High-purity low-enriched uranium denaturation process

Abstract

A novel semi-batch process is provided for converting high-assay low-enriched uranium (HALEU) from the uranium hexafluoride state to uranium dioxide and other chemical states useful as a feed for nuclear fuel in a nuclear reactor. This semi-batch process enables the use of a sufficiently small apparatus and a sufficiently low production rate to meet the nuclear criticality safety constraints for HALEU, and enables the safe, reliable and economical production of HALEU feed for nuclear fuel at a nominal capacity of up to approximately 20 MTU (metric tons of uranium metal) per year per denitration reactor.

Description

Detailed Description of the Invention

[0001] [Cross - Reference to Related Applications] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 340,893, entitled "HIGH ASSAY, LOW ENRICHED URANIUM DECONVERSION PROCESS", filed on May 11, 2022. The entire content thereof is incorporated herein by reference.

[0002] [Field of the Disclosure] The present disclosure relates to an efficient and effective process for deconverting fluorinated HALEU materials to produce HALEU feeds for nuclear fuel.

[0003] [Background] Currently, there is a need for high - assay, low - enriched uranium ("HALEU") feed materials for use in the production of fuel for advanced reactors. Uranium enrichment is the process of producing useful nuclear fuel from mined natural uranium by increasing the proportion of the uranium - 235 isotope, which enables a sustainable nuclear fission reaction. In the enrichment process, it is necessary to convert uranium into a gaseous state, which is achieved through a process called "conversion". In the conversion process, uranium oxide (usually uranium trioxide (UO 3 )) is converted into another compound (usually uranium hexafluoride (UF 6 ). This other compound becomes gaseous when heated at a relatively low temperature. Once the enrichment capacity is established, uranium hexafluoride needs to be deconverted into a chemical form useful as a feed for fuel manufacturers. Such chemical forms include uranium dioxide (UO 2 ), uranium octoxide (U 3 O 8 ), uranium tetrafluoride (UF 4) include metallic uranium (U) and combinations thereof. In a conventional nuclear reactor, the depleted enriched uranium, which is usually in powder form, can be compacted into small pellets, which are then heated to form a hard ceramic material. These small pellets are inserted into thin tubes called fuel rods. Those fuel rods are grouped together as a fuel assembly and loaded into the reactor core.

[0004] Natural uranium produced from mines usually contains about 0.7% by weight of uranium-235 isotope and the more stable uranium-238 isotope, which accounts for the remaining proportion. In known enrichment processes, UF 6 gas is fed into a centrifuge containing thousands of rapidly rotating vertical tubes. By the centrifuge, UF 6 gas is separated into two streams. One contains a higher proportion (usually 3 - 5%) of U-235 isotope and the other contains a very low concentration of U-235. At the maximum enrichment achievable by conventional uranium enrichment processes, the U-235 concentration is less than 5% by weight of the total uranium.

[0005] There are two types of processes for the depleting process of conventional enriched uranium, called the wet process and the dry process. In the wet process, UF 6 is mixed with water to form a UO 2 F 2 solution. Ammonia or ammonium carbonate is added to this mixture. UO 2 F 2 reacts with ammonia to produce ammonium diuranate, or UO 2 F 2 reacts with ammonium carbonate to produce ammonium uranyl carbonate. In either case, the slurry is then filtered, dried, and heated in a reducing atmosphere to obtain UO 2 .

[0006] An example of the dry process is described in U.S. Patent No. 4,830,841 granted to Urza. The described dry process is UF 6is fed into a continuous fluidized bed reactor and exposed to superheated steam in a gas-phase reaction to produce fine submicron particles of uranium tetrafluoride (UO 2 F 2 ). This is a continuous process. The uranium tetrafluoride particles are then agglomerated and densified in a fluidized bed of uranium oxide material having a uranium to oxygen ratio of 1:2.0 to about 1:2.67. The agglomerated and densified uranium tetrafluoride is defluorinated and reduced in the fluidized bed to obtain a fluoride-containing uranium oxide material having substantially the same composition as the composition of the fluidized bed. The fluoride-containing uranium oxide material is continuously withdrawn from the fluidized bed reactor and fed to another rotary kiln where it is treated with steam and hydrogen to obtain ceramic grade uranium oxide. In the continuous fluidized bed reactor, UF 6 cannot be completely defluorinated. To remove the remaining fluorine from the fluoride-containing uranium oxide particles discharged from the fluidized bed reactor, a secondary rotary kiln equipped with a steam and hydrogen supply line is required.

[0007] As the nuclear industry advances, the need for high-purity low-enriched uranium (HALEU) with enrichment levels significantly exceeding the conventional 3 - 5% is increasing. For the design of more compact, higher power density per unit volume, longer operating cycle, and more efficient advanced nuclear reactors compared to conventional reactors, it is necessary to enrich uranium up to about 20%. As the demand for HALEU increases, the need for a conversion process suitable for providing feed materials for the production of various types of HALEU fuels is also growing.

