Fission reactor with segmented cladding bodies having cladding arms with involute curve shape

Abstract

To provide alternative designs to increase design and manufacturing flexibility and reliability while meeting neutronics and thermal performance of fuel elements.SOLUTION: A plurality of layers form a nuclear fission reactor structure. Each layer has an inner segment body, an intermediate segment body, and an outer segment body. The layers include a plurality of cladding arms having involute curve shapes that spirally radiate outward from a radially inner end to a radially outer end. Chambers in the involute curve shaped cladding arm contain fuel compositions (and / or other materials such as moderators and poisons). The design of the involute curve shaped cladding arms and the composition of the materials conform to neutronic and thermal management requirements for the nuclear fission reactor, and are of sufficiently common design and / or have sufficiently few variations to reduce manufacturing complexity and manufacturing variability.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present disclosure generally relates to structures related to nuclear fission reactors and nuclear fission reactor spaces within nuclear fission reactors. In particular, heat-producing structures, such as fuel elements containing fissionable nuclear fuel compositions, are covered by a containment structure, such as a cladding. The heat-producing structures have an involute shape, and a plurality of such shapes are assembled to form a cylindrical reactor layer. Although the involute shape varies based on the radial position of the cylindrical reactor layer, uniformity of the involute shape minimizes the number of unique shapes of fuel elements (or other features, such as moderators and / or poisons) that are input to each heat-producing structure to achieve a desired reactor performance profile. The involute shape of the heat-producing structures allows for uniform thickness of the fuel elements and cladding, and allows for uniform coolant spaces between individual heat-producing structures. The present disclosure is particularly adapted for manufacturing at least the involute shape cladding structure of the heat-producing structures by an additive manufacturing process. The disclosed nuclear fission reactor is suitable for use in a variety of applications, including powering small vessels (such as spacecraft and satellites), nuclear thermal propulsion (NTP), and isotope production. [Background technology]

[0002] 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. Applicants expressly reserve the right to demonstrate that such structures and / or methods are not qualified as prior art against the present invention.

[0003] In designing new heat generating capabilities and structures for nuclear fission reactors, sufficient cooling of each fuel element throughout the nuclear fission reactor space is often a limiting design factor. In previous reactor designs, uranium fuel was encapsulated within rolled metal plates, for example, by a cold rolling process. Referring to the schematic diagram of FIG. 1, a layer 1 arrangement including a fuel composition layer 2 between two cladding layers (first cladding layer 4a and second cladding layer 4b) is fed into the nip of rollers 6 of a cold rolling machine. The cold rolling process reduces the thickness of the layer 1 arrangement from an initial thickness to a final thickness in one or more cold rolling steps. In this process, various layers of material (in the illustrated example, a fuel composition layer 2 and two cladding layers 4a and 4b) are metallurgically bonded into a single layer structure 8 (shown in cross section in FIG. 1 ) in which the cladding layers 4a and 4b provide encapsulation layers on either side of the fuel composition layer 2 (shown in cross section in FIG. 1 by dashed lines at the interfaces between the fuel composition layer 2 and the two cladding layers 4a and 4b). Whether formed in strips or plates, the unitary layer structure 8 can be further processed using conventional metal forming techniques. In one embodiment, such a plate-like unitary layer structure 8 is bent into an involute shape and incorporated into the core assembly (shown in partial cross section in FIG. 1 ) of the High Flux Isotope Reactor (HFIR) 10, a nuclear research reactor at Oak Ridge National Laboratory (ORNL). In the HFIR design, the involute shape 12 provides a uniform thickness uranium / clad plate disposed between the homogenized coolant spaces.

[0004] The single layer structure and involute shape in the HFIR have some drawbacks that reduce design flexibility. For example, to comply with neutronic and thermal management requirements, the composition of the fuel composition layer 2 is spatially non-uniform with respect to the position in the plate or band, and is adjusted based on the position in the core assembly. However, at the same time, the composition and layer distribution of the single layer structure are fixed during the process, e.g., cold rolling, of the fuel composition layer 2 and the two cladding layers 4a and 4b. Therefore, the structure of each position of the HFIR must have a uniquely constructed single layer structure, which is not compatible with other formats. Summary of the Invention

[0005] In view of the above, it would be more advantageous to have more flexibility in varying the shape, position, and composition of the clad fuel elements in the core assembly. Furthermore, it would be advantageous to meet the neutronics and thermal management requirements in nuclear fission reactor designs, as it would allow for less geometric and compositional variation of the clad fuel elements while also reducing the complexity of component manufacturing and assembly of the nuclear fission reactor. Furthermore, a modular, repeatable, and sufficiently large sized design would allow for the application of manufacturing methods such as additive manufacturing.

[0006] The neutronics and thermal performance of fuel elements in a nuclear fission reactor core design is affected, among other things, by the structure of the fuel elements, such as the shape, size, and relative position, the cladding surrounding the fuel elements, and the coolant channels, and by the thermal transport properties of the fuel elements, cladding, and coolant. As noted above, alternative designs are needed to improve design and manufacturing flexibility and reliability while still meeting the neutronics and thermal performance of the fuel elements.

[0007] In one example of an alternative design (see FIG. 2), a series of radially concentric layers of fuel rings 32 (a 60 degree portion 30 of the layer is shown in FIG. 2) are assembled into a cylindrical nuclear fission reactor space. In each fuel ring 32, the fuel ring edge 34a and the internal webbing 34b define a volume containing a fuel composition 36 that acts as a cladding and has a bowtie shape. The edge 34a and the webbing 34b may also define a shape of a coolant channel 38 that has a circular shape in cross section in FIG. 2. The volume containing the fuel composition 36 has the same cross-sectional area in each of the fuel rings 32. Similarly, the coolant channels 38 in each of the fuel rings 32 have the same cross-sectional area. For neutronics and thermal management purposes, each fuel ring 32 requires a different fuel composition (for a constant fuel cross-sectional area) or a different fuel shape (for a constant fuel composition). For example, a fuel composition sized to fit in ring 32b cannot be used in ring 32f and would not work well from a neutronics and thermal management standpoint. Thus, in a further example, the ten ring design shown in Figure 2 would require several different fuels with one or more varying fuel compositions and fuel geometries.

[0008] Another example of an alternative design (shown in FIGS. 3A and 3B ) assembles a layer (a 15° portion 50 of the layer is shown in FIGS. 3A and 3B ) that includes pockets 52 for fuel elements 54 distributed concentrically and radially within the portion 50. A plurality of portions 50 can be assembled into a cylindrical nuclear fission reactor space. Compared to the example of FIG. 2 , the example of FIG. 3A and 3B changes the shape of the fuel elements 54 from a bowtie shape to a more triangular or rectangular shape. Elliptical coolant holes 56 are disposed in a cladding web structure 58 between each pocket 52. As with the example of FIG. 2 , each differently sized and positioned fuel element 54 would require a different fuel composition or different fuel shape, and overall, the example of FIG. 3A and 3B would require a sufficiently large number of different fuels with one or more different fuel compositions and fuel shapes (although the change from a bowtie shape to a more triangular or rectangular shape simplifies the manufacture of such elements as well as the manufacture of such elements with various fuel compositions). However, neutronics and thermal performance analysis for the design shown in FIGS. 3A and 3B demonstrated that of the various different shapes and positions for the fuel elements, the only fuel element shape that could be adequately cooled was the radially outermost thin-shaped fuel element 54a, i.e., the fuel element with the largest length-to-width ratio.

[0009] The above two examples illustrate the challenges in designing heat generating functions and structures for nuclear fission reactors where the structures meet neutronic and thermal performance criteria, are of sufficiently common design and / or have sufficiently low variability to reduce manufacturing complexity and manufacturing variability (and thereby reduce the potential for manufacturing defects).

[0010] In general, the present disclosure relates to a nuclear fission reactor structure in which fuel elements containing a fissile nuclear fuel composition are arranged along an axis of an involute shaped encapsulating cladding structure. A plurality of such involute shaped cladding structures are arranged to form a ring, and a plurality of concentric rings are arranged to form a layer of the nuclear fission reactor structure. The layers themselves are assembled to form the nuclear fission reactor structure. In an exemplary embodiment, the nuclear fission reactor structure is an active core region of a nuclear fission reactor.

