Patent Application
20230211898
The present subject matter relates to examples of nuclear thermal propulsion (NTP) systems and nuclear reactor systems. The present subject matter also encompasses moderation and propulsion of nuclear thermal propulsion reactors with a combined moderator-propellant.
Conventional chemical-based propulsion systems commonly deployed in rockets rely on an oxidizer, such as oxygen, to generate a chemical reaction in order to create thrust. Nuclear thermal propulsion (NTP) systems have the potential to deliver thrust values that far exceed chemical based fuels. Typically, this is done by heating a propellant, typically low molecular weight hydrogen, to over 2,600 Kelvin by harnessing thermal energy from a nuclear reactor.
NTP is an appealing technology with prospects for becoming the propulsion system of choice for human missions beyond low earth orbit. Numerous mission architectures call NTP the preferred approach for a 2030s human Mars mission for its ability to produce significant amounts of thrust while operating at a high specific impulse.
The design of NTP systems dates back to the Nuclear Engine for Rocket Vehicle Applications (NERVA) work done by NASA. The NERVA design typically consists of a small nuclear fission reactor, turbopump assembly (TPA), nozzle, radiation shield, assorted propellant lines, pressure vessel, and support hardware. Thermal energy gained by the propellant during an expansion cycle is used to power the rocket.
In conventional NTP designs, a tank stores hydrogen (H2) as a propellant. This hydrogen propellant tank must be large enough to contain a sufficient amount of hydrogen for a mission, such as to space. Because the density and boiling point of hydrogen is not particularly high, the mass and size of the tank is usually very large. Hence, hydrogen propellant is difficult to store in a mass effective manner and small form factor within the tank.
Additionally, cryogenic equipment such as cryocoolers and multi-layer insulation (MLI) are needed to utilize the conventional hydrogen propellant. Cryogenic equipment is expensive, and thus is not conducive to a cost-effective mission, particularly in space. Accordingly, the conventional hydrogen propellant is not very cost-effective. The mass of the equipment needed for NTP systems using the conventional hydrogen propellant, including the cryogenic equipment and the tank is large and requires larger and more complex fairings for rockets to utilize the hydrogen propellant. An alternative propellant that can be stored as a dense liquid in a smaller tank that is lighter, with a smaller form factor, and with a relatively larger surface area to volume ratio compared to a hydrogen storing tank is needed.
Hence, there is room for further improvement in NTP systems and devices that incorporate such NTP systems. The combined moderator-propellant technologies disclosed herein increases the mass efficiency of an NTP system and improve the overall performance during operation. In contrast with the single purpose, non-moderating hydrogen propellant, the combined moderator-propellant technologies require little to no dedicated storage space for the majority of NTP operation. The combined moderator-propellant technologies advantageously allow a dual-purpose fluid to act as both a nuclear moderator as well as a propellant (e.g., for a rocket) in an NTP system, which makes the NTP system lighter, have a smaller form factor (less bulky), and more cost effective.
In an example, a nuclear thermal propulsion system includes a pressure vessel and a nuclear reactor core disposed in the pressure vessel. The nuclear reactor core includes a moderator region to flow a combined moderator-propellant and an array of fuel assemblies disposed within the moderator region. Each fuel assembly includes a nuclear fuel and an array of coolant channels formed within the nuclear fuel and coupled to the moderator region to flow the combined moderator-propellant to a thrust chamber. The combined moderator-propellant can include ammonia (NH3).
Each fuel assembly can further include an insulator layer surrounding the nuclear fuel and the array of coolant channels, an inner can surrounding the insulator layer, a combined moderator-propellant return disposed surrounding the inner can, and an outer can. The combined moderator-propellant return can be located between the inner can and the outer can. The outer can may be directly coupled to the moderator region, and the insulator layer can be formed of zirconium carbide (ZrC). The pressure vessel can be formed of a titanium alloy, an aluminum stainless steel alloy, or a nickel-chromium based superalloy. The inner can may be formed of a silicon carbide/silicon carbide (SiC—SiC) composite or a zirconium alloy. The outer can may be formed of the SiC—SiC composite, a beryllium (Be) composite, or a stainless steel alloy. The nuclear fuel can be comprised of coated fuel particles embedded inside a high-temperature matrix. The high temperature matrix can include silicon carbide, zirconium carbide, titanium carbide, niobium carbide, tungsten, molybdenum, or a combination thereof. The coated fuel particles can include tristructural-isotropic (TRISO) fuel particles, bistructural-isotropic (BISO) fuel particles, or TRIZO fuel particles. The BISO fuel particles can include a fuel kernel formed of uranium nitride (UN).
The nuclear thermal propulsion system can also include a reflector region disposed between the moderator region and the pressure vessel. The reflector region can be formed of a solid reflector material. The solid reflector material can be formed of beryllium (Be) or beryllium oxide (BeO).
Alternatively or additionally, the reflector region can be configured to flow the combined moderator-propellant. The nuclear thermal propulsion system can further include a moderator reflector separator disposed between the moderator region and the reflector region. The moderator reflector separator can be formed of a silicon carbide/silicon carbide (SiC—SiC) composite, beryllium (Be), or a stainless steel alloy.
The nuclear thermal propulsion system can include a coolant plenum located inside the pressure vessel and coupled to the moderator region to store and flow the combined moderator-propellant to the moderator region. Additionally, the nuclear thermal propulsion system can include a combined moderator-propellant pump. The combined moderator-propellant pump is configured to pump the combined moderator-propellant from the coolant plenum to the moderator region, and to pump the combined moderator-propellant from the moderator region to the array of fuel assemblies.
The nuclear thermal propulsion system can further include a plurality of circumferential control drums surrounding the moderator region. Each of the control drums includes a reflector portion within a first portion of an outer surface and an absorber material within a second portion of the outer surface. The reflector portion can be formed of a solid reflector material. The solid reflector material can be formed of beryllium (Be) or beryllium oxide (BeO). Alternatively or additionally, the reflector portion can include a control drum reflector chamber configured to flow the combined moderator propellant. The control drum reflector chamber is configured to flow the combined moderator-propellant while the combined moderator-propellant is in a pressurized or a supercritical state.
