WO2025185915A1

WO2025185915A1 - Nuclear fission power plant

Info

Publication number: WO2025185915A1
Application number: PCT/EP2025/053367
Authority: WO
Inventors: James BAULD; Megan J WAKELING; Joseph D LEE; Samuel PEPPER; Sam A BROWN
Original assignee: Rolls-Royce Submarines Ltd; Rolls Royce Submarines Ltd
Current assignee: Rolls-Royce Submarines Ltd; Rolls Royce Submarines Ltd
Priority date: 2024-03-08
Filing date: 2025-02-10
Publication date: 2025-09-12
Anticipated expiration: 2026-09-08
Also published as: GB202403378D0; GB2628902A; WO2025185915A8

Abstract

A nuclear fission power plant (10) for extra-terrestrial use, comprising: a nuclear reactor core (20) comprising a metallic fuel (30); a plurality of reactor heat pipes (40) at least partially extending within the nuclear reactor core; a neutron reflector (70) and a plurality of neutronic control elements (50) disposed around the periphery of the nuclear reactor core; a plurality of thermoelectric generators (80); a fluid circuit (90) comprising a heat exchanger (92) and a pump (94), wherein an end of the reactor heat pipes extends into the heat exchanger to transfer heat to a working fluid of the fluid circuit which transfers heat to the thermoelectric generators; a passive radiator (100); and a plurality of radiator heat pipes (86). The thermoelectric generators are thermally coupled to the fluid circuit and to at least one of the radiator heat pipes, which are thermally coupled to the passive radiator.

Description

NUCLEAR FISSION POWER PLANT

TECHNICAL FIELD

[0001] This disclosure relates to a nuclear fission power plant configured for extraterrestrial use and a kit of parts and method for a nuclear fission power plant configured for extra-terrestrial use.

BACKGROUND

[0002] In space applications, it is desirable to have a reliable and sustainable power source. Solar panels are often used for satellites; however their power density is low, and they do not generate electricity when in shadow. This is a particular problem for moon or planetary expeditions where a facility could be in shadow for prolonged periods of time. Solar panels could be supplemented with battery storage, but batteries add significant weight, which is not viable for a rocket launch. In any event, the low power density of solar panels limits their application. In particular, a moon or planet based facility may have a high power requirement.

[0003] The high-power density of a nuclear fission power plant and ability to continue generation without sunlight make nuclear fission power plants in extra-terrestrial applications an attractive option. However, an extra-terrestrial nuclear fission power plant would need to withstand the harsh environment of space (or moon/planet), require minimum maintenance, and survive the large vibrations associated with a rocket launch. The low or zero gravity force and lack of a readily available heat sink present additional challenges. Weight and size are also issues as any power plant would likely need to fit within the confines of a rocket.

[0004] The present disclosure seeks to address these issues.

SUMMARY

[0005] According to a first aspect there is provided a nuclear fission power plant configured for extra-terrestrial use, the nuclear fission power plant comprising: a nuclear reactor core, the nuclear reactor core comprising a metallic fuel; a plurality of reactor heat pipes, each reactor heat pipe at least partially extending within the nuclear reactor core; a neutron reflector disposed around a periphery of the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a plurality of thermoelectric generators; a fluid circuit comprising a heat exchanger and a pump, wherein a protruding end of the reactor heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to a working fluid of the fluid circuit, the fluid circuit being arranged such that the working fluid flowing through the fluid circuit transfers heat from the heat exchanger to the thermoelectric generators; a passive radiator; and a plurality of radiator heat pipes; wherein the thermoelectric generators have a first end thermally coupled to the fluid circuit and a second end thermally coupled to at least one of the radiator heat pipes, the radiator heat pipes being thermally coupled to the passive radiator such that heat dissipated at the second end of the thermoelectric generators is distributed across the passive radiator.

[0006] The metallic fuel may comprise High Assay Low Enriched Uranium (HALEU). The metallic fuel may be enriched to substantially 19.75% uranium-235. The metallic fuel comprises a solid fuel alloy, such as U-Zr, U-Mo etc.

[0007] The neutron reflector may be at least partially formed from beryllium oxide, BeO.

[0008] The nuclear reactor core may further comprise a moderator. The moderator may be at least partially formed from yttrium hydride (YtH2-x) or zirconium hydride (ZrH2-x).

[0009] Alternatively, the nuclear reactor core may comprise no moderator. The nuclear reactor core may be unmoderated. The nuclear reactor core may comprise a fast reactor.

