A nuclear fission power plant

Abstract

A nuclear fission power plant (10) comprising: a first fluid circuit (130) to circulate gas; a nuclear reactor core (20) comprising: a fuel (20) and a moderator (30); the nuclear fission power plant further comprising a neutron reflector (60), one or more primary control rods (70), one or more secondary control rods (80), and a containment vessel (90) substantially surrounding the nuclear reactor core and allowing gas in the gas circuit to flow through both the containment vessel and the nuclear reactor core, and an open Brayton power system coupled to the first fluid circuit via a second fluid circuit (160), the open Brayton power system comprising: a compressor (210); a turbine system (220); and a generator system (230); the open Brayton power system being arranged such that the turbine system is configured to drive the compressor and the generator system.

Description

[0001] 2024PF00139

[0002] 1

[0003] A NUCLEAR FISSION POWER PLANT

[0004] FIELD OF THE DISCLOSURE

[0005] The present disclosure relates to nuclear power systems, and more specifically 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.

[0006] BACKGROUND

[0007] Nuclear power stations are considered a favourable option for producing electrical energy in a manner which does not release carbon dioxide into the atmosphere. However, it is not always practical or necessary to construct a traditional large scale nuclear power station of the type that can produce hundreds of megawatts of energy, especially if the demand for energy is only of the order of a few megawatts, or temporary. Consequently, there is a desire to create smaller power supply stations comprising nuclear fission power plants which can be constructed in a shorter timescale, or even preconstructed off-site and transported to a location ready to be “switched on” when required. One such type of smaller power supply station has been dubbed the nuclear “microreactor”. Microreactor designs need to provide the same level of safety and reliability required by large scale nuclear power stations, but must achieve these things under the constraints of restrictive mass and volume limits, so that they can be transportable to different types of operating location.

[0008] The present disclosure seeks to provide a nuclear fission power plant suitable for use in a microreactor meeting these requirements.

[0009] SUMMARY

[0010] The present disclosure provides a nuclear fission power plant as set out in claim 1 , a microreactor as set out in claim 8, a kit of parts as set out in claim 10, and a method as set out in claim 17. Optional features are included in the dependent claims. 2024PF00139

[0011] 2

[0012] 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, the nuclear reactor core comprising: a fuel; a moderator; and at least one core inlet and at least one core outlet; a neutron reflector disposed around a periphery of the nuclear reactor core; a plurality of primary control rods, each primary control rod being configured to be selectively inserted into the nuclear reactor core; one or more secondary control rods configured to be selectively inserted into the nuclear reactor core; a containment vessel substantially surrounding the nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that a gas following the flow path flows from the containment vessel inlet towards the nuclear reactor core, into the nuclear reactor core via the at least one core inlet, out of the nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet such that the gas absorbs heat energy from the nuclear reactor core so as to cool the nuclear reactor core; a first fluid circuit configured to receive gas from the containment vessel outlet and deliver gas to the containment vessel inlet, wherein the first fluid circuit comprises a first passage through a first heat exchanger and a first pump; a second fluid circuit, wherein the second fluid circuit provides passage for a second fluid circuit working fluid, and comprises a second pump, a second passage through the first heat exchanger, and a third passage through a second heat exchanger; and an open Brayton cycle power system comprising: a compressor; a fourth passage through the second heat exchanger; a turbine system; and a generator system; wherein the open Brayton cycle power system is arranged such that air flows through the compressor to the fourth passage in the second heat exchanger, and from the fourth passage in the second heat exchanger to the turbine system, wherein the second heat-exchanger is configured to permit heat in the second fluid circuit working fluid to be transferred to the compressed air from the compressor, and the turbine system is configured to drive the compressor and the generator system.

[0013] The nuclear fission power plant may further comprise a recuperator configured to receive air from the turbine system and compressed air from the compressor so as to transfer heat energy from the turbine system to the compressed air from the 2024PF00139

[0014] 3 compressor prior to the compressed air entering the fourth passage in the second heat exchanger.

[0015] The nuclear fission power plant may further comprise a neutron shield disposed around the periphery of the nuclear reactor core. The neutron shield may comprise beryllium carbide (B4C).

[0016] The moderator of the nuclear fission power plant may comprise graphite.

[0017] The fuel of the nuclear fission power plant may comprise uranium oxycarbide (UCO).

[0018] The neutron reflector of the nuclear fission power plant may comprise beryllium oxide (BeO).

[0019] According to a second aspect there is provided a microreactor comprising the nuclear fission power plant of the first aspect. The power output of the microreactor may be in the range of 1 - 5MW.

