HEAT REMOVAL SYSTEM FOR A MOLTEN SALT REACTOR SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/341,652, filed on May 26, 2016, and entitled "Heat Removal System For A Molten Salt Reactor System," the entirety of which is hereby incorporated by reference.

TECHNOLOGICAL FIELD

[0002] The present disclosure relates generally to nuclear reactors, and, more particularly, to a heat removal system for use in a molten salt reactor (MSR) system.

BACKGROUND

[0003] The global demand for energy has largely been fed by fossil fuels. This typically involves taking reduced carbon out of the Earth and burning it. However, those hydrocarbons are in limited supply and burning the hydrocarbons produces carbon dioxide. According to the U.S. Environmental Protection Agency, more than 9 trillion metric tons of carbon are released into the atmosphere each year. Nuclear power is appealing due to possibilities of abundant fuel and carbon-neutral energy production.

[0004] Most nuclear energy has been provided by light water reactors (LWRs). In LWRs, light water (ordinary water) is used as the moderator as well as the cooling agent and the means by which heat is removed to produce steam used in generating electricity (e.g., turning turbines of electric generators). Although LWRs have been, and continue to be, relied upon for power generation, LWRs have drawbacks. For example, LWRs use solid fuel having very long radioactive half-lives (e.g., Uranium-235 has a half-life of approximately 700 million years). Also, LWRs operate at high pressure, thus requiring expensive engineering building materials to maintain LWRs. Additionally, since potential accidents associated with LWRs have high hazards, LWRs require expensive safety systems to deal with any accidents.

[0005] A molten salt reactor (MSR) is a class of generation IV nuclear fission reactor in which the primary nuclear reactor coolant, or even the fuel itself, is a molten salt mixture. A MSR may provide energy more safely and cheaply than LWRs. However, one challenge with MSRs is the management and control of heat generated as a result of nuclear fission within the reactor core, as well as decay heat released from radioactive decay of molten fuel salt. [0006] Some reactor designs include heat exchanger systems configured to actively transfer heated molten fuel salt away from the reactor core to other components to either utilize the heat for power generation (generation of electricity) or as a means of cooling the molten fuel salt for drawing heat away from the reactor core. For example, when a nuclear reactor has been shut down, and nuclear fission is not occurring at a large scale, heat still occurs within as a result of delayed decay of fission products releasing decay heat. It is important that the heat exchanger systems function properly to ensure consistent removal of heat from the reactor core. The removal of the decay heat is a significant reactor safety concern, especially shortly after normal shutdown or following a loss-of-coolant accident. Failure to remove decay heat may cause the reactor core temperature to rise to dangerous levels.

[0007] As such, current reactor designs may generally include safety protocols to account for systematic failure of one or more systems of a reactor, such as shutting down of the reactor in the event of power loss to, or failure of, the heat exchanger systems. However, the decay heat that follows the shutdown of a nuclear reactor following the loss of cooling function presents a challenge. In particular, if the heat is not removed efficiently from the reactor or in a timely manner, the temperature in the reactor may rise to unacceptable levels, which can lead to equipment damage and further compromise the structural integrity of the reactor itself, thereby resulting in catastrophic failure.

SUMMARY

[0008] Embodiments of the present disclosure can provide a heat removal system for use in molten salt reactor (MSR) system. The heat removal system can be configured to passively transfer heat from a reactor core to prevent elevated temperatures within the reactor and reduce the risk of catastrophic failure. Unlike some heat exchanger systems, or other powered systems which rely on a power source for operation (e.g., electricity-driver, fuel-driven, etc.), the heat removal system of embodiments of the present disclosure can be passive in that it can omit a power source in order to function as intended. Accordingly, in addition to transferring heat away from a reactor core during normal operation of the reactor for maintaining a constant temperature within the core, the heat removal system can be configured to continue functioning during a shutdown of the reactor without requiring a power source. Thus, the heat removal system can be configured to draw decay heat released by molten fuel salt that can follow as a result of the shutdown of the reactor, thereby reducing the temperature in the reactor to prevent the chance of catastrophic failure. [0009] Embodiments of the heat removal system can include a two-vessel configuration with a primary vessel and a secondary vessel. The primary vessel can house a reactor core and other components of the reactor system. The secondary vessel can surround the primary vessel. The primary vessel wall can include an outer surface including a first set of fins extending therefrom in an outward direction away from the primary vessel wall. The outer surface can further include voids defined between adjacent fins, such that the fins and voids are arranged in an alternating pattern along the outer surface. The secondary vessel wall can have an inner surface including a second set of fins extending therefrom in an inward direction toward the primary vessel wall. The second set of fins can be arranged in a similar fashion as the first set of fins, in that voids are defined between adjacent fins.

[0010] When assembled (i.e., when the primary vessel is enclosed within the secondary vessel), the first and second sets of fins can be generally interdigitated, or interleaved, with one another, such that fins of the first set are positioned within corresponding voids between the fins of the second set and the fins of the second set are positioned within corresponding voids between fins of the first set. However, when assembled, the primary and secondary vessels can avoid direct contact with one another. In other words, the first and second sets of fins can be configured such that they do not make contact with each other or with corresponding voids. Rather, a continuous gap or channel can be formed between the first and the second sets of fins. The continuous gap or channel can provide radiative heat transfer between the first and the second sets of fins, which can effectively draw heat away from the reactor and prevents the reactor temperature from rising to unacceptable levels.

