Actinide partitioning to isolate americium and curium during a used nuclear fuel recycling process

Abstract

A method of partitioning minor actinides includes directing a minor actinide aqueous solution into an actinide partitioning unit, the minor actinide aqueous solution comprising americium and curium in an aqueous solvent and the americium and the curium are each in a first oxidation state, directing a selective extracting solution into the actinide partitioning unit, wherein the selective extracting solution comprises an organic neutral extractant, an phase modifier, a hydrocarbon diluent, and sodium bismuthate, contacting the minor actinide aqueous solution with the selective extracting solution such that the curium binds with the selective extracting solution to form an organic phase curium solution and the sodium bismuthate induces an oxidation state increase in the americium from the first oxidation state to a second oxidation state, wherein the americium in the second oxidation state remains bound with the minor actinide aqueous solution, thereby partitioning the americium and the curium, and collecting the americium.

Description

SHQ0034WO / R24-3-PCT1ACTINIDE PARTITIONING TO ISOLATE AMERICIUM AND CURIUM DURING A USED NUCLEAR FUEL RECYCLING PROCESSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 722,172 filed on November 19, 2024, which is incorporated herein by reference in its entirety.BACKGROUND

[0002] The present disclosure relates generally methods and systems of processing used nuclear fuel.SUMMARY

[0003] According to an embodiment of the present disclosure, a method of partitioning minor actinides includes directing a minor actinide aqueous solution into an actinide partitioning unit, wherein the minor actinide aqueous solution comprises americium and curium in an aqueous solvent and the americium and the curium are each in a first oxidation state. The method further includes directing a selective extracting solution into the actinide partitioning unit, wherein the selective extracting solution comprises an organic neutral extractant, an phase modifier, a hydrocarbon diluent, and sodium bismuthate, contacting the minor actinide aqueous solution with the selective extracting solution such that the curium binds with the selective extracting solution to form an organic phase curium solution and the sodium bismuthate induces an oxidation state increase in the americium from the first oxidation state to a second oxidation state, wherein the americium in the second oxidation state remains bound with the minor actinide aqueous solution, thereby partitioning the americium and the curium, and collecting the americium.

[0004] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0005] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanyingSHQ0034WO / R24-3-PCT2 drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 schematically depicts a liquid-liquid extraction system, according to embodiments disclosed and described herein.DETAILED DESCRIPTION

[0007] Reference will now be made in detail to embodiments of used nuclear fuel processing that includes partitioning americium and curium after americium and curium are separated from a main process stream of used nuclear fuel, for example, after americium and curium are separated from a solution comprising minor actinides and lanthanides. The present disclosure comprises directing an aqueous solution of americium and curium into an actinide partitioning unit and directing a selective extracting solution into the actinide partitioning unit. The selective extracting solution comprises an organic neutral extractant, a phase modifier, a hydrocarbon diluent, and sodium bismuthate (NaBiCh). When the americium and curium enter the actinide partitioning unit, each are in the same oxidation state, for example, a +3 -oxidation state. In the +3 -oxidation state, both americium and curium readily bind with the organic neutral extractant of the selective extracting solution. However, the sodium bismuthate increases the oxidation state of americium, changing americium to a higher oxidation state, such as a +4, +5, +6, or +7-oxidation state, without altering the oxidation state of curium. In this higher oxidation state, the americium does not bind with the organic neutral extractant and remains in aqueous phase. Thus, the curium is partitioned from the aqueous solution of americium and curium into the organic phase, separating the americium from the curium.

