JPH0659095A - Decontamination treatment of radioactive contaminant - Google Patents

Abstract

PURPOSE:To provide a decontamination treatment method of a radioactive contaminant capable of removing a contaminant from the radioactive contaminant by means of a cleaning agent and also reusing the used cleaning agent. CONSTITUTION:This decontamination treatment method of a radioactive contaminant, after it decontaminates the radioactive contaminant with d-limonene, adds a produced decontaminated waste liquid with a radioactive substance separating agent not soluble with the decontaminated waste liquid, after stirring it, stands it and separates it in two phases, and after transferring a radioactive substance in a decontaminated waste liquid phase to a radioactive substance separating agent phase, fractionizes it into the radioactive substance separating agent phase and the decontaminated waste liquid phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decontaminating radioactive contaminants by removing the contaminants from the radioactive contaminants with a detergent and reusing the detergent used. Uses a cleaning agent to remove radioactive substances from the surface of clothes that are generated in large quantities as contaminants, especially those that occur in facilities that handle radioactive substances (hereinafter referred to as "nuclear facilities") such as nuclear power plants. Then, the present invention relates to a method for decontaminating radioactive contaminants, in which radioactive substances are separated and removed from the generated cleaning waste liquid by liquid-liquid exchange, and the cleaning agent is reused.

[0002]

2. Description of the Related Art Currently, clothing used in nuclear facilities is
Generally, cleaning is performed by a dry method using CFC or other organic solvent or a wet method using water and a detergent.
The purpose of cleaning in such a nuclear facility is different from that in general public cleaning. That is, in the city cleaning, dirt such as dirt, sebum, and food on the human body is washed, whereas in cleaning the nuclear power plant, the removal of radionuclides is the main purpose. Therefore, the cleaning method and the use of a large amount of the chelating agent are largely different from the cleaning methods in the market. Further, in recent years, the amount of radioactive waste liquid generated in the wet type cleaning is enormous, and a great deal of labor and energy is required to process the waste liquid. Therefore, the dry type cleaning is the mainstream. Most of the dry methods use CFC-113, which is easy to handle, as a cleaning solvent. Above CFC-113
Has been widely used because it has excellent properties as a dry cleaning solvent, evaporating by slight heating, easy to condense and reuse, and harmless to human body.

[0003]

However, in recent years,
It was confirmed that the above-mentioned CFC gas is destroying the ozone layer surrounding the earth, and it became clear that continuous CFC emission into the atmosphere could cause serious environmental damage. As a result of the examination of global ozone layer protection measures, the Ozone Layer Protection Law including the regulation of the use of CFCs was enacted, and the above-mentioned CFC-113
Is a specific CFC subject to regulation by this law, so supply and demand in the future is becoming difficult. On the other hand, in view of this situation, the use of non-regulated CFCs (so-called alternative CFCs) is being considered, but boiling point, detergency, toxicity,
There are various problems in terms of economical efficiency, and there is no prospect for practical use. Further, tetrachloroethylene and petroleum-based solvents have been conventionally used in the market as dry cleaning agents other than CFCs. However, since tetrachlorethylene is carcinogenic, it is designated as a Class 2 Specified Chemical Substance under the Chemical Substances Control Law or a Class 2 Organic Solvent under the Industrial Safety and Health Act, and the emission standards for the Water Pollution Control Act and the Sewer Act are also included. Has been defined. Further, the petroleum solvent is flammable, and there is a problem that petroleum odor remains on the clothes after cleaning. Furthermore, both tetrachloroethylene and petroleum-based solvents are used for the purpose of removing oily soil rather than removal of radioactive contamination, and it is hard to say that they replace CFC-113 described above. On the other hand, with respect to wet cleaning, as described above, a large amount of cleaning waste liquid is generated, and there is a problem that a large amount of labor and energy is required to process the cleaning waste liquid containing the radioactivity. However, in practice, it cannot be said that it is an alternative method to the dry cleaning using the above CFCs. As described above, in nuclear facilities and the like, due to the restrictions on the use of CFCs under the Ozone Layer Protection Act, a cleaning agent that is practically comparable to CFC-113 has been required in place of CFC-113, which will not be usable in the future.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that radioactive substances attached to clothes can be removed by washing the clothes with d-limonene, which has a proven record as a radioactive decontamination agent. I paid attention. This removal of radioactive substances by d-limonene is a known technique disclosed in Japanese Patent Application Laid-Open No. 62-165199 proposed by the present applicants. The feature of this technique is that radioactive contamination, especially human body It is characterized in that it is effective in removing contamination adhering to the surface and that radioactive waste can be easily reduced in volume by incineration after decontamination. Therefore, it is expected that if d-limonene is effective in removing the contamination adhering to the surface of the human body, it will also be effective in removing the radioactive substance adhering to clothing of the human body or helmet shoes. However, no matter how excellent the radioactive decontamination method is to remove radioactive substances using d-limonene, a large amount of d-limonene is consumed when a large amount of cleaning liquid is used for cleaning clothes. Is uneconomical and the CO ₂ gas generated during incineration is
It cannot be absolutely asserted that the technique is preferable for such applications because it may cause new air pollution.

[0005]

Therefore, the present inventor added the radioactive substance separating agent to the used waste liquid to add the radioactive substance in the waste liquid to the radioactive substance in the waste liquid based on the known radioactive contamination removal method by d-limonene. The present invention has been completed by studying a method for decontaminating radioactive contaminants that enables separation and removal and reuse of d-limonene. That is, in the present invention, after decontaminating radioactive contaminants with d-limonene, to the produced decontamination waste liquid, a radioactive substance separating agent that is incompatible with the decontamination waste liquid is added, and the mixture is left standing after stirring to form two phases. The radioactive contaminant in the decontamination waste liquid phase is transferred to the radioactive substance separation agent phase, and then the radioactive substance separation agent phase and the decontamination waste liquid phase are separated. Decontamination treatment method.

