering method.

[0037] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating includes a neutron moderator.

[0038] In another aspect that can be combined with any of the aforementioned aspects, the neutron moderator material comprises one or more of graphite or beryllium.

[0039] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating comprises CERCER material.

[0040] In another aspect that can be combined with any of the aforementioned aspects, the CERCER material comprises one or more borides, nitrides, or silicides.

[0041] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating includes an inner layer and an outer layer.

[0042] In another aspect that can be combined with any of the aforementioned aspects, the outer layer contains the same material composition as the matrix material surrounding the nuclear fuel particles.

[0043] In another aspect that can be combined with any of the aforementioned aspects, the inner layer comprises a low-density material having a lower density compared to the outer layer.

[0044] In another aspect that can be combined with any of the aforementioned aspects, the low-density material comprises at least one of graphite, silicon carbide, or zirconium carbide.

[0045] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating is materially compatible with the matrix material surrounding the nuclear fuel particles.

[0046] In another aspect that can be combined with any of the aforementioned aspects, the fuel core comprises at least one of oxides, carbides, oxycarbides, borides, or nitrides.

[0047] In another aspect that can be combined with any of the aforementioned aspects, at least one fuel coating covering the surface of the fuel core includes a single coating layer containing a porous material.

[0048] In another exemplary implementation, the method includes facilitating a nuclear fission process using multiple nuclear fuel elements, generating heat from the nuclear fission process, and using the heat generated from the nuclear fission process to produce electricity. Each of the multiple nuclear fuel elements includes a matrix material and a plurality of fuel particles arranged within the matrix material, and each fuel particle includes a fuel core and at least one fuel coating covering the surface of the fuel core.

[0049] In another exemplary implementation, a method for fabricating a nuclear fuel element includes using a sol-gel process to form a plurality of fuel particles, drying the fuel particles, calcining the fuel particles, sintering the fuel particles, coating the fuel particles with a fuel coating, filling the coated fuel particles into a matrix material, and sintering the coated fuel particles in the matrix material to form a nuclear fuel element.

[0050] Aspects that can be combined with exemplary implementations further include coating nuclear fuel elements in fuel element coating.

[0051] The functionally stepwise coated particle fuel implementations described herein can result in one or more of the following advantages. For example, the use of a single or two coating layers can simplify the production of the particle fuel and reduce its cost compared to particle fuel containing three layers. In some examples, the reduced number of coating layers can increase fissile density and improve the efficiency of power generation. In some examples, a single coating can be used around the fuel core, and the fuel particles can be placed within a matrix that provides retention of fission products. Thus, proper retention of fission products can be achieved with a reduced number of coating layers. Coated fuel particles with low-density coatings can be implemented to adapt to fission gases and fuel expansion. The disclosed systems and techniques allow for a better fuel particle filling fraction than other approaches because the minimum spacing between particles can be reduced. In addition, the disclosed systems and techniques can also be implemented to adapt to larger fuel particle sizes.

