CN115542368A - Device and method for measuring medium-low-emission nuclear waste bucket - Google Patents
Device and method for measuring medium-low-emission nuclear waste bucket Download PDFInfo
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Abstract
The invention discloses a device and a method for measuring a middle-low nuclear waste barrel, wherein the device comprises: the invention provides a transmission source, a transmission source collimation, a rotating platform, a detector collimation, a detector, a transmission source platform and the like, wherein the method comprises the steps of dividing a waste barrel into a plurality of layers along the axial direction and numbering, rotating the waste barrel, assuming that a medium and a radionuclide to be detected are uniformly distributed in a same-layer ring, obtaining the transmissivity of a characteristic energy peak of each ring in transmission measurement so as to obtain the equivalent density of each ring, and providing a method for correcting the reconstruction distortion of the transmission ring by using a dichotomy principle based on a layered ring-dividing gamma scanning digital simulation platform.
Description
Technical Field
The invention belongs to the technical field of nuclear industry, and particularly relates to a device and a method for measuring a medium-low-emission nuclear waste bucket.
Background
In view of the rapid development of nuclear power industry and the unprecedented increase of the number of nuclear power plants, a great amount of radioactive wastes will inevitably be generated. Sources of radioactive waste include the concentration and post-treatment stages of nuclear fuel cycles, nuclear power plant operating processes, radioisotope production and use processes, decommissioning of nuclear power facilities, and the nuclear weapons industry. The technical regulation for temporary storage of solid waste in low and medium horizontal radioactive state in nuclear power plant (GB 14589-1993) issued by the technical supervision agency states that the temporary storage location of waste has to specify the information of waste source, waste type and specific activity, surface radiation level and pollution level, and the waste barrel is required to enter the temporary storage warehouse to measure the radioactive substance therein, and the currently adopted methods include Segmented Gamma Scanning (SGS), chromatographic Gamma Scanning (TGS), SGS, which is a measurement principle that the waste barrel is axially divided into several layers, assuming that the substances and nuclides in the layers are uniformly distributed, and simultaneously the waste barrel is rotated at a constant speed (reducing the non-uniform distribution of the transverse medium and nuclides in the barrel), the radioactive nuclides are sequentially measured by a detector, and the total activity is obtained by summation, and in the SGS measurement, assuming that the medium density and radioactive nuclides are uniformly distributed in the layers, the actual measurement, the medium density and radioactive nuclides of the measured sample are difficult to completely satisfy the uniform conditions in the layers, and the reconstructed real activity value is quite large in error. TGS provided on the basis of SGS technology in the nineties of the twentieth century is an application of CT technology in gamma radioactive nuclide nondestructive quantitative measurement, the TGS technology not only carries out axial delamination on a sample to be measured, but also divides the delamination into a plurality of blocks, assumes that the radioactive nuclides and media in each block are uniformly distributed, then carries out delamination and ring measurement on the sample, estimates the content of the radioactive nuclides in each block after carrying out self-absorption correction on the basis, integrates the nuclide quantity of each block to obtain the nuclide content of the whole waste bucket, and compares the advantages and the limitations of the two to know, the SGS measurement process is simple, the efficient measurement time is short, the method is suitable for industrial batch detection, but the defect of low detection precision exists in the non-uniform object due to difficult accurate analysis, the TGS can accurately reconstruct the medium and radioactive distribution in the bucket, but the process is complex and the low efficiency, and the large-scale application of nuclear waste bucket detection is limited.
Disclosure of Invention
The invention belongs to the defects in the prior art, and provides a device and a method for measuring a medium-low radioactive nuclear waste barrel, which can not only keep the advantages of simple and quick layered gamma scanning, but also have the measurement accuracy comparable to the layered gamma scanning, and the measurement method can be called as an SRGS (segmented-Ring-transformed gamma scanning, SRGS) technology.
In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:
the utility model provides a well low-level nuclear waste bucket activity measuring device which characterized in that: the nuclear waste material analysis device comprises a transmission source, a transmission source collimator, a rotating platform, a detector collimator, a detector and an analysis module, wherein a middle-low-level nuclear waste barrel is arranged on the rotating platform, the rotating platform can drive the middle-low-level nuclear waste barrel to rotate along the vertical axis of the middle-low-level nuclear waste barrel as an axis, the transmission source collimator is arranged on one side of the transmission source, the detector collimator is arranged on one side of the detector, the transmission source and the detector are respectively arranged on two sides of the middle-low-level nuclear waste barrel, gamma rays emitted by the transmission source can be received by the detector after passing through the transmission source collimator, the middle-low-level nuclear waste barrel and the detector collimator, and the analysis module is connected with the detector and used for receiving and analyzing data transmitted by the detector.
