A nuclear fission power plant

Abstract

A nuclear fission power plant (10) comprising: a gas-cooled moderated nuclear reactor core (20) comprising: a fuel system (30); a moderator (35); and at least one core inlet (46) and at least one core outlet (48); a neutron reflector (70); a plurality of primary neutronic control elements (50); a secondary neutronic control system (60, 160); a containment vessel (40) substantially surrounding the gas-cooled moderated nuclear reactor core and allowing a gas to flow through both the containment vessel and the core; a fluid circuit (90) to receive hot gas from a containment vessel outlet (44) and deliver cooled gas to the containment vessel inlet (42); and an open Brayton power system coupled to the fluid circuit via a heat exchanger (92), the open Brayton power system comprising: a compressor (102); at least one turbine (104, 106); and a generator (108); the open Brayton power system being arranged such that the at least one turbine is configured to drive the compressor and the generator.

Description

A NUCLEAR FISSION POWER PLANTTECHNICAL FIELD

[0001] This disclosure relates to a nuclear fission power plant configured for use in a terrestrial environment and a kit of parts and method for a nuclear fission power plant configured for use in a terrestrial environment.BACKGROUND

[0002] It is desirable to have a reliable and low-carbon power source capable of deployment in a terrestrial environment. Terrestrial environments may include deserts, tundra, temperate climates, tropical rainforests, the Arctic, Antarctica, etc. Solar panels are often used as a means to generate electricity in terrestrial environments. However, their power density is low and they are limited to applications in sunlight. This is a particular problem for expeditions where a facility could be in darkness or in shadow for prolonged periods of time, e.g. a facility located in or substantially towards the Antarctic circle during the winter solstice, or a facility located beneath a tree canopy in a forest or jungle. The low power density of solar panels further limits their application. In particular, a facility in a terrestrial environment may have a high power requirement for which solar panels are not suited. Similarly, wind turbines may not be effective in locations with too low or too high an average wind speed for effective use of the turbine. Wind turbines also suffer from increased complexity in transportation and logistics, especially with regards to transporting the turbine blades, which may make it difficult to rapidly deploy a wind turbine to a terrestrial environment. On the other hand, diesel or gas generators are high-carbon energy sources, emit greenhouse gasses, and may be highly noise polluting.

[0003] The high-power density of a nuclear fission power plant and its ability to generate electricity independently from environmental conditions (e.g. sunlight or wind) make nuclear fission power plants an attractive option for use in terrestrial environments. However, it is desirable for a nuclear fission power plant to withstand harsh environmental conditions, require minimal maintenance, and be sufficiently robust to withstand damage in transit to a terrestrial environment. Weight and size are also issues as any power plant would likely need to fit within the confines of a container or containers in a transport vessel(s) capable of journeying to possibly remote and harsh environments.

[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 use in a terrestrial environment, 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 at least one core inlet and at least one core outlet; a neutron reflector disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums disposed around the periphery of the gas-cooled moderated nuclear reactor core; a secondary neutronic control system configured to selectively insert a secondary neutronic control element into a void in the gas-cooled moderated nuclear reactor core; a containment vessel substantially surrounding the gas-cooled moderated nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that gas following the flow path flows from the containment vessel inlet towards the gas-cooled moderated nuclear reactor core, into the gas- cooled moderated nuclear reactor core via the at least one core inlet, out of the gas-cooled moderated nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; 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 fuel system may comprise High Assay Low Enriched Uranium (HALEU). The fuel system may be enriched to substantially 19.75% uranium-235. The fuel system may comprise a solid fuel alloy, such as U-Zr, U-Mo etc.

[0007] The fuel system may comprise Tri-structural Isotropic (TRISO) particle fuel. The TRISO particle fuel may comprise a uranium, carbon and oxygen fuel kernel.

[0008] The neutron moderator may comprise zirconium hydride.

[0009] The neutron reflector may comprise graphite or aluminium oxide.

[0010] The fluid circuit may comprise a pump. The fluid circuit may comprise a heat exchanger. The electricity generating system may be coupled to the fluid circuit via the heat exchanger. The electricity generating system may be an open Brayton power system comprising a compressor, at least one turbine, and a generator. The open Brayton power system may be arranged such that air flows through the compressor, the heat exchanger, and the at least one turbine. The heat exchanger may be configured to permit heat in the gas flowing through the fluid circuit to be transferred to the compressed air from the compressor. The at least one turbine may be configured to drive the compressor and the generator.

[0011] The nuclear fission power plant may further comprise a neutron shield disposed around a periphery of the neutron reflector.

[0012] The primary and / or secondary neutronic control elements may comprise boron carbide, B4C.

