Radiation source estimation method, dose reduction countermeasure evaluation method, radiation source estimation device, dose reduction countermeasure evaluation device, radiation source estimation program, and dose reduction countermeasure evaluation program

Abstract

To provide a method for accurately estimating a radiation source.SOLUTION: A radiation source estimation method comprises the steps of: acquiring shape information of a space of an evaluation object; acquiring a gamma-ray intensity distribution image of the space; acquiring a measurement value of a radiation dose rate at each measurement position; setting a radiation source position and a radiation source shape on the basis of the gamma-ray intensity distribution image and shape information; setting the radiation dose intensity on the basis of a contribution ratio of the radiation source and the measurement value of the radiation dose rate; calculating the radiation dose rate distribution by performing radiation dose analysis; comparing the calculation result of the radiation dose rate distribution with the radiation dose rate measurement value; and correcting at least one of the radiation source position, radiation source shape and radiation dose intensity on the basis of the comparison result. The method repeats the correction step, the calculation step and the comparison step until the calculation result of the radiation dose rate distribution and the radiation dose rate measurement value match each other with target accuracy.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a radiation source estimation method, a dose reduction countermeasure evaluation method, a radiation source estimation device, a dose reduction countermeasure evaluation device, a radiation source estimation program, and a dose reduction countermeasure evaluation program. [Background technology]

[0002] In order to safely work in an environment where radioactive materials are widely distributed within a nuclear reactor facility, such as the Fukushima Daiichi Nuclear Power Plant, and their locations cannot be identified, it is necessary to implement dose reduction measures and improve the dose in the work environment. To implement effective dose reduction measures, it is necessary to accurately identify the location of the radiation source (the source of radiation). Patent Document 1 discloses a method for estimating the intensity distribution of a radiation source inside a structure using measurement results from outside the structure. However, if the location of the radiation source cannot be identified, it is difficult to estimate the intensity distribution using the method described in the above document. To implement effective dose reduction measures, it is necessary to accurately identify the location of the radiation source and then estimate the intensity distribution. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-193817 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need for a method to accurately estimate the radiation source.

[0005] The present disclosure provides a radiation source estimation method, a dose reduction countermeasure evaluation method, a radiation source estimation device, a dose reduction countermeasure evaluation device, a radiation source estimation program, and a dose reduction countermeasure evaluation program that can solve the above problems. [Means for solving the problem]

[0006] The radiation source estimation method according to the present disclosure includes the steps of: acquiring shape information of a space to be evaluated; acquiring a gamma-ray intensity distribution image that visualizes the gamma-ray intensity distribution in the space; acquiring a measured value of a dose rate at a predetermined measurement position in the space; setting a radiation source position and a radiation source shape in the space based on the gamma-ray intensity distribution image and the shape information; setting the radiation source position to a radiation source intensity calculated based on the contribution rate of the radiation source based on the gamma-ray intensity distribution image and the measured value of the dose rate; the radiation source position, the radiation source shape, and the radiation source intensity, performing a dose analysis based on the radiation source position, the radiation source shape, and the radiation source intensity to calculate a dose rate distribution in the space; comparing the calculation result of the dose rate distribution with the measured dose rate values; and correcting at least one of the radiation source position, the radiation source shape, and the radiation source intensity based on the result of the comparison, wherein the correction step, the calculation step of the dose rate distribution, and the comparison step are repeated until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate values ​​match with a predetermined target accuracy.

[0007] The dose reduction countermeasure evaluation method according to the present disclosure includes the steps of: setting a dose reduction countermeasure for each of the radiation source positions estimated by the radiation source estimation method; calculating a dose rate distribution after the dose reduction countermeasure is implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction countermeasure is implemented; and determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction countermeasure is implemented.

[0008] The radiation source estimation device according to the present disclosure includes a means for acquiring shape information of a space to be evaluated, a means for acquiring a gamma-ray intensity distribution image that visualizes the gamma-ray intensity distribution in the space, a means for acquiring a measured value of a dose rate at a predetermined measurement position in the space, a means for setting a radiation source position and a radiation source shape in the space based on the gamma-ray intensity distribution image and the shape information, a means for setting a radiation source intensity calculated based on a contribution rate of the radiation source based on the gamma-ray intensity distribution image and the measured value of the dose rate at the radiation source position, and a means for calculating a dose solution based on the shape information, the radiation source position, the radiation source shape, and the radiation source intensity. and means for comparing the calculation result of the dose rate distribution with the measured dose rate values; and means for correcting at least one of the radiation source position, the radiation source shape, and the radiation source intensity based on the result of the comparison, wherein the correcting means performs the correction, the calculating means calculates the dose rate distribution based on the correction, and the comparing means compares the dose rate distribution based on the correction with the measured dose rate values, repeatedly until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate values ​​match with a predetermined target accuracy.

[0009] The dose reduction countermeasure evaluation device according to the present disclosure includes: means for setting a dose reduction countermeasure for each of the radiation source positions estimated by the radiation source estimation device; means for calculating the dose rate distribution after the dose reduction countermeasure has been implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction countermeasure has been implemented; and means for determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction countermeasure has been implemented.

