Patent Application
20250218611
The present disclosure relates generally to nuclear fission reactors and structures related to nuclear fission reactors, in particular for propulsion. In particular, a fuel assembly core has stacked monolithic fuel bodies, insulation layers, an exhaust support plate, and an inlet flow structure. The fuel assembly core is mandrel-wound to form an assembled insulated fuel assembly core, which is positioned in a fuel assembly outer structure to form a fuel assembly. Fuel assemblies are incorporated into a nuclear thermal propulsion reactor, which may be used in various applications suitable for gas reactor designs, such as space, lunar and terrestrial environments.
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.
Twisted ribbon fuel forms have been previously used in reactor designs (see Burns et al, “Nuclear Thermal Propulsion Reactor Materials”, in Nuclear Materials, edited by P. Tsvetkov, London: IntechOpen, 2020), with (U, Zr) C fuel used for the low-temperature portion of the reactor design (i.e., propellant exit gas temperature≤2500 K), and (U, Zr, Nb) C used for the high-temperature portion of the reactor core. These conventional ribbon fuel forms were assembled into a tube with an insulation layer of NbC and ZrC and an outer casing of carbide-graphite material.
However, such conventional assembly allowed for several failure modes. Among these are cracking of the insulation layer, layer separation, and ablation forming holes. Each of these failure modes can allow hot propellant gas, such as hydrogen, to penetrate the layered tube structure, attack the layers, and ultimately cause failure of the casing.
There is a need for improvements in nuclear thermal propulsion reactors to address these failure modes and to, more generally, reduce defects and improve performance. In particular, improvements related to the geometry of the fuel itself and to the structures, arrangement and manufacturing of fuel assemblies, including of the various components of the fuel assembly, such as an exhaust support plate and an exhaust shield assembly. In addition, improvements related to the manufacture of insulated fuel assembly cores and fuel assemblies containing insulated fuel assembly cores are disclosed, which provide for improved manufacturability.
An embodiment of an insulated fuel assembly core comprises a plurality of fuel monoliths, an exhaust support plate, an exhaust shield assembly, and an insulation layer. The plurality of fuel monoliths is located axially along a longitudinal axis of the insulated fuel assembly core and each of the plurality of fuel monoliths has a shape of an eccentric cylinder and has a composition including a fissionable fuel component.
An embodiment of a method of manufacturing an insulated fuel assembly core comprises forming a tensioned fuel monolith stack mandrel assembly and forming an insulation layer on an outer surface of the tensioned fuel monolith stack mandrel assembly by mandrel winding. Forming the tensioned fuel monolith stack mandrel assembly includes: assembling a plurality of fuel monoliths into a stack along a longitudinal axis, wherein each of the plurality of fuel monoliths has a shape of an eccentric cylinder and includes a first end surface, a second end surface, a side surface connecting the first end surface to the second end surface, and a plurality of first channels extending axially from the first end surface to the second end surface; inserting an alignment drill rod through one of the plurality of first channels in a direction of the longitudinal axis; attaching an exhaust support plate to a first end of the assembled stack to form a core stack, wherein the exhaust support plate includes a first end face, a second end face, a circumferential surface connecting the first end face to the second end face, and a plurality of second channels extending from the first end face to the second end face and attaching the exhaust support plate inserts the alignment rod through one of the plurality of second channels; inserting a first set of tensioning cables through a first portion of the plurality of first channels in the plurality of fuel monoliths and through a first portion of the plurality of second channels in the exhaust support plate; attaching a plurality of second mandrel spacers to a second end of the core stack; inserting the first set of tensioning cables through the plurality of second mandrel spacers; attaching a plurality of first mandrel spacers to a first end of the core stack, wherein the first end of the core stack includes the exhaust support plate attached to the first end of the assembled stack; inserting a second set of tensioning cables through: (i) the plurality of first mandrel spacers, (ii) a second portion of the plurality of second channels in the exhaust support plate, (iii) a second portion of the plurality of first channels in the plurality of fuel monoliths, and (iv) the plurality of first mandrel spacers; tensioning the first set of tensioning cables and the second set of tensioning cables; and attaching a first threaded mandrel cap to a distal end of the plurality of first mandrel spacers and a second threaded mandrel cap to a distal end of the plurality of second mandrel spacers.
The disclosed insulated fuel assembly core can be incorporated into a fuel assembly by locating the insulated fuel assembly core within a fuel assembly outer structure and attaching an inlet connection assembly to an inlet end of the fuel assembly outer structure. Also, a plurality of fuel assemblies can be located in a different one of a plurality of fuel assembly openings in a moderator block to form a nuclear fission reactor structure.
Embodiments of the disclosed insulated fuel assembly core, fuel assembly, and structures and methods of fabrication have application in various fission reactor designs and application in a wide range of fields, including aerospace and industrial applications.
The foregoing summary, as well as the following detailed description of the embodiments, can be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown.
In some instances, dimensions of respective constituent elements are appropriately adjusted for clarity. For ease of viewing, in some instances only some of the named features in the figures are labeled with reference numerals.
In some embodiments, the plurality of channels 30 are arranged symmetrically relative to a longitudinal axis 40 of the body 20 of the fuel monolith 10. For example, the plurality of channels 30 can be arranged in groups of concentric rings, with a central channel 30′, an inner ring 52 of channels 30″, an intermediate ring 54 of channels 30″, and an outer ring 56 of channel 30″. Channels in any one ring can be evenly distributed in the circumferential direction or unevenly distributed in the circumferential direction. The concentric rings can be evenly distributed in the radial direction or can be unevenly distributed in the radial direction. In some embodiments, the axis of each of the plurality of channels 30 is parallel to the longitudinal axis 40. In other embodiments, the axis of a first portion of the plurality of channels 30 is parallel to the longitudinal axis 40 and the axis of a second portion of the plurality of channels 30 is skewed relative to the longitudinal axis 40. For example, the axis of the central channel 30′ and one or more of (a) the axis of the plurality of channels 30″ in inner ring 52 and (b) the axis of the plurality of channels 30″ in intermediate ring 54 can be parallel to the longitudinal axis 40, and the axis of the plurality of channels 30″ in outer ring 56 can be skewed relative to the longitudinal axis 40.
