A device and method for measuring low- and medium-level nuclear waste barrels

Abstract

The present invention discloses a device and method for measuring low- and medium-level nuclear waste barrels. The device includes: a transmission source, a transmission source collimator, a rotating table, a detector collimator, a detector, a transmission source platform, etc. The method is as follows: the waste barrel is divided into several layers along the axial direction and numbered. By rotating the waste barrel, it is assumed that the medium and the radioactive nuclides to be measured are evenly distributed in the same layer ring. The transmittance of the characteristic energy peak of each ring is obtained in the transmission measurement, thereby obtaining the equivalent density of each ring. Based on a layered and ring-scanning digital simulation platform, a method is proposed to correct the distortion of the transmission ring reconstruction using the dichotomy principle, and at the same time, the influence of crosstalk between rings is corrected. The total activity is obtained by summing the activities of each ring after correction. The present invention combines the advantages of the SGS and TGS measurement methods, improves the accuracy of the waste barrel activity analysis results while ensuring the measurement time, improves the application maturity of the γ scanning measurement technology, and expands its application field.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear industry, and in particular relates to a device and method for measuring low- and medium-level nuclear waste barrels. Background Art

[0002] Given the rapid development of nuclear power and the unprecedented growth in the number of nuclear power plants, the generation of large quantities of radioactive waste is inevitable. Sources of radioactive waste include enrichment and reprocessing in the nuclear fuel cycle, nuclear power plant operation, the production and use of radioisotopes, the decommissioning of nuclear power facilities, and the nuclear weapons industry. The "Technical Regulations for the Temporary Storage of Low- and Intermediate-Level Radioactive Solid Wastes from Nuclear Power Plants" (GB 14589-1993), issued by the State Administration of Technical Supervision, stipulates that information such as the source, type, specific activity, surface radiation level, and contamination level of waste entering and leaving temporary storage sites must be clearly identified. This also requires that the radioactive material within waste barrels entering temporary storage be measured. Currently used methods include segmented gamma scanning (SGS) and tomography gamma scanning (TGS). The SGS measurement principle involves dividing the waste barrel axially into several layers, assuming a uniform distribution of material and radionuclides within the layers. The barrel is then rotated at a constant speed (to minimize lateral uneven distribution of the medium and radionuclides within the barrel). The detector then measures each layer sequentially, summing the measurements to obtain the total activity. Because SGS measurements assume a uniform distribution of the medium and radionuclides within the layers, in actual measurements, the medium density and radioactivity distribution of the measured sample rarely fully meet this uniformity requirement within the layers, resulting in significant errors between the reconstructed activity and the true value. TGS, proposed in the 1990s based on SGS technology, is the application of CT technology in the non-destructive quantitative measurement of gamma radionuclides. TGS technology not only performs axial stratification on the sample to be tested, but also divides the stratification into several blocks, and assumes that the radionuclides and media in each block are uniformly distributed. The sample is then measured in layers and rings, and the content of radionuclides in each block is estimated after self-absorption correction. The number of nuclides in each block is accumulated to obtain the nuclide content of the entire waste barrel. Comparing the advantages, disadvantages and limitations of the two, it can be seen that the SGS measurement process is simple, efficient, and short in measurement time, making it suitable for industrial batch testing, but it is difficult to accurately analyze non-uniform objects and has the disadvantage of low detection accuracy. TGS can accurately reconstruct the medium and radioactivity distribution in the barrel, but the complexity of the process and low efficiency have limited its large-scale application in nuclear waste barrel detection. Summary of the Invention

[0003] The present invention aims to improve the deficiencies in the prior art and proposes a device and method for measuring barrels of low- and medium-level nuclear waste. The device and method can maintain the advantages of simplicity and speed of layered gamma scanning while having measurement accuracy comparable to that of tomographic gamma scanning. The measurement method can be called SRGS technology (segmented-Ringed gamma scanning, SRGS). Its principle is to divide the samples in each layer into several concentric rings of equal thickness and number them on the basis of SGS. The medium and nuclides in each ring are different, and the medium and the radioactive nuclides to be measured are evenly distributed within the ring. This assumption is more in line with the actual situation, improves the measurement accuracy of non-uniform samples to be measured, and greatly improves the detection accuracy compared to SGS. In addition, the measurement time is greatly reduced and the process is simpler compared to TGS, which has great practical significance. It will improve the application maturity of gamma scanning measurement technology and expand its field.

