JP2006084478A - Measuring method for radioactivity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring method for radioactivity for measuring radioactivity by determining a conversion factor without using an actual calibration radiation source. <P>SOLUTION: This method comprises a virtual modeling step 21 for arranging virtual three-dimensional models of a measurement subject and a radiation detector in a virtual three-dimensional space with the same positional relationship as an actual geometric positional relationship; a conversion factor setting step which is a step for associating the number of times of generation of a virtual radiation ray emitted from the virtual three-dimensional model of the measurement subject with the number of times of incidence of the virtual radiation ray upon the virtual three-dimensional model of the radiation detector to obtain a conversion factor, and has a virtual count calculating step 22 and a conversion factor calculating step 23; an actual counting rate calculating step 24 for actually counting the incidence of the radiation ray emitted from the measurement subject upon the radiation detector to obtain a counting rate; and a radioactivity calculating step 25 for calculating radioactivity of the measurement subject from the counting rate and the conversion factor. The detector and the measuring object are conceived as a group of a plurality of cells and as a group of parts opposed to the cells, respectively, and after the counting rate is calculated for each of the cells to determine radioactivity for every part of the measuring object, the radioactivity for the whole measuring object is determined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for measuring radioactivity. More specifically, the present invention relates to a radioactivity measurement method in which radioactivity is measured by obtaining a conversion coefficient without using an actual calibration radiation source.

  In order to obtain the radioactivity concentration and surface density of a measurement object such as demolition waste of a nuclear facility, it is necessary to first obtain the radioactivity of the measurement object. In the conventional measurement method of radioactivity, a conversion factor for calculating radioactivity from the count rate obtained from the count of the radiation detector was obtained by separately preparing a calibration radiation source with known radioactivity. Calculated by comparison with conversion factor.

  In order to measure the radioactivity surface density of the measurement object, it is necessary to first measure the radioactivity on the surface of the measurement object. To measure the radioactivity on the surface, β, which is less permeable than γ rays, is used. It is common to use lines. In other words, when γ-rays that are more permeable than β-rays are to be measured, whether the measured γ-rays are emitted from the surface of the measurement object or from the inside. It is difficult to discriminate and is not suitable for measuring the radioactivity on the surface of the measurement object. Therefore, a portable radiation detector called a survey meter specified in JIS (Japanese Industrial Standards) Z 4329 “Radioactive Surface Contamination Survey Meter” or an article specified in JIS Z 4337 “Surface Contamination Monitor for Stationary β-rays” Using the carry-out monitor, the radioactivity on the surface of the measurement object with β rays as the measurement object is measured.

Ogawa Iwao, Fundamental Atomic Energy Lecture 2 "Radiation", Corona Co., Ltd., November 15, 1976, 10th edition, pages 242-252

  However, in the surface radioactivity measurement method for obtaining the above-mentioned radioactivity surface density, the surface radioactivity is measured by measuring β-rays using a survey meter. In such cases, the survey meter cannot be inserted into the narrow tube, and it is difficult to measure the radioactivity on the inner peripheral surface of the narrow tube.

  In addition, in the radioactivity measurement method using γ-rays, which are more permeable than β-rays, the conversion factor for calculating the radioactivity is calculated by actually using a calibration radiation source. Since it is obtained by comparison with the coefficient, in order to obtain the radioactivity of the measurement object with high accuracy, it is necessary to create an optimal calibration radiation source according to the shape and size of the measurement object. It is not suitable for measuring the radioactivity of measurement objects of different sizes. For example, when measuring the radioactivity of demolition waste, etc. at nuclear facilities, it is practical to create an optimal calibration radiation source for each waste because wastes of various shapes and sizes are mixed. It is difficult to apply to the measurement of radioactivity of dismantled waste generated in large quantities.

  It is an object of the present invention to provide a radioactivity measurement method that does not require an actual calibration radiation source.

  In order to achieve this object, the radioactivity measurement method of the present invention arranges a virtual three-dimensional model of a measurement object and a radiation detector in the virtual three-dimensional space in the same positional relationship as the actual geometric positional relationship. A conversion factor for obtaining a conversion factor by associating the virtual modeling step, the number of generations of virtual radiation emitted from the virtual three-dimensional model of the measurement object, and the number of incidences of virtual radiation on the virtual three-dimensional model of the radiation detector A setting step, an actual count rate calculation step for actually counting the incidence of radiation emitted from the measurement object to the radiation detector to obtain a count rate, and determining the radioactivity of the measurement object from the count rate and the conversion factor A radioactivity calculation step is included.

  Here, the interaction between the radiation and the substance occurs with a certain probability, and it is possible to obtain the conversion coefficient without performing actual measurement using an actual calibration radiation source by reproducing this phenomenon in a pseudo manner. it can. That is, the three-dimensional shape and positional relationship between the measurement object and the radiation detector are virtually reproduced, and based on this, the number of generations of virtual radiation emitted from the virtual three-dimensional model of the measurement object and the radiation detector The conversion coefficient can be obtained by relating the number of incident virtual radiations to the virtual three-dimensional model. Then, the actual radioactivity of the measurement object is calculated from the calculated conversion factor and the count by the actual radiation detector.

  In the case of this radioactivity measurement method, the conversion coefficient setting step uses a Monte Carlo calculation method to generate virtual radiation randomly from the virtual three-dimensional model of the measurement object and to perform virtual conversion to the virtual three-dimensional model of the radiation detector. It is preferable to have a virtual count calculation step that counts the incidence of radiation to obtain a virtual count, and a conversion coefficient calculation step for obtaining a conversion factor from the number of occurrences of virtual radiation and the virtual count.

  By using the Monte Carlo calculation method, the three-dimensional shape and positional relationship between the measurement object and the radiation detector are virtually reproduced, and virtual radiation generated randomly from the virtual three-dimensional model of the measurement object is emitted as radiation. It is possible to simulate the incident on the virtual three-dimensional model of the detector. In this case, since the generation rate of the virtual radiation from the virtual three-dimensional model of the measurement object corresponds to the radioactivity of the virtual three-dimensional model, it is converted from the number of generations of the virtual radiation and the count in the virtual three-dimensional model of the radiation detector. The coefficient can be obtained. Then, the actual radioactivity of the measurement object is calculated from the calculated conversion factor and the count by the actual radiation detector.

