JPS61164195A - Method of treating nuclear power waste water - 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] (Industrial application field) The invention relates to a method for treating nuclear power generation wastewater.

(Prior technology) Nuclear power plants in Japan use book binding as cooling water in the heat exchangers in the plants, and also add chromate as a rust preventive to some of the cooling water in the circulation cooling system in the plants. In order to be used, the so-called floor drain wastewater in nuclear power plants contains radionuclide ions as well as various ions originating from seawater, in particular chloride ions and chromate ions originating from rust inhibitors. It contains about 100 ppm.

In this way, nuclear power generation wastewater containing radioactive ions as well as chlorine ions and chromate and chromate ions has conventionally been concentrated using a steam-heated evaporative concentrator and then solidified using cement. The evaporated water is collected, desalted, and reused as recovered water. However, this method has the problem that pitting corrosion and stress corrosion cracking are likely to occur in the stainless steel that is the constituent material of the evaporative concentrator because the wastewater contains the various ions mentioned above.

In order to solve these problems, a method has already been proposed in Japanese Patent Laid-Open No. 56-4034, in which reverse osmosis treatment and electrodialysis treatment are combined. but,
According to this method, due to the difference in the ion separation mechanisms between reverse osmosis treatment and electrodialysis treatment, it is important to harmonize the levels of both treatments in order to increase treatment efficiency, which requires extremely complicated treatment operations. is necessary. Furthermore, in order to increase treatment efficiency and prevent deterioration of the reverse osmosis membrane used, it is required to strictly control p■ of the wastewater. Furthermore, as is well known, high pressure is required to remove salts by reverse osmosis treatment, and there is also the problem that the membrane surface becomes contaminated and the amount of water permeated through the membrane decreases significantly over time.

The present invention was made in order to solve various problems in the conventional nuclear power generation wastewater treatment as described above, and in particular, there is no need for high pressure for P++ adjustment or treatment of wastewater, and further, It is an object of the present invention to provide a method for efficiently concentrating nuclear power generation wastewater and recovering deionized water without the problem of equipment corrosion.

A method for treating nuclear power generation wastewater according to the present invention is a method for treating nuclear power generation wastewater containing radionuclide ions, in which one side of a hydrophobic polymer porous membrane that allows water vapor to pass through but does not allow water to pass through is heated to a predetermined temperature. Nuclear power generation wastewater is brought into contact with the wastewater, steam is generated from this wastewater, and this is permeated through the other side of the porous membrane, cooled and condensed, thereby concentrating the wastewater and recovering deionized water. It is characterized by

In the method of the present invention, generated from nuclear power generation wastewater,
In order to cool and condense the water vapor that has passed through the hydrophobic polymer porous membrane, any of the following methods can be used.

The first method is to contact nuclear power generation wastewater at a predetermined temperature with one side of a hydrophobic polymer porous membrane that allows water vapor to pass through but does not allow solutes such as water and ions to pass through, and the other side of this porous membrane A heat transfer wall maintained at a predetermined low temperature is provided on the side at an appropriate distance from the membrane surface, and the wastewater generated from the nuclear power generation wastewater is
The water vapor that has passed through the porous membrane is cooled by the heat transfer wall soil and condensed to obtain deionized water. However, radionuclide ions, chloride ions, and chromate ions do not pass through the membrane, so this is It is concentrated in nuclear power generation wastewater with a high removal rate.

The second method is to contact one side of the hydrophobic polymer porous membrane with nuclear power generation wastewater at a predetermined temperature as described above, and contact the other side with a predetermined low-temperature cooling medium, such as cooling water. The water vapor generated from the nuclear power generation wastewater and permeated through the porous membrane is directly cooled and condensed in the cooling medium, and is obtained in the cooling medium, while the nuclear power generation wastewater is concentrated in the same manner as described above.

In the method of the present invention, the polymer porous membrane needs to be hydrophobic to nuclear power generation wastewater and have the property of not allowing water itself to pass therethrough but allowing water vapor to pass therethrough. Therefore, such a hydrophobic polymer porous membrane usually has micropores of about 0.05 to 50 μm, preferably about 0.1 to 5 μm, and preferably has a porosity of 50% or more. Further, the film thickness is not particularly limited, but is usually 1 to 2000 μm, preferably 5 to 1000 μm.
It is about m.

