Fuel moderator and absorber assembly

Abstract

A nuclear fuel, moderator, and absorber (FMA) assembly provides a mechanism to tailor the fissile material density, moderating power, and neutron absorbing functions at each lateral and axial location within the core; maintains the geometry of the materials required for these functions; retains gaseous fission products, solid fission products, and gaseous phases such as hydrogen as necessary. The FMA concept may be used in many different types of reactors to optimize reactor fuel utilization and safety performance. Advanced methods such as genetic algorithms or other methods that are currently available or become available and the use of artificial intelligence may be used to specify the components, materials, or features of each individual FMA for optimization of reactor core loading that results in superior reactor safety and economic performance. The Fuel Moderator and Absorber (FMA) assembly may be configured to enhance the retention of fission products, allowing siting of nuclear reactors with a minimal Emergency Planning Zone.

Description

NUCB.008WO PATENTFUEL MODERATOR AND ABSORBER ASSEMBLYINCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

[0001] Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. This application claims priority to U.S. Provisional Patent Application No. 63 / 658,569 filed on June 11, 2024.BACKGROUNDField

[0002] The present disclosure is directed to a nuclear fuel, moderator, and absorber (FMA) assembly, and more particularly to an integrated nuclear Fuel Moderator and Absorber (FMA) assembly.Description of the Related Art

[0003] There are currently many distinct designs and design concepts for reactors that use different types and arrangements of fissile nuclear fuel materials. In general, however, the type and arrangement of fissile nuclear materials within the reactor core is the same or very similar at each location throughout the core of the nuclear reactor. Using the same or very similar fuel design at each location results in less-than-optimal reactor performance in terms of fissile material utilization and reactor safety.SUMMARY

[0004] In accordance with one aspect of the disclosure, a nuclear fuel, moderator, and absorber (FMA) assembly is provided that provides a means to tailor the fissile material density, moderating power, and neutron absorbing functions at each lateral and axial location within the core; maintains the geometry of the materials required for these functions; retains gaseous fission products, solid fission products, and gaseous phases such as hydrogen as necessary. Advanced methods such as genetic algorithms or other methods that are currently available or become available and the use of artificial intelligence may be used to specify thecomponents, materials, or features of each individual FMA for optimization of reactor core loading that results in superior reactor safety and economic performance.

[0005] In accordance with on aspect of the disclosure, the configuration of each individual FMA assembly within a reactor core can be tailored by specifying the type, configuration, and density of fissile material, moderating material, and neutron absorbing material. Each FMA may be individually designed using advanced optimization algorithms, artificial intelligence, or other methods. Tailoring of each FMA results in a reactor core that is both laterally and axially designed to optimize nuclear fuel utilization and safety performance. The FMA may be configured to provide enhanced retention of fission products, reducing the required Emergency Planning Zone. The FMA may also be configured to retain hydrogen, allowing the use of solid hydride moderators at high temperatures.

[0006] In accordance with one aspect of the disclosure, a nuclear fuel assembly design is provided that incorporates multiple components necessary for the operation of a nuclear reactor into one integrated assembly. The same assembly may incorporate fissile material, fertile material, neutron moderator materials, neutron reflector materials, and neutron absorbing materials clad within a ceramic or metallic tube. This assembly is herein referred to as the Fuel Moderator Absorber (FMA) or ‘assembly’. The FMA allows the use of many different types and combinations of fissile components, fertile components, neutron moderator, neutron reflector, neutron absorbing materials, and spacers into a single FMA assembly to enable local tailoring of the operating conditions within the reactor core. Each individual FMA within a reactor core can be configured differently. For example, the use of a computer algorithm can be used to specify the design of each individual FMA within a reactor core to achieve reactor performance requirements and to increase the utilization of fissile nuclear material incorporated in the core. If the performance requirements, operating requirements, or operating constraints of the reactor change, the design of the FMA may be changed to accommodate these new conditions. The FMA can be designed and manufactured for use over a wide temperature range of from approximately room temperature to more than 1800 K through the appropriate selection of materials and fabrication parameters. The inclusion of one or more of fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials and thecomposition and properties of each type of material is dependent on the specific local operating requirements within the applicable nuclear reactor core.

[0007] The FMA can be manufactured in a factory where strict nuclear quality control requirements are easily applied. Combining the fuel and fertile material, moderator material, burnable neutron absorbers, and fixed neutron absorbers into a single FMA unit provides for simplified on-site assembly of a nuclear reactor through the combination of several components into a single assembly.

[0008] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile nuclear materials, fertile nuclear materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The outer sleeve may be sealed or left unsealed depending on the specific functions that the sleeve is required to perform, for example retention of fission products or gaseous phases. The inclusion of one or more types of material within each class, the specific type of material selected to perform a function, the tailored properties of each material, and the geometric and spatial configuration of materials within the FMA are dependent on the specific operating requirements within a specific region of the applicable nuclear reactor core.

[0009] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sealed outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The configuration of fissile material as a nuclear fuel contained within the FMA and the sealed ceramic or metallic outer sleeve encasing the FMA are constructed of a material designed to retain radioisotopes that result from nuclear fission (fission products) such that release of radionuclides during normal operating and accident conditions is negligible.

[0010] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sealed sleevefabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The moderator is a composed of a solid hydride material. The material used for fabrication of the outer ceramic or metallic sleeve encasing the FMA is selected, constructed, and sealed in a manner such that hydrogen introduced into the FMA as a gas or that may result from the dissociation of hydrogen from the solid neutron moderating material is retained so that the effectiveness of the moderator is not compromised.

[0011] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The fissile material is contained within coated nuclear fuel particles such as TRISO (TRi structural ISOtropic) particles embedded within carbonaceous material known as a fuel compact. The fertile materials, neutron moderating materials, burnable neutron absorber materials and fixed neutron absorber materials may be likewise dispersed as coated or uncoated particles within the TRISO fuel compact or outside of the TRISO fuel compact in separate compacts or cans.

[0012] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The fissile material may be dispersed within coated nuclear fuel particles such as TRISO (TRi structural ISOtropic) particles embedded within a carbonaceous cylinder known as a fuel compact. The radial thermal conductivity of the fuel compact is improved using a novel processing method. The improved thermal conductivity allows the use of fuel compacts greater than 2 cm in diameter while maintaining a small temperature gradient and low peak fuel temperature.

[0013] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The neutron moderating material may be distributed along the axial length of the FMA as elongated cylinder forms positioned inside of a central hole within one or more of the materials that may be included in the FMA.

[0014] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The neutron moderating material is distributed along the axial length of the FMA in the form of annular cylinders positioned around and partially or wholly encasing one or more of the materials that may be included in the FMA.

[0015] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. A solid hydride material is used as the neutron moderating material. The solid hydride moderator may be in the form of cylinders, discs, coarse or fine powder, or an assembly of shapes such as hexagons, cylinders, or rhombi placed in a sealed ceramic or metallic can inside of the FMA. The design of the cans containing the moderator and the sealing process are selected to locally retain hydrogen that may be released from the solid hydride moderator material during service. The sealed cans containing solid hydride moderator may be distributed axially and radially throughout theFMA depending on the specific operating requirements within a specific region of the applicable nuclear reactor core.

