Method and system for isotopic lithium separation

Abstract

A method and system for isotopically separating lithium-6 and lithium-7 from a mixture thereof. The method involves using molecular distillation with a heat exchange arrangement supplied by a nuclear reactor (1) to efficiently separate the isotopes. The system comprises a molecular distillation apparatus with a still (20), in combination with a nuclear reactor (1) equipped with a heat exchange arrangement to provide the required heat for the process.

Description

[0001] METHOD AND SYSTEM FOR ISOTOPIC LITHIUM SEPARATION

[0002] TECHNICAL FIELD

[0003] The disclosure relates to methods and systems for isotopic lithium separation of lithium-7 and lithium-6, in particular isotopic separation of lithium-7 and lithium-6 from naturally occurring lithium.

[0004] BACKGROUND

[0005] Naturally occurring lithium is a mixture of lithium-7 and lithium-6 in varying proportions due to the geological isotopic separation of the two, with the lithium-6 concentration varying roughly between 2% and 8%, with 5% being the norm.

[0006] Molten salt reactors utilizing lithium fluoride or chloride salts practically need to have highly enriched lithium-7 due to the large differences in the thermal capture neutron cross sections of lithium-6 and lithium-7, of 941 barn and 0.014 barn, respectively for thermal neutrons, and partly to minimize tritium production from neutron capture by lithium- 6.

[0007] Naturally occurring lithium has a thermal capture crosssection of roughly 65 barn, which is very high when compared to e.g. naturally occurring sodium, with a thermal capture cross-section of 0.5 barn, or naturally occurring potassium, with a thermal capture cross-section of 2 barn. For comparison 99.9% enriched lithium-7 (3N 7Li) has a thermal capture crosssection of 0.95 barn, 99.99% enriched lithium-7 (4N 7Li) has a thermal capture cross-section of 0.11 barn, and 99.999% enriched lithium-7 (5N 7Li) has a thermal capture crosssection of 0.02 barn. This means that 99.99% to 99.999% enriched lithium-7 (4-5N 7Li) is desired for the use of lithium in molten salt reactor salts.

[0008] Examples of lithium fluoride salt that can be used in molten salt reactor salts are 7LiF-BeF2, 7LiF-BeF2-UF4 , 7LiF-ThF4, 7LiF-ThF4 -UF4 , and 7LiF-ThF4-PuF3. Examples of lithium chloride salt that can be used in molten salt fast reactors are 7LiCl-KCl-UC13 , 7LiCl-UC13, 7LiCl-PuC13, 7LiCl-UC13- PuC13.

[0009] Highly enriched lithium-7 is especially important for thermal molten salt breeder reactors, which have the potential to scale much faster than other nuclear technologies given a constrained supply of fissile fuel. For scaling thermal molten salt breeder reactors to meet global energy demand in the coming decades, an annual enrichment capacity of lithium-7 of several tens of thousands of tonnes would be needed, which is a major challenge for scaling this type of reactor.

[0010] When lithium-6 captures a thermal neutron there is a high probability that it leads to tritium production. The production of tritium from lithium-6 is considered a radionuclide release hazard for nuclear reactors, while it is the goal in some fusion reactor blankets. Thus, nuclear (fission) reactors utilizing lithium need enriched lithium-7 while fusion reactors need enriched lithium-6, and the isotopic separation of lithium can serve both industries synergistically.

[0011] Examples of fluoride salts that can be used in fusion reactor blanket salts are 6LiF-BeF2 and 6LiF-7LiF-BeF2 , where the beryllium also serves as a neutron multiplier, and examples of molten metal alloys that can be used in fusion reactor blankets are Li, Li-Pb, and Li-Bi.

[0012] The predominant method for industrialized isotopic lithium separation is the COLEX process, which is a two-liquid-phase chemical exchange, between lithium hydroxide aqueous solution and a mercury-lithium amalgam, where lithium-6 has a slightly larger affinity for the mercury amalgam. The COLEX process involves large quantities of mercury and mercury compounds, which along with its high energy consumption makes the process unattractive for future isotopic lithium separation.

