Robust Nuclear Propulsion Fission Reactor with a 3-Pitch Pattern Core and Drum Absorbers

Abstract

The nuclear propulsion fission reactor structure has an active core region including fuel element structures, a reflector having rotatable neutron absorbing structures (such as drum absorbers), and a core support frame that conformally fits the outer surfaces of the fuel element structures to the reflector. The fuel element structures are positioned against the nearest fuel element structures in a three-pitch design. Cladding bodies defining coolant channels are inserted into and bonded to the upper and lower core plates to form a continuous structure that is the first portion of the containment structure. The nuclear propulsion fission reactor structure can be incorporated into a nuclear thermal propulsion engine for propulsion applications such as space propulsion.

Description

Technical Field

[0001] The present disclosure generally relates to nuclear reactors and structures associated with nuclear reactors, particularly for propulsion. Such nuclear propulsion reactors are applied to various non-terrestrial uses such as space and ocean environments.

Background Art

[0002] In the following description, specific structures and / or methods are referenced. However, the following references should not be construed as an admission that these structures and / or methods constitute prior art. The applicant expressly reserves the right to demonstrate that such structures and / or methods are not admitted as prior art to the present invention.

[0003] Various propulsion systems for non-terrestrial uses such as space have been developed. These include chemical-based propulsion systems, ion-based propulsion systems, and nuclear-based propulsion systems. Each of these propulsion systems balances thrust and specific impulse to provide performance tailored to a particular mission. For example, chemical-based propulsion systems have high thrust (e.g., greater than 10 7 propulsion pond (4.45×10 7 N)) but moderate specific impulse (e.g., 450 seconds or less) and are efficiently applied to heavy lift operations such as placing a payload in Earth orbit. Ion-based propulsion systems have low thrust (e.g., less than 10 propulsion pond (44.5 N)) but high specific impulse (e.g., 1,000 - 9,000 seconds) and are efficiently applied to long-term space travel such as interstellar travel. Nuclear power-based propulsion systems combine moderate thrust (e.g., thrust of 5,000 - 75,000 propulsion pond (22,250 - 333,750 N)) and moderate specific impulse (e.g., 600 - 1,000 seconds) and are efficiently applied to short-range space travel. Nuclear power-based propulsion systems are currently being evaluated as a propulsion option for NASA's Mars Design Reference Mission 5.0 human exploration.

[0004] Prior nuclear-based propulsion systems remain complex. For example, both the Nuclear Engine for Rocket Vehicle Application (NERVA) and the Rover program have developed nuclear thermal rocket designs. A typical design of a nuclear thermal propulsion reactor and engine 10 is shown in FIG. 1. The illustrated nuclear thermal propulsion reactor and engine 10 includes four main features, namely, an outer shell 20 having a reactor 22 housed within a reflector 24, a turbomachine 30 including a turbopump 32 and other piping and support equipment 34, a shield 40 separating the turbomachine 30 from the outer shell 20, and a nozzle section 50 including a nozzle 52 and a nozzle skirt 54.

[0005] However, these conventional nuclear-based propulsion systems still have drawbacks including utilizing complex decelerators and flow technologies and operating with minimal design margins that push the limits of design and related materials. Accordingly, there is still a need for a robust and simple design of a nuclear propulsion reactor, particularly for non-terrestrial applications such as space. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In view of the above, it would be advantageous to have a nuclear-based propulsion system with a robust single-pass propellant flow having a simplified core pattern for ease of manufacture. Further, a simplified design with a reduced number of weld points during manufacture is advantageous for reducing the risk of performance degradation. MEANS FOR SOLVING THE PROBLEMS

[0007] Generally, the present disclosure relates to a nuclear fission reactor structure suitable for use as an engine in a nuclear-based propulsion system. In an exemplary embodiment, the nuclear fission reactor structure utilizes fuel elements having a hexagonal cross-section arranged in a 3-pitch design and a rotatable drum neutron absorber for reactivity control. The nuclear fission reactor structure is housed within the outer shell of a nuclear thermal propulsion reactor and engine. The propellant gas is used as a coolant for the nuclear fission reactor structure. The propellant gas superheated within the nuclear fission reactor structure exits through a nozzle, generating thrust and impulse.

[0008] The embodiments disclosed herein include a plurality of fuel element structures, an active core region having an axial centerline defining the longitudinal axis of a nuclear propulsion reactor, a core support frame radially outside the active core region, a reflector radially outside the core modifier and having a radially inner surface oriented toward the active core region, and a plurality of neutron absorber structures disposed within the volume of the reflector. Each fuel element structure of the plurality of fuel element structures includes a clad body having an inner surface defining a coolant channel, a fuel composition body radially outside the clad body and surrounding the clad body, and a moderator composition body radially outside the fuel composition body and surrounding the fuel composition body. The coolant channel is located on the axial centerline of the fuel element structure. Further, the outer surface of the moderator composition body of the first fuel element structure abuts the outer surfaces of the moderator composition bodies of a plurality of nearest neighbor fuel element structures. The first fuel element structure among the plurality of fuel element structures includes a first coolant channel, a first clad body, a first fuel composition body, and a first moderator composition body. The second fuel element structure among the plurality of fuel element structures is the nearest neighbor fuel element structure to the first fuel element structure, and the second fuel element structure includes a second coolant channel, a second clad body, a second fuel composition body, and a second moderator composition body. In a cross-section between the first coolant channel of the first fuel element structure and the second coolant channel of the nearest neighbor fuel element structure, saidThe first coolant channel is separated from the second coolant channel by the first clad body, the first fuel composition body, the first moderator composition body, the second moderator composition body, the second fuel composition body, and the second clad body. only and is separated and the first coolant channel is separated from the second coolant channel without creating a gap between the first coolant channel and the second coolant channel The core support frame has a first surface radially inward of the second surface. The first surface is conformal to the radially outer surface of the active core region, and the second surface is conformal to the radially inner surface of the reflector. Each of the plurality of neutron absorption structures includes a neutron absorber body movable between a first position and a second position, and the first position is closer radially to the active core region than the second position.

[0009] Embodiments disclosed herein also include a nuclear thermal propulsion engine comprising a nuclear fission reactor structure and a housing disclosed herein. The active core region, the core support frame, the upper core plate, the lower core plate, the reflector, and the plurality of neutron absorption structures form a reactor structure, and the reactor structure is housed within the internal volume of the housing. When forming the nuclear thermal propulsion engine, a shield, a storage unit for cryogenically storing the propellant gas, a turbomachine, and a nozzle are operably attached to the reactor structure such that the upper core plate is oriented towards the first end of the housing and the lower core plate is oriented towards the second end of the housing within the internal volume of the housing. The shield, the turbomachine, and the storage unit are operably attached to the first end of the housing to provide a flow path from the storage unit to the nuclear propulsion reactor, and the nozzle is operably attached to the second end of the housing to provide a flow path for the superheated propellant gas exiting the nuclear propulsion reactor.

