Nuclear reactors for the generation of heat and power.

Abstract

The nuclear reactor power system includes a core including a plurality of nuclear fuel elements, each of the nuclear fuel elements including a first cooling channel passing through the nuclear fuel element and a second cooling channel passing through the nuclear fuel element and fluidically isolated from the first cooling channel, a first cooling system configured to transport a first fluid coolant through the core, the first cooling system being fluidly connected to the first cooling channel of each of the nuclear fuel elements, and a second cooling system configured to transport a second fluid coolant through the core, the second cooling system being fluidly connected to the second cooling channel of each of the nuclear fuel elements, the direction of the first fluid coolant flow through the first cooling channel being the same as the direction of the second fluid coolant flow through the second cooling channel.

Description

[Technical field]

[0001] The present disclosure relates generally to nuclear reactors, and more particularly to nuclear reactors designed for reliable power and heat production. [Background technology]

[0002] Global energy growth and the drive to reduce pollution and emissions are stimulating new activity surrounding the commercialization and design of new nuclear reactor technologies. Some of these technologies include nuclear reactors designed to provide long-lasting, resilient, and reliable power. Summary of the Invention [Means for solving the problem]

[0003] In an example implementation, a nuclear reactor power system includes a core including a plurality of nuclear fuel elements, each of the plurality of nuclear fuel elements including a first cooling channel passing through the nuclear fuel element and a second cooling channel passing through the nuclear fuel element and fluidly isolated from the first cooling channel, a first cooling system configured to transport a first fluid coolant through the core, the first cooling system fluidly connected to the first cooling channel of each nuclear fuel element, and a second cooling system configured to transport a second fluid coolant through the core, the second cooling system fluidly connected to the second cooling channel of each nuclear fuel element.

[0004] In an aspect that may be combined with example implementations, the first cooling system is fluidly isolated from the second cooling system.

[0005] In an aspect that may be combined with any of the preceding aspects, in a first operating mode, a first volume of a first fluid coolant flows through the first cooling system and a second volume of a second fluid coolant flows through the second cooling system, and in a second operating mode, the first volume of the first fluid coolant flows through the first cooling system and no second fluid coolant flows through the second cooling system.

[0006] In an aspect that may be combined with any of the preceding aspects, the power system is configured to operate at or near 100 percent of rated reactor power during operation in both the first mode of operation and the second mode of operation.

[0007] In an aspect that may be combined with any of the preceding aspects, during operation in the first operating mode, at least one of the first volume of the first fluid coolant or the second volume of the second fluid coolant is transported by natural circulation.

[0008] In an aspect that may be combined with any of the preceding aspects, the first fluid coolant is the same as the second fluid coolant.

[0009] In an aspect that may be combined with any of the preceding aspects, the first fluid coolant is different from the second fluid coolant.

[0010] In an aspect that may be combined with any of the preceding aspects, during operation in the second mode of operation, the first volume of the first fluid coolant is transported by natural circulation.

[0011] In an aspect that may be combined with any of the preceding aspects, during operation in the first operating mode, a first volume of a first fluid coolant flows from a first cooling system through a first cooling channel of each nuclear fuel element, and a second volume of a second fluid coolant flows from a second cooling system through a second cooling channel of each nuclear fuel element.

[0012] In an aspect that can be combined with any of the preceding aspects, the first cooling channel and the second cooling channel each have a cylindrical shape, and a cylindrical axis of the first cooling channel is parallel to a cylindrical axis of the second cooling channel.

[0013] In one aspect that may be combined with any of the preceding aspects, a direction of the first fluid coolant flow through the first cooling channel is the same as a direction of the second fluid coolant flow through the second cooling channel.

[0014] In an aspect that may be combined with any of the preceding aspects, the system includes a first heat exchanger configured to transfer heat from a first fluid coolant in the first cooling system to a first intermediate coolant of the first intermediate coolant loop, and a second heat exchanger configured to transfer heat from a second fluid coolant in the second cooling system to a second intermediate coolant of the second intermediate coolant loop.

[0015] In an aspect that may be combined with any of the preceding aspects, the intermediate coolant flows through the first intermediate coolant loop and the second intermediate coolant loop by natural circulation.

[0016] In an aspect that may be combined with any of the preceding aspects, the system includes a first heat exchanger configured to transfer heat from a first fluid coolant in the first cooling system to a first intermediate coolant of the first intermediate coolant loop, and a second heat exchanger configured to transfer heat from a second fluid coolant in the second cooling system to the first intermediate coolant of the first intermediate coolant loop.

[0017] In an aspect that may be combined with any of the preceding aspects, the first heat exchanger and the second heat exchanger are each configured to transfer heat at a level corresponding to a reactor power level at or near 100 percent of the rated reactor power.

[0018] In an aspect that may be combined with any of the preceding aspects, the system includes a third heat exchanger configured to transfer heat from the first intermediate coolant in the first intermediate coolant loop to the power conversion working fluid of the first power conversion system, and a fourth heat exchanger configured to transfer heat from the second intermediate coolant in the second intermediate coolant loop to the power conversion working fluid of the second power conversion system.

[0019] In an aspect that may be combined with any of the preceding aspects, at least one of the first intermediate coolant loop or the second intermediate coolant loop is configured to transfer heat to a plurality of power conversion systems.

[0020] In an aspect that may be combined with any of the preceding aspects, during operation, the first power conversion system and the second power conversion system each operate independently.

[0021] In an aspect that may be combined with any of the preceding aspects, the first power conversion system includes a first turbine, and the second power conversion system includes a second turbine, and the first turbine and the second turbine are each configured to operate at a power level corresponding to a reactor power level at or near 100 percent of the rated reactor power.

[0022] In an aspect that may be combined with any of the preceding aspects, each of the nuclear fuel elements further includes a third cooling channel passing therethrough and a fourth cooling channel passing therethrough, the first cooling system being fluidly connected to the third cooling channel of each of the nuclear fuel elements and the second cooling system being fluidly connected to the fourth cooling channel of each of the nuclear fuel elements.

[0023] In one aspect that can be combined with any of the preceding aspects, the third cooling channel and the fourth cooling channel each have a cylindrical shape, and a cylindrical axis of the third cooling channel is parallel to a cylindrical axis of the fourth cooling channel.

[0024] In an aspect that may be combined with any of the preceding aspects, a direction of the first fluid flow through the third cooling channel is the same as a direction of the second fluid flow through the fourth cooling channel.

[0025] In an aspect that may be combined with any of the preceding aspects, the first and second fluid coolants each include at least one of water, a liquid metal, a liquid salt, a supercritical fluid, or a gas.

