Environmental measurement system and environmental measurement method

Abstract

The object of the present invention is to provide an environmental measurement system and an environmental measurement method that can reduce the risk of failure of electronic equipment used for environmental measurement in a radiation environment. [Solution] The present invention relates to an environmental measurement system for measuring environmental information in a radiation environment, comprising: a detection unit equipped with a radiation emitter for detecting radiation; a first transport mechanism for installing the detection unit in a predetermined radiation environment; a second transport mechanism for retrieving the detection unit; and an analysis unit for analyzing environmental information where the detection unit is installed from measurement information measured by the retrieved detection unit. The detection unit is a measuring instrument that does not require power supply, and the second transport mechanism has a positioning function that identifies the location of the detection unit based on the light emitted from the radiation emitter.

Description

Technical Field

[0001] The present invention relates to an environmental measurement system and an environmental measurement method.

Background Art

[0002] In a radiation environment where people cannot easily approach, it is necessary to select equipment and investigation methods to be introduced in the situation where there is no light source and the situation such as radiation and the arrangement of structures is unknown. For example, in order to proceed with the decommissioning of the Fukushima Daiichi Nuclear Power Plant, appropriate environmental measurement technology is required, and it is necessary to clarify the situation step by step in order to grasp the position of the fuel debris. However, as the investigation progresses, the equipment has to be introduced into a new environment.

[0003] There is also a substance called a radiation-emitting element or a scintillator that emits light when irradiated with radiation. Generally, since the amount of light emission is proportional to the dose rate, it is used in a radiation detector. Depending on the type of radiation-emitting element, it is possible to capture this light emission visually or with a camera in a high dose rate environment.

[0004] In Patent Document 1, a device is disclosed that uses a radiation-emitting element attached to a remotely controlled robot as a marker to estimate the position and orientation of the robot from the position of the element that emits light in a radiation environment and to estimate the life of the robot from the amount of light emission. In Patent Document 2, analysis using a neutron absorber and derivation of a neutron beam are disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The types of electronic equipment usable in high-dose-rate environments are limited, and deploying remotely operated robots using general electronic equipment for extended periods carries a risk of malfunction. Furthermore, devices with independent power supply methods, such as wireless drones, require batteries. Given that these are small drones that need to move in confined spaces, and the weight of the batteries must be considered, there was a limitation that the equipment that could be carried had to be lightweight. For this reason, surveys using equipment that can be transported by drones or remote robots had to be conducted in environments where the dose rate was clearly below a certain level, or where the operation could be completed in a short amount of time.

[0007] One method for conducting long-term surveys in high-dose-rate environments is to transport stationary and storage-type sensors by drone, install them in the high-dose-rate area, and then have only the drone evacuate. In this case, if electronic equipment is used for sensing and for locating the sensors during retrieval, there is a possibility that the installed sensors may malfunction due to radiation.

[0008] The object of the present invention is to provide an environmental measurement system and an environmental measurement method that can reduce the risk of failure of electronic equipment used for environmental measurement in a radiation environment. [Means for solving the problem]

[0009] The present invention relates to an environmental measurement system for measuring environmental information in a radiation environment, comprising: a detection unit equipped with a radiation emitter for detecting radiation; a first transport mechanism for installing the detection unit in a predetermined radiation environment; a second transport mechanism for retrieving the detection unit; and an analysis unit for analyzing environmental information where the detection unit is installed from measurement information measured by the retrieved detection unit. The detection unit is a measuring instrument that does not require power supply, and the second transport mechanism has a positioning function that identifies the location of the detection unit based on the light emitted from the radiation emitter.

[0010] Alternatively, the environmental measurement method of the present invention is characterized by including the steps of: installing a radiation emitter that is placed in a radiation environment by a transport mechanism, and a detection unit consisting of the radiation emitter and an attached power-free measurement function in a measurement target area; retrieving the detection unit by a retrieval mechanism having a identification function that identifies the location of the installed detection unit based on the light emitted from the radiation emitter; and analyzing environmental information in which the detection unit is installed from the information of the measurement function. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an environmental measurement system and an environmental measurement method that can reduce the risk of failure of electronic equipment used for environmental measurement in a radiation environment.

