Patent Application
20240212871
Future space exploration beyond low-earth orbit brings significant engineering and environmental challenges to the forefront. Among these are the ability to provide reliable power at substantive scale for energy-intensive operations such as material processing, transportation, and thermal conditioning. NASA's trajectory towards returning to the Moon will involve significant human and machine presence in locations beyond those surveyed in the late 1960's and 1970's during Apollo.
For the six human landings on the Moon, all of the locations visited were in the hemisphere of the Moon which continually faces the Earth. Furthermore, these locations were all at relatively low lunar latitudes. While scientifically valuable, these six missions essentially comprise a very small sample of the ensemble lunar environment. With a surface area roughly equal to the continent of Africa, the Moon has many more environments left to explore.
The discovery of volatiles at the lunar poles—including up to six billion tons of water ice—opens up the possibility for resource utilization in-situ, including the manufacturing of propellant, oxygen for human consumption. The indigenous presence of water offers the potential for significant savings on the transportation a primary and essential material needed to support and sustain human presence.
However, the presence of water on the Moon is found to be locked up in locations that are perpetually dark. Cratered regions near the lunar poles, and in particular the South Pole Aitken Basin Region, possess geologically depressed areas which do not receive sunlight during any portion of the Moon's path around the Earth. These ‘cold traps’ have temperatures that can be as low as 20-30 K, and are the reason that volatiles such as water have not boiled off or been lost to the space environment. Adjacent to these locations are ‘peaks of eternal light’ where the sun is continually shining. Thus the valuable water resources needed to sustain exploration, and the access to power that might help one process these resources, are geographically located in a ‘mutually exclusive’ arrangement, separated not only in distance, but also in elevation, with significant harsh terrain in-between. Consequently, processing of volatiles found within perpetually-dark crater floors will require not only the basic energy needed to separate the volatiles from regolith, but also significant amounts of heat energy to keep the equipment warm, long-term sustainability to enable minimal energy resupply activities, be impervious to cosmic particle radiation, and serve many different tasks (charging vehicles, powering processing equipment, lights, heat, telemetry, etc.).
Mobility of any surface power supply itself is likely to be quite limited, either due to engineering constraints or terrain limitations. The logistical challenge of ‘stringing power cables’ from the areas of perpetual light into the floor of permanently shadowed craters is significant, and creates further failure modes, infrastructure maintenance, and reliability issues.
Therefore, there is a need for a self-contained nuclear power source (reactor) which is modularized to fit atop a dedicated small lunar lander, such as those being designed for early robotic missions in the ‘second wave’ of lunar exploration after Apollo. Implementations of the present disclosure are directed to these and other concerns.
Nuclear reactor cores and related systems are described herein. An example nuclear reactor core includes a plurality of fuel modules, where each of the plurality of fuel modules includes nuclear fuel; at least one fuel-module actuator mechanically coupled to at least one of the plurality of fuel modules, where the at least one fuel-module actuator is configured to rotate the at least one of the plurality of fuel modules; and at least one neutron source configured to emit neutrons and trigger a fission chain reaction in the at least one of the plurality of fuel modules.
Optionally, the fission chain reaction is in a subcritical condition. In some implementations, the at least one neutron source is further configured to sustain the fission chain reaction in the at least one of the plurality of fuel modules. Optionally, the fission chain reaction is in a critical condition.
In some implementations, the at least one neutron source is positioned inside of the at least one of the plurality of fuel modules, outside of the at least one of the plurality of fuel modules, or at or near a surface of the nuclear reactor core.
Alternatively or additionally, the nuclear reactor core includes at least one source actuator mechanically coupled to the at least one neutron source, where the at least one source actuator is configured to reposition the at least one neutron source.
In some implementations, the at least one neutron source is a plurality of neutron sources. Alternatively or additionally, each of the plurality of neutron sources is configured to emit neutrons and trigger the fission chain reaction in a respective one of the plurality of fuel modules. Optionally, in some implementations, each of the plurality of neutron sources is further configured to sustain the fission chain reaction in a respective one of the plurality of fuel modules. Alternatively or additionally, each of the plurality of source actuators is mechanically coupled to a respective one of the plurality of neutron sources, and where each of the plurality of source actuators is configured to reposition the respective one of the plurality of neutron sources.
In some implementations, the at least one neutron source includes an alpha-neutron (α, n) source. Optionally, the at least one neutron source includes Americium (Am)-beryllium (Be), plutonium (Pu)—Be, or radium (Ra)—Be.
In some implementations, each of each of the plurality of fuel modules has a cylindrical shape.
In some implementations, where the plurality of fuel modules is three fuel modules.
In some implementations, the nuclear fuel is distributed throughout each of each of the plurality of fuel modules. Alternatively or additionally, the nuclear fuel is arranged in one or more strips. Alternatively or additionally, where the nuclear fuel is arranged in one or more rings.
In some implementations, each of the plurality of fuel modules has a three-dimensional shape that defines an axial direction, and the nuclear fuel is arranged in at least one axial slice formed in at least one of the plurality of fuel modules. Alternatively, each of the plurality of fuel modules has a three-dimensional shape that defines a radial direction, and the nuclear fuel is arranged in at least one radial slice formed in at least one of the plurality fuel modules.