[0010] The radiation source estimation program according to the present disclosure includes the steps of: causing a computer to perform a dose analysis based on shape information of a space to be evaluated, a gamma-ray intensity distribution image that visualizes the gamma-ray intensity distribution in the space, a radiation source position and a radiation source shape in the space that are set based on the shape information, and a radiation source intensity at the radiation source position that is set based on a contribution rate of the radiation source based on the gamma-ray intensity distribution image and a measured value of a dose rate at a predetermined measurement position in the space, thereby calculating a dose rate distribution in the space; and comparing the calculated result of the dose rate distribution with the measured value of the dose rate. and when at least one of the radiation source position, the radiation source shape, and the radiation source intensity is corrected based on the result of the comparison, performing the dose analysis again by applying the corrected information of the radiation source position, the radiation source shape, and the radiation source intensity, and calculating the dose rate distribution in the space after applying the corrected information, and causing the device to repeatedly perform the steps of calculating the dose rate distribution in the space after applying the corrected information and the comparing step until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate match with a predetermined target accuracy.

[0011] The dose reduction measure evaluation program according to the present disclosure causes a computer to execute the steps of: setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation program; calculating the dose rate distribution after the dose reduction measure has been implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction measure has been implemented; and determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction measure has been implemented. [Effects of the Invention]

[0012] The radiation source estimation method, radiation source estimation device, and radiation source estimation program disclosed herein enable accurate estimation of a radiation source. The dose reduction countermeasure evaluation method, dose reduction countermeasure evaluation device, and dose reduction countermeasure evaluation program disclosed herein enable effective dose reduction countermeasures to be planned. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a block diagram illustrating an example of a radiation source estimation apparatus according to an embodiment. [Figure 2] 10 is a flowchart illustrating an example of a radiation source estimation process and a dose reduction countermeasure evaluation process according to the embodiment. [Figure 3] FIG. 10 is a diagram illustrating an example of shape information of an evaluation target space according to the embodiment. [Figure 4] FIG. 2 is a diagram showing an example of a gamma ray intensity distribution image according to the embodiment; [Figure 5] FIG. 10 is a diagram showing an example of a measurement result of a dose rate according to the embodiment. [Figure 6] FIG. 10 is a diagram showing an example of a dose analysis result according to the embodiment. [Figure 7] 10A and 10B are diagrams illustrating a process for setting radiation source intensity according to an embodiment. [Figure 8] FIG. 2 is a first diagram showing an example of a radiation source position and a measurement position according to the embodiment. [Figure 9] FIG. 2 is a second diagram showing an example of a radiation source position and a measurement position according to the embodiment. [Figure 10] FIG. 10 is a third diagram showing an example of a radiation source position and a measurement position according to the embodiment. [Figure 11] FIG. 1 is a diagram illustrating an example of a hardware configuration of a radiation source estimation apparatus according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Embodiment> The radiation source estimation device of the present disclosure will be described below with reference to FIGS. (composition) FIG. 1 is a block diagram showing an example of a radiation source estimation apparatus according to an embodiment. The radiation source estimation device 10 estimates the radiation source by confirming the validity of the set position, shape, and intensity of the radiation source based on the consistency between the analytical value of the dose rate distribution and the measured value. As shown in the figure, the radiation source estimation device 10 includes a gamma ray intensity distribution image acquisition unit 11, a measured value acquisition unit 12, an input acceptance unit 13, a control unit 14, and a memory unit 15.

[0015] The gamma-ray intensity distribution image acquisition unit 11 acquires an image (referred to as a gamma-ray intensity distribution image) captured by a gamma-ray camera. A gamma-ray camera is a device that acquires information on the relative ratio of radiation directionality and intensity using, for example, a semiconductor detector, and captures an image that visualizes the gamma-ray intensity distribution by superimposing and outputting the information on an image captured by the camera. For example, when a gamma-ray camera captures an image of a nuclear reactor facility where radioactive materials are widely distributed, an image is captured in which radiation sources are superimposed on the walls, floors, equipment, ducts, cable trays, etc. within the facility and displayed at their respective distribution locations. The radiation sources are displayed in colors such as red, yellow, green, and blue depending on their intensity. A location displayed in red indicates a high dose of gamma rays coming from that location, and the dose decreases as the color changes to yellow, green, and blue. By referring to the gamma-ray intensity distribution image, the location, distribution shape, and relative dose level of the radiation source can be determined, but the absolute value of the dose cannot be determined.

[0016] The measurement value acquisition unit 12 acquires gamma ray measurement values ​​measured by a gamma ray measuring device. For example, a worker may carry a measuring device and measure the gamma ray dose rate while moving around the facility, or the dose rate may be measured using a remote measuring device. Alternatively, the dose rate may be measured by installing measuring devices at multiple locations within the facility. The measurement value acquisition unit 12 acquires measurement values ​​taken at various locations within the facility. The gamma ray measurement values ​​acquired by the measurement value acquisition unit 12 are absolute values ​​of the dose rate.

[0017] The input receiving unit 13 receives various setting information and instruction information for instructing the start and end of processing, etc., input using an input device such as a keyboard, a mouse, a touch panel, or a button. For example, the input receiving unit 13 receives shape information of a space α to be evaluated. The space α to be evaluated is, for example, a nuclear reactor facility. The shape information includes, for example, CAD data showing the shape of the nuclear reactor facility at the time of construction, images of the interior of the nuclear reactor facility, and three-dimensional point cloud information measured inside the facility using a three-dimensional measuring device. The input receiving unit 13 also receives settings for the position, shape (thickness, range), and intensity of the radiation source. The input receiving unit 13 records the received information in the memory unit 15 or outputs it to the control unit 14.