[0013] The COLEX process COLEX separation is a mercury-based chemical approach for isotopic separation of lithium-6 and lithium-7, with aqueous lithium hydroxide (LiOH) contacted with lithiummercury amalgam, exploiting greater affinity of lithium-7 than Lithium-6 for the element mercury. The COLEX separation process involves passing a counter-flow of an aqueous lithium hydroxide flow up and a lithium-mercury amalgam flows down through a series of exchange columns containing a cation exchange resin. Mercury drains the lithium-6 fraction preferentially, although lithium-7 primarily flows with the hydroxide. The amalgam is separated from the lithium (enriched with lithium-6) at the bottom of the column, and the mercury is recovered for subsequent use. The lithium-7 fraction is electrolyzed to release the lithium hydroxide solution at the top. The operating temperature, flow rate, and column length all affect the enrichment that can be achieved with this process . Facilities at Oak Ridge, Tennessee using the COLEX process were operated between 1955 and 1963 to generate the current US stockpiles of 6Li and 7Li.

[0014] The COLEX has several downsides, such as:

[0015] Toxicity of the large amounts of mercury involved.

[0016] Tendency of amalgams to decompose in aqueous solutions. Formation of dangerous mercury-containing waste High energy consumption.

[0017] Potentially disastrous environmental implications since a substantial amount of mercury is required (24 million pounds were used in the U.S. between 1955 and 1963) and many opportunities for leaks into the environment exist.

[0018] Many methods have been researched and developed for the isotopic separation of lithium, including two-liquid-phase chemical exchange, ion exchange resins, ion exchange membranes, laser absorption, thermal diffusion, electromigration, fractional crystallization, microalgal, and molecular distillation. While multiple of these methods have been shown to work, none of them has shown to be an economical replacement for the COLEX process.

[0019] Isotopic separation of lithium metal using molecular distillation has seen limited research, with only a handful of articles published in the late 1950s and early 1960s and was ultimately abandoned, one reason being the high the high energy requirements and high temperature requirements of the process . CN115193253 discloses a method and a device for separating isotopes 6Li and 7Li using molecular distillation. Based on the difference of the atomic mass of 6Li and 7Li, 6Li and 7 Li are separated by a thermal evaporation method. The method is characterized in that in a vacuum chamber, after natural metal lithium is heated and evaporated and lithium vapor is kept under a certain pressure and is subjected to heat balance, 6Li is mainly distributed at the upper part of the vacuum chamber, and 7Li is mainly distributed at the lower part of the vacuum chamber. The boundary of 6Li and 7Li vapor can be determined according to the content proportion of 6Li and 7Li in natural metal lithium, the temperature and the pressure. And a partition plate which can be inserted or withdrawn at any time as required is arranged at the vapor boundary of 6Li and 7Li. During heat balance, the partition plate is inserted, then 6Li and 7Li vapor f < n > is released into respective cooling containers to be cooled into solids, and a protective layer is added, so that separation of 6Li and 7Li is realized.

[0020] SUMMARY

[0021] It is an object to provide a method and system for isotopic lithium separation that overcomes or at least reduces the problems above.

[0022] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures . Lithium metal melts at 180°C and boils at 1330°C, so simple distillation seems unattractive due to the high boiling point of molten lithium and low separation factor at high temperatures. However, the inventor realized that at temperatures well below the boiling point of lithium, the separation factor is enough that efficient isotopic separation can be performed, due to the high molecular mass difference of molten lithium-6 and lithium-7. The difference in molecular mass between lithium-6 and lithium-7 is enough that a theoretical separation factor of 1.08 can be achieved, with the differences in vapor pressure being small in comparison .

[0023] For efficient molecular distillation, the mean free path length of a vapor atom or molecule has to be on the order of or longer than the distance between the evaporation and condensation surfaces. The mean free path length of the lithium atom will depend on the quality of the still's vacuum and lithium vapor pressure, which in turn depends on the temperature of the lithium. The mean free path length of lithium vapor is roughly 50mm at 400°C, 20mm at 500°C, and 15mm at 550°C. Due to the longer free path length at lower temperatures, it is generally more effective to run the molecular distillation at lower temperatures but the rate of distillation will also be lower due to the lower evaporation rate. Thus, a balance needs to be found between efficient distillation and distillation rate for a particular still. The inventor arrived at an optimum evaporation surface temperature of approximately around 500-600°C with the cold side approximately 100°C colder, i.e. approximately 400-500°C for lithium molecular distillation The inventor arrived at the insight that liquid short-path molecular distillation of lithium is attractive since it allows for multiple stages which can have a very short path between the evaporating and condensing surfaces. Furthermore, the inventors arrived at the insight that the still can be constructed using commonly available materials and manufacturing methods since molten lithium is compatible with regular stainless steel, However, this type of stills needs simultaneous heating of the bottom of the still while cooling the top of the still at each stage, rendering it energy intensive .