[0008] 〔Overview〕 Due to nuclear criticality safety constraints, HALEU feed material (UF 6The transmutation requires a process that uses a very small device and provides safe, reliable, and economical production of HALEU feed for nuclear fuel. For the purposes of this disclosure, the term HALEU includes any uranium or uranium compound containing more than 5 wt% uranium component and up to about 20 wt% U-235 isotope. Examples of HALEU include metallic uranium and uranium compounds containing at least about 10 wt% U-235 isotope in the uranium component or at least about 15 wt% U-25 isotope in the uranium component. Also, examples of HALEU include high-grade commercially available HALEU containing about 19.75 wt% U-235 isotope based on the total amount of uranium. Conventional processes were designed for enrichment levels of 3 - 5%, but all such HALEU uranium-uranium compounds contain uranium enriched above that 3 - 5% level. This process is a semi-batch fluidized bed dry process for the transmutation of fluorinated HALEU materials to produce HALEU feed for nuclear fuel. The process 6 can use a device one order of magnitude smaller than the transmutation process. And the process currently has a nominal capacity of up to about 20 MTU (metric tons of metallic uranium) per reaction vessel per year, and as described herein, multiple reaction vessels can be used to achieve higher capacities. By this process, 6 complete (or nearly complete) defluorination of UF and production of defluorinated uranium oxide are achieved in a single fluidized bed reactor. And the process is a secondary rotary kiln, or UO 2It does not require other secondary reactors that are required by the known fluidized bed dry method for complete defluorination of the powder. A fluidized bed reactor is a type of reactor device. In a fluidized bed reactor, a fluid (i.e., a gas or a liquid) passes through solid powder (e.g., powder or larger granules) at a speed large enough to suspend the solid and make the solid behave as if it were a fluid. The solid material can be partially or completely suspended in the fluid and carried along with the fluid.

[0009] According to some embodiments, in a semi-batch process, an upright fluidized bed reactor vessel is utilized. The upright fluidized bed reactor vessel can have a cylindrical shape or other suitable shapes. In the first step a), a seed bed of uranium dioxide (UO 2 ) powder is provided in the lower part of the upright fluidized bed reactor vessel. The seed bed can have a mass of about 5% to about 20% of the target accumulated mass in the fluidized bed reactor. For example, if the fluidized bed reactor has a batch size represented by a target accumulated mass of about 10 kg of UO 2 powder, the seed bed can have a mass of about 0.5 kg to about 2 kg, preferably about 1 kg to about 1.5 kg. In some examples, the uranium component of the UO 2 powder contains more than 5 wt% of U-235 isotope, or at least about 10 wt% of U-235 isotope, or at least about 15 wt% of U-235 isotope, or about 19.75 wt% of U-235 isotope.

[0010] In the second step b), the UO in the seed bed 2The powder can be fluidized using an upward flow of an inert gas. The inert gas can be supplied to the lower portion of the fluidized bed reaction vessel and heated. As used herein, an "upflow stream" is a flow of gas or liquid that passes through granular solids in an upward direction and has the property of suspending the granular solids in the fluid flow. Heating can be achieved by using an electric heater or other heat source to heat both the reaction vessel and the inert gas entering the reaction vessel. The upward flow of the inert gas can be injected into the lower part of the fluidized bed reaction vessel with a velocity and volumetric flow sufficient to fluidize the UO 2 powder. The inert gas can be nitrogen, argon, or other suitable inert gas. The inert gas is preferably nitrogen due to its availability and low cost. In some examples, the initial heating is sufficient for the conversion from uranium hexafluoride (UF 6 ) to uranyl fluoride (UO 2 F 2 ) (which can occur at a reaction temperature of at least about 400 °C, preferably at least about 450 °C), and is also sufficient to enable the conversion from UO 2 F 2 to UO 2 powder (which can occur at a reaction temperature of at least about 600 °C). The initial heating at the upper (top) of the reaction vessel can be at a temperature of at least about 400 °C, preferably at least about 450 °C, to induce the initial hydrolysis reaction. The initial heating at the lower (bottom) of the reaction vessel can be at least about 600 °C so that the conversion from UO 2 F 2 to UO 2 powder can occur.

[0011] In the third step c), hydrogen gas and steam can be added and supplied to the upward flow of an inert (e.g., nitrogen) gas within the fluidized bed reaction vessel. This addition can be made at the same height within the reaction vessel as the addition of nitrogen at the lower part or just below the fluidized bed.

[0012] In step d), vaporized uranium hexafluoride (UF 6 ), which is preferably heated to about 100 °C, and additional steam are supplied in separate streams. The separate streams can, in some embodiments, be combined into a single inlet nozzle. The single inlet nozzle is preferably located at a higher position into the fluidized bed reaction vessel. The UF 6 feed is composed of uranium containing more than 5 wt% U-235 isotope, or at least about 10 wt% U-235 isotope, or at least about 15 wt% U-235 isotope, or about 19.75 wt% U-235 isotope. The UF 6 feed can be injected higher up in the reaction vessel. For example, the UF 6 feed can be injected into the upper part of the reaction vessel, or above or near the upper part of the fluidized bed. In some examples, the total amount of hydrogen gas and steam is an amount sufficient to carry out the following deconversion reaction. In the deconversion reaction, first, UF 6 is converted to UO 2 F 2 at about 450 °C (step e)), and then UO 2 F 2 is converted to UO 2 powder at a temperature of about 600 °C (step f)).

[0013]

Chemical formula

[0014]

Chemical formula

[0015] The total amount of steam added to the fluidized bed reactor can exceed the stoichiometric amount required to achieve the hydrolysis of uranium hexafluoride. The range of said total amount can be, for example, from about 4 moles to about 7 moles of steam per mole of uranium. An inert gas such as nitrogen acts as a diluent for the consistent fluidizing gas and steam. The range of said inert gas can be, for example, from about 0.5 moles to about 1.5 moles of inert gas per mole of uranium. The reaction vessel can be heated and / or cooled as necessary to maintain both reactions in a steady state. For example, steady cooling may be required at the upper part of the reaction vessel, and steady heating may be required at the lower part of the reaction vessel.

