Sic coated boron fuel burnable absorbers

Abstract

A fuel element (100) for a nuclear reactor, the fuel element comprising non-fissile particles (110) dispersed throughout fissile fuel (120), the non-fissile particles comprising a core comprising neutron absorbing material, wherein the neutron absorbing material is positioned at an innermost radial portion of the core, wherein the core is configured to remain stable at a temperature no less than 1000 °C; and an outer layer surrounding the core, the outer layer comprising silicon carbide.

Description

TITLEUSE OF SIC COATED BORON INTEGRAL FUEL BURNABLE ABSORBERSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Serial No. 63 / 565,880 filed March 15, 2024, entitled “USE OF SIC COATED BORON INTEGRAL FUEL BURNABLE ABSORBERS,” the contents of which is hereby incorporated by reference in its entirety herein.BACKGROUND

[0002] Current integral fuel burnable absorbers can lower initial reactivity of nuclear fuel but may still be present late in the fuel and continue to absorb neutrons, thereby potentially resulting in parasitic loss of reactivity. Other burnable fuel absorbers which are less likely to be parasitic absorbers later in the life of a fuel may be rapidly depleted and / or exacerbate issues associated with safety and operation. Accordingly, a need exists for alternative burnable absorbers.GOVERNMENT CONTRACT

[0003] This invention was made with government support under Contract No. DE-NE0009033 awarded by the Department of Energy. The government has certain rights in the invention.SUMMARY

[0004] The following summary is provided to facilitate an understanding of some of the innovative features unique to the aspects disclosed herein and is not intended to be a full description. A full appreciation of the various aspects disclosed herein can be gained by taking the entire specification, claims, and abstract as a whole.

[0005] In various aspects, a fuel element for a nuclear reactor is disclosed. In some aspects, the fuel element includes non-fissile particles. In some aspects, the non-fissile particles include a core comprising neutron absorbing material, and an outer layer surrounding the core. In some aspects, the neutron absorbing material is positioned at an innermost radial portion of the core. In some aspects, the core is configured to remain stable at a temperature no less than 1000 °C. In some aspects, the outer layer comprising silicon carbide.

[0006] In various aspects, a fuel pellet for a nuclear reactor is disclosed. In some aspects, the fuel pellet includes fissile fuel and non-fissile particles dispersed throughout the fissile fuel.In some aspects, each of the non-fissile particles includes an outer layer consisting of silicon carbide and a core enclosed by the outer layer. In some aspects, the silicon carbide comprises a columnar microstructure. In some aspects, the core comprises a boron-10 based neutron absorbing material, a first carbon-based interlayer deposited on an outer surface of the neutron absorbing material and a second second-based interlayer deposited on an outer surface of the first interlayer, the second interlayer comprising a greater density than the first carbon-based interlayer. In some aspects, the neutron absorbing material is positioned at a radially innermost portion of the core. In some aspects, the core is configured to remain stable during at least one of a formation of the outer layer around the core or a formation of the fuel pellet. In certain aspects, the graphite layer

[0007] These and other objects, features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of any of the aspects disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The various aspects described herein, together with objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings as follows.

[0009] FIG. 1 is a schematic representation of a fuel element, according to at least one nonlimiting aspect of the present disclosure.

[0010] FIG. 2 is a cross sectional view of a schematic representation of a non-fissile particle, according to at least one non-limiting aspect of the present disclosure.

[0011] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate various aspects of the present disclosure, in one form, and such exemplifications are not to be construed as limiting the scope of any of the aspects disclosed herein.DETAILED DESCRIPTION

[0012] Certain exemplary aspects of the present disclosure will now be described to provide an overall understanding of the principles of the composition, function, manufacture, and use of the compositions and methods disclosed herein. An example or examples of these aspects are illustrated in the accompanying drawing. Those of ordinary skill in the art will understand that the compositions, articles, and methods specifically described herein and illustrated in the accompanying drawing are non-limiting exemplary aspects and that the scope of the various examples of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary aspect may be combined with the features of other aspects. Such modifications and variations are intended to be included within the scope of the present disclosure.