In cross-section perpendicular to longitudinal axis 40, the body 20 of the fuel monolith 10 has the shape of an ellipse with a first diameter D1 that is different from a second diameter D2 (where the first diameter is perpendicular to the second diameter) resulting in the body 20 of the fuel monolith 10 having an eccentric cylindrical shape, e.g., an eccentric, right cylinder of height H1 with elliptical end surfaces. As an ellipse, the first diameter D1 is the major axis of the ellipse and the second diameter D2 is the minor axis of the ellipse. In exemplary embodiments, the difference in length of the first diameter D1 and the second diameter D2 is from greater than 0.5 mm to 5 mm, alternatively the difference in length is greater than 1.0 mm or greater than 2.5 mm and is less than 2.0 mm or less than 2.5 mm or less than 4.0 mm. In still further alternatives, the difference in length is about 2.0 mm (such as 1.8±0.1 mm, 1.6±0.1 mm, 1.4±0.1 mm, or 1.2±0.1 mm) or about 2.0 mm to about 5.0 mm (such as 4.5±0.1 mm, 4.0±0.1 mm, 3.5±0.1 mm, 3.0±0.1 mm or 2.5±0.1 mm). In exemplary embodiments, the eccentricity of the body 20 of the fuel monolith 10 is greater than zero to 0.6, alternatively greater than zero to 0.4 or greater than zero to 0.15, such as in a range from 0.01, 0.02, 0.05 or 0.10 to 0.6, 0.5, 0.4, 0.3, 0.2, 0.15, 0.10, or 0.05.
The eccentricity of the body 20 of the fuel monolith 10 facilitates alignment of the plurality of channels 30 in the fuel monoliths when the fuel monoliths are stacked together to form the fuel assembly core. In some embodiments, the first diameter D1 is 27 mm and the second diameter D2 is 26 mm, resulting in a 1.0 mm locking feature. In other embodiments, the first diameter D1 is 29.9 mm and the second diameter D2 is 28.9 mm, resulting in a 1.0 mm locking feature. The locking feature functions to maintain alignment of the channels 30 across the plurality of fuel monoliths 10 without the need for other mechanical locking features, such as alignment tubes, trapped spheres in pockets, keyways, or other geometrical locking means. The first diameter D1 and the second diameter D2 can have other sizes, with the difference D1-D2 being the size of the locking feature. As the difference in diameters increases, the strength of the locking feature increases. However, as the difference in diameters decreases less than 1 mm, the alignment of channels 30 between adjacent fuel monoliths 10 is less likely and results in the need for supplemental locking features, such as other mechanical locking features. Examples of suitable sizes for the locking feature are 1.0 mm to 4.0 mm.
In optional embodiments, in cross-section perpendicular to longitudinal axis 40, the body 20 of the fuel monolith 10 has the shape of circle and the fuel monolith 10 has a right cylindrical shape and an eccentricity of zero.
In exemplary embodiments, the fuel monolith 10 has a composition including a fissionable fuel component. One example of a fissionable fuel component is a uranium-based material, such as ZrUC or UC—ZrC—NbC. Other uranium-based materials include UO2, cermet of UO2 and W, UN with W cermet, and UO2 with Mo cermet. In exemplary embodiments, the composition is a solid solution including the fissionable fuel component. In one example, the composition of the fuel monolith 10 includes uranium having a U-235 assay above 5 percent and below 20 percent. Other compositions that can processed by injection molding techniques to form fuel monoliths 10 can also be used.
The exhaust support plate 130 includes a plurality of channels 132 that extend through the body of the exhaust support plate 130 from an inlet opening 134 in the first end face 136 to an outlet opening 138 in the second end face 140. The plurality of channels 132 provide a flow path for propellant gas, such as hydrogen, to flow through the exhaust support plate 130 during operation. The inlet openings 134 of the plurality of channels 132 are aligned with the plurality of channels 30 in the fuel monoliths 10 of the fuel assembly core 110 and can be arranged similarly to the arrangement of the plurality of channels 30 in the fuel monoliths 10, such as having the same symmetrical arrangement and/or being arranged in groups of concentric rings with even or uneven circumferential and/or radial distribution. The first end face 136 of the exhaust support plate 130 is planar to facilitate abutting to the end face of the adjacent fuel monolith 10 and the second end face 140 of the exhaust support plate 130 is concave to facilitate directing the flow of propellant gas exiting the outlet openings 138.
The exhaust support plate 130 is formed from a material with good corrosion resistance to the exhausting propellant gas. Both chemical corrosion and wear corrosion resistance are preferred. An example material for the exhaust support plate 130 is tungsten or a tungsten-based alloy or a W—Re alloys (for example, with a Re content between 3-50 wt %) or a carbide-based material, such as ZrC. In some example materials for the exhaust support plate 130, the material can be dispersion strengthened with carbides and oxides, for example, HfC, ThO2, and/or La2O3.
In exemplary embodiments, the exhaust shield assembly 150 includes a truncated conical section 152 and a tubular section 154. In exemplary embodiments, the truncated conical section 152 of the exhaust shield assembly 150 transitions from an elliptical shape at a first end (so as to mate to the elliptical shape of the eccentric cylindrical shape of the fuel monoliths 10 and exhaust support plate 130) to a circular shape at a second end, where the truncated conical section 152 is attached to the tubular section 154.
