JP3143855B2 - How to treat flame retardant waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing and treating a flame retardant waste containing a radioactive substance or a flame retardant waste contaminated with a radioactive substance.

[0002]

2. Description of the Related Art Nuclear facilities such as nuclear power plants generate a large amount of flame-retardant waste such as used ion-exchange resin obtained by treating radioactive waste. If you try to reduce the volume by burning this kind of flame-retardant waste directly in an incinerator,
It is virtually impossible to incinerate flame-retardant waste because the incinerator is damaged by the burning heat. Therefore, a method of solidifying flame-retardant waste with cement has been generally adopted. However, this method has a problem in volume reduction since the volume after cement solidification is increased by 5 times the original volume.

In order to solve this problem, a mixture of water and a used ion-exchange resin which has been treated with radioactive waste is heated under a condition of a so-called supercritical state at a temperature of 374 ° C. or more and a pressure of 215 atm or more. There has been proposed a method for treating radioactive waste in which the volume of the ion exchange resin is reduced (Japanese Patent Laid-Open No. 61-16569).

[0004]

Although radioactive wastes such as ion exchange resins can be reduced in volume by this method,
In order to completely decompose the ion exchange resin, there was a problem that the reaction time had to be extended. In addition, there is a possibility that the decomposed organic matter may remain in water as a solvent, and in this case, there is a problem in that waste liquid treatment becomes more difficult. An object of the present invention is to provide a method for treating flame-retardant waste, which simplifies the treatment process and reduces the amount of waste after treatment by quickly decomposing or burning the flame-retardant waste. . Another object of the present invention is to provide a method for treating flame-retardant waste, in which decomposed organic matter does not remain in water and waste liquid treatment is easy.

[0005]

The invention according to claim 1 is
As shown in FIG. 1, a step of preparing flame retardant wastes 10 and 13 containing a high-molecular organic compound containing a radioactive substance into a slurry 15 using water 14 as a dispersion medium, and converting the slurry 15 to a subcritical state or a supercritical state. And put the above flame retardant waste 10,1
3, a hydrolysis step of hydrolyzing 3 into light oil 21 and other heavy oils and solids 22, a step of separating light oil 21 decomposed in this decomposition step from heavy oils and solids 22, A step of incinerating the oil 21, a supercritical cracking step of adding oxygen or air to the remaining heavy oil and solid 22 to make the heavy oil and solid 22 supercritical and self-burning, A step of solid-liquid separating a residue after burning in the step to obtain a radioactive metal oxide 30 and water 31 separately.

The subcritical state in the above decomposition step is 200
374 ° C. and a pressure of 160-215 kg / cm ² , and the supercritical state in the decomposition step is 374-4
A temperature of 00 ° C. and a pressure of 215 to 300 kg / cm ² . The supercritical state in the supercritical decomposition step is 37.
A temperature of 4 to 600 ° C. and a pressure of 215 to 500 kg / cm ² . When the slurry is brought into a subcritical state or a supercritical state in the decomposition step, the physical properties of water as a dispersion medium are remarkably changed to become supercritical water, and the polymer organic compound of the slurry component and the supercritical water become a homogeneous phase. This supercritical water has a larger ionic product and a lower dielectric constant than liquid water, so that the hydrolysis reaction of the high molecular weight organic compound contained in the flame retardant waste is promoted. The light oil separated in the separation process is incinerated in a normal incinerator, and if the remaining heavy oil and solids are brought into a supercritical state by adding oxygen or air in a supercritical cracking process, high-speed oxidation, that is, self-combustion, occurs. As a result, wastewater (residue) is obtained in which solids precipitate while generating CO ₂ gas. When this residue is separated into solid and liquid by filtration or centrifugation, a radioactive metal oxide and wastewater are obtained separately.

The invention according to claim 2 is the invention according to claim 1, wherein the flame-retardant waste 10 containing a high-molecular organic compound containing a radioactive substance is contaminated with radioactive organic carbon. After the organic carbon is removed by contacting the contaminated flame retardant waste 10 with supercritical CO ₂ , the decontaminated flame retardant waste 13 is prepared into a slurry 15 using water 14 as a dispersion medium. This is a method of treating in a decomposition step. This supercritical state is at a temperature of 40-80 ° C and 150-350k
g / cm ² . When the flame retardant waste is contaminated with radioactive organic carbon, the radioactive organic carbon is easily removed by bringing the flame retardant waste into contact with supercritical CO ₂ .

[0008] The invention according to claim 3 is the invention according to claim 1 or 2, wherein the heat of combustion generated during self-combustion in the supercritical decomposition step is used as a heat source in the decomposition step for the treatment of flame-retardant waste. Is the way. By utilizing the combustion heat generated during self-combustion in the supercritical decomposition step as a heat source in the decomposition step, the amount of heat energy newly supplied in the decomposition step can be reduced.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. As shown in FIG. 1, a flame retardant waste 10 contaminated with radioactive organic carbon is brought into contact with supercritical CO ₂ . Here, as the compound containing radioactive organic carbon, formic acid, acetic acid, lower alcohol and the like having C (carbon) having a mass number of 14 can be mentioned. Examples of the flame retardant waste 10 include a flame retardant waste such as a used ion exchange resin obtained by treating a radioactive waste in a nuclear power plant. The contact is performed by placing the flame-retardant waste 10 in a pressure-resistant supercritical decomposition vessel 11 and then storing the CO ₂ stored in a high-pressure cylinder 12.
This is performed by blowing gas. The container 11 is maintained in a supercritical state at a pressure of 150 kg / cm ² and a temperature of 40 ° C., for example. After a lapse of about 10 to 30 minutes, the radioactive organic carbon is removed by the supercritical CO ₂ , and the decontaminated flame-retardant waste 13 is obtained. The flame-retardant waste 13 and water 14 are mixed to prepare a slurry 15 having a concentration of about 10%. When the flame-retardant waste is not contaminated with radioactive organic carbon, the flame-retardant waste and water are immediately mixed into a slurry without decontamination with supercritical CO ₂ .

