Separation method of fast reactor spent fuel
By employing selective extraction and back-extraction technologies, the problem of low radioactive element yield in fast reactor spent fuel has been solved, enabling efficient separation and recovery of plutonium and uranium, improving resource utilization, and promoting the closed-loop cycle of fast reactor spent fuel.
Patent Information
- Application Number
- CN202610002761.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-04
- Publication Date
- 2026-05-19
AI Technical Summary
The co-decontamination cycle of spent fuel in existing fast reactors is not ideal, resulting in low radioactive element yields and making it difficult to effectively recover and utilize plutonium and uranium.
Selective extraction and back-extraction techniques are employed. In the first extraction step, plutonium and uranium are selectively extracted. In the first washing step, impurities are blocked. In the first back-extraction step, the complexation of radioactive elements is destroyed. In the second extraction step, acidity is adjusted and a reducing agent is used to reduce plutonium. Finally, high-purity plutonium and uranium products are extracted separately in the separation step.
It improved the recovery rate of radioactive elements, promoted the optimization and recycling of resources, enhanced the utilization rate of uranium and plutonium, and achieved efficient recovery and purification of resources through a closed fuel cycle.
Smart Images
Figure CN122067833A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of spent fuel reprocessing technology, specifically relating to a method for separating spent fuel from fast reactors. Background Technology
[0002] Nuclear energy plays a vital role in ensuring energy security, protecting the environment, optimizing the energy structure, and achieving sustainable economic and social development in my country. Sustainable development of nuclear energy primarily requires addressing two major issues: optimizing the utilization of radioactive elements (uranium / plutonium) resources and minimizing radioactive waste.
[0003] Developing reprocessing technology for spent fast reactor fuel, separating radioactive elements from spent fast reactor fuel, and recycling these radioactive elements are effective ways to solve the two problems mentioned above.
[0004] The main purpose of fast reactor spent fuel reprocessing is to recover radioactive elements (uranium / plutonium) from spent fuel, use radioactive elements to manufacture mixed oxide (MOX) fuel elements, realize a closed-loop cycle of fast reactor spent fuel, and improve the utilization rate of radioactive elements.
[0005] The reprocessing technology for spent fuel from fast reactors mainly includes co-decontamination cycles and uranium purification cycles, as well as plutonium purification cycles. The co-decontamination cycle provided by existing technologies is not ideal, resulting in low radioactive element yields. Summary of the Invention
[0006] This application is made in view of the above-mentioned issues, and its purpose is to provide a method for separating spent fuel from fast reactors. This method can effectively separate radioactive elements from spent fuel from fast reactors through selective extraction and back-extraction techniques, thereby improving the yield of radioactive elements.
[0007] To address the aforementioned technical problems, this application provides a method for separating spent fuel from a fast reactor, comprising: a first extraction step: mixing spent fuel from a fast reactor, a first extractant, and a first washing agent in a mixing and clarifying tank; radioactive elements in the spent fuel are extracted into the first extractant to form a first organic phase; the first washing agent is used to form salts with impurity elements in the spent fuel to prevent impurity elements from entering the first organic phase; the radioactive elements include at least plutonium and uranium; and a first back-extraction step: mixing the first organic phase and the first back-extraction agent in a mixing and clarifying tank to allow radioactive elements in the first organic phase to enter the first back-extraction agent, forming a first organic phase. The process involves: forming a first back-extraction phase, where the first back-extraction agent is used to disrupt the complexation of radioactive elements, allowing them to enter the first back-extraction agent; a second extraction step, where the acidity of the first back-extraction phase is reduced and mixed with the second extractant and the first reducing agent in a mixing and clarifying tank, allowing uranium in the first back-extraction phase to enter the second extractant and form the second extraction phase, where the first reducing agent is used to reduce the oxidation state of plutonium in the first back-extraction phase from +4 to +3, so that the +3 plutonium remains in the first back-extraction phase; and a separation step, where plutonium is separated from the first back-extraction phase and uranium is separated from the second extraction phase.
[0008] In some implementations, the concentration of plutonium in the spent fuel of the fast reactor is from 15 g / L to 30 g / L, and the concentration of uranium is from 70 g / L to 90 g / L.
[0009] In some embodiments, the volume ratio of spent fuel from the fast reactor, the first extractant, and the first scrubbing agent is (0.5 to 2): (1 to 2.5): (0.3 to 1.3).