[0010] The embodiments disclosed in this specification also include a method of manufacturing a nuclear reactor structure. The method includes joining a first portion of each of a plurality of clad bodies to a lower core plate, each clad body having an inner surface that defines a coolant channel, the lower core plate including a plurality of openings extending from a first side surface of the lower core plate to a second side surface of the lower core plate, and the first portion of each clad body extending into a different one of the plurality of openings in the lower core plate. Next, each of the plurality of fuel composition bodies is disposed on an outer surface of a different one of the plurality of clad bodies, for example, by sliding, each fuel composition body having an annular cylindrical shape, and the fuel composition body surrounding the clad body with the inner surface of the annular cylinder of the fuel composition body facing the outer surface of the clad body. Then, each of the plurality of moderator bodies is disposed on an outer surface of a different one of the plurality of fuel composition bodies, for example, by sliding, where in cross section, each moderator body has a perimeter and an inner opening having a regular polygonal shape, and the moderator body surrounding the fuel composition body with the surface of the inner opening of the moderator body facing the outer surface of the annular cylinder of the fuel composition body. Next, a second portion of the clad body is joined to an upper core plate, the upper core plate including a plurality of openings extending from a first side surface of the upper core plate to a second side surface of the upper core plate, and the coolant channel of the clad body extending into one of the plurality of openings in the upper core plate. The assembled clad body, the fuel composition body radially outside the clad body, and the moderator composition body radially outside the fuel composition body define a fuel element structure, and in each fuel element structure, the coolant channel is the fuel element structure ofIt is arranged on the axial center line. In each fuel element structure, the cladding body includes a first portion that extends axially beyond the first axial end of the fuel composition body and a second portion that extends axially beyond the second axial end of the fuel composition body. Also, the outer surface of the moderator body of the first fuel element structure abuts against the outer surfaces of the moderator bodies of a plurality of nearest-neighbor fuel element structures. The first fuel element structure includes a first coolant channel, a first cladding body, a first fuel composition body, and a first moderator composition body. The first nearest-neighbor fuel element structure among the plurality of nearest-neighbor fuel element structures includes a second coolant channel, a second cladding body, a second fuel composition body, and a second moderator composition body. In a cross-section between the first coolant channel of the first fuel element structure and the second coolant channel of the first nearest-neighbor fuel element structure, the first coolant channel is separated from the second coolant channel by the first cladding body, the first fuel composition body, the first moderator composition body, the second moderator composition body, the second fuel composition body, and the second cladding body only is separated by and the first coolant channel is separated from the second coolant channel without creating a gap between the first coolant channel and the second coolant channel and is. A part of the upper core plate, a part of the lower core plate, and the cladding bodies of each fuel element structure form a first part of the containment structure of the nuclear propulsion reactor.

Brief Description of the Drawings

[0011] The foregoing summary and the following detailed description of the embodiments can be better understood when read in conjunction with the accompanying drawings. It should be understood that the illustrated embodiments are not limited to the exact arrangements and means shown.

[0012]

Figure 1

[0013]

Figure 2

[0014]

Figure 3

[0015]

Figure 4A

Figure 4B

Figure 4C

[0016]

Figure 5

[0017]

Figure 6A

Figure 6B

Figure 6C

Figure 6D

[0018]

Figure 7

[0019]

Figure 8

[0020]

Figure 9

[0021]

Figure 10A

Figure 10B

[0022]

Figure 11

[0023] For ease of viewing, in some examples, reference numerals are assigned only to some of the named features in the figures.

Embodiments for Carrying Out the Invention

[0024] FIG. 2 schematically shows an embodiment of a nuclear propulsion nuclear fission reactor structure. The nuclear propulsion nuclear fission reactor structure 100 includes a reactor core region 110, a core support frame 130, a reflector 150, and a plurality of neutron absorber structures 160.

[0025] The reactor core region 110 includes a plurality of fuel element structures 112 and has an axial centerline that defines the longitudinal axis 114 of the nuclear propulsion nuclear fission reactor structure 100. Each fuel element structure 112 includes a clad body 116 having an inner surface 118 that defines a coolant channel, a fuel composition object 120 radially outside the clad body 116, and a moderator composition object 122 radially outside the fuel composition object 120. When a plurality of fuel element structures 112 are arranged within the reactor core region 110, the outer surface 124 of the moderator composition object 122 of the first fuel element structure 112 abuts against the outer surfaces 124 of the moderator composition objects 122 of the plurality of nearest-neighbor fuel element structures 112. This is shown in FIG. 2 for the first fuel element structure 112a and a plurality of nearest-neighbor fuel element structures 112b - 112g. For example, in an exemplary embodiment, the side surfaces of the fuel element structures are in direct contact with the side surfaces of adjacent fuel element structures. The aggregate of the outer surfaces 124 of the moderator composition objects 122 of the fuel element structures 112 surrounding the reactor core region 110 defines the radially outer surface 126 of the reactor core region 110.

[0026] The core support frame 130 is located radially outside the active core region 110, and the reflector 150 is located radially outside the core support frame 130. The first surface 132 of the core support frame 130 is radially inside the second surface 134 of the core support frame 130. The first surface 132 of the core support frame 130 is conformal to the radially outer surface 126 of the active core region 110, and the second surface 134 of the core support frame 130 is conformal to the radially inner surface 152 of the reflector 150. The radially inner surface 152 of the reflector 150 faces the active core region 110, and the core support frame 130 functions to fit the shape of the radially outer surface 126 of the active core region 110 to the shape of the radially inner surface 152 of the reflector 150.

[0027] A plurality of neutron absorber structures 160 are disposed within the volume of the reflector 150. The neutron absorber structure 160 includes a neutron absorber body 162 that is movable between a first position and a second position, such as by rotation, and the first position is closer radially to the active core region than the second position. In an exemplary embodiment, the first position is the closest radially to the active core region, and the second position is the farthest radially from the active core region. In the embodiment shown in FIG. 2, the neutron absorber body 162 is shown in the first position that is closest radially. For purposes of illustration, the second radially distal position is shown using a virtual line (see the second position shown as 162'). The neutron absorber body 162 is movable between the first position and the second position to control the reactivity of the active core region 110. In the illustrated example, the neutron absorber body 162 is rotatable (R) about the axis 164 of the neutron absorber structure 160 from a first position that is closer radially (corresponding to the position shown for the neutron absorber body 162 in FIG. 2) to a second position 162'. However, other radial positions and / or directions of movement can be implemented as long as the various positions capable of moving the neutron absorber body 162 provide control of the reactivity of the active core region 110. In some embodiments, when a plurality of neutron absorber bodies 162 are each in the first position that is closer radially, each of the plurality of neutron absorber bodies 162 is equidistant radially from the axial centerline of the active core region 110.

[0028] Figure 3 is a partial top view of a part of a nuclear propulsion nuclear reactor structure. In Figure 3, a part of the reactor core region 110 is shown, and a part of the core support frame 130, the reflector 150, and the neutron absorber body 162 in the neutron absorption structure 160 are also shown. Some of the features that have already been shown and described in connection with Figure 2 are also shown in Figure 3.

