Microcell burnup test method based on quantitative analysis of 98Mo

Abstract

The invention relates to the technical field of nuclear fuel burnup detection, and particularly discloses a micro-zone burnup test method based on 98Mo quantitative analysis aiming at the problem of low accuracy of burnup detection of different micro-zones of nuclear fuel in an existing nuclear fuel burnup measurement method. The micro-zone burnup test method comprises the following steps: S1, taking a nuclear fuel sample, and determining the Mo content of the sample by adopting EPMA; s2, performing isotope test on fission nuclide 98Mo and isotope thereof in the sample by adopting SIMS; s3, the content C < 98Mo > of the 98Mo is calculated; s4, calculating a micro-area fuel consumption value Bu of the nuclear fuel according to the following formula; wherein B is a microcell burnup value, 9.380 is a coefficient, m < 98Mo > is the relative atomic weight of 98Mo, m < UO2 > is the relative atomic weight of UO2, and FY is the yield of nuclide obtained by fission of 235U into 98Mo. According to the method, the damage to the nuclear fuel sample is small, the micro-zone burnup in the micrometer size range of the nuclear fuel can be efficiently detected, the micro-zone burnup value of the nuclear fuel and the micro-zone burnup distribution at different positions of the fuel are obtained, the measurement range is more accurate, and the accuracy is higher.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel burnup detection technology, and more specifically, to a method based on... 98 Micro-area fuel consumption test method for quantitative analysis of Mo. Background Technology

[0002] UO2 fuel is currently the primary nuclear fuel used in commercial pressurized water reactor nuclear power plants. During operation, the burnup of UO2 fuel varies across different micrometer-sized regions, resulting in different microstructures within different micro-regions of the fuel. Particularly in the high-burnup regions at the fuel edges, the microstructure of UO2 fuel undergoes significant changes, such as the accumulation of fission products, radiation damage, fuel pellet cracking and remodeling, reducing the fuel's thermal and mechanical properties and affecting the operational safety of the nuclear power plant reactor. Therefore, research on micro-region burnup testing technology for UO2 fuel is urgently needed to obtain the micro-region burnup distribution at different radial locations of the nuclear fuel, which is of great significance for ensuring the operational safety of the reactor.

[0003] For example, patent CN113409972A provides a nuclear fuel burnup measurement process. It uses specific resin balls to selectively adsorb uranium and plutonium, efficiently separating uranium and plutonium from the complex matrix of the irradiated nuclear fuel solution. Using a solid coating method, the resin balls are directly loaded onto a rhenium wire with a U-shaped groove. The resin balls are used as a carrier to realize the loading of uranium and plutonium onto a thermal ionization mass spectrometer, thereby achieving the measurement of nuclear fuel burnup.

[0004] However, existing methods for measuring nuclear fuel burnup, as described above, all suffer from the problem of difficulty in detecting burnup in different micro-regions within extremely small size ranges, resulting in low accuracy in detecting burnup in different micro-regions of nuclear fuel. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of low accuracy in detecting the burnup of different micro-regions of nuclear fuel in existing nuclear fuel burnup measurement methods.

[0006] This invention is achieved through the following technical solution: This invention provides a method based on 98 The micro-area fuel consumption test method for quantitative analysis of Mo includes the following steps: S1. Nuclear fuel samples were taken, and the Mo content of the samples was determined using an electron probe microanalyzer. C Mo ; S2 uses a secondary ion mass spectrometer to analyze the fission nuclides in the above samples. 98 Isotope analysis was performed on Mo and its isotopes to calculate fission nuclides. 98 Mo isotope ratio A 98Mo ; S3 is calculated based on the measurement results of steps S1 and S2 using the following formula ①. 98 Mo content C 98Mo : ①; S4 Calculate the micro-zone burnup value B of nuclear fuel according to the following formula ②. u : ②; in, B u This represents the micro-zone fuel consumption value, with 9.380 being the coefficient for converting fuel consumption units from at% to MWd / tU. m 98Mo for 98 The relative atomic weight of Mo m UO2 This represents the relative atomic weight of UO2. FY for 235 U element fission 98 Production of Mo nuclides.

