Degradability range display method, degradation method, and degradability range display system

Abstract

This degradability range display method is for displaying a degradability range of an object to be degraded having a predetermined structure, and displays a degradability range corresponding to a predetermined sampling position of the object to be degraded on the basis of measurement information on a radiation dose and radiation energy at the sampling position and distribution information on a distribution of radioactivity in the depth direction corresponding to the sampling position.

Description

Decomposable range display method, decomposition method, and decomposable range display system

[0001] The present disclosure relates to a decomposable range display method, a decomposition method, and a decomposable range display system.

[0002] A known example of a device having an activated structure is the device disclosed in Patent Document 1. The device disclosed in Patent Document 1 is a self-shielded cyclotron that generates radiation during operation, and therefore, when it is disposed of, activated parts of the device's components and surrounding materials must be disassembled and disposed of as radioactive contaminated material.

[0003] Japanese Patent Application Laid-Open No. 2019-160462

[0004] Here, for decomposition objects such as the self-shield described above, it is necessary to distinguish between activated and non-activated parts. In particular, for such decomposition objects, activation may progress not only on the surface but also in the depth direction. In contrast, to measure the radioactivity concentration in the depth direction, it is necessary to obtain a sample by core drilling, divide it into several pieces in the depth direction, and measure the radioactivity concentration. This work must be performed at multiple points on the self-shield.

[0005] Therefore, an object of the present disclosure is to provide a decomposable range display method, a decomposition method, and a decomposable range display system for easily displaying a decomposable range.

[0006] A method for displaying a decomposable range according to one embodiment of the present disclosure is a method for displaying a decomposable range of a decomposable object having a predetermined structure, and displays the decomposable range corresponding to the sampling position based on measurement information of the radiation dose and radiation energy at a predetermined sampling position of the decomposable object and distribution information regarding the distribution of radioactivity in the depth direction corresponding to the sampling position.

[0007] This method for displaying a resolvable range displays a resolvable range corresponding to a sampling position based on measurement information of the radiation dose and radiation energy at a predetermined sampling position of an object to be decomposed and distribution information relating to the distribution of radioactivity in the depth direction corresponding to the sampling position. In this way, by using the measurement information and distribution information, it is possible to display a resolvable range corresponding to a sampling position. As described above, the resolvable range can be easily displayed.

[0008] The radiation dose and radiation energy at the sampling position may be measured using a radiation measuring device. In this way, measurement using a radiation measuring device allows for easy measurement without involving destruction such as core boring.

[0009] The decomposition target may include a radiation source that generates radiation and a shield that covers the radiation source with a shielding member. Since the shield covers the radiation source, activation progresses in the depth direction, but the present disclosure makes it possible to easily display the decomposable range.

[0010] The radiation source is a target device that is irradiated with particle beams from an accelerator, and the shield may be a self-shielded device that covers the target device. Because the activation pattern of a self-shielded device varies depending on the location, measurements must be taken at multiple sampling positions. Therefore, by adopting non-destructive measurements, the effect of being able to easily display the resolvable range becomes more pronounced.

[0011] The decomposition target may include, for example, steel plates and concrete.

[0012] The decomposable range display method may further include a calculation step of setting a virtual model of the decomposition object and calculating the radioactivity concentration at each position in the depth direction from the surface of the model, a measurement step of preparing the actual decomposition object, obtaining core samples extending in the depth direction from sampling positions in the actual object, and measuring the radioactivity concentrations of the core samples, and a distribution information acquisition step of acquiring distribution information regarding the distribution of the radioactivity concentration in the depth direction corresponding to the sampling positions based on the radioactivity concentrations obtained in the calculation step and the radioactivity concentrations obtained in the measurement step. In this case, by using the actual object in addition to the virtual model, the radioactivity concentration in the depth direction can be accurately and easily grasped.

[0013] A disassembly method according to an embodiment of the present disclosure may disassemble a disassembly target object based on the decomposable range displayed by the above-described decomposable range display method. By performing the disassembly work based on the range displayed by the above-described decomposable range display method, the disassembly work can be easily performed.

[0014] A decomposable range display system according to one embodiment of the present disclosure is a decomposable range display system that displays the decomposable range of a decomposable object having a predetermined structure, and includes a display unit that displays the decomposable range corresponding to a sampling position based on measurement information of the radiation dose and radiation energy at a predetermined sampling position of the decomposable object and distribution information regarding the distribution of radioactivity in the depth direction corresponding to the sampling position.

[0015] According to this decomposable range display system, it is possible to obtain the same effects and advantages as the above-mentioned decomposable range display method.