[0013] The secondary neutronic control system may comprise a plurality of reactivity control beads. The nuclear fission power plant may further comprise a bead control system. The bead control system may comprise a source of pressurised gas and a vessel configured to contain the plurality of reactivity control beads. The vessel may be in communication with the void of the gas-cooled moderated nuclear reactor core. The bead control system may further comprise a controller. The controller may selectively apply the source of pressurized gas to the vessel, to force the reactivity control beads contained in the vessel into the void of the gas-cooled moderated nuclear reactor core. The reactivity control beads may comprise one of more of Boron Carbide and Tantalum.

[0014] The primary neutronic control elements may be a primary form of control to control a reactivity level of the gas-cooled moderated nuclear reactor core, and may be used for fine control, such as during a normal operation mode.

[0015] The secondary neutronic control system may be a secondary form of control to control a reactivity level of the gas-cooled moderated nuclear reactor core, and may be used for coarse control, such as in an emergency or shut-down mode.

[0016] The neutron shield may comprise boron carbide.

[0017] The nuclear fission power plant may comprise at least one further fluid circuit and at least one further electricity generating system, the further fluid circuit being configured to be coupled to the electricity generating system or the further electricity generating system.

[0018] The nuclear fission power plant may comprise at least one further fluid circuit and at least one further open Brayton power system. The further fluid circuit may be configured to transfer heat from the gas-cooled moderated nuclear reactor core via the heat exchanger or via further heat exchangers to the open Brayton power system or the further open Brayton power system.

[0019] According to a second aspect there is provided a kit of parts for a nuclear fission power plant configured for use in a terrestrial environment, the kit of parts being configured at least partially for assembly at the terrestrial environment and comprising: a gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a fuel system; a moderator; and at least one core inlet and at least one core outlet; a neutron reflector configured to be disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums configured to be disposed around the periphery of the gas-cooled moderated nuclear reactor core; a secondary neutronic control system configurable to be selectively insert a secondary neutronic control element into a void in the gas-cooled moderated nuclear reactor core; a containment vessel which, when assembled, substantially surrounds the gas-cooled moderated nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configurable to define a flow path between the containment vessel inlet and the containment vessel outlet, such that in use, gas following the flow path flows from the containment vessel inlet towards the gas-cooled moderated nuclear reactor core, into the gas-cooled moderated nuclear reactor core via the at least one core inlet, out of the gas-cooled moderated nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; a fluid circuit configurable to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; andan electricity generating system couplable to the fluid circuit so as to generate an electrical current.

[0020] The electricity generating system of the kit of parts may be an open Brayton power system comprising a compressor, at least one turbine, and a generator. The open Brayton power system may be configured to be arranged such that in use, air flows through the compressor, the heat exchanger, and the at least one turbine. The heat exchanger may be configured such that in use, heat in the gas flowing through the fluid circuit is transferred to the compressed air from the compressor. The at least one turbine may be configured to drive the compressor and the generator.

[0021] The kit of parts may further comprise a neutron shield configured to be disposed around a periphery of the neutron reflector.

[0022] The secondary neutronic control system of the kit of parts may comprise a plurality of reactivity control beads, and the nuclear fission power plant may further comprise a bead control system, the bead control system comprising: a source of pressurised gas, and a vessel configured to contain the plurality of reactivity control beads, wherein the vessel is configured to be placed in communication with the void of the gas-cooled moderated nuclear reactor core; and a controller for selectively applying the source of pressurized gas to the vessel so as to be able to force the reactivity control beads contained in the vessel into the void of the gas-cooled moderated nuclear reactor core.

[0023] According to a third aspect there is provided a method for a nuclear fission power plant configured for use in a terrestrial environment, the method comprising controlling the nuclear fission power plant to: generate heat with a gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising a fuel system, a moderator, at least one core outlet, and at least one core inlet, wherein: a neutron reflector is disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums are disposed around the periphery of the gas-cooled moderated nuclear reactor core; a containment vessel is arranged to substantially surround the gas-cooled moderated nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between thecontainment vessel inlet and the containment vessel outlet, such that gas following the flow path flows from the containment vessel inlet towards the gas-cooled moderated nuclear reactor core, into the gas-cooled moderated nuclear reactor core via the at least one core inlet, out of the gas-cooled moderated nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; and a secondary neutronic control element is configured to be selectively inserted into a void in 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.

