WO2018026429A2

WO2018026429A2 - Split shield assembly for a reactor system

Info

Publication number: WO2018026429A2
Application number: PCT/US2017/034636
Authority: WO
Inventors: Andrew Mccall DODSON
Original assignee: Elysium Industries Ltd
Current assignee: Elysium Industries Ltd
Priority date: 2016-05-26
Filing date: 2017-05-26
Publication date: 2018-02-08
Anticipated expiration: 2018-11-26
Also published as: WO2018026429A3

Abstract

A split shield assembly for use in molten salt reactor (MSR) system can limit the occurrence of a fission reaction to the reactor core while also shielding the ambient environment from receiving inadvertent exposure to a fission reaction or fission products.

Description

SPLIT SHIELD ASSEMBLY FOR A REACTOR SYSTEM

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/341,649, filed on May 26, 2016, and entitled "Split Shield Assembly For A 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 split shield assembly for use in a molten salt reactor (MSR) system for limiting the occurrence of a fission reaction to the reactor core while preventing, or otherwise shielding, the ambient environment from receiving inadvertent exposure a fission reaction or fission products.

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 so as 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 fission reactions within the reactor core. In particular, during a reaction, neutrons may leak from the core and cause negative impact to surrounding structures, including the vessel wall. Accordingly, the reactor vessel wall may have a limited lifetime due to neutron fluence with both thermal and fast neutrons due to neutron leakage, which can weaken and damage the wall over time and potentially result in a reactor failure.

SUMMARY

[0006] Embodiments of the present disclosure provide a split shield assembly for use as a moderator in a molten salt reactor (MSR) system. The split shield assembly can help to manage fission reactions within the MSR system by preventing additional or inadvertent fission within the molten fuel salt. In other words, the split shield assembly can limit fission reactions to the reactor core while also shielding an outer wall of a reactor vessel from fission products. By shielding the outer wall of the reactor vessel, the split shield assembly can also help to shield the ambient environment.

[0007] In particular, the split shield assembly can shield other reactor components surrounding the reactor core from excessive neutron flux by absorbing and reflecting fast neutrons from the reactor core before the fast neutrons can reach the other reactor components. By reducing vessel damage caused by fast neutrons, such as helium embrittlement, the risk of a catastrophic accident (e.g., breakdown of the vessel wall and contamination of surrounding environment) can also be reduced. Accordingly, the split shield assembly of the present disclosure can improve the useful life of the reactor.

[0008] The split shield assembly can include a two-shield configuration configured for placement within a reactor vessel. The assembly can include a first shield coupled along a periphery of an inner vessel wall and it can include a thermal barrier layer positioned

immediately there between. The assembly can include a second shield positioned adjacent to a reactor core within the vessel and distanced away from, and opposing, the first shield such that a channel for receiving a flow of molten fuel salt can be formed between the first and second shields. The first and second shields can be composed of a radiation-tolerant or radiation- resistant material. As discussed in greater detail below, the first shield can be configured to moderate or absorb fast neutron products from flowing molten fuel salt while the second shield can be configured to reflect fast neutrons back towards the reactor core. In this manner, occurrence of fission reactions can be limited to the reactor core during flow of the molten fuel salt.

[0009] The split- shield configuration can also enable one of the shields to also function as a flow- separator or divider within the reactor system. This configuration can help to tune the flow parameters based on the desired application. For example, the reactor system can include one or more pumps configured to circulate fuel salt along flow paths, generally flowing downward along the vessel walls and upwards into the reactor core. The downward flow path of the fuel salt can be defined by the channel formed between the first and second shields. As fuel salt is circulated, fast neutrons from the reactor core, or other fission products (e.g., delayed neutrons), can be reflected by the second shield and they can be prevented from entering the channel between the first and second shields, thereby restricting the fission reaction to taking place in the core, as opposed to other areas within the reactor vessel. The first shield can be configured to moderate and/or absorb fast neutrons, thereby shielding the vessel wall from contact with additional fast neutrons from the fuel salt flowing within the channel. Accordingly, the split shield assembly can be configured to prevent the vessel wall from receiving inadvertent exposure to fission products or potential fission reaction, thereby improving the useful life of the vessel wall and reducing the potential risk of a catastrophic accident (e.g., breakdown of the vessel wall and contamination of surrounding environment).

