CN107942365B - Method and device for measuring radioactivity of waste barrel of nuclear power station - Google Patents
Method and device for measuring radioactivity of waste barrel of nuclear power station Download PDFInfo
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- CN107942365B CN107942365B CN201711064244.6A CN201711064244A CN107942365B CN 107942365 B CN107942365 B CN 107942365B CN 201711064244 A CN201711064244 A CN 201711064244A CN 107942365 B CN107942365 B CN 107942365B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/17—Circuit arrangements not adapted to a particular type of detector
- G01T1/178—Circuit arrangements not adapted to a particular type of detector for measuring specific activity in the presence of other radioactive substances, e.g. natural, in the air or in liquids such as rain water
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Abstract
The invention discloses a method for measuring radioactivity of a waste bin of a nuclear power station, which comprises the following steps: s1, establishing a waste barrel model base, weighing the total weight of the waste barrel, and calculating a linear attenuation coefficient according to the waste barrel model and the total weight; s2, screening and determining the measuring position of the detector relative to the waste bucket according to the objective function; s3, driving the detector and/or the waste barrel to move relatively to reach a measuring position, and scanning the waste barrel in multiple directions at the measuring position to obtain a counting rate vector; and S4, calculating the distribution and the total activity of the nuclide according to the detection efficiency and the counting rate vector. According to the measuring method provided by the invention, the waste barrel is partitioned and modeled, and media in each partition in the waste barrel model are uniformly distributed, so that the method is more consistent with the reality; in addition, the invention removes a transmission source device, and can reduce the pressure of radioactive source management and radiation protection of high radioactive sources in the daily measurement process of the waste barrel by establishing a waste barrel model and weighing to calculate the linear attenuation coefficient.
Description
Technical Field
The invention relates to a radioactive waste measurement technology, in particular to a method and a device for measuring radioactivity of a waste barrel of a nuclear power station.
Background
In the field of waste bin radioactivity measurement, nondestructive detection is commonly used, wherein gamma scanning is the most widely used waste bin detection method. Because different nuclides have characteristic gamma rays with different energies, different isotope types and activities in the radioactive waste barrel can be determined by scanning and measuring the gamma rays around the waste barrel.
The gamma-ray scanning measurement technique is classified into a segmented gamma-ray scanning technique (SGS method) and a tomographic gamma-ray scanning technique (TGS method).
The chromatographic gamma scanning technology has ideal measurement precision and wide application range, and is especially superior to other measurement methods in the measurement precision of uneven materials in the barrel. However, the higher precision depends heavily on the measurement times, and the decoupling process of simultaneously solving the equation set through multiple measurements leads to a more complex measurement process and an overlong measurement time, so that the method is not suitable for the measurement work of a large number of waste drums in the nuclear power plant.
In the traditional segmented gamma scanning technology, nuclides and filling materials in a waste bucket are uniformly distributed, which is not consistent with the actual technical process of a power plant and causes great deviation of a measurement result, the segmented gamma scanning technology of the double detectors is provided with two detectors, and transmission measurement is firstly carried out to obtain a linear attenuation coefficient of the materials in the bucket, so that the detection efficiency is calculated; establishing a monotonic function relation F (r) between the counting ratio of the two detectors and the annular distribution radius of the source item, determining the equivalent radius of the source item through the counting ratio, the F (r) and the initial detection efficiency matrix, calculating a new detection efficiency matrix under the equivalent radius of the source item to solve a new count, repeatedly iterating according to the sequence, taking the convergence value as a final count value, and summing the counts of each layer to obtain the total activity of the radionuclide in the barrel. The improved segmented gamma scanning technology introduces a decoupling variable with a radius dimension, so that a mathematical iteration process can be well utilized, and time and precision can be improved.
However, the improved segmented gamma scanning technique has the following disadvantages: (1) the constraint condition of optimal monotonicity of F (r) is not given, and the constraint condition only needs to be monotonous, so that the effect of mathematical iteration is greatly reduced; the selected initial detection efficiency is the efficiency calculated on the assumption of uniform distribution of nuclides, which is contradictory to the nonuniform distribution of the nuclides in the actual process; (2) the accuracy of detection efficiency calculation is the key for measuring the whole waste barrel, the linear attenuation coefficient of the material is the key for calculating the detection efficiency, for a small-volume barrel or a waste barrel with low filling medium density, the linear attenuation coefficient of each layer of material can be accurately measured by using a transmission source, but most of the solidification processes of the waste barrels of the nuclear power plants adopt the density of 2.0g/cm3The cement paste of (1) only a few high-energy rays can pass through, and very high activity of radioactive sources is needed, which puts very strict requirements on radioactive source management of waste barrel measurement and has very large data deviation of transmission measurement; (3) the double-detector arrangement has high requirements on the detector supporting platform, the relative position is not easy to adjust, and the difficulty in periodical calibration of the detector is high.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems of inconvenient measurement of the linear attenuation coefficient, inaccurate initial detection efficiency matrix and monotonicity of F (r) function in the existing measurement method, the measurement method and the measurement device for the radioactivity of the waste barrel are provided, wherein the relative position of the waste barrel and the detector can be flexibly adjusted, and the measurement precision is high.