  Further, in the radioactivity measurement method of the present invention, the conversion coefficient setting step includes a thickness of a medium existing between the measurement object and the radiation detector, an attenuation coefficient of the medium, a build-up coefficient of the medium, and It is also possible to obtain the conversion coefficient from the correlation of the number of radiations before and after passing through the medium approximately calculated based on the distance between the measurement object and the radiation detector.

For example, when considering shielding of radiation, shielding calculation is performed using a point decay kernel code. In this point attenuation core code, the number I of radiation after passing through a certain medium, the number of radiations I ₀ before passing through the medium, the thickness d of the medium, the attenuation coefficient μ of the medium, the build-up of the medium It is approximately obtained from Equation 1 which is a relational expression of the coefficient B and the distance r between the radiation source and the evaluation point.

<Equation 1>
I = (1 / (4πr ² )) I ₀ Be ^−μd
That is, the attenuation coefficient μ of the medium and the buildup coefficient B of the medium are determined according to the type of the medium, and the thickness d is determined according to the form of the measurement object, the position of the radioactive contamination, and the like. If the distance r between the radiation source and the evaluation point is known, the relationship between I and I ₀ can be derived approximately from the above relational expression, and the conversion coefficient can be obtained from the relationship between I and I _0. it can. That is, I ₀ corresponds to the number of virtual radiations emitted from the virtual three-dimensional model of the measurement object, I corresponds to the number of virtual radiations incident on the virtual three-dimensional model of the radiation detector, and I / I ₀ is the conversion factor. Then, the actual radioactivity of the measurement object is calculated from the calculated conversion factor and the count by the actual radiation detector.

  In addition, when it is clear that the radioactivity concentration and surface density of the measurement object are uniform, detection by a radiation detector consisting of one cell is sufficient, but the radioactivity concentration and radioactivity surface density are not uniform. If the distribution coefficient is unevenly distributed, the error is large in the conversion coefficient obtained on the assumption of a uniform distribution. Therefore, it is preferable to obtain the conversion coefficient in consideration of the uneven distribution situation (distribution of uneven distribution). In particular, when the radioactivity level of the measurement object is low, it is necessary to perform measurement with the radiation detector close to the measurement object. In such a case, the uneven distribution of radioactivity is greatly increased to the value of the conversion factor. Affect. In order to know the distribution of uneven distribution, the radiation detector is an aggregate of a plurality of small detectors (cells), that is, each of the radiation detectors is a cell, and the cells are assembled into one large radiation detector. Is effective. Then, the measurement object is divided into parts corresponding to the cells of the radiation detector, and a conversion coefficient is obtained for each cell for each part, so that the conversion coefficient takes into account the uneven distribution. The radioactivity of each part of the measurement object is obtained by the conversion coefficient thus obtained, and the radioactivity of the whole measurement object is obtained by the sum of the radioactivity of each part. In addition, it is possible to specify a part where a lot of radiation is detected by a large number of cells, and to estimate the radioactivity concentration and the like for each part of the specific object from the count information of each cell.

  Therefore, in the radioactivity measurement method of the present invention, the radiation detector is set as a set of a plurality of cells, and the measurement object is conceptualized as a set of parts facing the cells. A virtual three-dimensional model is formed as a collection of cells and a measurement object is converted into a virtual three-dimensional model as a collection of parts, and a conversion coefficient setting step is performed for each part of the virtual three-dimensional model of the measurement object. A conversion factor is calculated for each cell, and an actual count rate calculation step is performed for each cell of the radiation detector to obtain a count rate for each cell, and a radioactivity calculation step is performed for each site of the measurement object. After obtaining the radioactivity, the radioactivity of the entire measurement object is obtained from the radioactivity of each part.

  In this case, by obtaining a virtual count for each cell, highly accurate evaluation is possible even if radioactivity is unevenly distributed.

  The following radioactivity measuring device may be used. That is, the radioactivity measuring device includes a radiation detector that counts radiation emitted from the measurement object, and a three-dimensional spatial coordinate of the surface of the measurement object, and uses this to measure the measurement object and the radiation detector. 3D modeling means that virtually reproduces the geometric positional relationship of the object, and the number of virtual radiations emitted from the virtually reproduced 3D model of the measurement object and the radiation that is virtually reproduced Radiation for calculating the actual radioactivity of the measurement object based on the conversion factor setting means for obtaining the conversion factor by relating the number of incidents on the three-dimensional model of the detector, and the actual count rate and the conversion factor by the radiation detector. Performance calculating means is provided.

  Accordingly, the conversion factor setting means uses the virtual three-dimensional model of the radiation detector and the number of generations of the virtual radiation by using the virtual three-dimensional model of the measurement object and the radiation detector that are simulated by the three-dimensional modeling means. The conversion factor is obtained by relating the number of inputs to. The radioactivity calculation means obtains the actual radioactivity of the measurement object from the conversion coefficient thus obtained and the actually measured count rate of the radiation detector.

  In the case of this radioactivity measurement apparatus, the conversion coefficient setting means uses a three-dimensional Monte Carlo calculation code to randomly generate virtual radiation from a three-dimensional model of a measurement object and generate a radiation detector 3 that is virtually reproduced. A simulation means for simulating the incidence on the three-dimensional model, and a conversion coefficient calculation means for calculating a conversion coefficient based on the number of occurrences of virtual radiation and the count of the incidence of virtual radiation on the three-dimensional model of the radiation detector. It is preferable.

  Further, in the radioactivity measurement apparatus, the conversion coefficient setting means includes a thickness of a medium existing between the measurement object and the radiation detector, an attenuation coefficient of the medium, a build-up coefficient of the medium, and a measurement object. The conversion coefficient may be calculated from the correlation between the number of radiations before and after passing through the medium approximately calculated based on the distance between the radiation detector and the radiation detector.