[0010] The split shield assembly of the present disclosure can be configured to confine, or otherwise limit, the fission reaction to occur within the reactor core while reducing neutron flux in the ambient environment (e.g., outside of the vessel). Thus, the split shield assembly can replace the typical bulk moderators used in current reactors (e.g., LWRs, MSRs, etc.), such as, for example, regular (light) water, solid graphite, and heavy water, which have significant drawbacks. For example, graphite can have a limited lifetime in the core which can forced designers to either propose very low power density and thus very large cores, or to plan for periodic graphite replacement which is a difficult challenge. Furthermore, graphite use represents a significant disposal issue. The split shield assembly of the present disclosure can significantly reduce the complexity of design and operation, and can further have a longer lifespan, as compared to a graphite moderator, which can require replacement on a more frequent basis. This can help to extend the lifespan of the moderator because the useful life of graphite is limited to the local power density of the reactor. The reduced neutron flux at the wall (periphery) can also provide loss of far fewer neutrons to leakage, which can improve the conversion and/or breeding ratio.

[0011] In one embodiment, a split shield assembly is provided for a reactor system and can include a first shield and a second shield. The first shield can be configured to be coupled to an inner surface of a reactor vessel wall. The second shield can be configured to be positioned adjacent to a reactor core within the reactor vessel and positioned a distance away from, and opposing, the first shield such that a channel for receiving a flow of molten fuel salt is formed there between. Each of the first and second shields can be configured to absorb fast neutron products, from a molten fuel salt flowing in at least one of the channel between the first and second shields and the reactor core to thereby confine an occurrence of a fission reaction to the reactor core and shield an ambient environment from exposure to fission products.

[0012] The first and second shields can have a variety of configurations. In one aspect, each of the first and second shields can be formed from a radiation-tolerant or radiation-resistant material. In another aspect, at least one of the first and second shields is configured to reflect fast neutrons towards the reactor core. In another aspect, a thermal barrier layer can be interposed between the first shield and the inner surface of the reactor vessel wall.

[0013] In another embodiment, the first shield can have a thickness within the range between about 1 cm and about 10 cm. As an example, the first shield can have a thickness of about 5 cm.

[0014] In another embodiment, the second shield can have a thickness between the range between about 1 cm and about 15 cm. As an example, the second shield can have a thickness of about 5 cm.

[0015] In another embodiment, a distance between the first and second shields is approximately 5 cm. [0016] In one embodiment, a molten salt reactor system is provided and can include a vessel, a reactor core, a fuel salt, and a split shield assembly. The reactor core can be positioned within the vessel. The fuel salt can be configured to flow within the vessel and through the reactor core; and the split shield assembly can be positioned within the vessel and surround the reactor core. The split shield assembly can be configured to confine a fission reaction to the reactor core and is configured to shield ambient environment surrounding the reactor core from fission products.

[0017] In an embodiment, the split shield assembly can include a first shield and a second shield. The first shield can be coupled to an inner surface of a wall of the vessel. The second shield can be positioned adjacent to the reactor core within the vessel and positioned a distance away from, and opposing, the first shield such that a channel for receiving flow of fuel salt is formed there between. Each of the first and second shields can be configured to absorb fast neutron products, or other fission products, from fuel salt flowing in at least one of the channel between the first and second shields and the reactor core to thereby confine an occurrence of a fission reaction to the reactor core and shield an ambient environment from exposure to fission products.

[0018] Embodiments of the first and second shields can have a variety of configurations.

In one aspect, each of the first and second shields can be formed from a radiation-tolerant or radiation-resistant material. In another aspect, a thermal barrier layer of material can be positioned immediately between the first shield and the inner surface of the vessel wall.

