Nuclear reactor fuel assembly and process for production

Abstract

To provide a nuclear fuel assembly.SOLUTION: A nuclear fuel assembly for nuclear reactor cores includes at least one fuel compact including a fuel compact coating tube defining an inner volume and a plurality of fuel pins each including a pin coating tube defining an inner volume and a fissile fuel arranged in the inner volume of the pin coating tube. The plurality of fuel pins are arranged in the inner volume of the fuel compact coating tube; and the sectional shape of the fuel compact is defined by the fuel compact coating tube.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Claiming priority This application claims priority to U.S. Provisional Patent Application No. 62 / 794,320, filed January 18, 2019, the disclosure of which is incorporated herein by reference.

[0002] The presently disclosed invention relates generally to nuclear reactors, and more specifically to fuel assemblies for use in constructing reactor cores and processes for producing those fuel assemblies. [Background technology]

[0003] Concepts are known that utilize nuclear thermal propulsion to propel spacecraft during space travel. Existing propulsion concepts typically utilize a fuel assembly fabrication process known as a fuel dispersion method. The fuel dispersion method produces uranium-based fuel kernels, the kernels being on the order of 200 μm to 400 μm in diameter. The kernels are often fabricated by traditional internal gelation processes or advanced sol-gel processing methods. The kernels are coated with a metal matrix material (e.g., tungsten, etc.) to encapsulate the fuel kernel. Once coated, the particles are embedded in the metal matrix material (e.g., tungsten powder, etc.) and formed into a monolithic part by metallurgical compaction techniques such as hot isostatic pressing. However, various difficulties are known to exist with the fuel dispersion method for producing fuel assemblies. For example, challenges exist when producing fuel kernels less than 400 μm, as well as challenges exist with coating the fuel kernels with refractory metals (e.g., but not limited to, tungsten, molybdenum, etc.). Inconsistent coating of fuel kernels can be very problematic when attempting to achieve high fuel packing factors (such as those desired for fuel assemblies to be used in nuclear thermal propulsion applications). Specifically, improperly coated fuel kernels can come into contact with one another and agglomerate, which can lead to fuel meltdown and / or fuel loss. Moreover, core neutron analysis can be compromised because the exact location of the coated fuel kernels within the metal matrix material is not known. The need to prevent agglomeration of the coated fuel kernels requires that a sufficient amount of matrix material (tungsten powder) be used, which can impede the ability to achieve sufficient packing factors for fuel assemblies to be used in the aforementioned nuclear thermal propulsion applications.

[0004] Thus, at least one need remains for a fuel assembly suitable for use in nuclear thermal propulsion assemblies, and a process for producing the same. Summary of the Invention [Means for solving the problem]

[0005] One embodiment of the present invention provides a nuclear fuel assembly for a nuclear reactor core, the nuclear fuel assembly including at least one fuel cartridge having a lattice structure with an outer wall defining an interior volume, at least one flow channel extending through the interior volume of the lattice structure, at least one lattice site disposed within the lattice structure, and at least one fuel compact disposed within a corresponding one of the at least one lattice site, wherein a cross-sectional shape of the at least one fuel compact is the same as a cross-sectional shape of the corresponding one of the at least one lattice site.

[0006] Another embodiment of the present invention provides a nuclear fuel assembly for a nuclear reactor core, the nuclear fuel assembly having at least one fuel compact including a fuel compact cladding tube defining an internal volume, and a plurality of fuel pins, each fuel pin including a pin cladding tube defining an internal volume and a plurality of fuel pins including fissile fuel disposed within the internal volume of the pin cladding tube, the plurality of fuel pins being disposed within the internal volume of the fuel compact cladding tube, and a cross-sectional shape of the fuel compacts being defined by the fuel compact cladding tube.

[0007] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0008] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a nuclear reactor core including a fuel assembly constructed in accordance with an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of the fuel assembly shown in FIG. [Figure 3A] FIG. 3 is a perspective view of a lattice structure of the fuel assembly shown in FIG. [Figure 3B] FIG. 3 is an end view of a lattice structure of the fuel assembly shown in FIG. [Figure 4] FIG. 2 is a partial perspective view of a fuel pin according to an embodiment of the present invention. [Diagram 5] FIG. 2 is an end view of a fuel compact according to an embodiment of the present invention. [Figure 6A] FIG. 6 is an end view of a swaging operation being performed on the fuel compact shown in FIG. 5. [Figure 6B] FIG. 6 is an end view of a swaging operation being performed on the fuel compact shown in FIG. 5. [Figure 6C] FIG. 6 is an end view of a swaging operation being performed on the fuel compact shown in FIG. 5. [Figure 7] FIG. 2 is an end view of a finished fuel compact according to an embodiment of the present invention. [Figure 8] FIG. 2 is a partial perspective view of a fuel cartridge assembly according to an embodiment of the present invention. [Figure 9] FIG. 9 is an end view of the fuel cartridge shown in FIG. 8 after the fuel compact has been inserted into the grid. [Figure 10A]FIG. 10 is a perspective view of the fuel cartridge shown in FIG. 9 assembled to form a fuel assembly. [Figure 10B] FIG. 10 is a perspective view of the fuel cartridge shown in FIG. 9 assembled to form a fuel assembly. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Repeat use of reference characters in the present specification and drawings is intended to represent same or similar features or elements of the invention according to the present disclosure.