Additional objects, advantages and novel features of the examples will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The objects and advantages of the present subject matter may be realized and attained by means of the methodologies, instrumentalities and combinations particularly pointed out in the appended claims.
The drawing figures depict one or more implementations, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements.
100
101
102, 102A-B
107
113
114
120
140
151
170
171
172
173
204A-N
215
216
217
219A-F
220A-F
230
231
232
240
241
242
243
244
245A-N
246A-N
260
261
262
263
264
265
266
267
268
269
270
290
291
315
316
350
351A-F
390
391
400A-C
401
402
403
410
415
420
425A-D
430A-D
501
502
503
600
601
602
625
700
701
702
721
722
732
751
752
800
802
803
804
805
806
807
810
811-817
820
821-827
830
831-837
840
841-847
850
860
In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.
The term “coupled” as used herein refers to any logical or physical connection. Unless described otherwise, coupled elements or devices are not necessarily directly connected to one another and may be separated by intermediate components, elements, etc. The term “fluid communication” as used herein means that a substance, such as a liquid or a gas, can flow. In the examples herein, the combined moderator-propellant 102 is typically the substance. In some examples, during fluid communication the substance can flow between two or more chambers, channels, containers, tanks, or vessels such that when the substance settles, the substance balances out to the same level or pressure in all of the chambers, channels, containers, tanks, and vessels in fluid communication, regardless of the shape and volume of the chambers, channels, containers, tanks, and vessels.
Unless otherwise stated, any and all measurements, values, ratings, positions, magnitudes, sizes, angles, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. Such amounts are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. For example, unless expressly stated otherwise, a parameter value or the like may vary by as much as ± 5% or as much as ± 10% from the stated amount. The term “approximately” or “substantially” means that the parameter value or the like varies up to ± 10% from the stated amount.
The orientations of the nuclear thermal propulsion (NTP) system 100, nuclear reactor 107, nuclear reactor core 101, associated components, and/or any NTP system 100 incorporating the nuclear reactor core 101, fuel assemblies 204A-N, control drums 220A-F, such as shown in any of the drawings, are given by way of example only, for illustration and discussion purposes. In operation for a particular NTP system 100, the components may be oriented in any other direction suitable to the particular application of the NTP system 100, for example upright, sideways, or any other orientation. Also, to the extent used herein, any directional term, such as lateral, longitudinal, up, down, upper, lower, top, bottom, and side, are used by way of example only, and are not limiting as to direction or orientation of any NTP system 100 or component of the NTP system 100 constructed as otherwise described herein.
The various examples disclosed herein relate to combined moderator-propellant technologies that increase the mass efficiency and decrease the size (e.g., form factor) of a nuclear thermal propulsion (NTP) system 100 to improve the overall performance during operation. By combining the roles of moderator and propellant into a single fluid with a unified flow path, significant mass savings can be achieved within a lift vehicle implementing an NTP system 100. Utilizing propellant as a moderator allows for some or all of the moderator in the NTP system 100 to be ultimately used as propellant. Allowing the moderator to eventually be used as propellant gives the moderator a dual purpose, and obviates the need to add both a separate moderator (e.g., solid moderator blocks, such as graphite) and a separate propellant (e.g., hydrogen). Additionally, the NTP system does not require a separate tank for propellant. All of a combined-moderator propellant 102 can be stored within a pressure vessel 260 of the NTP system 100, and act as a moderator for the nuclear reactor 107 until expelled as propellant. The mass savings are substantial. An NTP system 100 utilizing combined moderator-propellant technologies potentially reduces the payload mass of the lift vehicle by as much or more than the weight of separate moderator and the tank of the separate propellant used in a conventional NTP-based lift vehicle.
The design paradigm of replacing elements of the nuclear reactor core 101 with the combined moderator-propellant 102 can be expanded further. In additional examples, not only are solid moderator blocks replaced with a moderator region 113 filled with liquid propellant acting as a moderator (the combined moderator-propellant 102), but control drums 220A-F of the nuclear reactor core 101 can be hollowed out (e.g., to form a cavity) and filled with combined moderator-propellant. This combined moderator-propellant 102 may need to be pressurized beyond the pressure within the moderator region 113 in order to allow the control drums 220A-F to reflect neutrons back into the nuclear reactor core 101.
Additionally, solid reflector block(s) that form a solid reflector region 215 at the periphery of the nuclear reactor core 101 can also be replaced with a fluid reflector region 315, filled with combined moderator-propellant 102. This combined moderator-propellant 102 may also need to be pressurized beyond the pressure within the moderator region 113 in order to allow the fluid reflector region 315 to reflect neutrons back into the nuclear reactor core 101. The mass savings of replacing either the solid control drum reflection portion 216 of the control drums 220A-F, the solid reflector block(s) in the solid reflector region 215, or both with a fluid that can ultimately be used as propellant is substantial. Very generally, when looking from above (as in
Reference now is made in detail to the examples illustrated in the accompanying drawings and discussed below.
In the example, the NTP system 100 is a type of nuclear reactor 107 that operates on the principle of an expansion cycle, which pumps a combined moderator-propellant 102, such as ammonia (NH3), through a combined moderator-propellant flow path 120. The expansion cycle is driven by a combined moderator-propellant pump 140 or turbopump assembly (TPA). The combined moderator-propellant pump 140, or pumps and turbines in a TPA, move the combined moderator-propellant 102 through the combined moderator-propellant flow path 120 and the combined moderator-propellant 102 becomes superheated in the nuclear reactor core 101 and expands to a gas, e.g., for thrust or power generation.
