JPH077098B2 - Radioactive liquid waste treatment equipment - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a treatment apparatus for radioactive liquid waste containing metal ions, and more particularly to removing metal ions suitable for a series of treatment apparatuses for oxidative decomposition of radioactive waste. The above-mentioned processing method for

[Technical background of the invention and its problems]

Although various solid or liquid radioactive organic wastes are generated at radioactive material handling facilities such as nuclear power plants,
At present, most of them are still in a fluid state because the final disposal method has not been established.For example, used ion-exchange resin and filter sludge, which are solid waste, are stored and stored in tanks as they are, and radioactive waste Volume reduction is an urgent and important issue. Since a large amount of radioactive organic waste such as used io-exchange resin is generated especially in solid waste, reducing the volume of this greatly contributes to the reduction of the amount of waste.

By the way, since radioactive organic waste is an organic polymer substance and can be decomposed in terms of chemical structure, conventional methods for volume reduction include dry incineration method, wet incineration method, thermal decomposition method, and chemical decomposition method. However, there are various problems as follows.

First of all, the dry incineration method is a method of incinerating waste as it is in an incinerator, and many methods are being studied or developed, but it is necessary to control the heat quantity and pretreatment, so operation There is a problem that the equipment becomes complicated. In addition, scattering of incinerated ash from the incinerator and harmful gas (SO _X , NO
_X ), etc., and it is necessary to take measures against them, including measures against radioactivity and equipment materials, and there are also problems such as migration of nuclides because radioactive substances are processed at high temperatures. With difficulty.

The wet incineration method involves waste in aqueous solution or in aqueous copper sulfate solution.
This is a method in which oxygen or air is fed under high temperature and high pressure of 20 to 100 atm and 200 to 300 ° C. for combustion, but there is a drawback that the volume reduction rate is inferior to that of the dry incineration method.

Pyrolysis is a method of thermally decomposing waste by cutting off the supply of oxygen, and it is generated compared to dry incineration because it decomposes radioactive organic waste at high temperature under an inert gas atmosphere. It has an advantage that the amount of dust is small. However, this method requires an additional step of burning cracked gas and has the problem of migration of radionuclides as in the case of the dry incineration method.

The chemical decomposition method oxidizes and decomposes waste resin by a chemical reaction with a drug, and the following methods have been studied.

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

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

The metal ions present in the oxidative decomposition liquid decomposed by the method of (1) are deposited and separated by electrolytic reaction to thereby facilitate the subsequent handling of the treatment liquid.

Using copper ions as a catalyst salt in the oxidative decomposition process targeting the used ion exchange resin by the method described above, the metal ions present in the oxidative decomposition liquid are separated by electrolysis to separate the metal, and then the treatment liquid is concentrated. A method of decomposing the sulfuric acid component in the treatment liquid by contacting it again with metallic copper (which may be copper on the electrode plate) at high temperature.

However, since the method of (1) handles strong acids and oxidizers at high temperatures, it has the drawback that the selection of equipment materials is very strict and that metal ions remain as they are.

In the method (1), the type of radioactive waste that can be decomposed by the existing metal ions may be limited, and the volume reduction effect is diminished by the added metal salt.

Although the metal ion is recovered by the method of 1, the recovered metal ion remains as a metal waste, and the anion of the metal salt remains as an acid in the treatment liquid, so that there is a problem that the volume reducing property is not improved so much. .

In this method, the metal salt (copper sulfate) can be reused as a catalyst to be added, and the acid generation due to the presence of the sulfone group in the resin can be further decomposed, so that the volume reduction property is greatly improved. . However, in this method, the metal ions are deposited in layers on the electrode on the flat plate, so there is a limit to the electrode area in the electrolytic cell volume, and the thickness of the deposited layer tends to vary. It is difficult to control.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object thereof is to efficiently recover metal ions from a radioactive liquid waste containing a metal ion obtained by oxidative decomposition of a radioactive organic waste at a high recovery rate. The purpose is to recover the radioactive organic waste in a form that can be easily reused for oxidative decomposition.

[Outline of Invention]

That is, the present invention comprises a liquid rectifying section having an inlet for introducing a radioactive liquid waste containing metal ions, and an electrolytic cell section installed above the liquid rectifying section via a dispersion plate, The tank part is the container wall that also serves as the collector of the negative electrode,
A lid that also functions as an electrode installed on the upper part of the container wall via packing, an anode fixed to this lid and installed in the central part of the electrolytic cell section, and a membrane installed around this anode with a space. And a conductive powder that does not pass through the film and is contained between the film and the container wall, and a discharge nozzle for discharging the conductive powder having a metal deposited on the surface of the container wall. And a radioactive liquid waste treatment apparatus.

