IP Library › Granted Patent US 12,626,829
Granted Patent B2
US 12,626,829 · App. 18/118,193 · Granted May 12, 2026

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

Inventors: Benjamin D. Fisher (Lynchburg, VA); John R. Salasin (Lynchburg, VA)
Assignee: BWXT Advanced Technologies LLC
G21C3/324G21C3/322G21C3/33G21C3/334G21C5/02G21C21/10B64G1/408G21C3/62G21D5/02
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Quick Facts
Patent No.
US 12,626,829
App. No.
18/118,193
Granted
May 12, 2026
Kind
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.

Claims (44)

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.

Assignments (2)
SECURITY INTEREST Recorded Nov 10, 2025
From: BWXT ADVANCED TECHNOLOGIES LLC; BWXT ISOTOPE TECHNOLOGY GROUP, INC.; BWXT NUCLEAR ENERGY, INC.
To: WELLS FARGO BANK, NATIONAL ASSOCIATION, AS ADMINISTRATIVE AGENT
Reel/Frame 073531/0358 →
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded Jul 14, 2025
From: FISHER, BENJAMIN D.; SALASIN, JOHN R.
To: BWXT ADVANCED TECHNOLOGIES LLC
Reel/Frame 071684/0833 →
Continuity (2)
Provisional Application 63317477 · Mar 7, 2022
Related Publication 20230282373A1 · Sep 7, 2023
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