[0016] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Burnable neutron absorber material in the form of cylinders, discs, hexagons, triangles, or other shapes may be distributed axially and radially throughout the FMA, and several types of burnable neutron absorber materials may be used in each FMA depending on the specific operating requirements within a specific region of the applicable nuclear reactor core.

[0017] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Fixed neutron absorber materials in the form of cylinders, discs, hexagons, triangles, or other shapes may be distributed axially and radially throughout the FMA, and several types of burnable neutron absorber materials may be used in each FMA depending on the specific operating requirements within a specific region of the applicable nuclear reactor core.

[0018] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Axial ceramic or metallic spacers in the form of discs, cylinders or other regular or irregular shapes as required are positioned at the interfaces between materials within the FMA to mitigate detrimental chemical reaction between the components.

[0019] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Axial spacers containing burnable neutron absorbers or fixed neutron absorbers in the form of discs or cylinders or other regular or irregular shapes as required may be positioned at the interfaces between materials within the FMA to mitigate chemical reactions between the components stacked within the FMA and to distribute burnable and / or fixed neutron absorbers axially within the FMA.

[0020] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Radial ceramic or metallic spacers in the form of annular cylinders or other regular or irregular shapes as required may be positioned at the interfaces between materials within the FMA to mitigate detrimental chemical reaction between the components. The chemical composition of the radial spacers is such that detrimental chemical reactions between the internal components of the FMA and the outer metallic sleeve are mitigated.

[0021] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sealed sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Radial ceramic or metallic spacers in the form of annular cylinders or other regular or irregular shapes as required may be positioned at the interfaces between materials within the FMA to mitigate detrimental mechanical interaction between the components. The design and mechanical properties of the radial spacers are such that dimensional changes such as those caused by thermal expansion orradiation-induced swelling prevent detrimental mechanical interaction between the internal components of the FMA and the outer ceramic or metallic sleeve.

[0022] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Radial ceramic or metallic spacers in the form of annular cylinders or other regular or irregular shapes as required may be positioned at the interfaces between materials within the FMA. The composition of the radial spacers may include burnable neutron absorber material and / or or fixed neutron absorber materials.

[0023] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Radial ceramic or metallic spacers in the form of annular cylinders or other regular or irregular shapes as required may be positioned at the interfaces between materials. The composition of the radial spacers may include neutron moderating materials.

[0024] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Neutron reflectors may be placed in the upper and lower regions of the FMA or as otherwise required to reflect neutrons otherwise lost back into the FMA to improve utilization of the fissile nuclear fuel and enhance the function of the fertile material depending on the specific operating requirements within a specific region of the applicable nuclear reactor core.

[0025] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sealed outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. Neutron reflectors in combination with neutron absorbers or without neutron absorbers are placed in the upper and lower regions of the FMA to reduce the neutron displacement damage to the closure joints that may be used to seal the FMA at its upper and lower ends.

[0026] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sealed sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. A gas plenum void of solid material may be placed within the upper, lower, or central regions of the FMA to accommodate the release of fission gas released from the fuel compacts, hydrogen gas released from a solid hydride moderator, or other gaseous materials that may be released from components internal to the FMA.

[0027] In accordance with another aspect of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises an outer sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, and neutron reflector materials. The inside surfaces of the ceramic or metallic tubes are coated partially or fully with neutron absorbing materials.

[0028] In some aspects, the techniques described herein relate to a combined nuclear fuel, moderator, and absorber assembly, including: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or moreneutron absorber materials disposed inside the sleeve; and one or more neutron reflector materials disposed inside the sleeve.

[0029] In some aspects, the techniques described herein relate to a combined nuclear fuel, moderator, and absorber (FMA) assembly, including: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron absorber materials disposed inside the sleeve; one or more neutron reflector materials disposed inside the sleeve; one or more axial spacers inside the sleeve between the one or more fissile nuclear material and the one or more neutron moderating materials; and one or more radial spacers inside the sleeve disposed about at least one of the one or more neutron moderating materials or about at least one of the one or more fissile nuclear materials, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of approximately 1000 to 1500 degrees Kelvin.

[0030] In some aspects, the techniques described herein relate to a combined nuclear fuel, moderator, and absorber (FMA) assembly, including: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron reflector materials disposed inside the sleeve; one or more radial spacers inside the sleeve about at least one of the one or more neutron reflector materials; and a gas plenum in the sleeve configured to retain one or more gaseous or non-gaseous fission products released by the one or more fissile nuclear materials inside the sleeve, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of less than 1000 degrees Kelvin.

[0031] In some aspects, the techniques described herein relate to a combined nuclear fuel, moderator, and absorber (FMA) assembly, including: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; a gas plenum in the sleeve configured to retain one or more gaseous or non-gaseous fission products released by the one or more fissile nuclear materials inside the sleeve; and one or more axial spacers between the gas plenum and at least one of the one or more fissile nuclear materials, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of more than 1500 degrees Kelvin.

[0032] In some aspects, the techniques described herein relate to a combined nuclear fuel, moderator, and absorber assembly, including: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; and one or more neutron reflector materials disposed inside the sleeve, wherein at least some of the one or more fissile nuclear material and one or more fertile nuclear material are mixed together.

[0033] In some aspects, the techniques described herein relate to a combined nuclear fuel, moderator, and absorber system including: a sealed or unsealed ceramic or metallic sleeve; a fissile material; a neutron moderating material; a burnable neutron absorber material; a fixed neutron absorber material; one or more axial spacers; one or more radial spacers; a neutron reflector material; and a gas plenum.BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 shows an example cross-sectional diagram of a Fuel, Moderator, and Absorber (FMA) assembly.

[0035] Figure 2 shows an example cross-sectional diagram of a Fuel, Moderator, and Absorber (FMA) assembly for use at approximately 1000 - 1500 Kelvin (K).

[0036] Figure 3 an example cross-sectional diagram of a Fuel, Moderator, and Absorber (FMA) assembly for use below approximately 1000 K.

[0037] Figure 4 shows an example cross-sectional diagram of a Fuel, Moderator, and Absorber (FMA) assembly for use above approximately 1500 K.

[0038] Figure 5 shows an example cross-sectional diagram of a Fuel, Moderator, and Absorber (FMA) assembly using fertile materials.DETAILED DESCRIPTION

[0039] Figure 1 provides a schematic cross-sectional diagram that indicates some of the configurations of the assembly. In accordance with aspects of the disclosure, an integrated nuclear Fuel Moderator and Absorber system is provided. The FMA comprises a sealed sleeve fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more of each class of materials including fissile materials, fertile materials, neutron moderating materials, burnable neutron absorbermaterials, fixed neutron absorber materials, and neutron reflector materials. Each class of material may be implemented in various forms, including axial spacers, radial spacers, cylindrical rods, or other shapes as necessary to function as specified depending on the specific operating requirements within a specific region of the applicable nuclear reactor core.

