Nuclear fission power plant

Abstract

A nuclear fission power plant (10) configured for extra-terrestrial use comprising a gas-cooled moderated nuclear reactor core (20) with a metallic fuel (30), a moderator (60), and a containment vessel (40) with a containment vessel inlet (42) and a containment vessel outlet (44). A neutron reflector (70) is disposed around a periphery of the gas-cooled moderated nuclear reactor core, and a plurality of neutronic control elements (50) comprising rotatable control drums disposed around the periphery of the gas-cooled moderated nuclear reactor core. A fluid circuit (90) is configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet. An electricity generating system (91) is coupled to the fluid circuit so as to generate an electrical current.

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, 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 a 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 gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a metallic fuel; a moderator; anda containment vessel comprising a containment vessel inlet and a containment vessel outlet; a neutron reflector disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the gas-cooled moderated nuclear reactor core; a fluid circuit configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; and an electricity generating system coupled to the fluid circuit so as to generate an electrical current.

[0006] The fluid circuit may comprise a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the fluid circuit is configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the turbine, heat dissipator and compressor. The electricity generating system may comprise an electrical generator, e.g., with a rotating element for generating an electrical current. The turbine may drive the compressor and the electrical generator.

[0007] Alternatively, the electricity generating system may comprise a plurality of thermoelectric generators and a passive radiator. A first end of the thermoelectric generators may be thermally coupled to the fluid circuit and a second end of the thermoelectric generators may be thermally coupled to the passive radiator. The fluid circuit may comprise a pump to circulate a working fluid in the fluid circuit.

[0008] 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.

[0009] The moderator may comprise graphite, such as nuclear grade graphite.

[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 heat dissipator may comprise a radiator arranged such that gas in the fluid circuit passes through or across the radiator and is in thermal contact with a radiator surface of the radiator. The heat dissipator may comprise a further radiator arranged such that the gas in the fluid circuit passes through the further radiator and is 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.

[0012] 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 a working fluid in the additional fluid circuit, a plurality of heat pipes and at least one radiator. A first end of each heat pipe may be thermally coupled to the working fluid of the additional fluid circuit and a second end of each heat pipe may be thermally coupled to the radiator or one of the radiators.

[0013] 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.

[0014] The nuclear fission power plant may further comprise at least one further fluid circuit. The further fluid circuit may comprise a further turbine, a further heat dissipator, and a further compressor arranged in flow series. The further fluid circuit may be configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the further turbine, further heat dissipator and further compressor. The nuclear fission power plant may comprise a further electrical generator. The further turbine may drive the further compressor and the electrical generator or the further electrical generator.

[0015] 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 gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a metallic fuel; a moderator; anda containment vessel comprising a containment vessel inlet and a containment vessel outlet; a neutron reflector disposable around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposable around the periphery of the gas-cooled moderated nuclear reactor core; a fluid circuit configurable to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; and an electricity generating system couplable to the fluid circuit so as to generate an electrical current.

[0016] The fluid circuit of the kit of parts may comprise a turbine, a heat dissipator, and a compressor configured to be arrangeable in flow series, wherein the fluid circuit when assembled is configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the turbine, heat dissipator and compressor; and the electricity generating means system of the kit of parts comprises an electrical generator, such that, when the electricity generating means system is assembled and in use, the turbine can drive the compressor and the electrical generator.

[0017] The heat dissipator of the kit of parts may comprise a radiator arrangeable such that, when the fluid circuit is assembled and in use, gas in the fluid circuit passes through or across the radiator and is in thermal contact with a radiator surface of the radiator.

[0018] 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 when assembled comprises a pump configured to circulate a working fluid in the additional fluid circuit, a plurality of heat pipes and at least one radiator, wherein a first end of each heat pipe is configured to be thermally coupled to the working fluid of the additional fluid circuit and a second end of each heat pipe is configured to be thermally coupled to the radiator or one of the radiators.

[0019] The electricity generating means system of the kit of parts may comprise a plurality of thermoelectric generators and a passive radiator, a first end of the thermoelectric generators being configured to be thermally coupled to the fluid circuit and a second end of the thermoelectric generators being configured to be thermally coupled to the passive radiator.

