Patent Application
20210354993
Nuclear power plants utilize nuclear fuel, which can degrade over time. The spent nuclear fuel has been typically viewed in some countries as a nuisance material, which may require particular precautions when handling. Additionally, recycling the spent nuclear fuel into new nuclear fuel or disposing of the spent nuclear fuel can be costly. These costs can be somewhat offset by utilizing some radioisotopes in the spent fuel for medical uses. The separations for medical uses, in particular, require high separation factors and good recovery of the valuable radioisotopes that may be present in very low concentrations and in very small amounts. There are challenges associated with the storage, transport, and/or recycling of spent nuclear fuel and the production of medical isotopes.
The present disclosure provides a method for separation of thorium from uranium and their decay products. The method comprises combining a nuclear fuel feedstock comprising thorium and uranium with a first acid to form a first solution. In various examples, the nuclear fuel feedstock can comprise other components, such as, for example, plutonium, other generated transuranic elements such as americium, curium, or combinations thereof. The first solution is contacted with an ion exchange resin that is selective for thorium or uranium. The thorium or uranium is at least partially removed from the first solution by binding the thorium or uranium to the ion exchange resin thereby forming a second solution. The second solution is combined with oxalic acid to precipitate uranium or thorium from the second solution to form a precipitate. In various examples, the thorium or uranium can be eluted from the ion exchange resin and then combined with oxalic acid to precipitate uranium or thorium to form the precipitate. The precipitate is separated from the second solution.
The present disclosure also provides a system for separation of thorium from uranium and their decay products. The system comprises an extraction vessel and a separation vessel. The extraction vessel comprises an extraction inlet, an ion exchange resin selective for thorium or uranium, and an extraction outlet. The extraction inlet is configured to receive a nuclear fuel feedstock comprising thorium and uranium and a first acid. The extraction vessel is configured to form a first solution from the nuclear fuel feedstock and the first acid. The extraction vessel is configured to contact the first solution with the ion exchange resin to form a second solution. The extraction outlet is configured to transport the second solution out of the extraction vessel. The separation vessel comprises a separation inlet and a separation outlet. The separation inlet is in fluid communication with the extraction outlet and is configured to receive the second solution and oxalic acid. The separation vessel is configured to combine the second solution and oxalic acid in order to precipitate the uranium or thorium in the second solution to form a precipitate.
It is understood that the inventions described in this specification are not limited to the examples summarized in this Summary. Various other aspects are described and exemplified herein.
The features and advantages of the examples, and the manner of attaining them, will become more apparent, and the examples will be better understood by reference to the following description of examples taken in conjunction with the accompanying drawing, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate certain examples, in one form, and such exemplifications are not to be construed as limiting the scope of the examples in any manner.
Certain exemplary aspects of the present disclosure will now be described to provide an overall understanding of the principles of the composition, function, manufacture, and use of the compositions and methods disclosed herein. An example or examples of these aspects are illustrated in the accompanying drawing. Those of ordinary skill in the art will understand that the compositions, articles, and methods specifically described herein and illustrated in the accompanying drawing are non-limiting exemplary aspects and that the scope of the various examples of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary aspect may be combined with the features of other aspects. Such modifications and variations are intended to be included within the scope of the present invention.
Reference throughout the specification to “various examples,” “some examples,” “one example,” “an example,” or the like, means that a particular feature, structure, or characteristic described in connection with the example is included in an example. Thus, appearances of the phrases “in various examples,” “in some examples,” “in one example,” “in an example,” or the like, in places throughout the specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in an example or examples. Thus, the particular features, structures, or characteristics illustrated or described in connection with one example may be combined, in whole or in part, with the features, structures, or characteristics of another example or other examples without limitation. Such modifications and variations are intended to be included within the scope of the present examples.
Spent nuclear fuel is typically only recycled into new nuclear fuel or vitrified for final disposal. During recycling, usually uranium is the desired product and thorium is thought of as a waste stream. However, the present inventors believe that the thorium-233U nuclear fuel cycle has the potential to provide isotopes of interest to the medical community if an effective technology were to be developed to extract these valuable isotopes from spent nuclear fuel from the thorium-233U cycle. The present inventors believe being able to extend the uses for the thorium-233U fuel cycle outside of power generation provides enhanced benefits for the use of the thorium-233U fuel cycle in nuclear power claims. Thus, the present disclosure provides methods and systems for separation of thorium from uranium and their decay products. The methods and systems according to the present disclosure can provide high purity medical grade thorium products, which may be used by the medical community or other industries. In various examples, the method and systems according to the present disclosure can provide high purity medical grade uranium products, which may be used by the medical community or other industries.