The technical means for solving the technical problems of the invention is as follows: in one aspect, a method for measuring radioactivity of a waste bin of a nuclear power plant is provided, which comprises the following steps:
s1, establishing a waste barrel model base, selecting a waste barrel model corresponding to the waste barrel from the waste barrel model base, weighing the total weight of the waste barrel, and calculating a linear attenuation coefficient according to the waste barrel model and the total weight;
s2, establishing a detection efficiency database according to the linear attenuation coefficient and the geometric condition of the waste bucket model, and screening and determining the relative measurement position of the detector and the waste bucket according to an objective function;
s3, driving the detector and/or the waste bucket to move relatively to the measuring position, and scanning the waste bucket in multiple directions at the measuring position to obtain a counting rate vector;
and S4, calculating the distribution and the total activity of the nuclide according to the detection efficiency and the counting rate vector.
Preferably, step S1 includes the following sub-steps:
s11, dividing the waste barrel into three types of models: the waste bin comprises a radiation area, a filling area and a bin wall area, and the waste bin model comprises the following parameters: the size of each partition, the material of each partition, and the initial density of each partition;
s12, calculating the weight of the filling area according to the size of the filling area and the density of the filling area, calculating the weight of the barrel wall area according to the size of the barrel wall area and the density of the barrel wall area, subtracting the weight of the filling area and the weight of the barrel wall area from the total weight to obtain the weight of the radiation area, and correcting the initial density of the radiation area by using the weight of the radiation area and the size of the radiation area;
s13, calculating the mass attenuation coefficient of each subarea according to the material of each subarea;
and S14, calculating the linear attenuation coefficient of each subarea according to the initial density of the filling area, the initial density of the barrel wall area, the corrected density of the radiation area and the mass attenuation coefficient of each subarea.
Preferably, step S2 includes the following sub-steps:
s21, calculating different source item distribution radiuses and detection efficiencies corresponding to different measurement positions according to the line attenuation coefficient and the partition model geometric conditions, and establishing a detection efficiency database;
s22, screening out the detection efficiency ratios of different measurement positions according to the detection efficiency database, calculating a plurality of groups of detection efficiency ratios, and judging whether the detection efficiency ratios are lower than 10 or not-3Sifting less than 10-3According to the screened detection efficiency ratio, a plurality of F (r) functions are established, wherein the F (r) functions are detection efficiency ratio relationsA function of the radius of the source term distribution;
s23, judging whether the F (r) functions meet monotonicity one by one, if so, turning to the next step, otherwise, directly excluding the F (r) functions;
s24, obtaining the radius range of the radiation area through the waste bucket model, approximating a plurality of F (r) function curves in the radius range of the radiation area by using straight lines, calculating the least square of the deviation of each F (r) function point and the fitted straight line as a target function, and selecting the optimal F (r) function according to the target function;
and S25, and the two positions corresponding to the optimal F (r) function are recommended measurement positions.
Preferably, the relative movement of the drive probe and/or the waste bin comprises: driving the detector to translate in the Y direction and the waste bin to translate in the X direction;
performing a multi-azimuth scan of the trash can includes: the waste barrel is driven to rotate around the axis of the waste barrel so as to realize circumferential acquisition of data in the waste barrel, and the detector is driven to move along the Z direction at the measuring position so as to scan the rotating waste barrel layer by layer.
Preferably, step S4 includes the following sub-steps:
s41, calculating a detection efficiency matrix and a source item distribution vector according to the line attenuation coefficient and the counting rate vector;
and S42, calculating the total activity of the nuclide according to the source item distribution vector.
Preferably, the substep S41 specifically includes:
s411, calculating the ratio of the counting rates of the two recommended measuring positions in each layer of the waste bucket according to the two recommended measuring positions;
s412, establishing an equation set, and solving an initial source item distribution vector by using an initial detection efficiency matrix and a measurement count rate vector;
s413, calculating theoretical activity values measured by the detector at the two recommended measuring positions when the source item in each layer is independently transported to the detector, and solving the ratio of the theoretical activities measured by the two recommended measuring positions;
s414, obtaining the new source item equivalent radius of each layer;
s415, interpolating and calculating detection efficiency matrixes Ea (K) and Eb (K) of the source items when the new source item equivalent radius Ri (K) is distributed from a detection efficiency database, wherein K represents the Kth iteration process;
and S416, calculating a new source item distribution vector.
Preferably, the substep S42 specifically includes:
s421, calculating activity distribution vectors IA and IB according to the final source item distribution vectors Ia (k +1) and Ib (k + 1);
and S422, calculating the total activities A and B of the waste barrel according to IA and IB, and taking the larger vector of A and B as the final total activity.
On the other hand, the device for measuring the radioactivity of the waste barrel of the nuclear power station comprises a weighing module, a control module, a driving module and a detector which are respectively connected with the waste barrel; wherein the content of the first and second substances,
the weighing module is connected with the waste barrel and used for weighing the total weight of the waste barrel;
the control module is connected with the driving module and the detector and used for establishing a waste barrel model library, selecting a waste barrel model corresponding to a waste barrel from the waste barrel model library, calculating a linear attenuation coefficient according to the waste barrel model and the total weight, establishing a detection efficiency database according to the linear attenuation coefficient and the geometric conditions of the waste barrel model, and screening and determining the relative measurement position of the detector and the waste barrel according to an objective function;
a drive module connected to the waste bin and the detector for driving the detector and/or the waste bin to move relative to each other and to the measuring position;
the detector is used for scanning the waste bucket in multiple directions at the measuring position to obtain a counting rate vector;
and the control module is also used for calculating the distribution and the total activity of the nuclides according to the detection efficiency and the counting rate vector.