[0011] In particular, the primary vessel can be configured to receive heat generated within the reactor, as a result of nuclear fission within the reactor core, decay heat released from radioactive decay of molten fuel salt, and combinations thereof. The gap formed between the primary and secondary vessels can serve as a radiative heat gap configured to assist in radiative transfer of heat from the first set of fins of the primary vessel to the second set of fins of the secondary vessel. For example, in some embodiments, the gap can be hermetically sealed and include a medium, such as an inert gas, configured to assist or enhance thermal radiation between the first and second sets of fins. In some cases, the medium can be a fluid selected to boil in response to the radiative heat (e.g., NaCL-AlCl ₄ ).

[0012] The radiative heat transfer can include the transfer of energy by emission of electromagnetic radiation from the first set of fins to the second set of fins. The second set of fins can be configured to absorb the heat, thereby drawing heat away from the primary vessel. In some embodiments, an additional buffer material or layer can surround, or can be in contact with, an exterior surface of the secondary vessel to further absorb heat from the secondary vessel (e.g., via convection, conduction, etc.) and further dissipate heat.

[0013] Embodiments of the heat removal system of the present disclosure can be

configurable, depending on the specific application and the amount of heat removal desired. For example, the arrangement of the first and second sets of fins of the primary and secondary vessel walls, respectively, can play a large role in determining the amount of heat that can be transferred. In particular, the amount of heat that can be transferred from the primary vessel to the secondary vessel can be dependent, in part, on the surface area of the fins. The fins can be tunable to have a specific surface area for transfer of a desired amount of heat. For example, for any given reactor system, there can be an acceptable range of temperatures in which the reactor core can operate (e.g., approximately 650°C or about 1,200°F). The physical dimensions of the fins (e.g., length and width), the number of fins, as well as the orientation of the fins, can be customized such that protrusion arrangement results in an amount of heat transfer sufficient to maintain the operating temperature of the reactor core within the acceptable temperature range.

[0014] The heat removal system of the present disclosure can be configured to function both during operation of the reactor and during a shutdown of the reactor. Accordingly, the heat removal system can be configured to efficiently draw heat away from the reactor core to maintain a constant temperature within the core within acceptable levels. For example, when a nuclear reactor shuts down, and nuclear fission is not occurring at a large scale, decay heat can still occur within the system. This decay heat can be non-trivial and, in some cases, decay heat can be between about 5% to about 6.5% of the previous core power if the reactor has had a long and steady power history. Therefore, passive heat removal using the interdigitated, or interleaved, fins and utilizing radiative heat transfer, can be configured to continue functioning in the event that there can be a reactor shutdown without requiring a power source. For example, the heat removal system can be configured to continue drawing heat from the reactor following a shutdown, wherein the heat can be in the form of decay heat released from molten salt fuel. Thus, embodiments of the disclosed heat removal system can overcome the drawbacks of current emergency backup cooling systems, which rely on power sources to deal with decay heat. Furthermore, radiative heat transfer can provide a much more efficient means of heat removal, in that the amount of energy transferred over a period time can be much greater than other heat transfer modes, such as convection or conduction. Thus, the heat removal system of embodiments of the present disclosure can provide a much more efficient and quicker manner of removing heat, thereby reducing the risk of temperature in the reactor rising to unacceptable levels and reducing the chance of catastrophic failure (e.g., breakdown of vessel wall and contamination of surrounding environment).

[0015] In one embodiment, a heat removal system is provided for a reactor and can include a primary vessel and a secondary vessel. The primary vessel can be configured to house a reactor core within and it can include a vessel wall with an outer surface. The outer surface can include a first set of fins extending outwardly therefrom and a first set of voids, where the first sets of fins and voids can alternate with one another. The secondary vessel can surround the primary vessel and have a vessel wall with an inner surface. The inner surface can include a second set of fins extending inwardly therefrom and a second set of voids, where the second sets of fins and the second set of voids can alternate with one another. The first set of fins can be positioned within the second set of voids and the second set of fins can be positioned within the first set of voids. The heat removal system can also include a gap defined between the outer surface of the primary vessel wall and the inner surface of the secondary vessel wall. The first set of fins can be configured to transfer heat from the reactor core to the second set of fins across the gap via radiative heat transfer.

[0016] Embodiments of the first and second set of fins can have a variety of configurations. In one aspect, the first set of fins and the second set of fins can be arranged along the primary and secondary vessel walls in a substantially similar manner. In another aspect, the first and second sets of fins can extend in a direction that is substantially parallel to a longitudinal axis of the primary and secondary vessel walls, respectively. In a further embodiment, the first and second sets of fins can extend along a length of the primary and secondary vessel walls, respectively. In an additional aspect, the first and second sets of fins can extend in a direction that is substantially parallel to a longitudinal axis of the primary and secondary vessel walls, respectively. In another aspect, the first and second sets of fins can be are arranged in a helical pattern.

[0017] In another embodiment, the primary vessel wall can include an inner layer forming an inner surface of the primary vessel wall and an outer layer forming the outer surface of the primary vessel wall. The inner layer can include a high nickel alloy or a molybdenum alloy. The inner layer can alternatively include HASTELLOY N. The outer layer can include a steel composition. As an example, the outer layer can include an austenitic stainless steel or a high-Cr martensitic steel HT-9.

[0018] In another embodiment, the gap can be hermetically sealed and contain an inert gas.

[0019] In another embodiment, the heat transferred between the first and second sets of fins can include heat generated as a result of nuclear fission within the reactor core.