[0029] For example, Figure 3 shows a plurality of fuel element structures 112 (arranged together with a plurality of nearest-neighbor fuel element structures), each having a clad body 116, a coolant channel 128, a fuel composition body 120, and a moderator composition body 122. The plurality of fuel element structures 112 collectively have translational symmetry. An example of translational symmetry is the 3-pitch design shown in Figure 3. In the 3-pitch design, there is translational symmetry between the fuel element structures 112, whereby features on one fuel element structure 112 are repeated on other fuel element structures 112 at a certain distance (or a certain pitch). For example, depending on whether comparing nearest neighbors or the next nearest neighbors, the repeating structure can be a multiple of the pitch. Exemplary suitable pitches are 3 cm to 10 cm, or 3 cm to 6 cm, or alternatively 4 cm, depending on the material selection and performance. Figure 3 shows an example of a 3-pitch design. The central axis of the coolant channel 128 is at a distance P1 from each of the central axes of the coolant channels 128 of the nearest-neighbor fuel element structures 112 and at a distance P2 (P2 = 2 × P1) from the next nearest neighbors. Each of the plurality of fuel element structures 112 has a polygonal cross-section. In the illustrated example, each of the plurality of fuel element structures 112 has a hexagonal cross-sectional shape. Other regular polygonal cross-sections can also be implemented. However, other shapes may require multiple shapes in one reactor core region design, such as a combination of octagons and squares.

[0030] Also, for example, Figure 3 shows the first surface 132 of the core support frame 130 that is conformal to the radial outer surface 126 of the reactor core region 110. Similarly, Figure 3 shows the second surface 134 of the core support frame 130 that is conformal to the radial inner surface 152 of the reflector 150, and the second surface 134 of the core support frame 130 is conformal to the radial inner surface 152 of the reflector 150.

[0031] The additional structure shown in FIG. 3 is the neutron absorber body 162 of the neutron absorption structure 160. FIGS. 4A-4C also show embodiments of the neutron absorption structure 160 and associated features within the reflector 150. As described herein, the neutron absorption structure 160 is disposed within the volume of the reflector 150, which volume is defined by the radially inner surface 152, radially outer surface 154, and top surface 156 and bottom surface 158 (not shown) of the reflector 150. As shown in FIGS. 3 and 4A-4C, the neutron absorption structure 160 includes a cylindrical drum 166 housed within a tube 168. The neutron absorber body 162 occupies a first portion of the cylindrical drum 166. This first portion of the cylindrical drum 166 is the volume of the cylindrical drum 166 that includes a portion of the outer surface of the cylindrical drum 166 (e.g., an arc of 120 degrees of the circumference of the cylindrical drum). When the tube 168 and the cylindrical drum 166 move as a unit, such as by rotating (R) with respect to the inner diameter surface of the reflector absorber housing, the cylindrical drum 166, the neutron absorber body 162, and the tube 168 slide along the inner surface of the reflector absorber housing. A motor (not shown in FIGS. 3 and 4A-4C) can be operably attached to the tube 168 by a drum shaft to rotate the neutron absorption structure 160. FIGS. 4B and 4C show an example where the first position of the neutron absorber body 162 is closer radially to the reactor core region than the second position (compare FIG. 4C showing the neutron absorber body 162 in the first position with FIG. 4B showing the neutron absorber body 162 in the second position), where in this case the first position in FIG. 4C is the closest radially to the reactor core region 110 and the second position in FIG. 4B is the farthest radially from the reactor core region 110.

[0032] The second part of the cylindrical drum 166, i.e., the part other than the part occupied by the neutron absorber body 162, functions as a secondary reflector. In some embodiments, the secondary reflector can be made of the same material as the reflector 150 such that the reflector 150 has substantially uniform neutron properties across the radial cross-section of the reflector 150 (regardless of whether the radial cross-section includes the neutron absorption structure 160). In certain embodiments, the reflector 150 and the cylindrical drum 166 are formed of suitable neutron moderating materials such as beryllium, beryllium oxide, and graphite, and combinations of such materials. However, in other embodiments, the secondary reflector and the reflector 150 are made of different materials. Suitable materials for the neutron absorber body 162 include B 4 C, europium(III) oxide, and dysprosium(III) oxide. Suitable materials for the tube 168 include combinations of most forms of steel, molybdenum, tungsten, and other exotic alloys. However, other materials may be used as long as they do not substantially interfere with the neutron absorption function of the neutron absorber body 162. In certain embodiments, the tube 168 is a stainless steel tube.

[0033] Other features of the exemplary embodiment of the nuclear propulsion nuclear fission reactor structure 100 include an upper core plate and a lower core plate. FIG. 5 schematically shows an upper cross-section of the nuclear propulsion nuclear fission reactor structure 100 including an example of the upper core plate 200. The upper core plate 200 has a first side surface 202 and a second side surface 204, and a plurality of openings 206. The openings 206 extend from the first side surface 202 to the second side surface 204 of the upper core plate 200. Each fuel element structure 112 (the outer surface 124 of the moderator body 122 of each fuel element structure 112 is shown by a dashed line in FIG. 5) is associated with one of the openings 206 such that a first portion of each cladding body 116, such as a first end 210, extends into a different one of the plurality of openings 206 and is joined to the upper core plate 200. For example, the first end 210 of the cladding body 116 can extend at least partially (with respect to length) into the opening 206. Alternatively, the first end 210 of the cladding body 116 extends into the opening 206 by a distance equal to the thickness (T) of the upper core plate 200. After extending the first end 210 into the opening 206, the first portion of each cladding body 116 is joined to the upper core plate 200 by any suitable means such as welding including resistance welding, full penetration welding, or by a suitable epoxy-based system such as J-B Weld (registered trademark). As seen in FIG. 5, the coolant channel 128 defined by the inner surface 118 of the cladding body 116 fits concentrically into one of the plurality of openings 206 of the upper core plate 200.

[0034] Although not shown in FIG. 5, the lower core plate has a feature corresponding to the upper core plate 200 and includes a first side surface and a second side surface, and a plurality of openings extending from the first side surface to the second side surface of the lower core plate 250. The lower core plate 250 is attached to the second end of the fuel element structure 112 in the same manner as the upper core plate 200 is attached to the first end of the fuel element structure 112. That is, the second end of the clad body 116 extends into a different one of the plurality of openings of the lower core plate 250. For example, the second end of the clad body 116 can extend at least partially (with respect to length) into the opening of the lower core plate. Alternatively, the second end of the clad body 116 extends into the opening of the lower core plate 250 by a distance equal to the thickness of the lower core plate 250. After the second end of the clad body 116 is extended into the opening of the lower core plate 250, the second portion of each clad body 116 is joined to the lower core plate 250 by any suitable means such as welding including resistance welding and full penetration welding, or by a suitable epoxy-based material such as J-B Weld (registered trademark). Also, similar to the upper core plate 200, the coolant channel 128 defined by the inner surface 118 of the clad body 116 fits into one of the plurality of openings of the lower core plate 250.

