JP2002207097A - Method and device for decontaminating radioactive substances - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and efficiently recover a radioactive substance adhering to a decontaminated object. SOLUTION: A method for decontaminating a radioactive substance includes a pretreatment process 11 where the decontaminated object to which a powdery radioactive substance adheres is put into contact with carbon dioxide in a supercritical or liquid state and a separation process 12 where the radioactive substance is separated from the contaminated object by decompressing carbon dioxide to convert it into a gaseous state. This method has a washing process 13 where carbon dioxide in a liquid state is supplied to the separated radioactive substance to flush it, a first recovery process 14 where the washed fluid is separated into an aggregate of the radioactive substance and a fluid and the aggregate is recovered, a decompression process 16 where the separated fluid is decompressed to convert carbon dioxide in a liquid state to that in a gaseous state, expand the volume of the carbon dioxide and give a flow velocity to the fluid, a second recovery process 17 where the radioactive substance is separated into fine grains and carbon dioxide in a gaseous state to recover the fine grains and a pressurizing process 18 where the separated carbon dioxide in a gaseous state is pressurized to convert the carbon dioxide into a supercritical or liquid state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decontaminating radioactive substances which can remove radioactive substances attached to radioactive wastes as contaminants. More specifically, the present invention relates to a method and an apparatus for decontaminating radioactive substances using the properties of carbon dioxide in a supercritical or liquid state.

[0002]

2. Description of the Related Art It is desirable that radioactive waste generated in nuclear facilities be decontaminated as much as possible during disposal to reduce the radioactivity level, and that the amount of generated radioactive waste be reduced by recycling as much as possible. Of the elements attached to radioactive waste, for example, plutonium, etc., even with a very small amount of a few mg, has a high radiation dose, and long-term storage as waste may be difficult. is necessary.

[0003] The surface condition of radioactive waste varies, and radioactive substances adhering to fine grooves and the like on the surface cannot achieve the expected decontamination effect by wiping. There is also a method of decontamination while polishing the waste surface with a decontamination medium such as alumina powder.However, the degree of decontamination such as re-adhering radioactive substances that have been decontaminated Has limitations. In contrast, cleaning with nitric acid can be expected to have a decontamination effect irrespective of the surface condition of radioactive waste, which is a contaminated material, and is effective when removing radioactive substances attached to fine grooves on the surface. It is. However, this cleaning method using nitric acid generates waste liquid after decontamination, so that it is not only necessary to treat the waste liquid, but also it is not possible to expect a sufficient effect on substances which are hardly soluble in nitric acid such as plutonium oxide.
There is also a method in which a nitric acid solution containing divalent silver ions is generated in an electrolytic cell and dissolved by the oxidizing action of these ions.
It is a special and complicated system. Furthermore, in the decontamination using a solution, when the radioactive substance is a substance requiring criticality control such as plutonium, the handling amount in the decontamination apparatus is limited, and the size of the decontamination apparatus is restricted. As mentioned above, there are several methods for decontamination of radioactive waste, but it is difficult to obtain the expected decontamination effect, or additional facilities are required, and from the viewpoint of criticality management There were restrictions on the amount of radioactive waste handled and the size of the equipment.

As a method of solving these problems of the above methods, there is a method of decontaminating carbon dioxide in a supercritical or liquid state. This method makes use of the high diffusivity of carbon dioxide in supercritical or liquid state and the property of carbon dioxide that easily evaporates due to pressure drop. Infiltrate supercritical or liquid carbon dioxide into the substance, then reduce the pressure, instantaneously vaporize the carbon dioxide, and rapidly expand the carbon dioxide to convert the radioactive substance into contaminated radioactive waste Separate from objects.