[0007] Preferably, in step S1, an LPET spectrophotometer is selected. First, the spectrophotometer is calibrated on a Fe-containing standard sample, and the PHA detector is calibrated with an accelerating voltage of 25 kV. Then, a pure metal Mo standard sample is used for calibration, and then the fission element Mo in the fuel micro-region is quantitatively tested.

[0008] Preferably, both the pure metallic Mo standard and the fuel sample to be tested need to be polished, then carbonized, and then placed into the electron probe sample chamber. Before calibration, the Mo standard should be peak-finding in WDS mode to determine the background position. This position should be input during calibration. The background should be linearly fitted, with a peak acquisition time of 30s and a background acquisition time of 15s.

[0009] Preferably, in step S1, the target region is screened by combining secondary ions and backscattering imaging under a small beam current of about 20~50nA; quantitative analysis uses a large beam current, ≥200nA, and the same quantitative time is required. The test parameters are verified on the sample, and the Mo signal quantity is recorded in real time to check for signal fluctuations; before the test, the peak of the Mo element in the target fuel needs to be searched to obtain the Mo element background. Two backgrounds are selected on the left and right sides, and an exponential fit is used; the characteristic peak of quantitative analysis is measured for 60s, and the background is measured for 30s.

[0010] Preferably, in step S2, the test parameters of the secondary ion mass spectrometer are as follows: The primary ion source is O 2+The oxygen source is equipped with primary and secondary ion beam accelerating voltages of +15kV and +5kV, respectively. The primary beam current is 20~100nA, the field aperture is 750 or 400μm, the contrast aperture is 400 or 150μm, and the scanning area is 100×100μm. 2 The maximum analytical area is 150×150μm. 2 The inlet slit width is 40~80μm, the outlet slit width is 80~160μm, the mass resolution is 1500~3000a.mu, and the energy slit width is 25~100eV.

[0011] Preferably, in step S2, the UO2 fuel sample is found 238 The secondary ion signal of U was used to focus the primary ion beam effectively by adjusting the L4 lens and the astigmatism correctors Stig X, Stig Y, and D5 S1; the sharpness of the exit and entrance slits was adjusted to make the entrance slit parallel to the exit slit; and the magnetic field was moved to locate... 98 The secondary ion signal of Mo is used to calibrate the position of the energy slit, so that... 98 The secondary ion signal intensity of Mo is the highest, and it scans the positions of the deflection plates DTCA and DTFA.

[0012] Preferably, in step S2, the direction of EPMA quantitative testing on the fuel sample is used for... 95 Mo、 97 Mo、 98 Mohe 100 Isotope testing was performed on Mo and other fission nuclides. The secondary ion signals of these fission nuclides were collected using an electron multiplier and calculated. 95 Mo、 97 Mo、 98 Mohe 100 Isotope ratios of Mo, etc.

[0013] The technical solution of the present invention has the following beneficial effects: This invention utilizes EPMA to quantitatively determine fission elements within the micrometer-scale range of UO2 fuel. Isotope analysis of the calibrated fission nuclides within this micro-region is performed using SIMS, obtaining the isotope ratios of the calibrated fission nuclides. The micro-region burnup of the UO2 fuel can then be calculated. This is based on the fact that secondary ion mass spectrometry (SIMS) and electron probe microanalysis (EPMA) are effective tools for characterizing and analyzing nuclear fuel fission products; SIMS can be used for depth profiling, isotope analysis, and surface analysis of fission products. EPMA is primarily used for the morphological characterization and quantitative analysis of fission products. Furthermore, this invention reveals that fission nuclides... 98Mo, as a stable nuclide, has a small neutron capture cross section, high natural abundance, and a high fission yield, making it easy to detect. It is an ideal burnup monitor and can be used as a fission nuclide for micro-area burnup calibration of nuclear fuel.