According to these radioactivity measuring devices, it is possible to measure the radioactivity of an object to be measured with high precision and speed without using an actual calibration radiation source, and in particular, various shapes. Therefore, it is possible to realize a measuring device suitable for processing a large amount of objects to be measured. In particular, when the conversion coefficient is obtained using the Monte Carlo calculation code, since the actual radiation emission phenomenon is simulated, the conversion coefficient in accordance with the actual phenomenon can be obtained. Further, when the conversion coefficient is obtained from the relationship between I and I ₀ obtained using the point decay kernel code, the calculation amount can be reduced, and the conversion coefficient can be calculated in a short time.

  In the radioactivity measuring apparatus, the radiation detector is a set of a plurality of cells, and the three-dimensional modeling means performs a virtual three-dimensional model of the radiation detector as a set of a plurality of cells, and a measurement object. Is converted into a virtual three-dimensional model as a collection of parts facing the cell, the conversion coefficient setting means obtains the conversion coefficient for each cell of the radiation detector for each part of the measurement object, and the radioactivity calculation means is the part of the measurement object In addition to obtaining the radioactivity every time, the radioactivity of the entire measurement object may be obtained from the radioactivity of each part.

  Therefore, a conversion coefficient is obtained for each cell of the radiation detector for each part of the measurement object, and the radioactivity for each part of the measurement object is calculated from these conversion coefficients and the count rate of each cell of the measured radiation detector. Further, the radioactivity of the entire measurement object is required.

  Moreover, you may make it measure a radioactivity density | concentration and a radioactivity surface density using the above-mentioned radioactivity measuring method and measuring apparatus.

  The radioactivity concentration measurement method includes a weight or volume measurement step for measuring the weight or volume of a measurement object, and the radioactivity obtained by any of the above-described radioactivity measurement methods divided by the weight or volume. And a radioactivity concentration calculating step for obtaining the concentration.

  The radioactivity concentration can be determined by dividing the radioactivity of the measurement object by weight or volume. Therefore, the radioactivity concentration can be obtained by dividing the radioactivity of the measurement object obtained by any of the aforementioned radioactivity measurement methods by the weight or volume measured in the weight or volume measurement step.

  Therefore, according to this radioactivity concentration measurement method, the radioactivity concentration of the measurement objects of various shapes and sizes can be measured with high accuracy and speed. Classification evaluation according to the radioactivity level of demolition waste expected to be performed can be performed quickly and rationally.

  The radioactivity concentration measuring device includes any one of the radioactivity measuring devices described above, a weight or volume measuring means for measuring the weight or volume of the measurement object, and the obtained radioactivity of the measurement object by weight or volume. And a radioactivity concentration calculating means for calculating the radioactivity concentration.

  The radioactivity concentration can be determined by dividing the radioactivity of the measurement object by weight or volume. Therefore, the radioactivity of the measurement object is obtained by any of the aforementioned radioactivity measurement devices, the weight or volume of the measurement object is obtained by the weight or volume measurement means, and the radioactivity is calculated by weight or volume by the radioactivity concentration calculation means. The concentration of radioactivity can be determined by dividing.

  Therefore, according to this radioactivity concentration measuring apparatus, an apparatus suitable for carrying out the above-described radioactivity concentration measurement method can be provided. In other words, the radioactivity concentration of objects to be measured in various shapes and sizes can be measured with high accuracy and speed, and the radioactivity of demolition waste that is expected to be generated in large quantities due to future decommissioning of nuclear reactors Classification evaluation according to the level can be performed quickly and rationally.

  Moreover, the measurement method of the radioactivity surface density is obtained by dividing the radioactivity obtained by any one of the radioactivity measurement methods described above by the surface area measurement step for measuring the surface area of the measurement object and the radioactivity surface density. It has a radioactive surface density calculation process.

  The radioactivity surface density can be determined by dividing the radioactivity of the measurement object by the surface area. Therefore, the radioactivity surface density can be obtained by dividing the radioactivity of the measurement object obtained by any of the above-described radioactivity measurement methods by the surface area of the measurement object measured in the surface area measurement step.

  Therefore, according to this radioactivity surface density measurement method, it is possible to measure the radioactivity surface density of objects of various shapes and sizes with high accuracy and speed. Classification evaluation according to the radioactivity level of demolition waste that is expected to be generated in a rapid and rational manner. In addition, it is possible to measure the radioactivity surface density inside the pipe having a small diameter so that the survey meter cannot be inserted with high accuracy and speed.

  Furthermore, the radioactivity surface density measuring device is one of the radioactivity measuring devices described above, surface area measuring means for measuring the surface area of the measurement object, and dividing the obtained radioactivity of the measurement object by the surface area to radiate. Radioactive surface density calculating means for calculating the active surface density is provided.

  The radioactivity surface density can be determined by dividing the radioactivity of the measurement object by the surface area. Therefore, the radioactivity of the measurement object is obtained by any of the above-described radioactivity measurement devices, the surface area of the measurement object is obtained by the surface area measurement means, and the radioactivity is divided by the surface area by the radioactivity surface density calculation means. The active surface density can be determined.

  Therefore, according to this radioactivity surface density measuring device, it is possible to provide an apparatus suitable for carrying out the radioactivity surface density measuring method. In other words, it is possible to measure the radioactivity surface density of measurement objects of various shapes and sizes with high accuracy and speed, and radiation of demolition waste that is expected to be generated in large quantities due to future decommissioning of nuclear reactors. Classification evaluation according to performance level can be performed quickly and rationally. In addition, it is possible to measure the radioactivity surface density inside the pipe having a small diameter so that the survey meter cannot be inserted with high accuracy and speed.

According to the radioactivity measurement method of the present invention, the radioactivity of a measurement object can be measured with high accuracy and speed without using an actual calibration radiation source, and various shapes can be obtained. It is possible to process a large amount and quickly of radioactivity measurement of a measuring object of a large size. In particular, when the conversion coefficient is obtained using the Monte Carlo calculation method, since the actual radiation emission phenomenon is simulated, the conversion coefficient in accordance with the actual phenomenon can be obtained. Further, when obtaining a conversion factor from the relationship between I and I ₀ obtained using the point attenuation nuclear code conversion in a short time since the calculation amount even worse the measurement accuracy as compared with the Monte Carlo technique is less A coefficient can be calculated.