[0024] The method may include generating electricity with an open Brayton power system coupled to the fluid circuit via a heat exchanger, the open Brayton power system comprising a compressor, at least one turbine, and a generator, the open Brayton power system being arranged such that air flows through the compressor, the heat exchanger, and the at least one turbine, wherein the heat exchanger is configured to permit heat in the gas flowing through the fluid circuit to be transferred to the compressed air from the compressor, and the at least one turbine is configured to drive the compressor and the 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.BRIEF 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 use in a terrestrial environment;

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

[0029] Figure 3 is a schematic diagram showing another example nuclear fission power plant configured for use in a terrestrial environment; and

[0030] Figure 4 is a flowchart depicting a method for a nuclear fission power plant configured for use in a terrestrial environment.DETAILED DESCRIPTION

[0031] With reference to Figure 1 , the present disclosure relates to a nuclear fission power plant 10 configured for use in a terrestrial environment. The nuclear fission power plant 10 is configured to be sufficiently robust, low-weight, deployable, and rugged to be transported to and used anywhere on the Earth’s surface, including remote and harsh environments such as desert regions, tropical rainforests, tundra, etc. Transportation / deployment to such environments may use any of ground / land-based vehicles (e.g. trucks, trains, etc.), aircraft (e.g. helicopters, airplanes, etc.), watercraft (e.g. boats, ships, etc.), or any other form of transportation. The nuclear fission power plant 10 may be fully assembled prior to transportation or may be at least partially assembled before transportation. Alternatively, the nuclear fission power plant 10 may be configured to be assembled where it is intended to be operated. For example, the nuclear fission power plant 10 may be transported in modular components or in sub-assemblies. Each module or sub-assembly may be transported, and the nuclear fission power plant 10 may subsequently be assembled.

[0032] The nuclear fission power plant 10 may be a micro-reactor. The micro-reactor may have a power output in the range of 1 - 5MW. The nuclear fission power plant 10 may be readily transportable, e.g. in a standard shipping container, or in a plurality of shipping containers for the distinct modules / sub-assemblies of the nuclear fission power plant 10.

[0033] 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.

[0034] 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 may 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 fissionisotopes into the environment, thereby improving an overall safety of the nuclear fission power plant 10. 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.

[0035] The nuclear reactor core 20 is moderated and comprises a moderator 35. The moderator 35 may improve the neutron economy of the nuclear reactor core 20. The moderator 35 may be provided within the nuclear reactor core 20 and may be interspersed throughout the nuclear reactor core. The moderator 35 may slow down the neutrons within the nuclear reactor core 20. The moderator may comprise zirconium hydride. Zirconium hydride may have a comparatively greater neutron slowing power than graphite or aluminium oxide. Using zirconium hydride as the moderator may therefore reduce an overall mass of the nuclear fission power plant. The moderator 35 may alternatively comprise any of graphite, aluminium oxide, yttrium hydride, or any other suitable moderator. However, zirconium hydride may be a good selection for deployable applications as it has an excellent ability to slow neutrons for only a small quantity of mass.

[0036] The nuclear reactor core 20 may be gas-cooled. The nuclear reactor core 20 may comprise at least one core inlet 46. The nuclear reactor core may comprise at least one core outlet 48. Heat may therefore be extracted from the nuclear reactor core 20 by virtue of a cooling gas that flows within the nuclear reactor core 20. The cooling gas may be configured to enter the nuclear reactor core 20 via the at least one core inlet 46. The cooling gas may be configured to exit the nuclear reactor core 20 via the at least one core outlet 48. The cooling gas may be helium, nitrogen, hydrogen, or any other appropriate cooling gas. A gas cooling system may allow higher core temperatures to be reached, as coolant evaporation issues (which can afflict pressurised water reactors) are eliminated. This, in turn, may allow for a greater thermodynamic efficiency of the nuclear fission power plant by creating a greater temperature difference between the reactor core 20 and heat sink.

[0037] The nuclear fission power plant 10 further comprises a plurality of primary neutronic control elements 50. The primary neutronic control elements 50 may be controlled to vary whether the primary 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 primary neutronic control elements 50 may comprise rotatable control drums disposedaround the periphery of the nuclear reactor core 20. Rotation of the drums by one or more first actuators 52 may vary whether the primary neutronic control elements 50 absorb or reflect neutrons from the nuclear reactor core 20. The first actuator(s) 52 may be controlled by a suitable first controller, which may receive data from one or more sensors. For example, the first actuators 52 may be controlled by first controller 54. The first controller 54 may be in communication with any suitable reactivity sensor system of the nuclear fission power plant 10, which may determine a rate of fission in the nuclear reactor core 20. Each drum may comprise a neutron reflecting material 51 (e.g. graphite or aluminium oxide) and may further comprise a neutron absorbing material 53 (e.g. boron carbide). 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 neutron absorbing material 53 is facing toward the core, thereby absorbing more neutrons to slow down the nuclear reactor. In this way, reactivity levels of the nuclear reactor core 20 may be controlled and the rotatable drums may provide the primary form of control. The primary 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 rotatable drums of the primary neutronic control elements 50 are advantageously compact and sufficiently robust for transportation.

[0038] The primary neutronic control elements 50 may comprise boron carbide, B4C, as the neutron absorbing material, and may comprise aluminium oxide, AI2O3, as the neutron reflecting material.