[0020] In another embodiment, the heat transferred between the first and second sets of fins can include decay heat released from radioactive decay of a fuel.

[0021] In one embodiment, a molten salt reactor system is provided an can include a primary vessel, a reactor core, a fuel salt, and a secondary vessel. The reactor core can be positioned within the primary vessel. The fuel salt can be configured to flow within the primary vessel and through the reactor core. The secondary vessel can surround the primary vessel and it can be configured to receive heat transferred from the primary vessel via radiative heat transfer.

[0022] In another embodiment, the primary vessel can include a vessel wall having an outer surface including a first set of fins extending outwardly therefrom and the secondary vessel can include a vessel wall having an inner surface including a second set of fins extending inwardly therefrom. The first and second sets of fins can be interdigitated or interleaved with one another.

[0023] In another embodiment, a gap can be defined between the first and second sets of fins of the outer surface of the primary vessel wall and the inner surface of the secondary vessel wall, respectively. The gap can be hermetically sealed and contain an inert gas.

[0024] In another embodiment, the first set of fins can be configured to transfer heat to the second set of fins across the gap via radiative heat transfer. The heat transferred between the first and second sets of fins can include heat generated as a result of nuclear fission within the reactor core. Alternatively, the heat transferred between the first and second sets of fins can include decay heat released from radioactive decay of the fuel salt. [0025] In another embodiment, the primary vessel can include and inner layer and an outer layer. The inner layer can include HASTELLOY ^® N. Alternatively, the outer layer can include austenitic stainless steel or a high-Cr martensitic steel HT-9.

[0026] In one embodiment, a heat removal system for a reactor is provided and can include a primary vessel and a secondary vessel. The primary vessel can be configured to house a reactor core within and it can include an outer surface having a first set of fins extending outwardly therefrom. The secondary vessel can surround the primary vessel and can have an inner surface with a second set of fins extending inwardly therefrom, where the first set of fins can be interleaved with the second set of fins. The heat removal system can also include a gap defined between the outer surface of the primary vessel wall and the inner surface of the secondary vessel wall. The first set of fins can be configured to transfer heat from the reactor core to the second set of fins across the gap via radiative heat transfer.

[0027] In another embodiment, the first set of fins and the second set of fins can be cooled by a fluid circulating within the gap. The fluid circulating within the gap can be configured to transfer heat from the reactor core via the first set of fins.

[0028] In another embodiment, the circulating fluid can be an inert gas or a liquid metal. The liquid metal can be NaCl-AlC .

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Features and advantages of the claimed subject matter will be apparent from the following detailed description of embodiments consistent therewith, which description should be considered with reference to the accompanying drawings, wherein:

[0030] FIG. 1 is a schematic diagram depicting a molten salt reactor system consistent with the present disclosure.

[0031] FIG. 2 is a schematic diagram depicting the chemical processing plant of the molten salt reactor system of FIG. 1 in greater detail.

[0032] FIG. 3 schematically illustrates the components of a molten salt reactor compatible with the system of FIG. 1.

[0033] FIG. 4 is a side view of a molten salt reactor including the heat removal system consistent with the present disclosure. [0034] FIG. 5 is an enlarged perspective view of one embodiment of a primary vessel compatible with the molten salt reactor of FIG. 3.

[0035] FIG. 6 is a cross-sectional view of a heat removal system including the primary vessel of FIG. 5 assembled with a corresponding secondary vessel taken along lines 6-6 of FIG. 4.

[0036] FIG. 7 is an enlarged cross-sectional view of the assembled primary and secondary vessels illustrating the interdigitated, or interleaved, arrangement of the first and second sets of fins.

[0037] FIG. 8 is an enlarged perspective view of another embodiment of a primary vessel compatible with the molten salt reactor of FIG. 3 illustrating the first set of fins being arranged along the primary vessel wall in a helical fashion.

[0038] FIG. 9 is a is a cross-sectional view of a heat removal system including the primary vessel of FIG. 8 assembled with a corresponding secondary vessel taken along lines 9-9 of FIG. 4.

[0039] For a thorough understanding of the present disclosure, reference should be made to the following detailed description, including the appended claims, in connection with the above-described drawings. Although the present disclosure is described in connection with exemplary embodiments, the disclosure is not intended to be limited to the specific forms set forth herein. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances can suggest or render expedient.

DETAILED DESCRIPTION

[0040] Embodiments of the present disclosure provide a heat removal system for use in molten salt reactor (MSR) system. The heat removal system can be configured to passively transfer heat from a reactor core to prevent elevated temperatures within the reactor and reduce the risk of catastrophic failure. Unlike some heat exchanger systems, or other powered systems which rely on a power source for operation (e.g., electricity-driver, fuel-driven, etc.), embodiments of the heat removal system of the present disclosure can be passive in that they can be configured to operate as intended without a power source. Accordingly, in addition to transferring heat away from a reactor core during normal operation of the reactor for maintaining a constant temperature within the core, embodiments of the heat removal system can be configured to continue functioning during a shutdown of the reactor without requiring a power source. Thus, the heat removal system can be configured to draw decay heat released by molten fuel salt that can follow as a result of the shutdown of the reactor, thereby reducing the temperature in the reactor to prevent the chance of catastrophic failure.

