GB2629745A - Nuclear reactor - Google Patents

Abstract

A nuclear reactor 10 configured for extra-terrestrial use (e.g. in space, orbit, on lunar surface) comprising a nuclear reactor core 20 with UO2 (Uranium Dioxide) fuel pellets 30, a moderator 60 comprising yttrium hydride (YH2), and a containment vessel 40. A neutron reflector 70 comprising beryllium oxide (BeO) is disposed around a periphery of the nuclear reactor core, and a plurality of control drums 50 disposed around the periphery of the nuclear reactor core. A fluid circuit 90 is configured to deliver gas heated by the nuclear reactor core to an electricity generating system 91, the system comprising a Brayton cycle engine coupled to the fluid circuit so as to generate an electricity. The fuel may comprise High-Assay-Low-Enriched-Uranium (HALEU). The nuclear reactor may be a micro-reactor and may be transportable e.g. via rocket. The Brayton power system may comprise: a compressor; a turbine system; and a generator.

Description

NUCLEAR REACTOR

TECHNICAL FIELD

[0001] This disclosure relates to a nuclear reactor configured for extra-terrestrial use and a kit of parts and method for a nuclear reactor 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 reactor and ability to continue generation without sunlight make nuclear reactors in extra-terrestrial applications an attractive option. However, an extra-terrestrial nuclear reactor 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 reactor configured for extra-terrestrial use, the nuclear reactor comprising: a containment vessel; a nuclear reactor core housed within the containment vessel, the nuclear reactor core comprising a fuel comprising UO2 pellets and a moderator comprising yttrium hydride; a neutron reflector housed within the containment vessel comprising beryllium oxide disposed around a periphery of the nuclear reactor core; a plurality of control drums disposed around the periphery of the nuclear reactor core; a fluid circuit configured to deliver gas to the nuclear reactor core to extract heat energy from the nuclear reactor core, deliver gas to an electricity generating system, receive gas from the electricity generating system; and return the gas to the nuclear reactor core; wherein the electricity generating system comprises a closed Brayton cycle engine so as to generate an electrical current using heat energy delivered by the electricity generating system by the fluid circuit.

[0006] The nuclear reactor fuel may comprise High-Assay Low-Enriched Uranium (HALEU).

[0007] The nuclear reactor fuel may be enriched to substantially 19.75% uranium-235.

[0008] The fluid circuit of the nuclear reactor may further comprise a pump.

[0009] The control drums of the nuclear reactor may be used for fine and coarse control of the nuclear reactor core.

[0010] The control drums of the nuclear reactor may be the sole form of control of the reactivity levels within the nuclear reactor core.

[0011] The closed Brayton cycle engine of the nuclear reactor may further comprise a heat dissipator arranged between the compressor and the turbine system such that gas flowing from the turbine system passes through the heat dissipator before the gas reaches the compressor.

[0012] 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.

[0013] According to a second aspect there is provided a kit of parts for building a nuclear reactor configured for extra-terrestrial use, the kit of parts being configured at least partially for assembly at the terrestrial environment and comprising: a containment vessel; a nuclear reactor core; a plurality of control drums; a neutron reflector comprising beryllium oxide; and an electricity generating system; the kit of parts being configured to be assembled to form a fluid circuit comprising: the containment vessel; and the electricity generating system; wherein the containment vessel is configured to contain at least the nuclear reactor core, the nuclear reactor core comprising a moderator comprising yttrium hydride; the nuclear reactor core being configured to accept a fuel system comprising UO2 pellets; the containment vessel further comprising a containment vessel inlet and a containment vessel outlet, the containment vessel inlet and containment vessel outlet being configured such that when assembled, gas can circulate around the fluid circuit, such that the gas can flow from the containment vessel inlet towards the nuclear reactor core, through the nuclear reactor core, and out of the nuclear reactor core towards the containment vessel outlet; wherein, when the kit of parts is assembled, the neutron reflector and plurality of control drums are disposed around a periphery of the nuclear reactor core; the electricity generating system being configured to be integrated with the fluid circuit, the electricity generating system comprising an open Brayton power system comprising: a compressor; a turbine system, and a generator; the electricity generating system being arranged such that when assembled, gas can flow from the containment vessel outlet to the turbine system via the fluid circuit, and from the compressor to the containment vessel inlet via the fluid circuit, wherein the turbine system is configured to drive the compressor and the generator.