[0011] The embodiments disclosed herein also include a nuclear fission reactor structure including a plurality of layers, each layer of the plurality of layers including an inner segment body including an inner opening extending axially from a first side of the inner segment body to a second side of the inner segment body, a middle segment body radially outward of the inner segment body, and an outer segment body radially outward of the middle segment body. A first interior interface separates the inner segment body and the middle segment body, and a second interior interface separates the middle segment body and the outer segment body. In a cross-sectional plan view in a plane perpendicular to the axially extending inner opening, the inner segment body includes a plurality of inner cladding arms having a first involute curve shape that radiates outward in a spiral manner from a first radially inner end adjacent the inner opening to a first radially outer end of the first interior interface. The intermediate segment body includes a plurality of intermediate cladding arms having a second involute curve shape radiating helically outward from a second radially inner end adjacent the first internal contact surface to a second radially outer end of the second internal contact surface, and the outer segment body includes a plurality of outer cladding arms having a third involute curve shape radiating helically outward from a third radially inner end adjacent the second internal contact surface to a third radially outer end of the radially outer surface of the outer segment body.

[0012] Embodiments disclosed herein also include a nuclear fission reactor comprising a plurality of layers as disclosed herein, the plurality of layers assembled into a nuclear fission reactor structure having a first end, a second end, and an exterior surface connecting the first end to the second end, a radial reflector disposed about the exterior surface of the active core structure, a pressure vessel, and a coolant system in fluid communication with the active core structure through an opening in the pressure vessel.

[0013] The embodiments disclosed herein also include a method of manufacturing the nuclear fission reactor structure disclosed herein, the method including manufacturing an inner segment body, a mid segment body segment, and an outer segment body segment, where each of the plurality of inner cladding arms, the plurality of intermediate cladding arms, and the plurality of outer cladding arms includes a plurality of chambers, assembling the inner segment body, the mid segment body segment, and the outer segment body segment into a layer, where the segment bodies are assembled by one of welding and bonding, disposing one of a fissile fuel composition and a moderator in the plurality of chambers to form a fuel-loaded layer, and assembling the plurality of fuel-loaded layers into the nuclear fission reactor structure.

[0014] In an alternative embodiment of the method of manufacturing a nuclear fission reactor structure disclosed herein, the method includes manufacturing a layer including an inner segment body, an intermediate segment body, and an outer segment body as a unitary structure, wherein each of the plurality of inner cladding arms, the plurality of intermediate cladding arms, and the plurality of outer cladding arms includes a plurality of chambers, disposing one of a fissile fuel composition and a moderator in the plurality of chambers to form a fuel loading layer, and assembling the plurality of fuel loading layers into the nuclear fission reactor structure.

[0015] Additionally, the disclosed reactors and cores, while having complex mechanical geometries, can be manufactured monolithically and repeatably layer by layer using additive manufacturing techniques, such as 3D printing of elemental metals or metal alloys, making the structures and features disclosed herein more readily manufacturable.

[0016] 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 is understood that the illustrated embodiments are not limited to the precise arrangements and instrumentalities. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram illustrating the structures and processes associated with the formation of cladding fuel structures in a prior art High Flux Isotope Reactor (HFIR); [Diagram 2] FIG. 1 is a schematic diagram of a 60 degree section of a layer of a design in which the assembled layer includes a series of radially concentric fuel rings in a first embodiment; [Figure 3A-3B] FIG. 3A is a schematic diagram of a 15 degree section of a layer of a design including pockets for concentrically and radially distributed fuel elements in a second embodiment, and FIG. 3B is a schematic diagram of the same section with fuel elements partially inserted in the pockets. [Figure 4] FIG. 13 is a partially exploded perspective schematic view of a simplified example of a nuclear fission reactor in which the active core region is assembled from layers of a third embodiment having a series of concentric segment bodies each including a cladding arm having a first involute curve shape; [Diagram 5] FIG. 1 is a top view diagrammatically illustrating a series of concentric segment bodies, each having an involute curve shape, assembled in layers; [Figure 6A-6C] FIG. 6A is a schematic top view of an embodiment of an inner segment body; FIG. 6B is an enlarged partial view of the inner segment body shown in FIG. 6A; and FIG. 6C is a diagram showing example surface features of the ends of the cladding arms. [Figure 7A-7B]FIG. 7A is a top view of a schematic representation of an embodiment of an intermediate segment body, and a partially enlarged view of the intermediate segment body shown in FIG. [Figure 8A-8B] FIG. 8A is a schematic top view of an embodiment of an outer segment body, and FIG. 8B is an enlarged partial view of the outer segment body shown in FIG. 8A. [Figure 9] FIG. 13 illustrates an example where the involute curved surface of the cladding arm is continuous across the inner segment body, the middle segment body, and the outer segment body. [Figure 10] FIG. 1 illustrates an example of layers in which each of the inner cladding arms can include six chambers, and each of the intermediate cladding arms and the outer cladding arms can include two chambers. [Figure 11] FIG. 1 is a schematic diagram of an example of a cladding arm; [Figure 12] FIG. 5 illustrates an embodiment of a layer including an inner body segment 502, a middle segment body 504, and an outer segment body, each including multiple chambers and multiple fuel composition bodies positioned on the respective segment bodies. [Figure 13A-13B] FIG. 13A shows the results of a thermal analysis study of an involute curve shaped cladding arm design disclosed herein, and FIG. 13B shows a close-up of a portion of the inner segment cladding arm shown in FIG. 13A. [Figure 14A-14D] FIG. 14A is a flow diagram showing the steps of assembling layers from various portions of a segment body; FIG. 14B is a flow diagram showing the steps of assembling layers from various portions of a segment body; FIG. 14C is a flow diagram showing the steps of fuel composition and / or moderator composition and interfering material loading into the layers; and FIG. 14D is a flow diagram showing the steps of assembling multiple layers into a nuclear fission reactor structure. [Figure 15] FIG. 1 is a side cross-sectional view of an embodiment of a nuclear fission reactor including multiple layers assembled into a nuclear fission reactor structure; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] For clarity, in some instances, only some of the named features in the figures are labeled with reference numbers.

[0019] 4 is a schematic, partially exploded view of a simplified exemplary embodiment of a nuclear fission reactor 100. The nuclear fission reactor 100 includes a plurality of layers 102 assembled into a nuclear fission reactor core structure 104 having a first end surface 106, a second end surface 108, and an outer surface 110 connecting the first end surface 106 and the second end surface 108 disposed along a longitudinal axis 112 of the active core structure 104. The layers 102 are defined by an inner segment body, a middle segment body, an outer segment body, a first internal interface surface, and a second internal interface surface, as described further herein. The nuclear fission reactor 100 also includes a radial reflector 114 disposed about the outer surface 110 of the active core structure 104. Although the active core structure 104 is shown as a cylindrical structure, any suitable geometric shape may be utilized so long as the active core structure exhibits the desired neutronics and thermal management characteristics. In an exemplary embodiment, the active core structure 104 is configured to have a diameter (D RX ) versus the length of the active core region (L RX ) is approximately 1 (i.e., L RX / D RX = 1 ± 0.05). In general, the radial reflectors 114 reduce neutron leakage in the nuclear fission reactor 100 by scattering (or reflecting) neutrons that would otherwise escape back into the core. This reduces the effective design multiplication factor (k eff ) and reduce the amount of fuel required to maintain criticality. A pressure vessel and a coolant system (shown diagrammatically as pressure vessel 120 and coolant system 130) are also provided that are in fluid communication with the active core structure through openings in the pressure vessel.

[0020] Any suitable radial reflector, pressure vessel, and coolant system may be incorporated into the nuclear fission reactor 100. For example, the coolant system may be liquid-based or gas-based. If the coolant system is gas-based, the layers 102 may be assembled into the active core structure 104 by welding adjacent layers 102 together at their outer periphery, i.e., contact surfaces corresponding to the outer surfaces of adjacent layers 102, and at their inner periphery to provide an airtight open cylindrical shape having an annulus shape in cross section, using welded joints. In a gas-based coolant system, only the outermost surface needs to be airtight since gas is permitted to circulate throughout the active core region. If the coolant system is liquid-based, the opposing surfaces of adjacent layers 102 are joined together such that the coolant channels are separate from each other while each provides a continuous path of coolant across the active core structure from a first end to a second end.

[0021] Alignment aids can be used to help align features, such as coolant channels, in one layer 102 with features in an adjacent layer 102. Clocking techniques can be applied that use protruding registry features on a surface of one layer 102 that fit or are inserted, for example, by inserting or being received, into receiving spaces on the adjacent surface of the adjacent layer 102. Other registry features can also be used, including pins, notches, molded protrusions, and the like. Additionally, other alignment aids, such as alignment channels or scribe marks, can also be used. Alignment aids can also be placed on one or more of a variety of suitable surfaces, including the adjacent inner surface and the continuous outer surface 110.