Preferably, the waste bin is divided into three categories: the waste bin comprises a radiation area, a filling area and a bin wall area, and the waste bin model comprises the following parameters: the size of each partition, the material of each partition, and the initial density of each partition;
the control module is further configured to:
calculating the weight of the filling area according to the size of the filling area and the density of the filling area, calculating the weight of the barrel wall area according to the size of the barrel wall area and the density of the barrel wall area, subtracting the weight of the filling area and the weight of the barrel wall area from the total weight to obtain the weight of the radiation area, and correcting the initial density of the radiation area by using the weight of the radiation area and the size of the radiation area;
calculating the mass attenuation coefficient of each subarea according to the material of each subarea;
and calculating the linear attenuation coefficient of each subarea according to the initial density of the filling area, the initial density of the barrel wall area, the corrected density of the radiation area and the mass attenuation coefficient of each subarea.
Preferably, the control module is further configured to:
calculating the detection efficiency corresponding to different source item distribution radiuses and different measurement positions according to the line attenuation coefficient and the partition model geometric condition, and establishing a detection efficiency database;
screening out the detection efficiency ratios of different measurement positions according to the detection efficiency database, calculating a plurality of groups of detection efficiency ratios, and judging whether the detection efficiency ratios are lower than 10-3Sifting less than 10-3Establishing a plurality of F (r) functions according to the screened detection efficiency ratios, wherein the F (r) functions are functions of the detection efficiency ratios with respect to the source term distribution radius;
judging whether the F (r) functions meet monotonicity one by one, if so, obtaining a radial range of the radiation area through a waste barrel model, approximating a plurality of F (r) function curves in the radial range of the radiation area by using straight lines, calculating the least square of the deviation of each F (r) function point and a fitted straight line as a target function, and selecting an optimal F (r) function according to the target function; otherwise directly excluding the F (r) function;
and the two positions corresponding to the optimal F (r) function are recommended measurement positions.
Preferably, the drive module comprises a trash can position drive unit, a detector height drive unit, and a rotary platform;
the waste barrel position driving unit comprises an X-axis fixing frame and an X-axis lead screw, and the X-axis lead screw is connected with an X-axis driving device and used for driving the X-axis lead screw to rotate so as to drive the waste barrel rack movably connected with the X-axis lead screw and a waste barrel above the waste barrel rack to translate along the X direction;
the detector height driving unit comprises a Z-axis fixing frame and a Z-axis lead screw, the Z-axis fixing frame is vertically fixed on the X-axis fixing frame, and the Z-axis lead screw is connected with a Z-axis driving device and used for driving a Z-axis lead screw to rotate so as to drive the Y-axis fixing frame movably connected with the Z-axis lead screw and a detector above the Y-axis fixing frame to move along the Z direction so as to scan the waste barrel layer by layer;
the detector position driving unit comprises a Y-axis fixing frame and a Y-axis screw rod, the Y-axis fixing frame is sleeved on the Z-axis screw rod in a vertically movable mode, and the Y-axis screw rod is connected with a Y-axis driving device and used for driving the Y-axis screw rod to rotate so as to drive the detector rack movably connected with the Y-axis screw rod and the detector above the detector rack to translate along the Y direction;
the rotating platform is installed on the waste bucket rack and used for driving the waste bucket to rotate around the axis of the waste bucket rack, and the detector is convenient for circumferentially collecting data in the waste bucket.
Preferably, the control module is further configured to calculate a detection efficiency matrix and a source item distribution vector according to the line attenuation coefficient and the count rate vector; and calculating the total activity of the nuclide according to the source item distribution vector.
The method and the device for measuring the radioactivity of the nuclear power station waste barrel have the following beneficial effects:
the measuring method provided by the invention divides the waste barrel into regions and carries out modeling, and the media in each region in the waste barrel model are uniformly distributed, which is more in line with the reality; in addition, the invention removes a transmission source device, and can reduce the pressure of radioactive source management and radiation protection of high radioactive sources in the daily measurement process of the waste barrel by establishing a waste barrel model and weighing to calculate the linear attenuation coefficient.
Drawings
FIG. 1 is a main flow chart of the method of measuring the radioactivity of a waste bin of the present invention;
FIG. 2 is a flow chart of the method of measuring the radioactivity of a waste bin of the present invention to obtain a line attenuation coefficient;
FIG. 3 is a schematic diagram of the operation of the waste bin radioactivity measuring device of the present invention;
fig. 4 is a schematic perspective view of a driving module of the radioactivity measuring device for a waste bin according to the present invention.
Detailed Description
The invention is further explained below with reference to the figures and examples.
Example one
The invention provides a method for measuring the radioactivity of a waste bin of a nuclear power station, and FIG. 1 is a main flow chart of the method for measuring the radioactivity of the waste bin, and referring to FIG. 1, the method comprises the following steps:
s1, establishing a waste barrel model base, selecting a waste barrel model corresponding to the waste barrel from the waste barrel model base, weighing the total weight of the waste barrel, and calculating a linear attenuation coefficient according to the waste barrel model and the total weight;
s2, establishing a detection efficiency database according to the linear attenuation coefficient and the geometric condition of the waste bucket, and screening and determining the relative measurement position of the detector and the waste bucket according to an objective function;
s3, driving the detector and/or the waste bucket to move relatively to the measuring position, and scanning the waste bucket in multiple directions at the measuring position to obtain a counting rate vector;
and S4, calculating the distribution and the total activity of the nuclide according to the detection efficiency and the counting rate vector.
