Clearance measuring device and clearance measuring method

Abstract

To accurately and sensitively measure and evaluate the radiation of a dismantled object and efficiently perform the whole disposal processing of the clearance object.SOLUTION: A clearance measurement device 1 includes: a radiation detector 2 in which at least one bundled plastic scintillation fiber is inserted in a flexible tube; a shape measuring unit 7 for measuring the shape of a dismantled object 11; a pressing mechanism 5 for pressing the radiation detector 2 against the dismantled object 11 on the basis of the result of measurement obtained by the shape measuring unit 7; a radiation measured value collecting unit 3 for collecting radiation measured values obtained by the radiation detector 2; and a radioactivity evaluation unit 9 for evaluating the radioactivity of the dismantled object 11 from the radiation measured values.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a clearance measurement device for accurately and efficiently evaluating the radioactivity of disassembled objects generated during the operation or decommissioning measures of nuclear power plants, and a clearance measurement method.

Background Art

[0002] During the operation or decommissioning of nuclear power plants, etc., a large amount of waste is generated, such as radioactive waste or waste contaminated by radioactivity, accompanying equipment replacement or facility disassembly. These wastes are classified according to the level of radioactivity concentration, such as the degree of radioactivity or radioactive contamination. Among these, those with a relatively high radioactivity concentration, collectively referred to as low-level radioactive waste, are disposed of by deep geological disposal such as intermediate-depth disposal. Those with a relatively low radioactivity concentration among low-level radioactive waste are disposed of by shallow geological pit disposal. For those with an extremely low radioactivity concentration among low-level radioactive waste, in-ground disposal such as trench disposal is carried out. Also, for high-level radioactive waste with a higher radioactivity concentration than low-level radioactive waste, formation disposal is carried out.

[0003] On the other hand, among the disassembled objects, there are some whose degree of radiation contamination is sufficiently small compared to the natural radiation level and the risk to human health can be ignored, and thus may be excluded from the regulations regarding radiation protection. These are called clearance objects.

[0004] Clearance objects do not need to be handled as radioactive substances. Therefore, clearance objects determined to have a radioactivity concentration below the clearance level can be carried out outside the nuclear power plant and, if reusable, reused as resources. If the reuse of clearance objects is not reasonable, they can be disposed of in the same way as ordinary industrial waste. The determination of whether it is below the clearance level is carried out by measuring the radiation of the disassembled object to be measured and evaluating the radioactivity from the measurement results.

[0005] One method for measuring and evaluating the radioactivity of dismantled materials is described in Patent Document 1. The method described in Patent Document 1 involves first measuring the shape of the dismantled material, and then, based on the shape measurement results, bringing a long plastic scintillation fiber (PSF) close to the surface of the dismantled material to a certain distance, and further scanning the surface while maintaining the close distance to take measurements. This makes it possible to measure the radioactivity of the entire large dismantled material with high accuracy and without missing any hot spots. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-70049 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The amount of clearance material generated is estimated to be tens of thousands of tons per standard light water reactor. In reality, even if material is clearance material, if its radioactivity concentration is determined to be higher than the clearance level based on radioactivity assessments using radiation measurements, it will be treated as radioactive waste.

[0008] The method described in Patent Document 1 makes it possible to measure large dismantled materials by using long plastic scintillation fibers that have shape flexibility. This makes it possible to reduce the shredding process when dismantling the clearance materials, thereby improving the overall efficiency of the processing and disposal of clearance materials.

[0009] However, in the method described in Patent Document 1, the plastic scintillation fiber is prone to bending due to its shape flexibility and length. As a result, it is not possible to maintain a constant distance between the plastic scintillation fiber and the surface of the dismantled material, leading to a problem where localized measurement sensitivity changes. Also for the same reason, a discrepancy may occur between the initially planned measurement position and the actual measurement position, making high-precision measurement difficult.