[0052] Details of one or more implementations of the subject matter described herein are described in the accompanying drawings and the following description. Other features, aspects, and advantages of the subject matter will be evident from this description, drawings, and claims. This specification also provides, for example, the following: (Item 1) A nuclear fuel system, wherein the nuclear fuel system is Matrix material and, A plurality of fuel particles arranged in the matrix material Equipped with, Each fuel particle is Fuel nuclei and, At least one fuel coating covering the surface of the fuel core and A nuclear fuel system equipped with these features. (Item 2) The nuclear fuel system described in item 1, wherein the fuel core comprises a fissile material. (Item 3) The nuclear fuel system according to item 2, wherein the fissile material comprises one or more of uranium-233, uranium-235, or plutonium-239, uranium oxide, uranium oxycarbide, uranium nitride, uranium silicide, or uranium boride. (Item 4) The nuclear fuel system according to any one of items 1-3, wherein the at least one fuel coating is functionally stepped in density. (Item 5) The nuclear fuel system according to any one of items 1-4, wherein the density of the at least one fuel coating increases along the outward radial direction with respect to the center of the fuel core. (Item 6) The nuclear fuel system according to any one of items 1-5, wherein the surface comprises the entire surface of the fuel core. (Item 7) The nuclear fuel system according to any one of items 1-6, wherein the at least one fuel coating is fabricated using a chemical deposition method or a discharge plasma sintering method. (Item 8) The nuclear fuel system according to any one of items 1-7, wherein the at least one fuel coating comprises a neutron moderator. (Item 9) The nuclear fuel system according to item 8, wherein the neutron moderator material comprises one or more of graphite or beryllium. (Item 10) The nuclear fuel system according to any one of items 1-9, wherein the at least one fuel coating comprises CERCER material. (Item 11) The nuclear fuel system according to item 10, wherein the CERCER material comprises one or more of borides, nitrides, or silicides. (Item 12) The nuclear fuel system according to any one of items 1-11, wherein the at least one fuel coating comprises an inner layer and an outer layer. (Item 13) The nuclear fuel system according to item 12, wherein the outer layer has the same material composition as the matrix material. (Item 14) The nuclear fuel system according to any one of items 12-13, wherein the inner layer comprises a material having a lower density compared to the density of the material of the outer layer. (Item 15) The nuclear fuel system according to item 14, wherein the material of the inner layer comprises at least one of graphite, silicon carbide, niobium carbide, hafnium carbide, tantalum carbide, titanium carbide, or zirconium carbide. (Item 16) The nuclear fuel system according to item 14, wherein the material of the inner layer comprises at least one of hafnium nitride, boron nitride, titanium nitride, or zirconium nitride. (Item 17) The nuclear fuel system according to item 14, wherein the material of the inner layer comprises at least one of hafnium boride, niobium boride, titanium boride, or zirconium boride. (Item 18) The matrix material is fabricated using a discharge plasma sintering method, as described in any one of items 1-17 of the nuclear fuel system. (Item 19) The nuclear fuel system according to any one of items 1-18, wherein the matrix material comprises one or more of silicon carbide, niobium carbide, hafnium carbide, tantalum carbide, titanium carbide, or zirconium carbide. (Item 20) The nuclear fuel system according to any one of items 1-19, wherein the matrix material comprises a neutron moderator. (Item 21) The nuclear fuel system according to any one of items 1-20, wherein the at least one fuel coating and the matrix material are materially compatible. (Item 22) A nuclear fuel system according to any one of items 1-21, further comprising a nuclear fuel compact manufactured by discharge plasma sintering, wherein the plurality of fuel particles and the matrix material are arranged within the nuclear fuel compact. (Item 23) The nuclear fuel system according to item 22, wherein the volume fraction of fuel particles is 35 percent or more of the volume of the nuclear fuel compact. (Item 24) The nuclear fuel system according to item 22, wherein the volume fraction of fuel particles is 50 percent or more of the volume of the nuclear fuel compact. (Item 25) The nuclear fuel system according to item 1, wherein the fuel core comprises at least one of oxides, carbides, oxycarbides, borides, or nitrides. (Item 26) The nuclear fuel system according to item 1, wherein the at least one fuel coating covering the surface of the fuel core comprises a single coating layer having a porous material. (Item 27) Nuclear fuel particles, wherein the nuclear fuel particles are Fuel nuclei and, At least one fuel coating covering the surface of the fuel core and Nuclear fuel particles possessing these properties. (Item 28) The aforementioned fuel core is a nuclear fuel particle as described in item 27, comprising a fissile material. (Item 29) The nuclear fuel particle according to item 28, wherein the fissile material comprises one or more of uranium-233, uranium-235, or plutonium-239. (Item 30) The nuclear fuel particles according to any one of items 27-29, wherein the at least one fuel coating is functionally stepped in density. (Item 31) The density of the at least one fuel coating increases along the outward radial direction with respect to the center of the fuel core, as described in any one of items 27-30, for the nuclear fuel particles. (Item 32) The nuclear fuel particle according to any one of items 27-31, wherein the surface comprises the entire surface of the fuel core. (Item 33) The nuclear fuel particles according to any one of items 27-32, wherein the at least one fuel coating is fabricated using a chemical deposition method or a discharge plasma sintering method. (Item 34) The at least one fuel coating comprises a neutron moderator, the nuclear fuel particles according to any one of items 27-33. (Item 35) The neutron moderator material comprises one or more of graphite or beryllium, as described in item 34, for the nuclear fuel particles. (Item 36) The nuclear fuel particles according to any one of items 27-35, wherein the at least one fuel coating comprises CERCER material. (Item 37) The CERCER material comprises one or more of borides, nitrides, or silicides, as described in item 36. (Item 38) The aforementioned at least one fuel coating comprises an inner layer and an outer layer, as described in any one of items 27-37, for nuclear fuel particles. (Item 39) The nuclear fuel particle according to item 38, wherein the outer layer has the same material composition as the matrix material surrounding the nuclear fuel particle. (Item 40) The nuclear fuel particles according to item 39, wherein the inner layer comprises a low-density material having a lower density compared to the outer layer. (Item 41) The nuclear fuel particle according to item 40, wherein the low-density material comprises at least one of graphite, silicon carbide, or zirconium carbide. (Item 42) The nuclear fuel particle according to any one of items 27-41, wherein the at least one fuel coating is materially compatible with the matrix material surrounding the nuclear fuel particle. (Item 43) The nuclear fuel particle according to any one of items 27-42, wherein the fuel core comprises at least one of oxides, carbides, oxycarbides, borides, or nitrides. (Item 44) The nuclear fuel particle according to any one of items 27-43, wherein the at least one fuel coating covering the surface of the fuel core comprises a single coating layer having a porous material. (Item 45) A method, wherein the said method is Using multiple nuclear fuel elements to accelerate the nuclear fission process, The process of generating heat from the nuclear fission process, To produce electricity using the heat generated from the nuclear fission process Includes, Each of the aforementioned plurality of nuclear fuel elements is Matrix material and, A plurality of fuel particles arranged in the matrix material Equipped with, A method wherein each fuel particle comprises a fuel core and at least one fuel coating covering the surface of the fuel core. (Item 46) A method for manufacturing nuclear fuel elements, wherein the method is Forming multiple fuel particles using a sol-gel process, Drying the fuel particles, The combustion of the aforementioned fuel particles, Sintering the aforementioned fuel particles, Coating the fuel particles with a fuel coating, The coated fuel particles are filled into the matrix material, The coated fuel particles in the matrix material are sintered to form the nuclear fuel element. Methods that include... (Item 47) The method according to item 46, further comprising coating the nuclear fuel element in the fuel element coating. [Brief explanation of the drawing]

