A nuclear fission power plant

Abstract

A nuclear fission power plant (10) comprising: a nuclear reactor core (20) comprising a fuel system (30) and a moderator (35); a plurality of heat pipes (40) that each at least partially extend within the core; a neutron reflector (70) disposed around the core; a plurality of primary neutronic control elements (50) disposed around the core; a secondary neutronic control element (60) configured to be inserted into a void in the core; a fluid circuit (90) comprising a first heat exchanger (92), a second heat exchanger (96), and a pump (94); and an open Brayton power system comprising: a compressor (102); one or more turbines (104, 106); and a generator (108), and being arranged such that air flows through the compressor, the second heat exchanger and the one or more turbines, wherein the second heat-exchanger is configured to permit heat from the core to be transferred to the compressed air from the compressor, and the one or more turbines 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 gases, 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 minimum 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 nuclear reactor core comprising a fuel system and a moderator; a plurality of heat pipes, each heat pipe at least partially extending within the nuclear reactor core; a neutron reflector disposed around a periphery of the nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a secondary neutronic control element configured to be selectively inserted into a void in the nuclear reactor core; a fluid circuit comprising a first heat exchanger, a second heat exchanger, and a pump, wherein an end of the heat pipes extends into the first heat exchanger to transfer heat from the nuclear reactor core to a working fluid of the fluid circuit; and an 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 second heat exchanger and the at least one turbine, wherein the second heat exchanger is configured to permit heat in the working fluid 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.

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

[0011] The secondary neutronic control element may comprise a linearly-movable control rod.

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

[0013] The secondary neutronic control element 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 nuclear reactor core. The bead control system may further comprise a bead control system controller for selectively applying the source of pressurized gas to the vessel and force the reactivity control beads contained in the vessel into the void of the 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 nuclear reactor core, and may be used for fine control, such as during a normal operation mode.

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

[0016] The nuclear fission power plant may further comprise a neutron shield. The neutron shield may be disposed around a periphery of the neutron reflector.

[0017] The neutron shield may comprise boron carbide.

[0018] The nuclear fission power plant may comprise at least one further fluid circuit and at least one further power conversion system. The further fluid circuit may be configured to transfer heat from the heat pipes or further heat pipes of the nuclear reactor core via the first and second heat exchangers or via further first and second heat exchangers to the power conversion system or the further power conversion 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 nuclear reactor core comprising a fuel system and a moderator; a plurality of heat pipes, each heat pipe at least partially extendable within the nuclear reactor core;a neutron reflector disposable around a periphery of the nuclear reactor core; a plurality of primary neutronic control elements comprising rotatable control drums disposable around the periphery of the nuclear reactor core; a secondary neutronic control element configurable to be selectively inserted into a void in the nuclear reactor core; a fluid circuit comprising a first heat exchanger, a second heat exchanger, and a pump, wherein, when assembled, an end of the heat pipes extends into the first heat exchanger to transfer heat from the nuclear reactor core to a working fluid of the fluid circuit; and an open Brayton power system comprising: a compressor; at least one turbine; and a generator; the open Brayton power system being arrangeable such that air flows through the compressor, the second heat exchanger and the at least one turbine, wherein the second heat-exchanger is configurable to permit heat in the working fluid 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.

[0020] The secondary neutronic control element of the kit of parts may comprise a linearly-movable control rod.

[0021] The secondary neutronic control element 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; 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 nuclear reactor core; and a controller for selectively applying the source of pressurised gas to the vessel so as to force the reactivity control beads contained in the vessel into the void of the nuclear reactor core.

[0022] The kit of parts of may further comprise a neutron shield configured to be disposed around a periphery of the neutron reflector.

[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 nuclear reactor core comprising a fuel system and a moderator, wherein a neutron reflector is disposed around a periphery of the nuclear reactor core, a plurality of primary neutronic control elements comprising rotatable control drums are disposed around the periphery of the nuclear reactor core, and wherein the nuclear fission power plant comprises a secondary neutronic control element configured to be selectively inserted into a void in the nuclear reactor core; transfer heat from the nuclear reactor core using a plurality of heat pipes, each heat pipe at least partially extending within the nuclear reactor core; transfer heat from an end of the heat pipes to a working fluid flowing in a fluid circuit, the fluid circuit comprising a first heat exchanger, a second heat exchanger and a pump, wherein the end of the heat pipes extends into the first heat exchanger to transfer heat from the nuclear reactor core to the working fluid of the fluid circuit; transfer heat from the working fluid of the fluid circuit to an open Brayton power system, wherein the open Brayton power system is arranged such that air flows from a compressor to the second heat exchanger, and from the second heat exchanger to at least one turbine, such that the heat is transferred via the second heat exchanger to air that has been compressed by the compressor; drive the compressor and a generator with the at least one turbine, wherein the at least one turbine is driven by the heated and compressed air of the open Brayton power system; and generate electricity by virtue of the driven generator.

