GB2628908A

GB2628908A - A nuclear fission power plant

Info

Publication number: GB2628908A
Application number: GB2403384.7A
Authority: GB
Inventors: D Lee Joseph; G Bauld James; A Brown Sam; J Wakeling Megan; Pepper Samuel
Original assignee: Rolls Royce Submarines Ltd
Current assignee: Rolls Royce Submarines Ltd
Priority date: 2024-03-08
Filing date: 2024-03-08
Publication date: 2024-10-09
Also published as: WO2025185916A8; WO2025185916A1; GB202403384D0

Abstract

A nuclear fission reactor 10 comprises: a plurality of heat pipes 40 configured to transfer heat from a reactor core 20 to a first heat exchanger 82; a fluid circuit 80 configured to transfer heat therefrom to a second heat exchanger 86; and an open Brayton power system 100 configured such that heat from the second heat exchanger is transferred to compressed air delivered by a compressor 102, the heated compressed air subsequently flowing through at least one turbine 104 & 106 configured to drive the compressor and an electrical power generator 108. The reactor core comprises: a fuel system 30, e.g. comprising High Assay Low Enriched Uranium (HALEU) enriched to 19.75% uranium-235; and moderator 35 comprising e.g. zirconium hydride. In addition to neutronic control elements in the form of rotatable control drums 50, a neutron reflector 60 is disposed around the periphery of the reactor core. A neutron shield (70, Fig. 2) may also be provided around the reactor.

Description

A NUCLEAR FISSION POWER PLANT

TECHNICAL 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 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 neutronic control elements comprising rotatable control drums disposed around the periphery of 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 electricity generating system coupled to the fluid circuit so as to generate an electrical current.

[0006] The electricity generating system may comprise an open Brayton power system. The open Brayton power system may comprise 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 second heat exchanger and the at least one turbine. The second heat-exchanger may be configured to permit heat in the working fluid 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.

[0007] 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. [0008] The fuel system may comprise Tri-structural Isotropic (TRISO) particle fuel. The TRISO particle fuel may comprise a uranium, carbon and oxygen fuel kernel.

[0009] The neutron moderator may comprise yttrium hydride or zirconium hydride.

[0010] The neutron reflector may comprise beryllium oxide, or graphite, or aluminium oxide.

[0011] The heat pipes may comprise a heat pipe working fluid comprising an alkali metal, such as sodium.

[0012] The neutronic control elements may comprise boron carbide, B4C.

[0013] The nuclear fission power plant may further comprise a neutron shield disposed around a periphery of the neutron reflector.

[0014] The neutron shield may comprise boron carbide.

[0015] 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.

[0016] The rotatable control drums may comprise a first set of rotatable control drums controlled by at least one first controller, and a second set of rotatable control drums controlled by at least one second controller. The at least one first controller may be configured to control the first set of rotatable control drums to selectively adjust a rate of fission during a normal operating mode. The at least one second controller may be configured to control the second set of rotatable control drums, e.g. when the rate of fission in the nuclear reactor core reaches a predetermined emergency threshold or shut down is required.

[0017] Each rotatable control drum may comprise a neutron-reflecting material and a neutron-absorbing material. The neutron-absorbing material may be disposed over at least a portion of an outer circumference of the rotatable control drum.

[0018] The neutron-reflecting material may comprise beryllium oxide. The neutron-absorbing material may comprise boron carbide.

[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, the plurality of heat pipes configured such that, when the kit of parts is assembled, each heat pipe at least partially extends within the nuclear reactor core; a neutron reflector disposable around a periphery of the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums disposable around the periphery of the nuclear reactor core; a fluid circuit comprising a first heat exchanger, a second heat exchanger, and a pump, wherein, when the kit of parts is assembled, an end of the heat pipes extends into the first heat exchanger so as to be able 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 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 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 kit of parts may further comprise a neutron shield configured to be disposed around a periphery of the neutron reflector.

[0021] The neutron shield of the kit of parts may comprise boron carbide.

