Method and apparatus for extracting protactinium from thorium-based breeding salts

Abstract

This application discloses a method and apparatus for extracting protactinium from thorium-based breeder salts, relating to the field of nuclear technology. The method for extracting protactinium from thorium-based breeder salts includes: mixing a thorium-containing alloy melt with a thorium-based breeder salt melt to reduce protactinium ions in the thorium-based breeder salt melt to metallic protactinium, and dissolving the metallic protactinium into the alloy melt to obtain a protactinium-containing alloy melt; allowing the melt after the reduction reaction to stand to separate the protactinium-containing alloy melt and the thorium-based breeder salt melt after the reduction reaction into layers, and removing the separated protactinium-containing alloy melt; and distilling the protactinium-containing alloy melt to separate the protactinium element.

Description

Technical Field

[0001] This application relates primarily to the field of nuclear technology, and in particular to a method and apparatus for extracting protactinium from thorium-based breeder salts. Background Technology

[0002] Thorium-based molten salt reactors (Th-MSRs), as a core direction of fourth-generation nuclear power technology, possess a key advantage in achieving efficient utilization of nuclear fuel and minimizing nuclear waste through the thorium-uranium conversion cycle. The crucial step in this cycle is that thorium-232 absorbs neutrons and converts into protactinium-233, which then undergoes beta decay (27-day half-life) to generate fissile uranium-233. However, because the thermal neutron capture cross-section of protactinium-233 is five times that of thorium-232, the gradual accumulation of protactinium-233 in the thorium-based molten salt reactor will capture a large number of neutrons. This not only consumes important uranium-233 precursors but also reduces the neutron economy of the thorium-based molten salt reactor. Therefore, it is necessary to promptly separate protactinium-233 from the thorium-based molten salt reactor, allowing it to decay back into uranium-233 before reuse. Currently, there are still many challenges in the separation technology of protactinium in molten salt systems, such as slow reaction rate, low separation selectivity, easy breeding salt pollution, and high energy consumption, which restrict the efficiency of thorium-uranium cycle and the economics of thorium-based molten salt reactors. Summary of the Invention

[0003] To address the aforementioned issues, this application proposes a method and apparatus for extracting protactinium from thorium-based breeding salts. This method and apparatus can efficiently extract protactinium and help reduce the extraction cost of protactinium.

[0004] This application proposes a method for extracting protactinium from a thorium-based breeding salt, comprising: mixing a thorium-containing alloy melt with a thorium-based breeding salt melt to reduce protactinium ions in the thorium-based breeding salt melt to metallic protactinium, and dissolving the metallic protactinium into the alloy melt to obtain a protactinium-containing alloy melt; allowing the melt after the reduction reaction to stand to separate the protactinium-containing alloy melt and the thorium-based breeding salt melt after the reduction reaction into layers, and removing the separated protactinium-containing alloy melt; and distilling the protactinium-containing alloy melt to separate the protactinium element.

[0005] This application also proposes an extraction device for protactinium from thorium-based breeder salts, including a melt separation unit comprising a first chamber, an inlet communicating with the first chamber, and a drain valve. The first chamber is used for a reduction reaction between the thorium-based breeder salt melt and a thorium-containing alloy melt, and for allowing the melt after the reduction reaction to stand so that the protactinium-containing alloy melt obtained from the reduction reaction separates from the thorium-based breeder salt melt after the reduction reaction. The drain valve is used to discharge the separated protactinium-containing alloy melt. The application also includes a distillation unit comprising a second chamber, a heating module, and a cooling module. The heating module is used to heat the protactinium-containing alloy melt located in the second chamber, the cooling module is used to cool the distilled alloy melt, and the distillation unit is used to distill the protactinium-containing alloy melt to separate the protactinium element.

[0006] Compared with the prior art, this application has the following advantages:

[0007] (1) The method for extracting protactinium from thorium-based breeding salts proposed in this application has a fast protactinium extraction rate, can match the half-life window of protactinium-233, and the single recovery rate of protactinium is not less than 80%.

[0008] (2) The thorium-based breeding salt melt after the reduction reaction can be recycled, which helps to reduce the extraction cost of protactinium.