[0039] Two or more independent first actuators 52 may be provided for redundancy. For example, a first 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 first 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. Therefore, although only one first controller 54 is shown, there may be two or more independent control systems. For example, an independent control system may be provided for each set of rotatable drums. Therefore, to achieve a desired level of reactivity in the nuclear reactor core 20, the first controller 54 or more than one independent controller may operate first actuators 52 to either cause eachrotatable drum of the nuclear fission power plant 10 to rotate, or cause a set of rotatable drums of the nuclear fission power plant 10 to rotate, or cause individual drums of the nuclear fission power plant 10 to rotate.

[0040] The nuclear fission power plant 10 further comprises a secondary neutronic control system 60, 160. The secondary neutronic control system 60, 160 is configured to selectively insert a secondary neutronic control element 64, 168 into a void 65 of the of the nuclear reactor core. This may occur by way of a second actuator 62 or valve 162 wherein the second actuator 62 or valve 162 is coupled or otherwise in communication with the secondary neutronic control element 60, 168. The second actuator 62 or valve 162 may be in communication with a second control system 63, 164.

[0041] In the example nuclear fission power plant of Figure 1 , the secondary neutronic control element 64 may comprise a control rod configured to be inserted into the void 65 of the nuclear reactor core 20. The secondary neutronic control element 64 may comprise one of boron carbide or tantalum.

[0042] Referring now to the example nuclear fission power plant of Figure 2, the secondary neutronic control system 160 of the nuclear fission power plant may comprise an emergency bead control system. The emergency bead control system may comprise at least one vessel 161 , the at least one vessel 161 may be configured to contain the secondary neutronic control element. In this example, the secondary neutronic control element 168 may comprise a plurality of reactivity control beads. Each reactivity control bead may be in the shape of e.g. a sphere. Each reactivity control bead may comprise a neutron absorbing material. In particular, each reactivity control bead may comprise one of boron carbide or tantalum. Each of the at least one vessel 161 may be coupled to the void 65 of the nuclear reactor core 20 and to at least one source of pressurized gas 166. The source of pressurized gas may be a gas-filled chamber. That is, a chamber configured to contain a pressurised gas. Alternatively, the source of pressurized gas 166 may be a factory pressurized air line, a compressor, or any other suitable means. An automatically controlled, and / or manually operable controller, such as valve 162, may be coupled to each of the at least one sources of pressurized gas 166. The valve 162 may be configured to permit the pressurized gas contained in the chamber to flow into the vessel 161 , thereby forcing the beads contained in the vessel 161 into the void 65 of the nuclear reactor core 20. The valve 162 may be configured to permit the pressurized gas to flow into the at least one vessel 161 upon a suitable reactivity sensor system of the nuclear fission power plant 10 determining that a rate of fission hasreached a predetermined threshold. The reactivity sensor system may thus be in communication with a control system, such as the second control system 164 shown in Figure 2, and the control system may be in communication with the valve 162. The valve may additionally be operable by an operator and / or manually operable by an operator.

[0043] The secondary neutronic control system 60, 160 may be used for coarse control, such as in an emergency or shut-down mode of the nuclear fission power plant 10. In the example nuclear fission power plant of Figure 1 , the control rod may be inserted quickly into the nuclear reactor core 20 in the event of an emergency. An emergency event may be determined by the suitable reactivity sensor system of the nuclear fission power plant 10. In the example nuclear fission power plant of Figure 2, the reactivity control beads may be inserted quickly into the nuclear reactor core 20 in the event of an emergency. The second control system 164 may be configured to cause the valve 162 to open such that the reactivity control beads are rapidly inserted into the nuclear reactor core 20 when the reactivity sensor system determines that a rate of fission has reached a predetermined threshold.

[0044] The nuclear fission power plant 10 may further comprise a neutron reflector 70 disposed around the nuclear reactor core 20. The neutron reflector 70 may be configured to reflect neutrons back towards the core. The neutron reflector 70 may at least partially surround the nuclear reactor core 20. In particular, the neutron reflector 70 may surround or substantially surround the nuclear reactor core. For instance, the neutron reflector may be disposed around a periphery of the nuclear reactor core 20. The neutron reflector 70 may improve a redundancy of the nuclear fission power plant 10, as neutrons which have not been reflected by a primary neutronic control element may be reflected by the neutron reflector 70. The neutron reflector 70 may comprise elongate cavities. Each elongate cavity may be configured to receive a corresponding primary neutronic control element 50 (e.g. a corresponding rotatable control drum). In this way, the primary neutronic control elements may be disposed around a periphery of the nuclear reactor core 20. The neutron reflector 70 may further comprise a bead or control rod through hole to permit the secondary neutronic control element (i.e. the beads or control rod) to be inserted into the void 65 of the nuclear reactor core 20. In addition, a plurality of channels may be formed in the neutron reflector 70. At least some of the plurality of channels (such as, e.g., channel 43) may be configured to permit a cooling gas to flow through the neutron reflector 70 and around the nuclear reactor core 20. Additionally, at least some of the plurality of channels may be configured to permit the cooling gas to enter and / or exit the nuclear reactor core 20. For example, the at least one core inlet 46 and the at least one core outlet 48 may be formed by virtue of a plurality of channels formed in the neutron reflector 70.The neutron reflector 70 may be formed from graphite or aluminium oxide. Aluminium oxide may be used as the neutron reflecting material, as its neutron reflecting properties are comparable to that of graphite, but with the added benefit of being easier to source and to machine, shape, cut, etc. which may consequently reduce a manufacturing cycle time of the nuclear fission power plant 10.