[0035] As shown, and partially in FIG. 5, as described above, at least a portion of the upper core plate 200, at least a portion of the lower core plate 250, and the clad body 116 of each fuel element structure 112 form a first portion of the containment structure of the nuclear propulsion nuclear fission reactor structure 100 (i.e., the propellant for fission product separation).

[0036] Figures 6A-6D show the components of an exemplary fuel element structure in schematic perspective views (Figs. 6A-6C) that are not assembled and a cross-sectional view (Fig. 6D) that is assembled. Fig. 6A shows one embodiment of the clad body 116. The clad body 116 is substantially in the shape of a tube having an outer surface 260 and an inner surface 118 that defines coolant channels. When the tube is a cylindrical tube, the outer surface 260 is an outer diameter surface and the inner surface 118 is an inner diameter surface. In some embodiments, the clad body 116 is a continuous extruded tube over the height of the active core region 110. By embodying the clad body 116 as an extruded tube, the need for seaming and welded joints in the clad body 116 is reduced or eliminated, the risk of failure of components during operation is reduced, and the manufacturing complexity is reduced.

[0037] Fig. 6B shows one embodiment of the fuel composition body 120. The fuel composition body 120 substantially has an annular cylindrical shape with a tube having an outer surface 270 and an inner surface 272. The inner surface 272 defines a space into which the clad body 116 fits. For example, when the clad body 116 is a cylindrical tube, the inner surface 272 is sized to complement the outer diameter surface of the clad body 116. The composition body 120 and the clad body 116 can be joined, for example, by sliding the clad body 116 into the space defined by the inner surface 272 of the fuel composition body 120 and press-fitting or bonding the two components in a hot isostatic pressing (HIP) operation.

[0038] FIG. 6C shows an embodiment of the moderator composition object 122. The moderator composition object 122 is in the shape of a substantially polygonal sleeve having a central opening 280 and a flat outer surface 124. In the illustrated embodiment, the moderator composition object 122 is an annular hexagon, but the moderator composition object 122 can take other shapes including other polygons and regular polygons. The annular hexagon of the moderator composition object 122 includes an outer surface 124 and a central opening 280 having an inner surface 282. The inner surface 282 defines a space into which the fuel composition object 120 (or the fuel composition object 120 joined to the cladding body 116) fits. The composition object 120 and the cladding body 116 can be assembled, for example, by sliding the fuel composition object 120 (or the fuel composition object 120 joined to the cladding body 116) into the space defined by the inner surface 282 of the moderator composition object 122. A tight attachment between the moderator composition object 122 and the outer surface of the fuel composition object 120 is not required, but the two components can be optionally joined, for example, by press-fitting or hot isostatic pressing.

[0039] FIG. 6D is a cross-sectional view of an embodiment of the assembled fuel element structure 112, showing the relative positions within the assembled fuel element structure 112 of the tubular cladding body 116, the annular cylindrical fuel composition object 120, and the moderator composition object 122 in the form of a polygonal sleeve.

[0040] Figure 7 is a schematic perspective view of a part of the upper surface of the reactor core region showing one end of a plurality of assembled fuel element structures. In the view of Figure 7, the assembled fuel element structure 112 is assembled in the reactor core region 110 in a state where the outer surface 124 of the moderator composition object 122 of the fuel element structure 112 abuts against the outer surfaces 124 of the moderator composition objects 122 of a plurality of nearest neighboring fuel element structures 112, resulting in an essentially continuous moderator body. In some embodiments, the plurality of fuel elements 112 can be manufactured together as a single component, i.e., as a reactor core part larger than one fuel element 112. The axial end faces of the moderator composition object 122 and the fuel composition object 120 are in (or substantially in) the same plane (with respect to each other) and form a substantially flat upper surface 190 of the reactor core region 110. In each fuel element structure 112, a part 220 of the clad body 116 extends axially beyond both the axial end of the moderator composition object 122 and the fuel composition object 120. Figure 7 corresponds to the end of the assembled fuel element structure 112 to which the upper core plate 200 is joined.

[0041] From Figure 7, it can be understood that the opposite end of the assembled fuel element structure 112 extends axially beyond both the axial end of the moderator composition object 122 and the fuel composition object 120 and has a similar substantially flat surface with a protruding portion of the clad body 116 corresponding to the end of the assembled fuel element structure 112 to which the lower core plate 250 is joined.

[0042] FIG. 8 is a schematic cross-sectional view of an embodiment of a reflector. Reflector 150 surrounds the active core region 110 and mates with a core support frame 130 that bridges the shape of the outer surface 126 of the active core region 110 (e.g., formed by the hexagonal surfaces 124 of the fuel element structure 112) with a uniform inner annular reflector surface 152. A neutron absorption structure 160 is contained within the volume of the reflector 150. In the embodiment of FIG. 8, the neutron absorber body 162 is shown with the drum-shaped cylindrical neutron absorption structure 160 facing inward at a position corresponding to the shutdown configuration of the nuclear propulsion nuclear fission reactor structure 100. The drum-shaped cylindrical neutron absorption structure 160 is configured such that the neutron absorber body 162 can be arranged equidistantly in the radial direction from the axial centerline of the active core region 110 so as to smooth the fission hot spots.

[0043] The reflector 150 functions to thermalize the "reflected" neutrons returning to the active core region 110 to increase the criticality and reduce the "leakage" of neutrons, which reduces the criticality potential of the nuclear propulsion nuclear fission reactor structure since there is no opportunity to generate a fission reaction. Second, the reflector houses a neutron absorption structure 160, which is a primary system for reactivity control. In FIG. 8, the embodiment of the neutron absorption structure 160 is in the form of a rotatable control drum. In order to house a neutron absorption structure 160 of sufficient size in the form of a rotatable control drum to control the reactivity, the reflector cannot be made overly thin (the width (W) between the inner surface 152 and the outer surface 154). In an exemplary embodiment, the width (W) of a beryllium-based reflector is between 15 cm and 30 cm. The width can vary based on the material of the reflector and the weight requirements for non-terrestrial applications of the nuclear propulsion nuclear fission reactor structure, and materials with lower neutron reflection characteristics require a thicker reflector, i.e., a wider width (W).

[0044] The nuclear propulsion nuclear fission reactor structure can further include an outer shell. FIG. 9 schematically shows an embodiment of a nuclear propulsion nuclear fission reactor structure 100 having an outer shell 300. A reactor structure including a reactor core region 110, a core support frame 130, an upper core plate 200, a lower core plate 250, a reflector 130, and a plurality of neutron absorption structures 160 is housed within an internal volume 302 of the outer shell 300. An upper reactor plate 304 is disposed above (or outside) a first side surface 202 of the upper core plate 200 and includes a plurality of holes 306 for passing a propellant gas. After the propellant gas passes through the plurality of holes 306, the plurality of holes are in fluid communication with a coolant channel 128 within the reactor core region 110 such that the propellant gas passes through the coolant channel 128 and functions as a coolant for the nuclear propulsion nuclear fission reactor structure 100. Similarly, a lower reactor plate 310 is disposed below (or outside) the lower core plate 250 and includes a plurality of holes 306 for passing the propellant gas exiting the coolant channel 128.

