JPS59116595A - Method of removing radioactive material in electrolyte in electrolytic decontamination - 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] The equipment, parts, etc. that were used at the nuclear power plant 6L station '4 and were contaminated with radioactive substances made of composite metal oxide lamps were to be decontaminated. The present invention relates to a method of removing radioactive substances that are released into an electrolytic solution and accumulated over time during decontamination by electrolytic polishing of the surface of a substrate.

From the surface of the object to be decontaminated, rl+, I 1
mThe released composite metal oxide is electric Ifg! circulation 131
It is relatively easy to separate i by solid-liquid separation means such as filtration and sedimentation.
i) Radioactive substances that can be taken out of the decomposition liquid system 1.Radioactive substances eluted from the decontamination object and dissolved in the electrolyte as metal ions cannot be removed in a concentrated form by solid-liquid separation methods such as those described above. It is not easy to make it possible to remove the electrolyte from the outside.

Continuing the electrolytic decontamination work under such conditions will increase the radioactivity in the electrolyte as radioactive substances such as metal ions accumulate and cause decontamination equipment operators to There is a risk of radioactive heat.

One way to avoid this risk is to
It is conceivable to extract some of the liquid from the system and remove the soluble radioactive substances using an ion exchange resin, and then recover this liquid, but if the electrolyte is highly concentrated and contains a large amount of metal ions, Since it is an acid solution, this method requires dilution with a large amount of water before treatment, and large equipment and a large amount of heat are required to condense and recover the diluted concentration solution after removing metal ions, etc. This method is impractical because it results in the production of radioactive secondary waste such as ion-exchange resins that adsorb metal ions. l
jIn addition to the ion exchange method described in I, one method is to neutralize and dispose of the τ electrolyte taken out of the system as pJ6r (M) without recovering it, but since a large amount of radioactive slurry is generated, it is difficult to dispose of it. All of these methods generate a large amount of radioactive secondary waste, and there is a risk that the radioactively contaminated area will expand considerably.

In the method of depositing the broken metal ions in the electrolyte on a collection electrode and collecting them out of the electrolyte, if an electrolyte with a simple composition consisting of one or several types of inorganic acids is used, If it is a concentrated liquid with high work efficiency, the hydrogen ion concentration is extremely high, and the hydrogen gas generation reaction takes priority over the precipitation reaction of metals such as iron, chromium, and nickel on the collection electrode. Therefore, in order to recover these metal ions, the -acid lQ degree must be made extremely low, resulting in an extreme decrease in work efficiency.

Therefore, in order to recover heavy metal ions such as νj, chromium, and nickel, it has been necessary to use an electrolytic solution containing components that form complex salts with these ions. But with this rinse! (The 7 metals are in the form of salts, and the secondary 1
;Q '4'E There is a large amount of material, and the axillary composition is complex, so liquid 7
i (rii) It's not easy.

Kibe 1! l; is 1. Electrolyte ((・
As a result of Y decontamination work, the electrolytic solution containing S of radioactive substances was put out into system 1 + t1 and electrolysis γ After solid-liquid separation of the radioactive suspension consisting of complex metal oxides released during the night, diffusion dialysis was carried out. A membrane separates the electrolyte into its main component, an inorganic acid, and metal ions, recovers all the acid, and collects the metal ions dissolved in the waste liquid, which contains a large amount of metal ions after the acid separation, through a collection layer. (It is characterized by preventing the accumulation of radioactive substances in the electrolyte by depositing them on a plate and extracting the metal ions from the waste liquid as solid metals out of the thread.)

Examples 1 and 1 of the invention will be described in detail below with reference to the drawings. FIG. 1 shows the basic 70-.

In Figure 1, it is an electrolytic cell for 1lld electrolytic and N decontamination, and in the C1 tree embodiment, 25vol is used as the electrolyte.
% sulfuric acid is filled. The surface is eluted and decontaminated by the electrolytic polishing method (/C) in the vV decontamination tank.As a result of several decontamination operations, the electrolyte is 48 g/
1. It now contains 85 g/e of t2m4 and gg/e of near ion. This liquid is pumped and separated into solid and liquid by a filter 12), and as a result of the decontamination work, a suspension consisting of a composite metal oxide is released from the surface of the object to be decontaminated and a diffusion dialysis membrane shown in (3) Removes particulates that cause performance deterioration. (4) is a dialysis tank, which is disposed of into the dialysis rooms (4a) and (4b) by means of a diffusion dialysis membrane 13). This dialysis membrane (3) has the property of selectively permeating acids, and its material is a polymer with a three-dimensional mesh structure, typically a styrene/divinylbenzene copolymer, which contains strong dissociation of quaternary amino groups, etc. PVC is a hydrophilic film in which a base is introduced as a fixed ion.

