Method and storage apparatus for radioactive waste

Abstract

To provide technology for the more appropriate long-term storage of radioactive waste. [Solution] The method for containing radioactive waste is a method for containing radioactive waste in a storage container. The method for containing radioactive waste comprises a dewatering step of supplying a slurry containing radioactive waste to a storage container and dewatering the slurry in the storage container, and a vacuum drying step of reducing the pressure of the storage container to dry the radioactive waste that was dewatered in the dewatering step. In the dewatering step, the pressure of the dewatering container, which contains the water discharged from the storage container, is reduced relative to the storage container, and the water in the storage container is transferred to the dewatering container. In the vacuum drying step, the pressure of the storage container is reduced and the storage container is heated to vaporize the water contained in the radioactive waste and dry the radioactive waste.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a method for storing radioactive waste and a storage device.

Background Art

[0002] As radioactive waste, for example, ion exchange resins used in facilities handling radioactive substances are known. In facilities handling radioactive substances, a large amount of ion exchange resins are used for purifying system water and water injected into the system in order to prevent corrosion of equipment. The radioactive waste (for example, ion exchange resins) after use is stored in a storage tank. For example, Patent Document 1 discloses an apparatus for dehydrating and storing radioactive waste.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When radioactive waste is dehydrated and stored using an apparatus such as that of Patent Document 1, maintenance during storage becomes easier and long-term storage becomes possible as compared with non-dehydrated slurry-like radioactive waste. However, even when radioactive waste is dehydrated using an apparatus such as that of Patent Document 1, a small amount of moisture remains in the storage container that houses the radioactive waste. In order to store radioactive waste for a long time, it is desirable to further remove the moisture contained in the radioactive waste.

[0005] This specification discloses a technology for more appropriately storing radioactive waste for a long time.

Means for Solving the Problems

[0006] A first aspect of the technology disclosed herein is a method for containing radioactive waste, which involves containing radioactive waste in a storage container. The method for containing radioactive waste comprises a dewatering step of supplying a slurry containing radioactive waste to a storage container and dewatering the slurry in the storage container, and a vacuum drying step of reducing the pressure of the storage container to dry the radioactive waste that was dewatered in the dewatering step. In the dewatering step, the pressure of a dewatering container, which contains water discharged from the storage container, is reduced relative to the storage container, thereby transferring the water in the storage container to the dewatering container. In the vacuum drying step, the pressure of the storage container is reduced, and the storage container is heated to vaporize the water contained in the radioactive waste and dry the radioactive waste.

[0007] In the above method for containing radioactive waste, the radioactive waste is dried in a vacuum drying process after the dewatering process. This further removes any water remaining in the storage container after the dewatering process. As a result, the radioactive waste can be stored more appropriately for a longer period of time. Although water in the radioactive waste can be removed by performing only the vacuum drying process without the dewatering process, performing the vacuum drying process after the dewatering process reduces the time and energy consumption compared to performing only the vacuum drying process. Furthermore, by heating and depressurizing the storage container during the vacuum drying process, the radioactive waste can be properly vacuum dried. In addition, the container (storage container) is depressurized in both the vacuum drying process and the dewatering process. As a result, it is possible to perform both the dewatering and vacuum drying processes using the same depressurization device. Therefore, it is possible to contain the radioactive waste in storage containers without using many different pieces of equipment.

[0008] Furthermore, a storage apparatus according to a first embodiment of the technology disclosed herein is a storage apparatus for storing radioactive waste. The storage apparatus comprises a storage container for dewatering and storing a slurry containing radioactive waste; a first filter disposed inside the storage container that allows water to pass through but prevents radioactive waste from passing through; a dewatering container for containing the water discharged from the storage container through the first filter; a depressurization device capable of depressurizing the storage container and the dewatering container, respectively; and a heating device for heating the storage container. The depressurization device depressurizes the dewatering container relative to the storage container so that the water in the storage container is discharged into the dewatering container, and depressurizes the storage container after the water in the storage container has been discharged into the dewatering container, thereby vaporizing the water contained in the radioactive waste in the storage container and drying the radioactive waste. The storage apparatus further comprises a heat exchanger for condensing the vaporized water that has been moved to the outside of the storage container.

[0009] The above storage apparatus allows for the dewatering of the slurry within the storage container, followed by vacuum drying of the radioactive waste inside the container. This ensures sufficient removal of moisture from the storage container, enabling more appropriate and longer-term storage of the radioactive waste. Furthermore, by incorporating a heating device, the storage container can be heated while simultaneously reducing pressure, allowing for optimal vacuum drying of the radioactive waste. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the schematic configuration of the storage apparatus according to Examples 1 and 2, illustrating the arrangement of the storage apparatus when supplying radioactive waste into the storage container. [Figure 2] This diagram shows the schematic configuration of the storage apparatus according to Example 1, illustrating the arrangement of the storage apparatus when vacuum-drying radioactive waste in a storage container. [Figure 3] A diagram showing the configuration of the storage container. [Figure 4] A diagram showing the structure of the inner container. [Figure 5] A flowchart illustrating an example of a method for storing radioactive waste in storage containers. [Figure 6]This diagram shows the schematic configuration of the storage apparatus according to Example 2, illustrating the arrangement of the storage apparatus when vacuum-drying radioactive waste in a storage container. [Modes for carrying out the invention]

