US-12620499-B2 - Fuel assembly

Abstract

A fuel assembly includes a plurality of elongated fuel elements. Each of the plurality of fuel elements has a spirally twisted, multi-lobed profile that defines a plurality of spiral ribs. Each of the plurality of fuel elements has a fuel kernel that includes fuel material disposed in a matrix of metal non-fuel material. The fuel material includes fissile material. A cladding surrounds the fuel kernel. A moderator: fuel ratio in a region of the fuel elements is 2.4 or less. The moderator: fuel ratio is an area ratio within a cross-section that is perpendicular to longitudinal axes of the plurality of fuel elements and extends through the plurality of fuel elements. The area ratio is a ratio of: (1) a total area available for moderator flow for the plurality of fuel elements to (2) a total area of the fuel kernels of the plurality of fuel elements.

Inventors

• Sergey Mikhailovich BASHKIRTSEV
• Valentin Fedorovich KUZNETSOV
• Valery Vladimirovich KEVROLEV
• Alexey Glebovich MOROZOV
• Michael H. MONTGOMERY

Assignees

• THORIUM POWER, INC.

Dates

Publication Date

20260505

Application Date

20231025

Claims (16)

1. 1 . A fuel assembly for a pressurized heavy water reactor, the fuel assembly comprising: a plurality of elongated fuel elements, each of said plurality of fuel elements having a spirally twisted, multi-lobed profile that defines a plurality of spiral ribs, each of said plurality of fuel elements comprising: a fuel kernel comprising fuel material disposed in a matrix of metal non-fuel material, the fuel material comprising fissile material, and a cladding surrounding the fuel kernel, wherein a moderator: fuel ratio in a region of the fuel elements is 2.4 or less, the moderator: fuel ratio being an area ratio within a cross-section that is perpendicular to longitudinal axes of the plurality of fuel elements and extends through the plurality of fuel elements, the area ratio is a ratio of: (1) a total area available for moderator flow for the plurality of fuel elements to (2) a total area of the fuel kernels of the plurality of fuel elements.
2. 2 . The fuel assembly of claim 1 further comprising a frame, including a first end plate and a second end plate.
3. 3 . The fuel assembly of claim 2 , wherein the frame spaces adjacent ones of said plurality of fuel elements from one another to prevent contact therebetween.
4. 4 . The fuel assembly of claim 1 , wherein the spiral ribs of adjacent fuel elements periodically contact one another over the axial length of the fuel elements to at least partially maintain the spacing of the fuel elements relative to each other.
5. 5 . The fuel assembly of claim 1 , wherein the multi-lobed profile includes lobe tips and intersections between adjacent lobes, and wherein the cladding is thicker at the lobe tips than at the intersections.
6. 6 . The fuel assembly of claim 1 , wherein the fuel kernel comprises δ-phase UZr 2 .
7. 7 . The fuel assembly of claim 1 , wherein each of the plurality of elongated fuel elements further comprises a displacer that extends along a central longitudinal axis of the fuel kernel.
8. 8 . The fuel assembly of claim 1 , wherein the non-fuel material comprises at least one of zirconium, aluminum, or a refractory metal.
9. 9 . The fuel assembly of claim 1 , wherein the fuel material comprises ceramic fuel material.
10. 10 . The fuel assembly of claim 1 , wherein the fuel material comprises a combination of uranium and thorium; plutonium and thorium; or uranium, plutonium and thorium.
11. 11 . A nuclear reactor comprising: a pressurized heavy water reactor; and a fuel assembly disposed in the pressurized heavy water reactor, the fuel assembly comprising: a plurality of elongated fuel elements mounted to each other, each of the plurality of fuel elements having a spirally twisted, multi-lobed profile that defines a plurality of spiral ribs, each of the plurality of fuel elements comprising: a fuel kernel comprising fuel material disposed in a matrix of metal non-fuel material, the fuel material comprising fissile material, and a cladding surrounding the fuel kernel, wherein a moderator: fuel ratio in a region of the fuel elements is 2.4 or less, the moderator: fuel ratio being an area ratio within a cross-section that is perpendicular to longitudinal axes of the plurality of fuel elements and extends through the plurality of fuel elements, the area ratio is a ratio of: (1) a total area available for moderator flow for the plurality of fuel elements to (2) a total area of the fuel kernels of the plurality of fuel elements.
12. 12 . The nuclear reactor of claim 11 , wherein the multi-lobed profile includes lobe tips and intersections between adjacent lobes, and wherein the cladding is thicker at the lobe tips than at the intersections.
13. 13 . The nuclear reactor of claim 11 , wherein the fuel kernel comprises 8 -phase UZr 2 .
14. 14 . The nuclear reactor of claim 11 , wherein each of the plurality of elongated fuel elements further comprises a displacer that extends along a central longitudinal axis of the fuel kernel.
15. 15 . The nuclear reactor of claim 11 , wherein each fuel assembly includes a frame that includes a first end plate and a second end plate, wherein the first and second end plates are mounted to opposite axial ends of each of the plurality of fuel elements.