[0010] Therefore, the present invention aims to measure and evaluate the radioactivity of dismantled materials with high sensitivity and accuracy, and to efficiently carry out the entire process of processing and disposal of clearance materials. [Means for solving the problem]

[0011] To solve the aforementioned problems, the clearance measuring device of the present invention is: A scintillator material that generates scintillation light through interaction with gamma rays was formed into an optical fiber shape. Plastic scintillation fiber In a bundle of multiple items A radiation detector inserted into a flexible tube, Measurement target A shape measuring unit that measures the shape of an object, and the radiation detector based on the measurement results from the shape measuring unit. Shape to the above Measurement target thing To match the shape A pressing mechanism for pressing, a radiation measurement value recording unit for recording radiation measurement values ​​measured by the radiation detector, and the radiation measurement values ​​from the Measurement target It is characterized by having a radioactivity evaluation unit that evaluates the radioactivity of a substance.

[0012] The clearance measurement method of the present invention is Measurement target The step of measuring the shape of an object, and the Measurement target From the shape measurement results of the object Multiple plastic scintillation fibers, each made by molding a scintillator material that generates scintillation light through interaction with gamma rays into an optical fiber shape, are bundled together and inserted into a flexible tube. The radiation detector Measurement target A step to calculate the direction in which to press against an object, and the radiation detector in the calculated direction of the pressing The shape is adjusted to match the shape of the object to be measured. The steps include pressing down, measuring radiation with the pressed radiation detector, and determining the measured radiation value from the measured radiation value. Measurement target The invention is characterized by having a step of evaluating the radioactivity of a substance. Other means will be described in the mode for carrying out the invention.

Advantages of the Invention

[0013] According to the clearance measurement apparatus and method of the present invention, it is possible to measure and evaluate the radioactivity of disassembled objects with high sensitivity and high precision, and to efficiently carry out the entire process of treating clearance objects.

Brief Description of the Drawings

[0014] [Figure 1] It is a diagram showing an example of a clearance measurement apparatus which is a first embodiment of the present invention. [Figure 2] It is a diagram showing a vertical cross section orthogonal to the longitudinal direction of a radiation detector used in the clearance measurement apparatus. [Figure 3] It is a flowchart of a measurement process by the clearance measurement apparatus. [Figure 4] It is a diagram showing an example of a pressing mechanism for pressing a radiation detector against a disassembled object in the clearance measurement apparatus. [Figure 5] It is a diagram showing an example of a clearance measurement apparatus which is a second embodiment of the present invention. [Figure 6] It is a diagram showing an example of a pressing mechanism for pressing a radiation detector against a disassembled object in the clearance measurement apparatus. [Figure 7] It is a flowchart of a measurement process by the clearance measurement apparatus. [Figure 8] It is a diagram showing an example of a clearance measurement apparatus which is a third embodiment of the present invention. [Figure 9] It is a flowchart of a measurement process by the clearance measurement apparatus.

Mode for Carrying Out the Invention

[0015] 《First Embodiment》 Hereinafter, a first embodiment of the present invention will be described with reference to the respective drawings. Figure 1 shows the clearance measuring device 1 in the first embodiment. In this figure, a large-diameter pipe (bent pipe) with a contaminated inner surface is cut in half to expose the contaminated surface as the dismantled object 11, and the measurement is taken by tracing this surface. However, the dismantled object 11 to be measured is not limited to the bent pipe or size shown in this figure.

[0016] The clearance measuring device 1 includes a shape measuring unit 7 and a transport unit 8. The shape measuring unit 7 measures the surface shape of the dismantled object 11. The transport unit 8 transports the dismantled object 11 into the clearance measuring device 1. The transport unit 8 is not mandatory; the shape measuring unit 7 may measure the surface shape of the dismantled object 11 while it is installed in the gantry 31, and is not limited to this configuration.

[0017] Furthermore, the clearance measuring device 1 includes a gantry 31, a radiation detector 2, a radiation measurement value recording unit 3, a radioactivity evaluation unit 9, a pressing mechanism 5, and a drive unit 6. The gantry 31 is a structure in which the four columns support the beam, and the pressing mechanism 5 can be moved in the forward, backward, left, and right directions.