[0040] Figures 2-4 provide example schematic cross-sectional diagrams of Fuel Moderator Assemblies that may be implemented using different combinations and configurations of ceramic or metallic outer sleeve, fissile material, fertile material, neutron moderating materials, burnable neutron absorbing materials, and fixed neutron absorbing materials.

[0041] Figure 2 provides one example of a specific implementation in which the FMA is designed to be used in a reactor operating within a temperature range of approximately 1000 - 1500 K and that requires minimal release of fission products.

[0042] Figure 3 provides one specific example of implementation of the FMA for use at lower temperature, for example at temperatures less than approximately 1000 K (e.g., about 900 K).

[0043] Figure 4 provides one specific example of implementation for use at temperatures greater than approximately 1500 K.

[0044] Figure 5 provides one specific example of implementation of an FMA which includes fertile materials. The quantity and placement of fertile material, fissile material, neutron moderating material, and neutron reflecting material within each separate FMA and the arrangement of these materials within each separate FMA is optimized to extend the operating lifetime of the core of a nuclear reactor.

[0045] Figure 1 shows components of a Fuel Moderator Assembly 100. The FMA has an outer sleeve or sheath 10 consisting of ceramic and / or metallic material. The ceramic and / or metallic outer sleeve 10 may be sealed (with end cap(s) 15) to prevent release of gaseous material. In another implementation, one or both end caps 15 are excluded so that the outer sleeve 10 is left unsealed. With reference to FIG. 1, the FMA 100 can have the outer sleeve 10 with end cap(s) 15 on both ends that are sealed, a type of neutron reflector referred to as a type 1 neutron reflector 25, a type of fixed neutron absorber referred to as a type 1 fixed neutron absorber 50, a type of fissile material referred to as a type 1 fissile nuclear material 40, an axial spacer 60, a type of neutron moderator referred to as a type 1 neutron moderator 45 positionedwithin the FMA within a radial spacer 70, an axial spacer 60, a type of fertile nuclear material referred to as a type 1 fertile nuclear material 80, a type of burnable neutron absorber material referred to as type 1 burnable neutron absorber 55, another type of fertile nuclear material referred to as type 2 fertile nuclear material 80, another type of burnable neutron absorber material referred to as type 2 burnable neutron absorber 55, an internal assembly referred to as a can 35 that may be sealed or unsealed and contain fissile nuclear material, fertile nuclear material, neutron moderator material, or other material required for the function of the FMA in various shapes and spatial arrangements, a type 2 neutron moderator material (or any other moderator material) 45 positioned within an annulus of type 2 fissile nuclear material (or any other type of fissile nuclear material) 40 which is further positioned within the FMA outer shell using a radial spacer 70 an axial spacer 65 that contains neutron moderating material in its composition, another type of fissile nuclear material referred to as type 3 fissile nuclear material 40 positioned within the FMA using radial spacers 75 that contain a neutron absorbing material, another type of fertile nuclear material referred to as type 3 fertile nuclear material 80, a type 2 fixed neutron absorber 50, a type 2 neutron reflector 30, and a radial spacer 70 that forms a lower gas plenum 20, a lower end cap 15 that seals the outer sleeve 10. The outer sleeve 10 material is selected based on properties such as operating temperature range, material behavior under neutron irradiation, neutron absorption, ability to be sealed, diffusion rate of fission products through a sealed outer sleeve, and the permeability of hydrogen through the sealed outer sleeve. The FMA may include a gas plenum 20 that provides a volume for the release of gas from the solid moderator, burnable absorbers, fissile material, and fertile material, and may be positioned anywhere within the outer sleeve of the FMA 100. Neutron reflectors 25, 30 may positioned in the upper and lower regions of the FMA 100 to reflect neutrons with an axially upward or downward trajectory toward the center of the core, or in any location within the FMA to reflect neutrons. The neutron reflectors 25, 30 may be in annular shapes (for example similar to the radial spacer 75), cylindrical shapes, or other shapes as required to optimally perform their function, and may alternate in a regular or irregular sequence with the other internal components as the specific reactor design dictates. Fissile material containing pellets or compacts 40 of varying composition, height, diameter, fuel loading, and enrichment and with cylindrical or annular geometries are positioned within the FMA outer sleeve, alternating in a regular or irregular sequence with the other internalcomponents of the FMA. Fissile material containing pellets or compacts may incorporate burnable absorber materials, fixed absorber materials, and / or solid moderator materials within the pellet, compact, or other shape as the specific FMA design within a specific reactor design dictates. Solid moderator materials 45 of varying chemical composition height, diameter, and moderator density, and with cylindrical or annular geometries, or with other geometries as the specific FMA design dictates, may be included within the FMA outer sleeve 10, and may alternate in a regular or irregular sequence with the other internal components of the FMA 100. Fixed 50 and burnable 55 neutron absorber materials of varying chemical composition, height, diameter, and density, and with cylindrical or annular geometries or other geometries as the specific design dictates, are positioned within the FMA outer sleeve 10, alternating in a regular or irregular sequence with the other internal components of the FMA. Axial spacers 60 with cylindrical or annular geometries, varying axial thickness, and variable chemical composition are placed at the interfaces between dissimilar materials within the FMA outer sleeve. The primary function of the axial spacers is to mitigate detrimental chemical reactions between dissimilar materials within the FMA 100, however axial spacers 65 may also include solid moderator materials, burnable neutron absorber materials, and / or fixed neutron absorber materials. The radial spacers 70 advantageously prevent detrimental chemical reactions between components within the outer sleeve 10 of the FMA 100 and the FMA outer sleeve material, and to accommodate volume changes of the internal components of the FMA 100. Radial spacers 70 may be used to create void spaces within the FMA 100 that can be used as gas plenums 20. Neutron absorber, neutron moderator, and or neutron reflector materials may also perform the function of radial spacers 75 as needed to optimize the design of the FMA with respect to the reactor core operating parameters. Fertile nuclear material 80 of different compositions may be included inside the FMA that may act as burnable poisons early in the reactor operating cycle and as a source of fissile material at a later time in the reactor operating cycle. The included fertile nuclear material may take the form of various shapes such as cylinders, annular cylinders, plates, or other shapes as required to meet reactor operating requirements. In some cases, it may be desirable to further isolate materials with a sealed ‘can’ 35 inside of the FMA as an additional barrier to the release of gas or other mobile materials or to allow optimization of the spatial configuration of complex assemblies of the internal components of the FMA.