[0026] In another example implementation, a nuclear reactor power system includes a reactor core, a primary cooling system configured to transport a primary fluid coolant through the reactor core, a first heat exchanger configured to transfer heat from the primary fluid coolant in the primary cooling system to a first intermediate coolant of a first intermediate coolant loop, and a second heat exchanger configured to transfer heat from the primary fluid coolant in the primary cooling system to a second intermediate coolant of a second intermediate coolant loop, the first intermediate coolant loop being fluidly isolated from the second intermediate coolant loop.

[0027] In certain aspects that can be combined with example implementations, the intermediate coolant flows through the first intermediate coolant loop and the second intermediate coolant loop by natural circulation.

[0028] In an aspect that may be combined with any of the preceding aspects, the first heat exchanger and the second heat exchanger are each configured to transfer heat at a level corresponding to a reactor power level at or near 100 percent of the rated reactor power.

[0029] In an aspect that may be combined with any of the preceding aspects, the system includes a third heat exchanger configured to transfer heat from the first intermediate coolant in the first intermediate coolant loop to the power conversion working fluid of the first power conversion system, and a fourth heat exchanger configured to transfer heat from the second intermediate coolant in the second intermediate coolant loop to the power conversion working fluid of the second power conversion system.

[0030] In an aspect that may be combined with any of the preceding aspects, at least one of the first intermediate coolant loop or the second intermediate coolant loop is configured to transfer heat to a plurality of power conversion systems.

[0031] In an aspect that may be combined with any of the preceding aspects, during operation, the first power conversion system and the second power conversion system each operate independently.

[0032] In an aspect that may be combined with any of the preceding aspects, the first power conversion system includes a first turbine, and the second power conversion system includes a second turbine, and the first turbine and the second turbine are each configured to operate at a power level corresponding to a reactor power level at or near 100 percent of the rated reactor power.

[0033] In another example implementation, a nuclear reactor power system includes a reactor core, a primary cooling system configured to transport a primary fluid coolant through the reactor core, a first heat exchanger configured to transfer heat from the primary fluid coolant in the primary cooling system to an intermediate coolant of an intermediate coolant loop, a second heat exchanger configured to transfer heat from the intermediate coolant in the intermediate coolant loop to a power conversion working fluid of a first power conversion system, and a third heat exchanger configured to transfer heat from the intermediate coolant in the intermediate coolant loop to a power conversion working fluid of a second power conversion system. The first power conversion system is fluidly isolated from the second power conversion system.

[0034] In an aspect that can be combined with an example implementation, during operation, the first power conversion system and the second power conversion system each operate independently.

[0035] In an aspect that may be combined with any of the preceding aspects, the first power conversion system includes a first turbine, and the second power conversion system includes a second turbine, and the first turbine and the second turbine are each configured to operate at a power level corresponding to a reactor power level at or near 100 percent of the rated reactor power.

[0036] In an aspect that may be combined with any of the preceding aspects, the system includes a third power conversion system that is fluidly isolated from the second power conversion system and the first power conversion system.

[0037] In certain aspects that may be combined with any of the preceding aspects, the system includes a fourth power conversion system that is fluidly isolated from the third power conversion system, the second power conversion system, and the first power conversion system.

[0038] In an aspect that may be combined with any of the preceding aspects, each power conversion system of the plurality of power conversion systems is configured to operate independently from each other power conversion system.

[0039] In an aspect that may be combined with any of the preceding aspects, the intermediate coolant flows through the intermediate cooling loop by natural circulation.

[0040] In an aspect that may be combined with any of the preceding aspects, the intermediate coolant flows through the intermediate cooling loop by forced circulation.

[0041] In an aspect that may be combined with any of the preceding aspects, the interstage cooling loop includes two or more pumps configured to drive forced circulation of the interstage coolant.

[0042] In an aspect that may be combined with any of the preceding aspects, the inter-cooling loop is coupled to at least one thermal energy storage unit.

[0043] In certain aspects that may be combined with any of the preceding aspects, the intermediate coolant includes at least one of water, a liquid metal, a liquid salt, a supercritical fluid, or a gas.

[0044] In another example implementation, a method includes operating a nuclear power system of any one of the preceding implementations to generate electrical power.

[0045] In an aspect that can be combined with exemplary implementations, during a first operating mode, two or more power conversion systems of the plurality of power conversion systems each operate at a power level corresponding to less than 100 percent of the rated reactor power.

[0046] In an aspect that may be combined with any of the preceding aspects, during operation of the two or more power conversion systems, the total power output of the reactor is 100 percent of the rated reactor power.

[0047] In an aspect that may be combined with any of the preceding aspects, during the second operating mode, a first power conversion system of the two or more power conversion systems operates at a power level corresponding to 100 percent of the rated reactor power, and a second power conversion system of the two or more power conversion systems is in a standby state.

[0048] In an aspect that may be combined with any of the preceding aspects, the method includes switching between operating the nuclear power system in a first operating mode and operating the nuclear power system in a second operating mode.

[0049] In an aspect that may be combined with any of the preceding aspects, switching between operating the reactor power system in a first operating mode and operating the reactor power system in a second operating mode is controlled by one or more of a battery, a capacitor, or power electronics.

[0050] In an aspect that may be combined with any of the preceding aspects, the method includes switching between operating the reactor power system in a first operating mode and operating the reactor power system in a second operating mode in response to a fault in the second power conversion system.

[0051] In another example implementation, a nuclear reactor power system includes a core including a fuel assembly region including a plurality of nuclear fuel elements arranged in parallel and extending from a first end of the fuel assembly region to a second end of the fuel assembly region, and a plate positioned adjacent to the first end of the fuel assembly region, the plate including one or more orifices, wherein a change in size of the one or more orifices causes a change in a flow volume of a fluid coolant through the core.

[0052] In certain aspects that may be combined with example implementations, the plate is positioned between the coolant inlet and the fuel assembly region, and the fluid coolant enters the fuel assembly region through one or more orifices in the plate.

[0053] In an aspect that may be combined with any of the preceding aspects, the plate is positioned between the coolant outlet and the fuel assembly region, and the fluid coolant exits the fuel assembly region through one or more orifices in the plate.

[0054] In an aspect that may be combined with any of the preceding aspects, the system includes a second plate positioned adjacent a second end of the fuel assembly region.

[0055] In an aspect that may be combined with any of the preceding aspects, the plate is formed from an expandable material that is configured to expand or contract with changing temperature.

[0056] In an aspect that may be combined with any of the preceding aspects, the plate is formed from an expandable material that is configured to expand or contract with changing radiation levels.

[0057] In an aspect that may be combined with any of the preceding aspects, expansion or contraction of the expandable material causes a change in size of one or more orifices.

