JP2013002971A - Method of treating radioactive waste water and treating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat radioactive waste water in large quantities quickly.SOLUTION: A treating apparatus for waste water containing radioactive substances, comprises: a pretreatment device selected from one of pretreatment devices including a strainer, a screen, or a precipitation device; a membrane separation device including a hollow fiber membrane or a flat membrane consisting of a fluororesin-made porous membrane containing a polytetrafluoroethylene; and a reverse osmosis membrane device. These devices are sequentially arranged and connected through piping.

Description

  The present invention relates to a processing method and a processing apparatus for radioactive liquid waste, and a processing method for efficiently removing radioactive material from the liquid waste when a nuclear facility is damaged due to natural disasters and a large amount of liquid waste containing the radioactive material is generated. The present invention relates to a processing apparatus.

Various methods for treating waste liquid containing radioactive substances have been proposed.
For example, in the treatment method of radioactive liquid waste disclosed in JP-A-6-130190, after pyrolysis treatment by a microwave heating method in a first treatment step, the residue after pyrolysis in a second treatment step Water is added to form a solution, and the precipitate is agglomerated and precipitated in the third treatment step, the membrane is separated in the fourth treatment step, and the final concentrated solution containing the radioactive component and the backwash solution of the separation membrane are washed in the fifth treatment step. Evaporation, melting, and solidification treatment is performed by heating by a microwave heating method.
Moreover, as shown in FIG. 8 in Japanese Patent Laid-Open No. 11-109092, a waste liquid containing a radioactive substance is once received in a cleaning drain tank 101 and then reverse osmosis membrane (RO membrane) 100 by a waste liquid transfer high-pressure pump 102. The waste water treatment is carried out by removing the radioactive material and separating it, and the Na concentration in the waste liquid before and after passing through the reverse osmosis membrane 100 is measured, and the reverse osmosis membrane is measured by the Na permeability calculated from the measured value. Degradation status is being evaluated.

JP-A-6-130190 Japanese Patent Laid-Open No. 11-109092

The processing method of Patent Document 1 requires a large number of steps, such as the first processing step to the fifth processing step, and microwave heating is necessary in the first processing step and the fifth processing step. It is unsuitable when processing high-concentration radioactive liquid waste quickly.
In addition, when the reverse osmosis membrane of Patent Document 2 is used, radioactive substances can be separated and removed from the waste liquid. However, as described in Patent Document 2, it is necessary to use the reverse osmosis membrane while checking the deterioration state. In addition, clogging is likely to occur immediately when turbidity enters, but the material of the reverse osmosis membrane is low in chemical resistance, so that it is difficult to clean, and frequent replacement of the reverse osmosis membrane is necessary. Therefore, there is room for improvement as a method for removing a large amount of high-concentration radioactive material from the waste liquid.

  The present invention provides a radioactive waste liquid treatment method and a treatment apparatus capable of separating and removing radioactive substances from a large amount of radioactive waste liquid mixed with a large amount of foreign substances including large solids and simultaneously separating and removing other foreign substances. Is an issue.

In order to solve the above problems, the present invention provides:
As a processing equipment for waste liquid containing radioactive materials,
A pretreatment device selected from a pretreatment device including a strainer, a screen and a sedimentation separator;
A membrane separation device comprising a hollow fiber membrane or a flat membrane made of a porous membrane made of a fluororesin containing polytetrafluoroethylene,
A reverse osmosis membrane device,
An apparatus for treating a radioactive liquid waste is provided, which is sequentially connected through a pipe.

  The hollow fiber membrane or flat membrane of the membrane separator is made of a polytetrafluoroethylene (PTFE) porous membrane, and is a microfiltration membrane (MF) that separates and removes suspended substances such as bacteria and ultrafine particles of a minimum of 0.1 to 1 μm. Film).

  As described above, before separating and removing radioactive substances with the reverse osmosis membrane device in the final process, the membrane separation device uses an MF membrane made of PTFE porous membrane and removes foreign matters of 0.1 to 1 μm in advance. Therefore, clogging of the reverse osmosis membrane can be reduced, and the separation and removal rate of ions of 1 nm or less contained in the radioactive substance can be increased. In addition, since the PTFE porous membrane used as the MF membrane has good chemical resistance, it does not deteriorate even if the backwash is frequently performed, and is suitable for the treatment of a large amount and rapid radioactive waste liquid.

