JPS6061697A - Method of decomposig and treating radioactive liquid organic waste - 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 [Technical Field of the Invention] The present invention relates to a power and method for decomposing radioactive liquid organic waste generated in facilities handling radioactive materials such as nuclear power plants.

[Technical background of the invention and its problems]

Facilities that handle radioactive materials such as nuclear power plants generate various kinds of waste, one of which is radioactive liquid organic waste. For example, it is an organic solvent used for reprocessing spent nuclear fuel. A treatment method for such radioactive liquid organic waste has not yet been established. For example, the organic solvent contains an organic phosphate ester such as tri-n-butyl phosphate (TBP).
P is currently stored untreated in tanks within the facility. If left untreated, storage tanks will suffer from corrosion, and the amount of corrosion is expected to increase in the future, so there is an urgent need to develop a safe treatment method. There is.

Regarding the treatment of these radioactive liquid organic wastes, various methods such as incineration, thermal decomposition, chemical decomposition, recovery and reuse, and solidification have been studied.

Among these, the incineration method is a method in which waste is literally incinerated in an incinerator, and many methods are being considered. It is difficult to do so, and there is a high possibility that radioactivity will be transferred into the combustion gas, so there are problems such as the need for special equipment for exhaust gas treatment.

The pyrolysis method is a method of non-oxidizing decomposition by heating to a high temperature with oxygen cut off. For example, a method in which liquid organic waste is sprayed into a furnace and heated to 700°C with water vapor (
JP-A-54-14700) and a method of suspending alkali such as calcium hydroxide in liquid organic waste and decomposing it at an ultra-high temperature of 5000°C (JP-A-57-52900).
etc. are being considered.

The latter method has the advantage of being applicable even to wastes containing phosphorus and halogens, but since it is processed at an ultra-high temperature of 5000°C, the material of the furnace becomes an issue.

Furthermore, both methods have the same problem as the incineration method, in which radioactivity is transferred into the waste gas.

Chemical decomposition method reduces 80% of waste containing phosphorus such as TBP.
This is a method of decomposing it into phosphoric acid, which is an inorganic substance, and a flammable organic compound that does not contain phosphorus by heating it with the above concentrated sulfuric acid at 110 to 150°C (1971 Atomic Energy Society of Japan Annual Meeting J14). However, in this method, the time required for decomposition is long, 10 to 24 hours, and the process of separating the decomposed maple material from phosphoric acid and separately burning it is necessary, making the system complicated.

The recovery and reuse method is a method in which radioactively contaminated liquid organic waste, especially waste solvents, is distilled and purified for reuse.
In the case of a thermally unstable substance such as BP, it is inevitable that a part of it will undergo thermal decomposition, and it is inevitable that radioactivity will remain in the solvent recovered by distillation.

The solidification method is a method in which liquid organic waste is solidified as it is or after adding other substances. Specifically, it is a method in which it is adsorbed on artificial mica and then sintered and solidified at 1000°C (Japanese Patent Laid-Open No. 5
3-143900), a method of solidifying by adding slaked lime and silicate, if necessary, and cement (Japanese Patent Laid-Open No. 54
-8300), a method of melting and solidifying with thermoplastic resin and/or asphalt (Japanese Patent Publication No. 51-12800)
, a method in which a vinyl compound such as styrene is polymerized and solidified together with other powdered radioactive waste or alone with a thermosetting resin such as an unsaturated polyester (Japanese Unexamined Patent Publication No. 50-20200, Publication No. 52-38540) There is a gado.

Among these solidification methods, the sintering solidification method requires a multi-stage process and is laborious, and uses high temperatures, making it difficult to select equipment materials, and also has problems with off-gas processing equipment. The method of solidifying by mixing slaked lime etc. has a problem with the safety of the solidified material, and when cement is used, there is a problem that the amount of solidified material increases, and the water resistance is low, so oozing is likely to occur. There are also problems. The melt-solidification method requires more than twice as many plates of solidifying material as the amount of waste, which actually increases the amount of waste. Moreover, assimilates have disadvantages such as having a specific gravity smaller than 1.0 and poor heat resistance and combustion resistance. Also, the cost is quite high.

In the polymerization solidification method, the organic compounds that are waste products may dissolve the assimilation material or interfere with polymerization, which limits the types of waste that can be treated, and also affects the properties of the solidified material itself. It is considerably inferior to the solidified form of solid waste.

As mentioned above, none of the treatment methods for radioactive liquid organic waste that have been considered to date are appropriate methods.

[Purpose of the invention]

In view of the current situation, the present invention is a method for treating radioactive liquid organic waste, which decomposes the waste almost completely into inorganic substances under mild conditions that are easy to implement. The purpose is to provide such a method.

[Summary of invention]

The present invention relates to a method for decomposing radioactive liquid organic waste, and is characterized in that the waste is decomposed by contacting it with an aqueous solution containing copper ions as a catalyst and hydrogen peroxide as an oxidizing agent. It is something that can be done. By decomposing the liquid organic waste in this manner, the carbon component is finally completely oxidized and decomposed to carbon dioxide and the hydrogen component to water, leaving only inorganic components in the decomposed liquid.