[0018] The radiation detector 2 is attached to the gantry 31 via the radiation detector holder 4. The radiation detector 2 consists of a flexible tube into which seven bundled plastic scintillation fibers are inserted, and photomultiplier tubes 20a and 20b provided at both ends of the flexible tube. By processing the signals detected by the photomultiplier tubes 20a and 20b, it is possible to detect the amount of radiation at each position of the plastic scintillation fibers inside the flexible tube.

[0019] The radiation measurement data recording unit 3 records the radiation measurements taken by the radiation detector 2. The radioactivity evaluation unit 9 evaluates the radioactivity from the radiation measurements collected by the radiation measurement data recording unit 3. The pressing mechanism 5 presses the radiation detector 2 against the dismantled object 11 in a direction approximately normal to the shape measuring unit 7. The drive unit 6 is attached to the gantry 31 and is capable of moving the pressing mechanism 5 vertically and freely horizontally within the gantry 31.

[0020] Figure 2 is a vertical cross-sectional view perpendicular to the longitudinal direction of the radiation detector 2. The radiation detector 2 is constructed by inserting a radiation detector made of plastic scintillation fiber 101 into a flexible tube such as a flexible interlock tube 103.

[0021] A plastic scintillation fiber 101 is a scintillator material that generates scintillation light through interaction with gamma rays, molded into an optical fiber shape. The radiation detector 2 measures the incident position and intensity of gamma rays from the difference in arrival time of the scintillation light incident on the photomultiplier tubes 20a and 20b at both ends of the plastic scintillation fiber 101. Plastic scintillation fibers 101 are available in lengths of approximately 10 to 20 m, and can output gamma ray intensity at intervals of, for example, 10 cm. They also have flexibility in shape, such as being bendable like optical fibers. By applying a long radiation detector 2 using a plastic scintillation fiber 101, it is possible to measure even dismantled materials 11 that are several meters long all at once. Therefore, it is not necessary to cut the dismantled materials 11 into sizes of several tens of centimeters to 1 m, and the cutting process can be reduced, making it possible to streamline the processing and disposal of clearance materials.

[0022] The plastic scintillation fiber 101 can be used not only individually, but also in bundles of multiple fibers. Figure 2 shows an example of using seven plastic scintillation fibers 101 bundled together, but it is also possible to use more than seven, or fewer than seven, bundled together depending on the radiation intensity of the object being measured.

[0023] Flexible tubes such as the interlock tube 103 are hollow tubes made of materials such as SUS, and can maintain their shape unless a new external force is applied to them. For example, if an external force is applied to the interlock tube 103 and it is bent, it can maintain that bent state. The interlock tube 103 is used for protecting optical fibers, various sensors, cables, etc., and in endoscopes, etc.

[0024] Because the plastic scintillation fiber 101 is shape-flexible, it may bend due to gravity or other influences unless an appropriate restraining force is applied along its length. Generally, in radiation measurements using the radiation detector 2, the measurement sensitivity changes as the distance between the object being measured and the radiation detector 2 changes. Therefore, the bending of the plastic scintillation fiber 101 causes the measurement sensitivity to change depending on the position of the plastic scintillation fiber 101 along its length. In contrast, by using the interlock tube 103, the plastic scintillation fiber 101 does not bend at any point along its length, making it possible to measure radiation at the initially planned measurement position.

[0025] Furthermore, the plastic scintillation fibers 101 are covered with a flexible material such as urethane 102. This prevents the position of the bundled plastic scintillation fibers 101 within the cross-section of the interlock tube 103 from changing. Now, consider the case where we want to maintain a distance d between the dismantled material 11 and the bundled plastic scintillation fibers 101. In this case, the radius of the imaginary circle inscribed in the bundled plastic scintillation fibers 101, shown as a dotted circle in Figure 2, is r. p Therefore, the outer radius is r d =(r p An interlock tube 103 having a radius of +d) is used. In other words, the radius of the flexible tube should be the sum of the distance between the plastic scintillation fiber 101 and the dismantled material 11 set in the measurement, and the radius of at least one bundle of plastic scintillation fibers 101.