As shown in FIG. 3, an apparatus for decontaminating radioactive substances using this method has a washing apparatus 1 that is sealed and can withstand a predetermined temperature and pressure. One of the cleaning devices 1 has a supply port 1
a is provided on the other side with an outlet 1b. The discharge port 1b is connected to the supply port 3a at the top of the filter 3 via the pipe line 2. A valve 2 a is provided in the middle of the pipe 2.
An outlet 3b is provided on the side of the filter 3. Outlet 3
b is connected to the compressor 6 via the pipe 4. A valve 4a and a buffer tank 4b are provided in the middle of the pipeline 4. The compressor 6 is connected to a supply port 1 a of the cleaning device 1 via a pipe 7. In the middle of the pipe 7, a valve 7a,
The buffer tank 7b and the valve 7c are provided in this order from the upstream side.

[0006] In the apparatus configured as described above, the cleaning apparatus 1 is used.
The contaminated substance to which the powdered radioactive substance attached to the inside is brought into contact with carbon dioxide in a supercritical or liquid state. Next, the valve 2a is opened to reduce the pressure in the cleaning device 1,
By instantaneously evaporating carbon dioxide, radioactive materials are separated from radioactive waste as contaminated material. This cleaning leaves powdered radioactive substances inside the cleaning device, circulation pipes, and the like. If the cleaning is performed repeatedly, the powdered radioactive substances may accumulate in pipes and the like and block them. Therefore, only the radioactive substance is separated and collected by the filter 3 from the fluid containing the carbon dioxide and the radioactive substance after washing. After capturing the radioactive material, the carbon dioxide is compressed by the compressor 6 and supplied to the cleaning device 1 again. As described above, since carbon dioxide is recycled, not only environmental considerations are taken, but also cleaning agents containing hydrogen atoms such as water and nitric acid cannot be used due to restrictions on criticality management, or use is restricted. Area (referred to as water-free area)
Is used as a method for decontamination of radioactive waste in the country. After the powdery radioactive material is collected by the filter, the filter or the like is periodically removed and replaced with a new one.

[0007]

However, this replacement of the filter is complicated because the entire decontamination apparatus is housed in a device such as a glove box for confining radioactive substances. In addition, it is necessary to recover the radioactive material from the collected filter, and there is a problem that the recovered filter itself becomes radioactive waste. An object of the present invention is to provide a method and an apparatus for decontaminating radioactive substances that can easily and efficiently collect radioactive substances attached to contaminated substances.

[0008]

According to the first aspect of the present invention,
As shown in FIG. 1, a pretreatment step 11 in which a contaminated substance to which a powdered radioactive substance is attached is brought into contact with carbon dioxide in a supercritical or liquid state, Or a separation step 12 of separating the radioactive substance from the contaminant by converting the carbon dioxide in a liquid state into a gaseous state, wherein the radioactive substance separated in the separation step 12 is converted into carbon dioxide in a liquid state. A washing step 13 for washing the radioactive material by supplying
A first recovery step 14 of separating the fluid containing the radioactive substance and the carbon dioxide in a liquid state washed in the cleaning step 13 into an aggregate of the radioactive substance and a fluid to collect the aggregate of the radioactive substance
And a pressure reducing step 16 in which the fluid separated in the first recovery step 14 is decompressed to convert the liquid carbon dioxide contained in the fluid into a gaseous state to increase the volume, thereby giving a flow rate to the fluid.
And a second recovery step 17 for separating the fluid into radioactive particles and gaseous carbon dioxide to recover the radioactive particles, and pressurizing the gaseous carbon dioxide separated in the second recovery step 17 And a pressurizing step 18 for converting carbon dioxide into a supercritical or liquid state. In the invention according to claim 1, by passing through the pretreatment step 11, the separation step 12, and the washing step 13, the high diffusivity of carbon dioxide in a supercritical or liquid state and the carbon dioxide that is easily vaporized due to a pressure drop The radioactive substance is separated from the contaminated material by utilizing the properties, and the radioactive substance aggregate having a large particle diameter is separated from the fluid in the first recovery step 14 to collect the radioactive substance aggregate. Decompression step 1
In step 6 and the second recovery step 17, carbon dioxide is converted into a gaseous state, a flow rate is given to the fluid, and fine particles of radioactive substance having a small particle diameter are separated from the fluid to recover fine particles of radioactive substance. In the pressurizing step 18, gaseous carbon dioxide is converted into supercritical or liquid carbon dioxide. In this way, the radioactive substance is efficiently decontaminated from the contaminated material by passing through the above steps.