[0010] The rotatable control drums may be used for fine and coarse control of the nuclear reactor core. The fine control may be used during a normal operating mode. The coarse control may be used in an emergency or shut-down mode. The rotatable control drums may be the sole (i.e. , only) form of control of the nuclear reactor core. The neutronic control elements, e.g., rotatable control drums, may comprise boron carbide, B4C.

[0011] The nuclear fission power plant may comprise a plurality of thermoelectric generator groups, with each group comprising a plurality of thermoelectric generators thermally coupled to the fluid circuit. The nuclear fission power plant may further comprise a plurality of intermediate fins. Each intermediate fin may be disposed between at least one of the radiator heat pipes and a corresponding group of the thermoelectric generators so as to conduct heat from the thermoelectric generators to the radiator heat pipes. The radiator heat pipes may extend beyond an edge of the intermediate fins. A common passive radiator may be provided for a plurality of thermoelectric generators or thermoelectric generator groups.

[0012] The radiator heat pipes may be elongate. The radiator heat pipes may be arranged perpendicular to a flow direction of the fluid circuit where a thermoelectric generator associated with the radiator heat pipe is thermally coupled to the fluid circuit.

[0013] The fluid circuit may comprise a plurality of parallel flow paths with at least one thermoelectric generator in thermal contact with each parallel flow path. A plurality of thermoelectric generators may be in thermal contact with each parallel flow path. The thermoelectric generators associated with a particular one of the parallel flow paths may be arranged in series.

[0014] The nuclear fission power plant may comprise a first plurality of thermoelectric generators thermally coupled to a first passive radiator via a first plurality of radiator heat pipes. The nuclear fission power plant may comprise a second plurality of thermoelectric generators thermally coupled to a second passive radiator via a second plurality of radiator heat pipes. The first passive radiator and the second passive radiator may be disposed either side of the fluid circuit.

[0015] The plurality of thermoelectric generators, the fluid circuit and passive radiator may be deployable from a stowed configuration to a deployed configuration in which the passive radiator may be opened out. The fluid circuit may be configured such that the thermoelectric generators and/or passive radiator are spaced apart from the nuclear reactor core, e.g. by 5 metres, by 10 metres or more.

[0016] According to a second aspect there is provided a kit of parts for a nuclear fission power plant configured for extra-terrestrial use, the kit of parts being configured at least partially for extra-terrestrial assembly and comprising: a nuclear reactor core, the nuclear reactor core comprising a metallic fuel; a plurality of reactor heat pipes, each reactor heat pipe configured such that when the kit of parts is assembled each reactor heat pipe at least partially extends within the nuclear reactor core; a neutron reflector configured to be disposed around a periphery of the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums configured to be disposed around the periphery of the nuclear reactor core; a plurality of thermoelectric generators; a fluid circuit that, when assembled, comprises a heat exchanger and a pump, wherein, when installed, a protruding end of the reactor heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to a working fluid of the fluid circuit, the fluid circuit being configured such that, when assembled, the working fluid can flow through the fluid circuit and transfer heat from the heat exchanger to the thermoelectric generators; a passive radiator; and a plurality of radiator heat pipes; wherein the thermoelectric generators have a first end thermally couplable to the fluid circuit and a second end thermally couplable to at least one of the radiator heat pipes, the radiator heat pipes being thermally couplable to the passive radiator such that, in operation, heat dissipated at the second end of the thermoelectric generators is distributable across the passive radiator.

[0017] The kit of parts of may comprise a moderator configured to be positioned within the nuclear reactor core.

[0018] According to a third aspect there is provided a method for a nuclear fission power plant configured for extra-terrestrial use, the method comprising controlling the nuclear fission power plant to: generate heat with a nuclear reactor core, the nuclear reactor core comprising a metallic fuel; wherein a neutron reflector is disposed around a periphery of the nuclear reactor core, and a plurality of neutronic control elements comprising rotatable control drums are disposed around the periphery of the nuclear reactor core; transfer heat from the nuclear reactor core using a plurality of reactor heat pipes, each heat pipe at least partially extending within the nuclear reactor core; transfer heat from a protruding end of the heat pipes to a plurality of thermoelectric generators using a working fluid flowing in a fluid circuit, the fluid circuit comprising a heat exchanger and a pump, wherein the protruding end of the heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to the working fluid of the fluid circuit; radiate heat using a passive radiator and a plurality of radiator heat pipes, wherein the thermoelectric generators have a first end thermally coupled to the fluid circuit and a second end thermally coupled to at least one of the radiator heat pipes, the radiator heat pipes being thermally coupled to the passive radiator such that heat dissipated at the second end of the thermoelectric generators is distributed across the passive radiator; and generate electricity by virtue of a temperature gradient across the thermoelectric generators.

