Nuclear fission power plant

Abstract

A nuclear fission power plant (10) for extra-terrestrial use, comprising: a gas-cooled moderated nuclear reactor core (20) comprising: a fuel system (30); a moderator (70); and a containment vessel (40); a linearly-movable neutron reflector (50) disposed around a periphery of the core; a neutron-absorbing control element (60) comprising a linearly-movable control rod; a first fluid circuit (81) comprising a first pump (86) and a first portion of a first heat exchanger (84), the first fluid circuit (81) receiving hot gas from the containment vessel and delivering cooled gas to the containment vessel; a second fluid circuit (82) comprising a second portion of the first heat exchanger, a turbine (87), a heat dissipator (96), and a compressor (88) arranged in flow series, a working fluid flowing through the second fluid circuit being arranged to drive the turbine (87) and transfer heat from the first heat exchanger (84) to at least one radiator (100) via the heat dissipator; and an electrical generator (90) driven by the turbine (87).

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 fuel system; a moderator; and a containment vessel comprising an inlet and an outlet;a linearly-movable neutron reflector disposed around a periphery of the gas-cooled moderated nuclear reactor core, a position of the linearly-movable neutron reflector being configured to at least partially control a reactivity level of the gas-cooled moderated nuclear reactor core; a neutron-absorbing control element comprising a linearly-movable control rod; a first fluid circuit comprising a first pump and a first portion of a first heat exchanger arranged in flow series, wherein the first fluid circuit is configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the first heat exchanger and the first pump; a second fluid circuit comprising a second portion of the first heat exchanger, a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the second fluid circuit is arranged such that a second fluid circuit working fluid flowing through the second fluid circuit drives the turbine and transfers heat from the first heat exchanger to the heat dissipator, wherein the heat dissipator comprises a plurality of heat pipes and at least one radiator, the heat pipes being configured to dissipate heat to the at least one radiator; and an electrical generator, wherein the turbine drives the compressor and the electrical generator.

[0006] The heat dissipator may comprise a first portion of a second heat exchanger in the second fluid circuit. The heat dissipator may further comprise a third fluid circuit comprising a second portion of the second heat exchanger, a second pump, the plurality of heat pipes and the at least one radiator. A first end of each heat pipe may be thermally coupled to a third fluid circuit working fluid of the third fluid circuit and a second end of each heat pipe may be thermally coupled to the radiator or one of the radiators. The third fluid circuit may be configured to circulate the third fluid circuit working fluid in the third fluid circuit and transfer heat from the second heat exchanger to the heat pipes and at least one radiator.

[0007] A first end of each heat pipe may be thermally coupled to a second fluid circuit working fluid of the second fluid circuit and a second end of each heat pipe may be thermally coupled to the radiator or one of the radiators. The second fluid circuit may be configured to circulate the second fluid circuit working fluid in the second fluid circuit and transfer heat from the first heat exchanger to the heat pipes and at least one radiator.

[0008] The fuel system may comprise High Assay Low Enriched Uranium (HALEU). Fuel in the fuel system may be enriched to substantially 19.75% Uranium-235.

[0009] The fuel system may comprise Tri-structural Isotropic (TRISO) particle fuel. The TRISO particle fuel may comprise a uranium, carbon and oxygen fuel kernel.

[0010] The linearly-movable neutron reflector may be a primary form of control to control a reactivity level of the gas-cooled moderated nuclear reactor core. The linearly- movable neutron reflector may be used for fine control, such as during a normal operating mode. The linearly-movable neutron reflector may comprise a reflection material consisting of beryllium oxide.

[0011] The linearly-movable control rod may be a secondary form of control to control a reactivity level of the gas-cooled moderated nuclear reactor core. The linearly-movable control rod may be used for coarse control, such as in an emergency or shut-down mode.

[0012] The moderator may comprise a moderator material consisting of yttrium hydride.

[0013] The heat pipes may comprise a heat pipe working fluid comprising an alkali metal, such as sodium.

