JPS61200497A - Removal of contamination due to radioactive material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a method for removing contamination by radioactive substances.

[Conventional technology]

Conventionally, in an environment such as a controlled area of a nuclear power plant, suspended matter contained in the air or water becomes radioactive and becomes radioactive, and adheres to the surface of equipment or tools. Accumulation often spreads to contaminated areas by flaking, falling off, or moving to other areas while adhering to objects it comes in contact with. Therefore, many methods have been developed to prevent the adhesion and accumulation of radioactive substances that cause such contamination. The main methods are listed below.

■ Dissolution method: This is a method in which the contaminated material is immersed in a strong acid or strong alkali solution, the metal surface is dissolved, and the process of washing with water is repeated. However, it is not applicable to non-metallic products such as rubber products and painted products. Not only is this not possible, but it is also limited by the size that can be put into the solution tank, and waste liquid treatment is not easy.

■ Blasting method: This is a method in which acid crystals or ice particles are mixed with high-pressure water and sprayed onto the metal surface to scrape off the contaminants along with a portion of the metal surface. Even when applied, the effect is small, and a large amount of waste liquid is generated, making post-treatment a major waste.

■ Electrolytic method: This is a method of electrolytically polishing contaminated metal surfaces in a weakly acidic solution, but it cannot be applied to non-metals, is limited to the size that can fit in an electrolytic tank, and requires treatment of waste liquid. It's not easy.

■Ultrasonic method: This is a method in which ultrasonic waves are applied to contaminated objects and the deposits are removed by minute vibrations, but this method can only be used underwater.
Therefore, the size of what can be treated is limited by the size of the water tank, and the effect can only be expected on loose contamination (contamination that is not stubbornly adhered).

■ Bubbling method: This is a method in which air or water vapor bubbles are injected from the bottom of a water tank containing contaminated substances, and the adhered substances are removed by the action of the bubbles and the water flow generated by the bubbles. Naturally, it can only be used underwater, the size of the material to be treated is limited by the size of the aquarium, and it can only be applied to loose contamination.

■ Strippable paint method: A strippable paint is applied to the surface of the contaminated object and dried to form a film.
This is a method of attaching contaminants to the inner surface and then peeling off the paint film, but there are two methods of attaching contaminants to the paint film: physical methods and chemical methods using paints with a chelate action mechanism. . However, the former, physical, is loose pollution, and the latter, chemical, is fixed pollution.
There are other methods such as washing with water, wiping, cutting, etc., but each method has its own problems.

[Problem that the invention seeks to solve]

As mentioned above, even though many pollution control methods have been developed, the size of the pollutants to be treated may be limited by the size of the treatment tank, or conversely, the treatment equipment may be seriously damaged. In some cases, a large amount of waste liquid is generated after treatment, which requires complicated countermeasures, and furthermore, the pollution control effect is not achieved because the mode of contamination is not sufficiently considered. No method of control has been found.

The technical object of the present invention is to eliminate these various drawbacks.

[Means for solving problems]

In order to solve the above problems, this invention applies an anionic surfactant aqueous solution whose pH value is adjusted to 3 to 6 on a surface contaminated with radioactive materials and substances, and then applies a polyvinyl alcohol-based chelate polymer. An anionic water-based paint with peelability as the main component is applied, and once this paint film has solidified, it is peeled off, and a synthetic rubber-based water-based emulsion is further applied to form a peelable organic insulating film. The present invention provides a method for preventing contamination of radioactive substances, which is characterized by the following, and the details thereof will be described below.

First, this invention involves a first step of applying an aqueous anionic surfactant solution with a pH value of 3 to 6 on the surface of equipment, tools, etc. contaminated with radioactive materials, and a polyvinyl alcohol based aqueous solution. A second step is to apply a peelable anionic water-based paint containing a chelate polymer as a main component, dry and solidify this paint film, and then peel it off. It consists of three steps, including the third step of applying an aqueous emulsion to form a peelable organic insulating film.

The mainstream of practical nuclear reactors for power generation is light water reactors, which are roughly divided into pressurized water reactors and boiling water reactors. Water is used as a coolant and for neutron moderation. Radioactive contaminants are the corrosion products of the constituent materials that come into contact with the coolant, which are released into the primary system, are activated and accumulate, and are composed of water-soluble radioactive metal ions (
O charge) and water-insoluble radioactive metal oxides (called cladding, which have a charge that depends on the hydrogen ion concentration pH of the system; for example, metal oxides in reactor water with a pH of 6 to 8 have a 0 or e charge).