[0020] 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 gas-cooled moderated nuclear reactor core comprising a metallic fuel, a moderator and a containment vessel comprising a containment vessel inlet and a containment vessel outlet, wherein a neutron reflector is disposed around a periphery of the gas-cooled moderated nuclear reactor core, and a plurality of neutronic control elements comprising rotatable control drums are disposed around the periphery of the gas-cooled moderated nuclear reactor core; receive hot gas from the containment vessel outlet to a fluid circuit; deliver cooled gas to the containment vessel inlet via the fluid circuit; and generate electricity with an electricity generating system coupled to the fluid circuit.

[0021] 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

[0022] 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:

[0023] Figure 1 is a schematic diagram showing an example of a nuclear fission power plant configured for extra-terrestrial use;

[0024] Figure 2 is a schematic diagram showing another example of a nuclear fission power plant configured for extra-terrestrial use;

[0025] Figure 3 is a schematic diagram showing another example of a nuclear fission power plant configured for extra-terrestrial use;

[0026] Figure 4 is a schematic diagram showing another example of a nuclear fission power plant configured for extra-terrestrial use; and

[0027] Figure 5 is a flowchart depicting a method for a nuclear fission power plant configured for extra-terrestrial use.DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The metallic fuel 30 may comprise a solid fuel alloy, such as U-Zr, U-Mo etc. Such 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 in pellet form and may be clad, e.g., in a tubular cladding.

[0032] The nuclear reactor core 20 may be gas-cooled. Heat may be extracted from the nuclear reactor core 20 by virtue of a cooling gas that flows within the nuclear reactor core 20. The nuclear reactor core 20 may comprise a containment vessel 40 that contains the cooling gas. The containment vessel 40 may comprise a containment vessel inlet 42 and a containment vessel outlet 44 for the cooling gas to flow through. The containment vessel 40 may define a flow path (see for example block arrows in Figure 1 , Figure 2, Figure 3, and Figure 4) between the containment vessel inlet 42 and containment vessel outlet 44 that forces the gas to flow over components within the nuclear reactor core 20. The cooling gas may be helium. However, nitrogen or hydrogen are also contemplated as possible cooling gases.

[0033] 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 controller 54. Although not depicted, it is envisaged that the controller 54 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, B4C). 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.

[0034] 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.

[0035] 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.

[0036] The nuclear reactor core 20 is moderated and comprises a moderator 60. The moderator 60 may be provided within the nuclear reactor core 20 and may be interspersed throughout the nuclear reactor core. The moderator 60 may slow down the neutrons within the nuclear reactor core 20. The moderator 60 may comprise graphite, e.g., nuclear grade graphite.

[0037] 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 graphite or aluminium oxide. Aluminium oxide (AI2O3) may be used as a reflection material, as it provides acceptable neutron reflection properties for its mass. Nuclear-grade graphite exhibits similar properties and could therefore also be used as the reflection material.

[0038] The nuclear fission power plant 10 further comprises an electricity generating system 91. The electricity generating system 91 can take different forms. For example, in Figure 2, the electricity generating system comprises an electrical generator 80, such as that with a rotating element for generating an electrical current.

[0039] The nuclear fission power plant 10 further comprises a fluid circuit 90 configured to supply fluid to, and remove fluid from, the electricity generating system 91.Continuing with the example of Figure 2, the fluid circuit 90 is configured to power a generator 80. The fluid circuit 90 is configured to receive hot gas from the containment vessel outlet 44 and deliver cooled gas to the containment vessel inlet 42. The fluid circuit 90 therefore shares a working fluid with the containment vessel 40 (i.e. , the working fluid of the fluid circuit 90 may be the cooling gas of the containment vessel 40). In the particular example shown in Figure 2, the fluid circuit 90 comprises a turbine 92, a heat dissipator 94, and a compressor 96 arranged in flow series. The hot gas from the nuclear reactor core 20 flows through and drives the turbine 92. The gas then passes through the heat dissipator 94 and then the compressor 96, before returning to the containment vessel 40 via the containment vessel inlet 42. The turbine 92 drives the compressor 96 and the electrical generator 80, e.g., by virtue of a connecting shaft 82. The gas flowing in the fluid circuit 90 and through the containment vessel 40 may follow the Brayton cycle. The fluid circuit 90 may be referred to as a direct Brayton circuit since it is directly connected to the containment vessel 40 of the nuclear reactor core 20.

[0040] In the example shown in Figure 2, the heat dissipator 94 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. 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.

[0041] The arrangement shown in Figure 2 advantageously eliminates the need for heat exchangers which might otherwise add complexity and mass to the system. In particular, the use of a radiator directly connected to the fluid cycle 90 eliminates the need for a heat exchanger, again reducing the complexity and mass of the design. Furthermore, the direct 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 92 and compressor 96.