[0014] The nuclear fission power plant may further comprise at least one further second fluid circuit. The further second fluid circuit may comprise the first heat exchanger or a further first heat exchanger in thermal communication with the first fluid circuit, a further turbine, the second heat exchanger or a further second heat exchanger, and a further compressor arranged in flow series. The further second fluid circuit may be arranged such that a further second fluid circuit working fluid flowing through the further second fluid circuit may drive the further turbine and transfer heat from the first heat exchanger or the further first heat exchanger to the second heat exchanger or the further second heat exchanger. The further turbine may drive the further compressor and the electrical generator or a further electrical generator.

[0015] The nuclear fission power plant may further comprise at least one further third fluid circuit. The further third fluid circuit may comprise the second heat exchanger or a further second heat exchanger in thermal communication with the second fluid circuit, a further second pump, a plurality of further heat pipes and at least one further radiator. A first end of each further heat pipe may be thermally coupled to the further third fluid circuit working fluid of the further third fluid circuit and a second end of each further heat pipe may be thermally coupled to the further radiator or one of the further radiators. The further third fluid circuit may be configured to circulate a further third fluid circuit working fluid in the further third fluid circuitand transfer heat from the second heat exchanger or the further second heat exchanger to the further heat pipes and at least one further radiator.

[0016] The or each radiator may be deployable from a stowed configuration to a deployed configuration in which the or each radiator may be opened out. The third fluid circuit may be configured such that the or each radiator is 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 gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a fuel system; a moderator; and a containment vessel comprising an inlet and an outlet; a linearly-movable neutron reflector disposable around a periphery of the nuclear reactor core, a position of the linearly-movable neutron reflector being configurable to at least partially control a reactivity level of the gas-cooled moderated nuclear reactor core; a neutron-absorbing control element comprising a linearly-movable control rod; a first fluid circuit comprising a first pump and a first portion of a first heat exchanger arrangeable in flow series, wherein the first fluid circuit is configurable to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the first heat exchanger and the first pump; a second fluid circuit comprising a second portion of the first heat exchanger, a turbine, a heat dissipator, and a compressor arrangeable in flow series, wherein, when assembled, a second fluid circuit working fluid can flow through the second fluid circuit to drive the turbine and transfer heat from the first heat exchanger to the heat dissipator, wherein the heat dissipator comprises a plurality of heat pipes and at least one radiator, the heat pipes being configured to dissipate heat to the at least one radiator; and an electrical generator, wherein, when assembled, the turbine drives the compressor and the electrical generator.

[0018] The heat dissipator of the kit of parts may further comprise a third fluid circuit, the third fluid circuit comprising a second heat exchanger, a first portion of the second heat exchanger being connected to the second fluid circuit; and a second portion of the secondheat exchanger being connected to a second pump, the plurality of heat pipes, and the at least one radiator, wherein a first end of each heat pipe is thermally coupled to a third fluid circuit working fluid of the third fluid circuit and a second end of each heat pipe is thermally coupled to the radiator or one of the radiators, and wherein the third fluid circuit is configured to circulate the third fluid circuit working fluid in the third fluid circuit and transfer heat from the second heat exchanger to the heat pipes and at least one radiator.

[0019] The fuel system of the kit of parts may comprise High Assay Low Enriched Uranium (HALEU).

[0020] The fuel system of the kit of parts may be enriched to substantially 19.75% uranium-235.

[0021] The fuel system of the kit of parts may comprise Tri-structural Isotropic (TRISO) particle fuel.

[0022] The moderator of the kit of parts may comprise a moderator material consisting of yttrium hydride.

[0023] The linearly-movable neutron reflector of the kit of parts may comprise a reflection material consisting of beryllium oxide.

[0024] 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 fuel system, a moderator, and a containment vessel comprising an inlet and an outlet, wherein a linearly-movable neutron reflector is disposed around a periphery of the gas-cooled moderated nuclear reactor core, a position of the linearly-movable neutron reflector being configured to at least partially control a reactivity level of the gas-cooled moderated nuclear reactor core, and wherein the nuclear fission power plant comprises a neutron-absorbing control element comprising a linearly-movable control rod; receive hot gas from the containment vessel outlet to a first fluid circuit comprising a first pump and a first portion of a first heat exchanger arranged in flow series; deliver cooled gas to the containment vessel inlet via the first heat exchanger and the first pump;heat a second fluid circuit working fluid flowing in a second fluid circuit comprising a second portion of the first heat exchanger, a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the second fluid circuit working fluid flowing through the second fluid circuit drives the turbine and transfers heat from the first heat exchanger to the heat dissipator, wherein the heat dissipator comprises a plurality of heat pipes and at least one radiator, the heat pipes being configured to dissipate heat to the at least one radiator; drive the compressor and an electrical generator with the turbine; and generate electricity with the electrical generator.