[0010] In some embodiments, the first extractant comprises a tributyl phosphate kerosene solution with a volume concentration of 10% to 30%.
[0011] In some embodiments, the first detergent comprises nitric acid with a molar concentration of 1 mol / L to 5 mol / L.
[0012] In some embodiments, the first back-extraction step includes: mixing a first organic phase and a first back-extraction agent such that radioactive elements in the first organic phase enter the first back-extraction agent to form a first mixture; washing the first organic phase with a second detergent such that residual radioactive elements in the first organic phase enter the second detergent to form a second mixture; and mixing the first mixture and the second mixture to obtain a first back-extraction phase.
[0013] In some embodiments, the first stripping agent comprises nitric acid with a molar concentration of 10 mol / L to 13 mol / L.
[0014] In some embodiments, the second detergent comprises nitric acid with a molar concentration of 0.01 mol / L to 1 mol / L.
[0015] In some embodiments, the volume ratio of the first organic phase to the first stripping agent is (0.5 to 2):(0.02 to 0.1).
[0016] In some embodiments, the volume ratio of the first organic phase to the second detergent is (0.5 to 2):(1 to 3).
[0017] In some embodiments, the first reducing agent includes at least one of methylhydrazine at a molar concentration of 0.2 mol / L to 1 mol / L and dimethylhydroxylamine at a molar concentration of 0.3 mol / L to 1 mol / L.
[0018] In some embodiments, the volume ratio of the first back-extraction phase, the second extractant, and the first reducing agent is (0.5 to 2):(0.2 to 2):(0.2 to 4).
[0019] In some embodiments, the second extractant is a tributyl phosphate kerosene solution with a volume concentration of 10% to 30%.
[0020] In some embodiments, the purification step of separating the plutonium product in the first back-extraction phase includes: oxidizing the chemical valence of the plutonium in the first back-extraction phase from +3 to +4; and separating the +4 plutonium in the first back-extraction phase by extraction.
[0021] In some embodiments, the step of separating uranium product from the second extraction phase includes: a second back-extraction step: mixing the second extraction phase with a second back-extractant so that uranium in the second extraction phase enters the second back-extractant to form a second back-extraction phase, wherein the second back-extractant is used to disrupt the complexation of uranium so that uranium enters the second back-extractant; and separating uranium product from the second back-extraction phase.
[0022] In some embodiments, the second stripping agent comprises nitric acid with a molar concentration of less than or equal to 0.1 mol / L.
[0023] In some embodiments, the volume ratio of the second extractant to the second back-extractant is 1:(1.1 to 1.5).
[0024] The method for separating radioactive elements from spent fuel in a fast reactor provided in this application firstly selectively extracts radioactive elements plutonium and uranium in a first extraction step, while simultaneously inhibiting the transfer of impurity elements using a first washing agent. Next, in a first back-extraction step, the complexation of radioactive elements is disrupted, enabling their transfer to the back-extraction agent. Then, through acidity adjustment and the use of a reducing agent in a second extraction step, uranium and plutonium are separated. Finally, in the separation step, high-purity plutonium and uranium products are extracted separately, thereby effectively improving the recovery rate of radioactive elements and promoting resource optimization and recycling through a closed fuel cycle. Attached Figure Description
[0025] Figure 1 This is a flowchart of a method for separating radioactive elements from spent fuel in a fast reactor according to an embodiment of this application; Figure 2 This is a flowchart of the method for separating radioactive elements from spent fuel in a fast reactor according to Example 1; Figure 3 This is a flowchart of plutonium purification in Example 1; Figure 4 This is a flowchart of uranium purification in Example 1. Detailed Implementation
[0026] The following detailed description, with appropriate reference to the accompanying drawings, discloses an embodiment of a method for separating spent fuel from a fast reactor. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of providing a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.
[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.
[0029] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.
[0030] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.
[0031] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.
[0032] Unless otherwise specified, the values of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.
[0033] The main purpose of fast reactor spent fuel reprocessing is to recover radioactive elements (uranium / plutonium) from spent fuel, use these radioactive elements to manufacture mixed oxide (MOX) fuel elements, achieve a closed-loop cycle of fast reactor spent fuel, and improve the utilization rate of radioactive elements. The reprocessing process for fast reactor spent fuel mainly includes: co-decontamination cycle and uranium purification cycle, and plutonium purification cycle steps. The co-decontamination cycle step provided by existing technologies is not ideal, resulting in low radioactive element recovery rates.