[0019] The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

BREIF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments will now be described by way of example only with reference to the accompanying drawings, which are purely schematic and not to scale, and in which:

[0021] Figure 1 is a schematic diagram showing an example of a nuclear fission power plant configured for extra-terrestrial use;

[0022] Figure 2 is a schematic diagram showing an example of a nuclear fission power plant configured for extra-terrestrial use;

[0023] Figure 3 is a schematic diagram showing an example arrangement of thermoelectric generators for the nuclear fission power plant;

[0024] Figure 4 is a schematic diagram showing another example arrangement of thermoelectric generators for the nuclear fission power plant;

[0025] Figure 5 is a schematic diagram showing another example arrangement of thermoelectric generators for the nuclear fission power plant; and

[0026] Figure 6 is a flowchart depicting a method for a nuclear fission power plant configured for extra-terrestrial use.

DETAILED DESCRIPTION

[0027] With reference to Figures 1 and 2, the present disclosure relates to a nuclear fission power plant 10 specifically configured for extra-terrestrial use, i.e., away from the Earth’s surface. The nuclear fission power plant 10 may be exclusively configured for extra- terrestrial use. As such, the nuclear fission power plant 10 may be referred to as an extraterrestrial nuclear fission power plant 10. However, the nuclear fission power plant 10 may be at least partially assembled on Earth and may be launched, e.g. from a rocket, into space. In a particular example, the nuclear fission power plant 10 may be intended for use on the lunar surface of the Moon orbiting Earth. However, the nuclear fission power plant 10 may also be used in space or on other planets and moons.

[0028] The nuclear fission power plant 10 may be a micro-reactor. As such, the nuclear fission power plant 10 may be readily transportable, in particular on a rocket.

[0029] As depicted, the nuclear fission power plant 10 comprises a nuclear reactor core 20. The nuclear reactor core 20 comprises a metallic fuel 30. The metallic fuel 30 may comprise High Assay Low Enriched Uranium (HALEU), e.g., with the concentration of the fissile isotope uranium-235 (U-235) being between 5% and 20% of the mass of uranium. In particular, the metallic fuel 30 may be enriched to substantially 19.75% uranium-235. This level of enrichment allows for better energy density whilst maintaining a safe level of enrichment.

[0030] The metallic fuel may comprise a solid fuel alloy, such as U-Zr, U-Mo etc. Such fuels may undergo fission from neutrons that have undergone moderation (slowing down). Furthermore, metallic fuels have a high density of fissile uranium atoms when compared to other fuel forms, meaning less mass of fuel is required to provide the required amount of energy. The metallic fuel 30 may be clad, e.g. in plated metal.

[0031] The nuclear reactor core 20 may be cooled using two-phase passive convection. For example, the nuclear fission power plant 10 may further comprise a plurality of heat pipes 40. Each heat pipe 40 extends at least partially within (e.g. substantially across a length of) the nuclear reactor core 20. The heat pipes 40 may be substantially elongate and may have a protruding end 42 that protrudes beyond the nuclear reactor core 20. The heat pipes 40 may be distributed within the nuclear reactor core 20, e.g., to ensure efficient heat transfer and heat distribution within the nuclear reactor core 20.

[0032] The heat pipes 40 are heat-transfer devices that use phase transition to transfer heat between two parts of the heat pipe. At the hot part of the heat pipe 40 (i.e., a part of the heat pipe within the nuclear reactor core 20), a volatile liquid within the heat pipe 40 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the heat pipe 40 to a cold part of the heat pipe (i.e., at the protruding end 42) and condenses back into a liquid, releasing the latent heat. The liquid then returns to the hot part of the heat pipe 40 and the cycle repeats.

[0033] Heat pipes 40 have been selected as they have excellent reliability, lifetime, and because a plurality of heat pipes are used, with the functioning of a single heat pipe being independent from the others, redundancy. The heat pipes 40 may use an alkali metal as their working fluid (for example sodium) as this provides excellent heat transportation when using the passive two-phase convection mechanism and operates within the 400-1000°C temperature range intended for the nuclear reactor core 20.