[0026] Furthermore, if the thickness of the interlock tube 103 is t, the plastic scintillation fiber 101 bundled with urethane 102 of thickness (dt) is covered and inserted into the interlock tube 103.

[0027] Figure 3 shows a flowchart of the measurement process when using the clearance measuring device 1 shown in Figure 1 and the radiation detector 2 shown in Figure 2. This measurement process consists of steps S10 to S12, which are pre-measurement preparation processes, and steps S13 to S18, which are measurement processes performed by the clearance measuring device 1.

[0028] In the pre-measurement preparation process, the shape measuring unit 7 first measures the shape of the dismantled object 11 (step S10). Based on the results of this shape measurement, the clearance measuring device 1 calculates planning data such as the measurement position of the dismantled object 11 by the radiation detector 2 and the scanning procedure of the radiation detector 2 on the dismantled object 11 (step S11). Based on the results of this shape measurement, the clearance measuring device 1 calculates the direction in which to press the radiation detector 2 against the dismantled object 11 (step S12).

[0029] Figure 4 shows an example of a pressing mechanism 5 that presses the radiation detector 2 against the dismantled object 11. The pressing mechanism 5 shown in Figure 4 is a specific illustration of the pressing mechanism 5 shown in Figure 1. When the clearance measuring device 1 presses the radiation detector 2 against the dismantled object 11, it follows the pressing direction calculated in step S12. The clearance measuring device 1 calculates the normal direction on the surface of the dismantled object 11 from point cloud data containing coordinate information measured by a shape measuring unit 7 using a laser scanning rangefinder, an infrared depth distance measuring instrument, a stereo camera, etc., and presses the radiation detector 2 in that normal direction. Note that the pressing direction of the pressing mechanism 5 is not limited and may be shifted by, for example, ±30 degrees from the normal direction on the surface of the dismantled object 11.

[0030] Returning to Figure 3, the explanation continues. During the measurement process by the clearance measuring device 1, the transport unit 8 transports the dismantled material 11 into the clearance measuring device 1 (step S13). Then, according to the planned data such as the measurement position of the dismantled material 11 by the radiation detector 2 and the scanning procedure of the radiation detector 2 for the dismantled material 11, calculated in step S12, the drive unit 6 moves the radiation detector 2 to the initial measurement position (step S14).

[0031] Next, the pressing mechanism 5 shown in Figure 4 presses the radiation detector 2 against the dismantled object 11 (step S15). In step S15, the pressing mechanism 5 sequentially presses the radiation detector 2 against the dismantled object 11 in the direction indicated by the dotted arrow along the radiation detector 2 in Figure 1. The radiation detector 2 changes its shape to match the shape of the dismantled object 11, thereby performing radiation measurement of the dismantled object 11 while maintaining measurement sensitivity along the length of the plastic scintillation fiber 101. Next, the radiation detector 2 performs the measurement (step S16). Once the measurement is completed at that position, it is determined whether this position is the final measurement position calculated in step S11 (step S17). If that position is the final position (Yes), the process shown in Figure 3 is terminated.

[0032] In step S17, if the radiation detector 2 is not in its final position, the clearance measuring device 1 moves the radiation detector 2 in the direction indicated by the solid arrow in Figure 1, which shows the inner surface of the dismantled object 11 (step S18), and returns to step S15. This is repeated until the radiation detector 2 reaches its final position. In step S17, if the position is not the final position (No), the clearance measuring device 1 terminates the process shown in Figure 3.

[0033] The first embodiment of the present invention described above has the effect of enabling highly sensitive and accurate evaluation of large-scale demolition materials, and furthermore, of efficiently carrying out the entire process of processing and disposal of clearance materials.

[0034] 《Second Embodiment》 A second embodiment of the present invention will be described with reference to Figures 5 to 7. The second embodiment of the present invention relates to an example of a method for avoiding contamination of the radiation detector 2 by contaminated material when the dismantled material 11 is contaminated, in the clearance measuring device 1 and method described in the first embodiment.

