A method for processing and analyzing spent fuel insoluble residue

Abstract

The present application relates to a kind of spent fuel insoluble residue processing and analysis method, comprising extracting residue, drying and weighing, strengthening dissolution, analyzing residue heavy uranium plutonium content and the like steps;Among them, through blank filter membrane contrast and eluent double baseline control, the interference influence of the filtration process in residue analysis is significantly reduced, so that nuclear material weighing result is more quantitative and reliable, conservative and reliable.Through in small sample amount, high radiation, complex multiphase matrix condition, using optimized mixed acid system proportioning and reaction time / temperature window, the full dissolution of trace target nuclide uranium / plutonium is realized, the purpose of quantitative analysis of target nuclide in high radioactivity residue is achieved, to ensure the accurate determination and safe and efficient processing of target nuclide in residue.The present application will soluble nuclide be transferred into liquid phase as far as possible, the source item intensity and volume of high-level solid residue are reduced to the greatest extent, the burden of final radioactive waste disposal is reduced, and it is suitable for insoluble residue component analysis in nuclear fuel reprocessing plant.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel reprocessing and analysis technology, specifically relating to a method for processing and analyzing insoluble residues from spent fuel. Background Technology

[0002] The dissolution process of spent fuel in nitric acid often produces a very small amount of residue with extremely high radioactivity. This residue typically exhibits a fine, multiphase morphology, containing insoluble components such as Ru / Mo / Zr and impurities such as fuel cladding fragments. Moreover, the actual content of the target nuclides (uranium, plutonium) in the residue is very low. If the process is not properly controlled, its weak signal can easily be interfered with by impurities or masked by the residual matrix, leading to inaccurate analytical quantification and causing deviations in nuclear material balance calculations.

[0003] Existing processes for treating residues mostly remain at the stage of "weighing + chemical analysis," lacking the identification of spurious signals in the residues and comprehensive criteria based on morphology and composition. Furthermore, there is a lack of targeted mixed acid compatibility and clear time-temperature windows for enhanced dissolution of residues, which may result in some poorly soluble phases not being fully dissolved or remaining without adequate evaluation.

[0004] Therefore, there is an urgent need for a closed-loop analytical procedure that can be performed under hot chamber conditions, is friendly to trace nuclides, and has high selectivity for complex matrices, in order to ensure the accurate determination and safe and efficient processing of target nuclides in residues. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for processing and analyzing insoluble spent fuel residues. This method is a closed-loop analysis process that can be performed under hot chamber conditions, is friendly to trace nuclides, and has high selectivity for complex matrices. It can achieve quantitative analysis of some elements in highly radioactive residues and obtain parameters such as residue morphology and particle size, thereby ensuring accurate determination and safe and efficient processing of target nuclides in the residues.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for treating and analyzing insoluble residues of spent fuel, the method comprising the following steps:

[0007] S1. Residue Extraction: The spent fuel nitric acid solution is filtered under negative pressure in a heated chamber to separate the insoluble residue from the filtrate. The filter membrane carrying the residue is removed, and a blank filter membrane is used as a blank control for the same negative pressure filtration and subsequent washing operations. The filter membrane carrying the residue is then acid-washed, and the eluent is collected for analysis reference. The blank eluent is also collected for comparative analysis. The mass change of the filter membrane carrying the residue before and after filtration and the volume of the eluent are recorded to establish a dual baseline for both chemistry and mass.

[0008] S2. Drying and weighing: After washing, the filter membrane carrying the residue is dried and weighed. Combined with the pre-determined blank mass of the filter membrane, the net mass of the residue is calculated.

[0009] S3. Enhanced dissolution: Transfer the dried residue to an inert and corrosion-resistant container, add a pre-prepared mixed acid of HNO3 and HF, heat to react, and release and dissolve the adsorbed or encapsulated trace amounts of target nuclides.

[0010] S4. Analysis of uranium and plutonium content in the residue: The uranium and plutonium content in the residue is calculated by analyzing the concentration of each element in the enhanced solution.

[0011] Furthermore, in step S1, the acid washing is performed by washing twice with a 0.1 mol / L nitric acid solution.

[0012] Furthermore, in step S2, the filter membrane carrying the residue after washing is placed in a desiccator at room temperature and dried for more than 48 hours, and then weighed. Color-changing silica gel is added to the desiccator.

[0013] Furthermore, the blank mass of the filter membrane is the mass of the blank filter membrane after negative pressure filtration, acid washing, and drying.