[0034] To address the aforementioned technical problems, this application provides a method for separating spent fuel from a fast reactor. This separation method effectively separates radioactive elements through selective extraction and back-extraction techniques, thereby increasing the yield of radioactive elements.
[0035] See Figure 1 This application provides a method for separating spent fuel from a fast reactor, the method comprising: First extraction step: Fast reactor spent fuel, first extractant and first detergent are mixed in a mixing and clarification tank. Radioactive elements in the fast reactor spent fuel are extracted into the first extractant to form a first organic phase. The first detergent is used to form salts with impurity elements in the fast reactor spent fuel to prevent impurity elements from entering the first organic phase. The radioactive elements include at least plutonium and uranium. First back-extraction step: The first organic phase and the first back-extraction agent are mixed in a mixing and clarification tank so that the radioactive elements in the first organic phase enter the first back-extraction agent to form the first back-extraction phase. The first back-extraction agent is used to destroy the complexation of the radioactive elements so that the radioactive elements enter the first back-extraction agent. The second extraction step involves reducing the acidity of the first back-extraction phase and mixing it with the second extractant and the first reducing agent in a mixing and clarification tank. This allows the uranium element in the first back-extraction phase to enter the second extractant and form the second extraction phase. The first reducing agent is used to reduce the oxidation state of plutonium in the first back-extraction phase from +4 to +3, so that the +3 plutonium element remains in the first back-extraction phase. Separation steps: Plutonium is separated in the first back-extraction phase, and uranium is separated in the second extraction phase.
[0036] The method for separating radioactive elements from spent fuel in a fast reactor provided in this application firstly selectively extracts radioactive elements plutonium and uranium in a first extraction step, while simultaneously inhibiting the transfer of impurity elements using a first washing agent. Next, in a first back-extraction step, the complexation of radioactive elements is disrupted, enabling their transfer to the back-extraction agent. Then, through acidity adjustment and the use of a reducing agent in a second extraction step, uranium and plutonium are separated. Finally, in the separation step, high-purity plutonium and uranium products are extracted separately, thereby effectively improving the recovery rate of radioactive elements and promoting resource optimization and recycling through a closed fuel cycle.
[0037] In this application, "first extractant" refers to a solvent that can dissolve plutonium and uranium in spent fuel from a fast reactor. By adding the first extractant to the spent fuel from the fast reactor, the initial separation of plutonium and uranium from other impurities can be achieved.
[0038] In this application, the "first detergent" is used to form salts with impurity elements in the spent fuel of the fast reactor to prevent the impurity elements from entering the first organic phase. In some embodiments, the first detergent is used to dissolve zirconium and ruthenium; and to form stable compounds with zirconium and / or ruthenium, so that zirconium and / or ruthenium remain in the first detergent.
[0039] In this application, "first back-extraction agent" refers to an agent capable of destroying the complex formed between the radioactive element and the extractant, thereby releasing the radioactive element into the back-extraction agent.
[0040] In this application, the "second extractant" is used as a solvent for selectively dissolving uranium from the first back-extraction phase.
[0041] In this application, "first reducing agent" refers to a reagent that can reduce plutonium in the high valence state (+4) to plutonium in the +3 valence state. Plutonium in the +3 valence state is easily soluble in the aqueous phase, so that the plutonium in the +3 valence state remains in the first back-extraction phase.
[0042] In some embodiments, the concentration of plutonium in spent fast reactor fuel is 15 g / L to 30 g / L, and the concentration of uranium is 70 g / L to 90 g / L. The method provided in this application can recover radioactive elements from spent fast reactor fuel with high concentrations of plutonium and uranium, and reprocess them for reuse in the fast reactor fuel cycle, significantly improving the utilization rate of uranium and plutonium resources.
[0043] For example, the concentration of plutonium in spent fuel from a fast reactor is 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 25 g / L, 30 g / L, or any value between two of these values.
[0044] For example, the concentration of uranium in the spent fuel of a fast reactor is 70 g / L, 72 g / L, 74 g / L, 76 g / L, 78 g / L, 80 g / L, 82 g / L, 84 g / L, 86 g / L, 88 g / L, 90 g / L, or any value between two of these two values.