[0046] Figure 2 provides one example of an implementation in which the FMA 100’ is designed to be placed within a reactor operating within a temperature range of approximately 1000 - 1500 Kelvin (K) and that requires minimal release of fission products. The FMA 100’ includes within a sealed sheath or outer sleeve 10 (sealed with end cap(s) 15) a neutron reflector 25, fixed neutron absorber 50, fissile nuclear material 40, axial spacer 60, solid moderator 45 and radial spacers 70 about it, an axial spacer 65 that contains a small amount of burnable neutron absorber in its composition, fissile nuclear material 40 and radial spacers 75 about it, fixed neutron absorber 50 and neutron reflector 30. In this specific example, the fissile material 40 is selected as TRISO (TRi- structural ISOtropic) particles embedded in a carbonaceous matrix (e g., TRISO fuel compacts). Some or all TRISO fuel compacts may also include burnable absorber material depending on the specific location of the FMA 100’ within the reactor core of a nuclear reactor. Additional shapes containing burnable absorber material 55 (see e.g., FIG. 1) may be distributed within the FMA 100’ as required. In the illustrated example, the sealed FMA outer sleeve 10 and end cap 15 are constructed of silicon carbide because of its neutron transparency, irradiation behavior, high radionuclide retention, and low hydrogen permeability, although other materials may also suffice. Graphite is specified as a neutron reflector material 25 and placed within the upper and lower regions of the FMA 100’ to optimize utilization of fissile material and to shield the upper and lower sealed closure joints of the outer sleeve 10 from neutron irradiation damage. The solid moderator material 45 is selected to be a high-temperature hydride moderator, such as yttrium hydride. The size, volume, spacing, shape, and hydrogen content of the solid moderator are tailored to the specific location in the reactor core. Chemically inert axial ceramic spacers 60 and radial spacers 70 with adequate radiation tolerance are placed between the yttrium hydride moderating material and the fissile TRISO fuel compacts and between the hydride moderator material and the sealed sheath 10 to mitigate potential chemical reactions that may be detrimental to the performance of these materials. The axial ceramic spacers 65 may contain a small quantity of fixed neutron absorber as required by the specific location within the reactor core. A second type of neutron absorber may be manufactured in the shape of an annular ring or in the shape of a radial spacer 75 and distributed as needed throughout the FMA 100’.

[0047] Figure 3 provides one example of an implementation of the FMA 100” for use at lower temperature, for example at temperatures less than 1000 K (e.g., approximately 900 K) in a reactor with a thermal or fast neutron spectrum. The FMA 100” includes within a sealed sheath or outer sleeve 10 (sealed with end cap(s) 15), a neutron reflector 25, fissile nuclear material 40, a solid moderator 45 that can be included for applications that require a thermal neutron spectrum, fertile nuclear material 80, fissile nuclear material 40, a gas plenum 20, a neutron reflector 30, and radial spacers 70 that at least partially form or define the gas plenum 20. In this case, the sealed sheath 10 (with end caps 15) may be constructed of a metal or metallic alloy with suitable radiation resistance, mechanical properties, and nuclear properties. The fissile material 40 may consist of cylindrical or annular pellets of uranium oxide, nitrides, or carbide compounds. Plutonium or mixtures of uranium and plutonium may also be used as the fissile material. Fertile material 80 may be included in the FMA 100” as a separate fuel pellet or in pellets containing both fissile and fertile elements. The solid moderator material (for thermal neutron spectrum) 45 may consist of beryllium or beryllium ceramic compounds in the form of discs placed as needed within the FMA 100”. Beryllium or ceramic beryllium compounds are used as upper and lower axial neutron reflectors 25 within the FMA 100”. A gas plenum 20 formed using one or more radial spacer(s) 70 is included in the lower section of the FMA 100” at lower temperature to accommodate gas release from the fuel pellets (of the fissile nuclear material 40).

[0048] Figure 4 provides one example of an FMA 100”’ for use at temperatures greater than approximately 1500 K. The FMA 100’” includes within a sealed sheath or outer sleeve 10 (sealed with end cap(s) 15) a gas plenum 20, burnable neutron absorber 55, fissile nuclear material 40, solid moderator 45, fissile nuclear material 40, and solid moderator 45. The sealed sheath 10 (and end caps 15) is manufactured from a ceramic material with radiation resistance, material properties, and nuclear properties suitable for the specific nuclear reactor application. The sealed sheath 10 contains fissile nuclear material 40 in the form of TRISO fuel compacts in a carbonaceous matrix, a high-temperature solid hydride moderator material 45 encased within a secondary gas-tight container (e.g., can) 47 that mitigates hydrogen release, and a gas plenum 20 (in an upper section of the sleeve 10) to account for expansion of gas at high temperature. The solid moderator 45 can is constructed of a material compatible with the encased hydride, the TRISO compacts, and the burnable neutron absorber. Burnableneutron absorber materials are formed into discs and placed as required within each individual FMA 100” ’as designed.

[0049] Figure 5 provides one example of an implementation of an FMA 100”” which includes fertile materials 80 along with fissile materials 40. The FMA 100”” includes within a sealed sheath or outer sleeve 10 (sealed with end cap(s) 15) neutron reflector material 25, fissile nuclear material 40, fertile nuclear material 80, fissile and fertile nuclear material 40, 80 and a solid moderator 45. Fertile materials may initially provide reactivity hold down of the reactor core through neutron capture. Neutron capture by the fertile material results in the production of fissile material. Fertile material may be placed in a pellet, compact, or other shape that contains only fertile material, may be placed in a pellet, compact, or other shape and diluted with an inert material which is neither fertile nor fissile, or may be placed in the same pellet, compact, or other shape along with fissile material. The fissile material produced through neutron capture by the fertile material in these forms adds reactivity to the core (of the nuclear reactor) over time, and may be used to extend the operating lifetime of the core. The quantity of fertile materials, fissile materials, solid moderator material and neutron reflector material within each separate FMA 100”” and the arrangement of these materials within each separate FMA 100”” is optimized to meet the operating requirements of the nuclear reactor. Other components, materials, or features such as the outer sleeve, the type and function of the seal on the outer sleeve, gas plenum, upper and lower reflectors, fixed neutron absorbers, burnable neutron absorbers, axial spacers, radial spacers, and axial and radial spacers containing neutron absorbing materials are included and arranged based on the design requirements for each individual FMA operating within the reactor core as required to meet reactor operating requirements.

[0050] The FMA assemblies described in Figure 1 through Figure 5 share the same basic structure, comprised of a sealed or unsealed sleeve or sheath 10 fabricated from ceramic or metallic materials or combinations of ceramic and metallic materials, and which may incorporate one or more types of each class of materials including fissile materials, fertile materials, solid neutron moderating materials, burnable neutron absorber materials, fixed neutron absorber materials, neutron reflector materials, axial spacers, radial spacers, axial and radial spacers containing neutron absorbing materials. A gas plenum may or may not be included in the FMA, depending on the specific types of fissile materials, fertile materials, andneutron absorbing materials included in the FMA. The specific design and implementation of each Fuel Moderator and Absorber (FMA) assembly consisting of or including these components may be tailored based on the specific type of nuclear reactor, the specific reactor operating objectives, and the specific location of the FMA within the reactor. The system components may be assembled and tested in a factory environment to yield a Fuel Moderator and Absorber (FMA) assembly designed for a specific reactor and a specific location within a reactor to optimize reactor performance.

