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EP-4742274-A2 - FUEL ASSEMBLY FOR THERMAL PROPULSION APPLICATIONS

EP4742274A2EP 4742274 A2EP4742274 A2EP 4742274A2EP-4742274-A2

Abstract

A fuel assembly includes first and second fuel elements contained within an outer structure of ceramic matrix composite material. An insulation layer formed of a first refractory ceramic material is interposed between an inner surface of the fuel assembly outer structure and an outer envelope surface of the first fuel element, spaced apart from the outer envelope surface of the first fuel element, and extends parallel to the first fuel element. First and second support meshes, each including a first region having a plurality of openings, interconnected internally within the first region and forming a flow path from a first side to a second side of the respective support mesh, are located at the respective end surfaces of the first fuel element. The second fuel element is separated from the first fuel element in a longitudinal direction by one of the support meshes. Each of the first and second fuel elements includes a plurality of elongated fuel bodies arranged in a fuel bundle, each elongated fuel body containing a fuel composition.

Inventors

  • BARRINGER, ERIC A.
  • KRECICKI, Matt
  • RIDGEWAY, Roger
  • JENSEN, RUSSELL R.
  • GUSTAFSON, Jeremy L.
  • ALES, Matt
  • BERGMAN, JOSHUA J.
  • SWANSON, Ryan T.
  • WITTER, Jonathan K.
  • GALICKI, Danny
  • INMAN, JAMES B.

Assignees

  • BWXT Advanced Technologies LLC
  • BWXT Nuclear Energy, Inc.

Dates

Publication Date
20260513
Application Date
20210812

Claims (20)