[0045] In some embodiments, the volume ratio of fast reactor spent fuel, the first extractant, and the first scrubbing agent is (0.5 to 2):(1 to 2.5):(0.3 to 1.3). When the three are mixed in the above volume ratio, the first extractant provides sufficient extraction volume and good flowability, enabling the fast reactor spent fuel to be fully dispersed in the first extractant; at the same time, the first scrubbing agent can fully react with impurities such as zirconium and ruthenium to generate inorganic salts, thereby improving the separation of target elements (plutonium and uranium) from impurity elements (zirconium and ruthenium).
[0046] In some embodiments, the first extractant is a tributyl phosphate kerosene solution with a volume concentration of 10% to 30%. Using the above-mentioned tributyl phosphate kerosene solution as the first extractant allows the phosphate groups in the tributyl phosphate to form stable complexes with plutonium and uranium, which is beneficial for the separation of target elements (plutonium and uranium) from impurity elements (zirconium and ruthenium).
[0047] In some embodiments, the first detergent comprises nitric acid with a molar concentration of 1 mol / L to 5 mol / L. A molar concentration of 1 mol / L to 5 mol / L nitric acid provides a suitable acidic environment for dissolving impurity elements (e.g., zirconium and ruthenium) without reacting with radioactive elements (plutonium and uranium) or disrupting the complexation between the radioactive elements and the first extractant. If the concentration of the first detergent is too low, it is not conducive to the sufficient dissolution of impurity elements, resulting in a high residual amount of impurity elements and affecting separation efficiency; if the concentration of the first detergent is too high, it is not conducive to protecting radioactive elements and may disrupt the complexation state between the radioactive elements and the first extractant, affecting the separation effect. Therefore, controlling the concentration of the first detergent within the above-mentioned range can further improve the separation effect of radioactive elements.
[0048] For example, the first detergent is a value with a molar concentration of 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, or any combination thereof.
[0049] In some embodiments, the first back-extraction step includes: mixing a first organic phase and a first back-extraction agent such that radioactive elements in the first organic phase enter the first back-extraction agent to form a first mixture; washing the first organic phase with a second detergent such that residual radioactive elements in the first organic phase enter the second detergent to form a second mixture; and mixing the first mixture and the second mixture to obtain a first back-extraction phase.
[0050] In this method, the effective transfer of radioactive elements is achieved by mixing the first organic phase with the first back-extraction agent. Simultaneously, washing the first organic phase with a second detergent further recovers residual radioactive elements, improving overall recovery efficiency. Finally, mixing the first mixture with the second mixture results in a first back-extraction phase with a higher content of radioactive elements, providing a better foundation for subsequent radioactive element separation and utilization.
[0051] In some embodiments, the first stripping agent comprises nitric acid with a molar concentration of 10 mol / L to 13 mol / L. Nitric acid at this concentration can effectively disrupt the complexation between the radioactive element and the first stripping agent, allowing the radioactive element to transfer from the first organic phase to the aqueous phase (the first stripping agent), thus achieving the stripping of the radioactive element.
[0052] For example, the first stripping agent comprises nitric acid with a molar concentration of 10 mol / L, 10.5 mol / L, 11 mol / L, 11.5 mol / L, 12 mol / L, 12.5 mol / L, 13 mol / L, or any combination thereof.
[0053] In some embodiments, the second detergent comprises nitric acid with a molar concentration of 0.01 mol / L to 1 mol / L. By using nitric acid with lower acidity to wash the first organic phase, this lower concentration of nitric acid detergent can further extract residual radioactive elements and improve the recovery rate of radioactive elements.
[0054] For example, the second detergent is nitric acid with a molar concentration of 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any combination thereof.
[0055] In some embodiments, the volume ratio of the first organic phase to the first stripping agent is (0.5 to 2):(0.02 to 0.1). By controlling the volume ratio of the first organic phase to the first stripping agent within the above range, sufficient amount of the first stripping agent is ensured to participate in the reaction, ensuring efficient stripping of radioactive elements from the first organic phase, achieving efficient transfer, and reducing the consumption of the first stripping agent, thereby saving costs.
[0056] For example, the volume ratio of the first organic phase to the first stripping agent is a value within a range of 0.5:0.02, 0.5:0.04, 0.5:0.06, 0.5:0.08, 0.5:0.1, 2:0.02, 2:0.04, 2:0.06, 2:0.08, 2:0.1, or any two of these.
[0057] In some embodiments, the volume ratio of the first organic phase to the second detergent is (0.5 to 2):(1 to 3). By controlling the volume ratio of the first organic phase to the second detergent within the above range, it is possible to ensure that the second detergent thoroughly cleans the first organic phase while avoiding excessive use of the second detergent.