[0008] The americium and curium may then each be collected separated. Most of the americium and curium present in used nuclear fuel comprise americium-241 and curium-244, respectively. Partitioning americium-241 allows it to be further processed to generate curium-242, a valuable radioisotope. For example, separated americium-241 may be irradiated, inducing neutron absorption to form americium-242, about 82% of which decays into curium-242. Curium-242 is not present in large quantities in used nuclear fuel and thus, separating americium from curiumSHQ0034WG / R24-3-PCT3 allows for the formation of valuable curium-242. The systems and methods described herein overcome some of the challenges of separating and isolating americium and curium from used nuclear fuel, allowing for the recycling of these useful materials, and incentivizing the reprocessing of used nuclear fuel, thereby reducing the longevity and long-term radiotoxicity of nuclear waste, and improving reprocessing economics. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0009] Referring now to FIG. 1, a liquid-liquid extraction (LLE) system 100 is schematically depicted. The LLE system 100 of FIG. 1 may be part of a used nuclear fuel processing system for partitioning and recycling used nuclear fuel. The LLE system 100 comprises an actinide- lanthanide extraction unit 110, a scrubbing unit 115, an actinide-lanthanide stripping unit 120, an actinide partitioning unit 130, and a solvent preparation unit 140. The actinide partitioning unit 130 is configured to isolate minor actinides and may be part of a used nuclear fuel processing system. Indeed, the LLE system 100 depicted in FIG. 1 may form a portion of a larger used nuclear fuel processing system, which may further include a fuel rod shearing system, a voloxidation system, a dissolution system, and additional LLE systems configured to selectively extract different subsets of the elements present in used nuclear fuel, for example, to selectively extract or co-extract uranium, plutonium, and neptunium from a main process stream before the main process stream reaches the actinide-lanthanide extraction unit 110.

[0010] The actinide-lanthanide extraction unit 110, the scrubbing unit 115, the actinide-lanthanide stripping unit 120, and the actinide partitioning unit 130 are each fluidly coupled, for example, using any fluid flow and control devices, such as piping, tubing, pumps, and tanks, and may each comprise one or more mixing devices. In operation, the mixing devices induce reactions between elements in an acidic liquid (i.e., in an aqueous phase) and elements in an organic liquid (i.e., in an organic phase). Example mixing devices include centrifugal contactors, pulse columns, counter- current columns, mixer settlers, or combinations thereof. In some embodiments, centrifugal contactors are useful because their compact size allows for the use of smaller hot cells, reducing the capital cost required for facility construction.

[0011] In operation, the LLE system 100 may receive liquid used nuclear fuel, for example, liquid raffinate from a uranium-plutonium extraction process, such as a uranium-plutonium codecontamination (CoDCon) process. This actinide-lanthanide containing raffinate includes minorSHQ0034WG / R24-3-PCT4 actinides (e.g., americium and curium), one or more lanthanides, one or more non-lanthanide fission products, and other components of used nuclear fuel not removed during the CoDCon process or another upstream process. The actinide-lanthanide containing raffinate is directed into the actinide-lanthanide extraction unit 110 in aqueous phase and an organic extracting solution is also directed into the actinide-lanthanide extraction unit 110 such that the organic extracting solution contacts the actinide-lanthanide containing raffinate. The organic extracting solution is configured to bind with the minor actinides and the one or more lanthanides, for example, when agitated using the one or more mixing devices of the actinide-lanthanide extraction unit 110, while the remainder of the raffinate, for example, the non-lanthanide fission products, remains in aqueous phase and exits the actinide-lanthanide extraction unit 110 for further processing. Indeed, the americum, the curium and the one or more lanthanides bind with the organic extracting solution to form an actinide-lanthanide organic solution.

[0012] The organic extracting solution comprises an organic neutral extractant, a phase modifier, and a hydrocarbon diluent (e.g., n-dodecane). The organic neutral extractant may comprise a neutral diglycolamide extractant. Example organic neutral extractants include N,N,N',N'-tetra(2- ethylhexyl)diglycolamide (T2EHDGA), N,N,N',N'-tetraoctyldiglycolamide (TODGA), and n- Octyl (phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO). Example phase modifiers include 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEHfEHP]) and di(2- ethylhexyl)phosphoric acid (HDEHP), N,N'-Dimethyl,N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), tributyl phosphate (TBP), octanal, or a combination thereof, and the hydrocarbon diluent comprises n-dodecane. For example, T2EHDGA may be present in the organic extracting solution in a range of from 0.01 M to 2 M, for example, from 0.02 M to 1.5 M, from 0.04 to 1 M, from 0.05 to 0.8 M, from 1 to 0.75 M, or the like. In embodiments in which the phase modifier comprises HEHfEHP] or HDEHP, the HEHfEHP] or HDEHP may be present in the organic extracting solution in a range of from 0.25 M to 2 M, for example, from 0.5 to 1.5 M. In embodiments in which the phase modifier comprises DMDOHEMA, the DMDOHEMA may be present in the organic extracting solution in a range of from 0.1 to 1 M, for example, from 0.2 to 0.7 M. In operation, the phase modifier increases the polarity of the organic extracting solution.