[0058] In another example implementation, a nuclear reactor power system includes a core including a fuel assembly region including a plurality of fuel pins, and a mass spectrometer positioned adjacent the fuel assembly, The mass spectrometer is configured to detect the presence of one or more failed fuel pins in the fuel assembly.

[0059] In certain aspects that can be combined with example implementations, the mass spectrometer is positioned within a cover gas plenum of the reactor core.

[0060] In an aspect that may be combined with any of the preceding aspects, the core is cooled by a liquid metal coolant, by a gas coolant, by water, or by a molten salt coolant.

[0061] In an aspect that may be combined with any of the preceding aspects, the mass spectrometer is configured to detect the presence of one or more failed fuel pins based on detecting the presence of at least one of fission gas or pre-filled fuel pin tag gas.

[0062] In an aspect that may be combined with any of the preceding aspects, the system includes a plurality of mass spectrometers configured to detect the presence of one or more failed fuel pins in the fuel assembly based on two or more of the mass spectrometers detecting the presence of at least one of the fission gas or the pre-filled fuel pin tag gas.

[0063] In an aspect that may be combined with any of the preceding aspects, the failed fuel pin includes a leaking fuel pin.

[0064] In an aspect that may be combined with any of the preceding aspects, a nuclear reactor power system includes a fuel including a fissile material, such as uranium-233, uranium-235, or plutonium-239, a coolant for transporting heat away from the fuel, a heat exchanger for transferring heat from the coolant or cooling device to a power conversion system, instrumentation, a support structure, and shielding.

[0065] In an aspect that may be combined with any of the preceding aspects, the fissile material can be contained within a fuel element. The fuel element can be held inside the reactor vessel.

[0066] In an aspect that may be combined with any of the preceding aspects, the primary coolant transfers heat from the fuel and conveys the heat to a heat exchanger where the heat is transferred to an intermediate coolant or to a power conversion working fluid.

[0067] In one aspect that may be combined with any of the preceding aspects, multiple heat exchangers are used that are independently sized, either individually or in redundant sets, to transfer heat at a desired power level up to 100 percent of the rated reactor power.

[0068] In an aspect that may be combined with any of the preceding aspects, the redundant heat exchanger system is part of a redundant and independent power conversion system.

[0069] In an aspect that may be combined with any of the preceding aspects, the reactor heat can be converted to usable heat or electricity via these independent heat transport paths.

[0070] In an aspect that may be combined with any of the preceding aspects, the nuclear reactor may be coupled to more than one turbine-generator system, each of which may operate at up to 100 percent of the reactor power.

[0071] In an aspect that may be combined with any of the preceding aspects, a decay heat removal supplemental cooling system is used to passively remove decay heat from the reactor vessel.

[0072] In an aspect that may be combined with any of the preceding aspects, the external cooling may remove heat from the reactor vessel system via a fluid, such as air or a liquid.

[0073] In an aspect that may be combined with any of the preceding aspects, the primary coolant is transported by natural circulation and transfers heat by natural convection.

[0074] In an aspect that may be combined with any of the preceding aspects, the primary coolant flows via natural circulation at steady state conditions ranging from reactor start-up through power levels to full output.

[0075] In an aspect that can be combined with any of the preceding aspects, the primary coolant can be water, a liquid metal, a liquid salt, a supercritical fluid, or a gas.

[0076] In an aspect that may be combined with any of the preceding aspects, the primary heat transport is accomplished using a heat pipe.

[0077] In an aspect that can be combined with any of the preceding aspects, one or more booster pumps are used to facilitate reactor startup by establishing a flow pattern via forced and mixed circulation, which transitions to natural circulation at a prescribed power level and the pumps are shut off.

[0078] In an aspect that may be combined with any of the preceding aspects, there are one or more intermediate cooling loops.

[0079] In an aspect that may be combined with any of the preceding aspects, the one or more interstage cooling loops operate in natural circulation.

[0080] In an aspect that may be combined with any of the preceding aspects, maintaining adequate coolant chemistry and purity control is provided to ensure useful life of the coolant and components.

[0081] In an aspect that may be combined with any of the preceding aspects, a passive coolant chemistry control system is used that is sized to reduce maintenance over the life of the plant.

[0082] In an aspect that may be combined with any of the preceding aspects, the independent heat transport and power conversion systems are operated such that only one is generating power while the other system is on standby.

[0083] In an aspect that may be combined with any of the preceding aspects, the independent heat transport and power conversion systems are operated such that more than one independent system is operated at a reduced capacity such that the total output is 100 percent of the rated power.

[0084] In an aspect that may be combined with any of the preceding aspects, the system includes a plurality of heat exchangers configured to transfer heat from the liquid metal coolant to the intermediate coolant.

[0085] In an aspect that may be combined with any of the preceding aspects, the system includes a heat exchanger configured to transfer heat from the liquid metal coolant to the power conversion working fluid.

[0086] In an aspect that may be combined with any of the preceding aspects, the heat exchanger is a low pressure drop heat exchanger.

[0087] In an aspect that may be combined with any of the preceding aspects, the one or more heat exchangers are rated to independently transfer at least 100 percent of the reactor power.

[0088] In an aspect that may be combined with any of the preceding aspects, the system includes a passively operated cold trap configured to purify the liquid metal coolant.

[0089] In an aspect that may be combined with any of the preceding aspects, during operation, the liquid metal coolant flows through the reactor by natural circulation.

[0090] In an aspect that may be combined with any of the preceding aspects, the liquid metal coolant is transported by natural circulation at steady state conditions at power levels ranging from reactor startup to full power.

[0091] In an aspect that may be combined with any of the preceding aspects, the system includes a booster pump configured to pump the liquid metal coolant through the reactor.

[0092] In an aspect that may be combined with any of the preceding aspects, the intermediate coolant comprises the same fluid as the liquid metal coolant.

[0093] In another example implementation, a method includes operating a nuclear power system of any one of the preceding implementations to generate electrical power.

[0094] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, drawings, and claims. [Brief description of the drawings]

[0095] [Figure 1A] FIG. 1A illustrates a top or bottom view of an exemplary fuel section of a nuclear reactor according to the present disclosure.

[0096] [Figure 1B] FIG. 1B shows an example cross-sectional view of two possible configurations of nuclear fuel elements according to the present disclosure.

[0097] [Diagram 2] FIG. 2 is a schematic diagram of a nuclear reactor power system in accordance with the present disclosure.

[0098] [Figure 3A] 3A and 3B are schematic diagrams of a nuclear reactor power system and a power conversion system in accordance with the present disclosure. [Figure 3B] 3A and 3B are schematic diagrams of a nuclear reactor power system and a power conversion system in accordance with the present disclosure.