[0016] The UO 2 powder produced in step f) can accumulate in the reaction vessel until the target mass is achieved. In some examples, the target mass can be at least about 3 times the mass of the initial seed bed of UO 2 powder, or at least about 5 times the mass of the initial seed bed of UO 2 powder, or at least about 7 times the mass of the initial seed bed of UO 2 powder. In one example, the mass of the initial seed bed of UO 2 powder can be from about 1 to 2 kg, and the target mass can be about 10 kg. When the UO 2 powder reaches its target mass in the fluidized bed, step g) can be carried out. In this step g), the supply streams of UF 6 and additional steam can be stopped. At this point, sufficient time can be given for the UF 6 remaining in the reaction vessel to react with the streams of hydrogen and steam being supplied to the lower part of the fluidized bed. Thereby, additional UO 2 powder is obtained, and said additional UO 2 powder accumulates in the fluidized bed. This step g) can be continued until all of the HALEU feed material in the fluidized bed reactor is completely defluorinated or defluorinated to the desired level. As a result, substantially defluorinated or completely defluorinated UO 2 powder remains in the fluidized bed.

[0017] When step g) is completed, step h) can be carried out. In this step h), a selected amount of UO 2 The flow (or flows) of hydrogen gas and steam entering the lower part of the fluidized bed can be stopped so that the selected amount of UO 2 powder can be discharged from the lower part of the reaction vessel. In some embodiments, a first amount of UO 2 powder is discharged from the reaction vessel, and a second amount of UO 2 powder can be left as a seed bed of UO 2 powder having approximately the same mass as the seed bed in step a). Then, steps b) to h) can be repeated a sufficient number of times until a desired amount of fluorinated HALEU material is deconverted and / or a desired amount of UO

[0018] powder is produced. 2 In some embodiments, the UO 2 powder discharged from the fluidized bed reactor can be used directly as a HALEU feed for nuclear fuel. In other embodiments, the UO 2 powder discharged from the fluidized bed reactor can be converted into different types of HALEU feeds for nuclear fuel using a subsequent fluidized bed reactor. The subsequent fluidized bed reactor can have the same or a similar size and configuration as the semi-batch fluidized bed reactor used to produce the UO

[0019] In some embodiments, the UO 2 powder is discharged from the fluidized bed reaction vessel and fed to a second fluidized bed reaction vessel, where it can be fluidized in the presence of an oxygen source (preferably air). Then, preferably by heating the incoming air simultaneously with the second reaction vessel, the fluidized bed can be heated to a temperature of at least about 140 °C. When the temperature of the fluidized bed reaches about 140 °C, an exothermic reaction begins and continues as the temperature rises to about 500 °C. And all of the UO 2 powder is converted to uranium trioxide (U 3 O 8 ) according to the following reaction:

[0020]

Chemical formula

[0021] Thereafter, the air source can be stopped or decelerated. And the second fluidized bed reactor can be cooled, or caused to cool, sufficiently to remove U 3 O 8 powder. U 3 O 8 is useful as a feed for nuclear fuel in some applications.

[0022] In some embodiments, the UO 2 powder can be discharged from the fluidized bed reaction vessel and fed to a second fluidized bed reaction vessel. The UO 2 powder is then fluidized within the second reaction vessel using an inert gas such as nitrogen, and preferably, by heating both the incoming nitrogen stream and the second reaction vessel, the upflow is heated to a temperature of about 400 °C to about 500 °C. Hydrogen fluoride gas is added to the second fluidized bed reactor, and this hydrogen fluoride gas reacts with the UO 2 powder to produce uranium tetrafluoride (UF 4 ) according to the following reaction:

[0023]

Chemical formula

[0024] Care can be taken so that the amount of HF required to complete the reaction is not greatly exceeded and any HF that may remain when the reaction is complete is properly discharged. The resulting UF 4 powder is in the form of a green salt, which is discharged into a suitable container and can be used as a feed for nuclear fuel in some applications.

[0025] In some embodiments, the aforementioned UF 4 powder can be reacted with an alkali metal, preferably calcium, to obtain metallic uranium. This reaction can occur within a pressure and heat resistant container heated to a temperature of at least about 400 °C. In some embodiments, UF 4The powder and an alkali metal (e.g., calcium) powder may be mixed and placed in a pressure and heat resistant container known as a "bomb reactor". After the container is heated until the exothermic reaction starts, the temperature rises due to the following exothermic reaction, and when the reaction proceeds to completion, it can reach up to about 1400 °C:

[0026]

Chemical formula

[0027] When metallic uranium falls to the bottom of the container, a pool of pure metal is formed. CaF 2 accumulates as "slag" on top of the metal. After the reaction vessel is cooled, or allowed to cool, the vessel can be opened and the slag can be separated from the metal. Pure metallic uranium is useful as a feed for nuclear fuel in some applications.

[0028] The foregoing features and advantages, as well as other features and advantages, will become more apparent by reading the following detailed description in conjunction with the drawings.