Region A in
The exhaust shield assembly 150 is formed from a material with good corrosion resistance to the exhausting propellant gas. Both chemical corrosion and wear corrosion resistance are preferred. An example material for the exhaust shield assembly 150 is tungsten or a tungsten-based alloy or a W—Re alloys (for example, with a Re content between 3-50 wt %) or a carbide-based material, such as ZrC. In some example materials for the exhaust support plate 130, the material can be dispersion strengthened with carbides and oxides, for example, HfC, ThO2, and/or La2O3.
In alternative embodiments, the transition from the eccentric cylindrical shape of the fuel monoliths 10 to a circular shape can occur in the exhaust support plate 130, with the first end face 136 of the exhaust support plate 130 having the elliptical shape of the eccentric cylindrical shape of the fuel monoliths 10 and the second end face 140 of the exhaust support plate 130 being circular shaped.
It should be noted that truncated conical section 152 and tubular section 154 can be manufactured as separate pieces and joined, for example, by welding. However, welding can leave a seam joint between the two pieces. Alternatively, the truncated conical section 152 and tubular section 154 can be manufactured as a unitary structure, such as by additive manufacturing or by machining, for example by sinker electrical discharge machining (EDM) manufacturing from a billet so that there is no welded seam joint between the two pieces.
In exemplary embodiments, R1 ranges from 10 mm to 50 mm (although the second end face 140 can optionally be planar with no radius), angle α ranges from 0 degrees to 20 degrees (such as 4 to 5 degrees, or 8 to 10 degrees), angle θ ranges from 0 degrees to 20 degrees (such as 4 to 6 degrees, or 8 to 12 degrees), angle β ranges from 0 degrees to 20 degrees (such as 6 to 10 degrees, or 10 to 15 degrees), and H2 (the height of the exhaust support plate 130) ranges from 5 mm to 50 mm (such as 12 to 20 mm). In some embodiments, α<θ<β, such as α=4.6 degrees, θ=5.4 degrees, and β=8 degrees.
Although the central region 144 is shown in
Details of the position and orientation of the channels 132′ are shown in the various cross-sectional views in correspond to the annotated cross-sections as follows: For the cross-sections in
In general, the various angles shown and labeled in
The angles orient the channels 132, 132′ so that they are essentially parallel to the face of the elliptical loft 142, e.g., within +5 degrees of parallel, alternatively within +1 degree of parallel. This angle is such that the openings of the channels 132,132′ on the second end face 140, i.e., the surface formed by R1, do not intersect with each other. The positions of inlet openings 134 of the channels are located so that the inlet openings 134 line up with the channels 30 in the fuel monolith 10.
The exhaust shield assembly 150 can be formed from separate parts joined together or can be formed as a unitary part. For example, a truncated conical section 152 and a tubular section 154 can be formed separately and joined tougher, for example, by resistance welding. Alternatively, a unitary exhaust shield assembly 150′ can have a truncated conical section 152′ and a tubular section 154′ that are formed as a singular part, which eliminates the welding joint.
In alternative embodiments of the unitary exhaust shield assembly is a unitary structure.
Step S110 prepares the fuel monolith 10, which may include manufacturing and post-manufacturing processing of the fuel monolith 10 or may include only post-manufacturing of a pre-manufactured fuel monolith 10. Manufacturing the fuel monolith 10 can be by various techniques. In an exemplary embodiment, the fuel monolith 10 is formed by injection molding techniques, such as ceramic injection molding, followed by debinding (e.g., by thermal-based or chemical-based debinding techniques) and sintering. Ceramic injection molding is highly precise and repeatable, resulting in dimensions and shape of the fuel monolith 10 being tightly controlled and substantially the same (within manufacturing tolerances) between production runs, particularly the side surface 26 and the eccentricity of the body 20 of the fuel monolith 10. Also, the first end surface 22 and the second end surface 24 are manufactured flat and parallel.
Where needed, the manufactured fuel monolith 10 can be subject to post-manufacturing processing. For example, surfaces of the manufactured fuel monolith 10 can be post-manufacturing processed by, for example, grinding to final dimension, such as by dual faced grinding and lapping techniques. Also, as needed, channels 30 of the manufactured fuel monolith 10 can be post-manufacturing processed to form channels 30 or to finish process the channels 30 to final shape, size and/or configuration. Other post-manufacturing processing can be used, such as wet polishing techniques to provide a smooth surface finish, or coatings, such as Nb2C or ZrC (depending on fuel type).
Step S120 assembles a plurality of fuel monoliths 10. In exemplary embodiments, the plurality of fuel monoliths 10 are stacked end face-to-end face. The eccentric shape of the fuel monoliths 10 provides a guide for aligning the channels 30 of the stacked fuel monoliths 10. Optionally, an additional guide, such as a drill rod 480, can be inserted into one or more channels 30, typically into the parallel channels, and used to align the stacked fuel monoliths 10. Preferably, at least two drill rods 480 and up to 6 or 7 drill rods 480 (as the number of parallel channels allows) are used as additional guides. For precision in alignment, clearance of the drill rod 480 to the interior diameter of the channel 30 is as small as possible, for example, 25 microns to 75 microns of clearance.
Step S130 attaches the exhaust support plate 130 and exhaust shield assembly 150 to the assembled plurality of fuel monoliths 10 to form a fuel assembly core 110. The eccentric shape of the exhaust support plate 130 provides a guide for aligning the channels 132 of the exhaust support plate 130 and the channels 30 of the stacked fuel monoliths 10. Optionally, the additional guide, such as a drill rod, can facilitate such alignment. The exhaust shield assembly 150 is attached to the exhaust support plate 130. For example, by an end portion 156 of the conical section 152 of the exhaust shield assembly 150 fitting over the circumferential surface 142 of the exhaust support plate 130.