[0051] The Fuel Moderator and Absorber assembly provides a mechanism to retain gaseous and non-gaseous radionuclides produced through nuclear fission using one or more barriers, a mechanism to retain hydrogen required for the function of solid hydride moderators through the use of one or more hydrogen retention barriers, a mechanism to configure and maintain the optimal geometry of the fissile material, fertile material, neutron moderating material, neutron reflecting material, and fixed and burnable neutron absorbing material, provides a mechanism to ensure the coolability of all components of the FMA, provides a mechanism to prevent detrimental chemical reactions between dissimilar components within and encasing the FMA, and provides a mechanism to accommodate irradiation-induced swelling of certain components.Additional Embodiments

[0052] In embodiments of the present disclosure, a Fuel Moderator and Absorber (FMA) assembly may be in accordance with any of the following clauses:

[0053] Clause 1. A combined nuclear fuel, moderator, and absorber assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron absorber materials disposed inside the sleeve; and one or more neutron reflector materials disposed inside the sleeve.

[0054] Clause 2. The assembly of clause 1, further comprising: one or more axial spacers inside the sleeve; one or more radial spacers inside the sleeve; and a gas plenum in the sleeve configured to retain one or more gaseous or non-gaseous fission products released by the one or more fissile nuclear materials inside the sleeve, wherein the one or more neutron absorber materials disposed inside the sleeve comprises one or more burnable neutron absorber materials and one or more fixed neutron absorber materials.

[0055] Clause 3. The assembly of clause 2, wherein the one or more fissile nuclear materials are three types of fissile nuclear material, the one or more fertile nuclear materials are three types of fertile nuclear materials, the one or more neutron moderating materials are two types of neutron moderating materials, the one or more nuclear reflector materials are two types of nuclear reflector materials, the one or more fixed neutron absorber materials are two types of neutron absorber materials, the one or more burnable neutron absorber materials are two types of burnable neutron absorber materials.

[0056] Clause 4. The assembly of clause 3, wherein one of the two neutron moderating materials is radially surrounded by one of the three types of fissile nuclear material.

[0057] Clause 5. The assembly of any of clauses 2-4, wherein the one or more radial spacers is disposed about at least one of the one or more fissile nuclear materials or one or more neutron moderating materials.

[0058] Clause 6. The assembly of any preceding clause, further comprising an end cap at each end of the sleeve to seal the sleeve.

[0059] Clause 7. The assembly of any preceding clause, wherein the sleeve comprises a ceramic material or a metallic material or a combination of a ceramic material and a metallic material.

[0060] Clause 8. The assembly of any preceding clause, wherein the one or more fissile nuclear materials comprise tri -structural isotropic (TRISO) particles embedded in a carbonaceous matrix.

[0061] Clause 9. The assembly of any of clauses 1-7, wherein the one or more fissile nuclear materials comprises a ceramic pellet.

[0062] Clause 10. The assembly of clause 9, wherein the ceramic pellet comprises a fissile metal oxide, carbide, or nitride compound.

[0063] Clause 11. The assembly of any of clauses 1-7, wherein the one or more fissile nuclear materials comprises a metallic alloy containing a fissile metal and a non-fissile metallic component.

[0064] Clause 12. The assembly of any preceding clause, wherein at least one of the one or more neutron moderating materials comprises a solid metal hydride material.

[0065] Clause 13. The assembly of any preceding clause, wherein at least one of the one or more neutron moderating materials comprises a graphitic or other carbonaceous material.

[0066] Clause 14. The assembly of any preceding clause, wherein at least one of the one or more neutron moderating materials comprises beryllium or a compound of beryllium.

[0067] Clause 15. The assembly of any preceding clause, wherein at least one of the one or more neutron reflector materials comprises a graphitic or other carbonaceous material.

[0068] Clause 16. The assembly of any preceding clause, wherein at least one of the one or more neutron reflector materials comprises beryllium or a ceramic or metallic compound of beryllium.

[0069] Clause 17. The assembly of any of clauses 2-16, wherein at least one of the one or more axial spacers prevent a chemical reaction of components at one or more horizontal interfaces inside the sleeve.

[0070] Clause 18. The assembly of any of clauses 2-17, wherein at least one of the one or more axial spacers include a burnable or fixed neutron absorber.

[0071] Clause 19. The assembly of any of clauses 2-18, wherein at least one of the one or more radial spacers prevent a chemical reaction of components at one or more vertical interfaces inside the sleeve.

[0072] Clause 20. The assembly of any of clauses 2-19, wherein at least one of the one or more radial spacers are configured to mitigate damage to the sleeve caused by expansion of materials internal inside the sleeve.

[0073] Clause 21. The assembly of any of clauses 2-20, wherein at least one of the one or more radial spacers include a burnable or fixed neutron absorber.

[0074] Clause 22. The assembly of any of clauses 2-21, wherein at least one of the one or more radial spacers include a neutron moderating material.

[0075] Clause 23. The assembly of any of clauses 2-22, wherein at least one of the one or more radial spacers include a neutron reflecting material.

[0076] Clause 24. A combined nuclear fuel, moderator, and absorber (FMA) assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron absorber materials disposed inside the sleeve; one or more neutron reflector materials disposed inside the sleeve; one or more axial spacers inside the sleeve between the one or more fissile nuclear material and the one or more neutron moderating materials; and one or more radial spacers inside the sleeve disposed about at least one of the one or more neutron moderating materials or about at least one of the one or more fissile nuclear materials, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of approximately 1000 to 1500 degrees Kelvin.

[0077] Clause 25. The assembly of clause 24, wherein the one or more neutron absorber materials include one or more fixed neutron absorber materials.

[0078] Clause 26. The assembly of any of clauses 24-25, further comprising an end cap at each end of the sleeve to seal the sleeve.

[0079] Clause 27. The assembly of clause 26, wherein the sleeve and end cap comprise silicon carbide.

[0080] Clause 28. The assembly of any of clauses 24-27, wherein at least one of the one or more axial spacers comprises a burnable neutron absorber material.

[0081] Clause 29. The assembly of any of clauses 24-28, wherein the one or more fissile nuclear materials comprise tri -structural isotropic (TRISO) particles embedded in a carbonaceous matrix.

[0082] Clause 30. The assembly of clause 29, wherein the TRISO particles are TRISO fuel compacts comprising burnable absorber material.

[0083] Clause 31. The assembly of any of clauses 24-30, wherein the one or more neutron reflector materials are two neutron reflector material volumes disposed in an upper region and a lower region of the sleeve.

[0084] Clause 32. The assembly of any of clauses 24-31, wherein the one or more axial spacers and one or more radial spacers are chemically inert.