[0014] Based on the above, the present invention provides a method based on... 98 A micro-area burnup testing method for quantitative analysis of Mo was developed. This method uses shielded EPMA to quantitatively analyze the fissile element Mo in micro-areas of irradiated UO2 fuel within the reactor, obtaining the Mo content. Shielded SIMS is then used to analyze the fissile nuclides within the fuel micro-areas. 98 Mo was subjected to isotope testing to obtain 98 The isotopic ratio of Mo was determined, and then the content of fissile nuclides Mo measured by EPMA was used to calculate the... 98 The content of Mo was determined, and the micro-zone burnup of UO2 fuel was calculated, thus establishing a basis based on 98 A micro-area burnup testing method for quantitative analysis of molybdenum (Mo). This method causes minimal damage to nuclear fuel samples and can efficiently detect micro-area burnup within the micrometer-scale range of nuclear fuel. It is minimally destructive, obtains micro-area burnup values ​​and micro-area burnup distributions at different locations on the fuel, and offers a more precise measurement range and higher accuracy. Attached Figure Description

[0015] Figure 1 This is a line graph showing the micro-zone fuel consumption values ​​of UO2 fuel at different radial positions in Example 1. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0017] This invention provides a method based on 98 The micro-area burnup testing method for quantitative analysis of Mo mainly uses EPMA to quantitatively test the fission element Mo in the micrometer-scale range of irradiated UO2 fuel samples, obtaining the content of fission element Mo. SIMS is then used to analyze the fission nuclides within the micro-area of ​​the fuel sample. 98 Isotope testing was performed on Mo and its isotopes to obtain... 98 The isotope ratio of Mo was determined, and then the fissile nuclide content of Mo was calculated based on the EPMA-measured content. 98 Mo content and micro-zone fuel consumption.

[0018] Specifically, the steps include the following: (1) Take a nuclear fuel sample and select several micro-regions with no or few precipitated phases on their surface as the analysis area. The number of selected micro-regions should be ≥5. Use an electron probe microanalyzer (EPMA) for calibration first, and then quantitatively test the fission element Mo in each micro-region. Combined with the standard sample, calculate the Mo content of multiple micro-regions and record it as c. Mo . Specifically, LPET spectrophotometer can be used for electron probe quantitative analysis. First, the spectrophotometer is calibrated on a Fe-containing standard sample, and the PHA detector is also calibrated. The accelerating voltage is 25 kV. Then, pure metal Mo standard sample is used for calibration, and then the fission element Mo in the fuel micro-region is quantitatively tested.

[0019] Andradite samples are typically used for calibration. Calibration requires maintaining a sharp focus on the optical microscope and ensuring the sample is positioned on the Rowland bulb. An appropriate beam current should be selected to ensure a maximum count (cps) > 3000 during calibration, and the count should not exceed 1 × 10⁻⁶. 4 cps.

[0020] Both the pure metallic Mo standard and the fuel sample to be tested need to be polished to ensure a smooth surface with no obvious scratches under micron-scale electron microscopy. Then, the Mo standard and the fuel sample to be tested are treated with carbon spraying to a thickness of about 20 nm. They are then placed in the electron probe sample chamber to avoid surface contamination and oxidation. The standard calibration uses a low beam current (about 33 nA) to avoid the influence of dead time. Before calibration, the Mo standard should be peak-finding in WDS mode to determine the background position. This position is input during calibration. Linear fitting is selected for the background, with a peak acquisition time of 30 s and a background acquisition time of 15 s.

[0021] The test area needs to be screened using secondary electron (SE) and backscattered electron (BSE) imaging at a low beam current of approximately 20–50 nA to ensure it is relatively clean, smooth, and free of obvious pores and detachment. Quantitative analysis uses a high beam current (≥200 nA) to ensure sufficient signal intensity, with a beam spot size of 10 μm to avoid sample damage and random errors caused by the test area. The same testing parameters as the quantitative analysis are used to verify the results on the sample, recording the Mo signal intensity in real time and checking for signal fluctuations. Before testing, peak finding for the Mo element in the test fuel is required to obtain the Mo background; two background values ​​are selected on each side, and an exponential fit is used. The characteristic peak measurement for quantitative analysis is 60 s, and the background measurement is 30 s.

