CA-3149582-C - ROBUST NUCLEAR PROPULSION FISSION REACTOR WITH TRI-PITCH PATTERNED CORE AND DRUM ABSORBERS

CA3149582CCA 3149582 CCA3149582 CCA 3149582CCA-3149582-C

Abstract

Nuclear propulsion fission reactor structure has an active core region including fuel element structures, a reflector with rotatable neutron absorber structures (such as drum absorbers), and a core former conformal mating the outer surface of the fuel element structures to the reflector. Fuel element structures are arranged abutting nearest neighbor fuel element structures in a tri-pitch design. Cladding bodies defining coolant channels are inserted into and joined to upper and lower core plates to from a continuous structure that is a first portion of the containment structure. The nuclear propulsion fission reactor structure can be incorporated into a nuclear thermal propulsion engine for propulsion applications, such as space propulsion.

Inventors

Craig D. GRAMLICH
Benjamin D. Fisher
WILLIAM E. RUSSELL II

Assignees

BWXT Advanced Technologies LLC

Dates

Publication Date: 20260505
Application Date: 20200825
Priority Date: 20200821

Claims (1)

CLAIMS 1. A nuclear propulsion fission reactor structure, comprising: an active core region including a plurality of fuel element structures and having an axial centerline defining a longitudinal axis of the nuclear propulsion reactor; a core former radially outward of the active core region; a reflector radially outward of the core former and having a radially inner surface oriented toward the active core region; and a plurality of neutron absorber structures located within a volume of the reflector, wherein each fuel element structure includes a cladding body having an inner surface defining a coolant channel, a fuel composition body radially outward of and surrounding the cladding body, and a moderator composition body radially outward of and surrounding the fuel composition body, wherein an outer surface of a moderator composition body of a first fuel element structure abuts an outer surface of a moderator composition body of a plurality of nearest neighbor fuel element structures, wherein the core former has a first surface radially inward of a second surface and the first surface is conformal to a radially outer surface of the active core region and the second surface is conformal to the radially inner surface of the reflector, and wherein each of the plurality of neutron absorber structures includes a neutron absorber body movable between a first position and a second position, the first position being radially closer to the active core region than the second position. 30 2. The nuclear propulsion fission reactor structure according to claim 1, wherein the fuel composition body has the shape of an annular cylinder, and wherein the fuel element structure has a cross section that has a polygonal shape. 3. The nuclear propulsion fission reactor structure according to claim1, wherein side surfaces of the fuel element structures are in direct contact with side surfaces of adjacent fuel element structures, and wherein an arrangement of the plurality of fuel element structures in the active core region has translational symmetry. 4. The nuclear propulsion fission reactor structure according to claim 1, wherein a fuel composition of the fuel composition body includes (i) uranium oxide that is less than 20% enriched, (ii) uranium with 10 wt.% molybdenum (U-10Mo), (iii) uranium nitride (UN), or (iv) a cermet of (i), (ii) or (iii). 5. The nuclear propulsion fission reactor structure according to claim 1, further comprising: an upper core plate; and a lower core plate, wherein the cladding body of each fuel element structure includes a first portion that extends axially past a first axial end of the fuel composition body and a second portion that extends axially past a second axial end of the fuel composition body, and 31 wherein the first portion of each fuel element structure is joined to the upper core plate and the second portion of each fuel element structure is joined to the lower core plate. 6. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the fuel composition body has the shape of an annular cylinder. 7. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the fuel element structure has a cross section that has a polygonal shape. 8. The nuclear propulsion fission reactor structure according to claim 7, wherein the fuel element structure has a cross section that has a regular polygonal shape. 9. The nuclear propulsion fission reactor structure according to claim 7, wherein the regular polygonal shape is a hexagon. 10. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein side surfaces of the fuel element structures are in direct contact with side surfaces of adjacent fuel element structures. 11. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein an arrangement of the plurality of fuel element structures in the active core region has translational symmetry. 32 12. The nuclear propulsion fission reactor structure according to claim 11, wherein a translation distance between the plurality of fuel element structures having translational symmetry is constant. 13. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein a fuel composition of the fuel composition body includes (i) uranium oxide that is less than 20% enriched, (ii) uranium with 10 wt.