Therefore, in the present invention, a porous membrane made of a fluororesin such as polytetrafluoroethylene resin is particularly preferably used as the porous membrane because it is hydrophobic and has excellent heat resistance. For example, a porous membrane obtained by extrusion molding a solution or melt of a fluororesin such as vinylidene fluoride resin or ethylene-tetrafluoroethylene copolymer resin is also preferably used.

However, even if a porous membrane is made of a hydrophilic resin such as polysulfone or cellulose resin, when the surface is coated with a water-repellent resin such as a fluororesin or silicone resin to provide a hydrophobic porous surface. Resin films can also be used.

Next, an apparatus suitable for carrying out the method of the present invention will be described based on the drawings.

1 and 2 show an example of an apparatus suitable for carrying out the first method described above.

That is, a membrane tube 2 made of a hydrophobic polymer porous membrane as described above is disposed coaxially within the outer tube 1, and nuclear power generation wastewater at a predetermined temperature is placed between the outer tube and the membrane tube. A stock solution passage 3 is formed for this purpose. Therefore, the outer tube preferably has heat retaining properties, and is made of resin, for example. An inlet pipe 4 and an outlet pipe 5 for nuclear power generation wastewater are connected to the raw solution passage 3, and the nuclear power generation wastewater is heated to a predetermined temperature by a heater 6 installed in these pipes as necessary.
It is circulated and distributed to the stock solution circuit. Nuclear power generation wastewater is appropriately replenished into the stock solution circuit through a supply pipe 8 equipped with a valve 7, and a portion is discharged from the stock solution circuit as necessary through a discharge pipe (not shown).

A heat transfer tube 9 is further disposed coaxially inside the membrane tube 2, and is spaced at an appropriate distance so as to have a steam space 10 between it and the membrane tube. It is preferable for the vapor diffusion space to be narrow from the point of view of water vapor condensation efficiency, but if it is made too narrow, it will actually create a flow resistance for the condensate, so it is usually 0.
．． Approximately 2 to 5 mm is suitable. A heat exchanger tube is a thin-walled tube made of a material with high heat conductivity, such as metal. An inlet pipe 11 and an outlet pipe 12 for a cooling medium are connected to the heat exchanger tube, and a cooling medium such as cooling water is circulated through the heat exchanger tube. Note that when a corrosive medium such as seawater is used as a cooling medium, it is desirable to line the inner wall surface of the heat exchanger tube with, for example, an epoxy resin. Further, a discharge pipe 13 for condensed water that has passed through the membrane tube, been cooled by the heat exchanger tube, and condensed is connected to the vapor diffusion space.

Note that, since the porous membrane constituting the membrane tube generally has low strength, it is preferably supported on a suitable support (not shown). Such a support only needs to be able to reinforce the porous membrane and allow water vapor to pass therethrough, and for example, a woven or nonwoven fabric made of polyamide or a porous tube made of ceramic is preferably used.

Further, as shown in FIG. 3, the device includes a plurality of membrane tubes 2 disposed inside an outer tube 1, each membrane tube having a heat transfer tube 9 inside, and a space between the outer tube and each membrane tube. FIGS. 4 and 5 also show examples of an apparatus for carrying out the first method, and the same members as in FIG. Reference numbers are provided. That is, outer tube 1
The membrane tube 2 is disposed coaxially inside the membrane tube, and the stock solution passage 3 is formed between the outer tube and the membrane tube, which is the same as the device shown in FIG. 1 described above. In this case, a spacer 14 is disposed on the inside of the membrane tube 2 in contact with it, and a heat exchanger tube 9 is further disposed on the inside of this spacer in contact with it. That is, since the spacer is cooled by the heat transfer tube, the spacer itself forms a cooled vapor diffusion space and also forms a passage for condensed water. Therefore, steam generated from nuclear power generation wastewater and permeated through the membrane tube is cooled by the spacer and the heat transfer tube 3, and the spacer is communicated with the condensed water outlet tube 13.

This spacer must be porous so that the steam that has passed through the membrane tube can pass through to the heat transfer tube, and must also have permeability in at least a predetermined direction for water that has been cooled and condensed by the heat transfer wall. Furthermore, it is preferable that the material has excellent thermal conductivity. In the illustrated apparatus, the spacer needs to have liquid permeability at least in the vertical direction so that the generated condensed water can flow down in the vertical direction.

Of course, the spacer may be bonded in advance to the porous membrane, the heat exchanger tube surface, or both.