[0085] Clause 33. A combined nuclear fuel, moderator, and absorber (FMA) assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron reflector materials disposed inside the sleeve; one or more radial spacers inside the sleeve about at least one of the one or more neutron reflector materials; and a gas plenum in the sleeve configured to retain one or more gaseous or non-gaseous fission products released by the one or more fissile nuclear materials inside the sleeve, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of less than 1000 degrees Kelvin.

[0086] Clause 34. The assembly of clause 33, further comprising an end cap at each end of the sleeve to seal the sleeve.

[0087] Clause 35. The assembly of any of clauses 33-34, wherein the one or more radial spacers at least partially define the gas plenum.

[0088] Clause 36. The assembly of clause 34, wherein the sleeve and end cap comprises a metal or metallic alloy.

[0089] Clause 37. The assembly of any of clauses 33-36, wherein the one or more fissile nuclear materials comprises cylindrical or annular pellets of uranium oxide, nitrides, carbon compounds.

[0090] Clause 38. The assembly of any of clauses 33-37, wherein the one or more neutron reflector materials or neutron moderating materials comprises beryllium or beryllium ceramic compounds.

[0091] Clause 39. The assembly of any of clauses 33-38, wherein the gas plenum is in a lower section of the sleeve.

[0092] Clause 40. A combined nuclear fuel, moderator, and absorber (FMA) assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; a gas plenum in the sleeve configured to retain one or more gaseous or non-gaseous fission products released by the one or more fissile nuclear materials inside the sleeve; and one or more axial spacers between the gas plenum and at least one of the one or more fissile nuclear materials, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of more than 1500 degrees Kelvin.

[0093] Clause 41. The assembly of clause 40, further comprising an end cap at each end of the sleeve to seal the sleeve.

[0094] Clause 42. The assembly of clause 40, wherein the gas plenum is in an upper section of the sleeve.

[0095] Clause 43. The assembly of any of clauses 40-42, wherein the or more fissile nuclear materials are two fissile nuclear materials and the one or more neutron moderating materials are two neutron moderating materials.

[0096] Clause 44. The assembly of any of clauses 40-43, wherein the one or more axial spacers comprises burnable neutron absorber material.

[0097] Clause 45. The assembly of any of clauses 40-44, wherein the one or more fissile nuclear materials comprise tri -structural isotropic (TRISO) fuel compacts in a carbonaceous matrix.

[0098] Clause 46. The assembly of any of clauses 40-45, wherein at least one of the one or more neutron moderating materials is a solid hydride moderator material encased within a gas-tight container that mitigates hydrogen release.

[0099] Clause 47. A combined nuclear fuel, moderator, and absorber assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; and one or more neutron reflector materials disposed inside the sleeve, wherein at least some of the one or more fissile nuclear material and one or more fertile nuclear material are mixed together.

[0100] Clause 48. The assembly of clause 47, further comprising an end cap at each end of the sleeve to seal the sleeve.

[0101] Clause 49. A combined nuclear fuel, moderator, and absorber system, comprising: a sealed or unsealed ceramic or metallic sleeve; a fissile material; a neutron moderating material; a burnable neutron absorber material; a fixed neutron absorber material; one or more axial spacers; one or more radial spacers; a neutron reflector material; and a gas plenum.

[0102] Clause 50. The system of clause 49, wherein the fissile material comprises tri-structural isotropic (TRISO) particles embedded in a carbonaceous compact.

[0103] Clause 51. The system of clause 49, wherein the fissile material comprises a ceramic pellet such as a fissile metal oxide, carbide, or nitride compound.

[0104] Clause 52. The system of clause 49, wherein the fissile material comprises a metallic alloy containing a fissile metal and a non-fissile metallic component.

[0105] Clause 53. The system of any of clauses 49-52, wherein the neutron moderating material comprises a solid metal hydride material.

[0106] Clause 54. The system of any of clauses 49-53, wherein the neutron moderating material comprises a graphitic or other carbonaceous material.

[0107] Clause 55. The system of any of clauses 49-54, wherein the neutron moderating material comprises beryllium or a compound of beryllium.

[0108] Clause 56. The system any of clauses 49-55, wherein the neutron reflector material comprises a graphitic or other carbonaceous material.

[0109] Clause 57. The system of any of clauses 49-56, wherein the neutron reflector material comprises beryllium or a ceramic or metallic compound of beryllium.

[0110] Clause 58. The system of any of clauses 49-57, where the one or more axial spacers prevent a chemical reaction of components inside the sleeve at horizontal interfaces.[01U] Clause 59. The system of any of clauses 49-58, wherein the axial spacers include a burnable or fixed neutron absorber.

[0112] Clause 60. The system of any of clauses 49-59, wherein the radial spacers prevent a chemical reaction of components inside the sleeve at vertical interfaces.

[0113] Clause 61. The system of any of clauses 49-60, wherein the radial spacers mitigate damage to the sleeve from expansion of materials inside the sleeve.

[0114] Clause 62. The system of any of clauses 49-61, wherein the radial spacers include a burnable or fixed neutron absorber.

[0115] Clause 63. The system of any of clauses 49-62, wherein the radial spacers include a neutron moderating material.

[0116] Clause 64. The system of any of clauses 49-63, wherein the radial spacers include a neutron reflecting material.

[0117] Clause 65: A Fuel Moderator and Absorber assembly with multiple components that may be individually tailored for use within a nuclear reactor core by including or excluding a variety of components or features to optimize reactor performance comprising: a sealed or unsealed ceramic or metallic sleeve that acts to maintain the geometry of components internal to the FMA, if sealed provides a means for retention of gaseous fission products released by the nuclear fuel internal to the FMA, if sealed provides a means for retention of non-gaseous fission products released from the nuclear fuel internal to the FMA, and if sealed may provide the capability to retain hydrogen as necessary for the optimal function of the solid hydride moderator materials that may be included in the FMA, one or more fissile nuclear materials that may be manufactured with dimensions, geometric configurations, and mass as necessary for the optimal function of the FMA, one or more fertile nuclear materials, if required, that may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA, one or more solid neutron moderating materials, if required, that may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA, one or more burnable neutron absorber materials, if required, that may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA, one or more fixed neutron absorber materials, if required, that may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA,one or more axial spacers that, if required, may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA, one or more radial spacers, if required, that may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA, one or more neutron reflectors, if required, that may be manufactured with dimensions, geometric configurations, chemical composition, and mass as necessary for the optimal function of the FMA,A gas plenum, if required, that may vary in location and dimensional volume as is necessary for the optimal function of the FMA.

[0118] Clause 66: The system of Clause 65, wherein the nuclear fuel comprises coated fissile particles such as TRISO or other coated particle fuels embedded in a carbonaceous compact.

[0119] Clause 67: The system of Clause 65, wherein the nuclear fuel comprises a ceramic pellet such as a fissile material composed of binary or ternary oxide, carbide, or nitride compounds.

[0120] Clause 68: The system of Clause 65, wherein the nuclear fuel comprises a metallic alloy containing a fissile metal and a non-fissile metallic component.