[0022] (2) Load the Si / Ta standard into the sample analysis chamber of the secondary ion mass spectrometer (SIMS), adjust the primary and secondary optical paths of the SIMS, and calibrate parameters such as the contrast aperture, field aperture, scanning area, maximum analysis area, entrance slit, exit slit, and energy slit. Set the primary beam current and calibrate the electron multiplier and Faraday cup.

[0023] The nuclear fuel sample to be tested is loaded into the sample analysis chamber of the SIMS. The shape of the primary ion beam is checked, the entrance and exit slits are adjusted, and the energy slit position, contrast aperture, DTCA, and DTFA are calibrated. Near the EPMA analysis region, the SIMS is used to analyze fissile nuclides in multiple micro-regions. 98 Isotope analysis was performed on Mo and its isotopes to obtain... 98 The average abundance ratio of Mo and its isotopes is denoted as a i .

[0024] In this case, the primary ion source of SIMS is O. 2+ The oxygen source is equipped with primary and secondary ion beam accelerating voltages of +15kV and +5kV, respectively. The primary beam current is 20~100nA, the field aperture is 750 or 400μm, the contrast aperture is 400 or 150μm, and the scanning area is 100×100μm. 2 The maximum analytical area is 150×150μm. 2 The inlet slit width is 40~80μm, the outlet slit width is 80~160μm, the mass resolution is 1500~3000a.mu, and the energy slit width is 25~100eV.

[0025] It should be found on the UO2 fuel sample. 238 The secondary ion signal of U was used to focus the primary ion beam effectively by adjusting the L4 lens and the astigmatism correctors StigX, StigY, and D5 S1; the sharpness of the exit and entrance slits was adjusted to make the entrance slit parallel to the exit slit; and the magnetic field was moved to locate... 98 The secondary ion signal of Mo is used to calibrate the position of the energy slit, so that... 98 The secondary ion signal intensity of Mo is the highest, and it scans the positions of the deflection plates DTCA and DTFA.

[0026] Along the direction of EPMA quantitative testing on the fuel sample 95 Mo、 97 Mo、 98 Mohe 100 Isotope testing was performed on Mo and other fission nuclides. The secondary ion signals of these fission nuclides were collected using an electron multiplier and calculated. 95 Mo、 97 Mo、 98 Mohe 100Isotope ratios of Mo, etc.

[0027] (3) Based on the content of the fission element Mo in the fuel sample obtained by EMPA testing and the content measured by SIMS... 98 The isotope ratio of Mo is calculated using the following formula ① to obtain the value of the micro-region. 98 Mo content C 98Mo .

[0028] ①; in, C 98Mo To calculate the fission nuclides obtained 98 Mo content, C Mo For the Mo content measured by electron probe, A 98Mo fission nuclides measured by secondary ion mass spectrometry 98 The isotope ratio of Mo.

[0029] (4) Based on the above calculations 98 Mo content and fuel consumption 98 The relationship with Mo, as shown in Formula ② below, allows for the calculation of the micro-area burnup value of nuclear fuel: ②; in, B u This represents the micro-zone fuel consumption value, with 9.380 being the coefficient for converting fuel consumption units from at% to MWd / tU. C 98Mo To calculate the fission nuclides obtained 98 Mo content (wt.%) m 98Mo for 98 The relative atomic weight of Mo m UO2 This represents the relative atomic weight of UO2. FY for 235 U element fission 98 Production of Mo nuclides, FY Take 0.5733.