In some implementations, the nuclear fuel is high enriched uranium or low enriched uranium.
In some implementations, the nuclear reactor core further includes a vessel, where the plurality of fuel modules are housed in the vessel. Optionally, the at least one neutron source is housed in the vessel. Alternatively or additionally, the at least one fuel-module actuator is optionally housed in the vessel.
In some implementations, the nuclear reactor core further includes a neutron moderator, where the neutron moderator is arranged within the nuclear reactor core. Optionally, the neutron moderator is arranged inside of the at least one of the plurality of fuel modules, outside of the at least one of the plurality of fuel modules, or at or near a surface of the nuclear reactor core. The neutron moderator is configured to reduce the speed of neutrons within the nuclear reactor core. Alternatively or additionally, the neutron moderator is configured to scatter neutrons back towards the nuclear fuel. Optionally, the neutron moderator includes graphite. Optionally, the at least one neutron source is configured to move relative to the neutron moderator.
In some implementations, each of the plurality of fuel modules includes a cooling channel.
An example nuclear reactor system is also described herein. The system includes a nuclear reactor core; and a controller comprising a processor operably coupled to a memory, the memory having computer-executable instructions stored thereon that, when executed by the processor, cause the processor to control the at least one fuel-module actuator and/or the at least one neutron source to control a rate of the fission chain reaction in the at least one of the plurality of fuel modules.
Another nuclear reactor system is also described herein. The system includes: a nuclear reactor core and an energy conversion system thermally coupled to the nuclear reactor core. Optionally, the energy conversion system is configured to convert heat from the fission chain reaction in the at least one of the plurality of fuel modules to electricity.
In some implementations, the energy conversion system is a thermionic energy converter. Optionally, the thermionic energy converter includes: an emitter electrode; a collector electrode; and a load line coupling the emitter and collector electrodes, where the emitter electrode is thermally coupled to the at least one of the plurality of fuel modules. Optionally, the emitter and collector electrodes are disposed in a vacuum chamber comprising a gas vapor.
In some implementations, the system includes a power source configured to store energy for nuclear reactor startup operations.
In some implementations, the system includes a heat exchanger thermally coupled to the nuclear reactor core and/or the energy conversion system, where the heat exchanger is configured to remove heat from the nuclear reactor core and/or the energy conversion system. Optionally, the heat exchanger is configured to circulate a fluid.
A modular system is also described herein. The system includes a plurality of nuclear reactor cores comprising a first nuclear reactor core and a second nuclear reactor core. Optionally, the system includes an energy conversion system thermally coupled to the plurality of nuclear reactor cores. Optionally, the energy conversion system is a thermionic energy converter. Alternatively or additionally, the system further includes a heat exchanger thermally coupled to the plurality of nuclear reactor cores and/or the energy conversion system, where the heat exchanger is configured to remove heat from the plurality of nuclear reactor cores and/or the energy conversion system.
An example fuel module is also described herein. The fuel module includes a cylinder with two flat end surfaces and a curvilinear surface extending between the two flat end surfaces; nuclear fuel arranged in at least one fuel channel formed on the curvilinear surface of the cylinder; and at least one coolant channel extending between the two flat end surfaces of the cylinder.
In some implementations, the nuclear fuel includes high enriched uranium or low enriched uranium. Optionally, where the at least one fuel channel is helically shaped.
Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be protected by the accompanying claims.
The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. As used in the specification, and in the appended claims, the singular forms “a,” “an,” “the” include plural referents unless the context clearly dictates otherwise. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. The terms “optional” or “optionally” used herein mean that the subsequently described feature, event or circumstance may or may not occur, and that the description includes instances where said feature, event or circumstance occurs and instances where it does not. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, an aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. As used herein, the terms “about” or “approximately” when referring to a measurable value such as an amount, a percentage, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, or ±1% from the measurable value.
Implementations of the present disclosure include nuclear reactor cores and systems that can be configured to generate thermal and/or electrical energy. In some implementations, the cores and systems operate in a subcritical condition. In other implementations, the cores and systems operate in a critical condition. With reference to
The reactor vessel 102 can include one or more rotating fuel modules 110. In the non-limiting examples in the present disclosure, the fuel modules are interchangeably described as “rotating fuel cylinders” and “rotating fuel drums.” However, this disclosure contemplates that the fuel modules 110 can be made in other geometric shapes. As described herein, each fuel module 110 can be mechanically coupled to a respective fuel-module actuator that is configured to rotate its fuel module. Motor(s) 114 shown in
The rotating fuel cylinders can optionally be partially or entirely surrounded by a neutron moderator 112. Neutron moderator 112 is configured to reduce the speed of neutrons travelling with the vessel 102. Alternatively or additionally, neutron moderator 112 is configured to scatter neutrons travelling within the vessel 102 back towards the nuclear fuel. A non-limiting example neutron moderator is graphite. Although graphite is provided as an example moderator, this disclosure contemplates that the moderator 112 can be made of a different material. A cross section of an implementation of a reactor vessel is illustrated in
The fuel modules 110 illustrated in
Based on the shape that the fuel strips/slices 302 form in the fuel modules 300, the configuration of the nuclear fuel can be changed by repositioning the neutron sources 202 and fuel modules 110 relative to one another. As described herein, the fuel modules 110, the neutron sources 202, or both fuel modules 110 and neutron sources 202 can be displaced by one or more actuators. Therefore, the relative positions of each of the neutron sources (e.g. the neutron sources 202 illustrated in
As illustrated in the perspective view of
The geometry of the fuel strips 302 can affect the rate of reaction of the nuclear fuel in the fuel strips. When the fuel drum 300 is used is used in a reactor core, e.g., as in the system 100 illustrated in
The present disclosure contemplates that different numbers of fuel strips can be used with different geometries and different amounts and types of fuel. As a non-limiting example, the fuel strips can be arranged helically around a curvilinear surface 306 of a cylinder, as shown in
In some implementations of the present disclosure, the fuel module 300 can include a shaft or attachment point 310 for turning the fuel drum 300.