[0013] Next, the actinide-lanthanide organic solution is directed to the scrubbing unit 115 for a scrubbing step in which the actinide-lanthanide organic solution is contacted with a scrubbing agent comprising a dicarboxylic acid and a scrub chelator. For example, the actinide-lanthanideSHQ0034WO / R24-3-PCT5 organic solution may be fed to the scrubbing unit 115 where it mixes with the scrubbing agent, which removes unwanted species (primarily non-lanthanide fission products and non-radioactive reagents not already removed during the extracting step or another upstream processing step) from the actinide-lanthanide organic solution. In some embodiments, the dicarboxylic acid is oxalic acid (H2C2O4) and the scrub chelator is N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA). The scrubbing agent may further include nitric acid, for example, 0.5 M to 1 M of nitric acid. Embodiments may include a second scrubbing step in which the actinide-lanthanide organic solution is contacted with a second scrubbing agent comprising a carboxylic acid, such as formic acid, lactic acid or a complex carboxylic, such as citric acid. In some embodiments, the second scrubbing agent also includes a second scrub chelator, which may comprise N,N,N',N'- tetraethyldiglycolamide (TEDGA). The second scrubbing agent may further include nitric acid, for example, 0.5 M to 1 M of nitric acid.

[0014] The minor actinides and lanthanides, now in organic phase as the actinide-lanthanide organic solution, are directed to the actinide-lanthanide stripping unit 120 for a stripping step that includes contacting the actinide-lanthanide organic solution with an actinide stripping agent comprising a first strip chelator and a first buffer, unbinding the minor actinides from the actinide- lanthanide organic solution, thereby stripping the minor actinides from the actinide-lanthanide organic solution and thereafter contacting the actinide-lanthanide organic solution with a lanthanide stripping agent comprising a second strip chelator and a second buffer, unbinding the one or more lanthanides from the actinide-lanthanide organic solution, thereby stripping the one or more lanthanides from the actinide-lanthanide organic solution. Without intending to be limited by theory, the minor actinide stripping agent is a more selective stripping agent and removes the minor actinides without removing the lanthanides, while the lanthanide stripping agent is a less selective stripping agent and removes the lanthanides together with any additional species remaining (e.g., any species not removed during the extraction or stripping steps, or other upstream processing of the used nuclear fuel). Thus, the minor actinide stripping agent is introduced before the lanthanide stripping agent.

[0015] In some embodiments, the first strip chelator (i.e., the chelator of the minor actinide stripping agent) comprises diethylene triamine pentaacetic acid (DTP A) and the first buffer comprises a citrate, such as ammonium citrate. Other example first strip chelator of the minor actinide stripping agent include nitric acid, TEDGA, cyclohexanediaminetetraacetic acidSHQ0034WO / R24-3-PCT6(CDTA), HEDTA, and acetohydroxamic acid (AHA). Other example first buffers of the minor actinide stripping agent include lactate, formate, and malonate. The first strip chelator may comprise concentration in the minor actinide stripping agent in a range of from 0.5 mM to 200 mM, for example, from 1 mM to 100 mM, from 10 mM to 80 mM, or from 25 mM to 75 mM, such as 5 mM, 10 mM, 20 mM, 25 mM, 50 mM, 75 mM, 100 mM, 125 mM, 150 mM, 175 mM, or the like. In some embodiments, the first buffer is compatible with the second scrubbing agent. For example, when the second scrubbing agent comprises lactic acid, the first buffer may comprise lactate and when the second scrubbing agent comprises formic acid, the first buffer may comprise formate. In operation, the first buffer adjusts the pH of the minor actinide stripping agent to a first pH, which may be a pH of from 3.5 to 4.5, for example, from 3.8 to 4.2. This pH adjustment also stabilizes the pH, which increases the stability of the process, making the process less sensitive to minor changes in pH.