In an alternative example, the nuclear reactor system that utilizes the combined moderator-propellant 102 can also be a terrestrial power system, such as a nuclear electric propulsion (NEP) system for fission surface power (FSP) system. NEP powers electric thrusters such as a Hall-effect thruster for robotic and human spacecraft. FSP provides power for planetary bodies such as the moon and Mars. In the NEP and FSP power applications, the nuclear reactor system enabled with combined moderator-propellant 102 technologies heats the working fluid (e.g., ammonia) through a power conversion system (e.g., Brayton) to produce electricity. Moreover, in the NEP and FSP power applications, the nuclear reactor system does not include a propellant, but rather includes the working fluid that passes through a reactor inlet when producing power. In the NEP and FSP power applications, the combined moderator-propellant 102 can be cooled via the reactor inlet working fluid (e.g., the flow coming out of a recuperator) before the working fluid passes through the fuel assemblies 204A-N. In NEP or FSP applications, a nuclear reactor system 100 may include a turbojet (e.g., a turbine and a compressor), instead of a turbopump assembly.
The NTP system 100 uses the nuclear reactor core 101, such as a compact fission reactor core that includes nuclear fuel, to generate many megawatts of thermal power (MWt) required to heat a combined moderator-propellant 102 to high exhaust temperatures for rocket thrust. The nuclear reactor core 101 provides thermal energy to drive the combined moderator-propellant pump 140. Operating the NTP system 100 during its various phases (startup, full thrust, and shutdown) is carried out by controlling the combined moderator-propellant 102 that is supplied via the combined moderator-propellant pump 140, to reach a desired reactor power level of the nuclear reactor core 101.
In
The combined moderator-propellant pump 140 includes one or more sub-pumps. These sub-pumps can be dispersed anywhere along the combined moderator-propellant flow path 120 to increase, decrease, or stop the flow of combined moderator-propellant 102 along the combined moderator-propellant flow path 120.
The combined moderator-propellant pump 140 transfers combined moderator-propellant 102 from the propellant tank 151 through the nuclear reactor core 101 along the combined moderator-propellant flow path 120. The combined moderator-propellant flow path 120 first flows the combined moderator propellant 102 through the moderator region 113.
The combined moderator-propellant 102 is stored as a liquid in the propellant tank 151 of the NTP system 100 propulsion stage. Then the combined moderator-propellant 102 is pressurized by a combined moderator-propellant pump 140, circulated though the moderator region 113 of the nuclear reactor core 101, and then circulated through the nuclear fuel region 114 of the nuclear reactor core 101, finally leaving the nuclear reactor core 101 as propellant. This approach removes the need and mass associated with a separate solid moderator, such as graphite or zirconium hydride (ZrH).
The moderator region 113 thermalizes fast neutrons resulting from nuclear fission events and is designed to generally decrease the speed of fast neutrons emitted by fuel assemblies 204A-N (see
The combined moderator-propellant 102 is initially heated while within the moderator region 113, as compared to the propellant tank 151. This initial heating will allow the fuel region 114 to overcome a smaller temperature differential between the temperature of the combined moderator-propellant 102 in the propellant tank 151. The initially heated combined moderator-propellant 102 then flows through the fuel region 114 where the heated combined moderator-propellant 102 is superheated. Finally, the combined moderator-propellant 102 ultimately flows to a chamber 170 (e.g., a thrust chamber, such as a rocket chamber).
The combined moderator-propellant flow path 120 may pass through the moderator region 113 multiple times, for example through a combined moderator-propellant return 241 in
The initially heated combined moderator-propellant fuel path 102 then exits the moderator region 113 and enters the fuel region 114. When within the fuel region 114, the combined moderator-propellant 102 is primarily acting in the role of a propellant. The fuel region 114 includes the fuel assemblies 204A-N, which superheat the combined moderator-propellant 102 passing through the fuel region 114 along the combined moderator-propellant flow path 120 toward the thrust chamber 170.
Selective fluid communication of the combined moderator-propellant 102 in the combined moderator-propellant flow path 120 can be achieved with a valve and an actuator. Each valve can be electronically or mechanically operated by one or more actuators. The valves can be spring loaded to one position and electrically actuated to another position to adjust valve position and hence propellant density via electric signals from a computer. Mechanically activated valves can be advantageous for control of liquid propellant flows; whereas, electrically activated valves can be used for lighter loads, such as gaseous propellant flows. For example, each valve facilitating selective communication of combined moderator-propellant 102 is controlled by an actuator via mechanical energy, such as hydraulic fluid pressure, pneumatic pressure, thermal energy, or magnetic energy. The actuator can be controlled by external mechanical energy or electronic circuitry, for example, the actuator can be driven by electric current control signals from a computer, microcontroller, digital or analog circuit, etc. The actuator can be a solenoid, variable displacement pump, electric motor, hydraulic cylinder, pneumatic, screw jack, ball screw, hoist, rack and pinion, wheel and axle, chain drive, servomechanism, stepper motor, piezoelectric, shape-memory, electroactive polymer, thermal bimorph, etc. In one example, the actuator is an internally piloted solenoid valve that acts directly on the valve. The valve and the actuator can collectively form a solenoid valve or a servovalve, such as an electrohydraulic servo valve. It may be advantageous for each valve to include multiple actuators, such as a solenoid driven by conveyed electric control signals that, in turn, acts on other actuators, such as a larger rack and pinion actuator, that in turns controls a pneumatically actuated valve, for example.
Using the combined moderator-propellant 102 removes the difficulties associated with the hydrogen (H2) propellant normally used in NTP systems. Hydrogen propellant as used in many NTP concepts must be stored at cryogenic temperatures (< 30 Kelvin (K)) and is a very low-density propellant. As such, the mass for tanks to store H2 and equipment for keeping H2 cryogenic have a large mass. As a particular example, in order to store 10,000 kg of propellant, when using cryogenic H2, the propellant tank would weigh an additional 8,621 kilograms (kg). As an alternative, 10,000 kg pressurized NH3 would only have a propellant tank 151 weighing an additional 780 kg. This results in a 600 kilogram per cubic meter (kg/m3) propellant density for NH3, as opposed to a 71 kg/m3 propellant density for cryogenic H2. Additionally, cryogenic H2 is only a liquid up to -253° C., as opposed to NH3 which is liquid up to 47° C. (C) at 2 megapascals (MPa). Liquids are more suited to acting as a moderator than gases, and so H2 is unlikely to serve well as a combined moderator-propellant 102.
