Small-scale nuclear reactor

Abstract

A small-scale nuclear reactor includes a reactor core, a primary heat transport system, a thermoelectric conversion system, a heat sink disposed externally of the reactor core, and a control system. The primary heat transport system is configured to circulate a working fluid (e.g., water) in a primary loop through the reactor core. The thermoelectric conversion system and the heat sink are thermally coupled to the primary heat transport system through heat exchangers. The thermoelectric conversion system comprises an Organic Ranking Cycle generator and a secondary heat transport system. The secondary heat transport system is configured to circulate an organic refrigerant in a secondary loop through the Organic Ranking Cycle generator. The control system regulates power output of the Organic Ranking Cycle generator by synchronously adjusting flow rates of the working fluid in the primary loop and the organic refrigerant in the secondary loop.

Description

SMALL-SCALE NUCLEAR REACTORREFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from United States Provisional Patent Application Serial No.63 / 761,672 filed Februaiy 21, 2025 entitled “NUCLEAR REACTOR CORE”. For the purposes of the United States, this application claims the benefit under 35 USC §119 of United States Provisional Patent Application Serial No. 63 / 761,672 filed February 21, 2025 entitled “NUCLEAR REACTOR CORE”, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates generally to nuclear reactors, and in particular to small-scale nuclear reactor core and fission assembly design. Some embodiments have example applications for generating power and providing heat in, for example, space, the lunar or planetary environment, or extreme and remote environments such as the Arctic.BACKGROUND

[0003] Small fission-based nuclear reactors are a promising source of power to support operations in extraterrestrial environments and in extreme or remote environments on Earth. These types of reactors may be used to establish microgrids in disaster relief zones and provide reliable power in remote communities. These types of reactors may also be utilized for hydrogen production and water desalination as clean water resources worldwide continue to decline, among other related applications.

[0004] In the Arctic, for example, there are significant infrastructure challenges and vulnerabilities within both military and civilian energy supply chains. Military installations often rely on fragile civilian power grids that are vulnerable to outages, and on regular fuel convoys that are logistically complicated and exposed to operational risks. These vulnerabilities not only hinder operational effectiveness but also pose a direct threat to continental security. The vulnerabilities have highlighted the need for safe, inexpensive, low-maintenance, kilowatt-scale energy systems that can be rapidly deployed to supply scalable, efficient, and sustainable off-grid or microgrid heat and power to regions like the Arctic.

[0005] In space and extraterrestrial environments, power is currently supplied primarily by low voltage power produced from photovoltaic (PV) and Radioisotope Thermoelectric Generator (RTG) systems. An RTG is a type of nuclear energy source that leverages the Seebeck effect and the temperature gradient across an array of thermocouples to convert the heat released by the decay of a suitable radioactive material (e.g., Pu-238) into electricity. However, RTGs are power-limited and cannot be controlled easily (i.e., without load-following capabilities). Current RTGs are typically used for power in the 1 to 500 W range and their specific power (i.e., electrical power per unit mass) decreases significantly as they are scaled to higher power outputs. For example, an RTG unit having a weight of about 38 kg including about 4.5 kg of Pu-238 can only provide enough heat to generate approximately 150 W of electrical power or 2 kW of thermal power. As such, RTG units cannot supply enough power to sustain long-term and power-demanding space operations (e.g., life support systems, industrial activities, etc.).

[0006] Advanced space exploration in the future (e.g, deep-space missions) will require a sustained presence on the Moon or another extraterrestrial body in the solar system. To sustain such a presence, reliable and continuous kW-scale heat and electrical power will need to be supplied on or to the extraterrestrial body for various mission-critical operations. Fission-based nuclear reactors, unlike photovoltaic (i.e., solar-based) solutions whose power production depends on illumination conditions, can be a reliable source of thermal energy and electrical power. Solar power is especially unfavourable for most locations on the Moon (i.e., at locations except the pole regions) because the lunar night spans about fourteen (14) days. Accordingly, fission-based nuclear reactors could be used to supply the power required to support mining operations and industrial processes on the Moon or other planetary bodies and to provide sustainable and long-lasting power for an extraterrestrial base, rovers, utility vehicles, propulsion systems for spacecrafts, and other mission-critical operations.

[0007] Unfortunately, no currently available Small Modular Reactors (SMRs) or Micro Modular Reactors (MMRs) are suitable for commercial or defense applications in extreme terrestrial or extraterrestrial environments, such as the Canadian Arctic or the lunar surface. While research reactors have been commissioned at universities throughout North America, they typically operate at relatively low temperatures and power levels and have limited fuel lifetime. Such reactors are impractical and uneconomical for commercial and defense power generation applications.Deployment of nuclear reactors to the Arctic and to space is subject to uncompromising logistical and technical requirements. Existing reactor designs have difficulties meeting these requirements due to their large size, high mass, and significant infrastructure needs. In addition, existing nuclearreactor designs usually rely on passive safety systems and convective heat transfer, which requires gravity and is not effective in the vacuum of space. Conventional nuclear reactors are also usually built with or otherwise rely on materials and components that are incompatible with the extreme environment of extraterrestrial bodies and space in general (e.g., lack of an atmosphere, extreme temperature, cosmic / solar radiation, and the presence of highly abrasive regolith). Existing nuclear reactor designs also tend to rely on construction and assembly methods that do not provide the structural integrity necessary to withstand the loads and stresses experienced during both transportation by military aircraft (e.g., C-17) and spacecraft and continuation operations in the extreme conditions of the lunar surface and the Arctic.