[0022] Each rotatable control drum of the kit of parts may comprise a neutron-reflecting material and a neutron-absorbing material, the neutron-absorbing material being configured to be disposed over at least a portion of an outer circumference of the rotatable control drum.

[0023] The neutron-reflecting material of the kit of parts may comprise beryllium oxide and the neutron-absorbing material may comprise boron carbide.

[0024] 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, and a plurality of neutronic control elements comprising rotatable control drums are disposed around the periphery of 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.

[0025] The method may further comprise the electricity generating system being an open Brayton power system. The open Brayton power system may comprise 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 second heat exchanger and the at least one turbine. The second heat-exchanger may be configured to permit heat in the working fluid 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.

[0026] 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

[0027] 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: [0028] Figure 1 is a schematic diagram showing an example nuclear fission power plant configured for use in a terrestrial environment; [0029] Figure 2 is a schematic diagram showing another example nuclear fission power plant configured for use in a terrestrial environment; and [0030] Figure 3 is a flowchart depicting an example method for a nuclear fission power plant configured for use in a terrestrial environment.

DETAILED DESCRIPTION

[0031] Wth 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 almost 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 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.

[0035] The nuclear reactor core 20 may be moderated and may comprise a moderator 35. The moderator 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 yttrium hydride. Yttrium hydride may have a comparatively greater neutron slowing power when compared to graphite, aluminium oxide, or zirconium hydride. Using yttrium 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, zirconium hydride, or any other suitable moderator. However, yttrium hydride may be selected due to its combination of neutron-slowing ability and comparatively high thermal stability when compared to other potential moderator materials. Along with reducing an overall mass of the nuclear fission power plant, yttrium hydride may also permit higher maximum core temperatures to be reached, thereby improving a thermodynamic efficiency of the nuclear fission power plant 10.

[0036] 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, which is to say, the extent of each heat pipe includes a section that passes through 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.

[0037] 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 of the 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.

[0038] 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.

[0039] The nuclear fission power plant 10 further comprises a plurality of neutronic control elements 50. The neutronic control elements 50 may be controlled to vary whether the neutronic control elements 50 absorb or reflect neutrons from the nuclear reactor core 20, and thereby control reactivity levels in the nuclear reactor core 20. The neutronic control elements 50 may comprise rotatable control drums disposed around the periphery of the nuclear reactor core 20. Rotation of the drums by an actuator 52 may vary whether the neutronic control elements 50 absorb or reflect neutrons from the nuclear reactor core 20. The actuator(s) 52 may be controlled by a suitable controller, which may receive data from one or more sensors. For example, the actuators 52 may be controlled by a first controller 54 and/or by a second controller 56. The first controller 54 may be part of or separate from the second controller 56. Although not depicted, it is envisaged that the first controller 54 and the second controller 56 may be in communication with multiple systems, including sensor system(s) of the nuclear fission power plant 10. The sensor systems may be configured to determine a rate of fission in the nuclear reactor core 20. Each drum may comprise a neutron-reflecting material 51 (e.g. graphite or beryllium oxide) and may further comprise a neutron-absorbing material 53 (e.g. boron carbide). Beryllium oxide has very good neutron reflecting properties for its mass, has a high thermal conductivity, and a high temperature stability. Using beryllium oxide as the neutron-reflecting material of the drum may therefore increase a performance of the drum, which may consequently permit a mass of the nuclear fission power plant 10 to be reduced. The neutron-absorbing material 53 may be disposed over at least a portion of an outer circumference of the drum. To promote reactivity, the control drums may be positioned such that more of the reflecting material 51 is facing toward the core, thereby directing more neutrons back into the nuclear reactor core. To slow down reactivity, each control drum cylinder may be rotated so that more of the 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 rotatable drums of the neutronic control elements 50 are advantageously compact and sufficiently robust for transportation.