[0011] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0012] In a second embodiment of the technology disclosed herein, in the first embodiment of the radioactive waste processing method described above, the storage container may be equipped with a filter placed inside the storage container that allows water to pass through but prevents radioactive waste from passing through. In the dewatering step, the water in the storage container may be moved to the dewatering container via the filter. In the vacuum drying step, the storage container may be depressurized via the filter. With such a configuration, in the dewatering step, by moving the water in the storage container to the dewatering container via the filter, it is possible to suppress the movement of radioactive waste to the outside of the storage container along with the water. Furthermore, in the vacuum drying step, by depressurizing the storage container via the filter, it is possible to suppress the movement of radioactive waste to the outside of the storage container along with the water when the inside of the storage container is depressurized.

[0013] In a third aspect of the radioactive waste containment method disclosed herein, in the second aspect of the radioactive waste processing method described above, the vacuum drying step may involve moving the vaporized water to the outside of the storage container via a filter. With this configuration, when moving the vaporized water to the outside of the storage container in the vacuum drying step, it is possible to suppress the movement of radioactive waste along with the water to the outside of the storage container.

[0014] In a fourth aspect of the radioactive waste containment method disclosed herein, in the first aspect of the radioactive waste processing method described above, the storage container may include a filter placed inside the storage container that allows water to pass through but prevents radioactive waste from passing through, and an exhaust port placed at the top of the storage container. In the dewatering step, the water inside the storage container may be moved to the dewatering container via the filter. In the vacuum drying step, the storage container may be depressurized via the exhaust port. With such a configuration, in the dewatering step, by moving the water inside the storage container to the dewatering container via the filter, it is possible to suppress the movement of radioactive waste to the outside of the storage container along with the water. In addition, in the vacuum drying step, depressurizing the storage container via the exhaust port makes it easier to depressurize the inside of the storage container.

[0015] In a fifth aspect of the technology disclosed herein, in the fourth aspect of the radioactive waste processing method described above, the vaporized water may be moved to the outside of the storage container through an exhaust port during the vacuum drying process. This configuration makes it easier to move the vaporized water to the outside of the storage container during the vacuum drying process.

[0016] A sixth aspect of the radioactive waste containment method disclosed herein may further include a condensation step in the third or fifth aspect of the radioactive waste treatment method described above, in which vaporized water moved outside the storage container is condensed. With such a configuration, the vaporized water moved outside the storage container can be properly treated.

[0017] In the storage device according to the second aspect of the technology disclosed in this specification, in the storage device according to the first aspect described above, the storage device may be disposed outside the storage container and further include a second filter that allows water to pass through and does not allow radioactive waste to pass through. The heat exchanger may condense the vaporized water that has been transferred outside the storage container via the second filter. According to such a configuration, even if radioactive waste is transferred outside the storage container together with the water vaporized in the storage container, the radioactive waste contained in the vaporized water is captured by the second filter. Therefore, it is possible to suppress the movement of radioactive waste to the heat exchanger.

[0018] In the storage device according to the third aspect of the technology disclosed in this specification, in the storage device according to the first or second aspect described above, the storage container may include an inner container that houses radioactive waste and an outer container that houses the inner container. The outer container may have a shielding structure that shields radiation. The inner container may not have a shielding structure. The heating device may be disposed on the outer surface of the inner container to heat the inner container. According to such a configuration, since the inner container does not have a shielding structure, it is possible to heat the inside of the inner container from the outside of the inner container. Therefore, the inside of the inner container can be heated by the heating device disposed on the outer surface of the inner container. As a result, the configuration of the heating device can be simplified, and it is possible to avoid the heating device from coming into contact with radioactive waste. Further, since the outer container has a shielding structure, even if the inner container does not have a shielding structure, the storage container can be shielded by disposing the inner container inside the outer container. Therefore, the storage container can be transferred outside the facility. By making the storage container have a double structure of an inner container and an outer container in this way, it is possible to easily heat the inside of the storage container (inner container) while the storage container has a shielding structure.

Example

[0019] (Example 1) Referring to the drawings, the storage device 10 according to the embodiment will be described. The storage device 10 is used for dehydrating and storing a slurry containing radioactive waste. In this embodiment, the radioactive waste is, for example, an ion exchange resin used in a facility that handles radioactive substances. The radioactive waste (for example, ion exchange resin) after use is in a slurry state and is stored in the storage tank 2. The radioactive waste is finally detoxified, but the detoxification process may be carried out after a long period has elapsed since it was stored in the storage tank 2. By using the storage device 10, the slurry containing radioactive waste can be dehydrated and stored. Therefore, it becomes easier to store radioactive waste for a long time.