[0035] Figure 5 shows a clearance measuring device 1 according to a second embodiment of the present invention. The clearance measuring device 1 shown in Figure 5 is configured to include a thin film dimension determination unit 22, a thin film installation unit 23, and a thin film decontamination unit 24, in addition to the configuration shown in Figure 1 of the clearance measuring device 1 of the first embodiment of the present invention.

[0036] The thin film dimension determination unit 22 determines the dimensions of the thin film sheet 21 covering the dismantled object 11 based on the measurement results of the dismantled object 11 by the shape measurement unit 7. The thin film installation unit 23 covers the surface of the dismantled object 11 with the thin film sheet 21 before pressing the radiation detector 2 against the dismantled object 11. After the dismantled object 11 is transported to the clearance measuring device 1 by the transport unit 8, the radiation detector 2 is pressed against the dismantled object 11 from above the thin film sheet 21 by the pressing mechanism 5. Figure 6 shows an example of how the radiation detector 2 is pressed against the dismantled object 11 from above the thin film sheet 21 by the pressing mechanism 5.

[0037] The pressing mechanism 5 shown in Figure 6 is a specific illustration of the pressing mechanism 5 shown in Figure 1. When the clearance measuring device 1 presses the radiation detector 2 against the dismantled object 11 from above the thin film sheet 21, it follows a pre-calculated pressing direction. The clearance measuring device 1 calculates the normal direction on the surface of the dismantled object 11 from point cloud data containing coordinate information measured by a shape measuring unit 7 using a laser scanning rangefinder, an infrared depth distance measuring device, a stereo camera, etc., and presses the radiation detector 2 in that normal direction. Note that the pressing direction of the pressing mechanism 5 is not limited to, for example, ±30 degrees from the normal direction on the surface of the dismantled object 11.

[0038] If it is suspected that radioactive material is attached to the surface of the dismantled material 11, the method shown in the first embodiment of the present invention may cause the attached radioactive material to adhere to and contaminate the radiation detector 2. Once the radiation detector 2 is contaminated by radioactive material, the measurement values ​​of the radiation detector 2 will constantly measure the radiation from the attached radioactive material, making it difficult to accurately measure the radiation from the dismantled material 11. Therefore, it is necessary to take measures to prevent the radiation detector 2 from being contaminated by radioactive material in advance, or to decontaminate it if it is contaminated by radioactive material. The thin film sheet 21 in the second embodiment of the present invention is intended to prevent contamination of the radiation detector 2 in advance.

[0039] The thin film sheet 21 must not shift relative to the dismantled object 11 when the radiation detector 2 is pressed against it by the pressing mechanism 5, and when the radiation detector 2 measures the object. The measurement is performed in the direction of the solid arrow shown on the surface of the dismantled object 11 in Figure 5.

[0040] This is because covering the dismantled material 11 with the thin film sheet 21 could cause radioactive material to adhere to the dismantled material 11. If the thin film sheet 21 shifts while radioactive material is attached, the position of the radioactive material will move, potentially leading to the same attached material being measured at least twice in different locations, which could make accurate measurements impossible.

[0041] For the thin film sheet 21, it is effective to use an adhesive wrap film on the side facing the dismantled material 11. The adhesiveness reduces the possibility of displacement when pressing the radiation detector 2 or during measurement. Another method to suppress displacement, although not shown in the figure, is to use a fixing jig such as placing a weight on the edge of the thin film sheet 21 or anchoring the edge. The thin-film decontamination unit 24 is a functional unit that decontaminates the thin-film sheet 21 before or after radiation measurement by the radiation detector 2. This makes it possible to reuse the thin-film sheet 21.

[0042] Figure 7 shows the flowchart of the measurement process using the clearance measuring device 1 described above. This measurement process consists of steps S20 to S24, which are pre-measurement preparation processes, steps S25 to S30, which are measurement processes using the clearance measuring device 1, and step S31, which is a thin film decontamination process.

