A quantitative method for fission nuclides based on the combined use of SIMS and EPMA

Abstract

This invention discloses a quantitative testing method for fissile nuclides based on the combined use of SIMS and EPMA. The steps are as follows: (1) Quantitative analysis of fissile elements in the micro-region of the irradiated nuclear fuel sample is performed using electron probe microanalysis (EPMA) combined with standard samples corresponding to fissile nuclides to obtain the fissile nuclide content; (2) Isotopic abundance of fissile nuclides in the micro-region tested by electron probe microanalysis (SIMS) is measured using secondary ion mass spectrometry (SIMS), and the precise content of fissile nuclides is calculated based on the fissile nuclide content and its isotopic abundance value. This invention combines EPMA and SIMS. First, quantitative testing of each fissile nuclide in the micro-region of the irradiated nuclear fuel is performed using EPMA combined with standard samples to obtain the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in the micro-region. This method can complete the quantitative testing of fissile nuclides in the micrometer scale range, and can accurately, conveniently and efficiently measure the fissile nuclide content in the nuclear fuel diameter range of 50 μm, greatly reducing the research scale of fissile nuclides.

Description

Technical Field

[0001] This invention relates to the field of quantitative testing technology for fission nuclides in micro-regions of irradiated nuclear fuel, and more specifically, to a quantitative testing method for fission nuclides based on the combined use of SIMS and EPMA. Background Technology

[0002] During the service life of nuclear fuel 235 U or 239 The fission of easily fissile nuclides such as Pu will produce a series of fissile nuclides, including 84 Kr、 132 Xe and other gaseous fission nuclides that can directly cause fuel swelling 131 I, 137 Corrosive semi-volatile fissile nuclides such as Cs and 98 Mo、 90 Zr and other solid fissile nuclides are readily released into fuel. Fissile nuclides readily diffuse, migrate, and are released into fuel. After irradiation, fissile nuclides within the fuel exhibit heterogeneous characteristics, with varying concentrations in different micro-regions. The behavior of fissile nuclides directly affects the thermodynamic properties of the fuel during service and is directly related to the safe operation of the reactor. Therefore, testing and analyzing fissile nuclides is of paramount importance for fuel design and development.

[0003] Existing methods for detecting fissile nuclides include chemical mass spectrometry, which involves dissolving irradiated nuclear fuel samples in acid and then using a mass spectrometer to analyze the fissile nuclides in the solution. This yields the average fissile nuclide content across the entire sample, but it cannot study fissile nuclides within a micrometer-scale region. Currently, there is no practically applicable method for quantitative detection of micro-area fissile nuclides.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] The current technology has the problem that existing chemical mass spectrometry methods for testing fissile nuclides only obtain the average fissile nuclide content of the entire sample, and cannot measure fissile nuclides in the micrometer-scale region. To solve the above technical problem, this invention provides a quantitative testing method for fissile nuclides based on the combined use of SIMS and EPMA. By combining EPMA and SIMS, EPMA is first used in conjunction with a standard sample to quantitatively test each fissile nuclide in the micro-region of irradiated nuclear fuel to obtain the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in the micro-region, thus completing the quantitative testing of fissile nuclides in the micrometer-scale range and obtaining the precise content of fissile nuclides.

[0006] This invention is achieved through the following technical solution: This invention provides a quantitative detection method for fission nuclides based on the combined use of SIMS and EPMA, comprising the following steps: (1) The fission elements in the micro-region of the irradiated nuclear fuel sample were quantitatively analyzed by using electron probe microanalysis (EPMA) combined with standard samples corresponding to fission elements to obtain the fission nuclide content. (2) The isotopic abundance of fission nuclides was measured in the micro-regions tested by electron probe microanalysis using a secondary ion mass spectrometer (SIMS). The precise content of fission nuclides was calculated based on the fission nuclide content and its isotopic abundance value.

[0007] Electron probe microanalysis (EPMA) is a micro-area compositional quantitative analysis instrument. Combined with standard samples, it enables non-destructive quantitative analysis of elements within the micrometer scale, offering high precision. Secondary ion mass spectrometry (SIMS) is a micro-area fissile nuclide analysis instrument capable of acquiring isotopic abundances of elements within the micrometer scale. This invention combines EPMA and SIMS. First, EPMA, combined with standard samples, is used to quantitatively analyze each fissile nuclide in a micro-area of ​​irradiated nuclear fuel, obtaining the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in this micro-area, thus completing the quantitative analysis of fissile nuclides within the micrometer scale and obtaining the precise content of fissile nuclides.