[0029] 〔Brief Description of the Drawings〕 Figure 1 schematically shows an embodiment of a semi-batch fluidized bed reactor suitable for implementing a process for producing HALEU UO 6 powder by deconverting a fluorinated HALEU feed material (e.g., UF 2 ). Also, the illustrated semi-batch fluidized bed reactor also represents a secondary fluidized bed reactor that can be used to convert HALEU UO 2 powder into other HALEU feeds for nuclear fuel (including U 3 O 8 and UF 4 ).

[0030] Figure 2 shows HALEU UO 2 powder from a primary fluidized bed reactor into another HALEU feed for nuclear fuel (U 3 O 8Schematically shows some embodiments of a semi-batch secondary fluidized bed reactor that can be used to convert (including) to.

[0031] Figure 3 schematically shows some embodiments of a semi-batch secondary fluidized bed reactor that can be used to convert HALEU UO2 powder from a primary fluidized bed reactor to another HALEU feed (including UF4) for nuclear fuel. This product can, according to some embodiments, be used directly as a feed for nuclear fuel or can also be used in the production of metallic uranium feed.

[0032] Figure 4 schematically shows, according to some embodiments, the process steps of the present disclosure in block diagram form.

[0033] 〔Detailed Description〕 Referring to Figure 1, the semi-batch process for de-converting a fluorinated HALEU material includes a semi-batch fluidized bed reactor 10. The semi-batch fluidized bed reactor 10 can have a much smaller size than the continuous dry process used for de-converting conventional low-purity uranium-based feed materials. The fluidized bed reactor 10 can have any suitable shape. Such shapes include, but are not limited to, the cylindrical shape shown in the figure. The fluidized bed reactor 10 can have a volume capable of producing from about 5 kg to about 20 kg, preferably from about 10 kg to about 15 kg of HALEU UO 2 powder in a single batch. The volume of the reactor 10 can be reduced by about 90% compared to the conventional volume of a continuous dry process fluidized bed reactor used for de-converting conventional low-purity uranium-based feed materials.

[0034] In some embodiments, the fluidized bed reactor 10 includes a gas dispersion plate 12. The gas dispersion plate 12 can be a sintered metal plate having a central opening 30. The gas dispersion plate 12 is used to inject a fluidizing gas evenly distributed near the lower part of the fluidized bed reactor 10. In the first step a), a seed bed 14 of (the above-described) HALEU uranium dioxide powder is provided on the gas dispersion plate 12. This can be achieved, for example, using a vertical (longitudinal) pipe (not shown) extending upward through the central opening 30. As a non-limiting example, for a 10 kg batch, the seed bed can have a mass of about 0.5 kg to about 2 kg, or about 1 kg to about 1.5 kg. In the second step b), a fluidizing flow of an inert gas (preferably nitrogen) is supplied to the gas dispersion plate 12 at an injection point 16 below the gas dispersion plate at a rate and volumetric flow sufficient to fluidize the seed bed 14. The fluidizing flow results in an upward flow that flows from the lower part to the upper part of the fluidized bed reactor 10.

[0035] The reaction vessel is heated to a temperature sufficient for the defluorination reaction to occur in the desired temperature range, preferably by heating both the inert gas flow and the fluidized bed reactor 10. The desired temperature range is at least about 400 - 450 °C for the conversion from UF 6 to uranium fluoride, and at least about 600 °C for the conversion from uranium fluoride to UO 2 powder. Initially, this may require different amounts of heat to be applied at the lower part and the upper part of the fluidized bed reactor 10. The lower part of the fluidized bed reactor 10 can be initially heated to at least about 600 °C, and the upper part of the fluidized bed reactor 10 can be initially heated to at least about 400 °C. Since the reaction that occurs can be a combination of exothermic and endothermic, for steady operation, it may be necessary to continuously remove heat near the upper part of the fluidized bed reactor 10 and continuously add heat near the lower part of the fluidized bed reactor 10. In the third step c), while heating the upward flow, steam and hydrogen gas can be added to the upward flow at the same injection point 16 as the inert gas, or near it.

[0036] When the reaction vessel reaches a suitable reaction temperature, in the fourth step d), the vaporized UF 6 , and separate streams of steam are added at the second injection point 18 (or two injection points at approximately the same location). Here, the injection point(s) 18 is / are at a significantly higher position within the reaction vessel than the first injection point 16. The injection point(s) 18 can be disposed above the upper part of the fluidized bed 14. The amount of hydrogen gas added at the first injection point 16, and the total amount of steam added at the first injection point 16 and the second injection point 18, need to be in sufficient amounts to carry out the following deconversion reaction. First, UF 6 is converted to UO 2 F 2 at about 450 °C in accordance with the following reaction in the fifth step e).

[0037]

Chemical formula

[0038] Second, UO 2 F 2 is converted to UO2 powder in accordance with the following reaction at a temperature of about 600 °C in the sixth step f).

[0039]

Chemical formula

[0040] The execution of step e) and the execution of step f) may have some overlap, but the two reactions start at different temperatures and may start at different positions within the reaction vessel. The reaction to produce uranium fluoride (step e)) starts at about 450 °C when UF 6 combines with steam in the inlet nozzle and is added to the reactor. On the other hand, the reaction to convert uranium fluoride to uranium dioxide (step f)) is for UO 2 F 2When formed and in contact with hydrogen, it starts at about 600 °C. When uranium fluoride is formed, the uranium fluoride first accumulates on a plurality of sintered metal filters 28 disposed at the upper part of the fluidized bed reactor 10, and a cake is formed on the filter surface. This cake is periodically discharged from the filter 28 using nitrogen blowback. As a result, the uranium fluoride is removed and dropped back into the fluidized bed. As the process cycle continues, the removed uranium fluoride is taken into the fluidized bed, and when the temperature in the upflow approaches 600 °C, it reacts with hydrogen gas to form uranium dioxide (step f)).