[0008] Accordingly, there remains a need for nuclear reactors that can overcome the abovementioned deficiencies. There remains a need for small-scale nuclear reactors, such as Micro Modular Reactors (MMRs), that can be rapidly deployed and effectively operated in extreme and remote environments (e.g., the Arctic, extraterrestrial bodies like the Moon, etc.). Such reactors should be designed or otherwise configured to provide a relatively high specific power (i.e., kW / kg) with relatively long refuelling cycles, while minimizing size and mass. Such reactors may be particularly useful for communities that rely heavily on diesel generators (e.g., communities in Canada’s Arctic), which contribute to carbon emissions, produce black soot that warms the Arctic at rates faster than global averages, and accelerate ice melt with permanent implications for Earth’s climate.SUMMARY OF THE DISCLOSURE

[0009] The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

[0010] One aspect of the invention relates to a small-scale nuclear reactor. The nuclear reactor includes a reactor core, a primary heat transport system, a thermoelectric conversion system, a heat sink disposed externally of the reactor core, and a control system. The primary heat transport system comprises a pump and at least two heat exchangers. The primary heat transport system is configured to circulate a working fluid (e.g., water) in a primary loop through the reactor core. The thermoelectric conversion system is thermally coupled to the primary heat transport system through aheat exchanger, and the heat sink is thermally coupled to the primary heat transport system through another heat exchanger. The thermoelectric conversion system comprises an Organic Ranking Cycle generator and its own secondary heat transport system. The secondary heat transport system is configured to circulate an organic refrigerant (e.g., a fluid having a boiling point lower than the boiling point of water) in a secondary loop through the Organic Ranking Cycle generator. The control system is operatively coupled to the primary heat transport system and the secondary heat transport system. The control system may be configured to regulate power output of the Organic Ranking Cycle generator by synchronously adjusting flow rates of the working fluid in the primary loop and the organic refrigerant in the secondary loop. A district heating system may be thermally coupled to the primary heat transport system or the secondary heat transport system.

[0011] In some embodiments, the heat exchangers are plate-type heat exchangers. In some embodiments, the primary heat transport system comprises a chemical and volume control system configured to remove unwanted substances from the working fluid. In some embodiments, the heat sink comprises a radiator having one or more exposed radiating surfaces adapted to dissipate heat through radiative heat transfer. In some embodiments, the primary heat transport system is operatively controlled by the control system to circulate the working fluid through the reactor core at a flow rate between 2.2 kg / s to 3.2 kg / s.

[0012] In some embodiments, the reactor core comprises a nuclear fuel cage contained in a vessel. The vessel may be pressurized by a pressurizer of the primary heat transport system. In such embodiments, the control system may include multiple control drums (e.g., three or more control drums) disposed externally around the pressurized vessel and outside the pressure boundary. The control drums may be configured to control reactivity of the reactor core to maintain a temperature of the working fluid to a range within, for example, 140°C and 340°C. In some embodiments, the reactor core includes a neutron reflector disposed around the pressurized vessel. The neutron reflector may be made of materials like beryllium, graphite, beryllium oxide, or a combination of any of the foregoing.

[0013] In some embodiments, the fuel cage comprises a top plate, a bottom plate, a central channel extending between the top and bottom plates, and a plurality of nuclear fuel rods connected between the top and bottom plates. In such embodiments, the nuclear reactor may include a primary shutdown system. The primary shutdown system is operated independently of the control system and comprises a central shutdown rod coated with neutron poisons. The primary shutdown system may be configured to detect overheating of the reactor core and insert the central shutdown rod into thecentral channel of the fuel cage during overheat. The nuclear reactor may also include a secondary shutdown system operated independently of the control system and the primary shutdown system. In some embodiments, the secondary shutdown system comprises a liquid neutron absorber release system and a plurality of shutdown drums disposed externally around the pressurized vessel. The secondary shutdown system may be configured to shut down the nuclear reactor during overheat by using either the shutdown drums and the liquid neutron absorber release system.

[0014] Another aspect of the invention relates to a nuclear fission reactor. The nuclear fission reactor comprises a reactor core, a primary heat transport system, a thermoelectric conversion system (e.g., a Stirling engine, a Rankine engine, etc.,), a cooling system, and a district heating system. The primary heat transport system comprises a pump and heat exchangers. The primary heat transport system is configured to circulate a primary working fluid in a primary loop through the reactor core. The thermoelectric conversion system and the cooling system are thermally coupled to the primary heat transport system through the heat exchangers. The thermoelectric conversion system comprises a thermoelectric generator and a secondary heat transport system. The secondary heat transport system is configured to circulate a secondary working fluid in a secondary loop to facilitate heat transfer from the primary working fluid to the thermoelectric generator. The cooling system comprising a heat sink and a tertiary heat transport system. The tertiary heat transport system is configured to circulate a tertiary working fluid in a tertiary loop to facilitate heat transfer from the primary working fluid to the heat sink. The district heating system is thermally coupled to the primary heat transport system, the secondary heat transport system, or the tertiary heat transport system.

[0015] In some embodiments, the district heating system is thermally coupled to the primary heat transport system through a supplementary heat exchanger disposed in the primary loop between the first heat exchanger and the second heat exchanger. In some embodiments, the district heating system is thermally coupled to the secondary heat transport system through a supplementary heat exchanger disposed in the secondary loop. In such embodiments, the third heat exchanger is configured to facilitate heat transfer from the secondary working fluid to the district heating system. In some embodiments, the district heating system is thermally coupled to the tertiary heat transport system through a supplementary heat exchanger disposed in the tertiary loop. In such embodiments, the third heat exchanger is configured to facilitate heat transfer from the tertiary working fluid to the district heating system before the tertiary working fluid is cooled by the heat sink.

