JPH0631866B2 - Volume reduction solidification method of radioactive metal-containing organic waste decomposition solution - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention is for reducing and solidifying a decomposition liquid obtained by oxidizing and decomposing radioactive metal-containing organic waste generated in a facility for handling radioactive materials such as nuclear power generation facilities. Volume solidification method of radioactive metal-containing organic waste decomposition liquid of the above.

[Technical background of the invention and its problems] In facilities handling radioactive materials such as nuclear power plants,
Although various radioactive solid wastes are generated, at present, most of them are not established as final disposal methods and are fluid, so used ion exchange resins and filter sludge, which are the main constituents of solid wastes, etc. Is stored mainly in tanks as it is, and reducing the amount of radioactive waste generated is an urgent and important issue for storage management.

Among such solid wastes, a large amount of radioactive organic wastes, such as used radioactive ion exchange resin, is generated. Therefore, reducing the volume of the radioactive organic wastes greatly contributes to the reduction of the amount of generated wastes.

By the way, radioactive organic waste is a polymer compound, and since it can be chemically structurally decomposed as a volume reduction method, it has been conventionally used in a dry incineration method, a wet incineration method, a thermal decomposition method,
Volume reduction methods such as the chemical decomposition method are being studied.

Of these, the dry incineration method is a method of literally incinerating in an incinerator as it is, and many methods have been studied and developed. However, when incinerating radioactive organic matter in an incinerator, it is necessary to control the amount of heat, so pretreatment such as drying and devising a method for supplying resin are required, which makes operation and equipment complicated. Further, since the incinerator itself does not have a function of suppressing the scattering of incineration ash, the scattering of radioactive incineration ash from the incinerator is very large (DF: decontamination factor is almost 1). Since harmful gases such as SOx and NOx are generated as radioactive gas as incineration gas, post-treatment called waste gas treatment is necessary including radioactive countermeasures, and these gases are highly corrosive and There are problems such as difficulty in selection. Further, in this method, since the radioactive organic waste is treated in a high temperature environment, there is a problem peculiar to radioactive handling, that is, so-called nuclide transfer, in which radioactive components are transferred to the incineration gas generated.

In addition, the wet incineration method uses 2 in an aqueous solution or an aqueous copper sulfate solution.
Although it is a method of burning radioactive organic matter by sending oxygen or air under high temperature and high pressure of 0 to 100 atm and 200 to 300 ° C., it has a drawback that the volume reduction rate is inferior to that of the dry incineration method. is there.

Furthermore, the thermal decomposition method is a method of thermally decomposing by cutting off the supply of oxygen, and since the radioactive organic matter is thermally decomposed at a high temperature in an inert gas atmosphere, the amount of soot and dust generated is greater than that of the dry incineration method. It has the advantage of being small. However,
This method requires an additional combustion step of decomposed gas and has the problem of migration of radionuclides as in the case of the dry incineration method.

On the other hand, the chemical decomposition method oxidizes and decomposes a resin by a chemical reaction with a drug, and the following methods are known.

A method in which radioactive organic matter is carbonized with hot concentrated sulfuric acid (130 to 300 ° C.), and then oxidatively decomposed with nitric acid or hydrogen peroxide.

A method of oxidatively decomposing an organic waste by contacting it with hydrogen peroxide solution in a solution containing mainly iron ion, copper ion, chromate ion or dichromate ion.

However, this method has a big problem that the selection of equipment materials is very strict because it handles strong acids and oxidizers at high temperatures, and metal ions remain as they are when radioactive metal-containing organic waste is targeted. In the method (1), the kind of organic waste that can be decomposed by the existing metal ions may be limited, and the salt effect is diminished by the added metal salt.

[Object of the Invention] The present invention has been made in response to such conventional circumstances.
Under mild conditions, which are easy to implement, reduce the concentration of waste liquid by removing metal ions, and achieve a high volume reduction rate when solidified. The purpose is to provide a method.