[0020] According to a third aspect there is provided a kit of parts for constructing a nuclear fission power plant comprising: a nuclear reactor core, the nuclear reactor core comprising: a fuel; a moderator; and at least one core inlet and at least one core outlet; a neutron reflector configured to be disposed around a periphery of the nuclear reactor core; a plurality of primary control rods, each primary control rod being configured to be selectively inserted into the nuclear reactor core; one or more secondary control rods configured to be selectively inserted into the nuclear reactor core; a containment vessel configured to substantially surround the nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured such that when the kit of parts is assembled a flow path is defined between the containment vessel inlet and the containment vessel outlet, such that a gas following the flow path flows from the containment vessel inlet towards the nuclear reactor core, into the nuclear reactor core via the at least one core inlet, out of the nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet such that the gas can absorb heat energy from the nuclear reactor core so as to cool the nuclear reactor core; a first heat exchanger, a second heat exchanger, a first pump, and a second pump, arrangeable into a first fluid circuit 2024PF00139

[0021] 4 and second fluid circuit; wherein the first fluid circuit is configured to receive gas from the containment vessel outlet and deliver gas to the containment vessel inlet, wherein the first fluid circuit comprises a first passage through the first heat exchanger and the first pump; and the second fluid circuit is configured to provide passage for a second fluid circuit working fluid, comprising the second pump, a second passage through the first heat exchanger, and a third passage through the second heat exchanger; and a compressor; a turbine system; and a generator system; configured to be assembled as an open Brayton cycle power system arranged such that air can flow through the compressor to a fourth passage in the second heat exchanger, and from the fourth passage in the second heat exchanger to the turbine system, wherein the second heat-exchanger is configured to permit heat in the second fluid circuit working fluid to be transferred to the compressed air from the compressor, and the turbine system is configured to drive the compressor and the generator system.

[0022] The kit of parts may further comprise a recuperator configurable to receive air from the turbine system and compressed air from the compressor so as to be able to transfer heat energy from the turbine system to the compressed air from the compressor prior to the compressed air entering the fourth passage in the second heat exchanger.

[0023] The kit of parts of may further comprise a neutron shield configured to be disposed around the periphery of the nuclear reactor core. The neutron shield may comprise beryllium carbide (B4C).

[0024] The moderator the kit of parts may comprise graphite.

[0025] The fuel of the kit of parts may comprise uranium oxycarbide (UCO).

[0026] The neutron reflector of the kit of parts may comprise beryllium oxide (BeO).

[0027] According to a fourth aspect there is provided a method for operating 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, the nuclear reactor core comprising a fuel, a moderator, at least one core outlet, and at least one core inlet, wherein: a neutron reflector is disposed around a periphery of the nuclear reactor core; a plurality of primary control rods are configured to be 2024PF00139

[0028] 5 selectively inserted into the nuclear reactor core; one or more secondary control rods are configured to be selectively inserted into the nuclear reactor core; and a containment vessel is arranged to substantially surround the nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that gas following the flow path flows from the containment vessel inlet towards the nuclear reactor core, into the nuclear reactor core via the at least one core inlet, out of the nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; deliver gas to the containment vessel inlet via the first fluid circuit; receive gas, heated by the nuclear reactor core, from the containment vessel outlet to a first fluid circuit; heat a second fluid circuit working fluid flowing through the first heat exchanger in a second fluid circuit; and generate electricity with an open Brayton cycle power system, the open Brayton cycle power system being coupled to the second fluid circuit via a second heat exchanger, the open Brayton cycle power system comprising a compressor, a turbine system, and a generator system, and being arranged such that air flows through the compressor, the second heat exchanger, and the turbine, wherein the second heat exchanger is configured to heat compressed air from the compressor passing through the second heat exchanger by the second fluid circuit working fluid, and the turbine is configured to drive the generator.

[0029] 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.

[0030] BRIEF DISCRIPTION OF THE DRAWINGS

[0031] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0032] FIG. 1 is a sectional side view of a schematic of an example nuclear fission power plant;

[0033] FIG. 2 is a schematic of an example of a control system for primary control rods; 2024PF00139

[0034] 6

[0035] FIG. 3 is a schematic of a further example control system for primary control rods;

[0036] FIG. 4 is a schematic of a further example control system for primary control rods;

[0037] FIG. 5 is a schematic of a further example control system for primary control rods;

[0038] FIG. 6 is a schematic of an example of a secondary control rod system;

[0039] FIG. 7 is a sectional side view of a schematic of a further example nuclear fission power plant;

[0040] FIG. 8 is a sectional side view of a schematic of a further example nuclear fission power plant;

[0041] FIG. 9 is a sectional side view of a schematic of a further example nuclear fission power plant;

[0042] FIG. 10 is a graphic representing a kit of parts for a nuclear fission power plant;

[0043] FIG. 11 is a graphic representing a method for operating a nuclear fission power plant; and

[0044] FIG. 12 is graphic representing a microreactor comprising a nuclear fission power plant.

[0045] DETAILED DESCRIPTION

[0046] Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0047] FIG. 1 shows a schematic sectional view of an example of a nuclear fission power plant 100 according to the present disclosure. The nuclear fission power plant 100 comprises a nuclear reactor core 10. The nuclear reactor core 10 comprises a fuel 20. The fuel 20 may comprise High Assay Low Enriched Uranium (HALEU), e.g., with the concentration of the fissile isotope uranium-235 (U-235) being between 5% and 20% of the mass of uranium. In particular, the fuel 20 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. 2024PF00139

[0048] 7

[0049] The fuel may comprise uranium oxycarbide, UCO. Uranium oxycarbide is sufficiently hard and strong, with a high melting point and resistance to radiation damage that allows it to be used in the extreme conditions of a nuclear reactor core. The fuel may be a coated particle fuel, such as a TRISO fuel. The fuel 20 may be in pellet form and may be clad, e.g. in plated metal or a tubular cladding. The fuel pellets may be stacked within a tube. The tube may be a metal tube. For example, pellets of fuel may be stacked within the metal tube, before the tube is welded closed, leaving a volume within the tube to trap fission gases. The fuel 20 may alternatively comprise any other suitable ceramic fuel, such as e.g. uranium carbide (UC), uranium dioxide (UO2), and uranium nitride (UN).