[0016] In some embodiments, the second strip chelator (i.e., the chelator of the lanthanide stripping agent) comprises DTP A, for example in a concentration in a range of from 50 mM to about 200 mM (e.g., 100), and the second buffer comprises a citrate, such as ammonium citrate. Other example first strip chelators of the lanthanide stripping agent include TEDGA, CDTA, HEDTA, and AHA. Other example second buffers of the lanthanide stripping agent include lactate, formate, and malonate. The second strip chelator may comprise concentration in the lanthanide stripping agent in a range of from 100 mM to 500 mM, for example, from 150 mM to 450 mM, from 200 mM to 400 mM, or from 100 mM to 300 mM, such as 100 mM, 125 mM, 150 mM, 175 mM, 200 mM, 225 mM, 250 mM, 275 mM, 300 mM, 325 mM, 350 mM, 375 mM, 400 mM, 425 mM, 450 mM, 500 mM, or the like. The lanthanide stripping agent may further include nitric acid, for example, 0.5 M to 1.5 M of nitric acid, such as 1 M of nitric acid. In some embodiments, the second buffer is compatible with the second scrubbing agent. For example, when the second scrubbing agent comprises lactic acid, the second buffer may comprise lactate and when the second scrubbing agent comprises formic acid, the second buffer may comprise formate. Moreover, it should be understood that, in some embodiments, the second buffer may be omitted from the lanthanide stripping agent. The concentration of the second strip chelator (i.e., the chelator in the lanthanide stripping agent) is higher than the concentration of the first strip chelator (i.e., the chelator in the minor actinide stripping agent). Without intending to be limited by theory, the lower concentration of the first strip chelator contributes to the increasedSHQ0034WO / R24-3-PCT7 selectivity of the minor actinide stripping agent. Moreover, the second buffer adjusts the pH of the minor actinide stripping agent to a first pH, which may be a pH of from about 4.0 to about 6.5, for example, from 4.3 to 6.0, from 4.5 to 5.5, or from 4.8 to 5.2. This pH adjustment also stabilizes the pH, which increases the stability of the process, making the process less sensitive to minor changes in pH. The first pH (e.g., the pH of the minor actinide stripping agent) is lower than the second pH (the pH of the lanthanide stripping agent).

[0017] In operation, the one or more mixing devices of the actinide-lanthanide stripping unit 120 may combine and agitate the organic phase minor actinides and the minor actinide stripping agent such that the minor actinides are removed from organic phase and combined with the minor actinide striping agent in aqueous phase to form the minor actinide aqueous solution. Similarly, the one or more mixing devices of the actinide-lanthanide stripping unit 120 may combine and agitate the organic phase lanthanides and the lanthanide stripping agent such that the lanthanides are removed from organic phase and combined with the lanthanide stripping agent in aqueous phase to form the lanthanide aqueous solution. Once partitioned, the minor actinide aqueous solution and the lanthanide aqueous solution may be collected and / or further processed.

[0018] Indeed, the minor actinide aqueous solution may be directed into the actinide partitioning unit 130 for further processing and a selective extracting solution is also directed into the actinide partitioning unit 130. The minor actinide aqueous solution comprises americium and curium, which are each in a first oxidation state, for example, a +3 -oxidation state. The selective extracting solution comprises an organic neutral extractant, a phase modifier, a hydrocarbon diluent, and sodium bismuthate in nitric acid. The selective extracting solution may be prepared in a solvent preparation unit 140, which is radiologically cold and is fluidly coupled to the actinide partitioning unit 130. In some embodiments, the selective extracting solution is formed by combining nitric acid with a powder of sodium bismuthate such that at least a portion of the sodium bismuthate dissolves, thereby forming a nitric acid sodium bismuthate solution and thereafter, combining the nitric acid sodium bismuthate solution with the organic neutral extractant and the phase modifier to form the selective extracting solution. Before combining with the nitric acid, the powder of sodium bismuthate may undergo a grinding process to reduce the average particle size, improving the dissolution process. When mixing the powder of sodium bismuthate with the nitric acid, heat may be applied, for example, the mixing may be done at a temperature of about 50 °C to 100 °C, such as about 70 °C, for a period of about 1 to 3 hours.SHQ0034WO / R24-3-PCT8