[0053] [Figure 1] Figure 1 provides a schematic illustration of an exemplary implementation of coated fuel particles according to the present disclosure.

[0054] [Figure 2] Figures 2A and 2B are schematic illustrations showing top cross-sectional views of exemplary implementations of the coated particle fuel compact according to the present disclosure.

[0055] [Figure 3] Figures 3A and 3B are schematic illustrations showing a side section view of an exemplary implementation of a coated particle fuel compact according to the present disclosure.

[0056] [Figure 4] Figure 4 is a flowchart illustrating an exemplary process for manufacturing a fuel element according to this disclosure. [Modes for carrying out the invention]

[0057] Embodiments of the present disclosure are described in detail herein with reference to the drawings, which are provided as illustrative examples of embodiments of the invention to enable those skilled in the art to practice the exemplary embodiments. In particular, the drawings and examples are not intended to limit the scope of the present disclosure to a single embodiment, and other embodiments are possible by the replacement of some or all of the elements described or illustrated. Furthermore, where any element of the present disclosure can be implemented in part or in whole using known components, only those parts of such known components necessary for understanding the present disclosure will be described, and detailed descriptions of other parts of such known components will be omitted so as not to obscure the exemplary embodiments.

[0058] The global energy increase and the desire to reduce pollution and emissions are stimulating new activity surrounding the commercialization and design of new reactor technologies. Some of these technologies include reactors that operate at high temperatures and are designed to use coated particle fuel to support high-temperature performance. Coated particle fuel designs can often use three layers of coating, often referred to as triple isotropic (TRISO) fuel. These coatings can include an inner graphite layer, a silicon carbide layer, and an outer graphite layer. These layers are included to hold fission products. Different materials used on each particle introduce complexity and cost in fabrication. To simplify fabrication, reduce costs, and increase fission density, a single coating can be used around the fuel, and the particles are placed within a matrix that provides retention of fission products.

