JPH0156720B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention processes waste liquid containing radioactive substances,
The present invention relates to a method and apparatus for suppressing the release of radioactive substances into the environment as much as possible. Specifically, the present invention provides radioactive wastewater containing chromate ions and chloride ions as well as radionuclide ions.
A method for efficiently concentrating the above ions for convenient disposal and recovering reusable deionized water by a clever combination of reverse osmosis and electrodialysis, and the apparatus used for this purpose. . Wastewater containing radioactive materials from nuclear power plants is treated in wastewater treatment equipment within the plant, and its release into the environment is suppressed. Conventionally, steam-heated evaporative concentrators have been mainly used to treat radioactive wastewater containing salts, and the concentrated liquid is transferred to a cement solidification device for solidification, while the evaporated water is cooled and disposed of. After condensing and passing through a desalination device,
The water is recycled as recovered water. Currently, all nuclear power plants in Japan are located on the coast, and this trend is expected to continue in the future. That the plant uses a large amount of seawater as cooling water in the heat exchanger within the plant, and that chromate is used as a rust preventive agent in some of the cooling water of the circulating cooling system within the plant. Therefore, salts in seawater, mainly sodium chloride, and chromates may be mixed into wastewater that is subject to radioactive wastewater treatment equipment. So-called "floor drain wastewater" is typical of wastewater containing chloride and chromate ions along with ions of these radionuclides. Although the radioactivity of such wastewater is not high, since it contains the above-mentioned salts and ions, there is a risk that pitting corrosion and stress corrosion cracking of the stainless steel, which is the material of the evaporative concentrator, may occur. The present inventors pursued a method to fundamentally solve the problems associated with the concentration treatment of wastewater containing ions that cause corrosion as described above, and adopted a combination of reverse osmosis and electrodialysis instead of evaporation concentration treatment. As a result of experiments, we found that radionuclide ions, chromate ions, and chloride ions in wastewater were efficiently concentrated by reverse osmosis treatment, and by applying electrodialysis treatment to the concentrated wastewater, we succeeded in achieving the above-mentioned results. The present invention was completed by confirming that ions can be concentrated into an aqueous salt solution with a sufficiently high concentration for final disposal such as cement solidification. The technology of concentrating ionic salts in water using reverse osmosis or electrodialysis is widely used industrially, and also for the treatment of radioactive wastewater, reverse osmosis is used for the treatment of so-called laundry wastewater from nuclear power plants. It was proposed to combine this with evaporative concentration. (Special Publication No. 54-871) Furthermore, the concept of combining reverse osmosis and electrodialysis to increase the effect of concentrating salts is already known. (For example, JP-A-50-75988, JP-A-54-8180) However, radioactive wastewater containing chlorine ions and chromate ions generated in nuclear power plants can be treated at the same level as conventional evaporative concentration. It was not known that reverse osmosis and electrodialysis could be effectively combined to treat the problem, and what operating conditions would make this possible. The present inventors investigated wastewater actually generated at nuclear power plants and found that it may contain several hundred ppm or more of chloride ions and chromate ions. As a result of researching the processing conditions of reverse osmosis and electrodialysis,
We succeeded in effectively combining these technologies,
The present invention was completed by determining process conditions for obtaining reusable recovered water that is highly concentrated and substantially free of salts and radioactive substances compared to conventional evaporative concentration processes. The method of treating radioactive wastewater of the present invention involves treating radioactive wastewater containing radionuclide ions, chromate ions, and chloride ions by a combination of reverse osmosis and electrodialysis, concentrating each of the above ions, and disposing of the radioactive wastewater. In a convenient and reusable method of recovering deionized water, the pH of the wastewater was adjusted to between 7 and 8 and then subjected to reverse osmosis treatment, resulting in a dilute solution with reduced ion concentration and an increased ion concentration. The former diluted liquid is collected and reused, and the latter concentrated liquid is concentrated by electrodialysis treatment for the purpose of ion transfer to obtain a diluted liquid and a concentrated liquid. Reverse osmosis is performed continuously, and the concentrated liquid separated is stored and subjected to batchwise electrodialysis to reduce the total ion concentration.
It consists of returning the diluted solution, which has been reduced to a predetermined value within the range of 300 to 1000 ppm, to reverse osmosis treatment. When treating radioactive wastewater, the first step is to check its pH.