[0045] The nuclear fission power plant 10 may further comprise a containment vessel 40. The containment vessel 40 may be disposed around the nuclear reactor core 20. In particular, the containment vessel 40 may at least partially surround the neutron reflector 70, the plurality of primary neutronic control elements 50, and the nuclear reactor core 20. For instance, the containment vessel 40 may be disposed around a periphery of the neutron reflector 70. The containment vessel 40 may be configured to contain a cooling gas. The cooling gas may be configured to cool the nuclear reactor core 20. The containment vessel may comprise an inlet 42. The containment vessel may comprise an outlet 44. The containment vessel inlet 42 may be configured to permit a cooling gas into the containment vessel 40. The containment vessel outlet 44 may be configured to permit the cooling gas out of the containment vessel 40. The containment vessel 40 may define a flow path (see for example block arrows in Figure 1 , Figure 2, and Figure 3) between the containment vessel inlet 42 and the containment vessel outlet 44. For example, the containment vessel 40 may comprise at least one inner surface 45. The at least one inner surface 45, in conjunction with other surfaces, e.g. of the containment vessel 40, may define a passage (i.e. the flow path) along which the cooling gas may flow. Accordingly, cooling gas may flow through the containment vessel 40 in a pre-determined manner. In this way, cooling gas following the flow path may flow from the containment vessel inlet 42 towards the nuclear reactor core 20. The flow path may direct the flow of the gas from the containment vessel inlet 42, through a channel formed in the neutron reflector 70 (e.g., channel 43), to the at least one core inlet 46. The cooling gas may then flow into the nuclear reactor core 20 via the at least one core inlet 46. The cooling gas may then flow through the nuclear reactor core 20, thereby forcing the gas to flow over, and absorb heat from, components within the nuclear reactor core 20. The cooling gas (which has now been heated by the components within the nuclear reactor core) may subsequently flow out of the nuclear reactor core 20 via the at least one core outlet 48. The flow path may direct the flow of the gas from the at least one core outlet 48 to the containment vessel outlet 44. The gas may then exit the containment vessel 40 via the at least one containment vessel outlet 44.

[0046] With reference to Figure 2 and Figure 3, the nuclear fission power plant 10 may further comprise a neutron shield 80 disposed around the nuclear reactor core 20. The neutron shield 80 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 80 may at least partially surround the containment vessel 40. In particular, the neutron shield 80 may surround or substantially surround the containment vessel 40. For instance, the neutron shield 80 may be disposed around a periphery of the containment vessel 40. The neutron shield 80 may thus improve a safety of the nuclear fission power plant 10, as neutrons which have not been absorbed or reflected by the primary neutronic control elements, or reflected by the neutron reflector 70, may be absorbed by the neutron shield 80. The neutron shield 80 may be formed from boron carbide, or any other suitable neutron absorbing material.

[0047] The neutron shield 80 and the containment vessel 40 may comprise primary through-holes. The number and location of primary through-holes formed in the neutron shield 80 and the containment vessel 40 may correspond with the number and location of elongate cavities formed in the neutron reflector 70. A primary neutronic control element 50 may thus be inserted into a corresponding elongate cavity of the neutron reflector 70 through a primary through-hole. Additionally or alternatively, the primary through-holes may allow e.g. cables, shafts, actuation systems, sensors, etc. to couple a first actuator 52 to a corresponding primary control element 50. The neutron shield 80 and the containment vessel 40 may further comprise a secondary through-hole, the secondary through-hole may correspond with the bead or control rod through hole of the neutron reflector 70, such as to permit the secondary neutronic control element (i.e. reactivity control beads or control rod) to be inserted into the void 65 of the nuclear reactor core 20. The neutron shield 80 may further comprise an outlet through- hole. The outlet through-hole hole formed in the neutron shield 80 may correspond with the containment vessel outlet 44. As such, cooling gas following the flow path defined by the containment vessel 40 may flow out of the containment vessel 40 and be received by e.g. a heat exchanging system.

