Cooling system

Abstract

A cooling system (900) for a heat source (500) that forms part of a nuclear fission reactor system (110). The cooling system (900) comprises a first coolant reservoir (902) for housing a first coolant (908), a condenser (904), and a first coolant system (906) configured to feed the first coolant (908) evaporated from the first coolant reservoir (902) by the heat source (500) into the condenser (904). The first coolant system (906) is also configured to return condensate (910) from the condenser (904) to the first coolant reservoir (902). The cooling system (900) further comprises a second coolant flow intake duct (922) extending from a second coolant flow intake duct inlet (924) to a second coolant flow intake duct outlet (926). The cooling system (900) further comprises a second coolant flow exhaust duct (932) extending from a second coolant flow exhaust duct inlet (934) to a second coolant flow exhaust duct outlet (936). The first coolant reservoir (902) comprises a second coolant inlet (928) of the first coolant reservoir and a second coolant outlet (930) of the first coolant reservoir. The second coolant flow intake duct outlet (926) is in fluid communication with the second coolant inlet (928) of the first coolant reservoir. The second coolant outlet (930) of the first coolant reservoir is in fluid communication with the inlet (934) of the second coolant flow exhaust duct. The second coolant flow intake duct (922), the first coolant reservoir (902), and the second coolant flow exhaust duct (932) are arranged in series to define the second coolant flow path (920).

Description

[Technical Field]

[0001] The present disclosure relates to a cooling system.

[0002] In particular, the present disclosure relates to a cooling system for a heat source forming part of a fission reactor system. [Background Art]

[0003] Fission reactor systems operate as heat engine systems and are used to provide power for many different applications. By way of example, a nuclear reactor is provided as a heat source for heating a working fluid passed through a closed cycle comprising a compressor and a turbine to rotate a shaft that can drive other machinery, for example a generator. A heat engine system comprises many components and interconnected subsystems.

[0004] Heat engine systems and / or components and / or subsystems of heat engine systems that result in improved safety and efficiency of the heat engine system during use are highly desirable. [Summary of the Invention]

[0005] According to the present disclosure, there are provided apparatuses, systems, and methods as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims and the following description.

[0006] Therefore, a fuel assembly (100) for a nuclear fission reactor system (110) may be provided. The fuel assembly (100) may extend along a longitudinal axis (112). The fuel assembly (100) may comprise a pressure tube (120) containing aluminum or an aluminum alloy. The fuel assembly (100) may comprise a sleeve member (132). The sleeve member (132) may be provided radially inward of the radially inward surface (134) of the pressure tube (120). The fuel assembly (100) may comprise a fuel compact unit (136). The fuel compact unit (136) may be located within the sleeve member (132) such that a gap (137) is maintained between the radially inward surface (139) of the sleeve member (132) and the fuel compact unit (136) to define a sleeve member flow path (140).

[0007] The sleeve member (132) and / or fuel compact unit (136) may contain silicon carbide.

[0008] The sleeve member (132) and / or fuel compact unit (136) may be coated and / or layered with an environmental barrier coating.

[0009] The first spacer element (150) extends between the fuel compact unit (136) and the sleeve member (132) to position the fuel compact unit (136) within the sleeve member (132) and maintain a gap (137) between the fuel compact unit (136) and the sleeve member (132).

[0010] End plugs (152) may be provided at the ends of the fuel compact unit (136) and the sleeve member (132), and a second spacer element (158) may extend from the end plugs (152) to the pressure pipe (120) to position the sleeve member (132) within the pressure pipe (120) and maintain an insulation gap (138) between the pressure pipe (120) and the sleeve member (132).

[0011] The fuel compact unit (136) can define a first flow path (160) extending from an inlet (162) provided at a first end (164) of the fuel assembly (100) to an outlet (166) provided at a second end (168) of the fuel assembly (100).

[0012] The fuel assembly (100) may be centered on its longitudinal axis (112).

[0013] The first flow path (160) may be centered on the longitudinal axis (112).

[0014] The fuel compact unit (136) may define a second flow path (170) extending from the inlet (162) to the outlet (166) of the fuel compact unit (136), the second flow path (170) being located radially outward of the first flow path (160).

[0015] The fuel compact unit (136) may define a plurality of second flow paths (170) extending from an inlet (162) to an outlet (166) of the fuel compact unit (136), each of which is located radially outward of the first flow path (160), and fin elements (172) are provided between each of the second flow paths (170).

[0016] The fuel compact unit (136) can be formed integrally.

[0017] A nuclear fission reactor system (110) comprising a reactor unit (200) having a fuel assembly (100) may be provided, wherein the inlet (162) of the fuel assembly is operable (i.e., configured) to be in fluid communication with a working fluid source (806). The outlet (166) of the fuel assembly may be operable (i.e., configured) to be in fluid communication with a working fluid exhaust port (840).

[0018] A heat engine system (300) may be provided. The heat engine system (300) may comprise a compressor (400) that defines a compressor fluid passage (402) extending from a compressor inlet (404) to a compressor outlet (406).

[0019] The heat engine system (300) may include a heat source (500) provided as a nuclear fission reactor system (110) according to the present disclosure.

[0020] The heat engine system (300) may include a turbine system (600) that defines a turbine fluid passage (602) extending from a turbine inlet (604) to a turbine outlet (606). The compressor (400), heat source (500), and turbine system (600) may define part of a working fluid flow circuit (700). The working fluid flow circuit (700) may further include a compressor-heat source duct (702) extending between the compressor outlet (406) and the heat source inlet (502), a heat source-turbine duct (704) extending between the heat source outlet (504) and the turbine inlet (604), and a turbine-compressor duct (706) extending between the turbine outlet (606) and the compressor inlet (404).

[0021] The heat engine system (300) may further comprise a wet compressible fluid source (850) in fluid communication with a compressor fluid passage (402).

[0022] The heat engine system (300) may further include a recuperator (810).

[0023] The heat engine system (300) may further include a heat exchanger (812).

[0024] The compressor-heat source duct (702) can provide fluid communication between the compressor outlet (406) and the heat source inlet (502) via the recuperator (810).

[0025] The turbine-compressor duct (706) can provide fluid communication between the turbine outlet (606) and the compressor inlet (404) via a recuperator (810) and a heat exchanger (812).

[0026] There may be provided a method of operating a heat engine system (300) according to the present disclosure, wherein the working fluid (800) comprises nitrogen and water vapor. The working fluid (800) may be fed into a compressor inlet (404) at pressure values and temperature values within a predetermined range.