  It is preferable to use a stretched PTFE (polytetrafluoroethylene) porous material as the hollow fiber. PTFE is stable against acids, alkalis and solvents, so it has excellent chemical resistance, can be washed repeatedly with a cleaning agent, can reduce the frequency of replacement, and has excellent non-adhesiveness due to the non-adhesive nature of the material. The suspension component consisting of can be made difficult to adhere. Furthermore, since it is also excellent in flexibility and strength, it is possible to generate a bubbling by pressurizing and injecting a gas from below, and to vibrate the hollow fiber with the bubbling, thereby making it difficult for foreign matter to adhere. Therefore, a large amount of waste liquid treatment can be performed quickly.

  The pretreatment device used in the pre-process of the membrane separation device may be any device that can separate and remove foreign matters of at least 10 μm, preferably exceeding 1 μm, and a plurality of types of pretreatment depending on the size of the foreign matter to be separated and removed. It is preferable to install the device.

  In addition, radioactive iodine, cesium, strontium, barium containing harmful ion components, before the membrane separator, between the membrane separator and the reverse osmosis membrane device, or after the concentrated water of the reverse osmosis membrane device, An adsorption device containing yttrium, radium, zeolite adsorbing these compounds, or organic or inorganic ion exchangers may be interposed.

Further, an ultrafiltration membrane (UF membrane) device or a nanofiltration membrane (NF membrane) device may be interposed between the membrane separation device provided with the MF membrane and the reverse osmosis membrane device.
However, in order to quickly process a large amount of radioactive liquid waste, it is preferable to dispose a reverse osmosis membrane device after the membrane separation device made of the PTFE porous membrane because the processing speed is delayed when the membrane separation device is installed in multiple stages. .

Furthermore, the present invention provides a method for treating a radioactive liquid waste, in which radioactive substances are separated and removed by the treatment apparatus and the radioactive substances are concentrated and reduced.
Further, in the treatment method, it is preferable that the radioactive substance is adsorbed and solidified with zeolite or the like from the reduced concentrated water.

  As described above, it is effective to use a reverse osmosis membrane to separate and remove radioactive substances, but the reverse osmosis membrane is easily clogged and needs to be replaced more frequently because of its low chemical resistance. One problem with the present invention is that a membrane separation device made of a PTFE porous membrane, which is superior in chemical resistance and has a high detergency, is placed in a reverse osmosis membrane before the reverse osmosis membrane. The foreign matter in the waste liquid to be supplied is set to a minimum of 0.1 to 1 μm to reduce the occurrence of clogging of the reverse osmosis membrane, so that it can be quickly processed even if the amount of radioactive waste liquid is large.

It is the schematic of the processing apparatus of 1st Embodiment of this invention. (A) (B) is a perspective view which shows the strainer used for a pre-processing apparatus. It is a schematic sectional drawing of a membrane separator. (A) is sectional drawing of the hollow fiber lower end of the hollow fiber membrane module used for a membrane separator, (B) is sectional drawing of a hollow fiber upper end. It is a perspective view of the 1st modification of the membrane separator of 1st Embodiment. It is a perspective view of the 2nd modification of the membrane separator of 1st Embodiment. It is the schematic of the processing apparatus of 2nd Embodiment. It is drawing which shows a prior art example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 schematically show a treatment apparatus for radioactive waste liquid according to a first embodiment.
A pretreatment device 2 including a strainer 3 that removes large foreign matters (sludge and scale) through a pipe 1A is disposed at a radioactive liquid waste outlet provided in a nuclear power generation facility. As shown in FIGS. 2 (A) and 2 (B), the strainer 3 is preferably arranged in multiple stages with the mesh gaps of the wire mesh tubes 3A and 3B accommodated inside the container being different in size. A membrane separation device 4 is installed via a pipe 1B at the drain of the pretreatment device 2 where the strainer is disposed, and a pipe 1C of the filtered liquid connected to the membrane separation device 4 is connected to the reverse osmosis membrane device 5, The drain port of the reverse osmosis membrane device 5 is connected to a drain storage pool or a discharge pipe 1D to the ocean.

  As shown in FIGS. 3 and 4, the membrane separation device 4 has a plurality of hollow fiber membrane modules 7 immersed in a filtration tank 6. Each hollow fiber membrane module 7 has a number of hollow fibers 10 made of PTFE porous membranes arranged with gaps, and upper and lower ends of these many hollow fibers 10 are resin-molded, and a fixing member molded with the resin 11 and 12 hold the hollow fiber 10 in position. The lower end opening of each hollow fiber 10 is sealed with the fixing member 12 as shown in FIG. 4 (A), while the upper end opening of the hollow fiber 10 faces the water collection header 13 as shown in FIG. 4 (B). The water collection header 13 is connected to the filtered liquid pipe 1C.