[0024] 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

[0025] 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:

[0026] Figure 1 is a schematic diagram showing an example nuclear fission power plant configured for use in a terrestrial environment;

[0027] Figure 2 is a schematic diagram showing another example nuclear fission power plant configured for use in a terrestrial environment;

[0028] Figure 3 is a schematic diagram showing another example nuclear fission power plant configured for in a terrestrial environment; and

[0029] Figure 4 is a flowchart depicting an example method for a nuclear fission power plant configured for use in a terrestrial environment.DETAILED DESCRIPTION

[0030] With reference to Figures 1 to 3, 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.

[0031] The nuclear fission power plant 10 may be a micro-reactor. The micro-reactor may have 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.

[0032] As depicted, the nuclear fission power plant 10 comprises a nuclear reactor core 20. The nuclear reactor core 20 comprises a fuel system 30. The fuel system 30 may comprise High Assay Low Enriched Uranium (HALEU), e.g., with the concentration of the fissile isotope uranium-235 (U-235) being between 5% and 20% of the mass of uranium. In particular, fuel of the fuel system 30 may be enriched to substantially 19.75% uranium-235. This level of enrichment allows for better energy density whilst maintaining a safe level of enrichment.

[0033] The fuel system 30 may comprise Tri-structural Isotropic (TRISO) particle fuel. Each TRISO particle fuel may comprise a uranium, carbon and oxygen fuel kernel, in particular a mixture of UO2 and UC. The TRISO fuel system 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 silicon carbide, SiC. The carbon and SiC-coated layers prevent the release of fission isotopes 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.

[0034] 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 35 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 compromise for deployable applications as it has an excellent ability to slow neutrons with only a small quantity of mass.

[0035] The nuclear reactor core 20 may be cooled using two-phase passive convection. For example, the nuclear fission power plant 10 further comprises a plurality of heat pipes 40. Each heat pipe 40 at least partially extends within the nuclear reactor core 20, e.g. across a substantial length of the nuclear reactor core 20. The heat pipes 40 may be substantially elongate and may have a protruding end 42 that protrudes beyond the nuclear reactor core 20. The heat pipes 40 may be distributed within the nuclear reactor core 20, e.g., to ensure efficient heat transfer and heat distribution within the nuclear reactor core 20.

[0036] The heat pipes 40 are heat-transfer devices that use phase transition to transfer heat between two parts of the heat pipe. At the hot part of the heat pipe 40 (i.e., in the nuclear reactor core 20), a volatile liquid within the heat pipe 40 turns into a vapour by absorbing heat from around the heat pipe. The vapour then travels along the heat pipe 40 to a cold part ofthe heat pipe and condenses back into a liquid, releasing the latent heat (i.e. , at the protruding end 42). The liquid then returns to the hot part of the heat pipe 40 and the cycle repeats.

[0037] Heat pipes 40 have been selected as they have excellent reliability, lifetime and redundancy (for example the nuclear power plant may continue to operate if a particular heat pipe has failed). The heat pipes 40 may use an alkali metal as their working fluid (for example sodium) as this provides excellent heat transportation when using the passive two-phase convection mechanism and operates within the 400-1000°C temperature range intended for the nuclear reactor core 20.

[0038] 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 disposed around the periphery of the nuclear reactor core 20. Rotation of the drums by a first actuator 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 54, which may receive data from one or more sensors. 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 (e.g. graphite) 51 and may further comprise a neutron absorbing material (e.g. boron carbide) 53. 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 the more of the neutron absorbing material 53 is facing toward the core, thereby absorbing more neutrons to slow down the rate of fission in 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.

[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 anotherarrangement, 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 more 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 each rotatable 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 may further comprise a secondary neutronic control element 60. The secondary neutronic control element 60 may comprise a linearly- movable control rod that may be selectively inserted into a corresponding void 64 (i.e., a cavity) in the nuclear reactor core 20. Movement of the control rod by a second actuator 62 may vary the number of neutrons the secondary neutronic control element 60 absorbs within the nuclear reactor core 20. The second actuator 62 may be controlled by a secondary neutronic control element controller 63, which may receive data from one or more sensors. The secondary neutronic control element controller 63 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. The secondary neutronic control element controller 63 may be part of or separate from the first controller 54. The secondary neutronic control element 60 may be used for coarse control, such as in an emergency or shut-down mode of the nuclear fission power plant 10. The control rod of the secondary neutronic control element 60 may be inserted quickly into the nuclear reactor core 20, e.g., 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. The secondary neutronic control element controller 63 may be configured to cause the second actuator 62 to rapidly insert the secondary neutronic control element 60 into the nuclear reactor core 20 when the reactivity sensor system determines that a rate of fission has reached a predetermined threshold.