The superheated combined moderator-propellant 102 then moves into the thrust chamber 170, where the superheated combined moderator-propellant 102 is pressurized and forced through a nozzle 171 that includes a throat 172 and a skirt 173. The superheated combined moderator-propellant 102 is pressurized and forced through the throat 171 of the nozzle 171 and then the skirt 173 of the nozzle 171, thereby generating propulsion of the NTP system 100.
The combined moderator-propellant pump 140 is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine. The rotodynamic pump and driving gas turbine can be mounted on the same shaft, or sometimes geared together. The combined moderator-propellant pump 140 produces a high-pressure fluid of combined moderator-propellant 102 for feeding the nuclear reactor core 101, cooling components of the NTP system 100, and moderating the amount of neutron fluence within the nuclear reactor core 101.
When the combined moderator-propellant 102 is superheated to a gas in the fuel region 114 of the nuclear reactor core 101, the combined moderator-propellant 102 accelerates and is exhausted from the thrust chamber 170 for expansion in the nozzle 171. The thermal expansion of the combined moderator-propellant 102 through the throat 172 and the skirt 173 of the nozzle 171 provides thrust. Some of the superheated combined-moderator propellant 102 can be used to turn a driving gas turbine of the combined moderator-propellant pump 140 to drive the rotodynamic pump. Of note, some of the superheated combined moderator-propellant 102 may be returned, for example bled from the nuclear reactor core 101 via a bypass, to turn the driving gas turbine of the combined moderator-propellant pump 140 to drive the rotodynamic pump. Subsequently, the expansion cycle repeats.
The generated thrust propels a vehicle that houses, is formed integrally with, connects, or attaches to the NTP system 100, such as a rocket, drone, unmanned air vehicle (UAV), aircraft, spacecraft, missile, etc. The vehicle can include various control nozzles for steering and other components. In the depicted example, the NTP system 100 with the nuclear reactor core 101 is utilized in a space environment. For example, the NTP system 100 that includes the combined moderator-propellant 102 can be a nuclear thermal rocket reactor, nuclear electric propulsion reactor, Martian surface reactor, or lunar surface reactor. In addition, the NTP system 100 can be used in the propulsion of submarines or ships.
A solid reflector region 215 surrounds the array of fuel assemblies 204A-N and the moderator region 113 of the nuclear reactor core 101. The solid reflector region 215 redirects free neutrons back toward the nuclear reactor core 101, increasing the number of fissile reactions, energy production, and nuclear reactor core 101 operating temperature.
A plurality of circumferential control drums 220A-F may surround the array of fuel assemblies 204A-N to change reactivity of the nuclear reactor core 101 by rotating the control drums 220A-F. Multiple control drums 220A-F may be positioned in an area of the solid reflector region 215 to regulate the neutron population and reactor power level during operation. The solid reflector region 215 can include one more sold reflector block(s).
A control drum 220A includes a solid control drum reflector portion 216, which in this example is generally formed of a material with a high elastic scattering neutron cross section. When the solid control drum reflector portion 216 faces inwards towards the nuclear reactor core 101, the neutron flux increases, which increases the reactivity and operating temperature of the nuclear reactor core 101. The control drum 220A also includes a control drum absorber material 217, which can be formed of a neutron poison. Neutron poisons are isotopes or molecules with a high absorption neutron cross section particularly suited to absorbing free neutrons. When the control drum absorber material 217 faces inwards towards the nuclear reactor core 101, the neutron flux decreases, which decreases the reactivity and operating temperature of the nuclear reactor core 101.
The control drums 220A-F can be implemented like any control drums 115A-U described in
Typically, the control drums 220A-F and fuel assemblies 204A-N are the same length; however, it should be understood that the lengths can differ depending on the implementation. A portion of the nuclear reactor core 101 is boxed and labeled as element 290 and this nuclear reactor core detail area 290 is magnified in
In a first example, the fuel assemblies 204A-N can be implemented like the fuel elements 310A-N described in
NTP system 100 includes a solid reflector region 215 (e.g., an outer reflector region) located inside the pressure vessel 260. Solid reflector region 215 includes a plurality of reflector blocks laterally surrounding the plurality of fuel assemblies 204A-N and the moderator region 113.
NTP system 100 includes the nuclear reactor core 101, in which a controlled nuclear chain reaction occurs, and energy is released. The neutron chain reaction in the nuclear reactor core 101 is critical – a single neutron from each fission nucleus results in fission of another nucleus – the chain reaction must be controlled. By sustaining controlled nuclear fission, the NTP system 100 produces heat energy. In an example implementation, the nuclear reactor system 100 is implemented as a gas-cooled high temperature nuclear reactor core 101. However, the combined moderator-propellant 102 can be included in a large utility scale nuclear reactor, heat pipe nuclear reactor, molten-salt-cooled nuclear reactor, fuel-in-salt nuclear reactor, or a sodium-cooled fast nuclear reactor. For example, combined moderator-propellant 102 can be included in an NTP system 100, such as a gas-cooled graphite-moderated nuclear reactor, a fluoride salt-cooled high-temperature nuclear reactor with a higher thermal neutron flux than the gas-cooled graphite-moderated nuclear reactor, or a sodium fast nuclear reactor with a faster neutron flux than the gas-cooled graphite-moderated nuclear reactor.
As noted above, the NTP system 100 can also be implemented instead as a nuclear power plant in a terrestrial land application, e.g., for providing nuclear power (e.g., thermal and/or electrical power) for remote region applications including outer space, celestial bodies, planetary bodies, and remotes regions on Earth. For example, the NTP system 100 with combined moderator-propellant 102 is utilized in a space nuclear reactor 107 for electrical power production on a planetary surface. The nuclear reactor system 100 with the combined moderator-propellant 102 can be a small commercial fission power system for near term space operations, lunar landers, or a commercial fission power system for high-power spacecraft and large-scale surface operations, such as in-situ resource utilization.
