Nuclear reactor fuels and related systems and methods

Abstract

Embodiments of nuclear fuel elements for various types of nuclear reactors are disclosed. One embodiment of a nuclear fuel element includes a plurality of solid nuclear fuel particles, such as tri-structure-isotropic (TRISO) fuel particles, mixed in a non-solid matrix that is substantially stagnated relative to the plurality of solid nuclear fuel particles. The non-solid matrix may include a liquid metal, a liquid metal alloy, and a liquid salt. Various embodiments of the non-solid matrix include tin, lead, sodium, aluminum, bismuth, and alloys thereof. Embodiments of a method of manufacturing a nuclear fuel and a nuclear fuel core including the nuclear fuel element are also disclosed.

Description

Citation of relevant applications

[0001] If an Application Data Sheet (ADS) or PCT Request Form (“Request”) was filed on the date of filing of this application, it is incorporated herein by reference. Any application in the ADS or Request that claims priority under 35 USC §§119, 120, 121, or 365(c), and any and all parent, grandparent, great-grandparent, etc., applications of such applications, are also incorporated by reference, including any priority claims made in those applications and any material incorporated by reference, provided that such subject matter does not conflict with this application.

[0002] In addition, this application relates to the following U.S. patent application, which is incorporated herein by reference in its entirety as if fully set forth herein: U.S. Provisional Patent Application No. 63 / 510,362 (LPF-1001P), filed June 26, 2023, entitled “Nuclear Reactor Fuel and Associated Systems and Methods,” which describes nuclear fuel cores and related methods for nuclear fission reactors. Technical Field

[0003] The embodiments of this invention belong to the field of nuclear technology. More specifically, the specific embodiments of this invention relate to nuclear fuel for various types of nuclear reactors. Background Technology

[0004] The statements in the background art are provided to help understand the invention and its applications and uses, and may not constitute prior art.

[0005] Breeder-burning nuclear fission reactors have a much higher "fuel efficiency" (total energy extracted from each initial uranium atom) than conventional fission reactors because they convert uranium into plutonium (breeding) instead of simply burning a small fraction of the uranium. This makes large fission reactors exceptionally economical and produce far less waste, while also allowing Earth's natural uranium and thorium resources to be sustained for much longer—providing the entire planet with a sustainable "clean air" energy source for hundreds of years.

[0006] However, existing fuel types used in these types of nuclear reactors have many limitations. Therefore, developing improved nuclear fuels for nuclear reactors (including but not limited to breeder reactors) would be an advancement in existing technology.

[0007] This invention was developed in response to this background. Summary of the Invention

[0008] The summary of this invention provides a broad overview of the invention, its applications and uses, and is not intended to limit the scope of the invention, which will become apparent when the detailed description is read in conjunction with the accompanying drawings.

[0009] Developing nuclear fuels for various types of nuclear reactors would be an advancement in existing technology. Therefore, implementation schemes for nuclear fuel elements for various types of nuclear reactors are disclosed.

[0010] According to a first aspect or in one embodiment, a nuclear fuel element is provided. The nuclear fuel element may comprise a plurality of solid nuclear fuel particles. Each of the plurality of solid nuclear fuel particles may comprise nuclear material. The nuclear fuel element may comprise a non-solid matrix. The plurality of solid nuclear fuel particles may be mixed in the non-solid matrix. The non-solid matrix may be substantially stationary relative to the plurality of nuclear fuel particles. The non-solid matrix may comprise a material selected from the group consisting of liquid metals, liquid metal alloys, and liquid salts.

[0011] In some implementations, multiple solid nuclear fuel particles comprise tri-structure isotropic (TRISO) particles.

[0012] In some implementations, the non-solid matrix is ​​selected from the group consisting of liquid metals and liquid metal alloys.

[0013] In some implementations, the non-solid matrix is ​​selected from the group consisting of tin, lead, sodium, aluminum, bismuth, zinc, magnesium, calcium, cerium, rubidium, zirconium, beryllium, potassium, yttrium, strontium, barium, and alloys thereof.

[0014] In some embodiments, the non-solid matrix comprises a quasi-metal. In some embodiments, the non-solid matrix also comprises an element selected from the group consisting of silicon and germanium.

[0015] In some embodiments, the non-solid matrix is ​​selected from the group consisting of tin, tin-aluminum alloy, tin-aluminum-gallium alloy, tin-zinc-aluminum alloy, tin-magnesium alloy, tin-aluminum-magnesium alloy and tin-magnesium-zinc alloy.

[0016] In some embodiments, the tin composition percentage in the non-solid matrix is ​​greater than 80% by mass fraction. In some embodiments, the tin composition percentage in the non-solid matrix is ​​greater than 90% by mass fraction.

[0017] In some implementations, the non-solid matrix is ​​selected from the group consisting of lead, lead-bismuth-tin alloys, and lead-magnesium alloys.

[0018] In some implementations, the non-solid matrix is ​​selected from the group consisting of sodium-lead alloys, sodium-lead-bismuth alloys, and sodium-bismuth alloys.

[0019] In some implementations, the non-solid matrix is ​​selected from the group consisting of lead-bismuth alloys and lead-bismuth eutectics.

[0020] In some implementations, the non-solid matrix is ​​liquid sodium.

[0021] In some implementations, the non-solid matrix is ​​liquid gallium.

[0022] In some embodiments, the non-solid matrix comprises an alloy selected from the group consisting of: alloys of tin, aluminum and gallium; alloys of tin, aluminum, lead and bismuth; alloys of lead and magnesium; alloys of aluminum and magnesium; alloys of magnesium and zinc; alloys of bismuth and sodium; and alloys of lead and sodium.

[0023] In some embodiments, the non-solid matrix comprises an alloy selected from the group consisting of: an alloy of lead and lithium; an alloy of tin and lithium; and an alloy of lead, bismuth, and lithium.

[0024] In some implementations, the non-solid matrix comprises liquid salt.

[0025] In other embodiments, the non-solid matrix further comprises a material selected from the group consisting of water, sulfur, supercritical fluids, organic liquids and inorganic liquids.

[0026] In some implementations, multiple solid nuclear fuel particles comprise tri-structure isotropic (TRISO) particles. The non-solid matrix can be selected from the group consisting of tin-aluminum alloys, tin-aluminum-gallium alloys, lead-bismuth alloys, and lead.

[0027] In some implementations, multiple solid nuclear fuel particles comprise particles selected from the group consisting of: tri-structure isotropic (TRISO) particles, bi-structure isotropic particles, and tetra-structure isotropic particles.

[0028] In some embodiments, at least one of the plurality of solid nuclear fuel particles comprises one or more materials selected from the group consisting of ceramic materials, metallic materials, carbon materials, and cermet materials.

[0029] In some implementations, at least one of the plurality of solid nuclear fuel particles contains an actinide fuel core.

[0030] In some embodiments, at least one of the plurality of solid nuclear fuel particles comprises a fuel core selected from the group consisting of UN core, UO2 core, UC core, and UCO core.

[0031] In some implementation schemes, the nuclear material is selected from the group consisting of fissile materials, transmutable materials, and proliferating materials.

[0032] In some implementations, multiple solid nuclear fuel particles contain fissile material selected from the group consisting of uranium, thorium, and plutonium.

[0033] In other embodiments, the plurality of solid nuclear fuel particles comprise transmutable or proliferating materials selected from the group consisting of thulium, thallium, gadolinium, silver, strontium, holmium, and lithium.

[0034] In some implementations, each of the multiple solid nuclear fuel particles has a diameter of less than 0.5 cm. 3 And greater than 6×10 -7 cm 3 The volume.

[0035] In some implementations, each of the plurality of solid nuclear fuel particles has a density of less than 1.5 × 10⁻⁶. -2 cm 3 And greater than 6×10 -7 cm 3 The volume.

