INTRODUCTION

[0001 ] The present invention relates inter alia to methods of reprocessing nuclear waste, to an apparatus therefor, and to products derived therefrom.

BACKGROUND

[0002] Nuclear waste, in the form of spent fuel from nuclear reactors (or indeed nuclear weapons), is highly radioactive and usually contains not only significant quantities of the original nuclear fuel material, but also nuclear by-products derived from the nuclear power generation process. These nuclear by-products generally fall into two categories - i) fission products (FPs); and ii) minor actinides. Typically these by-products are themselves very hazardous to most forms of life and also to the environment, which is why their storage and disposal is so heavily regulated by government. [0003] The radioactivity of a radioactive substance naturally decays over time. As such, nuclear waste and/or nuclear by-products are typically contained in appropriate storage/disposal facilities for a time sufficient for the radioactivity to have decayed to lower levels, at which stage the nuclear waste and/or by-products may be more safely disposed of. However, the time taken for such radioactive decay can vary enormously depending on the particular radioisotopes concerned, and can range from days (for very short-lived isotopes) to the order of millions of years for the spent nuclear fuel itself. Currently, radioactive waste is generally managed by segregating and storing short-lived waste, disposing of low level waste at near surface level ILW to a geological disposal facility (GDF), and disposing of or reprocessing high-level wastes.

[0004] Over the last 60 years the principal reason for reprocessing irradiated nuclear fuel has been to recover unused uranium and plutonium from the fuel elements and thereby close the fuel cycle, gaining some 25% to 30% more energy from the original uranium in the process and thus contributing to energy security. A secondary reason is to reduce the volume of material to be disposed of as high-level waste to about one fifth. In addition, the level of radioactivity in the waste from reprocessing is much smaller and after about 100 years falls much more rapidly than in used fuel itself.

[0005] Reprocessing irradiated fuel to recover uranium and plutonium avoids the wastage of a valuable resource. Most of it - about 96% - is uranium, of which less than 1 % is the fissile U- 235 and up to 1 % is plutonium. Both can be recycled as fresh fuel, saving up to 30% of the natural uranium otherwise required.

[0006] The recovery of this uranium and plutonium is accomplished by the separation from fission products (FPs) and minor actinides (MAs) in a ~3M nitric acid solution using the PUREX process (Plutonium Uranium Extraction Process), which involves liquid-liquid ion-exchange extraction. This process relies on the extraction of U and Pu from the nitric acid phase into an organic phase comprising of Tri butyl phosphate (TBP) and an appropriate diluent such as odourless kerosene. The FPs and MAs ultimately remain in the aqueous phase and appear in the high level liquid waste (HLW).

[0007] The PUREX process has many advantages, so much so that it is the industry standard for the reprocessing of nuclear fuels, and indeed no other reprocessing technique has been seriously entertained by those skilled in the art since its inception and regulatory enshrinement. However, the PUREX process does present a number of inherent challenges, namely:

1 . The TBP degrades radiolytically and hydrolytically to by-products that hinder the decontamination of the U and Pu from FPs and MAs if not removed.

2. Removal of these by-products requires a separate clean-up stage in the chemical separation circuit.

3. TBP is not a specific extractant, and the aqueous phase needs to be carefully controlled in order to provide the required selectivity.

4. The TBP and diluents used are sparing soluble in nitric acid and ultimately are discarded to the environment, with adverse consequences. 5. The separation circuit is multistage and complicated.

6. As U and Pu represent about 96% of the metals in the dissolved irradiated fuel the contactors (columns, mixer-settlers) used in the extraction circuit have to be sized accordingly. 7. The high-level-waste (HLW) requires further treatment to produce a stable solid waste appropriate for disposal.

8. FPs and MAs are not separated from each other by the PUREX process, and current nuclear waste reprocessing techniques do not allow for the separation and isolation of these ingredients.

[0008] Thus far, the nuclear industry has failed to conceive of a practical and sufficiently selective alternative to the PUREX process for use in the nuclear reprocessing industry. It is therefore an object of the present invention to solve at least one problem inherent in the prior art, and a particular object to develop a practical and selective alternative to the PUREX process.

BRIEF SUMMARY OF THE DISCLOSURE

[0009] According to a first aspect of the present invention, there is provided: i) a method of processing a mixture comprising nuclear material(s) and one or more nuclear by-products; ii) a method of separating nuclear material(s) from one or more nuclear byproducts; iii) a method of decontaminating nuclear material(s) contaminated with one or more nuclear by-products; iv) a method of reprocessing nuclear waste (or spent nuclear fuel) which comprises a mixture comprising nuclear material(s) and one or more nuclear by-products; v) a method of recovering nuclear material(s) from nuclear waste (or spent nuclear fuel), which nuclear waste comprises a mixture comprising nuclear material(s) and one or more nuclear by-products; vi) a method of processing a mixture comprising nuclear material(s) and one or more nuclear by-products to increase the proportion/concentration of nuclear material(s) within said mixture relative to the one or more nuclear by-products; or vii) a method of purifying a mixture comprising nuclear material(s) and one or more nuclear by-products to increase the proportion/concentration of nuclear material(s) within said mixture relative to the one or more nuclear by-products; the method comprising:

(a) providing a pre-contacted mobile phase comprising a/the mixture of the nuclear material(s) and the one or more nuclear by-products in a liquid medium; (b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s).

[0010] According to a second aspect of the present invention, there is provided a method of analyzing a mixture comprising nuclear material(s) and one or more nuclear by-products, the method comprising:

(a) providing a pre-contacted mobile phase comprising a/the mixture of the nuclear material(s) and the one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) eluting the stationary phase with an eluent;

(d) periodically or continuously analyzing the eluate. [0011 ] According to a third aspect of the present invention, there is provided a reprocessed nuclear material(s) obtained by, obtainable by, or directly obtained by the method of the first aspect.

[0012] According to a fourth aspect of the present invention, there is provided a use of a reprocessed nuclear material(s) of the third aspect as a nuclear fuel (i.e. a primary nuclear energy source) in a nuclear reactor or as a nuclear fuel/explosive (i.e. a primary nuclear energy source) in nuclear weapons.

[0013] According to a fifth aspect of the present invention, there is provided a nuclear fuel comprising the nuclear material(s) of the third aspect. [0014] According to a sixth aspect of the present invention, there is provided a nuclear reactor or a nuclear weapon comprising the nuclear fuel of the fifth aspect.

[0015] According to a seventh aspect of the present invention, there is provided a method of producing a nuclear fuel, the method comprising:

(a) providing a pre-contacted mobile phase comprising a mixture of nuclear material(s) and one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s);

(d) processing the nuclear material(s) contained within the mobile phase or nuclear material(s)-enriched eluate to produce a nuclear fuel.

[0016] According to an eighth aspect of the present invention, there is provided a nuclear fuel obtained by, obtainable by, or directly obtained by the method of the seventh aspect. [0017] According to a ninth aspect of the present invention, there is provided a method of producing a nuclear reactor or nuclear weapon, the method comprising:

(a) providing a pre-contacted mobile phase comprising a mixture of nuclear material(s) and one or more nuclear by-products in a liquid medium; (b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s);

(d) processing the nuclear material(s) containing within the mobile phase or nuclear material(s)-enriched eluate to produce a nuclear fuel; (e) incorporating the nuclear fuel within a nuclear reactor or nuclear weapon.

[0018] According to a tenth aspect of the present invention, there is provided a nuclear reactor or a nuclear weapon obtained by, obtainable by, or directly obtained by the method of the ninth aspect.

[0019] According to an eleventh aspect of the present invention, there is provided a method of isolating and/or purifying one or more nuclear by-products from a mixture comprising nuclear material(s) and one or more nuclear by-products, the method comprising:

(a) providing a pre-contacted mobile phase comprising a/the mixture of the nuclear material(s) and the one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s); (d) removing one or more of the one or more nuclear by-products from the stationary phase, optionally via elution of the stationary phase with an eluent to provide an eluate comprising (and suitably relatively enriched with) the one or more of the one or more nuclear by-products;

(e) isolating one or more of the one or more nuclear by-products (e.g. from a suitable eluate).

[0020] According to a twelfth aspect of the present invention, there is provided one or more nuclear by-products obtained by, obtainable by, or directly obtained by the method of the eleventh aspect.

[0021 ] According to a thirteenth aspect of the present invention, there is provided a use of one or more nuclear by-products of the twelfth aspect in electronics, in fuel cells, or as precious metals or catalysts.

[0022] According to a fourteenth aspect of the present invention, there is provided a method of disposing of one or more nuclear by-products, the method comprising:

(a) providing a pre-contacted mobile phase comprising a mixture of the nuclear material(s) and one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s); (d) either: i) removing the one or more nuclear by-products from the stationary phase (e.g. via elution of the stationary phase with an eluent to provide an eluate comprising the one or more nuclear by-products) and disposing of said nuclear by-products (optionally following their isolation or partial-isolation from the eluate); or ii) disposing of the one or more nuclear by-products with the stationary phase to which they remain associated.

[0023] According to a fifteenth aspect of the present invention, there is provided a method of treating decontamination liquors (e.g. liquors arising from nuclear decontamination operations, which contain nuclear by-products), the method comprising:

(a) providing a pre-contacted mobile phase comprising one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s).

(d) optionally thereafter removing the one or more nuclear by-products from the stationary phase (e.g. via elution of the stationary phase with an eluent to provide an eluate comprising the one or more nuclear by-products).

[0024] According to a sixteenth aspect of the present invention, there is provided a method of producing or purifying nuclear material(s), the method comprising:

(a) providing a pre-contacted mobile phase comprising nuclear material(s) and one or more nuclear by-products or impurities (e.g. which may cause the nuclear material(s) to be deemed "out-of-specification") in a liquid medium; (b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) or impurities relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution (or washing) of the stationary phase with an eluent (or washing medium), to provide a post- contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s).

[0025] According to a seventeenth aspect of the present invention, there is provided an apparatus or kit for: i) processing a mixture comprising nuclear material(s) and one or more nuclear by-products; ii) separating nuclear material(s) from one or more nuclear by-products; iii) decontaminating nuclear material(s) contaminated with one or more nuclear by-products; iv) reprocessing nuclear waste (or spent nuclear fuel) which comprises a mixture comprising nuclear material(s) and one or more nuclear byproducts; v) recovering nuclear material(s) from nuclear waste (or spent nuclear fuel), which nuclear waste comprises a mixture comprising nuclear material(s) and one or more nuclear by-products; vi) processing a mixture comprising nuclear material(s) and one or more nuclear by-products to increase the proportion/concentration of nuclear material(s) within said mixture relative to the one or more nuclear by- products; or vii) purifying a mixture comprising nuclear material(s) and one or more nuclear by-products to increase the proportion/concentration of nuclear material(s) within said mixture relative to the one or more nuclear by- products; viii) analyzing a mixture comprising nuclear material(s) and one or more nuclear by-products; the apparatus or kit comprising a stationary phase comprising one or more stationary phase matrix material(s), optionally arranged as a series of separate chromatography stations, wherein the stationary phase has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s).

[0026] According to an eighteenth aspect of the present invention, there is provided a reprocessing facility (or reprocessing plant) comprising the apparatus as defined in the seventeenth aspect.