[0041] As already explained, the total amount of steam added to the fluidized bed reaction vessel at both the injection point 16 and the injection point 18 can exceed the stoichiometric amount required to achieve the hydrolysis of uranium hexafluoride. An inert gas (e.g., nitrogen) functions as the fluidizing gas and acts as a diluent for the steam. The amount of hydrogen added should be as close as possible to the amount required to complete the conversion of uranium fluoride to uranium dioxide, and can be increased as necessary if the defluorination is not complete or if the defluorination is less than the desired target amount. Each of the two reactions generates a hydrogen fluoride (HF) by-product. The hydrogen fluoride by-product is discharged from the off-gas outlet 20 together with nitrogen and the excess steam and hydrogen. The hydrogen fluoride mixes with the excess steam to form hydrofluoric acid. The hydrofluoric acid condenses and separates from the nitrogen gas and hydrogen gas. As a result, separate streams 22 and 24 are produced. The nitrogen gas and hydrogen gas can be discarded or recycled. On the other hand, the hydrofluoric acid can be sold for other industrial uses.

[0042] When a uranium dioxide product is formed in step f), the uranium dioxide product accumulates as a powder and becomes part of the fluidized bed. As a result, the mass of the fluidized bed increases until it reaches the target mass. This target mass can be at least about 3 times, or at least about 5 times, or at least about 7 times, or more compared to the mass of the initial seed bed. For example, the size of the fluidized bed reactor 10 can be sized to operate with a seed bed of about 1 - 2 kg of uranium dioxide powder and a target mass of about 10 kg. When the fluidized bed reaches the target mass, step g) is performed. Step g) includes the step of stopping the inlet supply of UF 6 into the fluidized bed reactor 10 and reacting all the remaining UF 6 in the reactor 10 with a stream of hydrogen and steam to first produce uranium oxyfluoride (UO 2 F 2 ) and then to produce uranium dioxide (UO 2 ) powder that accumulates in the fluidized bed. Step g) can be continued until the fluidized bed contains substantially pure UO 2 powder and the fluorination intermediate product is substantially eliminated from the fluidized bed. At that point, the first batch of the UF 6 feed is completely defluorinated or defluorinated to the desired level.

[0043] UF 6 When a batch of UF 2 is completely defluorinated or defluorinated to the desired level in the fluidized bed reactor 10, the seventh step g) is performed. The seventh step g) includes the step of stopping the supply flow of hydrogen and steam at the first inlet 16 so that an amount of UO 2 powder can be discharged through the central opening 30 in the gas dispersion plate 12 and through the discharge port 32 at the bottom of the fluidized bed reactor 10. The inlet flow of nitrogen can be increased as needed to maintain sufficient fluidization for facilitating the discharge. The amount of UO 6 powder discharged is for assisting in the processing of the next batch of the UF 2An amount sufficient to leave a powder seed bed can be achieved, which can be about 80% to about 95% of the accumulated or target mass within the fluidized bed reactor 10. The UO discharged through the outlet 32 2 The powder can be fed to either or both of the two streams 34, 36. The illustrated stream 34 leads to a storage container where the UO 2 The powder can be used directly as a feed for nuclear fuel in some applications. The illustrated stream 36 leads to a second fluidized bed reactor where the UO 2 The powder can be converted to other feeds (U 3 O 8 , UF 4 is included but not limited to these) for nuclear fuel useful in some applications, and then (subsequent to conversion to UF 4 ) can be converted to metallic uranium.

[0044] When step g) is completed and sufficient UO 2 powder remains to replenish the seed bed, steps b) - h) can be repeated using a new batch of UF 6 feed. This process can be repeated the number of times necessary to produce sufficient UO 2 powder to meet current needs. The nominal capacity of a single fluidized bed reactor as described above, operating with a target mass of 10 kg of UO 2 powder, is estimated to be about 20 MTU per year. By configuring multiple fluidized bed reaction vessels 10 in parallel, the production rate can be increased. In that case, each of them can provide an annual production capacity of about 20 MTU per year.

[0045] Figure 2 schematically shows how an identical or very similar second semi - batch fluidized reactor 40 can be used to convert a batch of UO 2 powder from the first fluidized bed reactor 10 into a uranium octoxide (U 3 O 8 ) feed for nuclear fuel. Referring to Figure 2, the gas dispersion plate 12 receives the UO from the first reactor 10 2A full batch of powder (e.g., a batch having a mass of about 10 kg) can be supplied and a bed 44 can be formed above the dispersion plate 12. The bed can be fluidized using air entering the inlet 16 directly below the dispersion plate 12. The air contains 79% nitrogen and 21% oxygen. The oxidation vessel is preferably heated to a temperature of about 140 °C by heating both the incoming air and the second fluidized bed reactor 40, and an exothermic reaction starts. Once the exothermic reaction starts, the temperature rapidly rises to about 500 °C. UO 2 All of the powder is U 3 O 8 Until it is converted to powder, the following exothermic reaction proceeds rapidly:

[0046]

Chemical formula

[0047] Any U 3 O 8 powder accumulated on the sintered filter 28 can also be blown off using air or nitrogen. When the reaction is complete, the heat source is cut off, and after cooling, U 3 O 8 powder can be discharged from the second fluidized bed reactor through the opening 30, the outlet 32, and the flow 46 leading to the storage container.

