Nuclear fission power plant

Abstract

A nuclear fission power plant (10) for extra-terrestrial use comprising: a nuclear reactor core (20) comprising a metallic fuel (30) and a moderator (60); reactor heat pipes (40) that each at least partially extend within the nuclear reactor core; neutronic control elements (50) comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a neutron reflector (70) disposed around a periphery of the nuclear reactor core; a fluid circuit (90) comprising a turbine (94), a heat dissipator (96), and compressor (98) arranged in flow series, wherein an 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, which drives the turbine and transfers heat from the heat exchanger to the heat dissipator; and an electrical generator (80), wherein the turbine drives the compressor and electrical generator.

Description

NUCLEAR FISSION POWER PLANTTECHNICAL 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, the power density of solar panels 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; and a moderator;a plurality of reactor heat pipes, each reactor heat pipe at least partially extending within the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a neutron reflector disposed around a periphery of the nuclear reactor core; a fluid circuit comprising a turbine, a heat dissipator, and a compressor arranged in flow series, wherein an 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, wherein the fluid circuit is arranged such that the working fluid flowing through the fluid circuit drives the turbine and transfers heat from the heat exchanger to the heat dissipator; and an electrical generator, wherein the turbine is configured to drive the compressor and the electrical generator.

[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 moderator may be at least partially formed from yttrium hydride (YtH2-x) or zirconium hydride (ZrH2-x).

[0009] The reactor heat pipes may comprise a heat pipe working fluid comprising an alkali metal, such as sodium.

[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 deployable neutronabsorbing control balls. The deployable neutron-absorbing control balls may be selectively deployable into the nuclear reactor core to control reactivity levels. The deployable neutronabsorbing control balls may be used for coarse control, such as in an emergency or shut-down mode.

[0012] The heat dissipator may comprise a radiator arranged such that a gas in the fluid circuit may pass through the radiator and may be in thermal contact with a radiator surface of the radiator.

[0013] The heat dissipator may comprise a further radiator arranged such that the gas in the fluid circuit may pass through the further radiator and may be in thermal contact with a further radiator surface of the further radiator. The radiator and further radiator may be in parallel to each other in respect of the fluid circuit. Valves may be provided to isolate one of the parallel branches if necessary.

[0014] The heat dissipator may comprise a heat exchanger thermally coupled to an additional fluid circuit. The additional fluid circuit may comprise a pump configured to circulate an additional fluid circuit working fluid in the additional fluid circuit, a plurality of radiator heat pipes and at least one radiator. A first end of each radiator heat pipe may be thermally coupled to the additional fluid circuit working fluid of the additional fluid circuit and a second end of each radiator heat pipe may be thermally coupled to the radiator or one of the radiators.

[0015] The heat dissipator may comprise a plurality of radiator heat pipes and at least one radiator. A first end of each radiator heat pipe may be thermally coupled to the working fluid of the fluid circuit and a second end of each radiator heat pipe may be thermally coupled to the radiator or one of the radiators.

[0016] At least a portion of the heat dissipator (e.g. the radiator) may be deployable from a stowed configuration to a deployed configuration in which the at least a portion of the heat dissipator (e.g. the radiator) is opened out. The fluid circuit may be configured such that the heat dissipator (e.g. the radiator) may be spaced apart from the nuclear reactor core, e.g., by 5 metres, by 10 metres or more.

[0017] 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; and a moderator; a plurality of reactor heat pipes, each reactor heat pipe at least partially extendable within the nuclear reactor core;a plurality of neutronic control elements comprising rotatable control drums disposable around the periphery of the nuclear reactor core; a neutron reflector disposable around a periphery of the nuclear reactor core; a fluid circuit comprising a turbine, a heat dissipator, and a compressor arrangeable in flow series, wherein, when assembled, an 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, wherein the fluid circuit is arrangeable such that the working fluid flowing through the fluid circuit drives the turbine and transfers heat from the heat exchanger to the heat dissipator; and an electrical generator, wherein the turbine is configured to drive the compressor and the electrical generator.

[0018] The kit of parts may further comprise a plurality of deployable neutronabsorbing control balls, the deployable neutron-absorbing control balls being selectively deployable into the nuclear reactor core to control reactivity levels.

[0019] The heat dissipator of the kit of parts may comprise a radiator arrangeable such that when assembled and in use a gas in the fluid circuit passes through the radiator and is in thermal contact with a radiator surface of the radiator.

