JP2013002843A - Radiation dose reduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing a radiation dose with high safety, easily and at low costs for radiation contamination, in an overall contaminated area, especially, in agricultural lands, caused by leaking radioactive substances because of an accident in a nuclear plant.SOLUTION: Micronekton is brought into contact with radioactive substances (micronekton is soft porous ancient oceanic humus, indicates natural mineral resulting from burying, depositing and denaturing various oceanic lives or the like under natural phenomena such as crustal alteration in ancient times, and is mined from the Tanakura fracture zone in Fukushima prefecture). Micronekton powder is dispersed over the radioactive substances.

Description

  The present invention relates to a method for reducing the radiation dose from a radioactive substance by using mironectin.

In the accident at a nuclear power plant, a large amount of radioactive material was released, and what was released into the air diffused over a wide area and poured onto farmland, playgrounds, etc.
For this reason, some topsoil is removed, but it is difficult because the contaminated area covers a wide area. In particular, agricultural land is not only safe for farmers but also adsorbed by agricultural products, so that the safety of agricultural products is impaired. Therefore, countermeasures against a wide range of contamination by low-concentration radioactive materials are required.

  Patent Document 1 proposes a cement-based solidifying material for sealing a radionuclide, and zeolite is a radionuclide (for example, as an aggregate used as necessary for the cement-based solidifying material. , Cesium, strontium) adsorption performance is high, and even if the solidified container 8 containing the solidified body is damaged after being buried in the ground, it is preferable because leakage of radionuclides to the ground is suppressed, When the maximum particle size of zeolite is 2.5 mm or less, it is described that it is preferable because it has higher radionuclide adsorption ability. However, this includes zeolite as an aggregate in the cement and is not intended to be in direct contact with the radioactive material.

  On the other hand, Patent Document 2 has conventionally proposed an adsorption method, a bubble separation method, a solvent extraction method, and the like as a method for removing radioactive substances such as uranium. In such an adsorption method, the removal efficiency of radioactive substances is determined by the characteristics of the adsorbent used. Conventionally used adsorbents include hydrous titanium oxide, galena, manganese oxide, zirconium phosphate, inorganic adsorbents such as hydrous titanium oxide supported on activated carbon and alumina, acid oxime type chelate resins, and hexagonal resins. There are organic adsorbents such as carboxylic acids, but conventional adsorbents have low adsorption capacity, and technology has not been developed enough to remove medium to low levels of radioactive waste. An adsorbent for a radioactive substance containing an acid salt and a hydrated oxide of a tetravalent or / and divalent metal and a method for adsorbing a radioactive substance using the adsorbent have been proposed.

  However, in the above prior art, safety to the human body and the environment is unknown, and since it is expensive and cannot be easily treated, it is radiated from radioactive materials that have fallen and adhered to farmland, pastures, playgrounds, roads, etc. There is a need for a method for reducing the exposure dose of radiation in a safe, simple and inexpensive manner without particularly damaging the human body and animal and plant environments.

Japanese Patent Application Laid-Open No. 2008-241587 JP-A-5-146684

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for reducing the radiation dose from radioactive materials in a safe, simple and inexpensive manner.

  The invention according to claim 1 is a method for reducing the radiation exposure dose from a radioactive material, characterized in that mironekton is brought into contact with the radioactive material.

  Invention of Claim 2 is a radiation exposure dose reduction method characterized by spraying mironekton powder on the substance contaminated with the radioactive substance.

The present invention will be described in detail below.
The term “radiation” as used in the present invention refers to ionizing radiation that ionizes atoms constituting a substance through a charged particle when it hits the substance.
Radioactivity refers to the property of radioactive decay in which a certain kind of unstable nucleus changes to another kind of nucleus with radiation emission.

Although the materials and nuclides that emit radiation released in the accident at the Fukushima Daiichi Nuclear Power Station are not clear, ¹³¹ I and ¹³⁷ Cs are said to occupy a large proportion. ¹³¹ I and ¹³⁷ Cs are known to β ^- decay. ¹³¹ I has a half-life of about 8 days and ¹³⁷ Cs has a half-life of about 30 years. Radiation continues to be released from the nuclide, which is a substance that emits radiation, due to decay.

