JPS62192699A - Method of decomposing and processing radioactive water organic solvent - 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 [Object of the Invention] (Industrial Application Field) The present invention mainly relates to a method for decomposing radioactive waste organic solvents generated from spent nuclear fuel reprocessing facilities.

(Prior art) In nuclear power generation, in order to effectively utilize fuel resources, spent nuclear fuel is reprocessed to separate useful components such as uranium and plutonium from fission products, which are unnecessary components.
It is being reused as nuclear fuel. A common method for this reprocessing is to dissolve spent nuclear fuel in nitric acid and perform liquid-liquid extraction of the nitric acid solution with an organic solvent to separate and recover uranium and plutonium (PUREX method).

In this method, a phosphoric acid ester such as tri-n-butyl phosphate (TBP>) and an aliphatic hydrocarbon such as n-dodecane as a diluent are used as an organic solvent for extraction at a 3N (volume ratio).
A mixed solvent in a certain ratio is generally used. The uranium, J: and plutonium extracted with this mixed solvent are then back-extracted with diluted nitrate water, concentrated and processed. On the other hand, used waste solvents are radioactively contaminated and deteriorated due to radiation damage, and are disposed of as waste (waste solvents). The method for processing this used waste organic solvent is as follows:
Conventionally, two types of methods have been known as shown below.

■ A method in which the used waste organic solvent is treated with live phosphoric acid to separate it into an organic phosphate ester component and a diluent component, the former is then thermally decomposed, and the latter is reused or incinerated. (ET
R-287, (1980)) ■ A method in which both components are separated by a method similar to ■, and the separated phosphate ester component is directly solidified with asphalt or a thermoplastic resin. (K.F.
K-2212゜However, among the above two techniques, in the case of thermal decomposition method (①), anhydrous phosphoric acid and hydrocarbons are produced by decomposition, or the former may corrode the equipment materials, while the latter may cause condensation.・There is a problem that post-processing operations such as oil/water separation and incineration are required, making the process complicated.

Also, in the case of solidification method (■), waste (
Since it is not possible to increase the amount of mixed waste solvent (waste solvent), there are problems in that the volume reduction property is low and the properties of the solidified product are considerably worse than in the case of a solidified product of solid waste.

Based on the above background, the inventors have discovered that radioactive waste T
We proposed a wet oxidative decomposition treatment method for waste organic phosphate ester solvents such as AP or mixed organic solvents containing these (Japanese Patent Application No. 58-169205N and Japanese Patent Application No. 58-2125).
No. 92). These methods decompose the waste solvent into inorganic substances such as water, carbon dioxide, and phosphoric acid using hydrogen peroxide as an oxidizing agent in an aqueous solution of copper (II) salt (copper sulfate or phosphorus). It's a method.

However, even with these wet oxidation decomposition methods, there is a problem that the decomposition solution cannot be reused and becomes secondary waste when copper sulfate is used as a catalyst, while the method using phosphorus as a catalyst produces phosphorus. Since the image tone is insoluble in water, it must be used as a dilute phosphoric acid solution, so this phosphoric acid acts as a hydrogen peroxide stabilizer (hydrogen peroxide decomposition inhibitor) and removes the peroxide necessary for the reaction. There is a problem in that a very large amount of hydrogen water is required, resulting in high costs.

(Problems to be Solved by the Invention) The problems to be solved by the present invention are as follows: In a method for decomposing a radioactive waste organic solvent by wet oxidation decomposition of a radioactive waste organic solvent using an oxidizing agent, the required amount of the oxidizing agent is The aim is to reduce the amount of secondary waste generated.

[Structure of the Invention] (Means for Solving the Problems) The present invention solves the above problems by bringing a radioactive waste organic solvent into contact with an oxidizing agent in water in the presence of a copper oxide catalyst.

The waste solvents that are subject to oxidative decomposition in the present invention include:
Examples include the aforementioned organic phosphate esters, hydrocarbons, mixed solvents of both, and other arbitrary solvents, but among these, earth acids are also representative after being used in reprocessing by the Purex method. Waste TBP as waste extraction solvent
, and a waste mixed solvent consisting of TBP and its diluent n-dodecane.

Further, as the oxidizing agent, hydrogen peroxide, oxygen gas, oxygen mixed gas, etc. can be used. In the case of hydrogen peroxide, it is preferable to carry out the reaction under atmospheric pressure and at a temperature of about 80 to 100°C. Temperature 200 for oxygen gas or oxygen mixed gas
It is preferable to cause the reaction by blowing high-temperature, high-pressure gas at a temperature of about 300° C. and a pressure of 20 to 1100 at into water.