The exhaust support plate 130 and the truncated conical section 152 and the tubular section 154 forming the exhaust shield assembly 150 can be formed as separate pieces or formed as a unitary structure. The separate pieces can be joined by welding, such as resistance welding, or by a mechanical joint. When using resistance welding, addition of Rhenium in the alloy of the materials to be welded assists in resistive welding. Manufacturing techniques for forming the exhaust support plate 130 and the truncated conical section 152 and the tubular section 154 forming the exhaust shield assembly 150 as separate pieces include 3D wire electrical discharge machining (3D wire EDM) and EBEAM printing calibrated for tungsten production, such as the Arcam Spectra H electron beam melting system. EBEAM printing creates a roughened surface finish on the outer surface of the final part, which can be advantageous in subsequent application of the insulation layer 120. When manufactured as separate parts, the joining surfaces have tight tolerances to facilitate mating of the separate pieces. For example, 3D wire EDM manufacturing can be used with a true profile tolerance of, for example, 0.1 mm for interior holes and 0.03 mm for the exterior of the elliptical loft region. Manufacturing techniques for forming the exhaust support plate 130 and the truncated conical section 152 and the tubular section 154 forming the exhaust shield assembly 150 (or a subset of these pieces) as a unitary structure include additive manufacturing techniques. An advantage of additive manufacturing these pieces is the elimination of joints. Eliminating joints in these pieces reduces the potential for errors in manufacturing, makes the pieces faster to manufacture, and increases strength of the structure. However, unitary manufacture, particularly by additive manufacturing, affects the surface roughness of, e.g., the flow channels 132, which impacts flow 300 through the flow channels 132. Post-manufacturing processing, such as grinding or wet polishing techniques to provide a smooth surface finish, or high temperature coatings, can be used to reduce as-manufactured surface roughness of the flow channels 132 (similar to post-manufacturing processing of the channels 30).
Step S140 prepares a tensioned fuel monolith stack mandrel assembly 400. The structures and processes of preparing a tensioned fuel monolith stack mandrel assembly 400 are discussed further herein, in particular in connection with
Step S150 applies the insulation layer 120 to the tensioned fuel monolith stack mandrel assembly 400. The content and location of the insulation layer 120 can vary based on thermal requirements. For example, the most radially inward layers of insulation (as opposed to the most radially outward layers of insulation) and the insulation layer over the fuel assembly 200 at the second end 208 (as opposed to the first end 206) are exposed to the highest temperatures and are most susceptible to hydrogen corrosion. Anticipated operating conditions include and temperature of the inlet Hydrogen flow during full power thrust of approximately 300K, a temperature in the middle of the fuel assembly of approximately 1,300K during full power thrust, and a temperature of the exhaust Hydrogen flow during full power thrust of approximately 2750K. In high ISP embodiments, the temperature of the exhaust Hydrogen flow can be 3000K. Therefore, geometrical and material choices are made to provide the best resistance at these locations to the anticipated operating conditions.
As seen in
The inner insulation layer 120a is a compliant and compressive layer that is hydrogen resistive and has low thermal conductivity. In some embodiments, the inner insulation layer 120a is made from a random-orientation matting of ZrC fiber. Random-orientation matting is roll-wrapped around the tensioned fuel monolith stack mandrel assembly 400. The random-orientation matting is wrapped tightly, but it does not have to provide structural support. The primary role of inner insulation layer 120a is to provide high temperature resistance to hot Hydrogen and provide thermal shielding to the other layer(s) of insulation and to the fuel assembly outer structure 210. In exemplary embodiments, the inner insulation layer 120a is 1 mm thick but in alternate embodiments the inner insulation layer 120a is 2 mm thick or more. Fiber densities of the ZrC random-oriented matting can be 40-60%, with void spaces of 60-40%, respectively. Greater void space is generally desired to decrease the through-layer radial thermal conductivity and, therefore, increase the performance of the inner insulation layer 120a, as well as that of the overall insulation layer 120.
In alternative embodiments, the inner insulation layer 120a is made from ZrO2, SiC, carbon fiber, carbon fiber with surface conversion to ZrC or carbon fiber completely converted to ZrC using either tow strands and mandrel wrapping or using woven material and roll wrapping to form the inner layer. Chemical compatibility with hydrogen and high temperatures are the primary factors weighed when choosing an insulator material type, format (tow vs felt vs woven) and application method (mandrel wrapping vs roll wrapping).
In further alternative embodiments, the inner insulation layer 120a may be a thin tungsten spiral wrapped foil having a thickness of, for example, 25 microns to 50 microns. This tungsten layer may be used to seal hydrogen flow paths so that there is a high resistance for flowing hydrogen to escape the fuel assembly core 110.
Another example material suitable for the inner insulation layer 120a is to manufacture the inner insulation layer 120a separately and then apply it to the fuel assembly core 100. In this regard, carbon fiber can be basket weaved over a solid zirconia oxide mandrel, impregnated with phenolic and baked at 1300° C. to form a low temp C/C composite. The C/C composite is removed from the mandrel and surface converted to ZrC. Surface conversion to ZrC provides improvements to survival in the hydrogen environment at the hot end of the fuel assembly 200 (˜2700 K) and provides improvements to fuel assembly 200 performance. Thus, in some embodiments, surface conversion to ZrC may be implemented in the portion of the fuel assembly 200 toward the outlet end, and may not be implemented in the cooler, inlet end of the fuel assembly 200. The resulting composite can then be layed-up on the fuel assembly core 100 as inner insulation 120a.