[0018] The control unit 14 executes and controls the radiation source estimation process and includes an analysis unit 141, an evaluation unit 142, and an output unit 143. The analysis unit 141 analyzes the three-dimensional dose rate distribution in the space α using a three-dimensional transport calculation code that can precisely reproduce the behavior of gamma rays, such as MCNP (Monte Carlo N-Particle Transport Code), PHITS (Particle and Heavy Ion Transport code System), etc. For example, the analysis unit 141 inputs the shape information of the space α and information such as the position, shape, and intensity of the radiation source received by the input receiving unit 13 to MCNP or the like, and outputs the dose rate distribution in the space α analyzed by MCNP or the like. The evaluation unit 142 compares the dose rate distribution in the space α analyzed by the analysis unit 141 with the dose rates measured at multiple positions in the space α acquired by the measurement acquisition unit 12, and evaluates whether the two are consistent. The output unit 143 outputs various information such as shape information of the space α (Figure 3), a gamma ray intensity distribution image (Figure 4), the distribution of measurement values ​​(Figure 5), the dose rate distribution analyzed by the analysis unit 141 (Figure 6), and the evaluation results by the evaluation unit 142 to a display device, an electronic file, etc. The storage unit 15 stores calculation codes such as MCNP, data currently being processed, and the like.

[0019] (operation) Next, the radiation source estimation process and the dose reduction countermeasure evaluation process of this embodiment will be described. FIG. 2 is a flowchart showing an example of a radiation source estimation process and a dose reduction countermeasure evaluation process according to the embodiment.

[0020] (Radiation source estimation processing) First, the shape information of the space to be evaluated is set (step S11). For example, an analyst inputs CAD data of the space α, and information such as the size and installation position of the equipment to be installed in the space α. The CAD data includes three-dimensional information of the floors and walls of the space α as well as ducts and cable trays laid in the space α. The input receiving unit 13 acquires the shape information and records it in the storage unit 15. An example of the shape information of the space α is shown in FIG. 3.

[0021] Next, the gamma ray intensity distribution image acquisition unit 11 acquires a gamma ray intensity distribution image (step S12). The gamma ray intensity distribution image is captured at a predetermined position in the space α. The gamma ray intensity distribution image acquisition unit 11 acquires the input gamma ray intensity distribution image and records it in the storage unit 15. An example of the gamma ray intensity distribution image is shown in FIG. 4. (Information such as "C: Duct 10%" shown in FIG. 4 is not included in the gamma ray intensity distribution image. This information will be described later.)

[0022] Next, the measurement value acquiring unit 12 acquires the measurement value of the dose rate (step S13). The measurement value acquiring unit 12 acquires the measurement value of the gamma ray dose rate measured at each location in the space α. The measurement value acquiring unit 12 acquires the input measurement value and records it in the memory unit 15. An example of the measurement value measured at each location is shown in FIG. 5.

[0023] Next, the analyst sets the radiation source position and shape (step S14). For example, when the analyst performs a predetermined operation, the output unit 143 outputs a gamma ray intensity distribution image (e.g., FIG. 4) and a three-dimensional model of the space α (e.g., FIG. 3) based on the shape information set in step S11 to the display device. The analyst refers to the gamma ray intensity distribution image and identifies a position in the space α corresponding to the image position where a color such as red, yellow, green, or blue is displayed. For example, if a red circle is displayed in a certain portion of the gamma ray intensity distribution image, the analyst sets the position corresponding to that portion in the shape information of the space α as the radiation source. The analyst also sets the area corresponding to the red circle in a wall, duct, equipment, etc. present at the identified radiation source position and the thickness of the layer of radioactive material adhering to that area (e.g., 1 cm) as the shape of the radiation source. The analyst inputs the set position and shape of the radiation source in the radiation source estimation device 10. The input receiving unit 13 acquires the input position and shape of the radiation source and records (sets) them in the memory unit 15.

[0024] Next, the analyst sets the radiation source intensity (step S15). First, based on the color displayed in the gamma-ray intensity distribution image, the analyst calculates the contribution rate (contribution rate to the dose rate measured at the position where the gamma-ray intensity distribution image was captured) of each radiation source position set in step S14, and inputs the calculated contribution rate into the radiation source estimation device 10. In the gamma-ray intensity distribution image of FIG. 4, red is displayed superimposed on the equipment at position A, red is displayed on the hotspot at position B, green is displayed on the duct at position C, and green is displayed on the piping at position D. For example, the analyst sets a contribution rate of 40% for positions A and B, which are displayed in red, and a contribution rate of 10% for positions C and D, which are displayed in green. Next, the analyst sets a radiation source intensity according to the contribution rate and distance for each radiation source position. For example, as illustrated in FIG. 7, assume that the measured dose rate at position P, where the gamma-ray intensity distribution image was captured, is 10 (mSv / h). If the dose rate of 10 mSv / h at position P is allocated according to the above contribution rate, the dose rate of gamma rays reaching position P from position A is 4 mSv / h, the dose rate of gamma rays reaching position P from position B is 4 mSv / h, the dose rate of gamma rays reaching position P from position C is 1 mSv / h, and the dose rate of gamma rays reaching position P from position D is 1 mSv / h. Next, the analyst calculates the radiation source strength required to reach the allocated dose rate at position P based on the distance between position P and each of positions A to D. For example, taking into account the distance between position P and position A, the analyst reverse-calculates that the radiation source strength at position A must be 100 in order for the dose rate at position P to be 4 mSv / h. The analyst also reverse-calculates the radiation source strength at position B to be 10 based on the distance between position P and position B and the dose rate at position P of 1 mSv / h. Similarly, the analyst calculates the radiation source intensity 10 at position C and the radiation source intensity 20 at position D. The analyst inputs the calculated radiation source intensities at positions A to D into the radiation source estimation device 10. The input receiving unit 13 acquires the input radiation source intensities and records (sets) them in the memory unit 15.