[0036] In some implementations, the density of the non-solid matrix is ​​approximately the same as the density of multiple solid nuclear fuel particles.

[0037] In some implementations, the density of the non-solid matrix is ​​less than the density of multiple solid nuclear fuel particles.

[0038] In some other implementations, the density of the non-solid matrix is ​​greater than the density of multiple solid nuclear fuel particles.

[0039] In some implementations, nuclear fuel elements generate energy in nuclear reactors selected from the group consisting of: fast-spectrum fission reactors, thermal-spectrum fission reactors, ultrathermal-spectrum fission reactors, and fission-fusion hybrid reactors.

[0040] In some implementations, nuclear fuel elements generate energy in a nuclear reactor cooled by a coolant selected from the group consisting of liquid metal coolants, liquid salt coolants, gaseous coolants, water coolants, and heat pipes.

[0041] A nuclear fuel core for various nuclear fuel reactors is also provided. In some embodiments, the nuclear fuel core comprises a plurality of solid nuclear fuel particles, wherein each of the plurality of solid nuclear fuel particles contains nuclear material; a non-solid matrix, wherein the plurality of solid nuclear fuel particles are mixed in the non-solid matrix, the non-solid matrix being substantially stationary relative to the plurality of nuclear fuel particles, and the non-solid matrix comprising a material selected from the group consisting of liquid metals, liquid metal alloys, and liquid salts; and a plurality of coolant tubes penetrating the non-solid matrix, wherein each of the plurality of coolant tubes contains flowing coolant.

[0042] A nuclear reactor is also provided. In some embodiments, the nuclear reactor includes a power generation loop and a reactor. In some embodiments, the reactor includes nuclear fuel elements and a coolant. In some embodiments, the nuclear fuel elements include a plurality of solid nuclear fuel particles, wherein each of the plurality of solid nuclear fuel particles contains nuclear material; and a non-solid matrix. In some embodiments, the plurality of solid nuclear fuel particles are mixed in a non-solid matrix. In some embodiments, the non-solid matrix is ​​substantially stationary relative to the plurality of solid nuclear fuel particles. In some embodiments, the non-solid matrix comprises a material selected from the group consisting of liquid metals, liquid metal alloys, and liquid salts.

[0043] As shown and described herein, various nuclear fuel cores having the nuclear fuel elements described herein, as well as methods for manufacturing nuclear fuel elements, are within the scope of this invention.

[0044] Features described in the context of individual aspects and / or embodiments of the invention may be used together and / or interchangeable wherever possible. Similarly, for the sake of brevity, where features are described in the context of a single embodiment, those features may also be provided individually or in any suitable sub-combination.

[0045] Other aspects and embodiments of the invention will become apparent when the invention is read in conjunction with the accompanying drawings in its detailed description. Attached Figure Description

[0046] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the disclosed embodiments. For clarity, simplicity, and flexibility, not all elements, components, or specifications are defined in all the drawings. Not all drawings corresponding to specific steps or embodiments of the invention are drawn to scale. Rather, the focus is on illustrating the nature, function, and product of the manufacturing methods and apparatus described herein.

[0047] The embodiments of the invention described herein are exemplary and not restrictive. The embodiments will now be described by way of example with reference to the accompanying drawings, in which:

[0048] Figure 1 A fast breeder-burner or breeder nuclear reactor with a pool design is shown as an example reactor according to the prior art.

[0049] Figure 2 The filling of fuel pellets according to the prior art is shown.

[0050] Figure 3An enlarged cross-sectional view of fuel particles according to an embodiment of the present invention, a second enlarged cross-sectional view of fuel particles in a stagnant matrix, and fuel particles and a stagnant matrix filled in a fuel core are shown.

[0051] Figure 4 An enlarged cross-sectional view of a fuel core comprising fuel particles and a stagnant matrix within a containment vessel, according to an embodiment of the invention, is shown.

[0052] Figure 5 Another enlarged cross-sectional view of a fuel core comprising fuel particles and a stagnant matrix within a containment vessel, according to an embodiment of the invention, is shown.

[0053] Figure 6 This is yet another enlarged cross-sectional view of a fuel core comprising fuel particles and a stagnant matrix within a containment vessel, according to an embodiment of the invention.

[0054] Figure 7 A nuclear fuel reactor with a novel fuel core according to an exemplary embodiment of the present invention is shown.

[0055] Figure 8 Alternative embodiments of fuel pellets and stagnation matrix according to an embodiment of the present invention are shown.

[0056] Figure 9 An alternative embodiment of the fuel pellets according to an embodiment of the present invention is shown.

[0057] Figure 10 An alternative embodiment of the stagnant matrix according to an embodiment of the present invention is shown.

[0058] Figure 11 A flowchart of a method for preparing nuclear fuel according to an embodiment of the present invention is shown.

[0059] Figure 12 A photograph is shown of a batch of fuel particles mixed in a liquid stagnant matrix according to an embodiment of the present invention.

[0060] Figure 13 A photograph of a batch of fuel elements in solid form according to an embodiment of the present invention is shown.

[0061] Figure 14 A photograph of a batch of fuel elements in solid form according to an embodiment of the present invention is shown.

[0062] Figure 15 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the present invention.

[0063] Figure 16Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the present invention.

[0064] Figure 17 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the present invention.

[0065] Figure 18 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the present invention.

[0066] Figure 19 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the present invention.

[0067] Figure 20 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the present invention. Detailed Implementation

[0068] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without these specific details. Reference will now be made specifically to embodiments consistent with the invention, examples of which are illustrated in the accompanying drawings. Although the following description contains numerous details for illustrative purposes, those skilled in the art will understand that many variations and / or modifications to the suggested details are within the scope of the invention. Similarly, although many features of the invention are described by way of each other or in combination with each other, those skilled in the art will understand that many of these features may be provided independently of the others. Therefore, the description of the invention is set forth without prejudice to the generality of the invention and without imposing limitations on it.

[0069] This invention relates to a fuel design. The invention is described in conjunction with a breeder-combustion sodium-cooled fast reactor according to one embodiment. Various embodiments of the invention can be used or modified for any other type of nuclear system, including but not limited to fission reactors, fusion reactors, radioisotope energy systems, and accelerator systems.

[0070] Background of nuclear reactors

[0071] Figure 1A fast breeder-burner or breeder nuclear reactor with a pool design, according to an example reactor in the prior art, is shown. The reactor is characterized by its liquid metal coolant pool 114, typically filled with sodium or lead, which is used to cool the reactor core and facilitate heat transfer. The reactor typically contains a solid fissile fuel core 106, which is the primary source of nuclear fission. In existing designs, this core is typically composed of a mixture of breedable and fissile isotopes embedded in a solid matrix material (typically graphite). The solid fuel core 106 is immersed in the liquid metal coolant 114, which is pumped within and circulated in the reactor pool 120 by a reactor pool pump 110. The solid fuel core 106 may be surrounded by a breeder blanket 108 of breederable material, which is used to capture any escaped neutrons and convert them into additional fissile material, thereby further improving the reactor's efficiency. The fuel core may also be surrounded by a neutron reflector, which may be composed of liquid lead (Pb). Integrated within the reactor are control rods 102, which can be inserted or withdrawn to manage the fission reaction rate. These rods are made of neutron-absorbing materials, such as boron or cadmium, and their movement can be modulated to maintain the desired reactivity level within the core. Surrounding the reactor is a bio-shield 112, which may be composed of materials such as concrete or lead, and is designed to protect personnel and the environment from radiation emitted during reactor operation.