[0040] Two or more independent actuators 52 may be provided for redundancy. For example, an actuator may be provided at each end of a rotatable drum. In another arrangement, the rotatable drums may be arranged in two or more independent sets of rotatable drums with each set having its own actuator. The rotatable drums within a particular set may alternate with rotatable drums from another set. For example, there may be two independent sets of six rotatable drums interspersed with one another about the circumference of the nuclear reactor core 20. Therefore, although only one first controller 54 and only one second controller 56 is shown, there may be two or more independent first controllers 54, and similarly there may be two or more independent second controllers 56. 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 and second controllers 54, 56 or the more than one independent first and second controllers 54, 56 may operate 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.

[0041] The neutronic control elements 50 controlled by the at least one first controller 54 may be used for fine control, such as during a normal operating mode of the nuclear fission power plant 10. The at least one first controller 54 may be configured to control the rotatable control drums to selectively adjust a rate of fission during the normal operating mode of the nuclear fission power plant. For example, the at least one first controller 54 may be configured to cause actuators 52 to selectively rotate the neutronic control elements 50 based at least on a value representative of the current rate of fission in the core and a desired rate of fission in the core. The at least one first controller 54 may control a first set of rotatable control drums. The first controller 54 may cause, by way of corresponding actuators 52, the first set of rotatable control drums to selectively rotate based on a value representative of the current rate of fission in the core and a predetermined setpoint or an input from an operator.

[0042] The neutronic control elements 50 controlled by the second controller 56 may be used for coarse control, such as in an emergency or shut-down mode of the nuclear fission power plant 10. The at least one second controller 56 may cause the rotatable control drums to quickly rotate in the case of an emergency. For example, in the case of an emergency, each rotatable drum controlled by the second controller 56 may be caused to rotate such that a maximum surface area of the neutron-absorbing material 53 of each drum is facing towards the core. An emergency event may be determined by a suitable reactivity sensor system of the nuclear fission power plant 10. The at least one second controller 56 may control a second set of rotatable control drums. The at least one second controller 56 may be configured to cause a corresponding set of actuators to rapidly rotate the second set of rotatable control drums to a preset configuration when the reactivity sensor system determines that a rate of fission has reached a predetermined threshold.

[0043] The neutronic control elements 50 may comprise boron carbide, 134C, as the neutron-absorbing material.

[0044] The nuclear fission power plant 10 may further comprise a neutron reflector 60 disposed around the nuclear reactor core 20. The neutron reflector 60 may be configured to reflect neutrons back towards the core. The neutron reflector 60 may at least partially surround the nuclear reactor core 20. In particular, the neutron reflector 60 may surround or substantially surround the nuclear reactor core 20. For instance, the neutron reflector may be disposed around a periphery of the nuclear reactor core 20. The neutron reflector 60 may comprise elongate cavities. Each elongate cavity may be configured to receive a corresponding neutronic control element 50 (i.e. a corresponding rotatable control drum). In this way, the neutronic control elements may be disposed around a periphery of the nuclear reactor core 20. The neutron reflector 60 may further comprise insert cavities. Each insert cavity may be configured to allow a corresponding heat pipe 40 to be inserted into the nuclear reactor core 20, and to permit a protruding end 42 of a corresponding heat pipe 40 to protrude beyond the nuclear reactor core 20. The neutron reflector 60 may improve a redundancy of the nuclear fission power plant 10, as neutrons which have not been reflected by a neutronic control element may be reflected by the neutron reflector 60. The neutron reflector 60 may be formed from beryllium oxide, BeO. Alternatively, the neutron reflector 60 may be formed from graphite or aluminium oxide. However, beryllium oxide may provide higher neutron reflection for its mass when compared to graphite or aluminium oxide. Beryllium oxide also has a high thermal conductivity and high-temperature stability, making it suitable for use in proximity to a nuclear reactor core.