% molybdenum (U-10Mo), (iii) uranium nitride (UN), or (iv) a cermet of (i), (ii) or (iii). 14. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the neutron absorber body is movable between the first position and the second position to control reactivity of the active core region. 15. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein each cladding body is a continuous, extruded tube. 16. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the cladding body has a composition that includes (i) molybdenum, (ii) tungsten, (iii) rhenium, (iv) tantalum, (v) hafnium, (vi) alloys thereof of (i), (ii), (iii), (iv) or (v), or (vii) carbides of (i), (ii), (iii), (iv) or (v). 33 17. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein a first portion of the cladding body extends axially past a first axial end of the moderator composition body and a second portion of the cladding body extends axially past a second axial end of the moderator composition body. 18. The nuclear propulsion fission reactor structure according to claim 5, wherein a portion of the upper core plate, a portion of the lower core plate, and the cladding body of each fuel element structure form a portion of a containment structure for the nuclear propulsion reactor. 19. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the fuel composition body has the shape of an annular cylinder, wherein the moderator composition body is a polygon-shaped sleeve with a central opening, and wherein an inner diameter of the central opening defines a space in which the fuel composition body is located. 20. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein, when the neutron absorber body of each of the plurality of neutron absorber structures is at the first position, the neutron absorber body of each of the plurality of neutron absorber structures is radially equidistant from the axial centerline of the active core region. 34 21. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the neutron absorber body has a composition including beryllium, beryllium oxide, graphite, or combinations thereof. 22. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein each of the plurality of neutron absorber structures includes a cylindrical drum encased in a tube, wherein the neutron absorber body occupies a first portion of the cylindrical drum and a second portion of the cylindrical drum is a secondary reflector, and wherein the first portion of the cylindrical drum is a volume of the cylindrical drum that includes a portion of an exterior surface of the cylindrical drum. 23. The nuclear propulsion fission reactor structure according to claim 22, wherein the portion of the exterior surface of the cylindrical drum corresponds to a 120 degree arc of a circumference of the cylindrical drum. 24. The nuclear propulsion fission reactor structure according to claim 22, wherein the tube is stainless steel. 25. The nuclear propulsion fission reactor structure according to claim 22, wherein the cylindrical drum is rotatable relative to an inner diameter surface of the tube. 35 26. The nuclear propulsion fission reactor structure according to claim 22, further including a motor operatively attached to the cylindrical drum by a drum shaft to rotate the cylindrical drum. 27. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein a composition of the reflector includes beryllium, beryllium oxide or graphite. 28. The nuclear propulsion fission reactor structure according to claim 22, wherein a composition of the reflector includes beryllium, beryllium oxide or graphite, and wherein a composition of the secondary reflector includes beryllium, beryllium oxide or graphite. 29. The nuclear propulsion fission reactor structure according to claim 28, wherein the composition of the secondary reflector is the same as the composition of the reflector. 30. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the coolant is a propulsion gas and the nuclear propulsion reactor further comprises an upper reactor plate including a plurality of first holes for passage of the propulsion gas and a lower reactor plate including a plurality of second holes for passage of the propulsion gas. 31. The nuclear propulsion fission reactor structure according to claim 5, further comprising a hull, 36 wherein the active core region, the core former, the upper core plate, the lower core plate, the reflector, and the plurality of neutron absorber structures form a reactor structure, and wherein the reactor structure is housed within an interior volume of the hull. 32. The nuclear propulsion fission reactor structure according to claim 31, wherein the coolant is a propulsion gas and the nuclear propulsion reactor further comprises an upper reactor plate and a lower reactor plate, each reactor plate including a plurality of holes for passage of the propulsion gas. 33. The nuclear propulsion fission reactor structure according to claim 31, wherein the reactor structure is supported by a ledge attached to an interior surface of the hull or formed by a portion of the interior surface of the hull. 34. A nuclear thermal propulsion engine, comprising: the nuclear propulsion fission reactor structure according to claim 31, shielding; a reservoir for cryogenically storing a propulsion gas; turbomachinery; and a nozzle, wherein the upper core plate is oriented toward a first end of the hull and the lower core plate is oriented toward a second end of the hull, 37 wherein shielding, turbomachinery, and the reservoir are operatively mounted to the first end of the hull to provide a flow path from the reservoir to the nuclear propulsion reactor, and wherein the nozzle is operatively mounted to the second end of the hull to provide a flow path for superheated propulsion gas exiting the nuclear propulsion reactor. 