[0013] Reference throughout the specification to “various examples,” “some examples,” “one example,” “an example,” or the like, means that a particular feature, structure, or characteristic described in connection with the example is included in an example. Thus, appearances of the phrases “in various examples,” “in some examples,” “in one example,” “in an example,” or the like, in places throughout the specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in an example or examples. Thus, the particular features, structures, or characteristics illustrated or described in connection with one example may be combined, in whole or in part, with the features, structures, or characteristics of another example or other examples without limitation. Such modifications and variations are intended to be included within the scope of the present examples.

[0014] In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as “forward,” “rearward,” “left,” “right,” “above,” “below,” “upwardly,” “downwardly,” and the like are words of convenience and are not to be construed as limiting terms.

[0015] For longer burnup nuclear fuel, a burnable absorber is required in order to moderate initial reactivity. Gd2O3 and Er2O3 are currently used as integral fuel burnable absorbers for this purpose. While lowering initial reactivity by absorbing excess neutrons at the beginning of fuel life, however they are still present late in the cycle in the fuel as the fuel ages and continue to absorb neutrons becoming an unwanted parasitic loss. ZrB2is also used as a thin coating on UO2fuel and performs very well. However, this thin coating provides very little selfshielding of the boron absorber resulting in relatively rapid absorber depletion. Therefore, forlonger cycles and / or high-energy cores, ZrB2must often be supplemented with other neutron absorbers such as Gd2Os or Er2Os.

[0016] The reaction of the10B with neutrons is:

[0017] 10B + n =>7Li +4He + gamma

[0018] After absorbing a neutron, boron-10 becomes lithium-7 and helium-4 which absorb negligible amounts of neutrons. However, the He that is released increases the fuel rod internal pressure. While acceptable for lower enrichments (<~5%), at higher enrichments the additional B required results in unacceptable He pressures.

[0019] All pressurized water reactors (PWRs) utilize dissolved boron in the primary loop to help control excess reactivity. This increases operational complexity and costs and results in tritium discharges from the PWR. This dissolved boron cannot be replaced by increasing the ZrB2coatings because any increase in the coating thickness would lead to unacceptable rod internal pressure increases.

[0020] SiC coatings have been used to coat UCO and UO2, such as, for example, in making TRISO (TRi-structural ISOtropic) fuel but not just an integral fuel burnable absorber. In order to minimize the gas stresses on the SiC shell due to the He release as the B10 is reacted, the lowest molar density of B is desirable.

[0021] The use of boron or boron compounds or metal coated boron compounds coated with SiC can be made into small particles that can be mixed with UO2powders and pressed into pellets. The SiC coated boron compounds provide a miniature vessel to contain the He produced by the reaction of the B10 with neutrons and therefore will not increase the nuclear fuel rod internal pressure. The SiC coating also prevents the reaction of the B compounds with the UO2during sintering of the of the UO2pellets.

[0022] By having the B available as a particle rather than a very thin coating, the B will last longer than currently since the outer most layer of the B particle will be burned before exposing the next layer of the B particle to be burned, and so on. This allows the B to provide neutron reactivity hold-down for a much longer time period than does the current thin layer of B material.

[0023] This approach will allow the extension of the highly successful use of ZrB2 as an IFBA material for <5% U235 enrichments to the >5% U235 enrichments with LEU+ fuels. It could also lead to boron-free operations in primary coolant since the boron loading in the fuel could be increased without increasing the rod internal pressure.

[0024] Now referring to FIG. 1 , a schematic representation of a fuel element 100 for a nuclear reactor is disclosed, in accordance with at least one non-limiting aspect of the present disclosure. The fuel element 100 can be configured for use in a solid-fueled nuclear reactor, such as, for example, a PWR. For example, the fuel element 100 may be in the form of a pellet or a compact. Thus, the fuel element may be loaded into a fuel rod or a core. In various examples, the fuel element 100 includes non-fissile particles 110 which may be dispersed throughout a fissile material 120, such as a material comprising U-235. In certain examples, the fuel element 100 comprises fissile material 120 having U-235 enrichment levels of 5% or greater. Other configurations of the fuel element 100 are contemplated by the present disclosure. For example, the fuel element may be configured to exclude fissile material to be used in concert with other neighboring fissile fuel elements.