In order to optimize the technical scheme, the specific measures adopted further comprise:
the analysis module is a layered ring-divided gamma scanning digital simulation platform.
A method for measuring the activity of a waste bucket with a medium-low level nuclear comprises the following steps:
step 1: dividing the medium-low-level nuclear waste barrel into a plurality of layers along the height direction and numbering the layers, dividing the layers into a plurality of concentric rings with equal thickness and numbering the rings by taking a rotating shaft of the medium-low-level nuclear waste barrel as an axis, and assuming that the radioactivity distribution and the medium material distribution of samples in each layered ring are uniform;
step 2: detector and transmission sourcePerforming transmission measurement layer by layer from the bottommost layer of the middle-low radioactive nuclear waste barrel, setting a ring measuring line on each ring of each layer, enabling the ring measuring line to just horizontally penetrate through the position of half thickness of a sub-ring to be measured, adjusting the specific positions of a transmission source and a detector to enable a connecting line of the transmission source and the detector to be superposed with the ring measuring line, performing transmission measurement on the middle-low radioactive nuclear waste barrel ring by ring, and obtaining the transmissivity T of a characteristic energy peak of the transmission source at the ring measuring line of each layer c Wherein the inner ring profile necessarily passes through the corresponding ring and the outer ring;
and step 3: t obtained by transmission measurement c Calculating the line attenuation coefficient mu of the medium of each layer of loop measuring line c And equivalent density ρ c Equivalent density ρ c Correcting to obtain the corrected equivalent density of each ring of each layer;
and 4, step 4: the middle-low nuclear waste barrel rotates at a constant speed, the middle-low nuclear waste barrel performs self-emission measurement to obtain the activity of each ring of each layer, the equivalent density after distortion correction is reconstructed by each ring of each layer obtained in the step 3, and the system full-energy peak detection efficiency of each ring of each layer is obtained
And 5: and (4) performing inter-ring crosstalk correction, adding the corrected activities of the rings on the same layer, and adding the activities of the layers to obtain the total activity in the middle-low nuclear waste bucket.
In step 3, T obtained by transmission measurement is used c Calculating the line attenuation coefficient mu of the medium of each layer of loop measuring line c And equivalent density ρ c The specific formula used is:
wherein N is the total number of rings in the layer, mu i Is the linear absorption coefficient, L, of the ith ring medium to gamma rays with specific energy i,K When the Kth transmission measurement of the current layer is carried out, the transmission source beam passes through the diameter of the ith ringThe trace length is half value, the size is only related to the radius of the sample and the ring dividing strategy, the solution can be realized through geometric operation, the convention K =1 represents that the transmission source beam only passes through the outermost ring, namely the 1 st ring, mu m For measuring the mass attenuation coefficient of the object for the characteristic gamma-ray of a certain characteristic energy, p is the equivalent density,
transmissivity of I-th ring medium for gamma ray of specific energy, I and I 0 In order to obtain the full energy peak counting rate of certain characteristic energy of the transmission source by the beam opening measurement of the transmission source when the middle-low level nuclear waste barrel exists and the middle-low level nuclear waste barrel does not exist, the T of each ring in the transmission measurement is measured c The line attenuation coefficient mu of the medium of each layer of ring measuring line can be obtained by substituting the formula c And equivalent density ρ c And D is the path length of the transmitted ray penetrating the measurement object in the case of an ideal beam.