The NTP system 100 can be designed to, for example, travel into space, land on a planetary body, perform extended operations, and return to space. In such an example, the NTP system 100 would utilize the combined moderator-propellant 102 in the nuclear reactor core 101 to traverse space to the planetary body. Once affixed to the planetary body, the NTP system 100 can instead use the combined moderator-propellant 102 as a moderator and a coolant, looping the combined moderator-propellant 102 through the fuel region 114, and bleeding off heat to power other instrumentation, much like how the combined moderator-propellant pump 140 can operate based on extra heat from the combined moderator-propellant 102. Once the operations on the planetary body are complete, the NTP system 100 can return to using the combined moderator-propellant 102 as a moderator and a propellant, returning the NTP system 100 into space.
Therefore, the NTP system 100 can also be a terrestrial power system, such as a nuclear electric propulsion (NEP) system for fission surface power (FSP) system. NEP powers electric thrusters such as a Hall-effect thruster for robotic and human spacecraft. FSP provides power for planetary bodies such as the moon and Mars. In the NEP and FSP power applications, the NTP system 100 heats the combined moderator-propellant 102 through a power conversion system (e.g., Brayton) to produce electricity. Moreover, in the NEP and FSP power applications, the NTP system 100 does not necessarily utilize the combined moderator-propellant 102 as a propellant, but rather as a working fluid that passes through a reactor inlet when producing power. In the NEP and FSP power applications, the moderator region 113 is still filled with and can be cooled via the reactor inlet combined moderator-propellant 102 (e.g., the flow coming out of a recuperator) before the combined moderator-propellant 102 passes through the fuel assemblies 204A-N.
As shown in
The solid control drum reflector portion 216 and the control drum absorber material 217 can be on opposing sides of the cylindrical shape, e.g., portions of an outer circumference, of the control drums 220A-F. The solid control drum reflector portion 216 can include a reflector substrate shaped as a cylinder or a truncated portion thereof. The control drum absorber material 217 can include an absorber plate or an absorber coating. The absorber plate or the absorber coating are disposed on the reflector substrate to form the cylindrical shape of each of the control drums 220A-F. For example, the absorber plate or the absorber coating covers the reflector substrate formed of the reflector material to form the control drums 220A-F. When the solid control drum reflector portion 216 is the truncated portion of the cylinder, the control drum absorber material 217 is a complimentary body shape to the truncated portion to form the cylindrical shape.
Control drums 220A-F can be formed of a continuous surface, e.g., rounded, aspherical, or spherical surfaces to form a cylinder or other conical surfaces to form a quadric surface, such as a hyperboloid, cone, ellipsoid, paraboloid, etc. Alternatively or additionally, the control drums 220A-F can be formed of a plurality of discontinuous surfaces (e.g., to form a cuboid or other polyhedron, such as a hexagonal prism). As used herein, “discontinuous” means that the surfaces in aggregate do not form a continuous outer surface 165 that is round (e.g., circular or oval) perimeter of the control drums 220A-F. In
Rotating the depicted cylindrical-shaped control drums 220A-F changes proximity of the control drum absorber material 217 (e.g., boron carbide, B4C) of the control drums 220A-F to the nuclear reactor core 101 to alter the amount of neutron reflection. When the solid control drum reflector portion 216 is inwards facing towards the nuclear reactor core 101 and the control drum absorber material 217 is outwards facing, neutrons are scattered back (reflected) into the nuclear reactor core 101 to cause more fissions and increase reactivity of the nuclear reactor core 101. When the control drum absorber material 217 is inwards facing towards the nuclear reactor core 101 and the solid control drum reflector portion 216 is outwards facing, neutrons are absorbed and further fissions are stopped to decrease reactivity of the nuclear reactor core 101.
The outer solid reflector region 215 can be filler elements disposed between outermost nuclear fuel assemblies 204A-N and the control drums 220A-F as well as around the control drums 220A-F. The solid reflector region 215 can be formed of a moderator that is disposed between the outermost fuel assemblies 204A-N and an optional barrel (e.g., formed of beryllium). The solid reflector region 215 can include hexagonal or partially hexagonal shaped filler elements and can be formed of a neutron moderator (e.g., beryllium oxide, BeO). Although not required, NTP system 100 can include the optional barrel (not shown) to surround the bundled collection that includes the moderator region 113, fuel region 114, of the nuclear reactor core 101, as well as the solid reflector region 215. As depicted, the control drums 220A-F reside on the perimeter of the pressure vessel 260 and can be interspersed or disposed within the solid reflector region 215, e.g., surround a subset of the filler elements (e.g., solid reflector blocks) forming the reflector 140.
Pressure vessel 260 can be formed of aluminum alloy, carbon-composite, titanium alloy, a radiation resilient SiC composite, nickel-based alloys (e.g., Inconel™ or Haynes™), or a combination thereof. Pressure vessel 260 and NTP system 100 can be comprised of other components, including cylinders, piping, and storage tanks that transfer the combined moderator-propellant 102 that flows through the moderator region 113, the combined moderator-propellant return 241 (see
In
The combined moderator-propellant return 241 is then internally bounded by the inner can 242. Both the outer can 240 and the inner can 242 can be non-radioactive metal alloys, and serve the purpose of separating different volumes, portions, or segments of the combined moderator-propellant 102A from interacting with other combined moderator-propellant 102B at a different stage on the combined moderator-propellant flow path 120. The combined moderator-propellant return 241 can also be selectively coupled with the coolant channels 246A-N in order to behave as a dual pass heat exchanger. Adjusting a density of the combined moderator propellant 102 in the combined moderator-propellant return 241 can control the reactivity of the nuclear reactor core 101.
Between the nuclear fuel 244 itself and the inner can 242 is an outer insulator layer 243. Additionally, within the nuclear fuel 244 are multiple coolant channels 246A-N, with inner insulator layers 245A-N between each coolant channel 246A-N and the nuclear fuel 244. The inner insulator layer 245A and outer insulator layer 243 are formed of a high-temperature thermal insulator material with low thermal conductivity. The high-temperature thermal insulator material can include low density carbides, metal-carbides, metal-oxides, or a combination thereof. More specifically, the high-temperature thermal insulator material includes low density SiC, stabilized zirconium oxide, aluminum oxide, low density ZrC, low density carbon, or a combination thereof.