In the prior art, a transmission source is generally used for measuring the attenuation coefficient of a line, as the curing process of a waste barrel mostly adopts cement paste with the density of 2.0g/cm3, a common transmission source cannot penetrate a large-volume metal barrel filled with cement at all, and only a few high-energy rays can pass through the metal barrel; even if high-energy rays can pass through a high-density large-volume waste bin, the very high activity of the radioactive source is required for obtaining an accurate linear attenuation coefficient, so that very strict requirements are brought to the radioactive source management of waste bin measurement, and the data deviation of transmission measurement is very large; the method for obtaining the linear attenuation coefficient provided by the invention is more in line with the characteristics of a waste barrel solidification process, and can reduce the pressure of radioactive source management and radiation protection of a high radioactive source in the daily waste barrel measurement process.
Further, fig. 2 is a flowchart for obtaining the line attenuation coefficient, and referring to fig. 2, step S1 includes the following sub-steps:
s11, dividing the waste barrel into three types of areas: the waste bin comprises a radiation area, a filling area and a bin wall area, and the waste bin model comprises the following parameters: the size of each partition, the material of each partition, and the initial density of each partition;
s12, calculating the weight of the filling area according to the size of the filling area and the density of the filling area, calculating the weight of the barrel wall area according to the size of the barrel wall area and the density of the barrel wall area, subtracting the weight of the filling area and the weight of the barrel wall area from the total weight to obtain the weight of the radiation area, and correcting the initial density of the radiation area by using the weight of the radiation area and the size of the radiation area;
s13, calculating the mass attenuation coefficient of each subarea according to the material of each subarea;
and S14, calculating the linear attenuation coefficient of each subarea according to the initial density of the filling area, the initial density of the barrel wall area, the corrected density of the radiation area and the mass attenuation coefficient of each subarea. The line attenuation coefficient is equal to the product of the mass attenuation coefficient and the density.
The invention does not continue the assumption that nuclides and materials in the waste barrel are uniformly distributed in the prior art, but divides the waste barrel according to the mature and stable waste solidification process of the nuclear power plant, and the assumption is more consistent with the actual situation if the nuclides and the materials are uniformly distributed in each subarea in the waste barrel. Based on the partitions and assumptions, a reasonable and reliable waste barrel model library is established according to a mature and stable waste solidification process of the nuclear power station, the waste barrel model divides the interior of a waste barrel into an irradiation area, a filling area and a barrel wall area, and the size, the material composition and the initial density of each partition are defined according to a process.
And correcting the density of the radiation area by adopting a weighing waste bucket method according to the priority that the initial density of the bucket wall area and the initial density of the filling area are credible by default so that the density of the radiation area is closer to an actual value. The line attenuation coefficient calculated by the corrected emission area density is more accurate, and the accuracy of the line attenuation coefficient enables a detection efficiency matrix calculated later to be more accurate.
And according to the partition size of the waste barrel, the length of the sections passing through different materials in the linear transmission path from different positions in the waste barrel to the front end face of the detector is determined, so that the self-absorption part of the efficiency scale can be realized in the subsequent detection efficiency calculation in a mode extremely close to the actual physical process.
Further, step S2 includes the following sub-steps:
s21, calculating different source item distribution radiuses and detection efficiencies corresponding to different measurement positions according to the line attenuation coefficient and the partition model geometric conditions, and establishing a detection efficiency database;
s22, screening out the detection efficiency ratios of different measurement positions according to the detection efficiency database, calculating a plurality of groups of detection efficiency ratios, and judging whether the detection efficiency ratios are lower than 10 or not-3Sifting less than 10-3Establishing a plurality of F (r) functions according to the screened detection efficiency ratios, wherein the F (r) functions are functions of the detection efficiency ratios with respect to the source term distribution radius;
s23, judging whether the F (r) functions meet monotonicity one by one, if so, turning to the next step, otherwise, directly excluding the F (r) functions;
s24, obtaining the radius range of the radiation area through the waste bucket model, approximating a plurality of F (r) function curves in the radius range of the radiation area by using straight lines, calculating the least square of the deviation of each F (r) function point and the fitted straight line as a target function, and selecting the optimal F (r) function according to the target function;
and S25, and the two positions corresponding to the optimal F (r) function are recommended measurement positions.
The monotonicity of the f (r) function directly determines the time consumption and accuracy of the subsequent iteration process. In the prior art, no constraint condition with optimal monotonicity of the F (r) function is given, and the F (r) function is only required to be monotonous, so that the effect of subsequent mathematical iteration is greatly reduced. According to the invention, the optimal F (r) function is screened out through the constraint conditions in the steps S22 and S23 and the objective function in the step S24, so that the time consumption of the subsequent mathematical iteration process is short, the accuracy is high, and the optimal recommended measurement position of the detector and the waste bin is determined through the optimal F (r) function, so that the matching performance of the iterative algorithm related to the subsequent optimal F (r) function is higher, namely, the matching performance of the scanning process and the mathematical iteration is improved, and the accuracy of the calculation result of the iterative algorithm is further improved.
Further, the relative movement of the drive probe and/or the trash can comprises: driving the detector to translate in the Y direction and the waste bin to translate in the X direction;
the detector translates along the X direction and the waste bucket translates along the Y direction, so that the detector and the waste bucket reach opposite measurement positions for measurement;
performing a multi-azimuth scan of the trash can includes: the waste barrel is driven to rotate around the axis of the waste barrel so as to realize circumferential acquisition of data in the waste barrel, and the detector is driven to move along the Z direction at the measuring position so as to scan the rotating waste barrel layer by layer.
Further, step S4 includes the following sub-steps:
s41, calculating a detection efficiency matrix and a source item distribution vector according to the line attenuation coefficient and the counting rate vector;
and S42, calculating the total activity of the nuclide according to the source item distribution vector.