  1. A fuel assembly, comprising: a fuel assembly outer structure (110) formed of a ceramic matrix composite material; a first fuel element (105, 200) and a second fuel element (105, 200) contained within the fuel assembly outer structure; an insulation layer (160) formed of a first refractory ceramic material, wherein the insulation layer is interposed between an inner surface of the fuel assembly outer structure (110) and an outer envelope surface of the first fuel element (105, 200), and wherein the insulation layer (160) is spaced apart from the outer envelope surface of the first fuel element (105, 200) and extends parallel to the first fuel element (105, 200) from a first end surface of the first fuel element to a second end surface of the first fuel element; and a first support mesh (150a) located at the first end surface of the first fuel element and a second support mesh (150b) located at the second end surface of the first fuel element, wherein the second fuel element (105, 200) is separated from the first fuel element in a longitudinal direction by one of the first support mesh (150a) and the second support mesh (150b), wherein each of the first support mesh (150a) and the second support mesh (150b) includes a first region having a plurality of openings (152), wherein the plurality of openings (152) are interconnected internally within the first region and form a flow path from a first side to a second side of the respective support mesh, wherein each of the first fuel element and the second fuel element includes a plurality of elongated fuel bodies, wherein each elongated fuel body contains a fuel composition, and wherein the plurality of elongated fuel bodies are arranged in a fuel bundle.
  2. The fuel assembly according to claim 1, wherein each elongated fuel body longitudinally extends from a first end to a second end along a longitudinal axis of the respective elongated fuel body, wherein, in the fuel bundle, the plurality of elongated fuel bodies are arranged in spaced-apart relationship relative to each other, and wherein an empty space between the spaced-apart elongated fuel bodies in the fuel bundle is a coolant flow volume through which a coolant in a form of a propellant gas flows during operation of a reactor containing the fuel assembly.
  3. The fuel assembly according to claim 1, wherein the fuel assembly is elongated and is tubular-shaped and has an axial centerline defining a longitudinal axis of the fuel assembly, wherein the plurality of elongated fuel bodies of the first fuel element are located at positions that are axisymmetric about the longitudinal axis of the fuel assembly, as seen in cross-section in a plane perpendicular to the longitudinal axis of the fuel assembly.
  4. The fuel assembly according to claim 3, wherein, in a plane perpendicular to the longitudinal axis of the elongated fuel body, a cross-sectional shape of the elongated fuel body is a polygon, a circle, or an oval, preferably a regular polygon.
  5. The fuel assembly according to any one of preceding claims, wherein the fuel composition includes uranium having a U-235 assay above 5 percent and below 20 percent.
  6. The fuel assembly according to any one of claims 1-4, wherein the fuel composition is carbide based, the fuel composition preferably includes a binary carbide containing uranium or a ternary carbide containing uranium, more preferably includes (U,Zr)C or (U,Zr,Nb)C, and wherein, optionally, the first fuel element (105, 200) is refractory carbide coated.
  7. The fuel assembly according any one of the preceding claims, wherein the ceramic matrix composite material is a SiC-SiC composite.
  8. The fuel assembly according to any one of the preceding claims, wherein the first refractory ceramic material is porous with 60 to 85% of the volume consisting of void spaces.
  9. The fuel assembly according to any one of the preceding claims, wherein the first refractory ceramic material is 90% to 99.999% zirconium carbide having an open-cell foam structure or is 95% to 99.999% fibrous zirconium carbide.
  10. The fuel assembly according to any one of claims 1-7, wherein the first refractory ceramic material is a first zirconium carbide refractory ceramic material, wherein each of the first support mesh and the second support mesh is formed of a second refractory ceramic material, and wherein the second refractory ceramic material is a second zirconium carbide refractory ceramic material or a niobium carbide refractory ceramic material.
  11. The fuel assembly according to claim 10, wherein the second refractory ceramic material is porous with 30 to 70% of the volume consisting of void spaces.
  12. The fuel assembly according to claim 10, wherein the second refractory ceramic material is 90% to 99.999% zirconium carbide or 90% to 99.999% niobium carbide, and wherein the second refractory ceramic material has an open-cell foam structure.
  13. The fuel assembly according to any one of the preceding claims, wherein each of the first support mesh and the second support mesh includes an outer region enclosing a perimeter of the first region, wherein the outer region has a lower porosity than the first region, and wherein, optionally, the outer region is devoid of openings.
  14. The fuel assembly according to any one of the preceding claims, wherein a first end surface of the insulation layer abuts an outer region of the first support mesh and a second end surface of the insulation layer abuts an outer region of the second support mesh.
  15. The fuel assembly according to any one of the preceding claims, further comprising a third support mesh, wherein the third support mesh is located at an opposite end of the second fuel element from the one first or second support mesh separating the second fuel element from the first fuel element.
  16. The fuel assembly according to any one of the preceding claims, wherein the insulation layer interposed between the inner surface of the fuel assembly outer structure and the first fuel element is a first insulation layer and the first insulation layer extends longitudinally to also extend between the inner surface of the fuel assembly outer structure and the second fuel element, and the fuel assembly further comprises a second insulation layer, wherein the second insulation layer is interposed between an inner surface of the first insulation layer and the second fuel element.