[0041] Embodiments of the heat removal system can include a two-vessel configuration with a primary vessel and a secondary vessel. The primary vessel can house a reactor core and other components of the reactor system. The secondary vessel can surround the primary vessel. The primary vessel wall can have an outer surface including a first set of fins extending therefrom in an outward direction away from the primary vessel wall. The outer surface can further include voids defined between adjacent fins, such that the fins and voids are arranged in an alternating pattern along the outer surface. The secondary vessel wall can have an inner surface including a second set of fins extending therefrom in an inward direction toward the primary vessel wall. The second set of fins can be arranged in a similar fashion as the first set of fins, in that voids are defined between adjacent fins.

[0042] When assembled (i.e., when the primary vessel can be enclosed within the secondary vessel), the first and second sets of fins can be generally interdigitated, or interleaved, with one another, such that fins of the first set are positioned within corresponding voids between the fins of the second set and the fins of the second set are positioned within corresponding voids between fins of the first set. However, when assembled, the primary and secondary vessels can avoid direct contact with one another. In other words, in certain embodiments, the first and second sets of fins do not make contact with each other or with corresponding voids. Rather, a continuous gap or channel can be formed between the first and the second sets of fins. The continuous gap or channel can provide radiative heat transfer between the first and the second sets of fins, which can effectively draw heat away from the reactor and prevent the reactor temperature from rising to unacceptable levels.

[0043] In particular, the primary vessel can be configured to receive heat generated within the reactor, either as a result of nuclear fission within the reactor core or decay heat released from radioactive decay of molten fuel salt. The gap formed between the primary and secondary vessels can serve as a radiative heat gap configured to assist in radiative transfer of heat from the first set of fins of the primary vessel to the second set of fins of the secondary vessel. For example, in some embodiments, the gap can be hermetically sealed and include a medium, such as an inert gas, configured to assist or enhance thermal radiation between the first and second sets of fins. In some cases, the medium can be a fluid selected to boil in response to the radiative heat (e.g., NaCL-AlCl ₄ ). The energy created in the boiling medium can be captured via transfer to a second energy absorption medium positioned externally to the primary vessel. The energy or heat exchange can be, captured by a convention heat transfer mechanism, such as a heat exchanger, where energy from one fluid can be transferred to another fluid of a lower energy. An example of a convection heat transfer mechanism can be a shell and tube design. In this example, the heat energy can be transferred by convection through a metallic medium, such as a "tube" metal inside a heat exchanger.

[0044] Radiative heat transfer can include the transfer of energy by emission of

electromagnetic radiation from the first set of fins to the second set of fins. The second set of fins can be configured to absorb the heat, thereby drawing heat away from the primary vessel. In some embodiments, an additional buffer material or layer can surround, or be in contact with, an exterior surface of the secondary vessel to further absorb heat from the secondary vessel (e.g., via convection, conduction, etc.) and further dissipate heat.

[0045] Embodiments of the heat removal system of the present disclosure can be

configurable depending on the specific application and the amount of heat removal desired. For example, the arrangement of the first and second sets of fins of the primary and secondary vessel walls, respectively, can play a large role in determining the amount of heat that can be transferred. In particular, the amount of heat that can be transferred from the primary vessel to the secondary vessel can be dependent, in part, on the surface area of the fins. The fins can be tunable to have a specific surface area for transfer of a desired amount of heat. For example, for any given reactor system, there can be an acceptable range of temperatures in which the reactor core can operate (e.g., approximately 650°C or about 1,200°F). The physical dimensions of the fins (e.g., length and width), the number of fins, as well as the orientation of the fins, can be customized such that protrusion arrangement results in an amount of heat transfer sufficient to maintain the operating temperature of the reactor core within the acceptable temperature range.

[0046] Embodiments of the heat removal system of the present disclosure can be configured to function both during operation of the reactor and during a shutdown of the reactor.

Accordingly, the heat removal system can be configured to efficiently draw heat away from the reactor core to maintain a constant temperature within the core within acceptable levels. For example, when a nuclear reactor shuts down, and nuclear fission does not occur at a large scale decay heat can still occur within the system. This decay heat can be non-trivial and, in some cases, the decay heat can be within the range between about 5% to about 6.5% of the previous core power if the reactor has had a long and steady power history. Therefore, passive heat removal using the interdigitated, or interleaved, fins and utilizing radiative heat transfer, can be configured to continue functioning in the event that there is a reactor shutdown without requiring a power source. For example, the heat removal system can be configured to continue drawing heat from the reactor following a shutdown, where the heat can be in the form of decay heat released from molten salt fuel. Thus, embodiments of the disclosed heat removal system can overcomes the drawbacks of current emergency backup cooling systems, which can rely on power sources to deal with decay heat. Furthermore, radiative heat transfer can provide a much more efficient means of heat removal, in that the amount of energy transferred over a period time can be much greater than other heat transfer modes, such as convection or conduction. Thus, embodiments of the heat removal system of the present disclosure can provide a much more efficient and quicker means of removing heat, and can thereby reduce the risk of temperature in the reactor rising to unacceptable levels and reduce the chance of catastrophic failure (e.g., breakdown of vessel wall and contamination of surrounding environment).