[0019] In another embodiment, the first shield can have a thickness within a range between about 1 cm and about 10 cm. As an example, the first shield can have a thickness of about 5 cm.

[0020] In another embodiment, the second shield can have a thickness with a range between about 1 cm and about 15 cm. As an example, the second shield has a thickness of about 5 cm.

[0021] In another embodiment, a distance between the first and second shields can be about 5 cm. [0022] In one embodiment, a split shield assembly for a reactor system is provided and can include a first shield, a second shield, and a fuel-salt channel. The first shield can be positioned adjacent to an inner surface of a reactor vessel having a reactor core. The second shield can be positioned adjacent to the reactor core and opposite from the first shield. The fuel- salt channel can be between the first shield and the second shield and in fluid communication with the reactor core. The first shield and the second shield can be configured to reduce fission products within the fuel-salt channel.

[0023] Embodiments of the first and second shield can have a variety of configurations. In one aspect, the first shield and the second shield can be configured to reduce fission products by reducing a speed of fast neutrons within the fuel-salt channel. In another aspect, the first shield and the second shield can be configured to reduce fission products by absorbing fast neutrons. In a further aspect, the first shield and the second shield can be configured to reduce fission products by reflecting fast neutrons.

[0024] In another embodiment, the fuel- salt channel can be configured to receive a circulating fuel salt.

[0025] In another embodiment, the first shield can be non-structural.

[0026] In another embodiment, the first and second shields can be coupled to a closure head of the reactor vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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:

[0028] FIG. 1 is a schematic diagram depicting a molten salt reactor system consistent with the present disclosure.

[0029] FIG. 2 is a schematic diagram depicting the chemical processing plant of the molten salt reactor system of FIG. 1 in greater detail. [0030] FIG. 3 schematically illustrates the components of a molten salt reactor compatible with the system of FIG. 1.

[0031] FIG. 4 is an enlarged cross-sectional view of a portion of the molten salt reactor of FIG. 3 illustrating the split shield assembly in greater detail.

[0032] FIG. 5 is a schematic illustration of another embodiment of a split shield assembly configured for use with the molten salt reactor system of FIG. 1.

[0033] 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 may suggest or render expedient.

DETAILED DESCRIPTION

[0034] Embodiments of the present disclosure provide a split shield assembly that can be used as a moderator in a molten salt reactor (MSR) system. The split shield assembly can help to manage fission reactions within the MSR system by preventing additional or inadvertent fission within the molten fuel salt. In other words, the split shield assembly can limit fission reactions to the reactor core while also shielding an outer wall of a reactor vessel from fission products. By shielding the outer wall of the reactor vessel, the split shield assembly also helps to shield the ambient environment.

[0035] In particular, the split shield assembly can shield other reactor components surrounding the reactor core from excessive neutron flux by absorbing fast neutrons from the reactor core before the fast neutrons can reach the other reactor components. By reducing vessel damage caused by fast neutrons, the risk of a catastrophic accident (e.g., breakdown of the vessel wall and contamination of surrounding environment) can also be reduced. Accordingly, the split shield assembly of embodiments of the present disclosure can improve the useful life of the reactor. [0036] The split shield assembly can include a two-shield configuration configured to be placed within a reactor vessel. The assembly can include a first shield coupled along a periphery of an inner vessel wall and it can include a thermal barrier layer positioned immediately there between. The assembly can include a second shield positioned adjacent to a reactor core within the vessel. The second shield can be distanced away from, and opposing the first shield such that a channel for receiving a flow of a molten fuel salt is formed between the first and second shields. The first and second shields can be composed of a radiation-tolerant or radiation-resistant material and can be configured to moderate fast neutron products from flowing molten fuel salt so as to limit the occurrence of a fission reaction to the reactor core during flow of the fuel salt.