Further, the sub-step S41 specifically includes:
s411, counting rate vectors measured by the two recommended measuring positions are Ma and Mb respectively, the ratio of the counting rates of the two recommended measuring positions in each layer of the waste barrel is calculated according to the Ma and the Mb, the counting rate ratio of each layer is substituted into an optimal F (r) function to obtain a source item equivalent radius Ri of each layer, i represents the number of layers, detection efficiency matrixes Ea and Eb corresponding to the source item equivalent radius Ri are calculated in an interpolation mode from the detection efficiency database, and the Ea and the Eb are initial detection efficiency matrixes;
s412, establishing an equation set Ea Ia Ma and Eb Ib Mb, wherein Ia and Ib are source item distribution vectors corresponding to the two recommended measurement positions respectively, and solving the initial source item distribution vectors by using the initial detection efficiency matrix and the initial counting rate vector;
s413, according to the diagonal elements of the detection efficiency matrix in the previous step and the decoupling of the source item distribution vector in the previous step, calculating theoretical activity values measured by the detector at the two recommended measurement positions when the source items in each layer are independently transported to the detector, and solving the ratio of the theoretical activities measured by the two recommended positions;
s414, substituting the ratio of the theoretical activity into the optimal F (r) function to obtain a new source item equivalent radius Ri (K) of each layer, wherein i represents the number of layers, and K represents the K-th iteration process;
s415, interpolating and calculating detection efficiency matrixes Ea (K) and Eb (K) of the source items when the new source item equivalent radius Ri (K) is distributed from the detection efficiency database, wherein K represents the Kth iteration process;
s416, solving new source item distribution vectors Ia (k +1) and Ib (k +1) according to the equation system;
s417, judging inequality
If the difference is true, ξ is a relative deviation limit, ξ determines according to the precision requirement, Iai (k +1) represents the value corresponding to the ith layer of the trash can in the source item distribution vector Ia (k +1) in the k +1 th iteration, Iai (k) represents the value corresponding to the ith layer of the trash can in the source item distribution vector Ia (k) in the k +1 th iteration, if the inequality is true, Ia (k +1) and Ib (k +1) are determined to be the final source item distribution vector, and if the inequality is not true, the next iteration is performed by skipping step S4.
According to the embodiment, a high-precision passive efficiency scale algorithm is introduced to calculate the detection efficiency, a radius-dimension decoupling variable is introduced to enable a mathematical iteration process to be well utilized, and the measurement time and the measurement precision can be improved. In order to meet the non-negative condition, namely the solved activity value of each nuclide layer cannot be negative, the selectable mathematical iterative calculation method is very limited, and the commonly used iterative algorithm meeting the non-negative condition can only obtain local optimum and cannot give global optimum, so that the final calculation result is seriously dependent on the initial value. Therefore, it is important to determine accurate initial detection efficiency, and the initial detection efficiency calculated by the existing measurement method is obtained on the premise of assuming uniform distribution of the nuclides, which is not consistent with the fact that the nuclides are not uniformly distributed. The invention utilizes the counting rate measured by the detector to correct the initial detection efficiency matrix as the iterative initial detection matrix, which is closer to the actual value of the inhomogeneous distribution of nuclides. The calculation result of the iterative algorithm is more accurate. In order to satisfy the non-negative condition that the solved nuclide activity value of each layer cannot be negative, the selectable mathematical iterative calculation method is very limited, and the commonly used MLEM calculation mode is the preferred mode of the iterative process.
Further, the sub-step S42 specifically includes:
s421, calculating activity distribution vectors IA and IB according to the final source item distribution vectors Ia (k +1) and Ib (k + 1);
and S422, calculating the total activities A and B of the waste barrel according to IA and IB, and taking the larger vector of A and B as the final total activity. Although the deviation between A and B is very small, conservative consideration is given to the vector with the larger total activity in A and B as the final confirmed total activity.
The solving process of step S4 is repeated for each characteristic energy, so as to obtain activity values of all nuclides.
Example two
The invention also provides a device for measuring the radioactivity of the waste bucket of the nuclear power station, and referring to fig. 3, fig. 3 is a working principle diagram of the device for measuring the radioactivity of the waste bucket, and the device comprises a weighing module 1, a control module 2, a driving module 3 and a detector 4 which are respectively connected with the waste bucket; wherein the content of the first and second substances,
the weighing module 1 is connected with the waste barrel 5 and is used for weighing the total weight of the waste barrel 5;
the control module 2 is connected with the driving module 3 and the detector 4 and is used for establishing a waste barrel model library, selecting a waste barrel model corresponding to a waste barrel from the waste barrel model library, calculating a linear attenuation coefficient according to the waste barrel model and the total weight, establishing a detection efficiency database according to the linear attenuation coefficient and the geometric conditions of the waste barrel model, and screening and determining the relative measurement position of the detector 4 and the waste barrel 5 according to an objective function;
a drive module 3 connected to the waste bin 5 and to the detector 4 for driving the detector 4 and/or the waste bin 5 into relative movement and to the measuring position;
the detector 4 is used for scanning the waste barrel 5 in multiple directions at the measuring position to obtain a counting rate vector;
and the control module 2 is also used for calculating the distribution and the total activity of the nuclides according to the detection efficiency and the counting rate vector.