The coolant channels 246A-N are in the combined moderator-propellant flow path 120, between the moderator region 113 and the thrust chamber 170. The nuclear fuel 244 superheats the combined moderator-propellant 102 within the coolant channels 246A-N, placing approximately all of the combined moderator-propellant 102 in a superheated gaseous state as it enters the thrust chamber 170.
Each of the fuel assemblies 204A-N includes a nuclear fuel 244. The nuclear fuel 244 includes a fuel compact comprised of coated fuel particles, such as tristructural-isotropic (TRISO) fuel particles embedded inside a high-temperature matrix. In some implementations, the nuclear fuel 244 includes a fuel compact comprised of bistructural-isotropic (BISO) fuel particles embedded inside the high-temperature matrix. In yet another implementation, the nuclear fuel 244 includes a fuel compact comprised of a variation of TRISO known as TRIZO fuel particles. A TRIZO fuel particle replaces the silicon carbide layers of the TRISO fuel particle with zirconium carbide (ZrC). Alternatively, the TRIZO fuel particle includes the typical coatings of a TRISO fuel particle and an additional thin ZrC layer coating around the fuel kernel, which is then surrounded by the typical coatings of the TRISO fuel particle. In a further implementation, the nuclear fuel 244 includes a fuel compact comprised of a variation of BISO known as UN BISO fuel particles. A UN BISO fuel particle includes a fuel kernel of uranium nitride (UN). The high-temperature matrix includes silicon carbide, zirconium carbide, titanium carbide, niobium carbide, tungsten, molybdenum, or a combination thereof. Each of the TRISO fuel particles can include a fuel kernel surrounded by a porous carbon buffer layer, an inner pyrolytic carbon layer, a binary carbide layer (e.g., ceramic layer of SiC or a refractory metal carbide layer), and an outer pyrolytic carbon layer. The refractory metal carbide layer of the TRISO fuel particles can include at least one of titanium carbide (TiC), zirconium carbide (ZrC), niobium carbide (NbC), tantalum carbide, hafnium carbide, ZrC—ZrB2 composite, ZrC—ZrB2—SiC composite, or a combination thereof. The high-temperature matrix can be formed of the same material as the binary carbide layer of the TRISO fuel particles.
A description of TRISO fuel particles dispersed in a silicon carbide matrix to form a cylindrical shaped nuclear fuel compact is provided in the following patents and publications of Ultra Safe Nuclear Corporation of Seattle, Washington: U.S. Pat. No. 9,299,464, issued Mar. 29, 2016, titled “Fully Ceramic Nuclear fuel and Related Methods”; U.S. Pat. No. 10,032,528, issued Jul. 24, 2018, titled “Fully Ceramic Micro-encapsulated (FCM) fuel for CANDUs and Other Reactors”; U.S. Pat. No. 10,109,378, issued Oct. 23, 2018, titled “Method for Fabrication of Fully Ceramic Microencapsulation Nuclear Fuel”; U.S. Pat. Nos. US 9,620,248, issued Apr. 11, 2017 and 10,475,543, issued Nov. 12, 2019, titled “Dispersion Ceramic Micro-encapsulated (DCM) Nuclear Fuel and Related Methods”; U.S. Pat. Pub. No. 2020/0027587, published Jan. 23, 2020, titled “Composite Moderator for Nuclear Reactor Systems”; and U.S. Pat. No. 10,573,416, issued Feb. 25, 2020, titled “Nuclear Fuel Particle Having a Pressure Vessel Comprising Layers of Pyrolytic Graphite and Silicon Carbide,” the entireties of which are incorporated by reference herein. As described in those Ultra Safe Nuclear Corporation patents, the nuclear fuel can include a cylindrical fuel compact or pellet comprised of TRISO fuel particles embedded inside a silicon carbide matrix to create a cylindrical shaped nuclear fuel compact. A description of TRISO, BISO, or TRIZO fuel particles dispersed in a zirconium carbide matrix to form a cylindrical shaped nuclear fuel compact is provided in U.S. Pat. Pub. No. 2021/0005335 to Ultra Safe Nuclear Corporation of Seattle, Washington, published Jan. 7, 2021, titled “Processing Ultra High Temperature Zirconium Carbide Microencapsulated Nuclear Fuel,” the entirety of which is incorporated by reference herein.
Even without the major coolant plenum 261, however, there is both a photon shield 262 and a neutron shield 263 to protect sensitive components or humans. Much like the moderator region 113 and the control drum coolant gaps 219A-F, the photon shield 262 and neutron shield 263 are also filled with combined moderator-propellant 102, and in selective fluid communication with the combined moderator-propellant flow path 120. The combined moderator-propellant 102 can be highly pressurized in order to facilitate the functioning of the photon shield 262 and neutron shield 263.
On the combined moderator-propellant flow path 120, in order to properly distribute combined moderator-propellant 102 to the coolant channels 246A-N of the fuel assemblies 204A-N, the combined moderator-propellant 102 passes through a coolant intake manifold 269. The coolant intake manifold 269 includes an upper plate 264, and upper coolant plenum 265, a lower plate 266, and a lower coolant plenum 267. The upper coolant plenum 265 and lower coolant plenum 267 are in fluid communication with the combined moderator-propellant flow path 120, and properly structure the combined moderator-propellant 102 to serve as propellant. The coolant intake manifold 269 and the major coolant plenum 261 are protected from the radioactivity of the nuclear reactor core 101 by an inner pressure vessel 268.
Once the superheated combined moderator-propellant 102 is expelled from the coolant channels 246A-N, the superheated combined moderator-propellant 102 enters the thrust chamber 170. The thrust chamber 170 builds substantial pressure, forcing the gaseous superheated combined moderator-propellant 102 through the throat 172 and then out of the skirt 173 of the nozzle 171, thereby producing thrust. The nuclear reactor core 101 is protected from the chamber 170 by a bottom plate 270. The thrust chamber 170 is typically positioned at the bottom of the nuclear reactor core 101.