[0027] The pressure value may be in the range of 0 to 10 bar absolute pressure. The temperature value may be in the range of 0°C to 60°C.

[0028] There may be provided a cooling system (900) for a heat source (500) forming part of a fission reactor system (110). The cooling system (900) may comprise a first coolant reservoir (902) for containing a first coolant (908). The cooling system (900) may comprise a condenser (904). The cooling system (900) may comprise a first coolant system (906).

[0029] The cooling system (900) may further comprise the first coolant system (906). The first coolant system (906) may be configured to feed the first coolant (908) evaporated from the first coolant reservoir (902) by the heat source (500) to the condenser (904). The first coolant system (906) may be configured to return condensed water (910) to the first coolant reservoir (902).

[0030] The first coolant system (906) may comprise the first coolant reservoir (902) and / or the condenser (904).

[0031] The cooling system (900) may further comprise a second coolant flow intake duct (922) extending from a second coolant flow intake duct inlet (924) to a second coolant flow intake duct outlet (926).

[0032] The cooling system (900) may further comprise a second coolant flow exhaust duct (932) extending from a second coolant flow exhaust duct inlet (934) to a second coolant flow exhaust duct outlet (936).

[0033] The first coolant reservoir (902) may include a second coolant inlet (928) and a second coolant outlet (930).

[0034] The outlet (926) of the second coolant flow intake duct may be in fluid communication with the second coolant inlet (928) of the first coolant reservoir.

[0035] The second coolant outlet (930) of the first coolant reservoir may be in fluid communication with the inlet (934) of the second coolant flow exhaust duct.

[0036] A second coolant flow intake duct (922), a first coolant reservoir (902), and a second coolant flow exhaust duct (932) may be arranged in series to define a second coolant flow path (920).

[0037] The second coolant flow path (920) may be blocked by the first coolant (908) in the first coolant reservoir (902) when the first coolant (908) is above a predetermined level (L1) in the first coolant reservoir (902).

[0038] The second coolant flow path (920) can be opened to allow a second coolant flow from the second coolant flow intake duct inlet (924) to the second coolant flow exhaust duct outlet (936) when the first coolant (908) is below a predetermined level (L1) in the first coolant reservoir (902).

[0039] The first coolant (908) may be water.

[0040] The second coolant could be air.

[0041] The first coolant reservoir (902) may be in fluid communication with the first coolant fluid source (1000).

[0042] The present disclosure may provide a power plant (1100) comprising a heat source (500) and a cooling system (900) that form part of a nuclear fission reactor system (110).

[0043] The heat source (500) can define at least a portion of the section of the second coolant flow path (920) that extends between the second coolant inlet (928) and the second coolant outlet (930) of the first coolant reservoir.

[0044] The nuclear fission reactor system (110) may include a reactor unit (200) having a fuel assembly (100) having a pressure tube (120) configured to receive a flow of working fluid (800). The fuel assembly (100) may define a heat source (500). The pressure tube (120) may extend through a first coolant reservoir (902) to define at least a portion of a second coolant flow path (920).

[0045] The power plant (1100) may be configured such that the working fluid (800) is fluidly isolated from the first coolant (908) and the second coolant (940).

[0046] The pressure pipe (120) can define at least a portion of the section of the second coolant flow path (920) that extends between the second coolant inlet (928) of the first coolant reservoir and the second coolant outlet (930) of the first coolant reservoir.

[0047] The reactor unit (200) may comprise a plurality of fuel assemblies (100), each having a pressure tube (120) for receiving a flow of working fluid (800). The plurality of fuel assemblies (100) may define a heat source (500). The plurality of pressure tubes (120) may extend through a coolant reservoir (902) of a cooling system (900).

[0048] Multiple pressure tubes (120) can define at least a portion of the section of the second coolant flow path (920) that extends between the second coolant inlet (928) of the first coolant reservoir and the second coolant outlet (930) of the first coolant reservoir.

[0049] A gap may be maintained between adjacent pressure pipes (120), and the gap(s) may define at least a portion of the section of the second coolant flow path (920) that extends between the second coolant inlet (928) of the first coolant reservoir and the second coolant outlet (930) of the first coolant reservoir.

[0050] The pressure tubes (120) can be separated from each other so as to define a gap between them.

[0051] A method for operating a cooling system (900) for a heat source (500) that forms part of a nuclear fission reactor system (110) may be provided.

[0052] The cooling system (900) may define (i.e., include) a second coolant flow path (920) comprising a second coolant flow intake duct (922), a first coolant reservoir (902), and a second coolant flow exhaust duct (932) in series.

[0053] During operation, when the first coolant (908) is above a predetermined level (L1) in the first coolant reservoir (902), the second coolant flow path (920) may be blocked by the first coolant (908) in the first coolant reservoir (902).

[0054] During operation, when the first coolant (908) is below a predetermined level (L1) in the first coolant reservoir (902), the second coolant flow path (920) may be opened to allow a second coolant flow from the second coolant flow intake duct (922) to the second coolant flow exhaust duct (932).

[0055] Therefore, heat engine systems, as well as components and subsystems of heat engine systems, are provided that, when used, result in improved safety and efficiency compared to examples of related technologies.

[0056] Next, embodiments of the present invention will be described simply by reference to the drawings. [Brief explanation of the drawing]

[0057] [Figure 1] Figure 1 shows a schematic diagram of a heat engine system (e.g., a power plant) according to this disclosure. [Figure 2] Figure 2 shows a side cross-sectional view of the fuel assembly according to this disclosure. [Figure 3] Figure 3 shows an enlarged area of ​​the cross-sectional view of the fuel assembly shown in Figure 2. [Figure 4] Figure 4 shows a cross-sectional view of the end portion of the fuel assembly shown in Figures 2 and 3. [Figure 5] Figure 5 shows a perspective cross-sectional view of a portion of the fuel assembly shown in Figures 2 to 4. [Figure 6] Figure 6 shows an enlarged area of ​​a portion of the fuel assembly shown in Figures 2 to 4. [Figure 7] Figure 7 shows a schematic diagram of a part of a power plant equipped with the cooling system according to this disclosure. [Figure 8] Figure 8 shows an enlarged cross-sectional view of a portion of the power plant shown in Figure 7. [Figure 9] Figure 9 shows an enlarged view of a portion of the power plant shown in Figures 7 and 8. [Figure 10] Figure 10 shows an enlarged cross-sectional view of a portion of the power plant shown in Figures 7, 8, and 9. [Figure 11] Figure 11 shows an enlarged cross-sectional view of a portion of the power plant shown in Figure 8. [Modes for carrying out the invention]