The invention according to claim 2 is the invention according to claim 1, which is a method for decontaminating radioactive substances, wherein the first recovery step is performed by solid-liquid separation or sedimentation separation. According to the second aspect of the invention, in the first recovery step, aggregates of the radioactive substance having a large particle size are separated from the fluid by solid-liquid separation or sedimentation separation to collect the radioactive substance aggregates.

[0010] The invention according to claim 3 is the invention according to claim 1, which is a method for decontaminating radioactive substances, wherein the second recovery step is performed by solid-gas separation. In the invention according to claim 3,
In the second recovery step, fine particles having a small particle diameter are separated from the fluid by solid-gas separation to recover fine particles of a radioactive substance.

The invention according to claim 4 is the invention according to claims 1 to 3
The invention according to any one of the above, wherein the supercritical or liquid carbon dioxide obtained in the pressurizing step is supplied to the pretreatment step and a part of the supercritical or liquid carbon dioxide is reversed to the second recovery step. This is a method of decontaminating radioactive materials to be supplied and washed. In the invention according to claim 4, the supercritical or liquid carbon dioxide obtained in the pressurizing step is recycled to the pretreatment step.
In addition, a part of carbon dioxide in a supercritical or liquid state is backwashed and supplied to the second recovery step to prevent clogging of the filter in the second recovery step and to separate and recover effectively.

According to a fifth aspect of the present invention, as shown in FIG. 2, the radioactive material is separated from the contaminated material by washing the contaminated material to which the powdered radioactive material adheres with supercritical or liquid carbon dioxide. A cleaning device 21 for removing the fluid, a solid-liquid separator 23 for separating a fluid containing the radioactive substance removed in the cleaning device 21 and carbon dioxide in a liquid state into an aggregate of radioactive substances and a fluid, and a solid-liquid separator A venturi 27 that reduces the pressure of the fluid separated in 23 to convert the liquid carbon dioxide contained in the fluid into a gaseous state to increase its volume to increase the flow rate of the fluid, and to convert the fluid into fine particles of radioactive material and carbon dioxide in a gaseous state. This is a decontamination apparatus for radioactive substances, comprising: a solid-gas separator 26 that separates the gas into carbon dioxide; and a compressor 29 that pressurizes the gaseous carbon dioxide separated by the solid-gas separator 26.
In the invention according to claim 5, the radioactive substance is separated from the contaminated material by the cleaning device 21, and the radioactive substance aggregate having a large particle diameter is separated from the fluid by the solid-liquid separator 23. Venturi 2
By decompressing and evaporating the fluid in step 7, the flow rate is given to the fluid to facilitate separation of radioactive particles having a small particle size, and the solid-gas separator 26 separates radioactive particles.
Since the separation is performed in two stages as described above, the recovery rate of the radioactive substance can be improved. Further, since the carbon dioxide in the liquid state contained in the fluid is reduced to the carbon dioxide in the gas state by the venturi 27, the solid-gas separator 26 can be backwashed with the carbon dioxide in the supercritical or liquid state. Therefore, clogging of the filter can be prevented, and the frequency of replacement of the filter can be reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The powdery radioactive substance attached to radioactive waste has a very wide particle size distribution from extremely fine particles of less than 1 μm called submicron to agglomerates of powder of several mm or more. The particle size of the aggregate of the radioactive substance in the present invention is 100 μm to 30 mm, and the particle size of the fine particles of the radioactive substance is 0.1 to 500 μm.