[0012] Other issues, configurations, and effects not mentioned above will be clarified by the following description of the examples. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram of the environmental measurement system capable of localization in a radiation environment, as described in Example 1. [Figure 2] This diagram shows the basic operating procedures when targeting neutron measurements. [Figure 3] This diagram illustrates the light-off function, one method for identifying the retrieval location. [Figure 4] This diagram shows a detection unit composed of metal foil and a radiation emitter. [Figure 5] This figure shows an example where the metal penetration section is a double circle. [Figure 6] This figure shows an example where the metal piece is replaced with a metal wire and the shape of the radiation emitter is star-shaped. [Figure 7] This figure shows examples of measurement functions using metal foil and the same metal foil covered with a neutron-absorbing material. [Figure 8] This figure shows an example of an operation method when using a neutron-absorbing material. [Figure 9] This figure shows an example of an operation method when using multiple different types of radiation emitters.

Best Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments will be described with reference to the drawings. For those denoted by the same numerals in different drawings, the same objects are referred to, and thus the description thereof will be omitted.

Embodiment

[0015] Hereinafter, Embodiment 1 will be described with reference to FIG. 1. FIG. 1 is a schematic diagram of an environmental measurement system capable of position identification in a radiation environment of Embodiment 1. It is assumed to investigate inside the reactor pressure vessel of Fukushima Daiichi Nuclear Power Station using a drone. There is a reactor pressure vessel 12 inside the reactor containment vessel 11, and it is considered that there is fuel debris 13 inside it. An installation drone 15 equipped with a detection unit 14 is made to enter the reactor pressure vessel 12 from below from outside the reactor containment vessel 11. After installing the detection unit 14 at a position where fuel debris 13 may exist with the installation drone 15 which is the first transport mechanism, it passes through the lower part of the reactor pressure vessel 12 and retreats outside the reactor containment vessel 11. Here, although the transport mechanism of the detection unit 14 is made to enter and retreat from the lower part of the reactor pressure vessel 12, it may enter and retreat from other parts according to the situation during environmental measurement.

[0016] The detection unit 14 includes a radiation emitter 21 and detects radiation. With the installation drone 15 which is the first transport mechanism, the detection unit 14 is installed in a predetermined radiation environment. The radiation environment is measured in the state of being placed at a predetermined time. The detection unit 14 is recovered with a recovery drone 16 which is the second transport mechanism. In this system, an analysis unit for analyzing the environmental information where the detection unit 14 was installed from the measurement information measured by the recovered detection unit 14 is provided. The detection unit 14 is a measurement device that does not require power supply, and the recovery drone 16 which is the second transport mechanism has a specific function of specifying the position of the detection unit 14 based on the light emission from the radiation emitter. Also, in this system, a recording unit for recording information obtained by analyzing and calculating measurement information is provided.

[0017] In this way, electronic devices such as the installation drone 15 and the recovery drone 16 are temporarily exposed to the radiation environment, but it only takes a short time, and the risk of failure of the electronic devices due to radiation is reduced.

[0018] The detection unit 14 is a measuring device that does not require power supply and has the function of measuring radiation. Since it does not require a power supply, it is lightweight and suitable for transportation. In this embodiment, it has a configuration including a storage-type sensor. Affected by the environment of the installation location, the detection unit 14 changes and is recovered by the recovery drone 16, which is the second transportation mechanism, after a predetermined time has elapsed. At this time, the installation drone 15 used at the time of installation and the recovery drone 16 used at the time of recovery may or may not be the same. The recovered detection unit 14 can obtain the environmental information of the installation position inside the reactor pressure vessel 12 by analyzing the measurement information outside the reactor containment vessel 11.