[0041] The primary and / or secondary neutronic control elements 50, 60 may comprise boron carbide, B4C, as the neutron absorbing material.

[0042] As shown in Figure 2, it is envisaged that the nuclear fission power plant 10 may comprise (in addition to or as an alternative to the secondary neutronic control element 60, i.e. the linearly-movable control rod shown in Figure 1) an emergency bead control system 160. The emergency bead control system 160 may comprise at least one vessel 161 , the at least one vessel 161 may be configured to contain a plurality of reactivity control beads (not shown). Each reactivity control bead may be in the shape of 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 64 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 pressurised air line, a compressor, or any other suitable means. An automatically controlled (or manually operable) valve 162 may be coupled to each of the at least one (gas filled) chamber. The valve 162 may be configured to permit the pressurized gas contained in the chamber to flow into a corresponding at least one vessel 161 , thereby forcing the beads contained in the at least one vessel into the void 64 of the nuclear reactor core 20. The valve 162 may be configured to permit the pressurized gas to flow into a corresponding vessel upon a suitable reactivity sensor system of the nuclear fission power plant 10 determining that a rate of fission has reached a predetermined threshold. The reactivity sensor system may thus be in communication with a control system (e.g. bead control system controller 163), and the control system may be in communication with the valve. The valve may additionally be operable by an operator and / or manually operable by an operator.

[0043] 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 20. For instance, the neutron reflector 70 may be disposed around a periphery of the nuclear reactor core 20. 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 50 may be disposed around a periphery of the nuclear reactor core 20. The neutron reflector 70 may further comprise a rod through-hole to permit the secondary neutronic control element 60 (i.e. the control rod or beads) to be inserted into the void 64 of the nuclear reactor core 20. The neutron reflector 70 may further comprise insert cavities. Each insert cavity may be configured to allow acorresponding heat pipe 40 to be inserted into the nuclear reactor core, and to permit a protruding end 42 of a corresponding heat pipe 40 to protrude beyond 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 be formed from graphite or aluminium oxide. Nuclear-grade graphite may be used as a reflection material, as it provides acceptable neutron reflection properties for its mass. Aluminium oxide (AI2O3) exhibits similar properties and could therefore also be used as the reflection material.

[0044] With reference to Figures 2 and 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 neutron reflector 70. In particular, the neutron shield 80 may surround or substantially surround the neutron reflector 70. For instance, the neutron shield 80 may be disposed around a periphery of the neutron reflector 70. The neutron shield 80 may comprise primary through-holes. The number and location of primary through-holes formed in the neutron shield 80 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. The neutron shield 80 may further comprise a secondary through-hole, the secondary through-hole may correspond with the rod through-hole of the neutron reflector 70, such as to permit the secondary neutronic control element (i.e. the control rod or beads) to be inserted into the void 64 of the nuclear reactor core 20. The neutron shield 80 may further comprise insert through-holes. The number and location of insert through holes formed in the neutron shield 80 may correspond with the number and location of insert cavities formed in the neutron reflector 70. As such, heat pipes may be inserted into the nuclear reactor core, and a protruding end 42 of a heat pipe may protrude beyond the nuclear reactor core 20. 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 neutron-absorbing 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.

[0045] The nuclear fission power plant 10 may further comprise a fluid circuit 90 with a fluid circuit working fluid that flows through the fluid circuit. The fluid circuit 90 may comprisea first heat exchanger 92, a pump 94, and a second heat exchanger 96. The pump 94 may be operated to pump the fluid circuit working fluid around the fluid circuit. The protruding ends 42 of the heat pipes 40 extend into the first heat exchanger 92 to transfer heat from the nuclear reactor core 20 to the fluid circuit working fluid of the fluid circuit 90. The second heat exchanger 96 may be configured to transfer heat from the fluid circuit working fluid of the fluid circuit to a power conversion system working fluid of a power conversion system 100. As such, the fluid circuit 90 is arranged so that the fluid circuit working fluid flowing through the fluid circuit 90 transfers heat from the heat pipes 40 via the heat exchangers to the power conversion system working fluid of the power conversion system 100.