Next, the decontamination method of the present invention will be described with reference to FIG. First, the contaminated substance to which the powdered radioactive substance has adhered is brought into contact with carbon dioxide in a supercritical or liquid state (pretreatment step 11). In this step 11, supercritical or liquid carbon dioxide is brought into contact with the contaminant as a cleaning solvent. The temperature and pressure conditions of the supercritical or liquid carbon dioxide in this step 11 are 10 to 150 ° C., 4.5 to 25 M
Pa. The temperature and pressure conditions vary depending on various conditions such as contaminants and radioactive materials, but more preferably 20
５０50 ° C., 5.7 to 10 MPa. At the start of the process, carbon dioxide in a supercritical or liquid state is supplied from the outside as shown by a broken line in FIG. The supply from the outside is performed until the supercritical or liquid carbon dioxide obtained in the pressurizing step 18 described below is recycled as a cleaning solvent in the pretreatment step 11. Next, the pressure of the supercritical or liquid carbon dioxide contacted with the contaminated substance is reduced to gaseous carbon dioxide to separate the radioactive substance from the contaminated substance (separation step 12). In this step 12, the pressure of carbon dioxide is reduced to 0.
By reducing the pressure to a range of from 0.5 to 1 MPa, the carbon dioxide is changed to a gaseous state, and the radioactive substance is separated from the contaminated material by utilizing rapid volume expansion when changing to the gaseous state.

Next, carbon dioxide in a liquid state is supplied to the separated radioactive substance to wash the radioactive substance (flushing:
flushing) (washing step 13). In this step 13, in order to prevent the radioactive substance separated from the contaminated material from remaining in the cleaning device or the like, the radioactive material is flushed by supplying carbon dioxide in a liquid state to the cleaning device. Temperature and pressure conditions of carbon dioxide in a liquid state used for cleaning are 10 to 25.
C., 4.5 to 6.5 MPa is good. By this washing, the radioactive material forms a slurry with carbon dioxide. Cleaning process 1
The fluid containing the radioactive substance and the carbon dioxide in the liquid state washed in 3 is separated into the radioactive substance aggregate and the fluid to collect the radioactive substance aggregate (first recovery step 14). In this step 14, separation is performed by solid-liquid separation or sedimentation separation, and an aggregate of a radioactive substance having a relatively large particle size is recovered. The particle size of the aggregate of radioactive material to be separated is 100 μm
It is about 30 mm.

Next, the pressure of the liquid carbon dioxide contained in the fluid is reduced to gaseous carbon dioxide (decompression step 16). In this step 16, the carbon dioxide in a liquid state is decompressed to a gaseous state, thereby expanding the volume of the fluid and giving a flow velocity to the fluid. Increasing the flow rate makes it easier to separate the radioactive substance particles from the fluid in the second separation step 17 described later. Pressure condition is 0.05-1
Adjust to the range of MPa. Next, the fluid is separated into radioactive substance fine particles and gaseous carbon dioxide to collect the radioactive substance fine particles (second recovery step 17). This step 17
In the above, the fluid is separated into fine particles of radioactive substance having a particle size of 0.1 to 500 μm and carbon dioxide in a gaseous state by using the flow rate increased in the above-described decompression step 16. Finally, the pressure of the separated gaseous carbon dioxide is increased to supercritical or liquid carbon dioxide (pressure step 18). In this step 18, the gaseous carbon dioxide separated in the second recovery step 17 is pressurized into supercritical or liquid carbon dioxide. The pressure condition in this step is 4.5-25M
Pa. The obtained supercritical or liquid carbon dioxide is recycled as a washing solvent in the pretreatment step 11.
A part of the supercritical or liquid carbon dioxide is sent to the second recovery step 17 and used as a washing solvent for backwashing. Since the second recovery step 17 is a step of separating fine particles having a small particle diameter, the filter is clogged. By performing back washing, clogging of the filter is eliminated. Second
Since the pressure of carbon dioxide in the recovery step is lower than the pressure in the pressurization step, backwashing is possible.