[0024] According to a first aspect, there is provided a method of isotopically separating lithium-6 and lithium-7 from a mixture thereof, the method comprising:

[0025] - isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream by molecular distillation of the feed stream of molten lithium metal feed material, using a molecular distillation apparatus comprising a still or a series of stills,

[0026] - heating a heat exchange medium with a nuclear reactor to a temperature of at least 400 °C, and

[0027] - supplying the heated heat exchange medium to the molecular distillation apparatus.

[0028] By providing the heat for the molecular distillation process with a nuclear reactor, the, as such, very energy-intensive nuclear distillation process becomes less expensive due to the readily available and relatively inexpensive high temperature heat from the nuclear reactor, thereby substantially reducing the cost for molecular distillation, thereby rendering molecular distillation economically competitive with other known isotopic lithium separation methods .

[0029] According to a possible implementation form of the first aspect, the nuclear reactor is one of:

[0030] - a gas-cooled reactor preferably a high-temperature gas-cooled reactor (HTGR) or a very-high-temperature reactor VHTR,

[0031] - a liquid metal cooled reactor (LMR) ,

[0032] - a heat pipe cooled reactor (HPR) ,

[0033] - a molten salt reactor (MSR) .

[0034] According to a possible implementation form of the first aspect, an evaporator is operably connected to the still and comprises supplying the heated heat exchange medium to the evaporator .

[0035] According to a possible implementation form of the first aspect, the nuclear reactor comprises a reactor core, a primary heat exchange loop containing a primary heat exchange medium, the primary heat exchange loop passes through the reactor core and through a primary heat exchanger, and a secondary heat exchange loop containing a secondary heat exchange medium, the secondary heat exchange loop passes through the primary heat exchanger, comprising transporting heat from the reactor core to the secondary heat exchange medium by circulating the primary heat exchange medium in the primary heat exchange loop and circulating the secondary heat exchange medium in the secondary heat exchange loop.

[0036] According to a possible implementation of the first aspect, the secondary heat exchange loop passes through the evaporator .

[0037] According to a possible implementation form of the first aspect, the still comprises one or more of:

[0038] - a vertical column still,

[0039] - a horizontal still,

[0040] - a vacuum port for connection to a vacuum system for pulling a high or ultra-high vacuum,

[0041] - a feed port for receiving the mixture of molten lithium,

[0042] - a reflux port,

[0043] - a first upper outlet port for enriched vapor lithium-6,

[0044] - a second lower outlet port for enriched molten lithium-7,

[0045] - trace heating elements

[0046] - thermal insulation.

[0047] According to a possible implementation form of the first aspect, an evaporator is operably connected to the still, and the heat exchange medium that supplies heat to the evaporator comprises a molten salt preferably a nitrate, fluoride, or chloride salt with a suitable melting and boiling point.

[0048] According to a possible implementation form of the first aspect, a condenser is operably coupled to the still and comprises removing heat from the condenser with a heat exchange medium, preferably with a molten salt, preferably a nitrate, fluoride, or chloride salt. According to a possible implementation form of the first aspect, the heat exchange medium is circulated in a loop with one or more intermediate heat exchangers placed between the evaporator and the condenser comprising increasing the temperature drop between the evaporator and condenser, the one or more intermediate heat exchangers preferably comprising a counterflow recuperator.

[0049] According to a possible implementation form of the first aspect, the heat exchange medium comprises a NaNO3-KNO3 eutectic salt, with a melting point of approximately 250°C, comprising heating the evaporator to at least approximately 400°C, preferably to approximately 550°C, the NaNO3-KNO3 eutectic salt has a maximum operating temperature of 560°C due to thermal decomposition at higher temperatures.