[0011] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0012] Referring now to the figures, a reactor core 100 according to the present invention includes a plurality of modular fuel assemblies 110 received within a vessel shell 102, as best seen in FIGS. 1 and 2. Preferably, each fuel assembly 110 has a hexagonal cross-section and is formed by a plurality of fuel cartridges 112a, 112b, 112c, etc., as discussed in more detail below. Preferably, each fuel cartridge 112 includes a lattice structure 114 defining a plurality of lattice sites 122 therein and a plurality of fuel compacts 130 disposed therein. Each fuel compact 130 is received within a correspondingly shaped lattice site 122, as best seen in FIG. 8. It should be noted that while the fuel assemblies 110 discussed preferably have a hexagonal cross-section, in alternative embodiments, the fuel assemblies can have different cross-sectional shapes (e.g., but not limited to, triangular, square, rectangular, etc.).

[0013] As shown in FIGS. 3A and 3B , the lattice structure 114 includes a plurality of side walls 116 defining an elongated shell, a plurality of elongated tubes 118, and a plurality of inner walls 120, the plurality of elongated tubes 118 being disposed within the lattice structure 114 such that a central longitudinal axis of each of the elongated tubes 118 is parallel to a central longitudinal axis of the lattice structure 114, and the plurality of inner walls 120 defining a plurality of lattice sites 122 within the lattice structure. Each of the elongated tubes 118 extends the entire length of the lattice structure 114, thereby forming a channel through which reactor coolant may flow during reactor operation. Some inner walls 120a of the lattice structure 114 extend between pairs of the elongated tubes 118, while other inner walls 120b extend between corresponding elongated tubes 118 and adjacent side walls 116 of the lattice structure 114. As such, each lattice site 122 does not have the same cross-sectional shape. As best seen in FIG. 3B, the currently discussed embodiment of the lattice structure 114 includes 37 elongated tubes 118 and 96 full and partial lattice sites 122. However, it should be noted that in alternative embodiments, a different number of elongated tubes 118 and lattice sites 122 may be present. Preferably, the lattice structure 114 is formed by additive manufacturing (also known as metal 3D printing) and is comprised of a monolithic structure of the desired material (such as, but not limited to, molybdenum). Alternatively, the lattice structure 114 is formed by multiple cut sheets of the desired material (such as, for example, molybdenum), which are arranged into the desired lattice geometry and then resistance welded to form the component.

[0014] As best seen in FIG. 8, each fuel compact 130 of the fuel assembly 110 is formed such that its cross-sectional shape is the same as the cross-section of the corresponding lattice site 122. With additional reference to FIGS. 4 and 5, each fuel compact 130 is formed by a plurality of elongated fuel pins 132 that are disposed within an elongated fuel compact cladding tube 138 prior to a swaging process, as discussed in more detail below, to achieve the desired cross-sectional shape of the fuel compact. As best seen in FIG. 4, each fuel pin 132 includes a pin cladding tube 134 that is sealed by a top wall 133 and a bottom wall 135 such that the pin cladding tube 134 defines a sealed interior volume 139. The tube is sealed by the top wall 133 and the bottom wall 135 after fuel pellets 136 are disposed inside the pin cladding tube 134 such that the pin cladding tube 134 serves as cladding for the fuel. As shown, fuel pellets 136 are preferably utilized for the fuel pins, however, in alternative embodiments of the invention, fuel kernels, fuel powder, etc., rather than pellets, may be used.

[0015] Additionally, each assembled pin cladding tube 134 and fuel pellets 136 undergo a swaging process during which the desired final diameter of the fuel pins 132 is achieved. The pin diameter is selected to meet the desired fuel packing factor requirements of the fuel assembly. After swaging, each fuel pin 132 is disposed within a corresponding fuel compact cladding tube 138, as best seen in FIG. 5. It is noted that to achieve the desired fuel packing factor requirements, fuel pins 132 of different diameters are created to reduce the assembly volume defined by the interstitial spaces 141 within the fuel compact cladding tube. In the preferred embodiment shown, the pin diameters are selected such that the fuel pins 132 can be disposed within the fuel compact cladding tube 138 in a Warrington Seale configuration.

[0016] 6A-6C, after the fuel pins 132 are arranged in the desired pattern within the fuel compact cladding tube 138, a swaging process is performed on the fuel compact 130 to achieve the desired cross-sectional shape of the compact for subsequent insertion into the corresponding lattice sites 122 (FIG. 8). In the exemplary embodiment shown, the swaging process is performed in a press 142, which deforms the fuel compact cladding tube 138 into the desired cross-sectional shape. As shown, the cross-sectional shape of the fuel compact 130 is a perfect trilobe, which will allow the fuel compact 130 to be disposed in any of the lattice sites 122 that are not adjacent to the sidewall 116 of the lattice structure 114.