Synthetic fiber cloth such as PP is used as a reinforcing material. In general, a dialysis tank (last name, ke+su) is divided into multiple dialysis membranes; When water is passed through at a high flow rate, the acid preferentially migrates from chamber (4a) to chamber (4b) due to the difference in acid concentration between the two dialysis chambers and the selective permselectivity of @(3). Correspondingly, water flows from chamber (4b) to (4a
). As a result, about 80% of the acid in the electrolytic solution is recovered in the chamber (4b) and returned to the electrolytic cell (1), where the sulfuric acid concentration is adjusted 17 and reused. Room (4
In a), approximately 95% of the metal ions in the electrolyte remain;
The metal ions in the waste liquid at this time were iron 40 g/i',
Chromium 84g/V, = charge rb 8g/e. This waste liquid is led to the metal ion recovery tank (6), but since the hydrogen ion concentration is high up to this point, the hydrogen ion concentration is sufficiently low and The pH is adjusted to such a range that metal ions do not precipitate as hydroxides. The metal ion recovery tank (6) has an anode (8) connected to the anode of an external DC power source (7), and a cathode (9) connected to the cathode as well. The positive electrode 18) is generally made of a floating material such as a carbon rod, a lead plate, or a titanium plate plated with platinum, and the negative electrode (
9) may be made of an inexpensive material such as stainless steel or carbon steel, or may be a material to be decontaminated. In the recovery tank (6) containing the waste liquid, after adding sodium hydroxide to adjust the pH of the liquid to 2, when a current is applied from an external power source (7), the metal ions, which are cations, are transferred to the negative electrode (9). Precipitates as a metallic solid. In the wood example, titanium plated with platinum was used as the positive electrode (8), and SUS 804 was used as the negative electrode (9). After 100 hours of energization, the metal ion concentration in the waste liquid was reduced to 4.
0 g/e is 9g/eK, chromium is 84 g/l is 28
g/l, nickel could be reduced from 8 g/e to 5 g/l VC.

By removing these metal ions remaining in the electrolyte using an ion exchange resin, almost all of the radioactive substances in the electrolyte can be removed.Is it possible to collect and reuse this solution? Alternatively, it can be neutralized or diluted before being discharged.

According to Kippatsu 1!11 K, in a simple and highly efficient electrolyte of 25 vol 1% sulfuric acid, metal ions are recovered as metal solids, and most of the sulfuric acid is recovered and reused. Therefore, the amount of secondary waste generated as a result of the electrolytic dedying work is significantly reduced. Further, since the acid concentration and metal ion concentration in the waste liquid are reduced, subsequent waste liquid treatment is also easy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the process of treating an electrolytic solution in one embodiment of the present invention. (1)... Electrolytic cell, (2)... Filter, (3)...
Diffusion dialysis membrane, ]4) Diffusion dialysis tank, (4a) (4b)
...Dialysis room, 1ffil--water tank, (6)...metal ion recovery tank, (7)...external DC power supply, (8)...positive electrode, (9)...negative? 1! very. Patent applicant's representative name Patent attorney Hiroshi Kado H3 Yoshi-5.

Claims (1)

[Claims] In the process of decontaminating the metal surfaces of equipment, parts, etc. contaminated with radioactive materials using Electrolytic Research Institute Jv:, #
(11) After removing the separated metal oxide from the electrolyte, it is separated into gold α ions coexisting in the electrolyte and acid, which is the main component of the electrolyte, using a diffusion dialysis membrane. A radioactive substance in an electrolytic solution in electrolytic decontamination, which is characterized by recovering the acid and also precipitating metal ions dissolved in the waste liquid after acid separation onto a collecting electrode and extracting them from the waste liquid. Removal method.