[0008] The electron probe microanalysis combined with standard sample method used in this invention can accurately test the content of trace fissile nuclides with a content of less than 1 wt%, with a quantitative result deviation of usually less than 10%, and without damaging the test sample. Then, a secondary ion mass spectrometer can analyze the isotopic abundance of fissile nuclides in the micro-region. Finally, the precise content of each fissile nuclide is calculated based on the fissile nuclide content and its isotopic abundance value. Through this method, the fissile nuclide content in the range of 50 μm diameter of nuclear fuel can be measured accurately, conveniently and efficiently, which greatly reduces the research scale of fissile nuclides.

[0009] The precise calculation method for the content of each fission nuclide is as follows: Taking Mo as an example, the content of Mo measured by EPMA is a wt%, and the isotopic abundance of 98Mo measured by SIMS is b% (98Mo accounts for b%, 99Mo accounts for c%, and 100Mo accounts for d%). Then the content of 98Mo is a*b.

[0010] In a specific implementation, in step (1), the irradiated nuclear fuel is first prepared into a sample. The diameter of the irradiated nuclear fuel sample is the original diameter of the nuclear fuel (about 10 mm), the thickness is less than 1 mm, the dose at the 0 distance of the surface is less than 100 mSv, and the surface flatness and inclination are less than 1°. Then, the surface of the irradiated nuclear fuel sample is polished by sandpaper or polishing liquid with a particle size of less than 1 μm to make the surface smooth. Finally, after polishing, C, Au or Pt is sprayed onto the surface of the irradiated nuclear fuel sample to form a conductive film layer to improve the conductivity of the sample. The thickness of the coating should not be greater than 10 nm to avoid affecting the surface morphology of the sample.

[0011] In a specific implementation, in step (1), the standard sample corresponding to the fission element is: For semi-volatile CS elements, Cs(AlSi2O6) cesium garnet was used as the standard sample; For semi-volatile element I, LiIO3 was used as the standard sample; For Mo, pure metallic Mo was used as the standard sample; for Zr, ZrO2 was used as the standard sample. For gaseous Xe, since there were no standard samples, quantitative analysis was performed using the instrument's built-in theoretical calibration software.

[0012] In a specific implementation, the specific method of step (1) is as follows: The spectral efficiency of PET and LiF spectroscopic crystals was calibrated using standard samples; Standard samples of different elements were calibrated using PET and LiF spectrophotometers. Five points were selected at different locations on the standard sample for calibration to ensure that the deviation of the five calibration results was less than 1%. Specifically, Zr and Mo were calibrated and quantitatively analyzed using PET spectrophotometers, while I, Cs, and Xe were calibrated and quantitatively analyzed using LiF spectrophotometers. The micro-region to be tested in the irradiated nuclear fuel sample was found under secondary electron imaging, and the secondary electron images and backscattered electron images at 100X, 200X, 500X and 1000X were recorded respectively. At the same time, the average porosity of the micro-region to be tested in the irradiated nuclear fuel sample was calculated under the 100X secondary electron image. For irradiated nuclear fuel samples, a large beam current of 200-500 nA with a beam spot size of 50 μm is selected at 25 kV to perform quantitative analysis of fission nuclides in the micro-region to be measured. The analysis is repeated at least 5 times, and the deviation of the quantitative results of fission elements should be less than 5%. The final result is the average value. Then, the test results obtained by electron probe are divided by (1-porosity) to eliminate the influence of porosity in the micro-region to be measured and obtain the accurate fission nuclide content.

[0013] In a specific implementation, in step (1), the quantitative analysis specifically involves analyzing the La peak using Zr, Mo, and Xe elements, and analyzing the Lb peak using I and Cs elements.

[0014] In a specific implementation, in step (1), after calibrating standard samples of different elements using PET and LiF spectrophotometers, it is necessary to eliminate interference from overlapping characteristic peaks: The La peak of Mo needs to exclude the Lc peak of Zr (Δsinθ = 281 × 10⁻⁶). -6 )interference; The La peak of Xe needs to exclude the Lb3 peak of Te (Δsinθ = 273 × 10⁻⁶). -6 Interference between the L1 and L2 peaks of La elements; The Lb peak of Cs needs to exclude the L1 peak of Nd (Δsinθ=182×10). -6 ) and the La peak of the La element (△sinθ=445×10 ) -6 )interference; The Lb peak of I and the La peak of Zr do not overlap or interfere with each other.