[0034] The nuclear fission power plant 10 further comprises a plurality of neutronic control elements 50. The neutronic control elements 50 may be controlled to vary whether the neutronic control elements 50 absorb or reflect neutrons from the nuclear reactor core 20, and thereby control reactivity levels in the nuclear reactor core 20. The neutronic control elements 50 may comprise rotatable control drums disposed around the periphery of the nuclear reactor core 20. Rotation of the drums by an actuator 52 may vary whether the neutronic control elements 50 absorb or reflect neutrons from the nuclear reactor core 20. The actuator(s) 52 may be controlled by a suitable controller, which may receive data from one or more sensors. For example, the actuators 52 may be controlled by a first controller 55. Although not depicted, it is envisaged that the first controller 55 may be in communication with multiple systems, including sensor system(s) of the nuclear fission power plant 10. The sensor systems may be configured to determine a rate of fission in the nuclear reactor core 20. Each drum may comprise a neutron-reflecting material 51 (e.g. graphite or beryllium oxide) and may further comprise a neutron-absorbing material 53 (e.g. boron carbide). Beryllium oxide has very good neutron reflecting properties for its mass, has a high thermal conductivity, and a high temperature stability. Using beryllium oxide as the neutron-reflecting material of the drum may therefore increase a performance of the drum, which may consequently permit a mass of the nuclear fission power plant 10 to be reduced. The neutron-absorbing material 53 may be disposed over at least a portion of an outer circumference of the drum. To promote reactivity, the control drums may be positioned such that more of the reflecting material 51 is facing toward the core, thereby directing more neutrons back into the nuclear reactor core. To slow down reactivity, each control drum cylinder may be rotated so that more of the neutronabsorbing material 53 is facing toward the core, thereby absorbing more neutrons to slow down the nuclear reactor. In this way, reactivity levels of the nuclear reactor core 20 may be controlled and the rotatable drums may provide the primary form of control. The neutronic control elements 50 may be used for fine control, such as during a normal operating mode of the nuclear fission power plant 10. The neutronic control elements 50 may also be used for coarse control, such as in an emergency or shut-down mode of the nuclear fission power plant 10. The rotatable drums may be rotated quickly to rapidly increase their neutron absorbing properties, e.g., in the event of an emergency. The rotatable control drums may be the sole form of control of the nuclear reactor core 20. The rotatable drums of the neutronic control elements 50 are advantageously compact and sufficiently robust to withstand the vibrations of a rocket launch.

[0035] Two or more independent actuators 52 may be provided for redundancy. For example, an actuator may be provided at each end of a rotatable drum. In another arrangement, the rotatable drums may be arranged in two or more independent sets of rotatable drums with each set having its own actuator. The rotatable drums within a particular set may alternate with rotatable drums from another set. For example, there may be two independent sets of six rotatable drums interspersed with one another about the circumference of the nuclear reactor core 20. Likewise, two or more independent control systems for the actuator(s) may be provided for redundancy, for example an independent control system may be provided for each set of rotatable drums.

[0036] The rotatable drums are advantageously compact and very reliable compared with other control methods, such as linear control rods, which require more space. The rotatable drums also are less impacted by environmental conditions such as vibration and are therefore more robust. In contrast to linear control rods, the rotatable drums are also highly reliable since the space they occupy does not change and they do not rely on linear movement into a void.

[0037] As shown in Figure 2, the nuclear reactor core may further comprise a moderator 60. The use of a moderator may further reduce the mass of fuel required due to a better neutron economy. The moderator may be at least partially formed from yttrium hydride (YtH2-x). Yttrium hydride has exceptional neutron slowing power thus requiring less overall mass of moderator. YtFh-X also demonstrates outstanding thermal stability and therefore requires less cooling infrastructure when used in the reactor core. However, zirconium hydride (ZrH2-x) could be used in place of YtH2-x. ZrH2-x is almost as high performing as a moderator as YtH2-x.

[0038] The nuclear fission power plant 10 may further comprise a neutron reflector 70 disposed around a periphery of the nuclear reactor core 20. The neutron reflector may reflect neutrons back towards the nuclear reactor core 20. The neutron reflector may be formed from beryllium oxide, BeO. Beryllium oxide provides very high neutron reflection properties for its mass. Beryllium oxide also has high thermal conductivity and high temperature stability, making it ideal for use close to the reactor core 20. Alternatively, nuclear-grade graphite or aluminium oxide (AI2O3) may be used as a reflection material, as it provides acceptable neutron reflection properties for its mass.