[0027] According to an eighteenth aspect of the invention, there is provided a method of optimizing a multi-column chromatography apparatus and/or method for any of the aforesaid uses (e.g. reprocessing nuclear waste (or spent nuclear fuel) which comprises a mixture comprising nuclear material(s) and one or more nuclear by-products), the method comprising: i) determining relative concentrations of the individual nuclear by-products in the nuclear waste or in an initial mobile phase as defined herein; ii) Determining which are the most radioactive nuclear by-products or groups of nuclear by-products (e.g. by reference to half-life or radiation count); iii) Determining the net impact of specific nuclear by-products or of groups of nuclear by-products, by taking account of both radioactivity and concentration of the relevant nuclear by-products, and thereby determining a preferential order in which the nuclear by-products should be removed from the mobile phase (suitably with the most radiolyically damaging nuclear by-products being removed first before the least damaging); iv) Either or both: a. Performing multi-column chromatography upon a mobile phase sample of the relevant nuclear waste {via any of the methods defined herein where a plurality of interconnected individual columns, each comprising a different stationary phase matrix material(s) or mixture thereof, are used for a given stationary phase), with the columns arrange in-series in any given sequential order (where suitably each individual column is substantially the same size and comprises substantially the same weight of matrix material(s)), and sampling eluate before and after each individual column (i.e. the input and output of the mobile phase from each column) to determine the relative concentrations of the nuclear by-products in the mobile phase before and after each column, and thereby determining the impact of each individual column upon (i.e. the affinity of each column for) the various nuclear by-products; and/or b. Performing an individual column chromatography experiment, for each of the individual columns in the multi-column chromatography arrangement, upon successive identical mobile phase samples of the relevant nuclear waste, and determining the relative concentrations of the nuclear by-products in the mobile phase both before and after each column (i.e. the input and output of the mobile phase from each column), and thereby determining the impact of each individual column upon (i.e. the affinity of each column for) the various nuclear by-products; v) Optionally repeating step iv) part a) with the columns arranged in a different order; vi) Determining, from the observations made in steps iv) and v), a sequence of columns which selectively removes, from the mobile phase, some or substantially all of the most radioactive nuclear by-products or groups nuclear by-products towards the beginning of the column sequence (i.e. the first columns remove the most radioactive nuclear by-products).

[0028] Features, including optional, suitable, and preferred features of any aspect of the present invention may, where appropriate, be also features, including optional, suitable, and preferred features of any other aspect of the present invention.

BRIEF DESCRIPTION OF THE DRA WINGS

[0029] For a better understanding of the present invention, and to show how embodiments of the same are put into effect, reference is now made, by way of example, to the following figures, in which:

[0030] Figure 1 shows a flow chart illustrating the stages of an idealised reprocessing method;

[0031] Figure 2 is a schematic diagram illustrating continuous moving bed chromatography.

[0032] Figure 3 is a schematic diagram illustrating the principle of continuous annular chromatography (CAC).

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0033] Herein, the term "nuclear waste" refers to product(s) and/or by-products of nuclear technology, especially of nuclear power generation (e.g. from nuclear reactors), particularly that involving nuclear fission. However, in some embodiments, "nuclear waste" may arise from other applications of nuclear technology, for instance, including "nuclear waste" derived from nuclear weapons, medicine, or nuclear research. In particular embodiments, the relevant "nuclear waste" is that requiring decontamination and/or reprocessing. Typically the relevant "nuclear waste" is hazardous, and its storage and/or disposal is suitably regulated by government to safeguard human health and the environment. "Nuclear waste" may be processed to leave "radioactive waste" intended for disposal, which radioactive waste may be high level, intermediate, or low level radioactive waste. "Nuclear waste", in the context of the present application, is generally spent nuclear fuel comprising a mixture comprising nuclear material(s) and one or more nuclear by-products. Preferably the nuclear material(s) are separated from the one or more nuclear by-products, and the nuclear by-products become "radioactive waste".

[0034] Herein, "radioactive waste for storage" is radioactive waste that is intended for storage.

[0035] Herein, the term "nuclear material" refers to metal(s) and/or compound(s) thereof which are suitable, or processable to be suitable (i.e. precursor materials), for use as a nuclear fuel in a nuclear reactor or as a nuclear fuel/explosive in nuclear weapons. As such, references to a specific nuclear material by way of the metal only, may also include compound(s) thereof (this is customary in the art), though optionally it may also just refer to the metal (or metal ion) per se. As such, where the nuclear material(s) is said to consist of uranium and plutonium, this may include compounds of uranium and plutonium. A "nuclear material" generally comprises one or more "primary nuclear elements" (regardless of the form of the nuclear material - e.g. element, ionic, compound, solution, solid, etc.) that is/are primarily responsible for the generation of nuclear energy (e.g. uranium is the primary nuclear element of uranium dioxide). The "nuclear material" is distinct from by-products of nuclear reactions (herein "nuclear by-products"), for instance, by-products such as fission products (FP) and/or minor actinides (MA). Like the "nuclear materials" references to "nuclear by-products" general refers to element(s) and/or compound(s) thereof which are by-products of nuclear reactions, and reference to specific "nuclear by-products" by way of their element(s) may also include compound(s) thereof, though optionally it may also just refer to the element (or ion thereof) per se. The "nuclear material" may be enriched or unenriched, depending on the application (e.g. the particular type of nuclear reactor) in question. In the context of the present invention, relevant "nuclear material(s)" are those which are recovered and/or intended for recovery from mixtures including both the "nuclear material(s)" and associated "nuclear by-products" (e.g. fission products (FPs) and minor actinides (MAs) resulting from the "burn up" or nuclear reactions of the nuclear material(s)), whether said nuclear materials are for reuse or disposal. As such the "nuclear material(s)" are suitably integral to both inputs and outputs of the processes of the invention. The term "nuclear material" encompasses all forms of said material, be it the elemental form, ionic form, compound form, solid, liquid, or solution form of said material. In general, it is the properties of the primary nuclear element itself (rather than particular isotopic effects) that allow it to be separated from nuclear by-products in the methods of the invention.

[0036] Herein, a "nuclear fuel" is a material that may be "burned" by nuclear fission and/or fusion to produce nuclear energy. As such, a "nuclear fuel" is suitably a primary source of nuclear energy. In the context of the present specification, a "nuclear fuel" suitably refers to the material itself rather than articles comprising or consisting essentially of said material, for example, fuel rods.

[0037] Herein, where a particular material is said to be "radioactive" or "radioactively- contaminated", said material suitably exhibits elevated levels radioactivity or enrichment of radioactive isotopes (i.e. as compared to naturally occurring levels). Suitably, such a material has been exposed to nuclear radiation (e.g. radiation generated inside a nuclear reactor), for example, neutron radiation, alpha radiation, beta radiation, and gamma radiation. Suitably, such a material has been exposed to ionizing radiation, be it directly ionizing radiation (e.g. alpha and beta radiation) or indirectly ionizing radiation (e.g. neutron and gamma radiation). Suitably, such a material has been exposed to alpha, beta, gamma, or neutron radiation. In particular, said material has suitably been exposed to neutron radiation (e.g. as per that generated within a nuclear reactor). Throughout this specification, references to exposure or non-exposure to radiation refer to artificial and/or deliberate exposures as opposed to exposures to naturally occurring radiation. [0038] Herein, the term "burn up", "burnup", and "fuel utilization" are synonymous and are measures of the energy extracted from a primary nuclear fuel source, such as the nuclear materrial(s) and fuels described herein. "Burn up" is often measured in terms of the energy released per mass of initial fuel in Gigawatt days per metric ton of the relevant nuclear material(s) or at least the heavy metal(s) atoms thereof (GWd/t). [0039] References herein to "columns" in the context of column chromatography may also encompass other suitable contactor devices.

[0040] Herein, the terms "elution", "elute", "eluent", "eluate", etc. suitably relate to the elution of the stationary phase. Such elution may entail eluting nuclear by-products from the stationary phase (e.g. in the chromatographic sense), but may simply involve washing any occluded materials (e.g. nuclear materials) away from the stationary phase. Where such elution involves merely washing occluded materials (e.g. nuclear materials) away from the stationary phase, the eluent (which may instead be called a "washing medium" in this context if preferred) will in general be (substantially) the same (e.g. same acid concentration) as the feed material (e.g. the liquid medium of the pre-contacted mobile phase) so as to not affect the nuclear by-products (e.g. FPs or the MAs) distribution.

[0041] Herein, unless stated otherwise, the "weight percent (wt% or %w/w)" or "% by weight" of a particular component in relation to a given composition means the % of said component by weight relative to the total weight of the composition.

[0042] Herein, the term "consist essentially of", when used to describe the proportion of a given ingredient within a material, suitably means the material comprises at least 70 wt% of the given ingredient, more suitably at least 80 wt%, more suitably at least 90 wt%, more suitably at least 95 wt%, and most suitably at least 99 wt%.

[0043] Herein, the term "particle size" or "pore size" refers respectively to the length of the longest dimension of a given particle or pore. Both sizes may be measured using a laser particle size analyser and/or electron microscopes (e.g. tunneling electron microscope, TEM, or scanning electron microscope, SEM).

[0044] The term "mesoporous" is well known in the art, and herein generally refers to materials containing pores with diameters between 2 and 50 nm. [0045] Unless stated otherwise, any reference herein to an "average" value is intended to relate to the mean value.

General Methodology and Advantages of the Invention

[0046] The present invention provides a novel method to reprocess nuclear waste (i.e. spent nuclear fuel), be it nuclear waste from a nuclear reactor or nuclear weapons, though most suitably nuclear waste from a nuclear reactor. The method generally involves chromatographic separation of nuclear by-products (especially fission products, and minor actinide products) from nuclear material(s) so that the nuclear material(s) can be converted into nuclear fuel for reuse within nuclear reactors or nuclear weapons. Such chromatographic reprocessing methodologies are envisaged either as a replacement for established reprocessing technologies, such as PUREX, or as a reprocessing technology to be used alongside already established technologies in order to obtain more viable reprocessed nuclear material(s)/fuels and nuclear by-products which may be more viably disposed of or even used.

[0047] The reprocessing methods of the invention generally involve contacting a mobile phase, containing a mixture of nuclear material(s) and nuclear by-product(s) (i.e. the nuclear waste), with a stationary phase that selectively binds the nuclear by-product(s), so that the mobile phase can be subsequently separated from the stationary phase with a somewhat diminished nuclear by-product content, and therefore enriched in nuclear material(s). The process is suitably a chromatographic process, whereby the recovered mobile phase is obtained following elution of the stationary phase with a suitable eluent, to obtain a nuclear material(s)-enriched eluate that may then be further processed to produce a nuclear fuel for reuse, e.g. in a nuclear reactor or nuclear weapon. [0048] The reprocessing methods of the invention provide a surprisingly practical and selective alternative and/or complement to the PUREX process. Such methods unexpectedly selectively extract minor components from a complex mixture with remarkable efficiency. Furthermore, the components used in the methods of the invention (e.g. stationary phase) are sufficiently resistant to radiolytic and/or hydrolytic damage that nuclear materials can be effectively decontaminated without undue hindrance, and without the need for additional cleanup steps, thus reducing overall processing, radiation exposure, and costs. The methods of the invention also allow a high degree of tolerance, in terms of the inputs and operating parameters, without substantial loss of selectivity, and furthermore may be readily optimized for reprocessing individual batches of nuclear waste. The methods allow for clean separation of the various components, thereby reducing the risk of radioactive contamination of the environment following the disposal of waste streams. The methods of the invention are straight forward and relatively space-efficient, despite the fact that the nuclear materials intended for recovery still account for the vast majority of species within the reprocessing mixtures, and can be managed without complex multistage separation circuits. The methods of the invention directly yield stable solid state wastes which can be easily disposed of with minimal hazard. Furthermore, the methods of the invention surprisingly allow for the separation of fission products and minor actinides, thereby allowing for the safe and separate disposal of each, or indeed the separate use of each.