Therefore, in this invention, taking into consideration the characteristics and mode of the accumulated contaminants, in the first step, the pH is set to 3 to 6 in order to make the deposits more likely to float, that is, to convert the cladding surface charge to Anionic surfactants with high wetting and solubilizing abilities are applied to make the cladding hydrophilic through its micelle effect. Then, in the second step, metal ions with a charge of (1) are drawn into the coating film, these are chemically captured, and the coating film on which the soluble cladding has also been ionically adsorbed is peeled off.

Since the surface after the coating film is peeled off is in an activated state, a peelable coating film having an insulating function to prevent the ionization and adsorption of radioactive dust floating in the atmosphere is further formed in the third step.

In addition, in the first step, when adjusting the pH value of the surfactant solution, an acid such as oxalic acid, citric acid, ascorbic acid, boric acid, or EDTA (2Na) may be used. As the agent, for example, dodecylbenzenesulfonate (DBS), butyloctylbenzenesulfonate, acetylene diol, etc. may be used. In addition, the chelate polymer used in the second step is a chelate polymer ligand that has a donor atom that forms a complex with a metal in its molecule, and is a chelate polymer that is derived by etherifying polyvinyl alcohol. Examples include polymeric ligands such as polyvinyl alcohol, aliphatic diol, polycarbonyl, aromatic hydroxycarbonyl, and polycarboxylic acid. Anionic water-based paints containing such chelate polymers as main components are 30 to 50 parts of a water-based emulsion resin polymerized with a radical polymerization initiator such as an azo compound, peroxide compound, or cumene as an initiator to a mixture of acrylonitrile and butyl acrylate. 70 to 50 parts of a polyvinyl alcohol-based chelate polymer is added to the product, and in order to improve the wettability of the contaminated material and the surface to be coated,
It is made into a paint by adding a surfactant (for example, an anionic or nonionic one) to a concentration of 1 to 4 times the micelle concentration, and this paint contains fillers such as coloring pigments such as titanium oxide and carbon black. Even if , additives, etc. are blended, this invention will not be hindered. Furthermore, the water-based emulsion paint used in the third step needs to have an insulating film formed after curing, have appropriate elasticity and tensile strength, and be peelable. Examples include synthetic rubbers, such as acrylic rubbers. The concentration and amount of coating agent, paint, etc. used in each process are not particularly limited, and may be adjusted as appropriate depending on the degree of contamination, and the coating method also depends on the shape, size, etc. of the target object. Depending on the situation, an appropriate coating method may be selected from among the usual coating methods.

In the first step, this invention changes the electrical characteristics of the radioactive substance attached to the surface, changing the radioactive ionized substance and radioactive oxide into a state in which they are easily released from the surface to which they are attached, and in the second step, In the process of drying and solidifying the paint, radioactive ionized substances are chelated and chemically captured, and at the same time radioactive oxides are solubilized and physically adsorbed.The dried paint film is then peeled off, resulting in radioactive contamination that has adhered to the surface of objects. The substance is completely removed, and in the third step, it prevents contamination again and maintains a non-contaminated state for a long period of time.

〔effect〕

As mentioned above, according to the method of the present invention, the material of the target object is not limited to metal, but there is no problem even if it is rubber or synthetic resin, and even if it is a rubber product to which conventional methods cannot be applied. Even if it is painted, it can exhibit a sufficient pest control effect. Furthermore, this method is of great significance since it does not require any increase in the size of treatment equipment or consideration for waste liquid. Furthermore, the first step and the third step in this invention can be used as a pre-treatment and a post-treatment for decontamination methods other than the second step of this invention, respectively, and still exhibit sufficient effects and are extremely effective. be.

Claims (1)

[Claims] After applying an anionic surfactant aqueous solution with a pH value of 3 to 6 on the contaminated surface of radioactive contaminants, a peelable anionic water-based paint containing polyvinyl alcohol-based chelate polymer as the main component is applied. A radioactive substance characterized by: waiting for the coating film formed with this paint to solidify, peeling it off, and further applying a synthetic rubber-based aqueous emulsion to form a peelable organic insulating film. How to remove contamination by.