[0016] According to the present disclosure, it is possible to provide a decomposable range display method, a decomposition method, and a decomposable range display system that can easily display a decomposable range.

[0017] FIG. 1 is a schematic diagram showing a decomposable range display system for carrying out a decomposable range display method according to the present embodiment. FIG. 2 is a cross-sectional view of a self-shielded accelerator 1 in a plan view. FIG. 3 is a front view of the self-shielded accelerator 1, with the front side wall portion omitted. FIG. 4 is a process diagram showing a disassembly method. FIG. 5 is a process diagram showing detailed processing contents of a distribution information acquisition method (step S10). FIG. 6 is a process diagram showing detailed processing contents of a distribution information acquisition method (step S10). FIG. 7 is a diagram showing a virtual model. FIG. 8 is a table showing experimental conditions. FIG. 9 is a table showing calculation results of detection efficiency. FIG. 10 is a table showing the weight of a system of steel plates and concrete for each diameter. Rw Ｌ and Rw ｔｏｔａｌ 1 is a table showing the calculation results of Ｌ 3 is a graph showing the calculation results. A table summarizing the analysis results at sampling positions SP1 to SP8 and the radioactivity calculation conditions. A table summarizing the analysis results at sampling positions SP1 to SP8 and the radioactivity calculation conditions. A table summarizing the analysis results at sampling positions SP1 to SP8 and the radioactivity calculation conditions. A graph comparing the radioactivity depth distribution calculated using a virtual model with the depth distribution obtained by measuring an actual object. A graph comparing the radioactivity depth distribution calculated using a virtual model with the depth distribution obtained by measuring an actual object. A graph comparing the radioactivity depth distribution calculated using a virtual model with the depth distribution obtained by measuring an actual object. A graph comparing the radioactivity depth distribution calculated using a virtual model with the depth distribution obtained by measuring an actual object. A process diagram showing the decomposable range display process. A diagram showing the display contents of the display unit.

[0018] Hereinafter, a method for displaying a decomposable range according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In addition, the terms "upper" and "lower" may be used in the description, which correspond to the upper and lower directions in the drawings.

[0019] The decomposable range display method according to this embodiment is a method for displaying the decomposable range of a decomposition target 50 having a predetermined structure that should be decomposed by activation. Fig. 1 is a schematic diagram showing a decomposable range display system 100 for implementing the decomposable range display method according to this embodiment.

[0020] The decomposition target 50 is a structure that needs to be partially or completely decomposed by activation. The decomposition target 50 may include, for example, a radiation source that generates radiation and a shield that covers the radiation source with a shielding member. A self-shielded accelerator 1 as shown in FIGS. 2 and 3 may be used as such a decomposition target 50. In this case, the main radiation source is a target device 10. The shield is a self-shield 6 that covers the target device 10. The decomposition target 50 may include a steel plate 17 and concrete 18. However, the decomposition target 50 is not limited to a combination of the steel plate 17 and the concrete 18. For example, the self-shield 6 may be composed of only the concrete 18 or only the steel plate 17. "Heavy concrete" is used as the concrete 18 used for the self-shield 6. However, "ordinary concrete" may also be used as the concrete 18. In heavy concrete, the cobalt contained in the iron is activated (60Co), so the distribution of cobalt may be examined. The present inventors have discovered that cobalt is dominant in heavy concrete. On the other hand, in ordinary concrete, all we need to do is look at the distribution of activated europium.

[0021] The decomposition target 50 is not limited to the self-shielded accelerator 1, but may be a two-layer shielding wall in the case of a wall shield that is not self-shielded. For example, it may be a concrete / steel plate installed under the ceiling. The decomposition target 50 may also be a shielding wall in which an accelerator without a self-shield is installed. Accelerators without a self-shield may be accelerators for various purposes, such as accelerators for treatment devices that irradiate charged particle beams to treat cancer, accelerators for neutron capture therapy systems that treat cancer using boron neutron capture therapy (BNCT), accelerators for PET, accelerators for RI production, and accelerators for nuclear experiments. Furthermore, in the case of a particle beam therapy device, the main radiation source may be a collimator, deflector, damper, or the like installed inside the accelerator to process the beam emitted from the accelerator. The radiation source may also be a degrader (which attenuates energy) or a collimator located on the path of the particle beam emitted from the accelerator to the irradiation unit. The degrader scatters protons when it hits them, generating neutrons. In the case of BNCT, the radiation source may be a target that is irradiated with a proton beam to emit a neutron beam.