[0025] The radiation source intensities at positions A to D may be set by the radiation source estimation device 10. For example, an analyst inputs the measurement value at position P and the contribution rates of positions A to D to the radiation source estimation device 10. The input receiving unit 13 acquires the input contribution rates and records (sets) them in the storage unit 15. The control unit 14 then calculates the distances from position P to positions A to D based on the shape information of the space α, calculates the radiation source intensities at positions A to D based on the input measurement value (10 (mSv / h)) at position P, the contribution rates of each of positions A to D, and the calculated distances from position P to positions A to D, and records (sets) the calculated radiation source intensities at positions A to D in the storage unit 15. Alternatively, the analysis unit 141 may estimate the radiation source intensities using MCNP or the like. The contribution rates may be set by the radiation source estimation device 10, rather than by an analyst. For example, the radiation source estimation device 10 may be provided with a function for image processing a gamma ray intensity distribution image, and this function may be used to extract pixel regions of each color, red, yellow, green, and blue, from the gamma ray intensity distribution image. The control unit 14 may then set a contribution rate for each color so that the contribution rates of the red, yellow, green, and blue regions decrease in this order (red having the highest contribution rate and blue having the lowest). For example, in the case of red, the contribution rate can be calculated as follows: (relative intensity of red × number) / {(relative intensity of red × number) + (relative intensity of yellow × number) + (relative intensity of green × number) + (relative intensity of blue × number)} × 100. The same applies to other colors.

[0026] Next, the analysis unit 141 executes a dose rate distribution analysis (step S16). The analysis unit 141 inputs the shape information of the space α, the radiation source intensity and shape (range, thickness) of the radiation source positions A to D, etc. into a calculation code such as MCNP, executes a dose analysis, and calculates a three-dimensional dose rate distribution in the space α. For example, the analysis result of the dose rate distribution shown in Fig. 6 can be obtained (Fig. 6 shows a two-dimensional dose rate distribution diagram as an example).

[0027] Next, the evaluation unit 142 checks the reproducibility of the dose rate (step S17). The reproducibility of the dose rate refers to whether the dose rate distribution calculated by the dose rate distribution analysis reproduces the actual dose rate distribution, that is, whether the analysis result of the dose rate distribution matches the measured dose rate values ​​measured at each location. The evaluation unit 142 compares the analysis result of the dose rate distribution obtained in step S16 (e.g., FIG. 6) with the measured dose rate values ​​obtained in step S13 (e.g., FIG. 5) and determines whether the analytical value and the measured dose rate at each location match with a predetermined target accuracy (whether they match or whether the difference between them falls within a predetermined range). For example, if the differences between the measured and analytical values ​​at all measurement locations are within a predetermined range, the evaluation unit 142 determines that the reproducibility of the dose rate is good. If there is a significant difference at even one location, the evaluation unit 142 determines that the reproducibility of the dose rate is not good. If the evaluation unit 142 determines that the dose rate reproducibility is good (step S18; Yes), the position, shape, and intensity of the radiation source set in steps S14 to S15 are considered to be appropriate. The control unit 14 determines the radiation source defined by the position, shape, and intensity set in steps S14 to S15 as the radiation source distributed in the space α to be evaluated (step S19).

[0028] If the evaluation unit 142 determines that the reproducibility of the dose rate is not good (step S18; No), the output unit 143 outputs a message notifying the user that the reproducibility is low, such as "There is an error in the set radiation source position, shape, or intensity" (step S181), and repeats the processes from step S14 onward. For example, the analyst corrects at least one of the radiation source position, radiation source shape, and radiation source intensity and inputs the corrected information to the radiation source estimation device 10. The input receiving unit 13 acquires the corrected radiation source position, etc., and records (corrects) them in the storage unit 15 (steps S14 and S15). The analysis unit 141 then performs a dose rate distribution analysis based on the corrected radiation source position, etc. (step S16), and the evaluation unit 142 checks and determines the reproducibility of the dose rate (steps S17 and S18). This process is repeated until the evaluation unit 142 determines that the reproducibility of the dose rate is good.