[0042] The heat dissipator 94 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, gas in the fluid circuit 90 may pass through the further radiatorand 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.

[0043] With reference to Figure 3, in an alternative arrangement the heat dissipator 94 may comprise a heat exchanger 110 thermally coupled to an additional fluid circuit 120. The 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. The additional fluid circuit 120 may further comprise a plurality of heat pipes 124 and at least one radiator 126. A first end of each heat pipe 124 may be thermally coupled to the additional fluid circuit working fluid of the additional fluid circuit 120 and a second end of each heat pipe 124 may be thermally coupled to the radiator 126 or one of the radiators.

[0044] The heat pipes 124 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 124 (i.e. , coupled to the additional fluid circuit working fluid), a volatile liquid within the heat pipe 124 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the 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 heat pipe 124 and the cycle repeats.

[0045] 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 heat pipes 124 are also very effective at spreading heat across the radiator 126, which can improve heat dissipation. This improved performance helps to offset the increased complexity of including the additional fluid circuit 120. The 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.

[0046] Although not depicted, the nuclear fission power plant 10 may further comprise at least one further fluid circuit. The further fluid circuit may be similar to the fluid circuit 90 and may be arranged in parallel to the fluid circuit 90, e.g., such that the fluid circuit and further fluid circuit may operate independently of one another. Accordingly, the further fluid circuit may comprise a further turbine, a further heat dissipator, and a further compressor arrangedin flow series. The further fluid circuit may be configured to receive hot gas from the containment vessel outlet 44 and deliver cooled gas to the containment vessel inlet 42 via the further turbine, further heat dissipator and further compressor. Parallel flow branches (and optional valves) may be provided to divide the flow from the containment vessel outlet 44 for the fluid circuit 90 and further fluid circuit and recombine the flow at the containment vessel inlet 42. The further turbine may drive the further compressor and the electrical generator 80 or a further electrical generator. The heat dissipator and further heat dissipator may be as described with reference to any of Figures 1 to 4.

[0047] With reference to Figure 4, in a further alternative arrangement, the electricity generating system may comprise a plurality of thermoelectric generators 130 and a passive radiator 140. A first end of the thermoelectric generators 130 may be thermally coupled to the fluid circuit 90 and a second end of the thermoelectric generators 130 may be thermally coupled to the passive radiator 140. The fluid circuit 90 may comprise a pump 98 to circulate a working fluid in the fluid circuit. The passive radiator 140 may use the mechanism of conduction to transport heat away from the thermoelectric generators 130 and the mechanism of radiation to dissipate thermal energy out into space. In this way, a temperature gradient is provided across the thermoelectric generators 130 so that they may generate an electrical current.

[0048] 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 passive radiator 140 may be deployable from a stowed configuration to a deployed configuration in which the at least a portion of the heat dissipator or passive radiator is opened out. In particular, the radiator 100 or radiator 140 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 at least to the heat dissipator 94.

[0049] Once deployed, the fluid circuit 90 may be configured such that the radiator 100, 126 or 140 is spaced apart from the nuclear reactor core 20. The radiator 100, 126 or 140 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, 126 or 140 from the nuclear reactor core 20 may be achieved bythe fluid circuit 90 (and / or additional fluid circuit 120) having pipes (which may be flexible) with lengths that extend from the nuclear reactor core 20 to the desired location for the radiator 100, 126 or 140.

[0050] 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.

[0051] 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 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.

[0052] 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, hot gas from the containment vessel 40 is received by the fluid circuit 90. In a third action 230, cooled gas is delivered to the containment vessel 40 by the fluid circuit 90. In a fourth action 240, electricity is generated with an electricity generating system coupled to the fluid circuit 90.

[0053] The present disclosure advantageously provides a very energy efficient arrangement that is also compact, lightweight and robust. Having a fluid circuit that powers the electricity generation system and is fed directly from (and shares a common working fluid with) the containment vessel is a very energy efficient, compact and lightweight arrangement. The overall power to weight ratio of the nuclear power plant is therefore improved. This is a very important factor for rocket launches since it is desirable to maximise the power output of the nuclear power plant for a given maximum payload.

[0054] Furthermore, the direct gas Brayton cycle arrangement allows higher operating temperatures, which in turn allow greater thermal efficiency in power conversion. For example, the turbine can receive the high temperature gas from the nuclear reactor core. This reduces the mass within the system by reducing the size of the turbine and compressor.