[0016] In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. Features and advantages of the embodiments of the present invention will become apparent from the following detailed description, taken with reference to the appended drawings in which:

[0018] FIG. 1 is a schematic illustration of a small-scale nuclear reactor according to an example embodiment.

[0019] FIG. 2A is a side view of an exemplary nuclear reactor core of the FIG. 1 nuclear reactor. FIG. 2B is a cross sectional view the nuclear reactor core taken through line A-A’ shown in FIG. 2A.

[0020] FIG. 3 A is a perspective view of an exemplary vessel of the nuclear reactor core shown in FIG. 2A. FIGs. 3B and 3C are perspective views of an exemplary fuel cage of the nuclear reactor core shown in FIG. 2A.

[0021] FIG. 4A is a side view of a control drum of the nuclear reactor core shown in FIG. 2A. FIG.4B is a side view of a central shutdown rod of the nuclear reactor core shown in FIG. 2A.DETAILED DESCRIPTION

[0022] The description which follows and the embodiments described therein are provided by way of illustration of examples of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation and not limitation of those principles and of the invention. In some instances, certain structures and techniques have not been described or shown in detail in order not to obscure the invention.

[0023] FIG. 1 is a schematic illustration of a small-scale nuclear reactor 10 according to an example embodiment. Nuclear reactor 10 provides a means for generating heat and power in non-traditional environments like space, the lunar or planetary environment, extreme and remote environments suchas the Arctic, or in disaster relief zones. Nuclear reactor 10 is designed to operate by controlling the nuclear fission process taking place within the reactor core. As such, nuclear reactor 10 may also be referred to herein as a “fission reactor”, a “controlled reactor”, or a “controlled reactivity reactor”.

[0024] Fission reactor 10 comprises a nuclear reactor core 100, a primary heat transport system 200, a thermoelectric conversion system 300, a cooling system 400, a control system 500, and balance of plant systems and equipment. In contrast to conventional SMRs and MMRs with infrastructuredependent architectures, fission reactor 10 is designed to be transportable and incorporates advancements over historically successful research reactors (e.g., the SLOWPOKE-2), as described in more detail below. Compared to, for example, the SLOWPOKE-2 reactor which outputs only about 20 kW of thermal energy and does not any electrical power, fission reactor 10 can produce electric power and more thermal energy. In one embodiment, fission reactor 10 is designed or otherwise configured to output about 200 kW of thermal energy and between 10 kW to 25 kW of electrical power. In another embodiment, fission reactor 10 is designed or otherwise configured to output between 200kW to 1.5 MW of electrical power. Fission reactor 10 may be scaled to produce more or less power in other embodiments. Some embodiments of fission reactor 10 include interfaces compatible with lunar landers, rovers, and other utility vehicles.

[0025] Fission reactor 10 may be operated without an open pool in some cases, thereby reducing reactor footprint. This also allows fission reactor 10 to be deployed and used in environments where large volumes of water are unavailable. Fission reactor 10 may incorporate various types of working fluids as coolants and moderators for nuclear reactor core 100 (e.g., light water, heavy water, organic solutions, gas, liquid metal, and / or molten salt). In general, fission reactor 10 is less susceptible to risks like runaway nuclear reactions compared to convention nuclear reactors, thereby allowing fission reactor 10 to be provided in closer physical proximity to human-occupied communities. This can advantageously help reduce efficiency losses across power distribution and / or district heating systems. In some embodiments, the various components of fission reactor 10 are, individually or collectively, enclosable within standard size shipping containers, thereby enabling flexible and multimodal transportation (e.g., by truck, train, ship, barge, aircraft, spacecraft, etc.).

[0026] Fission reactor 10 comprises critical components and a nuclear reactor core 100 containing fuel which undergo nuclear reactions (e.g., fission reactions) to generate thermal energy. The fuel may, for example, comprise Low Enriched Uranium (LEU) (e.g., < 5% U-235) or High-Assay Low Enriched Uranium (HALEU) (e.g., 5-19.99% U-235). The fuel may be provided in the form of sintered UO2 elements enclosed within cladding tubes or fuel drums made of, for example, azirconium-alloy. As the energy released during fission heats reactor core 100, a working fluid (e.g., light water) may be circulated through the core via a pump to cool and carry heat away from reactor core 100. The working fluid may, in some cases, have a temperature between 140°C and 340°C when exiting nuclear reactor core 100. The working fluid may act as both a coolant and a moderator in some cases. The working fluid may be recirculated through reactor core 100 in a closed loop 12, as shown in FIG. 1. For the purposes of facilitating the description, the system 200 responsible for circulating the working fluid in this loop 12 is referred to herein as the “primary heat transport system” of fission reactor 10.

[0027] Fission reactor 10 relies on forced convection, instead of natural convection, to circulate the working fluid in primary loop 12. For example, a pump 202 may be provided as part of primary heat transport system 200 and used to circulate the working fluid through reactor core 100 as shown in FIG. 1. In addition, a pressurizer 203 may be provided and used in conjunction with pump 202 to actively control the pressure of the working fluid as it is circulated through loop 12 by primary heat transport system 200. Pump 202 and pressurizer 203 may be operatively connected to control system 500. In one embodiment, the working fluid is pressurized from around 3 MPa to around 15 MPa by pressurizer 203. Pressurizing the working fluid in primary loop 12 increases the saturation temperature of the working fluid, resulting in a higher outlet temperature for reactor core 100 and improved efficiency during thermal-electric conversion.