[0015] In a specific implementation, in step (2), before using a secondary ion mass spectrometer (SIMS) to test the isotopic abundance of fission nuclides in the micro-region to be tested, the primary and secondary optical paths are optimized and adjusted on the Si-Ta standard sample, and the test parameters are set. Then, the isotopic abundance of fission nuclides is measured on the irradiated nuclear fuel sample.

[0016] In a specific implementation, the specific parameters for measuring isotope abundance using a secondary ion mass spectrometer (SIMS) in step (2) are as follows: The primary ion beam accelerating voltage is 15 kV, the secondary ion beam accelerating voltage is 5 kV, the primary beam current is between 50 and 800 nA, the contrast aperture is 400 μm or 150 μm, the field aperture is 750 μm or 400 μm, the entrance slit is 10 to 40 μm, the exit slit is 20 to 80 μm, and the exit slit width is twice the entrance slit width. The energy slit width is 50 eV, and the scanning area is 100 × 100 μm to 200 × 200 μm.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The present invention provides a method for quantitative testing of fissile nuclides based on the combined use of SIMS and EPMA. By combining EPMA and SIMS, the fissile nuclides in the micro-region of irradiated nuclear fuel are first quantitatively tested using EPMA in combination with standard samples to obtain the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in the micro-region, thereby completing the quantitative testing of fissile nuclides in the micrometer scale range and obtaining the precise content of fissile nuclides. 2. The present invention provides a quantitative testing method for fissile nuclides based on the combined use of SIMS and EPMA. The electron probe combined with standard sample method can accurately test the content of trace fissile nuclides with a content of less than 1 wt%, and the quantitative result deviation is usually less than 10%. It does not damage the test sample. The secondary ion mass spectrometer can analyze the isotopic abundance of fissile nuclides in the micro-region. Through this method, the content of fissile nuclides in the range of 50 μm diameter of nuclear fuel can be accurately, conveniently and efficiently measured, which greatly reduces the research scale of fissile nuclides. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0019] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0020] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “an embodiment,” “an example,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0021] 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 understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" 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.

[0022] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating 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.

[0023] During the service life of nuclear fuel 235 U or 239 The fission of easily fissile nuclides such as Pu will produce a series of fissile nuclides, including 84 Kr、 132 Xe and other gaseous fission nuclides that can directly cause fuel swelling 131 I, 137 Corrosive semi-volatile fissile nuclides such as Cs and 98 Mo、 90Zr and other solid fissile nuclides are readily released into fuel. Fissile nuclides readily diffuse, migrate, and are released into fuel. After irradiation, fissile nuclides within the fuel exhibit heterogeneous characteristics, with varying concentrations in different micro-regions. The behavior of fissile nuclides directly affects the thermodynamic properties of the fuel during service and is directly related to the safe operation of the reactor. Therefore, testing and analyzing fissile nuclides is of paramount importance for fuel design and development.

[0024] Existing methods for detecting fissile nuclides include chemical mass spectrometry, which involves dissolving irradiated nuclear fuel samples in acid and then using a mass spectrometer to analyze the fissile nuclides in the solution. This yields the average fissile nuclide content across the entire sample, but it cannot study fissile nuclides within a micrometer-scale region. Currently, there is no practically applicable method for quantitative detection of micro-area fissile nuclides.

[0025] To address the aforementioned technical problems, this invention provides a quantitative testing method for fissile nuclides based on the combined use of SIMS and EPMA. By combining EPMA and SIMS, EPMA is first used in conjunction with standard samples to quantitatively test each fissile nuclide in a micro-region of irradiated nuclear fuel, obtaining the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in the micro-region, thereby completing the quantitative testing of fissile nuclides within the micrometer scale and obtaining the precise content of fissile nuclides.

[0026] The technical solution provided by this invention is as follows: A quantitative detection method for fission nuclides based on the combined use of SIMS and EPMA includes the following steps: (1) The fission elements in the micro-region of the irradiated nuclear fuel sample were quantitatively analyzed by using electron probe microanalysis (EPMA) combined with standard samples corresponding to fission elements to obtain the fission nuclide content. (2) The isotopic abundance of fission nuclides was measured in the micro-regions tested by electron probe microanalysis using a secondary ion mass spectrometer (SIMS). The precise content of fission nuclides was calculated based on the fission nuclide content and its isotopic abundance value.