[0020] The heat dissipator of the kit of parts may comprise a heat exchanger thermally couplable to an additional fluid circuit, wherein the additional fluid circuit comprises a pump configured to circulate a working fluid in the additional fluid circuit, a plurality of radiator heat pipes and at least one radiator, wherein a first end of each radiator heat pipe is thermally couplable to the working fluid of the additional fluid circuit and a second end of each radiator heat pipe is thermally couplable to the radiator or one of the radiators.

[0021] The heat dissipator of the kit of parts may comprise a plurality of radiator heat pipes and at least one radiator, wherein a first end of each radiator heat pipe is thermally couplable to the working fluid of the fluid circuit and a second end of each radiator heat pipe is thermally couplable to the radiator or one of the radiators.

[0022] 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 comprising a metallic fuel and a moderator, 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 reactor heat pipe at least partially extending within the nuclear reactor core; transfer heat from an end of the reactor heat pipes to a working fluid flowing in a fluid circuit, the fluid circuit comprising a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the end of the reactor heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to the working fluid of the fluid circuit; dissipate heat using the heat dissipator; drive the compressor and an electrical generator with the turbine; and generate electricity with the electrical generator.

[0023] 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

[0024] 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:

[0025] Figure 1 is a schematic diagram showing an example of nuclear fission power plant configured for extra-terrestrial use;

[0026] Figure 2 is a schematic diagram showing another example of a nuclear fission power plant configured for extra-terrestrial use;

[0027] Figure 3 is a schematic diagram showing another example of a nuclear fission power plant configured for extra-terrestrial use;

[0028] Figure 4 is a schematic diagram showing another example of a nuclear fission power plant configured for extra-terrestrial; and

[0029] Figure 5 is a flowchart depicting a method for a nuclear fission power plant configured for extra-terrestrial use.DETAILED DESCRIPTION

[0030] With reference to Figure 1 , 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 extra-terrestrial 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.

[0031] 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.

[0032] 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.

[0033] The metallic fuel 30 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 a tubular cladding.

[0034] The nuclear reactor core 20 may be cooled using two-phase passive convection. For example, the nuclear reactor core 20 may further comprise a plurality of reactor heat pipes 40. Each reactor heat pipe 40 extends at least partially within (e.g. substantially across a length of) the nuclear reactor core 20. The reactor heat pipes 40 may be substantially elongate and may have a protruding end 42 that protrudes beyond the nuclear reactor core 20. The reactor 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.

[0035] The reactor 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 reactor heat pipe 40 (i.e. , in the nuclear reactor core 20), a volatile liquid within the reactor heat pipe 40 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the reactor heat pipe 40 to a cold part of the heat pipe and condenses back into a liquid, releasing the latent heat (i.e., at the protruding end 42). The liquid then returns to the hot part of the reactor heat pipe 40 and the cycle repeats.

[0036] Reactor heat pipes 40 have been selected as they have excellent reliability, lifetime and redundancy (for example the nuclear power plant may continue to operate if a particular heat pipe has failed). The reactor 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.

[0037] 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(s) 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.

[0038] 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 neutronreflecting 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 neutronabsorbing 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 thereflecting 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 neutron-absorbing 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.

[0039] 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.

[0040] 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. 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.

[0041] However, with reference to Figure 2, it is also envisaged that the rotatable control drums may not be the sole form of control of the nuclear reactor core 20. For example, the nuclear fission power plant 10 may additionally comprise a plurality of deployable neutronabsorbing control balls 54. The deployable neutron-absorbing control balls 54 may be selectively deployable into the nuclear reactor core 20 to control reactivity levels. The deployable neutron-absorbing control balls 54 may be used for coarse control, such as in anemergency or shut-down mode. The rotatable control drums may continue to be used for fine control, such as during a normal operating mode of the nuclear fission power plant 10.

[0042] The deployable neutron-absorbing control balls 54 may be stored in a hopper 55 adjacent to the reactor core 20. In the event of an emergency reactor shut down, the deployable neutron-absorbing control balls 54 may be inserted into the nuclear reactor core 20 using gravity, gas pressure or any other method. This would increase negative reactivity in the nuclear reactor core 20 until the nuclear fission reaction has stopped. The deployable neutron-absorbing control balls 54 may be made from boron carbide, tantalum, or any other suitable neutron-absorbing material.

[0043] The nuclear reactor core 20 may further comprise a moderator 60. The use of a moderator may reduce the mass of fuel required as the moderator has the effect of improving the neutron economy. The moderator may be at least partially formed from yttrium hydride (YtH2-x), which can function as a neutron moderator at high temperatures. However, zirconium hydride (ZrH2-x) could be used in place of YtH2-x, as ZrH2-x can also act as a neutron moderator at high temperatures.