[0030] Example 1 (1) First, the pure Mo standard and the irradiated UO2 fuel sample were loaded into the sample chamber of the EPMA. The voltage was set to 25 kV and the current to 33 nA. The beam spot size was set to 10 μm. Five points were randomly selected on the Mo standard to calibrate the LPET crystal of the sp2 spectrum and the LPET of the sp3 spectrum. Then, the characteristic peak (La peak) of Mo was scanned within a range of ±2000 sinθ to the left and right by the spectrum. The left background of the La peak of Mo was set to -1235 sinθ and the right background to +1675 sinθ. The value of the characteristic peak Pk and the value of the background Bg were obtained by linear fitting of the two backgrounds. The net peak height of the Mo standard was calculated. I A std (cps / nA); (2) Select a voltage of 25kV and a current of 200nA, a beam size of 10μm, and a magnification of 5000x. Perform EPMA quantitative analysis on Mo from the center to the edge of the fuel sample. Select two background values ​​on each side of the characteristic peak (La peak) of Mo. The EPMA software automatically removes one background value with a large error. Linearly fit the remaining three background values ​​to obtain the value of the characteristic peak Pk of Mo and the value of the background Bg. Calculate the net peak height of the fission element Mo in the fuel sample. I A unk By combining quantitative analysis of pure Mo standard samples and using formulas ③ and ④, the content of Mo element at different radial positions in UO2 fuel was calculated.

[0031] ③; ④; in, C A unk This refers to the content (concentration) of Mo in UO2 fuel. C A std The concentration of Mo in the Mo standard. I A unk This represents the net peak height of Mo in the fuel. I A std G represents the net peak height of Mo in the Mo standard sample. ZAF G is the calibration coefficient. Z G is the determining factor for the generation of incident electron X-rays by EPMA. A G represents the degree of X-ray absorption by the sample. F This represents the degree of excitation of secondary X-rays generated within the sample.

[0032] (3) Using a primary beam of 2~15nA, the secondary and primary optical paths of the shielded SIMS oxygen ion source were optimized and adjusted on the Si-Ta optical path adjustment standard. The acceleration voltages of the primary ion beam and the secondary ion beam were +15kV and +5kV, respectively. The field aperture and contrast aperture of the SIMS were adjusted and centered. The exit slit and the entrance slit were adjusted so that the entrance slit was parallel to the exit slit. The electron multiplier was calibrated and parameters such as primary beam current, scanning area, maximum analysis area and energy slit width were set. (4) The primary beam current of the SIMS is selected as 20~100nA, the field aperture is 750 or 400μm, the contrast aperture is 400 or 150μm, and the scanning area is 100×100μm. 2 The maximum analytical area is 150×150μm. 2 The inlet slit width is 40–80 μm, the outlet slit width is 80–160 μm, the mass resolution is 1500–3000 a.mu, and the energy slit width is 25–100 eV. A moving magnetic field was used to locate [the slit] on the irradiated UO2 fuel sample. 238 To obtain the secondary ion signal from U, adjust the L4 lens and astigmatism correctors Stig X, Stig Y, and D5 S1 to ensure good focusing of the primary ion beam. Adjust the sharpness of the exit and entrance slits, ensuring the entrance slit is parallel to the exit slit. Move the magnetic field to find... 98 The secondary ion signal of Mo is then used to calibrate the position of the energy slit, so that... 98 The secondary ion signal intensity of Mo is the highest, and the positions of the DTCA and DTFA of the deflection plate are scanned. (5) Select the set SIMS test parameters for fission nuclides. 95 Mo、 97 Mo、 98 Mo, and 100 Mo was subjected to magnetic field correction, and then isotopic tests were performed on these nuclides along the direction of EPMA quantitative testing on the fuel sample. The secondary ion signals of these fission nuclides were collected using an electron multiplier, and then the ratio of each isotope of Mo was calculated according to formula ①.

[0033] (6) Based on the average content of the fission element Mo in the fuel samples obtained by EMPA testing and the content measured by SIMS... 98 The isotope ratios of Mo were calculated. 98 The content of Mo was determined, and the micro-area fuel consumption value of UO2 fuel was calculated using the fuel consumption calculation formula ②.