[0099] [Figure 4] 4A-4D are schematic diagrams of example configurations of nuclear reactor power systems and power conversion systems according to the present disclosure.

[0100] [Diagram 5] 5A and 5B show an example core including a passive flow orifice device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0101] Detailed Description Global energy growth and the drive to reduce pollution and emissions are stimulating new activity surrounding the commercialization and design of new nuclear reactor technologies. Some of these technologies include nuclear reactors designed to provide long-lasting, resilient, and reliable power in a more distributed manner.

[0102] The reactor system includes a fuel, including fissile material such as uranium-233, uranium-235, or plutonium-239, a coolant that uses a coolant to transport heat away from the fuel, a heat exchanger for transferring heat from the coolant or cooling device to a power conversion system, instrumentation, support structures, and shielding. The fissile material can be contained within fuel elements, which can be held inside the reactor vessel. The coolant transfers heat from the fuel to the heat exchanger, where it is transferred to an intermediate coolant or power conversion working fluid. The coolant can operate with natural circulation. When operating with natural circulation, the coolant flows without a motive force being applied to the coolant. For example, natural circulation can cause the coolant to flow through piping in the absence of an operating pump.

[0103] Multiple heat exchangers can be used, each or a combination of the multiple can be used to transfer up to 100 percent of the rated reactor power production. Rated reactor power is the maximum generating capacity of the reactor and is typically measured in megawatts (MW). Thus, multiple independent power conversion paths are provided, each rated at 100 percent of the rated reactor power.

[0104] An exemplary nuclear reactor system operates with a fluid coolant (e.g., a liquid metal coolant such as liquid sodium or liquid lead) that flows by natural circulation driven by the difference in density between the coolant in the core at its operating temperature and the coolant in the heat exchangers at their operating temperatures, in combination with the altitude difference between the core and the heat exchangers.

[0105] During operation of the reactor system, the primary coolant transfers heat from the fuel and carries the heat to the heat exchangers where it is transferred to an intermediate coolant or to a power conversion working fluid. The primary coolant is the coolant that flows through the reactor core. Multiple heat exchangers can be used, sized individually or in redundant sets to transfer heat at a desired power level up to 100 percent of the rated reactor power. The redundant heat exchanger systems can be part of redundant and independent power conversion systems.

[0106] In some implementations, the reactor heat can be converted to usable heat or electricity via independent heat transport paths. The reactor can be coupled to more than one turbine-generator system, each of which can operate at or near 100 percent reactor power.

[0107] In some implementations, the independent heat transport and power conversion systems are operated such that only one is generating power while the other is on standby.

[0108] In some implementations, the independent heat transport and power conversion systems are operated such that more than one independent system is operated at a reduced capacity so that the total output is at or near 100 percent of the rated power.

[0109] In some implementations, the system includes a plurality of heat exchangers configured to transfer heat from the liquid metal primary coolant to the intermediate coolant. In some implementations, the intermediate coolant includes the same fluid as the liquid metal coolant. In some implementations, the intermediate coolant is transported by natural circulation. In some implementations, the system includes one or more intermediate cooling loops that store the intermediate coolant. The one or more intermediate cooling loops can operate with natural circulation.

[0110] In some implementations, the system includes a heat exchanger configured to transfer heat from the liquid metal coolant to the power conversion working fluid. The heat exchanger may be, for example, a low pressure drop heat exchanger. In some implementations, the one or more heat exchangers are each rated to independently transfer at least 100 percent of the reactor power. In some implementations, multiple independent intermediate coolant loops are configured to transfer heat to independent power conversion systems. In some implementations, one independent intermediate coolant loop is configured to transfer heat to multiple independent power conversion systems.

[0111] FIG 1A shows a top or bottom view of an example fuel region of a nuclear reactor 100. FIG 1A depicts a cooling train that is fluidly connected to the cooling channels of the fuel elements. The top and bottom views of the reactor 100 are identical, and a single cooling train may be fluidly connected to the top and bottom of the same cooling channel.

[0112] 1A, nuclear reactor 100 includes a reactor vessel 102 that contains a reflector 104 and a core 110, which includes fuel elements. The fuel elements make up the core of nuclear reactor 100. Nuclear reactor 100 is cooled by two cooling systems or trains, including cooling train 140 and cooling train 150. Although shown as being cooled by two cooling trains, nuclear reactor 100 can be cooled by additional cooling trains, for example, three cooling trains, four cooling trains, five cooling trains, or more.

[0113] Cooling trains 140, 150 are fluidly isolated from one another such that coolant (e.g., liquid, gas, mixed phase fluid) from cooling train 140 does not mix with coolant from cooling train 150 and coolant does not flow between cooling trains 140 and 150. Cooling trains 140, 150 operate in parallel with one another.

[0114] During operation, cooling trains 140, 150 can be operated independently. In some embodiments, cooling trains 140, 150 are both operated such that coolant flows through both cooling trains 140, 150. In some embodiments, cooling train 140 can be operated while cooling train 150 is in a standby state such that coolant flows only through cooling train 140. In some embodiments, cooling train 150 can be operated while cooling train 140 is in a standby state such that coolant flows only through cooling train 150.

[0115] Each of the cooling trains 140, 150 can transport coolant through each fuel element of the core 110. For example, the cooling train 140 can transport coolant through a first half of the cooling channels of the fuel elements, and the cooling train 150 can transport coolant through a second half of the cooling channels of the fuel elements.

[0116] An exemplary fuel element of the core 110 is fuel element 120. FIG. 1B shows an exemplary cross-sectional view of two possible configurations of the nuclear fuel element 120. The fuel element 120 has a rectangular prismatic shape. In some embodiments, the fuel element 120 can have a cylindrical shape. The fuel element 120 can be formed from a material with high thermal conductivity, can have a low power density, or both.

[0117] In some implementations, the fuel element 120 has a thermal conductivity of 5 W / mK or greater (e.g., 8 W / mK or greater, 10 W / mK or greater, 20 W / mK or greater, 30 W / mK or greater). The high thermal conductivity of the fuel element 120 can improve heat transfer from the fuel to the coolant and can allow the nuclear fuel to be cooled when the nuclear reactor 100 operates with flow passing through less than all of the cooling channels. For example, in some operating modes, coolant may flow through the cooling channels that are fluidly coupled to the cooling train 140 and may not flow through the cooling channels that are fluidly coupled to the cooling train 150. The nuclear reactor 100 can operate at power levels at or near 100 percent of its rated capacity with reduced coolant flow due to the high thermal conductivity of the material that makes up the fuel element 120. A power level at or near 100 percent of rated capacity may include a power level within 10 percent (e.g., within 5 percent, within 3 percent, within 2 percent, within 1 percent) of the rated reactor power.