[0014] The kit of parts may further comprise a heat dissipator, the heat dissipator being arrangeable between the compressor and turbine system. The heat dissipator may comprise 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 radiative surface of the radiator.

[0015] According to a third aspect there is provided a method for a nuclear reactor configured for extra-terrestrial use, the method comprising controlling the nuclear reactor to: generate heat with a nuclear reactor core comprising a nuclear fuel and a moderator, the nuclear fuel comprising UO2 pellets and the moderator comprising yttrium hydride, the nuclear reactor core being housed in a containment vessel comprising a containment vessel inlet and a containment vessel outlet such that gas flowing from the containment vessel inlet to the containment vessel outlet flows through the nuclear reactor core, wherein a neutron reflector comprising beryllium oxide is disposed around a periphery of the nuclear reactor core, and a plurality of control drums disposed around the periphery of the nuclear reactor core; deliver, via a fluid circuit, gas heated by the nuclear reactor core from the containment vessel outlet to an electricity generating system; generate electricity with the electricity generating system, wherein the electricity generating system comprises a closed Brayton cycle engine coupled to the fluid circuit; and deliver, via the fluid circuit, gas cooled by the electricity generating system back to the containment vessel via the containment vessel inlet.

[0016] 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.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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: [0018] FIG. 1 is a schematic diagram showing a sectional view of an example of a nuclear reactor configured for extra-terrestrial use; [0019] FIG. 2 shows a sectional schematic side view of an example arrangement of a nuclear reactor core; [0020] FIG. 3 shows a sectional schematic plan view of an example arrangement of a nuclear reactor core; [0021] FIG. 4 shows a sectional schematic side view of an example of an arrangement of a nuclear reactor core; [0022] FIG. 5 shows a sectional schematic plan view of an example of an arrangement of a nuclear reactor core; [0023] FIG. 6 is a schematic diagram showing an example arrangement of control drums around a nuclear reactor core; [0024] FIG. 7 is a schematic diagram showing an example arrangement of control drum actuators; [0025] FIG. 8 is a schematic diagram showing another example arrangement of control drum actuators; [0026] FIG. 9 is a schematic diagram showing an example of an electricity generating system for the nuclear reactor of FIG. 1; [0027] FIG. 10 is a representation of a kit of parts for assembling a nuclear reactor; and [0028] FIG. 11 is a flowchart depicting a method for a nuclear reactor configured for extra-terrestrial use.

DETAILED DESCRIPTION

[0029] The present disclosure relates to a nuclear reactor specifically configured for extra-terrestrial use, i.e., away from the Earth's surface. The nuclear reactor may be exclusively configured for extra-terrestrial use. As such, the nuclear reactor may be referred to as an extra-terrestrial nuclear reactor. However, the nuclear reactor may be at least partially assembled on Earth from a kit of parts, and may be launched, e.g. from a rocket, into space. In a particular example, the nuclear reactor may be intended for use on the lunar surface of the Moon orbiting Earth. However, the nuclear reactor may also be used in space or on other planets and moons.

[0030] The nuclear reactor may be a micro-reactor. As such, the nuclear reactor may be readily transportable, in particular on a rocket.

[0031] FIG. 1 shows a schematic sectional view of a nuclear reactor 10 according to the present disclosure. The nuclear reactor 10 comprises a nuclear reactor core 20. The nuclear reactor core 20 comprises a fuel 30 (see FIG. 2, FIG. 3, FIG. 4, and FIG. 5), the fuel comprising UO2 pellets. The 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 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.

[0032] The fuel 30 may be clad, i.e. housed within in a cladding.