[0034] Among them, such as Figure 1 The figure shows the micro-zone fuel consumption values ​​calculated at different radial positions of UO2 fuel, from... Figure 1It can be seen that the micro-zone burnup value increases significantly at the edge of UO2 fuel, and the calculated average burnup value of UO2 fuel is 40506 MWd / tU.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 method based on 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, Includes the following steps: S1. Nuclear fuel samples were taken, and the Mo content of the samples was determined using an electron probe microanalyzer. C Mo ; S2 uses a secondary ion mass spectrometer to analyze the fission nuclides in the above samples. 98 Isotope analysis was performed on Mo and its isotopes to calculate fission nuclides. 98 Mo isotope ratio A 98Mo ; S3 is calculated based on the measurement results of steps S1 and S2 using the following formula ①. 98 Mo content C 98Mo : ①； S4 Calculate the micro-zone burnup value B of nuclear fuel according to the following formula ②. u : ②； in, B u This represents the micro-zone fuel consumption value, with 9.380 being the coefficient for converting fuel consumption units from at% to MWd / tU. m 98Mo for 98 The relative atomic weight of Mo m UO2 This represents the relative atomic weight of UO2. FY for 235 U element fission 98 Production of Mo nuclides.

2. The method based on claim 1 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, In step S1, an LPET spectrophotometer is selected. First, the spectrophotometer is calibrated on a Fe-containing standard sample, and the PHA detector is also calibrated. The accelerating voltage is 25 kV. Then, a pure metal Mo standard sample is used for calibration, and then the fission element Mo in the fuel micro-region is quantitatively tested.

3. The method based on claim 2 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, Both the pure metallic Mo standard and the fuel sample to be tested need to be polished, then carbonized, and then placed in the electron probe sample chamber. Before calibration, the Mo standard should be peaked in WDS mode to determine the background position. This position should be entered during calibration. Linear fitting should be selected for the background, with a peak acquisition time of 30s and a background acquisition time of 15s.

4. The method based on claim 2 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, In step S1, the target region is screened using secondary ions and backscattering imaging at a low beam current of approximately 20-50 nA. Quantitative analysis uses a high beam current of ≥200 nA, and the same quantitative time is required. This test parameter is verified on the sample, and the Mo signal quantity is recorded in real time to check for signal fluctuations. Before testing, peak finding is required for the Mo element in the target fuel to obtain the Mo element background. Two backgrounds are selected on the left and right sides, and an exponential fit is used. The characteristic peak of quantitative analysis is measured for 60 seconds, and the background is measured for 30 seconds.

5. The method based on claim 1 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, In step S2, the test parameters for the secondary ion mass spectrometer are as follows: The primary ion source is O 2+ The oxygen source is equipped with primary and secondary ion beam accelerating voltages of +15kV and +5kV, respectively. The primary beam current is 20~100nA, the field aperture is 750 or 400μm, the contrast aperture is 400 or 150μm, and the scanning area is 100×100μm. 2 The maximum analytical area is 150×150μm. 2 The inlet slit width is 40~80μm, the outlet slit width is 80~160μm, the mass resolution is 1500~3000a.mu, and the energy slit width is 25~100eV.

6. The method based on claim 1 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, In step S2, the UO2 fuel sample was found 238 The secondary ion signal of U is used to focus the primary ion beam well by adjusting the L4 lens and the astigmatism reducers Stig X, Stig Y and D5 S1; the sharpness of the exit slit and the entrance slit is adjusted so that the entrance slit is parallel to the exit slit. Move the magnetic field to find 98 The secondary ion signal of Mo is used to calibrate the position of the energy slit, so that... 98 The secondary ion signal intensity of Mo is the highest, and the positions of the DTCA and DTFA of the deflection plates are scanned.

7. The method based on claim 1 98 A micro-area fuel consumption test method for quantitative analysis of Mo, characterized in that, In step S2, the direction of EPMA quantitative testing on the fuel sample is followed. 95 Mo、 97 Mo、 98 Mohe 100 Isotope testing was performed on Mo and other fission nuclides. The secondary ion signals of these fission nuclides were collected using an electron multiplier and calculated. 95 Mo、 97 Mo、 98 Mohe 100 Isotope ratios of Mo, etc.

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