Next, the decontamination apparatus of the present invention will be described with reference to FIG. The radioactive substance decontamination device 20 has a cleaning device 21 that is sealed and can withstand a predetermined temperature and pressure.
One of the cleaning devices 21 is provided with a supply port 21a and the other is provided with a discharge port 21b. The outlet 21b is connected to the pipe 22
Is connected to the supply port 23a on the side of the solid-liquid separator 23. A valve 22 a is provided in the middle of the pipe 22. At the bottom of the solid-gas separator 23, a recovery port 23 for the aggregate of radioactive material is provided.
b, and a discharge port 23c is provided at the top. The discharge port 23c is connected to a supply port 26a on the side of the solid-gas separator 26 via a pipe 24. A venturi 27 is provided in the middle of the pipe 24. At the bottom of the solid-gas separator 26, there is provided a recovery port 26b for radioactive particles, and at the top, a backwash supply port 26c.
However, a discharge port 26d is provided on each side. The discharge port 26d is connected to a compressor 29 via a pipe 28. A buffer tank 31 is provided in the middle of the pipe 28. The compressor 29 is connected to the cleaning device 21 via a pipe 32.
Is connected to the supply port 21a. Three-way valves 32a and 32b are provided in the middle of the pipe 32, respectively. Three-way valve 32a
Is the backwash feed port 2 at the top of the solid-gas separator 26 via line 33
6c, and the three-way valve 32b is connected to the middle of the pipe 24 via the pipe 34. A pressure adjusting tank 36 and a valve 37 are provided in the middle of the pipe 34.

In the apparatus configured as described above, first, the contaminated substance supplied with the powdered radioactive substance supplied into the cleaning apparatus 21 is brought into contact with supercritical or liquid carbon dioxide. Next, the pressure in the cleaning device 21 is reduced by opening the valve 22a. Due to this pressure drop, carbon dioxide is instantaneously vaporized, and the carbon dioxide expands abruptly to separate radioactive substances from radioactive waste which is a contaminated substance. The gaseous carbon dioxide is returned to the liquid carbon dioxide by closing the valve 22a, and the inside of the cleaning device is flushed with the liquid carbon dioxide. The flushed liquid containing carbon dioxide in the liquid state and the radioactive substance is sent from the washing device 21 to the solid-liquid separator 23 via the pipe 22. Next, in the fluid sent to the solid-liquid separator 23, an aggregate of radioactive substances having a particle size of 100 μm to 30 mm is separated. The separated radioactive material aggregates are separated into a solid-liquid separator 2
3 Collected from the collecting port 23b at the bottom. The fluid is discharged from the top outlet 23c and sent to the venturi 27.
In the venturi 27, the pressure is reduced and the carbon dioxide contained in the fluid is turned into a gaseous state to expand the fluid and increase the flow velocity of the fluid. The expanded fluid is sent to a solid-gas separator, where the fluid is separated into fine particles of radioactive material having a particle size of 0.1 to 500 μm and gaseous carbon dioxide. The fine particles of the radioactive substance are recovered from the recovery port 26b at the bottom of the solid-gas separator, and the gaseous carbon dioxide is sent to the buffer tank 31 from the discharge port 26d at the side.

Next, the gaseous carbon dioxide stored in the buffer tank 31 is sent to the compressor 29, and the carbon dioxide is pressurized to 4.5 to 10 MPa by the compressor 29 and converted into supercritical or liquid carbon dioxide. Become. The pressurized supercritical or liquid carbon dioxide is sent to the supply port 21a of the cleaning device 21 again and recycled. A part of the supercritical or liquid carbon dioxide is supplied to the three-way valve 32a.
To switch the flow path and supply the gas through the backflow supply port 26c at the top of the solid-gas separator 26 via the pipe line 33 to backwash the solid-gas separator. Further, by switching the flow path by the three-way valve 32b, the pressure of the fluid depressurized by the venturi 27 is adjusted by the pressure adjusting tank 36 and the valve 37. In the embodiment of the present invention, the venturi 27 is used to reduce the pressure of the fluid. However, the pressure may be reduced by using an orifice, a choke, or the like. Further, a supply port 21c is provided on one side of the cleaning device 21,
Liquid carbon dioxide supply means 39 may be connected to the supply port 21c via a pipe 38, and a valve 41 may be provided in the middle of the pipe 38. Thus, the valve 41 can be opened to supply the liquid carbon dioxide from the liquid carbon dioxide supply means 39 to the cleaning device 21 to flush the inside of the cleaning device.