[0033] The nuclear reactor core 20 is gas-cooled, which is to say that heat energy is extracted from the nuclear reactor core 20 by virtue of a gas that flows around a fluid circuit 90, which includes flowing over, through, and around components within the nuclear reactor core 20. The nuclear reactor core 20 is housed within a containment vessel 40. The containment vessel 40 comprises a containment vessel inlet 42 where the gas can enter the containment vessel, and a containment vessel outlet 44 where the gas can exit the containment vessel. Within the containment vessel 40 the fluid circuit defines part of a flow path (see block arrows in FIG. 1 for example) between the containment vessel inlet 42 and containment vessel outlet 44 that forces the gas to flow over the components of the nuclear reactor core 20, and in doing so, to absorb heat energy from the components of the nuclear reactor core 20. Suitable gases for the purpose of extracting heat energy from the core include helium, nitrogen, hydrogen, and helium-xenon (i.e. a mixture of helium and xenon).

[0034] FIG. 2 shows a sectional schematic side view of an example arrangement of a nuclear reactor core 20. FIG. 3 shows a sectional schematic plan view of an example arrangement of a nuclear reactor core 20. In the examples of both FIG. 2 and FIG. 3, the main structure of the nuclear reactor core 20 is provided by a monolith 25. As its name suggests, the monolith 25 can be a single block of material, although it may instead be made up of connected pieces of material. A known material for constructing nuclear reactor cores is graphite, as graphite is resilient to high-temperature environments, and can be machined into shapes that allow for the insertion of (for example) fuel rods and the passage of gas coolant. In the examples of FIG. 2 and FIG. 3, the monolith contains compartments for fuel 30, and pieces of moderator 60 (in FIG. 3 the presence of the fuel 30 is symbolised by circles and the presence of the moderator 60 is symbolised by triangles). In FIG. 2 and FIG. 3, the sectional views show coolant channels (the presence of the coolant channels 28 being symbolised by hexagons in FIG. 2 and FIG. 3) in the monolith between blocks or rods of fuel 30 or moderator 60 which allow for the passage of gas travelling around the fluid circuit 90. As gas travels around the nuclear reactor core 20, or through the nuclear reactor core via one or more coolant channels 28, it will absorb heat energy from the monolith material, which has in turn been heated by the fuel 30. As a result, the gas will be much hotter as it leaves the nuclear reactor core than it was when it entered the nuclear reactor core.

[0035] The moderator 60 serves to slow down the neutrons within the nuclear reactor core 20. By slowing down the neutrons, the chances of the neutron interacting with uranium nuclei are increased, and so the rate of fission within the nuclear reactor core is increased, leading to the release of more heat energy. The moderator 60 comprises yttrium hydride. In the examples of FIG. 2 and FIG. 3, the nuclear reactor core 20 comprises distinct pieces of moderating material (i.e. moderator 60). Alternatively, I moderator may be integral to the monolith. For example, the core may comprise a graphite monolith having mixed within it an amount of yttrium hydride to moderate the neutrons passing through it. FIG. 4 shows a sectional schematic side view, and FIG. 5 shows a sectional schematic plan view, of an example of such an arrangement of a nuclear reactor core 20, where only distinct compartments of fuel and cooling channels are shown, as the yttrium hydride moderator material is dispersed within the material of the monolith. In FIG. 5, as with FIG. 3, the fuel 30 is symbolised by circles, and the coolant channels 28 are symbolised by hexagons.

[0036] Whilst in FIG. 3 the monolith is shown as having a circular cross-sectional shape, it is to be understood this is purely for illustrative purposes, and that the monolith may take other shapes depending on the space available for the nuclear reactor. One such example is shown in FIG. 5, which has a hexagonal cross-sectional shape. It is also to be understood that the particular arrangement of the fuel, moderator, and coolant channels shown in FIG. 2, FIG. 3, FIG. 4, and FIG. 5 is purely illustrative of the nature of the arrangement of the various constituents, i.e. to illustrate that each component is dispersed around the core, and that coolant channels, fuel, and moderator all neighbour each other around the core in order to perform their functions.