[0121] Clause 69: The system of any preceding clause, wherein the moderator material comprises a solid metal hydride material.

[0122] Clause 70: The system of any preceding clause, wherein the moderator material comprises graphite.

[0123] Clause 71 : The system of any preceding clause, wherein the moderator material comprises beryllium or a compound of beryllium.

[0124] Clause 72: The system of any preceding clause, wherein the reflector material comprises graphite.

[0125] Clause 73: The system of any preceding clause, wherein the reflector material comprises beryllium or a compound of beryllium.

[0126] Clause 74: The system of any preceding clause, wherein the system includes a gas plenum.

[0127] Clause 75: The system of any preceding clause, where the system includes an axial spacer that prevents chemical reaction of components internal to the FMA at horizontal interfaces.

[0128] Clause 76: The system of any preceding clause, where the system includes an axial spacer that incorporates a burnable or fixed neutron absorber material.

[0129] Clause 77: The system of any preceding clause, where the system includes a radial spacer that prevents chemical reaction of components internal to the FMA at vertical interfaces.

[0130] Clause 78: The system of any preceding clause, where the system includes a radial spacer that is designed to be a sacrificial system that mitigates damage to the outer sleeve that may be caused by expansion of materials internal to the FMA.

[0131] Clause 79: The system of any preceding clause, where the system includes a radial spacer that incorporates a burnable or fixed neutron absorber.

[0132] Clause 80: The system of any preceding clause, where the system includes a radial spacer that incorporates a neutron moderating material.

[0133] Clause 81 : The system of any preceding clause, where the system includes a radial spacer that incorporates a neutron reflecting material.

[0134] While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the systems and methods described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure. Accordingly, the scope of the present inventions is defined only by reference to the appended claims.

[0135] Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described in this section or elsewhere in this specification unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or processso disclosed, may be combined in any combination, except combinations where at least some of such components, materials, and features and / or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the components, materials, and features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0136] Furthermore, certain components, materials, and features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various components, materials, and features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable combination. Moreover, although components, materials, and features may be described above as acting in certain combinations, one or more components, materials, and features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination.

[0137] Moreover, while components, materials, or components, materials, and features may be depicted in the drawings or described in the specification in a particular order, such components, material, or components, materials, and features need not be implemented in the particular order shown or in sequential order, or that all components, material, or components, materials, and features be implemented, to achieve desirable results. Other components, material, or components, materials, and features that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional components, material, or components, materials, and features can be implemented before, after, simultaneously, or between any of the described components, material, or components, materials, and features. Further, the components, materials, or features may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual components, material, or components, materials, or features taken in the processes illustrated and / or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the components, materials, or features described above may be removed, others may be added. Furthermore, the components, materials, or features and attributes of the specific embodiments disclosed above may be combined indifferent ways to form additional embodiments, all of which fall within the scope of the present disclosure. Also, 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 described components and systems can generally be integrated together in a single product or packaged into multiple products.

[0138] For purposes of this disclosure, certain aspects, advantages, and novel components, materials, or features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0139] Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain components, materials, or features. Thus, such conditional language is not generally intended to imply that components, materials, or features are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these components, materials, or features are included or are to be implemented in any particular embodiment.

[0140] Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

[0141] Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of the stated amount.

[0142] The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.

[0143] Of course, the foregoing description is that of certain components, materials, or features, aspects and advantages of the present invention, to which various changes and modifications can be made without departing from the spirit and scope of the present invention. Moreover, the devices described herein need not feature all of the objects, advantages, components, materials, or features and aspects discussed above. Thus, for example, those of skill in the art will recognize that the invention can be embodied or carried out in a manner that achieves or optimizes one advantage or a group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. In addition, while a number of variations of the invention have been shown and described in detail, other modifications and methods of use, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is contemplated that various combinations or subcombinations of these specific components, materials, or features and aspects of embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various components, materials, or features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the discussed devices.

Claims

WHAT IS CLAIMED IS:

1. A combined nuclear fuel, moderator, and absorber assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron absorber materials disposed inside the sleeve; and one or more neutron reflector materials disposed inside the sleeve.

2. The assembly of claim 1, further comprising: one or more axial spacers inside the sleeve; one or more radial spacers inside the sleeve; and a gas plenum in the sleeve configured to retain one or more gaseous or non- gaseous fission products released by the one or more fissile nuclear materials inside the sleeve, wherein the one or more neutron absorber materials disposed inside the sleeve comprises one or more burnable neutron absorber materials and one or more fixed neutron absorber materials.

3. The assembly of claim 2, wherein the one or more fissile nuclear materials are three types of fissile nuclear material, the one or more fertile nuclear materials are three types of fertile nuclear materials, the one or more neutron moderating materials are two types of neutron moderating materials, the one or more nuclear reflector materials are two types of nuclear reflector materials, the one or more fixed neutron absorber materials are two types of neutron absorber materials, the one or more burnable neutron absorber materials are two types of burnable neutron absorber materials.

4. The assembly of claim 3, wherein one of the two neutron moderating materials is radially surrounded by one of the three types of fissile nuclear material.

5. The assembly of any of claims 2-4, wherein the one or more radial spacers is disposed about at least one of the one or more fissile nuclear materials or one or more neutron moderating materials.

6. The assembly of any preceding claim, further comprising an end cap at each end of the sleeve to seal the sleeve.

7. The assembly of any preceding claim, wherein the sleeve comprises a ceramic material or a metallic material or a combination of a ceramic material and a metallic material.

8. The assembly of any preceding claim, wherein the one or more fissile nuclear materials comprise tri-structural isotropic (TRISO) particles embedded in a carbonaceous matrix.

9. The assembly of any of claims 1-7, wherein the one or more fissile nuclear materials comprises a ceramic pellet.

10. The assembly of claim 9, wherein the ceramic pellet comprises a fissile metal oxide, carbide, or nitride compound.

11. The assembly of any of claims 1-7, wherein the one or more fissile nuclear materials comprises a metallic alloy containing a fissile metal and a non-fissile metallic component.

12. The assembly of any preceding claim, wherein at least one of the one or more neutron moderating materials comprises a solid metal hydride material.

13. The assembly of any preceding claim, wherein at least one of the one or more neutron moderating materials comprises a graphitic or other carbonaceous material.

14. The assembly of any preceding claim, wherein at least one of the one or more neutron moderating materials comprises beryllium or a compound of beryllium.

15. The assembly of any preceding claim, wherein at least one of the one or more neutron reflector materials comprises a graphitic or other carbonaceous material.

16. The assembly of any preceding claim, wherein at least one of the one or more neutron reflector materials comprises beryllium or a ceramic or metallic compound of beryllium.

17. The assembly of any of claims 2-16, wherein at least one of the one or more axial spacers prevent a chemical reaction of components at one or more horizontal interfaces inside the sleeve.

18. The assembly of any of claims 2-17, wherein at least one of the one or more axial spacers include a burnable or fixed neutron absorber.