[0050] The nuclear reactor core 10 comprises a moderator 30. The moderator 30 is situated within the nuclear reactor core 10 and may be interspersed throughout the nuclear reactor core, i.e. interspersed between regions containing fuel 20. Whilst in the example of FIG. 1 the moderator 30 is shown in distinct blocks (indicated with the diagonal hatching) between regions of fuel, it is to be understood that the moderator may also, or instead, surround or envelope the fuel. For example, the moderator may take the form of a monolith (the monolith being the structure in which the fuel is contained - not shown in FIG. 1 ) in which the fuel is encased.

[0051] The moderator 30 serves to slow down neutrons travelling within the nuclear reactor core 10, thus increasing their cross-section of interaction with uranium atoms within the core, leading to an increased number of fission events. Thus, the moderator improves the neutron economy of the nuclear reactor core 10, which is important given that the nuclear fission power plant 100 may be located in a remote location, and therefore challenging to refuel on a regular basis. The moderator 30 may comprise graphite. Graphite possesses a sufficient neutron-slowing power to increase the neutron economy of the nuclear reactor core, and is more rugged than other moderator materials, which is important as it will be more resilient to the shocks and vibrations the microreactor may be subject to during transport to its site of operation.

[0052] The nuclear reactor core 10 is gas-cooled. The nuclear reactor core 10 comprises at least one core inlet 40, and at least one core outlet 50. Heat is therefore extracted from the nuclear reactor core 10 by virtue of a gas that flows within and through the nuclear reactor core 10. The gas enters the nuclear reactor core 10 via the at least one core 2024PF00139

[0053] 8 inlet 40, and exits the nuclear reactor core 10 via the at least one core outlet 50. The gas may be helium, helium-xenon (a mixture of helium and xenon gases), nitrogen, hydrogen, or any other appropriate gas. A gas cooling system may allow higher core temperatures to be reached, as coolant evaporation issues (which can affect pressurised water reactors) are eliminated. This, in turn, may allow for a greater thermodynamic efficiency of the nuclear fission power plant by creating a greater temperature difference between the nuclear reactor core 10 and a heat sink.

[0054] The nuclear fission power plant 100 further comprises a plurality of primary control rods 70. The primary control rods 70 may be controlled to vary their neutron-absorbing effect on the nuclear reactor core and thereby control reactivity levels in the nuclear reactor core 10. The primary control rods 70 may be selectively inserted into corresponding primary control rod voids 72 (i.e. cavities) in the nuclear reactor core 10. FIG. 2 shows a schematic example of a control system for the primary control rods 70, with other items housed within the nuclear core removed for clarity. With reference to FIG. 2, movement of the primary control rods 70 by one or more first actuators 74 may vary the neutron-absorbing effect of the primary control rods 70 on the nuclear reactor core 10.

[0055] The one or more first actuators 74 may be controlled by a suitable controller, which may receive data from one or more sensors. For example, the one or more first actuators 74 may be controlled by a first controller 76. The first controller 76 may be in communication with any suitable reactivity sensor system 78 of the nuclear fission power plant 100, which may determine a rate of fission in the nuclear reactor core 10. The primary control rods 70 may be used for fine control, such as during a normal operating mode of the nuclear fission power plant 100. For example, the primary control rods 70 may be incrementally inserted or retracted from the nuclear reactor core 10. One or more first actuators 74 may cause the primary control rods to be gradually / incrementally inserted or retracted in response to a determined rate of fission in the nuclear reactor core 10 and operating instructions stored in the first controller 76. It is noted that the one or more first actuator(s) 74 may additionally be configured to cause the primary control rods 70 to be rapidly inserted into the primary control rod voids 72. For example, the primary control rods 70 may be rapidly inserted into the primary control rod voids 72 in the case of an emergency. 2024PF00139

[0056] 9

[0057] It is noted that the nuclear fission power plant 100 may comprise any number of primary control rods 70. Thus, although only two primary control rods 70 are shown in FIG. 1 and FIG. 2, it will be understood that the nuclear fission power plant 100 is not limited to having only two primary control rods, but rather can have several primary control rods positioned around and within the nuclear reactor core 10. It is envisaged that two or more independent first actuators 74 can be provided (per primary control rod) for redundancy. FIG. 3 shows a schematic of a further example control system, where each primary control rod 70 is provided with two independent first actuators, such that if one first actuator should fail, the position of the primary control rod can still be controlled by the other first actuator.

[0058] Furthermore, the primary control rods 70 may be arranged in two or more independent sets of primary control rods 70, with each set having its own first actuator. FIG. 4 shows a schematic of a further example control system, where the primary control rods 70 are arranged in two independent sets of primary control rods 70, with each set having its own first actuator 74.