[0004] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0005] A device for measuring the activity of low- and medium-level nuclear waste barrels is characterized by comprising a transmission source, a transmission source collimator, a rotating table, a detector collimator, a detector and an analysis module. The low- and medium-level nuclear waste barrels are placed on the rotating table. The rotating table can drive the low- and medium-level nuclear waste barrels to rotate along the vertical axis of the low- and medium-level nuclear waste barrels. The transmission source collimator is installed on one side of the transmission source, and the detector collimator is installed on one side of the detector. The transmission source and the detector are respectively placed on both sides of the low- and medium-level nuclear waste barrels. The gamma rays emitted by the transmission source can be received by the detector after passing through the transmission source collimator, the low- and medium-level nuclear waste barrels and the detector collimator. The analysis module is connected to the detector and is used to receive and analyze data transmitted by the detector.

[0006] To optimize the above technical solutions, specific measures taken also include:

[0007] The analysis module is a layered and ring-by-ring gamma scanning digital simulation platform.

[0008] A method for measuring the activity of low- and intermediate-level nuclear waste barrels comprises the following steps:

[0009] Step 1: Divide the low- and medium-level nuclear waste barrels into several layers along the height direction and number them. Within each layer, divide them into several concentric rings of equal thickness with the rotation axis of the low- and medium-level nuclear waste barrel as the axis and number them. It is assumed that the distribution of the radioactivity and the distribution of the dielectric material in each layer and ring is uniform.

[0010] Step 2: The detector and the transmission source perform transmission measurements on the barrels of low- and medium-level nuclear waste layer by layer and ring by ring starting from the bottom layer. A ring measurement line is set up on each layer and ring. The ring measurement line just passes horizontally through the position of half the thickness of the ring to be measured. The specific positions of the transmission source and the detector are adjusted so that the line connecting the transmission source and the detector coincides with the ring measurement line. The transmission measurement is performed on the barrels of low- and medium-level nuclear waste ring by ring to obtain the transmittance T of the characteristic energy peak of the transmission source at the ring measurement line of each layer. c , where the inner ring line must pass through the corresponding ring and the outer ring;

[0011] Step 3: Use the T obtained from the transmission measurement c Calculate the linear attenuation coefficient μ of the medium of each layer of the ring measurement line c and the equivalent density ρ c , for the equivalent density ρ c Correction is performed to obtain the corrected equivalent density of each layer and each ring;

[0012] Step 4: The medium and low level nuclear waste barrel rotates at a constant speed, and the self-emission measurement of the medium and low level nuclear waste barrel is carried out to obtain the activity of each layer and each ring. The equivalent density of each layer and each ring obtained in step 3 is reconstructed after distortion correction to obtain the system full energy peak detection efficiency of each layer and each ring.

[0013] Step 5: Perform inter-ring crosstalk correction, add up the corrected activities of each ring in the same layer, and then add up the activities of each layer to obtain the total activity in the low- and medium-level nuclear waste barrel.

[0014] In step 3, the T c Calculate the linear attenuation coefficient μ of the medium of each layer of the ring measurement line c and the equivalent density ρ c The specific formula used is:

[0015]

[0016] Where N is the total number of rings in the layer, μ i is the linear absorption coefficient of the medium of the i-th ring to the gamma ray of a specific energy, L i,K is the half value of the track length of the transmission source beam passing through the i-th ring during the K-th transmission measurement of the current layer. Its size is only related to the sample radius and the ring division strategy. It can be solved through geometric operations. It is agreed that K = 1 means that the transmission source beam only passes through the outermost ring, that is, the first ring. μ m is the mass attenuation coefficient of the measured object for a characteristic γ-ray of a certain characteristic energy, ρ is the equivalent density, is the transmittance of gamma rays of a specific energy to the medium of the i-th ring, I and I0 are the full energy peak count rates of a certain characteristic energy of the transmission source obtained by open beam measurement with and without the presence of low- and medium-level nuclear waste barrels, and the T of each ring in the transmission measurement is converted to cSubstituting the above formula, we can get the linear attenuation coefficient μ of the medium of each layer of the ring measurement line: c and the equivalent density ρ c , D is the path length of the transmitted ray penetrating the measurement object when it is an ideal beam.