[0050] According to a possible implementation form of the first aspect, the method comprises cooling down the condenser to approximately 300°C, preferably down to approximately 260°C. According to a possible implementation form of the first aspect, the method comprises using a LiNO3-NaNO3-KNO3 eutectic salt, with a melting point of approximately 120°C to heat the evaporator to approximately 400 °C, preferably to approximately 550°C and to cool down the condenser to approximately 150°C, the LiNO3-NaNO3-KNO3 eutectic salt having a maximum operating temperature of 560 °C due to thermal decomposition .

[0051] According to a possible implementation form of the first aspect, the method comprises using a LiF-NaF-KF eutectic salt, with a melting point of approximately 450 °C, comprising heating the evaporator to approximately 600°C and using the LiF-NaF-KF salt or a LiNO3-NaNO3-KNO3 eutectic salt to cool down the condenser to approximately 500°C, the LiF-NaF-KF eutectic salt preferably being operated at a maximum operating temperature of 700°C to prevent by excessive corrosion of the salt containment material.

[0052] According to a possible implementation form of the first aspect, the method comprises using a LiF-NaF-KF or NaNO3-KNO3 salt to heat the evaporator and using an organic coolant to cool the condenser.

[0053] According to a possible implementation form of the first aspect, the still comprises packing, preferably structured packing, and / or wherein the still is a vertical still.

[0054] According to a second aspect, there is provided a system for isotopically separating lithium-6 and lithium-7 from a mixture thereof, the system comprising:

[0055] - a molecular distillation apparatus comprising: at least one still configured for isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream, an evaporator operably coupled to the at least one still,

[0056] - a nuclear reactor comprising a reactor core, the system comprising a heat exchange arrangement for transferring heat from the nuclear reactor core to the evaporator using at least one heat exchange medium, the heat exchange arrangement being configured for supplying heat to the evaporator with a heat exchange medium having a temperature of at least 400°C.

[0057] According to a possible implementation form of the second aspect, the nuclear reactor comprises: a primary heat exchange loop containing a primary heat exchange medium, the primary heat exchange loop passes through the reactor core and through a primary heat exchanger, and a secondary heat exchange loop containing a secondary heat exchange medium, the secondary heat exchange loop passes through the primary heat exchanger.

[0058] According to a possible implementation form of the second aspect, the still comprises one or more of:

[0059] - a vertical column still,

[0060] - a horizontal still,

[0061] - a vacuum port for connection to a vacuum system for pulling a high or ultra-high vacuum,

[0062] - a feed port for receiving the mixture of molten lithium,

[0063] - a reflux port,

[0064] - a first upper outlet port for enriched vapor lithium-6,

[0065] - a second lower outlet port for enriched molten lithium-7,

[0066] - trace heating elements,

[0067] - thermal insulation.

[0068] According to a third aspect, there is provided a method of isotopically separating lithium-6 and lithium-7 from a mixture thereof, the method comprising: isotopically separating molten lithium metal material containing the mixture of lithium-6 and lithium-7 into enriched molten lithium-6 and enriched molten lithium-7 by molecular distillation of molten lithium metal material, using a molecular distillation apparatus comprising a still or a series of stills,

[0069] - heating a heat exchange medium with a nuclear reactor to a temperature of at least 400 °C, and

[0070] - supplying the heated heat exchange medium to the molecular distillation apparatus for driving the molecular distillation process .

[0071] According to a second aspect, there is provided a system for isotopically separating lithium-6 and lithium-7 from a mixture thereof, the system comprising:

[0072] - a molecular distillation apparatus comprising: at least one still configured for isotopically separating molten lithium metal material containing the mixture of lithium-6 and lithium-7 into enriched molten lithium-6 and enriched molten lithium-7, an evaporator operably coupled to the at least one still,

[0073] - a nuclear reactor comprising a reactor core, the system comprising a heat exchange arrangement for transferring heat from the nuclear reactor core to the evaporator using at least one heat exchange medium, the heat exchange arrangement being configured for supplying heat to the evaporator with a heat exchange medium having a temperature of at least 400°C.

[0074] These and other aspects will be apparent from the examples and embodiments described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

[0076] Fig. 1 is a diagrammatic representation of a system according to an embodiment comprising a molecular distillation apparatus and a nuclear reactor,

[0077] Fig. 2 is a diagrammatic representation of a system according to another embodiment comprising a molecular distillation apparatus and a nuclear reactor, and

[0078] Fig. 3 is a diagrammatic representation of yet another system according to another embodiment comprising a molecular distillation apparatus and a nuclear reactor.