Optionally, the controller can include one or more computing devices (e.g. the computing device illustrated in
The present disclosure contemplates that any kind of electrical generator 106 can be used to convert the heat produced by the reactor into electrical energy. In some implementations of the present disclosure, the electrical generator 106 is a thermionic generator, while other implementations of the present disclosure can use a gas-turbine generator. In some implementations of the present disclosure, the rotating fuel cylinders 110 can include cooling channels 118 configured for fluid (e.g., liquid or gas) flow through the rotating fuel cylinders. The fuel cylinders 110 illustrated in
Additionally, implementations of the present disclosure can include one or more control drums 116 located in the graphite moderator 112. The control drums 116 can include reflector materials configured to reflect neutrons back toward the fuel and/or absorber material configured to absorb neutrons. Additionally, the control drums 116 can include cooling channels 118. The control drums 116 illustrated in
The present disclosure contemplates that the system 100 can be operated as part of a larger system, e.g. as a single unit in a power plant with multiple nuclear reactors and generators. Similarly, the present disclosure contemplates that the system 100 can be operated using an external power source. For example, a secondary generator such as a solar panel or radioisotope thermoelectric generator (RTG). The present disclosure also contemplates that the system 100 can be operated in combination with an external power source that can provide backup power or startup power. For example, in some implementations the external power source can provide electrical energy to turn the motors 114 illustrated in
Additionally, the present disclosure contemplates that the system 100 can include any number of the components illustrated in
The present disclosure also contemplates that any number of reactor vessels 102 and generators 106 can be combined to create a power plant with a greater energy output than the individual generators. As a non-limiting example, the combined nuclear plant can include two of the reactor vessels illustrated in
It should be appreciated that the logical operations described herein with respect to the various figures may be implemented (1) as a sequence of computer implemented acts or program modules (i.e., software) running on a computing device (e.g., the computing device described in
Referring to
In its most basic configuration, computing device 2100 typically includes at least one processing unit 2106 and system memory 2104. Depending on the exact configuration and type of computing device, system memory 2104 may be volatile (such as random access memory (RAM)), non-volatile (such as read-only memory (ROM), flash memory, etc.), or some combination of the two. This most basic configuration is illustrated in
Computing device 2100 may have additional features/functionality. For example, computing device 2100 may include additional storage such as removable storage 2108 and non-removable storage 2110 including, but not limited to, magnetic or optical disks or tapes. Computing device 2100 may also contain network connection(s) 2116 that allow the device to communicate with other devices. Computing device 2100 may also have input device(s) 2114 such as a keyboard, mouse, touch screen, etc. Output device(s) 2112 such as a display, speakers, printer, etc. may also be included. The additional devices may be connected to the bus in order to facilitate communication of data among the components of the computing device 2100. All these devices are well known in the art and need not be discussed at length here.
The processing unit 2106 may be configured to execute program code encoded in tangible, computer-readable media. Tangible, computer-readable media refers to any media that is capable of providing data that causes the computing device 2100 (i.e., a machine) to operate in a particular fashion. Various computer-readable media may be utilized to provide instructions to the processing unit 2106 for execution. Example tangible, computer-readable media may include, but is not limited to, volatile media, non-volatile media, removable media and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. System memory 2104, removable storage 2108, and non-removable storage 2110 are all examples of tangible, computer storage media. Example tangible, computer-readable recording media include, but are not limited to, an integrated circuit (e.g., field-programmable gate array or application-specific IC), a hard disk, an optical disk, a magneto-optical disk, a floppy disk, a magnetic tape, a holographic storage medium, a solid-state device, RAM, ROM, electrically erasable program read-only memory (EEPROM), flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices.
In an example implementation, the processing unit 2106 may execute program code stored in the system memory 2104. For example, the bus may carry data to the system memory 2104, from which the processing unit 2106 receives and executes instructions. The data received by the system memory 2104 may optionally be stored on the removable storage 2108 or the non-removable storage 2110 before or after execution by the processing unit 2106.
It should be understood that the various techniques described herein may be implemented in connection with hardware or software or, where appropriate, with a combination thereof. Thus, the methods and apparatuses of the presently disclosed subject matter, or certain aspects or portions thereof, may take the form of program code (i.e., instructions) embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other machine-readable storage medium wherein, when the program code is loaded into and executed by a machine, such as a computing device, the machine becomes an apparatus for practicing the presently disclosed subject matter. In the case of program code execution on programmable computers, the computing device generally includes a processor, a storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. One or more programs may implement or utilize the processes described in connection with the presently disclosed subject matter, e.g., through the use of an application programming interface (API), reusable controls, or the like. Such programs may be implemented in a high level procedural or object-oriented programming language to communicate with a computer system. However, the program(s) can be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language and it may be combined with hardware implementations.
