Method for improving measurement precision of gamma radionuclide of gaseous effluent aerosol sample of nuclear power plant

Abstract

The invention discloses a method for improving gamma radionuclide measurement precision of a gaseous effluent aerosol sample of a nuclear power plant, which comprises the following steps: flatly placing a collected aerosol filter membrane in a plastic package bag, and carrying out annular plastic package; fixing the sample in the sample box; fixing the sample box on a detector of the measuring instrument through a sample fixing frame; efficiency scale and radioactive content preliminary calculation is carried out by using a reference source, then a correction coefficient conforming to addition is simulated and calculated by using passive efficiency scale software, and a preliminary calculation result is corrected to obtain a final value. By controlling the relative positions of the sample and the detector, the relative positions of the measured sample, the efficiency scale source and the detector can be strictly consistent, so that the efficiency scale is more accurate, and the measurement result is more accurate; and the placing position can be repeated when the sample is remeasured or different samples are measured, so that the different samples are different or identical. And a quantitative analysis method is improved by introducing a method combining active and passive efficiency scales, so that the measurement precision can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of radioactive detection, and in particular to a method for improving the measurement accuracy of gamma radioactive nuclides in aerosol samples of gaseous effluents from nuclear power plants. Background Art

[0002] Effluent monitoring is a key component of nuclear power plant radioactivity level monitoring, emergency management, and nuclear safety regulation. Measuring particles in gaseous effluent emitted from the main chimney of the nuclear island is a type of gaseous effluent monitoring project for nuclear power plants. These particles are typically collected using a filter membrane made of materials such as cellulose acetate with an effective diameter of approximately 40 mm and a thickness of less than 1 mm to form an aerosol sample, which is then quantitatively analyzed for its gamma radioactive nuclide content using gamma spectroscopy. During measurement, samples are often packaged in plastic bags and then placed in traditional sample boxes or directly placed on the detector surface for measurement. Because the aerosol filter membrane is very thin, the shape and position of the filter membrane within the plastic bag are difficult to control, making it very easy for the sample to stray from the detector surface, affecting the measurement results. Furthermore, some target nuclides exhibit cascade decay, which can cause the measurement results to deviate significantly from the true value (by more than 20%). Therefore, the accuracy of existing measurement methods needs to be improved. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a method for improving the measurement precision of gamma radionuclides in aerosol samples of gaseous effluents from nuclear power plants, thereby improving the measurement accuracy.

[0004] In order to solve the above technical problems, the purpose of the present invention is achieved through the following technical solutions:

[0005] A method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from a nuclear power plant comprises the following steps:

[0006] (1) Place the collected aerosol filter membrane flat in a plastic bag and perform circular plastic sealing to obtain a sample;

[0007] (2) Fix the sample in the sample box;

[0008] (3) Fix the sample box to the detector of the measuring instrument through the sample fixing bracket to ensure that the relative position of the sample box and the detector is fixed during each measurement;

[0009] (4) The measuring instrument performs detection measurement to obtain measurement results.

[0010] Preferably, in step (4):

[0011] The efficiency calibration and radioactive content are preliminarily calculated using a reference source, and then the passive efficiency calibration software is used to simulate the calculation to meet the additive correction coefficient, and the preliminary calculation results are corrected to obtain the final value.

[0012] Preferably, in step (2):

[0013] Placing the sample in the box body of the sample box;

[0014] The sample is fixed by anti-displacement fixings to prevent the sample from moving inside the box;

[0015] Close the lid.

[0016] Preferably, the sample is adhered to the box body of the sample box by means of adhesive tape.

[0017] Preferably, the anti-displacement fixing member is a pancake-shaped sponge, which is covered on the sample and then covered with a cover.

[0018] Preferably, in step (3), the sample holder has a fixing notch for fixing the sample box, the fixing notch corresponds to the position of the detection port of the detector, and the sample box is embedded in the fixing notch and fixed, so that it can be aligned with the detection port of the detector.

[0019] Preferably, the measuring instrument adopts a high-purity germanium gamma spectrometer for measurement.

[0020] The beneficial effects of the present invention compared with the prior art are:

[0021] (1) The present invention can ensure that the relative positions of the measured sample and the efficiency calibration source and the detector are strictly consistent by precisely controlling the relative positions of the sample and the detector, thereby making the efficiency calibration more precise and the measurement results more accurate; it can also ensure that the placement position of the sample can be repeated when retesting or measuring different samples, thereby improving the accuracy between different samples or the same sample.