[0022] 2 and 3, the configuration of a self-shielded accelerator 1, which is an example of the disassembly target 50, will be described. Fig. 2 is a cross-sectional plan view of the self-shielded accelerator 1. Fig. 3 is a front view of the self-shielded accelerator 1, with the front side wall portion omitted.

[0023] As shown in Figures 2 and 3, the self-shielded accelerator 1 is equipped with a target device 10. The self-shielded accelerator 1 functions as an RI production device that produces radioisotopes (RI). The self-shielded accelerator 1 can be used, for example, as a PET cyclotron, and the RI produced by the self-shielded accelerator 1 is used, for example, to produce radiopharmaceuticals (including radiopharmaceuticals) that are radioisotope-labeled compounds (RI compounds). Radioisotope-labeled compounds used in PET examinations (positron emission tomography examinations) in hospitals, etc. include: １８ F-FDG (fludeoxyglucose), １８F-FLT (fluorothymidine), １８ F-FMISO (fluorosonidazole), １１ C-Raclopride, etc.

[0024] 2 and 3 is a so-called self-shielded particle accelerator system, and includes an accelerator 2 that accelerates charged particles and a self-shield 6 that is a radiation shield that surrounds the accelerator 2 to shield it from radiation. In an internal space S formed so as to be surrounded by the self-shield 6, in addition to the accelerator 2, a target device 10 used to manufacture RI, a vacuum pump 4 for creating a vacuum inside the accelerator 2, and the like are disposed. Furthermore, the internal space S is also disposed with accessories necessary for operating the accelerator 2, accessory equipment used to cool the target device 10, and the like.

[0025] As shown in FIGS. 2 and 3, the target device 10 receives a charged particle beam B irradiated from the accelerator 2 to produce RI, and contains a raw material (e.g., target water; １８ The accelerator 2 has a storage section for storing the target device 10 (water). The target device 10 is covered by target shields 7 and 8 provided in the accelerator 2. The inner target shield 8 is made of a resin such as polyethylene. The outer target shield 7 is made of lead, for example.

[0026] The self-shield 6 is made up of multiple parts and is formed to cover the accelerator 2 and the target device 10. The self-shield 6 is a structure in which the accelerator 2 and the target device 10 are arranged, and in which the RI is manufactured by irradiating the target with a charged particle beam B from the accelerator 2. The self-shield 6 is a structure that shields radiation generated during the RI manufacturing process and prevents it from leaking outside the self-shield 6.

[0027] 2 , the self-shield 6 includes side walls 11 and 12 that face each other in the irradiation direction of the charged particle beam B, and side walls 13 and 14 that face each other in the horizontal direction perpendicular to the irradiation direction of the charged particle beam B. The side walls 11 and 12 are spaced apart from each other, and the side walls 13 and 14 are spaced apart from each other. One end of each of the side walls 13 and 14 is connected to both ends of the side wall 11, and the other end of each of the side walls 13 and 14 is connected to both ends of the side wall 12. As a result, the internal space S of the self-shield 6 is surrounded on all four sides by the side walls 11, 12, 13, and 14 without any gaps.

[0028] 3 , the upper end of the self-shield 6 is closed by an upper wall portion 15. That is, the upper wall portion 15 is connected to the upper ends of the side wall portions 11, 12, 13, and 14. The lower ends of the side wall portions 11, 12, 13, and 14 are placed on a floor 16. As a result, the internal space S surrounded by the side wall portions 11, 12, 13, and 14 is sealed by the upper wall portion 15 and the floor 16 without any gaps in the vertical direction.

[0029] 3, the self-shield 6 includes a steel plate 17 and concrete 18. Each of the walls 11, 12, 13, 14, and 15 of the self-shield 6 includes concrete 18 between the steel plate 17 that forms the outer shell and the steel plate 17 that forms the inner shell.

[0030] Returning to Fig. 1 , the decomposable range display system 100 is a system for displaying the decomposable range of the decomposition object 50 that should be decomposed by activation. The decomposable range display system 100 can non-destructively display the decomposable range without destroying the decomposition object 50 (for example, by extracting a core sample, etc.). The decomposable range display system 100 can non-destructively acquire the radioactivity concentration in the depth direction of the decomposition object 50. The decomposable range display system 100 includes a measurement unit 20, a calculation device 21, and a display unit 22.