[0059] The primary control rods 70 within a particular set may alternate with primary control rods 70 from another set. For example, there may be two independent sets of six primary control rods 70 interspersed with one another about the circumference of the nuclear reactor core 10. FIG. 5 shows a schematic of a further example control system, where the primary control rods 70 are arranged as two independent sets of six primary control rods 70 interspersed with one another. Therefore, although only one first controller 76 is shown in FIG. 2 and FIG. 3, there may be two or more independent control systems. For example, an independent control system may be provided for each set of primary control rods 70. Therefore, to achieve a desired level of reactivity in the nuclear reactor core 10, the first controller 76 or more than one independent first controllers 76 may operate the one or more first actuators 74 to either cause each primary control rod 70 of the nuclear fission power plant 100 to be selectively inserted / retracted, or cause a set of primary control rods 70 of the nuclear fission power plant 100 to be selectively inserted / retracted, or cause individual primary control rods 70 of the nuclear fission power plant 100 to be selectively inserted / retracted.

[0060] The nuclear fission power plant 100 further comprises one or more secondary control rod(s) 80. FIG. 6 shows a schematic of an example of a secondary control rod system, 2024PF00139

[0061] 10 with other items housed within the nuclear core removed for clarity. With reference to FIG. 6, the secondary control rod(s) 80 may comprise linearly movable control rods that may be selectively inserted into corresponding secondary control rod voids 82 (i.e., cavities) in the nuclear reactor core 10. As with the primary control rod(s) 70, movement of the secondary control rod(s) 80 by one or more second actuators 84 may vary the neutron-absorbing effect on the nuclear reactor core of the secondary control rod(s) 80. The second actuator(s) 84 may be controlled by a second controller 86. The second controller 86 may be part of or separate from the first controller 76. The second controller 86 may be in communication with any suitable reactivity sensor system 78 of the nuclear fission power plant 100, which may determine (for example) a rate of fission in the nuclear reactor core 10. The secondary control rod(s) 80 may be used for coarse control, such as in an emergency or shut-down mode of the nuclear fission power plant 100. The secondary control rod(s) 80 may be inserted quickly into the nuclear reactor core 10, 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 100. The second controller 86 may be configured to cause the one or more second actuator(s) 84 to rapidly insert the secondary control rod(s) 80 into the nuclear reactor core 10 when (for example) the reactivity sensor system 78 determines that a rate of fission or nuclear reactor core temperature has reached or exceeded a predetermined threshold.

[0062] Control systems shown in relation to the primary control rods 70 are equally applicable to the secondary control rods 80. For example, as with the primary control rods 70 as shown in FIG. 3, the one or more secondary control rods 80 may also have two or more independent second actuators 84 per primary control rod provided for redundancy. Additionally, as with the primary control rods 70 as shown in FIG. 4, in the case where there are multiple secondary control rods 80, the secondary control rods 80 may be arranged in two or more independent sets of secondary control rods 80, with each set having its own second actuator. Furthermore, in the case where there are multiple secondary control rods 80, the secondary control rods 80 may be arranged in two or more independent sets of secondary control rods 80, with each set having its own second actuator 84. The secondary control rods 80 within a particular set may alternate with secondary control rods 80 from another set. 2024PF00139

[0063] 11

[0064] The primary / secondary control rods 70, 80 may comprise any suitable neutron absorbing material. Examples of such materials include naturally-enriched boron carbide (B4C), boron carbide enriched with boron-10, or hafnium.

[0065] Referring back to FIG. 1 , the nuclear fission power plant 100 further comprises a neutron reflector 60 disposed around the nuclear reactor core 10. 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 10. In particular, the neutron reflector 60 may surround or substantially surround the nuclear reactor core. For instance, the neutron reflector may be disposed around a periphery of the nuclear reactor core 10. The neutron reflector 60 may comprise rod through holes to permit primary / secondary control rods 70, 80 to be inserted into a corresponding primary control rod void 72 or secondary control rod void 82 of the nuclear reactor core 10. Additionally, the at least one core inlet 40 and the at least one core outlet 50 may be formed by virtue of one or more channels formed in the neutron reflector 60. In the example system of FIG.1 , two such channels are formed in the neutron reflector 60; one channel provides an entry point for the core inlet 40, and the other provides an exit point for the core outlet 50. However, the skilled person will appreciate that further channels could be provided within the neutron reflector 60 so as to allow additional inlets and outlets as required, or that a single channel could provide passage for both the core inlet 40 and core outlet 50. The neutron reflector 60 may be formed from any suitable material. For example, the neutron reflector 60 may comprise beryllium oxide (BeO) which has a low density coupled with high neutron moderation and reflection capabilities. Alternatively, the neutron reflector 60 may comprise nuclear-grade graphite, as nuclear-grade graphite provides acceptable neutron reflection properties for its mass, or aluminium oxide (AI2O3), which exhibits similar properties and could therefore also be used as the reflection material for the neutron reflector 60.

