JPH02206800A - Decontaminating method for column vessel or the like - Google Patents

Abstract

PURPOSE:To improve the decontamination effect by filling a column and a vessel, etc., contaminated by a radioactive material with a decontamination use solution, giving an ultrasonic wave thereto and stirring the solution, and also, radiating an ultrasonic wave of a surface direct type ultrasonic vibrator to the contaminated surface. CONSTITUTION:The inside of a storage vessel 10 contaminated by a radioactive contaminant 12 is filled with a decontamination use solution 14. Subsequently, by supplying a signal generated from an ultrasonic wave generating device 30 to an ultrasonic vibrator 28 immersed therein, the decontamination use solution 14 is stirred. As a result, physical and chemical reactions are promoted, and the radioactive contaminant which is adhering is solved and eliminated. In this state, furthermore, a surface direct type ultrasonic vibrator 34 having directivity is used jointly. That is, an ultrasonic wave of the surface direct type ultrasonic vibrator 34 is radiated toward the surface part which is contaminated especially remarkably in the storage vessel 10, and the radioactive contaminant is peeled off and eliminated by a surface breakdown. In this case, the decontamination effect is high, and the generation quantity of a radioactive waste liquid used for decontamination such as an acid and alkali, etc. is decreased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for decontaminating towers and tanks containing radioactive solutions in various nuclear facilities, and more specifically,
This invention relates to a method of removing radioactive contaminants adhering to the inner wall surfaces of towers and tanks using ultrasonic waves.

[Prior Art] Nuclear facilities such as spent nuclear fuel reprocessing plants and nuclear fuel manufacturing plants have towers and tanks that contain radioactive solutions. Additionally, nuclear power plants and other facilities have fuel storage tanks. When these towers and tanks containing radioactive solutions are remodeled or removed, it is necessary to remove radioactive contaminants to reduce external and internal exposure.

Since the radioactive contaminants contained in the radioactive solution adhere to the inner surfaces of towers and tanks, conventional boat fishing methods involve dissolving and removing the radioactive contaminants using acid/alkaline solutions. For this purpose, acid/alkaline solutions are placed in towers and tanks, heated as necessary, and replaced with pumps. The radioactive contaminants that have adhered in this way are dissolved with an acid/alkaline solution9. Usually, the #i warm solution is first dissolved, and then the alkaline solution is used. By repeating this operation as many times as necessary, radioactive contaminants are removed and radiation exposure is reduced.

[Problem to be solved by invention E] As mentioned above, in the conventional technology, dissolution with an acid solution and dissolution with an alkaline solution are repeated as many times as necessary, resulting in the generation of a large amount of radioactive waste liquid, which requires a lot of cost to process and dispose of. However, there are disadvantages such as the fact that it takes a lot of time and that sufficient decontamination cannot be achieved despite the time it takes.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, generate less radioactive waste liquid, shorten decontamination work time, and improve the decontamination effect and reduce external and internal radiation exposure. The purpose of the present invention is to provide a method for decontaminating such towers and tanks.

[Means for Solving the Problems] The present invention, which can solve the above-mentioned technical problems, fills towers and tanks contaminated with radioactive substances with a decontamination solution, and agitates it by applying ultrasonic waves. In both cases, a method for decontaminating towers and tanks is to emit ultrasonic waves from a surface direct impact type (horn type) ultrasonic transducer toward the contaminated surface of the towers and tanks, and to peel off and remove the contaminated materials using surface destruction. It is. In the present invention, the term "towers and tanks" is used in a broad sense to include not only towers and tanks themselves, but also piping and other structures related thereto.

Here, a surface direct impact type ultrasonic transducer is movably supported, and it moves to target areas with significant surface contamination while removing contaminants.
It is desirable to remove it separately.

In addition, in order to carry out the above method, decontamination work can be carried out extremely easily if an opening or installation space is prepared in advance in which the ultrasonic transducer can be attached to the towers and tanks to be decontaminated. This is preferable.

[Effect] By applying ultrasonic vibration to the decontamination solution, the solution is stirred and physical and chemical reactions are promoted, thereby dissolving and removing contaminants adhering to the surfaces of towers and tanks. can. At the same time, by emitting directional ultrasonic waves from the surface direct impact type ultrasonic transducer toward the contaminated surface, surface destruction occurs and the radioactive contaminants are peeled off.

Therefore, by movably supporting a surface direct-impingement type ultrasonic transducer and emitting ultrasonic waves toward areas with significant surface contamination, #JR can be easily performed even on firmly attached radioactive contaminants. This allows decontamination work to be carried out more efficiently and in a shorter time.