[0020] As shown in FIGS. 1 and 2, the storage device 10 includes a storage container 20, a dehydration container 52, a decompression device 56, a heater 80, and a heat exchanger 84.

[0021] The storage container 20 is a container for storing radioactive waste. Specifically, the storage container 20 dehydrates the slurry containing radioactive waste and stores the dehydrated radioactive waste. As shown in FIG. 3, the storage container 20 includes an inner container 22 and an outer container 40.

[0022] As shown in FIG. 4, the inner container 22 includes an inner main body portion 24 and an inner lid portion 26. The inner main body portion 24 is a substantially cylindrical box shape with an open upper surface. The inner lid portion 26 is connected to the upper surface of the inner main body portion 24. Radioactive waste is accommodated in the space formed by the inner main body portion 24 and the inner lid portion 26. In this embodiment, the inner container 22 (that is, the inner main body portion 24 and the inner lid portion 26) does not have a shielding structure for shielding radiation.

[0023] The inner lid portion 26 is provided with an outlet 30 and a connection portion 34 to which a path for moving a slurry containing radioactive waste is connected. When supplying radioactive waste into the storage container 20 (i.e., the inner container 22), one end of the first drainage path 60 (see Figure 1) is connected to the outlet 30, and one end of the first slurry supply path 62 (see Figure 1) is connected to the connection portion 34. Furthermore, as will be described later, when vacuum drying the radioactive waste in the storage container 20, one end of the third depressurization path 82 (see Figure 2) is connected to the outlet 30.

[0024] A filter 28 and a discharge pipe 29 are arranged inside the inner container 22. The filter 28 is positioned near the inner surface of the bottom of the inner main body 24. The filter 28 is configured to allow water to pass through, but to prevent radioactive waste (e.g., ion exchange resin, etc.) from passing through. One end of the discharge pipe 29 is connected to the filter 28, and the other end is connected to the outlet 30. The discharge pipe 29 discharges the water in the inner container 22 that has passed through the filter 28 to the outside of the inner container 22 (specifically, to the dewatering container 52, which will be described later) via the outlet 30 and the first drainage path 60. The discharge pipe 29 also discharges the gas (water vapor) in the inner container 22 that has passed through the filter 28 to the outside of the inner container 22 (specifically, to the heat exchanger 84, which will be described later) via the outlet 30 and the third depressurization path 82.

[0025] As shown in Figure 3, the outer container 40 comprises an outer body portion 42 and an outer lid portion 44. The outer body portion 42 is a roughly cylindrical box shape with an open top. The outer lid portion 44 is detachably attached to the top surface of the outer body portion 42. The outer body portion 42 is configured to accommodate an inner container 22 inside. That is, the inner diameter of the outer body portion 42 is larger than the outer diameter of the inner container 22, and in this embodiment, the outer body portion 42 is configured to accommodate one inner container 22. In addition, the height dimension of the outer body portion 42 (specifically, the distance from the top surface of the bottom of the outer body portion 42 to the top edge of the side) is larger than the height dimension of the inner container 22.

[0026] The outer body portion 42 and the outer lid portion 44 have a shielding structure that shields against radiation. The shielding structure is designed to shield against radiation emitted from radioactive waste (i.e., radioactive waste stored in the storage container 20 in this embodiment). For example, the outer body portion 42 and the outer lid portion 44 are made of a material that is difficult for radiation to pass through, and are made with a thickness that can shield against radiation.

[0027] Because the outer container 40 (i.e., the outer body 42 and the outer lid 44) ​​has a shielding structure, radiation emitted from the radioactive waste inside the outer container 40 (specifically, the radioactive waste in the inner container 22 housed inside the outer container 40) can be prevented from leaking to the outside of the outer container 40. Therefore, by housing the radioactive waste in the storage container 20 (specifically, the inner container 22 housed inside the outer container 40), the radioactive waste inside the storage container 20 can be transported to the outside of a facility with a shielding structure. Furthermore, by making the storage container 20 a double structure consisting of an inner container 22 and an outer container 40, only the inner container 22 can be placed in the storage facility (however, limited to facilities with a shielding structure) to store the radioactive waste (inner container 22). Because the outer container 40 has a shielding structure, its outer diameter is large. By placing only the inner container 22 in the storage facility, many inner containers 22 can be placed in the storage facility, and thus a large amount of radioactive waste can be stored in the storage facility. Furthermore, since only the inner container 22, which does not have a shielding structure, can be placed in the storage facility, the capacity of the storage facility can be reduced.

[0028] In this embodiment, the outer container 40 was configured to accommodate one inner container 22, but the configuration is not limited to this. For example, the outer container may be configured to accommodate multiple inner containers 22. By accommodating multiple inner containers 22 in one outer container, many inner containers 22 can be transported simultaneously. Furthermore, the plate thickness of the outer container 40 may be set according to the type of radiation emitted from the radioactive waste stored in the storage container 20 (i.e., the inner container 22). In this embodiment, the storage container 20 has a double-walled structure. Therefore, by appropriately setting the plate thickness of the outer container 40, it is possible to appropriately handle the storage and transport of radioactive waste containing various radioactive materials without changing the shape of the inner container 22.