[0058] This disclosure relates to a fuel assembly 100 for a nuclear fission reactor system 110. This disclosure also relates to a nuclear fission reactor system 110 comprising a reactor unit 200 comprising the fuel assembly 100. This disclosure also relates to a heat engine system 300 and a method for operating the heat engine system 300. This disclosure further relates to a cooling system 900 for a heat source 500 that forms part of the nuclear fission reactor system 110, and a method for operating the cooling system 900 for a heat source 500 that forms part of the nuclear fission reactor system 110. This disclosure also relates to a power plant 1100 comprising a heat source 500 that forms part of the nuclear fission reactor system 110. Thus, the power plant 1100 may be equipped with a heat source 500, and the heat source 500 may form part of the nuclear fission reactor system 110.

[0059] This disclosure may also relate to facilities or vehicles having any aspect of this disclosure. Vehicle 10 may be a land vehicle, a ship such as a surface vessel, or a submersible such as a submarine.

[0060] Figure 1 illustrates a heat engine system 300. The heat engine system 300 may include a heat source 500 provided as a nuclear fission reactor system 110. The heat source 500 is provided with a heat source inlet 502 and a heat source outlet 504. During operation, the working fluid 800 enters the heat source 500 through the heat source inlet 502, is heated, and then discharged through the heat source outlet 504. The working fluid 800 may contain nitrogen.

[0061] The nuclear fission reactor system 110 may include a reactor unit 200 comprising a fuel assembly 100 according to this disclosure. The fuel assembly 100 may define at least a portion of a heat source 500.

[0062] The heat engine system 300 may include a compressor 400 that defines a compressor fluid passage 402 extending from a compressor inlet 404 to a compressor outlet 406.

[0063] The heat engine system 300 may include a turbine system 600 that defines a turbine fluid flow path 602 extending from a turbine inlet 604 to a turbine outlet 606.

[0064] Both the compressor fluid passage 402 and the turbine fluid passage 602 are configured so that the working fluid 800 flows through them.

[0065] As illustrated in Figure 1, the compressor 400, heat source 500, and turbine system 600 define a portion of the working fluid flow circuit 700 through which the working fluid 800 flows. The working fluid flow circuit 700 further comprises a compressor-heat source duct 702 extending between the compressor outlet 406 and the heat source inlet 502. The working fluid flow circuit 700 further comprises a heat source-turbine duct 704 extending between the heat source outlet 504 and the turbine inlet 604. The working fluid flow circuit 700 further comprises a turbine-compressor duct 706 extending between the turbine outlet 606 and the compressor inlet 404.

[0066] The heat engine system 300 further comprises a wet compressible fluid source 850 in fluid communication with the compressor fluid passage 402. The wet compressible fluid source 850 may be in fluid communication with the compressor fluid passage 402 at the compressor inlet 404 and / or between the compressor inlet 404 and the compressor outlet 406 via a spray unit 852 to the compressor fluid passage 402. The spray unit 852 may be configured to produce droplets having a diameter of 10 microns or less.

[0067] Adding a wet compressible fluid (e.g., water) to the working fluid 800 can be controlled to maintain a 100% relative humidity state as the working fluid 800 passes through the compressor 400 (i.e., during compression). As is known in the art, the action of compressing water droplets together with the working fluid 800 results in droplet evaporation, maintaining a 100% relative humidity state.

[0068] In other words, during operation, the fluid passing along at least a portion of the working fluid flow circuit 700 may contain nitrogen and water vapor, thereby humidifying the working fluid 800. That is, the relative humidity of the working fluid 800 may be 100%.

[0069] The heat engine system 300 may further comprise a housing 802 that is operable to be sealed in order to define a system reservoir 804 in which a compressor 400, a heat source 500, a turbine system 600, and a working fluid flow circuit 700 are located. The system reservoir 804 may also be provided as a working fluid source 804.

[0070] The heat engine system 300 may further comprise a recuperator 810. The heat engine system 300 may further comprise a heat exchanger 812. The compressor-heat source duct 702 may provide fluid communication between the compressor outlet 406 and the heat source inlet 502 via the recuperator 810. The turbine-compressor duct 706 may provide fluid communication between the turbine outlet 606 and the compressor inlet 404 via the recuperator 810 and the heat exchanger 812.

[0071] The recuperator 810 is configured to recover heat lost from the working fluid 800 by, for example, adding heat from the working fluid 800 passing through / along the turbine-compressor duct 706 (from the turbine 600) to the working fluid 800 passing through / along the compressor-heat source duct 702 (which is fed from the compressor 400 to the heat source 500).

[0072] The heat exchanger 812 is in heat flow communication with the heat sink 820, thereby removing thermal energy from the working fluid 800 that flows along the turbine-compressor duct 706 after the working fluid 800 has been discharged from the recuperator 810.

[0073] The heat exchanger 812 may be configured to produce condensate 910 fluid, which is supplied to the fluid source 850. That is, the heat exchanger 812 may be configured to act as a condenser for producing condensate 910 fluid, which is supplied to the fluid source 850. The fluid source 850 may be in fluid communication with the compressor fluid passage 402 via the water heater 822. The water heater 822 may be in heat-flux communication with the recuperator 810 so as to receive thermal energy from the recuperator 810.

[0074] An embodiment of the fuel assembly 100 of the reactor unit 200 is illustrated in Figures 2 to 6. The fuel assembly 100 is located within the reactor unit 200 and forms part of the heat source 500. During operation, the working fluid 800 passes through the fuel assembly 100. That is, the fuel assembly 100 defines at least a portion of the working fluid flow path between the heat source inlet 502 and the heat source outlet 504.

[0075] The fuel assembly 100 may extend along the longitudinal axis 112. The fuel assembly 100 may be centered on the longitudinal axis 112. The fuel assembly 100 may include a pressure pipe 120 that is centered on and extends along the longitudinal axis 112.

[0076] The pressure tube 120 may include aluminum or an aluminum alloy. That is, the pressure tube 120 may be made from aluminum or an aluminum alloy. The pressure tube 120 may be manufactured primarily from aluminum or an aluminum alloy. The pressure tube 120 may be configured to reflect the heat radiation generated by the fuel compact 136 and return it to the fuel compact 136. That is, the pressure tube 120 may be configured as a heat radiation shield. A pressure tube 120 made from aluminum can reflect 95% of the heat radiation and return it to the fuel compact 136.