[0043] In the pre-measurement preparation process, the shape measuring unit 7 first measures the shape of the dismantled object 11 (step S20). Based on the results of this shape measurement, the clearance measuring device 1 calculates planning data such as the measurement position of the dismantled object 11 by the radiation detector 2 and the scanning procedure of the radiation detector 2 for the dismantled object 11 (step S21), and calculates the size of the thin film sheet 21 (step S22). The required size of the thin film sheet 21 is calculated based on the shape measurement results of the dismantled object 11, for example, the maximum and minimum values ​​of the X, Y, and Z axes of the coordinate values ​​(X, Y, Z) of the point cloud data.

[0044] The thin film installation unit 23 then lays the thin film sheet 21 on the dismantled object 11 (step S23). The clearance measuring device 1 calculates the direction in which to press the radiation detector 2 against the dismantled object 11 based on the results of this shape measurement (step S24).

[0045] During the measurement process by the clearance measuring device 1, the transport unit 8 transports the dismantled material 11 into the clearance measuring device 1 (step S25). Then, according to the planned data such as the measurement position of the dismantled material 11 by the radiation detector 2 and the scanning procedure of the radiation detector 2 for the dismantled material 11, calculated in step S11, the drive unit 6 moves the radiation detector 2 to the initial measurement position (step S26).

[0046] Next, the clearance measuring device 1 presses the radiation detector 2 against the dismantled object 11 using the pressing mechanism 5 shown in Figure 6 (step S27). In step S27, the pressing mechanism 5 sequentially presses the radiation detector 2 against the dismantled object 11 in the direction indicated by the dotted arrow along the radiation detector 2 in Figure 5. The radiation detector 2 changes its shape to match the shape of the dismantled object 11, thereby performing radiation measurement of the dismantled object 11 while maintaining measurement sensitivity along the length of the plastic scintillation fiber 101. Next, the radiation detector 2 performs the measurement (step S28). Once the measurement is completed at that position, it is determined whether or not this position is the final measurement position calculated in step S21 (step S29).

[0047] In step S29, if the radiation detector 2 is not in its final position (No), the clearance measuring device 1 moves the radiation detector 2 in the direction indicated by the solid arrow in Figure 5, which shows the inner surface of the dismantled object 11 (step S30), and returns to step S27. This is repeated until the radiation detector 2 reaches its final position. In step S29, if the position of the radiation detector 2 is the final position (Yes), the clearance measuring device 1 performs decontamination of the sheet (step S31) and returns to step S20.

[0048] In the measurement process shown in Figure 7, compared to the measurement process shown in Figure 3 in the first embodiment of the present invention, the sheet size is calculated in step S22 and the thin film sheet 21 is laid in step S23.

[0049] Furthermore, in this measurement process, after the measurement of one or a set of dismantled items 11 is completed, the thin film sheet 21 is decontaminated when measuring another dismantled item 11 (step S31). This allows the thin film sheet 21 to be reused.

[0050] There is a concern that the thin film sheet 21 may become contaminated with radioactive material upon contact with the dismantled material 11, potentially creating new contaminated waste. In the second embodiment, the thin film sheet 21 is decontaminated to suppress the increase in contaminated waste. In this case, it is preferable to prepare at least two thin film sheets 21 and to carry out the decontamination of one thin film sheet 21 and the measurement of the dismantled material 11 by the clearance measuring device 1 in parallel. This makes it possible to avoid step S31 of the sheet decontamination process becoming a bottleneck.

[0051] The second embodiment of the present invention described above allows for highly sensitive and accurate evaluation of large dismantled materials while avoiding contamination of the radiation detector 2 with radioactive materials. Furthermore, it enables efficient processing and disposal of clearance materials.

[0052] 《Third Embodiment》 A third embodiment of the present invention will be described with reference to Figure 8. The third embodiment of the present invention is an example of a system for decontaminating the radiation detector 2 as one of the countermeasures against contamination of the radiation detector 2 by radioactive materials, as described in the second embodiment. The clearance measuring device 1 shown in Figure 8 is configured by adding a radiation detector decontamination unit 25 to the configuration shown in Figure 1 of the clearance measuring device 1 of the first embodiment of the present invention. The radiation detector decontamination unit 25 decontaminates the radiation detector 2.