In step 3, presetting an equal proportion model of the middle-low nuclear waste barrel in advance on a layered ring-dividing gamma scanning digital simulation platform, recording the transmissivity of a characteristic energy peak under different equivalent densities and transmission ray penetration measuring object path lengths, and carrying out equivalent density rho pair on the layered ring-dividing gamma scanning digital simulation platform c Adopting dichotomy to carry out iterative processing, obtaining the corrected equivalent density of each ring of each layer by correction, starting from the outermost ring of a certain layer, sequentially correcting from the outer ring to the inner ring, and specifically, firstly setting an interval containing the density of each ring and bringing the interval into the iterative equivalent density rho c * Obtaining an iterative equivalent transmission T C * Comparing T C And T C * Size of (C), T C * Greater than T C The iterative equivalent density at this time is rho c * As the minimum value of the set density interval, T C * Less than T C The iterative equivalent density at this time is rho c * As the maximum value of the set density interval, and then taking the average value of the minimum value and the maximum value as the iteration equivalent density rho of the next iteration c * When adjusted T C * Close to the actually measured transmission T C Then completing the correction of one-ring transmission reconstruction distortion, wherein the equivalent density after the correction of the outermost ring is rho c * 。
In step 3, density correction is performed on the inner ring again based on the result of the correction of the outer adjacent ring, each time according to the method of claim 5 until the density correction of each ring in the current layer is completed, then density correction is performed on each ring of all layers, and finally the corrected equivalent density of each ring of each layer is obtained.
In step 4, when the self-emission measurement is performed on the middle-low-level nuclear waste bucket to obtain the activity of each layer of rings, the activity of the inner ring is inevitably influenced by the outer ring when the activity of the inner ring is measured due to ring division, so that the inter-ring crosstalk of the activity of each ring is corrected, and a correction factor is added to deduct the counting contribution of other rings to the current ring.
The correction factors are selected as follows: considering all related nuclides and mediums in the nuclear waste bucket, establishing a database of the activity of each ring and corresponding correction factors obtained by the fact that each ring is under different mediums and nuclides based on a layered ring-division gamma scanning digital simulation platform, searching the closest value of the activity of each ring measured through experiments and data in the database, and taking the corresponding correction factor as the correction factor of the activity of each ring in actual measurement.
In step 4, the system full energy peak detection efficiency of each ring of each layer is obtained as follows: based on a layered ring-dividing gamma scanning digital simulation platform, equivalent density is obtained through transmission ring-dividing reconstruction distortion correction to carry out experimental model reconstruction, the characteristic energy gamma counts obtained by a detector are obtained by sequentially setting each layer of rings as a single source from the measurement of the gamma count of a first layer of first rings, the ratio of the characteristic energy gamma counts obtained by the detector to the corresponding emitted characteristic gamma counts is the system full-energy peak detection efficiency of the ring detector corresponding to the nuclide of the layer in different layers and different rings, and after the simulation measurement of the system full-energy peak detection efficiency of the first layer of first rings is completed, the simulation of the system full-energy peak detection efficiency of each layer of each corresponding ring is sequentially carried out when the gamma counts of different layers of different rings are measured in a simulated manner until the system full-energy peak detection efficiency of each layer of each ring is completed.
In the step 5, the method for calculating the total activity in the medium-low-level nuclear waste bucket comprises the following steps:
S(E)'＝S(E)·η
(3)
S(E) c ＝∑S(E)”
(5)
wherein S (E) is the total energy peak count of E, eta is a correction factor, which is the ratio of the count obtained when only the current ring is in the subject to the count obtained when the current ring and other rings are in the subject, S (E) 'is the count of E, which is the corrected characteristic energy of crosstalk of a ring, S (E)' is the total energy peak count of E, which is the emission characteristic energy of a ring, S (E) C The sum of the counts of the rings in the layer, t is the single measurement time of each ring, and the measurement time of each ring is consistent, S (E) T Is the reconstructed value of the total activity of gamma rays with characteristic energy E emitted by the nuclear element in the waste bin, S 0 The total activity of gamma rays with characteristic energy E emitted by the kernel element in the bucket is sigma of the relative error between the real value and the reconstructed value of the activity of the radioactive source in the bucket, and epsilon is the system full energy peak detection efficiency of each ring.
The invention has the beneficial effects that:
1. based on a layered ring-dividing gamma scanning digital simulation platform, transmission ring-dividing reconstruction distortion correction is carried out on the linear attenuation coefficient of each ring obtained by transmission measurement, the equivalent density of each ring can be corrected accurately, the significance is brought to the ring-dividing reconstruction of the waste bucket, the system detection efficiency of each ring can be simulated accurately, and the accuracy of measuring the total activity of the waste bucket is improved.
2. Compared with the traditional SGS, in the SRGS, in the rotation measurement process by utilizing a cylindrical waste barrel, a medium and the radionuclide to be measured which are non-uniformly distributed in the SRGS are axially and symmetrically distributed to a certain degree relative to a detector, on the basis, a layered ring-divided SRGS measurement analysis model is established, the inside of the SRGS is divided into a plurality of ring sources, the medium and the nuclide of each ring are different, the radioactivity distribution and the medium material distribution of a sample in each layered ring are uniform, the homogenization assumption of the SGS measurement is changed into non-uniformity treatment which accords with the actual condition, and the detection precision is greatly improved.