[0047] As previously described, embodiments of the heat removal system can be compatible with one or more embodiments of an MSR, described below in detail. FIG. 1 depicts a molten salt reactor system 100 configured for the generation of electrical energy from nuclear fission. The molten salt reactor system 100 can include a molten salt reactor 102 which can contain a molten fuel salt 104, which can include a mixture of chloride and fluoride salts. The molten fuel salt can include fissile materials, fertile materials, and combinations thereof. Examples of fissile materials can include, but are not limited to, thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), and curium (Cm). In certain embodiments, the fissile materials can include one or more of the following isotopes, in any combination: Th-225, Th-227, Th-229, Pa-228, Pa-230, Pa-232, U-231, U-233, U- 235, Np-234, Np-236, Np-238, Pu-237, Pu-239, Pu-241, Am-240, Am-242, Am-244, Cm- 243, Cm- 245, and Cm- 247). Examples of fertile materials can include, but are not limited to, ²³² ThC14, ²³⁸ UC1 ₃ and ²³⁸ UC1 ₄ . In an embodiment, the molten fuel salt 104 can include fissile materials including ²³³ UC1 ₃ , ²³⁵ UC1 ₃ , ²³³ UC1 ₄ , ²³⁵ UC1 ₄ , and ²³⁹ PuCl ₃ ; and carrier salts including sodium chloride (NaCl), potassium chloride (KC1), and/or calcium chloride (CaCl ₂ ). [0048] Upon absorbing neutrons, nuclear fission can be initiated and sustained in the molten fuel salt 104, generating heat that elevates the temperature of the molten fuel salt 104 (e.g., about 650°C or about 1,200°F). The heated the molten fuel salt 104 can be transported via a pump from the molten salt reactor 102 to a heat exchange unit 106, as discussed below with respect to FIG. 3. The heat exchange unit 106 can be configured to transfer the heat generated by the nuclear fission from the molten fuel salt 104.

[0049] The transfer of heat from the molten fuel salt 104 can be realized in various ways. For example, the heat exchange unit 106 can include a pipe 108, through which the heated molten fuel salt 104 travels, and a secondary fluid 110 (e.g., a coolant salt) that surrounds the pipe 108 and absorbs heat from the molten fuel salt 104. Upon heat transfer, the temperature of the molten fuel salt 104 can be reduced in the heat exchange unit 106 and the molten fuel salt 104 can be transported from the heat exchange unit 106 back to the molten salt reactor 102. The system 100 can also include a secondary heat exchange unit 112 configured to transfer heat from the secondary fluid 110 to a tertiary fluid 114 (e.g., water), as the secondary fluid 110 can be circulated through secondary heat exchange unit 112 via a pipe 116.

[0050] The heat received from the molten fuel salt 104 can be used to generate power (e.g., electric power) using any suitable technology. For example, when the tertiary fluid in the secondary heat exchange unit 112 can be heated to a steam and transported to a turbine 118. The turbine 118 is can be turned by the steam and drive an electrical generator 120 to produce electricity. Steam from the turbine 118 can be conditioned by an ancillary gear 122 (e.g., a compressor, a heat sink, a pre-cooler, and a recuperator) and it can be transported back to the secondary heat exchange unit 112.

[0051] Additionally, or alternatively, the heat received from the molten fuel salt 104 can be used in other applications such as nuclear propulsion (e.g., marine propulsion), desalination, domestic or industrial heating, hydrogen production, or a combination thereof.

[0052] Additionally, or alternatively, transfer of heat from the molten fuel salt 104 occurs via the heat removal system described in greater detail herein, which can be used as a means of drawing heat from the molten salt reactor 102 and the molten fuel salt 104 both during operation of the molten salt reactor 102 and during a shutdown of the molten salt reactor 102. Thus, in addition, or alternatively, to transfer of heat via the heat exchange unit 106, the heat removal system can be used to efficiently draw heat away from the reactor core to maintain a constant temperature within the core within acceptable levels while the molten salt reactor 102 can be operating and, in the event that the reactor is shutdown, the heat removal system can be configured to continue functioning to manage the transfer of decay heat released from molten fuel salt 104.

[0053] During the operation of the molten salt reactor 102, fission products can be generated in the molten fuel salt 104. The fission products will include a range of elements. The fission products can include, but are not limited to, rubidium (Rb), strontium (Sr), cesium (Cs), and barium (Ba), an element selected from lanthanides, palladium (Pd), ruthenium (Ru), silver (Ag), molybdenum (Mo), niobium (Nb), antimony (Sb), technetium (Tc), xenon (Xe), or krypton (Kr).

[0054] The buildup of fission products (e.g., radioactive noble metals and radioactive noble gases) in the molten fuel salt 104 can impede or interfere with the nuclear fission in the molten salt reactor 102 by poisoning the nuclear fission. For example, xenon- 135 and samarium- 149 have a high neutron absorption capacity, and can lower the reactivity of the molten salt. Fission products can also reduce the useful lifetime of the molten salt reactor 102 by clogging components, such as heat exchangers or piping.

[0055] Therefore, it can be desirable to keep concentrations of fission products in the molten fuel salt 104 below certain thresholds to maintain proper functioning of the molten salt reactor 102. This goal can be accomplished by a chemical processing plant 124 configured to remove at least a portion of fission products generated in the molten fuel salt 104 during nuclear fission. During operation, molten fuel salt 104 can be transported from the molten salt reactor 102 to the chemical processing plant 124, which can processes the molten fuel salt 104 so that the molten salt reactor 102 functions without loss of efficiency or degradation of components.

[0056] In certain embodiments, the system 100 can also include an actively cooled freeze plug 126. The freeze plug 126 can be configured to allow the molten fuel salt 104 to flow into a set of emergency dump tanks 128 in case of power failure and/or on active command.

