JPH034198A - Contamination removing method for radioactive contaminated metal waste - Google Patents

Abstract

PURPOSE:To remove contamination without increasing secondary waste by peeling and removing part of the coating of the radioactive contaminated metal waste and forming an electric feeding surface, performing electrolytic contamination removal, and peeling and removing the remaining coating of the metallic waste after the electrolytic contamination. CONSTITUTION:Piping 10 whose contamination is to be removed is cut to specific length and fitted rotatably on a blast contamination removing device 16. A nozzle 14 jets a plastic blast material 18 toward the external surface 10b of the piping 10 together with compressed air. Consequently, part of the coating on the external surface 10b is peeled and removed away to form the electric feeding surface 10c where the metal base material is exposed. The piping 10 is dipped in an electrolyte 32, and a DC voltage is applied from a power source 34 through an electric feeding jig 38 to remove the contaminated oxide film of the internal surface 10a. Then the piping 10 is fitted rotatably on the blast contamination removal device 44. The blast injection nozzle 42 jets the blast material 18 and compressed air toward the external surface 10b. Consequently, the coating of the external surface 10b is all peeled and removed to obtain clean metallic waste 11.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for decontaminating radioactively contaminated metal waste, and in particular to a method for decontaminating radioactively contaminated metal waste in nuclear power plants. Regarding decontamination methods.

[Conventional technology]

Conventionally, metal waste contaminated with radioactivity is cut into pieces, compressed into drums, and stored in a waste building. However, as the number of drums increases every year, securing storage space has become a problem. Under these circumstances, it is desired to reduce the volume of metal waste, and various waste treatment techniques have been developed.

Currently, the waste treatment techniques include a high-pressure compression method, a melting method, and an electric discharge dyeing method, among which the electric discharge dyeing method is attracting particular attention. The electrolytic decontamination method involves immersing radioactively contaminated metal waste (object to be decontaminated) in an electrolytic solution and passing an electric current through the electrolyte to quickly remove contaminated oxide skin M (crud) from the object to be decontaminated. , and is a method for completely dissolving and removing. The electrolytic solution used includes mineral acids such as phosphoric acid and sulfuric acid, and neutral salts such as sodium nitrate and sodium sulfate.

According to the electrolytic decontamination method, the radioactivity of the object to be decontaminated can be reduced to the level of radioactivity of general waste, so it is expected to significantly reduce the volume of decontamination.

By the way, when an object to be decontaminated whose surface has been painted is electrolytically destained, the radioactivity in the electrolyte penetrates into the uneven parts of the coating, or if the uneven areas reach the metal base material of the object to be decontaminated, the paint is removed. Because it penetrates into the lower surface, trace amounts of radioactivity often remain on the painted surface. Further, if radioactive substances or the like are fixed between the undercoat surface and the topcoat surface of the paint, the radioactive substances cannot be removed by the electrostatic release dyeing method. Therefore, when decontaminating a painted object to be decontaminated, a worker scrapes off the paint with a file, grinder, etc. to expose the metal base material.

For example, when decontaminating a cylindrical pipe whose inner surface is contaminated with radioactive substances and whose surface is painted, the paint is first scraped off with a file, grinder, etc. to expose the metal base material.

Next, the pipe with the exposed metal base material is immersed in an electrolytic solution. An electrode is installed on the central axis of the pipe immersed in the electrolytic solution, and a conductive electrode is attached to the exposed surface of the metal base material.

In this state, a current is applied from the electrode to dissolve and remove the cladding on the inner surface of the pipe. This decontaminates the piping.

[Problem to be solved by the invention]

However, if all the paint is removed, the exposed surface of the metal base material of the object to be decontaminated, such as piping, has a lower electrical resistance than the inner cladding, so there is a drawback that the efficiency of using electrolytic current decreases.

Furthermore, if all the coating is scraped off, the uncontaminated metal base material will be melted, resulting in an increase in the amount of used electrolyte, ie, the amount of secondary waste.

Furthermore, if the object to be decontaminated is contaminated with high levels of radioactivity, there is a problem that workers will be exposed to radioactivity when scraping off the paint.

The present invention has been developed in view of these circumstances, and is capable of completely decontaminating objects to be decontaminated without increasing secondary waste, as well as scraping off the paint on objects to be decontaminated without being exposed to radioactivity. The purpose of this study is to provide a method for decontaminating radioactively contaminated metal waste.