Adjusting to a range of 7 to 8 provides high deionization ability for radionuclide ions and chromate ions in reverse osmosis treatment, as well as increases current efficiency in electrodialysis treatment, increasing the concentration reached in the concentrate. This is because it can be expensive. Once this PH range is selected, there is no need to adjust the PH during subsequent processing. Generally, it has been thought that it is best to concentrate ions by reverse osmosis in a neutral to slightly acidic pH range. However, according to the experience of the present inventors, it is quite surprising that as far as the wastewater to be treated is concerned, neutral to weakly alkaline wastewater is particularly effective for concentrating radioactive substance ions and chromate ions. Better results can be obtained in the PH region. The experimental data below is for wastewater containing NaCl 490ppm Na ₂ CrO ₄ 920ppm radioactivity 8×10 ^-4 μCi/ml, the pH of which was adjusted by adding hydrochloric acid or caustic soda, using reverse osmosis membrane Dowex250.
(Cellulose acetyl acetate membrane) Operating pressure: 14 kg/cm ² Recovery rate: 75% Temperature: Obtained by reverse osmosis at room temperature.

[Table] The reason why the removal rate decreased after long-term operation at the highest pH is thought to be due to deterioration of the membrane due to hydrolysis. Therefore, the pH of reverse osmosis in this case should be 7 to 8. On the other hand, the inventors' experiments regarding electrodialysis for the purpose of ion transfer revealed that, as shown below,
It was found that desalination was performed efficiently at a pH of 7 or higher. Radioactive wastewater containing NaCl 1.5×10 ³ ppm Na ₂ CrO ₄ 1.9×10 ³ ppm Radioactivity 3×10 ^-3 μCi/ml was treated with Aciplex (registered trademark of Asahi Kasei Industries, Ltd.) as an ion exchange membrane at various pH values. ) 10 pieces each of K-101 and A-201,
Electrodialysis was performed using an electrodialysis device assembled with a gasket spacer so that the current-conducting area was 1 dm ² and equipped with an electrode frame at both ends, under the conditions of a bath applied voltage of 15 V (constant voltage), temperature of room temperature, and batch operation. The results are as follows.

【table】

[Table] As can be seen from the table above, when the pH is as low as 6, the current value is low and the current efficiency is also low. Since the movement of ions is small, the concentration of the concentrate does not increase much. This is thought to be mainly because the ion exchange membrane permeability of chromate ions is greatly influenced by pH. Chromate ions have a stronger property of oxidizing other substances on the acidic side than on the weakly alkaline and alkaline sides. Furthermore, when electrodialysis was continued for a long time at pH 6 or lower, it was observed that the ion exchange membrane deteriorated and changed color. The above-mentioned current efficiency in electrodialysis and durability of the ion exchange membrane have important meanings in determining process conditions. When treating radioactive wastewater, the treatment equipment is also susceptible to contamination by radionuclides, so it is important to maximize the desalting and concentration efficiency and make the equipment compact, and to increase the durability of the equipment to ensure long-term use. This is because it is particularly strongly desired to be able to use it over a period of time. To prevent problems, it is necessary to completely remove the solids contained in wastewater that is subjected to reverse osmosis treatment. Therefore, in practice, many operations should be carried out in advance. By adjusting the pH of the wastewater to the above range of 7 to 8, certain metal ions become poorly soluble and precipitate.
A part of it can be physically separated and removed at this stage. It is desirable that this ray be caused by an ultraviolet ray. Next, regarding the relationship between reverse osmosis treatment and electrodialysis treatment in the method of the present invention, in order to carry out both most efficiently and maximize the significance of the combination, it is necessary to adjust the level of each treatment. It is necessary to harmonize. The present inventors have determined that it is appropriate to set the limit of desalination that should be achieved by electrodialysis treatment for the purpose of ion transfer, and to use wastewater whose salt concentration has decreased to that limit as the feed solution for reverse osmosis treatment. I thought that there was, and through experiments I confirmed that this idea was correct. The basic principle of electrodialysis treatment is that ions in the liquid move due to the action of an electric field, so if the ion concentration is extremely low, the efficiency is poor. Therefore, it is usually best to apply it to an aqueous solution with an ion concentration of several hundred ppm or more. On the other hand, in reverse osmosis treatment, when the concentration of salts is high, the osmotic pressure increases, which not only requires high operating pressure but also tends to reduce the removal rate of salts. There are certain difficulties. In the present invention, the degree of deionization achieved by electrodialysis for the purpose of ion transfer is set within the range of 300 to 1000 ppm in terms of salt concentration, taking into consideration the purpose of the treatment and the characteristics of both processes described above. The dilution was made so that a dilution of the same value could be obtained. Electrodialysis is inefficient when operating with dilute solutions that do not reach 300 ppm.