Therefore,
Each fuel assembly 204A-N can further include: an insulator layer (shown as an outer insulator layer 243 in
In this example, the outer can 240 can be directly coupled to the moderator region 113. The insulator layer (shown as an outer insulator layer 243 in
The NTP system 100 can include a reflector region (e.g., either a solid reflector region 215 as shown in
The NTP system 100 can further include a coolant plenum (shown as major coolant plenum 261 in
NTP system can include a plurality of circumferential control drums 220A-F surrounding the moderator region 113. Each of the control drums 220A-F includes a reflector portion (e.g., either a solid reflector portion 216 as shown in
Additionally, the solid control drum reflector portion 216 in each control drum 220A-F has been replaced with a fluid control drum reflector portion 316. Therefore, in this example the fluid control drum reflector portion 316 is also is in fluid communication or selective fluid communication with the combined moderator-propellant flow path 120, along with the moderator region 113, and the fluid reflector region 315. At a certain point in the operation of the NTP system 100, the fluid control drum reflector portion 316 of any of the control drums 220A-F may be emptied, and the combined moderator-propellant 102 within the fluid control drum reflector portion 316 will be pumped by the combined moderator-propellant pump 140 out of the fluid control drum reflector portion 316, and ultimately into the coolant channels 246A-N to be used as propellant for the NTP system 100. Alternatively, only portions of the solid control drum reflector portion 216 are replaced with the fluid control drum reflector portion 316 comprised of the combined moderator-propellant 102. The combined moderator-propellant 102 may need to be pressurized within the fluid control drum reflector portion 316 in order to function in a similar manner to the solid control drum reflector region 216.
A portion of the nuclear reactor core 101 is boxed and labeled as element 390 and this nuclear reactor core detail area 390 is magnified in
In a similar manner, in order to keep the combined moderator-propellant 102 of the control drum coolant gaps 219A-F separate from the combined moderator-propellant 102 of the fluid control drum reflector portion 316 of the control drums 220A-F, a respective control drum reflector chamber 351A-F is formed in each control drum 220A-F. The control drum reflector chamber 351A can be a hollowed-out cavity or reservoir to hold the combined moderator-propellant 102. The control drum reflector chamber 351A can include at least one opening that is selectively opened/closed a valve that is controlled by an actuator. This control drum reflector chamber 351A-F allows for the combined moderator-propellant 102 of the control drum coolant gaps 219A-F to be kept at a separate pressure from the combined moderator-propellant 102 of the fluid control drum reflector portion 316 of the control drums 220A-F when the control drum coolant gap 219A-F is not in fluid communication with the fluid control drum reflector portion 316.
The sequence of couplings of the moderator region 113, control drum coolant gaps 219A-F, control drum reflector chambers 351A-F, fluid reflector region 315, combined moderator-propellant return 241, major coolant plenum 261, upper coolant plenum 265, and lower coolant plenum 267 can be varied, and any of the above components may flow combined moderator propellant 102 into any other component above. In this illustrated example, however, the fluid reflector region 315, control drum reflector chambers 351A-F, control drum coolant gaps 219A-F, and major coolant plenum 261, all selectively flow the combined moderator-propellant 102 into the moderator region 113. The moderator region 113 selectively flows the combined moderator-propellant 102 into the combined moderator-propellant return 241. The combined moderator-propellant return 241 flows the combined moderator-propellant 102 into the upper coolant plenum 265 and lower coolant plenum 267 of the coolant intake manifold 269. The coolant intake manifold 269 then flows the combined moderator-propellant 102 into the coolant channels 246A-N, which then flow into the thrust chamber 170, and the nozzle 171 (e.g., including throat 172 and skirt 173) before being expelled from the NTP system 100 to generate thrust.
Varying the pressure (which directly relates to density) of the combined moderator-propellant 102 in the components listed above can noticeably increase the reactivity of the nuclear reactor core 101. Higher pressure combined moderator-propellant 102 further reduces the speed of fast neutrons, more than lower pressure combined moderator-propellant 102. By increasing the pressure of the combined moderator-propellant 102 substantially, particularly in the moderator region 113, it is possible to affect the reactivity of the nuclear reactor core 101 without turning the control drums 220A-F. Therefore, the NTP system 100 that implements the combined moderator-propellant 102 can be constructed without control drums 220A-F based on the propellant density control techniques disclosed in U.S. Pat. No. 10,643,754 to Ultra Safe Nuclear Corporation of Seattle, Washington, issued May 5, 2020, titled “Passive Reactivity Control of Nuclear Thermal Propulsion Reactors” the entirety of which is incorporated by reference herein.
In
Therefore,
The NTP system 100 can include a reflector region (e.g., either a solid reflector region 215 as shown in
NTP system 100 can include a plurality of circumferential control drums 220A-F surrounding the moderator region 113. Each of the control drums 220A-F includes a reflector portion (e.g., either a solid reflector portion 216 as shown in
In
The performance calculations heavy lift vehicle plot 400A shows that the NH3 NTP system 100 is more efficient over the storable bipropellant system. The NH3 NTP performance line 401 is to the right of the storable bipropellant performance line 402, and the storable bipropellant performance line 402 never crosses the NH3 NTP performance line 401. Additionally, the NH3 NTP system 100 is able to transport between 2,500 kg and 4,000 kg more in maximum payload mass 415 for any given reasonable delta-v 410 mission velocity. The NH3 NTP system 100 is able to produce 700 to 3000 km/s more in delta-v 410 velocity for any reasonable maximum payload mass 415.
A central theme of
Hence, in
Geo mission equivalent 425A is the amount of delta-V 410 needed to move a heavy lift vehicle into a geospatial orbit, or an equivalent mission. Fast Mars orbit one way equivalent 425B is the amount of delta-V 410 needed to move a heavy lift vehicle into an orbit of Mars with no return to Earth, or an equivalent mission. LLO (lunar orbit) round trip equivalent 425C is the amount of delta-V 410 needed to move a heavy lift vehicle into an orbit of the moon with a return to Earth, or an equivalent mission. Ryugu round trip equivalent 425D is the amount of delta-V 410 needed to move a heavy lift vehicle to the Ryugu asteroid with a return to Earth in a manner similar to the Hayabusa2 mission, or an equivalent mission.