[0044] 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.

[0045] The nuclear fission power plant 10 may further comprise an electrical generator 80, such as that with a rotating element for generating an electrical current, and a fluid circuit 90 configured to power the electrical generator 80. The fluid circuit 90 may comprise a heat exchanger 92. The protruding ends 42 of the reactor heat pipes 40 may extend into the heat exchanger 92 to transfer heat from the nuclear reactor core 20 to a working fluid of the fluid circuit 90.

[0046] The fluid circuit 90 may further comprise a turbine 94, a heat dissipator 96, and a compressor 98 arranged in flow series. The hot working fluid from the heat exchanger 92 flows through and drives the turbine 94. The gas then passes through the heat dissipator 96and then the compressor 98, before returning to the heat exchanger 92. The turbine 94 drives the compressor 98 and the electrical generator 80, e.g., by virtue of a connecting shaft 82. The working fluid flowing in the fluid circuit 90 may follow the Brayton cycle.

[0047] In the example shown in Figure 1 , the heat dissipator 96 comprises a radiator 100 arranged such that gas in the fluid circuit 90 passes through or across the radiator 100 and is in thermal contact with a radiator surface of the radiator. For example, heat may flow from the working fluid of the fluid circuit 90 via at least conduction into the radiator body, and then to the radiator surface of the radiator, from which it can radiate away into the surrounding environment (for example, space). The fluid circuit 90 may flow through a tortuous flow path thermally coupled to the radiator 100, e.g., to maximise the heat transfer from the fluid circuit 90 to the radiator 100. Heat can dissipate by radiation from the radiator surface. The radiator 100 is advantageously structurally simple, with no moving parts or components, making it a reliable configuration for rejecting excess thermal energy. The radiator 100 also lends itself to being foldable or divisible such that it can be readily stowed for transportation.

[0048] The arrangement shown in Figure 1 advantageously eliminates the need for additional heat exchangers which might otherwise add complexity and mass to the system. Furthermore, the gas Brayton cycle provides benefits such as reaching higher temperatures allowing for greater thermal efficiency in power conversion. This also reduces the mass of the system by reducing the size of the turbine 94 and compressor 98.

[0049] The heat dissipator 96 may comprise at least one further radiator arranged in parallel (or in series) with the radiator 100. The further radiator may be structurally similar to the radiator 100. For example, the working fluid in the fluid circuit 90 may pass through the further radiator and may be in thermal contact with a further radiator surface of the further radiator. The radiator and further radiator may be in parallel branches of the fluid circuit 90. Valves may be provided to isolate one of the parallel branches if necessary.

[0050] With reference to Figure 3, in an alternative arrangement, the heat dissipator 96 may comprise an additional heat exchanger 110 thermally coupled to an additional fluid circuit 120. The additional heat exchanger 110 may thermally couple the fluid circuit 90 and the additional fluid circuit 120. The additional fluid circuit 120 may comprise a pump 122 configured to circulate an additional fluid circuit working fluid in the additional fluid circuit 120. The additional fluid circuit 120 may further comprise a plurality of radiator heat pipes 124 and at least one radiator 126. A first end of each radiator heat pipe 124 may be thermally coupledto the additional fluid circuit working fluid of the additional fluid circuit 120 and a second end of each radiator heat pipe 124 may be thermally coupled to the radiator 126 or one of the radiators.

[0051] The radiator heat pipes 124, much like the reactor heat pipes 40, are heattransfer devices that use phase transition to transfer heat between two parts of the heat pipe. At the hot part of the radiator heat pipe 124 (i.e., coupled to the additional fluid circuit working fluid), a volatile liquid within the radiator heat pipe 124 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the radiator heat pipe 124 to a cold part of the heat pipe and condenses back into a liquid, releasing the latent heat at the radiator 126. The liquid then returns to the hot part of the radiator heat pipe 124 and the cycle repeats.

[0052] The arrangement shown in Figure 3 advantageously reduces the flow length of the fluid circuit 90, which reduces flow resistance and can increase flow rate. The radiator heat pipes 124 are also very effective at spreading heat across the radiator 126, which can improve heat dissipation and improve compactness. This improved performance helps to offset the increased complexity of including the additional fluid circuit 120. The radiator heat pipes 124 are also highly reliable and provide additional redundancy, e.g., in case a particular heat pipe fails or the radiator 126 is struck by a meteorite. Having a high degree of redundancy can reduce the amount of shielding required, which in turn reduces the overall weight.