[0045] Also shown in FIG. 9 is a motor 320 operably attached to a cylindrical drum 166 of the neutron absorption structure 160 by a drum shaft 322 for rotating the cylindrical drum 166. In the illustrated embodiment, the motor 320 is external to the outer shell 300 and the drum shaft 322 passes through the outer shell 300, for example, by a port or other opening 324 of the outer shell 300.

[0046] Embodiments of the outer shell 300 are formed from a sheet of material such as stainless steel and can include ribs or other reinforcing structures to provide additional structural support. As seen in FIG. 10A, the outer shell 300 can be a single continuous component. However, in other embodiments, the outer shell 300 can then be a plurality of components that are assembled with fasteners. The inner ledge 330 of the outer shell 300 supports the reflector 130 and the active core region 110. The inner ledge 330 can be attached to the inner surface of the outer shell 300 or can be formed by a portion of the inner surface of the outer shell 300. FIG. 10B (an enlarged view of portion P1 of FIG. 10A) shows an exemplary interface between the reactor structure and the outer shell 300. The lower core plate 250 of the active core region 110 is placed on the lower core plate ledge portion 332 of the inner ledge 330 to form a mechanical interface.

[0047] During operation and before the nozzle throat reaches Mach 1, the incoming flow must overcome the increasing pressure within the converging nozzle section. This can potentially cause a reverse flow condition if there are cracks in the space within the outer shell 300, for example, below the reactor structure, below the active core region 110. Therefore, the seal of the mechanical interface between the lower core plate ledge portion 332 and the lower core plate 250 should be as stable as possible during startup to prevent leakage to the reflector 130 and the active core region 110. Under steady-state conditions during operation (i.e., in the case of nozzle throat Mach 1) and after the shock exits the bifurcation section, the acceleration of the flow through the bifurcated nozzle section "pulls" the flow and forms a seal between the lower core plate ledge portion 332 and the lower core plate 250 due to a negative dynamic pressure difference.

[0048] The present disclosure also relates to a nuclear thermal propulsion engine that includes a nuclear propulsion nuclear fission reactor structure 110 within a housing 300. The nuclear thermal propulsion engine further includes, for example, a shield, turbomachinery, and a nozzle section that is attached to or supported by the housing 300, consistent with that illustrated and described in connection with FIG. 1. In an exemplary embodiment, the reactor core region 110 is placed on the lower core plate ledge portion 332 of the inner ledge 330, the reflector 130 is attached to the reflector ledge portion 334 of the inner ledge 330 by fasteners such as bolts or pins, the drum shaft 322 operably attaches a motor 320 (e.g., fixed to the housing via a motor support plate) to the neutron absorption structure 160 and passes through the upper opening 324 of the housing 300. The nozzle section is bolted to the bottom of the housing 300, and the shield and turbomachinery are fixed to the upper portion of the housing 300. A storage section for cryogenically storing the propellant gas is operably connected, along with the shield and turbomachinery, to provide a flow path from the storage section to the nuclear propulsion reactor, and the nozzle section is operably connected to provide a flow path for the superheated propellant gas exiting the nuclear propulsion reactor.

[0049] The nuclear propulsion nuclear fission reactor structure (and nuclear thermal propulsion engine including the nuclear propulsion nuclear fission reactor structure) can be manufactured using suitable means. Generally, the nuclear propulsion nuclear fission reactor structure is manufactured by a method that includes joining a clad body to a lower core plate, sliding a fuel composition body and a moderator body to a predetermined position over a radially inner feature, for example, sliding the fuel composition body onto the clad body and the moderator body onto the assembled fuel composition body-clad body to form a fuel element structure, and joining an upper core plate to a portion of each clad body that extends axially beyond the fuel composition body and the moderator body. Subsequently, a reflector is placed around the outer surface of the assembled fuel element structure, and the inner surface of the reflector is fitted to the outer surface of the assembled fuel element structure by a core support frame.

[0050] FIG. 11 is a flow diagram showing the basic steps in one embodiment of a method for manufacturing a nuclear propulsion nuclear fission reactor structure. Method 400 includes a step 410 of joining a first portion of each of a plurality of clad bodies to a lower core plate. Each clad body 116 has an inner surface 118 that defines a coolant channel 128, and the lower core plate 250 includes a plurality of openings that extend from a first side surface of the lower core plate to a second side surface of the lower core plate. When joining the clad body 116 to the lower core plate 250, the first portion of each clad body 116 extends into a different one of the plurality of openings of the lower core plate 250. When joining the clad body 116 to the lower core plate 250, it is preferable to join the entire interface between the first portion and the lower core plate together, for example, by welding, to form a continuous metal body including the clad body 116 and the lower core plate 250.

[0051] Method 400 also includes a step 420 of sliding each of a plurality of fuel composition bodies on an outer surface of a different one of the plurality of clad bodies. Each fuel composition body 120 has an annular cylindrical shape. When the fuel composition body 120 is disposed on the outer surface 260 of the clad body 116, the inner surface 272 of the annular cylinder of the fuel composition body 120 is oriented toward the outer surface 260 of the clad body 116. Since the first portion of the clad body 116 extends into the opening of the lower core plate 250, the fuel composition body 120 is prevented from extending to the same axial position as the end of the clad body 116 by the lower core plate 250. Thus, the first portion of the clad body 116 extends axially beyond the first axial end of the fuel composition body 120. Similarly, a second portion of the clad body 116 extends axially beyond the second axial end of the fuel composition body 120 to provide a portion of the clad body 116 for joining to the opening 206 of the upper core plate 200. After disposing the fuel composition body 120 on the outer surface 260 of the clad body 116, the fuel composition body 120 and the clad body 116 can be fixed to each other or otherwise joined, for example, by press fitting or hot isostatic pressing (HIP).

[0052] Method 400 also includes step 430 of sliding each of the decelerator bodies on a different one of the outer surfaces of the plurality of fuel composition bodies. Each decelerator body 122 has a perimeter having a regular polygon (hexagon in a particular embodiment) in cross-section and an inner opening 280. When the decelerator body 122 is disposed on the outer surface 270 of the fuel composition body 120, the surface 282 of the inner opening 280 of the decelerator body 122 is oriented toward the outer surface 270 of the annular cylinder of the fuel composition body 120. A tight attachment between the decelerator composition body 122 and the outer surface 270 of the fuel composition body 120 is not required, but the two components can be optionally joined, for example, by press-fitting or hot isostatic pressing.