[0017] In step 3, a scale model of a medium and low level nuclear waste barrel is preset in advance on the digital simulation platform for layered and ring-shaped γ scanning, and the transmittance of the characteristic energy peak under different equivalent densities and the path length of the transmission ray penetrating the measurement object is entered. c The bisection method is used for iterative processing to obtain the corrected equivalent density of each ring in each layer. Starting from the outermost ring of a certain layer, the correction is carried out from the outer ring to the inner ring. The specific steps are to first set the interval containing the density of each ring, and then bring in the iterative equivalent density ρ c * Get an iterative equivalent transmittance T C * , compare T C and T C * Size, T C * Greater than T C The iterative equivalent density ρ at this time c * As the minimum value of the set density range, T C * Less than T C The iterative equivalent density ρ at this time c * As the maximum value of the set density interval, then take the average of the minimum and maximum values as the iterative equivalent density ρ of the next iteration c * , when the adjusted T C * Close to the actual measured transmittance T C When the correction of one ring of transmission reconstruction distortion is completed, the equivalent density of the outermost ring after correction is ρ c * .

[0018] In step 3, the density of the inner ring is corrected based on the result of the correction of the outer adjacent ring. Each correction is performed according to the method described in claim 5 until the density correction of each ring in the current layer is completed. Then, the density correction is performed on each ring of all layers, and finally the corrected equivalent density of each ring in each layer is obtained.

[0019] In step 4, when measuring the activity of each ring in each layer through self-emission measurements of the low- and medium-level nuclear waste barrels, the activity of the inner ring will inevitably be affected by the outer ring due to the ring division. Therefore, the activity of each ring is corrected for inter-ring crosstalk, and a correction factor is added to deduct the contribution of other rings to the count of the current ring.

[0020] The correction factors are selected as follows: considering all the nuclides and media involved in the nuclear waste barrel, a database of the activity of each ring and the corresponding correction factor is established based on the layered and ring-by-layer γ scanning digital simulation platform to obtain the activity of each ring under different media and nuclide conditions. The closest value is found between the activity of each ring measured experimentally and the data in the database, and the corresponding correction factor is taken as the correction factor for the activity of each ring in the actual measurement.

[0021] In step 4, the system full energy peak detection efficiency of each layer and each ring is obtained as follows: based on the layered and ring-by-layer γ scanning digital simulation platform, the equivalent density is obtained by transmission ring-by-ring reconstruction distortion correction to reconstruct the experimental model, starting from measuring the γ count of the first ring of the first layer, each layer and each ring is set as a single body source to obtain the characteristic energy γ count obtained by the detector, and the ratio of the characteristic energy γ count obtained by the detector to the corresponding characteristic γ count of the emission is the system full energy peak detection efficiency of the corresponding nuclide in the detector of the layer and the ring in different layers and rings. After completing the simulation measurement of the system full energy peak detection efficiency of the first layer and the first ring, the simulation of the system full energy peak detection efficiency of each ring and each layer corresponding to the γ counts of different rings and layers is carried out in sequence until the system full energy peak detection efficiency of all layers and rings is completed.

[0022] In step 5, the total activity in the barrel of low- and intermediate-level nuclear waste is calculated as follows:

[0023] S(E)'=S(E)·η (3)

[0024]

[0025] S(E) c =ΣS(E)” (5)

[0026]

[0027]

[0028] Where S(E) is the full energy peak count of a ring with a characteristic energy of E, η is the correction factor, which refers to the ratio of the count obtained when only the current ring is the body source to the count obtained when the current ring and other rings are the body sources, S(E)' is the count of a ring with a characteristic energy of E after crosstalk correction, S(E)" is the full energy peak count of a ring with a characteristic energy of E, and S(E) Cis the sum of the counts of each ring in the layer, t is the single measurement time of each ring, and the measurement time of each ring is consistent. T is the reconstructed value of the total activity of gamma rays with characteristic energy E emitted by the nuclides in the waste barrel, S0 is the total activity of gamma rays with characteristic energy E emitted by the nuclides in the barrel, σ is the relative error between the true value and the reconstructed value of the activity of the radioactive source in the barrel, and ε is the system full energy peak detection efficiency of each ring.