[0066] The nuclear fission power plant 100 further comprises a containment vessel 90. The containment vessel 90 is disposed around the nuclear reactor core 10. In particular, the containment vessel 90 may at least partially surround the neutron reflector 60, the plurality of primary control rods 70, the secondary control rod(s) 80, and the nuclear reactor core 10. For instance, the containment vessel 90 may be disposed around a periphery of the neutron reflector 60. The containment vessel 90 may be configured to 2024PF00139

[0067] 12 contain a gas. The gas may be configured to cool the nuclear reactor core 10. The containment vessel comprises a containment vessel inlet 110 and a containment vessel outlet 120. The containment vessel inlet 110 may be configured to permit a gas into the containment vessel 90. The containment vessel outlet 120 may be configured to permit the gas out of the containment vessel 90. The containment vessel 90 may define a flow path (see for example block arrows in FIG.1 ) between the containment vessel inlet 110 and the containment vessel outlet 120 along which the gas may flow. Accordingly, gas may flow through the containment vessel 90 in a pre-determined manner. In this way, gas following the flow path may flow from the containment vessel inlet 110 towards the nuclear reactor core 10. The flow path may direct the flow of the gas from the containment vessel inlet 110 to the at least one core inlet 40. The gas may then flow into the nuclear reactor core 10 via the at least one core inlet 40. The gas may then flow through the nuclear reactor core 10, thereby forcing the gas to flow over components within the nuclear reactor core 10, and in doing so, absorb heat energy from the components within the nuclear reactor core. The gas, now heated, may subsequently flow out of the nuclear reactor core 10 via the at least one core outlet 50. The flow path may direct the flow of the gas from the at least one core outlet 50 to the containment vessel outlet 120. The gas may then exit the containment vessel 90 via the at least one containment vessel outlet 120.

[0068] The nuclear fission power plant 100 further comprises a first fluid circuit 130 configured to receive gas from the containment vessel outlet 120 and deliver gas to the containment vessel inlet 110, wherein the first fluid circuit 130 comprises a first passage 142 through a first heat exchanger 140, and a first pump 150. The first pump 150 may be operated to pump the first fluid circuit working fluid (i.e. , the gas) around the first fluid circuit. As such, gas may be pumped (by the first pump 150) from the first fluid circuit 130 into the containment vessel 90 via the containment vessel inlet 110. The gas, guided by the flow path defined by the containment vessel 90, may flow through the nuclear reactor core 10. The gas may therefore absorb heat energy from the components within the nuclear reactor core 10 before flowing out of the containment vessel outlet 120 and being received by the first fluid circuit 130. The gas, now heated, may then flow through the first passage 142 of the first heat exchanger 140. The first heat exchanger 140 is configured to transfer heat energy from the gas of the first fluid circuit 130 to the working fluid of a second fluid circuit 160. 2024PF00139

[0069] 13

[0070] The second fluid circuit 160 provides an intermediate transport loop for the heat energy extracted by the gas from the nuclear reactor core 10. The second fluid circuit 160 comprises a second pump 170, a second passage 144 through the first heat exchanger 140, and a third passage 182 through a second heat exchanger 180. As the second fluid circuit working fluid passes through the second passage 144 in the first heat exchanger 140 it is heated up by the gas (i.e. the working fluid of the first fluid circuit) passing through the first passage 142 in the first heat exchanger 140 that has flowed round the first fluid circuit 130 and been heated by the nuclear reactor core 10. The second fluid circuit working fluid then flows further round the second fluid circuit until it reaches a third passage 182 in the second heat exchanger 180. As the second fluid circuit working fluid passes through the third passage 182 in the second heat exchanger 180, it transfers heat energy to compressed air passing through a fourth passage 184 in the second heat exchanger 180. The second fluid circuit working fluid may be helium, helium-xenon, nitrogen, hydrogen, or any other appropriate gas.

[0071] It is to be understood that whilst the first 142, second 144, third 182 and fourth 184 passages are, for simplicity, schematically represented in FIG.s 1 , 7, 8, and 9 by straight channels, they will in reality be formed as per channels in heat exchangers known in the art, and may therefore (for example) take the form of a network of intertwined pathways with thermally connected surfaces of types which allow for the transfer of heat energy between (in these examples) the two fluids flowing through the heat exchangers, without the fluids being allowed to mix or come into physical contact.

[0072] The fourth passage 184 is part of an open Brayton cycle power system 200. The open Brayton cycle power system comprises a compressor 210, the fourth passage 184 in the second heat exchanger 180, a turbine system 220, and a generator system 230. Air from the atmosphere surrounding the nuclear fission power plant 100 will be sucked into, and compressed by, the compressor 210, before flowing into the fourth passage 184 of the second heat exchanger 180, where it will be heated by thermal interaction with the second fluid circuit working fluid passing through the third passage 182 of the second heat exchanger 180. The air, now compressed and heated, can pass through the turbine system 220, where it will drive rotation of the turbine(s) within the turbine system. It will be understood that the turbine system can comprise one or more turbines. The one or more turbines of the turbine system 220 can be linked or separate. If linked, 2024PF00139

[0073] 14 they can be linked in series or parallel. For example, parallel separate turbine systems may be useful as a means of providing redundancy in the turbine system 220, such that the turbine system can continue to provide motive force even if one turbine within the turbine system should fail or be required to stop functioning. Series-linked turbine systems may extract more energy from the heated compressed air than a single turbine. For similar reasons, even though only a single compressor is referred to, the open Brayton cycle power system may include a plurality of compressors that can be linked or separate.