The inner insulation layer 120a is typically applied dry, without a binder. This decreases the thermal conductivity of inner insulation layer 120a. The dry, inner insulation layer 120a is held in place by the subsequent layers of the insulation layer 120.
The inner insulation layer 120a may use a variety of geometrical wrapping patterns, such as helical winding patterns or basket weave helical patterns. Basket weave helical patterns are used to decrease fiber density and therefore decrease radial thermal conductivity in both the inner insulation layer 120a and the other layers of the insulation layer 120. Basket weave patterns are formed by increasing the fiber bandwidth in CNC mandrel wrapping control software beyond the actual fiber width as applied to the mandrel. By increasing this fiber bandwidth, an open weave with high porosity can be achieved. For example, a basket weave pattern can have 2 mm thick fibers oriented at 45 degrees, with an ˜2 mm space between each tow.
The inner insulation layer 120a can optionally be retained by a gripping feature, which consists of a roughened surface finish or other mechanical features, such as spiked protrusions, on the outer circumferential surface of the fuel assembly core 110. Application of the other layers of the insulation layer 120, such as the outer insulation layer 120b, compresses the inner insulation layer 120a to engage with the gripping feature. The gripping feature can be located at separate regions along the length of the fuel assembly core 110 and prevents motion of the inner insulation layer 120a relative to the fuel assembly core 110 during thermal cycling. Gripping features may also be applied to the outer circumferential surface of the exhaust support plate 130 and/or the exhaust shield assembly 150.
The outer insulation layer 120b is created by mandrel wrapping with a twin tow machine and is made using carbon fiber. In alternative embodiments, the outer insulation layer 120b is made using SiC fiber or ZrO2 fiber tows. Wrapping using twin tows (No. 56) can be advantageous relative to wrapping with a single tow since it has been observed the tension of a single fiber causes deflection in the insulated fuel core assembly 100. Twin tow winding orients the two tows 180 deg apart, which prevents this deflection.
The outer insulation layer 120b can consist of multiple layers, such as from one to twenty sublayers depending on the fiber type used for the insulator winding and the thickness of the overall insulator. In exemplary embodiments, inner sublayers (such as sublayers one to three) are applied dry, without a binder so as to decrease the thermal conductivity. The dry sublayers are held in place by the subsequent sublayers of the outer insulation layer 120b. Outer sublayers (such as the three to five most outer sublayers) are applied wet using a phenolic resin (BK 5236M Phenolic Impregnating Resin from Bakelite Synthetics, or similar). The low viscosity of this phenolic resin has desirable properties for the wet layup stage of mandrel winding. Ideal viscosity of the phenolic resin is in the range of 300-700 Cps.
The insulation layer 120, e.g., the inner insulation layer 120a and the sublayers of the outer insulation layer 120b, are applied over an axial length of the tensioned fuel monolith stack mandrel assembly 400 that is greater than the length of the fuel assembly core 100. This is done so that any variation in the tow winding, such as due to the change in direction of the winding equipment at each turnaround region, does not occur at a location coincident with the fuel assembly core 100. For example, the turnaround region can be located where the mandrel spacers of the tensioned fuel monolith stack mandrel assembly 400 are located. By having any variation in the tow winding occur axially spaced from the fuel assembly core 100, the winding of the insulation layer 120 at the fuel assembly core 100 is more uniform.
For application of the insulation layers in Step S150, an axial tension can be applied to the tensioned fuel monolith stack mandrel assembly 400. For example, pneumatic chucks can be incorporated into the winding system and attached to the axial ends of the tensioned fuel monolith stack mandrel assembly 400 e.g., via threaded mandrel end caps 440, 470, and a tension applied from the winding equipment to the tensioned fuel monolith stack mandrel assembly 400. Depending on the amount of tension already applied to the tensioned fuel monolith stack mandrel assembly 400 from internal tensioning components (as discussed herein), only a minor amount of axial tension (for example, less than 1500 Newtons (337 lbf), such as 222 Newtons (50 lbf), 445 Newtons (100 lbf) or 1245 Newtons (280 lbf)) is needed to be applied to the tensioned fuel monolith stack mandrel assembly 400 to maintain the tensioned fuel monolith stack mandrel assembly 400 straight during application of the insulation layers. Excess axial tension (for example, above 445 Newtons) can cause stretching of the internal tension components, and therefore gaps between the fuel monoliths 10 can occur. Excess axial tension also increases the overall torque on the tensioned fuel monolith stack mandrel assembly 400 due to bearing drag on the idle chuck where the axial tension is applied. If higher tensions are to be used, the idle chuck can be actively driven using a motor synchronized with the primary drive chuck.
Once the outer sublayers are impregnated with phenolic resin, the wound and impregnated tensioned fuel monolith stack mandrel assembly 400 is then cured according to the heat treatment schedule applicable to the phenolic resin. The cure process can be conducting in a controlled manner in a suitable heating system, such as a tubular heating system with insulation, which allows for even heating of the phenolic resin while the wound and impregnated tensioned fuel monolith stack mandrel assembly 400 is slowly rotated inside using the rotation axis of the mandrel winding machine. Slowly rotating the wound and impregnated tensioned fuel monolith stack mandrel assembly 400 helps maintain straightness during the phenolic resin cure cycle.
Further and/or alternative details on mandrel wound insulation is contained in U.S. patent application Ser. No. 18/118,193, the entire contents of which are incorporated herein.
In Step S160, the mandrel winding components and tensioning components are disassembled from the cured tensioned fuel monolith stack mandrel assembly 400. The structures and processes of disassembling the mandrel winding components and tensioning components are discussed further herein, in particular in connection with
Once disassembled, the insulated fuel assembly core 100 can be optional post-processed and then inserted into a fuel assembly outer structure 210. Post processing can include, for example, machining to final dimensions. Example machining processes include centerless grinding.