[0039] Referring to Figures 1 to 3, the nuclear fission power plant 10 may further comprise a plurality of thermoelectric generators 80. The thermoelectric generators 80 may generate an electrical current by virtue of a temperature gradient across each thermoelectric generator. The thermoelectric generators 80 may generate electricity from the diffusion of electrons across the temperature gradient. The thermoelectric generators 80 may be electrically coupled together and may supply an electrical current to one or more loads. The thermoelectric generators 80 advantageously have excellent reliability and long lifespans and the nuclear fission power plant 10 can continue to operate in the event of one or more thermoelectric generators 80 failing.

[0040] The nuclear fission power plant 10 may further comprise a fluid circuit 90 with a working fluid that flows through the fluid circuit. The fluid circuit 90 may comprise a heat exchanger 92 and a pump 94. The pump 94 may be operated to pump the working fluid around the fluid circuit. The protruding ends 42 of the heat pipes 40 extend into the heat exchanger 92 to transfer heat from the nuclear reactor core 20 to the working fluid of the fluid circuit 90. The thermoelectric generators 80 have a first end thermally coupled to the fluid circuit 90. As such, the fluid circuit is arranged so that the working fluid flowing through the fluid circuit 90 transfers heat from the heat pipes 40 via the heat exchanger 92 to the thermoelectric generators 80.

[0041] Referring to Figure 3, the nuclear fission power plant 10 may comprise a plurality of radiator heat pipes 86. The second end of the thermoelectric generators 80 may be coupled to a radiator heat pipe 86. In a particular example, the radiator heat pipes 86 may be elongate and may be arranged perpendicular to a flow direction of the fluid circuit 90 where a thermoelectric generator 80 associated with the radiator heat pipe is thermally coupled to the fluid circuit 90. The radiator heat pipes 86 may be thermally coupled to a passive radiator 100 such that heat dissipated at the second end of the thermoelectric generators 80 is distributed across the passive radiator 100. The passive radiator 100 may be comprised of a thin metal sheet or fin. The passive radiator 100 presents a surface area from which heat may be radiated. The passive radiator 100 may use the mechanism of radiation to dissipate thermal energy out into space. In this way, a temperature gradient is provided across the thermoelectric generators 80 so that they may generate an electrical current. The radiator heat pipes 86 may extend beyond an edge of the thermoelectric generators 80 so that heat from the second end of the thermoelectric generators may be transferred to a greater area of the radiator 100.

[0042] As with the heat pipes 40, the radiator heat pipes 86 are heat-transfer devices that use phase transition of an internal working fluid to transfer heat between two parts of the heat pipe. At the hot part of the radiator heat pipe 86 (i.e., directly or indirectly coupled to the second end of the thermoelectric generators 80), a volatile liquid within the radiator heat pipe 86 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the radiator heat pipe 86 to a cold part of the radiator heat pipe and condenses back into a liquid, releasing the latent heat at the radiator 100 (e.g., at a point spaced apart from the second end of the thermoelectric generator 80). The liquid then returns to the hot part of the radiator heat pipe 86 and the cycle repeats.

[0043] The passive radiator 100 is advantageously structurally simple, with no moving fluids or components, so as to provide a reliable configuration for rejecting excess thermal energy. The passive radiator 100 also lends itself to being foldable or divisible such that it can be readily stowed for transportation.

[0044] With reference to Figure 4, the nuclear fission power plant 10 may comprise a plurality of thermoelectric generator groups 82 (examples of which are indicated by the dashed line boxes), with each group 82 comprising a plurality of thermoelectric generators 80 thermally coupled to the fluid circuit 90.

[0045] With reference to Figure 5, the nuclear fission power plant 10 may comprise a first plurality of thermoelectric generators 80a thermally coupled to a first passive radiator 100a via a first plurality of radiator heat pipes 86a on a first side of the fluid circuit 90. The nuclear fission power plant 10 may comprise a second plurality of thermoelectric generators 80b thermally coupled to a second passive radiator 100b via a second plurality of radiator heat pipes 86b on a second side of the fluid circuit 90. As such, the first passive radiator 100a and the second passive radiator 100b may be disposed either side of the fluid circuit 90. This arrangement may maximise the number of thermoelectric generators 80b and the passive radiator surface area. The first and second passive radiators 100a, 100b may be vertically orientated, e.g., with respect to a moon or planetary surface.