[0058] For example, the volume ratio of the first organic phase to the second detergent is nitric acid in a range of 0.5:1, 0.5:2, 0.5:3, 2:1, 2:2, 2:3, or any combination thereof.
[0059] In some embodiments, the first reducing agent includes at least one of methylhydrazine at a molar concentration of 0.2 mol / L to 1 mol / L and dimethylhydroxylamine at a molar concentration of 0.3 mol / L to 1 mol / L. Methylhydrazine and dimethylhydroxylamine can reduce plutonium (+4 valence) to plutonium (+3 valence), thereby transferring plutonium to the first back-extraction phase while uranium remains in the organic extraction phase, thus achieving separation of plutonium and uranium and contributing to improved purity of both elements.
[0060] For example, the molar concentration of dimethylhydroxylamine is a value within a range of 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any combination thereof.
[0061] For example, the molar concentration of methylhydrazine is a value within a range of 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any combination thereof.
[0062] In some embodiments, the volume ratio of the first back-extraction phase, the second extractant, and the first reducing agent is (0.5 to 2):(0.2 to 2):(0.2 to 4). By controlling the volume ratio of the three components within the above range, on the one hand, the appropriate use of the first back-extraction phase can ensure the effective transfer of radioactive elements, and on the other hand, the appropriate ratio of the second extractant and the reducing agent helps to further separate and purify radioactive elements. In particular, through the action of the reducing agent, selective dissolution of radioactive elements in specific valence states can be achieved. This precise ratio not only improves recovery efficiency and reduces the loss of radioactive elements during processing, but also helps to reduce the consumption of chemical reagents, thereby reducing processing costs and improving the environmental friendliness and economy of the entire nuclear fuel reprocessing process.
[0063] In some embodiments, the second back-extraction agent is nitric acid with a molar concentration of less than or equal to 0.1 mol / L. In back-extraction step 1C, using nitric acid (dilute nitric acid) with a molar concentration of less than or equal to 0.1 mol / L as the second back-extraction agent disrupts the complexation equilibrium due to the acidic environment provided by the dilute nitric acid, causing uranium to transfer from the organic extraction phase to the inorganic first back-extraction phase, thus achieving the separation of uranium from the second extractant and facilitating the acquisition of a high-purity uranium product.
[0064] For example, the second back-extraction agent is nitric acid with a molar concentration of 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, or any combination thereof.
[0065] In some embodiments, during the initial extraction step, the volume ratio of the first mixture, the second extractant, and the reducing agent is (0.5 to 2):(0.2 to 2):(0.2 to 4), which facilitates the separation of uranium and plutonium.
[0066] In some embodiments, the volume ratio of the organic intermediate phase to the reducing agent in the intermediate extraction step is (0.5 to 2):(0.2 to 1).
[0067] In some embodiments, the reducing agent includes at least one of methylhydrazine at a molar concentration of 0.2 mol / L to 1 mol / L and dimethylhydroxylamine at a molar concentration of 0.3 mol / L to 1 mol / L. Methylhydrazine and dimethylhydroxylamine can reduce plutonium (+4 valence) to plutonium (+3 valence), thereby transferring plutonium to the first back-extraction phase while uranium remains in the organic extraction phase, thus achieving separation of plutonium and uranium and contributing to improved purity of both elements.
[0068] For example, the molar concentration of dimethylhydroxylamine is a value within a range of 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any combination thereof.
[0069] For example, the molar concentration of methylhydrazine is a value within a range of 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any combination thereof.
[0070] In some embodiments, the second extractant is a tributyl phosphate kerosene solution with a volume concentration of 10% to 30%. A tributyl phosphate kerosene solution with a volume concentration within this range can fully complex with uranium, retaining uranium in the organic extract phase, which is beneficial for improving the separation efficiency of plutonium and uranium.
[0071] In some embodiments, the chemical valence of plutonium in the first back-extraction phase is oxidized from +3 to +4; the +4 plutonium is then separated from the first back-extraction phase by extraction. By oxidizing the plutonium in the first back-extraction phase from +3 to +4, the extraction efficiency of plutonium can be effectively improved. +4 plutonium is more easily captured by the extractant than +3 plutonium, thus allowing for more efficient separation of +4 plutonium in subsequent extraction processes.