3. Compared with TGS, SRGS simplifies the process, greatly reduces the measurement time, and has no obvious difference from the detection precision of SRGS. Compared with the SGS, the SRGS detection precision is greatly improved, the precision of waste barrel activity measurement is improved while the measurement time is ensured, and the split-ring density reconstruction distortion is corrected by combining a digital simulation platform, so that the measurement process is simplified, the split-ring reconstruction can be accurately performed, the measurement result is greatly improved, and the accuracy of the activity of the measured sample is ensured.
Drawings
FIG. 1 is a schematic view of the sample split ring of the present invention
FIG. 2 is a schematic view of the sample split ring of the present invention.
Fig. 3 is a schematic view of the layered ring-divided gamma scanning transmission measurement of the present invention.
FIG. 4 is a schematic diagram of distortion correction algorithm for split-ring reconstruction according to the present invention.
Fig. 5 is a schematic diagram of the layered and looped gamma scan self-emission measurement of the present invention.
Fig. 6 is a schematic diagram of inter-layer ring crosstalk.
The reference numbers in the figures are: the device comprises a transmission source 1, a transmission source collimator 2, a rotary table 3, a detector collimator 4, a detector 5 and a middle-low-level nuclear waste bucket 6.
Detailed Description
Embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
The invention provides a new detection technology for the measurement of the medium-low level nuclear waste barrel, and the method not only keeps the advantages of simplicity and rapidness of SGS measurement, but also achieves the aim of small difference with TGS measurement precision, and can guarantee the efficiency and the measurement precision, thereby guaranteeing the accuracy of nuclear waste barrel measurement data.
The invention will be described in further detail with reference to the accompanying drawings, in which:
as shown in fig. 1 and 2, the nuclear waste barrel is divided into a plurality of layers along the height direction and numbered, the sample is divided into a plurality of concentric rings with equal thickness and numbered in the layer by taking the rotating shaft as the center, and the radioactivity distribution and the medium material distribution of the sample in each sub-ring are assumed to be uniform. Numbering the sub-rings in the barrel, and numbering the sub-rings in the barrel in a descending order from the sample: 1,2, \ 8230, wherein S and S are total number of layers, and the sub-rings are numbered in ascending order from outside to inside: 1,2, \ 8230;, N i ，N i Is the total number of split rings of the ith tier.
As shown in fig. 3, transmission measurement is performed on a sample to be measured layer by layer, and the specific process is as follows: and adjusting the transmission source, the collimator of the transmission source, the detector and the specific collimating position of the detector, horizontally moving the sample barrel to be measured to a position where a connecting line of the transmission source and the detector just penetrates through half of the thickness of the sub-ring to be measured, and then performing transmission measurement to obtain the transmissivity of the characteristic energy peak of the transmission source at the position.
After the characteristic energy peak transmissivity of the transmission source in each ring is obtained, the density obtained by ring division reconstruction is corrected, and the transmissivity T obtained based on the cone-beam transmission measurement data is obtained through a layered ring division gamma scanning measurement device C And obtaining corresponding T obtained by transmission measurement by using Beer formula c Calculating the line attenuation coefficient mu of the medium of each layer of loop measuring line c And equivalent density ρ c ：
Wherein N is the total number of rings in the layer, mu i Is specific to the ith ring mediumLinear absorption coefficient of energy gamma ray, L i,K When the Kth transmission measurement of the current layer is carried out, the length of the track of the transmission source beam passing through the ith ring is half, the size of the track is only related to the radius of a sample and a ring dividing strategy, the solution can be obtained through geometric operation, and the convention K =1 indicates that the transmission source beam only passes through the outermost ring, namely the 1 st ring, mu m For measuring the mass attenuation coefficient of the object for the characteristic gamma-ray of a certain characteristic energy, p is the equivalent density,
transmissivity of ith ring medium for gamma rays of specific energy, I and I 0 The full energy peak counting rate of certain characteristic energy of the transmission source is obtained by the transmission source beam-opening measurement when the middle-low level nuclear waste barrel exists and the middle-low level nuclear waste barrel does not exist, and the T of each ring in the transmission measurement c The line attenuation coefficient mu of the medium of each layer of ring measuring line can be obtained by substituting the formula c And equivalent density ρ c And D is the path length through the measurement object with the transmitted ray as the ideal beam.