[0046] As best shown in Figure 5, each group 82 of thermoelectric generators 80 may have an intermediate plate or fin 84 disposed between the passive radiator 100 and the group 82 of thermoelectric generators. The intermediate fin 84 may assist in conducting heat from the thermoelectric generators 80. The intermediate fin 84 may have a dimension that extends beyond the thermoelectric generators 80. This may help even out the temperature distribution on the passive radiator 100. The passive radiator 100 may be common to a plurality of the thermoelectric generators 80 or groups 82 of thermoelectric generators 80. The intermediate fins 84 may thus facilitate heat transfer from individual groups of thermoelectric generators 80 to a common passive radiator 100.

[0047] The combination of the radiator heat pipes 86 and radiator 100 is more compact and efficient than an arrangement with thermoelectric generators directly coupled to a radiator. Furthermore, the heat pipes 86 are extremely reliable due to their lack of moving parts and have excellent redundancy due to the ability to have a large number of heat pipes. The radiator heat pipes 86 are also very effective at spreading heat across the radiator 100, which improves heat dissipation. This improved performance more than offsets the increased complexity of including the radiator heat pipes 86.

[0048] As shown in Figures 1 and 2, the fluid circuit 90 may comprise a plurality of parallel flow paths with at least one thermoelectric generator 80 or group 82 of thermoelectric generators 80 in thermal contact with each parallel flow path. Thermoelectric generators 80 or groups 82 of thermoelectric generators 80 may be arranged in series within a particular one of the parallel flow paths.

[0049] Although not depicted, it is envisaged that the nuclear fission power plant 10 may comprise at least one further fluid circuit similar to fluid circuit 90. The further fluid circuit may be configured to transfer heat from the heat pipes 40 or further heat pipes of the nuclear reactor core 20. The further fluid circuit may transfer heat via the heat exchanger 92 or a further heat exchanger to the thermoelectric generators 80 or further thermoelectric generators. The further fluid circuit may have a further pump for circulating a working fluid in the further fluid circuit. The further fluid circuit may effectively be parallel to the fluid circuit 90 and may improve the robustness of the nuclear fission power plant 10 since it can continue to operate in the event of one of the fluid circuits failing. [0050] The nuclear fission power plant 10 may be deployable from a stowed configuration (e.g., in which the nuclear power plant may be stowed within a rocket for transportation) to a deployed configuration (e.g., in which the nuclear power plant may be operated to generate electricity). For example, the plurality of thermoelectric generators 80, the fluid circuit 90 and passive radiator 100 may be deployable from a stowed configuration to a deployed configuration in which the passive radiator 100 is opened out. In particular, the passive radiator 100 may be flexible and/or foldable. The deployability of the nuclear fission power plant 10 may be at least partially enabled by the fluid circuit 90 having flexible pipes connecting the various components. Also, clustering the thermoelectric generators into groups 82 may facilitate the radiator 100 to be packaged down into a smaller volume, e.g. by separating or folding sections of the radiator 100 associated with each group 82.

[0051] Once deployed, the fluid circuit 90 may be configured such that the passive radiator 100 and thermoelectric generators 80 are spaced apart from the nuclear reactor core 20. The passive radiator 100 and thermoelectric generators 80 may be spaced apart from the nuclear reactor core 20 by 5 metres, by 10 metres or more. This may allow the passive radiator 100 to be spread out over a greater area and it may increase the radiative capacity of the passive radiator 100 by being further from the nuclear reactor core 20. The spacing of the thermoelectric generators 80 from the nuclear reactor core 20 may be achieved by the fluid circuit 90 having pipes (which may be flexible) with lengths that extend from the heat exchanger 92 to the desired location for the thermoelectric generators 80.

[0052] The present disclosure also relates to a kit of parts for the nuclear fission power plant 10. The kit of parts may comprise at least some of the above-described components. The kit of parts may be configured for placement within a rocket to be launched into space. The kit of parts may also be configured at least partially for extra-terrestrial assembly. Once deployed in space, the kit of parts may automatically assemble or may be assembled with the assistance of a robot, an astronaut or any other space operative.

[0053] With reference to Figure 6, the present disclosure also relates to a method 200 for the nuclear fission power plant 10. The method 200 comprises controlling the nuclear fission power plant 10. The control of the nuclear fission power plant 10 may be at least partially carried out remotely, for example on a lunar base, from Earth or any other location.