[0009] (3) The thorium-based breeder salt melt and the alloy melt have good system compatibility, which reduces the risk of thorium-based breeder salt being contaminated. Attached Figure Description

[0010] The accompanying drawings are included to provide a further understanding of this application; they are incorporated into and constitute a part of this application. The drawings illustrate embodiments of this application and, together with this specification, serve to explain the principles of this application. In the drawings:

[0011] Figure 1 This is a schematic flowchart of the method for extracting protactinium from thorium-based breeding salts provided in this application embodiment;

[0012] Figure 2 This is a schematic diagram of the state of the melt separation unit in the extraction device provided in this application before the reduction reaction;

[0013] Figure 3 This is a schematic diagram of the state of the melt separation unit in the extraction device provided in this application after the reduction reaction;

[0014] Figure 4 This is a schematic diagram of the state of the distillation unit in the extraction apparatus provided in this application embodiment during the distillation process;

[0015] Figure 5 This is a schematic diagram of the state of the distillation unit in the extraction device provided in this application embodiment after distillation is completed.

[0016] Reference numerals: melt separation unit 210, first chamber 211, feed inlet 212, liquid delivery pipe 2121, drain valve 213, third container 214, distillation unit 220, cooling module 221, air inlet 2211, air outlet 2212, isolation membrane 2213, second chamber 222, upper second chamber 2221, lower second chamber 2222, first container 223, second container 224. Detailed Implementation

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0018] As indicated in this application, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0019] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0020] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0021] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0022] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0023] Flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, various steps can be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0024] The following specific embodiments illustrate the extraction method (hereinafter referred to as the "extraction method") and extraction apparatus for protactinium from thorium-based breeding salts of this application.

[0025] refer to Figure 1 The extraction method in one embodiment includes the following steps:

[0026] Step S110: Mix the thorium-containing alloy melt with the thorium-based breeding salt melt to reduce the protactinium element and dissolve it into the alloy melt, thereby obtaining the protactinium-containing alloy melt;

[0027] Step S120: Allow the molten metal after the reduction reaction to stand still, so that the molten metal containing protactinium alloy and the molten metal containing thorium-based breeding salt after the reduction reaction are separated into layers, and then remove the molten metal containing protactinium alloy after separation;

[0028] Step S130: Distill the protactinium-containing alloy melt to separate the protactinium element.

[0029] The following is a detailed explanation of steps S110 to S130.

[0030] In step S110, the thorium-based breeder salt melt can be a product derived from dry processing of spent fuel from a thorium-based molten salt reactor. The components of the thorium-based breeder salt melt include lithium fluoride (LiF), beryllium fluoride (BeF2), thorium tetrafluoride (ThF4), and protactinium tetrafluoride (PaF4). As an feasible approach, the composition ratio of the thorium-based breeder salt melt is approximately 15% by mass of ThF4, 0.1%-2% by mass of PaF4, and the remainder being a matrix molten salt including LiF and BeF2. This composition ratio ensures that the thorium-based breeder salt melt possesses good fluidity and chemical stability at the extraction temperature.

[0031] Thorium (Th) and protactinium (Pa) have high optimal separation factors, allowing protactinium to be selectively reduced into thorium-containing alloy melts, thus efficiently separating protactinium from thorium-based breeder salt melts. The concentration of thorium in the alloy melt can be saturated, which is beneficial for separating protactinium from thorium-based breeder salt melts.

[0032] As an feasible approach, the thorium-containing alloy melt contains bismuth (Bi) or lead (Pb), or both bismuth and lead. The reason for choosing bismuth, lead, and thorium to form the alloy melt is that the alloy melt formed by thorium with bismuth or lead has few or no side reactions with the thorium-based breeder salt melt, reducing the risk of contamination of the breeder salt. In particular, the alloy melt formed by bismuth and thorium is liquid within the operating temperature range of the thorium-based breeder salt melt, so no additional temperature control is required to match the operating temperature of the thorium-based breeder salt melt. For ease of description, the thorium-containing alloy melt mentioned below includes bismuth but excludes lead, but the scope of protection of this application is not limited to this.

[0033] As one feasible approach, before mixing the thorium-containing alloy melt with the thorium-based breeder salt melt, the thorium-based breeder salt melt is allowed to stand to remove air bubbles and homogenize its concentration. During this standing period, the thorium-based breeder salt melt is heated to maintain its molten state.