[0046] 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 second heat exchanger 96, the second heat exchanger 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 second heat exchanger 96. The second heat exchanger 96 may be configured to transfer heat from the fluid circuit working fluid 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 may drive the compressor 102. The second turbine 106 may be coupled to the generator, and 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 second heat exchanger 96, 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.

[0047] 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 ontodistinct 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 may comprise the nuclear reactor core 20 with the protruding ends 42 of the heat pipes 40 extending into the first heat exchanger 92, the primary neutron-absorbing control elements 50, the secondary neutron-absorbing control element(s) 60, the neutron reflector 70, the neutron shield 80. A second sub-assembly may comprise the pump 94, the second heat exchanger 96, and any interconnecting piping. A third sub-assembly may comprise the power conversion system 100. A fourth sub-assembly may comprise the first controller 54, the secondary neutronic control element controller 63, and any actuators 52, 62 of the primary / secondary neutron-absorbing control elements. This is but one example, it will be understood that other sub-assemblies are possible, and that the configuration of sub-assemblies may be adapted to best suit the means of transport. For example, first and second actuators 52, 62 of the primary / secondary neutron-absorbing control elements may be assembled into the first subassembly instead of being separately transported in the fourth 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.

[0048] 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 the heat pipes 40 or further heat pipes of the nuclear reactor core 20. The further fluid circuit may transfer heat via the first heat exchanger 92 or a further heat exchanger to the working fluid of the power conversion system 100. The further fluid circuit may have a further pump for circulating a working fluid 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.

[0049] 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 second heat exchanger 96 or to a further second 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 fissionpower plant 10 since it can continue to operate in the event of one of the open Brayton power systems failing.

[0050] The present disclosure also relates to a kit of parts for the nuclear fission power plant 10. The kit of parts may comprise at least some of the above-described components. The kit of parts may be configured for placement within at least one container, such as a standard 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.

[0051] 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).

[0052] The method 200 controls the nuclear fission power plant 10 such that in a first action 210, the nuclear fission power plant 10 generates heat with the nuclear reactor core 20. In a second action 220, the nuclear fission power plant 10 transfers heat from the nuclear reactor core using the plurality of heat pipes 40. In a third action 230, the nuclear fission power plant 10 transfers heat from the protruding end 42 of the heat pipes 40 to the power conversion system working fluid in the power conversion system 100 via the fluid circuit working fluid flowing in the fluid circuit 90. In a fourth action 240, the nuclear fission power plant 10 drives the compressor 102 with at least one turbine 104, 106. In a fifth action 250, the nuclear fission power plant 10 drives the generator 108 with the at least one turbine 104, 106 of the power conversion system 100. In a sixth action 260, the nuclear fission power plant 10 generates electricity by virtue of the driven generator.

[0053] The present disclosure advantageously provides a lightweight, yet rugged, safe, and resilient nuclear fission power plant. These advantages are particularly beneficial for deployment to a remote environment. Weight and ruggedness are important factors for transport considerations, a high level of safety is crucial especially in remote and substantially inaccessible environments, and resilience helps to ensure a long life span with minimal maintenance. The specific use of TRISO (coated) fuel, a neutron reflector, a neutron shield,heat pipes, rotatable control drums, a linear control rod or emergency bead control system, an intermediate fluid circuit, and an open Brayton system contribute to these advantages.

[0054] The TRISO fuel system improves the safety of the nuclear fission power plant, as the fission isotopes are securely contained within a coated shell. Although the TRISO fuel form may have a lower fissile density, this is countered by the reflector and moderator, which make better use of the available neutrons. 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 achieved by the neutron shield, which may absorb any neutrons that are not reflected by the neutron reflector, and the intermediate 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 (e.g. the linear control rod and / or the emergency bead control system), enables a controller 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.

[0055] 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.

[0056] It is further noted that the Brayton cycle generator provides excellent power to weight performance when compared to other power conversion technologies. The open Brayton cycle 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 application range of the nuclear fission power plant, as it may confidently function in almost all terrestrial environments.

[0057] A robustness of the nuclear fission power plant is further improved by the heat pipes in the reactor core, which have few moving parts and are therefore less likely to requiremaintenance. Further, the heat pipe arrangement is resilient due to the high level of redundancy since a particular heat pipe can fail without affecting operation of the remaining components. The heat pipes also promote a flat temperature distribution within the reactor core, which improves reactor performance. The overall efficiency of the nuclear power plant is therefore improved.

[0058] 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.

[0059] The above-described features combine to improve the safety, robustness and resilience of the overall nuclear power plant, whilst maintaining good efficiency and energy output.