16. 16 . The nuclear reactor of claim 11 , wherein the spiral ribs of adjacent fuel elements periodically contact one another over the axial length of the fuel elements to at least partially maintain the spacing of the fuel elements relative to each other.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a divisional application of U.S. application Ser. No. 17/237,683, filed Apr. 22, 2021, which in turn is a divisional application of U.S. application Ser. No. 15/900,071, filed Feb. 20, 2018, which in turn is a continuation of Ser. No. 13/695,792, filed Jun. 3, 2013, which is a U.S. National Stage application under 35 USC § 371 of PCT/US2011/036034 filed 11 May 2011, which claims priority benefit under the Paris Convention from U.S. Provisional Application No. 61/333,467, filed May 11, 2010, U.S. Provisional Application No. 61/393,499, filed Oct. 15, 2010, and U.S. Provisional Application No. 61/444,990, filed Feb. 21, 2011, all three of which are titled “METAL FUEL ASSEMBLY,” the entire contents of which are hereby incorporated by reference herein. BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to nuclear fuel assemblies used in the core of a nuclear reactor, and relates more specifically to metal nuclear fuel elements. Description of Related Art U.S. Patent Application Publication No. 2009/0252278 A1, the entire contents of which are incorporated herein by reference, discloses a nuclear fuel assembly that includes seed and blanket sub-assemblies. The blanket sub-assembly includes thorium-based fuel elements. The seed sub-assembly includes Uranium and/or Plutonium metal fuel elements used to release neutrons, which are captured by the Thorium blanket elements, thereby creating fissionable U-233 that burns in situ and releases heat for the nuclear power plant. Conventional nuclear power plants typically use fuel assemblies that include a plurality of fuel rods that each comprise uranium oxide fuel in a cylindrical tube. SUMMARY OF EMBODIMENTS OF THE INVENTION The surface area of the cylindrical tube of conventional fuel rods limits the amount of heat that can be transferred from the rod to the primary coolant. To avoid overheating the fuel rod in view of the limited surface area for heat flux removal, the amount of fissile material in these uranium oxide fuel rods or mixed oxide (plutonium and uranium oxide) fuel rods has conventionally been substantially limited. One or more embodiments of the present invention overcome various disadvantages of conventional uranium oxide fuel rods by replacing them with all metal, multi-lobed, powder metallurgy co-extruded fuel rods (fuel elements). The metal fuel elements have significantly more surface area than their uranium oxide rod counterparts, and therefore facilitate significantly more heat transfer from the fuel element to the primary coolant at a lower temperature. The spiral ribs of the multi-lobed fuel elements provide structural support to the fuel element, which may facilitate the reduction in the quantity or elimination of spacer grids that might otherwise have been required. Reduction in the quantity or elimination of such spacer grids advantageously reduces the hydraulic drag on the coolant, which can improve heat transfer to the coolant. Because the metal fuel elements may be relatively more compact than their conventional uranium oxide fuel rod counterparts, more space within the fuel assembly is provided for coolant, which again reduces hydraulic drag and improves heat transfer to the coolant. The higher heat transfer from the metal fuel rods to the coolant means that it is possible to generate more heat (i.e., power), while simultaneously maintaining the fuel elements at a lower operating temperature due to the considerably higher thermal conductivity of metals versus oxides. Although conventional uranium oxide or mixed oxide fuel rods typically are limited to fissile material loading of around 4-5% due to overheating concerns, the higher heat transfer properties of the metal fuel elements according to various embodiments of the present invention enable significantly greater fissile material loadings to be used while still maintaining safe fuel performance. Ultimately, the use of metal fuel elements according to one or more embodiments of the present invention can provide more power from the same reactor core than possible with conventional uranium oxide or mixed oxide fuel rods. The use of all-metal fuel elements according to one or more embodiments of the present invention may advantageously reduce the risk of fuel failure because the metal fuel elements reduce the risk of fission gas release to the primary coolant, as is possible in conventional uranium oxide or mixed oxide fuel rods. The use of all-metal fuel elements according to one or more embodiments of the present invention may also be safer than conventional uranium oxide fuel rods because the all-metal design increases heat transfer within the fuel element, thereby reducing temperature variations within the fuel element, and reducing the risk of localized overheating of the fuel element. One or more embodiments of the present invention provide a fuel assembly for a pressurized heavy water