[0037] Referring back to FIG.1, also housed within the containment vessel 40 is a neutron reflector 70. The neutron reflector is disposed around a periphery of the nuclear reactor core 20. Part of the fluid circuit 90 within the containment vessel 40 passes through the neutron reflector 70. For example, this may be by virtue of a conduit within the neutron reflector, and/or one or more channels formed within the material of the neutron reflector itself. Whilst in FIG. 1 the fluid circuit is shown entering and exiting the containment vessel on the same edge of the containment vessel 40, which is to say the containment vessel inlet 42 and the containment vessel outlet 44 are on the same side of the containment vessel 40, it is to be understood that this is purely an illustrative example, and that the containment vessel inlet 42 and the containment vessel outlet 44 can be on different edges to those shown in FIG. 1, and can be on different edges to each other, i.e. the containment vessel inlet 42 and the containment vessel outlet 44 do not have to be on the same edge of the containment vessel, but can be positioned according to the layout of the nuclear reactor and the space around the nuclear reactor. The neutron reflector reflects neutrons emanating from the nuclear reactor core 20 back towards the nuclear reactor core 20. The neutron reflector comprises beryllium oxide. Beryllium oxide has high thermal conductivity, high temperature stability, and very good neutron reflecting properties for its mass.

[0038] The nuclear reactor 10 further comprises a plurality of control drums 50. The control drums 50 are configured to be disposed around the periphery of the nuclear reactor core 20. In the example of FIG. 1, the control drums are shown in cavities within the neutron reflector 70. Whilst only two control drums 50 are visible (in sectional view) in FIG. 1, it is to be understood that more control drums could be arranged around the nuclear reactor core, an example of such an arrangement being shown in FIG. 6. The control drums 50 may be controlled to vary the degree to which they absorb or reflect neutrons from the nuclear reactor core 20, and thereby control reactivity levels in the nuclear reactor core 20. Specifically, it is rotation of the control drums by one or more actuators 52 (omitted from FIG. 6 for clarity -instead see FIG. 1, FIG. 7, and FIG. 8) that varies the degree to which the control drums 50 absorb or reflect neutrons from the nuclear reactor core 20. The actuator(s) 52 may be controlled by a suitable controller 54, which may receive data from one or more sensors. It is envisaged that the controller 54 may be in communication with multiple systems, including sensor system(s) (not shown) of the nuclear reactor 10. The sensor systems may be configured to determine a rate of fission in the nuclear reactor core 20.

[0039] Each control drum 50 comprises a neutron-reflecting material 51 (e.g. graphite or beryllium oxide) and a neutron-absorbing material 53 (e.g. boron carbide (B4C)). As mentioned earlier, beneficial properties of beryllium oxide as a reflector include its stability at high temperatures and high thermal conductivity. Using beryllium oxide as the neutron-reflecting material of the control drum may therefore increase a performance of the control drum, which may consequently permit a mass of the nuclear reactor 10 to be reduced. The neutron-absorbing material 53 is disposed over at least a portion of an outer circumference of the control drum. To promote reactivity, the control drums may be rotated such that more of the reflecting material 51 is facing toward the nuclear reactor core 20, thereby directing neutrons back into the nuclear reactor core that might otherwise have escaped from the nuclear reactor core. To slow down reactivity, each control drum may be rotated so that more of the neutron-absorbing material 53 is facing toward the nuclear reactor core 20, thereby absorbing more neutrons escaping from the core in order to slow down the rate at which fission reactions are occurring within the nuclear reactor. In this way, reactivity levels of the nuclear reactor core 20 may be controlled and the control drums may provide the primary form of control. The control drums 50 may be used for fine control, such as during a normal operating mode of the nuclear reactor 10. The control drums 50 may also be used for coarse control, such as in an emergency or shut-down mode of the nuclear reactor 10. The control drums may be rotated quickly to rapidly increase their neutron-absorbing properties, e.g., in the event of an emergency. The control drums may therefore be the sole form of control of the nuclear reactor core 20.

[0040] Control drums are advantageously compact compared with other control methods, such as linear control rods, which require more space. Specifically, unlike linear control rods, the space occupied by control drums does not change as they do not rely on linear movement into a void. The control drums also are less impacted by environmental conditions such as vibration, and are therefore more robust.