[0022] (2) The present invention improves the quantitative analysis method by introducing a combination of active and passive efficiency scales, which can effectively improve the measurement accuracy and solve the problem of lack of repeatability and comparability of measurement results.

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 Schematic diagram of the structure of a γ-radionuclide measurement sample box in this embodiment.

[0026] Figure 2Schematic diagram of the structure of a γ-radionuclide measurement sample box in this embodiment.

[0027] Figure 3 Schematic diagram of the structure of a γ-radionuclide measurement sample box in this embodiment.

[0028] Figure 4 Schematic diagram of the structure of a γ-radionuclide measurement system in this embodiment.

[0029] Figure 5 Schematic diagram of the structure of the sample fixing frame in this embodiment.

[0030] Figure 6 The detection efficiency changes with the distance from the sample to the detector surface (d represents the sample elevation distance) compared to when the sample is close to the detector surface.

[0031] Description of the symbols in the figure:

[0032] 1. γ-radionuclide measurement sample box; 11. Box body; 12. Cover; 13. Sample; 14. Anti-displacement fixing piece;

[0033] 2. Sample fixing frame; 21. Fixing notch;

[0034] 3. Detector. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0037] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used in the specification and appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0039] This embodiment provides a method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from a nuclear power plant, comprising the steps of:

[0040] (1) Place the collected aerosol filter membrane flat in a plastic bag and perform circular plastic sealing to obtain a sample;

[0041] (2) Fix the sample in the sample box;

[0042] (3) Fix the sample box to the detector of the measuring instrument through the sample fixing bracket to ensure that the relative position of the sample box and the detector is fixed during each measurement;

[0043] (4) The measuring instrument performs detection measurement to obtain measurement results.

[0044] The measuring instrument in this embodiment is a high-purity germanium gamma spectrometer.

[0045] Among them, the sample box 1 in this embodiment has various structural forms. In this embodiment, it includes a box body 11 for placing a sample 13, a cover body 12 matched with the box body 11, and an anti-displacement fixing member 14 for preventing the sample 13 in the box body 11 from moving.

[0046] In this embodiment, the sample 13 is placed in the box body 11 and then fixed by the anti-displacement fixing member 14. This can keep the position of the sample 13 unchanged during measurement, thereby improving measurement accuracy. In addition, the sample box 13 in this embodiment can be used to measure different samples 13 and can be reused.

[0047] In this embodiment, the anti-displacement fixing member 14 can have various structural forms. For example, some downward pressing structures can be set in the box body 11. When the sample 13 is placed in the box body 11, the sample 13 is fixed by downward pressing. Of course, it can also be achieved in many other ways.

[0048] In one embodiment, the bottom of the box body 11 is adhesively connected to the sample 13 .

[0049] In this embodiment, the sample 13 can be pasted and fixed in the box body 11, so that the sample 13 can be kept flat at the bottom of the box body 11, the flatness of the sample 13 is improved, and errors caused by shape changes are avoided. At the same time, combined with the action of the anti-displacement fixing member 14, the sample 13 is fixed more firmly to avoid movement.

[0050] In one embodiment, the sample 13 includes a sample 13 collection filter membrane and a plastic sealing bag for plastic sealing the sample 13 collection filter membrane.

[0051] In this embodiment, the sample 13 collection filter membrane (collected aerosol filter membrane) is sealed in a plastic bag to address the potential unevenness of the filter membrane and prevent dust from falling off the collected filter membrane or the volatilization of potentially volatile radionuclides. Specifically, during the plastic sealing process, the collected aerosol filter membrane is placed flat in a plastic bag and sealed in an annular shape using a plastic sealing process. Care is taken to exclude as much air as possible during the sealing process.

[0052] In one embodiment, the bottom of the box body 11 is connected to the plastic bag by adhesive tape.

[0053] In this embodiment, the plastic bag can be connected to the bottom of the box body 11 by adhesive tape, for example, double-sided tape is used, which is convenient and quick to operate and easy to disassemble and assemble.

[0054] In order to facilitate the positioning of the sample 13, in one embodiment, the box body 11 has a pasting positioning area for pasting the sample 13. In this embodiment, the pasting positioning area can be provided, and the sample 13 can be pasted and fixed in the pasting positioning area.

[0055] In this embodiment, the box body 11 can have various structural forms. In one embodiment, the box body 11 is circular. Of course, the box body 11 in this embodiment can also have other shapes and can be configured in various ways according to actual needs.