[0027] Electron probe microanalysis (EPMA) is a micro-area compositional quantitative analysis instrument. Combined with standard samples, it enables non-destructive quantitative analysis of elements within the micrometer scale, offering high precision. Secondary ion mass spectrometry (SIMS) is a micro-area fissile nuclide analysis instrument capable of acquiring isotopic abundances of elements within the micrometer scale. This invention combines EPMA and SIMS. First, EPMA, combined with standard samples, is used to quantitatively analyze each fissile nuclide in a micro-area of ​​irradiated nuclear fuel, obtaining the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in this micro-area, thus completing the quantitative analysis of fissile nuclides within the micrometer scale and obtaining the precise content of fissile nuclides.

[0028] The electron probe microanalysis combined with standard sample method used in this invention can accurately test the content of trace fissile nuclides with a content of less than 1 wt%, with a quantitative result deviation of usually less than 10%, and without damaging the test sample. Then, a secondary ion mass spectrometer can analyze the isotopic abundance of fissile nuclides in the micro-region. Finally, the precise content of each fissile nuclide is calculated based on the fissile nuclide content and its isotopic abundance value. Through this method, the fissile nuclide content in the range of 50 μm diameter of nuclear fuel can be measured accurately, conveniently and efficiently, which greatly reduces the research scale of fissile nuclides.

[0029] In a specific implementation, in step (1), the irradiated nuclear fuel is first prepared into a sample. The diameter of the irradiated nuclear fuel sample is the original diameter of the nuclear fuel (about 10 mm), the thickness is less than 1 mm, the dose at the 0 distance of the surface is less than 100 mSv, and the surface flatness and inclination are less than 1°. Then, the surface of the irradiated nuclear fuel sample is polished by sandpaper or polishing liquid with a particle size of less than 1 μm to make the surface smooth. Finally, after polishing, C, Au or Pt is sprayed onto the surface of the irradiated nuclear fuel sample to form a conductive film layer to improve the conductivity of the sample. The thickness of the coating should not be greater than 10 nm to avoid affecting the surface morphology of the sample.

[0030] In a specific implementation, in step (1), the standard sample corresponding to the fission element is: For semi-volatile CS elements, Cs(AlSi2O6) cesium garnet was used as the standard sample; For semi-volatile element I, LiIO3 was used as the standard sample; For Mo, pure metallic Mo was used as the standard sample; for Zr, ZrO2 was used as the standard sample. For gaseous Xe, since there were no standard samples, quantitative analysis was performed using the instrument's built-in theoretical calibration software.

[0031] In a specific implementation, the specific method of step (1) is as follows: The spectral efficiency of PET and LiF spectroscopic crystals was calibrated using standard samples; Standard samples of different elements were calibrated using PET and LiF spectrophotometers. Five points were selected at different locations on the standard sample for calibration to ensure that the deviation of the five calibration results was less than 1%. Specifically, Zr and Mo were calibrated and quantitatively analyzed using PET spectrophotometers, while I, Cs, and Xe were calibrated and quantitatively analyzed using LiF spectrophotometers. The micro-region to be tested in the irradiated nuclear fuel sample was found under secondary electron imaging, and the secondary electron images and backscattered electron images at 100X, 200X, 500X and 1000X were recorded respectively. At the same time, the average porosity of the micro-region to be tested in the irradiated nuclear fuel sample was calculated under the 100X secondary electron image. For irradiated nuclear fuel samples, a large beam current of 200-500 nA with a beam spot size of 50 μm is selected at 25 kV to perform quantitative analysis of fission nuclides in the micro-region to be measured. The analysis is repeated at least 5 times, and the deviation of the quantitative results of fission elements should be less than 5%. The final result is the average value. Then, the test results obtained by electron probe are divided by (1-porosity) to eliminate the influence of porosity in the micro-region to be measured and obtain the accurate fission nuclide content.

[0032] In a specific implementation, in step (1), the quantitative analysis specifically involves analyzing the La peak using Zr, Mo, and Xe elements, and analyzing the Lb peak using I and Cs elements.