[0037] The split- shield configuration can also enable one of the shields to also function as a flow- separator or divider within the reactor system. This can help to tune the flow parameters based on the desired application. For example, the reactor system can include one or more pumps configured to circulate fuel salt along flow paths, generally flowing along the vessel walls (e.g., downward) and into the reactor core (e.g., upwards). As an example, a downward flow path of the fuel salt can be defined by a channel formed between the first and second shields. When a fuel salt is circulated, fast neutrons from the reactor core, or other fission products, can be absorbed by the second shield and prevented from entering the channel between the first and second shields, thereby restricting the fission reaction to taking place in the core, as opposed to other areas within the reactor vessel. The first shield can be configured to absorb and shield the vessel wall from contact with any additional fast neutrons from the fuel salt flowing within the channel.

[0038] Accordingly, the split shield assembly can be configured to prevent the vessel wall from receiving inadvertent exposure to fission products or potential fission reaction, thereby improving the useful life of the vessel wall and reducing the potential risk of a catastrophic accident (e.g., breakdown of the vessel wall and contamination of surrounding environment).

[0039] As described herein, a split shield assembly of the present disclosure can be configured for use in a fast-spectrum molten-salt reactor (FS-MSR). An FS-MSR, also sometimes referred to as a "fast neutron reactor" or simply a "fast reactor," can include nuclear reactors in which the fission chain reaction can be sustained by fast neutrons, as opposed to slow, or thermal, neutrons used in a thermal reactor. The term "thermal" can refer to a thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and structure, which can be at a much lower energy than the fast neutrons initially produced by fission. Thermal reactors can rely on a neutron moderator for reducing the speed of neutrons so as to make them capable of sustaining a nuclear chain reaction. The moderator can slow neutrons until they approach the average kinetic energy of the surrounding particles (i.e., reducing the speed of the neutrons to low velocity thermal neutrons), thereby remaining uncharged and allowing them to penetrate deep in the target and close to the nuclei. Fast reactors, however, can avoid the requirement of a neutron moderator, but can also use fuel that is relatively rich in fissile material when compared to that required for a thermal reactor.

[0040] 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 containing the molten fuel salt 104, which can include a mixture of chloride and fluoride salts. The molten fuel salt 104 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), 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,

2 "32"ThCl₄, 2 "3^J8^OUCl₃ and 2 "3^J8^OUCl₄. In an embodiment, the molten fuel salt 104 can include a mixture of fissile materials including ²³³UC1₃, ²³⁵UC1₃, ²³³UC1₄, ²³⁵UC1₄, and ²³⁹PuCl₃; and carrier salts including sodium chloride (NaCl), potassium chloride (KC1), and/or calcium chloride (CaCl₂).

[0041] 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 (shown in FIG. 3) 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. [0042] 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 is circulated through secondary heat exchange unit 112 via a pipe 116.

[0043] The heat received from the molten fuel salt 104 may be used to generate power (e.g., electric power) using any suitable technology. For example, when the tertiary fluid 114 in the secondary heat exchange unit 112 is water, it can be heated to a steam and transported to a turbine 118. The turbine 118 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.

[0044] 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.

[0045] During the operation of the molten salt reactor 102, fission products can be generated in the molten fuel salt 104. The fission products can 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).

[0046] 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 can 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.

[0047] 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 process the molten fuel salt 104 so that the molten salt reactor 102 functions without loss of efficiency or degradation of components.

[0048] 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.

[0049] 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 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.

[0050] 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.

[0051] 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 canbe 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).

[0052] 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 (UC1₄), U(III) can be in the form of uranium trichloride (UC1₃), and the redox ratio can be a ratio E(o)/E(r) of UC /UCI₃. Although UC1₄ can corrode the molten salt reactor 102, the existence of UC1₄ can reduce the melting point of the molten fuel salt 104. Therefore, the level of the redox ratio, UCVUCI₃, 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.

[0053] 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.

[0054] The salt exchange unit 208 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. [0055] 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 vessel 300 having a vessel wall 302. The vessel wall 302 can include one or more layers or can include one or more materials, as will be described herein. For example, the vessel wall 302 can include an inner surface 304 formed from a first material and an intermediate surface or layer 306 (e.g., a gamma shield) formed from at least a second material, and an outer surface formed from a third material. The third material can be different than or the same as the first and/or second materials.