The present disclosure provides a method for separation of thorium from uranium and their decay products. The method can comprise combining a nuclear fuel feedstock comprising thorium and uranium and their decay products with a first acid to form a first solution. The first solution can be contacted with an ion exchange resin that is selective for thorium or uranium. The ions with a higher selectivity to the resin can be preferentially adsorbed to the ion exchange resin while the lower selectively species can pass through the ion exchange resin, hence separating the elemental species from one another. For example, thorium or uranium can be at least partially removed from the first solution by binding the thorium or uranium to the ion exchange resin thereby forming a second solution. In various examples, the second solution can be recycled for further exposure to additional ion exchange resin to improve the recovery of uranium or thorium. Once sufficient recovery has been achieved, the second solution can be combined with oxalic acid to precipitate the desired species, uranium or thorium. In various examples, if the second solution contains actinides and/or decay product impurities, a secondary solution comprising tributyl phosphate (TBP) and optionally a hydrocarbon, can be introduced to the second solution which can dissolve actinides and/or decay product impurities. Thereafter, dilute nitric acid can be introduced to a mixture of the second solution and secondary solution which can preferentially remove thorium from the mixture prior to exposure to oxalic acid (e.g., relative to other actinides and/or decay product impurities). Regardless of whether the secondary solution is used, the precipitate can be separated from the second solution. The precipitate can be processed into various products.
In various examples, the thorium or uranium can be eluted from the ion exchange resin and then combined with oxalic acid to precipitate uranium or thorium to form the precipitate. The precipitate can be processed into various products. In various examples, if the solution eluted from the ion exchange resin contains actinide or decay product impurities, a secondary solution comprising tributyl phosphate (TBP) can be introduced to the eluted solution which can dissolve actinides and/or decay product impurities. Thereafter, dilute nitric acid can be introduced to a mixture of the eluted solution and secondary solution which can preferentially remove thorium from the mixture prior to exposure to oxalic acid.
The ion exchange resin can be selective for thorium (e.g., thorium (IV)) or uranium (e.g., uranium (VI)) depending on the composition of the resin and the acid solution used for dissolution. Separation of actinides utilizing ion exchange resins is described in “SOLID-PHASE EXTRACTION FOR THE SEPARATION OF ACTINIDES FROM RADIOACTIVE WASTE” by S. Maischak and J. Fachinger, WM'01 Conference, Feb. 25-Mar. 1, 2001, Tucson Arizona which is hereby incorporated by reference. For example, the ion exchange resin and acid combination can be selective for uranium (e.g., comprise a greater affinity for binding with uranium (VI) than for thorium (IV)). An ion exchange resin that can be selective for uranium can comprise diamyl amylphosphonate, such as, for example, a UTEVA resin available from EIChroM Darien, Ill. The UTEVA resin is described in EIChroM ideas Newsletter Volume 4, Issue No. 2, published June 1997 entitled “UTEVA Resin” which is hereby incorporated by reference. The diamyl amylphosphonate can form nitrato complexes with actinide elements. An ion exchange resin that can be selective for uranium can comprise a quaternary ammonium salt, such as, for example, a TEVA resin available from TRISKEM International, France. The TEVA resin is described in the product sheet entitled TEVA resin by TRISKEM International available at “https://www.triskem-international.com/scripts/files/5c5855b887c4f4.23796223/PS_TEVA-Resin_EN_160927.pdf” which is hereby incorporated by reference.
As illustrated in the process schematic of
As illustrated in
The second solution can be combined with oxalic acid to precipitate the thorium from the second solution to form a precipitate comprising thorium (e.g., thorium oxalate which can comprise a reduced solubility in acidic solutions), 110. Precipitation of uranium and/or thorium can proceed according to “PARAMETRIC STUDY ON CO-PRECIPITATION OF U/TH in MOX FUEL OF AHWR” by S. K. Tiwari, et al., International Thorium Energy Conference (ThEC 2015) Oct. 12-15, 2015, Mumbai, India which is hereby incorporated by reference. The inventors of the present disclosure surprisingly discovered the combination of first removing uranium utilizing the ion exchange resin and then precipitating the thorium from the first solution could result in an unexpectedly enhanced purity and/or yield of products produced from the thorium precipitate. In various examples, the concentration of hydrochloric acid in the second solution can be kept at a sufficient level (e.g., greater than 5 Normal) to limit precipitation of uranium. In various other examples, the thorium in the second solution can be converted into a salt and precipitated out of the second solution by altering the pH of the second solution to reduce the solubility of the dissolved salt.