As shown in fig. 4, a middle-low nuclear waste barrel equal proportion model is preset in advance on a layered ring-divided gamma scanning digital simulation platform, the transmissivity of a characteristic energy peak under different equivalent densities and transmission ray penetration measuring object path lengths is recorded, and the equivalent density rho is measured on the layered ring-divided gamma scanning digital simulation platform c Adopting dichotomy to carry out iterative processing, obtaining the corrected equivalent density of each ring of each layer by correction, starting from the outermost ring of a certain layer, sequentially correcting from the outer ring to the inner ring, and specifically, firstly setting an interval containing the density of each ring and bringing the interval into the iterative equivalent density rho c * Obtaining an iterative equivalent transmission T C * Comparison of T C And T C * Size of (D), T C * Greater than T C The iterative equivalent density rho at the moment c * As the minimum value of the set density interval, T C * Less than T C The iterative equivalent density rho at the moment c * As the maximum value of the set density interval, and then taking the average value of the minimum value and the maximum value as the iteration of the next iterationGeneration of equivalent density rho c * When adjusted T C * Close to the actually measured transmission T C Then completing the correction of one-ring transmission reconstruction distortion, wherein the equivalent density after the correction of the outermost ring is rho c * And performing density correction on the inner ring based on the correction result of the outer adjacent ring until the density correction of all the rings is completed, and performing density correction on each ring of all the layers to obtain the corrected equivalent density of each ring of each layer.
As shown in fig. 5 and 6, after the transmission reconstruction distortion correction is completed, the self-emission measurement (without adding a transmission source) is performed, the steps of the self-emission measurement are consistent with those of the transmission measurement, the density of each ring after the ring reconstruction distortion correction is adopted, and the system total energy peak detection efficiency epsilon of each ring is obtained based on the layered and layered ring-divided gamma scanning digital simulation platform, so that the activity of each ring is obtained.
The correction factors are selected as follows: considering all related nuclides and mediums in the nuclear waste bucket, establishing a database of the activity of each ring and corresponding correction factors obtained by the fact that each ring is under different mediums and nuclides based on a layered ring-division gamma scanning digital simulation platform, searching the closest value of the activity of each ring measured through experiments and data in the database, and taking the corresponding correction factor as the correction factor of the activity of each ring in actual measurement.
The activity obtained by multiplying the activity of each ring by the correction factor is the final activity of each ring, and the final activities are added layer by layer one by one to obtain the total activity.
S(E)'＝S(E)·η
(3)
S(E) c ＝∑S(E)”
(5)
Wherein S (E) is the total energy peak count of E, eta is a correction factor, which is the ratio of the count obtained when only the current ring is in the body source to the count obtained when the current ring and other rings are in the body source, S (E) 'is the count of E after crosstalk correction of a ring, S (E)' is the total energy peak count of E in one ring of emission characteristic energy, S (E) C Is the sum of the counts of the rings in the layer, t is the single measurement time of each ring, and the measurement time of each ring is consistent, S (E) T Is the reconstructed value of the total activity of gamma rays with characteristic energy E emitted by the nuclear element in the waste bin, S 0 The total activity of gamma rays with characteristic energy E emitted by the kernel element in the bucket is sigma of the relative error between the real value and the reconstructed value of the activity of the radioactive source in the bucket, and epsilon is the system full energy peak detection efficiency of each ring.
The above are only preferred embodiments of the present invention, and the scope of the present invention is not limited to the above examples, and all technical solutions that fall under the spirit of the present invention belong to the scope of the present invention. It should be noted that modifications and adaptations to those skilled in the art without departing from the principles of the present invention may be apparent to those skilled in the relevant art and are intended to be within the scope of the present invention.
Claims (10)
1. The utility model provides a well low nuclear waste bucket activity measuring device which characterized by: the nuclear waste material analysis device comprises a transmission source, a transmission source collimator, a rotating platform, a detector collimator, a detector and an analysis module, wherein a middle-low-level nuclear waste barrel is arranged on the rotating platform, the rotating platform can drive the middle-low-level nuclear waste barrel to rotate along the vertical axis of the middle-low-level nuclear waste barrel as an axis, the transmission source collimator is arranged on one side of the transmission source, the detector collimator is arranged on one side of the detector, the transmission source and the detector are respectively arranged on two sides of the middle-low-level nuclear waste barrel, gamma rays emitted by the transmission source can be received by the detector after passing through the transmission source collimator, the middle-low-level nuclear waste barrel and the detector collimator, and the analysis module is connected with the detector and used for receiving and analyzing data transmitted by the detector.