Wherein the waste bin is divided into three categories: the waste bin comprises a radiation area, a filling area and a bin wall area, and the waste bin model comprises the following parameters: the size of each partition, the material of each partition, and the initial density of each partition;
further, the control module 2 is further configured to:
calculating the weight of the filling area according to the size of the filling area and the density of the filling area, calculating the weight of the barrel wall area according to the size of the barrel wall area and the density of the barrel wall area, subtracting the weight of the filling area and the weight of the barrel wall area from the total weight to obtain the weight of the radiation area, and correcting the initial density of the radiation area by using the weight of the radiation area and the size of the radiation area;
calculating the mass attenuation coefficient of each subarea according to the material of each subarea;
and calculating the linear attenuation coefficient of each subarea according to the initial density of the filling area, the initial density of the barrel wall area, the corrected density of the radiation area and the mass attenuation coefficient of each subarea.
The measurement apparatus provided in this embodiment is based on the measurement method provided in the first embodiment, and therefore the measurement apparatus has the same technical effects as the measurement method provided in the first embodiment, and details thereof are not repeated herein. Generally use two detectors to detect the count rate vector of two different positions among the prior art, the setting of two detectors requires highly to supporting platform, is difficult for adjusting the relative position of detector and garbage bin, and the detector is regularly calibrated the degree of difficulty great. The embodiment only uses one detector to respectively execute two cyclic scanning measurements, the two scanning cycles correspond to different relative measurement positions of the detector and the waste bucket, and the position of the detector is easy to adjust and the height of the detector is easy to control by arranging one detector.
The detector 4 and the waste barrel 5 are moved by the driving module 3, so that the relative positions of the detector 4 and the waste barrel 5 are changed, the detector 4 is moved by the driving module 3 so as to realize the measurement of different heights of the waste barrel 5, and the control module 2 is used for coordinating and controlling, so that all parts coordinate to complete the measurement steps in the first embodiment and automatically calculate. Therefore, the technical effect that can be achieved by the first embodiment can also be achieved by the apparatus, and details are not described herein.
The control module 2 is further configured to:
calculating the detection efficiency corresponding to different source item distribution radiuses and different measurement positions according to the line attenuation coefficient and the partition model geometric condition, and establishing a detection efficiency database;
screening out the detection efficiency ratios of different measurement positions according to the detection efficiency database, calculating a plurality of groups of detection efficiency ratios, and judging whether the detection efficiency ratios are lower than 10-3Sifting less than 10-3Establishing a plurality of F (r) functions according to the screened detection efficiency ratios, wherein the F (r) functions are functions of the detection efficiency ratios with respect to the source term distribution radius;
judging whether the F (r) functions meet monotonicity one by one, if so, obtaining a radial range of the radiation area through a waste barrel model, approximating a plurality of F (r) function curves in the radial range of the radiation area by using straight lines, calculating the least square of the deviation of each F (r) function point and a fitted straight line as a target function, and selecting an optimal F (r) function according to the target function; otherwise directly excluding the F (r) function;
and the two positions corresponding to the optimal F (r) function are recommended measurement positions.
Further, referring to fig. 3, the driving module 3 includes a trash can position driving unit 31, a probe position driving unit 32, a probe height driving unit 33, and a rotating platform 34;
referring to fig. 4, fig. 4 is a schematic perspective view of a driving module, the waste bin position driving unit 31 includes an X-axis fixing frame X1 and an X-axis screw bar X2, the X-axis screw bar X2 is rotatably fixed on the X-axis fixing frame X1, an X-axis guide rail X4 is further disposed on the X-axis fixing frame X1, a waste bin rack X5 capable of sliding along the X-axis guide rail X4 is disposed on the X-axis guide rail X4, the waste bin is mounted on the waste bin rack X5, and the X-axis screw bar X2 is connected to an X-axis driving device X3;
the operating principle of the trash can position driving unit 31 is: x axle drive arrangement X3 drive X axle lead screw X2 is rotatory, and then drives the waste bin rack X5 with X axle lead screw X2 swing joint and translate along the X direction, and waste bin 5 moves along with waste bin rack X5, and X axle guide rail X4 provides the guide effect for waste bin 5's removal.
The detector height driving unit 33 comprises a Z-axis fixing frame Z1 and a Z-axis lead screw Z2, the Z-axis fixing frame Z1 is vertically fixed on an X-axis fixing frame X1, the Z-axis lead screw Z2 is movably fixed on a Z-axis fixing frame Z1, a Z-axis guide rail Z4 is further arranged on the Z-axis fixing frame Z1, a Y-axis fixing frame Y1 capable of sliding along a Z-axis guide rail Z4 is arranged on the Z-axis guide rail Z4, the detector is installed on the Y-axis fixing frame Y1, and the Z-axis lead screw Z2 is connected with a Z-axis driving device Z3;
the working principle of the detector height driving unit 33 is as follows: z axle drive arrangement Z3 drive Z axle lead screw Z2 is rotatory, and then drives Y axle mount Y1 with Z axle lead screw swing joint and reciprocate along the Z direction, and detector 4 follows Y axle mount Y1 and moves along the Z direction together so that the layer by layer scans the waste bin, Z axle guide rail Z4 provides the guide effect for detector 4's the reciprocating.
The detector position driving unit 32 comprises a Y-axis fixing frame Y1 and a Y-axis lead screw Y2, the Y-axis fixing frame Y1 is sleeved on the Z-axis lead screw Z2 in a vertically movable manner, the Y-axis lead screw Y2 is rotatably fixed on a Y-axis fixing frame Y1, a Y-axis guide rail Y4 is further arranged on the Y-axis fixing frame Y1, a detector rack Y5 capable of sliding along a Y-axis guide rail Y4 is placed on the Y-axis guide rail Y4, the Y-axis lead screw Y2 is rotatably arranged in the detector rack Y5 in a penetrating manner, the detector 4 is mounted on the detector rack Y5, and the Y-axis lead screw Y2 is connected with a Y-axis driving device Y3;
the detector position drive unit 32 operates on the following principle: the Y-axis driving device Y3 drives the Y-axis lead screw Y2 to rotate, so that the detector rack Y5 movably connected with the Y-axis lead screw Y2 is driven to move in a translation mode along the Y direction, the detector 4 moves along with the detector rack Y5, and the Y-axis guide rail Y4 provides a guiding effect for the movement of the detector 4.