Examples of the spacer include woven fabrics, non-woven fabrics made of 10 to 1000 meshes of natural or synthetic fibers, such as polyethylene, polyester, polyamide, etc.
Carbon fiber cloth, metal mesh, etc. are preferably used. The thickness of the spacer is not particularly limited, but if it is too thick, it will actually reduce the steam condensation efficiency, so normally,
A value of 5 cranes or less, particularly a range of 0.2 to 3111, is preferred. That is, by using a spacer with a small thickness, the interval between the vapor diffusion spaces can be reduced, and at the same time, the efficiency of condensing water vapor and the acquisition rate of condensed water can be increased.

The raw solution passage 3 has an inlet pipe 4 and an outlet pipe 5 for nuclear power generation waste water.
is connected, and a heater 6 is provided in this conduit as necessary. It is the same as in the previous device that the nuclear power generation wastewater is replenished into the raw solution circuit through a supply pipe 8 equipped with a valve 7. Also,
As mentioned above, the heat exchanger tube includes an inlet pipe 11 for the cooling medium.
and the outlet pipe 12 are connected, and the cooling medium is circulated through the heat transfer tube.

In the first device shown in FIGS. 1 and 2, nuclear power generation wastewater at a predetermined temperature is introduced into the raw solution passage 3, and the water vapor generated from the nuclear power generation wastewater passes through the membrane tube 2 and passes through the vapor space. 10, the condensed water is cooled on the surface of the heat exchanger tube 9, flows down the surface of the heat exchanger tube, and is led out of the apparatus through the condensed water outlet tube 13. Ions in the stock solution are blocked from permeation by the membrane tube and concentrated in the stock solution. According to this device,
Nuclear power generation wastewater can be concentrated and substantially deionized water can be obtained as condensed water.

According to the apparatus shown in FIG. 4, water vapor generated from nuclear power generation wastewater passes through the membrane tube 2, is cooled by the spacer 14 and the heat transfer tube 9, is condensed, and flows down the spacer to the condensed water outlet tube 13. is guided outside the device.

6 and 7 show an example of an apparatus suitable for carrying out the second method described above, in which the same parts as in FIG. 1 are given the same reference numerals.

A membrane tube 2 made of a hydrophobic polymer porous membrane as described above is disposed coaxially within the outer tube 1, and a stock solution passage 3 is formed between the outer tube and the membrane tube. Nuclear power generation wastewater at a predetermined temperature is passed through the membrane tube, and deionized water is passed through the membrane tube as a cooling medium. That is, the nuclear power generation wastewater and the cooling medium are brought into contact through the membrane tube. An inlet pipe 4 and an outlet pipe 5 for distributing nuclear power generation wastewater are connected to the raw solution passage 3, and similarly, an inlet pipe 11 and an outlet pipe 12 for distributing a cooling medium are connected to the membrane tube 2. There is.

According to this second device, generated from nuclear power generation wastewater,
The water vapor that has passed through the membrane tube wall is immediately cooled and condensed using deionized water as a cooling medium, and is recovered in deionized water. As described above, the nuclear power generation wastewater is replenished from the supply pipe 8 as necessary, heated in the heater 6, and circulated through the raw liquid circuit through the pipes 4 and 5. Cooler 14 installed in the cooling medium circuit according to
The cooling medium is circulated through the cooling medium circuit while being cooled to a predetermined temperature by
is taken out of the device.

According to this second device, the nuclear power generation wastewater at a predetermined temperature is brought into direct contact with the cooling medium through the membrane tube, so the water vapor generated from the nuclear power generation wastewater is immediately cooled by the cooling medium and condensed. , stored and recovered in a cooling medium. Therefore, not only is the vapor permeation rate high, but it can also be made more compact than a device that provides a steam space between the membrane tube and the heat transfer wall, and the effective membrane area per unit volume is large, so it can be used efficiently to treat nuclear power generation wastewater. deionized water can be recovered.

Although not shown, as a modification of the device shown in FIG. 6, the device includes a plurality of membrane tubes housed in an outer tube, a cooling medium is circulated in each membrane tube, and a space outside the membrane tubes in the outer tube serves as a stock solution passage. It may be formed as shown in FIG.

In addition, in the case of any of the above-mentioned devices, the present invention has been described in detail assuming that nuclear power generation wastewater is passed through the raw solution passage 3 between the outer tube and the membrane tube, and a cooling medium is circulated within the membrane tube. However, it goes without saying that the cooling medium may be passed through the raw liquid passage, while the raw pre-power generation wastewater may be passed through the cooling medium passage.