[0077] The sleeve member 132 may be provided radially inward of the radially inward surface 134 of the pressure pipe 120. The sleeve member 132 may be separated from the radially inward surface 134 of the pressure pipe 120 so as to form an insulating gap 138 between the sleeve member 132 and the radially inward surface 134 of the pressure pipe 120. That is, the sleeve member 132 is provided so as to form an insulating gap 138 between the sleeve member 132 and the pressure pipe 120, and this insulating gap 138 contains stagnant (i.e., non-flowing) insulating gas (during use).

[0078] The sleeve member 132 may be centered on and extend along the longitudinal axis 112.

[0079] The fuel assembly 100 may include a fuel compact unit 136. The fuel compact unit 136 may be centered on and extend along the longitudinal axis 112.

[0080] The pressure pipe 120, sleeve member 132, and fuel compact unit 136 may be arranged concentrically around the longitudinal axis 112. The pressure pipe 120, sleeve member 132, and fuel compact unit 136 may be nested, with the fuel compact unit 136 separated from the pressure pipe 120 by the sleeve member 132.

[0081] The fuel compact unit 136 may be positioned within the sleeve member 132 such that a gap 137 is maintained between the radially inner surface 139 of the sleeve member 132 and the fuel compact unit 136, defining a radiative shielding channel 140 that is operable to receive the working fluid 800. That is, during operation, the working fluid 800 passes along the radiative shielding channel 140.

[0082] The sleeve member 132 and / or fuel compact unit 136 may contain silicon carbide. That is, the sleeve member 132 and / or fuel compact unit 136 may contain silicon carbide. That is, the sleeve member 132 and / or fuel compact unit 136 can be made from silicon carbide. The sleeve member 132 and / or fuel compact unit 136 can be manufactured mainly from silicon carbide.

[0083] The sleeve member 132 and / or the fuel compact unit 136 are fitted with a coating and / or layer of an environmental barrier coating. The sleeve member 132 is mainly made from silicon carbide and may be fitted with a coating and / or layer of an environmental barrier coating. The fuel compact unit 136 is mainly made from silicon carbide and may be fitted with a coating and / or layer of an environmental barrier coating (EBC).

[0084] Environmental barrier coatings for silicon carbide are configured for high-temperature environments. The environmental barrier coating may comprise a two-layer coating comprising a mullite bond coat (3Al2O32SiO2) and an upper protective coat (sometimes called a YAS coating) composed of yttrium oxide, aluminum oxide, and / or silicon oxide (Y2O3-Al2O3-SiO2). Such coatings are durable and corrosion-resistant. Additionally, these components provide a relatively low neutron cross-section on a volume basis, comparable to that of the silicon carbide substrate.

[0085] As shown in Figures 4 and 5, the first spacer element 150 extends between the fuel compact unit 136 and the sleeve member 132, positioning the fuel compact unit 136 within the sleeve member 132 and maintaining a gap 137 between the fuel compact unit 136 and the sleeve member 132, thereby defining the radiation shielding flow path 140. A plurality of first spacer elements 150 may be provided spaced apart around the periphery of the fuel compact unit 136. The first spacer element 150, or each first spacer element 150, may be provided as fins, arrangements of pin features, or spiral ribs configured to improve heat transfer to the working fluid flowing through the radiation shielding flow path 140.

[0086] As shown in Figure 3, the second spacer element 158 ​​extends between the sleeve member 132 and the pressure pipe 120, positioning the sleeve member 132 within the pressure pipe 120, thereby maintaining an insulating gap 138 between the sleeve member 132 and the pressure pipe 120. Multiple second spacer elements 158 may be provided spaced apart around the sleeve member 132.

[0087] An end plug 152 may be provided at the end of the fuel compact unit 136 and the sleeve member 132, and a second spacer element 158 ​​may extend from the end plug 152 to the pressure pipe 120 to position the sleeve member 132 within the pressure pipe 120, thereby maintaining an insulating gap 138 between the pressure pipe 120 and the sleeve member 132.

[0088] The end plugs 152 may be provided at both ends of the fuel assembly 100.

[0089] Therefore, in an example where multiple fuel compacts 136 are arranged in series, these fuel compacts 136 can be held together using a sleeve member 132, and the end plugs 152 provide retaining features at both ends of the assembly.

[0090] The fuel compact unit 136 defines a first flow path 160 extending from an inlet 162 at a first end 164 of the fuel assembly 100 to an outlet 166 at a second end 168 of the fuel assembly 100. The first flow path 160 may be centered on the longitudinal axis 112. During operation, the working fluid 800 passes along the first flow path 160.

[0091] The fuel compact unit 136 may define a second flow path 170 extending from the inlet 162 to the outlet 166 of the fuel compact unit 136, the second flow path 170 being located radially outward of the first flow path 160. During operation, the working fluid 800 passes along the second flow path 170.

[0092] The fuel compact unit 136 may define a plurality of second flow paths 170 extending from the inlet 162 to the outlet 166 of the fuel compact unit 136, each of which is located radially outward of the first flow path 160. Fin elements 172 are provided between each of the second flow paths 170, thereby dividing the flow and supporting the outer portion of the fuel compact 136 on the inner portion of the fuel compact 136.

[0093] The fuel assembly inlet 162 is operable to be in fluid communication with the working fluid source 806, and the fuel assembly outlet 166 is operable to be in fluid communication with the working fluid exhaust port 840.

[0094] Specifically, the fuel assembly inlet 162 is in fluid communication with the compressor-heat source duct 702 and is operable to receive the working fluid 800 from the compressor-heat source duct 702, and the fuel assembly outlet 166 is in fluid communication with the heat source-turbine duct 704 and is operable to discharge the working fluid 800 to the heat source-turbine duct 704.

[0095] In other words, the fuel assembly 100 defines a portion of the working fluid flow circuit 700.

[0096] The fuel compact unit 136 can be formed integrally. That is, the outer portion and the inner portion of the fuel compact 136 can be made from a single silicon carbide structure. In an alternative example, the outer portion and the inner portion of the fuel compact 136 can be formed separately (for example, the fuel compact 136 may be an assembly of two separate elements).