The rotating platform 34 is mounted on the waste bin rack X5, supports the waste bin 5, and is used for driving the waste bin 5 to rotate around the axis of the waste bin 5, so that the waste bin 5 rotates to be conveniently scanned by the detector 4 in the circumferential direction.
Further, the control module 2 is also used for calculating a detection efficiency matrix and a source item distribution vector according to the linear attenuation coefficient and the counting rate vector; and calculating the total activity of the nuclide according to the source item distribution vector.
The measuring device provided by the invention sets two degrees of freedom, namely distance and eccentricity, in the degree of freedom for adjusting the relative positions of the driving device, the detector and the waste barrel, can obtain more measuring positions, improves the flexibility of the scanning process of the system, can automatically find the optimal detection efficiency ratio F (r) function and the corresponding position, does not need manual adjustment of personnel, reduces the time cost and the accuracy deviation of the personnel operation, and improves the efficiency and the reliability of the waste barrel measurement.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (10)
1. A method for measuring the radioactivity of a nuclear power station waste bin is characterized by comprising the following steps:
s1, establishing a waste barrel model base, selecting a waste barrel model corresponding to the waste barrel from the waste barrel model base, weighing the total weight of the waste barrel, and calculating a linear attenuation coefficient according to the waste barrel model and the total weight;
s2, establishing a detection efficiency database according to the linear attenuation coefficient and the geometric condition of the waste bucket model, and screening and determining the relative measurement position of the detector and the waste bucket according to an objective function;
s3, driving the detector and/or the waste bucket to move relatively to the measuring position, and scanning the waste bucket in multiple directions at the measuring position to obtain a counting rate vector;
s4, calculating the distribution and the total activity of nuclides according to the detection efficiency and the counting rate vector; step S1 includes the following substeps:
s11, dividing the waste barrel into three types of areas: the waste bin comprises a radiation area, a filling area and a bin wall area, and the waste bin model comprises the following parameters: the size of each partition, the material of each partition, and the initial density of each partition;
s12, calculating the weight of the filling area according to the size of the filling area and the density of the filling area, calculating the weight of the barrel wall area according to the size of the barrel wall area and the density of the barrel wall area, subtracting the weight of the filling area and the weight of the barrel wall area from the total weight to obtain the weight of the radiation area, and correcting the initial density of the radiation area by using the weight of the radiation area and the size of the radiation area;
s13, calculating the mass attenuation coefficient of each subarea according to the material of each subarea;
s14, calculating the linear attenuation coefficient of each partition according to the initial density of the filling area, the initial density of the barrel wall area, the corrected density of the radiation area and the mass attenuation coefficient of each partition; step S2 includes the following substeps:
s21, calculating different source item distribution radiuses and detection efficiencies corresponding to different measurement positions according to the line attenuation coefficient and the partition model geometric conditions, and establishing a detection efficiency database;
s22, screening out the detection efficiency ratios of different measurement positions according to the detection efficiency database, calculating a plurality of groups of detection efficiency ratios, and judging whether the detection efficiency ratios are lower than 10 or not-3Sifting less than 10-3Establishing a plurality of F (r) functions according to the screened detection efficiency ratios, wherein the F (r) functions are functions of the detection efficiency ratios with respect to the source term distribution radius;
s23, judging whether the F (r) functions meet monotonicity one by one, if so, turning to the next step, otherwise, directly excluding the F (r) functions;
s24, obtaining the radius range of the radiation area through the waste bucket model, approximating a plurality of F (r) function curves in the radius range of the radiation area by using straight lines, calculating the least square of the deviation of each F (r) function point and the fitted straight line as a target function, and selecting the optimal F (r) function according to the target function;
and S25, and the two positions corresponding to the optimal F (r) function are recommended measurement positions.
2. The method of measuring the radioactivity of a waste bin of claim 1,
the relative movement of the drive probe and/or the waste bin comprises: driving the detector to translate in the Y direction and the waste bin to translate in the X direction;
performing a multi-azimuth scan of the trash can includes: the waste barrel is driven to rotate around the axis of the waste barrel so as to realize circumferential acquisition of data in the waste barrel, and the detector is driven to move along the Z direction at the measuring position so as to scan the rotating waste barrel layer by layer.
3. The method for measuring the radioactivity of a waste bin as claimed in claim 2, wherein the step S4 comprises the following sub-steps:
s41, calculating a source item distribution vector according to the detection efficiency and the counting rate vector;
and S42, calculating the total activity of the nuclide according to the source item distribution vector.
4. A method for measuring the radioactivity of a waste bin as claimed in claim 3, wherein the sub-step S41 comprises:
s411, calculating the ratio of the counting rates of the two recommended measuring positions in each layer of the waste bucket according to the two recommended measuring positions;
s412, establishing an equation set, and solving an initial source item distribution vector by using an initial detection efficiency matrix and a measurement count rate vector;
s413, calculating theoretical activity values measured by the detector at the two recommended measuring positions when the source item in each layer is independently transported to the detector, and solving the ratio of the theoretical activities measured by the two recommended measuring positions;
s414, obtaining the new source item equivalent radius of each layer;
s415, interpolating and calculating detection efficiency matrixes Ea (K) and Eb (K) of the source items when the new source item equivalent radius Ri (K) is distributed from a detection efficiency database, wherein K represents the Kth iteration process;
and S416, calculating a new source item distribution vector.