In general, the radionuclides involved in the atomic bombing of nuclear power plants are mainly ⁶⁰ Co, ⁵⁸ Co, ⁵⁴ Mn, etc. produced in reactor water, and these include Fe ₂ O ₃ in the pollutants. It is known that they exist in a state of being incorporated in fine particles of an iron-based oxide called a clad. The known mechanism of decontamination of radioactivity by d-limonene has not been clarified, but the presence of two double bonds in the molecule increases the free electron density of the d-limonene molecule. It is presumed that heavy metals such as Co and Mn are bound to these by weak bonds such as π bonds to form a complex, so that radioactive substances such as ⁶⁰ Co, ⁵⁸ Co and ⁵⁴ Mn can be easily incorporated. To be However, since the π bond has a very weak bonding force, the bond is easily broken when an external force is applied. For example, d-limonene molecule and ⁶⁰ Co, ⁵⁸ Co or ⁵⁴
When a highly viscous substance is added to a liquid containing a complex in which a heavy metal such as Mn is π-bonded and stirred and shaken, the π-bond is broken and heavy metal ions such as ⁶⁰ Co, ⁵⁸ Co, and ⁵⁴ Mn are removed. , Will be transferred to the sticky substance side. In the present invention, the aqueous solution containing the adhesive substance as described above is referred to as a radioactive substance separating agent. The present invention is characterized in that the radionuclide released by d-limonene is transferred to the side of the radioactive substance separating agent. The radioactive substance separating agent according to the present invention is a mixture of one or a plurality of the following components. Polyvinylpyrrolidone 10 ppm to 1% by weight Polyvinyl alcohol 10 ppm to 1% by weight Polyacrylamide 10 ppm to 1% by weight Polyacrylic acid 10 ppm to 1% by weight Carboxymethyl cellulose 10 ppm to 1% by weight Water

[0007]

As described above, in the method for decontaminating radioactive contaminants of the present invention, the radioactive contaminants are decontaminated with d-limonene and then added to the produced decontamination waste solution. Since a radioactive material separating agent that is incompatible with the decontamination waste liquid is used, by allowing the mixture to stand after stirring, d-limonene and the radioactive material separating agent can be favorably separated into two phases, and as a result, The radioactive material (separating agent layer) can be easily separated and separated. Further, in the method for decontaminating radioactive contaminants of the present invention, the radioactive substance in the decontamination waste liquid phase is transferred to the radioactive substance separating agent phase, and then the radioactive substance separating agent phase and the decontaminating agent are removed. Since it was decided to separate the dye waste liquid phase, the d-
Limonene can again be used as a decontaminant of radioactive contaminants. Therefore, the consumption of d-limonene is reduced, and the cleaning cost can be reduced. Also,
Since most of d-limonene is reused, the amount of radioactive waste liquid inevitably becomes extremely small and the waste liquid treatment becomes easy.

[0008]

EXAMPLE An example of the method for decontaminating radioactive contaminants of the present invention will be shown below to clarify the radioactive decontamination effect of the present invention. (1) To a separating funnel containing 200 ml of d-limonene, add 0.2 ml of about 4 × 10 ⁵ Bq / cm ³ of 0.1 wt% ⁶⁰ CoCl aqueous solution, and use a reverse well type NaI scintillation detector to separate the funnel. The radioactivity of the aqueous solution was measured to be 6.2 × 10 ⁴ Bq (before decontamination). The NaI scintillation detector used at this time had a diameter of 2 inches and the measurement time was 60 minutes. (2) Next, prepare 200 ml of the radioactive substance separating agent prepared in the following mixing ratio. did. Polyvinylpyrrolidone 1000ppm Polyvinyl alcohol 2000p
pm polyacrylamide
500ppm Carboxymethyl cellulose 2000ppm Water Add the radioactive substance separating agent 200ml prepared in (2) to the aqueous solution in the separating funnel of (3) (1) above, and shake for 200 cycles at a shaking speed. Shake for 2 minutes / minute. (4) After standing for 5 minutes, the lower layer of the liquid separated into two layers in the separating funnel (radioactive substance separating agent layer) was collected, and the residual radioactivity of the d-limonene layer remaining in the separating funnel was measured. NaI as in (1)
8.4 × 10 ¹ Bq measured by scintillation detector
(After decontamination).

Claims (3)

[Claims] 1. After decontaminating radioactive contaminants with d-limonene, a radioactive substance separating agent that is incompatible with the decontamination waste liquid is added to the produced decontamination waste liquid, and the mixture is left standing after stirring to form a two-phase mixture. Separate
Decontamination of radioactive contaminants, characterized in that the radioactive substance in the decontamination waste liquid phase is transferred to the radioactive substance separating agent phase, and then the radioactive substance separating agent phase and the decontamination waste liquid phase are separated. Processing method. 2. A method of decontaminating clothing contaminated with radioactivity with d-limonene, and d-
The method for decontamination treatment of radioactive contaminants according to claim 1, wherein 2 to 60% by weight based on the amount of limonene is added, the mixture is allowed to stand after stirring, and radioactivity is separated to the separating agent phase side by liquid-liquid exchange. 3. The radioactive substance separating agent phase and the decontamination waste liquid phase are separated, and the separated decontamination waste liquid phase d-limonene is repeatedly reused as a decontaminating agent for radioactive contaminants. The method for decontaminating radioactive contaminants according to claim 1 or 2.