[0025] FIG. 2 illustrates a cross-sectional view of a schematic representation of a non-fissile particle 110 according to at least one non-limiting aspect of the present disclosure. Now referring to FIGs. 1 and 2, the non-fissile particles 110 include a core 112 comprising a neutron absorbing material 113 and an outer layer 116. The outer layer 116 surrounds the core 112. The neutron absorbing material 113 is positioned at an innermost radial portion of the core 112. For example, in examples where the non-fissile particle 110 is spherical, the core 112 and the outer layer 116 are concentric spheres, the neutron absorbing material 113 being positioned at the center of the non-fissile particle 110 and the outer layer 116 being in the form of a hollow spherical shell enclosing the core 112 and / or the neutron absorbing material 113. In various examples, the non-fissile particles 110 have an outer diameter in a range of 0.1 mm to 2 mm and the core 112 can have an outer diameter in a range of 100 microns to 1000 microns. Other geometries of the non-fissile particle 110 are contemplated by the present disclosure. For example, in some implementations, the non-fissile particle 110 may have a non-spherical geometry, such as a cylindrical geometry, or the outer layer 116 may be a spherical shell encapsulating a non-spherical core 112.

[0026] In various examples, the neutron absorbing material 113 is a boron-10 based material, such as natural boron or an enriched boron having B10 concentrations of no less than 19 % by weight based on the entire weight of boron isotopes of the boron-10 based material. The boron-10 based material can include elemental boron and / or a compound thereof, such as boron carbide (B4C), boron nitride (BN), and / or other metal-rich boride compounds. For example, the neutron absorbing material 113 can include one or more borides of any one of titanium, zirconium, hafnium, yttrium, calcium, samarium, europium, or dysprosium, or a borate compound comprising cadmium. Other configurations of the neutron absorbing material 113 are contemplated by the present disclosure. For example, in someimplementations, the neutron absorbing material 113 can include a borate, such as cadmium- based Cd3(BO3)2, or non-boron based materials such as oxides of gadolinium and / or erbium.

[0027] The outer layer 116 comprises silicon carbide (SiC). In various examples, the SiC of the outer layer 116 comprises columnar grains of (3-SiC. Alternatively, or additionally, the majority of the outer layer 116 can be comprised of a-SiC and in some cases, may consist entirely of a-SiC, such as, for example, when the outer layer 116 is formed via a process comprising a sintering temperature of no less than 1700 °C. In certain examples, the outer layer 116 has a thickness in a range of 50 microns to 500 microns. In some respects, this configuration of the outer layer 116 can provide the strength required to withstand any increases in internal pressure in the non-fissile particle 110 normally encountered during operation of a nuclear reactor, such as from expansion of helium gas produced by a boron- based neutron absorbing material 113 upon exposure to a neutron flux. Thus, the fuel element 100 can be configured to provide a flattening of reactivity over the life of the fissile fuel therein while containing the gases normally responsible for increasing pressure exerted on the fuel rods within the non-fissile particles 110, thereby maintaining dimensional stability of the non- fissile particles 110 upon exposure to a neutron flux in a reactor environment and safe operating pressures within an operating reactor incorporating the fuel elements. Other configurations of the non-fissile particles 110 are contemplated by the present disclosure. For example, in some implementations, the core 112 may be surrounded by a high porosity carbon layer, a dense carbon layer, an SiC layer, or any combination thereof, such as a high porosity carbon layer, followed by a dense carbon layer, followed by an SiC layer, followed by a carbon layer.

[0028] In various examples, the core 112 is configured to remain stable at a temperature encountered thereby during manufacture of the fuel element 100, such as a temperature no less than 1000 °C. For example, the neutron absorbing material 113 can be configured such that a melting point thereof is no less than a temperature of 1400 °C, or no less than 1700 °C, or no less than 1785 °C. In some examples, the neutron absorbing material 113 comprises B, BN, B4C, TiB2, ZrB2, HfB2, YB4, YBe, CaBe, SmBe, S1T1B4, EuBe, DyB4, or DyBe.