[0049] The nuclear by-product extraction methods of the present invention may also be advantageously employed upstream from the existing PUREX process, since the present invention allows for initial removal of highly radioactive materials (e.g. high β/γ emitters such as Cesium and Strontium fission products) which would otherwise compromise the TBP (via radiolysis) in the PUREX process. Nuclear Waste and Mixtures of Nuclear Materials and Nuclear By-Products

[0050] The nuclear waste (e.g. spent nuclear fuel) used in accordance with the invention suitably comprises a mixture comprising nuclear material(s) and one or more nuclear byproducts. As such, the nuclear material(s) and the one or more nuclear by-products are suitably as defined anywhere herein. However, references herein to "nuclear waste" may be interchagable with a "mixture comprising nuclear material(s) and one or more nuclear byproducts", which may or may not be nuclear waste as such.

[0051 ] Suitably, the nuclear waste is derived from a nuclear reactor (suitably from the nuclear fuel thereof), suitably from an operational nuclear reactor, suitably a nuclear reactor operating pursuant to said nuclear fuel for at least one year, suitably at least two years. Suitably, the nuclear waste is the nuclear fuel of said reactor.

[0052] In a particular embodiment, the nuclear reactor in question is a pressurized water (PWR) reactor, most suitably a light water reactor. Suitably, the nuclear reactor in question is an enriched-uranium nuclear reactor. In future the relevant nuclear reactor may be a GEN IV system, i.e. fast reactor.

[0053] The nuclear waste is suitably (derived from) irradiated uranium nuclear material. Suitably, the uranium nuclear material is (slightly) enriched uranium. Suitably said uranium nuclear material (i.e. in its original form prior to irradiation within a nuclear reactor) comprises at least 1 % w/w U-235, suitably at least 2% w/w U-235, more suitably at least 3% w/w U-235, suitably about 3.5% w/w U-235.

[0054] The nuclear waste in question suitably has a "burn up" of at least 5 Gigawatt days per ton of nuclear material (e.g. uranium) (GWd/t), suitably at least 10 GWd/t, more suitably at least 20 GWd/t, and most suitably at least 30 GWd/t. The nuclear waste in question suitably has a "burn up" of at most 100 Gigawatt days per ton of nuclear material (e.g. uranium) (GWd/t), suitably at most 80 GWd/t, more suitably at most 50 GWd/t, and most suitably at most 40 GWd/t.

[0055] Suitably, the nuclear waste in question has been allowed to "cool" (i.e. outside the nuclear reactor or warhead) for at least 1 year, suitably at least 2 years, suitably at least 4 years, and more suitably at least 5 years. Suitably, the nuclear waste in question has been allowed to "cool" (i.e. outside the nuclear reactor or warhead) for at most 10 years, suitably at most 6 years.

[0056] In a particular embodiment, the nuclear waste is irradiated pressurized water reactor 3.5% U-235 fuel, suitably with a burn up of about 33 GWd/t, suitably cooled for about 5 years.

[0057] Suitably, the nuclear waste comprises at least 70% w/w nuclear material(s), suitably at least 90% w/w, more suitably at least 95% w/w, most suitably at least 96% w/w. Suitably, the nuclear waste comprises at most 99.5% w/w nuclear material(s), suitably at most 98% w/w, more suitably at most 97% w/w. Suitably, the nuclear waste comprises between 94% w/w and 98% w/w uranium (or compound(s) thereof) and between 0.5 and 1 .5% w/w plutonium (or compound(s) thereof). Suitably, the nuclear waste comprises at least 0.5% w/w nuclear byproducts, suitably at least 2% w/w, more suitably at least 3% w/w. Suitably, the nuclear waste comprises at most 10% w/w nuclear by-products, suitably at most 5% w/w, more suitably at most 3.5% w/w. [0058] Suitably, the weight ratio of nuclear material(s) to nuclear by-products is between 70:30 and 99.5:0.5, suitably between 90:10 and 98:2, most suitably between 95:5 and 97:3.

Nuclear Material(s)

[0059] Nuclear materials, in the context of the present invention, are metal(s) and/or compound(s) thereof which are suitable, or processable to be suitable (i.e. precursor materials), for use as a nuclear fuel (i.e. a primary nuclear energy source) in a nuclear reactor or as a nuclear fuel/explosive (i.e. a primary nuclear energy source) in nuclear weapons. In a particular embodiment, the nuclear material(s) in question are suitable for use as a nuclear fuel in a nuclear reactor. [0060] A nuclear material suitably comprises a "primary nuclear element" (regardless of the form of the nuclear material - e.g. element, ionic, compound, solution, solid, etc.) that is primarily responsible for the generation of nuclear energy (e.g. uranium is the primary nuclear element of uranium dioxide). The nuclear material(s) may be in any chemical or physical form, and references to specific nuclear material(s) by reference to the element only may equally encompass compounds of said elements.

[0061 ] A nuclear material is distinct from by-products of nuclear reactions (herein "nuclear byproducts"), for instance, by-products such as fission products (FP) and/or minor actinides (MA). [0062] In preferred embodiments, the nuclear material comprises (or the primary nuclear element is) uranium, plutonium, thorium and/or compound(s) thereof. Most suitably, the nuclear material comprises (or the primary nuclear element is) uranium, plutonium, and/or compound(s) thereof.

[0063] The nuclear material may be a "source material", which is typically natural or depleted uranium (including uranium ore concentrates), or a "special fissionable material", which is typically enriched uranium (U-235), uranium-233, and/or plutonium-239. The nuclear material may be enriched or unenriched, depending on the application (e.g. the particular type of nuclear reactor) in question.

[0064] In preferred embodiments, a nuclear material comprises fissile nuclear material(s), or nuclear material(s) which are processable to become fissile (i.e. precursors to fissile materials), including materials which may be transformed into fissile materials through neutron bombardment. Such fissile nuclear material(s) suitably comprise heavy fissile elements capable of nuclear fission, especially when they are struck by neutrons. Suitably such fissile nuclear material is capable of a self-sustaining chain reaction that releases energy in a controlled manner in a nuclear reactor or in a rapid uncontrolled manner in a nuclear weapon.

[0065] The nuclear material may suitably comprise, consist essentially of, or even consist of, uranium and plutonium or compound(s) thereof. The nuclear material may suitably comprise uranium-235 ( ²³⁵ U) and/or plutonium-239 ( ²³⁹ Pu), and/or compound(s) thereof, which are fissile materials commonly used in the nuclear industry. The nuclear material may suitably comprise at least 80% w/w uranium (regardless of isotope), more suitably at least 90% w/w uranium, more suitably at least 95% w/w uranium, most suitably at least 98% w/w uranium. The nuclear material may suitably comprise at least 0.1 % w/w plutonium (regardless of isotope), suitably at least 0.5% w/w plutonium, most suitably at least 0.9% w/w plutonium. In a particular embodiment, the nuclear material comprises 90-99.5% w/w uranium (or compound(s) thereof) and 0.5-10% w/w plutonium (or compound(s) thereof), more suitably 98-99.5% w/w uranium and 0.5-2% w/w plutonium. The nuclear material may suitably comprise uranium, of which at least 1 % w/w of said uranium is U-235, suitably at least 2% w/w is U-235, most suitably at least 3% w/w is U-235. The nuclear material may suitably comprise uranium, of which at most 10% w/w of said uranium is U-235, suitably at most 5% w/w is U-235, most suitably at most 4% w/w is U- 235. In a particular embodiment, the nuclear material is or comprises PWR 3.5% U-235 fuel.

[0066] Within a nuclear fuel, the nuclear material(s) in question are usually in a form appropriate for the application in question, and such forms are well known in the art. For instance, enriched uranium fuels/materials (often used in PWRs) are typically in the form of a hard ceramic oxide (UO2) which is used to form the nuclear reactor fuel elements. However, it is well understood that such hard ceramic U0 ₂ is produced by extracting uranium from uranium ore, converting said extracts into U ₃ 0 ₈ before subsequently converting it to U0 ₂ , then UF ₄ , and then into gaseous UF ₆ to facilitate uranium enrichment before said uranium is converted back into the hard ceramic U0 ₂ product used to form the fuel elements. [0067] The nuclear material(s) may be considered in terms of "input nuclear material(s)" (i.e. those which are exposed to the processes of the invention) and "output nuclear material(s)" (i.e. products of the processes of the invention). Suitably, the nuclear material(s) are the same in both cases, and suitably the composition of any nuclear material(s), for instance where multiple materials are involved (e.g. where both uranium and plutonium are present), are substantially the same, suitably at least in terms of the primary nuclear elements themselves (for instance where the chemical or physical forms may have changed during the course of the processes of the invention).

[0068] Suitably, the nuclear material(s) products, in terms of the output of the method(s) of the present invention, comprises or consist essentially of uranium and plutonium, which mixture may form the basis of reprocessed fuel for reuse in nuclear reactors. It is in some senses advantageous that these two nuclear materials are not separated, for instance, to reduce threats from nuclear proliferation. Nuclear By-Product(s)

[0069] In the context of the present invention, the nuclear by-products are suitably distinct from the nuclear material(s). The nuclear by-products are suitably by-products of the nuclear material(s) undergoing a nuclear reaction, for instance in a nuclear reactor during its operational lifetime.

[0070] The nuclear by-products are themselves suitably radioactive. Suitably, the nuclear byproducts are emitters of alpha, beta, gamma, and/or neutron radiation.

[0071 ] The nuclear by-products suitably comprise or consist essentially of fission products (FP) and/or minor actinides (MA), suitably derived from nuclear reactions of the nuclear material(s), suitably nuclear reactions which take place during "burn up" inside a nuclear reactor. The FPs and MAs may be in any chemical or physical form, and references to specific FPs and MAs by reference to the element only may equally encompass compounds of said elements.

Fission Products (FPs)

[0072] Fission products (FPs) are the atomic fragments remaining after large atomic nuclei (e.g. uranium) split into two or more smaller nuclei (though generally just two), whilst generally also releasing neutrons and some heat energy and gamma radiation in the process. The fission products are themselves generally radioactive, which is why they pose a disposal and storage hazard in their own right. The fission products suitably include one or more (suitably at least two) or all of: Germanium (e.g. Ge-72, 73, 74, 76), Arsenic (e.g. As-75), Selenium (e.g. Se-77, 78, 79, 80, 82), Bromine (e.g. Br-81 ), Krypton (e.g. Kr-83, 84, 85, 86), Rubidium (e.g. Rb-85, 87), Strontium (e.g. Sr-88, 89,90), Yttrium (e.g. Y-89), Zirconium (e.g. Zr-90 to Zr-96), Niobium (e.g. Nb-95), Molybdenum (e.g. Mo-95, 97, 98, 100), Technetium (e.g. Tc-99), Ruthenium (e.g. Ru-101 to Ru-106), Rhodium (e.g. Rh-103), Palladium (e.g. Pd-105 to Pd-1 10), Silver (e.g. Ag- 109), Cadmium (e.g. Cd-1 1 1 to Cd-1 16), Indium (e.g. ln-1 15), Tin (e.g. Sn-1 17 to Sn-126), Antimony (e.g. Sb-121 , 123), Tellurium (e.g. Te-125, 127 to 132), Iodine (e.g. 1-127, 129, 131 ), Xenon (e.g. Xe-131 to Xe-136), Cesium (e.g. Cs-133, 134, 135, 137), Barium (e.g. Ba-138, 139), and lanthanides, such as lanthanum (e.g. La-139), cerium (e.g. Ce-140 to Ce-144), neodymium (e.g. Nd-142 to Nd-146, 148, 150), promethium (e.g. Pm-147), and samarium (e.g. Sm-149, 151 , 152, 154). Suitably the fission products may include compound(s) of any of the elements or isotopes listed. The fission products of the nuclear by-products suitably comprise one or more of the above-listed FPs, suitably two or more thereof.