[0019] In some embodiments, the selective extracting solution is formed by combining nitric acid with the organic neutral extractant and the phase modifier to form an extracting solution, and thereafter dissolving a powder of sodium bismuthate in the extracting solution to form the selective extracting solution. Before combining with the extracting solution, the powder of sodium bismuthate may undergo a grinding process to reduce the average particle size, improving the dissolution process. When mixing the powder of sodium bismuthate with the extracting solution, heat may be applied, for example, the mixing may be done at a temperature of about 50 °C to 100 °C, such as about 70 °C, for a period of about 1 to 3 hours. It should be understood that embodiments are contemplated in which not all the sodium bismuthate combined with the nitric acid dissolves in the nitric acid. In some embodiments, the sodium bismuthate in nitric acid comprises 10 to 100 mM of sodium bismuthate in 3 to 6 M of nitric acid.

[0020] The minor actinide aqueous solution and the selective extraction solution are contacted using the actinide partitioning unit 130. For example, the one or more mixing devices of the actinide partitioning unit 130 may combine and agitate the minor actinide aqueous solution and the selective extracting solution such that certain elements are removed from the minor actinide aqueous solution (which is in an aqueous phase) and combined with the organic phase portion of the selective extracting solution. The curium, which is in the first oxidation state, binds with the organic phase portion of the selective extracting solution to form an organic phase curium solution. However, the sodium bismuthate induces an oxidation state increase in the americium from the first oxidation state to a second oxidation state and in the second oxidation state, americium does not bind with the organic phase portion of the selective extracting solution. Instead, the americium in the second oxidation state remains in aqueous phase, for example, remains bound with the minor actinide aqueous solution, thereby partitioning the americium and the curium. The second oxidation state is a +4-oxidation state, a +5-oxidation state, a +6-oxidation state, or a +7-oxidation state. The americium, which remains in aqueous phase in the minor actinide aqueous solution may be collected. The collected americium may next be separated from the actinide aqueous solution by calcination, precipitation, or a combination thereof.

[0021] Without intending to be limited by theory, sodium bismuthate is in a +5-oxidation state when in organic phase, for example, when in when in nanodroplets of nitric acid dispersed in the organic phase of the selective extracting solution, but bismuth has a preferred oxidation state of +3. Moreover, americium is stable in a number of higher oxidation states, such as +5, whileSHQ0034WG / R24-3-PCT9 curium and the one or more lanthanides are not stable in the +5-oxidation state. In operation, when sodium bismuthate in the selective extraction solution contacts americium, two electrons swap from the sodium bismuthate to the americium, as shown in simplified form in Equation 1 and in more detail in Equation 2. n 1)(Equation 2)

[0022] Unlike americium, the curium does not swap electrons with the sodium bismuthate. In the higher (e.g., +5) oxidation state, the americium does not bind with the organic phase portion of the selective extracting solution, while the curium, which remains in the lower (e.g., +3) oxidation state and the sodium bismuthate, now in the lower +3 oxidation state, binds with the organic phase portion of the selective extracting solution. The americum in the higher (e.g., +5) oxidation state remains bound with the minor actinide aqueous solution, separating the americium and the curium.

[0023] The organic neutral extractant of the selective extracting solution comprises T2EHDGA, TODGA, CMPO, or a combination thereof, the phase modifier comprises HEH[EHP], HDEHP,N,N'-Dimethyl,N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), tributyl phosphate (TBP), octanal, or a combination thereof, and the hydrocarbon diluent comprises n-dodecane. For example, T2EHDGA may be present in the selective extracting solution in a range of from 0.01 M to 2 M, for example, from 0.02 M to 1.5 M, from 0.04 to 1 M, from 0.05 to 0.8 M, from 1 toO.75 M, or the like. In embodiments in which the phase modifier comprises HEH[EHP] or HDEHP, the HEH[EHP] or HDEHP may be present in the selective extracting solution in a range of from 0.25 M to 2 M, for example, from 0.5 to 1.5 M. In embodiments in which the phase modifier comprises DMDOHEMA, the DMDOHEMA may be present in the selective extracting solution in a range of from 0.1 to 1 M, for example, from 0.2 to 0.7 M. In operation, the phase modifier increases the polarity of the selective extracting solution. The sodium bismuthate may be present in selective extracting solution as 10 to 100 mM of sodium bismuthate in 3 to 6 M of nitric acid. In some embodiments, the organic neutral extractant, the phase modifier, and the hydrocarbon diluent of the selective extracting solution are the same as the organic neutral extractant, the phase modifier, and the hydrocarbon diluent of the organic extracting solution used in the actinide-lanthanide extraction unit 110 to partition the minor actinides and lanthanides fromSHQ0034WO / R24-3-PCT10 the actinide-lanthanide containing raffinate, reducing the material complexity of the americium and curium separation process.