[0079] DETAILED DESCRIPTION

[0080] Fig. 1 shows an embodiment of a system for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. The system comprises a molecular distillation apparatus and a nuclear reactor 1. The molecular distillation apparatus comprises at least one still 20 configured for isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium- 6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream. The molecular distillation apparatus may comprise several stills 20 in series. In the embodiment shown in Fig. 1, the still 20 comprises a vertical column 22, a vacuum port 29 for connection to a vacuum system 40 for pulling a high or ultra- high vacuum, a feed port 24 for receiving the mixture of molten lithium, a reflux port 26, a first upper outlet port

[0081] 27 for enriched vapor lithium-6, a second lower outlet port

[0082] 28 for enriched molten lithium-7, structural packing 23, trace heating elements 31, and thermal insulation 32. However, it should be understood that this is just an example of a still 20 that can be used in the distillation apparatus, and other types of stills, such as horizontal stills (not shown) can also be used. Molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 is fed to the vertical column 22 by a feed conduit that leads to the feed port 24, preferably as a substantially constant stream, but this could also be an intermittent stream. The vacuum port 29 is connected to a vacuum pump 4 that creates a high or ultra- high vacuum in the interior of the vertical column 22. An evaporator 25 is operably coupled to still 20 at two separate positions by an evaporator conduit 29 that has an inlet at the lowest area of the vertical column 22 and an outlet slightly above the lowest area of the vertical column 22. In the present embodiment, the inlet of the evaporator conduit

[0083] 29 is connected to the second lower outlet 28, but it should be understood that the evaporator, 29 may just as well have its own port into the lowest area of the vertical distillation column 22. Enriched molten lithium-7 is circulated through the evaporator conduit 29 and the evaporator 25 by a circulation pump (not shown) or other device capable of forcing the circulation of molten lithium-7.

[0084] The packing material 23, preferably structured packing 23, provides a large surface area with counterflowing molten lithium metal and lithium metal vapor. The structured packing material 23 is preferably optimized for short-path molecular distillation of lithium, taking the operating temperature of the still 20 into consideration in the design of the structured packing 23. A relatively long column of packing 23 serves as multiple theoretical stages allowing for a large separation factor in one or more packing columns 23. The distillation process happens above the melting point of molten lithium, but preferably below the boiling point of molten lithium .

[0085] The first upper outlet 27 connects to the inlet of a condenser 30 and the outlet of the condenser 30 is split into a reflux 26 and an off-stream 21 of enriched molten lithium-6.

[0086] The condenser 30 is operably coupled to the still 20 for removing heat from the stream of enriched vapor lithium-6 coming from the upper outlet 27 to thereby condense at least partially the stream of enriched vapor lithium-6 coming from the upper outlet 27 in the condenser 30. The condenser 30 is cooled with a heat exchange medium to remove heat from the condenser 30. The exchange medium is in an embodiment a molten salt, preferably a nitrate, fluoride, or chloride salt.

[0087] The system comprises a heat exchange arrangement for transferring heat from the nuclear reactor 1 to the evaporator 25 using at least one heat exchange medium, the heat exchange arrangement being configured for supplying heat to the evaporator 25 with a heat exchange medium supplied to the heat exchange arrangement having a temperature of at least 400°C. The nuclear reactor 1 comprises reactor core 2, a primary heat exchange loop 3 containing a primary heat exchange medium, the primary heat exchange loop 3 passes through the reactor core 2 and through a primary heat exchanger 4. The primary heat exchange loop 3 comprises a primary circulation pump 5 for circulating the primary heat exchange medium in the primary heat exchange loop 3.

[0088] The system comprises a secondary heat exchange loop 1 containing a secondary heat exchange medium, the secondary heat exchange loop 12 passes through the primary heat exchanger 4 and through the evaporator 25, for transferring heat from the nuclear reactor 1 to the evaporator 25. A circulation pump (not shown) can be provided in the secondary heat exchange loop 12.

[0089] To provide the necessary heat for the molecular distillation process, the secondary heat exchange medium is heated to a temperature of approximately 400°C or higher using a nuclear reactor 1.