[0073] The fission products suitably constitute at least 90% w/w of the nuclear by-products, more suitably at least 92% w/w, more suitably at least 95% w/w, most suitably at least 96% w/w. The fission products suitably constitute at most 99.5% w/w of the nuclear by-products, more suitably at most 99% w/w, more suitably at most 98% w/w, most suitably at most 97% w/w.

Minor Actinides (MAs)

[0074] Minor actinides (MAs) are the actinide elements present in nuclear waste other than uranium and plutonium, which are instead generally termed major actinides. The minor actinides may suitably include one or more (suitably at least two) or all of neptunium, americium, curium, berkelium, californium, einsteinium, and fermium, and are themselves typically radioactive, thus creating a waste disposal and storage hazard. In terms of radioactivity, the most crucial minor actinide isotopes in nuclear waste are neptunium-237, americium-241 , americium-243, curium-242 to curium-248, and californium-249 to californium-252. Suitably the minor acitindes may include compound(s) of any of the elements or isotopes listed. The minor actinides of the nuclear by-products suitably comprise neptunium, americium, and suitably also curium.

[0075] The minor actinides suitably constitute at least 0.5% w/w of the nuclear by-products, more suitably at least 1 % w/w, suitably at least 2% w/w, most suitably at least 3% w/w. The minor actinides suitably constitute at most 10% w/w of the nuclear by-products, more suitably at most 5% w/w, most suitably at most 4% w/w.

Particular embodiments

[0076] In a particular embodiment, the nuclear by-products comprise neptunium, americium, curium, cesium, rubidium, strontium, barium, yttrium, one or more lanthanides, zirconium, selenium, tellurium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, tin, antimony, and/or compound(s) thereof. Suitably all the compounds and elements defined as "nuclear by-products" are radioactive.

Mobile Phase and the Provision thereof

[0077] In the context of the present invention, the mobile phase comprises a mixture of nuclear material(s) and one or more nuclear by-products. This "mixture" may suitably be "nuclear waste" or derived from "nuclear waste" (e.g. following dissolution or other treatments). The mobile phase additionally comprises a liquid medium. Suitably the nuclear material(s) and one or more nuclear by-products are dissolved, dispersed, or otherwise suspended within the liquid medium. Suitably at least 50% w/w of the nuclear waste (or the "mixture") is dissolved in the liquid medium, suitably at least 70% w/w, more suitably at least 90% w/w, most suitably at least 95% w/w. Suitably, the mobile phase is a solution, with the relevant solutes being dissolved in the relevant liquid medium (see below).

[0078] "Providing the mobile phase" suitably involves mixing the liquid medium with the nuclear waste or mixture of the nuclear material(s) and the one or more nuclear by-products. Such a process suitably involves dissolving (completely or partially, but preferably substantially completely) said nuclear waste (or the "mixture") in the liquid medium. Suitably dissolution is performed in hot acid (e.g. hot nitric acid or hot sulphuric acid). Suitably the resulting solution is 0.2 to 6M in the relevant acid, more suitably 0.5 to 3M in the relevant acid. The acid used to dissolve the nuclear waste may be a concentrated acid (e.g. 7M nitric acid), though typically the acid concentration will be diminished prior to contacting the mobile phase with the stationary phase. The dissolving process may involve first partially dissolving the relevant material(s) before a further round of contact with the acid takes place.

[0079] Suitably, the mobile phase is relative concentrated. Suitably the mobile phase comprises at least 50g/L of nuclear waste (or of the "mixture"), suitably at least 100g/L, suitably at least 200g, suitably at least 280g/L. Suitably, the mobile phase comprises at most 500g/L of nuclear waste, suitably at most 400g/L, suitably at most 350g/L. [0080] Relative proportions and ratios of nuclear material(s) and nuclear by-products (e.g. in the nuclear waste or the "mixture") are detailed above, and are equally applicable to the mobile phase. As such, it is straightforward to calculate suitable quantities and concentrations of solutes based on the aforementioned proportions. However, in a particular embodiment, the mobile phase comprises 250-350 g/L nuclear material(s) and 5 to 15 g/L nuclear by-products. In a particular embodiment, the mobile phase comprises the following materials within +/- 20% of the stated concentrations, suitably within +/- 10% of the stated concentrations, suitably within +/- 5% of the stated concentrations:

[0081 ] Since the nuclear by-products are separated from the nuclear material(s) during the process of the present invention, strict control of dissolution in the formation of the mobile phase is not essential, in contrast to the established PUREX process, where dissolution control is critical. Though the mobile phase may be filtered prior to being provided to the method of the invention or contacted with the stationary phase, this is optional.

[0082] The composition of the "input mobile phase" (i.e. the pre-contacted mobile phase entering the method of the invention) is suitably different from the "output mobile phase" (i.e. the mobile phase exiting the method of the invention, or the relevant eluate) in terms of the relative proportions of nuclear material(s) to nuclear by-products. Suitably the "output mobile phase" (or relevant eluate, which may be more dilute than the input mobile phase) has a higher proportion of nuclear material(s) to the nuclear by-products. [0083] The liquid medium is suitably selected for mutual compatibility with the stationary phase, and for optimal separation factors in terms of the stationary phases binding/association affinity for the nuclear by-products relative to the nuclear material(s). However, the stationary phase may be selected for compatibility with the liquid medium, and the liquid medium selected for another reason (e.g. solubility of the relevant materials). The liquid medium suitably dissolves the nuclear material(s) and the nuclear by-product(s). The liquid medium suitably is or comprises an acid. Suitably the liquid medium is or comprises an inorganic acid, such as sulphuric acid or nitric acid. Suitably the liquid medium prevents or minimizes any precipitation of plutonium. Suitably the liquid medium prevents or minimizes the formation of colloidal suspensions. In a particular embodiment, the liquid medium is sulphuric acid. In a particular embodiment, the liquid medium is nitric acid. The acid is suitably 0.5 to 8M acid, suitably 1 to 4M acid. The nitric acid is suitably 0.5M to 4M nitric acid. The ultimate molarity of the acid in the mobile phase may be suitably between 0.2 and 8M, though is more suitably 0.5 to 4M.

Stationary Phase and contact of Mobile Phase therewith [0084] The stationary phase has a higher affinity for one or more of the nuclear by-products than for the nuclear material(s), at least in the form in which the nuclear by-products and nuclear materials are present within the mobile phase. Suitably the stationary phase has a higher affinity for two or more of the nuclear by-products than for the nuclear material(s).

[0085] The stationary phase comprises at least one stationary phase matrix material. The stationary phase may comprise a plurality of different stationary phase matrix materials. Suitably different stationary phase matrix materials exhibit differential affinities for different nuclear by-products. As such, one of the nuclear by-products may have a preferential affinity for one of the stationary phase matrix materials over another stationary phase matrix material. [0086] The stationary phase may be a single bulk material (be it a packed monolith, as in a chromatographic column or cartridge, or particulate material intended to be slurried or monolithically packed), comprising either a single stationary phase matrix material or a mixture of a plurality of different stationary phase matrix materials. Where a stationary phase comprises a single bulk material comprising a plurality of different stationary phase matrix materials, the different matrix materials may selectively bind different nuclear by-products so that the single bulk material is multifunctional. As such, different matrix materials within the single bulk may be judiciously chosen to optimize the extraction of nuclear by-products from the mobile phase. In fact, the methods of the invention may involve a step of analyzing the composition of the nuclear waste/mixture (or the mobile phase) to determine the optimal composition of the stationary phase, prior to preparing the stationary phase. Such stationary phases may be simply prepared by mixing (substantially homogenously) the relevant different stationary phase matrix materials, optionally in the (air) dry state or in a slurried state. Suitably, such stationary phases having mixtures of matrix materials within a single bulk are packed into a monolith (e.g. a column) such that "contacting" the mobile phase and stationary phase (i.e. step (b)) and suitably also the subsequent "separating" of the mobile phase from the stationary phase (i.e. step (c)) is characterized by liquid chromatography (e.g. column chromatography).

[0087] Alternatively, the stationary phase may comprise a plurality of distinct bulk materials (optionally each distinct bulk being as per the "single bulk material(s)" defined above - e.g. a series of separate stationary phase monoliths). Each distinct bulk material suitably comprises either a single stationary phase matrix material or a mixture of a plurality of different stationary phase matrix materials. The different stationary phase matrix materials suitably exhibit differential affinities for different nuclear by-products. In such embodiments, the individual distinct bulk materials of the stationary phase are suitably arranged in series in fluid communication with each other (i.e. fluidly interconnected) such that the mobile phase (and any eluent that may be used) can be successively contacted with each distinct individual bulk material in sequence. Distinct bulk materials may be packed directly adjacent to one another (i.e. so that they are in direct contact with each other) and/or may be physically separated (so that they do not contact each other directly), for instance, by a fluid flow channel. In an embodiment, the plurality of distinct bulk materials may be packed as a series of separate monoliths that are arranged in series along a fluid channel (i.e. through which the mobile phase and any eluents may pass), so that "contacting" (i.e. step (b)) and optionally also "separating" (i.e. step (c)) can be characterized by liquid chromatography (e.g. column chromatography), albeit via a series of distinct chromatography stations. Again, different bulk materials and different stationary phase matrix materials (or different mixtures thereof) may be employed throughout the stationary phase in such an "in-series" arrangement. Different stationary phase matrix materials may be mixed together as part of any one of the individual distinct bulk materials along the "in-series" stationary phase arrangement. Alternatively, each of two or more individual distinct bulk materials (i.e. stationed at different points) may comprise or essentially consist of a different but single stationary phase matrix material. By way of example, the stationary phase may comprise a series of individual monoliths (or individual packed columns), wherein each monolith (or column) comprises a different stationary phase matrix material or different composition of stationary phase matrix materials, depending on whether a particular monolith comprises a single stationary phase matrix material or mixture of a plurality of stationary phase matrix materials. Again, the different stationary phase matrix materials within the stationary phase arrangement suitably exhibit differential affinities for different nuclear byproducts. Therefore, each individual monolith or column along the path of the stationary phase may selectively extract one or more particular nuclear by-products from the mobile phase. Such an arrangement may be envisaged as a sequence of smaller columns, each comprising a different stationary phase matrix material, as opposed to having a larger column comprising a plurality of different stationary phase matrix materials.

[0088] Though preferably the stationary phase is fluidly interconnected along its entire path, in certain embodiments, the stationary phase may have a fluid disconnect such that the output mobile phase (or eluate) from one part of the stationary phase may be introduced as a input mobile phase in a another part of the stationary phase.