35. A method of manufacturing a nuclear propulsion fission reactor structure, the method comprising: joining a first portion of each of a plurality of cladding bodies to a lower core plate, wherein each cladding body has an inner surface defining a coolant channel, wherein the lower core plate includes a plurality of openings extending from a first side of the lower core plate to a second side of the lower core plate, and wherein the first portion of each cladding body extends into a different one of the plurality of openings in the lower core plate; sliding each of a plurality of fuel composition bodies over an outer surface of a different one of the plurality of cladding bodies, wherein each fuel composition body has the shape of an annular cylinder, and wherein an inner surface of the annular cylinder of the fuel composition body is oriented toward and surrounds the outer surface of the cladding body; sliding each of a plurality of moderator bodies over an outer surface of a different one of a plurality of fuel composition bodies, wherein, in a cross-section, each moderator body has a periphery having a regular polygonal shape and an inner 38 opening, and wherein a surface of the inner opening of the moderator body is oriented toward and surrounds an outer surface of the annular cylinder of the fuel composition body; and joining a second portion of the cladding body to an upper core plate, wherein the upper core plate includes a plurality of openings extending from a first side of the upper core plate to a second side of the upper core plate and wherein the coolant channel of the cladding body extends into one of the plurality of openings in the upper core plate, wherein the assembled cladding body, fuel composition body that is radially outward of and surrounds the cladding body, and moderator composition body that is radially outward of and surrounds the fuel composition body define a fuel element structure, wherein, in each fuel element structure, the cladding body includes a first portion that extends axially past a first axial end of the fuel composition body and a second portion that extends axially past a second axial end of the fuel composition body, wherein an outer surface of a moderator body of a first fuel element structure abuts an outer surface of a moderator body of a plurality of nearest neighbor fuel element structures, and wherein a portion of the upper core plate, a portion of the lower core plate, and the cladding body of each fuel element structure form a first portion of a containment structure for the nuclear propulsion reactor. 39 36. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, wherein forming the plurality of cladding bodies includes extruding the cladding body in the form of a seamless tube. 37. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, wherein joining the first portion of each of the cladding bodies to the lower core plate includes welding. 38. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, wherein forming the plurality of fuel composition bodies includes a fuel compaction technique or an additive manufacturing technique. 39. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, further comprising affixing the fuel composition body to the cladding. 40. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 39, wherein affixing the fuel composition body to the cladding includes press fitting or hot isostatic pressing. 41. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, wherein joining the second portion of each of the cladding bodies to the upper core plate includes welding. 40 42. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, further comprising positioning a reflector about an outer surface of assembled fuel element structures and mating an inner surface of the reflector to an outer surface of the assembled fuel element structures with a core former. 43. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 42, wherein the inner surface of the reflector forms a second portion of the containment structure for the nuclear propulsion reactor. 44. The method of manufacturing a nuclear propulsion fission reactor structure according to claim 35, the method further comprising one or more of: forming the plurality of cladding bodies; forming the plurality of fuel composition bodies; and forming the plurality of moderator bodies. 45. The nuclear propulsion fission reactor structure according to claims 1 or 5, wherein the fuel composition body has a shape of an annulus having an inner surface defining an opening and an outer surface, and wherein the coolant channel is radially inward of the inner surface and the moderator composition body is radially outward of the outer surface. 41 46. The nuclear propulsion fission reactor structure according to claim 1, wherein, in each fuel element structure, the moderator composition body directly contacts the fuel composition body. 42