The radioactive liquid waste containing metal ions to be treated by the treatment apparatus of the present invention is, for example, one obtained by reacting radioactive waste with hydrogen peroxide in the presence of a metal salt as a catalyst to undergo oxidative decomposition, and its representative The typical one is a cation or anion exchange resin used for the treatment of radioactive waste liquid in a nuclear power plant by oxidative decomposition. As the catalyst, for example, ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate, iron typified by copper sulfate, copper, cobalt,
Examples thereof include salts of metals such as nickel, lead, manganese, chromium and cerium.

In the above-mentioned oxidative decomposition reaction, the carbon component and hydrogen component in the ion exchange resin are oxidized and removed mainly as carbon dioxide and water vapor, and the remaining oxidative decomposition liquid is the sulfate ion decomposed by the sulfur-containing component and the metal salt of the catalyst. Alternatively, it is a transparent liquid containing metal ions and the like adsorbed by ion exchange. A method of injecting an oxygen-containing gas under heat and pressure (about 200 to 300 ° C., 20 to 100 atm) instead of oxidative decomposition with hydrogen peroxide is also possible. Become.

The conductive powder used in the present invention is preferably carbon particles, but any conductive powder that can serve as a cathode may be used, for example, a powder of copper, platinum, or the like is used.

Further, as the material of the container wall also serving as the current collector of the anode and the negative electrode used in the present invention, any of the anode material and the cathode material conventionally used in the electrolytic cell can be used, and among them, in the radioactive waste liquid. Those that can be used in are suitable. Examples of the anode include platinum, carbon, lead, and various metal materials (for example, iron, iron alloys, copper, lead, carbon, etc.) to which platinum is attached, and the like. On the other hand, cathode materials include carbon, platinum, corrosion resistant alloys, stainless steel (depending on the properties of the waste liquid), titanium, iron with platinum, lead with platinum, etc. Of these, those having good workability are preferable.

Example of Invention

 Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view of a radioactive liquid waste device which is an embodiment of the present invention. As shown in FIG. 1, the processing apparatus is configured to have a liquid rectifying section 1 below and an electrolytic cell section 2 above, and a dispersion of a perforated plate or the like is provided between the liquid rectifying section 1 and the electrolytic cell section 2. Board 3
Is installed. The liquid introducing port 4 is installed at the bottom of the liquid rectifying unit 1, while the electrolytic bath unit 2 is made of a stainless steel container wall 5 acting as a current collector of the negative electrode, and a platinum installed in the center. Of the anode 6, a membrane 7 that is placed around the anode 6 and is impermeable to the conductive powder, and a lid 8 that also serves to fix the electrode. A voltage is applied between the lid 8 and the container wall 5. A packing 9 that also serves as insulation is inserted between the two. The electroconductive powder 10 exists in a floating state inside the electrolytic cell unit 2 (only part of which is shown in the drawing), an overflow pipe 11 is installed in the upper part, and a discharge nozzle 12 is installed in the lower part.

When electrolytically treating a liquid radioactive organic waste with the above-mentioned treatment apparatus, first, a waste liquid is introduced through the treatment liquid introduction port 4 and introduced into the electrolytic bath section 2 through the dispersion plate 3. The electroconductive powder (carbon particles in this embodiment) 10 in the electrolytic cell section 2 floats in the introduced waste liquid, contacts the container wall 5 connected to the power source, and becomes a cathode, and the carbon particles which become a cathode. Center anode 6
Electrolysis is carried out between and. After the electrolysis is completed, the waste liquid is discharged from the overflow pipe 11, while the carbon particles are deposited on the surface of the metal to increase the specific gravity thereof, and the carbon particles are transferred to the bottom of the electrolytic cell portion 2 and taken out by the discharge nozzle 12. An example of the deposition reaction of metal ions on carbon particles is as follows.

Fe ²⁺ ＋ 2e ⁻ → Fe Fe ³⁺ ＋ 3e ⁻ → Fe Cu ²⁺ ＋ 2e ⁻ → Cu By such reaction, almost 100% of the metal ions in the waste liquid are deposited on the negative electrode and can be separated and recovered. Some of the metal ions are adsorbed by the ion exchange resin, and since these are activated, the radioactive concentration of the waste liquid can be reduced by separating such metal ions.