[0054] The method 200 controls the nuclear fission power plant 10 such that in a first action 210, the nuclear fission power plant 10 generates heat with the nuclear reactor core 20. In a second action 220, the nuclear fission power plant 10 transfers heat from the nuclear reactor core using the plurality of heat pipes 40. In a third action 230, the nuclear fission power plant 10 transfers heat from the protruding end 42 of the heat pipes 40 to the plurality of thermoelectric generators 80 using the working fluid flowing in the fluid circuit. In a fourth action 240, the nuclear fission power plant 10 radiates heat using the passive radiator 100. In a fifth action 250, the nuclear fission power plant 10 generates electricity by virtue of the temperature gradient across the thermoelectric generators 80.

[0055] The present disclosure advantageously provides a lightweight, yet rugged and resilient nuclear fission power plant. These advantages are particularly beneficial for space applications where weight and ruggedness are important factors for a rocket launch and resilience helps to ensure a long life span with minimal maintenance. The specific use of heat pipes, rotatable control drums, thermoelectric generators and a passive radiator contribute to these advantages. The reactor core, heat pipes, thermoelectric generators and passive radiator have few moving parts and are therefore very robust. The rotatable drums are also highly reliable since the space they occupy does not change and they are not relying on linear movement into a void. The heat pipe and thermoelectric generator arrangement is resilient due to the high level of redundancy since a particular heat pipe or thermoelectric generator can fail without affecting operation of the remaining components.

[0056] The heat pipes also promote a flat temperature distribution within the reactor core, which improves reactor performance. The resulting improvement in heat output compensates for the less efficient thermoelectric generators. The overall efficiency of the nuclear power plant is therefore maintained at a high level.

[0057] Furthermore, the selected moderator and reflector materials are high performing, which improves power output and allows a more compact reactor. The increased heat output can lead to more current being output by the thermoelectric generators. The more efficient core design can also save weight since less uranium fuel is required.

[0058] The above-described features combine to improve the robustness and resilience of the overall nuclear power plant, whilst providing a high performing nuclear reactor with good efficiency and energy output.

[0059] In addition, the present disclosure provides a lightweight and compact design. For example, the metallic fuel system provides a high energy density and lightweight arrangement, and the rotatable drums minimize the volume required since the occupied space does not change when the drums are actuated. The fluid circuit also provides a simple but effective design that allows a modular and readily deployable arrangement. The overall package size and weight is therefore lower.

[0060] The fluid circuit may also provide a thermal buffer between the reactor core and the thermoelectric generators. The fluid circuit may thus reduce the impact of any thermal fluctuations in the reactor core.

[0061] Moreover, not having linearly actuated control rods saves weight, reduces complexity, and provides a more robust arrangement. Examples given herein and therefore more robust owing to the fact they do not require linearly actuated control rods in order to function safely.

[0062] Various examples have been described, each of which feature various combinations of features. It will be appreciated by those skilled in the art that, except where clearly mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub- combinations of one or more features described herein.

Claims

1 . A nuclear fission power plant configured for extra-terrestrial use, the nuclear fission power plant comprising: a nuclear reactor core, the nuclear reactor core comprising a metallic fuel; a plurality of reactor heat pipes, each reactor heat pipe at least partially extending within the nuclear reactor core; a neutron reflector disposed around a periphery of the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a plurality of thermoelectric generators; a fluid circuit comprising a heat exchanger and a pump, wherein a protruding end of the reactor heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to a working fluid of the fluid circuit, the fluid circuit being arranged such that the working fluid flowing through the fluid circuit transfers heat from the heat exchanger to the thermoelectric generators; at least one passive radiator; and a plurality of radiator heat pipes; wherein the thermoelectric generators have a first end thermally coupled to the fluid circuit and a second end thermally coupled to at least one of the radiator heat pipes, the radiator heat pipes being thermally coupled to the at least one passive radiator such that heat dissipated at the second end of the thermoelectric generators is distributed across the at least one passive radiator.

2. The nuclear fission power plant of claim 1 , wherein the metallic fuel comprises High Assay Low Enriched Uranium (HALEU).

3. The nuclear fission power plant of claim 1 or 2, wherein the metallic fuel is enriched to substantially 19.75% uranium-235.

4. The nuclear fission power plant of any preceding claim, wherein the metallic fuel comprises a solid fuel alloy.

5. The nuclear fission power plant of any preceding claim, wherein the neutron reflector is at least partially formed from beryllium oxide, BeO.

6. The nuclear fission power plant of any of the preceding claims, wherein the nuclear reactor core further comprises a moderator.

7. The nuclear fission power plant of claim 6, wherein the moderator is at least partially formed from yttrium hydride (YtH₂-x) or zirconium hydride (ZrH₂-x).