Copper oxide used as a catalyst is insoluble in water, but may be used after being suspended in water. Copper oxide in any shape can be used, but it is most preferably in the form of fine powder because it has a large surface area and the reaction system can be effectively homogenized by stirring.

(Function) In the present invention, when the radioactive waste organic solvent is brought into contact with an oxidizing agent in water in the presence of a copper oxide catalyst, the radioactive waste organic solvent is easily oxidized and decomposed.

For example, when hydrogen peroxide is used as the oxidizing agent, ON radicals are generated by the catalytic action of copper oxide in the reaction system, and the waste solvent is oxidized and decomposed by these 0* radicals.

When a radioactive waste organic solvent is oxidized and decomposed, carbon dioxide and water are produced in the case of a hydrocarbon solvent, and phosphoric acid is also produced in the case of an organic phosphate ester such as a TBP solvent.

When the TBP solvent is oxidatively decomposed, part or all of the phosphoric acid produced reacts with part or all of the copper oxide catalyst present in the system due to the action of the oxidizing agent to form a phosphorus tone,
It dissolves in a decomposition solution containing phosphoric acid to form a homogeneous aqueous solution. Therefore, the composition of the oxidative decomposition solution of the organic solvent containing TBP is a dilute phosphoric acid aqueous solution with a phosphor effect, which is used to oxidize and decompose TBP using the previously proposed dilute phosphoric acid aqueous solution with a phosphor effect as a catalyst. The composition is the same as that of the decomposition liquid in the method, and it can be reused as the catalyst liquid in the method.

When a hydrocarbon solvent such as n-dodecane is partially oxidized and decomposed, the decomposition products are only carbon dioxide and water, and therefore the copper oxide used as a catalyst remains unreacted as a precipitate.

(Example) The present invention will be described in detail.

Example 1 In an oxidative decomposition tank equipped with an external heater and stirrer, 320 d of pure water, 18.5 g of TBP and 1.0 g of copper oxide powder
g (0,054g/91BP, converted to copper amount 0.0
43! ? /gTBP> were heated to 100° C. while thoroughly stirring and mixing the mixture to be uniform. The moisture that evaporates at this time is refluxed into the reaction solution using a water-cooled condenser. Next, add 35% hydrogen peroxide solution to this mixture.
30 ml was added continuously using a pump at a constant rate over 2 hours.

After the addition of the hydrogen peroxide solution was completed, the reaction solution was kept under the same conditions for an additional hour, and a pale blue, transparent, homogeneous aqueous solution was obtained. When the total organic carbon content (TOC) in the decomposed solution was measured, it was found to be 1/10 of the total carbon content in the TBP originally used.
In other words, it was confirmed that the decomposition rate using TOC as an index was 90% or more.

Comparative Example 1 0.033 mol/2 of 25% phosphoric acid solution with phosphor tone
20rd (metallic copper ions in the liquid: 2.049.0.
127 g/g TBP) was used as the catalyst solution, and
The oxidative decomposition of 16 g of TBP was carried out using twice the amount of hydrogen peroxide as an oxidizing agent as in Example 1.

The final TOC decomposition rate of the decomposition liquid in this case was 90%, which is almost the same as in Example 1.

Comparative Example 2 Using the same phosphoric acid solution catalyst as in Comparative Example 1,
The amount of hydrogen peroxide used was the same as in Example 1, 330 Inl.
An attempt was made to oxidize and decompose 16g of TBP.

However, the organic phase remained in the liquid after the reaction was completed, and it was separated into two phases. Therefore, it was revealed that TBP was not decomposed under these reaction conditions.

Example 2 Under exactly the same conditions as Example 1, TBP was used instead of TBP.
Oxidative decomposition was performed using a mixed solvent of /n-dodecane = 9/1. The decomposition liquid was a homogeneous and transparent aqueous solution as in Example 2, and the TOC decomposition rate was 90% or more.

Example 2
The test was carried out under the same conditions using a 70-fold scaled-up amount. The final TOC decomposition rate of the decomposition solution was 90%.

As shown in the above eight examples, in the case of decomposition of TBP, when phosphorus is used as a catalyst, the amount of catalyst is at least 0.1279 per 1.0 g of TBP in terms of copper ions.
required. On the other hand, when copper oxide according to the invention is used as a catalyst, 0.0.
Even with a copper amount of 0439, sufficient decomposition was possible.