[0029] The beneficial effects of the present invention are:

[0030] 1. Based on the layered and ring-by-ring γ scanning digital simulation platform, the linear attenuation coefficient of each ring obtained by transmission measurement is corrected for transmission ring reconstruction distortion. The equivalent density of each ring can be corrected more accurately, which is of great significance for the ring reconstruction of the waste barrel. It can accurately simulate the system detection efficiency of each ring and improve the accuracy of the total activity of the waste barrel.

[0031] 2. Compared with traditional SGS, SRGS utilizes the rotating measurement process of a cylindrical waste barrel. The non-uniformly distributed medium and radionuclides to be measured present a certain degree of axisymmetry relative to the detector. Based on this, a layered and ringed SRGS measurement and analysis model is established. The barrel is divided into several ring sources, each with different media and nuclides. The radioactivity distribution and medium material distribution of the sample in each layer and ring are "uniform". This changes the uniformity assumption of SGS measurement to non-uniformity treatment, which is in line with the actual situation and greatly improves detection accuracy.

[0032] 3. Compared to TGS, SRGS simplifies the process and significantly reduces measurement time, while maintaining comparable detection accuracy. Compared to SGS, SRGS significantly improves detection accuracy. By improving the accuracy of waste drum activity measurements while maintaining measurement time, and by combining a digital simulation platform to correct for distortion in ring density reconstruction, SRGS simplifies the measurement process and enables more accurate ring reconstruction, significantly improving measurement results and ensuring the accuracy of the measured sample activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the sample ring of the present invention

[0034] Figure 2 Schematic diagram of sample ring division of the present invention.

[0035] Figure 3 It is a schematic diagram of the layered and ring-by-ring γ scanning transmission measurement of the present invention.

[0036] Figure 4 It is a flow chart of the ring reconstruction distortion correction algorithm of the present invention.

[0037] Figure 5 It is a schematic diagram of the layered and ring-divided γ scanning self-emission measurement of the present invention.

[0038] Figure 6 This is a schematic diagram of inter-layer and inter-ring crosstalk.

[0039] The reference numerals in the figure are: transmission source 1, transmission source collimator 2, rotating table 3, detector collimator 4, detector 5, and medium and low-level nuclear waste barrel 6. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in further detail below with reference to the accompanying drawings.

[0041] The present invention provides a new detection technology for the measurement of medium- and low-level nuclear waste barrels. This method retains the advantages of SGS measurement, which is simple and fast, while achieving the goal of having a measurement accuracy not much different from TGS. It can ensure both efficiency and measurement accuracy, thereby ensuring the accuracy of the nuclear waste barrel measurement data.

[0042] The present invention will be further described in detail with reference to the accompanying drawings:

[0043] like Figure 1 , Figure 2 As shown, the nuclear waste barrel is divided into several layers along the height direction and numbered. With the rotation axis as the center, the sample is divided into several concentric rings of equal thickness within the layer and numbered. It is assumed that the distribution of radioactivity and dielectric material in each ring is "uniform". The rings in the barrel are numbered, and the layers are numbered in ascending order from the sample to the bottom: 1, 2, ..., S, where S is the total number of layers. The rings are numbered in ascending order from the outside to the inside: 1, 2, ..., N i , N i is the total number of sub-rings in the i-th layer.

[0044] like Figure 3 As shown, the transmission measurement is performed on the sample to be tested layer by layer and ring by ring. The specific process is: adjust the specific positions of the transmission source and its collimator, the detector and its collimation, move the sample barrel to the position horizontally so that the line connecting the transmission source and the detector just passes through half the thickness of the ring to be tested, and then perform transmission measurement to obtain the transmittance of the characteristic energy peak of the transmission source at this position.

[0045] After obtaining the characteristic energy peak transmittance of the transmission source in each ring, the density obtained by ring segmentation reconstruction is corrected, and the transmittance T obtained based on the cone beam transmission measurement data is obtained by the layered ring segmentation γ scanning measurement device. C The Beer formula is used to obtain the corresponding T obtained by transmission measurement. c Calculate the linear attenuation coefficient μ of the medium of each layer of the ring measurement line c and the equivalent density ρ c :

[0046]

[0047]