Copper ion involved as a catalyst is 500 to 110,000p
When used as an aqueous solution with a concentration in the range of p, decomposition proceeds rapidly, and the amount is desirably 5 parts by weight or more relative to the waste. As a copper ion source, any compound can be used as long as it is a copper salt that is soluble in water at the concentration mentioned above and completely ionizes in an aqueous solution, but if an organic acid salt is used, its organic group will also decompose. It is not suitable because it becomes a target and decomposes, reducing the decomposition performance for waste. Further, halogen salts are not very suitable from the viewpoint of equipment corrosion. Copper sulfate is most preferred.

Hydrogen peroxide is 100% by weight on the folding material to be treated.
It is desirable that the amount is 10 times or more in terms of H, O, and in particular, to completely decompose TBP and the like, it is desirable to use a set that is 30 times or more. There are two ways to add hydrogen peroxide, such as a batch method in which the required amount is added at once, or a semi-batch method in which continuous addition is performed using a constant flow method. A semi-batch method is suitable for performing the decomposition.

To carry out the decomposition reaction, the liquid organic waste, an aqueous solution containing chloride ions, and hydrogen peroxide are placed in a decomposition tank, mixed (the mixed solution may be an aqueous solution or an emulsion), and thoroughly stirred. The decomposition reaction proceeds due to the heat of reaction without any particular external heating; however, in order to speed up the reaction rate, it is preferable to increase the reaction temperature by external heating, especially in the range of 80 to 10
Preference is given to decomposition at a temperature of 0°C.

The decomposed liquid is obtained as a clear aqueous solution, and after neutralization if necessary, it can be released into the environment depending on its radioactivity level, or it can be used as a normal waste liquid in the same way as high conductivity radioactive waste liquid such as recycled waste liquid. It can be processed in the processing system.

[Embodiments of the invention]

The present invention will be explained by examples.

Example 1 T in an oxidative decomposition tank equipped with an external heater and stirrer
B P 16F and 0.1 mol/l copper sulfate aqueous solution 3
20m/ (Copper ion concentration in solution 6350ppm)
Stir and mix to make it homogeneous and give 90 to 1
The mixture was heated to 00° C., and the evaporated water was refluxed, and 480 μm of hydrogen peroxide solution with a concentration of 60% was continuously added to this solution at a constant rate over 2 hours using a pump. After the addition of the hydrogen peroxide solution was completed, the reaction solution was kept under the same conditions for another 30 minutes, and the reaction solution became a clear homogeneous aqueous solution.
No presence of water-insoluble components was observed. When the total organic carbon content (TOC) in the solution was measured, it was found that 87% of the total carbon content in 1BP before decomposition had decreased, and therefore 87% had been decomposed.

Example 2 A decomposition reaction was carried out under the same conditions as Example 1, except that the amount of hydrogen peroxide added was twice that of Example 1. The amount of TOC in the decomposition solution was 98% of the original volume had been reduced.

〔Effect of the invention〕

As described above, the present invention makes it possible to decompose radioactive liquid organic waste, for which no conventional treatment method has been established, using a simple device and method. Oxidative decomposition according to the present invention ultimately converts the waste into carbon dioxide and water (steam).
Since it decomposes into inorganic substances, only inorganic substances remain in the treated decomposition liquid. Furthermore, since the decomposition reaction of the present invention is carried out at 100°C or lower and does not use corrosive chemicals, there is no need to pay special attention to the material of the equipment, and radioactivity does not scatter or migrate into the generated gas. There's not much to do. Therefore, waste gas treatment does not require any special equipment and can be treated in a normal off-gas system.

Continuation of page 1 @Inventor Rihan Sahara Kawasaki Gravity Inside the laboratory

Claims (6)

[Claims] (1) A method for decomposing radioactive liquid organic waste, which comprises bringing the radioactive liquid organic waste into contact with an aqueous solution containing copper ions and hydrogen peroxide for oxidative decomposition. (2) The decomposition treatment method according to claim 1, wherein the radioactive liquid organic waste is an organic solvent consisting of tributyl phosphate. (3) The decomposition treatment method according to claim 1, wherein the aqueous solution containing copper ions is an aqueous copper sulfate solution. (4) The concentration of copper ions in the aqueous solution is 500 to 11,000.
The decomposition treatment method according to claim 1, wherein the decomposition treatment method is 0pp. (5) The amount of copper ions is 5% for the organic waste to be decomposed.
The decomposition treatment method according to claim 1, wherein the amount is at least % by weight. (6) The decomposition treatment method according to claim 1, wherein the amount of hydrogen peroxide is 10 times or more (Kyofu) in terms of 100% H10 relative to the organic waste to be decomposed. The decomposition treatment method according to claim 1, wherein the oxidative decomposition reaction is carried out at a temperature range of 80 to 100°C.