JPH077104B2 - Decontamination method for radioactive contaminants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention applies radioactive vibration polluted in a nuclear facility, for example, to ultrasonic vibration in the presence of a specific chemical solution. The present invention relates to a decontamination method for radioactive contaminants to be decontaminated.

(Prior Art) It is necessary to decontaminate all radioactive pollutants contaminated with radioactivity in nuclear facilities, such as tools and protective equipment used in nuclear facilities. Conventionally, as the decontamination method, an electro-deletion dyeing method or a blasting method has been widely used. Further, recently, a decontamination apparatus that uses water or an organic solvent as a decontamination solution and performs ultrasonic cleaning as necessary has been disclosed in JP-A-59-83097.

(Problems to be Solved by the Invention) However, the above-mentioned electro-deletion dyeing method has a drawback that it cannot be used for decontaminating non-conductor materials such as rubber and plastic. Further, the blast method can be used for decontaminating non-conductive materials, but it is difficult to decontaminate deep inside surfaces such as pipes, and there is the disadvantage that small objects such as tools must be decontaminated one by one. there were. Furthermore, the ultrasonic decontamination device using the organic solvent described above was effective for decontamination when contaminants were fats, paints, loose contamination, etc., but for other contaminations, decontamination of radioactivity was performed. There was a drawback that could not be done completely.

The object of the present invention is to eliminate the above-mentioned inconvenience, and to decontaminate radioactive pollutants to a level at which they can be handled as general waste regardless of their materials, and to almost completely decontaminate even complicated shapes. It is intended to provide a decontamination method for radioactive contamination that can be performed.

(Means for Solving Problems) In the method for decontaminating radioactive contaminants of the present invention, radioactive contaminants contaminated with radioactive substances are converted into sulfuric acid: 5 to 15%, oxalic acid: 1 to 5%.
At least one of the above and phosphoric acid: 5-30% is immersed in a decontamination solution containing a chemical solution, and ultrasonic waves are placed in the decontamination tank under heating at 80 ° C or less. The decontamination is performed by directly applying ultrasonic vibration with a container.

(Operation) In the present invention, ultrasonic cleaning is performed in a specific chemical containing at least one chemical selected from phosphoric acid, sulfuric acid and oxalic acid to almost completely decontaminate radioactive contaminants. is doing. Further, even if the radioactive contaminant has a complicated shape, it can be almost completely decontaminated by ultrasonic cleaning in a specific chemical solution.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of an apparatus for carrying out the decontamination method of the present invention. In the embodiment shown in FIG. 1, in the decontamination tank 1, phosphoric acid 5-30% (preferably 10-15%), sulfuric acid 5-25% (preferably 10-20%), oxalic acid 1-5 %
It is filled with the decontamination liquid 2 containing at least one or more chemical liquids (preferably 2 to 3%) as a main component and an additive such as a chelating agent. An ultrasonic wave oscillator 3 is provided at the bottom of the decontamination tank 1, and ultrasonic wave oscillators 4, 5, 6 and 7 are provided on the four side walls of the decontamination tank 1, respectively, in FIG. To arrange. Further, a movable ultrasonic oscillator 8 is provided on the upper surface of the decontamination tank 1, the decontamination basket 9 is set in the decontamination tank 1, and then the oscillator 8 is installed at the position shown in FIG. The decontamination tank 1 is provided with a heater 15 for adjusting the temperature of the decontamination solution 2, and a filter 16 and a decontamination solution circulation pump 17 are provided for removing impurities in the decontamination solution 2 inside for decontamination. Liquid 2 is being purified.

The decontamination basket 9 made of, for example, Hastelloy, which is a corrosion-resistant material, containing the substance 13 to be decontaminated is controlled to move up and down by a lifting motor 10, and after the decontamination process is completed, the decontamination basket 9 It is configured so that it can be set in the rinse liquid 12. As the rinse liquid 12 in the rinse tank 11, for example, water or the like that can wash the decontamination liquid 2 attached to the decontamination object 13 after the decontamination process is used, and the ultrasonic oscillator 14 provided at the bottom of the rinse tank 11 is used. And ultrasonic cleaning.