[0034] One feasible approach is to inject thorium-based breeder salt molten material into thorium-containing alloy molten material. Specifically, the thorium-based breeder salt molten material is injected into the thorium-containing alloy molten material at an appropriate rate, and the injection process can be continuous. This allows for sufficient contact between the thorium-based breeder salt molten material and the thorium-containing alloy molten material, increasing the reduction reaction rate. Furthermore, by continuously injecting the thorium-based breeder salt molten material, protactinium can be continuously extracted without shutting down the reactor, a method that meets the requirements of online processing.

[0035] During the mixing process, thorium in the thorium-containing alloy melt is reduced to thorium ions (Th). 4+ Thorium ions are added to the thorium-based breeder salt melt, maintaining the stability of the thorium concentration in the melt. The protactinium ions (Pa) in the thorium-based breeder salt melt... 4+ It is reduced to metallic protactinium, and the reaction formula is: Pa 4+ +4 →Pa, while protactinium dissolves into the alloy melt, forming a protactinium-containing alloy melt. The composition of the thorium-based breeding salt melt after the reduction reaction includes LiF, BeF2, and ThF4, as well as a small amount of unreduced PaF4.

[0036] In step S120, the mixed melt comprising the protactinium-containing alloy melt and the thorium-based breeder salt melt after reduction reaction is allowed to stand. The density difference between the two melts causes them to separate into layers: the upper layer is the thorium-based breeder salt melt after reduction reaction, and the lower layer is the protactinium-containing alloy melt. In some embodiments, after step S120, 80% by mass of protactinium in the thorium-based breeder salt melt dissolves into the lower layer of the protactinium-containing alloy melt, meaning that the protactinium recovery rate is not less than 80% in a single extraction process of the thorium-based breeder salt melt.

[0037] As an feasible approach, the reduced thorium-based breeder salt melt is returned to the reactor. Specifically, after separating the protactinium-containing alloy melt from the mixed melt, the remaining melt is mainly the reduced thorium-based breeder salt melt. The reduced thorium-based breeder salt melt is then directly returned to the reactor, thus achieving recycling.

[0038] In step S130, the protactinium-containing alloy melt is distilled to obtain a distilled alloy melt whose main component is bismuth and a residual alloy melt whose main component is protactinium. In one embodiment, the protactinium-containing alloy melt is placed in a sealed space, the sealed space is evacuated to a high vacuum, and then heated to a set temperature at an appropriate rate for isothermal distillation. The bismuth in the protactinium-containing alloy melt vaporizes into a gaseous state, and then liquefies into a liquid state upon cooling, thereby obtaining the distilled alloy melt, and the remaining part is the residual alloy melt, thus separating protactinium from the protactinium-containing alloy melt.

[0039] As a feasible approach, the distillate alloy melt can be recycled for the next extraction. Specifically, the main component of the distillate alloy melt is bismuth, containing a small amount of protactinium. By adding thorium to replenish the thorium concentration, it can be used as a thorium-containing alloy melt for reducing protactinium, and then reused for the next protactinium extraction. This recycling of the distillate alloy melt reduces the cost of protactinium extraction.

[0040] refer to Figure 2 and Figure 4 This application also proposes an extraction device for protactinium in thorium-based breeding salts, the extraction device comprising: a melt separation unit 210 and a distillation unit 220.

[0041] refer to Figure 2 and Figure 3 The melt separation unit 210 has a first chamber 211, an inlet 212 communicating with the first chamber 211, and a drain valve 213 communicating with the first chamber 211. Thorium-based breeder salt melt is fed into the first chamber 211 through the inlet 212, which can be located at the top of the first chamber 211. The first chamber 211 is used for the reduction reaction between the thorium-based breeder salt melt and the thorium-containing alloy melt, and for allowing the mixed melt after the reduction reaction to stand so that the protactinium-containing alloy melt and the reduced thorium-based breeder salt melt separate into layers. The first chamber 211 can be made of molybdenum and filled with high-purity argon gas to isolate the influence of water and oxygen on the reduction reaction. The drain valve 213 is used to drain the molten protactinium-containing alloy after stratification (located at the bottom of the first cavity 211). The drain valve 213 can be a controllable valve made of Hastelloy-N. The third container 214 is used to hold the molten protactinium-containing alloy discharged by the drain valve 213.