[0072] Solid fuel core 106 generates heat through a nuclear fission process, and this heat is transferred to liquid metal coolant 114 surrounding the fuel core 106. Heat exchanger 116 facilitates heat transfer from the liquid metal coolant 114 in the reactor pool 120 to the intermediate loop 122. In the power generation loop 130, the heat from the liquid metal coolant is used in steam generator 118 to generate steam 132, which powers a power turbine 134 to generate electricity. Water 136 flows back from the power turbine 134 to the steam generator 118. Flow baffles 104 can be positioned in the reactor pool 120 to facilitate coolant flow and enhance heat transfer from the fuel core 106 to the liquid metal coolant 114 within the reactor pool 120.

[0073] Figure 2The filling of fuel particles 210 according to the prior art is shown. Fuel particles 210 are filled in solid nuclear fuel briquettes 220, which are placed within solid fuel rods 230, which are subsequently arranged together with coolant tubes 244 within a solid fuel assembly 240. According to one embodiment of the invention, a tri-structure isotropic (TRISO) fuel particle 210 is shown in an enlarged three-dimensional cross-sectional view. At the core of the particle is a fuel core 218, typically composed of uranium, thorium, or plutonium. This fuel core acts as the primary source of nuclear fission. Surrounding the fuel core 218 is a porous carbon buffer layer 216. This layer is designed to absorb fission gases and alleviate stress on the outer layer caused by heat and radiation from the fuel core. Surrounding the porous carbon buffer layer 216 is one of two pyrolytic carbon layers 212. This inner pyrolytic carbon layer is dense and acts as an additional barrier against the escape of fission products. The next layer, 214, is made of silicon carbide, a material renowned for its excellent heat resistance and mechanical strength. This silicon carbide layer 214 provides a robust barrier against the release of fission products, even under extreme conditions. Finally, the outermost layer is another pyrolytic carbon layer 212, similar to the inner pyrolytic carbon layer. This outer layer provides additional containment and protection for the fuel core 218. The multi-layered design of the TRISO particles is essential to their role in enhancing nuclear reactor safety.

[0074] Next, TRISO particles 210 are embedded within solid fuel briquettes 220, which are then stacked within fuel rods 230. The fuel rods house fuel briquettes 234 (fuel briquettes 220 being one example) within graphite sleeves 236. The fuel rods are located within channels in the fuel assemblies 240 of the reactor core, adjacent to coolant tubes 224. More specifically, the solid fuel briquettes 220, containing a plurality of TRISO particles, are designed to provide an additional containment layer and facilitate efficient heat transfer. Solid fuel briquettes 234 are typically made of a graphite matrix and are arranged within fuel rods 230, which may have surrounding graphite sleeves 236 and plugs 232 to secure the fuel briquettes 234 within the fuel rod. Fuel rods 242 (fuel rods 230 being one example) are arranged within the fuel assemblies 240, immediately adjacent to the coolant tubes. Fuel assemblies 240 are typically constructed of solid, high-strength, corrosion-resistant materials such as zirconium alloys, capable of withstanding the high temperatures and pressures within the reactor core. Coolant tubes 244, filled with liquid sodium coolant, are designed to maintain the reactor core temperature by removing heat generated during fission. However, this arrangement of solid fuel briquettes 234 within the solid fuel assembly 240 with liquid sodium coolant tubes 244 causes stability issues due to the positive “cavitation value” of the sodium coolant, leading to undesirable positive reactivity feedback in the reactor. This invention addresses this problem and other issues associated with related embodiments using a novel fuel design.

[0075] Improved nuclear fuel and fuel core design

[0076] Figure 3 A nuclear fuel element 320 according to an embodiment of the invention is shown. The fuel element 320 comprises nuclear fuel particles 322 mixed in a substantially stagnant matrix 324. As used herein, “stagnant” means that the relative motion of the matrix with respect to the TRISO fuel particles is negligible. The matrix is ​​substantially stagnant because it is stationary relative to the fuel particles, except for thermal expansion and mixing. The fuel particles mixed in the matrix may be submerged, immersed, suspended, embedded, or floated in the matrix. The matrix is ​​not a coolant, does not flow through the turbine or external heat exchanger, and is stationary relative to the fuel particles except for the aforementioned thermal expansion and mixing. Figures 8 to 10 Alternative material options for fuel pellets 322 and stagnation matrix 324 are shown in the figure.

[0077] Fuel particles 322 are mixed in a stagnant matrix 324 with a high volumetric fill rate. In some embodiments, the density of the stagnant matrix 324 is substantially the same as the density of the fuel particles 322. In other embodiments, the density of the stagnant matrix 324 is less than the density of the fuel particles 322, and in still other embodiments, the density of the stagnant matrix 324 is greater than the density of the fuel particles 322. In some embodiments, the fuel particles 322 are spherical. It should be noted that when the fuel element 320 is presented as a two-dimensional (2D) cross-sectional slice as shown, the apparent volumetric fill rate of the spherical particles is lower than the actual three-dimensional (3D) volumetric fill rate. However, it will be apparent to those skilled in the art that the teachings of this disclosure can be extended to use any type of spherical fuel particles in any type of matrix at any fill rate.

[0078] In some embodiments, the substantially stagnant matrix 324 is a non-solid matrix. According to one embodiment, the substantially stagnant matrix 324 may be a mixture of liquid lead (Pb) and liquid sodium (Na), for example, a mixture of 60% lead and 40% sodium. The density of liquid lead is greater than the density of fuel particles 322. The density of liquid sodium is less than the density of fuel particles 322. According to another embodiment, the stagnant matrix 324 may be a mixture of lead (Pb) and lithium (Li). Additional embodiments are described in the section on alternative embodiments of fuel element composition.

[0079] According to one embodiment, the nuclear fuel particles 322 mixed in the stagnant matrix 324 can be TRISO fuel particles. An embodiment of the fuel particles 322 including TRISO fuel particles is shown in an enlarged three-dimensional cross-sectional view 310. At the core of the fuel particles is a fuel core 318, which is typically composed of uranium, thorium, or plutonium. This fuel core 318 serves as the primary source of nuclear fission. Surrounding the fuel core 318 is a porous carbon buffer layer 316.

[0080] This layer is designed to absorb fission gases and alleviate stress on the outer layer caused by heat and radiation from the fuel core. Surrounding the porous carbon buffer layer 316 is one of two pyrolytic carbon layers 312. This inner pyrolytic carbon layer is dense and acts as an additional barrier against the escape of fission products. The next layer 314 is made of silicon carbide (SiC), a material known for its excellent heat resistance and mechanical strength. This silicon carbide layer 314 provides a robust barrier against the release of fission products, even under extreme conditions. Finally, the outermost layer is another pyrolytic carbon layer 312, similar to the inner pyrolytic carbon layer. This outer layer provides additional containment and protection for the fuel core 318. The multi-layered design of the TRISO particles is essential to their role in enhancing nuclear reactor safety.

[0081] As further detailed in the simulation results section and the section on advantages over existing designs, in some embodiments, when the stagnant matrix surrounding the fuel particles is in liquid form, it has high thermal expansion, which provides a negative reactive feedback that dominates any positive reactive feedback from the sodium coolant present in sodium-cooled reactor designs. In some embodiments, TRISO fuel particles are used to further encapsulate fission products within the fuel particles, thereby preventing undesirable reactions between fission products in larger fuel cores. In summary, the fuel element of the present invention allows for high fuel utilization, with safe, stable reactivity and a very low risk of radiation release.

[0082] The configuration and / or composition of fuel particles 322 are not limited to the embodiments described above. Rather, it should be understood that, depending on the desired characteristics of the fuel particles 322, fuel particles 322 conforming to this disclosure may include one or more additional layers, or one or more layers may be omitted.

[0083] The disclosed fuel design can be extended to any solid macroscopic ceramic particles (e.g., TRISO particles) mixed in any matrix (e.g., liquid metal, molten salt), wherein mixing includes immersion, infiltration, suspension, or floating of the particles. Further embodiments are described in the following sections.