[0118] The lower power density of the fuel elements 120 can reduce the fuel temperature and allow the nuclear fuel to be cooled when the reactor 100 operates with flow passing through less than all of the cooling channels. The reactor 100 can operate at power levels at or near 100 percent even with reduced coolant flow due to the lower power density of the fuel elements 120.

[0119] Fuel element 120a includes cooling channels 141a and 142a for cooling train 140 and cooling channels 151a and 152a for cooling train 150. Cooling channels 141a and 142a transport coolant from cooling train 140, while cooling channels 151a and 152a transport coolant from cooling train 150. Fuel element 120a also includes graphite filler 124 and fuel pins 122. Cooling channels 141a, 142a, 151a, and 152a pass through the graphite filler of fuel element 120a.

[0120] Fuel element 120b includes cooling channels 141b and 142b for cooling train 140 and cooling channels 151b and 152b for cooling train 150. Cooling channels 141b and 142b transport coolant from cooling train 140, while cooling channels 151b and 152b transport coolant from cooling train 150. Fuel element 120b also includes a fuel matrix or fuel meat 132.

[0121] The cooling channels 141b, 142b, 151b, and 152b pass through the fuel meat 132 of the fuel element 120b. The fuel meat 132 may include a mixture of nuclear fuel material and a moderator material. The fuel meat 132 may include a metallic material.

[0122] In some embodiments, cooling channels 141b, 142b, 151b, and 152b each have a cylindrical shape. The cylindrical axes of the cooling channels can extend parallel to one another. For example, the cylindrical axis of cooling channel 141b can be parallel to the cylindrical axis of cooling channel 142b.

[0123] In some implementations, coolant from the cooling train 140 enters the cooling channels 141b, 142b of the fuel element 120 at the top of the fuel element and flows downward through the fuel element 120, e.g., in the direction of gravity. The coolant exits the cooling channels 141b, 142b of the fuel element 120 at the bottom of the fuel element 120 and returns to the cooling train 140. Similarly, coolant from the cooling train 150 enters the cooling channels 151b, 152b of the fuel element 120 at the top of the fuel element and flows downward through the fuel element 120. The coolant exits the cooling channels 151b, 152b of the fuel element 120 at the bottom of the fuel element 120 and returns to the cooling train 150. Thus, the fluid flow through the cooling channels 141b, 142b, 151b, and 152b may be in parallel uniform directions, e.g., downward in the direction of gravity.

[0124] In some implementations, coolant from the cooling train 140 enters the cooling channels 141b, 142b of the fuel element 120 at the bottom of the fuel element and flows upward through the fuel element 120, e.g., relative to the direction of gravity. The coolant exits the cooling channels 141b, 142b of the fuel element 120 at the top of the fuel element 120 and returns to the cooling train 140. Similarly, coolant from the cooling train 150 enters the cooling channels 151b, 152b of the fuel element 120 at the bottom of the fuel element 120 and flows upward through the fuel element 120. The coolant exits the cooling channels 151b, 152b of the fuel element 120 at the top of the fuel element 120 and returns to the cooling train 150. Thus, fluid flow through cooling channels 141b, 142b, 151b, and 152b may be in a parallel uniform direction, for example, upward with respect to the direction of gravity.

[0125] In some implementations, the fluid flow through the cooling channels 141b, 142b, 151b, and 152b can be in a non-uniform direction. For example, coolant can enter the cooling channels 141b, 142b from the cooling train 140 at the top of the fuel element 120 and enter the cooling channels 151b, 152b from the cooling train 150 at the bottom of the fuel element 120. Thus, the fluid coolant flow through the cooling channels 141b, 142b can be in an opposite, parallel direction to the direction of the fluid coolant flow through the cooling channels 151b, 152b.

[0126] Although shown as having four cooling channels 141b, 142b, 151b, and 152b, the fuel element 120 can include more or fewer cooling channels. For example, the fuel element 120 can include two cooling channels, with two cooling trains each fluidly coupled to one of the cooling channels. In some examples, the fuel element 120 can include six cooling channels, with two cooling trains each fluidly coupled to three of the cooling channels, or three cooling trains each fluidly coupled to two of the cooling channels. Other combinations of cooling trains and channels are also possible (e.g., three cooling trains and three cooling channels per fuel element, four cooling trains and four cooling channels per fuel element, two cooling trains and eight cooling channels per fuel element).

[0127] 2 is a schematic diagram of a nuclear reactor power system 200. System 200 includes nuclear reactor 100 and power conversion trains 230a and 230b. Power conversion trains 230a and 230b are independent power conversion trains. Power conversion trains 230a and 230b are driven by heat from nuclear reactor 100. Heat is transported from reactor 100 to power conversion trains 230a and 230b by cooling loops 240 and 250, respectively. Coolant can be transported by cooling loop 240 using natural or forced circulation.

[0128] Cooling loops 240 and 250 are fluidly isolated from each other and operate in parallel with each other. Cooling loop 240 includes a hot leg 242 for transporting hot coolant to power conversion train 230a and a cold leg 244 for transporting cold coolant to reactor 100. Cooling loop 250 includes a hot leg 252 for transporting hot coolant to power conversion train 230b and a cold leg 254 for transporting cold coolant to reactor 100.

[0129] In some embodiments, cooling loops 240 and 250 transport primary coolant. For example, cooling loops 240 and 250 can include cooling trains 140 and 150 of FIGURE 1A. In this embodiment, primary coolant from cooling train 140 flows from reactor 100 through cooling loop 240 to power conversion train 230a, and primary coolant from cooling train 150 flows from reactor 100 through cooling loop 250 to power conversion train 230b.

[0130] In some embodiments, cooling loops 240 and 250 can transport an intermediate coolant. For example, cooling train 140 can be cooled by an intermediate coolant in cooling loop 240, and cooling train 150 can be cooled by an intermediate coolant in cooling loop 250. In some embodiments, reactor 100 includes a single primary cooling train, and cooling loops 240 and 250 are each configured to remove heat from the single primary cooling train.

[0131] 3A and 3B are schematic diagrams of a system including a nuclear reactor power system and multiple power conversion systems. Referring to FIG. 3A, system 300 includes nuclear reactor 100, cooling loops 240 and 250, and heat exchangers 330a, 330b. Heat exchangers 330a and 330b transfer heat from cooling loops 240 and 250, respectively, to a power conversion working fluid. Reactor 100, cooling loops 240 and 250, and heat exchangers 330a and 330b are located within containment vessel 340.