As described above, the electrolytic treatment of the present invention is most effective when applied to a radioactive waste liquid obtained by oxidizing and decomposing radioactive waste such as an ion exchange resin with hydrogen peroxide in the presence of a metal salt catalyst. Becomes That is, the electrolytic treatment of the present invention not only has a high recovery rate of the metal, but can be directly used in the next step without peeling the metal deposited on the conductive powder, and after consuming the metal. The conductive powder of 1 has the advantage that it can be used again for electrolytic treatment. This series of radioactive waste treatment steps is shown in FIG. 2 and briefly described below.

That is, in FIG. 2, the radioactive waste 21 such as an ion exchange resin is oxidatively decomposed by contacting with hydrogen peroxide in the presence of the metal salt catalyst to become an oxidative decomposition liquid 22. Next, this oxidative decomposition liquid
22 (containing metal ions) is electrolyzed according to the present invention to deposit a metal, and the remainder becomes an electrolytic reaction residual liquid 23. The electrolytic reaction residual liquid 23 is heated and concentrated while being brought into contact with a reducing agent such as charcoal and sulfur, or a metal such as copper having a lower ionization tendency than hydrogen, whereby sulfate ions are reduced to sulfur dioxide and removed. This reaction is, for example, as shown below.

2H ₂ SO ₄ + C → 2SO ₂ ↑ + CO ₂ ↑ + 2H ₂ O Cu + 2H ₂ SO ₄ → CuSO ₄ + SO ₂ ↑ + 2H ₂ O As shown in this reaction formula, when a reducing agent such as charcoal is used, sulfate ion is It becomes sulfur dioxide and is almost completely decomposed. When a divalent metal such as copper is used, theoretically that
50% is decomposed. As the metallic copper used here, it is convenient to use the metallic copper deposited on the conductive powder (carbon particles) in the previous electrolysis. The deposited metal copper has a very large specific surface area and good reactivity. Further, the carbon particles whose metallic copper has been consumed by the reaction can be returned to the processing device and used for the electrolytic reaction. Since the carbon particles can be recycled in this way, they do not become secondary waste.

Sulfur dioxide generated in this desulfurization reaction has a very small transfer to radioactivity like carbon dioxide and water vapor accompanying the above-mentioned oxidative decomposition reaction, and can be treated by the conventional waste gas treatment technology.

The decomposition residual liquid 24 after the desulfurization reaction can be used for the initial oxidative decomposition reaction. If the radioactivity concentration in the reaction liquid exceeds the permissible amount, copper is deposited again as necessary, or the waste liquid 25 is directly treated in the waste liquid treatment system. Alternatively, after neutralization and drying treatment, the obtained dry residue 26 on the powder is mixed with a solidifying material such as polyester resin to form a solidified body 27. According to this method, the amount of the solidified product generated 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 of the solidification of plastic after dry powdering.

Next, examples of the present invention will be described more specifically.

The radioactive liquid waste to be electrolyzed is about 1 Kg of powdered ion-exchange resin (trade name: Powdex, a mixture of cation resin and anion resin in a dry weight of 1: 1) using a copper sulfate aqueous solution as a catalyst salt. About 100 ℃ in 50 glass containers
It was decomposed by heating to and continuously adding hydrogen peroxide. By the above operation, the decomposition solution for 3 batches was prepared.

The decomposition solution 20 (copper amount: about 2 mol) was electrolyzed by the treatment apparatus shown in FIG. 1, and copper was deposited and recovered on the carbon particles at a recovery rate of almost 100%.

For comparison, the same oxidative decomposition solution as described above was electrolyzed in a conventional electrolytic cell. The electrolytic cell used has the structure shown in FIG. 3, and a carbon cathode 32 and an anode 33 having a platinum foil on its surface are suspended in the electrolytic cell 31. The waste liquid 34 was placed in this electrolytic cell, and a voltage was applied between both electrodes for electrolysis.

The results of the both electrolytic treatments are shown in FIGS. 4 and 5. FIG. 4 shows the change over time of the copper recovery rate, and FIG. 5 shows the change over time of the total current efficiency. In both cases, the solid line shows the case of the present invention and the broken line shows the case of the conventional method. . As can be seen from these figures, the method of the present invention shows almost the same recovery data as the conventional method, but since the electrolytic cell volume is 4 in the method of the present invention and 40 in the conventional method, the present invention is extremely It can be seen that the miniaturized electrolytic cell has almost the same effect.