[0025] 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

[0026] 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:

[0027] Figure 1 is a schematic diagram showing an example nuclear fission power plant configured for extra-terrestrial use;

[0028] Figure 2 is a schematic diagram showing another example nuclear fission power plant configured for extra-terrestrial use; and

[0029] Figure 3 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 fuel system 30. The fuel system 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, fuel of the fuel system 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 fuel system 30 may comprise Tri-structural Isotropic (TRISO) particle fuel. Each TRISO particle fuel may comprise a uranium, carbon and oxygen fuel kernel, in particular a mixture of UO2 and UC. The TRISO fuel system which will undergo fission from neutrons that have undergone moderation (slowing down). The TRISO fuel may be coated with layers of carbon and a layer of SiC. The carbon and SiC coated layers prevent the release of fission isotopes into the environment. These small, coated particles (around the size of a poppy seed) may then be manufactured into compacts, with a matrix material holding the particles together. The matrix holding the particles together may be substantially cylindrical and may be provided in pellet form. The pellets may be clad, e.g. in one or more layers of ceramic or one or more layers of metal or any combination of ceramic and metal layers.

[0034] The nuclear reactor core 20 is 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 an inlet 42 and an 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 and Figure 2) between the inlet 42 and 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.

[0035] The nuclear fission power plant 10 may further comprise a linearly-movable neutron reflector 50 disposed around a periphery of the nuclear reactor core 20. The neutron reflector 50 may reflect neutrons back towards the nuclear reactor core 20. A position of the linearly-movable neutron reflector 50 may be configured to at least partially control a reactivity level of the nuclear reactor core 20. An actuator 52 may linearly move (e.g., slide) the neutron reflector 50. For example, the neutron reflector 50 may be at least partially retracted such thatfewer neutrons are reflected back into the nuclear reactor core 20. In this way, reactivity levels of the nuclear reactor core 20 may be controlled. The neutron reflector 50 may be a primary form of control to control the reactivity level of the nuclear reactor core 20. For example, the neutron reflector 50 may be used for fine control, such as during a normal operating mode of the nuclear fission power plant 10.

[0036] The neutron reflector 50 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 nuclear 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.

[0037] Two or more independent actuators 52 may be provided for redundancy. For example, an actuator may be provided at each end of the linearly-movable neutron reflector 50. In another arrangement, the linearly-movable neutron reflectors 50 may be arranged in two or more independent sets of neutron reflectors 50 with each set having its own actuator. The linearly-movable neutron reflectors 50 within a particular set may alternate with linearly- movable neutron reflectors from another set. For example, there may be two independent sets of six linearly-movable neutron reflectors 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 linearly-movable neutron reflectors 50.

[0038] The nuclear fission power plant 10 may further comprise at least one neutronabsorbing control element 60. The neutron-absorbing control element 60 may comprise a linearly-movable control rod that may be selectively inserted into a corresponding cavity in the nuclear reactor core 20. Movement of the control rod by an actuator 62 may vary the neutron absorbing properties of the neutron-absorbing control element 60. The secondary neutronabsorbing control element 60 may be used for coarse control, such as in an emergency or shut-down mode of the nuclear fission power plant 10. The control rod of the neutronabsorbing control element 60 may be inserted quickly into the nuclear reactor core 20, e.g., in the event of an emergency. The neutron-absorbing control element 60 may comprise boron carbide, B4C, as the neutron absorbing material.

[0039] The nuclear reactor core 20 may be moderated and may comprise a moderator 70. The moderator may improve the neutron economy of the nuclear reactor core 20. Themoderator 70 may be provided within the nuclear reactor core 20 and may be interspersed throughout the nuclear reactor core 20. The moderator 70 may slow down the neutrons within the nuclear reactor core 20. The moderator 70 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. YtH2-X also demonstrates outstanding thermal stability and therefore requires less cooling infrastructure when used in the nuclear reactor core 20. 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.

