JP2013120109A - Radioactive cesium acquisition filtration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and method for acquiring and removing radioactive materials leaked out of vegetable sediment of a forest and a field contaminated by the radioactive materials.SOLUTION: Radioactive materials are acquired and concentrated in a filtration device by facilitating to separate radioactive materials including plant opal from plant bodies while preserving vegetable sediment, rice straw, or the like for a long term by sealing them in a container to make leaf mold, and removing moisture content through the filtration device which sandwiches mica fragments with partition walls having a vertical directivity. Radioactive materials are filtered to effectively perform decontamination by installing the filtration device or a mat made of the same material quality in water culture, a waterway, or the like into which water contaminated with radioactive materials is caused to flow.

Description

  The present invention relates to an apparatus and method for capturing and removing radioactive material leaking from plant deposits in forests and wilderness contaminated by radioactive material.

Due to the massive earthquake that occurred in the eastern part of Japan on March 11, 2011, and the huge tsunami just after that, several reactors at the Tokyo Electric Power Fukushima Daiichi Nuclear Power Station eventually became extremely severe. A major accident occurred. During this process, a large amount of radioactive material scattered due to hydrogen explosions in the reactor building was not limited to the Fukushima prefecture where the power plant is located. It contaminates the land and continues to have a great physical and psychological impact on the daily lives of the residents. In particular, the actual damage caused by the scattering of radioactive cesium with a long half-life is enormous, and immediate decontamination measures are required. A considerable decontamination effect is recognized by high pressure washing in residential areas where many people live, roads, schools, etc., and by physical removal of surface soil in areas where soil is exposed such as schoolyards and fields. Has been implemented in various places. On the other hand, in the land where plants are prosperous, such as forests and grasslands, which occupy most of the contaminated area, radioactive materials that have fallen on plant deposits such as deciduous leaves and dead trees are removed from the surface soil. Decontamination by simple physical means such as is difficult. If exposed to rain, there is a concern that the attached radioactivity will leak over time and diffuse into the surrounding soil and water veins, and may be transferred to crops. In fact, some examples of such cases have been reported, but no effective countermeasures have yet been proposed. Furthermore, for crops produced in such contaminated areas, even if the measured value of residual radioactivity is below the reference value, distribution is difficult due to the public's psychological resistance, so-called reputation, and secondary damage Is also enormous.

Therefore, it prevents the spread of radioactive materials to the surroundings and the transition to crops and water veins in large areas of forests, wilderness, and cultivated land contaminated with radioactive materials, and is also effective for the subsequent decontamination treatment. There is an urgent need to develop practical, innovative measures that are effective / expensive.

Regarding decontamination of radioactively contaminated soil, the method of washing clay with water, the method of heat treatment of unfractionated contaminated soil, the method of distributing glaze based on the accumulation of radioactivity in clay , Etc., have been published in press or academic conferences, but all are still small scale exploration stages, many of which remain to shield or immobilize radioactivity. In principle, it is assumed that it is necessary to spend a considerable amount of money for both equipment and materials to implement on a wide range of soils.

As a result of the investigation and analysis using the contaminated soil generated by the accident at the nuclear power plant, the applicant has found that most of the radioactive material is a fine clay component, especially a fine part that constitutes an equivalent part of the soil in the affected area. It was found that the radioactivity that was strongly adsorbed by the mica particles and once adsorbed was extremely difficult to elute even after various physical and chemical treatments. Further, according to the subsequent investigation, it is a known fact described in many literatures in Japan and overseas that cesium, which is a radioactive substance, is selectively and strongly adsorbed by mica components. Therefore, if only the mica particles can be isolated from other components and other components with less pollution can be returned to the original land, the volume of contaminated soil can be greatly reduced, effectively removing large volumes of soil. Dyeing is possible. In fact, one of the applicants has devised an apparatus and method for efficiently and inexpensively removing only fine mica pieces from various components constituting the soil, and has already filed applications (Japanese Patent Application Nos. 2011-196687 and 2011-2011). 20476: Applicant: Isamu Kawakami).