[0055] The moderated reactor also improves efficiency and saves weight. The more efficient reactor design and efficient Brayton cycle combine to provide a very efficient power plant that also has low weight.

[0056] Moreover, not having linearly actuated control rods saves weight, reduces complexity and provides a more robust arrangement. The present disclosure is less likely to be damaged during rocket launch by not having linearly actuated control rods. By contrast, linearly-actuated control rods are essentially cantilevers with a distal end that is vulnerable to the high vibration loads encountered during rocket launch.

[0057] 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.

[0058] 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 gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a metallic fuel; a moderator; and a containment vessel comprising a containment vessel inlet and a containment vessel outlet; a neutron reflector disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the gas-cooled moderated nuclear reactor core; a fluid circuit configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; and an electricity generating system coupled to the fluid circuit so as to generate an electrical current.

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 of the preceding claims, wherein the moderator comprises graphite.

6. 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.

7. 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.

8. The nuclear fission power plant of any of the preceding claims, wherein the fluid circuit comprises a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the fluid circuit is configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the turbine, heat dissipator and compressor; and the electricity generating system (91) comprises an electrical generator, wherein the turbine drives the compressor and the electrical generator.

9. The nuclear fission power plant of claim 8, wherein the heat dissipator comprises a radiator arranged such that gas in the fluid circuit passes through or across the radiator and is in thermal contact with a radiator surface of the radiator.

10. The nuclear fission power plant of claim 8, 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 a working fluid in the additional fluid circuit, a plurality of heat pipes and at least one radiator, wherein a first end of each heat pipe is thermally coupled to the working fluid of the additional fluid circuit and a second end of each heat pipe is thermally coupled to the radiator or one of the radiators.

11. The nuclear fission power plant of any of claims 1 to 7, wherein the electricity generating system comprises a plurality of thermoelectric generators and a passive radiator, a first end of the thermoelectric generators being thermally coupled to the fluid circuit and a second end of the thermoelectric generators being thermally coupled to the passive radiator.

12. 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 gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a metallic fuel; a moderator; and a containment vessel comprising a containment vessel inlet and a containment vessel outlet;a neutron reflector disposable around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposable around the periphery of the gas-cooled moderated nuclear reactor core; a fluid circuit configurable to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; and an electricity generating system couplable to the fluid circuit so as to generate an electrical current.

13. The kit of parts of claim 12, wherein the fluid circuit comprises a turbine, a heat dissipator, and a compressor arrangeable in flow series, wherein the fluid circuit configured such that when assembled the fluid circuit can receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the turbine, heat dissipator and compressor; and the electricity generating system comprises an electrical generator, configured such that, when the electricity generating system is assembled, the turbine can drive the compressor and the electrical generator.

14. The kit of parts of claim 13, wherein the heat dissipator comprises a radiator arrangeable such that, when the fluid circuit is assembled, gas in the fluid circuit can pass through or across the radiator and is in thermal contact with a radiator surface of the radiator.

15. The kit of parts of claim 12, wherein the heat dissipator comprises a heat exchanger thermally couplable to an additional fluid circuit, wherein the additional fluid circuit when assembled comprises a pump configured to circulate a working fluid in the additional fluid circuit, a plurality of heat pipes and at least one radiator, wherein a first end of each heat pipe is configured to be thermally coupled to the working fluid of the additional fluid circuit and a second end of each heat pipe is configured to be thermally coupled to the radiator or one of the radiators.

16. The kit of parts of claim 12, wherein the electricity generating system comprises a plurality of thermoelectric generators and a passive radiator, a first end of the thermoelectric generators being configured to be thermally coupled to the fluid circuit and a second end of the thermoelectric generators being configured to be thermally coupled to the passive radiator.

17. 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 gas-cooled moderated nuclear reactor core comprising a metallic fuel, a moderator and a containment vessel comprising a containment vessel inlet and a containment vessel outlet, wherein a neutron reflector is disposed around a periphery of the gas-cooled moderated nuclear reactor core, and a plurality of neutronic control elements comprising rotatable control drums disposed around the periphery of the gas-cooled moderated nuclear reactor core; receive hot gas from the containment vessel outlet to a fluid circuit; deliver cooled gas to the containment vessel inlet via the fluid circuit; and generate electricity with an electricity generating system coupled to the fluid circuit.

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