[0028] Other components of primary heat transport system 200 include a first heat exchanger 210 for transferring heat from the working fluid to a secondary loop 14 for the purposes of thermal electric conversion, and a second heat exchanger 220 for transferring residual heat from the working fluid to a cooling system or ultimate heat sink. First heat exchanger 210 and second heat exchanger 220 are provided in and form a part of primary loop 12. Compared to second heat exchanger 220, first heat exchanger 210 is located relatively proximate to an outlet of reactor core 100 as shown in FIG. 1. Therefore, the temperature of the working fluid as it passes through first heat exchanger 210 is typically higher than the temperature of the working fluid as it passes through second heat exchanger 220.

[0029] Primary heat transport system 200 may, optionally, include a chemical and volume control system (CVCS) 230, and an emergency core cooling system (ECCS) 240. CVCS 230 may comprise coarse filters, particulate filters, ion exchange columns, or other purification systems for removing unwanted substances form the working fluid. This may be particularly desirable where printed-circuit heat exchangers are used, as described in more detail below. In some embodiments, CVCS 230comprises means for degassing or modifying chemical levels of the working fluid. CVCS 230 may, for example, be configured introduce boron, gadolinium, hydrogen, in some chemical form, or demineralized water to the working fluid to return its pH and chemistry to optimal levels before it is recirculated into reactor core 100. CVCS 230 may be supported by pressure reducing valves and supplementary heat exchangers to prevent the working fluid from damaging its components.

[0030] ECCS 240 provides reactor core 100 with heat removal during accident scenarios when other methods of cooling are impaired or require assistance to maintain core temperatures within safe margins. ECCS 240 may comprise multiple injection systems for various pressure levels as well as a recirculation system for sustained low pressure cooling. In some embodiments, ECCS 240 includes a high-pressure injection system configured to inject a coolant driven by inert gas into reactor core 100 during emergencies, an intermediate-pressure injection system designed to address small to medium loss of coolant accidents, and a low-pressure system. The intermediate-pressure injection system may be driven in the same manner as the high-pressure system. For the low-pressure system, a coolant may be positioned physically above reactor core 100. The coolant flows into the pressure vessel during emergencies and lost coolant is recirculated by redundant containment sump-pumps through coarse strainers to prevent entry of large debris into the core. In some embodiments, ECCS 240 is configured to rely on natural convection to create a thermosiphon to cool reactor core 100 without the use of external power or pump flow.

[0031] In the embodiment shown in FIG. 1, fission reactor 10 comprises a thermoelectric energy conversion system 300 for converting heat into electricity. Examples of suitable types of thermoelectric energy conversion systems 300 include, but are not limited to, thermoelectric generators (TEGs), Stirling engines, Brayton engines, and Rankine (steam or organic) cycle generators. In the illustrated embodiment, thermoelectric conversion system 300 is thermally coupled to primary heat transport system 200 through first heat exchanger 210. For the purposes of facilitating the description, the term “thermally coupled” is used herein to refer to a coupling that facilitates heat exchange either directly or indirectly. Two systems or components are considered to be “thermally coupled” to each other if they are capable of exchanging heat, either directly or indirectly.

[0032] In the illustrated embodiment, thermoelectric conversion system 300 comprises a thermoelectric generator 310 and its own heat transport system 320. Thermoelectric conversion system 300 works by extracting heat from the working fluid exiting out of reactor core 100, and using thermoelectric generator 310 to convert the heat to electricity. In some embodiments,thermoelectric generator 310 is an Organic Rankine Cycle generator and heat transport system 320 is configured to circulate a secondary working fluid in a secondary loop 14 passing through first heat exchanger 210 and Organic Rankine Cycle generator 310. In such embodiments, the secondary working fluid may be an organic refrigerant (e.g., hydrofluorocarbons, fluorocarbons, etc.). The organic refrigerant may start in a liquid phase before it is circulated by secondary heat transport system 320 to extract heat through heat exchanger 210. Due to its low boiling point, the organic refrigerant may vaporize into a gas phase before entering the Organic Rankine Cycle generator 310, thereby improving the efficiency of the heat to electricity conversion. A condenser (not shown) may be included as part of the thermoelectric conversion system to condense the organic refrigerant back to a liquid before it is recirculated again by heat transport system 320.

[0033] Cooling system 400 is provided as part of fission reactor 10 to extract residual heat from the primary working fluid after the primary working fluid has been circulated through first heat exchanger 210. In some embodiments, cooling system 400 comprises a heat sink 410 and a means for heat sink 410 to extract residual heat from the working fluid via the second heat exchanger 220. For example, cooling system 400 may include its own heat transport system 420 configured to extract residual heat from the working fluid by circulating a tertiary working fluid in a tertiary loop 16 as shown in FIG. 1. In some embodiments, a radiator is thermally coupled to the second heat exchanger 220 to allow residual heat in the working fluid to be dissipated to the environment. The radiator may, for example, comprise one or more radiator panels having exposed radiating surfaces adapted to dissipate heat through radiative heat transfer. This provides a passive and efficient mechanism to cool the working fluid in situations where fission reactor 10 is used at locations with sub-zero ambient temperatures (e.g., the Arctic). By incorporating a radiator as part of cooling system 400, fission reactor 10 can be deployed to locations where there are no rivers or lakes, since decay and residual heat from the heat transport systems can be rejected directly to the environment (e.g., by using radiator fins or air-cooled heat exchangers). This allows fission reactor 10 to generate energy without relying on the cooling towers required to operate conventional large-scale nuclear systems.