[0020]

Next, embodiments of the present invention will be described. <Example 1> First, a contaminated substance to which 100 mg of uranium oxide had been adhered was prepared as a simulated substance of the contaminated substance to which a powdered radioactive substance had adhered. First, this contaminated material was supplied into the cleaning device of the decontamination device shown in FIG. 2 and was brought into contact with carbon dioxide at a temperature of 20 ° C. and a pressure of 5.7 MPa. Next, the pressure in the cleaning device was reduced to 0.2 MPa to separate the attached uranium oxide from contaminants. Next, a liquid containing carbon dioxide and uranium oxide in a liquid state was sent to the solid-liquid separator 23 to separate the uranium oxide aggregates. next,
The fluid was depressurized by a venturi 27 to convert carbon dioxide contained in the fluid into a gaseous state and sent to a solid-gas separator to separate fine particles of uranium oxide. Finally, uranium oxides separated by the solid-liquid separator and the solid-gas separator were respectively recovered.

Example 2 The same decontamination apparatus as in Example 1 was used except that a contaminant to which 50 mg of cobalt oxide had adhered was used as a simulated substance. The oxide was recovered. <Example 3> The same decontamination apparatus as in Example 1 was used except that a contaminant to which 75 mg of ruthenium oxide had adhered was used as a simulated substance. Collected. <Example 4> The same decontamination apparatus as in Example 1 was used except that a contaminant to which 40 mg of strontium oxide had adhered was used as a simulated substance, and strontium oxide was used under the same conditions as in Example 1. Collected.

Comparative Example 1 The same simulated substance as in Example 1 was prepared. First, this simulated substance was supplied into the cleaning apparatus of the decontamination apparatus shown in FIG. 3 and was brought into contact with carbon dioxide at a temperature of 20 ° C. and a pressure of 10 MPa. Next, the pressure in the cleaning device is set to 0.2.
The uranium oxide adhering to the reduced MPa was separated from the simulated substance. Next, a fluid containing carbon dioxide and uranium oxide in a liquid state was sent to a filter to separate and collect uranium oxide. <Comparative Evaluation 1> Table 1 shows removal rates and residual rates of elements from contaminated substances in Examples 1 to 4 and Comparative Example 1. In addition, the amount of element attachment in Table 1 shows the weight of the radioactive substance in an oxide form.

[0023]

[Table 1]

As is clear from Table 1, in Comparative Example 1, it is considered that the residual ratio of the elements was high and remained in the cleaning device. In contrast, in Examples 1 to 4, the recovery rates were high. Of the removed uranium oxide,
About 95% was recovered from the solid-liquid separator, and the remaining about 5% was recovered from the solid-gas separator. The particle size of the uranium oxide recovered from the solid-liquid separator is approximately 200 μm to 10 mm, and the particle size of the uranium oxide recovered from the solid-gas separator is approximately 1 μm to 3 μm.
It was 00 μm.

[0025]

As described above, according to the present invention, first, the contaminated substance to which the powdered radioactive substance has adhered is brought into contact with carbon dioxide in supercritical or liquid state in the pretreatment step, The radioactive substance is separated from the contaminant by decompressing the carbon dioxide in the critical or liquid state to convert the carbon dioxide in the supercritical or liquid state into a gaseous state. Next, the radioactive substance separated in the washing step is flushed with liquid carbon dioxide to wash out the remaining radioactive substance, and the fluid containing the radioactive substance washed in the first recovery step and the liquid carbon dioxide is subjected to particle size reduction. Separates into a radioactive substance aggregate having a size of 100 μm to 30 mm and a fluid, and collects the radioactive substance aggregate. Next, the fluid separated in the depressurizing step is decompressed to convert the liquid carbon dioxide contained in the fluid into a gaseous state to increase the volume, thereby giving a flow rate to the fluid.
In the recovery step, the radioactive substance fine particles having a particle size of 0.1 to 500 μm are separated into gaseous carbon dioxide and the radioactive substance fine particles are recovered. Finally, the gaseous carbon dioxide separated in the pressurizing step is pressurized to be supercritical or liquid carbon dioxide. The carbon dioxide pressurized in the pressurization step is sent to the second recovery step for backwashing, thereby eliminating clogging of the filter, drastically reducing filter replacement, and recovering radioactive substances from the replaced filter. Work can be omitted. Radioactive substances attached to contaminated materials can be collected simply and efficiently.