Step S170 inserts the insulated fuel assembly core 100 into a fuel assembly outer structure 210, such as by inserting the insulated fuel assembly core 100 into the fuel assembly outer structure 210.
Once inserted into the fuel assembly outer structure 210, other components can be attached as necessary to form the fuel assembly 200. For example, the inlet connection assembly 220 can be attached, for example, using crimp 232.
The tensioned fuel monolith stack mandrel assembly 400 extends along axis 402 from a first end 404 to second end 406 and includes (i) the fuel assembly core 100 (shown with insulation layer 120), (ii) internal tensioning components (see also
Mandrel spacers 420, 450 can be made of aluminum (such as 6061 Aluminum) or stainless steel (such as 17-4PH Stainless Steel or 304 stainless steel), or other suitable material.
The internal tensioning components are shown in
The first set of tensioning cables 490a extend from a first end at an end surface of the endmost mandrel spacer 420a to a second end at the second end face 140 of the exhaust support plate 130. Thus, the first set of tensioning cables 490a extend through the first mandrel spacers 420 in the first mandrel spacers section 430, through the fuel monoliths 10 and the exhaust support plate 130 of the fuel assembly core 100. In the exhaust support plate 130, the first set of tensioning cables 490a are located in the non-parallel channels 132 at the periphery of the exhaust support plate 130.
The first set of tensioning cables 490a are tensioned and then terminated at each of the first end and the second end so as to maintain the tension in the first set of tensioning cables 490a. Termination can be by suitable means, such as by a crimp 494 or with a termination fixture.
The second set of tensioning cables 490b extend from a first end at an end surface of the endmost mandrel spacer 420a to a second end at an end surface of endmost mandrel spacer 450a. Thus, the second set of tensioning cables 490b extend through the first mandrel spacers 420 in the first mandrel spacers section 430, through the fuel assembly core 100 (including the fuel monoliths 10 and the exhaust support plate 130 and the exhaust shield assembly 150), and through the second mandrel spacers 450 (both the second mandrel spacers 450 in the second end 106 of the fuel assembly core 100 and the second mandrel spacers section 450 in the second mandrel spacers section 460). In the exhaust support plate 130, the second set of tensioning cables 490b are located in both the parallel channels 132 and the non-parallel channels 132 radially inward from the non-parallel channels 132 in which the first set of tensioning cables 490a are located.
The second set of tensioning cables 490b are tensioned and then terminated at each of the first end and the second end so as to maintain the tension in the second set of tensioning cables 490b. Termination can be by suitable means, such as by a crimp 492 or with a termination fixture.
It should be noted that not all channels 30 of the fuel monoliths 10 and not all channels 132 of the exhaust support plate 130 contain an internal tensioning component. Rather, some channels 30, 132 are left empty in the tensioned fuel monolith stack mandrel assembly 400.
The tension cables can be any suitable cable, such as stainless-steel cable made of 316L or tungsten cables. Examples include Bare 7×49, commercial (SS or W) and Bare 1×19, commercial (SS) cables available from Carl Stahl Sava Industries, Inc., Riverdale, New Jersey.
Also illustrated are drill rods 480, which are used to align components of the fuel assembly core 100 during assembly, such as when stacking the fuel monoliths 10 and the exhaust support plate 130. While the drill rods 480 provide strength to the tensioned fuel monolith stack mandrel assembly 400 and help prevent bowing, they do not apply significant, if any, compressive forces on the tensioned fuel monolith stack mandrel assembly 400. In some embodiments, the drill rod 480 that is located in central channel 30′ of the fuel monoliths 10 can include threaded ends for application of threaded terminations that can be used to tension the drill rod 480 in channel 30′. In addition, a threaded drill rod allows the application of compressive forces on the tensioned fuel monolith stack mandrel assembly 400, e.g., by threading a termination nut.
Returning to Step S160 in method S100 and
In the alternative embodiment of the tensioned fuel monolith stack mandrel assembly 400′, the threaded mandrel end caps 440, 470 have been replaced by mandrel tensioning caps 440′, 470′ at each of the first end 404′ and the second end 406′. Also, one or more tensioning cables in an inner grouping of channels have been replaced by drill rods 480′. In exemplary embodiments, a plurality of drill rods 480′, for example, five to nine drill rods 490′, alternatively seven drill rods 490′, are used. The drill rods 480′ are close slip fit to the interior channels 30′ of the fuel element, the support plate, and the spacers of the tensioned fuel monolith stack mandrel assembly 400′. The drill rods 480′ are threaded on each end to allow for threaded nuts to be used to tension the drill rods 480′. The threaded ends of the drill rods 480′ extend past end surfaces of the mandrel tensioning caps 440′, 470′ so that the threaded nuts can be attached to threaded ends and tightened to place the fuel monolith stack mandrel assembly 400′ in tension. The use of drill rods 490′ in place of tensioning cables simplifies assembly and increases rigidity to the tensioned fuel monolith stack mandrel assembly 400′ in resistance to torsion during winding.
Subsequently, tensioning cables 490c can be added as described herein in relation to the first embodiment of the fuel monolith stack mandrel assembly 400, and as shown in
The method S200 optionally uses an alignment jig (see Step S210) to assist with placing and aligning the various components and for alignment support during the tensioning process. Placing into the alignment jig can occur any time before tensioning the tensioning cables (Step S260). After tensioning is complete in Step S250, the assembly is removed from the alignment jig (Step S270). Removing from the alignment jig can occur either before or after attaching the threaded mandrel end caps 440, 470 (Step S280).