[0022] The disclosed nuclear fission reactor structure comprises a plurality of layers. Each layer includes a series of concentrically arranged segment bodies. Each segment body includes a cladding arm having an involute curve shape. FIG. 5 is a top view that diagrammatically illustrates a series of concentric segment bodies 210, 240, 270. Each of them includes a cladding arm having a first involute curve shape assembled in a layer 200. In an exemplary embodiment, the nuclear fission reactor structure comprises an inner segment body 210, a middle segment body 240, and an outer segment body 270. The middle segment body 240 is radially outward of the inner segment body 210, and the outer segment body 270 is radially outward of the middle segment body 240. An interface separates one segment body from a radially adjacent consecutive segment body. For example, a first interior contact surface 212 separates the inner segment body 210 and the mid-segment body 240 , and a second interior contact surface 242 separates the mid-segment body 240 and the outer segment body 270 .

[0023] The nuclear fission reactor structure includes an inner opening that extends axially from a first axial end of the nuclear fission reactor structure to a second axial end of the nuclear fission reactor structure (typically corresponding to a longitudinal axis of the nuclear fission reactor structure). The inner opening may function as a coolant channel, but may also function (in combination with or separate from the coolant channel) to accommodate reactor controls, control rods, sensors, or radioisotope production equipment. Each layer has a corresponding inner opening that defines a portion of the inner opening when multiple layers are assembled into the nuclear fission reactor structure.

[0024] FIG. 5 illustrates an embodiment of a layer 200 in a plane perpendicular to the axis of an axially extending inner opening 202 in a top view for the layer and in a cross-sectional plan view for an assembled nuclear fission reactor. The layer 200 includes an inner segment body 210 including an inner opening 202 that extends axially from a first side 204 of the layer 200 to a second side 206 of the layer 200. The layer 200 also includes a middle segment body 240 that is radially outward of the inner segment body 210 and an outer segment body 270 that is radially outward of the middle segment body 240. The concentrically arranged segment bodies 210, 240, 270 are joined together to form the layer 200 at a contact surface. The segment bodies can be joined to form the contact surface by any suitable means. In some embodiments, the segment bodies can be joined to form the contact surface by welding. In other embodiments, the segment bodies can be joined to form the contact surface by a compression fitting. In either case, a first interior contact surface 212 separates the inner segment body 210 and the mid-segment body 240 , and a second interior contact surface 242 separates the mid-segment body 240 and the outer segment body 270 .

[0025] FIG. 6A illustrates an embodiment of the inner segment body 210 in a top view for the inner segment body 210 and in a cross-sectional plan view for an assembled nuclear fission reactor structure, in each case in a plane perpendicular to the axis of the axially extending internal opening 202. FIG. 6B illustrates an enlarged view of a portion P1 of the inner segment body 210 illustrated in FIG. 6A. The inner segment body 210 includes a plurality of inner cladding arms 214 having a first involute curve shape that radiates outward in a spiral manner from a first radially inner end 216 adjacent the internal opening 202 to a first radially outer end 218 of an outer edge 220 that forms or is part of the first internal contact surface 212 in the assembled layer 200. The plurality of inner cladding arms 214 include a plurality of chambers 222. The plurality of chambers 222 are distributed along the length of the inner cladding arms 214. In each cladding arm 214, each chamber 222 is contained within a web 224 of material forming the inner segment body 210, such that each chamber 222 is surrounded by the web 224, with a first chamber 222a separated from an adjacent chamber 222b by a portion of the web 224. As described herein, the chamber 214 contains a fissile fuel composition (or other composition, such as moderator and interfering material), and the web 224 serves as a cladding for the fissile fuel composition or other composition.

[0026] One or more coolant openings 230 are disposed between the chambers 222 of one cladding arm 214 and the chambers 222 of the adjacent inner cladding arm 214 (e.g., chamber 222c of one inner cladding arm 214a and chamber 222d of the adjacent cladding arm 214b (see FIG. 6B )). The coolant openings 230 extend through the inner cladding arm 214 in a thickness direction of the inner segment body 210 from a first side 204' of the inner segment body 210 to a second side 206' of the inner segment body 210.

[0027] The coolant openings 230 can be in a variety of forms. For example, if the web 224 of the inner segment body 210 is a unitary body, the coolant openings 230 are one or more passages, channels, or other openings that can be formed in the web during initial web manufacture, such as during a layer-by-layer deposition process of an additive manufacturing process, or can be formed in the web after web manufacture by a material removal process such as drilling, milling, plunge milling, or using an electrical discharge machining (EDM) process. In another example, where each cladding arm 214 is formed as a unitary body and multiple cladding arms 214 are joined to form the inner segment body 210, the coolant openings 230 are passages or other openings formed by features at an edge of the inner cladding arm 214, i.e., an edge bounded by a surface of the inner cladding arm 214 forming a first side 204' of the inner segment body 210, a surface of the inner cladding arm 214 forming a second side 206' of the inner segment body 210, a surface of a first radially inner end 216 of the inner cladding arm 214, and a surface of a first radially outer end 218 of the inner cladding arm 214. In this regard, the edge of the cladding arm 214 may include grooves, ribs, protrusions, or other surface features that form one or more passages, channels, or other openings when contacted by an edge of an adjacent cladding arm 214.

[0028] In some embodiments, the surface features are discreet areas located along the perimeter of the edge. In other embodiments, the surface features extend continuously or discontinuously along at least one opposing side from a first end toward a first side of the inner segment body to a second end toward a second side of the inner segment body. Combinations of different surface features can also be implemented. Furthermore, the surface features may be present on only one edge of the cladding arm or may be located on both edges of the cladding arm. In one example, the surface features are protrusions. Non-limiting examples of protrusions include features that have in common with bumps, knobs, or mesa-like features, including both regular and irregular shapes.

[0029] The surface feature has an upper surface that is distal from at least one opposing side from which the projection protrudes. When assembled to a segment body with an adjacent cladding arm, the upper surface of the projection contacts the opposing side of the adjacent cladding arm, and the height or projection distance of the projection provides a stand-off separation between the two cladding arms. This stand-off separation forms a channel between the two cladding arms. If present, in some embodiments, such a surface feature may be offset along the radially extending length of the cladding arm 214 such that the location of the surface feature does not coincide with the portion of the web 224 that separates the first chamber 222a from the adjacent chamber 222b. A combination of different coolant openings may also be implemented. As an example, FIG. 6C shows a surface feature (in this case, a rib 234) on an edge of a cladding arm (in this case, an example of an inner cladding arm 214). However, surface features may be present on edge surfaces and on one or more of the inner cladding arm 214 , the intermediate cladding arm 244 , and / or the outer cladding arm 272 as well.

[0030] In some embodiments, it is preferred that the inner segment body 210 is formed as a unitary body to avoid welds or other structures on the surface that form the inner diameter of the opening 202 that would otherwise be present from joining individual cladding arms 214 or groups of cladding arms 214.

[0031] To facilitate visualization of the involute curved shape of the inner cladding arm 214, an embodiment of the inner cladding arm 214 is shown diagrammatically in FIG. 6A. In the illustrated embodiment, the two curving sides 232a, 232b of the involute curved shape of the inner cladding arm 214 are located on a line connecting the midpoints of the webs 224 located between the chambers 222 in one cladding arm 214 and the chambers 222 in the adjacent cladding arm 214. The involute curved shape itself may be constant in width (i.e., the width is the distance between the two opposing curving sides 232a, 232b of the involute curved shape of the inner cladding arm 214) as a function of position along the axis of the involute curved shape that extends from the midpoint of the first radially inner end 216 to the midpoint of the first radially outer end 218. Alternatively, the involute curve shape may vary in width as a function of position along an axis of the involute curve shape that extends from the midpoint of the first radially inner end 216 to the midpoint of the first radially outer end 218. For example, the involute curve shape may continue to increase in width or decrease in width as a function of position along an axis of the involute curve shape that extends from the midpoint of the first radially inner end 216 to the midpoint of the first radially outer end 218.

[0032] Figure 7A illustrates an embodiment of the middle segment body 240 in a top view for the middle segment body 240 and in a cross-sectional plan view for the assembled nuclear fission reactor structure, in each case in a plane perpendicular to the axis of the axially extending internal opening 202. Figure 7B illustrates an enlarged view of portion P2 of the middle segment body 240 shown in Figure 7A. In Figure 7A, the middle segment body 240 is shown in the context of the inner segment body 210 and the outer segment body 270 that form the layer 200.