[0024] Without intending to be limited by theory, including the phase modifier in the selective extracting solution minimizes and may prevent the formation of a third phase emulsion when combining and agitating the minor actinide aqueous solution and the selective extraction solution, even at large volumes of the minor actinide aqueous solution and the selective extraction solution. Equipment used in liquid-liquid extraction is designed to operation with two phases (i.e., aqueous phase and organic phase) and the presence of a third phase emulsion would contaminate each phase, causing equipment damage and failure. By minimizing the third phase emulsion, large, commercial volumes of used nuclear fuel can be processed. For example, directing the minor actinide aqueous solution into the actinide partitioning unit 130 comprises directing at least 250 mL of the minor actinide aqueous solution into the actinide partitioning unit 130, for example, at least 500 mL, at least 750 mL, at least 1 L, at least 5 L, at least 10 L, at least 20 L, or the like. The used nuclear fuel that the present disclosure contemplates processing may comprise at least 2.5 parts per billion (ppb) of americium and at least 2.1 x 10'8ppb of curium.

[0025] Once the minor actinide aqueous solution and the selective extracting solution interact, the curium bound with the selective extracting solution that forms the organic phase curium solution may next be contacted with an aqueous stripping agent such that the curium unbinds from the organic phase curium solution to form an aqueous phase curium solution. The collected curium, now in aqueous phase, may next be separated from the remainder of the aqueous phase curium solution by calcination or precipitation. In some embodiments, the aqueous stripping agent comprises deionized water. In some embodiments, the aqueous stripping agent comprises comprise nitric acid, such as dilute nitric acid.

[0026] Most of the americium and curium present in used nuclear fuel comprise americium-241 and curium-244, respectively. After the americium-241 is partitioned and isolated, it can be further processed to generate curium-242, a valuable radioisotope. For example, the americium- 241 may be irradiated with neutrons such that at least a portion of the americium-241 undergoes a neutron absorption reaction, thereby transmuting the at least a portion of the americium-241 into americium-242, about 82% of which decays into curium-242 via beta decay. Curium-242 is not present in large quantities in used nuclear fuel and thus, separating americium from curium allowsSHQ0034WO / R24-3-PCT11 for the formation of valuable crucium-242. In some embodiments, an accelerator-based system is used to irradiate the americium-241 with neutrons, for example, an accelerator-based system that generates neutrons by fusion, such as deuterium / tritium fusion, spallation, or any other accelerator-based neutron generation technique. In some embodiments, a nuclear reactor is used to irradiate the americium-241 with neutrons, for example, a power reactor, a research reactor, or any other known or yet to be developed nuclear reactor. Moreover, americium-241 has a half-life of about 432 years and contributes a significant of the total decay heat generated in long term storage of used nuclear fuel. In contrast, curicum-242 has much shorter half-life of about 162 days. Thus, transmuting the americium-241 to curium-242 also reduces the total repository volume and long-term decay heat of used nuclear fuel.

[0027] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

[0028] As utilized herein, the terms “approximately,” “about,” “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Indeed, such terms refer to the subsequently listed property or measurement within normal manufacturing tolerances and imperfections in the relevant field. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical values or idealized geometric forms provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the disclosure as recited in the appended claims.

[0029] The term “coupled” and variations thereof, as used herein, means the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent orSHQ0034WO / R24-3-PCT12 fixed) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members coupled directly to each other, with the two members coupled to each other using a separate intervening member and any additional intermediate members coupled with one another, or with the two members coupled to each other using an intervening member that is integrally formed as a single unitary body with one of the two members. If “coupled” or variations thereof are modified by an additional term (e.g., directly coupled), the generic definition of “coupled” provided above is modified by the plain language meaning of the additional term (e.g., “directly coupled” means the joining of two members without any separate intervening member), resulting in a narrower definition than the generic definition of “coupled” provided above. Such coupling may be mechanical, electrical, or fluidic.