[0060] Various examples have been described, each of which feature various combinations of features. It will be appreciated by those skilled in the art that, except where clearly mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

CLAIMS1. A nuclear fission power plant configured for use in a terrestrial environment, the nuclear fission power plant comprising: a nuclear reactor core comprising a fuel system and a moderator; a plurality of heat pipes, each heat pipe at least partially extending within the nuclear reactor core; a neutron reflector disposed around a periphery of the nuclear reactor core; a plurality of primary neutron-absorbing control elements comprising rotatable control drums disposed around the periphery of the nuclear reactor core; a secondary neutronic control element configured to be selectively inserted into a void in the nuclear reactor core; a fluid circuit comprising a first heat exchanger, a second heat exchanger, and a pump, wherein an end of the heat pipes extends into the first heat exchanger to transfer heat from the nuclear reactor core to a fluid circuit working fluid of the fluid circuit; and an 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 second heat exchanger and the at least one turbine, wherein the second heat exchanger is configured to permit heat in the fluid circuit working fluid 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 graphite or aluminium oxide.

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

9. The nuclear fission power plant of any of the preceding claims, wherein the secondary neutronic control element comprises a linearly-movable control rod.

10. The nuclear fission power plant of any of claims 1 to 8, wherein the secondary neutronic control element 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 nuclear reactor core; and a bead control system controller for selectively applying the source of pressurised 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 nuclear reactor core.

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

12. The nuclear fission power plant of any of the preceding claims, wherein the primary neutron-absorbing control elements are a primary form of control to control a reactivity level of the nuclear reactor core, and are used for fine control.

13. The nuclear fission power plant of any of the preceding claims, wherein the secondary neutronic control element is a secondary form of control to control a reactivity level of the nuclear reactor core, and is used for coarse control.

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

15. The nuclear fission power plant of claim 14, wherein the neutron shield comprises boron carbide.

16. 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 nuclear reactor core comprising a fuel system and a moderator; a plurality of heat pipes, each heat pipe at least partially extendable within the nuclear reactor core; a neutron reflector disposable around a periphery of the nuclear reactor core; a plurality of primary neutron-absorbing control elements comprising rotatable control drums configured to be disposed around the periphery of the nuclear reactor core; a secondary neutronic control element configurable to be selectively inserted into a void in the nuclear reactor core; a fluid circuit comprising a first heat exchanger, a second heat exchanger, and a pump, wherein, when the fluid circuit is assembled, an end of the heat pipes extends into the first heat exchanger to transfer heat from the nuclear reactor core to a fluid circuit working fluid of the fluid circuit; and an open Brayton power system comprising: a compressor; at least one turbine; and a generator; the open Brayton power system being arrangeable such that, when assembled and in use, air flows through the compressor, the second heat exchanger and the at least one turbine, wherein the second heat-exchanger is configurable to permit heat in the fluid circuit working fluid 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.

17. The kit of parts of claim 16, wherein the secondary neutronic control element comprises a linearly-movable control rod.

18. The kit of parts of claim 16, wherein the secondary neutronic control element 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 nuclear reactor core; and a bead control system controller for selectively applying the source of pressurised gas to the at least one vessel so as to force the reactivity control beads contained in the at least one vessel into the void of the nuclear reactor core.

19. The kit of parts of any of claims 16, 17, or 18, further comprising a neutron shield configured to be disposed around a periphery of the neutron reflector.

20. 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 nuclear reactor core comprising a fuel system and a moderator, wherein a neutron reflector is disposed around a periphery of the nuclear reactor core, a plurality of primary neutron-absorbing control elements comprising rotatable control drums are disposed around the periphery of the nuclear reactor core, and wherein the nuclear fission power plant comprises a secondary neutronic control element configured to be selectively inserted into a void in the nuclear reactor core; transfer heat from the nuclear reactor core using a plurality of heat pipes, each heat pipe at least partially extending within the nuclear reactor core; transfer heat from an end of the heat pipes to a fluid circuit working fluid flowing in a fluid circuit, the fluid circuit comprising a first heat exchanger, a second heat exchanger and a pump, wherein the end of the heat pipes extends into the first heat exchanger to transfer heat from the nuclear reactor core to the fluid circuit working fluid of the fluid circuit; transfer heat from the working fluid of the fluid circuit to an open Brayton power system, wherein the open Brayton power system is arranged such that air flows from a compressor to the second heat exchanger, and from the second heat exchanger to at least one turbine, suchthat the heat is transferred via the second heat exchanger to air that has been compressed by the compressor; drive the compressor and a generator with the at least one turbine, wherein the at least one turbine is driven by the heated and compressed air of the open Brayton power system; and generate electricity by virtue of the driven generator.

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