Concentration of concentrate does not increase. Therefore, the processing capacity of the device is low, and the above-mentioned demand for compactness cannot be met. On the other hand, it is disadvantageous to subject a substance with a concentration exceeding 1000 ppm to reverse osmosis treatment for the reasons mentioned above. The reverse osmosis treatment and the electrodialysis treatment are combined in the manner described above to exert their respective functions, but in the present invention, the ion concentration of the electrodialysis diluent reaches the set value described above. Once this is done, the electrodialysis is stopped, and the resulting diluted solution is returned to the reverse osmosis treatment and processed again. Thereby, water in the diluent can be recovered and reused, and the operating conditions of the entire treatment process can be stabilized. In order to industrially implement a process that includes electrodialysis, an electrical conductivity measurement device that has a certain correlation with ion concentration is attached to the electrodialysis device, and operation is performed based on the information obtained from the device. It is better to control Electrodialysis treatment, which aims to move ions, has two purposes. The first is to electrically move ions in the wastewater into another aqueous solution (concentrate) through an ion exchange membrane and extract them, reducing the salt concentration in the wastewater to the required value. The aim is to increase the concentration of ions transferred from the ion to the concentrate as much as possible. To satisfactorily achieve these objectives, it is desirable or usually necessary for the electrodialysis process to be operated in a batch manner. Therefore, a batch type electrodialysis was adopted in the present invention. Batch operation also has the advantage that the most appropriate current can be applied at each point in time depending on the concentration of the diluent flowing through the dialyzer, resulting in a higher average current density than continuous operation, which applies only a constant current. . This increases the throughput of the device, making it easier to make it more compact, and also allows the concentration of the concentrated liquid to reach a higher concentration. While reverse osmosis treatment is performed continuously, electrodialysis is performed batchwise. Therefore, the concentrated liquid with increased ion concentration obtained by reverse osmosis treatment is stored in a tank and then subjected to batchwise electrodialysis treatment. It is necessary to turn it into If continuous operation reverse osmosis and batch operation electrodialysis are smoothly connected in this way, the entire process can be carried out continuously by controlling the batch operation based on the setting of the limit salt concentration mentioned above. It can be driven stably. Reverse osmosis, electrodialysis and especially ultrafiltration techniques are all well known and practiced in various fields. These existing techniques can also be used to implement the method of the present invention. Judging from the above data, the dilute solution separated by reverse osmosis treatment can usually be reused as is, but if necessary, it can be further deionized using an ion exchange resin to completely deionize it. It can also be turned into water and then reused. The final separated liquid containing ions concentrated by electrodialysis treatment for the purpose of ion transfer is similar to that obtained by conventional evaporative concentration.