Additional processing of the tensioned fuel monolith stack mandrel assembly 400 can occur, as needed, prior to proceeding with applying the insulation layer 120 (Step S150), such as dimensional verifications and correction as needed, such as for straightness,
Step S220 inserts one or more drill rods 480 into the fuel assembly core 100. Fuel Monoliths 10 are aligned in a stack using the interior diameters of the channels 30 and drill rods inserted into the same. If using an alignment jig or other support, it can be used to cradle the fuel assembly core 100 while inserting the one or more drill rods 480. The clearance of the drill rod to the interior diameter of the channel 30 is as small as possible, for example, 25 microns to 75 microns of clearance. The drill rods provide rotational restraint and at least two drill rods 480 are used, alternatively 6-7 drill rods 480 are used. At least one drill rod 480 is provided in the central channel 30′ and extends axially beyond each end of the fuel assembly core 100. Other of the plurality of drill rods 480 may optionally also extend axially beyond each end of the fuel assembly core 100. These axially extending drill rods 480 provide alignment for the subsequent attachment of the mandrel spacers 420, 450.
Step S230 attaches a first set of tensioning cables 490a. The first set of tensioning cables 490a are installed in a plurality of non-parallel channels 132 at the peripheral region of the exhaust support plate 130. Using the non-parallel channels 132 guides the first set of tensioning cables 490a to respective channels 30″″ in the outer ring 56 of exhaust support plate 130. The second end of each of the first set of tensioning cables 490a has a termination 494 and the first end of each of the first set of tensioning cables 490a are inserted through the channels 30 in the fuel monolith until the respective termination 494 seats against the exhaust support plate 130. The terminations 494 can be chamfered and short so that they fit in the void space between the exhaust support plate 130 and the truncated conical section 152 of the exhaust shield assembly 150. In alternative embodiments, one or more or all of the first set of tensioning cables 490a can be replaced by threaded rods and the terminations 494 can be a threaded nut.
Step S240 attaches exhaust end mandrel spacers 450 and the inlet end mandrel spacers 420. The axially extending drill rods 480 are inserted into the holes 422 in the mandrel spacers 420,450 and the mandrel spacers 420,450 are sequentially attached to build up the respective mandrel spacer sections 430,460. The number of mandrel spacers 420,450 can vary, as long as the length of the first mandrel spacer section 430 and the length of the second mandrel spacer section 460 provides a sufficient runout space for the turnaround region of the helical winding process used in the formation of the insulator layer 120. A sufficient runoff space results in the helical winding process being uniform over the entire length of the finished insulated fuel assembly 100.
The mandrel spacers can be installed in any sequence between exhaust end and inlet end, as long as the proper type of mandrel spacer is used at each end. Inlet end mandrel spacers 420 have the same basic geometry as the fuel monoliths 10 (see
At the same or separate time from attaching the mandrel spacers 420,450, the first set of tensioning cables 490a are inserted into the holes 422 in the inlet end mandrel spacers 420.
Step S250 attaches a second set of tensioning cables 490b. The second set of tensioning cables 490b are installed from the distal end of one of the mandrel sections 430,460 and are threaded through holes 422,452 in the respective mandrel spacers 420, 450 and through the correspondingly aligned channels in the exhaust support plate 130 and the fuel monoliths 10. Typically, the second set of tensioning cables 490b are installed starting from the exhaust end by inserting a first end of each tensioning cable 490b into a respective hole 452 in the exhaust end mandrel spacers 450. The holes 422,452 in the respective mandrel spacers 420, 450 are selected so that the second set of tensioning cables 490b extend through holes 30 in the intermediate ring 54 of the fuel monoliths 10. The second end of each of the second set of tensioning cables 490b has a termination 492 and the first end of each of the second set of tensioning cables 490b are inserted until the respective termination 492 seats against the end face of the respective end mandrel spacers 420,450 (depending on which end from which the insertion begins). In alternative embodiments, one or more or all of the second set of tensioning cables 490b can be replaced by threaded rods and the terminations 492 can be a threaded nut.
At the same time as or separate time from attaching the second set of tensioning cables 490b, the second set of tensioning cables 490a are inserted into the holes 422 in the inlet end mandrel spacers 420.
The second set of tensioning cables 490b can be the same tensioning cables or different tensioning cables from the first set of tensioning cable 490a.
In example embodiments, there are 18 tensioning cables 490a in the first set of tensioning cables 490a and 6 tensioning cables 490b in the second set of tensioning cables 490b. Other arrangements can be used, such as a plurality of inner threaded drill rods and a plurality of outer tensioned cables, e.g., seven inner threaded drill rods and four to eight outer tensioned cables.
Step S260 tensions the tensioning cables 490a, 490b. Cable tensioning is done to balance the forces on the fuel monolith stack mandrel assembly 400. For example, one or two pairs of tensioning cables, i.e., two tensioning cables or four tensioning cables, in the same set of tensioning cables, i.e., the first set of tensioning cables 490a or the second set of tensioning cables 490b, can be simultaneously tensioned to balance out any adverse moments inside the fuel monolith stack mandrel assembly 400. Such adverse moments would otherwise tend to cause the fuel monolith stack mandrel assembly 400 to bend. When tensioning the pairs of tensioning cables, opposing tensioning cables are used.
The tensioning sequence begins with the center grouping of second set of tensioning cables 490b. It should be noted that the first set of tensioning cables 490a are more easily tensioned from the inlet side because of the arrangement of structures in the exhaust end, such as the exhaust end mandrel spacers 450 and the exhaust shield assembly 150. While the second set of tensioning cables 490b can be tensioned from either end. For convenience, the assembly sequence and insertion of the tensioning cables 490a,490b can result in both the first set of tensioning cables 490a and the second set of tensioning cables 490b being tensioned from the same end, such as at the first end 404, which corresponds to the first end 104 (or inlet end) of the insulated fuel assembly core 100.