[0132] The power conversion working fluid is transported from heat exchanger 330a through piping system 333a to turbine 350a. The power conversion working fluid is also transported from heat exchanger 330b through piping system 333b to turbine 350b. In some embodiments, heat exchanger 330a and turbine 350a are part of a first power conversion train, e.g., power conversion train 230a of FIG. 2. In this embodiment, heat exchanger 330b and turbine 350b are part of a second power conversion train, e.g., power conversion train 230b of FIG. 2.

[0133] In some embodiments, heat exchangers 330a and 330b are cooled by a single inter-cooling loop. For example, the inter-cooling loop can transport heat from a primary coolant in reactor 100 to both heat exchangers 330a and 330b. In this embodiment, reactor 100 can be cooled by a single primary cooling train or by multiple primary cooling trains that transfer heat to a single inter-cooling loop.

[0134] In some implementations, a bypass 334 connects piping system 333a to piping system 333b. The bypass 334 can be implemented such that power conversion working fluid from heat exchanger 330a can flow through the bypass 334 and power turbine 350b and / or power conversion working fluid from heat exchanger 330b can flow through the bypass 334 and power turbine 350a. In this manner, heat from either the first cooling system or the second cooling system can be used to power both turbines 350a, 350b.

[0135] 3B, system 301 includes a reactor module 302, which includes a reactor core 306, a primary coolant system 305, and an intermediate heat exchanger 304. The heat exchanger 304 is cooled by a single inter-cooling loop 308. The inter-cooling loop 308 transports heat from the primary coolant system 305 to a power conversion heat exchanger 310. System 301 also includes power conversion systems 315a and 315b, and heat sinks 316a and 316b.

[0136] In some embodiments, the intermediate coolant flows through the intermediate cooling loop 308 by natural circulation. In some embodiments, the intermediate coolant is forced through the intermediate cooling loop 308 by motive force provided by one or more pumps. Redundant pumps can be included in the intermediate loop to provide forced circulation. The redundant pumps provide improved reliability of the intermediate system such that it is fault tolerant if one pump goes offline.

[0137] The intermediate loop can be designed to include thermal energy storage via a thermal storage medium, including structure and / or coolant, to allow for continued power generation in the event of a reactor shutdown. The thermal energy storage can also allow for power peaking using the combined capacity of the power conversion systems. For example, system 301 includes thermal energy storage 311.

[0138] In some embodiments, the intermediate coolant is a liquid metal. The intermediate coolant system can be sized to store a significant amount of thermal energy to be used to support increased power generation in excess of 100 percent of the rated reactor power by including an increased mass of coolant and / or through the use of a solid or phase change heat storage medium in a storage tank fluidly connected to the intermediate coolant loop.

[0139] 4A-4D are schematic diagrams of example configurations of a nuclear reactor power system and a power conversion system. Referring to FIG. 4A, a nuclear reactor 410a provides heat through two cooling loops 412 to a first power conversion train 401a and a second power conversion train 402a.

[0140] Referring to FIG. 4B, a first reactor 410b provides heat to the first power conversion train 401b and the second power conversion train 402b through two cooling loops 414, and a second reactor 420b provides heat to the third power conversion train 403b and the fourth power conversion train 404b through two cooling loops 416.

[0141] Referring to FIG. 4C, a first reactor 410c provides heat to the first power conversion train 401c and the third power conversion train 403c through a shared cooling loop 418, a second reactor 420c provides heat to the first power conversion train 401c and the second power conversion train 402c, and a third reactor 430c provides heat to the second power conversion train 402c and the third power conversion train 403c.

[0142] Referring to FIG. 4D, the first reactor 410d provides heat to the first power conversion train 401d and the second power conversion train 402d through a partially shared cooling loop 422, and the second reactor 420d provides heat to the second power conversion train 402d and the third power conversion train 403d.

[0143] Using the disclosed techniques, nuclear reactor power systems can achieve high operational uptime by incorporating redundancy such that the nuclear reactor power system can continue to operate at full power even if one or more power conversion systems are offline.

[0144] In some embodiments, the nuclear reactor power system operates in a first mode of operation in which the multiple power conversion trains are each operating at a power level corresponding to greater than zero percent of the rated reactor power but less than 100 percent of the rated reactor power, and the combined power output of the reactors can be up to 100 percent of the rated reactor power.

[0145] The reactor power system can also operate in a second mode of operation in which one power conversion train is operating at a power level corresponding to 100 percent of the rated reactor power and the other power conversion train is on standby. The reactor system can quickly switch between operating in the first mode of operation and operating in the second mode of operation. For example, with two power conversion trains operating in a "hot" mode, the system can switch from operating two power conversion trains to operating a single conversion train without performing a start-up from a cold or zero power condition. This also allows for a power management system of reduced complexity. The rotational inertia of the operating turbines can quickly pick up loads while reducing the possibility of large voltage disruptions.

[0146] In some implementations, a decay heat removal supplemental cooling system is used to passively remove decay heat from the reactor vessel. In some implementations, external cooling can remove heat from the reactor vessel system via a fluid, such as air or liquid.

[0147] In some implementations, the primary coolant is transported by natural circulation and transfers heat by natural convection. The primary coolant may flow via natural circulation at steady-state conditions ranging from reactor start-up to full power levels. The primary coolant may include, for example, water, liquid metal, liquid salt, supercritical fluid, or gas.

[0148] In some implementations, primary heat transport is accomplished using heat pipes. According to some embodiments, one or more booster pumps are used to facilitate reactor startup by establishing a flow pattern through forced and mixed circulation, which then transitions to natural circulation at the desired power level. The booster pumps can be shut off once natural circulation is established.

[0149] Maintaining adequate coolant chemistry and purity control is important to ensure the useful life of the coolant and components. In some implementations, a passive coolant chemistry control system is used that is sized to allow for minimal maintenance over the life of the plant operation. In some implementations, the system includes a passively operated cold trap configured to purify the liquid metal coolant.

[0150] In some implementations, during operation, the liquid metal coolant flows through the reactor by natural circulation. The liquid metal coolant can flow by natural circulation at steady state conditions at power levels ranging from reactor startup to full power. In some implementations, the system includes a booster pump configured to pump the liquid metal coolant through the reactor.

[0151] In an example implementation, a nuclear power reactor vessel system includes an inner vessel defining an inner volume sized to at least partially enclose a nuclear reactor cooled by a primary coolant, such as a liquid metal coolant, and an outer vessel sized to fully or substantially enclose the inner vessel. The nuclear reactor includes a plurality of nuclear fuel elements. In some embodiments, at least some of the nuclear fuel elements are at least partially enclosed within cladding.