[0019] As an example of measuring neutrons with a storage-type sensor in the detection unit 14, a metal piece can be considered. The metal piece becomes radioactive by neutron irradiation and changes into a radioactive substance with a predetermined half-life. The gamma rays emitted by this radioactive metal are different for each type of metal. The metal piece can be appropriately selected according to the situation based on the size of the reaction cross-section with neutrons, the energy of the gamma rays emitted by radioactivation, the half-life of the radioactive metal, etc. For example, gold, nickel, samarium, europium, lanthanum, dysprosium, praseodymium, indium, cobalt, manganese, sodium, iron, niobium, tungsten, scandium, tantalum, silver, etc. can be used.

[0020] Regarding such a neutron measurement method using radioactivation, Patent Document 2 discloses analysis using a neutron absorber and derivation of a neutron beam. FIG. 2 is a diagram showing a basic operation method in the case of targeting neutron measurement. Basically, it has the same content and flow as the description in FIG.

[0021] In FIG. 2, mainly, it includes steps S1 of installing the sensor, step S2 of recovering the sensor, and step S3 of analyzing the sensor information in the analysis unit.

[0022] Step S1 involves a transport mechanism equipped with a neutron measurement device entering the measurement target area, installing the neutron measurement device in the measurement target area, and returning the transport mechanism. Subsequently, the neutron measurement device is left in the measurement target area for a predetermined period of time.

[0023] Step S2 involves entering the measurement target area with a retrieval mechanism equipped with a receiving function, locating the neutron measurement mechanism, retrieving the neutron measurement mechanism, and returning the retrieval mechanism.

[0024] Step S3 measures the energy of gamma rays from the neutron measurement mechanism and calculates the neutron flux from the peak count rate. This information is then recorded in the recording unit.

[0025] A radiation emitter, which is a radiation-emitting element, is used as a transmission function to communicate the retrieval location of the detection unit 14 to the retrieval drone 16. The radiation emitter emits light when irradiated with radiation such as gamma rays. The emission wavelength (color) varies depending on the type of radiation emitter. Since no power source is required for emission, there is no need to supply power, and the weight can be reduced. In addition, because a radiation emitter is used, it is possible to determine the retrieval location even in environments with no light source and high dose rates.

[0026] Therefore, for neutron measurement purposes, since neither the metal piece nor the radiation emitter requires power supply, the detection unit 14 is relatively small and lightweight, mitigating the limitations on transportation by drone. The retrieval location can be determined by capturing the light emitted by the radiation emitter using the retrieval drone 16.

[0027] Figure 3 illustrates the light-off function, one method for identifying the retrieval location. It schematically shows the method for identifying the retrieval location. The retrieval drone 16 is typically equipped with a camera 31 and lighting 32, which are image recognition means, for surveying and confirming the direction of travel. The emission wavelength of the radiation emitter of the detection unit 14 is visible light so that the location can be identified using a general image recognition means.

[0028] By making the emission wavelength of the radioactive emitter visible light, the retrieval drone 16 does not require any additional equipment to be mounted to identify the retrieval location. The light 32 has a function to turn off, and for example, by stopping the retrieval drone 16 and turning off the light 32 for a short time, it is possible to make it easier to detect the emission of the radioactive emitter. Possible methods for turning off the light 32 include switching it on and off at any time via remote control, or configuring it to be a flashing light from the start. Methods for detecting the emission of the radioactive emitter include not only having a person identify it through a camera, but also identifying the emission location using image processing.

[0029] Various shapes are possible for the metal piece. Figure 4 shows a detection unit composed of metal foil and a radioactive emitter. Figure 4 shows the configuration when a metal sheet (foil) is used as a sensor that does not require power supply. The radioactive emitter 21 is assumed to be a thin plate. In a practical configuration, at least one of the wide surfaces of the radioactive emitter 21 will be covered with metal foil 22. If at least one of the top surface (upper side of the paper in Figure 4) or bottom surface (lower side of the paper in Figure 4) of the radioactive emitter 21 is covered with metal foil 22, the other surface is likely to be in contact with the ground, and visible light will be emitted outside the detection unit 14 only from the thin side of the radioactive emitter 21. If the positional relationship allows the camera 31 to distinguish the emission from the side of the radioactive emitter 21, the retrieval location can be identified, but to further improve the possibility of identification, a metal penetration part 23 is provided in the metal foil 22. With this configuration, the camera 31 will be able to capture the emission from surfaces other than the side. [Examples]