  17. The fuel assembly according to claim 16, wherein a first end surface of the second insulation layer abuts an outer region of the second support mesh and a second end surface of the second insulation layer abuts an outer region of the third support mesh.
  18. The fuel assembly according to any one of the claims 1-15, wherein the insulation layer interposed between the inner surface of the fuel assembly outer structure and the first fuel element is a first insulation layer, wherein an insulation layer interposed between the inner surface of the fuel assembly outer structure and the second fuel element is a second insulation layer, and wherein the first insulation layer is longitudinally separated from the second insulation layer by the one first or second support mesh separating the second fuel element from the first fuel element.
  19. The fuel assembly according to any one of the preceding claims, wherein the insulation layer interposed between the inner surface of the fuel assembly outer structure and the first fuel element extends an entire length of the fuel assembly outer structure.
  20. The fuel assembly according to any one of the preceding claims, further comprising an inlet flow adapter at a first end of the fuel assembly and an outlet flow adapter at a second end of the fuel assembly, wherein the fuel assembly outer structure connects the inlet flow adapter to the outlet flow adapter.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT The invention described herein was made in the performance of work under Subcontract 00212687 to DOE Award No. DE-AC07-05ID14517 and NASA Prime Contract 80MSFC17C0006, and is subject to the provisions of section 2035 of the National Aeronautics and Space Act (51 U.S.C. § 20135). The Government has certain rights in this invention. TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY The present disclosure relates generally to nuclear fission reactors and structures related to nuclear fission reactors, in particular for propulsion. Such nuclear propulsion fission reactors may be used in various non-terrestrial applications, such as space and ocean environments. In particular, the disclosure relates to a carbide-based fuel assembly that can be incorporated into a nuclear reactor for nuclear thermal propulsion and which is capable of heating hydrogen propellant to temperatures required to achieve specific impulse (Isp) values in the range of 900 to 1000 seconds, alternatively 950 to 1000 seconds. The fuel assembly includes uranium-bearing fuel elements, preferably using high-assay low-enriched uranium (HALEU), and a carbide-based insulator and other structural material. BACKGROUND In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention. Various propulsion systems for non-terrestrial applications, such as in space, have been developed. A typical design for a nuclear thermal propulsion (NTP) reactor and engine 10 is shown in FIG. 1. The illustrated nuclear thermal propulsion reactor and engine 10 includes four main features: a vessel 20 having a reactor 22 contained within a reflector 24, turbomachinery 30 including turbo pumps 32 and other piping and support equipment 34, shielding 40 (which is shown as internal shielding in between the turbomachinery 30 and the vessel 20, but can also be external shielding), and a nozzle section 50 including a nozzle 52 and a nozzle skirt 54. Various fuel element structural and fuel materials have been considered. Typically, prior nuclear rocket programs utilized high-enriched (weapons grade) uranium (HEU), enriched to around 90% U-235. In one example, coated uranium carbide particles or uranium carbide-zirconium carbide particles were dispersed in a graphite matrix that was coated with zirconium carbide or niobium carbide to prevent hydrogen erosion of the graphite. A hydrogen propellant/coolant temperature of 2550K was reached during integrated nuclear engine testing. In another example, a cermet fuel consisting of uranium oxide embedded in a refractory metal matrix was used. Structural forms for NTP reactors have, in one example, included particle bed reactors (PBR), in which the hydrogen propellant flowed radially through a bed of coated UCx fuel particles and then axially outward from the center of the fuel element into the nozzle chamber, and in a second example, included propellant/coolant flowing axially over bundles of fuel rods. Despite the state of the art for NTP reactors, there remains a need for improved designs, and particularly designs that incorporate HALEU fuel, and manufacturing techniques to realize propulsion systems for NTP applications that balance thrust, specific impulse, and mass to provide performance that is tailored to specific missions. SUMMARY Presently, there is a need for improvements directed to NTP applications in which the specific impulse is in the range of 900 to 1000 seconds. This translates to propellant (i.e., hydrogen propellant) exit temperatures from the reactor in excess of 2700K (kelvin), and thus fuel temperatures in excess of 2900K. In example embodiments utilizing hydrogen propellant, exit temperature of the hydrogen propellant is on the order of 2950K for a specific impulse of 950 seconds. Additionally, there is a need to implement HALEU fuels, so as to reduce or eliminate the use of HEU fuel. However, reactors using HALEU fuel require significant neutron moderation to produce a thermal neutron energy spectrum. In general, the disclosure is directed to a nuclear fission reactor structure suitable for use in a nuclear-based propulsion system, such as nuclear thermal propulsion. In exemplary embodiments, the nuclear fission reactor structure utilizes a carbide-based fuel assembly containing one or more uranium-bearing fuel elements. The carbide-based fuel assembly includes a fuel assembly outer structure and also includes a carbide-based insulation layer interposed between an inner surface of the fuel assembly outer structure and one or more uranium-bearing fuel elements located in the assembly. One or more carbide-based support meshes are positioned at the longitudin