[0041] As illustrated in FIG. 7, Two or more independent actuators 52 may be provided for redundancy. For example, an actuator may be provided at each end of a control drum. In another arrangement, an example of which is illustrated in FIG. 8, the control drums 50 may be arranged in two or more independent sets of control drums with each set having its own actuator 52. The control drums within a particular set may alternate with control drums from another set. For example, there may be two independent sets of six control 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 control drums.

[0042] Referring back to FIG. 1, the nuclear reactor 10 further comprises an electricity generating system 91. The electricity generating system 91 can take different forms. In the example system of FIG. 9, the electricity generating system comprises an electrical generator 80, such as that with a rotating element for generating an electrical current.

[0043] In the example system of FIG. 9, the fluid circuit 90 is configured to power the generator 80. The fluid circuit 90 is configured to receive gas, heated by the components within the nuclear reactor core, from the containment vessel outlet 44, and deliver gas, which has been cooled after passing around the fluid circuit 90, to the containment vessel inlet 42. In the particular example shown in FIG. 9, the fluid circuit 90 comprises a turbine 92, a heat dissipator 94, and a compressor 96 arranged in flow series. The gas, heated by the nuclear reactor core 20, flows through and drives the turbine 92. The gas then passes through the heat dissipator 94, which removes residual heat energy from the gas which was not removed by the turbine 92, and then passes through 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 follows the Brayton cycle. The fluid circuit 90 may be referred to as a direct Brayton cycle circuit since it is directly connected to the containment vessel 40 of the nuclear reactor core 20, and as such the same gas which flows through the nuclear reactor core also flows through the Brayton cycle circuit, i.e. the fluid circuit 90. As the Brayton cycle engine is not open to the surrounding environment, but rather recirculates the same gas, it may be referred to as a closed Brayton cycle circuit, or a closed Brayton cycle engine.

[0044] In the example system shown in FIG. 9, 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 radiative 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 then 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 adapted for the space available, i.e. it can be shaped to fit a variety of volumes.

[0045] The use of a direct circuit which takes heated gas straight from the nuclear reactor core advantageously eliminates the need for heat exchangers which might otherwise add complexity and mass to the system. Furthermore, the direct gas Brayton cycle provides benefits such as reaching higher temperatures allowing for greater thermal efficiency in power conversion. This can also allow for reductions in the mass of the system, by enabling a reduction in the size of the turbine 92 and compressor 96.

[0046] The heat dissipator 94 may comprise at least one further radiator (not shown) 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 radiator and may be in thermal contact with a further radiative 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.

[0047] Although not depicted, the nuclear reactor 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 arranged in 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 generator 80 or a further generator. The heat dissipator and further heat dissipator may be as described with reference to FIG. 9.

[0048] Although not depicted, the fluid circuit or further fluid circuit may comprise a pump. The pump may be useful for example during startup of the nuclear reactor to establish a direction of gas flow around the fluid circuit or further fluid circuit.

[0049] Although not depicted, the nuclear reactor 10 may further comprise a neutron shield at least partially disposed around the nuclear reactor core 20. The neutron shield may be configured to substantially reduce a likelihood of neutrons escaping from the nuclear reactor core 20 and into the surrounding environment. The neutron shield may at least partially surround the neutron reflector 70. For instance, the neutron shield may be disposed around a periphery of the neutron reflector 70. The neutron shield 80 may thus improve the safety of the nuclear fission power plant 10, as neutrons which have not been absorbed or reflected by the neutron-absorbing material 53 of the control drums 50, or reflected by the neutron reflector 70, may be absorbed by the neutron shield. The neutron shield may be formed from boron carbide, or any other suitable neutron-absorbing material.

[0050] The nuclear reactor 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 may be deployable from a stowed configuration to a deployed configuration in which the at least a portion of the heat dissipator is opened out. In particular, the radiator 100 may be flexible and/or foldable. The deployability of the nuclear reactor 10 may be at least partially enabled by the fluid circuit 90 having flexible pipes connecting at least to the heat dissipator 94.

[0051] Once deployed, the fluid circuit 90 may be configured such that the radiator is 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 fluid circuit 90 having pipes (which may be flexible) with lengths that extend from the nuclear reactor core 20 to the desired location for the radiator 100.