[0074] The one or more turbines of the turbine system 220 are used to drive the compressor 210. In addition, the one or more turbines of the turbine system 220 are coupled to a generator system 230, and thus the turbine system 106 may drive the generator system 230 to generate electrical power. The electrical power may be distributed via a suitable power distribution network to users.

[0075] With reference to FIG. 7, the nuclear fission power plant 100 may further comprise a neutron shield 190 disposed around the nuclear reactor core 10. The neutron shield 190 may be configured to substantially reduce a likelihood of neutrons escaping from the nuclear reactor core 10 and into the surrounding environment. The neutron shield 190 may at least partially surround the containment vessel 90. In particular, the neutron shield 190 may surround or substantially surround the containment vessel 90. For instance, the neutron shield 190 may be disposed around a periphery of the containment vessel 90. The neutron shield 190 may thus improve a safety of the nuclear fission power plant 100, as neutrons which have not been absorbed by the primary or secondary control rods 70, 80, or reflected by the neutron reflector 60, may be absorbed by the neutron shield 190. The neutron shield 190 may be formed from boron carbide, or any other suitable neutron-absorbing material.

[0076] The neutron shield 190 and the containment vessel 90 may comprise control through holes. The number and location of control through holes formed in the neutron shield 190 and the containment vessel 90 may correspond with the number and location of control rod through holes formed in the neutron reflector 60. A primary or secondary control rod 70, 80 may thus be inserted into a corresponding primary or secondary control rod void 72, 82 of the nuclear reactor core 10 through a control through hole. Additionally or alternatively, the control through holes may allow e.g. cables, shafts, 2024PF00139

[0077] 15 actuation systems, sensors, etc. to couple a first or second actuator 74, 84 to a corresponding primary / secondary control rod 70, 80. The neutron shield 190 may further comprise one or more outlet through holes. An outlet through hole formed in the neutron shield 190 may correspond with the containment vessel outlet 120. As such, gas following the flow path defined by the containment vessel 90 may flow out of the containment vessel 90 and be received by, for example, a heat exchanging system.

[0078] With reference to FIG. 8, the nuclear fission power plant 100 may further comprise a recuperator 240. The recuperator is configured to receive both air that has passed through the turbine system 220, and compressed air that has passed through the compressor 210, and to enable the transfer of residual heat energy present in the air that has passed through the turbine system to the compressed air that has passed through the compressor, prior to the compressed air entering the fourth passage 184 in the second heat exchanger 180. An advantage of including the recuperator in the nuclear fission power plant 100 is that it uses “waste heat” from the turbine system to increase the temperature of the compressed air prior to it arriving in the second heat exchanger 180, improving the thermodynamic efficiency of the power conversion system.

[0079] The nuclear fission power plant 100 may comprise at least one further open Brayton cycle power system 200. FIG. 9 shows a schematic example of a nuclear fission power plant 100 having a further open Brayton cycle power system 200. The at least one further open Brayton cycle power system 200 may be configured to absorb heat from the working fluid of the second fluid circuit 160. The further open Brayton cycle power system 200 may therefore be coupled to the second heat exchanger 180. The further open Brayton cycle power system 200 may effectively be parallel to the open Brayton cycle power system 200 and may improve the robustness of the nuclear fission power plant 100 since the nuclear fission power plant 100 can continue to operate in the event of one of the open Brayton cycle power systems 200 failing.

[0080] It is envisaged that the nuclear fission power plant 100 may be constructed from a kit of parts 300. 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 2024PF00139

[0081] 16 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.

[0082] With reference to FIG. 10, by providing the nuclear fission power plant 100 as a kit of parts, the parts of the nuclear fission power plant 100 can be grouped into a plurality of sub-assemblies 310, which in turn can be more easily transported to the intended operation location of the nuclear fission power plant 100 prior to assembly. Each of the plurality of sub-assemblies 310 may be loaded into its own shipping container, or the plurality of sub-assemblies may be loaded into 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 10, the primary control rods 70, the secondary control rod(s) 80, the neutron reflector 60, the containment vessel 90, and the neutron shield 190. A second sub-assembly may comprise the first pump 150, the first heat exchanger 140, and any interconnecting piping of the first fluid circuit 130. A third sub-assembly may comprise parts of the second fluid circuit, for example the second pump 170, second heat exchanger 180, and the piping to be connected to the first heat exchanger 140, and the components of the open Brayton cycle power system 200. A fourth sub-assembly may comprise the first controller 76, the second controller 86, and any first or second actuators 74, 84 of the primary / secondary control rods 70, 80. 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 actuators 74 of the primary control rods 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 100 to be completely assembled, loaded onto a container, and transported to the appropriate terrestrial location.

[0083] With reference to FIG. 11 , the present disclosure also relates to a method 400 for operating the nuclear fission power plant 100. The method 400 comprises controlling the nuclear fission power plant 100. The control of the nuclear fission power plant 100 may be at least partially carried out remotely. For example, the nuclear fission power plant 100 may be controlled from a control facility that is located remote to the location of the nuclear fission power plant 100. Alternatively, control of the nuclear fission power 2024PF00139

[0084] 17 plant 100 may be carried out locally (i.e., at the location of the nuclear fission power plant 100).