[0029] Here, with reference to FIGS. 8 to 10, factors that reduce the reproducibility of the radiation source position and the like set in steps S14 and S15 will be described. Radiation source estimation is relatively easy if the relationship between the hotspot E and the measurement position P on the gamma-ray intensity distribution image is such that direct rays from the radiation source E reach the measurement position P, as shown in FIG. 8. However, as shown in FIG. 9, if a structure F1 exists between the true radiation source F and the measurement position P on the gamma-ray intensity distribution image, and gamma rays bypass the structure F1, strike a wall F3, and are scattered, the scattered rays reach the measurement position P, the gamma-ray intensity distribution image taken at the measurement position P will display red or yellow at the scattering position F2. If the radiation source position is set with reference to this gamma-ray intensity distribution image, F2 will be set as the radiation source position. In this case, for example, a discrepancy will occur between the actual dose rate measured at a position P1 close to the true radiation source F and the dose rate at position P1 indicated by the dose rate distribution analyzed using the scattering position F2 as the radiation source position. If only one measurement result (e.g., position P) is available, setting F2 as the radiation source position will not reveal any errors in the radiation source position. However, comparing the measured dose rates at multiple positions with the analytical values ​​can reveal errors in the radiation source position. Furthermore, as shown in Figure 10, if a high-dose device is located on the opposite side of measurement position P across wall F3, and a gamma-ray camera captures streaming rays (streaming rays are radiation rays that pass through narrow spaces such as gaps between walls or through holes in walls) that reach measurement position P through a locally thinned region F4 of wall F3, red or yellow will appear at transmission position F4 in the gamma-ray intensity distribution image captured at measurement position P. Setting the radiation source position based on this gamma-ray intensity distribution image will identify transmission position F4 as the radiation source position. In this case, there is a high possibility that the measured dose rates at locations other than measurement position P will differ from the analytical results obtained by MCNP or other methods. By comparing the measured dose rates at multiple locations with the analytical results of the dose rate distribution in this way, errors in the estimated radiation source position, etc. can be detected.When low reproducibility is output (step S181), the analyst makes an engineering judgment while referring to the shape information of the space α, for example, by considering the possibility that the radiation source shown in the gamma ray intensity distribution image is a scattered ray or a streaming ray, resets the radiation source position, radiation source shape, and radiation source intensity, and repeats the process from step S14.

[0030] Note that gamma ray intensity distribution images may be captured at multiple positions within the space α. In this case, gamma ray intensity distribution images captured at multiple positions are acquired in step S12. Then, the processes of steps S14 to S18 are performed for each gamma ray intensity distribution image. In this case, a step of comparing the radiation source position, radiation source shape, and radiation source intensity determined based on each gamma ray intensity distribution image may be further provided, and the radiation source position, etc. may be further adjusted based on the comparison results. Alternatively, an analyst may set the radiation source position, shape, and intensity based on multiple gamma ray intensity distribution images (steps S14 to S15), and then repeatedly perform the process of checking the reproducibility of these settings (steps S16 to S18). In addition, in steps S14 to S15, where the analyst sets the position, shape, and intensity of the radiation source, this can be substituted by setting the position, shape, and intensity of the radiation source by estimation using, for example, a statistical model using a data assimilation method based on the data acquired in steps S12 to S13.

[0031] (Dose reduction measures evaluation process) Once the radiation source is determined by the above process, it becomes possible to execute the process of evaluating dose reduction measures. First, the analyst sets the dose contribution rate for each radiation source (step S20). The analyst sets the contribution rate of each radiation source to each location in the space α, taking into consideration direct rays, scattered rays, and streaming rays from the radiation source. Next, the analyst sets a dose reduction target for each radiation source (step S21). For example, the analyst sets a target to reduce the dose rate from "radiation source 1" present on the floor from 7 (mSv / h) to 0.1 (mSv / h), and inputs the target value into the radiation source estimation device 10. The input receiving unit 13 acquires the input target value and records (sets) it in the memory unit 15. Next, the analyst sets dose reduction measures (step S22). For example, the analyst sets dose reduction measures for each radiation source determined in step S19, such as implementing shielding measures to deal with "radiation source 2" present in the cable tray, and implementing cleaning or wiping to deal with "radiation source 3" present in the wall and "radiation source 4" present on the ceiling, and inputs the dose reduction measures into the radiation source estimation device 10. The input receiving unit 13 acquires the input dose reduction measures for each radiation source and records (sets) them in the storage unit 15. The radiation source estimation process can accurately estimate the position, shape, and intensity of the radiation source, so that in step S22, it is possible to appropriately set dose reduction measures to achieve the goal set in step S21 based on the estimation results.

[0032] Next, the dose rate distribution after the dose reduction measures are implemented is evaluated (step S23). For example, the analyst sets the intensity and shape (area, thickness) of each radiation source after the dose reduction measures set in step S22 are implemented, and inputs these values ​​to the radiation source estimation device 10. The input receiving unit 13 acquires the intensity and shape of each input radiation source and records (sets) them in the storage unit 15. Next, the analysis unit 141 inputs the shape information of the space α, the position of each radiation source determined in step S19, the radiation source intensity and shape after the dose reduction measures are implemented, etc. into MCNP or the like, and executes the calculation code. As a result, the dose rate distribution in the space α shown in FIG. 6 is obtained. The control unit 14 compares the analysis result by the analysis unit 141 with a predetermined target value and determines whether the dose rate in the space α after the dose reduction measures are implemented has reached the target (step S24). For example, if the analysis result of the dose rate distribution by the analysis unit 141 indicates that the dose rate is equal to or less than the target value at any position in the space α, the control unit 14 determines that the target has been reached, and if not, determines that the target has not been reached. When the control unit 14 determines that the target has been reached (step S24; Yes), the analyst plans dose reduction measure construction based on the dose reduction measure set in step S22 (step S25).