[0090] The nuclear reactor 1 may be a gas-cooled reactor, such as a high-temperature gas-cooled reactor (HTGR) or a very-high- temperature reactor (VHTR) , a liquid metal cooled reactor (LMR) , a heat pipe cooled reactor (HPR) , or a molten salt reactor (MSR) . Accordingly, the first heat exchange medium can be gas, liquid metal, or molten salt, and the second heat exchange medium can be gas, liquid metal, or molten salt, and any combinations of the material used for the first and second heat exchange medium are possible. Accordingly, the heated secondary heat exchange medium is supplied to the molecular distillation apparatus, where it is utilized in an evaporator 25, to drive the isotopic separation process .

[0091] The secondary heat exchange medium utilized in the evaporator 25 comprises or is in an embodiment a molten salt with a suitable melting and boiling point, such as NaNO3-KNO3 eutectic salt with a melting point of approximately 250°C. The evaporator 25 is heated to at least approximately 400°C, preferably to approximately 550°C.

[0092] The secondary heat exchange medium utilized in the evaporator 25 comprises or is in another embodiment LiNO3-NaNO3-KNO3 eutectic salt with a melting point of approximately 120°

[0093] The secondary heat exchange medium utilized in the evaporator 25 comprises in yet another embodiment a LiF-NaF-KF eutectic salt, with a melting point of approximately 450°C, to heat the evaporator to approximately 600°C, preferably to approximately 700°C.

[0094] Fig. 2 shows another embodiment of the system for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. In this embodiment, structures, and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. This embodiment is essentially the same as the first embodiment, except that the secondary heat exchange loop 12 passes both through the evaporator 25 and the condenser 30. Accordingly, the components and elements of the system that are the same and their functionality are not described again, instead, reference is made to the embodiment above .

[0095] At least one intermediate heat exchanger 50 is placed between the evaporator 25 and the condenser 30 to increase the temperature drop between the evaporator 25 and the condenser 30. The at least one intermediate heat exchangers 50 preferably comprises a counterflow recuperator. The heat that is removed from the intermediate heat exchanger 50 / counterf low recuperator can be used for other purposes, e.g. power generation or district heating. Another heat exchanger 52 can be arranged downstream of the condenser 30. The heat that is removed from the other heat exchanger 52 can be used for other purposes, e.g. power generation or district heating .

[0096] For cooling the condenser 30 the heat exchange medium may be a molten salt, such as the LiNO3-NaNO3-KNO3 eutectic salt with a melting point of approximately 120°C, which allows cooling down the condenser to approximately 150°C, preferably approximately 130°C.

[0097] Alternatively, a LiF-NaF-KF eutectic salt, with a melting point of approximately 450°C, can be used to heat the evaporator to approximately 600 °C, preferably to approximately 700°C, and the LiF-NaF-KF salt or a LiNO3-NaNO3- KNO3 eutectic salt can be used to cool down the condenser to approximately 550°C, preferably to approximately 400°C. In some embodiments, an organic coolant can be used to cool the condenser 30 while maintaining the high temperature required for isotopic separation.

[0098] Fig. 3 shows another embodiment of the system for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. In this embodiment, structures, and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. This embodiment is essentially the same as the first embodiment, except that the secondary heat exchange loop 12 passes through a multi-stage horizontal still 62. Accordingly, the components and elements of the system that are the same and their functionality are not described again, instead, reference is made to the embodiment above.