On the other hand, the method cannot be applied as it is in forests and wilderness where the soil is covered with plants or plant deposits. According to applicant's experiments, the binding of radioactive material to general plant deposits is apparently relatively loose, and when exposed to wind and rain, the radioactive material diffuses to the surroundings and is absorbed by crops to become secondary There is concern about possible contamination. We closely observed the time course and found that most of the radioactive material leaked out in the process of plant deposits being decomposed into humus. Therefore, an application was filed for a method of capturing radioactive cesium eluted during the humicification process of plant deposits with mica fragments previously distributed (Japanese Patent Application No. 2011-249605: Applicant: Eisaku Katayama, Isamu Kawakami).
Subsequent investigation revealed that silicic acid compounds with a particle size of several to 100 μm, called plant stones, were found in plant sediments, especially leaves of monocotyledons such as ferns, mosses, and gramineous plants. The possibility of accumulating a large amount and binding radioactive cesium as well as the mica component in the soil emerged. That is the reason why radioactive cesium accumulates in rice straw. The vegetation stones come off the plant body as the sediment turns into humus, but the cesium moves with the vegetation stones at that time, so it does not adsorb and migrate to the mica fragments. It can only be treated by decontamination of the soil itself. To prevent leakage of radioactive cesium from general plant deposits or rice straw into the environment and to perform sufficient decontamination, treat these plant deposits as a closed system enclosed in a suitable container, It is desirable to remove it as a cesium / plant stone complex.

In the United States in 1987, there is a preceding example (US Pat. No. 4,808,318 (2/28/1989)) which prevents the diffusion of radioactive cesium by adsorbing to phlogobite. However, as an example of the use of mica, only filtration of contaminated water is not mentioned.

As a decontamination method for stored water contaminated with radioactive substances, materials and techniques (Japanese Patent Application No. 2011-124004) for immersing a material carrying a metal salt in a graft chain grown from nylon fibers have been reported. Is limited to liquids and cannot be used for soil decontamination.

Prior to this application, one of the applicants filed a method for selectively collecting mica components from soil (Japanese Patent Application Nos. 2011-196680 and 2011-20476).

Prior to this application, we distributed bacterial groups promoting foliarization and mica fragments adsorbing radioactive material to contaminated plant sediments, and selectively recovering mica components bound to radioactive material by the above method. Filed a method (Japanese Patent Application No. 2011-249605). According to it, a considerable part of the plant stone in the soil is removed together with the mica component, but it is not quick and complete.

The main object of the present invention is to promote the leakage of radioactive materials in a state where a large amount of plant sediment contaminated in forests and wilderness is isolated from the outside, and to almost completely remove the pollutants through an appropriate filtration device. To provide a quick, safe and inexpensive means for very easily proceeding with the subsequent decontamination work.

Still another object of the present invention is to provide a means for decontaminating a large amount of reserve water or running water in hydroponic land or the like at a very low cost.

As used herein and in the claims, terms such as “radioactive material” and “contamination” refer to isotopic forms with unstable nuclides that decay and most commonly emit energy as alpha particles, beta particles, and gamma rays. Means elemental contamination. Such radioactive materials are mainly fission products or reactor by-products or nuclear bomb unreacted materials. Representative examples include radionuclides such as Cs137, Co60, K40, Pu236, U2355, U238, Ru103, Te, Sr, Rb, Y, Re, Rh, Pd, Tc, Np and Am. In the present invention, the effect was confirmed for Cs137.

As used herein and in the claims, the term “long term” or “sufficient period” means a period up to the time when the plant deposits accumulated in the container according to the present invention become humus, but are closed. Since it is a system, post-processing may be delayed. “Plant deposits” is a general term that includes rice straw in addition to general vegetation.

The invention according to claim 1 of the present invention encloses contaminated forest and wilderness plant deposits in a sufficiently strong and lightweight container such as a flexible plastic bag for general waste, and if necessary, It is characterized in that it is packed with a bacterial group that decomposes sediments into humus, or livestock excretion containing it, and a nutrient medium that promotes the growth of the bacteria. Due to biological or chemical degradation of the sediment, plant stones that were part of the plant and radioactive material bound to it are released from the plant along with the eluted ions, but remain in the container and are filtered as described below. Captured at the top of the device.

The invention according to claim 2 of the present invention is a filtration device in which a considerable amount of mica fragments are sandwiched from above and below as a partition wall that does not leak. The upper surface of the device is provided with a coarse mesh of about 10 mm and two or more stages through which fine particles of about 1 mm or less permeate to prevent clogging. To prevent leakage of fine particles. Furthermore, a lid that fits tightly to the frame of the filtration device can be installed at the bottom, and a tightening ring for fitting to the opening of the container can be installed at the top, or can be installed easily by using a tapered shape. It has a mechanism. A filtration device adapted to the opening of the above-mentioned container enclosing a bacterial group that converts plant deposits to humus is placed under the container and stored for a long time. During this time, the sediment turns into humus under anaerobic conditions, and the water leaked at that time is discharged by gravity through the filtration device and is accumulated at the bottom of the device. At that time, free cesium dissolved in water -Radioactive materials in a state of being bound to ions and mica components in the contaminated soil and plant stones are all trapped in the filtration device.