[0084] In some embodiments, nuclear fuel 334, comprising a substantially stagnant matrix 324 and a mixture of nuclear fuel particles 322, including nuclear fuel element 320, may be contained within a large container 332 within the nuclear fuel core 330. The nuclear fuel 334 is permeated by a plurality of coolant pipes 335. These coolant pipes contain coolant for removing or transferring heat from or to the fuel core 330. The nuclear fuel 334 comprises a stagnant matrix containing a mixture of fuel particles, filling the entire volume of the container 332 of the fuel core 330 except for the coolant pipes 335 that contain the coolant.

[0085] According to one embodiment, the fuel core 330 may be a nuclear reactor core. In some embodiments, the internal portion of the fuel core 332 exhibits 1 / 6 symmetry (e.g., a hexagonal cross-section that remains unchanged at integer multiples of 60 degrees of rotation). The coolant tube 336 may be formed of a material (e.g., ceramic) capable of withstanding extremely high radiation damage over long periods of time. In some embodiments, the ceramic material is silicon carbide (SiC) or zirconium carbide (ZrC).

[0086] Figure 4 An initial embodiment of the invention is shown in Figure 3 The diagram shows a top view 410 and a side view 420 of a nuclear fuel core 330. The fuel core 330 includes a large container 332 containing nuclear fuel elements 334, which comprise a substantially stagnant matrix and a mixture of nuclear fuel particles. The fuel element 334, containing particles within the matrix, is punctured by multiple coolant tubes 336.

[0087] Figure 5 A first enlarged cross-sectional view of a nuclear fuel element 334 comprising a substantially stagnant matrix and mixed fuel particles, according to an embodiment of the invention, is shown, wherein the stagnant matrix is ​​pierced by a plurality of coolant tubes 336. The coolant tubes 336 may contain individually flowing coolant 502.

[0088] Figure 6 A second enlarged cross-sectional view of a fuel element 334 and a coolant conduit 336 according to one embodiment of the invention is shown. The fuel element 334 may comprise a substantially stagnant matrix mixed with a plurality of fuel particles. The fuel element 334, containing particles in the matrix, is further pierced by a conduit 336 containing a separately flowing coolant 502. In one embodiment, the coolant 502 may be a liquid sodium (Na) coolant.

[0089] Figure 7 An example embodiment of a fast breeder-burning nuclear reactor with a pool design according to some embodiments of the invention is shown, which utilizes a novel fuel core 330 with novel fuel elements. At the core of the reactor is the innovative fuel core 330, which comprises fuel particles mixed in a stagnant matrix. In one embodiment, previously in Figure 3 As shown in and Figure 4 The fuel core 330, shown in top and side cross-sectional views, consists of fuel particles immersed in a substantially stagnant matrix of the same density as the fuel particles, such that the fuel particles are suspended in the matrix. Recall that "stagnant" means that the relative motion of the matrix with respect to the fuel particles is negligible. The fuel core is pierced by multiple coolant tubes that contain individually flowing coolant. In some embodiments, the coolant tubes are ceramic coolant tubes, and the flowing coolant is liquid sodium or lead. In some embodiments, the fuel particles are TRISO fuel particles.

[0090] Coolant flows out from liquid metal coolant 714 in reactor pool 720. Liquid metal coolant 714, typically filled with sodium or lead, is used to cool reactor fuel core 330 and facilitate heat transfer. Liquid metal coolant 714 is pumped within reactor pool 720 by reactor pool pump 710 and circulates within reactor pool 720. Fuel core 330 may be surrounded by a breeder blanket 708 of breederable material, which is used to capture any escaped neutrons and convert them into additional fissile material, thereby further improving reactor efficiency. Fuel core may also be surrounded by a neutron reflector, which may be composed of liquid lead (Pb).

[0091] Fuel core 330 generates heat through a nuclear fission process, and this heat is transferred to liquid metal coolant 714 surrounding the fuel core 330 and flowing through coolant pipes within the fuel core 330. Heat exchanger 716 facilitates heat transfer from the liquid metal coolant 714 in the reactor pool 720 to the intermediate loop 722. In the power generation loop 730, the heat from the liquid metal coolant is used to generate steam 732, which powers the power turbine 734 to generate electricity. Water 736 flows from the power turbine 734 back to the steam generator 718. Flow baffles 704 may be positioned in the reactor pool 720 to facilitate coolant flow and enhance heat transfer from the fuel core 330 to the liquid metal coolant 714 within the reactor pool 720.

[0092] Alternative implementation scheme for fuel element composition

[0093] Figure 8 A tree diagram illustrating various potential embodiments of the invention is presented. The diagram begins with the main concept of the fuel element 810 at the root and branches into two main categories: nuclear fuel particles 820, which have corresponding subtrees rooted at 820; and a stationary matrix 830, which has corresponding subtrees rooted at 830. As described, the fuel particles are mixed in a matrix that is substantially stationary relative to the fuel particles.

[0094] The subtree rooted at nuclear fuel particle 820 is further divided into various types of fuel particles that can be used, including the various materials used in the fuel particle 822, the composition of the fuel particle core 824, and the size of the fuel particle 826. Each of these fuel types is further subdivided into different possible configurations, such as... Figure 9 As detailed in the text.

[0095] Sub-trees 830 for the stagnant matrix explore different materials that can be used to form the matrix in which fuel particles are mixed. This includes branches of fluids 840 (including liquids 842 and supercritical fluids 844) and solids 850 with predetermined properties constituting the matrix. Each sub-branch is further divided into different possible properties, compositions, and structures, such as different density values ​​and material compositions relative to the density of the fuel particles. Figure 10 The details are further elaborated in the text.

[0096] Figure 8 The tree diagram illustrates the versatility and adaptability of this invention in fuel design, highlighting its potential to be customized to meet specific reactor requirements or operating conditions.

[0097] Figure 9 A tree diagram is presented, which shows the initial state at... Figure 8The tree introduced herein branches into subtrees rooted at nuclear fuel particle 820, and various embodiments of the invention are illustrated. It should be understood that these examples are not intended to limit the scope of this disclosure, but are provided as possible implementations. Nuclear fuel particles can be composed of different materials 822, including but not limited to ceramic, carbon, and metallic materials. In some embodiments, nuclear fuel particles can also be composed of cermet materials. As a composite material consisting of ceramic and metallic components, cermet can provide a balance between the high-temperature resistance and hardness of ceramics and the thermal conductivity of metals. This balance can potentially enhance the performance of fuel particles, particularly in the high-temperature environments typically encountered within nuclear reactors. The ceramic component of a cermet can be designed to encapsulate the nuclear fuel, while the metallic component can facilitate heat conduction away from the fuel, thereby contributing to the overall efficiency and safety of reactor operation. Examples of partially ceramic and partially carbon nuclear fuel particles include particles in group 934, listed in Table 2. Furthermore, Table 3 lists the types of fuel cores that can be used in group 936 of TRISO particles, bi-structure isotropic (BISO) particles, and quadri-structure isotropic (QUADRISO) particles in some embodiments of the invention. Nuclear fuel particles can have various fuel compositions 824, including but not limited to fissile materials, transmutable materials, and propagating materials, including materials used for activation, propagation, or radioisotope production. Table 1 lists fissile materials 932, including but not limited to uranium, thorium, plutonium, and other actinide elements, which can be used in nuclear fuel particles in some embodiments of the present invention. Table 4 lists transmutable materials 938 used for activation, propagation, or radioisotope production, which can be used in fuel particles in some embodiments of the present invention. Nuclear fuel particles can also have various sizes 826, including but not limited to any predetermined volume, medium size (volume < 0.5 cm). 3 Small size (volume <0.015cm) 3 ) or fine size (any volume > 6 × 10 -7 cm 3 And the volume is <0.015cm³ 3 Nuclear fuel particles can be larger than 6 × 10⁻⁶. -7 cm 3 The dimensions mentioned are not intended to limit the scope of this disclosure, but are provided as possible implementations.