[0014] Furthermore, in step S2, the total mass of the filter membrane carrying the residue after drying is weighed using a precision balance, and the blank mass of the filter membrane is subtracted to obtain the net mass of the insoluble residue, which serves as the basis for subsequent nuclide balance calculations.

[0015] Furthermore, the mixed acid is 9–12 mol / L HNO3 + 0.05 mol / L HF.

[0016] Furthermore, the heating reaction conditions are: reacting for 12–30 hours in the range of 90–130°C.

[0017] Furthermore, in step S4, ICP-MS is used to quantitatively analyze the uranium and plutonium content in the enhanced solution.

[0018] Furthermore, the method also includes the following microscopic characterization steps:

[0019] Before the enhanced dissolution treatment, a portion of the dried residue sample was taken and subjected to scanning electron microscopy morphology observation, energy scattering X-ray spectroscopy composition analysis, and particle size analysis.

[0020] The beneficial effects of this invention are as follows: The method for processing and analyzing insoluble spent fuel residue provided by this invention includes steps such as residue extraction, drying and weighing, enhanced dissolution, and analysis of the heavy uranium and plutonium content in the residue. The dual baseline control using a blank filter membrane and eluent significantly reduces the interference of the filtration process in residue analysis, making the nuclear material balance results more quantitative, reliable, and conservative. By using optimized mixed acid system ratios and reaction time / temperature windows under conditions of small sample volume, high radiation, and complex multiphase matrix, the complete dissolution of trace target nuclides uranium / plutonium is achieved, enabling quantitative analysis of target nuclides in highly radioactive residues. This ensures accurate determination and safe and efficient processing of target nuclides in the residues.

[0021] Furthermore, this invention utilizes a "triple" approach of morphology, particle size, and elemental composition to explain the reasons for the undissolved residue, the properties of the undissolved matter, and corresponding enhanced dissolution strategies, providing clear quantitative guidance for process equipment improvement and formulation scale-up. Simultaneously, this invention transfers soluble nuclides into the liquid phase as much as possible, minimizing the source term intensity and volume of high-level radioactive solid residues, reducing the burden of final radioactive waste disposal, and is applicable to the analysis of insoluble residue components in nuclear fuel reprocessing plants. In addition, this invention can also provide a basis for decision-making regarding the subsequent resource utilization of radioactive waste by confirming the enrichment characteristics of precious metal elements (Ru, Pd, Rh, etc.) in the residue. Attached Figure Description

[0022] Figure 1 A schematic diagram illustrating the method for treating and analyzing the insoluble residue of spent fuel provided in an embodiment of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be further clearly and completely described below with reference to the accompanying drawings and examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that in the description of the embodiments of the present invention, the terms "upper," "lower," "front," "rear," "front," "back," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and 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. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] This invention provides a method for processing and analyzing insoluble spent fuel residues. It is a closed-loop analytical process that can be performed under hot chamber conditions, is friendly to trace nuclides, and exhibits high selectivity for complex matrices. By providing an optimized mixed acid system ratio and reaction time / temperature window under conditions of small sample volume, high radiation, and complex multiphase matrices, it achieves complete dissolution of trace target nuclides (uranium / plutonium) and ensures that the above process can be replicated and scaled up in engineering. This achieves the purpose of quantitatively analyzing some elements in highly radioactive residues and obtaining parameters such as residue morphology and particle size, thus ensuring accurate determination and safe and efficient processing of target nuclides in the residues.

[0026] like Figure 1 As shown in this embodiment, a method for treating and analyzing insoluble residues from spent fuel is provided. The method includes the following steps:

[0027] S1. Residue Extraction: The spent fuel nitric acid solution is filtered under negative pressure in a heated chamber to separate the insoluble residue from the filtrate. The filter membrane carrying the residue is removed, and a blank filter membrane is used as a control for the same negative pressure filtration and subsequent washing operations. The filter membrane carrying the residue is then acid-washed, and the eluent is collected for analysis reference. The blank eluent is also collected for control analysis. The mass change of the filter membrane carrying the residue before and after filtration and the volume of the eluent are recorded to establish a dual baseline for both chemistry and mass.

[0028] Specifically, insoluble residues and filtrate in spent fuel nitric acid solution are separated by 80 kPa negative pressure filtration.

[0029] In one specific embodiment, the method for removing the filter membrane carrying the residue is as follows: after filtering the spent fuel nitric acid solution under negative pressure using a special filter for the hot chamber in the hot chamber, a robotic arm is used to remove the filter element with the filter membrane, place it in a special transfer box for the filter element, and transfer the transfer box together with the filter element to the glove box or fume hood of the radioactive laboratory, and then remove the filter membrane installed in the filter element.