[0056] As shown in FIG. 3, the molten salt reactor 102 can also include a reactor core 308. The reactor core 308 can include a reactor core portion 310 configured to contain nuclear fuel components where the nuclear reactions take place and where heat is generated.

[0057] The molten salt reactor 102 can also include one or more neutron reflectors 312. The neutron reflectors can be configured to elastically scatter neutrons during fission reactions occurring within the reactor core 308. In some cases, a control rod 314 can be lowered into the reactor core 308 to help initiate nuclear fission.

[0058] The molten salt reactor 102 can also include a split shield assembly. As described in greater detail below, the split shield assembly can be configured for placement within the vessel 300 and it can function to confine and limit fission products within the reactor core 308, thereby limiting the occurrence of a fission reaction to the reactor core 308. The split shield assembly can also be configured to prevent, or otherwise shield, the vessel wall 302 from neutron damage.

[0059] As shown in FIG. 3, the split shield assembly can include a two-shield configuration, including a first shield 316 and a second shield 318. The first shield 316 can be coupled along a periphery of the inner surface 304 of the vessel wall 302 and can further include a thermal barrier layer 317 interposed between the vessel wall 302 and the first shield 316. The second shield 318 can be positioned adjacent to the reactor core 308, distanced from and opposing the first shield 316. So configured, the first and second shields 316, 318 can form a channel 319 for receiving a flow of molten fuel salt 104. The first and second shields 316, 318 can be composed of a radiation-tolerant and/or radiation-resistant material and they can be configured to absorb fast neutron products from flowing molten fuel salt 104. In this manner, the first and second shields 316, 318 can limit the occurrence of a fission reaction to the reactor core 308 during flow of molten fuel salt 104, as will be described in greater detail herein.

[0060] While the molten salt reactor system 100 is shown in FIG. 1 as having one primary heat exchanger, multiple heat exchangers can be used. As an example, FIG. 3 shows the molten salt reactor 102 including two heat exchangers 320. During use, pumps 322 can be configured to circulate a molten fuel salt 104 along paths within the vessel 300 (as indicated by arrows 324a- 324e). For example, a molten fuel salt 104 can be pumped through and out of the heat exchangers 320 (indicated by arrow 324a), at which point fuel salt 104 can flow through channel 319 defined between the first and second shields 316, 318 (indicated by arrow 324b).

Subsequently, fuel salt 104 can flow into and through the reactor core 308 (indicated by arrows 324c and 324d, respectively) and through a channel 326 before returning to the heat exchangers 320.

[0061] FIG. 4 is an enlarged cross-sectional view of a portion of the molten salt reactor 102 illustrating the split shield assembly in greater detail and the flow of a fuel salt 104 therethrough. As shown, the first shield 316 can be coupled adjacent to a periphery of the inner surface 304 of the vessel wall 302, including a thermal barrier layer 317 positioned immediately there between. The second shield 318 can be positioned adjacent to the reactor core 308 and generally opposing the first shield 316 so as to form the channel 319 there between.

[0062] The vessel wall 302 can be formed of a high nickel alloy such as HASTELLOY N, or any other suitable material such as molybdenum alloy TZM (titanium- zirconium-molybdenum alloy), or 316FR steel. The vessel wall 302 can further have a thickness (THKi) of approximately 3 cm. The first shield 316 can have a thickness (THK₂) between 1 and 10 cm. In some embodiments, the THK₂ of the first shield 316 may be approximately 5 cm. The second shield 318 can have a thickness (THK₃) between 1 and 15 cm. In some embodiments, the THK₃ of the second shield 318 can be approximately 5 cm or less. A distance D between the first and second shields 316, 318 can be approximately 5 cm. Thus, the channel 319 can have a width of approximately 5 cm.