[0045] With reference to Figure 2, the nuclear fission power plant 10 may further comprise a neutron shield 70 disposed around the nuclear reactor core 20. The neutron shield 70 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 70 may at least partially surround the neutron reflector 60. In particular, the neutron shield 70 may surround or substantially surround the neutron reflector 60. For instance, the neutron shield 70 may be disposed around a periphery of the neutron reflector 60. The neutron shield 70 may comprise primary through-holes. The number and location of primary through-holes formed in the neutron shield 70 may correspond with the number and location of elongate cavities formed in the neutron reflector 60. A neutronic control element 50 may thus be inserted into a corresponding elongate cavity of the neutron reflector 60 through a primary through-hole. The neutron shield 70 may further comprise insert through-holes. The number and location of insert through holes formed in the neutron shield 70 may correspond with the number and location of insert cavities formed in the neutron reflector 60. 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 70 may thus improve a safety of the nuclear fission power plant 10, as neutrons which have not been absorbed or reflected by the neutronic control elements 50, or reflected by the neutron reflector 60, may be absorbed by the neutron shield 70. The neutron shield 70 may be formed from boron carbide, or any other suitable neutron-absorbing material.

[0046] The nuclear fission power plant 10 may further comprise a fluid circuit 80 with a fluid circuit working fluid that flows through the fluid circuit. The fluid circuit 80 may comprise a first heat exchanger 82, a pump 84, and a second heat exchanger 86. The pump 84 may be operated to pump the fluid circuit working fluid around the fluid circuit 80. The protruding ends 42 of the heat pipes 40 extend into the first heat exchanger 82 to transfer heat from the nuclear reactor core 20 to the fluid circuit working fluid of the fluid circuit 80. The second heat exchanger 86 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 80 is arranged so that the fluid circuit working fluid flowing through the fluid circuit 80 transfers heat from the heat pipes 40 via the heat exchangers to the power conversion system working fluid of the power conversion system 100.

[0047] 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 86, 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. Therefore in this example the power conversion system working fluid of the power conversion system comprises air taken from the surrounding environment. The air, having been compressed, may then flow into the second heat exchanger 86. The second heat exchanger 86 may be configured to transfer heat from the fluid circuit working fluid of the fluid circuit 80 to the compressed air flowing through 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 86, 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.

[0048] 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 may comprise the nuclear reactor core 20 with the protruding ends 42 of the heat pipes 40 extending into the first heat exchanger 82, the neutronic control elements 50, the neutron reflector 60, the neutron shield 70. A second sub-assembly may comprise the pump 84, the second heat exchanger 86, and any interconnecting piping. A third sub-assembly may comprise the power conversion system 100. A fourth sub-assembly may comprise the at least one first controller 54, the at least one second controller 56, and any actuators 52 of the neutronic control elements. This is but one example, it will be understood that other subassemblies are possible, and that the configuration of sub-assemblies may be adapted to best suit the means of transport. For example, actuators 52 of the neutronic control elements may be assembled into the first sub-assembly 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.

[0049] 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 80. 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 82 or a further heat exchanger to the power conversion system working fluid of the power conversion system 100. The further fluid circuit may have a further pump for circulating a further fluid circuit working fluid in the further fluid circuit. The further fluid circuit may effectively be parallel to the fluid circuit 80 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.

[0050] 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 fluid circuit working fluid of the fluid circuit 80 or further fluid circuit. The further open Brayton power system may therefore be coupled to the second heat exchanger 86 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 fission power plant 10 since it can continue to operate in the event of one of the open Brayton power systems failing.

[0051] 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.

[0052] With reference to Figure 3, the present disclosure also relates to a method 200 for the nuclear fission power plant 10. The method 200 comprises controlling the nuclear fission power plant 10. The control of the nuclear fission power plant 10 may be at least partially carried out remotely. For example, 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).

[0053] 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 80. In a fourth action 240, the nuclear fission power plant 10 drives the compressor 102 with the first turbine 104. In a fifth action 250, the nuclear fission power plant 10 drives the generator 108 with the second turbine 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. In an alternative example fifth action 250, the nuclear fission power plant 10 comprises a single turbine 104 which also drives the generator 108 of the power conversion system 100.

[0054] The present disclosure advantageously provides a lightweight, yet rugged, compact, safe, efficient, and resilient nuclear fission power plant. These advantages are particularly beneficial for deployment to a remote environment. Weight, ruggedness, and compactness 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, an intermediate fluid circuit, and an open Brayton power system contribute to these advantages.