[0034] In some embodiments, nuclear reactor 10 may be adapted to provide district heating. In such embodiments, nuclear reactor 10 comprises a district heating system (not shown) thermally coupled to primary heat transport system 200, secondary heat transport system 320, or tertiary heat transport system 420. District heating system works by extracting thermal energy remaining in the primary working fluid, the secondary working fluid, or the tertiary working fluid, as the case may be. The thermal energy may be extracted by circulating a coolant circulating in a supplementary loop. Thesupplementary loop may pass through buildings and infrastructure to provide district heating. In one embodiments, the district heating system is thermally coupled to primary heat transport system 200 through a heat exchanger provided in primary loop 12 at a location between first heat exchanger 210 and second heat exchanger 220. In another embodiment, the district heating system is thermally coupled to secondary heat transport system 320 through a heat exchanger provided in secondary loop 14 at a location downstream of thermoelectric generator 310. In this embodiment, district heating system works by extracting heat from the secondary working fluid circulating in secondary loop 14. In another embodiment, the district heating system is thermally coupled to the tertiary heat transport system 420 through a heat exchanger provided in tertiary loop 16 at a location upstream of heat sink 410. In this embodiment, the district heating system works by extracting heat from the tertiary working fluid circulating in tertiary loop 16.

[0035] The heat exchangers described herein may comprise plate heat exchangers (i.e., exchangers which rely on metal plates to transfer heat between two fluids), shell and tube heat exchangers (i.e., exchangers consisting of a series of tubes with one set carrying hot fluid and another set carrying cold fluid), printed-circuit heat exchangers, etc. Due to the size of small-scale reactor 10, plate-type heat exchangers and printed-circuit heat exchangers may be preferred over other types of heat exchangers in some cases. Compared to the heat exchangers used in conventional nuclear reactors, the plate-type heat exchanger is capable of achieving higher heat transfer rates per unit volume with lower temperature differences, and using this type of heat exchanger allows residual heat in the primary working fluid to be transferred to the secondary and tertiary working fluid more efficiently.

[0036] Other ancillary components may be included as part of nuclear reactor 10. Examples of such ancillary components, include but are not limited to: a containment structure, external emergency and safety systems (e.g., backup power source, fire suppression, ventilation), and semi-autonomous electronic systems driven by, for example, artificial intelligence for remotely monitoring and / or remotely controlling the reactor.

[0037] Referring now to FIGs. 2A and 2B, shown therein is an exemplary design of a nuclear reactor core 100 of nuclear reactor 10. The reactivity of reactor core 100 is controlled by control system 500 to regulate the power level of reactor 10. A combination of control rods (i.e., rods that may be inserted into or withdrawn from reactor vessel 120) and control drums (i.e., drums positioned around the perimeter of reactor vessel) may be included as part of control system 500. In the illustrated embodiment, control drums 510 with mechanically-restricted speeds are disposed outside the pressure boundary of the reactor core to eliminate the risk of rapid withdrawal.

[0038] Reactor core 100 comprises a fuel cage 110 contained in a vessel 120 (e.g., see FIG. 3 A), an inlet 122 for facilitating flow of a coolant into core 100, and an outlet 124 for facilitating flow of the coolant away from core 100. Vessel 120 is pressurized in some embodiments (e.g., by pressurizer 203) and may also be referred to herein as a pressure vessel. In the illustrated embodiment, pressure vessel 120 comprises an inlet 122 located at the bottom and an outlet 124 located at the top. In other embodiments, pressure vessel 120 may comprise multiple outlets and / or inlets, and the inlet(s) / outlet(s) may be located along the side of pressure vessel 120. The temperature within pressure vessel 120 may be regulated by an active cooling module of control system 500. Pressure vessel 120 may be made of stainless steel, zirconium alloy, or other suitable materials for the application. Although vessel 120 is typically pressurized, this is not necessary in some cases.

[0039] Fuel cage 110 may be suspended in or fastened and secured to the inner walls of pressure vessel 120. In some embodiments, fuel cage 110 comprises a top plate 112 and a bottom plate 114 with holes provided throughout. The holes may be shaped or otherwise designed to receive and support fuel pins 116, and to provide flow channels 118 between the top and bottom plates (e.g., see FIGs. 3B and 3C). Top plate 112 and the bottom plate 114 may be disk shaped and mechanically fastened to pressure vessel 120. Top plate 112 and / or bottom plate 114 may also comprise a central hole for supporting a central channel 119 extending therebetween as shown in FIG. 3B.

[0040] The specifications of fuel cage 110 may be designed or selected based on, for example, the desired power output and operating conditions of reactor 10. Examples of these design specifications include: the number and dimensions of fuel pins, the length of the fuel pins, pitch and configuration of the fuel pins and flow holes, fuel cage diameter, sheath or cladding thickness, sheath or cladding material (e.g., stainless steels, silicon carbides, or zirconium alloys), and fuel form (e.g., sintered uranium dioxide pellets or other advanced fuel like Tri-structural Isotropic (TRISO) particle fuel or uranium zirconium hydride).

[0041] In one embodiment, fuel cage 110 comprises between 300 to 400 (e.g., 342) fuel pins 116 and between 600 to 700 (e.g., 665) flow holes 118. In another embodiment, fuel cage 110 comprises up to 2700 fuel pins and up to 6000 flow holes 118. In general, the number of fuel pins 116 and flow holes 118 may be increased to enhance the power output of fission reactor 10. Fuel pins 116 extend between top plate 112 and bottom plate 114 as shown in FIG. 3B. The end portions of fuel pins 116 may be deformed and secured in place against top and / or bottom plates 112, 114 to prevent fuel pins 116 from sliding out of place after loading.