[0048] The nuclear fission power plant 10 may therefore further comprise a fluid circuit 90 with a gas that flows through the fluid circuit. The fluid circuit 90 may comprise a heat exchanger 92 and a pump 94. The pump 94 may be operated to pump the working fluid (i.e., the gas) around the fluid circuit. The fluid circuit 90 may be configured to deliver cooling gas to the containment vessel inlet 42 via a fluid circuit outlet 96. The fluid circuit 90 may further be configured to receive hot gas from the containment vessel outlet 44 via a fluid circuit inlet 98. As such, cooling gas may be pumped (by the pump 94) from the fluid circuit 90 into thecontainment vessel 40 via the containment vessel inlet 42. The gas, guided by the flow path defined by the containment vessel 40, may flow through the core of the nuclear reactor 20. The cooling gas may therefore absorb heat from the nuclear reactor core 20 before flowing out of the containment vessel outlet 44 and being received by the fluid circuit 90. The hot gas may then flow through the heat exchanger 92. The heat exchanger 92 may be configured to transfer heat from the gas of the fluid circuit 90 to the working fluid of a power conversion system 100.

[0049] The power conversion system 100 may comprise an open Brayton power system. The power conversion system may therefore comprise a compressor 102, a first turbine 104, a second turbine 106, and a generator 108. A fluid duct 110, such as an air duct, may fluidically couple the compressor 102 to the heat exchanger 92, the heat exchanger 92 to the first turbine 104, and the first turbine to the second turbine 106. The fluid duct 110 may comprise an intake portion 112, the intake portion being configured to permit air from the environment into the compressor 102. The compressed air may then flow into the heat exchanger 92. The heat exchanger 92 may be configured to transfer heat from the working fluid (i.e., the gas) of the fluid circuit 90 to the compressed air of the power conversion system 100. The heated and compressed air may subsequently flow into the first turbine 104 and then flow into the second turbine 106. The first turbine 104 may be mechanically coupled to the compressor 102, e.g. via a shaft, and thus the first turbine 104, being driven by the air, may drive the compressor 102. The second turbine 106 may be coupled to the generator, and thus the second turbine may drive the generator 108, to generate electrical power. The electrical power may be distributed via a power distribution network 114 to users. The air, following the fluid duct 110, therefore passes through the compressor 102, the heat exchanger 92, the first turbine 104, and the second turbine 106, before being exhausted back into the environment via an exhaust portion 116 of the fluid duct 110. The air released back into the environment may subsequently act as a heatsink, thereby improving a thermodynamic efficiency of the power conversion system 100. Although the first and second turbines 104, 106 are depicted on separate shafts, it is also envisaged that the first and second turbines may be provided on a common shaft. Likewise, a single common turbine may be provided that powers both the compressor 102 and generator 108.

[0050] Although not depicted, it is envisaged that the nuclear fission power plant 10 may be transported in distinct sub-assemblies. Each sub-assembly may be loaded onto distinct shipping containers, or onto the same container, and may be assembled ‘in-situ’ at the terrestrial location, e.g. where power is required. As an example, a first sub-assembly maycomprise the nuclear reactor core 20, the primary neutronic control elements 50, the neutron reflector 70, the containment vessel 40, and the neutron shield 80. A second sub-assembly may comprise the pump 94, the heat exchanger 92, and any interconnecting piping of the fluid circuit 90. A third sub-assembly may comprise the power conversion system 100. A fourth sub-assembly may comprise the emergency bead control system 160. A fifth sub-assembly may comprise the at least one first controller 54, the at least one second control system 164, and any first actuators 52 of the primary neutronic control elements. This is but one example, it will be understood that other sub-assemblies are possible, and that the configuration of subassemblies may be adapted to best suit the means of transport. For example, first actuators 52 of the primary neutronic control elements 50 may be assembled into the first sub-assembly instead of being separately transported in the fifth sub-assembly. It is also possible for the nuclear fission power plant 10 to be completely assembled, loaded onto a container, and transported to the appropriate terrestrial location.

[0051] Although not depicted, it is envisaged that the nuclear fission power plant 10 may comprise at least one further fluid circuit similar to fluid circuit 90. The further fluid circuit may be configured to transfer heat from cooling gas flowing through the further fluid circuit or further to the working fluid of the power conversion system 100 via the heat exchanger 92 or a further heat exchanger. The further fluid circuit may have a further pump for circulating a gas in the further fluid circuit. The further fluid circuit may effectively be parallel to the fluid circuit 90 and may improve the robustness of the nuclear fission power plant 10 since it can continue to operate in the event of one of the fluid circuits failing.

[0052] Although not depicted, it is envisaged that the nuclear fission power plant 10 may comprise at least one further power conversion system 100. The nuclear fission power plant 10 may thus comprise at least one further open Brayton power system (e.g. like that described above). The further open Brayton power system may be configured to absorb heat from the working fluid of the fluid circuit 90 or further fluid circuit. The further open Brayton power system may therefore be coupled to the heat exchanger 92 or to a further heat exchanger. The further open Brayton power system may effectively be parallel to the open Brayton power system and may improve the robustness of the nuclear fission power plant 10 since it can continue to operate in the event of one of the open Brayton power systems failing.