[0029] Alternatively, or in addition to the above, the core 112 can include one or more interlayers 114 surrounding the neutron absorbing material 113. For example, a neutron transparent carbon-based material having a melting point no less than 1000 °C, such as, for example, porous carbon and / or graphite, can be deposited onto, or encapsulate, the outer surface of the neutron absorbing material 113, thereby forming the interlayer 114. In examples where the core 112 comprises a carbon-based interlayer 114, the carbon-based material may be deposited by a physical vapor deposition and / or chemical vapor deposition process suchthat the interlayer 114 is at least 50% dense based on the bulk volume of the interlayer 114. As used herein, the term “bulk volume” refers to a volume occupied by an amount of a material, including any pores or cavities thereof, and not necessarily an entire volume occupied by a geometric footprint of a material. For example, the bulk volume of a hollow sphere having a wall thickness comprised of a porous material refers to a volume occupied by only the material and the pore volume thereof making up the wall thickness and not the hollow portion within the walls of the sphere. Thus, a density based on the bulk volume of a material may refer to a fraction of the bulk volume taken up by volume attributed to a mass of the material and not any portion of the bulk volume that is attributed to any gaps or pores. In certain examples, the core 112 can include an interlayer 114 having a thickness in a range of 50 microns to 700 microns. In some respects, this configuration of the interlayer 114 can maintain a physical state of the neutron absorbing material 113, and / or and / or a material containment thereof, upon exposure to high temperatures and / or otherwise abnormal conditions. For example, the core 112 may be subjected to temperatures exceeding a temperature associated with a phase change, or melting point, of the neutron absorbing material 113 during a sintering operation of the non-fissile particle 110 and / or the fuel element 100. Further, the core 112 may encounter temperatures associated with an increased likelihood of a chemical reaction and / or interaction between the neutron absorbing material 113 and the outer layer 116, or a precursor to the outer layer 116, during a formation of outer layer 116. Accordingly, the core 112 can be configured to withstand process conditions associated with the formation of the outer layer 116 around the core 112 and / or manufacture of the fuel element 100. Other configurations of the core 112 are contemplated by the present disclosure. For example, in some implementations, the neutron absorbing material 113 can be coated with a first carbon-based interlayer and a second carbon-based interlayer, having a greater density than the first interlayer, may be deposited on the first interlayer.

[0030] The present disclosure also provides a fuel pellet for a nuclear reactor. The fuel pellet comprises fissile fuel and non-fissile particles. The non-fissile particles are similar in many respects to the non-fissile particles 110 disclosed hereinabove, which are not described in detail for the sake of brevity. In various examples, the non-fissile particles comprise an outer layer consisting of silicon carbide and a core enclosed by the outer layer, the core comprising a boron-10 based neutron absorbing material. The neutron absorbing material is positioned at a radially innermost portion of the core, and one or more carbon and / or graphite layers is deposited on an outer surface of the neutron absorbing material. The silicon carbide comprises a columnar microstructure.

[0031] The core of the fuel pellet disclosed above can be configured similarly to other cores described elsewhere in the present disclosure. Thus, the non-fissile particles of the fuel pellets can comprise a core configured to remain stable during at least one of a formation of the outer layer around the core or a formation of the fuel pellet. In some examples, the core is configured to maintain a physical state of the neutron absorbing material at a temperature associated with at least one of the formation of the outer layer around the core or the formation of the fuel pellet, such as a sintering temperature no less than 1700 °C. In certain examples, the core comprises a boron-10 based neutron absorbing material, a low density graphite first interlayer deposited on an outer surface of the neutron absorbing material, and a high density second interlayer of graphite surrounding the first interlayer.