Can be treated by cement hardening. At that time, if the wastewater is filtered after adjusting the pH to separate solids, it is a good idea to treat them at the same time. When using the treatment method of the present invention, the problem of corrosion of equipment is almost eliminated because conventional evaporation concentration is not carried out when treating radioactive wastewater containing chromate ions and chloride ions that cause corrosion. This is an advantage because all operations can be performed at room temperature without the need for heating. Solving the corrosion problem makes it unnecessary to use stainless steel, a high-grade and therefore expensive material, which has been unavoidable in the past, making it possible to reduce construction costs. In terms of energy consumption, the total amount of electricity used for operating the pressure pump for reverse osmosis and electrodialysis is smaller than for evaporation due to heating, which satisfies the need for energy conservation. This reduction in operating costs is due to
Coupled with the fact that the construction cost of the wastewater treatment facility is low, the economic efficiency of the method of the present invention is ensured. As the examples below will show, the level of radioactive and corrosive substances can be increased even further than what was achieved with conventional evaporation concentrations, which is advantageous because the amount of final processing such as cement solidification is reduced. be. The invention also relates to a device for carrying out the method for treating radioactive wastewater as described above. below,
Typical aspects thereof will be described with reference to drawings showing flow sheets. The device of the present invention treats radioactive wastewater containing radionuclide ions as well as chromate and chloride ions by a combination of reverse osmosis and electrodialysis, concentrating each of the above ions to make them convenient for disposal and reuse. A device for recovering deionized water, including a tank for adjusting the pH of the wastewater, a device for filtering the wastewater adjusted to pH 7-8, a tank for storing the liquid and supplying it to the reverse osmosis device, A reverse osmosis device for treating wastewater and separating it into a concentrated liquid and a dilute liquid, a tank for storing the concentrated liquid from the reverse osmosis device and supplying it to the electrodialysis device, and an ion generator for further concentrating the concentrated liquid. It consists essentially of an electrodialysis device for transport purposes, the retentate outlet of the reverse osmosis device being connected to said reverse osmosis supply tank through a pressure reducing valve, and the electrodialysis device having a diluent tank, a concentrate tank and It is equipped with an polar liquid tank and respective circulation pumps, and can be operated in batches.The concentrated liquid is supplied from the electrodialysis supply tank to the diluent tank, which is converted into a diluted liquid by electrodialysis, and all ions are extracted. The diluted solution whose concentration has been reduced to a predetermined value within the range of 300 to 1000 ppm is circulated to the reverse osmosis supply tank. The wastewater to be treated stored in the wastewater PH adjustment tank 1 is added with acid or alkali from the PH adjustment agent tank 2 to adjust the pH to between 7 and 8, and then pump P
-1 circulates through the ultrafiltration device 4, and insoluble solid particles therein are separated. It is advantageous to use a backwash type ultrafiltration device, and it is recommended to combine this with a cartridge type filtration device 3 and remove the solids concentrated in the former with the latter.
Such measures ensure smooth operation of the limit device. However, since various solid-liquid separators other than those described above can be used to remove solid particles contained in the wastewater to be treated and insoluble substances generated by adjusting the pH, various solid-liquid separators other than those described above can be used. There are no particular limitations on the model. There are various types of reverse osmosis devices, such as a tubular type, a plate and frame type, a spiral type, and a hollow-eye bar type, and any of these types can be used. By performing the pretreatment using the ultraviolet rays described above, performance deterioration due to deposits on the semipermeable membrane can be sufficiently prevented. The ultra-violet liquid is transferred from the liquid tank/reverse osmosis supply tank 5 to the reverse osmosis device 6 by the pressure pump P-3.
-1. The device shown in the figure uses two stages of reverse osmosis modules in series, the permeated water from the first stage reverse osmosis device 6-1 is received in a tank 7, and a pressure pump P is used.
-4 and put into the second stage reverse osmosis device 6-2. The concentrated liquid, which is non-permeated water in the first stage, is sent through the pressure reducing valve V-3 to the concentrated liquid tank and electrodialysis supply tank 8 located in front of the electrodialysis apparatus. Since the non-permeate water in the second stage has a relatively low salt concentration, it is also passed through the pressure reducing valve V-4 to the reverse osmosis supply tank 5.
Return to. For reverse osmosis treatment, depending on the ion concentration of the wastewater and the quality of the recovered water, one module may be sufficient, or a two-stage system may be appropriate as described above. It is of course possible to have three or more stages, but it is usually not necessary. Even if there are 3 or more steps,
The concentrated liquid with a relatively high ion concentration from the non-permeated water outlet in the first stage is depressurized and sent to the electrodialysis supply tank, and the concentrated liquid with a relatively low ion concentration from the non-permeated water outlet in the final stage is passed through a pressure reducing valve. The principle of returning to the reverse osmosis supply tank remains the same. Since most of the radioactive substances and salts contained in permeated water from reverse osmosis treatment have been removed, it can usually be reused as recovered water. If necessary, the sample is further passed through an ion exchange resin layer to almost completely remove the small amount of remaining ions before use. The concentrated liquid with increased salt concentration received in the concentrated liquid tank 8 then enters the diluted liquid tank 9 of the electrodialysis machine, and is circulated through the electrodialysis tank 10 by the circulation pump P-5, during which ions are removed. The radioactive substances and salts contained in this state migrate to the concentrated liquid side. The concentrate is also circulated between the electrodialyzer 10 and the concentrate tank 12 by the pump P-7, and is gradually concentrated. In the illustrated example, the concentrate tank 8 from the reverse osmosis process and the electrodialysis dilute tank 9 are connected in series; Since this system is designed to enable batch operations, based on the principle, two or more tanks are installed in parallel, and while one tank stores concentrated liquid from reverse osmosis, another tank can be stored at the same time. Of course, an embodiment is also possible in which one tank is used for circulating the electrodialysis diluted solution and the tank is switched after one operation of concentration by electrodialysis is completed. When the concentration of the diluted solution obtained by transferring ions to the concentrated solution side by electrodialysis for the purpose of ion transfer has decreased to a predetermined value within the range of 300 to 1000 ppm in terms of total ion concentration, valve V-7 is activated. Open it and
This diluted solution is returned to the reverse osmosis supply tank 5. The electrical conductivity corresponding to an ion concentration of 300 to 1000 ppm in the liquid varies depending on the type of ion, but in terms of what is being treated in the present invention, it is approximately 500 ppm.