[0097] As shown in Figure 2, the fuel assembly 100 may comprise a plurality of fuel compacts 136 arranged end-to-end along the longitudinal axis 112 inside the sleeve member 132. In such an arrangement, projections 180 (as shown in Figure 5) are provided on the end faces of the fuel compact units 136 for engagement with recesses on the end faces of adjacent fuel compact units 136, thereby preventing these adjacent fuel compact units 136 from rotating relative to each other around the longitudinal axis 112.

[0098] In some examples, several fuel assemblies 100 may be joined end to end. As shown in Figure 6, the end plugs 152 are configured to stack together in a way that aligns the flow path to prevent gas from flowing through the adiabatic gap 138 (i.e., annular space 138) between the fuel assembly and the pressure pipe 120, thereby ensuring that the adiabatic gap 138 remains a “dead” (i.e., stagnant) volume and thus functions as an insulator. The joint does not have to be airtight, but it may be provided as a meandering path to increase the pressure loss for any gas flowing into the adiabatic gap 138.

[0099] As shown in Figures 7 to 10, the cooling system 900 may include a first coolant reservoir 902 for housing a first coolant 908. The first coolant 908 may include water, for example, demineralized water.

[0100] In Figures 7 to 10, it will be understood that parts of the equipment (e.g., housing, components, and other structures) have been removed to illustrate the internal features of the cooling system 800 that are important for its configuration and operability. The cooling system 900 may form part of the reactor unit 200 shown in Figure 1.

[0101] The cooling system 900 may include a condenser 904.

[0102] The cooling system 900 may include a first coolant system 906. The first coolant system 906 may include a first coolant reservoir 902 and / or a condenser 904. The first coolant system 906 can be defined by the first coolant reservoir 902 and / or a condenser 904.

[0103] The first coolant system 906 may be configured to send the first coolant 908 (shown as 908' in Figure 11), which has evaporated from the first coolant reservoir 902 due to the heat from the heat source 500, to the condenser 904. The first coolant system 906 may also be configured to return the condensate 910 formed by the condenser 904 back to the first coolant reservoir 902.

[0104] As best illustrated in Figures 9 and 11, the first coolant system 906 may define a flow path (e.g., a flow communication means) for transporting the evaporated first coolant 908 (shown as 908' in Figures 9 and 11) from the first coolant reservoir 902 to the condenser 904. The first coolant system 906 may define a flow path (e.g., a flow communication means) for returning the condensate 910 formed by the condenser 904 back to the first coolant reservoir 902.

[0105] The cooling system 900 may include a second coolant flow path 920 comprising a second coolant flow intake duct 922 extending from a second coolant flow intake duct inlet 924 to a second coolant flow intake duct outlet 926. The second coolant may contain air. The second coolant may be drawn in from the local environment.

[0106] The first coolant reservoir 902 may define a portion of the second coolant flow path 920 between the second coolant inlet 928 of the first coolant reservoir and the second coolant outlet 930 of the first coolant reservoir. The outlet 926 of the second coolant flow intake duct may be in fluid communication with the second coolant inlet 928 of the first coolant reservoir.

[0107] The cooling system 900 may include a second coolant flow exhaust duct 932 extending from a second coolant flow exhaust duct inlet 934 to a second coolant flow exhaust duct outlet 936, and the second coolant outlet 930 of the first coolant reservoir is in fluid communication with the second coolant flow exhaust duct inlet 934. The second coolant flow exhaust duct outlet 936 is operable to discharge hot air; that is, during use, hot air is discharged through the second coolant flow exhaust duct outlet 936.

[0108] The second coolant flow intake duct 922, the first coolant reservoir 902, and the second coolant flow exhaust duct 932 may be arranged in series to define the second coolant flow path 920. That is, the second coolant flow path 920 may be defined in series by the second coolant flow intake duct 922, the first coolant reservoir 902, and the second coolant flow exhaust duct 932.

[0109] The second coolant flow intake duct inlet 924, the second coolant flow intake duct outlet 926, the second coolant inlet 928 of the first coolant reservoir, the second coolant outlet 930 of the first coolant reservoir, the second coolant flow exhaust duct inlet 934, and the second coolant flow exhaust duct outlet 936 may be arranged in series to define the second coolant flow path 920. That is, the second coolant flow path 920 may be defined in series by the second coolant flow intake duct inlet 924, the second coolant flow intake duct outlet 926, the second coolant inlet 928 of the first coolant reservoir, the second coolant outlet 930 of the first coolant reservoir, the second coolant flow exhaust duct inlet 934, and the second coolant flow exhaust duct outlet 936.

[0110] The second coolant flow path 920 may be blocked by the first coolant 908 in the first coolant reservoir 902 when the first coolant 908 is above a predetermined level (L1) in the first coolant reservoir 902, as illustrated in Figure 11.

[0111] As illustrated in Figures 8 and 11, the second coolant inlet 928 and the second coolant outlet 930 of the first coolant reservoir may be located on the upper side 950 of the first coolant reservoir 902 and / or may be defined by the upper side 950 of the first coolant reservoir 902. The second coolant inlet 928 of the first coolant reservoir may be defined by the first duct / housing 952 extending from the upper side of the first coolant reservoir 902. The second coolant outlet 930 of the first coolant reservoir may be defined by the second duct / housing 954 extending from the upper side 950 of the first coolant reservoir 902.

[0112] A predetermined level (L1) of the first coolant 908 may be a level at which the first coolant 908 substantially fills the first coolant reservoir 902 and thus reaches the second coolant inlet 928 and / or the second coolant outlet 930 of the first coolant reservoir. A predetermined level (L1) of the first coolant 908 may be a level at which the first coolant 908 rises in the ducts / housings 952, 954 that define the second coolant inlet 928 and / or the second coolant outlet 930 of the first coolant reservoir, thereby blocking the second coolant inlet 928 and / or the second coolant outlet 930 of the first coolant reservoir.

[0113] As illustrated in Figures 8 and 11, the second coolant flow intake duct 922 and / or the second coolant flow exhaust duct 932 may extend upward away from the first coolant reservoir 902.

[0114] The second coolant flow intake duct 922 may extend upward away from the first duct / housing 952 that defines the second coolant inlet 928 of the first coolant reservoir.

[0115] The second coolant flow exhaust duct 932 may extend upward away from the second duct / housing 954 that defines the second coolant outlet 930 of the first coolant reservoir.