The oxalic acid can be added to the second solution at a substantially stoichiometric ratio to the thorium present in the second solution. For example, the oxalic acid may be added in a range of 0.001% to 1% by weight of the second solution. In various examples, keeping the oxalic acid at a substantially stoichiometric ratio to the thorium can limit excess oxalic acid present in the second solution and thus limits the present of the oxalic acid in the filtered solution. Therefore, the filtered solution can be recycled back into the process to be combined with the nuclear fuel feedstock, 114. The recycling can capture additional thorium, uranium, plutonium, or other decay products that remain in solution.
The thorium precipitate can be separated from the second solution by various processes, such as, for example, filtration to form a filtered thorium material and a filtered solution, 112. The filtered thorium material and optionally, ashless filter paper which can be used in the filtration process, may be oxidized by, for example, heating in an oxidizing environment (e.g., heating the filtered thorium material in a range of 200 degrees Celsius to 500 degrees Celsius in air), 116. The thorium dioxide can be processed to form a thorium product, 118.
In various examples, the ion exchange resin can also bind a portion of the thorium. In order to remove the bound thorium, the ion exchange resin can be washed with hydrochloric acid to elute preferentially the thorium for further separation at 110. The uranium may be recovered from the resin by elution with an acid or solvent or the uranium can be left adsorbed to the resin and/or immobilized such that is can be suitable for disposal.
In certain other examples, the ion exchange resin can be selective for thorium (e.g., comprise a greater affinity for binding with thorium (IV) than for uranium (VI)). An ion exchange resin that can be selective for thorium can be comprise a quaternary ammonium salt, such as, for example, a TEVA resin available from TRISKEM International, France. The TEVA resin can be selective for uranium by the use of hydrochloric acid as the first acid or selective for thorium by the use of nitric acid as the first acid.
As illustrated in the process schematic of
The second solution can be combined with oxalic acid to precipitate the uranium from the second solution to form a precipitate comprising uranium (e.g., uranium oxalate), 210. The inventors of the present disclosure surprisingly discovered the combination of first removing thorium utilizing the ion exchange resin and then precipitating the uranium from the first solution could result in an unexpectedly enhanced purity and/or yield of products produced from the uranium precipitate. In various examples, the concentration of nitric acid in the second solution can be kept at a sufficient level to limit precipitation of thorium.
The oxalic acid can be added to the second solution at a substantially stoichiometric ratio to the uranium present in the second solution. For example, the oxalic acid may be added in a range of 0.001% to 1% by weight of the second solution. In various examples, keeping the oxalic acid at a substantially stoichiometric ratio to the uranium can limit excess oxalic acid present in the second solution and thus limit the presence of the oxalic acid in the filtered solution. Therefore, the filtered solution can be recycled back into the process to be combined with the nuclear fuel feedstock if desired.
The uranium precipitate can be separated from the second solution by various processes, such as, for example, filtration to form a filtered uranium material and a filtered solution, 212. The filtered uranium material and optionally, ashless filter paper which can be used in the filtration process, may be oxidized by, for example, heating in an oxidizing environment (e.g., heating the filtered uranium material in a range of 200 degrees Celsius to 500 degrees Celsius in air) to form triuranium octoxide, 214. The triuranium octoxide can be processed to form a uranium product, 216
In various examples, the thorium bound to the ion exchange resin can be eluted utilizing an acid (e.g., <5 molar hydrochloric acid or no greater than 0.1 molar nitric acid), a solvent, or a combination thereof, to form a third solution comprising the thorium and the acid, 220. The third solution can then be processed through precipitation 110, filtration 112, oxidation 116, and processing into a product 118 as described with reference to
In various examples, the second solution or third solution can be further purified utilizing a second ion exchange resin prior to the separating utilizing precipitation 110 or 210. In certain examples, the second solution and/or the third solution can be further purified using a liquid-liquid extraction with a secondary solution comprising TBP and optionally a hydrocarbon (e.g., a liquid hydrocarbon) and thereafter introducing a dilute nitric acid prior to the separating utilizing precipitation 110 or 210. The liquid hydrocarbon can be in the liquid state at standard temperature and pressure.