[0033] The intermediate segment body 240 includes an inner cladding arm 244 having a second involute curve shape that radiates outward in a spiral manner from a second radially inner end 246 adjacent an inner opening 248 that forms or is part of the first inner contact surface 212 in the assembled layer 200 to a second radially outer end 250 at an outer edge 256 that forms or is part of the second inner contact surface 242 in the assembled layer 200. The multiple intermediate cladding arms 244 include at least one chamber 252, or alternatively multiple chambers 252a, 252b (see also, e.g., FIGS. 9 and 10). In FIG. 7B, the chambers 252 are shown in only two intermediate cladding arms 244, but additional intermediate cladding arms 244, or alternatively all intermediate cladding arms 244, may include one or more chambers 252. The chamber 252 extends along the length of the intermediate cladding arm 244, or, if multiple chambers are included, the chambers 252a, 252b are distributed along the length of the intermediate cladding arm 244. The chambers 252 (or, if multiple chambers are included, the chambers 252a, 252b) are contained within a web 254 of material forming the intermediate segment body 240, such that an individual chamber 252 in each intermediate cladding arm 244 is enclosed within the web 254. Furthermore, if multiple chambers 252 are included, a first chamber 252a is separated from an adjacent chamber 252b by a portion of the web 254 (see also Figures 9 and 10). As described herein, the chambers 252 may include a fissile fuel composition (or other compositions, such as moderators and interfering materials), and the web 254 serves as a cladding for the fissile fuel composition or other compositions.

[0034] Similar to the inner segment body 210, the middle segment body 240 can include one or more coolant openings 258 that can be located between a chamber 252 or chambers 252a, 252b in one middle cladding arm 244 and a chamber or chambers 252a, 252b in an adjacent middle cladding arm 244. The coolant openings 258 extend through the middle cladding arm 244 in the thickness direction of the middle segment body 240 from a first side 204'' of the middle segment body 240 to a second side 206'' of the middle segment body 240.

[0035] Also, like the inner segment body 210, the coolant openings 258 associated with the middle segment body 240 can be of various forms (although the coolant openings 258 associated with the middle segment body 240 can be the same as or different from the coolant openings 230 in the inner segment body 210). For example, if the web 254 of the middle segment body 240 is a unitary body, the coolant openings are one or more passages, channels, or other openings that can be formed in the web during initial web manufacture, e.g., during a layer-by-layer deposition process of an additive manufacturing process, or can be formed in the web after web manufacture by a material removal process such as drilling, milling, plunge milling, or using an electrical discharge machining (EDM) process. In another example, where each intermediate cladding arm 244 is formed as a unitary body and multiple intermediate cladding arms 244 are joined to form the mid-segment body 240, the coolant openings 258 may be passages or other openings formed by surface features at an edge of the intermediate cladding arm 244, i.e., an edge bounded by a surface of the intermediate cladding arm 244 forming a first side 204'' of the mid-segment body 240, a surface of the intermediate cladding arm 244 forming a second side 206'' of the mid-segment body 240, a surface of a second radially inner end 246 of the intermediate cladding arm 244, and a second radially outer end 250 of the intermediate cladding arm 244. In this regard, the edge of the cladding arm 244 may include grooves, ribs, or other surface features that form one or more passages, channels, or other openings when contacted by an edge of an adjacent intermediate cladding arm 244. In this regard, the edge of the intermediate cladding arm 244 may include any of the surface features described and / or illustrated herein with respect to the inner cladding arm 214 and FIGURE 6C. If present, in some embodiments, such surface features may be offset along the radially extending length of the intermediate cladding arm 244 such that the location of the surface features does not coincide with a portion of the web 254 that separates the first chamber 252a from the adjacent chamber 252b.A combination of different coolant openings may also be implemented.

[0036] In some embodiments, it is preferred that the intermediate segment body 240 be formed as a unitary body to avoid welds or other structures at the surface 260 that forms the inner diameter of the opening 248 that would otherwise be present from joining individual intermediate cladding arms 244 or groups of intermediate cladding arms 244. In some embodiments, one or both of the surface 260 that forms the inner diameter of the opening 248 and the outer edge 256 of the intermediate segment body 240 may be smooth surfaces (as seen in the surface 260) or may be ridged (as seen in the surface of the outer edge 256) having a series of peaks and valleys. The surface morphology of the surface 260 and the outer edge 256 that form the opening 248 may be complementary to their adjacent surfaces within the assembled layer 200. However, if not perfectly complementary, there may be gaps that can act as coolant channels, or adapter structures may be used to accommodate non-conforming surfaces at the interface. For example, the first internal interface may include a plurality of secondary coolant channels that traverse the active core structure from a first end to a second end. Also, if the surfaces are not complementary, an adapter structure may be used to mate the incompatible surfaces at the interface. As a further alternative, a combination of secondary coolant channels and adapter structures may also be implemented.

[0037] To facilitate visualization of the involute curve shape of the intermediate cladding arm, an embodiment of the intermediate cladding arm 244 is shown diagrammatically in FIG. 7A. In the illustrated embodiment, the two curved sides 262a, 262b of the involute curve shape of the intermediate cladding arm 244 lie on a line connected to the midpoint of the web 254 located between the chamber or chambers 252a, 252b of one intermediate cladding arm 244 and the chamber or chambers 252a, 252b of the adjacent intermediate cladding arm 244. The involute curve shape itself may be of constant width (i.e., where the width is the distance between the two opposing curved sides 262a, 262b of the involute curve shape of the intermediate cladding arm 244) as a function of axial position of the involute curve shape extending from the midpoint of the second radially inner end 246 to the midpoint of the second radially outer end 250. Alternatively, the involute curve shape may vary in width as a function of position along an axis of the involute curve shape that extends from the midpoint of the second radially inner end 246 to the midpoint of the second radially outer end 250. For example, the involute curve shape may continue to increase in width or decrease in width as a function of position along an axis of the involute curve shape that extends from the midpoint of the second radially inner end 246 to the midpoint of the second radially outer end 250.

[0038] Figure 8A illustrates an embodiment of the outer segment body 270 in a top view for the outer segment body 270 and in a cross-sectional plan view for the assembled nuclear fission reactor structure, in each case in a plane perpendicular to the axis of the axially extending inner opening 202. Figure 8 illustrates an enlarged view of portion P3 of the outer segment body 270 shown in Figure 8A.

[0039] The outer segment body 270 includes outer cladding arms 272 having a third involute curve shape that radiates outward in a spiral manner from a third radially inner end 274 adjacent an inner opening 276 that forms or is part of the second internal contact surface 242 in the assembled layer 200 to a third radially outer end 278 at an outer edge 280 that forms or is part of the radially outermost edge in the assembled layer 200 (or forms or is part of an additional contact surface in the assembled layer 200 if additional segment bodies are included beyond the three shown). The multiple outer cladding arms 272 include at least one chamber 282, or alternatively multiple chambers 282a, 282b (see also, e.g., FIGS. 9 and 10). In FIG. 8B, the chambers 282 are shown in only two outer cladding arms 272, but additional outer cladding arms 272, or alternatively all of the outer cladding arms 272, may include one or more chambers 282. The chamber 282 extends along the length of the outer cladding arm 272, or if multiple chambers are included, the chambers 282a, 282b are distributed along the length of the outer cladding arm 272. The chamber 282 (or chambers 282a, 282b, if multiple chambers are included) is contained within a web 284 of material forming the outer segment body 270, such that an individual chamber 282 in each outer cladding arm 272 is enclosed within the web 284. Furthermore, if multiple chambers 282 are included, a first chamber 282a is separated from an adjacent chamber 282b by a portion of the web 284 (see also Figures 9 and 10). As described herein, the chambers 282 may contain a fissile fuel composition (or other compositions, such as moderators and interfering materials), and the web 284 serves as a cladding for the fissile fuel composition or other compositions.

[0040] Similar to the inner segment body 210 and the middle segment body 240, the outer segment body 270 can include one or more coolant openings 286 that can be located between a chamber 282 or chambers 282a, 282b in one outer cladding arm 272 and a chamber 282 or chambers 282a, 282b in an adjacent outer cladding arm 272. The coolant openings 286 extend through the outer cladding arm 272 and in the thickness of the outer segment body 270 from a first side 204''' of the outer segment body 270 to a second side 206''' of the outer segment body 270.