  The membrane separation device 4 is an immersion type suction filtration device. The pump 15 provided in the pipe 1C sucks the hollow fiber 10 to allow the radioactive waste liquid supplied into the filtration tank 6 to pass through the hollow fiber 10 for filtration. The spent liquid is taken out from the water collection header 13 through the hollow fiber 10 to the pipe 1C.

In the hollow fiber membrane module 7 arranged in the filtration tank 6, an interval of 0.5 to 10 mm is provided between adjacent hollow fibers 10. The hollow fiber 10 formed from the expanded PTFE porous material has an inner diameter of 0.5 to 12 mm, an outer diameter of 1.5 to 14 mm, a film thickness of 0.5 to 1 mm, a length of about 1000 mm, and an ultrafine pore diameter. Of 50 to 1000 nm, porosity of 50 to 80%, tensile strength of 3 kgf or more, and transmembrane pressure difference of 0.1 to 1.0 MPa.
In this embodiment, an inner diameter of 1 mm, an outer diameter of 2 mm, and a length of 1000 mm are used as the hollow fiber 10, and 400 to 500 of these hollow fibers 10 are converged, and the diameter of one hollow fiber membrane module 7 is about 150 mm.

  As shown in FIG. 3, a bubbling air diffuser 20 is disposed below the hollow fiber membrane module 7. One end of the air diffuser 20 is a closed end 20a, and the other end 20b is detachably connected via a packing (not shown) so that the air introduction header 23 can be kept airtight. The air introduction header 23 is connected to the blower 25 through an air introduction pipe, and 100 to 300 kPa of pressurized air is introduced into the air introduction header 23. An injection hole 21 is formed in the air diffusion tube 20, pressurized gas is injected from the injection hole 21, and bubbling is supplied to adjacent gaps of the hollow fibers 10 that are converged, causing the hollow fibers 10 to sway. ing.

  The hollow fiber 10 is an MF membrane that can capture foreign matters having a minimum size of 0.1 μm to 1 μm. Therefore, the foreign matters of 0.1 μm to 1 μm are removed from the filtered liquid of the radioactive waste liquid taken out from the membrane separation device 4 to the pipe 1C. A pressure pump 26 is provided downstream of the suction pump 15 in the pipe 1C, and the filtered liquid flowing through the pipe 1C is pressurized and supplied to the reverse osmosis membrane device 5.

  The reverse osmosis membrane device 5 includes an RO membrane 28 made of a polyamide-based composite membrane or the like. By pressing the osmotic pressure of 0.75 to 1.5 MPa or more and allowing the RO membrane 28 to permeate, the radioactive substances are removed. The waste liquid can be taken out.

In the radioactive waste liquid treatment apparatus, if at least 1 μm or more of foreign matter is separated and removed from the waste liquid supplied to the reverse osmosis membrane apparatus 5 in the previous step, the reverse osmosis membrane apparatus 5 can reduce the occurrence of clogging of the RO membrane 28. A large amount of radioactive liquid waste can be processed quickly.
Therefore, the function of the hollow fiber membrane module 7 in which the hollow fibers 10 are converged in the membrane separation device 4 in the previous process of the reverse osmosis membrane device 5 is very important.

  In the membrane separation device 4, the waste liquid introduced and filled in the filtration tank 6 passes through the hollow fiber 10 by driving the pump 15, and solid-liquid separation is performed by membrane filtration. In order to exfoliate and remove suspended components deposited on the surface of the hollow fiber 10 or between the membranes by continuing the membrane filtration, the blower is operated constantly or intermittently from the air introduction pipe and the air introduction header 23 to the diffusion pipe 20. Pressure air is introduced and pressure air is injected from the injection hole 21. The jetted pressurized air rises in contact with the surface of the adjacent hollow fiber 10 and gives vibration to the hollow fiber 10 to peel and remove the suspended component from the surface of the hollow fiber 10.

  In this way, since pressurized air is directly injected from the air diffusing tube 20 into the gap between the hollow fibers 10, a considerably strong vibration can be applied to the hollow fibers 10, and the suspension that adheres and accumulates on the surface of the hollow fibers 10. The turbid component can be strongly peeled and removed. Moreover, even if a stronger vibration force is applied to the hollow fiber 10 than before, the hollow fiber 10 is formed of PTFE having a tensile strength of 3 kgf or more, so that the hollow fiber 10 can be prevented from being damaged by vibration.