[0042] Flow holes 118 are typically smaller on top plate 112 and larger on bottom plate 114. In the illustrated embodiment, fuel cage 110 is oriented with fuel pins 116 extending in a direction (e.g., vertical direction as shown) that is generally parallel to the direction of fluid flow between inlet 122 and outlet 124. As described above, various design adjustments to fuel cage 110 are possible, such as increasing the length and / or diameter of fuel pins 116 within fuel cage 110 and / or adjusting the positioning of (e.g., distance between) fuel pins 116 inside fuel cage 110, to increase the power output of reactor 10.

[0043] Neutron reflectors 130 are positioned around fuel cage 110 to prevent or limit the number of neutrons from escaping core 100. In the illustrated embodiment, reflectors 130 are disposed externally of vessel 120 and outside of the pressure boundary. Reflectors 130 may be made of or include a material or a combination or composite of the following materials: beryllium metal, graphite, beryllium oxide, heavy water, and the like. In the illustrated embodiment, reflector 130 is cylindrical in shape with an annular body portion and top and bottom portions shaped like a disk. Reflector 130 may, optionally, include holes and / or channels for supporting peripheral control drums 510 of control system 500, other instrumentation (e.g., flux detectors), etc.

[0044] Reflector 130 and pressure vessel 120 may be contained within a radiation shield. The shield may be tubular shaped and made of one or a combination of materials, such as boron carbide, water and lead (e.g., when nuclear reactor 10 is used on Earth) or regolith (e.g., when reactor core is used on the Moon). In one embodiment, the radiation shield has a diameter that is in the range of about 1 meters to 3 meters (e.g., 2 meters), and a height that is in the range of about 3 meters to 5 meters (e.g., 4 meters).

[0045] Control system 500 is designed or otherwise configured to regulate the power level of reactor 10 and provide both control and fail-safe shutdown mechanisms. The power level of reactor 10 can be regulated by, for example, controlling the temperature of the working fluid flowing away from reactor core 100 using an active cooling system (not shown) or by adjusting the reactivity within reactor 10 using control system 500. This can be achieved in some embodiments by maintaining the temperature of the working fluid exiting reactor core 100 at a certain temperature (e.g., 185°C) and / or by adjusting the flow rate of the working fluid (e.g., 2.4 kg / s). In another embodiment, control system 500 is configured to automatically reduce the reactor power or initiate shutdown mechanisms if the outlet of core 100 exceeds a certain temperature (e.g., 245°C) or if the temperature rise across core 100 exceeds a certain level (e.g., more than 20°C). In such embodiments, the temperature of theworking fluid circulating in primary loop 12 may range between a desired lower temperature (e.g., 165°C) and upper temperature (e.g., 185°C), depending on the desired power level.

[0046] Control system 500 may include both components that are housed within vessel 120 and components that are located outside of vessel 120. Some of the components may, for example, be embedded within the annular or top portions of reflector 130 as depicted in FIG. 2B. The components include control drums 510 and electronics for controlling the orientation of the control drums. As depicted in FIG. 2B, the control drums 510 of control system 500 may be located outside of and positioned around vessel 120 to control the reactivity and thermal output of reactor 10. By using the control drums 510 outside of vessel 120, the risk of ejection is reduced. Control drums 510 may be made of the same material as reflector 130. Control drums 510 may be made of (or comprise a segment coated with) materials like boron carbide, cadmium, silver, hafnium, indium, or a combination of any of the foregoing. Control drums 510 may, optionally, be protected with a layer of cladding. The dimensions and specifications of the cladding may be adjusted or designed based on the desired application for fission reactor 10.

[0047] In general, control system 500 serves as the primary controller of the primary, secondary and tertiary heat transport systems. Control system 500 may be configured to adjust flow rates in each loop in a synchronized manner to facilitate electrical load following (i.e., matching output of the thermoelectric generator to the required demand of the electrical consumers). Control system 500 may also be configured to control the amount of excess heat allocated for district heating or required to be dissipated through the ultimate heat sink. Control system 500 may include temperature sensors, flow rate sensors, pressure sensors, and electrical demand sensors. The sensors may be connected to a central processor of control system 500. The central processor receives information from the sensors and use the information to dynamically adjust flow rates of the pumps in the primary, secondary, and tertiary heat transport systems. This allows nuclear reactor 10 to be adapted for operation under a wide range of temperature inputs (e.g., in the secondary and tertiary loops), different secondary and tertiary working fluids, and potential configurations for the district heating system.

[0048] In some embodiments, fission reactor 10 comprises a safety system 600 that operates independently of control system 500. The safety system may include and control a primary shutdown system and an independent secondary shutdown system. The primary shutdown system comprises electronics and a central shutdown rod 610 (e.g., see FIG. 4B) for insertion into central channel 119 of fuel cage 110 during emergencies. Pressure vessel 120 may include a channel toaccommodate central shutdown rod 610. The primary shutdown system may, optionally, incorporate additional rods distributed within the fuel cage assembly. The independent secondary shutdown system comprises electronics, a liquid neutron absorber release system, and shutdown drums that are provided in the periphery of the reactor vessel (e.g., embedded in the reflector 130). The shutdown drums are controlled independently from control drums 510 of control system 500. The liquid absorber release system may rely on boron solution, heavy water, liquid metals, gadolinium nitrate solutions, molten salt, or lead / lead-bismuth eutectic solutions to shut down reactor 10, including in the event of an emergency. In one embodiment, the secondary shutdown system works by introducing a liquid neutron absorber to the working fluid circulating in primary loop 12. The liquid neutron absorber may be introduced into the working fluid via a specialized injection pump and / or a specialized tank in the CVCS 230. In another embodiment, the liquid neutron absorber is injected directly into pressure vessel 120. In this embodiment, the liquid neutron absorber may be removed via the CVCS 230 if it is found in the working fluid.