Description

WO 2021/071599 PCT/US2020/04 7722 ROBUST NUCLEAR PROPULSION FISSION REACTOR WITH TRI-PITCH PATTERNED CORE AND DRUM ABSORBERS TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY [0001] 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 have applications in various non-terrestrial applications, such as space and ocean environments. BACKGROUND [0002] 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. [0003] Various propulsion systems for non-terrestrial applications, such as in space, have been developed. These include chemical-based propulsion systems, ion-based propulsion systems, and nuclear-based propulsion systems. Each of these propulsion systems balances thrust and specific impulse to provide performance that is tailored to specific missions. For example, chemical-based propulsion systems have high thrust (e.g., > 107 lbs thrust(> 4.45 x 107 N)), but modest specific impulse (e.g., s 450 sec) and are efficiently applied to heavy lift operations, such as placing payloads into earth orbit. Ion-based propulsion systems have low thrust (e.g.,< 10 lbs thrust(< 44.5 N)), 1 CA 03149582 2022-2-25 WO 2021/071599 PCT/US2020/04 7722 but high specific impulse (e.g., 1,000 - 9,000 sec) and are efficiently applied for long term space travel, such as inter-stellar travel. Nuclear-based propulsion systems combines modest thrust (e.g., 5,000- 75,000 lbs thrust (22,250 - 333,750 N)) and modest specific impulse (e.g., 600- 1,000 sec) and are efficiently applied to near-space travel. Nuclear-based propulsion systems are currently being evaluated as a propulsion option for NASA's Human Exploration of Mars Design Reference. Architecture 5.0. [0004] Previous nuclear-based propulsion systems are still complex. For example, both Nuclear Engine for Rocket Vehicle Application (NERVA) and Project Rover have developed nuclear thermal rocket designs. A typical design for a nuclear thermal propulsion reactor and engine 1 O is shown in FIG. 1. The illustrated nuclear thermal propulsion reactor and engine 1 O includes four main features: a hull 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 separating the turbomachinery 30 from the hull 20, and a nozzle section 50 including a nozzle 52 and a nozzle skirt 54. [0005] However, these prior nuclear-based propulsion systems still have drawbacks, including utilizing complex moderators and flow techniques, operating with minimal design margins that push the limits of the design and associated materials. Accordingly, there is still a need for robust and simple designs for nuclear propulsion reactors, particular for non-terrestrial applications, such as in space. SUMMARY [0006] Considering the above, it would be advantageous to have a robust, single pass propellant flow, nuclear-based propulsion system with a simplified core pattern for ease 2 CA 03149582 2022-2-25 WO 2021/071599 PCT/US2020/04 7722 of manufacturing. Additionally, a simplified design with reduced number of weld points in manufacturing is advantageous to reduce the risk of performance degradation. [0007] In general, the disclosure is directed to a nuclear fission reactor structure suitable for use as an engine in a nuclear-based propulsion system. In exemplary embodiments, the nuclear fission reactor structure utilizes a fuel element with a hexagonal cross-section arranged in a tri-pitch design and rotatable drum neutron absorbers for reactivity control. The nuclear fission reactor structure is housed in a hull of a nuclear thermal propulsion reactor and engine. A propulsion gas is used as a coolant for the nuclear fission reactor structure. Propulsion gas superheated in the nuclear fission reactor structure exits through a nozzle and generates thrust and impulse. [0008] Embodiments disclosed herein include a nuclear propulsion fission reactor structure comprising an active core region including a plurality of fuel element structures and having an axial centerline defining a longitudinal axis of the nuclear propulsion reactor; a core former radially outward of the active core region; a reflector radially outward of the core reformer and having a radially inner surface oriented toward the active core region; and a plurality of neutron absorber structures located within a volume of the reflector. Each fuel element structure includes a cladding body having an inner surface defining a coolant channel, a fuel composition body radially outward of the cladding body, and a moderator compos