  Furthermore, since PTFE is strong in chemical resistance, an automatic cleaning device using a sodium hypochlorite solution, a sodium hydroxide solution, and a mixture thereof as a chemical solution for cleaning is attached. When the cleaning chemical solution is supplied to the hollow fiber 10 by cross flow and periodically cleaned, the hardly soluble component adhering to the surface of the hollow fiber 10 can be dissolved, and the surface of the hollow fiber 10 can be easily slipped to be suspended components. Easy to remove.

  As described above, bubbling from the air diffusing tube 20 is imparted to the hollow fiber 10 so that the hollow fiber 10 is shaken to make it difficult for the suspended components to adhere to the surface of the hollow fiber 10, and a strong cleaning liquid is used periodically. By washing, occurrence of clogging of the hollow fiber 10 can be reduced. As a result, when a large amount of radioactive liquid waste is generated, it can be rapidly filtered by the membrane separation device 4, and the waste liquid after the filtration treatment is pressurized and supplied to the reverse osmosis membrane device 5 by the membrane separation device, thereby reverse osmosis. Occurrence of clogging of the reverse osmosis membrane of the membrane device 5 can be significantly reduced, and radioactive substance ions can be removed quickly in the reverse osmosis membrane device 5.

The hollow fiber membrane module 7 of the membrane separation device 4 is not limited to the above-described embodiment. As shown in the first modification of FIG. 5, the configuration presented in Japanese Patent Application No. 2006-175129 of the applicant's previous application, The hollow fiber 10 may be folded in two in a U shape and converged.
Furthermore, as shown in the second modification of FIG. 6, a flat membrane type separation membrane module 30 in which flat membrane elements 28 using a flat membrane made of PTFE are converged may be used.

FIG. 7 shows a second embodiment.
In the second embodiment, an adsorption device 40 including a container 36 filled with zeolite 35 is interposed between the membrane separation device 4 and the pretreatment device 2 including the strainer 3. By passing the radioactive waste liquid through the adsorption device 40, the radioactive substances in the waste liquid can be adsorbed and removed. Other configurations are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted.
The adsorption device 40 may be interposed between the membrane separation device 4 and the reverse osmosis membrane device 5.

The present invention is not limited to the first and second embodiments, and instead of the strainer 3, screens and precipitation separators may be used, or pretreatment devices corresponding to foreign substances to be removed may be provided in multiple stages.
Further, the membrane separator may be provided in multiple stages with a hollow fiber membrane or a flat membrane according to the size of foreign matter that can be membrane filtered.
Furthermore, the reverse osmosis membrane device may be provided with a multi-stage reverse osmosis membrane device with different pressures.

1A, 1B, 1C piping
2 Pretreatment device 4 Membrane separation device 5 Reverse osmosis membrane device 6 Filtration tank 7 Hollow fiber membrane module 10 Hollow fiber

Claims (5)

As a processing equipment for waste liquid containing radioactive materials,
A pretreatment device selected from a pretreatment device including a strainer, a screen and a sedimentation separator;
A membrane separation device comprising a hollow fiber membrane or a flat membrane made of a porous membrane made of a fluororesin containing polytetrafluoroethylene,
A reverse osmosis membrane device,
A processing apparatus for radioactive liquid waste, characterized in that it is sequentially connected via piping.   The hollow fiber membrane or flat membrane of the membrane separation device is made of a porous PTFE membrane, and is a microfiltration membrane (MF membrane) for separating and removing suspended substances such as bacteria and ultrafine particles having a minimum of 0.1 to 1 µm. The processing apparatus of radioactive waste liquid of 1.   Radioactive iodine, cesium, strontium, barium, yttrium containing harmful ion components at the front stage of the membrane separation apparatus, between the membrane separation apparatus and the reverse osmosis membrane apparatus, or after the concentrated water of the reverse osmosis membrane apparatus. The apparatus for treating a radioactive liquid waste according to claim 1 or 2, wherein an adsorption device containing zeolite, radium, zeolite adsorbing these compounds, or an organic or inorganic ion exchanger is interposed.   The processing method of the radioactive waste liquid which concentrates and reduces a radioactive substance while separating and removing a radioactive substance with the processing apparatus of any one of Claim 1 thru | or 3.   The method for treating a radioactive liquid waste according to claim 4, wherein the radioactive substance is adsorbed and solidified by zeolite or the like from the reduced concentrated water.

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