[Means to solve problems]

In order to achieve the above object, the present invention provides a method for decontaminating radioactively contaminated metal waste whose surface is coated, in which a part of the coating of the radioactively contaminated metal waste is peeled off and a current-carrying surface is removed. , and the metal waste on which the conductive surface has been formed is immersed in an electrolytic solution to de-dye the metal waste, and the remaining coating of the de-dyed metal waste is peeled off and the radioactive substances are removed. It is characterized by

[Effect]

According to the present invention, first, the electrical surface (IO) of the object to be decontaminated (10) is
Only the coating in c) is peeled off and removed by blasting. Next, the object to be decontaminated (lO) on which the current-carrying surface (IOc) has been formed is immersed in the electrolytic solution (32) to perform electrolytic dedying. Next, the remaining coating on the object to be decontaminated (10) that has been electro-destained is peeled off and removed. Thereby, the object to be decontaminated (10) can be completely decontaminated without increasing secondary waste.

〔Example〕

Preferred embodiments of the method for decontaminating radioactively contaminated metal waste according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a system diagram showing an embodiment of the method for decontaminating radioactively contaminated metal waste according to the present invention.

In FIG. 1, the inner surface 10a of the pipe 10 is contaminated with radioactivity and the outer surface 10b is painted.

The piping 10 is cut to a predetermined length, and the cabinet 1
2. It is rotatably installed in a blast decontamination device 16 that includes a blast injection nozzle 14 and the like.

The blast injection nozzle 14 is communicated with a hopper 20 in which a combustible plastic blasting material 18 is stored.

Further, the blast injection nozzle 14 sends the blast material 18 sucked by the pressurized air from the air source 22 to the outer surface 10 b of the rotating pipe 10 .
Spray toward. As a result, the pipe 10 has an outer surface 1
Since a part of the coating 0b is peeled off and removed by the collision of the blasting material 18, it is possible to form the current-carrying surface 10C in which the metal base material is exposed.

Meanwhile, the cabinet 12 is formed in a hopper shape, and the bottom thereof is communicated with the recovery device 24. Therefore, the piping ip
The waste blasting material, peeled paint powder, and radioactive substances contained therein are collected into the collection device 24. The waste blasting material, paint powder, and radioactive materials collected by the collection device 24 are passed through a filter 26 by pressurized air from the air source and separated from the air, and then transported to an incineration bag [28] and incinerated.

On the other hand, the pipe 10 on which the current-carrying surface 10c is formed is connected to the electrolytic cell 3
It is immersed in an electrolytic solution 32 stored in a tank. An electrode 3 connected to a current power supply 34 is attached to the center axis of the immersed pipe 1O.
6 is arranged, and a current-carrying jig 38 connected to a DC power source 34 is attached to the current-carrying surface 10c of the pipe IO. Therefore, the DC voltage of the DC voltage #34 is applied to the electrode 36, energized to the pipe IO via the electrolytic solution 32, and flows to the energizing jig 38. As a result, the pipe 10 is electrolytically destained, so that the contaminated oxide film (kraft) on the inner surface 10a can be dissolved and removed.

After drying, the de-dyed piping lO is placed in cabinet 4.
0, and is rotatably mounted within a blast decontamination device 44 consisting of a blast injection nozzle 42 and the like. The blast injection nozzle 42 communicates with the hopper 20 described above. Therefore,
The blast injection nozzle 42 blows the blast material 18 inside the hopper 20 sucked by pressurized air from the air source 22.
is applied to the outer surface 1 of the rotating pipe 10 along with pressurized air.
Spray toward painting 0b. With this, the pipe 10
Since the coating on the outer surface 10b is completely peeled off by the collision with the blasting material 18, the radioactive substances fixed in the coating are removed and the metal waste 11 becomes clean.

The cabinet 40 is formed into a hopper shape similar to the cabinet 12 described above, and the bottom thereof communicates with the collection bag [24] described above. Therefore, the waste plastic material that collided with the coating on the surface 10b of the pipe 10, the peeled paint powder, and the radioactive substances contained therein are collected in the recovery device 24, passed through the filter 26, and then sent to the incineration device 28. be incinerated.

Next, a specific embodiment of the method for decontaminating radioactively contaminated metal waste according to the present invention will be described with reference to FIGS. 1, 2, and 3.

FIG. 2 shows a first example showing the progress of a decontamination test.

The test sample piping lO has an initial counting rate of 2.0xlO
'cps is used, and the electrolytic solution 32 is a 20% sodium sulfate solution with a current density of 0.3^/cj and a liquid temperature of 30°C.