[0030] Optionally, the pore size of the filter membrane is 1 μm.

[0031] Optionally, in step S1, the acid washing is performed by washing twice with a 0.1 mol / L nitric acid solution.

[0032] S2. Drying and weighing: After drying the filter membrane carrying the residue, weigh it and calculate the net mass of the residue by combining it with the pre-determined blank mass of the filter membrane.

[0033] Optionally, in step S2, the filter membrane carrying the residue after washing is placed in a desiccator at room temperature and dried for more than 48 hours, then taken out and weighed. Color-changing silica gel is added to the desiccator.

[0034] Specifically, the blank filter mass is the mass of the blank filter membrane after negative pressure filtration, acid washing, and drying.

[0035] In step S2, the total mass of the filter membrane carrying the residue after drying is weighed using a precision balance. The blank mass of the filter membrane is then subtracted to obtain the net mass of the insoluble residue, which serves as the basis for subsequent nuclide balance calculations.

[0036] S3. Enhanced dissolution: Transfer the dried residue to an inert and corrosion-resistant container, add a mixed acid pre-prepared from HNO3 and HF, and heat to react; the enhanced dissolution step can selectively destroy the insoluble oxides containing elements such as U, Pu, and Zr in the residue, as well as the carrier structure such as Ru-Mo rich inclusions, and release and dissolve the adsorbed or encapsulated trace target nuclides.

[0037] Optionally, the mixed acid is 9–12 mol / L HNO3 + 0.05 mol / L HF. The heating reaction conditions are: reaction at 90–130 °C for 12–30 hours.

[0038] In a preferred embodiment, the mixed acid is 10 mol / L HNO3 + 0.05 mol / L HF; the heating reaction conditions are: a closed reaction at a constant temperature of 120 °C for 24 hours.

[0039] S4. Analysis of uranium and plutonium content in the residue: By analyzing the concentration of each element in the enhanced solution, especially the concentration of uranium and plutonium, the uranium and plutonium content in the residue can be calculated.

[0040] Optionally, in step S4, ICP-MS is used to quantitatively analyze the uranium and plutonium content in the enhanced solution.

[0041] Specifically, a series of prepared standard solutions were first measured using ICP-MS, and a standard curve was plotted. Then, the uranium and plutonium content in the enhanced solution was measured using ICP-MS.

[0042] Optionally, the method further includes the following microscopic characterization steps:

[0043] A portion of the dried residue sample scraped off before enhanced dissolution was retained for morphological observation using scanning electron microscopy (SEM) and energy-scattered X-ray spectroscopy (EDS) to identify the microscopic morphological characteristics, main elemental composition, and distribution ratio of the residue particles. Microscopic analysis distinguished non-nuclear background materials such as filter membrane fibers from the residue particles that actually carry nuclides. Particle size analysis was simultaneously employed to statistically analyze the particle size distribution and aggregation state. A comparative analysis of the changes in residue composition and quantity before and after enhanced dissolution was conducted to determine the composition, properties, and forms of undissolved matter. This information is used to study the formation mechanism of insoluble residues from spent fuel and methods for controlling insoluble residues.

[0044] The method provided in this embodiment significantly reduces the interference of the filtration process in residue analysis through dual baseline control of blank filter membrane and eluent, making the nuclear material balance results more quantitative, reliable, and conservative. It utilizes "triple" evidence of morphology, particle size, and elemental composition to explain the reasons for residue insolubility, the properties of undissolved substances, and corresponding enhanced dissolution schemes, providing clear quantitative guidance for process equipment improvement and formulation scale-up. Furthermore, by confirming the enrichment characteristics of precious metal elements (Ru, Pd, Rh, etc.) in the residue, it provides a basis for decision-making regarding the subsequent resource utilization of radioactive waste. Simultaneously, this method transfers soluble nuclides into the liquid phase as much as possible, minimizing the source term intensity and volume of high-level radioactive solid residues and reducing the burden of final radioactive waste disposal.

[0045] The following examples further illustrate specific embodiments of the present invention.

[0046] Example 1

[0047] This embodiment 1 provides a baseline-traceable method for residue extraction and weighing, including the following steps:

[0048] (1) After completing the nitric acid dissolution experiment of spent fuel elements in a certain reprocessing hot chamber, the insoluble residue and filtrate in the spent fuel nitric acid dissolution solution were separated by filtration under negative pressure of 80 kPa. At the same time, a blank filter membrane was used for filtration and washing twice with 0.1 mol / L nitric acid solution according to the same procedure, and the blank eluent was collected for control analysis.