[0032] A method for producing a fuel pellet of the present disclosure is also provided. In various examples, the method includes preparing a mixture comprising the fissile fuel and the non-fissile particles dispersed therein, forming the mixture into a compact, and sintering the compact to produce the fuel pellet. In some examples, the compact is sintered at a temperature no less than 1000 °C, which may also be a temperature no greater than a melting point of any of the fissile fuels, the non-fissile particles, and / or one or more components of the non-fissile particles. In certain examples, the method includes preparing the non-fissile particles. Preparing the non-fissile particles can include providing kernels of neutron absorbing material having a diameter in the range of 100 microns to 1000 microns, depositing a layer of SiC around the neutron absorbing material with a CVD or PVD process, such as a CVD process with methyltrichlorosilane and hydrogen at a temperature in a range of 1300 °C to 1500 °C (with an inert gas such as Ar to act as carrier and to adjust the partial pressures of the two reactive species) and sintering the SiC coated kernels at a temperature no less than 1700 °C. In certain examples, preparing the non-fissile particles includes depositing an interlayer of carbon or graphite via a CVD or PVD process onto the neutron absorbing material prior to depositing the SiC. In one example, the interlayer of carbon is deposited through CVD using a mixture of alkenes and alkynes, such as propene and / or acetylene, as precursors. Thus, the method for producing a fuel pellet can provide fuel pellets which maintain safe operating conditions in a nuclear reactor without sacrificing reactor output.

[0033] Various features and characteristics are described in this specification to provide an understanding of the composition, structure, production, function, and / or operation of the disclosure, which includes the disclosed methods and systems. It is understood that the various features and characteristics of the disclosure described in this specification can be combined in any suitable manner, regardless of whether such features and characteristics are expressly described in combination in this specification. The Inventors and the Applicantexpressly intend such combinations of features and characteristics to be included within the scope of the disclosure described in this specification. As such, the claims can be amended to recite, in any combination, any features and characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Furthermore, the Applicant reserves the right to amend the claims to affirmatively disclaim features and characteristics that may be present in the prior art, even if those features and characteristics are not expressly described in this specification. Therefore, any such amendments will not add new matter to the specification or claims and will comply with the written description, sufficiency of description, and added matter requirements.

[0034] With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those that are illustrated or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.

[0035] The invention(s) described in this specification can comprise, consist of, or consist essentially of the various features and characteristics described in this specification. The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. Thus, a method or system that “comprises,” “has,” “includes,” or “contains” a feature or features and / or characteristics possesses the feature or those features and / or characteristics but is not limited to possessing only the feature or those features and / or characteristics. Likewise, an element of a composition, coating, or process that “comprises,” “has,” “includes,” or “contains” the feature or features and / or characteristics possesses the feature or those features and / or characteristics but is not limited to possessing only the feature or those features and / or characteristics and may possess additional features and / or characteristics.

[0036] The grammatical articles “a,” “an,” and “the,” as used in this specification, including the claims, are intended to include “at least one” or “one or more” unless otherwise indicated. Thus, the articles are used in this specification to refer to one or more than one (i.e., to “at least one”) of the grammatical objects of the article. By way of example, “a component” meansone or more components and, thus, possibly more than one component is contemplated and can be employed or used in an implementation of the described compositions, coatings, and processes. Nevertheless, it is understood that use of the terms “at least one” or “one or more” in some instances, but not others, will not result in any interpretation where failure to use the terms limits objects of the grammatical articles “a,” “an,” and “the” to just one. Further, the use of a singular noun includes the plural, and the use of a plural noun includes the singular, unless the context of the usage requires otherwise.

[0037] In this specification, unless otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term “about,” in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described herein should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0038] Any numerical range recited herein includes all sub-ranges subsumed within the recited range. For example, a range of “1 to 10” includes all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Also, all ranges recited herein are inclusive of the end points of the recited ranges. For example, a range of “1 to 10” includes the end points 1 and 10. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any subrange subsumed within the ranges expressly recited. All such ranges are inherently described in this specification.

[0039] As used in this specification, particularly in connection with layers, the terms “on,” “onto,” “over,” and variants thereof (e.g., “applied over,” “formed over,” “deposited over,” “provided over,” “located over,” and the like) mean applied, formed, deposited, provided, or otherwise located over a surface of a substrate but not necessarily in contact with the surface of the substrate. For example, a layer “applied over” a substrate does not preclude the presence of another layer or other layers of the same or different composition located between the applied layer and the substrate. Likewise, a second layer “applied over” a first layer does not preclude the presence of another layer or other layers of the same or different composition located between the applied second layer and the applied first layer.