[0030] If there are light-emitting objects other than the radiation-emitting element 21 or light-reflecting materials in the survey area, it may interfere with the identification of the detection unit 14. In addition, radiation irradiation may introduce noise into the camera image. In such an environment, in order to identify the detection unit 14, it is conceivable to make the shape of the light emitted from the radiation-emitting element 21 characteristic. In Figure 4, the metal penetration portion 23 is shown as three ellipses. As another example, the metal penetration portion could be made into a double circle as shown in Figure 5. By using such a shape, the accuracy of image recognition can be improved. As an image recognition method, it is also possible to improve the accuracy of identification by learning shapes set in advance using machine learning or the like. When measuring multiple locations within the measurement area simultaneously, it is also possible to link the location information with the installed detection unit 14 by changing the shape of the metal penetration portion 23 for each installation location. [Examples]

[0031] As shown in Figure 6, a thin metal such as a metal wire 24 may be used as the metal piece instead of metal foil. In Figure 6, the shape of the radiation emitter 21 is made star-shaped to facilitate the identification of the detection unit 14 by image. The metal wire 24 is wrapped multiple times around a part of the radiation emitter 21. Figure 6 shows an example where it is wrapped three times around each vertex of the star shape, but the number of wraps may be less or more than three. The characteristic shape does not have to be star-shaped; a more distinctive and complex shape may also be used. When measuring multiple locations within the measurement target area simultaneously, it is possible to link the positional information with the installed detection unit 14 by changing the shape of the radiation emitter 21 for each installation location. [Examples]

[0032] Neutrons produced by nuclear fission reactions have relatively high energies, averaging 2 MeV. These neutrons are slowed down by water and other substances, becoming lower-energy neutrons that are more likely to trigger nuclear fission reactions. Knowing the ratio of low-energy to high-energy neutrons in the environment where neutrons are being measured provides information to estimate whether the neutrons incident on the environment were slowed down by water or other substances after their generation. This is important for evaluating criticality safety and considering methods for removing fuel debris.

[0033] One possible method for separately measuring high-energy and low-energy neutrons is to install the detector 14 in Figure 4 in close proximity to the detector 40 in Figure 7. The detector 14 consists of a metal foil 22, a radiation emitter 21, and a neutron absorber. Figure 7 shows an example of a measurement function where the metal foil and the same metal foil are covered with a neutron absorber. The neutron absorber 41 is placed on top of the metal foil 22. Suitable neutron absorbers are materials with a large nuclear reaction cross-section with low-energy neutrons, such as cadmium, gadolinium, boron, and hafnium. Similar to the metal foil 22, to prevent interference with the emission from the radiation emitter 21, an absorber penetration portion 42 is provided in the metal foil 22, aligned with the position of the metal penetration portion 23. The neutron absorber absorbs low-energy neutrons and can prevent nuclear reactions of the metal foil 22 caused by low-energy neutrons.

[0034] The nuclear reactions that are likely to occur between low-energy neutrons and the metal foil 22 are different from those that are likely to occur between high-energy neutrons and the metal foil 22. The activated metal produced differs for each type of nuclear reaction, and the energy of the emitted gamma rays also differs. Therefore, if low-energy neutrons are present in the area where the detection unit 14 and detection unit 40 are installed, the energy distribution of gamma rays emitted from the metal foil 22 of each detection unit 14 and detection unit 40 after a certain period of time will be different. As a result, it is possible to estimate the presence and extent of low-energy neutrons by analyzing the energy of the gamma rays after recovery.

[0035] Figure 8 shows an example of an operation method when using a neutron absorber. It is a calculation flow for estimating the amount of low-energy and high-energy neutrons using a neutron absorber.