  Further, by obtaining a virtual count for each cell, highly accurate evaluation is possible even if radioactivity is unevenly distributed.

  Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.

  FIG. 1 shows an embodiment of a radioactivity measurement method of the present invention, and FIG. 2 shows an example of an embodiment of a radioactivity measurement apparatus that implements the radioactivity measurement method. The measurement apparatus includes a radiation detector 1 that counts radiation emitted from the measurement object 18, such as γ-rays, and a three-dimensional shape measurement apparatus 11 that measures the surface shape of the measurement object 18 and captures it as three-dimensional spatial coordinates. And the geometric positional relationship between the measurement object 18 and the radiation detector 1 using the three-dimensional spatial coordinate data of the surface of the measurement object obtained by the three-dimensional shape measurement apparatus 11 (see FIG. 3A). Is virtually reproduced (see FIG. 3B), and virtual radiation, for example, virtual γ-rays are randomly generated from the three-dimensional modeling means 2 and the three-dimensional model 16 of the measurement object 18 virtually reproduced. Simulation means 3 for simulating the reproduction of the reproduced radiation detector 1 on the three-dimensional model 17, the number of generations of virtual radiation, and the count of the incidence of virtual radiation on the three-dimensional model 17 of the radiation detector 1 By A conversion factor calculation unit 4 that calculates a conversion factor and a radioactivity calculation unit 5 that calculates the actual radioactivity of the measurement object 18 based on the actual count rate and conversion factor of the radiation detector 1 are provided. That is, in the present embodiment, the number of virtual radiations emitted from the three-dimensional model 16 of the measurement object 18 virtually reproduced and the incidence on the three-dimensional model 17 of the radiation detector 1 virtually reproduced. A conversion coefficient setting means for obtaining a conversion coefficient by associating a number is constituted by a simulation means 3 and a conversion coefficient calculation means 4.

  In the present embodiment, at least one arithmetic processing unit 6 such as a CPU or MPU, an interface 7 for inputting / outputting data, a computer 9 having a memory 8 for storing programs and data, and a predetermined control or arithmetic program. Thus, the three-dimensional modeling means 2, the simulation means 3, the conversion coefficient calculation means 4, and the radioactivity calculation means 5 are realized. That is, the arithmetic processing unit 6 uses the control program such as the OS stored in the memory 8, the program specifying the procedure such as the radioactivity measurement method, the necessary data, etc., and the above three-dimensional modeling means 2, simulation means 3, conversion The coefficient calculation means 4 and the radioactivity calculation means 5 are realized. The computer 9 is connected to an output device 10 such as a CRT display or a printer.

  As the three-dimensional shape measurement apparatus 11, for example, a device that detects the spatial coordinates of the surface of the measurement object 18 as point cloud data and measures the three-dimensional shape is used in this embodiment. The three-dimensional shape measuring apparatus 11 is a non-contact type three-dimensional laser scanner, which scans the surface by applying laser light to the measurement object 18 and forms an image of the scattered light on a CCD by a condenser lens. The image position is input as a counter value and converted into distance data by the principle of triangulation. Multipoint point group data can be obtained by scanning the optical axes of the laser projector and the light receiver at high speed with a galvanometer mirror. The three-dimensional coordinates of the measuring object 18 measured by the three-dimensional shape measuring apparatus 11 are input to the computer 9 via the interface 7. Specifically, for example, the spatial coordinates of the surface of the measurement object 18 can be detected at high speed using a “three-dimensional scanner TDS3100” manufactured by Pulstec Industrial Co., Ltd., and obtained as three-dimensional spatial coordinate data.

  As the radiation detector 1, for example, a plastic scintillation detector that measures γ-rays can be used, and is arranged in parallel above and below the measurement object 18. Count data from the radiation detector 1 is input to the computer 9 via the interface 7.

  Next, a method for measuring radioactivity will be described. This radioactivity measurement method takes in the three-dimensional spatial coordinates of the surface of the measurement object and uses it to place the measurement object 18 and the virtual three-dimensional models 16 and 17 of the radiation detector 1 in the virtual three-dimensional space. A virtual modeling step 21 arranged in the same positional relationship as the actual geometric positional relationship, virtual radiation, for example, γ-rays are randomly generated from the virtual three-dimensional model 16 of the measurement object 18 and the virtual 3 of the radiation detector 1 is generated. A virtual count calculation step 22 that counts the incidence of virtual radiation on the dimensional model 17 to obtain a virtual count, a conversion factor calculation step 23 that obtains a conversion factor from the number of occurrences of virtual radiation and the virtual count, and a discharge from the measurement object 18 The actual count rate calculating step 24 that actually counts the incident radiation, for example, the incidence of γ-rays on the radiation detector 1 to obtain the count rate, and the radioactivity of the measuring object 18 is obtained from the count rate and the conversion factor. Radioactivity calculation step 25. That is, in the present embodiment, the number of virtual radiation emitted from the virtual three-dimensional model 16 of the measurement object 18 and the number of virtual radiation incident on the virtual three-dimensional model 17 of the radiation detector 1 are related and converted. A conversion coefficient setting step for obtaining a coefficient includes a virtual count calculation step 22 and a conversion coefficient calculation step 23.

  In the present embodiment, a phenomenon in which radiation is emitted from the measurement object 18 and counted by the radiation detector 1 is simulated using a three-dimensional Monte Carlo calculation method performed on the computer 9 of the measurement apparatus shown in FIG. By doing so, the conversion factor is obtained. Therefore, in the virtual modeling step 21, the shapes of the radiation detector 1 and the measurement target 18 when actually counting the radiation emitted from the measurement target 18 using the radiation detector 1 in the actual count rate calculation step 24. In addition, so-called three-dimensional modeling is performed to express these geometric positional relationships in a format suitable for a three-dimensional Monte Carlo calculation code. That is, in the virtual modeling step 21, first, the three-dimensional shape measurement apparatus 11 measures the three-dimensional shape of the radiation detector 1 and the measurement object 18 and their positional relationship, and the three-dimensional coordinate data is converted into three-dimensional data. For example, as shown conceptually in FIG. 3B, the measurement object 18 and the three-dimensional models 16 and 17 of the radiation detector 1 are virtually reproduced in a virtual three-dimensional space and input to the modeling means 2. Place in the same positional relationship as the relationship. Then, what is arranged in this way is expressed in the format of a three-dimensional Monte Carlo calculation code to form an input file (three-dimensional modeling). In this input file, data on at least the form of the measurement object 18, the form of the radiation detector 1, and the form of other space medium are recorded. Examples of the form of the measurement object 18 include a three-dimensional shape, a distribution of radioactive contamination (contamination only on the surface or whether it is uniformly contaminated to the inside, etc.), energy of γ rays to be generated, and the like. Examples of the form of the radiation detector 1 include a three-dimensional shape, composition, and density. As other forms of the medium in the space, for example, there is a vacuum or air, and whether or not there is lead shielding.