[Example] FIG. 1 is a schematic diagram showing an example of an apparatus configuration for carrying out the method of the present invention. The storage tank 1O is a container used to contain a radioactive solution in a nuclear facility, etc., and has radioactive contaminants 12 attached to its inner surface.The present invention is a method for decontaminating such towers and tanks.

The inside of the storage tank IO is filled with a decontamination solution 14.

These decontamination solutions 14 are acid, alkaline solutions, water, or the like, and are supplied from an auxiliary decontamination tank 16. One end of a discharge pipe 18 is open at the bottom of the storage tank 10, and the discharge pipe 18 is connected to a pump 20 that rises outward from the upper part of the storage tank 10 and pumps out the decontamination solution. pump 20
The outlet side is branched into three routes, one of which leads to the waste liquid treatment system via a valve 21. The other side is connected to the filter device 2 via the valve 22.
4, and further reaches the decontamination liquid auxiliary connector 16.

These constitute a circulation loop for decontamination solutions.

Note that the necessary new decontamination solution is directly supplied to the auxiliary decontamination tank 16. An electric heater 25 is installed outside the storage tank 10.
is provided.

An ultrasonic transducer 28 is inserted through an opening 26 formed in the upper part of the storage tank 10. A signal from an ultrasonic generator 30 is supplied to the ultrasonic transducer 28 via a cable 32.

The operation of this equipment is as follows. The inside of the storage tank 10 contaminated with radioactive contaminants 12 is filled with a decontamination solution 14, and the signal from the ultrasonic generator 30 is supplied to the ultrasonic transducer 28 immersed in the decontamination solution 14. Solution 14 is stirred. This promotes physical and chemical reactions to dissolve and remove attached radioactive contaminants. However, it is difficult to efficiently remove radioactive contaminants that are firmly bound to the tank wall using only this method.

Therefore, as shown in Figure 2, a directional surface direct hit type (
A horn-type) ultrasonic vibrator 34 is also used. Emit ultrasonic waves from the surface-direct ultrasonic transducer 34 toward a particularly heavily contaminated surface portion of the storage tank 10 (near the radioactive contaminant 12),
Radioactive contaminants are peeled off and removed by surface destruction. This surface-direct type ultrasonic transducer 34 can move a submarine equipped with an ultrasonic transducer that can move freely underwater by remote control so that it can move and remove contaminants from areas with significant surface contamination. The ultrasonic transducer used here is a type with directivity coupled with a horn, and the operating frequency range is 20 to 5.
It is preferable that the frequency is 0 kHz and the usable temperature range is from room temperature to about 100°C.

The radioactive contaminants that have been peeled off and suspended or dissolved in the solution are discharged by a pump 20 via a discharge pipe 18. The clean decontamination solution is then filtered through the valve 22 by the filter device 24 and returned to the auxiliary decontamination tank 16. The shortage is supplied to the storage tank 10 from the auxiliary decontamination tank.

In addition, in order to promote the reaction in the storage tank 10 and increase the decontamination efficiency, the solution temperature can be lowered to 10% using an external heating source such as an electric heater 25.
It is preferable to carry out the work at a suitable temperature in the range up to 00°C.

[Effects of the Invention] As described above, the present invention uses ultrasonic waves to agitate the decontamination solution in tanks, and also radiates directional ultrasonic waves toward contaminated surfaces to destroy the surface. Because it is a method that strips and removes contaminated materials, it has a high decontamination effect, which reduces the amount of radioactive waste liquid used for decontamination such as acids and alkalis, and shortens decontamination work time, reducing external and internal radiation exposure. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus for implementing the method of the present invention, and FIG. 2 is an explanatory diagram showing the main parts of the apparatus for implementing the method of the present invention. lO...Storage tank, 12...Radioactive contaminants, 14...
Decontamination solution, 28... Ultrasonic transducer, 34... Surface direct impact type ultrasonic transducer. Figure 1 Patent applicant Power reactor and nuclear fuel development corporation Shigeru Rihito Miyoshi

Claims (1)

[Claims] 1. Filling towers and tanks contaminated with radioactive substances with a decontamination solution, applying ultrasonic waves to the solution and stirring it,
A decontamination method for towers and tanks, characterized by emitting ultrasonic waves from a surface-direct type ultrasonic transducer toward the contaminated surfaces of towers and tanks, and peeling off and removing radioactive contaminants using surface destruction. 2. The method for decontaminating towers and tanks according to claim 1, wherein the surface direct impact type ultrasonic transducer is movably supported and the radioactive contaminants are peeled off while moving the surface-directed ultrasonic transducer to target areas with significant surface contamination.