[0031] The measurement unit 20 measures the radiation dose and radiation energy at a predetermined sampling position of the decomposition object 50 using the radiation measurement device 23. The radiation measurement device 23 transmits measurement information to the calculation device 21. For example, a survey meter may be used as such a radiation measurement device 23. The radiation measurement device 23 can measure the nuclide (energy) of radiation. The radiation measurement device 23 can measure, for example, ５４ Mn, ６０ Co, etc. The radiation measuring device 23 can also measure the quantity of nuclides. The radiation measuring device 23 performs measurement by bringing the end face 23a into contact with the surface 50a of the decomposition object 50. Therefore, the radiation measuring device 23 can measure the radiation dose and radiation energy of the surface 50a of the decomposition object 50. A scintillation counter is used as the radiation measuring device 23. Alternatively, a semiconductor detector capable of gamma-ray spectrum measurement may be used as the radiation measuring device 23.

[0032] The properties of the radiation irradiated to the decomposition target 50 are determined by the positional relationship between the target device 10 (the target therein), which serves as the radiation source, and the self-shield 6, as well as the structures present between them. The sampling position at which the measurement unit 20 performs measurements on the decomposition target 50 is linked to the radioactivity concentration distribution. This is because the shape of the decomposition target 50 and the positions of objects (e.g., targets irradiated with accelerated particles) placed around the decomposition target 50 while the decomposition target 50 is in use affect the neutron energy distribution. In this embodiment, the target device 10 (the target therein), which serves as the radiation source, is located on both sides of the accelerator 2. Target shields 7 and 8 are provided around the target device 10, and the distances from the target device 10 to each of the walls 11, 12, 13, 14, and 15 are also different. Therefore, sampling positions are set at each of the walls 11, 12, 13, 14, and 15.

[0033] FIG. 3 shows an example of sampling positions. For example, sampling positions SP1 to SP8 may be used as the sampling positions. These sampling positions SP1 to SP8 are set based on the positional relationship with the target devices 10 on both sides, which are radiation sources. Sampling positions SP6 to SP8 are set toward the back side of the paper, and are set relative to the sidewalls on the back side of the paper in FIG. 3. Sampling positions are also set on the sidewalls on the front side of the paper in FIG. 3. For example, sampling positions may be set at locations opposite sampling positions SP6 and SP7. In FIG. 3, sampling positions SP1 to SP8 are shown as viewed from the target device 10 (or the accelerator 2, which has a close relationship with the target device 10), which is the radiation source, to the self-shield 6. Therefore, the location where the measurement unit 20 performs measurement is the location corresponding to the surface 6a of the self-shield 6 when viewed from sampling position SP1.

[0034] As shown in FIG. 1 , the display unit 22 is a device that displays various information to the worker. The display unit 22 may be configured with, for example, a monitor. After the decomposable range is identified, the display unit 22 may display the decomposable range to the worker. Note that if the computing device 21 does not perform the identification described below, the estimation result of the estimation unit 26 may be displayed on the display unit 22, and the worker may identify the decomposable range by looking at the display result. Note that in addition to the display unit 22, audio output means such as a speaker may be provided.

[0035] The content displayed by display unit 22 is not particularly limited, but the decomposable range may be directly displayed as the radioactivity concentration, or may display a range in which decomposition is recommended (without directly displaying the radioactivity concentration).The method of displaying the decomposable range by display unit 22 is not particularly limited, and may display a diagram as shown in display content EA in Figure 21, or a combination of numerical values ​​and text information as shown in display content EB.

[0036] The calculation device 21 is a device that performs various calculations in the decomposable range display system 100. The calculation device 21 may be configured by a computer system or the like. The calculation device 21 includes an estimation unit 26, a decomposable range specification unit 27, a distribution information acquisition unit 28, and a storage unit 29.

[0037] The estimation unit 26 estimates the distribution of radioactivity concentration in the depth direction corresponding to the sampling position based on the measurement information from the measurement unit 20 and pre-stored distribution information on the surface radiation dose and the depth direction radioactivity distribution corresponding to the sampling position. The depth direction refers to the thickness direction of each wall portion 11, 12, 13, 14, and 15 when the inner surface 6a of the self-shield 6 is used as the reference. For example, at sampling position SP1 (see FIG. 3 ), the depth direction corresponds to the horizontal direction from the inner surface 6a of the side wall portion 11 toward the outer surface 6b. The estimation method by the estimation unit 26 will be described in detail later.

[0038] The decomposable range specifying unit 27 specifies the decomposable range based on the estimation result by the estimation unit 26. The decomposable range specifying unit 27 determines the extent to which activation has progressed from the surface 6 a of the self-shield 6 based on the estimation result of the distribution of radioactivity concentration in the depth direction from the surface 6 a of the self-shield 6, and specifies the range to be decomposed.