19. The assembly of any of claims 2-18, wherein at least one of the one or more radial spacers prevent a chemical reaction of components at one or more vertical interfaces inside the sleeve.

20. The assembly of any of claims 2-19, wherein at least one of the one or more radial spacers are configured to mitigate damage to the sleeve caused by expansion of materials internal inside the sleeve.

21. The assembly of any of claims 2-20, wherein at least one of the one or more radial spacers include a burnable or fixed neutron absorber.

22. The assembly of any of claims 2-21, wherein at least one of the one or more radial spacers include a neutron moderating material.

23. The assembly of any of claims 2-22, wherein at least one of the one or more radial spacers include a neutron reflecting material.

24. A combined nuclear fuel, moderator, and absorber (FMA) assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron absorber materials disposed inside the sleeve; one or more neutron reflector materials disposed inside the sleeve; one or more axial spacers inside the sleeve between the one or more fissile nuclear material and the one or more neutron moderating materials; and one or more radial spacers inside the sleeve disposed about at least one of the one or more neutron moderating materials or about at least one of the one or more fissile nuclear materials, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of approximately 1000 to 1500 degrees Kelvin.

25. The assembly of claim 24, wherein the one or more neutron absorber materials include one or more fixed neutron absorber materials.

26. The assembly of any of claims 24-25, further comprising an end cap at each end of the sleeve to seal the sleeve.

27. The assembly of claim 26, wherein the sleeve and end cap comprise silicon carbide.

28. The assembly of any of claims 24-27, wherein at least one of the one or more axial spacers comprises a burnable neutron absorber material.

29. The assembly of any of claims 24-28, wherein the one or more fissile nuclear materials comprise tri-structural isotropic (TRISO) particles embedded in a carbonaceous matrix.

30. The assembly of claim 29, wherein the TRISO particles are TRISO fuel compacts comprising burnable absorber material.

31. The assembly of any of claims 24-30, wherein the one or more neutron reflector materials are two neutron reflector material volumes disposed in an upper region and a lower region of the sleeve.

32. The assembly of any of claims 24-31, wherein the one or more axial spacers and one or more radial spacers are chemically inert.

33. A combined nuclear fuel, moderator, and absorber (FMA) assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; one or more neutron reflector materials disposed inside the sleeve; one or more radial spacers inside the sleeve about at least one of the one or more neutron reflector materials; and a gas plenum in the sleeve configured to retain one or more gaseous or non- gaseous fission products released by the one or more fissile nuclear materials inside the sleeve, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of less than 1000 degrees Kelvin.

34. The assembly of claim 33, further comprising an end cap at each end of the sleeve to seal the sleeve.

35. The assembly of any of claims 33-34, wherein the one or more radial spacers at least partially define the gas plenum.

36. The assembly of claim 34, wherein the sleeve and end cap comprises a metal or metallic alloy.

37. The assembly of any of claims 33-36, wherein the one or more fissile nuclear materials comprises cylindrical or annular pellets of uranium oxide, nitrides, carbon compounds.

38. The assembly of any of claims 33-37, wherein the one or more neutron reflector materials or neutron moderating materials comprises beryllium or beryllium ceramic compounds.

39. The assembly of any of claims 33-38, wherein the gas plenum is in a lower section of the sleeve.

40. A combined nuclear fuel, moderator, and absorber (FMA) assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; a gas plenum in the sleeve configured to retain one or more gaseous or non- gaseous fission products released by the one or more fissile nuclear materials inside the sleeve; and one or more axial spacers between the gas plenum and at least one of the one or more fissile nuclear materials, wherein the FMA assembly is configured for use in a nuclear reactor configured to operate within a temperature range of more than 1500 degrees Kelvin.

41. The assembly of claim 40, further comprising an end cap at each end of the sleeve to seal the sleeve.

42. The assembly of claim 40, wherein the gas plenum is in an upper section of the sleeve.

43. The assembly of any of claims 40-42, wherein the or more fissile nuclear materials are two fissile nuclear materials and the one or more neutron moderating materials are two neutron moderating materials.

44. The assembly of any of claims 40-43, wherein the one or more axial spacers comprises burnable neutron absorber material.

45. The assembly of any of claims 40-44, wherein the one or more fissile nuclear materials comprise tri-structural isotropic (TRISO) fuel compacts in a carbonaceous matrix.

46. The assembly of any of claims 40-45, wherein at least one of the one or more neutron moderating materials is a solid hydride moderator material encased within a gas-tight container that mitigates hydrogen release.

47. A combined nuclear fuel, moderator, and absorber assembly, comprising: a sleeve; one or more fissile nuclear materials disposed inside the sleeve; one or more fertile nuclear materials disposed inside the sleeve; one or more neutron moderating materials disposed inside the sleeve; and one or more neutron reflector materials disposed inside the sleeve, wherein at least some of the one or more fissile nuclear material and one or more fertile nuclear material are mixed together.

48. The assembly of claim 47, further comprising an end cap at each end of the sleeve to seal the sleeve.

49. A combined nuclear fuel, moderator, and absorber system, comprising: a sealed or unsealed ceramic or metallic sleeve; a fissile material; a neutron moderating material; a burnable neutron absorber material; a fixed neutron absorber material; one or more axial spacers; one or more radial spacers; a neutron reflector material; and a gas plenum.

50. The system of claim 49, wherein the fissile material comprises tri-structural isotropic (TRISO) particles embedded in a carbonaceous compact.

51. The system of claim 49, wherein the fissile material comprises a ceramic pellet such as a fissile metal oxide, carbide, or nitride compound.

52. The system of claim 49, wherein the fissile material comprises a metallic alloy containing a fissile metal and a non-fissile metallic component.

53. The system of any of claims 49-52, wherein the neutron moderating material comprises a solid metal hydride material.

54. The system of any of claims 49-53, wherein the neutron moderating material comprises a graphitic or other carbonaceous material.

55. The system of any of claims 49-54, wherein the neutron moderating material comprises beryllium or a compound of beryllium.

56. The system any of claims 49-55, wherein the neutron reflector material comprises a graphitic or other carbonaceous material.

57. The system of any of claims 49-56, wherein the neutron reflector material comprises beryllium or a ceramic or metallic compound of beryllium.

58. The system of any of claims 49-57, where the one or more axial spacers prevent a chemical reaction of components inside the sleeve at horizontal interfaces.

59. The system of any of claims 49-58, wherein the axial spacers include a burnable or fixed neutron absorber.

60. The system of any of claims 49-59, wherein the radial spacers prevent a chemical reaction of components inside the sleeve at vertical interfaces.

61. The system of any of claims 49-60, wherein the radial spacers mitigate damage to the sleeve from expansion of materials inside the sleeve.

62. The system of any of claims 49-61, wherein the radial spacers include a burnable or fixed neutron absorber.

63. The system of any of claims 49-62, wherein the radial spacers include a neutron moderating material.

64. The system of any of claims 49-63, wherein the radial spacers include a neutron reflecting material.