2. The activity measuring device for the middle-low nuclear waste bin as claimed in claim 1, wherein: the analysis module is a layered ring-divided gamma scanning digital simulation platform.
3. A method for measuring the activity of a waste material bucket with a medium-low radioactive core is characterized by comprising the following steps: the method comprises the following steps:
step 1: dividing the medium-low-level nuclear waste barrel into a plurality of layers along the height direction and numbering the layers, dividing the layers into a plurality of concentric rings with equal thickness and numbering the rings by taking a rotating shaft of the medium-low-level nuclear waste barrel as an axis, and assuming that the radioactivity distribution and the medium material distribution of samples in each layered ring are uniform;
step 2: the detector and the transmission source perform transmission measurement layer by layer from the bottommost layer of the middle-low nuclear waste barrel, each ring of each layer is provided with a ring measuring line, the ring measuring line just horizontally passes through the position of half of the thickness of the sub-ring to be measured, the specific positions of the transmission source and the detector are adjusted to ensure that the connecting line of the transmission source and the detector is superposed with the ring measuring line, the transmission measurement is performed ring by ring on the middle-low nuclear waste barrel, and the transmissivity T of the characteristic energy peak of the transmission source at the ring measuring line of each layer is obtained c Wherein the inner ring profile necessarily passes through the corresponding ring and the outer ring;
and step 3: t obtained by transmission measurement c Calculating the line attenuation coefficient mu of the medium of each layer of loop measurement line c And equivalent density ρ c Equivalent density ρ c Correcting to obtain the corrected equivalent density of each ring of each layer;
and 4, step 4: the middle-low nuclear emptying waste bucket rotates at a constant speed, the middle-low nuclear emptying waste bucket carries out self-emission measurement to obtain the activity of each layer of ring, the equivalent density after distortion correction is rebuilt by each layer of ring obtained in the step 3, and the system full energy peak detection efficiency of each layer of ring is obtained
And 5: and (4) inter-ring crosstalk correction is carried out, the corrected activities of the rings on the same layer are added, and then the activities of the layers are added to obtain the total activity in the middle and low-level nuclear waste barrel.
4. The method for measuring the activity of the waste bucket with the medium-low radioactive cores as claimed in claim 3, wherein the method comprises the following steps:
in step 3, T obtained by transmission measurement is used c Calculating the line attenuation coefficient mu of the medium of each layer of loop measuring line c And equivalent density ρ c The specific formula used is:
wherein N is the total number of rings in the layer, mu i Is the linear absorption coefficient, L, of the ith ring medium to gamma rays with specific energy i,K When the Kth transmission measurement of the current layer is carried out, the length of the track of the transmission source beam passing through the ith ring is half, the size of the track is only related to the radius of a sample and a ring dividing strategy, the solution can be obtained through geometric operation, and the convention K =1 indicates that the transmission source beam only passes through the outermost ring, namely the 1 st ring, mu m For measuring the mass attenuation coefficient of the object for the characteristic gamma-ray of a certain characteristic energy, p is the equivalent density,
transmissivity of I-th ring medium for gamma ray of specific energy, I and I 0 The full energy peak counting rate of certain characteristic energy of the transmission source is obtained by the transmission source beam-opening measurement when the middle-low level nuclear waste barrel exists and the middle-low level nuclear waste barrel does not exist, and the T of each ring in the transmission measurement c The line attenuation coefficient mu of the medium of each layer of ring measuring line can be obtained by substituting the formula c And equivalent density ρ c And D is the path length through the measurement object with the transmitted ray as the ideal beam.