[0063] When in use, a fuel salt 104 can circulate through the molten salt reactor 102 flow paths 324a-324e. As shown in FIG. 4, a fuel salt 104 can flow through channel 319 defined between the first and second shields 316, 318, respectively, as indicated by arrow 324b (e.g., downward). The first shield 316 can include a radiation-tolerant or radiation-resistant material configured to absorb fast neutrons from within fuel salt 104, as indicated by arrows 400. Similarly, as fuel salt 104 flows upward through the reactor core portion 310 (as indicated by arrow 324d), the second shield 318 can also include a radiation-tolerant or radiation-resistant material configured to absorb fast neutrons from within a fuel salt 104, as indicated by arrows 406. Additionally, or alternatively, in some embodiments, at least one of the first and second shields 316, 318 can be configured to reflect or repel fast neutrons. For example, an outer surface of the second shield 318 (e.g., a surface generally oriented in a direction facing towards the first shield 316 and vessel wall 302) can be configured to receive and reflect fast neutrons from a fuel salt 104 within the channel 319, as indicated by arrows 402 and 404, respectively. Accordingly, the split shield can function to absorb fast neutrons, or other fission products, from within a fuel salt 104 so as to prevent ambient environment outside of the reactor core 308 from being exposed to such products and further confining the fission reaction to take place within the reactor core 308, as opposed to other areas within the vessel 300.

[0064] Accordingly, the split shield assembly can be configured to limit the occurrence of a fission reaction to the reactor core 308 while preventing, or otherwise shielding, the ambient environment, including the vessel wall 302, from receiving inadvertent exposure a fission reaction or fission products. In particular, the split shield assembly can be configured to shield components surrounding the reactor core 308 from excessive neutron flux by absorbing fast neutrons from the reactor core 308, thereby reducing the potential neutron damage to the vessel wall 302 and thus reducing the potential risk of a catastrophic accident (e.g., breakdown of the vessel wall 302 and contamination of surrounding environment). Accordingly, the split shield assembly of embodiments of the present disclosure can further improve the useful life of the molten salt reactor 102 and it can allow for high power density applications.

[0065] FIG. 5 illustrates an alternative embodiment of a molten salt reactor 500 suitable for use with the molten salt reactor system 100. As shown, the molten salt reactor 500 can include the vessel 300 with a closure head 502 and a split shield assembly 504. The split shield assembly 504 can be similar to the split shield assembly discussed above with respect to FIGS. 3-4. As an example, the split shield assembly 504 can be dimensioned for receipt within the vessel 300, interposed between the vessel wall 302 and reactor core (not shown) and it can include two or more shields 506 having channels 319 therebetween for receipt of a flow of a molten fuel salt 104. So configured, the split shield assembly can shield the vessel wall 302 from exposure to fission products (e.g., soluble and insoluble fission products) that can flow with the molten fuel salt 104 and can contribute to helium embrittlement of the vessel wall 302. However, in contrast to the split shield assembly of FIGS. 3-4, the split shield assembly 504 can be secured to the closure head 502 rather than vessel wall 302. As an example, the split shield assembly 504 can be coupled to an upper ring 510 that is in turn coupled to an upper reflector 512 that is secured to the closure head 514. The upper reflector can be configured to shield control rods 514 from fast neutrons and reflect fast neutrons back towards the core. Thus, when the closure head 502 is removed from the vessel 300, the split shield assembly 504 can also be removed.

Beneficially, this arrangement can allow replacement of the split shield assembly 504 and further extend the life of the vessel 300.

[0066] 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 may be combined in any suitable manner in one or more embodiments.

[0067] 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

[0068] 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

[0069] 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 in its various equivalents thereof.

Claims

CLAIMS What is claimed is:

1. A split shield assembly for a reactor system, the split shield assembly comprising:

a first shield configured to be coupled to an inner surface of a reactor vessel wall; and a second shield configured to be positioned adjacent to a reactor core within the reactor vessel, the second shield positioned a distance away from, and opposing, the first shield such that a channel for receiving a flow of molten fuel salt is formed there between;

wherein each of the first and second shields is configured to absorb fast neutron products from a molten fuel salt flowing in at least one of the channel between the first and second shields and the reactor core to thereby confine an occurrence of a fission reaction to the reactor core and shield an ambient environment from exposure to fission products.