[0089] Suitably the stationary phase, whether arranged as a single bulk or multiple distinct bulk materials, is configured for liquid column chromatography, wherein suitably the or each bulk material is packed into a column. As such, the stationary phase (be it a single column/part or comprising multiple separate columns/parts) suitably defines a stationary phase path though which the mobile phase passes during "contacting" of the mobile phase with the stationary phase.

[0090] Contacting the mobile phase with a stationary phase may merely involve slurrying the stationary phase (be it a single stationary phase matrix material or mixture of different materials) with the mobile phase. However, suitably "contacting" involves "loading" the mobile phase to a column of stationary phase matrix material (whether a single or mixture of said materials), by methods well known in the art of liquid chromatography (e.g. via gravity or via a pump). The mobile phase is then suitably passed through the column (e.g. whether under positive or negative pressure, or under gravity), and optionally through subsequent columns (where a plurality of columns characterize the stationary phase) by methods well known in the art of chromatography.

[0091 ] "Contacting" suitably comprises binding, extracting, absorbing, or adsorbing one or more of the nuclear by-products onto/into the stationary phase or a part thereof. Equally "contacting" may be considered to comprise removing one or more of the nuclear by-products from the mobile phase (suitably with the stationary phase or a part thereof). During contact between the mobile phase and the relevant stationary phase (or relevant part thereof), suitably nuclear by-products preferentially bind the stationary phase (or relevant part thereof) whilst the nuclear material(s), and optionally other nuclear by-products, remain within the mobile phase. Contact between the mobile phase and the stationary phase (or relevant part thereof) may be maintained for a time sufficient to ensure that the relevant nuclear by-products preferentially bind to the stationary phase. The flow rate of the mobile phase through the stationary phase (where chromatography is involved) may be judiciously controlled to optimize nuclear byproduct extraction rates.

[0092] Suitably the mobile phase is contacted with the stationary phase in a manner so that the stationary phase is saturated (in terms of binding sites) to at least 50% capacity, suitably at about 75% capacity, suitably at about 95%.

[0093] Ultimately, the (post-contacted) mobile phase is separated from the stationary phase. Suitably the output (post-contacted) mobile phase is enriched in nuclear material(s) relative to nuclear by-product(s) relative to the input (pre-contacted) mobile phase. [0094] The methods of the invention suitably involve eluting the stationary phase (especially where chromatographic methods are used) with an eluent, suitably after loading the stationary phase with the pre-contacted mobile phase. The output mobile phase may ultimately be separated from the stationary phase as an eluate comprising the mobile phase diluted with eluent.

[0095] The eluent is suitably miscible with the mobile phase, or at least with the liquid medium thereof. Suitably the eluent is substantially the same (or a diluted form - e.g. with water) as the liquid medium of the mobile phase. As such, in certain embodiments, the eluent is an acid, such as sulphuric acid or nitric acid. In a particular embodiment, the acid is nitric acid. The acid is suitably 0.5 to 8M acid, suitably 1 to 4M acid. The nitric acid is suitably 0.5M to 4M nitric acid.

[0096] The stationary phase suitably comprises a stationary phase matrix material that is a solid state ion-exchange material, suitably a cation exchange material. Such a cation-exchange material suitably allows cationic forms of the element(s) of the one or more nuclear by-products to be selectively extracted from the mobile phase by the ion-exchange material. [0097] The stationary phase suitably comprises one or more microporous and/or mesoporous stationary phase matrix materials, most suitably mesoporous stationary phase matrix materials. The stationary phase suitably comprises a stationary phase matrix material that comprises modified silica, suitably a cation-exchange silica, suitably a meso-porous silica cation exchange material. The silica may, for instance, be modified through being doped with one or more of boron, aluminium, and/or gadolinium.

[0098] Microporous and/or mesoporous materials suitable for use in the stationary phase are outlined in Dyer et al, "Synthesis and Characterisation of mesoporous silica phases containing heteroatoms, and their cation exchange properties. Part 1 . Synthesis of Si, Al, B, Zn substituted MCM-41 materials and their characterisation", Microporous and Mesporous Materials, 126 (2009), p.192-200, which is hereby incorporated by reference. This document describes production of the relevant matrix materials as well as their characterization. Mesoporous gadolinium-based matrix materials are described in Liu et al, "Disordered Mesoporous Gadolinosilicate Nanoparticles Prepared Using Gadolinium Based Ionic Liquid Emulsions: Potential as Magnetic Resonance Imaging Contrast Agents", Australian Journal of Chemistry, 201 1, 64(5) 617-624 (https://pubiications.csiro.au/rpr/downloaci?pjd=csiro:EP1 1562£dsid=PS3) which is also hereby incorporated by reference. Though these gadolinium matrices were developed for an entirely different purpose, they have been used as effective cation-exchange stationary phase matrix materials in accordance with methods of the present invention. [0099] In an embodiment, the stationary phase comprises one or more stationary phase matrix materials (suitably two or more) selected from the group including:

• Variously functionalized amorphous or crystalline silica(s), or mixtures thereof.

• Amorphous or crystalline silica(s) which have boron cations inserted thereinto, or mixtures thereof. · Amorphous or crystalline silica(s) which have aluminium cations inserted thereinto, or mixtures thereof.

• Amorphous or crystalline silica(s) which have gadolinium cations inserted thereinto.

• Amorphous or crystalline silica(s) impregnated with calixarene, or mixtures thereof.

• Amorphous or crystalline silica(s) impregnated with crown ethers, or mixtures thereof. · Amorphous or crystalline silica(s) impregnated with tributyl phosphate, or mixtures thereof.

• Mesoporous mobil composition of matter materials (e.g. MCM-41 and MCM-48).

[00100] As explained above, the stationary phase may comprise a plurality of different ion- exchange resin or materials, and/or different modified silica-based cation-exchange resins. The stationary phase may comprise amorphous or crystalline silica incorporating appropriate ligands for binding one or more of the nuclear by-product(s) (e.g. FPs and MAs). As such, one or more stationary phase matrix materials may be or comprise amorphous or crystalline silica incorporating appropriate ligands for binding one or more of the nuclear by-product(s) (e.g. FPs and MAs).

[00101] Some potentially advantageous characteristics of the stationary phase and matrix material(s) thereof which have been developed and/or selected for use in accordance with the present invention, include:

1 . Radiation stability;

2. Acid stability, and

3. Selectivity for the nuclear by-products or family of nuclear by-products (e.g. whether differentiated by size, oxidation state, or otherwise)

4 Availability

5 Cost

6 Durability i.e. low attrition

7 Appropriate physical properties such as size, density, porosity, surface area etc.

8 Appropriate chemical characteristics such as fast kinetics, reversible extraction, medium/high capacity for the appropriate radionuclide/s, etc.

[00102] The stationary phase and/or matrix material(s) thereof, are suitably (substantially) free of organic materials, though in certain embodiments downstream parts of the stationary phase may include organic materials where upstream parts of the stationary phase are arranged to remove the most radioactive nuclear by-products from the mobile phase.

[00103] The stationary phase may, as abovementioned, comprise several chromatography stations, each comprising different or a different mixture of stationary phase matrix materials (preferably each being a monolith/packed column). Different chromatography stations are suitably designed to extract different nuclear by-products. The sequential order of the different chromatography stations may be judiciously arranged so that, when the mobile phase is passed therethrough, nuclear by-products are selectively extracted in a certain order to minimize damage to the stationary phase and optimize efficiency. For instance, the most radioactive nuclear by-products (which generally have the shortest half-life) could be the first to be extracted from the mobile phase onto the stationary phase (at one of the early chromatography stations) whilst (relatively) less radioactive nuclear by-products (which generally have longer half-lives) could potentially be extracted later, e.g. further downstream on the stationary phase at one of the later chromatography stations. Suitably the stationary phase and/or matrix material(s) thereof chemical differentiate between different radioactive species (i.e. in terms of binding affinity), since selective chromatographic separation of specific isotopes of the same element is extremely difficult.

[00104] A suitable process may involve a first stage, comprising removing some or (substantially) all of the fission products from the mobile phase, suitably onto or into a first part of the stationary phase (or onto/into a first or first set of matrix material(s), be them mixed or arranged separately as a series of individual chromatography stations); and a second stage, comprising selectively removing some or (substantially) all of the minor actinides from the mobile phase, suitably onto or into a second part of the stationary phase (or onto/into a second or second set of matrix material(s), whether mixed or separate). The first and second state may be in any order, but in a particular embodiment they are carried out in sequence with the first stage followed by the second. The first stage may itself be split into sub-stages 1 A and 1 B, wherein Stage 1 A preferentially removes from the mobile phase fission products with the shortest half-lives, whilst Stage 1 B preferentially removes from the mobile phase fission products with longer half-lives than those in Stage 1 A. The process may comprise a third stage, preferably after the first and second stages, the third stage comprising removing some or (substantially) all remaining fission products and/or minor actinides (suitably with the longest half-lives) from the mobile phase, suitably onto or into a third part of the stationary phase (or onto/into a third or third set of matrix material(s), whether mixed or separate). The third part of the stationary phase may comprise one or more matrix materials comprising an organic polymeric material(s), since suitably by this stage the mobile phase has had the majority of the most radioactive nuclear by-products removed. The second part of the stationary phase may comprise one or more matrix materials comprising an organic polymeric material(s), since by this stage the mobile phase may have had a significant amount of the most radioactive nuclear by-products removed. The relevant organic polymeric material(s) may be suitably functionalized with an appropriate ligand, for example, which selectively binds one or more of the nuclear byproducts.

[00105] The first stage most suitably comprises a plurality of chromatography stations arranged in series, each comprising a different stationary phase matrix material, suitably for absorbing a different or different composition of fission products. Likewise, the second stage may suitably comprise a plurality of chromatography stations arranged in series, each comprising a different stationary phase matrix material, suitably for absorbing a different or different composition of minor actinides.

[00106] Suitably, some or all of the stationary phase matrix materials employed (e.g. in the first stage and/or suitably the second stage and optionally also the third stage), comprise modified silica and/or mesoporous molecular sieves (suitably as defined herein). Suitably the relevant matrix material(s) may be functionalized through appropriate modification. Suitably the relevant matrix material(s) is mesoporous, comprises mesoporous particles, or comprises particles with mesoporous parts. The stationary phase matrix materials(s) may comprise particles having a mesoporous core (suitably having an ordered framework with substantially uniform mesopores) and an amorphous silica wall, suitable examples being mobil composition of matter materials (e.g. MCM-41 or MCM-48). Suitably such matrix material(s) can be produce with a controlled pore size, suitably through judicious adaptations of the synthesis conditions, for instance, using different surfactants. Suitably the pore size is between 1 .5 and 20 nm.

[00107] Silica matrix material(s) used in accordance with the invention may be modified by methods well known in the art, for instance the: a) insertion of a hetero-cation, such as boron, aluminium etc, during the preparation of the silica matrix; b) impregnation of the matrix with an appropriate extractant/ligand, such as tributyl phosphate, calixarene, crown ethers, etc.; c) Co-condensation of a ligand into the matrix during preparation of the silicate; and/or d) Attachment of ligand/s to the polymeric silica structure.

[00108] Silica matrix material(s) may be classified into crystalline or amorphous forms, both of which have been prepared and developed as metal/cation exchangers. The crystalline forms are the most suitably for use with the present invention, since they are advantageously easier to characterize at the meso-scale, which thereby facilitates attribution of the desired functionality and location thereof. Identifying the location of functionality in amorphous materials is somewhat more difficult. [00109] In the context of the invention, suitable silica matrix material(s) are amorphous or crystalline silica matrices having a heterocation inserted thereinto, such as boron, aluminium, or gadolinium.