[0041] Also, like the inner segment body 210 and the middle segment body 240, the coolant openings 286 associated with the outer segment body 270 can be of various shapes (although the coolant openings 286 associated with the outer segment body 270 can be the same as or different from one or more of the coolant openings 258 in the middle segment body 240 and the coolant openings 230 in the inner segment body 210). For example, if the web 284 of the outer segment body 270 is a unitary body, the coolant openings are one or more passages, channels, or other openings that can be formed in the web during initial web manufacture, e.g., during a layer-by-layer deposition process of an additive manufacturing process, or can be formed in the web after web manufacture by a material removal process such as drilling, milling, plunge milling, or using an electrical discharge machining (EDM) process. In another example, where each outer cladding arm 272 is formed as a unitary body and multiple outer cladding arms 272 are joined to form the outer segment body 270, the coolant openings 286 may be passages or other openings formed by surface features at an edge of the outer cladding arm 272, i.e., an edge bounded by a surface of the outer cladding arm 272 forming the first side 204''' of the outer segment body 270, a surface of the outer cladding arm 272 forming the second side 206''' of the outer segment body 270, a surface of a third radially inner end 274 of the outer cladding arm 272, and a surface of a third radially outer end 278 of the outer cladding arm 272. In this regard, the edge of the outer cladding arm 272 may include grooves, ribs, or other surface features that form one or more passages, channels, or other openings when contacted by an edge of an adjacent outer cladding arm 272. In this regard, the edge of the intermediate cladding arm 244 may include any of the surface features described and / or illustrated herein with respect to the inner cladding arm 214 and FIG. 6C.If present, in some embodiments such surface features may be offset along the length of the radially extending outer cladding arm 272 such that the location of the surface features does not coincide with the portion of the web 284 that separates the first chamber 282a from the adjacent chamber 282b. Combinations of different coolant openings may also be implemented.

[0042] In some embodiments, one or both of the surface 288 forming the inner diameter of the opening 276 and the outer edge 280 of the outer segment body 270 may be smooth (as seen in the surface 288) or ridged (as seen in the surface of the outer edge 280) with a series of peaks and valleys. The configuration of the surface 288 forming the inner diameter of the opening 276 may be complementary to the surface to which it abuts within the assembled layer 200. Also, if an additional segment body is radially outward of the outer segment body 270, the configuration of the surface of the outer edge 280 may be complementary to the surface to which it abuts within the assembled layer 200. However, if the surfaces are not perfectly complementary, there may be gaps that can function as coolant channels. For example, the second inner contact surface may include multiple secondary coolant channels that traverse the active core structure from the first end to the second end. Also, if these surfaces are not perfectly complementary, adapter structures may be used to mate the mismatched surfaces at the contact surface. As a further alternative, a combination of secondary coolant channels and adapter structures may be implemented.

[0043] To facilitate visualization of the involute curve shape of the outer cladding arm, an embodiment of the outer cladding arm 244 is shown diagrammatically in FIG. 8A. In the illustrated embodiment, the two curved sides 292a, 292b of the involute curve shape of the outer cladding arm 272 lie on a line connected to the midpoint of the web 284 located between the chamber or chambers 282a, 282b in one outer cladding arm 272 and the chamber or chambers 282a, 282b in the adjacent intermediate cladding arm 272. The involute curve shape itself may be of constant width (i.e., where the width is the distance between the two opposing curved sides 292a, 292b of the involute curve shape of the outer cladding arm 244) as a function of position along the axis of the involute curve shape that extends from the midpoint of the third radially inner end 274 to the midpoint of the third radially outer end 278. Alternatively, the involute curve shape may vary in width as a function of position along an axis of the involute curve shape that extends from the midpoint of the third radially inner end 274 to the midpoint of the third radially outer end 278. For example, the involute curve shape may continue to increase in width or decrease in width as a function of position along an axis of the involute curve shape that extends from the midpoint of the third radially inner end 274 to the midpoint of the third radially outer end 278.

[0044] In some embodiments, when considered collectively, the first involute curve shape, the second involute curve shape, and the third involute curve shape share a common involute curve shape. Thus, the surface of the inner cladding arm, the surface of the intermediate cladding arm, and the surface of the outer cladding arm form a continuous involute curve shape that extends from the inner opening to the radially outer surface of the outer segment body. For example, as shown in FIG. 9, when the surfaces of the curved sides 232a, 232b of the first involute curve shape of the inner cladding arm protrude across the first inner contact surface 212, the protrusion coincides with the surfaces of the curved sides 262a, 262b of the second involute curve shape of the intermediate cladding arm. As a result, there is one continuous involute curve shape including the surfaces of the curved sides 232a, 232b of the first involute curve shape of the inner cladding arm and the surfaces of the curved sides 262a, 262b of the second involute curve shape of the intermediate cladding arm. As a further example, if the continuous involute curve shape described above protrudes further across the second inner contact surface 242, the protrusion also coincides with the surfaces of the curved sides 292a, 292b of the third involute curve shape of the outer cladding arm. As a result of this further protrusion, there is one continuous involute curve shape including the surfaces of the curved sides 232a, 232b of the first involute curve shape of the inner cladding arm, the surfaces of the curved sides 262a, 262b of the second involute curve shape of the intermediate cladding arm, and the surfaces of the curved sides 292a, 292b of the third involute curve shape of the outer cladding arm. Also, as shown in FIG. 9, the first involute curve shape, the second involute curve shape, and the third involute curve shape each correspond to a different portion of a continuous involute curve shape extending from the inner opening to the radially outer surface of the outer segment body.

[0045] In another embodiment, the surfaces of the curved edges 232a, 232b of the first involute curve shape of the inner cladding arm, the surfaces of the curved edges 262a, 262b of the second involute curve shape of the middle cladding arm, and the surfaces of the curved edges 292a, 292b of the third involute curve shape of the outer cladding arm correspond to the curvature of a continuous involute curve shape, but one or more of the segment bodies are rotated relative to an adjacent segment body. When rotated less than a quantized value that maintains the alignment of the surfaces, the rotation causes the surface of the curved edge to be rotationally offset from the projection of the continuous involute curve shape. In such an arrangement, the surfaces of the curved edges of the involute curve shapes of the cladding arms on each side of the relevant affected contact surface are discontinuous in that they are connected by a step change.

[0046] In yet other embodiments, when considered collectively, the first involute curve shape, the second involute curve shape, and the third involute curve shape have different curvatures. Thus, the surface of the inner cladding arm, the surface of the intermediate cladding arm, and the surface of the outer cladding arm form a discontinuous involute curve shape that extends from the inner opening to the radially outer surface of the outer segment body. Such an embodiment is shown in layer 200 illustrated in FIG. 5.

[0047] In some embodiments, some or all of the surfaces of the inner cladding arm, the intermediate cladding arm, and the outer cladding arm form discontinuous involute curve shapes, but such surfaces still collectively spiral radially in the same direction, i.e., either in a right-handed (clockwise) direction (as shown in FIG. 5) or a left-handed (counterclockwise) direction.

[0048] In yet further embodiments, one or more (but not all) of the first involute curve shape, the second involute curve shape and the third involute curve shape share a common involute curve shape, such that some of the surfaces of the inner cladding arm, the intermediate cladding arm and the outer cladding arm form a continuous involute curve shape extending across their respective surfaces, while other portions of the surfaces of the inner cladding arm, the intermediate cladding arm and the outer cladding arm form discontinuous involute curve shapes extending across their respective surfaces.

[0049] In the embodiments shown and described in Figures 6A-6B, 7A-7B, and 8A-8B, each of the inner cladding arms, the intermediate cladding arms, and the outer cladding arms may individually include one or more chambers. In some embodiments, the inner cladding arms have more chambers than either the intermediate cladding arms or the outer cladding arms. For example, as shown in Figure 5, each of the inner cladding arms of the inner segment body 210 can include six chambers 222 (see also chamber 222 in Figure 6A), and each of the intermediate cladding arms and the outer cladding arms includes one chamber (252 and 282, respectively) (see also chamber 252 in Figure 7B and chamber 282 in Figure 8B). As another example, as shown in Figure 10, each inner cladding arm can include six chambers 222 (see also chamber 222 in Figure 6A), while the intermediate cladding arm and the outer cladding arms include two chambers (252 and 282, respectively). In an exemplary embodiment, the total number of chambers in the inner cladding arm, the intermediate cladding arm, and the outer cladding arm is ten or less.

[0050] FIG. 10 also illustrates alternative embodiments of the middle segment body 240 and the outer segment body 270. In the alternative embodiment, the cladding arms are manufactured as a unit, such as unit 300 including the middle cladding arms and unit 310 including the outer cladding arms. Manufacturing the cladding arms as a unit provides advantages when using additive manufacturing processes. Additionally, when manufactured as a unit, the units can use less material to form the web (at least in part because adjacent cladding arms can have less web material between any chambers included in those adjacent cladding arms compared to separate cladding arms located adjacent to each other), minimizing the number of weld joints required to assemble a complete segment body.

[0051] As mentioned above, in various examples of cladding arms, the individual chambers are surrounded by webs. Typically, during manufacture, the webs form the sides and bottom of the chambers, and one side of the chamber, such as the top, is initially open and can be loaded with a fissile fuel composition (or other compositions, such as moderators and interfering materials). After loading, the one open side of the chamber is closed by a cap attached to the web.