[0116] In other words, the system is configured such that when the first coolant 908 is above a predetermined level (L1) in the first coolant reservoir 902, the second coolant flow path 920 is blocked by the presence of the first coolant 908. The second coolant flow path 920 may be blocked by the first coolant 908 at or between the second coolant inlet 928 and the second coolant outlet 930 of the first coolant reservoir.

[0117] That is, when the first coolant 908 is above a predetermined level (L1), the second coolant inlet 928 of the first coolant reservoir may be filled with the first coolant 908, thereby preventing the flow of the second coolant through the second coolant inlet 928 of the first coolant reservoir, and thereby preventing the flow of the second coolant through the first coolant reservoir 902. When the first coolant 908 is above a predetermined level (L1), the second coolant outlet 930 of the first coolant reservoir may be filled with the first coolant 908, thereby preventing the flow of the second coolant through the second coolant outlet 930 of the first coolant reservoir, and thereby preventing the flow of the second coolant through the first coolant reservoir 902.

[0118] That is, when the first coolant 908 is above a predetermined level (L1), the first coolant 908 may spread over the second coolant inlet 928 of the first coolant reservoir, thereby preventing the flow of the second coolant through the second coolant inlet 928 of the first coolant reservoir, and thereby preventing the flow of the second coolant through the first coolant reservoir 902. When the first coolant 908 is above a predetermined level (L1), the first coolant 908 may spread over the second coolant outlet 930 of the first coolant reservoir, thereby preventing the flow of the second coolant through the second coolant outlet 930 of the first coolant reservoir, and thereby preventing the flow of the second coolant through the first coolant reservoir 902.

[0119] The second coolant flow path 920 can be opened to allow a second coolant flow from the second coolant flow intake duct inlet 924 to the second coolant flow exhaust duct outlet 936 when the first coolant 908 is below a predetermined level (L1) in the first coolant reservoir 902. That is, the system is configured such that the second coolant flow path 920 is open (i.e., not blocked) when the first coolant 908 is below a predetermined level (L1) in the first coolant reservoir 902. In other words, the system is configured such that when the first coolant 908 is below a predetermined level (L1) in the first coolant reservoir 902, the first coolant 908 no longer fills the first coolant reservoir 902, and therefore a path (e.g., a section of the second coolant flow path 920) is opened, allowing the flow of the second coolant through the first coolant reservoir 902. This system is configured such that when the first coolant 908 is below a predetermined level (L1) in the first coolant reservoir 902, the level of the first coolant 908 is below the level of the second coolant inlet 928 of the first coolant reservoir 902, and the first coolant 908 is below the level of the second coolant outlet 930 of the first coolant reservoir 902, thereby allowing the second coolant to flow freely through at least a portion of the first coolant reservoir 902 between the second coolant inlet 928 and the second coolant outlet 930 of the first coolant reservoir.

[0120] Therefore, as the level of the first coolant 908 in the first coolant reservoir 902 decreases within the first coolant reservoir 902, the volume of the second coolant path 920 within the first reservoir increases. When there is no first coolant 908 in the first coolant reservoir 902, the entire volume of the first coolant reservoir 902 defines the second coolant path 420 passing through the first coolant reservoir 902.

[0121] This system is configured such that, with the second coolant flow path 920 open, the heated second coolant is discharged from the second coolant flow exhaust duct 932, thereby drawing the second coolant into the second coolant flow intake duct 922 (as illustrated in Figures 1 and 8).

[0122] During normal use (i.e., when the first coolant 908 is above a predetermined level L1 in the first coolant reservoir 902, for example, indicated by "L2" in Figure 11), the second coolant flow intake duct 922 and the second coolant flow exhaust duct outlet 936 are operable to function as flues for water vapor from the first coolant reservoir 902.

[0123] As shown in Figure 7, the first coolant reservoir 902 may be in fluid communication with the first coolant fluid source 1000, for example, a nearby large water tank storage unit.

[0124] The heat source 500 can define at least a portion of the second coolant flow path 920 that extends between the second coolant inlet 928 of the first coolant reservoir and the second coolant outlet 930 of the first coolant reservoir.

[0125] As described above, the nuclear fission reactor system 110 may comprise a reactor unit 200 equipped with fuel assemblies 100 for receiving a working fluid 800. Thus, in this example, the fuel assemblies 100 define a heat source 500. The pressure tubes 120 of the fuel assemblies 100 may extend through the first coolant reservoir 902 to define at least a portion of the second coolant flow path 920.

[0126] The working fluid 800 can be fluidically isolated from the first coolant 908 and the second coolant 940.

[0127] The pressure pipe 120 can define at least a portion of the second coolant flow path 920 that extends between the second coolant inlet 928 of the first coolant reservoir and the second coolant outlet 930 of the first coolant reservoir.

[0128] The reactor unit 200 may comprise a plurality of fuel assemblies 100 for receiving a flow of working fluid 800. The plurality of fuel assemblies 100 may define a heat source 500. The plurality of pressure tubes 120 of the fuel assemblies 100 may extend through a coolant reservoir 902 of the cooling system 900. The plurality of pressure tubes 120 may be called a “pressure tube bundle”.

[0129] Multiple pressure tubes 120 can define at least a portion of the second coolant flow path 920 that extends between the second coolant inlet 928 of the first coolant reservoir and the second coolant outlet 930 of the first coolant reservoir.

[0130] As shown in Figure 9, gaps may be maintained between adjacent pressure pipes 120, and these gaps define at least a portion of the second coolant flow path 920 that extends between the second coolant inlet 928 of the first coolant reservoir and the second coolant outlet 930 of the first coolant reservoir.

[0131] The pressure pipes 120 can be spaced apart from each other so as to define a gap between them.

[0132] During operation of the heat engine system 300 of this disclosure, the working fluid 800 contains nitrogen and water vapor so that the working fluid 800 is humidified. That is, the relative humidity of the working fluid 800 may be 100%. The working fluid 800 is fed into the compressor inlet 404 at a predetermined range of pressure and temperature values ​​to achieve the desired efficiency of the heat engine.

[0133] The pressure of the working fluid 800 at the compressor inlet 404 can be controlled to be within the range of 0 to 10 bar absolute pressure. The pressure of the working fluid 800 at the compressor inlet 404 can be controlled to be within the range of 0 to 5 bar absolute pressure. The pressure of the working fluid 800 at the compressor inlet 404 can be controlled to be within the range of 1 to 5 bar absolute pressure. The pressure of the working fluid 800 at the compressor inlet 404 can be controlled to be approximately 1 bar absolute pressure (i.e., atmospheric pressure).