[0059] Figure 1 is a schematic illustration of an exemplary implementation of coated fuel particles 100 according to the present disclosure. A reactor may contain fuel comprising fissile material such as uranium-233, uranium-235, or plutonium-239. The fissile material may be in the form of fuel nuclei 110. The fuel nuclei 110 may be, for example, a spherical nucleus of fissile material. The fuel nuclei 110 are coated in a fuel coating 120 comprising one or more layers 121, 122 of porous coating material surrounding the fuel. A matrix material 130 surrounds the coated fuel particles 100.

[0060] The reactor can be cooled by a coolant such as a gas, supercritical fluid, or liquid. The fissile material can be contained within a fuel compact or fuel element, and the fuel element can be held inside the reactor vessel.

[0061] The fissile material can be an oxide, carbide, oxycarbide, boride, or nitride. When a boride is used, boron can be isotope-enriched within isotope boron 11. The fuel core 110 can have a radius 115 of, for example, 0.03 centimeters (cm) or more, 0.10 cm or more, or 0.2 cm or more.

[0062] The fuel core 110 is surrounded by a fuel coating 120, which includes one or more coating layers 121, 122. The fuel coating 120 functions as a porous buffer layer between the fuel core 110 and the matrix material 130. The fuel coating 120 can have a thickness 123 of, for example, 0.01 cm or less, 0.02 cm or less, or 0.03 cm or less.

[0063] In some implementations, the fuel coating 120 includes a single coating layer having a porous material. In some implementations, the single coating layer has a uniform material composition.

[0064] In some implementations, the fuel coating 120 includes an inner layer 121 and an outer layer 122. In some implementations, the fuel coating 120 may include an additional coating layer between the inner layer 121 and the outer layer 122. In some implementations, each coating layer 121, 122 has a different material composition from each other.

[0065] In some implementations, the inner layer 121 is formed from a low-density material such as graphite, silicon carbide, or zirconium carbide to accommodate fuel expansion and fission gas release.

[0066] In some implementations, the outer layer 122 has the same material composition as the matrix material. In some examples, the fuel coating 120 and the matrix material 130 are materially compatible. For example, the outer layer 122 may include a material that is physically and chemically compatible with the matrix material 130 at high temperatures (e.g., 1,500°C to 3,000°C, and optionally above 3,000°C). A compatible material may, for example, be resistant to oxidation and corrosion when in contact.

[0067] In some examples, the fuel coating 120 may include materials made from borides, nitrides, or silicides. In some examples, the materials of the fuel coating 120 may be combined as ceramic particles (e.g., CERCER material) dispersed within a ceramic matrix.

[0068] The fuel coating 120 can be functionally graded in terms of density. Density is described herein in terms of relative density. Relative density can be defined as the ratio of the volume of the solid material to the total volume of the material. Relative density can be expressed in terms of void volume fraction, for example, the ratio of the volume of voids to the total volume of the material. This means that the sum of the void fraction and the relative density is 100 percent, in relation to the porosity or void fraction of the material. For example, a material with a void fraction of 70 percent can be described as having a density of 30 percent.

[0069] Functionally stepped coating materials can have diverse compositions and structures. For example, a functionally stepped fuel coating 120 may be denser near its outer surface, with the density gradually decreasing along the inward radial direction. The inward radial direction can be defined as the direction from the outer surface of the fuel coating 120 toward the center 125 of the fuel core 110. In some implementations, the density decreases almost linearly along the inward radial direction through the fuel coating 120. In some implementations, the density decreases stepwise along the inward radial direction through the fuel coating 120.

[0070] Therefore, the portion of the fuel coating 120 closer to the fuel core 110 is generally less dense than the portion of the fuel coating 120 further away from the fuel core 110. The lower-density material of the fuel coating 120 adjacent to the fuel core 110 can adapt to fission gases and fuel expansion.

[0071] A functionally stepped coating can have a density ranging, for example, from about 30 percent to about 70 percent. In an exemplary implementation, the internal portion of the fuel coating 120 (e.g., the portion closest to the fuel core 110) has a density of 30 percent or more, while the external portion of the fuel coating 120 (e.g., the portion furthest from the fuel core 110) has a density of 70 percent or less.