[0029] As shown in Figure 1, the dewatering container 52 receives the slurry-like radioactive waste stored in the storage tank 2 and supplies the received slurry-like radioactive waste to the storage container 20. The dewatering container 52 may directly receive the radioactive waste from the storage tank 2, or it may move the radioactive waste from the storage tank 2 to another tank (hereinafter also referred to as the primary storage tank), and then move the radioactive waste from the primary storage tank to the dewatering container 52. For example, it may not be possible to install the storage device 10 of this embodiment near the storage tank 2. In such cases, the radioactive waste in the storage tank 2 can be stored in the storage container 20 at a location away from the storage tank 2 by storing the radioactive waste in the primary storage tank and then transporting the primary storage tank with the radioactive waste inside. Hereinafter, the storage tank 2 and the primary storage tank described above will be collectively referred to as "storage tank 2". The dewatering container 52 has a filter 54 inside. The filter 54 is configured to allow water to pass through, but to prevent radioactive waste (e.g., ion exchange resin, etc.) from passing through.

[0030] A second slurry supply path 64 and a second drainage path 66 are provided between the dewatering container 52 and the storage tank 2. A pump 65 is installed in the second slurry supply path 64. The second slurry supply path 64 supplies slurry containing radioactive waste from the storage tank 2 to the dewatering container 52 by operating the pump 65. The end of the second drainage path 66 on the dewatering container 52 side is connected to a filter 54. When slurry or water is supplied to the dewatering container 52 from an external source (storage tank 2 or storage container 20), the water in the dewatering container 52 is sent to the second drainage path 66 via the filter 54. The water sent to the second drainage path 66 moves to the storage tank 2.

[0031] A first drainage route 60 and a first slurry supply route 62 are installed between the dewatering container 52 and the storage container 20. The first drainage route 60 and the first slurry supply route 62 are installed when supplying radioactive waste into the storage container 20. The dewatering container 52 supplies slurry-like radioactive waste to the storage container 20 via the first slurry supply route 62. The dewatering container 52 also receives water from the storage container 20 via the first drainage route 60.

[0032] The depressurization device 56 is a vacuum pump that can individually depressurize the space inside the dewatering container 52 and the space inside the storage container 20. When supplying a slurry containing radioactive waste into the storage container 20 and dewatering the slurry inside the storage container 20, the depressurization device 56 can be connected to a first depressurization path 68 connected to the storage container 20, and can also be connected to a second depressurization path 70 connected to the dewatering container 52. When the depressurization device 56 is operated while connected to the first depressurization path 68, the space inside the storage container 20 is depressurized via the first depressurization path 68. When the depressurization device 56 is operated while connected to the second depressurization path 70, the space inside the dewatering container 52 is depressurized via the second depressurization path 70. Furthermore, as shown in Figure 2, when vacuum drying the radioactive waste inside the storage container 20, the depressurization device 56 can be connected to a third depressurization path 82 connected to the storage container 20. When the depressurizing device 56 is operated while it is connected to the third depressurizing path 82, the gas inside the storage container 20 is exhausted via the third depressurizing path 82, and the space inside the storage container 20 is depressurized.

[0033] The heater 80 is in sheet form and is detachably wrapped around the entire outer circumference of the side of the inner body 24 in the circumferential direction. The heater 80 is installed on the outer circumference of the inner body 24 when vacuum drying the radioactive waste inside the storage container 20 (specifically, the inner container 22). By heating the inner container 22 with the heater 80, the temperature inside the inner container 22 rises. Also, when vacuum drying the radioactive waste inside the storage container 20, a pressure sensor 81 is installed in the storage container 20. The pressure sensor 81 measures the pressure inside the storage container 20.

[0034] The heat exchanger 84 is installed in the third depressurization path 82. The third depressurization path 82 reduces the pressure inside the inner container 22 and discharges the gas (water vapor) inside the inner container 22 when vacuum drying the radioactive waste in the storage container 20. The heat exchanger 84 condenses the gas discharged from the inner container 22. The condensed water condensed in the heat exchanger 84 is discharged from the heat exchanger 84 to a drainage container (not shown). Alternatively, the condensed water condensed in the heat exchanger 84 may be discharged to a dewatering container 52.

[0035] Next, a method for storing radioactive waste in the storage container 20 will be described. As mentioned above, slurry-like radioactive waste may be subjected to detoxification treatment after a long period of time. In this embodiment, in order to facilitate the long-term storage of radioactive waste, the slurry-like radioactive waste is dewatered before storage.