[0042] As one implementation method, refer to Figure 2 The feed inlet 212 of the melt separation unit 210 includes a delivery pipe 2121 that extends into the first cavity 211. The delivery pipe 2121 is used to inject the thorium-based breeder salt melt into the thorium-containing alloy melt, so that the thorium-based breeder salt melt and the thorium-containing alloy melt can be in full contact.

[0043] refer to Figure 4 and Figure 5The distillation unit 220 includes a heating module, a cooling module 221, and a second chamber 222. The distillation unit 220 is used to distill the protactinium-containing alloy melt to separate the protactinium element. The heating module is used to heat the protactinium-containing alloy melt located in the second chamber 222, and the cooling module 221 is used to cool the distilled alloy melt. As one embodiment, the heating module can be a heating furnace.

[0044] As one implementation method, refer to Figure 4 and Figure 5 The cooling module 221 includes several air inlets 2211, several air outlets 2212, and an isolation membrane 2213. The isolation membrane 2213 divides the second cavity 222 into an upper second cavity 2221 and a lower second cavity 2222. The air inlets 2211 and the air outlets 2212 communicate with the upper second cavity 2221. The air inlets 2211 are used to supply cooling gas to the upper second cavity 2221, and the air outlets 2212 are used to discharge cooling gas. The distillation unit 220 also includes a first container 223 and a second container 224 located in the lower second cavity 2222. The first container 223, which can be a graphite crucible, is disposed in the second cavity 222 to hold the protactinium-containing alloy melt. The second container 224 is located below the lower edge of the isolation membrane 2213 to collect the distilled alloy melt left along the isolation membrane 2213. The protactinium-containing alloy melt is heated by a heating module to vaporize the bismuth in the melt. The vaporized bismuth liquefies upon encountering the separating membrane 2213 and flows along the membrane into the second container 224, resulting in a distilled alloy melt whose main component is bismuth, containing a small amount of protactinium. The residual alloy melt in the first container 223 is primarily composed of protactinium, containing a small amount of bismuth.

[0045] To better understand the extraction method and apparatus of this application, a specific non-limiting embodiment is provided here, in which the main components of the thorium alloy melt are bismuth and thorium. (Refer to...) Figures 2 to 5 The embodiment includes the following steps 1 to 7.

[0046] Step 1: Prepare thorium-based breeding salt melt.

[0047] In this step, the thorium-based breeder salt melt is derived from the dry reprocessing of spent fuel from a thorium-based molten salt reactor.

[0048] Step 2: Input the thorium-based breeding salt melt into the first cavity 211 of the melt separation unit 210.

[0049] In this step, the first cavity 211 is filled with argon gas with a purity of ≥99.999%.

[0050] Step 3: Heat the thorium-based breeding salt melt in the first cavity 211 to 650°C and keep it at a constant temperature for 30-60 minutes. Then, inject the thorium-containing alloy melt into the thorium-based breeding salt melt through the infusion tube 2121.

[0051] In this step, the thorium-based breeding salt melt is completely melted by heating, the thorium element in the thorium-containing alloy melt is at a saturated concentration, and the injection rate of the thorium-containing alloy melt is 1L / min.

[0052] Step 4: Carry out the reduction reaction.

[0053] In this step, protactinium ions in the thorium-based breeding salt melt are reduced to metallic protactinium and dissolved into the thorium-containing alloy melt to obtain a protactinium-containing alloy melt, thus achieving selective transfer of protactinium.

[0054] Step 5: After the reduction reaction, let the melt stand at 650°C.

[0055] In this step, the density difference between the protactinium-containing alloy melt and the thorium-based breeding salt melt after the reduction reaction is used to separate the two into layers. The density of the protactinium-containing alloy melt is 9.5 g / cm³-10.5 g / cm³, and the density of the thorium-based breeding salt melt after the reduction reaction is 2.5 g / cm³-3.5 g / cm³.

[0056] Step 6: The lower layer of protactinium-containing alloy melt is discharged into the third container 214 through the drain valve 213 of the melt separation unit 210, and then the upper layer of thorium-based breeding salt melt after reduction reaction is retained.

[0057] Step 7: Transfer the molten protactinium-containing alloy after the reduction reaction to the distillation unit 220 for distillation treatment.