[00110] The mobile phase exiting the stationary phase (which may also be termed the "eluate", particularly where an eluent is used to facilitate passage of the mobile phase through the stationary phase) is suitably a product (e.g. a nuclear material(s)-enriched eluate) comprising the nuclear materials in a proportion that is higher, relative to the nuclear by-products, than in the original pre-treated mobile phase mixture. Such a product may be further processed to isolate the nuclear materials for their subsequently intended purpose (e.g. reuse, deposal, etc.). [00111] The weight of stationary phase matrix material(s) relative to the weight of nuclear waste being purified may be customized to optimize the process for any particular batch of nuclear waste. Suitably, the weight of stationary phase matrix material(s) is selected based on the total weight of nuclear by-products (within the nuclear waste), since it is said nuclear by-products that are suitably extracted from the mobile phase by the stationary phase matrix material(s). Suitably, the weight ratio of stationary phase matrix material(s) to nuclear by-products is between 50:1 and 100,000:1 , suitably between 100:1 and 10000:1 , suitably between 500:1 and 2000:1 .

Passing the Mobile Phase through the Stationary Phase [00112] "Contacting" of the mobile phase with the stationary phase suitably involves passing the mobile phase through the stationary phase (i.e. along a path defined by the stationary phase and the matrix material(s) of which it is composed, be it along a path defined by a single or multiple separate parts/columns), suitably from an "upstream end" (i.e. start point) to a "downstream end" (i.e. end point). Suitably, during this process, the mobile phase makes contact with (substantially) all parts of the stationary phase. Suitably the process of passing the mobile phase through the stationary phase is characterized by liquid chromatography, and suitably the stationary phase comprises one or more chromatography stations as defined herein. Suitably, the stationary phase is eluted during the passage of the mobile phase through the stationary phase. Suitably such elution facilitates the passage of the mobile phase through the stationary phase, and suitably the eluate emanating from the downstream end of the stationary phase represents a post-treated mobile phase (i.e. wherein nuclear by-products have been removed from the original mobile phase). References herein to mobile phase may be synonymous with "eluate" where the stationary phase has been eluted to facilitate passage of the mobile phase therethrough. [00113] The mobile phase may be passed through the stationary phase in a range of manners well known to those skilled in the art. For instance, the mobile phase may be pumped through the stationary phase, under the influence of either positive or negative pressure, suitably with a suitable eluent. Alternatively, the mobile phase may be passed through the stationary phase under the influence of gravity. Preferably, a pump is used in conjunction with an eluent to facilitate passage of the mobile phase through the stationary phase.

[00114] Any suitable eluent may be used in the method(s) of the invention. A suitability eluent is typically compatible with the stationary phase, the mobile phase, and the contents thereof. Most suitably, the eluent comprises the liquid medium, or at least some components of the liquid medium, used in the provision of the initial pre-treated mobile phase. The eluent may suitably have any of the properties or characteristics defined in relation to the liquid medium. For instance, the eluent is suitably selected for mutual compatibility with the stationary phase, and for optimal separation factors in terms of the stationary phases binding/association affinity for the nuclear by-products relative to the nuclear material(s). The eluent suitably mobilizes the nuclear material(s) and the nuclear by-product(s). The eluent suitably is or comprises an acid. Suitably the eluent is or comprises an inorganic acid, such as sulphuric acid or nitric acid. Suitably the eluent prevents or minimizes any precipitation of plutonium. Suitably the eluent prevents or minimizes the formation of colloidal suspensions. In a particular embodiment, the eluent is sulphuric acid. In a particular embodiment, the eluent is nitric acid. The acid is suitably 0.5 to 8M acid, suitably 1 to 4M acid. The nitric acid is suitably 0.5M to 4M nitric acid.

[00115] In a particular embodiment, the process of passing the mobile phase through the stationary phase is characterized by batch liquid chromatography, again optionally with one or more chromatography stations as defined herein. This may involve applying the initial mobile phase to the "upstream end" (i.e. the start/top) of the stationary phase, suitably to at the start of a packed column of one or more stationary phase matrix material(s) (suitably at the start of the first column, where multiple columns are used in series), before the stationary phase is then eluted (e.g. by continuously feeding an eluent though the "upstream end") to pass the mobile phase through the stationary phase such that the nuclear by-products contained in the mobile phase are removed by the stationary phase. Such a batch chromatography process may include one or more chromatography stations along the stationary phase, though suitably all such chromatography stations are fluidly interconnected. However, in certain embodiments, the stationary phase may be split, such that eluates must be transferred and reapplied to a further stationary phase, optionally defined as herein. [00116] In a particular embodiment, the process of passing the mobile phase through the stationary phase is characterized by continuous liquid chromatography, again optionally with one or more chromatography stations as defined herein. Such continuous chromatography can be accomplished via simulated moving bed (SMB) or continuous annular chromatography (CAC). In such systems, the stationary phase is in constant motion relative to the "feed point" (i.e. where the initial pre-treated mobile phase is introduced). This can be accomplished by either moving the bed and keeping the feed points stationary, or moving the feed points and keeping the bed stationary. In addition, this motion can be designed such that the feed flow and the bed movement may be in a counter current or crosscurrent direction. Systems with truly constant motion between the "feed points" and the bed (i.e. stationary phase) will be continuous, whereas those that merely simulate this motion will be semi-continuous. A semi- continuous process can approach the continuous process by making smaller and smaller discrete movements. For instance, in a cascade of fixed beds operated in a "merry-go-round" sequence, product can be collected from one bed and feed fed to another while the remaining columns are at an intermediate stage of the process. If timed in such a way that product is always being collected at one of the different column outlets, an apparently continuous process exists.

Further Processing of Recovered Mobile Phase

[00117] Suitably, in the method(s) of the invention, once the mobile phase has been suitably "contacted" with the stationary phase to remove sufficient nuclear by-products from said mobile phase, the post-treated mobile phase is then suitably separated from the stationary phase, most suitably via a process of elution (or washing) which allows recovery of an eluate comprising the nuclear material(s) in a more purified form than within the original pre-contacted mobile phase.

[00118] This eluate/output mobile phase may be suitably further processed, suitably in any number of ways well known in the art. For instance, the eluate/output mobile phase may undergo any one or more of the following post-treatments, including: i) any number of further reprocessing treatments well known in the art - this may involve extracting the nuclear material(s) from the eluate/output mobile phase, modifying the nuclear materials, enriching the nuclear materials, and forming nuclear fuel or fuel elements therefrom; ii) liquid-liquid ion-exchange, for instance, using the established Plutonium Uranium Extraction process (PUREX); iii) reprocessing the nuclear material(s) into nuclear fuel for nuclear reactors or nuclear weapons (e.g. if necessary processing the eluate/output mobile phase; iv) incorporating any reprocessed nuclear fuel into a nuclear reactor or nuclear weapon.

[00119] The nuclear material(s) may, with or without the abovementioned further processing, be stored or converted into a storable form prior to such storage.

[00120] According to an aspect of the present invention, there is provided a reprocessed nuclear material(s) obtained by, obtainable by, or directly obtained by the aforementioned method(s).

[00121] According to a further aspect of the present invention, there is provided a use of a reprocessed nuclear material(s) as a nuclear fuel (i.e. a primary nuclear energy source) in a nuclear reactor or as a nuclear fuel/explosive (i.e. a primary nuclear energy source) in nuclear weapons.

[00122] According to a further aspect of the present invention, there is provided a method of producing a nuclear fuel, the method comprising:

(a) providing a pre-contacted mobile phase comprising a mixture of nuclear material(s) and one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution of the stationary phase with an eluent, to provide a post-contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s);

(d) processing the nuclear material(s) contained within the mobile phase or nuclear material(s)-enriched eluate to produce a nuclear fuel. [00123] According to a further aspect of the present invention, there is provided a nuclear fuel obtained by, obtainable by, or directly obtained by the aforementioned method.

[00124] According to a further aspect of the present invention, there is provided a nuclear fuel comprising the aforementioned reprocessed nuclear material(s). According to a further aspect of the present invention, there is provided a nuclear reactor or a nuclear weapon comprising the aforementioned nuclear fuel.

[00125] According to a further aspect of the present invention, there is provided a method of producing a nuclear reactor or nuclear weapon, the method comprising:

(a) providing a pre-contacted mobile phase comprising a mixture of nuclear material(s) and one or more nuclear by-products in a liquid medium; (b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution of the stationary phase with an eluent, to provide a post-contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s);

(d) processing the nuclear material(s) contained within the mobile phase or nuclear material(s)-enriched eluate to produce a nuclear fuel;

(e) incorporating the nuclear fuel within a nuclear reactor or nuclear weapon.

[00126] According to a further aspect of the present invention, there is provided a nuclear reactor or a nuclear weapon obtained by, obtainable by, or directly obtained by the aforementioned method.

Recovery of Nuclear By-products

[00127] According to an aspect of the present invention, there is provided a method of isolating and/or purifying one or more nuclear by-products from a mixture comprising nuclear material(s) and one or more nuclear by-products, the method comprising:

(a) providing a pre-contacted mobile phase comprising a/the mixture of the nuclear material(s) and the one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution of the stationary phase with an eluent, to provide a post-contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s);

(d) removing one or more of the one or more nuclear by-products from the stationary phase, optionally via elution of the stationary phase with an eluent to provide an eluate comprising (and suitably relatively enriched with) the one or more of the one or more nuclear by-products;

(e) isolating one or more of the one or more nuclear by-products (e.g. from a suitable eluate).

[00128] According to a further aspect of the present invention, there is provided one or more nuclear by-products obtained by, obtainable by, or directly obtained by the aforementioned method.

[00129] The eluate containing the one or more nuclear by-products may be collected as one or more separate fraction(s) to the eluate containing the nuclear material(s). Suitably, the eluate containing the nuclear by-products is collected after collection and separation of the eluate containing the nuclear materials.

[00130] The eluent used to extract the nuclear by-products from the stationary phase may be the same or different from any eluent used during the "contacting" and/or "separation" of the mobile phase with/from the stationary phase during the purification of the nuclear material(s). Suitably the eluent may be different, since the eluent system used during "contacting" and/or "separation" is suitably selected to optimize separation of the nuclear materials and nuclear byproducts so that the nuclear by-products are retained by the stationary phase whilst the nuclear materials are washed away from the stationary phase within the eluent.

[00131] Any eluent containing the nuclear by-product(s) may be further processed prior to isolation of the one or more nuclear by-products. For instance, the liquid phase (i.e. eluent) may be removed, or the nuclear by-products may be extracted using liquid-liquid ion exchange.

[00132] The nuclear by-products may then be used, stored, or disposed of.

Disposing of Nuclear By-products [00133] The nuclear by-products may be disposed of either with the stationary phase matrix material(s) to which they are associated/bound (i.e. if said by-products have not been "stripped" from the stationary phase through elution), with the eluent within which they have been eluted from the stationary phase, or in an isolated form (i.e. following separation from the stationary phase matrix material(s) to which they were formally associated/bound). Regardless of the form in which they are disposed, the nuclear by-products may first be stored for a period of time (e.g. to allow "cooling") prior to disposal.