[0098] Figure 10 A tree diagram is presented, showing the subtree rooted at stagnant matrix 830, which is the original subtree in... Figure 8 The tree branches introduced in the text illustrate various embodiments of the invention. The stagnant matrix 830, designed to mix nuclear fuel particles, can be composed of a non-solid matrix or a solid matrix having predetermined properties. The non-solid matrix may contain a fluid 840, which may be further classified as a liquid 842 or a supercritical fluid 844.

[0099] The liquid matrix 842 may have a variety of densities 1040 relative to the mixed particles, including but not limited to lower, equal to, or higher densities compared to the nuclear fuel particles dispersed therein. The composition 1050 of the liquid matrix may include, but is not limited to, liquid metals, liquid metal alloys, liquid quasi-metals, molten salts, water, organic fluids, glass, or other suitable materials. Specific examples of liquid metals 1052 and molten salts 1054 that can be used as the matrix are listed in Tables 5 and 6, respectively. In some embodiments, the liquid matrix comprises a Sn-Al liquid metal alloy. In some embodiments, the matrix comprises tin, lead, sodium, aluminum, bismuth, zinc, magnesium, calcium, cerium, rubidium, zirconium, silicon, beryllium, potassium, yttrium, strontium, germanium, barium, and alloys thereof. Stagnant matrices may comprise metals and quasi-metals, such as silicon and germanium. In some embodiments, the matrix comprises tin, tin-aluminum alloys, tin-aluminum-gallium alloys, tin-zinc-aluminum alloys, tin-magnesium alloys, tin-aluminum-magnesium alloys, and tin-magnesium-zinc alloys. For tin alloys, a composition percentage of tin greater than 80% or alternatively greater than 90% by mass fraction may be used. In some embodiments, the matrix comprises liquid metals or liquid metal alloys such as lead, lead-bismuth-tin alloys, lead-magnesium alloys, sodium-lead alloys, sodium-lead-bismuth alloys, sodium-bismuth alloys, lead-bismuth alloys, or lead-bismuth eutectic. The matrix may also comprise liquid sodium or liquid gallium. In some embodiments, the matrix may comprise alloys of tin, aluminum, and gallium; alloys of tin, aluminum, lead, and bismuth; alloys of lead and magnesium; alloys of aluminum and magnesium; alloys of magnesium and zinc; alloys of bismuth and sodium; or alloys of lead and sodium. In some embodiments, the matrix may comprise alloys of lead and lithium; alloys of tin and lithium; or alloys of lead, bismuth, and lithium. In some embodiments, the matrix may also comprise liquid salts, water, sulfur, supercritical fluids, and / or another organic or inorganic liquid or semi-liquid. It should be noted that in the Pb-Al and Pb-Bi-Al embodiments shown in Table 5, liquid Al is located on top of liquid Pb because Pb and Al do not form an alloy, and the medium-density fuel particles are suspended around the Al-Pb boundary.

[0100] The water used in the matrix may include either light or heavy water, option 1056. In some embodiments, the liquid matrix may be composed of other materials 1058, including but not limited to S or S compounds, P or P compounds, and Br or Br compounds. Supercritical fluid 844 may also be used as the matrix and includes materials 1060 such as S-CO2, S-H2O, S-CH4, S-C2H6, etc. For solid matrix 850 with predetermined properties, materials 1070 such as polyethylene, other plastics or polymers, and metal hydrides (including but not limited to ZrH, YH, CaH) may be used according to some embodiments of this disclosure.

[0101] Tables 1 to 4 show the material composition of alternative fuel pellets. Tables 5 and 6 show the material composition of alternative stagnation matrices.

[0102] Table 1. Alternative Material Composition Options for Fissile Materials Used in Fuel Pellets (see Table 1) Figure 9 )

[0103] uranium thorium plutonium Other actinide elements

[0104] Table 2. Alternative Material Composition Options for Fuel Pellets (see Table 2) Figure 9 )

[0105] TRISO granules BISO Granules QUADRISO granules Other particles

[0106] Table 3. Alternative options for the material composition of the fuel core used in fuel pellets (see Table 3) Figure 9 )

[0107] UN Core <![CDATA[UO2 kernel]]> UC Core UCO Core Other actinide core compounds

[0108] Table 4. Materials for fuel particles used in transmutation (activation, proliferation, or radioisotope) (see Table 4) Figure 9 )

[0109]

[0110] Table 5. Alternative material compositions for liquid metals used in the matrix (see Table 5) Figure 10 )

[0111]

[0112] *Pb and Al do not form alloys; liquid Al sits on top of liquid Pb.

[0113] Table 6. Alternative material compositions for liquid salts used in the matrix (see Table 6) Figure 10 )

[0114] Preferred implementation scheme Alternative Implementation Plan LiF <![CDATA[FLiBe(LiF+BeF2)]]> <![CDATA[BeF2]]> FLiNaK(LiF+NaF+KF) NaF <![CDATA[BaF2]]> KF <![CDATA[PbF2]]> NaCl <![CDATA[PbF4]]> <![CDATA[ZrF4]]> <![CDATA[CeF3]]> Any other fluoride salt <![CDATA[CeF4]]> Any other chloride salt <![CDATA[BiF3]]> Any other salt <![CDATA[BiF5]]>

[0115] Exemplary methods for manufacturing and using nuclear fuel

[0116] Figure 11 A flowchart of a method for preparing nuclear fuel according to one embodiment of the present invention is shown. In step 1102, a particle-matrix mixture is produced by mixing solid fuel particles (such as TRISO particles) with a matrix (such as a mixture of liquid lead and liquid sodium). The matrix may have a larger, smaller, or equal density compared to the fuel particles. In step 1104, the method then moves to a cooling and solidification stage, where the mixture is allowed to cool in a mold or casting. As the mixture cools, it may change from a liquid to a solid state, thereby forming a plurality of solidified fuel briquettes. In step 1106, the plurality of solidified fuel briquettes are inserted into a reactor core to prepare fuel for the reactor. In step 1108, during reactor operation, the solidified fuel may be in a liquid state at the operating temperature and used as liquid fuel within the reactor. During operation, the matrix is ​​substantially stagnant relative to the fuel particles. During operation, the fuel solution may need to be periodically mixed or stirred.

[0117] Although the method for preparing nuclear fuel has been described with reference to the specific sequence of steps involving the use of TRISO particles and a liquid metal matrix, those skilled in the art will understand that various modifications can be made and its elements can be substituted with equivalents without departing from the scope of this disclosure. For example, other types of fuel particles can be used, or the cooling and solidification processes can be modified.

[0118] Furthermore, many modifications can be made to adapt the method to different types of reactors or fuels, or to optimize the method for specific operating conditions, without departing from the scope of this disclosure. For example, the method may be adapted for use with different types of coolants, or the fuel may be prepared in different forms or shapes. Therefore, this disclosure is not intended to be limited to the specific method disclosed as a preferred mode of carrying out this disclosure, but rather this disclosure will include all variations and modifications within the spirit and scope of this disclosure.

[0119] Experimental results

[0120] Figures 12 to 20 Photographs are shown of exemplary batches of fuel elements containing solid particles mixed in a stagnant matrix. These batches used yttrium oxide-stabilized zirconia (YSZ) ceramic spheres (1 mm in diameter) as an alternative to TRISO nuclear fuel particles. The particles remained well suspended, although their density was not exactly the same as that of the immersed metallic alloy fluid. When the spheres are small enough, the surface area to volume ratio becomes sufficiently high. Furthermore, buoyancy and gravity are proportional to volume, while viscosity-related forces are proportional to surface area. Therefore, when the density of the spheres is on the same order of magnitude as the fluid density, these particles are small enough that viscous forces dominate buoyancy and gravity, thus significantly slowing particle movement. While viscous forces do not permanently fix the particles, they slow particle movement over timescales much longer than the transients in most relevant nuclear reactors.