[0049] In some embodiments, the safety system includes a mechanism for automatically moving fuel cage 110 away from reflector(s) 130 to rapidly decrease reactivity at instances of potential failure. The mechanism may be implemented in various ways, including through the use of a cable system to move vessel 120 (and the enclosed fuel cage 110) away from reflector(s) 130, or a cable system to move reflector(s) 130 away from the vessel 120 (and the enclosed fuel cage 110).

[0050] A wide variety of supplementary features and variations are possible within the scope of the present disclosure. Examples of such features include: continuously pumping water through ion exchange columns to maintain water chemistry and control corrosion, utilizing a pool of water for additional shielding and passive cooling with an insulated lid to enclose a gas space, continuously circulating air and water vapor through a purification system and hydrogen recombiner, and limiting the primary loop to a certain temperature and automatically reducing the reactor power if the core outlet exceeds a certain temperature.

[0051] Other features related to improved reactor core designs for enabling higher-powered operations and deployment to extraterrestrial environments or extreme and remote environments on Earth and Moon, while maintaining safety. These features may be based on or otherwise incorporate one or more of the following principles: (1) increase the number of fuel pins and / or amount of fuel contained within the reactor core of existing research or experimental reactor designs (e.g., the SLOWPOKE, SLOWPOKE-2 and SLOWPOKE-3 reactors); (2) add burnable poison(s) into the reactor core; (3) isolate the fuel cage from the outer pool by, for example, placing the fuel cage of thereactor core inside a containment or pressure vessel; (4) place additional circular plates or structural supports inside the fuel cage; (5) increase the number of structural rods along the edge of the fuel cage;(6) stack multiple fuel cages or reactor cores within the same vessel;(7) modify the length of the fuel pins; (8) modify fuel element diameter and / or the sheath wall thickness of the fuel pins and adjust the diameter of the fuel pin holes in the circular fuel plates accordingly; (9) adjust distance and configurations between fuel pins (e.g., modify lattice pitch and the water to pin ratio within the core) to improve performance and reliability and adjust the diameter of the fuel cage plates accordingly;(10) use of tristructural-isotropic (TRISO) or uranium zirconium hydride fuel instead of pellets; (11) use alternative materials, such as stainless steels, silicon carbide, and zirconium alloys, for the fuel pin sheaths; (12) increase the number of control rods or drums located within the reactor core but outside of any pressurized region; and (13) incorporate a liquid neutron absorber injection system as an additional independent shutdown mechanism. Some embodiments of the nuclear reactors described herein may be provided as part of an overall system, such as the systems described in Patent Cooperation Treaty Publication No. PCT / CA2023 / 050730 entitled “Lunar and planetary nuclear reactor”, the contents of which are hereby incorporated by reference in their entirety.

[0052] The examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein.

[0053] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the scope of the invention. The scope of the claims should not be limited by the illustrative embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. For example, various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments.Embodiments of the invention may include zero, any one or any combination of two or more of such features. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible).

[0054] Embodiments of the invention, such of the control and safety systems described herein, may incorporate computer hardware implemented in a variety of forms, including but not limited to specifically designed hardware, configurable hardware, programmable data processors, or combinations thereof. Examples of specifically designed hardware include: logic circuits, application-specific integrated circuits (“ASICs”), large scale integrated circuits (“LSIs”), very large scale integrated circuits (“VLSIs”), and the like. Examples of configurable hardware include: one or more programmable logic devices such as programmable array logic (“PALs”), programmable logic arrays (“PLAs”), and field programmable gate arrays (“FPGAs”)). Examples of programmable data processors include: microprocessors, digital signal processors (“DSPs”), embedded processors, graphics processors, math co-processors, real-time controllers, safety-rated controllers, and the like. Aspects of the control and safety systems described herein may be realized in hardware, software, firmware, or any combination thereof, and the described functional operations may be implemented as computer-executable instructions, logic blocks, modules, or circuits without departing from the scope of the invention. In some embodiments, one or more programmable data processors may be included in a control circuit and configured to perform the control, monitoring, and safety functions described herein by executing software instructions, firmware, or a combination thereof stored in one or more memories accessible to the processors.

[0055] Unless the context clearly requires otherwise, throughout the description and the claims: “comprise”, “comprising”, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense. “Herein”, “above”, “below”, and words of similar import, when used to describe this specification shall refer to this specification as a whole and not to any particular portions of this specification. “Or” in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. The singular forms “a”, “an”, and “the” also include the meaning of any appropriate plural forms.

[0056] Where a component is referred to above, unless otherwise indicated, reference to that component should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[0057] Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied tosystems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and / or acts with equivalent features, elements and / or acts; mixing and matching of features, elements and / or acts from different embodiments; combining features, elements and / or acts from embodiments as described herein with features, elements and / or acts of other technology; and / or omitting combining features, elements and / or acts from described embodiments.

[0058] Although the present invention has been described and illustrated with respect to preferred embodiments and preferred uses thereof, it is not to be so limited since modifications and changes can be made therein which are within the full, intended scope of the invention as understood by those skilled in the art.