[0039] The distribution information acquisition unit 28 acquires distribution information relating to the distribution of radioactivity in the depth direction corresponding to the sampling position. The distribution information acquisition unit 28 acquires the distribution information and stores it in the storage unit 29 before the processing of the estimation unit 26 and the decomposable range identification unit 27 is performed. Detailed processing content of the distribution information acquisition unit 28 will be described later. Note that the distribution information acquisition unit 28 may be provided as a device separate from the calculation device 21. In this case, after the distribution information acquisition unit 28 acquires the distribution information, it transmits the distribution information to the storage unit 29 of the calculation device 21.

[0040] Next, a disassembly method including a decomposable range display method according to this embodiment will be described with reference to FIG. 4 . FIG. 4 is a process diagram illustrating the disassembly method. As shown in FIG. 4 , in the disassembly method, first, distribution information is acquired (step S10), then the decomposable range display method is executed (step S20), and finally, the decomposition target 50 is decomposed based on the displayed decomposable range (step S30). Note that the distribution information acquisition method (step S10) is performed in advance at a different work site before the decomposable range display method (step S20) and the disassembly method (step S30) are performed. The distribution information obtained by the distribution information acquisition method is stored in the memory unit 29.

[0041] 5 and 6 are process diagrams showing detailed processing contents of the distribution information acquisition method (step S10). The distribution information acquisition method includes a calculation step S200, a measurement step S300, and a distribution information acquisition step S400. The calculation step S200 is a step of setting a virtual model (model) that virtually simulates the decomposition target 50 and calculating the radioactivity concentration at each position in the depth direction from the surface of the virtual model. The measurement step S300 is a step of preparing an actual decomposition target 50, obtaining a core sample extending in the depth direction from a sampling position in the actual object, and measuring the radioactivity concentration of the core sample. The distribution information acquisition step S400 is a step of obtaining distribution information regarding the distribution of radioactivity concentration in the depth direction corresponding to the sampling position based on the radioactivity concentration obtained in the calculation step S200 and the radioactivity concentration obtained in the measurement step S300. The calculation step S200 and the distribution information acquisition step S400 are executed by the distribution information acquisition unit 28.

[0042] The calculation step S200 will be described in detail with reference to FIG. 5 and FIGS. 7 to 12. As shown in FIG. 5, first, a virtual model 70 is prepared (step S40). In step S40, a virtual model 70 simulating the self-shield 6 is prepared, and multiple types of radiation source systems are created. As shown in FIG. 7, the virtual model 70 is obtained by cutting out the surface 6a of the self-shield 6 into a cylindrical shape with a predetermined diameter and a predetermined thickness. The virtual model 70 includes a steel plate 51 and a concrete 52. The steel plate 51 on the surface of the virtual model 70 is measured by the radiation measurement device 23. A single steel plate 51 with a predetermined thickness is used. The number of concrete 52 layers ranged from two to five depending on the model. Four types of virtual models 70, "MA," "MB," "MC," and "MD," with diameters and thicknesses set to arbitrary values, were prepared. The thicknesses of the virtual models 70 decrease in order of "MA," "MB," "MC," and "MD." The number of layers and density of the concrete 52 in each of the four types of virtual models 70 may be shown, for example, in a table such as that shown in FIG. 8 . The steel plate 51 is the layer "L0," and the concrete 52 layers are "L1 to L5" in order from the surface 6a side. Three patterns, X, Y, and Z, were adopted as the radioactivity ratio F / C between the steel plate 51 and the concrete 52. Note that, since values ​​corresponding to the simulation settings and calculated values ​​may be inserted into the columns for each item in the table of FIG. 8 , specific numerical values ​​are omitted here. In FIG. 8 , any number may be inserted in place of "*." The same applies to the tables shown in FIG. 9 and subsequent figures. In FIG. 9 and subsequent figures, any value may be inserted in place of "***."

[0043] Next, the detection efficiency η for gamma rays of multiple energies was calculated (step S50, FIG. 5). Regarding the relative radioactivity intensity, the concrete 52 was measured using the decay rate e －０．０１２５ｄ The calculation results of the detection efficiency may be summarized in a table such as that shown in FIG.

[0044] Next, the radioactivity of the entire system is calculated from the ratio of radioactivity in each layer (step S60, FIG. 5). The value of the entire calculation system may be inserted into the detection efficiency in FIG. 8. A method for decomposing the above values ​​into each layer will now be described. Each layer L0 to L5 has a unique relative radioactivity: R inserted in FIG. 8. Ｌ is assigned. Ｌ is treated as a concentration per weight, so the weight of each layer: w Ｌ Multiplying by this gives the percentage of radioactivity in the whole: Rw Ｌ Therefore, the radioactivity of the entire system can be expressed as in equation (2). The weight of the entire system is calculated (step S70, FIG. 5). The weight of the system of steel plates 51 and concrete 52 for each diameter may be summarized in a table such as that shown in FIG. 10. Rw Ｌ and Rw ｔｏｔａｌ The calculation results may be summarized in a table such as that shown in FIG.