First, a part of the pipe 10 to be painted is blasted using the nozzle 14.
A melamine resin-based plastic blast material 18 is used to peel and remove the melamine resin-based plastic blasting material 18 to form a current-carrying surface 10c. Next, the piping IO having the current-carrying surface tOC formed thereon is immersed in the electrolytic solution 32 stored in the electrolytic bath 30, and de-dyed for 30 minutes to dissolve and remove the contaminated oxide film (cladding) on the inner surface 10a. Here, the counting rate of the pipe lO after 30 minutes is the second
3. As shown in the figure. Although the OX has decreased to 10"cp-, it has not reached the count rate of 7Qcpm, which is comparable to general metal waste (B, G). Next, the pipe 10 that has been electrolytically destained is washed with water. By washing with water, the pipe The counting rate of lO is 3.
Although the amount decreased slightly from OX 10'cpa+, it has not yet reached the above counting rate. Next, after drying the pipe 10 that has been washed with water, the blasting material 1 is discharged from the blasting nozzle 42.
8 to peel off the remaining coating on the pipe 10 and remove the radioactive substance fixed in the coating. by this,
It was found that the count rate of the pipe 10 reached 70 cpm, which is an 81G count rate.

FIG. 3 shows the Kanji Example showing the progress of the decontamination test.

The test sample piping 10 has an initial counting rate of 6.7X 1
0' is used, and the electrolytic solution 32 has a current density of 0.
An 80% phosphoric acid solution with a temperature of 1^/ci and a liquid temperature of 60°C is used.

First, a part of the coating on the pipe IO is peeled off and removed using the flammable melamine-based plastic blasting material 18, as described above, to form the current-carrying surface IOC.

Next, the pipe 10 with the current-carrying surface 10C formed thereon is immersed in the electrolytic solution 32, and de-dyed for 60 minutes to dissolve and remove the cladding on the inner surface 10a. Here, the counting rate of the pipe 10 after 60 minutes has passed is 4.6 as shown in FIG. OxlQ
'cps but BSG count rate 7Qcpm
has not been reached. Next, the pipe IO that has been subjected to electrolytic dedying is washed with water. By washing with water, the count rate of the pipe 10 is 4.
Although the amount of Ox decreased slightly from 10"cpm, it still did not reach the above counting rate.

Next, after drying the pipe 10 which has been washed with water, the blasting material 18 is injected from the blasting material injection nozzle 42 to peel off the remaining coating on the piping 10 and remove the radioactive substance fixed in the coating. As a result, the counting rate of piping IO is B, G
It was found that the counting rate reached 7Qcpm.

In addition, when used waste blasting material is incinerated in the incinerator 128 and the waste gas is analyzed, it is found that no SOx, HCl, etc. are generated, and the ash content is only 2% of the original blasting material. did.

This also makes it possible to suppress the generation of secondary radioactive substances due to the blasting method.

〔Effect of the invention〕

As explained above, according to the method for decontaminating radioactively contaminated metal waste according to the present invention, a part of the coating is peeled off and removed to form an energized surface, and the object to be decontaminated on which the energized surface is formed is de-energized. dyed,
Since the remaining coating on the object to be decontaminated after electrolytic decontamination has been peeled off and removed, the object to be decontaminated can be completely decontaminated without increasing secondary waste.

Furthermore, since the coating was removed by blasting, the coating can be removed without being exposed to radioactivity.

[Brief explanation of drawings]

Figure 1 is a system diagram showing an embodiment of the method for decontaminating radioactively contaminated metal waste according to the present invention, and Figure 2 is an explanatory diagram showing the progress of decontamination when sodium sulfate is used as the electrolyte. ,′! Figure J3 is an explanatory diagram showing the progress of electrolytic de-dying when phosphoric acid is used as the electrolyte. lO... Piping, 14... Blast injection nozzle,
18...Flammable plastic blasting material, 32...
・Electrolyte solution. Figure 2

Claims (2)

[Claims] (1) In a method for decontaminating radioactively contaminated metal waste whose surface has been painted, a part of the coating of the radioactively contaminated metal waste is peeled off to form a current-carrying surface, and the current-carrying surface is formed. Radioactively contaminated metal waste, characterized in that the metal waste is immersed in an electrolytic solution to be electrolytically destained, and the remaining coating of the electrolytically dedyed metal waste is peeled off to remove radioactive substances. How to decontaminate objects. (2) The method for decontaminating radioactively contaminated metal waste according to claim 1, wherein the coating on the radioactively contaminated metal waste is peeled off and removed by a blasting method.