[0072] In some embodiments, the step of separating uranium product from the second extraction phase includes a second back-extraction step: mixing the second extraction phase with a second back-extractant to allow uranium in the second extraction phase to enter the second back-extractant, forming a second back-extraction phase. The second back-extractant is used to disrupt the complexation of uranium, allowing uranium to enter the second back-extractant; and separating the uranium product from the second back-extraction phase. By using a second back-extractant to disrupt the complexation of uranium, the transfer of uranium from the second back-extraction phase to the second back-extractant can be effectively promoted, thereby achieving efficient separation of uranium. This method can improve the extraction purity and recovery rate of uranium while reducing the content of impurities and residues.
[0073] In some embodiments, the volume ratio of the second extractant to the second back-extractant is 1:(1.1 to 1.5). In the second back-extraction step, the volume of the second back-extractant is greater than that of the second extractant, which can sufficiently promote the dissociation of uranium from the second extractant and its transfer to the second back-extractant, thus ensuring the efficiency of uranium back-extraction.
[0074] For example, the volume ratio of the second extractant to the second back-extractant is a value between 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or any combination thereof.
[0075] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Unless otherwise stated, reagents or instruments used without a specified manufacturer are all conventional products that can be obtained commercially.
[0076] Example 1 See Figure 2 The separation methods include: First extraction step: Take a volume ratio of 1:1.3:0.65 for the fast reactor spent fuel solution (which may be referred to as fast reactor spent fuel in this application), a first extractant (a 30% volume concentration of tributyl phosphate kerosene solution), and a first detergent (3 mol / L HNO3).
[0077] The spent fuel solution from the fast reactor, the first extractant, and the first scrubbing agent undergo a 12-stage extraction process. Spent fuel solution is added in stage 6, the first extractant in stage 1, and the first scrubbing agent in stage 12. Radioactive elements (plutonium and uranium) in the spent fuel are extracted into the first extractant, forming the first organic phase.
[0078] First reverse extraction step: Measure the volume ratio of the first organic phase, the first stripping agent (11 mol / L HNO3), and the second detergent (0.01 mol / L HNO3) in a ratio of 1:0.057:1.585.
[0079] A 16-stage back-extraction process is performed. A first organic phase is added in stage 1, a first back-extraction agent is added in stage 8, and a second detergent is added in stage 16. Radioactive elements in the first organic phase enter the first back-extraction agent, forming the first back-extraction phase.
[0080] Second extraction step: To reduce the acidity of the first back-extraction phase, measure the first back-extraction phase (volume ratio 1:0.33:0.33), the second extractant (30% tributyl phosphate kerosene solution), and the first reducing agent (0.6 mol / L dimethyl hydroxylamine, 0.3 mol / L methylhydrazine, and 0.35 mol / L HNO3).
[0081] In the second extraction step, a total of 16 extraction stages are performed. During the fourth extraction stage, a mixture of the first reverse extraction phase, the second extractant, and the first reducing agent is added.
[0082] The process allows uranium in the first back-extraction phase to enter the second extractant to form the second extraction phase. The first reducing agent is used to reduce the oxidation state of plutonium in the first back-extraction phase from +4 to +3, so that the +3 plutonium remains in the first back-extraction phase.
[0083] Separation steps: The second back-extraction step involves mixing the second back-extraction phase with a second back-extraction agent (0.01 mol / L nitric acid) to allow uranium from the second extraction phase to enter the second back-extraction agent, forming a second back-extraction phase. The second back-extraction agent is used to disrupt the complexation of uranium, allowing it to enter the second back-extraction agent. The ratio of the second extraction phase to the second back-extraction agent is 1:1.1.
[0084] See Figure 3 Uranium purification: Adding 30% tributyl phosphate kerosene solution 2DX and 1 mol / L nitric acid 2DS to the second back-extraction phase yields a mixture 2DU, wherein the volume ratio of the second back-extraction phase 2DF:nitric acid 2DX to 30% tributyl phosphate kerosene solution 2DX is 1:3.5:0.55. This allows uranium in the second back-extraction phase 2DF to coordinate with the 30% tributyl phosphate kerosene solution 2DX, thereby being extracted into the 30% tributyl phosphate kerosene solution to obtain mixture 2DU.
[0085] Extraction was performed by adding 0.1 mol / L nitric acid 2EX to the mixture 2DU, yielding an aqueous phase 2EW and an oil phase 2EU. Uranium products were separated from the oil phase 2EU, with a volume ratio of 2DF:2EX of 1:7.7.