The invention according to claim 3 of the present invention is characterized by a method of removing and collecting the filtration device that has captured the radioactive substance by the above method. When collecting the filtration device, if the plant deposits remaining in the container are washed by replenishing a small amount of water several times from the top, most of the radioactivity will flow out and filter even the plant stones. Since it is captured by the apparatus, the deposit can be discarded as it is or can be used for the original purpose as humus. As long as the upper part of the adsorption layer is in a wet state, the accumulated fine particles and plant stones will not come off, so the whole may be reversed with the container. Since the whole is treated as a closed system, only the mica component which is the filtration device or its contents can be selectively recovered without escaping most of the radioactive material to the outside. The work can be done quickly because a large number of devices can be processed in parallel, and the volume and weight of the contaminated objects to be finally isolated are significantly reduced. Significant savings on disposal or storage space. Further, only the silicic acid compound is recovered, and the subsequent disposal process is simple and easy to perform.

  Invention of Claim 4 of this invention is an instrument which raises the discharge | emission rate of a water | moisture content by connecting with a vacuum cleaner etc. and performing pressure reduction, when the leakage of a water | moisture content is inadequate in the filtration process. Two pipes are connected in a T-shape, and one pipe protruding upward is attached instead of the lid of the above-mentioned filtration device and sucked. The amount of radioactive material adsorbed on silicic acid components such as mica and plant stone is considered to be extremely small. When the value of the radioactivity trapped by the filtration device is low, the same filtration device can be used repeatedly.

The invention according to claim 5 of the present invention is a filtration device in which mica fragments are wrapped in a coarse nonwoven fabric and formed into a thin mat shape in the same manner as described above. There is no frame, and it is used in the form of laying on the bottom of a hydroponic land or waterway. In the former, a slow water flow is directed downward. In the latter case, it is best to install in the direction perpendicular to the water flow. Since the filtration device is thinly molded, it does not interfere with the water flow in either case.

According to the present invention, decontamination of plant deposits and rice straw in forests and wilderness, which has been difficult to decontaminate against radioactive contamination so far, more completely, quickly, safely and inexpensively, The final waste can be greatly reduced in volume and volume.

The bird's-eye view and sectional view of the filtration device by the present invention. a) Outer frame, b) Coarse sieve, c) Fine sieve, d) Bulkhead, such as non-woven fabric or filter paper, which allows water to pass but not fine particles, e) Vermiculite fragments packed inside, f) Lid below the filter . The upper part is fitted into the opening of a container filled with plant deposits. The installation method of the filtration apparatus by this invention. A plant deposit contaminated with radioactive material is packed in a strong container such as a flexible plastic trash bag, along with bacteria and culture medium that promote humus, and b) the filtration device of Fig. 1 C) Seal upside down. After that, it is left to stand upside down, but it may be left still upward. Use of the filtration device according to the invention. After a sufficient period of time has elapsed, a) When the bag is facing up, reverse the top and bottom, and b) drain the water through the filtration device. Radioactive material is trapped inside the filtration device. If the amount of water discharged is small, d) make a small hole in the top of the bag and replenish a small amount of water in several degrees to wash the humus. If the water discharge rate is slow, attach the device e), and apply a negative pressure with a vacuum cleaner to forcibly discharge the water. To maintain negative pressure, connect another container to the drain. Sectional drawing of the mat | matte containing the mica fragment according to this invention. a) Mica fragments wrapped in non-woven bulkheads. The material of the upper and lower partition walls conforms to the filtration device described above.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a filtration device in which vermiculite particles finely crushed to a particle diameter of about 1 mm are sandwiched between upper and lower partitions. The upper surface of an apparatus with an outer frame made of plastic or metal (assuming the use of filter paper, which is disk-shaped in the figure, but does not matter), has a coarse mesh of about 10 mm and fine particles of about 1 mm or less. A two-stage mesh is arranged to prevent clogging, and a partition wall that only allows moisture to pass is arranged on the lower surface to prevent leakage of fine particles such as plant stones. Furthermore, a lid that matches the frame of the filtration device is provided at the bottom, and a tightening ring or a fitting mechanism using a tapered shape is provided at the top to easily fit the opening of the container.

Packing plant deposits and rice straw collected in radioactively contaminated forests and wilderness into a non-permeable container made of a sufficiently strong material such as a flexible plastic bag, and narrowing its opening Install and seal the filtration device. In that case, you may add a small amount of water and the bacteria which promote humus formation, its culture medium, etc. as needed. Let stand for a long time and wait for humus.

