JPH0552916B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a method for controlling temperature and sulfuric acid concentration, which are reaction conditions, in a chemical reaction for removing sulfuric acid ions in the oxidative decomposition solution of radioactive organic waste as sulfur dioxide. Regarding.

[Technical background of the invention and its problems] One of the ways to treat radioactive waste generated from nuclear power plants is to treat the radioactivity of solid or liquid materials such as used radioactive ion exchange resins and radioactive organic waste solvents used for water purification. There is processing of organic waste. As a treatment method for these wastes, chemical decomposition methods are being considered; for example, so-called acid digestion methods using sulfuric acid and nitric acid, or sulfuric acid and hydrogen peroxide, or ferrous sulfate and ferric sulfate. Alternatively, there is a method of oxidative decomposition with hydrogen peroxide using copper sulfate as a catalyst salt, or a method of oxidative decomposition in water by blowing oxygen or air at high temperature (200°C or higher) and high pressure (40 atmospheres or higher).

Among these methods, in the method of oxidative decomposition with hydrogen peroxide using copper sulfate as a catalyst salt, the copper ions in the decomposition solution are collected on an electrode plate using the principle of electrolysis, and the remaining sulfate ion-containing solution is used with a reducing agent or metallic copper (copper metal). A method is being considered in which the sulfuric acid component is decomposed by contacting it with metallic copper (using metallic copper on an electrode plate) and removed as sulfur dioxide. This is shown in the following equation when metallic copper is used.

Cu＋2H ₂ SO ₄ →CuSO ₄ ＋SO ₂ ↑＋
2H ₂ O Generally A (aqueous solution) + B (solid) → C↑ (gas) +
In the reaction D↓ (precipitation), products C and D exit the reaction system as gas and precipitate, respectively, so as the reaction progresses, the concentration of reactant A gradually decreases, and The reaction rate also decreases accordingly. This is shown in FIG. FIG. 2 shows the change in the decomposition rate of sulfuric acid with the passage of reaction time, and the broken line in the figure shows the decomposition rate when the reaction is carried out without heating. In this case, the reaction rate decreased because the sulfuric acid concentration in the reaction solution decreased, and the decomposition rate of sulfuric acid decreased. On the other hand, the solid line represents the case of the present invention, which was carried out while controlling the reaction conditions by the method described below.

In order to prevent this reduction in reaction rate, it is necessary to evaporate water by heating to prevent a reduction in the concentration of the reactants. However, when the increase in concentration due to heating exceeds the decrease in concentration as the reaction progresses, the concentration of the reactant increases and exceeds the optimum range. Therefore, it is necessary to control both temperature and concentration to control the reaction system.

In the reaction (1) above, the decomposition conditions for the sulfuric acid component are said to be preferably a temperature of 150° C. or higher and a sulfuric acid concentration of about 70% or higher, but it is difficult to continuously measure such a high sulfuric acid concentration.

On the other hand, equipment materials for reaction vessels used under such conditions are limited, and metal materials are used exclusively in the field of nuclear energy, so it is undesirable for the sulfuric acid concentration to increase too much, and it is preferable within a certain range. It is desirable to keep it to around 70%.

From the above, in the above reaction, it is strongly desired to control the sulfuric acid concentration within a certain range, although it is difficult to continuously measure the sulfuric acid concentration.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to heat and concentrate the oxidized decomposition solution of radioactive organic waste in the presence of a reducing agent or metallic copper, and to concentrate the oxidized decomposition solution in the decomposition solution. An object of the present invention is to provide a method in which temperature and sulfuric acid concentration can be simultaneously controlled in a reaction for converting a sulfuric acid component into sulfur dioxide.

[Summary of the Invention] The present invention provides a method for producing radioactive organic waste by subjecting an oxidative decomposition solution of radioactive organic waste to a heating reaction in the presence of a reducing agent or metal copper to decompose the sulfuric acid component in the decomposition solution into sulfur dioxide. In the processing method of
The method is characterized in that the reaction solution is heated to boiling, the boiling point is measured, and dilution water is injected so that the measured temperature value is always within the approximate range of the boiling point corresponding to the optimum concentration of the reaction solution. Concerning a method for disposing of radioactive organic waste.

