JPS5936240B2 - Decontamination methods for items contaminated with radioactive materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for decontaminating tools, equipment such as waste pumps, articles, etc., contaminated with radioactive substances.

Conventionally, the following methods have been used to decontaminate items contaminated with radioactive substances.

That is, first, items to be contaminated are placed in a decontamination solution and decontaminated by rubbing with a brush or the like, or wiped off with a paper towel, rag, or the like. On the other hand, decontamination waste liquid is treated with a decontamination waste liquid treatment system that includes, for example, a filter that removes undissolved solids and a distiller that evaporates and concentrates the filtrate. For example, it was mixed with cement and solidified.

On the other hand, paper towels and rags have been disposed of as solid waste.

As a result, the amount of secondary waste generated increases, which has become a problem.

Furthermore, in such conventional decontamination methods, the decontamination work takes a long time and is not very efficient, and radiation exposure during this time has also been a problem.

In addition, with this method, decontamination of simple tools is not a problem, but for decontamination of single pieces of highly radioactively contaminated equipment such as waste pumps, remote control is desirable in order to reduce radiation exposure for workers. It was extremely difficult to operate.

The present invention was made in order to eliminate such conventional drawbacks, and in decontaminating articles contaminated with radioactive substances, the articles are treated with a low boiling point organic solvent heated at a temperature about 5° C. lower than the boiling point. The above-mentioned drawbacks can be overcome by cleaning the organic solvent under ultrasonic vibration in a vacuum chamber, and after cleaning, the low-boiling organic solvent is passed through a filter to remove undissolved solids, and then distilled and reused. The aim is to provide a method for decontaminating items contaminated with radioactive materials.

The details of one embodiment shown in the drawings will be explained below. The drawing shows a system diagram of an embodiment of the invention. In the figure, reference numeral 1 indicates a decontamination bath, and a low boiling point organic solvent 2 is accommodated in the decontamination bath 1.

As this low boiling point organic solvent 2, low specific heat and low boiling point organic solvents such as various fluorocarbons and perchlorethylene are suitable. An immersion heater 3 is inserted into the decontamination bath 1 to heat the organic solvent 2 to a temperature approximately 5°C lower than the boiling point of the organic solvent. A condenser 4 is arranged to condense the vapor of 2.

Furthermore, an oscillator 6 of an ultrasonic oscillator 5 is immersed in the low boiling point organic solvent 2 of the decontamination bath 1. An organic solvent transfer pipe T is connected to the lower part of the decontamination bath 1, and is connected via a transfer pump 8 to the inlet end of a filter 9 for purifying the organic solvent. A transfer pipe 10 extending from the outlet end of the filtration filter 9 is branched, one side is opened to the decontamination bath 1 via an on-off valve 11, and the other side is opened to an on-off valve 12.
is connected to the inlet end of a distillation column 13 for purifying organic solvents. 14 is a heater for the distillation column 13.

A steam pipe 15 connected to the outlet end of the distillation column 13 is connected to an inlet end of the condenser 16, and the steam pipe 15 is connected to the inlet end of the condenser 16.
The organic solvent vapor sent from 5 is condensed here and becomes an organic solvent, which is transferred into the decontamination bath 1 through the transfer pipe IT. The method of the present invention is carried out as follows using the apparatus as described above.

First, a low-boiling organic solvent 2 is poured into a decontamination bath 1,
Immersion heater 3 is energized to lower the liquid temperature by 5°C below the boiling point of this solvent.
After raising the temperature to a moderately low temperature and further activating the condenser 4 to prevent volatilization of solvent vapor, the article to be decontaminated is placed in the decontamination bath 1, and the ultrasonic oscillator 5 is activated to hold it for a certain period of time.

In this case, the radioactive substances attached to the items to be decontaminated are quickly separated from the items to be decontaminated by the dissolving action of the heated organic solvent and the mechanical action of ultrasonic vibrations.
Dissolved or dispersed in organic solvents. Thereafter, the decontaminated articles are taken out of the decontamination bath and transferred to a drying device equipped with a solvent vapor recovery device (not shown) for drying. If necessary, a solvent recovery tank and a solvent recovery device may be attached to the solvent purification system described later, and the washed organic solvent may be temporarily stored in the solvent recovery tank and dried in the decontamination bath 1. You may also do so.

On the other hand, the organic solvent 2 after washing is sent to the filtration filter 9 by the transfer pump 8, and after solid impurities are removed, it is sent to the decontamination bath 1 again through the on-off valve 11.

In addition, when a large amount of soluble components are dissolved in the organic solvent and the decontamination effect is reduced, the organic solvent that has passed through the filtration filter 9 is sent to the distillation column 13 via the on-off valve 12 and evaporated.
After being condensed and liquefied by the condenser 16, it is sent to the decontamination bath 1. The evaporation residue remaining in the distillation column 13 is sent to a waste tank via a discharge valve 18. Distillation column 13
The evaporation residue and the used filter 9 are mixed with, for example, a curable resin, filled into a radioactive waste container, and solidified and disposed of.

As described above, according to the present invention, the cleaning effect is extremely good because cleaning is performed in a low-boiling point organic solvent heated at a temperature lower than the boiling point while being excited by ultrasonic waves, and decontamination is difficult with conventional methods. Waste pump parts, tools, various equipment items, etc. that have been contaminated can be easily cleaned. Furthermore, since the organic solvent can be purified and reused, the amount of secondary waste generated by washing is extremely small, and the amount of time and effort required for waste treatment can be greatly reduced. Furthermore, since this method can be easily operated remotely, the radiation exposure of workers is greatly reduced.

[Brief explanation of drawings]

The drawing is a system diagram of a decontamination device used in the present invention. 1...Decontamination bathtub, 2...Low boiling point organic solvent, 3...Immersion heater, 4,16...
・Capacitor, 5... Ultrasonic oscillator, T, lO
...Transfer pipe, 8...Transfer pump,
9...filtration filter, 11, 12...
Opening/closing valve, 13... Distillation column.

Claims (1)

[Claims] 1. When decontaminating articles contaminated with radioactive substances, the articles are washed in a low-boiling organic solvent heated at a temperature lower than the boiling point under ultrasonic vibration, and the low-boiling organic solvent after cleaning is A method for decontaminating items contaminated with radioactive substances, which comprises passing through a filter to remove undissolved solids, followed by distillation and reuse.