~2000μmho/cm. Therefore, a device is installed to measure the electrical conductivity of the diluted solution, and the device is configured to automatically open valve V-7 when its concentration drops to the point where it should be circulated to reverse osmosis treatment. Good. The flow explained above is appropriate when the raw wastewater to be treated has a normal concentration or lower, that is, when the conductivity is 1000 to 500 μmho/cm or less, and after pH adjustment. The filtered wastewater is first subjected to reverse osmosis treatment, and the concentrated liquid obtained is treated by electrodialysis until a diluted liquid with a conductivity close to the lower limit of the above set value, that is, close to 500 μmho/cm, is obtained. by doing
A typical operation is to return the diluted solution to the tank 5, mix it with the raw wastewater, and repeat the reverse osmosis treatment. On the other hand, if the raw wastewater to be treated has a high ion concentration and an electrical conductivity of 2000 μmho/cm or more, direct reverse osmosis treatment is disadvantageous for the reasons mentioned above. Valve V-9 is closed and V-10 is opened, and the waste water after filtration is sent to tank 9 via tank 8, and electrodialysis treatment is performed first until the diluted solution reaches 500μmho/
It is advisable to deionize the material until it exhibits an electrical conductivity of about cm, then send it to the tank 5, where it is subjected to reverse osmosis treatment. In this case, the concentrated liquid from the first-stage reverse osmosis module 6-1 is placed in the tank 8, mixed with raw wastewater, and subjected to electrodialysis treatment. The device of the present invention can be used in various ways depending on the situation, all of which are within the scope of the present invention. Finally, the liquid on the concentration side of the electrodialysis treatment is transferred to the concentrate tank 12 and the electrodialysis tank 1 by pump P-7.
0 and the ion concentration gradually increases. If the concentration becomes extremely high, the driving force for back-diffusion of ions through the ion exchange membrane to the diluent side increases, which tends to reduce dialysis efficiency and may also lead to a decrease in membrane performance. Concentration should be stopped at However, in the wastewater treated by the present invention,
It is easy to increase the final salt concentration of the concentrate to about 10%. Once the ion concentration of the concentrate has reached a predetermined value within these limits, i.e. when the desired concentration for wastewater has been achieved, valve V-8 is opened to transfer the concentrate to a final stage such as cement solidification. Move on to the processing step. Example A pilot plant was constructed to implement the process shown in the flow sheet, and wastewater containing radioactive substances as well as chromate ions and chloride ions was treated. The results are shown below. (Treated wastewater) NaCl 490ppm Na ₂ CrO ₄ 920ppm Radioactivity 8×10 ^-4 μCi/ml PH Adjusted to 7.5 (Treatment amount) 3000 (Result)

[Table] As shown above, the raw wastewater was concentrated 100 times. This level has been difficult to achieve with conventional evaporation concentrations.

[Brief explanation of drawings]

The drawing is a flow sheet showing an example of the apparatus for treating radioactive wastewater of the present invention. 1...Wastewater PH adjustment tank, 2...PH regulator tank,
3... Cartridge type overloader, 4... Ultra limiter, 5
...Liquid tank and reverse osmosis supply tank, 6-1, 6-
2... Reverse osmosis device, 8... Concentrated liquid tank and electrodialysis supply tank, 9... Diluted liquid tank, 10... Electrodialysis tank, 12... Concentrated liquid tank, 13... Extreme liquid tank, P
-1 to P-7...Pump, V-1 to V-10...Valve.