[0072] In some implementations, one or more of the coating layers surrounding the fuel core 110 may have a specific density such that the density is uniform throughout the coating layer. For example, the inner layer 121 may have a first density, and the outer layer 122 may have a second density greater than the first density.

[0073] In some implementations, one or more coating layers around the fuel core 110 may have stepped densities within the coating layers. For example, within the inner layer 121, the density may increase along the outward radial direction. Similarly, within the outer layer 122, the density may increase along the outward radial direction. The outward radial direction can be defined as the direction from the center 125 of the fuel core 110 toward the outer surface of the fuel coating 120.

[0074] In some implementations, the fuel coating 120 may include at least one coating layer having a uniform density and at least one coating layer having a stepped density. For example, the inner layer 121 may have a uniform density, and the outer layer 122 may have a density that increases along the outward radial direction.

[0075] Figures 2A and 2B are schematic illustrations showing top cross-sectional views of exemplary implementations of coated particle fuel compacts 210 according to the present disclosure. For example, the fuel compact 210 has a solid cylindrical shape. Figure 2A shows a perspective view of the fuel compact 210 and includes a top cross-sectional view of coated fuel particles 100 within the fuel compact 210. Figure 2B shows a top cross-sectional view of the fuel compact 210. The fuel compact 210 is shown in close proximity to other fuel compacts 211, 212, 213, and 214.

[0076] Figures 3A and 3B are schematic illustrations showing exemplary side cross-sectional views of an exemplary implementation of the coated particle fuel compact 210 according to the present disclosure. Figure 3A shows a perspective view of the fuel compact 210 and includes a cross-sectional side view of the coated fuel particles 100 within the fuel compact 210. Figure 3B shows a cross-sectional side view of the fuel compact 210.

[0077] As shown in Figures 2A, 2B, 3A, and 3B, the fuel compact 210 has a cylindrical shape, but in some examples the fuel compact can have a spherical shape. In some examples the fuel compact can have an annular cylindrical shape. In some examples the fuel compact can have a rectangular prism or a cuboid shape.

[0078] The fuel compact 210 includes coated fuel particles 100 in a matrix material 130. The coated fuel particles 100 can be filled together in a volume fraction or filling fraction ranging from less than 35 percent to more than 60 percent of the fuel compact volume. In some implementations, the volume fraction of coated fuel particles 100 in the matrix material 130 is 40 percent or more (e.g., 45 percent or more, 50 percent or more, 55 percent or more).

[0079] The matrix material 130 can be fabricated, for example, by a discharge plasma sintering method and can function as a barrier against the emission of fission products. The matrix material 130 may include graphite, silicon carbide, zirconium carbide, zirconium diboride, or a combination of these materials. The matrix material 130 can have a density of approximately 75 percent to 100 percent. In some implementations, the matrix material 130 has a density of 90 percent or more (e.g., 92 percent or more, 95 percent or more, 97 percent or more). In some implementations, the matrix material 130 has a density of 90 percent or more, and the fuel compact 210 does not have a fuel element coating 220. In some implementations, the matrix material 130 has a density of less than 90 percent, and the fuel element coating 220 is applied to the fuel compact 210. The fuel element coating 220 can be completely high density, for example, having a density of 90 percent to 100 percent.

[0080] The fuel coating 120, the matrix material 130, or both may include composite materials. The fuel coating 120, the matrix material 130, or both may include composite materials to achieve desired performance characteristics such as resistance to degradation due to hydrogen or oxygen exposure. In some examples, the fuel coating 120 or the matrix material 130 may function as a fixed absorbent or a flammable toxin. In some examples, the fuel coating 120, the matrix material 130, or both may function as a moderator or may include a neutron moderator such as a metal hydride.

[0081] Figure 4 is a flow chart of an exemplary process 400 for fabricating a fuel element according to the present disclosure. Process 400 includes forming gel fuel particles using a sol-gel process (402). A sol-gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides. The process involves the conversion of monomers into a colloidal solution (sol), which serves as a precursor for separate particles or an integrated network (or gel) of a network polymer.