[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 at least one container, such as astandard shipping container to be loaded onto a ship or a truck. The kit of parts may also be configured at least partially for assembly at the desired terrestrial deployment location. Once deployed in the terrestrial environment, the kit of parts may automatically assemble, or may be assembled with the assistance of a robot or any other operative.

[0054] With reference to Figure 4, 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, the nuclear fission power plant 10 may be controlled from a control facility that is located remote to the location of the nuclear fission power plant 10. Alternatively, control of the nuclear fission power plant 10 may be carried out locally (i.e., at the location of the nuclear fission power plant 10).

[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 moderated nuclear reactor core 20. In a second action 220, cooled gas is delivered to the containment vessel 40 by the fluid circuit 90. In a third action 230, hot gas from the containment vessel 40 is received by the fluid circuit 90. In a fourth action 240, a working fluid flowing in the power conversion system 100 is heated by virtue of the heat exchanger 92. In a fifth action 250, the compressor 102 and generator 108 are driven by at least one turbine, such as the first turbine 104 and the second turbine 106. In a sixth action 260, electricity is generated by the generator 108.

[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.

[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 reflector and the moderator, which make better use of the available neutrons.

[0058] Safety of the nuclear fission power plant is improved by reducing a likelihood of neutrons and radioisotopes from being released into the environment. This is at least partly achieved by the neutron shield, which may absorb any neutrons that are not reflected by the neutron reflector, and the fluid circuit, which provides a further barrier between the reactor core and the power conversion system, thereby reducing a risk of radioisotopes being released into the environment. The rotatable drums provided, in combination with a further emergency control system (i.e. , the control rod or emergency bead control system), enables a controller or controllers to exert both fine and coarse control over the rate of fission in the core of the reactor. This further enhances a safety of the nuclear fission power plant.

[0059] The fluid circuit may also provide a thermal buffer between the reactor core and the power conversion system. The fluid circuit may thus reduce the impact of any thermal fluctuations in the reactor core. As an example, the thermal inertia provided by the fluid circuit may reduce a thermal load experienced by components of the power conversion system, and therefore reduce a thermal fatigue of those components. This, in turn, may improve a life span of the nuclear fission power plant, and reduce an amount of maintenance required.

[0060] It is further noted that the Brayton power system generator provides excellent power to weight performance when compared to other power conversion technologies. The open Brayton power system is configured to use air from the surrounding environment as the working fluid of the system, and to use the air from the environment as the heat sink. A nuclear fission power plant that uses a steam Rankine cycle is confined to operating in environments with a water source. On the other hand, the nuclear fission power plant of the present disclosure may be deployed even to environments with no nearby water source. Such as, e.g. dry and arid desert environments like the Australian outback. This improves a robustness and versatility of the nuclear fission power plant, as it may confidently function in almost all terrestrial environments.

[0061] A transportability and utility of the nuclear fission power plant is improved through the ability to either transport the nuclear fission power plant in distinct sub-assemblies, or to transport an ‘already’ assembled nuclear fission power plant. As such, if transport constraints (e.g. regulations) demand smaller shipping containers, this may be accommodated by transporting the nuclear fission power plant in sub-assemblies configured to be easily assembled at the environment. Where no such constraints exist, the nuclear fission power plant may be fully or substantially assembled (e.g. at a factory) before being transported to the environment, thereby reducing a complexity for an end operative.

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

Claims

CLAIMS1 . A nuclear fission power plant configured for use in a terrestrial environment, 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 at least one core inlet and at least one core outlet; a neutron reflector disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums disposed around the periphery of the gas-cooled moderated nuclear reactor core; a secondary neutronic control system configured to selectively insert a secondary neutronic control element into a void in the gas-cooled moderated nuclear reactor core; a containment vessel substantially surrounding the gas-cooled moderated nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that gas following the flow path flows from the containment vessel inlet towards the gas-cooled moderated nuclear reactor core, into the gas- cooled moderated nuclear reactor core via the at least one core inlet, out of the gas-cooled moderated nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; a fluid circuit configured to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; and an open Brayton power system coupled to the fluid circuit via a heat exchanger, the open Brayton power system comprising: a compressor; at least one turbine; and a generator; the open Brayton power system being arranged such that air flows through the compressor, the heat exchanger, and the at least one turbine, wherein the heat exchanger is configured to permit heat in the gas flowing through the fluid circuit to be transferred to the compressed air from the compressor, and the at least one turbine is configured to drive the compressor and the generator.

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

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

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

5. The nuclear fission power plant of claim 4, wherein the TRISO particle fuel comprises a uranium, carbon, and oxygen fuel kernel.