[0052] FIG. 11 is a schematic diagram of an example of a cladding arm 400. In the example cladding arm 400, several features discussed herein are illustrated. For example, the example cladding arm 400 has multiple chambers (three chambers 402a, 402b, 402c in the illustrated embodiment). Also illustrated is a fuel composition 404. The fuel composition 404 is illustrated at different points in the loading process. In one example, the fuel composition 404 is a pre-formed body 406 having suitable dimensions for insertion into the chamber. Suitable dimensions include a size where the body 406 has thermal transfer contact between an outer surface of the body 406 of the fuel composition 404 and an inner surface of the chamber 402. Alternatively, the body 406 has a minimal standoff distance between an outer surface of the body 406 of the fuel composition 404 and an inner surface of the chamber 402, and a heat transfer material, such as a salt or metal that melts at the operating temperature, is also loaded into the chamber 402. Also, the volume of the body 406 is sufficiently smaller than the volume of the chamber 402 to accommodate the by-products of the fission reaction and operation at elevated temperatures, such as the volume to accommodate fission gases and volume changes due to the fission reaction, as well as any thermal expansion volume changes. As seen in connection with chamber 402b, the body 406 of fuel composition is inserted into the chamber, and as seen in connection with chamber 402c, a cap 408 closes the chamber, for example, by welding the cap to a portion of the web that forms the periphery of the opening of the chamber. When closed by the cap 408, the chamber is isolated from the environment and the fuel composition 404 is surrounded by the web of the cladding arm 400 (or by a combination of the web of the cladding arm 400 and the cap, if the cap is not considered part of the web after closing the chamber).

[0053] Another exemplary feature shown in the embodiment of the cladding arm 400 is a surface feature 420 on one edge 422 of the cladding arm 400. As previously mentioned, either or both of the edges 422, 424 are bounded by a surface 426 of the cladding arm 400 that forms / will form a first side of the segment body, a surface 428 of the cladding arm 400 that forms / will form a second side of the segment body, a surface 430 of the radially inner end of the cladding arm 400, and a surface 432 of the radially outer end of the cladding arm 400. In the example illustrated in FIG. 11, the surface feature 420 is a rib that extends on the surface of the edge 422. As can be easily seen from FIG. 11, when the edge 422 contacts the edge of the adjacent cladding arm, the surface feature 420 offsets a portion of the edge 422 from the edge of the adjacent cladding arm by a distance corresponding to the distance that the surface feature 420 extends on the surface of the edge 422. Thereby, a channel is formed that extends from a surface 426 of the cladding arm 400 that forms / will form a first side of the segment body to a surface 428 of the cladding arm 400 that forms / will form a second side of the segment body.

[0054] FIG. 12 illustrates a layer 500 including an inner body segment 502, a middle segment body 504, and an outer segment body 506. Each body segment has a plurality of chambers. A plurality of fuel composition bodies 508 are disposed on each segment body corresponding to the shape (including involute curve shape) and the number of chambers present in each segment body in which the fuel composition bodies are loaded. For example, a fuel composition body 508a is loaded into the radially inner chamber 510a of the inner segment body 502, a fuel composition body 508g is loaded into the radially inner chamber 510g of the middle segment body 504, and a fuel composition body 508j is loaded into the radially outer chamber 510j of the outer segment body 506. Furthermore, in some embodiments, the fuel composition within each fuel composition body varies, resulting in chambers containing different fissile fuel compositions at different locations along the cladding arms.

[0055] 11 and 12 with respect to the fuel composition, in one or more examples where the fuel composition is loaded into the chamber, it may be substituted with a moderator composition or a mixture of moderator compositions or interfering material compositions. Such substitution may be performed in accordance with the neutronics and thermal management design of the reactor.

[0056] 13A and 13B show the results of a thermal analysis study on the involute curved cladding arm design disclosed herein. The thermal analysis was performed based on a nuclear fission reactor including such an involute curved cladding arm design. The involute curved cladding arm design of FIG. 13A shows a cladding arm 600 (corresponding to an embodiment of the inner segment body cladding arm) having a first set of six fuel composition bodies 602, a cladding arm 604 (corresponding to an embodiment of the middle segment body cladding arm) having a second set of four fuel composition bodies 606, and a cladding arm 608 (corresponding to an embodiment of the outer segment body cladding arm) having a third set of four fuel composition bodies 610. Overall, the thermal analysis showed that there was sufficient cooling on both sides of the cladding arms of each segment body to prevent the fuel composition in the chamber from melting.

[0057] Of the cladding arms and fuel composition of FIG. 13A, thermal analysis showed temperatures ranging from about 1256.3 K (for the cladding at concave surface 620 and tip 622) to a maximum of 2504.6 K for the hottest heat rise, which occurs in a region of the cladding arms of the inner segment body located toward the radially outer end (corresponding to section P4 of FIG. 13A and shown as regions 630a and 530b in the close-up of FIG. 13B). Region 630a is associated with the fuel composition body of chamber 602e and occurs at the curved edge of the cladding arms of the inner segment body at temperatures between 2227.2 K and 2504.6 K. This result was interpreted as the fuel composition body in chamber 602e expanding during operation, causing an increase in the curvature of the fuel composition body, resulting in the fuel composition body no longer making contact with the inner surface of chamber 602e in region 630a. This gap formed between the fuel composition body and the inner surface of chamber 602e reduced heat transfer and increased temperature. It should be noted that this test did not include a heat transfer material such as salt or liquid metal buffer. The presence of the heat transfer material is expected to fill the gap and improve heat transfer, lowering the temperature in region 620. However, the portion 622 of the web collocated in region 620 maintains a much lower temperature between 2356.3K and 1395K.

[0058] The involute curve shaped cladding arms, segment bodies, and layers disclosed herein can be manufactured by any suitable process. Figures 14A-14D are flow diagrams illustrating exemplary steps in the assembly of layers from various portions of segment bodies (Figures 14A-14B, loading of fuel and / or moderator compositions and interfering materials into layers (Figure 14C)) and assembly of multiple layers into a nuclear fission reactor structure (Figure 14D).

[0059] In a first manufacturing process, the involute curve shaped cladding arm 700 includes multiple chambers, and the webs of the involute curve shaped cladding arm define a cladding structure that is manufactured by metallurgical processes. These metallurgical processes include, in one example, additive manufacturing processes. The inner segment body 702 structure is preferably formed as a single structure (as shown in FIG. 14A ) to minimize bonding of the inner diameter surfaces of the openings. Furthermore, using a suitable additive manufacturing process, the entire structure of the layer 720, including the inner segment body 702, the middle segment body 704, and the outer segment 706 structure features of the inner segment body 702, can be formed as a single structure.

[0060] In other embodiments, the involute curve shaped cladding arms forming the intermediate segment body 704 and the involute curve shaped cladding arms forming the outer segment body 706 may be fabricated separately and bonded to the layers, or may be formed as a single body forming a unit that is bonded to layer 720 (see FIG. 14B), as shown in FIG. 14A.

[0061] Other structures of the involute cladding arms, such as chambers and coolant openings, are typically fabricated at this point in the process. The chambers in each involute cladding arm are first fabricated (in an additive manufacturing process or by machining the material of the involute cladding arm) to the point where the openings remain defining the chambers, i.e., cavities with sidewalls and one closed end.

[0062] Joining the involute curve shaped cladding arms to form layer 720 (FIG. 14B) can be done by any suitable means, including welding and bonding.

[0063] After forming the layer 720, the chamber is loaded with fissile fuel composition 742 (or other materials such as moderators or interfering materials) (see FIG. 14C, where the loading process is indicated by arrows). Optionally, a heat transfer material is also placed in the chamber. Once the chamber is loaded, a cap is placed over the opening and sealed, for example, by welding or a hot isostatic pressing (HIP) process, to form the assembled involute curve shaped cladding arms.

[0064] Next, as shown in FIG. 14D, the multiple assembled layers 740 are further assembled into a nuclear fission reactor structure 780. The layers are placed one on top of the other into corresponding internal structures, such as coolant openings. As previously described, clocking techniques using protruding registry features can be used for alignment purposes. In an exemplary construction, up to ten layers 740 are assembled to form the nuclear fission reactor structure 780. The layers 740 are assembled by any suitable means, such as welding or gluing. Additionally, a plate 782 can be placed on either end of the nuclear fission reactor structure 780. The plate can have suitable openings, for example, to accommodate the coolant openings, accommodate the internal openings, and / or accommodate the light load openings. The assembled nuclear fission reactor structure 780 is placed within a radial reflector 784. The radial reflector is optional based on the fuel material and the core design.