[0058] In this step, the second chamber 222 of the distillation unit 220 is evacuated to a high vacuum, with a pressure range of 1 Pa to 100 Pa. The heating module heats the protactinium-containing alloy melt to 1200 °C at a rate of 5 °C / min to 8 °C / min for isothermal distillation. Bismuth vaporizes into a gaseous state, liquefies upon contact with cooling air, and is collected in the second container 224. Protactinium metal with a purity ≥99.5% is also obtained in the first container 223.

[0059] This application uses specific terms to describe embodiments of the application. Terms such as "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of the application. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0060] It should be noted that, in order to simplify the description of the present application and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of the embodiments of the present application sometimes combines multiple features into a single embodiment, drawing, or description thereof. However, this disclosure method does not imply that the subject matter of the application requires more features than those mentioned. In fact, the embodiments contain fewer features than all the features of the single embodiments disclosed above.

[0061] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used to describe embodiments are sometimes modified by the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in this application are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of range in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

Claims

1. A method for extraction of the element protactinium from a thorium-based breeder salt, characterized in that, The method comprises the following steps: mixing a thorium-containing alloy melt with a thorium-based fertile salt melt, reducing the plutonium ions in the thorium-based fertile salt melt into metallic plutonium, and dissolving the metallic plutonium into the alloy melt to obtain a plutonium-containing alloy melt; resting the melt after the reduction reaction, separating the plutonium-containing alloy melt from the thorium-based fertile salt melt after the reduction reaction, and taking out the plutonium-containing alloy melt after the separation; distilling the plutonium-containing alloy melt to separate the plutonium element.

2. The method of claim 1, wherein the thorium-based fertile salt is thorium dioxide (Th02). The thorium-containing alloy melt contains bismuth and / or lead.

3. The method of claim 1, wherein the thorium-based fertile salt is thorium dioxide (ThO2). The method further comprises the following steps: Before mixing the thorium-containing alloy melt with the thorium-based fertile salt melt, resting the thorium-based fertile salt melt to remove bubbles in the thorium-based fertile salt melt and homogenize the concentration of the thorium-based fertile salt melt.

4. The method of claim 1, wherein the thorium-based fertile salt is thorium dioxide (Th02). The method of mixing the thorium-containing alloy melt with the thorium-based fertile salt melt comprises the following step:

5. The method of claim 1, wherein the thorium-based fertile salt is thorium dioxide (ThO2). The method further comprises the following step: Stacking the thorium-based fertile salt melt after the reduction reaction.

6. The method of claim 1, wherein the thorium-based fertile salt is thorium dioxide (ThO2). The method further comprises the following step: Recycling the distilled alloy melt obtained by the distillation to the next extraction.

7. The method of claim 1, wherein the thorium-based fertile salt is thorium dioxide (ThO2). The method uses a melt separation unit to take out the plutonium alloy melt, the melt separation unit comprising a first cavity, a feed inlet and a discharge valve, the first cavity being used for the reduction reaction of the thorium-based fertile salt melt with the thorium-containing alloy melt, and for resting the melt after the reduction reaction to separate the plutonium-containing alloy melt obtained by the reduction reaction from the thorium-based fertile salt melt after the reduction reaction, the discharge valve being used for discharging the plutonium-containing alloy melt after the separation; The method uses a distillation unit to separate the plutonium element, the distillation unit comprising a second cavity, a heating module and a cooling module, the heating module being used for heating the plutonium-containing alloy melt in the second cavity, and the cooling module being used for cooling the distilled alloy melt.

8. The method of claim 7, wherein the thorium-based fertile salt is thorium dioxide (Th02). The feed inlet of the melt separation unit comprises a liquid delivery tube extending into the first cavity, wherein the liquid delivery tube is used for injecting the thorium-based fertile salt melt into the thorium-containing alloy melt.

9. The method of claim 7, wherein the thorium-based fertile salt is thorium dioxide (Th02). The cooling module comprises a plurality of air inlets, a plurality of air outlets and a separation membrane, the separation membrane dividing the second cavity into an upper second cavity and a lower second cavity, the plurality of air inlets and the plurality of air outlets being in communication with the upper second cavity; The distillation unit further comprises a first container and a second container in the lower second cavity, the first container being used for containing the plutonium-containing alloy melt, and the second container being located below the lower edge of the separation membrane to collect the distilled alloy melt left along the separation membrane.

10. The method of claim 7, wherein the thorium-based fertile salt is thorium dioxide (Th02). The heating module is a heating furnace.

Images