[0036] As shown in Figure 5, first, the parts of the storage device 10 are arranged near the storage tank 2 (S100). That is, the storage device 10 in this embodiment is not permanently installed, but is installed and used in a removable manner near the storage tank 2 to be processed. For this reason, the storage device 10 is first installed near the storage tank 2 to make the radioactive waste in the storage tank 2 ready for processing. In step S100, as shown in Figure 1, the parts of the storage device 10 are arranged to supply radioactive waste to the storage container 20 (specifically, the inner container 22). Specifically, a dewatering container 52 and a depressurization device 56 are installed near the storage tank 2, and a second slurry supply route 64 and a second drainage route 66 are connected between the dewatering container 52 and the storage tank 2. In addition, the inner container 22 is installed, and a first drainage route 60 and a first slurry supply route 62 are connected between the inner container 22 and the dewatering container 52. In addition, a first depressurization route 68 is connected to the inner container 22. As mentioned above, instead of storage tank 2, the components of the storage device 10 may be placed near the primary storage tank.

[0037] Next, the slurry-like radioactive waste contained in the storage tank 2 is supplied to the dewatering container 52 (S110). Specifically, the pump 65 is operated. As a result, the slurry-like radioactive waste is supplied from the storage tank 2 to the dewatering container 52 via the second slurry supply path 64. Also, the water in the dewatering container 52 is sent to the second drainage path 66 via the filter 54 and moved to the storage tank 2 (S120). As a result, the concentrated slurry-like radioactive waste is contained in the dewatering container 52.

[0038] In this embodiment, the water discharged from the dewatering container 52 in step S120 was returned to the storage tank 2, but the configuration is not limited to this. For example, the water discharged from the dewatering container 52 may be discarded without being returned to the storage tank 2, or it may be sent to another processing device (not shown) and detoxified before being discarded.

[0039] Next, the space inside the inner container 22 is depressurized (S130). Specifically, the depressurization device 56 is operated while connected to the first depressurization path 68. As a result, the space inside the inner container 22 is depressurized via the first depressurization path 68.

[0040] Next, the slurry-like radioactive waste supplied into the dewatering container 52 in step S110 is moved to the inner container 22 via the first slurry supply path 62 (S140). In step S130, the space inside the inner container 22 is depressurized. As a result, a pressure difference is created between the space inside the inner container 22 and the space inside the dewatering container 52. This pressure difference allows the slurry-like radioactive waste to be easily moved from the dewatering container 52 to the inner container 22.

[0041] When slurry-like radioactive waste moves from the dewatering container 52 to the inner container 22, the space inside the dewatering container 52 is depressurized (S150). Specifically, the depressurization device 56 is operated while connected to the second depressurization path 70. As a result, the space inside the dewatering container 52 is depressurized via the second depressurization path 70. The space inside the inner container 22 is opened to the atmosphere and its pressure is higher than that inside the dewatering container 52.

[0042] Next, the water in the inner container 22 is moved to the dewatering container 52 via the first drainage path 60 (S160). As described above, in step S150, the space inside the dewatering container 52 is depressurized, and a pressure difference is created between the space inside the inner container 22 and the space inside the dewatering container 52. This pressure difference allows water to be easily moved from the inner container 22 to the dewatering container 52. The first drainage path 60 is connected to the filter 28 via the outlet 30 and the discharge pipe 29. Therefore, only water that can pass through the filter 28 moves to the dewatering container 52 via the discharge pipe 29, the outlet 30, and the first drainage path 60, and radioactive waste that cannot pass through the filter 28 (ion exchange resin in this embodiment) remains in the inner container 22. Since only the water in the inner container 22 moves to the dewatering container 52, the slurry-like radioactive waste is dewatered in the inner container 22. The water that has moved into the dewatering container 52 is sent to the second drainage path 66 via the filter 54 and then moves to the storage tank 2.

[0043] In this embodiment, the water in the inner container 22 was returned to the dewatering container 52 in step S160, but the system is not limited to this configuration. For example, the water in the inner container 22 may be discharged into another container instead of being returned to the dewatering container 52. Also, in step S160, the water that moved into the dewatering container 52 was returned to the storage tank 2, but the system is not limited to this configuration. For example, the water that moved into the dewatering container 52 may be discarded without being returned to the storage tank 2, or it may be sent to another processing device (not shown) and detoxified before being discarded.

[0044] Next, it is determined whether the inner container 22 is full of radioactive waste (S170). Since the water in the inner container 22 is drained in step S160, the amount of contents (i.e., radioactive waste) in the inner container 22 decreases by the amount drained. If the inner container 22 is not full (NO in step S170), the process returns to step S110, and steps S110 to S170 are repeated until the inner container 22 is full.

[0045] When the inner container 22 is full (YES in step S170), the arrangement of each part of the storage device 10 is changed (S180). Specifically, the arrangement is changed from one for supplying slurry containing radioactive waste to the inner container 22 and dewatering the slurry within the inner container 22 (arrangement in Figure 1) to one for vacuum drying the radioactive waste inside the inner container 22 (arrangement in Figure 2). Specifically, the first drainage path 60, the first slurry supply path 62, and the first depressurization path 68 connected to the inner container 22 are removed. Also, the second depressurization path 70 installed between the dewatering container 52 and the depressurization device 56 is removed. Then, a third depressurization path 82 is connected between the outlet 30 of the inner container 22 and the depressurization device 56. In addition, a heater 80 and a pressure sensor 81 are installed in the inner container 22.