[0053] Figure 9 shows a flowchart of the measurement process in the third embodiment of the present invention. The measurement process in Figure 9 consists of steps S40 to S42, which are pre-measurement preparation processes, and steps S43 to S50, which are measurement processes by the clearance measuring device 1.

[0054] In the pre-measurement preparation process, the shape measuring unit 7 first measures the shape of the dismantled object 11 (step S40). Based on the results of this shape measurement, the clearance measuring device 1 calculates planning data such as the measurement position of the dismantled object 11 by the radiation detector 2 and the scanning procedure of the radiation detector 2 against the dismantled object 11 (step S41). Based on the results of this shape measurement, the clearance measuring device 1 calculates the direction in which to press the radiation detector 2 against the dismantled object 11 (step S42).

[0055] During the measurement process by the clearance measuring device 1, the transport unit 8 transports the dismantled material 11 into the clearance measuring device 1 (step S43). Then, according to the planned data such as the measurement position of the dismantled material 11 by the radiation detector 2 and the scanning procedure of the radiation detector 2 for the dismantled material 11, calculated in step S42, the drive unit 6 moves the radiation detector 2 to the initial measurement position (step S44).

[0056] Next, the pressing mechanism 5 shown in Figure 4 presses the radiation detector 2 against the dismantled object 11 (step S45). In step S45, the pressing mechanism 5 sequentially presses the radiation detector 2 against the dismantled object 11 in the direction indicated by the dotted arrow along the radiation detector 2 in Figure 1. The radiation detector 2 changes its shape to match the shape of the dismantled object 11, thereby performing radiation measurement of the dismantled object 11 while maintaining measurement sensitivity along the length of the plastic scintillation fiber 101. Next, the radiation detector 2 performs the measurement (step S46). Once the measurement is completed at that position, it is determined whether this position is the final measurement position calculated in step S41 (step S47). If that position is the final position (Yes), the process in Figure 9 is terminated.

[0057] In step S47, if the radiation detector 2 is not in its final position, the clearance measuring device 1 decontaminates the radiation detector 2 (step S48), and performs a confirmation measurement after decontamination (step S49). The clearance measuring device 1 moves the radiation detector 2 in the direction indicated by the solid arrow in Figure 1, which shows the inner surface of the dismantled material 11 (step S50), and returns to step S45. This is repeated until the radiation detector 2 reaches its final position.

[0058] In step S48, the radiation detector 2 is moved from near the surface of the dismantled material 11 to a decontamination device for the radiation detector 2, and decontaminated by the device. In step S49, after the decontamination of the radiation detector 2 has been performed, the radiation detector 2 is measured in an environment unaffected by radioactive materials to confirm that the decontamination has been successfully carried out and that the same measurement values ​​as before the start of the measurement are obtained. Then, it is moved to the next measurement position and radiation measurement is performed.

[0059] The third embodiment of the present invention described above has the effect of removing radioactive contamination from the radiation detector 2, evaluating large dismantled items with high sensitivity and accuracy, and furthermore, efficiently carrying out the entire process and disposal of clearance materials.

[0060] Variant form The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. It is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0061] Each of the above configurations, functions, processing units, and processing means may be implemented in part or in whole by hardware, such as an integrated circuit. Each of the above configurations and functions may also be implemented in software by a processor interpreting and executing a program that implements each function. Information such as programs, tables, and files that implement each function can be stored in a recording device such as memory, a hard disk, or an SSD (Solid State Drive), or on a recording medium such as a flash memory card or a DVD (Digital Versatile Disk).