In the present invention, the reason why the reaction temperature and sulfuric acid concentration can be controlled simultaneously by maintaining the boiling point of the reaction solution at a constant value will be explained below.

As mentioned above, the temperature conditions for the sulfuric acid decomposition reaction in the present invention are 150°C or higher, and the sulfuric acid concentration in the reaction solution is 70°C.
%, but such conditions are close to the boiling point conditions of the reaction solution in this reaction. In other words, the boiling point curve of sulfuric acid is shown in Figure 3. For example concentration
The boiling point of 70% sulfuric acid is approximately 164°C, as shown by the dotted line in FIG. If the concentration increases beyond this, the boiling point will also increase. Therefore, when the boiling point reaches this temperature, by injecting dilution water to maintain the boiling point at this temperature, the sulfuric acid concentration will be maintained at about 70% at the same time as the temperature.

[Embodiments of the invention] An embodiment of the present invention will be described with reference to FIG.

In FIG. 1, a reactor 1 is equipped with a stirrer 2, a heater 3, a temperature sensor 4, and a condenser 5. Reaction liquid (sulfuric acid aqueous solution) in reaction vessel 6
reacts with reactant (metallic copper) 7 to produce sulfur dioxide, water and copper sulfate 8. Sulfur dioxide and water exit the system via the condenser 5 as gases. The reactor 1 is constantly heated by a heater 3, and the temperature of the reaction liquid is constantly detected by a temperature sensor 4. As the reaction and heating proceed, the temperature of the reaction liquid rises, and when it exceeds the set boiling point temperature, the dilution water injection pump 10 is activated under the supervision of the controller 9 based on the temperature signal from the temperature sensor 4. Start up and pour diluent 1 from dilution tank 11.
2 is injected into reactor 1. By injecting this dilution water 12, the concentration of the reaction liquid 6 is lowered and the temperature is also lowered. If the temperature sensor 4 detects a temperature lower than the set temperature, the dilution water injection pump 1 is activated by the controller 9.
0 stops. By repeating these operations, the reaction temperature and sulfuric acid concentration can be maintained at predetermined values.

FIG. 4 is a graph comparing the case where the temperature of the reaction solution was controlled by the above method and the case where such control was not performed. As is clear from FIG. 4, in the case of the present invention, the temperature of the reaction solution is controlled to be constant, and the reaction proceeds under conditions of a constant sulfuric acid concentration. On the other hand, if the method of the present invention is not adopted,
The temperature of the reaction solution increases, water evaporates, and the sulfuric acid concentration increases, creating unstable reaction conditions and affecting the equipment materials.

[Effects of the Invention] As explained above, according to the method of the present invention, the boiling point of the reaction solution is maintained at a predetermined value by measuring the temperature of the reaction solution. Concentration can also be controlled.
Therefore, when decomposing the sulfuric acid component in the oxidative decomposition solution of radioactive organic waste, the sulfuric acid concentration can be controlled by measuring only the temperature, and the reaction can proceed efficiently.

Further, by controlling the temperature and the sulfuric acid concentration in this way, it is possible to avoid these abnormal increases, and therefore it is also possible to prevent adverse effects on the materials of the reactor.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus showing an example of an apparatus for carrying out the method of the present invention, and Fig. 2 shows changes in the sulfuric acid decomposition rate with the passage of reaction time, in the case without heating and in the case of the present invention. Figure 3 is a graph showing the relationship between the concentration of sulfuric acid and boiling point. Figure 4 is a comparison between when the temperature of the reaction solution is controlled according to the present invention and when it is not controlled. 2 is a graph showing changes in reaction temperature. 1... Reactor, 3... Heater, 4... Temperature sensor, 6... Reaction liquid, 7... Reactant, 9... Controller, 10... Dilution water injection pump, 11... Dilution water tank .

Claims (1)

[Claims] 1. In a method for treating radioactive organic waste, which comprises subjecting an oxidative decomposition solution of radioactive organic waste to a heating reaction in the presence of a reducing agent or metallic copper to decompose the sulfuric acid component in the decomposition solution into sulfur dioxide, the reaction solution is heated to boiling point, and the boiling point is measured and controlled by injecting dilution water so that the measured temperature value is always within the approximate range of the boiling point corresponding to the optimum concentration of the reaction solution. How to dispose of organic waste.