5. The method for measuring the radioactivity of a waste bin as claimed in claim 4, wherein the substep S42 comprises:
s421, calculating activity distribution vectors IA and IB according to the final source item distribution vectors Ia (k +1) and Ib (k + 1);
and S422, calculating the total activities A and B of the waste barrel according to IA and IB, and taking the larger vector of A and B as the final total activity.
6. The device for measuring the radioactivity of the waste bucket of the nuclear power station is applied to the method for measuring the radioactivity of the waste bucket according to claim 1, and is characterized by comprising a weighing module, a control module, a driving module and a detector which are respectively connected with the waste bucket; wherein the content of the first and second substances,
the weighing module is connected with the waste barrel and used for weighing the total weight of the waste barrel;
the control module is connected with the driving module and the detector and used for establishing a waste barrel model library, selecting a waste barrel model corresponding to a waste barrel from the waste barrel model library, calculating a linear attenuation coefficient according to the waste barrel model and the total weight, establishing a detection efficiency database according to the linear attenuation coefficient and the geometric conditions of the waste barrel model, and screening and determining the relative measurement position of the detector and the waste barrel according to an objective function;
a drive module connected to the waste bin and the detector for driving the detector and/or the waste bin to move relative to each other and to the measuring position;
the detector is used for scanning the waste bucket in multiple directions at the measuring position to obtain a counting rate vector;
and the control module is also used for calculating the distribution and the total activity of the nuclides according to the detection efficiency and the counting rate vector.
7. A waste bin radioactivity measuring device as claimed in claim 6, wherein the waste bin is divided into three categories: the waste bin comprises a radiation area, a filling area and a bin wall area, and the waste bin model comprises the following parameters: the size of each partition, the material of each partition, and the initial density of each partition;
the control module is further configured to:
calculating the weight of the filling area according to the size of the filling area and the density of the filling area, calculating the weight of the barrel wall area according to the size of the barrel wall area and the density of the barrel wall area, subtracting the weight of the filling area and the weight of the barrel wall area from the total weight to obtain the weight of the radiation area, and correcting the initial density of the radiation area by using the weight of the radiation area and the size of the radiation area;
calculating the mass attenuation coefficient of each subarea according to the material of each subarea;
and calculating the linear attenuation coefficient of each subarea according to the initial density of the filling area, the initial density of the barrel wall area, the corrected density of the radiation area and the mass attenuation coefficient of each subarea.
8. The apparatus of claim 7, wherein the control module is further configured to:
calculating the detection efficiency corresponding to different source item distribution radiuses and different measurement positions according to the line attenuation coefficient and the partition model geometric condition, and establishing a detection efficiency database;
screening out the detection efficiency ratios of different measurement positions according to the detection efficiency database, calculating a plurality of groups of detection efficiency ratios, and judging whether the detection efficiency ratios are lower than 10-3Sifting less than 10-3Establishing a plurality of F (r) functions according to the screened detection efficiency ratios, wherein the F (r) functions are functions of the detection efficiency ratios with respect to the source term distribution radius;
judging whether the F (r) functions meet monotonicity one by one, if so, obtaining a radial range of the radiation area through a waste barrel model, approximating a plurality of F (r) function curves in the radial range of the radiation area by using straight lines, calculating the least square of the deviation of each F (r) function point and a fitted straight line as a target function, and selecting an optimal F (r) function according to the target function; otherwise directly excluding the F (r) function;
and the two positions corresponding to the optimal F (r) function are recommended measurement positions.
9. The waste bin radioactivity measuring device of claim 6, wherein the drive module comprises a waste bin position drive unit, a detector height drive unit, and a rotating platform;
the waste barrel position driving unit comprises an X-axis fixing frame and an X-axis lead screw, and the X-axis lead screw is connected with an X-axis driving device and used for driving the X-axis lead screw to rotate so as to drive the waste barrel rack movably connected with the X-axis lead screw and a waste barrel above the waste barrel rack to translate along the X direction;
the detector height driving unit comprises a Z-axis fixing frame and a Z-axis lead screw, the Z-axis fixing frame is vertically fixed on the X-axis fixing frame, and the Z-axis lead screw is connected with a Z-axis driving device and used for driving a Z-axis lead screw to rotate so as to drive the Y-axis fixing frame movably connected with the Z-axis lead screw and a detector above the Y-axis fixing frame to move along the Z direction so as to scan the waste barrel layer by layer;
the detector position driving unit comprises a Y-axis fixing frame and a Y-axis screw rod, the Y-axis fixing frame is sleeved on the Z-axis screw rod in a vertically movable mode, and the Y-axis screw rod is connected with a Y-axis driving device and used for driving the Y-axis screw rod to rotate so as to drive the detector rack movably connected with the Y-axis screw rod and the detector above the detector rack to translate along the Y direction;
the rotating platform is installed on the waste bucket rack and used for driving the waste bucket to rotate around the axis of the waste bucket rack, and the detector is convenient for circumferentially collecting data in the waste bucket.
10. A waste bin radioactivity measuring device as claimed in claim 8, wherein said control module is further adapted to calculate a source term distribution vector from the detection efficiency and count rate vectors; and calculating the total activity of the nuclide according to the source item distribution vector.
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