[0134] The temperature of the working fluid 800 at the compressor inlet 404 can be controlled to be within the range of 0°C to 60°C. The temperature of the working fluid 800 at the compressor inlet 404 can be controlled to be within the range of 0°C to 40°C. The temperature of the working fluid 800 at the compressor inlet 404 can be controlled to be within the range of 5°C to 40°C. The temperature of the working fluid 800 at the compressor inlet 404 can be controlled to be approximately 15°C.

[0135] The evaporation of the wet compressible fluid added to the working fluid 800 causes a cooling effect that lowers the working fluid temperature at the compressor outlet, thereby reducing the workload of the compressor. As a result, more power becomes available to the turbine, increasing its ability to recover heat from the recuperator, improving cycle efficiency and power density.

[0136] During the operation of the cooling system 900, as shown in Figure 11, when the first coolant 908 is above a predetermined level L1 in the first coolant reservoir 902, the second coolant flow path 920 is blocked by the first coolant 908 in the first coolant reservoir 902.

[0137] When the first coolant 908 is below a predetermined level L1 in the first coolant reservoir 902, the second coolant flow path 920 is open to allow a second coolant flow from the second coolant flow intake duct 922 to the second coolant flow exhaust duct 932.

[0138] Therefore, in the example where the cooling system 900 is used during operation as part of the fission reactor system 110, i.e., as a moderator tank (e.g., a first coolant reservoir 902) housing the pressure tube 120, the heat removal paths for decay heat, through which heat is transferred to the working fluid 800 in the moderator tank, are by conduction and thermal radiation. Essentially, the pressure tube 120 of the moderator tank functions as a heat transfer tube for rejecting reactor decay heat.

[0139] During normal operation (i.e., when the first coolant 908 is above a predetermined level L1 in the first coolant reservoir 902, for example, level L2, and as a result the second coolant flow path 920 is blocked by the first coolant 908 in the first coolant reservoir 902), the fuel at the inlet is kept at a low temperature by the incoming coolant, which minimizes the total amount of heat released from the moderator tank. When the coolant flow stops and the pressure is reduced (either due to a malfunction or a normal shutdown), the fuel temperature is normalized to be nearly isothermal between the core inlet and core outlet, thereby increasing the amount of heat that can be released to the moderator for a given fuel temperature. This heat is usually released via boiling of the moderator (along with heat from gamma and neutron radiation heating of the moderator and tank structure), and this boiling moderator is then condensed on the reactor moderator condenser 904.

[0140] If the cooling flow through the condenser 904 is lost, the reactor 110 shuts down, and the generated steam in the moderator tank (first coolant reservoir 902) is then discharged into the second coolant flow exhaust duct 932, where it is released into the environment. As this process continues, the water level in the first coolant reservoir 902 drops (for example, from level L2), which can serve as an initial reserve of cooling water.

[0141] The coolant level may continue to decline in the first coolant reservoir 902 until a second coolant flow path 920 is created between (and including) the inlet air duct and the outlet air duct (i.e., the second coolant flow intake duct 922 and the second coolant flow exhaust duct 932) for indefinitely continuing decay heat removal via natural convection (for example, when the first coolant level falls below level L1, as shown in Figure 11).

[0142] Due to the lower heat transfer properties of air compared to boiling water, the temperature of the pressure tube 120 can rise to approximately 300°C when the first coolant level has decreased and / or been completely lost, opening the second coolant flow path 920. From this point onward, the pressure tube 120 is continuously and indefinitely cooled to the atmosphere, while this transition to the final cooling stage does not require any pressurization / depressurization of any system and / or components.

[0143] One example, though not shown in the illustration, may include the addition of a flap valve that closes under buoyancy and opens under gravity as the water level decreases, in order to isolate the moderator water from the environment during normal operation.

[0144] An additional water supply may be maintained nearby (e.g., a first coolant fluid source 1000) primarily for replenishing moderator losses during normal operation and maintaining the coolant level, and can be easily supplied to the moderator tank.

[0145] Therefore, a heat engine system, and / or components and / or subsystems of a heat engine system, are provided that, when used, result in improved safety and efficiency of the heat engine system.

[0146] The fuel assembly 100 is configured to enable the fission reactor system 110 to operate under conditions that support the wet compression operating performance of the heat engine system 300. In other words, the fuel assembly 100 of the present disclosure is configured to enable the heat engine compressor 400 to operate under a wet compression closed cycle.

[0147] In the example of the present disclosure, the use of a water moderator / coolant (which may be unpressurized, for example) enables the structure of the reactor unit 200 to operate at low temperatures using a low-cost aluminum structure, and the thermal radiation reflectivity of aluminum, in combination with the fuel compact unit 136 of the present disclosure, enables high reactor outlet gas temperatures that enable high plant efficiency.

[0148] Additionally, structural materials (e.g., aluminum and silicon carbide) are resistant to oxidizing environments and allow for the possibility of wet compression systems where the working fluid contains a significant proportion of water vapor. These structural materials would be rapidly oxidized within high-temperature gas-cooled reactor plants of related technologies (e.g., which may include graphite structures).

[0149] The fuel compact unit 136 can operate at a temperature of approximately 1300°C. The pressure tube 120 is kept well below its melting point by a coolant / moderator fluid that surrounds the pressure tube 120 and actively cools the tube 120 to a temperature close to the moderator / coolant temperature (100°C). Aluminum is ideally suited for this application because it has a constant low thermal emissivity and high resistance to oxidation even at high temperatures. The first coolant 908 around the outside of the pressure tube 120 keeps the aluminum below its melting point.

[0150] In addition, the selection of materials for the fuel assembly 100 of this disclosure also allows for the use of water (e.g., demineralized water) as the first coolant 908, which is readily available.

[0151] Aluminum and / or aluminum alloys are inherently more corrosion-resistant and have higher radiation resistance than other materials conventionally used in this application. Additionally, in these applications, pressure tubes operate at temperatures close to the melting point (i.e., annealing point) of aluminum, meaning that under these operating conditions, aluminum or aluminum alloys have high resistance to radiation damage (e.g., high-temperature steel), and consequently, the pressure tubes of this disclosure, operating at these lower temperatures, will inherently have a longer lifespan than those of related technologies. Furthermore, aluminum has high thermal conductivity and is therefore useful for temperature control in the fission reactor system 110. Another consideration is that aluminum alloys are also relatively low-cost compared to more specialized materials that may be used in the construction of pressure tubes for the fission reactor system 110.