[0052] The present disclosure also relates to a kit of parts 300 for the nuclear reactor 10, the kit of parts being symbolically represented in FIG. 10. The kit of parts may comprise at least some of the above-described components. For example, the kit of parts may comprise a containment vessel, and a nuclear reactor core, the nuclear reactor core being configured to use a fuel comprising UO2 pellets and comprising a moderator comprising yttrium hydride. The kit of parts may further comprise a plurality of control drums, a neutron reflector comprising beryllium oxide, and an electricity generating system. The kit of parts should be configured to be assembled to form a fluid circuit comprising the containment vessel and the electricity generating system.

[0053] When the kit of parts is assembled, the neutron reflector and plurality of control drums should be disposed around a periphery of the nuclear reactor core, and the electricity generating system should be integrated with the fluid circuit. The electricity generating system will comprise an open Brayton power system comprising a compressor, a turbine system, and a generator. The electricity generating system is arranged such that when assembled, gas can flow from the containment vessel outlet to the turbine system via the fluid circuit, and from the compressor to the containment vessel inlet via the fluid circuit, wherein the turbine system is configured to drive the compressor and the generator.

[0054] The kit of parts can further comprise a heat dissipator. The heat dissipator can be arranged between the compressor and turbine system. The heat dissipator can comprise a radiator, the radiator being 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 radiative surface of the radiator.

[0055] The kit of parts may be configured to be subdivided into sub-assemblies 310 for placement within one or more rockets to be launched into space, the sub-assemblies being connectable once they arrive at their site of use. 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.

[0056] Wth reference to FIG. 11, the present disclosure also relates to a method 200 for the nuclear reactor 10. The method 200 comprises controlling the nuclear reactor 10. The control of the nuclear reactor 10 may be at least partially carried out remotely. for example on a lunar base, from Earth, or any other location.

[0057] The method 200 controls the nuclear reactor 10 such that in a first action 210, the nuclear reactor 10 generates heat with the nuclear reactor core 20. The nuclear reactor core will comprise a nuclear fuel and a moderator, with the nuclear fuel comprising UO2 pellets and the moderator comprising yttrium hydride. The nuclear reactor core is housed in a containment vessel comprising a containment vessel inlet and a containment vessel outlet. The arrangement of the containment vessel inlet and the containment vessel outlet on the containment vessel is such that gas flowing from the containment vessel inlet to the containment vessel outlet flows through the nuclear reactor core, where the gas absorbs heat energy from components of the nuclear reactor core. A neutron reflector comprising beryllium oxide is disposed around a periphery of the nuclear reactor core, and a plurality of control drums are disposed around the periphery of the nuclear reactor core.

[0058] In a second action 220, gas heated by the nuclear reactor core flows via a fluid circuit from the containment vessel 40 to an electricity generating system 91. In a third action 230, electricity is generated by the electricity generating system coupled to the fluid circuit 90. The electricity generating system comprises a closed Brayton cycle engine coupled to the fluid circuit. In a fourth action 240, gas cooled by the electricity generating system is delivered back to the containment vessel 40 via a containment vessel inlet 42 by the fluid circuit 90.

[0059] The electricity generating system 91 can take different forms. For example, the electricity generating system may comprise an electrical generator 80, such as that with a rotating element for generating an electrical current.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Moreover, the use of control drums as the sole means to control the reactivity levels within the nuclear reactor core saves weight, reduces complexity and provides a more robust arrangement compared with systems that use linearly actuated control rods. The present disclosure is less likely to be damaged during rocket launch by not having linearly actuated control rods, as linearly-actuated control rods are essentially cantilevers with a distal end that is vulnerable to the high vibration loads encountered during rocket launch.

[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 sub-combinations of one or more features described herein.