[0062] In each embodiment, the control lines and information lines shown are those deemed necessary for explanation and do not necessarily represent all control lines and information lines in the actual product. In practice, it can be assumed that almost all components are interconnected. [Industrial applicability]

[0063] By using the clearance measurement device and method of the present invention, it becomes possible to measure and evaluate the radioactivity of dismantled materials with high sensitivity and accuracy, and to efficiently carry out the entire process and disposal of clearance materials. Furthermore, the present invention can be used not only for clearance materials but also as a device for evaluating the radioactivity of low-level radioactive waste. [Explanation of Symbols]

[0064] 1. Clearance measuring device 2. Radiation detector 3. Radiation measurement data recording unit 4. Radiation detector holder 5. Pressing mechanism 6 Drive Unit 7 Shape measurement section 8. Conveying section 9. Radioactivity Assessment Department 11 Demolition 21 Thin film sheet 22 Thin film dimension determination section 23 Thin film installation part 24 Thin film decontamination section 31 Gantry 101 Plastic scintillation fiber 102 Urethane 103 Interlock Tube

Claims

1. A radiation detector comprising a flexible tube in which multiple plastic scintillation fibers, each formed by molding a scintillator material that generates scintillation light through interaction with gamma rays into an optical fiber shape, are bundled together and inserted into the flexible tube, A shape measuring unit that measures the shape of the object to be measured, Based on the measurement results from the shape measuring unit, a pressing mechanism presses the shape of the radiation detector to match the shape of the object to be measured, A radiation measurement value recording unit that records radiation measurement values ​​measured by the aforementioned radiation detector, A radioactivity evaluation unit that evaluates the radioactivity of the object to be measured from the radiation measurement values, A clearance measuring device characterized by having the following.

2. The radius of the flexible tube is the sum of the distance between the plastic scintillation fiber and the object to be measured, and the radii of the bundled plastic scintillation fibers, as set during the measurement. The clearance measuring device according to feature 1.

3. The flexible tube is capable of maintaining its bent state when bent by an external force. The clearance measuring device according to feature 1.

4. The radiation detector has a thin film installation section which installs a thin film on the surface of the object to be measured before pressing it against the object to be measured. The clearance measuring device according to feature 1.

5. The system includes a thin film dimension determination unit that determines the dimensions of the thin film to be placed on the surface of the object to be measured based on the measurement results of the shape measurement unit. The clearance measuring device according to feature 4.

6. The thin film has adhesive properties on the side facing the object to be measured. The clearance measuring device according to feature 4.

7. The thin film is installed, and a jig for fixing the thin film is also installed. The clearance measuring device according to feature 4.

8. The system has a thin film decontamination unit that decontaminates the thin film before or after radiation measurement by the radiation detector, The clearance measuring device according to claim 4 or 5, characterized in that it is the same as described in claim 4 or 5.

9. The system includes a radiation detector decontamination unit that decontaminates the radiation detector before or after radiation measurement by the radiation detector. The clearance measuring device according to claim 1 or 2, characterized in that it is the same as described in claim 1 or 2.

10. The device further includes a transport unit for transporting the object to be measured into the clearance measuring device. The clearance measuring device according to claim 1 or 2, characterized in that it is the same as described in claim 1 or 2.

11. A step of measuring the shape of an object to be measured, The steps include: calculating the direction in which a radiation detector, which is inserted into a flexible tube and consists of multiple bundles of plastic scintillation fibers (formed from scintillator material that generates scintillation light through interaction with gamma rays) inserted into a flexible tube, should be pressed against the object to be measured, based on the shape measurement results of the object to be measured; The steps include pressing the shape of the radiation detector against the object to be measured in the calculated pressing direction, and The steps include measuring radiation using the radiation detector that is pressed against the body, A step of evaluating the radioactivity of the object to be measured from the measured radiation values, A clearance measurement method characterized by having [a certain feature].

12. Based on the shape measurement results of the object to be measured, the normal direction on the surface of the object to be measured is calculated, and the radiation detector is pressed against the object in the direction of the normal direction. The clearance measurement method according to feature 11.

13. Based on the shape measurement results of the object to be measured, a thin film is placed on the surface of the object to be measured, and the radiation detector is pressed against the object to be measured from above the thin film. The clearance measurement method according to feature 12.

14. After the radiation measurement of the object to be measured by the radiation detector is completed, the thin film is decontaminated. The clearance measurement method according to feature 13.

15. After performing radiation measurements at one measurement location using the aforementioned radiation detector, the radiation detector is decontaminated, and then moved to the next measurement location to perform radiation measurements. The clearance measurement method according to claim 11 or 12, characterized by the features described herein.

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