[0030] References herein to the positions of elements (e.g., “top,” “bottom,” “above,” “below”) are merely used to describe the orientation of various elements in the FIGURES. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

[0031] Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from what is depicted and described, unless specified differently above. Also, two or more steps may be performed concurrently or with partial concurrence, unless specified differently above. Such variation may depend, for example, on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations of the described methods could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps, and decision steps.

Claims

SHQ0034WO / R24-3-PCT13CLAIMS1. A method of partitioning minor actinides, the method comprising: directing a minor actinide aqueous solution into an actinide partitioning unit, wherein: the minor actinide aqueous solution comprises americium and curium in an aqueous solvent; and the americium and the curium are each in a first oxidation state; directing a selective extracting solution into the actinide partitioning unit, wherein the selective extracting solution comprises an organic neutral extractant, a phase modifier, a hydrocarbon diluent, and sodium bismuthate; contacting the minor actinide aqueous solution with the selective extracting solution such that the curium binds with the selective extracting solution to form an organic phase curium solution and the sodium bismuthate induces an oxidation state increase in the americium from the first oxidation state to a second oxidation state, wherein the americium in the second oxidation state remains bound with the minor actinide aqueous solution, thereby partitioning the americium and the curium; and collecting the americium.

2. The method of claim 1, wherein the first oxidation state is a +3-oxidation state.

3. The method of claim 1, wherein the second oxidation state is a +4-oxidation state, a +5- oxidation state, a +6-oxidation state, or a +7-oxidation state.

4. The method of claim 1, wherein the organic neutral extractant comprises T2EHDGA, TOGDA, or a combination thereof, and the phase modifier comprises HEHfEHP], HDEHP, DMDOHEMA, TBP, octanal, or a combination thereof.

5. The method of claim 4, wherein the selective extracting solution comprises from 0.05 to 0.8 M T2EHDGA.

6. The method of claim 4, wherein the selective extracting solution comprises from 0.5 to 1.5 M HEH[EHP],SHQ0034WO / R24-3-PCT147. The method of claim 4, wherein the selective extracting solution comprises from 0.2 to 0.7 M DMDOHEMA.

8. The method of claim 1 , wherein the selective extracting solution comprises from 10 to 100 mM of sodium bismuthate in 3 to 6 M of nitric acid.

9. The method of claim 1, wherein the hydrocarbon diluent comprises n-dodecane.

10. The method of claim 1, wherein the selective extracting solution is formed by combining nitric acid with a powder of sodium bismuthate such that at least a portion of the sodium bismuthate dissolves, thereby forming a nitric acid sodium bismuthate solution and thereafter, combining the nitric acid sodium bismuthate solution with the organic neutral extractant and the phase modifier to form the selective extracting solution.

11. The method of claim 1 , wherein the selective extracting solution is formed by combining nitric acid with the organic neutral extractant and the phase modifier to form an extracting solution, and thereafter dissolving a powder of sodium bismuthate in the extracting solution to form the selective extracting solution.

12. The method of claim 1, further comprising contacting the organic phase curium with an aqueous stripping agent such that the curium unbinds with the organic phase curium solution to form an aqueous phase curium solution and collecting the curium.

13. The method of claim 12, wherein collecting the curium comprising collecting the curium in the aqueous phase curium solution and the method further comprises separating the curium from the aqueous phase curium solution by calcination or precipitation.

14. The method of claim 1, wherein the actinide partitioning unit comprises a plurality of mixing devices.SHQ0034WO / R24-3-PCT1515. The method of claim 14, wherein the plurality of mixing devices comprise centrifugal contactors, pulse columns, mixer settlers, or a combination thereof.

16. The method of claim 1, wherein collecting the americium comprising collecting the americium in the minor actinide aqueous solution and the method further comprises separating the americium from the minor actinide aqueous solution by calcination or precipitation.

17. The method of claim 16, wherein the americium comprises americium-241 and the method further comprises irradiating the americium-241 with neutrons after collecting the amercium-241 such that at least a portion of the americium-241 undergoes a neutron absorption reaction, thereby transmuting the at least a portion of the americium-241 into americium-242, wherein at least a portion of the americium-242 beta decays into curium-242.

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