[0033] If the control unit 14 determines that the target has not been reached (step S24; No), the output unit 143 outputs a message notifying that the dose reduction measures are insufficient and the analysis results of step S23 (step S241), and repeats the processes from step S21 onwards. This makes it possible to formulate dose reduction measures that can achieve the target dose rate.

[0034] (effect) As described above, according to this embodiment, it is possible to accurately estimate the position, shape, and intensity of radiation sources distributed in a space to be evaluated. Furthermore, it is possible to determine effective dose reduction measures based on the results of radiation source estimation.

[0035] FIG. 11 is a diagram illustrating an example of a hardware configuration of a radiation source estimation apparatus. The computer 900 includes a CPU 901 , a main memory device 902 , an auxiliary memory device 903 , an input / output interface 904 , and a communication interface 905 . The radiation source estimation apparatus 10 described above is implemented in a computer 900. The above-described functions are stored in the auxiliary storage device 903 in the form of a program. The CPU 901 reads the program from the auxiliary storage device 903, loads it into the main storage device 902, and executes the above-described processing in accordance with the program. The CPU 901 also allocates a storage area in the main storage device 902 in accordance with the program. The CPU 901 also allocates a storage area in the auxiliary storage device 903 for storing data being processed in accordance with the program.

[0036] A program for implementing all or part of the functions of the radiation source estimation apparatus 10 may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed to perform processing by each functional unit. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. If a WWW system is used, the term "computer system" also includes a homepage providing environment (or display environment). The term "computer-readable recording medium" refers to portable media such as CDs, DVDs, and USBs, as well as storage devices such as hard disks built into the computer system. If the program is distributed to the computer 900 via a communication line, the computer 900 may load the program into the main storage device 902 and execute the processing described above. The program may be for implementing part of the functions described above, or may be capable of implementing the functions described above in combination with a program already stored in the computer system.

[0037] As described above, several embodiments according to the present disclosure have been described, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as defined in the claims, as well as in the scope and spirit of the invention.

[0038] <Additional Notes> The radiation source estimation method, the dose reduction countermeasure evaluation method, the radiation source estimation device, the dose reduction countermeasure evaluation device, the radiation source estimation program, and the dose reduction countermeasure evaluation program described in the embodiments can be understood, for example, as follows.

[0039] (1) A radiation source estimation method according to a first aspect includes the steps of: acquiring shape information of a space to be evaluated; acquiring a gamma-ray intensity distribution image that visualizes the gamma-ray intensity distribution in the space; acquiring a measured value of a dose rate at a predetermined measurement position in the space; setting a radiation source position and a radiation source shape in the space based on the gamma-ray intensity distribution image and the shape information; setting the radiation source position to a radiation source intensity calculated based on the contribution rate of the radiation source set based on the gamma-ray intensity distribution image and the measured value of the dose rate; the step of performing dose analysis based on the radiation source shape and the radiation source intensity to calculate a dose rate distribution in the space; the step of comparing the calculation result of the dose rate distribution with the measured dose rate value; and the step of correcting at least one of the radiation source position in the space, the radiation source shape, and the radiation source intensity based on the result of the comparison, wherein the correction step, the step of calculating the dose rate distribution, and the step of comparing are repeated until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate value match with a predetermined target accuracy. This allows the radiation source to be estimated with high accuracy.

[0040] (2) A radiation source estimation method according to a second aspect is the radiation source estimation method of (1), in which, when setting the radiation source intensity, the measured value of the dose rate measured at the same position as the shooting position of the gamma ray intensity distribution image is allocated based on the contribution rate, and the radiation source intensity is set based on the allocated value and the distance between the measurement position and the radiation source position. This allows a specific value of the radiation source intensity to be set.

[0041] (3) A radiation source estimation method according to a third aspect is the radiation source estimation method of (1) to (2), wherein in the step of comparing the calculated result of the dose rate distribution with the measured value of the dose rate, the measured values ​​of the dose rates at a plurality of positions are compared with the calculated result of the dose rate distribution, and the correction step, the step of calculating the dose rate distribution, and the comparison step are repeated until the measured value of the dose rate at each of the plurality of positions matches the calculated result of the dose rate distribution with the target accuracy. This allows the validity of the initially set radiation source position, radiation source shape, and dose to be confirmed. If the calculated dose rate distribution differs from the dose measurement values ​​at each location, the settings for the radiation source position, etc. are corrected. This allows the radiation source position to be estimated with high accuracy.

[0042] (4) A radiation source estimation method according to a fourth aspect is the radiation source estimation method of (3), further comprising a step of notifying that there is an error in any of the radiation source position, the radiation source shape, and the radiation source intensity, if there is any inconsistency as a result of comparing the measured dose rates at the multiple positions with the calculated dose rate distribution. This makes it possible to notice an error when, for example, a radiation source is set incorrectly due to the influence of scattered rays or streaming rays.

[0043] (5) A radiation source estimation method according to a fifth aspect is the radiation source estimation method according to any one of (1) to (4), further comprising the step of notifying whether or not the comparison results in a match at the target accuracy. This makes it possible to determine whether the set radiation source position, radiation source shape, and radiation source intensity are appropriate.