[0152] In some embodiments, the submersion fluid cools components of the system. The submersion fluid stores thermal energy generated by the reactor. In some embodiments, the submersion fluid is the same fluid as the liquid metal coolant. In some embodiments, the submersion fluid and the liquid metal coolant are fluidically or hydraulically connected. The submersion fluid and the liquid metal coolant can be fluidically connected by one of a flow diode, a pressure gate, a permeable membrane, or a height difference. In some embodiments, the system includes a modular package of reactor vessel components. The modular package can be removable from the system.

[0153] In some embodiments, the reactor power system includes a mass spectrometer detector to detect failed fuel pins. Typically, a gamma spectrometer is used to detect fission products. The mass spectrometer can be located in a cover gas plenum outside the active core of the reactor. The system can be used to detect fission gases and / or pre-charged fuel pin tag gases. The presence of these materials in the cover gas plenum is likely to result from a failed or leaking fuel pin since gas would not otherwise be present and no other source of gas is present. Multiple mass spectrometers can be used to ensure redundancy and redundancy and the ability to confirm detection of abnormal gas with a match of more than one positive signal. The spectrometer can be part of the overall reactor instrumentation and control system and can be used to determine if the failed fuel element should be replaced.

[0154] The mass spectrometer detector can be located, for example, in the cover gas region of a liquid metal cooled nuclear reactor. The mass spectrometer detector can also be located in a gas cooled reactor or a molten salt reactor where a cover gas region or gas plenum exists. The mass spectrometer can also be located in a coolant chemistry and control system where the mass spectrometer can detect fission products that are indicative of a fuel pin failure.

[0155] 5A and 5B show example reactor cores 501, 502 that include passive flow orifice devices or orifice plates. The passive flow orifice plates can be positioned at the top end of the fuel assembly area, at the bottom end of the fuel assembly area, or at both the top and bottom ends of the reactor fuel assembly area.

[0156] The core 501 includes a coolant inlet 521. The core 501 includes a fuel assembly region 511 that includes a plurality of fuel elements or fuel pins 513. The fuel assembly region 511 has a top end 515 and a bottom end 517. In some embodiments, the top end 515 is located above the bottom end 517 in the direction of gravity, e.g., the z-direction. Each fuel pin 513 has a length in the z-direction.

[0157] The core 501 includes a passive flow orifice device 510 at a bottom end 517 of the fuel assembly region 511. The passive flow orifice device 510 includes a flow orifice 508 and a passive thermal expansion orifice plate 509. Although shown as having three orifices 508, the plate 509 can include more or fewer orifices 508.

[0158] The passive flow orifice device 510 is positioned between the coolant inlet 521 and the fuel assembly area 511. Fluid coolant enters the fuel assembly area 511 through an orifice in the plate 509. The passive flow orifice device 510 is positioned with the surface of the plate 509 extending in a direction perpendicular to the length of the fuel pins 513. For example, the fuel pins 513 extend in the z direction and the surface of the plate 509 extends in the xy plane. The passive flow orifice device 510 can passively and automatically respond to temperature changes by expanding or contracting. The expansion and contraction of the passive flow orifice device 510 causes an increase or decrease in flow volume at the assembly level based on the local power to flow ratio.

[0159] The core 502 includes a coolant outlet 522. The core 502 includes a fuel assembly region 512 that includes a plurality of fuel pins 514. The fuel assembly region 512 has a top end 516 and a bottom end 518. In some embodiments, the top end 516 is located above the bottom end 518 in the direction of gravity, e.g., the z-direction. Each fuel pin 514 has a length in the z-direction.

[0160] The core 502 includes a passive flow orifice device 520 at an upper end 516 of the fuel assembly region 512. The passive flow orifice device 520 includes a flow orifice 528 and a passive thermal expansion orifice plate 529. The passive flow orifice device 520 includes a disk 519 positioned within the orifice 528. An annulus 530 is formed between the orifice 528 and the disk 519. Expansion and contraction of the disk 519, the plate 529, or both changes the cross-sectional area of ​​the annulus 530. The changing size of the annulus 530 changes the flow volume of the fluid coolant through the passive flow orifice device 520. The disk 519 can be suspended within the orifice 528 using wires or a suspension arm. The disk 519 can be centered within the orifice 528 so that the coolant flow around the disk 519 is radially uniform.

[0161] A passive flow orifice device 520 is positioned between the fuel assembly area 512 and a coolant outlet 522. Fluid coolant exits the fuel assembly area 512 through an orifice 528 in a plate 529. The passive flow orifice device 520 can passively and automatically respond to temperature changes by expanding or contracting. The expansion and contraction of the passive flow orifice device 520 causes an increase or decrease in flow volume at the assembly level based on the local power to flow ratio.

[0162] The passive flow orifice devices 510, 520 can either respond to increased coolant temperature based on the element's nuclear fission power production, or can employ materials that lead to increased radiative heating based on reactions with photons and neutrons generated within the element. These can include small amounts of fissile materials, boron, or high-Z materials. The passive flow orifice devices 510, 520 can also be designed to respond to both temperature and radiative heating.

[0163] Passive flow orifices can alleviate the need for fixed or difficult to move flow orifices and allow for easier fuel shuffling. The expanding and contracting passive flow orifice devices can adjust the coolant flow rate over time throughout the life of the core to accommodate changes in temperature and radioactivity. Thus, the passive flow orifice devices can remain in place for long periods during the life of the core without being replaced, reducing the amount of maintenance required.

[0164] The flow orifices ensure a flat fuel element coolant exit temperature distribution, improving reactor performance. Passive flow orifice devices can use solid materials or liquid or gas expanders that expand as they experience higher temperatures, increasing the flow area, reducing pressure drop, and allowing more primary coolant flow to flow through the orifice device. Gases and liquids have favorable expansion properties that can compensate for their increased complexity. Responding to coolant temperature, radiative heating, or both would couple temperature and power behavior with the desired orifice expansion behavior.

[0165] Although this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or claimed subject matter, but rather as descriptions of features specific to particular implementations of a particular invention. Certain features described herein in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations, separately or in any suitable subcombination. Also, although features may be described above as acting in a combination and even initially claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and the claimed combination may also be subject to subcombinations or variations of the subcombination.

[0166] Similarly, although operations are depicted in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order shown, or in a sequential order, or that all of the illustrated operations be performed, to achieve desirable results. In some situations, multitasking and parallel processing may be advantageous. Also, it should be understood that the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and that the program components and systems described may generally be integrated together in a single software product or packaged within multiple software products.

[0167] Several implementations have been described. Nevertheless, it should be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. For example, the example operations, methods, or processes described herein may include more or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in a different sequence than described or illustrated in the figures. Thus, other implementations are within the scope of the following claims.

