JP2013019876A - Decontamination agent for radionuclide cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the risk aversion from radiation exposure is an urgent subject because of leakage and dispersion of radionuclide caused by a nuclear power plant disaster and it is required to provide means for a release from the radiation exposure by capturing radionuclide cesium that is contaminating all substances.SOLUTION: In order to solve the problem, radionuclide cesium is to be adsorbed/captured. Bentonite of an adsorbent is used for capturing radionuclide cesium and in order to stably and effectively derive the characteristics thereof, a pH buffer solution, an adhesive compound binder, and a surfactant are allowed to coexist.

Description

The present invention relates to a decontamination agent for the purification of non-decontaminated matter contaminated with radionuclide cesium.

JP-A-11-101894 JP 2006-78336 A JP 2009-52955 A

EUROPA Radiocesium Fear "Russia Gives Up Removal" Cycle mechanism technology No. 23 2004.6 "Adsorption behavior of Cs on bentonite colloid"

  Radionuclides are scattered and leaked in the nuclear power plant accident, and pollution is spreading in various places. In particular, removal of radionuclides that continue to emit radiation everywhere is a pressing issue.

  In situations where radionuclides are attached or mixed in soil, concrete, plants, sludge, dust, etc., the opportunity for radiation exposure is large and dangerous. Moreover, the reality is that there are local people who are exposed to the fear of invisible radionuclides and radiation and have to live every day.

  While contamination by radionuclides is wide-ranging, it is important to purify the contamination of building materials such as concrete and timber, soil and plants in order to ensure the safety of living areas. In particular, it is said that the radionuclide cesium, which has a relatively long half-life, is highly reactive and cannot be removed when adsorbed. This is famous for giving up the purification of the radionuclide cesium after the explosion at the Chernobyl nuclear plant in Russia. However, there is no means to release the danger of radiation exposure without removing the radionuclide cesium, and the invention for decontamination of radionuclide cesium is an urgent issue.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by the following means.
That is, in order to purify the non-decontaminated matter contaminated with the radionuclide cesium, it is adsorbed and captured by contact with the radionuclide cesium as a decontamination agent and passivated to purify the non-decontaminated product. It turns out that the problem can be solved.

  Bentonite is used as an adsorbent for the radionuclide cesium used in the present invention, and it is already known that the adsorbent captures cesium present in water. However, it has been said that decontamination is impossible when the radionuclide cesium is adsorbed and bound to a non-decontaminated product. (Non-Patent Documents 1 and 2) The Fukushima nuclear accident this time is unexpected, and no countermeasures have been prepared, and there is little knowledge and no prior art exists.

  Therefore, the inventors studied repeatedly focusing on the adsorption performance of bentonite to cesium. As a result, in the adsorption reaction, it is important to maintain the contact time of the decontaminating agent and the non-decontaminated product, the water content and pH of the reaction system in a certain region. Bentonite is highly reactive in the presence of moisture, but it expands and loses its shape, increasing its viscosity and difficult to handle. Therefore, the present invention has been devised to coexist with a pressure-sensitive adhesive having excellent hydrophilicity, wettability and flexibility, and to keep the decontamination agent in a non-decontamination product for a certain period of time.

Further, since the allowable range of the relationship between the reaction region of bentonite and pH fluctuation is relatively narrow, the pH of the reaction system greatly affects the reaction efficiency. For this reason, by using a pH buffer solution, even if some acid and alkali entered the system, stabilization of the reaction and its maintenance could be secured.
In the adsorption reaction of the radionuclide cesium, it is important that the decontaminant bentonite and the non-decontaminated product maintain moisture and increase the contact time and that the fluctuation in pH is small.

  Although the final step of the decontamination work is washing with water, it was solved by including a water-soluble pigment in the decontamination agent so that the degree of washing could be visually determined.

Furthermore, the adsorbed radioactive material must be stored for a long period of time, but the decontaminant bentonite that adsorbs the decontaminated radionuclide cesium is in an insolubilized form and is unlikely to cause secondary contamination. .

  In the present invention, any object contaminated with a radionuclide is used as a decontamination object, and the radionuclide is removed with a bentonite decontamination agent, so that the chance of radiation exposure can be greatly reduced. In the living sphere, decontamination was performed on rooftops, walls, soil, walls and water, and roof tiles, walls and walls made of concrete. The radionuclide can be passivated (insolubilized) by carrying out the present invention together with decontamination of soil, water and the like. In other words, the captured radionuclide cannot suppress the release of radiation, but since the nuclide does not move again or cause a reaction, no secondary contamination can occur under normal control. By performing the decontamination of the present invention at various places, it is possible to release from the danger of radiation exposure.

  In particular, infants, children, and pregnant women are said to be greatly affected by radiation exposure. The accident at the nuclear power plant in Fukushima is an accident that occurred in the vicinity of a living area that humankind has not yet experienced, and in reality it is impossible to predict future effects. The contribution of the present invention is very significant in considering how to protect living persons from radiation, including children in the future who are greatly affected by radiation.

  The radionuclide cesium decontamination agent used in the present invention is bentonite. In the place of contact between the decontaminating agent for adsorption and the contaminated material to be decontaminated, it is important to control the presence of water and pH. If this condition was ensured, the performance of the adsorbent bentonite could be demonstrated, and an efficient decontamination work could be performed.

The present invention is a decontaminating agent that captures radionuclide cesium with an adsorbent bentonite. In order to draw out the characteristics of the adsorbent, the present invention relates to a buffer material for coping with pH fluctuations and an adhesive for maintaining the adsorption time.
Hereinafter, the present invention will be described using examples.
However, the present invention is not limited to the following examples.