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric.
Implementations of the present disclosure can be used as power sources for space exploration applications. As an example, implementations of the present disclosure can be configured to deliver up to a few megawatts of usable power, and be modular and self-contained payloads that can be landed directly at a site where power is required, serve as a ‘charging base’ for vehicles, processing equipment, and constitute an important source of heat for permanently shadowed areas (e.g., portions of the moon). The reactor design can include of three rotating cylinders, with fuel distributed throughout each cylinder in fuel strips in a ‘barber pole’ arrangement. By tuning the geometry of the fuel, and the rotation of the cylinders, fine control of both the amount of generated power and the longevity of the reactor can be performed.
Example implementations of these reactor designs show that the reactor fits within a volume envelope of approximately 1 m3, and up to three individual reactor/landers can be arranged within the cross-section of a 3.5 m diameter rocket fairing. Consequently, these can be launched in bulk, either on a dedicated mission for a smaller launch vehicle, or as auxiliary/secondary payloads aboard larger vehicles such as NASA's Space Launch System (SLS). An example implementation can be configured to provide 3 MWatt of continuous power, with an expected lifetime of 5 years. Such a reactor can be manufactured ‘at scale,’ and is comprised of high enriched uranium (HEU) or low enriched fuel (LEU) with TRISO fuel.
The Small Modular Reactor (SMR) with the features of an evolutionary and lifetime core, simple and modular design, multiple “walkaway” passive safety systems, and autonomous control system with assorted instrumentation is disclosed that is also safe-guardable, cost competitive, and commercially viable. The Rotating Fuel Core with Fuel Strip (ROFFUS) SMR has a containment layout based on a sealed two chamber containment for the reactor vessel and the thermal power conversion system. Primary cost reduction is achieved by a compact design of each chamber that is a factory fabricated component and transportable by truck or rail to a nuclear power site.
Three sets of passive safety systems can be present that can remove the core decay heat without any AC power source or even any operator intervention for an indefinite period of time. In order to: (i) burn the fuel effectively, (ii) operate without refueling complexity, and, (iii) control the reactivity autonomously for operational and safety constraints, ROFFUS has: (1) inherent safety and intrinsic characteristics to avoid the need for continuous shifts of operators and security forces, (2) a lifetime core (a design choice), (3) a scalable design, and does not depend on novel components (such as a new fuel type) that require a multi-decade development program.
ROFFUS core can include several motor-operated rotating cylinders (RCs) to achieve a lifetime core and effective autonomous core control. The RCs can include: (i) three to six closely packed cylinders with a non-traditional fuel assembly, and, (ii) additional several cylinders that are typically control drums containing reflector and absorber material. The number of rotating fuel cylinders and total diameter can depend upon the desired power level. Each cylinder contains fuel and vertical cooling channels (CCs). The cylinders are imbedded in a larger cylindrical structure of graphite with no fuel and sufficient CCs to avoid overheating the graphite during operations from neutron and gamma heating. The integration of the components or inclusion in nuclear context, as well as the “candy stripe” fuel cylinders, are novel.
Two alternative evolutionary life-time core designs using RCs are considered in this example implementation of the present disclosure: (1) RCs with neutron absorbers (illustrated in
For RCs with neutron absorbers, both fuel and neutron absorbers can be used in RCs. The internal structure of each cylinder can contain separate fuel channels with TRISO fuel particles—the same basic fuel design of a prismatic-block high temperature gas cooled reactor (HTGR). The fuel cylinders can have the same cross section at any elevation but the TRISO fuel particles can have a special loading pattern in the vertical direction that is similar to a candy stripe—a spiral fuel loading pattern where at any horizontal level there is fuel on one side of the graphite cylinder but not on the other side. When the fuel cylinders are rotated so the fuel at a particular horizontal level is toward the reactor center, the reactor can go critical in that vertical position and produces power. This occurs at only one level of the cylinder because of the spiral pattern of fuel loading—at other levels the fuel in each cylinder is facing further outward. The reactor initiates operations with the fuel zone of each cylinder facing each other at the top of the reactor core. As that fuel zone is burnt out, the cylinders are rotated so the reactor zone moves downward in the reactor core. It is possible for rotation of the cylinders to move the active core region up and down on a regular basis to obtain relatively uniform burnup over the vertical height of each cylinder-a rotation over a period of several months. A long core life can be achieved by choosing an appropriate height for the reactor core. This design can also use neutron absorbers outside of the red ring 802 as illustrated
As illustrated in
Implementations of the present disclosure include a Source Driven Small Modular Reactor (SD-SMR) design that can operate autonomously for a long time in harsh environments (high cosmic ray and low temperatures). Implementations of the present disclosure which allow for the reactor operation in a subcritical condition can remove the need for control rods, simplify the reactor operation control, allow for natural cooling, the use of a “walkaway” passive safety system, provide flexibility in the use of different fuel compositions, and significantly diminish the feedback effects caused by the fuel burnup.