[0053] With reference to Figure 4, in an alternative arrangement the additional heat exchanger 110 of the example depicted in Figure 3 may be omitted. In other words, the heat dissipator 96 may comprise just the plurality of radiator heat pipes 124 and at least one radiator 126. A first end of each radiator heat pipe 124 may be thermally coupled to the working fluid of the fluid circuit 90 and a second end of each radiator heat pipe may be thermally coupled to the radiator 126 (or one of the radiators 126). The heat pipes 124 may thus be directly thermally coupled to the working fluid of the fluid circuit 90.

[0054] 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. Accordingly, the further fluid circuit may comprise a further turbine and a further compressor arranged in flow series. The further fluid circuit may also comprise a further heat dissipator or share the heat dissipator 96 with fluid circuit 90. The further fluid circuit may be configured to transfer heat from the reactor heat pipes 40 or further reactor 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 theheat dissipator 96 or further heat dissipator. The further turbine may drive the further compressor and the electrical generator 80 or a further electrical generator. 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.

[0055] 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, at least a portion of the heat dissipator 94 or radiator 100, 126 may be deployable from a stowed configuration to a deployed configuration in which the at least a portion of the heat dissipator or radiator is opened out. In particular, the radiator 100 or radiator 126 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 and / or connections connecting at least to the heat dissipator 94.

[0056] Once deployed, the fluid circuit 90 may be configured such that the radiator 100 (or radiator 126) is spaced apart from the nuclear reactor core 20. The radiator 100 (or radiator 126) may be spaced apart from the nuclear reactor core 20 by 5 metres, by 10 metres or more. This may allow the radiator to be spread out over a greater area and it may increase the radiative capacity of the radiator by being further from the nuclear reactor core 20. The spacing of the radiator 100 (or radiator 126) from the nuclear reactor core 20 may be achieved by the fluid circuit 90 (and / or additional fluid circuit 120) having pipes (which may be flexible) with lengths that extend from the heat exchanger 92 to the desired location for the radiator 100 (or radiator 126).

[0057] 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.

[0058] With reference to Figure 5, the present disclosure also relates to a method 200 for the nuclear fission power plant 10. The method 200 comprises controlling the nuclearfission 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.

[0059] 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, heat from the nuclear reactor core 20 is transferred to the plurality of reactor heat pipes 40. In a third action 230, heat is transferred from the heat pipes to the working fluid of the fluid circuit 90. In a fourth action 240, heat is dissipated from the heat dissipator 96. In a fifth action 250, the compressor 98 and electrical generator 80 are driven by the turbine 94. In a sixth action 260, electricity is generated with the electrical generator 80.

[0060] The present disclosure advantageously provides a very compact micro-reactor design. This advantage is particularly beneficial for space applications where compactness is an important factor for a rocket launch. The compact design is achieved thanks to various factors. For example, the rotatable drums minimize the length and volume required since the occupied space does not change when the drums are actuated. The metallic fuel system provides a high energy density and therefore compact and lightweight arrangement. The selected hydride moderator and BeO reflector materials are high performing, which improves power output and allows a more compact reactor. The more efficient core design can also save weight since less uranium fuel is required. The Brayton cycle generator also provides excellent power to weight and volume performance when compared to other power conversion technologies. The overall package size and weight is therefore lower.

[0061] The heat pipes also promote a flat temperature distribution within the reactor core, which improves reactor performance. The resulting improvement in heat output (and the particular material choices mentioned above) compensates for the absorption of neutrons by the heat pipes. The use of heat pipes also avoids having a gas cooled core and all of the associated components. The overall efficiency of the nuclear power plant is therefore maintained at an acceptable level, whilst providing a very compact package.

[0062] The present disclosure also provides a rugged and resilient nuclear fission power plant. These advantages are particularly beneficial for space applications where ruggedness is an important factor 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, and a passive radiator contribute to these advantages. The reactor core, heat pipes, and passiveradiator have few moving parts and are therefore very robust. The rotatable drums are also highly reliable since they only require rotational movement to operate. The heat pipe arrangement is resilient due to the high level of redundancy since a particular heat pipe can fail without affecting operation of the remaining components.

[0063] The fluid circuit provides a simple but effective design that allows a modular and readily deployable arrangement. The fluid circuit may also provide a thermal buffer between the reactor core and the electrical generator. The fluid circuit may thus reduce the impact of any thermal fluctuations in the reactor core.

[0064] 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 subcombinations of one or more features described herein.