  Even if the shape or the like of the measurement object 18 changes each time, the data about the three-dimensional shape of the radiation detector 1 and the distance between the radiation detector 1 and a reference surface such as a table on which the measurement object 18 is placed, Since the positional relationship does not change, it is not necessary to perform measurement of the radiation detector 1 by the three-dimensional shape measuring apparatus 11 every time, and the time and effort of measuring and inputting each time using previously or previously input three-dimensional data can be saved. be able to. In this case, the time for acquiring and inputting the data of the three-dimensional shape can be shortened.

  Next, in the virtual count calculation step 22, virtual radiation is randomly generated from the virtual three-dimensional model 16 of the measurement object 18 using a three-dimensional Monte Carlo calculation method, and radiation detection is performed among the generated virtual radiation. A count is obtained by counting those incident on the virtual three-dimensional model 17 of the vessel 1. In other words, γ rays are emitted from radioactive materials isotropically (with equal probability in all directions), and the emitted γ rays pass through or collide with the material, or are absorbed and separated into new energy γ rays. To do. This interaction between γ-rays and matter occurs with a certain probability, and this phenomenon can be approximated and expressed by a mathematical model. In the three-dimensional Monte Carlo calculation code, γ rays emitted in all directions from the virtual three-dimensional model 16 of the measurement object 18 on the computer 9 by the simulation means 3 in an isotropic or equal probability are used by using the mathematical model described above. Can be tracked. Therefore, the probability (a value close to detection efficiency) of how much the γ-rays emitted from the measurement object 18 are incident on the radiation detector 1 installed at a remote location can be obtained by calculation. The arithmetic processing unit 6 of the computer 9 serving as the simulation means 3 simulates the state in which radiation is emitted from the measurement object 18 using a three-dimensional Monte Carlo calculation code, and obtains the count by the radiation detector 1 in a pseudo manner. As the three-dimensional Monte Carlo calculation code, for example, an MCNP code, which is a public code developed at the Los Alamos National Laboratory in the United States, can be used.

  Next, in the conversion coefficient calculation step 23, the ratio between the number of γ rays virtually generated and the count value counted by the detector model 17 in the conversion coefficient calculation means 4 realized in the arithmetic processing unit 6 of the computer 9. Calculate the conversion factor. Now, assuming that A γ-rays are generated from the virtual three-dimensional model 16 of the measurement object 18, B γ-rays are incident on the virtual three-dimensional model 17 of the radiation detector 1, that is, the virtual count is B. Assuming that, the conversion coefficient is A / B.

  In the next actual count rate calculation step 24, the radiation detector 1 measures the γ rays actually emitted from the measurement object 18 to obtain the count rate. At this time, the positional relationship between the radiation detector 1 and the measurement object 18 is made the same as the positional relationship virtually reproduced on the computer 9. In the radioactivity calculation step 25, the radioactivity of the measurement object 18 is calculated by multiplying the calculated count rate by the conversion coefficient. Now, assuming that the actually obtained count rate is C, the radioactivity of the measurement target 18 is determined by C × A / B / (gamma ray release rate of the measurement target radioactive substance). This calculation is performed in the radioactivity calculation means 5 realized in the calculation processing device 6.

  As described above, in the radioactivity measurement method and measurement apparatus of the present invention, the conversion factor can be obtained using the three-dimensional Monte Carlo calculation method. Therefore, the calibration radiation that must be created according to the measurement object 18. The radioactivity of the measuring object 18 can be measured quickly and with high accuracy without using a source.

  Next, a radioactivity concentration measuring method and measuring apparatus will be described.

  FIG. 4 shows an embodiment of the radioactivity concentration measuring method of the present invention, and FIG. 5 shows an example of an embodiment of the radioactivity concentration measuring apparatus for carrying out the radioactivity concentration measuring method. This radioactivity concentration measurement apparatus is obtained by adding the functions of weight or volume measurement means 13 and radioactivity concentration calculation means 12 to the radioactivity measurement apparatus of FIG.

  The radioactivity concentration calculation means 12 calculates the radioactivity concentration by dividing the radioactivity of the measurement object 18 obtained by the radioactivity calculation means 5 by the weight or volume. In this embodiment, for example, the arithmetic processing of the computer 9 is performed. The radioactivity calculation means 5 is realized by a program that causes the apparatus 6 to perform arithmetic processing for dividing the radioactivity of the measurement object 18 by weight or volume. Further, the weight or volume measuring means 13 measures the weight or volume of the measuring object 18 and is a measuring instrument that measures the weight of the measuring object 18 in this embodiment. The measurement result by the measuring instrument 13 is input to the radioactivity concentration calculating means 12 of the computer 9 via the interface 7.

  The radioactivity concentration measurement method carried out by such a measuring device is based on the above-described radioactivity measurement method by the weight or volume measurement step 31 for measuring the weight or volume of the measurement object 18 and the radioactivity measurement method described above. It includes a radioactivity concentration calculation step 33 for obtaining the radioactivity concentration by dividing the obtained radioactivity by weight or volume.