[00134] Where the nuclear by-products are bound to a silica-based stationary phase matrix material, they are particular well suited for direct storage and/or disposal. [00135] As such, an aspect of the present invention provides a method of disposing of one or more nuclear by-products, the method comprising:

(a) providing a pre-contacted mobile phase comprising a mixture of the nuclear material(s) and one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) separating the mobile phase from the stationary phase, optionally following elution of the stationary phase with an eluent, to provide a post-contacted mobile phase (or eluate) that is enriched (suitably in terms of the relative proportions of nuclear material(s) to nuclear by-product(s)), relative to the pre-contacted mobile phase, in the nuclear material(s);;

(d) either: i) removing the one or more nuclear by-products from the stationary phase (e.g. via elution of the stationary phase with an eluent to provide an eluate comprising the one or more nuclear by-products) and disposing of said nuclear by-products (optionally following their isolation or partial-isolation from the eluate); or ii) disposing of the one or more nuclear by-products with the stationary phase to which they remain associated.

Uses of Nuclear By-products

[00136] According to a thirteenth aspect of the present invention, there is a use of one or more nuclear by-products of the twelfth aspect in electronics, fuel cells, or as precious metals or catalysts. The present invention will effectively increase the abundance of otherwise rare electronic and precious components. Analvical uses of the method of the invention

[00137] The aforementioned chromatographic techniques used in accordance with the present invention may be easily adapted, by methods well known in the art, to produce analytical chromatographic methodologies. For instance, the mobile phase(s), stationary phase(s), eluent(s), and contact/elution method(s), etc., may be employed in exactly the manner as hereinbefore described, though suitably on a smaller scale, to afford an analytical liquid chromatography method, apparatus, or system. Suitably, in analytical methods of the invention, the stationary is eluted, be it by isocratic and/or gradient elution, to afford chromatographic eluate fractions or eluates that are analysed by techniques well known in the art (e.g. mass spectroscopy, radiation detection methods, etc.), suitably to quantitatively and/or qualitatively determine the composition of said fractions or eluates.

[00138] As such, an aspect of the present invention provides a method of analyzing a mixture comprising nuclear material(s) and one or more nuclear by-products, the method comprising:

(a) providing a pre-contacted mobile phase comprising a/the mixture of the nuclear material(s) and the one or more nuclear by-products in a liquid medium;

(b) contacting the mobile phase with a stationary phase (wherein the stationary phase suitably has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s));

(c) eluting the stationary phase with an eluent; (d) periodically or continuously analyzing the eluate.

[00139] Suitably the analytical method involves analyzing the eluate for nuclear material(s) and/or nuclear by-product(s), and suitably quantifying said by-products.

[00140] Suitably the analytical method may be used to establish a suitably method for purifying the nuclear material(s) - i.e. in method development. Apparatus / Plant

[00141] According to an aspect of the present invention, there is provided an apparatus or kit for: i) processing a mixture comprising nuclear material(s) and one or more nuclear by-products; ii) separating nuclear material(s) from one or more nuclear by-products; iii) decontaminating nuclear material(s) contaminated with one or more nuclear by-products; iv) reprocessing nuclear waste (or spent nuclear fuel) which comprises a mixture comprising nuclear material(s) and one or more nuclear byproducts; v) recovering nuclear material(s) from nuclear waste (or spent nuclear fuel), which nuclear waste comprises a mixture comprising nuclear material(s) and one or more nuclear by-products; vi) processing a mixture comprising nuclear material(s) and one or more nuclear by-products to increase the proportion/concentration of nuclear material(s) within said mixture relative to the one or more nuclear byproducts; or vii) purifying a mixture comprising nuclear material(s) and one or more nuclear by-products to increase the proportion/concentration of nuclear material(s) within said mixture relative to the one or more nuclear byproducts; viii) analyzing a mixture comprising nuclear material(s) and one or more nuclear by-products; the apparatus or kit comprising a stationary phase comprising one or more stationary phase matrix material(s), optionally arranged as a series of separate chromatography stations, wherein the stationary phase has a higher affinity for one or more of the nuclear by-product(s) relative to the nuclear material(s).

[00142] The apparatus or kit may comprise any of the aforementioned items for use with the method(s) of the present invention. Likewise, the apparatus or kits may incorporate features and arrangements of features (e.g. "in-series" columns) as described herein in relation to the methods of the invention.

[00143] The present invention also provides a reprocessing facility (or plant) comprising the apparatus as defined herein.

Method of Optimising the Arrangement of Columns for In-Series Multiple Column Chromatography

[00144] According to an aspect of the invention, there is provided a method of optimizing a multi-column chromatography apparatus and/or method for any of the aforesaid uses (e.g. reprocessing nuclear waste (or spent nuclear fuel) which comprises a mixture comprising nuclear material(s) and one or more nuclear by-products), the method comprising: i) determining relative concentrations of the individual nuclear by-products in the nuclear waste or in an initial mobile phase as defined herein; ii) Determining which are the most radioactive nuclear by-products or groups of nuclear by-products (e.g. by reference to half-life and/or radiation count, suitably taking into account any "cooling" that the nuclear waste may have previous undergone); iii) Determining the net impact of specific nuclear by-products or of groups of specific FPs and MAs, by taking account of both radioactivity and concentration of the relevant nuclear by-products, and thereby determining a preferential order in which the nuclear by-products should be removed from the mobile phase (suitably with the most radiolyically damaging nuclear by-products being removed first before the least damaging); iv) Either or both: a. Performing multi-column chromatography upon a mobile phase sample of the relevant nuclear waste {via any of the methods defined herein where a plurality of interconnected individual columns, each comprising a different stationary phase matrix material(s) or mixture thereof, are used for a given stationary phase), with the columns arrange in-series in any given sequential order (where suitably each individual column is substantially the same size and comprises substantially the same weight of matrix material(s)), and sampling eluate before and after each individual column (i.e. the input and output of the mobile phase from each column) to determine the relative concentrations of the nuclear by-products in the mobile phase before and after each column, and thereby determining the impact of each individual column upon (i.e. the affinity of each column for) the various nuclear by-products; and/or b. Performing an individual column chromatography experiment, for each of the individual columns in the multi-column chromatography arrangement, upon successive identical mobile phase samples of the relevant nuclear waste, and determining the relative concentrations of the nuclear by-products in the mobile phase both before and after each column (i.e. the input and output of the mobile phase from each column), and thereby determining the impact of each individual column upon (i.e. the affinity of each column for) the various nuclear by-products; v) Optionally repeating step iv) part a) with the columns arranged in a different order; vi) Determining, from the observations made in steps iv) and v), a sequence of columns which selectively removes, from the mobile phase, some or substantially all of the most radioactive nuclear by-products or groups nuclear by-products towards the beginning of the column sequence (i.e. the first columns remove the most radioactive nuclear by-products). [00145] The above optimization protocol for the sequential order of the columns may be advantageously conducted at low mobile phase loadings, so that the individual columns are running well under 100% capacity (in terms of saturation of binding sites). This helps to isolate the column binding selectivity issue. Suitably, each column comprises an equal weight of stationary phase matrix material (or mixtures thereof), suitably to help eliminate any column size variables when establish the optimal column sequence.

[00146] However, the above protocol may be modified so that not only the sequential order of columns can be optimized by also the relative sizes of said columns. Suitable modifications may include performing/repeating step iv)b) at different relative loadings (i.e. weight of mobile phase per weight of matrix material(s) in the relevant column). Step iv)a) may also be performed/repeated with different relative loadings for different columns to deduce an optimized purification system for any particular nuclear waste.

[00147] Any of the methods or apparatuses defined herein may be suitably optimized using the above method.

EXAMPLE

[00148] The present invention is now further illustrated by reference to the following non-limiting example. It will be readily apparent to those skilled in the art that the various specific features and parameters of the example can be readily modified without departing from the scope of the present invention.

Materials and Equipment

[00149] In general chemicals were purchased from Fischer Scientific and/or Sigma Aldrich and, where necessary, from specialist suppliers. Nuclear waste materials were obtained as described. "Simulation" experiments may employ non-radioactive or less-radioactive

counterparts to the relevant nuclear materials and/or nuclear by-products, which are well known in the art and readily commercially available and relatively safe to handle. Stationary phase matrix materials were either purchased (e.g. mesoporous mobil composition of matter materials, e.g. MCM-41 and MCM-48) form commercially available sources, or produced in accordance with the procedures outlined in either:

• Dyer et al, "Synthesis and Characterisation of mesoporous silica phases containing heteroatoms, and their cation exchange properties. Part 1 . Synthesis of Si, Al, B, Zn substituted MCM-41 materials and their characterisation", Microporous and Mesporous Materials, 126 (2009), p.192-200; or

• Liu et al, "Disordered Mesoporous Gadolinosilicate Nanoparticles Prepared Using Gadolinium Based Ionic Liquid Emulsions: Potential as Magnetic Resonance Imaging Contrast Agents", Australian Journal of Chemistry, 64(5) 617-624.

Preparation of Mobile Phase

[00150] In the present example, spent nuclear fuel (i.e. nuclear waste) is taken from a pressurized water reactor (PWR), cooled for 5 years, and the cooled fuel is subsequently reprocessed according to the following example. The nuclear waste in question is typically irradiated PWR 3.5 % Uranium-235 fuel with a burn up of 33 GWD/t.

[00151] The nuclear waste, which is initially in the form of irradiated nuclear ceramic oxide fuel encased in either stainless steel or zircaloy, is first chopped into small segments and these are exposed to -40% hot nitric acid (or -7-8M hot nitric acid) to dissolve the ceramic oxide fuel'. The solution is subsequently clarified, if necessary, by centriguation to afford a nitric acid solution containing radionuclides in the concentrations shown in Table 1 (which were predicted using a nuclear inventory code such as FISPIN (used by the UK), ORIGEN (US code part of SCALE suite of codes), which is a method well known in the art for calculating or predicted concentrations of radionuclides). The concentrations may, however, be analytically determined by alternative methods well known in the art.

Table 1 Concentrations of Radionuclides in initial mobile hase (nitric acid solution).

[00152] The uranium and plutonium represent the nuclear materials intended for recovery and reprocesses, the neptunium, americium, and curium represent minor actinides (MAs), which need to be separated from the nuclear materials, and the remaining radionuclides represent fission products (FPs), ranging from radioactively short lived to long lived species, which again require separation from the nuclear materials. The fission products and minor actinides are collectively nuclear by-products.

[00153] The clarified nitric acid solution is then purified (to extract subject to one of two different chromatographic purification techniques.

First Chromatographic Purification Example

[00154] The clarified nitric acid solution of the nuclear waste is loaded onto the top of a large upright ion-exchange column, which contains a packed monolith comprising a mixture of various different stationary phase matrix materials, including:

• A mixture of amorphous and crystalline silicas which are variously functionalized.

• A mixture of amorphous and crystalline silicas which have inserted thereinto (during the silica preparation) boron cations.

• A mixture of amorphous and crystalline silicas which have inserted thereinto (during the silica preparation) aluminium cations.

• A mixture of amorphous and crystalline silicas which have inserted thereinto (during the silica preparation) gadolinium cations.

• A mixture of amorphous and crystalline silicas impregnated with calixarene. • A mixture of amorphous and crystalline silicas impregnated with crown ethers.

• A mixture of amorphous and crystalline silicas impregnated with tributyl phosphate.

• A mixture of mesoporous mobil composition of matter materials (MCM-41 and MCM-48).

[00155] The individual stationary phase matrix materials are prepared by methods well known in the art (suitably as described above) and subsequently mixed together to produce a single mixed matrix material which is then packed into a single monolithic column in accordance with standard chromatographic column packing.