Claims

CLAIMS1 . 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; and a moderator; a plurality of reactor heat pipes, each reactor heat pipe at least partially extending within the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a neutron reflector disposed around a periphery of the nuclear reactor core; a fluid circuit comprising a turbine, a heat dissipator, and a compressor arranged in flow series, wherein an 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, wherein the fluid circuit is arranged such that the working fluid flowing through the fluid circuit drives the turbine and transfers heat from the heat exchanger to the heat dissipator; and an electrical generator, wherein the turbine is configured to drive the compressor and the electrical generator.

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 moderator is at least partially formed from yttrium hydride (YtH2-x) or zirconium hydride (ZrH2-x).

7. The nuclear fission power plant of any of the preceding claims, wherein the reactor heat pipes comprise a heat pipe working fluid comprising an alkali metal.

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 claims 1 to 8, wherein the nuclear fission power plant comprises a plurality of deployable neutron-absorbing control balls, the deployable neutron-absorbing control balls being selectively deployable into the nuclear reactor core to control reactivity levels.

11. The nuclear fission power plant of any of the preceding claims, wherein the heat dissipator comprises a radiator arranged such that a gas in the fluid circuit passes through the radiator and is in thermal contact with a radiator surface of the radiator.

12. The nuclear fission power plant of any of claims 1 to 10, wherein the heat dissipator comprises a heat exchanger thermally coupled to an additional fluid circuit, wherein the additional fluid circuit comprises a pump configured to circulate an additional fluid circuit working fluid in the additional fluid circuit, a plurality of radiator heat pipes and at least one radiator, wherein a first end of each radiator heat pipe is thermally coupled to the additional fluid circuit working fluid of the additional fluid circuit and a second end of each radiator heat pipe is thermally coupled to the radiator or one of the radiators.

13. The nuclear fission power plant of any of claims 1 to 10, wherein the heat dissipator comprises a plurality of radiator heat pipes and at least one radiator, wherein a first end of each radiator heat pipe is thermally coupled to the working fluid of the fluid circuit and a second end of each radiator heat pipe is thermally coupled to the radiator or one of the radiators.

14. 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; anda moderator; a plurality of reactor heat pipes, each reactor heat pipe being configured such that, when the kit is assembled, each reactor heat pipe at least partially extends within 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 neutron reflector configured to be disposed around a periphery of the nuclear reactor core; a fluid circuit comprising a turbine, a heat dissipator, and a compressor arrangeable in flow series, wherein, when assembled, an 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, wherein the fluid circuit is configured to be arranged such that the working fluid flowing through the fluid circuit drives the turbine and transfers heat from the heat exchanger to the heat dissipator; and an electrical generator, wherein the turbine is configured to drive the compressor and the electrical generator.

15. The kit of parts of claim 14, further comprising a plurality of deployable neutronabsorbing control balls, the deployable neutron-absorbing control balls being selectively deployable into the nuclear reactor core to control reactivity levels.

16. The kit of parts of claims 14 or 15, wherein the heat dissipator comprises a radiator arrangeable such that when assembled and in use a gas in the fluid circuit passes through the radiator and is in thermal contact with a radiator surface of the radiator.

17. The kit of parts of any of claims 14 or 15, wherein the heat dissipator comprises a heat exchanger thermally couplable to an additional fluid circuit, wherein the additional fluid circuit comprises a pump configured to circulate an additional fluid circuit working fluid in the additional fluid circuit, a plurality of radiator heat pipes and at least one radiator, wherein a first end of each radiator heat pipe is thermally couplable to the additional fluid circuit working fluid of the additional fluid circuit and a second end of each radiator heat pipe is thermally couplable to the radiator or one of the radiators.

18. The kit of parts of any of claims 14 or 15, wherein the heat dissipator comprises a plurality of radiator heat pipes and at least one radiator, wherein a first end of each radiatorheat pipe is thermally couplable to the working fluid of the fluid circuit and a second end of each radiator heat pipe is thermally couplable to the radiator or one of the radiators.

19. 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 comprising a metallic fuel and a moderator, 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 reactor heat pipe at least partially extending within the nuclear reactor core; transfer heat from an end of the reactor heat pipes to a working fluid flowing in a fluid circuit, the fluid circuit comprising a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the end of the reactor heat pipes extends into the heat exchanger to transfer heat from the nuclear reactor core to the working fluid of the fluid circuit; dissipate heat using the heat dissipator; drive the compressor and an electrical generator with the turbine; and generate electricity with the electrical generator.

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