[0053] Method 400 also includes step 440 of joining a second portion of the cladding body to the upper core plate. The upper core plate 200 includes a plurality of openings 206 extending from a first side surface 202 of the upper core plate 200 to a second side surface 204 of the upper core plate 200. The second portion of the cladding body 116 (extending axially beyond the axial end of the fuel composition body 120) is inserted into the opening 206 and joined to the upper core plate 200. When joining the cladding body 116 to the upper core plate 200, it is preferred to join the entire interface between the second portion and the upper core plate together, for example, by welding, to form a continuous metal body including the cladding body 116 and the upper core plate 200. Note that by joining the cladding body 116 of each fuel element structure to the upper core plate 200 and the lower core plate 250, a part of the upper core plate forms the first part of the containment structure of the nuclear propulsion fission reactor structure 100. Also, since the inner surface 118 of the cladding body 116 defines a coolant channel 128 having a first portion and a second portion inserted into the openings of the lower core plate and the upper core plate, respectively, the coolant channel 128 of the cladding body 116 also extends into the openings of the lower core plate and the upper core plate.

[0054] Each fuel element structure 112, which is assembled to include a clad body 116, a fuel composition object 120 radially outside the clad body 116, and a moderator composition object 122 radially outside the fuel composition object 120, is arranged in the active core region 110 such that the outer surface 124 of the moderator body 122 of the first fuel element structure abuts the outer surfaces 124 of the moderator bodies 122 of a plurality of nearest neighboring fuel element structures, for example, in a relationship of 3 pitches.

[0055] After assembling the fuel element structures 112 in the active core region 110, the reflector 150 is arranged around the outer surface 126 of the assembled fuel element structures 112. The core support frame 130 helps the inner surface 152 of the reflector 150 to fit onto the outer surface 126 of the assembled fuel element structures 112. The core support frame 130 also fits with the upper core plate 200 and the lower core plate 250, so the reflector 150 forms the second part of the containment structure of the nuclear propulsion fission reactor structure 100.

[0056] Note that other features and structures of the nuclear propulsion fission reactor structure 100 can be manufactured as part of the method or supplied for use in the method. Thus, the method 400 can optionally include one or more of forming a plurality of clad bodies 116, forming a plurality of fuel composition objects 120, and forming a plurality of moderator bodies 122. The step of forming the plurality of clad bodies 116 is performed by any suitable technique including metalworking techniques such as extrusion. The step of forming the plurality of fuel composition objects 120 can be performed by any suitable technique including fuel compression techniques or additive manufacturing techniques. The step of forming the plurality of moderator bodies 122 can be performed by any suitable technique including powder compression or additive manufacturing techniques.

[0057] In some manufacturing methods or steps of the manufacturing method, the characteristic parts and structures (or a part thereof) of the nuclear propulsion nuclear fission reactor structure 100 are manufactured as an integral one-piece structure, for example, using an additive manufacturing process. As used herein, the additive manufacturing process includes any technique for constructing a 3D object by adding materials layer by layer. Examples of suitable additive manufacturing processes utilize 3D printing of metal alloys such as molybdenum-containing metal alloys, zircaloy-4 or hastelloy X, or 3D printing of ceramics such as uranium or beryllium oxide to form the above-described structural features such as cladding or fuel. In other embodiments, the fissile nuclear fuel composition and / or heat transfer agent and / or moderator material and / or poison used as part of the nuclear propulsion nuclear fission reactor structure 100 can be included in an integral structure when a suitable multi-material additive manufacturing process having a plurality of metals and ceramics in the feedstock is used. If molten metal is not included in the additive manufacturing process, the additive manufacturing process can be paused, a volume of molten metal is placed in the fuel cavity (either in liquid or solid form), and the additive manufacturing process is continued to complete the structure of the closed chamber. Other alloys that can be used when a suitable multi-material additive manufacturing process having a plurality of metals in the feedstock is used include steel alloys, zirconium alloys, and molybdenum-tungsten alloys (for cladding and / or containment structures), beryllium alloys (for reflectors), and stainless steel (for containment structures). Even if not manufactured by an additive manufacturing process, the above materials can be used for manufacturing the various characteristic parts and structures disclosed herein.

[0058] Furthermore, although the disclosed reactors and cores have complex mechanical shapes, the structures and characteristic parts disclosed herein can be more easily manufactured by using additive manufacturing techniques such as 3D printing of elemental metals or metal alloys to manufacture integrally and repeatedly layer by layer.

[0059] Additive manufacturing techniques for producing monolithic and unitary structures can include additional steps of (a) predictive and causal analysis, (b) in-situ monitoring and accelerated processing during fabrication of the structure layer-by-layer in combination with machine vision, (c) automated analysis in combination with machine learning components, and (d) virtual inspection of the digital representation of the structure upon completion. Further, additive manufacturing techniques can create complex geometries and, when combined with in-situ sensors, machine vision imagery, and artificial intelligence, enable adjustment of manufacturing quality when components are built on an additive basis layer-by-layer (in many cases these layers are on the order of 50 microns), providing predictive quality assurance for the manufacture of such reactors and structures.

[0060] As used herein, a cladding is a layer of fuel that includes features positioned between a coolant and nuclear fuel. The cladding functions as a safety barrier to prevent radioactive fission fragments from escaping the fuel and contaminating the coolant. Some design constraints of the cladding include neutron absorption, radiation resistance, and temperature behavior. The cladding is typically made of a corrosion-resistant material with a low thermal neutron absorption cross-section. Exemplary materials include zircaloy or steel, but other materials may be used, such as compositions including metal and ceramic bases (Be, C, Mg, Zr, O, Si), and alloys thereof including molybdenum, tungsten, rhenium, tantalum, hafnium, and carbides, if suitable for the conditions of the reactor. In some embodiments, the cladding material can be isotope enriched to increase reactivity by reduction of isotopes having a higher neutron absorption cross-section; for example, molybdenum enrichment Mo-92 has a lower parasitic neutron absorption cross-section than elemental molybdenum. In embodiments of the disclosed nuclear propulsion fission reactor structures, the upper and lower core plates are made of cladding material, preferably having the same composition as the cladding body.

[0061] The fissile nuclear fuel composition can be high assay low enriched uranium (HALEU) having an assay greater than 5% and less than 20% U 235 or greater than or equal to 20% U 235It can be highly enriched uranium (HEU) having uranium. Suitable fissile nuclear fuel compositions applicable to the disclosed fuel element structures include uranium oxide (UO 2 ) with less than 20% enrichment, uranium containing 10 wt% molybdenum (U-10Mo), uranium nitride (UN), and other stable fissile fuel compounds. Burnable poisons may also be included. Typically, the fissile nuclear fuel composition is in the form of a cermet such as UO 2 containing W or Mo and UN containing W or Mo. In some embodiments, molten metal can also function as the "metal" part of the cermet.