In this case, the catalytic copper loss is 0.064g/gT B P (
If the amount is less than 0.05 mol/R, all of the catalytic copper oxide used becomes phosphorous and dissolves in the liquid, but if more than that is used, the excess copper becomes hydrocarbons such as n-dodecane. As in the case of the decomposition of other substances, it remains unreacted as a precipitate.

Regarding hydrogen peroxide required for decomposition, when the target waste solvent is only TBP, hydrogen peroxide is 30% per 1.03 sample in a method using a copper phosphate catalyst as a catalyst.
% aqueous solution requires 12'Om1 or more, but in the method using copper oxide as a catalyst according to the present invention, this is 607! can be reduced to

As described above, the decomposition treatment method of the present invention can reduce the amount of chemicals used compared to the conventional method of using phosphorus as a catalyst, reducing costs and reducing the amount of waste solvent used. It is excellent in both size and capacity.

In addition, as mentioned above, when TAP is oxidatively decomposed in the present invention, the decomposed solution is a dilute phosphoric acid solution in a phosphorescent style, so this can be used as is, or after being concentrated, as a new waste organic solvent It can be reused as a catalyst liquid during the oxidative decomposition of

Roughly speaking, if the copper ions dissolved in the oxidized decomposition solution of the present invention are separated and recovered as metallic copper by some method, the recovered metal shell will contain almost no radioactivity. It is also possible to reuse it as a catalyst in a new decomposition reaction. Although any method can be used to separate and recover copper ions, electrolysis is the most suitable method because it generates little secondary waste, is easy to operate, and is low cost. be. This can be carried out, for example, by using platinum as an anode and copper, graphite, etc. as a cathode, and applying a DC voltage of about 3 V between the two electrodes. As a result, copper ions dissolved in the decomposition solution are easily deposited as metallic copper on the surface of the cathode plate and recovered. This step of separating, recovering, and reusing copper can be repeated any number of times, so it becomes possible to decompose a large amount of waste solvent with a small amount of copper used for two reactions.

Note that the oxidized decomposition solution after recovering copper can be reused as a separation agent for waste organic solvents as described in the section of the prior art. If the radioactivity level is high and reprinting is difficult, evaporate the water after adjusting H as necessary, and add a solidifying agent to the solid residue to assimilate and stabilize it. In this case, since the copper is solidified after being recovered from the decomposition liquid, it is expected that the volume reduction will be even greater than the method in which the decomposition liquid is solidified as it is. be done.

On the other hand, as mentioned above, in the case of oxidative decomposition of hydrocarbon solvents, etc., the copper oxide used as a catalyst remains unchanged as a precipitate, so this is filtered and collected, and after washing, it becomes a new waste solvent. It can be reused as a catalyst in the oxidative decomposition reaction of

[Effects of the Invention] As described above, according to the present invention, radioactive waste organic solvent, for which no effective treatment method has been established, can be easily oxidized and decomposed into inorganic substances under mild conditions using a simple device. can do. Moreover, the present invention has the advantage that the amount of copper catalyst and stimulant required are both small compared to the wet oxidative decomposition methods proposed so far.

Furthermore, the decomposition liquid produced by the decomposition process of the present invention can be reused as it is or after being concentrated as a separating agent or catalyst for radioactive waste organic solvents. The amount generated can be significantly reduced.

(8733) Agent Patent Attorney Yoshiaki Inomata (Baka
1 person)

Claims (4)

[Claims] (1) A method for decomposing a radioactive waste organic solvent, which comprises bringing the radioactive waste organic solvent into contact with an oxidizing agent in water in the presence of a copper oxide catalyst. (2) Claim 1 in which the radioactive waste organic solvent is an organic phosphate ester, a hydrocarbon, or a mixed solvent of both.
A method for decomposing radioactive waste organic solvents as described in Section 1. (3) Using hydrogen peroxide as an oxidizing agent at a temperature of 80 to 10
A method for decomposing a radioactive waste organic solvent according to claim 1, which is carried out at 0° C. and atmospheric pressure. (4) The method for decomposing a radioactive waste organic solvent according to claim 1, which is carried out at a temperature of 200 to 300°C and a pressure of 20 to 100 atmospheres using oxygen or a mixed gas containing oxygen as an oxidizing agent.