[0121] For illustration, assume the particles have a slightly higher density than the fluid. Initially, they will be stationary, stacked or piled at the bottom (fill rate approximately 64%). As the particles suddenly heat up due to a surge in thermal power, the fluid will thermally expand, and if the fluid is viscous enough, the particles will initially move upwards with the fluid (fill rate decreases). This provides a very strong negative reactive feedback for reactor safety. The particles will then gradually settle back to their original positions at a much slower rate. High viscosity is key to ensuring that this resettling timescale is longer than the nuclear transient timescale and for the initial thermal expansion of the fluid.

[0122] Figure 12A photograph is shown of a batch of fuel elements in liquid form according to one embodiment of the invention. YSZ particles are immersed in a liquid metal matrix. In this exemplary experiment, a tin-indium alloy is used as the liquid metal alloy matrix and was chosen because of its low melting point, which is advantageous in the initial testing phase. Figure 12 The earliest experiments conducted were filmed to verify whether YSZ particles remained suspended and immersed in a liquid metal matrix, and the results showed that the YSZ particles did indeed remain suspended and immersed in the liquid metal matrix. The tin-indium alloy was chosen primarily as a proof-of-concept, and it should be noted that due to indium's strong neutron absorption properties, tin-indium alloys are practically unlikely to be used in nuclear reactors. Various matrix compositions that can be used in reactors are shown in [the image / image / etc.]. Figures 13 to 20 In the middle. And as described above in this disclosure.

[0123] Figure 13 A photograph of a cross-section of a batch of fuel elements in solid form according to one embodiment of the invention is shown. The fuel elements comprise a tin-zinc-aluminum alloy matrix and YSZ ceramic spheres as an alternative to TRISO particles.

[0124] Figure 14 Another photograph shows a cross-section of a batch of fuel elements in solid form according to one embodiment of the invention. The fuel elements comprise a tin-zinc-aluminum alloy matrix and YSZ ceramic spheres as an alternative to TRISO particles.

[0125] Figure 15 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the invention. The fuel elements comprise a tin-zinc-aluminum alloy matrix and YSZ ceramic spheres as an alternative to TRISO particles.

[0126] Figure 16 Another photograph shows a cross-section of a batch of fuel elements in solid form according to one embodiment of the invention. The fuel elements comprise a tin-zinc-aluminum alloy matrix and YSZ ceramic spheres as an alternative to TRISO particles.

[0127] Figure 17 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the invention. The fuel elements comprise a tin-zinc-aluminum alloy matrix and YSZ ceramic spheres as an alternative to TRISO particles.

[0128] Figure 18 Another photograph shows a cross-section of a batch of fuel elements in solid form according to one embodiment of the invention. The fuel elements comprise a lead-bismuth eutectic alloy matrix and YSZ ceramic spheres as a substitute for TRISO particles.

[0129] Figure 19Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the invention. The fuel element comprises a lead-magnesium alloy matrix and YSZ ceramic balls as an alternative to TRISO particles.

[0130] Figure 20 Another photograph shows a cross-section of a batch of fuel elements in solid form according to an embodiment of the invention. The fuel elements comprise a lead-sodium alloy matrix and YSZ ceramic spheres as a substitute for TRISO particles.

[0131] Model simulation results

[0132] Simulation results are shown below, demonstrating the feasibility of using one embodiment of the invention as fuel in a breeder-fire fission reactor. In one embodiment, spherical TRISO particles with a uranium metal fuel core (800 μm diameter) are suspended in a liquid mixture of approximately 60% Pb metal and 40% Na metal (volume fraction). The volumetric fill factor of these spherical particles is 64%, where fill factor refers to the proportion of the total fluid volume occupied by the particles. The fuel is permeated by a number of coolant tubes, which are SiC tubes filled with flowing liquid Na metal coolant. The entire core is surrounded by a pure liquid Pb neutron reflector. According to one embodiment of the invention, Table 7 shows the basic reactor core parameters, including core and neutron reflector dimensions and fuel particle volumetric fill factor.

[0133] Table 7. Exemplary fuel core parameters

[0134] fuel core parameters result unit Active core height 400 cm outer diameter of active core 300 cm Axial reflector thickness 100 cm Radial reflector thickness 100 cm fuel pellet volume fill rate 64% volume%

[0135] According to one implementation, the stagnant matrix surrounding fuel particles exhibits significant thermal expansion, leading to large negative reactivity feedback that readily offsets the positive reactivity feedback of the sodium cavitation value. Here, the sodium cavitation value refers to the change in reactivity or nuclear fission rate when sodium coolant in the reactor is removed or "cavitated." A positive sodium cavitation value means increased reactivity when sodium is cavitated, which could lead to increased reactor power output and potentially hazardous conditions. Additionally, reactivity... 7Feedback refers to a reactor's response to changes in conditions such as temperature or power output. Positive reactivity feedback occurs when an increase in power output leads to conditions that further increase reactivity, creating a self-amplifying cycle. This can potentially lead to a rapid increase in power output, known as reactor runaway, which can be dangerous. Positive sodium cavitation values ​​can contribute to positive reactivity feedback, potentially leading to unsafe conditions in nuclear reactors. The design of this invention counteracts this effect due to the thermal expansion of the fluid matrix surrounding fuel particles, resulting in net negative reactivity. The combustion-breeding fast reactor is able to achieve high fuel utilization on a very large scale with very stable reactivity, while still enjoying the high power density and economic efficiency of sodium coolant.

[0136] Table 8. Exemplary fuel core characteristics

[0137] Exemplary fuel core characteristics result Neutrons are "k-effective" in the early stages of their lifespan. 1.0085±0.0009 Fission "conversion rate" in the early stages of lifespan 1.0072±0.0015 "Delayed neutron fraction" in the early stages of life 0.00797±0.368%

[0138] The neutron k-effectiveness is a dimensionless neutronics parameter that represents the effective neutron multiplication factor of a reactor. If k-effectiveness is greater than 1.0, the neutron chain reaction reactor has reached criticality, and the reactor may be started. The results shown in Table 8 above indicate that k-effectiveness is 1.0085 ± 0.0009, which exceeds the 1.0 threshold.

[0139] The fission conversion rate is the ratio of the production rate of fissile plutonium-239 (Pu-239) atoms to the destruction rate of fissile uranium-235 (U-235) atoms and fissile Pu-239 atoms. The production rate of fissile Pu-239 atoms is primarily through neutron absorption and subsequent decay of U-238 atoms. The destruction rate of fissile U-235 and fissile Pu-239 atoms is primarily through fission. If the fission conversion rate is greater than 1.0, the reactor produces more fissile atoms (fuel used for fission) than it consumes. The results shown in Table 8 above indicate a fission conversion rate of 1.0072 ± 0.0015, which exceeds the 1.0 threshold. This demonstrates that the embodiments of this disclosure can achieve true breeder-combustion physics, i.e., very high fuel utilization.

[0140] The delayed neutron fraction is the fraction of all neutrons emitted from the core that are not directly produced by fission. Instead, these delayed neutrons are produced by the decay of various fission products after the fission products have emerged from fission. The presence of delayed neutrons on the timescale (seconds to minutes) of fission product decay allows fission reactors to be safely controlled, primarily because the timescale of the fission reaction is extremely short (microseconds to milliseconds). The reactor is stable as long as any rapid perturbation in the reactor causes a fraction of k-effective change that is less than the delayed neutron fraction, which occurs only if its "reactivity coefficient" (as defined below) is negative.