[0040] The nuclear fission power plant 10 may further comprise a first fluid circuit 81 carrying a first fluid circuit working fluid, and a second fluid circuit 82 carrying a second fluid circuit working fluid. The first fluid circuit 81 may be thermally coupled to the second fluid circuit 82 via a first heat exchanger 84.

[0041] The first fluid circuit 81 may comprise a first pump 86 and a first portion of the first heat exchanger 84 arranged in flow series. The first fluid circuit 81 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 first heat exchanger 84 and the first pump 86. The first fluid circuit 81 may therefore share a working fluid with the containment vessel 40, i.e., the first fluid circuit working fluid may be the cooling gas of the containment vessel 40.

[0042] The second fluid circuit 82 may comprise a second portion of the first heat exchanger 84, a turbine 87, a heat dissipator 96, and a compressor 88 arranged in flow series. The second fluid circuit 82 is arranged such that a second fluid circuit working fluid flowing through the second fluid circuit drives the turbine 87 and transfers heat from the first heat exchanger 84 to the heat dissipator 96. The heat dissipator 96 may dissipate heat from the second fluid circuit 82. The second fluid circuit working fluid flowing in the second fluid circuit 82 may follow the Brayton cycle. The 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 87 and compressor 88. The working fluid flowing in the second fluid circuit 82 may be nitrogen (N2), carbon dioxide (CO2), such as supercritical CO2, or any other appropriate fluid.

[0043] The nuclear fission power plant 10 may further comprise an electrical generator 90, such as that with a rotating element for generating an electrical current. The second fluid circuit 82 may be configured to power the electrical generator 90. For example, the turbine87 may drive the compressor 88 and the electrical generator 90, e.g., by virtue of a connecting shaft 92.

[0044] The heat dissipator 96 comprises a plurality of heat pipes 110 and at least one radiator 100. The heat pipes 110 are configured to dissipate heat to the at least one radiator 100. The heat dissipator 96 may comprise at least one radiator 100 and a plurality of heat pipes 110. A first end of each heat pipe 110 may be thermally coupled to the second fluid circuit working fluid of the second fluid circuit 82 and a second end of each heat pipe 110 may be thermally coupled to the radiator 100.

[0045] The heat pipes 110 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 110 (i.e., coupled to the second fluid circuit working fluid in the second fluid circuit 82), a volatile liquid within the heat pipe 110 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the heat pipe 110 to a cold part of the heat pipe (i.e., coupled to the radiator 100) and condenses back into a liquid, releasing the latent heat at the radiator 100. The liquid then returns to the hot part of the heat pipe 110 and the cycle repeats. The released latent heat may then radiate from a surface of the radiator 100. The heat pipe working fluid may comprise sodium.

[0046] The heat pipes 110 are very effective at spreading heat across the radiator 100, which can improve heat dissipation. The heat pipes 110 are also highly reliable and provide additional redundancy, e.g., in case a particular heat pipe fails or the radiator 100 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. The radiator 100 also lends itself to being foldable or divisible such that it can be readily stowed for transportation.

[0047] In the particular example shown in Figure 2, the heat dissipator 96 comprises a third fluid circuit 83 with a third fluid circuit working fluid. The third fluid circuit 83 is thermally coupled to the second fluid circuit 82 by virtue of a second heat exchanger 85. A first portion of the second heat exchanger 85 may be in the second fluid circuit 82 between the compressor 88 and turbine 87. The third fluid circuit 83 may comprise a second portion of the second heat exchanger 85, a second pump 89, the at least one radiator 100 and the plurality of heat pipes 110 arranged in flow series. A first end of each heat pipe 110 may be thermally coupled to the third fluid circuit working fluid of the third fluid circuit 83 and a second end of each heat pipe 110 may be thermally coupled to the radiator 100. The third fluid circuit 83 is configured to circulate the third fluid circuit working fluid in the third fluid circuit and transfer heat from thesecond heat exchanger 85 to the heat pipes 110 and at least one radiator 100. The third fluid circuit working fluid flowing in the third fluid circuit 83 may be water (H2O), ammonia (NH3) or any other appropriate fluid.