[0049] (2) Place the filter membrane carrying the residue in a desiccator at room temperature. The desiccator contains color-changing silica gel. After drying for 48 hours, take it out and weigh it. Combine the pre-determined blank mass of the filter membrane after filtration and two acid washes to calculate the net mass of the residue.

[0050] The net weight of the residue measured in this experiment was extremely small, but the reliability of the quality data was ensured by the use of blank control and precise weighing calibration, which established a quality benchmark for subsequent nuclide recovery rate calculations.

[0051] Example 2

[0052] This embodiment 2 employs enhanced dissolution to ensure that the target nuclide enters the liquid phase, thereby enabling accurate measurement of the target nuclide. The steps include:

[0053] The dried residue obtained in Example 1 was transferred into a polytetrafluoroethylene (PTFE) reaction vessel, and about 200 mL of a prepared mixed acid (concentration of 10 mol / L HNO3 + 0.05 mol / L HF) was added. The mixture was then sealed and reacted at a constant temperature of 120 °C for 24 hours.

[0054] If necessary, gentle stirring can be applied during the dissolution process to promote the contact reaction between the acid and the residue.

[0055] After the reaction was completed and cooled, the system was filtered again to obtain a clear liquid. ICP-MS was then used to quantitatively analyze the uranium and plutonium content in the enhanced solution. In Example 2, a series of prepared standard solutions were first measured using ICP-MS, and a standard curve was plotted. Then, ICP-MS was used to measure the uranium and plutonium content in the enhanced solution.

[0056] This Example 2 demonstrates that by employing the mixed acid system strategy provided by the present invention, almost all target nuclides such as uranium and plutonium in spent fuel residue can be dissolved into the liquid phase.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for treating and analyzing insoluble residues from spent fuel, characterized in that, The method includes the following steps: S1. Residue Extraction: The spent fuel nitric acid solution is filtered under negative pressure in a heated chamber to separate the insoluble residue from the filtrate. The filter membrane carrying the residue is removed, and a blank filter membrane is used as a blank control for the same negative pressure filtration and subsequent washing operations. The filter membrane carrying the residue is then acid-washed, and the eluent is collected for analysis reference. The blank eluent is also collected for comparative analysis. The mass change of the filter membrane carrying the residue before and after filtration and the volume of the eluent are recorded to establish a dual baseline for both chemistry and mass. S2. Drying and weighing: After washing, the filter membrane carrying the residue is dried and weighed. Combined with the pre-determined blank mass of the filter membrane, the net mass of the residue is calculated. S3. Enhanced dissolution: Transfer the dried residue to an inert and corrosion-resistant container, add a pre-prepared mixed acid of HNO3 and HF, heat to react, and release and dissolve the adsorbed or encapsulated trace amounts of target nuclides. S4. Analysis of uranium and plutonium content in the residue: The uranium and plutonium content in the residue is calculated by analyzing the concentration of each element in the enhanced solution.

2. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, In step S1, the acid washing involves washing twice with a 0.1 mol / L nitric acid solution.

3. A radioactive liquid filtration device suitable for hot chamber environments according to claim 1, characterized in that, In step S2, the filter membrane carrying the residue after washing is placed in a desiccator at room temperature and dried for more than 48 hours, then taken out and weighed. Color-changing silica gel is added to the desiccator.

4. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, The blank mass of the filter membrane is the mass of the blank filter membrane after negative pressure filtration, acid washing, and drying.

5. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, In step S2, the total mass of the filter membrane carrying the residue after drying is weighed using a precision balance. The blank mass of the filter membrane is then subtracted to obtain the net mass of the insoluble residue, which serves as the basis for subsequent nuclide balance calculations.

6. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, The mixed acid is 9–12 mol / L HNO3 + 0.05 mol / L HF.

7. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, The heating reaction conditions are: reacting for 12–30 hours in the range of 90–130°C.

8. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, In step S4, ICP-MS is used to quantitatively analyze the uranium and plutonium content in the enhanced solution.

9. The method for treating and analyzing insoluble residues of spent fuel according to claim 1, characterized in that, The method further includes the following microscopic characterization steps: Before the enhanced dissolution treatment, a portion of the dried residue sample was taken and subjected to scanning electron microscopy morphology observation, energy scattering X-ray spectroscopy composition analysis, and particle size analysis.

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