  For example, the case where the radioactivity concentration is obtained by weight will be described as an example. First, the radioactivity concentration on the computer 9 is measured by measuring the weight of the measurement object 18 by the weighing instrument 13 in the weight or volume measurement step 31 prior to the radioactivity measurement. Input to the calculation means 12. Thereafter, in the radioactivity measurement routine 32, the method of FIG. Then, the radioactivity concentration calculation means 12 calculates the radioactivity concentration by dividing the radioactivity obtained by the radioactivity calculation means 5 by the weight obtained by the measuring instrument 13 (radioactivity concentration calculation step 33). For example, when the weight of the measurement object 18 is D and the radioactivity is E, the radioactivity concentration is obtained by E / D. The obtained radioactivity concentration is output to the output device 10 and displayed or printed in an arbitrary form.

  In addition, when calculating | requiring a radioactive concentration with a volume instead of a weight, the volume measuring means which can measure the volume of the measuring object 18 is used as a weight or volume measuring means 13. FIG. The volume measuring means in this case is for obtaining the volume based on, for example, the three-dimensional shape data of the measurement object 18 measured by the three-dimensional shape measuring apparatus 11, and the arithmetic processing unit 6 of the computer 9 is usually used as the volume measuring means. Make it work. Assuming that the volume of the measurement object 18 thus obtained is F, the radioactivity concentration calculation step 33 calculates E / F to obtain the radioactivity concentration.

  As described above, in the radioactivity concentration measuring method and measuring apparatus of the present invention, the radioactivity of the measuring object 18 is measured without using a different calibration radiation source for each measuring object 18. It is possible to accurately measure the radioactivity concentration of the measurement object 18 with high accuracy and with respect to the measurement object 18 of various shapes and sizes.

  Next, a measuring method and measuring apparatus for the radioactivity surface density will be described.

  FIG. 6 shows an embodiment of the radioactive surface density measuring method of the present invention, and FIG. 7 shows an embodiment of a measuring apparatus for carrying out the radioactive surface density measuring method. This radioactivity surface density measuring apparatus is obtained by adding the functions of the surface area measuring means 14 and the radioactivity surface density calculating means 15 to the radioactivity measuring apparatus of FIG.

  The radioactivity surface density calculation means 15 calculates the radioactivity surface density by dividing the radioactivity of the measurement object 18 obtained by the radioactivity calculation means 5 by the surface area. In this embodiment, for example, the calculation process of the computer 9 is performed. It implement | achieves by making the apparatus 6 function as the radioactive surface density calculation means 15 by a program. Further, the surface area measuring means 14 obtains the surface area from the shape data of the measuring object 18 measured by, for example, the three-dimensional shape measuring apparatus 11, and in the present embodiment, for example, the arithmetic processing unit 6 of the computer 9 sets a predetermined program. This is realized by functioning as the surface area measuring means 14 for obtaining the surface area by performing a calculation based on the calculation.

  The radioactivity surface density measurement method carried out by such a radioactivity surface density measurement apparatus includes a surface area measurement step 42 for measuring the surface area of the measurement object 18 and the radioactivity measurement described above. It includes a radioactivity surface density calculating step 43 for determining the radioactivity surface density by dividing the radioactivity obtained by the method by the surface area.

  The radioactivity surface density measurement method will be specifically described. First, the radioactivity measurement routine 41 performs the radioactivity measurement method of FIG. 1 to measure the radioactivity of the measurement object 18. In this case, in the virtual count calculation step 22 of FIG. 1, radiation, for example, γ rays are virtually generated from the surface of the virtual three-dimensional model 16 of the measurement object 18. That is, the surface contamination of the measurement object 18 is simulated. Then, in the next surface area measuring step 42, the surface area of the measuring object 18 is calculated based on the data relating to the three-dimensional shape of the measuring object 18 in the surface area measuring means 14 realized by the arithmetic processing unit 6 of the computer 9 and a predetermined arithmetic program. Is calculated. Thereafter, in a radioactivity surface density calculation step 43, the radioactivity surface density is calculated by dividing the radioactivity related to the surface contamination of the measurement object 18 by the surface area of the measurement object 18. Now, assuming that the surface area of the measuring object 18 is G, the radioactive surface density is obtained by E / G. The obtained radioactivity surface density is output to the output device 10 and displayed or printed in an arbitrary form.

  In this radioactivity surface density measurement method, the surface area of the measurement object 18 is obtained after obtaining the radioactivity of the measurement object 18, that is, after the execution of the radioactivity measurement routine 41, the surface area measurement step 42 is performed. In order to obtain the radioactivity of the measurement object 18, the virtual model executed at the stage of measuring the three-dimensional shape of the measurement object 18 in the virtual modeling step 21, that is, the radioactivity measurement routine 41 is executed. In the conversion step 21, the surface area of the measurement object 18 may be obtained.

  Thus, in the measuring method and measuring apparatus of the radioactivity surface density of the present invention, the radioactivity of the measuring object 18 is measured without using the calibration radiation source corresponding to the measuring object 18, so that It is possible to accurately measure the radioactivity surface density of the measurement object 18 with high accuracy and with respect to the measurement object 18 of various shapes and sizes. In addition, since the measurement of the radioactivity surface density is performed on the γ-rays emitted from the measurement object 18, unlike the case of measuring the radioactivity surface density on the β-rays, it is not possible to insert a survey meter. For example, the radioactivity surface density of the inner peripheral surface of the thin tube can be measured with high accuracy.

  FIG. 8 shows an example of a concept of a system that verifies the radioactivity level of demolition waste generated by, for example, reactor decommissioning using the above-described radioactivity concentration measurement method and radioactivity surface density measurement method.

  By decommissioning the reactor, a large amount of demolition waste 51 (measurement object 18) of various shapes, sizes, radioactivity levels, etc. is generated. These radioactive wastes 51 are conveyed to the shape measuring unit 52 and the three-dimensional shape measurement apparatus 11 measures the three-dimensional shape. The radiation detector 1 and the measuring instrument 13 are installed in the next radiation / weight measuring unit 53 to measure the weight of the radioactive waste 51 on which the shape measurement has been performed and to emit radiation emitted from the radioactive waste 51. Count and determine the radioactivity concentration and surface density. Then, after the verification about the radioactivity concentration and the radioactivity surface density is performed by the verification unit 54, each demolition waste 51 is appropriately disposed and reused according to each level. By checking the radioactivity level of the demolition waste 51 in this way, it becomes possible to quickly check a large amount of the demolition waste 51, which may be generated in large quantities due to future nuclear reactor decommissioning. It is possible to cope with the expected disposal and reuse of the dismantled waste 51.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, the radioactivity may be measured as described above, but in the present invention, the radioactivity is further measured as follows. That is, when the virtual γ rays emitted from the three-dimensional model 16 of the measurement object 18 by the simulation using the three-dimensional Monte Carlo calculation code are counted by the three-dimensional model 17 of the radiation detector 1, the upper and lower three-dimensional models 17 are respectively determined. As an aggregate of a large number of cells, the incidence of virtual γ rays may be counted for each cell.