Once each tensioning cable has been tensioned to the final tension, the end is terminated. Termination can be by suitable means, such as by a crimp 492 or with a termination fixture.
The tensioning the second set of tensioning cables 490b, the tensioning sequence continues with tensioning of the first set of tensioning cables 490a, which proceeds in similar fashion to that of tensioning the second set of tensioning cables 490b.
In one aspect, a twin bore hydraulic tensioner system can be used to tension the fuel monolith stack mandrel assembly.
In some embodiments, an end plate is positioned over the terminus end of each mandrel spacer section 430, 460, which distributes the forces associated with tensioning the tension cables 460a,490b. In exemplary embodiments, the force in each tensioning cable 460a,490b is about 85 N/M to about 450 N/m, alternatively about 225 N/m (20 lbf to 100 lbf, alternatively 50 lbf).
In optional embodiments, a stack of small Bellville washers may be used between the end plate and the termination. This addition of high force springs can make the overall tensioned assembly more resilient to adverse deflection when the assembly process is completing attachment of mandrel spacers 420
In other optional embodiments, a high tensile monofilament plastic wire replaces one or more or all of the metal tensioning cables. High tensile monofilament plastic wire maintains tension down the cable better than metal tensioning cables. When used, tension may be applied to the high tensile monofilament plastic wire until it yields in elastic or plastic deformation, and then the termination can be applied.
Although described above in the sequence of Steps S220 to S250, in that order, other orders of Steps S220 to S250 can be used. For example, some or all of the mandrel spacers 420,450 can be placed prior to attaching the first set of tensioning cables 490a by, for example, placing the mandrel spacers 420,450 on the drill rod 480. Also for example, the second set of tensioning cables 490b can be attached prior to completing the attachment of all the mandrel spacers 420,450 by, for example, attaching the second set of tensioning cables 490b after attaching the mandrel spacers 420 of the first mandrel spacer section 430.
Other variations can also be used, as long as the sequence results in an assembly ready for tensioning in Step S260 with (a) a first termination 494 of each of the first set of tensioning cables 490a is adjacent the second end face 140 of the exhaust support plate 130 and a second end each of the first set of tensioning cables 490a projects from a first set of holes 422 in the most distal mandrel spacer 420 at the other end of the assembly, e.g., the first end 404, and in a position to be able to be tensioned and (b) a first termination 492 of each of the second set of tensioning cables 490b is adjacent the distal end of the most distal mandrel spacer 450 on the second end 406 and a second end each of the second set of tensioning cables 490b projects from a second set of holes 422 in the most distal mandrel spacer 420 at the other end of the assembly, e.g., the first end 404, and in a position to be able to be tensioned
Step S280 attaches the threaded mandrel end caps 440,470 in preparation for application of mandrel wound insulation layer 120 (Step S150). Threaded mandrel end caps 440,470 can also be attached earlier in the method S200, once access to the end on which that threaded mandrel end cap is attached is no longer needed.
An interface structure 1125, which may or may not include supplemental radial restraint, is radially outward of the active core region 1110 and a reflector 1135 is radially outward of the interface structure 1125. A first surface of the interface structure 1125 is conformal to the outer surface of the active core region 1110 and a second surface of the interface structure 1125 is conformal to an inner surface of the reflector 1135. The inner surface of the reflector 1135 is oriented toward the active core region 1110, and the interface structure 1125 functions to mate the geometry of the outer surface of the active core region 1110 to the geometry of the inner surface of the reflector 1135, thus allowing various geometries and arrangements for the active core region 1110, such as cylindrical or polygonal
Note how the seals 230 contact the inner surface of the opening 1118 and provide freedom of motion for change in axial dimension due to thermal expansion.
The nuclear fission reactor structure can further comprise a vessel 1140.
As shown in
Embodiments of the vessel 1140 are formed from machined forgings and generally use high strength aluminum or titanium alloys due to weight considerations. The vessel 1140 can be multiple components that are then assembled together, for example, with fasteners. However, in other embodiments, the vessel 1140 can be one contiguous component or a welded together assemblage.
Additional disclosure related to the nuclear fission reactor structure and its components can be found in U.S. patent application Ser. No. 16/999,244, the entire contents of which are incorporated by reference.
The disclosure is also directed to a nuclear thermal propulsion engine that includes the nuclear fission reactor structure 1100 within a vessel 1140 within a reactor section 1170. The nuclear thermal propulsion engine further includes a shielding section 1175, a turbo machinery section 1180, and a nozzle section 1185 attached to or supported by the vessel 1140, for example, as consistent with that shown in
It is contemplated that various supporting and ancillary equipment can be incorporated into the disclosed nuclear fission reactor structure and nuclear thermal propulsion engine. For example, at least one of a moderator (such as a zirconium hydride, beryllium, beryllium oxide, and graphite), a control rod for launch safety, a neutron source to assist with start-up, and a scientific instrument (such as a temperature sensor or radiation detector) can be incorporated into the nuclear propulsion fission reactor structure.
The disclosed arrangements pertain to any configuration in which a heat generating source including a fissionable nuclear fuel composition, is incorporated into a fuel bundle. Although generally described herein in connection with a gas-cooled nuclear thermal propulsion reactors (NTP reactors), the structures and methods disclosed herein can also be applicable to other fission reactor systems.
Nuclear propulsion fission reactor structure disclosed herein can be used in suitable applications including, but not limited to, non-terrestrial power applications, space power, space propulsion, and naval applications, including submersibles.
While reference has been made to specific embodiments, it is apparent that other embodiments and variations can be devised by others skilled in the art without departing from their spirit and scope. The appended claims are intended to be construed to include all such embodiments and equivalent variations.
This application is based on and claims priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 63/459,450, filed Apr. 14, 2023, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63459450 | Apr 2023 | US |