[0065] In some manufacturing methods or steps of the manufacturing method, the involute curve shaped cladding arm portion, segment body, and / or layers are manufactured as an integral single structure, for example using an additive manufacturing process. As used herein, an additive manufacturing process includes any technique for building a 3D object by layering material. An example of a suitable additive manufacturing process utilizes 3D printing of metal alloys such as molybdenum-containing metal alloys, Zircaloy-4, or Hastelloy X to form the aforementioned structural features. In other embodiments, if a suitable multi-material additive manufacturing process with multiple metals in the feedstock is employed, fissile nuclear fuel composition and / or heat transfer material and / or moderator and / or interference material may be included in the integral single structure. If molten metal is not included in the additive manufacturing process, the additive manufacturing process can be paused and a volume of molten metal can be placed in the fuel cavity (either in liquid or solid form) and the additive manufacturing process can be continued to complete the construction of the closed chamber. If a suitable multi-material additive manufacturing process is employed having multiple metals in the feedstock, other alloys that may be used include alloy steels, zirconium alloys, and molybdenum tungsten alloys (for the core shell), beryllium alloys (for the reflector), and stainless steels (for the containment vessel). The above-mentioned materials may be used in the manufacture of the various structures disclosed herein, even if not manufactured by an additive manufacturing process.

[0066] Additive manufacturing techniques for the production of integral single structures can include additional steps of (a) predictive and causal analysis, (b) in-situ monitoring combined with machine vision and accelerated processes during the layer-by-layer production of the structure, (c) automated analysis combined with machine learning components, and (d) virtual inspection of the digital representation of the completed structure. Furthermore, additive manufacturing techniques can form complex shapes. When combined with in-situ sensors, machine vision images, and artificial intelligence, additive manufacturing techniques provide predictive quality assurance for the production of such reactors and structures, as the components are additively manufactured layer by layer (often these layers are on the scale of 50 microns), allowing for the adjustment of the manufacturing quality.

[0067] As used herein, cladding is the outer casing of the fuel that includes features and is located between the coolant and the nuclear fuel. The cladding acts as a safety barrier to prevent radioactive fission fragments from escaping and contaminating the coolant. Some design constraints for the cladding include neutron absorption, radiation resistance, and temperature behavior. The cladding is typically made of a corrosion-resistant material that has a low absorption cross section for thermal neutrons. Exemplary materials include Zircaloy or steel, although other materials, such as metal-based and ceramic-based (Be, C, Mg, Zr, O, and Si), can be used if appropriate for the conditions of the reactor. In some embodiments, the cladding material can be isotopically enriched to increase reactivity through reduction of isotopes with high neutron absorption cross sections. For example, molybdenum enriched Mo-92 has a smaller parasitic neutron absorption cross section than elemental molybdenum.

[0068] Suitable fissionable nuclear fuel compositions applicable to the disclosed nuclear fission reactor and included in the heat generating source include uranium oxide enriched to less than 20%, uranium with 10 wt% molybdenum (U-10Mo), uranium nitride (UN), and other stable fissionable fuel compositions. Burnable interfering materials may also be included. Typically, the fissionable nuclear fuel compositions are in the form of ceramic materials.

[0069] The molten metal contained in the disclosed nuclear fission reactor and suitable for inclusion in the fuel cavity is: Sodium (Na), sodium potassium (NaK), potassium (k), and iron (Fe).

[0070] It is contemplated that various support and auxiliary devices may be incorporated into the disclosed nuclear fission reactor. For example, at least one of moderators (such as zirconium hydride (ZrH), beryllium oxide (BeO), water, and graphite), control rods (such as iridium control rods), and scientific instruments (such as temperature sensors or radiation detectors), and isotope generators may be incorporated into the nuclear fission reactor. Additionally, the control rods may also contain neutron poisons that absorb neutrons and may be used to adjust the criticality of the nuclear fission reactor. The neutron poisons may absorb enough neutrons to shut down the nuclear fission reactor (e.g., when the control rods are fully inserted into the reactor space) or may be axially positioned to maintain the criticality of the nuclear fission reactor (e.g., when the control rods are withdrawn from the core a distance that allows the nuclear fission chain reaction to continue). Any suitable number of control rods and moderators may be used and may be appropriately distributed throughout the reactor space to obtain one or more of the desired flux profile, power distribution, and operating profile. In an exemplary embodiment, the control rods are threaded, helping to conserve axial space, maximizing control rod diameter, and allowing direct contact to the roller nut for reliable SCRAM operation. All or some of the control rods can be individually controlled by individual motors to provide individual reactive control and / or power shaping.

[0071] FIG. 15 is a side cross-sectional view illustrating a schematic of an embodiment of a nuclear fission reactor 800 including multiple layers 802 assembled into a nuclear fission reactor structure 804 and disposed along a longitudinal axis 806 of the nuclear fission reactor structure 804. As previously disclosed and described in embodiments herein, the layers 802 are defined by an inner segment body, a middle segment body, an outer segment body, a first internal interface surface, and a second internal interface surface. The nuclear fission reactor 800 also includes a radial reflector 810 disposed about an outer surface of the nuclear fission reactor structure 804. The nuclear fission reactor structure 804 may be of any suitable geometry so long as it exhibits suitable neutronics and thermal management characteristics. As described herein, the diameter (D RX ) versus the length of the active core region (L RX ) is approximately 1 (i.e., L RX / D RX =1±0.05), the exemplary embodiment has enough layers 802. In general, the radial reflectors 810 reduce neutron leakage from the nuclear fission reactor 800 by scattering (or reflecting) neutrons that would otherwise escape into the core. This reduces the design effective multiplication factor (k eff ) and reduce the amount of fuel required to maintain criticality. The pressure vessel 820, among other things, surrounds the nuclear fission reactor structure 804 and has openings 822 through which the active core structure can be in fluid communication (coolant flow indicated by arrows 824) with a coolant system (not shown). Some of the various auxiliary equipment associated with the nuclear fission reactor are also shown in FIG. 15, including control rod assemblies 830 and shutdown devices such as poison rods 832 axially movable within the inner openings of the nuclear fission reactor structure 804. Any suitable radial reflector, pressure vessel, and coolant system may be incorporated into the nuclear fission reactor 800, as previously disclosed and described in the embodiments herein.

[0072] The disclosed arrangements relate to any configuration in which a heat generating source, including a fissile nuclear fuel composition, whether a fuel element or the fissile nuclear fuel composition itself, is surrounded by cladding. Although generally described herein in the context of pressurized water reactors (PWR reactors) and water as a primary coolant, the structures and methods disclosed herein may also be applied to other nuclear reactor systems. This includes boiling water reactors (BWR reactors), deuterium oxide (heavy water) moderator reactors such as CANDU reactors, light water reactors (LWR reactors), pebble bed reactors (PBR reactors), nuclear thermal propulsion reactors (NTP reactors), both commercial and research reactors, utilizing other primary coolants such as helium, hydrogen, methane, molten ore, liquid metal, etc. Any fuel cladding configuration in these various reactors may produce better core safety and performance characteristics when utilizing the molten metal fuel buffer technology disclosed herein.

[0073] The nuclear fission reactors disclosed herein can be used in any suitable application, including, but not limited to, terrestrial power, remote power or off-grid applications, space power, space propulsion, isotope production, directed energy applications, commercial power applications, and desalination.

[0074] Although particular embodiments have been referenced, it will be apparent that other embodiments and variations can be devised by others skilled in the art without departing from the spirit and scope thereof, and it is intended that the appended claims be construed to include all such embodiments and equivalent variations.

Claims

1. 1. A nuclear fission reactor structure comprising a plurality of layers, Each of the plurality of layers comprises: an inner segment body including an inner opening extending axially from a first side of the inner segment body to a second side of the inner segment body; an intermediate segment body radially outward of the inner segment body; an outer segment body radially outward of the intermediate segment body; a first internal contact surface separating the inner segment body and the middle segment body; a second internal contact surface separating the intermediate segment body and the outer segment body; Including, In a plan cross-sectional view taken along a plane perpendicular to the axially extending inner opening, the inner segment body includes a plurality of inner cladding arms having a first involute curve shape that radiates spirally outwardly from a first radially inner end adjacent the inner opening to a first radially outer end of the first internal contact surface; the intermediate segment body includes a plurality of intermediate cladding arms having a second involute curve shape that radiates outwardly in a spiral manner from a second radially inner end adjacent the first internal contact surface to a second radially outer end of the second internal contact surface; the outer segment body includes a plurality of outer cladding arms having a third involute curve shape that radiates outwardly in a spiral manner from a third radially inner end adjacent the second internal contact surface to a third radially outer end at a radially outer surface of the outer segment body; wherein the first involute curve shape, the second involute curve shape, and the third involute curve shape form a continuous involute curve shape extending from the inner opening to the radially outer surface of the outer segment body; each of the first involute curve shape, the second involute curve shape, and the third involute curve shape having a different curvature; the plurality of inner cladding arms, the plurality of intermediate cladding arms, and the plurality of outer cladding arms include a plurality of chambers; chambers at different locations along the cladding arm contain different fissile fuel compositions; chambers at different locations along the cladding arm contain different moderators; the inner cladding arm has opposing sides extending from the first side of the inner segment body to a second side of the inner segment body; At least one protrusion projects outwardly from at least one of said opposing sides. Nuclear fission reactor structure.