    The present invention has been invented by discovering that the amount of radiation from the soil surface is drastically reduced when milonecton powder is sprayed on soil contaminated with radioactive material released in the accident at the Fukushima Daiichi nuclear power plant. .

Here, mironekton is a soft porous ancient marine humus, and various marine animals and plants (algae, plankton, coral, seafood, etc.) were buried and deposited by natural phenomena such as crustal deformation in the ancient times. Sea mud is a natural mineral that is mined from the Tanakura Shatter Zone in Fukushima Prefecture.
Milonecton is a porous body mainly composed of silicic acid and Al ₂ O ₃ , contains 66 or more elements, and has micropores with an average pore radius of 50 nm. Since silicic acid is a type of SiO ₃ O ₉ or SiO ₆ O ₁₈ , it has a sustained release of oxygen and a strong ion exchange power. Mined from the mironekton deposit and then crushed and adsorbed, hygroscopic, and cation-exchangeable, it is used as a natural resource powder for animal plant growth aids and water quality improvement. As the powdered mironekton, products such as “Minegreen” and “Minegrette” with the trade names of registered trademarks of Yahata Industry Co., Ltd. can be used.

In order to reduce the radiation exposure from radioactive materials present on the ground and shallow soil, it is only necessary to contact milonecton with radioactive materials, and mironecton powder is applied to bare fields, playgrounds, crop vegetation, etc. It can be made to contact simply. For spraying, the powder may be sprayed in a dry state, and water may be sprayed after the powder is sprayed, or may be mixed with water to form a slurry.
Powder spraying may be performed by any method, and a conventional agricultural chemical spraying machine or the like can be used effectively.
Further, after spraying or directly into the topsoil layer of the cultivated land, it may be brought into contact with the radioactive substance by, for example, swallowing mironecton powder.
Milonecton may be thrown into radioactively contaminated water such as rivers, pond water, etc., and solidified and sintered mironecton can be used to reduce radiation from radioactive pollutants in the water. .

The radiation-reducing substance containing mironectin as a component may be mironectone alone or a mixture of materials such as zeolite that do not inhibit the effect of mironectone to reduce radiation.
In order to reduce the exposure over a wide area, it is preferable to increase the contact area and the covering area by pulverizing mironecton powder.
The amount of the mironecton powder to be sprayed may be appropriately set according to the intensity of radiation emitted from the target soil or the like, or may be sprayed in several degrees.

According to the first aspect of the present invention, the amount of radiation emitted from the radioactive substance can be reduced by bringing mironecton into contact with the radioactive substance.
Although the mechanism of action is not clear, in addition to the effect of being simply shielded by the radioactive material being coated, the radioactive material scattered from the nuclear power plant is considered to be in the form of fine particles. Various types of radiation that constitutes pores by being physically or chemically adsorbed in the pores of mironecton, or trapped in the pores by the ion exchange ability of mironectin and spatially confined It is presumed that this may be due to shielding by a substance containing an element.

It is a graph showing transition of the difference of the radiation dose before and after Minnegreen spraying which measured the radiation dose with time in Example 1 just above soil. It is a graph showing transition of the difference of the radiation dose before and after Minne Green spraying which measured the radiation dose over time in 20 cm of soil in Example 1. FIG. In Example 4, it is a photograph showing a mode that Minine green is sprayed on a paddy field by the broadcaster connected to the tractor.

  Hereinafter, the present invention will be further described with reference to examples of the present invention.

Laboratory experiment Milonecton powder was used for the topsoil of the field collected in Iidate-mura, Soma-gun, Fukushima. As the powder of mironekton, “registered trademark Minne Green” used as a plant growth promoter in the form of a powder obtained by pulverizing mironekton from Yawata Corporation was used.
500 g of topsoil (raw soil) was laid flat on three A4 size bats, and 100 g or 30 g of mince green was sprayed thereon, and the radiation dose before and immediately after spraying was measured. After spraying minne green and measuring the radiation dose, each bat was sprayed with 100 g of water. After 40 hours, 91 hours, 19 days, and 24 days after spraying Minne Green, the radiation dose immediately above the soil or Minne Green spray surface and 20 cm above was measured. S. E. An International Inspector EXP Plus was used. Hereinafter, Examples 2, 3, and 4 were also measured with the same measuring device. Minine Green has a bulk specific gravity of about 0.9. The measurement was performed by moving the probe of the Geiger counter horizontally at a predetermined height for 1 minute to obtain the highest value among the indicated values. In addition, the measurement 40 hours after Minne Green spraying was performed on 15 cm instead of 20 cm.
The results are shown in Table 1.