[0099] The heat exchange medium in the secondary heat exchange loop 12 is heated to a high temperature in the primary heat exchanger 4 by exchanging heat with the heat exchange medium in the primary heat exchange loop 3. High-temperature heat exchange medium in the secondary heat exchange loop 12 leaving the primary heat exchanger 4 is fed to a lower passage extending along the lower horizontal side of the horizontal still 62 for heating the molten lithium in the lower portion of the horizontal still 62 and from there the heat exchange medium passes through a heat exchanger 54 where it exchanges heat with a cooling medium so that the temperature of the heat exchange medium entering the upper portion of the horizontal still 62 is lowered. From the heat exchanger 54, the heat exchange medium is fed to an upper passage extending along the upper horizontal side of the horizontal still 62 with its condensing elements 130, and from there the heat exchange medium is fed back to the primary heat exchanger 4. Molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 is fed to the horizontal still column 62 by a feed conduit that leads to the feed port 24 at the lower portion of the horizontal still 62, preferably as a substantially constant stream, but this could also be an intermittent stream. The horizontal still comprises a plurality of horizontally distributed stages (three are shown as an example in this embodiment) but a still would typically constitute more than 100 stages. Each still can comprise one or more trays, which in turn can comprise multiple stages. In case of multiple trays, they are preferably connected to each other to provide a certain enrichment capacity. Molten lithium flows through the bottom of each tray from one stage to the next. The bottom of the tray is heated while the top is cooled to allow lithium metal to evaporate across the bottom of the tray and condense on the top of the tray. The tray is constructed such that lithium flow from one stage to the other is serial. While the lithium passes through the bottom of a stage some of the lithium will evaporate and condense on the lid of the stage that forms a condensing element 130, which is slanted to let the condensed lithium metal fall into the bottom of the previous stage. This drives the condensed lithium backward towards the first stage, while the condensed lithium dripping into the bottom of the stages displaces molten lithium forwards and potentially the tray bottom is slanted to drive the molten lithium forwards. In this way counter flowing streams of lithium are provided where the consensed lithium which is lithium-6 rich flows backward through the stages to the first outlet port 67 and the remaining lithium which is lithium-7 rich flows forward through the stages towards the second outlet port 68. In this way, enriched lithium 6 is concentrated at the start of the tray and enriched lithium 7 is concentrated at the end of the tray.

[0100] The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed sub ect-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0101] The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g. , cross-hatching, arrangement of parts, proportion, degree, etc. ) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

Claims

CLAIMS1. A method of isotopically separating lithium-6 and lithium- 7 from a mixture thereof, the method comprising:- isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream by molecular distillation of the feed stream of molten lithium metal feed material, using a molecular distillation apparatus comprising a still (20) or a series of stills (20) , characterized by- heating a heat exchange medium with a nuclear reactor (1) to a temperature of at least 400 °C, and- supplying the heated heat exchange medium to the molecular distillation apparatus.

2. The method of claim 1, wherein the nuclear reactor is one of :- a gas-cooled reactor preferably a high-temperature gas-cooled reactor or a very-high-temperature reactor,- a liquid metal cooled reactor,- a heat pipe cooled reactor,- a molten salt reactor.

3. The method of claim 1 or 2, wherein an evaporator (25) is operably connected to the still (20) , comprising supplying the heated heat exchange medium to the evaporator (25) .

4. The method of any one of claims 1 to 3 wherein the nuclear reactor (1) comprises a reactor core (2) , a primary heat exchange loop (3) containing a primary heat exchange medium,the primary heat exchange loop (3) passes through the reactor core (2) and through a primary heat exchanger (4) , and a secondary heat exchange loop (12) containing a secondary heat exchange medium, the secondary heat exchange loop (12) passes through the primary heat exchanger (4) , comprising transporting heat from the reactor core (2) to the secondary heat exchange medium by circulating the primary heat exchange medium in the primary heat exchange loop (3) and circulating the secondary heat exchange medium in the secondary heat exchange loop (12) .

5. The method of claim 4, wherein the secondary heat exchange loop (12) passes through the evaporator (25) .

6. The method of any one of claims 1 to 5, wherein the still (20) comprises one or more of:- a vertical column still (22) ,- a horizontal still (62) ,- a vacuum port (29) for connection to a vacuum system (40) for pulling a high or ultra-high vacuum, a feed port (24) for receiving the mixture of molten lithium,- a reflux port (26) ,- a first upper outlet port (27) for enriched vapor lithium-6,- a second lower outlet port (28) for enriched molten lithium-7,- trace heating elements (31) ,- thermal insulation (32) .

7. The method of any one of claims 1 to 6, wherein an evaporator (25) is operably connected to the still (20) , and wherein the heat exchange medium that supplies heat to the evaporator (25) comprises a molten salt preferably a nitrate, fluoride, or chloride salt with a suitable melting and boiling point .

8. The method of any one of claims 1 to 7, wherein a condenser (30) is operably coupled to the still (20) , comprising removing heat from the condenser (30) with a heat exchange medium, preferably with a molten salt, preferably a nitrate, fluoride, or chloride salt.

9. The method of claim 8, when depending on claim 7 wherein the heat exchange medium is circulated in a loop (12) with one or more intermediate heat exchangers (50) placed between the evaporator (25) and the condenser (30) comprising increasing the temperature drop between the evaporator (25) and condenser (30) , the one or more intermediate heat exchangers (50) preferably comprising a counterflow recuperator (50) .