  That is, the radiation detector is a set of a plurality of cells and the measurement object is a concept of a set of parts facing the cell. In the virtual modeling step, the radiation detector is a set of a plurality of cells to be a virtual three-dimensional model. And a virtual three-dimensional model of the measurement object as a collection of parts, and performing a conversion coefficient setting step for each part of the virtual three-dimensional model of the measurement object to obtain a conversion coefficient for each of the cells for each part, The actual count rate calculation process is performed for each cell of the radiation detector to obtain the count rate for each cell, the radioactivity calculation process is performed to determine the radioactivity for each part of the measurement object, and then the radioactivity of each part Further, the radioactivity of the entire measurement object may be obtained.

  Specifically, for example, when the radiation detector 1 is configured as an assembly of four cells 1a as shown in FIG. 9, a measurement object 18 to be measured on the radiation detector 1 is measured. It is conceptualized as a set of parts 18a facing the cell 1a. Then, assuming that the radioactivity concentration and the radioactivity surface density are uniform in each part 18a, a conversion coefficient is obtained for each cell in each part of the three-dimensional model by performing simulation.

  First, the counting efficiency (conversion factor) when the radiation emitted from the first part of the three-dimensional model 16 is counted in the first to fourth cells of the three-dimensional model 17 is the shape of the measurement object 18. Based on the measurement result, a three-dimensional Monte Carlo calculation code is used. For example, the efficiency (conversion factor) when counting in the first cell is 0.4, the efficiency (conversion factor) when counting in the second cell is 0.15, and the result is It is assumed that the efficiency (conversion coefficient) at the time of counting is 0.15, and the efficiency (conversion coefficient) at the time of counting by the fourth cell is 0.07.

  Similarly, the conversion factor when the radiation emitted from the second to fourth parts of the three-dimensional model 16 is counted in the first to fourth cells of the three-dimensional model 17 is the shape of the measurement object 18. Based on the measured results, the three-dimensional Monte Carlo calculation code is used. These results are assumed to be the values shown in Table 1.

  On the other hand, the actual count of the cell 1a of the radiation detector 1 is 100 for the first cell 1a, 50 for the second cell 1a, 50 for the third cell 1a, and 40 for the fourth cell 1a. .

  When the above results are expressed in a matrix, the relationship between the radioactivity R1 to R4 for each part 18a and the count rate in the four cells 1a of the radiation detector 1 is expressed by Equation 2. The radioactivity of the first part 18a is R1, the radioactivity of the second part 18a is R2, the radioactivity of the third part 18a is R3, and the radioactivity of the fourth part 18a is R4.

  Thus, after calculating | requiring the radioactivity R1-R4 of the 1st-4th site | part 18a, the sum total of these radioactivity R1-R4 is calculated | required. In the above example, since Equation 3 is obtained, the radioactivity of the entire measurement object 18 is 308.3 Bq.

<Equation 3>
Radioactivity of the entire measurement object 18 = R1 + R2 + R3 + R4
= 225.1 + 18.7 + 19.8 + 44.7 = 308.3

  When the radioactivity concentration and the radioactivity surface density are not uniform but unevenly distributed in various places, the conversion factor obtained assuming a uniform distribution has a large error. In particular, when the radioactivity level of the measurement object 18 is low, it is necessary to perform measurement by bringing the radioactivity detector 1 close to the measurement object 18, and the radioactivity detector 1 is measured close to the measurement object 18. In some cases, the uneven distribution of radioactivity greatly affects the value of the conversion factor. However, the conversion factor can be obtained in consideration of the uneven distribution state (distribution of uneven distribution) by doing as described above, and even if the radioactivity of the measurement object 18 is unevenly distributed, the radioactivity concentration and the radioactivity surface Highly accurate evaluation of density is possible.

  In the specific example described above, the radiation detector 1 is a set of four cells 1a, but the number of cells 1a is not limited to four. By increasing the number of cells 1a, the radioactivity distribution of the measurement object 18 can be evaluated in more detail.

  The radioactivity measurement apparatus that implements such a method is, for example, the radioactivity measurement apparatus shown in FIG. 2, in which the radiation detector 1 is a set of a plurality of cells, and the three-dimensional modeling means 2 is the radiation detector 1. And a virtual three-dimensional model as a collection of a plurality of cells and a virtual three-dimensional model of a measurement object as a collection of parts facing the cell, and the conversion coefficient setting means is provided for each part of the measurement object. A conversion coefficient is obtained for each cell, and the radioactivity calculation means 5 is configured to obtain the radioactivity for each part of the measurement object and obtain the radioactivity of the whole measurement object from the radioactivity of each part.

  In the above description, the conversion coefficient is obtained by performing a simulation using a three-dimensional Monte Carlo calculation code. However, the method for setting the conversion coefficient is not limited to this. For example, a conversion coefficient may be obtained using a code for shielding calculation called a point attenuation kernel code.

  That is, in the conversion coefficient setting step, the thickness of the medium existing between the measurement object and the radiation detector, the attenuation coefficient of the medium, the build-up coefficient of the medium, and between the measurement object and the radiation detector Alternatively, a radioactivity measurement method may be used in which a conversion coefficient is obtained from the correlation between the number of radiations before and after passing through the medium approximately calculated based on the distance.

  More specifically, when the radiation emitted from the measurement object 18 passes through the medium existing between the measurement object 18 and the radiation detector 1, the relationship between the number of radiations before and after the passage is as follows: Approximate expression 4 can be obtained.