[0152] Silicon carbide is also inherently less corrosive than other materials conventionally used in the reactor core and fuel structural materials, as well as the sleeve member 132. Therefore, the use of a silicon carbide matrix portion in the fuel assembly enables wet compression.

[0153] Operating a heat engine to perform a wet compression process results in improved thermal efficiency (e.g., 45%–50% thermal efficiency) and power density (e.g., 1.5–2 times power increase) compared to examples of related technologies where wet compression is not used. Conventional heat engine systems, including nuclear fission reactor systems, have not been operated using wet compression due to problems associated with corrosion of core structural materials and the high-temperature operation required for gas turbine technology.

[0154] The cooling system 900 of the present disclosure is configured to be used in combination with or independently of the wet compression configuration of the fuel assembly and closed-cycle heat engine of the present disclosure to improve the safety of the fission reactor system 110.

[0155] The main advantages of the cooling system 900 of this disclosure are its cooling capacity under normal operating conditions and its configuration that allows for an immediate transition to its cooling capacity in the event of loss of operating performance and / or loss of coolant of the condenser 904. The structure of the cooling system 900 is such that the transition can be performed without requiring any physical configuration of the cooling system, for example, without valves, switches, or any additional equipment to be operated and / or deployed.

[0156] Attention is drawn to all documents and literature filed concurrently with or prior to this specification in connection with this application and made available to the public together with this specification, and the contents of all such documents and literature are incorporated herein by reference.

[0157] All features disclosed herein (including any appended claims, abstracts, and drawings) and / or all steps of any method or process so so disclosed may be combined in any combination, except for any combination in which at least some of such features and / or steps are mutually exclusive.

[0158] Each feature disclosed herein (including any attached claims, abstract, and drawings) may be replaced by an alternative feature serving the same, equivalent, or similar purpose unless otherwise specified. Therefore, unless otherwise specified, each disclosed feature is merely an example of a general set of equivalent or similar features.

[0159] The present invention is not limited to the details of the embodiments described above. The present invention extends to any novel one or any novel combination of features disclosed herein (including any appended claims, abstract and drawings), or any novel one or any novel combination of steps of any method or process so so disclosed.

Claims

1. A cooling system for a heat source forming part of a nuclear fission reactor system, wherein the cooling system is A first coolant reservoir for housing the first coolant, Condenser and A first coolant system configured to send the first coolant evaporated from the first coolant reservoir by the heat source to the condenser, and to return condensate to the first coolant reservoir, Equipped with, The cooling system is, A second coolant flow intake duct extending from the inlet of the second coolant flow intake duct to the outlet of the second coolant flow intake duct, A second coolant flow exhaust duct extending from the inlet to the outlet of the second coolant flow exhaust duct, Furthermore, The first coolant reservoir comprises a second coolant inlet of the first coolant reservoir and a second coolant outlet of the first coolant reservoir, The outlet of the second coolant flow intake duct is in fluid communication with the second coolant inlet of the first coolant reservoir. The second coolant outlet of the first coolant reservoir is in fluid communication with the inlet of the second coolant flow exhaust duct. A cooling system comprising a second coolant flow intake duct, a first coolant reservoir, and a second coolant flow exhaust duct, all arranged in series to define a second coolant flow path.

2. The cooling system according to claim 1, wherein the second coolant flow path is blocked by the first coolant in the first coolant reservoir when the first coolant is above a predetermined level (L1) in the first coolant reservoir.

3. The cooling system according to claim 2, wherein the second coolant flow path is open to allow a second coolant flow from the inlet of the second coolant flow intake duct to the outlet of the second coolant flow exhaust duct when the first coolant is below a predetermined level (L1) in the first coolant reservoir.

4. The cooling system according to any one of claims 1 to 3, wherein the first coolant is water and the second coolant is air.

5. The cooling system according to any one of claims 1 to 4, wherein the first coolant reservoir is in fluid communication with the first coolant fluid source.

6. A power plant comprising a heat source that forms part of a nuclear fission reactor system, and a cooling system according to any one of claims 1 to 5.

7. The power plant according to claim 6, wherein the heat source defines at least a portion of the second coolant flow path extending between the second coolant inlet of the first coolant reservoir and the second coolant outlet of the first coolant reservoir.

8. The power plant according to claim 6 or 7, wherein the nuclear fission reactor system comprises a reactor unit having a fuel assembly having a pressure tube configured to receive a flow of working fluid, the fuel assembly defining the heat source, and the pressure tube extending through the first coolant reservoir to define at least a portion of the second coolant flow path.

9. The power plant according to claim 8, wherein the working fluid is configured to be fluidly isolated from the first coolant and the second coolant.

10. The power plant according to claim 8 or 9, wherein the pressure pipe defines at least a portion of the second coolant flow path extending between the second coolant inlet of the first coolant reservoir and the second coolant outlet of the first coolant reservoir.

11. The power plant according to any one of claims 8 to 10, wherein the reactor unit comprises a plurality of fuel assemblies, each having a pressure tube for receiving a flow of working fluid, the plurality of fuel assemblies defining the heat source, and the plurality of pressure tubes extending through the coolant reservoir of the cooling system.

12. The power plant according to claim 11, wherein the plurality of pressure pipes define at least a portion of the second coolant flow path extending between the second coolant inlet of the first coolant reservoir and the second coolant outlet of the first coolant reservoir.

13. The power plant according to claim 12, wherein a gap is maintained between adjacent pressure pipes, and the gap defines at least a portion of the second coolant flow path extending between the second coolant inlet of the first coolant reservoir and the second coolant outlet of the first coolant reservoir.

14. The power plant according to claim 13, wherein the plurality of pressure pipes are spaced apart from each other so as to define the gap between them.

15. A method for operating a cooling system for a heat source forming part of a nuclear fission reactor system, wherein the cooling system defines a second coolant flow path comprising a second coolant flow intake duct, a first coolant reservoir, and a second coolant flow exhaust duct arranged in series, During operation, when the first coolant is above a predetermined level (L1) in the first coolant reservoir, the second coolant flow path is blocked by the first coolant in the first coolant reservoir. A method wherein, when the first coolant is below a predetermined level (L1) in the first coolant reservoir, the second coolant flow path is open to allow a second coolant flow from the second coolant flow intake duct to the second coolant flow exhaust duct.

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