Claims

CLAIMS1. A small-scale nuclear reactor comprising:a reactor core;a primary heat transport system configured to circulate a working fluid in a primary loop through the reactor core, the primary heat transport system comprising a pump, a first heat exchanger, and a second heat exchanger;a thermoelectric conversion system thermally coupled to the primary heat transport system through the first heat exchanger, the thermoelectric conversion system comprising an Organic Ranking Cycle generator and a secondary heat transport system configured to circulate an organic refrigerant in a secondary loop through the Organic Ranking Cycle generator;a heat sink disposed externally of the reactor core and thermally coupled to the primary heat transport system through the second heat exchanger; anda control system operatively coupled to the primary heat transport system and the secondary heat transport system, wherein the control system is configured to regulate power output of the Organic Ranking Cycle generator by synchronously adjusting flow rates of the working fluid in the primary loop and the organic refrigerant in the secondary loop.

2. The nuclear reactor of claim 1, wherein the first heat exchanger comprises a plate-type heat exchanger.

3. The nuclear reactor of claim 2, wherein the primary heat transport system comprises a chemical and volume control system configured to remove unwanted substances from the working fluid passing through the plate-type heat exchanger.

4. The nuclear reactor of claim 1, wherein the heat sink comprises a radiator having one or more exposed radiating surfaces adapted to dissipate heat through radiative heat transfer.

5. The nuclear reactor of claim 1, wherein the primary heat transport system is operatively controlled by the control system to circulate the working fluid through the reactor core at a flow rate between 2.2 kg / s to 3.2 kg / s.

6. The nuclear reactor of claim 1, wherein the primary heat transport system comprises a pressurizer, and wherein reactor core comprises a nuclear fuel cage contained in a pressurized vessel.

7. The nuclear reactor of claim 6, wherein the control system comprises a plurality of control drums disposed externally around the pressurized vessel.

8. The nuclear reactor of claim 7, wherein the plurality of control drums are configured to control reactivity of the reactor core to maintain a temperature of the working fluid to a range within 140°C and 340°C.

9. The nuclear reactor of claim 6, wherein the reactor core comprises a neutron reflector disposed around the pressurized vessel.

10. The nuclear reactor of claim 9, wherein the neutron reflector comprises one or more of the following: beryllium, graphite, and beryllium oxide.

11. The nuclear reactor of claim 6, wherein the fuel cage comprises a top plate, a bottom plate, a central channel extending between the top and bottom plates, and a plurality of nuclear fuel rods connected between the top and bottom plates.

12. The nuclear reactor of claim 11, comprising a primary shutdown system operated independently of the control system, wherein the primary shutdown system comprises a central shutdown rod coated with neutron poisons, and wherein the primary shutdown system is configured to detect overheating of the reactor core and insert the central shutdown rod into the central channel of the fuel cage during overheat.

13. The nuclear reactor of claim 12, comprising a secondary shutdown system operated independently of the control system and the primary shutdown system, wherein the secondary shutdown system comprises a liquid neutron absorber release system and a plurality of shutdown drums disposed externally around the pressurized vessel, and wherein the secondary shutdown system is configured to shut down the nuclear reactor duringoverheat by using at least one of the shutdown drums and the liquid neutron absorber release system.

14. The nuclear reactor of claim 1, wherein the working fluid comprises water, and wherein the organic refrigerant comprises a fluid having a boiling point lower than the boiling point of water.

15. The nuclear reactor of claim 1, comprising a district heating system thermally coupled to the primary heat transport system.

16. A nuclear fission reactor comprising:a reactor core;a primary heat transport system configured to circulate a primary working fluid in a primary loop through the reactor core, the primary heat transport system comprising a pump, a first heat exchanger, and a second heat exchanger;a thermoelectric conversion system thermally coupled to the primary heat transport system through the first heat exchanger, the thermoelectric conversion system comprising a thermoelectric generator and a secondary heat transport system configured to circulate a secondary working fluid in a secondary loop to facilitate heat transfer from the primary working fluid to the thermoelectric generator;a cooling system thermally coupled to the primary heat transport system through the second heat exchanger, the cooling system comprising a heat sink and a tertiary heat transport system configured to circulate a tertiary working fluid in a tertiary loop to facilitate heat transfer from the primary working fluid to the heat sink; anda district heating system thermally coupled to one of the primary heat transport system, the secondary heat transport system, and the tertiary heat transport system.

17. The nuclear fission reactor of claim 16, wherein the district heating system is thermally coupled to the primary heat transport system through a third heat exchanger disposed in the primary loop between the first heat exchanger and the second heat exchanger.

18. The nuclear fission reactor of claim 16, wherein the district heating system is thermally coupled to the secondary heat transport system through a third heat exchanger disposed in thesecondary loop, and wherein the third heat exchanger is configured to facilitate heat transfer from the secondary working fluid to the district heating system.

19. The nuclear fission reactor of claim 16, wherein the district heating system is thermally coupled to the tertiary heat transport system through a third heat exchanger disposed in the tertiary loop, and wherein the third heat exchanger is configured to facilitate heat transfer from the tertiary working fluid to the district heating system before the tertiary working fluid is cooled by the heat sink.

20. The nuclear fission reactor of claim 16, wherein the thermoelectric conversion system comprises at least one of a Stirling engine and a Rankine engine.

21. Systems having any new and inventive feature, combination of features, or sub-combination of features as described herein.

22. Methods having any new and inventive steps, acts, combination of steps and / or acts or subcombination of steps and / or acts as described herein.

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