New Horizons dry mass equivalent 430A is the mass of the New Horizons spacecraft, or an equivalent mass. X-37B dry mass equivalent 430B is the mass of the X-37 Boeing orbital test vehicle, or an equivalent mass. GOES-17 weather satellite equivalent 430C is the mass of the GOES-17 environmental satellite, or an equivalent mass. Two average GEO satellite equivalent 430D is the average mass of two geospatial satellites, or an equivalent mass.
As in
In the performance calculations medium lift vehicle plot 500A of
Likewise, storable bipropellant performance line 402 of
In the depicted performance calculations Europa Clipper plot 600, the curves of the NH3 NTP performance line 601 and the storable bipropellant performance line 602 of
Likewise, storable bipropellant performance line 402 has an X-intercept at around 6.75 km/s delta-V, and a Y-intercept near 15,000 kg maximum payload mass 415, whereas storable bipropellant performance line 602 has an X-intercept at around 6.75 km/s delta-V, and a Y-intercept near 24,000 kg maximum payload mass 415.
The performance calculation Europa Clipper plot 600 indicates that the NH3 NTP system 100 would be able to transport 9,300 kg on a Jupiter transfer mission equivalent 625: meaning a 300 kg net payload could be transported. The storable bipropellant system is unable to generate enough Delta-V 410 to transport an unladen Europa Clipper on a Jupiter Transfer mission equivalent 625A, as the Europa Clipper is itself too massive.
Therefore,
The pressurized NH3 propellant tank 751 has a pressurized NH3 propellant tank diameter 721 of 3.2 meters (m) in order to hold 10,000 kg of pressurized NH3 propellant 701. This pressurized NH3 propellant tank diameter 721 of 3.2 meters results in an area of 10.24 meters squared (m2) and a volume of 68.9 meters cubed (m3).
The cryogenic H2 propellant tank 752 would have a cryogenic H2 propellant tank height 722 of 11.2 m, and a cryogenic H2 propellant tank diameter 732 of 4 m. This notional cryogenic H2 propellant tank height 722 of 11.2 m and notional cryogenic H2 propellant tank diameter 732 of 4 m results in a top area of 16 m2, a side area of 44.8 m2, and a volume of 179.2 m3. Therefore, the volume of the notional pressurized NH3 propellant tank 751 required to store the same mass of propellant as the notional cryogenic H2 propellant tank 752 is one third, which is a significant mass and form factor savings. Additionally, because the height reduction is so significant moving from the tall cylindrical notional cryogenic H2 propellant tank 752 to the pressurized NH3 propellant tank 751 that is spherical shaped, the pressurized NH3 propellant tank 751 has a smaller form factor and thus will be able to fit in substantially more NTP systems, while also utilizing smaller and more efficient fairings. Additionally, the pressurized NH3 propellant tank 751 is more likely to fit into fairings currently utilized in existing NTP systems, whereas the cryogenic H2 propellant tank 752 will fit in far fewer existing fairings, and would require substantial redesign of the existing fairings of existing NTP systems.
In addition, due to the fact that hydrogen propellant as used in many NTP concepts must be stored at cryogenic temperatures (< 30 Kelvin (K)), the mass of a notional cryogenic H2 propellant tank 752 to store H2 and the equipment for keeping H2 cryogenic are quite large. As a particular example, in order to store 10,000 kg of cryogenic H2 propellant 702, the cryogenic H2 propellant tank 752 would weigh an additional 8,621 kilograms (kg). As an alternative, 10,000 kg pressurized NH3 propellant 701 would only have a pressurized NH3 propellant tank 751 weighing an additional 780 kg. This results in a 600 kilogram per cubic meter (kg/m3) propellant density for NH3 in the pressurized NH3 propellant tank 751, as opposed to a 71 kg/m3 propellant density for cryogenic H2 propellant 702 in the notional cryogenic H2 propellant tank 752. Additionally, cryogenic H2 propellant 702 is only a liquid up to 253° C., as opposed to pressurized NH3 propellant 701 which is liquid up to 47° C. (C) at 2 megapascals (MPa). Liquids are more suited to acting as a moderator than gases, and so cryogenic H2 propellant 702 is unlikely to serve well as a combined moderator-propellant 102. Therefore, using the pressurized NH3 propellant 701 as the combined moderator-propellant 102 removes the difficulties associated with the cryogenic H2 propellant 702 normally used in NTP systems.
The potential propulsion technology chart 800 has row headers identifying criteria for determining whether a certain propulsion technology 860 is suited for a particular extraterrestrial mission. The criteria include: utilizing non-cryogenic propellants 810; whether the technology fits into commercial launch vehicle (CLV) fairings with room for payloads 820; whether the propulsion technology is green 830 like the propulsion technology tested for the Green propellant infusion mission by NASA; whether the propulsion technology is performs well in rapid and low gravity-loss orbital maneuvers 840; and whether the technology utilizes no more than a single fluid 850. As the results 811-817, 821-827, 831-837, 841-847, 851-857 indicate, only the NH3 NTP system 100 has results 811, 821, 831, 841, 851 with all passing marks. All other propulsion technologies 802-807 disclosed have some failing results 812-814, 822, 827, 835, 846-847, 853-855, 857 indicating that those technologies 802-807 are not as suited to extraterrestrial propulsion as the NH3 NTP system 100 based on these criteria 810, 820, 830, 840, 850. In particular, H2 NTP 802 as discussed in
The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows and to encompass all structural and functional equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections 101, 102, or 103 of the Patent Act, nor should they be interpreted in such a way. Any unintended embracement of such subject matter is hereby disclaimed.
It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “containing,” “contain”, “contains,” “with,” “formed of,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises or includes a list of elements or steps does not include only those elements or steps but may include other elements or steps not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by “a” or “an” does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various examples for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed examples require more features than are expressly recited in each claim. Rather, as the following claims reflect, the subject matter to be protected lies in less than all features of any single disclosed example. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present concepts.
This application claims priority to U.S. Provisional Pat. Application No. 63/066,422, filed on Aug. 17, 2020, titled “Combined Ammonia-Based Moderator and Propellant for Nuclear Thermal Propulsion Stages,” the entire disclosure of which is incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/046274 | 8/17/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63066422 | Aug 2020 | US |