[0085] The method 400 controls the nuclear fission power plant 100 such that in a first action 410, the nuclear fission power plant 100 generates heat within the nuclear reactor core 10. In a second action 420, gas is delivered to the containment vessel 90 by the first fluid circuit 130. In a third action 430, gas from the containment vessel 90, heated by the nuclear reactor core, is received by the first fluid circuit 130. In a fourth action 440, the second fluid circuit working fluid flowing in the second fluid circuit 160 is heated by the gas flowing through the first heat exchanger 140. In a fifth action 450, compressed air from the open Brayton cycle power system compressor 210 is heated as it passes through the second heat exchanger 180 by the second fluid circuit working fluid. In a sixth action 460, the generator 108 is driven by the turbine system 220 of the open Brayton cycle power system. In a seventh action 470, electricity is generated by the generator 108.

[0086] The present disclosure advantageously provides a highly efficient and reliable nuclear fission power plant. This is at least partly because the ceramic fuel is resilient to high temperatures and a gaseous coolant cannot change state at high temperatures in the way a liquid coolant can. This in turn can improve thermodynamic efficiency by providing a greater temperature gradient across the system.

[0087] Safety of the nuclear fission power plant is improved by reducing a likelihood of neutrons and radioisotopes from being released into the environment. This is at least partly achieved by the neutron shield, which may absorb any neutrons that are not reflected by the neutron reflector, and the second fluid circuit 160, which provides a further barrier between the reactor core and the open Brayton cycle power system, thereby reducing a risk of radioisotopes being released into the environment. The use of coated particle (for example TRISO) fuel form would also reduce the likelihood of radioisotopes being released due to the additional layer of containment around all the nuclear fuel material. The primary and secondary control rods, in combination with the control systems provided, allows both fine and coarse control to be exerted over the rate of fission in the core of the reactor. This further enhances a safety of the nuclear fission power plant. 2024PF00139

[0088] 18

[0089] The second fluid circuit 160 may also provide a thermal buffer between the reactor core and the power conversion system. The second fluid circuit 160 may thus reduce the impact of any thermal fluctuations in the reactor core. As an example, the thermal inertia provided by the second fluid circuit 160 may reduce a thermal load experienced by components of the open Brayton cycle power 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.

[0090] 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 desired deployment location, thereby reducing a complexity for an end operative.

[0091] The moderator 30 may alternatively comprise any of zirconium hydride, aluminium oxide, or yttrium hydride, all of which have suitable neutron-slowing properties.

[0092] The present disclosure relates to a nuclear fission power plant 100 configured for use in a terrestrial environment. The nuclear fission power plant 100 is configured to be sufficiently robust, reliable, 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.

[0093] The nuclear fission power plant 100 may be part of a microreactor, as illustrated in FIG. 12. The microreactor may have a power output in the range of 1 - 5MW, which is suitable for most of the remote applications which may require the use of such a microreactor. 2024PF00139

[0094] 19

[0095] It will be understood that the invention is not limited to the embodiments abovedescribed and various modifications and improvements can be made without departing from the concepts described herein. Except where 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

2024PF0013920Claims1. A nuclear fission power plant 100 configured for use in a terrestrial environment, the nuclear fission power plant comprising: a nuclear reactor core 10, the nuclear reactor core comprising: a fuel 20; a moderator 30; and at least one core inlet 40 and at least one core outlet 50; a neutron reflector 60 disposed around a periphery of the nuclear reactor core; a plurality of primary control rods 70, each primary control rod being configured to be selectively inserted into the nuclear reactor core; one or more secondary control rods 80 configured to be selectively inserted into the nuclear reactor core; a containment vessel 90 substantially surrounding the nuclear reactor core, the containment vessel comprising a containment vessel inlet 110 and a containment vessel outlet 120, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that a gas following the flow path flows from the containment vessel inlet towards the nuclear reactor core, into the nuclear reactor core via the at least one core inlet, out of the nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet such that the gas absorbs heat energy from the nuclear reactor core so as to cool the nuclear reactor core; a first fluid circuit 130 configured to receive gas from the containment vessel outlet and deliver gas to the containment vessel inlet, wherein the first fluid circuit comprises a first passage 142 through a first heat exchanger 140 and a first pump 150; a second fluid circuit 160, wherein the second fluid circuit provides passage for a second fluid circuit working fluid, and comprises a second pump 170, a second passage 144 through the first heat exchanger, and a third passage 182 through a second heat exchanger 180; and an open Brayton cycle power system 200 comprising: a compressor 210; a fourth passage 184 through the second heat exchanger; a turbine system 220; and a generator system 230;2024PF0013921 wherein the open Brayton cycle power system is arranged such that air flows through the compressor to the fourth passage in the second heat exchanger, and from the fourth passage in the second heat exchanger to the turbine system, wherein the second heatexchanger is configured to permit heat in the second fluid circuit working fluid to be transferred to the compressed air from the compressor, and the turbine system is configured to drive the compressor and the generator system.

2. The nuclear fission power plant of claim 1 , further comprising a recuperator 240 configured to receive air from the turbine system and compressed air from the compressor so as to transfer heat energy from the turbine system to the compressed air from the compressor prior to the compressed air entering the fourth passage in the second heat exchanger.