[0062] When used, a heat transfer agent such as a salt or metal that melts at the operating temperature can be included in the fuel element structure to improve the thermal coupling between the fuel composition body and the cladding body. Further, the heat transfer agent can occupy cracks or other defects within the fuel element structure (whether present initially or generated during the operation of the reactor) to promote thermal coupling. Molten metals included in the disclosed nuclear propulsion nuclear reactor structures and suitable for inclusion in the fuel element structure to provide thermal transfer contact include sodium (Na), sodium-potassium (NaK), potassium (K), iron (Fe), copper (Cu), silver (Ag), lead (Pb), and bismuth (Bi), or alloy compositions thereof.

[0063] It is contemplated that various support auxiliary devices can be incorporated into the disclosed nuclear propulsion nuclear reactor structures and nuclear thermal propulsion engines. For example, at least one of a moderator (such as zirconium hydride (ZrH), beryllium (Be), beryllium oxide (BeO), water, graphite, etc.), control rods for launch safety (such as iridium control rods), and scientific instruments (such as temperature sensors or radiation detectors) can be incorporated into the nuclear propulsion nuclear reactor structure.

[0064] The disclosed configurations relate to any configuration in which a heat source containing a fissile nuclear fuel composition, whether a fuel element or the fissile nuclear fuel composition itself, is surrounded by a cladding. Although generally described herein in the context of a gas-cooled nuclear thermal propulsion reactor (NTP reactor), the structures and methods disclosed herein may be applicable to other nuclear reactor systems as well.

[0065] The nuclear propulsion nuclear reactor structures disclosed herein can be used in suitable applications including, but not limited to, non-terrestrial power applications, space power, space propulsion, and marine applications including submarines.

[0066] Although specific embodiments have been referred to, it is clear that other embodiments and variations can be devised by those 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.

Explanation of Reference Numerals

[0067] 100 Nuclear propulsion nuclear reactor structure 110 Active core region 112 Fuel element structure 116 Cladding body 120 Fuel composition object 122 Moderator composition object 128 Cooling body channel 130 Core support frame 150 Reflector 160 Neutron absorption structure 200 Upper core plate 250 Upper core plate

Claims

Claim 1 A nuclear propulsion nuclear fission reactor structure (100), comprising: A reactor core region (110) including a plurality of fuel element structures (112) and having an axial center line defining the longitudinal axis of the nuclear propulsion reactor; A core support frame (130) radially outside the reactor core region (110); A reflector (150) radially outside the core support frame (130) and having a radially inner surface oriented towards the reactor core region; A plurality of neutron absorber structures (160) disposed within the volume of the reflector (150); Each fuel element structure of the plurality of fuel element structures (112) includes a clad body (116) having an inner surface defining a coolant channel (128), a fuel composition body (120) radially outside the clad body (116) and surrounding the clad body (116), and a moderator composition body (122) radially outside the fuel composition body (120) and surrounding the fuel composition body (120). The coolant channel (128) is located on the axial center line of the fuel element structure (112); The outer surface of the moderator composition body (122) of the first fuel element structure (112) abuts against the outer surfaces of the moderator composition bodies (122) of a plurality of nearest-neighbor fuel element structures (112); The first fuel element structure among the plurality of fuel element structures (112) includes a first coolant channel (128), a first clad body (116), a first fuel composition body (120), and a first moderator composition body (122); The second fuel element structure among the plurality of fuel element structures (112) is the nearest-neighbor fuel element structure (112) to the first fuel element structure. The second fuel element structure includes a second coolant channel (128), a second clad body (116), a second fuel composition body (120), and a second moderator composition body (122); In a cross-section between the first coolant channel (128) of the first fuel element structure and the second coolant channel (128) of the nearest fuel element structure, the first coolant channel (128) is separated from the second coolant channel (128) only by the first cladding body (116), the first fuel composition body (120), the first moderator composition body (122), the second moderator composition body (122), the second fuel composition body (120), and the second cladding body (116), and the first coolant channel (128) is separated from the second coolant channel (128) without creating a gap between the first coolant channel (128) and the second coolant channel (128). The core support frame (130) has a first surface radially inside the second surface, the first surface being conformal to the radially outer surface of the active core region (110), and the second surface being conformal to the radially inner surface of the reflector (150). Each of the plurality of neutron absorption structures (160) includes a neutron absorber body (162) movable between a first position and a second position, the first position being closer radially to the active core region (110) than the second position, a nuclear propulsion nuclear fission reactor structure (100).

2. An upper core plate (200); A lower core plate (250); and further includes The cladding body (116) of each fuel element structure (112) includes a first portion axially extending beyond the first axial end of the fuel composition body (120) and a second portion axially extending beyond the second axial end of the fuel composition body (120). The first portion of each fuel element structure (112) is joined to the upper core plate (200), and the second portion of each fuel element structure (112) is joined to the lower core plate (250). The nuclear propulsion nuclear fission reactor structure (100) according to claim 1.

3. The fuel composition body (120) has an annular cylindrical shape, and the fuel element structure (112) has a polygonal cross-section, the nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

4. The side surface of the fuel element structure (112) is in direct contact with the side surface of an adjacent fuel element structure (112), the nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

5. The nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2, wherein the arrangement of the plurality of fuel element structures (112) in the active core region (110) has translational symmetry.

6. The nuclear propulsion nuclear fission reactor structure (100) according to claim 5, wherein the distance between repeating elements in the structure is constant.

7. The fuel composition of the fuel composition object (120) includes uranium oxide with less than 20% enrichment, uranium containing 10 wt% molybdenum U-10Mo, uranium nitride UN, or a cermet thereof, in the nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

8. The neutron absorber body (162) is movable between the first position and the second position to control the reactivity of the active core region (110), in the nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

9. Each cladding body (116) is a continuous extrusion tube, and the cladding body (116) has a composition including molybdenum, tungsten, rhenium, tantalum, hafnium, or an alloy thereof, in the nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

10. The first portion of the cladding body (116) extends axially beyond the first axial end of the moderator composition object (122), and the second portion of the cladding body (116) extends axially beyond the second axial end of the moderator composition object (122), in the nuclear propulsion nuclear fission reactor structure (100) according to claim 2.

11. A part of the upper core plate (200), a part of the lower core plate (250), and the cladding body (116) of each fuel element structure (112) form a part of the containment structure of the nuclear propulsion reactor, in the nuclear propulsion nuclear fission reactor structure (100) according to claim 2 or 10.

12. The fuel composition object (120) has an annular cylindrical shape, and the moderator composition object (122) is a polygonal sleeve having a central opening (280), and the inner diameter of the central opening (280) defines the space in which the fuel composition object (120) is disposed, in the nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

13. The nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2, wherein when each of the plurality of neutron absorber bodies (162) is in the first position, each of the plurality of neutron absorber bodies (162) is equidistant radially from the axial center line of the active core region (110).

14. Each of the plurality of neutron absorption structures (160) includes a cylindrical drum (166) housed in a tube (168), the neutron absorber body (162) occupies a first portion of the cylindrical drum (166), a second portion of the cylindrical drum (166) is a secondary reflector, and the first portion of the cylindrical drum (166) is the volume of the cylindrical drum (166) including a part of the outer surface of the cylindrical drum (166). The nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

15. The nuclear propulsion nuclear fission reactor structure (100) according to claim 14, wherein the part of the outer surface of the cylindrical drum (166) corresponds to an arc of 120 degrees of the circumference of the cylindrical drum (166).