[0048] Figure 3 schematically shows how the same or very similar second semi-batch fluidized reactor 50 can be modified to convert a batch of UO 2 powder from the first fluidized bed reactor 10 to uranium tetrafluoride (HF 4 ). This uranium tetrafluoride (HF 4 ) can then be used directly as a feed for nuclear fuel or converted to metallic uranium feed in a later process. Referring to Figure 3, the gas dispersion plate has UO from the first reactor 10 2A full batch of powder (e.g., a batch having a mass of about 10 kg) can be supplied and a bed 44 can be formed above the dispersion plate 12. The bed can first be fluidized using a nitrogen upflow entering the inlet 16 directly below the dispersion plate 12. Preferably, by heating both the incoming nitrogen stream and the reaction vessel 50, when the upflow is heated to a reaction temperature of about 400 °C to about 500 °C, hydrogen fluoride gas is metered into the upflow in the fluidized bed, and UO 2 powder can be converted to HF according to the following reaction 4 :

[0049] [Chemical formula]

[0050] Off-gas containing nitrogen, water vapor from the reaction, and residual HF exits the reactor through the outlet 20. Thereafter, the outlet stream splits into a gas stream 22 of nitrogen gas and a liquid stream 24 of hydrofluoric acid formed by the mixing of HF gas and condensed water vapor. UF 4 The product exists as a green salt, and the green salt is discharged from the fluidized bed reaction vessel 50 through the opening 30 and the discharge port 32. The discharge stream of UF discharged through the outlet 32 can be supplied to either or both of two streams 54, 56. The illustrated stream 54 leads to a storage container where the UF 4 salt can be used directly as feed for nuclear fuel in some applications. The illustrated stream 56 leads to a "bomb reactor", which is a sealed container, where the UF 4 salt can react with metallic calcium to produce metallic uranium. The bomb reactor can be lined with an inert material (e.g., magnesium oxide). The reaction can start at a temperature of about 400 °C and an exothermic reaction begins. Thereafter, the temperature rises due to the following exothermic reaction and can reach up to about 1400 °C when the reaction proceeds to completion: 4 [Chemical formula]

[0051] [Chemical formula]

[0052] Approximately 10 kg of UF 4 Assuming the salt as the starting batch, the reaction in the bomb reactor typically yields about 8 kg of metallic uranium and about 2 kg of calcium fluoride slag separable from uranium. This metallic uranium can then be used as a feed for nuclear fuel in some applications.

[0053] The illustrated fluidized bed reaction vessel 10 provides a very effective and efficient small reactor that meets nuclear safety standards for converting fluorinated HALEU feed materials into HALEU feeds for various useful nuclear fuels. In one embodiment, the reaction vessel 10 may have a diameter of only about 4 - 5 inches and may have an upper, somewhat expanded vapor space to assist in the desorption of fluidized powder from the sintered metal filter. UO 2 To convert UO powder into HALEU feeds for various alternative nuclear fuels, two reaction vessels of substantially the same size and configuration can be provided in series. This fluidized bed reaction vessel is particularly suitable for the conversion of fluorinated HALEU feed materials as it is an order of magnitude (about 90%) smaller than conventional continuous dry process conversion reactors.

[0054] Figure 4 shows an exemplary process flow for converting UF to UO through a batch process or a semi - batch process, as described throughout various embodiments presented herein. As described above in various embodiments, in block 400, a seed bed of UO is provided within the fluidized bed reactor. The seed bed of UO contains uranium with more than 5 wt% U - 235 isotope. In block 402, UO 6 to UO 2 In block 400, a seed bed of UO is provided within the fluidized bed reactor as described above in various embodiments. The seed bed of UO contains uranium with more than 5 wt% U - 235 isotope. In block 402, UO 2 A seed bed of UO is provided within the fluidized bed reactor. The seed bed of UO contains uranium with more than 5 wt% U - 235 isotope. 2 The seed bed of UO contains uranium with more than 5 wt% U - 235 isotope. 2It is fluidized by a flow of an inert gas (which may be nitrogen). In block 404, a flow of hydrogen and steam is supplied into the reactor. In block 406, vaporized uranium hexafluoride and additional steam are supplied to the reactor described above. The vaporized uranium hexafluoride contains uranium with more than 5 wt% U-235 isotope. In block 408, uranium hexafluoride is reacted with steam to obtain uranyl fluoride. In block 410, uranyl fluoride is reacted with hydrogen to obtain additional UO 2 is obtained. In block 412, a first amount of UO 2 is removed from the reactor. In block 414, a second amount of UO 2 is left for use as a seed bed for a later batch process. In some cases, the first amount of UO 2 removed from the reactor contains uranium having more than 5 wt% U-235 isotope, or uranium having more than 10 wt% U-235 isotope, or uranium having more than 15 wt% U-235 isotope, or uranium having more than 17 wt% U-235 isotope, or uranium having more than 19 wt% U-235 isotope.