2. 1. A nuclear fission reactor structure comprising a plurality of layers, Each of the plurality of layers comprises: an inner segment body including an inner opening extending axially from a first side of the inner segment body to a second side of the inner segment body; an intermediate segment body radially outward of the inner segment body; an outer segment body radially outward of the intermediate segment body; a first internal contact surface separating the inner segment body and the middle segment body; a second internal contact surface separating the intermediate segment body and the outer segment body; Including, In a plan cross-sectional view taken along a plane perpendicular to the axially extending inner opening, the inner segment body includes a plurality of inner cladding arms having a first involute curve shape that radiates spirally outwardly from a first radially inner end adjacent the inner opening to a first radially outer end of the first internal contact surface; the intermediate segment body includes a plurality of intermediate cladding arms having a second involute curve shape that radiates outwardly in a spiral manner from a second radially inner end adjacent the first internal contact surface to a second radially outer end of the second internal contact surface; the outer segment body including a plurality of outer cladding arms having a third involute curve shape radiating outwardly in a spiral manner from a third radially inner end adjacent the second internal contact surface to a third radially outer end at a radially outer surface of the outer segment body. Nuclear fission reactor structure.

3. the first involute curve shape, the second involute curve shape, and the third involute curve shape form a continuous involute curve shape extending from the inner opening to the radially outer surface of the outer segment body.

3. The nuclear fission reactor structure of claim 2.

4. the continuous involute curved surface projection extends across the first and second internal contact surfaces and coincides with each of a surface of one of the plurality of inner cladding arms, a surface of one of the plurality of intermediate cladding arms, and a surface of one of the plurality of outer cladding arms; 4. The nuclear fission reactor structure of claim 3.

5. each of the first involute curve shape, the second involute curve shape, and the third involute curve shape corresponds to a different portion of a continuous involute curve shape extending from the inner opening to a radially outer surface of the outer segment body.

3. The nuclear fission reactor structure of claim 2.

6. the continuous involute curved surface projection extends across the first and second internal contact surfaces and coincides with each of a surface of one of the plurality of inner cladding arms, a surface of one of the plurality of intermediate cladding arms, and a surface of one of the plurality of outer cladding arms; 6. The nuclear fission reactor structure of claim 5.

7. each of the first involute curve shape, the second involute curve shape, and the third involute curve shape having a different curvature; A nuclear fission reactor structure according to any one of claims 1 to 6.

8. the continuous involute curved surface projection extends across the first and second internal contact surfaces and coincides with each of a surface of one of the plurality of inner cladding arms, a surface of one of the plurality of intermediate cladding arms, and a surface of one of the plurality of outer cladding arms; A nuclear fission reactor structure according to any one of claims 1 to 7.

9. each of the plurality of inner cladding arms, the plurality of intermediate cladding arms, and the plurality of outer cladding arms includes a plurality of chambers; A nuclear fission reactor structure according to any one of claims 1 to 8.

10. the chambers of each of the cladding arms are separated from each other by a web; 10. The nuclear fission reactor structure of claim 9.

11. each said inner cladding arm having more chambers than each said outer cladding arm; 11. A nuclear fission reactor structure according to claim 9 or 10.

12. The plurality of chambers is 10 or less.

12. A nuclear fission reactor structure according to any one of claims 9 to 11.

13. each said intermediate cladding arm having the same number of chambers as each said outer cladding arm; 13. A nuclear fission reactor structure according to any one of claims 9 to 12.

14. the chamber containing one of a fissile fuel composition and a moderator; A nuclear fission reactor structure according to any one of claims 9 to 13.

15. chambers at different locations along the cladding arm contain different fissile fuel compositions; 15. The nuclear fission reactor structure of claim 14.

16. Chambers at different locations along the cladding arm contain different moderators.

16. A nuclear fission reactor structure according to claim 14 or 15.

17. when the fissile fuel composition is located within a chamber, a gap exists between at least a portion of an inner surface of one of the chambers and at least a portion of an outer surface of one of the bodies forming the fissile fuel composition; 15. The nuclear fission reactor structure of claim 14.

18. the inner cladding arm has opposing sides extending from the first side of the inner segment body to a second side of the inner segment body; At least one protrusion projects outwardly from at least one opposing side surface; 18. A nuclear fission reactor structure according to any one of claims 1 to 17.

19. each projection extends continuously along the at least one opposing side surface from a first end toward the first side surface of the inner segment body to a second end toward the second side surface of the inner segment body; 20. The nuclear fission reactor structure of claim 18.

20. each projection extends discontinuously along the at least one opposing side surface from a first end toward the first side surface of the inner segment body to a second end toward the second side surface of the inner segment body; 20. The nuclear fission reactor structure of claim 18.

21. the projection has a top surface distal to at least one opposing side from which the projection projects; when assembled to the inner segment body with a first inner cladding arm immediately adjacent to a second inner cladding arm, a top surface of a protrusion on the first inner cladding arm contacts an opposing side of the second inner cladding arm to form a channel between the first inner cladding arm and the second inner cladding arm.

21. A nuclear fission reactor structure according to any one of claims 18 to 20.

22. the inner segment body, the intermediate segment body, the outer segment body, the first interior contact surface, and the second interior contact surface define a layer.

22. A nuclear fission reactor structure according to any one of claims 1 to 21.

23. a plurality of layers as claimed in claim 2 assembled into a nuclear fission reactor structure having a first end, a second end, and an exterior side connecting said first end and said second end; a radial reflector disposed about the outer side of the nuclear fission reactor structure; A containment vessel; a coolant system in fluid communication with the nuclear fission reactor structure through an opening in the containment vessel; Equipped with Nuclear fission reactor.

24. The nuclear fission reactor structure has a cylindrical structure.

24. The nuclear fission reactor of claim 23.

25. The coolant system is liquid-based or gas-based.

25. A nuclear fission reactor according to claim 23 or 24.

26. the first and second internal contact surfaces of each of the plurality of layers including a plurality of secondary coolant channels traversing the active core structure from the first end to the second end.

26. The nuclear fission reactor of any one of claims 23 to 25.

27. the plurality of first layers are assembled to the nuclear fission reactor structure by welding; 27. The nuclear fission reactor of any one of claims 23 to 26.

28. a plurality of first layers are assembled to the nuclear fission reactor structure by adhesive bonding; 27. The nuclear fission reactor of any one of claims 23 to 26.

29. 3. A method of manufacturing a nuclear fission reactor structure as claimed in claim 2, comprising the steps of: manufacturing the inner segment body, the intermediate segment body segments, and the outer segment body segments, wherein each of the inner cladding arms, the intermediate cladding arms, and the outer cladding arms includes a plurality of chambers; assembling the inner segment body, the intermediate segment body segments, and the outer segment body segments into layers, the segment bodies being assembled by one of welding and gluing; disposing one of a fissile fuel composition and a moderator in the plurality of chambers to form a fuel loading layer; assembling a plurality of said fuel loaded layers into said nuclear fission reactor structure; Including, method.

30. the inner segment body, the intermediate segment body segments, and the outer segment body segments are manufactured using an additive manufacturing process.

30. The method of claim 29.

31. 3. A method of manufacturing a nuclear fission reactor structure as claimed in claim 2, comprising the steps of: fabricating a layer including the inner segment body, the intermediate segment body, and the outer segment body as a unitary structure, wherein each of the inner cladding arms, the intermediate cladding arms, and the outer cladding arms includes a plurality of chambers; disposing one of a fissile fuel composition and a moderator in the plurality of chambers to form a fuel loading layer; assembling a plurality of said fuel loaded layers into said nuclear fission reactor structure; Including, method.

32. the unitary structure of the inner segment body, the middle segment body, and the outer segment body is manufactured using an additive manufacturing process; 32. The method of claim 31 .

33. disposing the nuclear fission reactor structure within a radial reflector; 33. The method of claims 29, 30, 31, and 32.

34. The nuclear fission reactor structure has a cylindrical shape. The method of claims 29, 30, 31, 32, and 33.

Images