[0033] In a specific implementation, in step (1), after calibrating standard samples of different elements using PET and LiF spectrophotometers, it is necessary to eliminate interference from overlapping characteristic peaks: The La peak of Mo needs to exclude the Lc peak of Zr (Δsinθ = 281 × 10⁻⁶). -6 )interference; The La peak of Xe needs to exclude the Lb3 peak of Te (Δsinθ = 273 × 10⁻⁶). -6 Interference between the L1 and L2 peaks of La elements; The Lb peak of Cs needs to exclude the L1 peak of Nd (Δsinθ=182×10). -6 ) and the La peak of the La element (△sinθ=445×10 ) -6 )interference; The Lb peak of I and the La peak of Zr do not overlap or interfere with each other.

[0034] In a specific implementation, in step (2), before using a secondary ion mass spectrometer (SIMS) to test the isotopic abundance of fission nuclides in the micro-region to be tested, the primary and secondary optical paths are optimized and adjusted on the Si-Ta standard sample, and the test parameters are set. Then, the isotopic abundance of fission nuclides is measured on the irradiated nuclear fuel sample.

[0035] In a specific implementation, the specific parameters for measuring isotope abundance using a secondary ion mass spectrometer (SIMS) in step (2) are as follows: The primary ion beam accelerating voltage is 15 kV, the secondary ion beam accelerating voltage is 5 kV, the primary beam current is between 50 and 800 nA, the contrast aperture is 400 μm or 150 μm, the field aperture is 750 μm or 400 μm, the entrance slit is 10 to 40 μm, the exit slit is 20 to 80 μm, and the exit slit width is twice the entrance slit width. The energy slit width is 50 eV, and the scanning area is 100 × 100 μm to 200 × 200 μm. Example

[0036] This invention provides a method for quantitative testing of fission nuclides based on the combined use of SIMS and EPMA, comprising the following steps: (1) Sample preparation and loading First, the irradiated nuclear fuel is prepared into a sample, which is then loaded into an electron probe. The diameter of the irradiated nuclear fuel sample is the original diameter of the nuclear fuel (approximately 10 mm), the thickness is less than 1 mm, the dose at the zero distance from the surface is less than 100 mSv, and the surface flatness and inclination are less than 1°. Then, the surface of the irradiated nuclear fuel sample is polished with sandpaper or polishing liquid with a particle size of less than 1 μm to make the surface smooth. Finally, after polishing, C, Au, or Pt is sprayed onto the surface of the irradiated nuclear fuel sample to form a conductive film layer to improve the conductivity of the sample. The thickness of the coating should not exceed 10 nm to avoid affecting the surface morphology of the sample.

[0037] (2) Standard sample calibration and elimination of characteristic peak overlap interference (2.1) The spectral efficiency of the PET and LiF spectrophotometers was calibrated using a series of standard samples according to the instrument software requirements; The standard samples corresponding to fission nuclides are: For semi-volatile CS elements, Cs(AlSi2O6) cesium garnet was used as the standard sample; For semi-volatile element I, LiIO3 was used as the standard sample; For Mo, pure metallic Mo was used as the standard sample; for Zr, ZrO2 was used as the standard sample. For gaseous Xe, since there were no standard samples, quantitative analysis was performed using the instrument's built-in theoretical calibration software.

[0038] (2.2) Standard samples of different elements were calibrated using PET and LiF spectrophotometers. Five points were selected at different locations on the standard sample for calibration, and the deviation of the five calibration results was ensured to be less than 1%. Specifically, Zr and Mo elements were calibrated and quantitatively analyzed using a PET spectrophotometer, while I, Cs, and Xe elements were calibrated and quantitatively analyzed using a LiF spectrophotometer. The quantitative analysis was as follows: the La peak of Zr, Mo, and Xe elements was analyzed, and the Lb peak of I and Cs elements was analyzed.

[0039] (2.3) After calibrating standard samples of different elements using PET and LiF spectrophotometers, it is necessary to eliminate interference from overlapping characteristic peaks: The La peak of Mo needs to exclude the Lc peak of Zr (Δsinθ = 281 × 10⁻⁶). -6 )interference; The La peak of Xe needs to exclude the Lb3 peak of Te (Δsinθ = 273 × 10⁻⁶).-6 Interference between the L1 and L2 peaks of La elements; The Lb peak of Cs needs to exclude the L1 peak of Nd (Δsinθ=182×10). -6 ) and the La peak of the La element (△sinθ=445×10 ) -6 )interference; The Lb peak of I and the La peak of Zr do not overlap or interfere with each other.