8. The nuclear fission power plant of any of the preceding claims, wherein the rotatable control drums are used for fine and coarse control of the nuclear reactor core.

9. The nuclear fission power plant of any of the preceding claims, wherein the rotatable control drums are the sole form of control of the nuclear reactor core.

10. The nuclear fission power plant of any of the preceding claims, wherein the nuclear fission power plant comprises a plurality of thermoelectric generator groups, with each group comprising a plurality of thermoelectric generators thermally coupled to the fluid circuit.

11. The nuclear fission power plant of claim 10, wherein the nuclear fission power plant further comprises a plurality of intermediate fins, each intermediate fin being disposed between at least one of the radiator heat pipes and a corresponding group of the thermoelectric generators so as to conduct heat from the thermoelectric generators to the radiator heat pipes.

12. The nuclear fission power plant of claim 11 , wherein the radiator heat pipes extend beyond an edge of the intermediate fins.

13. The nuclear fission power plant of any of the preceding claims, wherein the radiator heat pipes are elongate and are arranged perpendicular to a flow direction of the fluid circuit where a thermoelectric generator associated with the radiator heat pipe is thermally coupled to the fluid circuit.

14. The nuclear fission power plant of any of the preceding claims, wherein the fluid circuit comprises a plurality of parallel flow paths with at least one thermoelectric generator in thermal contact with each parallel flow path.

15. The nuclear fission power plant of claim 14, wherein a plurality of thermoelectric generators is in thermal contact with each parallel flow path, the thermoelectric generators associated with a particular one of the parallel flow paths being arranged in series.

16. The nuclear fission power plant of any of the preceding claims, wherein the nuclear fission power plant comprises a first plurality of thermoelectric generators thermally coupled to a first passive radiator via a first plurality of radiator heat pipes and a second plurality of thermoelectric generators thermally coupled to a second passive radiator via a second plurality of radiator heat pipes.

17. The nuclear fission power plant of claim 16, wherein the first passive radiator and the second passive radiator are disposed either side of the fluid circuit.

18. A kit of parts for a nuclear fission power plant configured for extra-terrestrial use, the kit of parts being configured at least partially for extra-terrestrial assembly and comprising: a nuclear reactor core, the nuclear reactor core comprising a metallic fuel; a plurality of reactor heat pipes, each reactor heat pipe configured to be at least partially extendable within the nuclear reactor core; a neutron reflector configured to be disposed around a periphery of the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums configured to be disposed around the periphery of the nuclear reactor core; a plurality of thermoelectric generators; a fluid circuit that, when assembled, comprises a heat exchanger and a pump, wherein, when installed, a protruding end of the reactor heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to a working fluid of the fluid circuit, the fluid circuit being configured such that when assembled the working fluid can flow through the fluid circuit and transfer heat from the heat exchanger to the thermoelectric generators; a passive radiator; and a plurality of radiator heat pipes; wherein the thermoelectric generators have a first end thermally couplable to the fluid circuit and a second end thermally couplable to at least one of the radiator heat pipes, the radiator heat pipes being thermally couplable to the passive radiator such that, in operation, heat dissipated at the second end of the thermoelectric generators is distributable across the passive radiator.

19. The kit of parts of claim 18, further comprising a moderator configured to be positioned within the nuclear reactor core.

20. A method for a nuclear fission power plant configured for extra-terrestrial use, the method comprising controlling the nuclear fission power plant to: generate heat with a nuclear reactor core, the nuclear reactor core comprising a metallic fuel; wherein a neutron reflector is disposed around a periphery of the nuclear reactor core, and a plurality of neutronic control elements comprising rotatable control drums are disposed around the periphery of the nuclear reactor core; transfer heat from the nuclear reactor core using a plurality of reactor heat pipes, each heat pipe at least partially extending within the nuclear reactor core; transfer heat from a protruding end of the heat pipes to a plurality of thermoelectric generators using a working fluid flowing in a fluid circuit, the fluid circuit comprising a heat exchanger and a pump, wherein the protruding end of the heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to the working fluid of the fluid circuit; radiate heat using a passive radiator and a plurality of radiator heat pipes, wherein the thermoelectric generators have a first end thermally coupled to the fluid circuit and a second end thermally coupled to at least one of the radiator heat pipes, the radiator heat pipes being thermally coupled to the passive radiator such that heat dissipated at the second end of the thermoelectric generators is distributed across the passive radiator; and generate electricity by virtue of a temperature gradient across the thermoelectric generators.