[0044] (6) A sixth aspect of the radiation source estimation method is the radiation source estimation method of any one of (1) to (5), wherein the step of acquiring gamma-ray intensity distribution images includes the steps of acquiring gamma-ray intensity distribution images taken at a plurality of positions in the space, and for each of the gamma-ray intensity distribution images, setting a radiation source position, the radiation source shape, and the contribution rate in the space, setting the radiation source intensity, calculating a dose rate distribution in the space by the dose analysis, comparing the calculation result of the dose rate distribution with the measured dose rate values, the correction step, and repeating the correction step, the calculation step of the dose rate distribution in the space, and the comparing step until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate values ​​are consistent with the target accuracy, and further includes the step of comparing the radiation source position, the radiation source shape, and the radiation source intensity obtained based on each of the gamma-ray intensity distribution images. This allows the position, shape, and intensity of the radiation source to be calculated based on multiple gamma-ray intensity distribution images, and the results can be compared.If there are discrepancies in the radiation source position or dose within the same area, the possibility of scattering or streaming can be considered, and the exact source position can be estimated.

[0045] (7) A radiation source estimation method according to a seventh aspect is a radiation source estimation method according to any one of (1) to (6), wherein in the step of calculating the dose rate distribution, the dose analysis is performed using a three-dimensional transport calculation code that can reproduce the behavior of gamma rays. This makes it possible to calculate the dose rate distribution.

[0046] (8) A dose reduction measure evaluation method according to an eighth aspect includes the steps of: setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation methods of (1) to (7); calculating the dose rate distribution after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction measure is implemented; and determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction measure is implemented. This allows for the planning of dose reduction measures that will achieve the target.

[0047] (9) A radiation source estimation device according to a ninth aspect includes: a means for acquiring shape information of a space to be evaluated; a means for acquiring a gamma-ray intensity distribution image that visualizes the gamma-ray intensity distribution in the space; a means for acquiring a measured value of a dose rate at a predetermined measurement position in the space; a means for setting a radiation source position and a radiation source shape in the space based on the gamma-ray intensity distribution image and the shape information; a means for setting a radiation source intensity calculated based on the measured value of the dose rate and a contribution rate of the radiation source set based on the gamma-ray intensity distribution image at the radiation source position; and a means for performing a dose analysis based on the shape information and the radiation source intensity. The system includes a means for calculating a dose rate distribution in the space, a means for comparing the calculation result of the dose rate distribution with the measured value of the dose rate, and a means for correcting at least one of the radiation source position in the space, the radiation source shape, and the radiation source intensity based on the result of the comparison, and the correcting means performs the correction, the calculating means calculates the dose rate distribution based on the correction, and the comparing means compares the corrected dose rate distribution with the measured value of the dose rate repeatedly until the calculation result of the dose rate distribution by the dose analysis matches the measured value of the dose rate with a predetermined target accuracy.

[0048] (10) A dose reduction countermeasure evaluation device according to a tenth aspect includes a means for setting a dose reduction countermeasure for each radiation source position estimated by the radiation source estimation device described in (9), a means for calculating the dose rate distribution after the dose reduction countermeasure is implemented based on the radiation source strength and the radiation source shape for each radiation source position after the dose reduction countermeasure is implemented, and a means for determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction countermeasure is implemented.

[0049] (11) A radiation source estimation program according to an eleventh aspect includes, in a computer 900, a step of performing a dose analysis based on shape information of a space to be evaluated, a gamma-ray intensity distribution image visualizing a gamma-ray intensity distribution in the space, a radiation source position and a radiation source shape in the space that are set based on the shape information, and a radiation source intensity at the radiation source position that is set based on a contribution rate of the radiation source based on the gamma-ray intensity distribution image and a measured value of a dose rate at a predetermined measurement position in the space, to calculate a dose rate distribution in the space; and a step of comparing the calculated result of the dose rate distribution with the measured value of the dose rate. and when at least one of the radiation source position, the radiation source shape, and the radiation source intensity is corrected based on the result of the comparison, performing the dose analysis again by applying the corrected information of the radiation source position, the radiation source shape, and the radiation source intensity, and calculating a dose rate distribution in the space after applying the corrected information, wherein the process of calculating the dose rate distribution in the space after applying the corrected information and the comparing step are repeated until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate match with a predetermined target accuracy.

[0050] (12) A dose reduction measure evaluation program according to a twelfth aspect causes a computer 900 to execute the steps of: setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation program described in (11); calculating the dose rate distribution after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction measure is implemented; and determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction measure is implemented. [Explanation of symbols]

[0051] 10...Radiation source estimation device 11. Gamma-ray intensity distribution image acquisition unit 12 Measurement acquisition section 13 Input reception section 14. Control section 141...Analysis Department 142...Evaluation section 143 Output section 15...Storage section 900···Computer 901 CPU 902...Main memory 903...Auxiliary storage device 904 Input / Output Interface 905···Communication Interface

Claims

1. acquiring shape information of a space to be evaluated; acquiring a gamma ray intensity distribution image that visualizes the gamma ray intensity distribution in the space; obtaining dose rate measurements at predetermined measurement locations in the space; setting a radiation source position and a radiation source shape in the space based on the gamma ray intensity distribution image and the shape information; a step of setting a radiation source intensity calculated based on a contribution rate of the radiation source based on the gamma ray intensity distribution image and the measured value of the dose rate at the radiation source position; performing a dose analysis based on the shape information, the radiation source position, the radiation source shape, and the radiation source intensity, and calculating a dose rate distribution in the space; comparing the calculated dose rate distribution with the measured dose rate; modifying at least one of the source position, the source shape, and the source intensity based on the results of the comparison; and repeating the correction step, the calculation step of the dose rate distribution, and the comparison step until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate match with a predetermined target accuracy. Source estimation method.

