Functionally graded lattice cermet fuel structure with shape corresponding to a mathematically-based periodic solid, particularly for nuclear thermal propulsion
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 lower and upper core plates to from a continuous structure that is a first portion of the containment structure. The body of the fuel element has a structure with a shape corresponding to a mathematically-based periodic solid, such as a triply periodic minimal surface (TPMS) in a gyroid structure. The nuclear propulsion fission reactor structure can be incorporated into a nuclear thermal propulsion engine for propulsion applications, such as space propulsion.
1. A nuclear fuel lattice structure, comprising:
a body having a structure including a plurality of webbings having outer surfaces that define a network of interconnected channels located within an envelope surface of the body,
wherein a baseline of the webbings is an implicit surface of a mathematically-based periodic solid,
wherein the mathematically-based periodic solid is a triply periodic minimal surface (TPMS),
wherein at least a portion of the channels extend from a first outer surface of the body to a second outer surface of the body,
wherein the structure has a volumetric density of 35% to 85%,
wherein a composition of the structure includes a nuclear fissionable fuel having an enrichment of up to 20%, and
wherein a specific enrichment of the structure (% enrichment per unit volume) is constant ±2%.
2. The nuclear fuel lattice structure according to claim 1 , wherein the triply periodic minimal surface (TPMS) is a gyroid structure, and wherein the implicit surface is defined by a gyroid equation (sin x cos y+sin y cos z+sin z cos x)=0.
3. The nuclear fuel lattice structure according to claim 2 , wherein each webbing has a thickness relative to the baseline, and, within the body, the thickness of the webbing varies in accordance with a vector field.
4. The nuclear fuel lattice structure according to claim 3 , wherein the thickness of the webbings is symmetric relative to the baseline.
5. The nuclear fuel lattice structure according to claim 1 , wherein a uranium content of the nuclear fissionable fuel varies by spatial location in the body.
6. The nuclear fuel lattice structure according to claim 5 , wherein the variation in uranium content by spatial location in the body includes increasing a content of U235 due to an increased density of the lattice.
7. The nuclear fuel lattice structure according to claim 1 , wherein the mathematically-based periodic solid is biased to effect a flow rate of a medium flowing through the network of interconnected channels.
8. The nuclear fuel lattice structure according to claim 1 , wherein the body is disc-shaped and occupies a volume that includes a radial side surface corresponding to a thickness of the body between the first outer surface and the second outer surface.
9. The nuclear fuel lattice structure according to claim 1 , wherein the triply periodic minimal surface (TPMS) is a Schwarz minimal surface.
10. The nuclear fuel lattice structure according to claim 1 , wherein the nuclear fissionable fuel is high-assay low-enriched uranium (HALEU) with a U 235 assay equal to or greater than 5 percent to equal to or lower than 20 percent.
11. The nuclear fuel lattice structure according to claim 1 , wherein the nuclear fissionable fuel includes uranium oxide that is less than 20% enriched, uranium with 10 wt. % molybdenum (U-10Mo), uranium nitride (UN), or a cermet thereof.
12. The nuclear fuel lattice structure according to claim 3 , wherein the thickness of the webbings is asymmetric relative to the baseline.
13. A nuclear fuel segment, comprising:
the nuclear fuel lattice structure according to claim 1 ; and
a cladding layer deposited on the outer surfaces of the plurality of webbings that define the network of interconnected channels.
14. The nuclear fuel segment according to claim 13 , wherein the cladding layer has a composition including molybdenum, tungsten, rhenium, tantalum, hafnium and alloys thereof, including carbides.
15. A nuclear reactor structure, comprising:
an active core region including a plurality of nuclear fuel segments according to claim 13 ,
wherein the plurality of nuclear fuel segments are arranged along an axial centerline defining a longitudinal axis of the nuclear reactor structure.
16. The nuclear reactor structure according to claim 15 , wherein the network of interconnected channels in the body of adjacent nuclear fuel segments are aligned to provide fluid communication from a first end surface of the active core to a second end surface of the active core.
17. A nuclear thermal propulsion engine, comprising:
the nuclear reactor structure according to claim 15 , wherein the nuclear reactor structure is housed within an interior volume of a hull;
shielding;
a reservoir for cryogenically storing propulsion gas;
turbomachinery; and
a nozzle,
wherein the shielding, the turbomachinery, and the reservoir are operatively mounted to a first end of the hull to provide a flow path from the reservoir to the nuclear reactor structure, and
wherein the nozzle is operatively mounted to a second end of the hull to provide a flow path for superheated propulsion gas exiting the nuclear thermal propulsion engine.