[00156] The column is loaded with a sufficient amount of the nitric acid solution to saturate the stationary phase to 75% capacity (in terms of its binding capacity for the fission products and minor actinides present in the nitric acid solution, though this loading can easily be modified to suit the circumstances and optimize the process). The column is then eluted/washed with 3M nitric acid to remove any occluded interstitial uranium and plutonium trapped in the stationary phase, and the eluate duly collected. It should be noted though, that if initial loading of the mobile phase took place with 1 M nitric acid, the eluent used to remove occluded interstitial nuclear materials would then be 1 M nitric acid as well. Analysis of the eluate revealed that it was indeed relatively richer in the nuclear materials (U and Pu) relative to the nuclear byproducts (FPs and MAs) than the original pre-chromatographed solution. Once all the nuclear materials were eluted from the column, the FPs and MAs bound to the stationary phase are then removed therefrom, if so desired, through elution with 0.1 M to 1 M nitric acid or even alkaline solutions. Again, the eluent system can be chosen to optimize the removal of the nuclear by-products, and to optimize separation between the various fractions. The stationary phase may optionally then be reused, because there is surprisingly no significant radiolytic damage.

[00157] Alternatively the stationary phase with the FPs and MAs bound thereto may be stored and/or disposed of. Second Chromatographic Purification Example

[00158] The clarified nitric acid solution of the nuclear waste is loaded to the first of a plurality of in-series and fluidly interconnected packed ion-exchange columns, each of which contains a packed monolith comprising a different stationary phase matrix material, where the individual stationary phase matrix materials for each column were:

• A mixture of amorphous and crystalline silicas which are variously functionalized.

• A mixture of amorphous and crystalline silicas which have inserted thereinto (during the silica preparation) boron cations.

• A mixture of amorphous and crystalline silicas which have inserted thereinto (during the silica preparation) aluminium cations.

• A mixture of amorphous and crystalline silicas which have inserted thereinto (during the silica preparation) gadolinium cations.

• A mixture of amorphous and crystalline silicas impregnated with calixarene.

• A mixture of amorphous and crystalline silicas impregnated with crown ethers. · A mixture of amorphous and crystalline silicas impregnated with tributyl phosphate.

• A mixture of mesoporous mobil composition of matter materials (MCM-41 and MCM-48).

[00159] The individual stationary phase matrix materials are prepared as explained above and, where relevant, mixed together to produce a single matrix material which is then packed into a single monolithic column in accordance with standard chromatographic column packing. In the present example, the individual columns were arranged in the series in no particular order. However, it is envisaged that the arrangement could be optimized to minimize radiolytic damage to the stationary phase system as a whole by removing the most radioactive nuclear byproducts first, thereby minimizing damage to later columns. This is discussed in the alternative embodiments below. [00160] The series of columns are loaded with a sufficient amount of the nitric acid solution to saturate the entire stationary phase (including all columns) to 75% capacity (in terms of its binding capacity for the fission products and minor actinides present in the nitric acid solution). The entire stationary phase system is then eluted/washed with 3M nitric acid to remove any occluded interstitial uranium and plutonium trapped in the stationary phase, and the eluate duly collected. Analysis of the eluate revealed that it was indeed relatively richer in the nuclear materials (U and Pu) relative to the nuclear by-products (FPs and MAs) than the original pre- chromatographed solution.

[00161] Once all the nuclear materials were eluted from the column, the FPs and MAs bound to the individual columns of the stationary phase are then removed therefrom, if so desired, through elution with weaker acid than that use for the initial elution, an alkaline solution, or other suitable reagent. The stationary phase may optionally then be reused, because there is surprisingly no significant radiolytic damage.

[00162] Alternatively the stationary phase matrix materials with the FPs and MAs bound thereto may be stored and/or disposed of.

Alternative Embodiments [00163] Under development are more optimized variants of the second chromatographic purification example above, whereby the individual columns are arrange in-series in a sequential order to optimise separation and minimise radiolytic damage to the stationary phase as a whole. This is achieved by removing the most radioactive nuclear by-products towards the start of the column series, thereby minimizing damage to the later columns in the series. [00164] Discerning this optimal in-series sequence is straightforward by: i) Determining relative concentrations of the FPs/MAs or groups of FPs/MAs within the relevant nitric acid solution of nuclear waste (i.e. the initial mobile phase); ii) Determining the most radioactive FPs/MAs or groups of FPs/MAs (e.g. by reference to half-life and/or current radioactivity levels in view of any "cooling" that may have taken place), examples being Sr-90, Cs-137, Ru-106, Sb-125, Pm-147, Eu-154; iii) Determining the net impact of specific FPs and MAs, or of groups of specific FPs and MAs, when taking account of both the relevant FP/MA radioactivity and relative concentrations, and thereby determining a preferential order in which the FPs/MAs or groups of FPs/MAs should be removed (i.e. with the most damaging being removed first, and the least damaging being removed last);

Either: a. Performing column chromatography, according to the method of the second chromatographic purification example (i.e. with the in-series individual columns arranged in any particular order; suitably each column has a substantially equal weight of the relevant matrix material), upon a sample of the nitric acid solution of nuclear waste (i.e. initial mobile phase) and sampling eluate before and after each individual column (i.e. the input and output of the mobile phase from each column) to determine the relative concentrations of the fission products and minor actinides in the mobile phase at each point, and thereby determining the impact of each individual column upon the various FPs/MAs or groups of FPs/MAs; and/or b. Performing an individual column chromatography experiment, for each of the individual columns of the second chromatographic purification example, upon successive identical samples of the nitric acid solution of nuclear waste (i.e. initial mobile phase), and determining the relative concentrations of the fission products and minor actinides in the mobile phase both before and after each column (i.e. the input and output of the mobile phase from each column), and thereby determining the impact of each individual column upon the various FPs/MAs or groups of FPs/MAs;

Optionally repeating step vi) part a) with the columns arranged in a different order;

Determining, from the observations made in steps vi) and v), a sequence of columns which selectively removes, from the mobile phase, the most radioactive FPs/MAs or groups of FPs/MAs towards the beginning of the column sequence (i.e. the first columns remove the most radioactive FPs/MAs).

[00165] Though step v)a) should ideally be repeated with the columns in a different order one or more times, since a different sequential order may give results indicating a different match between specific columns and FPs/MAs, improvements may be gained by running through the above sequence only once, preferably also employing step v)b) as a cross-check.

[00166] The above optimization protocol for the sequential order of the columns may be advantageously conducted at low loadings, so that the individual columns are running well under 100% capacity (in terms of saturation of binding sites). This helps to isolate the binding selectivity issue. Suitably each column therefore comprising an equal weight of stationary phase matrix material (or mixtures thereof) - this helps to eliminate any column size variables.

[00167] However, the above protocol may be modified so that not only the sequential order of columns can be optimized by also the relative sizes of said columns. Suitable modifications may include performing/repeating step v)b) at different relative loadings (i.e. weight of mobile phase per weight of matrix material(s) in the relevant column). Step v)a) may also be performed/repeated with different relative loadings for different columns to deduce an optimized purification system for any particular nuclear waste.

[00168] FIG. 1 illustrates an embodiment of an idealised reprocessing method, in which: - The nuclear waste is dissolved, suitably as defined above, to provide an initial mobile phase.

- Stage 1 removes, from the mobile phase, the most short-lived and highly radioactive fission products (e.g. being Sr-90, Cs-137, Ru-106, Sb-125, Pm-147, Eu-154) through a series of in-line individual columns arranged in an optimized order established by the abovementioned protocol.

- Stage 2 removes, from the mobile phase, medium-lived fission products, through either a series of in-line individual columns (optionally optimized as above) or through an individual column comprising a mixture of stationary phase matrix materials (e.g. as per the First Chromatographic Purification Example above). - Stage 3 removes, from the mobile phase, minor actinides, through either a series of inline individual columns (optionally optimized as above) or through an individual column comprising a mixture of stationary phase matrix materials (e.g. as per the First Chromatographic Purification Example above). There is scope to use organic polymeric materials at this stage, when the most radioactive nuclear by-products have been removed from the mobile phase.

Stage 4 is a final clean-up which removes, from the mobile phase, long-lived fission products, through either a series of in-line individual columns (optionally optimized as above) or through an individual column comprising a mixture of stationary phase matrix materials (e.g. as per the First Chromatographic Purification Example above). There is scope to use organic polymeric materials at this stage, when the most radioactive nuclear by-products have been removed from the mobile phase.

- Finally purified uranium and plutonium isotopes are separated from the stationary phase. [00169] In alternative embodiments, continuous chromatography is accomplished via simulated moving bed (SMB) or continuous annular chromatography (CAC). In these types of contacting systems there is constant motion of the bed/stationary phase (or parts thereof) relative to the "feed point". This can be accomplished by either moving the bed and keeping the feed points stationary, or moving the feed points and keeping the bed stationary. In addition, this motion can be designed such that the feed flow and the bed movement may be in a counter current or crosscurrent direction. Those systems with truly constant motion between the inlet points and the bed will be continuous, while those that simulate this motion will be semi-continuous. A semi-continuous process can approach the continuous process by making smaller and smaller discrete movements. For instance, in a cascade of fixed beds operated in a merry-go-round sequence, product can be collected from one bed and feed fed to another while the remaining columns are at an intermediate stage of the process. If timed in such a way that product is always being collected at one of the different column outlets, an apparently continuous process exists. A conceptual view of the corresponding idealized moving-bed process is illustrated in FIG. 2. [00170] Referring to FIG. 2, for the separation of a two-component (A and B) system the system contains four zones defined by the introduction and withdrawal of process liquid. In zone I, the sorbent adsorbs component A; in zone 1 1 , component B is desorbed; in zone 1 1 1 , the desorbent D strips component A from the sorbent; and finally, in zone IV, B replaces the desorbent D on the sorbent. The feed, A and B, enters between zones I and 11 where the more strongly retained species, A, is carried upward by the sorbent. In the upper portion of the column, A is stripped off and exits at the top of the column. The more weakly retained component, B, moves downward where it is stripped and finally exits at the bottom of the column. In the actual Sorbex process, the sorbent remains stationary and the liquid fed and withdrawal points are moved through a cascade of fixed beds using a rotary valve system to simulate the sorbent movement. In this way, the difficulties of solids handling are avoided.

[00171] The continuous annular chromatographic apparatus is illustrated in FIG. 3. In this apparatus, the sorbent (i.e. stationary phase or part(s) thereof) is packed in the space between two concentric cylinders. For isocratic operation, the eluent is uniformly distributed throughout the annulus and flows downward toward the bottom of the bed. The feed mixture to be separated is fed at the top of the annular bed at a point that remains fixed in space while the entire bed assembly is slowly rotated on its vertical axis. If the feed Components have different affinities for the sorbent, they will travel along paths with different slopes, exiting at different angular locations relative to the feed point. The least-retained components will emerge closest to the feed port, while the more- retained components will exit at increasing angles from the feed port in the direction of rotation. Simply continuous annular chromatography, or CAC, replaces the one-dimensional, unsteady-state process of conventional chromatography with a two-dimensional, steady-state process. In conventional chromatography the separated components exit at different times; here they exit at different angles.

Conclusion

[00172] The chromatographic methodologies of the invention for the purification of nuclear materials show a surprising ability to withstand radiolytic damage to afford viable and improved methods for reprocessing nuclear waste. The scope of the invention is significant, and allows for customised reprocessing treatments for particular batches of nuclear waste.