[Summary of the Invention] That is, according to the present invention, oxidative decomposition is performed by bringing hydrogen peroxide into contact with a radioactive metal-containing organic waste in a liquid in the presence of a metal salt or by injecting an oxygen-containing gas under heat and pressure. Oxidative decomposition step for producing a decomposition solution containing metal ions, a metal precipitation electrolysis step for precipitating and separating a metal from the decomposition solution containing the metal ions by electrolytic reaction, and the decomposition solution after the metal precipitation electrolysis step is adjusted to pH. A method for reducing the volume of a radioactive metal-containing organic waste decomposed solution, which comprises a drying step of adjusting and removing water, and a solidification treatment step of solidifying a dry residue obtained by the drying step with a solidifying material. is there.

The drawings are process drawings for explaining one embodiment of the present invention.

In this embodiment, first, radioactive metal-containing organic waste 1
Is oxidatively decomposed by contact with hydrogen peroxide in the presence of an oxidation catalyst, for example, a metal salt described later, to give an oxidative decomposition liquid 2.

As a typical example of the metal-containing organic waste to be the subject of the present invention, a cation or a mixed ion exchange resin of cation and anion which is generally used for treating radioactive waste liquid in a nuclear power plant, for example, styrene and divinylbenzenesulfonic acid are copolymerized. There is a powdery or granular ion exchange resin having a sulfone group or an amino group inside the synthetic resin, or a mixture of this with an aqueous metal salt solution.

As the metal used in the above-mentioned oxidation catalyst, one or more metals selected from ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate and copper sulfate are used.
The concentration of these metal salts is 500 as the metal content in the reaction solution.
Appropriate is the extent of existence of 10,000 ppm. The concentration of the hydrogen peroxide solution is 1 to H ₂ O _{2 in} the aqueous solution of the reaction system.
About 40% is suitable. The reaction proceeds even at room temperature, but it is preferable to heat the reaction to proceed the reaction. The reaction temperature is preferably 50 ° C or higher, particularly 90 to 100 ° C.

In addition, instead of the method of contacting the radioactive metal-containing organic waste with hydrogen peroxide, a gas containing oxygen is injected under pressure into the liquid containing the radioactive metal-containing organic waste to remove the radioactive metal-containing organic waste. It is also possible to oxidatively decompose. The heating and pressurizing conditions in this case are a temperature of 200 to 300 ° C. and a pressure of 20 to 10
A range of 0 atm is suitable.

In the oxidative decomposition reaction, carbon components and hydrogen components in the ion exchange resin are oxidized to generate mainly carbon dioxide gas and water vapor, and a transparent liquid product is obtained as an oxidative decomposition liquid. Since this oxidative decomposition reaction is carried out at a lower temperature than in the dry incineration method, the transfer of radioactivity to the generated carbon dioxide gas and water vapor is extremely small, and it can be processed by the conventional waste gas processing technology. The oxidative decomposition liquid 2 contains, for example, sulfate ions generated when the sulfur-containing ion exchange resin having a sulfone group or the like is oxidatively decomposed,
It contains metal salts or metal ions adsorbed by ion exchange and sulfate ions.

The oxidative decomposition liquid 2 containing this metal ion is then subjected to an electrolytic reaction to remove the metal ion. In this electrolytic reaction, for example, an electrolytic refining tank having Pt as an anode and Cu or Fe as a cathode is used, and the metal ions present in the oxidative decomposition solution 2 are deposited on the cathode by the reaction represented by the following formula, for example. .

^{Fe 2+ + 2e - --- → Fe} Fe 3+ + 3e - --- → Fe Cu 2+ + 2e - --- → Cu by such reaction, metal ions in the oxidative decomposition solution to precipitate nearly 100% negative electrodes Can be collected.
Some of the metal ions adsorbed by ion exchange have been activated, and since these can also be removed from the waste liquid, the radioactive concentration of the waste liquid can be reduced, and the effect of reducing exposure can be expected.

The electrolytic reaction residue liquid 3 from which the metal ions have been separated and separated in this way is then heated and concentrated while being brought into contact with a reducing agent such as charcoal or sulfur, or a metal such as Cu having a lower ionization tendency than hydrogen. It is desirable to reduce the sulfate ion to sulfur dioxide and remove it.