[0046] Next, the space inside the inner container 22 is depressurized (S190). Specifically, the depressurization device 56 is operated while connected to the third depressurization path 82. As a result, the space inside the inner container 22 is depressurized via the third depressurization path 82. The third depressurization path 82 is connected to the filter 28 via the outlet 30 and the outlet pipe 29. Therefore, when depressurizing the space inside the inner container 22 via the third depressurization path 82, it is possible to prevent the radioactive waste contained inside the inner container 22 from moving to the outside of the inner container 22.

[0047] When the pressure inside the inner container 22 is reduced to a preset first pressure value, the pressure reducing device 56 is stopped and the heater 80 heats the inside of the inner container 22 (S200). By heating the inside of the inner container 22 while the pressure inside the inner container 22 is reduced in step S190, any water remaining inside the inner container 22 boils and vaporizes.

[0048] Next, it is determined whether the pressure inside the inner container 22 has stabilized (S210). The pressure inside the inner container 22 is measured by the pressure sensor 81. While the water inside the inner container 22 is vaporizing, the pressure inside the inner container 22 continues to rise. If the pressure inside the inner container 22 is rising (NO in step S210), the system waits until the pressure inside the inner container 22 stabilizes.

[0049] Once the pressure inside the inner container 22 stabilizes (YES in step S210), the gas is discharged from the inner container 22 (S220). Specifically, the depressurization device 56 is operated while connected to the third depressurization path 82. As a result, the gas inside the inner container 22 is discharged to the outside of the inner container 22 via the third depressurization path 82. By discharging the gas inside the inner container 22 to the outside of the inner container 22, the amount of water remaining in the inner container 22 that was not discharged when the water inside the inner container 22 was discharged in step S160 can be further reduced. The third depressurization path 82 is connected to the filter 28 via the outlet 30 and the discharge pipe 29. Therefore, when the gas inside the inner container 22 is discharged to the outside of the inner container 22, it is possible to avoid the radioactive waste contained in the inner container 22 moving to the outside of the inner container 22. Note that in step S220, the gas inside the inner container 22 is discharged using the depressurization device 56. As a result, the gas inside the inner container 22 is discharged, and the space inside the inner container 22 is depressurized.

[0050] When the gas in the inner container 22 is discharged, the depressurization device 56 is stopped (S230). When the gas in the inner container 22 is discharged in step S220, the amount of gas in the inner container 22 decreases, and the pressure inside the inner container 22 drops to a preset second pressure value (the second pressure value may be the same as or different from the first pressure value). Also, because the gas in the inner container 22 is discharged using the depressurization device 56, the pressure inside the inner container 22 is reduced as the gas is discharged. Therefore, if there is still moisture remaining in the inner container 22, the water inside the inner container 22 will vaporize. Then, as time passes, the pressure inside the inner container 22 will rise again. So, after stopping the depressurization device 56, the measurement value of the pressure sensor 81 is monitored to determine whether or not the pressure inside the storage container 20 has risen (S240). If the pressure inside the inner container 22 has risen (YES in step S240), it can be determined that the water inside the inner container 22 has vaporized. Therefore, the process returns to step S210 and repeats steps S210 to S240.

[0051] On the other hand, if the pressure inside the inner container 22 does not rise (NO in step S240), it can be determined that there is almost no water remaining inside the inner container 22 and that almost no vaporized water has been generated inside the inner container 22. Therefore, the vacuum drying of the inner container 22 (processing in steps S180 to S240) is terminated. Then, the third depressurization path 82 is removed (S250). Also, the heater 80 and pressure sensor 81 are removed from the inner container 22. Next, the inner container 22 is placed inside the outer container 40 (S260). This completes the placement of the radioactive waste into the storage container 20.

[0052] In this embodiment, the inner container 22 is not housed in the outer main body 42, and the radioactive waste is housed in the inner container 22. However, the configuration is not limited to this. For example, the inner container 22 may be housed in the outer main body 42 when the slurry containing the radioactive waste, as described in steps S100 to S170, is supplied into the inner container 22 for dewatering. In this case, during the processing in step S100, the inner container 22 is housed in the outer main body 42, and the various parts of the storage device 10 are arranged. Then, during the processing in step S180, when the various parts of the storage device 10 are arranged to vacuum dry the inside of the inner container 22, the inner container 22 is removed from the outer main body 42, and the heater 80 is installed around the inner container 22. Alternatively, the slurry containing the radioactive waste may be supplied into the inner container 22 for dewatering while the inner container 22 is housed in the outer main body 42, and the inside of the inner container 22 may be vacuum dried. In this case, during step S100, the inner container 22 can be housed in the outer main body 42 with the heater 80 installed around it. Alternatively, during step S100, the inner container 22 without the heater 80 installed around it can be housed in the outer main body 42, with the parts of the storage device 10 arranged, and during step S180, the inner container 22 without the heater 80 installed around it can be housed in the outer main body 42, with the arrangement of the parts of the storage device 10 changed. In this case, during step S180, the heater 80 can be installed around the outer main body 42.