That is, according to the device of the present invention, about 1 / of the conventional electrolytic cell
Despite the electrolytic cell volume of 10, the same recovery effect is achieved in a shorter time than before. This is because the carbon particles come into contact with the container wall, which is a fixed negative electrode, before the metal ions to form a fluidized particle negative electrode, and the electrolytic reaction is performed between this and the central anode. Shows.

The metallic copper obtained by the above treatment method of the present invention is deposited on the carbon particles in a very uniform thickness. The copper on the carbon particles was used as it was, and the sulfuric acid ion decomposition of the waste liquid after copper deposition was carried out as follows.

The waste liquid for which one batch of copper had been recovered was taken out, put into a glass flask of about 3 little by little, and heated and concentrated to a liquid temperature of 160 ° C. At this point, when three batches of recovered metallic copper were added to this solution, generation of a large amount of SO ₂ gas was observed. In addition, the waste liquid after the copper collection for the remaining 2 batches is completed,
When the flask was added to maintain the liquid temperature at 160 ° C, SO ₂ gas continued to be generated, and the final SO ₂ gas generation amount exceeded 90% as the decomposition rate of sulfuric acid. Obtained.
For comparison, sulfate ions were similarly decomposed using the deposited copper obtained by electrolysis by the conventional plate electrolysis. Results are shown in FIG. As is clear from the figure, the decomposition rate is improved when decomposed by the copper treated and recovered by the apparatus of the present invention.

The carbon particles remaining in the residual waste liquid after the above-described sulfuric acid decomposition was washed and the cleaning liquid was added to the residual waste liquid. Almost no metallic copper residue was found on the carbon particles. The carbon particles were reused in the electrolytic reaction, while the waste liquid diluted with the cleaning liquid was a solution containing copper sulfate as a main component and could be used again as a catalyst salt for decomposition of the waste resin. When such reuse was not performed, the diluted waste liquid was adjusted in pH, dried, concentrated, further pulverized, and solidified by using the polyester resin as a solidifying agent. It was possible to reduce the volume to about 1/2 of that when it was solidified by oxidative decomposition alone. This volume reduction ratio can be further increased by repeating copper recovery and desulfurization.

〔The invention's effect〕

As described above, the treatment apparatus of the present invention can efficiently collect metal ions in radioactive liquid waste in a smaller space than conventional apparatuses. Further, since the conductive powder after use can be used as it is for the decomposition of sulfate ion in the waste liquid, if the treatment device of the present invention is used as one step of a series of radioactive liquid waste treatment, the waste treatment is extremely efficient. It is also possible to reuse the conductive powder. Then, finally, the volume of the solidified body to be discarded can be greatly reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view of a radioactive liquid waste treatment apparatus which is an embodiment of the present invention, and FIG. 2 is a process diagram of a series of radioactive waste treatment including a treatment using the treatment apparatus of the present invention as one step,
FIG. 3 is an explanatory view of an electrolytic cell used for electrolysis of a conventional radioactive waste liquid, and FIG. 4 is a view showing a comparison of changes over time in copper recovery rate between the method using the treatment apparatus of the present invention and the conventional method, FIG. 5 is a diagram showing a comparison of changes with time of the total current efficiency, and FIG. 6 is a diagram comparing changes with time of sulfuric acid decomposition rates of copper recovered by the present invention and copper recovered by a conventional method. 2 ... Electrolyzer part, 3 ... Dispersion plate, 4 ... Treatment liquid inlet port, 5 ... Wall also serving as collector of negative electrode, 6 ... Anode, 7 ... Membrane, 10 ... Carbon Particle, 11 …… Overflow pipe, 12 …… Discharge nozzle.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Unoki 4-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Nuclear Power Co., Ltd. (56) Reference JP-A-60-57300 (JP, A) JP 60-18798 (JP, A)

Claims (1)

[Claims] 1. A liquid rectifying section having an inlet for introducing a radioactive liquid waste containing metal ions, and an electrolytic cell section installed above the liquid rectifying section via a dispersion plate, wherein the electrolysis is performed. The tank part was a container wall that also served as the collector of the negative electrode, a lid that also served as an electrode installed on the top of this container wall via a packing, and was fixed to this lid and installed in the center of the electrolytic cell part. An anode, a film placed at a distance around the anode, a conductive powder that does not pass through the film and is contained between the film and the container wall, and is installed at the bottom of the container wall. A radioactive liquid waste treatment device comprising: a discharge nozzle for discharging a conductive powder having a metal deposited on its surface.