US-12626829-B2 - Fuel bundle with twisted ribbon fuel rodlets for nuclear thermal propulsion applications, structures for manufacture, and methods of manufacture

US12626829B2US 12626829 B2US12626829 B2US 12626829B2US-12626829-B2

Abstract

Fuel bundle has plurality of twisted ribbon fuel rodlets arranged in hexagonal packing or circle packing arrangement in a reactor core encased in a multilayer casing. Arrangement of twisted ribbon fuel rodlets is facilitated by rodlet seating fixture with seating surface having a plurality of protrusions that form a receiving space for ends of the twisted ribbon fuel rodlets. Manufacture of the fuel bundle incorporates fiber manufacturing technologies and, optionally, infiltration of spaces in the reactor core by infiltrant. Twisted ribbon fuel rodlet manufacturing system has sub-systems that impart twist periodicity to extruded ribbons, inspect twisted extruded ribbons, and cut twisted extruded ribbons to length. Inspection sorts twisted ribbon fuel rodlets as well as provides feedback to adjust operation of sub-systems. The fuel bundle (and optional fuel bundle support) can be incorporated into a fuel assembly of nuclear propulsion fission reactor structure of, for example, a nuclear thermal propulsion engine.

Inventors

Benjamin D. Fisher
John R. SALASIN

Assignees

BWXT Advanced Technologies LLC

Dates

Publication Date: 20260512
Application Date: 20230307

Claims (17)

1 . A fuel bundle, comprising: a multilayer casing having an inner volume defining a reactor core; and a plurality of twisted ribbon fuel rodlets arranged in the reactor core, the plurality of twisted ribbon fuel rodlets forming a core region, wherein the plurality of twisted ribbon fuel rodlets have a composition including a fissionable fuel component, wherein the multilayer casing includes an inner layer, an inner intermediate layer an outer intermediate layer, and an outer layer, wherein the inner layer is a graphite compressive felt insulation layer, wherein the inner intermediate layer is a composite reinforcement and compressive layer, wherein the outer intermediate layer is a first compressive prepeg layer, and wherein the outer layer is a second compressive prepeg layer.
2 . The fuel bundle according to claim 1 , wherein, in a cross-section perpendicular to a longitudinal axis of the fuel bundle, cross-sections of the plurality of twisted ribbon fuel rodlets are arranged in a hexagonal packing arrangement, and wherein the hexagonal packing arrangement extends to outermost twisted ribbon fuel rodlets at a periphery of the core region.
3 . The fuel bundle according to claim 2 , further comprising a plurality of filler rods at a plurality of locations about the periphery of the core region.
4 . The fuel bundle according to claim 1 , wherein, in a cross-section perpendicular to a longitudinal axis of the fuel bundle, cross-sections of the plurality of twisted ribbon fuel rodlets are arranged in a circle packing arrangement, and wherein the circle packing arrangement extends to twisted ribbon fuel rodlets that are inward from a periphery of the core region.
5 . The fuel bundle according to claim 4 , wherein there are areas of non-symmetry at the periphery of the core region.
6 . A method of manufacturing a fuel bundle, the method comprising: forming a core region of the fuel bundle, wherein forming the core region includes seating first ends of each of a plurality of twisted ribbon fuel rodlets in a respective receiving space of a rodlet seating fixture, wherein the rodlet seating fixture includes a seating surface having a plurality of protrusions, the plurality of protrusions are distributed on the seating surface and have a height from a base surface of the seating surface, and side surfaces of a plurality of adjacent protrusions define the respective receiving space; attaching an end cap to second ends of each of the plurality of twisted ribbon fuel rodlets to form a pre-bundle; optionally introducing an infiltrant into the pre-bundle to occupy void spaces in the assembled twisted ribbon fuel rodlets; encasing the pre-bundle in a multilayer casing including an inner layer, an inner intermediate layer, an outer intermediate layer, and an outer layer; removing the rodlet seating fixture and end cap; and optionally removing the infiltrant, wherein the plurality of twisted ribbon fuel rodlets have a composition including a fissionable fuel component, wherein the inner layer is a graphite compressive felt insulation layer, wherein the inner intermediate layer is a composite reinforcement and compressive layer, wherein the outer intermediate layer is a first compressive prepeg layer, and wherein the outer layer is a second compressive prepeg layer.
7 . The method according to claim 6 , further comprising: supporting an axial length of the seated twisted ribbon fuel rodlets by a support housing during forming of the core region of the fuel bundle, wherein the support housing is in contact with a periphery of the rodlet seating fixture, and removing the support housing prior to encasing the pre-bundle in the multilayer casing.
8 . The method according to claim 7 , further comprising completely enclosing the assembled twisted ribbon fuel rodlets, wherein optionally introducing the infiltrant into the pre-bundle includes vacuum assisted infiltration.
9 . The method according to claim 8 , wherein encasing the pre-bundle in the multilayer casing includes manual layup of one or more of the inner layer, the inner intermediate layer, the outer intermediate layer, and the outer layer.
10 . The method according to claim 8 , wherein encasing the pre-bundle in the multilayer casing includes mandrel winding of one or more of the inner layer, the inner intermediate layer, the outer intermediate layer, and the outer layer.
11 . The method according to claim 8 , wherein, in a cross-section perpendicular to a longitudinal axis of the core region, cross-sections of the plurality of twisted ribbon fuel rodlets are arranged in a hexagonal packing arrangement, and wherein the hexagonal packing arrangement extends to outermost twisted ribbon fuel rodlets at a periphery of the core region.
12 . The method according to claim 11 , further comprising locating a plurality of filler rods at a plurality of locations about the periphery of the core region, wherein ends of each of the plurality of filler rods are seated in the rodlet seating fixture.
13 . The method according to claim 8 , wherein, in a cross-section perpendicular to a longitudinal axis of the core region, cross-sections of the plurality of twisted ribbon fuel rodlets are arranged in a circle packing arrangement, and wherein the circle packing arrangement extends to twisted ribbon fuel rodlets that are inward from a periphery of the core region.
14 . The method according to claim 6 , wherein, in a cross-section perpendicular to a longitudinal axis of the core region, cross-sections of the plurality of twisted ribbon fuel rodlets are arranged in a hexagonal packing arrangement, and wherein the hexagonal packing arrangement extends to outermost twisted ribbon fuel rodlets at a periphery of the core region.
15 . The method according to claim 14 , further comprising locating a plurality of filler rods at a plurality of locations about the periphery of the core region, wherein ends of each of the plurality of filler rods are seated in the rodlet seating fixture.
16 . The method according to claim 6 , wherein, in a cross-section perpendicular to a longitudinal axis of the core region, cross-sections of the plurality of twisted ribbon fuel rodlets are arranged in a circle packing arrangement, and wherein the circle packing arrangement extends to twisted ribbon fuel rodlets that are inward from a periphery of the core region.
17 . The method according to claim 6 , wherein encasing the pre-bundle in the multilayer casing includes (i) manual layup of one or more of the inner layer, the inner intermediate layer, the outer intermediate layer, and the outer layer or (ii) mandrel winding of one or more of the inner layer, the inner intermediate layer, the outer intermediate layer, and the outer layer.