[0048] Although not depicted in the Figures, the nuclear fission power plant 10 may further comprise at least one further second fluid circuit. The further second fluid circuit may be similar to the second fluid circuit 82 and may be arranged in parallel to the second fluid circuit 82, e.g., such that the further second fluid circuit transfers heat from the first fluid circuit 81 to the third fluid circuit 83 (or a further third fluid circuit). Accordingly, the further second fluid circuit may comprise a portion of the first heat exchanger (or a further first heat exchanger) in thermal communication with the first fluid circuit 81 and a portion of the second heat exchanger (or a further second heat exchanger) in thermal communication with the third fluid circuit 83 (or a further third fluid circuit). The further second fluid circuit may also comprise a further turbine and a further compressor arranged in flow series. The further second fluid circuit may be arranged such that a further second fluid circuit working fluid flowing through the further second fluid circuit drives the further turbine and transfers heat from the first heat exchanger (or the further first heat exchanger) to the second heat exchanger (or the further second heat exchanger). The further turbine may drive the further compressor. The further turbine may also drive the electrical generator 90 or a further electrical generator.

[0049] Again, although not depicted, the nuclear fission power plant 10 may further comprise at least one further third fluid circuit. The further third fluid circuit may be similar to the third fluid circuit 83 and may be arranged in parallel to the third fluid circuit 83, e.g., such that the further third fluid circuit transfers heat from the second fluid circuit 82 (or further second fluid circuit) to the radiator 100 (or a further radiator). Accordingly, the further third fluid circuit may comprise a portion of the second heat exchanger (or a further second heat exchanger). The further third fluid circuit may also comprise a further second pump and at least one further radiator with a plurality of further heat pipes arranged in flow series. As for the third fluid circuit 83, a first end of each further heat pipe may be thermally coupled to the further third fluid circuit working fluid of the further third fluid circuit and a second end of each further heat pipe may be thermally coupled to the further radiator.

[0050] The nuclear fission power plant 10 may comprise one or more (e.g., a single) first fluid circuit 81. The first fluid circuit 81 may be provided within a combined protective reactor housing that may protect the components inside from damage, e.g. from space debris or meteorites. The second fluid circuit(s) 82 may also be provided in the protective reactorhousing. The third fluid circuit(s) 83, however, may be provided outside of the protective reactor housing. This may minimise the mass and volume of the protective reactor housing.

[0051] 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 radiator 100 may be deployable from a stowed configuration to a deployed configuration in which the at least a portion of the radiator is opened out. In particular, the radiator 100 may be flexible and / or foldable. The deployability of the nuclear fission power plant 10 may be at least partially enabled by at least the third fluid circuit 83 having flexible pipes connecting to the radiator 100 and heat pipes 110.

[0052] Once deployed, the radiator 100 may be spaced apart from the nuclear reactor core 20. The radiator 100 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 from the nuclear reactor core 20 may be achieved by the first, second and / or third fluid circuits 81 , 82, 83 having pipes (which may be flexible) with lengths that extend to the desired location for the radiator 100.

[0053] 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.

[0054] With reference to Figure 3, 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.

[0055] 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 gas-cooled and moderated nuclear reactor core 20. In a second action 220, hot gas from the containment vessel 40 is received by the first fluid circuit 81. In a third action 230, cooled gas is deliveredto the containment vessel 40 by the first fluid circuit 81. In a fourth action 240, a second fluid circuit working fluid flowing in the second fluid circuit 82 is heated by virtue of the first heat exchanger 84. In a fifth action 250, the compressor 88 and generator 90 are driven by the turbine 87. In a sixth action 260, electricity is generated by the generator 90.

[0056] The present disclosure advantageously provides a very efficient nuclear power reactor plant with a high power to weight ratio. Using a gaseous coolant in conjunction with TRISO fuel allows for the nuclear reactor core to reach much higher temperatures than other fuel forms and cooling methods. This is at least partly because the TRISO coating makes it resilient to high temperatures and a gaseous coolant cannot change state at high temperatures in the way a liquid coolant can. This in turn can improve thermodynamic efficiency by providing a greater temperature gradient across the system. Furthermore, the Brayton cycle generator provides excellent power to weight performance when compared to other power conversion technologies. In addition, the sliding reflector used for control provides a more compact arrangement since a separate controller is not required. This further reduces the overall mass and volume and improves the power to weight ratio.