10. The method of any one of claims 7 to 9, wherein the heat exchange medium comprises a NaNO3-KNO3 eutectic salt, preferably with a melting point of approximately 250°C, comprising heating the evaporator (25) to at least approximately 400°C, preferably to approximately 550°C.

11. The method of claim 10, comprising cooling down the condenser (30) to approximately 300°C, preferably down to approximately 260°C.

12. The method of any one of claims 7 to 9, comprising using a LiNO3-NaNO3-KNO3 eutectic salt, with a melting point of approximately 120 °C to heat the evaporator (25) to approximately 400°C, preferably to approximately 550°C and to cool down the condenser (30) to approximately 150°C, preferably approximately 130°C13. The method of any one of claims 7 to 9, comprising using a LiF-NaF-KF eutectic salt, with a melting point of approximately 450 °C to heat the evaporator (25) to approximately 600°C, preferably to approximately 700°C and using the LiF-NaF-KF salt or a LiNO3-NaNO3-KNO3 eutectic salt to cool down the condenser (30) to approximately 550°C, preferably to approximately 400°C.

14. The method of any one of claims 7 to 9, comprising using a LiF-NaF-KF or NaNO3-KNO3 salt to heat the evaporator (25) , and using an organic coolant to cool the condenser (30) .

15. The method of any one of claims 1 to 14, wherein the still(20) comprises packing (23) , preferably structured packing(23) , and / or wherein the still (20) is a vertical still (20) .

16. A system for isotopically separating lithium-6 and lithium-7 from a mixture thereof, the system comprising:- a molecular distillation apparatus comprising: at least one still (20) configured for isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 andlithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream, an evaporator (25) operably coupled to the at least one still (20) , characterized by- a nuclear reactor (1) comprising a reactor core (2) , the system comprising a heat exchange arrangement for transferring heat from the nuclear reactor core (2) to the evaporator (25) using at least one heat exchange medium, the heat exchange arrangement being configured for supplying heat to the evaporator (25) with a heat exchange medium having a temperature of at least 400°C.

17. The system of claim 16, wherein the nuclear reactor comprises a primary heat exchange loop (3) containing a primary heat exchange medium, the primary heat exchange loop (3) passes through the reactor core (2) and through a primary heat exchanger (4) , and the system comprises a secondary heat exchange loop (12) containing a secondary heat exchange medium, and the secondary heat exchange loop (12) passes through the primary heat exchanger ( 4 ) .

18. The system of claim 16 or 17, wherein the still (20) comprises one or more of:- a vertical column still (22) ,- a horizontal still (62) ,- a vacuum port (29) for connection to a vacuum system (40) for pulling a high or ultra-high vacuum, a feed port (24) for receiving the mixture of molten lithium,- a reflux port (26) ,- a first upper outlet port (27) for enriched vapor lithium-6,- a second lower outlet port (28) for enriched molten lithium-7,- trace heating elements (31) ,- thermal insulation (32) .

19. A method of isotopically separating lithium-6 and lithium- 7 from a mixture thereof, the method comprising: isotopically separating molten lithium metal material containing the mixture of lithium-6 and lithium-7 into enriched molten lithium-6 and enriched molten lithium-7 by molecular distillation of molten lithium metal material, using a molecular distillation apparatus comprising a still or a series of stills,- heating a heat exchange medium with a nuclear reactor to a temperature of at least 400 °C, and- supplying the heated heat exchange medium to the molecular distillation apparatus for driving the molecular distillation process .

20. A system for isotopically separating lithium-6 and lithium-7 from a mixture thereof, the system comprising:- a molecular distillation apparatus comprising: at least one still configured for isotopically separating molten lithium metal material containing the mixture of lithium-6 and lithium-7 into enriched molten lithium-6 and enriched molten lithium-7, an evaporator operably coupled to the at least one still,- a nuclear reactor comprising a reactor core,the system compri sing a heat exchange arrangement for trans ferring heat from the nuclear reactor core to the evaporator using at least one heat exchange medium, the heat exchange arrangement being conf igured for supplying heat to the evaporator with a heat exchange medium having a temperature of at least 400 ° C .

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