When the humus has been sufficiently developed, the filter device is placed in a downward direction as shown in FIG. 2, and the lower lid is removed to allow the moisture in the interior to flow out. At this time, most of the ionized cesium and the plant stones deviated from the plant body are captured in the filtration device. If necessary, some small holes may be drilled in the top of the bag and refilled with water to clean it.

When the moisture is insufficiently discharged, a negative pressure is applied as shown in FIG. 3 by using a discharge promoting device in which a T-shaped pipe is fitted to the lower part of the filtering device to forcibly discharge the water.

Fine particles such as vermiculite and collected plant stones in the filtration device are disposed of as radioactive waste by vitrification. The humus remaining in the container can be used as it is for the purpose of improving the original soil as long as the radioactive decontamination state is sufficient, but it may be discarded.

The filtration device formed into a thin mat is used for the same purpose as described above by installing it in the bottom of a hydroponic land or in a water channel. In the former, a slow water flow is directed downward. In the latter case, it is best to install in the direction perpendicular to the water flow. In any case, since the mat is thinly formed, the water flow is not hindered.

Example 1
The fact that vermiculite fragments strongly adsorb liberated cesium ions is clear in the literature and in our own experiments, so this time we examined the ability of non-woven plant stones to be captured as a partition wall under the filter.

As a result of verifying to what extent the contained plant stones pass through the non-woven fabric used in the filtration device through the water suspended in the existing humus soil and the bottom soil of the lake, all the plant stones detected microscopically It was proved that it remains on the upper side of the nonwoven and does not leak at all. Moreover, since there was no clogging even when a large amount of sample was placed, it was confirmed that the practical performance was sufficient.

    Vermiculite produced by the sintering of meteorite is a kind of “mica” originally contained in large quantities in rock and soil clay. Radioactive cesium is adsorbed specifically and stably over a long period of time due to the structure and chemical nature of the layer opening at the stump. It is a natural material that is harmless, extremely safe and inexpensive, and will not cause any environmental problems if it is confirmed that harmful asbestos, which is also a kind of mica, is not included in the same vein. Fukushima Prefecture is one of its production areas. In the present invention, an inexpensive and effective filtration suitable for large-scale treatment such as a large amount of plant deposits or rice straw that has been polluted extensively by an accident at a nuclear power plant and no suitable treatment method has yet been found. The material is used as the contents of the device. Since everything is handled in a closed system when using this device, not only cesium ions released in water but also a large amount of silicate compounds leaking from the plant can be captured together, allowing almost complete decontamination. Since the device itself has a simple structure, it is easy to manufacture, and it is possible to work using a large number of devices in parallel. Moreover, since the contents of the filtration apparatus in which the contaminants are concentrated are also raw materials for glass and cement, it is convenient for subsequent radioactive containment treatment. These features can be used very effectively for handling accidents at nuclear power plants.

Claims (5)

Enclose plant deposits of forests and wilderness contaminated by radioactive material scattering and rice straw in a sufficiently strong and lightweight container such as a flexible plastic bag for general waste, decompose the deposits, and humus A method for liberating radioactive substances in a closed system, which includes a group of bacteria to be converted into or a livestock dung containing the bacteria and a nutrient medium that promotes the growth of the bacteria. A filtration device that sandwiches a considerable amount of mica debris from above and below as a partition wall that does not leak. On the upper surface of the device, a coarse mesh of about 10 mm and a two-stage mesh of about 1 mm or less through which fine particles permeate are arranged to prevent clogging. The A container such as a lid that fits into the frame of the apparatus at the bottom and does not escape moisture, and a tightening ring or taper-shaped fitting to fit the opening of the container of claim 1 at the top. Filtration device that has a mechanism that can be easily attached to the camera. A method for removing and collecting a filtration device that has captured radioactive material by the method and apparatus of claims 1 and 2. When collecting the filtration device, if the plant deposits remaining in the container are cleaned by replenishing a small amount of water several times from the top, most of the radioactive material including plant stones will flow out and be filtered. Captured by the device. Since the actual amount of radioactive material adsorbed on the silicic acid component is considered to be small, it is possible to repeatedly use the same filtering device when the radioactivity of the entire filtering device is low. An instrument that increases the water discharge rate by connecting a vacuum cleaner and reducing the pressure when water leakage is insufficient during the filtration process. Two pipes are connected in a T shape, and one side is attached in place of the lid of the filtration device. It has a structure in which mica fragments are enclosed in a coarse bag-shaped container made of a water-permeable material, and is installed in water or in a water channel to absorb and capture radioactive substances contained in water to mica fragments. Radioactive material filtration device characterized by the purpose of preventing reflow.

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