[0053] Furthermore, in this embodiment, the inside of the inner container 22 was vacuum-dried while monitoring the pressure inside the inner container 22, but the configuration is not limited to this. For example, the inside of the inner container 22 may be vacuum-dried by adjusting the heating temperature of the heater 80. When the pressure is reduced, the boiling point of water decreases, and water vaporizes at a temperature lower than 100°C. By adjusting the heating temperature of the heater 80 so that the temperature inside the inner container 22 reaches the target temperature for vacuum drying, the inside of the inner container 22 can be vacuum-dried until the desired amount of residual moisture is achieved.

[0054] Alternatively, instead of vacuum drying the inside of the inner container 22 while monitoring the pressure inside the inner container 22, the amount of moisture removed from the inner container 22 may be monitored, and the inside of the inner container 22 may be vacuum dried until the desired amount of residual moisture is reached. During vacuum drying, the water vapor removed from the inner container 22 is condensed in the heat exchanger 84 and discharged into a drainage container (or dewatering container 52) not shown. The amount of water discharged per unit time (specifically, the mass of water) into the drainage container (or dewatering container 52) during vacuum drying may be monitored, and the vacuum drying process may be terminated when the amount of water discharged per unit time falls below a predetermined value. In this case as well, by appropriately setting the predetermined value, the inside of the inner container 22 can be vacuum dried until the desired amount of residual moisture is reached.

[0055] Alternatively, instead of vacuum drying the inner container 22 while monitoring the pressure inside the inner container 22, the inner container 22 may be vacuum dried while monitoring the temperature inside the inner container 22. In this case, a temperature sensor (not shown) for measuring the temperature inside the inner container 22 is installed. During vacuum drying, the inner container 22 is heated by the heater 80. While water is vaporizing under reduced pressure, the pressure (vapor pressure) inside the inner container 22 remains approximately constant, and the temperature inside the inner container 22 hardly changes. On the other hand, when there is no more water vaporizing inside the inner container 22, it is heated by the heater 80, and the temperature inside the inner container 22 rises. For this reason, the vacuum drying process may be terminated when the temperature inside the inner container 22 reaches a predetermined temperature or higher. In this case as well, the inner container 22 can be vacuum dried until the desired amount of residual moisture is achieved.

[0056] (Example 2) In the above-described embodiment 1, the gas inside the storage container 20 (specifically, the inner container 22) was discharged to the outside of the storage container 20 via a filter 28 inside the storage container 20, but the configuration is not limited to this. For example, as shown in Figure 6, the gas discharged from the storage container 20 may pass through a filter 86 located outside the storage container 20.

[0057] In the storage apparatus 110 of this embodiment, a third depressurization path 182 is connected between the depressurization device 56 and the storage container 20 when the radioactive waste in the storage container 20 is vacuum-dried. The third depressurization path 182 differs from the third depressurization path 82 of Embodiment 1 above in that the end on the storage container 20 side is connected to a connection part 34 (see Figure 4), and a filter 86 is installed between the storage container 20 and the heat exchanger 84. The filter 86 is configured to allow water to pass through, but to prevent radioactive waste (e.g., ion exchange resin, etc.) from passing through.

[0058] The connection part 34 is not connected to the filter 28 and discharge pipe 29 inside the storage container 20. Therefore, when the process of discharging gas from the inner container 22 via the connection part 34 (S220 in Figure 5) is performed, the gas located at the top of the storage container 20 is easily discharged. As a result, water vapor vaporized by reduced pressure is easily discharged outside the storage container 20.

[0059] On the other hand, when a process to reduce the pressure inside the storage container 20 via the connection part 34 (S190 in Figure 5) or a process to discharge gas from the storage container 20 (S220 in Figure 5) is performed, the gas is discharged outside the storage container 20 without passing through the filter 28 inside the storage container 20. As a result, there is a risk that radioactive waste will be discharged outside the inner container 22 along with the gas inside the storage container 20. In this embodiment, a filter 86 is placed in the third pressure reduction path 182. Therefore, even if radioactive waste is discharged outside the storage container 20 along with the gas from the connection part 34, the filter 86 can capture the radioactive waste discharged outside the storage container 20.