[0082] Process 400 comprises at least one of drying, calcining, or sintering (404) the particles. Drying is the thermal removal of (chemically unbonded) liquid moisture from a material. Drying is typically carried out by bringing a wet solid into contact with a hot combustion gas. Calcining refers to heating a solid to a high temperature in the absence of air or oxygen. Sintering is the process of compressing a material by heat or pressure at a temperature below its melting point, forming a solid mass of the material, and causing the aggregation of mineral particles into a porous and uneven mass by initial fusion caused by heat produced by the combustion of a solid fuel within the mass itself. Atoms within the material diffuse across the particle boundaries, fusing the particles together to produce a single solid piece. Sintering is carried out as a heat treatment and can increase the strength and structural integrity of the material. The drying, calcining, and sintering processes are carried out to obtain nuclei of a desired size and density.

[0083] Process 400 includes coating particles with a porous protective film (406) or filling a mold with particles and a matrix material (408). For example, in some aspects, particles can be coated separately, or particles can be placed in an uncoated matrix material. Sintering dynamics with respect to the matrix / particle interface can induce desired functional stepping, or desired functional stepping can be suppressed through sintering control so that the coating has full density around the particles. This can be done when functional stepping, such as for short-duration nuclear thermal propulsion systems using fuel particles, is not required.

[0084] The particles can be coated with a porous protective film using vapor deposition or discharge plasma sintering. Discharge plasma sintering is a sintering method that may also be known as electric field-assisted sintering, pulsed current sintering, or plasma pressure compaction. During discharge plasma sintering, heat results in the densification of the powder compact, which results in achieving improved density at lower sintering temperatures compared to conventional sintering techniques. The heat generation is internal and facilitates very high heating or cooling rates (up to 1,000 K / min). Therefore, the sintering process is generally very fast (e.g., within a few minutes).

[0085] Vapor deposition, such as chemical vapor deposition, is a vacuum deposition method used to produce high-quality and high-performance solid materials. The process can be used to produce and apply thin films. In vapor deposition, a substrate is exposed to one or more volatile precursors, which react and / or decompose on the substrate surface to produce a desired deposit. Vapor deposition can be used to deposit shape-matched films and enhance the substrate surface. Vapor deposition can be used to produce coatings with sufficient thickness and uniformity. Particles are coated with a porous protective film to produce coated fuel particles 100.

[0086] Process 400 includes the step (410) of discharging plasma sintering particles in a matrix. The matrix can be made from matrix material 130. The particles sintered in the matrix form fuel elements, such as fuel compacts 210.

[0087] Process 400 optionally includes a step (412) of coating the fuel element. For example, with respect to a fuel element accompanied by a matrix material 130 having a density of less than 90 percent, the fuel element can be coated with a completely high-density fuel element coating 220. The fuel element coating 220 may be formed from a material having a density of 100 percent or close to 100 percent, for example, a density of 95 to 100 percent. As an example, the fuel element coating may be one or more of graphite, silicon carbide, niobium carbide, hafnium carbide, tantalum carbide, titanium carbide, or zirconium carbide. The fuel element coating may also be a nitride such as hafnium nitride, boron nitride, titanium nitride, or zirconium nitride. The fuel element coating may also be a boride such as hafnium boride, niobium boride, titanium boride, or zirconium boride.

[0088] In this specification, embodiments showing individual components should not be considered limiting; rather, this disclosure is intended to encompass other embodiments including multiple identical components unless expressly described otherwise herein, and vice versa. Furthermore, the applicants do not intend that any term in this specification or claims should be considered non-generic or of a special meaning unless expressly described as such. In addition, this disclosure includes, for illustrative purposes, current and future known equivalents to known components referenced herein.

[0089] This specification includes many specific implementation details, but these should not be interpreted as limitations on the scope of any invention or claimed content, but rather as descriptions of features specific to a particular implementation of a particular invention. In the context of separate implementations, certain features described herein may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented in multiple implementations, individually or in any preferred secondary combination. Furthermore, features described above as acting in a combination and initially claimed as such, but one or more features from the claimed combination may, in some cases, be removed from that combination, and the claimed combination may be subject to secondary combinations or variations of secondary combinations.