[Brief description of the drawings]

FIG. 1 is a diagram showing the order of steps in a method for decontaminating radioactive substances of the present invention.

FIG. 2 is a schematic diagram of a radioactive substance decontamination apparatus of the present embodiment.

FIG. 3 is a schematic diagram of a conventional radioactive substance decontamination apparatus.

[Explanation of symbols]

 Reference Signs List 11 Pretreatment step 12 Separation step 13 Cleaning step 14 First recovery step 16 Depressurization step 17 Second recovery step 18 Pressurization step 21 Cleaning device 23 Solid-liquid separator 26 Solid-gas separator 27 Venturi 29 Compressor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsunori Shinohara 1-3-3 Koishikawa, Bunkyo-ku, Tokyo Mitsubishi Materials Corporation System Business Center (72) Inventor Osamu Kanehira 1-3-25 Koishikawa, Bunkyo-ku, Tokyo No. Mitsubishi Materials Corporation System Business Center

Claims (5)

[Claims] 1. A pretreatment step (11) in which a contaminated substance to which a powdery radioactive substance is attached is brought into contact with carbon dioxide in a supercritical or liquid state; A separation step (12) of separating the radioactive substance from the contaminated substance by converting carbon dioxide in a supercritical or liquid state into a gaseous state, wherein the radioactive substance is separated in the separation step (12). Washing step of supplying liquid-state carbon dioxide to the washed radioactive material to wash the radioactive material
(13) a first method of separating the fluid containing the radioactive substance and the liquid carbon dioxide washed in the cleaning step (13) into an aggregate of the radioactive substance and a fluid to collect the aggregate of the radioactive substance; Collection process
(14), and decompressing the fluid separated in the first recovery step (14) to increase the volume of carbon dioxide in a liquid state contained in the fluid in a gaseous state to increase the volume, thereby providing a flow rate to the fluid. Step (16), a second recovery step (17) of separating the fluid into fine particles of radioactive material and carbon dioxide in a gaseous state to recover fine particles of radioactive material, and separation in the second recovery step (17). Pressurizing the gaseous carbon dioxide into supercritical or liquid carbon dioxide (18). 2. The method according to claim 1, wherein the first recovery step (14) is performed by solid-liquid separation or sedimentation. 3. The method according to claim 1, wherein the second recovery step (17) is performed by solid-gas separation. 4. The supercritical or liquid carbon dioxide obtained in the pressurizing step (18) is supplied to the pretreatment step (11), and a part of the supercritical or liquid carbon dioxide is recovered in the second step. The method for decontaminating a radioactive substance according to any one of claims 1 to 3, wherein the step (17) is carried out by backwashing. 5. A cleaning device (21) for cleaning a contaminated substance to which a powdered radioactive substance is attached with carbon dioxide in a supercritical or liquid state to separate and remove the radioactive substance from the contaminated substance. A solid-liquid separator (23) for separating a fluid containing the radioactive substance and carbon dioxide in a liquid state removed by the washing device (21) into an aggregate of the radioactive substance and a fluid, and the solid-liquid separator (23) A venturi (27) that gives a flow rate to the fluid by decompressing the fluid separated and reducing the volume of the carbon dioxide in a liquid state contained in the fluid to a gaseous state and increasing the volume thereof; Decontamination of radioactive materials comprising a solid-gas separator (26) for separating carbon dioxide in a gaseous state, and a compressor (29) for pressurizing the gaseous carbon dioxide separated by the solid-gas separator (26) apparatus.