Hereinafter, the decontamination method of the present invention will be described. First, a substance to be decontaminated 13 which is a radioactive pollutant is contained in a decontamination basket 9 and at least one of phosphoric acid, sulfuric acid and oxalic acid adjusted to the above-mentioned concentration is used. It is dipped in the decontamination solution 2 containing the chemical solution by driving the ascending motor 10. After heating the temperature of the decontamination liquid 2 to 80 ° C. or lower, preferably 40 to 60 ° C. by the heater 15, the ultrasonic wave oscillator 3 to 8 is used.
An ultrasonic wave is applied to the decontamination liquid 2 at 10 to 30 KHz, preferably about 20 KHz to perform ultrasonic cleaning. The decontamination time at this time is about 2 to 30 minutes. Further, in order to enhance the decontamination efficiency, air may be blown from below the decontamination tank 1, and the decontamination object 13 may be swung in the decontamination liquid 2. The decontamination object 13 that has been decontaminated as described above is rinsed with the decontamination basket 9 by driving the lifting motor 10.
The decontamination liquid 2 is washed by being immersed in the rinse liquid 12 in 11 and performing ultrasonic cleaning. The decontaminated material 13 after decontamination is reused as a tool or discarded as general waste.

The reason for limiting the temperature of the decontamination solution to 80 ° C. or lower in the present invention is that decontamination treatment cannot be effectively performed at 80 ° C. or higher.

Example 1 A 100φ pipe contaminated with radioactivity was decontaminated by variously changing the composition of the decontamination solution and the temperature of the decontamination solution as shown in Table 1 described later. The frequency of the ultrasonic transducer applied during decontamination is 20
The KHz and power density were 0.8 to 1.5 W / cm ³ . In addition, the decontamination basket during decontamination is 3-5 cm
The distance (for one wavelength or more) was moved up and down at a speed of 2-3 times / minute. The number and position of ultrasonic transducers were the same as those in the examples shown in FIGS. 1 and 2. After the decontamination process is completed, wash the decontaminated material in the rinse tank and obtain the radioactivity concentration with the monitoring device as the measured value (count / min) of the GM tube. Compare the measured value before decontamination with the decontamination performance. Decontamination index (D
F) was asked as. The results are shown in Table 1.

The present invention is not limited to the above-described embodiments, but various modifications and changes can be made. For example, it goes without saying that the number and arrangement of the ultrasonic oscillators described above are merely examples, and other configurations can be adopted.

(Effects of the Invention) As is clear from the above description, according to the method for decontaminating a radioactive contaminant of the present invention, the radioactive contaminant is made of a material by ultrasonic decontamination in a specific chemical solution. Regardless of the type of waste, it can be decontaminated in a short time to a level at which it can be handled as general waste, and radioactive contaminants of complicated shapes can be decontaminated relatively easily. Moreover, decontamination can be performed without damaging the radioactive contaminants.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an apparatus for carrying out the decontamination method of the present invention, and FIG. 2 is a front view of a decontamination tank of the apparatus shown in FIG. 1 ... Decontamination tank, 2 ... Decontamination solution 3,4,5,6,7,8,14 ... Ultrasonic oscillator 9 ... Decontamination basket 10 ... Elevating motor, 11 ... Rinse Tank 12 …… rinse liquid, 13 …… decontamination object 15 …… heater

Claims (3)

[Claims] 1. A radioactive contaminant contaminated with radioactivity was mixed with at least one of sulfuric acid: 5 to 15% and oxalic acid: 1 to 5%, and phosphoric acid: 5 to 30%. Radiation characterized by being immersed in a decontamination solution containing a chemical solution, and being decontaminated by directly applying ultrasonic vibrations with an ultrasonic generator placed in the decontamination tank under heating at 80 ° C or less. Decontamination method for active pollutants. 2. The method for decontaminating radioactive contaminants according to claim 1, wherein the ultrasonic vibration has a frequency of 10 to 30 KHz. 3. The method for decontaminating radioactive contaminants according to claim 1, wherein the chemical solution is heated to 40 to 60 ° C.