Claims (1)

[Claims] 1 Radioactive wastewater containing chromate and chloride ions along with radionuclide ions is treated by a combination of reverse osmosis and electrodialysis to concentrate each of the ions to make them convenient for disposal and for recycling. In the method of recovering usable deionized water, the pH of the wastewater is adjusted to between 7 and 8 and then subjected to reverse osmosis treatment to form a dilute solution with a reduced concentration of the above ions and a concentrated solution with an increased ion concentration. The former diluted solution is collected and reused, and the latter concentrated solution is concentrated by electrodialysis treatment for the purpose of ion transfer to obtain a diluted solution and a concentrated solution. At that time, reverse osmosis is continuously performed. The concentrated solution separated is stored and subjected to batchwise electrodialysis, and the diluted solution whose total ion concentration has been reduced to a predetermined value within the range of 300 to 1000 ppm is again subjected to the above-mentioned reverse osmosis treatment. A method for treating radioactive wastewater, which comprises returning the radioactive wastewater. 2. The method for treating radioactive wastewater according to claim 1, wherein the radioactive wastewater is floor drain wastewater of a nuclear power plant. 3. The method for treating radioactive wastewater according to claim 1, wherein the pH of the wastewater is adjusted to 7 to 8, and then filtered, suspended solids are removed, and then reverse osmosis treatment is performed. 4. A method for treating radioactive wastewater according to claim 1, wherein the diluted liquid separated by reverse osmosis treatment is further deionized using an ion exchange resin and reused. 5. The method for treating radioactive wastewater according to claim 1, wherein the ion concentration of the diluted solution obtained by electrodialysis treatment for the purpose of ion transfer is measured by measuring its electrical conductivity. 6. The method of treating radioactive wastewater according to claim 3, which comprises solidifying solids separated by filtration and concentrated liquid by electrodialysis together into cement. 7 Radioactive wastewater containing radionuclide ions as well as chromate and chloride ions is treated by a combination of reverse osmosis and electrodialysis to concentrate each of the above ions, making it convenient for disposal and producing deionized water that can be reused. In equipment for collecting wastewater, tanks for adjusting the pH of wastewater, PH
A device for filtering wastewater adjusted to 7 to 8, a tank for storing the filtrate and supplying it to the reverse osmosis device, a reverse osmosis device for treating this wastewater and separating it into concentrated liquid and diluted liquid, and a device for removing water from the reverse osmosis device. It consists essentially of a tank for storing the concentrate and supplying it to the electrodialysis machine, as well as an electrodialysis machine for the purpose of transferring ions to further concentrate said concentrate, and the retentate outlet of the reverse osmosis machine is The electrodialysis machine is connected to the reverse osmosis supply tank through a pressure reducing valve, and is equipped with a diluent tank, a concentrate tank, and a polar solution tank, as well as respective circulation pumps, and is capable of batch operation. The above concentrated solution is supplied from the supply tank to the diluent tank and converted into a diluted solution by electrodialysis until the total ion concentration is 300~
1. An apparatus for treating radioactive wastewater, characterized in that the diluted solution reduced to a predetermined value within the range of 1000 ppm is returned to the reverse osmosis supply tank. 8. The apparatus for treating radioactive wastewater according to claim 7, wherein the filtration device is an ultrafiltration device. 9. The apparatus for treating radioactive wastewater according to claim 8, which comprises a cartridge type filtration device in combination with an ultrafiltration device. 10 The reverse osmosis device is configured as a multi-stage series system, with a pressure pump placed between the stages, and the concentrated liquid with a relatively high ion concentration from the non-permeate water outlet of the first stage is sent to the electrodialysis supply tank, and the non-permeate water outlet of the final stage is sent to the electrodialysis supply tank. 8. The apparatus for treating radioactive wastewater according to claim 7, wherein the concentrated liquid having a relatively low ion concentration is returned to the reverse osmosis supply tank through a pressure reducing valve. 11. The apparatus for treating radioactive wastewater according to claim 7, comprising an ion exchange device for further desalting the dilute solution from the reverse osmosis device. 12 The means for measuring the ion concentration in the diluted solution is a conductivity meter, and the measured value is 500 to 2000 μmho/cm.
8. An apparatus for treating radioactive wastewater according to claim 7, wherein the diluent is returned to the reverse osmosis supply tank when the diluent drops below a predetermined value within the range of .