[0086] See Figure 4 Plutonium purification: The chemical valence of plutonium in the first back-extraction phase 1BP is oxidized from +3 to +4, allowing the +4 plutonium to enter the organic phase, resulting in a mixture 2AF.
[0087] A mixture was prepared by adding 3.5 mol / L nitric acid (2AX) and 30% tributyl phosphate kerosene solution (2DX). The organic phase (2AP) was then separated from the mixture. The volume ratio of 2AX, 2AF, and 2AS was 1:3.5:0.45.
[0088] 0.3 mol / L of nitric acid 2BX was added to the organic phase 2AP, and extraction was performed to separate the plutonium product from the organic phase 2BP.
[0089] Example 2 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: In the first extraction step, the number of extraction stages, the number of stages into which the spent fuel solution from the fast reactor enters, the number of stages into which the first extractant enters, and the number of stages into which the first detergent enters are shown in Table 1.
[0090] Example 3 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: The first extraction step: the number of extraction stages, the number of stages into which the spent fuel solution from the fast reactor enters, the number of stages into which the first extractant enters, and the number of stages into which the first detergent enters are shown in Table 1.
[0091] Example 4 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: The first extraction step involves a volume ratio of 1:1:0.65 for spent fast reactor fuel, the first extractant, and the first washing agent.
[0092] Example 5 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: The first extraction step involves a volume ratio of fast reactor spent fuel, first extractant, and first detergent of 1:1.5:0.65.
[0093] Example 6 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: First back-extraction step: See Table 2 for the number of back-extraction stages, the number of the first organic phase entering the stage, the number of the first back-extraction agent entering the stage, and the number of the second detergent entering the stage.
[0094] Example 7 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: First back-extraction step: See Table 2 for the number of back-extraction stages, the number of the first organic phase entering the stage, the number of the first back-extraction agent entering the stage, and the number of the second detergent entering the stage.
[0095] Example 8 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: In the first extraction step, the number of extraction stages, the number of stages into which the spent fuel solution from the fast reactor enters, the number of stages into which the first extractant enters, and the number of stages into which the first detergent enters are shown in Table 1.
[0096] The second extraction step involves 16 stages of extraction. In the fifth stage, a feed solution containing both U and Pu (the first back-extraction phase) is used. In the first stage, a second extractant is added, and in the sixteenth stage, a first reduction back-extraction agent is added.
[0097] And the first reverse extraction step is not performed.
[0098] Example 9 The same method as in Example 1 was used to recover uranium and plutonium from spent fuel in a fast reactor, with the difference being: In the first extraction step, the number of extraction stages, the number of stages into which the spent fuel solution from the fast reactor enters, the number of stages into which the first extractant enters, and the number of stages into which the first detergent enters are shown in Table 1.
[0099] The second extraction step involves 16 stages of extraction. In the third stage, a feed solution containing both U and Pu (the first back-extraction phase) is used. In the first stage, a second extractant is added, and in the sixteenth stage, a first reducing back-extraction agent is added.
[0100] And the first reverse extraction step is not performed.
[0101] Comparative Example 1 The plutonium element in the spent fuel of the fast reactor is directly separated using the plutonium wire from the example, and the uranium element in the spent fuel of the fast reactor is separated using the uranium wire from the example.
[0102] Table 1
[0103] Table 2
[0104] In Table 1, the extraction volume ratio refers to the volume ratio of spent fuel solution from the fast reactor, the first extractant, and the first scrubbing agent.
[0105] In Table 2, the back-extraction volume ratio refers to the volume ratio of the first organic phase, the first back-extraction agent, and the second detergent.
[0106] The data in Tables 1 and 2 show that the separation method for spent fast reactor fuel provided in this application can effectively separate radioactive elements from spent fast reactor fuel through selective extraction and back-extraction technologies, thereby improving the yield of radioactive elements.
[0107] Although this application has been described with reference to its specific exemplary embodiments, many different variations, modifications, etc. will become apparent to those skilled in the art.
[0108] Furthermore, the separation method provided in this application achieves a decontamination coefficient of 1000 for Ru and Cs, as the removal effect of these two elements is of significant concern in the post-processing flow. These are elements with high gamma radioactivity; their removal reduces gamma radioactivity in subsequent post-processing steps, helps extend equipment life, and also mitigates the radiolytic impact on organic extractants. The achievement of such high coefficients demonstrates the feasibility and practical value of this process.
[0109] By studying the disclosure and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments when practicing this application.