Claims

1. 1. A nuclear reactor power system comprising:

1. A reactor core comprising a plurality of nuclear fuel elements, each of the plurality of nuclear fuel elements comprising: a first cooling channel passing through the nuclear fuel element; a second cooling channel passing through the nuclear fuel element and fluidly isolated from the first cooling channel; a reactor core comprising: a first cooling system configured to transport a first fluid coolant through the reactor core, the first cooling system fluidly connected to the first cooling channel of each nuclear fuel element; a second cooling system configured to transport a second fluid coolant through the core, the second cooling system fluidly connected to the second cooling channels of each nuclear fuel element; 1. A nuclear reactor power system comprising:

2. 10. The nuclear reactor power system of claim 1, wherein the first cooling system is fluidly isolated from the second cooling system.

3. in a first mode of operation of the nuclear reactor power system, a first volume of a first fluid coolant flows through the first cooling system and a second volume of a second fluid coolant flows through the second cooling system; In a second operating mode of the nuclear reactor power system, a first volume of a first fluid coolant flows through the first cooling system and a second volume of a second fluid coolant does not flow through the second cooling system.

10. The nuclear reactor power system of claim 1.

4. 4. The nuclear power system of claim 3, wherein the nuclear power system is configured to operate at or near 100 percent of rated reactor power during operation in both the first mode of operation and the second mode of operation.

5. 4. The nuclear reactor power system of claim 3, wherein during operation in the first mode of operation, at least one of the first volume of first fluid coolant or the second volume of second fluid coolant is transported by natural circulation.

6. 4. The nuclear reactor power system of claim 3, wherein during operation in the second mode of operation, the first volume of first fluid coolant is transported by natural circulation.

7. During operation in the first mode of operation: the first volume of first fluid coolant flows from the first cooling system through the first cooling channel of each nuclear fuel element; the second volume of first fluid coolant flows from the second cooling system through the second cooling channel of each nuclear fuel element; 4. The nuclear reactor power system of claim 3.

8. 4. The nuclear reactor power system of claim 3, wherein the first cooling channel and the second cooling channel each comprise a cylindrical shape, and a cylindrical axis of the first cooling channel is parallel to a cylindrical axis of the second cooling channel.

9. 2. The nuclear reactor power system of claim 1, wherein a direction of first fluid coolant flow through said first cooling channel is the same as a direction of second fluid coolant flow through said second cooling channel.

10. a first heat exchanger configured to transfer heat from the first fluid coolant in the first cooling system to a first intermediate coolant in a first intermediate coolant loop; a second heat exchanger configured to transfer heat from the second fluid coolant in the second cooling system to a second intermediate coolant in a second intermediate coolant loop; 10. The nuclear reactor power system of claim 1, comprising:

11. the first intermediate coolant flows through the first intermediate coolant loop by natural circulation; the second intermediate coolant flows through the second intermediate coolant loop by natural circulation; 11. The nuclear reactor power system of claim 10.

12. a first heat exchanger configured to transfer heat from the first fluid coolant in the first cooling system to a first intermediate coolant in a first intermediate coolant loop; a second heat exchanger configured to transfer heat from the second fluid coolant in the second cooling system to the first intermediate coolant in the first intermediate coolant loop; 10. The nuclear reactor power system of claim 1, comprising:

13. 11. The nuclear reactor power system of claim 10, wherein each of the first heat exchanger and the second heat exchanger is configured to transfer heat at a level corresponding to a reactor power level at or near 100 percent of rated reactor power.

14. a third heat exchanger configured to transfer heat from the first intermediate coolant in the first intermediate coolant loop to a power conversion working fluid of a first power conversion system; a fourth heat exchanger configured to transfer heat from the second intermediate coolant in the second intermediate coolant loop to a power conversion working fluid of a second power conversion system; and 11. The nuclear reactor power system of claim 10, comprising:

15. 11. The nuclear reactor power system of claim 10, wherein at least one of the first intermediate coolant loop or the second intermediate coolant loop is configured to transfer heat to a plurality of power conversion systems.

16. 15. The nuclear reactor power system of claim 14, wherein during operation, the first power conversion system and the second power conversion system each operate independently.

17. the first power conversion system includes a first turbine; the second power conversion system includes a second turbine; each of the first turbine and the second turbine is configured to operate at a power level corresponding to 100 percent of rated reactor power or near a reactor power level; 15. The nuclear reactor power system of claim 14.

18. Each of the nuclear fuel elements further comprises: a third cooling channel passing through the nuclear fuel element; a fourth cooling channel passing through the nuclear fuel element; and Equipped with the first cooling system is fluidly connected to the third cooling channel of each nuclear fuel element; the second cooling system is fluidly connected to the fourth cooling channel of each nuclear fuel element; 10. The nuclear reactor power system of claim 1.

19. 20. The nuclear reactor power system of claim 18, wherein the third cooling channel and the fourth cooling channel each comprise a cylindrical shape, and a cylindrical axis of the third cooling channel is parallel to a cylindrical axis of the fourth cooling channel.

20. 20. The nuclear reactor power system of claim 18, wherein a direction of first fluid coolant flow through said third cooling channel is the same as a direction of second fluid coolant flow through said fourth cooling channel.

21. 10. The nuclear reactor power system of claim 1, wherein each of the first and second fluid coolants comprises at least one of water, a liquid metal, a liquid salt, a supercritical fluid, or a gas.

22. the reactor core comprises a fuel assembly region including a plurality of nuclear fuel elements arranged in parallel and extending from a first end of the fuel assembly region to a second end of the fuel assembly region; a plate positioned adjacent a first end of the fuel assembly region, the plate including one or more orifices configured to vary in size to cause a change in flow volume of a fluid coolant through the core; 10. The nuclear reactor power system of claim 1, comprising:

23. the plate is positioned between the coolant inlet and the fuel assembly area; fluid coolant enters the fuel assembly region through the one or more orifices in the plate; 23. The nuclear reactor power system of claim 22.

24. the plate is positioned between the coolant outlet and the fuel assembly area; fluid coolant exits the fuel assembly region through the one or more orifices in the plate; 23. The nuclear reactor power system of claim 22.

25. A nuclear reactor power system as described in claim 22, wherein the plate comprises a first plate and the system comprises a second plate positioned adjacent to the second end of the fuel assembly area.

26. 23. The nuclear reactor power system of claim 22, wherein the plate is formed from at least one expandable material configured to expand or contract with changing temperature.

27. 23. The nuclear reactor power system of claim 22, wherein the plate is formed from at least one expandable material configured to expand or contract with changing radiation levels.

28. 27. The nuclear reactor power system of claim 26, wherein expansion or contraction of the at least one expandable material causes a change in size of the one or more orifices.

29. A nuclear reactor power system as described in claim 27, wherein expansion or contraction of the at least one expandable material causes a change in size of the one or more orifices.

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