[0055] 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. In addition, the intermediate fluid circuit may provide 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, in combination with the independent control systems provided, enables a controller to selectively adjust a rate of fission in the core of the reactor during normal operation, and to quickly shut down the reactor in the case of an emergency. This further enhances a safety of the nuclear fission power plant. Rotatable drums may be more compact and robust than other neutronic control elements, such as e.g. linear control rod systems, and may therefore improve a transportability of the nuclear fission power plant without compromising its operational safety.

[0056] 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.

[0057] 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 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.

[0058] 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 require maintenance. 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.

[0059] It is also noted that the moderator may comprise yttrium hydride, and that yttrium hydride may provide excellent neutron slowing power when compared to other alternative moderator materials. Therefore, an yttrium hydride moderator may provide an improved neutron economy within the core when compared to e.g. a graphite moderator of an equivalent mass. An overall mass of the nuclear fission power plant may thus be reduced as less moderator material is required to produce the desired neutron slowing effect. Using yttrium hydride may therefore allow a greater core temperature to be reached, which may consequently improve a thermodynamic efficiency of the nuclear fission power plant. An increase in mass of the neutron reflector (as a result of the increased core temperatures) may be mitigated by using beryllium oxide as the neutron reflector material. Beryllium oxide has very good neutron reflection properties for its mass, has a high thermal conductivity and a high temperature stability. The nuclear fission power plant of the present disclosure may therefore have a relatively low weight without compromising its ability to safely operate at higher temperatures and achieve improved thermodynamic efficiencies.

[0060] 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.

[0061] The above-described features combine to improve the safety, robustness and resilience of the overall nuclear power plant, whilst simultaneously improving its efficiency and energy output.

[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 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 neutronic control elements comprising rotatable control drums disposed around the periphery of 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.
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 yttrium hydride or zirconium hydride.
7. The nuclear fission power plant of any preceding claim, wherein the neutron reflector comprises beryllium 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 preceding claim, further comprising a neutron shield disposed around a periphery of the neutron reflector.
10. The nuclear fission power plant of claim 9, wherein the neutron shield comprises boron carbide.
11. The nuclear fission power plant of any preceding claim, wherein each rotatable control drum comprises a neutron-reflecting material and a neutron-absorbing material, the neutron-absorbing material being disposed over at least a portion of an outer circumference of the rotatable control drum.
12. The nuclear fission power plant of claim 11, wherein the neutron-reflecting material comprises beryllium oxide and the neutron-absorbing material comprises boron carbide.
13. A kit of parts for a nuclear fission power plant configured for use in a terrestrial environment, the kit of parts comprising: a nuclear reactor core comprising a fuel system and a moderator; a plurality of heat pipes, each heat pipe being configured such that, when the kit of parts is assembled, each heat pipe at least partially extends within the nuclear reactor core; a neutron reflector configured to be disposed around a periphery of the nuclear reactor core; a plurality of neutronic control elements comprising rotatable control drums configured to be disposed around the periphery of the nuclear reactor core; a fluid circuit comprising a first heat exchanger, a second heat exchanger, and a pump, wherein, the plurality of heat pipes are configured such that when the kit of parts is 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 configured to be arranged such that air can flow 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.
14. The kit of parts of claim 13, further comprising a neutron shield configured to be disposed around a periphery of the neutron reflector.
15. The kit of parts of claim 14, wherein the neutron shield comprises boron carbide.
16. The kit of parts of any of claims 13, 14, or 15, wherein each rotatable control drum comprises a neutron-reflecting material and a neutron-absorbing material, the neutron-absorbing material being configured to be disposed over at least a portion of an outer circumference of the rotatable control drum.
17. The kit of parts of claim 16, wherein the neutron-reflecting material comprises beryllium oxide and the neutron-absorbing material comprises boron carbide.
18. 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, and a plurality of neutronic control elements comprising rotatable control drums are disposed around the periphery of 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, 35 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; 5 and generate electricity by virtue of the driven generator.