[0040] (3) Quantitative analysis of fission elements by EPMA and photographic recording of the test micro-area The micro-region to be tested in the irradiated nuclear fuel sample was found under secondary electron imaging, and the secondary electron images and backscattered electron images at 100X, 200X, 500X and 1000X were recorded respectively. At the same time, the average porosity of the micro-region to be tested in the irradiated nuclear fuel sample was calculated under the 100X secondary electron image. For irradiated nuclear fuel samples, a large beam current of 200-500 nA with a beam spot size of 50 μm is selected at 25 kV to perform quantitative analysis of fission nuclides in the micro-region to be measured. The analysis is repeated at least 5 times, and the deviation of the quantitative results of fission elements should be less than 5%. The final result is the average value. Then, the test results obtained by electron probe are divided by (1-porosity) to eliminate the influence of porosity in the micro-region to be measured and obtain the accurate fission nuclide content.

[0041] (4) Isotope analysis using SIMS After transferring the irradiated nuclear fuel sample into the SIMS, the micro-region to be tested by the electron probe was first located, and a significant change in the apparent color of the area bombarded by the electron beam could be observed. Then, the primary and secondary optical paths of the SIMS were optimized and adjusted on the Si-Ta standard. After setting the test parameters for measuring isotopic abundance, high-resolution mass spectrometry of fission nuclides was performed on the irradiated UO2 fuel sample to obtain sufficient mass resolution and eliminate interference from interfering atomic groups on the mass spectrum peaks of fission nuclides. The specific test parameters are as follows: Oxygen source was selected as the primary ion source, primary ion beam accelerating voltage was 15 kV, secondary ion beam accelerating voltage was 5 kV, primary beam current was between 50 and 800 nA, contrast aperture was 400 μm or 150 μm, field aperture was 750 μm or 400 μm, entrance slit was 10 to 40 μm, exit slit was 20 to 80 μm, and the exit slit width was twice the entrance slit width. Energy slit width was 50 eV, and scanning area was 100 × 100 μm to 200 × 200 μm. Isotope analysis was performed on the fission nuclides of the irradiated UO2 fuel samples. The secondary ion signals of each fission nuclide were recorded using an electron multiplier, and the isotopic abundance of the fission nuclides was calculated using the isotope analysis software of SIMS.

[0042] (5) Calculate the content of each fission nuclide based on the precise fission nuclide content obtained in step (3) and the isotopic abundance of each fission nuclide obtained in step (4). The precise content calculation method for each fission nuclide is as follows: Taking Mo as an example, the content of Mo is a wt% measured by EPMA, and the isotopic abundance of 98Mo is b% measured by SIMS (98Mo accounts for b%, 99Mo accounts for c%, and 100Mo accounts for d%). Then the content of 98Mo is a*b.

[0043] Electron probe microanalysis (EPMA) is a micro-area compositional quantitative analysis instrument. Combined with standard samples, it enables non-destructive quantitative analysis of elements within the micrometer scale, offering high precision. Secondary ion mass spectrometry (SIMS) is a micro-area fissile nuclide analysis instrument capable of acquiring isotopic abundances of elements within the micrometer scale. This invention combines EPMA and SIMS. First, EPMA, combined with standard samples, is used to quantitatively analyze each fissile nuclide in a micro-area of ​​irradiated nuclear fuel, obtaining the precise content of fissile elements. Then, SIMS is used to measure the isotopic abundance of fissile elements in this micro-area, thus completing the quantitative analysis of fissile nuclides within the micrometer scale and obtaining the precise content of fissile nuclides.

[0044] The electron probe microanalysis combined with standard sample method used in this invention can accurately test the content of trace fissile nuclides with a content of less than 1 wt%, with a quantitative result deviation of usually less than 10%, and without damaging the test sample. Then, a secondary ion mass spectrometer can analyze the isotopic abundance of fissile nuclides in the micro-region. Finally, the precise content of each fissile nuclide is calculated based on the fissile nuclide content and its isotopic abundance value. Through this method, the fissile nuclide content in the range of 50 μm diameter of nuclear fuel can be measured accurately, conveniently and efficiently, which greatly reduces the research scale of fissile nuclides.