3. The nuclear fission power plant of claim 1 or claim 2, further comprising a neutron shield 190 disposed around the periphery of the nuclear reactor core.

4. The nuclear fission power plant of claim 3, wherein the neutron shield comprises beryllium carbide (B4C).

5. The nuclear fission power plant of any preceding claim, wherein the moderator comprises graphite.

6. The nuclear fission power plant of any preceding claim, wherein the fuel comprises uranium oxycarbide (UCO).

7. The nuclear fission power plant of any preceding claim, wherein the neutron reflector comprises beryllium oxide (BeO).

8. A microreactor comprising the nuclear fission power plant of any preceding claim.

9. A microreactor according to claim 8, wherein the power output of the microreactor is in the range of 1 - 5MW.2024PF001392210. A kit of parts for constructing a nuclear fission power plant comprising: a nuclear reactor core 10, the nuclear reactor core comprising: a fuel 20; a moderator 30; and at least one core inlet 40 and at least one core outlet 50; a neutron reflector 60 configured to be disposed around a periphery of the nuclear reactor core; a plurality of primary control rods 70, each primary control rod being configured to be selectively inserted into the nuclear reactor core; one or more secondary control rods 80 configured to be selectively inserted into the nuclear reactor core; a containment vessel 90 configured to substantially surround the nuclear reactor core, the containment vessel comprising a containment vessel inlet 110 and a containment vessel outlet 120, and being configured such that when the kit of parts is assembled a flow path is defined between the containment vessel inlet and the containment vessel outlet, such that a gas following the flow path flows from the containment vessel inlet towards the nuclear reactor core, into the nuclear reactor core via the at least one core inlet, out of the nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet such that the gas can absorb heat energy from the nuclear reactor core so as to cool the nuclear reactor core; a first heat exchanger, a second heat exchanger, a first pump, and a second pump, arrangeable into a first fluid circuit and second fluid circuit; wherein the first fluid circuit 130 is configured to receive gas from the containment vessel outlet and deliver gas to the containment vessel inlet, wherein the first fluid circuit comprises a first passage through the first heat exchanger 140 and the first pump 150; and the second fluid circuit 160 is configured to provide passage for a second fluid circuit working fluid, comprising the second pump 170, a second passage through the first heat exchanger, and a third passage through the second heat exchanger 180; and a compressor 210; a turbine system 220; and a generator system 230;2024PF0013923 configured to be assembled as an open Brayton cycle power system arranged such that air can flow through the compressor to a fourth passage in the second heat exchanger, and from the fourth passage in the second heat exchanger to the turbine system, wherein the second heat-exchanger is configured to permit heat in the second fluid circuit working fluid to be transferred to the compressed air from the compressor, and the turbine system is configured to drive the compressor and the generator system.

11. The kit of parts of claim 10, further comprising a recuperator configurable to receive air from the turbine system and compressed air from the compressor so as to be able to transfer heat energy from the turbine system to the compressed air from the compressor prior to the compressed air entering the fourth passage in the second heat exchanger.

12. The kit of parts of claim 10 or claim 11 , further comprising a neutron shield configured to be disposed around the periphery of the nuclear reactor core.

13. The kit of parts of claim 12, wherein the neutron shield comprises beryllium carbide (B4C).

14. The kit of parts of any of claims 10, 11 , 12, or 13, wherein the moderator comprises graphite.

15. The kit of parts of any of claims 10, 11 , 12, 13, or 14, wherein the fuel comprises uranium oxycarbide (UCO).

16. The kit of parts of any of claims 10, 11 , 12, 13, 14, or 15, wherein the neutron reflector comprises beryllium oxide (BeO).

17. A method for operating 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, the nuclear reactor core comprising a fuel, a moderator, at least one core outlet, and at least one core inlet, wherein:2024PF0013924 a neutron reflector is disposed around a periphery of the nuclear reactor core; a plurality of primary control rods are configured to be selectively inserted into the nuclear reactor core; one or more secondary control rods are configured to be selectively inserted into the nuclear reactor core; and a containment vessel is arranged to substantially surround the nuclear reactor core, the containment vessel comprising a containment vessel inlet and a containment vessel outlet, and being configured to define a flow path between the containment vessel inlet and the containment vessel outlet, such that gas following the flow path flows from the containment vessel inlet towards the nuclear reactor core, into the nuclear reactor core via the at least one core inlet, out of the nuclear reactor core via the at least one core outlet, and towards the containment vessel outlet; deliver gas to the containment vessel inlet via the first fluid circuit; receive gas, heated by the nuclear reactor core, from the containment vessel outlet to a first fluid circuit; heat a second fluid circuit working fluid flowing through the first heat exchanger in a second fluid circuit; and generate electricity with an open Brayton cycle power system, the open Brayton cycle power system being coupled to the second fluid circuit via a second heat exchanger, the open Brayton cycle power system comprising a compressor, a turbine system, and a generator system, and being arranged such that air flows through the compressor, the second heat exchanger, and the turbine, wherein the second heat exchanger is configured to heat compressed air from the compressor passing through the second heat exchanger by the second fluid circuit working fluid, and the turbine is configured to drive the generator.

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