The core of the proposed SD-SMR is comprised of HEU or LEU TRISO fuel and graphite moderator. The TRISO fuel is placed in three cylindrical annuli, surrounded by graphite and the reactor vessel. To achieve a neutron balance, moveable neutron sources are placed within the fuel annuli, for example, as illustrated in
To achieve a power of 3-4 MW, a neutron flux of about 1.0×10{circumflex over ( )}12 #/cm-2 s can be required. For an Am—Be source,
Implementations of the disclosed reactor design can be suitable for commercial exploitation to provide power on the surface of the Moon.
The disclosed rector design can be a derivative High Temperature Gas Reactor (HGTR). Challenges in the neutronics modeling of HTGRs that were overcome include: (1) high burnup and high temperatures expected, (2) dealing with double fuel heterogeneity and spatial power oscillations, and (3) quantification of uncertainties. The MCNP and SERPENT codes were used to perform burnup calculations for the disclosed rector design and to develop a predictive model to optimize the rotation of the cylinders and movement of the sources to achieve uniform burnup over the vertical height, including possible impact of uncertainties.
Thermionic energy conversion (TEC) methods can be used to convert heat to electricity. Electrons evaporate from a hot cathode (heated by nuclear fuel) into a vacuum and can be collected by anode (cooled by helium coolant) to generate electric current. Implementations of the disclosed rector design's nuclear core can be cooled by helium gas flowing through the CCs in the RCs and control drums as well as bearing clearance, as illustrated in the thermal hydraulic model shown in
Materials aspects of the disclosed rector design are very similar to a HTGR and therefore rely on the knowledge developed under the U.S. Department of Energy (DOE) activities to qualify TRISO fuel particle, graphite and other structural components. Analysis was conducted to ensure that the disclosed rector design operation conditions fit into the irradiation conditions on the moon. The primary focus was verifying that the existing data were sufficient to ensure integrity of materials component under operating conditions suitable for autonomous control, online monitoring of components for maintenance and accident conditions, specifically focusing on reactivity insertions and decay heat removal.
Implementations of the present disclosure can include Direct Brayton Cycle based power generation cycle (PGC) as illustrated in
The design basis accidents and operational transients with disruptive consequences were evaluated using the RELAP5-3D and MELCOR codes. Safety assessment of the disclosed rector design was supported using a dynamic probabilistic safety assessment (DPSA) approach. DPSA is particularly appropriate for systems with passive safety features and digital instrumentation and control systems as with the disclosed rector design.
Implementations of the disclosed rector design can simplify the in-core instrumentation and reduce the number of required sensors, which, as a consequence, can reduce the complexity of the sensor network and the sensor fault probability. On the other hand, autonomy can require deployment of a larger number of sensors for reactor control and safety monitoring. Line sensors for distributed temperature sensing and sensor networks for flux mapping can be used to replace point sensors to provide both safety and health monitoring with less numbers but adequate information. One challenge is the inadequate radiation hardness evaluation for new sensor materials. A targeted experiment was performed for the down selection of the sensor candidates for temperature and neutron flux mapping.
The mass and dimensions of implementations of the disclosed rector design can it ideal for launch either in multiples within a dedicated launch vehicle, or as a secondary payload on a launch to Trans-Lunar Injection. Implementations of the disclosed rector design can be a dedicated, single, and modular payload aboard a robotic lander base, such as the small/medium Lander Designs pursued by NASA/Marshall Space Flight Center and the Johns Hopkins Laboratory in 2010. The construction models of ROFFUS4Space chambers were designed to reduce capital cost, while meeting U. S. Nuclear Regulatory Commission requirements for safety. Isolation systems were designed in ANSYS/ABAQUS platforms to reduce potential seismic effects from moonquakes—caused by lunar tides and meteoroid impacts—on safety-critical components and to achieve a nearly uniform design independent of characteristics of sites.
A modularized design can allow for shorter construction times to reduce financial exposure and schedule risk, primary reasons for nuclear terrestrial power plant high capital costs. The high degree of factory manufacturing and assembly results in less total need for construction support resources for project management and quality assurance and control.
A small lander (e.g., 155 kg dry mass) and its disclosed rector design payload can be decelerated in the lunar environment through the use of a STAR 30BP solid rocket motor attached to the bottom of the lander. Landing can be accomplished using three 445 N bi-propellant axial divert and attitude control system DACS engines which reduce the vertical and lateral velocity to ˜1 m/s, as well as six 30 N vernier engines to control spacecraft attitude.
All landing can be automated. Once landed, the reactor can be commissioned to provide all required heat and power for the duration of the mission. A warm-gas testing program of the prototype lander was accomplished successfully at NASA/Marshall in the early 2010's, making this technology high enough on the TRL scale (approximately TRL 7) to minimize further development costs.
Implementations of the present disclosure include source-driven subcritical reactor design that can operate autonomously for a long period of time in harsh environments (high cosmic ray and low temperatures). These implementations are referred to as Monet (autonoMous sOurce driveN rEacTor), and allow for the reactor operation in subcritical condition, removes the need for control rods, simplifies the reactor operation control, allows for natural cooling, allows for the use of a “walkaway” passive safety system, provides flexibility in the use of different fuel compositions, and significantly diminishes the feedback effects caused by the fuel burnup. The present disclosure includes a high level description of the proposed reactor concept and describes the power conversion system and space flight system integration.