Claims (12)

1. CLAIMS1. A nuclear reactor configured for extra-terrestrial use, the nuclear reactor comprising: a containment vessel; a nuclear reactor core housed within the containment vessel, the nuclear reactor core comprising a fuel comprising UO2 pellets and a moderator comprising yttrium hydride; a neutron reflector housed within the containment vessel comprising beryllium oxide disposed around a periphery of the nuclear reactor core; a plurality of control drums disposed around the periphery of the nuclear reactor core; a fluid circuit configured to deliver gas to the nuclear reactor core to extract heat energy from the nuclear reactor core, deliver gas to an electricity generating system, receive gas from the electricity generating system, and return the gas to the nuclear reactor core; wherein the electricity generating system comprises a closed Brayton cycle engine so as to generate an electrical current using heat energy delivered by the electricity generating system by the fluid circuit.
2. 2. The nuclear reactor of claim 1, wherein the fuel comprises High-Assay Low-Enriched Uranium (HALEU).
3. 3. The nuclear reactor of claim 1 or 2, wherein the fuel is enriched to substantially 19.75% uranium-235.
4. 4. The nuclear reactor of any of the preceding claims, wherein the fluid circuit further comprises a pump.
5. 5. The nuclear reactor of any of the preceding claims, wherein the control drums are used for fine and coarse control of the nuclear reactor core.
6. 6. The nuclear reactor of any of the preceding claims, wherein the control drums are the sole form of control of the reactivity levels within the nuclear reactor core.
7. 7. The nuclear reactor of any of the preceding claims, wherein the closed Brayton cycle engine further comprises a heat dissipator arranged between the compressor and the turbine system such that gas flowing from the turbine system passes through the heat dissipator before the gas reaches the compressor.
8. 8. The nuclear reactor of claim 7, 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.
9. 9. A kit of parts for building a nuclear reactor configured for extra-terrestrial use, the kit of parts being configured at least partially for assembly at the terrestrial environment and comprising: a containment vessel; a nuclear reactor core; a plurality of control drums; a neutron reflector comprising beryllium oxide; and an electricity generating system; the kit of parts being configured to be assembled to form a fluid circuit comprising: the containment vessel; and the electricity generating system; wherein the containment vessel is configured to contain at least the nuclear reactor core, the nuclear reactor core comprising a moderator comprising yttrium hydride; the nuclear reactor core being configured to accept a fuel system comprising UO2 pellets; the containment vessel further comprising a containment vessel inlet and a containment vessel outlet, the containment vessel inlet and containment vessel outlet being configured such that when assembled, gas can circulate around the fluid circuit, such that the gas can flow from the containment vessel inlet towards the nuclear reactor core, through the nuclear reactor core, and out of the nuclear reactor core towards the containment vessel outlet; wherein, when the kit of parts is assembled, the neutron reflector and plurality of control drums are disposed around a periphery of the nuclear reactor core; the electricity generating system being configured to be integrated with the fluid circuit, the electricity generating system comprising an open Brayton power system comprising: a compressor; a turbine system; and a generator; the electricity generating system being arranged such that when assembled, gas can flow from the containment vessel outlet to the turbine system via the fluid circuit, and from the compressor to the containment vessel inlet via the fluid circuit, wherein the turbine system is configured to drive the compressor and the generator.
10. 10. The kit of parts of claim 9, wherein the kit of parts further comprises a heat dissipator, the heat dissipator being arrangeable between the compressor and turbine system.
11. 11. The kit of parts of claim 10, 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 radiative surface of the radiator.
12. 12. A method for a nuclear reactor configured for extra-terrestrial use, the method comprising controlling the nuclear reactor to: generate heat with a nuclear reactor core comprising a nuclear fuel and a moderator, the nuclear fuel comprising UO2 pellets and the moderator comprising yttrium hydride, the nuclear reactor core being housed in a containment vessel comprising a containment vessel inlet and a containment vessel outlet such that gas flowing from the containment vessel inlet to the containment vessel outlet flows through the nuclear reactor core, wherein a neutron reflector comprising beryllium oxide is disposed around a periphery of the nuclear reactor core, and a plurality of control drums disposed around the periphery of the nuclear reactor core; deliver, via a fluid circuit, gas heated by the nuclear reactor core from the containment vessel outlet to an electricity generating system; generate electricity with the electricity generating system, wherein the electricity generating system comprises a closed Brayton cycle engine coupled to the fluid circuit; and deliver, via the fluid circuit, gas cooled by the electricity generating system back to the containment vessel via the containment vessel inlet.