[0056] In one embodiment, the anti-displacement fixing member 14 matches the internal shape of the box body 11. When the sample 13 is placed in the box body 11, the anti-displacement fixing member 14 covers the sample 13 to flatten the sample 13 and prevent it from moving.

[0057] The anti-displacement fixing member 14 in this embodiment can have various structural forms. In one embodiment, the anti-displacement fixing member 14 is a pancake-shaped sponge.

[0058] In this embodiment, a pancake-shaped sponge structure is adopted. The pancake-shaped sponge is light and easy to place. After the sample 13 is placed in the box body 11, the pancake-shaped sponge is covered on the sample 13, and then the cover body 12 is covered. The pancake-shaped sponge can press down the sample 13, making the sample 13 more flat and fixed in position.

[0059] In this embodiment, the sample box 1 can be positioned and fixed by a sample fixing rack 2. The sample fixing rack 2 in this embodiment can have various structural forms. For example, it can be set to a detachable form, such as being fixed to the detector 3 by means of snap connection, etc. The method of fixing the γ radionuclide measurement sample box 1 can also be a snap connection, etc.

[0060] In one embodiment, the sample holder has a fixing notch 21 for fixing the sample box 1 , and the fixing notch 21 corresponds to the position of the detection port of the detector, so that the γ-radionuclide measurement sample box 1 is aligned with the detection port of the detector.

[0061] In this embodiment, the sample holder is provided with a fixing notch 21. The sample box 1 is then inserted into the fixing notch to be snap-fitted and positioned within the fixing notch. The fixing notch corresponds to the detection port of the detector, so that the sample box 1 can be aligned with the detection port and the relative position remains unchanged. This ensures that the relative positions of the measured sample, the efficiency calibration source, and the detector are strictly consistent, making the efficiency calibration more precise and the measurement results more accurate. It also ensures that the sample placement position is repeatable when retesting or measuring different samples, thereby improving the comparability of different samples or multiple measurement results of the same sample.

[0062] When quantitatively calculating the gamma energy spectrum of a sample, the radioactivity of the nuclide is inversely proportional to the detection efficiency of the detection system for gamma rays of corresponding energy, and the detection efficiency is directly related to the specific measurement geometric conditions.

[0063] In practice, effluent aerosol filter measurements often involve packaging samples in plastic bags, placing them in traditional sample boxes, or simply placing the bags on the detector surface for measurement. Because aerosol filters are very thin, the shape and position of the filters in the bags are difficult to control. Consequently, the sample can easily drift away from the detector surface, affecting measurement results.

[0064] To illustrate the influence of the uncontrollable filter shape and position on the measurement results, the passive efficiency calibration software (LabSOCS) was used to simulate and calculate the change in detection efficiency when the distance d between the sample and the detector surface was different.

[0065] With a step size of 1 mm, the changes in detection efficiency of common nuclide energy points in the energy range of 50 keV to 2000 keV are calculated when the spacing d changes to 5 mm (relative to d = 0 mm). The results are shown in Figure 6 Simulations show that for every 1 mm of elevation, the detection efficiency decreases by approximately 4%. This shows that the measurement results are strongly dependent on the distance between the sample and the detector.

[0066] In actual measurements, the position of the filter membrane in the plastic bag is uncontrollable, which can easily lead to deviations of several millimeters or even centimeters. By using the multiple quality control measures introduced by the container and measurement method designed by the present invention, the shape and position of the filter membrane can be effectively controlled, making the measurement results more accurate and repeatable.

[0067] In addition, in one embodiment, in step (4):

[0068] The efficiency calibration and radioactive content are preliminarily calculated using a reference source, and then the passive efficiency calibration software is used to simulate the calculation to meet the additive correction coefficient, and the preliminary calculation results are corrected to obtain the final value.

[0069] In this embodiment, the γ-radionuclide content of the sample is analyzed, and the nuclides with cascade effect are quantitatively calculated by combining active and passive efficiency calibration methods.

[0070] Many target nuclides in effluent aerosol samples exhibit cascade decay phenomena. When the sample is placed on the detector surface for measurement, an obvious cascade coincidence addition effect will occur. Therefore, corrections are made in this embodiment. The correction methods used in this embodiment include the single energy efficiency curve method, the decay scheme theoretical calculation method, the Monte Carlo simulation calculation method, and software specifically used for simulation calculation of gamma spectrometer detector efficiency, such as LabSOCS and Angle.