[0141] The stability of reactors with negative reactive feedback was verified by calculating the "reactivity coefficient." The reactivity coefficient is the ratio of k—the effective sensitivity to temperature changes in various core materials. The reactivity coefficients were calculated due to thermal expansion of accumulating fuel (fuel particles + Na-Pb liquid) and only Na-Pb liquid without fuel particle movement. The reactivity coefficients due to thermal expansion of liquid sodium coolant, silicon carbide coolant tubes, and liquid lead neutron reflectors were also calculated. The simulation results for the reactivity coefficients are shown in Table 9.

[0142] The k-efficiency change is expressed as dk / kk = 1 / keff1 - 1 / keff2. It can also be expressed in dollars or cents, where one "dollar" equals the "slow-emission neutron fraction" (0.00797 in this case). For similar comparisons at the same temperature change, each reactivity coefficient is multiplied by the coefficient of thermal expansion (CTE) (1 / K) of each material to obtain results in cents / K.

[0143] The Doppler reactivity coefficient in the fuel was also calculated, which is caused by the Doppler effect on the microscopic neutron cross section of uranium due to the atomic motion varying at different temperatures.

[0144] Table 9. Simulation results of reactivity coefficients

[0145] Thermal expansion: dk / kk / % density cents / % density CTE (1 / k), volume cents / K Aggregate fuel <![CDATA[-1.07x10 -3 ]]> -13.4 not applicable -0.24 Pb-Na fluid only <![CDATA[-9.85x10 -6 ]]> -0.12 <![CDATA[1.80x10 -4 ]]> <![CDATA[-2.22x10 -3 ]]> SiC coolant pipes <![CDATA[-1.97x10 -5 ]]> -0.25 <![CDATA[4.00x10 -6 ]]> <![CDATA[-9.89x10 -5 ]]> Na coolant <![CDATA[-1.08x10 -5 ]]> -0.14 <![CDATA[2.60 10 -4 ]]> <![CDATA[-3.54x10 -3 ]]> Pb reflector <![CDATA[-1.97x10 -6 ]]> <![CDATA[-2.47x10 -2 ]]> <![CDATA[1.20x10 -4 ]]> <![CDATA[-2.97x10 -4 ]]> Doppler: Fuel Doppler effect not applicable not applicable not applicable <![CDATA[-1.46x10 -5 ]]>

[0146] The net reactivity coefficient is strongly negative, primarily due to the expansion of aggregated fuel—the Pb-Na fluid pushes aside suspended fuel particles. The thermal expansion reactivity coefficient of liquid Na coolant is slightly negative here. In some embodiments of the invention, a large negative fuel coefficient can dominate and overwhelm any positive coolant coefficient that might result.

[0147] Advantages over existing designs

[0148] This disclosure provides a novel design for breeder-combustion fission reactors that offers several advantages over existing designs. One of the key advantages is the use of a stagnant matrix surrounding TRISO particles. As described in the preceding sections, when this matrix is ​​in liquid form, it exhibits significant thermal expansion, leading to a large negative reactivity feedback. This feedback effectively counteracts the positive reactivity feedback associated with sodium (referred to as the sodium cavitation value). As a result, the reactor is able to achieve breeder-combustion equilibrium at scale, characterized by high fuel utilization, while maintaining stable reactivity. This contributes to the safety of reactor operation. Furthermore, the reactor benefits from high power density due to the favorable thermal properties of the sodium coolant, which enhances its economic viability.

[0149] These desired properties contrast with existing breeder-combustion reactor designs, which suffer from the high cavitation value of their sodium coolant. This leads to positive reactive feedback in the critical neutron chain reaction when sodium density decreases due to any increase in temperature. Other approaches attempt to mitigate the sodium cavitation value problem by moderating neutrons with lead or gaseous coolants. However, to achieve the high neutron energy spectrum required for the breeder-combustion process, the equilibrium burnup (defined as the fraction of uranium atoms undergoing fission when the reactor's breeder and burnup rates eventually reach equilibrium) may exceed a threshold that any solid uranium-based fuel can maintain while preserving structural and mechanical integrity. This could potentially lead to problematic decomposition of the solid fuel.

[0150] The present invention’s design of blended fuels, made from fuel particles mixed in a matrix, provides additional benefits through the properties of solid fuel particles. In some embodiments of the invention, TRISO fuel particles are used to further encapsulate fission products within the fuel particles, thereby preventing undesirable reactions between fission products in larger fuel cores. This differs from molten salt reactors (MSRs), which also address the reactivity stability issues of liquid fuels but result in the mixing of fission products within the fuel core, leading to a “periodic soup” and an increased risk of radiation release.

[0151] More specifically, TRISO fuel particles contain carbon atoms in each of their layers, which weakly moderate neutron energies. While the neutrons are still fast enough to achieve breeder-burn fuel efficiency, the equilibrium burnup is also very high. Here, equilibrium burnup is the fraction of uranium atoms that fission occurs when the reactor's breeder and burnup rates eventually reach equilibrium. In some implementations, TRISO particles are able to maintain structural integrity while withstanding extremely high burnup levels.

[0152] The fuel containing TRISO fuel particles in the matrix disclosed in this invention has a significantly lower risk of radiation leakage compared to currently known solutions in the art. The TRISO fuel particles 310 mixed in a stagnant matrix are structurally more resistant to neutron radiation, corrosion, oxidation, and high temperatures. Furthermore, when a uranium atom undergoes fission, it splits into two smaller atoms called fission products or fission fragments, which are typically radioactive and may differ in size and atomic number, and are produced with varying probabilities. Most of these fission products are radioactive and decay into other fission fragments. Each TRISO fuel particle acts as its own containment system, retaining fission products under all reactor conditions and preventing undesirable reactions of fission products within the larger fuel core.

[0153] Therefore, the use of TRISO particles in this design significantly reduces the risk of radiation release compared to reactors using non-TRISO solid fuel. This eliminates the need for extensive, multi-year chemical research testing, further enhancing the practicality and feasibility of this design. Table 10 summarizes the advantages and benefits of the fuel design of this invention. One embodiment of the invention is presented in the last column of Table 10 and, as shown, exhibits good performance across all considered criteria, including fuel utilization, power density (and economic viability), radiation and coolant leakage risk, safety and stability regarding coolant cavitation value, and technical risks due to the unknown chemical properties of new nuclear materials or reaction byproducts. In summary, the fuel design of this invention allows for high fuel utilization, with safe, stable reactivity and a very low risk of radiation release.

[0154] Table 10. Comparison and advantages of the disclosed implementation scheme compared to other designs

[0155]

[0156] Additional exemplary applications and implementation schemes

[0157] In some aspects, the disclosed embodiments of the nuclear fuel can be used to generate energy in fast-spectrum fission reactors, thermal-spectrum fission reactors, hyperthermal-spectrum fission reactors, or fission-fusion hybrid reactors. In other aspects, the disclosed embodiments of the nuclear fuel can be used to generate energy in nuclear reactors cooled by liquid metal coolants, liquid salt coolants, gaseous coolants, water coolants, or heat pipes.

[0158] This invention is also advantageous to the fusion energy industry in future fusion reactors and fission-fusion hybrid reactors. In fusion reactors, the design may or may not include the same cooling pipes. TRISO particles can be immersed in a lead-lithium fluid mixture. Lithium allows neutron breeding of tritium, and the first fusion reactor must produce tritium to replenish its deuterium-tritium fuel. For fission-fusion hybrid technology, TRISO fuel for the fission component is ideal because there is no leakage of fission products. The breeder-combustion and very stable reactivity characteristics of the fuel design will also be very attractive for the more efficient use of fission fuel by breeding plutonium. This disclosure encapsulates fission products within TRISO while employing a matrix that can be mixed (effectively stirred) without removal from the reactor; this combination makes it an attractive option for fission-based fusion energy enhancement. Various embodiments of the invention can be used or modified for any other type of nuclear system, including but not limited to fission reactors, fusion reactors, fission-fusion hybrid reactors, radioisotope energy systems, and accelerator systems.