Description

RELATED APPLICATION DATA The application is based on and claims priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 63/317,477, filed Mar. 7, 2022, the entire contents of which are incorporated herein by reference. 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 applications suitable for gas reactor designs, such as space, lunar and terrestrial environments. In particular, the disclosure relates to twisted ribbon fuel rodlets formed of a composition including a fissionable fuel component and assembled into a fuel bundle that will be incorporated into a fuel assembly for a thermal propulsion reactor, to structures for manufacture of the twisted ribbon fuel rodlets and for assembly of the fuel bundle, and methods for fabricating such twisted ribbon fuel rodlets and fuel bundles. 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. Development and testing of twisted ribbon fuels occurred in the USSR from approximately 1975 to 1990 and have been reported in Burns et al, “Nuclear Thermal Propulsion Reactor Materials”, in Nuclear Materials, edited by P. Tsvetkov, London: IntechOpen, 2020. (U, Zr) C fuel was used for the low-temperature portion of the USSR reactor design (i.e., propellant exit gas temperature≤2500 K), and (U, Zr, Nb) C was used for the high-temperature portion of the reactor core. Fuel ribbons were extruded and twisted on their long axis, sintered and assembled into a tube. Dimensions of the ribbon and the twist rate were (1.5 mm×2.8 mm, S=30 mm). The simple tube restraint system used in this prior work allowed for several failure modes. As reported in Lanin, “Nuclear Rocket Engine Reactor”, Springer Series in Materials Science, Volume 170, Wang et al. (Eds.), Springer-Verlag Berlin Heidelberg (2013), high temperature, multiple-cycle operation damaged the twisted ribbon fuels. For example, fuel element plasticity at elevated temperatures and a twisting failure mode caused by increasing axial forces as reactor differential pressure increased were observed. Also, hot hydrogen ablation of the insulation and casing materials was observed. SUMMARY There is a need for improvements in twisted ribbon fuel rodlets, in structures for manufacture of the twisted ribbon fuel rodlets and for assembly of the fuel bundle, and in methods for fabricating such twisted ribbon fuel rodlets and fuel bundles. In particular, improvements related to the radial restraint of twisted ribbon fuel rodlets in the fuel bundle and in structures and materials of the fuel bundle and its casing. Thus, a method of radial restraint for the twisted ribbon fuel rodlets in the fuel bundle uses geometric-specific end fixtures, supports, and fiber architectures and also manufacturing methods to address failure modes, to improve internal distribution and restraint of the twisted ribbon fuel rodlets, to improve distribution forces, and to strengthen the twisted ribbon fuel rodlets (and materials of the fuel bundle casing) against fracture by keeping the entire fuel bundle in radial compression. In addition, improvements related to the manufacture of twisted ribbon fuel rodlets are disclosed, which provide for improved manufacturability including preparation of materials for twisted ribbon fuel rodlets, methods of manufacture including extrusion of ribbon fuel rodlets and twisting of ribbon fuel rodlets to form twisted ribbon fuel rodlets that have uniform characteristics, and defect detection in manufactured twisted ribbon fuel rodlets. Improved twisted ribbon fuel rodlets contribute to improvements in overall fuel bundle performance and reduced failures. In fuel assemblies, improvements to the distribution of forces are also disclosed, particularly distribution of forces in the high temperature, ductile regions of the fuel assembly such as the region of the outlet fuel bundle(s). The geometry of fuel bundle supports, such as tapered outer circumference surfaces, translate axial loading of the twisted ribbon fuel rodlets caused by reactor differential pressure from the fuel bundle and its components to the fuel assembly outer surface. An embodiment of a fuel bundle comprises a multilayer casing having an inner volume defining a reactor core and a plurality of twisted ribbon fuel rodlets arranged in the reactor core. The plurality of twisted ribbon fuel rodlets have a composition including a fissionable fuel component. In a cross-section perpendicular to a longitudinal axis of the fuel bundle, cros