[0071] To improve measurement accuracy, a method combining active and passive efficiency calibrations is proposed to quantitatively measure the activity of nuclides with additive effects. This method was actually applied to three simulated aerosol samples during the 2019 International Atomic Energy Agency (IAEA) proficiency testing to verify the accuracy of the analytical method and illustrate the influence of the additive effect on the results.

[0072] (1) Instruments, equipment and methods

[0073] γ spectrometer: CANBERRA BE3830 high purity germanium spectrometer, relative efficiency 30%, energy resolution 1.52keV ( 60 Co point source @1.33MeV).

[0074] Samples: 3 simulated aerosol filter membrane samples (numbered S05, S06, and S07) were obtained from the IAEA. The sample diameter is 43 mm and the thickness is about 0.2 mm. Analysis showed that the radionuclides contained are 134 Cs and 137 Cs, here we only discuss the cascade decay phenomenon 134 Cs.

[0075] Reference Source: Create a reference source with a geometry and medium similar to the sample being measured. Specifically, mark a 43mm diameter circular area on the sticky side of a piece of clear tape. Place a thin layer of a certified simulated fallout powder source within the area and cover it with another layer of tape to prevent the powder from falling. The amount of powder source used is determined by weighing it on an analytical balance before and after applying the tape.

[0076] Measurement and analysis method: The sample is placed in a sample box and placed on the center of the detector surface through a sample holder for measurement. Each sample is measured for 48 hours. When analyzing the data, the reference source is used to calibrate the active efficiency and perform preliminary calculations. 134Cs activity, and then simulate the calculation with the passive efficiency scale (LabSOCS is used here) to meet the addition correction factor, and correct the preliminary calculation results to obtain 134 Final activity of Cs.

[0077] (2) Measurement results

[0078] The measurement results of the three samples are shown in Tables 1 to 3. 134 Cs emits multiple gamma rays, and here we analyze the five spectral lines with the highest emission probability. It can be seen that the largest relative deviation of the three sample analysis results occurs at the 563.2keV full energy peak of the S07 sample, which is -5.7%. 134 The arithmetic mean of the five Cs spectral line results was taken, and the relative deviations between the analysis results of the three samples and the IAEA reference values ​​were between 0.0% and -1.6%, verifying the accuracy of the analysis method.

[0079] 134 The combined coincidence correction coefficients for the five Cs peaks ranged from 0.729 to 0.829, with corrections reaching up to 27% (at the 569.3 keV peak). The corrected results agreed well with the reference values. This suggests that not performing cascaded coincidence corrections can lead to significant deviations from the true values, thus affecting the accuracy of effluent emission statistics.

[0080] Table 1 Analysis results of S05 simulated aerosol filter membrane

[0081]

[0082] Table 2 Analysis results of S06 simulated aerosol filter membrane

[0083]

[0084] Table 3 Analysis results of S07 simulated aerosol filter membrane

[0085]

[0086] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants, characterized in that: Including steps: (1) Place the collected aerosol filter membrane flat in a plastic bag and perform circular plastic sealing to obtain a sample; (2) Fix the sample in the sample box; (3) Fix the sample box to the detector of the measuring instrument through the sample fixing bracket to ensure that the relative position of the sample box and the detector is fixed during each measurement; (4) The measuring instrument performs detection measurement to obtain measurement results.

2. The method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants according to claim 1, characterized in that: In step (4): The efficiency calibration and radioactive content are preliminarily calculated using a reference source, and then the passive efficiency calibration software is used to simulate the calculation to meet the additive correction coefficient, and the preliminary calculation results are corrected to obtain the final value.

3. The method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants according to claim 2, characterized in that: In step (2): Placing the sample in the box body of the sample box; The sample is fixed by anti-displacement fixings to prevent the sample from moving inside the box; Close the lid.

4. The method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants according to claim 3, characterized in that: Stick the sample into the sample box with adhesive tape.

5. The method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants according to claim 4, characterized in that: The anti-displacement fixing member is a pancake-shaped sponge, which is covered on the sample and then covered with a cover.

6. The method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants according to any one of claims 1 to 5, characterized in that: In step (3), the sample holder has a fixing notch for fixing the sample box, and the fixing notch corresponds to the position of the detection port of the detector. The sample box is embedded in the fixing notch and fixed, so that it can be aligned with the detection port of the detector.

7. The method for improving the measurement accuracy of gamma radionuclides in aerosol samples of gaseous effluent from nuclear power plants according to claim 1, characterized in that: The measuring instrument adopts a high-purity germanium gamma spectrometer for measurement.

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