[0057] FIG. 2 shows additional detail of the chemical processing plant 124. During a typical state of reactor operation, the molten fuel salt 104 can be circulated continuously (or near- continuously) by way of the pump 202 from the molten salt reactor 102 through one or more of the functional sub-units of the chemical processing plant 124. As discussed below, examples of the sub-units can include, but are not limited to, a corrosion reduction unit 204, a froth floatation unit 206, and a salt exchange unit 208.

[0058] In an embodiment, the corrosion reduction unit 204 can be configured to limit or reduce the corrosion of the molten salt reactor 102 by the molten fuel salt 104. The molten salt reactor 102 can be constructed of metallic alloy including one or more of the following elements: iron (Fe), nickel (Ni), chromium (Cr), manganese (Mn), carbon (C), silicon (Si), niobium (Nb), titanium (Ti), vanadium (V), phosphorus (P), sulfur (S), molybdenum (Mo), nitrogen (N), any of the cermet alloys, or a variant thereof, stainless steels (austenitic stainless steel), or a variant thereof, zirconium alloy, or a variant thereof, or tungsten alloy, or a variant thereof.

[0059] During reactor operation, the molten fuel salt 104 can be transported from the molten salt reactor 102 to the corrosion reduction unit 204 and from the corrosion reduction unit 204 back to the molten salt reactor 102. The transportation of the molten fuel salt 104 can be driven by pump 202, which can be configured to adjust the rate of transportation. The corrosion reduction unit 204 can be configured to process the molten fuel salt 104 to maintain an oxidation reduction (redox) ratio, E(o)/E(r), in the molten fuel salt 104 in the molten salt reactor 102 (and elsewhere throughout the system 100) at a substantially constant level, where E(o) is an element (E) at a higher oxidation state (o) and E(r) is that element (E) at a lower oxidation state (r).

[0060] In one embodiment, the element (E) can be an actinide (e.g., uranium (U)), E(o) can be U(IV) and E(r) can be U(III). In this embodiment, U(IV) can be in the form of uranium tetrachloride (UC1 ₄ ), U(III) can be in the form of uranium trichloride (UCI ₃ ), and the redox ratio can be a ratio E(o)/E(r) of UCI ₄ /UCI ₃ . Although UCI ₄ can corrode the molten salt reactor 102, the existence of UCI ₄ can reduce the melting point of the molten fuel salt 104.

Therefore, the level of the redox ratio, UCI ₄ /UCI ₃ , can be selected based on at least one of a desired corrosion reduction and a desired melting point of the molten fuel salt 104. For example, the redox ratio can be at a substantially constant ratio selected between about 1/50 to about 1/2000. More specifically, the redox ratio can be at a substantially constant level of about 1/2000. [0061] The froth flotation unit 206 can be configured to remove at least part of insoluble fission products and/or dissolved gas fission products from the molten fuel salt 104.

Examples of insoluble fission products can include one or more of the following, in any combination: krypton (Kr), xenon (Xe), palladium (Pd), ruthenium (Ru), silver (Ag), molybdenum (Mo), niobium (Nb), antimony (Sb), and technetium (Tc). Examples of gas fission products can include one or more of xenon (Xe) and krypton (Kr). As an example, the froth flotation unit 206 can generate froth from the molten fuel salt 104 that includes the insoluble fission products and/or the dissolved gas fission products. The dissolved gas fission products can be removed from the froth, and at least a portion of the insoluble fission products can be removed by filtration.

[0062] The salt exchange unit 208 which can be configured to remove at least a portion of the soluble fission products dissolved in the molten fuel salt 104. Examples of the soluble fission products can include one or more of the following, in any combination: rubidium (Rb), strontium (Sr), cesium (Cs), barium (Ba), and lanthanides. The removal of soluble fission products can be realized through various mechanisms.

[0063] FIG. 3 schematically illustrates an embodiment of a molten salt reactor 102 configured for use with the molten salt reactor system 100. As shown, the molten salt reactor 102 can include a primary vessel 300 having a primary vessel wall 302. The primary vessel wall 302 can include one or more layers or can be formed from one or more materials, as will be described herein. For example, the primary vessel wall 302 can include an outer surface 304 and the inner surface 306. The primary vessel wall 302 can further be formed from one or more layers of different materials.

[0064] As will be described in greater detail herein, the primary vessel 300 can form part of a heat removal system of the present disclosure. For example, the heat removal system can include a two-vessel configuration, including a primary vessel (e.g., the primary vessel 300) and a secondary vessel 400 surrounding the primary vessel 300. The secondary vessel 400 can include a secondary vessel wall 402 having an outer surface 404 and an inner surface 406. Accordingly, when the primary vessel 300 and the secondary vessel 400 are assembled with one another, as shown, the outer surface 304 of the primary vessel wall 302 can face the inner surface 406 of the secondary vessel and a gap can be formed between the primary vessel wall 302 and the secondary vessel wall 402, in which heat transfer can occur for drawing heat in a direction away from the molten salt reactor 102 to prevent the reactor from rising to unacceptable levels.

[0065] The molten salt reactor 102 can further include a reactor core 308, which can include the reactor core portion 310 of the molten salt reactor 102 containing the nuclear fuel components where the nuclear reactions take place and the heat can be generated. The molten salt reactor 102 can further include one or more neutron reflectors 312 to elastically scatter neutrons during a fission reaction. In some cases, a control rod 314 can be lowered into the reactor core 308 to help initiate nuclear fission. In some embodiments, the molten salt reactor 102 can also include a neutron absorber 316 configured to function to confine fission products within the molten salt reactor 102.