[0045]

[0046] Finally, the radioactivity concentration per 1 cps in each layer is calculated (step S80, FIG. 5). The radioactivity concentration per 1 cps is calculated using the above-mentioned formula (3). The calculation results for gamma rays α keV are shown in FIG. Ｌ An example of a graph of the calculation results of A is shown. Based on the result of step S80, the radiation source saturation region is confirmed (step S90, FIG. 5). It is preferable that the error range of the result of each radiation source system is within 10%. If the radiation source system is saturated with respect to γ ​​rays reaching the radiation measuring device 23, A Ｌ The value of should not change.

[0047] Next, the measurement step S300 and the distribution information step S400 will be described with reference to FIGS. 6 and 13 to 19. First, a real model is prepared (step S100, FIG. 6). For example, if the self-shield 6 of the disassembly target 50 is "HM-12S," the real model 60 (see FIG. 3) in step S100 also employs the "HM-12S" self-shield 6. Next, core samples are obtained from the real model, and the radioactivity concentration of each core sample is measured (step S110, FIG. 6). Core samples may be obtained from sampling positions SP1 to SP8 shown in FIG. 3. In this case, a core sample CS extending from the inner surface 6a to the outer surface 6b of the self-shield 6 is extracted at the corresponding sampling position. The extracted core sample CS is then used to measure the radioactivity concentration at each depth position using a measuring device.

[0048] Next, the radioactivity concentration in the depth direction in the virtual model is calculated for the locations corresponding to the sampling locations where core samples were taken from the actual model (step S120, Figure 6). Here, analysis is performed at sampling locations SP1 to SP8 in the virtual model using a method similar to the measurement method described in Figure 5. The analysis results (cps, statistical error) at sampling locations SP1 to SP8 and the radioactivity calculation conditions (detection efficiency derivation system, ５４ Mn and ６０ The radioactivity ratio F / C of Co between the steel plate 51 and the concrete 52 may be summarized in the tables shown in Figures 13 to 15. Ｌ represents the radioactivity concentration per 1 cps for each layer. By multiplying this value by the cps of the α keV, β keV, and γ keV peaks obtained in the experiment after correcting for the half-life and branching ratio, ５４ Mn and ６０ The radioactivity concentration of Co can be derived.

[0049] The distribution information acquisition unit 28 acquires distribution information regarding the distribution of radioactivity in the depth direction corresponding to each sampling position SP1 to SP8 based on the calculation result obtained in step S120 and the measurement information obtained in step S110 (step S400, FIG. 6). For example, the radioactivity depth distribution obtained in step S120 and the depth distribution obtained in step S110 are compared using graphs such as those shown in FIGS. 16 to 19. As shown in the graph on the left side of FIG. 16, the graph G1 with a large value ６０ The graph G2 shows the estimated value of Co. ５４ Graphs of estimated values ​​calculated using a virtual model can also be drawn for other F / C ratios, but here only graphs that are close to the measured values ​​of the actual model are shown. The same applies to the other graphs in Figures 16 to 19. ６０ For Co, the radioactivity concentrations for β keV and γ keV were calculated using equation (3), and then the weighted average was calculated (also shown in Figures 14 and 15). ５４ Mn and ６０ (The estimated Co radioactivity values ​​are shown.) As shown in Figures 16 to 19, the estimated values ​​from measurements using the virtual model generally well reproduced the measured values ​​from the actual model. There was particularly good agreement at the sampling points with high radioactivity. In "Core 4" and "Core 5," buildup was observed and the depth distribution differed from the other sampling points, but the estimated values ​​well reproduced the core analysis values. In "Core 3," "Core 5," and "Core 7," the estimated values ​​from the virtual model were lower than the core analysis values. This is thought to be because upward measurements created a gap between the self-shielding surface and the detector, which did not reproduce the calculation system in Figure 1. In other words, by correcting in the direction of decreasing detection efficiency, the estimated values ​​can be increased, thereby reducing the difference with the core analysis values. In "Core 1" and "Core 8," ６０ The estimated value for Co exceeded the core analysis value. This is because a target was present nearby at the time of measurement, and the amount of Co emitted was due to activation of the target and its surroundings. ６０ It is thought that this was due to the influence of Co.