[0057] A further advantage of the present disclosure is that it is particularly rugged and effective at retaining nuclear isotopes. This is due to the TRISO fuel system securely containing fission isotopes within a coated shell. Although the TRISO fuel form may have a lower fissile density, this is countered by the high performing reflector and moderator materials, which make better use of the available neutrons.

[0058] Furthermore, the addition of three fluid circuits means that even if both heat exchangers fail there is a low risk of potentially radioactive coolant being released to the environment. Having a separate third fluid circuit also gives greater and more independent control over the heat being rejected and provides a thermal buffer, which can help smooth out temperature fluctuations, for example if the nuclear power plant is in shadow. Moreover, the use of heat pipes within the radiator provides excellent redundancy if some heat pipes are damaged. This reduces the risk of the nuclear reactor core overheating due to sub-par heat removal. Having two distinct forms of reactor neutron control is also safer.

[0059] 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 fuel system; a moderator; and a containment vessel comprising an inlet and an outlet; a linearly-movable neutron reflector disposed around a periphery of the gas-cooled moderated nuclear reactor core, a position of the linearly-movable neutron reflector being configured to at least partially control a reactivity level of the gas-cooled moderated nuclear reactor core; a neutron-absorbing control element comprising a linearly-movable control rod; a first fluid circuit comprising a first pump and a first portion of a first heat exchanger arranged in flow series, wherein the first fluid circuit is configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the first heat exchanger and the first pump; a second fluid circuit comprising a second portion of the first heat exchanger, a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the second fluid circuit is arranged such that a second fluid circuit working fluid flowing through the second fluid circuit drives the turbine and transfers heat from the first heat exchanger to the heat dissipator, wherein the heat dissipator comprises a plurality of heat pipes and at least one radiator, the heat pipes being configured to dissipate heat to the at least one radiator; and an electrical generator, wherein the turbine drives the compressor and the electrical generator.

2. The nuclear fission power plant of claim 1 , wherein the heat dissipator comprises: a second heat exchanger, a first portion of the second heat exchanger being connected to the second fluid circuit; and a third fluid circuit, a second portion of the second heat exchanger being connected to the third fluid circuit, the third fluid circuit further comprising a second pump, the plurality of heat pipes and the at least one radiator, wherein a first end of each heat pipe is thermally coupled to a third fluid circuit working fluid of the third fluid circuit and a second end of each heat pipe is thermally coupled to the radiator or one of the radiators, and wherein the third fluidcircuit is configured to circulate the third fluid circuit working fluid in the third fluid circuit and transfer heat from the second heat exchanger to the heat pipes and at least one radiator.

3. The nuclear fission power plant of claim 1 , wherein a first end of each heat pipe is thermally coupled to a second fluid circuit working fluid of the second fluid circuit and a second end of each heat pipe is thermally coupled to the radiator or one of the radiators, and wherein the second fluid circuit is configured to circulate the second fluid circuit working fluid in the second fluid circuit and transfer heat from the first heat exchanger to the heat pipes and at least one radiator.

4. The nuclear fission power plant of any of the preceding claims, wherein the fuel system comprises High Assay Low Enriched Uranium (HALEU).

5. The nuclear fission power plant of any of the preceding claims, wherein the fuel system is enriched to substantially 19.75% uranium-235.

6. The nuclear fission power plant of any of the preceding claims, wherein the fuel system comprises Tri-structural Isotropic (TRISO) particle fuel.

7. The nuclear fission power plant of claim 6, wherein the TRISO particle fuel comprises a uranium, carbon and oxygen fuel kernel.

8. The nuclear fission power plant of any of the preceding claims, wherein the linearly- movable neutron reflector is a primary form of control to control a reactivity level of the gas- cooled moderated nuclear reactor core.