[0040] Whereas particular examples of this disclosure have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present disclosure may be made without departing from the disclosure as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A fuel element for a nuclear reactor, the fuel element comprising: non-fissile particles, the non-fissile particles comprising: a core comprising neutron absorbing material, wherein the neutron absorbing material is positioned at an innermost radial portion of the core, wherein the core is configured to remain stable at a temperature no less than 1000 °C; and an outer layer surrounding the core, the outer layer comprising silicon carbide.

2. The fuel element of claim 1 , wherein the neutron absorbing material comprises a boron-10 based material.

3. The fuel element of claim 2, wherein the boron-10 based material comprises at least one of elemental boron or a boron compound.

4. The fuel element of claim 3, wherein the boron compound comprises boron carbide, boron nitride, a borate, a boride, or a combination thereof.

5. The fuel element of claim 4, wherein the boron compound comprises a boride of any one of titanium, zirconium, hafnium, yttrium, calcium, cadmium, samarium, europium, or dysprosium.

6. The fuel element of claim 3, wherein the boron-10 based material comprises elemental boron, BN, B4C, TiB2, ZrB2, HfB2, YB4, YBe, Cd3(BC>3)2, CaBe, SmBe, SmB4, EuBe, DyB4, or DyBe, or any combination thereof.

7. The fuel element of claim 1 , further comprising fissile material enriched to a U-235 level of 5% or greater.

8. The fuel element of claim 7, wherein the fuel element is in the form of a pellet or a compact, wherein the non-fissile particles and the fissile material are dispersed throughout the fuel element.

9. The fuel element of claim 1 , the core of the non-fissile particles further comprising one or more interlayers positioned between the neutron absorbing material and the outer layer, wherein the interlayer comprises a carbon-based material.

10. The fuel element of claim 9, wherein the melting point of the carbon-based material is no less than 1000 °C.11 . The fuel element of claim 9, wherein the carbon-based material is at least 50% dense based on the bulk volume of the carbon-based material.

12. The fuel element of claim 9, wherein the carbon-based material is graphite.

13. The fuel element of claim 1 , wherein the non-fissile particles are configured to maintain an outer diameter following an exposure to a neutron flux.

14. The fuel element of claim 1 , wherein the outer layer has a thickness in a range of 50 microns to 500 microns.

15. The fuel element of claim 1 , wherein the silicon carbide of the outer layer comprises a columnar microstructure.

16. The fuel element of claim 15, wherein the silicon carbide comprises a-SiC, p-SiC, or a combination thereof.

17. A fuel pellet for a nuclear reactor, the fuel pellet comprising: fissile fuel; and non-fissile particles dispersed throughout the fissile fuel, each of the non-fissile particles comprising: an outer layer consisting of silicon carbide, wherein the silicon carbide comprises a columnar microstructure; and a core enclosed by the outer layer, the core comprising: a boron-10 based neutron absorbing material, wherein the neutron absorbing material is positioned at a radially innermost portion of the core; and a first carbon-based interlayer deposited on an outer surface of the neutron absorbing material; and a second second-based interlayer deposited on an outer surface of the first interlayer, the second interlayer comprising a greater density than the first carbon-based interlayer,wherein the core is configured to remain stable during at least one of a formation of the outer layer around the core or a formation of the fuel pellet.

18. The fuel pellet of claim 17, wherein the core is configured to maintain a physical state of the neutron absorbing material at a temperature associated with at least one of the formation of the outer layer around the core or the formation of the fuel pellet.

19. The fuel pellet of claim 17, wherein the temperature associated with at least one of the formation of the outer layer around the core or the formation of the fuel pellet is no less than 1700 °C.

20. A method for producing the fuel pellet of claim 17, the method comprising: preparing a mixture, the mixture comprising the fissile fuel and the non-fissile particles; forming the mixture into a compact; and sintering the compact to produce the fuel pellet.

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