2. When setting the radiation source intensity, the measured value of the dose rate measured at the same position as the imaging position of the gamma ray intensity distribution image is allocated to the radiation source position based on the contribution rate; setting the radiation source intensity based on the allocated value and the distance between the imaging position and the radiation source position; The radiation source estimation method according to claim 1 .

3. In the step of comparing the calculated result of the dose rate distribution with the measured value of the dose rate, comparing the measured dose rates at a plurality of positions with the calculated dose rate distribution; repeating the correcting step, the calculating step of the dose rate distribution, and the comparing step until the measured value of the dose rate at each of the plurality of positions and the calculated result of the dose rate distribution match with the target accuracy. The radiation source estimation method according to claim 1 or 2.

4. a step of notifying that there is an error in any of the radiation source position, the radiation source shape, and the radiation source intensity, if there is any inconsistency as a result of comparing the measured values ​​of the dose rates at the plurality of positions with the calculated results of the dose rate distribution; The radiation source estimation method according to claim 3, further comprising:

5. a step of notifying whether the comparison results in a match at the target accuracy; The radiation source estimation method according to claim 1 or 2, further comprising:

6. In the step of acquiring the gamma ray intensity distribution image, gamma ray intensity distribution images captured at a plurality of positions in the space are acquired, For each of the gamma ray intensity distribution images, setting the radiation source position and the radiation source shape; setting the radiation source intensity; calculating the dose rate distribution; comparing the calculated dose rate distribution with the measured dose rate; the modifying step; repeating the correction step, the calculation step of the dose rate distribution in the space, and the comparison step until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate values ​​match with the target accuracy; Run further comparing the radiation source position, the radiation source shape, and the radiation source intensity obtained based on each of the gamma ray intensity distribution images; The radiation source estimation method according to claim 1 , comprising:

7. In the step of calculating the dose rate distribution, the dose analysis is performed using a three-dimensional transport calculation code that can reproduce the behavior of gamma rays. The radiation source estimation method according to claim 1 or 2.

8. a step of setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation method according to claim 1 or 2; calculating the dose rate distribution after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each radiation source position after the dose reduction measure is implemented; determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction measure has been implemented; A dose reduction measure evaluation method having the following.

9. A means for acquiring shape information of a space to be evaluated; a means for acquiring a gamma ray intensity distribution image that visualizes the gamma ray intensity distribution in the space; means for acquiring a measured value of a dose rate at a predetermined measurement position in the space; a means for setting a radiation source position and a radiation source shape in the space based on the gamma ray intensity distribution image and the shape information; a means for setting a radiation source intensity at the radiation source position, the radiation source intensity being calculated based on the contribution rate of the radiation source based on the gamma ray intensity distribution image and the measured value of the dose rate; a means for performing a dose analysis based on the shape information, the radiation source position, the radiation source shape, and the radiation source intensity, and calculating a dose rate distribution in the space; means for comparing the calculated dose rate distribution with the measured dose rate; means for modifying at least one of the source position, the source shape, and the source intensity based on the results of the comparison; and the correcting means performs the correction, the calculating means calculates the dose rate distribution based on the correction, and the comparing means compares the dose rate distribution based on the correction with the measured dose rate values, repeatedly until the calculation result of the dose rate distribution by the dose analysis matches the measured dose rate values ​​with a predetermined target accuracy; Source estimation device.

10. a means for setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation device according to claim 9; a means for calculating the dose rate distribution after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each radiation source position after the dose reduction measure is implemented; a means for determining whether or not the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction measures have been implemented; A dose reduction measure evaluation device having the same.

11. On the computer, a step of performing a dose analysis based on shape information of a space to be evaluated, a gamma-ray intensity distribution image that visualizes the gamma-ray intensity distribution in the space, a radiation source position and a radiation source shape in the space that are set based on the shape information, and a radiation source intensity at the radiation source position that is set based on a contribution rate of the radiation source based on the gamma-ray intensity distribution image and a measured value of a dose rate at a predetermined measurement position in the space, and calculating a dose rate distribution in the space; comparing the calculated dose rate distribution with the measured dose rate; when at least one of the radiation source position, the radiation source shape, and the radiation source intensity is corrected based on the result of the comparison, performing the dose analysis again by applying the corrected information of the radiation source position, the radiation source shape, and the radiation source intensity, and calculating a dose rate distribution in the space after applying the corrected information; and a process of repeatedly performing a step of calculating the dose rate distribution in the space after the application and the step of comparing until the calculation result of the dose rate distribution by the dose analysis and the measured dose rate match with a predetermined target accuracy; A radiation source estimation program that executes the above.

12. On the computer, a step of setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation program according to claim 11; calculating the dose rate distribution after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each radiation source position after the dose reduction measure is implemented; determining whether the dose rate in the space has reached a predetermined target based on the dose rate distribution after the dose reduction measure has been implemented; A dose reduction measures evaluation program that implements the above.

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