The bentonite of the present invention is a derivative Izumo bentonite (Kasanen Kogyo Co., Ltd.) and has an average particle size of 10 to 30 μm. A phosphate buffer solution (pH 5.8 to 8.0) was used as the pH buffering agent.
The phosphate buffer was prepared as follows.
(1) Sodium dihydrogen phosphate dihydrate (MW 156.01): 1.56 g
(2) Disodium hydrogen phosphate dodecahydrate (MW 358.14): 3.58 g
(1) and (2) were dissolved in 2 L of water, and 300 g of the bentonite was added and spread to make a decontamination agent.

A concrete decontamination test was performed using the bentonite decontamination agent.
Date of measurement: July 2, 2011 Location: Nakanouchi, Iizaka-cho, Fukushima Prefecture Hotel garden and gutter radiation measuring instrument: Digital Geiger Counter MIRION RDS-30
(Made in Sweden)
Measuring method:
Concrete as a decontamination target was about 1 m ² . First measure the surrounding radiation dose, then wash the decontamination object with water, measure the radiation dose after brushing (after decontamination 1), wash the decontamination object with the invention and measure the radiation (decontamination After 2) The weight loss was observed.
The results are shown in a table simultaneously with “Example 2”, “Example 3”, and “Example 4”.

  0.2% of hydroxypropylmethylcellulose (trade name: METOROSE Shin-Etsu Chemical Co., Ltd.) was dissolved in 2 L of water of Example 1, and 0.01% of polyoxyethylene polyoxypropylene block polymer (surfactant as a surfactant) New Paul PE78: Sanyo Kasei Co., Ltd.) was introduced, and the rest was the same as Example 1.

  An abrasive (trade name: Homing Kao Co., Ltd.) 5 g / 2 L was added to the formulation of Example 2 and the same treatment as above was performed.

In the formulation of Example 2, decontamination work was performed at pH around 5.0 using citric acid-phosphoric acid as the pH buffer solution. At this time, a small amount of the blue No. 1 dye was added to serve as a guide for brushing and cleaning, but the blue color is a mark, and the progress of the work is well understood and effective.
The “result” is as follows.

コンクリートの下にあって、苔の部分は異常に高い値であった。特に屋根から落ちる雨が溜まる部分は値が高い。表中の８．４５は異常な値であるので（）に平均値を記した。
測定地周辺は放射線（γ線）値は高いが、場所による変動幅も大きい。The measured values around the place where the measurement was made on that day were as follows. (300m area of measurement site)

Under the concrete, the moss part was unusually high. The value is particularly high where rain falls from the roof. Since 8.45 in the table is an abnormal value, the average value is indicated in parentheses.
Radiation (γ-ray) values are high around the measurement site, but the fluctuation range varies depending on the location.

The results of Examples 1 to 4 were as follows.

In Example 1, the radiation loss was about 39% from the value before decontamination, but the radionuclide of the decontaminated product was removed because the blank value around the measurement site was almost the same as the value after decontamination 2. It seems to be. In Example 2, it is estimated that the pressure-sensitive adhesive is effective. In Example 3, it is conceivable that the amount of radiation loss has a positive effect when some concrete is ground with an abrasive. Further, Example 4 was carried out by selecting a place where the radiation dose was particularly high, but the effect was exhibited as in Examples 1, 2, and 3. Throughout the pH, it is desirable that the pH is close to neutral and the trapping efficiency is good and that the adhesive has a contact time. However, in the actual place of decontamination, it must be used properly depending on the object. For example, in soil decontamination, it is possible to reduce the radiation dose by spraying a mixture of bentonite and buffer material, and mixing and embedding it in the soil. Thus, it was proved again that bentonite decontamination agent is an excellent material for capturing radionuclide cesium. Since the cleaning liquid in this case was below the standard limit, it was poured into the sewer for treatment.

  Everything contaminated with radionuclides is decontaminated and it is a huge amount. By inventing a radionuclide cesium decontamination agent that was previously impossible, the field of release from radiation will increase. In addition to ensuring a safe life zone for human beings, the spiritual relief of releasing from invisible fear is also great.

Claims (6)

A radionuclide characterized by purifying the decontaminated material by contacting a decontaminant with bentonite as an adsorbent with a non-decontaminated product contaminated with the radionuclide cesium, adsorbing and passivating the radionuclide cesium. Cesium decontamination agent. The radionuclide cesium decontamination agent is characterized in that the decontamination agent according to claim 1 coexists with a pH buffer solution in order to widely maintain the radionuclide cesium adsorption performance. 3. The decontamination reagent according to claim 2, wherein the pH buffer comprises at least one of sodium phosphate buffer, citrate-phosphate buffer, Tris-HCl buffer, HEPES buffer, Britton-Pobinsonno buffer. A radionuclide cesium decontamination agent characterized by this. The decontamination agent according to claim 1, 2 or 3, wherein ethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, xanthan gum, sodium alginate, polyvinyl acetate, vinyl acetate / acrylic copolymer A radionuclide cesium decontamination agent characterized by comprising at least one of the coalescence. The decontamination agent according to claim 1, 2, 3 or 4, wherein surfactant is alkylbenzene sulfonate, glycerin monostearate, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyethylene glycol fatty acid ester. A radionuclide cesium decontamination agent characterized by comprising at least one of them. A decontamination agent for a radionuclide cesium according to claim 1, wherein the decontamination agent has a colorant readily soluble in water.