[0090] Similarly, while actions are depicted in a specific order in the diagrams, this should not be understood as requiring that such actions be performed in a specific or sequential order shown to achieve the desired result, or that all illustrated actions be performed. In some situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the program components and systems described may generally be integrated together within a single software product or packaged within multiple software products.

[0091] Several implementations are described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of this disclosure. For example, the exemplary operations, methods, or processes described herein may include more or fewer steps than those described. Furthermore, the steps in such exemplary operations, methods, or processes may be performed in a different arrangement than those described or illustrated in the figures. Thus, other implementations are within the scope of the following claims.

Claims

1. A nuclear fuel system comprising nuclear fuel particles (100), wherein the nuclear fuel particles are Fuel nucleus (110) and, A single fuel coating layer (120) covering the surface of the fuel core and It is equipped with, A nuclear fuel system wherein the fuel coating layer comprises a porous material, the fuel coating layer is functionally stepped in density, and the void volume fraction of the fuel coating layer increases substantially linearly along the inward radial direction with respect to the center (125) of the fuel core through the fuel coating.

2. The nuclear fuel system according to claim 1, wherein the fuel core comprises a fissile material.

3. The nuclear fuel system according to claim 2, wherein the fissile material comprises one or more of uranium-233, uranium-235, or plutonium-239.

4. The nuclear fuel system according to any one of claims 1 to 3, wherein the surface comprises the entire surface of the fuel core.

5. The nuclear fuel system according to any one of claims 1 to 4, wherein the fuel coating is manufactured using a chemical deposition method or a discharge plasma sintering method.

6. The nuclear fuel system according to any one of claims 1 to 5, wherein the fuel coating comprises a neutron moderator.

7. The nuclear fuel system according to claim 6, wherein the neutron moderator comprises one or more of graphite or beryllium.

8. The nuclear fuel system according to any one of claims 1 to 7, wherein the fuel coating comprises a CERCER material.

9. The nuclear fuel system according to claim 8, wherein the CERCER material comprises one or more of borides, nitrides, or silicides.

10. The nuclear fuel system according to any one of claims 1 to 9, wherein the fuel core comprises at least one of oxides, carbides, oxycarbides, borides, or nitrides.

11. Matrix material (130), A plurality of fuel particles arranged in the matrix material The nuclear fuel system according to any one of claims 1 to 10, further comprising:

12. The nuclear fuel system according to claim 11, wherein the matrix material is manufactured using a discharge plasma sintering method.

13. The nuclear fuel system according to any one of claims 11-12, wherein the matrix material comprises one or more of silicon carbide, niobium carbide, hafnium carbide, tantalum carbide, titanium carbide, or zirconium carbide.

14. The nuclear fuel system according to any one of claims 11-13, wherein the matrix material comprises a neutron moderator.

15. The nuclear fuel system according to any one of claims 11-14, wherein the fuel coating and the matrix material are materially compatible.

16. The nuclear fuel system according to any one of claims 11-15, further comprising a nuclear fuel compact (210) manufactured by discharge plasma sintering, wherein the plurality of fuel particles and the matrix material are arranged within the nuclear fuel compact.

17. The nuclear fuel system according to claim 16, wherein the volume fraction of fuel particles is 35 percent or more of the volume of the nuclear fuel compact.

18. The nuclear fuel system according to claim 17, wherein the volume fraction of fuel particles is 50 percent or more of the volume of the nuclear fuel compact.

19. A method, wherein the said method is Using multiple nuclear fuel elements to accelerate the nuclear fission process, The process of generating heat from the nuclear fission process, To produce electricity using the heat generated from the nuclear fission process Includes, Each of the aforementioned plurality of nuclear fuel elements is Matrix material (130), A plurality of fuel particles (100) arranged in the matrix material and It is equipped with, Each fuel particle comprises a fuel core (110) and a single fuel coating layer (120) covering the surface of the fuel core. The fuel coating layer comprises a porous material, the fuel coating layer is functionally stepped in density, and the void volume fraction of the fuel coating layer increases substantially linearly along the inward radial direction with respect to the center (125) of the fuel core through the fuel coating.

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