5. The method for measuring the activity of the middle-low radioactive nuclear waste bucket as claimed in claim 4, wherein the method comprises the following steps: in step 3, presetting an equal proportion model of the middle-low nuclear waste barrel in advance on a layered ring-dividing gamma scanning digital simulation platform, recording the transmissivity of a characteristic energy peak under different equivalent densities and transmission ray penetration measuring object path lengths, and carrying out equivalent density rho pair on the layered ring-dividing gamma scanning digital simulation platform c Adopting dichotomy to carry out iterative processing, obtaining the corrected equivalent density of each ring of each layer by correction, starting from the outermost ring of a certain layer, sequentially correcting from the outer ring to the inner ring, and specifically, firstly setting an interval containing the density of each ring and bringing the interval into the iterative equivalent density rho c * Obtaining an iterative equivalent transmittance T C * Comparison of T C And T C * Size of (D), T C * Greater than T C The iterative equivalent density rho at the moment c * As the minimum value of the set density interval, T C * Less than T C The iterative equivalent density at this time is rho c * As the maximum value of the set density interval, and then taking the average value of the minimum value and the maximum value as the iteration equivalent density rho of the next iteration c * When adjusted T C * Close to the actually measured transmission T C Then completing the correction of one-ring transmission reconstruction distortion, wherein the equivalent density after the correction of the outermost ring is rho c * 。
6. The method for measuring the activity of the waste bucket with the medium-low radioactive core as claimed in claim 5, wherein: in step 3, density correction is performed on the inner ring again based on the result of the correction of the outer adjacent ring, each time according to the method of claim 5 until the density correction of each ring in the current layer is completed, then density correction is performed on each ring of all layers, and finally the corrected equivalent density of each ring of each layer is obtained.
7. The method for measuring the activity of the waste bucket with the medium-low radioactive cores as claimed in claim 6, wherein the method comprises the following steps: in step 4, when the self-emission measurement is performed on the middle-low-level nuclear waste bucket to obtain the activity of each layer of rings, the activity of the inner ring is inevitably influenced by the outer ring when the activity of the inner ring is measured due to ring division, so that the inter-ring crosstalk of the activity of each ring is corrected, and a correction factor is added to deduct the counting contribution of other rings to the current ring.
8. The method for measuring the activity of the waste bucket with the medium-low radioactive core as claimed in claim 7, wherein: the correction factors are selected as follows: considering all related nuclides and mediums in the nuclear waste bucket, establishing a database of the activity of each ring and corresponding correction factors obtained by the ring under different medium and nuclide conditions based on a layered ring-division gamma scanning digital simulation platform, searching the closest value of the activity of each ring measured through experiments and data in the database, and taking the corresponding correction factor as the correction factor of the activity of each ring in actual measurement.
9. The method for measuring the activity of the waste bucket with the medium-low radioactive core as claimed in claim 8, wherein: in step 4, the system full energy peak detection efficiency of each ring of each layer is obtained in the following manner: based on a layered ring-dividing gamma scanning digital simulation platform, equivalent density is obtained through transmission ring-dividing reconstruction distortion correction to carry out experimental model reconstruction, each layer of rings is sequentially set as a single source from the measurement of gamma count of a first layer of first rings to obtain characteristic energy gamma count obtained by a detector, the ratio of the characteristic energy gamma count obtained by the detector to the corresponding emitted characteristic gamma count is the system full-energy peak detection efficiency of different rings of corresponding nuclides of the ring detector of the layer, and after the system full-energy peak detection efficiency simulation measurement of the first layer of first rings is completed, the system full-energy peak detection efficiency simulation of each layer of corresponding rings is sequentially carried out when the gamma counts of different rings are measured in a simulation mode until the system full-energy peak detection efficiency of each layer of all layers is completed.
10. The method for measuring the activity of the waste bucket with the middle or low radioactive nuclear as claimed in claim 9, wherein: in the step 5, the method for calculating the total activity in the medium-low-level nuclear waste bucket comprises the following steps:
S(E)'＝S(E)·η (3)
S(E) c ＝∑S(E)” (5)
wherein S (E) is the total energy peak count of E, eta is a correction factor, which is the ratio of the count obtained when only the current ring is in the body source to the count obtained when the current ring and other rings are in the body source, S (E) 'is the count of E after crosstalk correction of a ring, S (E)' is the total energy peak count of E in one ring of emission characteristic energy, S (E) C Is the sum of the counts of the rings in the layer, t is the single measurement time of each ring, and the measurement time of each ring is consistent, S (E) T Is the reconstructed value of the total activity of gamma rays with characteristic energy E emitted by the nuclear element in the waste bin, S 0 The total activity of gamma rays with characteristic energy E emitted by the kernel element in the barrel is sigma, the relative error between the real value and the reconstructed value of the activity of the radioactive source in the barrel is sigma, and the system total energy peak detection efficiency of each ring is epsilon.
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