[0055] The general nature of the embodiments of the present disclosure is such that, without departing from the general concept of the embodiments of the present disclosure, the knowledge of those skilled in the art can be applied so that others can easily modify and / or adapt specific embodiments for various applications without undue experimentation, as will be apparent from the foregoing description of such specific embodiments to a sufficient extent. Therefore, such adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments based on the teachings and guidance presented herein. The syntax or terminology herein is for the purpose of explaining the terms or syntax of the present specification so that they are interpreted by those skilled in the art in light of the teachings and guidance presented herein, and not for the purpose of limitation.

[0056] The breadth and scope of the embodiments of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

[0057] Unless otherwise specified or understood differently within the context in which it is used, terms related to conditions, such as in particular "can", "could", "might" or "may", generally convey that while a particular implementation may include a particular feature, element and / or operation, other implementations do not include the particular feature, element and / or operation. Thus, such terms related to conditions generally do not intend that a feature, element and / or operation is required in any way in one or more implementations, or that the logic for determining whether these features, elements and / or operations are included in any particular implementation, or whether these features, elements and / or operations are to be performed in any particular implementation, is necessarily included in one or more implementations regardless of the presence or absence of user input or prompts.

[0058] Those skilled in the art will recognize that any process or method disclosed herein can be modified in many ways. The process parameters and order of the steps described and / or illustrated herein are provided by way of example only and can be varied as desired. For example, the steps illustrated and / or described herein may have been shown or discussed in a particular order, but these steps do not necessarily have to be performed in the order illustrated or discussed.

[0059] Also, in the various exemplary methods described and / or illustrated herein, one or more of the steps described or illustrated herein may be omitted, or additional steps may be included in addition to the disclosed steps. Further, the steps of any method disclosed herein can be combined with any one or more of the steps of any other method disclosed herein.

[0060] Also, in the various exemplary methods described and / or illustrated herein, one or more of the steps described or illustrated herein may be omitted, or additional steps may be included in addition to the disclosed steps. Further, the steps of any method disclosed herein can be combined with any one or more of the steps of any other method disclosed herein.

[0061] Of course, for the purpose of describing the various features of the present disclosure, it is impossible to describe all possible combinations of elements and / or methods. However, those skilled in the art will recognize that a greater number of additional combinations and permutations of the disclosed features are possible. Accordingly, various changes can be made to the present disclosure without departing from the scope or spirit of the present disclosure. Further, other embodiments of the present disclosure may become apparent by considering the specification and the attached drawings, and by practicing the disclosed embodiments presented herein. The examples presented in the specification and the attached drawings should be considered in all respects to be illustrative rather than restrictive. Specific terms are used in this specification, but they are used only in a general and explanatory sense and not for the purpose of limitation.

[0062] Unless otherwise specified, the terms "a" or "an" as used herein are to be construed to mean "at least one of". Finally, for ease of use, the terms "including" and "having" (and their derivatives) as used herein are interchangeable with the term "comprising" and have the same meaning.

[0063] From the above description and the accompanying drawings, while specific implementations are described herein for illustrative purposes, it will be understood that various modifications can be made without departing from the spirit and scope of the appended claims and the elements recited in the claims. In addition, while specific aspects are presented below in specific claim forms, the inventors contemplate various aspects in any available claim form. For example, while some aspects may currently be described as being embodied only in a specific configuration, other aspects may likewise be so embodied. Various modifications and changes can be made that will be apparent to those skilled in the art who obtain the benefits of this disclosure. All such modifications and changes are intended to be included, and thus the above description should be considered in an illustrative rather than a limiting sense.

Brief Description of the Drawings

[0064]

Figure 1

Figure 2

Figure 3

Figure 4

Claims

1. A semi-batch process for the deconversion of a fluorinated HALEU material for the production of a HALEU feed for nuclear fuel, a) A step of providing a seed bed of uranium dioxide (UO ２ ) powder in a fluidized bed reactor vessel, wherein the UO ２ powder contains uranium containing more than 5 wt% of U-235 isotope; b) While heating the reaction vessel, using an upward flow containing an inert gas to fluidize the UO ２ powder in the reaction vessel; c) supplying a flow of hydrogen and steam to the upward flow of the inert gas; d) A step of supplying vaporized uranium hexafluoride (UF ６ ) and additional steam to the fluidized bed reaction vessel, wherein the UF ６ contains uranium containing more than 5 wt% of U-235 isotope; e) reacting the UF ６ with a portion of the water vapor to obtain uranyl fluoride (UO ２ F ２ ); f) reacting said UO ２ F ２ with said hydrogen in said upflow to obtain additional UO ２ powder that accumulates in said fluidized bed; g) When the UO in the fluidized bed ２ reaches the target mass, stop the supply of UF ６ and additional steam, and react the residual UF in the reaction vessel ６ with the flow of hydrogen and steam to obtain additional UO ２ powder accumulating in the fluidized bed; and h) stopping the flow of hydrogen and steam so that a certain amount of said UO ２ powder can be discharged from the reaction vessel A process comprising.

2. UO in step a) ２ said UO sufficient to leave a powder seed bed ２ discharging the powder from the reaction vessel, The step of repeating steps b) to h), The process according to claim 1, further comprising.

3. The target mass in step g) is at least about three times the mass of the seed bed in step a), the process according to claim 1.

4. The target mass in step c) is at least about five times the mass of the seed bed in step a), the process according to claim 1.

5. The uranium in steps a) and d) contains more than about 10 wt% U-235 isotope, the process according to claim 1.

6. The uranium in steps a) and d) contains more than about 15 wt% U-235 isotope, the process according to claim 1.

7. The inert gas in step b) contains nitrogen, the process according to claim 1.

8. The heating in step b) is sufficient heating to enable the execution of step e) at a temperature of at least about 450 °C, the process according to claim 1.