16. The cylindrical drum (166) is rotatable with respect to the inner diameter surface of the tube (168), and the nuclear propulsion nuclear fission reactor structure (100) further includes a motor (320) operably attached to a drum shaft (322) that rotates the cylindrical drum (166). The nuclear propulsion nuclear fission reactor structure (100) according to claim 14.

17. The coolant is a propellant gas, the nuclear propulsion reactor further includes an upper reactor plate (304) and a lower reactor plate (310), and each reactor plate includes a plurality of holes (306) for passing the propellant gas. The nuclear propulsion nuclear fission reactor structure (100) according to claim 1 or 2.

18. Further comprising an outer shell (300), The active core region (110), the core support frame (130), the upper core plate (200), the lower core plate (250), the reflector (150), and the plurality of neutron absorption structures (160) form a reactor structure, The nuclear propulsion nuclear fission reactor structure (100) according to claim 2, wherein the reactor structure is housed within the internal volume of the outer shell (300).

19. The coolant is a propellant gas, and the nuclear propulsion reactor further includes an upper reactor plate (304) and a lower reactor plate (310). Each reactor plate includes a plurality of holes (306) for passing the propellant gas, and the reactor structure is attached to the inner surface of the outer shell (300) or supported by a ledge (330) formed on a part of the inner surface of the outer shell (300). The nuclear propulsion fission reactor structure (100) according to claim 18.

20. A nuclear thermal propulsion engine, comprising: the nuclear propulsion fission reactor structure (100) according to claim 18; a shield (40); a storage section for storing the propellant gas at an extremely low temperature; a turbomachine (30); and a nozzle (52). The upper core plate (200) is oriented toward the first end of the outer shell (300), and the lower core plate (250) is oriented toward the second end of the outer shell (300). The shield (40), the turbomachine (30), and the storage section are operably attached to the first end of the outer shell (300) so as to provide a flow path from the storage section to the nuclear propulsion reactor. The nozzle (52) is operably attached to the second end of the outer shell so as to provide a flow path for the superheated propellant gas exiting the nuclear propulsion fission reactor structure. A nuclear thermal propulsion engine.

21. A method for manufacturing a nuclear propulsion fission reactor structure (100), comprising: joining a first portion of each of a plurality of clad bodies to a lower reactor plate (250), each clad body (116) having an inner surface defining a coolant channel, and the lower reactor plate (250) including a plurality of openings extending from a first side surface of the lower reactor plate (250) to a second side surface of the lower reactor plate (250), the first portion of each clad body (116) extending into a different one of the plurality of openings of the lower reactor plate (250), step (410); sliding each of a plurality of fuel composition objects on an outer surface of a different one of the plurality of clad bodies, each fuel composition object (120) having an annular cylindrical shape, and the fuel composition object (120) surrounding the clad body with the inner surface of the annular cylinder of the fuel composition object (120) facing the outer surface of the clad body, step (420); Sliding each of a plurality of decelerator bodies on the outer surface of a different one of a plurality of fuel composition objects, wherein in cross-section, each decelerator body (122) has a periphery having a regular polygonal shape and an inner opening, and the decelerator body (122) surrounds the fuel composition object (120) with the surface of the inner opening of the decelerator body (122) facing the outer surface of the annular cylinder of the fuel composition object (120) (step 430). Joining a second portion of the clad body (116) to the upper core plate (200), wherein the upper core plate (200) includes a plurality of openings extending from a first side surface of the upper core plate (200) to a second side surface of the upper core plate (200), and the coolant channel (128) of the clad body (116) extends into one of the plurality of openings of the upper core plate (200) (step 440), including. The assembled clad body (116), the fuel composition object (120) radially outside the clad body (116), and the decelerator composition object (122) radially outside the fuel composition object (120) define a fuel element structure (112). In each fuel element structure (112), the coolant channel (128) is disposed on the axial center line of the fuel element structure (112). In each fuel element structure (112), the clad body (116) includes a first portion extending axially beyond a first axial end of the fuel composition object (120) and a second portion extending axially beyond a second axial end of the fuel composition object (120). The outer surface of the decelerator body of the first fuel element structure (112) abuts against the outer surfaces of the decelerator bodies of a plurality of nearest-neighbor fuel element structures (112). The first fuel element structure includes a first coolant channel (128), a first clad body (116), a first fuel composition object (120), and a first decelerator composition object (122). The first nearest-neighbor fuel element structure among the plurality of nearest-neighbor fuel element structures (112) includes a second coolant channel (128), a second clad body (116), a second fuel composition object (120), and a second decelerator composition object (122). In a cross-section between the first coolant channel (128) of the first fuel element structure and the second coolant channel (128) of the first nearest fuel element structure, the first coolant channel (128) is separated from the second coolant channel (128) only by the first cladding body (116), the first fuel composition body (120), the first moderator composition body (122), the second moderator composition body (122), the second fuel composition body (120), and the second cladding body (116), and the first coolant channel (128) is separated from the second coolant channel (128) without creating a gap between the first coolant channel (128) and the second coolant channel (128). A method for manufacturing a nuclear propulsion fission reactor structure (100), wherein a part of the upper core plate (200), a part of the lower core plate (250), and the cladding body (116) of each fuel element structure (112) form a first part of the containment structure of a nuclear propulsion reactor. Claim 22 The method for manufacturing a nuclear propulsion fission reactor structure (100) according to claim 21, wherein the step of forming the plurality of cladding bodies includes extruding the cladding body (116) in a seamless tube shape. Claim 23 The method for manufacturing a nuclear propulsion fission reactor structure (100) according to claim 21, wherein the step of forming the plurality of fuel composition bodies includes fuel compression technology or additive manufacturing technology. Claim 24 The method for manufacturing a nuclear propulsion fission reactor structure (100) according to claim 21, further comprising the step of fixing the fuel composition body (120) to the cladding body, and the step of fixing the fuel composition body (120) to the cladding body includes press-fitting or hot isostatic pressing. Claim 25 The method for manufacturing a nuclear propulsion fission reactor structure (100) according to claim 21, further comprising the step of disposing a reflector (150) around the outer surface of the assembled fuel element structure (112), and the step of fitting the inner surface of the reflector (150) to the outer surface of the assembled fuel element structure (112) by a core support frame (130). Claim 26 The method for manufacturing a nuclear propulsion fission reactor structure (100) according to claim 25, wherein the inner surface of the reflector (150) forms a second part of the containment structure of the nuclear propulsion reactor. Claim 27 The step of forming the plurality of cladding bodies, and The step of forming the plurality of fuel composition objects; One or more of the steps of forming the plurality of decelerator main bodies; The method for manufacturing a nuclear propulsion nuclear fission reactor structure (100) according to claim 21.

Images