[0017] 8, each fuel compact 130 is inserted into a corresponding lattice site 122 of the lattice structure 114 with an interference fit. Preferably, the interference fit is achieved by heating the lattice structure 114 prior to inserting the fuel compact 130 into the corresponding lattice site 122. After each lattice site 122 receives a corresponding fuel compact 130 therein, a top wall 133 and a bottom wall (not shown) are resistance welded to the top and bottom ends of the lattice structure 114 to complete the construction of the fuel cartridge 112, as shown in FIG. 9. Both the top and bottom walls include a plurality of apertures 137, each corresponding to a location of an elongated tube 118 of the lattice to allow reactor coolant to flow therethrough.

[0018] 10A and 10B, each fuel assembly 110 is fabricated, such as by stacking a desired number of fuel cartridges 112a, 112b, until a fuel assembly of a desired length is achieved. The stacked fuel cartridges 112a, 112b are then consolidated by methods such as, but not limited to, diffusion bonding, resistance welding, mechanical fastening, and the like. In that each fuel assembly 110 is constructed from individual fuel cartridges 112, which are then fastened together, the material composition of the fuel in each fuel cartridge 112 may be varied from the remaining fuel cartridges 112. As such, the material gradient of each fuel assembly 110 may be varied along its axial linkage. For example, referring again to FIG. 2, a reduced amount of tungsten may be used in the fuel cartridge 112a forming the upper portion of the fuel assembly 110, as compared to the fuel cartridge 112c forming the bottom portion of the fuel assembly 110. While it may be desirable to have an increased amount of tungsten in the bottom fuel cartridge 112c (due to the increased temperature in that portion of the core), it may be desirable to reduce the amount of tungsten in the fuel cartridges 112a and 112b because temperatures are lower higher in the core. This may be advantageous in that tungsten may be difficult to isotopically enrich and is heavier than various other materials (e.g., molybdenum) that may be used in locations where lower temperatures are encountered.

[0019] These and other modifications and variations to the present invention may be practiced by those skilled in the art without departing from the spirit and scope of the present invention, which is more particularly described in the appended claims. For example, in an alternative embodiment of the present invention, rather than disposing fuel compacts in corresponding lattice sites when constructing a fuel cartridge, as described above, a fuel dispersion method may be used to fill the interior of a lattice structure surrounding a flow channel. In addition, it should be understood that aspects of the various embodiments may be interchanged in whole or in part. Moreover, those skilled in the art will recognize that the foregoing description is merely exemplary, and is not intended to limit the invention as further described in such appended claims. Thus, the spirit and scope of the appended claims should not be limited to the exemplary descriptions of the versions contained herein.

Claims

1. A nuclear fuel assembly for a nuclear reactor core, the nuclear fuel assembly including at least one fuel compact, the at least one fuel compact comprising: a fuel compact cladding tube defining an interior volume; a plurality of fuel pins, each fuel pin including a pin cladding tube defining an interior volume, and fissile fuel disposed within the interior volume of the pin cladding tube; Including, 11. A nuclear fuel assembly, comprising: a fuel compact cladding tube having a cross-sectional shape defined by said fuel compacts; a fuel pin cladding tube having a cross-sectional shape defined by said fuel compact cladding tube;

2. 10. The nuclear fuel assembly of claim 1, wherein the fissile fuel in the plurality of fuel pins is one of a fuel pellet, a plurality of fuel kernels, and a fuel powder.

3. 10. The nuclear fuel assembly of claim 1, wherein each fuel pin of each fuel compact and said fuel compact cladding tube are substantially cylindrical in shape prior to the swaging process that results in the cross-sectional shape of said fuel compact.

4. The nuclear fuel assembly further includes at least one fuel cartridge, the at least one fuel cartridge comprising: a lattice structure including an outer wall defining an interior volume; at least one flow channel extending through the interior volume of the lattice structure; at least one lattice site disposed within the lattice structure; Including, at least one fuel compact disposed within a corresponding one of the at least one lattice site; 4. The nuclear fuel assembly of claim 3, wherein a cross-sectional shape of the at least one fuel compact is the same as a cross-sectional shape of the corresponding one of the at least one lattice site.

5. 5. The nuclear fuel assembly of claim 4, wherein the at least one fuel cartridge comprises a plurality of fuel cartridges, each fuel cartridge further comprising a top wall and a bottom wall disposed on opposite sides of the lattice structure such that each lattice site defines a sealed volume.

6. 5. The nuclear fuel assembly of claim 4, wherein the top and bottom walls of each fuel cartridge define a plurality of apertures, each aperture corresponding to a location of a corresponding flow channel of the fuel cartridge.

7. 7. The nuclear fuel assembly of claim 6, wherein the nuclear fuel assembly includes a plurality of fuel cartridges, the plurality of fuel cartridges being disposed end-to-end and secured to one another.

Images