2. The split shield assembly of claim 1, wherein each of the first and second shields comprises a radiation-tolerant or radiation-resistant material.

3. The split shield assembly of claim 1, wherein at least one of the first and second shields is configured to reflect fast neutrons towards the reactor core.

4. The split shield assembly of claim 1, wherein a thermal barrier layer is interposed between the first shield and the inner surface of the reactor vessel wall.

5. The split shield assembly of claim 1, wherein the first shield comprises a thickness within the range between about 1 cm and about 10 cm.

6. The split shield assembly of claim 5, wherein the first shield has a thickness of about 5 cm.

7. The split shield assembly of claim 1, wherein the second shield comprises a thickness between the range between about 1 cm and about 15 cm.

8. The split shield assembly of claim 7, wherein the second shield has a thickness of about 5 cm.

9. The split shield assembly of claim 1, wherein the distance between the first and second shields is approximately 5 cm.

10. A molten salt reactor system comprising:

a vessel:

a reactor core positioned within the vessel;

a fuel salt configured to flow within the vessel and through the reactor core; and a split shield assembly positioned within the vessel and surrounding the reactor core, wherein the split shield assembly is configured to confine a fission reaction to the reactor core and is configured to shield ambient environment surrounding the reactor core from fission products.

11. The molten salt reactor system of claim 10, wherein the split shield assembly comprises: a first shield coupled to an inner surface of a wall of the vessel; and

a second shield positioned adjacent to the reactor core within the vessel, the second shield positioned a distance away from, and opposing, the first shield such that a channel for receiving flow of fuel salt is formed there between;

wherein each of the first and second shields is configured to absorb fast neutron products, or other fission products, from fuel salt flowing in at least one of the channel between the first and second shields and the reactor core to thereby confine an occurrence of a fission reaction to the reactor core and shield an ambient environment from exposure to fission products.

12. The molten salt reactor system of claim 11, wherein each of the first and second shields comprises a radiation-tolerant or radiation-resistant material.

13. The molten salt reactor system of claim 11, wherein a thermal barrier layer of material is positioned immediately between the first shield and the inner surface of the vessel wall.

14. The molten salt reactor system of claim 11, wherein the first shield comprises a thickness within a range between about 1 cm and about 10 cm.

15. The molten salt reactor system of claim 14, wherein the first shield has a thickness of about 5 cm.

16. The molten salt reactor system of claim 11, wherein the second shield comprises a thickness with a range between about 1 cm and about 15 cm.

17. The molten salt reactor system of claim 16, wherein the second shield has a thickness of about 5 cm.

18. The molten salt reactor system of claim 11, wherein the distance between the first and second shields is about 5 cm.

19. A split shield assembly for a reactor system, the split shield assembly comprising:

a first shield positioned adjacent to an inner surface of a reactor vessel having a reactor core;

a second shield positioned adjacent to the reactor core and opposite from the first shield; and

a fuel-salt channel between the first shield and the second shield and in fluid

communication with the reactor core,

wherein the first shield and the second shield are configured to reduce fission products within the fuel-salt channel.

20. The split shield assembly of claim 19, wherein the first shield and the second shield are configured to reduce fission products by reducing a speed of fast neutrons within the fuel- salt channel.

21. The split shield assembly of claim 19, wherein the first shield and the second shield are configured to reduce fission products by absorbing fast neutrons.

22. The split shield assembly of claim 19, wherein the first shield and the second shield are configured to reduce fission products by reflecting fast neutrons.

23. The split shield assembly of claim 19, wherein the fuel-salt channel further is configured to receive a circulating fuel salt.

24. The split shield assembly of claim 19, wherein the first shield is non-structural.

25. The split shield assembly of claim 19, wherein the first and second shields are coupled to a closure head of the reactor vessel.