[0036] First, in step S1, a transport mechanism such as a drone equipped with the detection unit 14 and detection unit 40 enters the measurement target area, such as inside a pressure vessel. Next, the detection unit 14 and detection unit 40 mounted on the transport mechanism are placed in the measurement target area, and the transport mechanism retreats to an area with a low dose rate. After that, a time set appropriately according to the situation, such as the type of metal fragment, is waited for.

[0037] In step S2, a retrieval mechanism equipped with a camera as a receiving function enters the measurement target area during retrieval. The camera captures the emission of light from the radiation emitter 21, and the detection unit 14 and detection unit 40 are retrieved. After that, the retrieval mechanism retreats from the measurement target area. In step S3, the detection unit 14 and detection unit 40 are transported to a location where analysis is possible, and the energy of the gamma rays is analyzed using measurement information from a high-purity germanium semiconductor detector or the like.

[0038] At the analysis site, the peak count rate of gamma rays generated by activation with low-energy neutrons and the peak count rate of gamma rays generated by activation with high-energy neutrons are measured for each metal foil 22. By comparing these measured peak count rates, the amount of low-energy neutrons (low-energy neutron flux) and the amount of high-energy neutrons (high-energy neutron flux) are calculated.

[0039] As described above, by determining the amounts of low-energy and high-energy neutrons, we can obtain advantageous information for inferring whether neutrons incident on the environment being measured have been slowed down by water or other means after their generation. This is important for evaluating criticality safety and considering fuel debris removal methods. [Examples]

[0040] Various elements can be used for the radiation emitter 21. Different types emit different wavelengths, resulting in different colors visible to the camera. By changing the type of radiation emitter 21 for each installation location, it is possible to link the location information with the detection unit 14 (or detection unit 40). By using different radiation emitters 21 for each location in this way, the detection unit 14 (or detection unit 40) can be retrieved and then irradiated with X-rays or other means to examine the emission wavelength (color). This allows the linked information to be recorded and verified in the recording unit after retrieval. [Examples]

[0041] So far, we have presented several pieces of information that characterize the detection unit, such as the shape of the penetration section, the shape of the radiation emitter, and the emission wavelength from the radiation emitter. This characterizing information can also be used to link to the recovery time. For example, if a metal piece with a high probability of reaction with low-energy neutrons and a neutron absorber 41 are used as the detection unit 40, there may be cases where there are few incident neutrons and it is desirable to irradiate the detection unit 40 equipped with the neutron absorber 41 for a longer period than the detection unit 14 without the neutron absorber.

[0042] Figure 9 shows an example of an operation method when using multiple radiation emitters of different types. The difference from the flow shown in Figure 8 is that the timing of retrieving the detection unit 14 and the detection unit 40 is different. In the flow of Figure 9, the steps of installing the detection unit 14 and the detection unit 40 (step S1), retrieving the detection unit 14 (step S2), analyzing the information of the detection unit 14 (step S3), retrieving the detection unit 40 (step S2), and analyzing the measurement information of the detection unit 40 (step S3) are performed sequentially.

[0043] In other words, in the first step S2, the location of the neutron measurement mechanism not covered by the neutron absorber is first identified, and only the neutron measurement mechanism and the detection unit 14 that are not covered by the neutron absorber are recovered. Then, in the first step S3, the energy of the gamma rays from the neutron measurement mechanism not covered by the neutron absorber is measured, the peak count rate (A) is calculated by gamma ray energy analysis, and the neutron flux (B) is calculated. After that, a predetermined time is waited until the detection unit 40 is recovered.

[0044] Next, in the second step S2, the location of the neutron measurement mechanism covered with the neutron absorber is identified, and the neutron measurement mechanism and the detection unit 40 are recovered by the recovery mechanism. At this time, the recovery mechanism that recovered the detection unit 14 and the recovery mechanism that recovered the detection unit 40 may be the same or different. In the second step S3, the energy of the gamma rays from the neutron measurement mechanism covered with the neutron absorber is measured for the recovered detection unit 40, and the peak count rate is calculated in the same way as for the detection unit 14.