When reducing agents such as charcoal and sulfur are used, the sulfate ions become sulfur dioxide almost completely, and when divalent metals such as Cu are used, 50% of them are theoretically decomposed. It

That is, in the former case, for example, the sulfate ion becomes sulfur dioxide by the following reaction, and 2H ₂ SO ₄ + C −− → 2SO ₂ ↑ + CO ₂ ↑ + 2H ₂ O ↑ In the latter case, the liquid temperature becomes 130 ° C. or higher. Sulfuric acid and copper in the oxidative decomposition liquid react with each other in the following manner to form copper sulfate in an equimolar amount with sulfur dioxide.

Cu + 2H ₂ SO ₄ −− → Cu SO ₄ + SO ₂ ↑ + 2H ₂ O ↑ That is, in the reaction with Cu, 1 mol of copper sulfate is produced from 1 mol of metallic copper and at the same time 1 mol of sulfate ion is converted into sulfur dioxide as oxidative decomposition solution. Will be removed from. Therefore, even if metallic copper is used, 50% of sulfate ions can be removed.

The sulfur dioxide generated in this desulfurization reaction, like carbon dioxide and water vapor accompanying the oxidative decomposition reaction of the resin described above, has a very small transfer to radioactivity and can be treated by conventional waste gas treatment technology. is there.

In addition, the reduction residue liquid 4 remaining in the desulfurization reaction using metallic copper
Since it can be reused to decompose the radioactive ion exchange resin, using this reaction solution eliminates the need to newly use copper sulfate for oxidative decomposition and almost completely decomposes and removes sulfate radicals. can do. If the radioactivity concentration in the reaction solution exceeds the permissible amount, copper is deposited again as required, or the waste solution 5 is treated as it is in a conventional waste solution treatment system. Alternatively, after the neutralization and the drying treatment, the obtained powdery dry residue 6 is mixed with, for example, a polyester resin and solidified to obtain a solidified body 7. According to this method, the solidified body generated is generated. The amount of can be 1/100 of the case where the conventional ion-exchange resin is solidified with cement as it is, and 1/20 of the case where it is solidified with plastic after drying.

[Examples of the Invention] Examples of the present invention will be described below.

Example 1 To a four-necked flask equipped with a condenser and a stirrer, a powdery mixed ion-exchange resin (trade name: Powdex) in a dry state and 5000 parts of water per 100 parts of this ion-exchange resin were added and thoroughly mixed, then _H 2 _O concentration as a ₂ is 10% the amount of hydrogen peroxide and Fe ₂ (S
Ferric sulfate was added in an amount such that the concentration as O ₄ ) ₃ was 0.01 mol / mol, and the mixture was heated to 100 ° C., and mixing and stirring was continued at this temperature for 1 hour. Gas is generated as the reaction progresses,
The solution becomes cloudy in the beginning, but finally becomes a clear liquid. The gas generated here was condensed in a condenser, and after condensation was returned to the reaction residual liquid in the reactor, and the gas was directly introduced to the next gas treatment step.

Next, the reaction residue liquid was electrolyzed in an electrolytic refining tank in which the anode was Pt and the cathode was Fe, and about 100% of Fe in the liquid was deposited on the electrode. Next, a theoretical amount of charcoal powder was added to the electrolytic residue solution and the mixture was heated and concentrated. At about 130 ° C, generation of sulfur dioxide and carbon dioxide gas was observed from the liquid due to the reaction of sulfate ion with charcoal, and at 180 ° C, it was confirmed that the sulfate ion was decomposed at about 100 ° C. This liquid residue can be disposed of by treating with a conventional waste liquid treatment system after pH adjustment, and the liquid material after pH adjustment was evaporated to dryness and solidified with a polyester resin to solidify the plastic, which resulted in oxidative decomposition. Just neutralize,
The volume could be reduced to about 1/5 as compared with the case of evaporating and drying and solidifying the plastic.