9. The heating in step b) is sufficient heating to enable the execution of step f) at a temperature of at least about 600 °C, the process according to claim 1.

10. Said certain amount of UO ２ The step of discharging the powder from the reaction vessel, The discharged UO ２ powder is reacted with oxygen to obtain triuranium octoxide (U ３ O ８ ), and a step of obtaining The process according to claim 1, further comprising.

11. The discharged UO ２ powder is reacted with oxygen to obtain U ３ O ８ The process according to claim 10, wherein the step of obtaining is carried out in a second fluidized bed reaction vessel at a temperature of at least about 140 °C.

12. Said certain amount of UO ２ The step of discharging the powder from the reaction vessel, The discharged UO ２ powder is reacted with hydrogen fluoride gas to obtain uranium tetrafluoride (UF ４ ), and a step of obtaining The process according to claim 1, further comprising.

13. The discharged UO ２ powder is reacted with hydrogen fluoride gas to obtain UF ４ The process according to claim 12, wherein the step of obtaining is carried out in a second fluidized bed reaction vessel at a temperature of about 400 ° C to about 500 ° C.

14. The UF ４ The process according to claim 12, further comprising a step of reacting the UF with an alkali metal to obtain metallic uranium (U).

15. The alkali metal contains calcium (Ca), UF ４ The process according to claim 14, wherein the step of reacting UF with calcium is carried out in a pressure and heat resistant vessel at a temperature of at least about 400 °C.

16. A semi-batch process for the deconversion of a fluorinated HALEU material for the production of a HALEU feed for nuclear fuel, a) A step of providing a seed bed of uranium dioxide (UO ２ ) powder in a fluidized bed reactor vessel, wherein the UO ２ powder contains uranium containing at least about 10 wt% of the U-235 isotope; b) While heating the reaction vessel to a temperature of at least about 450 °C at the upper part of the reaction vessel and to a temperature of at least about 600 °C at the lower part of the reaction vessel, using an upward flow containing nitrogen gas, fluidize the UO ２ powder in the reaction vessel; c) supplying a flow of hydrogen and steam into the upward flow of the inert gas; d) A step of supplying vaporized uranium hexafluoride (UF ６ ) and additional steam into the upper part of the fluidized bed reaction vessel, wherein the UF ６ contains uranium containing at least about 10 wt% of U-235 isotope; e) hydrolyzing the UF within the upper portion of the fluidized bed reactor to obtain uranyl fluoride (UO ６ F ２ ); ２ step; f) Reacting said UO ２ F ２ with said hydrogen in said upward flow to obtain additional UO ２ powder that accumulates in said fluidized bed; g) When the UO in the fluidized bed ２ reaches the target mass, stop the supply of UF6 and additional steam, and react the residual UF in the reaction vessel ６ with the flow of hydrogen and steam to obtain additional UO powder accumulated in the fluidized bed; and ２ a step of obtaining; h) A step of stopping the flow of hydrogen and steam so that a certain amount of the UO ２ powder can be discharged from the reaction vessel A process comprising.

17. The UO formed in step e) ２ F ２ collecting step using a sintered metal filter disposed near the upper part of the reaction vessel; Using the nitrogen blowback of the filter, periodically blow off the UOF from the filter and drop the UOF towards the fluidized bed; ２ F ２ and a step of dropping the UOF ２ F ２ towards the fluidized bed; The process according to claim 16, further comprising.

18. said UO ２ F ２ The process according to claim 17, wherein step f) of reacting said F with said hydrogen in said upward flow is carried out in said fluidized bed.

19. The uranium in steps a) and d) contains at least about 15 wt% U-235 isotope, the process according to claim 16.

20. A semi-batch process for the deconversion of a fluorinated HALEU material for the production of a HALEU feed for nuclear fuel, a) A step of providing a seed bed of uranium dioxide (UO ２ ) powder in a fluidized bed reactor vessel, wherein the UO ２ powder contains uranium containing about 19.75 wt% of U-235 isotope; b) While heating the reaction vessel, using an upward flow containing an inert gas to fluidize the UO ２ powder in the reaction vessel; c) supplying a flow of hydrogen and steam to the upward flow of the inert gas; d) A step of supplying vaporized uranium hexafluoride (UF ６ ) and additional steam to the fluidized bed reaction vessel, wherein the UF ６ contains uranium containing about 19.75 wt% of the U-235 isotope; e) reacting the UF ６ with a part of the water vapor to obtain uranyl fluoride (UO ２ F ２ ); f) reacting said UO ２ F ２ with said hydrogen in said upward flow to obtain additional UO ２ powder that accumulates in said fluidized bed; g) When the UO in the fluidized bed ２ reaches the target mass, stop the supply of UF6 and additional steam, and react the residual UF in the reaction vessel ６ with the flow of hydrogen and steam to obtain additional UO powder accumulated in the fluidized bed; and ２ a step of obtaining; h) stopping the flow of hydrogen and steam so that a certain amount of the UO ２ powder can be discharged from the reaction vessel A process comprising.

21. UO in step a) ２ said UO sufficient to leave a powder seed bed ２ a step of discharging the powder from the reaction vessel, a step of repeating steps b) to h); The process according to claim 20, further comprising

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