[0050] From the above, the distribution information acquisition unit 28 generates the graphs G1 and G2 (or corrected graphs) shown in FIGS. 16 to 19.６０ Co, ５４ The distribution information acquisition unit 28 associates the acquired distribution information at each of the sampling positions SP1 to SP8 with the surface dose values ​​at each of the sampling positions SP1 to SP8 measured by the radiation measurement device 23, and stores the information in the storage unit 29. Note that Figures 17 to 19 show distribution information under some conditions, and distribution information is acquired by executing the measurement step S300 and the calculation step S200 under many more conditions, and is stored in the storage unit.

[0051] The method for displaying the decomposable range will be described in detail with reference to Figure 20. First, the measurement unit 20 measures the radiation dose and radiation energy at the sampling positions of the self-shield 6 of the decomposition target 50 using the radiation measurement device 23 (step S140). The radiation dose is information on the magnitude of the radioactivity concentration. The radiation energy is information on identifying the radioactive nuclide. The sampling positions may be sampling positions SP1 to SP8, but if the memory unit 29 also has data on other sampling positions, measurements may be made at the other sampling positions.

[0052] The estimation unit 26 estimates the distribution of radioactivity concentration in the depth direction corresponding to the sampling position based on the measurement information in step S140 and the information on the radiation dose on the surface and the distribution information on the distribution of radioactivity in the depth direction corresponding to the sampling position stored in advance (step S150). The estimation unit 26 acquires measurement information of the radiation dose and radiation energy of the surface 6a at the sampling position from the measurement unit 20. The estimation unit 26 also acquires distribution information corresponding to the sampling position by referencing the information stored in the storage unit 29 with the sampling position measured by the measurement unit 20. The estimation unit 26 estimates (calculates) the distribution of radioactivity concentration in the depth direction at the sampling position using the measurement information by the measurement unit 20 and the distribution information and dose information stored in the storage unit 29. The calculation method used by the estimation unit 26 is not particularly limited, but may be, for example, －０．０１２５ｔ" may be used. "A: radioactivity concentration, "C: coefficient determined by information on the radiation dose on the surface, and "t: depth from the surface (excluding the thickness of the steel plate)."

[0053] The decomposable range specifying unit 27 specifies a decomposable range based on the estimation result in step S150 (step S160). The decomposable range specifying unit 27 determines the depth-wise radioactivity concentration at the sampling positions SP1 to SP8 and determines the depth to which activation has progressed at each of the sampling positions SP1 to SP8. The decomposable range specifying unit 27 then specifies the range (depth) to be decomposed at each of the sampling positions SP1 to SP8. For example, the decomposable range specifying unit 27 may specify a range greater than a reference radioactivity concentration value as the decomposable range. For locations other than the sampling positions SP1 to SP8, the decomposable range specifying unit 27 may set the decomposable range based on the decomposable range at the sampling positions SP1 to SP8. The display unit 22 displays the decomposable range specified in step S160 (step S180).

[0054] Once the disassembly range is displayed in the process shown in FIG. 20 , disassembly work is carried out. For example, chipping work, which destroys the wall from the surface 6 a side, may be used as a disassembly method. Note that the disassembly method is not limited to chipping work, and other methods such as cutting may also be used. The disassembled parts of the self-shield 6 are disposed of as radioactive waste. Portions that are estimated to be unactivated are disposed of as general waste. Note that in the case of the self-shield 6, the polyethylene and lead shielding members may be removed in advance for measurement. Polyethylene may become less activated if it contains fewer impurities. For lead, the radiation dose should be measured, and any lead that should be disposed of as radioactive waste should be packed into drums and disposed of.

[0055] Next, the actions and effects of the decomposable range method, decomposition method, and decomposable range display system 100 according to this embodiment will be described.

[0056] This method of displaying a resolvable range displays a resolvable range corresponding to a sampling position based on measurement information of the radiation dose and radiation energy at a predetermined sampling position of the decomposition object 50 and distribution information relating to the distribution of radioactivity in the depth direction corresponding to the sampling position. In this way, by using the measurement information and distribution information, it is possible to display a resolvable range corresponding to the sampling position. As described above, the resolvable range can be easily identified.

[0057] The radiation dose and radiation energy at the sampling position may be measured using the radiation measuring device 23. In this way, measurement using the radiation measuring device 23 allows for easy measurement without involving destruction such as core boring.

[0058] The decomposition target 50 may include a radiation source that generates radiation and a shield that covers the radiation source with a shielding member. Since the shield covers the radiation source, activation progresses in the depth direction, but the present disclosure makes it possible to easily display the decomposable range.