[0048] Where N is the total number of rings in the layer, μ i is the linear absorption coefficient of the medium of the i-th ring to the gamma ray of a specific energy, L i,K is the half value of the track length of the transmission source beam passing through the i-th ring during the K-th transmission measurement of the current layer. Its size is only related to the sample radius and the ring division strategy. It can be solved through geometric operations. It is agreed that K = 1 means that the transmission source beam only passes through the outermost ring, that is, the first ring. μ m is the mass attenuation coefficient of the measured object for a characteristic γ-ray of a certain characteristic energy, ρ is the equivalent density, is the transmittance of gamma rays of a specific energy to the medium of the i-th ring, I and I0 are the full energy peak count rates of a certain characteristic energy of the transmission source obtained by open beam measurement with and without the presence of low- and medium-level nuclear waste barrels, and the T of each ring in the transmission measurement is converted to c Substituting the above formula, we can get the linear attenuation coefficient μ of the medium of each layer of the ring measurement line: c and the equivalent density ρ c , D is the path length of the transmitted ray penetrating the measurement object when it is an ideal beam.

[0049] like Figure 4 As shown in the figure, a scale model of a medium and low level nuclear waste barrel is preset in advance on the digital simulation platform of layered and ring-shaped γ scanning, and the transmittance of the characteristic energy peak under different equivalent densities and the path length of the transmission ray penetrating the measurement object is entered. c The bisection method is used for iterative processing to obtain the corrected equivalent density of each ring in each layer. Starting from the outermost ring of a certain layer, the correction is carried out from the outer ring to the inner ring. The specific steps are to first set the interval containing the density of each ring, and then bring in the iterative equivalent density ρ c * Get an iterative equivalent transmittance T C * , compare T C and T C * Size, T C * Greater than T C The iterative equivalent density ρ at this time c * As the minimum value of the set density range, T C * Less than T C The iterative equivalent density ρ at this time c * As the maximum value of the set density interval, then take the average of the minimum and maximum values as the iterative equivalent density ρ of the next iterationc * , when the adjusted T C * Close to the actual measured transmittance T C When the correction of one ring of transmission reconstruction distortion is completed, the equivalent density of the outermost ring after correction is ρ c * , based on the result of the correction of the outer adjacent ring, the density of the inner ring is corrected until the density correction of all rings is completed, and then the density correction is performed on each ring of all layers, and finally the corrected equivalent density of each ring in each layer is obtained.

[0050] like Figure 5 、 Figure 6 As shown in the figure, after the transmission reconstruction distortion correction is completed, the self-emission measurement is performed. The self-emission measurement (without an external transmission source) is consistent with the transmission measurement steps. The density of each ring after the distortion correction is reconstructed by ring division. The system full-energy peak detection efficiency ε of each ring is obtained based on the layered layered ring division γ scanning digital simulation platform, thereby obtaining the activity of each ring. Due to the ring division, the activity of the inner ring will inevitably be affected by the outer ring. Therefore, the activity of each ring needs to be corrected for inter-ring crosstalk. We need to deduct the counting contribution of other rings to the current ring.

[0051] The correction factors are selected as follows: considering all the nuclides and media involved in the nuclear waste barrel, a database of the activity of each ring and the corresponding correction factor is established based on the layered and ring-by-layer γ scanning digital simulation platform to obtain the activity of each ring under different media and nuclide conditions. The closest value is found between the activity of each ring measured experimentally and the data in the database, and the corresponding correction factor is taken as the correction factor for the activity of each ring in the actual measurement.

[0052] The activity obtained by multiplying the activity of each ring by the correction factor is the final activity of each ring, and the total activity is obtained by adding them up layer by layer and ring by ring.

[0053] S(E)'=S(E)·η (3)

[0054]

[0055] S(E) c =∑S(E)” (5)

[0056]

[0057] Where S(E) is the full energy peak count of a ring with a characteristic energy of E, η is the correction factor, which refers to the ratio of the count obtained when only the current ring is the body source to the count obtained when the current ring and other rings are the body sources, S(E)' is the count of a ring with a characteristic energy of E after crosstalk correction, S(E)" is the full energy peak count of a ring with a characteristic energy of E, and S(E)C is the sum of the counts of each ring in the layer, t is the single measurement time of each ring, and the measurement time of each ring is consistent. T is the reconstructed value of the total activity of gamma rays with characteristic energy E emitted by the nuclides in the waste barrel, S0 is the total activity of gamma rays with characteristic energy E emitted by the nuclides in the barrel, σ is the relative error between the true value and the reconstructed value of the activity of the radioactive source in the barrel, and ε is the system full energy peak detection efficiency of each ring.