[0066] While the molten salt reactor system 100 is shown in FIG. 1 as having one primary heat exchanger, multiple heat exchangers can be used. For example, FIG. 3 shows the molten salt reactor 102 including two heat exchangers 318. During use, one or more pumps 320 circulate the molten fuel salt 104 along paths within the primary vessel 300 (as indicated by arrows 322a-322e). For example, the molten fuel salt 104 can be pumped through and out of the heat exchangers 318 (indicated by arrow 322a), at which point the fuel salt flows through a channel defined between the inner surface 306 of the primary vessel wall 302 and the neutron reflector 312 (indicated by arrow 322b), then flows into and through the reactor core 308 (indicated by arrows 322c and 322d, respectively) and through a channel 324 before returning to the heat exchangers 318.

[0067] FIG. 4 is a side view of an embodiment of the molten salt reactor 102 including a heat removal system of the present disclosure. FIG. 4 illustrates the assembly of the primary vessel 300 and the secondary vessel 400 relative to one another. As shown, the secondary vessel 400 can at least a portion of, if not all, the primary vessel 300 and it can be configured to draw heat from the primary vessel 300 to assist in the heat removal process for preventing the molten salt reactor 102 (e.g., the reactor core 308 and the molten fuel salt 104), from reaching unacceptable temperatures.

[0068] FIG. 5 is an enlarged perspective view of one embodiment of a primary vessel 300. As shown, a primary vessel wall 302a can be formed from one or more layers having different materials. For example, the primary vessel wall 302a can include a first layer 326 generally forming the inner surface 306 of the wall 302a and a second layer 328 forming the outer surface 304 of the wall 302a. The first layer 326 can include a high nickel alloy (e.g.,

®

HASTELLOY N), or any other suitable material such as a molybdenum alloy (e.g., titanium-zirconium-molybdenum (TZM)) or 316FR steel. The second layer 328 can include a steel composition, such as austenitic stainless steel or a high-Cr martensitic steel (e.g., HT-9).

[0069] As shown, the outer surface 304 of the primary vessel wall 302a (i.e., the outer surface of the second layer 328) can include a set of the fins 330 extending therefrom in an outward direction away from the primary vessel wall 302a. The fins 330 can be can extend in a direction substantially parallel with a longitudinal axis X of the primary vessel wall 302a. Accordingly, when assembled, the fins 330 can be characterized as vertical fins in that they have a vertical orientation relative to the ground or horizon. The vertical fins 330 can extend along an entire length of the wall 302a or can extend only along a portion of the length of the wall 302a. The outer surface can also include at least one void 332 defined between two adjacent fins 330, such that the fins 330 and the voids 332 are arranged in an alternating pattern along the outer surface.

[0070] FIG. 6 is a cross-sectional view of an embodiment of a heat removal system including the primary vessel 300 shown in FIG. 5 assembled with a corresponding secondary vessel 400, taken along lines 6-6 of FIG. 4. As shown, the secondary vessel wall 402a can include a single layer including one or more materials configured to draw heat from the primary vessel wall 302a in a manner described in greater detail herein. For example, the secondary vessel wall 402a can include a steel composition, such as an austenitic stainless steel or a high-Cr martensitic steel (e.g., HT-9). In some embodiments, the secondary vessel wall 402a can include a molten salt configured to receive heat from the primary vessel wall 302a.

[0071] As shown, the inner surface of the secondary vessel wall 402a can include a set of the fins 408 extending therefrom in an inward direction toward the primary vessel wall 302a. The inner surface further includes voids 410 defined between adjacent fins 408, such that the fins 408 and voids 410 can alternate with one another along the inner surface of the vessel wall 402a.

[0072] The fins 408 can be arranged in a similar fashion as the fins 330 of the primary vessel wall 302a. In particular, the fins 408 can share the same orientation as the fins 330, such that, when the primary vessel 300 and the secondary vessel 400 are assembled with one another, the first and second sets of the fins 330, 408 can be generally interdigitated, or interleaved, with one another. For example, the fins 330 of the primary vessel wall 302a can be positioned within corresponding voids 410 of the second vessel wall 402a and fins 408 of the secondary vessel wall 402a can be positioned within corresponding voids 332 of the primary vessel wall 302a. However, when assembled, the primary vessel 300 and the secondary vessel 400 can avoid direct contact with one another. In other words, the first and second sets of the fins 330, 408 do not make contact with each other or with corresponding voids 332, 410. Rather, a continuous gap 500, or channel, can be formed between the vessel walls 302a, 402a. As will be described in greater detail herein, the gap 500 can be configured in such as manner to provide radiative heat transfer between the first set of the fins 330 and the second set of the fins 408 to effectively draw heat away from the molten salt reactor 102 and prevent the molten salt reactor 102 from rising to unacceptable temperatures.

[0073] FIG. 7 is an enlarged cross-sectional view of the primary vessel 300 and the secondary vessel 400 that illustrates the interdigitated, or interleaved, arrangement of the fins 330, 408 of the primary and secondary vessel walls 302a, 402a. As shown, for example, a first fin 330(1) of the primary vessel wall 302a can be positioned within a void 410 defined between adjacent first and second fins 408(1) and 408(2) of the secondary vessel wall 402a. Accordingly, the primary and secondary vessel walls 302a, 402a can include the same number of the fins and voids to achieve the interdigitated, or interleaved, arrangement shown.