Reactor Core: The core of implementations of the present disclosure is subcritical and is comprised of a variable enrichment low enriched (LEU) TRISO (TRi-structural ISOtropic particle) fuel, graphite moderator, and Am—Be neutron source. Implementations of the present disclosure can offer a safe, scalable, and autonomous design that can operate in the harsh moon environment. The subcriticality can eliminate the potential for reactor criticality accidents, provides significant flexibility in the fuel choice and its enrichment, and consequently can simplify reactor control. Additionally, to achieve a more uniform fuel burnup and eliminate the need for control rods, implementations of the present disclosure can perform rotation of fuel drums with variable fuel enrichment resulting in a barber-pole configuration (e.g. by forming one or more strips or slices of fuel in the fuel drums in a helical or “barber-pole” shape).
Implementations of the present disclosure can include different core designs with different amount of fuel, moderator, and source.
The common features among the above designs are: three fuel drums containing fuel annuli with sectors of different enrichments including 19.75%, 3.5%, and 0.72% (natural uranium); and, a central region of movable source. They differ in the thinner fuel annuli and presence of an outer source drum 1402 (light green region) in the implementation of the present disclosure illustrated in
For example implementation #1 (
For an implementation of the present disclosure with a drum design with 4 annuli of 2 cm thickness each, the fuel height used to achieve a given degree of subcriticality was determined. Additionally, the need for reflector outside the source regions was evaluated.
Additionally, for the core height of 73 cm, the self-shielding effect of each fuel annulus was examined by reducing the thickness from 2 cm to 1.5 cm and 1.0 cm, and also varying the number of annuli. The table 1, below, compares Monet mass and eigenvalue (i.e., degree of subcriticality) for a few cases.
The table above indicates that a reasonable degree of subcriticality can be achieved in implementations of the present disclosure by varying number and thicknesses of the annuli per fuel drum. Multi-variable the optimization studies can be performed considering key parameters such as the core weight and size, amount of the external source, the operating life, fuel drum rotation frequency, simplicity of reactor control system, feasibility of manufacturing, and the cost to determine an optimal core configuration depending on the mission objectives. For example, for the core designs presented in Table 1, the estimated total mass of the core is between 7 t to 8 t to generate about 10 kW. This mass can be reduced in some implementations by placing the source at regions with high neutron importance, which can be evaluated by determining the importance function associated with the fission neutrons throughout the reactor core. Additionally, in some implementations, it can be more effective if the required power is produced by a combination of smaller of modules that meet the existing weight limitation (i.e., 0.6 t) for placing the reactor on the surface of the moon. For example, for this non-limiting example implementation, 10-12 modules can meet the weight limitation and deliver the required power. This approach can introduce flexibility in the deployment and use of the reactors on the moon. Finally, it is important to note that the maximum power of the Monet design can be adjusted (due to its subcriticality condition) because it is directly related to the amount and arrangement of the external sources used. A machine learning (ML) algorithm can be used to enable adjustment of the rotation frequency of the fuel drums, and the movement of the sources for reactor control during normal and accident conditions.
Monte Carlo calculations were conducted to examine key system parameters such as degree of subcriticality, and the core mass and size.
Additionally,
The reactor mass increases from about 10 t to 31 t with increasing fuel drum diameter with graphite and fuel representing the major portion of this mass.
The present disclosure contemplates the use of other designs and combinations of fuel, moderator and source.
Our studies to date have demonstrated that maximum reactor power can easily be adjusted by changing the amount of source for the same reactor core design. Additionally, the core neutron economy (i.e., keff and subcritical multiplication M), fuel burnup, core life, and core weight can be optimized by considering different combinations of fuel, moderator, and source positioning and amount, different enrichments, and different rotation speeds. Alternative implementations of the present disclosure can include a single fuel drum, larger number of drums, different sizes of fuel regions of different enrichments, a single fuel enrichment, and other source placements (e.g., an external source annulus for each drum rather than the one annulus used in some implementations of the present disclosure, and reducing the amount of outside graphite.
To develop optimum designs of some implementations of the present disclosure, a detailed multi-variable study considering the parameters disclosed herein can be performed. Additionally, multiphysics studies can be performed to account for cooling strategies, temperature effects, and corresponding source movement, and an autonomous control system will be developed using machine learning algorithms which can utilize online measurements and computation.
Implementations of the present disclosure can be designed using ordinary manufacturing techniques and reactor fuels. This can increase the manufacturability of implementations of the present disclosure and/or reduce the cost of implementations of the present disclosure.
In some implementations of the present disclosure, a thermionic energy conversion (TEC) method can be used to convert heat to electricity.
Thermionic energy conversion is a direct conversion of heat energy into electrical energy. Therefore implementations of the present disclosure including thermionic energy conversion can perform the energy conversion with few or no moving parts, and increased reliability.