According to Table 1, the amount of radiation on the soil differs from bat to bat, but in all cases, the amount of radiation decreases with time. This is probably due to the ¹³¹ I decay.

  In order to clarify the effect of spraying mineral green directly on the soil, Fig. 1 shows the measurements of mineral green 100g sprayed, mineral green 30g sprayed, and mineral green that was not sprayed on the raw soil or mineral green. The change over time of the change value (difference) from the initial value of the value is shown. The vertical scale is μSv / h. As can be seen from FIG. 1, the sprayed mineral green shows a large radiation dose reduction effect for both sprayed amounts of 30 g and 100 g.

In order to clarify the effect of mince green spraying 20 cm above the soil, Fig. 2 shows the initial values of the measured values measured 20 cm above for the raw soil that is not sprayed with 100 g minmine green, 30 g minine green. It represents the change over time of the change value (difference). The vertical scale is μSv / h.
With the passage of time, the radiation dose of the untreated soil also decreased, which may be due to the decay of ¹³¹ I, which has a short half-life. The effect of 30 g of sprayed mineral green appears to be more effective than that of 100 g of minne green, but it seems that the 30 g sprayed material was associated with a higher radiation dose of the original raw soil.

For the evaluation in the field, the following effects were measured with the cooperation of farmers in Iitate Village, Soma-gun, Fukushima, which is a low-concentration contaminated area due to radioactivity.
Experiment date May 31, 2011 Place 580 Iwagi, Iitate, Iidate-mura, Soma-gun, Fukushima
Minne green spray amount 85kg (100 liters)
Spreading area approx. 100m ²
Under the above-mentioned conditions, “green” was sprayed on the “garden” and the radiation was measured.
The pre-dispersion measurement of 7.756 microsieverts was reduced to 5.118 microsieverts after spraying, and the pre-spread measurement of 9.748 microsieverts was reduced to 5.142 microsieverts after spraying. It was.

Experiment day May 31, 2011 Place Soba field, Iidate-mura, Soma-gun, Fukushima Minna green spray amount 51kg (60 liters)
Which approximately 100m ² of the spray area buckwheat field 3,000m ²
Under the above conditions, Minna Green was sprayed on the buckwheat field and the radiation was measured.
Minine green spraying areas were 8.408 microsieverts and 5.624 microsieverts, but when unspreading grounds were measured, they were 9.426 microsieverts and 10.000 microsieverts. Admitted.

Experiment day June 3, 2011 Place Paddy field, Iidate-mura, Soma-gun, Fukushima Pref.
Minne green spread 476kg (560 liters)
Minine green was sprayed on paddy fields using a broadcaster connected to a tractor.

Under the above-mentioned conditions, an experiment for confirming the radioactive reduction effect was conducted in Iidate Village paddy field.
Point A What was 15.08 microsievert before spraying Minine Green was reduced to 10.02 microsievert after spraying (down 5.06 microsievert).
Point B What was 15.20 microsievert before spraying Minine Green was reduced to 8.936 microsievert after spraying (down 6.264 microsievert).

The damage caused by the contamination of the whole area, especially farmland, etc. caused by radioactive material leakage due to an accident at a nuclear power plant is large, and it is desired to solve it early. ADVANTAGE OF THE INVENTION According to this invention, the amount of radiation emitted from a radioactive substance can be reduced easily and cheaply with high safety only by contacting mironecton with the radioactive substance, and can be effectively used.
Further, according to the present invention, the amount of radiation emitted from farmland or the like can be effectively reduced by simply spraying mironecton powder on the farmland or the like, and the radiation dose emitted from the farmland or the like can be reduced easily and inexpensively.

Claims (2)

  A method for reducing the radiation dose from a radioactive material, characterized by bringing mironectin into contact with the radioactive material.   A method for reducing radiation dose, characterized by spraying mironectin powder on a substance contaminated with a radioactive substance.