6. The nuclear fission power plant of any preceding claim, wherein the moderator comprises zirconium hydride.

7. The nuclear fission power plant of any preceding claim, wherein the neutron reflector comprises aluminium oxide.

8. The nuclear fission power plant of any preceding claim, further comprising a neutron shield disposed around a periphery of the neutron reflector.

9. The nuclear fission power plant of any of the preceding claims, wherein the secondary neutronic control system comprises a plurality of reactivity control beads, and wherein the nuclear fission power plant further comprises a bead control system, the bead control system comprising: a source of pressurised gas; at least one vessel configured to contain the plurality of reactivity control beads, wherein the at least one vessel is in communication with the void of the gas-cooled moderated nuclear reactor core; and a secondary control system4 for selectively applying the source of pressurized gas to the at least one vessel and forcing the reactivity control beads contained in the at least one vessel into the void of the gas-cooled moderated nuclear reactor core.

10. The nuclear fission power plant of claim 9, wherein the reactivity control beads comprise one of more of boron carbide and tantalum.

11. The nuclear fission power plant of any of the preceding claims, wherein the primary neutronic control elements are a primary form of control to control a reactivity level of the gas- cooled moderated nuclear reactor core, and are used for fine control.

12. The nuclear fission power plant of any of the preceding claims, wherein the secondary neutronic control system is a secondary form of control to control a reactivity level of the gas- cooled moderated nuclear reactor core, and is used for coarse control.

13. The nuclear fission power plant of claim 8, wherein the neutron shield comprises boron carbide.

14. A kit of parts for a nuclear fission power plant configured for use in a terrestrial environment, the kit of parts being configured at least partially for assembly at the terrestrial environment and comprising: a gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising: a fuel system; a moderator; and at least one core inlet and at least one core outlet; a neutron reflector configured to be disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums configured to be disposed around the periphery of the gas-cooled moderated nuclear reactor core; a secondary neutronic control system configurable to selectively insert a secondary neutronic control element into a void in the gas-cooled moderated nuclear reactor core; a containment vessel which, when assembled, substantially surrounds the gas-cooled moderated nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configurable to define a flow path between the containment vessel inlet and the containment vessel outlet, such that in use, gas following the flow path flows from the containment vessel inlet towards the gas-cooled moderated nuclear reactor core, into the gas-cooled moderated nuclear reactor core via the at least one core inlet,out of the gas-cooled moderated nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; a fluid circuit configurable to receive hot gas from the containment vessel outlet and deliver cooled gas to the containment vessel inlet; and an open Brayton power system couplable to the fluid circuit via a heat exchanger, the open Brayton power system comprising: a compressor; at least one turbine; and a generator; the open Brayton power system being arrangeable such that air can flow through the compressor, the heat exchanger, and the at least one turbine, wherein the heat exchanger is configurable to permit heat in the gas flowing through the fluid circuit to be transferred to the compressed air from the compressor, and the at least one turbine is configurable to drive the compressor and the generator.

15. The kit of parts of claim 14, further comprising a neutron shield configured to be disposed around a periphery of the neutron reflector.

16. The kit of parts of claim 14 or claim 15, wherein the secondary neutronic control system comprises a plurality of reactivity control beads, and wherein the nuclear fission power plant further comprises a bead control system, the bead control system comprising: a source of pressurised gas; at least one vessel configured to contain the plurality of reactivity control beads, wherein the at least one vessel is configured to be placed in communication with the void of the gas-cooled moderated nuclear reactor core; and a controller for selectively applying the source of pressurized gas to the at least one vessel so as to be able to force the reactivity control beads contained in the at least one vessel into the void of the gas-cooled moderated nuclear reactor core.

17. A method for a nuclear fission power plant configured for use in a terrestrial environment, the method comprising controlling the nuclear fission power plant to: generate heat with a gas-cooled moderated nuclear reactor core, the gas-cooled moderated nuclear reactor core comprising a fuel system, a moderator, at least one core outlet, and at least one core inlet, wherein:a neutron reflector is disposed around a periphery of the gas-cooled moderated nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums are disposed around the periphery of the gas-cooled moderated nuclear reactor core; a containment vessel is arranged to substantially surround the gas-cooled moderated nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that gas following the flow path flows from the containment vessel inlet towards the gas-cooled moderated nuclear reactor core, into the gas-cooled moderated nuclear reactor core via the at least one core inlet, out of the gas-cooled moderated nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; and a secondary neutronic control system is configured to selectively insert a secondary neutronic control element into a void in 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 open Brayton power system coupled to the fluid circuit via a heat exchanger, the open Brayton power system comprising a compressor, at least one turbine, and a generator, the open Brayton power system being arranged such that air flows through the compressor, the heat exchanger, and the at least one turbine, wherein the heat exchanger is configured to permit heat in the gas flowing through the fluid circuit to be transferred to the compressed air from the compressor, and the at least one turbine is configured to drive the compressor and the generator.

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