[0074] The primary vessel wall 302a can be configured to receive heat generated within the molten salt reactor 102, either as a result of nuclear fission within the reactor core 308 or decay heat released from radioactive decay of the molten fuel salt 104. The gap 500 formed between the primary and secondary vessel walls 302a, 402a can serves as a radiative heat gap configured to assist in radiative transfer of heat from the first set of the fins 330 of the primary vessel wall 302a to the second set of the fins 408 of the secondary vessel wall 402a. For example, in some embodiments, the gap 500 can be hermetically sealed and it can be configured to receive a medium to assist or enhance thermal radiation between the first and second sets of the fins 330, 408. In some embodiments, medium can be nitrogen. In other embodiments, the medium can be a fluid selected to boil in response to the radiative heat (e.g., NaCL-AlC ). The energy created in the boiling medium can be captured via transfer to a second energy absorption medium positioned externally to the primary vessel. The energy or heat exchange is, or can be, captured by a convention heat transfer mechanism, such as a heat exchanger, where energy from one fluid can be transferred to another fluid of a lower energy through a shell and tube design, for example. In this instance, the heat energy can be transferred by convection through a metallic medium which usually can be the "tube" metal inside a heat exchanger.

[0075] The radiative heat transfer can include the transfer of energy by emission of electromagnetic radiation (as illustrated by broken line arrows) from the first set of the fins 330 to the second set of the fins 408 across the gap 500. In turn, the fins 408 of the secondary vessel 402 can be configured to absorb the energy, thereby drawing heat away from fins 330 of the primary vessel wall 302. In some embodiments, an additional buffer material or layer can surround, or can be in contact with, an exterior surface of the secondary vessel 400 to further absorb heat from the secondary vessel 400 (e.g., via convection, conduction, etc.) and further dissipate heat.

[0076] Embodiments of the heat removal system of the present disclosure can be

configurable depending on the specific application and the amount of heat removal desired. For example, the arrangement of the first and second sets of the fins 330, 408 of the primary vessel wall 302 and the secondary vessel wall 402, respectively, can influence an amount of heat that can be transferred. In particular, an amount of heat that can be transferred from the primary vessel wall 302 to the secondary vessel wall 402 can be dependent, in part, on a surface area of the fins 330, 408. Thus, the fins 330, 408 can be tunable to have a specific surface area for transfer of a desired amount of heat. For example, for a given reactor system, there can be an acceptable range of temperatures in which the reactor core can operate (e.g., approximately 650°C or 1,200°F). The physical dimensions of the fins 330, 408 (e.g., length and width), the number of the fins 330, 408, as well as the orientation of the fins 330, 408, can be customized such that protrusion arrangement results in an amount of heat transfer sufficient to maintain the operating temperature of the reactor core 308 within a selected acceptable temperature range. Thus, as shown in FIGS. 5-7, the fins 330, 408 can be formed along the primary and the secondary vessel walls 302a, 402a in a vertical orientation.

However, other dimensions, orientations, arrangements, and the like are contemplated herein.

[0077] For example, FIG. 8 is an enlarged perspective view of another embodiment of a primary vessel wall 302b illustrating fins 330 arranged in a helical pattern. FIG. 9 is a cross- sectional view of the primary vessel 302b and the secondary vessel wall 402b assembled with one another, as taken along lines 9-9 of FIG. 4. As shown, the fins 330 can be arranged in a horizontal orientation when the primary vessel wall 302b is positioned and assembled with the secondary vessel wall 402b. The fins 408 of the secondary vessel wall 402b can be arranged in a similar helical pattern, such that, during assembly, the primary and the secondary vessel walls 302b, 402b can be assembled in a threaded engagement, similar to a nut and bolt arrangement. As an example, the vessel walls 302b, 402b can be rotated relative to one another to thread and advance the helical fins 330, 408 within the voids 332, 410.

[0078] Embodiments of the heat removal system of the present disclosure can be configured to function both during operation of the reactor and during a shutdown of the molten salt reactor 102. Accordingly, the heat removal system can be configured to efficiently draw heat away from the reactor core to maintain a constant temperature within the core within acceptable levels. Because the heat removal system can utilize radiative heat transfer, the heat removal system can be configured to continue functioning in the event that there is a reactor shutdown without requiring a power source. For example, the heat removal system can be configured to continue drawing heat from the reactor following a shutdown, wherein the heat can be in the form of decay heat released from molten salt fuel.

[0079] In this manner, embodiments of the disclosed heat removal system can overcome the drawbacks of current emergency backup cooling systems, which can rely on power sources to deal with decay heat. Furthermore, radiative heat transfer can provide a much more efficient means of heat removal, in that the amount of energy transferred over a period time can be much greater than other heat transfer modes, such as convection or conduction. Thus, embodiments of the heat removal system of the present disclosure can provide a much more efficient and quicker means of removing heat, and can thereby reduce the risk of temperature in the reactor rising to unacceptable levels and reducing the chance of catastrophic failure (e.g., breakdown of vessel wall and contamination of surrounding environment).

[0080] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. [0081] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications are possible within the scope of the claims. Accordingly, the claims are intended to cover all such equivalents.

Incorporation by Reference

[0082] References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes.

Equivalents

[0083] Various modifications of the disclosed embodiments and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification and guidance that can be adapted to the practice of the disclosed

embodiments and equivalents thereof.