After storing the slurry 15 in a slurry storage tank 16, a high-pressure pump 17 is used to disassemble the heat-resistant and pressure-resistant decomposition vessel 1.
To 9 At the same time, water 14 for hydrolyzing the flame retardant waste 13 is supplied. Here, PVC is used as the flame retardant waste 13.
NaOH, KO when a chlorine compound such as
An aqueous alkaline solution 18 such as H is added. This is to neutralize the reaction during decomposition and to make the wastewater neutral. The container 19 has, for example, a pressure of 300 kg / cm ² and a temperature of 400 kg / cm ² .
It is maintained in a supercritical state of ° C. After about 10 to 30 minutes, about 80% by weight or more of the flame retardant waste 13 is hydrolyzed by the supercritical water. The aqueous solution after the reaction has a brown color, and a small amount of oil (light oil) is phase-separated. This aqueous solution is sent to a separator 20 where it is separated into a light oil 21 and other heavy oils and solids 22 when the pressure is reduced. The heavy oil content and the solid content are less than about 20% by weight of the flame retardant waste 13.
The light oil 21 is incinerated in a normal incinerator 23.

After storing the heavy oil component and the solid component 22 in a storage tank 24, the heavy oil component and the solid component are placed in a heat-resistant and pressure-resistant supercritical cracking vessel 25. In order to promote these combustions, it is preferable to add a hydrogen peroxide solution 26 as a source of oxygen to the heavy oil component and the solid component in advance. Air 28 is pumped into the container 25 by the compressor 27. Although not shown, O ₂ gas stored in a high-pressure cylinder may be blown instead of adding the hydrogen peroxide solution. The container 25 is maintained in a supercritical state at a pressure of, for example, 300 kg / cm ² and a temperature of 400 ° C., similarly to the container 19. After two minutes, heavy oil and solids are self-burned and decomposed by O _{2 in} a supercritical state. The heat generated by the self-combustion is used as a heat source in a decomposition step for hydrolysis of the first flame-retardant waste 13 via a heat medium. The aqueous solution after the heavy oil component and the solid component are self-burned and decomposed is colorless and transparent, and has no oil component. The aqueous solution is sent to a separator 29 where the pressure is reduced, and solid-liquid separation such as filtration or centrifugation is performed to separate the aqueous solution into a radioactive metal oxide 30 and wastewater 31. The CO ₂ gas generated by the reaction is released to the atmosphere. The waste water 31 is subjected to a waste water treatment 32, a part of which is used for hydrolysis of the flame-retardant waste 13, and the rest is discharged.

[0012]

As described above, according to the present invention, a flame-retardant waste such as a used ion-exchange resin which has been treated at a nuclear facility and which has been treated with a radioactive waste is efficiently decomposed or processed in a short time. Can be burned. Since the processing time is short, the size of the apparatus itself can be reduced, and furthermore, since the processing efficiency is good, an excellent effect that little secondary waste is generated is exhibited. There is also an advantage that the decomposed organic matter does not remain in the water and the waste liquid treatment is easy.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a method for treating flame-retardant waste according to the present invention.

[Explanation of symbols]

 10,13 Flame retardant waste 14,31 Water 15 Slurry 21 Light oil 22 Heavy oil and solid content 30 Radioactive metal oxide

Continued on the front page (72) Inventor Shinichi Hasegawa 6-headed Mukoyama, Naka-machi, Naka-machi, Ibaraki Prefecture 1414 Mitsubishi Materials Corporation Naka Energy Research Laboratory (72) Inventor Akira Tanaka, Naka-machi, Naka-machi, Ibaraki Prefecture 6-headed character at 1002 14 Naka Energy Research Laboratory, Mitsubishi Materials Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) G21F 9/30

Claims (3)

(57) [Claims] 1. A step of preparing a flame retardant waste (10, 13) containing a high molecular organic compound containing a radioactive substance into a slurry (15) using water (14) as a dispersion medium; A subcritical or supercritical state to hydrolyze the flame-retardant waste (10, 13) into light oil (21) and other heavy oils and solids (22); Separating the light oil (21) decomposed in the above from the heavy oil component and the solid component (22); incinerating the separated light oil component (21); and the remaining heavy oil component and the solid component (22). A supercritical cracking step of adding oxygen or air to the heavy oil component and the solid component (22) in a supercritical state by self-burning, and solid-liquid separation of the residue after burning in the supercritical cracking process A method for treating flame-retardant waste, comprising the steps of separately obtaining a radioactive metal oxide (30) and water (31). 2. The flame-retardant waste (10) containing a high-molecular-weight organic compound containing a radioactive substance is contaminated with radioactive organic carbon, and the flame-retardant waste (10) contaminated with the radioactive organic carbon is brought into a supercritical state. after removal of the organic carbon by contacting the CO _2, wherein the treatment with decomposition step to prepare flame retardant wastes the decontamination (13) the slurry (15) to a dispersion medium of water (14) Item 1
The method for treating the flame-retardant waste described in the item. 3. The method for treating a flame-retardant waste according to claim 1, wherein the heat of combustion generated during self-combustion in the supercritical decomposition step is used as a heat source in the decomposition step.