As illustrated in
The separation vessel 310 can comprise separation inlets 312 and 314 and a separation outlet 316. The separation inlet 312 can be in fluid communication with the extraction outlet 306. The separation inlet 312 can be configured to receive the second solution and the separation inlet 314 can be configured to receive oxalic acid. The separation vessel 302 can be configured to combine the second solution and oxalic acid in order to precipitate the uranium or thorium in the second solution to form a precipitate. The separation outlet 316 can be configured to transport the precipitate and/or second solution out of the separation vessel 310.
In various examples, the separation outlet 316 can be in fluid communication with a filtration system. The filtration system can be configured to recycle a filtered solution to the extraction vessel 302 via a recycle line. In certain other examples, the system 300 can comprise a furnace to oxidize the precipitate separated in the filtration system. In some examples, the system 300 can comprise other processing equipment.
Those skilled in the art will recognize that the herein described methods and systems, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken as limiting.
Various features and characteristics are described in this specification to provide an understanding of the composition, structure, production, function, and/or operation of the invention, which includes the disclosed methods and systems. It is understood that the various features and characteristics of the invention described in this specification can be combined in any suitable manner, regardless of whether such features and characteristics are expressly described in combination in this specification. The Inventors and the Applicant expressly intend such combinations of features and characteristics to be included within the scope of the invention described in this specification. As such, the claims can be amended to recite, in any combination, any features and characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Furthermore, the Applicant reserves the right to amend the claims to affirmatively disclaim features and characteristics that may be present in the prior art, even if those features and characteristics are not expressly described in this specification. Therefore, any such amendments will not add new matter to the specification or claims and will comply with the written description, sufficiency of description, and added matter requirements.
Wth respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those that are illustrated or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.
The invention(s) described in this specification can comprise, consist of, or consist essentially of the various features and characteristics described in this specification. The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. Thus, a method or system that “comprises,” “has,” “includes,” or “contains” a feature or features and/or characteristics possesses the feature or those features and/or characteristics but is not limited to possessing only the feature or those features and/or characteristics. Likewise, an element of a composition, coating, or process that “comprises,” “has,” “includes,” or “contains” the feature or features and/or characteristics possesses the feature or those features and/or characteristics but is not limited to possessing only the feature or those features and/or characteristics and may possess additional features and/or characteristics.
The grammatical articles “a,” “an,” and “the,” as used in this specification, including the claims, are intended to include “at least one” or “one or more” unless otherwise indicated. Thus, the articles are used in this specification to refer to one or more than one (i.e., to “at least one”) of the grammatical objects of the article. By way of example, “a component” means one or more components and, thus, possibly more than one component is contemplated and can be employed or used in an implementation of the described compositions, coatings, and processes. Nevertheless, it is understood that use of the terms “at least one” or “one or more” in some instances, but not others, will not result in any interpretation where failure to use the terms limits objects of the grammatical articles “a,” “an,” and “the” to just one. Further, the use of a singular noun includes the plural, and the use of a plural noun includes the singular, unless the context of the usage requires otherwise.
In this specification, unless otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term “about,” in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described herein should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Any numerical range recited herein includes all sub-ranges subsumed within the recited range. For example, a range of “1 to 10” includes all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Also, all ranges recited herein are inclusive of the end points of the recited ranges. For example, a range of “1 to 10” includes the end points 1 and 10. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited. All such ranges are inherently described in this specification.
Any patent, publication, or other document identified in this specification is incorporated by reference into this specification in its entirety unless otherwise indicated but only to the extent that the incorporated material does not conflict with existing descriptions, definitions, statements, illustrations, or other disclosure material expressly set forth in this specification. As such, and to the extent necessary, the express disclosure as set forth in this specification supersedes any conflicting material incorporated by reference. Any material, or portion thereof, that is incorporated by reference into this specification, but which conflicts with existing definitions, statements, or other disclosure material set forth herein, is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material. Applicant reserves the right to amend this specification to expressly recite any subject matter, or portion thereof, incorporated by reference. The amendment of this specification to add such incorporated subject matter will comply with the written description, sufficiency of description, and added matter requirements.
Whereas particular examples of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