[0159] Other embodiments of the invention will be apparent to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. The specification and examples are to be considered exemplary only, and various other embodiments and alternative implementations are within the scope of the invention.

Claims

1. A nuclear fuel element comprising: a plurality of solid nuclear fuel particles, wherein each solid nuclear fuel particle of the plurality of solid nuclear fuel particles comprises a nuclear material; and a non-solid matrix, wherein the plurality of solid nuclear fuel particles are mixed in the non-solid matrix, wherein the non-solid matrix is substantially stagnant with respect to the plurality of solid nuclear fuel particles, and wherein the non-solid matrix comprises a material selected from the group consisting of a liquid metal, a liquid metal alloy, and a liquid salt.

2. The nuclear fuel element of claim 1, wherein the plurality of solid nuclear fuel particles comprise tristructure-isotropic (TRISO) particles.

3. The nuclear fuel element of claim 1, wherein the non-solid matrix is selected from the group consisting of a liquid metal and a liquid metal alloy.

4. The nuclear fuel element of claim 1, wherein the non-solid matrix is selected from the group consisting of tin, lead, sodium, aluminum, bismuth, zinc, magnesium, calcium, cerium, rubidium, zirconium, beryllium, potassium, yttrium, strontium, barium, and alloys thereof.

5. The nuclear fuel element of claim 1, wherein the non-solid matrix further comprises an element selected from the group consisting of silicon and germanium.

6. The nuclear fuel element of claim 1, wherein the non-solid matrix is selected from the group consisting of tin, a tin-aluminum alloy, a tin-aluminum-gallium alloy, a tin-zinc-aluminum alloy, a tin-magnesium alloy, a tin-aluminum-magnesium alloy, and a tin-magnesium-zinc alloy.

7. The nuclear fuel element of claim 6, wherein the composition percentage of tin in the non-solid matrix is greater than 80% tin by mass fraction.

8. The nuclear fuel element of claim 1, wherein the non-solid matrix is selected from the group consisting of lead, a lead-bismuth-tin alloy, and a lead-magnesium alloy.

9. The nuclear fuel element of claim 1, wherein the non-solid matrix is selected from the group consisting of a sodium-lead alloy, a sodium-lead-bismuth alloy, and a sodium-bismuth alloy.

10. The nuclear fuel element of claim 1, wherein the non-solid matrix is selected from the group consisting of a lead-bismuth alloy and a lead-bismuth eutectic.

11. The nuclear fuel element of claim 1, wherein the non-solid matrix is a liquid sodium.

12. The nuclear fuel element of claim 1, wherein the non-solid matrix is a liquid gallium.

13. The nuclear fuel element of claim 1, wherein the non-solid matrix comprises an alloy selected from the group consisting of: an alloy of tin, aluminum, and gallium; an alloy of tin, aluminum, lead, and bismuth; an alloy of lead and magnesium; an alloy of aluminum and magnesium; an alloy of magnesium and zinc; an alloy of bismuth and sodium; and an alloy of lead and sodium.

14. The nuclear fuel element of claim 1, wherein the non-solid matrix comprises an alloy selected from the group consisting of: an alloy of lead and lithium; an alloy of tin and lithium; and an alloy of lead, bismuth, and lithium.

15. The nuclear fuel element of claim 1, wherein the non-solid matrix comprises a liquid salt.

16. The nuclear fuel element of claim 1, wherein the non-solid matrix further comprises a material selected from the group consisting of water, sulfur, a supercritical fluid, an organic liquid, and an inorganic liquid.

17. The nuclear fuel element of claim 1, wherein the plurality of solid nuclear fuel particles comprise tristructure- isotropic (TRISO) particles, and wherein the non-solid matrix is selected from the group consisting of tin-aluminum alloys, tin-aluminum-gallium alloys, lead-bismuth alloys, and lead.

18. The nuclear fuel element of claim 1, wherein the plurality of solid nuclear fuel particles comprise particles selected from the group consisting of tristructure- isotropic (TRISO) particles, dual structure-isotropic particles, and quadruple structure- isotropic particles.

19. The nuclear fuel element of claim 1, wherein at least one of the plurality of solid nuclear fuel particles comprises one or more materials selected from the group consisting of ceramic materials, metallic materials, carbon materials, and cermet materials.

20. The nuclear fuel element of claim 1, wherein at least one of the plurality of solid nuclear fuel particles comprises an actinide fuel kernel.

21. The nuclear fuel element of claim 1, wherein at least one of the plurality of solid nuclear fuel particles comprises a fuel kernel selected from the group consisting of UN kernels, U02 kernels, UC kernels, and UCO kernels.

22. The nuclear fuel element of claim 1, wherein the nuclear material is selected from the group consisting of fissile materials, transmutation materials, and fertile materials.

23. The nuclear fuel element of claim 1, wherein the plurality of solid nuclear fuel particles comprise a fissile material selected from the group consisting of uranium, thorium, and plutonium.

24. The nuclear fuel element of claim 1, wherein the plurality of solid nuclear fuel particles comprise a transmutation material or fertile material selected from the group consisting of thulium, thallium, gadolinium, silver, strontium, holmium, and lithium.

25. The nuclear fuel element of claim 1, wherein each solid nuclear fuel particle of the plurality of solid nuclear fuel particles has a volume less than 0.5 cm 3 and greater than 6 x 10 -7 cm 3 .

26. The nuclear fuel element of claim 1, wherein each solid nuclear fuel particle of the plurality of solid nuclear fuel particles has a volume less than 1.5 x 10 -2 cm 3 and greater than 6 x 10 -7 cm 3 .

27. The nuclear fuel element of claim 1, wherein the non-solid matrix has approximately the same density as the plurality of solid nuclear fuel particles.

28. The nuclear fuel element of claim 1, wherein the non-solid matrix has a density that is less than the density of the plurality of solid nuclear fuel particles.

29. The nuclear fuel element of claim 1, wherein the non-solid matrix has a density that is greater than the density of the plurality of solid nuclear fuel particles.

30. The nuclear fuel element of claim 1, wherein the nuclear fuel element generates energy in a nuclear reactor selected from the group consisting of fast spectrum fission reactors, thermal spectrum fission reactors, epithermal spectrum fission reactors, and fission-fusion hybrid reactors.

31. The nuclear fuel element of claim 1, wherein the nuclear fuel element generates energy in a nuclear reactor that is cooled by a coolant selected from the group consisting of liquid metal coolants, liquid salt coolants, gas coolants, water coolants, and heat pipes.

32. A nuclear reactor, comprising: a power generation circuit; and a reactor, wherein the reactor comprises a nuclear fuel element and a coolant, wherein the nuclear fuel element comprises: a plurality of solid nuclear fuel particles, wherein each of the plurality of solid nuclear fuel particles comprises a nuclear material; and a non-solid matrix, wherein the plurality of solid nuclear fuel particles are mixed in the non-solid matrix, wherein the non-solid matrix is substantially stagnant with respect to the plurality of solid nuclear fuel particles, and wherein the non-solid matrix comprises a material selected from the group consisting of a liquid metal, a liquid metal alloy, and a liquid salt. wherein the plurality of solid nuclear fuel particles are mixed in the non-solid matrix, wherein the non-solid matrix is substantially stagnant with respect to the plurality of solid nuclear fuel particles, and wherein the non-solid matrix comprises a material selected from the group consisting of a liquid metal, a liquid metal alloy, and a liquid salt.

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