Claims
1. A method for separating spent fuel from a fast reactor, characterized in that, include: First extraction step: Fast reactor spent fuel, first extractant and first detergent are mixed in a mixing and clarification tank. Radioactive elements in the fast reactor spent fuel are extracted into the first extractant to form a first organic phase. The first detergent is used to form salts with impurity elements in the fast reactor spent fuel to prevent the impurity elements from entering the first organic phase. The radioactive elements include at least plutonium and uranium. First back-extraction step: The first organic phase and the first back-extractant are mixed in a mixing and clarification tank so that the radioactive element in the first organic phase enters the first back-extractant to form a first back-extraction phase. The first back-extractant is used to destroy the complexation of the radioactive element so that the radioactive element enters the first back-extractant. The second extraction step involves reducing the acidity of the first back-extraction phase and mixing it with the second extractant and the first reducing agent in a mixing and clarification tank, so that the uranium element in the first back-extraction phase enters the second extractant to form the second extraction phase. The first reducing agent is used to reduce the oxidation state of plutonium element in the first back-extraction phase from +4 to +3, so that the +3 plutonium element remains in the first back-extraction phase. Separation steps: Plutonium is separated from the first back-extraction phase, and uranium is separated from the second extraction phase.
2. The separation method according to claim 1, characterized in that, In the spent fuel of the fast reactor, the concentration of plutonium is from 15 g / L to 30 g / L, and the concentration of uranium is from 70 g / L to 90 g / L.
3. The processing method according to claim 1, characterized in that, The first extraction step satisfies at least one of the following: (1) The volume ratio of the fast reactor spent fuel, the first extractant and the first scrubbing agent is (0.5 to 2): (1 to 2.5): (0.3 to 1.3); (2) The first extractant comprises a tributyl phosphate kerosene solution with a volume concentration of 10% to 30%; (3) The first detergent includes nitric acid with a molar concentration of 1 mol / L to 5 mol / L.
4. The processing method according to claim 3, characterized in that, The first back-extraction step includes: The first organic phase and the first stripping agent are mixed so that the radioactive element in the first organic phase enters the first stripping agent to form a first mixture; The first organic phase is cleaned with a second detergent so that the radioactive elements remaining in the first organic phase enter the second detergent to form a second mixture; The first mixture is mixed with the second mixture to obtain the first back-extraction phase.
5. The processing method according to claim 4, characterized in that, The first back-extraction step satisfies at least one of the following: (1) The first stripping agent comprises nitric acid with a molar concentration of 10 mol / L to 13 mol / L; (2) The second detergent comprises nitric acid with a molar concentration of 0.01 mol / L to 1 mol / L; (3) The volume ratio of the first organic phase to the first stripping agent is (0.5 to 2): (0.02 to 0.1); (4) The volume ratio of the first organic phase to the second detergent is (0.5 to 2): (1 to 3).
6. The separation method according to claim 1, characterized in that, The first reducing agent includes at least one of methylhydrazine with a molar concentration of 0.2 mol / L to 1 mol / L and dimethylhydroxylamine with a molar concentration of 0.3 mol / L to 1 mol / L.
7. The processing method according to claim 6, characterized in that, The second extraction step satisfies at least one of the following: (1) The volume ratio of the first back-extraction phase, the second extractant, and the first reducing agent is (0.5 to 2): (0.2 to 2): (0.2 to 4); (2) The second extractant is a tributyl phosphate kerosene solution with a volume concentration of 10% to 30%.
8. The processing method according to any one of claims 1 to 7, characterized in that, The purification steps for separating the plutonium product in the first back-extraction phase are as follows: The chemical valence of plutonium in the first back-extraction phase is oxidized from +3 to +4. Plutonium with a +4 valence was separated in the first back-extraction phase by extraction.
9. The processing method according to any one of claims 1 to 7, characterized in that, The steps for separating the uranium product in the second extraction phase include: Second back-extraction step: The second extractant phase is mixed with the second back-extractant so that the uranium element in the second extractant phase enters the second back-extractant to form the second back-extractant phase. The second back-extractant is used to break the complexation of the uranium element so that the uranium element enters the second back-extractant. The uranium product is separated in the second back-extraction phase.
10. The processing method according to claim 9, characterized in that, The second back-extraction step satisfies at least one of the following: (1) The second stripping agent comprises nitric acid with a molar concentration of less than or equal to 0.1 mol / L; (2) The volume ratio of the second extractant to the second back-extractant is 1: (1.1 to 1.5).