A part of thermal energy generated in the reactor core is directly translated into electricity by thermionic converters, and the leftover portion is removed as waste heat through the coolant system and radiator. Thermo-mechanical parameters, such as electrode temperatures, interelectrode irradiation coefficient, interelectrode gap size, could or might exert significant influence on characteristics of thermionic conversion. To achieve more precise predictions, thermionic conversion and circuits are coupled as shown in
Implementation of the present disclosure can be configured as a ‘lander agnostic’ payload, to the greatest extent possible, to enable delivery and operation across the broadest portfolio of NASA-selected landers within the Commercial Lunar Payload Services (CLPS) program, and to therefore also enable the broadest range of lunar surface applications. This approach is possible, in part, because implementation of the present disclosure can be powered off for launch, flight, and landing, and therefore can be essentially an inert mass for most of the dynamic phases of spaceflight.
Accordingly, implementations of the present disclosure can model the space flight system dimensions against basic mass, center-of-gravity, vibration, and thermal environments in the power-off configuration, thereby placing only minimum reliance (e.g., possible heaters for thermal maintenance) on the launch vehicle, lander, or spacecraft bus during all phases of the mission prior to activation on the lunar surface. This approach can simplify spacecraft/payload interfaces, reduce complexity, facilitate greater modularity in testing and development, and reduce cost.
A non-limiting example of a suitable lander that can include or transport implementations of the present disclosure is the lunar lander sold under the trademark Griffin, designed and built by Astrobotic of Pittsburgh, PA. This lander was selected by NASA to deliver the VIPER (Volatiles Investigating Polar Exploration Rover) rover to the vicinity of the Moon's south pole, in search of water and other volatiles essential for sustained human exploration.
An example of the Griffin is illustrated in
Additionally, the present disclosure contemplates that one or more parts of the reactor and/or generator can be transported separately and combined in situ. As an example, one lander can transport the reactor, while a second lander can transport the generator. Alternatively, one lander can transport some parts of the reactor and/or generator while other landers can transport other parts of the reactor and/or generator.
Implementations of the present disclosure can be derivative High Temperature Gas Reactors (HGTR). Challenges in the neutronics modeling of HTGRs can include: (1) high burnup and high temperatures expected, (2) dealing with double fuel heterogeneity and spatial power oscillations, and (3) quantification of uncertainties. The MCNP and SERPENT codes will be used to perform burnup calculations for implementation of the present disclosure and to develop a predictive model to optimize the rotation of the cylinders and movement of the sources to achieve uniform burnup over the vertical height, including possible impact of uncertainties.
Thermionic energy conversion (TEC) method can be used to convert heat to electricity. Electrons evaporate from hot cathode (heated by nuclear fuel) into a vacuum and are collected by anode (cooled by helium coolant) to generate electric current. The power generation cycle will be designed and optimized to maximize the generated electricity by using RELAP5-3D/SCDAP. The modified Reactor Excursion and Leak Analysis Program (RELAP5) with the implement of thermionic energy converter properties and heat transfer correlations is adopted to analyze the thermal-hydraulic (TH) characteristics of the space nuclear reactor. The power generation cycle will be designed and optimized to maximize the generated electricity by using RELAP5-3D/SCDAP. A RELAP5 model including the thermionic fuel elements (TFEs), reactor core, radiator, coolant loop and volume accumulator will be established. The temperature reactivity feedback effects of the fuel, TFE emitter, TFE collector, reflector, moderator and the reactivity insertion effects of control drums and safety drums will be considered in the model. The steady state condition will be simulated and analyzed. The maximum temperatures of the fuel and TFE components will be predicted to design the coolant channels of the fuel elements. The size and geometry of the coolant channels, the connections to the rest of the power conversion system will be designed and simulated in this task.
In some implementations of the present disclosure, strong feedback effects between TH and neutronics can be expected for small size HTGRs. Therefore, the transient behavior of an implementation of the present disclosure can be modeled by advanced coupled tools, such as RELAP/SCDAP and NESTLE, to capture the feedback effects of thermal-hydraulics, reactor kinetics, and fuel behavior. The coupling of codes models not only TH and neutronics of the fuel elements but also structural components of the power conversion system. Furthermore, the neutronic component is not limited to the sole core solver. The coupled code system encompasses TH material performance of the fuel, neutronic solver, and neutronic data preparation. This can provide a framework for coupling RELAP5/SCDAPSIM/MOD4.0 with a suite of neutron kinetics codes that includes NESTLE, DRAGON and/or a version of the ENDF library. This task will use nodal power distributions to calculate mechanical and thermal parameters such as heat-up, and meltdown of fuel rods and control rods, the release of fission products from fuel rods, and the disintegration of fuel rods into porous debris. On the neutronics side, this work will use the NESTLE and DRAGON codes. NESTLE solves up to four energy groups neutron diffusion equations utilizing the Nodal Expansion Method (NEM). The DRAGON code, developed at Ecole Polytechnique de Montreal, performs lattice physics calculations based on the neutron transport equation and is capable of using very fine energy group structures. In this work, the coupling approach to exchange data among the various modules will be used. In the coupling process, the generated nuclear data (in fine multigroup energy structure) will be collapsed down into two- or four-group energy structures for use in NESTLE. The power distribution results of the neutronic calculations will be transmitted to the thermal-hydraulics code. The spatial distribution of coolant density and the fuel-moderator temperature, which result from the TH calculations, will be transmitted back to the neutron kinetics codes and then the loop is closed using new neutronics results.