[0059] The radiation source is a target device 10 that is irradiated with particle beams from the accelerator 2, and the shield may be a self-shield 6 that covers the target device. Since the activation state of the self-shield 6 varies depending on the location, measurements must be taken at multiple sampling positions. Therefore, by adopting non-destructive measurements, the effect of being able to easily display the resolvable range becomes more pronounced.

[0060] The decomposition target 50 may include, for example, a steel plate 17 and concrete 18 .

[0061] The decomposable range display method may further include a calculation step of setting a virtual model of the decomposition object 50 and calculating the radioactivity concentration at each position in the depth direction from the surface of the model, a measurement step of preparing the actual decomposition object 50, obtaining core samples extending in the depth direction from sampling positions in the actual object, and measuring the radioactivity concentrations of the core samples, and a distribution information acquisition step of obtaining distribution information regarding the distribution of the radioactivity concentration in the depth direction corresponding to the sampling positions based on the radioactivity concentrations obtained in the calculation step and the radioactivity concentrations obtained in the measurement step. In this case, by using the actual object in addition to the virtual model, the radioactivity concentration in the depth direction can be accurately and easily grasped.

[0062] The disassembly method according to this embodiment may disassemble a disassembly target object within a decomposable range specified by the above-described decomposable range display method. By performing the disassembly work based on the range specified by the above-described decomposable range display method, the disassembly work can be easily performed.

[0063] The decomposable range display system 100 of this embodiment is a decomposable range display system that displays the decomposable range of a decomposable object 50 having a predetermined structure, and is equipped with a display unit 22 that displays the decomposable range corresponding to a sampling position based on measurement information of the radiation dose and radiation energy at a predetermined sampling position of the decomposable object 50 and distribution information regarding the distribution of radioactivity in the depth direction corresponding to the sampling position.

[0064] According to this decomposable range display system 100, it is possible to obtain the same effects and advantages as the above-mentioned decomposable range display method.

[0065] The above describes one embodiment of the present disclosure, but the present disclosure is not limited to the above embodiment and may be modified within the scope that does not change the gist of the claims.

[0066] For example, the steps shown in Figures 4 to 6 and Figure 20 are merely examples, and the content and order may be changed as appropriate, and some processing may be omitted, without departing from the spirit of the present disclosure.

[0067] 2...Accelerator, 6...Self-shield, 10...Target device, 20...Measurement unit, 22...Display unit, 23...Radiation measuring device, 26...Estimation unit, 27...Decomposable range identification unit, 50...Decomposition object, 100...Decomposable range display system.

Claims

1. A method for displaying a decomposable range of a decomposable object having a specified structure, which displays the decomposable range corresponding to a specified sampling position based on measurement information of the radiation dose and radiation energy at the specified sampling position of the decomposable object and distribution information regarding the distribution of radioactivity in the depth direction corresponding to the sampling position.

2. The method for displaying a resolvable range according to claim 1, wherein the radiation dose and radiation energy are measured at the sampling positions using a radiation measuring device.

3. A method for displaying a decomposable range as described in claim 1, wherein the object to be decomposed comprises: a radiation source that generates radiation; and a shield that covers the radiation source with a shielding member.

4. The method for displaying a resolvable range according to claim 3, wherein the radiation source is a target device irradiated with a particle beam from an accelerator, and the shield is a self-shielding shield that covers the target device.

5. The method for displaying a decomposable range according to claim 3, wherein the object to be decomposed includes a steel plate and concrete.

6. A method for displaying a decomposable range as described in claim 1, further comprising: a calculation step of setting up a model that virtually simulates the decomposition object and calculating the radioactivity concentration at each position in the depth direction from the surface of the model; a measurement step of preparing an actual object of the decomposition object, obtaining core samples extending in the depth direction from sampling positions in the actual object, and measuring the radioactivity concentrations of the core samples; and a distribution information acquisition step of obtaining distribution information regarding the distribution of radioactivity concentration in the depth direction corresponding to the sampling positions based on the radioactivity concentrations obtained in the calculation step and the radioactivity concentrations obtained in the measurement step.

7. A decomposition method for decomposing the object to be decomposed according to the decomposable range displayed by the decomposable range display method according to any one of claims 1 to 5.

8. A decomposable range display system for displaying the decomposable range of a decomposable object having a specified structure, comprising a display unit for displaying the decomposable range corresponding to a specified sampling position of the decomposable object based on measurement information of radiation dose and radiation energy at the specified sampling position of the decomposable object and distribution information regarding the distribution of radioactivity in the depth direction corresponding to the sampling position.