9. The nuclear fission power plant of any of the preceding claims, wherein the linearly- movable control rod is a secondary form of control to control a reactivity level of the gas-cooled moderated nuclear reactor core.

10. The nuclear fission power plant of any of the preceding claims, wherein the moderator comprises a moderator material consisting of yttrium hydride.

11. The nuclear fission power plant of any of the preceding claims, wherein the linearly- movable neutron reflector comprises a reflection material consisting of beryllium oxide.

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

13. 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 fuel system; a moderator; and a containment vessel comprising an inlet and an outlet; a linearly-movable neutron reflector configured to be disposed around a periphery of the nuclear reactor core, a position of the linearly-movable neutron reflector being configurable to at least partially control a reactivity level of the gas-cooled moderated nuclear reactor core; a neutron-absorbing control element comprising a linearly-movable control rod; a first fluid circuit comprising a first pump and a first portion of a first heat exchanger configured to be arranged in flow series, wherein the first fluid circuit is configurable to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet via the first heat exchanger and the first pump; a second fluid circuit comprising a second portion of the first heat exchanger, a turbine , a heat dissipator, and a compressor configured to be arranged in flow series, wherein the second fluid circuit can be arranged such that in operation a second fluid circuit working fluid flows through the second fluid circuit, drives the turbine, and transfers heat from the first heat exchanger to the heat dissipator, wherein the heat dissipator comprises a plurality of heat pipes and at least one radiator, the heat pipes being configured to dissipate heat to the at least one radiator; and an electrical generator, wherein, when assembled, the turbine drives the compressor and the electrical generator.

14. The kit of parts of claim 13, wherein the heat dissipator further comprises: a third fluid circuit, the third fluid circuit comprising a second heat exchanger, a first portion of the second heat exchanger being connected to the second fluid circuit; and a second portion of the second heat exchanger being connected to a second pump, the plurality of heat pipes, and the at least one radiator, wherein a first end of each heat pipe is thermally coupled to a third fluid circuit working fluid of the third fluid circuit and a second end of each heat pipe is thermally coupled to the radiator or one of the radiators, and wherein the third fluid circuit isconfigured to circulate the second working fluid in the third fluid circuit and transfer heat from the second heat exchanger to the heat pipes and at least one radiator.

15. The kit of parts of claim 13 or claim 14, wherein the fuel system comprises High Assay Low Enriched Uranium (HALEU).

16. The kit of parts of claim 13, 14, or 15, wherein the fuel system is enriched to substantially 19.75% uranium-235.

17. The kit of parts of claim 13, 14, 15, or 16, wherein the fuel system comprises Tri- structural Isotropic (TRISO) particle fuel.

18. The kit of parts of claim 13, 14, 15, 16, or 17, wherein the moderator comprises a moderator material consisting of yttrium hydride.

19. The kit of parts of claim 13, 14, 15, 16, 17, or 18, wherein the linearly-movable neutron reflector comprises a reflection material consisting of beryllium oxide.

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 gas-cooled moderated nuclear reactor core comprising a fuel system, a moderator, and a containment vessel comprising an inlet and an outlet, wherein a linearly-movable neutron reflector is disposed around a periphery of the gas-cooled moderated nuclear reactor core, a position of the linearly-movable neutron reflector being configured to at least partially control a reactivity level of the gas-cooled moderated nuclear reactor core, and wherein the nuclear fission power plant comprises a neutron-absorbing control element comprising a linearly-movable control rod; receive hot gas from the containment vessel outlet to a first fluid circuit comprising a first pump and a first portion of a first heat exchanger arranged in flow series; deliver cooled gas to the containment vessel inlet via the first heat exchanger and the first pump; heat a second fluid circuit working fluid flowing in a second fluid circuit, the second fluid circuit comprising a second portion of the first heat exchanger, a turbine, a heat dissipator, and a compressor arranged in flow series, wherein the second fluid circuit working fluid flowing through the second fluid circuit drives the turbine and transfers heat from the first heat exchanger to the heat dissipator, wherein the heat dissipator comprises a plurality of heatpipes and at least one radiator, the heat pipes being configured to dissipate heat to the at least one radiator; drive the compressor and an electrical generator with the turbine; and generate electricity with the electrical generator.

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