Material aspects of some implementations of the present disclosure can be similar to a HTGR and therefore design methods can rely on the knowledge developed under the U.S. Department of Energy (DOE) activities to qualify TRISO fuel particle, graphite and other structural components. Analysis can be conducted to ensure that implementations of the present disclosure conditions fit into the irradiation conditions on the moon. This can include verifying that the existing data are sufficient to ensure integrity of materials component under operating conditions suitable for autonomous control, online monitoring of components for maintenance and accident conditions, specifically focusing on reactivity insertions and decay heat removal.
The design basis accidents and operational transients with disruptive consequences can be evaluated using the RELAP5-3D and MELCOR codes. A RELAP5 model including the thermionic fuel elements (TFEs), reactor core, radiator, coolant loop and volume accumulator can be established. The temperature reactivity feedback effects of the fuel, TFE emitter, TFE collector, reflector, moderator and the reactivity insertion effects of control drums and safety drums will be considered in the model. Three severe transient accidents including reactivity insertion accident (RIA), loss of flow accident (LOFA) and loss of coolant accident (LOCA), will be simulated and analyzed. Test matrix can be prepared based on the wide range of boundary conditions will be used to run RELAP5. All these transients can define which transients and special boundary conditions can be considered as the limiting design basis accident(s). The maximum temperatures of the fuel and TFE components will be compared against the melting temperature of the components. In addition, the time for operator's response for the progress of these accidents can be predicted with the simulators to show that the calculation results prove that the reactor is a safe and reliable system or not.
Safety assessment can be supported using a dynamic probabilistic safety assessment (DPSA) approach. DPSA allows a unified framework to account for the joint effects of aleatory and epistemic uncertainties in predicting the distribution of risk associated with the system response and is particularly appropriate for systems with passive features as with the proposed concept due to the possible interaction of process, hardware and software in a compact design. The inputs for DPSA can be: #1: a time-dependent system model (which can be based on the system models described herein); #2: possible normal and abnormal system configurations (which can be based on the system configurations described herein), and, #3: transition probabilities (or rates) among the chosen configurations.
Additionally, the present disclosure contemplates that multiple phases of risk assessment can be performed. For example, the first phase can correspond to the launch phase where the reactor can be inert within the confines of the spacecraft. This can present a relatively low risk but can lead to damage of the reactor core. The second phase can correspond to the phase during which the reactor core is moved out of the spacecraft using the lander and deposited on the moon surface. Here again the risk can be limited to damaging the core. The third phase can correspond to the reactor installation phase. The final phase can correspond to reactor operation. It should be understood that these phases are intended only as examples, and that the safety of implementations of the present disclosure can be modeled using any number of phases where the phases include different activities from those described herein.
Common cause failures can be modeled as a separate system configuration or using other techniques (e.g., beta factor method) depending on data availability. Non-limiting examples of tools that are suitable for performing this analysis include DPSA tools ADAPT and RAVEN which can be coupled to the neutronic and TH codes used in the design process to identify and quantify the likelihood of possible risk modes. Determining data for transition probabilities can be a challenging input to the risk assessment since data can be scarce (if at all available) for hardware behavior under lunar conditions. If data are not available to quantify such behavior, then DPRA results on combination of system component failure modes that lead to undesirable consequences for the mission can be used to identify data needs for quantification. In addition, expert opinion elicitation in combination with Bayesian analysis can also be performed to obtain relevant estimates. The safety analysis can be performed iteratively based on experimental data. Additionally, modifiers can be used in the safety analysis to approximate the conditions of different environments (e.g., the moon's surface, outer space, etc.).
The construction models of reactor chambers can be designed to reduce capital cost, while meeting U. S. Nuclear Regulatory Commission requirements for safety. Moreover, the design of implementations of the present disclosure can take into account the types of forces that are likely to be encountered where the reactor is deployed. For example, isolation systems can be designed in ANSYS/ABAQUS platforms to reduce potential seismic effects from moonquakes—caused by lunar tides and meteoroid impacts—on safety-critical components and to achieve a nearly uniform design independent of characteristics of sites. A modularized design will allow shorter construction times to reduce financial exposure and schedule risk, primary reasons for nuclear terrestrial power plant high capital costs. The high degree of factory manufacturing and assembly will result in less total need for construction support resources for project management and quality assurance and control.
The mass and dimensions of implementations of the present disclosure can make it ideal for launch either in multiples within a dedicated launch vehicle, or as a secondary payload on any launch to Trans-Lunar Injection. Therefore, these implementations can be suitable as a dedicated, single, and modular payload aboard a robotic lander base, such as the small/medium Lander Designs pursued by NASA/Marshall Space Flight Center and the Johns Hopkins Laboratory in 2010. This can include configuring the implementations of the present disclosure so that they meet mass limits, volume constraints, launch and other acceleration loads, thermal environments that include cruise-phase and surface operations, telemetry, and power distribution. This design process can include several design and analysis iteration cycles.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
This application claims the benefit of U.S. provisional patent application No. 63/181,676, filed on Apr. 29, 2021, and titled “ROTATING FUEL CORE WITH FUEL STRIPS FOR SMALL MODULAR REACTOR,” the disclosure of which is expressly incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/027044 | 4/29/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63181676 | Apr 2021 | US |