<Equation 4>
I = (1 / (4πr ² )) I ₀ Be ^−μd

Here, I is the number of radiation after passing through a certain medium, I ₀ is the number of radiation generated before passing through a certain medium, μ is an attenuation coefficient (cm ⁻¹ ), and d is the radiation of the measurement object 18. Is the thickness (cm) of the part through which B passes, B is the build-up coefficient, and r is the distance between the measurement object and the radiation detector 1. The attenuation coefficient μ and the build-up coefficient B are values determined according to the type of the medium, and the thickness d is a value determined according to the form of the measurement object 18, the position of radioactive contamination, and the like. The distance r can be obtained based on the positional relationship between the virtual three-dimensional models 16 and 17 formed in the virtual model process 21. The thickness d may be obtained based on the positional relationship between the virtual three-dimensional models 16 and 17. In the point decay kernel method used for radiation shielding calculation, calculation is performed using the above formula.

Since the relationship between I and I ₀ is known from the above equation, the conversion coefficient can be obtained in the conversion coefficient calculation step. That is, I ₀ corresponds to the number of virtual radiations emitted from the virtual three-dimensional model 16 of the measurement object 18, and I corresponds to the number of virtual radiations incident on the virtual three-dimensional model 17 of the radiation detector 1. , I / I ₀ is a conversion factor. And after calculating | requiring a conversion factor, the radioactivity of a measuring object is calculated | required in the same procedure as the above-mentioned case, and a radioactivity density | concentration and a radioactivity surface density are calculated | required. In this radioactivity measurement method, the measured radioactivity is an approximate value, but the calculation amount is small, so that the radioactivity can be easily determined in a short time.

  As shown in FIG. 10, the radioactivity measuring apparatus that implements this method includes a radiation detector 1 that counts radiation emitted from the measurement object 18, and a measurement object 18 and the radiation detector 1. The number of radiation before and after passing through the medium approximately calculated based on the thickness of the existing medium, the attenuation coefficient of the medium, the build-up coefficient of the medium, and the distance between the measurement object 18 and the radiation detector 1 The conversion coefficient setting means 19 for calculating the conversion coefficient from the correlation of the above and the radioactivity calculation means 5 for calculating the actual radioactivity of the measurement object based on the actual count rate and the conversion coefficient by the radiation detector 1 are provided. Is done. Then, for example, by adding the functions of the weight or volume measuring means 13 and the radioactive concentration calculating means 12 shown in FIG. 5 to the measuring apparatus of FIG. 10, the radioactive concentration measuring apparatus is configured. Further, for example, by adding the functions of the surface area measuring means 14 and the radioactive surface density calculating means 15 shown in FIG. 7 to the measuring apparatus of FIG. 10, the radioactive surface density measuring apparatus is configured.

  Further, even when a simulation is performed using a point decay kernel code to obtain a conversion coefficient, the upper and lower three-dimensional models 17 are calculated in the same manner as when a simulation is performed using a three-dimensional Monte Carlo calculation code to obtain a conversion coefficient. May be counted as an aggregate of a large number of cells, and the incidence of virtual γ rays may be counted for each cell.

It is a flowchart which shows an example of embodiment of the measuring method of the radioactivity of this invention. It is a schematic block diagram which shows an example of embodiment of the measuring device of the radioactivity of this invention. The conceptual diagram which shows the positional relationship of a radiation detector and a measurement object, (A) is a conceptual diagram which shows actual geometric positional relationship, (B) is the conceptual diagram which shows the positional relationship virtually modeled in three dimensions It is. It is a flowchart which shows an example of embodiment of the measuring method of the radioactive concentration of this invention. It is a schematic block diagram which shows an example of embodiment of the measuring apparatus of the radioactive concentration of this invention. It is a flowchart which shows an example of embodiment of the measuring method of the radioactive surface density of this invention. It is a schematic block diagram which shows an example of embodiment of the measuring apparatus of the radioactive surface density of this invention. It is a conceptual diagram of the system which verifies the radioactivity level of the demolition waste generated by the nuclear reactor decommissioning. It is a conceptual diagram of the radiation detector which consists of a collection of a some cell (radiation detector). It is a schematic block diagram which shows the other example of embodiment of the measuring device of the radioactivity of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation detector 2 Three-dimensional modeling means 3 Simulation means 4 Conversion coefficient calculation means 5 Radioactivity calculation means 12 Radioactivity concentration calculation means 13 Measuring instrument (weight or volume measurement means)
14 Surface area measuring means 15 Radioactive surface density calculating means 16 Three-dimensional model of measurement object 17 Three-dimensional model of radiation detector 18 Measurement object 21 Virtual modeling process 22 Virtual count calculation process 23 Conversion coefficient calculation process 24 Actual count rate Calculation step 25 Radioactivity calculation step 31 Weight or volume measurement step 33 Radioactivity concentration calculation step 42 Surface area measurement step 43 Radioactivity surface density calculation step

Claims (1)

A virtual modeling step of arranging a virtual three-dimensional model of the measurement object and the radiation detector in the same positional relationship as the actual geometric positional relationship in the virtual three-dimensional space, and emitting from the virtual three-dimensional model of the measurement target A conversion coefficient setting step for obtaining a conversion coefficient by associating the generated number of generated virtual radiations with the number of incident virtual radiations to the virtual three-dimensional model of the radiation detector, and the radiation emitted from the measurement object An actual count rate calculating step for actually counting the incidence on the radiation detector to obtain a count rate; and a radioactivity calculating step for obtaining the radioactivity of the measurement object from the count rate and the conversion factor, The radiation detector is set as a set of a plurality of cells and the measurement object is considered as a set of parts facing the cells. In the virtual modeling step, the radiation detector is set as a set of a plurality of cells. And a virtual three-dimensional model of the measurement object as a collection of parts, and performing the conversion coefficient setting step for each part of the virtual three-dimensional model of the measurement object, A conversion factor is determined for each of the cells, and the actual count rate calculation step is performed for each cell of the radiation detector to determine a count rate for each of the cells, and the radioactivity calculation step is performed to determine the measurement object. A radioactivity measurement method, wherein after obtaining radioactivity for each part, the radioactivity of the whole measurement object is obtained from the radioactivity of each part.

Images