[0060] In the above-described embodiment 1, the filter 86 was not placed in the third depressurization path 82 (see Figure 2), but the configuration is not limited to this. For example, the filter 86 may also be placed in the third depressurization path 82 in the above-described embodiment 1. In this case, when the radioactive waste in the storage container 20 is vacuum-dried, the gas in the storage container 20 passes through the filter 28 inside the storage container 20 and is discharged outside the storage container 20, and also passes through the filter 86 placed in the third depressurization path 82 and is sent to the heat exchanger 84. By having the gas in the storage container 20 pass through both the filter 28 inside the storage container 20 and the filter 86 placed in the third depressurization path 82, it is possible to more reliably prevent the radioactive waste from moving outside the storage container 20. In addition, in the above-described embodiments 1 and 2, the first drainage path 60 may also be equipped with a filter configured to allow water to pass through but prevent radioactive waste from passing through. In this case, when the process of dewatering the slurry-like radioactive waste contained in the storage container 20 (S160 in Figure 5) is performed, the water in the storage container 20 passes through the filter 28 inside the storage container 20 and is discharged outside the storage container 20, and also passes through a filter located in the first drainage path 60 and is moved to the dewatering container 52. Therefore, it is possible to more reliably prevent the radioactive waste from moving outside the storage container 20.

[0061] The following points should be noted regarding the storage device 10 described in the embodiment. The filter 28 in the embodiment is an example of a "filter" and a "first filter," the connection part 34 is an example of an "exhaust port," the heater 80 is an example of a "heating device," and the filter 86 is an example of a "second filter."

[0062] The specific examples of the technology disclosed herein have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples described above. Furthermore, the technical elements described herein or in the drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated herein or in the drawings achieves multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness. [Explanation of Symbols]

[0063] 2: Storage tank 10, 110: Storage device 20: Storage container 22: Inner container 28: Filter 29: Discharge pipe 30: Outlet 34: Connection part 40:Outer container 42:Outer body part 44:Outer lid part 52: Dehydration container 56: Pressure reducing device 60: First drainage route 62: First slurry supply route 64: Second slurry supply route 66: Second drainage route 68: First decompression path 70: Second decompression pathway 80: Heater 82, 182: Third decompression path 86: Filter 84;heat exchanger

Claims

1. A method for storing radioactive waste in storage containers, A dewatering step involves supplying the slurry containing the radioactive waste to the storage container and dewatering the slurry within the storage container. The system includes a vacuum drying step in which the storage container is depressurized to dry the radioactive waste that has been dehydrated in the dehydration step, In the dewatering step, the dewatering container that holds the water discharged from the storage container is depressurized relative to the storage container, and the water in the storage container is transferred to the dewatering container. A method for containing radioactive waste, wherein in the vacuum drying step, the storage container is depressurized and the storage container is heated to vaporize the water contained in the radioactive waste and dry the radioactive waste.

2. The storage container is equipped with a filter placed inside the storage container that allows water to pass through but prevents the radioactive waste from passing through. In the dewatering step, the water in the storage container is transferred to the dewatering container via the filter. The method for containing radioactive waste according to claim 1, wherein the vacuum drying step reduces the pressure of the storage container through the filter.

3. The method for containing radioactive waste according to claim 2, wherein in the vacuum drying step, the vaporized water is moved to the outside of the storage container via the filter.

4. The aforementioned storage container is A filter is placed inside the storage container and allows water to pass through but prevents the radioactive waste from passing through. The storage container is equipped with an exhaust port located at the top of the container, In the dewatering step, the water in the storage container is transferred to the dewatering container via the filter. The method for containing radioactive waste according to claim 1, wherein the storage container is depressurized through the exhaust port during the vacuum drying step.

5. The method for containing radioactive waste according to claim 4, wherein in the vacuum drying step, the vaporized water is moved to the outside of the storage container through the exhaust port.

6. A method for containing radioactive waste according to claim 3 or 5, further comprising a condensation step of condensing the vaporized water that has been moved to the outside of the storage container.

7. A storage device for storing radioactive waste, A storage container for dewatering and storing the slurry containing the aforementioned radioactive waste, A first filter is placed inside the storage container and allows water to pass through but prevents the radioactive waste from passing through. A dewatering container for containing the water discharged from the storage container through the first filter, A vacuum device capable of reducing the pressure of the storage container and the dewatering container, respectively. The system includes a heating device for heating the aforementioned storage container, The aforementioned pressure reducing device is The water in the storage container is discharged into the dewatering container by reducing the pressure of the dewatering container relative to the storage container, After the water in the storage container is discharged into the dewatering container, the storage container is depressurized to vaporize the water contained in the radioactive waste in the storage container and dry the radioactive waste. The storage device further comprises a heat exchanger for condensing the vaporized water that has been moved to the outside of the storage container.

8. The storage container is further equipped with a second filter located outside the container, which allows water to pass through but prevents the radioactive waste from passing through. The storage apparatus according to claim 7, wherein the heat exchanger condenses the vaporized water that has been moved to the outside of the storage container via the second filter.

9. The aforementioned storage container is An inner container for containing the aforementioned radioactive waste, It comprises an outer container that houses the inner container, The outer container has a shielding structure that shields against radiation. The inner container does not have the shielding structure, The storage apparatus according to claim 7 or 8, wherein the heating device is arranged on the outer surface of the inner container and heats the inner container.

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