[0058] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for measuring the activity of low- and intermediate-level nuclear waste drums, using a device for measuring the activity of low- and intermediate-level nuclear waste drums, characterized by: The measuring device includes a transmission source, a transmission source collimator, a rotating table, a detector collimator, a detector and an analysis module. The low- and medium-level nuclear waste barrel is placed on the rotating table. The rotating table can drive the low- and medium-level nuclear waste barrel to rotate along the vertical axis of the low- and medium-level nuclear waste barrel. The transmission source collimator is installed on one side of the transmission source, and the detector collimator is installed on one side of the detector. The transmission source and the detector are respectively placed on both sides of the low- and medium-level nuclear waste barrel. The gamma rays emitted by the transmission source can be received by the detector after passing through the transmission source collimator, the low- and medium-level nuclear waste barrel and the detector collimator. The analysis module is connected to the detector and is used to receive and analyze data transmitted by the detector. The measuring method comprises the following steps: Step 1: Divide the low- and intermediate-level nuclear waste barrels into several layers along the height direction and number them. Within each layer, divide the barrels into several concentric rings of equal thickness and number them, with the rotation axis of the barrel as the axis. Assume that the distribution of the radioactivity and the distribution of the dielectric material in each layer and ring is uniform. Step 2: The detector and the transmission source perform transmission measurements on the barrels of low- and medium-level nuclear waste layer by layer and ring by ring starting from the bottom layer. A ring measurement line is set up on each layer and ring. The ring measurement line just passes horizontally through the position of half the thickness of the ring to be measured. The specific positions of the transmission source and the detector are adjusted so that the line connecting the transmission source and the detector coincides with the ring measurement line. The transmission measurement is performed on the barrels of low- and medium-level nuclear waste ring by ring to obtain the transmittance T of the characteristic energy peak of the transmission source at the ring measurement line of each layer. c , where the inner ring line must pass through the corresponding ring and the outer ring; Step 3: Use the T obtained from the transmission measurement c Calculate the linear attenuation coefficient μ of the medium of each layer of the ring measurement line c and the equivalent density ρ c , for the equivalent density ρ c Correction is performed to obtain the corrected equivalent density of each layer and each ring; Step 4: The low- and medium-level nuclear waste barrel rotates at a constant speed, and self-emission measurements are performed on the barrel to obtain the activity of each layer and each ring. The distortion-corrected equivalent density of each layer and each ring obtained in Step 3 is reconstructed to obtain the system full energy peak detection efficiency of each layer and each ring. In step 4, when measuring the activity of each ring in each layer through self-emission measurements of the low- and medium-level nuclear waste drums, the activity of the inner ring will inevitably be affected by the outer ring due to the ring separation. Therefore, the activity of each ring is corrected for inter-ring crosstalk, and a correction factor is added to deduct the contribution of other rings to the count of the current ring. The correction factor is selected as follows: considering all the nuclides and media involved in the nuclear waste drum, a database of the activity and corresponding correction factors of each ring under different media and nuclide conditions is established based on a layered and ring-by-ring gamma scanning digital simulation platform. The activity of each ring measured experimentally is compared with the data in the database to find the closest value, and the corresponding correction factor is used as the correction factor for the activity of each ring in the actual measurement; Step 5: Perform inter-ring crosstalk correction, add up the corrected activities of each ring in the same layer, and then add up the activities of each layer to obtain the total activity in the low- and medium-level nuclear waste barrel.

2. The method for measuring the activity of low- and intermediate-level nuclear waste barrels according to claim 1, wherein: The analysis module is a layered and ring-by-ring gamma scanning digital simulation platform.

3. The method for measuring the activity of low- and intermediate-level nuclear waste barrels according to claim 2, wherein: In step 3, the T c Calculate the linear attenuation coefficient μ of the medium of each layer of the ring measurement line c and the equivalent density ρ c The specific formula used is: Among them, N is the total number of rings in the layer, μ i is the linear absorption coefficient of the medium of the i-th ring to the gamma ray of a specific energy, L i,K is the half value of the track length of the transmission source beam passing through the i-th ring during the K-th transmission measurement of the current layer. Its size is only related to the sample radius and the ring division strategy. It can be solved through geometric operations. It is agreed that K = 1 means that the transmission source beam only passes through the outermost ring, that is, the first ring. μ m is the mass attenuation coefficient of the measured object for a characteristic γ-ray of a certain characteristic energy, ρ is the equivalent density, is the transmittance of gamma rays of a specific energy to the medium of the i-th ring, I and I0 are the full energy peak count rates of a certain characteristic energy of the transmission source obtained by open beam measurement with and without the presence of low- and medium-level nuclear waste barrels, and the T of each ring in the transmission measurement is converted to c Substituting the above formula, we can get the linear attenuation coefficient μ of the medium of each layer of the ring measurement line: c and the equivalent density ρ c , D is the path length of the transmitted ray penetrating the measurement object when it is an ideal beam.