[0045] The information obtained in the first step S3, which is the peak count rate (A) or neutron flux (B), is combined with the information obtained in the second step S3 to calculate the low-energy neutron flux and the high-energy neutron flux. In this way, the low-energy neutron flux and the high-energy neutron flux can be calculated from the calculation results for the detection unit 14 and the calculation results for the detection unit 40. [Examples]

[0046] The above has described metal pieces as examples of storage-type sensors that do not require power supply, but there are no restrictions on the material used as a sensor as long as it undergoes irreversible changes in response to the environment. For example, when measuring temperature, there are temperature sensors that change color irreversibly. Even in this case, the radiation emitter 21 can be used for position identification, and it is preferable to provide a penetration when the radiation emitter is covered by the temperature sensor. The shape of the cover over the radiation emitter can also be made distinctive to facilitate position identification. [Explanation of Symbols]

[0047] 11: Reactor containment vessel, 12: Reactor pressure vessel, 13: Fuel debris, 14: Detection unit, 15: Installation drone, 16: Recovery drone, 21: Radiation emitter, 22: Metal foil, 23: Metal penetration, 24: Metal wire, 31: Camera, 32: Lighting, 40: Detection unit, 41: Neutron absorber, 42: Absorber penetration.

Claims

1. In an environmental measurement system that measures environmental information in a radiation environment, A detection unit equipped with a radiation-emitting material for detecting radiation, A first transport mechanism for installing the detection unit in a predetermined radiation environment, A second transport mechanism for recovering the detection unit, The system includes an analysis unit that analyzes environmental information of the area where the detection unit is installed, based on the measurement information measured by the detection unit that has been recovered. The detection unit is a measuring instrument that does not require power supply. The environmental measurement system is characterized in that the second transport mechanism has a specific function that identifies the position of the detection unit based on the light emitted from the radiation emitter.

2. In the environmental measurement system according to claim 1, An environmental measurement system characterized in that the aforementioned specific function is an image recognition means.

3. In the environmental measurement system according to claim 1, An environmental measurement system characterized in that the measuring instrument, which does not require power supply, is a metal piece.

4. In the environmental measurement system described in claim 3, An environmental measurement system characterized in that the metal piece has a through-hole that allows light from the radiation emitter to pass through.

5. In the environmental measurement system according to claim 4, An environmental measurement system characterized in that the aforementioned specific function identifies the position of the detection unit to be recovered from the shape of the penetration portion using an image recognition means.

6. In the environmental measurement system according to claim 1, The environmental measurement system is characterized in that the aforementioned specific function identifies the position of the detection unit to be recovered from the shape of the radiation emitter.

7. In the environmental measurement system according to claim 1, An environmental measurement system characterized by comprising a neutron absorber in the detection unit.

8. In the environmental measurement system according to claim 7, The environmental measurement system is characterized in that the neutron absorbing material has a perforating portion that allows light from the radiation emitter to pass through.

9. In the environmental measurement system according to claim 1, An environmental measurement system characterized by having a recording unit that records the emission wavelength and installation location, with each of the detection units being composed of different types of radiation emitters, at multiple locations within the measurement target area.

10. In the environmental measurement system according to claim 1, The measuring instrument that does not require power supply is made of a metal piece. An environmental measurement system characterized in that the metal piece contains at least one of the following: gold, nickel, samarium, europium, lanthanum, dysprosium, preseodymium, indium, cobalt, manganese, sodium, iron, niobium, tungsten, scandium, tantalum, and silver.

11. In the environmental measurement system according to claim 1, The detection unit is equipped with a neutron absorber. The environmental measurement system is characterized in that the neutron absorbing material contains at least one of cadmium, gadolinium, boron, and hafnium.

12. The steps include: installing a radiation emitter, which is placed in a radiation environment by a transport mechanism, and a detection unit consisting of the radiation emitter and an attached power-free measurement function, in the area to be measured; The steps include: recovering the detection unit using a recovery mechanism having a function to identify the position of the detection unit installed based on the light emitted from the radiation emitter; An environmental measurement method characterized by including the step of analyzing environmental information in which the detection unit is installed from the information of the measurement function.

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