Example 2 A powdered mixed ion-exchange resin (commercial name: Powdex) in a dry state was added to the four-necked flask used in Example 1, and 1500 parts of sulfuric acid having a concentration of about 6000 ppm as metallic copper per 100 parts of this ion-exchange resin. An aqueous copper solution was added and heated to a temperature of 80 to 100 ° C. Then, while stirring with a stirrer, an aqueous solution of hydrogen peroxide having a concentration of 60% was added at a constant flow rate at a constant flow rate of 30 ml per 1 g of the dry ion exchange resin to oxidize the ion exchange resin, and decomposed into a gaseous product and a liquid residue. The rest of the above decomposition solution is electrolyzed in an electric refining tank with an anode Pt and a cathode Cu, and the Cu content in the liquid is almost 100% in the Cu electrode.
It was deposited. Thereafter, the electrolytic residue solution was heated and concentrated while being brought into contact with the deposited metallic copper. It was confirmed that sulfur dioxide was generated from the liquid due to the decomposition of sulfate ions at about 130 ° C., and that 50% of the theoretical amount of sulfate ions was decomposed at 150 ° C. After adjusting the pH of this liquid residue, it can be disposed of by treating with a conventional waste treatment system. Also, the liquid substance after pH adjustment was evaporated to dryness and solidified with a polyester resin to solidify the plastic. Neutralize with,
The volume could be reduced to about 1/2 as compared with the case of evaporating and drying and solidifying the plastic.

In addition, the copper sulfate-containing residue solution that decomposed this sulfate ion was used in combination with an aqueous solution of hydrogen peroxide to perform the same waste ion exchange resin decomposition treatment again. In this case as well, when an aqueous solution of a metal salt and an aqueous solution of peroxide were used. It was found that it had a similar ability to decompose organic waste containing sulfur.

[Effects of the Invention] As is clear from the above description, according to the method of the present invention, a higher volume reducing property can be obtained as compared with the conventional method.

Further, since the metal ions derived from the metal-containing organic waste are recovered as metals, the amount of secondary waste becomes extremely small.

[Brief description of drawings]

 The drawings are process drawings schematically showing the process of the present invention. 1 ... Radioactive metal-containing organic waste 2 ... Oxidative decomposition solution 3 ... Electrolysis reaction residue solution 4 ... Reduction residue solution 5 ... Waste solution 6 ... Dry residue 7 ... Solidified body

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuaki Sato 4-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Nuclear Power Co., Ltd. (56) References JP-A-53-88500 (JP, A) ) JP-A-58-72099 (JP, A) JP-A-58-146899 (JP, A) JP-A-57-52899 (JP, A)

Claims (6)

[Claims] 1. A radioactive metal-containing organic waste in a liquid is contacted with hydrogen peroxide in the presence of a metal salt, or an oxygen-containing gas is injected under heat and pressure to oxidize and decompose to contain a metal ion. Oxidative decomposition step to generate a decomposition solution that generates, a metal deposition electrolysis step that deposits and separates a metal from the decomposition solution that contains this metal ion by an electrolytic reaction, and the pH of the decomposition solution after this metal deposition electrolysis step is adjusted to remove water. And a solidification treatment step of mixing the dried residue from the drying step with a solidifying material and solidifying the mixture, thereby reducing the volume of the radioactive metal-containing organic waste decomposition liquid. 2. The metal salt comprises one or more selected from ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate and copper sulfate. A method for solidifying a volume of a decomposed solution of a radioactive metal-containing organic waste described in the above. 3. The concentration of the metal salt in the liquid is 500 to 10,000 ppm in terms of metal ion.
Item 3. A method for reducing the volume of a radioactive metal-containing organic waste decomposed solution according to Item 2 or 2. 4. The method for reducing and solidifying the volume of a radioactive metal-containing organic waste decomposition solution according to claim 1, wherein the concentration of hydrogen peroxide in the solution is 1 to 40% in terms of H ₂ O ₂ . 5. The oxidative decomposition step according to claim 1, wherein the radioactive metal-containing organic waste is contacted with hydrogen peroxide in the presence of a metal salt at a temperature of 80 to 100 ° C. for oxidative decomposition. Item 10. A method for solidifying a volume of a radioactive metal-containing organic waste decomposed liquid according to any one of items 1 to 3. 6. The oxidative decomposition step is performed at a temperature of 200 to 300 ° C.
The method for reducing the volume of a radioactive metal-containing organic waste decomposed solution according to claim 1, wherein a gas containing oxygen is injected at a pressure of 20 to 100 atm to oxidatively decompose the radioactive metal-containing organic waste.