4. The method for measuring the activity of low- and intermediate-level nuclear waste barrels according to claim 3 is characterized by: In step 3, a scale model of a medium and low level nuclear waste barrel is preset in advance on the digital simulation platform for layered and ring-shaped γ scanning, and the transmittance of the characteristic energy peak under different equivalent densities and the path length of the transmission ray penetrating the measurement object is entered. c The bisection method is used for iterative processing to obtain the corrected equivalent density of each ring in each layer. Starting from the outermost ring of a certain layer, the correction is carried out from the outer ring to the inner ring. The specific steps are to first set the interval containing the density of each ring, and then bring in the iterative equivalent density ρ c * Get an iterative equivalent transmittance T C * , compared with T C and T C * Size, T C * Greater than T C The iterative equivalent density ρ at this time c * As the minimum value of the set density range, T C * Less than T C The iterative equivalent density ρ at this time c * As the maximum value of the set density interval, then take the average of the minimum and maximum values as the iterative equivalent density ρ of the next iteration c * , when the adjusted T C * Close to the actual measured transmittance T C When the correction of one ring of transmission reconstruction distortion is completed, the equivalent density of the outermost ring after correction is ρ c * .

5. The method for measuring the activity of low- and intermediate-level nuclear waste barrels according to claim 4, wherein: In step 3, the density of the inner ring is corrected based on the result of the correction of the outer adjacent ring. Each correction is performed according to the method described in claim 4 until the density correction of each ring in the current layer is completed. Then, the density correction is performed on each ring of all layers, and finally the corrected equivalent density of each ring in each layer is obtained.

6. The method for measuring the activity of low- and intermediate-level nuclear waste barrels according to claim 5, wherein: In step 4, the system full energy peak detection efficiency of each layer and each ring is obtained as follows: based on the layered and ring-by-layer γ scanning digital simulation platform, the equivalent density is obtained by transmission ring-by-ring reconstruction distortion correction to reconstruct the experimental model, starting from measuring the γ count of the first ring of the first layer, each layer and each ring is set as a single body source to obtain the characteristic energy γ count obtained by the detector, and the ratio of the characteristic energy γ count obtained by the detector to the corresponding characteristic γ count of the emission is the system full energy peak detection efficiency of the corresponding nuclide in the detector of the layer and the ring in different layers and rings. After completing the simulation measurement of the system full energy peak detection efficiency of the first layer and the first ring, the simulation of the system full energy peak detection efficiency of each ring and each layer corresponding to the γ counts of different rings and layers is carried out in sequence until the system full energy peak detection efficiency of all layers and rings is completed.

7. The method for measuring the activity of low- and intermediate-level nuclear waste barrels according to claim 6, wherein: In step 5, the total activity in the barrel of low- and intermediate-level nuclear waste is calculated as follows: S(E)'=S(E)·η (3) S(E) c =∑S(E)” (5) Where S(E) is the full energy peak count of a ring with a characteristic energy of E, η is the correction factor, which refers to the ratio of the count obtained when only the current ring is the body source to the count obtained when the current ring and other rings are the body sources, S(E)' is the count of a ring with a characteristic energy of E after crosstalk correction, S(E)" is the full energy peak count of a ring with a characteristic energy of E, and S(E) C is the sum of the counts of each ring in the layer, t is the single measurement time of each ring, and the measurement time of each ring is consistent. T is the reconstructed value of the total activity of gamma rays with characteristic energy E emitted by the nuclides in the waste barrel, S0 is the total activity of gamma rays with characteristic energy E emitted by the nuclides in the barrel, σ is the relative error between the true value and the reconstructed value of the activity of the radioactive source in the barrel, and ε is the system full energy peak detection efficiency of each ring.

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