Furthermore, when the device has a spacer between the membrane tube and the heat transfer tube, the spacer itself is also cooled by the low-temperature heat transfer wall, so the vapor that permeates through the membrane is immediately cooled by the spacer and the heat transfer wall. As a result, the steam condensation rate is increased, and nuclear power wastewater can be concentrated and deionized water can be obtained with high efficiency.

In addition, in all of the illustrated devices, the raw liquid passage or the cooling medium passage is formed in an annular shape, but a flat membrane wall in place of the membrane tube and a flat heat transfer wall in place of the heat transfer tube are placed between them. At least one set is arranged facing each other with or without a diffusion space, and each passage is enclosed in a suitable container corresponding to the outer tube, and each passage is used for circulation of a stock solution or a cooling medium. By connecting these circuits, it is possible to obtain a device having a stock solution passage and a cooling medium passage each having a rectangular cross section, corresponding to each of the above-mentioned devices. Furthermore, by arranging the membrane wall and the heat transfer wall in contact with each other via a spacer, a device corresponding to FIG. 4 can be obtained.

It will be clear that such an apparatus can also be suitably used to carry out the method of the invention.

As described above, the method of the present invention involves bringing nuclear power generation wastewater at a predetermined temperature into contact with a hydrophobic polymer porous membrane, and cooling and condensing the water vapor generated from the nuclear power generation wastewater and permeated through the membrane. In this way, nuclear power generation wastewater is concentrated and deionized water is obtained as condensed water. Therefore,
According to the method of the present invention, unlike the above-mentioned reverse osmosis method which uses a pressure difference as a driving force, the driving force is a temperature difference, so pressurization is not required, and the heat source is a nuclear power plant. The waste heat generated can be used.

Furthermore, according to the method of the present invention, it is not necessary to adjust the pH of nuclear power generation wastewater during treatment, and there is no problem of corrosion of equipment, and nuclear power generation wastewater can be efficiently concentrated and deionized water can be used. It can be recovered.

Examples of the present invention are listed below.

Example 1 As shown in Fig. 1, a membrane tube with a diameter of 25mm made of a porous polytetrafluoroethylene membrane lined with a porous polyamide woven fabric was coaxially placed inside a synthetic resin outer tube with a diameter of 40mm. Further, a stainless steel heat exchanger tube having a diameter of 23 mm was disposed within the membrane tube so that the distance between the tube walls was IN to construct an apparatus. Note that the above porous membrane has an average pore diameter of 0.
．． It had micropores of 2 μm, a porosity of 80%, and an effective membrane area of 240 cJ in the device.

In addition to the above device, seawater at a temperature of 25°C is passed through the heat transfer tube as cooling water, and as shown below, seawater at a temperature of 60°C, which contains chromate ions, chloride ions, etc. in addition to radionuclide ions, is used as cooling water. Nuclear power generation wastewater is circulated and supplied to the raw solution passage, and the sodium chloride concentration in the concentrated solution is 36,000 p.
It was processed until it reached pm. As the results are shown in the table, the condensed water can essentially be reused as deionized water.

The condensate acquisition rate is 8.5 kg/kg at the beginning of the process.
It was time. Also, for 1000 hours, 8.2 kg/
ITr·hr, and almost no change over time in the rate of acquisition of condensed water was observed.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of an apparatus suitable for carrying out the method of the present invention, FIG. 2 is a sectional view taken along the line A-A in FIG. 4 is a longitudinal sectional view showing another apparatus suitable for carrying out the method of the present invention; FIG. 5 is a sectional view taken along line B--B in FIG. 4; FIG. 7 is a longitudinal cross-sectional view showing yet another device, and FIG. 7 is a cross-sectional view taken along the line B--B in FIG. 6. 1... Outer tube, 2... Membrane tube, 3... Stock solution passage, 9...
...Heat transfer tube, 10...Vapor diffusion space, 13...Condensed water outlet pipe, 14...Spacer, 15...Cooling medium outlet pipe.

Claims (1)

[Claims] (1) In a method for treating nuclear power generation wastewater containing radionuclide ions, nuclear power generation wastewater at a predetermined temperature is brought into contact with one side of a hydrophobic polymer porous membrane that allows water vapor to pass through but does not allow water to pass through; Nuclear power generation wastewater characterized by generating water vapor from this wastewater, passing it through the other side of the porous membrane, cooling and condensing it, thereby concentrating the wastewater and recovering deionized water. processing method.