[0045] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA, characterized in that, Includes the following steps: (1) The fission elements in the micro-region of the irradiated nuclear fuel sample were quantitatively analyzed by using electron probe microanalysis (EPMA) combined with standard samples of fission elements to obtain the fission nuclide content. (2) The isotopic abundance of fission nuclides was measured in the micro-regions tested by electron probe microanalysis using a secondary ion mass spectrometer (SIMS). The precise content of fission nuclides was calculated based on the fission nuclide content and its isotopic abundance value.

2. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 1, characterized in that, In step (1), the surface of the irradiated nuclear fuel sample is polished and then coated with a conductive film layer with a thickness of no more than 10 nm.

3. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 2, characterized in that, In step (1), the surface of the irradiated nuclear fuel sample is polished with sandpaper or polishing liquid with a particle size of less than 1 μm, and then C, Au or Pt is sprayed on the surface to form a conductive film layer.

4. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 2, characterized in that, In step (1), the standard sample corresponding to the fission element is: For semi-volatile CS elements, Cs(AlSi2O6) cesium garnet was used as the standard sample; For semi-volatile element I, LiIO3 was used as the standard sample; For Mo, pure metallic Mo was used as the standard sample; for Zr, ZrO2 was used as the standard sample. For gaseous Xe, since there is no standard sample, quantitative analysis is performed using the instrument's built-in theoretical calibration software.

5. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 1, characterized in that, The specific method for step (1) is as follows: The spectral efficiency of PET and LiF spectroscopic crystals was calibrated using standard samples; Standard samples of different elements were calibrated using PET and LiF spectrophotometers; The micro-region to be tested in the irradiated nuclear fuel sample was located under secondary electron imaging, and secondary electron images and backscattered electron images at different magnifications were recorded respectively. At the same time, the average porosity of the micro-region to be tested in the irradiated nuclear fuel sample was calculated under secondary electron imaging. Quantitative analysis of fission nuclides in the micro-regions of irradiated nuclear fuel samples was performed to obtain the fission nuclide content.

6. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 5, characterized in that, In step (1), a large beam current of 200~500 nA is selected at 25kV, and the beam spot size is 50μm to perform quantitative analysis on the micro-region to be measured.

7. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 5, characterized in that, In step (1), the fission nuclide content is obtained by dividing the electron probe test result by (1-porosity) to eliminate the influence of porosity, which yields the accurate fission nuclide content.

8. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 5, characterized in that, In step (1), secondary electron images and backscattered electron images are recorded at 100X, 200X, 500X and 1000X respectively, and the average porosity of the micro-region to be tested in the irradiated nuclear fuel sample is calculated under the 100X secondary electron image.

9. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 5, characterized in that, In step (1), Zr and Mo elements are calibrated and quantitatively analyzed using a PET spectrophotometer, while I, Cs, and Xe elements are calibrated and quantitatively analyzed using a LiF spectrophotometer.

10. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 9, characterized in that, In step (1), the quantitative analysis specifically involves analyzing the La peak using Zr, Mo, and Xe elements, and analyzing the Lb peak using I and Cs elements.

11. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 10, characterized in that, In step (1), after calibration, it is necessary to eliminate interference from overlapping characteristic peaks: The La peak of Mo needs to exclude the interference of the Lc peak of Zr. The La peak of Xe needs to exclude the interference of the Lb3 peak of Te and the L1 peak of La. The Lb peak of Cs element needs to exclude the interference of L1 peak of Nd element and La peak of La element; The Lb peak of I and the La peak of Zr do not overlap or interfere with each other.

12. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 1, characterized in that, In step (2), the specific parameters for measuring the isotopic abundance of fission nuclides in the micro-region to be tested using a secondary ion mass spectrometer (SIMS) are as follows: The primary ion beam accelerating voltage is 15 kV, the secondary ion beam accelerating voltage is 5 kV, the primary beam current is between 50 and 800 nA, the contrast aperture is 400 μm or 150 μm, the field aperture is 750 μm or 400 μm, the entrance slit is 10 to 40 μm, the exit slit is 20 to 80 μm, and the exit slit width is twice the entrance slit width. The energy slit width is 50 eV, and the scanning area is 100 × 100 μm to 200 × 200 μm.

13. The quantitative detection method for fissile nuclides based on the combined use of SIMS and EPMA according to claim 12, characterized in that, In step (2), before testing the isotope abundance using a secondary ion mass spectrometer (SIMS), the primary and secondary optical paths are optimized and adjusted on the Si-Ta standard sample, and the test parameters are set. Then, the isotope abundance of fission nuclides is tested on the irradiated nuclear fuel sample.